Class Z376^/ Copyright^ 10 . COPYRIGHT DEPOSIT. ENGINEERING OF POWER PLANTS ENGINEERING OF POWER PLANTS V^ BY ROBERT H: FERNALD, M. E., A. M., Ph. D. WHITNEY PROFESSOR OP DYNAMICAL ENGINEERING, UNIVERSITY OP PENNSYLVANIA AND GEORGE A. ORROK, M. E. CONSULTING ENGINEER, NEW YORK FORMERLY MECHANICAL ENGINEER THE NEW YORK EDISON COMPANY First Edition McGRAW-HILL BOOK COMPANY, Inc. 239 WEST 39TH STREET. NEW YORK LONDON: HILL PUBLISHING CO., Ltd. 6 & 8 BOUVERIE ST., E.C. 1916 Copyright, 1916, by the McGraw-Hill Book Company, Inc. fa? NOV 27 1916 THB MAPLE PRE9S YORK PA ©CLA445843 PREFACE This work is not a treatise on power plants. It is simply an epitome of the subject arranged by the authors for convenient classroom use. Originally compiled by one of the authors in 1908 for use at the Case School of Applied Science, these notes have been used for eight years at that institution and for four years at the University of Pennsylvania as the fundamental course in power plants for all senior engineering students, including mechanical, electrical, chemical, civil and mining engineers. Besides offering much general material relating to the Engineering of Power Plants, the two underlying thoughts in the preparation of this text for classroom use have been — (a) To bring to the student a realization of the fact that engineering, although based on the exact sciences, is not itself an exact science but requires, on the part of the successful engineer, a natural fund of "common sense" and the application of engineering judgment — a realization of the fact that accuracy may mean within twenty per cent, and not the seventh place to the right of the decimal point; and (b) To give the student some idea of the commercial side of engineer- ing — a field too seldom touched upon in many engineering courses. The cost figures presented must be used with caution as market variations are such and local conditions so different that such data can be at best only approximate. Although the authors have endeavored to give credit for data copied from various sources, much of the material has been so subdivided and used by so many different writers that it has not been feasible to trace it to its original source. The authors desire to acknowledge their appreciation of the excellent service rendered by Paul J. Kiefer in checking the material presented in these notes. R. H. F. G. A. O. vu CONTENTS Page Preface vii Chapter I. Sources of Energy 1 II. The Steam Engine 18 III. Electric Generators and Motors 76 IV. Foundations 82 V. Condensers 87 VI. The Steam Boiler 121 VII. Chimneys and Mechanical Draft 166 VIII. Smoke and Smoke Prevention 190 IX. Boiler Auxiliaries 197 X. Piping 215 XI. Coal and Ash Handling 232 XII. The Steam Power Plant 239 XIII. Variable Load Economy 269 XIV. Cost of Power 285 XV. Hints on Steam Plant Operation . . 315 XVI. Power Transmission 319 XVII. District Heating 341 XVIII. The Power Plant of the Tall Office Building 354 XIX. The Power Plant of the Steam locomotive 362 XX. Fuels 372 XXI. Internal-combustion Engines 398 XXII. Producer Gas and Gas Producers 435 XXIII. Comparative Efficiencies and Operating Costs for Different Types of Installations 491 XXIV. Compressed Air 511 XXV. Refrigerating Machinery 525 XXVI. Hydraulic Power 530 Index 571 IX ENGINEERING OF POWER PLANTS CHAPTER I SOURCES OF ENERGY For industrial purposes energy is derived from : (a) Vital forces; muscular power of men and animals. (b) Gravity; energy of the wind and flowing water. (c) Chemical forces; energy of fuel. In considering the various types of power, it is convenient to further subdivide item (c) into: (d) Steam. (e) Gas. if) Compressed air, hot water and refrigeration. (g) Hydraulic power; with application to pumps, elevators, cranes, etc. (h) Electric. Unit of Power. — The unit 1 of power is the horsepower (hp.). One horsepower = 33,000 ft. -lb. per minute or 550 ft. -lb. per second in American and English practice. The metric horsepower used in Europe = 542.47 ft.-lb. per second or 0.9863 English horsepower. The metric horsepower is known as the pferde starke (P.S.) in German and cheval de vapeur in French. The unit used in electrical measurements of power is international and is called the watt, of which 746 correspond to the mechanical energy in 1 hp. The metric horsepower = 736 watts. Efficiency of a Machine. — Kent states that the efficiency of a machine is a fraction expressing the ratio of the useful work to the whole work performed, which is equal to the energy expended. The limit to the efficiency of a machine is unity, denoting the efficiency of a perfect machine in which no work is lost. The difference between the energy expended and the useful work done, or the loss, is usually expended either in overcoming friction or in doing work on bodies surrounding the machine from which no useful work is received. Thus in an engine propelling a vessel part of the energy exerted in the cylinder does the useful work of giving motion to the vessel, and the remainder is spent in overcoming the friction of the machinery and in making currents and eddies in the surrounding water. 1 In 1913, Mr. H. C. Stott suggested a double unit called the Myriawatt as a standard for steam-electric power. This standard has not yet been adopted. For discussion, see Journal A. S. M. E., February, 1913. 1 ENGINEERING OF POWER PLANTS A common and useful definition of efficiency is " output divided by input." Muscular Power of Men and Animals. — In dealing with living motors, it must be borne in mind that the motors are seldom alike, that the same motor varies at different times and that such motors can be used only intermittently as rest is absolutely essential. The various treatises on the subject point out that such motors will differ with: (a) The health of the specimen, his muscular development, his nervous tempera- ment, his disposition, his degree of stimulus of interest and will. (6) The species of animal, the race of man. (c) The amount of practice, the degree of training. (d) The abundance of food and air; the climate. These items are all important but it is hardly possible to determine their exact effect upon the motor. The more tangible elements that effect the work accomplished are: (e) The relation of the working hours to those of rest in the 24 hr. of the day. (/) The relation between the maximum exertion possible and the force actually exerted. (g) The speed in feet per second. (h) The nature of the machine receiving the effort of the motor force. The effort of the application of energy should be to secure the greatest foot-pounds in a continuous day's work. Labor of Men. — Man's labor is usually in lifting, pushing or pulling, or in transporting weights. Experimental data are as follows: Work of Men against Known Resistances (Rankine) Kind of exertion Resist- ance, lb. Velocity, ft. per sec. Hours per day Ft.-lb. per sec. Ft.-lb. per day (8 hr.) 1. Raising his own weight up stair or ladder 2. Hauling up weights with rope and lowering the rope unloaded 3. Lifting weights by hand 4. Carrying weights upstairs and returning un- loaded 5. Shoveling up earth to a height of 5 ft. 3 in. . . . 6. Wheeling earth in barrow up slope of 1 in 12^, horiz. veloc. 0.9 ft. per sec, and returning un- loaded 7. Pushing or pulling horizontally (capstan or oar) . . 8. Turning a crank or winch i 9. Working pump. 10. Hammering 143.0 0.5 8 71.5 40.0 0.75 6 30.0 44.0 0.55 6 24.2 143.0 0.13 6 18.5 6.0 1.3 10 7.8 132.0 0.075 10 9.9 26.5 2.0 8 53.0 12.5 5.0 ? 62.5 18.0 2.5 8 45.0 20.0 14.4 2 min. 288.0 13.2 2.5 10 33.0 15.0 ? 8? ? 2,059,200 648,000 522,720 399,600 280,800 356,400 1,526,400 1,296,000 1,188,000 480,000 JFlJ Note. — See Taylor's study on "Handling Pig at Bethlehem," "Principles of Scientific Management," Harpers, 1911, p. 25. SOURCES OF ENERGY Records show that men have pulled once 182, 208, 227 and 267 lb. Ordinarily, at a crank a man will exert from 15 to 18 lb. continuously and from 25 to 30 or even 40 if applied intermittently. Such a crank will turn from 26 to 30 revolutions per minute. At 18 lb., the foot-pounds per day are 1,296,000, while for an engine horsepower they are 15,840,000, or the man has one-twelfth or one- thirteenth the power of an engine horsepower. Clark says that the average net daily work of an ordinary laborer at a pump, a winch, or a crane may be taken at 3300 ft. -lb. per minute, or Jf o hp-j f or 8 hr. a day; but for shorter periods from four to five times this rate may be exerted. Rowing in races is calculated to exact 4,000 lb. raised 1 ft. high per minute, or nearly 3^ hp. The action of the heart limits the stress which can be put on the human organism. For a short time like 2J^ min., records of 11,550 ft. -lb. per minute have been recorded, but usually 3,000 ft. -lb. per minute is too high for acceptable service. Performance of Men in Transporting Loads Horizontally (Rankine) Kind of exertion Load, lb. Velocity, ft.-sec. Hours per day Lb. con- veyed. 1 ft. per sec. Lb. con- veyed, 1 ft. per day 11. Walking, unloaded, transporting his own weight. 12. Wheeling load L in 2-whld. barrow, return un- loaded 13. Wheeling load L in 1-wh. barrow, return un- loaded 14. Traveling with burden 15. Carrying burden, returning unloaded 16. Carrying burden, for 30 sec. only I 140 5.0 10 700.0 224 m 10 373.0 132 m 10 220.0 90 2H 7 225.0 140 m 6 233.0 252 0.0 0.0 126 11.7 . . . 1,474.2 23.1 0.0 25,200,000 13,428,000 7,920,000 5,670,000 5,032,800 Coignet's apparatus was a hoist, in which dirt on one platform was lifted out of an excavation by the descent of laborers on a similar plat- form attached to rope passing over a pulley at the top. The laborers lifted their weight out of the excavation by climbing up ladders, and their descending weight over-balanced the material to be lifted. Brakes controlled the speed. Where weights are lifted by men hauling over pulleys, about 40 lb. is an average pull. Emerson states that to spade up a section of land would take an active man's energy for 500 years. With oil power tractors and gang plows three men can turn over 640 acres of land in 36 hr. It is good hard work to make a broad jump of 20 ft. at a speed of 10 miles an hour, 4 ENGINEERING OF POWER PLANTS rising 4 ft., from the ground, but aeroplanes at the international contest this year (1912) will fly 80 miles at a speed which may reach 110 miles an hour, and fly as easily at an altitude of 5,000 ft. as at 50. Formerly a man could carry a maximum load of 100 lb.; today his trains drag 6,000 tons and his ships carry 30,000 tons. As pointed out by Greenfield 1 "One of the serious objections to the use of man-energy for motive purposes lies in the impracticability of securing large amounts of power from even large groups of men. A little calculation will make this point clear: The power plant of a modern "department store" may contain, let us say, eight steam boilers with an aggregate capacity of some 4,800 hp. To produce 5,000 hp. by the use of men it would be necessary to employ 5,000 X 10 = 50,000 men, who are supposed to drive the electric generators, treadwheel fashion. Assigning a floor space of 2 ft. by 4 ft. to each man, these workers would require a total floor space of 50,000 X 8 = 400,000 sq. ft., which is about one-fifth of the total floor space in the Philadelphia store of John Wanamaker." This point will be more fully emphasized by the following problem. 1. The total indicated horsepower of the turbine steamer Mauretania is 70,000. If the average demand is 60 per cent, of her rated horsepower, how many men would be required for a trans-Atlantic trip if man-power were substituted for the turbines on this steamer? The most efficient way to use a man's effort is to have him lift his own weight, either by treadmill, tread-power or by using his weight as a counterpoise for the dead weight to be lifted. Here he does 4,000 ft. -lb. per minute as a counterweight or in treadmills, 3,000 ft.-lb. 2,600 to 2,750 ft.-lb. is a figure for use with a crank. A heavy flywheel (200-400 lb.) is very useful in machines for human motors to equalize the unequal effort in parts of the revolution where the man can exert but little power. All things considered a man seems to be most efficient for continued service when he works one-third of his day of 24 hr. at a speed of one- third of his maximum and exerts one-third of his maximum force. Animal Motors. — Work of Horses against a Known Resistance (Rankine) Kind of exertion Resist- If ^ ance, lb. ft ' P er sec. Hours per day Ft.-lb. ! Ft.-lb. per sec. per day 1. Cantering and trotting, drawing a light rail- [ way carriage (thoroughbred) 1 2. Horse drawing cart or boat, walking (draught- min. 22^ mean 30^ max. 50 120 100 66 } UH 3.6 3.0 6.5 .... 4 8 8 447J-S 432 300 429 6,444,000 12,441,600 3 Horse drawing a gin or mill, walking 8,640,000 4. Horse drawing a gin or mill, trotting 6,950,000 1 Cassiers Magazine, 1911, " Human Energy as a Motive Power" by B. S. Green- field. SOURCES OF ENERGY Kent states that the average power of a draught-horse, as given in line 2 of the above table, being 432 ft.-lb. per second, is 432/550 = 0.785 of the conventional value assigned by Watt to the ordinary unit of the rate of work of prime movers. It is the mean of several results of experiments, and may be considered the average of ordinary performance under favorable circumstances. Performance of Horses in Transporting Loads Horizontally (Rankine) Kind of exertion Load, lb. /elocity, Hours Trans- ft. per per port sec. day per sec. Transport per day 5. Walking with cart, always loaded 6. Trotting with cart, always loaded 7. Walking with cart, going loaded, returning empty; V, mean velocity 8. Carrying burden, walking 9. Carrying burden, trotting . . 1,500 3.6 10 5,400 750 7.2 m 5,400 1,500 2.0 10 3,000 270 3.6 10 972 180 7.2 7 1,296 194,400,000 87,480,000 108,000,000 34,992,000 32,659,200 This table has reference to conveyance on common roads only, and those evidently in bad order as respects the resistance to traction upon them. A horse towing or drawing at a walk will average a pull of 120 lb. at Z}/2 ft. per second or 2.3 miles per hour. At a trot the pull will be but 66 lb. at 6^ ft. per second. In a whin or gin at a brisk walk, or at 3 ft. per second, the pull will be about 100 lb. The curved track lowers the efficiency of the draft. Forty feet is the usual diameter of circle for large machines. In towing the average figures are: Miles per hour Hours per day Load in tons Miles per hour Hours per day Load in tons 2.5 11.5 520.0 6.0 2.0 30.0 3.0 8.0 243.0 7.0 1.5 19.0 3.5 5.9 153.0 8.0 1.12 13.0 4.0 4.5 102.0 9.0 0.75 9.0 5.0 2.9 52.0 10.0 0.55 6.3 In horse power or horse gears the slow speed of the motor requires multiplying mechanism for high-speed machinery. The losses here limit the field for these motors. Although the engine horsepower is 33,000 ft.-lb. per minute, the living horse does not keep this rate up all day. In pumping with horses the records are: 23,412 ft.-lb. per 8 hr. per day. 24,360 ft.-lb. per 6 hr. per day. 27,056 ft.-lb. per 4.5 hr. per day. 32,943 ft.-lb. per 3 hr. per day. 6 ENGINEERING OF POWER PLANTS The average is from 21,000 to 25,000 ft.-lb. per minute. Other animals used for draught purposes are the ox, the mule, the ass, the elephant, the reindeer and the dog. The ox-power is about 12,000 ft.-lb. per minute, the mule 10,000; the ass 3,500. Rankine favors two-thirds speed and same load for the ox as compared with the horse; for the mule one-half load and same velocity; for the ass one- quarter load and same velocity as for the horse. For transporting burdens the camel, the dromedary and the llama may be added to the list. The load of a freight camel is 550 lb. carried 30 miles per day for 4 days; for dromedary the load is 770 lb.; the llama, 110 lb. Animal motors are used in frontier or colonial conditions for farming and forest service; for crushing and grinding sugar, for cotton work, for sawing, pumping, irrigation, etc. 1 GRAVITY— ENERGY OF WIND AND WATER Windmills. 2 — Horizontal-shaft four-sailed windmills of the " Dutch" type have been used for many years. A- few vertical shaft wheels have also been used. These types, although efficient, were costly and hard to control and have been superseded by the " American" type which has spread over the entire globe. If P = wind pressure in pounds per square foot, V = wind velocity, miles per "hour, then from Stanton's ex- periments, P = 0.0036F 2 If W = work in foot-pounds per second, then for European mills of the Dutch type, W = 0.001 IF 3 (Coulomb) This value of W is likely to be higher than shown by average practice. For mills of the American type W = 0.00045 7 3 (Wolff) W = 0.000507 3 (Griffiths) 1 See A.S.M.E., vol. 14, p. 1014, paper by Thomas H. Briggs, "Haulage by Horses." 2 Note. — Among early experimenters the work of Smeaton and Coulomb stands out conspicuously. Excellent theoretical treatments will be found in "Windmills" by A. R. Wolff and in the Encyclopedia Britannica, 11th edition by W. C. Unwin. See also "Modern Tests" in Water Supply Papers Nos. 1 and 8, U. S. Geological Survey. For wind-pressure formulas, see Stanton in Proceedings I.C.E., vol. 156 and works of Eiffel and Hagen. SOURCES OF ENERGY If D = diameter of wheel in feet, hp. = horsepower, then hp. = D 2 7 3 853,000 <- -Pull-out Pole Fig. 1. The efficiency of modern wheels varies from 5 to 30 per cent., 10 to 18 per cent, representing standard practice. Much of the power is lost in the gearing. The best wind velocity is about 15 miles per hour, the useful range being from 10 to 20 miles. The best wheel diameter seems to be about 12 ft., although wheels s ENGINEERING OF POWER PLANTS from 8 to 16 ft. in diameter give excellent results; 80-ft. wheels have, however, been successfully used. A few wide blades are more efficient than many narrower ones. The vanes should not cover more than from 75 to 80 per cent, of the wheel area for best results and should never overlap. The governing of windmills is done almost entirely by putting the wheel into the plane of the wind. Certain foreign wheels govern by feathering the vanes and some American wheels by swinging sections of vanes into the plane of the wind. Windmills should be erected on towers or other elevated structures, but should not be set on hilltops or windy headlands. Reports of the U. S. Weather Bureau show that the useful hours (those with V between 10 and 20) are rarely over 3,000 per year in wooded locations, but in the Western plains and in certain favored localities in the East they may be much higher. Pumping is the best method of utilizing wind-power but many windmills are geared to run feed cutters and other agricultural machinery. Successful American manufacturers are reported by Wolff to be meeting the following guarantees. Capacity of Windmills. — Designa- tion of mill Vel. of wind, in miles per hour Revolu- tions of wheel per minute G 25 ft. allons of to 50 ft. water r an elev 75 ft. aised p< ation o' 100 ft. :r minu 150 ft. te 200 ft. Equiva- lent useful hp. de- veloped Average No. of hours per day during which this results will be obtained Wheel, ft. 16 16 16 16 16 16 16 16 70 to 75 60 to 65 55 to 60 50 to 55 45 to 50 40 to 45 35 to 40 30 to 35 6.162 19.179 33.941 45.139 64 . 600 97.682 124.950 212.581 3.016 0.04 0.12 0.21 0.28 0.41 0.61 0.78 1.34 8 10 9.563 6.638 4.750 8.485 11.246 16.150 24.421 31.248 49.725 8 12 14 16 18 20 25 17.952 22 . 569 31.654 52.165 63.750 106.964 11.851 15.304 19.542 32.513 40.800 71.604 5.680 7.807 9.771 17.485 19.284 37.349 4.998 8.075 12.211 15.938 26.741 8 8 8 8 8 8 In comparing Wolff's figures with those given by the formula it should be remembered that the values for horsepower as given in the table are overall horsepowers and include pump and pipe friction while the formula gives the horsepower available at the wheel shaft. For windmill economy, Wolff gives: SOURCES OF ENERGY 9 Economy of Windmills. — Gal. of water raised 25 ft. per hour Equiva- lent ac- tual useful hp. developed Avg. No. of hours per day during which this quantity will be raised Expenses for ictual useful power developed, in cents, per hour Desig- nation of mill For interest on 1st cost (1st cost including cost of wind- mill, pump and tower 5 per cent, per annum) For repairs and deprecia- tion (5 per cent, of 1st cost per annum) For atten- dance For oil Total Expense per hp., in cents, per hour Wheel, ft. m 370 0.04 8 0.25 0.25 0.06 0.04 0.60 15.0 10 1,151 0.12 8 0.30 0.30 0.06 0.04 0.70 5.8 12 2,036 0.21 8 0.36 0.36 0.06 0.04 0.82 5.9 14 2,708 0.28 8 0.75 0.75 0.06 0.07 1.63 5.8 16 3,876 0.41 8 1.15 1.15 0.06 0.07 2.43 5.9 18 5,861 0.61 8 1.35 1.35 0.06 0.07 2.83 4.6 20 7,497 0.79 8 1.70 1.70 0.06 0.10 3.56 4.5 25 12,743 1.34 8 2.05 2.05 0.06 0.10 4.26 3.2 Based on the figures quoted by Wolff in the fifth column the cost of the installations including windmill, pump and tower is approximately: Wheel, Cost, ft. $ 8.5 145 10.0 175 12.0 . . 210 14.0 -. 435 16.0 670 18.0 * 790 20.0 1,000 25.0 1,200 American Windmill and Tower Prices Diam., ft. Mill alone Tower Rated hp. Rated r.p.m. Weight machinery, lb. Price f.o.b., Chicago Height, ft. Weight, lb. Price f.o.b., Chicago Wooden mill. . 10 12 14 16 18 20 25 0.08 0.12 0.25 0.40 0.55 0.75 1.00 1.25 35 35 30 28 25 22 20 16 400 500 700 1,010 1,685 1,880 2,990 4,300 $28.50 33.00 42.00 75.00 114.00 128.00 194.00 352.00 20 30 40 40 40 40 40 40 203 500 950 1,300 1,450 1,450 2,935 2,935 $15.60 30.00 50.00 82.50 92.00 92.00 186.00 186.00 Steel mill 8 10 12 0.08 0.12 0.25 30 25 20 325 500 950 22.50 36.25 66.00 20 30 40 203 500 950 15.60 30.00 50.00 Steel mill 8 10 12 14 16 20 1.5-3 2-4 3-6 30.00 50.00 70.00 120.00 175.00 360.00 25 25 25 60 60 60 435 435 585 1,435 2,550 5,400 26.50 26.50 38.50 88.00 160.00 410.00 10 ENGINEERING OF POWER PLANTS Bulletin No. 105 of the North Dakota Agricultural Experiment Station contains a description of a 1.4-kw. electric light and power plant deriving its power from a 16-ft. aeromotor windmill on a 20-ft. wooden tower. In connection with the generator a 62-cell 40-amp.-hr., 110-volt Plante type storage battery is used. Cost of 16-ft. wheel, tower and governing pulley $200.00 Cost of house 35.00 Cost of dynamo 1.4 kw., 150 volts, 1,800 r.p.m 110.00 Cost of battery 550.00 Cost of switchboard 150 . 00 $1,045.00 Yearly charges: Interest, 6 per cent $62.70 Dep. 10 per cent 104.50 Attendance 12 . 80 Oil 5.00 Repairs $185.00 Year 1912 — kilowatt-hours at switchboard per year 3,300. Cost per kilowatt-hour = 5.6 cts. This wheel gave a maximum of 1,009 hp.-hr. in April and a minimum of 332 hp.-hr. in August. The two important factors in the success of this installation were the governor and an automatic regulator which cut the battery out and into the circuits as required. The attendance charged to the apparatus seems very small and the absence of repair charges is remarkable. Tide and Wave Motors. — Albert W. Stahl, U.S.N., finds 1 the energy of ocean waves to be as follows: Total Energy of Deep-sea Waves in Terms of Horsepower per Foot of Breadth Ratio of length Length of waves in feet height of waves 25 50 1 75 100 150 200 300 400 50 0.04 0.23 0.64 1.31 3.62 7.43 20.46 42.01 45 0.05 0.29 0.79 1.62 4.47 9.18 25.30 51.94 40 0.06 0.36 1.00 2.05 5.65 11.59 31.95 65.58 35 0.08 0.47 1.30 2.68 7.37 15.14 41.72 85.63 30 0.12 0.64 1.77 3.64 10.02 20.57 56.70 116.38 25 0.16 0.90 2.49 5.23 14.40 29.56 80.85 167.22 20 0.25 1.44 3.96 8.13 21.79 45.98 126.70 260.08 15 0.42 2.83 6.97 14.31 39.43 80.94 223.06 457.89 10 0.98 5.53 15.24 31.29 86.22 177.00 487.75 1,001.25 5 3.30 18.68 51.48 105.68 291.20 597.78 1,647.31 3,381.60 1 See "The Utilization of the Power of Ocean Waves," Transactions A.S.M.E., vol. 13, p. 438. SOURCES OF ENERGY 11 Commenting on the practical utilization of this form of energy he divides the subject into: 1. The various motions of the water which may be utilized for power purposes. 2. The wave-motor proper — that is, the portion of the apparatus in direct contact with the water, and receiving and transmitting the energy thereof; together with the mechanism for transmitting this energy to the pumping or other suitable machinery for utilizing the same. 3. Regulating devices, for obtaining a uniform motion from the more or less irregular and variable action of the waves, as well as for adjusting the apparatus to the state of the tide and condition of the sea. 4. Storage arrangements for ensuring a continuous and uniform output of power during a calm or when the waves are comparatively small. Taking up first the consideration of the motions that may be utilized for power purposes, we find the following: 1. Vertical rise and fall of particles at and near the surface. 2. Horizontal to-and-fro motion of particles at and near the surface. 3. Varying slope of surface of wave. 4. Impetus of waves rolling up the beach in the form of breakers. 5. Motion of distorted verticals. Mr. Stahl further states: "Possibly none of the methods described in this paper may ever prove com- mercially successful; indeed the problem may not be susceptible of a financially successful solution. My own investigations, however, so far as I have yet been able to carry them, incline me to the belief that wave-power can and will be utilized on a paying basis." Wave motors are of two forms, the paddle type and the float type. In the former the paddle swings backward and forward with the wave motion, moving a shaft or pair of shafts by rachets. In the latter a heavy- float is lifted by the waves and in falling drives a shaft by means of rachets. Many attempts in this direction have been made but no successful machine has been developed that can withstand the tremendous power of severe storms. A float-type motor erected near Los Angeles, Cal., developing suffi- cient power for about 30 incandescent electric lights, withstood the storms for one year. In this locality the waves, though high are regular. A storage battery was used for storing the energy developed during the day. There are several tide mill ponds along the Connecticut and New York shores. One such pond at Stamford is reported to have an area of some 10,000,000 sq. ft. One writer on the subject estimates that about 50 hp.-hr. can be realized per million square feet of pond area. 12 ENGINEERING OF POWER PLANTS A plant that attracted much attention at the time of its construction is the hydraulic air compressor of the Rockland Power Co., Rockland, Maine. • The plant is described as follows: "The plant consists of two basins, a high- and a low-water one, as in the Decoeur system. Each basin has an area of 1 sq. mile and there is a tide of 10 ft. From the high-water basin a 15-ft. shaft extends vertically downward for 203 ft., and then is connected by a horizontal tunnel to a 35-ft. shaft extending upward to the low-water tank. At the top of the down-flow shaft there are 1 ,500 half -inch air inlet tubes, through which air is drawn into the water and carried to the bottom of the shaft. The air separates at the bottom and accumulates in an air chamber while the water flows up the larger shaft to the low-water tank. The air is under a head of water of 195 ft. and is piped to the surface through a 14-in. pipe which joins a 30-in. main. This apparatus develops 5,000 hp. and has an efficiency of 75 per cent. It has no moving parts to break or get out of order. Air compressed by this method is very dry, being about three times as dry as the atmosphere and this is a decided advantage as the pipe resistance of dry air is very low and velocities as high as 70 ft. per second may be used. Dry air also can be used cold for expansion purposes and will not freeze. As an actual test an 80-hp. Corliss engine was run for 10 hr. on this air, the admission temperature being 5.3°F. and the exhaust — 40°F. After the run there was no trace of frost in the exhaust port or passage. The only cost in connection with the operation of this compressor is the salary of a watchman to keep ice, timber, etc., from entering the inlet shaft. The construction cost of this particular plant amounted to about $100 per horsepower. Each basin of 1 acre area and with a tide of 9 ft. can produce about 5 hp. A basin with an area of 200 acres and so located that it would not require more than 3 ft. of dam per acre would be a commercial success if de- veloped into an air-compressing plant." Apparently the most successful tide machines have taken advantage of the rising tide for storing water in tanks or basins from which it is passed through waterwheels or turbines. Solar Engines. 1 — Using HerschelFs data, Ericsson about 1870 esti- mated the direct heat energy of the sun in 45° latitude to be equivalent to 13,000,000 hp. per square mile. Buchanan in Egypt in 1882 by means of better apparatus recorded the extremely high rate of 3,245 B.t.u. per square foot per minute, which is equivalent to 214,000,000 hp. per square mile. Solar engines are not direct in their action, but use steam as an intermediary. The main interest is, therefore, in the boiler. Monehart's apparatus, exhibited in Paris in 1878, consisted of a conical mirror 112 in. in diameter, which concentrated the sun's rays on a boiler containing about 44 lb. of water. With 45 sq. ft. of reflecting surface he succeeded in evaporating 11 lb. of water from a feed tem- perature of 68°F. into steam at 75 lb. pressure. 1 See Engineering News, May 13, 1909 and Nov. 17, 1910. SOURCES OF ENERGY 13 Ericsson's apparatus consisted of a parabolic mirror 11 by 16 ft. which concentrated the sun's rays on a boiler 6J4 in. in diameter and 11 ft. long. This machine, erected in New York in 1883, developed about 3.25 hp. in a 6-in. diameter by 8-in. stroke engine. The steam was evaporated at 20 lb. gage pressure. A good condenser was used with this plant. Many similar machines have been built with varying success. Most of these machines were mounted on equatorial mountings and were swung to meet the sun but fixed boilers or rather evaporators have been proposed. Shuman in 1907 built at Tacony, Pa., an experimental plant, each unit of which consisted of a sheet-iron boiler 3 ft. square with a Fig. 2. — Original Shuman sun power plant, Aug., 1907, Tacony, Pa. water space % in. wide. This is placed on a table with a mirror on each side. The plant contained 26 banks of 22 units each, a total of 5,000 sq. ft. of boilers and 5,300 sq. ft. of mirrors, 10,300 sq. ft. in all. 4,800 lb. of water were evaporated in 8 hr. of sunshine at atmospheric pressure. A special engine was designed to work under this low range of pressures and from 20 to 32 hp. was developed. This plant was tested by Prof. R. C. Carpenter (see Engineer, London, July 5, 1912). Later Shuman in his plant at Meadi, Cairo, Egypt, went back to the moving parabolic mirrors with a 15-in. wide flat cast-iron boiler in the focus. This plant has five reflectors 204 ft. long, 13^ in. wide with a thermostat control to keep the axis in the sun's plane. The total re- flecting surface is 19,000 sq. ft, This plant averages 1,100 lb. of steam evaporated per hour for 10-hr. day. The engine at Tacony was a 24 by 24-in. special engine with extra large exhaust valves running 12-150 r.p.m. The Cairo engine was a 14 ENGINEERING OF POWER PLANTS 36 by 36-in. running at 110 r.p.m. The Cairo plant cost, exclusive of land, $7,600 or $140 per brake horsepower. Shuman figures that sun-power is economical in Egypt when coal costs more than $2.40 per ton. In the Shuman invention a tract of land is rolled level, forming a shallow trough. This is lined with asphaltum pitch and covered with about 3 in. of water. Over the water about }/§ in. of paraffine is flowed, leaving between this and a glass cover about 6 in. of dead air space. It is estimated that a power plant of this type to cover a heat-absorption area of 160,000 sq. ft., or nearly 4 acres, would develop about 1,000 hp. Provision is made for storing hot water in excess of the requirements of a low-pressure turbine during the day, to be utilized for running the turbine during the period when there is no absorption of heat. The heated water is run from the heat absorber to the storage tank, thence to the turbine, through a condenser and back to the heat absorber. The water enters the thermally insulated storage tank, or the turbine, at about 202°F. With a vacuum of 28 in. in the condenser, the boiling point of the water is reduced to 102°, and as it enters the turbine nearly 10 per cent, explodes into steam. Mr. Shuman estimates that a 1,000-hp. plant built upon his plan would cost about $40,000. Willsie's plant at the Needles, Cal., built in 1908-09, utilizes the sun's heat to vaporize sulphur dioxide through the medium of water heated in a pipe coil encased in glass. His apparatus developed 20 net hp. He figures his apparatus to cost as follows: 400-hp. plant, per horsepower Solar heater $100.00 Heat storage plant (100 hr.) 10.00 Engine and pumps 20 . 00 SO2 vaporizers 15 . 00 Condenser 15 . 00 Emergency boiler 2 . 75 S0 2 1.25 $164.00 Operating cost per horsepower-hour Interest dep., etc . 19 Labor 0.27 Supplies 0.15 0.61 cts. Willsie compares the cost per horsepower-hour in a 400-hp., steam-electric and solar-electric power plant, and finds that the steam plant would have to obtain its coal for $0.66 a ton to compete with the sun-power plant in districts favorable to the latter. SOURCES OF ENERGY 15 The following table presents a brief summary of the development of the sun motor to date. Year Inventor Location Reflecting surface, sq. ft. Water evaporated per hour, lb. Square foot of reflect- ing surface per pound of evaporation 1878 Mouchot Paris 45 11 4.09 1883 Ericsson New York 162 * 1911? Shuman Tacony 10,300 600 17.16 1913 Shuman Cairo 19,000 1,100 17.28 * 3.25 hp. developed in engine. The efficiency of the evaporative apparatus depends on the quality of the heat insulation. Ericsson's plant was much better in this regard than any of the others. Shuman's Tacony plant was nearly twice as good as the Cairo plant but was more costly. All modern plants use the steam at or near the atmospheric pressure and must have plenty of condensing water for the vacuum. It would appear that the turbine is the best form of apparatus to use steam between these limits. Prof. Fessenden's proposition (see British Association Adv. Science, 1912) including windmills, turbines, a 1,000-ft. well, exhaust turbines and flat solar heaters, has not as yet been experimentally tried. Energy of Fuel. — In coal and other fuels an enormous capacity for doing work is stored in very compact bulk. It is liberated from the fuel gradually as required, and the limits of the available quantity have not yet been reached, although the time limit on anthracite coal and possibly other fuels appears to be close at hand. Such fuels are to be had in nearly all regions and where they are not native they are easily transported. If desired the energy resident in them can be transported in the form of gas to the place where it is to be used. It should not be forgotten that but a very small percentage of the heat energy in the fuel is actually converted into useful work at the machine. Roughly, if the fuel be used in a steam plant, 30 per cent, of the heat is lost by radiation and up the stack. Of the possible 70 per cent, that goes to the engine, nearly 90 per cent, is carried away by the condensing water or dissipated in the exhaust. Of the 10 per cent, or less converted into work a portion is used in overcoming friction, so that the useful work at the machine or busbars represents, in efficient steam plants, between 5 per cent, and 10 per cent, of the heat energy of the fuel thrown into the furnace under the boiler. In the latest large unit installations efficiencies of 17 and 18 per cent, have been reached, but these are very exceptional. 16 ENGINEERING OF POWER PLANTS Similar losses, although not necessarily of the same magnitude are evident in all present methods of power development from fuel. Analysis of Development in a Power Plant. — Hutton states that in the typical power plant there are five steps: 1. Generation or liberation of the stored or accumulated energy. 2. The storage or accumulation of the energy of heat thus liberated from the fuel in a suitable vessel or reservoir from which it can be drawn off as required. (In the steam plant this is the boiler.) 3. The appliance whereby the energy stored in the boiler as potential energy is transformed into actual energy by being made to exert force through a pre- scribed path under the control of capable intelligence. (This is the engine.) 4. The controlled force acting through the controlled space or path is to be transmitted from the engine or prime mover to the machine or apparatus which is to be driven. (This gives rise to mechanism and transmission machinery.) 5. The industrial work of manufacturing, propelling or whatever may be the function of the generated power, is the last link in the chain. In water-power plants the liberation or storage of energy is done for the engineer before his work begins. This is also true of the windmill motor. In the gas, hot-air, or direct-combustion engine there is no storage step in the process, but the energy must be utilized as fast as it is released. On the other hand, for the gas-engine plant which produces its own gas there is a step of accumulation of energy which is lacking when solid fuel is burned directly under the boiler. D. B. Rushmore has estimated the amount of power used in the United States as follows: Horsepower Horses and mules 25,000,000 Automobiles 25,000,000 Steam and naval vessels 5,000,000 Steam railroads 50,000,000 Irrigation 500,000 Mines and quarries 6,000,000 Flour, grist and saw mills 1,250,000 Manufactures 25,000,000 Central stations 8,000,000 Isolated plants 4,250,000 Electric railways 4,000,000 Total 154,000,000 Excluding the first four divisions, it is evident that about 49,000,000 hp. are used in the ordinary manufacturing, heating, lighting and electric railway business. Of this power at least 25,000,000 hp. or over 50 per cent, is used in the form of electric energy. It is probable that nearly SOURCES OF ENERGY 17 30,000,000 hp. are produced by steam; 12,000,000 hp. by water and about 7,000,000 hp. by gas or oil motors. The transmission of power in its various fields of electrical trans- mission, compressed air, high-pressure water, shafting, belting, gearing or linkage is an extensive subject in itself, but will be touched upon briefly later in these notes. Although the reciprocating steam engine may be regarded by many as obsolescent, it holds an important place in power production. Its mechanism and method of operation are better known by the average engineer than those of the more recent forms of prime movers. It is, therefore, used in these notes as a basis for the development of the essential principles of a power plant. CHAPTER II THE STEAM ENGINE Horsepower of a Cylinder. — Let P = pressure on piston in lb. per square inch. = mean effective pressure (m.e.p.). L = length of stroke in feet. A = area of piston in square inches. N = number times per minute that piston is acted upon by the then hp. = pressure. PLAN 33,000 " Fig. 3. — Simple slide-valve engine, throttling governor. In an engine once constructed A and L are fixed or constant and the factor 33,000 is constant. If then K denotes the fraction -Q— oo,U0u the hp. formula may be written hp. = PNK in which K is called the engine constant. It is not necessary that the piston travel back and forth in a straight . 18- THE STEAM ENGINE 19 line, as in reciprocating engines, although this is the common type. When the piston or area receiving the steam pressure travels in a circular path continuously in the same direction the engine is called a rotary steam engine. The following handy rule is given for estimating the horsepower of a single-cylinder engine. Square the diameter and divide by 2. This is correct whenever the product of the mean effective pressure and the piston speed (in feet per minute) = 21,000. viz., whenm.e.p. = 30 and S = 700. m.e.p. = 33 and S = 600. m.e.p. = 38 and S = 550. m.e.p. = 42 and S = 500. Fig. 4. — Simple steam engine. These conditions correspond to those of ordinary practice with both Corliss and shaft-governor high-speed engines. Essential Parts of a Reciprocating Steam Engine. — The crank and connecting rod are used almost universally for converting reciprocating into rotary motion. The piston traverse in the cylinder = 2 X the effective length of the crank. Length of Typical Reciprocating Engine. — Between head end and crankpin the length is made up of: (a) Cylinder = two cranks. (6) Piston rod = two cranks. (c) Connecting rod = six cranks (four to eight). (d) All allowances for stuffing-box, cylinder heads, metal in piston, crosshead, etc. 20 ENGINEERING OF POWER PLANTS Total = something over ten cranks. The oscillating engine, having no connecting rod, is only about four cranks long. The trunk engine, having no piston rod, is about five cranks long. Engines 1 Classified by Position of Cylinder Axis. — (a) Horizontal; (6) Vertical; (c) Inclined. — Horizontal engines are most usual and cheap- est where room or floor space is not limited. Horizontal Engines. — Advantages. — 1. Cheapness. 2. Convenience of access from ground level to all parts. 3. Weight distributed over large area for support. Fig. 5. — Simple Corliss engine. Disadvantages. - 1. Action of gravity adds to friction. Bad for stuffing-boxes. Piston springs often necessary. 2. Tendency of cylinder to wear oval. Vertical Engines. — Advantages. — 1. Diminished ground area. 2. Avoidance of cylinder friction and unequal wear. 3. Require very little cylinder oil. The small ground-area requirement has made vertical engines prac- 1 Much of the descriptive material relating to steam engines is from "The Mechanical Engineering of Power Plants," by F. R. Hutton, John Wiley & Sons, 1908. THE STEAM ENGINE 21 tically universal for screw-propelled ships, which are deep-water vessels, and in crowded power plants in cities where ground is costly. Disadvantages . — 1. Effort on crankpin is greater when weight of mechanism is acting downward with gravity. This must be counteracted to prevent unequal effort on crankpin and irregular speed. Three methods for accomplishing this are used: (a) counterweighting the crank on the side opposite the reciprocating parts; (b) steam cylinders so calculated as to balance ; (c) by steam distribution to the two ends of the cylinder. Fig. 6. — Cross-compound vertical reversing engine. 2. In large engines the different parts are on different levels, or stories, increasing the number of men required to handle or superintend them. Beam Engines. — Advantages. — 1. Steam cylinder can be vertical. 2. Cylinder and its weight can be kept low down and shaft may also be directly attached to bedplate near the foundation. 3. Long stroke for piston is possible and yet not too much space in ground plan consumed. Great advantage in side- 22 ENGINEERING OF POWER PLANTS wheel practice and pumping. R.p.m. may be kept low but piston speed high. 4. Flexibility in alignment of cylinder axis in relation to shaft axis. 5. Where there are several working cylinders, the beam makes easy means of operating them. Some cylinders vertical, others inclined, etc. Disadvantages. — 1. Too many joints. 2. Weight of beam so far above the center of gravity of the hull. Fig. 7. — Compound beam pumping engine. 3. In warships, vulnerable part exposed. Destruction of this part fatal. This consideration resulted in the back-acting beam type. Classicatfiion of Engines by Their Use of Steam. — A. High-speed, low-speed, and moderate speed of rotation. B. Single- and double-acting. (7. Expansive and non-expansive. D. Condensing and non-condensing. E. Simple, compound or multiple expansion. THE STEAM ENGINE 23 High-speed Engines. — Consequences of high rotative speed are: 1. Small cylinder volume. 2. Item 1 means engine light in weight. 3. Short length of cylinder means a small crankarm, short connecting rod, and an engine short in length. 4. Variations of either effort or resistance are more promptly met and less noticeable as compared with mean effort or resistance of any given minute. 5. Regulating mechanism tends to equalize effort and re- sistance in less interval of time than with slower types. 6. Decrease in economy with use, as valves cannot be kept tight. Low-speed Engines. — Limitations of speed are often imposed by the resistance to be overcome. This condition is met in pumping engines, blowing engines, paddle-wheel engine, marine engines, etc. It is possible to secure a large product of L X N by making L large when N is small. Engines not making over 125, r.p.m. are classed as low-speed. Advantages of Low-speed are the Disadvantages of High. — 1. Rapid alternating of admission and compression of steam through ports to cylinder of high-speed engine compel large port areas. 2. Rapid motion of piston compels generous clearance allow- ance at each end between piston and cylinder heads. 3. Wear per unit of surface greater in short stroke. 4. Heating and abrasive wear goes on rapidly, resulting in possible increase in expense for maintenance and repairs in high-speed engines. 5. Lubrication compelled to be generous to the point of waste- fulness in high-speed engines. 6. The above five conditions compel a standard of workman- ship in fitting, alignment, provisions for wear, etc., which make high-speed engines costly to build and successful only when well made. Piston Speed as Distinguished from Rotative Speed. — Piston speed in feet per minute = L X N, Less than 500 ft. per minute = low speed. 600 to 800 ft. per minute = moderate speed. Above 900 ft. per minute = high speed. As may readily be understood a low rotative speed engine does not necessarily have a low piston speed, as for example, an 18 by 48 Corliss engine making 85 r.p.m. Piston speeds as high as 1,400 ft. have been used. 24 ENGINEERING OF POWER PLANTS Single- and Double-acting Engine. — The single-acting engine takes steam on one side of the piston only. In the vertical engine of this type, the steam acts with gravity and in one direction only. This results in: (a) Silent running at high speeds. (6) Less danger of overheated bearings. Fig. 8. — Westinghouse single-acting engine. Single-acting vertical steam engines are usually made with twin cylinders. This construction gives a simple inexpensive engine. Although a few such types are still on the market, reduction of space occupied per horsepower of output and greater uniformity of turning moment on the crankpin have led to the general adoption of the double- acting principle. Expansive and Non-expansive Engines. — If steam is allowed to enter the cylinder at full boiler pressure during the entire stroke and is, at the end of the stroke, exhausted at this same pressure, the effort upon the THE STEAM ENGINE 25 piston has been constant and the steam has been used in the cylinder non-expansively. If, however, advantage is taken of the elastic quality of steam, it may be admitted to the cylinder at full boiler pressure for a portion of the stroke only and then allowed to expand during the remainder of the stroke. Under these conditions, the effort upon the piston decreases from the moment the steam supply to the cylinder is shut off until the end of the stroke. Single-cylinder direct-acting pumps and many elevator engines use steam non-expansively, but the majority of power-plant engines take advantage of the greater economy secured by operating expansively. Thermal Efficiencies. — The increase in the theoretical thermal efficiency by operating expansively and by condensing is readily seen by an examination of the following figures. If Ti = absolute temperature of steam entering the cylinder. T2 = absolute temperature of steam leaving the cylinder. Then T x -T 2 efficiency T, = efficiency of " ideal" or Carnot cycle. Steam-engine Efficiency Gage pressure, lb. Absolute pressure, lb. °F. = t °F. abs. = T -13 2 126 586 1 16 216 676 100 115 338 798 114 129 347 807 150 165 366 826 200 215 388 848 798 - 676 122 798 807 - 676 807 798 - 586 798 826 - 676 826 848 - 676 848 826 - 586 826 798 131 807 212 798 150 826 172 848 240 826 = 15.3 per cent, efficiency between 115 and 16 lb. abs. = 16.3 per cent, efficiency between 129 and 16 lb. abs. = 26.6 per cent, efficiency between 115 and 2 lb. abs. = 18.2 per cent, efficiency between 165 and 16 lb. abs. = 20.3 per cent, efficiency between 215 and 16 lb. abs. = 29.0 per cent, efficiency between 165 and 2 lb. abs. 26 ENGINEERING OF POWER PLANTS The steam engine cannot approach this "ideal" or Carnot cycle. On this account it is customary to compare the thermal efficiency of the actual engine with a modified cycle known as the Rankine cycle with complete expansion. The outline of this comparison is as follows : Actual cycle where ab = abedefa. steam admission. be c de = expansion. = point of release. = exhaust stroke. ef = compression. A B HT *V\ f D \ 'j ^^^ oy = Pressure Axis ^^^e ox = YoJume Axis \f |Z> 2 ^^>j^ ■ v a 2=^(7 O V\ = Steam Line Pressure P2= Condenser or Exhaust Line Pressure Fig. 9. Rankine cycle with complete expansion (also called Clausius cycle) = ABCD. Where AB BC CD DA steam admission, complete adiabatic pressure, exhaust stroke, a constant-volume pressure rise. expansion down to condenser The thermal efficiency of the Rankine cycle (E R ) is the ratio of the heat changed into work per pound of steam if expanded adiabatically (#i - H 2 ) to the heat necessary to raise feed water from the temperature of exhaust to the temperature in the boiler and evaporate it (H l - q 2 ), or E R = H 1 -H. ; where Hi = total heat per pound of steam at pressure p x . H 2 = total heat per pound of steam at pressure p 2 after adiabatic expansion from pressure p lm q 2 = heat of the liquid at pressure p 2 . The thermal efficiency of an actual steam engine (E A ) may be expressed as the ratio of the heat actually delivered as work per pound THE STEAM ENGINE 27 of steam to the heat supplied per pound, measured above the heat of the liquid at the exhaust pressure. The heat equivalent of 1 hp.-hr. is 2 545 2,545 B.t.u. Then ' w is the heat equivalent of the useful work ob- tained per pound of steam, W being the pounds of steam supplied 2 545 per horsepower-hour. Therefore, the thermal efficiency = W /u \* Efficiency ratio is a term expressing the ratio between the thermal efficiency of the actual engine and the thermal efficiency of the ideal engine operating on the Rankine cycle with complete expansion between the same pressure limits. Its value will then be the ratio of E^ to E R , or Efficiency ratio = «- 2,545 ^ ffi - H 2 ~ W(H 1 - q 2 ) : H l -q 2 2,545 ~ W(Hi - H 2 ) Example. — Determine (a) the thermal efficiency, (6) the Rankine cycle efficiency, and (c) the efficiency ratio of a condensing engine operating with an economy of 13 lb. of dry saturated steam per horse- power-hour, initial pressure 140 lb. absolute, exhaust pressure 2 lb. absolute. (a) Hi = 1,192.2 (from steam tables). q 2 = 94.0 (from steam tables). 2 545 195 8 Thermal efficiency = io/i iq o 2 — Q4^ = 1 OQft o = 0-178 = 17.8 per cent. (6) Hi = 1,192.2 (from steam tables). H 2 = 914 (by use of total heat — entropy or "Mollier" diagram). q 2 = 94 (from steam tables). i™= • *t> i- 1 1,192.2-914 278.2 A oe „ Efficiency 01 Rankine cycle = ., ., no n ttt = -, r>r>o r> = 0.257 = 25.7 J J 1,192.2 — 94 1,098.2 per cent. f\W 4.' 2 > 545 195 ' 8 n *nr (c) Efficiency ratio = 13(M92 . 2 _ 9 14) = 27^2 = °' 695 or from above = ttt = »' „ = 0.695. (0) 0.257 Condensing and Non-condensing Engines. — Advantages of the Condensing Type. 1. With cylinder of given area, stroke, and piston speed the net effective pressure is greater than in non-condensing engines. 28 ENGINEERING OF POWER PLANTS Fig. 10. — 24 and 38 X 48 cross-compound engine Allis-Chalmers Co. Fig. 11. — Section of high-speed compound engine. THE STEAM ENGINE 29 . 2. Another way of putting it is, same power can be secured by a smaller cylinder with the condensing type. 3. Less volume of steam drawn from boiler per stroke, there- fore less coal required per horsepower-hour. 4. Due to more complete expansion the condensing engine utilizes the heat imparted to the steam by the fuel more per- fectly than the non-condensing. 5. Efficiency. T 2 might be brought to about 60°F., the ordinary temperature of the cooling water, but it is not often convenient to use so much water, or the cost is prohibitive; Fig. 12. — Armington & Sims tandem compound high-speed engine. consequently the temperature is usually about 100° to 130°F. In non-condensing plant, T 2 will be 212°F. or over. Hence the efficiency for the condensing engine is greater. 6. Condensing engine preheats the water to be fed to boiler. This saves fuel and is of advantage to the boiler. Disadvantages of the Condensing Type. — 1. Low final temperature increases condensation in cylinder thereby reducing economy. 30 ENGINEERING OF POWER PLANTS 2. Vacuum must be maintained. Engine must do work to accomplish this. Usually circulating water must also be handled. 3. Oil in condensed steam troublesome. Often has to be removed to prevent boiler troubles and clogging of passages. 4. Cannot be used where circulating water is expensive. Fig. 13. — Section of una-flow engine cylinder. Una-flow Engines. — An attempt has been made to combine the advantages of the single-acting engine with those of the double-acting engine by Professor Stumpf , whose una-flow engine is a first-class example of good theory coupled with clever design. The cylinder of this engine is practically twice as long as the ordinary engine cylinder, and the depth of the piston is the stroke of the piston minus the width of the Boiler Pressure Boiler Pressure Fig. 14. Absolute Vacuum Absolute Vacuum -Indicator cards from non-condensing and condensing una-flow engines. exhaust ports which are located circumferentially around the center line of the travel of the piston. The admission valves are double-beat poppet valves, located in the cylinder heads. By this construction many of the disadvantages of the double-acting engine are overcome and the good results of the single-acting cylinder are also obtained. Another result of this construction, the ability to carry out the expansion very much further is an advantage of this design. It is possible to expand the steam as fully and as economically in one of these cylinders THE STEAM ENGINE 31 as in the two cylinders of the ordinary compound engine. 1 As the steam upon exhausting does not come into contact with the admission ports relatively high-cylinder wall temperatures are maintained at the admission ends of the cylinder, thus materially reducing cylinder con- densation. High superheats and high vacuums can be readily taken care of and guarantees as low as 8.8 lb. of steam per indicated horsepower- hour have been made by German builders. Fig. 15. — Tandem compound Corliss engine. Compound and Multiple -expansion Engines. — Advantages. — 1. High expansion and greater difference between initial and final temperature in steam is secured with admission through a longer portion of stroke. Also more favorable crank angles. 2. Greater expansion means higher possible boiler pressure. 3. Strain on mechanism less by receiving high pressure on smaller piston area. 4. More advantageous arrangement for admitting and cutting off steam. 5. Any leakage past valves in high-pressure cylinder goes to low-pressure cylinder and not to waste. 6. Condensation in high-pressure cylinder evaporates and does work in low. 1 Full details and tests of this construction may be found in Prof. Stumpf's book, "The Una-flow Steam Engine," published by the D. Van Nostrand Co., New York. 32 ENGINEERING OF POWER PLANTS 7. When so arranged that the several engines have independ- ent crankpins there is an advantage both in size of pin and in crank effort. 8. With cranks quartering or at the proper angles turning effort is equalized thus diminishing weight of flywheel. 9. With reheater the quality of steam may be improved during expansion. 10. Hottest steam in smallest cylinder, thus reducing loss. 11. Range of temperature between initial and final states of each cylinder is less than it would be if expansion were in one cylinder only. Disadvantages. — 1. Cost of cylinders, other than low. 2. Additional weight and bulk. 3. Friction loss of extra cylinder and valve-chest. 4. Difficulties in governing. 5. Danger of water in low-pressure cylinder, especially trouble- some in locomotives. Throttling and Cut-off Engines. — Advantages of Throttling. — 1. Engine cheap to build and buy. 2. Steam pressure exerted through considerable portion of stroke, hence less inequality in steam effort at beginning and end of stroke. 3. Throttling effect has a tendency to dry out moisture in steam and to diminish moisture in cylinder. Disadvantages of Throttling. — 1. Not as sensitive as cut-off engine to instantaneous varia- tion in the resistance. 2. Does not regulate as closely to speed as cut-off type. 3. Exhaust usually at higher pressure than in cut-off, causing rejection of more heat. Advantages of Cut-off Engine. — 1. Effort controlled per stroke of engine. 2. Engine sensitive immediately to variations in resistance. 3. More certain to be kept at uniform speed by governor. 4. Full boiler pressure exerted on piston until cut-off. 5. Full advantage from expansive working. THE STEAM ENGINE 33 Disadvantages . — 1. Wide difference of effort at two ends of stroke requiring massive flywheel. 2. Design and complication of valve-gear. 3. Engine costly to build and buy. 4. Cylinder condensation increased by lower terminal pressure and temperatures. For many classes of work in power-house service variations are so wide that automatic cut-off is essential. Where effort is constant, as Fig. 16. — Nordberg four-cylinder steam hoisting engine. Calumet & Arizona Mining Co. in pumping, in railway and in marine practice, throttling is close enough, especially when the engine driver has to be in constant attendance. The automatic cut-off is usually more economical, and the engine is usually better built. When desirable to cut off later than one-third stroke there is little gain in carrying boiler pressure much higher than 80 lb. gage. For simple engines the steam pressure is seldom above 80 lb. gage, but for compound it ranges from 80 to 250 lb. 3 34 ENGINEERING OF POWER PLANTS Fig. 17. — Manhattan type duplex cross-compound engine. Subway Power House, New York. (fas) Fig. 18. — Size and types of portable engines. THE STEAM ENGINE 35 Triple- and quadruple-expansion engines are used little save for pumping and for marine work. The steam pressure for these engines usually runs from 125 to 250 lb. Special Classification. — 1st. Stationary; 2d Traction; 3d Marine. — The first is subdivided into: (a) Factory or mill, including power-house; (6) Pumping engines, including blowing engines and air compressors; (c) Hoisting engines; (d) Locomobiles; (e) Miscellaneous engines. The second is subdivided into: (a) Locomotives, traction engines, including road-rollers and self-propelled steam fire engines, auto trucks and automobiles and agricultural engines. The third consists of engines for marine service. Fig. 19. — Nordberg poppet-valve engine, tandem compound. Rotary Steam Engines. — Advantages. — 1. Effort of steam applied directly to produce rotary motion. 2. No reciprocating parts, therefore no inertia effects. 3. No dead centers. 4. Absence of reciprocating parts makes it easy to run at high speed. 5. Very compact. Occupies little room. 6. Either no valve gearing, or very simple if any. 7. Cheap to build. Should be cheap to buy. 8. No reciprocating rods or dead centers, hence condensed steam in cylinder does no harm. 9. Increased construction and item 8 adapt it to outdoor service. 10. No skill required to handle it. 36 ENGINEERING OF POWER PLANTS Disadvantages. — 1. Difficulty of satisfactorily packing surfaces which do not move through equal spaces in equal times. 2. Expense connected with proper lubrication. If efficiently lubricated they consume an excessive amount of oil. 3. Excessive waste space to be filled with steam each revolu- tion. 4. In simple type, non-expansive. This coupled with items 1 and 2 make it uneconomical. Fig. 20. — Section of Herrick rotary engine. 5. Difficult to design for large horsepowers. Structure becomes inconvenient the moment large areas are desired in order to make P X A large. Difficult to secure high-piston speed in feet per minute without making the engine excessively large. Economy may be secured by arranging in series upon a shaft, so that the steam rejected from No. 1 drives No. 2 of larger volume. Few if any rotary engines have been commercially successful. In view of this fact it may be well to record the general data for a rotary engine tested by one of the authors. THE STEAM ENGINE 37 38 ENGINEERING OF POWER PLANTS Fig. 22. — Section of Nordberg poppet-valve engine cylinder. Fig. 23. — Oscillating marine steam engine, section through air pump. THE STEAM ENGINE 39 1. The simple steam motor of 20-b.hp. rating occupied only approxi- mately 12 cu. ft. of space overall. 2. The motor which was under load for 5 hr. continuously showed no indications of heating or variations in uniformity of action. Its speed regulation for varying loads was remarkable. 3. The steam consumption of this unit was exceptional, clearly sur- passing the corresponding consumption of the average reciprocating unit of similar capacity. 4. After one year of service this rotary engine showed an increased steam consumption per brake horsepower-hour of only 4.6 per cent. STEAM TURBINES Basic Principles. — The steam turbine, like the water turbine, utilizes the kinetic energy of fluid in motion. Whenever a moving fluid impinges on moving vanes which change the direction of flow and reduce the velocity of the fluid, the energy of the fluid is converted into mechanical work and is available through the shaft on which the moving vanes are placed. Differences between Steam and Water Turbines. — There are two important distinctions between steam and water turbines. First, pro- vision must be made in the steam turbine for converting the heat energy of the steam into kinetic energy or the energy of motion. To accomplish this the steam turbine is furnished with nozzles so designed as to control the expansion of the steam in a way to augment its velocity. These nozzles are of two types, diverging and converging. Where the drop of pressure is large the diverging nozzle is used. In this nozzle the walls diverge in the direction of the flow of the steam, so that its outlet area is larger than its inlet area. Where the drop of pressure is smaller the converging nozzle is used. These nozzles differ from the nozzle of the water turbine in that they perform two functions, they not only direct the flow of steam, but they assist in the necessary expansion re- quired to convert the heat energy into kinetic energy. In the Parsons type the fixed blades form a series of nozzles. Second, although jet velocities higher than 300 ft. per second are common on the Pacific Coast, in water turbines the ordinary water velocities are w T ell below this figure. In the steam turbine the velocities are very much greater and the turbine must be adapted to velocities as high as 3,000 to 4,000 ft. per second. It is interesting to compare this speed with the muzzle velocity of a modern rifle ball, which leaves the barrel at about 2,600 ft. per second, or in the neighborhood of 30 miles per minute. This is 40 ENGINEERING OF POWER PLANTS the speed of steam discharging into the atmosphere from a nozzle of the best shape under a pressure of 50 lb. gage. In the successful steam turbine: 1. As much of the heat energy of the steam as possible must be converted into kinetic energy. 2. The rotor, nozzles and guide passages must be capable of utilizing the kinetic energy of the steam in the most efficient manner. 3. The casing, rotor and blading must hold their form under the heat strains and centrifugal strains and must be tight against leakage. 4. The apparatus must run at the proper speed at the point of delivery of power and all parts must run within safe limits. Comparison with the Steam Engine. — In the steam turbine the process of expansion of the steam as in the steam engine is duplicated, except that the flow of steam is continuous instead of intermittent. The steam engine may be termed a ratchet mechanism, while the steam turbine is a continuous mechanism. The difference in form of the turbine and engine is due to the fact that the turbine is designed to work by changing the direction of motion of the flowing steam, while the engine is designed to operate by the direct pressure of the steam. The turbine is thus a velocity motor and the steam engine a pressure motor. Impulse and Reaction Turbines. — In an impulse turbine the wheel is moved by the impulse of a jet of steam impinging on the blade surfaces. In the true reaction turbine the jet of steam issues from the moving part and impinges on the atmosphere or a fixed blade, thus moving the rotor by reaction. These terms are not used in this way at the present time and the distinction usually made is that in the impulse wheel the expan- sion of the steam is complete within the nozzle, while in the reaction wheel the expansion is not completed until after the steam enters the moving bucket. These terms are not good terms to use to distinguish the different types of turbines. Another way of stating this difference is that impulse turbines are partial-entry or ventilated turbines, while reaction turbines are full-entry or drowned turbines. It is better not to use these terms. Classification of Turbines. — Turbines may be classified first as to size into small turbines and large turbines, the small turbine being built in sizes up to 750 hp. or 500 kw., the large turbine, commencing at this size and going up to the limit of mechanical construction, which at the present time may be from 30,000 to 60,000 kw. or larger. Large turbines are usually classified by the names of their inventors or manu- facturers and the following types may be distinguished: Parsons, Curtis, Rateau, Zoelly and composite. All of these turbines are very much alike in principle, but differ widely in mechanical design and construction. THE STEAM ENGINE 41 The Parsons turbine was the first of the large turbines to be successful and is now manufactured in both Europe and America. The con- struction is of the drum type in which the blades are fixed in grooves on the outside of a cylindrical drum for the rotor, the fixed blades being held in grooves on the inside of the casing. All Parsons turbines are full intake machines and require for complete expansion from 200 lb. steam pressure down to 28 in. of vacuum, about 80 rows of blades, 40 fixed and 40 moving. No glands are necessary to prevent leakage between the stages, as the pressure differences are quite small, and the clearances at the end of the blades very small indeed. Each manufacturer of Parsons turbines varies the design in minor details, such as thrust bearing, loca- Fig. 24. — Westinghouse double flow turbine on erecting floor. tion of dummies, type of blading and mechanical construction of the drum and casing. The Rateau turbine is of the partial-entrance type and so-called multi-cellular construction. The drum system of construction is rarely used, the guide blades are held in diaphragms with glands to prevent leakage where the shaft passes through them. About 20 stages are usually used for the range of expansion between 200 lb. pressure and 28-in. vacuum. The Zoelly turbine is of the full intake type, but closely follows the Rateau construction in general lines with the exception that more cast iron and cast steel are used in its construction and considerably less riveted-steel work. In this turbine it is very rare that more than 12 stages are used for the expansion of steam from 200 lb. to 28-in. vacuum. The Curtis turbine, which originated in America, has been classed 42 ENGINEERING OF POWER PLANTS as the multiple-velocity stage type. It is always partial intake and from three to six stages are necessary for the expansion from 200 lb. to 28-in. vacuum. The particular feature of this type is that in each stage two or more velocity stages may be used. The construction is somewhat similar to the Zoelly machine, with the exception that the shaft has been placed in a vertical position and held by a step bearing. The clearances in this machine can be very generous, as they are in the Zoelly and Rateau types. The diaphragms between the stages are provided with a gland where the shaft passes through them, thus preventing leakage from stage to stage. Fig. 25. — 7000-kw., 1800-r.p.m., Curtis steam turbine. The Parsons, Zoelly, and Rateau constructions seem to give much better results in that part of the expansion between atmosphere and 28 in. of vacuum. The Curtis and Rateau types appear to give a trifle better result in the part of the expansion between 200 lb. and atmosphere. When these facts became known some manufacturers started building what we have termed the composite type of machine by using a Curtis wheel for the first stage and the Parsons, Zoelly, or Rateau machine for the low-pressure end. This construction resulted in a shorter, stiffer and cheaper machine and the economies obtained were extremely good. Shortening the machine and decreasing the number of stages enabled the manufacturers to build machines of a size much larger than the old construction, and the simplified wheel constructions enabled higher speeds to be used with the attending economies. Any combination of the various type machines may be THE STEAM ENGINE 43 made and at the present time practically every turbine manufacturer is turning out the composite machine as the bulk of his product, although machines of the straight Parsons, Zoelly and Curtis type are being built. ^ I1A ^ V - ^g^SBgS \n1F az! Sm** Fig. 26. — Brown, Bouverie & Co. composite-type turbine. Fig. 27. — 1400 kw. Ljungstrom turbine and condenser, Sandriken, Sweden. It should be noted that the governing of all full intake machines is of the throttling or puff type, while the governing of the partial intake machines is almost entirely of the nozzle type, that is the steam is 44 ENGINEERING OF POWER PLANTS admitted at full pressure to one or more nozzles, depending on the load on the turbine. Quite recently in Sweden the Ljungstrom turbine has been placed on the market, which differs materially from the other types of large turbines. The Ljungstrom turbine is a radial-flow machine, in which the steam is admitted through the center of the shaft and passes through the blades in a radial direction to the condenser. There are no fixed blades, but two sets of working blades moving in opposite directions. By this means bucket speeds may be kept high with reasonable low shaft revolutions. Tests of this machine are extremely good and if Fig. 28. — Bergmann (Curtis-Rateau) composite type turbine. the blade construction, which at first sight appears very flimsy, bears the test of time, it may be classed as a fifth-basic type of turbine. Small Turbines. — Small turbines are of many types, but may be classified by the method in which the steam is used in the wheel. In the DeLaval the steam is expanded in a nozzle and is passed once through the buckets of a single wheel. This was the first successful turbine and has been used to a great extent. This naturally leads to high bucket speeds and in the small sizes to a very high speed of rotation, in some cases as high as 12,000 revolutions per minute. In order to make the turbine a usable proposition a special reduction gearing was made for reducing this speed to the proper point. In the small turbine of the Curtis manufacture the wheel is provided THE STEAM ENGINE 45 with two or more sets of blades and the steam is used a number of times on the same wheel, each velocity stage using a portion of the jet velocity. In the Riedler-Stumpf turbine the nozzle has a number of return passages behind it returning the steam to the wheel buckets. In the Terry type the nozzle carries behind it a number of ventilated- return passages, by which the steam after passing through the wheel is returned two or three times to the wheel buckets on the entrance side. In the Electra or Westinghouse type, the steam having passed once through the buckets of the wheel, is caught by a return passage, which returns the steam to the wheel on the discharge side and passes it through the buckets in a contrary direction. Fig. 29. — Zoelly steam turbine. In the Kerr type the buckets are almost exactly similar to those of the Pelton waterwheel and the steam is used only once in a set of buckets. This necessitates a number of stages when economy is to be secured. Most of these turbines, when built in the larger sizes, have more than one wheel and as they increase in size, approach in construction some one of the large turbine types. By far the largest use for the small steam turbine is for auxiliary work and they are largely run non-condensing. In this case the economy is not quite so good as that of a good steam engine when kept in good con- dition, the difference being that with the engine the economy will not hold up, whereas with the turbine there is no falling off of steam economy with age and wear. The larger sizes are almost always run condensing, giving economies not quite so good as those of a first-class steam engine under the same conditions. 46 ENGINEERING OF POWER PLANTS Rating of Steam Turbines. — Turbine ratings are usually based on maximum sustained load. Momentary overload capacity is very large and moderate overloads of considerable duration can be carried but may require the admission of high-pressure steam to low-pressure stages by means of a secondary valve. Small turbines for driving pumps, blowers, etc., are rated in horsepower. Turbines used to drive electric generators are usually rated in connection with the generator, the combined unit or turbo-generator being rated in kilowatts. Note. — For a review of present turbine construction practice, see paper by Prof. A. G. Christie, vol. 34, A.S.M.E. Transactions, p. 435. Vol. 31 of the same Trans- actions contains a paper by one of the authors which gives sections and steam-con- sumption curves of most of the types of small turbines. Efficiency and Losses. 1 — The maximum theoretical efficiency of a steam turbine is the efficiency of the Rankine ideal engine between the temperatures of admission and exhaust. The several losses which tend to reduce the efficiency of turbines below the theoretical maximum are (1) residual velocity, or the kinetic energy due to the velocity of the steam escaping from the turbine; (2) friction and imperfect expansion in the nozzles; (3) windage, or friction due to rotation of the wheel in steam; (4) friction of the steam traveling through the blades; (5) shocks, impacts, eddies, etc., due to imperfect shape or roughness of blades; (6) leakage around the ends of the blades or through clearance spaces; (7) shaft friction; (&) radiation. The sum of all these losses amounts to about 25 per cent, of the available energy in the largest and best designs and to 50 per cent, or more in small sizes or poor designs. Oil Required by Steam Turbines. — No cylinder oil is required for the turbine and the exhaust may be condensed and used over and over again as feed water for the boilers without danger, providing exhausts from oily condenser auxiliaries are not permitted to mix with the con- densed steam. The only oil required by the turbine is the medium machine oil used for the turbine bearing. This oil is small in quantity, since the bearings of small machines are ring oiled and require to be filled up only about once per month. All large machines have a forced lubrication system for the bearings with a filter and pump attached to the turbine and the oil is used over and over again. Noise. — The earlier turbo-generators were very noisy, due to the fan action of the rotor. Modern design encloses the stator and the forced ventilation, provided by the fan action of the rotor or an outside blower reduces this noise to a reasonable amount. Where, however, a number of large generators are ventilated from one duct it is well to make pro- visions for a dampening action and to take particular precautions that 1 "American Handbook for Electrical Engineers," p. 1399. THE STEAM ENGINE 47 an organ-pipe effect is not produced. A great deal of attention has been given to the reduction of noise in turbo-generators, and while it is not possible to entirely eliminate it, the noise has been reduced to a reasonable amount. Mechanical Efficiency of Steam Engines. — The mechanical efficiency of the same engine will often vary considerably from time to time, depending upon the operating conditions. In general the mechanical efficiency of various types of engines varies from 0.80 to 0.94, although better figures have been secured under test and poorer results are frequently encountered in practice. The following table gives a few efficiencies secured from tests of engines under normal but good working conditions. The influences of work- manship in the construction of the engine and the variation in operating conditions are apparent from the variation in efficiencies shown. Kind of engine Horsepower Efficiency Simple engines: Horizontal portable Horizontal portable High-speed, stationary High-speed, stationary Corliss, condensing Corliss, non-condensing Compound : Portable Horizontal, stationary Horizontal, mill engine Corliss, condensing High-speed, condensing Pumping engine Vertical three-cylinder compound electric-lighting engine Triple-expansion : Vertical pumping engines 25 80 50 100 150 100 80 75 300 100 46 650 6,000 800 0.86 0.91 0.92 0.90 0.85 0.86 0.88 0.90 0.86 0.90 0.87 0.93 0.97 0.94 to 0.97 The following results, secured from three triple-expansion pumping engines under test at St. Louis, indicate the possibilities under condi- tions of superior workmanship and exceptionally refined conditions of operation. No. 1 No. 2 No. 3 I.hp. Eff. I.hp. Eff. I.hp. Eff. 873 96.6 875 96.8 859 97.7 48 ENGINEERING OF POWER PLANTS Although, strictly speaking, there is no relation between the horse- power capacity of engines and mechanical efficiency, a small engine often being more efficient than a large one, yet in general it is probably true that considering workmanship as a whole, the number of cheap engines of relatively small size and the greater skill and care usually exercised in the operation of large units, a sufficiently close relation between mechanical efficiency and size may be assumed to warrant the use of the following tables of approximate mechanical efficiencies for reciprocating steam engines. Mechanical efficiency of reciprocating steam engines, rated load Mechanical efficiency of steam engines in per cent, of rated load efficiency I.hp. Efficiency, per cent. Per cent, of rated load Per cent, of rated load efficiency 5 25 50 200 400 500 1,000 2,000 3,000 80.0 83.5 85.0 86.5 89.0 90.0 90.8 92.5 94.0 100 90 80 70 60 50 40 30 100.0 99.0 97.2 95.2 92.5 89.0 83.4 74.0 Steam-engine Economy. — F. W. Dean says 1 in speaking of the economy of steam plants: "It is well known that the economics of such plants are very variable and differ from each other. In some cases great care is taken to have good plants carefully operated, while in others they are neglected and incompetent men are employed." He further says: "In the case of engines there are non-condensing and condensing engines and turbines, and they can be simple or compound. In addition there are steam engines that are being devised which are likely to surpass in economy any that are now on the market, and these improved engines are on the verge of being introduced (December, 1914). In addition superheated steam is being intro- duced. By its use it is easy to save 10 per cent, of coal without any accompanying disadvantages. The advantage of using better condensing apparatus is being realized and such apparatus is being introduced with improved economy." Average Steam Consumption of Reciprocating Steam Engines. — Although the range of steam consumption per horsepower per hour is wide for engines of a given size and of different types, depending upon the quality of construction and the degree of refinement called for by commercial demands, an idea of the average economy of reciprocating steam engines may be had from the following table. 1 A.S.M.E. Transactions, vol. 36, p. 839. THE STEAM ENGINE 49 Pounds of Dry Steam per Indicated Horsepower-hour of Full Rated Load Simple high-speed Simple low-speed Compound high-speed Compound low-speed I.hp. Non-con- Con- Non-con- Condens- Non-con- Condens- Non-con- Condens- densing densing densing ing densing ing densing ing 10 65.0 50.0 15 57.0 44.0 20 52.5 40.0 25 49.0 38.0 30 46.5 36.0 40 42.5 33.0 50 40.0 30.2 60 38.0 28.5 75 35.5 26.2 100 33.0 23.4 27.0 21.6 29.3 22.5 23.6 20.0 150 30.4 21.5 26.3 21.0 28.6 22.0 23.1 19.5 200 29.5 20.6 25.7 20.5 27.9 21.5 22.7 19.0 250 29.0 20.2 25.2 20.0 27.3 21.0 22.3 18.5 300 28.5 20.0 24.8 19.6 26.6 20.5 21.9 18.1 400 24.1 18.8 25.4 19.5 21.1 17.3 500 23.7 18.3 24.2 18.6 20.4 16.5 600 23.4 17.9 23.3 17.9 19.8 15.8 700 23.2 17.7 22.7 17.5 19.2 15.3 800 23.0 17.6 22.3 17.2 18.7 15.0 900 22.9 17.5 22.1 17.0 18.4 14.7 1,000 22.8 17.4 22.0 16.9 18.2 14.5 1,500 * 13.8 2,000 13.5 2,500 13.2 5,000 - 12.5 Probable Gain in Steam Consumption by Condensing. — The follow- ing table serves to illustrate the marked gain in steam consumption of condensing engines over non-condensing. The figures given are approxi- mations only. Pounds Dry Steam per Indicated Horsepower-hour Type of engine Non-condensing Probable limits Assumed for com- parison Condensing Probable limits Assumed for com- parison Per cent, gained by condens- ing Simple high-speed Simple low-speed . Comp. high-speed Comp. low-speed . Triple high-speed . 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O CO ? o c c ce r 1 6 i — ■ - IH : cstj :flg CO co « co a Cfl o Seym ooper ice & 3 O * t< rH CB -1-5 a 3 5 O w 2% O-u a l-H foffi cq OOh H i-l CN CO Tf O co N. co«> w CO CO ■ro CO 2 i-i 2 o= 3Q M ft oo t*o oo CNCO ■*00 N-CO 00 ^H l-HCN NCN 00 1-t . -H IC io X • »o O ^H I I ^HO lON- coco CNCN talc •o o S I c ° a J ?^ * a OS C a -a u 3 3T> 41 co a) a *-> ,1) o o * n *J — 1 n cd a aj 4h i-i t- C ° 2 o^a 43 3 ■J -t a - a efl r -3 V o C a T3 u 1) 1) 09 a ■ Q 1 o8 — En o a t- BE) a T7 00 ~* £ 3 CD *j •jj -3 J3 pq a) i! a 52 ENGINEERING OF POWER PLANTS The probable steam consumption of condensing engines of different types with different pressures of steam is given in a set of curves by R. H. Thurston and L. L. Brinsmade, Transactions A.S.M.E., 1897, from which curves Kent has derived the following approximate figures. Steam Pressure, Absolute Pounds per square inch 400 300 250 200 150 100 75 50 Ideal engine (Rankine cycle) . . Quadruple exp. wastes 20 per cent 6.95 8.75 Triple exp. wastes 25 per cent. 9.25 Compound wastes, 33 per cent. 10 . 50 Simple engine wastes, 50 per cent 14.00 7.5 9.15 9.95 11.25 15.00 7.9 9.75 10.50 11.80 15.80 8.45 10.50 11.15 12.70 16.80 9.20 10.50 11.60 13.00 12.30 14.00 13.90 15.60 18.40 11.40 14.00 15.10 16.90 20.40 22.70 12.90 15.60 16.70 18.90 25.20 These engines are of the usual ratios of expansion. A 1 to 7 com- pound will be as economical as a 1 to 7 triple or quadruple expansion engine. It is conservative to say that compound engines may now be built to produce an indicated horsepower on 12.5 lb. of saturated steam per hour. With high degree of superheat the 10-lb. mark has been passed but if results were calculated on the basis of saturated steam the figures would barely reach 10 lb. From 23 four-valve engines in commercial operation, Barrus reports : 1 falls below 12 lb. per horsepower-hour 3 fall below 13 lb. per horsepower-hour 16 fall below 14 lb. per horsepower-hour only 3 fall above 14 lb. per horsepower-hour The table on pages 50 and 51 gives an excellent idea of the rela- tive steam economy of different types of engines under test conditions. One of the recent developments of the reciprocating steam engine in this country (long used in Europe) is the Lentz compound engine which in many respects resembles the modern horizontal, tandem double- acting gas engine. Tests of a 143^ and 24% by 273^-In. Engine Are Steam pressure, lb., gage Vacuum, in., Hg. Superheat, °F. R.p.m. Lb. steam per i.hp.-hr. I.hp. under initial condi- tions 170 170 26 26 150 167 167 366 366 12.3 10.4 Tests have recently been reported by the manufacturers which give the steam consumption of a 115-hp. Buckeye-mobile, running at 248 THE STEAM ENGINE 53 r.p.m.; steam at 210 lb.; initial superheat, 171°F.; non-condensing, as 13.3 lb. per indicated horsepower-hour. This unit produced an in- Fig. 30. — Compound locomobile using superheated steam and surface condensers. ^0698) *Y(59fk (1770) ^(955) 15.19'™ Wfc ~(4&30~j V&» Fig. 31. — Sizes and types of locomobiles. dicated horsepower-hour on 1.33 lb. of coal having a calorific value of 14,500 B.t.u. per pound. A 169-hp. unit running at 200 r.p.m.; steam at 209 lb.; initial superheat, 218°F.; vacuum 25.7 in., showed a water 54 ENGINEERING OF POWER PLANTS rate of 9.2 lb. per indicated horsepower-hour. The coal consumption, using fuel with a calorific value of 14,209 B.t.u. per pound, was 1.08 lb. per indicated horsepower-hour.* The effect of superheating upon the steam consumption is brought out more clearly by the following test results. The consumption is given in pounds per horsepower-hour of superheated steam and also in equivalent pounds of saturated steam. I.hp. Superheat, °F. Lb. steam, i.hp.-hr. Equivalent, sat. steam B.t.u. per i.hp.-hr. 222 0.0 12.08 12.08 15,000 226 43.7 11.58 11.77 14,600 227 97.7 11.00 11.44 14,200 223 151.7 10.67 11.33 14,000 223 221.2 9.81 10.69 13,300 218 310.9 8.89 10.01 12,000 The result shows that for every 100°F. superheat the steam con- sumption per indicated horsepower-hour was reduced 1 lb. or 8.5 per cent, and that the consumption expressed in terms of equivalent saturated steam was reduced 0.6 lb. per indicated horsepower-hour. It should be remembered that the poorer the engine the larger the gain from the use of superheat. In a first-class engine the gain in economy is rarely over 5 per cent, per 100°F. superheat, but in a poor simple non-condensing engine it may be 50 per cent, for the first 100° superheat. Steam Consumption of Small Steam Turbines. — The majority of small steam turbines are run non-condensing and are rated on the brake horsepower instead of the indicated. Although the steam consumption for different-sized turbines may vary with the speed, an estimate of the average consumption for non-condensing units may be secured from the following table. Pounds op Dry Steam per Brake Horsepower-hour at Full Rated Load (180 lb. steam pressure, moderate superheat, no back pressure) B.hp. Lb. per b.hp.-hr. 10 60 25 50 50 45 100 40 150 35 200 30 250 28 THE STEAM ENGINE 55 Fig. 32. — Section of Terry steam turbine. The values would be materially increased by back pressure. Esti- mates of the probable steam consumption of the larger condensing steam turbines may be made from the following tables, keeping in mind that the figures recorded are test results under the best operating conditions. Records of Steam Consumption for Turbines Turbine Nominal power Steam used per hr., lb. Estimated equivalent B.hp. E.hp. Kw. per i.hp. With saturated steam Westinghouse Parsons Westinghouse Parsons Rateau Curtis (American) .... DeLaval Zoelly 400 kw. 1,250 kw. 300 hp. 500 kw. 300 hp. 500 hp. 13.63 14.13 18.95 14.90 13.63 15.17 16.05 21.50 12.68 12.72 13.11 12.68 13.96 14.12 56 ENGINEERING OF POWER PLANTS Record of Steam Consumption for Turbines (Continued) Turbine Nominal power Steam used per hr„ lb. Estimated l equivalent per B.hp. J E.hp. Kw. i.hp. With superheated steam, not exceeding 150°F. Parsons ; 3,000 kw. Westinghouse Parsons 400 kw. Curtis (American) 500 kw. 1,500 kw. 500 hp. 1,250 kw. 300 hp. 300 kw. Curtis (English) I 500 kw. Parsons Zoelly Westinghouse Parsons. DeLaval Parsons 11.79 15.80 12.07 13.28 17.79 13.44 18.00 14.05 18.82 13.78 18.48 13.94 14.96 10.06 15.29 20.50 | 10.85 11.23 11.95 12.10 12.36 12.40 12.82 13.16 13.76 With highly superheated steam, superheat from 180° to 290°F. Parsons Curtis (American) Curtis (American) 5,000 kw. 500 kw. 2,000 kw. Westinghouse Parsons j 400 kw. 10.12 10.14 10.36 10.39 Economy Tests of Turbines (Marks and Davis Tables) In calculating Rankine B.t.u. an efficiency of 90 per cent, is assumed for turbine and generator Turbines Load, kw. Steam press, abs. Super- heat, °F. Vac. 29.92 in. Bar. Lb. steam per kw.- hr. B.t.u. per kw.- I Rankine cycle, j B.t.u. per kw.- min. Eff. ratio Dunstan Parsons A. E. G. Rummelsburg Erste Brunner Chic-Edison Curtis A. E. G. Moabit Carville Parsons Bergman Zoelly Charlottenburg Erste Brunner Zoelly Augsburg Nurnberg Boston Edison Curtis Richmond Allis Brown Boveri City Elec. Westinghouse . . B. R. T. Westinghouse Manchester Howden N. Y. E. Westinghouse N. Y. E. Curtis No. 10. . . . Varberg DeLaval 6,257 2,177 6,000 8,191 3,169 5,164 1,545 2,052 2,000 1,250 5,195 4,328 3,500 8,563 11,601 6,383 9,870 8,921 1,570 204.0 176 272 194 198.5 191.0 199.0 143 185.0 215 215.0 121 195.0 201 200.0 202 161.5 118 188.0 204 189.0 142 186.0 108 162.0 133 183.0 59 192.0 114 203.0 137 192.0 97 190.0 111 172.3 170 29. 29. 28. 29. 29, 28. 28. 28 27. 28, 28, 27, 28. 28 27, 27 27, 28, 5 28, 02 11 32 11 12.12 36 12 00 12 96 13 54 12 39 13 82 13 79 13 74 13 97 14 80 13 10 14 82 14 40 14 19 15 10 14 49 16 ,95 ,77 .58 .68 70 .18 97 .05 ,84 10 52 .02 ,72 .43 ,23 .30 .05 249.4 257.1 259.5 263.9 268.4 268.8 270.3 271.6 274.5 274.5 276.1 278.3 278.6 280.5 282.8 285.8 294.6 86 296.0 47 337.9 190.8 180.9 205.6 184.1 192.8 192.4 199.1 200.5 218.4 196.2 199.3 211.6 203 211 212 213 219 208.8 206.6 76.4 70.4 79.2 69.8 71.8 71.6 73.6 73.9 79.6 71.5 72.2 76.0 72.9 75.5 75.1 74.8 74.5 70.5 61.2 THE STEAM ENGINE 57 References Turbine Dunstan Parsons A. E. G. Rummelsberg Erste Brunner Chicago Edison Curtis A. E. G. Moabit Carville Parsons Bergman Zoelly Charlottenburg Erste Brunner Zoelly Augsburg Nurnberg Boston Edison Curtis Richmond Allis Brown Boveri City Electric Westinghouse B. R. T. Westinghouse Manchester Howden N. Y. E. Westinghouse N. Y. E. Curtis Varberg DeLaval for Economy Tests of Turbines Reference London Engineering, Mar. 10, 1911. Stodola, p. 404, 4th edition. Zeit. V. D. I., Dec. 10, 1910, p. 2104. Report on Tests by Breckenridge, 1907. Zeit. V. D. I., 1907, p. 386. Stodola, 439, 4th edition. Zeit. V. D. I., Dec. 10, 1910, p. 2104. Escher Wyss Leaflet. Zeit. V. D. I., Dec. 10, 1910, p. 2104. Zeit. V. D. I., Dec. 10, 1910, p. 2104. N. E. L. A. Proceedings, 1907, p. 433. Sibley Journal, January, 1911. Zeit. V. D. I., Dec. 10, 1910, p. 2104. A.S.M.E., Journal, December, 1910, p. 2089. Operating Co. London Engineer, 1909, p. 462. N. Y. E. Tests, 1907. N. Y. E. Tests, Whitham, 1907. Power, May 3, 1910, p. 798. F. W. Dean (Power, May 6, 1913) gives the following comparative figures for steam consumption for reciprocating steam engines and steam turbines. Guaranteed Steam Consumption Pounds per Kilowatt-hour (150 lb. steam pressure) Capacities, kw. Engine sat. steam 100°F. superheat Turbine 100°F. super- (Vac. = 26 in.) heat (vac. = 28 in.) 500 1,000 1,500 2,000 18.67 18.80 18.80 18.93 16.8 16.9 16.9 17.0 17.7 18.0 16.8 16.6 Low-pressure or Exhaust, Bleeder and Mixed-pressure Turbines. — Since that portion of the turbine which utilizes the expansion of the steam from around atmospheric pressure to the best obtainable vacuum is much more efficient than the high-pressure portion of the turbine, it was proposed very early in the turbine development to install low- pressure or exhaust turbines in connection with non-condensing engines already installed. The combination unit gave nearly double the power of the engine unit alone, was somewhat less costly per unit capacity and resulted in a saving of from 5 to 10 per cent, or even more in operating costs. These savings were particularly large in connection with the exhaust from rolling mill, hoisting and reversing engines and steam hammers, but as these machines were of intermittent service some 58 ENGINEERING OF POWER PLANTS method of providing steam during the period of rest had to be intro- duced. This led Professor Rateau, one of the earliest to use this type of machine, to invent his regenerator, which provided storage to tide over the intermittent periods of stopping. Other manufacturers got around the difficulty in another way by the introduction of an auxiliary Curtis high-pressure wheel ahead of the low-pressure element and providing a governor valve which admitted high-pressure steam to run the turbines during the periods when no low-pressure steam, or not enough, was available. These machines are known as mixed-pressure turbines and have become quite common, as they are well suited to certain conditions. The Rateau regenerator practically consists of a large cast-iron tank Fig. 33. — Section of Kerr turbine. acting as a jet condenser at atmospheric pressure. A slight reduction in the pressure vaporizes some of the stored water, thus providing steam for the low-pressure turbine. Combinations of regenerator and mixed- pressure turbines are also used with good success. (For the theory of regenerators, see paper by F. G. Gasche, Engineers' Society of Western Pennsylvania, Nov. 19, 1912.) It is sometimes convenient, especially in district lighting and heating systems, to abstract steam from the turbine at a little above atmospheric pressure, this steam to be used in the heating system or for similar uses. Such a turbine is known as a bleeder turbine. The steam is taken off through a specially designed valve arranged to maintain any predeter- mined pressure in the bleeder main. By combining 1 the superior efficiency of the engine in the pressure 1 "American Handbook for Electrical Engineers," p. 1395. THE STEAM ENGINE 59 range above the atmosphere with that of the turbine below the atmos- pheric range a resultant superior to the efficiency of either single type may be secured. Standard piston engines are able to sustain full rated load when run non-condensing and often will carry from 25 to 50 per cent, above rated load without danger of excessive wear. Under such conditions the water rate per kilowatt-hour is high but all the heat rejected in the exhaust is available to a low-pressure turbine; hence the net economy of the combined engine and turbine may be considerably superior to that of the engine when run condensing. By proportioning the turbine to efficiently utilize the exhaust steam and by connecting to it a high-vacuum condenser, the initial capacity of the unit may be doubled or even trebled, and if the engine is in good condition, the resultant efficiency may be superior to that obtainable from a new complete-expansion turbine of equal capacity. Combined Engine and Turbine Unit. — Owners of first-class recipro- cating steam-engine plants will often be confronted with the desirability of the extension of their plants. This may be done in a number of ways, by the duplication of the engine units, by the purchase of complete expansion turbines, or by installing low-pressure turbines, to operate on the exhaust steam from the existing steam engines. It is difficult to say which of these ways is the best, as the local condition will largely govern the problem, but it is safe to say that in no case at the present time in plants of 1,000 hp. or larger, will the reciprocating engine plant be duplicated. In a few cases it has been found advisable to install low-pressure turbines, but in most instances complete expansion turbines, replacing the original engines, will be the most economical solution. Each case, however, should be considered by itself, bearing in mind that the cost of the low-pressure steam turbine will be about two-thirds of that of a complete expansion turbine capable of developing the power of the engine and low-pressure turbine combined. Economy of Combined Engine and Turbine. — An improvement of from 20 to 25 per cent, in steam economy is obtained in combining the low-pressure turbine with a compound condensing engine of normal cylinder proportions, and from 40 to 45 per cent, with the same engine non-condensing. Considering a single-cylinder Corliss engine in connection with the low-pressure turbine, the customer's coal bill could be decreased from 50 to 60 per cent. With the use of a low-pressure turbine the excellent performance of large, efficient reciprocating engines can be bettered by about 2.5 lb. or over 14 per cent. Messrs. Stott and Pigott reported 1 the following results from com- 1 A.S.M.E. Journal, March, 1910. 60 ENGINEERING OF POWER PLANTS bining a 7,500-kw. Manhattan-type engine with a 7,500-kw. low-pressure turbine. (a) An increase of 100 per cent, in maximum capacity of' plant. (6) An increase of 146 per cent, in economic capacity of plant. (c) A saving of approximately 85 per cent, of the condensed steam for return to the boilers. (d) An average improvement in economy of 13 per cent, over the best high-pres- sure turbine results. Fig. 34. — Section of Dake-American turbine. (e) An average improvement in economy of 2.5 per cent, (between the limits of 7,500 and 15,000 kw.) over the results obtained by the engine units alone. (/) An average thermal efficiency between the limits of 6,500 and 15,500 kw. of 20.6 per cent. Variable -load Steam Consumption. — The steam consumption given both for reciprocating engines and turbines are for full rated load. For other loads the economy is not as good. The average variation of steam consumption per horsepower-hour or per kilowatt-hour with change of load, expressed in terms of per cent, of full-load economy, may be taken as: THE STEAM ENGINE 61 Per Cent, of Full Load Steam Consumption per Horsepower-hour or per Kilowatt-hour Load = 2 /4 ■u y* H Engine 160 Turbine (small non-condensing) 135 Turbine (large condensing) (185 lb. and 100°F. superheated steam, 28 in. vac.) 114 120 110 107 105 105 101 100 100 100 103 101 101 Duty of Pumping Engines. — The duty, efficiency and economy of reciprocating triple-expansion pumping engines are shown by the following table of " Official Trials." Location Rated capac- ity mil- lions of U. S. gal- lons Water actu- ally pump- ed, mil- lions of U. S. gallons 24 hr. Net head pump- ed a- gainst, lb. per sq. in. a ft Ini- tial gage pres- sure Indi- cated horse- pow- er Devel- oped horse- power Me- chan- ical effi- cien- cy Dry steam per i.hp.- hour Duty Type Per thou- sand lb. of dry steam Per one mil- lion B.t.u. in steam Holly Holly Louisville, Ky. Frankfort, Pa. Albany, N. Y. Brockton, Mass. Cleveland, Boston, Mass. St. Louis, Mo. St. Louis, Mo. Milwaukee, Wis. 24.0 20.0 12.0 6.0 2.5 30.0 20.0 15.0 12.0 24.111 21.219 12.193 6.316 2.142 30.314 20.070 15.121 12.430 90.0 95.7 139.5 130.6 180.7 61.0 104.0 127.0 121.0 24.0 20.1 22.3 40.1 62.3 17.7 16.5 16.4 20.4 155.1 180.2 153.0 150.0 149.6 185.5 140.6 126.2 124.6 925.7 158.7 801.5 859.2 801.6 673.0 879.4 817.0 726.0 334.0 151.9 747.8 839.6 726.3 618.0 95.0 9.641 195.01 184.4 182.1 164.5 Holly Holly 170.0 Holly Allis Allis Allis Allis 95.8 93.3 97.7 90.6 91.8 11.51 10.33 10.66 10.67 10.82 164.6 178.5 181.3 179.4 175.4 148.8 163.9 158.8 158.1 151.0 109°F. superheat at throttle. Complete details of three such pumping engines are presented. Make and type Holly vertical Holly vertical Worthington horizontal Contract price Weight, tons Capacity, gal., 24 hr... Diameter, cyls., in Stroke, ft Diameter, plungers, in. R.p.m Condensers Steam pressure, lb. gage Water pressure, lb Duty, ft.-lb. per million B.t.u Duty per 1,000 lb. 150° superheated steam Duty per 1,000 lb. saturated steam I.hp $124,700 970 25,000,000 32, 60, 90 5 36 21.89 Jet 150 80 151,000,000 179,000,000 Water hp Mech. efficiency Steam per w.hp.-hr., lb. . Steam per i.hp.-hr., lb. 1 966 896 94.5 11.071 10.250 $112,679 970 25,000,000 34, 64, 98 5V 2 34% 21.356 Surface 160 108 160,000,000 193,500,000 1,118 1,074 96.3 10. 23 1 9.86 1 $5,500 15,000,000 36, 72 4 36M 13.142 Jet 100 80 125,000,000 560 15.8 i 150°F. superheat. 62 ENGINEERING OF POWER PLANTS Cost of Simple, High-speed Engines. — I.hp. Cost f.o.b. Cost per i.hp. f.o.b. Cost erected Cost per i.hp. erected 50 $760 $15.20 $910 $18.20 75 910 12.10 1,070 14.30 100 1,090 10.90 1,270 12.70 125 1,260 10.00 1,420 11.30 150 1,410 9.40 1,625 10.80 200 1,735 8.70 1,990 10.00 250 2,050 8.20 2,350 9.40 Fig. 35. — Section of 125-kw. two-stage Curtis turbine. The above figures are averages of several quotations for different makes of engines and serve as a basis for approximate cost estimates. The f.o.b. cost in dollars for these engines may be represented by the formula 435 + 6.5 X i.hp. THE STEAM ENGINE 63 Many such formulae are presented by different writers. Naturally they vary considerably in accordance with the types of engines con- sidered and the state of the market. Many authors subdivide into many divisions, but for work of this character this seems unnecessary. The average of six such formulae for simple, high-speed engines up to 500 i.hp. is, cost in dollars = 200 + 10 X i.hp. Above 500 i.hp. the approximate formula seems to approach more nearly to, cost in dollars = 200 + 6 X i.hp. The erecting cost of such engines is reported by Potter 1 as Engine, i.hp. 75 100 150 300 450 600 Erecting cost $125 to 150 150 to 200 200 to 300 300 to 400 400 to 450 400 to 600 The erecting costs indicated for the engines listed on page 62 follow roughly the formula, erecting cost in dollars = 100 + 0.8 X i.hp., which averages about 16.5 per cent, of f.o.b. cost of engine. Another set of figures for average costs of such engines, erected, including foundations, compiled from the wide experience of one con- sulting engineer, is as follows: Engine horse- power Cost per horse- power 10 $36.50 12 14 $36.00 $35.50 15 $35.00 20 30 $34.50 $28.50 40 $21.50 50 $17.40 75 $15.50 Cost of Simple Non-condensing Corliss Engines. — -The cost of simple, low-speed engines may be obtained from the table below. It should, however, be borne in mind that the prices given may now be seriously affected by steam-turbine competition. When such is the case, it is probable that the cost of steam engines may be reduced to approximately 70 per cent, of the f.o.b. prices given. In order to establish the ratio of cylinder size to horsepower of the engine, the dimensions of the various engines are included. The horsepowers are based on 80 lb. gage pressure and cut-off at 34 stroke. 1 Power, Dec. 30, 1913. 64 ENGINEERING OF POWER PLANTS ouiq ^ituiq THE STEAM ENGINE Cost of Simple Non-condensing Corliss Engines 65 Size Hp. Engine f.o.b. Per hp. Founda- tion Erecting Piping Total Total per hp. 14 X36 14 X 42 16 X 36 16 X42 18 X36 18 X42 18 X48 20 X 42 20 X48 22 X42 22 X 48 42 X48 26 X48 28 X48 28 X 54 30 X48 100 $1,700 110 1,800 125 1,950 140 2,000 155 2,150 175 2,350 200 2,600 210 2,600 230 2,850 250 3,000 280 3,500 320 4,000 380 4,650 425 5,150 450 5,300 500 5,800 $17.00 16.40 15.60 14.30 13.90 13.40 13.00 12.40 12.35 12.00 12.50 12.50 12.20 12.10 10.80 11.60 $275 300 325 350 375 400 425 500 525 550 600 700 800 900 1,050 1,200 $175 200 210 225 240 250 260 270 275 300 325 375 440 500 575 600 $165 175 180 190 200 210 220 230 250 310 340 390 560 800 950 1,070 &2,315 2,475 2,665 2,765 2,965 3,210 3,505 3,600 3,900 4,160 4,765 5,465 6,450 7,350 7,875 8,670 $23.15 22.50 21.30 19.75 19.15 18.35 17.50 17.10 16.95 16.65 17.00 17.10 16.95 17.30 17.50 17.30 The variation in prices listed is considerable and precludes the application of a positive formula. The following will, however, approximate the values sufficiently closely for preliminary estimates. Cost in dollars, f.o.b. = 700 + 10 X i.hp. The averages of other formulae given by different writers for the cost of simple Corliss engines are: Up to 400 i.hp. 820 + 10.3 X i.hp. Above 400 i.hp. 375 + 10.2 X i.hp. which are in reasonable agreement with the formula above. The erecting cost of these engines, including foundations, seems to be from 35 per cent, to 50 per cent, of the f.o.b. cost of the engines, averaging about 37 per cent. The following formulae may serve in this connection. Erecting cost in dollars = (up to 400 i.hp.) 275 + 3.5 X i.hp. (above 400 i.hp.) 250 + 5.0 X i.hp. 66 ENGINEERING OF POWER PLANTS Cost of Compound High-speed Non-condensing Engines Size Hp.i Cost f.o.b. Cost per hp. f.o.b. 8 and 13 X 12 60 $1,190 $19.85 8 and 16 X 12 80 1,420 17.75 10 and 18 X 12 100 1,520 15.20 11 and 19 X 14 125 1,830 14.65 12 and 20 X 16 150 2,285 15.20 13 and 22 X 16 200 2,620 13.10 15 and 25 X 16 250 2,890 11.55 16 and 28 X 18 300 3,580 11.90 17 and 30 X 18 350 4,150 11.85 20 and 36 X 18 400 4,590 11.50 1 Hp. based on 100 lb., steam pressure. Although these quotations vary considerably, they correspond approximately to: Cost in dollars = 500 + 10.5 X i.hp. The averages of several other formulae for the cost of such engines are: Cost in dollars = (below 250 i.hp.) 775 + 10.5 X i.hp. (above 250 i.hp.) 625 + 9.5 X i.hp. With no data at hand relating to the cost of setting compound high- speed engines, it may be assumed that this item amounts to about the same percentage of the initial engine costs as in the high-speed simple engine. This will give a basis for forming approximate estimates. Cost of Compound Condensing Corliss Engines. — Size Hp. Wt. lb. inc., condenser Wt. per hp. Cost 1 f.o.b. Cost per hp. Foundation and erecting Total cost Total per hp. Based on 100 lb. steam pressure 14 X 28 X 42 200 18 X 34 X 42 300 20 X 38 X 48 400 22 X 42 X 48 500 24 X 46 X 48 600 60,000 85,000 110,000 140,000 170,000 300 $4,565 $22.80 283 5,700 19.00 275 7,300 18.25 280 8,480 16.95 284 10,000 18.85 $1,050 1,025 1,250 1,400 1,675 $5,615 6,725 8,550 9,880 11,675 $28.10 22.40 21.35 19.75 19.60 Based c >n 120 lb. steam pressure 13 X 26 X 42 200 60,000 300 4,465 22.80 1,050 5,515 27.55 16 X 32 X 42 300 85,000 283 5,500 18.33 1,025 6,525 21.75 18 X 36 X 48 400 110,000 275 7,100 17.75 1,250 8,350 20.85 20 X 40 X 48 500 140,000 280 8,280 16.55 1,400 9,680 19.35 22 X 44 X 48 600 170,000 284 9,900 16.50 1,675 11,575 19.30 Prices include condensers. THE STEAM ENGINE 67 The prices given apply to both tandem and cross-compound engines, the cost of the former being less than 10 per cent, lower in smaller sizes and somewhat greater in large sizes. The corresponding approximate f ormulae are : Cost in dollars, f.o.b. = 1,800 + 13.6 X i.hp. and cost in dollars, f.o.b. = 1,600 + 13.6 X i.hp. The average of other formulae for compound Corliss engines up to600hp. is: Cost in dollars, f.o.b. = 1,500 + 9.8 X i.hp. The cost of foundations and setting seems to be about 18 per cent, of the f.o.b. cost of the engine, for units of the sizes given. One firm manufacturing Corliss engines of from 200 to 3,000 hp. gives the weights of engines as from 200 to 250 lb. per horsepower and the price from 6 to 8 cts. per pound. Cost of Compound Condensing Engines. — Figures reported by one consulting engineer indicate that in general the average cost per horse- power, erected, for various types of compound condensing engines is approximately as follows: Engine, horse- power. ..... Cost per horsepower. 100 $25 200 $24 300 $23 400 $22 500 $21.50 600 $21.25 700 $21 800 $20.75 900 1,000 $20.50$20.25 1,500 $19.50 2,000 $19 Cost of Steam Turbines. — Small turbines for driving pumps, blowers, etc., cost from $20 to $40 per horsepower. All types of turbines cost approximately the same. Turbine costs are subject to considerable variation, the tendency being a decided decrease in the cost per kilowatt from year to year. The costs given should therefore be checked against actual quotations, even when used in preliminary estimates. Approximate Cost of Steam Turbines and Generators In Dollars per Kilowatt, Rated Capacity Size, kw. 100 300 500 750 1,000 2,500 5,000 7,500 10,000 Direct-current condens- ing 60-cycle A.C. condens- ing 25-cycle A.C. condens- ing 48 38 36 22 30 28 16 25 13.50 17.00 12.00 14.00 11.00 12.50 10.50 68 ENGINEERING OF POWER PLANTS F. W. Dean 1 gives the comparative cost of turbine and reciprocating engine units on the basis of real outputs at 80 per cent, power factor including apparatus and exciters, all erected, including foundations as: Comparative Costs Horizontal four-valve engine units Turbine units Capacities, Ratio engine to kw. Total cost Cost per kv.a. Total cost Cost per kv.a. turbine 500 $22,700 $45.40 $12,250 $24 . 50 1.85 1,000 40,200 40.20 17,900 17.90 2.24 1,500 62,200 41.50 23,800 15.85 2.61 2,000 76,400 38.20 30,500 15.25 2.50 Commercial Aspects of the Turbine. — Limitations. The field of the turbine is limited by its relatively high speed and the fact that it is non- reversible. Because of its high speed it cannot be used for driving machinery by belting. In view of this restriction the turbine is limited to driving direct-connected apparatus, such as electric generators, centrifugal pumps, fans and blowers, ship propellers, etc. The turbine is essentially a central station apparatus. Field of the Reciprocating Engine. — The power for rollingmills, blast furnaces, mine and water-works pumping, mine hoisting, air and am- monia compressors, etc., will be furnished by the piston engine for a long time, and Corliss engines or similar types will still be used for mill work where belt or rope driving is preferred. Turbine Advantages. — The advantages of the turbine are high economy under variable loads, small floor space, uniform angular velocity and close speed regulation, freedom from vibration, inexpensive founda- tions, ease in erecting and usually quickness in starting, steam economy not seriously impaired by age, small cost of maintenance and attendance, adapted to use with high superheat, water of condensation free from oil. Engine Advantages. — Rather than call attention to special features engine builders point to reliability, simple and cheap condensing system requiring only a small quantity of condensing water, and to the fact that nearly as good economy as the best turbine economy may be ob- tained without the use of highly superheated steam. It is only fair to say that in the last 5 years all of the builders of large-sized engines for land work have practically gone out of business, although many engine builders still remain in the field. It is noticeable that only the builders of the higher-class engines and the lower-class engines in the medium and small sizes remain in the field. 1 Paper before National Association of Cotton Mfgrs., Boston, April, 1913. THE STEAM ENGINE 69 Turbines vs. Engines in Units of Small Capacity. — Under this title K. S. Barstow presented the following summary before the A.S.M.E. in December, 1915, for units of less than 500-hp. capacity. APPLICABILITY OF TURBINES 1. Direct-connected units, operat- ing condensing. 60-cycle generators in all sizes, also 25-cycle generators above 1,000-kw. capacity. (This paper is, however, not intended to deal with units of this size.) Direct-current generators in sizes up to 1,000-kw. capacity, including ex- citer units of all sizes. Centrifugal pumping machinery operating under substantially constant head and quantity conditions, and at moderately high head, say from 100 ft. up, depending upon the size of the unit. Fans and blowers for delivering air at pressures from 1^-in. water column to 30 lb. per square inch. 2. Direct-connected units, operat- ing non-condensing for all the above purposes, in those cases wherein steam economy is not the prime factor or where the exhaust steam can be com- pletely utilized, and, in the latter case, particularly where oil-free exhaust steam is desirable or essential. 3. Geared units, operating either condensing or non-condensing for all the above-mentioned applications, and in addition, many others which would otherwise fall in the category of the steam engine, on account of the rela- tively slow speed of the apparatus to be driven. APPLICABILITY OF ENGINES 1. Non-condensing units, direct-con- nected or belted and used for driving : 70 ENGINEERING OF POWER PLANTS Electric generators of all classes excepting exciter sets of small capacity, un- less, belted from the main engine. Centrifugal pumping machinery, operating under variable head and quality conditions and at relatively low heads, say up to 100 ft., depending on the capacity of the unit. Pumps and compressors for delivering water or gases in relatively small quantities and at relatively high pressures in the case of pumps at pressures above 100 lb. per square inch and in the case of compressors at pressures from 1 lb. per square inch and above. Fans and blowers (including induced draft fans) for handling air in variable quantities and at relatively low pressures, say not over 5-in. water column. Line shafts of mills, where the driven apparatus is closely grouped and the load factor is good. All apparatus requiring reversal in direction of rotation, as in hoisting engines and engines for traction purposes. 2. Condensing units direct-connected or belted, for all the above purposes, particularly where the condensing water supply is limited, and where the water must be recooled and recirculated. The Saving of Space. — The introduction of the composite type of machine has made possible large improvements in the space require- ments of turbines. At the present time 60,000 kw. in turbines with their condensing apparatus can be placed in the space occupied by 8,000 kw. of vertical engines with direct-connected generators and jet-con- densing apparatus. A few years ago, three 20,000-kw. machines were placed in the space formerly occupied by four 4,500-kw. engine units. A few years earlier an 8,000-kw. turbine was placed in the space occupied by a 4,000-kw. vertical engine. Where horizontal engines have been in use the space saving is of course much larger and 60,000 kw. could be placed today with its condensing apparatus in the space occupied by a 1,500-kw. duplex tandem compound horizontal unit. In the smaller sizes the saving of space is nearly as well marked, but is always a function of the speed of the turbine, slow-speed turbines being very large and high-speed turbines comparatively very small. A 250-hp. medium- speed non-condensing turbine can be put inside of a 4-ft. cube, and a 150-hp. high-speed turbine might be put in a 30-in. cube. There seems to have been no great saving in space with the vertical-shaft turbine over the horizontal-shaft turbine when condensers and auxiliaries are taken into account. Based on the overall dimensions of the generating units but not including condensers and auxiliaries, W. F. Fisher reports (Power, vol. 34, page 275) the average approximate floor space per engine horsepower to be: THE STEAM ENGINE Comparative Space per E.hp. 71 Turbine units Corliss engines units Capacities, hp. Type Sq. ft. per e.hp. Type Sq. ft. per e.hp. 2,000 2,000 5,000-8,000 5,000-8,000 5,000-8,000 Westinghouse-Parsons Curtis horizontal Westinghouse-Parsons Curtis horizontal Curtis vertical 0.146 0.098 0.100 0.060 0.040 Horiz. cross-comp. Vert, cross-comp. Manhattan Vert, three-cyl. comp. 0.64 0.36 0.48 0.20 A ratio of the average space occupied by the engine units to that of the turbine units reported is 4.7 to 1. A similar table has been compiled from a paper by F. W. Dean 1 based on real output of the units at an 80 per cent, power factor. Besides the generating units, the condensing apparatus and exciters are included . Comparative Space per Kilovolt-ampere Capacities, kw. Turbines Engines Ratio engines to turbines Dimensions, ft. Sq. ft. per kv.a. Dimensions, Sq. ft. per ft. kv.a. 500 1,000 1,500 2,000 14 X 6 14 X 8 19 X 9 21 X 9 0.168 0.112 0.114 0.094 18 X26 24 X 30 26 X 35 28 X 37 0.935 0.720 0.605 0.518 5.57 6.43 5.30 5.51 Although the possibilities of great space reduction by installing turbines in place of reciprocating engines are clearly shown by the figures given above, it is peculiarly interesting to note that the present- day tendency toward less-crowded conditions in central stations makes the actual space reduction per kilowatt of plant rating less real than generally supposed as shown by the following tables compiled from published 2 data from 23 well-known central stations. 1. Capacity, ult. kw. 2. Boiler capacity, ult. hp. 3. Boiler hp. per rated kw. 4. Square feet per kw. (ground-floor plan). 5. Square feet per kw. (total single-deck plan). 6. Square feet per kw. (total generating room). 7. Square feet per kw. (net gen. room exc. switchboard). 8. Square feet per kw. (boiler room actual floor plan). 9. Square feet per kw. (boiler room total single-deck plan). 10. Square feet per boiler hp., boiler room (single-deck plan). 1 Paper before National Association of Cotton Mfgrs., Boston, April, 1913. 2 "Recent Developments on Steam Power Station Works," by J. R. Bibbins, paper before A. S. and T. Ry. E. A., 1907 convention. 72 ENGINEERING OF POWER PLANTS 18 Turbines 5 Corliss, vertical and engines horizontal . F Ratio ~ A, Max. B, Min. C, Avg. D, Max. E, Min. F, Avg. 1 77,500 3,000 30,000 70,000 38,500 50,000 2 62,500 2,500 22,500 43,000 23,000 33,500 3 0.948 0.435 0.71 0.833 0.614 0.67 0.945 4 3.46 0.817 1.84 1.985 0.958 1.44 0.783 5 3.46 1.206 2.04 3.01 1.33 2.24 1.10 6 1.71 0.30 0.81 1.16 0.634 0.82 1.01 7 1.15 0.208 0.59 0.784 0.524 0.65 1.10 8 1.746 0.49 1.13 1.063 0.384 0.66 0.585 9 1.746 0.679 1.28 2.12 0.768 1.42 1.110 10 2.65 0.778 1.77 2.75 1.08 2.10 1.19 Fig. 38. — Comparative size of 1000-hp. pumping engine and 2500-hp. torpedo-boat engine. THE STEAM ENGINE 73 Engine Flywheels. — Flywheels are necessary in the majority of in- stallations. Marine engines require no flywheels, or rather the water- wheel and propeller serve this purpose. The locomotive requires no flywheels since the driving wheels and the living force of the engine and train serve this purpose. When there are two cranks at 90°, or three at 120°, the weight of the flywheel diminishes rapidly. For rough work in rolling mills, etc., with quartering cranks the flywheel is often dispensed with to facilitate quick reversal of the engine. The size of the wheel depends upon the regulation required of a given engine. A variation of 5 per cent, in the speed is often allowable in factory engines while in certain types of electric lighting stations the allowable variation is only 1 per cent. On large, important 60-cycle installations a variation either side of perfect rotation of one-fourth of a geometrical degree has been specified. A fair guarantee to ask is that the speed of the engine shall not vary more than from 2 to 2J^ per cent, above or below the normal speed under any conditions of load. First Cost vs. Economy of Operation. — The first cost of engines of the different types in a measure varies inversely as the economy and durability, but as a rule the saving in the coal bill due to the operation of engines of the better grade will more than pay the excess in the first cost during the first few years of operation, which in some respects might be considered as paying interest on the investment. It is not always true that plants containing the most expensive engines have as a whole the highest initial cost, as the more economical type of engine requires less boiler capacity, and the saving in boiler- room cost may be enough to cover the extra engine cost. For convenience it may be stated that a boiler horsepower requires the evaporation of approximately 30 lb. of water at the usual tem- peratures of feed water and at ordinary steam pressures. As already seen the amount of steam required by different engines varies from about 10 lb. per horsepower-hour in best practice to 50 or 60 in poor grades of engines. This would indicate that with the most economical types of engines 1 boiler horsepower would be sufficient to supply 3 engine horsepower, while with the poorer types 1 boiler horsepower would supply steam for about J£ an engine horsepower. In one case the boiler would have to be of six times the capacity of the other to supply the same amount of power. This may be put in another form as follows : 1 boiler horsepower = 33,480 B.t.u. per hour. In reasonably large plants an indicated horsepower = 12,000 to 24,000 B.t.u. per hour. 74 ENGINEERING OF POWER PLANTS Then in general in large plants it is sufficient to provide only enough boiler horsepower to equal one-half the engine indicated horsepower as this will not only meet the normal engine demand for steam, but will give sufficient margin to cover the cutting out of boilers for cleaning and repairs. For small amounts of power or for intermittent use inexpensive engines will prove satisfactory, but when the cost of power is a large item and when the engine is run continuously, the best is none too good. Engines are usually designed to give the rated power when working with the best ratio of expansion. The most economical use of steam is usually found, therefore, when engines are working under normal full load, provided they are working under favorable conditions. Engines must be properly proportioned for the load they are to carry, if high economy is to be maintained. The best results are invariably found with engines operating under steady load. In electric-power stations the load generally varies within wide limits and a number of tests of such stations shows that the same grade of engine consumes about 50 per cent, more steam for the same work than for service where the load is uniform. Compounding is advisable for large units if the load is reasonably uniform. With a fluctuating load the simple engine governs better and is about as economical. PROBLEMS 2. Engine is 12 in. by 18 in. Piston rod 2.in.; m.e.p. for head end = 40 lb. and for crank end = 37 lb.; 250 r.p.m. Find (a) Horsepower of head end. (6) Horsepower of crank end. (c) Total indicated horsepower (i.hp.). 3. Engine is 6 in. by 9 in. Piston rod 1}£ in.; m.e.p. for head end = 33 lb. and crank end = 30.5 lb.; 300 r.p.m. Find same as in problem 1. 4. A locomotive running at the rate of 45 miles per hour has 72-in. driving wheels and cylinders 18 in. by 30 in. Piston rod 2% in.; m.e.p. 100 lb. Find the indicated horsepower of the locomotive. 5. In problems, 2, 3 and 4, find the horsepower constant for both head and crank end of each engine. 6. An engine is required to indicate 37 hp. with m.e.p. = 40 lb., stroke = 18 in., r.p.m. = 90. Required the diameter of the cylinder. 7. Test the "Handy Rule" on page 19 in problems 2, 3 and 6. 8. A small factory has a 450-i.hp. simple, high-speed, non-condensing engine and a 450-i.hp. compound, low-speed, condensing engine. If the steam used by the two engines is allowed to waste, what will be the difference in the steam consumption of the two engines for a month of 26 days, when operating at full load for 10 hr. each day? 9. What size compound, high-speed, non-condensing engine would give the same total steam consumption as the 450 i.hp. simple engine in problem 8? What size compound high-speed condensing engine would give the same total steam consumption? 10. In a recent engine test the following readings were secured : (a) When running non-condensing ; length of run, 10 hr. ; reading of feed-water meter at beginning of test, THE STEAM ENGINE 75 26,958.7 cu. ft. and at end, 27,324.5 cu. ft.; average temperature of feed water at meter, 195°F.; voltmeter, 230; ammeter, 130. (b) When running condensing; time, 10 hr.; feed-water meter, 34,652.0 and 34,911.6; feed water, 120°F.; load as in (a). Find per cent, gain in water consumption per e.hp.-hr. by running condensing. 11. Given the following data for a steam pumping engine: Diameter cylinders, inches 32 60 90 Diameter piston rods, inches 3 6 9 (rods pass entirely through cylinders) Stroke, feet 5 M.e.p., pounds 68 19 8.5 Water pumped per 24 hr., gallons 36,000,000 Head on pumps, or lift, feet 160 Steam used per hour (containing 2 per cent, moisture) pounds 12,500 Guaranteed duty, foot-pounds, per 1,000 lb. dry saturated steam 140,000,000 Bonus, $1,000 per million ft.-lb. above 140 Forfeiture, $2,000 per million ft.-lb. below 140 R.p.m 21.8 Determine : 1. The indicated horsepower of the engine. 2. The water horsepower of the engine and the mechanical efficiency. 3. The consumption of dry saturated steam per hour per indicated horsepower and per water horsepower. 4. The bonus or forfeiture, if any. 12. The following is the operating performance of a two and three quarter (2%) million gallon centrifugal pumping unit- consisting of two pumps (in series), gear- driven by a condensing steam turbine. Discharge head = 158 lb. per square inch. Suction lift =12 ft. Rate of pumping = 1,890 g.p.m. Steam per hour = 3,965 lb. Steam pressure = 150 lb. per square inch gage and dry saturated. Exhaust pressure = 0.5 lb. per square inch absolute. Determine : 1. The water horsepower; 2. Pounds of steam per water horsepower-hour. 3. Duty per million B.t.u. How does this duty compare with the average performance of reciprocating triple- expansion pumping engine? What considerations might justify the installation of the lower duty centrifugal unit? What brake horsepower rating should be specified for the turbine in the above case? 13. For purposes of preliminary estimate, determine the approximate size of building (square feet of floor area) for a steam-turbine installation of 3,000-kw. capacity. (a) Turbine room; (6) Boiler room; (c) Plant. 14. Determine the heat economy, thermal efficiency, and efficiency ratio of the 169-hp. Buckeye-mobile described on page 53. CHAPTER III ELECTRIC GENERATORS AND MOTORS Efficiency and Cost. — The discussion of electric transmission of power and of the relative merits of the D.C. and A.C. systems will be presented later. The efficiency and cost of this type of equipment are, however, presented at this point. Mechanical Efficiency of Generators. Per Cent. Kw. Load = \i % n H 50 72.0 81.0 84.0 88.0 100 74.5 83.5 86.0 91.0 250 76.0 85.5 89.0 93.0 500 77.5 87.0 90.5 94.5 750 78.0 87.5 91.0 95.0 1,000 78.0 88.0 91.5 95.5 1,500 78.5 88.5 92.0 96.0 2,000 79.0 89.0 92.5 96.5 5,000 79.0 89.0 92.5 96.5 The efficiency of generators at other than full load may be found approximately from the following table. Efficiency of Generators in Per Cent, of Full-load Efficiency Per cent, of rated load 100 Per cent, of full-load efficiency 100.0 90 80 70 60 50 40 30 99.4 98.4 96.8 94.7 92.0 88.0 84.0 With direct-connected engine-generator sets in which the sizes of the two machines are properly proportioned to each other, the individual efficiencies may be combined, giving the following combined mechanical and electrical or the overall full-load efficiencies and relative efficiencies with fractional loads as indicated on p. 77. A convenient method for the conversion of kilowatt generator rating to indicated horsepower engine rating is by combining into one factor the ratio L.„ (746 watts = one hp.), or 1.34, and the above overall efficiencies. For example, the 50-kw. generator set will require at 75.3 per cent. 76 ELECTRIC GENERATORS AND MOTORS 77 Full load Fractional load Rating of generator, kw. Per cent, overall efficiency of unit Per cent, of the rated load on generator Per cent, of the full-load overall efficiency of unit 50 75.3 100 100.0 100 78.5 90 98.5 250 82.8 80 96.1 500 85.4 70 92.6 1,000 87.7 60 89.0 1,500 89.5 50 84.5 2,000 91.2 40 79.4 3,000 91.5 30 72.5 20 62.9 10 50.8 50 X 1.34 overall efficiency, an engine indicated horsepower rating of — n -- ' — = 50 X 1.78 = 89 i.hp., 1.78 being the resultant conversion factor. These factors will be as follows for the several sizes listed. Conversion Factor (Full Rated Load) Rating of generator, Factor 50 1.78 100 1.71 250 1.62 500 1.57 1,000 * 1.53 1,500 1.50 2,000 1.47 3,000 1.465 At fractional loads the factors must be increased with the decrease of the overall efficiency. The conversion factor corresponding to the unit rating may be divided by the proper per cent, of full-load overall efficiency or may be multiplied by its reciprocal. The reciprocals of the per cent, values in the above table, expressed as multipliers, are given below. Fractional Load Multiplying Factor Per cent, load on generator Factor 100 1.00 90 1.015 80 1.04 70 1.08 60 1.12 50 1.18 40 1.26 30 1.38 20 1.59 10 1.97 78 ENGINEERING OF POWER PLANTS The approximate cost of generators and motors is contained in the following tables and diagrams : Direct-current Belted Generators, 1 Cost per Kilowatt Kw. Slow-speed ■ Moderate-speed High-speed 5 $37.00 (1,200 r.p.m.) 28.50 (1,000 r.p.m.) 16.00 (1,300 r.p.m.) 8.50 (100 r.p.m.) $30.00 (1,800 r.p.m.) 10 23.00 (1,800 r.p.m. ) 25 100 $17.00 (900 r.p.m.) 12.30 (675 r.p.m.) Alternating- current Belted Generators Kv.a. Speed Cost per kv.a. 15 1,800 $22 50 25 1,800 18.00 100 900 14.00 500 360 10 00 Alternating-current Direct-connected Generators Kv.a. Speed Cost per kv.a. 50 300 $20.00 75 277 17.00 250 200 11.00 500 120 11.00 1,000 ioo- 10.00 $100 $200 $300 $400 $500 $600 $700 $800 $900 Fig. 39. — Cost of direct-current shunt and compound motors. 115 and 230 volts. (Prepared by L. B. Beatty, 1915.) 1 These costs of generators per kilowatt are taken from the section on costs, " Ma- chine Shop Electrical Handbook," by C. E. Clewell, McGraw-Hill Book Co., N. Y. ELECTRIC GENERATORS AND MOTORS 79 a 20 $100 $200 $300 Fig. 40. — Cost of direct-current shunt and compound motors. (Prepared by L. B. Beatty, 1915.") 550 volts. $200 $300 $600 $700 Fig. 41. — Cost of induction motors — squirrel-cage. 110 to 550 volts, 60-cycle. (Prepared by L. B. Beatty, 1914.) 80 ENGINEERING OF POWER PLANTS 50 Pi X 40 o T-t v II 30 S 20 10 w ##4 YA ^W ,- '// / A- / J&& #\ + / §100 $200 $300 $400 $500 Fig. 42. — Cost of induction motors — phase-wound 2-<£ and 3-tf> (Prepared by L. B. Beatty, 1915.) $600 $700 $800 110 to 550 volts, 60-cycle, 50 £40 o Z <^- o c a £20 o 10 *F — & f 9&* w v * f V '°y °* y / /C^ X 100 500 600 700 200 500 400 Cost in Dollars Fig. 43. — Cost of induction motors — phase wound. 110 to 550 volts, 60-cycle, 2-cf> and 3-(/>. (Prepared by L. B. Beatty, 1915.) PROBLEMS 15. The engine of problem 10 is a simple, high-speed unit. (a) What was the approximate steam consumption per brake horsepower-hour un- der the two conditions of the test shown? (6) What was the approximate steam consumption per indicated horsepower-hour under the two conditions? 16. A test of a compound Corliss engine with D.C. generator, direct-connected, gave the following readings when running non-condensing: Length of run, 5 hr. ELECTRIC GENERATORS AND MOTORS 81 Water-meter readings, 72,850 and 73,500 cu. ft. Voltmeter, 240; ammeter, 1,500. What was the approximate steam consumption per indicated horsepower-hour? 17. The owner of a small factory has installed two simple high-speed non-condens- ing steam engines with direct-connected D.C. generators. Engine A is guaranteed not to consume more than 63 lb. of dry saturated steam per kilowatt-hour at full load. At the time of the test the following data were obtained. Cylinder diameter Stroke Diameter piston rod M.e.p. head end M.e.p. crank end R.p.m. Total steam used per hour = 10 in. = 15 in. = 2 in. = 40 lb. = 42 lb. = 250 = 2,1001b. Engine B is guaranteed not to consume more than 29 lb. of dry saturated steam per indicated horsepower-hour at full load. At the time of the test the following data were obtained. Voltmeter reading Ammeter reading Total steam used per hour = 230 = 230 = 2,850 lb. 1. Was engine A safely within the guarantee? 2. Was engine B safely within the guarantee? 3. Which engine showed the better economy? Approximately how much better? 18. The following are the full-load performances of a 500-kw. direct-connected engine and a 500-kw. turbo-generator operating under conditions as noted : Steam consumption, lb. per hr. Initial press ^ b " per sq - in " Vacu ^ in - of j Superheat Determine for each and compare : (a) The steam economy in pounds per kilowatt-hour. (6) The heat economy in B.t.u. per kilowatt-hour. (c) The thermal efficiency in per cent. (d) The heat economy of a Rankine cycle for the conditions given, in B.t.u. kilowatt-hour. (e) The efficiency of a Rankine cycle for the conditions given, in per cent. (/) The efficiency ratio. per CHAPTER IV FOUNDATIONS 1. Must support concentrated weight of engine upon the ground by distributing the weight over sufficient area to prevent settling. 2. Must go far enough below surface to be beyond settling either from frost, vibra- tions, or influence of loads borne by adjacent ground. Rarely safe to permit a depth less than 3 ft. below the general level. In cold regions effect of frost is felt down to a depth of 6 ft. The foundations for small engines are rarely less than 43^ ft., while for large units the depth is sometimes as great as 20 to 25 ft. Engine foundation depths are usually decided by other considerations than weight, such as location of auxiliaries, cellar or basement, etc. 3. Must have mass and weight enough to hold engine still against unbalanced forces. 4. Must have mass enough to take up vibrations if bedplate is not massive enough. The rules for allowable weight per square foot on different soils vary in different cities, but in general the supporting power in tons per square foot may be taken as (Baker, " Treatise on Masonry Construction"): Rock — granite, etc., in hard compact strata 200 to Rock — limestone, equal to best masonry 25 to 30 Rock — sandstone, equal to best brick masonry 15 to 20 Rock — broken and well compacted 7 to 20 Rock — soft and pliable as shale, equal to poor brick masonry 15 to 20 Hard pan — gravel and sand, well cemented with clay 8 to 10 Clay — thick beds and dry 4 to 6 Clay — thick beds and moderately dry 2 to 4 Clay — soft, wet, confined 1 to 2 Gravel — coarse and dry, well compacted and confined 8 to 10 Sand — dry, compact, well cemented with clay 4 to 6 Sand — clear and dry, confined in natural beds 2 to 4 Quicksand — marshy and alluvial soils, etc., confined 0.5 to 1 If the soil is of low bearing power, piling must be used. Formerly piles were usually of spruce or hemlock. At the present time yellow or red pine, oak, birch and beech are used. Steel piles and concrete piles are also meeting with favor. Wooden piles are at least 5 in. in diameter at the point and 10 in. at the butt for piles 20 ft. or less in length; 6 in. at the point and 12 in. at the butt for piles over 20 ft. long. The "Engineering News Pile Formula/' often used, is, safe bearing power in tons = twice the weight of hammer in tons multiplied by height of fall in feet divided by one + penetration of pile in inches under last blow. 82 FOUNDATIONS 83 Often the tops are cut level and the soil excavated for a foot. Con- crete is then filled in over the heads of the piles, sometimes to a depth of several feet. The Metropolitan Street Ry. 96th Street power house, New York City, and the Kent Avenue Power House, Brooklyn, are on 8-ft. beds of concrete over piles 30-in. centers. Engine Foundations Proper. — The engine builder always furnishes an engine foundation plan, showing the various footings which must be supported and the location and sizes of the various anchor bolts. It is customary to build a wooden template covering the entire foundation and supporting square wooden boxes about 1}^ in. larger internally than the diameter of the foundation bolts. These act as forms and when removed from the foundation allow plenty of play for the founda- tion bolts. The heavy cast-iron washers or anchor plates are set in the concrete form at the base of these boxes and pockets are provided below them so that the nut on the lower end of the foundation bolt may be reached by a wrench. At the present time foundations are always built of concrete in monolithic masses as far as possible, and the foundation is usually allowed to set a week or 10 days before any heavy weights are placed upon it. Good concrete is made by mixing 1 part of good Portland cement, 3 parts of sand and 5 parts of broken stone or gravel, the latter small enough to pass through a 2-in. ring. This should be mixed very wet. Another proportion sometimes used for engine foundations is 1 :2 :4. Concrete foundations weigh approximately 150 lb. per cubic foot. Cost of Concrete Foundations. — Large foundations or foundations of the simplest form may be put in for from $6 to $8 per cubic yard. If the foundations are small or irregular, requiring special forms and considerable template work the price will often be about double the above figures or $13 or $14 per cubic yard complete, including all ex- cavating and carpenter work. Another basis of estimating foundation costs is : Excavation without shoring in soft material 50 cts. to $1 per cu. yd. Excavation without shoring in rock $1 to $4 per cu. yd. Concrete $6 to $7 per cu. yd. Forms 15 cts. per sq. ft. Waterproofing (if used) 40 cts. per sq. ft. Average cost figures for concrete work of a large project recently reported 1 are: Group 1. — For plain concrete used for walls, approaches, bins, con- duits, etc. Group 2. — Miscellaneous concrete foundations. 1 See "Unit Construction Costs" by E. H. Jones, McGraw-Hill Book Co. 84 ENGINEERING OF POWER PLANTS Group 3. — Reinforced-concrete walls, foundations, sumps, etc. Group 4. — Items 1, 2 and 3 combined. Group No. Total amount, cu. yd. Labor cost per cu. yd. Material cost per cu. yd. Total cost per cu. yd. Max. Min. Avg. Max. Min. Avg. Max. Min. Avg. 1 2 3 4 7,779 8,706 2,830 19,315 $8.07 6.85 7.49 8.07 $0.75 2.01 3.40 0.75 $2.85 2.99 3.37 3.37 $8.82 8.90 9.48 9.48 $3.37 3.42 6.42 3.37 $4.82 5.36 5.48 5.48 $16.11 13.52 16.35 16.35 $5.53 6.00 10.35 5.53 $7.67 8.36 13.53 8.85 Anchor dolts Pockets Fig. 44. — Foundation for cross-compound engine A consulting engineer of large experience shows the cost of all the foundations required in steam-power plants to be approximately as follows : Cost of Foundations per Engine Horsepower For Simple Non-condensing: I.hp. of plant Cost per horsepower For Simple Condensing I.hp. of plant Cost per horsepower. . I.hp. of plant Cost per horsepower. For Compound Condensing: I. hp. of plant Cost per horsepower I.hp. of plant Cost per horsepower. 10 $5.70 10 $8.50 40 $7.00 100 $5.70 700 $5.10 12 $5.50 12 5.40 50 5.70 14 $5.40 14 J. 30 75 5.00 200 300 $5 .60 $5 . 50 800 $5.00 900 $4.90 15 5.35 15 $8.10 100 $5.70 400 $5.40 1,000 $4.80 20 $5.25 20 $7.80 30 $5.15 30 $7.40 40 50 $5.05 $4.90 500 600 55.30 $5.20 1,500 $4.40 2,000 $4.10 75 $4.60 FOUNDATIONS 85 Foundation Bolts. — Foundation bolts for small engines are rarely below % in. in diameter and from this they increase in size with the engine and the stresses to 2J^ to 3 in. on large vertical engines up to 10,000 hp. These bolts may be of medium steel and the larger sizes always have upset ends with the threads of a larger size than the body of the bolt. They should not be too long on account of temperature and stress changes, but should run down far enough into the foundations to get sufficient weight of concrete between the engine bed and the anchor plate. The anchor plates are always of cast iron, designed after the manner of column bases and usually have lugs cast on their bottom surface to hold the lower nut. It is not customary to use locknuts on anchor bolts, but they are sometimes used, especially for vertical engines on those bolts which pass through the bearings and are also used to hold down the bearing caps. Grouting. — The bedplate, after being placed on the foundation, is lined up and leveled by means of shims and steel wedges. After this is done the anchor bolts are inserted and the nuts tightened up hand- tight, using a proper wrench for the size of the nut. This leaves a joint between the bedplate and the foundation, which varies from }£ in. in small engines to 1 to 1J^ in. in large engines. A clay dam is now built around the bedplate and cement grout, usually neat or at worst 1 part cement to 2 parts sand, is poured into this space through holes which are left for this purpose in the bedplate. Where the bedplate is hollow it is quite customary to fill it with this cement grout. Care must be taken that there are no air bubbles left under the bedplate and that the cement runs out until held by the dam on all sides of the bedplate. The grout is now allowed to set for 3 or 4 days, the dam and the ragged edges of the grout chipped away and then the foundation bolt nuts are tightened to full bearing by sledging, taking care that the alignment and the level of the bedplate are not changed. Other materials have been used instead of the cement grout, such as a rust joint made out of iron filings and sal ammoniac, melted sulphur, type metal, oakum, felting and in some cases even wooden wedges, but at the present time practically the only material used is the cement grout. Alignment. — If the bedplate is in one casting, as is usual in small engines, it is only necessary to level up the planed surfaces of the guides in two directions at right angles to each other, and even this is not absolutely necessary. Where the bedplate is in two or more parts the problem becomes a much more difficult one. The various sections of the bedplate are assembled on the foundations in approximately their final positions. They are then bolted together, or the T-headed links are heated and placed in the holes provided for them, thus bringing the 86 ELINEERING OF POWER PLANTS parts of the bedplates into close contact by the shrinking of the links. The bedplate, then, as a whole is wedged up until it is level in both directions. It is frequently necessary during this period, especially in vertical engines, to have one part of the bedplate slightly higher than its final position in order that the deflection caused by the added weights placed on the plate may just bring the bedplate to a true level. This work will be greatly expedited by the use of an engineer's level, although on smaller engines it is customary to level and center the bedplate from wires which have been stretched through the final axis of the cylinder and shaft. It should be remembered that with large shafts and with considerable distance between the bearings there will be measurable deflection, in which case, with vertical engines, the cylinders will not be set in the vertical plane, but will be inclined so that the cylinder axis will be at right angles to the shaft in its deflected position. The cylinders of a 5,000-hp. cross-compound vertical engine, with the flywheel and generator between the cylinders may be as much as %>{$ in. closer together than the centers of the cranks. In one case on an engine of this size where the generator and flywheel were outboard of the engine, the outboard bearing had to be set nearly % in. above a true level to produce quiet and cool running. PROBLEMS 19. Estimate the size and cost of foundations for the following steam engines. (a) 50-hp. simple high-speed. (b) 500-hp. tandem compound Corliss. (c) 2,000-hp. Manhattan-type Corliss compound. 20. The dimensions of bedplate of a 1,000-kw. turbo-generator are 6 ft. 6 in. by 17 ft. in. The distance from basement floor to turbine-room floor is 14 ft. The soil below basement level is moderately dry clay. Sketch a proposed foundation for the turbine and estimate the cost of the same. 21. Eight steam-engine and generator units of 2,500 kw. each, weighing with auxiliaries 350 lb. per indicated horsepower, are to be erected on a pile foundation. The area covered is 100 ft. by 100 ft. Piles, 4 ft. center to center. In driving the piles a 2,000-lb. hammer was used; drop, 10 ft. ; last penetration of pile, 1 in. Is the founda- tion safe? If so, how much leeway is there for each pile, in pounds? If not safe, how much excess load is there for each pile, in pounds? CHAPTER V CONDENSERS Condensation may be considered as of two kinds; mixed condensation when the steam and cooling water are brought together in the same vessel or machine as in the jet, barometric and ejector types, and surface condensation when a film of metal prevents mixing as in the surface and atmospheric types. STEAM ENTRANCE <— K-> Parallel-flow type Fig. 45. Mixed Condensation. — C3T Counter-current type Barometric condenser heads. Let t 8 be the temperature of the steam to be condensed. t be the temperature of the injection water. t\ be the temperature of the outlet or hotwell water. H be the total heat in the steam at t a . h be the heat in the liquid at t\. w be the pounds of steam per hour to be condensed. Q be the pounds of water per hour needed for condensing. Then = R = H~h (1) and R is the ratio of water to steam w h — t required for condensation. ti theoretically is equal to t 8 but in practice h is from 5° to 10° lower than t 8 owing to the presence of air and imperfect mixing. In pro- 87 88 ENGINEERING OF POWER PLANTS portioning ordinary jet or barometric condensers w is the normal amount of steam to be condensed and a 50 per cent, overload is common at some reduction of vacuum. Let G = the cubical contents of the cone in cubic feet. Then G = 0.00143w + 8.25 cu. ft. The allowable velocity in the tail pipe is 5 ft. per second. Then / = 0.073 \/jv in. A = 15.7 VG in. B = 0.3A C = 1.2A J-l for small sizes. J-2 for large sizes. ^5 for 26-27 in. Increase slightly for 28 in. (2) (3) (4) H = I = Steam velocity in K about 600 ft. per second. K = abt. (5) The height of the flange x above the level of the hotwell should never be less than 35 ft. and may be greater to advantage. Size of condenser, lb. of steam per hr. 5,000 10,000 15,000 20,000 25,000 30,000 40,000 50,000 60,000 80,000 100,000 Exhaust K 10" 14" 17" 20" 22'/ 24" 28" 32" 35" 40" 45" Tail pipe J 6 8 9 10 11 12 14 16 18 20 24 Injection H 5 7 8 9 10 11 12 14 16 18 20 Air J 2 38 3 45 3 48 3 52 4 56 5 60 5 63 6 68 6 72 7 78 8 Diameter A 82 B 9 13 14 16 17 18 19 20 21 23 25 C 45 54 57 62 67 72 75 81 86 94 99 D 28 33 36 38 40 42 46 50 52 57 60 E 56 66 72 76 80 84 92 100 104 114 120 The condenser bell should be as near to the exhaust flange as possible as friction and velocity head count up very fast with good vacua. The barometric pipe may be replaced by a pump of some kind. In the ordinary jet condenser the bell is placed over the suction chamber of the pump. In all arrangements of this type there must always be a suf- ficient head of water over the suction valves to ensure their rising. Ejector condensers follow the same principle as the ordinary type when a tail pipe is used and the throat of the ejector is usually figured for a velocity of 15 to 20 ft. per second. Here K = w 50 as before, inches H = 0.073 Vw - 1 in. CONDENSERS 89 T = 0.6# in. J = 0.073 Vw in. = 5K about The flange X should be about 40 ft. above the level of the tail water. [Injection I K-w— >) Exhaust ~~A Fig. 46. — Ejector condenser, Bulkley type. Fig. 47. — Ejector condenser, Schiite & Koerting type. SCHUTTE Eductoe Condenser Pounds steam per hour A B C D E G 520 9 6M m 2 w IK 1,040 123^ 8 ±% 3 2 2 2,240 isy 2 11 5 4 3 3 3,300 2iy 2 13 5M 5 3^ 33^ 4,800 25^ 15 VA 6 4 4 6,600 30K 17 7K 7 43^ 43^ 9,000 35M 19 8 8 5 5 12,000 41 21V 2 9 9 6 6 15,000 46K 23H 10 10 7 7 21,000 53 27 11 12 8 8 28,500 61M 30 12 14 9 9 36,000 70 34 14 16 10 10 24,000 80 38 15 18 12 12 60,000 90 43 18 20 14 14 90,000 108 51 21 24 16 16 90 ENGINEERING OF POWER PLANTS Ejector condensers without the tail pipe are common and when properly installed and operated work very well. Condenser bells of most any shape may be used and are equally efficient if the water and steam are brought into contact and the air is collected and carried away. This may be done by a separate dry air pump, or the air pipe may be led into the throat of the tail pipe. Surface Condensation. — The steam is condensed on the outer surface of metallic tubes through which the condensing water flows. Let N = total heat to be transmitted per hour, B.t.u. S = outside surface of tubes, total in square feet. 6 m = mean temperature difference of water and steam, °F. K = coefficient of heat transmission, B.t.u. per square foot per hour, per °F., diff. in temperature. Then N = K$JS Q = w ^^4 (6) and N = w(H - h) S = -^ — '- = -^ — -' (7) Let t a = vacuum temperature. For practical work K may be taken as constant for any one con- dition, although it has been shown by experiment to be subject to small variations with 6 m . The mean temperature difference for rough calculation with small rise in temperature of the circulating water may be the arithmetical mean without serious error, but for "most calculation the geometrical mean should be used. A- = -^~i (8) The quantity of circulating water Q is a function of the number and size of the tubes, the number of water passes in the condenser and the velocity of the water in the tubes. The values of K depend on the velocity of the water also as well as on the material of the tube, its cleanliness and the richness of the steam and air mixture in the condenser. The general formula for K is K = kcp 2 U\/V w (9) Where k equals 350 a constant, c equals the cleanliness coefficient varying from 1.0 to 0.50, P 8 p equals the air richness ratio ^ ? - ■Lt U equals the material coefficient. 1.0 for copper. 0.98 for admiralty mixture. 0.97 for admiralty mixture oxidized. CONDENSERS 91 0.95 for Muntz metal. 0.92 for aluminum bronze. V w = water velocity in tubes, feet per second. The water velocity should be about 8 ft. per second. The material coefficient may usually be taken at 0.95 and the cleanliness coefficient at about 0.9 for such waters as New York or Chicago. The air richness coefficient is exceedingly difficult to measure experimentally but for tight condensers with efficient air pumps it may be taken at from 0.95 to 0.97. Under these conditions K = 782. The value of K = 782 is thus under the best conditions and should not be taken for design since tight condensers and air pumps are not the rule but the exception and tubes soon oxidize or become coated with dirt and scale. In com- mercial work K = 350 seems to be the usual figure but values as high as 600 have been guaranteed. It should be remembered that a surface condenser is rarely tested to its limit. In condenser design the given quantities usually are w, t and the required vacuum. It is important that the place of measurement of the vacuum should be stated and this is usually in the nozzle connect- ing the prime mover to the condenser. The best vacuum will always be found at the air-pump suction, less in the body of the condenser, and the worst in the nozzle. The vacuum inside the prime mover will be less by the velocity head necessary to give motion to the exhaust and by friction in the nozzle. The allowable velocity in a turbine nozzle is about 600 ft. per second. Starting with the vacuum in the nozzle certain assumptions must be made; first, the loss in the condenser known as drop — this in a well- designed condenser should not exceed 0.2 in. of mercury and t 8 should be taken as the temperature corresponding to this reduced vacuum. For good practice h should be from 8° to 10°F. lower than t a and h — t Q is now known. H and h are known from the steam tables and Q may be calculated. — the ratio of cooling water to condensed steam usually ranges from 50 to 100 and it should be remembered that a large ratio means more power required in the circulating pumps. Having t 8 , t and ti the mean temperature difference may be calculated from (8) and the surface from (7). Small tubes are best for the transmission of heat but cannot be used with dirty water so that the usual sizes are % in., Y± in., 1 in. and in some cases with very bad water 1J^ in. or even larger. Let a = area of tube in square inches. I — length of tube in feet (sum of all passes). d = diameter of tube in inches. 92 ENGINEERING OF POWER PLANTS n = number of tubes in one pass. A = area of one pass in square feet. / = number of passes. Then 144A Q f . n a ~ 1,560(17* U ; and i = ^ (ii) The length of a single tube is -- and the tube ratio is -;. This should be between 30 and 50. The best value of this ratio has not been estab- lished by experiment. Some adjustments may be necessary due to space and other con- siderations which can be made at this time. Tube spacing is important as there must be room for the glands and sufficient metal between them for strength. The minimum allow- able spacing or pitch of tubes is \ %-in. tubes 1 ^{Q-m. pitch 192 tubes per square foot. %-in. tubes lK6-i Q - pitch 147 tubes per square foot. J£-in. tubes 134 -i n - pitch 106 tubes per square foot. 1 -in. tubes \% -in. pitch 88 tubes per square foot. 1^-in. tubes \% -in. pitch - 63 tubes per square foot. The number of tubes per square foot of tube-sheet surface is given w k 166 roughly by n = p^- 2 . Glands should be of the same metal as the tubes and be provided with an inside lip to prevent creeping of tubes. The entrance of the gland should be rounded. Rubber rings are much used for packings on European condensers with fresh condensing water, but the screw gland with corset-lace pack- ing put in with an automatic gun is probably best. Tube packings may be fiber, woven hose or corset lacing. No animal or vegetable fats should be used on the packing as they form soluble compounds with copper, paraffine is the best wax to use with woven packings. Tube sheets should be Muntz metal or brass. A rolled sheet will give the best service although cast sheets are used. The thickness of tube sheets should be }/% in. to % in. larger than the tube diameter. Condenser shells are usually of cast iron ribbed outside against collapsing pressure but may be of steel plate or sheet brass (navy practice) stiffened with angles. Tubes should be supported at distances of 60 to CONDENSERS 93 70 diameters by supporting plates usually of cast iron, drilled with 3^6' m - clearance around the tube. Water boxes should be large and designed to offer as little friction as possible to the passage of the water. A hole }/% in. in diameter in the partition will allow the upper box to drain when not in use and the condenser is usually set on a slope of 1 in. in 15 ft. so that the tubes may drain. Where possible the steam should enter from the top and water at the bottom (counter-current principle) but this is not essential as parallel flow condensers give good results. tXMAUJT STLAM INLET COMOCMATt Fig. 48. — Cross-section spiroflow surface condenser. The bottom of the circulating water outlet should be above the highest point of the tube bank. If this cannot be done at the water box the pipe should be carried up to the same height away from the condenser. The steam passage should be direct to the tube bank and if possible the nozzle should be spread so no dead spots may be left away from the path of the steam. The upper bank of tubes may have a wider spacing than the lower or channels may be left open into the tube surface to afford a free passage for the steam. Baffle-plates and guide plates are also used for the same purpose but are not as efficient. The steam flow should be directed to the coldest part of the condenser and here the dry air suction should be taken out. The suction should be screened to prevent water being carried into it. 94 ENGINEERING OF POWER PLANTS Water connections should be figured for a velocity of 10 ft. per second and the air connection should be at least twice the hotwell water size which should be figured for about 6 ft. per second. Owing to the wide range of steam consumptions for engines no definite relation exists between engine horsepower and required con- denser surface. Similarly no definite relation exists between the con- densing surface and the amount of steam condensed unless the cooling water temperature is constant. An average figure commonly quoted is 10 lb. of steam condensed per square foot of condensing surface for 24 to 26-in. vacuum with 70°F. cooling water. Fig. 49. — Cross-section Westinghouse surface condenser. Although the circulating water required per pound of steam con- densed varies widely in practice, depending on the vacuum maintained, the difference between the temperature of the steam due to the vacuum and the temperature of the condensate leaving the condenser, and the amount of air in the condenser, yet the following figures will serve as an indication of the variation in the amount of circulating water required due to differences in initial temperature of the circulating water. CONDENSERS 95 Pounds circulating water per pound steam condensed ( = R) H-h t\ — t t\ = t s — 5 R = Vac. H-h U h R to = 50 V/X;A-,. W/%* Fig. 91. — Stirling-type boiler. Cost of Fire-tube Boilers. — Hp. Average size Cost f.o.b. factory Cost per hp., f.o.b. factory Cost of setting Cost of boiler set Cost set per hp. 50 60 70 80 100 125 150 175 200 54" X 14' 54" X 16' 60" X 14' 60" X 16' 66" X 16' 72" X 16' 78" X 18' 565 620 700 850 1,000 1,170 1,310 1,400 $9.65 9.42 8.85 8.75 8.50 8.00 7.80 7.50 7.00 260 295 300 310 385 450 500 540 $725 825 915 1,000 1,160 1,385 1,620 1,820 1,940 $14.50 13.75 13.10 12.50 11.60 11.10 10.80 10.30 9.70 THE STEAM BOILER 135 These figures may be reduced to the following approximate formulae for the cost of horizontal fire-tube boilers. Cost f.o.b. factory ($) = 180 + 6.4 X hp. Cost of setting ($) = 140 + 2 X hp. Other cost figures reported give results considerably below those of the formula above, the average of three such formulae being f.o.b. cost ($) = 100 + 4.5 X hp. Fig. 92. — Heine-type boiler. Cost of Water-tube Boilers. — The following table gives the average prices for several different makes of water-tube boilers f.o.b. factory. Hp. Total cost Cost per hp. 100 $1,360 $13.60 * 125 1,540 12.30 150 1,730 11.50 175 1,950 11.15 200 2,200 11.00 250 2,600 10.40 300 3,100 10.30 400 4,100 10.20 500 5,000 10.00 136 ENGINEERING OF POWER PLANTS From these figures the following formula is derived : Cost f.o.b. factory ($) = 425 + 9 X hp. For want of better average figures on price of settings for water- tube boilers, the formula for settings for fire-tube boilers may be used, viz.: Cost of setting ($) = 140 + 2 X hp. Fig. 93. — Herreshoff boiler. Another estimate for the cost of the brickwork for boiler settings is: $3.50-$3.00 per hp. up to 100 hp. 2.50- 2.00 per hp. up to 200 hp. 2.00- 1.00 per hp. above 200 hp. ($1.00 at 500 hp.) Potter's formula? (Power, Dec. 30, 1913)— slightly modified— for the cost in dollars of the usual sizes of water-tube boilers are: For vertical boilers = 900 + 6.3 X hp. For horizontal boilers = 150 + 8.2 X hp. The following table gives the prices of high-grade water-tube boilers, f.o.b. factory in 1916. THE STEAM BOILER 137 Fig. 94. — Almy water-tube boiler. Horizontal Water-tube Boilers with Cast-iron Headers, 160 Lb. Pressure Single boiler Two in battery Hp. each boiler Total cost Cost per hp. Total cost Cost per hp. 200 $3,000 $15.00 $5,900 $14.75 300 4,000 13.35 7,750 12.90 400 4,800 12.00 9,350 11.70 500 6,000 12.00 11,350 11.35 600 7,200 12.00 Horizontal Water-tube Boilers with Wrought-steel Headers, 200 Lb. Pressure Single boiler Two in battery Hp. each boiler Total cost Cost per hp. Total cost Cost per hp. 200 $3,900 $19.50 $7,600 $19.00 300 5,000 16.70 9,600 16.00 400 5,800 14.50 11,500 14.40 500 7,050 14.10 14,000 14.00 600 8,750 14.60 138 ENGINEERING OF POWER PLANTS Average Cost of Boilers. — The average cost of boilers including set- ting, as reported by one consulting engineer, on the basis of boiler capacity required for the indicated horsepower rating of the plant is : Cost of Boilers per Engine Horsepower (Including Setting) Simple non-condensing Engine horsepower. . . . Cost per horsepower. . . Simple condensing: Engine horsepower. . . . Cost per horsepower. . , Engine horsepower. . . . Cost per horsepower. . . Compound condensing: Engine horsepower. . . . Cost per horsepower. . . Engine horsepower. . . . Cost per horsepower. . . 10 12 14 15 20 30 40 50 75 $56.00 $51.00 $46.00 $43.50 $32.00 $26 . 00 $24.00 $20.50 $17.30 10 12 14 15 20 30 $35.50 $33.10 $29.60 $28.50 $25.10 $20.50 40 50 75 100 $17.80 $15.80 $14.80 $14.20 100 200 300 400 500 600 700 800 $8.00 $7.60 $7.40 $7.30 $7.25 $7.20 $7.15 $7.05 900 1,000 1,500 2,000 $6.90 $6.80 $6.60 $6.40 Furnace Design. — There is no other apparatus in a power plant upon which so much depends as the boiler furnace. This is usually the place to look for increased economy. Considering the design of the furnace, there are three essential features: First. — A grate must be provided upon which to burn the coal. Second. — Means must be provided for the admission of a proper amount of air to facilitate combustion. Third. — A combustion chamber must be installed, of the proper shape and capacity, for the gases which are to be burned. Flat grates are used when coal is fired by hand. They may be classified as shaking and dumping grates. The shaking grate is best adapted for burning coal which has a limited amount of ash, and which does not clinker badly. The dumping grate is adapted, as well as any, to practically all kinds of fuel, though generally it is more expensive than the shaking grate. When forced draft is installed, the air is generally admitted in the front of the ashpit which forms a chamber large enough to allow the air to come to rest, the pressure in this chamber forcing the air through the fire more or less uniformly. When the induced draft system is used, the ashpits are left open and the air is drawn in under the grate, or through the fire-door, or at any other place where there may be a leak. THE STEAM BOILER 139 When forced draft is produced by a steam jet — which is frequently used in very small installations — it is common practice to place this steam jet in the side wall in the ashpit. These steam jets are commonly believed by the operating engineers to be especially advantageous on account of the prevention of clinker in the ash. This is a very poor FORD. Fig. 95. — Babcock & Wilcox marine boiler. means for preventing clinker, however, as clinker formation is reduced because the steam cools the fire below the clinkering temperature. Re- cently a combination turbine-driven disk-fan has been used, which is very well adapted to these small installations on account of the fact that a much less percentage of steam is passed into the grates along with the air. The warm air is a great help to the combustion of the coal, but few attempts have been made to preheat the air before introducing it under the grate. 140 ENGINEERING OF POWER PLANTS One system which has been used to a small extent, is that of forcing the air through passages in the bridge-wall and side walls, but these chambers gradually become clogged, and the maintenance expense is usually too high to make the advantage derived from the warm air worth while. For internally fired boilers the Howden and Ellis-Eaves systems are much used in marine practice and also in stationary practice abroad. In Howden's system the air, driven by a fan, is forced through tubes in the uptake. Here it is heated and then led into the ashpit and also above the grate. The Ellis-Eaves system includes the induced draft principle and is usually applied to boilers with larger tubes than the Howden system. The most important consideration in the design of the furnace is in the combustion chamber. The more volatile matter the coal contains, the more difficulty this problem presents. In burning the fine grades of anthracite, it is possible to have the heating sur- 1 JfilS|PlP%f1 faces of the boiler relatively close to the grate, as practically no hydrocarbons are distilled from this coal. With horizontal multitubular boilers, the distance from the top of the grate to the underside of the boiler is not over 2 to 3 ft., and in many cases, under these conditions, this coal is burned with fairly good results. When soft coal, however, is burned in the same furnace, it invariably produces a large amount of smoke, ^|jj| and the furnace efficiency is very low. When p IG 96 —Boiler econ- ^ e hydrocarbon content of the coal is distilled omiser, superheater and off, before it can be sufficiently mixed with the ^mJSkw? air t0 burn ' ** comes int0 contact with the sur " face of the boiler, and is chilled to a point below the combustion temperature. To prevent this, an arch or arches may be provided under the shell of the boiler, or the furnace may be built in the form of the well-known Dutch oven. A very good setting is produced by springing several arches across the grate, between the side walls of the boiler, leaving an area between these arches, through which the gases" may pass, about equal to the area blocked by the arches. The height at which the boiler shell should be set above the grate depends upon the amount of volatile constituent in the coal. With coal containing from 15 to 20 per cent, volatile matter, this distance should be not less than 4 to 5 ft. ; and if the coal contains a larger amount of volatile matter, this distance should be increased as far as possible. The Dutch oven, of course, will produce a better result than the construction just described, but it is more expensive to install, and it THE STEAM BOILER 141 must be built out in front of the boiler, taking up a considerable amount of space. The maintenance is also probably in excess of that of the arches. When water-tube boilers are installed, the design of the furnace takes a somewhat different form. In the first place it is always much wider than for fire-tube boilers; and, again, constructive considerations make it easier to obtain the required volume for the combustion chamber when burning highly volatile coal. In burning fine grades of anthracite, in many cases a plain, flat grate only is provided, and this gives fairly good results. The Webster furnace which has been used in some very large installa- tions of late years, is designed, primarily, for burning fine anthracite, and has given excellent satisfaction. This furnace consists of four fire- brick arches sprung across the grate between the side walls of the boiler, their object being to prevent the cooling of the fire when the doors are opened for firing. This is a very important matter, especially when induced draft is used, as in this case the pressure of the atmosphere is anywhere from ^{q to 1 in. of water above that over the fire; and when the doors are open an immense amount of cold air will rush in, chilling the tubes and cooling the fire. When forced draft is in use, the difference in pressure between the air outside and that over the fire is only sufficient to carry away the flue gases, and is seldom over }{q or %o in. of water, as the air is forced through the fire by the draft. For burning bituminous coal under the water-tube boiler, the number of different types of furnaces used is almost infinite. With the boilers of the Babcock and Wilcox type, the Murphy furnace — which is essentially a Dutch oven — is frequently applied, and generally produces good re- sults. These boilers are, however, most always used with some form of mechanical stoker, and will be considered later. The plain Dutch oven is sometimes used, but only on coals of rela- tively high volatile content. One of the most effective ways of in- creasing the volume of the combustion chamber, and keeping the volatile gases from contact with the water surfaces of the Babcock and Wilcox type of boiler, is to provide a baffle covering the lower portion of the first and second passes, thus circulating the products of combustion first over the bridge-wall, thence up through the third pass, down the second, and up the first pass to the uptake. This makes possible a firebrick roof over the whole grate, extending some 3 or 4 ft. back of the bridge-wall, and has all the effect of a Dutch oven without the dis- advantages of the latter. The scheme does not require any extension front built out from the boiler. A very important consideration, irrespective of the type of furnace put in, is the height of the boiler tubes above the floor or, what amounts 142 ENGINEERING OF POWER PLANTS 5 13 tJ-H ill rrT-i i ' i ' i v~r s 3 i , i . i, i . i T^T^T 1,1,1 I I I I 1 .1.1,1. 1 .1. T~T III G^T ' ii*ii i i i i 7~r -Air Space ; i i i i i i — r 1 I II I ill T~T EZZ III I III 5=ft K-H-l-> J 1 III III I II ill II i i i i i i i 2E GROUND PLAN I I I rS 1 1 , 1,1 1, 1 ,1 ^ II ' I ' T I I I I I -Air Space | | | | | | | | | | I I I -ZL 1, 1 , 1 L=C I I I I III I I I I I I C I , I 1=3* ' ' ' "^ T i_ K It x I v-y — AE- H i i i i i ~r ^^^^^^^^^^^^^^^^^^ XX 1 FRONT ELEVATION !«— H- #mMM»MM^^^ SECTION ON LINE A.B. ] Fig. 97. — Setting for flush-front boilers. THE STEAM BOILER 143 FRONT ELEVATION ■ Fig. 98. — Setting for arch-front boilers. Floo r Level H-^j h— H — H • SECTION ON LINE A.B. , 144 ENGINEERING OF POWER PLANTS to the same thing, above the grate. Formerly it was considered customary to install the B. & W. boiler with the bottom of its front header about 7 ft. 6 in. above the floor line. This distance has been gradually in- creased for burning the high-volatile bituminous coals, to 9 ft. ; and now, in some of the most recent installations, has been made 10 to 12 ft. above the floor line. Even this figure might well be increased for burning western coals which contain 30 per cent, or more volatile matter. Another type of furnace, although not very widely used, for which a great deal is claimed, is the Hawley down draft furnace. This con- Fig. 99. — Bigelow-Hornsby boiler. sists, essentially, of an ordinary flat grate above which, some 2 ft. or more, is a secondary grate composed of tubes through which the boiler water circulates. The coal is fed onto this secondary grate. The gases are distilled from it here, breaking the coal up and allowing it to fall through the bars onto the main grate. The gases from the fresh coal, as it is coked on the secondary grate, pass down through the incandescent coal which lies underneath, and thence into the combustion chamber. Here the gases, which by this time are more or less thoroughly mixed with air, are burned by the heat of the burning coke on the main grate below. THE STEAM BOILER 145 In considering the amount of coal which can be burned per square foot of grate surface, we find variations under different conditions of from 12 to 125 lb. per hour. In central-station practice, burning the finer Fig. 100. — Large Stirling boiler as installed at Hauto, Pa. grades of anthracite where forced draft is almost universally employed, it is customary to burn, under normal conditions, in the neighborhood of from 25 to 30 lb. of coal per square foot of grate. On the peak loads by in- creasing the draft on the fire, this figure may be, and very often is, in- 10 146 ENGINEERING OF POWER PLANTS creased to 50 lb. per square foot. The economy when this latter amount of coal is burned, is somewhat diminished, due largely to the fact that the draft necessary to burn this amount of coal is sufficient to cause a certain percentage of it to pass into the back combustion chambers of the boilers, and to be deposited in the flues unburned, causing con- siderable loss. Soft coal is very seldom burned on flat grates in any of the reasonably large central power stations, some form of mechanical stoker being em- ployed. When soft coal is burned on flat grates, however, it is usually customary to burn not over 20 lb. per square foot, as it is very difficult with hand-firing, to produce an even distribution of air, and in conse- quence, if sufficient time is not given the air to mix with the volatile gases, a large part of these will pass off unburned. Furnace Losses. — The most serious furnace losses are: (a) Heat necessary to create draft. (6) Heating air used for combustion. (c) Heating ash. (d) Radiation. (e) Incomplete combustion, smoke, etc. (/) Imperfect transfer of heat. Mechanical Stokers. — The Stoker Problem. — In considering whether or not mechanical stokers should be installed in a proposed plant many technical factors and local conditions must be taken into account. The kind of coal to be burned and its cost are important factors. In general it may be stated that unless the firemen are expert and exception- ally well handled, coal will be burned more economically by using a reasonably well-designed mechanical stoker than by the hand-fired method. The quality of the labor at hand if not of a good character gives added weight to the stoker as it does not require such intelligent firemen to handle the stokers properly as it does to fire the coal by hand with equal efficiency. The labor problem is also important in the larger plants on account of the possibility of strikes. In small plants it is always a question whether the saving in labor and coal will warrant the investment for stokers. In localities where the finer grades of anthracite,, such as the buckwheat sizes, are available at a low price it will generally be more economical especially in the smaller plants to fire the coal by hand. In the larger plants the price of the coal must be weighed care- fully against the other conditions previously noted and the decision must be made on the merits of the individual case. There is one other point which perhaps gives some advantage to hard coal and that is when large storage capacity is required. Hard coal may be stored in practically unlimited amounts, while it is well known that great difficulty due to spontaneous combustion is experienced in storing THE STEAM BOILER 147 large quantities of bituminous coal especially when it runs high in volatile content. A number of plants for the storing of bituminous coal under water to prevent loss by spontaneous combustion have been installed. Fig. 101. — Green chain-grate stoker under Stirling boiler. Fig. 102. — Green chain-grate stoker. Types of Stokers. — There are three general types of mechanical stokers, although there are several which cannot be conveniently placed in any one of these classes. The first is the chain-grate stoker consisting of an endless chain placed 148 ENGINEERING OF POWER PLANTS in the furnace of the boiler with its top side revolving slowly from the front of the furnace toward the back. The coal is fed onto this moving grate in front and is burned as it passes toward the bridge-wall, where, when the grate is moving at its proper speed, the coal will have been completely burned to ash which will drop down into the ashpit below. Some representative stokers of the chain-grate type are the Babcock and Wilcox, the Green, the Playford and the American. The second type of stoker is the inclined overfeed type, of which the Roney, the Ross, the Murphy and the Wilkinson are examples. These stokers consist of movable bars forming an inclined grate with a Sectional Throat Piece (Always specify number of pieces wanted)_ Hopper-End - Boiler Front ^p Cover Angle \ I Stoker Number Here Hopper Shaft ^ Hand Wheel . Stud- Hand Wheel - Agitator Sector-. Agitator -~ Sheath-Nut' Sheath' Face-Nut - Lock-Nut - Eccentric' Eccentric Strap' Dumping Grate Handle 1 Connecting Kod Guard Handle Guard Handle Catch' Door Handle Grate Bar Top 2rRequired for each web - Cross Bar Dumping Grate Bearer "Bearer Key Center Bearer Shoe Side Bearer or Middle Bearer Shoe Fig. 103. — Section of Roney stoker. mechanism for moving these bars in such a manner as to cause the coal which is fed in at the top to be pushed gradually down the grates until it reaches the dumping grate at the bottom, at which point it should be completely burned. The third type is the underfeed of which the Taylor, the Jones and the American are typical examples. In these stokers the coal is fed onto the grate or up under the grate in such a manner that the fresh coal is always close to the grate while the coal which is being burned is at the top. The air is also introduced at the bottom and while passing up through the bed of coal is heated and thoroughly mixed with the volatile gases distilled from the coal and when passing through the incandescent THE STEAM BOILER 149 layer at the top reaches its temperature of combustion, so that generally no arches are necessary. There are several other stokers which are used to a greater or lesser extent and work on somewhat different principles, perhaps the most notable being the so-called "finger" stoker which has several oscillating paddles which pick up the coal and throw it into the furnace. There is another stoker somewhat of this order in which the coal is mechanically shovelled into the furnace. These stokers, however, have not reached any extensive application as yet and in general are only applicable to particular conditions. Chain Grates. — The one great advantage of the chain-grate stoker over most of the others is that it is suitable for burning with natural draft Transverse Section Fig. 104. — Murphy stoker. bituminous coals of very high volatile content. In plants where the load is reasonably steady and where sudden peaks are not thrown upon the boilers this stoker makes a first-class installation. There are two serious troubles with this type of stoker which always have to be contended with. The first of these is the leakage around the back of the stoker which, in most installations, is very large and cools the combustion chamber beyond the point at which volatile gases are ignited. This has been obviated to a large extent by certain of the manufacturers by placing a long flat arch from the bridge-wall toward 150 ENGINEERING OF POWER PLANTS Fig. 105. — American underfeed stoker. Fig. 106. — Taylor underfeed stoker. THE STEAM BOILER 151 the front so that the air which pours up from the back of the chain grate will be heated to a sufficient temperature so that it will not cool off the combustion chamber. The other trouble which must be looked after carefully is the very large percentage of combustible in the ash which always occurs with a chain-grate stoker in spite of the fact that the ash- pit only covers, in most cases, less than one-third of the area under the grate. The method of feeding the coal on to the moving grate varies in the different makes. In the Playford and the Babcock and Wilcox stokers no feeding device is used, the coal coming from the hopper directly onto the grate. In the Green stoker the coal from the hopper is coked on a series of movable bars which feed it down onto the chain grate. The American stoker has no device for feeding the coal to the chain grate but at the bridge-wall end a separate dumping grate is used instead of allowing the ashes to merely fall over the end of the grate. The coking arches vary but very little in all of these makes, these variations being due primarily to the different volatile contents of the coals to be burned. Combustion. — The student will find available an unlimited amount of good material relating to combustion. One of the most satisfactory presentations of this subject is that of H. deB. Parsons in his book on "Steam Boilers" 1 from which much of the following material is taken. "When heat is applied to coal, the resulting combustion is effected as follows: first, the absorption of heat; second, the vaporization of the bituminous or hydro- carbon portion and its combustion; and third, the combustion of the solid or carbonaceous part. These actions are entirely separate and distinct, and must take place in the order as given. The hydrocarbon or bituminous portion consists of marsh gas, olefiant gas, tar, pitch, naphtha, etc. The flame is derived from the gaseous portion, and this explains why the soft or bituminous coals burn with more flame than the anthracites. Coal gas, taken by itself, is not inflammable, as a lighted taper placed in a jar of coal gas will be extinguished. In order to consume it oxygen must be sup- plied, that is, the gas must be mixed with air. When this is done the gas will be consumed instantly, provided the proper temperature be present. When a charge of fresh coal is thrown on a fire we cannot control the amount of gas that may be generated, but we can control the supply of air. Therefore it is essential, when soft coals are to be burned, that a certain amount of air be admitted in addition to the regular supply through the grate, during the periods of evolution of the gases. This can be accomplished by permitting air to enter above the grate, or directly into the combustion chamber behind the bridge wall, or both. The quantity admitted should bear some suitable relation to the per- centage of the hydrocarbons contained in the fuel. It is best in all cases to pro- vide ample passages for the air, and then to admit the proper quantity as deter- mined by trial and observation of the smoke produced. In order to burn the coal economically, it has been found necessary that an 1 "Steam Boilers," by H. deB. Parsons, 4th edition, p. 15. 152 ENGINEERING OF POWER PLANTS excess of air should be allowed to enter the furnace. If only the theoretical quantity be supplied, a large proportion of the carbon will either not be con- sumed or be only half burned to carbon monoxide (CO). On the other hand, too great an excess, as well as a deficiency of air, is a detri- ment to the economical working of the furnace. Much depends upon the design, especially with soft coals, for the requisite quantity may be supplied in a manner as not to be available; that is, the particles of oxygen may not come into contact with particles of carbon. In short, the air and particles of fuel may not mix, but rush to the chimney in " stream-lines." "The temperature at which some of the physical and chemical changes take place when a fresh charge of coal is thrown on a fire are about as follows: 1 (a) Previous to putting on a charge of coal the temperature of the bed of coals is from dull red heat (700°C. or 1,292°F.) up to a bright white heat (1,400°C. or 2,552°F.) or even higher. (b) The coal, when fired, is about 15°C. or 60°F. (temperature of the room). As soon as it reaches a fire-bed it begins to heat by conduction from the hot coals beneath. The hot gases, products of combustion of the coal beneath, also heat the new charge of coal. (c) The heating of the coal causes the volatile matter to distil off. The amount distilled at any given temperature is unknown, but it is certain that traces of volatile combustible matters are given off as low as 110°C. (220°F.). (d) At about 400°C. or 750°F. the coal reaches the temperature of ignition and burns to carbon dioxide. (e) At about 600°C. or 1,100°F. most of the gases given off by coal (hydrogen, marsh gas and other volatile hydrocarbons) will ignite if oxygen be present. (/) At 800°C. (1,470°F.) the carbon dioxide, as soon as formed from the coal, will give up one atom of its oxygen to burn more coal, thus: CO2 + C = 2CO. The carbonic oxide will burn back to carbon dioxide if mixed with oxygen at the necessary temperature, which is between 650° and 730°C. (1,200° and 1,350°F.). (g) At about 1,000°C. or 1,832°F. the H 2 formed by the burning of the hydro- gen in the volatile matter in the coal begins to dissociate. (h) At about 1,000°C. or 1,832°F. any carbon dioxide not previously burned to carbonic oxide begins to dissociate to carbonic oxide and oxygen. (i) The various hydrocarbons which begin to be distilled at 110°C. and possi- bly lower, undergo many changes, dissociations and breakings up at the various temperatures they pass through. So many of these are unknown that it is use- less to state the few we do know. About 700°C. (1,300°F.) both the hydrocarbons and the carbonic oxide will unite with oxygen if the latter be present and intimately mixed with them. If they do not burn, the tendency is always to break up into simpler and more volatile compounds as the temperature rises. The composition of the gases from combustion may be found in almost any ratio. The following volumetric analyses will afford some idea of the ratio found. The last two are given on the authority of George H. Barrus, the last one being the products from Pocahontas (semi-bituminous) coal: 1 Steam Users' Association, Boston, Circular No. 9, R. S. Hale's Report on Effi- ciency of Combustion. THE STEAM BOILER 153 Poor. Per cent. Average. Per cent. Excellent. Per cent. Carbon dioxide (C0 2 ) Oxygen (O) Carbon monoxide (CO) Nitrogen, vapor of water, etc., by difference. 8.0 4.4 7.6 80.0 100.0 9.0 11.5 Trace 79.5 100.0 12.0 7.5 0.1 80.4 100.0 15.1 4.0 0.7 80.2 100.0 These gas analyses can be made by the Orsat or some similar apparatus, by tapping the flue and extracting a measured volume by means of a pressure bottle, such as is used in a chemical laboratory, and a graduated burette. The sample is then forced in succession through three pipettes containing caustic potash, pyrogallic acid and caustic potash, and cuprous chloride in hydrochloric acid, which will absorb respectively the carbon dioxide, the oxygen and the carbon monoxide. The loss of volume at each operation is measured in the burette. The refuse from a fuel is that portion which falls into the ashpit and that car- ried off by the draft, consisting of ashes, unburnt or partially burnt fuel and cin- ders. Loss by Unbttrned Coal in Ashpit Remarks — authority Per cent, refuse Per cent. combustible in refuse Per cent. in total coal E. B. Coxe (Trans. N. E. Cotton Mfg. Assn., 1895), using his traveling grate, on small-sized anthracite coal... .-. . / 10.05 1 23.70 f 13.35 \ 14.31 16.10 10.30 9.20 18.50 13.61 18.70 8.10 10.30 40.00 14.00 4.8 18.68 11.92 31.0 25.0 25.0 37.2 31.3 29.3 67.8 67.2 26.0 30.0 83.0 51.4 50.0 2.2 2.7 W. H. Bryan (Trans. A. S. M. E., vol. 16, p. 773), using soft coal - 4.3 3.6 Pennsylvania coal, bars 1^6 in. wide, 1 in. apart 4.0 Other tests 3.8 2.9 Other tests 5.4 Other tests with mechanical stoker 9.2 Other tests with mechanical stoker 12.6 Arkansas State Geological Survey Report, 1888, vol. 3, p. 73, Pittsburgh coal 2.1 Ditto Arkansas coal 3.1 Ditto Arkansas coal 33.2 Ditto Arkansas coal 7.2 Dampfkessel Revision Verein Berlin Geschafts Bericht, 1895, p. 79. Coal dust 2.4 The following is from a report of R. S. Hale, Steam Users' Association, Boston, Circular No. 9: "The amount of loss by unburned coal in the ashpit depends on so many factors that it is impracticable to express it by any formula. A statement of the factors and a collection of examples must, therefore, suffice. (a) The loss by unburned coal in the ashpit depends on the width of the open- ing in the grate bars, and increases as the width increases. (b) The loss depends on the size of the coal, and increases as the size of the coal decreases. 154 ENGINEERING OF POWER PLANTS (c) The loss is probably greater for a non-caking than for a caking coal. (d) The loss probably increases as the amount of earthy matter in the coal increases, but not the same ratio. (e) 1 The loss is less with a fan blast than with a steam blast. (/) 2 The loss is greater the more the fire is disturbed. This is especially noticeable in automatic stokers with moving grate bars." The following formula of Dulong is convenient for determining the theoretical quantity of air that is required for the combustion of any fuel whose composition is known. Let C, H and O denote respectively the weight of carbon, hydrogen and oxygen in the fuel; and W and V the weight and volume of air required. Other ingredi- ents may be neglected, as they have but a slight effect on the result. Then or W = 11.61C + 34.78 (h - jj), W = 12C + 35 (h - jj) , nearly; and V = 152.56C + 457.04 (h - jj) , or V = 153C + 457 (H - ^) , nearly. The value of W per pound is about 12 for anthracite and good bituminous coals, 6 for wood, and 11 for charcoal. It is found impossible in practice to obtain complete combustion unless the air supplied to the furnace be in excess of that theoretically required. Experience dictates that for ordinary natural draft nearly twice the theoretical quantity of air should be admitted, or about 24 lb. per pound of coal. With mechanical drafts and with natural drafts when the mixing effects are strong and positive, the excess of air may be considerably reduced. The volume of air supply per pound of coal, in ordinary factory practice, with natural draft is about 300 cu. ft. ; and may be as low as 200 cu. ft. when the mixing effect is strong." The actual volume may be estimated by using an anemometer, or may be closely calculated from a flue gas analysis by using the following formula. A = 11.6 where co 2 + ^ + o 2 C0 2 + CO XC + 3(H-gj A = weight of dry air per pound of dry coal; C0 2 , CO, and O2 = per cent, volume of each in the flue gas; C, H and O = the weight of each in 1 lb. of dry coal. The total weight of the dry products of combustion passing out of the stack will be / co 2 + c 2 ° + oA W, = C X \l + 11.6 CQ2 + C0 ) + 26.8(H - g) + N 1 Report of Coal Waste Commission, Pa., 1893, p. 31. 2 Report of Coal Waste Commission, Pa., 1893, p. 31. THE STEAM BOILER 155 or, expressed in terms of "A," above Wi = A + C+N- S^H - jj) where Wi = total weight of dry combustion products per pound of dry coal; N = the weight of nitrogen in 1 lb. of dry coal. The specific heat of the dry flue gas may be taken at 0.24 for ordinary purposes of calculation of B.t.u. loss. The loss due to an incomplete combustion of the carbon to CO will be, in units of B.t.u. loss per pound of fuel, _ 10,160XC O B.t.u.loss = CX-^+c^' "The conclusions drawn by R. S. Hale 1 are: that ordinary firing is apt to give 10 to 20 per cent, worse results than the best skilled firing, the low results being caused by using too much air and by getting poor combustion. That it is easier for firemen to get better results in some boiler furnaces than others, but that this difference becomes large only with poor soft coal. That many but not all of the patent devices (down-draft grates, stokers, etc.) in common use will with moderately skilled firemen give better results than those obtained by ordinary firemen in ordinary furnaces. That it is probable, but not proved, that ordinary firemen can get better re- sults from these devices than can ordinary firemen on ordinary grates. Heat of Combustion. — The heat produced by the combustion of 1 lb. of various substances is given in the following table in British thermal units: Total Heats of Combustion B.t.u. per lb. Hydrogen 62,032 Carbon to carbon dioxide 14,500 Carbon to carbon monoxide 4,400 Carbon monoxide to carbon dioxide 4,330 defiant gas 21,344 Liquid hydrocarbons vary in proportion to weight from 19,000 to 22,600 Charcoal, wood 13,500 Charcoal, peat 11,600 Wood, dry, average 7,800 Wood, 20 per cent, moisture 6,500 Peat, dry, average 9,950 Peat, 25 per cent, moisture 7,000 Coal, anthracite, best qualities, about 15,000 Coal, anthracite, ordinary, about 13,000 Coal, bituminous, dry, about 14,000 Coal, cannel, about 15,000 Coal, ordinary poor grades, about : 10,000 These figures are slightly altered by different authors. The above list may fairly be taken as an average." 1 Steam Users' Circular, No. 9. 156 ENGINEERING OF POWER PLANTS Boiler Rating. — It has been customary in the past to rate fire-tube boilers at 11.5 sq. ft. of heating surface per horsepower, water-tube boilers at 10 sq. ft. of heating surface, and internally fired boilers at 8.5 sq. ft. of heating surface per horsepower, a horsepower being understood to be the " Centennial rating/' 343^ lb. of water evaporated per hour from and at 212°F. This rating is in use today, but most engineers buy square feet of heating surface and not horsepower, this being due to the great advances which have been made in the art of firing boilers. At the time of the formulation of the " Centennial rating" 3.5 lb. of evaporation per square foot of surface per hour was considered very good work and the economical point of evaporation. At the present time with better designed boilers and our better knowledge of combustion problems it is not uncom- mon to obtain 9 or 10 lb. of evaporation, with good economy, from large- tube boilers and as much as 15 to 18 lb. with the smaller tube types. Prof. Bone, with his surface combustion boiler, has evaporated from 30 to 45 lb. of water per square foot of surface per hour over a considerable time, with excellent economy. Considerable discussion has arisen regarding the measurement of heating surface, i.e., whether such measurements should be based on the inside or outside diameters of the tubes. The American Society of Mechanical Engineers favors using the surfaces which receive the heat — the outside diameter of water-tube and the inside diameter of fire-tube boilers. Boiler Efficiency. — Boiler efficiency may be graded as follows: 50 to 60 per cent, poor; 60 to 70 per cent, fair; 70 to 75 per cent, good; over 75 per cent, excellent. The last is seldom obtained. Pounds of Water per Horsepower-hour. — James Watt's figure was 1 cu. ft., or 62.5 lb. The standard of 1876, Centennial, adopted by the American Society of Mechanical Engineers was 30 lb. evaporated from a temperature of 100°F. (feed water) into steam at 70 lb. gage pressure. This is equivalent to 34.5 lb. from and at 212°F. As has already been pointed out there is no direct relation between boiler and engine horsepower. For convenience in comparing the evaporative results of boilers operat- ing under different conditions of feed-water temperature and steam pressure, it is necessary to reduce all such variable conditions to a defi- nite standard. The conditions agreed upon, which have been in use many years, are those of a feed-water temperature of 212°F. and the evaporation of the water at that temperature into steam at atmospheric pressure, with a temperature of 212°F. This has been shortened into either " Equivalent evaporation" or " Evaporation from and at 212°." Factor of Evaporation. — At the pressure of one atmosphere (14.7 lb. per square inch) and at 212°F., the heat necessary to make water at THE STEAM BOILER 157 that temperature into steam at that pressure is approximately 970 B.t.u. If, then, the total heat, Q, required to vaporize a weight of water, W, be observed from a test, in which the feed water was introduced at t f , and the evaporation took place into steam at t, the total heat which went into the evaporated water was the product Q X W. If the evaporation had taken place from and at 212°F. Q would have been 970 for each pound, so that 970H would have been the equiva- lent heat absorbed if H is the corresponding weight of water evaporated from and at 212°F. Equating these, ^™ QW = 970H or H = ~~ gives the pounds of water which would have been evaporated from and at 212°. q A table giving the value of the factor ^^ has been computed and may be found in various books dealing with boiler tests. This factor is designated, " Factor of Evaporation." For example, given feed water at 40°F. evaporated into steam at 100 lb. gage, what is the factor of evaporation? If q = the heat of the liquid at 40°F. = 8.1 q l = the heat of the liquid at 100 lb. gage (338°F.) = 309 r = the heat of vaporization at 100 lb. gage = 879.5 then qi - q = 309 - 8.1 = 301 then total heat = 301 + 879.5 = 1,180.5 B.t.u. per pound ' ' - = 1.22 = factor of evaporation, that is, the evapora- tion of 1 lb. of water from a feed-water temperature of 40°F. into steam at 100 lb. gage pressure is equivalent to evaporating 1.22 lb. from water at 212°F. into steam at 212°F. The average factor of evaporation for the wide range of feed-water temperatures and steam pressures in common use is roughly 1.15. This approximate factor may be used for all general calculations that do not require close refinement. This corresponds to the evaporation of 30 lb. of water per horsepower-hour under ordinary commercial 34.5 conditions as \rr? — 30. 1.15 Pounds of Water Evaporated per Pound of Dry Coal (from and at 212°).— Maximum theoretical 15 Maximum under conditions of practice 12 Excellent practice 10 Fair practice 8 Common practice (small plants) 7 158 ENGINEERING OF POWER PLANTS Pounds of Coal per Square Foot of Grate Area per Hour. — (a) With chimney draft: Slowest rate, Cornish boilers 4- 6 Ordinary rate, Cornish boilers 10- 15 Ordinary rate for anthracite 15- 20 Ordinary rate for bituminous 20- 25 (b) With forced draft: Stationary water-tube boilers 25- 50 Locomotives 40-100 Torpedo boats 60-125 Boiler Deterioration. — Boilers are subject to many deteriorating forces which may be summed up as: (a) Internal corrosion. (b) External corrosion. (c) Pitting. (d) Grooving. (e) General wear and tear. Idle Boilers. — When boilers are out of service for any length of time they should receive the following treatment as specified by Parsons. "The outside should be cleaned and painted with a good metallic paint, applied directly to the cleaned and dried surface. If the boiler be covered by lagging, the lagging should not be allowed to absorb moisture from the atmosphere. On the fire side, the soot and ashes should be thoroughly removed and the surface cleaned. These surfaces should then be kept dry and not exposed to damp air. Fresh lime in pans or trays,- renewed as required, will absorb the moisture in the air. Occasional small fires of tarred wood will be beneficial, as the heat will dry the metallic surfaces and the resinous condensations from the thick smoke will cover the tubes and shell with a protective coating. On the water side, corrosion may be active at the water line if the boiler be left partly full. Idle boilers should, therefore, be entirely dry or completely filled with water. If the laying off is a short time only, it is a good plan to fill the boiler with water made alkaline by a little soda. If for a long period, it seems best to empty the boiler and dry out the inside by a small fire built in a pan, which can be inserted through the lowest manhole. The manhole and hand- hole covers can be put back and the boiler made tight so that the oxygen will be consumed by the fire, or the covers can be left off and lime in trays used to absorb any moisture. Boiler Explosions. — Parsons states that explosions occur when the steam pressure exceeds the resisting strength of the metal structure. In a well-designed boiler the parts are of approximately equal strength throughout. It is good practice so to design a boiler that those parts shall have an excess of strength which are expected to suffer most rapidly from corrosion or wear and tear. Then as the boiler advances in age, the various parts become more nearly equal in strength. THE STEAM BOILER 159 Should a boiler become weakened and a rent occur, the steam pressure will be suddenly reduced, thus releasing the heat stored in the water. A portion of the water instantly flashing into vapor probably accounts for the great destructive effects produced by an explosion. While the rent primarily occurs at some weak spot, the fracture may not and seldom does follow a line of structural weakness. The new forces set up at the instant of explosion no doubt account for this phenomenon. All things being equal, the damaging effect by explosion of water- tubular boilers will be less than of fire-tubular boilers of equal rating, since the former contain a smaller proportion of water, and since extra time will be required for complete release, because the bursting part is small. Failures of boilers are usually due to wear and tear, produced chiefly by expansion and contraction, to corrosion, to overheating and to care- lessness. Overheating may be caused by low water or by scale or grease. Important fixtures, such as main stop valves, may become attacked, or the main steam pipe may be burst by water-hammer, thus causing a sudden release of pressure, which, if quick enough, may be followed by an explosion. When an explosion does occur, it is frequently difficult to determine the cause, and hasty judgment should always be withheld. A good piece of metal may show a poor quality of fracture on account of the suddenness of the rupture. Opinion as to the quality of the metal should only be given after a close and careful analysis of physical and chemical tests. The best way to prevent explosion is to employ intelligent labor and not neglect proper and regular inspection." Boiler Inspection. — The requirements and regulations regarding inspection are given in the American Society of Mechanical Engineers' Code. Number of Boilers to do Given Work. — The subdivision of heating surface into the proper number of boilers is important, for a careful study may result in much saving in first cost and in cost of operation. For instance, if boiler capacity to evaporate 33,600 lb. of water per hour from and at 212° is required, approximately 9,600 sq. ft. of heating surface will be needed. If each square foot of heating surface may be overloaded 33^ per cent, (which is quite possible in ordinary practice) it is evident that if the 9,600 sq. ft. were divided among four boilers, one boiler might be shut down for repairs or cleaning, and the other three run at 33}i per cent, overload and still evaporate 33,600 lb. of water. If the total heating surface were divided into three boilers, each of 3,200 sq. ft. of heating surface, two might not be able to run the plant alone, so a fourth or spare boiler would have to be supplied. This would 160 ENGINEERING OF POWER PLANTS be poor division of power as the money spent on the spare boiler would represent so much capital lying idle most of the time. Selection of Boiler Type. — The choice of type will depend much upon the conditions of service. For high pressures such as are used for modern power plants, water- tube boilers are safer. They are also probably more economical and meet the varying demands better than fire-tube boilers. For reasonably low pressures in relatively small power plants and for heating installations the ordinary fire-tube boiler meets the requirements well if overload capacity is not an essential factor. Such boilers are cheaper and probably cost less for repairs than water-tube boilers. The tendency with fire-tube boilers is toward hand-fired furnaces, which are often objectionable because of excessive smoke production which may make them undesirable for urban conditions. Saving by Use of Mechanical Stokers.— The difference between good and bad firing may easily amount to from 5 to 20 per cent, of the amount of fuel fired; hence, there is no investment around a steam plant which will pay better than the extra amount paid to secure good boiler practice. Automatic stokers are now developed to a remarkable degree of per- fection, and when suited to the fuel have an advantage over hand-firing in that under all conditions they are reliable, can be adjusted to the minimum of air and the maximum of load, and can be depended upon to operate continuously with the minimum amount of skilled labor. The economic saving will depend on the basis of comparison and the method of operation. Compared with an ordinary or poor fireman, they should show a large saving. Whether a stoker will save labor in the fire room depends upon the size of the plant. As a rule, mechanical stokers are not labor-saving devices in plants containing less than six to eight boilers (1,500 to 4,800 hp.). One man can handle the coal and ashes, fire the boilers and attend to the water level of 200 hp. of boilers equipped with the common hand- fired furnace. With shaking or dumping grates 300 hp. may be con- trolled by one man. With large boilers equipped with dumping grates one man will fire around 1,000 boiler hp. when using the steam sizes of anthracite coal, but the coal must be delivered in front of the boiler and a water tender is usually provided for every 24 boilers. With soft coal about 700 boiler hp. may be fired by one man under similar cirumstances. In a large plant containing twelve 650 B. & W. boilers, equipped with stokers, a water tender, one fireman and one helper are required per watch for their efficient operation. In stations of this size the ash men are in the basement, and the change from hand- to stoker-firing would make no difference in their number. One authority states that stokers save 30 to 40 per cent, of the boiler THE STEAM BOILER 161 labor in plants using over 200 tons of coal per week; 20 to 30 per cent, in plants using from 50 to 200 tons of coal per week, and no saving in plants below 50 tons. It should be remembered that unless the type of stoker is suited to the kind of fuel obtainable, the maintenance of the stoker plant is likely to be extremely high, running in some cases twice or three times as high as fire-room labor under hand-fired conditions. Cost of Mechanical Stokers. — In general, mechanical stokers cost from $3.50 to $6.50 per boiler horsepower, but the cost depends more on the width of the stoker than on the horsepower of the boiler. Chain- grate stokers cost in the neighborhood of from $180 to $250 per foot of width. Inclined-grate stokers of the Roney, Acme, Wilkinson or similar types, from $140 to $225 per foot of width. Underfeed stokers from $200 to $300 per foot of width. The length of the stokers is usually standard and depends on the type of coal to be burned. These prices differ considerably with the amount of auxiliary material furnished with the stoker, such as fronts, air boxes, coking arches, stoker drives and speed-changing devices, but are based on labor and material costs current in New York prior to the European war. The following is the approximate cost of stokers suitable for a water- tube boiler of 350-hp. rated capacity with 45 sq. ft. of grate surface; height of chimney above grate, 175 ft.; coal burned, Illinois screenings. The cost of the installation is not included. 1. Burke smokeless furnace 1,000 2. Wilkinson stoker 1,200 3. Roney stoker 1,300 4. Hawley down-draft furnace 1,350 5. Murphey furnace and stoker 1,350 6. Jones underfeed stoker. . 1,400 7. Chain grate and appurtenances 1,500 8. Taylor stoker 2,000 R. J. S. Pigott (Proceedings Am. Elec. Ry. Assoc, 1914) gives the following data for mechanical stokers. Average Data for Stokers Type of stoker Step and slope overfeed V over- feed Chain over- feed Gravity under- feed Horizontal retort underfeed Average price per rated boiler horsepower Normal forcing ability in per cent, of rating Price per maximum horsepower develop- able Maintenance per ton coal fired, in cents. . . Attendance in man-hours per active hour . Pounds coal per square foot grate surface (maximum) 11 $3.60 $3.60 190 175 $1.90 $2.06 10-12 11-14 0.45 0.45-0.50 35-38 35-42 $3.50-$6.55 260 $2.52 6-10 0.20-0.30 45-48 $5.65 300-350 $1.62-$1.88 2.5-4 0.08-0.10 60-75 $4.44 300 $1.48 4-6 0.30-0.40 50-65 162 ENGINEERING OF POWER PLANTS Operation and Care of Boilers. — Full instructions regarding the opera- tion and care of steam boilers will be found in the Code published by The American Society of Mechanical Engineers (1916). Among the most important points upon which the power plant engineer should be informed are : (a) Water level. (h) Blowing off. (6) Leaks. (t) Grease. (c) Getting up steam. (j) Efficient operation. (d) Cutting in boilers. (k) Banking fires. (e) Low water. (I) Scale prevention. (J) Foaming. (m) Shutting down. (g) Safety valves. (n) Inspection and repairs. (o) Laying up boilers. PROBLEMS 32. Given the following data from a boiler test: 1. Kind of boiler, Heine, water-tube. 2. Kind of fuel, West Virginia, briquettes. 3. Furnace, hand-fired. 4. Duration of trial, hours 10.25 5. Grate surface, square feet 40 . 55 6. Water heating surface, square feet 2,031 .0 7. Steam pressure, gage, pounds per square inch 83 . 7 8. Temperature of feed water, °F 52 . 9 9. Temperature of escaping gases from boiler, °F 590 . 10. Total weight of coal as fired, pounds 7,515.0 11. Moisture in coal, per cent 2 . 32 12. Ash and refuse in dry coal, per cent 10. 36 13. Calorific value per pound of dry coal, B.t.u 15,235.0 14. Calorific value per pound of combustible, B.t.u 16,266.0 15. Moisture in steam, per cent 0.8 16. Total weight of water fed to boiler, pounds 62,641 . 17. Factor of evaporation 1.20 Find the following: 1. Ratio of water heating surface to grate surface. 2. Total weight of dry coal consumed, pounds. 3. Total ash and refuse, pounds. 4. Total combustible consumed, pounds. 5. Dry coal consumed per hour, pounds. 6. Combustible consumes per hour, pounds. 7. Dry coal per square foot of grate surface per hour, pounds. 8. Quality of steam (dry steam = unity). 9. Water actually evaporated, corrected for quality of steam, pounds. 10. Water evaporated per hour, corrected for quality of steam, pounds. 11. Equivalent evaporation per hour from and at 212°, pounds. 12. Equivalent evaporation per hour from and at 212°, per square foot of water heating surface, pounds. 13. Horsepower developed. THE STEAM BOILER 163 14. Builders' rated horsepower. 15. Percentage of builders' rated horsepower developed. 16. Water evaporated under actual conditions per pound of coal as fired. 17. Equivalent evaporation from and at 212° per pound of coal as fired. 18. Equivalent evaporation from and at 212° per pound of combustible. 19. Equivalent evaporation from and at 212° per pound of dry coal. 20. Efficiency of boiler; heat absorbed by boiler per pound of combustible, divided by the heat value of 1 lb. of combustible, per cent. 21. Efficiency of boiler and grate; heat absorbed by boiler per pound of dry coal, divided by heat value of 1 lb. of dry coal, per cent. 33. Given the following data from a boiler trial : 1. Heine water-tube boiler. 2. Iowa coal. 3. Duration of trial in hours 9 . 92 4. Grate surface, square feet 40 . 55 5. Water heating surface, square feet 2,031.0 6. Steam pressure, gage, pounds per square inch 82 . 5 7. Temperature of feed water, °F 48 . 8. Temperature of flue gases, °F 627 . 9. Total weight of coal as fired, pounds 10,986. 10. Moisture in coal, per cent 14 . 88 11. Ash and refuse in dry coal, per cent 17.4 12. B.t.u. per pound of dry coal 11,497.0 13. B.t.u. per pound of combustible 13,385.0 14. Moisture in steam, per cent 0.91 15. Total weight of water fed to boiler, pounds 55,180.0 16. Factor of evaporation 1 . 205 Determine the values indicated in problem 32. ^ — 34. An office building contains 7,500 sq. ft. of radiation for steam heating, supplied from a low-pressure fire-tube boiler of 950 sq. ft. of heating surface. The engine used for power purposes, running non-condensing and exhausting into the atmosphere consumed in an 8-hr. run 27,700 lb. of steam supplied from a water-tube boiler of 950 sq. ft. of heating surface. What boiler horsepower was being developed by each boiler? What per cent, of the manufacturer's rating was developed in each case? How much coal was probably used in the 8 hr. run for all purposes if the coal con- tained 5 per cent, moisture? What was the consumption of the engine per indicated horsepower-hour if the switchboard readings were 240 volts and 260 amperes? D.C. generator. 35. What are the approximate boiler efficiencies corresponding to the table of equivalent evaporations per pound of dry coal on page 157. 36. Find the (a) factor of evaporation; (6) the equivalent evaporation; (c) the B.t.u. output of boiler per hour, and a (d) the boiler horsepower required for each of the following installations. 1. A heating system using 2,200 lb. of steam per hour, the steam being delivered from the boiler under 5 lb. per square inch gage pressure and at 96 per cent, quality, and the condensate being returned to the boiler at 175°F. 2. A non-condensing steam engine carrying 150 i.hp.load, requiring with the aux- iliaries 29 lb. of steam per indicated horsepower-hour; steam pressure 125 lb. per square inch gage; quality 98.9 per cent.; feed-water temperature 110°F. 164 ENGINEERING OF POWER PLANTS 3. A 500-kw. steam turbine, requiring with auxiliaries 18 lb. of steam per kilowatt hour; steam pressure 160 lb. per square inch gage; superheat 100°F.; feed-water temperature 210°F. 37. A boiler plant consisting of three 250-hp. hand-fired boilers uses No. 3 buck- wheat anthracite coal, costing $2.50 per long ton as delivered. Twelve hundred tons are used per month at an average equivalent evaporation of 7 lb. per pound of coal as fired. The operating labor is in three shifts, each consisting of two firemen and one coal passer, paid $2.50 and $2, respectively, per day, 7 days per week. The per cent, of ash in the coal by analysis is 14, but the total ash and refuse are approxi mately 19 per cent., costing 40 cts. per ton for removal. The use of soft coal and underfeed stokers is considered, the coal costing $3 per long ton delivered, the ash content being 8 per cent. An evaporation of 9 lb. is anticipated, the labor for operation being reduced to one fireman and one coal passer per 8-hr. shift, at the same wage rates. What, if any, will be the reduction in cost per 1,000 lb. of steam? On the basis of the same future demand for steam would the investment seem advisable? 38. If the above plant were to operate under the same load only 10 hr. per day (one shift, $2.50 and $2 per day wage rate), 5}i days per week, and if it had previously been using the $3 soft coal and obtaining an evaporation of 9 lb., would the stoker investment still be justified? 39. Coal of the following analysis is being used in a hand-fired furnace. Per cent. by weight Carbon 70.5 Hydrogen 4.9 Nitrogen 1.8 Oxygen 8.2 Sulphur 0.9 Ash : 13.7 100.0 B.t.u. per pound dry 12,750 Analysis of the flue gas gives the following results : Per cent, by volume C0 2 7.6 O 11.9 CO 0.3 N 80.2 Determine : (a) The pounds of air theoretically required for perfect combustion per pound of coal. (6) The pounds of air actually supplied per pound of coal, (c) The per cent, excess air. 40. On the basis of the analyses in problem 39, with a boiler-room temperature of 70°F. and a flue temperature of 580°F., how many B.t.u. are lost in the dry flue gases per pound of dry coal. What per cent, of the heat value of the coal is this heat loss? 41. After closing up the leaks in the boiler setting of problems 39 and 40 and adopting better methods of firing the following average flue gas analysis is obtained. THE STEAM BOILER 165 Per cent, by volume C0 2 13.1 6.5 CO 0.4 N 80.0 100.0 If in both cases the losses other than the sensible heat in the flue gas are assumed as 16 per cent, of the heat in the coal, what would be the probable yearly saving in coal bill, coal costing $3.50 per ton; the former consumption having been 1,500 tons per year. CHAPTER VII CHIMNEYS AND MECHANICAL DRAFT Chimneys. — Chimneys are built primarily for two purposes; first, to furnish draft to enable a sufficient quantity of combustible to be burnt, and second, to discharge hot or noxious gases at a sufficient height to avoid a nuisance. Theoretically, the draft power of a chimney depends on the height of its top above the grate bars and the respective densities of the hot gases and the outside air. Let H = height of the chimney above the grate in feet. U = 493°F. absolute temperature at 32°F. ti = absolute temperature of outside air. t 2 = absolute temperature of gases. 5 = theoretical draft power in inches of water. a = 0.01549tf g - 1) This formula is based on the supposition that t 2 is the mean tem- perature of the hot gases in the stack. Assuming a mean stack tempera- ture of 600°F. with the external air at 62°F. the above formula reduces to 5 = 0.00736#, on which the following table is based: H 5 H s H s H s 10 0.074 60 0.441 110 0.810 160 1.178 20 0.147 70 0.515 120 0.883 170 1.251 30 0.220 80 0.589 130 0.957 180 1.325 40 0.294 90 0.662 140 1.030 190 1.398 50 0.368 100 736 150 1.104 200 1.472 In practice, chimney height may be determined from the draft re- quirements by the following formula: H = 0.00736 135.875 The required draft power depends upon the loss of head due to fric- tion in ashpit air admission openings, to friction in passing through grate and fuel bed, to losses by leakage of cold air into combustion cham- ber, to friction in the boiler passes and finally to flue, economizer and 166 (F-iy CHIMNEYS AND MECHANICAL DRAFT 167 stack frictions and the difference of temperature necessary to produce the flow in the stack. Of these, the loss due to the grate and the fuel bed amounts to from 50 to 75 per cent, of the total. The loss from leakage of cold air into combustion chamber, from friction in the boiler passes, flues, economizer and stacks amounts to from 15 to 35 per cent., leaving often as little as 4 per cent, to produce velocity in the chimney gases. No satisfactory method has been devised for calculating the necessary draft. The height may also be determined from the desired fuel consumption per square foot of grate per hour. Let F = pounds of coal burnt per hour per square foot of grate. Then following Thurston : For anthracite coal 8 = 0.001875(7^ - l) 2 and H For best Penn. or Welsh 8 = 0.00148F 2 and H = ^. 5 For Pittsburgh or Illinois ™ 2 8 = 0.000833F 2 and H = g- These formulas have only a limited application. Natural draft greater than 1.5 in. of water is seldom necessary, and higher intensities can much better be obtained by forced or induced draft. This limits the height of chimneys to about 200 ft., which is perhaps above the economical limit from a cost and construction standpoint. Chemical and metallurgical works in the neighborhood of towns require excessively high chimneys to remove the noxious gases and a number have been built exceeding 400 ft. in height. In many works, however, means have been taken to utilize sulphurous, arsenical and other -vapors with a large measure of success. All chimney formulas are based on the hypothesis that the capacity or theoretical coal consumption of a chimney varies directly as the area (or effective area) and the square root of the height. Let C = coal consumption in pounds per hour. A = area of chimney in square feet. H = height above the grates in feet. Then the typical formula may be written thus : c = kaVh, where K = a constant. It may be written C = K(A - 0.6 VA) VH (Kent's formula), where (A — O.Q^A) is the " effective area." 168 ENGINEERING OF POWER PLANTS L-. n'6' $£1,346' Section atEiev43'6 # Sectior\atElev.200'0» Section at Elev. I5'0* Fig. 107. — Common brick chimney, 96th St. Power House, Metro politan St. Ry. Co , New York. CHIMNEYS AND MECHANICAL DRAFT 169 The value of the constant K, as given by different authorities, varies greatly. Toldt gives K = 5; Prechtl, K = 6.4; Molesworth, K = 9; Ser, K = 9.3; Hutton, K = 10 to 16; Seaton and Rounthwaite, K = 12; Henthorn, K = 16.6, and Kent, K = 16.65 (using the effective area for A); Brinckerhoff (average), K = 18.1. Toldt and Prechtl refer mainly to German metallurgical practice, Ser to general French practice, Moles- worth and Hutton to English practice, Seaton and Rounthwaite to marine practice, Henthorn to American mill practice. An average of 30 stacks of various sizes now doing good work gives K = 9.4. An average of three notoriously overworked stacks gives K = 17.9. Ser's figure K = 9.3, was obtained theoretically by allowing for twice the amount of air necessary for perfect combustion. By allowing an excess of one-half the amount necessary for perfect combustion, which result can readily be obtained by the use of automatic stokers, the constant K = 12 will be obtained. For preliminary calculations the above formula with K = 12, gives practical results, but the chimney should be checked by comparison with known stacks of similar diameter and height for the final calculations. The value of K = 12 applies only to brick-lined stacks. In case an unlined iron or steel stack is being considered, the value of K may be increased to 14 or 15, and for small stacks 16 may be used. The base of a brick stack should rarely be less than one-tenth of the height. The allowable batter according to different authorities varies from 1 in 192 to 1 in 20 on each side, but the best practice lies between 1 in 30 and 1 in 40 for ordinary brick, with 1 in 60 to 1 in 80 for the Custodis or hollow-tile method of construction. In brick chimneys practice varies as to the thickness of the walls. The linings are not exposed to wind pressure, and consequently can be much thinner than the outside wall, but 100 ft. is about the practical limit of each step. The usual practice is to make the steps about 50 ft. high and 4 in. thick at the top up to a height of 150 ft. For higher chimneys the lining should be 8 in. thick at the top. The outside walls for chimneys up to 150 ft. high may be 8 in. thick at the top, with the steps about 50 ft. high or the upper steps may be as high as 60 ft., with 50 ft. for the lower steps. For stacks built on the Custodis principle the top courses are from 8 to 13 in. thick, depending on the height. The thickness of the moulded brick is increased 2 in. every 5 meters, or about every 16J^ ft. All brick stacks should be topped with a waterproof cap, usually of cast iron, although in many cases it is made of stone or monolithic concrete. Lightning rods are considered by many engineers as a neces- sity, and there is no doubt that many stacks have been saved by their 170 ENGINEERING OF POWER PLANTS Fig. 108.— Typical hollow-tile chimney. Fig. 109.— Steel stack, Wilmerding, Pa. Fig. 110. — Tapered rein- forced-concrete chimney, M. W. Kellog Co. CHIMNEYS AND MECHANICAL DRAFT 171 use. If furnished at all, care should be taken that the conductor and ground connections are good. The best constructions for steel stacks include a number of vertical stiffeners riveted to the shell which support horizontal cast-iron or steel rings on which the linings are built. The vertical stiffeners are usually spaced about 5 ft. apart, and the horizontal rings about 20 ft. apart. By this method any section of the lining may be replaced without dis- turbing the other sections. The thickness of the metal at the top of the stack in such cases is usually % in., increasing J^ in. every 50 ft. Stacks in which the linings are not supported may be J4 m - thick at the top, increasing 3^6 m - every 30 ft. Guyed stacks of light sheet iron are frequently used for single boilers and even for quite large plants especially where the expected life of the plant is short. The smaller stacks are made up in lengths of about 20 ft. of 3^-in. steel connected by angle rings on the outside or the whole stack may be riveted in one piece on the ground and erected with a gin pole. For these stacks the value of K in the general formula may be as high as 20 as they are usually connected directly to the boiler uptake and are exposed to high temperatures. Such stacks deteriorate very rapidly and cannot be considered a desirable construction, but occasionally circumstances will require their use. Galvanized stranded wire cables form the best guys and the anchors may be concrete blocks for the larger sizes. For the smaller sizes the guys usually lead to the steel building structure. During the last 15 years the use of reinforced concrete as a stack material has become quite common. These stacks are of many patterns and have been quite successful. The later stacks resemble the brick stacks on the outside, but cylindrical and bottle shapes are used to some extent. The advantages claimed for this type of stack are.: 1. Absence of joints, the construction being monolithic. 2. Rapidity of construction. 3. Great strength in compression and tension. 4. Light weight, requiring little foundation. Disadvantages . — 1. Difficulties with forms. 2. The break at the end of each day's work. 3. No data concerning life available. Many good stacks of this type have been erected in the last few years and their cost, appearance and performance compares favorably with the other types. 172 ENGINEERING OF POWER PLANTS Evase Stacks. — During the last few years a type of stack has been developed in Europe which offers marked advantages both as to cost and ease with which the draft may be controlled. The stack action is based on the injector principle, but the theory has not been well worked out as yet. The stack resembles a Venturi meter set up on end, the upper cone or diffuser enclosing an angle of 7°. These stacks are rarely over 60 or 70 ft. in height and are usually applied to single boilers or batteries, in order that the control may be perfect. It is usually possible to attain an evaporation of about 2 lb. of water per square foot of boiler surface with the stack alone. For the higher ratings air is injected just below the Venturi throat, thereby inducing a higher rate of suction than the height of the stack would make. It is possible so to proportion the stack and blower capacities that a suction draft of 3 or 4 ins. of water may be obtained, but this is usually unnecessary, as drafts of from 1 in. to 1}^ in. will fulfil most of the requirements. The following empirical rules may be followed in the tentative design of these stacks : 1. Figure the area and diameter of the base of the stack from the maximum num- ber of cubic feet of flue gases per second, using 40 ft. per second as the velocity. 2. Make the area of the throat 50 per cent, of the stack area. 3. Figure the height of the suction cone (30° included angle). 4. The height of the diffuser will be seven times the throat diameter and the diameter of the stack at the top of the diffuser will be 1.85 times the throat diameter. 5. The next thing to settle is the size of the air nozzle for inducing draft. This is a matter of the static pressure of the available fans and is smaller as this static pres- sure is larger. It is usually taken in the neighborhood of 15 in. of water. The formula for the diameter ratios then becomes v r 111^1 suction pressure R ' \ motive air pressure Both pressures in inches of water. From this ratio the diameter and area of the nozzle may be readily calculated. 6. The amount of motive fluid must next be calculated, using w = 0.9 area ■\/lg X 70 X water gage of motive air. Knowing the cubic feet of motive air per second and the area of the nozzle, its velocity can readily be calculated, also the veloc- ity head, which added to the static head gives the total head furnished by the induced-draft fan, whose horsepower can then be calculated by the following formula htAVXQO hp - " 6,395 X y where y is the fan efficiency, usually 0.50. h t is the total pressure, inches of water. A is area of outlet. V is velocity in feet per second. These stacks have been used in a large number of the best modern stations in Europe, South America and also in the Rand in Africa. CHIMNEYS AND MECHANICAL DRAFT 173 Flues and Uptakes. — The uptakes on standard boilers are usually designed for a normal evaporation of 3J^ lb. of water per square foot of surface per hour. This, ordinarily with soft coal, corresponds to }4 lb. of coal per square foot of heating surface per hour or 133 cu. ft. of flue gases per hour per square foot of heating surface. Taking the velocity Fig. 111. — Section of boiler house with Evase* stacks. of the gas at rating to be 10 ft. per second this would correspond to a flue area of 0.0037 sq. ft. for every square foot of heating surface. With a 50 per cent, overload on the boiler this will give sufficiently low velocities to make sure that the minimum portion of dust will be carried up the stack. Where soft coal is used this area may be safely reduced to 0.003 174 ENGINEERING OF POWER PLANTS per square foot of heating surface, in fact, on some installations as low a value as 0.0025 has been used with success. From the beginning of the uptake to the base of the stack the tem- perature of the flue gas continually decreases and it is good practice to take into account the drop in temperature and also to consider a 25 per cent, increase in velocity in the same space. Where increasing again in the stack the velocities are approximately: Normal Overload Velocity at uptake 10 to 15 ft. 15 to 20 ft. Velocity at end of flue 13 to 18 ft. 18 to 23 ft. Main velocity in stack 20 to 30 ft. 25 to 40 ft. * 51—4 2 l 13 /,8 -,A-A __£ ^i [— 3':.?A{ i Fig. 112. — Evase stack. These figures will be modified more or less due to variable amounts of excess air present in the flue gas. Flues and uptakes should be as straight as possible and of as large CHIMNEYS AND MECHANICAL DRAFT 175 an area as is consistent with the general design of the station. Sharp right-angled bends should be avoided and if possible the bottoms of the flues should be semicircular in section. The main portions of the flue for permanent work should be built of steel 34 m -> or thicker, the best practice being around % in., well stiffened with longitudinal angles at corners and cross angles or tees on the outside. No rivets should be used in the building up of the flue but square-headed bolts with square- headed nuts may be used. Where changes occur, plates should be bent wherever possible avoiding sudden contractions and expansions. Fig. 113. — Evase" stacks at a German plant. No paint should be used on the interior of the flue. The best pro- tective covering for this purpose is a wash of Portland cement and water mixed to a consistency of cold-water paint and applied with a stiff brush. The outside of the flue should be covered with 2 in. of asbestos or magnesia covering fastened onto wire mesh, which has been wired securely to the stiffening angles, the usual construction leaving an inch air space between the flue and the covering. Suitable expansion joints must be provided if the flue is of any great length. The methods of hanging the flue deserve careful attention, the best way being to support it by steel straps from I-beams properly spaced and located just above the top plate of the flue. Suitable clean-out doors should be provided and pipes or chutes through which the flue dust may be taken away without being scattered over the neighboring machinery. 176 ENGINEERING OF POWER PLANTS Chimney Dimensions. — The following table of chimney dimensions may serve as a guide in checking dimensions determined by the given formulae. Table of Chimney Dimensions Diameter Height, in feet in inches 75 80 85 90 95 100 110 120 130 140 150 175 200 Commercial horsepower 24 75 78 81 26 90 92 95 98 28 106 110 114 117 120 30 122 127 130 133 137 32 144 149 152 156 164 34 162 168 171 176 185 36 188 192 198 208 215 40 237 244 257 267 279 44 287 296 310 322 337 48 352 370 384 400 413 54 445 468 484 507 526 60 577 600 627 650 672 66 697 725 758 784 815 72 862 902 932 969 1,044 84 1,173 1,229 1,270 1,319 1,422 96 ... 1,584 1,660 1,725 1,859 1,983 108 2,058 2,102 2,181 2,352 2,511 120 2,596 2,693 2,904 3,100 Draft Pressure Required for Combustion of Different Fuels Kind of fuel Total draft in inches of water Kind of fuel ! Total draft in inches I of water Straw Wood Sawdust Peat, light Peat, heavy Sawdust mixed with small coal Steam coal, round 0.20 0.30 0.35 0.4 0.5 0.6 0.4-0. Slack, very small Coal dust Semi-anthracite coal Mixture of breeze and slack. . . . Anthracite, round Mixture of breeze and coal dust Anthracite slack 0.7-1 0.8-1 0.9-1. 1.0-1. 1.2-1, 1.2-1. 1.3-1. CHIMNEYS AND MECHANICAL DRAFT Cost of Guyed Iron Stacks. — 177 Approx. hp. Height, ft. Diam., in. Price complete 25 40 16 $60 • . • 40 18 70 50 18 85 75 50 20 90 • • • 50 26 105 60 22 110 100 60 24 125 60 26 135 • . • 60 28 150 125 60 28 190 . . • 60 32 205 150 60 34. 165 200 60 36 215 225 60 38 230 250 60 42 260 300 60 46 290 400 60 52 340 100 60 500 Cost of Brick Chimneys. — Approx. hp. Height, ft. Diam. flue Square base Outside wall Cost fire- brick lining Vi, height Cost con- crete fdtn. Total cost No. brick Cost at $14 per M 85 135 200 300 400 750 1,000 1,650 2,500 80 90 100 110 120 130 140 150 160 25" 30" 35" 43" 51" 61" 74" 88" 110" 7' 5" 8' 3" 9' 10" 10' 2" 11' 2" 12' 6" 13' 11" 15' 1" 17' 10" 32,000 40,000 65,000 75,000 87,000 131,000 151,000 200,000 275,000 $448 560 910 1,050 1,218 1,834 2,114 2,800 3,850 $60 82 113 190 261 334 432 482 720 $90 144 198 252 306 360 414 468 525 $598 786 1,226 1,492 1,785 2,528 3,060 3,750 5,095 The following approximate costs of various sizes of a well-known radial brick chimney give an idea of the variation in cost due to increase in diameter and height. 12 178 ENGINEERING OF POWER PLANTS Size of chimney Cost Size of chimney Cost Height, Diameter, Height, Diameter, ft. ft. ft. ft. 75 4 $1,350 175 8 $7,050 75 6 1,950 175 10 7,525 75 8 2,650 175 12 8,050 75 10 3,725 175 14 9,725 .... 181 21 11,500 125 6 3,500 200 6 9,250 125 8 4,250 200 10 10,500 125 9 3,345 200 11 7,990 125 10 4,675 200 12 11,100 125 12 5,125 200 14 12,500 150 8 6,150 250 10 16,500 150 10 4,350 250 12 18,250 150 10 • 7,125 250 14 21,500 150 12 7,750 250 16 20,000 150 14 8,275 250 16 24,250 Cost of Special Chimneys. — Christie ("Chimney Design and Theory") gives the following cost of chimneys 150 ft. high and 8 ft. internal diameter. Approximate cost Common red brick $8,500 Radial brick 6,800 Steel, self-supporting, full lined 8,300 Steel, self-supporting, half lined 7,800 Steel, self-supporting, unlined 5,820 Steel, guyed * 4,000 Average Cost of Stacks and Flues. — The average cost of stacks and flues (erected) for several installations ranging from 10 hp. to 2,000 hp. is reported by one consulting engineer as follows: Cost of Stacks and Fwbls per Engine Horsepower Simple non-condensing: Engine horsepower Cost of stack, per horsepower Cost of flues, per horsepower. Engine horsepower Cost of stack, per horsepower Cost of flues, per horsepower. Simple condensing: Engine horsepower Cost of stack, per horsepower Cost of flues, per horsepower. Engine horsepower Cost of stack, per horsepower Cost of flues, per horsepower. 10 $16.00 2.30 30 $8.70 2.20 10 $12.00 2.30 40 $5.70 2.10 12 $14.80 2.30 40 $7.30 2.15 12 $10.70 2.30 50 $5.25 2.05 14 $13.40 2.30 50 $6.30 2.10 14 $9.70 2.30 75 $4.80 2.05 15 $13.00 2.30 75 $5.60 2.00 15 $9.40 2.30 100 $4.55 2.00 20 $11.60 2.25 20 $8.50 2.20 30 $6.30 2.15 CHIMNEYS AND MECHANICAL DRAFT uu Cost op Stacks and Fwbls per Engine Horsepower. — {Continued) Compound condensing: Engine horsepower Cost of stack, per horsepower. Cost of flues, per horsepower. Engine horsepower Cost of stack, per horsepower. Cost of flues, per horsepower. 179 100 200 300 400 500 $4.55 $4.00 $3.65 $3.30 $3.10 1.95 1.80 1.60 1.35 1.10 700 800 900 1,000 1,500 $2.90 $2.85 $2.80 $2.75 $2.70 0.90 0.80 0.70 0.55 0.55 600 $2.95 1.00 2,000 $2.70 0.55 Forced and Induced Draft. — In the ordinary power plant the chimney furnishes the draft necessary to burn the fuel. Systems of forced and induced draft have, however, been developed where it has been neces- sary to burn more coal, or where because of other difficulties, a better command was needed over the draft than could be obtained by a chimney. In the forced-draft system the stack is allowed to carry away the products of combustion, but the air necessary for the combustion of the fuel is forced under the grate by means of some type of blower so located as to Fig. 114. — Forced draft. deliver into a closed ashpit or into an air-tight fire room. In the induced- draft system a much larger fan, working at a lower pressure, is intro- duced into the flue, leading from the boilers to the stack, and the draft pressure of the stack is augmented by the pressure developed by the fan. Of the two systems the forced-draft system is most used, since the fan in the induced-draft system is particularly liable to deterioration on account of its being exposed to the action of the hot chimney gases. It was formerly claimed by the advocates of induced draft that the expense of a chimney could be saved by the adoption of this system, and this is 180 ENGINEERING OF POWER PLANTS true in some few cases. In the large majority of cases, however, the plant is so located that a stack of considerably greater height than would be considered necessary for draft alone must be provided to carry the noxious gases and smoke a sufficient distance above neighboring struc- tures. Forced draft came into prominence through the use of the finer steam sizes of anthracite for fuel, as it was found that these sizes of anthracite could not be burned with any degree of satisfaction with a draft above the fire-bed. Some of the more successful of the modern types of stokers require forced draft for the burning of bituminous coal, and the ease of manipulation of a fire with the combination of forced Fig. 115. — Induced draft. draft and chimney, has made the use of forced draft quite general. In cases where the plant is located at a distance from habitations the induced- draft system may be the best to install. The best results may be obtained where forced draft is used to force the air through the fire-bed keeping a pressure of 0.01 to 0.03 in. of water in the furnace above the fuel and allowing the chimney draft to carry away the products of combustion. A number of systems using both forced- and induced-draft fans connected by automatic devices for maintaining such a condition have been devised but the older method with hand regulation will usually give better results. CHIMNEYS AND MECHANICAL DRAFT 181 The initial cost of a brick chimney will usually be two or three times that of the mechanical-draft apparatus, but the larger the plant the less will be the relative cost. In small plants, 100 to 150 hp., the cost of a guyed steel stack 75 ft. in height, would be considerable less than that of a mechanical-draft system, and once erected would cost practically nothing for operation, while the power required to operate a fan in a plant of that size would be 5 per cent, or over of the total steam capacity. A tall self-supporting chimney for larger plants, however, is very costly as compared with a fan system of equal capacity. For example, a brick chimney 175 ft. high and 10 ft. in internal diameter capable of furnish- ing the necessary draft for a 3,000-hp. plant, will cost, including foun- dation, about $10,000. A duplicate-fan induced-draft system of equivalent capacity will cost about $5,000, a single-fan induced-draft system, $3,500, and a forced-draft system, $2,500. Capacity of Fans and Power Required. — Ordinary fans are built with radial blades and are usually sized by the height of the casing in inches : thus a 60-in. fan has an impeller of say 42 in. in diameter but the casing height is 60 in. They may be built with a single- or double-inlet. The double inlet impeller is usually considerably wider than the single- inlet. The usual proportions of the runner and case are determined from the "blast area" which is the area through which the fan will discharge giving a velocity equal to the peripheral velocity of the impeller. This, WD for the standard steel-plate fans, is a = — ^— where a = blast area, W = width of blades at the tips and D = the diameter of the impeller. W is usually about 0.4D. The radial depth of the blades is usually 0.15 D. The inlet is then about 0.562) in diameter and the width of the casing is the same as the diameter of the inlet. Let Q = cubic feet of 0.4D 2 air per second and let N = r.p.m. Then a = - — ^— = 0.133D 2 and ^ • \ i i ''•+ DN DN niQQn2 19.1Q n3 the peripheral velocity = t -^r = -r^-. and 0.133D 2 = nA/ . or D 3 = 144Q ny for dimensions in feet or roughly for Q = cubic feet per minute, 0AND z = Q. For multi vane fans the formula is 1.09iVD 3 = Q. These deliveries are based on certain total pressures (static + velocity) which are dependent on the orifice, the peripheral velocity and type of fan and may be shown by characteristic curves or taken from the tables. When the conditions are known the theoretical horsepower may be calculated by hp. = fi »., , where Q = cubic feet per minute and h t = total head in inches of water. The theoretical horsepower must be divided by the efficiency to give the actual horsepower. 182 ENGINEERING OF POWER PLANTS Steel-plate Fan Table of Air Pressures, Capacity and Horsepower Water gage, inches Capacity, cubic feet per minute per square inch of blast area Theoretical horsepower to move the given volume 0.2 12.2 0.0004 0.4 17.2 0.0011 0.6 21.15 . 0020 0.8 25.0 0.0031 1.0 27.3 0.0043 1.5 33.8 0.0079 2.0 38.8 0.0122 2.5 43.3 0.0169 3.0 47.5 0.0224 3.5 51.4 0.0282 4.0 54.8 0.0344 5.0 61.2 0.0481 6.0 66.9 0.0630 There are many designs of fans on the market which do not agree with these formulas and most builders publish tables for distribution giving sizes, dimensions and performances of their fans under all ordinary conditions. It should be remembered that these published figures refer to the delivery and pressure at the fan outlet. Where delivery is through ducts, the friction and other losses of the ducts must be calculated and added to the conditions at the fan in order that a proper selection may be made. Multiblade fans of the Sirrocco and Sturtevant types differ from the ordinary fans in having very narrow blades curved forward in the direc- tion of rotation. These blades are from 0.05D to 0. ID in radial depth and are considerably more efficient than the radial-bladed fans for many services. High-pressure blowers used for cupola blowing and other high-pres- sure work have generally cast housings and are made with slightly curved vanes. Their efficiency is also high as compared with the steel-plate fan. Propeller fans of many types are manufactured ranging from the Blackman with very low volumetric efficiency to the Seymour, and McEwen type with 30 to 60 per cent, volumetric efficiency. Guided propeller fans of the Rateau or Parsons type have higher efficiencies. The characteristic curves for steel-plate, multiblade and cupola fans for the same diameter of impeller and r.p.m. are given below. When a fan has been tested it becomes possible to draw a character- istic for that fan which will give a view of its performance over a wide range. Such a characteristic is given in Fig. 117. CHIMNEYS AND MECHANICAL DRAFT 183 Stock fans are usually purchased without guarantee but where good results are desired it is better to specify exact conditions and obtain a 2.6 2,4 2.2 2.0 1.8 >> •5 1.6 o o > 1.4 ll.2 .&1.0 Cupalo Blowers 1 ite< >1 1 5 la e j 7 ai .S TP ^ ^ c. -^ ^ 6 a' <^> $* < lyi 1> -5 y =y E P_ JS^ ■^b. - Thp Q 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 10 20 £0 40 50 60 70 80 90 100 Ratio of Opening Fig. 116. — Characteristic curves of fans. 20000 30000 40000 Q Cu.Ft.per Minute Fig. 117. — Performance curve of Massachusetts fan. 50000 guarantee as to delivery and efficiency. In involved cases the fan and duct system should be purchased as a unit. 184 ENGINEERING OF POWER PLANTS Depreciation and Maintenance of Stacks and Mechanical Draft Systems. — The depreciation on a well-designed masonry or concrete stack is very low. A properly constructed steel stack, lined with brick, requires only painting on the outside every 2 years. The depreciation Fig. 118. — Steel-plate fan casing, American Blower Co. Dimensions of Steel-plate Blowers Size A B c D E F G H I j K 50 24% 19% 22 29 3 20 21 16% 18 18 24% 60 2934 23% 26% 34 3 23 24% 19% 21% 21% 28 70 33% 27 30% 40 3 26 28 23% 24% 24% 31 80 38% 31 34% 45 3 30 31% 26% 27 27 35 90 42% 34% 39% 50 3 -34 36 30% 30% 30% 39 100 47% 38% 43% 55 3 38 39 33% 34% 34% 42 110 52 42% 47% 51% 60 3 42 42% 37% 37H 37% 45% 120 57 46% 66 3 46 47 41% 41% 41% 51% 140 66 54% 60 76 3 53 53% 48 48 48 58 160 75% 62 68% 86 3 60 60% 54 54 54 65 180 84 % 69% 77 96 3 68 68% 60% 60 60 72% 200 93% 77% 85% 106 3 76 75% 66% 66 66 79% 220 103 85 94 116 3 84 82 73 72 72 90 240 112% 92% 102% 126 3 92 89 79% 78 78 97 260 121% 100% 111 136 4 100 96 85 84 84 104 280 130% 108% 119% 146 4 108 102 92 90 90 110 300 140 116 128 156 4 116 109% 98 96 96 117 Size L M „ o p Q B 8 T u V 50 20 31 9 39 17 18% 17% 12 4 15 9 60 23 35 9 43 17 21 20 14 4 15 9 70 27 38 9 46 17 23% 22% 16 4 15 9 80 29% 41 9 49 17 24% 23% 18 4 15 9 90 33 45 9 53 17 26% 25% 20 4 15 9 100 36% 49 9 57 17 30% 28% 22 6 15 9 110 40 52 9 60 17 32 30% 24 6 15 9 120 44 61 9 70 17 35% 33% 37% 26 6 23 9 140 51 67 13 76 22 39% 30 8 23 13 160 57 73 13 82 22 43 41% 32 8 23 13 180 63% 80 13 89 22 46 44% 36 8 23 13 200 69% 86 13 95 22 52% 50 40 10 23 13 220 81 100 13 109 22 59 55% 44 12 35 13 240 87 106 13 115 22 62 58% 48 12 35 13 260 93 112 13 121 22 67 63% 52 14 35 13 280 100 118 13 127 22 70 66% 56 14 35 13 300 106 124 13 133 22 74 69% 60 16 35 13 CHIMNEYS AND MECHANICAL DRAFT 185 Speeds, Capacities and Horsepowers op "ABC" Steel-plate Fans at Varying Revolutions ^ g Fan PS 1 5 60 70 80 90 100 110 120 140 160 180 200 220 240 100 Per V. Pres. oz. Cu. ft. Hp. 785 .017 682 .150 942 .025 1121 .222 1100 .034 1870 .370 1257 1414 .044 .055 2652 3840 .476 .672 1571 .068 5475 1.01 1728 .082 6395 1.37 1885 .100 9565 2.03 2200 2513 .134 .175 1491621750 3.46' 5.47 2837 .231 30221 7.7 3141 .273 41608 12.0 3455 .335 55201 17.1 3769 .401 71941 25.1 125 Per V. Pres. oz. Cu. ft. Hp. 981 .027 852 .175 1178 1375 .089 .053 14022338 .284 .439 1571 .060 3158 .588 1768 .089 4809 .934 1964 .108 6844 1.34 2160 .132 7992 2.06 2356 .153 11945 2.90 2750 .212 18645 5.00 3141 .276 27170 8.15 3533 .350 37767 12.5 3926 .435 52010 19.3 4318 .525 68997 29.2 4711 .626 99910 43.5 150 Per V. Pres. oz. Cu. ft. Hp. 1177 .039 1023 .200 1413 1650 .056 .075 1681 2805 .325 .531 1886 .100 3979 .756 2121 2356 .130] .160 5760 8110 1.27 1.86 2592 .190 9580 2.74 2827 .230 14360 3.90 3300 3770 .300! -400 22374 32610 7.22j 11.3 4240 4711 .5031 .626 45325J 62412 19. 6| 32.1 5182 .758 82811 46.2 5653 .904 108120 68.6 175 Per V. Pres. oz. Cu. ft. Hp. 1374 1649 1925 .053 .076 .104 119411962 3274 .225 .393 .647 2200 .134 4622 1.01 2474 .172 6729 1.74 2749 .212 9594 2.46 3024 .258 11200 3.55 3297 .306 16715 5.52 3850 1 4380 .420 .554 26100 38043 9.91 17.3 4947 .687 52883 27.9 5496 .848 72814 44.2 6046 1.02 96626 67.1 6596 1.21 126089 103.0 200 Per V. Pres. oz. Cu. ft. Hp. 1570 1884 2200 .069 .101 .134 13642242 3740 .262;.478i.855 1 i 2511 .175 5304 1.26 2828 .225 7690 2.05 3142 .274 10960 3.16 3456 .333 12830 4.69 3770 .392 19150 7.01 4400! 5026 .537i .700 29850 43520 13.3 23.7 5654 .903 60442 39.2 6282 1.12 83231 62.1 6910 1.34 110422 96.8 7538 1.59 143902 154.5 225 Per V. Pres. oz. Cu. ft. Hp. 1766 .087 1534 .300 2120 2475 .1261.172 2523 '4207 .581 1.03 2829 .225 5969 1.57 3182 .285 8655 2.61 3534 .351 12334 4.09 3888 .421 14385 5.95 4241 .507 21500 9.29 4950 .690 33560 17.0 5654 .901 48680 31.1 6360 1.14 68000 52.8 7065 1.41 93634 87.9 7774 1.69 124217 142.5 250 Per V. Pres. oz. Cu. ft. Hp. 1963 .109 1706 .375 23552750 .056. 213 2793 '4675 .684' 1.22 3143 .280 6332 1.79 3535 .360 9600 3.32 3927 .430 13705 4.97 4320 .520 16000 7.44 4712 .630 23950 11.6 5500 .860 37310 22.5 6283 1.12 54200 41.2 7067 1.48 75558 71.7 7852 1.73 104036 121.4 275 Per V. Pres. oz. Cu. ft. Hp. 2159 2591 3025 .1311.189 .258 1876 3083:5142 .4361.821 1.45 3457 .337 7294 2.35 3889 4319 .426 .526 10578115773 3.92 6.09 4731 .623 17394 3.09 5183 .756 26278 14.5 6050 1.04 41020 29.4 6911 1.35 58328 54.7 7774 1.71 83104 89.3 300 Per V. Pres. oz. Cu. ft. Hp. 2355 .160 2046 .500 2826 1 3300 .225 .302 3363 5610 .975 1.73 3771 .401 7957 2.86 4242 4712 .520 ! .630 11520 16250 4.63 7.44 5184 .760 19200 11.4 5654 . 910 28800 18.1 6600 1.26 44750 37.5 7539 1.62 63629 69.3 350 Per V. Pres. oz. Cu. ft. Hp. 2747 .216 2387 .663 3297 3850 .306J.418 3923 6545 1.282.38 4399 .550 9282 3.89 4949 .693 13410 6.65 5447 .850 19110 10.7 6048 .970 22395 17.2 6597 1.25 33400 28.3 7700 1.68 52206 55.8 400 Per. V. Pres. oz. Cu. ft. Hp. 3140 3768 4400 .277 .399 1.546 2729 438417480 .750 1.70 3.19 5028 .713 10620 5.04 5656 .904 15400 9.34 6282 1.14 21950 15.3 6912 1.42 25574 25.2 7540 1.63 38300 39.2 and maintenance charges on a mechanical-draft system will range from 5 to 15 per cent, of the cost and in the case of induced systems may be considerably higher. Efficiency With Stacks and Mechanical Draft Systems. — With mechanical draft a much thicker fire can be maintained on the grates, thus permitting a high rate of combustion and minimum draft per pound of fuel, both of which result in increased boiler efficiency. Where the forced-draft system is used a proper manipulation of stack dampers and fan speeds leads to a balanced draft from which exceedingly good results can be obtained. In this case the chimney has only to furnish 186 ENGINEERING OF POWER PLANTS Fig. 119. — Cast-iron case volume blower. American Blower Co. Dimensions 0> S) to A B c D E F G H I J K L M N O P Q R S 1 7% 6% 7 9 434 5 5% 434 6% 4 8% 8% 3 2% 3% 6 l X« 7 2 2 9% 7% ay?. 10% 5% 6 64 5% 84 5 HM fi H%6 4 3 5% 6% 'He 8% 2% 3 10% w m 12 H 6% 7 7% 7 934 5% 12% 12% 15% 5 3% 5% 8 16 4 fi 10 3 4 13% n% 12% 16 8 9 /ffi 9 9% 8«4 12% R 7% 15% 6 4 7 11% 1M« 13 3% 5 16% 14% 15% 19% 10% 11 11% 10% 15% 9 17% 17% 7 4% 8 13 1%6 16 4% 6 20 % 16% 18'H 6 23% 12% 13 14 13 17% 10% 20 20 8 5% 9%: 15% l% fi 19 5% 7 23% 19% 214 27 14% 15 16 15% 20% 12% 23% 23% 9 0% 11% 18 I'M 6 22 6 8 26 21% 24 30% 16% 17 18% 17% 234 144 26 26 10 7% 13 20% l 9 4 fi 25 6% 9 29 24% 26% 34% 18% 19 20% 19% 26 16 29 29 11 8% 14% 23 1^6 28 7% Speed, Capacity and Horsepower Required for the "ABC" Volume Blowers Dia. of Width at Cir. in 1%0 1. pressure 1% Oz. pressure 2 Oz. pressure Size wheel per- iphery feet R.p.m. Cu. ft. Hp. net R.p.m. Cu. ft. Hp. net R.p.m. Cu. ft. Hp. net 1 8% 2 2.22 3300 348 0.350 3560 376 0.445 3810 402 0.545 2 10% 2% 2.75 2650 512 0.520 2880 554 0.655 3080 590 0.800 3 12 34 4% 3.15 2320 711 0.728 2510 770 0.918 2690 822 1.17 4 15% 4.06 1800 1210 1.24 1950 1305 1.55 2080 1395 2.53 5 19 5% 4.98 1470 1830 jl.87 1590 1980 2.35 1700 2110 3.83 6 22% 6% 5.90 1240 2600 2.66 1340 2810 3.33 1440 3000 5.45 7 26 7% 6.80 1075 3420 3.50 1160 3700 4.37 1250 3960 7.20 8 29% 8% 7.73 950 4130 4.54 1025 4800 5.68 1100 5125 9.30 9 33 9% 8.65 845 5580 5.72 915 6020 7.15 980 6440 11.7 Size Dia. of wheel Width at per- iphery Cir. in feet 3 Oz. pressure R.p.m. I £,"■ Hp. net 4 Oz. pressure R.p.m. Cu. ft. Hp. net 5 Oz. pressure R.p.m. Cu. ft. Hp. net 8% 2 2.22 4670 492 1.00 5400 568 10% 2% 2.75 3770 725 1.47 4360 835 12 3% 3.15 3300 1005 2.06 3810 1160 15% 4% 4.06 2560 1705 3.46 2960 1970 19 5% 4.98 2080 2590 5.75 2410 2980 22% 6% 5.90 1760 3670 7.45 2040 4250 26 7% 6.80 1530 4850 9.85 1770 5600 29% 8% 7.73 1340 6270 12.8 1550 7250 33 9% 8.65 1200 7875 16.0 1390 9100 1.54 2.26 3.17 5.35 8.07 11.5 15.2 19.7 24.7 6100 4900 4300 3330 2720 2300 2000 1750 1570 635 935 1300 2200 3340 4750 6250 8100 10180 2.15 3.17 4.44 7.45 11.3 16.2 21.2 27.4 34.4 CHIMNEYS AND MECHANICAL DRAFT 187 sufficient draft to remove the products of combustion, while the forced draft maintains the combustion at the proper rate and produces a slight plenum above the fire, thus preventing the large losses due to inrush of cold air when the fire-doors are opened. With mechanical draft the amounts of air and pressure can be readily regulated for any- sudden increase or decrease of the requirements practically independent of boiler performance. Damp muggy days appreciably affect the draft of the chimney as do adverse air currents and high winds, but these k J >- r K =4 Fig. 120. — -Niagara conoidal fan. Dimensions of Niagara Conoidal Fan Overhung Pulley Full Housing — Bottom Horizontal Discharge Dimensions in Inches Size A B C D E F G H I J K L M X Y 3 3% 4 12 14 16 15% 18% 21 17% 20 22% HKe 13 u% 15% 18%6 21%6 13% 15% 6 17% 20i% 6 24% 27% 22 25% 29 16% 18% 20% 11% 13 14% 14 16 18 27% 29% 31% 15 16 17 3% 3% 3% 8 9 10 4% 5 5% 18 20 22 23% 26% 28% 25% 28% 31% 16% 18% 20% 6 23% 26% 29% 19% 22% 6 24% 31% 34i% 6 38% 6 32% 36 39% 22% 24% 26% 16% 18% 20% 6 20 22 24 33% 36 37 18 19% 19% 3% 3% 3% 11 12 14 6 7 8 24 28 32 31% 36% 42 34% 39% 45% 22% 6 26 29% 31 1 %6 37% 42% 26% 30% 35^1 6 41% 48% 6 55% 43 50% 56% 28% 32% 36% 22% 6 26 29% 26 30 34 41% 50 56 22 25% 29 4% 5% 6% 16 18 20 9 10 11 36 40 44 47% 52% 57% 51% 56% 62% 33% 37% 6 40i ^ 6 47i% 6 53 58% 6 39% 44% 48% 62% 6 69% 76% 6 64 70% 78 40% 44% 49% 33% 37% 6 40i% 6 38 42 46% 63% 67% 75% 32 34 38 8% 8% 8% 24 26 28 12 13 14 48 52 56 63 68% 73% 68 73% 79 44% 48% 52% 6 63% 68% 74% 6 52i% 6 57% 61% 83% 90% 6 97% 85 92 99 53% 58% 62% 44% 48% 52% 6 50% 55 59 81 85% 95% 41 43 48 10 11 13 30 34 36 15 16 17 60 64 68 78% 84 89% 83% 90% 96 55% 59% 63% 79% 84% 90% 6 66% 6 70% 75 104% 6 111 H71%6 106 112% 119% 66% 71% 76% 55% 59% 63% 63 67% 72 100% 109 115 50 54 56% 15 38 40 44 18 19 20 72 76 80 94% 99% 105 101% 107 112% 66i% 6 70i% 6 74% 95% 100i% 6 106 79% 6 83i% 6 88% 124% 131i% 6 138% 126% 133% 140% 80% 66i% 6 84%i70i% 6 88% 74% 76 80 84 122% 128 130 61 63 63% 46 48 50 188 EXGIXEERIXG OF POWER PLAXTS conditions with mechanical draft will not affect the burning of coal, since the amount of chimney draft used is much smaller than the capacity of the chimney. It is claimed that smokeless combustion is more readily effected with artificial draft than with natural draft, as a thicker fire can be carried and the correct proportion of air more readily adjusted. Fig. 121. — Runner of conoidal fan, Buffalo Forge Co. Capacity Table Buffalo Fans Fan Mean dia. of blast- wheel y 2 " Total press. 1" Area or 0.288 oz. of Total press, or 2" 0.577 oz. Total press, or 1 . 154 oz. 3" Total press, or 1.734 oz. no. out- let, sq.ft. > -i d $ "3 > ft £ i 3 > o 75 > d — — 3 3H 4 152£" 18J4" 21" 1.31 478 1,720 0.19 675 1.79 409 2,350 0.26 579 2.33 358 3,070 0.34 506 2,440 3,320 4,340 0.54 0.74 0.97 955 818 716 3,450 1 . 54 4,690 2.09 6,130 2.73 1,169 1,002 877 4,220 5,750 7,510 2.83 3.85 5.02 4K 5 23M" 26"" 28K" 2.95 318 3 . 64 287 4.41 260 3,880 0.43 4,790 0.53 5,800 0.65 450 405 368 5,490 6,770 8,200 1.22 1.51 1.83 636 573 521 7,760 3.46 9,580 4.27 11,590 5.47 780 702 638 9,500 11,730 14,190 6.36 7.84 9.49 6 7 8 31M" 36>2" 42" 5.25 239 7.14 205 9.33 179 6,900 0.77 9,400 1.05 12,260 1.37 338 289 253 9,750 13,280 17,340 2.17 2.96 3.87 477 409 358 13,790 6.15 18,770 8.37 24,520 10.90 585 501 439 16,890 23.000 30,040 11.30 15.40 20.10 9 10 11 48" 52" 57H" 11.81 159 14. 5S 143 17.64 130 15,520 1.73 19,160 2.14 23,180 2.58 225 203 184 21,950 27,090 32,780 4.89 6.04 7.31 318 286 260 31,020 13.80 38,310 17.10 43,360 20.70 390 351 319 38,010' 46,930" 56,780. 25.40 31.40 38.00 12 13 14 63" 68" 73" 21.00 119 24.65 110 28.56 102 27.590 3.08 32,370 3.61 37,550 4.19 169 156 145 39,010 45,780 53,100 8.70 10.20 11.80 239 220 205 55,170 24.60 64,730 28.90 75,090 ,33.50 292 270 251 67,570 79,300 91,970 45.20 53.00 61.50 15 16 17 78 H" 83 3Y' 89" 32.81 96 37.33 90 42.14 84 43,100 4.80 49,040 5.47 55,370 6.17 135 127 119 60,960 69,360 78,300 13.60 191 15.50 179 17.50 189 86,200 38.40 98,060 43.70 110,720 49.40 234 219 206 105, 5S0 120,130 135,620 70.60 80.30 90.70 18 19 20 94" 99" 105" 47.25 80 62,060 6.92 52.65 75 69,160 7.71 58.33 72 76,640 8.54 113 107 101 87,780 97,800 108,370 19.60 159 21.80 151 24.20 143 124,110 55.30 138,280 61.70 153,250 68.30 195 185 175 152,020 169,400 187.6S0 101.70 113.30 12o.50 CHIMNEYS AND MECHANICAL DRAFT 189 The advantages of forced and induced draft may be summed up as follows: (1) Draft not limited by atmospheric conditions or height of stack; (2) increased capacit}^ of plant, within limits, at will; (3) possibility of burning inferior fuel with advantage. Disadvantages: (1) High operating cost of the machine; (2) occupies space which often is valuable; (3) uses from 1 to 5 per cent, of the steam generated by the boiler. PROBLEMS 42. The height of a chimney at the plant of Fall River Iron Co., Boston, is 350 ft.; internal diameter, 11 ft. Determine the number of pounds of coal that can be burned per hour and the horsepower of the chimney. 43. The power plant of the Passaic Print Works, Passaic, N. J., has a chimney 9 ft. in internal diameter which handles the gases from 13,855 lb. of coal per hour. Deter- mine the height of the stack. 44. The plant of the Amoskeag Mills, Manchester, N. H., has a stack 230 ft. high which handles the gases from 19,195 lb. of coal per hour. What is the diameter? 45. (a) Two boilers in the market have the following heating surface: (A) Is a water-tube boiler with 3,350 sq. ft. (B) Is a fire-tube boiler with 2,590 sq. ft. Under test (A) actually evaporated 144,000 lb. of water in 12 hr., and (B) 108,000 lb. What was the approximate per cent, of rating carried by each boiler? (6) On the basis of the evaporation given in (a), and usual operating conditions, how much coal was fired under each boiler per 12 hr. if the coal contained 10 per cent, moisture? (c) On the basis of (6), what would be the diameter and height of stack required for this plant, if one stack serves both boilers? (d) With a stack of the dimensions determined in (c), how does its commercial horsepower, as given in the table on page 176, compare with that of the given plant? 46. A plant containing five 300-hp. boilers, four of which are in continuous service under approximately 33 per cent, overload, has a chimney 7^ ft. in internal diameter and 160 ft. high. Additional steam demands will require the installation of two 300- hp. boilers, these to run at about the same overload. The. fuel used is run of mine bituminous coal, about 13,000 B.t.u. per pound. Will the present stack be of sufficient capacity? 47. In connection with the above plant, it is finally decided to erect another stack to have sufficient capacity to handle three 300-hp. boilers at 50 per cent, overload, burning the same grade of coal. The boilers have a ratio of heating surface to grate surface of 50 to 1. Estimate the height and the diameter of stack to be used. 48. Determine a "Handy" (approximate) figure for the required capacity of (1) a forced-draft fan in terms of cubic feet per minute per pound of coal burned per hour; (2) an induced-draft fan. 49. It is desired to provide a forced-draft fan of the steel-plate type for a battery of boilers of 1,000 hp. rated capacity but from which it is intended to be able to take 100 per cent, overload. The boilers are to be equipped with underfeed stokers, on which the manufacturers guarantee 100 per cent, boiler overload capacity with 3.5 in. of water draft. Determine the impeller diameter and width, the r.p.m., and the horse- power rating of engine drive required for a steel-plate type of draft fan. CHAPTER VIII SMOKE AND SMOKE PREVENTION Smoke is a result of imperfect or improper combustion. The Stand- ard Dictionary states that smoke is the volatilized products of the com- bustion of an organic compound, as coal, wood, etc., charged with fine particles of carbon. The definition of the word ''smoke" given in the recent (1915) report on Smoke Abatement and Electrification of Railway- Terminals in Chicago is "the gaseous and solid products of combustion, visible and invisible, including, in the case of certain industrial fires, mineral and other substances carried into the atmosphere with the products of combustion." Smoke consists then of: 1. Visible properties. 2. Solid constituents. 3. Gaseous constituents. The ordinary conception of smoke is based upon the effect of particles of carbon upon the eye, and the fact' is generally lost sight of that, other than from an esthetic standpoint, more damage may result from the nearly colorless gases issuing from a chimney than from the more offensive black smoke. So pronounced is this color impression that the majority of ordinances relate specifically to the density of the smoke as determined by color charts. The universal standard is a system of charts known as the Ringelmann system, which, when placed at the proper distance from the observer, give graduations of gray between pure white and black. Although the more harmful portions of smoke are practically colorless, it is nevertheless true that the color graduation may be an index of the efficiency of combustion and may indicate the proportion of inju- rious gases that are issuing from a given stack. In the ordinary furnace under a steam boiler we find the grate upon which the fuel is placed; the openings in the grate through which air is supplied ; the combustion chamber in which the oxygen of the air and the gases of combustion are thoroughly mixed; and the chimney or stack for producing the necessary draft and for carrying away the products of combustion. 190 SMOKE AND SMOKE PREVENTION 191 black 2 per For perfect combustion there are three primary requisites, namely, carbon, oxygen and a chemical combination of these elements. In the regular proc- esses commercially employed the carbon is secured by the use of coal, wood, oil or other fuel; the oxygen is secured directly through an ample air supply; and the chemical combination of these elements is secured by maintaining sufficiently high temperatures. It is apparent that there are four factors that determine to what extent a boiler plant in commercial operation will smoke: 1. The character of the fuel used. 2. The character of the equipment used for burning the fuel. 3. The care exercised by the fireman. 4. The state of the atmosphere. It is obvious that the problem of smoke preven- tion is the problem of perfect combustion. Smoke consumption is not possible and there is no such thing as a smoke consumer. A very common erroneous impression exists re- garding the amount of carbon or "good coal" that issues from chimneys in the form of smoke. Wild statements of enthusiasts on the subject of smoke prevention are frequently made to the effect that this carbon loss amounts to one-quarter or one- third of the fuel charged into the furnace. Such statements are absurd, as the amount of carbon thus issuing probably seldom exceeds cent, at the most. Smoke is made up of carbon, ash, tar, acids, ammonia and sometimes small amounts of arsenic. Recent reports from one city show the relation between in- dustrial and domestic soot issuing from chimneys to be: Fig. 122.— Fuel grate, air passage, combustion chamber and stack of typical plant. -K 192 ENGINEERING OF POWER PLANTS Industrial plants, per cent. Domestic plants Kitchen, per cent. Drawing room, per cent. Carbon 27.00 1.68 1.14 61.80 53.34 3.68 12.46 17.80 37.22 Hydrogen Tar 3.51 40.38 Ash 4.94 It is readily seen that the amount of carbon and tar from domestic chimneys is relatively far greater than from industrial chimneys. It is also correspondingly apparent that the ash from domestic chimneys is relatively far less than from industrial chimneys. Domestic chimneys are seen, therefore, to have a record that is far from clear and must be taken into account in considering the ultimate solution of the smoke problem. Effects of Smoke. — Briefly, the effects of smoke may be summarized as : 1. Effect on buildings and building materials. 2. Effect on vegetation. 3. Effect on weather conditions. 4. Effect on health and conduct. The smoke nuisance has become such an important factor in connec- tion with urban power-plant installations that it deserves the serious consideration of all students of engineering. From the exhaustive report of the Chicago Association of Commerce relating to Smoke Abatement and Electrification of Railway Terminals (1915) the following conclusions are taken: "A survey of the atmosphere of several of the world's great cities shows an improvement in atmospheric conditions during recent years. It shows also that Chicago suffers less from the effects of smoke than certain other large cities of this and other countries. The comparison of the air of cities with that of the country has revealed char- acteristics which may and apparently must be attributed to the smoke of the cities; but it has also been shown that they may in part be attributed to other sources, as, for example, leakage from gas mains, the pollution due to sewers, the dust of the streets and decaying organisms. Air analysts have admittedly not been able to separate the products of combustion as dispersed in the air from other agents of air pollution. The industrial activity of all important cities has brought about an increase in coal consumption which is greater than the increase in population. Smoke formation and the consequent pollution of the atmosphere by smoke have in re- cent years tended to increase, and have done so except so far as the adoption of various means in smoke prevention have proved effective. The fact is repeatedly pointed out that, in securing results of scientific value for use in abating smoke, SMOKE AND SMOKE PREVENTION 193 no one individual and no one city can accomplish the work that must be done. The observations must be numerous and must extend over decades. The fact appears firmly established that there is a well-defined relation be- tween smoke and fog and that the presence of smoke induces fog. It is agreed that sunshine is a function of the amount of smoke present in the atmosphere. Certain investigations have shown that the amount of carbon dioxide in the atmosphere of cities is, as a rule, only about 1 per cent, greater than that in coun- try air. The sulphur compounds in the atmosphere are generally due to the combustion of coal. Among the sources of pollution of city air by smoke, the world over, domestic chimneys are conspicuous. The mention of them by observers and students is much more frequent than the mention of any other source. The most successful means which have been employed to abate smoke have included not only legal prohibition but also the development of cooperative and educative measures. With reference to the effects of smoke, the following conclusions seem justified by the literature on the subject: (a) There is a general agreement among sanitary authorities that polluted air is harmful to health, but at the present time there exists no accurate method of measuring this harm nor of determining the relative responsibility of the differ- ent elements which enter into the mixture of gases and solids commonly referred to as atmospheric air. (6) The direct effects of smoke or of any of its attributes, including soot, dust and gases, in amounts which may ordinarily pervade the atmosphere of a smoky city are not shown to be detrimental to persons in normal health, but the general physical tone is lowered as the result of long-continued breathing of pol- luted air. (c) The direct effect of smoke upon those who are ill has been most extensively studied in connection with tuberculosis and pneumonia. It appears that smoke does not in any way stimulate the onset of the tubercular process nor militate against the rapidity of recovery when once this disease has been contracted, but that it has a direct antiseptic effect and tends to localize the disorder. In cases of pneumonia, the effect becomes seriously detrimental. (d) The tarry matter and sulphur compounds present in coal smoke have been shown by experiments to affect certain classes of vegetation when applied in sufficient quantities. (e) Smoke is popularly regarded as a source of loss and damage in its effects upon building materials, objects of virtu, clothing and other property. While these effects of smoke seem obvious, it has not been possible to estimate their extent with any degree of accuracy." "Smokeless combustion of bituminous coal, as defined by present practice involves compliance with certain well-defined principles, the more important of which may be described as follows: 1. The fresh coal should be introduced into the furnace at such a point and distributed in such manner that the gases distilled from it will be required to pass over the incandescent portions of the fire. Observance of this condition exposes 13 194 ENGINEERING OF POWER PLANTS the distillates to high temperatures, aids in their ignition and thereby promotes their combustion. The distillates, if not thoroughly burned are prolific sources of smoke. 2. The stream of gases arising from the fresh fuel must be heated as quickly as practicable and must be kept at a high temperature until the process of com- bustion is well advanced. The presence of a firebrick arch under which the dis- tillates may be burned is an aid in securing this condition. 3. The interposition of heat absorbing surfaces in close proximity to the fresh coal or the burning distillates tends to cool the gases, to suppress combustion and to produce smoke. 4. The admission of air, by which combustion is stimulated, should be pro- vided for at proper points and should be subject to careful regulation. 5. The proportions of the furnace should be such as will provide an ample flameway. This condition is necessary in order that the time occupied by the gases in passing through the furnace may be sufficient to permit them to burn completely. Where the length of the furnace is limited, the flameway may be extended by the use of baffle arches which require the gaseous stream to meander through the furnace, producing in effect an elongation of the flameway and pro- moting the mixing of the gases. A brick arch in the comparatively small furnace of the locomotive serves to increase the length of the flameway, promotes the in- termixing of gases and maintains the temperature required for igniting the gases. 6. Where the dimensions of the furnace are necessarily restricted, and where the air admitted cannot be perfectly distributed, the use of small steam jets with induced air discharged into the furnace serves to promote the mixture of gases, and by so doing, to improve combustion. The use of such jets with induced air on locomotive fireboxes is known to be of material service in suppressing visible smoke." To obtain entirely satisfactory results from hand-fired furnaces, certain recom- mendations for the guidance of firemen are laid down by different authorities. Among these are the following: 1. Fuel should be supplied to the fire periodically in small quantities. "A furnace well designed and operated will burn many coals without smoke up to a certain number of pounds per hour, the rate varying with different coals depend- ing on their chemical composition. If more than this amount is burned, the efficiency will decrease and smoke will be made owing to the lack of capacity to supply air and mix gases." 1 2. The accepted methods of supplying coal to hand-fired furnaces are four in number, as follows: (a) The "spreading or sprinkling" method; uniform stoking of the entire surface of the grate. (6) The " coking" method; covering the front part of the grate after pushing back the glowing coal. (c) The "ribbon" method; partially covering the surface of the grate by stok- ing the entire length of the grate and only partially covering the sides, or by stok- ing one-half of the grate surface. 1 United States Geological Survey, Bulletin 373, 1912. SMOKE AND SMOKE PREVENTION 195 (d) The "alternate" method; used when the grate has two or more doors through which to feed the fuel." "A review of the literature relating to mechanical, physical and chemical means of abating smoke shows: 1. That among the means which have been suggested to reduce the amount of smoke in the atmosphere of cities are: (a) The removal of fuel consuming industries to points remote from the city. {b) The construction of smoke sewers, or community chimneys, of such size and height as to permit of directing the discharges from many flues into one stack and thereby delivering the combined stream far above the city. (c) The establishment of central heating and power plants combining the activities of many small coal consuming plants into a few large centers which may possibly be located at points removed from areas of congested population. (d) The employment of devices for washing smoke discharges before emission into the atmosphere. (e) The condensation and deposition of smoke particles by means of electric devices. (/) The abolition of many small coal fires through an extension of the use of gas and electricity. (g) Improvement in methods of firing. 2. That fires of bituminous coal may be maintained without becoming sources of visible smoke, providing certain principles are recognized in the design of furnaces and in the manner in which they are fired. 3. That it is possible to secure smokeless combustion of fuel fired under sta- tionary boilers by hand-firing, though such a result implies careful supervision. 4. That many types of automatic stokers are available, the operation of which, under favorable conditions, is unattended by the production of visible smoke. 5. That various aids to combustion are recognized which, when applied to furnaces, tend to suppress smoke. The more important of these are: (a) The brick arch as applied to stationary boilers and as applied to locomo- tive boilers. (b) The use of baffle walls in furnaces. (c) The use of the steam jet with induced air for accelerating the process of combustion." The complete elimination of smoke in Chicago is set forth by the Commission as follows: "The complete electrification of Chicago railway terminals would not suffice to make the city smokeless. It has been estimated that only from 30 to 50 per cent, of all the smoke which pollutes the atmosphere of Chicago comes from loco- motives. The remainder is from domestic and industrial fires, small and large. Large industrial fires may, through the use of appliances which are well known, readily be made smokeless, and it is to fires of this class that the City Smoke Department has given most attention. A large percentage of the total smoke comes from domestic fires or from industrial fires so small as to make difficult the bestowal of sufficient care upon them to secure the prevention of smoke. Any plan, therefore, which aims at the development of a smokeless city must deal 196 ENGINEERING OF POWER PLANTS effectively with such small fires. Interpreting this problem, in terms of Chicago's fuel resources and our present knowledge of the art, requires a very strict enforce- ment of City ordinances not only for the suppression of smoke from equipment already installed, but very stringent regulations governing installation of new furnace apparatus. With the present administration of the Department of Smoke Prevention, under the direction of a competent commission, it is probable that a new and better ordinance than that now in force could be of limited value at the present time, but the future will impose requirements not dealt with at present. While the policies and methods at present employed in the conduct of the Department of Smoke Inspection are, without doubt, correct in a general way, there are several matters that should receive particular attention, as follows: (a) Much smoke is produced at night, on Sundays and holidays, when the city smoke inspectors are not at work. As this smoke is fully as objectionable as the smoke made during other times, the immediate establishment of smoke inspection service during these periods is recommended. (b) When an enlarged organization of the Department has been effected, the ordinance should be changed to deal with different grades of smoke instead of dense smoke only, as at present. (c) The small heating boiler used in apartment houses, small flat buildings and residences is a very crude appliance. The state of the art in its application to apparatus of this character is in the same undeveloped stage as that of the standard type of boiler furnace years ago and its development has remained stationary while that of the power boiler has made great advances. Therefore, the development of improved types of low-pressure heating boilers should be encouraged and within reasonable time their use made compulsory. (d) The use of such smokeless fuels as gas and coke should be encouraged. Each is an ideal fuel for domestic and small intermittent fires. The only limita- tion to their employment is that of cost and anything that will reduce that cost should be encouraged. (e) The extension of the plan for supplying steam for heat and power to adjacent buildings from a plant centrally or conveniently located with reference to those to be served, is a scheme having great possibilities for the elimination of smoke, as it makes possible the generation of steam under more favorable conditions than prevail in small plants. (J) The installation of automatic stokers in the smaller steam-power plants should be enforced. (g) As there appears to be no way of operating river tug boats without ob- jectionable smoke except by the use of anthracite coal, the boats on the Chicago River should be required to use such fuel. (h) Passenger and freight steamers in the Chicago River should either be required to use a better grade of fuel than at present, or mechanical stokers should be installed to use the fuel now employed. (i) There are many special problems in connection with the prevention of smoke that have and will present themselves from time to time, requiring special and particular study. Such problems consist in the suppression of smoke from furnaces of rolling mills, brickyards, malleable-iron plants, terra-cotta works and in similar industries, as well as from automobiles, etc. CHAPTER IX BOILER AUXILIARIES Feed Pumps. — In the majority of cases an extremely wasteful steam engine is used to operate the steam pump for supplying the boiler with feed water. As the power required for pumping the feed water is only a small portion of the entire amount, an extremely uneconomical pump does not represent a great percentage loss of the entire fuel. Further than this, as the exhaust steam from the auxiliaries is usually needed for heating the feed water the actual steam consumption chargeable to the feed pump is not over 10 per cent, of its water rate. Fig. 123. — Worthington three-stage centrifugal feed pump with Terry turbine drive. Steam Consumption of Feed Pumps. — With compound steam ends well lagged and covered 100 lb. of steam per indicated horsepower-hour should be safe consumption for feed pumps of large size, while in small pumps, 200 lb. appears to be nearer the mark. The pump efficiency should not be less than 80 per cent. The following illustrates the method of determining the amount of steam required by the feed pump to supply a given amount of water against a given head. Suppose the main engine, radiation and leakage, and all auxiliaries with the exception of the feed pump, require 8,000 lb. of steam per hour when operating at full rated load, and the boiler pressure is 150 lb. gage. 197 198 ENGINEERING OF POWER PLANTS The feed pump must now pump not only the 8,000 lb. of water against 150 lb. pressure, but, in addition, the actual amount of steam required to operate the feed pump itself. Assuming the economy of the pump to be 200 lb. of steam per indicated horsepower-hour and its efficiency to be 80 per cent., and letting "s" Fig. 124. — Turbine-driven centrifugal feed pump, A.E.G., Berlin. represent the total steam used by the feed pump per hour, the value of "s" may be found from the following: (8,000 + s) X 150 X 2.31 X 200 S ~ 3j3<3O0X 60 X 0.80 Centrifugal Feed Pumps. — About 10 years ago it was found to be a comparatively easy matter to design a centrifugal pump to deliver water at pressures in excess of 200 lb., and the search for an ideal feed pump ended in the adoption of centrifugal pumps, using two to five stages, driven by steam turbines or electric motors. These pumps were con- tinuous in their action, thus putting no severe strains on the feed piping, as did the intermittent action of the old duplex or triplex pumps. If the feed valves were all shut off by some chance, no accident occurred, since the centrifugal pump simply churned the water, but did not deliver it. It was found that the pumps were much smaller, required almost no at- BOILER AUXILIARIES 199 tendance and a large saving was made, due to the absence of pump- valve renewals, which with hot water, had amounted to a rather large figure. The steam consumption of the turbines, even when run non- condensing, was reasonably low, due to the high rate of rotation, and did not increase with age, as in the case of the reciprocating pumps. It was no uncommon thing to find the steam consumption of a 6 by 4 by 6-in. duplex feed pump to be 180 lb. per horsepower when new, and this con- sumption would increase with the age of the pump until the pump was dismantled and the steam valves ground tight. Even when the centrifu- gal pump ran at as low a speed as 1,800 r.p.m., the steam consumption of the turbine, when run non-condensing, would not exceed 50 lb. per Fig. 125. — Section of double-suction three-stage centrifugal feed pump. horsepower, and this consumption would not increase with age. The only defect in the centrifugal feed pump is that 200 gal. per minute is about the smallest size which will pay for manufacture, the three common sizes being 500, 750 and 1,000 gal. per minute. The price of the cen- trifugal feed pump with the turbine drive is about 50 per cent, in excess of the reciprocating pump of the same capacity, and the maintenance of the pump valves in the reciprocating pump will usually be larger than the additional fixed charges. All centrifugal feed pumps should be provided with a check valve on the discharge side, with a bypass provided with a spring valve between the discharge and suction, for use when all of the feed valves happen to be closed, and with a pump governor of some type, which will slow down the turbine when much water is not required. Cost of Feed Pumps. — The cost of feed pumps is a small item in the cost of the station, varying from 20 to 50 cts. per kilowatt of station capacity, or from 15 cts. to $1 per boiler horsepower the lower prices 200 ENGINEERING OF POWER PLANTS Cost of Feed Pumps (Installed) per Engine Horsepower Simple non-condensing: Engine horsepower Cost per horsepower. . . . Simple condensing: Engine horsepower. . Cost per horsepower. Engine horsepower . Cost per horsepower. Compound condensing: Engine horsepower. . . . Cost per horsepower . . . Engine horsepower. . Cost per horsepower. 10 12 14 15 20 $5.70 $5.50 $5.50 $5.40 $4.50 10 12 14 15 20 $5.70 $5.70 $5.70 $5.70 $5.40 40 50 75 100 $3.10 $2.75 $2.10 $1.70 100 200 300 400 500 $0.95 $0.60 $0.45 $0.40 $0.30 900 1,000 1,500 2,000 $0.25 $0.25 $0.25 $0.20 30 $3.80 30 40 $3.15 600 | 700 $0 .30 $0 . 30 50 $2.75 800 $0.25 75 $2.10 300 450 600 750 Gallons per Minute Fig. 126. — Characteristic curve varying conditions, centrifugal pump. 150 100 F= m135 90 2120 80 £105 o w 90 75 e 60 g O 45 y t [S^s v & < if. / ^ \ V D o* e t k^ i /& ifiP. P"^- VI II ii i 400 800 1200 1600 Gallons per Minute 2000 Fig. 127. — Characteristic curve, 8-in. high- speed centrifugal pump. «60 o CD fa a 50 eJ £40 120 110 100 . 90 i 80 •g 70 30 W 60 a so 10 30 20 10 "20' o i ' *10 o 1- o W o ^f r V? 9* A/ ri y / V jio r »e f s^ S 300 600 900 1200 1500 1800 Gallons per Minute 2100 2400 Fig. 128. — Characteristic curve, variable head and constant-speed centrifugal pump. applying to the larger station. Duplex direct-acting pumps, of the Worthington type, and suitable for boiler feeding, vary in capacity from BOILER AUXILIARIES 201 the 6 by 4 by 6-in., 100-gal. pump to the larger pot-valved pumps with compound steam ends 14 and 20 by 10 by 15 in. delivering 500 gal. per minute. The price varies from about $300 for the small size to around $2,000 for the large size, with the intermediate sizes at proportional prices. Centrifugal feed pumps, turbine-driven, run from 200 to 1,000 gal. per minute, in about four sizes, and cost about $1,500 in the 200-gal. size and about $3,200 in the 1,000-gal. size. Motor-driven centrifugal pumps are about 10 per cent, higher in price, and triplex motor-driven pumps often run from 100 to 200 per cent, higher. The Injector. — Injectors are sometimes used instead of feed pumps or to supplement them. They have to be carefully adjusted for the steam pressure used. The temperature of feed water supplied to the injector must be below 150°F. Advantages. — 1. Cheap in small sizes. 2. Compact. 3. No moving parts. No cost for repairs. 4. Delivers water hot to boiler. 5. No exhaust to care for. 6. Delivers warmed water without use of feed-water heater. These advantages make its use almost universal for locomotives. Disadvantages. — 1. Stops on reduction of steam pressure. 2. After stopping by failure in steam pressure, often hard to start. 3. Feed water cannot be much over 100°F. in actual operation. 4. Is of little use in large sizes. The injector uses about as much steam as the feed pump. The in- jector would seldom be used with boilers above 100 hp. except in loco- motive practice where its use saves the installation of feed-water heaters. Feed-water Heaters. — The exhaust from the feed pump and other auxiliaries can be largely utilized by the employment of feed-water heat- ers, wherein the feed water is heated nearly to the exhaust temperature by the exhaust steam. The following claims are made for feed-water heaters: for every 11° that the feed water is warmed there is a saving of 1 per cent, in the fuel burned; with sufficient exhaust steam available, cold feed water may be raised to 205°-210°, saving from 10 to 15 per cent, of the fuel. In some localities a heater will pay for itself in a few months, depending on the price of fuel. Heaters are of two kinds, closed and open. In the closed heater the feed water is pumped through copper tubes around which the exhaust steam is led. The heat of the exhaust steam is transferred through the copper tubes to the feed water and the condensed steam may go either 202 ENGINEERING OF POWER PLANTS to the feed-water tank or to the sump if it is oily. Closed heaters are rarely used at the present time, unless the exhaust steam is so dirty that the condensate must be thrown away. 600 500 ^Projected ) j ~^F» / / n'^ /(200 V Head7 / (185 H.P /& 200 400 600 800 . 100( 1200 1400 16,01 /c gf | | Capacity in Gals/Min. 100,000 200,000 300,000 400,000 500,000 600,000 700,000 800,000 900,000 Capacity in Lbs ./Hour Fig. J29. — Characteristic curves of Westinghouse house and fire service pump. Open heaters consist of a chamber in which the exhaust steam and feed water are mixed. They usually are of such a size that considerable storage is obtained. Where the feed water is very hard they may be Feed Steam Outlet or Inlet Feed Mud Blow Fig. 130. — Closed heater, Berryman type. provided with trays on which the carbonates thrown down by the heat are deposited, and frequently they are provided with a sand or excelsior filter which catches other impurities. These heaters, when furnished with this apparatus, might be termed heater purifiers and are largely used. BOILER AUXILIARIES 203 The closed heater is practically a surface condenser working at atmos- pheric pressure, while the open heater is a jet condenser, in some cases with purifying attachments. There is a third type of heater which was introduced a number of years ago but has made little headway toward common use. A tray or trays are placed in the steam space of the boiler and the feed water is delivered into the upper tray, overflowing and being heated by Fig. 131. — " Cochrane " open heater. the steam. The impurities collect in the trays, and are removed by what corresponds to a surface blowoff pipe. Theoretically there can be no saving by the use of a live steam feed water heater. Actually the reported savings are from 1 to 3 per cent. The most valuable feature of this type is the surface blowoff and the assurance that no cold water can touch the hot boiler surfaces. See Fig. 132. Cost of Feed-water Heaters. — The ordinary closed heater has from M to % sq. ft. of heating surface for each boiler horsepower, and costs from 75 cts. to $1 per horsepower. 204 ENGINEERING OF POWER PLANTS Cost of Feed-water Heaters Installed per Engine Horsepower Simple non-condensing: Engine horsepower Cost per horsepower. . . . Simple condensing: Engine horsepower . . Cost per horsepower. Engine horsepower. . Cost per horsepower. Compound condensing: Engine horsepower. . . . Cost per horsepower. . . Engine horsepower. . Cost per horsepower. 10 12 14 15 20 30 40 50 $2.95 $2.75 $2.70 $2.60 $2.50 $2.20 $2.15 $2.05 10 12 14 15 20 30 $2.95 $2.75 $2.70 $2.65 $2.50 $2.30 40 50 75 100 $2.15 $2.10 $2.00 $1.80 100 200 300 400 500 600 700 800 $2.85 $2.55 $2.25 $2.00 $1.75 $1.40 $1.10 $1.10 900 1,000 1,500 2,000 $1.00 $1.00 $0.95 $0.95 75 $1.90 Fig. 132. — Double deck boiler with internal-feed water heater. Economizers. — Under advantageous conditions, the large waste of heat to the chimney may be very largely reduced by the use of a special form of feed-water heater of the water-tube type, which may be provided with soot cleaners and is located in the flue between the boiler and chimney. Such a heater is called an " economizer." Economizers are of value in plants operating with steady load in which little exhaust steam is available. The annual maintenance usually amounts to 10 per cent, or more of the original cost. Save under excep- tional conditions, boiler heating surface is cheaper and usually gives better results. One writer states that economizers are guaranteed by the manufac- turers to save 6.5 per cent, when the temperature of the water entering BOILER AUXILIARIES 205 them is as high as 200°F., the economizers having 4.5 sq. ft. of heating surface per boiler horsepower and the boilers working at normal rating. Several tests show a saving of 10 per cent, with low stack temperatures, and an average of 12 per cent, with ordinary stack temperatures. The amount saved would ordinarily pay for the cost of the economizers in about 3 years. They cost about $5.40 per boiler horsepower for plants of 1,000 boiler hp. and over on the basis of 4.8 sq. ft. per boiler horsepower; or $6 per Fig. 133. — Economizer. boiler horsepower on the basis of 5 sq. ft. This includes the cost of de- livering, erecting, brick setting, etc. It is claimed that 3 per cent, of the investment will more than pay for the cost of operation, cleaning and repairs. This same writer gives the following illustrative example : 1,000-hp. plant. Operating 300 10-hr. days per year. Coal consumption, 33^ lb. per boiler horsepower-hour. Coal, $3 per ton. Annual fuel cost would be $15,750. Economizer saving, 12 per cent. = $1,890. Cost of economizer, 5.40 per boiler horsepower = $5,400. 8 per cent, for interest, repairs, operating and cleaning = $432. Net saving = $1,458 which is sufficient to pay for the economizer in less than 4 years. If plant were operated continuously, fuel cost = $45,990. Net saving = $5,085, sufficient to pay for economizer in about one year. 206 ENGINEERING OF POWER PLANTS Barrus reports the following results of economizer tests: Heating surface, boiler, square feet j 1,894 Heating surface, economizer, square feet Temperature of gases leaving boiler, degrees Temperature of gases leaving economizer, degrees .... Temperature of feed water entering economizer, degrees Temperature of feed water entering boiler, degrees j 175 Increased evaporation produced by economizer, per cent 1,894 1,058 5,592 1,600 1,920 1,280 376 361 403 231 254 299 95 79 111 175 145 169 10.5 7 9.3 3,126 1,600 435 279 84 196 12.8 and W. R. Roney (Transactions A. S. M. E., vol. 15) reports: Plants tested Gases entering economizer, degrees . . . Gases leaving economizer, degrees .... Water entering economizer, degrees.. . Water leaving economizer, degrees . . . Gain in temperature of water, degrees Fuel saving, per cent 1 610 340 110 287 117 16.7 2 505 212 84 276 192 3 550 205 185 305 120 17.1 11.7 4 522 320 155 300 145 13.8 5 505 320 190 300 110 10.7 6 465 250 180 295 115 7 490 290 165 280 115 8 495 190 155 320 165 9 595 299 130 311 181 11.2 11.0 15.5 16.8 The N. E. L. A. in the June, 1915 Report of its Committee on Prime Movers points out that: " Exactly how far to push the question of feed-water heating by economizer depends on investment cost, depreciation, operating cost, space required and the economy obtained. The increase in economy due to the economizer described above amounts to from 10 to 12 per cent. If the feed water were supplied to the boiler at the temperature of the steam it would mean an economy of from 16 to 17 per cent., or a further gain of about 6 per cent. This would reduce the tem- perature of the discharge gases to about 200°F. The cost of accomplishing this must be more than offset by the gain in economy to warrant such an installation — and each case must be considered separately. If the temperature of the gas is lowered below the dew point, a deposit of moisture occurs on the tubes, with resultant scale and incrustation, and has a further objection with western coals, in that the moisture combines with the sulphur in the flue gas, forming sulphuric acid. The cleaning of economizer tubes of soot does not as yet appear to be satis- factorily solved. The scrapers as ordinarily fitted have the effect of rolling the deposit on the tubes, making it difficult to remove. Blowing, both with steam and air, has been tried, but generally it has not been successful, or has introduced other difficulties which more than offset its usefulness. With the present tendency to increase the operating pressure of boilers, it is very evident that some change will be necessary in the materials used in econo- mizer construction, to assure their adoption, even though the economies obtain- able are relatively large. With boilers operating at 225 lb., the feed-line pres- BOILER AUXILIARIES 207 sures may exceed 250 lb., and may even at times reach 300 lb., which is generally considered too high a pressure to be safely sustained by cast-iron construction. The question of steel construction is possibly not entirely settled though the cost would be materially increased and there is the liability of excessive corrosion due to the chemical properties of certain coals. Percentage op Steam Generated Used by Auxiliaries (Surface-condensing Plants — Steam-driven Pump) Feed pump Circ pump Air pump "Wh"i Steam used, per cent. Kind of plant Econ., Eff., Econ., Eff., Econ., Eff., lb. per cent. lb. per cent. lb. per cent. 75- to 500-kw. horizontal direct- 500 12.50 acting auxiliaries. 200 80 150 80 150 60 1,000 1,500 2,000 2,500 15.75 19.00 22.00 24.75 500- to 1,000-kw. horizontal direct- 500 9.00 acting auxiliaries. 150 80 100 80 100 60 1,000 1,500 2,000 2,500 11.50 13.75 16.00 18.25 100- to 600-kw. engine-driven cen- 500 8.75 trifugal circulating pumps, 1,000 11.00 crank and flywheel air pumps, 200 80 60 50 50 60 1,500 13.00 direct-acting feed pumps. 2,000 2,500 15.25 17.25 600- to 1,000-kw. engine-driven 500 7.50 centrifugal, circulating pumps, 1,000 9.50 drank and flywheel air pumps, 150 80 50 52 45 60 1,500 11.50 direct-acting feed pumps. 2,000 2,500 13.50 15.50 Above 1,000-kw. engine-driven 500 7.50 centrifugal circulating pumps, 1,000 7.75 crank and flywheel, air pumps, 100 80 40 55 40 60 1,500 8.25 direct-acting feed pumps. 2,000 2,500 10.00 11.50 1 " W" is the number of pounds of circulating water per pound of exhaust steam. " h" is total head on circulating pump in feet. 208 ENGINEERING OF POWER PLANTS Percentage of Steam Generated Used by Auxiliaries (Jet-condensing Plants — Steam-driven Pump) Feed pump Circ. pump Air pump "Wh" Steam used, per cent. Kind of plant Econ., Eff., Econ., Eff., Econ., Eff., lb. per cent. lb. per cent. lb. per cent. 50- to 300-kw. horizontal direct- 200 13.00 acting auxiliaries 200 80 150 80 150 70 300 500 1,000 1,500 16.75 20.75 25.75 30.00 300- to 800-kw. horizontal direct- 200 9.00 acting auxiliaries. 150 80 100 80 100 70 300 500 1,000 1,500 200 11.50 14.75 18.50 25.00 8.00 150- to 500-kw. engine-driven cen- 300 9.50 trifugal injection pumps, crank 500 11.50 and flywheel air pumps, direct- 1,000 14.75 acting feed pumps. 200 80 60 50 50 70 1,500 200 19.75 6.00 500- to 1,000-kw. engine-driven 300 7.50 centrifugal injection pumps, 500 9.25 crank and flywheel air pumps, 1,000 12.00 direct-acting feed pumps. 150 80 50 52 45 70 1,500 200 16.75 4.50 Above 1,000-kw. engine-driven - 300 5.75 centrifugal injection pumps, 500 7.25 crank and flywheel air pumps, 100 80 40 55 40 70 1,000 9.75 direct-acting feed pumps. 1,500 13.75 Radiation and Leakage. — In well-designed plants, with properly- covered pipe lines, the radiation and leakage losses may be taken as low as 3 per cent, of the total evaporation, but usually will run much in excess of this figure. Oil Pumps. — Small duplex steam pumps are usually used for feeding oil to the burners. They are exceedingly uneconomical and a steam consumption of over 200 lb. of steam per indicated horsepower-hour may be considered a fair average. The efficiency of these pumps is also very low, varying between 40 and 50 per cent. It is customary to assume the steam consumption of the oil pumps as being 1 jper cent, of the total evaporation, which is conservative. Centrifugal oil pumps have been used to some extent and are much less inefficient and some- what higher in cost. Oil Burners. — There is a great variety of oil burners on the market, some of which have given good satisfaction. They may be divided into BOILER AUXILIARIES 209 three classes, depending on the atomizing agent used and the method of its mixture with the oil. 1. Burners using steam for atomizing. 2. Burners using high-pressure air for atomizing. 3. Burners using low-pressure air for atomizing. Practically all commercial oil-burning installations on land use a burner of the first type, as it is simpler, more convenient and more eco- nomical. These burners may be again divided into those in which the oil and atomizing agent are mixed inside the burner, and those in which they are not mixed until they leave the burner. Oil-firing does not usually meet with the best results, unless large properly shaped combustion spaces are provided, and this is best secured with some of the more modern types of water-tube boiler. The steam used for atomizing the oil at the burners is a direct loss, escaping up the stack as superheated steam. The best results show a steam consumption of about 3^3 lb. of steam per pound of oil, which is something over 2 per cent, of the gross evaporation. In ordinary cases the use of atomizing steam amounts to from 3 to 5 per cent. Boiler Feed Water. — Although this is a large subject, the essential features, as stated by Shealy in his " Steam Boilers," 1 are here presented in modified form. "The waters of our lakes, rivers, springs, and underground streams contain more or less mineral substances that have been dissolved by the water in its passage through the earth, and also more or less dirt, mud, and vegetable matter which have been taken up and carried along by the water. When water is evapo- rated in a boiler, all of these impurities are left behind and are usually deposited in solid form. In some cases these substances merely settle as a soft mud and can be blown off, but more often they form a hard scale on the heating surface, which is difficult to remove. The scale thus formed is a very poor conductor of heat and its presence, therefore, reduces the efficiency and capacity of a boiler by reducing the amount of heat that can pass through the heating surface. It is much better, as far as possible, to prevent the scale-forming substances from entering the boiler, as, once inside, they will form a more or less hard scale which must be removed. Even though the scale formed is soft and easily re- moved, its presence involves a certain expense in laying off the boiler and cleaning it. To prevent the formation of scale, requires a knowledge of the chemistry of feed water and of the proper treatment by which the mineral salts may be removed before feeding the water into the boiler, or they may be changed in nature so that they will not form a hard scale but will settle as a soft scale or as_mud which can be blown off or easily removed. Impurities in Feed Waters. — The impurities most often found, and found in the largest quantities, are given below together with their chemical formulae: l " Steam Boilers," E. M. Shealy, McGraw-Hill Book Co. 14 210 ENGINEERING OF POWER PLANTS Calcium carbonate CaCC>3 Magnesium carbonate MgCC>3 Calcium sulphate CaSC>4 Magnesium sulphate MgSCh The impurities less frequently found and in smaller quantities are : Iron carbonate Fe2CC>3 Magnesium chloride MgCl 2 Calcium chloride CaCL 2 Potassium chloride KCL Sodium chloride NaCL Besides these there may be iron oxides, calcium phosphate, silica, and organic matter, which usually occur in very small quantities. The Carbonates. — Calcium carbonate and magnesium carbonate do not dis- solve very readily in pure water, but most water contains carbonic acid (CO 2) and if this is present, the carbonates dissolve very readily. The carbonates unite with the carbonic acid and form the bicarbonates of calcium and magnesium, which are very soluble. This combination can, however, be broken up by heating, which drives off the carbonic acid gas and returns the carbonates to the insoluble form, when they will be deposited. The action described above, begins when the water is heated to 180°F. and by the time it has reached 200°F., the greater part of the carbonates will be deposited. It requires a temperature of about 290°F. to deposit all of the carbonates, but the larger part is deposited between the temperatures of 180° and 200°F. If the feed water enters the boiler at a temperature lower than 180°F. the carbonates will be deposited inside the boiler, but, if some device is used whereby the feed water is heated to a temperature of about 210° or 212° before it enters the boiler, there will be very little of the carbonates deposited in it and it will be easily cleaned. The Sulphates. — Calcium sulphate and magnesium sulphate are the most troublesome impurities as they form an exceedingly hard scale which is difficult to remove. The solubility of calcium sulphate in grains per gallon is given in the following table. Temperature, °F. Soli ability, grains per gall 212 125.0 300 40.0 350 15.5 400 12.0 450 11.0 500 10.5 When other salts are present the solubility is somewhat larger. Live-steam feed-water heaters will usually throw down a portion but chemical means must be taken to prevent scaling in the boiler as the water becomes concentrated. The sulphates possess very active cementing qualities, and not only form a very hard scale themselves, but become mixed with mud and other sediment, BOILER AUXILIARIES 211 cementing it also into a very dense, hard scale. The best and cheapest chemical for this purpose is carbonate of soda, which is also known by the names of soda ash, soda crystals, sal soda, washing soda, Scotch soda, concentrated crystal soda, crystal carbonate of soda, black ash, and alkali. At temperatures above 200°F., carbonate of soda or soda ash acts on the sulphate of calcium and magnesium, and also sodium sulphate. The carbonates thus formed become insoluble and deposit at this temperature. The sodium sulphate thus formed remains in solution and passes into the boiler where it gradually accumulates in the water till it can hold no more, when it is deposited. Before it begins to deposit, however, the boiler may be blown down and refilled with fresh water. The Hartford Steam Boiler Inspection and Insurance Co. states that with an average water, such as that of Lake Michigan, requiring 1 lb. of soda ash per 10-hr. day for a 75-hp. horizontal return tubular boiler, the boilers should be blown down two gages every 12 hr., and should be emptied and refilled with water not less than once in 3 weeks. Chlorides. — Magnesium chloride gives trouble because of its cementing properties. The other chlorides such as calcium, sodium and potassium give little trouble from incrustation unless allowed to concentrate until the water will hold no more in solution, when they are deposited and increase the bulk of the scale. Magnesium chloride is generally supposed to have a corrosive action on the steel plates of the boiler as it reacts with the water, under the influence of heat, forming magnesium hydrate and hydrochloric acid, the acid then attacking the metal of the shell and tubes. Preventing Scale. — The formation of scale and the troubles caused by it have already been explained. The feed water should be analyzed and steps taken either to prevent the scale-forming elements from entering the boiler or to cause their deposit within the boiler in a form that will not adhere to the metal but can readily be blown out. If scale has already formed within a boiler, chemicals should be introduced to soften it and it should then be removed by washing, if softened sufficiently, or if not, by mechanical means. If the scale is very hard and flinty, it indicates that there is a considerable percentage of the sul- phates present. The carbonates form a very soft scale. Foaming and Priming. — A boiler is said to foam if the steam space is partially filled with unbroken bubbles of steam, and to prime if the steam carries water with it from the boiler. Foaming is caused by any materials, either dissolved in the water or suspended in it, which retard or interfere with the free escape of steam from the water in the boiler. A collection of scum on the surface of the water is also a common cause of foaming. Scum may be caused by oil, vegetable matter, or sewage which collects on the surface of the water, forming a coating which is hard for the steam bubbles to break when they rise to the surface. If the water contains an alkali, and any animal or vegetable oil becomes mixed with it, the alkali will change the oil into soap, which forms suds and causes foaming. In many power plants the exhaust from engines or pumps is condensed, collected into hotwells, and fed back into the boilers. If the cylinders are lubricated with animal or vegetable oil, there is dan- ger of its getting into the boiler and causing foaming. For this reason, only a mineral oil should be used in the cylinder but, even with this, great care should be taken to prevent its entering the boiler, as it is a frequent cause of burned plates. 212 ENGINEERING OF POWER PLANTS Oil extractors placed in the exhaust pipe will aid in removing oil. Open feed- water heaters are usually provided with oil extractors, and feed water taken from such heaters is almost entirely free from oil. Foaming may also be caused by the concentration of certain salts in the water. Priming is, in general, caused by the following conditions, all of which should be looked after: 1. Failure to blow down regularly and sufficiently (chief cause). 2. Failure to clean the boilers regularly. 3. Presence of oil, alkalies or vegetable matter. 4. Type of boiler. Corrosion. — Corrosion is most often caused by the presence of a free acid in the feed water. The free acid may result from the supply of water being con- taminated, from adulterants in the cylinder oil which find their way into the boiler, or from the splitting up of certain salts in the water. All water contains more or less air, which is liberated when the water is heated and which attacks metal surfaces. Air absorbed in water is more active in at- tacking metal than free air. This is probably due to the fact that more oxygen than nitrogen is absorbed by the water. The ordinary ingredients of scale, carbonate and sulphate of lime, have little or no direct corrosive action unless the scale becomes too thick and causes over- heating. In fact a slight coating of these salts acts as a protection and, in some cases, when the water fed into the boiler is exceptionally pure, the interior of the boiler may be lime washed at cleaning time with advantage. Another frequent cause of pitting and corrosion is a galvanic action which goes on in some boilers, particularly in marine practice. This may be stopped by placing pieces of zinc in various parts of the boiler. The zinc will be eaten in- stead of the steel and, therefore, will need" replacing frequently. Treatment of Feed Waters. — In case the feed water is known to contain impurities, a sample of it should be submitted to a chemist who makes a specialty of analyzing feed water, for analysis and prescription for the remedy of be applied. This course should also be followed in the case of a new plant. When the location for a new plant is to be chosen, particular care should be taken to secure a suffi- cient supply of good water. The term "good" as applied to feed water is only relative, but the following designations are generally used, based on the number of grains of scale-forming substance in each gallon of the feed water: Less than 8 gr. per gallon Very good. From 8 to 12 gr. per gallon Good. From 12 to 15 gr. per gallon Fair. From 15 to 20 gr. per gallon Poor. From 20 to 30 gr. per gallon Bad. More than 30 gr. per gallon Very bad. Water containing as much as 20 to 30 gr. of scale-forming materials to the gallon should never be used unless the water is first purified. For convenience of reference, the different impurities to be found in feed water and the remedies to be applied are collected in the following table : BOILER AUXILIARIES 213 Troublesome substance Trouble Remedy Sediment, mud, clay, etc Bicarbonates of lime, magnesium and iron Sulphate of lime Chloride and sulphate of magnesium Carbonate of soda in large quantities Acid Incrustation Incrustation Incrustation Incrustation Incrustation and corrosion Priming Corrosion Corrosion Foaming Priming Corrosion Filtration, blowing off. Blowing off. Heating feed. Addition of caustic lime. Addition of carbonate of soda or barium chloride. Addition of carbonate of soda. Addition of barium chloride. Alkali. Dissolved carbonic acid and oxygen Grease (from condensed water) Organic matter (sewage) Organic matter Heating feed water. Addition of slacked lime. Slacked lime and filtering. Carbonate of soda. Substitute mineral oil. Precipitate with alum, or ferric chloride and filter. Precipitate with alum, or ferric chloride and filter. The Permutit water purification process which has been recently introduced depends, for its action, upon the power of "base exchange" possessed by zeolites. The process consists of pumping the raw feed water through a tank containing an artificial zeolite made by fusing kao- lin, feldspar, pearlash and soda. This material is broken up into small pieces and packed in the shell. The calcium and magnesium compounds are converted into sodium compounds which are very soluble. When the Permutit becomes exhausted, it is regenerated by a strong solution of common salt which is allowed to remain in contact with it for about 8 hr. This process is not practical with a large amount of lime salts in solution as the cost is prohibitive. Cold processes for water softening are quite largely used and with bad waters are beneficial but are somewhat costly The cost of treating may vary from J^ ct. per 1,000 gal. to as high as 7 or 8 cts. per 1,000 gal. Where the Permutit process may be used its cost should not exceed 4 cts. per 1,000 gal. Hot processes are best worked in the open feed-water heater which should be provided with large water- storage capacity and filtering arrangements. Soot Blowers. — In modern installations of both water- and fire-tube boilers, soot blowers are regularly installed as a part of the permanent equipment and are used as often as may be necessary to secure good opera- tion. These tube cleaners consist of a set of nozzles so set that all the tubes of a fire-tube boiler can be cleaned at once. In water-tube boilers a set of nozzles are provided for each pass and the nozzles are so arranged that practically the whole heating surface may be covered. Steam or air is used and the tubes are cleaned while the boiler is in light service. The installation cost varies from 50 cts. to $2.50 per boiler horsepower. 214 ENGINEERING OF POWER PLANTS Fig. 134. — Vulcan soot blowers applied to Babcock & Wilcox boiler. PROBLEMS _ 60. The owner of a maufacturing plant is about to install a 400-hp. compound con- densing Corliss engine with surface condenser, water-tube boilers and the necessary auxiliaries. The cooling tower will be placed on the roof of the building, 70 ft. above the pump pit. 1. How much steam ought the boilers to supply per hour when the engine is oper- ating at full rated load? 2. He proposes to install three boilers of equal size, two of which shall supply the steam demand in (1) when operating at 25 per cent, above the manufacturer's rating. How many square feet of heating surface should each boiler contain? 51. Determine the amount of steam used by a feed pump per hour for each plant indicated in problem 18, page 81. CHAPTER X PIPING Although the choice and arrangement of certain generators and prime movers determine in a general way the efficiency under which a generating station can work, yet the piping systems may influence this result to a much greater extent than is generally believed. The size and arrangement of the various pipes and valves have a very important influence on the efficient and economical operation of the plant. The piping system may be classified under the following heads : High-pressure steam piping, main and auxiliary. High-pressure drip piping and boiler returns. The feed- water piping (high pressure). The exhaust piping. The circulating water piping for condensation. The hotwell and low-pressure drip piping. The make-up feed piping and city water supply. The jacket and wetting-down piping. Compressed-air piping. Oil piping, both low-pressure for lubrication and high-pressure for step bearings, and The fire lines, which are ordinarily considered part of the plumbing contract and put in separately from the pipe job. In the design of these various systems consideration must be given to drainage and returns (traps and steam loops), expansion bends, slip joints, etc., vibration, angles and supports, and the various materials which are proper to use for the different purposes which the piping sys- tems must fulfill. The joints or flanges, the gaskets to be used between the flanges, the design of the fittings, elbows, tees, etc., the types and designs of the valves, must all be considered in connection with each class of piping. Pipe. — The material for steam pipe, whether high or low pressure, is now almost uniformly openhearth steel. This may be made by the acid or basic process, but Bessemer pipe or wrought-iron pipe should not be used if the best results are to be obtained. The use of Bessemer-steel pipe brings in difficulty in flanging and bending is usually uncertain at the welds. It has in its composition rather more phosphorus and sulphur than is considered good when severe strains are to be placed on the mate- 215 216 ENGINEERING OF POWER PLANTS rial. Wrought-iron pipe, when it can be obtained, may be very good for certain uses but it is almost impossible to flange a piece of wrought-iron pipe satisfactorily and its use is now confined mainly to unimportant work at localities close to the place where the pipe is made. Steel pipe when used for oil or salt water is often galvanized and its thickness should be proportioned to meet the pressures in use. Where warm water is to be distributed, cast-iron pipe has been and is the standard. Cast-iron pipe, when properly made, has proved to be the best for large and small water mains for either low or high pressures. Where the water pipe is small or where many bends are required, or where the heat and wear are excessive, bronze pipe has been substituted for cast-iron with very good results. The smaller sizes of pipe used in the oiling system are almost invariably made of brass. The use of copper pipe for steam work has been almost entirely superseded, the introduction of superheated steam with the resulting action of the high temperature on the copper rendering it unfit for such employment. There are many stations in which nothing but openhearth steel and cast-iron piping are used and it may be noted that this practice is increasing and these materials will be the standard for the future. Joints. — Pipe joints have been a great source of trouble in the past and the various kinds and " standards" have been as many almost as there were individual engineers. For low-pressure pipe work the screwed joint with the standard pipe thread and cast-iron flanges has been and is the standard for the best work. For pressures above 100 lb., however, another type of joint should be adopted if the best work is desired. For this purpose there has been no joint found better than the so-called Van Stone joint. This is made by flanging the end of the pipe against the outside of a steel or cast-iron flange. There are many varieties of welded flanges in which the flange is welded directly to the pipe, but these do not seem to have been as popular or as good in construction as the so- called Van Stone, although many people use them. All welded flanges have the disadvantage that they cannot be turned on the pipe, making great care necessary to avoid mistakes in drilling them. The best joints are made by grinding the seats to a perfect surface and then bolting them together without a gasket. This, however, takes a high grade of mechanic and has been satisfactory only when made in the proper manner. Instead of grinding the faces, it is now considered at least as good to fine tool finish them and insert a gasket which in the best work has been made of very soft steel approximately Jfoo m - thick. Duralite and other indurated fibers make good gaskets. Copper gaskets appear to deteriorate very rapidly in this position and are not used on high-pressure work as much as formerly. The tongue and groove joint cannot be recommended for steam work as it is almost impossible to PIPING 217 bring two joints to the same degree of tightness. For the lower steam pressures copper gaskets work very nicely and are now standard. These are usually stamped with corrugations which flatten out when the bolts are tightened up, assuring a surface practically the whole width of the face. For exhaust work rubber with wire insertion such as the " Rain- bow 5 ' is mostly used. For water, whether hot or cold, the "Common Sense" or other babbit composition gaskets are quite satisfactory. The gasket made up of a soft lead ring with a copper wire ring outside of it has also been largely used with very good results and " Rainbow" gaskets are satisfactory when the pressures are not too high. Fittings. — For low-pressure work, either steam, exhaust or water, the Master Steam Fitters' Association has adopted a standard of pipe fitting which is practically used throughout the United States and it is only for pressures higher than 300 lb. that special fittings are required. Up to 200 lb. steam pressure with no superheat, cast iron or gun iron forms the ideal material for pipe fittings and is practically the only material in use. With the advent of superheated steam, however, the cast-iron fittings soon proved themselves to be useless with the high heats and semi-steel and steel fittings were tried with the best of results. Today no plant using superheated steam installs cast-iron fittings for high-temperature work. All fittings should be provided with proper means of draining and drainage pockets or outlets should be placed at the lowest points for the attachment of the drainage system. Valves. — For low-pressure work the standard cast-iron valves with bronze seats have been more than satisfactory. They are now made of a great many types, all of which give very good results. The solid wedge gate is perhaps the earliest and the best known. The spilt-wedge type and the parallel two-gate type are also well known and largely sold. Globe valves are not usually used for steam work on account of the resist- ance offered to the passage of the steam, but for throttle valves and for stop valves are still the standard. For high-pressure work and especially with superheated steam the use of the steel-body valve with steel seats and discs has become standard and many varieties of valves are now on the market, some of which are doing excellent work. Nickel-bronze and nickel are also used for seats and stems with good results. In choosing a valve for high-pressure and high-temperature work, great stress should be laid on the absence of chance for unequal expansion in the body and gates. The metal should be so placed that what expansion occurs will be equable in all directions and the gates so designed that they cannot spring out of true under different degrees of heat. Such mechanism as may be used between the gates in a double-gate valve to press them up against the seats should be as carefully designed as the body of the valve, as small deflections in this part of the mechanism will prevent tightness. 218 ENGINEERING OF POWER PLANTS The most satisfactory valves for this work have been of the double- wedge type, although there are good parallel seat and solid-wedge valves on the market which have stood severe tests. Bolts. — It has been customary in ordinary work to use the standard sizes of bolts as provided by the Master Steam Fitters' Association, using a number of bolts of reasonably small diameter. These bolts are the or- dinary iron or Bessemer-steel stock with square heads and semi-finished hexagonal nuts. If these bolts are made of good openhearth steel and are set up in the proper manner, it is an insurance against troubles in the pipe joints whereas the ordinary bolt will probably stretch enough to cause more or less trouble, not to say anything of the action of the hot steam upon the bolts. A leaky pipe is more than a nuisance, for when it has persisted for some time it means that the flanges must be refinished before a tight joint can be obtained. High-pressure Steam Piping, Main and Auxiliary. — The high-pressure steam piping of a power station consists first of a steam line taking the steam from the boiler drums and delivering it into, second, the first steam main or steam header, and third, the connections from the steam header to the various prime movers. The auxiliary steam may be taken from the boiler drums into the auxiliary header with connections to the aux- iliaries, or the connections to the auxiliaries may be made from the main itself, or from the connections to the prime movers. All of these systems are in satisfactory use. The type of the main steam lines, however, depends very largely upon the layout of the station. With the end-to-end layout, in which the boilers are placed at one end of the station and the prime movers at the other end with main steam line connecting the two, the piping may be likened to a tree, the boiler piping being the roots, the trunk of the tree the steam main and the branches of the tree the feeders of the prime movers. This type of station is very rarely built at the present day on account of the sizes necessary for the steam main through which all of the steam must pass. For stations larger than about 5,000 kw. it is never used and the ordinary arrangement is the back-to-back where the boilers are ar- ranged in one line and the prime movers in another parallel line, with the steam line parallel to both and between them. The boiler connections then are taken directly to the main and the leads of the prime movers directly from the mains to the prime movers. This system is modified into a unit system by leaving out the steam main and by introducing small equalizing pipes between the unit lines connecting a group of boilers with the prime movers. Further modifications of this layout were brought out by the use of the double-decked station in which the prime movers are placed in the basement with the boilers overhead or the boilers PIPING 219 are placed in the basement with prime movers overhead. Stations of both of these types have been in operation for a long time. There are also stations with the prime movers in the center and a double line of boilers on either side of the engine room. This brings in complications in the steam piping, but is frequently economical in cost. Disadvantages of Various Systems. — The first system described, or the trunk system, is quite a costly system to install and as all of the steam had to pass through one section of the main it necessitates very large pipes and the consequent serious increase in the cost; the expansion difficulties are magnified by the length of the main steam line and except for very small plants it is no longer used. The parallel system is probably the most used of all systems and the unit system and ring-header system are modifications of it. In the ring- header system the steam main is a continuous ring which may extend around the prime movers, or may be simply a loop between the prime movers. The unit system is frequently turned into a ring-header system with smaller pipe connections between the parts of the unit system. Figs. 135, 151, and 157, show various steam-pipe layouts of these types. The unit system almost invariably presents the cheapest and most satisfactory system of piping, the steam lines being smaller in size. It suffers the disadvantage that when the prime mover is out of service the boilers connected to it are also out of service. The parallel system is probably more popular than the unit system and is very frequently used. The cost of this stands next to the unit system and is about the same as the unit system with the cross-ties, which, in reality, convert the unit system into a parallel system. The ring-header system is probably the most used and is without doubt the most flexible, but is also much more costly to install on account of the double line of main headers which are usually the largest steam pipes in the station. There is a great difference of opinion among engineers as to the best method to be followed in these layouts. Formerly it was considered necessary to install a duplicate system of steam mains, each boiler having a connection to each of the two mains and each prime mover con- nections to both mains also. This led to a complete duplicate set of steam piping which was extremely costly and usually gave a great deal of trouble. It is very easy to keep a steam line tight when it is hot all the time, but a steam line first hot and then cold is usually much more troublesome. In cases where the duplicate system was installed, one of the lines has been removed and the stations are now running on a single system with much better results. The losses in a steam piping system are entirely due to radiation, the drop in steam pressure due to the friction in the pipe being manifested in heat and radiated from the surface of the pipe. It is now considered the best practice to make these pipes 220 ENGINEERING OF POWER PLANTS PIPING 221 as small as possible allowing at least from 3 to 5 per cent, drop between the boiler drum and the prime mover. By cutting down the size of the pipe the surface is reduced and as the radiation is directly proportionate to the surface large savings are made. Formerly steam mains of 18 to 24 in. in diameter were considered necessary in small stations and the radiation owing to the poor quality of pipe covering then used was enormous. At the present time very few mains are put in of larger size than 14 in. I.D. and in some cases a 10- or 12-in. main is considered sufficient. The drop in pressure between boiler and prime mover is considerably larger than formerly but the actual heat loss due to friction and radiation is very much less than it was. This reduction in pipe sizes also brought in great economies in the upkeep cost of the steam lines as with the high pressures carried at the present day it would be almost impossible to keep a 20-in. or 24-in. main tight under the conditions of actual service. Steam Speeds. — For years standard practice for the speed of steam in steam lines was 4,000 ft. per minute as the minimum, 6,000 as the average and 8,000 as the maximum. This was considered the standard in the days when 125 lb. steam pressure was carried without superheat. At the present time with 200 lb. pressure and superheat which may extend as high as 200°F. above the saturation temperature, the minimum steam speeds are much higher and very few engineers are using as the minimum speed less than 8,000 ft. per minute, the maximum in some cases running as high as 18,000 ft. with no bad results. Details. — Starting from the boiler it is good practice today to connect the various boiler drums with what is known as a crossover header con- sisting of a steel casting with ball-and-socket joint connections to the vari- ous boiler drums and provided with a single outlet at the top from which the steam supply may be taken. This header is connected to the boiler drums by means of cast-steel nozzles which are riveted to the drums and which have on their upper flanges a ball-and-socket joint. On top of this crossover is placed some variety of automatic stop check valve which is required by the police regulations of certain cities. This stop check valve is made in many styles and performs a variety of functions. It is usually so arranged that when the pressure in the boiler drops below the main pressure the valve will shut preventing the steam from returning to the boiler. It is usually provided with an automatic clos- ing device so that when a steam pipe breaks and a sudden drop of pressure occurs in the main the valve will also shut. It is also provided with a hand closing and opening device. Such valves are shown in Figs. 92 and 136. From the outboard flange of this valve the main boiler connection is taken to the main. This is of bent steel pipe with Van Stone flanges 222 ENGINEERING OF POWER PLANTS and is not usually larger than 10 in. for a 650-hp. boiler. Of late the sizes have been cut down to 8 in. and in some cases to 6 in. with very good results. Between this connection and the steam main a gate valve is always placed so that there may be two valves between the boiler drums and the steam main. This is good practice apart from the police regula- tions which usually require that every connection to the boiler shall have at least two valves between the boiler and the main. The steam main itself is divided into sections by means of gate valves some of which may be provided with hydraulic or electrical closing and opening devices so that they may be operated from a distance if necessary in cases of emer- gency. But all valves of this type should be provided with hand closing and opening gear as well as the mechanical gear. From the steam main at a convenient point the connection to the prime mover is made. At the steam main a gate valve is located and the lead is taken by the most direct methods with large bends to the throttle valve of the prime mover. It is not usual to place a second valve between the gate valve and the throttle on the prime mover as the automatic throttle and the throttle valve itself are considered as giving sufficient safety. Auxiliary Steam Piping. — It was formerly considered the best practice to have the auxiliary steam piping entirely separate from the main steam line and to this end a separate connection was made with a small valve to the end of the crossover pipe on t<— — 15 Fig. 136. — Automatic-stop check every boiler, these connections being led into an auxiliary main of smaller size extend- ing across the rear of the boilers. This was an entirely separate system connected in no way with the main system. It has the customary two valves between the boiler and the main and a single valve at the main where the connection is made to the auxiliary, the throttle valve of the auxiliary engine acting as the second valve between the engine and the main. It is now considered better practice that the steam connections with those auxiliaries that are intimately connected with a prime mover should be taken directly from the steam connections of the prime mover near the throttle valve. In many of the latest stations this scheme has been PIPING 223 carried out with very good results. This means, however, that a separate system must be provided in the boiler house for the feed pumps, fire pumps and other boiler room auxiliaries which is usually done by means of a similar separate piping system either taken from the boiler drums or else from certain points on the steam main that must always be in service. This is without doubt the best system where superheat is used in both prime movers and the auxiliaries. High-pressure Drip Piping and Boiler Returns. — It is customary to install a drip system along the under side of a high-pressure steam main to return the water of condensation to the drip tank or boiler. This system is usually built up of small pipe with screw joints, pipe not over 2 in. size being used for this purpose. Every fitting and valve in the main is tapped for a drip connection and a nipple is screwed in with a valve. Similar drips should be installed in the boiler connections next to the main. One of the drips on each boiler connection should be so arranged that it may lead into the ashpit of the boiler where it can be observed and this pipe is left open when the boiler is open for inspection showing that there is no steam next to the stop check valve. As the high-pressure drips are among the most important pipes in the station it is customary to make these of extra heavy pipe and a great deal of care is usually taken that all of the joints are tight and that the system is a substantial one in every respect. Feed-water Piping (High Pressure). — The high-pressure feed-water piping consists of all of the piping connecting the feed-water pumps with the boilers themselves. This includes the lines through the closed heaters when they are installed and also lines to and from- the economizers. This pipe is almost invariably made of cast iron and for ordinary work does not exceed 8 in. in diameter even in the largest stations. Such pipe is usually from % to 1 in. thick with heavy flanges and raised seats. This piping system usually consists of a run of piping under each row of boilers from which a loop is taken up over each battery and down again connect- ing with the main on the other side. This loop is most always of 3-in. pipe and is provided at a point above the floor with a check valve and sometimes with a hose connection. The stop valves and check valves are usually of brass and the piping running over the boilers and between check valves is usually brass pipe, iron-pipe size, with brass flanges screwed on and sweated. In the middle of the battery above the boilers a gate valve is placed to separate the two parts of the loop, and brass fittings are inserted above the drums to provide for the 2-in. connections to the front ends of the boiler drums. These connections are bent brass pipe, iron-pipe size, and at the drum are provided with a combination stop and check valve so that any line may be thrown out of service if desired. This is not the standard arrangement, however. The standard consists 224 ENGINEERING OF POWER PLANTS Safety Release Valve Oi' Operating Cylinder of a double line of 3-in. pipe extending up at the middle of the battery and connecting with a 2-in. line to each of the three drums. This line usually interferes with stoker installations or with the middle column which runs up between the two boilers of a battery and in large stations the installation is almost always made as first described. Each boiler maker usually has his own type of stop check valve at the drums and this valve is usually furnished with the boiler. The check valves and stop valves and the gate valve in the middle of the boiler over- head are usually also furnished by the boiler contractor. The piping below the main 3-in. stop valves is usually cast iron and is furnished by the pipe contractor. These mains run below the lines of boilers and are connected to the main feed line which may run the length of the station. This line is sometimes made as a ring header or closed loop. Sometimes it consists of a double line of mains with crossovers protected by gate valves which are usually of cast iron. Suitable air chambers for equalizing the pulsations are provided when reciprocating pumps are used. The use of steel pipe for feed-water lines is not to be recommended under any circum- stances. The hot pure water affects the material very badly causing pittings which, with certain impurities that are present, will probably destroy the pipe in a very short time. Cast iron seems to stand this sort of work much better than anything else which has been used and is very satis- factory. In many cases where steel has been used it has had to be removed within a very short time and cast-iron pipe substituted. Exhaust Piping. — The smaller sizes of exhaust piping up to 6 or 8 in. are usually made of standard cast-iron pipe with cast-iron flanges for say 50 lb. pressure. Between 8-in. and 30-in. spiral riveted galvanized pipe with steel flanges riveted on is commonly used; and riveted steel pipe for sizes above 30 in. Allowable speeds of exhaust steam in these pipes are very much larger than are allowable for pressure steam speeds, as high as 35,000 ft. per minute being permissible in certain cases. When a prime mover is arranged to be run continuously the exhaust connection to the condenser is usually made very short and of cast iron. The at- mospheric exhaust is connected into this pipe between the prime mover Fig. 137. — Atmospheric valve. relief PIPING 225 and condenser and is provided with an atmospheric relief valve which is arranged to open wide whenever the vacuum drops to a certain amount. Fig. 137 shows a type of relief valve which has proved satisfactory in service. They are almost always balanced valves of the globe type, provided with weights and dashpots to prevent chattering and arranged for quick and full opening under operating conditions. Hydraulic devices are usually installed to allow opening or closing from a distance. The smaller apparatus, which is always run non-condensing, is provided with a direct exhaust pipe to the heaters where the steam is condensed at atmospheric pressure for heating the feed water. When turbine- driven auxiliaries are used and run non-condensing it is very important that there be no back-pressure at the exhaust nozzle of the turbine and great care should be taken that the exhaust pipes are suf- ficiently large and straightaway, that no pressure may be devel- oped at the exhaust nozzle. All exhaust piping should be laid out with a fall to the heater or else should be properly graded with drip piping of sufficient size. In a small plant where the ex- haust is allowed to go to the atmo- sphere, suitable mufflers should be installed at the top of the exhaust line to prevent noise. (See Fig. 143.) Determining Pipe Sizes. — Many formulae have been used for determining pipe sizes for steam engines, but most of them are now obsolete. In Power for Jan. 19, 1915, F. W. Salmon presents results secured by plotting the necessary data from a large number of suc- cessful plants. If A = area of pipe bore in square inches, d = diameter of pipe bore in inches, W = average pounds of steam per hour, C = a constant for a given pressure in the pipe, , , tXC then or Fig. 138. — Anchor for steam main. iv — tx uunoteu 4 W = A X C = = d 2 XK W d 2 = " - a R Salmon presents the following tables for determining suitable pipe sizes: 15 226 ENGINEERING OF POWER PLANTS Constants Vacuum, inches, Hg. 28 26 24 22 20 18 16 13 6 Gage pressure, square inches . C 50 84 105 122 134 144 151 162 176 187 80 267 100 275 125 284 150 291 175 298 200 304 K 39.2 66.0 82.5 95.7 102.0 113.0 118.6 127.0 138.0 147.0 210.0 216.0 223.0 229.0 234.0 239.0 Grading of Pipe. — The slope of the pipe line should be toward the engine as water is often prevented from flowing back against the steam current. Drip pockets should be used in all fittings. The main line should pitch about 1 in. in each 10 ft. of run. Pipe lines always need draining. 1- to 2J^-in. drain pipes should be used. It is frequently _h_ i^,^^^^ w^^^m^^^ -Q- Fig. 139. — Slip expansion joint. Fig. 140. — Wainwright expansion joint. convenient to use the drip lines as bypasses instead of bypassed valves in high-pressure work. Expansion of Pipe. — The coefficient of expansion for ordinary steam pipe seems to be about 0.000006 of its length for each degree F. A rough and ready rule is to allow ^ in. for every 100 ft. for every 100°F. differ- ence of temperature. All pipe lines should be laid out to take care of this expansion, and to this end large radius bends should be employed wherever possible. It is usual to cut the pipe so it will be the right length when it is hot, making up the joints and pulling them together, PIPING 227 Jp "^[bc k. F" Fig. 141. — Baragwanath expan- sion joint. so that an initial stress is put in the cold pipe. When the pipe becomes hot, this stress disappears and the pipe will then be in equilibrium. Suitable hangers should be provided every 10 or 12 ft. to support the pipe in its proper place. These may consist of a band around the pipe with a rod hanger from some of the floor beams overhead, or the pipe may be supported from below on a roller. Anchors should also be provided at certain places so that the direction of expansion may be controlled. On very long lines sliding expansion joints become necessary, or the corru- gated-steel expansion joint may be used. Pipe Coverings. — The best covering is 85 per cent, carbonate of magnesia, 1 in. thick on exhaust piping and 2 in. thick on high-pressure steam piping. This should be covered with J^-in. asbestos board and with sewed and pasted canvas. Remov- able flange coverings should be used. (See paper by McMillan, A. S. M. E., December, 1915.) Badly erected and leaky lines of steam piping may cause excessive waste. More steam (250 boiler hp.) can leak through a 1-in. hole in a steam pipe at 150 lb. steam pressure than one fireman would usually supply by steady coaling. Leaks in steam pipe are usually regarded as insignificant but they rapidly dissipate the heat generated in the consumption of a large amount of coal. Uncovered steam pipes also waste large amounts of coal and load the steam with water; water in the steam causes pounding or water- hammer in the pipes, which often produces serious results. A good steam covering will save some 80 per cent, of the loss of heat which takes place from the naked pipe and the investment in a good pipe covering will usually more than repay 100 per cent, interest. Cost of Piping. — The cost of piping in a steam power plant varies greatly with the type of installation and with the size of the plant, ranging all the way from $10 to $15 per rated horsepower installed in small plants, to $1.50 to $2.50 per rated horsepower installed in plants of from 3,000 to 5,000 hp., using 125 lb. steam pressure. For turbine plants and engine plants using 175 to 200 lb. steam pressure with superheat, the piping cost for plants of 3,000 to 5,000 hp. will vary from $2.50 to $6. In large turbine plants using high-pressure steam and high superheat the cost may be in excess of $8 per horsepower. In one engine plant of 28,000 hp. the steam piping system cost $4.35 per horsepower; the feed-water system, 30 cts.; the drip system, 25 cts.; the blowoff system, 10 cts.; the condensing water piping for jet condens- 228 ENGINEERING OF POWER PLANTS ers, 30 cts.; the house, fire and heating piping, 15 cts.; the jacket piping, 10 cts.; and the oil system and piping, 75 cts. This system used steam at 175 lb. pressure with no superheat. The use of steel fittings and the careful construction necessary for high-pressure superheated steam work has greatly increased the cost of steam piping. The one item of laboi has practically doubled in the last 10 years. The list prices of pipe and fittings should be discounted from 50 to 75 per cent. Eighty-five per cent, magnesia, 1 in. thick, costs in the neighborhood of 30 cts. per square foot in place. In general such covering costs about one-half list price including labor. One writer states that one man will cover 100 ft. of straight pipe or 40 fittings per day up to 4-in. pipe size. Above 4 in. the cost per 100 ft. of pipe length will be greater owing to the increased labor of handling. One consulting engineer reports the plant piping cost per indicated horsepower rating of the plant as follows : Simple non-condensing Engine horsepower Cost per horsepower . . . Simple condensing: Engine horsepower. . . . Cost per horsepower. . . Simple condensing: Engine horsepower. . . . Cost per horsepower . . . Compound condensing: Engine horsepower. . . . Cost per horsepower. . . Compound condensing: Engine horsepower. . . . Cost per horsepower. . . 10 12 14 15 20 30 40 50 $8.30 $8.00 $7.60 $7.40 $6.70 $5.70 $5.10 $4.60 10 12 14 15 20 30 $11.20 $11.00 $10.70 $10.20 $9.50 $8.00 40 50 75 100 $7.70 $7.30 $6.10 $5.70 100 200 300 400 500 600 700 $13.80 $11.20 $9.10 $8.00 $7.40 $6.80 $6.50 800 900 1,000 1,500 2,000 $6.25 $6.00 $5.75 $5.10 $4.55 75 $3.90 Exhaust Heads and Oil Extractors. — The atmospheric exhaust pipe which usually leads into the air above the roof of the station would be very noisy and likely to create a nuisance from the water entrained in the exhaust steam. To avoid the noise and save the water a muffler or exhaust head is fitted to the top of this pipe. This usually consists of a conical or cylindrical chamber two or three times the diameter of the pipe in which are placed wire screens and other baffles breaking up the flow of the steam and the organ pipe effect which would otherwise be pro- duced. Suitable baffles are also installed to catch the entrained water which is piped back to the heater or sump. Where the condensate from the exhaust steam from engines is to be used over again it is necessary to install a grease or oil extractor in the PIPING 229 exhaust line. This usually consists of a set of baffles in an enlarged sec- tion of the pipe very similar in design to the steam separator, but of much larger size, as the velocities must be very low in order that the oil may be deposited. It should be remembered that if the oil becomes emulsified or volatilized it will be practically impossible to catch it. In such cases it will be better to change the quality of the oil or throw away the water. There are also grease extractors made to remove the Fig. 142. — "Lagonda" oil filter and grease extractor. Fig. 143. — Exhaust head. emulsified oil from water by means of electrical currents. These machines are good in their way, but are costly and take up a great deal of space. Another type of grease extractor is the pressure filter with car- tridges of absorptive material, such as excelsior. These ma- chines are also bulky and not much used. Steam Traps. — The high- pressure engine drips should, if possible, be led back direct to the boiler, but if this is not pos- sible, the next best place is the open heater. The low-pressure drips contain more or less oil, and Fig. 144. — Steam trap, float type. should be thrown away. If, however, it is necessary to save them, a steam trap may be used which will lift the returns to a sufficient height to enable them to flow by gravity to a heater or storage tank. Steam 230 ENGINEERING OF POWER PLANTS U traps may also be used in the high-pressure line, returning the condensed water to the boiler direct. The steam trap is usually a closed container provided with a small valve controlled by a float or bucket in such a manner that when the container becomes full of condensed water a small valve is opened and the steam pressure forces the condensate through the pipes to its destination. These small valves require an enormous amount of care to keep tight, otherwise the high-pressure steam blows through the trap and is a continual waste. Use as few traps as possible. The receiver with pump is a better device than the trap and is used in the better class installations. Steam Loop. — A much better device than the trap for returning drips to the boiler is the steam loop of which there are a number of varieties. In general the system consists of a riser from the drip point, a length of uncovered pipe slightly sloping toward the discharge end and a drop leg connected to the mud drum of the boiler with a check stop valve and bleeder. The condensation and cooling in the uncovered horizontal pipe creates a sufficient drop in pressure to bring mixed steam and water to the upper level of the apparatus where it cools and by its weight forces itself past the -■ ■ |~ check valve into the mud drum. The steam loop is m — |jek somewhat modified in the larger systems but although S successful when well installed is not as good a system as the receiver and pump. Steam Separators. — The separator is an enlarge- ment of the piping system in which the steam velocity is reduced and the particles forced to travel in a zigzag direction against surfaces, corrugated or provided with lips to catch and retain the liquid particles which run down in the wake of the lips out of contact with the steam into a receiver. Some separators have screen baffie, others grids, but all embody the two principles, change of direction and reduction of velocity. Separators are built with either cast-iron, cast-steel, or riveted- steel shells but the heads are always castings. Although absurdly high efficiencies are claimed by manufacturers of steam separators, efficiencies which cannot be realized in commercial practice, yet no separator should be retained in service that does not remove at least 80 per cent, of the water carried by the steam approach- ing the separator. PROBLEMS Fig. 145. — Cochrane separator. 52. A 6-in. pipe line 150 ft. long carrying steam at 125 lb. gage pressure, was put up without expansion joints. At the end of the 150-ft. run the direction of the pipe was changed abruptly 90° and the pipe rigidly held in the new direction. Close to the 150- PIPING 231 ft. point several short 2^-in. connections were tapped into the 6-in. main. As soon as steam was turned on the 6-in. ell was ruptured and every connection torn off. Why? How much did the pipe move at the point in question? 63. Determine the proper steam and exhaust pipe sizes for a 325-i.hp. non-condens- ing Corliss engine. What would be the pipe sizes if this engine were designed to run condensing? What would be the sizes for a 6,000-hp. condensing engine? 64. A 100-hp. Corliss compound condensing engine requires the following steam per indicated horsepower-hour. Percentage of load 25 50 75 100 125 Pounds steam per indicated horsepower-hour. ... 32 24 21 20 20.5 If the steam pressure is 100 lb. gage, what size steam and exhaust pipes ought the engine to have? What is the velocity of the steam in the pipes for the various loads on the engine? 66. Calculate the velocities in the various pipes as given by Salmon's formula. Plot them with pressures as abscissae. Deduce the equation to the curve. Plot the curve 36,000 y = and compare. CHAPTER XI COAL AND ASH HANDLING Coal Handling. — For small plants coal is usually hauled by wagons and dumped in the boiler room in front of the boilers, but it is better practice, even in these small plants, to provide a pocket above the boilers Fig. 146. — Coal handling machinery Williamsburg Power House Transit Develop- ment Co., Brooklyn, N. Y. with some means for getting the coal into it. The coal may be dumped from the car or wagon into a small receiving hopper, which feeds a travel- ing belt, conveyor bucket or elevator system, which transfers the coal to the overhead pocket. In some stations the car is unloaded by means of 232 COAL AND ASH HANDLING 233 a grab bucket on a telpher system which transfers the coal, a bucketful] at a time, from the car or wagon to the coal pocket. Coal Elevator Coal. Weighing and Distributing Crane Coal Bin over each Producer tt^-H-- Operating Gear for Producer Gas Producer Hughes Self Cleaning Coal Car Fig. 147. — Typical coal-handling apparatus for gas producers or boilers. Where it is not possible to install a coal pocket it is customary to have a storage pile in the neighborhood of the fire room. Industrial railway tracks are run from the pile to the boiler fronts and small cars may be 234 ENGINEERING OF POWER PLANTS loaded either by hand or by a small locomotive crane and run along the tracks in front of the boilers, the hand-firing being done direct from the cars. This outside coal storage has been adopted for a number of larger stations, but small hoppers are provided above each boiler capable of holding 2 or 3 tons of coal and a car system, or telpher system, has been installed from the coal pile to the fire room to keep these hoppers full. The design of coal-handling machinery depends largely on local con- ditions. In one station of 15,000 hp. the location is on a hillside, the coal supply being obtained by wagons which drive onto the roof of the Co'- 1 Fig. 148. — Typical coal-handling tower, one-man type. station and dump their coal directly into the coal pocket. At Carville, near Newcastle, England, the railroad siding is extended over the roof of the boiler house and the coal is delivered direct from cars to pocket. Most of the larger stations in the Eastern States receive their coal by water. The coal is removed from the boats by means of clamshell buck- ets, often as large as 2 tons capacity, which are hoisted at once to a maxi- mum height required for delivering the coal. This amounts in some stations to a hoist of 140 ft. The coal is dumped from the clamshell bucket into a receiving pocket and then passed through a crusher which reduces the coal to the proper size for firing. From the crusher it goes into the cars of a cable railroad or conveyor, which delivers it to the various coal COAL AND ASH HANDLING 235 pockets from which large downtakes lead to each stoker or firing door. The cable railroad is usually the cheapest conveyor to install, maintain and operate. Next comes the traveling belt. The bucket conveyor is the most costly of the three. Forty to 50 tons of coal may be unloaded per 8-hr. day by one man. One man has fired as much as 16 tons of coal per watch of 8 hr. Cost of Coal Handling. — In small plants the cost of coal handling may be as large as 40 to 45 cts. per ton fired. Where machinery is installed the cost drops with careful design and increase of size of plant to the neighborhood of 8 to 12 cts. per ton with good sized plants. For the larger of the central stations this cost should not exceed 4 cts. per ton. The cost of stacking in well-designed storage piles should not exceed 2 cts. per ton and the cost of reclaiming will be about the same. It should be remembered that in small plants a good man and one mule will handle a considerable amount of coal at an exceedingly cheap rate, and in most of the smaller plants it will not pay to install coal-handling machinery. An idea of the saving to be secured by mechanically handling the coal may be obtained from the following figures: A plant of 7,500 hp. in boilers was operated for some time without coal-handling machinery other than small hand cars which were loaded by hand from railway cars outside of the building, and which were then hauled up a straight incline to the boiler house, so that the fuel could be dumped in front of the furnaces. The coal-handling machinery later introduced was so arranged that the coal was only handled by hand in shoveling it out of railway cars onto the conveying system. Wages Tons burned Cost per ton Hand operation: 16 firemen and 1 helper, 11 coal and ash men. Ash removed by contract. Mechanical operation: 3 firemen and 2 helpers, 80 634.66 287.75 11 coal and ash men, 2 conveyor men 654. 50 .229 0.1478 0.041 0.0938 The saving in wages of firemen and helpers amounted to 18.8 cts. per ton, which is 82.1 per cent, or $1,311.30 per month. The saving on coal and ash handling is 5.4 cts. per ton, which is 41.4 per cent, or $376.55 per month, or a total saving of $1,687.85 per month or over $20,000 per year. If the coal did not have to be shoveled from coal cars onto the conveyor in this plant the saving on labor might be even greater. 236 ENGINEERING OF POWER PLANTS The total cost of handling coal from coal car to ash car in large cen- tral stations is roughly 10 to 18 cts. per ton. Letters from owners of about 600 boilers to Mr. R. S. Hale of the Steam Users' Association, indicate that it costs to move coal by hand (wheelbarrow) about 1.6 cts. per ton-yard up to distances of 5 yd., then about 0.1 ct. per ton-yard for each additional yard. One man, besides a night man, can run an engine and fire up to about 10 tons of coal per week. One man, besides an engineer and night man, can fire up to about 35 tons per week. Settling Chamber Special C.I.Tee and Plug Direction . | ^nv|^Flangea of Ash b=a n \M Plug Fig -Diagrammatic view of pneumatic ash-conveyor plant, Armour Glue Works, Chicago, 111. Two men, besides an engineer and night man, can fire up to about 80 tons per week. These figures assume that the night man does all he can of the banking, cleaning and starting. Mr. Hale further reports that mechanical stokers save 30 to 40 per cent, of labor in plants burning from 50 to 150 tons per week, and save no labor in small plants. Boiler attendants were paid about $1.50 per day of 10 or 12 hr. Average cost of firing coal was reported to be 48 cts. per ton; maximum, 71 cts. per ton; minimum, 26 cts. per ton. Ash Handling. — In small hand-fired plants and in most of the older plants no ash pockets were provided under the grates, the firemen pulling the ashes out of the ashpit with a hoe and then shoveling them into ash COAL AND ASH HANDLING 237 cans, wheelbarrows or cars for removal. Where the power plant has a basement ash hoppers allowing the storage of about 8 hr. ashes are usu- ally provided. These hoppers have suitable gates at the bottom, through which the ashes may be dumped into steel dump cars which are hauled by an electric locomotive outside the station. In the country the ashes are generally used for filling in adjoining land; in the interior cities they are usually valuable, in some cases bringing as high a price as 50 cts. per cubic yard. Where they cannot be used for these purposes the dump cars deliver into a skip or ash hoist which delivers the ashes into a pocket from which they may be delivered into boats, cars or wagons for disposal. At the Armour Glue Factory in Chicago is installed a pneumatic ash sys- tem, taking care of the ashes from 22 B. & W. boilers of 300 hp. each. In this installation an 8-in. cast-iron pipe is run along the front of the ash hop- pers which are large enough for 24-hr. storage. The hopper is provided on an 8 by 12-in. aperture in the pipe and the ashes are pulled from the ash hopper into the pipe by hand. A vacuum of from 10 to 15 in. of water is maintained in the pipe by an exhauster of the Conner sville double- impeller type placed at the outboard end of the 8-in. line. In front of the exhauster a separator is placed similar in principle to the standard shaving separator and discharged through a valve in the bottom into the ash pocket. With this system the ashes are conveyed horizontally 200 ft. around numerous bends, and vertically 70 ft. before being discharged into the hopper. The ashes must be dry and all large lumps and clinkers must be broken up. The operation is by one man and is said to take not over 2 hr. per day. Traveling belts and bucket conveyors have also been used for hand- ling ashes, but the upkeep on this apparatus is very large indeed. Cost of Ash Handling. — The cost of getting the ashes out of the sta- tion and into the ash pocket will vary from 25 cts. per ton of coal fired in small stations to as low as 4 or 5 cts. per ton of coal fired in very large stations with well-designed apparatus. The cost of removing ashes varies with the locality and may be a source of revenue under certain conditions. No figures can be given for the maintenance of ash-handling plants, but as a general rule, the maintenance will be at least as large as the labor cost, as ash-handling machinery wears out rapidly. The cost of ash handling varies also with the kind and quality of coal, being larger as the percentage of ash increases, and much larger with clinkering coal. Coal Storage. — It is usual in power stations to provide coal pocket space for from 7 to 10 days' supply of coal. This, however, is insufficient for a central station and further storage must be provided outside of the station. This usually consists of a coal pile, ranging from 10,000 to 200,000 tons capacity, depending on the size of the central-station system, it usually being considered that from 3 to 6 months' supply is sufficient 238 ENGINEERING OF POWER PLANTS to insure continuity of operation under all circumstances. These piles are provided with stacking and loading machinery and are of two general types, one in which the pile is spanned by a bridge carrying the loading and unloading machinery, and the second type in which the pile is made by means of trestles and cable cars, while the unloading is done by means of locomotive cranes and the cable-car system. A third type, largely used by the hard-coal railroads, consists of conical piles about 400 ft. in diameter and 90 ft. high, in which the small sizes of anthracite coal are taken to the top of the pile by means of inclined flight conveyors, and the reclaiming is done by a movable horizontal flight conveyor. CHAPTER XII THE STEAM POWER PLANT OPERATING COST Design of Power Plant. — No better service can be rendered the non- expert about to construct a power plant than to advise him to engage a capable engineer to design the plant and to superintend its installation. Methods of Buying Apparatus. — (a) Bids. (b) Have reputable manufacturer build it and pay what he asks. (c) Have engineer state in specifications requirements of apparatus wanted, permitting manufacturer to vary details enough to enable him to use standard designs. (d) Have engineer design the whole plant in detail buying standard apparatus where possible but developing new designs to meet new con- ditions. Location. — The most important factors governing the location of the power plant are: (a) Availability of water supply, especially for condensing. (b) Economical handling of fuel and ash. (c) Storage capacity for fuel. (d) Ease of power distribution. (a) The supply of water must be guaranteed and must be abundant. Wells do not usually furnish desirable water for boiler purposes, lake or river water being preferable. Ferranti states: "The water supply is enormously important today and I see no method so long as the converting process is thermal, that is to say, where there is a rise and a reduction in temperature, where the cooling water will not play a most impor- tant part." (b) If possible, the boiler house should be so located that coal can be delivered directly from boats or cars to the storage bins. If the grade can be so arranged as to avoid elevating the coal, a saving of from 25 to 50 cts. per ton may often be effected. (c) Ample coal storage capacity should be provided to serve in times of strikes, blockages, etc. (d) This depends upon the character and purpose of the plant. Pro- visions should always be made for future enlargements and extensions. Constructions. — The type of building is determined by the price of land and the available space. The engine and boiler house should be 239 240 ENGINEERING OF POWER PLANTS separate from the other buildings, to avoid danger from fire and to pre- vent troubles from vibration. Where the ground is not too expensive the entire plant may be on one level. In this case a one-story building with brick walls, steel-truss roof, and cement floor is most common. A well-drained and well-lighted basement should be provided if the plant is large for pipes, condensers, ash hoppers, traps and such apparatus as is necessary below grade. In large plants basements are often 20 to 25 ft. in the clear. .- Reinforced Cinder Concrete r^i^JSf.^.Js^ Fig. 150.— Spy Run Power House, Ft. Wayne and Northern Indiana Traction Co. Where ground is expensive it is necessary to build in stories, but this practice should be avoided when possible. It is a question whether engines or boilers should be placed above. Formerly the boilers were placed above the engines, but of late the plan has been reversed. All pumps, heaters, etc., should be on the main floor where practicable for the sake of light and cleanliness. The engines and boilers should be in separate rooms with a tight partition between to keep dust and THE STEAM POWER PLANT 241 ,j o O i—i a .2 "•+3 o 03 o M o 02 a> o d o +3 •r-( a> 1G 242 ENGINEERING OF POWER PLANTS moisture from the engines. All power stations should be fireproof. Wooden floors should not be used as the fire risk is too great. Arrangement. — The boilers should be located in batteries of two along the side of the boiler house opposite the coal supply, and each battery should be easily accessible on all sides. Special attention should be paid to facilities for cleaning shell, tubes, flues and combustion chambers. It is always desirable to have at least one spare engine in case of breakdowns. If there are several engine units it is more economical to have different sizes, that the engine power may be adapted to the load at any time. The engines should be arranged with steam nozzles in line and con- necting with the horizontal header. If there is no basement, all exhaust pipes and drips should be carried in conduits under the floor and be easily accessible. Have no pipe where it cannot be readily seen and handled. If the engines are non-condensing, the exhaust steam should be run first through a feed-water heater and the balance of the heat used for warming the building. If the vacuum system of heating is used, there will be less back-pressure on the engine. There should be one main feed line connecting the pumps with all the boilers. It is also well in small plants to have an injector connected di- rectly to each boiler to use in emergencies but this is too expensive for boilers above 50 hp. Some provision must be made for filling the boilers when cold either from the city mains or by hand pumps. The fundamental requirements of station systems are reliability, accessibility and durability. The engineer is concerned in the design of stations that will never require a shutdown of the entire system. The conditions of service must determine the system. If the service is 24 hr. a day, running for 8 hr. at half load only, then the system should provide for repairs being made, at the same time maintaining the capacity. If the station is required to generate at all times two-thirds of its total capac- ity, the plant should not have less than three units all of the same size. No unit should be so large that the station cannot be operated without it by overloading the other machinery to the permissible limit. For good service and economy in large central stations all units should be of the same size and the number of generating units should not be less than five nor more than eight, one unit in reserve, the others for carrying the load. In any case the original installation should be for a two-division, three- division or four-division plant with provision for future divisions. If the plant is to be a two-division plant it may be built with two units, each of a capacity slightly larger than the minimum load conditions demand, and the future unit may be made twice the capacity of these smaller ones. THE STEAM POWER PLANT 243 244 ENGINEERING OF POWER PLANTS This arrangement of units would be permissible in a plant which ordi- narily delivers only half of the power called for on Sundays, holidays, etc. It has been found ordinarily that a three-division plant is more suitable for permitting repairs to be made and also requires less investment for reserve capacity. If the plant is to be a three-division plant, the boilers should be in three divisions, say, 6, 9, or 12 in number. The auxiliaries should be in pairs, not necessarily together, but each sufficient for the entire plant, and they should be connected to the differ- ent divisions so that when one division is out of service the other auxiliary will be on operating division. Let it be assumed that a station requires three units for an output of two-thirds of the total capacity of the units and later will require an addi- tional unit. There is but one solution for the problem under these conditions and that is that the station shall ultimately be a four-divi- sion plant for output of three-quarters of the total capacity of the units. The boilers must be arranged in three units so as to allow one to be out of condition for cleaning and repairs. Assuming the engines to be of 2,000 hp. each, then two 500-hp. boilers would be required for each engine, but by assuming three engines of 2,000 hp. each or a total of 6,000 hp. there would be 3,000 hp. in boilers to be divided into five units, so as to allow one boiler to be out of service. This would give five 600-hp. boilers. If the fourth engine unit is likely to be ordered before the three units are called upon to carry full load for a large part of the time it would be safe to estimate on 8,000 hp. of engines or 4,000 hp. of boilers, or seven boilers, each of 555 hp., which is a some- what better arrangement for the four-unit plant. Types of Station Design. — In the United States, where fuel has as a rule been reasonably cheap, the standard type of power station includes the boiler and engine with steam-driven auxiliaries. Economizers are very rarely used and the auxiliaries are run non-condensing, the exhaust steam being led to a heater and used for heating the feed water. This may be termed standard American design, and exceedingly good results may be obtained from it. In Europe, where coal is as a rule poorer and more costly than in America, and where interest charges have been considerably less, another type of station is more usual. Economizers are the rule and usually at least one-half as much surface is furnished in the economizer as in the boilers. The auxiliaries are driven direct from the prime mover or by electric motors, and no feed-water heaters are used because of the lack of available exhaust steam. The condensate is used over again, being pumped directly into the economizers. Such stations, when well de- signed, are capable of exceedingly good economy, but apparently no better than is given by the American type of plant. THE STEAM POWER PLANT 245 246 ENGINEERING OF POWER PLANTS There are a number of American plants following to some extent the European types, but differing from them widely in the types of apparatus. In these plants both economizers and feed-water heaters are present, together with a number of other heat-saving devices. The auxiliaries are electrically driven from current supplied by a separate auxiliary unit, which has a jet condenser, in which the feed water of the station is used as the condensing water. There are many modifications of this type possible, and notable examples exist in the Conners Creek station of the Detroit Edison Co. and the Cleveland Municipal Plant. It is doubtful whether better results under similar conditions will be obtained by this type of station. TURBO GENERATOR UNIT M0.3 j yTo Stack HURLim "WATER RESERVOIR ECONOMIZERS BOILER. HOT-WATER RESERVOIR k^ DISCHARGE TUNNEL ^INTAKE TUNNEL Fig. 154. — Diagram of steam and water circuits Northwest Station, Commonwealth Edison Co., Chicago, 111. These three types may well be represented by the apices of an equi- lateral triangle ; between them lies the whole field of the many variations which occur in design. Given the same load factor and use factor and with equally careful design, it is probable that similar economic results may be obtained from any type of plant, but to secure these results the design must be of the very best and the local conditions must be good. In particular the design must be suited to the local conditions and the type of fuel procurable in that locality. A fourth type of power station, which perhaps under modern condi- tions might be as economical as any, is the power plant of the steamer Inch Dene, a 10-knot freighter using Scotch marine boilers, superheated steam, multiple expansion engines, with the auxiliaries driven from the engine itself. The economical results from these ships have been exceed- ingly good, but it should be remembered that the use factor in this case THE STEAM POWER PLANT 247 is practically 90 per cent. Particulars of a test of this vessel may be found in Marine Engineering, vol. 6, p. 332. At the present time there is renewed agitation for the use of higher pressure steam, and a number of manufacturers are ready to supply boil- ers designed to furnish steam at 600 lb. pressure and 200° superheat. The turbine manufacturers are prepared to offer turbines to utilize this high-pressure steam. Whether these changed conditions will result in a new type of station cannot be stated, but it is certain that additional operating economies may be secured, although the total economy, when fixed charges are considered, may not be much better. It is not probable that any one type of station will become standard, but that the development of the three types with their variations will proceed along similar lines until a change takes place in our method of generating power. Cost of Buildings. — The estimated cost of buildings is most readily determined on the basis of cost per square foot of floor space or cost per cubic foot of space for the entire building. The following figures represent the averages of several quotations : Cost per square foot, Cost per cubic foot, cents Mill construction Fireproof stores, factories and warehouses with brick, con- crete, stone and steel construction Concrete or reinforced-concrete shops, factories and ware- houses Plain power houses with concrete floors and with brick and steel superstructure Power houses under city conditions with superior archi- tectural details 0.80-1.10 2.00-3.00 1.25-1.75 2.00-2.75 3.00-4.50 6.5- 8.5 14.0-25.0 8.0-16.0 9.0-12.0 15.0-30.0 A consulting engineer of large experience finds the cost of boiler houses, engine houses and coal pockets to run approximately as follows when based on the cost per engine horsepower installed. Cost op Buildings per Engine Horsepower Simple non-condensing engines: Engine horsepower Boiler house, cost per hp Engine house, cost per hp Coal pocket, cost per hp Simple condensing engines: Engine horsepower Boiler house, cost per hp Engine house, cost per hp Coal pocket, cost per hp 10 $37.15 4.80 20.00 10 $33.70 14.40 19.00 12 $33.00 4.35 18.00 12 $29.60 12.60 17.90 14 $30.00 4.00 16.00 14 $27.50 11.30 16.60 15 $28.50 3.90 15.00 15 $26.20 10.90 15.80 20 $24.50 3.30 13.70 20 $21.60 8.60 13.60 30 $20.50 2.75 11.00 30 $18.20 7.75 11.00 40 $18.00 2.50 9.80 50 $16.00 2.30 8.30 75 $13.00 2.15 6.00 248 ENGINEERING OF POWER PLANTS Cost of Buildings per Engine Horsepower. — {Continued) Engine horsepower Boiler house, cost per hp Engine house, cost per hp. . . . Coal pocket, cost per hp Compound condensing engine Engine horsepower Boiler house, cost per hp. Engine house, cost per hp. Coal pocket, cost per hp. . . Engine horsepower Boiler house, cost per hp. . . Engine house, cost per hp. . Coal pocket, cost per hp. . . 40 $16.00 6.40 8.70 100 $28 . 50 5.70 700 $5.35 6.30 2.10 50 $14.80 5.35 8.50 200 $24.00 4.00 800 $5.00 5.60 2.05 75 $11.30 4.90 6.30 300 $11.20 11.20 3.10 900 $4.70 5.35 1.95 100 $9.70 4.30 5.70 400 $8.00 9.35 2.60 1,000 $4.55 5.00 1.80 500 $6.40 8.50 2.40 1,500 $4.10 4.75 1.75 600 $5.70 7.20 2.25 2,000 $3.95 4.55 1.60 Incidentals. — In erecting a power plant, there are always a lot of mis- cellaneous items that add to the total expense but which are very difficult to determine before the installation is made. These always amount to considerably more than anticipated, usually averaging in the neighbor- hood of 10 to 15 per cent, of the cost of the project. If based on the engine horsepower, the incidentals reported by one consulting engineer run about as follows : Cost op Incidentals per Engine Horsepower Simple non-condensing: Engine horsepower Incidentals, cost per horsepower Engine horsepower Incidentals, cost per horsepower Simple condensing: Engine horsepower Incidentals, cost per horsepower. Engine horsepower Incidentals, cost per horsepower Compound condensing: Engine horsepower Incidentals, cost per horsepower Engine horsepower Incidentals, cost per horsepower 10 12 14 15 20 $20.00 $18.00 $16.00 $15.00 $13.70 30 40 50 75 $11.00 $9.80 $8.30 $6.00 10 12 14 15 20 $18.00 $17.60 $17.00 $16.60 $14.70 40 50 75 100 $10.80 $10.30 $8.70 $7.80 100 200 300 400 500 $9.70 $8.00 $6.80 $6.50 $6.25 700 800 900 1,000 1,500 $5.75 $5.50 $5.25 $5.00 $4.75 30 $11.80 600 $6.00 2,000 $4.60 Cost of Installations Complete. — An idea of the approximate cost of complete installations may be had from the following table. THE STEAM POWER PLANT 249 ore 250 ENGINEERING OF POWER PLANTS Approximate Cost per Kilowatt of Steam Turbine-driven Installations Siz e of plants — kilowatts 5,000 10,000 20,000 30,000 40,000 50,000 Building, real estate and excavating Turbines and generators $17.50 28.25 6.85 34.50 5.75 1.20 1.90 4.20 2.50 1.30 8.50 1.80 5.75 $14.60 23.50 5.70 28.70 4.80 1.00 1.60 3.50 2.10 1.10 7.10 1.50 4.80 $13.10 21.20 5.15 25.80 4.30 0.90 1.45 3.15 1.90 1.00 6.40 1.35 4.30 $11.65 18.75 4.50 23.00 3.85 0.80 1.30 2.80 1.70 0.90 5.70 1.20 3.85 $10.95 17.65 4.30 21.50 3.60 0.75 1.20 2.60 1.60 0.85 5.30 1.10 3.60 $10.20 16.50 Condensers 4.00 Boilers, stokers, superheaters and stacks. . . Bunkers, and conveyors 20.00 3.40 Boiler feed and service pumps Feed- water heaters 0.70 1.10 Exciters 2.50 1.50 Foundation (machinery) 0.75 Piping and conduits 5.00 Crane 1.00 3.35 $120.00 $100.00 $90.00 $80.00 $75.00 $70.00 Averaging the figures above shows the percentage distribution of cost to be approximately: Per cent, of total cost Building, real estate and excavating 14. 6 Turbines and generators 23 . 5 Condensers : 5.7 Boilers, stokers, superheaters and stacks 28 . 7 Bunkers and conveyors 4.8 Boiler feed and service pumps 1.0 Feed-water heaters 1.6 Switchboard and wiring 3.5 Exciters 2.1 Foundation (machinery) 1.1 Piping and conduits 7.1 Crane 1.5 Supt. and engineering, etc 4.8 100.00 Comparative Cost of Steam Power Stations, Complete. — The follow- ing values will illustrate the relative cost of different types of power stations. The figures are for complete plants including engines, genera- tors, boilers, piping, feed pumps and heaters, stacks and buildings. Direct-connected generators — one reserve unit. THE STEAM POWER PLANT 251 Cost op Steam Power Stations Horsepower i Simple non-condensing high-speed. . . . Compound non-condensing high-speed Compound condensing DeLaval turbine Vertical condensing low-speed Horizontal condensing low-speed Parsons turbine 100 200 400 600 1,200 2,000 $12,960 14,140 15,230 14,860 $19,280 21,180 22,740 21,180 $32,210 34,370 37,400 36,050 52,280 51,420 $43,950 45,940 49,890 48,300 69,470 69,490 60,060 $78,300 79,860 85,990 84,240 108,990 102,500 88,090 155,930 148,310 122,100 Cost per Kilowatt of Several Stations Electric Ry. Econ- omy, 1903, Mc- Graw Pub. Co. Max. Min. Yorkshire Power Co., 6,000 kw. Thornhill 10,000- kw. engine plant 90,000- kw. turbine plant 150,000- kw. plant (London) Green- wich London, 34,000 kw. Land Foundations Buildings Stacks Total building Boilers Superheaters Stokers Economizers Coal and ash Piping Heaters and pumps. Prime movers Condensers Crane Exciters Switchboard cables. Incidentals Total equipment . . . Total $3.50 15.00 2.00 20.50 17.00 3.00 4.50 7.50 12.00 3.00 53.00 10.00 2.00 112.00 132.50 $1.50 8.00 1.00 10.50 9.00 2.50 2.50 3.00 4.00 2.00 38.00 4.50 2.00 67.50 78.00 1.43 13.4 78.00 91.40 $1.22 9.70 1.22 12.14 12.10 2.42 1.46 1.94 7.30 0.97 58.30 6.30 1.46 2.42 94.67 106.81 52.14 4.17 17.80 10.55 2.67 37.33 $1.60 14.50 16.10 > 6.45 1.94 3.40 13.85 2.13 27.77 43.87 $56.55 > 14 . 69 1.56 > 7.86 > 28.40 1.07 [ 5.12 ' 58.70 115.25 Stevens and Hobart Snell, 1912. Rider, I. E. E., 1909. Operating Expenses. — Before deciding on the best and most eco- nomical plant for a given set of conditions, it is necessary to consider the relative yearly expense. This may be divided into fixed charges which are a function of the cost of the plant and must be paid whether or not power is produced; and operating cost or as it is often termed, station cost. The original division by Hopkinson in 1892 was into two similar categories: (a) a fixed charge depending on the maximum rate at which the energy may be demanded and independent of the time over which the demand may extend; and (b) a running charge proportional to the time the demand is kept up. His fixed charge might be termed a " readi- ness to serve charge" and included interest on cost, taxes, insurance, amortization plus the expense for labor, fuel, stores, etc., needed to keep 252 ENGINEERING OF POWER PLANTS the plant running light and ready to work. His running charge 1 included the additional fuel, labor, repairs, and stores necessary for the carrying of the load. Hopkinson's categories proved to be subject to disadvantages due to the difficulty of segregating " light running charges" from the other run- ning charges but the substantial accuracy of the method has never been Barometric Condenser . House Alternator Exhaust Adjustable Back Pressure Valve Head Tank Oyer flow to Storage Tank 20.000 Kw. Turbine ^JS* %'".?. 35.000 Sg Ft. Condenser -(31500 y Sq. Ft now instal- I C3 q D CD led) -.. Ja Exhaust 1000 Kw House' Alternator(Turbine Boiler Feed Driven) Pump (Turbine Driven) Hot Well Pump Barometric Injection Pump Overflow Storage ;; Tank ■Surge Pump Fig. 156. — Diagram of auxiliary connections Conners Creek Station, Detroit Edison Co. tt. denied. He gave figures for a 2,500-kw. plant in which the "running light" charges amounted to $136,000 and the fully loaded charges to $288,000. The " light running" charge per kilowatt of demand is not far from $54.30 and the corresponding costs of production including standing and running charges for the various use factors are given in the following table. Per cent, use factor Cost, cents Per cent, use factor Cost, cents 5 12.72 55 1.74 10 6.68 60 1.66 15 4.66 65 1.58 20 3.66 70 1.52 25 3.06 75 1.46 30 2.66 80 1.40 35 2.38 85 1.36 40 2.16 90 1.32 45 1.98 95 1.28 50 1.86 100 1.26 1 A very good account of the discussion of these principles may be found in Word- ingham's "Central Electrical Stations" and in the Transactions of the Institute of Electrical Engineers (London, Eng.). THE STEAM POWER PLANT 253 The later and present practice is to include interest, depreciation, taxes and insurance in fixed charges and fuel, labor, including superin- tendence, water, oil, waste and supplies, and maintenance in station cost or operating cost. The sum of the two is called total cost or better, production cost. These may be tabulate as follows: Fixed Charges: (a) Interest on investment. (6) Depreciation (replacement). (c) Taxes, (city, state, etc.). (d) Insurance. Station Charges: (a) Fuel. (b) Labor (including superintendence). (c) Oil, waste and supplies. (d) Water. (e) Maintenance. Interest. — It is usually fair to allow 6 per cent, for interest on invest- ment but small industrial plants usually have to pay higher rates, say 7 or 8 per cent. Municipalities may pay as low as 4 per cent, and it has been possible in Europe in the past to figure on a smaller return. For the general run of problems it is safe to use 6 per cent. Depreciation. — Structures and machinery grow old and unfit for the purpose for which they were erected or purchased. They may be kept in reasonable repair by the ordinary running maintenance but there will come a time when the plant is worn out and must be replaced if the busi- ness is to continue. If the business ends with the life of the plant, as in some mining propositions, the capital has been destroyed and the investor only gets the interest return which in this particular case must be high. To meet the above conditions, it has grown to be the custom to set aside every year a sum of money which is known by various names, depending on how it enters into the accounts, such as sinking fund, depreciation or amortization. It may be paid to the stockholders either as extra divi- dends or by putting it into improving the value of the plant and these two ways are considered the best methods for private business and small close corporations. For public corporation plants the sinking-fund method is the best as in these plants the capital is furnished by the sale of bonds which must be redeemed at a certain time. All corporations other than close corporations should use the depreciation method and invest the depreciation fund so that when the old plant wears out or is superseded the money will be available to build a new one. The very rapid development of the power generation and distribution business in the last 30 years has shown the difference between the actual 254 ENGINEERING OF POWER PLANTS life of power-generating machinery and its useful life; or its life up to the time that its use is superseded by larger and more economical apparatus or a machine better suited to changed conditions of power generation. The following table shows the actual life which has been estimated for various portions of steam power-plant equipment. Approximate Useful Life of Various Portions of Steam Power-plant Equipment Years Buildings, brick or concrete 50 Buildings, wooden or sheet-iron 15 Chimneys, brick 50 Chimneys, self-sustaining steel 25 to 40 Chimneys, guyed sheet-iron 5 to 10 Boilers, water-tube 30 to 50 Boilers, fire-tube 15 Engines, slow-speed 25 Engines, high-speed 15 Turbines 10 to 20 Generators, direct-current 5 to 20 Generators, alternating-current 5 to 20 Motors 10 to 20 Pumps 25 Condensers, jet 10 to 20 Condensers, surface 10 to 20 Heaters, open 30 Heaters, closed 20 Economizers 5 to 10 Wiring - 20 Belts 7 Coal conveyor, bucket 5 to 10 Coal conveyor, belt 2 to 5 Transformers, stationary 30 Rotary converters 25 Storage batteries 3 to 5 Piping, ordinary 12 Piping, first-class 20 to 30 So much depends upon the design and the conditions of operation that no fixed values can be definitely assigned and the above figures should be used with caution. Practice shows that most power-plant appliances become obsolete long before the limit of their useful life is reached. The Traction Valuation Commission in Chicago in 1906 gave the following percentages for plant depreciation: Per cent. Engines, Corliss, low-speed 3 to 5 Engines, automatic, high-speed 5 to 10 Cable-winding machinery 3 THE STEAM POWER PLANT 255 Per cent. Generators, direct-connected, modern 5 Generators, belted (depending on date) 5 to 10 Traveling cranes 2 Switchboard and all wiring 2 Piping 3J5 Pumps 5 Heaters, closed 6 to 10 Heaters, opened, if cast iron only 3 Breeching and connections, brick 5 Breeching and connections, steel 10 Boilers and settings, horizontal tubular 10 Boilers and settings, water-tube 3.5 Grates 10 Coal-handling machinery 6 Ash-handling machinery 8 Combined coal- and ash-handling machinery 7 Storage bins, steel 3 to 10 Miscellaneous items 5 "The above annual rates of depreciation have been used as a basis in depreciating the power-plant equipment. Apparatus has been depreci- ated at these rates down to 20 per cent, of the wearing value, the wearing value being determined by subtracting the scrap value from the cost new. All power-plant equipment has been considered as worth 20 per cent, of its wearing value as long as it is in operating condition. Depreciation is applied to wearing value, as the apparatus is always worth scrap value." The above percentages applied to a particular plant of 2,900-kw. capacity give an approximate depreciation for the whole plant of 4 per cent. It is idle to attempt to figure actual depreciation on a power plant from the above figures as many extraneous conditions enter into the prob- lem. The difference between good and bad feed water might vary the 10 per cent, allowed for boilers from 4 to 20 per cent. For a well-maintained plant the allowance might be only about one- half as much for depreciation as for one poorly maintained. For design and comparison purposes it is best to assume a fixed percentage for de- preciation. It is customary to use 6 per cent, and the error from the use of this figure is not likely to be large in the present state of the art. Taxes and Insurance. — Taxes will vary from 1 to 2 per cent, of the value of the property. Insurance of buildings and machinery will vary from 0.5 to 1.5 per cent. These two items are usually combined for estimating purposes at 2 per cent. TOTAL FIXED CHARGES. Fixed charges for estimating purposes may then be taken as: Interest, 6 per cent. 256 ENGINEERING OF POWER PLANTS Depreciation, 6 per cent. Insurance and taxes, 2 per cent. Total, 14 per cent. This value may be used in estimates and for solving the problems in these notes. This total allowance of 14 per cent, for fixed charges may be regarded as fair when the operating portions of such installations are alone con- sidered. When the buildings of brick or concrete make up a large proportion of the investment, an average of 11 per cent, for fixed charges is perhaps a better figure. STATION COST. Fuel. — The available fuels for power-station purposes are the steam sizes of anthracite coal, bituminous coal, oil and natural gas. The steam sizes of anthracite include all the finer grades from pea coal down to the refuse or culm. Culm which may contain as high as 35 per cent, ash costs about 25 cts. a ton at the mine, No. 3 buckwheat or rice coal about 50 cts., No. 1 buckwheat about 80 cts. and pea coal about $1. Bitumin- ous coal, which varies greatly in quality, also varies much in price at the mines averaging from 90 cts. to $1.50 per ton. The average freight rate on coal is 1J£ cts. per ton-mile. Anthracite coal is used in the anthracite regions and to a consider- able extent in the regions round about extending to New York and Phila- delphia, but the steam fuel of the whole country as a rule is bituminous coal. The price at the power station will vary from $12 in certain unac- cessible localities down to 90 cts. near the mines. Oil, usually the crude oil of commerce, varies in price per barrel of 42 gal. at the well from 40 to 60 cts. Oil is handled by pipe lines in the regions near the wells but a good deal of it is water-borne and the freight is relatively much lower than for coal. Contracts for Mexican and Texas oil have been offered in New York and Philadelphia for $1.25 per barrel. Oil will probably be an available fuel only in the Pacific States where coal is high and poor and in Texas and Oklahoma. At a distance from the wells the price usually runs from 2 to 4 cts. per gallon. Although natural gas is found in limited quantities in many sections of the United States, its use for power-plant purposes is largely in the region of Pennsylvania, Ohio and West Virginia. The gas is piped from the wells and costs from 10 to 30 cts. per 1,000 cu. ft. The cost of fuel must always be ascertained for the particular locality as large variations in price occur in an unexpected way due to local condi- THE STEAM POWER PLANT 257 tions. Before the discovery of the Californian oil fields most of the steam fuel used in San Francisco was Welsh coal brought out as ballast or to help make up a cargo. For the same reason Canadian coal was largely used in Westphalia, Germany, before the outbreak of the European war. SCALE OF FEET 10 20 30 40 50 60 70 80 90 100 Fig. 157. — Carville Power Station, Wallsend on Tyne. The price of the coal is not the only fuel cost. The coal must be put into the station bunkers, the ashes must be removed and disposed of and these costs should be added to the cost of coal. If the coal is insured, this cost is fuel cost and if stored for any time the interest cost should be added. 17 258 ENGINEERING OF POWER PLANTS o o O S-l o Pk bC "2 3 o W O Ph 02 O 00 THE STEAM POWER PLANT 259 For known conditions the fuel consumption should be determined by- using the B.t.u. value of the fuel and a proper boiler and furnace efficiency. Some idea of the average coal consumption of plants of different sizes may be obtained from the following table, based on the coal per horse- power-hour. Coal per Horsepower per Hour Simple non-condensing: Engine horsepower Total coal, pounds Engine horsepower Total coal, pounds Simple condensing: Engine horsepower Coal, running times, pounds . Total coal, pounds Engine horsepower Coal, running times, pounds Total coal, pounds Compound condensing: Engine horsepower Coal, running times, pounds Total coal, pounds Engine horsepower Coal, running times, pounds Total coal, pounds 2 3 4 6 8 10 13.0 10.5 8.5 7.9 7.6 7.4 14 15 20 30 40 50 7.0 6.5 6.0 5.5 4.75 4.5 10 12 14 15 20 6.1 5.9 5.7 5.25 4.80 7.0 6.75 6.50 6.00 5.50 30 40 50 75 100 4.60 4.20 3.75 3.40 3.10 5.25 4.75 4.25 3.70 3.50 100 200 300 400 500 600 2.75 2.45 2.40 2.35 2.30 2.25 3.15 2.85 2.75 2.70 2.65 2.60 800 900 1,000 1,500 2,000 2.15 2.10 1.95 1.80 1.75 2.50 2.45 2.25 2.05 2.00 12 7.25 75 4.0 700 2.20 2.55 Kent states 1 that small engines and engines with fluctuating loads are usually very wasteful of fuel. The following figures, illustrating their low economy, are given by Professor Unwin, Cassier's Magazine, 1894. Small Engines in Workshops in Birmingham, England Probable i.hp. at full load Average i.hp. during observation Coal per i.hp. per hour during observe tion, pounds 12 2.96 36.0 45 7.37 21.25 60 8.2 22.61 45 8.6 18.13 75 23.64 11.68 60 19.08 9.35 60 20.08 8.50 It is largely to replace such engines as the above that power will be distributed from central stations. Labor. — This charge should include the wages of all stokers, oilers, engineers, laboratory men, switchboard operators, electricians, clerks, janitors, watchmen and such portion of superintendence as is given to the station. The wages of all men employed on repairs should be charged to maintenance. 1 "Mechanical Engineers' Pocket-book/' p. 964. 260 ENGINEERING OF POWER PLANTS UIOJJ. THE STEAM POWER PLANT 261 The cost of attendance will depend upon the size of the plant, in gen- eral, being less for a large plant, i.e., relatively less. The cost of engine attendance is greater for high-speed than for Corliss, and is also increased by the introduction of compounding or condensing engines. The salaries paid engineers vary from $60 per month to $150 for ordi- nary plants. Firemen receive from $50 to $90 per month, the average being about $65 for 12-hr. days. Coal passers and ash wheelers receive about $30 to $55 per month. In New York and Philadelphia firemen and coal passers receive in the neighborhood of $2 to $2.25 per 8-hr. day. In general the yearly (3,080) hours cost of attendance will run about: For simple non-condensing plants: Engine horsepower 2 $99 15 $202 10 $178 40 $350 3 $109 20 $230 12 $190 50 $405 4 $116 30 $287 14 $202 75 $535 6 $136 40 $338 15 $210 100 $670 8 $154 50 $390 20 $238 10 $173 75 $520 30 $297 12 $184 14 Attendance $194 Engine horsepower Attendance For simple condensing plants: Engine horsepower Attendance Engine horsepower Attendance One man attends engine, fires boiler and is supposed to do other work besides. On the 10-hp. plant one-half of his time is charged to attend- ance and three-fourths of his time on the 100-hp. plant. For compound condensing plants: Engine horsepower Number of men and wages Total attendance Engine horsepower Number of men and wages Total attendance 100 1 at $16 700 1 at $17 2 at $22 1 at $10 $2,650 200 300 400 500 1 at $16 1 at $16 1 at $16 1 at $16 1 at $7 1 at $7 1 at $10 1 at $13 1 at $7 1 at $7 $1,220 $1,220 $1,760 $1,930 800 900 1,000 1,500 1 at $18 1 at $18 1 at $19 1 at $22 2 at $22 2 at $25 2 at $26 3 at $36 1 at $10 1 at $10 2 at $20 2 at $20 $2,700 $2,930 $3,480 $4,400 600 1 at $17 1 at $13 1 at $10 $2,100 2,000 1 at $25 4 at $50 2 at $20 $5,200 These costs are below the average for the larger sized plants. The following figures represent the cost of attendance for a large electric steam-turbine central station. The wages involved in the cost of power delivered by one unit (14,000- 262 ENGINEERING OF POWER PLANTS kw. Curtis turbine, 8 B. & W., boilers of 5,000 sq. ft. of heating surface each and auxiliaries) to the switchboard are: General Engineering Force: Cost per day One chief engineer at $250 per month, % of his time $1 .40 One assistant chief engineer at $200 per month, % of his time 1.11 One chief electrician at $200 per month % of his time 1.11 One assistant chief electrician at $150 per month, % of his time. ... 0.83 Three load despatchers at $100 per month, \i of their time 1 . 66 One boiler-room foreman at $100 per month, % of his time . 55 Operators for One Generating Unit: 1 Three watch engineers at $4 per day of 8 hr $12 . 00 Three oilers at $2.50 per day of 8 hr 7. 50 Three switchboard attendants at $2.50 per day of 8 hr 7 . 50 Three firemen at $2.50 per day of 8 hr 7 . 50 Three water tenders at $2.50 per day 7 . 50 One boiler washer at $2.50 per day of 8 hr 2 . 50 One pipe fitter at $3 per day of 8 hr 3 . 00 One pipe fitter helper at $1.50 per day of 8 hr 1 . 50 Four laborers at $2 for coal handling 8 . 00 Total $63.66 Herrick has given a table of interest in connection with the labor item. Plant Rating, Output, Total station Labor per kw.-hr., Total station cost, kw.-hr., Number of station kw. kw.-hr. wages cents cents employees A 6,000 8,776,165 $25,937 0.296 1.21 22 B 5,000 6,043,204 20,920 0.346 1.23 20 C 4,000 5,400,192 19,429 0.360 1.24 28 D 2,000 3,288,623 9,954 0.302 1.42 11 E 2,000 4,305,003 9,663 0.224 1.27 13 F 1,250 1,470,066 6,844 0.465 1.56 8 G 950 1,479,898 8,771 0.595 2.05 7 H 700 889,760 6,669 0.750 2.34 8 I 630 730,458 5,017 0.685 1.80 6 Plant Kw. per station employee Wages per kw. station capacity A 272.0 $4.31 B 250.0 4.18 C 136.0 5.10 D 182.0 4.97 E 154.0 4.83 F 157.0 5.45 G 136.0 9.25 H 87.5 9.52 I 105.0 7.95 1 In the plant upon which these figures are based, there is a watch engineer and an oiler employed to look after each unit. THE STEAM POWER PLANT 263 Maintenance. — This is the cost of maintaining the building and ma- chinery in good working order and includes both materials and labor, the object being to have the plant in as good condition as a going concern as it was when built. There are many standards of good running order and an increase in this item usually means a de- crease in the fuel item. Six per cent, of the station charges is a fair average allowance for maintenance. Oil, Waste and Supplies. — Good cylinder oil in small quantities costs from 30 to 60 cts. per gallon. In quantity it maybe purchased from 25 to 40 cts. Bearing oil is cheaper and runs from 18 to 30 cts. Good bearing oil in quantity should cost from 23 to 27 cts. a gallon. The amount of oil required varies greatly with the type of in- stallation, the periods of continuous service and the care of the engine operator. So great is this varia- tion that average figures mean little, but they will serve in making esti- mates of operation costs. A com- parison of many returns shows the amount of cylinder oil and the amount of engine oil used to be practically equal for reciprocat- ing steam engines. The average returns from a number of installations show the consumption of each kind of oil to be approximately 1 pt. per 1,000 hp.-hr. or 1 pt. per 1,000,000 sq. ft. rubbed over. Turbines require no cylinder oil and use bearing oil only. As each unit has its oil system only the make-up and auxiliary oil have to be considered. It has been the 264 ENGINEERING OF POWER PLANTS custom of some oil companies to contract to furnish all the oil needed at a certain price per kilowatt-hour generated. The prices have varied between 0.01 and 0.02 ct. per kilowatt-hour. White waste of good grade may be purchased in 150-lb. bales at about 9 cts. per pound (variation 7 to 11 cts.). This item may amount to con- siderable unless care is taken. Relatively large financial savings may be made by using a waste and oil separator. By this means waste may be used six or eight times and large amounts of oil are recovered which, after filtering, may be reused. One small station of about 750- or 1,000-hp. capacity installed such a separator at a cost of $150, and saved $90 in oil and waste the first month. The average saving per month in this plant is over $100. In the larger stations washable cheesecloth towels have replaced waste. Supplies include such small articles as packings, small pipes, valves and fittings, tools, wrenches, gaskets and other small articles which must be kept in stock. They should include laboratory supplies, stationery, janitors' supplies, and other items of this kind. These three items are usually lumped together and form a small part of the station cost in a large plant. One consulting engineer reports the yearly (3,080 hr.) cost of oil, waste and supplies to run approximately as follows: Simple non-condensing: Engine horsepower Oil, etc Engine horsepower Oil, etc Simple condensing: Engine horsepower Oil, etc Engine horsepower Oil, etc Compound condensing:. Engine horsepower Oil, etc Engine horsepower Oil, etc 2 $13.20 15 $26.50 10 $22.80 40 $53.00 100 $143.00 800 $420.00 3 $14.30 20 $31.20 12 $24 . 80 50 $64.00 200 $205.00 900 $445.00 4 - $14.30 30 $41.50 14 $26.70 75 $89.00 300 $240.00 1,000 $470.00 6 $17.60 40 $51.00 15 $27.60 100 $114.00 400 $285.00 1,500 $600.00 $20.00 50 $61 . 50 20 $32 . 50 500 $315.00 2,000 $685.00 10 $22.00 75 $85.50 30 $43.00 600 $350.00 12 $23.80 700 $385.00 14 $25 . 80 These costs are below the average for the larger size plants. Water. — This expense will be relatively small with a condensing sta- tion even where city water is used. In many cities the cost of water for manufacturing purposes is 40 cts. per 1,000 cu. ft. or $5.35 per 1,000 gal. For New York City the price is $1 per 1,000 cu. ft. Where fresh water is used for condensation the feed water can usually be taken from the THE STEAM POWER PLANT 265 tail pipe and will cost nothing. With turbine stations and surface con- densers the make-up is very small and the water item is smaller than the oil item. Caution should be exercised in using Artesian or other well water as feed water if its chemical composition is not known. PROBLEMS 56. Estimate the cost of a small power plant of 125 i.hp. The estimate is to be based on the assumption that the engine and boiler are not more than 20 ft. apart; that water supply is brought into the engine room by customer; that exhaust valve and safety-valve exhaust are to be carried outside of the engine room a distance of not more than 20 ft.; that sewer connection is made in engine room to which drip pipes and blowoff pipes may be carried. 1. 125-hp. simple non-condensing engine, on cars. 2. Freight to destination, estimated. 3. Cartage and handling to position, about $5 per ton. 4. Foundation. 5. Boiler, horizontal fire-tube horsepower. 6. Freight. 7. Handling. 8. Setting. 9. Iron stack. 10. Erecting. 11. Feed pump. 12. Feed-water heater. 13. Pipe connections, steam, exhaust and water pipe. 14. Pipe covering for all steam pipe. 15. Man to superintend erection (customer furnishing all laboring help in handling heavy pieces) 5 days at $5 per day. 16. Railroad expenses from factory and board. 17. Add to above for contingencies, 5 to 10 per cent. 18. Add consulting engineer's or agent's commission, if any. 19. Add expense of test after erection, if required. 57. An equipment is to be selected for a steam power plant capable of developing 750 hp. Three estimates are to be made as follows : A. Two 300-hp. compound, high-speed, non-condensing engines and one 150-hp. compound, high-speed, non-condensing engine. Return tubular boilers. Equal units. Two in operation, and one in reserve. Flat grates, hand-fired. Equivalent evaporation 7.5 lb. water per pound of coal. B. Two 300-hp. compound, condensing Corliss engines and one 150-hp. compound, condensing high-speed engine. Water-tube boilers and mechanical stokers. Same arrangement of boilers as in "A." Equivalent evaporation 8 lb. water per pound coal. C. Two 375-hp. compound, condensing Corliss engines. Boiler equipment and conditions as in "B." Determine the best plant to install: (a) If water is purchased and wasted to sewer, (fr) If water costs nothing but pumpage. Note. — Standby losses need not be considered in this problem. 266 ENGINEERING OF POWER PLANTS Investment "A." 1. Two 300-hp. engines, erected 2. Foundations for two engines 3. One 150-hp. engine, erected 4. Foundation for engine 5. boilers, hp. each, including setting 6. Brick stack 7. Flues 8. Two feed pumps 9. Two feed-water heaters 10. Piping 1 1. Boiler house 12. Engine house 13. Coal pocket 14. Incidentals Total Investment "B." 1. Two 300-hp. engines and condensers, erected 2. Foundations for two units 3. One 150-hp. engine and condenser, erected 4. Foundation • 5. boilers, hp. each, including setting 6. Brick stack 7. Flues 8. mechanical stokers 9. Two feed pumps 10. Two feed-water heaters 11. Piping * 12. Boiler house 13. Engine house 14. Coal pocket 15. Incidentals Total Investment "C." 1. Two 375-hp. engines and condensers, erected 2. Foundations for two units 3. boilers, hp. each, including setting 4. Brick stack 5. Flues 6. mechanical stokers 7. Two feed pumps 8. Two feed-water heaters 9. Piping 10. Boiler house 11. Engine house 12. Coal pocket 13. Incidentals Total THE STEAM POWER PLANT 267 Estimated Operating Cost. — Service 10 hr. per day, 308 days per year. Load on engine = 85 per cent, of full-load rating. Plant "A" Amount $ per per day day 1. Coal: Tons for two 300-hp. engines Tons for one 150-hp. engine Tons for auxiliaries and leakage 2. Attendance: engineers at $ firemen at $ coal passers at $ 3. Oil : Cylinder oil for all engines Engine oil for all engines 4. Waste and supplies 5. Water: M cu. ft. for two 300-hp. engines M cu. ft. for one 150-hp. engine M cu. ft. for auxiliaries and leakage 6. Maintenance, 6 per cent, on % Operating expenses only $ 7. Fixed charges at per cent, on $ Total operating cost and fixed charges $ Plant "B" Amount $ per per day day 1. Coal: Tons for two 300-hp. engines Tons for one 150-hp. engine Tons for auxiliaries and leakage 2. Attendance: engineers at $ firemen at $ - . . . coal passers at $ 3. Oil: Cylinder oil Engine oil 4. Waste and supplies 5. Water: M cu. ft. for auxiliaries and leakage M cu. ft. for circulating water 6. Maintenance, 6 per cent, on $ Operating expenses only $ 7. Fixed charges at per cent, on $ Total operating cost and fixed charges $ Plant "C" Amount $ per per day day 1. Coal: Tons for two 375-hp. engines Tons for auxiliaries and leakage 2. Attendance: engineer at $ firemen at $ coal passers at $ 3. Oil: Cylinder oil Engine oil 268 ENGINEERING OF POWER PLANTS 4. Waste and supplies 5. Water: M cu. ft. for auxiliaries and leakage M cu. ft. for circulating water 6. Maintenance, 6 per cent, on $ Operating expenses only $ 7. Fixed charges at per cent, on $ Total operating cost and fixed charges Summary ABC Investment Excess cost over " A" Total operating cost per year Saving in operation cost per year over " A" Time to make up difference in first cost by saving in operating expenses Total indicated horsepower-hours Cost per indicated horsepower-hour 68. Assuming the same types for the installation as in problem 56 estimate the operating cost for 24 hr. service for 365 days per year. CHAPTER XIII VARIABLE LOAD ECONOMY The making of power, up to a very few years ago, was entirely a local business, each mill, shop or factory was located at the power supply, or when steam was used the engine was located in or near the factory build- ing. The transmission to the machines was by shafting, gears or belts. About 60 years ago rope transmission and a little later hydraulic and compressed-air transmissions were introduced in certain localities in order that the power might be used at some distance from the point of generation. About 30 years ago electrical transmission came into use Fig. 161. — Jumbo dynamo and Armington & Sims engine. Station unit, built June, 1881. The first Central and with it the central station became an established fact. Both the hydraulic transmission, so well applied at London and Geneva, and the compressed-air transmission, as it was used in Paris, might have been capable of development, but the essential convenience and economy of the electrical transmission and drive soon gave it first place, and today when one speaks of the central-station supply of power the electrical system is implied. The electrical transmission of power has its disadvantages, the chief being the impossibility of storing power in any quantity. Electricity 269 270 ENGINEERING OF POWER PLANTS must be used as generated. This means that there will be a varying load on the central station at all times and that the generators must be large enough to generate the maximum power required at one time and also must be run at something below the best efficiency most of the time. This variation of load is best shown by a load curve, plotted with time 250 200 150 100 50 1 1 Max. Load 20 Total Consul] Load Factor Jan.l 1 K.W. Occured iption Per Mont 34 Per Cent 312 | from n 510" 8 K a 6.3 W. I P.A rs. [. 125 100 75 | | Jan.1912 | Max. 1 Load 83 K.W. lOecured from 3.30 to 4 P.M. Total Consumption Per Montb 31450 K.W. Hrs. Load Factor 54 Per' Cent r'v b- J i 1 ! r^in u r- <* ) _r ^vl L " 50 25 / > ^ ■L r __T j > .Tl_ s ■Sj- — Lf J 12 M. 6 8 A.M. 10 8 10 12 P.M. 12 2 M. 6 8 A.M. 10 8 10 12 Fig. 162. — Load curve of average size department store. Fig. 163.— Load curve of U. S. Post Office Building. Gov't. for the abscissae and power for the ordinates. Such load curves for cen- tral stations with various kinds of load are shown in the accompanying figures. These load curves will vary from day to day and season to season, but for each kind of business a characteristic curve can be drawn. 125 100 75 50 25 Max Tota Loa Load 85 I 1 Consump 1 Factor 4 Jan.1912 L.W. | Occured f tion Per Montb Per Cent om ] 8007 .30 t I K.1 1 2 P r. h» .M. 8. 1500 1200 900 600 300 Loa 1 Factor Jjan.1912 55.1 Per Cent jJ Li"- rin r" JL J f JL 1 J r n 1. I J 1 L, J I (Or ,rL H r i i r if" LrT 1 r L / 12 2 M. 4 6 8 10 12 2 4 6 8 10 12 A.M. N. P.M. 12 2 4 6 M. A.M. 10 12 2 4 6 8 10 12 N. P.M. Fig. 164. — Load curve of newspaper Fig. 165. — Combined load curve of nine plant. largepower consumers. Through the courtesy of The Detroit Edison Co., Figs. 166 and 167 are presented showing the change in load distribution due to the recent change from central to eastern time in that city. One blue print is plotted on clock time as a basis; the other is plotted on sun time. In each case the ordinates are based on the peak of the curve before the change of time, this peak being called 100 per cent. VARIABLE LOAD ECONOMY 271 In comparing these curves it should be noted that the change occurred in the late spring and that there would naturally have been an increase in the depth of the valley preceding the peak, as well as a decrease in the height of the peak itself. 100 80 Q* U 60 8 40 20 — -* / / / N A /">o», \ \ / / » V / Vv / » i / \\ /' \\ i \ \ / / \ \ s 1 I V A; \\ »' / v/ \\ w 1 / \\ at 1 \ \_/ «/ / / / \ \ / / — \ \ i /.« / / fc. \' / I ' 1. -i ^ i*£ 1 •1 1 K^ P ° wer B 4000 3200 2400 1600 800 12 2 4 6 8 10 12 2 4 6 8 10 12 12 2 4 6 8 10 12 2 4 6 M. A.M. N. P.M. M. A.M. N. P.M 8 10 12 Fig. 170. — Winter load curve power and Fig. 171. — Summer load curve power lighting. and lighting. taken over a short period, such as 15 min., or an hour, within that interval. In each case the interval of maximum load should be definitely specified. It is dependent upon the local conditions and the purpose for which the VARIABLE LOAD ECONOMY j 273 load factor is to be determined. For electric-light plants and for oper- ating statistics it is usual to consider the load factor as the ratio of the average load for the day to the maximum 5-min. peak. In a street-rail- way plant where the momentary swings are larger, the period for deter- mining the maximum may to advantage be made as large as 30 min. or even 1 hr., and the maximum peak taken as the average during that period. The yearly load factor is the average load for the year divided by the maximum during the year. Station economies depend on load factors to a considerable extent and high load factors are uncommon, except in metallurgical plants, where a load factor of 90 per cent, may be at times attained. Railway plants give load factors varying between 3 per cent, and 50 per cent. Lighting stations rarely exceed 30 per cent, and the smaller lighting plants are sometimes as low as 3 per cent. Williams and Tweedy in " Commercial Engineering for Central Stations," give a list of 24 central stations with varying output from 900,000 kw.-hr. per year to over 32,000,000 kw.-hr. per year, in which the lowest load factor is 19.2, the highest load factor 36.5, and the average for the 24 plants 28 per cent. A station with a high load factor should have few units and large ones and the most economical apparatus will quickly pay for itself. A low load factor will mean smaller units and a larger number of them and the economy of at least half of the apparatus is of no great consequence, since it is only used a few hours every year. In some of the larger lighting plants as much as 97 per cent, of the output is generated on less than 50 per cent, of the ap- paratus, the remaining half of the machines are in use less than 60 hr. out of the 8,760 hr. of the year. A. F. Strouse in the Electric Journal has given the following table of industrial load factors which may be useful: Per cent. Per cent. Boiler shops 10-20 Foundries 5-15 Shoe factories 15-25 Knitting mills 25 Breweries 45 Machine shops 5-25 Cement plants 60-90 Clay products 15-20 Coal mines 15-30 Tanneries 10-20 Cotton mills 20-30 Textiles (general) 25 Flour mills 20-25 "Woodworking ships 5-30 Diversity Factor. — It will be noted that load factor is a measure of the load on the central-station system, and is independent of the type or kind of power generation. There is another factor which also deals with the system load, which is of great importance to the operator and designer. It has been noticed that while one piece of apparatus on an electrical supply main may occasionally take its maximum power, two such machines will not take double the power, because their maximums do not come at the same time. If we take the sum of the maximums of all the 18 274 ENGINEERING OF POWER PLANTS connected loads on the system and divide them by the maximum load on the system we have a factor which has been called the diversity factor, and in every case is greater than one, and in some systems may be as large as four or five. The National Electric Light Association, in 1912, changed the definition of this factor while retaining the name, as follows : " diversity factor is the ratio between the simultaneous demand of a number of individual services for a specified period, and the sum of the individual demands of those services for the same period." This defini- tion expressed as a fraction or as a percentage (never greater than one) is now universally accepted. The diversity factor of a purely lighting load may be as low as 25 per cent. With motor loads the factor is 50 per cent, or higher. Gear (Electrical World, Nov. 10, 1910) gives the following table of block diversity factors and load factors for three classes of electrical service : Analysis of Customer's Diversity Factors Group Number of 'customers Kw. con- nected per customer Sum of con- sumer's maxima Maximum of group Diver- sity factor Average consumers load factor Group load* factor Residence Lighting Block A. Block B. Block C. Average 34 185 167 128 0.53 0.53 0.87 0.68 12 68 93 57 3.6 20.0 28.0 17.2 0.3 0.294 0.302 0.299 7.0 7.0 7.3 7.1 23.3 23.8 24.0 23.9 Commercial Lighting Group D Group E. . . . Group F. . . . Group G 1 . . . Average 46 79 160 221 95 1.28 0.74 0.53 2.70 0.70 46 36 62 403 48 33.0 26.0 41.0 270.0 33.0 0.714 0.714 0.662 0.675 0.685 13.0 11.0 10.0 13.0 10.8 18.0 16.0 15.0 19.0 15.7 General Motor Service Group H Group I Group J Group K. . . . Average 29 18 11 25 21 0.1 hp. 3.3 11.8 6.0 4.5 30 kv.a. 40 90 100 65 21 kv.a. 25 65 70 45 0.7 0.625 0.719 0.7 0.695 15.0 16.0 18.0 21.0 15.5 21.0 26.0 28.0 30.0 26.0 A and B, apartments; C, apartments and residences; D, small stores, saloons, restaurants; E, small stores above; F, apartments above stores, lodge halls, etc.; G, office building; H, I, J, K, mostly clothing manufacturers. 1 G is not included in average of group. VARIABLE LOAD ECONOMY 275 Use Factor. — The designing engineer uses a factor analogous to load factor which is known as the use factor and sometimes as the utility fac- tor. This may be defined as the ratio between the average power sent out by the station to the maximum 24-hr. rating of the station. This factor is in all cases lower than the load factor by the amount of reserve. The load factor and diversity factor tell what part of the installation is used and how much it is used, but they do not show the capacity of the generating station. The use factor does this and may be used for design. Readiness to Serve. — "The readiness to serve" item plays a large part in station economy. If we know what the load will be 15 min. or }/2 hr. ahead due preparations can be made with ease and certainty. Where this is not known machinery must be run light in anticipation of a load that may never come. That such loads do come at times is shown by the "thunderstorm peaks/' which may increase the load 50 per cent, in 5 min. Central Station Design. — The power-station problem, as presented to the designing engineer, usually takes the form of a deductive analysis, 65,000 60,000 55,000 50,000 2 45,000 S 40,000 o Q 35,000 30,000 25,000 20,000 c o £ 20 80 wJek p.j) Lo«a, V *A i (i l\ , nl . . , ^^iLiOTilSilT _^w ^An^Lt^iiia n ^^fy T T + ^^ > Sunday and Holiday Loads i « ' V \ '~ N Atmospheric Temperature , ^^A\^J&^^Aa , ^/V^Y^ wf+-<* -* -^v- f r" 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Day 8 Fig. 172. — Boston Elevated Ry. load curve showing effect of temperature on a railway load. starting from several given conditions which are at once the basis and the limitation of the problem. These conditions may be scheduled as follows: First, method of power generation; second, the type of load, that is, the load factor and diversity factor; third, the locality over which the power is to be distributed and used; fourth, various restrictions depend- ing on peculiar physical, political or commercial considerations. Of these conditions the last two are always beyond the control of the designing engineer, while the first two are more or less directly under his control, and should be the subject of careful studies to insure the best solution. Under location, it is necessary to consider the territory to be covered, the 276 ENGINEERING OF POWER PLANTS distribution of population, lines and distribution of travel and manufac- turing and commercial localities. If the central station is to supply a lighting load, a power load, a railway load or any combination of these, the locality must be studied with reference to these conditions. The various political, commercial and artistic restrictions, under the fourth category, must be taken into consideration in the analysis, leading up to the centers of distribution of population. With these studies it will be possible to approximate quite closely to what may be expected regarding the use of current at all times in the 24 hr., and a load curve may be laid out and the load factor ascertained. The proper location of the central station may then be picked out with reference to ease and economy of distribution. During the foregoing analysis the following points will have been considered and tentatively settled; the maximum load, the average yearly and daily load, the system of distribution, the location of the central station, the location of the various distribution lines, sub- stations, feeders and mains, and finally the types of prime movers. The en- gineer is now ready to roughly design the various parts of the system and to make the preliminary layouts and estimates from which the investor must decide as to whether the project will be commercially successful. Standby Losses. — In the commercial operation of a plant under change- able load conditions it is necessary to retain steam pressure on boilers « w m v o; 19 >— -> 1 ^~W 1 ^ ^ 1 C 41 ^ t \ l « 5 a H I I t t •_.;» L T if t f . 4 X Jt t *t I ± o S * ^ ± S j_ . ^--it * _L _L It 12 12 12 12 12 12 Night Nigh-t Night Fig. 173. — Boiler load curve of a large central heating station o 12 Time (Josse.) which are otherwise idle in order to provide sufficient reserve capacity for sudden power demands and to keep up steam pressure during periods when the plant is shut down. Owing to radiation, leakage, and other losses, this requires considerable fuel. Take the case of an office-building plant operating 18 hr. per day. There are 6 hr. during which no power is being turned out. It is there- fore necessary either to keep up sufficient fire to maintain the normal boiler pressure during this period or else to close all dampers and openings and make up the reduced pressure before starting up the plant. Again, during the busy hours of the day — say from 5 to 6 o'clock when all ele- vators are running and, if in the winter time, nearly all the lights are burning — the power requirement reaches its maximum and all the boilers are operating at a high capacity. But during the light run — say 8 or 9 o'clock on a bright summer morning — only part of the boilers are re- quired, and (if the plant be a large one) probably only one of the generat- VARIABLE LOAD ECONOMY 277 ing sets. And, as in the case when the plant is completely shut down, steam pressure must be either maintained or reestablished before the boilers are brought into service. Then there are the losses due to turning over reserve engines preparatory to their being "cut in," and the warm- ing up of idle units, etc. It will be noted that all of this requires fuel while not adding in any degree to the power output. The fuel losses caused by these conditions are known as " standby losses" and are com- mon to every plant. Their magnitude depends upon the load factor, hours of operation per day, number of units, design and construction of plant, kind and ef- fectiveness of non-conducting covering, climatic conditions, etc., and is, therefore, a very difficult factor to accurately determine. For first-class plants the standby losses are probably about 6 per cent, of the fuel required at normal boiler rating over a period of time All Units H-^ — — >+< — 1-75 Kw. 300 250 200 Shut Down £150 :§100 M 50 12 2 4 6 8 10 12 2 4 6 8 10 12 Midnight Noon Midnight Fig. 174. — Load curve of office building. 1-150 Kvf A'l^ T * 1-150 Kw> equal to the standby period. The average is probably nearer 10 per cent. The simplest manner in which to explain this standby loss is by refer- ence to an actual example (see Fig. 174). The plant consists of two units of 75 kw. each (one of which is used as a reserve unit only) and one of 150 kw. rated capacity; and three water-tube boilers of 150 hp. each (one being for reserve purposes). The generating sets are high-grade, tandem-compound, self-oiling, automatic, direct-connected, non-condensing, piston-valve units. The general method of determining probable standby losses is first to establish the points on the load curve where different boilers should be cut in and out, thus dividing the day into several periods during each of which certain boilers are operated. From this is obtained the total boiler capacity idle and the number of hours of such idleness from which the standby loss may be approximated in accordance with the above. 278 ENGINEERING OF POWER PLANTS This, of course, involves a knowledge of boiler efficiencies and engine economies. For the case in hand the exhaust steam from the engines is more than sufficient for furnishing heat for the building so that all the steam gener- ated in boilers is used by the engine and auxiliaries. Now, in order to determine the proper time for cutting in or out various boilers it is first necessary to predetermine just when different generating units will be required in service. It will be noted that in the example under considera- Kw. 8000 7000 6000 5000 4000 3000 2000 1000 J\ f \ k . Jan. Feb. Alar. Apr. May June July fff] Aug. Af\A Sept. Oct. Nov. Al\ Dec. Kw. 8000 7000 6000 5000 4000 3000 2000 1000 Fig. 175. — Curve of daily maximum demands. Wangen, a. A. tion the entire day of 24 hr. has been divided primarily into five divisions, as follows: 1. From 12:00 midnight to 6:00 a.m. 2. From 6:00 a.m. to 12:00 noon. 3. From 12:00 noon to 4:45 p.m. 4. From 4:45 p.m. to 7:00 p.m. 5. From 7:00 p.m. to 12:00 midnight. From midnight until 6 o'clock in the morning the entire plant is out of service. The second period — that during the morning hours — is well taken care of by one 75-kw. set. During the third of these periods the maximum output is 150 kw. VARIABLE LOAD ECONOMY 279 bfi - c3 3 ft O T5 3 CO o fa 280 ENGINEERING OF POWER PLANTS and the average about 100 kw. One unit is kept in service, viz., the 150-kw. machine. During the fourth period the load rapidly increases to a maximum of 275 kw., the average being about 180 kw. One 150-kw. and one 75-kw. unit take care of these conditions operating at a slight overload for about lhr. The fifth period is taken care of quite economically by the original 150-kw. machine, the smaller unit having been shut down at 7:00 p.m. The determination of the amount of steam required and therefore the number of boilers necessary at any moment is now an easy matter. Say for instance, the plant is started up at 6:00 a.m. with one boiler in service. The steam requirements are easily within the capacity of this boiler until the load suddenly increases late in the afternoon. At 4:00 p.m. 100 kw. is being generated, the unit being operated at about two- thirds of its rated load at that instant. Assuming the steam consumption to be 25 lb. per indicated horsepower-hour and a combined engine and generator efficiency of above 90 per cent., there will at that moment be required steam at the rate of approximately 4,300 lb. per hour. This allows about 15 per cent, for auxiliaries, etc., and is roughly equiva- lent to 145 boiler hp. This is a very small load for a good water-tube boiler of 150-hp. capacity, but the load increases very suddenly after 4:00 p.m. so that it is necessary to cut in the second boiler at that time. At 6 o'clock the load has reached its maximum of 275 kw. and there is then required for the entire plant steam at the rate of about 12,000 lb. per hour or 400 boiler hp. This condition is, however, only instantaneous, the demand increasing and decreasing very rapidly before and after this time. Two 150-hp. boilers are, therefore, easily capable of caring for these conditions until about 10:00 p.m. when one boiler is cut out, leaving the remaining one in operation until the plant is shut down at midnight. It is easily seen that the day is further divided into four periods of operation in the boiler room which may be summarized as follows: 1. From 12:00 midnight to 6:00 a.m., no boilers used. 2. From 6:00 a.m. to 4:00 p.m., one boiler used. 3. From 4:00 p.m. to 10:00 p.m., two boilers used. 4. From 10:00 p.m. to 12:00 midnight, one boiler used. From this is developed the number of boiler horsepower idle during the day, neglecting the reserve boiler which is always idle and which is not considered for the reason that it is not kept under steam and therefore uses no fuel. There are two boilers idle from 12:00 midnight to 6: 00 a.m. — or 6 hr. each. There is one boiler idle, but under steam, from 6:00 a.m. (when plant VARIABLE LOAD ECONOMY 281 is started up) until 4 : 00 p.m. — or 10 hr. ; there is one boiler idle from 10 : 00 p.m. to 12:00 midnight or 2 hr. This is equivalent to a 150-hp. boiler idle (2 X 6) + 10 + 2 = 24 hr. If this one 150-hp. boiler were actually operating at full load for 24 hr. there would be developed 150 X 24 or 3,600 boiler hp.-hr. 282 ENGINEERING OF POWER PLANTS If oil were used as fuel and if its calorific value be 18,500 B.t.u. per pound and the boiler efficiency 70 per cent., there would be required (3,600 X 34.5 X 970) + (336 X 18,500 X 70) barrels of oil, or 27.5 bbl. on the basis of 336 lb. per barrel. The standby loss is about 6 per cent, of this or about 1.65 bbl. per day. As a further illustration of standby losses, consider the following abstract of a letter 1 from John Hunter, Chief Engineer of Power Plants, Union Electric Light and Power Co., St. Louis, describing the practice at the Ashley Street Station in banking fires. " There are two general conditions under which boilers are maintained in a banked condition. First, boilers only required for 2 hr. at the peak in the after- noon and known as a short bank, where the minimum amount of coal is burned and where the steam pressure in the boiler is allowed to drop as low as 60 lb. To maintain a banked fire on a 100-sq. ft. chain grate in this condition requires 130 lb. of coal per hour. The other condition is what is known as a long bank, in which about 450 lb. of coal per hour are burned on the grate and the boiler is kept on the header, but delivers only a small amount of steam. These boilers are used for varying load. Under present condition of operation at Ashley Street, three boilers more than the number required for carrying the steam load at any time are always carried on a long bank. With 22 boilers under fire the maximum number required on the load during the peak is 19 boilers. On the 528 boilers hours each day there are 223, or 42.2 per cent., which are banking hours. Seventy-two of these banking hours are at the rate of 450 lb. of coal per hour (boilers on the long bank), consuming a total of 32,400 lb. of coal. The remain- ing 151 banking hours (boilers on the short bank), are at the rate of 130 lb. per hour, consuming a total of 19,630 lb. The total amount of coal used for banking during the 24 hr. is 52,030 lb. or 26 tons, which at a cost of $1.10 per ton amounts to $28.60 per day. The amount of coal for banking amounts to 5.1 per cent, of the total consumption for the station. When notice is given of a storm existing anywhere along the transmission line, or when there is any possibility of an interruption in the service, standby boilers are started up and kept in readiness to pick up the load. The banking consump- tion on the standby boilers at such times will run about 450 lb. of coal per hour." Carrying Peak Loads Economically. — The sources of power for peak loads are: (a) Storage batteries. {b) Purchased power. (c) Hydroelectric power. {d) Gas engine. (e) Steam turbine. (/) Old apparatus. 1 Report of Committee on Prime Movers, N.E.L.A., 1914. VARIABLE LOAD ECONOMY 283 A summary of the deductions regarding each of these methods of meeting peak loads follows. (a) Storage Batteries. — Fixed charges excessive on a battery capable of discharging at maximum rate for 2 hr. (6) Purchased Power. — Heavy fixed charges per kilowatt of maximum demand ($15 to $25 per kilowatt) plus charge per kilowatt-hour of actual service. (c) Hydroelectric Power. — If transmitted any distance shows heavy fixed charges. id) Gas Engine. — Low fuel cost while idle, but heavy fixed charges. (e) Steam Turbines. — Good because of low first cost. (/) Old Apparatus. — Best because the interest on first cost must be paid or written off as depreciation. As apparatus becomes obsolete, it is kept a few years as peak apparatus. As a matter of fact any unit, no matter how uneconomical, is good peak apparatus since it is only used a few hours per year and the cheapest fixed charge determines what is best for that small amount of service. PROBLEMS 59. Given a 1,200-kw. condensing railroad unit — direct-connected type — compris- ing the following apparatus: Boilers. — Two batteries of two boilers each, three corresponding to the full rated capacity of the plant, one for reserve. Engines. — One unit — cross, compound gridiron valve type — developing rated capacity with 160 lb. gage pressure and 24-in. effective vacuum. Condensers. — Surface type, for 26.6-in. vacuum in shell, with circulating water at 70°F. ; ratio, water to steam 40 to 1 ; head on circulating pump, 25 ft. Air and Circulating Pumps. — Horizontal, single, steam-driven, direct-acting. Feed and Oil Pumps. — Horizontal, duplex, direct-acting, steam-driven. Heater. — Open type, steam from feed, air and circulating pumps. Fuel. — Cal. crude oil, 18,500 B.t.u. per pound, 336 lb. per barrel. Required : (a) The full-load test economy of the plant in terms of kilowatt-hours output at the switchboard per barrel of oil burned, with constant full load. (b) The test economy of the plant in terms of kilowatt-hours output at the switch- board per barrel of oil burned, including all standby losses, if demand on the plant is as follows : 6 :00 a.m.-8 :00 a.m 1,200 kw. 8 :00 a.m.-9 :30 a.m 850 kw. 9 :30 a.m.-3 :00 p.m 425 kw. 3: 00 p.m -4: 30 p.m 850 kw. 4 : 30 p.m.-6 : 30 p.m 1,200 kw. 6 : 30 p.m.-midnight . 425 kw. Midnight-6 : 00 a.m 250 kw. 60. A power plant consists of: 1. A 200-hp. simple non-condensing steam engine with direct-connected 125-kw. D.C. generator. This unit cost compIeteTerected, $5,000. 284 ENGINEERING OF POWER PLANTS 2. Two B. & W. boilers of 2,550 sq. ft. of heating surface each, costing complete with chain-grate stokers, erected, $9,300; two feed pumps at $200 each and feed-water heater costing $500. 3. A brick stack costing $4,250. 4. Boiler and engine houses and coal pockets costing $15,400. 5. Incidental erecting costs $3,355. The output of the plant during the last year, operating 10 hr. per day for 308 days, was 346,000 kw.-hr. The plant was also called upon to supply heat 10 hr. per day for a total of 5,400 sq. ft. of radiation. The exhaust steam was used for heating. An electric company makes a proposition to supply the power at 2.5 cts. per kw.- hr., from its central station, the heating still to be done by the private plant. To take advantage of the central station power, it will be necessary to change from the D.C. to the A.C. system. If this is done the new A.C. motors will cost $11,500. About $3,675 (40 per cent, of initial cost) can be realized on the D.C. motors. The D.C. wiring cost $10,200. The additional wiring to change to A.C. system will amount to $1,870. The labor required during the past year consisted of one engineer at $1,100, one fireman at $780, one fireman 6 months at $300. Will it pay to purchase power and simply use the isolated plant for heating, or is it best to turn down the proposition of the electric company? A. Cost of Operating Private Plant. Determine cost of: 1. Water for power and exhaust steam heating. 2. Water for live steam heating, if any. 3. Coal for power and exhaust steam heating. 4. Coal for live steam heating, if any. 5. Oil, waste, etc. 6. Attendance. 7. Fixed charges. B. Cost with Purchased Power. Determine cost of: 1- Power purchased. 2. Water for heating. 3. Coal for heating. 4. Oil, waste, etc. 5. Attendance. 6. Fixed charges. 61. It is probable that in 2 years the demand upon the plant in problem 60 will double the kilowatt-hour output. At the same time the manufacturing business will require heat 10 months, 24 hr. per day, the radiating surface amounting to 32,500 sq. ft. Will it pay to purchase power and run the isolated heating plant or will it be better to operate the isolated plant for both power and heat, adding a 500-hp. engine with 325-kw. D.C. direct-connected generator? The cost of this unit erected, com- plete, will be $15,000. The motor installations of problem 60 will be ample to take care of the extra demand. CHAPTER XIV COST OF POWER The Iron Age, July 27, 1911, gives the following figures for the cost per kilowatt-hour for a 2,000-hp. plant located near the colliery mouth using slack coal at 30 cts. per ton at the mine and 90 cts. per ton delivered. The plant furnished power for the railway shops and all uses of power were reduced to the kilowatt-hour basis. Output for the year 2,472,513 units (kw.-hr.) Coal fired. 15,414 tons Coal per kilowatt-hour 13 . 95 lb. Coal per kilowatt-hour .'. . . . 56 cts. Average yearly cost per kilowatt-hour (sta- tion cost) . 877 cts. The steam plant cost $250,000 Fixed charges per kilowatt-hour 1.215 cts. Total cost 2.092 cts. 30000 28000 26000 24000 22000 20000 » 18000 % 16000 ° 14000 "g 12000 W 10000 8000 6000 4000 2000 1000 2000 3000 4000 5000 6000 7000 80008760 Fig. 178. — Load duration curve of Rochester Railway Light & Power Co. The Engineering Record, Jan. 21, 1911, gives the following figures for the station of the Edison Electric 111. Co. of Brocton, Mass. : 285 age-^- LF= p44% 286 ENGINEERING OF POWER PLANTS Year Output, kw.-hr. Use factor, per cent. Load factor, per cent. Cost of coal, cents Labor, cents Coal per ton, dollars 1907... 1909... 1910... 2,831,000 21.0 26.5 1.23 0.34 4.91 5,868,000 22.3 28.6 0.62 0.29 4.45 8,079,000 30.7 33.1 0.56 0.29 4.27 Engine plant, 1,700 kw. Turbine station, 3,000 kw. Turbine station, 3,000 kw. Unfortunately in America but few good steam-plant station costs are published on a comparable basis. In England much more publicity is given to these figures and Lighting and a few other papers publish in 12 2 4 A.M. 8 10 12 2 4 6 Hours 10 12 P.M. Fig. 179. — Load curve of large central station. (Josse.) every issue a table of the costs, outputs, and other data for most of the lighting and traction plants. These figures have now been published for many years and are of great interest. The following tables have been taken from these reports. Stahl und Eisen, Dec. 21, 1911, published a table giving the station costs for 37 steam stations covering plants in Germany, Austria, Russia, COST OF POWER 287 Table Showing Cost of Power in English Electric Stations (Municipally owned) Electric supply stations Year Yearly load, kw.-hr. Coal and other fuel Oil, waste, water and stores Wages of work- men Repairs and main- tenance Total cost Max. load on feeders Load factor Plant capac- ity at end of year St. Marylebone Aberdeen Birmingham. . . Bolton Bradford Brighton Edenburgh. . . . Glasgow Leeds Liverpool Manchester. . . . Nottingham. . . Salford Sheffield Stalybridge. . . . Sunderland .... West Ham 1910 1910 1911 1911 1910 1911 1910 1910 1911 1910 1911 1911 1910 1910 1911 1911 1911 10,776,459 5,436,065 32,866,835 11,156,084 18,737,857 10,285,680 15,309,493 36,479,243 14,372,765 36,089,627 83,308,848 11,944,527 14,719,170 10,317,933 13,295,341 10,208,493 22,690,266 0.586 0.630 0.366 0.550 0.325 0.750 0.530 0.428 0.305 0.429 0.407 0.731 0.530 0.325 0.325 0.345 0.470 .0406 .0203 .0203 .0408 .0610 .0460 .0407 .0407 .0203 .0407 .0203 .1420 .0610 .0203 .0202 .0202 .0203 0.244 0.183 0.162 0.163 0.142 0.265 0.102 0.184 0.122 0.184 0.203 0.285 0.122 0.184 0.081 0.122 0.122 0.426 0.183 0.245 0.184 0.245 0.428 0.366 0.265 0.225 0.143 0.184 0.285 0.203 0.325 0.061 0.265 0.203 1.300 1.016 0.793 0.938 0.773 1.489 1.039 0.917 0.672 0.797 0.814 1.443 0.916 0.854 0.487 0.752 0.815 7,824 3,218 15,553 5,019 7,922 5,140 11,424 21,719 7,980 18,071 37,520 6,316 6,707 6,870 5,300 5,235 8,123 15.72 19.28 24.12 25.37 27.00 22.84 15.30 19.17 20.56 22.80 25.35 21.69 25.05 17.14 28.64 22.26 31.89 12,000 4,649 22,040 7,600 8,180 7,200 15,217 37,478 15,740 37,000 47,301 10,850 7,000 11,400 8,003 9,590 11,400 Table Showing Cost of Power in English Electric Stations (Privately owned) Electric supply stations Year Yearly load, kw.-hr. Coal and other fuel Oil, waste, water and stores Wages of work- men Repairs and main- ] cost tenance Total Max. load on feeders Load factor Plant capac- ity at end of year Central Charing Cross .... Chelsea City of London. . . County of London London Metropolitan Westminster Newcastle Dist. . . Hackney Ashton on Lyne . . Bury Cambuslang Coventry Darlington Dewsbury Loughborough .... Motherwell Wolverhampton. . Prescot 1909 1910 1910 1910 1910 1909 1910 1909 1909 1910 1910 1911 1910 1911 1911 1910 1911 1910 1910 1910 17,282,370 25,733,222 4,144,936 25,183,380 16,985,687 10,308,537 12,287,674 18,546,815 10,479,253 4,785,053 2,838,295 4,014,247 J12.527 7,443,937 2,192,036 1,209,675 531,886 2,444,944 8,289,720 4,560,397 0.547 0.770 1.112 0.608 0.648 0.709 0.770 1.032 0.405 0.528 0.508 0.406 0.101 0.324 0.386 0.527 0.345 0.406 0.426 0.345 0.061 0.040 0.081 0.020 0.040 0.061 0.040 0.101 0.081 0.041 0.081 0.041 0.264 0.020 0.041 0.081 0.041 0.081 0.041 0.041 0.142 0.284 0.506 0.243 0.182 0.284 0.446 0.304 0.162 0.162 0.243 0.142 0.426 0.142 0.203 0.406 0.365 0.182 0.122 0.162 0.162 0.912 8,616 0.426 1.520 13,231 0.588 2.287 2,769 0.304 1.175 17,767 0.507 1.377 10,350 0.386 , 1.440 7,756 0.507 1.763 7,800 0.467 1.904 10,169 0.162 0.810 5,530 0.162 0.893 2,857 0.446 1.278 1,391 0.182 0.771 2,022 0.487 1.278 120 0.122 0.608 4,769 0.162 0.792 1,235 0.609 1.623 960 0.487 1.238 355 0.122 0.791 1,280 0.304 0.893 4,181 0.162 0.710 1,803 22.90 22.20 17.09 16.18 18.73 15.17 17.98 20.82 21.63 19.12 23.29 22.66 10.70 19.01 20.26 14.38 17.10 21.80 22.64 28.87 12,830 21,440 3,500 25,000 16,500 17,250 18,500 17,225 9,000 4,800 1,760 2,000 200 6,600 1,970 1,050 600 1,910 5,230 2,260 Table Showing Cost of Power in English Electric Tramway Stations Electric railway stations Year Yearly load, kw.-hr. Coal and other fuel Oil, waste, water and stores Wages of workmen Repairs and main- tenance Total cost Dublin Glasgow Leeds Newcastle-on-Tyne Sheffield Cardiff Huddersfield Leicester Preston 1910 1910 1910 1910 1910 1910 1911 1910 1910 11,771,939 26,860,126 14,793,687 8,213,651 13,960,753 4,047,580 4,751,903 5,799,492 1,596,645 0.510 0.245 0.470 0.305 0.385 0.590 0.366 0.366 0.407 0.041 0.041 0.041 0.020 0.020 0.041 0.020 0.061 0.020 0.203 0.203 0.143 0.184 0.142 0.163 0.184 0.203 0.142 0.102 0.162 0.041 0.203 0.162 0.061 0.470 0.0815 0.245 0.858 0.651 0.695 0.712 0.712 0.860 1.040 0.710 0.815 288 ENGINEERING OF POWER PLANTS < m w Q H ll> cd o 1> f ) CO -P CO '. W ft g I? § 2.2 o3 O 2 1 in co M -O CI 3 o3 »H° 3 ft pq "P fa d co 3 "S« co ai^^SO a 3 o o e4 Cl' Q • .2 i- a i2 ° ET3 g 03 -SCO .3 O O "S .2 -^ o3T)3 '. co osrs > pq u o u o o u r3 p. D o W o Si oooooooooo o ooooo ooooo oooooooooo o ooooo ooooo ©COHOOO©CCt>.00»0 O CNiOtN hh NMtJihO t>o co cncocococo coocnco© >0 CN ■* »# CO CO CO CO CO »0 CO CO-^COCOCO CO'OCO'O-'* ooo oo ooo oo CO00O3 '"i T * i>ti*o* ioco CO CO CO CO CN ooo ooo ■*<©© OOO •COCO • 00 O O ■* 00 00 00 CO CN TjHiO -HlO • H rj< CN CO iJH CO O O CM © -NHO CO .0>COtJ< 1-Hi-I -CNH • lO i-l iH H t-I i-l H O i-t -©CNCOCO H -TjlH -OOO -©HCO©CN00 • t* CN CN t> i-l O -COH -itfi-H •HrtNOHQ -OCOOOt^ O -©CO© ■* -lO CO H H 'UJi-IH COCO ■O00 1-HO OO -OO -CNO -OOOOOO -©hhO oo i-i co t»CO OOO ©CO ■HHtJI o»o coco COIN ■lOiO •©CO •COIN ••* • CO 00 CO >C •>■ 00 -COiOCTiO ■CO •00-^COOOCO •OOOt^rti •O 'ONONHH -OOOCO »o •owes CN -Ol-^i-i CO 'OHO OiCO -lO -IN t^O •© • © OO -IN •© •OCN ooo OO -oo • oooooo -oooo ■ooo Tt«CN 00 CO CNCO •IO00 •(NO • com ■OOK5K300NOO •(OOK3K5 O • (N t>. 00 © (N iO CO (N lO -COCOHH rf( • (N CO Tf( ■lO-^CO C>iO • © •*•» t-i-* -iO -O Nri •!> -iH O -lOO 00 -CO i-l Tj4 -CO »0 o»o t>.iO CO-* OO -OO -rHOOOOOOOO -©ooo i-HO -i-iCM • CO i-( CO rH CO (N i-H O O OO -O© -©©(NO©©©©© OHHO i-l • i-H i— I i-l •o©o© © -oo© ON- -N HO -i-H oo -o ■0 -H COO -00CN • 00 CO Tt< tJ< CO oo -t-iO • ^ 00 »o N t» CO ■* -»o •(NhiOO I> .(NOOiO ■»O00OC0 CO -Hi-iCN •rJI-HHOCO lO •NQ0I> OO 00© COIN CO -HO (N -CBK3 t>- 'ION CO»C COO OOCO OO •©© 'HOOOOOO ■COOOHtNOOOO-HH ■HCOCNCOCOOOt^OO© •■HHCNCOCO-HHCOCOININCO ©©©©©00©©0©0©©0©©00 ©0©©iO©0©0©-H<©iOiO©00©© CO >o »C lO H lO CO *o t> O CO 00 CN CO © © IO 00 © CN CO CO CO CO* CO CN CO O H ^ O* lO CO -HH o" CO ©* "3 tH i-H H l-l t-I H i-l rH CN H H >-l H i-H l-H i-H i-l ©o©o©o©ooo© oo©oo©oo©oo l> CO O (N N CN CO_ CO_ 00_ * CO CN H CO* CN H ©* CN CO* O" iO H © © ■* CN 00 00 ■* O ■* © •© CN »o •* O CO CO r>» CN H lO -CN 00©©0©©©0© ••HHTf#COHH00 •COHCOCOHOCOOOCNCOiOCNiOiOCO •CNi-li-li-ICN'HHi-li-lrHi-li-lcNCOi-HOi-1 •©©©©©©OOOOO©©©©© (N* CO r^TjiCNCO Oi-H »0 i-H CO COCO i-li-H H HCNH© CN HIOOCO-H^COHCNCOOCO-* • CO O 00 00 N »C O lO CO © CN CN © iO CN 00 N OOOOOiOOOOOOOOOt^CN'OHCO •MM«NO)iO(OCOH(O^HOO>NNt» ■HHOOCOiOOCN CO CN 00 O ■* CO CNCOCO^CNCNCNCOCOCOCNCOCO -Ttit>.COTllC0CO00COHrJlrHTt<00CO-HHHlO -COCN •* NffiiJIHO^ (N-^CNHCDCOOOO-^OOHCOCN • CO •* tJ( CN ■* * lO -©lOOO* cOTt<00Ht~© O ^(OOOOONO'ONN'HN'* • H iO CO »C O ^.Hi-itHHCNHHCNHCNHCNi* CNCNC0HCN l> .©OOOCO H -CNHtNH C0*O00»O© HNHHHCO CO © IO © OH CN H CN CO HCN 00©O©»0t~©'HHc0cN©CD©©C000C0©t>cN 00C0OO»OHTtl T tO©C0C0C0C0'* a, H io' CN ■*' o' CN O CO 00* CO CO* Tji CO •* ■* CO CO t>. CO HHHtHHHHHCOHCNHHWCOHHHHH (N O00OC0HC0 COHCOOOOO lOCNTtKNHiO CN »-l i-H i-H i-l CN CNHb-iO^cO t>»00-H<0»00 COCNOCNOOO l-l 00 i-l rH H rH Oi O O o> H CN CN CN c3 X "J 4>P N It s ^ fl^—a s <» 2'3 M 2 S"2^5 So3o3££^3^^o£:3£ ^pqfqpqfqpqpqoMQPPW tit m (n+irt 2 „ 5-0 A o3, 05 g fl "c1 ro o3 m t, 03 OJ S CP . > ^ o*2 P* bfl to o3 C^j,Q Hiss CO 03 03 CO.rt OtHWWM 3-S BfifrQ 03 03 O N CO -•§ CO . <-, - 3J3^T3 03 So fa rl 03 u CO .R_o s? o hJ= « O ^OPhPh d o3lJ a> a as 03 03 O o ^3 a a In co o C CO 0Q 0Q CQ ^ tt HCNCO-HHiOCOt>.CjOO©HCNCO-*iOCOt^OOO© f-tHrHi-lr-lt-(i-ti-ltHHCN r^ooooHCN co CNCNCNCOCOCO CO 1)1 IO (O Is CO CO CO CO COST OF POWER 289 -, 6 I = a ? o Oh Goal .... - \y t '— "h. i >• ^, -\ 1/ r— ^j" ^ I /' Water I i7 vS v — — * i 1 1 *5 - / ^ ■c^ J 12 12 Night 12 12 Night 12 12 Night 100 H T3 50 £2i 25 ^c o £ 12 Time Fig. 180. — Curve showing water and coal consumption of a large heating station. (Josse.) C 3 a M 2 . a 1- a O 100,000 3 5 7 9 1,000,000 12 14 Yearly Load Yearly Load Fig. 181. — Operating cost steam power plants Fig. 182. — Influence of cost of fuel up to 1000 kw. capacity. (Josse.) on total operating cost. (After Josse.) 3 " 2 -a w -a" u -0^1 2 ,Tot al Oj >erat ng ( lost 1 /i uel ^Sa arie 3 & ' iVage ' s """I sN aintf nance /Lubri — Fi cants 4 5 6 J _l 9 10 11 12 13 14 Mlllion_K.W,Hr. I ' I ' 20 Million Xfi.H;P.Hr. 11 16 18 2 4 6 8 10 12. Yearly Load Fig. 183. — Operating costs steam power plants, reciprocating engines and steam turbines. (Josse.) JXI 2 M u «* i CU 1 Fig. 184. 19 11 12 13 Million K.W.Hr. 1 1 I 1 10 12 14 16 IB 20 Million E2.H.P.Hrj Yeafly Load -Operating costs larger sizes of steam turbine plants. (Josse.) 290 ENGINEERING OF POWER PLANTS Sweden, Denmark and Holland. These figures are extremely interesting and will repay careful study. In his "Neuere Kraftanlangen," Professor Josse of Charlottenburg has collected figures from practically all the larger plants in Germany and both his figures and curves are of great value. The book also con- tains similar tabulations for gas and oil engines. Figs. 180 to [l85_are reproduced from his book. ■ 60 40 20 Cost X of Wages.] Maintenance Lubrication Packings in if, of (Total Operating Cost. ^Operating Cost in Cents per Eff. H.P.& per K for an Average Year ' ^ .W. Hr. etc. 100,000 2 3 4 l__l I I I I L 7 8 9 1,000,0001.1 1.2 Million 1,000,000 , i *' wu l ' vw i x "- l ^-R.W. Hr. 100,000 3 5 7 9 1.1 1.3 1.5 1.7 Million Eff. Yearly Load H.P:Hr. Fig. 185. — Curves of direct operating expenses. (Josse.) The following tables of station costs for stoker-fired stations and hand-fired stations have also been calculated in percentages for easier comparison. The following figures have been published for the station cost of tur- bine stations with mechanical stoking: Output Brussells (Greenwich (Eng.),. 43XoofoOOkw.-hr. 2 2,000?000 kwl-hr. |»35»bK5£ Cents Per cent. Cents Per cent. Cents Per cent. Cents Per cent Coal Labor Oil and waste Water Maintenance. Total 0.394 0.0897 0.0123 0.0079 0.0288 0.5327 74.0 16.8 2.3 1.5 5.4 100.0 0.46 0.104 0.004 0.04 0.608 75.6 17.1 0.7 6.6 100.0 0.389 80.3 0.4731 0.0662 13.66 0.0718 0.0125 2.58 0.0159 0.0167 3.45 0.0366 0.4844 99.99 0.5974 79.1 12.0 28.0 6.1 100.0 CO © CO »OCN HO CO_r-H CM*C CN1-H rHU3 LOCO i>co OCi-h CO co" CO !> co" O CO CN <* »OOi CN-* o_os CN o o CO CO* CN 00 CN CO CN CO CO I-H co CN C75 >o 00 I-H O 00 1—1 CN co CM <* O CN CO CN CN •>* co CN co © o 00 T-l CO i-H -<* 1— 1 o" CN o co i-H c I 3,721,153 m CO 0> GO o co CO o © © co" CO CO CO O o o LO" o co_ CN lO i-H «s CN co" 00 00 © 00* CN 0» o o 00 t>" co i-H CN o o» 00* 0» 00 o CN co CO o o ■^1 1-H CO CN* O CO CN 00 CO o o iH CO CN CN c c c c I lO o 0» o o r—i o 1— 1 O o CN t-H o o CN o o co_ o o-c £ °. c c T-< o cp u tx CN 1* -Q o 05 £ +="73 e3 CP t- ■** QJ U c « cp C cX . o CO « c « 3 *> >12 • •r" d *■> .5 > I a cp TS 09 « CD fl s o o o cp u ■3 ■ cn'S -O'E cpt3 •*= i -O.S r co *e > Ot3 CJ i s-° o o o £ Cp -^ O 3 3„ 53 CO u .S 2 * to CO 1 CP fl "5 c CP CN B0 U o 03 a u CP "3 i o -O . i- CO ** a 1 CP o > CN d « C o CP CP w c . o m o ■^ i •£-S 3 cp . cp'^3 O ^CN g 4S.5 cp S8« CN c d 'O'O d cp o o o ai w d - O CO o •*= 1 •s-s 3 cp . - - cb^: o 3 e K -5.5 ^ > bC ^■^^ -L cc — O cp cp JO C J2 CX--H CN d* 3 c d 13T3 - v 5 *» o o « CP n d . o CO o •a-i 3 cp . ^CN g -5.3 cp ^IS"° ^-"3 CP ' co — O CP CP CN -d d d cp O c£ o x"° z. cp O CP cp a CN g ^"V 3 cp d^3 5 *= d-r< ^ SR ro ' i d o O'ri-u J CP CP 1— 1 cog o° 2d *! 3 d CP 73 > -^-5 CP gl» «°°.s .5t3'm XICC S3 CP CO cog a •a-° 3 d CP 73 > ol3 CP g^ o^ I§» Tt t - 3 CP "°°.s -5t3'"J -Odd S3 cp CO i i ©■* >OtJ< '"'co CO o ■*> 03 > co" 2 ° d eg — 03 73 =3 £ c C „ O CP CP « > £ ■rH 03 O.T3-d d i co S"cp -- CN 1 o o "O o3 MM O d o '-3 T3 T3 03 CP 5^ ■g CP s" t c cpIo i S 03 43 ! ? < CO PQ CO I-H < pq 00 I— 1 © o IN o CN O o (lll-kw. lurlx.-ftH.-ri.iitor; total ,,f i:. ,-..|,,T ; .t..r ;i . 5.000 8,216,207 18.8 9,684 Bitumii ' 3.35 0.54 \TfK',i?afa',r» a a 8 „r" H 0.28 0.172 0.065 0.07- 0.31 0.049 0.013 ' 2 5D Viies ■M&^s'gCTMatare.Vvwai "■"'" 8,770.165 In. 7 1 :,:.. 3 coal passers, 4 sw. bd, men. 0.28 0.20 O.B0 OA 2 1,500-kw. turbo-alternators. 3,00, 2.51, 5,858,255 22.3 26.6 8,120 Bituniiriuus 3.1 0.02 4 mc,1!Tcoalpas°s i e rs a ' 4 ^ H 0.29 0.051 0.0023 0.0533 0.097 1.06 OB 2 1,500-kw. turbo-alternators. 3,000 33.5 Bituminous 0.50 4 engineers, 3 oilera, 7 fire- " 0.23 0.80 7 3 comp. cond. direct-con -t. -1 .-ngiix- units; 2 L'.M'-kiv iiiot<>r-MH.fr,U..rH for d.-O. molor load. bitumtaJu/ 3.67 0.42 2 cowpawers, Hwf bd°m?n; H 0.30 0.22 0.04 8A i'Mi'i'-lnv.ii .mils ,,f 2,2.'.0-l,,v ,1 ratine; Gs.rmlllH-lt-drivci,Kor»THt..r.H 4.50C 5,754,208 14.6 3.3 0.68 21 total. H 0.34 0.23 1.25 SB 1 1,500-kw. turbo-alternator; 3 en- , i i t f * M ill 4.50C 7,120,314 [8 , 3.1 0.62 23 total. H 0.28 0.13 1.03 " - 7.,,il,|, . ' .■.:.'" ii-!, ( 1 1 ...iirrr.-,,,, 5,00t i,,ui:t,2u 13.8 Bituminous ' " 0.088 2 coal pas a s'ers,°4 sw,' bd^roen. H 0.34 0.059 0.045 0.02 0.124 0.054 0.018 1.23 10A 1 turbine unit of 2.000 hp.; 3 comp, .■nnd-.-nKih- .,...« of 2.HUI .o,.m- 3.40C 4,715,000 14.7 32.6 lffi .' 7 3.3 " ' ; fittera, ?1luremon™2 aw. bd. M 0.31 0.072 0.014 ,l 1,7 0.109 ll 11,7, 0.02 0.021 1.08 ■ OB \^ 1 ,lHp'^ntcV 1 mp ,1 rVnd , V I ^£"^L.", f 3,40 1,081 5,513,03' is.-. 31.8 Bituminous : "" %™&r5 , -i'w m n s t n tOT ' M ,.26 1.05 " inn :i non ! lp : l 1 .'.no hp.; 1 1,500- 4.00C 5,400.000 15.4 B.tummous 4.7S 3.2 0.70 H 0.30 0.034 0.14 1.24 12 1 1,500-kw. and 2 500-kw turbo- altornators. 2,50C 4.873.250 28.4 Bituminous 3.3. 0.51 0.25 0.23 0.09 13A -t engine units both direct-connected and bolted generators. 2.50C 3,106,000 Bituminous | 4.5 3.3 0.74 14 total. 0.41 0.158 0.011 0.03 0.203 1.41 I3B f online units both direct-coin, eeted and belted generators. 4.71 .; .-, 0.74 3 engineers, 3 firemen, 2 elcaners, 2 ro:.l pu^.-rs, 1 nmelmd-U, 3 sw. bd. men. H U.J. 0.170 III.,., 0.05 0.239 (i i.i;:-t (1 024 1.36 14A 3 comp. cond. engine units with dir. ■.■,-.■,,-,, „■<■<, ■,! generators. 1,210 3.288,023 IS. 8 31 2?S4S Bituminous 1 '; ""' ■t eiiRin.ers. 3 oilera. 3 fire men, 3 helpers. " 0.30 0.003 0.00 0.151 0.038 1.42 14B > dbS > «£l±d SS£toS d " ith 2,000 ,,611 ■1,000.157 22.6 IS Bituminous : ;; 0.74 4 m° e n nTnclpe 3 r 8 ° Uerfl ' B firC " 0.31 0.041 0.072 0.01 0.13 ' 1.24 14C 3 di^icon C n°eSd SttaS** ^ 2,00. 1,651 •1,461,580 25.4 J;": Bituminous :! 1, 0.07 .. 0.20 — 1.07 15 2 1.000-kw. turbine units. 2,000 4.410,201 25 ■ 0.47 ii 20 0.02 0.72 ISA belted^nerator eng " , ° ""'' W '' h 2,300 1,67 3,721,153 18.6 25.4 0,076 'nkulninoS' •' " 0.65 bd. men, 2 helpers. 0.28 0.003 2 l,liiin-l;w. turbo-alternators. 2 non- ■■Nji.l oiK-me Units will, bolt-driver, 2,800 1,050 4.40S.S05 18.0 25.8 7,31, ,.u,7"',','.'-"!'. - .1 7 -.I M 0.25 0.055 0.018 0.02 17A Kni-im-drivm .mit.i. ,..-i 1( -rat..r:= l,.-lt- d,iv..„ and .hr-.t-ounected, mostly '■'"''■ " 3 ' 990 ' 634 23.2 Bituminous 3:1 3 engineers, 3 firemen, 2 coa " 0.24 0.008 0.028 0.00 0.10 0.02 0.02 1.25 17B 6 Ai t driven d uniS t0Qb * 00Ilne0teden " .1! 1,000 4,357,648 20.4 26.2 "^,'."l','i",',"t- i:?! 0.78 3 engineers, 3 firemen, 2 coa 1177 0.008 0.015 0.01 0.097 0.016 0.017 0.01! 1.16 18 6 engines, all but one comp. cond.. 15 2,158 ■:. :>'... 22.8 IS ""eSiSg"" 4 , 5; 5.5 0.876 %nS. 5 3 'help fi e r rT eU,2CO0 0.224 0.17 1.27 19 2 500-kw. turbo-alternators, 2 en«ine- 1,001 3,275,152 23.4 5 'l3l "—'"-" is 4.1 0.82 6 engineers. 2 oilers. 3 fire 0.34 0.055 ti 03S 0.00 7 0.101 0.013 1.28 20A 2 750-kw. turbine units, 3 cond. en- .'i.ie, ilnvii,,; 2 .br.ot-eonneotcd and 2,330 1,928,088 0.40 ;i.7,i- Bituminous , 37 0.85 5 engineers, 3 firemen, 2 0.055 o.ooi 0.01 10.069 0.001 0.000 0.01 1.27 20B 2 750-kw. turbine units, 3 cond. en- l.ih. ^Irivii.H 2 direet-r uPll ,e.'h-.l ;i .id 1 belted generator. 2,330 1,450 2,137,800 10.4 16.8 3,77- bitumVimus' '' S " ., ■! ii. I.', 5 „eSr- 3 — ■ 2 H n .1, 0.046 0.002 0.00 3 0.053 0.003 0.031 ii ,, 0.38 1.10 20C 2 750-kw. turbine units. 3 cond. en- L-m-sdriviTiK 2 dir,et-.-,.-,t,neeled and 2,330 '■"'" 2,428,04. 11.8 23.1 4. -'» Bituminous .1 '» 3.9 0.08 helper" "*' <"<•••<"•■ " " : " 1.18 21 Bituminous 3. 86 ii 7,7 3 engineers, 3 firemen. H 0.30 0.077 0.051 1.07 22A .'.ml Slid |;w. diiv.-n by comp. cond. 1,250 1,470,006 13.4 2 ffi D.i.ji.nn,..., 2:'! 4.5 0.82 4 engineers, 4 firemen. " 0.46 0.006 007 0.05 0.167 - 1.56 22B and NO') kw. driven by comp. cond. :.ss 1,602,371 14.7 3,301 ^.n'.u'n'n- 2 : "r 4.6 0.70 helper. H 0.48 1.54 23A bell-drivei, 1.11,,1,-ilur,.; .ils,. :> -1 |-ku: 582 1.010.382 20.4 oSSSr- i% ii..-., 3 2fc" i meI S 'At y ™i°'°»n? n ' 1 '' r ' II 0.60 0.087 0.004 0.00 5 0.096 0.078 0.021 1.71 23B Sum.' with tin.' nd.lini.n uf a .Mlll-l.-.v. 1,082 1,227,017 13.0 (■.'.>•:; e'' ).'!'"" i:U 3 engineers, 1 dynamo tender. H 0.011 J 0.185 1.05 23C S Cbineunit e *""'"' "' " 5 °°' k "'' 0,082 W']; ''it'>i"- r,;; 1.00 3 engineer.. 1 ,..,,ii.,„, lender. H 0.327 0.017 O.00 10.363 0.0S4 0.036 n.47 2.05 23D 1,082 1,400,045 15.6 1.20C t'..k. lal,,,,,, nous breeze :l ii 0.56 3 o en„ineers. 1 dynan.o tender, H 0.61 0.04 0.035 l nl 1 0.116 2.04 21 SYooo'S: °Stbi»»°SSf driv *° 800 1,140,173 10.3 2,485 Bituminous , 2! 1 -7 0.917 2 "ginee,.. 2 firemen, 2 11 0.40 nr 26 050 031,040 11.2 2,213 Bituminous 2:25 0.40 1.09 3 engineers. 4 firemen. U 1.03 0.178 0.047 3~iT 2CA \ns cm tfcszt,i[sr ""■ 675 050,880 2,417 B.tummou 9 i - 1.79 H 0.103 ii Ui.7 2.89 725 886,800 13.0 2.175 ,,- i - 4 ' 1 .•.■ ■^engineer,. 4 firemen, 2 H 0.71 0.025 2.14 20C ^iSe^onSXenerSr """ 725 889.700 14.0 2.200 Bituminous 5.79 '■" 3 oi e»,inee,s. 3 firemen. 2 H cS 0.160 2^T 27 5 drivfi™' tSffii f5 a 8 ,„ i r.o„': o ° d ' 008 487 878,140 11.0 20.5 ;,,7.-,.. ( 2 7, 1 16 H — — 0.2! 0.005 2.00 28 3 eo'Sie5™ d ner*a n £;r """' *"""" 030 730,468 13.2 1,620 Bituminous 4.99 0.025 3 engineers, 3 firemen. H 0.686 0.11 rio - Plan Pie!! Plor Plot N.. (■. C.nliul ..f..!;.... (city of ,0,11011 gelro a engine,.. ] P ant N, 11.0 12. C L3, C 14. C n? < 17. C 18. L Jmi.r. »!..! r:i •S 35,00 40,00 •Hl.llii 40,00 stati ))• Pla, ). Us )■ Plan ). ?i.: Plan t No. 1 X^ 7 : cc! 1 w C,.[ . Cen trul su i.l -i: ay Cpo ion (p pulat ..ii. ,ii, i Hi.,,, on, 30, n, 20,0 on, :iu. .Ll). No.. 11 00). 0). . 290 Sweden, and will In hi has colle and botl tains sin reproduc The hand-fir compari The bine sta Out Coal.... Labor. . . Oil and w Water. . . Mainten; Total COST OF POWER 291 The following figures have been published for hand-fired stations with both engine and turbine machinery: Output Engine station Cambridge, 7,344,392 kw.-hr. Engine station Boston Edison kw.hr. Turbine station Hudson Co., 20,000,000 kw.-hr. Cents Per cent. Cents Per cent. Cents Per cent. Engine station, 886,600 kw.-hr. Engine station, 5,952,936 kw.-hr. Cents Per cent. Cents Per cent. Coal Labor Oil and waste.. \ Water / Maintenance 0.46 0.30 0.22 47 31 22 Total. 0.98 100 0.3750 54.5 0.2123 31.0 0.0279 4.0 0.0308! 4.5 0.04061 6.0 0.6866 0.195 0.173 0.02 0.025 100.0 0.413 47.2 41.9 4.8 6.1 1.22 0.705 0.031 0.025 0.160 100.0 2.141 57.0 0.575 33. 0J 0.341 1.4| 0.016 l.ljO.052 7.5 0.070 54.5 32.3 1.5 4.9 6.6 100. o! 1.054 99.8 It will be noticed that with stoker-fired stations the fuel cost varies from 74 to 80.3 per cent, of the station cost. These figures date from 1908 to 1911 and are all from comparatively medium-sized plants, the plant of the Boston Edison Co. being the largest. With larger sized plants and 1915 conditions this percentage will probably be nearer 90 per cent, and for stoker-fired plants in general with turbines for prime movers it is safe to take the fuel cost as 80 to 85 per cent, of the station cost. In hand-fired engine stations the fuel cost varies from 47 to 57 per cent, of the station cost. In more modern turbine plants the percentage may increase to 65 or 70 per cent, with size and good operating. Sixty per cent, is a fair figure for estimates for a turbine plant and 50 to 55 per cent, for an engine plant. Williams and Tweedy give the inserted table of kilowatt-hour cost of electric power in steam-driven generating plants of various sizes. As a general rule the better the plant, the larger the plant and the better the operating, the higher will be the percentage of fuel cost to the total station cost. Standards of Good Operation. — While the station cost may be used as a criterion of good operation, the cost of coal and its quality, the pre- vailing rates for labor and a number of smaller factors must be known before two station costs can be compared with any degree of certainty. For stations under the same management the station cost is a good crite- rion but even here there may be defects in the design of the plant which will prevent economical operation, or a low use factor which will greatly increase the unit costs. The coal consumption, pounds per horsepower-hour or per kilowatt- hour, has-been-used _as_ a_j}riterion_.aiid_is. ..ajsomewhal better one Jthan 292 ENGINEERING OF POWER PLANTS station cost since only two accounts must be kept to determine it accu- rately and these two accounts are always kept by both large and small plants. The water rate per kilowatt-hour has also been used but is very rarely obtained with accuracy, requiring the installation of many very accurate water meters in the ordinary large plants. The ordinary city water meters can be used for the make up if calibrated very frequently. Station Lb., coal per kw.-hr. B.t.u. per lb. of coal B.t.u, per kw.-hr. L.F., per cent. Carville, 6 mos. ending June 30, 1905. Glasgow Corporation, 1905 Manchester (Stuart Street), 1905. . . Powell-Duffryn Steam Coal Co., 1905 City and South London Co., 1905. . . Charing Cross Co. Bow Stat,, 1905. . Charing Cross Co. Bow Stat., 1904. . Sheffield Neepsend, 1905 Metropolitan East Side Co., 1905. . . Central Co., 1905 County of London Co., 1905 Salford, 1905 Leeds, 1906 St. James & Pall Mall Co., 1905 London Elec. Co., 1905 Bradford, 1905 Westminster Co., 1905 Berlin, 1905 Berlin, 1904 Vienna, 1904 Eberfeld, 1904 Hamburg Zollverein, 1904 Frankfort a/Main, 1904 Hamburg Combined, 1904 Cohn a/Rhine, 1904 Munich, 1904 Copenhagen, 1904 Charlottenburg, 1904 Oberschlesischer Indus., 1904 Dresden Power, 1905 Dresden Light, 1904 Brussells Tramways, 1907 Buenos Ayres, 1904 Brocton, Mass., 1907 Brocton, Mass., 1909 Brocton, Mass., 1910 Redondo, Cal., 15-day test Redondo, Cal., 16 mos., 1908-09 14,604,800 20,558,500 28,189,455 4,500,000 6,644,131 12,174,104 10,340,657 3,499,428 22,711,000 7,102,960 11,350,000 10,666,001 8,436,817 6,654,217 14,235,423 14,723,356 11,61-6,914 141,059,129 113,389,947 45,939,840 7,206,950 12,914,177 16,431,832 27,188,640 13,126,850 12,888,991 13,280,515 6,747,000 27,286,995 12,528,657 5,464,405 21,913,000 32,722,381 2,831,000 5,868,000 8,079,000 3.13 4.50 3.57 3.75 4.41 3.64 3.43 4.04 4.64 4.20 5.50 4.37 15 54 60 12 96 2.38 3.10 2.70 00 00 30 40 60 70 90 4.50 4.80 6.50 7.20 2.09 3.00 5.62 3.21 3.41 11,000 10,500 13,500 13,000 11,500 14,000 15,000 13,000 11,800 14,000 11,000 14,320 11,000 14,200 12,000 13,000 14,394 12,368 12,576 11,938 12,420 13,500 13,500 13,500 12,870 12,765 12,519 11,340 10,800 8,244 7,560 12,000 13,500 14,000 14,000 14,000 34,430 47,250 48,200 48,750 50,720 50,960 51,450 52,520 54,750 58,800 60,500 62,580 78,650 78,670 55,200 53,560 71,390 29,440 38,980 32,230 37,260 40,500 44,550 45,900 46,330 47,230 48,820 51,030 51,840 53,580 54,430 25,100 40,500 78,800 45,000 47,700 24,438 26,200 37.0 17.4 36.3 37.0 35.0 13.7 13.4 13.4 22.0 12.5 18.9 28.0 14.5 18.6 25.0 28.0 27.0 30.4 31.1 35.2 27.2 38.6 29.9 284 37.8 24.2 29.3 24.0 35.2 30.8 22.9 40. 0(?) 42. 0(?) 26.5 26.6 31.3 60.0 55.0 COST OF POWER 293 Station water rates as low as 14 lb. per kilowatt-hour over a period of one year have been reported from stations using electric auxiliaries but rates from 17 to 20 lb. are very good and rates from 25 to 50 lb. or higher are not uncommon. Any figure between 2 and 3 lb. of coal per kilowatt- hour is good practice and there are very few reported figures below 2 lb. 90000 80000 70000 60000 W .£50000 \4 P.40000 H 30000 20000 10000 1 41 < — ! i 1 1 1 J = Load Factors 4- = Use Factors A = Eberswalde Fi 1 1' t 1 ;ures 1 \ " ■ 1 \ (J \ 6 1 ° " V \ 0c \° + \ -7 \ \°. \ c \ V ° -8 \ * \ 4 + Y \ \ D ° \ "9 V *- + ° A \ \ \ -10 \ \ s + v Sc ■__ "^ ^•^-, y = 595000 = 18000+ x ._ lb . ^13000 + Tl° -15 g — U A \ \ >^ y = - A ■-^. y = X—5 nnnn . 735000 - 8000+ x _ 5 oints have been arily Assumed -30 These P Arbitr -50% -100% Fig. 10 20 30 40 50 60 70 80 30 100 Per Cent Load Factor 186. — Relation between load factor and thermal units in fuel. per kilowatt-hour. Five pounds of coal per kilowatt-hour with very low load factor is good. Perhaps the best method of stating station economy is to give the B.t.u.'s in the coal per kilowatt-hour. This eliminates price and quality of the coal and if the load factor is stated, say 28,000 B.t.u's. per kilowatt- hour at 30 per cent, load factor, we have a very good criterion of both the design and operation of the station. This was recognized as far back as 294 ENGINEERING OF POWER PLANTS 1905 by Patchell who, in a paper in the Proceedings Institute of Electrical Engineers (London), vol. 39, 1905, gives the figures for a large number of stations. The preceding table is taken largely from Patchell's paper with other figures that have been published since that time. These values of B.t.u's. per kilowatt-hour have been plotted as ordinates against load factors as abscissas in Fig. 186. The points ob- viously cannot lie on any one curve since the stations are of all sorts and conditions, and the operators are of various degrees of skill, but the points all lie in a field of elongated curved shape and the outside limits may be sketched in with substantial accuracy. In this field all reasonable values will appear. The median curve through the length of this field corresponds to the equation (X — 5)(y — 13,000) = 665,000. It will be observed that good records lie to the left of the curve and poor records to the right. 600 S £ 500 3 10 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 .1914 Fig. 187. — Detroit Edison Co., development curves. (See Hirschfeld's paper, A.S.M.E., Dec., 1916.) This measure of efficiency, B.t.u.'s per kilowatt-hour, may be turned into thermal efficiency by dividing it into 3,410 as shown by the second scale of ordinates appearing on the figure. Of the two efficiencies B.t.u's. per kilowatt-hour appears to be the better to use from an operating standpoint since the coal is generally bought on a B.t.u. basis and the cost of 1,000 B.t.u's. in the coal is usually well known. It is well to be cautious in accepting figures published in the technical press relating to station economy. As they usually appear they are mainly defective, that is, conditions are not wholly stated. A particularly good station cost may be quoted leaving out load factor and cost of coal. Sometimes the coal cost is given as lb. per kilowatt and the fact that it is kilowatt-hours generated and not kilowatt-hours leaving the busbars is not stated. As much as 10 to 20 per cent, may be used in the station. COST OF POWER 295 The loss after leaving the feeder switches should be charged to distribu- tion, but all losses and used current in the station are not part of output. Load factors should always be yearly. It would be still better if use factors were used but this is not general practice as yet. Many cost figures leave out repairs or maintenance and make no note of it. One company bought about one-third of its output from a water- power company but the entire operation was charged to the steam and no note made of the water in the publication. In a great many cost fig- ures the time over which they are taken is not stated and many excellent figures of days or weeks run have been published without qualification. As no repairs were made in this time nor oil purchased, these items do not appear. M fioo.ooo % g 90,000 g 80,000 O-l ° 70,000 *< *£ ^ ^ 21 ,ooo,c 00 J? taP* $W 5 tets f^!\ & $P* — -r v ^ / / 500 /1903- 4^ . s 12 1903 1904 1905 1906 1907 1908 1909 1910 Fig. 190. — Development curve, Melbourne Elec. supply. 12 3 Noon 12 Fig. 191. — Load curve of maximum days, Melbourne Elec. supply. peaks of demand of train acceleration are not felt by the central-station system. Figure 187 taken from Hirshfeld's paper (A.S.M.E., December, 1916) shows the continuation of growth in its relation to population, and similar curves are given in Figs. 190, 191 and 192 for Melbourne, Australia. Curves of daily maximum loads show the variation of demand throughout the year and should be studied very carefully as much may be learned from them. Cost Curves at Variable Loads. — Dr. Klingenberg, in " Bau. Gr. Elek.," has shown a very convenient method for showing graphically the econ- omy of central stations. This is possible where it is convenient to get the actual cost at two or three ratings over a sufficient period of time to reduce errors to small dimensions. If the total cost in dollars, including fixed charges, is plotted as ordi- nates, against the load in kilowatts as abscissae, the resulting curve will be a straight line intercepting the F-axis at a fixed distance above the origin. 302 ENGINEERING OF POWER PLANTS If the cost curve be transposed, making the 7-axis the X-axis, extend the new X-axis to the right and erect upon this a daily load curve, the hourly cost can be read off directly with suitable scales at any portion of the curve. 1,000 ,.000 900,000 800,000 700,000 600,000 500.000 400,000 300,000 200 000 >&. % N^O nT „ fe 3 < Daily LoiLd K.W. Hrs. ?. 8 Fig. 192. — Curves of monthly outputs, Melbourne Elec. Supply. Fig. 193. — Coal consumption curve, Markische E. W. If the intercept of the economy curve be transferred to the F-axis below the origin and each point of the load curve be projected to the econ- omy curve and thence transferred to the fourth angle, as in Fig. 196, an 500 450 400 350 300 250 200 150 100 50 3° O O O/' Daily Load K.W. Hrs. Fig. 194. — Steam consumption curve, Markische E. W. Daily Load K.W. Hrs. Fig. 195. — Station cost curve, Markische E. W. area will result whose ordinates will be cost and from which the constant and variable costs can be scaled off for any hour of the day. If yearly records are available and a plot be made with the economy curve in the second angle and the average load of each hour of the year COST OF POWER 303 plotted in the first angle in the order of their magnitude, commencing with the maximum hour, and these two curves be combined as before in the fourth angle, a yearly cost curve will be obtained. The area under the yearly load curve in the first angle will be the output of the station in kilowatt-hours and the shape of the curve will show how much the machinery is used and to what advantage. Similar curves may be drawn for the yearly steam consumption and coal consumption. In London Engineering, Nov. 13, 1914, R. H. Parsons has shown curves of a similar character, but not so well developed, and S. A. Fletcher, in the Electric Journal, has done similar work along this line. It should be noted that the diagrams show that the smaller the use factor the greater will be the effect of the constant cost portion of the area under the curve. The full-load efficiency of the machines, which is often the criterion, will Load Curve Fig. 196. influence but little the cost of production. To obtain the most econom- ical results we must aim at the reduction of the three factors, invested capital, constant operating losses and the attendance cost. This saving is to be sought by means of correct design and arrangement, but not at the expense of quality and safety. The constant portion of the load should be carried by the most economical machines, reserving the cheaper equip- ment for the variable portion of the load. Figs. 197 and 198 give oper- ating results on this basis for one of the most interesting of central stations. On pages 66 to 73 of the same book, Dr. Klingenberg has estimated the cost and calculated the station economy for three different sizes of power plants, 1,000-kw., 5,000-kw. and 2Q,000 kw. He has worked these 304 ENGINEERING OF POWER PLANTS figures out on the basis of various use factors from 10 per cent, to the lim- iting condition, 100 per cent., and his results, which are shown in Figs. 199 and 200, are very interesting. These curves are analogous to the economy curve for steam engines, given so long ago by Emery. Yearly Load Curve Total Yearly Steam. Consumption Fig. 197. S .o o ^2 '11 20 8 M 19 is 17 16 1.50 1.00 P- 0.50 a 50000 ^. ^^-»£ iiL£ons_ miption B.T. & a o \% ump d o O ^atCon sumption 20000 S 09 o \<^ E 8 6 w 0.1 0.2 0.3 0.4 0.5 Use Factor Fig. 198. — Economical results Eberswalde Station, Markische E. W. In "Bau. Gr. Elek." he has given figures regarding the Eberswalde plant of the Markischer Elektrizitatswerke. This plant, illustrated in Figs. 96 and 160, had 7,400 kw. installed in 1,500-r.p.m. turbines at that COST OF POWER 305 time and cost $393,000 including $7,150 for land and bulkhead work. This is the cheapest central station reported and is a fine example of clever design, being well suited to the work expected of it. The cost per kilowatt installed is $53 and the fixed charges at 12 per cent, are $47,100 or $6.36 per kilowatt. Very careful records were kept for the 3-year period which the figures cover and the following table indicates first-class results following careful design and good operation. Use factor, per cent. Coal, lb. per kw.-hr. B.t.u.'s per kw.-hr. Lb. water evaporated per lb. coal Station water rate Operating cost Fixed charges, 12 per cent. Total station cost 10 3.24 41,200 6.72 21.76 0.794 0.726 1.520 20 2.495 31,700 7.47 18.66 0.590 0.363 0.953 30 2.247 28,533 7.83 17.63 0.523 0.242 0.765 40 2.133 26,950 8.05 17.11 0.490 0.181 0.671 50 2.048 26,000 8.20 16.80 0.466 0.145 0.611 Economizers are used in this station but no heaters. The auxiliaries are electrically driven with the exception of the feed pumps and condenser pumps which are driven by small steam turbines. Table 1. — Klingenberg's Estimate No. Items Power plants A = 20,000 kw. B = 5,000 kw. \ C = 1 ,000 k w. 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Boiler eff. full load including power for draft, chain grates and feed pumps, % No-load boiler consumption in per cent, full load Boiler, % Auxiliaries, % Feed pumps, % Total, % Heat drop in turb. and cond. (185#-197° S.H.) B.t.u./# Steam at full load including excit. and aux., #/kw.-hr Heat equiv. of 1 kw.-hr., B.t.u Eff. of turb. = item 5 -5- (item 3 X item 4) , % No-load cons, per cent, full-load consumption, % Live-steam piping surface, sq. ft Heat loss, B.t.u./sq. ft./hr Eff. of piping excl. of throttle loss, % Power cons, (light.etc, in station) in % full load, % Installation cost per kw., $ Water, etc., per kw. year, $ Wages per kw. year, $ Repairs per kw. year (1 % station cost), $ Interest & renewals per kw. year (12 % sta. cost) $ Heating value of coal, B.t.u./#, Cost of coal delivered to boiler per ton (2,000 jf) . . Cost per million B.t.u., $ 20 78 9.00 1.50 0.50 11.00 1,240 12.8 3,415 21.5 10.0 1,940 368 99.8 0.5 35.70 0.07 0.70 0.36 4.28 13,500 3.24 0.12 76 9.75 1.50 0.50 11.75 1,240 14.3 3,415 19.1 12.5 1,400 368 99.7 0.75 47.60 0.10 1.00 0.48 5.71 13,500 3.24 0.12 75 10.00 1.50 0.50 12; 00 1,240 16.5 3,415 16.6 15.0 1,076 368 99.6 1 71 0.14 1.43 0.73 8.56 13,500 3.24 0.12 00 10 306 ENGINEERING OF POWER PLANTS Table 2 Items Heat consumption of plants at full load No. A = 20,000 kw. B = 5,000 kw. C = 1,000 kw. Con- stant part Vari- able part Total Con- stant part Vari- able part Total Con- stant part Vari able part Total 20 Boiler (1-2) Received 11.00 89.00 100.00 78.00 11.75 88.25 100.00 76.00 12.00 88.00 100.00 Delivered 75.00 21 Piping (10) Received 0.16 77.84 78.00 77.84 0.23 75.77 76.00 75.77 0.30 74.70 75.00 Delivered 74.70 22 Turbine (6-7) Received 7.78 70.06 77.84 16.70 9.45 66.32 75.77 14.50 11.20 63.50 74.70 Delivered 12.40 23 Light and power Received 0.08 16.62 16.70 16.62 0.11 14.39 14.50 14.39 0.12 12.28 12.40 Delivered 12.28 24 Total balance Received Delivered 19.02 80.98 100.00 16.62 21.54 78.46 100.00 14.39 23.62 76.38 100.00 12.38 25 Total balance per kw.-hr. full load Delivered, B.t.u 3,900 16,600 20,500 •3,415 5,150 18,600 23,750 3,415 6,580 21,220 27,800 3,415 26 Coal per kw.-hr., § 0.29 1.23 1.52 0.38 1.38 1.76 0.49 1.57 2.06 Table 3 Items Operating cost in cents per kw.-hr. at full load No. A = 20,000 kw. B = 5,000 kw. C = 1,000 kw. Constant part Variable part Total Constant part Variable part Total Constant part Variable tpart Total 27 28 29 30 31 Coal (19-25) . . Water (13) Repairs Interest and renewals Total 0.047 0.001 0.008 0.004 0.049 0.109 0.199 0.199 0.246 0.001 0.008 0.004 0.049 0.308 0.062 0.001 0.011 0.005 0.065 0.144 0.223 0.223 0.285 0.001 0.011 0.005 0.065 0.367 0.079 0.002 0.016 0.008 0.098 0.203 0.255 0.255 0.334 0.002 0.016 0.008 0.098 0.458 COST OF POWER 307 Table 4 Units Symbol Power plant Items A 20,000 kw. B 5,000 kw. C 1,000 kw. Heat consumption at no load (25 1 ) Additional heat consumption (25) Operatingcost withoutcoal (32) (27) Cost of coal (19) B.t.u. per kw.-hr. B.t.u. per kw.-hr. Cents per kw.-hr. Cents per mill B.t.u. b w c g 3,900 16,600 0.062 12 5,150 18,600 0.082 12 6,580 21,220 0.124 12 Table 5 No. Items Units Power plant A = 20,000 kw. B = 5,000 kw. C = 1,000 kw. Momentary heat con- sumption, B.t.u. /kw.-hr. Wt = 3,900— +16,600 TO W t = 5,150— + 18,600 TO Wt = 6,580— + 21,220 TO Average yearly heat con- sumption, B.t.u. /kw.-hr. W m = 3,900-/ +16,600 n W m = 5,150-/+ 18,600 W m = 6,580-/+ 2 1.220 n If (/ = 1), B.t.u./kw.-hr. W m i = 3,900- +16,600 n W m i = 5, 150- + 18,600 n TF m i = 6,580- + 21,220 n If (/ = «), B.t.u./kw.-hr. W mi = 20,500 W m 2 = 23,750 W m i = 27,800 Average yearly operating cost, cents/kw.-hr tf = 0.062l + 12X ^ n 1,000,000 X = 0.082 1 +^^ Wl - n l.OpO.OOO K = 0.124i+- 12XTF * n 1,000,000 Table 6 Limit / = 1, n = m Equation #5,, Limit f — n Equation #6 Use factor B.t.u. per kw.-hr. Percentage 20,500 = 100% B.t.u. per kw.-hr. A B C A B c A B C 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 20,500 20,930 21,470 22,170 23,100 24,400 26,350 29,600 36,100 55,600 23,750 24,320 25,020 24,950 27,170 28,900 31,500 35,800 44,400 70,100 27,800 28,520 29,420 30,620 32,170 34,420 37,670 43,120 54,020 86,920 100.0 98.0 95.5 91.8 88.9 84.1 77.9 69.4 56.7 36.8 86.1 84.2 81.9 79.0 75.6 71.0 65.2 57.2 46.4 29.3 74.0 72.1 69.6 67.0 63.8 59.8 54.7 47.5 37.9 23.6 20,500 20,500 20,500 20,500 20,500 20,500 20,500 20,500 20,500 20,500 23,750 23,750 23,750 23,750 23,750 23,750 23,750 23,750 23,750 23,750 27,800 27,800 27,800 27,800 27,800 27,800 27,800 27,800 27,800 27,800 308 ENGINEERING OF POWER PLANTS Table 7 A 0.062 B 0.082 c 0.124 A 12 X W m B 12 X W m C 12 X Wm n n n 1,000,000 1,000,000 1,000,000 0.062 0.082 0.124 0.246 0.285 0.334 0.069 0.091 0.138 0.252 0.292 0.342 0.078 0.102 0.155 0.258 0.300 0.352 0.089 0.103 0.117 0.137 0.177 0.207 0.266 0.278 0.312 0.326 0.368 0.386 0.124 0.164 0.248 0.293 0.347 0.413 0.155 0.205 0.310 0.316 0.378 0.452 0.206 0.273 0.413 0.356 0.430 0.517 0.310 0.410 0.620 0.433 0.535 0.650 0.620 0.820 1.240 0.667 0.840 1.040 Table 7 (Continued) Use factor Limit / = 1 Equations 5 and 7 Power plant A 20,000 kw. cts./kw.-hr. B 5,000 kw. cts./kw.-hr. C 1,000 kw. cts./kw.-hr. Limit / = n Equations 6 and 7 Power plant A 20,000 kw. cts./kw.-hr. B 5,000 kw. cts./kw.-hr. C 1,000 kw. cts./kw.-hr. 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.308 0.321 0.336 0.357 0.381 0.417 0.471 0.562 0.743 1.287 0.370 0.385 0.406 0.431 0.463 0.514 0.586 0.706 0.948 1.660 0.458 0.480 0.507 0.545 0.593 0.661 0.762 0.930 1.270 2.280 0.308 0.315 0.324 0.335 0.349 0.370 0.401 0.452 0.556 0.866 0.369 0.379 0.390 0.408 0.425 0.452 0.493 0.564 0.703 1.105 0.458 0.472 0.489 0.511 0.541 0.582 0.644 0.747 0.954 1.574 Annual Cost of Power. — Harrington Emerson says: 1 "In China men are paid $0.01 an hour for climbing treadmills actuating stern wheels which propel river boats. These Coolies convert their stored human muscular energy into mechanical foot-pounds. From experience with treadmills in British prisons we know exactly the mechanical equivalent of hard labor. It is a climb of 8,640 ft. each 24 hr. This is the limit of human endurance for a succession of days. To convert this into horsepower we must know the man's weight and the number of hours he works each day. The average weight of man is about 150 lb. A man of this weight climbing 8,640 ft. in 24 hr. yields 1,296,000 ft.-lb. A horsepower for 24 hr. is 47,530,000 ft. -lb. It would therefore take 36.6 Chinamen to yield a continuous horsepower and the wages of these China- men would amount to $3.66 per day, or $1,336 a year. "From Niagara you can buy a horsepower year for $20. It costs the paper mills which have their own power about $12 a year for continuous horsepower. 1 Proceedings S.P.E.E., vol. 20, 1912. COST OF POWER 309 Human energy at $0.01 a day costs one hundred and ten times as much as this water-power energy, although the supervising human labor receives an average of $3 a day. "The substitution of uncarnate energy for human muscular energy has in- creased wages thirty-fold and has cheapened power to 1 per cent, of its cheapest muscular price. This is not all. When men are used as power generators the supply is strictly limited and can be easily monopolized. Uncarnate energy is 90000 85000 80000 75000 70000 5* 65000 2.4 2.2 2.0 W 1.8 1 1.4 1 1.2 a O a 1 -° 1 0.8 D 0.6 0.4 0.2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0s3 Factor For(/U) Heavy Lines For (f=n) Light Weight Lines Fig. 199. — Klingenberg's cost curves. (KjC- J3- A \c B A -c- B A ^ 60000 g 55000 p. D 50000 H n 45000 a £40000 d. | 35000 a o 30000 | 25000 20000 15000 10000 5000 °0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Use Factor For(/=l) Heavy Lines For (/=?l) Light Weight Lines Fig. 200. — Klingenberg's heat consump- tion curve. without limit as long as there is coal and oil and gas, as long as the sun shines and makes organic fuels or draws up water from the surface of the ocean. "For strictly limited horsepower at $1,336 a year we now have unlimited horse- power at a minimum price of $12." Although the cost of a horsepower varies greatly with local conditions and with the cost of fuel, water, labor and supplies yet a fair idea of the average cost may be obtained from the following tables prepared by different students of power costs. 310 ENGINEERING OF POWER PLANTS Yearly Costs of Steam Power, 308 Days, 10 Hr. per Day, Simple Non-con- densing Engine Table A. — Engine and Boiler Combined 1. Horsepower of engine 2. Total coal consumption in pounds per horse- power-hour 3. Cost of plant per horsepower 4. Fixed charges on plant at 11 per cent 3 5. Cost of coal at $5 per long ton i 6. Attendance i 7. Oil, waste and supplies S 8. Total yearly cost, coal at $5 per ton i 9. Total yearly cost, coal at $4 per ton i 10. Total yearly cost, coal at $3 per ton i 11. Yearly cost per horsepower, coal at $5 per ton. $ 12. Yearly cost per horsepower, coal at $4 per ton J 13. Yearly cost per horsepower, coal at $3 per ton . 5 13.0 200 . 00 44.00 180.00 99.00 13.20 336.00 300.00 265.00 168.00 152.00 132.00 10 152 50 215 109 14 388 345 300 130 116 102 .50 8 .00J133 .00 58 .00(233 .00 116 .30 15 00J424, ,00385, ,00 340, ,00 106, 00 95, ,00 83, 6 7 110 72, 325 136, 17, 8 550.00 495 430 92 81 72, 7, 89, 78, 420, 154, 20, 672, 610. 530. 84. 76. 66. 10 7, 83, 91, 510, 173, 22. 796. 720. 630. 79. 72. 63. 12 7.25 78.00 102.00 00 600.00 00 184.00 00 23.80 00910.00 00810.00 00 710.00 76.00 68.00 59.00 Table B. — Engine and Boiler — Independent 1. Horsepower of engine 10 12 14 15 20 2. Total :o; 1 consumption in pounds per horse- power-hour 7.40 10.00 7.25 194.00 7.00 182.00 6.50 174.00 6.00 3. Cost of plant per horsepower ....$ 153.00 4. Fixed charges on plant at 11 per cent ....$ 230.00 255 . 00 280.00 285 . 00 337.00 5. Cost of coal at $5 per long ton .....$ 510.00 600 . 00 675.00 690 . 00 830 . 00 6. Attendance ..-.'.$ 173.00 184.00 194.00 202.00 230.00 7. Oil, waste and supplies ....$ 22.00 23.80 25.80 26.50 31.20 8. Total yearly cost, coal at $5 per ton . ...9 935.00 1,063.00 1,175.00 1,203.00 1,428.00 9. Total yearly cost, coal at $4 per ton . , . .$ 840.00 960.00 1,050.00 1,080.00 1,260.00 10. Total yearly cost, coal at $3 per ton . . . . s 740.00 830.00 920.00 950.00 1,100.00 11. Yearly cost per horsepower, coal at $5 per ton.S 93.50 88.00 83.00 80.00 71.00 12. Yearly cost per horsepower, coal at $4 per ton.S 84.00 79.00 74.00 72.00 64.00 13. Yearly cost per horsepower, coal at $3 per ton.S 74.00 68.00 64.00 62.00 56.00 Table B (Continued) 1. Horsepower of engine 2. Total coal consumption in pounds per horsepower-hour . . 3. Cost of plant per horsepower 4. Fixed charges on plant at 11 per cent 5. Cost of coal at $5 per long ton 6. Attendance 7. Oil, waste and supplies 8. Total yearly cost, coal at $5 per ton 9. Total yearly cost, coal at $4 per ton 10. Total yearly cost, coal at $3 per ton 11. Yearly cost per horsepower, coal at $5 per ton 12. Yearly cost per horsepower, coal at $4 per ton 13. Yearly cost per horsepower, coal at $3 per ton 30 5.50 126.00 415.00 1,100.00 287.00 41.50 18.43 1,660.00 1,450.00 60.00 54.00 47.00 40 4.75 107.00 475.00 1,310.00 338.00 51.00 2,194.00 1,960.00 1,710 00 55.00 49.00 42.00 50 4.50 96.00 525.00 1,540.00 390 . 00 61.50 2,516.00 2,250.00 1,960.00 50.00 45.00 39.00 75 4.00 79.00 650.00 2,050.00 520.00 86.00 3,306.00 3,000.00 2,650.00 44.00 39.00 34.00 COST OF POWER 311 Table C 10 12 14 15 20 2. Total coal per horsepower per hour, pounds 7.00 6.75 8.50 6.00 5.50 3. Cost of plant per horsepower $ 220 . 00 204.00 192.00 186.00 163.00 4. Fixed charges on plant at 11 per cent $ 242.00 270.00 295.00 307.00 360.00 5. Cost of coal at $5 per long ton $ 480.00 560.00 625.00 670.00 750.00 178.00 190.00 202.00 210.00 238.00 7. Oil, waste and supplies $ 22.80 24.80 26.70 27.60 32 . 50 8. Total yearly cost, coal at $5 per ton $ 923.00 1,045.00 1,149.00 1,215.00 1,380.00 9. Total yearly cost, coal at $4 per ton $ 830.00 940.00 1,030.00 1,100.00 1,240.00 10. Total yearly cost, coal at $3 per ton $ 730.00 820.00 900.00 960 . 00 1,080.00 11. Yearly cost per horsepower, coal at $5 per ton. . $ 92.30 87.00 82.00 80.00 69.00 12. Yearly cost per horsepower, coal at $4 per ton. . $ 83.00 78.00 74.00 72.00 62.00 13. Yearly cost per horsepower, coal at $3 per ton. . $ 73.00 68.00 65.00 63.00 54.00 Table C (Continued) 1. Horsepower of engine 2. Total coal per horsepower per hour, pounds. . . 3. Cost of plant per horsepower 4. Fixed charges on plant at 11 per cent 5. Cost of coal at $5 per long ton 6. Attendance 7. Oil, waste and supplies 8. Total yearly cost, coal at $5 per ton 9. Total yearly cost, coal at $4 per ton 10. Total yearly cost, coal at $3 per ton 11. Yearly cost per horsepower, coal at $5 per ton . 12. Yearly cost per horsepower, coal at $4 per ton. 13. Yearly cost per horsepower, coal at $3 per ton. 30 5.25 134.00 440.00 1,040.00 297.00 43.00 1,720.00 1,550.00 1,360.00 57.00 51.00 44.50 40 4.75 120.00 530.00 1,310.00 350.00 53.00 2,243.00 2,020.00 1,770.00 56.00 50.00 43.50 50 4.25 108.00 590.00 1,470.00 405.00 64.00 2,529.00 2,270.00 2,010.00 51.00 46.00 40.00 75 3.70 93.00 765.00 1,910.00 535.00 89.00 3,299.00 2,961.00 2,600.00 44.00 39.40 34.50 100 3.50 81.00 890.00 2,420.00 760.00 114.00 4,094.00 3,700.00 3,250.00 41.00 37.00 32.50 Yearly Cost of Steam Power, 308 Days, 10 Hr. per Day, Compound Condensing Engine Table D 1. Horsepower of engine 2. Total coal per horsepower-hour, pounds 3 Cost of plant per horsepower 4. Fixed charges on plant at 11 per cent 5. Cost of coal at $5 per long ton 6. Attendance 7. Oil, waste and supplies 8. Total yearly cost, coal at $5 per ton 9. Total yearly cost, coal at $4 per ton 10. Total yearly cost, coal at $3 per ton 11. Yearly cost per horsepower, coal at $5 per ton 12. Yearly cost per horsepower, coal at $4 per ton 13. Yearly cost per horsepower, coal at $3 per ton 100 2.75 105.00 ,160.00 ,910.00 880 . 00 143.00 ,198.00 ,780.00 ,300.00 42.20 37.80 33.20 200 2.45 93.30 2,060.00 3,370.00 1,220.00 205.00 6.948.00 6,200.00 5,400.00 35.10 31.50 27.70 300 2.40 86.40 2,850.00 5,100.00 1,220.00 240.00 9,496.00 8,550.00 7,500.00 31.50 28.40 25.00 400 2.35 76.20 3,350.00 6,700.00 1,760.00 285.00 12,171.00 11,000.00 9,700.00 30.50 27.00 23.80 312 ENGINEERING OF POWER PLANTS Table D (Continued) 1. Horsepower of engine 2. Total coal per horsepower-hour, pounds 3. Cost of plant per horsepower $ 4. Fixed charges on plant at 11 per cent $ 5. Cost of coal at $5 per long ton $ 6. Attendance $ 7. Oil, waste and supplies $ 8. Total yearly cost, coal at $5 per ton $ 9. Total yearly cost, coal at $4 per ton $ 10. Total yearly cost, coal at $3 per ton $ 11. Yearly cost per horsepower, coal at $5 per ton . $ 12. Yearly cost per horsepower, coal at $4 per ton . . $ 13. Yearly cost per horsepower, coal at $3 per ton . . $ 500 2.30 71.20 3,920.00 8,380.00 1,930.00 315.00 14,596.00 13,200.00 11,500.00 29.20 26.10 23.00 600 2.25 67.30 4,451.00 9,650.00 2,100.00 350.00 16,818.00 15,700.00 13,200.00 27.70 24.90 21.90 700 2.20 64.40 4,952.00 11,000.00 2,650.00 385.00 19,050.00 17,200.00 15,200.00 27.30 24.60 21.50 800 2.16 62.20 5,492.00 12,500.00 2,700.00 420 . 00 21,674.00 19,500.00 17,100.00 26.10 23.50 20.60 Table D (Continued) 1. Horsepower of engine 2. Total coal per horsepower-hour, pounds 3. Cost of plant per horsepower 4. Fixed charges on plant at 11 per cent 5. Cost of coal at $5 per long ton 6. Attendance 7. Oil, waste and supplies 8. Total yearly cost, coal at $5 per ton 9. Total yearly cost, coal at $4 per ton 10. Total yearly cost, coal at $3 per ton 11. Yearly cost per horsepower, coal at $5 per ton. 12. Yearly cost per horsepower, coal at $4 per ton, 13. Yearly cost per horsepower, coal at $3 per ton, 900 2.10 59.30 5,910.00 14,300.00 2,930.00 445.00 23,644.00 21,200.00 18,500.00 25.20 22.60 19.90 1,000 2.00 55.70 6,130.00 14,500.00 3,480.00 470.00 24,595.00 22,200.00 19,500.00 24.50 22.00 19.40 1,500 1.80 54.40 9,000.00 18,600.00 4,400.00 600.00 35,100.00 31,500.00 27,500.00 23.50 20.30 17.90 2,000 1.75 53.20 11,880.00 24,200.00 5,200.00 685.00 42,018.00 37,800.00 33,000.00 21.00 18.90 16.60 Another estimate is presented in Table "E." pared by Mr. Webber in 1903. This table was pre- Cost of Steam Power per Indicated Horsepower of 3,080 Hr. Table E 1. Horsepower of plant 2. Total plant per i.hp. including buildings . 3. Fixed charges, 14 per cent 4. Coal per hp.-hr., lb 5. Cost of coal at $4 6. Attendance 7. Oil, waste and supplies 8. Total with $4 coal 9. Total with $2 coal 100 $170.00 23.80 7.00 38.50 12.00 2.40 200 $146.00 24.40 6.00 35.70 10.00 2.00 300 $126.00 17.65 6.00 33.00 8.60 1.72 400 L10.00 15.40 5.50 32.00 7.25 1.45 500 $96.00 13.45 5.00 27.50 6.20 1.24 600 $85.00 11.90 4.50 24.70 5.40 1.08 76.70 57.45 68.10 50.25 60.97 44.47 56.10 40.10 48.39 34.64 43.08 30.73 COST OF POWER 313 Table E (Continued) Horsepower of plant Total plant per i.hp. including buildings Fixed charges, 14 per cent Coal per hp.-hr., lb Cost of coal at $4 Attendance Oil, waste and supplies Total with $4 coal Total with $2 coal 700 $76.00 10.65 4.00 22.00 4.70 0.94 800 $69.00 9.65 3.50 19.20 4.15 0.83 900 $64.00 8.95 3.00 16.50 3.75 0.75 1,000 $60.00 8.40 2.50 13.75 3.50 0.70 1,500 $58.00 8.12 2.00 11.00 3.25 0.65 2,000 $56.00 7.85 1.50 8.25 3.00 0.60 38.29 27.29 33.83 24.23 29.95 21.75 26.35 19.47 23.02 17.52 19.75 15.50 $60 per horsepower-year at the machine is a common assumption where steam is the motive power. !!>eu $70 $60 $50 " $40 $?0 $?0 10 20 30 40 50 60 Horse-power 70 80 90 $4. 100 Fig. 201. — Cost of producing a horsepower-year of 3080 hours with simple non- condensing stationary engines with coal at $3.00, $4.00 and $5.00 per long ton. $80 $70 $60 $50 $40 $30 «<>n 10 20 30 40 50 60 Horse-power 70 80 90 100 Fig. 202. — Cost of producing a horsepower-year of 3080 hours with simple condensing engines with coal at $3.00, $4.00 and $5.00 per long ton. The accompanying diagrams show other estimates of the yearly cost of producing steam power under various conditions and costs of coal when 314 ENGINEERING OF POWER PLANTS running 10 hr. a day for 6 days a week with fairly steady load. They are intended to show the expense of running under everyday conditions on such a plant as a prudent man would install with ordinary skill. Cost of 24-hr. power for 365 days per year is about 2.2 times the cost for 10-hr. power for 308 days. 900 1100 Horse -power Fig. 203. — Cost of producing a horsepower-year of 3080 hours with compound con- densing engines with coal at $3.00, $4.00 and $5.00 per long ton. Cost of 24-hr. power for variable load cannot be stated without know- ing all conditions. For varying load, usually add about 20 per cent, to coal consumption required for steady load. CHAPTER XV HINTS ON STEAM PLANT OPERATION The following hints regarding the operation of steam power plants are given with the idea that they may be of service to the young engineer dur- ing the trials and tribulations that come with early responsibility. The operation or running of steam power plants with the accumulated experience of more than a century and a half might seem to most any one who has not been in the actual working to be a very simple problem, which throughout the last century at least had been standardized and was well understood. Indeed by talking to many operators whose duty it is to run steam plants, he would be sure that the last word had been said and that there was nothing to learn from further study. When one commences to investigate these plants from which such rose-colored re- ports are received and to note down and compare the figures, he will find discrepancies of a very serious nature, loop holes that are very wide indeed and he will soon find that his information is largely a matter of guesswork. If the investigator is an engineer, his scientific training will show him that the reported results are impossible and in searching around for the reasons he will find that his informant either is ignorant of the proper methods to apply and thus fooling himself with incorrect results, or he is simply hiding his own lack of knowledge by giving results he knows are not true. The man who reports a horsepower-hour on 1 lb. of coal or an evapora- tion of 14 lb. of water per pound of coal, is in the class with the man who sprinkles a small amount of some chemical on ashes and reports that he gets more heat from the ashes than from an equal amount of good coal. This same man is likely to tell you his furnace temperature is 3,200° and his flue gases 200°. The object of a power plant is to furnish power. When a power plant fulfills its purposes it must furnish power when it is wanted and in such quantities as wanted. It must be so run that power must be available whenever it is needed, that is, continuity of operation is essential and finally it must make and deliver power at as low a cost as is consistent with the circumstances of its design and location. To fulfill the above conditions the operator must study the plant as a whole and in detail with reference to the following: 1. The plant must be studied to discover its strong points and weak- nesses, that is, how well the designer has attacked the problem. What 315 316 ENGINEERING OF POWER PLANTS has he forgotten or left out and how can the omissions be corrected? What particular parts cost more than the return from them warrants? 2. Each piece of machinery must be gone over and a proper under- standing obtained of what may be expected of it. Is it fitted for the work it has to do? What would it cost to replace it with the best machine of its kind? Does it pay to run it? How should it be run to get the best results? 3. Fuel, being the largest single item in station cost, should receive the most careful study. A study of the fuel supply of the district is most profitable and may show that you can obtain a better and cheaper supply of fuel without difficulty. Look into the methods of shipping and marketing the coal. It may be possible to buy the same coal in a different way to better advantage. How much water does the coal contain when delivered and what do you pay for the water? Look into the methods of storing, does the water evaporate or increase in the storage? Every pound of water evaporated from the coal in the furnace costs nearly as much to evaporate as if it were in the boiler and it is then wasted. Are the coal-handling arrange- ments bad or good? Sometimes conveyors cost more than coal handling with a horse and cart, or even a few sections of industrial railway. The percentage of refuse is important as well as the combustible in the ash. If the refuse is more than a few per cent, more than the ash content, something is wrong with the grates or with the firing. If the combustible in the ash is high, over 50 per cent., the firing is bad or the cleaning of the fires has not been done properly. Be careful that your samples are average samples. Many incorrect results are due to imperfect sampling. Watch the combustion and air supply. Carbonic-acid determinations from beyond the bridge-wall and in the flue should be regularly made. The apparatus is simple and cheap and when carefully made the results are valuable. The results will not be absolute, however, but comparable. For accurate results, very careful sampling and analysis are required and these are not usually obtainable except in plants of the maximum size where one man is trained to do only this work. It is quite difficult for anyone to duplicate results. 4. Feed Water. — Is it pure or a good boiler water? A good boiler water is not necessarily pure. In fact pure water is too good a solvent and is not desirable. Is boiler compound needed? Do you buy patent medicine? The usual patented compounds are 50 cts. worth of lime and soda ash dissolved in a barrel of water and sold for 30 to 60 cts. per gallon. Learn what the scaling salts are and how they occur in the boiler water; and use the least amount of soda ash and lime that will soften the water. A little scale is not a bad thing. How much water do you blow off in the blowoff system? How much from the safety valves. What is the HINTS ON STEAM PLANT OPERATION 317 leakage loss in the pipe system. Is there another source of feed water and how much does it cost? Are your water meters correct? Do they run fast on light loads? A known plant paid 40 per cent, more for water than it should, due to incorrect meters, so check them against weighing devices or a meter of the Venturi type once in a while. Are the steam pipes covered? What do you lose by condensation in the pipes? Are your drips thrown away or do they leak away? All clean drips should go to the boilers and there should be few dirty drips. 5. Oil. — How do you lubricate the machinery in the plant? If you have an oil system, is it working well? How much oil do you use? How is it purchased? How do you check up the quality of the oil? Some operators buy on a kilowatt-hour basis. Other operators buy by the gallon or barrel. Do you use compounded oil? You will hear some operators claim that cylinder oil will not lubricate unless it contains a certain proportion of tallow — say 10 or 12 per cent. This is fallacious but it dies hard. Do you oil through the carrying action of the incoming steam or do you feed the oil drop by drop where it is needed and when it is needed? How much care is exercised in saving oil? Waste and Supplies. — How much waste do you use and how do you handle it? Will washable towels be better and cheaper than waste? Can you save oil that way? How do you look after packing gaskets and pump valves? Pump valves make good rubber heels. Do any of yours go that way? What small supplies do you keep and how are they issued and accounted for? 6. Maintenance. — In this particular item the operating man may save or lose quite a little money. Boilers must be cleaned, engines must be overhauled, pumps must be packed and valves replaced. Condensers must be cleaned and tubes replaced. If oil is present in the condensate the steam side of condensers should be boiled out with a soda solution occasionally. The dust must be blown out of electrical machinery. Dust and dirt must be kept out of everything and heat should be saved everywhere. Regular schedules of overhauling help, and if the work can be done between times, with the regular force, a saving will be made. How do you handle extraordinary repairs? 7. Labor. — Is your organization good or are you suffering from dead- wood, dry rot, soldiering or incompetency. How do you run your force — on the team work principle or individual plan ? Are your men ambitious for more work and responsibility or for more pay? Are they real me- chanics or just workmen? Do they take pride in their work? Finally. — Do you know the efficiency of your plant? Are you run- ning on 8 lb. of coal per kilowatt-hour, or on, say, 2.5 lb. or better yet, do you turn out a kilowatt-hour for 35,000 B.t.u. in the fuel or 50,000 B.t.u., or even higher? Do you know your station water rate? Is it 318 ENGINEERING OF POWER PLANTS 20 lb. or 40 lb., and how accurately do you know it? What is your aver- age boiler efficiency over a year, coal against water? What is your bank- ing loss? Do you know your load factor and use factor? Can you by changing the use of your units improve your station economy? Which engine uses the most steam and which the least? Are the economy curves flat or deeply hollow? Do you know your costs? Who keeps them and are they kept accurately? Do you know what each piece of apparatus costs per year to keep it in good working operation? Costs are illusive and the operating man should look after them very carefully. How are your gages, thermometers and meters? Where and how were they rated? Do you keep standards to use for comparison? Are your valves tight? Do you keep the stems packed and what leakage do you have? Do you ever weigh your coal? How much does it lose in weight in the bunker? Do you wet down your coal? CHAPTER XVI POWER TRANSMISSION Shafting and Belting. — The oldest and most common method of trans- mitting power from the engine to the consumer is by means of shafting, gearing and belting. Until within 25 years hardly any other method was considered except in special cases. Chief Objection to this System. — The two chief objections to this system are its friction losses and its lack of adaptability. Experiments made by various engineers have shown losses between engine and machine in ordinary machine shops of from 50 to 60 per cent, of the total power transmitted by the engine. This loss is greatest in shops where large machines are employed, located at some distance from each other and it is here that other kinds of transmission can be used to advantage. Two incidental objections to shafting and belting are dirt and interference with proper lighting. These are objections of considerable importance in some shops as dirt and dust from the processes of manufacture are kept stirred up by the moving belts, often causing inconvenience to the work- men, and dark shops are not only objectionable from general standpoints but may lead to accidents. Cost of Shafting and Belting. — The cost of shafting, including the necessary hangers, couplings and pulleys will vary according to size be- tween $2 and $6 per linear foot. A rough rule which may be used in preliminary work is to allow $1 per linear foot per inch of diameter. The cost of belts will vary from $5 to $50 for such widths and lengths as are used in ordinary shop practice. The discount on all kinds of belt- ing usually ranges from 50 to 70 per cent, of the list price. Rope Driving. — Ropes may take the place of belts in special cases, but cannot be said, in any sense, to have replaced them for ordinary use. Manila and cotton ropes are sometimes used for main drives to connect the engine with the head shaft, and less frequently for distributing the power to the different floors. It may be said in general that the first cost of ropes is less than of belts, but that they wear out much faster, are more difficult to splice, and are less efficient. They are sometimes valuable for carrying power at different angles. Wire ropes have been used to a considerable extent in the past for carrying power comparatively long distances, especially in places exposed 319 320 ENGINEERING OF POWER PLANTS to the weather, but electricity has almost entirely supplanted them. The initial cost of a wire-rope transmission for distances from 300 to 1,000 ft. is very small, and the running expense is no greater than that of electricity but the rope drive is much more limited in its application. Steam Transmission. — Where the area covered by an establishment is Large it is often more economical to have a central boiler house and to transmit high-pressure steam to the various buildings, there to be used for both power and heating. The loss in transmission, although heavy, is probably much less than for shafting and belting if the pipes arc of proper size and properly insulated. Efficiency of Transmission. — Rather extravagant claims have been made as to the advantage of electricity over shafting and belting in the matter of efficiency. Experiments on several group installations in machine shops have shown a loss of from 40 to 60 per cent, of the total power of the engine before reaching the machine, as previously pointed out. These losses are due partly to the shafting and belting and would be reduced with independent motors. Direct tests on 16 large machines driven by independent motors in a locomotive works showed an average of 8.85 hp. for the machine and its work and 2.35 hp. for the power consumed by the motor and countershaft. This means an effi- ciency of Less than (SO per cent, for the motors, not counting the losses in the generator and transmission lines. On the other hand, it may be said that although the friction losses in shafting and belting remain nearly constant at all loads, the electrical losses will diminish as the load falls off. The following sections relating to "Electric Drive 4 Versus Shafting and Belting" have been thoroughly revised and brought down to date by ( 5. E. Clewell, Assistant Professor of Electrical Engineering at the University of Pennsylvania, whose articles in American Machinist (1914-15) relating to this subject are well known. Electric Drive Versus Shafting and Belting. — The main advantages of the electric drive are included under the heads of " Location of Machines," "Head Room," "Centralized Power," "Reliability," and the "Ability to Study Machine Performance." 1 Flexibility in the location of machinery with electric drive has come to be an acknowledged advantage in machine-shop work and particularly in the use of portable tools. The clear head room resulting from the use of individual motor-driven machines and the eliminating of overhead belting, adapts manufacturing spaces to improved lighting and venti- lating conditions, and to more effective crane service, since the interfer- ence of overhead belts often dictates just what portions of a shop may be served by the crane and which may not. Furthermore, a centralized 1 "American Handbook for Electrical Engineers," John Wiley and Sons, New York, p. 972. POWER TRANSMISSION 321 power station is made possible through the medium of electric power distribution, thus making changes and extensions of the plant practically independent of the power supply. Under reliability, it follows that the breakdown of a single motor which is individually connected to its own machine tool, affects the operation of that machine only, whereas a break- down in the belting or shafting of a line-shaft drive, often causes interrup- tion for a larger group of machinery. The study of machine performance which is a valuable accompani- ment to improved production methods, and to the application of so-called "scientific management" to machinery practice, has practically been made possible for the first time, through the use of the recording and graphic electric meters which may be used in conjunction with indi- vidually motor-driven machinery. This feature of electric drive is be- ginning to be recognized as one of its most important advantages. Methods of Motor Drive. — These may be classified as individual and as group drives. In the former, each machine is fitted with its own motor, either driven directly or through a countershaft, and there is an entire absence of overhead belts. This system is particularly applicable to shops having large machines located some distance apart and perhaps varying in character. It is necessary, however, in such cases to control the speed of the machine directly through the speed control of the motor, and this may be done by any one of the various methods of motor speed control. Ranges of speeds of 4 to 1 are common, but in some special cases speed ranges as high as 10 to 1 are available for motor drive. In the group method, several machines are arranged in a group and are driven by a short line shaft which is driven in turn by a motor. This makes it possible to use a constant-speed motor because the speed adjust- ments of the machine tool are effected in the ordinary manner through the medium of cone pulleys or gears. The size of the motor may also be smaller than that of the motors used for the corresponding machine tools with the method of individual motor drive, on account of the diversity factor of the group of machines. On the other hand, with the group method of driving, the overhead belts are only partially done away with, and there is not that freedom of arrangement which makes the individual method of driving so desirable. It is also necessary in this connection to distinguish between the use of direct- and alternating-current motors. In general, individual motor drives necessitate direct-current motors, because of their adaptability to flexible speed control, while in the group method either direct- or alternating-current motors may be used since the motor under this con- dition may usually be of the constant-speed type. The choice of direct or alternating current for machine-shop drives depends also to some extent upon whether there is a possibility or likeli- 21 322 ENGINEERING OF POWER PLANTS hood of throwing over, at certain times, to an outside power company's circuits. If the ready-to-serve charge is not too great, the alternating- current distribution from this one standpoint may be best, because the alternating current which is usually employed by the large central power stations, could thus be relied upon at certain times. In the case of an individual shop power plant in which the amount of power required by the shop is large and there is no public service corpora- tion to rely upon in the neighborhood, the question of direct or alternating current is partly dependent on the area covered by the plant, and partly dependent on the need for adjustable-speed motors. Alternating current is satisfactory both for small and for large plants from the viewpoint of distribution, but from this same viewpoint, direct current is hardly suit- able for a plant extending over a considerable area, because of the large drop in voltage due to the long lines required and the relatively low supply voltages usually employed with direct-current systems of distribution. Adjustable-speed motors, however, are mainly of the direct-current type, and where their use is essential, it may be found desirable to employ alternating current for the main distribution circuits, and to transform from alternating to direct current by rotary converters or motor-generator sets, to meet the need of a source of direct current for motors of this type. In some plants, therefore, circuits of both types will be found, those of the alternating-current type being depended upon for lighting, and con- stant-speed motors, and those of the direct-current type supplying the adjustable-speed motors and sometimes certain electric lamps which are operative only on direct-current circuits. Some years ago a great deal of discussion took place about the possi- bility of adjustable-speed motors for the various forms of machine-tool drive. Motors of this type are now available and are widely used. Machine-tool builders, who in the past have found it necessary to design their tools so as to get speed changes mechanically, now in many cases find it desirable to adapt the design of their machines for operation by individual electric motors. The amount of power drawn for any given tool varies usually over a wide range, and a motor should be put on an individual tool which can take care of the largest load that the tool is apt to require, although its rated capacity need not be determined by this maximum demand on account of the liberal overloads which modern motors can develop for short intervals without excessive heating. In general, if a number of tools are grouped together, a motor that is appreciably smaller than the sum of the individual horsepower capacities required on the different tools may be installed. This is illustrated by the fact that even in the case of the group drive, the actual power drawn from the generator may be less than the total rated capacity of the motors connected to the gener- POWER TRANSMISSION 323 ator. It must be remembered, however, that the power required to drive a machine tool is very small in proportion to the total cost of production chargeable to that tool, and hence other advantages of the individual motor drive may entirely offset the small gain in reduced motor size when the group method is employed in contrast to the individual method of drive. In the installation of all motors, because of low efficiency at low loads, care should be taken that motors not too large for the work are chosen. With alternating-current motors, the fractional loads are also accom- panied by low power factor; hence for this additional reason it is better to operate an alternating-current motor at or near its full rated capacity rather than at a load much below normal for a large part of its operation. To summarize the matter of group versus individual methods of drive, it may be stated that there is still much difference of opinion regard- ing their relative advantages, although these differences of opinion are not so marked as was the case 10 years ago. Both methods are quite widely used, and each individual case requires careful study before an intelligent decision can be reached as to the actual merits of each method. In many cases both methods of driving will be found in the same plant. Three items 1 stand out as most important in this question: (a) the influence of the character of the load; (6) the influence of speed; and (c) the influence of relative cost. Under (a) there is a general acceptance of the conclusion that where machines are operated intermittently, the method of individual drive is to be preferred. With the group method, the total load is made up partly of friction and other mechanical losses which go on continuously, and partly by the demand of the machine tools themselves when working. If, therefore, the load factor of the machines is low, the friction losses form a larger percentage of the total power consumed, and the group system thus becomes less efficient than where the machine load factor is high. Under (6) the wide range and fine gradations of speed with an indi- vidual adjustable-speed motor give it a decided advantage in the matter of speeds over the group or line-shaft drive. The modern interpole, ad- justable-speed motor possesses excellent commutation characteristics both at heavy and at light loads for a wide range of speeds, thus overcom- ing one of the larger difficulties in earlier types. Under (c) it may be said that the choice between individual and group drives is essentially one of relative cost. While the first cost of the motor equipment for individual driving is greater than the cost of the motor equipment for group driving, the economic returns through increased production by the use of indi- vidual motors may actually offset the higher first cost in a relatively short 1 "American Handbook for Electrical Engineers," John Wiley and Sons, New York, p. 973. 324 ENGINEERING OF POWER PLANTS time interval. Moreover, what may be termed secondary advantages, such as a more open shop space, better illumination and ventilation, and improved crane service, all form additional advantages in favor of the individual drive, which, while difficult to evaluate into cost equivalents, are now recognized as being of distinct economic value to any plant. Sizes of Motors Recommended to Drive Machine Tools. — The ac- companying tables contain the sizes and speeds of motors usually em- ployed with the average duty indicated for machine tools. The average load factor for motors driving lathes is from 10 to 25 per cent. On some special machines, as driving-wheel and car-wheel lathes, the cuts are all heavy, which increases the average load factor to from 30 to 40 per cent. For extension boring mills, 5-hp. motors are used to move the housings on from 10-ft. to 16-ft. mills, 7K-hp. for from 14-ft. to 20-ft. mills and 10-hp. for from 16-ft. to 24-ft. mills. The load factor of the driving motor on boring mills averages from 10 to 25 per cent. The load factor of motor-driven drills is about 40 per cent., when the larger drills applicable thereto are used. If the smaller drills are used, the load factor averages 25 per cent, and lower. For the average milling operations the load factor averages from 10 to 25 per cent. On slab-milling machines where large quantities of metal are renewed it will average from 30 to 40 per cent. On planers the load factor averages between 15 and 20 per cent. The motor must be large enough to reverse the bed quickly, yet this peak load occurs for such short intervals that it does not increase the average load per cycle very much. The work done on shapers is of a varying character. With light work the load factor will not exceed 15 to 20 per cent.; with heavy work, the load factor will be as high as 40 per c^nt. The conditions encountered on slotters are similar to those on shapers. In the following tables 1 the horsepower recommended is based on average practice; it may therefore be decreased for very light work and must often be increased for heavy work. For convenience, the class of motor is indicated by the symbols A, B and C, which have the following meanings: (A) refers to the adjustable-speed shunt-wound direct-current motor, used wherever a number of different speeds are essential. (B) refers to the constant-speed shunt-wound direct-current motor, where the speeds are obtained by a gear-box or cone-pulley arrangement or where one speed only is required. (C) refers to the squirrel-cage induc- tion motor for use in alternating-current circuits and used or adapted to those cases where direct current is not available. A gear-box or cone- pulley arrangement must be used to obtain different speeds. 1 Based on the practice of the Westinghouse Electric and Manufacturing Co. POWER TRANSMISSION Table I. — Engine Lathes Motor A, B or C 325 Swing, inches Horsepower Average Heavy 12 1H 2 14 %tol 2 to 3 16 1 to 2 2 to 3 18 2 to 3 3 to 5 20 to 22 3 iy 2 to 10 24 to 27 5 7)4 to 10 30 5 to 7% 7Y 2 to 10 32 to 36 iy 2 to 10 10 to 15 38 to 42 10 to 15 15 to 20 48 to 54 15 to 20 20 to 25 60 to 84 20 to 25 25 to 30 Axle Lathes Horsepower Single 5, 7K, 10 Double 10, 15, 20 Wheel Lathes Size, inches Horsepower Tail stock motor, 1 horsepower 48 51 to 60 79 to 84 90 100 15 to 20 15 to 20 25 to 30 30 to 40 40 to 50 5 5 5 5to7K 5to7K 1 Standard machine-tool traverse motor. Table II. — Bolt and Nut Machinery Single Double Triple Bolt Cutters, Motor A, B or C Size, inches Horsepower i, IK, V4 1 to 2 1M,2 2 to 3 2^,3K 3 to 5 4, 6 5to7K 1, IX 2 to 3 2, 2y 2 3 to 5 1, 1H, 2 3to7M Bolt Pointers, Motor, B or C 1 to 2 326 ENGINEERING OF POWER PLANTS Four-spindle Six-spindle Ten-spindle Table II. — Bolt and Nut Machinery. — {Continued) Nut Tappers, Motor, A, B or C 1, 2 3 2 3 2 5 Nut Facing, Motor, B or C 1, 2 2 to 3 Bolt Heading, Upsetting and Forging, Motor, A, 1 B 2 or C 3 Size, inches Horsepower %toiy 2 5 to iy 2 \y 2 to 2 10 to 15 2Y 2 to 3 20 to 25 4 to 6 30 to 40 1 Speed variation is sometimes desired when different sizes of bolts are headed on the same machine. 2 Compound-wound direct-current motor. 3 Wound secondary or squirrel-cage motor with approximately 10 per cent. slip. Table III. — Boring and Turning Mills Size 37 to 42 in. 50 in. 60 to 84 in. 7 to 9 ft. 10 to 12 ft. 14 to 16 ft. 16 to 25 ft. Motor, A, B or Average 5 to iy 2 iy 2 to 10 10 to 15 10 to.15 15 to 20 20 to 25 Horsepower Heavy iy 2 to 10 iy 2 to 10 10 to 15 30 to 40 Drilling and Boring Machines, Motor, A, B or C Horsepower Sensitive drills up to y in. Upright drills, 12 to 20 in. Upright drills, 24 to 28 in. Upright drills, 30 to 32 in. Upright drills, 36 to 40 in. Upright drills, 50 to 60 in. Radial drills, 3-ft. arm Radial drills, 4-ft. arm Heavy 3 to iy 2 to iy 2 Horsepower ■4 to y± i 2 3 5 5 to iy 2 Average 1 to 2 2 to 3 3 to 5 5 to iy 2 Radial drills, 5 to 6 and 7-ft. arm 5 Radial drills, 8 to 9 and 10-ft. arm iy to 10 Cylinder Boring Machines, Motor, A, B or C Horsepower Diameter of spindle, inches 4 6 8 Max. boring diam., inches 20 30 40 10 15 POWER TRANSMISSION 327 Table III.— Boring and Turning Mills. — (Continued) Pipe Threading and Cutting-Off Machines, Motor, A, B or C Size pipe, inches Horsepower H Vi l IK 2 3 4 8 to 2 to 3 to 4 to 6 to 8 to 10 to 12 to 18 24 2 3 3 3 to 5 3 to 5 5 5 7H 10 Table IV. — Bulldozers or Forming or Bending Machines Motor, B 1 or C 2 Width, inches Head in n chH ment ' 29 14 34 16 39 16 45 18 63 20 Buffing Lathes, Motor, B or C Wheels No. Diam., inches 2 6 2 10 2 12 2 14 1 Compound-wound motor. 2 Wound secondary or squirrel-cage motor with approximately 10 per cent. slip. For brass tubing and other special work use about double the above horsepower. Horsepower 5 7K 10 15 20 lorsepower MtoK 1 to 2 2 to 3 3 to 5 Table V. — Planers Motor, , A, 1 B l or c Width, inches Under rail, inches Horsepower 22 22 3 24 24 3 to 5 27 27 3 to 5 30 30 5 to iy 2 36 36 10 to 15 42 42 15 to 20 48 48 15 to 20 54 54 20 to 25 60 60 20 to 25 72 72 25 to 30 84 84 30 100 100 40 Normal length of bed in feet is about one-fourth the width in inches. 1 Compound-wound motor. 328 ENGINEERING OF POWER PLANTS Table V. — Planers. — (Continued) Rotary Planers, Motor, A, B or C Diam. of cutter, inches Horsepower 24 5 30 7H 36 to 42 10 48 to 54 15 60 20 72 25 84 30 96 to 100 40 Table VI.- —Hydrostatic Wheel Presses Motor, B or C Size, tons Horsepower 100 5 200 7V 2 300 7y 2 400 10 600 15 Table VII. — Punching and Shearing Machines Presses for Notching Sheet Iron, Motor, A, B or C, K to 3 lip. Punches, Motor, B 1 or C 2 Diam., inches Thickness, inches Horsepower % H 1 y 2 y 2 2 to 3 % % 2 to 3 H H 3 to 5 Vs H 5 1 y 2 5 1 7y 2 IK iy 2 to 10 m 10 to 15 2 10 to 15 2V 2 IK 15 to 25 1 Compound-wound motor. 2 Wound secondary or squirrel- ■cage motor with approximately 10 per cent, slip on the larger sizes. Shears, Motor, B 1 or C 2 Horsepower Width, inches Cut, 1$ in. iron Cut, \i in. iron 30 to 42 3 5 50 to 60 4 7y 2 72 to 96 5 10 • Bolt shears iy hp. Double-angle shears 10 hp. 1 Compound-wound motor. 2 Wound secondary or squirrel-cage induction motor with 10 per cent. slip. POWER TRANSMISSION 329 Table VII. — Punching and Shearing Machines. — (Continued) Lever Shears, Motor, B 1 or C 2 Size, inches Horsepower 1X1 5 m x \y 7y 2 2X2 10 6 XI 2K X 2K 15 1 X7 2% X 2% 20 1H X8 3>i X 3K 30 43^ round 1 Compound-wound motor. 2 Wound second or squirrel-cage motor with approximately 10 per cent. slip. Plate Shears, Motor, B 1 or C 2 Size of metal Cut per Length of „ cut, inches minute stroke, inches Horsep % X 24 35 3 10 1 X 24 20 3 15 2 X 14 15 4M 30 1 X 42 20 4 20 IV 2 X 42 15 4K 60 IH X 42 18 6 75 1^ X 72 20 5K 10 1^ X 100 10 to 12 7y 2 75 1 Compound-wound motor. 2 Wound secondary or squirrel-cage motor with approximately 10 per cent. slip. Plate Squaring Shears, Motor, B or C Size of plates, inches Cuts per minute Horsepower 54 X 54 30 7H He packs 72 X 72 30 7y %g packs Table VIII. — Shapers Motor, A, B or C Stroke, inches Horsepower, single head 12 to 16 2 18 2 to 3 20 to 24 3 to 5 30 5to7K Traverse Head Shaper 20 7M 24 10 330 ENGINEERING OF POWER PLANTS Table VIII. — Shapers. — (Continued) Rolls — Bending and Straightening, Motor, B l or C 2 Width, feet Thickness, inches Horsepower 4 % 5 6 He 5 6 Vie 7V 2 6 *A 15 8 Vs 25 10 IX 35 10 1H 50 24 l 50 1 Standard bending roll motor. 2 Wound secondary induction motor. Size of saw, inches 20 26 32 Stroke, inches 6 8 10 12 14 Saws, Cold and Cut Off, Motor, A, B or C Horsepower Size of saw, inches 3 5 7V 2 36 42 48 Slotting and Key Seating, Motor, A, B or C Horsepower 3 3 to 5 5 5 5to7K Stroke, inches 16 18 20 24 30 Horsepower 10 to 15 20 25 Horsepower 7y 2 7H to 10 10 to 15 10 to 15 10 to 15 Horizontal Boring, Drilling and Milling Machines, Motor, A, B or C Size of spindle, inches V/2 to 43^ 4^ to 53^ 5H to QH Horsepower for single spindle 5 to iy 2 iy 2 to io 10 to 15 For machines with double spindles use motors of double the horsepower given. Size of drills, inches 3^2 to M Heto^ %6tO^ Kto^ %tol 2 2 2 Table IX. — Multiple Spindle Drill Motor, A, B or C Ma t X ospfnd < le illS Horsepower 6 3 10 5 10 7V 2 10 10 10 10 to 15 4 7y 2 6 10 8 15 POWER TRANSMISSION 331 Table IX. — Multiple Spindle Drill. — (Continued) Emery Wheels, Grinders, Etc., Motor, B or C Wheels No. Size, inches Horsepower 2 6 y 2 to 1 2 10 2 2 12 3 2 18 5 to iy 2 2 24 iy 2 to 10 2 26 iy 2 to 10 Miscellaneous Grinders, Motor, B or C Horsepower Wet-tool grinder 2 to 3 Flexible swinging, grinding and polishing machine .... 3 Angle-cock grinder 3 Piston-rod grinder 3 Twist-drill grinder 2 Automatic-tool grinder 3 to 5 Table X. — Milling Machines Vertical Slabbing Machines, Motor, A, B or C Width of work, inches Horsepower 24 iy 2 32 to 36 10 42 15 Vertical Milling Machines Height under work, inches Horsepower 12 5 14 iy 2 18 10 20 15 24 20 Plain Milling Machines Table feed, inches Cross feed, inches Vertical feed inches •i Horse- power 34 10 20 7K 42 12 20 10 50 12 21 15 Universal Milling Machines Machine No. Horsepower Machine No Horsepower 1 1 to 2 3 5 to 7% w 1 to 2 4 iy 2 to 10 2 3 to 5 5 10 to 15 Horizontal Slab Millers Width between housings, inches Average Horsepower Heavy 24 7y to 10 10 to 15 30 iy 2 to 10 10 to 15 36 : 10 to 15 20 to 25 60 25 50 to 60 72 25 75 332 ENGINEERING OF POWER PLANTS Table XI. — Grinding Machines (Grinding Shafts, Etc.) Motor, A, B orC [Diana, wheel, Length work, Horsepower inches inches Average work Heavy work 10 50 5 7M 10 72 5 7y 2 10 96 5 7y 2 10 120 5 7y 2 14 72 10 15 18 120 10 15 18 144 10 15 18 168 10 15 Gear Cutters, Motor, A f 5 or C Size, inches Horsepower Size, inches Horsepower 36 X 9 2 to 3 60 X 12 5 to iy 2 48 X 10 3 to 5 72 X 14 iy 2 to 10 30 X 12 5to7K 64 X20 10 to 15 Hammers, Motor, B l or C 2 Size, pounds Horsepower 15 to 75 y 2 to 5 100 to 200 5 to iy 2 Bliss drop hammers require approximately 1 hp. for every 100-lb. weight of hammer head. 1 Compound-wound motor. 2 Wound secondary squirrel-cage motor with approximately 10 per cent. slip. Selection of Motors and Speed Requirements for Machine Service. — The selection of the proper motor for given service requirements necessi- tates a careful study into the characteristics of the work to be performed by the machine tool. Both power and speed requirements vary widely in different tools, and a motor well adapted to one class of work may be unsuited to another. Expert advice should be secured in such a problem at least in the first cases until the factors involved are thoroughly under- stood, and the characteristics of the various types of motors on the market are mastered in their relation to the power and speed conditions to be supplied for given machines. The importance of speed is at once realized when one considers that production depends to a great extent on the use of the most economical cutting speed for given operations. The 4 to 1 adjustable-speed motor now commonly employed in machine-shop work will be found to meet most conditions. It is recommended 1 that given machine tools be re- stricted to a certain range of diameters of work and thus make possible a close speed adjustment within this range, rather than to work a maxi- mum range of diameters on a given tool with less refinements in the speed 1 Westinghouse practice. POWER TRANSMISSION 333 adjustment. Useful charts are available from the larger electrical manu- facturers by means of which the horsepower requirements for given depths of cut, cutting speeds and feed, may be determined conveniently. Simi- larly, charts are available from which the relation between feeds, cutting speeds, diameters of work, and spindle speeds may be determined con- veniently. The following table 1 is also useful in this general connection: Horsepower per cubic Metal foot of metal per minute Cast iron 0.3 to 0.5 Wrought iron 0.6 Machinery steel 0.6 Steel, 50 carbon and harder 1 . to 1 . 25 Brass and similar alloys . 2 to . 25 For drills, the cubic inches of metal removed per minute are found by the formula : Q = 0.7854 X d 2 f where d is the diameter of the drill in inches and / the feed in inches per minute. The constants for drills are approximately double those given in the previous table. Cost of a Horsepower at the Machine. — The cost of power trans- mitted electrically to the consumer will depend on the original cost at the engine or water power. Power transmitted from a large waterfall by electricity frequently sells for $25 per horsepower-year for short dis- tance transmission. (It is reported that Niagara power sells from $12 to $24 per horsepower-year.) Mr. W. C. Webber estimates the total cost at the machine of electrical transmission in shops as follows, allowing for interest and depreciation and including repairs, attendance, etc. : Per horsepower-year of 3,080 hr $52 Per horsepower-year of 7,392 hr 57 Per horsepower-year of 8,760 hr 66 These are computed on a basis of 100 hp. produced at the engine for $35 per horsepower-year at 3,080 hr. One authority states that with coal at $3 per ton a simple non-con- densing, high-speed engine will produce 500 hp. at a cost of $36 per horse- power-year of 3,080 hr., while a triple-expansion condensing engine will furnish the same power for $24. The probable costs in an electric system for furnishing power to a machine shop might be summarized as follows: 1 Westinghouse Electric and Manufacturing Co. The table refers to lathes, planers, etc., when round-nose tools are used. 334 ENGINEERING OF POWER PLANTS Cents per kilowatt-hour Coal at $3.50 per ton •>. 0.5 Labor 0.4 General expenses 0.2 Fixed charge 0.4 Total 1.5 This does not allow for the cost or losses of distribution, but represents the cost at the switchboard, and corresponds very nearly to $35 per horse- power-year of 3,080 hr. The following data has been compiled by the Bullock Electric Manu- facturing Co. for the cost of power compared with output of the factory for different systems of transmission: (a) Ordinary belting and shafting 1 . 7 to 2 . per cent. (b) Electric group drive . 8 to 1 . per cent. (c) Individual motor drive 0.4 per cent. It is evident that there is a marked saving in power through the use of individual motor drive, but it is also apparent that in most factories the important factor is increase in output, and if one system of power effects an increase of even 50 per cent, in the power consumption, this increase is relatively a small factor in the total cost of production. In this con- nection, it may be stated that there is abundant testimony that the in- stallation of individual motor drive in large shops has effected from 20 to 40 per cent, increase in the output for given machine tools, and an equal or even greater economy in room. Through the cooperation of Professor H. B. Dates the following notes relating to electrical machinery are given: Direct Current versus Alternating Current. — For equal low voltages usually found in the small machine shop of say 250 volts, both systems require the same amount of copper in general terms in the matter of dis- tribution about the buildings of the plant. If the three-wire system is used with the direct-current and the two-wire system with the alternating- current, the advantage is in favor of the direct-current system. The advantage of the alternating-current system lies in the flexible method of transformation from low to high voltages and vice versa by means of the transformer, thus permitting the use of high voltage for the power trans- mission at low current and consequently low line losses and low copper costs. Direct current is usually generated at comparatively low voltage and it cannot readily be transformed from one voltage to another as with the alternating current. Direct-current motors, however, are essential where adjustable-speed service is a requirement. Incandescent lamps may be operated on either direct- or alternating-current circuits. Lamps of the 110- volt class, however, are better than those designed for opera- tion on 220-volt circuits. POWER TRANSMISSION 335 High voltages, which are desirable for economy in the transmission of power over long distances, are more or less out of place in most manu- facturing plants, and consequently in the smaller plants where the dis- tances to be covered are relatively small, direct current is used. With a low-voltage direct-current system, 110 or 220 volts, there are no trans- formers to install and maintain, there is no danger from very high volt- ages, and the system as a whole is characterized by simplicity both in design and operation. As extensions are made to such a plant, however, the difficulties in power transmission become greater due to the heavy copper losses at low voltage, and it may be desirable to use alternating current at a higher voltage. From these circuits, lamps and constant- speed motors may be supplied, and where adjustable-speed direct-current motors must be used, special direct-current circuits may be employed, the transformation from alternating to direct current being effected by the rotary converter (also known as the synchronous converter) or by a motor-generator set. Direct-current Motors, Types and Where Used. — Shunt motors possess good starting torque and favorable operating characteristics for many operations. Their speed regulation is usually very good. They may be used where the load at starting is fairly high and where practically constant speed is desired at all loads, i.e., for line shafting, group drives, and for many machine tools. Series motors are used only where they can be geared or securely coupled to their load, to prevent the excessive speeds which result when the load on a series motor is thrown off. They are adapted for heavy starting duty where variations in speed are not objectionable. In such motors the speed varies approximately inversely as the square of the load. Series motors are adapted to street-car service, to cranes, hoists, fans and similar loads. Compound motors, cumulatively wound, have characteristics which depend upon the relative strength of shunt and series field coils. These motors have operating features which result from the combined effects of series and shunt windings, so that in a measure the action is partly like that of a shunt motor and partly like that of a series motor. Cumu- lative-wound compound motors possess a good starting torque, but are apt to have poorer speed regulation, that is, a greater drop in speed with increases in load, than in the case of the straight shunt motor. Compound-wound motors of the cumulative type are sometimes used on loads where fairly large torque is required at one portion in each cycle and where the load is relatively light for the rest of the cycle. They are used quite extensively for elevator work, heavy planers, and for similar loads. It should be noted that a portion of the torque in this motor is due to its series-motor characteristics, but when the speed increases, the 336 ENGINEERING OF POWER PLANTS field flux does not tend to decrease therewith as in the series motor, be- cause the current in the shunt circuit remains practically constant. The employment of the shunt field in addition to a series field thus prevents the speed from exceeding safe limits at low loads. Interpole or Commutating-pole Motors. — This type has come into very wide use during recent years for adjustable-speed machine-shop service. The interpoles render commutation practically perfect under wide ranges of speeds and loads. Adjustable-speed motors with wide speed ranges cost more than constant-speed motors of the same horse- power rating. Temperature rise, rather than commutation, is the limiting factor in the output which can be supplied by a given motor. For constant-speed service the use of interpoles is not as essential as in the adjustable-speed service. In constant-speed service, however, where the load is subject to rapid and violent fluctuations and where very large overloads must be carried, the design should be such as to take care of the main heating effects, while interpoles may be employed to maintain perfect commuta- tion under severe load conditions. Therefore, for intermittent constant- speed service, the interpole motor is more desirable than the motor of usual design. In direct-current railway service the use of interpoles enables motors to withstand large loads for short periods, or, where artificial ventilation is used, to operate continuously at overloads without excessive sparking as a limiting factor. This statement also applies in a general way to series motors used for mill purposes. Shunt motors, when used for adjustable-speed service, have theii performance greatly improved with interpoles, and it is possible to reverse a 5-hp. shunt motor when interpoles are used, under full-load conditions, without sparking. This is not possible with ordinary shunt motors. The interpole motor is simple in construction, requires but two service wires, works at maximum voltage, that is, from circuits of normal voltage, may have its speed control accomplished by the insertion of a rheostat in the field circuit in the ordinary manner, and operates throughout a large speed range at almost constant efficiency. Direct-current motors of the interpole type, therefore, especially lend themselves to machine- tool work where adjustable speed is required and where good speed regu- lation under fixed positions of the controller is necessary. They are successfully used from about K2 to 1,500 hp. and larger in mill and shop work. Alternating-current Motors. — Polyphase, that is, two- and three- phase induction motors are chiefly used on alternating-current circuits in the shop. Sometimes the single-phase induction motor is used in the POWER TRANSMISSION 337 smaller sizes but for power work the polyphase type is nearly always employed. The induction motor is inherently a constant-speed motor and it is largely used as such. If the rotor of an induction motor is of the phase- wound type (rather than the squirrel-cage type) with the use of auxiliary resistances in the rotor circuit it can be made to operate as an adjustable- speed motor but to a very limited extent and at the expense of efficiency and good speed regulation under various loads. Probably the greatest usefulness of the induction motor, therefore, is as a constant-speed machine. In this form, it is simple and rugged in construction, has no commutator or brushes, and when completely enclosed requires a mini- mum of attendance. It has a wide application in certain kinds of mill work, for example, for cement and paper mills and in reduction works. In addition to the use of auxiliary resistance in the wound rotor circuit for obtaining speed changes as well as greater torque at starting, speed changes may also be produced to a limited extent in the induction motor by the "potential," "change of poles," "change of frequency," or " cascade control" methods. "Cascade Control" Methods. 1 — Where power is purchased from a central power station, the supply is most commonly alternating current. In such a case the induction motor will be satisfactory for most constant- speed work, and should be employed unless adjustable-speed motors are essential, thus calling for direct-current circuits. Since the usual sources of alternating-current supply are at relatively high voltages and since it is customary to utilize the power at relatively low voltages, the use of a transformer is necessary for stepping down the voltage. Very large induction motors are often run at voltages as high as 6,600 volts, i.e., direct from the line without the interposition of transformers. The steel plant at Gary, Ind., successfully uses induction motors of 6,000 hp. on the rolls. The motors are equipped with heavy flywheels and the design is such that the peak loads are taken by the flywheels. Generators. — Direct-current generators have reached a high stage of development in multipolar types and at lower speeds than formerly. They have been improved mechanically and there has been a transition from the belted to the direct-connected type. The belted type is higher speed than the direct-connected, is lighter in weight for given output, and consequently is lower in first cost. In the direct-connected type there is a saving in floor space, no belting with its dust and dirt, less noise and a saving of one bearing in moder- ate-sized machines as the generator is mounted on an extension of the engine shaft. In buying a direct-connected set, if the engine is bought from one 1 For information on these methods see "American Handbook for Electrical Engi- neers," John Wile}' & Sons, New York, pp. 1009-1011. 22 338 ENGINEERING OF POWER PLANTS manufacturer and the generator from another, it is customary for the engine manufacturer to furnish the shaft. Details are furnished the gen- erator manufacturer and the shaft is sent to him. He then mounts the rotating member of the generator upon it. In modern practice only the smaller units are belt-driven. Alternating-current generators in the earlier designs were of the single- phase type, with high frequency, 125 to 133 cycles (now obsolete), and were usually of small capacity and designed for belted operation. Rapid development has been made in polyphase types both two- and three-phase, 60 and 25 cycles. Single-phase motors are not good in large sizes, owing to the fact that they are not self-starting, except by the use of special starting devices which in general do not afford good starting torque. Polyphase systems are dictated from power considerations since the polyphase motor is self-starting, and gives highly satisfactory service. The polyphase generator is superior to the single-phase in performance (regulation), cost and weight. Distribution is cheaper with three-phase than with single-phase. Single-phase systems are limited to small plants where the motor load is very light. A single-phase machine of 200-kw. capacity is very rare. Lighting and power systems may both be fed from the same polyphase lines, although lighting circuits should always be kept separate from the power circuits so as to eliminate voltage fluctuations and the consequent flicker and unsteadiness usually found when lamps and motors are sup- plied from the same circuit. A three-phase generator may be loaded to 58 per cent, of its total three-phase output when operated single-phase. There seems to be little reason for installing single-phase generators at the present time. Three-phase systems are usually preferable to two-phase systems and are most generally used today. Where two-phase current is desired for special uses it may be obtained from the three-phase circuit by the Scott transformer connection. Three-phase systems are always used for economical transmission. Alternating-current generators have voltages which are seldom as low as 440 volts; 2,300 volts is common. Where transmission is over a fairly short distance, from say 6 to 15 miles, generators may and usually do operate at line voltages of 6,600, 11,000 or 13,200 volts. Generators are thus built to develop voltages as high as 13,200 volts. Where transformers have been used to step up to higher line voltages for longer transmission distances, generators are commonly built at one of the following voltages: 2,300, 4,000, 6,600, 11,000, or 13,200. Alter- nating-current generators driven by steam turbines are now in operation with capacities as high as 35,000 kv.a. POWER TRANSMISSION 339 Standard voltage for alternating-current circuits may be listed as follows: 110, 220, 440, 2,300, 6,600, 11,000, 13,200, 22,000, 33,000, 66,000, 90,000, 110,000 and 150,000. Standard frequencies in this country are 25 and 60 cycles per second with some 40-cycle installations. Arc lamps do not in general operate satisfactorily on circuits with a frequency below about 40 cycles. Incandescent lamps may be operated on 25-cycle circuits but with slightly less satisfactory results than with higher frequencies. Twenty-five-cycle current is preferable for motors, especially so for rotary converters and synchronous motors. It is also preferable for transmission on account of better line regulation. For general purposes as mixed lighting and power, 60-cycle current is used; or power purposes, 25-cycle current. Exciters for Alternators. — All alternating-current generators require direct current for excitation of fields. In large stations exciters are direct-connected to prime movers. In small installations they are frequently direct-connected to or belted to the alternator itself. Exciter plant must be absolutely reliable; hence a reserve of good capacity is required either in the form of additional units or in storage battery or both. Capacity Required in Exciters. — For medium speed, small-sized alter- nators, the exciter capacity is usually about 2.5 per cent, of that of the generator. In large steam-turbine units, high-speed, it is about 0.5 per cent. Ratings by Output. — All electrical apparatus should be rated by out- put and not by input. Generators, transformers, etc., should be rated by electrical output; motors, by mechanical output. Rating in Kilowatts. — Electrical power should be expressed in kilo- watts except when otherwise specified. Apparent Power, Kilovolt -amperes. — Apparent power in alternating- current circuits should be expressed in kilovolt-amperes as distinguished from real power in kilowatts. When the power factor is 100 per cent., the apparent power in kilovolt-amperes is equal to the kilowatts. Rated (Full-load) Current. — Is that current which with the rated terminal voltage gives the rated kilowatts or the rated kilovolt-amperes. Determination of Rated Current. — If P be the rating or true watts, assuming a power factor of unity, and E be the full-load terminal voltage, then rated current per terminal is : / = P/E in a direct-current machine or single-phase alternating-current generator. I = 0.58 X P/E in a three-phase alternating-current generator. / = 0.50 X P/E in a two-phase alternating-current generator. If the power factor is other than unity, divide P by the power factor in per cent. Temperature Rise. — Under regular service conditions the temperature 340 ENGINEERING OF POWER PLANTS should never be allowed to remain at a point which will result in perma- nent deterioration of the insulating material in the machine. It has been recommended 1 that the following temperature rises re- ferred to room temperatures of 40°C. be never exceeded. (These are to be considered as maximum permissible temperature rises above 40°C. allowable; manufacturers should keep within these limits.) A. For cotton, silk, paper and similar materials, when so treated or impregnated as to increase the thermal limit, or when permanently immersed in oil, also enameled wire, 65°C. B. Mica, asbestos and other materials capable of resisting high temperatures, in which any class A material or binder is used for structural purposes only, and may be destroyed without impairing the insulating or mechanical qualities of the insula- tion, 85°C. C. Fireproof and refractory materials such as pure mica, porcelain, quartz, etc. no limit specified. Effects of Semi and Totally Enclosing Direct-current Motors. — With semi-enclosing, at normal temperature rise, the output is reduced. Fully enclosing the motor reduces the rating still more below normal. Forced cooling raises the rating above normal. The general plan today is to operate one large central station and locate at various centers substations for local distribution. Irrespective of the form in which power is distributed, i.e., alternating current or direct current, the power is delivered to the substations from the main generating plant (alternating-current plant usually now) as three-phase, high-voltage and at the substation it is transformed either as regards e.m.f. or in addition from alternating to direct current ac- cording to the demand. For transmission a general figure of about 1,000 volts per mile may be used up to present limits of say 150,000 volts. 1 See Standardization Rules of the American Institute of Electrical Engineers, edition of July 1, 1915. CHAPTER XVII DISTRICT HEATING Although the discussion of heating from central stations belongs primarily to courses on " Heating and Ventilation,'' yet the transmis- sion of steam or hot water for this purpose is so closely allied with power generation that brief notes relating to this subject are added. The material presented is largely from the published 1 data of Bushnell and Orr, and Gifford. There are two distinct systems of central heating, steam and hot water. Central heating as a byproduct has proved very attractive financially in many cases and either system, steam or water, should give excellent results if properly installed and managed and, for this reason, both sys- tems have become popular and have increased in number. Central heating as a utility is very similar to any other business. To be successful the heat must be manufactured as economically as possi- ble. It must be marketed economically and it must be made attractive both as to price and quality of service. Advantages to the Public. — 1. Comfort, even heat, always ready. 2. Cleanliness around the premises. 3. Reduction of labor. 4. Reduction of cartage through city streets. 5. Reduction of smoke nuisance. 6. Safety. The Byproduct Plant. — The thermal efficiency of an electric plant is very low. Even after the steam is generated 70 to 90 per cent, of the heat is exhausted after passing through the prime mover. If this steam is exhausted to the atmosphere, the waste is enormous. If it is condensed, the heat in the exhaust steam is transmitted to the cooling water and liberated, either through the cooling tower or pond. At any rate, it is wasted, but, of course, not so much of it is wasted in the condensing plant. However, when an electric plant is so located that it can serve a good heating territory, it can make a kilowatt of electric energy for considerably less in conjunction with a heating plant than it can by running alone con- densing. It is a problem that must be worked out for each situation, but, as a general rule, the revenue from the heat sales will more than pay 1 District Heating," Bushnell and Orr, Heating and Ventilating Magazine Co., N. Y. "Central Station Heating," Gifford, Heating and Ventilating Magazine Co., N. Y. 341 342 ENGINEERING OF POWER PLANTS the coal bills after deducting from the heat income interest, maintenance and depreciation on the heating investment. Combining these two utilities then increases the net earnings of each. It increases the load factor of the boiler plant and causes it to operate more economically because of the better load conditions. It increases the heat units utilized and sold. It should not increase the labor cost as the same crew can handle both. It increases the electrical output because it does away with isolated electric and power plants. If the central plant can serve its patrons with heat, light and power, it is not half so difficult to get this business because, as a rule, the owners of the isolated plants can buy these commodities from the central plant for less money than they can make them themselves, but if heat is not furnished by the central plant they cannot afford to buy electricity and make their own heat, as they heat with the exhaust steam from their own plant which, they naturally figure, costs them practically nothing. This kind of business materially helps the electric plant because it in- creases its load and its net earnings. In general, the combining of these two utilities is very satisfactory and advantageous to both. Methods of Selling Heat. — The methods of charging for heat may be divided into five classes: (A) Flat rates per square foot of radiation for hot-water systems. (B) Flat rates per square foot of radiation for steam-heating systems. (C) Flat rates per square foot of radiation, theoretically required ac- cording to the company's formulae. * (D) Flat rate per year based on estimates of service requirements, or else based on estimate of what the customer would be willing to pay. (E) Schedule prices based on the amount of steam used as shown by either steam or condensation meters. Class "A" — Flat Rates for Hot-water Heating. — It can readily be seen that the price for heating during the heating season in the Southern States ought to be very much lower than in a State like Maine or Minne- sota. The majority of heating plants are located in the Northern States and the variation in price would be approximately from 15 to 25 cts. per square foot of radiation, with 20 cts. as an average price in the neighbor- hood of Chicago, 111. Class "B" — Flat Rates for Steam Heating. — The rate for steam radia- tion is about 50 per cent, higher than that for hot-water radiation, the price varying from about 25 to 35 cts. per square foot of radiation for districts having a temperature condition approximately like that of Chi- cago, 111. The difference in rates between steam and hot-water radiation is due to the fact that steam radiation usually transmits about 50 per cent, more heat per square foot of radiating surface than is transmitted by hot-water radiation. DISTRICT HEATING 343 Class "C" — Contracts Based on Theoretical Required Radiation. — Contracts are also based on a flat rate dependent on the amount of radia- tion required as determined by the formulae of the company. In this form of contract the price is governed not only by the amount of radiation installed, which is the minimum, but also by the theoretical radiation required to heat the building, according to the formula? adopted by the company. Class "D" — Flat Contract. — Unfortunately with a great many heating companies many of the contracts are based on a flat price, which has been arrived at in a manner similar to that of a peddler in selling his wares. In other words, neither the buyer nor the seller has a very correct idea of what the service is worth, but after due discussion arrive at a price which becomes the basis of their agreement. There is always a tempta- tion on the part of customers toward wastefulness where the service is based on a flat price per year and all formulae used in figuring such con- tracts should take account of this fact. The average result in New York and Chicago shows that the consumer will use about 25 per cent, more steam when operating under flat-rate contracts, than when operating on a meter basis. Class "E" — Contracts Based on Meter Readings. — In Class "E" the contracts are based on the amount of steam used as shown by either steam or condensation meters. This contract is used: 1. By central steam companies who furnish a house-to-house service and deliver the steam from a central plant to the curb wall of the customer. 2. By maintenance companies which operate the boiler plants in various buildings and supply steam to the owner from his own plant on a meter basis. The result of an examination of the meter rates for steam heat for 39 cities is shown by the following table. Meter Rates for Steam Heat Pounds of steam per month Cents, per 1,000 lb. Maximum Minimum Average 1st 10,000 10,000 10,000 10,000 10,000 25,000 25,000 50,000 50,000 300,000 500,000 100 90 90 87 85 80 80 73 70 67 50 60 50 50 45 45 43 40 38 38 36 35 80.0 2d 70.0 3d 67.5 4th 65.0 5th 62.5 Next 60.0 Next 57.5 Next 52.5 Next 50.0 Next 47.5 Over 41.5 344 ENGINEERING OF POWER PLANTS In a hot-water heating franchise the meter rate is not necessary, because there are no meters on the market. When they do come, they will probably be the heat-unit meter, and in that event 1,000,000 B.t.u. would be the logical basis of charge. On a meter basis for steam heating, 1,000 lb. of steam is the basis of charge On a flat-rate basis for hot water or steam heating the charge per annum or per season is either per square foot of radiation or per 1,000 cu. ft. of space heated. When the charge per square foot of radiation is used as a basis it should be stated clearly that it is the radiation required to heat the build- ing and not the radiation that is installed in the building. The required radiation is the amount necessary to install so that the company can guarantee to maintain a comfortable temperature. With the flat rate per square foot basis, thermostatic control is almost essential to good operation and economical use of heat in the residences and buildings. The flat-rate basis charge, of so much per thousand cubic feet of space, is not as equitable as the per square foot of radiation basis. For each and every 1,000 cu. ft. of contents do not require the same amount of heat, owing to the difference in location and difference in use. For in- stance, 1,000 cu. ft. in a corner drug store requires more heat at zero out- side than does 1,000 cu. ft. in a dentist's office at zero outside. This method is not used very much at the present time. The most scientific method of charge and one that is finding universal favor in connection with public utility service is the " ready to serve" or " maximum demand" rate. For example, assume a building that uses heat only 6 hr. out of 24 hr. in a day. This building demands a place on the line and requires the capacity, both in the mains and at the heating station, to supply its maximum demand. The heating company must be ready to serve this building at any time it requires service. In return for that required con- dition, the heating company only receives pay for 6 hr. service, while the building using heat for 18 hr. pays the company three times the revenue paid by the other building. It is also the case with churches or auditoriums where heat is used only two or three days out of the week. The heating company must reserve capacities for these buildings, but in return receives only about one-sixth the revenue it would receive from other buildings requiring the capacities that these churches, etc., require. It is obvious, therefore, that a rate based on the number of pounds of steam condensed is far from equitable. It is here that the " maximum demand" or " ready to serve" rate shows its strong points as an equitable rate. As stated before, this DISTRICT HEATING 345 rate is based on the cost of the service to the utility, plus an equitable profit. In making a rate for service per season it is desirable to know the per- centage of heat used in any one month during the heating season for two reasons: First, the collections are often made monthly; second, it some- times happens that a credit or debit is given for certain months during the season, when the service is started or stopped in mid-season. The following table will be useful in this connection. Heat Consumption Table Per cent. Heat used up to Oct. 31 6 From Oct. 31 to Nov. 30 12 From Nov. 30 to Dec. 31 18 From Dec. 31 to Jan. 31 21 From Jan. 31 to Feb. 28 19 From Feb. 28 to Mar. 31 13 From Mar. 31 to Apr. 30 8 From Apr. 30 to May 15 3 100 The following division is used extensively in flat rate contracts and is easily remembered by the consumers : 5 per cent, of contract price payable Oct. 1. 15 per cent, of contract price payable Nov. 1. 20 per cent, of contract price payable Dec. 1. 20 per cent, of contract price payable Jan. 1. 20 per cent, of contract price payable Feb. 1. 15 per cent, of contract price payable Mar. 1. 5 per cent, of contract price payable Apr. 1. Before leaving the subject of rates, it might be well to call attention to the two-rate system, which has been frequently advocated, viz., the adoption of a primary charge based on the theoretical amount of radia- tion connected and a secondary charge based on the meter readings. This kind of rate is perhaps more thoroughly sound than the single sliding- schedule, due to the fact that the primary rate can be made to closely approximate the investment charge, while the secondary rate can be used on the operating costs. The chief objection to this rate is that it requires that the theoretical radiation for each customer be figured from a basic formula and such estimates of theoretical radiation required are more open to controversy than the reading of a satisfactory meter. Another point in favor of the simple sliding-schedule based on meter readings is that it is more easy to explain this method of charging to the customer. While it is very possible that the two-rate system will be the future 346 ENGINEERING OF POWER PLANTS basis for the sale of steam, just as it is already to a large extent the basis for the sale of electricity, yet it is questionable as to whether the time for this change has arrived. One two-rate system in use in an eastern city is applied as follows : (a) Reduce the cubic feet of heated contents to a cube of equal con- tents. (b) Base the rate on the area of one side of this cube and on the actual steam consumption. For the city in question the rate is 1 ct. per square foot of the equiva- lent cube plus 30 cts. per 1,000 lb. of steam. Take a house of approximately 20,000 cu. ft. of heated contents. Equivalent cube = 27 X 27 X 27. Fixed charge each month of heating season (8 months) = 27 X 27 X $0.01 = $7.29. If the steam consumption for a month were 20,000 lb., the bill for the month would be Fixed charge = $7 . 29 20 X 30 cts. = 6.00 $13.29 If the consumption for the month were 50,000 lb. then the bill would be Fixed charge = $7 . 29 50 X 30 cts. = 15.00 $22.29 Cost of Exhaust Steam Heating. — The Wisconsin Railroad Commis- sion, in its reports, vol. 2, page 302, states that, with coal at $2 per ton, exhaust steam could be sold at 50 cts. per 1,000 lb. safely; that is, with a secure profit, but it also states that where live steam is sold there would be small profits unless large quantities of steam were sold. The engineer of a company of recognized standing states that the charge which his company makes to the different buildings and depart- ments for the use of exhaust steam for heating is at the rate of 2 cts. per month per square foot of radiating surface for 6 months of the year. He finds in practice that when using exhaust steam 1 lb. will supply about 3 sq. ft. of radiation with steam for 1 hr. He figures that if 1 lb. of coal will produce 8 lb. of steam, it will supply about 25 sq. ft. of radia- tion for 1 hr., and when coal costs $2 per ton the fuel necessary to supply 1 sq. ft. of radiation for one month, making proper allowance for the value of the steam used in the engine, will cost about 1 ct., assuming that steam is supplied to the radiator for only 10 or 12 hr. per day. Also assuming that the amount of boiler-room expense will just about equal the fuel cost, he estimates the cost for exhaust steam as 2 cts. per DISTRICT HEATING 347 square foot per month during the months when heat is necessary. It is very doubtful whether many heating plants can be operated for heating alone and supply live steam at a cost of 2 cts. or less per square foot per month. The normal consumption of steam in radiators per season under ordinary conditions in a climate similar to that of Chicago, 111., runs from 600 to 800 lb. of steam per square foot where the radiating surface is properly proportioned. There are buildings, however, which cannot be depended upon to run very close to this average. Occasionally the con- sumption will be very much above this amount in one building and in another building it will be very much below, the amount used running all the way from 300 to 3,000 lb. per square foot of radiating surface during the heating season. The following summaries present interesting data showing the varia- tions in steam consumption in different latitudes. Class of buildings — office buildings, retail stores, residences, saloons, hotels, apartments, garages, light manufacturing buildings, wholesale stores, clubs, schools, churches, offices, banks, lodges, factories, theatres, restaurants, post offices, Y. M. C. A.'s, halls, telephone companies, hos- pitals, city halls, court houses, etc. Large City in the Middle West Mean Temperature during Heating Season 41°F. Number of consumers Cubic feet of space Square feet of radiation Total condensa- tion per season, pounds Season's average per 1,000 cu. ft. of space, pounds Season's average per sq. ft. radia- tion, pounds 162 20,505,000 229,842 117,196,000 5,715 510 Eastern City Mean Temperature during Heating Season 41.3°F. 187 7,258,293 94,993 63,249,000 8,714 665 Large Southern City Mean Temperature during Heating Season 54.7°F. 149 24,546,000 194,702 84,711,000 3,451 435 Steam Co nsumption of various classes of buildings in a clty West, Indicating the Economy Effected by Meter Meter rate of the Middle Rates 39 7,103,028 65,132 38,012,000 5,352 584 Flat rate 95 7,859,357 78,062 74,318,000 9,456 951 348 ENGINEERING OF POWER PLANTS Estimating Miscellaneous Steam Requirements in Large Buildings. — In addition to heating service the district-heating company may be called upon to supply steam for many other purposes. The owner of the modern first-class building is obliged to provide the highest quality of service for his tenants, and this is accomplished only by the installation of a system of auxiliary apparatus of various kinds, many of which are operated by steam. Among these may be included the following: 1. Hot-water heaters, supplying heated water for industrial or manufacturing purposes, or for domestic uses, such as scrubbing and lavatories. 2. Vacuum pumps, used in connection with steam-heating systems for removing air and condensation from the radiation. 3. Ejectors used in a manner similar to vacuum pumps. 4. House pumps used for elevating the domestic water supply to the roof of the building where it is stored in a tank. 5. Boiler-feed pumps. 6. Steam-hydraulic elevator pumps. 7. Direct-steam elevator engines. 8. Fire-pumps. 9. Air compressors. (a) General use. (6) Sewer-ejector system. (c) For pressure-tanks on hydraulic system. 10. Steam syphons and jets. 11. Refrigerating machinery. (a) Compression systems. (6) Absorption systems. 12. Brine pumps or other auxiliary refrigerating apparatus. 13. Drinking-water pumps. 14. Stoker engines. 15. Ventilating fan-engines. 16. Warming and cooking apparatus for restaurants. 17. Laundry apparatus. 18. Miscellaneous industrial uses, varying with the class of building and tenants. To determine with any degree of certainty just how extensive the use of steam for these purposes will be in each building, usually requires a specialist in this particular line of engineering — one who is enabled to draw from experience and observation for verification of estimates. Whenever possible, it is needless to say one should be guided by com- parison with buildings already supplied with approximately similar service. The cost of heating service is made up of the following items which should be figured on the basis of 1,000 lb. of steam generated or a mul- tiple of that quantity. DISTRICT HEATING 349 1. Fixed charges based on investment in: Building, Dynamos, Boilers, Furnaces, Piping, Engines. and various accessories for the above. (a) Amortization. (6) Obsolescence. (c) Interest. (d) Taxes. (e) Rental value of space. (/) Marginal charge for diversion of capital. Salaries Operating costs: Chief engineer. Assistant engineers. Firemen. Coal-passers. Oilers. Electricians. Steam-fitters. Boiler-washers. Elevator repair men. Helpers. Engineer's clerk. Office labor for metering and billing. Employer's liability insurance and salaries paid to injured employees when off duty. Also a portion of the time of the management used in buying supplies and looking after the operating organization. ' Fuel. Transportation of ashes. Oil, waste, water. Shovels, fire-tools. Electricity for lighting and power in boiler room. Miscellaneous supplies and expenses. Supplies < All of the above are direct costs which are directly chargeable to the cost of operating a plant. In addition to the above costs, there are other costs which might be termed indirect charges which often come as a result of power-plant operation. 1. Throwover Switch Service from Central-station Service. — As a rule, the cost per kilowatt-hour for throwover switch service is greater than the rate where complete service is furnished, and often a minimum bill is required in addition to the higher rate. 2. Danger of Breakdown in the Service and Consequent Loss if Throwover Switch is not Installed. 3. Losses on Account of Decreased Rental Value of the Building. — The majority of isolated plants operated with high-speed engines shows a marked fluctuating quality in the light. This is usually increased at irregular intervals where high-speed electric elevators are operating on 350 ENGINEERING OF POWER PLANTS the same plant. It is also frequently found that in the summertime the space directly above the boiler is hard to rent on account of the heat coming up through the floor from the engine room below. There is also the damage and annoyance caused by vibration in the building. 4. Losses of Time on Account of Obstruction of Entrances by Coal Teams. — Some of the firms which have discontinued the use of their own plants and gone on central-station service have been particularly desirous of getting the steam service also in order that they might discontinue the delivery of coal to their buildings, and thereby be able to receive and deliver goods without any interference with coal teams. 5. Losses on Account of Smoke Fines, or Dirt in the Building, due to Operation of the Boilers. — In large Western cities where soft coal is used, there has been an active campaign started to prevent the emission of smoke, and a number of these cities have laws imposing fines on the owners of smoky chimneys. 6. Losses on Account of Strikes, due to Labor Troubles. — If the above costs of operation are carefully tabulated and are based not on the theo- retical economy of apparatus operating at maximum load when new and under special conditions, but on the average operating economy as found in plants, they will show a substantial saving by the use of central- station service, providing the rates for central-station service correspond with those recently made in many of our large cities. Heating Station. — Gifford states that in the heating station we have the same general subdivision in our subject, (1) steam and (2) water. Steam systems divided into (a) vacuum and (6) pressure, and water systems are divided into (a) open and (6) closed systems. Steam System. — The vacuum system has a low pressure on the steam main and a vacuum or suction on the return main. Pumps are used to create the vacuum and thereby to cause the return water to come back to the plant. Its operation is as follows: The steam is generated in the boiler and passes either through the engines, after which the oil is extracted, or direct to the pipe line. Through the pipe line it goes to the buildings. It is there condensed and the condensation returns to the plant via the return line and is usually emptied into a storage tank. Here it is stored until the boilers need it. It passes from the tank to the feed-water heater, then through the economizer, if one is used, and then into the boiler again. The pressure system is like the above except that there is no return and, consequently, no vacuum pump. The pressure carried on this system is optional with the designer, but better practice seems to be to keep the pressure as low as possible, especially if the engines exhaust into the heat- ing mains. Some engineers design, in straight-fuel-burning plants, DISTRICT HEATING 351 high-pressure systems and reduce the pressure at the service of each building or in the high-pressure feeder lines, but this practice has never been very popular and its advantages have never been proven. The mod- ern practice seems to be a low-pressure system (3 to 10 lb.) with high- pressure feeders to be used as such only when necessary. The operation of a pressure system is very simple. The steam is gen- erated in the boilers and goes from there to the engines and then to the pipe line, if an exhaust steam plant. If not, the steam goes direct to the pipe line and through the pipe line to the buildings. Here it is condensed and the condensed water cooled as much as possible and then dumped into the sewer. The pressure system is used more extensively than the vacuum system. The vacuum system allows a somewhat lower pressure on the engines and also furnishes the return water for reuse, which is a benefit sometimes. Water Systems. — The open system of hot-water heating gets it name from the fact that the system is open to the atmosphere at one point. In this system we find the open heater or com-mingler used. The operation is as follows : The water returns from the pipe line and passes through a relief valve to the open heater or com-mingler where it is reheated to as high a degree as there is exhaust or live steam to heat it. It then goes through the circulating pump and is forced, if sufficiently heated, out into the line again. If not sufficiently hot it is forced through a closed high-pressure condenser or heater, or through a circulating boiler where it is reheated more, before going out into the pipe line and to the buildings. After it goes through the buildings it returns to the plant again. In this system the steam and circulating water mix in the open heater or the com-mingler and water is, therefore, added to the system. Con- sequently, it is necessary to supply some means of relief which is done by placing a relief valve on the return line; when the pressure exceeds a certain point, which it will do if water is added, the valve will open and discharge into the storage tank. This can also be accomplished by float- ing the storage tank on the return line and letting the overflow go direct to the tank, but this arrangement does not allow any appreciable change in the return pressure, which change is sometimes desirable. The advantage of this system is that all the heat in the steam is transferred into the circulating water, this giving us a high efficiency in the transmission of the heat, but it requires more energy in the pump- ing of the water due to the reduction in the pressure which is necessary in order to mix the steam and water and liberate the air. Liberating or extracting the air is simple in an open heater because the pressure on the heater is the same as the atmosphere and a vent open to the air will carry off the air. In a com-mingler where from 3 in. to 16 352 ENGINEERING OF POWER PLANTS in. of vacuum is maintained on the exhaust steam line it is not so simple, but this can be accomplished by means of tanks which work very well. The difference in operation between a com-mingler and an open heater is that the com-mingler will create a vacuum on the engine exhaust and the open heater will not. However, the com-mingler will operate at atmospheric pressure if it is desired. The open system throws all the condensed steam into the heating mains, which is an advantage in one way, in that it keeps the heating mains full of good water and is a disadvantage in that it takes this water away from the boiler. But with a tight pipe line the water discharged from the overflow of the pipe line soon becomes fairly good because all make-up water is condensation and, consequently, the water for the boil- ers, which should be taken from the storage tank, will soon be diluted with sufficient good water to make the feed water fairly good, so that this disadvantage is not troublesome. The closed system of hot-water heating operates as follows: The water returns to the plant and goes through the circulating pumps. In this way the pumps handle the coolest water, which is some advantage. Then it goes through the exhaust steam condenser or heater and then, if not sufficiently warm, it goes through the high-pressure steam heater or the circulating or reheater boilers. Sometimes the circulating water is forced through economizers. This is a very good arrangement. After the water is reheated sufficiently, it is forced out through the pipe line through the buildings and back to the plant. The closed system operates on less power requirements in its circula- tion of water. The fact that it does not mix the steam with the water insures good feed water for the boilers. The heat transmission of the condensers or closed heaters in this system is not as great as in the open heater or com-mingler in the open system. All water entering the sys- tem should be treated so as to take out as many of the impurities as pos- sible and thus keep the line in good shape by putting in only good water. Which system to adopt is a question that can be decided only after local conditions are known. It is a difficult matter sometimes to deter- mine — and generalities in this connection are misleading. If a steam plant is decided upon, it is not difficult to figure out which system, vacuum or pressure, will be the most economical. If a water plant has been chosen, it is more difficult to decide whether an open or a closed system will be the better. If a vacuum is desired on the engines, an open system with a com-mingler is a desirable and logical choice. If there are no engines to be considered as, for instance, in a straight-fuel-burning plant, a closed system answers the purpose better than an open system because it requires less power to handle the circulation. A closed system will create a vacuum if the condenser surface is sufficiently large and the water DISTRICT HEATING 353 temperature is not carried too high and if there is not too much steam to condense. As a general rule, if the hot-water plant is a byproduct to an electric plant, an open system is the better. If not a byproduct plant, the closed system is, perhaps, preferable. After the system has been decided upon, the details of the design can be determined. In deciding upon these points capacity and efficiency are the main features to be considered. Durability is also important and so is the expense of maintenance. 23 CHAPTER XVIII THE POWER PLANT OF THE TALL OFFICE BUILDING 1 Probably the best illustration of compact power installations to meet the heating, ventilating, lighting, power and sanitary demands of a good- sized town or small city is found in the plants of tall office buildings and modern hotels. Data from 17 such plants show the cost of electric current to be made up of labor, coal and handling ashes, water, lamps, oil and supplies, re- pairs, central station service where used for periods of minimum consump- tion to allow shutting down of the plant, and interest and depreciation. Roughly these figures average : labor, }i ; coal, }i ; interest and depre- ciation, J^fo or more; and the sum giving the cost of power as made up of the minor items. The mean load throughout the day is usually about 50 per cent, of the full load. The maximum load is required only an hour or two in the after- noon during the winter months. It is customary to allow about 50 per cent, reserve over the estimated peak loads in designing the boiler plant. Division of the Load. — The average power required during the differ- ent portions of the year is shown in the following table: Per cent, of total Lights, kw. Power, kw. Total, kw. Absolute peak load 70 60 30 30 20 16 214 184 92 92 62 49 20 20 20 20 20 20 234 Average peak and running load, dark days Average peak load for 8 months 203 112 Average day load for 8 months 112 Average day load for 6 months 82 Average low days for 12 months 69 Average nights, Sundays and holidays 50 In addition to the above there is usually an increase of 10 per cent, over the above running loads on account of the special needs of tenants. Under ordinary conditions it is customary to allow 1.6 hp. in engines for each kilowatt output of the generator and 1.8 hp. in boilers for each kilowatt in generators. Selection of Plant. — In accordance with the above the following main plant would be selected, which gives elasticity in its working and will take care of the following conditions: Summarized from "The Power Plant of the Tall Office Building" by J. H. Wells, Transactions A.S.M.E., vol. 25, p. 685. 354 POWER PLANT OF THE TALL OFFICE BUILDING 355 1. Maximum load 70 per cent, of total connected load + 10 per cent. = 257 kw. 2. Average day load for 8 months 30 per cent, of total connected load + 10 per cent. = 123 kw. To operate under these conditions the following plant will meet the requirements. Two generators of 125-kw. capacity each, either of which will carry the average peak running load, or both connected will carry the absolute peak loads which are on for short isolated periods only. One generator of 100-kw. capacity to carry early running and low average loads for 12 months. One generator of 50-kw. capacity as an auxiliary unit for nights, holidays, Sundays and odd times. Such a plant in operation was called upon for the following : Kilowatt-hours of lighting load January 33,670 May 19,301 September 17,688 February 25,388 June 18,200 October 25,542 March 24,462 July 16,600 November 33,696 April 19,950 August 17,928 December 40,425 Assuming, therefore, a total output through the busbars of 431,050 kw.-hr. per year, the engines would generate 1.6 X 431,050 = 689,680 hp.-hr. and the boilers would generate 1.8 X 431,060 = 775,890 hp.-hr. Assuming an engine guarantee of 24 lb. of steam per hp.-hr. and 8 lb. of water per pound of coal, then the total coal will be 1,164 tons and the water required will be 297,942 cu. ft. It is safe to assume that only 50 per cent, of the water is wasted and the remainder returned to the boilers. Taking cost of coal at $3.75 per ton; water at 10 cts. per 100 cu. ft. (New York prices); oil and waste at $4.60; interest and depreciation (if one-half be charged to this account), $3,000; ash removal, $218.25 (5 per cent, of cost of coal) ; and charging one-half the cost of the force in the fire and engine rooms to this account, or $2,500, makes the total cost of operating the electric plant $10,632, or approximately 2.5 cts. per kw.-hr. Estimating Boiler Capacity Required. — Hubbard gives the following methods of computing the boiler capacity required in office buildings. Heating. — Boiler power for heating is usually obtained from the amount of radiating surface to be supplied, and for all practical purposes the following ratios may be used, in which it is assumed that 1 boiler 356 ENGINEERING OF POWER PLANTS hp. will supply 130 sq. ft. of direct cast-iron radiation, 100 sq. ft. of direct wrought-iron pipe coils, 50 sq. ft. of indirect cast-iron radiation. Boiler power computed in this manner should be increased about 5 per cent, for losses due to radiation from steam and return mains. Ventilation. — Boiler power required for ventilation is based on the volume of air to be supplied. This may be found by the rule that the horsepower is equal to the cubic feet of air to be warmed per hour from zero to 70°, multiplied by 1.3 and divided by 33,000. Power for Lights. — In finding the boiler power for lighting, first determine the electrical energy to be supplied at the lamps, then find the indicated horsepower of the engines necessary to produce this, and then compute the probable quantity of steam required from the type of engine to be used. In computing the approximate electrical horsepower at the lamps it may be assumed that in general for offices, assembly halls, etc., approxi- mately 1.25 watts will be required per square foot of working plane for good lighting. The efficiency of a first-class generating set, including the losses in transmission, may be taken as about 75 per cent, when located in or near the building to be lighted, so that the electrical horsepower necessary to supply the lamps divided by 0.75 will give the indicated horsepower of the engines. The total weight of steam required, in pounds per hour, divided by 30, will give the approximate boiler horsepower. Driving Fans. — Power for driving the fan motors may be included with the power for lighting, by assuming 1 hp. of electrical energy deliv- ered to the motors for each 2,000 cu. ft. of air to be removed by the fans per minute. Hot Water. — The boiler power for hot-water heating may be deter- mined by multiplying the number of gallons of water to be heated per hour by the increase in temperature and by 8.3, then divide by 33,000 to reduce to horsepower. The temperature increase may be taken as 140° under average conditions. Elevators. — The horsepower required for raising an elevator is found by multiplying the sum of the live load, which averages about 70 lb. per square foot of floor space in the car, and the unbalanced weight of car, which may be taken as approximately 25 lb. per square foot of floor space in hydraulic elevators, and for drum and duplex electric elevators, by the speed in feet per minute, average 400 to 600. Divide this product by the efficiency, average about 0.6, and divide again by 33,000 to reduce to horsepower. Allowing for stops and time when the elevators are idle it is customary to consider that each elevator is in operation 0.7 of the time. As hydrau- POWER PLANT OF THE TALL OFFICE BUILDING 357 lie elevators are not counterweighted up to their full weight, they descend by gravity, so power is required only on the upward trip. The above rule is for a continuous upward movement, hence, if the elevator is in operation only 0.7 of the time, and one-half the time that it is in actual operation is occupied in downward trips, requiring no power, the results found by the above calculation should be multiplied by 0.7 times 0.5 when considering a hydraulic elevator. Substituting the average values as given above shows the required horsepower for each square foot of floor space in the car to be (70 + 25) X 400 X 0.7 X 0.5 -f- 0.6 X 33,000 = 0.7 Hence, the total square foot floor area of the elevator cars multiplied by 0.7 will give the horsepower to be delivered by the pumps. The necessary boiler power will depend upon the type of pump used. The .following table gives the average steam consumption in pounds per delivered horsepower per hour for different types of duplex pumps. Rate of steam ^Pe of pump Toundfpe?' horsepower-hour Simple non-condensing 150 Compound non-condensing 85 Triple non-condensing 45 High-duty non-condensing 35 The total horsepower required multiplied by the rate of steam con- sumption divided by 30 will give the boiler horsepower. For electric elevators the foot-pounds per minute are readily deter- mined and hence the horsepower for each square foot of floor surface in the cars. Assuming a combined efficiency of 0.65 for the engine, generator and motor, the indicated horsepower of engine square feet of floor surface in the cars is determined and this multiplied by the total floor space, in square feet, will give the total indicated horsepower of the engines. From this point on the method of obtaining the boiler horsepower is the same as already described in the case of electric lighting. Refrigeration. — The capacity of a refrigerating plant is commonly ex- pressed in two ways: " ice-melting effect" and "ice making." For ex- ample, a 20-ton machine will produce the same cooling effect in 24 hr. as the melting of 20 tons of ice, or in other words, will extract the same amount of heat from the brine as would be required to melt 20 tons of ice into water at a temperature of 32°. Theoretically, the extraction of this amount of heat from 20 tons of water, at an initial temperature of 32° should change into ice; but in practice there are various losses not present in the simple process of cool- ing, so that it is customary to allow for twice the boiler power per ton 358 ENGINEERING OF POWER PLANTS for ice making as for the process of cooling or ice-melting effect. The indicated horsepower required per ton of refrigeration depends upon the suction and condenser pressure, which in turn are governed by the temperature and amount of the condensing water used. Under conditions where condensing water must be obtained at average city prices the most economical results are obtained with suction pressures ranging from 20 to 30 lb. and condenser pressures of 140 to 150 lb. Under these conditions one i.hp. in the steam cylinder will produce about 60 lb. of ice-melting effect per hour, or 0.75 ton per 24 hr. This will, of course, vary somewhat with the range of pressures and also with the size and type of machine, but in the absence of more exact data, may be used for approximate results. Another method in common use is to provide 1.5 i.hp. per ton of refrigeration, which is slightly more than the previous case. Knowing the indicated horsepower of the compressor, the probable steam consumption can be determined for the particular type of engine used. Comparative Costs of Private and Central Station Heating and Power. ■ — To illustrate the comparative costs of private plants vs. central station heating and power, Bushnell and Orr present 1 the following figures from a building recently analyzed in Chicago. This building is a large office building about 200 ft. square and 21 stories in height. It has a court in the center above the first floor 73 ft. square. The original estimate of the steam consumption based on formulae was 63,2Q0,000 lb. The actual consumption during the year 1913 as shown by meters was in round numbers 64,300,000 or about 1,100,000 lb. over the estimate. As the steam consumption in any building will vary ordinarily a much larger percentage from season to season, the estimate given may be con- sidered fairly accurate. The original estimate for consumption of elec- tricity was 1,250,000 kw.-hr. The consumption in 1913 was 1,100,000 kw.-hr. If a plant had been installed in the building, the consumption would probably have been about 50,000 kw.-hr. more, and as the building is not quite rented a complete rental of the building would probably bring the current consumption very nearly up to the estimate. The actual consumption for this building was in round numbers 500,000 kw.-hr. for tenants' lighting, 150,000 kw.-hr. for public lighting and 450,000 kw.-hr. for power, of which about three-quarters was con- sumed by the elevator equipment. Assuming a price for electricity of 2J-2 cts. per kw.-hr. from the central-station service and a price of 40 cts. per 1,000 lb. for steam on central-station service, it is very easy to figure the cost of central-station service on this basis. Let us assume that the building will be fully rented and that the total consumption is 1 Bushnell and Orr, "District Heating." POWER PLANT OF THE TALL OFFICE BUILDING 359 1,150,000 kw.-hr. We will also assume that the building purchases its entire requirements both for steam and electricity and retails the elec- tricity to its own tenants. The total bills for the building would be: 1,150,000 kw.-hr. at 2% cts. per kilowatt-hour $28,750 64,300,000 lb. of steam at 40 cts. per 1,000 lb 25,720 Total $54,470 In figuring the cost of isolated plant service, it will be necessary to add the cost of electricity for lights in engine and boiler rooms, and also the cost for ventilating same. Assuming, therefore, that this amounts to 50,000 kw.-hr. per year, the total electricity used by the plant would be 1,150,000 kw.-hr. plus 50,000 kw.-hr. or 1,200,000 kw.-hr. per year. The average steam consumption in office building plants as shown by a number of tests taken on typical installations is about 60 lb. of steam per kilowatt-hour throughout the year. While the above would represent average conditions, in this comparison it would be better to assume 50 lb. since in a large building such as this, it would be possible to get an economy above the average. 1,200,000 kw.-hr. of electricity at 50 lb. per kilowatt-hour would require 60,000,000 lb. of steam per year. It is fair to assume that about 40 per cent, of this would be saved for heating by utilizing the exhaust from the engines. This would leave a net steam consumption of 60 per cent, of 60,000,000 or 36,000,000 lb. It has been shown by meter readings that the heating requirements of the buildings are 64,300,000 lb. of steam. Adding together the steam required for electricity and the steam for heating, gives a total of 100,300,000 lb. or in round numbers 100,000,000 lb. of steam per annum. The average evaporation in this plant runs about 5 lb. of steam per pound of coal. If a power plant were operated all summer long the average evaporation would be somewhat higher, say 5J£ lb. of steam per pound of coal. On the basis of 100,000,000 lb. of steam, the annual coal consumption would be 18,181,818 lb., or in round figures 9,000 tons. On this basis the operating expenses would be as follows: Supplies 9,000 tons of coal at $2.75 per ton $24,750 Ash removal, 6 per cent 1,485 Water, for steam supply, washing out boiler and engine room, etc 1,000 Oil, waste and packing 1,200 Tools and miscellaneous supplies 1,200 Boiler and fire insurance 60 Total $29,695 360 ENGINEERING OF POWER PLANTS Labor Chief engineer $3,000 Assistant to chief engineer 1,500 Three watch engineers 3,600 Two oilers 1,920 Engineer's clerk 480 Three firemen at $840 2,520 Two ashmen at $720 1,440 Liability insurance and losses from sickness among employees 1,000 Time of office, including manager's time for super- vising 1,000 16,460 Total operating expenses $46,155 In addition to the operating costs we must include the: Fixed Charges. — To take care of this building which has an aggregate installation of about 15,000 50-watt lamps, 200 hp. in general power and 600 hp. in elevator power, or a total connected equipment of about 1,800 hp., it will be necessary to install a plant of about 1,200 kw. which would cost complete at $50 per kilowatt about $60,000. The plant would also require space of upward of 6,000 sq. ft. On the above basis the fixed charges would be as follows : Amortization at 3 per cent $1,800 Obsolescence at 5 per cent 3,000 Interest at 6 per cent 3,600 Repairs at 2 per cent -. 1,200 Taxes at 1 per cent 600 Rental value of space at 50 cts. per square foot 3,000 Marginal charge for diversion of capital at 5 per cent 3,000 Total $16,200 Summarizing the above gives: Operating charges $46,155 Fixed charges 16,200 Total $62,355 It will be noted that the cost for labor to take care of the elevators, electric fans, etc., as well as the radiation has been omitted from both estimates as they are practically equal in both propositions. Comparing this with the above cost of central-station operation, we find a saving of about $8,000 per year. As a matter of fact the central station costs in Chicago are slightly under these figures. If the price for electricity, however, were 4 cts. per kilowatt-hour and the price of steam 50 cts. per 1,000 lb., the situation would be reversed, and there would be a saving of POWER PLANT OF THE TALL OFFICE BUILDING 361 about $16,000 in the operation of an isolated plant. In other words, the result is not determined by the cost of isolated plant operation, but by the rates offered by the central-station company. The above figures are given as average figures and may be found to be higher or lower in different localities and in different plants. The fact that some of the largest buildings in Chicago now operating plants are running at considerably higher expense than that assumed in this esti- mate tends to show that the estimated cost of isolated plant service is conservative. Problems ^^-—62. A 10-story office building occupies a ground area of 15,000 sq. ft. and has a cubic capacity of 2,000,000 cu. ft. There is 1 sq. ft. of direct cast-iron radiating sur- face installed per 90 cu. ft. of space. The elevator equipment is four 10-passenger elevators, 600 ft. per minute; one 1-ton freight elevator, 400 ft. per minute. All elevators are motor-driven. The first floor is ventilated, 10 changes of air being provided per hour. Hot-water service heaters will provide 1,000 gal. of water per hour at 180°F. The engines are simple high-speed, arranged to run condensing in summer and to exhaust into the heating system in winter. Determine the capacity of generating equipment required for the building. Will extra boiler capacity be required for heating? If so, what is total capacity required. CHAPTER XIX THE POWER PLANT OF THE STEAM LOCOMOTIVE The most compact steam power plant in daily commercial use is found in the locomotive. Horsepower. — The indicated horsepower of the locomotive may be computed as for any steam engine, but it is sometimes more convenient to use the following formula: Let p = mean effective pressure in pounds per square inch. d = diameter of cylinder in inches. S = length of stroke in inches. M = speed in miles per hour. D = diameter of driving wheel in inches. Then for two cylinders pd*SM lhp ' = "375D ' The indicated horsepower of some of the latest type compound loco- motives runs as high as 2,500. Efficiency. — The power required to overcome the friction of the mov- ing parts of the locomotive and to drive the locomotive and tender varies from 10 to 30 per cent, of the developed power. Tractive Force. — Simple Locomotives. — Let F = indicated tractive force in pounds. p = mean effective pressure in the cylinder in pounds per square inch. S = stroke of piston in inches. Wk d — diameter of cylinders in inches. D = diameter of driving wheels in inches. Then 4:*d 2 pS d 2 pS. F = 4irD D If the drop in pressure of the steam due to expansion, friction and wire drawing be taken into account, then the formula becomes 0.$Pd 2 S Actual tractive force = D in which P = boiler pressure in pounds per square inch. 362 THE POWER PLANT OF THE STEAM LOCOMOTIVE 363 Compound Locomotives. — The Baldwin Locomotive Works formulae for compound locomotives of the Vauclain four-cylinder type are ' C 2 SX0.67P „ c 2 SX0.25P F = D + W— in which C = diameter of high-pressure cylinder in inches, c = diameter of low-pressure cylinder in inches. For a two-cylinder cross-compound the formula is simply „ C 2 S X 0.67P F = D The formulae apply for speeds not over 10 miles per hour above which the tractive power rapidly falls off. The limit of hauling capacity of a locomotive is usually from one-fifth to one-fourth of the weight on the drivers. Drawbar Pull. — The drawbar pull or tractive force of a locomotive is the force exerted at the drawbar or connection to the train as indicated on a dynamometer. This force is limited by the weight on the driving wheels and by the power of the engine. The drawbar pull at that point where the driving wheels begin to slip is known as the adhesion of the locomotive. Adhesion varies with the coefficient of friction between steel and steel under given track conditions. The use of sand under the drivers is to increase the coefficient of friction. Values of Coefficient of Friction Good conditions, dry rail / = . 20 to . 25 Maximum with sand / = . 33 Wet sloppy rail as in fog / = . 15 Worst condition / = . 125 Tractive force = weight on drivers X /. Under good conditions the drawbar pull necessary to haul 1 ton of 2,000 lb. varies from 6 to 8 lb. on level track and increases with curves and grades. Two formulae in general use for determining the resistance are V R = 2 + -7 {Engineering News formula). V R = 3 + -x (Baldwin Locomotive Works formula). in which R = resistance in pounds per ton (2,000 lb.) on straight, level track, and V = velocity in miles per hour. The increased resistance due to grade is as follows: 364 ENGINEERING OF POWER PLANTS If the grade be 1 ft. per mile, the pull required to lift 2,000 lb. will be 2,000 Q7C _ tubt, = 0.3788 lb. 5,z©U Total resistance due to grade in pounds per ton (2,000 lb.) = 0.3788 X rise in feet per mile. If the grade is expressed in per cent, the resistance in pounds per ton (2,000 lb.) will reduce to 20 lb. for 1 per cent, grade. The resistance due to curves is not easily determined. G. R. Hender- son in " Locomotive Operation" estimates this resistance at 0.7 lb. per ton (2,000 lb.) per degree of curve. (Degree of curve = the angle at the center subtended by a chord of 100 ft.) Resistance in pounds per ton = 0.7 c. in which c = number degrees of curve. This value is greater for locomotives, often being as high as 1.4 c. y2 2 _ y 2i Resistance due to acceleration = 70 ~ in which Vi and Vi = velocities in miles per hour and S = distance in feet. Increased Economy with Increase of Pressure. — Tests reported (Bulletin No. 26, University of Illinois Experiment Station) show the following increase in economy with increase in boiler pressure : Boiler pressure, lb. per sq. in 120 140 160 180 200 220 240 Steam per i.hp.-hr., lb 29.1. 27.7 26.6 26.0 25.5 25.1 24.7 Coal per i.hp-hr., lb 4.0 3.8 3.6 3.5 3.4 3.4 3.3 Effect of Speed on Average Steam Pressure. — C. H. Quereau points out (Engineering News, Mar. 8, 1894) that the mean steam pressure (and consequently the power of the engine) decreases as the speed of the loco- motive increases. He gives the following figures: Miles per hour 46 51 51 53 54 57 60 66 R.p.m 224 248 248 258 263 277 292 321 Pressure, lb. sq. in 51.5 44.0 47.3 43.0 41.3 42.5 37.3 36.3 Two- cylinder compound Single-expansion Revolutions Miles per hour Water per i.hp. per hour Revolu- tions Miles per hour Water per i.hp. per hour 100 to 150 21 to 31 18.33 1b. 151 31 21.70 150 to 200 31 to 41 18.91b. 219 45 20.91 200 to 250 41 to 51 19.71b. 253 52 20.52 250 to 275 51 to 56 21.4 1b. 307 63 20.23 321 66 20.01 THE POWER PLANT OF THE STEAM LOCOMOTIVE 365 Effect of Speed on Steam Consumption. — Mr. Quereau also gives in the same article the foregoing table relating to the variation of steam con- sumption with speed. Depreciation of Locomotives. — Kent quotes the Baldwin Locomotive Works as suggesting that for the first 5 years the full second-hand value of the locomotive (75 per cent, of first cost) be taken; for the second 5 years 85 per cent, of this value; for the third 5 years, 70 per cent.; after 15 years, 50 per cent, of the second-hand value; and after 20 years, and as long as the engine remains in use, 25 per cent, of the first cost. Use of Superheated Steam. — Superheated steam is now quite gen- erally used in locomotive practice. Its use has resulted in increased steam economy and less trouble from water of condensation in the cylin- ders. The saving in water consumption per horsepower-hour is reported to be some 10 or 12 per cent, over that with saturated steam, with a cor- responding saving of 10 to 15 per cent, in fuel consumption. Mechanical Stokers for Locomotives. — The use of mechanical stokers on locomotives is rapidly developing. Mr. W. S. Bartholomew 1 reports that in September, 1915, there were about 1,000 such stokers in use in the United States. The special gains by the use of stokers is summed up by Mr. Bar- tholomew as follows: It is evident that the railroad companies and the enginemen both profit by the application of mechanical stokers to locomotives. Locomotive capacity is increased, while, strange as it may seem, the fireman's labor in shoveling coal and his suffering from the heat are materially reduced. The railroads secure a return on their investment from the increased tonnage, less expensive fuel, and other economies effected, and the men, individually, make more money per month with less effort. Small locomotives are made larger, and large locomotives are made possible. These and other results are being accomplished by stokers designed to be applied to existing power with the necessary limitations that come thereby, and much more may reasonably be expected in the future, now that the stoker has established itself for permanent use, as stokers will be taken seriously into account in the designing of new heavy power to be built in the future for capacity as well as economy. The best idea of the performance of the steam locomotive is probably secured by an examination of the conclusions of the special committee appointed to cooperate with the Pennsylvania R. R. in conducting tests 1 See complete review of "Mechanical Stoking of Locomotives," by W. S. Bar- tholomew, Journal of the Franklin Institute, September, 1915. 366 ENGINEERING OF POWER PLANTS of locomotives at the St. Louis plant during the Exposition of 1904. The conclusions are as follows: BOILER PERFORMANCE 1. Contrary to common assumption, the results show that when forced to maximum power the large boilers delivered as much steam per unit area of heating surface as the small ones. 2. At maximum power, a majority of the boilers tested delivered 12 or more lb. of steam per square foot of heating surface per hour; two de- livered more than 14 lb.; and one, the second in point of size, delivered 16.3 lb. These values expressed in terms of boiler horsepower per square foot of heating surface are 0.34, 0.40 and 0.47 respectively. 3. The two boilers holding first and second place with respect to weight of steam delivered per square foot of heating surface are those of passenger locomotives. 4. The quality of the steam delivered by the boilers of locomotives under constant conditions of operation is high, varying somewhat with different locomotives and with changes in the amount of power developed between the limits of 98.3 per cent, and 99.1 per cent. 5. The evaporative efficiency is generally maximum when the power delivered is least. Under conditions of maximum efficiency most of the boilers tested evaporated between 10 and 12 lb. of water per pound of dry coal. The efficiency falls as the state of evaporation increases. When the power developed is greatest its value commonly lies between limits of 6 and 8 lb. of water per pound of dry coal. 6. The smoke-box temperature for all boilers, when working at light power, is not far from 500°F. As the power is increased the tempera- ture gradually rises, the maximum value depending upon the extent to which the boiler is forced. For the locomotives tested it lies between 600° and 700°F. 7. With reference to grate area, the results prove beyond question that the furnace losses due to excess air are not increased by increasing the area. In general, it appears that the boilers for which the ratio of grate surface to heating surface is largest are those of greatest capacity. 8. A brick arch in the firebox results in some increase in furnace temperature and improves the combustion of the gases. 9. The loss of heat through imperfect combustion is in most cases small, except as represented by the discharge from the stack of solid particles of fuel. 10. Relatively large firebox heating surface appears to give no ad- vantage either with reference to capacity or efficiency. The fact seems to be that the tube-heating surface is capable of absorbing such heat as may not be taken up by the firebox. THE POWER PLANT OF THE STEAM LOCOMOTIVE 367 11. The value of the Serve tube over the plain tube of the same outside diameter, either as a means for increasing capacity or efficiency, was not definitely determined. 12. The draft in the front end for any given rate of combustion, as measured in inches of water, depends upon the proportions of the locomotive and the thickness and condition of the fire. Under light power its value may not exceed an inch, but it increases rapidly as the power increases. Representative maximums derived from the tests lie between the limits of 5 in. and 8.8 in. 13. Insufficient openings in the ash-pans and the mechanism of the front end, especially the diaphragm, are shown by the tests to lead to the dissipation of considerable portions of the draft force. THE ENGINE 14. The indicated horsepower of the modern simple freight locomotive tested may be as great as 1,000 or 1,100; that of a modern compound passenger locomotive may exceed 1,600. 15. The maximum indicated horsepower per square foot of grate surface lies, for the freight locomotives, between the limits of 31.2 and 21.1; for passenger locomotives, between 35.0 and 28.1. 16. The steam consumption per indicated horsepower-hour necessarily depends upon the conditions of speed and cut-off. For the simple freight locomotives tested the average minimum is 23.7. The consumption when developing maximum power is 23.8, and when under those conditions which proved to be least efficient, 29.0. 17. The compound locomotives tested, using saturated steam, con- sumed from 18.6 to 27 lb. of steam per indicated horsepower-hour. Aided by a superheater, the minimum consumption is reduced to 16.6 lb. of superheated steam per indicated horsepower-hour. 18. In general the steam consumption of simple locomotives decreases with increase of speed, while that of the compound locomotive increases. From this statement it appears that the relative advantages to be de- rived from the use of the compound diminish as the speed is increased. 19. Tests under a partially opened throttle show that when the degree of throttling is slight the effect is not appreciable. When the degree of throttling is more pronounced, the performance is less satisfactory than when carrying the same load with a full throttle and a shorter cut-off. THE LOCOMOTIVE AS A WHOLE 20. The percentage of the cylinder power which appears as a stress in the drawbar diminishes with increase of speed. At 40 r.p.m. the 368 ENGINEERING OF POWER PLANTS maximum is 94 and the minimum 77; at 280 r.p.m. the maximum is 87 and the minimum 62. 21. The loss of power between the drawbar and the cylinder is greatly affected by the character of the lubricant. It appears from the tests that the substitution of grease for oil upon axles and crankpins increases the machine friction from 75 to 100 per cent. 22. The coal consumption per dynamometer horsepower per hour for the simple freight locomotives tested is, at low speeds, not less than 3.5 lb., nor more than 4.5 lb., the value varying with the running condi- tions. At the highest speeds covered by the tests the coal consumption for the simple locomotives increased to more than 5 lb. 23. The coal consumption per dynamometer horsepower per hour for the compound freight locomotives tested is, for low speeds, between 2 and 3.7 lb. Results at higher speeds were obtained only from a two- cylinder compound, the efficiency of which under all conditions is shown to be very high. The coal consumption per dynamometer horsepower-hour for locomotive at the higher speed increases from 3.2 to 3.6 lb. 24. The coal consumption per dynamometer horsepower-hour for the four compound passenger locomotives tested varies from 2.2 to more than 5 lb., depending upon running conditions. In the case of all these locomotives the consumption increases rapidly as the speed is increased. 25. A comparison of the performance of the compound freight locomotives with that of the simple freight locomotives, is very favorable to the compounds. For a given amount of power the compound shows an average saving over the best simple of over 10 per cent., while the best compound shows a saving over the poorest simple of not far from 40 per cent. It should be remembered, however, that the conditions of the tests, which provide for the continuous operation of the locomotives at constant speed and load throughout the period covered by the observa- tions, are all favorable to the compound. 26. It is a fact of more than ordinary significance that a steam loco- motive is capable of developing a horsepower at the drawbar upon the consumption of but a trifle more than 2 lb. of coal per hour. This fact gives the locomotive high rank as a steam power plant. 27. It is worthy of mention that the coal consumption per horsepower- hour developed at the drawbar by the different locomotives testedjpre- sents marked differences. Some of these are easily explained from a consideration of the characteristics of the locomotives involved. Where the data are not sufficient to permit the assignment of a definite cause there can be no doubt that an extension of the study already made will reveal it. THE POWER PLANT OF THE STEAM LOCOMOTIVE 369 Average Heat Balance for Test Locomotive. — Percentages of Total Heat Available Absorbed by the water in the boiler 52 Absorbed by the steam in the superheater 5 Lost in vaporizing moisture in the coal 5 Lost through the discharge of CO 1 Lost through the high temperature of escaping gases, the products of combustion 14 Lost through unconsumed fuel in the form of front-end cinders 3 Lost through unconsumed fuel in the form of cinders or sparks passed out of the stack 9 Lost through unconsumed fuel in the ash 4 Lost through radiation, leakage of steam and water, etc 7 100 Fuel Expense of Locomotives. — The fuel bills of a railroad constitute ordinarily about 10 per cent, of the total expense of operation, or from 30 to 40 per cent, of the actual cost of running the locomotive. There were in 1906, on the railroads of the United States 51,000 locomotives. It is estimated that these locomotives consumed during the year not less than 90,000,000 tons of fuel, which is more than one- fifth of all the coal, anthracite and bituminous, mined in the coun- try during the same period. The coal thus used cost the railroad $170,500,000. Observations on several representative railroads have indicated that not less than 20 per cent, of the total fuel supplied to locomotives per- forms no function in moving trains forward. It disappears in the incidental ways just mentioned or remains in the firebox at the end of the run. The fuel consumption accounted for by the heat balance is, there- fore, but 80 per cent, of the total consumed by the average locomotive in service. Applied on this basis to the total consumption of coal for the country, the heat balance may be converted into terms of tons of coal as follows : Summary of results obtained from fuel burned in locomotives. Tons 1. Consumed in starting fires, in moving the locomotive to its train, in backing trains into or out of sidings, in making good safety-valve and leakage losses, and in keeping the locomotive hot while standing (estimated) 18,000,000 2. Utilized, that is, represented by the heat transmitted [to water to be vaporized 41,040,000 3. Required to evaporate moisture contained by the coal.. . 3,600,000 4. Lost through incomplete combustion of gases 720,000 5. Lost through heat of gases discharged from the stack 10,080,000 6. Lost through cinders and sparks 8,640,000 7. Lost through unconsumed fuel in the ash 2,880,000 8. Lost through radiation, leakage of steam and water, etc. 5,040,000 90,000,000 24 370 ENGINEERING OF POWER PLANTS Elimination of the Steam Locomotive. — During the past few years much has been written regarding the electrification of terminals and even of main lines. The development is slowly but surely coming. Although it is not within the field of these notes to present any lengthy discussion of this subject, yet the conclusions of the Chicago Association of Com- merce presented in its report relating to " Smoke Abatement and Elec- trification of Railway Terminals" (1915) are of sufficient significance to warrant presentation. The conclusions regarding terminal electrifica- tion in Chicago are: . (a) That it is practicable from an engineering standpoint. (6) That when effected it will be of economic advantage to the railroads. (c) That it will present no greater element of danger to passengers and employes, if properly installed, than now exists with steam opera- tion. (d) That the most serious and difficult feature of the problem is the financial one. " Conclusions Concerning the Feasibility of Eliminating the Steam Locomotive from the Railroad Terminals of Chicago and of Meeting all Operating Requirements without Resort to Complete Electrification." Basing judgment upon the present-day achievement, 1 the following general conclusions seem to be justified: 1. There is available at this time no form of locomotive, carrying its own power and capable of handling the traffic of the Chicago railroad terminals, which would be substituted for the steam locomotive, and there is no prospect of the immediate development of any such locomotive. 2. The design of a gasoline internal-combustion locomotive capable of handling the traffic of the Chicago terminals would involve such a multiplication of engine cylinders as to make its adoption almost, if not quite, prohibitive. 3. The adoption of a gasoline internal-combustion locomotive, should the design of such a machine become practicable, would not insure smoke- less operation. As in the case of an automobile engine, such machines emit smoke when starting, and the amount of the smoke discharged is a function of the power developed. 4. The possibilities of an internal-combustion locomotive, in which the source of power is an oil engine, constitute a promising field for work. No such locomotive, possessing the power of a modern steam locomotive, has thus far been developed. The elaborate experiments of Dr. Rudolph Diesel are significant, but the results derived from them do not indicate that the problem of design has been solved. 5. The adoption of an oil-engine locomotive of the Diesel type, as- suming the details of a satisfactory design to have been worked out, will 1 April, 1914. THE POWER PLANT OF THE STEAM LOCOMOTIVE 371 not in itself suffice to secure smokeless operation. Oil engines are smoke- less only when the fuel and air supply are adjusted to suit the load. Whether an oil engine will be more or less objectionable, because of its smoke, than the existing steam locomotive, can be determined only by tests under service conditions. 6. The compressed-air storage locomotive, the hot-water storage loco- motive and the storage-battery locomotive are all devices which, judged by the present state of the art, can be made serviceable only under special or peculiar conditions where more efficient devices cannot be used. It is not to be expected that such locomotives can be introduced for general work in the Chicago terminal. 7. There are certain short stretches of track in yards and industries to which it appears impracticable to apply any form of electric contact system; in the event of the complete elimination of the steam locomotive from the Chicago terminals, it would be practicable to work this trackage with some one of the specialized forms of locomotive described, notwith- standing the fact that no one of these locomotives is sufficient for the general work of the terminals. 8. The self-propelled motor cars of any of the various types described are most valuable for a light, diversified and not too frequent traffic. The field of usefulness for such cars within the limits of the Chicago terminals, where business is segregated and the passenger movement heavy, is not extensive. 9. The complete elimination of the steam locomotive from the rail- road terminals of Chicago would, under present conditions, necessitate the abandonment of the service or the complete electrification of these terminals. CHAPTER XX FUELS Solid Fuels. — The solid fuels used for power-plant purposes may be divided into the following general classes: 1. Coal. 2. Lignite. 3. Peat. 4. Wood. According to the classification of the U. S. Geological Survey, 1 the various groups of coal and allied compounds are: (a) Graphite. (b) Anthracite. (c) Semi-anthracite. (d) Semi-bituminous. (e) Bituminous. (/) Sub-bituminous. (g) Lignite. (h) Peat. (i) Wood, cellulose. The forms of wood in common use are : wood, bagass, tan bark, straw and stubble. Coke, charcoal and artificial fuel briquettes are fuels prepared from coal and wood. Graphite. — Graphite cannot be burned with sufficient ease to warrant its use as a fuel. There are, however, extensive deposits of graphitic anthracite in Rhode Island and Massachusetts that have been exploited from time to time as fuel. Its composition is approximately carbon, 78 per cent.; volatile matter, 2.60 per cent.; silica, 15.06 per cent.; phos- phorus, 0.045 per cent. Under special treatment it has been made to burn in boiler furnaces, but with difficulty. Under suitable conditions it may be used for the generation of^producer gas. Anthracite. — The principal anthracite mines are in eastern Pennsyl- vania, although semi-anthracite coal is found in one or two other sections of the country. Anthracite is largely carbon. The commercial sizes are usually known as lump, broken, egg, stove, chestnut, pea, 1 and 2 buck- 1 Transactions A.S.M.E., May, 1905. 372 FUELS 373 wheat, rice and barley. These last two are known as No. 3 in the New York market. The heating value of the smaller sizes is considerably below that of the larger sizes as the amount of non-combustible earthy material is naturally higher in the smaller sizes. To handle the finer sizes to advantage for power-plant purposes requires specially constructed grates and forced draft. Semi-bituminous Coals. — The combustible portion of semi-bituminous coals is very uniform in composition. The volatile matter is usually from 18 to 22 per cent, of the combustible matter. Such fuels are usually low in moisture, ash and sulphur, and rank among the best steaming coals in the world. Among these coals are the Pocahontas, New River, Cumberland and Clearfield coals of Virginia, West Virginia and Maryland. These are the highest grade coals in the United States. They run low in ash, 3 to 8 per cent, and their heating value is in the neighborhood of 14,500 B.t.u. per pound or better, for the higher grades. Bituminous Coals. — Bituminous coal is found extensively in the United States especially in Pennsylvania, Ohio, Kentucky, Tennessee, Indiana, Illinois, Iowa and Wisconsin. There is a wide variation in the ash content and heating value. In general the Eastern varieties are of a higher grade than the Western. Many bituminous coals are of the caking variety thus requiring considerable attention on the part of the firemen. Sub-bituminous coal, as its name implies, is a grade between bitu- minous coal and the true lignites. It is frequently called black lignite. Some of the sub-bituminous coals, however, resemble bituminous coal so closely in physical appearance that it is hard to distinguish between them except by analysis. Its calorific value is usually less than that of bitu- minous coal. It is usually high in sulphur. It is found in the Rocky Mountain and Pacific States. Lignite. — Lignite usually shows clearly a woody structure. Fre- quently the form of the bark of trees is plainly visible, although some lig- nites have more the appearance of brown clay. The lignites of the United States resemble the brown coals of Germany. The amount of moisture is very high in the lignites, often running from 30 to 40 per cent. The localities in which lignite is found are chiefly North Dakota, South Dakota, Texas, Arkansas, Louisiana, Mississippi and Alabama. Kent states that the relation of the volatile matter and of the fixed carbon in the combustible portion of the coal enables us to judge the class to which the coal belongs, as anthracite, semi-anthracite, semi-bituminous, bituminous or lignite. Coals containing less than 7.5 per cent, volatile matter in the combustible, would be classed as anthracite, between 7.5 and 12.5 per cent, as semi-anthracite, between 12.5 and 25 per cent, as 374 ENGINEERING OF POWER PLANTS semi-bituminous, between 25 and 50 per cent, as bituminous and over 50 per cent, as lignitic coals or lignites. In the classification of the U. S. Geological Survey the sub-bituminous coals and lignites are distinguished by their structure and color rather than by analysis. In summarizing tests of the U. S. Geological Survey (Bulletins 261, 290 and 323 and Professional Paper 48) Kent presents the following valu- able table and calls attention to the fact that the table shows approxi- mately the range of heating values per pound of combustible, as deter- mined by the Mahler calorimeter, and the range of percentages of fixed carbon in the combustible (total of fixed carbon and volatile matter) in the coals from the several States. The extreme figures, 10,200 and 15,950 fairly represent the whole range of heating values of the combustible of the coals of the United States, but the figures for each State do not nearly cover the range of values in that State, and in some cases, as in Indiana and Illinois, the figures are much lower than the average heating values of the coals of the States. Fixed C, per cent. B.t.u. per pound of combustible Pennsylvania anthracite West Virginia semi-bituminous Arkansas semi-bituminous Pennsylvania bituminous West Virginia bituminous Eastern Kentucky Western Kentucky Alabama Kansas Oklahoma Missouri Illinois Iowa Indiana New Mexico Wyoming Montana Colorado North Dakota Texas 80 84 67 55 61 62 56 50 59 57 50 48 48 44 89 to 76.5 to 77.0 67 5 to 55.0 60 to 50.5 5 to 59.0 to 53.5 to 51.0 5 to 47.0 .0 to 47.5 to 53.5 49 5 to 47.0 0to41.5 48.5 46 5 to 42.5 5 to 34.0 14,900 15,950 to 15,650 15,250 to 15,500 15,500 15,500 to 15,000 15,000 14,400 to 13,700 14,800 to 14,200 14,800 to 14,100 14,600 to 13,100 14,300 to 12,600 13,700 to 12,400 13,600 to 12,700 13,300 12,500 to 12,300 13,300 to 10,900 12,100 11,500 10,200 to 11,400 10,900 to 11,000 The following analyses of representative coals of the six classes speci- fied as given by Professor N. W. Lord are: Class 1. Anthracite culm. Class 2. Semi-anthracite. Class 3. Semi-bituminous. Pennsylvania. Arkansas. West Virginia. FUELS 375 Class 4 (a). Bituminous coking. Connellsville, Pa. Class 4 (6). Bituminous non-coking. Hocking Valley, Ohio. Class 5. Sub-bituminous. Wyoming, black lignite. Class 6. Lignite. Texas. Composition of Illustrative Coals, Car-load Samples. op "Air-dried" Sample Proximate Analysis Class Moisture Vol. comb Fixed carbon Ash 1 2.08 7.27 74.32 16.33 2 1.28 12.82 73.69 12.21 3 0.65 18.80 75.92 4.63 4a 0.97 29.09 60.85 9.09 46 7.55 34.03 52.57 5.85 5 8.68 41.31 46.49 3.52 6 9.88 36.17 43.65 10.30 Loss on air drying 3.40 1.10 1.10 4.20 Undet. 11.30 23.50 Ultimate Analysis op Coal Dried at 105°C. Hydrogen Carbon . . . Oxygen . . . Nitrogen . Sulphur. . Ash 2.63 3.63 4.54 4.57 5.06 5.31 76.86 78.32 86.47 77.10 75.82 73.31 2.27 2.25 2.68 6.67 10.47 15.72 0.82 1.41 1.08 1.58 1.50 1.21 0.78 2.03 0.57 0.90 0.82 0.60 16.64 12.36 4.66 9.18 6.33 3.85 4.47 64.84 16.52 1.30 1.44 11.43 Results Calculated to an Ash- and Moisture-free Basis Vol. comb 8.91 91.09 14.82 85.18 19.85 80.15 32.34 67.66 39.30 60.70 47.05 52.95 45.31 Fixed carbon 54.69 Ultimate Analysis Hydrogen Carbon . . . Oxygen.., Nitrogen . Sulphur. . 3.16 4.14 4.76 5.03 5.41 5.50 92.20 89.36 90.70 84.89 80.93 76.35 2.72 2.57 2.81 7.34 11.18 16.28 0.98 1.61 1.13 1.74 1.61 1.25 0.94 2.32 0.60 1.00 0.87 0.62 5.05 73.21 18.65 1.47 1.62 Calorific Value in B.t.u. per Pound, by Dulong's Formula Air-dried coal 12,472 15,286 13,406 15,496 15,190 16,037 13,951 15,511 12,510 14,446 11,620 13,235 10,288 Combustible 12,889 Dulong's formula is total heat = 14,600C + 62,000(tf - -"-) + 4,000S o 376 ENGINEERING OF POWER PLANTS in which C, H, and S represent the proportions of carbon, hydrogen, oxygen and sulphur. An approximate formula sometimes used is total heat = 154.8 (100 — (per cent, of ash + per cent, of moisture)). From a table presented by Meyer (" Steam Power Plants," page 23) the following data are selected to indicate the relative value of the differ- ent classes of steam coals: Kind of coal Relative evaporative power " Equivalent evaporation," pounds Pounds of coal per square foot of grate per hour Pocahontas, W. Va. 1 100.0 91.6 80.0 80.0 67.5 84.0 79.0 74.0 9.5 8.7 7.6 7.6 6.4 8.0 7.5 7.0 15 Youghioheny, Pa. 2 17 Hocking Valley, O. 2 18 Big Muddy, 111. 2 20 Mt. Olive, 111. 2 20 Lackawanna, Pa., 3 pea Lackawanna, Pa., 3 No. 1 buckwheat Lackawanna, Pa., 3 rice 15 13 12 1 Semi-bituminous. 2 Bituminous. 3 Anthracite. Peat. — Peat is defined by Davis 1 as partly decomposed and disinte- grated vegetable matter that has accumulated in any place where the ordinary decay or chemical decomposition of such material has been more or less suspended, although the form and a considerable part of the struc- ture of the plant organs are more or less destroyed. In its natural state peat contains about 10 per cent, combustible and about 90 per cent, water. Although peat has long been used in Europe as fuel for heating and other domestic purposes, it is but recently that it has been utilized for power purposes. Although it is estimated that in the United States, exclusive of Alaska, peat deposits cover an area of over 11,000 sq. miles, aggregating approximately 13,000,000,000 tons of available fuel, yet its use in this country can hardly be said to be beyond the experimental stage. A good idea of the heating value of peat may be had from the following table : 1 "The Uses of Peat" by C. A. Davis, Bureau of Mines Bulletin No. 16. FUELS Air-dried Peat 377 Kind of peat Locality Water Ash Sul- phur Heating value, B.t.u. Calo- Air- dried Water- free Brown, fibrous . . . Brown, fibrous . . . Light-brown, fibrous Dark-brown Brown, structureless Brown Brown, fibrous ... Brown Brown, fibrous ... Brown Brown, fibrous ... Salt marsh , Black Light-brown, struc tureless Brown, fibrous .... Brown, sandy Black Fremont, N. H Hamburg, Mich. . . . Rochester, N. H... . Westport, Conn. . . . New Durham, N. H. New Fairfield, Conn. Westport, Conn. . . . Kent, Conn Cicero, N. Y Black Lake, N. Y. La Martine, Wis. . . Kittery, Me Greenland, N. H.... Waupaca, Wis. Madison, Wis. . Kent, Conn N. Y... 6.34 7.93 0.69 5,161 9,290 7.50 6.55 0.28 5,050 9,090 11.64 4.06 0.22 5,042 9,083 12.70 4.12 0.24 4,772 8,590 6.06 17.92 0.88 4,415 7,947 9.63 7 93 0.46 4,367 7,861 19.69 3.23 0.19 4,273 7,691 12.10 7.22 0.83 4,269 7,684 14.57 7.42 0.25 4,209 7,576 8.68 16.61 0.99 4,179 7,522 9.95 16.77 0.79 4,149 7,468 13.50 12.04 1.94 4,066 7,319 6.62 24.11 1.01 3,992 7,186 6.62 24.44 0.65 3,872 6,970 8.99 18.77 0.38 3,857 6,943 9.06 36.06 1.46 3,291 5,924 6.52 28.50 0.57 2,867 5,161 9,920 10,026 10,280 9,839 8,460 8,690 9,578 8,743 8,869 8,237 8,293 8,462 7,695 7,465 7,628 5,924 5,521 A typical proximate analysis of a good grade of Florida peat is: Moisture 17.21 Volatile matter 5i . 01 Fixed carbon ■. 24.85 Ash 6.93 Sulphur 0.49 B.t.u. per pound of dry fuel 10,082 Wood. — Wood is now little used as power-plant fuel. Dry wood con- sists of about 50 per cent, carbon, the remaining 50 per cent, being oxygen and hydrogen. Some woods, such as the evergreens, contain small quan- tities of turpentine. The heat value of dry wood seems to run from about 6,600 B.t.u. per pound for white oak to 9,900 for long-leaf pine. The ash content varies, according to different writers, from 0.03 to 5.0 per cent. When fresh cut the moisture content varies from 30 to 50 per cent., but after a few months of drying in the air this is reduced to 20 or 25 per cent. Approximately 2J4 lb. of dry wood are required to equal 1 lb. of aver- age bituminous coal. Pound for pound the fuel value of different dry woods is practically the same. Bagass. — Bagass is the refuse cane from the sugar manufacture. The composition of bagass is approximately: 378 ENGINEERING OF POWER PLANTS Per cent Wood fiber 37 to 45 Combustible salts 10 to 9 Water 53 to 46 10O-100 and the corresponding heat value from 3,000 to 3,500 B.t.u. per pound. E. W. Kerr reports 1 an equivalent evaporation of 2.25 lb. of water per pound of wet bagass having a net heating value of 3,256 B.t.u. per pound. He recommends a rate of burning of not less than 100 lb. per square foot of grate per hour. Tan Bark. — D. M. Meyers states 1 that the calorific value of spent tan averages: 9,500 B.t.u. per pound, dry. 2,665 B.t.u. per pound as fired (65 per cent, moisture). He reports the following economic results: Equivalent evaporation per pound of tan as fired, pounds 1 . 48 Equivalent evaporation per pound of dry tan, pounds 4 . 30 Straw. — A summary of the data given by Kent 3 is: Per cent. of volume - Dry winter-wheat straw Mean for wheat and barley straw c 46.2 5.6 0.4 43.7 4.1 36.0 H 5.0 N ■ 0.5 O 38.0 Ash 4.8 Water 15.7 100.0 100.0 B.t.u. per pound Winter-wheat straw, dry 6,290 Winter-wheat straw, 6 per cent, water 5,770 Winter-wheat straw, 10 per cent, water 5,448 Buckwheat straw, dry 5,590 Flax straw, dry 6,750 1 Bulletin 117, Louisiana Agricultural Experiment Station, Baton Rouge, La. 2 Transactions A.S.M.E., vol. 31, p. 685. 3 "Mechanical Engineers' Pocketbook," 9th edition, 1916, p. 839. FUELS 379 Coke. — Coke is made from coal by one of two processes. Gas-works coke is the residue from the distillation of coal in gas making. Oven coke is produced by a process of partial combustion in specially designed ovens. For fuel purposes the latter is usually the better. With the beehive-oven process of coke making the percentage yield of coal in coke averages about 60 per cent, for the United States, the range being from 44 to 75 per cent. With the byproduct coke-oven process the yield should average from 68 to 72 per cent, with good coal. The average of 29 sam- ples of coke from six different States shows approximately the following composition : Per cent. Fixed carbon 90 Ash 9 Sulphur 1 Charcoal. — By driving off the volatile matter from wood or peat by a process of partial combustion or by a process of distillation, charcoal may be produced. The charcoal yield is from 45 to 60 bu. per cord of wood. It is far too expensive to be used much as a power-plant fuel. Fuel Briquets. — By grinding coal, lignite or peat and pressing in forms fuel briquets may be produced. If coal is used a binder is necessary. Investigations by the Bureau of Mines show the following binders to be commercially available: Binder Amount required, per cent. Cost of binder per ton of briquets, cents Petroleum residuum Water-gas tar pitch 4 5 to 6 6.5 to 8 45 to 60 50 to 60 Coal-tar pitch 65 to 90 Many other binders have been used, but as a rule with less success or at greater cost. The cost of petroleum residuum is much higher now (1916) than when the report of the Bureau of Mines was made. Lignite and peat briquets have been made with the use of no addi- tional binder, but to date (1916) not on an extended commercial basis in the United States. Although average values are often misleading, if properly used the following table of the average of a large number of determinations of the heating value of fuels may be of service. Unless otherwise specified the values are B.t.u. per pound of dry fuel. 380 ENGINEERING OF POWER PLANTS B.t.u. per pound Anthracite coal (small) 12,500 Anthracite coal (large) 14,000 Semi-anthracite 13,400 Semi-bituminous 15,000 Bituminous coal (as fired) 12,300 Bituminous coal (dry) 13,200 Sub-bituminous 12,000 Lignite (as fired) 8,300 Lignite (dry) 11,300 Asphalt 17,000 Peat (as fired) 8,100 Peat (dry) 10,300 Wood (dry) 6,600 to 9,900 Bagass (45 to 55 per cent, water) 3,000 to 3,500 Tan bark (with 65 per cent, water) 2,700 Tan bark (dry) 9,500 Straw 5,400 to 6,700 Weight and Volume of Solid Fuels. — One ton (2,000 ltO Approximate cpace of required, cu. ft. Anthracite lump 28 . 8 Anthracite broken 30 . 3 Anthracite egg 30 . 8 Anthracite stove 31.1 Anthracite chestnut 31 . 9 Anthracite pea 32 . 8 Max. Avg. Min. Bituminous coal 45.6 37.8 34.3 The weight of a bushel of coal, pounds In Indiana 70 In Pennsylvania 76 In Alabama, Colorado, Georgia, Illinois, Ohio, Ten- nessee and West Virginia 80 Weight of a bushel of coke, pounds Maximum Average Minimum 50 40 33 When buying coal it is well to remember that: 1. The heating power per pound of combustible is about constant; and more attention should be paid to the per cent, of earthy matter than to the calorific value per pound of coal. 2. The earthy matter appears to increase by about lj^ per cent, for each size of coal as it becomes smaller, but the price often diminished in a greater ratio. FUELS 381 3. The amount of refuse is always much in excess of the earthy matter reported by analysis. 4. With anthracite, the best qualities are indicated by the sharpest angles and the brightest appearance. If the coal is dull and shows seams and cracks, it will split up in the fire and not prove economical. 5. Bituminous coals showing whitish films or rusty stains should be avoided, as they indicate the presence of sulphur and pyrites. The Purchase of Coal under Government and Commercial Specifica- tions on the Basis of its Heating Value. — Until recent years, coal consum- ers purchased coal merely on the statement of the dealer as to its quality, relying on his integrity and on the reputation of the mine or district from which the coal was obtained. Even today this method must be followed by small consumers, by local dealers and even by some fairly large con- sumers. Only the Government and very large consumers, or a combina- tion of small consumers, can offer to buy by specification at the present time. The purchase of coal by specification is an important step toward the conservation of our national mineral resources, for it results in an in- creased use of the lower grades of coal. The poorer coals find a market by competing with the better grades, not as to the price per ton but as to the cost of an equal number of heat units. Factors Affecting Value. — Some of the factors that may influence the commercial results obtained in a boiler are cost of the coal as determined by price and heating value, care in firing, design of the furnace and boiler setting, size of grate, formation of excessive amounts of clinker and ash, available draft and size of coal. Of the physical characterisitcs of coal the following have a direct bearing on the value as a power-plant fuel: (a) Moisture. (6) Ash. (c) Volatile matter and fixed carbon. (d) Sulphur and clinker. (e) Size of coal. (/) Heat units. (a) Moisture in the coal is worthless, costs money for freight and cart- age and loss of heat. (6) Non-combustible material, called ash, is worthless to the pur- chaser. In commercial coals this proportion of ash ranges from 4 to 25 per cent. As a rule the higher the percentage of ash, the poorer the coal. A fusible ash may be a very serious matter. (c) Although furnaces designed for high-volatile coals may give results that make the coal as desirable as one low in volatile matter, yet in gen- 382 ENGINEERING OF POWER PLANTS eral the coal containing the higher percentage of fixed carbon is more efficiently handled or " burns better. " (d) Sulphur in the free state gives little trouble, but if combined with iron and other impurities may seriously reduce the efficiency of a furnace. Iron sulphide usually makes a fusible ash and causes clinker troubles and excessive grate-bar renewals. (e) For efficient furnace results, coal should be fairly uniform in size. Very fine coals or coal dust, tend to check the draft and usually require special furnace construction. It is important to know the caking quali- ties of coal. (/) In general the efficiency and value of coals will vary directly with the B.t.u. value, but as indicated above, the character of the ash and the form of the sulphur present, may destroy this relation. Suitable furnace construction is also an important factor. In general, then, considerable care must be exercised in purchasing coal to meet properly the requirements imposed by local plant conditions as to character and variation of load, type of furnace, etc. Specification Standards. — Kent 1 summarizes the standards as follows: "Anthracite and Semi-anthracite. — The standard is a coal containing 5 per cent, volatile matter, not over 2 per cent, moisture, and not over 10 per cent. ash. A premium of 0.5 per cent, on the price will be given for each per cent, of volatile matter above 5 per cent, up to and including 15 per cent., and a reduction of 2 per cent, on the price will be made for each 1 per cent, of moisture and ash above the standard. Semi-bituminous and Bituminous. — The standard is a semi-bituminous coal containing not over 20 per cent, volatile matter, 2 per cent, moisture 6 per cent. ash. A reduction of 1 per cent, in the price will be made for each 1 per cent, of volatile matter in excess of 25 per cent., and of 2 per cent, for each 1 per cent, of ash and moisture in excess of the standard. For Western coals in which the volatile matter differs greatly in its percentage of oxygen, the above specification based on proximate analysis may not be sufficiently accurate, and it is well to introduce either the heating value as determined by a calorimeter or the percentage of oxygen. The author has proposed the following for Illinois coal: The standard is a coal containing not over 6 per cent, moisture and 10 per cent, ash in an air-dried sample, and whose heating value is 14,500 B.t.u. per pound of combustible. For lower heating value per pound of the combustible, the price shall be reduced proportionately, and for each 1 per cent, increase in ash or moisture above the specified figures, 2 per cent, of the price shall be deducted." The United States Government has been purchasing coal under 1 "Mechanical Engineers' Pocketbook," 9th edition, p. 830. FUELS 383 specification for some years. The essential points of the Government specifications are as follows : BITUMINOUS COAL Description of Coal Desired 1. The coal must be a good coal and must be adapted for successful use in the particular furnace and boiler equipment. 2. Bidders are required to specify the coal offered in terms of moisture, "as received;" ash, volatile matter, sulphur, and British thermal units, "dry coal." Such values become the standards for the coal of the successful bidder. In addition the bidders are required to give the trade name of the coal offered, the name or other designation of coal bed, name of mine or mines, location of mine or mines (town, county, and State), railroad on which mine or mines are located, and name of operator of mine or mines. Note. — Bids not supplying the foregoing information may be considered informal and rejected. Coal of the description and analysis specified is herein known as the contract grade. Bidders are cautioned against specifying higher standards than can be maintained, for to do so will result in deductions in price and may result in the rejection of delivered coal or cancellation of the contract. In this connection it should be recognized that the small "mine samples" usually indicate a coal of higher economic value than that actually delivered in carload lots because of the care taken to separate extraneous matter from the coal in the "mine samples." Award 3. In determining the award of this contract, consideration will be given to the quality of the coal (expressed in terms of ash in "dry coal," of moisture in coal "as received," and British thermal units in "dry coal") offered by the respective bidders, to the operating results obtained on the same and similar coals on previous contracts or by test, as well as to the price per ton. 4. Bids may be rejected from further consideration if they offer coals regard- ing which the Government has information that they possess unsuitable physical characteristics or excess volatile matter or sulphur or ash contents, or that they are unsatisfactory because of clinkering or excessive refuse, or because of having failed to meet the requirements of city smoke ordinances, or for other cause that would indicate that they are of a character or quality that the Government considers unsuited for use in its storage space or in its power-plant furnace equipment. 5. In order to compare bids as to the quality of the coal offered all proposals shall be adjusted to a common basis. The method used shall be to merge the four variables — ash, moisture, heating value, and price bid per ton — into one figure, the cost of 1,000,000 B.t.u., so that one bid may readily be compared with another. The procedure under this method will be as follows: (a) All bids shall be reduced to a common basis with respect to moisture by dividing the price quoted in each bid by the difference between 100 per cent, and the percentage of moisture guaranteed in the bid. The adjusted bids shall be figured to the nearest tenth of a cent. 384 ENGINEERING OF POWER PLANTS (b) The bids shall be adjusted to the same ash percentage by selecting as the standard the proposal that offers coal containing the lowest percentage of ash. The difference in ash content between any given bid and this standard shall be divided by 2 and the price in such bid, adjusted in accordance with the above, multiplied by the quotient. The result shall be added to the above adjusted price. The adjusted bids shall be figured to the nearest tenth of a cent. (c) On the basis of the adjusted price, allowance shall then be made for the varying heat values by computing the cost of 1,000,000 B.t.u. for each coal offered. This determination shall be made by multiplying the price per ton adjusted for ash and moisture contents by 1,000,000 and dividing the result by the product of 2,000, multiplied by the number of British thermal units guaranteed. 6. After the elimination of undesirable bids the selection of the lowest bid of the remaining bids on the basis of the cost per 1,000,000 B.t.u. may be con- sidered by the Government as a tentative award only, the Government reserving the right to have practical service test or tests made under the direction of the Bureau of Mines, the results to determine the final award of contract. The interested bidder or his authorized representative may be present at such test. Causes for Rejection 7. It is understood that coal containing 3 per cent, more moisture, or 4 per cent, more ash, or 3 per cent, more volatile matter, or 1 per cent, more sulphur, or 4 per cent, less British thermal units than the specified guarantees as the standards for the coal hereunder contracted for, or if coal is furnished from mine or mines other than herein specified by the contractor, unless upon the written permission of the Government, shall be considered subject to rejection, and the Government may, at its option, either accept or reject the same. Should the Government have used a part of such coal subject to rejection, such shall not impair the Government's right to cause the contractor to remove the coal remain- ing of the delivery subject to rejection. 8. It is agreed that if the contractor furnishes coal in three consecutive deliveries, or in case more than 20 per cent, of the amount of the coal delivered to any date during the life of this contract which contains 3 per cent, more moisture, or 2 per cent, more ash, or 3 per cent, more volatile matter, or 1 per cent, more sulphur, or 2 per cent, less British thermal units than the specified guarantees as the standards for the coal hereunder contracted for, or if coal is furnished from mine or mines other than herein specified, unless upon the written permission of the Government, then this contract may, at the option of the Government, be terminated, or the Government may, at its option, purchase coal in the open market until it may become satisfied that the contractor can furnish coal equal to the standards guaranteed, and the Government shall have the right to charge against the contractor any excess in price of coal so purchased over the corrected price which would have been paid to the contractor had the coal been delivered by him. 9. The contractor shall be required to remove, without cost to the Govern- ment, within a reasonable time after notification, coal which has been rejected by the Government. Should the contractor not remove rejected coal within the said reasonable time, the Government shall then be at liberty to have the said FUELS 385 coal removed from its premises and charge any and all costs incidental to its removal against the account of the contractor and to deduct the cost thereof from any money then due or thereafter to become due to the contractor. Price and Payment 10. The Government hereby agrees to pay the contractor within 30 days after the completion of an order or delivery for each ton of 2,000 lb. of coal delivered and accepted in accordance with all the terms of this contract the price per ton determined by taking the analysis of the sample, or the average of the analyses of the samples if more than one sample is analyzed, collected from the coal delivered upon the basis of the price herein named adjusted as follows for variations in heating value, ash, and moisture from the standards guaranteed herein by the contractor. (a) Considering the coal on a " dry-coal" basis, no adjustment in price shall be made for variations of 2 per cent, or less in the number of British thermal units from the guaranteed standard. When the variation in heat units exceeds 2 per cent, of the guaranteed standard, the adjustment shall be proportional and shall be determined by the following formula: B.t.u. delivered coal (" dry-coal" basis) . ., — — — — — - X bid price = price resulting for B.t.u. (dry-coal basis) specified in contract B.t.u. variation from the standard. The adjusted price shall be figured to the nearest tenth of a cent. As an example, for coal delivered on a contract guaranteeing 14,000 B.t.u. on a "dry-coal" basis at a bid price of $3 per ton showing by calorific test results varying between 13,720 and 14,280 B.t.u., there would be no price adjustment. If, however, by way of further example, the delivered coal shows by calorific test 14,350 B.t.u. on a "dry-coal" basis, the price for this variation from the contract guaranty would be, by substitution in the formula: 14. nno X $3 = $3,075. (b) No adjustment in price shall be made for variations of 2 per cent, or less below or above the guaranteed percentage of ash on the "dry-coal" basis. When the variation exceeds 2 per cent, the adjustment in price shall be determined as follows: The difference between the ash content by analysis and the ash content guar- anteed shall be divided by 2 and the quotient shall be multiplied by the bid price, and the result shall be added to or deducted from the British thermal units adjusted price or the bid price, if there is no British thermal unit adjustment, according to whether the ash content by analysis is below or above the percentage guaranteed. The adjustment for ash content shall be figured to the nearest tenth of a cent. As an example of the method of determining the adjustment in cents per ton for coal containing an ash content varying by more than 2 per cent, from the standard, consider that coal for which the above-mentioned heat-unit adjust- ment is to be made has been delivered on a contract guaranteeing 10 per cent, ash and shows by analysis an ash content of 7.50 per cent, the adjustment in price would be determined as follows: 25 386 ENGINEERING OF POWER PLANTS The difference between 10 and 7.50, which is 2.50, would be divided by 2, and the quotient of 1.25 multiplied by $3, resulting in an adjustment of 3.7 cts. per ton, which in this case would be an addition. The price after adjustment for the variations in heating value and ash content would be $3,075 plus $0,037, or $3,112. (c) The price shall be further adjusted for moisture content in excess of the amount guaranteed by the contractor, the deduction being determined by mul- tiplying the price bid by the percentage of moisture in excess of the amount guaranteed. The deduction shall be figured to the nearest tenth of a cent. As an example, consider the coal for which the above-mentioned heat unit and ash adjustments are to be made, and as having been delivered on a contract guaranteeing 3 per cent, moisture, and that the coal shows by analysis 4.58 per cent, moisture, then the bid price would be multiplied by 1.58 (representing excess moisture), giving 4.7 cts. as the deduction per ton. The price to be paid per ton for the coal would then be $3,112, less $0,047, or $3,065. 11. If coal on visual inspection by the officer in charge appears to meet the contractor's guarantees, the said officer will have the right, immediately on the completion of an order, to make payment on 90 per cent, of the amount of the bill, based on the tonnage delivered and at the bid price per ton. The 10 per cent, withheld is to cover any deduction on account of the delivery of coal which on analysis and test is subject to an adjustment in price. If the 10 per cent, withheld should not be sufficient to cover the deduction, then the amount due the Government may be taken from any money thereafter to become due to the contractor, or may be collected from the sureties. Sampling 12. The contractor shall have the privilege of having a representative present to witness the collection and preparation of the samples to be forwarded to the laboratory. 13. The samples shall be collected and prepared in accordance with the method given in Appendix A, attached hereto as a part of these specifications and proposals. Analyses 14. The samples shall be immediately forwarded to the Bureau of Mines, Department of the Interior, Washington, D. C, and they shall be analyzed and tested in accordance with the method recommended by the American Chemical Society and by the use of a bomb calorimeter. The expense of such analyses and tests shall be made at no cost to the contractor. The results shall be reported by the Bureau of Mines to the officer in charge in not more than fifteen (15) days after the receipt of the sample — if more than one sample is received from the same delivery, the fifteen (15) days shall date from the receipt of the last sample taken. Method of Sampling. — Proper sampling of coal is difficult. So much depends upon it that it must be properly done. For instructions in this field/the student is referred to the Bulletins of the Bureau of Mines and to the reports of Committee D-5, A. S. T. M. (1916). FUELS 387 Use of Briquets. — Briquets are good fuel. The only drawback is the cost of the binder, as it usually does not pay to briquet if the binder costs more than 25 cts. per ton of briquets. An elaborate and carefully executed series of tests involving the use of natural coals and of briquets made from the same coal, previously crushed, has been carried out on a locomotive mounted at the testing plant of the Pennsylvania Railroad Co. at Altoona, Pa., under the direc- tion of the Government Testing Station. Less extensive tests were made on several other railroads and some preliminary experiments involving the use of briquets in marine service have been made in connection with one of the Government's torpedo boats. Results of Experiments. — The results obtained in these tests are said to sustain the following general conclusions: 1. The briquets made on the Government's machines have well with- stood exposure to the weather and have suffered but little deterioration from handling. 2. In all classes of service involved by the experiments the use of briquets in place of natural coal appears to have increased the evaporative efficiency of the boilers tested. 3. The smoke produced has in no test been more dense with the bri- quets than with coal; on the contrary, in most tests the smoke density is said to have been less when briquets were used. 4. The use of briquets increases the facility with which an even fire over the whole area of the grate may be maintained. 5. In locomotive service the substitution of, briquets for coal has re- sulted in a marked increase in efficiency, in an increase in boiler capacity, and in a decrease in the production of smoke. It has been specially noted that careful firing of briquets at terminals is effective in diminishing the amount of smoke produced. General Deductions. — At the usual rate of combustion in locomotives the equivalent evaporation with either kind of briquet is 10 to 15 per cent, higher than with run-of-mine coal. So far as blackness of smoke is concerned there seems to be little ad- vantage in briquets over run-of-mine coal. However, the loss in sparks is less, and especially with the larger size of briquets. It is a great deal easier to raise and to keep up steam with briquets than with run-of-mine coal as they contain no fines. Higher rates of combustion are feasible and consequently higher power, which is of espe- cially great advantage on long grades. As to efficiency, there is practically no difference between the two sizes of briquets, but the smaller ones are easier to handle. Torpedo-boat Service. — In, torpedo-boat service the substitution of briquets for coal improves the evaporative efficiency of the boiler. It 388 ENGINEERING OF POWER PLANTS does not appear to have affected, favorably or otherwise, the amount of smoke produced. Steam can be raised more quickly with briquets than with run-of- mine coal. Run-of-mine coal is transferred much more readily than briquets from the coal bunker to the fire room. With briquets the capacity of a coal bunker is reduced by 23 to 27 per cent. Use of Low-grade Fuels. — The Reports of the U. S. Geological Survey show that, if the rate of increase of fuel consumption in this country that has held for the past 50 years is maintained, the supply of easily available coal will be exhausted before the middle of the next century. As is Fig. 204. — Average yearly production of coal in the United, States. shown in Fig. 204, the annual production of coal in the United States increased from less than 20,000,000 tons 60 years ago to nearly 500,000,- 000 tons in 1913; if the industries of the country continue to develop at a sufficient pace to maintain this rate of increase, then the limit of our coal supply will be reached in about 200 years. The fuel consumption per capita is actually increasing much faster than the population, so that the question of the continuation of this rate of increase is one of consider- able importance. It is interesting to note that the production of coal in the United States has been for some years greater than that in any other country. The world's production of coal by countries is given in Fig. 205. Investigations into the waste of coal in mining have shown the enor- mous extent of this waste, aggregating from 200,000,000 to 300,000,000 tons yearly, of which at least one-half might be saved. Attention is FUELS 389 being directed to the practicability of reducing this waste through more efficient mining methods. It has also been demonstrated that the low- COUNTRY United States (1913) Great Britain (1913) Germany (1912) Austria-Hungary (1912) France (1913) Russia (1912) Belgium (1912) Japan (1912) China (1912) India (1912) Canada (1913) New South Wales (1913) Spain (1912) Transvaal (1911) Natal (1911) New Zealand (1912) Holland (1912) Queensland and Victoria (1912) Chile (1912) Asiatic Russia (1910) Mexico (1912) Bosnia and Herze govina (1912) Turkey (1912) Italy (1912) Dutch East Indies (1912) Sweden (1912) Other Countries SHORT TONS 100.000,000 200.000,000 300.000,000 400.000.000 500.000,000 600.000,000 Fig. 205. — World's production of coal. grade coals high in sulphur and ash now being left underground can be used economically in the gas producer for power and light, and should, 390 ENGINEERING OF POWER PLANTS therefore, be mined at the same time that the high-grade coal is removed. The following low-grade fuels should, therefore, receive thoughtful consideration: 1. High-ash fuels, which are regarded at present as practically worth- less. 2. Extensive deposits of lignite found in various sections of the country. 3. Peat from vast areas of swamps and bogs. A study of the situation leads to the belief that the utilization of these fuels, which have until recently been regarded as of little or no value, may increase the fuel resources of the United States approximately (on the basis of present marketable grades) : Per cent. (a) Low-grade bituminous and anthracite 75 to 100 (6) Sub-bituminous, lignite and peat 60 or roughly, a total of 150 per cent. In considering the use of such fuels, it must not be overlooked that the percentage of ash is high in the low-grade bituminous and anthracite fuels and the percentage of moisture high in many of the lignites and in the peats. These conditions practically prohibit transportation and necessitate the use of these grades in close proximity to the mine or bog. Liquid Fuels. — The liquid fuels which are used on a large enough scale to warrant consideration as power-plant fuels are : fuel oil, gasoline, kerosene and alcohol. The heating values and weights of these fuels run about as follows : POU ga d llo P n r B.t.u. per pound Fuel oil 8.3 to 6.7 18,400 to 20,400 Gasoline (high-grade) 6.0 20,500 Kerosene 6.6 19,900 Denatured alcohol 6.8 11,600 With the possible exception of denatured alcohol these fuels need no definition. Denatured alcohol as used for power purposes consists of grain alcohol (C 2 H 6 0) made poisonous and repulsive by the addition of wood alcohol and benzine in the following proportions: 100 parts grain alcohol, 10 parts wood alcohol, 3^ part benzine. Oil versus Coal under Boilers. — Of these fuels the only one used on a commercial basis for steam generation in boilers is fuel oil. It is, there- fore, important to compare the relative results from coal and oil for this purpose. Kent gives 1 the following table based on the assumed data: B.t.u. per pound of oil, 19,000; weight of oil, 7.57 lb. per gallon; 1 bbl. = 42 gal. = 315 lb. 1 "Mechanical Engineers Pocketbook," 9th edition, p. 842. FUELS 391 Coal, B.t.u. per pound 1 lb. oil = pounds coal 1 bbl. oil = pounds coal 1 ton coal = . . . .barrels oil 10,000 1.9 598 3.34 11,000 1.73 544 3.68 12,000 1.58 499 4.01 13,000 1.46 460 4.34 14,000 1.36 427 4.68 15,000 1.27 399 5.01 This table shows that if coal of a heating value of only 10,000 B.t.u. per pound costs $3.34 per ton and coal of 14,000 B.t.u. per pound costs $4.68 per ton, then the price of oil will have to be as low as $1 per barrel to compete; or, on this basis oil will be the cheaper fuel if it is below $1 per barrel. In general it may be said that the heating value of crude petroleum is from 1.44 to 1.6 times that of average good coal, even after deducting the steam used to operate the pulverizers, which steam amounts to about 4 per cent, of the total evaporation of the boilers. With the best types of apparatus this can be reduced to 2 per cent. Under good conditions good fuel oils will evaporate from 16 to 17 lb. of water from and at 212°F. per pound of oil. If the weight of a gallon of oil be 6.8 lb. and the cost per barrel (42 gal.) be $0.94, then the cost of 2,000 lb. would be $6.58 and at a commer- cial efficiency of 1 to 1.6 the values of the fuels would be the same when coal delivered, including handling of ashes, costs $4.12. The boilers at the Chicago World's Fair gave the following average results : Consumption of oil per hour 22 . 792 lb. Equivalent evaporation per pound of oil from and at 212° . . 14.88 lb. Cost of oil per hour $56.20 Cost of oil per boiler horsepower-hour $0 . 0057 Cost of labor per boiler horsepower-hour $0 . 0006 Experiments on express locomotives in England gave 1 lb. of oil (max.) was equivalent to 2.4 lb. coal. 1 lb. of oil (min.) was equivalent to 2.0 lb. coal. 1 lb. of oil (avg.) was equivalent to 2.2 lb. coal. Advantages of Liquid Fuel. — 1. Reduction in number of firemen in proportion of 5 or 6 to 1. 2. Easy lighting of fires and more regular supply of heat. 3. Fires readily regulated to suit demand for steam, and can promptly extinguished. 4. Small proportion of refuse and its easy disposal. be 392 ENGINEERING OF POWER PLANTS 5. Storage tanks can be located to best advantage, while coal bins must be near the boilers. 6. No sparks; no dust; no loss by banking. Disadvantage of Liquid Fuel. — 1. Fire risk. Use prohibited by some city ordinances. 2. Offensive odor. Use prohibited by some cities. 3. Vapor forms explosive mixture with air. 4. Supply limited. 5. Burners make objectionable roaring noise. 6. Heating surface apt to become coated with residue. 7. Tendency of the oil to creep by valves and leak. 8. Necessity for auxiliary apparatus to start oil fire or maintain it or both. Boiler Efficiency with Oil Fuel.- — Although boiler efficiencies as high as 82 per cent, or above are reported with oil-burning furnaces, the aver- age is probably nearer 72 per cent, if the average with coal burning fur- naces be taken as 70 per cent., i.e., the efficiency with oil is about 2 per cent, higher than with coal. As the other liquid fuels are largely used in internal-combustion en- gines no further discussion of them will be given at this point. Purchase of Fuel Oil under Specification. — The Bureau of Mines presents in Technical Paper No. 3 specifications for the purchase of fuel oil as applied by the Government. The essential features are: 1. It should not have been distilled at a temperature high enough to burn it, nor at a temperature so high that flecks of carbonaceous matter began to separate. 2. It should not flash below 60°C. (140°F.) in a closed Abel-Pensky or Pensky-Martens tester. 3. Its specific gravity should range from 0.85 to 0.96 at 15°C. (59°F.) ; the oil should be rejected if its specific gravity is above 0.97 at that tem- perature. 4. It should be mobile, free from solid or semisolid bodies, and should flow readily, at ordinary atmospheric temperatures and under a head of 1 ft. of oil, through a 4-in. pipe 10 ft. in length. 5. It should not congeal nor become too sluggish to flow at 0°C. (32°F.). 6. It should have a calorific value of not less than 10,000 calories per gram (18,000 B.t.u. per pound); 10,250 calories to be the standard. A bonus is to be paid or a penalty deducted as the fuel oil delivered is above or below this standard. 7. It should be rejected if it contains more than 2 per cent, water. ° Calories X 1.8 = British thermal units per pound. FUELS 393 8. It should be rejected if it contains more than 1 per cent, sulphur. 9. It should not contain more than a trace of sand, clay or dirt. Causes for Rejection. — 1. A contract entered into under the terms of these specifications shall not be binding if, as the result of a practical service test of reasonable duration, the fuel oil fails to give satisfactory results. 2. It is understood that the fuel oil delivered during the term of the contract shall be of the quality specified. The frequent or continued failure of the contractor to deliver oil of the specified quality will be con- sidered sufficient cause for the cancellation of the contract. Price and Payment. — 1. Payment for deliveries will be made on the basis of the price named in the proposal for the fuel oil corrected for variations in heating value, as shown by analysis, above or below the standard fixed by the contractor. This correction is a pro rata one and the price is to be determined by the following formula: Delivered calories per gram (or B.t.u. per pound) X contract price Standard calories per gram (or B.t.u. per pound) price to be paid. Water that accumulates in the receiving tank will be drawn off and measured periodically. Proper deduction will be made by subtracting the weight of the water from the weight of the oil deliveries. Gas. — Several different kinds of gas are commercially used as fuel. The most important are: (a) Natural gas. (6) Illuminating gas. (c) Coke-oven gas. (d) Producer gas. (e) Blast-furnace gas. The heating values of these different gases vary considerably under varying conditions — the first with different geographical locations; the others with variations in the fuels used and in details of operation in their manufacture. The following figures are fair average heating values for the gases under standard conditions (60°F. and 14.7 lb. per square inch). B.t.u. per cubic foot of standard gas Natural gas 1,000 Illuminating gas 570 Coke-oven gas 550 f Up-draft plants 150 Producer gas \ Double-zone plants 115 [ Down-draft plants 110 Blast-furnace gas 90 394 ENGINEERING OF POWER PLANTS Natural Gas under Steam Boilers. — Tests with natural gas under steam boilers indicate the consumption of " standard gas" per boiler horsepower to be from 38 to 60 cu. ft. in general although consumptions as high as 74 cu. ft. are reported. The corresponding efficiencies seem to range from 60 to 75 per cent, for normal commercial conditions with 1,000-B.t.u. gas. At an efficiency of 74 per cent, the consumption would be approximately 45 cu. ft. per boiler horsepower. Absurd figures are sometimes reported which indicate test results as low as 17 or 18 cu. ft. of gas per boiler horsepower. In addition to the figures above, it may be well to point out that even with a gas of 1,100 B.t.u. per cubic foot and a furnace efficiency of 100 per cent, the consumption must be 30.3 cu. ft. as shown below. One boiler horsepower = 970 X 34.5 = 33,400 B.t.u. which must be transmitted to the water. 33,400 1,100 = 30.3. Even with this high heat value gas and an efficiency of 75 per cent, the amount of gas required per boiler horsepower will be 33 > 400 a* n u = 40.5 cu. ft. 1,100 X 0.75 J. M. Whitham (Transactions A. S.M.E., 1905) gives the following conclusions as a result of a series of investigations to determine the rela- tive value of blue flame and white flame gas under boilers : "1. There is but little advantage possessed by one burner over another. "2. As good economy is made with blue as with white or straw flame, and no better. "3. Greater capacity may be made with a straw- white flame than with a blue flame. "4. An efficiency as high as from 72 to 75 per cent, in the use of gas is seldom obtained under the most expert conditions. "5. The 'air for dilution' is greater with gas than with coal, so possible coal efficiencies are impossible with gas. "6. Don't expect in good commercial practice to get a boiler horsepower on less than from 43 to 45 cu. ft. of natural gas (standard). "7. Fuel costs are the same under best conditions with natural gas at 10 cts. per 1,000 cu. ft. and semi-bituminous coal at $2.87 per 2,240 lb. (based on 3.5 lb. of wet coal per boiler horsepower-hour or 45 cu. ft. of gas). "8. Expressed otherwise a long ton of semi-bituminous coal is equivalent to 28,700 cu. ft. of natural gas. "9. As compared with hand-firing with coal in a plant of 1,500 boiler hp., coal being $2 per 2,240 lb., the labor saving by the use of gas is such that natural gas should sell for about 10 cts. per 1,000 cu. ft." FUELS 395 It has been stated that the boiler horsepower handled by one fireman is seven or eight times as much with gas-fired boilers as with coal fired. Natural Gas for Domestic Heating. — As a result of investigations into the use of natural gas for domestic heating, W. F. M. Goss reached the following conclusions: 1. In comparison with anthracite coal, gas is worth 6.8 cts. per 1,000 cu. ft. for each $1 per ton charged for coal. 2. In comparison with bituminous coal, gas is worth 8.1 cts. per 1,000 cu. ft. for each $1 per ton charged for coal. 3. In comparison with first-class hickory wood, gas is worth 11.1 cts. per 1,000 cu. ft. for each $1 per cord charged for wood. For example, taking values common in central Indiana, in comparison with anthracite coal at $7 per ton, gas is worth 47.6 cts.; per 1,000 cu. ft., with bituminous coal at S3. 50, gas is worth 28.4 cts.; with hickory at $6 per cord, gas is worth 66.6 cts. COST OF ENERGY IN FUELS Kind of fuel Cost, $ B.t.u. as fired Number B.t.u. for $1 Small anthracite . . Large anthracite . . Bituminous coal. . Bituminous coal. . Lignite Peat Fuel oil Fuel oil Gasoline Gasoline Kerosene "Kerosene Denatured alcohol Denatured alcohol Natural gas Natural gas Illuminating gas . . Coke-oven gas .... Producer gas Producer gas Producer gas Producer gas Blast-furnace gas. Blast-furnace gas. 3.00 per ton 7 . 00 per ton 3.00 per ton 1 . 50 per ton 3.00 per ton 3 . 00 per ton 0.04 gal. 0.02 gal. 0.30 gal. 0.10 gal. 0.30 gal. 0.10 gal. 0.40 gal. 0.30 gal. 0.30 0.10 0.80 0.80 0.04 0.02 0.04 0.02 0.02 0.01 M cu. ft. M cu. ft. M cu. ft. M cu. M cu. M cu. M cu. M cu. ft. M cu. ft. M cu. ft. ft. ft. ft. ft. 12,500 per lb. 14,000 per lb. 14,500 per lb. 12,300 per lb. 8,300 per lb. 8,100 per lb. 19,400 19,400 20,500 20,500 19,900 19,900 11,600 11,600 1,000 1,000 570 550 150 150 110 110 90 90 per lb. per lb. per lb. per lb. per lb. per lb. per lb. per lb. per cu. per cu. per cu. per cu. per cu. per cu. per cu. per cu. per cu. per cu, ft. ft. ft. ft. ft. ft. ft. ft. ft. ft. 8,350,000 4,000,000 9,680,000 16,440,000 5,520,000 5,400,000 3,600,000 7,300,000 410,000 1,230,000 440,000 1,320,000 197,000 263,000 3,333,000 10,000,000 712,000 689,000 3,750,000 7,500,000 2,750,000 5,550,000 4,500,000 9,000,000 B C D E 14,200 13,800 14,500 12,700 2.0 3.5 1.9 6.2 9.2 7.5 5.2 8.5 28.0 26.5 21.0 30.4 0.9 1.0 0.7 1.2 396 ENGINEERING OF POWER PLANTS PROBLEMS 63. Check by Dulong's formula and by the approximate formula of page 376 the values of B.t.u. per pound for the fuels of page 375. 64. Does the approximate formula of page 376 give a reasonable check for the B.t.u. value for Florida peat given on page 377? 65. In response to a call for bids the following were received: A B.t.u. (dry) 13,500 Moisture, per cent 1.5 Ash, per cent 8.0 Volatile matter, per cent 29 . 5 Sulphur, per cent 1.1 Price per ton (2,000 lb.) $3.00 3.15 3.05 3.45 2.70 Which bid offers the lowest cost per 1,000,000 B.t.u.? 66. A coal contract specifies 13,500 B.t.u. (dry), 10 per cent, ash and 5 per cent, moisture at $2.50 per ton of 2,000 lb. delivered. The first lot of 1,000 tons averaged 13,700 B.t.u. (dry) and 12 per cent, ash and 56.2 per cent, moisture. What should be the basis of payment per ton and what is the total bonus or forfeiture for the coal company on the 1,000 tons? 67. Two boilers, one fired with oil and one with the coal delivered in problem 66, each evaporate 180,000 lb. of water as metered during a 12-hr. run. The boiler efficiency was 72 per cent, with oil and 68 per cent, with coal. With oil at 3 cts. per gallon, what was the total cost of fuel for each of the 12-hr. runs? 68. A 500-hp. boiler is run 85 per cent, above rating. Determine : (a) The fuel cost for the plant for each of the fuels listed below for a period of one month of 30 days, 24 hr. per day, not including standby. (6) Determine the equivalent evaporation per pound of dry coal, per pound of oil, and per 1,000 cu. ft. of gas. Bituminous coal: Contract Delivered 13,500 B.t.u. dry. 14,000 B.t.u. dry. 6.5 per cent, moisture. 6.0 per cent, moisture. Oil: 8 per cent, ash in dry coal. 12.5 per cent, ash in dry coal. $3.00 per ton (2,0001b.). 19,800 B.t.u. per pound. $0.90 per barrel (42 gal.). Natural gas: 1,050 B.t.u. per cu. ft. $0.25 per 1,000. 69. A 650-hp. boiler is run 200 per cent, above rating. Determine : (a) The fuel cost for the plant for each of the fuels listed below for a period of 6 days, 24 hr. per day. (6) The equivalent evaporation per pound of dry coal, per pound of oil, and per 1,000 cu. ft. of gas. FUELS 397 Bituminous coal: Contract 14,200 B.t.u. dry. 4.5 per cent, moisture. 7.5 per cent, ash in dry coal. $2.20 per gross ton. Oil: 19,300 B.t.u. per pound. Natural gas: 975 B.t.u. per cubic foot. Delivered 13,900 B.t.u. dry. 3 . 8 per cent, moisture. 6 . 9 per cent, ash in dry coal. $1.00 per barrel (42 gal.). 25 cts. per 1,000. 70. (A) Determine the estimated fuel cost of evaporating in a steam boiler, 1,000 lb. of water, under commercial operating conditions, with each of the following fuels: (a) Bituminous coal, 14,200 B.t.u. dry, 8 per cent, ash, 1.3 per cent, sul- phur, 7 per cent, moisture at $3.15 per ton of 2,240 lb. (6) Oil, 19,450 B.t.u. per pound at $1.20 per barrel of 42 gal., making allowance for the steam required for atomizer. (c) Natural gas, 990 B.t.u. per cubic foot at 25 cts. per 1,000 cu. ft. (B) With the least expensive fuel as a basis, determine the allowable cost of each of the other two fuels to make the fuel cost of evaporating 1,000 lb. of water the same for all three fuels. (C) Determine the equivalent evaporation: (a) Per pound of dry coal. (6) Per pound of oil. (c) Per 1,000 cu. ft. CHAPTER XXI INTERNAL-COMBUSTION ENGINES In internal-combustion engines the pressure upon the piston is pro- duced by the expansion of a so-called "explosive mixture. ,, This explo- sive mixture consists of a combustible gas, vapor or oil mixed with air in such proportions that the mixture is easily ignited and upon ignition burns with such rapidity that a high temperature and high pressure are produced. The rate of burning is so rapid that it is commonly called an explosion. Four-cycle and Two-cycle Engines. — Two types of internal-combus- tion engines are commercially in use today, the four-cycle and the two- POWER- STROKE 1 EXHAUST - STROKE 2L Volume COMPRESSION - STROKE 4 Volume Closed Open -^) Fig. 206. cycle. In the four-cycle, or better four-stroke cycle gas engines, the events take place as indicated by the diagram, Fig. 206. Obviously there is, for a single-acting, single-cylinder engine but one power stroke for every two revolutions, and in commercial operation this power stroke may occasionally be missed, due to light load, improper gas mixture or failure of the ignition. This four-stroke cycle is frequently called the " Otto-cycle' ' in honor of the inventor of the engine, Dr. Otto. 398 INTERNAL-COMBUSTION ENGINES 399 In the two-cycle engine the suction stroke or pump stroke of the engine and the exhaust stroke are practically done away with. Two auxiliary pumps are used for supplying to the engine cylinder gas and air at a pressure of about 10 lb. per square inch. The exhaust valves are annular openings in the cylinder wall near the end of the cylin- der and are uncovered by the piston as it nears the end of its stroke and 70 80 90 Fig. 207. 40 50 60 % of Stroke -Indicator card — two-cycle gas engine. 100 promptly covered by the piston as it reaches the same point on the return stroke. When the piston has completed about 0.9 of its stroke the ex- haust ports are uncovered, the burnt gases rush out and are followed by a rush of air from the air pump. This air tends to "scavenge" the cylinder or free it from burnt gases. This air is immediately followed by gas in such proportions as to make an POWER Exhaust Suction Compression Compression POWER Exhaust Suction Y Suction Exhaust * m Compression Suction ■<- POWER Compression ■■ Exhaust dawud <- POWER 1st Stroke 2nd Stroke 3rd Stroke 4th Stroke Fig. 208. — Sequence of events in the four-cycle double-acting system tandem cylinders. explosive mixture. This mixture is compressed upon the return stroke of the piston, ignited and expanded as in the four-stroke type. The ex- haust, scavenging and admission must take place in the time allowed for about 10 per cent, of one stroke. For an engine whose piston speed is 750 ft. per minute this means that these operations must be accomplished in about 0.05 sec. This short time interval means high fluid friction losses. 400 ENGINEERING OF POWER PLANTS The irregularity of power impulses in the four-cycle engine may be readily overcome by placing two or more cylinders side by side and work- ing all on a single crankshaft, as is widely practiced with marine steam en- gines. Thus the three-cylinder engine gives a power impulse regularly at every two-thirds of a revolution, which has been found sufficient for very exacting work. Cranks are spaced 120° apart, or one-third of a circum- ference, so that power impulses occur at successive intervals of 240° rotation. The relative advantages and disadvantages of the two-cycle and four- cycle engines as pointed out by W. H. Adams 1 for engines of the Diesel type practically hold good for all types of two- and four-cycle internal- combustion engines. Mr. Adams states that the two-cycle type gives POWER Compression POWER Compression Exhaust POWER Exhaust POWER Suction Exhaust Suction Exhaust Compression Suction Compression Suction Suction Exhaust Suction Exhaust Compression Suction Compression Suction POWER Compression POWER Compression Exhaust POWER Exhaust POWER > 1st Stroke 1st Stroke 2nd Stroke 2nd Stroke 3rd Stroke 3rd Stroke 4th Stroke ! 4th Stroke Fig. 209. — Sequence of events four-cycle, double-acting twin tandem type. almost twice as much power for the same size of cylinder, as it has two working strokes for one in the four-cycle. (Actual value is 170 to 180 per cent.) This means less weight, less space and less first cost. As usually constructed, the piston acts as its own valve and so air inlet and exhaust valves are not required. (This is not true of some of the better class of two-cycle Diesel engines, as will be explained later.) In marine work the reduction in number of valves makes it easier to reverse a two- cycle engine. The use of the two-cycle type has also made large units possible, and single-acting engines for 1,200 hp. per cylinder have been built. On the other hand, there is to be said for the four-cycle type of Diesel engine: 1 "The Diesel Engine and Its Application in Southern California," by W. H. Adams, Transactions A.S.M.E. INTERNAL-COMBUSTION ENGINES 401 (a) It is older than the two-cycle type and so has become a more stable construction. (b) It gives better fuel economy, as expansion can be carried to the end of the stroke and no power is required for the scavenging pump. The gain is about 10 per cent. (c) The mean temperature is lower. There is more time to remove the heat and not so much heat to remove per unit of cylinder surface. (In a two-cycle engine 90,000 B.t.u. per hour have to be removed for every square foot of cylinder surface. In four-cycle engines the figure is 40,000 B.t.u. In an ordinary water-tube boiler working at 300 per cent, of rating, it is 10,000 B.t.u.) Fig. 210. — Single-cylinder, single-acting, vertical gas engine. (d) The valve gear runs at one-half the speed of the main shaft. (e) In the high-speed two-cycle engine, it has been difficult to get the burnt gases out of the cylinder in the short time available, so that such engines have not been quite as successful as four-cycle engines. The tendency in this country and abroad is to use four-cycle engines up to from 700 to 1,000 hp. and above that two-cycle. This is due to the reduced first cost of the two-cycle type in the large sizes and the excessive diameter of cylinder required in large four-cycle engines. As progress is made in design, the two-cycle type may supersede the four-cycle, but this is not evident at present in the smaller sizes. 26 402 ENGINEERING OF POWER PLANTS Horsepower. — The indicated horsepower of internal-combustion en- gines is found by the use of the same formula as for steam engines, viz : I.hp. = PLAN 33,000 in which P L A N m.e.p. in pounds per square inch. stroke in feet. effective piston area in square inches. number of times per minute the pressure is exerted on the piston. Although it is frequently convenient to determine the indicated horse- power of gas engines, and it is often desirable to do so, yet it should be remembered that although the indicated horsepower is generally used in Fig. 211. — Single-cylinder, single-acting horizontal gas engine. purchasing steam engines, the brake, or effective, horsepower is used in contracts of sale of gas engines. In computing the brake horsepower from the cylinder dimensions and speed of four-cycle engines it is customary to assume mean effective pres- sures of 66, 68 or 70 lb. per square inch and a mechanical efficiency of 85 per cent. An idea of the relation between cylinder dimensions and horsepower for two-cylinder, tandem, double-acting, four-cycle engines may be had from the following table: INTERNAL-COMBUSTION ENGINES 403 Diam. cyl., in Stroke cyl., in , Rev. per min Piston speed, ft. per min Rated b.hp Factor C Diam. cyl., in Stroke, in Rev. per min Piston speed, ft. per min Rated b.hp Factor C 18 24 150 600 260 0.8 34 42 100 700 1,105 20 24 150 600 320 0.8 36 48 92 736 1,300 0.96 1.00 21 30 125 625 370 0.84 38 40 48 48 92 92 736 736 1,460 1,630 1.01 1.02 22 24 30 30 125 125 625 625 405 490 0.84 0.85 42 54 86 774 1,875 1.06 24 36 115 690 545 0.95 44 54 86 774 2,080 1.07 26 36 115 630 0.93 46 54 86 774 2,280 1.08 28 36 115 690 690 740 0.94 48 60 78 780 2,475 1.07 30 42 100 700 855 0.95 50 60 78 780 2,720 1.09 32 42 100 700 985 0.96 52 62 78 780 2,950 1.09 For determining the approximate horsepower of small automobile- type gasoline engines, the A.L.A.M. has adopted a formula diam. 2 X no. cylinders b.hp. = 2.5 This assumes a piston speed of 1,000 ft. per minute. On this basis the following ratings are derived, as given by Kent (page 1101, 9th edition) : Bore, in Bore, mm Hp., 1 cylinder. Hp., 2 cylinders Hp., 4 cylinders Hp., 6 cylinders 2.5 64.0 2.5 5.0 10.0 15.0 3.0 76.0 3.6 7.2 14.4 21.6 3.5 89.0 4.9 9.8 19.6 29.4 4.0 102.0 6.4 12.8 25.6 38.4 4.5 114.0 3.1 16.2 32.4 48.6 5.0 127.0 10.0 20.0 40.0 60.0 5.5 140.0 12.1 24.2 48.4 72.6 6.0 154.0 14.4 28.8 57.6 86.4 For two-cycle engines of the power-boat type the American Power Boat Association uses: b.hp. = area of piston X no. cylinders X length of stroke X 1.5 It should be remembered that the rating of gas engines is such, due to increased economy with increase of load, that they cannot respond to heavy overload demands. In order that the purchaser may have a definite idea of what he is buying and feel sure of an " overload leeway," the prevailing practice seems to be so to rate gas engines that they will respond to and maintain a load 20 per cent, above that specified in the contract as the normal rating of the engine. It must not be forgotten that the power of a gas engine varies with the atmospheric pressure and consequently with change in elevation. 404 ENGINEERING OF POWER PLANTS If p = barometric pressure at sea level, p e = barometric pressure at elevation, hp. = horsepower at sea level, hp.« = horsepower at elevation, then hp-e = ^hp. Fig. 212. — Section of single-acting, four-cycle vertical gas engine. Piston Speeds. — Gas-engine piston speeds run approximately as fol- lows : Small stationary engines, 400 to 600 ft. per minute. Large stationary engines, 500 to 1,000 ft. per minute. Automobile engines, 600 to 1,000 ft. per minute. Regulating or Governing. — Levin states 1 that the factors that deter- mine the output of an engine are: The amount of gas admitted, the 1 "Modern Gas Engine and the Gas Producer," by A. M. Levin, John Wiley and Sons. INTERNAL-COMBUSTION ENGINES 405 amount of air admitted, the compression effected, and the timing of the ignition. To effect governing, two or more of these features are generally changed simultaneously. In the hit-or-miss system the gas alone, or the gas and air, are shut off entirely at excessive speeds, but other features remain unchanged. In throttling an already completed mixture the gas and air volumes are changed proportionally, and, thus, the quality of the charge remains unchanged, but the compression will be diminished. Fig. 213. — Three-cylinder, four-cycle, single-acting vertical gas engine. By having the gas and air throttle controlled separately, the quality of the mixture may be changed, but the quantity unchanged, and thus the compression unchanged. Between these proportions the quality of the charge may be changed to any extent, resulting in a more or less decreased compression. It may even be possible to dilute the charge to such an extent that its quantity and compression become greater at reduced loads. Mechanical Efficiency of Gas Engines. — Tests of both four- and two- cycle engines show the following relative mechanical efficiencies: Four-cycle 74 to 92 Avg. = 85 Two-cycle 63 to 75 Avg. = 70. 406 ENGINEERING OF POWER PLANTS Owing to the difficulty often encountered in obtaining the indicated horsepower of gas engines under operating conditions, and owing to the lack of reliability in determining the indicated horsepower from indicator cards save by experienced men, it is advisable to determine the friction INTERNAL-COMBUSTION ENGINES 407 horsepower of a gas engine by careful tests and thereafter use this value in determining the mechanical efficiency of the engine, as many investi- gations have shown the friction horsepower of such engines to be suffi- ciently constant to warrant this procedure. For example, take the tests on gasoline and alcohol engines reported in IL S. Bureau of Mines, Bulletin No. 43. Brake horsepower Indicated horsepower Friction horsepower Per cent, rated load Mechanical efficiency b.hp. i.hp. X 100 b.hp. b.hp. + avg. f.hp X 100 Otto 15-hp. gasoline engine 17.16 19.34 2.18 114.3 88.8 88.3 15.98 18.30 2.37 106.7 87.3 87.6 15.40 17.70 2.30 102.8 87.0 87.1 14.80 16.90 2.10 98.6 87.5 86.7 14.18 16.22 2.04 94.5 87.4 86.2 13.66 15.87 2.21 91.0 86.1 85.8 12.41 14.70 2.29 82.9 84.4 84.6 9.98 12.29 2.31 66.5 81.4 81.5 7.60 10.18 2.58 50.7 75.3 77.0 5.09 7.49 2.40 34.0 68.0 69.2 Avg. frictional horse- power for 245 tests .... 2.27 Nash 10-hp. gasoline engine 15.10 17.74 2.64 151.0 85.2 86.4 13.78 15.75 1.97 137.8 87.5 85.2 14.00 15.04 1.04 140.0 91.6 85.4 12.80 16.11 3.31 128.0 79.5 84.3 11.73 13.89 2.16 117.3 84.5 83.1 11.28 13.82 2.54 112.8 81.6 82.6 10.76 12.58 1.82 107.6 85.6 81.9 10.51 13.19 2.68 105.1 79.6 81.5 10.17 12.14 1.97 101.7 83.8 81.0 9.36 12.05 2.69 93.6 77.8 79.7 8.22 10.78 2.56 82.2 76.3 77.5 7.99 9.87 1.88 79.9 81.0 77.0 7.08 9.55 2.47 70.8 74.5 74.8 6.06 8.20 2.14 60.6 73.9 71.7 4.72 7.25 2.53 47.2 65.9 66.4 Avg. frictional horse- power for 104 tests .... 2.39 408 ENGINEERING OF POWER PLANTS The figures above represent test conditions. The following data from engines operating under rather harsh conditions are, therefore, of com- parative interest. These tests on pumping engines in operation in Cali- fornia were made under the direction of the Government. They show that the power consumed in friction is approximately constant for a given speed, without regard to the useful work done. They also show the uneconomical results that come from using an engine too large for the work. Brake horsepower Indicated horsepower Friction horsepower Mechanical efficiency Per cent, rated load b.hp. i.hp. X 100 b.hp. b.hp. + avg. f .hp. X 100 Fairbanks-Morse 25-hp. gasoline engine 9.3 16.9 7.6 37.2 55.0 56.4 8.0 15.2 7.2 32.0 52.6 52.6 6.7 13.4 6.7 26.8 50.0 48.2 5.4 12.6 7.2 21.6 42.8 42.8 4.0 11.6 7.6 16.0 34.5 35.7 0.0 6.7 6.7 0.0 0.0 00.0 Avg 7.2 White and Middleton 30-hp. gasoline engine 11.8 18.5 6.7 39.0 64.0 64.0 8.0 16.0 7.1 26.7 50.0 54.4 5.9 11.7 5.8 19.7 50.4 46.8 2.9 10.1 7.2 9.7 28.7 30.2 Avg 6.7 Thermal Efficiency and Economy. — If there are no losses, 1 B.t.u- per minute would give 778 ft.-lb. per minute behind the piston, 60 B.t.u. per hour would give the same. B.t.u. per i.hp.-hr. = 33,000 X 60 778 = 2,545 with no losses of any kind. rp, , ~ . i.hp. X 33,000 Thermal efficiency = =5-7 *—-. — : — * — r Ky nno ' J B.t.u. per mm. in fuel X 778 «, , ~ . b.hp. X 33,000 Thermal efficiency = ^-r — ^—. — r-^ — . w ,_ -• J B.t.u. per mm. in fuel X 778 Although very wild claims are made by some manufacturers regarding the thermal efficiencies of their engines, it is probable that the maximum thermal efficiency of such engines under the most favorable operating INTERNAL-COMBUSTION ENGINES 409 410 ENGINEERING OF POWER PLANTS conditions 1 is about 38 per cent., based on the indicated horsepower, or 30 per cent, based on the brake horsepower. One engine is reported to have developed a brake horsepower-hour on 7,200 B.t.u. but this is very exceptional. Under working conditions gas engines are expected to produce a brake horsepower on from 9,000 to Fig. 216. — Horizontal, twin-tandem, double-acting four-cycle gas engine. 12,000 B.t.u. per hour. The average of several quotations from different manufacturers is as follows: Per cent, rated load 100 75 50 25 B.t.u. per b.hp.-hr. 10,000 12,000 14,700 20,000 One reliable firm guarantees under operating conditions for the same per cent, of load 10,500, 11,500, 14,000, 20,000 B.t.u. per hour. These guarantees will, of course, vary somewhat with the gas used, but the average values will give a fair basis for estimates. Comparative Results from Denatured Alcohol and Gasoline. — The possibilities from denatured alcohol in internal combustion engines are so good that a brief summary of the important results from 2,000 tests with gasoline and alcohol at the United States Bureau of Mines Testing Station is presented : 1 The theoretically possible thermal efficiency of the Otto engine is 52 per cent, and of the Diesel 57 per cent. INTERNAL-COMBUSTION ENGINES 411 Gasoline Alcohol Hp. of engines 10 and 15 10 and 15 Best compression pressure, lb., sq. in 70 180 Maximum explosion pressure, lb., sq. in. . . . .... 600 to 700 Fuel per b.hp.-hr., lb 0.60 0.71 Fuel per b.hp.-hr., gal 0.10 0.10 General Conclusions. — (a) For engines of the same cylinder size, but with 70 lb. compression for gasoline and 180 lb. for alcohol, the maximum available horsepower of the alcohol engine is about 30 per cent, greater. Fig. 217. — 500-hp. vertical marine gas engine. (6) With the compression pressures indicated, the engines required equal volumes of gasoline and denatured alcohol, respectively, per horse- power-hour, namely, about 1 pt. (c) If alcohol be used in an engine with a compression designed for gasoline, the engine will require about 50 per cent, more alcohol than gaso- line per horsepower-hour. (d) Alcohol diluted with water in any proportion up to about 50 per cent, can be used in gasoline or alcohol engines if the engines are properly adjusted. Pressures and Temperatures. — The degree of compression possible with explosive mixtures used in internal combustion engines varies with the fuel used. Under normal conditions with engines working on the Otto cycle the allowable compression pressure will be approximately: 412 ENGINEERING OF POWER PLANTS Fuel Pounds per square inch Kerosene 50 to 75 Gasoline 70 to 90 Alcohol 70 to 200 Illuminating gas 70 to 90 Natural gas 90 to 140 Producer gas 120 to 200 Blast-furnace gas 130 to 200 After combustion the pressure is much higher, usually running from 250 to 400 lb. per square inch and not infrequently reaching 600 or 700 lb. per square inch. The temperature after combustion usually reaches 2,200°F. to 2,500°F. and may at times reach 3,000°F. In the Diesel engine the initial compression reaches 500 to 550 lb. per square inch and the compression temperature is in the neighborhood of 1,000°F. The two great sources of heat loss in internal combustion engines are due to the high temperature of the exhaust gases and the heat trans- ferred through the cylinder walls to the jacket water. The temperature of the gases at release is often from 1,500 to 1,800°F. Circulating Water. — To remove the excess heat from the cylinder walls and in large engines from the pistons, piston rods and exhaust valves, water is circulated through cored passageways. The amount of cooling water required per horsepower-hour is stated by different investigators as: t~ „o+:„„*~„ Cubic feet per Investigator horsepower-hour a 0.67 to 0.93 b 0.83 to 1.03 c 0.40 to 0.80 d 0.73 to 0.73 e 1.20 to 1.47 / 0.67 to 1.07 Average 0.75 to 1.00 The U. S. Bureau of Mines figures average for a large number of tests 0.82 cu. ft. per horsepower-hour for a three-cylinder, single-acting engine of 250-hp. rating. The wide variation in practice in commercial plants may be seen by comparing the following figures covering long-time periods for plants in daily operation. The high average is undoubtedly due in part to the fact that water cost little or nothing at most of these plants. The initial temperatures reported for the cooling water for these INTERNAL-COMBUSTION ENGINES 413 Plant 1 2 3 4 5 6 Cubic horsepo feet wer- per bour 3 .36 2 .80 2 .56 1 ,01 2 .18 2 .56 Average 2.41 installations range from 50° to 90°F. and the outlet temperatures from 86° to 160°F., the average being 115°F. In general there may be said to be at present a tendency toward higher temperatures of circulating water than in the past. Until within a few years 160° was regarded as about the upper commercial limit but recent practice in special plants has been to put the jacket water under pressure and to increase its temperature to about 300°F. or more. For small engines it may pay to install tanks or reservoirs for the cir- culating water. If this is done and the circulation is maintained by the difference in the specific gravity of the hot and cold water, the size of the tanks should be sufficiently large to enable the engine to run smoothly at maximum load for several hours consecutively. The reservoirs should then have a capacity of 50 to 65 gal. per horsepower hour. For large installations when water is expensive, cooling towers are often installed or spray ponds built as in condensing steam-engine practice. Lubrication. — Owing to the high temperatures that prevail in the cylinder of the internal-combustion engine, the question of proper lubrication is a serious one. Cylinder oil should be exceedingly pure, free from acids, and composed of hydrocarbons that leave no residue after combustion. Only mineral oils, therefore, are suitable for the purpose. The ignition point of good cylinder oil should not be lower than 535°F. The losses in power due to poor lubrication of gas engines may amount to 10 or 15 per cent. The amount of oil required per horsepower-hour varies with the char- acter of the installation and the method of operation. For full-load 24-hr. service, the proportion per horsepower-hour is, of course, greater than for a plant running under light load for a 9- or 10-hr. day. The average of several figures given by the engine manufacturers for the amount of engine oil required is 0.508 gal. per 1,000 hp.-hr. The operators of plants, however, report their commercial require- ments to be : The average of a number of returns from the operators of reciprocating steam engines indicates the consumption of cylinder oil and engine oil 414 ENGINEERING OF POWER PLANTS Gallons PER 1,000 Hp.- Hr. Horsepower of engines Hours of service per day Cylinder oil Engine oil Other lubricants 100 8 2.0 100 1.8 1.3 1.25 40, 160 16 2.8 190 24 1.0 500 24 1.25 80, 160, 200, 375 12 1.5 3.0 200, 500 24 1.26 300 24 0.75 0.4 0.8 750 10 0.5 0.17 0.07 125 0.13 0.4 0.1 150, 250, 300, 600 0.5 1.0 500 10 0.5 0.6 0.14 500, 1,000 10 0.4 0.6 300, 2,000 24 2.7 5.3 0.7 115, 300, 750 24 24 0.25 1.25 0.5 Average 1.17 1.11 0.51 to be approximately the same and to equal 0.13 gal. each per 1,000 hp.-hr. On this basis the oil consumption of gas engines seems to be approximately eight or nine times as much as that of reciprocating steam engines. This is perhaps not unreasonable as the .lubricating requirements of the gas engine are much more severe than those of the steam engine, but the ratio seems rather high. Advantages of the Internal-combustion Principle. — 1. The energy of the heat liberated by combustion operates directly upon the piston of the engine to produce motion, without intervening appliances. 2. The economy in fuel per horsepower is greater than with steam. No fuel consumed wastefully in getting the motor ready to start. In plants, other than producer-gas plants, more nearly portable than steam plants. 3. Insurance lowered by absence of boiler under pressure but some- times offset by gas-holder, or stored liquid fuel. 4. Absence of boiler avoids necessity of licensed operators. 5. Motor ready to start without previous preparation except with gas producer. 6. When fuel cut off, engine stops, not always a gain with gas producer. 7. Advantage of subdivided power, as each motor may receive its gas without loss through pipes, or from fuel tanks. INTERNAL-COMBUSTION ENGINES 415 8. No storage of large amounts of energy under pressure, in a contain- ing vessel, the rupture of which will cause disaster. 9. No boiler to cause trouble from bad water. 10. Normal and proper combustion smokeless. 11. Reduction in dust, sparks, ashes, etc., even with producers. Disadvantages. — 1. In Otto cycle only one stroke in four is power stroke. In two-cycle only one in two. On this account for a given mean pressure a large cylinder volume is required, especially for single-acting engines. 2. Irregular crank effort. Heavy flywheel needed. If a number of cylinders are used the engine itself becomes heavy. 3. Motor does not start from rest by a simple motion of a lever or valve. This involves a clutch. 4. No way of increasing the power beyond the limit set by the diame- ter of the cylinder. 5. No storage of energy for overload demands, etc., as in the boiler, save in the producer system. 6. Have to cool cylinder and other parts of the engine with water. 7. Large amount of heat carried away, unutilized, by the jacket water. 8. In spite of cooling water, the valves become leaky and require attention. 9. If not carefully looked after in making the installation, the ex- haust is noisy. 10. High temperature makes lubrication difficult. 11. If combustion not complete odor of exhaust offensive. 12. May get explosions in exhaust pipes or reservoirs. 13. Governing difficult on variable loads. 14. Not usually reversing in action. 15. Efficiency a maximum only near full load and when up to speed. Rapid Development of the Gas Engine. — It was during the latter part of the nineteenth century that the gas engine found its way on to the market, and, although many types have been produced in the past 30 or 40 years, it is only within the past 10 or 15 years that the deve- lopment of large engines has been noted. This development started in England, Belgium and Germany but marked progress has been limited to the past dozen years. For many years the natural fuel of these internal-combustion engines was city gas, but even this was too expensive except for engines of small capacity. It was seldom found feasible to operate engines of more than 75 hp. on this fuel. Cheap gas was essential for the development of the gas engine, but early attempts in this direction were somewhat discouraging, and for a 416 ENGINEERING OF POWER PLANTS time the probabilities of encroaching to any extent upon the field occu- pied by the steam engine were very remote. The theoretical possibilities of the internal-combustion engine oper- ated upon cheap fuel promised so much that the practical difficulties were rapidly overcome with the result that steam boilers and engines in many plants were replaced by gas engines, and at the present time the internal-combustion engine is a serious rival of the steam engine in many of its applications. The development of the gas engine in point of size has been exceedingly rapid. It was in 1900 that a 600-hp. engine exhibited at the Paris Ex- position was regarded as a wonder, but today four-cycle, twin-tandem, double-acting engines of 2,000 to 3,500 hp. can be found in nearly all up-to-date steel plants, and there are installations in this country con- taining several units rated at 5,400 hp. each. Marine engines of the Diesel type have reached 1,200 hp. per cylinder, or 7,000 hp. in six cylinders, all single-acting. Proper Location for a Gas Engine. — A gas engine should be located in a well-lighted place, accessible for inspection and maintenance and should be kept entirely free from dust. As a general rule the engine space should be enclosed. An engine should not be located in a cellar, on a damp floor, or in badly illuminated and ventilated places. The pipes by which fuel is conducted to engines, the gas bags, etc., are rarely altogether free from leakage, especially if the fuel used be street gas, or natural gas. For this reason the engine room should be as well ventilated as possible in the interest of safety. Long lines of pipe between the meter and the engine should be avoided, for the sake of economy, since the chance for leakage increases with the length of pipe. Not infrequently the leakage of a pipe 30 to 50 ft. long, supplying a 30-hp. engine, may be as much as 90 cu. ft. per hour. An engine should be supplied with gas as cool as possible, which con- dition is seldom realized if long pipe lines be employed for city or natural gas, extending through workshops, the temperature of which is usually higher than that of the underground piping. On the other hand, pipes should not be exposed to the freezing temperature of winter, since the frost formed within the pipe, and particularly the crystalline deposits of naphthaline, reduces the cross-section and sometimes clogs the passage. Often it happens that water condenses in the pipes; consequently, the piping should be so arranged as to avoid pockets. In places where water can collect, a drain pocket or plug should be provided so that liquid can be introduced to dissolve the naphthaline. Starting Gas Engines. — Various methods have been used for starting these engines. Among the most common are: 1. Hand-starting with flywheel or independent crank. INTERNAL-COMBUSTION ENGINES 417 2. In multi-cylinder engines, by hand pumps. 3. Compressed air [most usual today]. 4. Storage of compressed explosive mixture. 5. Independent engine for starting in large plants. 6. Various explosives. Exhaust Pipe. — If the exhaust pipe must be long, the use of elbows or sharp bends should be avoided as far as possible. In the case of very long pipes it is advisable to increase their diameter every 16 ft. from the exhaust. For the sake of safety, at least that portion of the piping which is near the engine should be located at a proper distance from woodwork and other combustible material. Great care must be taken if the exhaust be discharged into a sewer or chimney, even though the sewer or chimney be not in use; for the unburnt gases may be trapped, and dangerous ex- plosions may ensue at the moment of discharge. When several engines are installed near each other, each should be provided with a special exhaust pipe, especially if the engines are to be in operation at the same time; otherwise the exhaust of one may cause excessive back-pressure on the others. Exhaust Noises. — Among the most difficult noises to muffle is that of the exhaust. The most commonly employed means is to extend the exhaust pipe upward as far as possible, even well above the roof. This reduces the noise to some extent, but is not very efficient and produces back-pressure on the engine. Exhaust mufflers help to some extent, and the employment of pipes of sufficiently large cross-section to constitute expansion boxes in themselves will also muffle the exhaust. Consider- able benefit has been derived from specially designed exhaust pipes, con- structed on such lines that the gases have an opportunity for rapid ex- pansion immediately after leaving the engine. This condition is secured by a gradual expansion of the pipe for a distance of a few feet from the engine. A more complete solution of the problem is obtained by causing the exhaust pipe after leaving the muffler to discharge into a masonry trough having a volume equal to 12 times that of the engine cylinder. One authority states that the trough should be divided into two parts, sepa- rated by a horizontal iron grating. Into the lower part, which is empty, the exhaust pipe discharges; in the upper part paving blocks or hard stones not likely to crumble with the heat are placed. Between this layer of stones and the cover it is advisable to leave considerable space. Here the gases expand after having been divided into many parts in passing through the spaces left between adjacent stones. The trough should not be closed by a rigid cover; for although efficient muffling may be attained, yet an explosive mixture may be formed in the trough and damage caused. 27 418 ENGINEERING OF POWER PLANTS The explosion is, however, less dangerous than noisy. Some authorities claim the only use of stones in the pit is to prevent the possibility of accident to careless people. Weight of Gas Engines. — It is interesting to note the wide variation in weights per horsepower of different types of gas engines. Weight per Type horsepower, pounds Aero 2 . 5 to 4 Motor boat 35 to 40 City gas, natural gas or gas- oline 200 to 250 Oil 250 to 500 Producer gas or blast-furnace gas 200 to 600 Avg. 300 in Europe. 400 in United States. COST OF GAS ENGINES Cost of Gas Engines for City or Natural Gas Horsepower Engine, f.o.b., dollars Cost per horse- power, f.o.b., dollars Horsepower Engine, f.o.b., dollars Cost per horse- power, f.o.b., dollars 20 700 35.00 100 3,550 35.50 20 860 43.00 100 3,830 38.30 22 775 35.20 125 4,100 32.80 25 875 35.00 125 4,475 35.80 27 1,250 46.30 - 135 4,200 31.10 30 1,130 37.70 140 6,980 49.90 35 1,600 45.75 150 4.856 32.40 50 1,650 33.00 160 5,230 32.70 50 1,800 36.00 175 5,750 32.80 50 1,960 39.20 175 6,275 35.80 50 2,000 40.00 195 7,300 37.40 100 3,400 34.00 200 5,600 28.00 360 13,400 37.25 Cost of Kerosene Engines Horsepower Engine, f.o.b., dollars Cost per horse- power, f.o.b., dollars Horsepower Engine, f.o.b., dollars Cost per horse- power, f.o.b., dollars 1 2 4 6 8 121 204 324 444 568 121.00 102.00 81.00 74.00 71.00 10 15 20 30 40 60 650 855 1,060 1,450 2,020 2,820 65.00 57.00 53.00 48.40 50.50 47.00 INTERNAL-COMBUSTION ENGINES 419 Cost of Producer Gas Engines Horsepower Cost, Cost Founda- Cost of f.o.b. of tion, founda- factory erecting cubic feet tion Cost of engine erected including foundation Cost per horsepower F.o.b. factory Erected, including founda- tion 20 55 60 60 75 80 80 80 80 85 85 100 110 110 112 130 135 160 160 250 400 400 600 1,000 2,000 1,000 2,800 2,900 3,610 3,400 3,250 3,830 4,150 3,550 4,-925 4,950 4,960 4,200 5,250 6,600 5,500 6,100 6,650 12,000 12,800 17,400 33,750 64,850 175 150 100 300 875 350 375 2,000 2,160 5,400 50 105 150 150 225 520 560 1,400 1,150 2,400 3,935 3,300 6,770 7,360 67,125 55.00 46.70 48.40 48.10 42.50 40.70 40.90 48.90 41.80 49.25 45.00 45.10 37.50 40.40 48.80 35.00 38.10 26.60 30.00 32.00 29.00 33.75 32.43 43.70 52.40 41.20 42.30 29.40 33.56 The Oil Engine. — Although the oil engine is but a form of internal- combustion engine and has, therefore, been reviewed in a general way in the preceding pages, it is attracting so much attention at the present time (1916) that further details regarding it are presented. As early as 1873 Brayton tried kerosene oil in a two-cycle engine, burning the fuel directly in the cylinder at constant pressure. Theoretic- ally this should have given an efficiency of more than 50 per cent. Unfortunately, the losses attendant on the compression of the air and the fuel, with the difficulties of finding a burner and controlling the con- stant-pressure flame became so serious that the manufacture of the engine was discontinued. 420 ENGINEERING OF POWER PLANTS The first attempt to develop an oil engine on the Otto cycle was prob- ably that of Priestman, who in 1888 succeeded in constructing an engine which worked on heavy petroleum distillate in a very satisfactory man- Fig. 218. — DeLaVergne type F. oil engine. ner. Priestman used an ordinary four-cycle Otto engine, but injected his oil into a vaporizer by means of -the reflex rose spray nozzle, the oil dropping into the center of the spray by gravity and the small pump \\\\\\\\\\v\\^M'^ Fig. 219. — Nordberg heavy oil engine. compressing the air for use in this apparatus. The spray was received in a cast-iron outside-heated vaporizer and the ordinary Otto cycle was carried on with this gas in the customary manner. Most of the engines built in England from that time to this have been INTERNAL-COMBUSTION ENGINES 421 more or less on the Priestman principle, although the Hornsby Akroid which came out in 1892 uses an externally heated extension of the cylinder compression space as a vaporizer, the oil being forced into this chamber by means of a small pump and as the piston returns on the compression stroke the heating of the charge of air reaches a point at which the density of the mixture is such that it will ignite directly from the hot chamber. In the Brayton engine flame ignition was necessary. In the Priestman engine electrical ignition was used and with the Hornsby Akroid what amounts to hot-tube ignition is the standard. Many varieties of these engines are in use today. In many of these engines there is sufficient heat developed in the compression space to ignite the charge, in others Fig. 220. — Horizontal Diesel engine, 30 b.hp. the hot-tube ignition must be used. Among the successful engines of this type are the DeLaVergne, the Mietz and Weiss and many others. It is to be noted that most of these modern oil engines employ com- paratively low compression. One hundred and fifty pounds is high, from 80 to 100 is perhaps higher than the average. Some trouble results from the carbonization of the fuel in the compression space from imperfect burning and from the gumming up of the small oil passages. In most of these engines the cylinder heads and the vaporizing hot tubes must be cleaned once or twice in 24 hr. if economical running is at all a necessity. There is another type of engine in which an auxiliary compression cylinder in the cylinder head is used to compress a small portion of the mixture up to the ignition point. A number of small engines have been built on this principle. 422 ENGINEERING OF POWER PLANTS There are three methods of securing the vaporized mixture. The first is the spray and outside-heated hot vaporizer, in which a very rich mixture of atomized oil and air is heated in a cast-iron receptacle. The entrance into the hot tube is constricted and the air admission is by a separate valve into the cylinder itself. The compression of the air on the return stroke of the piston forces a sufficient volume of air into the hot tube to get the required mixture for explosion. The second is the comparatively large vaporizer with many baffles which is heated by the exhaust gases of the engine. Into this vaporizer the oil is fed drop by drop, falling on the hot surfaces where it is vaporized. This chamber is in communication with an inlet valve and the air passes through the vapor- izer making a proper mixture for explosion. The first plan is self -igniting, the second plan requires an electrical igniter. The third system is a modification of the second in which the air supply is partly used in atomizing the fuel and is partly taken in in the ordinary way. This also requires electric ignition. — A Fig. 221. — Indicator card of Diesel engine. In all of these engines the fuel consumption, while comparatively good, does not in general run much below 1 lb. of oil per brake horsepower- hour. The compression does not, as a rule, run much above 60 or 70 lb. per square inch and usually is not so high in engines using hot-bulb igni- tion. The construction of these engines is practically the same as that of ordinary gas engines with the slight variations due to the vaporizer. In fact, a great many builders of engines up to 200 hp. make only slight modifications in their engines for the use of various fuels. The addition of the carburetter to the engine makes the ordinary producer gas engine fit for using gasoline. The addition of the vaporizer converts it into a kerosene engine. Otherwise the details are not modified in any way. In 1893 Dr. Rudolf Diesel published a book entitled "The Theory and Construction of the Rational Heat Motor," in which he described a new engine with the following characteristics: First, the production of the highest temperature of the cycle not by and during combustion, but before and independently of it entirely by mechanical compression of the air. Second, the gradual introduction of a small and carefully regulated quantity of finely divided combustible into the highly compressed and INTERNAL-COMBUSTION ENGINES 423 heated air, in such a way that no increase of temperature takes place and all the heat generated is at once carried off by the expansion of the gases of combustion. Third, introduction of a large excess of air while main- taining a proper combustion of the fuel. Fig. 222. — Section Busch-Sulzer Bros. Diesel engine. This paper created great interest among engineers because of the almost revolutionary ideas which it contained. Dr. Diesel in his first proposals attempted to compress the air isothermally to pressures exceed- ing 250 atmospheres. This he soon found to be impossible of achieve- ment and he modified his motor by using adiabatic compression to around 60 atmospheres. He also proposed using powdered coal as a fuel, but 424 ENGINEERING OF POWER PLANTS soon had to give this up because of the impossibility of getting rid of the ash which in a very short time stopped the working of the engine. The Diesel motor made very little progress from the date of its invention until about 1898 when small-sized engines of this type were put on the market by a number of manufacturers. The Diesel engine at first was built on the ordinary four-cycle prin- ciple. Of late years, however, the two-cycle engine has been rather largely built, an auxiliary air pump being introduced to provide proper scavenging. Fig. 223. — Sulzer Bros. Diesel engine, 1000 b.hp. Although there have been many variations introduced by manufac- turers, nearly all are today confining their attention to the standard Diesel principle with compression in the working cylinder up to 500 lb. per square inch (1,000°F.), using a multiple-stage air pump to provide the injection air at 600 to 850 lb. per square inch. The extremely high pressures and temperatures of the Diesel system have put a limit to the cylinder diameter at about 30 in., which corre- sponds to an approximate cylinder output of say 400 hp. at 150 revolu- tions with four-cycle practice. It does not seem advisable to use more than six cranks on account of shafting difficulties and today the largest motors of this type might have 800 hp. per crank or 4,800 hp. for a six- cylinder engine. This power may be nearly doubled by the adoption of the two-cycle system. INTERNAL-COMBUSTION ENGINES 425 The four-cycle type of engine seems to be preferable for small sizes, although difficulties with the exhaust valve are of considerable importance and increase with the size of the engine. When the two-cycle type is used, in practically all large engines, the only serious difficulties have been from the inlet valves, which usually have to be gone over about once in from 6 to 8 weeks. The horizontal type of engine may be used in small sizes, but the best results on engines of any size have been obtained with the vertical engines. The DeLaVergne Co. in New York manufactures an engine designated as their F. H. type which operates on a variation of the Diesel principle. It is a four-cycle engine and compresses the air only to 250 to 300 lb., using a hot bulb to secure ignition. Fig. 224. — Types of oil-engine vaporizers. There are many methods of governing a Diesel engine, but in most cases the governing is done by bypassing the oil pump so that only the proper amount of oil for the work to be done is introduced into the cylinder. Among the auxiliaries required by a Diesel engine is an air compressor which must be of the two-stage type and have four valves. There must be an adjusting device to regulate the amount of air and it is customary to supply storage tanks, usually of the Mannesmann bottle type, in which the air is kept at a pressure of from 750 to 1,000 lb. The regulation of the air pressure for the engine at light loads is done by hand, otherwise the large amount of air admitted with the small charge of fuel might prevent ignition. It has been noted that the results of chemical analyses of different fuels do not furnish sufficient exact information regarding their suita- 426 ENGINEERING OF POWER PLANTS bility for use in the Diesel engine. This suitability can apparently only be determined by actual test. Two fuels of similar chemical analysis may give widely different results in the engine. There is a large selec- tion of cheap fuels available, such as crude mineral oil, mineral-oil residue and gas oil, that is, the intermediate products from oil re- Fig. 225. — Werkspoor 1100 b.hp. marine Diesel engine. fineries from which benzine and kerosene have been distilled, and the tar oils, tar from the water gas machine, byproducts from the distilla- tion of coal and paraffin, wood tar and paraffin oils. When tar is used, a small amount of gasoline is first injected to insure operation before the engine is warmed up. INTERNAL-COMBUSTION ENGINES 427 With such a choice of fuels it is probable that the Diesel engine will prove a favorite motor in many localities. Piston speeds of 600 to 1,000 ft. per minute are used. Speeds lower than 200 ft. per minute are not advisable on account of the leakage and difficulties with compression. An interesting development in the Diesel engine field is the adaptation of the Oeckelhauser type of engine to the Diesel principle. This has been done by Prof. Junkers, who has obtained 1,000 hp. from a single cylinder by his construction. In this engine three balanced cranks and connecting rods are used and the cylinders have no heads. Two pistons opposed to each other slide back and forth in the cylinder uncovering the exhaust ports at the ends of the stroke, the pumps being driven from the crossheads similarly to the ordinary marine steam engine. These engines are being built in the tandem type for marine use and promise to be of great im- portance, particularly for freighters whose principal business is oil carry- ing. The practical limit of cylinder dimensions for this type of engines will be much in excess of the 30-in. limit of the ordinary type of engine and with present materials there is little doubt that a 60-in. cylinder of 72-in. stroke could be constructed today with good results. Fullager has also built engines of this type. At present the largest Diesel engines for land service are four-cylinder engines of approximately 2,400 b.hp. These engines are running for electric-light service with admirable results on a guaranteed oil consump- tion not to exceed 0.4 lb. of oil per brake horsepower-hour. They are of the two-cycle type. Four-cycle engines have an oil consumption of practically 90 per cent, of this figure, or about 0.36 lb. of oil per brake horsepower. The thermal efficiency of these engines is between 30 and 40 per cent. Twenty-five to 30 per cent, of the heat is carried away in the cooling water and the rest in the exhaust gases. COST OF FOUR-CYCLE DIESEL ENGINES Horsepower Engine, f.o.b., dollars Cost per horsepower, f.o.b., dollars 100 7,700 77 200 12,600 63 300 17,100 57 400 21,600 54 500 26,500 53 600 30,000 50 800 39,200 49 1,000 48,000 48 About 20 per cent, of the waste heat may possibly be utilized for heat- 428 ENGINEERING OF POWER PLANTS ing purposes and the claim is made that if a proper utilization of this heat be obtained the efficiency of the Diesel unit might be brought up to about 80 per cent. The cost of two-cycle engines of large size is somewhat less, approxi- mately $35 to $40 per horsepower for engines of 1,000 hp. Foundations will cost from $2.50 to $4 per horsepower. Erecting labor will cost from $2 to $3 per horsepower. Summary of General Data on Diesel Engines. — Size: Smallest 6% by 8%, two-cycle, four-cylinder, 110 b.hp. for four cylinders. Largest 32.2 by 39.4, two-cycle, one-cylinder, 1,250 b.hp. for one cylinder. Weight: 250 to 500 lb. per horsepower in United States. Speed : 150 to 250 r.p.m. Submarine service 350 to 550. 600 to 900 ft. per minute piston speed. Mechanical Efficiency: Per cent, rated load 30 50 75 100 120 Mechanical efficiency 43 62 70 75 78 Thermal Efficiency: Per cent, rated load 50 75 100 120 Thermal efficiency 25 30 31 30 Economy: Per cent, rated load 30 50 75 100 120 Pounds, oil per brake horsepower-hour (Test) 0.71 0.55 0.46 0.43 0.44 Pounds, oil per brake horsepower-hour (Mfgrs. guarantee) (Oil, 18,000 B.t.u. per pound 0.60 0.53 0.50 Pressure for Spray: 800 to 1,100 lb. per square inch. Air Required: 16 to 34 cu. ft. free air per brake horsepower-hour. Power for Compressor: 4 to 7 per cent, of engine power. Cooling Water: 0.4 to 1.2 cu. ft. per brake horsepower-hour. Temperature Cooling Water: 130° to 140°R, max. 180°F. INTERNAL-COMBUSTION ENGINES 429 Lubricating Oil: 1.25 gal. per 1,000 hp.-hr. Attendance : One man to 1,000 to 1,500 hp. Life and Repairs: Uncertain. The Humphrey Pump. — Probably no single power-plant development has attracted more widespread attention during the past few years than the Humphrey pump. The operation of this device as described by Messrs. Potter and Trump in Practical Engineer, Feb. 15, 1915, is as follows : "Operation of the Humphrey gas pump is similar to the four-stroke Otto cycle with the exception that in this pump there is complete expansion, whereas in the Otto cycle the losses from exhaust taking place under a high back-pressure are considerable. Fig. 226. — Humphrey pump. Fig. 227. — Valve gear, Humphrey pump. "To start the pump, the proper mixture of air and gas is forced into the cylinder by a small gas-engine-driven air compressor of the two-cylinder type, one cylinder pumping air and the other gas. Two separate systems of ignition are furnished, one consisting of special spark plugs operated from storage bat- teries and the other from an electric generator. "After the proper mixture of air and gas is in the cylinder, all the valves being closed, the charge is exploded by an electric spark, directly over the surface of the water, no piston or moving parts being used, and the increase in pressure 430 ENGINEERING OF POWER PLANTS resulting therefrom drives the water in the pump head downward, setting the whole column of water in the play pipe in motion. This column of water acquires kinetic energy during the period when work is being done upon it by the expand- ing gases. By the time these gases have expanded to atmospheric pressure, the water in the play pipe is moving at a high velocity, and as the motion of this column of water cannot be suddenly arrested, the pressure in the explosion chamber falls below atmospheric, when both scavenging and water valves open. A certain amount of water enters through the suction valves, most of which fol- lows the moving column in the play pipe, while the rest rises in the explosion chamber. To assist the scavenging action, a certain amount of air is admitted to the explosion chamber to mix with the spent gases. "Most of the kinetic energy in the moving column is expended in forcing water into the surge tank, and, as soon as the column of water in the play pipe comes to rest, it starts to move back toward the pump, gaining velocity until the water reaches the level of the exhaust valves, which are shut by constriction and impact. A certain quantity of the burned products mixed with the scavenging Fig. 228. — Diagram of Humphrey-pump installation. air is now imprisoned in the cushion space and the kinetic energy of the moving column is expended in compressing this to a much greater pressure than that due to the static pumping head. "As a result of the energy stored in these entrapped gases, the column of water is again forced outward; the pressure in the gas head is again reduced below atmospheric pressure, when a fresh charge of gas and air is drawn into the explo- sion chamber. Again the column of water returns and compresses the charge of gas and air which is then ignited to start a fresh cycle of operation. "Primarily, the period of cycle of the pump is determined by the length of the reciprocating column of water in the play pipe. This motion is similar to the swing of the pendulum of a clock, and its period of vibration is governed by the length of the water column in the same way as is the period of swing of a pendulum by its length. As a general rule, assuming the column to be of uniform section, the period of vibration is almost proportional to the square root of the length of the water column." Although extensive installations of this pump have been made in Europe and INTERNAL-COMBUSTION ENGINES 431 in Egypt, a brief description of one of the first plants to be installed in the United States is recorded by the same writers in the article mentioned as follows: "In reporting upon the project to irrigate certain lands in Texas along the Rio Grande, extending from Del Rio to within 10 miles of Eagle Pass, the engi- neers employed had to decide between a gravity system involving the construc- tion of a supply canal some 16 miles long to water approximately 12,000 acres of land, and a pumping project to irrigate at once some 6,700 acres and to be extended to meet future needs. " Tentative plans and reports showed that the supply canal of the gravity project could be constructed for about $300,000 with an annual expense for fixed charges, maintenance and operation of approximately $40,000 irrespective of the use made of the canal. On the other hand, it was found the pumping project could be built for $60,000 and would entail an annual expense for fixed charges and depreciation of $6,000, and for maintenance and operation, $7,700. As the pumping project appeared so much more attractive financially than the gravity projects, its adoption was recommended. " The pumping engine selected is made under Humphrey and Smyth patents by the Humphrey Gas Pump Co., Syracuse, N. Y., and is guaranteed to pump not less than 20,000 gal. per minute against a static head of 37 ft. As it is believed that it will deliver in the neighborhood of 30,000 gal. per minute, all structures have been designed accordingly. The thermal efficiency of this pump is guaran- teed by the manufacturer to be not less than 20 per cent, of heat energy in the gas turned into work on the water when using producer gas having a heat value of not less than 100 B.t.u. per cubic foot. The Del Rio pump will make between 12 and 20 complete cycles per minute." Reported test figures for an installation near London, using producer gas from anthracite, show: Efficiency of gas plant, not including fuel used by auxiliary boiler, per cent 82 Anthracite per water horsepower-hour pounds (guaran- tee was 1.1 lb.) 0.796-0.957 Thermal efficiency based on water pumped, per cent 22-27 Gas Turbines. — There may be three varieties of the gas turbine: first, the air turbine in which air is the working fluid and the furnace is outside the system. This turbine is analogous to the hot-air engine and may or may not have regenerative features. The air turbine is a toy and can never be of importance, because of the impossibility of transmitting the heat to the air at a sufficiently rapid rate and because of the excessive size of the pumps and other auxiliaries. The theoretical efficiency could never exceed 10 per cent, and might be as low as 3 per cent. The com- mercial efficiency would be considerably lower. Second, the gas turbine in which gas alone is used, predicating an inside furnace, compressors, regenerators and other complications. This turbine has more possibili- ties and an efficiency of 30 per cent, might theoretically be obtained. 432 ENGINEERING OF POWER PLANTS The size of the apparatus is large and the power used by the pumps be- comes prohibitive, if an attempt at high pressures is made. High tem- peratures are necessary for economy and the experimental apparatus has usually burned up or fused before a test could be obtained. Third, the steam and gas turbine in which water is injected to reduce the temperature and increase the efficiency of the apparatus. The steam and gas turbine may attain an efficiency equal to the engine, or say about 35 per cent., but this efficiency is dependent very largely on the furnace temperature. At 500°F. the theoretical efficiency is 3 per cent.; at 1,000°F., 12 per cent.; at 1,500°F., 20 per cent.; and at 2,000°F. around 27 per cent. The water injection helps to carry off the heat and by regeneration these efficiencies might be somewhat increased. There are 10 or 12 gas turbines of various kinds running at the present time. The economy, however, is not good, and in no case have real tests been reported. One of the latest machines, intended for 1,000 hp., built by Brown, Bouverie and Co. for the inventor, Holzworth, has been run somewhat successfully, but his published tests are not in a shape to quote. His machine is an air-cooled gas turbine, the air is admitted at atmos- pheric pressure, the gas is compressed in a centrifugal blower, while an exhaust or furnishes the vacuum. These two fans are driven by a steam turbine using steam made from the exhaust gases in a regenerator. Al- most any kind of gas or oil fuel may be used, and he even used powdered Cannel coal in one of his tests. The 1,000-hp. unit weighs 25 tons and consists of a number of explosion chambers, each provided with valves, igniters and nozzle. The explosion chambers form the bedplate of the machine and the wheel is a two-stage impulse wheel with vertical shaft. PROBLEMS 71. If a 500-hp. gas engine requires 11,500 B.t.u. per horsepower-hour at full load, how many cubic feet of each of the following gases will be required per hour when the engine is developing (A) 300 hp.; (B) 100 hp.? (a) Natural gas. (6) Illuminating gas. (c) Up-draft producer gas. (d) Down-draft producer gas. (e) Blast-furnace gas. 72. Given a 100-hp. gas engine consuming 1,200 cu. ft. of natural gas per hour at full load with the barometer reading 29.35 in. and under a manometer pressure of 7 in. of water with the temperature of the gas 85°F. The heat value of the gas is 940 B.t.u. per cubic feet as measured. Determine : (a) The consumption of standard gas (60°F. and 30 in. Hg.) per horsepower-hour. (b) The B.t.u. per horsepower-hour. (c) The thermal efficiency (based on the heat value of the gas and the brake horse- power). (d) The amount and cost of water required by this engine for one month's oper- ation (26 days, 10 hr. per day). INTERNAL-COMBUSTION ENGINES 433 73. A customer purchased a 200-hp. gas engine guaranteed to consume not over 3,300 cu. ft. of illuminating gas per hour when running at full rating. When he received his gas bill for the first month amounting to $566 he felt that it was excessive and entered a protest. The records showed that the direct-connected D.C. generator had developed 17,800 kw.-hr. for the month, operating with uniform load 9 hr. a day for 26 days. Cost of gas $1 per 1,000 cu. ft. 1. Based on the guarantee was he justified in his protest or was the bill correct? 2. If the bill is incorrect, how much is it out? 74. Another customer with a 200-hp. gas engine guaranteed to consume not over 2,200 cu. ft. of natural gas per hour when running at full rating protested his bill of $110 for the month. The records showed that the direct-connected D.C. generator had developed 17,800 kw.-hr. for the month, operating with uniform load 9 hr. a day for 26 days. Cost of gas 30 cts. per 1,000 cu. ft. 1. Based on the guarantee was he justified in his protest or was the bill correct? 2. If the bill is incorrect, how much is it out? 75. If running under normal conditions, how many gallons of gasoline should a 250-hp. gas engine consume per 10-hr. day when developing: (a) 50 hp. (6) 80 hp. (c) 100 hp. (d) 175 hp. (e) 225 hp. 76. An acceptance test of a 100-hp. gas engine operating on illuminating gas shows it to be consuming 1,810 cu. ft. of gas per hour at a load of 75 b.hp., the gas being metered at a temperature of 70°F. and under a pressure of 3 in. of water above atmos- phere (barometer = 29.58). The heat value of the gas at standard conditions (60°F. and 30 in. barometer) is 600 B.t.u. per cu. ft. The engine is guaranteed to give a full-load thermal efficiency (on b.hp.) of 25 per cent. Would the test results justify claims of failure to meet the guarantee? What gas consumption (as metered) should have been expected? 77. Given a 150-kw. gas power plant with direct-current generator, direct-con- nected to a four-cycle gas engine. Fuel, natural gas. 970 B.t.u. per cubic foot. Determine the test economy of the plant in terms of cubic feet of gas per kilowatt- hour output at the switchboard if the demand on the plant is as follows: 6.00 a.m. to 8.30 a.m. 100 kw. 8.30 a.m. to 10.30 a.m. 150 kw. 10.30 a.m. to 3.00 p.m. 70 kw. 3.00 p.m. to 7.00 p.m. 125 kw. 7.00 p.m. to midnight 90 kw. Midnight to 6.00 a.m. 60 kw. 78. A manufacturer is considering the installation of a generating set to deliver a rated load of 200 kw. (direct-connected). Three types of installations are under consideration : (A) A simple, high-speed, non-condensing steam engine and direct-connected generator, hand-fired, water-tube boilers (two in service, one in reserve), closed feed- water heater, and feed pumps. (B) A four-cycle, two-cylinder, Diesel-type oil engine with direct-connected generator, to operate on crude oil at 3 cts. per gallon. (C) A four-cycle gas engine with generator, to operate on natural gas at 20 cts. per 1,000 cu. ft. 28 434 ENGINEERING OF POWER PLANTS Coal used in the steam plant will be bituminous coal costing $3 per ton. Water costs 40 cts. per 1,000 cu. ft. A building to house the plant is available, without cost, but foundations, stack, etc., must be provided. The plant will carry full load 10 hr. per day, 308 days per year. Estimate the total installation cost, the total yearly operating costs including fixed charges, and the resultant cost per kilowatt-hour generated. CHAPTER XXII PRODUCER GAS AND GAS PRODUCERS Producer Gas. — Gas of some kind and quality can be made from almost anything that will burn and nearly all gases used for power, heat- ing and lighting, with the exception of natural gas, are derived from the combustion of solid fuels or the vaporization of liquid fuels. From the standpoint of practical convenience and economy the fuels commercially employed for making producer gas are generally coal, coke, charcoal, lig- nite and peat, although wood, sawdust, straw, oil, etc., may be advan- tageously used under certain conditions. In the most familiar process of gas making, namely the manufacture of coal gas, the coal is subject to destructive distillation. The resulting gas is high in illuminating qualities and has a relatively high heat value per cubic foot. In this process there is a valuable byproduct in the form of coke which finds a ready market at a remunerative price. In another process of gas making from coal a limited supply of air, with or without water vapor or steam, is passed through a thick fuel bed. By the proper regulation of this air supply a partial or incomplete com- bustion of the fuel is maintained resulting in the gradual consumption of the entire combustible portion. Instead of having a large coke yield as a byproduct, as in the former process, the coke is utilized in the gas mak- ing. Gas made according to this latter method is known as producer gas and the apparatus in which the gas is developed is called the gas producer. Composition of Producer Gas. — In the manufacture of any gas it is found that its definite composition will vary considerably from time to time unless the details involved in the gas production are definitely controlled. The essential constituents are found in all kinds of fuel gas but in such widely different proportions that the gases resulting from the differ- ent systems of manufacture vary greatly in their range and manner of commercial application. The heat value of any gas is determined by the proportion of com- bustible gases present in any mixture and by the relative percentage of each of the individual gases. The non-combustible gases of course add nothing to the heat value but rather act in the opposite direction, that is, as diluents. 435 436 ENGINEERING OF POWER PLANTS These combustible and non-combustible portions usually embody the following constituents in varying proportions in the different types of gas: (1) Combustible gases Hydrogen, H2 Carbon monoxide, CO Methane, CH4 (marsh gas) Ethylene, C 2 H 4 (2) Non-combustible gases Nitrogen, N 2 Carbon dioxide, CO2 Oxygen, 2 Not only is there a wide variation in the composition of various types of gases, but considerable variation will often be found in gases of the same general type. Typical analyses of producer gas are: Composition by Volume, Per Cent. From anthracite From bituminous coal From lignite From peat From wood Up-draft plants Hydrogen, H 2 Carbon-monoxide, CO Methane, CH 4 Ethylene, C 2 H 4 Oxygen, 2 Carbon dioxide, C0 2 . . Nitrogen, N 2 15.5 12.90 13.74 18.50 22.7 18.28 18.72 21.00 0.0 3.12 3.44 2.20 0.0 0.18 0.17 0.40 0.3 0.04 0.16 0.00 5.5 9.84 10.55 12.40 56.0 55.60 53.22 45.50 100.0 100.00 100.00 100.00 4.0 13.6 8.0 0.0 0.0 12.9 61.7 100.0 Hydrogen, H 2 Carbon monoxide, CO Methane, CH 4 Ethylene, C 2 H 4 Oxygen, O Carbon dioxide, C0 2 . . Nitrogen, N 2 Down-draft plants 12.01 14.76 10.19 21.05 16.01 16.91 0.49 0.98 0.66 0.01 0.00 0.06 0.13 0.01 0.41 6.22 11.87 10.94 60.09 56.37 60.83 100.00 100.00 100.00 Besides the constituents mentioned, fuel gases often contain vapors which do not appear in the analysis, but which may prove useful or detrimental in the commercial application of the gas. Many of these vapors are hydrocarbon compounds, the most familiar of which and the most important are tarry matters. PRODUCER GAS AND GAS PRODUCERS 437 As is readily seen, the simplest producer gas is made by passing dry air through a thick bed of carbon, commercially either charcoal or coke. If a producer be filled with charcoal or coke and a fire be kindled in the lower portion then as the dry air enters from below the oxygen of the air will combine with a limited portion of the carbon in the incandescent zone thus supporting the combustion and developing a CO2 gas. If now this carbon dioxide gas be passed through the deep bed of charcoal or coke (carbon) above the burning zone, the oxygen and carbon tend to unite to form carbon monoxide, CO, if the proper temperatures prevail. This gas is the simplest of producer gases, but it is low in heat value, and difficult to produce on an economical commercial basis. The usual pro- cedure in producer gas making is to utilize coal as the fuel and to add a certain amount of steam with the air. This steam not only has the effect of enriching the gas but also tends to reduce the fuel-bed temperatures which otherwise may become too high for the successful generation of this gas. Steam, upon meeting an incandescent fuel bed, is decomposed so that the combination of carbon and steam is theoretically broken up into carbon monoxide and hydrogen (C + H 2 = CO + 2H 2 ). The enrichment of the gas from the steam is due to the additional hydrogen. It is also essential that sufficient care be exercised in the use of steam to prevent the chilling of the bed to such a point that the necessary decompo- sition cannot take place. The amount of steam that can be used to advantage is, therefore, limited. It is possible to maintain combustion with the air which is supplied and at the same time supply such a large amount of steam that its complete decomposition cannot follow owing to lack of temperature in the fuel bed. The result is usually an excess of carbon dioxide and the mechanical mixture of a certain portion of the steam still undecomposed with the gas issuing from the generator. When coal is used in place of coke there is usually considerable volatile material, especially in bituminous coals, which is distilled from the fresh coal at the top of the producer by the heat in the gas which passes up through the fuel bed. Besides this coal gas there is usually considerable tarry material given off by coal which may or may not be objectionable in the application of the gas according to the method of utilization. If these tarry products or hydrocarbon compounds are allowed to chill they may be very objectionable in certain types of plants owing to their tend- ency to clog pipe lines, valves, engine governors, etc. It is important, therefore, when this gas is to be used for operating engines that this tar be eliminated from the gas or be itself converted into a gas which may be utilized as a part of the regular output of the plant. The methods of handling these tarry products will be discussed later. As previously pointed out, carbon monoxide, hydrogen, ethylene and methane are desirable constituents in producer gas. The application of 438 ENGINEERING OF POWER PLANTS the gas in various industrial uses depends somewhat upon the relative proportions of these different constituents. Gases with a high percentage of hydrogen may be well adapted to certain types of metallurgical appli- cation but for power purposes involving the use of the gas in internal- combustion engines it is found necessary to keep the percentage of hy- drogen within certain limits. For this reason the methods of operating producer plants for power purposes are often quite different from those applied when the gas is to be used for metallurgical work. As will be noted in the above analyses, oxygen usually appears in very small percentages. Nitrogen has no special effect but simply acts as a diluent. The third diluent, carbon dioxide, is an undesirable constituent in producer gas and the percentage present should always be the minimum possible with any given grade of coal or method of manipulation. The chief objections to carbon dioxide in the gas are that it indicates the de- velopment of more heat than is required in the process of gas making; shows the presence of a larger percentage of nitrogen than would be the case with more perfect operation and also indicates that a certain portion of the carbon monoxide has been burned in the producer or that the thick- ness of the fuel bed was not sufficient to reduce the carbon dioxide evolved in the incandescent zone to carbon monoxide before leaving the producer. The principle causes of an excess of carbon dioxide are a thin incandescent fuel bed without sufficient depth of carbon to properly decompose the carbon dioxide produced in this incandescent bed and too low temperature in the fuel bed, usually due to an over-supply of steam. Types of Gas Producers. — Two distinct processes of making producer gas are in use — the up-draft process and the down-draft process. For commercial purposes these processes are applied by different manufac- turers in different ways resulting in the following four general types of producers : (a) Up-draft suction producers. (6) Up-draft pressure producers. (c) Down-draft producers. (d) Double-zone producers. The Up-draft Suction Producer. — As originally manufactured the suction, or reduction of pressure below that of the atmosphere, was pro- duced entirely by the suction stroke of the engine. Today this reduction in pressure is more often produced by the introduction of a mechanical exhaust or, thus simplifying the operation. The operation of the engine-type suction plant is described below. As shown in Fig. 229 the essential parts of a suction-producer plant are the gas generator or furnace, the steam generator or boiler, and the gas cleaner or scrubber. A fire is made with shavings, wood, etc., on the grate of the gas generator, the air necessary for combustion being PRODUCER GAS AND GAS PRODUCERS 439 supplied by means of the blower shown at D. As soon as the fire is sufficiently kindled the fuel to be used for gas making — charcoal, coke or anthracite — is gradually charged into the producer. The blower for the air supply is driven by hand, or in large plants by electric or other power, until gas of sufficiently good quality to operate the engine is generated. The quality of the gas is roughly ascertained by means of a test-cock at which the gas is lighted. As soon as the test flame shows the right color, which can be readily determined after a little experience, the gas is turned into the engine. The smoke and poor gas developed during the early stages of combustion are discharged into the outside air by means of the purge pipe shown at E. As soon as the engine is started, the blowing of Wr JLI ii Fig. 229. — Engine-type suction gas producer plant. the producer is stopped, and the necessary air for maintaining combustion is drawn into the base of the producer by means of the suction produced in the engine cylinder. If air alone is supplied, even in restricted quantities, the temperature of the fuel bed in the producer rises so high as to hinder the production of satisfactory gas. It is necessary, therefore, as previously stated, to cool the fuel bed by adding steam. The methods of producing this steam vary in detail in plants of different design, but the principles involved are essentially the same. At C is shown the steam generator or boiler for this particular type of producer. Steam at atmospheric pressure is generated by the heated 440 ENGINEERING OF POWER PLANTS gas, which leaves the producer at the point F on its way to the scrubber. The steam thus generated is picked up by the air supply passing into the base of the producer. The mixture of air and steam is then drawn up through the incandescent fuel bed. The oxygen of the air and the oxygen of the steam combined with the highly heated carbon in the lower part of the bed, producing complete combustion and developing carbon diox- ide. The gas thus formed passes up through a thick fuel bed above and the carbon dioxide is largely reduced to carbon monoxide. The hydrogen liberated by the decomposition of the steam greatly enriches the product. Scrubbing the Gas. — The gas after leaving the gas generator at the point F passes to the base of the scrubber G. The scrubber is usually a a ;:; ^^ - .I fi'TfCfjSliSSi^Sii'firnfii " ' , H9HHH^^bM~- v f\" ' *l : % Vv i. ■■ : ' ; ' I ■■ f . "'^ SB >:/ ■ SBki^H^^H '-■'■ < ^isi jfl ; 5S fess*?* Fig. 230. — Smith gas producer. cast-iron or sheet-steel tower in which dust, soot, tar and other im- purities are removed from the gas. As usually constructed it consists of a simple cylindrical shell filled with coke, over which water is sprayed. The dirty hot gas enters the base of the scrubber and flows upward; it is divided, in passing through the coke, into separate streams which are met by a fine water spray flowing in the opposite direction. The gas and the water are thus brought into intimate contact and the particles of dirt and other foreign matter carried by the gas are largely washed out. The wash water from the scrubber passes into a water seal shown at K, from which it overflows into the drain, or, in large installations, into a settling basin or reservoir. If the gas is to be used in an engine it is essential that it be thoroughly freed from gritty material in order to pre- vent scoring of the engine cylinders. It is equally important that tarry PRODUCER GAS AND GAS PRODUCERS 441 compounds be removed, in order to prevent clogging of the engine valves and governor. Owing to the fact that the draft of air and steam through the fuel bed is produced by the suction stroke of the engine, it is important that the resistance offered by the fuel bed, scrubber and connections should at all times be a minimum in order that the power from the engine avail- able for commercial use may not be too seriously reduced, by the demands for operating the producer plant itself. With this in view it is essential Fig. 231. — Smith gas producer plant. that the grate be kept free from the accumulation of ash and that clinker- ing in the fuel bed be reduced to a minimum. It should further be borne in mind that owing to this suction action of the engine any tarry products or other foreign matter that may have passed by the scrubber will be drawn directly into the engine valves. Any large amount of tar condens- ing and cooling in the valves or governor attachments of the engine tends to interfere with its successful operation. For this reason fuels containing large percentages of tar are not available for use in this type of suction producer. This of necessity restricts the fuels in regular use in these in- 442 ENGINEERING OF POWER PLANTS stallations to charcoal, coke and anthracite coal. Even with certain cokes and anthracite coals there is a slight tar production which has to be properly cared for. By the introduction of an exhauster of the Root or Connersville type the pressure through the gas-generating system may be maintained below that of the atmosphere without depending upon the suction stroke of the engine. The application of these exhausters is readily seen by reference to Figs. 232, 235, 235A and 237. The pressure on one side of the exhauster is, of course, negative and on the other positive. This arrangement makes possible the introduction of additional gas-cleaning devices and the possible use of bituminous coal and other tarry fuels. Fig. 232. — Charging floor Smith producer showing tar extractor. The largest single unit installed to date is an up-draft suction producer in which the reduction of pressure is maintained by an exhauster as shown by Figs. 231 and 232. The producer is of simple construction of sheet steel and channels. It is made on the sectional principle and can easily be enlarged by the ad- dition of one or more sections. As operated, the plant shown by the cuts has a fuel-bed area of 210 sq. ft. and burns about 2,750 lb. of Illinois coal per hour. Owing to the fact that the fuels generally used in the engine-type suc- tion plants are high in price, the installations of this type, although nu- merous, are of comparatively small power, seldom exceeding 300 hp. per unit and in the majority of cases not exceeding 100. PRODUCER GAS AND GAS PRODUCERS 443 The Up -draft Pressure Producer. — The pressure producer develops its gas under slight pressure (usually 2 to 8 in. of water). This pressure is produced by means of steam introduced through the blast pipe shown in the cut. The air enters the producer through this same pipe, being Fig. 233. — Up-draft pressure gas producer. drawn in by means of induced currents produced by the steam. The steam is supplied at a pressure of from 40 to 80 lb. by an auxiliary boiler. In this type of producer it is necessary to carry an ash bed deep enough to protect the blast pipe. On top of this ash bed is the incandescent zone and above this 444 ENGINEERING OF POWER PLANTS PRODUCER GAS AND GAS PRODUCERS 445 the deep fuel bed, supplying the carbon for reconverting the C0 2 gas into CO. The other essential parts of the up-draft pressure producer-gas plant are a preheater for heating the air entering the producer by means of the sensible heat of the hot gas from the producer; a scrubber for cleansing the gas; a tar extractor and tar drips; a pressure regulator; and sometimes a purifier for removal of sulphur from the gas. The elevation of such a plant is shown in Fig. 234. The Down-draft Producer. — By the mechanical extraction of tar a large part of the heat value of the gas is lost. As already stated, this may not be a serious matter in plants where the sale of the tar for commercial uses brings a good financial return, but in installations where the tar is thrown away the loss is sufficiently serious to warrant the attempt to devise some means of converting this tar into a gas of suitable quality for engine use. Attempts have been made to accomplish this result by manufacturers in this country and abroad, and the success attained has been sufficient to warrant the building of such plants on a commercial basis. Operation of a Typical Plant. General Description. — A typical plant of this character manufactured in the United States is shown in Fig. 235. This plant consists of two gas generators made of steel shells with firebrick linings. As in the types previously mentioned, the essential features of this type of plant are the gas generators or producers, the steam generator or boiler, the gas-cleaning apparatus or scrubbers (both wet and dry), the gas holder or receiver, and the necessary auxiliary piping, etc. In operating the producer plant the gas generators are charged with coke to a height of 3 or more ft. above the grates, and lumps of coal about 4 in. in diameter are added on top of the coke to the depth about 6 in. A wood fire is then kindled on top of this charge. The valves in the pipes at the base of the producers leading to the boiler being open, the exhauster a is started and the entire portion of the plant to its left is thus placed under suction. The air for supporting combustion is drawn in through the charging doors shown above the operating floor at b, downward through the fuel bed and pipe line into the base of the boiler, up through the boiler tubes and pipe line to the base of the scrubber, and then up through the scrubber into the exhauster. From the exhauster the gas is under pressure and may be sent through the dry scrubber c into the gas holder, or by simply opening the valve may be sent through the purge pipe d, into the outside air. When starting the fire, smoke and impure gas are diverted through the purge pipe until such time as the test flame shows the gas is suitable for turning into the holder. After the coke has become incandescent and the fire in the upper portion of the fuel bed well established, green fuel is added through the 446 ENGINEERING OF POWER PLANTS 2 O f-t ft o3 T3 i o Q CO 6 PRODUCER GAS AND GAS PRODUCERS 447 charging doors b as the condition of the fire and the quality of the gas require. The steam required by the plant is generated in the tubular boiler e by the heat of the gases as they pass from the generator to the scrubber. Sufficient heat is furnished in this manner to supply steam at 60 or 80 lb. pressure in the average plant of this type, although occasionally it is found best to install an auxiliary boiler. The steam which enters the producer above the fuel bed at the point / mingles with the air entering at b and the mixture passes down through the fuel bed, as previously outlined. The gas is cleaned by the coke scrubber, although in this particular type of plant the scrubber is fitted with partitions or shelves, upon which the coke is placed. The water spray which meets the ascending gas currents is shown at g. The upper portion of this scrubber is generally filled with excelsior, thus making a dry scrubber which removes consider- able moisture from the gas besides impurities. The additional dry scrub- ber, shown at c, is also filled with excelsior, and consists of two chambers, with valve connections so arranged that either chamber may be bypassed for cleaning. Conversion of Tarry Vapors into Fixed Gases. — By this down-draft process the hydrocarbon compounds and volatile material distilled from the green coal in the top of the fuel bed are drawn into the incandescent zone, where the tarry material is to a certain extent converted into a fixed gas. The completeness of the conversion is determined by the coal used, the conditions of the fuel bed, and the method of operating. Some- times the process is exceedingly satisfactory and the tarry products are practically all transformed into a good grade of gas; at other times a portion of this material is transformed into gas and a portion is burned in the incandescent zone. One of the criticisms of the system is that at some plants much lampblack is produced. Although this may cause no serious results so far as the operation of the engine is concerned, yet lamp- black is a disagreeable substance to handle in any quantity and tends to collect in every nook and crevice. If it is not properly removed when coals containing a high percentage of sulphur are used there is a possi- bility of a weak solution of sulphuric acid forming in certain portions of the plant and gradually eating away any iron or steel with which it may come into contact. "Shooting" the Fuel Bed. — After operating this plant for a few hours by the method described, the fuel bed in each of the generators gradually becomes clogged with tarry matter, soot, dust, ash, etc., and the suction required of the exhauster becomes excessive. If the plant is clean this suction amounts to possibly 5 or 6 in. of water, and gradually increases as the fuel bed becomes clogged. In the majority of plants it is not 448 ENGINEERING OF POWER PLANTS deemed wise to allow the suction to exceed about 20 in. of water, although there are plants in daily operation in which 60 in. are carried without difficulty. When this suction becomes excessive, it is necessary to clean the fuel bed. This cleaning, which must be done without stopping the plant, is carried on as follows: Suppose the fuel bed in the generator marked A, Fig. 235, requires cleaning. The charging doors b, b are closed, then the valve connecting the base of the producer A to the boiler is also closed by means of a wheel manipulated from the operating floor, and the steam entering the top of the producer is cut off and steam at full pressure, namely, 60 to 100 lb., is discharged into the base of the producer just below the grate. This high- pressure steam rushing through the fuel bed tends to dispel the tar, soot, dirt, ash, and other foreign material. The process is called " shooting." During the process the current through the fuel bed is, of course, reversed ; that is, made to flow upward instead of downward. In the shooting a jet of live steam is turned upon an incandescent fuel bed, and a water gas is formed which is quite different from the gas produced during the down- draft operation of the plant. The heat value of this gas averages about 200 B.t.u. per cubic foot instead of a little over 100 B.t.u., which is the heat value of the gas normally made by the producer. During the process of shaking up and cleaning the fuel bed the water gas is passed up through the fuel bed into the top of the generator A; through the bypass pipe behind the boiler, shown at h ; down through the fuel bed of the generator B; and then on through the boiler and scrubber to the exhauster, as in the normal working of the plant. The method of cleaning generator B is the same, except, of course, that the operation of the two generators is in reverse order. Utilization of Water Gas. — The gas produced during the cleaning process, high in hydrogen and of relatively high fuel value, differs so materially from the gas regularly made that many operators of down- draft plants find it inadvisable to mix the two gases, and provide two DESCRIPTION OF FIG. 235A. 1. Air intake. 2. Producer. 3. Fuel. 4. Waste gas stack. 5. Removable stack. 6. Center charging door. 7. Secondary vaporizer and Water-cooled top. 8. Side charging door. 9. Mixture inlet. 10. Peek hole. 11. Vaporizer. 12. Vaporizer inspection hand hole. 13. Vaporizer water supply. 14. Vaporizer overflow gauge. 15. Top of ash bed. 16. Ash pier concrete. 17. Foundation piers. 18. Waterseal pit. 19. Gas off-take (from prod.). 20. Sprayer column No. 1. 21. Sprayer column No. 2. 22. Water trap. 23. Sprayers. 24. Water supply for trap. 25. Water drain for trap. 26. Up-draft air connection. 27. By-pass connection. 28. Grate for supporting coke in wet scrubber. 29. Wet scrubber. 30. Scrubber sprays. 31. Scrubber gas off-take. 32. Exhauster Del. gas to expansion tank and Engine. 33. Drain. 34. By-pass and up-draft connection. 35. Waste gas stack. 36. Auto. By-pass valve (sending surplus gas back to scrubber). 37. Gas to engine. 38. Combined expan. tank and purifier. 39. Scrubber drain (sealed 1 ). 40. Baffle plate. PRODUCER GAS AND GAS PRODUCERS 449 i! i^ mmmH 29 450 ENGINEERING OF POWER PLANTS gasometers, one for the regular producer gas, or air gas, as it is sometimes called, the other for the gas generated during the shooting process, which is generally termed water gas. The discharge of these two types of gas to their respective gasometers is controlled by the operator on the charg- Fig. 236. — Westinghouse double-zone gas producer. ing floor. The number of times a bed should be shot during the day de- pends largely upon the character of the fuel used, the demands on the plant, and the methods of manipulation. It is not deemed desirable to utilize the water gas jin some plants used only for power purposes, and the PRODUCER GAS AND GAS PRODUCERS 451 gas is discharged into the atmosphere through the purge pipe. In certain plants with high-grade fuels and proper manipulation it is necessary to shoot the bed only two or three times a day. As the period required for the operation is not over a minute or two, the resultant loss from the discharge of gas through the purge pipe amounts to very little. In other plants where producer gas is used for heating, annealing, tempering, forge work, etc., in addition to its use for the development of power, it is ad- visable to generate as much of the higher heat-value water gas as possible. To this end, the bed is shot as often as may be done without chilling the incandescent zone below an efficient temperature. Single generator down-draft plants are now in use from which the ash may be withdrawn without shutting down the gas generator thus allowing continuous operation as shown by Fig. 235A. Fig. 237. — Westinghouse double-zone gas-producer plant. The Double-zone Producer. — The double-zone producer is, as its name implies, a combination of the up-draft and down-draft principles. Two incandescent zones are maintained and the gas is withdrawn at the center or waist-line of the producer. The CO2 gas formed in both of these zones is thus drawn through the central coke zone where it is recon- verted to CO. After the initial fires are started and the plant in operation, the fresh fuel is charged at the top and the volatile matter drawn down through the upper incandescent zone where the hydrocarbons are either burned or converted into a fixed gas, thus destroying the tar. The cen- tral coke zone supplies the lower incandescent zone with fuel and in turn is maintained by the coke formed in the upper zone. Care in controlling 452 ENGINEERING OF POWER PLANTS the distribution of air to the upper and lower zones is required to insure the proper balance for continuous operation. Vaporizers. — As already pointed out steam is essential in producer-gas making. It is introduced with the air. In many plants it is generated Fig. 238. — Smith tar extractor. Capacity 250,000 cu. ft. per hour. Fig. 239. — Section of Smith tar extractor. by the sensible heat of the gases as shown in Fig. 229, but for the pressure plants it is usually generated in an auxiliary boiler. For suction plants the steam is at atmospheric pressure or a little below this pressure, while in the down-draft plant of the type shown in Fig. 235, the steam pressure PRODUCER GAS AND GAS PRODUCERS 453 is in the neighborhood of 60 to 80 lb. This is also the usual pressure carried by the auxiliary boilers of the pressure-type installations. Scrubbers and Tar Extractors. — Ideas regarding the best method of cleaning the gas seem to vary greatly. At one extreme is a scrubber without coke or other solid material, completely filled with finely atomized water or fog, through which the gas passes. At the other extreme is a tall tower-like scrubber with the water pelting down in large drops or globules and supposedly beating the dust and dirt out of the gas. The ordinary practice, however, is to use coke-filled scrubbers and water spray. In passing through the scrubber the gas is more or less cleansed, de- pending on the character of the fuel used and the process of gas making. In the down-draft process additional scrubbers filled with excelsior are used for removing moisture and lampblack from the gas. For up-draft Fig. 240. — Details of a Smith tar extractor. The above is a photograph of the tar extractor for a 200-hp. producer. The previous illustration shows a section of this apparatus on a plane through the parallel axes of the tar extractor and gas line. Either of the two extractor heads may be cut in or out of service without affecting the operation of the plant. The heads are ported so that the gas passes through the extractor when its axis is parallel to that of the gas main, and when turned ninety degrees the extractor is out of service. In this illustra- tion the head on the left is out of service and the screens and holder, in which the glass-wool diaphragm is mounted, are dissembled. The coverplate is removed from the head on the right, showing the dia- phragm assembled and in place. plants using tar-producing fuels, some process of tar extraction must be introduced. The most common type of tar extractor removes the tar by centrifugal action, the extractor resembling a centrigufal pump. From the extractor the gas passes through tar drips to water-sealed pits. A liberal supply of water is required for this process, and the speed of rota- tion of the fan is of vital importance. A recent form of static tar extractor 1 requiring no water is shown in Figs. 238, 239 and 240. The descriptive paragraphs are from the manufacturers catalogue. 1 For a complete description of this tar extractor see Transactions A.S.M.E., vol. 35, p. 837. 454 ENGINEERING OF POWER PLANTS Special Producer-gas Engine Conditions. — As previously stated, it is necessary in order to make producer gas suitable for use in an engine that it be thoroughly scrubbed and cleaned and that it be sent to the en- gine at a low temperature. By keeping the temperature low a given volume of gas contains a large number of heat units and, consequently, is capable of developing more power in the engine cylinder than the cor- responding volume of the weaker gas. Another advantage in sending the gas cold to the engine is the fact that there is no danger of any con- densation of tarry vapors or water vapor after reaching the engine cylin- der. This is probably a minor advantage as the engine cylinders are usually kept at a sufficiently high temperature to prevent any possibil- ity of such condensation even if the gas be delivered at a relatively high temperature. Producers for Metallurgical and Heating Purposes. — Producer gas has for years been extensively used in various types of furnaces in the manufacture of iron and steel. This use has become more and more general during the last few years. In districts where the steel mills have had an abundant supply of natural gas no necessity for a substitute has been felt and no incentive for economizing the fuel supply has existed. The supply of natural gas, however, is by no means unlimited — in some places it has failed altogether — and the time when it will no longer be available in large quantities is near. Large users of this remarkable natural resource have had to recognize these conditions and to hold them- selves in readiness to use artificial gas when the supply of natural gas becomes inadequate. The solution of the problem is found in the gas producer, and at the present time there are within the natural-gas regions large installations of gas producers used for the operation of openhearth furnaces. In the manufacture of producer gas for metallurgical processes the gas goes to the furnace directly from the producer without any cooling or cleaning. It therefore enters the furnace highly heated, carrying with it all volatile hydrocarbons and tarry matter, as gases or vapors, and these add much to the heat value of the gas. The simplicity of the gas-pro- ducer equipment required where cleaning of the gas is not essential is shown clearly in Fig. 241. The gas passes directly from the producers to the gas header. Other Applications as a Fuel. — The abundance of natural gas and the multiplicity of uses to which it has been applied have led to a much greater appreciation of the advantages of gaseous fuel, and have helped to empha- size the value of the gas producer. During the past few years there has been great development in the utilization of producer gas not only for power purposes and in the manufacture of iron and steel, but in other industries as well. PRODUCER GAS AND GAS PRODUCERS 455 Among the uses to which producer-gas fuel has been put are annealing, japanning, enameling, soldering, brazing, galvanizing, drying, evaporat- ing, tempering, casehardening, type casting, yarn singeing and heating molds, wash kettles, ladles, stoves, bakers' ovens, and cooking. It has 1 Fig. 241. — Gas-producer plairtffor metallurgical purposes. also been used quite extensively in brick, lime and cement kilns, and in various types of ore-roasting furnaces. Fuels Used. — Anthracite. — Little difficulty has been experienced in handling good grades of anthracite coal in gas producers. Occasionally some trouble is experienced due to the character of the ash or to a low 456 ENGINEERING OF POWER PLANTS ash-fusing temperature. In the main, however, this fuel has been found very satisfactory. For most sections of the country the price of anthra- cite is relatively too high to warrant its use in plants of large capacity. It is, therefore, largely utilized in plants not exceeding 500 hp. Little has been done in this country with gas producers for the utilization of anthracite screenings or material from the culm pile. Anthracite coal may be utilized to good advantage in plants of either the up-draft or the down-draft type. Inasmuch as it is comparatively free from tar, anthracite is commonly used in the up-draft producer of the suction type. A single installation of 4,000 hp. of down-draft producers is using an- thracite at $11.30 per ton in preference to bituminous coal for which the plant was designed. Although the company owns bituminous mines, it places a value of $8 per ton upon its books for the bituminous coal. On this basis of $8 per ton for the bituminous coal and $11.30 per ton for the anthracite, a year's operation shows financially in favor of the anthracite. Outside of two or three installations, the individual anthracite plants of this country do not exceed a few hundred horsepower. Bituminous Coal. — Satisfactory gas producers have been designed for the use of both bituminous coals and lignites of good quality. There is comparatively little difficulty in handling, on a commercial scale, such plants provided the fuel is low in ash, has a fairly high ash-fusing tempera- ture and does not give serious trouble from caking and clinkering. Un- fortunately these restrictions are too exacting to fit usual practice in the United States with low-priced fuel. The European situation, where they are able to specify quite definitely the characteristics of the coal, is very different. The answer to a query as to whether producers have been successfully designed for the use of bituminous coals and lignites, is "Yes" for bitu- minous coals and lignites of high grades and although it is not "No" for other grades of bituminous coals and lignites, yet it is realized that low- grade fuel, high in ash and prone to clinker troubles, is not regarded in the majority of cases as worth the time and effort required. Bituminous coals and lignites of good grade may be successfully used in the up-draft producer if adequate equipment is installed for scrubbing the gas and removing the tar and in the down-draft producer of the continuous type and in the double-zone producer. One of the largest single generators in the United States has 210 sq. ft. of fuel bed area burning 2,750 lb. of Illinois bituminous coal per hour. There is no apparent reason why single-shell producers of this type should not be built four times this capacity. Lignite and Peat. — Both lignite and peat have been successfully used in various types of producer plants. Many commercial installations are PRODUCER GAS AND GAS PRODUCERS 457 operating on the former fuel in this country. Peat has not been com- mercially developed in the United States, but in Europe it is extensively used as a producer gas fuel. Amount of Fuel Used by Producer-gas Power Plants in the United States. — An estimate of the horsepower capacity of gas producers in operation for power purposes in the United States in 1915 and the amount of fuel used by these plants is : Horsepower For anthracite coal: Plants of more than 500 hp. rating 40,000 hp. Plants of less than 500 hp. rating 95,000 hp. For bituminous coal 130,000 hp. For lignite 15,000 hp. A corresponding estimate of the annual fuel consumption of these plants is: Anthracite 240,000 short tons. Bituminous 400,000 short tons. Lignite 60,000 short tons. 700,000 short tons. Use of Low-grade Fuels. — In the United States the majority of plants are using good-grade fuels, but economic conditions will necessitate before many years use of so-called low-grade material. Although commercial conditions make reliability of operation and plant capacity imperative, many plants could today utilize to advantage relatively cheap, poor grades of fuel with an assurance of both reliability and capacity and a net financial gain. The most difficult problem seems to be that of securing thoroughly competent men for the careful supervision of such installations. As indicated below the Bureau of Mines has demonstrated beyond a doubt the possibilities of actually using the following fuels in gas producers. Fuel from Variety or size Per cent, ash Per cent, moisture Pounds of fuel, as fired consumed in, producer per b.hp.-hr. New Mexico . . Tennessee .... Iowa Wyoming Wyoming Illinois Brazil, S. A. . . West Virginia. Pennsylvania . Pennsylvania . West Virginia, Run-of-mine Run-of-mine Run-of-mine Bone Run-of-mine Bone Washery refuse Washery refuse Bone 19.63 20.57 20.70 20.72 21.73 23.12 23.44 28.08 30.35 31.89 43.74 3.62 3.55 16.69 9.44 8.65 8.67 10.96 2.91 2.68 2.25 0.47 1.10 1.45 1.56 1.70 1.83 2.88 2.02 1.26 2.34 2.76 1.65 458 ENGINEERING OF POWER PLANTS Pounds of Fuel per Square Foot of Fuel-bed Area per Hour. — One of the most important commercial items connected with the design and also with the operation of gas producers is the determination of the number of pounds of fuel consumed per square foot of fuel-bed area per hour. This rate of fuel consumption varies radically with different types of plants and with different grades and different types of fuel and has led to much difficulty in designing and in rating producers. Early work in this coun- try followed European practice almost entirely and thereby occasioned a great deal of trouble in properly rating the pioneer plants and brought about the ultimate failure of many of them. Under certain European conditions, in which fuels of a definite grade are specified, high rates of fuel consumption may be obtained. It is not impossible to secure similar rates of consumption under corresponding circumstances in this country, but as selected fuels are seldom obtainable except under test conditions, it has been found that in general in the United States the rate of fuel con- sumption per square foot of fuel-bed area does not average much over one-half the amount originally guaranteed by early manufacturers. This fact has, of course, led to a decided modification in the design and proportions of many plants. Returns from the operators of plants throughout the United States indicate the following rates of fuel consumption per square foot of fuel- bed area to be good average commercial practice. Anthracite coal Avg. Max. Bituminous coal Lignite Peat Avg. Max. Avg. Max. Avg. Wood Avg. Up-draft plants : (a) Fuel, as fired. (b) Fuel, dry Down-draft plants: (a) Fuel, as fired. (6) Fuel, dry Double-zone plants: (a) Fuel, as fired. (6) Fuel, dry 10.0 10.0 14.0 13.5 8.5 8.0 17.5 16.5 13.5 12.5 14.0 13.0 23.5 22.0 18.5 17.5 12.0 8.5 26.5 18.5 21.5 15.0 17.0 12.0 31.5 22.0 27.0 19.0 15.0 12.0 35.5 25.5 14 Pounds of Fuel per Horsepower per Hour. — Producer-gas investiga- tions of the United States Geological Survey and the Bureau of Mines conducted with plants not above the average in efficiency showed the following approximate fuel consumption per brake horsepower per hour. PRODUCER GAS AND GAS PRODUCERS Pounds per Brake Horsepower per Hour 459 Bituminous coal Lignites Peat 1 Avg. Max. Min. Avg. Max. Min. avg. Fuel as fired . . . Fuel, dry 1.3 1.2 2.0 0.8 1.8 0.8 2.0 1.63 2.8 2.02 1.5 1.35 2.6 2.0 Although these figures were secured during the progress of regular tests, yet the conditions outlined in reports of the Bureau of Mines indi- cate clearly that equally good results should be readily secured in the average commercial producer-gas plant. A more direct comparison between the results of commercially oper- ated plants and those from the Government Station may be had by an inspection of the following table. Pounds of Fuel as Fired per Brake Horsepower per Hour Anthracite coal Bituminous coal Lignite Peat 1 avg. Wood* Avg. Max. Min. Avg. Max. Min. Avg. Max. Min. avg. Bureau of Mines. . . Commercial plants 1.3 1.5 1.3 1.3 1.4 2.0 2.4 0.8 1.0 2.0 2.5 2.8 3.0 1.5 2.0 2.6 3.3 The relation between the pounds of fuel per brake horsepower-hour and the calorific value of the fuel may be seen by referring to the following Fig. 242. W « ® 3 Q, O „W2J w a < « O J P 02 B *S c3 a c3 o o o o o CO -t-=> d o3 i— i a a> d Bb d 3 s ^ ■§ o o M a O 10 — — i-l o o S3 e3 os co CO 'C * 13 -o oq a 00 ~. o3 g-o;3 > '. 73 O (g « M w fl v h co o3_ J3 g.2 o3 >>0 ^ °d« «-73 I* B j-tf 2 * .2 9 S"^a fe a ® g CI a>^) * O 3 5oo CfOOOi-Ci-iWOOacSTHirOcNOOOOiOCOiO W'*rfC>00XN00iO©NI»O'*HH!0OlP3N W « M M h N «' rt «' «' N h N N ei W N N N CN ■*NO"3HO)OOM'U5NfflM'i(N O O O »h O i-h O O O i-i o o o o o c id i-J © o HMaNMN(ONh O oooooodoodoood dddodd OOOiCOOOO»C(MiCM 00NMM(OO)O>(»e<5Nffl(D OOOOCOiOO© NNHhOOOOOO) i-H I-H iH I-H O O c a ^H a o a a o i—i T-H o c — i o o o o 1-H -r o 3 N 00 s a OS 50 o c c o a 00 a o 00 c a i-H l> o a CO io o a 50 X a c a a a IO a a 05 CO a a OS -r a a 1—1 o a 0! to a a a 50 a a OS CO o o CO IO IO <* oo to O to oo c OS ■re o co 1— I re i-H T— 1 a i—i oo 00 03 CI CO rH IO a M to co to DO CI o a CO a IO a GO to ■oo o o cc a a i-H CO co 00 OOOOCNrtTjIHOnNOJCONMlWOHNOOO NOniOONM'-iHMHMfflMM'liM*»H HHNHffiNCCtOiOiOhOOffliOM^iONfflO rH rH >-i IO O rH (N CN i-H ooaaaaoaooo oioioaioooiooioo NHNOSifNOHNOH oo^oornc CO T* 73 a a 3 3 o o a a o o cq ro cct jej co co a t, a a a 3 '3 '3 '3 ** a a a <-h CO CD CO . 73 73 73 ci M M a a a a a a 3 3 3 CO CD CD O O O . • . C -. C C C O. a a a a a a O O O o o o O CJ o o o o rACQCQQOtncQCQOOCQCOCOQOCOtnCQCOaOCOCncQ JJCDVCOCDCDCDCDCOCDCDCD oooooooooo j3J2-O^^X!XlX3J2^ _ CD CD O C O O J3 X -Q -O CO CO CO CO CD o O ^2 J2 c9 S T3 a be a EFFICIENCIES AND OPERATING COSTS 503 H O tf H fa o ° a ro o E-" o J o P iJ OS O ^ i 1 N "3 ■* o ■43 00 c3-a CQ fl oS O in O o o o o o o M •S 43 03 <_ 2 icants, kings nd •plies ,_| ,+i ,_( r# fr. lO ,41 b- CO 00 i-i ■& ■* CO O O 1-" CM rH O O 09 <- O 03 » a -Q c3 3 o o o o o o o O 3ft oq 1-3 CO tN ■* iC t- 00 "3 4) lO Tjl T(( H (O CO O i-i 3 CO H N O O) N OS Ph i-H i-H O *-i O O O _ d 0«j lO • • • ■* CO • •HH • r~ t> • u oJ . O t- CO © © t~ tN C5 © ~*A O O tN 00 ■* ■* t^ >> '. iH <3 >0 "<* TH tN tN £* i-< 00 N H to O N 03^ fl io o w h o n 0J H H CO CO 00 r* ■a <*H C ' o o3 2 !h « 43 00 " fl 2 t- o o • • o ■ o o tianic trical inery .,dol kw. CO CO • tN g CT> 00 • • Ci • c3 mec elec ch kw aximum ontinu- us load, kw. iO O O O O O CO CO t- CO 00 O IO iO H H f) CO CO §°o J ft It V o o o o o O l-l i-H rH 43 43 +3 o3 cS * oo oo 03 a a > i B OJ 11) -* ^ a ]B 3 oo © a s a 43 43 O O O Cj oJ o o o '3 „ ™ o o o oo 05 -h i-H »— i OB «3 *> 43 43 43 43 -2 ID 0) OJ 03 a O O J J J 03 fl fl ^ fci U □ S 03 03 03 5 o o a a a 2 2 3 3 3 ib m « rt ° ° i" .2 iJ 43 43 T3 "d T) •J 'S tj tj fl fl fl -5 -5 43 03 3 3 3 2°J3J oo o a S jj 53 a a a 8 8 a a S S S O o 3 3 O O O _S _5 33 X O « O tN CJ N CI CN CO ^ tf < w H O « is d oo »o tN tN I-H CO o l-< o o o o J* c c tN 43 03 CO a c IE 3 43 S 00 4= < i - 4J oe tN m OJ B H 3 ■>J 504 ENGINEERING OF POWER PLANTS T3 c3 o I— I 03 o p p •rH -r= CI o o r* 3 o w 1-H ^ rH 0) w r> o o <1 ^-^ PH- IS > GO .a sa P H ■ft -H 0) % O Ph S 03 a; -t-> tc « b() (H aj H-J O ° o I. 00 O CO CO tJ4 00 n h © n oon sj o3 ^ 3 r2 ^ "o3-d w a sq cm 8 >h o o3 ft rO o3 3 d ft «° M e3 2d — o u ~h3 >> '. oc 3 a 03 o.2 ^ a 3 o3 o3-3 PM OJ <0 Ih — i a * o3 — • =2 U rr< P- +3 d - u rS t "J Or* 1 "3 d ad o £ a * 3 t> C rH CN rH i-H i-H l-H i— I © O r- < r- li-Hr-li-li-l OWOMNNO^OHN M»K5nO"3'l5(OiOOON 0 CO o 00 GO p co 00 o CD o CO o o CO o o CO o 10 i-0 o 01 CO o CO o 00 LO o r-H 1—1 Ol o IO o CO 'CO a so o CO o CO rH ooooooooooooooo O O O O O CO O iO O O O CO Tji CO O CO O^tDHOCCNffl^ OOONHifNCCOOiO CNC005tN00rHiOl>iOC0CDiMO co r^ CO Of) on H Ol th r^ eo 00 O rH c o to ~* CO C-j b- rH CO rH rH "* OS r^ CO ■- -* rH rH 0) rH cc co CO' rH r- t* 05 rH 01 o rH rH CO i— i o oc a o o iO O CO — a o o o a o o o o o o c o • 00 • co i-H rH n CD CO rH Ol OS CO co co co CO rH CO 00 CO rH IO 30 t^ • OCOOOCOOiOOOOOOOO o^ootaooowiooooooHO HHHNMJUJOOiCfflOONO H H H H N M W M 3 3* hO m rQ 3 13 3 3 * rO rrj rrj rrj fl fl 3 ri Cj cj c3 T3 T3 3 3 3 3 c3 c« T3 T3 3 3 c3 rt T3 13 3 3 03 c3 rfl m Bl Tr IB m BO m If) m ff) oo hli hi: M tl! bli bit hli bl Ml td bl' M G G C C C d d d d d d a CU OJ a> a> 4) V V o 0) ftftftftftftaftftftftft T5 T3 3 T) 3 c3 3 03 . c$ . 00 . 00 M tn M 3 M 3 c z c ft • ft o ft o ooooooocoocu ■* ■^ ■* CO »o t- W5 IO •* O o OS — i ■* Tf* n rf; Bfl on 00 on no m Rl 00 00 II) 01 h rl t-. Ih u tl r< u Ih %~ Ih Ih M Ih h c O CO OJ 0) 93 01 ■Zj m OJ U OJ U O) OOOOOOOOOOOOOO rQrQrQrQrQrQrQrQrQ-QrOHQrQrQrQ lO^COiOcOOOOOCNCOrHtNcO-^CO rH CNrHrHrHCNi-Hi-HCN EFFICIENCIES AND OPERATING COSTS 505 Table 4 shows results for large steam plants (of over 1,000-kw. capacity). In such plants more reciprocating engines than turbines are found. Table 5 gives results for steam-turbine plants of more than 1,000-kw. capacity. Lubrication expense is reduced and the cost of fuel and wages determine the cost of operation which in one plant is reduced to 0.525 cts. per kilowatt-hour with a thermal efficiency of 12.3 per cent. Table 6 gives a tabulation for gas power plants. These costs differ depending on the fuel used. Most plants use anthracite or coke or both, the specific cost being lower with coke. Reliable information was not available of plants using lignite briquettes, but these are somewhat under those for coke. Gas plants are thermally superior to steam plants. The diversity in the specific cost of fuel is partly explained by the difference in price. The cost of fuel decreases as the load increases only up to 300,000 kw.-hr. yearly load, and the expense of fuel is independent of the size of plant. The fuel cost varies for two similar plants of the same yearly load from 0.38 ct. to 0.88 ct. per kilowatt-hour. The cost of maintenance and the cost of lubrication are about the same as for the steam plant. For small gas plants the maintenance cost is greater than for the steam plant, but for a yearly load of 700,000 kw.-hr. the costs remain below that for steam plants. The total costs vary from 1.5 cts. to 2.66 cts. per kilo- watt-hour. At about 600,000 kw.-hr. the total operating cost is about \Yl times the fuel cost. Up to 10 years ago there were no gas engines built of more than 1,000 hp. capacity. Now ,there are more than 1,000,000 hp. in operation in the world. Two fuels are in common use: Blast-furnace gas and coke-oven gas. In Table 7 are given the operating results for two large gas-engine plants. This sort of information is difficult to secure as these plants are just beginning to arrange for the exact measurement of gas used. The total cost is low, ranging from 0.264 ct. to 0.357 ct. In Table 8 are shown Diesel engine results. The thermal efficiency is nearly the same for all the plants (about 31 per cent.) with the excep- tion of the smallest. The cost of lubricants, etc., is somewhat higher than for steam and gas plants. The maintenance can be almost neg- lected. The unit costs for salaries decrease inversely with the yearly load. In general they require more skilled attendance. The total cost of operation amounts to 1.79 cts. for small plants and falls to 1.095 cts. for a plant with a yearly load of 1,000,000 kw.-hr. The total cost amounts to 1.7 times the fuel cost for plants of large size and about double the fuel cost for small plants. Fig. 185 shows, in the lower half of the diagram, how the total operat- ing costs and the fuel costs for steam, gas and Diesel engines compare. 506 ENGINEERING OF POWER PLANTS 73 O d O d d « 8 H .s «< o3 tf iQ O O O H P CO w > o «+H 09 H-3 a d •i— i ,Q a +3 CD *H ft o «o-S 2 H »"? w .S to a> ' o3 cN.«_a O 9* h U ^ U H o w. fit CD 13 ° * a §3 S g.2 cs >.-o fe Eg-S°-5 S3 so . .3 d c3 F § ° oooo io on CO CO CO CO CN CM ■* lO i-l 00 N tO iH i-H i-t O O O CO a r>. a> i—i I-H I— 1 CM 'O i-i on CO i-H o O o O o o O o o o o I— 1 ^H to to 1— 1 lO t» "rff co 1—1 eo OJ CO iQ Ui CN t-H o o o o o o o CO -H co N t>- CO o CO Ttl tO ^ CO o o o o o o 0} -H IQ CO CO CO r^ C5 O CN c o o I-H 1-4 o o o o o CO i-i o o © o CO © © i-H © © CN iH O CN CN O o" N 00 ffi "5 O* i-H »C O O CN O O CN ^ i-H CO CO o o o o © o O S «3 tJI lO N b- O O iO o o CO O K) CN O O i-H lO 00 H © O H H H M © 115 co co co cq tn go eo a> a) cd a> a) q a a d a J3 -^ x: 42 x> S £ 3 3 3 •** -** HJ +» +j rt -* CO Ol CO EFFICIENCIES AND OPERATING COSTS 507 b B O CO < -t-> fc oi < ft fa *H o 0) to Eh •J o ft P 02 «3 OS B O c© B hh* 9 OS O «3 d 03 03 ^ 03 O 2 » ^•8 43 43 T3 ID in 3 d 43 43 03 03 3.3. - w briq g gas briq g gas 0) 03 03 ^4 44 ^ o o o C3 o o 03 c3 -3 bfl fl bfl * 03 93 03 08 bfl bfl bfl bfl fo 03 c3 .9 03 .3 03 03 03 03 5 -9 .9 .9 .-£ O 43 O 43 3 O 03 o c3 43 43 43 43 'o 'S '3 '3 ■jj 5 +> 3 5 ■£ '5 43 OS 03 ga.Sfl.2 c3 c3 c3 c3 2-2 § d d . L* u u u ja&S^S © j2 ja j j A B 3 8 I 3 2i2 2* 3 3 3 3 3 d^'S <3 HH ^33 3 3 <1pqppqa O <*«!OiOOOOOOOiCOO OOiflOO Hi O O (DiOO)(NtDOO'tH(000 N N O 00 O) IN CO COO)HTjltONil5H3aiOOM iO t> O iO lO iO N H °C® NH^HNNHNHi-ilN 1— 1 t-( CN i-H I-H CN i-H .s ^ t+i 00 • COCNi-HCNOOOrH CN CO CO CO CO O Hi I COCO •Ttll-HNOt^TtlTHOi O O) CO Tjl 00 CC 03 M u 03 a -* 03 g ^ 03 43 CO CN ■H(DNNiONNO oo -oooooooo H H (N « OOOO O CO 000 03 3 Salarie and wages 00©COO»0©iO©COiO UJ N iO C O CN lO -2 CO->#CNCO00COTtl00COlOCO t> CO ->+i ■* CN Hi CN a o MHOt»00)NN<0(»K3 i-llHrHO'-HOOOOOO >C t>- t>. CN OOOO 00 ■* Hi 000 DO o o «2 _ MiO^OOTtOOOOiO O CN iO O CO 1-1 00 3 cs « ts a «3HNMfflWOOO)N«3 MOON CO CO CN bfl 0)hiO^HO«30B!OW 00 IN C3 CO OO t^ Tj< a OOOi-hi-h©Oi-hO©i-h OOOO OOO 43 cS (i 03 Q O, 00 OOO^HOOOOOOO OOOO OOO iliflOOONOiOONOfl co 00 10 10 CO CO Hi o "a! i-iOCNO-r CO CN >» -M "5O(0O00^H(0(N(0N 'i-H t^ T*l rH C i-H b» ^•DJ? OOOOOOi-HCOt^COt-CO CO CO CO 00 c>- O CO c3 e3 '. «3Hi00N(OtO©l<3MNN Hi Tj( CO CO C\ CN •*+! K^.2 £ ^ ^ (OhoONiOONMIOhN t>- OS CN O ec CN O i-H MHNCCM^MN CN ■* ■* CO l> CN CO i-H CO *>"e 5 i >a 2 « 3 o t! * » o o o o o o O C c O O O-- h £)»-< 03 •> 03 o o o O Hi O 000 c O O ■^ I and e trie machi per k dolla kw «5 O H CO l> - OS IO 00 CT> O m n © co 1- os ► con- tinu- ous load, kw. (N O b- O 00 -tf C O * N C c CN C O c S CO >0 CO O O "# C co co in cc (- CO C t* c t^ % H ri H C( CM CM (M CN CN CO Tt f IC IO ■* 1-1 d 03 bfl 03 M 03 03 V - ^ t- o o c 43 43 43 4i a a c3 c3 c CO 03 o 43 c3 - Lh (- a 03 03 a d d c co Pi 03 03 0. 03 o* 03 43 a o3 5 03 0Q 03 bfi bO hi D.d nerato nerato eras. . . O 43 03 ) 2 d 0) bfl 03 M 03 03 0. - - - ^ 3 = 03 03 O: CO 03 & 03 03 0. 'bi d 03 btl 03 0) .. H 60 bfl M J3 a bo o o a a c d 43 hi 3 N N -43 CN (N CO CN . 03 '■+; 03 03 rt - 03 03 03 03 2 0) 03 03 03 03 DC i 1 - 03 03 a t- ■ .s .s a .s 9 9 d d c X5 C 3 1 g 42 b 3 % *Sb 'So 3 '5b 'Si "So b£ bfl bi r a a ~ a a a d d c 13 t- 03 03 H? 03 03 03 03 03 a £ "a -£ 03 3 3 a a cq a 03 o o O 3 o CO o CO I-H i— 1 PE| © d « < d >< 01 "Si i- 1 CN s a> d «< .3 « CO -1-3 H -• J5 3 43 3 43 fc 'a m «" o o o c o o c o o o o o o c o a "tf O O CN i-i 0C lO CO CO CO CO O "" > I-I H CO 4» a 03 5 43 43 +: SOS oo oo a O O C S 2 £ D O ( c3 o3 o! .5 2 5 a a c 'Si '3) 'S a a c J 73 T3 T3 1 a oc X CO CD © CE 03 03 03 03 03 03 03 03 03 ■»» -+3 +s .5 .2 .£ a a a a s s 'Ei '3 '5 ) M M M M be bl ) a a a C 3 C 3 C 3 .3 X> ,0 03 03 03 03 03 03 03 03 03 go go or 00 00 Of CO GO 00 00 00 Of o3 c3 oi o3 o3 o; o3 o3 o3 o3 o3 oi Si tO Q '.i ti -. -i a a a it a CD FH r— CO -H CI CO N H N :n rH 1 EFFICIENCIES AND OPERATING COSTS 509 s 3 o CO H P CQ oo CD C 03 03 o .2 a 03 o3 ^ PI "c3T3 to a ■£ Ml k. oa o a a 5 J3 • § gift's S CO Ph SCO 3 3 o .5 PI o3 03 Q Oh O CO OS CO l> 00 O O O O O iO N THNH00O O 00 h ^ Ki Ol CN CN rH <-< r-H ,-H O h n n CN CD 00 O CN O CD 05 00 • O • CN c 00 CO O 1— 1 CO 10 to CN 00 O O • O 1-* O 1— 1 r-i O DO M C CD re CO I— 1 oc CO 00 co CO 1—1 co co O O O O O O O Moomoomioo tO00CO00CN-*(NCO ■* CO i-H OOOOOOOOOO CO CO CD O CO re O • O • CN • co re 1— 1 M 00 co >o .-H CN O CO CO CO O O O • O 000 CO 10 1T~ I— 1 OS 00 CO CN O »o O O O OS CN CO 1— C 00 1— 1 OS X re CN CO q CO O 000 iO o o I-H i-H i-H O ■* O O O "# ^ CN CO CO CO -# CD CD CN CN CO CO •* CO CD ft o o CD ft eecseeecsee .a -3 « 03 03 0) <0 . . ft ft J3 * O o o IO H tn 03 CO CD .2 .2 '5b "3b a a CO co ft O o co g'Q r- CO ^ CO £3 • CO 00 .3 ^ /-v (3 1 >> CNCNCNCNCNCNCOCOCO ft ft 510 ENGINEERING OF POWER PLANTS In the upper portion the cost for wages, maintenance, lubricants, etc., are expressed in percentage to the total cost for each of these types of engines. The gas engine shows the smallest fuel expense; the Diesel engine the smallest total operating expense, the steam-engine plant being in both cases the most expensive. In the upper chart, the Diesel engine is the lowest and the gas engine the highest. CHAPTER XXIV COMPRESSED AIR Compressed air is used for transmitting power, for the storage of energy for many purposes, and for producing refrigeration. Air at mod- erate pressures is used in blast-furnace work and in the Bessemer process; air at higher pressures for the transmission of power, the operation of cranes, hoists and presses, and for the working of motors such as drills, coal-cutting machinery, hoists, street cars and similar applications. High-pressure air has been used for storage, for refrigeration and in cer- tain chemical processes. Air at low pressures, between atmospheric and 5 or 6 lb. per square inch, produced by centrifugal fan blowers or the so- called positive blowers, is used for the ventilation of mines, buildings and ships and for producing forced and induced draft for steam boilers. The storage of energy by compressed air usually differs from the transmission of power, in that the compressed air, which is forced into the receiver at high pressure, is generally used at a much lower pressure in the air motor. Although compressed air has been used in engineering operations for a period of probably 200 years, the modern application of compressed air is probably due to Messrs. Kraft and Sommeiller whose extensive experi- ments at the Cockerill works at Seraing in Belgium, resulted in the use of compressed air at the Marie colliery in Seraing in 1856. The Som- meiller compressor built by the Cockerill Co. compressed the air for the work in the Mount Cenis tunnel in 1861. The air pressure used was 106 lb. per square inch and the longest transmission lines exceeded 20,000 ft. The air motors worked expansively, the cylinders being heated to prevent freezing. The Sommeiller compressor (see Fig. 257) consisted of a plunger working between two containers filled with water, the water serving to cool the air and acting as the piston of the compressor. These compressors were quite economical and more modern constructions on the same principle, such as the Leavitt compressor at the Calumet and Hecla copper mines, have given very good service. This compressor has double-acting cylinders, 60 by 42 in. and runs at the comparatively high speed of 25 r.p.m. About 1868 the dry compressor came into use, the cooling being imperfect. This was improved shortly afterward by the introduction of the spray injection by Prof. Colladon. Spray injection is now no longer used and both cylinders and pistons are water-cooled to reduce the loss by heating as far as possible. It was soon found that it 511 512 ENGINEERING OF POWER PLANTS was much better to make the compressor a compound or two-stage machine and to install intercooling coils between the cylinders. Modern air compressing dates from about 1877, when Mekarski and Popp com- menced the installation of compressed-air plants for the driving of railways and the distribution of power. In the United States the development of compressed air has followed the development of the mining industry, and most of the compressors have been built and sold for the working of air drills and similar machinery in the mining and quarrying fields. About 15 years ago the " pneumatic tool" came into the market and since Fig. 257. — Sommeiller hydraulic compressor. that time no shop or manufactory is complete without its compressed-air line, which supplies power for the use of an infinite variety of tools. Kraft in the years 1854-8 used compressed air for the cranes at the Cocke- rill works at Seraing and many of these cranes are still in use. Pneumatic lifts and cranes are now installed in many places. Air-compression machinery may be divided into (a) piston com- pressors and blowing engines; (b) rotary blowers of the positive-pressure type; (c) centrifugal blowers or fans including the turbo-blower and com- pressor; and (d) the hydraulic air compressor. Piston Compressors and Blowing Engines. — Piston compressors and blowing engines differ only in the pressure to which they work. Blowing engines for the blast furnace usually work from 8 to 15 lb. per square inch above the atmosphere. Blowing engines for the Bessemer converter work between 18 and 35 lb. gage. Ordinary air compressors of the piston type for power purposes are usually built to deliver air between 50 and 80 lb. per square inch for single-cylinder compression. From about 70 to 120 lb. per square inch they are usually compounded and for higher COMPRESSED AIR 513 Fig. 258. — Riedler valve. pressures, up to 2,000 to 2,500 lb. per square inch, three- and four-stage compression is used with intercoolers between each two stages. The construction is practically that of a steam engine, Fig. 269, the only differ- ences being the unusual care taken with the jacketing and intercoolers, the excessively small clearance and the type, location and area of the valves. The early air compressors used the standard steam-engine valves with the consequence that the volu- metric efficiencies were in many cases below 50 per cent. This almost immediately led to the use of poppet discharge valves and very large mechanically moved inlet valves, and finally to mechanically controlled valves of very large area for both suction and discharge. The well-known Reidler valves, Fig. 258, were invented for this use. These valves, however, have been superseded on the more modern machines by a very light spring-controlled multiported diaphragm valve, known as the Borsig type, Fig. 259, which is now used by prac- tically all of the better class of builders on low- and medium-pressure work. The International Pump Co. make a straight leaf valve of this type. For the large blowing tubs of blast-furnace and steel-mill work the Slick system has been very largely used. Here the cylinder heads are firmly fixed to the base of the machine, while the cylinder barrel is provided with slotted suction openings on each end and is moved backward and forward at the proper time, to ensure full valve opening as in Fig. 261. The discharge valves are located as usual in the heads. Some of these blow- ing tubs have been built as large as 100 in. in diameter with a stroke of 7 ft. Bessemer blowing engines are usually of much smaller size and are built either on the Slick system or with the Borsig valves (see Trinks paper, vol. 33, Transactions A.S.M.E.). The positive pressure blower, Fig. 262, consists of two shafts carrying two- or three-lobed impellers running in a casing with extremely small clearances. These blowers may be used up to about 15 lb. per square 33 Fig. 259.- -Borsig valve for blowing engines or air compressors. 514 ENGINEERING OF POWER PLANTS inch and are built with much success in this country by such firms as the Connersville Blower Co. and the P. & F. M. Root Co. These blowers fezgzggz^^^ r fe zz asBZZzz-gz ^VVVWVWWVAV <.».///////// //////////////// Fig. 260. — Compressor cylinder with piston intake. Rockersbaft Air Discharge Fig. 261. — "Stick" blowing tub. Westinghouse Machine Co. may be used either as blowers or exhaustors or as pumps (see Transactions A.S.M.E., vol. 24, paper by J. T. Wilkin; vol. 28, paper by Gregory). The centrifugal blowers are of two varieties, the volume blower, used COMPRESSED AIR 515 exclusively for low pressures and large volumes, up to say 15 or 20 in. of water, and the so-called high-pressure blower or cupola blower, which delivers a smaller volume at pressures not exceeding 2 or 3 lb. per square inch. Centrifugal compressors of the " turbo" variety with many stages, Fig. 263, may be built for use up to a pressure of about 150 lb. per square inch. Turbo-blowers and compressors are similar machines, differing only in the delivery pres- sures and the number of stages and delivery volume. They are usually built on the prin- ciple of the centrifugal pump, that is, the fluid to be compressed is conducted in radial paths, the only design departing from this arrangement is the Parsons, where the flow direction is axial. Turbo-blowers for blast- furnace work will deliver from 17,000 cu. ft. per minute to 60,000 per minute. Bessemer blowers deliver up to about 30,000 cu. ft. per minute. Turbo-compressors have in general a much lower capacity, not usually exceeding 20,000 cu. ft. a minute at from 75 to 135 lb. gage. Larger turbo-com- pressors have been built, up to a capacity of 50,000 cu. ft. per minute. Steam-turbine drive is usually used where great capacity fluctuations obtain, whereas with constant capacity the high-speed electric motor is most used. With smaller outfits the steam turbine is almost invariably found, as with this drive higher speeds may be obtained Inlet Fig. 262.— Connersville blower or pump. Fig. 263. — Rotary air compressor, turbine driven. and the number of stages kept down. The number of stages varies between one for very low-pressure machines to 28 for the higher pressures. Up to 14 stages compressors are usually built on one shaft and in one casing. With a higher number of stages two casings are used. All of these machines are very carefully water-cooled, but the cooling does not appear to be as efficient in the lower stages as in 516 ENGINEERING OF POWER PLANTS the upper ones. For high-pressure work this is a disadvantage for the turbo-compressor. However, the cooling in the upper stages is so good that the discharge temperature of the air, when working at 115-lb. pressure can be brought down to about 165°F. with water at the ordinary temperatures. A 1,000-hp. compressor, under these conditions, will use about 1,600 cu. ft. of water per hour for cooling. The minimum size of compressors, up to 100 lb., is in the neighborhood of 2,500 cu. ft. per minute, while for blowers at 20 lb., the minimum may be taken at 5,000 cu. ft. per minute. The speeds of .revolution run from 5,000 to 6,000 in the smaller sizes down to 3,000 in the larger sizes of machines. The construction of the impellers is usually of radial buckets riveted between two nickel-steel disks, although cast wheels have also been used. Pressures up to 90 lb. have frequently been obtained in as low as 12 stages, but the buckets in this case were not radial. (See paper by Richard S. Rice, Transactions A.S.M.E., vol. 33, p. 381, for discussion of the turbine blower with efficiencies and costs.) t^^^^^^^^^^^^mi Fig. 264. — Section of turbine air Fig. 265. — Section of three-stage turbine air compressor showing water-cooling compressor, arrangement. In the hydraulic air compressor, see Fig. 266, a descending column of water is allowed to draw into itself a certain amount of air. At the lowest point of the apparatus a sudden enlargement of section and change of direction slows down the water velocity to such an extent that the entrained air is set free and is collected in a pocket. This air, which is compressed to the pressure due to the head of water at this point, is piped to the surface for distribution and use. Such a plant is installed near Greenville, Conn., on the Quinnebaug River and has been quite successful. The efficiency of the apparatus is very high, but it is large and costly and can only be used in very advantageous locations. For an COMPRESSED AIR 517 account of the Greenville plant see Webber's paper, A.S.M.E., vol. 22, page 599. Frizell's paper in the Journal of the Franklin Institute, 1880, also contains a test on a plant of this kind, but a full discussion of the subject is in Parker, "The Control of Water." Compressed-air motors are usually of the type of the steam engine but for small powers a rotary machine of the impulse turbine type has been used. Pulsometer, Emerson and other fluid pressure pumps are worked occasionally by air, especially where there is danger of flooding and occasionally it is convenient to use air in the ordinary duplex pump. Fig. 266. — Hydraulic air compressor. Economy in the use of air can be secured by preheating either by steam or outside heat or by a gas flame in the air current. Where pre- heating is used it may be possible to get more power out of the air than the work of compression and the higher the pressure and degree of pre- heating the larger is the saving. Where a compound motor is used as in some of the mine hoists both preheating and reheating may be practised with consequent economy. In the Porter compound mining locomotive the air is preheated, used in the high-pressure cylinder and expanded to a low temperature, possibly — 30°. It is reheated by the heat of the atmos- phere blown through the reheater and then used in the low-pressure cylinder. Air-lift Pump. — The air-lift pump, Fig. 267, is the reverse of the hydraulic air compressor and finds a wide application in pumping deep wells. Compressed air is led through a small pipe to the bottom of the casing and the difference in weight between the water outside the casing and the mixture of air and water inside starts the well flowing. (See A.S.M.E. Transactions, vol. 31, page 311 and Parker, "The Control of Water.") 518 ENGINEERING OF POWER PLANTS The mechanical efficiency of first-class air compressors, driven by first-class steam or gas engines, is about 85 per cent. ; ordinary machines will run below this. The mechanical efficiency of turbo-blowers and compressors will usually run around 90 per cent. The overall efficiency in the best machines will run from 70 per cent, downward. Urn ^ \ A \ \ Air 1 f 7 I W// r i (B) Fig. 267.— Air lifts. Fig. 268. — Belt-driven duplex compressor. Volumetric Efficiency. — The actual capacity of compressor cylinders is not equal to the apparent capacity, due to the effect of clearance, heat- ing of the intake air and imperfect valve action. There have been very few tests made to show measured volumetric efficiencies, but where they have been made, as in the case of the Rand mines these efficiencies were shown to be around 60 per cent. Standard machines should give from COMPRESSED AIR 519 85 to 95 per cent, volumetric efficiency under ordinary conditions. It frequently happens that the air ducts bringing the outside air to the intake valves of the compressors are so designed that a considerable rise of temperature takes place within them, together with a loss of pressure. Such arrangements have often resulted in the reduction of volumetric efficiency by as much as 15 to 20 per cent. Oil. — A number of explosions have taken place in air storage tanks and compressing cylinders due to the vaporization of the lubricating oil used in the air cylinders, hence the greatest care should be taken in the choice of the lubricant, and only the necessary quantity should be used. Some compressors have been lubricated with colloid graphite, and water lubrication has been used with success. Turbo-compressors need no lubrication and will probably be more largely used on this account. Fig. 269. — Tandem compound steam and two-stage air compressor straight-line type. The transmission of power by compressed air has been quite attract- ive in the past, especially where power for compression was cheap and abundant, and although displaced by electric transmission for many purposes, has still a large field for use. As the first extensive experiments were made at Seraing in connection with the mines, so in mining operations compressed-air transmission finds its greatest development today. It is also used for operating cranes and other machines where power is used only at intervals, as the condensation of steam, when used directly, is excessive and^ hydraulic power is liable to give trouble from freez- ing. The first large system installed for actual commercial work was at Paris, where Popp in 1881 built the St. Fargeau station (2,000 hp.) and later the station at the Quai de la Gare (10,000 hp.). The system had 34 miles of air mains, including 4J^ miles of 20-in. main. The losses at the farthest ends of these mains rarely exceed 8 lb. per square inch and the pressure carried was 90 lb. The system was well patronized on account of its convenience for delivering small powers, or in places where 520 ENGINEERING OF POWER PLANTS the cold exhaust could be used for refrigeration. The trouble from freez- ing was avoided by passing the air through a coil of pipe heated externally by a charcoal fire. A number of motors of a size exceeding 100 hp. were installed. At this plant it was reported that the cost of compressing 33 lb. of air to a pressure of 90 lb. per square inch was a trifle less than 1 ct. It is the convenience and safety of the transmission and storage of energy by compressed air which has made it so important and widespread a feature of modern engineering. The convenient return of the exhaust to the atmosphere is in many places an advantage, as in underground or submarine work, and the harmlessness of the air in case of accident, break- age or leakage, is often a valid reason for the use of air engines. Many of the collieries and mineral mines in this country and abroad have compressed-air transmissions approaching in size the Paris installa- Fig. 270. — Cross-compound horizontal-vertical ammonia compressor. tion. A coal mine producing 3,000 tons per day will use about 2,000 hp. in compressors and may have from 3 to 10 miles of mains depending on the size and depth of the workings. Some of the copper mines in the upper Michigan peninsula have large compressed-air transmissions, 20-in. pipe being used in a number of cases. Compressed-air System at Butte and Anaconda. — The Anaconda Copper Mining Co. operates 22 shafts at Butte. In 1912 they com- menced using compressed air for hoisting and installed a compressor plant electrically driven. Each compressor has a capacity of 7,500 cu. ft. (465 lb.) of free air (12 lb. abs.) compressed to 90 lb. gage and is run by a 1,200-hp. 2,200-volt synchronous motor. There are eight com- pressors in all. The system furnishes air for about 40,000 hp. of hoists, the diversity and load factors being low. Seven of these compressors are COMPRESSED AIR 521 run continuously the eighth being held in reserve, the excess air being used in the drills. About 13,500 hp. of motors are in use driving smaller compressors in the various mines for furnishing air for drilling and blowing Fig. 271. — Cross-compound air compressor. out the workings. There is a hydrostatic storage plant for the hoisting service of 66,000 cu. ft. capacity and the air is distributed by something over 3 miles of mains with a pressure drop of about 3 lb. Storage reser- Fig. 272. — Nordberg two-stage motor-driven air compressor, Anaconda Copper Min- ing Co., 7500 cu. ft. free air per mine. voirs of about 8,400 cu. ft. capacity are installed at each of the large hoists to prevent excessive loss of pressure in the lines. After various electric systems had been considered the compressed-air system was installed for the following reasons: 522 ENGINEERING OF POWER PLANTS 1. Total cost was lower, due to the fact that the existing steam hoists could be readily changed over at small expense for air working. Fig. 273. — Nordberg duplex-geared air hoisting engine, Mond Nickel Co. 2. Large power storage capacity could be cheaply provided to over- come excessive inrush in starting. Fig. 274. — Straight line air compressor, Meyer cut off. 3. Synchronous motors could be used in the compressing plant main- taining the power factor and load factor at 100 per cent. 4. Excess air could be used with great advantage in the drill system. COMPRESSED AIR 523 5. A steam drying plant in existence at each mine rendered reheating cheap and easy and largely increased the efficiency. It was found by test that from 1.4 to 1.5 kw. were used per indicated horsepower in the hoist. See papers by Nordberg, Gillie and Hebgen, Transactions A.I.M.E., vol. 46. See also paper by Pauly, Transactions A.I.M.E., vol. 42. The most modern and also the largest installation of this kind is the plant of the Rand Mines Power Supply Co., Ltd., in South Africa, which was installed in 1909-1 1 . The compressor station is located at the Robin- son Central Deep, where 12 motor-driven compressors of the centrifugal type are installed, and in addition four turbo-compressors are installed at Rosherville, 5 miles away. Twenty-seven and one-half miles of main Fig. 275. — Tandem duplex compressor. piping 27J^ to 9 in. in diameter served to distribute the air to the 13 cus- tomers whose own mains extend throughout their underground workings. The larger compressors are driven by a 7,000-kw. motor and deliver 2,900 lb. of air per minute at 100 lb. gage. The smaller compressors are half this size. The pipe lines have a capacity of 310,000 cu. ft. and 46,000 lb. of air are thus stored in the lines between the pressures of 90 and 120 lb. (the allowable variation). The yearly output in 1914 was 2,826,500,000 lb. of air at 34 per cent, load factor, with a maximum demand of 15,800 lb. per minute. The air is used for operating small hoists, ore pocket gates, etc., for blowing out the working places after blasting and for oper- ating rock drills, the last being the principle use. Both the fixed- and loose-hammer percussive-type rock drill is used, the rock being too hard for rotary drill. All air is sold on meter readings, the Rand Co. supplying 524 ENGINEERING OF POWER PLANTS Venturi meters and the mining corporations swinging gate meters, the mean of the two readings being taken. The air unit is a purely com- mercial unit and was fixed by local considerations at 27.441 lb. of air at 100 lb. gage pressure, corresponding to 0.641 kw.-hr. See paper by A. E. Hadley, I.E.E., 1913, and paper of J. H. Rider, I.E.E., 1915; also Klingenberg, Ban. Groz. Elek. Storage of compressed air in small bulk and with little weight in strong tanks led to its use for street car service as early as 1878, and a number of street car systems were installed. In all cases these systems proved to be cheaper and better than the horsecar system which they dis- placed. The system usually used the air at about 300 lb. per square inch. A number of reservoirs consisting of Mannesmann bottles about 9 in. in diameter and 6 ft. long located under the seats, held the supply air at a much higher pressure, usually around 2,500 lb. per square inch. Most of the systems included a tank of superheated water, through which the air was passed on its way to the motors. The system was, however, too costly to compete with the electric trolley system and has been almost entirely abandoned in the various localities where it was installed. CHAPTER XXV REFRIGERATING MACHINERY The use of so-called freezing mixtures for the abstraction of heat has been known for many years and is still used for domestic purposes and for a few other applications. Mechanical refrigeration had been in use for about 100 years when the first machine using ether was invented. Since that time air, water vapor, sulphur dioxide, ammonia, carbon diox- ide and other fluids have been used as refrigerating mediums, but today only air, carbon dioxide and ammonia are of practical importance. The two chief uses of refrigeration are for cold storage and transportation and the making of artificial ice. We may classify modern refrigerating machinery as dense-air, com- pression machines using carbon dioxide or ammonia and ammonia ab- sorption machines. The dense-air machine, used to quite an extent in BriaeTank t£X Expansion Valve I Condenser Uf 7T H Brine Tank mu Power Cylinder mpressor JJ Expansion Cylinder jCJoo ZA- Power Cylinder mpressor -Uondenser- Cooling Water AMMONIA OR CARBON DIOXIDE COMPRESSION SYSTEM Cooling Water DENSE AIR SYSTEM Fig. 276. marine practice, consists of a compressing cylinder, in which the air is compressed to about 225 lb., a water cooler which cools the compressed air, an expansion cylinder in which the compressed air is expanded to about 65 lb. and the refrigerating coils, where the expanded and cooled air absorbs the heat. This is known as the dense-air system and appa- ratus of economical size may be employed due to the high pressures used. This system is largely used for ice making and ice-box cooling on ship- board because of its safety (no dangerous fumes in case of leakage in confined spaces) but it is not efficient. In the compression systems using CO2 and NH 3 the gas is compressed to such pressure that when cooled in the condenser by the cooling water it will liquefy. The liquid is then expanded through a valve into the refrigerating coils where it absorbs sufficient heat to evaporate the liquid 525 526 ENGINEERING OF POWER PLANTS and the gas is then led to the suction side of the compressor to again begin the cycle. These machines are much more efficient than the dense-air machine and with CO2 pressures as high as 900 lb. must be used. They are largely employed in marine practice especially in the frozen-meat trade. An additional reason for their use is the fact that they can be applied to the extinguishing of cargo or bunker fires. The ammonia compression machine is used on land to a much greater extent than the others and more economical results are obtained than with the CO2 or dense-air systems. The ammonia used is anhydrous and the only serious troubles Brine Tank <£ I) Cooling Water Inlet r^\ Absorber U[V] Expansion Valve v^y Pump 1 ^ >l V ^ (£ 2) ^ Condenser Interchanger- Rectifier s Separator Jl Cooling Water Outlet Analyzer- Steam Coils w Generator Fig. 277. — Absorption system. come from leakage of ammonia into the air and water into the ammonia. A tight system will avoid these troubles. In the ammonia-absorption system a solution of NH 3 in water is used. The strong NH 3 solution is heated by steam coils in the generator, and the NH 3 driven off at a pressure of about 150 lb. The gas passes through the analyzer and rectifier and then to the condenser where the ammonia is liquefied by the cold-water circulation. The liquefied ammonia is ex- panded through the cooling coils to the absorber in which the evaporated ammonia is absorbed by water thus keeping a low pressure in the coils. The liquor is then pumped to the generator to go through the C3^cle again. This system is not efficient in small units and is better adapted to re- frigerating than to ice making. Many of the large systems in abattoirs, REFRIGERATING MACHINERY 527 cold-storage plants and central stations for refrigeration are of this type. The efficiency of the ammonia absorption and compression systems are practically equal under commercial conditions. In the direct-expansion system the refrigerating fluid is circulated in the cold room in pipes but when air is the medium the room becomes part of the system. This system is comparatively little used on account of the regulation troubles, presence of moisture and difficulties of leakage when CO2 or NH 3 is the medium. The more usual and better system is the brine circulation system in which the expansion coils are submerged in a brine tank, the cold brine (a solution of salt or calcium chloride) being circulated by a pump through coils in the cold room. The unit of refrigeration is the "ton of ice melting per 24 hr." The latent heat of ice is approximately 144 B.t.u. so the ton of refrigeration = 288,000 B.t.u. per 24 hr. or 200 B.t.u. per minute. The ice-making capacity is somewhat less than half this figure. In a refrigerating system the lower temperature is fixed by the room temperature required for refrigeration and the upper temperature is fixed by the amount and temperature of the circulating water. The pressures are fixed when these temperatures and the medium are known. In the American Society of Mechanical Engineers' rating the tempera- tures are taken as 0° and 90°F. and the economy is taken as the ice-melt- ing effect per pound of coal or per indicated horsepower. The usual piston displacements in the compressor per ton of rated capacity vary between 3.5 and 5 cu. ft. per minute and the power required varies from 1 to 2.5 i.hp. per ton of refrigeration. Good average efficiencies are about 25 lb. of ice-melting effect per pound of coal with either compression or absorption system. The dense- air machine is not nearly as efficient say 3 to 8 lb. of ice-melting effect per pound of coal. About twice the theoretical amount of cooling water is required for good work. Practical figures lie between 1 and 3 gal. per minute per ton of capacity. Ice Making. — Artificial ice, one of the important applications of refrigeration, may be made either by the plate system or can system. In the plate system a series of compartments from 12 to 16 in. wide, 4 to 6 ft. deep and 10 to 20 ft. long, are constructed from cast iron or steel plates behind which the brine circulates. A movable brine circulating coil is sometimes used in the center of the compartment to cool the water to the freezing temperature. After the freezing has begun this coil is swung out of the way. On the completion of the freezing process which may take from 30 hr. to a week warmer brine is pumped through the passages loosening the plate ice and the plate is lifted by a crane and sawed into blocks of suitable size for marketing. 528 ENGINEERING OF POWER PLANTS In the can process steel cans holding from 100 to 600 lb. of water are suspended in the cold brine tank. The freezing takes from 2 to 24 hr. and the tanks are emptied and handled by similar machinery to that employed in the plate system. Clear ice is obtained in both systems by a process of agitation. There is a third system in which a revolving cylinder, in which the brine circulates, dips in the water tank and becomes covered with ice crystals. These are scrapped off and pumped with some water into a hydraulic press which converts the slush into a cake of ice by squeezing out the water. It is difficult to obtain clear ice in this process. Cold Storage. — The brine-circulation system requires about 50 to 100 per cent, more surface in the pipe coils than the direct-expansion system. For freezing fish and meat the surface may be 100 per cent, larger still. The following table of lineal feet of 1-in. pipe required per cubic foot of cold storage space has been adapted from Siebel. Size of room in Room temperature, F°. Direct-expansion system cubic feet 0° 10° 20° 30° 40° 50° 100 1,000 10,000 30,000 100,000 Average Insulation 4.0 1.25 0.8 0.6 0.4 2.0 0.3 0.2 0.15 0.12 0.5 0.2 0.14 0.1 0.07 0.4 0.15 0.1 0.07 0.05 0.3 0.1 0.07 0.04 0.03 0.2 0.07 0.04 0.03 0.02 For brine circulation multiply by 1.75. For lj^-in. pipe multiply by 0.8. For lj^-in. pipe multiply by 0.65. For 2-in. pipe multiply by 0.55. Number of cubic feet per ton of refrigerating capacity per 24 hr. Direct expansion. For brine circulation multiply by 0.57. Size room 0° 10° 20° 30° 40° 50° 100 120 500 650 800 1,300 2,500 1,000 400 2,000 2,500 3,200 5,000 11,000 10,000 600 2,500 3,200 5,000 8,500 16,000 30,000 800 4,000 5,000 7,000 12,000 23,000 100,000 1,200 6,000 8,000 12,000 18,000 35,000 PROBLEMS 87. The poultry, vegetable, meat and wine rooms on a passenger steamer occupy a space approximating 7,000 cu. ft. The dense-air system with brine circulation is REFRIGERATING MACHINERY 529 used. Assuming that a temperature of 30° is maintained, what will be the amount of 1-in. pipe coil required, the rating of the dense-air machine and the horsepower required ? 88. A cold storage company has a building 80 ft. wide, 100 ft. deep and four stories high. Assume one floor for machinery and 10 per cent, of the other floors for elevators and stairs, ceilings 10 ft. high, and a general business requiring an average temperature of 40° in the rooms, brine circulation system. Find the length of pipe coils, rating of the machine, horsepower required and amount of cooling water per day assuming a rise of 30°. Assuming an ammonia-compression system, find the size of compressor if the piston speed is 300 ft. per minute. Estimate the coal used per day. 34 CHAPTER XXVI HYDRAULIC POWER Although the generation of power by heat engines is a development of the last 200 years, hydraulic and air-power have been known and used for a much longer period and their beginnings go back at least to the Christian era. Air-power is of small relative importance, but hydraulic- power, water-power, in favored localities is of great importance and must always be considered by the power engineer. BREAST WHEEL UNDERSHOT WHEEL Fig. 278. The potential energy of water may be measured by its weight (IF) — the force available — multiplied by the available fall (h) — the space through which the force is to be exerted — or E = IT'/?. The theoretical power (horsepower) of water in motion is given by the formula hp. = WV 2 where T T is the velocity in feet per second, IT is the weight of 550 X 2g water per second and g the acceleration due to gravity Qh For an efficiency of 80 per cent, this formula reduces to yr = hp. where Q = cubic feet 530 HYDRAULIC POWER 531 per second, h = head in feet, which may be easily remembered for rough calculations. The earliest waterwheels were " current" wheels." These were large wheels, Fig. 278, with paddles which dipped in the stream and were turned by the velocity of the current. They were mainly used for raising water for irrigation purposes or for driving an archimedean screw. The efficiency was very low, 3 to 5 per cent. A few modern current wheels have been built and a little higher efficiencies have been secured. All current wheels depend on the natural velocity of the stream and an early improvement led the water through an artificial channel or flume where a greater velocity could be secured and the wheel was made with ^Nozzle Fig. 279.— Flash wheel. small clearance at the bottom and sides so that practically the whole of the water was made available to drive the wheel. This improved wheel was known as the " undershot" wheel, Fig. 278, and efficiencies from 25 to 40 per cent, were obtained. Later the bottom of the flume was built up with very small clearances to the height of the center of the wheel making the modification known as the breast wheel, Fig. 278, with efficiencies as high as 50 or 55 per cent. All of these wheels had straight buckets or paddles. Poncelet improved the breast wheel by curving the paddles and making them deeper and by utilizing the breast as a dam and allowing the water to spurt out near the lowest portion of the wheel increasing the efficiency to 60 to 65 per cent. 532 ENGINEERING OF POWER PLANTS Many wheels of this type were built in the eastern United States for sawmill work using heads up to 18 to 20 ft. The wheel was usually a built-up wooden wheel with flat buckets about 2 in. deep in a radial direc- tion by sufficient width to give the power required. A rectangular penstock brought the water to the wheel level where the wooden breast and bottom of the penstock formed the nozzle. These wheels were termed " flash wheels/' Fig. 279, in the Catskills but were known by other Fig. 280. — Boyden-Fourneyron turbine, Tremont mills. names in other parts of the country. No good tests of these wheels are extant but fully 50 to 60 per cent, efficiency must have been secured in the better class of wheels. The " overshot" wheel, Fig. 278, came into use soon after the under- shot wheel especially for slower moving mechanisms such as hammers and bellows for the early blast furnaces. The wheel was built with buckets capable of holding the water which were filled from the flume HYDRAULIC POWER 533 when they were at the top of their travel. The weight of the water turned the wheel and efficiencies exceeding 85 per cent, were often reached. Very large wheels of this type have been built, some of them exceeding 60 ft. in diameter. One of the most famous in America was the "big" Fig. 281.— 14000 H.P. Pelton-Doble water-wheel unit. wheel of the Burden Iron Works at Troy, N. Y., which was 20 ft. wide, 60 ft. in diameter and produced 278 hp. at 85 per cent, efficiency (see Proceedings A.S.C.E., vol. 79, p. 708). Fig. 282. — "Free deviation" or Girard turbine. The turbine was invented in France and was introduced into the United States by Elwood Morris of Pennsylvania in 1843, but its develop- ment here was largely due to Uriah A. Boy den, who in 1844 designed a 75-hp. wheel for use at Lowell, Mass. (Fig. 280). This was an outward 534 ENGINEERING OF POWER PLANTS flow wheel but in 1849 J. B. Francis designed for the Boott Cotton Mills at Lowell the inward-flow Francis turbine, now the standard wheel for low-head work both in this country and Europe. These wheels of modern construction give a maximum efficiency of over 90 per cent. The flash wheel is the probable predecessor of the impulse wheel which came in use shortly after 1870. The impulse wheel is a high-head type and the water is jetted from a nozzle into buckets on the periphery of the wheel (Fig. 281). These wheels are generally known as the Pelton type although the Pelton patent of 1880 was antedated 5 years by the Atkins patent which was not utilized. These wheels give an efficiency of 80 to 85 per cent. A European type of impulse turbine which has been used to a considerable extent is the Girard, also known as a free deviation turbine (Fig. 282). The water is led inside the ring of buckets and jetted outward. High efficiencies have been obtained. Water turbines may be classified as impulse or reaction turbines with more justice than steam turbines, but the terms, partial intake or full intake, better describe the classification. They may also be classified as to the direction of water flow as axial or radial flow, and inward or outward flow, but practically all modern turbines fall into two classes, the inward-flow central discharge turbine, known generally as the Francis turbine, and the class in which a free jet impinges on an open bucket generally known as the tangential or Pelton type. With the current wheel no serious constructions were required as the wheel was supported by floats or cribs in the moving current of the stream, but with the better types of machinery flumes and masonry supports had to be constructed, dams became necessary to artificially increase the available head and to store water to secure a uniform flow. The study of the variation of stream flow became a necessity and rainfall and run-off records were kept and compared. These records are now made and published by the Government in the Water Supply Reports for the run-off of streams and by the Weather Bureau for rainfall. To secure stream flow or run-off records the stream must be rated and a gage maintained and read at least once each day usually at 8.00 a.m. A cross-section of the stream is chosen where the river is straight for a considerable distance on both sides and where the bottom and sides are rock or hard gravel or hard clay not liable to change during floods or low water. This cross-section is accurately surveyed and a gage is established with its zero at the lowest low-water level on record. Next the velocity of flow of the stream is obtained at as many gage readings as possible. This is usually done by means of a current meter (Fig. 283). The cross-section is divided into many small areas and a velocity reading is obtained at the center of gravity of each area. These readings are averaged for the mean velocity and the discharge is calculated HYDRAULIC POWER 535 in cubic feet per second for that gage reading. Where a current meter is not available floats or rods weighted to float in an upright position may be used; the velocities being obtained by timing the floats in passing a given distance downstream. After the discharges have been obtained for a number of gage heights a rating curve may be plotted connecting each gage height of the stream with a discharge. When the daily dis- charges are plotted a curve known as a hydrograph is obtained in which all the variation of the flow of the stream is shown graphically. The daily discharge is always given in cubic feet per second or cusecs. The aver- Lead Weight Fig. 283. — Current meter. age yearly and monthly discharges are also given as inches of water on the watershed or catchment area in order that they may be compared with the rainfall. Maximum and minimum discharges are also noted and stated in cubic feet per second and also in second-feet per square mile of catchment area. There have been a great many attempts to connect rainfall with run- off so that in the absence of long term gaging records nearly correct figures for a given watershed might be obtained from the rainfall records which usually cover a much longer period. There are a number of papers and much discussion of this subject in the Transactions of the A.S.C.E., 536 ENGINEERING OF POWER PLANTS 1913-14 and 1915, but this method should be used with discretion and only when gagings are not available. It should be remembered that while the water flowing in the streams is due to rainfall, some portion of this is evaporated, much is absorbed by vegetation at certain periods of the year, and a considerable fraction may be stored in the earth for long periods. Many experiments have been made to ascertain these quantities under certain conditions and details may be found in Rafter, "Hydrology of New York;" Mead, " Hydrology;" and the Transactions of the A.S.C.E. Having the gagings of a stream for a number of years the mean monthly flows can be calculated and a curve plotted showing the summation of these flows. This curve is called a mass curve and examples are shown in Figs. 284 and 285. A straight line passing through the origin and tangent 1905 1906 1907 1908 1909 1910 1911 Fig. 284. to the lowest portion of the curve will give the largest average flow to be obtained from the stream and the necessary storage can easily be calcu- lated. It usually will not pay to provide this amount of storage but a discussion of the mass curve and a survey of the available locations for storage reservoirs and dams will soon show the economical size of storage and the economical mean flow to be provided for. The longer the set of gagings the better will be the work especially if they include a minimum year. It is interesting to plot the variations of the yearly rainfall for the available years as a curve in conjunction with the hydrographs. A study of these curves for any watershed will well repay the trouble. It is, however, important that a sufficient number of well-located rainfall stations be present on the watershed or the curves will be misleading. The creation of a large storage reservoir is usually a costly operation both as to dam and land damages. The following table of the cost of A. 800-jt-jt r ::::::::::::::::_l;tz" '_^^ «■£-■* 7K0 ^2 ' 7 * * ? , 7flft 4^ ^ ,' / -fe-Lobij-r- / 7 / S sS^^.S^^*^ I 1 . 7 > / yS ^ ^A^ !> /y^^^^^^^^^v , ■ / / ' /^/\/^^ \„Q 1 r j ::£::::::::::::::: _f.- : -"-ql4lO-- H - _ X^^ I rnn v 7 j "=>"«» ^g;^ " |10 uuu ^ J / 'f0s$^z /' , ' = — —J o / f RATE VECTOR. LOCKAGES PER 24-HOURS 1 / / IMK10 if .4-fJ~~ \\\X\\ -fc--^^frli>)9-M" Inches, Land Area Feet, Gatun Area GRAPHICAL SCALE 1,624 Inches Storage on oter-shed Equivalent to 67 Feet Storage on Lake Gatun at Elevation-}-, 87) i ' y ' ' ,.-• ->1 1 1 %£' L^^'-l III 1 . j&s ,<--'' m | | | I I | mjJjaso <$- A"----^\ J - 8 ~>» —- ^5 I X w OF LEAST YIELD 3HED FOR 1901-11 >l THAT WOULD I0US RATES .'■tiyJa j- - -J®/* **' ' ,4 ' IKS! /'■-'^•°" ^'ttl Mill ~ ' rr-fp\ rf <*■ is' • II If ; ■ 1 M J J A SO ! j ] \/ t_Y\ t*-, 1 _!!2i£SS SHOWING MAXIMUM DEPLETIO -S200-"- H '^ HAVE OCCURRED WITH VAR % — i i 1 1 ^ | 1 tfuX " n} jab 3 -- *Ml _ /'[ W i ] ■ T J9M— -s- "2 i .- Y'" it 180 :: 1 TfTr -„_ w iii>£. 1 -- T ? MT"" 1 M3-4j- s •?, -,; ■S oas IasoWd jIf mJaUjIjI K6oUlo|jWt>IAM J iiSOl Time Monthg Fig. 285. (Facing page 536) HYDRAULIC POWER 537 large storage reservoirs has been compiled from various authorities and shows the extreme variations of cost. Compare the differences of the cost of the Ashokan and Croton reservoirs on small streams with the cost of the Assuan storage on the Nile. Cost of Storage Reservoirs Location Storage, billions of cubic feet Assuan, Egypt (new) Assuan, Egypt (old) Ashokan, N. Y Christiana & Harts River, Transvaal Belle Fourche, S. D Wachusett, Mass Aziscohas, Maine New Croton, N. Y Chattanooga, Tenn. (approx.) Buena Vista, Cal Laramie River, Wy Indian River, N. Y Croton, N. Y Lake MacMillan, Pecos, N. M Bear Valley, Cal Cost per billion, cubic feet $238,000 343,000 792,000 1,560,000 94,000 269,000 125,000 973,000 533,000 21,000 23,000 19,000 972,000 47,000 39,000 Dams may be classed as : 1. Earth. 2. Earth with core wall. 3. Hydraulic-filled earth. 4. Timber. 5. Masonry. 6. Concrete and cyclopean masonry. 7. Hollow, Ambursen or reinforced concrete. 8. Steel with or without rock fill. 9. Moveable or Bear trap (barages). The earth dam is a simple bank of earth. The top soil is usually cleared away to good firm soil and then the dam is built in thin horizontal layers well watered and compacted by rollers as the work progresses. The upstream slope is usually 4 or 5 to 1 and protected by riprap or pitched with cobble or flagstones. The downstream slope is 2 or 3 to 1 and is sodded. These dams should not be built over 8 to 10 ft. in height if they are expected to be tight and the width of the horizontal top should be equal to the height. Ample spillways of masonry or solid timber should be provided. In some localities such as irrigation work in India these dams have been built much higher and the percolation through the dam has been regulated with good success. 538 ENGINEERING OF POWER PLANTS Earth dams for higher heads should be constructed with core walls to prevent seepage and percolation which would eventually lead to the destruction of the dam. The core wall may be of puddled clay, timber sheet piling, stone, concrete, or steel. The core should start a sufficient distance below the foundation of the dam to prevent dangerous seepage. The core must be thick enough to be impervious and should be carried up nearly to the crest of the dam and above the spillway level. Many experiments have been made to determine the line of ground water in an earth dam but this seems to depend on the nature of the materials, which should be thoroughly investigated before construction and all improper earth thrown away. At Gatun, Panama, the 30-mile lake of the Panama Canal is held back by the Gatun dam, a hydraulic-filled dam with rock toes and riprap facings. The toes were first placed of heavy rock and then soft mud and sand pumped in to fill the interior as the riprap slopes were carried up. This dam is 120 ft. high and about a mile wide. It sustains a head of water exceeding 80 ft. The Necaxa dam of the Mexican Light and Power Co. is of this type and is 190 ft. high, the highest earth dam in the world. It has a puddled clay core, riprap slopes and a hydraulic fill. Timber dams are built by sinking square cribs of timber which are filled with riprap to hold them in place. On these cribs the covering planks are laid. Another good way on a small stream is to drive a line of wooden sheet piling across the stream. To the sheet piling is spiked a 12- by 12-in. mudsill as low down as possible on the upstream side. Cribs of round poles are placed downstream of the sheet piling supporting the wales and the cover planks are spiked to both mudsill and wales. The dam soon silts up on the upstream side and remains tight as long as the silt is there. The whole length of the dam is usually the spillway in which case an apron of planking is necessary on the downstream side to take the impact of the spill water and prevent undercutting. Masonry dams built of brick or cut stone are of all sections, the plain rectangular wall with a capstone sloping downward upstream being very common for low heads. The best form for a masonry dam is dependent on the kind and weight of the masonry and whether it is also to be used for a spillway. For this purpose the ogee form is the most frequently adopted as giving the maximum effect with the smallest cost and such dams are often submerged 10 to 15 ft. without danger. Masonry dams are rarely built except upon a rock foundation. Concrete may be used instead of masonry or the so-called cyclopean concrete in which very large stones often exceeding 10 tons are imbedded in the concrete. It is said to be important that these stones do not touch but at least one large dam was constructed by piling up the large stones in the forms and then grouting the pile thoroughly. This con- HYDRAULIC POWER 539 struction cannot be recommended. Small dams have been built of rein- forced concrete in sections similar to a retaining wall but for large con- structions and a solid dam steel reinforcing is not necessary. All masonry and concrete dams should go deep enough into the solid rock to prevent failure by shear or moving bodily downstream. In the dam at Austin, Texas, which failed by moving downstream, the toe was at the upstream end of the section and was only 24 in. wide. The dam at Austin, Pa., failed in the same manner. SbwJjS^^^^^^SSc Fig., 286. — Section of Estocada dam and power house, Portland Railway Light & Power Co., Ore. The hollow or Ambursen concrete dam is usually built "A" section in bays of proper width and the usual design of reinforced-concrete struc- tures is followed. The design has been criticised by some engineers who maintain that concrete under water is not sufficiently impervious to pre- serve steel from deterioration but the oldest Ambursen structures have shown no sign of deterioration up to date. In this type of dam the power house may be placed in the interior of the dam and remarkably economical construction results. Steel dams are of two types. The commoner consists of a set of " A' ' 540 ENGINEERING OF POWER PLANTS frames with buckle plates riveted to the upstream flanges. These plates may be protected from deterioration by a thin layer of concrete. The second type has been used in the rocky canyons of the Western States where a steel-plate core has been anchored in the side walls and bottom of the canyon and broken rock has been dumped on both sides of the plate to provide stability. In some cases the plate has been protected by a light concrete wall on both sides. The bear-trap or movable dam was developed during the canalization of the European rivers and has been extensively used by the United States Government engineers on the Ohio and its tributaries in the im- provement of navigation. During a flood the dam is lowered to the bot- tom of the river but as soon as the flood subsides the dam is raised and a pool sufficient for navigation is formed. The bear-trap dam consists of a number of units or palets about 24 in. wide and the height of the dam. These palets are hinged at their bottom ends to a heavy masonry construc- tion at the bottom of the river. At the point of center of pressure at the downstream side a strut is attached, which fits in a lock at the bottom of the river below the hinge and holds the palet in a nearly vertical position. In another type the strut is hinged at the downstream end and the con- nection of strut and palet is so placed that the unit when set up is stable until the water reaches a certain height when the palet is overbalanced and falls to the bottom. Other types have "A" frames supporting a platform and longitudinal girders on which square logs of wood are sup- ported. These are removed by the attendants in time of flood and re- placed afterward. Spillways. — Every dam should be provided with a spillway of suffi- cient capacity to take care of the maximum flood. Frequently the whole crest of the dam is used as a spillway as at Holyoke and Hales Bar and such dams must be made heavy to prevent overturning when the water is at its maximum height above the crest. Where the floods are of smaller moment a portion of the crest is made lower and walled in at the sides to act as a spillway as at the Delta and Hinckly dams, N. Y. The spillway is often placed at a distance from the main dam where rock is available and a first-class construction secured at less cost, as at Ashokan, N. Y. Where floods are severe and of very rapid rise it is common to provide a small spillway for normal use and to install gates of sufficient size in the dam itself to take care of the flood waters. Examples of this type of construction may be seen at Chevres on the Rhone, Switzerland, where large gates of the "Stoney" type are in use and at the Scotland Dam on the Shetucket, Conn., where gates of the "Taintor" variety are installed. It is usual to allow a rise of about 5 ft. over the crest of the spillway at maximum floods. During ordinary seasons the crest of the spillway is increased in height HYDRAULIC POWER 541 Iron Rod May be as by flashboards. The simplest construction consists of pieces of ordinary pipe 10 ft. apart imbedded about 1 ft. in the concrete crest of the dam. Into these pipes, pieces of round iron 1 in. to 1}4 in. in diameter and ex- tending in some cases 3 ft. above the crest, are inserted. On the upstream side of these rods pieces of 2 by 12-in. planking are laid on edge thus raising the crest 3 ft. (see Fig. 287) . The planks are held in place by the water. In case of a sudden flood topping the crest the iron rods bend over, allowing the planks and water to escape down the spillway. There are a num- ber of patented flashboard constructions but the commoner type is the best and cheapest. Hydraulic -station Layouts .• — Hydraulic- station layouts are almost always determined by the physical conditions of the case in question, since the local geological condi- tions usually determine the site of the dam and power house, the quantity of water and head available. At times there may be a choice of types, but this usually happens only when the head is on the dividing line between the Pelton and Francis types, or when the head is so low that a number of wheels must be used on one Fig. 287.— Flashboards. h— s'o' ^6 Drain Valre Fig. 288. — Section through penstock and power house, Uncas Power Co., Scotland, Conn. shaft. There always remains, however, the choice between horizontal and vertical shaft wheels. Where the stream regimen is fairly constant and the power house is a part of the dam itself three arrangements should receive careful considera- tion; the horizontal shaft wheel extending into the head race with the shaft parallel to the flow of the stream, and the draft tube to carry the 542 ENGINEERING OF POWER PLANTS Fig. 289. — Typical cross-section of power house, Coosa River, Lock 12 development. HYDRAULIC POWER 543 water away; the horizontal shaft wheel with the shaft at right angles to the flow of the stream, necessitating a penstock and with the draft tube as before. Both of these plans necessitate a power house below the dam, although the Ambursen type, with the power house inside the dam, may be used. Third, the vertical shaft wheel, either submerged or with a draft tube. Here the power house may be above the crest of the dam if desirable. In the first and third cases the penstock is an open one. In the second case the penstock is very short, sometimes only a foot or two longer than the wheel casing. Due to the short connection, there is no trouble from surges or water inertia. With higher heads, or where the power house is located at some distance from the dam, penstocks with or without canals or flumes, are necessary, and either the vertical or hori- Fig. 290. — Stoney gates, Manchester ship canal. zontal shaft wheel can be used. The two or three permissible arrange- ments are usually laid out and quick preliminary estimates are made to determine the best plan. Where plenty of water is available with low heads two or even three or four wheels may be used on one shaft, or a number of wheels may be geared to one shaft. Where there are two good ways of solving the problem it is sometimes advisable to secure proposals on both types of installation and use the most advantageous. Due regard should be given to the convenience of repair, which may well be in certain cases the deciding factor. There are certain plants in which it is necessary to draw down the pond 10 ft. or more in order to make repairs on one wheel. That plan is usually the best which puts the wheel above the tail water and provides a gate between the head race and the wheel. In good installations a turbine can be opened, examined 544 ENGINEERING OF POWER PLANTS and put back into service in less than an hour. This is not usually pos- sible with submerged wheels. Large headgates cannot be handled quickly and pumping a wheel pit is a slow and troublesome operation. Many installations must be built with wheel pits and submerged wheels. In such cases the headgates should be very carefully designed and, if large and heavy, cranes should be provided for their rapid and efficient handling. Up to a width of about 5 ft. and a head of 8 to 10 ft., the ordinary wooden stop logs make the best and cheapest headgate for concrete or stone constructions. Above these dimensions steel gates of the Stoney type with roller supports may be used (see Broome gate, Fig. 291), but the construction should be solid and in larger sizes should WW Gate Closed Gate Partly Opened Fig. 291. — Broome gate. be of the cellular construction used in lock gates. Where rollers are used, cast-iron roller races should be bolted to the concrete or stonework. The smaller sizes of gates are worked by the ordinary screw and winch handles. Many large installations are provided with the Taint or gates for use as headgates. These gates consist of a 30° to 60° section of the surface of a cylinder and are hung on a horizontal axis on the downstream side. They are sometimes as wide as 20 ft. and may be 8 or 10 ft. high, with leather or rubber washers on the sides and bottom of the gate to keep them watertight. They are handled with the ordinary screw control in the smaller sizes, or by a hoist for the larger sizes. At the admirable water-power installation at Chevres on the Rhone below Geneva these gates are used to close the wheel pits on the upstream side, and the HYDRAULIC POWER 545 sump pump is of such a size that it is possible to examine the three wheels on one shaft and get them back into service in less than 2 hr. Most rivers and lakes contain more or less floating trash, sticks, leaves, logs of wood, and, in the winter, ice. Suitable means must be provided to prevent this rubbish from entering the penstocks and wheels. Float- ing debris is usually controlled by a floating boom which directs this class of rubbish over the spillway. The rubbish which passes below the boom must be caught on a rack or screen. These racks are usually made of flat bars, set edgewise and properly spaced and stayed. They must be kept clean, which is usually done by means of a rake and cheap labor. Occasionally, as at Chevres, where the trash is troublesome and the rack is over 300 ft. long, a power rake electrically operated is used. This rake El.84.0 Normal Tailwater Corrugated Steel Bheet Piling- Fig. 292. — Tainter gates, Scotland dam. is on a car which travels the entire length of the screen, raking and deliver- ing into dump cars. The trash in this case has a fuel value and is dried and burned. In northern localities the same booms and screens are used to divert ice, and in some situations the raking must be continuous during the winter. At Rochester, on Brown's race, the raking for three 600-hp. wheels often requires three shifts of eight men for days at a time. In this race the ice forms on the bottom of the race as well as at the water surface, which makes the trouble very serious. "Anchor ice" is ice that forms on the bottom of passages or races. " Frazil ice" is fine needles of ice, which in certain localities form all through the body of the stream, and when caught in the wheel passages may freeze solid. Reserve. — When laying out a hydraulic power plant the question of reserve must be considered in connection with the expected load, the water 35 546 ENGINEERING OF POWER PLANTS available, and the diversity of water-supply peak and load peaks. As a general rule, one unit of the largest size should be installed as reserve. Where no water is available for reserve or where the minimum water does not coincide with the minimum peak, a heat-engine reserve or standby plant may be necessary. Many hydraulic installations require this heat-engine reserve, and where the variation in water supply is consider- able, the steam reserve may be nearly as large as the water power itself. At Utica the Trenton falls plant of 6,000 kw. has a steam auxiliary of 4,000 kw. and both plants will probably be increased in the future in about the same proportions. There are many cities whose lighting and traction supplies are generated by water power, which have steam auxil- iaries capable of carrying the full load, in case of breakdown or low water. The Rochester company, taking 10,000 kw. from Niagara Falls, keeps the same capacity in steam power with banked fires as a standby. Frequently water power has been sold for delivery only when water power is available. This is known as secondary power and of course brings a lower price. There are cases where tertiary power is also sold, which may be cut off by the hydraulic company at any time it sees fit. Water Storage Batteries. — It has often been proposed to pump the tail water back into the pond by cheap machinery, or in the time of low load, and to utilize it again at the peak. At the Rheinfall at Newhausen such a water storage is in use. Here a fall of about 60 ft. is available but owing to state re- strictions only a certain portion of the water may be used. The load curve is of the usual light power and traction type, with about 50 per cent, load factor. Two combination units have been installed, each consisting of a high-head centrifugal pump, a water turbine and an electrical unit capable of being used either as a motor or generator, all on the same shaft. The turbines in the main plant, at time of light load, furnish electrical energy which is used by the motor and centrifugal pump portion of the unit to pump water to a storage reservoir situated in the hills about 240 ft. above the station. When the peak comes on, the cycle is reversed, and the water in the reservoir is used in the turbine, driving the electric machine as a generator to supply the additional power. There are a number of these installations in Europe, and the idea seems to have originated with Sulzer Bros, who have Fig. 293. — Gelpke's standard types. Kaplan's types are similar. HYDRAULIC POWER 547 furnished the pumps and have charge of the installations; Escher, Wyss and Co. furnishing the turbine and Brown, Bouverie and Co. the electric apparatus. It has also been proposed to use the Humphrey pump to pump the tail water back into the pond, but no installations of this kind have been made. Design and Proportions of Turbines and Runners. — Gelpke in "Turbinien und Turbinienlangen" has given particulars of the design of •eight standard types of Francis wheels which are tabulated below with changes to suit American practice (see Fig. 293) . Type c Rev. at 1- ft. head X diam., mD. V D* P n = 0.8 Gelpke's max. value of rj Moody's best values of t\ (see curve) B D Diam. exit edge of vanes, D VIII 10.8 77 0.222 0.020 0.83 0.885 0.08 0.66 VII 13.1 80 0.302 0.027 0.84 0.89 0.10 0.67 VI 16.6 83 0.441 0.040 0.845 0.903 0.125 0.70 V 22.2 89 0.685 0.062 0.86 0.915 0.16 0.75 IV 29.4 96 1.03 0.094 0.87 0.918 0.20 0.86 III 40.6 107 1.58 0.144 0.87 0.918 0.25 0.97 II 54.5 121 2.23 0.203 0.83 0.91 0.30 1.10 I 70.4 138 2.87 0.260 0.77 0.87 0.35 1.23 As the speed n, horsepower, hp. and head H are known, C or the "unit speed," i.e., the speed which under 1-ft. head will develop one hp., 13 12 11 S3 O W 9 fa 8 -> ** 7 fc> 6 s. System. 80 90 100 i i i i i i i j .P. VIor •is ( 3o. / /W ellm an Seav er I (Lori 'an yo% — r • .Sa mso n T irbi nes 1 y ' 7 •"*"■"■> v. *"v . Swedish T arbi ties 1 V Gra if & D r ["hoi na N . X \ 80%J il "X V s \ N \ \ 7Ri ich( J^ BEST REPORTED TEST RESULTS CURVES BY PROF. MOODY TRANS. ASCE-VOL-LXV1 \ \ \ / Nae ■enb ach \ \ Allis-Chalmei s * > \ 70<7/i \ \ Pel ton Wheels Pra ncis i-T irbi nes \ < >\ jrirard \ Vhe ;ls 20 40 60 80 100 120 140 160 180 200 220 210 260 280 300 320 340 360 380 400 420 440 460 480 500 Specific Speeds (Metric System) R.P.M. Fig. 295. A wheel of this diameter at 300 r.p.m. and 50-ft. head will develop about P • 580 hp. at 80 per cent, efficiency. ™ = 0.203; multiplying this by D 2 and H H gives 583 hp. 107 X \/50 P Taking type III, mD is 107 and - Qnr T~ ' = 2.52 ft. diam. ^ 2 is 0.44. 144 X 2.52 2 X 50 3/i = 324 hp. This wheel is much too small. It will probably be possible to find a stock wheel which will more closely fit the conditions than type II. HYDRAULIC POWER 549 D. W. Mead has plotted the characteristic curves of the various makes of stock American wheels in his discussion of Larner's paper in vol. 66 of the Transactions of A.S.C.E. These curves are plotted with r.p.m. per minute under 1-ft. head as abscissae and hp. under 1-ft. head as 20 24 28 32 36 40 44 Discharge in Cubic Feet per Second under One Foot Head. ordinates. A modified reproduction of these curves is given in Fig. 296. If the efficiency is 80 per cent, the ordinates of these curves multiplied by 11 will give q, the quantity of water used at 1-ft. head and q at any other efficiency may be readily found. ft\/hp. If the "unit speed" C = m and the head H are known it will 550 ENGINEERING OF POWER PLANTS be possible to pick out innumerable combinations of power and speed depending on the size of the runner used. Values of C from 1 to 6 or 7 indicate the Pelton or tangential type; from 10 to 100 the Francis type. The values between 7 and 10 indicate the field of the outward radial-flow turbine of the Girard type often called "a free deviation turbine" and hardly known in America. _. _ . -'.ii *, peripheral speed of runner The coefficient of peripheral speed = is a very convenient runner characteristic indicating whether 0.00653£>tt Vh certain high or low values of C are due more to a high or low speed (large or small bucket angles) or to a high or low capacity. According to Zowski for low-speed runners C = 10 to 28, = 0.58 to 0.7. Thus from C = 28 to 60 would indicate medium-speed wheels with values of from 0.6 to 0.8. High-speed runners would have C > 60 with values of > 0.7. The square of C is called by Mead K$ = specific speed and by Parker, the type constant. In the Journal of Electric Power and Gas, May 25, Aug. 3 and Nov. 9, 1912, G. J. Henry, Jr., presents some interesting tables on both tangential (Pelton) and Francis wheels. He divides the Francis wheels into five types as in the following table: Types B C D E Unit speed C Peripheral speed R.p.m. at 1-ft. head. Q f full gate Efficiency \ % gate. [ y 2 gate. 80-68 82-79 32-155 2-50 + 0.72 0.75 0.68 68-50 79-73 26-160 25-45 0.77 0.79 0.73 50-38 73-68 20-160 0.8-40 0.80 0.82 0.76 38-24 68-64 15-160 0.5-38 0.81 0.83 0.77 24-10 64-60 15-160 0.3-22 0.80 0.82 0.76 For the Pelton wheels he gives the following table where D = pitch diameter of buckets, d = jet diameter. D d 10 11 12 13 14 15 16 18 22 26 30 C 5.35 4.85 4.46 4.11 3.83 3.56 3.35 2.97 2.43 2.06 1.79 Efficiencies Full gate % gate . . }4 gate . . H gate . . 0.60 0.70 0.76 0.79 0.80 0.81 0.82 0.82 0.82 0.81 0.80 0.83 0.81 0.85 0.86 0.87 0.86 0.86 0.85 0.84 0.68 0.75 0.80 0.82 0.84 0.84 0.84 0.84 0.82 0.80 0.62 0.72 0.77 0.80 0.82 0.82 0.82 0.81 0.80 0.77 0.81 0.83 0.77 0.73 HYDRAULIC POWER 551 for tangential wheels varies between 0.40 and 0.47. Parker in his " Control of Water" gives good methods of checking up designs of both types of wheels. Moody in his discussion of Larner's paper gives some curves of maxi- mum efficiencies attained by modern waterwheels of the Francis and tangential types. These curves slightly modified are reproduced in Fig. 295. The detailed design of a turbine and casing is mainly concerned with the angles of entrance and discharge of the vanes or buckets in the runner and of the direction of the entering water from the guide vanes. This is a highly specialized subject and beyond the scope of this book. Zowski in Engineering News, Jan. 6 and Feb. 10, 1910, gives perhaps the best treatment of this subject in English although Parker in his "Control of Water" gives the treatment in good form. The general turbine equa- tion may be written: 2gH = (U 2 - U 2 2 ) + (W 2 - W2 2 ) + (V 2 - 7 2 2 ). Where U and U 2 are runner velocities, W and W 2 are absolute velocities of the water and V and V 2 are relative velocities of the water. This equation may be transformed into: 2gH = AQ 2 + BQn + Cn 2 where H = head, Q = quantity of water, n = r.p.m. and A, B and C are coefficients depending on bucket angles, friction and the proportions of the machine. This is also the general equation of the centrifugal pump with the signs changed: - 2gH = AQ 2 - BQn - Cn 2 . This is the equation of a hyperbolic paraboloid. The analysis has been very carefully worked out by Grunebaum in his pamphlet, Zur Theorie der Zentrifugalpumpen, Berlin, 1905. W. F. Uhl in Transactions A.S.M.E., vol. 34, page 418, has published a variation of Gelpke's types, which is convenient to use. He uses six types instead of eight. The Holyoke Testing Flume. — The Holyoke testing flume grew out of the testing of waterwheels started by James Emerson at Lowell in the late sixties. In 1870 the Holyoke Water Co. invited Mr. Emerson to move to Holyoke and to establish a flume there. The present Holyoke flume built by Clemens Hersehell dates from 1883 and up to date more than 2,000 runners have been tested there. The flume is adapted for testing runners from 27 to 42 in. in diameter under a maximum head of about 16 to 17 ft. Capacities up to 250 cu. ft. per second may be used which reduces the available head to about 10 ft. Quantities higher than this cannot be measured with accuracy. The accuracy and application to general practice of the Holyoke 552 ENGINEERING OF POWER PLANTS tests have been attacked very often, especially where a high-head turbine has been tested under the Holyoke conditions. However, at the present time these tests hold " a position of gen- erally accepted reliability" and it is the opinion of many engineers that the results shown in the flume may be bettered in a careful field test (see Larner's paper). Testing in place is now quite common and when proper precautions are taken may be quite accurately done. The Holyoke test sheets usually contain 60 to 70 tests of 3 to 5 min. duration from which the following data is secured : number of experiment, percentage of gate opening, percentage of full discharge of wheel, head, duration of experiment, revolutions per minute, quantity of water dis- charged by wheel, horsepower developed, efficiency of wheel. From these data it is possible to construct a set of characteristic curves covering the whole field of the operation of the turbine. Mead has shown this in Fig. 295 and 247 of his " Water Power Engineering." Fig. 247 is reproduced here. In this method the discharges per second under 1-ft. head are used as abscissae with r.p.m. under 1-ft. head as ordinates. The efficiency under each gate opening and speed is plotted in its proper place with the above coordinates and the curves of equal efficiency are then drawn in. If hp. at 1-ft. head is now marked on each of the plotted points curves of equal horsepower may be drawn. From these curves the entire performance of the runner under all circumstances may be seen. Mechanical Details. — The standard wheel consists of two crowns between which the buckets are placed. The buckets are either made of formed steel plates placed in the molds and cast into the crowns or they may be made of the same material as the rest of the runner in which case the mold is built up with cores. Cast wheels are practically uni- versal now. No attempt at finishing is usually made except to chip or file off the fins left by the core junctions and some of the very highest efficiencies have been obtained from runners in this condition proving that surface friction does not play nearly as large a part as was formerly supposed. Careful design and good workmanship usually go together in which case much hand-finishing is not necessary. Balancing is not as necessary as in steam turbines but is done to some extent especially on tangential wheels where the buckets are usually of forged or cast steel bolted to the rim of the wheel. The larger diameter wheels are usually built on the tension-spoke principle. Clearances between fixed and moving parts in well-built wheels are not larger than }^6 m -> although with careful design the water wasted through a clearance as large as % in. would not be excessive when the wheel is running. When the wheel is not running the leakage is deter- HYDRAULIC POWER 553 mined by the kind and tightness of the gates. It is always best to have a valve in the penstock just above the wheel so that when not in use the wheel may be drained and leakage prevented. For this purpose butter- fly valves of very heavy design, actuated by power have been found valuable but the best valve for low and medium heads is a plain gate valve actuated by a hydraulic cylinder. These valves should not be supposed to take the place of the stop logs or other headworks gates, but should be in addition to them. Casings. — The casings of water turbines may be of almost any form and a good designer may display his individual taste to the full. With open penstocks the casing need only consist of the guides and the two narrow crowns holding them in place. With the closed penstock the scroll or spiral casing when well designed is the best. Cylindrical casings are used to a large extent especially when two or more wheels are on one shaft and when the casing supports the bearings in horizontal wheels. In designing casings the attempt should be made so to proportion the casing that at the loading at which the turbine is most often used the water will be brought to the guides at the required velocity without eddys and with a smooth stream flow. Draft Tubes. — Draft tubes should be so designed that there is a uni- form reduction of velocity from runner to tail water. The upper end of the draft tube should be the same diameter as the outside of the runner with a little flare at this point in the case of large-capacity runners to take care of the outward discharge from the buckets. From this point the tube should enlarge consistently to the discharge point and a flare of 1 ft. in diameter to 3 ft. in length is the maximum that may be allowed. One foot in 4 or 5 is much better. Knowing the height of the tube, the outlet is known and the loss of head can be calculated. This loss may vary from less than 1 per cent, of the total head to as much as 12 or 15 per cent, in poorly designed installations. Gating. — Turbine gates for regulating the amount of water entering the runner are of three kinds: 1. Cylinder gates in which a thin cylinder moves axially in the clear- ance space between guide vanes and runner blocking more or less of the breadth of the passages. This gate leads to eddys and inefficiency unless cross-partitions are cast between the vanes of the runner to control the formation of eddys (Fig. 297). 2. Register gates in which the thin cylinder in the clearance space is perforated with holes to correspond to the guide passages and is moved circumferentially to control the size of the discharge openings in the guide passages. These gates are not used very much since they increase the friction and eddy losses seriously (Fig. 298). 3. Wicket gates in which the guide vanes are pivoted and opened or 554 ENGINEERING OF POWER PLANTS closed to admit more or less water to the runner. This method also creates eddys at all positions but one, but they can be better controlled by this construction and wicket gates are adopted for the better class of turbines (see Fig. 299). Regulation. — The problem of waterwheel regulation is much more complicated than the regulation of gas or steam prime movers. The Fig. 297. — Cylinder gate. Fig. 298. — Register gate. steam engine, with its two or more maximum impulses per revolution, presents a very simple problem, since a medium-weight flywheel can store enough energy from impulse to impulse to maintain a nearly uniform rotation until the cutoff or throttling governor can control the size of the next impulse. In a slow-moving single-cylinder engine the flywheel Fig. 299.— Wicket or Fink gate. has only to store energy for ${ q sec. The regulating machinery is light in a throttling governor weighing only a few pounds, and a very small simple flyball governor furnishes sufficient power for quick and efficient working. With the steam turbine the same small and light machinery will do the work if a throttling governor is used. When nozzle governing or HYDRAULIC POWER 555 puff governing is used the relay principle is introduced. Here, as in the steam engine, the action is practically instantaneous and the flywheel effect of turbine and generator is always sufficient for good regulation. A single-cylinder, single-acting, four-cycle internal-combustion engine presents a much more difficult problem. With 75 r.p.m., the impulses are a little over 2 sec. apart and the loads can vary much in 2 sec. Four cylinders would bring the interval down to }4 sec - an d four double- acting cylinders to J4 sec, but in this case the mechanisms to be moved are large and heavy, as are the friction and inertia. It is possible to design a flyball governor having sufficient power to operate them, but the oil relay is easier, cheaper and more certain. In these types of prime movers the working fluid is very light even at high pressure and the inertia of the moving fluid is negligible, but when Time in Seconds 12 3 4 5 6 10 Fig. 300. — RegulatiorTcurves. dealing with water as a source of power the weight of the fluid is the source of energy and the governing mechanisms must be strong enough to take care of the heavy shocks due to the inertia of the moving water. The gate mechanisms of turbines are usually larger than the wheel itself and generally as heavy, while the connecting links are also very heavy. All of this heavy machinery cannot be put in motion, or stopped quickly, but luckily the flywheel effect of the revolving parts is usually large and the sudden impulses are not of the order of those in steam or gas engines. With small wheels and low heads a relay governor is used, but with higher heads or large wheels the relay does its work through a third mechanism, usually a rack and pinion. The usual arrangement includes a flyball governor which actuates two ratchets on a bar which is recipro- cated continually by the relay. When the speed rises, one of the ratchets 556 ENGINEERING OF POWER PLANTS is brought into play on the ratchet wheel and the reciprocating motion moves the wheel around, tooth by tooth, closing the gate. There is always a small speed variation at which no motion of the gate follows. 39 H"- . 132-8 — 31% ft — UH- oh"-- im Fig. 301. — Waterwheel governor, Sanitary District of Chicago. In this kind of a governor there is always a lag and the length of lag is adjusted to take care of some of the inertia of the water column. Much trouble in the earlier governors was caused by the attempt to run ignumvitae Cast Iron Fig. 302. — Step bearings. Fig. 303. — Step bearings. them without lag and trouble also results if the lag is too much. The correct amount seems to depend on head, revolutions, size of penstock and weight of gate mechanism. Two general principles may be stated: first, the gate must be opened HYDRAULIC POWER 557 only as fast as gravity can supply the water to the wheel; and second, the gates must be closed so slowly that no serious strains will be devel- oped in the penstock from the inertia of the water. Wherever it is possible, the gate mechanism should be in static balance, except as to friction. This is not always possible, but it can be partially done in every case and the governor is then relieved of work which it should not be called upon to do. Fig. 300 shows the curves of opening and closing of a modern type of governor, and Figs. 301 and 304 show the governors Fig. 304. — Waterwheel governor. and the relay mechanism. For parallel running of waterwheels and steam or gas engines it is essential that the flyball governors of the machines have the same characteristics, although there are modifying influences, such as flywheel action. The difficulty of dividing the load between water and steam units has been largely overcome, and with the modern governors the troubles experienced are small. Practically the only auxiliaries of a waterwheel, besides the governor are the thrust bearing and oiling system, and on the horizontal shaft 558 ENGINEERING OF POWER PLANTS turbines thrust bearings are usually not required. For small wheels the old lignum vitae step bearing or phosphor-bronze button, run with water lubrication, is still the best construction, see Figs. 302, 303, but shafts larger than 5 in. and very fast-running shafts do not work well unless the design is ample. In the larger modern designs the thrust bearing is placed near the top of the shaft below the generator, where it may be supported from the floor framing, or with the later Kingsbury thrust the bearing is placed above the generator on the spider which supports the upper bearing. The older thrusts consist of two cast-iron surfaces, face to face, the lower one fixed and the upper revolving with the shaft. To the center of pressure of these surfaces oil or water is piped under sufficient Fig. 305. — Kingsbury thrust bearing. pressure to raise the shaft one or two-thousandths of an inch. The oil or water escapes through the orifice and the upper shoe will run on the film of fluid so made. In the Kingsbury bearing the revolving surface is replaced by a number of smaller rectangular shoes, supported at a point behind the center of pressure. These shoes are babbeted on the face side and scraped to a true surface, but the forward edges are eased to allow the oil to enter under them. The lower shoe is covered with about 3 in. of oil which may be circulated to keep it cool. These bearings are shown in Fig. 305 and Fig. 306 shows the oil-pressure bearing for the same weight, such as was used at Niagara Falls. Where the pressure bearing is used a rather complicated oil- or water-supply system is neces- sary and pressures up to 700 or 800 lb. per square inch are often used. HYDRAULIC POWER 559 Tyhe oiling systems are usually gravity systems, provided with a sump for the dirty oil, from which it is pumped through niters to supply tanks near the roof of the station. If the head necessary to work the governor relays is higher than the gravity head in the station, two small pumps and an accumulator are usually installed for this purpose. On horizontal- shaft machines of small size, ring oiling bearings are usually used, but lignum vitse bearings with water lubrication are also common. For the larger horizontal shaft turbines the regular gravity oiling system should be installed. Flood lubrication, with higher bearing pressures, surface speeds and oil temperatures are the tendency at the present time. For Electric Oil Catcher Fig. 306. — Oil-pressure thrust bearing. Niagara Falls Power Co. Head Races, Canals and Flumes. — It is frequently necessary in order to take advantage of the total fall, to place the dam at the narrowest portion of the stream where good foundations are available and locate the power house a considerable distance down stream bringing the water to the power house in open channels, such as head races, earth or rock canals, or tunnels or pipe lines. Wooden flumes of rectangular section were formerly used for small powers or in localities where lumber was very cheap. The sides and bottom were usually made of two thicknesses of planking with broken joints. The deterioration in these flumes was very rapid. 560 ENGINEERING OF POWER PLANTS When the canal is in earth or rock it usually pays to line it with con- crete. A velocity of 2 ft. per second may be allowed in unlined earth canals and 8 ft. per second in lined canals. It is not unusual to find these canals exceeding 6,000 ft. in length. In all cases the head lost in the canal must be more than made up by the lower location of the power house. From both canals and flumes penstocks of wood or metal must be used to convey the water to the wheels or the canal or flume may be replaced by metal or wood stave pipe. The local configuration of the country usually determines which is the better plan to be used. If the stream is terraced, the canal may be the much better method. If rock ridges exist between the dam and the proposed power house site with a wind- ing stream and broken country, pressure tunnels in the solid rock have been driven in a straight line to the wheels, thus saving much distance and consequent loss of head. Water from a dam in one watershed has been taken in a tunnel under the ridges to the adjoining watershed and utilized to better advantage there. The lining of these tunnels should be very smooth. Very good results are obtained from this construction. The reports of the Board of Water Supply of the City of New York contain much interesting information, but the best data on these tunnels is to be found in the report on the Hetch-Hetchy Water Supply for San Francisco by John R. Freeman, Past President, A.S.M.E. This report is a model of its kind and will repay careful study by the engineer. For figuring the slope and loss of head in canals, flumes and tunnels the tables given in Williams and Hazens " Hydraulic Tables" (Wiley) are most convenient. Wood pipe should not be painted but, for a good length of life, should be covered in with earth (not a very good plan as then the pipe cannot be inspected) or protected by a house. Steel pipe is protected by the Augus Smith HYDRAULIC POWER 561 covering and either buried or unprotected. All pipes should have a large air vent near the intake end to prevent collapsing when the water is drawn off and on long pipes additional vents are often installed. Air valves should be placed on high points. The plant at Salmon Falls, N. Y., illustrated in Fig. 307, is a good example of the use of tunnel, wood pipe and steel pipe. Water Tower or Standpipe. — If an open penstock is possible, this form of construction will undoubtedly be the best as fluctuations of head or pressure due to inertia will be very small indeed. With canal con- struction and low heads the surplus water can easily be taken care of by a small spillway. When closed penstocks of any length are necessary, the inertia of the moving water, as its velocity fluctuates due to the governing of the wheels to meet changes of load, may create dangerous pressures or surges. In a small installation at low head or even up to 200 ft. it has been usual to place a standpipe as close to the turbines as possible with its height great enough to reach above the dam level. In addition to this spring loaded relief valves are always furnished at the end of the penstock to further relieve the undue rise in head. The water tower may be of the plain cylindrical type as at Trenton Falls or the two diameter or differential type as at Salmon Falls (Fig. 307). They may be built of steel or reinforced concrete up to 200 ft. high, but usually the cheaper and stronger construction is steel above 100 ft. high. A valuable chapter on the design and use of the water tower may be found in D. W. Mead's "Water Power Engineering" and a discussion of the formulas and methods of design in Parker's " Control of Water." Speeds of Turbine and Generator. — In most cases hydro-develop- ments are utilized by means of electric generation and transmission and it becomes important to place the r.p.m. of the turbine at such a figure that the electric generator will be reasonably cheap and suited to the serv- ice. Francis wheels may be built for many permissible speeds, in fact for any horse-power and head combination the range of speeds is very large. Table A has been calculated for C = 90 to C = 10 and for heads from 100 to 600 ft. giving minimum and maximum speed values for a number of generators from 200 kw. to 10,000 kw. The figures under C = 10 are the lower speed limits for that head, under C = 90 the higher limits. It is well not to approach either limit too closely. Most of the hydro-systems in this country have been designed to use 60-cycle current but a few plants have been built using 40 cycles and a considerable number using 25 cycles. In Europe other frequencies are sometimes used. Table B gives the speeds of 60-, 40- and 25-cycle 2 X 60 X cvcles generator, with common pole numbers. 1 — = r.p.m. 36 562 ENGINEERING OF POWER PLANTS Table A.— ■Possible Revolutions Pee , Minute C 10 90 10 90 10 90. 10 90 10 90 10 90 Kw Hp. Head 100-ft. 200 ft. 300 ft. 400 ft. 500 ft. 600 ft. 10,000 13,800 27 243 63 567 106 954 152 1,368 202 1,818 253 2,277 5,000 6,900 38 342 90 810 150 1,350 215 1,935 282 2,538 358 3,222 2,000 2,760 61 549 143 1,287 237 2,133 341 3,069 450 4,050 566 5,094 1,000 1,380 85 765 202 1,818 335 3,015 480 4,320 635 5,715 798 7,182 500 690 121 1,089 286 2,574 474 4,266 680 6,120 900 8,100 1,130 10,170 300 413 157 1,413 370 3,330 614 5,526 882 7,938 1,164 10,476 1,464 13,176 200 276 182 1,638 453 4,077 750 6,750 1,078 9,702 1,425 12,825 1,790 16,110 Table B— R.P.M. Poles 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 36 40 72 60 cycles 40 cycles 3,600 2,400 1,500 1,800 1,200 750 1,200 800 500 900 600 375 720 480 300 600 400 250 514 343 214 450.0 300.0 187.5 400 367 167 360 240 150 327 218 136 300 200 125 277.0 185.0 115.5 257 172 107 240 160 100 225 150 94 200 184 84 180:100 120 92 75 42 Of Francis wheels from 200 kw. to 10,000 kw. installed in the last few years on heads up to 600 ft. the r.p.m. have varied from about 94 to 514, these being the limits in which the cost of the generator has balanced against the turbine cost. Six hundred r.p.m. seems to be a favorite speed for both small and large units of the tangential type but speeds as high as 900 and as low as 200 have been used. In many cases the spacing of the units and design of the headworks settle the permissible diameters and speeds. Cost of Hydraulic Installations. The total cost of a hydraulic instal- lation may be divided into two parts: first, the dam, land damages, spillway, canals, flumes, pipe lines or penstocks and other details relating to the storage and transportation of the water; and second, the power house, turbines and electrical apparatus. The first group will usually amount to 50 per cent, of the total cost in small low-head plants, rising to 65, 70 and sometimes 80 per cent, in large high-head installations. Where a large amount of storage is constructed the storage itself may in large plants amount to 50 per cent, of the total cost. The installation cost per kilowatt varies greatly, depending on local conditions, from $50 per kilowatt, where the best conditions prevail, to as high as $300 or more, where the conditions are not good. It is usually considered that a cost of $125 per kilowatt represents the limit of economical construction, with interest at 6 per cent. Where the capitalist will put up with a smaller return than 6 per cent., higher-cost HYDRAULIC POWER 563 plants may be possible. Not infrequently unknown physical con- ditions largely increase the cost of installation of a water power. When this occurs the project usually goes into a receiver's hands and enough capital is written off so that the work may proceed. In a number of cases this accounts for the very low reported costs of certain plants. The construction of the dam is largely a matter of excavation and masonry or concrete. Earth excavation may be figured as low as 25 cts. Fig. 308. — Section through 17,500 turbine unit Coosa River, Lock 12 development. per cubic yard under good conditions, but where much hauling has to be done or difficult conditions must be met, prices as high as $1 to $1.25 must be used. Rock excavation is rarely cheaper than $1 per cubic yard under the best conditions, and may go to $3 in bad locations and as high as $10 to $15 in caisson work. Concrete and masonry can easily be figured when the prices of sand, cement and rock are known. Concrete usually runs from $4.50 to $10 per yard in place, $5.50 to $7 is about the average where concrete can be placed in mass and the forms are simple. The 564 ENGINEERING OF POWER PLANTS HYDRAULIC POWER 565 local price of lumber determines the cost of the forms which will rarely be higher than $2 per yard, in which case steel forms should be con- sidered. Lumber delivered at $40 or higher usually means that con- siderable steel may, with economy, be used in the forms. Cut-stone work may run from $12 to $25 per yard, but is very rarely used in commercial construction at the present day. Power houses and switch and trans- former houses should be figured as in steam plants. The steel contract will average from 8 cts. per cubic foot in small buildings to 16 cts. per cubic foot in large heavy buildings, all on the basis of $80 per ton erected. The masonry contract will run from 12 cts. to 30 cts. per cubic foot de- pending on locality, materials and amount of terra cotta, tile and cut stone and other ornaments. Hydraulic machinery and governors vary in price with head and size; small low-head turbines cost approximately $15 per kilowatt, while large low-head machines may be bought as low as $7. Medium-head apparatus (from 200 to 600 ft.) may vary from $13 to $7.50 per kilo- watt. High-head turbines of the Pelton type run from $10 per kilowatt in small sizes down to $5 in large sizes. Generators, switchboard, exciters and cable vary from $24 per kilowatt for small low-head (low- speed apparatus) to $8 per kilowatt for large high-head high-speed machinery. Transformers cost $6 to $8 per kilowatt. Penstocks or pressure pipes of riveted steel vary in cost from 3 cts. to 6 cts. per pound erected, plus freight and haulage. Wood stave pipe, used to such a large extent for low-head pressure pipes, will cost about 15 cts. per foot board measure, erected, with bands, for medium sizes and pressures. Gates of the Taintor type will not usually run above 5 cts. a pound erected, plus freight and haulage. Stoney gates in small sizes may run to 8 cts., but in the large sizes should not exceed 5 cts. Cranes for use inside the power station of both the alternating-current and direct-cur- rent types, may be figured at $4.50 per ton lifted per foot of span for small short-span cranes, down to $2.50 per ton-foot for heavy long-span cranes. Special cranes, used outside the power house for handling gates, may cost anywhere from $3 to $10 per ton-foot, depending on the design. The question of land damages, due to flooding caused by the creation of the pond, is an extremely important one. This cost in certain plants in the West, where the flooded lands were far from a settled district, have been as low as $1 per acre, while in certain of the large city water-supply reservoirs, the land damages amounted to over $250 per acre. On an average for developments reasonably removed from towns, prices from $70 to $115 per acre have been paid. Railroads and highways usually follow rather closely the flow line of a river, and these constructions must be relocated previous to the con- 566 ENGINEERING OF POWER PLANTS struction of the dam. $3,000 per mile is a fair price for country highway relocation and from $5,000 to $8,000 per mile will cover the relocating of a good State road in localities where good materials are common. The cost of railroad relocation is another matter. Single-track little- used roads may usually be relocated at a cost not exceeding $60,000 a mile, but the cost of relocating a double-track express road has usually been found so high that it has not been attempted. Table of Estimated Cost per Horsepower of Water-power Plants Having horizontal turbines, steel penstocks, and walled tailraces (dam and buildings not included) Hp. "L" 10 ft. fall 15 ft. fall 20 ft. fall 30 ft. fall 40 ft. fall 1,000 f 100 $65.14 $40.92 $29.37 $19.40 $14.60 \ 600 98.75 63.75 46.70 30.95 23.55 900 \ 100 65.35 41.00 29.55 19.55 14.80 \ 600 98.95 63.90 46.95 31.00 23.85 800 f 100 65.50 41.10 29.65 19.70 15.00 \ 600 99.15 64.00 47.00 31.15 23.95 700 f 100 65.70 41.20 29.85 19.90 15.10 \ 600 99.50 63.95 47.25 31.35 24.15 600 f 100 65.85 41.55 30.00 20.00 15.35 1 600 100.10 64.40 47.40 31.80 24.55 500 J 100 66.00 41.70 30.25 20.25 15.50 1 600 100.10 64.00 47.85 31.80 24.45 400 J 100 66.30 42.05 30.55 20.80 16.00 1 600 100.00 65.15 48.05 32.35 25.10 300 J 100 66.85 42.65 31.10 21.50 16.50 1 600 101.00 65.80 48.50 33.20 25.65 200 \ 100 68.50 44.20 32.45 22.60 17.60 \ 600 102.85 67.35 50.60 34.45 26.95 100 | 100 71.40 46.65 34.75 24.75 19.80 i 600 106.60 70.30 52.90 36.85 30.80 "L" = distance from feeder head to end of tailrace, cost of canal, if any, not included. Cost of Hydro -electric Developments. — The cost of hydro-electric developments depends upon many conditions, such as water rights, real estate, right-of-way, the cost of the development, and the distribution system. Further, the depreciation, repairs, taxes, insurance, interest on the investment, operating expenses, etc., enter into the account. The cost of the enterprise depends very much on the character and the conditions under which the development is carried out, and the cost per unit capacity depends upon the total capacity of the plant. It occurs quite frequently that the unit cost in large propositions is greater than in small ones, although it would appear that it should be smaller. HYDRAULIC POWER 567 Table I. — Estimate of Cost of Various Developments Location of development Natural head Available head Power developed, hp. Estimated capital cost Cost per hp. Healey's Falls, Lower Trent River . . . Middle Falls, Lower Trent River. . . Rauney's Fall Rapids above Glen Miller Rapids above Trenton Maitland River 1 Sangeen River Beaver River (Eugenia Falls) Severn River (Big Chute) 2 South River St. Lawrence River, Iroquois, Ont . . . Mississippi River, High Falls, "A" 3 . Mississippi River, High Falls, "B" 4 . Montreal River, Fountain Falls, Ont. Dog Lake, Kaministiquia River 3 Cameron Rapids Slate Falls , 60 8,000 30 5,200 35 6,000 18 3,200 18 3,200 80 1,600 40 1,333 420 2,267 52 4,000 85 750 12 1,200 78 2,400 78 1,100 27 2,400 I < 547 310 13,676 1 r 547 310 6,840 j 39 16,350 \ 39 8,250 J 31 40 3,686 I 31 40 1,843 $675,000 475,000 425,000 350,000 370,000 325,000 250,000 291,000 350,000 150,000 179,000 195,000 123,000 214,000 832,000 619,700 815,000 600,000 357,600 260,000 $84.38 91.37 69.67 109.38 115.63 203.12 187.53 128.28 87.50 153.33 149.16 81.25 181.82 89.16 61.00 91.00 50.00 73.00 97.00 141.00 1 Dam rather expensive. 3 With storage development. 2 Headworks and canal less expensive than ordinary. 4 Including 3,500 ft. of head water tunnel. Table II. — Estimate of Cost of Hydro-electric Plants at Niagara Falls 24-hr. power capacity 50,000-hp. development 75,000-hp. development 100,000-hp. development Tunnel tailraces $1,250,000 450,000 500,000 300,000 1,080,000 760,000 350,000 100,000 75,000 $1,250,000 450,000 700,000 450,000 144,000 910,000 525,000 100,000 75,000 $1,250,000 450,000 Headworks and canal Wheel pit 700,000 Power house 600,000 Hydraulic equipment 1,980,000 1,400,000 Electrical equipment Transformer station and equipment . Office building and machine shop . . . Miscellaneous 700,000 100,000 75,000 Engineering and misc. 10 per cent, of above making total construction cost $4,865,000 $5,350,000 436,560 $5,900,000 $6,490,000 529,548 $7,255,000 $7,980,000 651,168 Interest, 2 years at 4 per cent Total capital cost $5,786,560 $114 $7,019,584 $94 $8,631,168 $86 Per horsepower 568 ENGINEERING OF POWER PLANTS This is due to the fact that in many large propositions a heavy expense is involved in the harnessing of great volumes of water. Table I, accompanying, gives figures on the estimated costs of various developments tabulated by the Ontario Hydro-electric Power Commis- sion, and Table II gives the estimated cost of a hydro-electric plant at Niagara Falls, as given in the report of above-named Commission. It will be noticed by reference to Table I that the cost of hydro- electric plants per horsepower, varies greatly (from $61 to $203) and may vary even more. Correct estimates can be arrived at only by thorough investigation of all the factors, considering with especial care the impor- tant element of depreciation. In estimating the cost of power (that is, the generation and dis- tribution, which of course depends very much upon the load factor) administration and operating expense, maintenance, depreciation, inter- est, insurance, etc., must also be well considered. The following table clearly illustrates the cost of power at the development of the Chicago Sanitary District System. Table III. — Cost of Power, Chicago Sanitary District System Total cost of development and transmission $3,500,000 Estimates of cost Interest on investment at 4 per cent $140,000 . 00 Taxes on real estate, buildings, etc 7,200.00 Depreciation on buildings at 1 per cent. 3,650.00 Depreciation on waterwheels at 2 per cent 2,027 . 32 Depreciation on generators at 2 per cent 1,824.60 Depreciation on pole lines at 3 per cent 2,020.50 Depreciation on other electrical appliances at 3 per cent 3,995.52 Total fixed charge 161,137.94 Operating expenses Power and substation labor $63,240 . 00 Repairs to machinery and building 3,700.00 Incidental expenses 1,200 . 00 Operating Lawrence Avenue pumping station 43,960 . 00 Operating 39th Avenue pumping station 120,380.00 Interest on investment 39th Street pumping station . . 15,599 . 76 Total operating expense 248,079.76 Total cost to sanitary district $409,217.76 Capacity, 15,000 hp., cost per hp. per annum 26 . 40 A most important item in determining the cost of power is the cost of distribution. This is particularly true in long-distance transmission HYDRAULIC POWER 569 systems where the skill of the engineer is of vital importance in selecting the proper route and the kind of systems to be employed. Whether a long-distance power-transmission project will pay will depend upon the cost of generating the power, the cost of transmission, the transmission loss, etc., and the value of energy at the point of dis- tribution, i.e., the cost at which energy might be generated at this point by some other system, as, for instance, by a steam power plant. The difference between the cost of power at the generating end and its value at the point of distribution represents the maximum cost of transmission allowable. INDEX Actual fuel consumption and cost of oper- ation of existing plants, 501 Advantages, engine, 68 of revolving-grate producers, 469 of the internal-combustion principle, 414 Advantages, turbine, 68 Air, compressed, 511 compressor cylinders, oil in, 519 compressors, volumetric efficiency of, 518 condensers, 96 » -lift pump, 517 -pump system, the kinetic, 108 system at Butte and Anaconda, com- pressed, 520 Alcohol and gasoline, comparative re- sults from denatured, 410 Alignment, 85 Alternating current, direct current vs., 334 motors, 336 Alternators, exciters for, 339 Amount of fuel used by producer-gas power plants, 457 Anaconda, compressed-air system at Butte and, 520 Analysis of development in a power plant, 16 Animal motors, 4 Animals, muscular power of men and, 2 Annual cost of power, 308 Anthracite, 372 Apparatus for turbines, condensing, 95 Apparent power, kilovolt amperes, 339 Arrangement of the power plant, 242 Ash handling, 236 coal and, 232 cost of, 237 Aspects of the turbine, commercial, 68 Auxiliaries, boiler, 197 condenser, 99 Auxiliaries, percentage of steam gener- ated used by, 207 power required by producer, 463 Auxiliary steam piping, 218, 222 Average cost of boilers, 138 of stacks and flues, 178 heat balance for test locomotive, 369 steam consumption of reciprocating steam engines, 48 Axis, engines classified by position of cylinder, 20 B Bagass, 377 Bark, tan, 378 Basic principles of steam turbines, 39 Beam engines, 21 Belting, cost of shafting and, 319 electric drive vs. shafting and, 320 shafting and, 319 Bituminous coals, 373, 383, 456 semi-, 373 Blast furnace as a gas producer, the, 486 -furnace gas-electric plants, cost of, 488 power, cost of, 488 gas power, cost of steam and, 499 Bleeder and mixed pressure turbines, low-pressure, 57 Blowing engines, piston compressors and, 512 Blowers, soot, 213 Boiler auxiliaries, 197 capacity required by office buildings, estimating, 355 construction, specifications for, 128 deterioration, 158 efficiency, 156 with oil fuel, 392 explosions, 158 feed water, 209 inspection, 159 materials, 126 performance, locomotive, 366 571 572 INDEX Boiler pressure, maximum, 128 rating, 156 returns, high-pressure drip piping and, 223 -room piping details, 221 settings, 130 the steam, 121 types, dependability of the different, 126 selection of, 160 Boilers, average cost of, 138 cost of fire-tube, 134 water-tube, 135 cylindrical-flue, 122, 124 hanging or supporting, 133 horsepower rating of, 130 idle, 158 natural gas under steam, 394 oil vs. coal under, 390 operation and care of, 162 return-tubular, 122, 125 to do given work, number of, 159 types of, 121 water-tube, 123, 125 Bolts, 218 foundation, 85 Brick chimneys, cost of, 177 Briquets, fuel, 379 in torpedo-boat service, 387 results of experiments with, 387 use of, 387 Buck-stays and tie-rods, 132 Building, the power plant of the tall office, 354 Buildings, cost of, 247 division of the load in tall office, 354 estimating boiler capacity required by office, 348 miscellaneous steam requirements in large, 355 refrigeration for office, 357 selection of plant for tall office, 354 Burners, oil, 208 Butte and Anaconda, compressed-air system at, 520 Buying coal, when, 380 Byproduct coke-oven gas plants, 485 heating plant, the, 341 producer-gas plants, 478 operating results and working costs of, 482 C Canals and flumes, head races, 559 Capacity of fans and power required, 181 of windmills, 8 required in exciters, 339 Care of boilers, operation and, 162 Carrying peak loads economically, 282 "Cascade control" methods, 337 Casings of water turbines, 553 Central station design, 275 heating and power, comparative costs of private and, 358 Centrifugal feed pumps, 198 Chain grates, 149 Charcoal, 379 Chimney dimensions, 176 Chimneys, 166 and mechanical draft, 166 cost of brick, 177 special, 178 Circulating pumps, 99 water, 412 Classification of engines by their use of steam, 22 special, 35 of turbines, 40 Cleaning the gas generator, 462 Coal and ash handling, 232 factors affecting value of, 381 handling, 232 cost of, 235 per square foot of grate area per hour, pounds of, 158 pounds of water evaporated per pound of dry, 157 specification standards for purchase of, 382 storage, 237 the purchase of, under specifications, 381 under boilers, oil vs., 390 when buying, 380 Coals, bituminous, 373, 383, 456 semi-bituminous, 373 Coke, 379 Coke-oven gas plants, byproduct, 485 Cold storage, 528 Combined engine and turbine, economy of, 59 unit, 59 Combustion, 151 INDEX 573 Combustion engines, horsepower of in- ternal, 402 internal, 398 lubrication of internal, 413 pressures and temperatures in internal, 411 Commercial aspects of the turbine, 68 Commutating-pole motors, interpole or, 336 Comparative cost of operating different types of power installations, examples of, 495 costs of private and central station heating and power, 358 cost of steam power stations, com- plete, 250 efficiencies and operating costs for different types of installations, 491 results from denatured alcohol and gasoline, 410 Comparison of steam turbine with steam engine, 40 Composition of producer gas, 435, 459 Compound and multiple-expansion en- gines, 31 condensing Corliss engines, cost of, 66 engines, cost of, 67 Compressed air, 511 -air system at Butte and Anaconda, 520 Compressor cylinders, oil in air, 519 Compressor, and blowing engines, piston, 512 volumetric efficiency of air, 518 Concrete foundations, cost of, 83 Condensate pumps, 100 Condensation, mixed, 87 surface, 90 Condenser auxiliaries, 99 installations, cost of individual, 115 pumps, power required for, 112 Condensers, 87 air, 96 cost of, 113 evaporative, 97 formulae for use of, 115 Condensing and non-condensing engines, 27 apparatus for turbines, 95 Corliss engines, cost of compound, 66 Condensing engines, cost of compound, 67 Conditions, special producer-gas engine, 454 Construction, specifications for boiler, 128 Constructions, power plant, 239 Consumption of feed pumps, steam, 197 of reciprocating steam engines, aver- age steam, 48 of small steam turbines, steam, 54 variable-load steam, 60 Conversion of tarry vapors into fixed gases, 447 Cooling ponds, 115 towers, 116 cost of, 118 Corliss engines, cost of compound con- densing, 66 cost of simple non-condensing, 63 Corrosion, 212 Cost curves at variable loads, 301 of a horsepower at the machine, 333 of ash handling, 237 of blast-furnace gas electric plants, 488 power, 488 of boilers, average, 138 of brick chimneys, 177 of buildings, 247 of byproduct producer-gas plants, operating results and working, 482 of coal handling, 235 of compound condensing Corliss engines, 66 condensing engines, 67 of concrete foundations, 83 of condensers, 113 formulas for, 115 of cooling towers, 118 of Diesel engines, 427 of electric generators and motors, efficiency and, 76 power in New York City, the, 298 of energy in fuels, 395 of exhaust steam heating, 346 of feed pumps, 199 of feed-water heaters, 203 of fire-tube boilers, 134 of fuel with different types of instal- lations, relative, 492 of gas engines, 418 574 INDEX Cost of gas producers, 473 of hydraulic installations, 562 of guyed iron stacks, 177 of hydraulic installations, 562 of hydro-electric developments, 566 of individual condenser installations, 115 of installations complete, 248 of mechanical stokers, 161 of oil, waste and supplies, 263 of operating different types of power installations, examples of com- parative, 495 of operation of existing plants, actual fuel consumption and, 501 of piping, 227 of power, 285 annual, 308 of producer-gas installations, 474 power plants, operating, 475 of shafting and belting, 319 of simple, high-speed engines, 62 non-condensing Corliss engines, 63 of special chimneys, 178 of stacks and flues, average, 178 of steam and blast-furnace gas power, 499 and producer-gas plants, relative, 474 of steam power stations complete, comparative, 250 of steam turbines, 67 of water, 119, 264 of water-tube boilers, 135 station, 256 fuel, 256 labor, 259 maintenance, 263 vs. economy of operation, first, 73 Costs for different types of installations, comparative efficiencies and operating, 491 of private and central station heat- ing and power, comparative, 358 Coverings, pipe, 227 Cubic feet of gas per pound of fuel, 461 Current, rated, 339 Curves at variable loads, cost, 301 load, 300 Cut-off engines, throttling and, 32 Cylinder axis, engines classified by posi- tion of, 20 Cylinder, horsepower of a, 18 Cylindrical-flue boilers, 122, 124 D Dams, 537 Data on Diesel engines, summary of general, 428 Denatured alcohol and gasoline, com- parative results from, 410 Dependability of the different boiler types, 126 Depreciation, 253 and maintenance of stacks and mechanical draft systems, 184 of locomotives, 365 Design and proportions of turbines and runners, 547 central station, 275 furnace, 138 of power plant, 239 types of station, 244 Details of water turbines, mechanical, 552 Deterioration, boiler, 158 Determining pipe sizes, 225 Development in a power plant, analysis of, 16 of the gas engine, rapid, 415 Diesel engines, cost of, 427 summary of general data on, 428 Difference between steam and water turbines, 39 Different boiler types, dependability of the, 126 types of installations, comparative efficiencies and operating costs for, 491 relative cost of fuel with 492 of power installations, examples of comparative cost of operat- ing, 495 Dimensions, chimney, 176 of gas producers, 472 Direct-current motors, types and where used, 335 Direct current vs. alternating current, 334 Disadvantages of the internal-combus- tion principle, 414 of various pipe systems, 219 INDEX 575 Distribution, gas, 485 District heating, 341 Diversity factor, 273 Division of the load in tall office build- ings, 354 Domestic heating, natural gas for, 395 Double-acting engines, single- and, 24 -zone producer, the, 451 Down-draft producer-gas plant, opera- tion of a typical, 445 producer, the, 445 Draft, chimneys and mechanical, 166 forced and induced, 179 systems, depreciation and mainte- nance of stacks and mechanical, 184 efficiency with stack and mecha- nical, 185 tubes, 553 Drawbar pull of the locomotive, 363 Drawing fires, time between periods of, 463 Drip piping and boiler returns, high- pressure, 223 Driving, rope, 319 Dry coal, pounds of water evaporated per pound of, 157 Dulong's formula, 375 Duty of pumping engines, 61 E Eccentric-grate gas producer, revolving, 467 Economizers, 204 Economy of combined engine and tur- bine, 59 of gas engines, thermal efficiency and, 408 of operation, first cost vs., 73 of windmills, 9 steam engine, 48 tests of steam engines, 50 of turbines, 56 variable load, 269 with increase of steam pressure in the locomotive, increased, 364 Effect of speed on average steam pres- sure, 364 Effects of semi and totally enclosing direct-current motors, 340 of smoke, 192 Efficiencies and operating costs for differ- ent types of installations, com- parative, 491 of different types of engines, thermal, 491 thermal, 25 Efficiency and cost of electric generators and motors, 76 and economy of gas engines, thermal, 408 boiler, 156 of air compressors, volumetric, 518 of a machine, 1 of and losses in steam turbines, 46 of gas engines, mechanical, 405 producers, 470 of steam engines, mechanical, 47 of the locomotive, 362 of transmission, 320 with oil fuel, boiler, 392 with stack and mechanical draft systems, 185 Electric developments, cost of hydro-, 566 drive vs. shafting and belting, 320 generators and motors, 76 efficiency and cost of, 76 plants, cost of blast-furnace gas, 488 power, cost of blast-furnace gas, 488 in New 'York City, the cost of, 298 Elimination of the steam locomotive, 370 Energy in fuels, cost of, 395 of fuel, 15 of wind and water, 6 sources of, 1 Enclosing direct-current motors, effects of semi and totally, 340 Engine advantages, 68 and turbine economy of combined, 59 and turbine unit, combined, 59 comparison of steam turbine with steam, 40 conditions, special producer-gas, 454 economy, steam, 48 essential parts of a reciprocating steam, 19 field of the reciprocating, 68 flywheels, 73 foundations proper, 83 length of typical reciprocating, 19 of the locomotive, the, 367 576 INDEX Engine, piston speeds, gas, 404 proper location for a gas, 416 rapid development of the gas, 415 the oil, 419 the steam, 18 Engines, average steam consumption of reciprocating steam, 48 beam, 21 classification of, by their use of steam, 22 classified by position of cylinder axis, 20 compound and multiple-expansion, 31 condensing and non-condensing, 27 cost of compound condensing, 67 Corliss, 66 of Diesel, 427 of gas, 418 of simple, high-speed, 62 non-condensing Corliss, 63 duty of pumping, 61 economy tests of steam, 50 expansive and non-expansive, 24 four-cycle and two-cycle, 398 high-speed, 23 horizontal, 20 horsepower of internal combustion, 402 internal combustion, 398 low-speed, 23 lubrication of internal combustion, 413 mechanical efficiency of gas, 405 of steam, 47 piston compressors and blowing, 512 pressures and temperatures in in- ternal combustion, 411 regulating or governing gas, 404 rotary steam, 35 single- and double-acting, 24 solar, 12 special classification of, 35 starting gas, 416 summary of general data on Diesel, 428 thermal efficiencies of different types of, 491 efficiency and economy of gas, 408 throttling and cut-off, 32 turbines vs., in units of small ca- pacity, 69 Engines, una-flow, 30 vertical, 20 weight of gas, 418 Essential parts of a reciprocating steam engine, 19 Estimating boiler capacity required by office buildings, 355 miscellaneous steam requirements in large buildings, 348 Evaporation, factor of, 156 per pound of dry coal, 157 Evaporative condensers, 97 Evase' stacks, 172 Examples of comparative cost of operat- ing different types of power in- stallations, 495 Exciters for alternators, 339 capacity required in, 339 Exhaust heads and oil extractors, 228 low-pressure or, bleeder and mixed pressure turbines, 57 noises, 417 pipe, 417 piping, 224 steam heating, cost of, 346 Expansion joints, 110 of pipe, 226 Expansive and non-expansive engines, 24 Expense of locomotives, fuel, 369 Expenses, operating, 251 Experiments with briquets, results of, 387 Explosions, boiler, 158 Extractors, scrubbers and tar, 453 F Factor, diversity, 273 load, 271 of evaporation, 156 use, 275 Factors affecting value of coal, 381 Fans, capacity of, and power required, 181 Feed pipe, 129 pumps, 197 centrifugal, 198 cost of, 199 steam consumption of, 197 water, boiler, 209 -water heaters, 201 cost of, 203 impurities in, 209 INDEX 577 Feed water piping, 223 treatment of, 212 Field of the reciprocating engine, 68 Fires, time between periods of drawing, 463 Fire-tube boilers, cost of, 134 First cost vs. economy of operation, 73 Fittings, pipe, 217 Fixed gases, conversion of tarry vapors into, 447 Flues and uptakes, 173 average cost of stacks and, 178 Flumes, head races, canals and, 559 Flume, the Holyoke testing, 551 Flywheels, engine, 73 Foaming and priming, 211 Forced and induced draft, 179 Formula, Dulong's, 375 Formulae for cost of condensers, 115 Foundation bolts, 85 Foundations, 82 cost of concrete, 83 engine, proper, 83 Four-cycle and two-cycle engines, 398 Fuel, 256 -bed area, pounds of fuel per square foot of, per hour, 458 bed, shooting the, 447 boiler efficiency with oil, 392 briquets, 379 consumption and cost of operation of existing plants, actual, 501 cost, station, 256 cubic feet of gas per pound of, 461 energy of, 15 expense of locomotives, 369 oil under specifications, purchase of, 392 per horsepower per hour, pounds of, 259 per square foot of fuel-bed area per hour, pounds of, 458 standby, 463 used by producer-gas power plants, amount of, 456 with different types of installations, relative cost of, 492 Fuels, 372 cost of energy in, 395 heating value of, 379 in gas producers, use of low-grade, 457 37 Fuels, liquid, 390 solid, 372 used in gas producers, 455 use of low-grade, 388 weight and volume of solid, 380 Furnace design, 138 losses, 146 Fusible plugs, 129 G Gage-cocks, water glass and, 129 Gage, steam, 129 Gain in steam consumption by condens- ing, probable, 49 Gas, 393 and gas producers, producer, 435 composition of producer, 435, 459 distribution, 485 -electric plants, cost of blast-furnace, 488 -electric power, cost of blast-furnace, 488 engine conditions, special producer, 454 piston speeds, 404 proper location for a, 416 rapid development of the, 415 engines, cost of, 418 mechanical efficiency of, 405 regulating or governing, 404 starting, 416 thermal efficiency and economy of, 408 weight of, 418 for domestic heating, natural, 395 generator, cleaning the, 462 heat value of producer, 460 installations, cost of producer-, 474 per pound of fuel, cubic feet of, 461 plant, operation of a typical down- draft producer, 445 plants, byproduct coke-oven, 485 byproduct producer-, 478 operating results and working costs of byproduct producer-, 482 relative cost of steam and pro- ducer, 474 uses of tar from producer-, 464 power, cost of steam and blast- furnace, 499 578 INDEX Gas power plants, amount of fuel used by producer-, 457 producer, 435 revolving eccentric-grate, 467 the blast furnace as a, 486 producers, cost of, 473 dimensions of, 472 efficiency of, 470 fuels used in, 455 producer gas and, 435 slagging, 484 types of, 438 use of low-grade fuels in, 457 relative results from steam and pro- ducer, 471 scrubbing the, 440 turbines, 431 under steam boilers, natural, 394 utilization of water, 448 various uses of producer-, 454 Gases, conversion of tarry vapors into fixed, 447 heating value of various, 393 Gasoline, comparative results from de- natured alcohol and, 410 Gating, 553 General data on Diesel engines, summary of, 428 Generator, cleaning the gas, 462 speeds of turbine and, 561 Generators, 337 and motors, efficiency and cost of electric, 76 Good operation, standards of, 291 Governing gas engines, regulating or, 404 Grading of pipe, 226 Graphite, 372 Grate area, pounds of coal per square foot of, per hour, 158 Grates, chain, 149 Gravity, energy of wind and water, 6 Grouting, 85 Guyed iron stacks, cost of, 177 H Handling, ash, 236 coal, 232 and ash, 232 cost of ash, 237 of coal, 235 Hanging or supporting boilers, 133 Head races, canals and flumes, 559 Heat balance for test locomotive, aver- age, 369 methods of selling, 342 value of producer gas, 460 Heaters, cost of feed-water, 203 feed-water, 201 Heating and power, comparative costs of private and central station, 358 cost of exhaust steam, 346 district, 341 natural gas for domestic, 395 plant, the byproduct, 341 purposes, producers for metallurgi- cal and, 454 station, 350 steam system of, 350 value of fuels, 379 of various gases, 393 water systems of, 351 High-pressure drip piping and boiler returns, 223 steam piping, 218 -speed engines, 23 cost of simple, 62 Hints on steam plant operation, 315 Holyoke testing flume, the, 551 Horizontal engines, 20 Horsepower, cost of a, at the machine, 333 -hour, pounds of water per, 156 of a cylinder, 18 of internal combustion engines, 402 of the locomotive, 362 rating of boilers, 130 Hotwells, 109 Humphrey pump, the, 429 Hydraulic installations, cost of, 562 power, 530 -station layouts, 541 Hydro-electric developments, cost of, 566 Ice making, 527 Idle boilers, 158 Impulse and reaction turbines, 40 Impurities in feed water, 209 Incidentals, 248 Increased economy with increase of steam pressure in the locomotive, 364 Individual condenser installations, cost of, 115 INDEX 579 Induced draft, forced and, 179 Injector, the, 200 Inspection, boiler, 159 Installations, cost of, complete, 248 cost of hydraulic, 562 producer-gas, 474 , Insurance, taxes and, 255 Interest, 253 Internal combustion engines, 398 horsepower of, 402 lubrication of, 413 pressures and temperatures in, 411 -combustion principle, advantages of the, 414 disadvantages of the, 415 Interpole or commutating-pole motors, 336 Iron stacks, cost of guyed, 177 Jacket, use of water, 469 Joints, expansion, 110 K Kilovolt-amperes, apparent power, 339 Kilowatts, rating in, 339 Kinetic air-pump system, the, 108 Labor, 259 cost, station, 259 of men, 2 Leakage, radiation and, 208 Length of typical reciprocating engine, 19 Lignite, 373, 456 Liquid fuels, 390 Load curves, 300 factor, 271 in tall office buildings, division of the, 354 Location for a gas engine, proper, 416 of power plant, 239 Locomotive as a whole, the, 367 average heat balance for test, 369 boiler performance, 366 drawbar pull of the, 363 efficiency of the, 362 elimination of the steam, 370 Locomotive, horsepower of the, 362 increased economy with increase of steam pressure in the, 364 the engine of the, 367 the power plant of the steam, 362 tractive force of the, 362 Locomotives, depreciation of, 365 fuel expense of, 369 mechanical stokers for, 365 Loop, steam, 230 Losses, furnace, 146 in steam turbines, efficiency of and, 46 standby, 276 Low-grade fuels in gas producers, use of, 457 use of, 388 -pressure or exhaust, bleeder and mixed pressure turbines, 57 -speed engines, 23 Lubrication of internal combustion en- gines, 413 M Machine, cost of a horsepower at the, 333 efficiency of a, 1 service, selection of motors and speed requirements for, 332 tools, sizes of motors recommended to drive, 324 Machinery, refrigerating, 525 Maintenance, 263 cost, station, 263 of stacks and mechanical draft sys- tems, depreciation and, 184 Materials, boiler, 126 Maximum boiler pressure, 128 Mechanical details of water turbines, 552 draft, chimneys and, 166 systems, depreciation and main- tenance of stacks and, 184 efficiency with stack and, 185 efficiency of gas engines, 405 of steam engines, 47 stokers, 146 cost of, 161 for locomotives, 365 saving by use of, 160 Mechanically stirred and revolving- grate producers, 465 580 INDEX Men, labor of, 2 muscular power of, and animals, 2 Metallurgical and heating purposes, pro- ducers for, 454 Method of sampling, 386 Methods of motor drive, 321 of selling heat, 342 Mixed condensation, 87 pressure turbines, low-pressure or exhaust, bleeder and, 57 Motor drive, methods of, 321 Motors, alternating-current, 336 and speed requirements for machine service, selection of, 332 animal, 4 direct-current, types and where used, 335 effects of semi and totally enclosing direct-current, 340 efficiency and cost of electric gene- rators and, 76 electric generators and, 76 interpole or commutating-pole, 336 recommended to drive machine tools, sizes of, 324 tide and wave, 10 Multiple-expansion engines, compound and, 31 Muscular power of men and animals, 2 N Oil burners, 208 engine, the, 419 extractors, exhaust heads and, 228 fuel, boiler efficiency with, 392 in air compressor cylinders, 519 pumps, 208 required by steam turbines, 46 under specifications, purchase of fuel, 392 vs. coal under boilers, 390 waste and supplies, 263 Operating costs for different types of installations, comparative effi- ciencies and, 491 of producer-gas power plants 475 different types of power installations, examples of comparative cost of, 495 expenses, 251 hints on steam plant, 315 results and working costs of by- product producer-gas plants, 482 Operation and care of boilers, 162 of a typical down-draft producer- gas plant, 445 of existing plants, actual fuel con- sumption and cost of, 501 standards of good, 291 Output, ratings by, 339 Natural gas for domestic heating, 395 under steam boilers, 394 Noise of turbo-generators, 46 Noises, exhaust, 417 Non-condensing Corliss engines, cost of simple, 63 engines, condensing and, 27 Non-expansive engines, expansive and, 24 Number of boilers to do given work, 159 O Office buildings, division of the load in tall, 354 estimating boiler capacity required by, 355 refrigeration for, 357 selection of plant for tall, 354 the power plant of the tall, 354 Parts of a reciprocating steam engine, essential, 19 Peak loads, carrying economically, 282 Peat, 376, 456 Percentage of steam generated used by auxiliaries, 207 Performance, locomotive boiler, 366 Periods of drawing fires, time between, 463 Pipe coverings, 227 exhaust, 417 expansion of, 226 feed, 129 fittings, 217 grading of, 226 sizes, determining, 225 systems, disadvantages of various, 219 INDEX 581 Piping, 215 auxiliary steam, 218, 222 cost of, 227 details, boiler-room, 221 exhaust, 224 feed-water, 223 high-pressure drip and boiler re- turns, 223 steam, 218 Piston compressors and blowing engines, 512 speed as distinguished from rotative speed, 23 speeds, gas engine, 404 Plant for tall office buildings, selection of, 354 of the steam locomotive, the power, 362 of the tall office building, the power, 354 operation, hints on steam, 315 Plugs, fusible, 129 Ponds, cooling, 115 spray, 116 Position of cylinder axis, engines classi- fied by, 20 Pounds of coal per square foot of grate area per hour, 158 of fuel per horsepower per hour, 259 per square foot of fuel-bed area per hour, 458 of water evaporated per pound of dry coal, 157 of water per horsepower-hour, 156 Power, annual cost of, 308 comparative costs of private and central station heating and, 358 cost of, 285 blast-furnace gas-electric, 488 of steam and blast-furnace gas, 499 hydraulic, 530 in New York City, the cost of elec- tric, 298 installations, examples of compara- tive cost of operating different types of, 495 of men and animals, muscular, 2 plant, analysis of development in a, 16 arrangement of the, 242 constructions, 239 Power plant, design of, 239 location of, 239 of the steam locomotive, the, 362 of the tall office building, the, 354 the steam, 239 plants, amount of fuel used by pro- ducer-gas, 457 operating costs of producer-gas, 475 required by producer auxiliaries, 463 for condenser pumps, 112 stations, comparative cost of steam, complete, 250 transmission, 319 unit of, 1 Pressure, effect of speed on average steam, 364 in the locomotive, increased economy with increase of steam, 364 maximum boiler, 128 producer, the up-draft, 443 Pressures and temperatures in internal combustion engines, 411 Preventing scale, 211 Priming, 110 foaming and, 211 Principles of steam turbines, basic, 39 Private and central station heating and power, comparative costs of, 358 Probable gain in steam consumption by condensing, 49 Problems, 4, 74, 80, 86, 119, 162, 189, 214, 230, 265, 283, 361, 396, 432, 489, 528 Producer auxiliaries, power required by, 463 gas, 435 and gas producers, 435 composition of, 435, 459 engine conditions, special, 454 heat value of, 460 installations, cost of, 474 plant, operation of a typical down- draft, 445 plants, byproduct, 478 operating results and working costs of byproducts, 482 relative cost of steam and, 474 uses of tar from, 464 power plants, amount of fuel used by, 457 operating costs of, 475 582 INDEX Producer gas, relative results from steam and, 471 various uses of, 454 revolving eccentric-grate gas, 467 the blast furnace as a gas, 486 the double-zone, 451 the down-draft, 445 the up-draft pressure, 443 suction, 438 Producers, advantages of revolving-grate, 469 cost of gas, 473 dimensions of gas, 472 efficiency of gas, 470 for metallurgical and heating pur- poses, 454 fuels used in gas, 455 mechanically stirred and revolving- grate, 465 producer gas and gas, 435 slagging gas, 484 types of gas, 435 use of low-grade fuels in gas, 457 Proper location for a gas engine, 416 Proportions of turbines and runners, de- sign and, 547 Pull of the locomotive, drawbar, 363 Pump, air-lift, 517 the Humphrey, 429 Pumping engines, duty of, 61 Pumps, centrifugal feed, 198 circulating, 99 condensate, 100 cost of feed, 199 feed, 197 oil, 208 power required for condenser, 112 steam consumption of feed, 197 Purchase of coal, specification standards for, 382 of coal under specifications, the, 381 of fuel oil under specification, 392 R Radiation and leakage, 208 Rapid development of the gas engine, 415 Rated current, 339 Rating, boiler, 156 in kilowatts, 339 of boilers, horsepower, 130 of steam turbines, 46 Ratings by output, 339 Reaction turbines, impulse and, 40 Readiness to serve, 275 Reciprocating engine, field of the, 68 length of typical, 19 steam engine, essential parts of a, 19 steam engines, average steam con- sumption of, 48 Refrigeration for office buildings, 357 Refrigerating machinery, 525 Regulating or governing gas engines, 404 Regulation, waterwheel, 554 Relative cost of fuel with different types of installations, 492 cost of steam and producer-gas plants, 474 results from steam and producer gas, 471 Results and working costs of byproduct producer-gas plants, operating, 482 from denatured alcohol and gasoline, comparative, 410 from steam and producer gas, rela- tive, 471 of experiments with briquets, 387 Return-tubular boilers, 122, 125 Returns, high-pressure drip piping and boiler, 223 Revolving eccentric-grate gas producer, 467 -grate producers, advantages of, 469 mechanically stirred and, 465 Rope driving, 319 Rotary steam engines, 35 Rotative speed, piston speed as dis- tinguished from, 23 Runners, design and proportions of tur- bines and, 547 S Safety valves, 129 Sampling, method of, 386 Saving by use of mechanical stokers, 160 of space with turbines, the, 70 Scale, preventing, 211 Scrubber water required, 464 Scrubbers and tar extractors, 453 Scrubbing the gas, 440 Selection of boiler type, 160 of motors and speed requirements for machine service, 332 of plant for tall office buildings, 354 INDEX 583 Selling heat, methods of, 342 Semi-bituminous coals, 373 Separators, steam, 230 Serve, readiness to, 275 Settings, boiler, 130 Shafting and belting, 319 cost of, 319 electric drive vs., 320 Shooting the fuel bed, 447 Simple, high-speed engines, cost of, 62 non-condensing Corliss engines, cost of, 63 Single- and double-acting engines, 24 Sizes of motors recommended to drive machine tools, 324 Slagging gas producers, 484 Small steam turbines, steam consump- tion of, 54 turbines, 44 Smoke and smoke prevention, 190 effects of, 192 Solar engines, 12 Solid fuels, 372 weight and volume of, 380 Soot blowers, 213 Sources of energy, 1 Space, the saving of, with turbines, 70 Special chimneys, cost of, 178 classification of engines, 35 producer-gas engine conditions, 454 Specification standards for purchase of coal, 382 Specifications for boiler construction, 128 purchase of fuel oil under, 392 the purchase of coal under, 381 Speed, effect of, on average steam pres- sure, 364 piston, as distinguished from rotative speed, 23 requirements for machine service, selection of motors and, 332 Speeds, gas engine piston, 404 of turbine and generator, 561 steam, 221 Spillways, 540 Spray ponds, 116 Stack and mechanical draft systems, efficiency with, 185 Stacks and flues, average cost, 178 and mechanical draft systems, de- preciation and maintenance of, 184 Stacks, cost of guyed iron, 177 Evase, 172 Standards for purchase of coal, speci- fication, 382 of good operation, 291 Standby fuel, 463 losses, 276 Standpipe, water tower or, 561 Starting gas engines, 416 Station cost, 256 design, central, 275 types of, 244 fuel cost, 256 heating, 350 labor cost, 259 layouts, hydraulic-, 541 maintenance cost, 263 Steam and blast-furnace gas power, cost of, 499 and producer-gas plants, relative cost of, 474 relative results from, 471 and water turbines, difference be- tween, 39 boiler, the, 121 boilers, natural gas under, 394 classification of engines by their use of, 22 consumption of feed pumps, 197 of reciprocating steam engines, average, 48 of small steam turbines, 54 probable gain in, by condensing, 49 variable-load, 60 engine, comparison of steam turbine with, 40 economy, 48 essential parts of a reciprocating, 19 the, 18 engines, average steam consumption of reciprocating, 48 economy tests of, 50 mechanical efficiency of, 47 rotary, 35 gage, 129 heating, cost of exhaust, 346 locomotive, elimination of the, 370 the power plant of the, 362 loop, 230 piping, auxiliary, 218, 222 584 INDEX Steam piping, high pressure, 218 plant operation, hints on, 315 power plant, the, 239 stations, comparative cost of, com- plete, 250 pressure, effect of speed on average, 364 in the locomotive, increased econ- omy with increase of, 364 requirements in large buildings, esti- mating miscellaneous, 348 separators, 230 speeds, 221 system of heating, 350 transmission, 320 traps, 229 turbine, comparison of, with steam engine, 40 turbines, 39 basic principles of, 39 cost of, 67 efficiency of and losses in, 46 oil required by, 46 rating of, 46 steam consumption of small, 54 used by auxiliaries, percentage of, 207 use of superheated, 365 Stokers, cost of mechanical, 161 for locomotives, mechanical, 365 mechanical, 146 saving by use of mechanical, 160 types of, 147 Stop valve, 129 Storage batteries, water, 546 coal, 237 cold, 528 Straw, 378 Suction producer, the up-draft, 438 Summary of general data on Diesel engines, 428 Superheated steam, use of, 365 Supplies, oil, waste and, 263 Supporting boilers, hanging or, 133 Surface condensation, 90 System, the kinetic air-pump, 108 Tall office building, the power plant of the, 354 buildings, division of the load in, 354 Tall office buildings, selection of plant for, 354 Tan bark, 378 Tar extractors, scrubbers and, 453 from producer-gas plants, uses of,. 464 Tarry vapors, conversion of, into fixed gases, 447 Taxes and insurance, 255 Temperature in internal combustion engines, pressures and, 411 Testing flume, the Holyoke, 551 Test locomotive, average heat balance for, 369 Tests of steam engine, economy, 50 of turbines, economy, 56 The blast furnace as a gas producer, 486 byproduct heating plant, 341 cost of electric power in New York City, 298 down-draft producer, 445 double-zone producer, 451 engine of the locomotive, 367 Holyoke testing flume, 551 Humphrey pump, 429 injector, 200 kinetic air-pump system, 108 locomotive as a whole, 367 oil engine, 419 power plant of the steam locomotive, 362 of the tall office building, 354 purchase of coal under specifications, 381 saving of space with turbines, 70 steam boiler, 121 engine, 18 power plant, 239 up-draft pressure producer, 440 up-draft suction producer, 438 Thermal efficiencies, 25 of different types of engines, 491 efficiency and economy of gas en- gines, 408 Throttling and cut-off engines, 32 Tide and wave motors, 10 Tie-rods, buck-stays and, 132 Time between periods of drawing fires, 463 Tools, sizes of motors recommended to drive machine, 324 Torpedo-boat service, briquets in, 387 Tower of standpipe, water, 561 INDEX 585 Towers, cooling, 116 cost of cooling, 118 Tractive force of the locomotive, 362 Transmission, efficiency of, 320 power, 319 steam, 320 Traps, steam, 229 Treatment of feed water, 212 Tubes, draft, 553 Turbine advantages, 68 and generator, speeds of, 561 commercial aspects of the, 68 comparison of steam, with steam engine, 40 economy of combined engine and, 59 unit, combined engine and, 59 'Turbines and runners, design and proportions of, 547 basic principles of steam, 39 casings of water, 553 classification of, 40 condensing apparatus for, 95 cost of steam, 67 • difference between steam and water, 39 •economy tests of, 56 efficiency of and losses in steam, 46 gas, 431 impulse and reaction, 40 low-pressure or exhaust, bleeder and mixed pressure, 57 mechanical details of water, 552 oil required by steam, 46 rating of steam, 46 small, 44 steam, 39 consumption of small steam, 54 the saving of space with, 70 vs. engines in units of small capacity, 69 Turbo-generators, noise of, 46 Two-cycle engines, four-cycle and, 398 Types of boilers, 121 of gas producers, 435 of installations, comparative effi- ciencies and operating costs for different, 491 relative cost of fuel with different, 492 of power installations, examples of comparative cost of operating different, 495 Types of station design, 244 of stokers, 147 Typical down-draft producer-gas plant, operation of a, 445 reciprocating engine, length of, 19 U Una-flow engines, 30 Unit, combined engine and turbine, 59 of power, 1 Units of small capacity, turbines vs. en- gines in, 69 Up-draft pressure producer, the, 440 suction producer, the, 438 Uptakes, flues and, 173 Use factor, 275 of briquets, 387 of low-grade fuels, 388 in gas producers, 457 of mechanical stokers, saving by, 160 steam, classification of engines by their, 22 of superheated steam, 365 of water jacket, 469 Uses of producer-gas, various, 454 of tar from producer-gas plants, 464 Utilization of water gas, 448 V Value of coal, factors affecting, 381 of fuels, heating, 379 of producer gas, heat, 460 of various gases, heating, 393 Valve, stop, 129 Valves, 217 safety, 129 Vaporizers, 452 Vaporizer water required, 463 Vapors, conversion of tarry, into fixed gases, 447 Variable load economy, 269 steam consumption, 60 loads, cost curves at, 301 • Various pipe systems, disadvantages of, 219 uses of producer-gas, 454 Vertical engines, 20 Volume of solid fuels, weight and, 380 Volumetric efficiency of air compressors, 518 586 INDEX W Waste and supplies, oil, 263 Water, 264 boiler feed, 209 circulating, 412 cost of, 119 energy of wind and, 6 evaporated per pound of dry coal, pounds of, 157 gas, utilization of, 498 glass and gage-cocks, 129 impurities in feed, 209 jacket, use of, 469 per horsepower-hour, pounds of, , 156 required, scrubber, 464 vaporizer, 463 storage batteries, 546 systems of heating, 351 Water tower of standpipe, 561 treatment of feed, 212 -tube boilers, 123, 125 cost of, 135 turbines, casings of, 553 difference between steam and, 39 mechanical details of, 552 Waterwheel regulation, 554 Wave motors, tide and, 10 Weight and volume of solid fuels, 380 of gas engines, 418 When buying coal, 380 Wind and water, energy of, 6 Windmills, 6 capacity of, 8 economy of, 9 Wood, 377 " Working costs of byproduct producer- gas plants, operating results and, 482