LAND,^ MRINE,: ;& -DdGOMOl^iVi: BRYAN :P0KKIS, M. IKST. G.E, BOUGHT WITH THE INCOME PROM THE SAGE ENDOWMENT FUND THE GIFT OF Henrg W. Sage 1S91 ^... l.^..z...L^.f. , ±.5-...!:}?^.. TJ 285.068'""" """""'<*y Library IJ;S,)Jeat efficiency Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004607440 THE HEAT EFFICIENCY OF STEAM BOILERS STANDAR D WORKS FOR EN GINEERS. /^AC? rkii ANTr» AID PMrilMP^- A Praetieal Text-Book on Internal UAS, UlL, A1>U /\1K. i:il>UIl>E^. Combustion Motors without Boiler. By BRYAN" DONKIN, M.Inst.C.E. Second Edition, Revised throughout and Enlarged. With numerous additional Illustrations. Large 8vo. 25s. General Contents.— Gas Engines :—Greneral Description— History and Development— British, French, and German Gas Engines— Gas Production for Motive Power— Theory of the Gas Engine— Chemical Composition of Gas in Gas Engines— Utilisation of Heat— Explosion and Combustion. Oil Motors :— History and Development— Various Types— Priestman's and other Oil Engines. Hot-Air Engines :— History and Development— Various Types : Stirling's, Ericsson's, etc., etc. " The BEST BOOK now published on Gas, Oil, and Air Engines."— rAe Engineer. BOILERS, MARINE AND LAND : Their Construction and Strength. A Hand- book of Kules, Formulae, Tables, etc., relative to Material, Scantlings, and Pressures, Safety Valves, Springs, Fittings, and Mountings, etc. By T. W. Tbaill, M.InstO.E., F.E.R.N., Late Engineer Surveyor-in-Chief to the Board of Trade. Third Edition, Revised and Enlarged. Pocket size, leather, 12s. 6d. ; also larger size for office use, cloth, 12s. 6d. *,* To the Second and Thikd Editions many New Tables for Pkessches up to 200 lbs. per Square Inch have been added. "The MOST valuable wokk on Boilers published in England."— SAi^jJingr World. " Contains an Enormous Quantity oe Infokmation arranged in a very convenient form. ... A most useful volume, sup- plying information to be had nowhere else."— TAe Engineer. MUNRO'S STEAM BOILERS : Their Defects, Management, and Construction. By R. D. MuNRO, Engineer of the Scottish Boiler Insurance and Engine Inspecting Company. Thikd Edition. Illustrated. 4s. 6d. *»* This little book has been specially designed for the use of Young Engineers and Boiler Attendants. FUEL AND WATER : A Manual for Users of Steam and Water. By Prof. Fkanz Sohwaokhofek, of Vienna, and Walter R. Browne, M.A., C.E., late Fellow of Trinity College, Cambridge. Demy 8vo, with numerous Illustrations. 9s. A MANUAL OF THE STEAM ENGINE AND OTHER PRIME MOVERS. By W. J. Maoquorn Rankine, LL.D., F.R.S., late Regius Professor of Civil Engineering in the University of Glasgow. With a Section on Gas, Oil, and Air Engines. By Bryan Donkin, M.Inst.C.E. Crown 8vo, cloth, 12s. 6d. Fottrteenth Edition. A MANUAL OF MARINE ENGINEERING. The Designing, Construction, and Working of Marine Machinery. By A. E. Seaton, M.Inst.C.E., M.Inst. Mech.E., M.Inst.N.A. Thirteenth Edition. With a Section on Water-Tube Boilers. 21s. "Mr Seaton's Manual has no rival."— Tfte Kmcs. MARINE ENGINEERING RULES AND TABLES. For Marine Engineers, 'Na.vsX Architects, and others. By A. E. Seaton, M.Inst.C.E., and H. M. Rounthv^taite, M.Inst. Mech.E. With Illustrations. Leather." Fourth Edition. 8s. 6d. "Admirably fulfils its purpose."— Jfamie Engineer. STEAM AND STEAM ENGINES (A Text- Book of). By Prof. Jamieson, M.Inst.C.E., M.lnst.E.E., F.R.S.E., Glasgow and West of Scotland Technical College. With over 200 Illustrations, Folding Plates, and Examination Papers. Twelfth Edition. 8s. 6d. "The BEST BOOK yet published for Students." — The Engineer. JAMIESON'S ELEMENTARY MANUAL OF STEAM AND THE STEAM ENGINE. Fifth Edition. 3s. 6d. " Quite the RIGHT sort of boolj."- TAc Engineer. VALVES AND VALVE-GEARING : Including the Corliss Valve and Trip Gears. By Charles Httrst, Practical Draughtsman, Large 8vo. With numerous Illustrations and Plates. 7s. 6d. "Almost every type of Valve and its Gearing is clearly set forth, so as to be READILY understood and practically applied."— Industries and Iron. " Will prove a VERY VALUABLE aid." — Manne Engineer. LOCOMOTIVE ENGINES: Their Design and Construction. A Practical Text-Book for the Use of Engine-Builders, Designers, and Draughtsmen, Railway Engineers, and Students. By William Frank Pettigrbw, M.Inst.C.E. Large 8vo. With numerous Illustrations and Plates. With Sections on Continental and American Engines. By Albert F. Ravenshear, B.Sc, of H.M. Patent Office. ENGINE-ROOM PRACTICE. A Handbook for Engineers and Officers in the Koyal Navy and Mercantile Marine. Including the Management of the Main and Auxiliary Engines on Board Ship. By John G. Liveksidge, Engineer, E.N., A.M.lnst.C.E., Instructor in Applied Mechanics, Royal Naval College, Greenwich. With numerous illustrations LONDON: CHARLES GRIFFIN & COMPANY, LTD., EXETER ST., STRAND. >^ El I— I Pi ■ a M P H H Pi o I— I P9 a THE HEAT EFFICIENCY OF STEAM BOILERS- LAND, MARINE, AND LOCOMOTIVE. WITH TESTS AND EXPERIMENTS ON DIFFERENT TYPES, HEATING VALUE OF FUELS, ANALYSES OF GASES, EVAPORATION, AND SUGGESTIONS FOR TESTING BOILERS. BY , BRYAN pONKIN, MEMBER OF THE INSTITUTION OF CIVIL ENGINEERS ; MEMBER OF THE INSTITUTION OF MECHANICAL ENGINEERS ; MEMBER OF THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS ; MEMBER OF THE VEREIN DEUTSCHER ING^NIEURE ; AUTHOR OF " A TEXT-BOOK OF GAS, OIL, AND AIR ENGINES," ETC. WITH NUMEROUS TABLES, PLATES, AND ILLUSTRATIONS IN THE TEXT. LONDON: CHARLES GRIFFIN & COMPANY, LIMITED, EXETER STREET, STRAND. 1898. [All Rights Reserved.} 'ii^b \-*»\ ^') ^. a^^(J.S' ^ PREFACE. In his professional career the Author has had frequent opportunities, during the last twenty-five years, of making Tests on Steam Boilers. Some time ago he began to tabulate many experiments, and, as the list continually increased, he considered that it might prove useful as a collection of facts, if thrown into the shape of a book. With this object he has added the results of various trials made by others, as well as chapters on combustion and kindred subjects. He has endeavoured to make the book as practical as possible, and useful as a reference for Engineers, and those interested in the economical production of steam. The history of Steam Boilers, which dates back 100 to 150 years, is not touched upon, as it would be foreign to his purpose. Boiler tests, in his opinion, are useless and even misleading, unless the heating value of the fuel, analysis of gases, evaporation of water, and boiler efficiency are given. Many engineers are satisfied with recording only the evaporative results in lbs. of water per lb. of fuel ; but, considering how largely fuels differ in their heating value and percentage of incombustible matter, such tests cannot be regarded as satisfactory or exhaustive. So much heat is given to a boiler in the shape of fuel, the greater part of which is usefully employed in evaporating water, while a certain percentage, large or small, is wasted. Many manufacturers, even in England, will now guarantee a certain boiler efficiency with a given fuel. In other words, with coal of known quality and heating value (without economiser) they will guarantee that, say, 70% of the heat shall be converted into steam of a certain pressure from a certain temperature of feed water, and so many lbs. of water evaporated per square foot . of heating surface per hour. Boilers cover so large a field that the Author has been obliged to confine himself only to those parts of the subject which deal with tests, combustion, smoke, etc., and has not VI PREFACE. touched upon other questions, which are treated fully in many books. On the very important topic of the composition of all kinds of fuel, — solid, liquid, and gaseous, — both in England and elsewhere, the reader is referred to other works, especially those treating of the analysis of combustibles and their heating value. The titles of some of these books will be found in the Bibliography. It is mainly by collating and comparing a large number of reliable tests, that the principles governing combustion and efficiency in different types of boilers can be de- termined. The Author hopes, therefore, that his contribution to the heat question, by breaking comparatively new ground, will lead the way, and incite others to make more complete collections of careful boiler experiments, the only mode in which the subject can be thoroughly and practically studied. Most of the well-known boiler types made by leading English and foreign engineers will be found represented in the Tables of Tests. The trials have been drawn from trustworthy sources, such as The Proceedings of the Institution of Civil Engineers, Proceedings of the Institution of Mechanical Engineers, of the Institution of Naval Architects, and of the North- East CocLst Engineers and Shipbuilders, as well as The Engineer, Engineering, from Zeit- schrift des Vereines deutscher Inginieure, and many other technical journals and periodicals, both here, on the Continent, and in America. Some Boiler Insurance Companies in England and abroad now publish in their yearly reports experiments made by their own engineers, and many of these careful trials (in which the heating value of, the fuel, analysis of gases, &c., are given) have been selected, especially when made by such competent authorities as Mr M. Longridge and others. It is difficult to estimate the number of steam boilers of all kinds used in all countries on land. At the end of the last century only a few thousand were working, and there were no locomotive or marine boilers. Now the number is probably about three-quarters of a million. This does not include the number of locomotives in the world, which may be taken approximately at 124,000. On the Continent all boilers must be legally registered, and marked with a Government stamp; but as no such law exists in England, the number in use is not easily known. Very large sums of money, representing many millions sterling, have been invested in steam boilers, and thousands of engineers are continually studying economy in coal. The question of heat efficiency is, therefore, not a small one. To generate steam a very large amount of fuel is consumed every year, and much is wasted. If 10% or 15% could be economised, a very moderate estimate, it would represent a great gain to the world at large. The total annual production of coal in all countries a few years ago was 400 millions of tons. We shall not be far wrong in estimating that one-half, or 200 million tons, is used PREFACE. vu yearly for generating steam. Putting the cost per ton at the low average price of 10s., we get 100 million pounds sterhng as about the annual value of the fuel consumed under stationary, semi-portable, locomotive, and marine boilers. The gradual increase in the pressures of steam is also very striking. At the beginning of the century the steam pressure was only a few lbs. per square inch : now pressures of 150 to 200 lbs. and more are common. In the Tables of Eesults, English weights and measures have been used, although the Author would have much preferred to keep to the more convenient Metric System, but the time has hardly arrived for its general adoption in this country. Several gentlemen have been kind enough, at the Author's request, to make special boiler tests for this book. To his personal and other engineering friends in Great Britain, the United States, and on the Continent, who have helped him much in various ways, he gratefully acknowledges his indebtedness. The Donkin and Kennedy series of 21 tests on different types of boilers, all with the same coal, originally published in Engineeriiig, have been incorporated in the Tables. Mr C. J. Wilson, the eminent chemist, kindly consented to look through the chapter on Combustion, and advantage has been taken of some of his valuable criticisms. The Author will gratefully receive notice of any errors, and will also be glad to have, for insertion in a future edition, duly signed particulars of careful boiler tests, according to the headings adopted and in the order given in the Tables. At the end of the book a collection of drawings of various types of ancient and modern steam boilers will be found. B. D. Rbigatb, May 1898. TABLE OF CONTENTS. CHAPTEK I. CLASSIFICATION OF DIFFERENT TYPES OF BOILERS. Division I. Division II. Internally Fired Boilers. PASE Externally Fired Boilers. PAGE Cornish with and without smoke tubes. 1 Cylindrical, 9 Lancashire with and without smoke tubes, 3 Lancashire, 10 , , with short smoke tubes, 4 Elephant, . 10 ,, with three furnace tubes, . 4 Two-storey, 11 Dry back, .... 4 Water tube. Babcook and Wilcox, 12 Wet back. 5 Stirling, . . 12 Lancashire with smoke tubes. Spence's experi- ,, Thornyoroft, . 13 ments on, 6 ^^ Belleville, 13 Locomotive and Agricultural, 6 Yarrow, . 14 Two-storey Cornish, 8 Various types, 14 Two-storey Lancashire,. 9 Vertical, . 14 CHAPTER II. EXPLANATION OF THE HEADINGS OF THE TABLES. Explanation of columns I. to IX. , Explanation of columns X. to XXIII., . Explanation of columns XXIV. to XXVI. 16 17 18 Remarks, Priming of steam. 18 18 CHAPTER III. TABLES OF EXPERIMENTS ON BOILERS. Internally Fired. Cornish without smoke tubes, }j it ,, with smoke tubes, 21 23 25 27 Lancashire — no smoke tubes. Machine firing, }) Hand firing, . 29 31 33 35 37 39 HEAT EFFICIENCY OF STEAM BOILERS. Chaptbb III. — Tables of Experiments on Boilers — contirmed. Lancashire — no smoke tubes. Hand firing, ,, Berlin trials, — no smoke tubes. Hand firing, .... ,, Dlisseldorf trials, — no smoke tubes. Hand firing, .... ,, German trials, ,, with smoke tubes. Hand firing, , , three flues, no smoke tubes, Dry back, with smoke tubes, ,, cold air, chimney draught (Spenoe), ,, ,, forced ,, ,, ;) 3} 1i M -J , , hot forced draught, , Summary, Spenoe's experiments, . Wet back with smoke tubes. At sea, Locomotire. Stationary, >i J) Agricultural, Locomotive. Semi-portable, Locomotive. Running on rails, . PAGE PAGE 41 Two-storey with smoke tubes. 85 43 ,, Lancashire with smoke tubes, 87 45 n 9) J} >) 89 47 49 51 Externally Tired. 53 Return smoke tubes. 91 Lancashire, . 93 55 Elephant without smoke tubes. 95 57 , , with , , 97 59 Two-storey with smoke tubes, 99 61 Water tube. Babcock and Wilcox, 101 63 >j jj )? 103 65 ,, Various, .... 105 67 , , Various. Frankfort Exhibition, 107 69 Stirling, 107 71 Various, 109 71 , , Niclausse, 111 73 ,, Thornycroft, . 111 75 Belleville, . 113 77 Vertical 113 79 Summary of all experiments. Internally fired, 115 81 ,, ,, Externally fi.xeA, 117 83 Summary of boiler efficiencies, 118 CHAPTER IV. FIRE GRATES OF VARIOUS TYPES. Fire bars, . 119 Grates— Donneley, Excess of air. 119 Godillot, Grates — Tenbrink, . 120 , , Dulac, . ,, Knhn, . 120 , , Wackarnie- -Belpaire, „ Pellatt, . . 121 ,, Kudlicz, Stepped grates, . 121 ,, Cario, . Marsilly 121 Ferret, . „ Barber, . 121 , , Meldrum, „ Munich, 121 ,, Empire, Grates — Seipp, . 122 , , Ferrando, ,, Rinne, 122 American down-draught furnaces. „ Stauss, 122 }> it Hawley, Adam, . 122 CHAP! MECHANICA :er v. L STOKERS. Baldwin, Advantages and disadvantages, 126 Proctor, Coking and sprinkler stokers. 126 Cass, . Vicars, 127 Whitaker, . Bennis, 127 Frisbie, . Juckes, 128 Wilkinson, . M'Dougal, 128 Coxe, . Eodgkinson, . . 129 Babcock and Wilcox, Leach, . 129 Roney, . Henderson, . 129 Hale's report, 122 122 123 123 123 123 123 124 124 124 124 124 125 129 129 130 130 130 130 130 131 131 CONTENTS. XI CHAPTER VI. COMBUSTION OF FUEL IN BOILERS. Conditions of combustion, Admission of air, . Heating value of fuel, . ,, ,, formula, . Calculation of air required, . Chemical process of combustion, Hoadley's experiments, Analysis of flue gases, . PAGE 133 133 134 134 135 135 135 136 PAGE Quantity of air required for combustion, 137 Percentage of CO2 in escaping gases, . 137 Methods of calculation, . . 138 Places for sampling gases, 138 Spence's experiments, . 139 Process of combustion in practice, . 139 Methods of regulating it, . . 140 CHAPTER VII. TRANSMISSION OF HEAT THROUGH BOILER PLATES, AND THEIR TEMPERATURE. General remarks, ... . 142 Plotted results of French locomotive trials, 143 Examples of transmission of heat, 143 Blechyndeu's experiments, . 145 Results, . 153 Durston's experiments, 153 Hirsch's experiments, . Witz's Kirk's „ Ti-ansmission through Serve tubes, Hudson on heat transmission, 158 159 160 160 160 CHAPTER VIII. FEED WATER HEATERS, SUPERHEATERS, FEED PUMPS, ETC. Feed water heaters, Efficiency of economisers, Economisers. English type. Green, Scheurer-Kestner's trials, French feed water heaters. Hale on economisers, General conclusions, Pimbley's economiser, . Heating feed water by exhaust steam, Trial of an economiser. Superheating steam in boiler flues, 164 165 165 165 166 166 167 167 168 168 170 Superheaters. Hicks, M'Phail & Simpson, Schwoerer, Gehre, . Sinclair, SerpoUet, Schmidt, Supply of feed water to boilers. Table of superheating steam, Injectors, Longridge on feeding boilers. 171 171 172 172 172 173 173 173 174 174 175 CHAPTER IX. SMOKE AND ITS PREVENTION. Smoke from factories, . . 176 I. Nature of smoke, . . . 176 Chemical combinations, . . 177 II. Methods of preventing smoke, . 178 Conditions for good combustion,. 178 Method of introducing air, . 179 Spence's experiments, 179 Gaseous fuel, . . . . 180 Down-draught furnaces, . . 180 Powdered coal firing, .... 180 III. Smoke scales 181 Prussian smokecommission, scale adopted by, 182 III. IV. Smoke scales — continued. Silence's experiments. Precipitation of soot, . New smoke scale, Ringelmann's smoke scale, Diagi'am of five smoke scales. Smoke commission reports, . English commissions, Prussian smoke commission, Lewicki's trials, Paris smoke trials, 182 183 183 184 184 184 185 185 186 186 Xll HEAT EFFICIENCY OF STEAM BOILERS. I. Sampling and analysing gases, Sampling — Waller's system, Analysing, Orsat apparatus, Winkler , , Bunte ,, Elliott Dasymeter, Eoonometer, II. Measurement of temperatures, Pyrometers, Ball thermometers, Anemometers, U-water gauge. CHAPTER X. , USED IN TESTING BOILERS. PAGE . 187 III. Fuel calorimeters, 188 Prof. Thomson's, 189 Berthelot and Mahler, . ]90 Carpenter, . 190 IV. Steam calorimeters. 190 Hirn, 190 Carpenter's separating calorimeter, 191 Superheating calorimeter, 191 Barrus 192 Eateau, 192 Peabody's throttling calorimeter, 192 " Salt test," 193 Other instruments. . 193 PAGE 193 194 195 196 196 196 196 197 197 197 197 199 200 CHAPTER XI. MARINE AND LOCOMOTIVE BOILERS. General remarks, 201 Stoking, 202 Draught, ... 202 Eoonomisers, or feed water heaters, 202 Weir's „■ „ . 202 Evaporators, .... 203 Weir's evaporators, . 203 Howden's system of hot forced draught, . 204 Serve smoke tubes, . . ; . 205 Eetarders in smoke tubes, . 206 Comparison of Scotch and water tube boilers, 206 Internally fired marine boilers, 206 Scotch ,, ,, 206 Gunboat ,, 207 Externally fired boilers. Water tube type, Table of weights of different marine boilers, Belleville water tube boiler, Babcock and Wilcox , , Niclausse , , Normajid , , Thorny croft ,, Yarrow , , Various ,, Number of boilers in steamships. Locomotive boilers for marine work' „ onra _ . Statistics of locomotive boilers, Locomotive trials on a French railway, . 207 208 208 209 210 210 210 211 211 211 212 212 213 218 Need of coal testing stations, Difficulties, . Advantages, English trials, Wigan trials. Foreign trials. Dantzig, CHAPTER XII. FUEL TESTING STATIONS. 214 \ Brieg trials, .... 214 ' Munich trials, . 215 i Bunte's results, . 215 i German Imperial Navy trials, 215 ' Belgian trials, . . . 216 Donkin and Kennedy experiments. 216 216 218 219 220 220 CHAPTER XIII. DISCUSSION OF THE TRIALS AND CONCLUSIONS. Table of efficiencies. Discussion, Variations in boiler efficiency with different rates of evaporation, Graphic diagram of , , , , , , 221 222 223 Saiivage on efficiency, 224 Barrus ,, .,• 225 Loss of heat due to different amounts of COj, . 226 Illustrative diagram . 226 CONTENTS. Xlll CHAPTER XIV. ON THE CHOICE OF A BOILER, AND TESTING OF LAND, MARINE, AND LOCOMOTIVE BOILERS. Choosing a boiler. Heating surface required. Notes for making boiler tests, Coal, Fires, Gases, Smoke, . Feed water. Instruments required, . Blank sheets for use in land boiler trials, I'AGE 227 Weekly return of fuel and water, PAGE . 232 . 227 Example of results of a trial. 233 229 American rules for land boiler trials, . 235 229 Preliminary regulations, 235 . 230 Blank report for a trial. 240 . 230 Explanatory details, 242 230 Locomotive boiler trials. 244 230 Preparations and instructions, 245 . 230 Blank sheets of data and results, 246 . 231 APPENDICES. Appendix I. On the cost of generating steam in factories, .... . 249 ' , , II. Table and formulae from Hudson's article on the transmission of heat, . . 252 , , III. "Warm blast steam boiler furnace. By J. C. Hoadley, . . . . . .254 , , IV. List of boilers at the Hydraulic Power Company's and the Electric Lighting Company's Stations, London, .... . . . 256 , , V. Notes on the De Laval water tube steam boiler, . . . 257 , , VI. Spenoe's experiments on the colour of flames, 257 , VII. Heating surfaces of Cornish and Lancashire boilers, . 259 , , VIII. Paris smoke trials, with tables, . . . .260 BlBLlOGEAPHY, 269 Plates of Steam Boilers — Land, marine, and locomotive, illustrating — a, progress made during the present century ; 5, best modern practice. Index, .... .',■■''.■■ 272-303 305 LIST OF ILLUSTRATIOIfS. Frontispiece — The Behevillb Boiler, Water tube. Marine type. No. OF Fig. rig. 1. Plain Cornish boiler, . 2. Cornish boiler with return smoke tubes, 3. Cornish boiler with smoke tubes, 4. Cornish boiler with short smoke tubes, 5. Cornish boiler with small smoke tubes, 6. Lancashire boiler, 7. Lancashire boiler with short smoke tubes, 8. Lancashire boiler with three furnace tubes, 9. Dry back boiler, 10. Wet back boiler, lOas. ,, ,, ,, double, 11. Lancashire boiler — Spenoe's experiments, llffl. \ ,, ■ > Plotted results of Spence's experiments, Ud. ) 12. Locomotive boiler, 13. Two-storey boiler 14. Cornish below, . ,, ,, ,, ,, smoke tubes above. ,, ,, ,, ,, cylindrical above, Two-storey boiler. Lancashire below, ,, „ ,, ,, smoke tubes above. Plain cylindrical boiler, .... 19. Cylindrical boiler with return smoke tubes, 20. Lancashire boiler with external grate, 21. Elephant boiler, one " bouilleur, " ,, ,, two " bouilleurs," ,, ,, three "bouilleurs," ,, ,, with smoke tubes. Two-storey boiler, externally fired, , , with smoke tubes, ,, two water lines, Babcook and Wilcox water tube boiler, 29. Stirling boiler, 30. Thornycroft boiler, 31. Belleville boiler, 32. Yarrow boiler, 33. Vertical boiler with cylindrical shell, 34. ,, ,, with water tubes, 35. ,, ,, with vertical smoke tubes, 36. Experiments on locomotive boiler, 37. Transmission of heat through boiler plates, 38. 39. 15. 16. 17. 18. 22. 23. 24. 25. 26. 27. 28. PAGE 2 2 2 2 3 3 4 4 5 5 5 6 8 . . 8 9 9 9 9 9 10 10 10 10 10 11 11 11 12 12 13 13 13 14 14 14 15 . 143 . 144 . 144 . 144 LIST OF ILLUSTRATIONS. XV No. OP f 10. Kg. 40.Bleohyndeii experimental boiler, 4jl.Bleehynden experiments, Plate A. 1*187" 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 0'75" 0'562" „ 0-25" 1 " Plate B. 0-468" ,, 0-375" 0-156' 0-812" 4" 1-187" 0-187" thick, Plate C. „ D. ,, E. 53. Durston's experiments, No. 1 54. „ E6. „ 56. „ 57. Durston's Expts. 58. „ „ ^.^ ,, „ Fall of temperature of gases, Hirsch experimental boiler. No. 2, No. 5, No. 6, Small experimental boiler used in No. 9. 59. 60. 61. Drawing of smoke tubes. 62. Hirsch's experiments plotted, . 63. Wright's feed water heater, 64. Smoke diagram. Wegener powdered coal firing, 65. Smoke diagram. Ringelmaun. No. 0, 66. „ „ ,, No. 1, 67. „ ,, ,, No. 2, ' 68. „ „ „ No. 3, 69. ,, ,, ,, No. 4, 70. „ „ „ _ No. 5, 71. Waller's gas sampling and analysing apparatus, 72. U-water gauge, 73. Fuel calorimeter, 74. Peabody steam calorimeter, .... 75. Serve smoke tubes, . . . . 76. Babcook and Wilcox marine boiler, .... 77. Graphic diagram of boiler efficiencies for different rates of evaporation, 78. , , , , of loss of heat due to varying amounts of CO2, 79. Hoadley's experiments with hot air for combustion, 80. Old stationary boiler, 1775 (Smeaton), ) „ , 81. Modern Lancashire boiler— Two internal fires ) ^° ^^™^ ^^^^' 82. Boilers of steamship " Luoania " "I ™ , 83. Old marine boiler, 1820 j-lo same scale, . 84. Great Western Kail way. Modern express locomotive \ m 1 85. Old locomotive, 1825 (Stockton and Darlington Railway) /■^° ^^™ ^''*'®' 86. Steamship " Lucania," general view \,^ , 87. Margate Steam Yacht, 1815 '/ ^° ^*™^ '^°*^^' 88. Three flue marine boiler with smoke tubes, modem, 89. „ „ ,, ,, back to back type, ,, 90. Howden's method of heating air for combustion by hot gases, 91. Belleville water tube boiler — modern, y^. ,, ,, J J ,, 93. Watt stationary boiler, 1788, 94. Newcomen stationary boiler, 1772, 95. Old stationary boiler, 1750, . . . . 96. Old locomotive boiler, 1815, . ... 97. Lancashire boiler, showing dirt, soot, etc., as in an actual boiler, 98. ,, ,1 ,, ,, cross section, 99. Cornish boiler with smoke tubes, cross section (modern), 100. „ ., 1) ,, longitudinal section (modern), 101. Lancashire boiler (modern), cross section, 102. ,, I) >i longitudinal section, 103. Longitudinal and cross section of Cornish boiler. Special type. FAOG 146 147 147 148 148 149 • . 149 150 150 . 151 151 . 152 . 152 . 154 155 155 156 . 157 157 158 158 159 159 . 168 . 181 To face page 184 189 193 196 198 205 209 223 225 255 272 273 274 275 276 276 276 277 277 278 278 278 278 279 279 280 280 280 280 281 XVI HEAT EFFICIENCY OF STEAM BOILERS. No. OF Fig. page Fig. 104. Cross section, Cornish boiler, . . .... 281 105. Dry back boiler with two furnaces and smoke tubes, . . 281 106. Cornish boiler with Ferret grate, longitudinal section, . . . 282 107. ,, „ ,, „ cross section, . . . 282 108. Lancashire boiler, three flue. General view, external, . . 283 109. ,, ,, two flue. „ ,, „ ■ . 284 110. Lancashire boiler, front view and section, showing brick setting, . . 285 111. Dry back boiler, two farnace tubes and smoke tubes, 286 112. Vertical boiler with smoke tubes, elevation, . . 287 113. ,, ,, ,, ,, section, . 287 114. Vertical boiler with water tubes, section, . . 287 115. Vertical boiler with large water tubes, . . 288 116. „ ,, ,, . . 288 117. Vertical boiler with inclined water tubes, 288 118. „ „ ,, 288 119. Two-storey boiler, longitudinal section, 289 120. ,, ,, cross section, . . 289 121. Thornycroft water tube boiler, external view, . . . 290 122. ,, ,, ,, showing tubes, . 290 123. ,, ,, ,, general view, . 290 124 Yarrow small water tube boiler, . . 291 125. Serpollet water tube boiler (two views), 291 126. Climax small water tube boiler I ,, . ^ o, [ three views, 292 i^i- ,, ,, ,, ) 128. Water tube boiler, . . . 293 129. Cross section of water tube boOer, . 293 130. Normand small water tube boiler, . . 293 131. Clarke Chapman small water tube boiler, 294 132. Hornsby large water tube boiler, . . 294 133. Babcock and Wilcox large water tube boiler, 295 134. Haythorn's small ,, ,, . 296 135. Vicars' stoker, cross section, . . 297 136. Hodgkinson's stoker, elevation, . . . 297 137. Vicars' stoker, general view with several boilers, . . 298 138. „ ,, elevation, . . 299 139. Green's economiser, elevation, 300 140. ,, ,, plan, . . -300 141. Small feed water heater, copper coil, . . 301 142. I I ^. /< Examples of joints between furnace tubes and front plates V . . 301 145; ( j 146. Feed water heater, small tubes. Two views, . . . 302 147. 1 ) 148. -j Examples of corrugated furnace tubes for internally fired boilers \ . 303 149. I J *^* In each of the Tables of Tests a small drawing of the boiler used is given, but not numbered. STEAM BOILERS AND THEIR HEAT EFFICIENCY. CHAPTEE I. Classification of Different Types of Boilers. Internally Fired Boilers — Cornish, five types — Lancashire, three types — Dry Back — Wet Back or Marine — Lanca- shire, Spence's Experiments — Locomotive— Two-storey, five types — Externally Fired Boilers — Cylindrical — Lancashire — Elephant, four types — Two-storey — Water tube — Babcock and Wilcox — Stirling — Thornycroft — Belleville — Yarrow — Vertical Boilers. Steam boilers may be divided into three classes, according to the uses to which they are applied, namely : — 1. Stationary boilers for mills or factories, having generally a fixed chimney. 2. Boilers having an iron chimney, which are semi-portable and often in motion while at work, such as marine and locomotives. 3. Boilers forming an intermediate class be- tween the two former, which are gener- ally at rest while working, but portable on wheels, with a short iron chimney. This type includes the large agricultural class, steam rollers and traction engines, road carriages, fire engines, tramways, etc. The boilers treated in this book are classified into two main divisions: I. Internally fired, the grates or furnaces being placed inside the boiler and surrounded by water ; and II. Exter- nally fired, or those having their fires external to the water of the boiler, and the grate and furnace underneath, or at the front. In both these two classes stoking may be carried on either by hand or automatically, by means of mechanical stokers, and natural, forced, or in- duced draught may be used. Different Types. — In the following pages drawings and descriptions are given of five dif- ferent types of Cornish boilers, both with and without smoke tubes, three kinds of Lancashire boilers, the dry back, wet back or marine type, locomotive and agricultural, running or fixed, and four types of two-storey boilers. All these are internally fired. Of externally fired boilers the following are described with drawings : — Several types of water tube boilers, three types of elephant boilers, two-storey cylindrical with smoke tubes, and various kinds of vertical boilers. DIVISION I. INTERNALLY fired boilers may be again sub-divided into the following types : — li Cornish boilers, so caUed because they were first made in Cornwall, and are still much used there. They are distinguished by having HEAT EFFICIENCY OF STEAM BOILERS. Fier. 1. only one furnace tube, one grate, and no smoke tubes. An example of this type is shown in fig. 1. It has generally a brick-work casing, three horizontal brick flues, and a horizontal cylindrical boiler shell, with a single furnace tube wholly surrounded by water, and carried the whole length of the boiler. The hot gases pass first direct through the furnace tube to the back of the boiler, then return to the front along the bottom of the cylindrical shell, and divide into two streams on both sides, being thus carried horizontally three times the length of the boiler, from the grate to the chimney. As an alter- nate arrangement, the gases after leaving the furnace tube are sometimes directed first through the two side flues and then along the bottom of the boiler to the chimney. This type is without any smoke tubes, but has often a few conical water tubes, and sometimes a corrugated furnace tube. Twenty-five experiments on it with coal or gas coke and chimney draught will be found on pages 21 to 25. In these experiments the boiler efficiency, without economisers, varies from 53% to 81|%. The best results were obtained with an evaporation of from 2J to 3 lbs. per square foot of heating surface per hour, and with 10 to 20 lbs. of coal burnt per square foot of grate per hour. The highest efficiencies were produced when evaporating 3 lbs. of water per square foot of heating surface per hour. Three experiments, all with chimney draught, are added on page 25, with Cornish externally fired boilers, which should have been placed among the second series of trials. The boiler efficiency in them was from 60% to 66%. With the latter 2j lbs. water were evaporated per square foot of heating surface per hour. 2. Cornish boiler with return smoke tubes (fig. 2). — This boUer generally has external brick flues and a cylindrical shell. The iron furnace tube is carried the whole length of the boiler, and the grate is placed inside it. The tube is not in the centre of the shell, and space is left on one side for a series of smoke tubes running parallel with it from end to end, as shown. Fig. 2. The direction of the hot gases is first through the fiirnaee tubej back through all the smoke tubes, returning either through the bottom or side brick flues to chimney. Xo experiments on this type of boiler are given in the Tables. 3. Cornish boiler with cylindrical shell (fig. 3), central furnace tube, and smoke tubes. — The furnace tube is carried only partly Fig. 3. through the boiler, and a set of short smoke tiibes are placed between it and the back, as shown. A second set surrounding the furnace tube run the whole length of the boiler. The direction of gases is through the furnace tube and short smoke tubes, then through the long smoke ' tubes to the front, and so through the external brick flues to the chimney. No experi- ments on this type will be found in the Tables. 4. Cornish boiler (fig. 4), with one set of short smoke tubes at the end of the furnace tube. This boiler is somewhat similar to the last, with external brick flues, cylindrical shell, — _ "'^^^^^ —■-^iap^ Fig. 4. and central furnace tube. The latter is carried about half way through the shell, as shown, and the passage of the gases continued in the short smoke tubes to the end of the boiler. The direction of gases is through the furnace and smoke tubes, they then pass two or three times along the external brick flues to the chimney. Five experiments will be found on page 27 on this type of boiler with chimney draught, at different rates of coal burnt per square foot of grate, and evaporation per square foot of heating surface per hour. The boiler efficiencies without economisers vary from 55% to 76%. The best COENISH AND LANCASHIRE BOILEES. Fig. 5. results seem to have been obtained with about 2 lbs. of water evaporated per square foot of heat- ing surface per hour, and very inferior results with ^ lb. per square foot. All these varieties of Cornish boilers with internal grates, with and without smoke tubes, are common both here and on the Continent, and are chiefly used for stationary purposes. 5. Cornish boiler with smoke tubes (fig. 5). — This type has also a cylindrical shell similar _ to the last. Here the furnace tube is placed centrally to the horizontal shell, and carried right through, with a series of small smoke tubes running along both sides of it, the whole length of the boiler, as shown. The direc- tion of gases is first through the furnace tube, then through the smoke tubes, and round through the external brick-work flues to the chimney as before. Four experiments are given on page 27 on this boiler, with efiiciencies from 66% to 81%. With the latter 2 lbs. of water were evaporated per square foot of heating surface per hour, with chimney draught and no economiser. 6. Lancashire boiler (fig. 6). — The difi'erence between this type and the Cornish is that it has two furnace tubes, and two internal grates in- stead of one. It is a favourite boiler in Lanca- shire, whence its name, and is much used in mills, factories, and other large industrial works. It has a horizontal cylindrical shell and furnace tubes set in brick-work with external brick flues. The furnace tubes are plain or corrugated, and are carried right through the boiler. The direction of the gases varies somewhat, but is generally as follows : — Through each furnace tube, then under bottom brick flue to the front of the boiler, where they divide and pass through the two side flues to chimney. Sometimes after leaving the furnace tubes the gases are carried first through the two side flues, then unite and pass along the bottom flue to chimney. This boiler is very largely used in England for stationary purposes, and a good deal in Germany and Austria. The furnace tube is often provided with cross GaUo- Tlfr. 6. way conical water tubes. In this type there are no smoke tubes. The numerous experiments on this boiler on pages 29 to 59 are divided into machine and hand stoking trials. Tests with machine firing or mechanical stokers. — Forty-two experiments are given on pages 29 to 35, with and without economisers, and chiefl.y with chimney draught. About seven or eight difierent types of machine firing were used, with different rates of coal burnt per square foot of grate surface, and of evaporation per square foot of heating surface per hour. Most of these experiments were made in England. The boiler efiiciencies, with different conditions of soot or deposit, varied much, from 52% to 74% without economisers. The gain in efficiency with the latter varied from 6% to 15%, accord- ing to their area, condition, dirty or clean, and other circumstances. The total efficiencies of boiler and economiser together varied from 62% to 87%. The best results with economisers were obtained when evaporating from 4 to 5^ lbs. of water per square foot of heating surface per hour. The maximum lbs. of coal burnt per square foot of grate per hour was 56 lbs., and the minimum 9 lbs. with small economisers. Tests with hand stoking. — A hundred and fourteen experiments are given on pages 37 to 57, both with and without economisers, and chiefly with chimney draught. Most of them were made in England, but some on the Continent. The rates of firing, evaporation, and boiler efficiency vary much, as might be expected, owing to the great variety of fuels, grates, draughts, stokers, temperature of gases, excess of air in gases, quantity of soot and deposit, and other working conditions. It is difficult to summarise such a large number of experiments. "Without economisers the best results seem to be with 3 to 4-| lbs. of water evaporated per square foot of heating surf ace per hour, and 70% to 77% boiler efficiency ; with economisers the best results are 4 to 51- lbs. of water per square foot of heating surface per hour, and an efficiency of 83%. From 6% to 12% may be added for the efficiency of the economisers alone, according to their area, etc. Dusseldorf Exhibition experiments (1880). — These, given on page 55, furnish an interest- ing set of sixteen experiments, all on the same Lancashire boiler, with the same stoker and HEAT EFFICIENCY OF STEAM BOILERS. steam pressure, but witliout economiser, and burning eight different kinds of coal. Taking the set of eight experiments with cast-iron grate bars only, the efficiencies varied from 56J% to 69%, the water evaporated per square foot of heating surface per hour ranged from 4 to 4 "8 lbs., the latter giving about the best results. The coal was of good heating value. The excess of air at the end of the furnace tube and at the damper is not given, but the difference in excess of air at these two places, beyond that theoretically required for combustion, is shown, and proved that there was air leakage through the brick- work. These experiments are arranged in order of boiler efficiency. They were very carefully carried out, and the author was fortunate enough to witness some of them. Prussian Smoke Commission. — Eight experi- ments will be found on page 53 on the same Lancashire boiler, without economiser, made by very competent German engineers, under the auspices of the Prussian Smoke Commission. Also another set of three experiments on another Lancashire boiler. In the latter the maximum boiler efficiency was 80% without economiser, with an evaporation of 4^ lbs. water per square foot of heatiag surface, and 24 lbs. fuel per square foot of grate surface per hour. In these good experi- ments the gases were carefully analysed in two different places, at the end both of the furnace tube and of the boiler flues, and the results always show leakage of air through the brick- work, although care was taken to prevent any infiltration. 7. Lancashire boiler with short smoke tubes (fig. 7).^ — -This type has a cylindrical shell and two furnace tubes, with internal grates like the last. The furnace tubes, however, are not carried to the end of the boiler, but are followed by _ ■ -^ — — -K^ :M ^^^= Fig. 7. smoke tubes, as shown. The gases pass through the furnace and smoke tubes, then through the different external brick flues, as before, to the chimney. This boiler is used both in England and on the Continent. Ten experiments on it will be found at page 59, all made without an economiser, by skilful engineers, and supervised by the Vienna Boiler Association. The boiler efficiency varied from 65|% to 74^%. The best results were obtained with an evaporation of 2 lbs. water per square foot of- heating surface per hour. The temperature of the smoke gases was low, but the percentage excess of air was considerable, even with chimney draught, showing that a better result might have been obtained. 8. Lancashire boiler with three furnace tubes and three internal grates (fig. 8). — This type has been introduced of late years, and has met with some success. There is an outer cylindrical shell set in brick-work, which com- pletely surrounds the three cylindrical furnace tubes. The hot gases pass to the chimney in the same direction as in No. 6, the only difference being that there are three furnace tubes instead of two. With this type more priming water is found in the steam than when two furnace tubes are used. On page 61 six experi- ments on this type, all with economisers, will be found. Different rates of firing are used, from 15 lbs. to 30 lbs. coal being burnt per square foot of grate per hour. From 5 to 6 lbs. water were evaporated per square foot of heating surface per hour. The total efficiency of boiler and economiser varied from 61% to 73f%. All the above boilers, Nos. 1 to 8, are nearly always used on land, in mills, etc., or for stationary purposes. They are always set in brick-work, with fixed chimneys. 9. Dry back boiler (fig. 9). — This boiler has been much used in England during the last few years in electric light stations, factories, etc.,. and is similar to the marine boiler next described.. It has two furnace tubes below, like a Lancashire boiler, and a horizontal cylindrical shell. In the upper part there is a series of smoke tubes running the whole length. At the back it is cased in brick-work, forming a dry combustion chamber, hence the name given to the boiler.- The direction of gases is back through the two furnace tubes, forward through all the smoke tubes, and either direct or round the- Fig. 8. DRY BACK AND WET BACK BOILERS. boiler shell to the chimney. This boiler is used on land, and is usually set in brick-work. Kve experiments on this type, with chimney draught and hand firing, and without economisers, will be found on page 63.. The water evaporated per square foot of heating surface per hour varied from 3 to 4^ lbs., and 15 J to 21| lbs. of coal were burnt per square foot of grate surface per hour. The boiler eificiency was not high, varying from 55% to 65%. The most economical rate of evaporation with this type is about 3J lbs. water per square foot of heating surface per hour. One experiment on this boUer with mechanical stoking and without an economiser is also given, in which the efficiency was 73^%, but this result was obtained with superheated steam, when evaporating 8^ lbs. of water per square foot of heating surface per hour (see also pages 65 to 71 for Spence's experiments on a boiler of similar type). 10. Wet back or Fig. 10. marine type (fig. 10). — This boiler is similar to No. 9, having two Lancashire furnace tubes below, and smoke tubes above, but^they do not run the whole length of the boiler, a water heat- ing surface being left at the back, hence the name of wet back. The direction of gases is through the furnace tubes, then forward through the small smoke tubes, and thence to chimney. This type is much used at sea, and sometimes for stationary purposes. Pig. 10a shows two of these boilers, each with three furnace tubes, arranged back to back for steam-ships, forming one boUer with six grates and six firing doors. Six experiments are given on page 73, five made at sea and one on land. All are with hand firing, some with forced, some with chimney draught, none with economisers. The boiler efficiency varied from 62% to 70%, and the water evaporated per square foot of heating surface from 2f to 9f lbs. per hour. Combustion was fairly good, some- times as much as 13% of COg by volume being obtained from the analysis of the gases. The coal burnt per square foot of grate per hour varied from 19 to 31 lbs. The best result at sea was with an evaporation of 2"7 lbs. per square foot. Unfortunately very few experiments have been or are made on boilers at sea. The measurement of the hot feed water from the surface condenser is rather troublesome in very confined and warm engine-rooms. It is also a somewhat tedious operation to weigh the coal in baskets by a spring balance, in all the dust and dirt between the coal bunkers and the stoke hole floor, opposite the hot boiler furnaces, especially if the weather is rough. The analysis of gases and taking the temperatures of the funnel gases in rain, wind, and snow, on deck, next the hot chimney, is also not agreeable, but there is no real diificulty. Care and attention are necessary, and the conditions of work in very warm spaces cannot be called pleasant. As one of the members of the committee, the author was present at most of the marine trials arranged by the Institu- tion of Mechanical Engin- eers, and speaks from personal experience. 11. Lancashire boiler with two internal furnace tubes ending in a series of short smoke tubes, forming a con- tinuation (fig. 11), is similar to No. 7. The G HEAT EFFICIENCY OF STEAM BOILERS. gases pass in this case direct from the fires through the smoke tubes, up the chimney. Although it resembles the dry back type, it is occasionally used in ship-yards. On pages 65 to 71 will be found twenty -seven interesting experiments made by Mr Spence at Newcastle, ^=?— ^- "^SE^ — ^5"^ "=^:=^ =. -- j^-j rig. 11. all on the same boiler of this type, stoked by hand, with the same coal and steam pressure, but without economisers or brick flues. Chimney draught in some experiments, and forced draught in others were used, and the air for com- bustion was introduced sometimes cold, some- times heated. The quantity of air admitted was greatly and purposely varied, to get the minimum of smoke and the maximum boiler efficiency. Unfortunately the gases were not analysed, which is much to be regretted. The eleven experiments on page 65 were made with chimney draught and air at atmospheric pressure. The boiler efiiciency varied from a minimum of 65% to a maximum of 73%. The water evaporated per square foot of heating surface per hour did not vary much, viz., from 5 J to 6 lbs. The coal burnt per square foot of grate per hour varied from 17 to 19 lbs. The gases of combustion in all Mr Spence's experi- ments escaped at too high a temperature to give the best results. Accuracy, not economy, was the object aimed at. The five experiments on page 67 were made with forced air supply at atmospheric tempera- ture. The boiler eflSciency varied from 64f% to 67f % ; the water evaporated per square foot of heating surface per hour varied from 5 '4: lbs. to 8 '8 lbs. The best result was obtained with an evaporation of 6| lbs. From 30 to 43 lbs. of coal were burnt per square foot of grate per hour. In the eight experiments on page 69, with forced air supply at atmospheric temperature, the boiler efficiency varied from 66 to 75f%. The water evaporated per square foot of heating surface per hour varied from 5 J to 7 lbs. ; the coal burnt per square foot of grate per hour from 31 J to 47^ lbs. Three experiments are given at page 71 with forced air supply heated to a tem- perature of 242° F. to 261° F. Here the boiler efficiency varied from 75^% to 78|% ; the water evaporated from 5| to 6 lbs. . per square foot of heating surface per hour, the coal burnt per square foot of grate per hour from 30 to 40 lbs. Of all these experiments No. 27, with forced supply of warm air, gave the best results. The ' boiler efficiency reached 78^-%. Five and a half lbs. of water were evaporated per square foot of heating surface per hour, and 20 lbs. of coal burnt per square foot of grate surface per hour. Even here, however, the gases escaped at 362° F. above the temperature of the steam, and had this differ- ence in temperature been reduced, the results would have been still better. On page 71 will be found a summary of the four best experiments, that is, the experiment giving the highest boiler efficiency in each of the four sets. Figs. 11a, 11&, lie, lid show the results plotted for all the experiments. The ordinates represent the numbers of the trials, the abscissae the results, namely, lbs. of coal per square foot of grate per hour, lbs. of water per lb. of coal from and at 212°, lbs. of air per lb. of coal, and boiler efficiency. The value of these experiments would have been greatly enhanced had the gases been analysed. 12. Locomotive and agrictiltural boilers (fig. 12). — This old and simple but efficient type . is extensively used in all countries on railways, and for all agricultural purposes, and portable applications. It consists of a cylindrical shell, an internal grate with rectangular fire box and combustion chamber, and a nest of smoke tubes running nearly the whole length of the boiler, and ending in the smoke box at the foot of the short iron chimney. The gases pass direct to the smoke tubes, and through them up the chimney. Although these boilers are chiefly portable, they are sometimes used at sea for torpedo boats and small sliips, and also on land. They are usually mounted on wheels, and there are no brick flues or settings. With this type in- duced draught is produced by the exhaust steam sent from the cylinders up the chimney. Experi- ments on this class of boiler under normal work- ing conditions, that is, while running, are rather rare, and only a few good trials are available. To sample the gases and take the temperatures from a smoke box in front of a locomotive going SPENCE'S EXPERIMENTS. hi SI Lbs. oF Air per lb. of Coal. ^ , 9° ? ^ e,s,7 Lbs. of Coal pef Six. Ft of Crafe per hour. ' ■'. i^' ' I — ' if ' — '"'' — ' J. ' — I — I ' fe ' Lbs. of Water per lb. of Coal from i at 212. Si Lbs. of Wat.er per /t>. of Coal from and at 212 . 1,2.3 § to if Dl 9 Lbs. of Air per lb. of coat Boil S:£ffielep Lbs.ofcoel perStfFtof'Srate per^ hour. Lbs. of Water pcr/b. of coal frfm and af 3 to Ss 2/2 : ■-I'S'S-C'M ED CD S ^ Q 31% rt (B ri cgi^ A6s o/* Ws/ci" per lb. of Coal from & af 2/2.' 8 HEAT EFFICIENCY OF STEAM BOILERS. Fig. 12. at fifty to sixty miles an hour is not easy or agreeable, and is seldom done. Forty-six experiments on the locomotive type of boiler will be found on pages 75 to 83 ; thirty-five are on stationary or semi-portable, and eleven on locomotive boilers running on rails, at page 83. With stationary, semi-fixed boilers feed water heaters are sometimes used, but not economisers. Pages 75, 77, and 81 give the boiler efficiency of twenty-six stationary boilers. In nearly all of them it is high, varying from 53-7% to 81-J%, although there was no doubt some prim- . ing. The water per square foot of heat- ing surface per hour ranges from 1 1- to 8^ lbs. ; that evaporated per lb. of coal from and at 212° is often 11 lbs., sometimes higher with good coal, but the best efficiencies are obtained when the evaporation is from 2 to 6 lbs. of water per square foot of heating surface per hour. Page 79 gives an interesting set of experiments very carefully carried out at Newcastle, by the Royal AgriculturalSociety's well- knownengineers, on nine different sizes of stationary agricultural boilers, none of them large, and all worked with induced draught. No feed water heaters were used. All the experiments were made with the same coal, but with different stokers. The boiler efficiencies varied from 59% to 84% even under very similar conditions. The water evaporated per lb. of same coal, from and at 212° F., varied from 10 lbs. to 13 lbs. ; the lbs. of water per square foot of heating surface per hour from 1| to 5 J, the latter giving the minimum efficiency ; the best was obtained when not more than 1^ to 2 lbs. of water were evaporated per square foot of heating surface per hour. From 9|- to 30 lbs. of coal were burnt per square foot of grate per hour. The maximum quantity of CO2 in the gases was 15f % by volume. For these boilers, all nominally of 8 HP., the various makers supplied very different heating surfaces, and it seemed as if they had been constructed without a sufficient number of preliminary tests, to .determine the best proportions for obtaining the highest results. It is from systematic and accurate trials of this kind that a great deal can be learnt, and much exact information obtained. At page 83, where eleven experiments on three running locomotives are given, the boiler efficiency varied between 66% and 82%. Un- fortunately, few accurate experiments on running locomotives, in which the water was carefully measured, have been published, nor is it an easy task to carry out such trials. The best results seem to be with an evaporation of 5 to 7 lbs. of water per square foot of heating surface per hour. With 8 or 9 lbs. evaporated, the results are lower. The water per lb. of coal from and at 212° varied from 9^ to 12| lbs., but doubtless the boilers primed a little. 13. Two-storey boiler (fig. 13), Cornish, with short smoke tubes and a plain cylinder above. — In this type the lower boiler has a l-T^ -fcJ- J^m ^ ^S '— ' -i Fig. 13. single furnace tube and short smoke tubes beyond, as shown. The direction of gases is through the furnace and smoke tubes, returning round the external brick flues to the chimney. Four experiments will be found at page 85 on a boiler of this class, with economiser, machine fired, with two kinds of coal. Excluding the economiser, the boiler efficiency varied from 64% to 75%, the latter result being obtained with an evaporation of 6 lbs. of water per square foot of heating surface per hour. The efficiency of the boiler and economiser taken together varied from 72J% to 86|%. The lbs. of water evaporated per lb. of coal were from 8^ to llf lbs. Combustion was good, and in one case the CO2 was 12% in the gases ; their temperature was very low. This type is a good deal used on the Continent and also in England. Another trial, page 89, No. 19, was made at Dusseldorf on this type of boiler in which the efficiency was 56%, and 3 lbs. water were evaporated per square foot of heating surface per hour. The analysis, of the gases showed a large excess of air. For want of a better name the author has classified this and the four following boilers as TWO-STOREY AND EXTERNALLY FIRED CYLINDRICAL BOILERS. 9 the two-storey type. They form, in fact, two boilers, one above the other, joined together, and both producing steam. Sometimes the two are alike in shape and diameter, sometimes dis- similar. They are more used abroad than in this country, and always for stationary purposes, with a fixed chimney. They give good efficiencies generally, although there is a large external brick-work surface for radiation. The tempera- ture of the escaping gases is generally low. 14. Two-storey boiler, Cornish below, with smoke tubes above (fig. 14). — Here the upper boiler is provided with smoke tubes along its whole length. The direc- tion of gases is through the furnace tube, then through the smoke tubes, and generally outside both cylindri- cal shells to the chimney. A trial on this boiler, hand fired with brown coal, and without econo- miser, will be found at page 87, No. 12. The boiler efficiency was 68%, with an evaporation of 3 lbs. water per square foot of heating surface per hour, and 35 lbs. of coal were burnt per square foot of grate per hour. Considering the poor quality of the coal used, this is a good result. 15. Two-storey boiler (fig. 15), Cornish below and plain cylindrical above. — In this type the lower boiler is Cornish with a single furnace tube and shell, and a plain cylindrical boiler above, without smoke tubes. The boiler is surrounded with brick flues, giving considerable radiating surface. The direction of gases is usually through the one furnace tube, and round the outside brick flues surrounding them, but it is often varied in dififerent There are no experiments on this type Tables. Two-storey boiler, Lancashire below, tubes above, with one water line (flg. 1 6). This boiler has two cylinders, one above the other, of equal diameter, the lower one con- taining two Lancashire furnace tubes, the upper a series of smoke tubes. The direction of the gases is first through the furnace tubes, returning through the smoke tubes of the upper boiler and then generally round the external brick flues of both shells to chimney. Three experiments on this boiler will be found at page 85, seven on ways, in the 16. £moke Fig. 16. page 87, Nos. 9 and 13 to 18, and several on page 89, both hand and machine fired. Most of them were made abroad with different kinds of grates, and no economisers were used. The boiler efiiciency was generally high, rang- ing from 61 to 81%. With the latter only 2 lbs. water per square foot of heating surface per hour were evaporated. The lbs. fuel burnt per square foot of grate varied from 13 to 31 lbs. 17. Two-storey Lancashire boiler with smoke tubes above (fig. 17). — Similar to the last, the only difference being that there are two water lines instead of one. Two experiments on this type will be found at page 85, Nos. 5 and 6, made by the Vienna Boiler Association. The efficiencies varied from 70 to 71^%, and the evapora- tion per square foot of heating surface per hour was about 2 lbs. water in both the experiments. Another trial wUl be found on page 89, and two on page 87, all without economisers. Fig. 17. DIVISION II. EXTEENALLY FIRED BOILERS.— In this second division the grate is always external to the boiler itself, and placed sometimes below, some- times at the end of the cylindrical shell contain- ing the water. 18. Plain cylindrical or egg-ended boiler (fig. 18). — This is the simplest type, and lias a horizontal cylindrical shell, without either smoke or water tubes, under which the grate is fixed. An outer brick casing incloses the grate and boiler. The ends are generally hemispherical, and hence the name egg-ended. The direction of gases is through the furnace chamber under the boiler, then through the brick flues, round the external part of the surface to the chimney. This is an old type, and is only employed on land for stationary purposes. It is generally set in brick-work with a fixed chimney, and is often used in collieries. It is Fig. 18. 10 HEAT EFFICIENCY OF STEAM BOILERS. Kg. 19. not very economical, and is only suitable for low pressures; no good experiments on it have been found. Colliery owners pay little attention to their boilers. Tests are hardly ever made, and there is often much waste of heat. 19. Cylindrical boiler (fig. 19), with return smoke tubes carried through the water the whole length of the boiler, as shown. This is a favourite type in the United States, where it is largely used, and considered to be very economical, an opinion which seems to be borne out by the tests. It is a cheap boiler to make, but is little used in England. The direction of gases is from the grate along the bottom of the boiler, returning through all the smoke tubes to the chimney. Sometimes the gases also pass round the outside shell. The boiler is used on land for stationary purposes, with a fixed chimney and natural or forced draught, and is usually set in brick-work, and often worked with an econo- miser. The gases escape at a fairly low tempera- ture. Eleven experiments on this boiler are given at page 91, with heating surfaces varying from 330 to 1700 square feet. The diameter of the smoke tubes was 3 in., 4 in., 4^ in., 6 in., and 10 in. respectively, the boiler efficiency varied from 56|^% to 81%. The temperature of the exit gases was rather low. From 2 to 9 lbs. of water were evaporated per square foot of heating surface per hour. The best efficiency was obtained with an evaporation of 2 to 3h lbs. of water. The coal burnt per square foot of grate per hour was from 10 to 43f lbs. Several tests were made with the Hawley down draught furnace, consist- ing of two grates, one above the other. This ingenious arrangement seems to give practically no smoke, but requires a good draught. 20. Lancashire boiler with external grate (fig. 20). — This boiler, generally set in brick- work, consists of a oyhndrical shell with two large central smoke tubes and a grate below. The direction of gases is first round the shell, then back through the tubes to the chimney. Many of these boilers are used in Germany, with inclined grates in front, or grates in steps to burn poor coal, such as brown coal, lignite, and also other fuels containing much water. In some experiments there was about 50 to 55% moisture in the coal. Eight experiments on this type, all made in Germany, are given at page 93. The water evaporated per square foot of heating surface per hour varied from 2 to i^ lbs.; the boiler efficiency from 53% to 74%. The latter result was obtained when evaporating 4 lbs. of water per square foot of heating surface per hour. The evapora- tion per lb. of fuel is naturally very low with these coals of small Fig. 20. heating value, and varies from 2J to 5^ lbs. The percentage of COg in the gases is generally very good, with only a small excess of air. 21, 22, 23. Elephant boilers (figs. 21, 22, and 23). — These three types and the following form a class by themselves, much used in France and elsewhere on the Continent. They are called in England "Elephant Boilers," and in France "Chaudieres a Bouilleurs," houilleurs being the name applied in each case to the large lower water tubes. No. 21 has only one bouilleur; No. 22 two; and No. 23 three, arranged beneath the central horizontal cylindrical boiler shell. Fig. 21. Fig. 23. with which they are connected. The external grates are under the houilleurs, and the whole is inclosed in brick flues. The direction of gases is generally first under the houilleurs, then forwards and backwards, below and around the boiler shell, the usual plan being to pass them two or three times along it, before they escape to the chimney. There are no smoke tubes in the three types here considered. They are frequently used in mills and for other stationary purposes with brick setting, fixed chimneys, and natural draught. Economisers are seldom applied, but feed water heaters are very often added on the Continent. These are simply horizontal cylindri- cal tubes, 1 or 1 J feet in diameter, which act as ELEPHANT BOILERS— TWO-STOREY B0ILER8. II economisers, and are placed in the flues; the gases circulate round them after leaving the boiler on their way to the chimney. These boilers are in great favour on the Continent, but hardly used in England. On page 95 will be found ten experiments on this type, with two and three bouiUeurs. The boiler efficiency varies from 55% to 65%, without feed water heaters. With the latter the total efficiency is from 55 to 78%. With the highest efficiency 5 lbs. of water were evaporated per square foot of heating surface per hour. The best results without feed water heaters were obtained with an evaporation of 4 lbs. of water per square foot per hour. Ten to eighteen lbs. of coal were burnt per square foot of grate per hour. This type of boiler, without smoke tubes or economisers, does not seem to give a very good efficiency, and the gases escape at too high a temperature for the best results. 24, Elephant boiler with smoke tubes (fig. 24). — This boiler is similar to those just de- scribed, but is arranged with the external grate below the two bouiUeurs, and a horizontal cylindrical boiler shell above, provided with a large number of small smoke tubes running the whole length of the boiler. The direction of gases is from the grate under the bouiUeurs, returning through the smoke tubes, and outside the boiler shell to the chimney. Feed water heaters are sometimes used, but are not as necessary as in some boilers, as the temperature of the gases is already considerably reduced by the smoke tubes. Set in brick-work, with natural draught and fixed chimney, this boiler is much in request for mill and stationary purposes, especially in France. Eight experiments are given on it at page 97, in which the boiler efficiency without feed water heaters varies from 59 to 70%. With the latter it rises from 61 to 71%. The water evaporated per square foot of heat- ing surface per hour is from 21 to 3| lbs. The coal burnt per square foot of grate per hour varies from 12 to 30 lbs. These four types are practically two-storied boilers of unequal diameter. If the water used is bad, they are rather difficult to clean internally. 25, 26. Two-storey boilers (figs. 25 and 26). — The next two types consist practically of two Fig. 24. boilers, one above the other, connected as shown. They are heated by one external grate placed below. In No. 25 the lower boiler is a plain cylindrical shell, and the upper, of the same diameter, is provided with a large number of smoke tubes running through its whole length. The direction of gases is underneath the bottom shell, through the smoke tubes, and either partly or wholly round both shells to chimney. The arrange- ment in No. 26 is the same, but the lower boiler, although it has a grate underneath it, is shaped hke a Cornish, with one large central smoke tube. The direction of gases is first under the bottom of the lower boiler, then through the large Cornish tube, next through all the smoke tubes, and round the outside of the two shells to the chimney. These two types of two-storey boilers, set in brick-work and worked with natural draught, are used in factories and for stationary jDurposes. Feed water heaters are seldom added, the heat of the gases being almost wholly absorbed by the numerous smoke tubes before they escape to the chimney. The boilers are not often employed in England, but largely on the Con- tinent, where the author has often seen them at work. Nine experiments, all made abroad, are given on page 99. They are all on boilers like fig. 25, with smoke tubes. None on the other type, fig. 26, with Cornish tube below, appear to have been published. Without economisers the boiler efficiency varies from 57 to 79%, and the evaporation per square foot of heating surface per hour from 2 to 4 lbs. of water. An evapora- tion of 2 to 3 lbs. gave the best results. The temperature of the escaping gases was generally too high for the best economy. 27. Two-storey boiler with two water lines (fig. 27). — Like the last two types, this boiler has two cylindrical shells placed one above the other, with an external grate beneath the lower. The peculiarity of this compound type is that it has two distinct water lines, with connections re- spectively between the water and the steam in the two shells, as shown. There are no smoke tubes. The direction of gases is first under the 12 HEAT EFFICIENCY OF STEAM BOILERS. Fig. 27. lower boiler shell, then round the external flues of both shells to the chimney. The boiler is set in brick-work, and. used with natural chimney draught. All two-storied boilers have the dis- advantage of giving a very large area of radiation through the brick-work, particularly when fixed separately. No experiments on this type are given in the Tables. Water tube boilers. — These form a large and important distinct class. Although foreshadowed in the earlier part of the century, they date in their present shape from recent times, and have mostly been designed to meet modern requirements, especially for high steam pressures and rapid evapora- tion. Their distinguishing characteristic is that, instead of the greater part of the water being contained in a large cylindrical shell or shells, it is presented for evaporation in relatively small tubes, horizontal, vertical, inclined, or curved. These tubes are carried round, above, or at the side of the furnace or combustion chamber, and thus a comparatively small body of water is exposed to the heat of com- bustion. There is less circulation to and fro of the hot gases, which simply pass through the combustion chamber and about the tubes in a zig-zag direction to the chimney. A quick and good circulation of water is a great necessity in this class of boilers. In most of them the tubes do not contain water only, but water and steam, and the tendency, when not forced, is for the steam to become dry and even slightly superheated, thus sometimes obstruct- ing the circulation of the water. (See page 207 for further remarks on this subject.) The grates are external, generally with cast-iron fire bars, and stoked by hand. These boilers are mostly used on land, but sometimes at sea ; when forced they are inclined to prime, and to produce wet steam. 28. The Babcock and Wilcox water tube boiler (fig. 28), although originally made in America, is now a good deal used in this country. The horizontal grate is below. The boiler consists of a number of inclined water tubes, generally about 4 in. diameter, con- nected by vertical tubes to the steam drum, a large horizontal cylindrical tube placed above, which receives both the heated water and the steam. Through the vertical tubes at the side a good circulation of water is maintained. The hot gases pass outside the inclined water tubes, first in a vertical direction from the grate, then round the battery of tubes on their way to the chimney, then- course being deflected by a couple of baifles. The tubes contain water, or water and steam. This type of boiler is not suitable for bad water, as the tubes are difficult to clean. It is very largely used in America on land, and is begin- ning to be adopted for rivers and marine work. For land purposes it is always set in brick-work ; at sea it is inclosed in a wrought-iron casing. It is worked with natural, forced, or induced draught, either with or without economisers. Where the latter are used, they are of the same type as the boiler itself, and consist of a series of 4-in. water tubes, with the hot gases led outside them, the feed water passing through them. Separate 4-in. pipes are sometimes added for • superheating the steam by the gases from the fire, and have worked well in many cases, if placed at a proper distance, neither too near nor too far from the furnace. Thirteen experiments on Babcock and Wilcox boilers, with and without economisers, and with chimney and force draught, are given on pages 101 and 103, showing from 50 to 74% boiler efficiency. Eleven of the boilers were fired by hand, mechanical stokers were used with two. The evaporation per square foot of heating surface per hour varied from 2 to 4 lbs. water ; the best results (74% efficiency) were with 2| lbs. evaporated. As long as the temperature of the escaping gases is reduced, it does not much matter whether the heat is withdrawn from them in the boiler, or in the 4-in. tubes of the economiser. The coal burnt per square foot of grate per hour varied from 13 to 47| lbs. Three experiments are also given on page 103 on another water tube boiler, similar to the Babcock. In two of them the boiler efficiency was low, in the third it was 72%. 29. Stirling water tube boiler (fig. 29).— This is another type with small water tubes 1^ to 2 in. in diameter, suitable for high steam pressures. The boiler consists of three steam THORNYCROFT AND BELLEVILLE BOILERS. 13 Fig. 29. drums above and one large water drum below, the external grate being placed at the side near the lower water drum. Three sets of water tubes inclined at slightly different angles lead from the water drum below to the upper steam drums. This boiler was introduced in America, and is more' often used on land with a brick setting than at sea. The gases rise from the grate, are de- flected from the vertical by the brick fire bridges, and pass in a zigzag direction around the numerous tubes to the chimney, their course being regulated by baffles. Any kind of draught, forced, natural, or induced, may be applied. On page 107 two experiments, made in America, are given, in which the boiler efficiency was 74|^ to 76f %. Three lbs. of water were evaporated per square foot of heating surface per hour. The boilers were hand fired, with chimney draught, and no economisers were used. 30. Thornycroft's water tube boiler (fig. 30). — Like the last this boiler has a large number of snaall tubes over the fire, but they are curved, as shown, instead of straight. The tubes are now made of steel, and are f in. diameter for small boilers and l^ in. for large. They start from the cylindrical water drum below, curve outwards so as to expose a considerable portion of their surface to the flames, and are con- nected with the steam drum above, delivering their con- tents of mingled water and steam into it above the water line. The grate in two divisions is placed a Httle below the lowest part of the tubes, and alongside the lower water drum. The direction of gases is vertically upwards through the series of water tubes to the chimney above, passing round the steam drum. This boiler is designed for raising steam quickly and for high pressures, and is used for torpedo and other high speed boats, and also on land. It is inclosed in a wrought-iron casing, no brick- work being used. Force draught is generally applied, but it can also be worked with induced draught. ■ Fig. 30. On page 111 four experiments are given, form- ing an interesting series, all made by Sr Kennedy on the same boiler and with the same coal, but with difierent pressures of air in the stoke hole, and at evaporations varying greatly from 1 J lbs. to 8^ lbs. water per square foot of heating surface per hour. The quantity of coal burnt also differed much, ranging from 8 lbs. to 67 lbs. per square foot of grate per hour. The boiler efficiencies were very good, from 66 to 86f%, the highest being attained with an evaporation of IJ lbs. water per square foot of heating surface and 7f lbs. coal burnt per square foot of grate per hour. The temperature of the escaping gases was very low, only 165° above that of the steam, with 3;^ lbs. water evaporated per square foot of heating surface. These trials, however, were unfortunately of very short duration. 31. BeUeviUe boiler (fig. 31).— This is a foreign type, which has been employed in France for land purposes for many years, and has lately ISSSSSS^ ui«& . Fig. 31. been improved in design, and adapted for marine work. The boiler is now extensively adopted by the French Navy for large ships and for marine purposes generally. The English Admiralty has also during the last few years applied it to many ships in the Navy, and it is now made by several large ship-building firms here, but has not yet been employed in the English mercantile marine. The boiler consists of a large number of steel water tubes, 4 in. diameter, placed zigzag one above the other. The connections between them, which at first caused much difficulty, to insure a proper water circulation, are ingeniously contrived. The tubes are arranged at a very slight inchne ; the grate is placed below, and the steam drum above, as shown. The gases rise vertically through all the water tubes to the chimney above. In most Government ships forced blast is used, but the boiler is suitable to any kind of mechanical or 14 HEAT EFFICIENCY OP STEAM BOILERS. natural draught, and tlie highest pressures of steam can be generated with it. Like most types of water tube boilers the Belleville vnll not work well if the water is very bad, but in marine apphcations the same water is generally used over and over again, and very little or no oil is applied to lubricate the cylinders. On land the boiler is set in brick- work, and at sea in a •double wrought-iron casing with isolating material between. Few experiments on this boiler have been published, as the feed water is seldom measured at sea, but three trials are given at page 113. They were all made on land, though on the marine type of boiler. The efficiency was high, from 75 to 78%. The evaporation was from 5 to 6J lbs. of water per square foot of heating surface, and from 24 to 36 lbs. of coal were burnt per square foot of grate per hour. Doubt- less there was a little priming. Economiser pipes to heat the feed water are often added to these boilers. 32. Yarrow's water tube boiler (No. 32). — This is a type the design of which has only been perfected within the last few years. It consists ■of a large number of small straight steel water tubes, 1 in. or 1^ in. diameter, placed at an angle immediately over the fire, and discharging the steam into a cylindrical drum at the top, and below the water line. There are two collectors at the bottom, forming connection with the steam drum above, so that a good circulation of water is established, which the straight tubes do not obstruct. These form a sort of boundary to the hot gases and flames rising from the grate and passing through them. The direction of gases is vertically upwards between the tubes, and round the steam drum to the chimney. This boiler is especially designed for marine purposes and high pres- sures, and is largely used for torpedo and •other boats, where strength and speed are required. It is not set in brick-work, but is inclosed in a sheet-iron casing. Either natural, induced, or forced draught is employed, the latter usually at sea. Economisers are not used. The boiler is also sometimes worked on land, with brick-work setting. An experiment on it is given at page 105, with 66% boiler efficiency, and an evaporation of 6 lbs. of water per square foot of heating surface per hour. The author has not found any series of experiments on this interesting type of boiler. No doubt, in future tests, the efficiency will be higher. Many other types of water tube boilers will be found mentioned in the chapter on marine boilers, as the Seaton, Blechynden, Herreshoif, and several French types, the Normand, D'Allest, Niclausse, etc. Experiments on the De Naeyer, Steinmiiller, Walther, Buttner, Heine, Seaton, Almy, Golirig, Hermann, and other boilers will be found on pages 105 to 1 11. Among them may be noted three trials on the Niclau.sse, page 111, made by Dr Kennedy and Professor Unwin, in which the efficiency was 72 and 73% without ■economisers, when evaporating 3^ to 6^ lbs. water per square foot of heating surface per hour. These water tube boilers, however, are in general so similar in type to the Babcock that it has not been considered necessary to treat or sum- marise them separately. They are mostly French, German, and Belgian, The efficiencies vary from 55 to 76^% without econo- misers, the water, evaporated per square foot of heating surface per hour varies from 1| to &^ lbs., an evaporation of i^ lbs. giving the best results. 33. Vertical boiler (fig. 33), with cylindrical shell and inclined large water tube carried across the furnace. — The gases pass vertically upwards round the water tubes and so to chimney. There are endless varieties of these little vertical boilers, which are much used for cranes, fire engines, and other small semi- portable purposes. They are seldom set in brick, and are usually of the simplest description, with grate, fur- nace chamber, and chimney all in one vertical line. In America large vertical boilers are used, but very seldom in England or on the Continent. It is difficult to cool the gases sufficiently to get a good economy of heat in the smaller Kg- 34. types. 34. Vertical boiler (fig. 34), with cylindrical shell differing from the last in having a series of small inclined water tubes carried across VERTICAL BOILERS. 15 the furnace. The direction of the hot gases is straight upwards between these tubes to the vertical chimney above. Some- times the boiler is surrounded with brick flues. 35. Vertical boiler with vertical smoke tubes (fig. 35). — This simple type of boiler requires little explanation, as its construction is shown in the p,.^ .,. sketch. It has a vertical cylindrical "' ' ' shell, sometimes set in brick-work, a central fiirnace chamber and grate below, and smoke tubes above. The gases rise directly from the furnace, and pass through the smoke tubes upwards to the chimney. Five experiments on small and medium sizes of these vertical boilers are given at page 113. The boiler efficiencies are low with the very small types, as economy is not so important for intermittent work as simplicity. They vary from 44% to 76%, the evaporation from 1| to 13 lbs. water per square foot of heating surface per hour, and from 5 to 34 lbs. of coal burnt per square foot of grate per hour. CHAPTEE II. Explanations of the Headings of the Tables. The various types of boilers have been tabu- lated in a uniform manner, in vertical columns. It was the wish of the author to diminish the number of columns as much as possible, and only to give in them what was absolutely essential to understand the experiments. We wUl now describe these various headings, which apply to nearly all the different types of boilers, although, of course, in many of them economisers or feed water heaters were not used. In some cases the various columns have been left blank, as the author wished to keep the Tables as uniform as possible. There are, however, a few modifications for some special experiments. Column I. gives the total heating surface of the boiler tested, in square feet. This surface is for one boiler. In some cases three, four, and five boilers were tested, but in these experiments the results have been similarly divided, so as only to have the results of one boiler for each trial. Column II. gives the total heating surface of the economiser only, when one was used. Columns III. and IV. give the general dimen- sions of the boiler in length and diameter. In some cases these dimensions have not been men- tioned by the experimenter. The heating sur- face is really much more important than the dimensions. Column V. shows the amount of vacuum or draught in the chimney, as measured in inches of water by the U gauge placed generally at the bottom of the chimney. In some cases the vacuum has been given both on the boiler side of the damper and in the chimney. In the majority of the experiments the draught was produced by the chimney alone, and, where nothing is stated in this column, chimney draught 16 is meant. Forced draught was, however, some- times used, or air delivered under pressure below the grate, either at atmospheric temperature or heated. Some other tests were made with induced draught, which is independent of any chimney, and is created by a fan driven at con- siderable speed, drawing the hot gases from the boiler flues. "With locomotive or agricultural boilers the draught is created by the exhaust steam delivered into the short chimney or funnel, and giving an induced current, as with these boilers high chimneys are out of the question. Forced and induced draught are largely used in marine practice, sometimes with air at atmospheric temperature, and sometimes heated. Induced draught is employed on all railways, and with locomotives in all countries. Column VI. gives the grate area in each case in square feet. "When nothing is mentioned the ordinary horizontal grates with cast-iron bars are understood to have been used, but many of the experiments M'ere made with various types of grates, vertical, inclined, or specially constructed ; sometimes with jets of steam under the bars; sometimes with the fire bars dipping into water. An account of different kinds of grates will be found in Chapter I"V. The fuel was put on either by hand or by automatic mechanical stokers, and it will be seen in the Tables that the boilers are classed under the heading of Hand and Mechanical Stoking. Columns VII., VIII., and IX. refer to heat eflScienoies. Column VII. gives the heat efficiency of the boiler only, apart from that of the economiser, or, in other words, the percentage of heat value in the fuel utilised in evaporating EXPLANATION OF HEADINGS OF TABLES. 17 water into steam. This is tlie figure of merit adopted to compare the different boiler tests, and it is now much used in France, Germany, Switzerland, the United States, and other countries. Column VIII. giyes the efficiency due to the economiser or feed water heater only, and Column IX. the combined efficiency of boiler and economiser together. Column X. shows the steam pressure by gauge in lbs. per square inch, and the corre- sponding steam temperature. Columns XI. and XII. refer to the tempera- ture of the furnace gases. Column XI. gives the temperature of these gases at the end of the boiler. Underneath this temperature is placed that of the steam ia the boiler, and the difference between the two, as shown, is important, because it, giyes the excess of temperature of the gases over and above that of the steam. Of course, when economisers are not used, this excess should be as low as possible for the best economy. Colvunn XII. gives the temperature of the gases at the chimney side of the economiser when one is used, and before the gases are dis- charged to the clumney. It is very important that this temperature also should be reduced to a minimum for the highest economy, as, after passing the economiser, all heat goes to waste. It wiU be seen, however, that in many cases it is much too high. Columns XIII., XIV., and XV. refer to the analysis of the various gases by volume, or the percentage of COg, 0, and CO at the particular places where the samples were taken. This is generally done on the boiler side of the damper, but often also at the end of the first run of the gases, viz., at the end of the fire tubes. In some cases two sets of analyses from each of these places are given in the Tables. The difference in the analysis of the gases at these two points is important and instructive, as showing generally large infiltration of air, either through various cracks, or often through porous bricks of the boiler setting and other parts. This leakage should be stopped as much as possible, as is sometimes done, but it does not seem possible to check it entirely. Column XVI. gives the lbs. of water evapo- lated per hour per boiler, showing the quantity actually evaporated hourly during the experi- ment. Generally speaking, ia good trials, the water is measured in tanks, but piston type water-meters have been sometimes used by the experimenters, and should, of course, be tested both before and after every trial. Column XVII. gives the lbs. of water evaporated per lb. of fuel from and at 212° F. This is the standard usually adopted in England, in order to compare the evaporation of different boilers all reduced to the same pressure and temperature. On the Continent another standard is employed, from 0° C. to 100° C, equal to from 32° F. to 212° F. In all the Continental experiments this value has been coiiverted to the English standard. Columns XIX., XX., XXI., and XXII. refer to the fuel used. Column XIX. gives the name of the fuel, and coal is understood when not otherwise noted. A great variety of fuels were burnt in the different trials, from the very best down to poor brown coal, also mixtures of different coals, and in various cases gas coke, and a mixture of coal and coke. Column XX. gives the heating value of the dry coal or fuel in T.U. per lb. It is generally determined in an instrument called a fuel calorimeter, but in some few cases this important heat value has been calculated by competent experimenters from the analysis of the coal. Sometimes both methods have been used, and the two should agree within a small percentage. Column XXI. gives the ashes and clinkers in. the fuel, in percentage to the total fuel burnt. This will be seen in the varioiis experiments to differ very much, from 2% and 3% to as much as 30% to 40%. It is essential to know this percentage, as it shows the poorness or richness in incom- bustible matter of the fuel burnt. Column XXII. refers to the lbs. of fuel burnt per square foot of grate per hour ; this will be seen in the various experiments to vary largely. Column XXIII. refers to the admission of air, whether too much or too little. This is a very important point, because it gives the percentage of air at the end of the boiler, near the damper, over that required for the combustion of the fuel. It very rarely happens that too little air ia admitted, but it is nearly always in excess. The numbers in the column are calculated from the analysis of the gases given in columns XIII., XIV., and XV. It is necessary for the best economy that the percentage excess of air should be reduced as much as possible, say to within 50% 18 HEAT EFFICIENCY OF STEAM BOILERS. of the theoretical quantity required for the combustion of the particular fuel used. Column XXIV. shows the year of the test. Colmnn XXV. gives the names of the experi- menters, with the authority, reference, remarks, etc. In the case of several experiments with one boiler the figures are indicated in this column, as,, in many cases, two, three, and even as many as ten experiments have been made with the same boiler and coal. Column XXVI. gives the leferencs number of each experiment. Bemarks. — It has not been thought necessary to add the number of hours each trial lasted. The time varied from eight to twelve hours, and .sometimes longer. "When the tests were very short they have been omitted altogether. As the object in these Tables was to make them as simple as possible, the total coal used per hour is not stated, but it can be calculated from column XXII., giving the lbs. of fuel per square foot of grate per hour, and from column v., giving the area of the grate. Priming of steam. — This is rarely touched upon in these trials with different boilers and by different experimenters. Unfortunately, tests have been very seldom made as to the amount of water in the steam generated, and it is only of late years that reliable instruments have been available. Even now it is somewhat doubtful which is the best to use. More experiments have been made in this direction in the United States than in other countries with steam calori- meters. The subject will be found fully treated at page 196. When boilers are forced they are much more liable to prime than when they are not fired hard. The type of boiler appears also to affect the question, as priming seems to take place more frequently in water tube boilers when forced than in others. In some of the trials with locomotive boilers there have also been evident signs of priming. CHAPTEE III. 425 EXPERIMENTS ON ENGLISH AND FOREIGN BOILERS WITH THEIR HEAT EFFICIENCIES— SHOWN IN FIFTY TABLES. 1!) 10 EXPERIMKNTS ON CORNISH TYPE OF BOILER WITH ONE INTERNAL FURNACE, Boiler Epficibncibs from 62 to 79 per cent. PAailODLAES OP BOIIEE TESIKD. 1 as O !-• Gases Waibb Etapoeated. Heating Surface Total. eeueral Dimensions. .So 1 ill o or per cent, of Heal Value in Fuel utUised. Teniperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler wben not otberwise stated). 1^ IS (l Lbs. of Cold Water eva- pprated per sq. ft. Heating Surface per hour, Boiler only. op do O Sq. ft. 1 11 m i 1 5 1 At end of Boiler and difference above Steam Temn. 11 Percentage by Volume. r 853 W.2 COa. 0. 00. Sq. ft. m. Ft. Ins. Sq.ft % 7. V. Lbs. sq. in. F." F.° °/o 7. 7. Lbs. Lbs. Lbs. 324 18-7 5-5 0-6 16-7 61-8 61 -S 514 299° 533° 299 234 7-7 112-1 2100 9-1 7'4 427 20 5-7 0-3 16-5 63-0 63 50 297° 620° 297 323 No t tak en. 960 8-1 2*2 Do. Do. Do. Do. Do. 68-0 68-0 504 298° 618° 298 320 Do. 910 8-7 2-1 Do. Do. Do. Do. Do. 75-0 75 62 309° 706° 309 397 Do. 1190 9-8 2-8 Do. Do. Do. Do. Do. 77-0 78-0 77 64 311° 732° 311 421 Do. 123,0 10 2-9 Do. Do. Do. Do. Do. 78-0 49 297° 698° 297 401 Do. 1280 9-6 3-0 Do. Do. Do. Do. Do. 79 -C 79-0 50 297° 690° 297 393 Do. 1230 9-6 2-9 496 26-5 5-5 21-7 65-0 650 115 347° Do. 1710 9-9 32 457 640 26 '0 50 0-25 18-0 73-6 4-5 78-1 98 336° 3284° •171 9-7 9-8 1147 11-8 2-5 J 700 30 5-75 0-5 21 78i 78i 37 283° 485° 283 202° 10-2 7-8 0-3 1470 11-4 I 2-3 i ■I HAND FIRING— BRICK SETTING WITHOUT SMOKE TUBES. With and -without Economiseks— Chimney Deaitoht. 21 Foil. AlB, Tear of Test. ^^ o d o 1 Name of Coal or Puel. "3.S ■ 1 .S3 ll 111 H if Excess of Air at End of Boiler in per cent, over tbat required for Com- bustion of Coal. f= ^ ■ ^ COKJSISH BOlLiiiK,, V%fm^y STATIONARY. Coal when not noted. N^^ TV. 7. Lbs. % Authority, Tleference, Experimenter, Locality, Remarks, Ac. Chimney Draught when not Mentioned. Nixon Navlga- * tion. 15,560 6-8 15-7 165 1894 Central Institute — Doukin and Kennedy, series No. 19. Unwin— Conical water tubes— fire 8" thick. Engineering, June 15, 1894. T; Units per aq. ft. heating surf. p. m. = 120. 1 Gas Coke. 12,350 14-5 8-6 Do. Donkin — Vauxhall Gas Works, London. 6 Experiments at increasing rates of evaporation, all on same boiler and with gas coke — 87„ moisture in coke. Boiler and flues fairly clean. 79% max. boiler efficiency. 637„ min. do. 7% moisture. 6 Expts. arranged in order of boiler efficiency. 7% moisture. 107o moisture. Boiler efficiency highest with 3 lbs. evaporation per sq. ft. ■ per hr. 6J7o moisture. Best efficiency this page. ,_ , 5J /o moisture. 2 3 4 5 6 7 J Do. Do. 11-7 7-5 ... Do. Do. 12,600 10-8 8-8 Do. Do. Do. 11-4 8-9 ... Do. Do. 11,700 9-1 91 Do. Do. Do. 10-8 9-3 ... Do. Welsh. 14,900 8 7-8 1895 Unwin's Report — Margate. 6 conical water tubes in furnace flue. 8 Do. 14,654 6 6 100 1890 Kennedy's Report— Addington Water Works. Conical water tubes in furnace flue. 54 T.U. per sq. ft. per min. average transmission of heat. 9 Nixon Naviga- tion. 15,560 9-3 6-8 100 1891 Donkin and Kennedy, series No. 8— East London Water Works. Engineering, May 15, 1891. 3 conical water tubes in flue— 10" fire. T.U. per sq. ft. p. m. = 38. 10 11 EXPERIMENTS ON CORNISH TYPE OF BOILER WITH ONE INTERNAL FURNACE, BOILEII ErFICIENCIES FROM 53 TO 81f PER CENT. Particdiars of Boiler Tested. Efffciencies or per cent, of Heat Value in Fuel utilised. & i a 1 Gases. Water Etaposated. Heating Surface Total. General Dimensions. .So ill > g o o ■5 Temperature of Furnace Oases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). III II =■3 Lbs. of Cold Water eva- porated per sq. ft. Heatinff Surface per Hour, Boiler only. 1 1 i g 1 r §1 Ob MS B 3 At end of Boiler and difference above Steam Temp. ■s'l |g Percentage by Volume. 002. 0. CO. Sq.ft. Sq.fi;. St. Et. Ins. Sq.ft. 7. 7. '/, Us. sq. in. F." F.° Vo 7. 7o Lbs. Lbs. Lbs. 389 31 7-2 0-5 15-8 53-0 53-0 71 317° 792° 317 475 110 7-8 0-1 2172 8-56 5-6 841 Do. Do. 0-35 Do. 71-8 71-8 70 316° 387° 316 71 8-6 10-2 0-4 3058 11-56 3-56 256 15 5-5 8'2 53-7 53-7 01b. Atmos. 212° 478° 212 266 7-5 O'l 960 7-5 3-75 Do. Do. Do. Do. 61-8 61-8 Do. 397° 212 185 6-5 780 8-6 3-0 890 25-5 7 '8 0-5 0-35 16 64-0 64 '0 105 341° 870° 341 529 13 6 10'7 5 '2 8-6 10 05 3680 6-3 4-1 Do. Do. Do. 0-3 0-3 Do. 64-5 64-5 106 342° 800° 342 458 12-2 8-9 7-6 10-1 0-50 0-40 2350 7-4 2-6 Do. Do. Do. 0-5 0-4 Do. 66-0 66-0 103 340° 865° 340 525 13-3 10-6 5-6 9 08 0-05 3540 90 4 175 12 4-5 0-3 11-2 58-5 58-5 24 265° 665° 265 400 No t tak en. 620 8-57 3-5 Do. Do. Do. Do. Do. 64-3 64-3 23 263° 739° 263 476 Do. 860 9-42 4-9 645 25 4 0-3 15-5 73-5 73-5 120 350° 589° 350 239 114 6-8 00 3290 10-3 5-1 600 28 6 ... 16-0 81-7 81-7 79 323° 439° 323 116 No t tak en. 1700 12-4 2'9 HAND FIRING— BRICK SETTING WITHOUT SMOKE TUBES. No ECONOMTSERS — ChIMNBY DRAUGHT. .23 Fdei. AlE. Tear of Test. ^-^ Name of Coal or Fuel. ■3.9 II Iss. ■S3 M O ill Excess of Air at. End of Boiler ill per cent. over tbat required for Com- bustion of Coal. f^— ^ CORJ^ISH BOILER, ; '^^faroiiwpi/ STATIONARY. Coal when not noted. T.U. 7. Lbs. °L Authority, Reference, Experimenter, LocalitT. Bemar]£S, &e. Chimney Draught when not Mentioned. Elizabeth Pit Essen. 15,540 3-5 19-5 60 1880 Gases through furnace tube, under bottom and then over top. In No. 12 direct through furnace tube to chimney without pass- ing round outside boiler shell, or two journeys less than No. 11.— -The difference is marked in eflaciency and temperature, (j) Dusseldorf Tests — Corrugated furnace tube by Schultz Knaudt —Cost of Boiler, £534. Brick work, 1303 cub. ft. = £36. Two Expts. on same boiler and same fuel. W 11 12 Do. Do. 4 20-4 158 Do. Clifton Colliery. 13,880 9 18-0 155 1893 Two Expts., both on same boiler, provided with boiler plate pro- jecting ribs on outside of boiler at bottom and in furnace tube top. Total surface =■ 772 sq. ft.— apparently no gain in evap. or effic. Turnace flue 2 ft. 9 ins. Longridge— Manchester — annual report. 13 ; 14 Do. Do. .7 13 195 Do. Bohemian Lignite. 9o50 3-4 43-7 32 66 1894 Inclined Kuhu grate— Large cross tube over fire— Hopper for coal — Air admitted over grate. Temp, and analysis gases taken at end furnace tube and also at end boiler flue— Chimney 108 feet. '. Prussian State Smoke Commission Report— Schneider and De Grahl, chief engineers. Corrugated furnace tube with three conical water tubes. Direction gases, through furnace tube, under bottom over top. Three Expts. at different rates firing and evaporation. Max. efBc. 66%. .15 i \ ) 16 17 Moravian Lignite. 11,100 3-7 23-2 56 90 Do. Silesian Hard. 13,150 2-7 29-5 33 65 Do. Nixon Naviga- tion. 14,150 2-7 7-0 1896 Donkin— London. Two Expts. at two different rates of firing and evaporation. Direction gases, through furnace tube, three times along boiler to chimney. 18 19 20 21 Do. Do. 4-7 8-9 Do. Clean Ruhr Nuts. 13.712 8 24-5 307„ end flue, 60% end boiler. 1891 Report Erankfort Exh. tests.-Special fire bk. bridge for heating air for combustion. Another expt. gave boiler efiic. 797o- Schultz boiler— corrugated flue. Welsh Coal. 14,500 2-2 9-9 1893 Unwin's Report— West Middlesex Water Works. One of the trials was made also with three boilers, with practi- cally same result as in this case. Best efficiency this page. 4 EXPERIMENTS ON CORNISH TYPE OF BOILER WITH ONE INTERNAL FURNACE, Boiler EEFiciBNcy from 55 to 75f Per Cent. Pabticdiaes op Boiiek Tested. Efficiencies a k if Gases. Water Evaporated. Heating Surface Total. General Dimensions. 11 ill 1 o o a S < or percent, of Heat value ill Fuel utilised. Temperature of Furnace Gases. Analysis Of Furnace Gases (at end of Boiler when not otherwise stated). So ■ ^« is. =11 1^ "Si, W it Lbs. of Cold 'W'ater Eva- porated per sq. ft. Heating Surface per hour, Boiler only. .1 P m ■a S 1 It so ea o s. a a s 1 At end of Boiler and difference above Steam Temp. o'i l« Percentage by Volume. CO2. 0. CO. Sq.ft. Sq. ft. Ft. rt. Ins. Sq. ft. % 7. V. Lbs. sq. in. F.' R« ^ % 7. %,• libs. Lbs. Lbs. 303 20-3 5-6 0-4 22 55 55-0 14 248° 641° 248 393 6-1 7-0 12-2 12-0 1505 6-64 5-0 710 28-6 6-56 0'4 21-5 70-8 70-8 135 358° 816° 358 458 16 2-0 5273 10-4 7-27 Do. Do. Do. 0-3 Do. 75-5 75-5 Do. 658° 358 300" 15 3-3 3720 11-2 513 466 22 6-5 0-2 18 74-2 74-2 33 278° 485° 278 207 No t tak en. 2067 8-2 2-2 3 EXPERIMENTS ON CORNISH TYPE OF BOILER WITH ONE EXTERNAL FURNACE, Boiler EFrioiENCY, 60 to 66 Per Cent. 327 20-3 5-6 0-2 8-6 60 60 18 256° 707° 256 451 8-9 8-6 8-6 8 1 ... 1485 6-3 4-44 Do. u Do. Do. 0-26 Do. 62-4 62-4 18 256° 703° 256 447 12-5 12-4 5-4 5-7 ... 1472 7-6 4.4 520 23 5-9 0-25 12-9 65-9 65-9 91 332° 501° 332 169 14-5 11-9 4-1 6-1 ... 1338 5-93 2-5 HAND FIRING— BRICK SETTING. Chimney DKAtroHT — no Economisers. 25 Fuel. Air. Tear of Test. ^—^ [ONARY. :s. 1 s ■s ! a S 1 Name of Coal or Fuel. 1^ "eh O.S II . n .S3 ji Is. II Hi Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. ^ ^=- =^ ^^ CUKJSI ISH T y en, STAT. ¥^'=fanmnrpj' ^0 SMOKE TUBI Ooal when not noted. H^^ T.U. 7. Lbs. 7o Authority, Reference, Experimenter, Locality, Bemarlca, &c. Hard Coal, Zwickau. 11,600 10 12 210 170 1890 Levicki— Report— Dresden, 1896. Chemnitz Railway Workshops. No water tubes in flues — T.U. per sq. ft. p. m. = 94. Gases taken at end furnace flue and end boiler. (9) 22 Nut Coal. 13,590 6 27 20 1896 Z.V.D.I.— 15th May, 1897. Sohultz-Knaudt boiler — Corrugated fire tube. 2 Expts. on same boiler at two diff. rates firing and eva- poration—about 407„ more evaporation and 5°/^ only less eflSciency. Direction gases — through tube, forward one side and back other side. Best Bxpt. — this page. 23 24 • Do. Do. 5 18 30 Do. Gas Coke. 10,625 18 7-7 1897 Donkin — Bermondsey. 25 HAND FIRIN( FURNAC] }— BRI E IN Fb CK SETTINC ONT OF BOILE •. }— CHIMNEY DRAUGHT. \ ^^ R — NO Smoke tubes. ' f 1 Coal, ^ Brown Coal. 10,150 11 32 100 109 1890 Levicki— Report — Dresden, 1896. — Chemnitz. Inclined grate, 45° in front boUer — Fire tube conical — no cross water tube. Transmission T.U. per sq. ft. p. m. = 86. (8) Do. do. do. 2 Expts. on same boiler — difif. coals. T.U. per sq. ft. p. m. = 85. (7) 26 27 Hard Coal. 11,800 13 26 45 46 Do. Brown Coal, Saxony. 8,700 20 25 52 Do. Same authority Saxony. Donneley vert, grate bars— small water tubes in front boiler. 13 conical water tubes in furnace flue. T.U. per sq. ft. p. m. = 49. (5) 28 9 EXPERIMENTS ON CORNISH TYPE OF BOILER WITH ONE INTERNAL FURNACE, BoiLEK Efficiencies from 55 to 81 per cent. PAEIIOOIiARS OF BoilBB TkSIED. Efficiencies 1 ll 1^ Oases. Waibb Etapokatid. Heating Surface Total. General Dimensions. ^ o n S.S > 1 o o s or per cent, of Heat Value ill Fuel utUised. Temperature of Furnace Oases. Analysis of Furnace Oases (at end of Boiler when not otherwise stated). IS p* .gpffl Hi 1 '=■3 Lbs. of Cold Water Eva- porated per sq, ft. Heating Surface per hour, Boiler only. 1 = |1 1 i3 It BS s 1 At end of Boiler and difference abOTe Steam Temp. .1 •si 5 Percentage by Volume. CO2. 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. % 7. 7. Lbs. sq. in. F.« F.« 7. 7. •/. Lbs. Lbs. Lbs. 560 Three 8 Pieces 5-5 oh. 10-5 55-0 55-0 35 281° 261° 281 No t tak en. 282 8-15 0-51 Do. D o. ... 15-0 56-2 56-2 41 288° 256° 288 Do. 322 8-32 0-6 Do. D o. 10'5 70'7 70-7 48 296° 460° 296 164 Do. 1084 10-47 1-95 Do. D 0. 150 75-9 75-9 41 288° 529° 288 341 Do. 1163 11-23 2-1 804 19 6-3 0-6 200 66-6 66-6 72-5 319° 732° 319 413 12-8 5-3 3920 10-35 5-0 538 8-3 66-5 66-5 69 315° 330° 315 15 No t giv en. 1076 7-34 2-0 215 ... ... 4-5 68-5 68-5 74 319° 380° 319 61 Do. 495 8-74 2-3 538 8-3 81-0 81-0 77 321° 325° 321 4 Do.. 1020 7-95 1-9 J 1193 16-5 6-5 0-45 19-7 68-8 1 1 68-8 70 316° 33.3° 316 17 9-5 91 0-4 3532 11-0 2-95 HAND FIRING— BRICK SETTING WITH SMOKE TUBES. No EcoNOMisERs— Chimnby Draught. 27 FOEL. Name of Goal Is .9g 1' or Fuel. =.3 II 5*i (>■" •dug Coal when s^^ §s.^ not noted. |S < T.U. 7. of Air at £ndof Boiler in per cent. over that reqoirecl for Com- bustion of Coal. Year of Test. CORNISH WITH SMOKE TUBES, STATIONARY. Authority, Reference, Experimenter, Locality, Renijiiks, &c. Chimney Draught wheu not Mentioned. Welsh. 14,300 Do. Do. Do. Do. Do. 3-7 1882 3 Do. Do. 11-5 8-0 Nixon Naviga- tion Welsh. 15,560 2-5 20-8 Do. Diff. Expt. at diff. rates, firing, and evaporation, all with same coal — Area grate varied. Arranged in order of boiler efficiency. Too little work for a good result. Cowper, at Simpson's, London. Each boiler made in three pieces, for transport. 1st piece— Plain, Cornish — 1 tube. 2nd „ — 1 tube furnace, with conical water tubes. 3rd „ — Smoke tubes. Do. See Engineering, March 3, 1882. No brick -setting. 60 1894 Donkin and Kennedy, No. iO— Engineering, July 20, Office Daily Telegraph, London. 4-f t. corrugated flue. T. U. per sq. ft. p. m. = 87. 52 short smoke tubes, 4" diam. at end furnace tube. Bohemian Small Coal. 9,478 210 94 1895 Boiler Association, Vienna— All these three Expts. with same direction gases — Through furnace tube, forward through all smoke tubes (whole length of boiler and on each side furnace tube) round outside of shell to chimney. (32) Silesian Nuts. 12,350 16-6 100 Silesian Nuts, Small. Elizabeth Pit, Essen. 10,670 15,540 3-7 19-4 72 Do. Do. Do. Do (5) Expts. on same boiler at diff. rates evap. (26) Best efficiency this page. 19-7 90 1880 Dusseldorf Expt. Tests— Report. Schultz-Knaudt boiler— Corrugated furnace tube. Direction gases, through furnace tube, then through smoke tube (whole length boiler) and back through two larger smoke tubes in steam space. Boiler cost £572— Cub, contents bk. wk. 311=£9. (c) 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, Boiler ErnciENCiES alone varying between 55 and 60 pee cent. Pakhculars of Boiibe Tustid. Cf «:«:»« «;«*» s. . fflg ■il u Gases. Water Evaporated, Heating Surface Total. General Dimensions So 'i 1 u o 1 or per cent, of Heat Value in Fuel utilised. Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). Lbs. of Cold Water eva- porated per sq. ft. Heatms Surface per Hour, Boiler only. o p .| 03 i fi d 0^ Boiler only. Econo- misep onlv. ri S At end of Boiler and difference above Steam Temp. At end of Economiser. Percentage by Volume. CO2 0. CO. Sq. ft. Sq. ft. Ft. rt. Ins. Sq. ft. 7o % 7. Lbs. sq. in. F.» F.° 7. 7, 7o Lbs. Lbs. Lbs. Not given. ... 7 0-3 Not given. 55 8-0 63-0 69 315° 580° 315 265 400° Not given ... 7090 7-6 Cold Feed. Do. Do. 7 0-25 Do. 55-0 7-5 62-5 74 319° ... 11-4 6-6 4650 7-6 Cold. 970 28 7-5 0-6 29-1 55-2 55-2 90 331° 580° 331 249 ... 6-2 13-1 3500 6-2 4-0 538 24 7 0-3 27 .56 56 32 277° 695° 277 418 7-7 11-2 3748 7-2 7-87 1300 893 30 7-5 0-3 38 57-9 10-8 68-7 88 330° 674° 330 344 418° 11-2 6-2 5970 7-94 4-6 1130 Not 1200 30 8-0 0-7 35 58 8-0 57-3 112 345° 422° 345 77 315° 7300 7-1 6-45 given. 8-0 0-2 66-0 57 -S 88 330° 650° 330 320 280° 100 ... 5700 8-02 Cold. 542 25 7'0 0-25 25 57-8 34 279° 578° 279 299 6-7 11-0 0-5 3070 6-4 57 ' Not given. 8-0 58 5 9-0 67-5 86 328° ... 8-2 7320 Hot. 7-8 ! t _ Do. Do. 7 0-3 59 9 68 -0 66 312° 400° 5i 14 4590 Hot. 6-8 ...J 28 'M MACHINE FIRING— BRICK SETTING. With and without Economiser — Chimney Draught. 2&- Edel. Am. Year of Test. S s o i 1 ■s Name of Coal or ExiBl. •3.9 111 ill k I II Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Ooal. /-J — _-»-< X LANCASHIRE STATIONARY jp'^^^-^^^^i BOILER. Coal when not noted. \^Uw^j^f^^»^ NO SMOKE TUBES. T.U. 7. Lbs. % Authority, Reference, Experimenter, Locality, Remarl^s, &c. : , Harley ' Slack. 12,900 6 1892 Report, 1895 — Committee testing smoke preventing appliT ances — England. Bennis sprinkling stoker. Smoke not given. 1 i West Haughton IS, 080 15 24 80 1893 Same authority — Barlow & Jones — Bolton. Proctor's sprinkling stoker. 2 Wilson Dross. 10,846 19 18-5 200 Do. Same authority — also Thomson, Report No. 10. Brown, Stewart — Dalmarnock — furnaces 2' 11"— five cross tubes each — no smoke. Sinclair coking stoker— 5" fires. 1 3 Earnock Dross. 12,446 64 21-7 150 1891 Same authority — Thomson, No. 3 — 44" fires. Orr-Ewing & Co.— Dumbarton — furnace 2' 9"— six cross tubes each. Bennis sprinkling stoker — smoke not given. 4 •Nuts. 13,: 00 8 19-7 75 1895 Donkin — St. Mary Cray. Vicar's stoker. Five conical tubes each flue. 5 Mande Rough Small. 12,000 Si 32-3 1896 Abbey Mills Pumping Station— P. I.e. Eng., Vol. 129. Approx. sample coal sent author by chief engineer, C.C. Vicar's stoker. 6 Haughton Slack. 13,080 11 ... 90 1892 Same authority as No. 1 . Barlow & Jones — Bolton. Sinclair coking stoker. 7 Earnock Dross. 10,745 9i 22 156 1891 Same authority— No. 4 Thomson. Orr-Ewing & Co. — ^Dambarton- conical tubes in furnace flues. Coal small, wet, dirty — 7i" fires. Hodgkinson's coking stoker — smoke not observed. 8 12,950 10 24 ... 1893 Same authority. Cross & Winkworth— Bolton. Cass coking stoker. 9 2nd Best. 11,250 114 250 1892 Same authority. Cross & Winkworth— Bolton. Bennis sprinking stoker— Best efficiency — this page. 10 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, Boiler Eppiciencies alone varying between 61 and 65 per cent. Particdiaes or Boilee Tested. ■3 1 OQ Gapes. Wateb Evapokatjib. Healing Surface Total. General Dimensions. .So i Pa PI So? s 2 o o s or per cent, of Heat Value in Fuel utilised. Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Bo/Jer when not otherwise stated). ■sgl 1^ 1^ i Lbs. of Cold Water eva- g pprated per sq. ft. » HcatinB Surface per Hour, Boiler only. One Boiler only. m s 1 1 a It 1' O b 3 At end of Boiler and difference above Steam Temp. 31 si Percentage by Volume. C02. 0. CO. S(j.ft. Sq, ft. Ft. FL Ins Sq.ft. 7. 7. 7. Lbs. sq. in. P." S." 7. 7. 7. Lb.. Lbs. 1069 34 7-4 0-8 18 611 61-1 60 307° 664° 307 357^ No t tak en. 8280 9-3 7-7 Do. Do. Do. 0-7 Do. 61-5 61-5 60 307° 688° 307 381 Do. 8210 9-3 7-7 960 30 8 0-6 61-5 61-5 73 318° 842° 318 624 8-7 10-2 0-3 6450 8-26 6-4 Not given. ... n 0-3 ... 61-5 7 68-5 87 329° 489° 329 160 273° 3-2 2860 Hot 8-9 .... 1 D 0. 8 0-3 ... 62-4 12 74'4 157 368° 803° 368 435 381° 9-6 ... 7300 8-3 ... D 0. 8-5 0-4 63-6 6 69-6 90 331° 520° 331 189 320° 14-0 ... 7350 7-8 Do. ... 8'0 0-6 63-8 7-6 71-4 95 334° 725° 334 391 261° 11-2 8070 SO Do. 7-5 0-3 ... 64-5 64-5 50 298° 475° 298 177 7-3 12-5 4020 91 Do. 8-0 06 ... 65-6 65-6 82 325° 9-9 6-6 6940 8-3 ... 1008 2880 30 8 0-3 33-2 63-1 12 '4 75-5 157 369° 803° 369 434 381° 96 8-7 7300 10-36 Cold Feed. 7-25 MACHINE FIRmG— BRICK SETTING. With and without Economisek— Chimney Dbaught. 31 Fuel. Am. Year or Test. /^^^^^^ LANCASHIRE STATIONARY (^■"^rT^"^ BOILER. s o 1 Name of Coal orFueL Sop. if ill p II Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. Coal when not noted. VgWHwwztmnmj/ ^S^_<^1:"V-1^ NO SMOKE TUBES. T.U. /. Lbs. % Authority, Eeference, Experimenter, Locality. Remarks, &c. Slack. 14,623 7-4 56-6 1895 Fletcher— sent to Author. No economiser. Vicar's coking stoker — Liverpool. See No. 38 for another Expt. on this boiler with smaller evap. and greater efficiency. 11 12 13 Do. 14,533 7-7 55-3 Do. Wigan. 13,051 13 25i 120 1890 Report, 1895 — Committee smoke preventing. Yates & Thorn, Blackburn — bars rocked by hand. Proctor's sprinkling stoker — no economiser. Durham Slack. 13,770 14i 17 500 1891 Hyd. Power Co., Westr. London. Same authority — with economiser. Vicar's coking stoker. 14 15 Shaw Slack, Wigan. 12,963 5i 24 100 1893 Spinning Co., Hey wood. Same authority — economiser. Bennis sprinkling stoker. Rougli Slack. 11,900 114 35 1892 Musgrave — ^Bolton. Same authority — economiser. Vicar's coking stoker. 16 17 Do. 12,180 8i ... 70 1893 Same authority. Musgrave's, Bolton — economiser. Vicar's coking stoker. Denaby Nut. 13,480 64 204 ■ 160 1891 Same authority. Royal Arsenal, Woolwich — no economiser. Proctor's sprinkling stoker. 18 19 Atherton Slack. 12,270 11 ... 90 1892 Same authority. Dobson & Barlow, Bolton— no economiser. Bennis stoker. Best efficiency this page. Shaw Slack. 12,963 54 24 100 1893 Crossland— 3% priming. Heywood — furnace flues 3' 2" — economiser. Oases — through furnace, under bottom — split sides. Bennis stoker. 20 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, BOILEK ErWClENCIES ALONE VARYING BETWEEN 65 AND 69 PEK CENT. Pakticulabs ofBoiibe Tesibd. E-ff :..:»•■. «E«n t3 Gases Water Etafobatbd. ' Heating Surface TotaL General Dimensions. 5 = If III 1 O 1 or per cent, of Heat value in Fuel utilised. Temperature of Furnace Oases. Analysis of Furnace Gases (at end of Boiler wben not otherwise stated). i la Lbs. of Cold Water eva- gwated per sq. ft. eating Surface per hour. Boiler only. _ 8°- s m ■s s S It >> i At end of Boiler and difference above Steam Temp. O § §8- Percentage by Volume. C02. 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ina, Sq.ft 7. V. 7.' Lbs. sq. in. F." F.° Vo 7. 7. Lbs. Lbs. Lbs. 1300 2680 34 8 0-3 38 65-2 14-2 79'4 87 329° 706° 329 377 366° No ttak en. 4580 9-06 3-5 971 28 7-5 0-6 33-5 '66-6 66-6 60 307° 730° 307 423 10 8-2 5814 7-35 6-1 1040 1920 30 7-5 0-8 36 67-2 10-5 77-7 155 368° 700° 368 332 388° 9 10 01 4762 11-38 4-58 Do. Do. Do. Do. Do. Do. 68 3 11-3 79-6 155i 368° 730° 368 362 375° 9-9 8-8 O'l 4694 11-68 4-51 1300 2680 34 8-0 0-3 38 67-3 11-8 79-1 70i 316° ... ... No ttak en. 5350 9-34 4-1 Do. Do. Do. Do. 0-4 Do. 67-8 13-7 81-5 89 330° 592° 330 262 350° Do. 3770 9 05 2-9 1035 1290 30 7-5 0-5 28 68-5 9'7 78-2 93J 333° 519° 333 186 256° 5 15 3160 8-42 3-0 Do. Do. Do. Do. Do. Do. 67-7 110 78-7 94 334° 548° 334 214 298° 3 17-7 3610 9-65 3-5 947 5120 29-5 7-1 ... 22 680 12-0 80-0 78 322° 750° 322 428 333° 10-3 8-0 0-2 4685 1000 4-95 971 28 7-5 0-5 33-5 69 69-0 63 310° 705° 310 395 11-0 8 6151 6-55 7-6 i 32 MACHINE FIRING— BRICK SETTING. With and without Economisee — Chimney Dkaught. 33 FVEL. AlK. Year of Test. 4^ s a •g a K W ■s 1 1 NameofCoal or Fuel. 0.0 111 B .93 VCtH 111 B ■gin is is a Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. |^?''~^-_^>'~SH BOILER. Coal when not noted. ^"Ijj^"'^ NO SMOKE TUBES. T.U. 7. Lbs. 7o Authority, Kefeieuce, Experimenter, Locality, Remarks, &c. Small Coal. 13,400 6 12-8 1895 Donkin— St. Mary Cray — 7 cross tubes in each furnace flue. Very large economiser — 14i7o gain. Vicar's coking stoker. 21 Greenfield Virgin Dross. 10,657 18 28-4 90 1891 Report, 1895, smoke testing — No. 7, Thomson. Thornliebank coking stoker and hollow fire bars, Davidson's. 12 conical water tubes — 8" fires — no smoke. 22 Townley Slack. 13,843 74 14 110 1893 Crossland— Yorkshire. See Engineer, May 5, 1893 — 3' furnace and 5 water tubes each. 5 conical water tubes each furnace flue. Proctor's stoker. Livet setting— chimney 180 ft. high. 23 24 J - 26 Do. Do. 8i 13J 90 Do. Small. 13,398 8-1 15-1 1895 Donkin — St. Mary Cray. Vicar's coking stoker — 7 cross water tubes each flue. Same boiler as No. 21, above. 2 Expts. on same boiler at difi'. rates firing and evap, — about same efficiency. Very Small. 12,896 8-7 10-8 Do. Ordinary SmaU. 11,800 5 14-5 280 1892 Donkin — Hyd. Power Co., Millbank. 2 trials in same boiler, rather diff. rates. 5 conical water tubes each furnace flue. Vicar's coking stoker. Difl". coal — about same efficiency. 27 28 29 30 Welsh Small. 13,950 1-3 13-5 530 Do. Small Coal. 11,962 ... 17-2 80 1887 Longridge Report. Proctor's stoker — some hand firing also. Virgin Dross, Wet. 11,053 13 28 70 1891 Thornliebank Works — No. 6, Thomson. Do. coking stoker - Smoke Report. Hollow fire bars — Best Expt.— this page. 6 conical water tubes each flue — 8" fires — no smoke. 12 EXPERIMENTS ON LANCASHIRE TYPE OF BOILEK WITH TWO INTERNAL FURNACES, BonER Efficiencies vaeyins between 52 and 74 pek cent. • Partiodlabs of Boilee Tested. ■a il is Gases Watee Evapokated. 1 Heating Surface Total. General Dimensions. S'S as °^ . m 1 i < or per cent, of Heat Value in Fuel utilised. Temperature of Fm-nace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). • u it ill .J 1 ■°i. hi' u fl-g n 1 Q ta i! W.2 S •i 1 At end of „ Boiler and ■„ difference above Steam Temp. Percentage by Volume. CO2. 0. CO. Sq. ft. Sq.ft. Ft. Ft. Ins. Sq. ft. 7. ■', 7. Lbs. sq. in. F.° 7, "/o 7„ Lbs. Lbs. Lbs 400 19-7 5-2 0-2 16i 519 51-9 68 314° 530° 314 216 5-4 14-3 0-06 785 6-5 1-96 Do. Do. Do. Do. H 618 61-8 70 315° 550° 315 235 ... 4-8 14-6 877 77 2-17 1130 3600 30 8 0-6 31-7 ... 637 89 330° 333° 330 3 207° No t tak en. 6886 7-9 6-1 - 811 28 7-2 0-4 31 66 3 66-3 52 300° 671° 300 371 13-3 10-2 5-6 8-4 ... 4028 8-2 4-9 Do. Do. Do. 0-33 Do. 690 69 -0 51 299° 624° 299 325 147 11 -8 3-9 6-9 4147 8-4 5-0 936 1142 28 7-5 0-6 21 69-5 12-0 81-5 79 323° 566° 323 243 372° 57 13-5 3552 Hot. 10 '8 3-87 Hot. L Do. Do. Do. Do. Do. Do. 71-3 9-7 81 '0 Do. 401° 323 78 278° No t tak en. 3760 Hot. 11 '2 4-2 Hot. 1069 34 28 7 '4 0-8 18 70-7 70-7 60 307° 636° 307 329 Do. 6700 10-3 6-2 905 7 0-6 32 70-7 707 62 309° 633° 309 324 10-5 87 6202 675 6-9 935 1200 30 7 30-2 72 72 1 15-0 87 '0 76-1 89 330° Not taken. No t tak en. 5400 10-2 5-6 1350 23 7 '6 1'8 34 4'0 Air heat'i 68 314° 559° 314 245 406° End air heater. 7-9 10-5 7497 9-6 5 -56 Not given. •" 8 0'5 ... 740 11-0 85-0 40 287° 680° 287 893 250° 12-5 ... ... 8700 7-4 34 MACHINE FIRING— BRICK SETTING. With and without Ecokomisers— Chimney and Induced Draught, 35 Fdkl. Air. Tear of Test. ^^-^ 1 S E a. •s 6 3 Name of Goal or Fuel. III -3 it- Ill |g5 w II Excess of Air at End of Boiler In per cent, over that requii-ed for Com- bustion of Coal. i^-=^''^=^=-=A LANCASHIRE STATIONARY. \^?mJ|Um^ NO SMOKE TUBES. Coal when not noted. T.U. % Lbs. % Authority, Reference, Experimenter, Locality, Remarisa, &e. Saxon Coal. . 12,135 7i H 250 1893 Saxon Boiler Association — Munster — at Jena. Ordinary horizontal grates— Heating value given as wet coal con- taining 8J% water. Sent to author. Do. do. Kowitzky grate. 31 32 Do. Do. Do. 15 300 Do. Maude Royal Small. 12,000 8i 29i 1896 Abbey Mills Pumping Station— P.I.C.E., Vol. 129. Sample coal sent Author by chief engineer, C.C. Very large eoonomiser — ^generally used for more boilers. Vicar's stoker. 33 Hard Coal, Saxony. 11,910 3 18 41 83 1890 Levicki Report, 1896 — Leach stoker— Chemnitz. Horizontal grate — 5 cross water tubes, each flue. Gases in two places^end tube and end boiler. Transmission — T.U. per sq. ft. p. m. = 95. Gases through furnace tubes— under bottom, over top and sides. T.U. persq. ft. p. m.=98. 34 35 Do. 11,830 4 18 28 60 Do. Nixon Naviga- tion, Welsh. 15,560 3 16 260 1891 Donkin and Kennedy, No. 9-10— Hyd. Power Co., Bankside. Migineering, Oct. 2, 1891. Vicar's coking stokers — fires 11" thick. 2 Expts. on same boiler — same rates. Same efficiency. Direction gases — through furnaces under boiler — split sides to chimney. 36 j 37 Do. Do. Do. 17 ... Do. Slack. 14,077 8 42 ... 1895 Fletcher — sent to Author. Liverpool. Vicar's coking stokers. 38 Virgin Dross, Wet. 11,053 13i 284 80 1891 Thornliebank Works, coking stoker and hollow bars. No. 5, Thomson. Galloway boiler, oval flue. Furnace 2' 9J"— 33 cross water tubes — 8" fires — no smoke. 39 ... 13,600 11 19i ... 1882 Longridge's Report — Blackburn. Gases through furnace flue — along two sides, under bottom. Proctor's stokers. 40 Wigan Slack. 13,065 13 24i 140 1894 Guinness' Brewery, Dublin— Tests given to Author by chief engineer — smoke tubes at end furnace flue — no brick work — gases through furnace and smoke tubes, then through air heat- ing tubes to chimney — induced draught fan — Cass stoker — air heated to 340° F. 41 Small dirty. 9,740 26 30^ 50 1893 Smoke Report, 1895— Cross & Winkworth, Bolton. Hard firing — Best efiiciency this page. Cass coking stoker. 42 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, BoiiiEE Efficiencies varying from 42 to 58 per cent. PAETIODlABa OF BOILEE TESTED. Efficiencies or per cent, of Heat Value in Fuel utilised. ■a •"^ ia II CO Gases. Water Evaporated. Heating Surface Total. General Dimensions. 11 ill > f a ■s 1 Temperature of Fm-nace Oases. Analysis of Furnace Oases (at end of Boiler when not otherwise stated). |l ! OS li Lbs. of Cold Water eva- Derated per sq. ft. Heating Surface per Uour, Boiler only. fe o . c o o 1 P t n M.S •i 1 of ■d a Percentage by Volume. CO2. 0. CO. Sq.ft. Sq. ft. Ft. Ft. Ins. Sl. ft. °L °l. Lbs. sq. in. F.° F." °U °U ■'■" Lbs. Lbs. Lbs. 998 30 7-5 0-3 35 42-1 42-1 36 282° 489° 282 207 No t tak en. 2592 4-9 2-6 570 26 7-0 0-5 34-6 46-0 46-0 35 281° 407° 281 126 3-0 17-5 3554 5-6 6-2 907 2408 30 7-0 0-7 32 48-3 10 '8 59-1 125 352° 580° 352 228 345° No t tak en. 4640 6-9 5-1 550 23 6-2 0-2 19-5 50-4 50-4 53 301° 730° 301 429 9-2 9-7 2050 5-2 3-7 907 2408 30 7 0-7 32 52-0 53-0 11-9 63-9 122 351° 572° 351 221 345° No t tak en. 4520 7-1 5-0 1058 4128 30 8 1-2 88 8-2 61-2 92 332° 587° 332 255 353° Do. 7590 7-5 7-2 998 1 30 7-5 0-4 35 53-7 53-7 69 315° 497° 315 182 ... 10-1 8-5 7 '3 2981 6-6 3'0 Not given. 28 7 0-3 56-5 7-5 11-7 11-9 64-0 66 312° ... 3670 7-3 ... 808 640 26 7 0-3 35 55-8 57-9 67-5 69-8 58 305° 729° 305 424 417° 8-5 10-2 0-2 3795 10-0 4-7 Do. Do. Do. Do. Do. Do. 59 306° 735° 306 429 409° 8 '4 10-7 0-1 3860 10-4 47 ; 1 HAND FIRINO— BRICK SETTING. With and without Economisees — Chimney Dkaught. 37 FtJEL. Are. Tear of Test. z-^. i i s- ■s i s o 1 2 Name of Coal or Fuel. t lit 33 ft |fi ^ ft Excess ot Air at Endoi Boiler in percent. over that required for Com- bustion of Coal. /^:^^^=S=V LANCASHIRE STATIONARY. OTumJ^Uw^ NO SMOKE TUBES. Coal when not noted. T.IT. % Lis. X Authority, Keference, Experimenter, Locahty, Eemarks, &c. Splints and Dirty Coal. 11,200 344 17-6 ... 1897 Donkin— North England. 9" fires — very dirty coal — cast-iron bars. Air pressure under bar, rV'> with steam jet. Earnoch. 11,802 9i 20 530 1891 Smoke Report, 1895 — Thomson, No. 1. Orr-Ewing & Co. — Dumbarton. Auld air bridge. 6 water tubes each furnace flue. Slack, Bolton. 14,659 11 20-3 ... 1895 Fletcher. Caddy's hollow bars. Bolton. 3 Bohemian 9978 9 24 100 1894 Dachau Paper Mills — Germany, Munich Boiler Association — Gyssling. 4 5 6 Slack, Bolton. 14,342 Hi 19 1895 Fletcher — sent to Author. Bolton. Caddy's hollow bars. Worsley Slack. 13,694 14-7 28 ... 1895 Fletcher — sent to Author. Bolton. Steam jet under grates. Hntton Seam. 11,880 25 13 '8 90 1897 Donkin — North of England. Air pressure under fire bars, jV", with steam jet Dirty coal. Same boiler as No. 1. 7 ... 12,300 7-2 16 120 1892 Smoke Report, 1895. Crossland & Winkworth — Bolton. Hollow fire bars — Caddy's — split bridge. 8 Burgy Coal. 14,280 8 12'9 120 1894 Crossland Report. Wakefield. Best efficiency on this page. 9 10 Do. 14,448 6i 12-6 125 Do. 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, BoiLEK Efficiencies feom 52J to 57i pee Cent, PABTiorr,*ns OP BoitiB Tested. Efficiencies or per cent, of Heat Value In Fuel utilised. steam Pressure by Gauge and Steam Temperature P. Gases, Watee Evapohated. Heating Surface Total. General Dimensions. SI u ^ a ^3 ^&. HI > 1 a •s S .■5 Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). iJ .Sol 3 Lbs. of Cold Water eva- porated per sq. ft. Heating Surface per Hour, Boiler only. It 11 i i 5 If e m a 1 At end of Boiler and difFei-ence above Steam Temp. 1 •d a O Percentage by Volume. CO2. 0. CO. Sq. ft. Sq. ft Ft. Ft. Ins. Sq. ft. % 7. % Lljs. sq. in. F." F." °U X 7. Lbs. Lbs. Lbs, 733 685 27 7 - 34 52-5 10-0 62-5 62 309° 705° 309 396 395° 8-0 6-8 End End B'l'r. Eco. 3490 9-19 4-77 Do. Do. Do. Do. Do. 53-2 9-8 630 62 309° 688° 309 379 425° 8-0 6-9 End End B'l'r. Ego. 3735 8-19 5i Do. Do. Do. Do. ... Do. 55-6 11-2 66-8 6J 308° 705° 308 397 386° 8-1 7-0 End End B'l'r. Eco. 8574 8-15 4-9 Do. Do. Do. Do. Do. 56-1 11-9 68-0 Do. 702° 308 394 406° 8-6 7-6 End End B'l'r. Eco. 3808 8-37 5-2 717 640 26-2 7 0-4 35 55-7 11-1 66 '8 58 305° 722° 305 417 431° 7-4 11-0 3745 9-95 5-2 Do. Do. Do. Do. Do. Do. 56-4 10-8 67-2 68 305° 726° 305 421° 412° 8-0 10-8 3885 10 '2 5-4 733 685 27 7 34 56-1 10-2 66-3 63 310° 665° 310 355 365° 5-2 3835 10-8 5-2 735 640 20-5 7 35 54-4 11-6 66 56 303° 68&° 303 385 439° No t tak en. 3665 8-5 5-0 Do. Do. Do. Do. Do. 56-2 57-5 11-0 67-0 Do. 671° 303 368 421° Do. 3705 8 '5 5-0 Do. Do. Do. Do. Do. 10'6 68-1 58 305° 667° 305 36'.! 367° Do. 8800 8 -97 5-1 3S HAND FIRING— BRICK SETTING. All with Economisbrs— Chimney Draught. 39 Name of Coal or Fuel. Fuel. Coal when not noted. ^ °.a e3 O < b a <1 < ^ a h! Sq. ft. Sq. ft. Ft Ft. Ins. Sq. ft. 7. 7. 7. Lbs. sq. in. ¥.' F.' 7. 7. 7. Lbs. Lbs. Lbs. 808 640 26 7 0-2 35 55-8 11-7 67-5 58 729° 305 417° 8-5 10-2 0-2 3795 10-0 4-7 305° 424 m. Do. Do. Do. Do. Do. 56-5 10-9 67-4 59 705° 306 401° 8-3 10-8 0-1 3620 10-0 .4-5 . 306° 399 53 750° 550 23 6-2 0'3 19J 56-7 66-7 301 10-2 8-9 2000 5-2 3-6 301° 449 Not given. 7-5 0-2 57-2 57-2 48 295° 550° 295 255 13-0 ... ... 5320 6-86 ... 800 28 8 0-7 39 51-3 51-3 84 327° 670° 327 343 No t tak en. 6100 7-4 7-6 Do. Do. Do. Do. Do. Do. 54-4 54-4 90 331° 670° 331 339 Do. 7170 7-8 8-9 Do. Do. Do. Do. Do. Do. 54-9 54-9- 99 337° 700° 337 363 Do. 6540 7-9 8-1 Do. Do. Do. Do. Do. Do. 55-7 55-7 94 333° 650° 333 317 Do. 6000 8-0 7-4 : Do. Do. Do. Do. Do. Do. 62-3 62-3 98 336° 670° 336 334 Do. 7830 9-0 9-7 5-6 1130 1200 30 8 0-6 38 59-0 115 406° 347 294° Do. 6382 7-3 347° 59 HAND FIRING— BRICK SETTING. Without and with Economiser— Chimney DEAueHT. 41 Fdel. AlB. Tear of Test. ^— . 4^ a 1 ■s 1 STameofCoal or Fuel. ■8.0 P. lis Sop. Ill © rt 2 1^" II Excess of Air at Bndot BoUer in per cent, over that required for Com- bustion of Coal. ^^^^^^i LANCASHIRE STATIONARY, \^l^3w*m^ NO SMOKE TUBES. Coal when not noted. T.TJ. % Lbs. % Authority, Reference, Experimenter, Locality, Remarks, Ac. CoY 14,280 8 13 120 1894 Crossland Report, 1894. Wakefield— economiser trials. 6 cross water tubes, each furnace flue (2' 8J"). 2 tests on same boiler at about same rate of evaporation, same coal giving about same efficiency. 21 22 Do. Do. Do. 12-3 130 Do. Penz- berger. 8936 14i 23 70 1894 Dachau Paper Mill — Germany, Munich Boiler Association — Gyssling — Report. 23 ... 12i 50 1892 English Smoke Report, 1895. Cross & Sons— Bolton. Grids open in doors all time — much smoke. 24 Washed Nuts, Rother- hain. 14,000 6-9 25J ... 1896 Radford— Sheffield — at Davey brothers. 5 Expts. all on same boiler, but with 5 diSerent stokers, but same coal — press, steam about same. lbs. water evap. from 212° p. fBest man stoker 9"0 lbs. lb. coal. t Worst „ „ 7-4 Diff. = 1-6 = 22% vtnii^r. „ffl„^ / Best 62-3 man Boiler effioy. ^^^^^^ 5^.3 Diff. 11-0 = 18% Therefore the difference between best and worst man made a gain of 22% in evap. and 18% in boiler efficy. with same boiler and coal. These 5 Expts. formed a prize competition of hand-stoking, and show the great difference stokers can make. No economiser. Best Expt. this page. Low boiler efficiency. Temperature of gases too high for best economy. 25 26 27 28 29 Do. Do. 7-6 28 Do. Do. Do. 6-8 25^ Do. Do. Do. 6-5 23 ... Do, Do. Do. 7-4 27 ... Do. Maude Rough Small. 12,000 10-7 25 ... 1896 Abbey MUl Pumping Station— P.I. C.E., Vol. 129. Approx. sample coal sent Author by chief engineer, CO. Small coal cost 9s. 3d. p, ton. 30 10 EXPERIMENTS ON LANCASHIRE. TYPE OE BOILER WITH TWO INTERNAL FURNACES, BoiLEE Efficiencies fkom 594 to 64 per cent. PAETICnr.A'Rfl OP BOILEK TESTED. Efficiencies or per cent, of Heat Value In Fuel utilised. S og ti ii m Gases. Water Evapokated. Heating Surface Total. General Dimensions. ".2 ill > 1 ■s 1 Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). 3^ ■S|3 Lbs. of Cold Water eva- porated per sq. ft. Heating Surface per Hour, Boiler only. 1 o cA i s 1 5 ■r i! s 7. 3 5 At end of Boiler and difference above Steam Temp. ,1 11 Percentage by Volume. CO2. 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. °L 7. TJbs. sq. in. F.' p. 7. 7. 7. Lbs. Lbs. Lbs. 860 Not 25 59-6 59-6 98 336° 700° 336 364 No t giv en. 2750 7-0 3-2 given. 30 7 60 2 61-0 60-2 61 308° 680° 308 372 12-0 1-5 5365 7-6 ... 886 32 61-0 85 328° 690° 328 362 No t giv en. 3280 5-0 37 780 28 6-5 0-5 23-5 61-7 61-7 95 334° 530° 334 196 5-6 13-4 2400 4-4 3-1 ' s 883 26 7-7 0-2 34 60-6 60-6 34 280° 717° 280 437 9-5 7-6 1-5 5256 6-3 6-9 ' 538 25 7 0-2 27 62 62-0 31 275° 657° 275 382 0. 7-0 11-0 0-2 3775 7-7 7-0 ; 999 30 7-4 0-2 35 61-9 61-9 69 315° 8-2 8-6 953 8-0 0-95 1068 33 7 0-5 36-6 62-8 62-8 71 311° 522° 311 211 9-3 9'6 0-3 3464 101 3-2 i 582 21 7 0-4 15 63-7 63-7 46 294° 367° 294 73 No 11-7 t tak en. 1438 8-1 2'5 i ! Not given. ... 8-5 0-4 ... 64-0 7-0 71-0 85 327° ■ ... 7180 7-8 42 m HAND FmmG— BRICK SETTING. WitH AND WITHOUT ECONOMISBKS— CHIMNEY DeAFGHT. 43 Fuel. . Am. rear of Test. ^^ i ■s d s s Name of Coal or Fuel. % .Op, 111 t Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. ^= — --t:^^^ I.ANUASHIKK STATION AKy. \^mnJ[% mi 1 o •S ■5 Temperature of Furnace Gases, Analysis of Furnace Gases (at end of Boiler when not otherwise stated). it 3^ ="2 h3 Lbs. of Cold Water eva- porated per sq. ft. Heating Surface per Hour. Boiler only. o I. 1* i a 3 1 i 5 4 o o B Hi At end of Boiler and difference {ibove Steam Temp. i ■a a ^ S °S1 Percentage by Volume. C02. o. 00 SiJ. ft. Sq ft. Ft. Ft. Ins. Sq. ft. % 7. % Uba. sq. in. F." F.' 7, 7. •/, Lbs. Lbs. Lbs. : 7 0-5 64-2 64-2 lO'O 3870 9 '3 ... 385 17 5-5 0-2 134 64-2 64-2 90 331° 500° 331 169 7-2 11-8 ... 850 9-1 2'2 1103 Not given. 26 7-2 0-4 32i 62-0 92 332° 617° 7-8 11 '2 5470 7-4 4-8 1150 3280 30 8-5 0-7 35 65-1 5-7 70 '8 66 313° 560° 313 •247 264° No t tak en 5880 9-1 5'1 1076 30 7-5 30 65-7 65-7 92 332° 684° 332 352 11-3 9-9 1-1 4250 8-6 3-95 900 1200 30 7 31-5 64-2 Not given 61 308° 583° 308 275 313° 14-0 0-2 7625 8-6 8-47 Do. Do. Do. Do. Do. 34 63-4 ... Do. 64-3 56 304° 588° 304 284 325° 13-3 ... 0-4 7298 8-5 8'11 923 64-3 62 309° 800° 309 491 No t giv en. 4100 7-7 4-4 860 23 64-7 64-7 92 332° 600° 332 268 Do. 2310 7-9 2-7 : 780 28 6-5 0-5 23i 67-0 67-0 96 335° 410° 335 75 7-5 11-5 ... 2220 4-8 2-8 44 HAND FIRING— BRICK SETTING. With and without Eoonomisbrs— Chimney and Foecbd Draught. 45- Fuel. AlE. Excess ot Air at End of Boiler in percent, over that required for Com- bustion of Coal. Tear of Test. ^^ 4J a a 'S ■s i s la Name of Coal or Fuel. "a 1^^ it H" II 11 So 3" ^ssz:^^:^^^i LAJ^ CASH IRE STATION ARV. ^miJ[|Ln>^ NO SMOKE TUBES. Coal when not noted. T.U. % Lbs. % Authority, Reference, Experimenter, Locality, Remarks, &e. York- shire, 13,982 3i 14 90 1890 Smoke Report, 1895. Egret MiUs-T-Ashton— Greave's firebrick baffles. Grid doors always open. 41 Ruhr. 13,830 7J 8 160 1895 Munich Boiler Association— Gyssling — 1895. Flour Mills. 42 Bohemian Coal. 11,560 11 26 142 1893 Do. do. Chemical Works — Ingolstadt. 43 Anthra- cite and Durham. 13,600 8 20 1892 Donkin — ^Wandsworth — Ferret Grate. Forced bLast under grate. Large economiser giving only 5'7%. 44 Small Coal. 12,700 6 18 70 1890 Donkin— East London — Ferret Grate. Slight forced air pressure under grate. 45 South Yorkshire Coal. 12,886 11 32i 40 1892 Longridge Report, 1892 — Nr. Manchester. 2' 8J" furnaces — boiler clean — large economiser. Calculated temp, furnace, 3960° (46). \ Do. do. 3640 (47). / 2 tests on same boiler with same coal, and about same evapora- tion, giving ^bput same efficiency. 46 47 Do. Do. 13 30J 42 Do. Washed Coal, EmmaPit. 11,570 ... m 89 1895 Report, Boiler Association, Vienna, 1895. 48 , Austrian Coal. 11,850 ... 14 ... Do. Do. do. 49 Mixed Coal. 6910 10 22J 150 1895 Munich Boiler Association Report, 1895 — Gyssling. Spinning mills — Best efficiency this page. 50 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, Boiler Efficiencies fkom 62J to 71J per cent. PARTICUr,AT?fl OP BOILEB TESTED. Efficiencies or per cent, of Heat Value in Fuel utilised. 1 h as S% ll ll Gases. I Wateb Evapobateo. 1 Heating Suiface Total. General Dimensions. Ms > i 1 Tenmevature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise .stated). ll p o°3 s ll 51 ' 1. ■ st o f 1 Q if "3 ^.1 lllii .1 :3« Percentage by Volume. CDs. CO. [ Sq. It. Sq. ft. Ft. Ft. Ins. Sq. ft. ■/. •/. °u Lbs. sq. in. F.' F," 'to •/. "/. Lbs. Lbs. Lbs. 998 30 7'5 0-3 35 67-6 67-6 60 307° 469° 307 162 14-7 2-7 4722 9-1 4-73 582 21 7 0-4 15 67-5 67-5 57 304° 630° 304 326 12-55 7-2 0-3 2369 10-0 4 Do. Do. Do. 0'35 15 70-4 70-4 50 297° 399° 297 102 8-7 10'4 1277 9-9 2-2 1 I 1 1 582 Do. Do. 0-4 Do. 68-7 68-7 50 297° 400° 297 103 400° 291 109 8-4 10-2 1177 9-9 2-0 Do. Do. Do. 0-4 Do. 69-3 69-3 44 291° No t tak en. 1326 6-0 2 '3 , 935 400 30 7 ... 33 62-8 8'1 70-9 84 327' 700° 327 373 450° 8-9 11-5 5326 9-9 57 Do. Do. Do. Do. ... Do. 71-6 6-8 78-4 83 326° 648° 326 322 390° 11-8 7-7 5266 10-1 5'6 Not stiveu. 640 26-5 7 0-6 35 67-8 11-0 78 '8 56 303° 671° 303 368 421° No t talc Do. en. 7410 9-4 ... Do. Do. Do. Do. Do. 0-5 Do. 68-8 12-1 80-9 56 303° 688° 303 385 429° 7330 9-4 ... 600 27-5 6-2 18-2 68-5 68'5 62 309° 625° 309 216 14-8 2-3 0-01 2659 10-0 4-4 46 HAND FIRING— BRICK SETTING. With and without Eoonomisee— Chimney Dkaught. 47 Fdel. AlK. 1 1 ■s d Z a a 2 1 Name of Coal 01- Fuel. ■fi ill ft Excess of Air at End of Boiler In per cent, over that required for Com- bustion of Coal. Tear of Teat. /^^^\ &;;^^-^^^\ LANCASHIRE STATIONARY. ^^M^m^ ^Q SMOKE TUBES. not noted. T.U. z Lbs. % Authority, Reference, Experimenter, Locality, Eemarlis, be. Horton Small. 13,100 6-7 15-9 80 1897 Donkin — Newcastle— Empire fire bars. Furnace tubes 2' llj" diam. — 5 cross water tubes. 10" fires — 2 steam jets, under eacli grate, and pressure under bars A". 51 Nixon's Naviga- tion, Welsh. 15,560 3-8 18i 55 1887 Donkin & Kennedy — No. 3'Expt., Donkin's Wks., Bermondsey. Ferret water grate — air pressure below bars. EngiTieermg, August 1, 1890. Gases through tubes — split sides and under boiler to chimney — 6" fire. Do. do. No. 2 Expt. Engineering, August 1, 1890. Conical water tubes in each furnace flue — 8J" fire. 2 Expts. at very different rates evaporation — same coal. 52 53 Do. Do. 7-0 lOi 120 Do. Do. 15,955 7-0 lOJ 120 Do. Donkin — Bermondsey Works — Ferret grate. Forced draught,^/' under bars— 8 J" fire— direction gases as above. 5% moisture in coal. Do. do. 4" fire. ^" air pressure under fire bars. 3% moisture in coal. 2 Expts. on same boiler — diflferent fuels — with practically same efficiencies. 54 55 56 57 58 59 Gas Breeze. 8403 20 17 1886 Wigan. 13,363 ... 18i 110 60 1888 Longridge— Report, 1889— Fu-e 6". Gases through furnace — under bottom — split sides to chimney — 2 Expts. with different excess air — better boiler efficiency — same rate of evaporation. More CO2— same coal. Economiser not clean — Best Expt. on this page. 2' 9" furnace tubes — 5 water tubes in each. Do. Do. ... 16i Do. Burgy. 16,020 ... 12J ... 1894 Fletcher's Report on economiser (Green's) — Wakefield, 1894. 2 Expts. on same boiler with same coal, at same rate, and with nearly the same efficiencies. Do. Do. 12-6 ... Do. Coal, West- phalia. 14,110 4 17 28 1896 Saxon Boiler Association — Erfurt. Ordinary horizontal grate. 1J% moisture in coal. 60 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, Boiler Efficiencies fkom 59 to 78"7 pek cent. Pahticdlabs of Boiler Tested. Efficiencies or per cent, of Heat value in Fuel utilised. 1 1 Gases. Watek Evapokated, 1 Heating Surface Total, General Dimensions. £■3 ^ is ^& III > 5 1 Temperature of Furnace Oases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). 11 Sg S Pi ■s|l i la ¥1 §"3 t 1 a CO i! u 0> B 1 a Hill ^1 ■d a g8 5^ Percentage by Volume. CO2. 0. CO. Sq. ft. Sq. ft Ft. Ft. Ins. Sq. ft. °u % % Lbs. sq. in. F.' F." ■/. °U 7. Lbs. Lbs. Lbs. r 965 Not given . 26 6-5 0'15 23-4 69-6 93 333° ... 450° 8-6 10-4 2050 6-89 2-14 Do. Do. Do. Do. 0-20 Do. ... 70-9 95 334° ... 430° 7-9 10-9 1950 6-28 2-03 860 Do. 22 6'5 0-15 20-0 72-2 93 333° 350° 6-5 12-5 ... 1400 10-26 1-63 1 Do. Do. Do. Do. 0-12 25-0 75-8 92 332° ... 308° 6-1 12-8 1230 7-25 1-43 693 400 22 6 0-6 27-5 58-7 5-0 63-7 83 326° 801° 326 475 384° 8-3 9-2 2360 7-87 3-4 Do. Do. Do. Do. Do. Do. 69-8 8-0 77-8 80 324° 818° 324 494 462° 6 '9 10-6 2170 9-46 3-1 665 24 7 0-3 33 74-8 74 '8 59 306° 750° 306 444 9-5 9-1 11-6 9-2 2410 7-67 3-6 Do. L Do. Do. Do. Do. 75-0 75-0 64 311° 667° 311 356 9-2 2610 7-60 3-9 975 28 7'5 30 74-3 74-3 97 336° 507° 336 171 3845 11-4 3-9 Do. Do. Do. ... Do. 78-7 78-7 95 334° 340° 334 6 ... ... 2794 12-1 2'86 ] I. 48 ■:• HAND FIRING— BEICK SETTING. WITH AND WITHOUT EoONOMISEES — ChIMNBT DRAUGHT. 49 Xameof Coal or Fuel. Coal when not noted. Sf^ "Hi.! ^ s o ^1 ft is. Ais. Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. Tear of Test. LANCASHIRE STATIONARY. NO SMOKE TUBES. Autliority, Reference, Experimenter, Locality, Remarks, &c. Austrian, Bavarian, Saar. Bavarian. Small "Welsh Mixed. Do. Clifton Colliery, Notting- ham. Do. Nixon's Nav. ,' Welsh. Do. 9658 16i 15 8434 16 13,700 8^ 9220 20 12,950 12 13,100 n 9900 54 10'8 9800 11-8 14,878 13-6 Do. 9-3 120 1896 140 Do. Munich Boiler Association Report, 1896— Gyssling. At spinning mill — Augsberg. 2 feed water heaters in boiler flues. 2 Expts. on same boiler — same evaporation — same eflcy. — not same coal. 190 Do. 210 Do. Same authority. 2 feed water heaters in flues. 2 Expts. on same boiler — same rate evap. , diff. coal. 130 Do. 170 Do. Donkin — Pellatt hollow fire bars — blocked up. North of London — Ordinary air admission — Galloway boiler. Do. do. — Air passing through hollow bars and through vertical openings. 2 Expts. on same boiler — No. 66 much better efficiency.' IDO Do. 110 Do. Donkin — Pellatt hollow fire bars — blocked up — no air passing through bars. Nottingham — Ordinary air admission — much smoke. Do. — Air going through hollow bars and through vertical opening to back bridge. 2 Expts. on same boiler and with same coal— practically no smoke. 65 1897 1896 ITnwin — "West Middlesex Water yToi\s— Engineer, September 24, 1897. 2 Expts. at difi'erent rates evap. The lower evap. giving best boiler efficiency. Best efficiency this page — Coal 1% moisture. 61 62 64 65 66 67 68 69 70 8 EXPERIMENTS ON LANCASHIRE TYl'E OF BOILER WITH TWO INTERNAL FURNACES, Boiler Effioibncibs fkom 54 to 77 pee cent. Paetiodlaes op Boiler Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. 1 Ss II i 1" Gases. Watkb Evapohated. Heating Surface Total. General Dimensions. 11 1; iil f o ■s Temperature of Fui-nace Oases. Analysis of Furnace Gases (at end of Boiler when not othervise stated). Hi =3 i ■SB Lbs. of Cold Water eva- porated per sq. ft. Heating Surface per Hour, Boiler only. ir 1 it m i ! •SO B il a 6 At end of Boiler and difference above Steam Temp. 1 1^' Percentage by Volume. CO2. 0. CO. Sq. ft. Sq. ft. rt. Ft. Ins. Sq. ft. 7. °u % Lbs. sq. In. F." F." •/. •/. V. Lbs. Lbs. Lbs. 612 J25 ! 6 26 69-8 ..: 69-8 49 297° No t tak en. 1728 10-0 2 '8 Doi Do. Do. Do. 771 77-1 83-7 52 300° Do. 1673 2640 11-0 2-6 645 322 25-5 6-2 ... 105 341° ... 295° 9-0 10-8 4-1 1050 33 -a 7-2 0-4 34 '8 540 54-0 80 " 324° 700° 324 376 ... 6-9 End 10-0 fire 0-0 tube. 4186 6-64 4-0 867 33 6-9 0-6 32-6 640 64-0 65-2 77 321° 716° 321 395 ... 11-2 End 7-1 fire 0-0 tube. 4758 3360 6-17 5-51 960 34i 10-8 0-45 31-0 65-2 ... 85 328° 600° 328 272 ... 13 3-7 0-2 5-5 3-6 477 19-1 6-6 0-2 32-9 691 74-2 69-1 52i 300° 568° 300 268 484° 305 179 9-9 9-5 10-1 10-3 0-02 0-0 1804 6-96 3-8 Do. Do. Do. 1 Do. ... 74-2 58 305° ... 17-4 12-7 2-3 6-9 0-4 1936 9-25 4-0 £0 HAND FIRING— BRICK SETTING, With and without Eoonomisbk — Chimney Dkaught. 51 Fuel. AlK. Year of Test. /^~~\ 4i ■s d 15 Name of Goal or Fuel. ■Sc St- ill 111 || ll 1 Excess t Air at End of Boiler in )er cent. over that equii-ed or Com- bustion of Coal. ^s=zs^:^^s^ LANCASHIRE STATIONARY. ^^mm^^mtmm uo SMOKE TUBES. Coal when not noted. T.V. % ■ Lbs. X Authority, Reference, Experimenter, Locality, Remarks, &c. Welsh, 13,700 7 7-6 ... 1881 Donkin— Barnet Water AVovks. P.I.C.E., Vol. 66, 1881— 3" fires. Gases — through furnaces — under bottom — split sides to chimney, 2 Expts. on same boiler at different rates evaporation — lower evaporation better efficiency. Fires 8" thick. 71 72 Do. Do. 8i 6-7 ... Do. German Hard Coal. 12,745 10 „. 110 1894 Brauer Report— Carlsruhe, Feed water heater— Best eflciency this page. 73 Saxony Coal, 13,980 5 21-7 166 1891 LevickiReport—Hermsdorf— Chemnitz. Horizontal grate — 11 water tubes each furnace flue. Direction gases — through furnace tubes — two sides — under bottom. Transmission heat per sq. ft. p. m. = 76 T.D. (15) 74 Do. Mixed. 11,020 134 28-7 60 End tube. 1889 Same authority— Quarry Works— Dresden. Paucksch — Furnace tubes different diameter— no water tubes. Horizontal grate— Direction gases as above. Transmission, 10"4 T.U. p. m. through boiler plates. (1) 1 75 Brown Coal. 8250 1 23-5 50 1892 Same authority — Brick Works— Saxony. Schreiber grate — no water tubes in furnace flues. Direction gases as above. Transmission, 65 T.U. per sq. ft. p. m. through plates, (23) 76 77 Gas Coke and Coal Mixed. 11,560 19 9-2 110 119 1892 Same authority — Gas Works — Dresden, Horizontal grate — Direction gases as above. Gases taken end 1st run and at end boiler. Transmission, 71 T.U. p. m, (18) 'Gas ! Coke. 14,410 ■6 7-4 26 66 Da No water tubes in furnace flues. 2 Expts. on same boiler at different rates evaporation. Transmission— 75 T.U, p, m, (19) 78 11 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, Boiler Efficiencies feom 57 to 80 pee cent. Pakticulaes of Boiler Tested. Efficienoies or per cent, of Heat Value in Fuel utilised. k u is Gases. Watek Evapoeated. Heating Surface Total. General Dimensions. i Ill 3 Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not , otherwise stated). i 1^ ■S|2 s 'S'S ¥1 9-1 .5 -rt ;," Pi? ■g§ o 1 t 5 0° ca S •s ■s E-1 If Percentage by Volume. CO2. a CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. 7. % 7. Lbs. sq. in. F.° F." 7, 7. °l. Lbs. Lbs. Lbs. 1 640 24-5 6-25 07 21 57 57-0 81 324° 800° 660° 324 336 11-6 9-1 6-7 10-0 0-23 0-16 3400 7'6 5-3 ■ Do. Do. Do. 0-6 Do. 66 6 60-6 Do. 1050° 610° 324 286 12-6 10-4 6-8 8-5 0-13 0-04 4050 6-0 6-3 Do. Do. Do. 0-3 Do. 70-6 70-6 85 328° 850° 460° '■328 332 9-0 7-8 10-2 10-9 0-21 0-19 2500 9-2 3-8 Do. Do. Do. 0-5 Do. 71-2 71 '2 84 327° 960° 735° 327 408 11-7 10-4 7-3 8-6 0-04 0-04 3760 9'1 5-9 ; 640 24-5 6-25 Do. 62-4 62-4 72 317° 750° 660° 317 343 12-1 10-1 5-9 9-9 0-01 0-01 3220 5-3 5-0 Do. Do. Do. Do. 68-4 68-4 79 323° 810° 690° 323 367 11-6 10-3 7-4 9 '4 0-0 0-0 3810 8-7 6-0 Do. Do. Do. 69-7 69-7 70 316° 930° 570° 316 254 9'2 81 10-4 9-2 9-7 11-7 8-9 10-0 0-0 0-0 2670 8-3 4-2 Do. 6 Do. Do. 71-0 71-0 76 321° ... 530° 321 209 0-0 0-0 2520 91 3-9 1070 31 7 '5 0-5 22-6 73 6 73 '6 44 291° 450° 291 159 9-4 8-2 9-4 11-2 O'O 0-0 3620 6-5 3-4 Do. Do. Do. 0-5 Do. 76-5 76-5 48 295° "460° 295 165 10-2 8-9 8-4 9-9 0-0 0-0 4600 9-5 4-3 ■ Do. Do. Do. Do. 80-3 80-3 43 290° 465° 290 175 12-1 10-5 7i 9-9 0-0 4860 10-0 4-5 HAND FIRING— BRICK SETTING. No EooNOMiSBR — Chimney Draught. 53 FnEi,. AlE. Year of Test. ^^-— "»^ Eleven Expts. by the Berlin Prussian jr >. SmoJce Commission, 1894, by Chief 1 1 O d CO o 1 Name of Coal or Fuel. Oh 1 lis 111 i ■II Excess of Air at End of Boiler in percent. OYer that required for Com- bustion of Coal. y^:^--^-^^ Engineers Schnbidee. and U. ueahl [^'*'~"^_^ "Vi at and near Berlin, on \^Wnwlfemin^ TWO LANCASHIEE STATIONARY ^^;-^'~^'~y BOILERS. ^<^iM^ NO SMOKE TUBES. Coal when not noted. T.XJ. % Lbs. % Authority, Reference, Experimenter, Locality, Remarlcs, &c. English Coal. 12,8.50 8 26 46 88 1893 4 different Expts. with different coals at different rates firing and evap. — Increasing boiler efficiencies — All 4 on same boiler, with Stauss special air admission behind bridge. Direction gases— through furnace tube— under bottom — along two sides and back along top of boiler. _ _, Two furnace tubes 2' 4" diameter each — 4 conical water tubes. Temperature gases taken at end furnace tube and at end boiler — sampled gases also at both places. 1st at end furnace tubes. 2nd at end boiler. All 1 hour tests —Different rates evaporation— different eflSciencies. All with ordinary horizontal grates. 79 80 81 82 83 84 85 86 Bohemian Brown Coal. 9600 3i 39 37 65 Do. Upper Silesian Coal. 12,300 a 16 91 105 Do. Do. Do. i 23J 50 66 Do. Bohemian Brown Coal. 8200 H 3ii 37 88 Do. Same boiler as Nos. 79-82. Direction gases as above. 4 Expts. with Chubb's air admission at bridge — at different rates^ different coals — decreasing rates of coal and water, and increasing efficiencies. Expts. arranged. in order of boiler efficiency. Silesian Nuts. 12,340 9 25 53 78 Do. Do. 11,500 12i 18 83 122 Do. Upper Silesian. 12,350 44 15i 70 88 Do. Bohemian Brown Coal. 8500 3 28 80 110 Do. 3 Expts. with different coals— on same boiler — increasing rates coal per sq. ft. grate, increasing efficiency and increasing rates water evaporation per sq. ft. 2 furnaces 2' 10" diameter each, with 8 cross water tubes. Kowitzke air admission at bridge. Direction gases as above — ordinary grates. Best efficiency on this page. 87 88 89 Silesian Small. 12,000 6 24i 63 85 Do. Do. Do. 6 24J 50 90 Do. 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES^ BOIT.ER E-FFICIENOIFS FEOM 54 TO 69 PER CENT. PARTICULAnS OF BOILER TESTED. h OS it Gases. 1 Water Evaporated Heating Surface Total. General Dimensions. « ^£ U °^ . Ill > 1 O < or per cent, of Heat Value in Fuel utilised. Temperature of Furnace Oases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). rt >■ ^ o Is PS, 3s 0fi Lbs. of Water Evapor- ated per sq. ft. Heating Surface per hour.Boiler only. o M f 1 > i! B "a g iilii < ■gl ■d a Percentage by Volume. COj. 0. CO. Sq.ft. Sq. ft. rt. Ft. Ins. Sq. ft. X X % Lbs. sq. in. F.° F.» % X % Lbs. Lbs. Lbs. 1068 32-6 6-6 0-50 0-45 36-5 Oast Bars. Wro't. Bars. 56-7 55-5 56-7 55-5 72 Both. 310° 71 311° 483° 477° 12-8 11-4 4-6 6 '3 1-6 1-3 5033 4211 8-5 8-3 4-73, 3-95 ■ Do. Do. ... 0-45 0-47 Cast, Wro't. 58-4 56 58-4 56-0 420° 463° 11-9 11-8 5-6 5-3 0-9 1-6 4756 5194 8-5 8-2' 4-47 i 4-88 ; Do. Do. ... 0-45 0-47 Cast. Wro't. Cast. Wro't. 59 4 60-5 59-4 60-5 71 311° 323° 350° 12-5 12-3 6-0 5'5 0-7 1-1 4539 4645 7-9' 8'0 4 •26- . 4-36 Do. Do. 0-50 0-40 60-4 58-4 60-4 58-4 71 311° 467° 560° 10-5 12-3 8-2 5-6 0'8 0'6 . 4250! 4534 9'3 9-6 4'0 4'2 4 '53 ' 4-36 Do. Do. 0-48 0-43 Cast. Wro't. 60-5 64-5 60-5 64-5 71 311° 480° 465° 12-5 11-8 5-8 7-0 01 0-0 4825. 464r 1 9-2 1 9'8 Do. Do. 0-45 0-45 Cast. Wro't. 61-9 53-9 61-9 53 '9 71 311° 485° 509° 12-7 12 '7 5 '2 4-2 1-9 2'2 5087 4478 l:0i-2. 8-9 478 4-20 Do. Do. 0-46 0-46 Cast. Wro't. 66 60-3 66-0 60-3 71 311° 464° 413° 11-7 10-6 6-8 8-1 01 0-8 51 56. 423.7' 9-3 ■ 8-5 1 4-84 3-98 Do. Do. 0-50 0-55 Cast. Wro't. 69-0 64-8 69-0 64-8 71 311° 488° 459" 13-2 12-6 6 '3 5-3 0-0 0-3 5130 4846 10.-O! 9-4 4-82 4'55 H HAND FIRING— BRICK SETTING. No EcoNOMisEK— Chimney Deattght. 55 Fuel. Air. Tear of Test. ^^ ^N. Special set of 16 Expts. made at 1 ■s 1 KameofCoal or Fuel. §1 •23 111 n Excess g >; ofAivat ftg End of ■gM Boiler In b u pe)^ cent. S g. over _, ? that S-g requu-ed S^ for Com. .^ bustion ^S of Coal. hy^—^ =^^^^^^ Report, Reiche — all on same Boiler an d ^RUumlHuuiku.^ same Stoker ; same press, steam. X^w^'^Xj^ LANCASHIRE STATIONARY. ^%r=^-r^ NO SMOKE TUBES. Coal when not noted. T.TT. % Lbs. % Authority, Reference, Experimenter, Locality, Remarks, &c. Rhenish. 14,646 10-0 10-0 19 164 27 41 1880 Sv/mmary of the Mxperimenls. All these Expts. were made on same boiler (Moeller) and in pairs — same coal only for a pair of Expts. — of each . / one with east iron grate bars. P \ one with wrought iron grate bars. 16 Expts., 8 kinds flaming coals, to find out most suitable bars for each coal. Cast iron bars had 11-5 sq. ft. air space. \ Wrought iron bars had 16 '3 sq. ft. air space. J Total grate area same in all =36 "5 sq. ft. 2 furnace flues, 2' 9 J" diam., with 14 conical water tubes in each — furnace flues not corrugated. Each Expt. 8 hours. Direction gases — through furnaces — split sides — under bottom to chimney. Boiler cost £420— Bk. wk., 1540 c.f.— £47. % air in excess over that required for coal from 24 to 61. Lbs. coal per sq. ft. grate varied from 15 to 20 '5. Evap. per sq. ft. heating surface p. hour from 4 to 4'9 lbs. i Cast iron bars with smaller air spaces between bars generally \ 1 gave best boiler efSciency with these 8 kinds coals. / Arranged in order boiler efflciencies with cast iron gi-ate bars. 80 SI 82 S3 84 95 96 97 98 99 100 101 102 103 104 105 Dutch. 14,176 14-0 9-0 18 204 35 33 Do. Konig's Grube. 12,837 11-0 13 18J 18i 39 35 Do. Boni- facius. 14,859 13-0 130 15 164 1 62 36 Do. Pluto. 14,674 6 5-0 17 164 37 48 Do. Schid. 15,966 8-0 15-0 16 16^ 33 24 Do. Zoll- verein. 13,621 14-0 190 18 16i 46 61 Do. German- icus. 14,070 12-0 10-0 16i 16| 32 33 Do. 9 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, Boiler Efficieis"oibs fkom 53 to 74 per cent. Pajiticui-ahs of Boiler Tested. EfFiciencies 1 n as >° s £ d. SS IS ss Gases. ■Water Evapokated. Heating Surface Tofcil. General Dimensions. =■3 n m 1 o o P or per cent, of Heat Value in Fuel utilised. Temperature of Fui'nace Gases. Analysis of Furnace Gases [at end of Boiler when not otherwise stated). h i| li =■3 ^^1 i ill! is i 1 S 1 Ed ui s ■§sl 1 Percentage by Volume. COj. 0. CO. i S^. ft. Sq. It. Ft. Ft. Ins. Sq. ft. % % % Lbs, sq. in. F." J.. X % X Lbs. Lbs. Lba. 356 No t giv en. 17-8 52-8 52-8 137 359° 610° 359 251 No t giv en. 1700 6-95 4-8 Do. Do. Do. 53-7 63-7 142 362° 711° 362 349 Do. 1880 7-06 6 -3 Do. Do. Do. 60-2 60-2 140 361° 545° 361 184 Do. 1100 7-93 3'1 900 32-8 6-8 0-9 en. 30 70 70-0 75 320° 790° 320 470 13-0 6-4 7200 10-2 8-0 1075 No t giv 33 72 72-0 77 321° 610° 321 289 10-4 7-7 6300 7-6 5-9 ,1 907 Do. 33-2 66-3 66-3 61 308° 676° 308 368 Do. 6100 7-8 6-7 Do. Do. Do. 70-7 70-7 65 312° 691° 312 379 Do. 5900 8-7 6 '5 Do. Do. Do. Do. 72-7 72-7 57 305° 581° 305 276 Do. 6100 9-2 6-7 Do. Do. 74.-1 ... 74-1 51 299° 628° 299 329 Do. 6420 8-7 7-1 HAND FIRING— BRICK SETTING. No ECONOMISEKS — CHIMNEY DRAUGHT. 57 Fdbi,. Air. Tear of Test. ^— ^ 1 1 6 !zi 1 Same of Coal or Fuel. II .S3 1 g' It If Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. Lr-~^-=._ ^=-J\ LANCASHIRE STATIONARY. \^nm^|^m^ NO smoke tubes. Coal when not noted. T.U. % Lbs. % Authority, Reference, Experimenter, Locality, Remarks, fto. Prussian Coal. 12,700 ... 17-6 1897 Vienna Boiler Association, 1897— Report. Corrugated furnace tubes. 3 Expts. on same boiler with same coal at different rates firing and evaporation — Better efficiency with less evaporation. (7) 106 107 108 Do. Do. ... 18'5 107 Do. Do. Do. ... 15-0 42 Do. English Coal. 14,100 li 27 1891 Paucksch Boiler— Magdeburg. 2 furnace tubes made of 16 short pieces with flanges. Largest diameter, 2-6 ft. \ Vo™;„„ M^^^t-^r.^ SmSlest „ 2-1 ft. / ^^^^""^ diameters. Authority as above. 109 Silesian Coal. 11,800 7 24i 80 1891 Paucksch Boiler — Schroeder — Dantzig. Same kind furnace tubes. Authority as above. 110 Lower Silesian . Small Coal. 11,360 ... 26i Do. Authority as above. Paucksch Boiler. For drawing this boiler see p. 281. (31) Furnace flues in' short pieces of different diameters. 4 Expts. on same boiler with different coals and rates evaporation. (23) (15) Best Expt. this page. (32) 111 112 113 114 Lower Silesian Coal. 11,930 ... 22-7 ... Do. Upper Silesian Coal. 12,200 22-5 Do. ^ Do. Do, ... 24 ... Do. 10 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH TWO INTERNAL FURNACES, Boiler Efficiencies from 65J to 74J per cent. Pabticulaes op Boiler Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. 1 h il Gases. Wateb Etaporaieii. Heating Surface Total. General Dimensions. £■8 U |l ill > 1 < Temperature of Furnace Gases. Analysis of Fumaco Gases (at end of Boiler when not otherwise stated). il 3S il il fHKg O p 1 1 1 |§ o CO ii B 1 At end of Eoiler and difference abOYo Steam Temp. Si °l < Percentage by Volume. C0„. 0. CO. Sij. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. X % % Lbs. sq. in. F." J.. % % °4 Lbs. Lbs. Lbs. 1722 No t giv en. 33 65-6 65-6 85 328° 550° 328 222 Tak no in en, t t giv repo at en rt. 5500 5-9 3-2 2022 Do. 35 67-6 67 '6 77 321° 435° ,321 114 Do. 4650 5-5 1 2-3 ' 2350 Do. 38i 71-7 71-7 94 334° 490° 334 156 Do. 6100 8-2 2-6 ^ 2350 Do. 38i 71-9 71-9 94 334° 478° 334 144 Do. 6100 7-8- 2-6 ' 2300 Do. 374 73-0 73-0 57 305° 470° 305 165 Do. 6330 8-6 2-3^ 1744 Do. 33 73-4 73-4 109 343° 460° 343 1L7 Do. 3488 6-1 2'0 1 ' 915 Do. 17-2 73-5 73-5 76 321° 410° 321 89 Do. 1820 7-9 2-0 ! Do. Do. Do. 73-5 73-5 88 330° 435° 330 105 Do. 2200 8-4 2.4, 1614 Do. Do. 26-2 74-3 74-3 156 368° 482° 368 114 Do. 3700 9 '3 8-8 23 i 2350 38i 74-6 74-6 88 330° 487° 330 167 Do. 6800 J $8 HAND FIRING— BRICK SETTING, WITH SMOKE TUBES. No EooNOMisER — Chimney Drattght. 59 FtTEL. AlK. Tear of Test. 1 1 1 O 6 O NameofCoal or Fuel. II i p Excess ot Aiv at End of Boiler in per cent, over that required for Com- bustion of Coal. ^ /''^^ ; — ^^ -= — OKE TUBES. ! Coal when not noted. ^^:==^- STATIONARY, WITH SM T.U. X Lbs. % Authority, Reference, Experimenter, Locality, Remarks, &c. Coal and Brown Coal. 8708 Not given. 31 81 1895 Vienna Boiler Association Reports of 1895-1896— all Expts. on this page. 1 2 Brown Coal Nuts. 7939 27 190 Do. Silesian Coal. 11,200 20 95 1896 (35) 2 Expts. on same boiler and with same coal. Same evaporation, same efficiency. (40) 3 4 ' Do. 10,470 21 85 Do. i(' Austrian Coal. 11,400 184 116 Do. (29) 5 ■ 6 ' 7 8 H Small Slack. 8015 19-7 73 1895 ;•! Small Coal. 10,380 17 120 Do. 2 Expts. on same boiler, at rather different rates of evapora- ' tion — same efficiency. Do. 11,070 18 100 Do. Prussian Coal. 12,070 ... m 120 1896 (18) 9 10 oilesian Coal. 11,385 ... 21 83 Do. This is third Expt. on this boiler at different rates. See Nos. 3-4 above. This (No. 10) is best efficiency this page. (30) 6 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH THREE INTERNAL FURNACES,-: Boiler Efficiencies from 52 to 667 pee cent. . Pahticulaes op Boiler Tested. Eff inie ncie^ II If en Gases. Water Evapoeaiej)," 1 Heating Surface Total. General Dimensions. > 1 o 4 or per cent, of Heat Value in Fuel utilised. Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). St, P 11 1.:! ¥1 1.1 1 t 1 r W.S S 7. At end of Boiler and difference above Steam Temp. 1 o i Tj a ^ S Percentage by Volume. CO2. 0. CO. . Sq, Jt. Sq. ft. Ft. Ft. Ins. Sq. ft. 7. 7, Lbs. sq. in. F.' F.' 7. V. 7. Lbs. Lbs. Lb.. 1 1300 960 30 8-5 1-0 33-8 52-0 10-0 62-0 98J 336° 636° 336 300 469° 4-8 14-8 oa5 7720 8-7 5'9 Do. Do. Do. Do. Do. Do. 57 8-0 65-0 98 336° 568° 336 232 395° 5-0 14-5 0-02 7293 9-4 5'6.: 1270 1033 30 8 '5 0-9 38 54-2 7'0 61-2 96 335° 450° 335 115 395° No t tak en. 7810 7-3 -f- 51 ( 1186 852 30 8-2 36 66.1 7-0 73-1 100 338° 666° 338 328 403° 11-0 3-7 0-4 6027 9-3 Do. Do. Do. Do. ... Do. 667 7-0 73-7 100 338° 656° 338 318 356° 12-4 2-9 0-4 5895 9 '3 4'9 1 EXPERIMENT ON A LANCASHIRE BOILER WITH THREE INTERNAL FORNACES, 1014 2060 27 8 0-6 45-7 60 5 4'8 65-3 73 318° 608° 318 290 ... No t tak en. ' 5300 9-0 J HAND FIRING— BRICK SETTING. With Economisee — Chimney Dkaitght. 61 Fuel. XamtfofCoal or Fuel, Coal when not noted. ^ a ■» 5 5 as Lbs. of Air at Endot BoUer in per cent, over that required for Com- bustion of Coal. Tear of Test, 3 FURNACE TUBES. NO SMOKE TUBES. STATIONARY. Authority, Reference, Experimenter, Locality, Remarks, &c. Not given. Do. Dirty, "Wet Slack. Burnley. Do. 12,869 11 26-4 12,869 13 .24- 13,050 13 30 13,492 8-5 19-3 Do. 9-8 18 '8 300 1892 280 Do. Crossland — Engineer, March 11, 1892. Blackburn 160 ft. chimney. 5% priming. 2 Expta. on same boiler. 1891 Fletcher — "Balls" tipping bars — Blackburn. Test from Fletcher Manchester to Author. 70 1891 50 Do. Longridge's Report, 1891 — Manchester. 2 Expts. on same boiler — There is risk priming with these boilers. T.U. per sq. ft. of surface p. m. = 152. Through boiler plates — Best efficiency this type. Burnley. BRICK SETTING— MACHINE FIRING— NO SMOKE TUBES. With Economisek— Chimkey Deaught. 14,495 7-6 15 1895 Fletcher — Halifax — Whittaker stoker — hollow bars with steam jets. From Fletcher Manchester to Author. 6 EXPERIMENTS ON DRY BACK TYPE OF BOILER WITH TWO INTERNAL FURNACES, BoiLEE Efficiencies fkom 55 to 73^ pee cent. Paeticulars or Bohee Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. •a S k It 11 Gases. Water Evapoeated. Heating Surface Total. General Dimensions. II ill 1 •3 4 Temperature of Furnace Oases. Analysis of Fm-nace Gases (at end of Boiler when not otherwise stated). k Son 0^ ¥1^ 1° 1' J 1 5 SI a 1 At end of Boiler and difference above Steam Temp. 1 og 11 5^ Percentage by Volume. CO2. 0. CO. Sq.ft. Sq. ft. Ft. Ft. Ins. Sq. ft. 7. 7. 7. Lba. sq. in. F.° F." 7. 7. 7. Lbs. Lbs. Lbs, ;] 1030 10 8 0-25 284 54-8 54-8 57 304° 635° 304 331° 5-5 14-7 2980 6-6 - 2-9 ^ 1030 10 8 0-3 28i 55-0 55-0 59 306° 707° 306 401 7-5 11-0 3360 6-6 3>3 1200 10 8 0-6 35 56-4 56-4 62 309° 669° 309 360 '7-3 10-0 0-5 5400 6-8 4 '5 402 8 7-2 0-2 12 61-7 61-7 81 324° 574° 324 250 No t tak en. 1793 8-5 4-5 1200 10 8 0-45 35 65-0 65-0 66 312° 623° 312 311 8-5 i 10-0' ! 4340 7-7 3'6 1 EXPERIMENT ON A DRY BACK WITH TWO INTERNAL FURNACES WITH SMOKE TUBES, 930 12 10-5 73-4 73-4 160 370° 584° 370 214 9-5 ... 8000 9-56 8'6 ! HAND FIRING— BRICK SETTING— ON LAND. No EcoNOMisBE — Chimney Dkaxjght. 63 Fuel. Name of Coal or Fuel. Coal when not noted. ■so II 1§S oO Pi n T.U. .S3 ■et% gS.1 ^ Air. Excess ol Airat End of Boiler in per cent, over that required for Com- bustion of Coal. Tear of Test. DRY BACK BOILER, WITH SMOKE TUBES. STATIONARY. Authority, Reference, Ezperimenter, Locality, Remarks, &c. Blantyre Dross. Blantyre Dross. EU Dross. Nixon's Navig. Ell Dross. 11,675 Do. 11,734 13,280 11,514 11 n 10 15-7 19 21 21-5 16 240 150 160 120 1892 1892 1892 1897 1892 English Smoke Report, 1895— Geddes fire doors. Brick combustion chamber at back of boiler. English Smoke Report — Geddes fire doors — brick setting. Spread firing — alternate. Hele Shaw — Liverpool University College. 30 4" smoke tubes — 8 ft. long. Test made Author's request — No brick setting. English Smoke Report, 1895 — Firing alternately. At Messrs Laidlaw, Glasgow — brick setting — Geddes fire doors. DRY BACK, WITH SMOKE TUBES. MACHINE FIRING— ON LAND— NO ECONOMISER— CHIMNEY DRAUGHT. Scotch. .40 to 45 100 1895 Kennedy — 3J' furnaces — 166 3" smoke tubes — steam super- heated 60°-80° — Edinburgh — 26 small superheating pipes above boiler — partly brick setting. I. M. Eng., 1896— Sinclair's stoker. 11 EXPERIMENTS ON DRY BACK TYPE OF MARINE BOILER WITH TWO INTERNAL FURNACES, ' Air at temperature of atmosphere (60° to 70° F.). Top of fire bars to crown of furnace, 1' 3 J" — all with same coal Particulars of Boiler Tested. . Efficiencies or_per[cent. of Heat Value in Fuel utilised. ■a § . 11 Si ii Water Evaporated. Fuel. Air, S n H ■s 1 Beating Surface Total. General Dimensions. i ■S.S 11 =3 §•■3 II =1 Lbs. of Water ETapoiated per sq. ft. Heating Sur- face per liour, BoUer only, from 212°. Name of Coal or Fuel. ■S.9 1"' lil. t U §^ So. It Lbs. Air admitted per lb. Coal. 9 o a O J i Boiler oniy. Sill 13 Coal when not noted. Sq. ft. rt. in. Ft. in. Sq. ft. % Ms. sq. in. F." Lbs. Lbs. Lba. T.U. % Lbs. Lbs. Incli Water 446 14' 9" 6'0" 14-6 65-0 55 303° 779° 303 476 2353 9-16 5-27 Stella Nuts, New- castle. 13,620 1-2 17-5 12-25 Do. Do. Do. Do. 657 Do. 815° 303 51ii 2455 9-26 5-5 Do. Do. 1-1 18-1 13-1 Do. Do. Do. Do. 66-4 Do. 728° 303 425 2447 9-36 5-48 Do. Do. 1-2 17-8 13-8 Do. Do. Do. Do. 65-8 Do. 768° 303 465 2562 9-28 5-74 Do. Do. 1-4 18-6 14-0 Do. Do. Do. Do. 67-1 Do. 764° 303 461 2580 9-46 5-78 Do. Do. 1-5 18-6 16-8 Do. Do. Do. Do. 68-2 Do. 757° 303 464 2657 9 '62 5-95 Do. Do. 2-6 18-8 16-6 Do. Do. Do. Do. 68-6 Do. 775° 303 472 2612 9-68 5-85 Do. Do. 2-3 18-4 17-3 Do. Do. Do. Do. 71-0 Do. 748° 303 445 2710 10-01 6-07 Do. Do. 2-1 18-5 18-2 Do. Do. Do. Do. 72-2 Do. 788° 303 485 2532 1019 5-67 Do. Do. 2-2 17-0 20-4 Do. Do. Do. Do. 73-2 Do, 767° 303 ,464 2646 10-33 5-93 Do. Do. 1-8 17-5 17-3 Do. Do. Do. Do. 72-7 Do. 701° 303 398 2637 10-25 5-91 Do. Do. 2-2 17-4 18-5 In above 11 Experiments with natural draught, with same boiler, coal, stolier, and steam pressure, the quantity of ! better combustion. Fire bars too high. In 3rd and 4th sets of Experiments the bars were lowered 3 inches. -For plotted Gases not analysed. ilr admitted was grafliiaW results of these 11 Expn"'! HAND FIRING, WITH 88 SMOKE TUBES— NO BRICK SETTING— NO ECONOMISER. FiKE Tubes, 2' 3" diam. — Chimney Dkaught. stoker, and steam pressure.— Speacc's Expe,rvm',ni.s, North-East Coast Engineers and Shipbuilding, 1888, Vol. 4. STATIONARY, DRY BACK. Object was gradually to increase quantity of air fromaninsuffioientc|uantityofl241bs. 1 jQ.^ H,3_ ^^i to a sumoient quautity oi l7i lbs. J ° theoretically required for coal combustion. Other condi- tions very little varied. Boiler efficiency gradually increased from 65 to 73%. 88 25" smoke tubes, 5' 9" long. All trials 6 hours. Expts. made in 1887. 65 All air going through fire bars, none admitted top of bridge. Thick smoke after stoking and raking. Much blue CO flames. Fires 9" to 10" thick. (1, 2, 3) In this set some holes open to bottom of bridge. Better efficiency, better evaporation, less smoke. (4, 5, 6) More air at bottom of bridge, better efficiency, better evaporation, less smoke, and less temperature of gases. (7, 8, 9) More air at bottom of bridge, efficiency, etc. , about same as last. (10, 11, 12) Very much less smoke in this experiment than in first (50% less). Some air admitted at the two doors, and air admitted at bottom of bridge also. (13, 14, 15) More air admitted at the two doors, and also at bottom of bridge. (16, 17, 18) In the four experiments same quantity of air admitted bottom of bridge, but quantity admitted at doors gradu- ally increased. Better efficiency, better evaporation, less smoke, less temperature of gases. (No air at top of bridge.) (19, 20, 21) More air admitted at the two doors, and at bottom of bridge also. (22, 23, 24) Air at doors and bottom of bridge, but now admitted first time at top of bridge. Grates 14-6 sq ft. / 6-1 sq. ft. openings ( .^^ ^^^ ^j^^ ^^^^^^ experiments. 29 fire bars, i" I 8 -5 , , bars. \ (25, 26, 27) Air at doors, bottom of bridge, and at top of bridge. Best result this page. Only 27 fire bars (two removed to give more air). (28) Air at doors, bottom of bridge, and at top of bridge. Only 25 fire bars (two removed to give more air). (29, 30, 31) More air, better results, less smoke. increased from 12i lbs. per lb. coal (boiler efflciency 65) to 17J (boiler efficiency 73), all other conditions being about the same. .50/^ less smolce, ments see Fig. 11a, page 7. Lbs. coal p. sq. ft. grate p. hr., 17J to 19— lbs. water p. sq. ft. heating surface p. hr. , 5\ to 6. Tubes cleaned daily. 5 EXPERIMENTS ON DRY BACK TYPE OF MARINE BOILER WITH TWO INTERNAL FURNACES, Air at atmospheric temperature (55° to 75° F. ). Top of fire bars to crown PAETICTTLATtS OF BOILEE TESTED. Efficiencies s Gases. Water Evapoeated. Heating Surface Total. G-eneral Dimensions. =■3 1-9 u > 1 a o S < or per cent, of Heat Value in JFuel utilised. Temperature of Furmice Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). ijWg s la III 1. It o Is i 1 S 1 ■3 At end of Boiler and difference above Steam Temn. .1 °i 11 Percentage by Volume. COj. o. CO. Sq. ft. Sq. ft. Ft. in Ft. in Ins. Sq. ft. % % X Lbs. sq. in. F.° F.- % % X Lb.i Lbs. Lbs. 446 14'9" 6'0" ... 10-1 64-7 ... 55 303° 1100° 303 797 919° 303 616 No t tak Do. en. 3924 9-06 8-79 Do. Do. Do. • »• 7-5 67-8 Do. 2904 9'57 6-5 Do. Do. Do. ... 6-38 64-8 Do. 944° 303 641 Do. 2951 9-15 6-6 Do. Do. Do. Do. 8-25 66-8 Do. 872° 303 569 Do. 2429 9-43 5-4 Do. Do. lO'l 66-6 Do. 934° 303 631 Do. 2842 9-39 6-4 1 In the above 5 experiments with forced draught, same boiler, coal, stoker, and steam pressure ; air admission first then decreased, 64J to 68 ; then decreased to 66. Lbs. of water per sq. ft. of heating surface varied between 9 and SJ, , Higher temperature of gases. Fire bars placed too high. For plotted results of these five experiments, see fig. US, ■ Comparing experiments, page 65, with natural draught, with this page, with forced draught— Not These 5 experiments with the quantity air admitted through the holes above HAND FIRING— NO BRICK SETTING. NO EOONOMISER— COLD FORCED DRAUGHT, of furnace, 1' SJ". Area of Grates reduced. — Spence's Experiments, 1887. 67 AlB. 4J s < 1 1 1 1 6 1 /^ "\ Name of Coal or Fuel. |1 III w .S3 IS Ill a -- If Lbs. Air Coal. ^7 =^ . r=^ — — g^^^ ■'^^^^^ ^^0 Coal when not noted. STATIONARY, DRY BACK. 88 SMOKE TUBES, 2f'— 5' 9" Long. T.TT. % Lbs. Lbs. Ins. Water.' Remarks, &c. Stella Nuts, Newc'stle. 13,620 3-5 42-7 18-6 1-4 No air except through bars. (1,2) 12 13 14 Do. Do. 3-5 40-4 26-6 1-4 More air, better efficiency, better evaporation. Air admitted through doors — Best this page. (3,4) Do. Do. 3-5 39-0 23-0 1-0 Less efficiency, less evaporation— more air admitted through doors — less total air than in last case. (S) Do. Do. 2-5 31-1 20-7 0-6 Less air — better efficiency — better evaporation — less air admitted through doors. (7,8) 15 16 Do. Do. 2-5 29-8 17-5 0-6 About same as last. More air through doors. (9, 10) increased from 18-6 lbs. to 27 lbs., then decreased to 17J lbs. per lb. of coal. Boiler efl5ciency first increased and Lbs. fuel per sq. ft. of grate per hour varied from 43 to 30. Maximum efBciency lower than on last two pages. page 7. sneh good boiler efficiency. Too much air admitted. Much more coal burnt per sq. ft. grate. doors varied sometimes more or less. No air below bridges— very little above. 8 EXPERIMENTS ON DRY BACK TYPE OF MARINE BOILER WITH TWO INTERNAL FURNACES, Air at atmosplierio temperature. Giates 3" lower= 1' 6J" from crown of Paktiouiaes or Boilek Tested. Efficiencies 1 Is Gases. Watek Evapoeated, Heating Surface Total. General Dimensions. £■8 II 1 a o •5 or per cent, of Heat Value in Fuel utilised. Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). ill 1-^ l'-.-?a Hi 1 i 3 i ■ s > 1 1^ S 3 o Eh ■ggl OSS'" o 5 Percentage by Volume. COj. 0. CO. Si. ft. Sq. ft. rt. in Ft. In Ins. Sq. ft. % % X Lbs. sq. in. F.' r." Z % % Lbs. Lbs. Lbs. 446 14' 9" 6'0" 7-2 66-7 55 303° 760° 303 457 No t lak en. 26S7 9-41 6-0 Do. Do. Do. 7-2 75-7 ... Do. 783° 303 480 Do. 2853 10-67 6-4 Do. Do. Do. 7-2 73-6 Do. 764.° 303 461 Do. 2833 10-39 6-3 Do. Do. Do. Do. Do. 6-8 70-5 ... Do. 835° 303 , 532 Do. 3145 9-95 . 7-0 Do. Do. 9-3 65-9 ... Do. 834° 303 531 Do. 3135 9-29 7-0 Do. Do. 5-8 73-4 Do. 739° 303 436 ' Do. 2873 10-35 6-4 Do. Do. Do. Do. Do. 6-2 75-5 72-8 ... Do. 741° 303 438 Do. 2424 10-65 5-4 Do. 8-2 Do. 692° 303 389 Do. 2660 10-27 5-9 Fire bars in these 8 Expts. g" thick, ^" spaces, and i In the above 8 experiments with forced draught at temperature of atmosphere, with same boiler, coal, stoker, and steam mm. Lbs. of water per sq. 'ft. of heating surface varied from 6^ to 7. Coal per sq. ft. of grate per hour from 31i Compared with page 67, the results are better— better HAND FIRING— NO BRICK SETTING. NO EGONOMISER^-COLD FORCED DRAUGHT, furnaces. Same coal, stoker, and steam pressure.— jSpewce's Experiments, Name of Coal or Fuel. Coal when not noted. 6?: gg ri O o So a. .3 ■a li ■Sliio 5S O (3 go Lbs. Air fer b. CoaL ^^LH DRY BACK. 88 SMOKE TUBES, 2i"— 5' 9" Long. 69 Inch Watar. Stella Nuts, Newc'stle. 13,620 Do. Do. Do. Do. Do. Do. Do. Do. Do. Do. Do. Do. Do. Do. 39-5 37-0 37-7 i M 46-3 36-3 47-5 31-5 17-1 20 '3 20-; 22-0 20-0 21-8 22-9 18-0 0-4 Same rate of evaporation as with natural draught. All air going in below bars — none above. This experiment gave 2J% better efficiency than natural draught. (1.2) 0-4 More air per lb. of coal, better efficiency, better evaporation per lb. of coal — ^less smoke. Boiler efficiency about 4% better than with natural draught. Some air above bars — Best efficiency this page. (3, 4) 0-4 More air, less boiler efficiency, less lbs. of water per lb. of coal. Same grate in experiments 17, 18, and 19. (5, 6, 7) 0-75 More air, increased evaporation per sq. ft. heating surface. Less efficiency — less lbs. of water per lb. of ooal. (8, 9) 0-35 Increased evaporation per sq. ft. — less boiler efficiency — less lbs. of water per lb. of coal. (10, 11) 0-66 Less rate of evaporation. Greater boiler efficiency — More lbs. of water per lb. of coal. (14) 0-43 Less rate of evaporation per sq. ft. of heating surface — ^more lbs. of water per lb. of coal. Efficiency higher — 'a little more air admitted. (15, 16) 0-3 Less coal per sq. ft. of grate. Lower pressure in ash-pit — Less boiler efficiency. (17, 18) . placed crossways. Air spaces f total grate area. ■pressure; quantity of air varied from 17 to 23 lbs, per lb. of ooal. Boiler efficiency from 76-7, max., to 66, to 47i lbs. Grate bars lowered, with better results. For plotted results of these 8 experiments see fig. lie, page 7. toiler efficiency — less air admitted per lb. coal. 3 EXPERIMENTS ON DRY BACK TYPE OE MARINE BOILER WITH TWO INTERNAL FURNACES, With hot air at 242° to 261° F, Grates 1' SJ" from crown of furnaces.— PAKTIODI.AES OF BOILEH TESTED. Efficiencies or per cent, of Heat Value in Fuel utUised. S a. ig |l 01 Gasgs, Water Evaporated. Heating Surface Total. General Dimensions. £■8 u n u 1 o o d g < Temperature ol Furnace Gases. Analysis of Furnace Gases (at end of Boiler wlien not otherwise stated). a. « Fh l«a m .sis =°3 II sag*' O it 1° i 1 5 1 O U .O (0 e At end of Boiler and difference above Steam Temp. .s oi ' •a c II < Percentage by. Volume. COg. o. CO. Sq. a Sq. ft. Ft. in Ft. in Ins. Sq. ft. % % X Lbs. sq. in. F.. F.» X X X Lbs. Lbs. Lbs. 446 14' 9" 6' 0" 7-2 76-1 55 303° 701° 303 398 No t tak en. 2700 10-74 6-0 Do. Do. Do. 8-2 756 Do. 719° 303 416 Do. 2675 10-66 6-0 1' Do. Do. Do. 5-8 78-4 ... Do. 665° 303 362 Do. 2517 11-06 6-6 In the above 3 experiments with hot forced draught at a temperature from 242° to 261° — same boiler, coal, stoker, 78i max. Water per sq. ft. per hour of heating surface varied from 5i to 6 lbs. Lbs. of coal per sq. ft. of grate per hour, ' Works, Newcastle. Vacuum in chimney not given — gases of combustion not analysed in any of experiments, ; SUMMARY OF 4 BEST RESTTLTS in PEBOEDING 4 PAGES, 65, 67, 69, 71— All with same boiler, coal, stoker, steam pressui'e, etc. 446 14' 9" 6'0" ... 7-5 67-8 ... 55 303°" 919° 303 616 Best of 5exp erim ents. 2904 9-57 6-6 Do. Do. Do. 14-6 73-2 Do. 767° 303 464 Best of Ilex perim ents. 2646 10-33 5-9 Do. Do. Do. 7-2 75-7 ... Do. 783° 303 480 Best of 8exp erim ents. 2853 10-67 6-4 Do. Do. Do. ... 5-8 78-4 ... ... Do. 665° 303 362 Best of 3exp erim ents. 2517 11 -OS 6-6 70 HAND FIRING— NO BKICK SETTING— NO ECONOMISER— HOT FORCED DRAUGHT. Same coal, stoker, and steam pressure. Spence's Experiments. 71 Air. S •s < ■g 1 i' ■s 6 1 /^^"\ 1 ^ Name of Coal HcJ ■"1 5°..:! r Lbs. Air Coal. -. -. - -: ^- ^p or Fuel. ■s.g '■'^^^==1 Coal when not noted. i— —. g g a o 5 Temperature of Furnace Oases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). 1:.. •S83 s 1 o Li B . .9 t 1 5 B ■i o H At end of • Boiler and difference above Steam Temp. ^1 5" Percentage by Volume, CO2. 0. 1 CO. 1 Sq ft. Si. ft. Ft. Ft. Ins. Sq. ft. 62-0 7. 7. Lbs. sq. in. F.' 791° 363 428 F.° 7. 7. 7. Lbs. Lbs. Lbs. 3324 16 13-5 0-31 104 62-0 145 363° 12-9 5-5 0-8 14,930 8-20 4-5 2910 18-2 13-0 0-36 no 62-0 62-0 80 324° 835° 324 511 9-5 lC-3 0-2 21,510 8-53 7-4 1835 10 13-0 1 07 59 66-0 66-0 105 342° 910° 342 563 11-9 8-2 16,545 9-84 ' 9-0 2257 11 13-2 0'28 52 67-2 C7-2 56 304° 578° 304 274 7-7 11-8 7860 8-87 3-5 j i 1580 10 13-2 0-25 21 69-2 69-2 165 373° 452° 373 79 8-4 11-4 4308 10-63 27 1 EXPERIMENT ON WET BACK BOILER WITH TWO INTERNAL FURNACES WITH SMOKE TUBES, 502 8-5 8-5 22-5 70-0 70 '0 70 316° No t tak en. 4920 8-8 9'8 INTERNAL FURNACES, WITH SMOKK TUBES— HAND FIRING— NO BRICK SETTING— AT SEA, Forced and Chimney Dbattqht — No Eoonomiser. 75 Fuel. Air. Bxeesa of Air at Endot Boiler in per cent, over that required for Com- bustion of Coal. Tear of Teat. 1 O 1 1 1 BOILERS AT SEA. Pro. I. M. Engineers Marine Committee, 1894. Name of Coal or Fuel. "Set ■21 ft go ^^^^ Coal when not noted. "===^=-^ T.V. X Lta. 1 X Remarks, &c. Scotch Coal. 12,770 H 19 45 1889 Meteor, s.s. Natural draught — corrugated furnace tubes. Two double ended boilers— 6 fires and furnaces. 1 Yorkshire and Notting- ham. 13,280 6k 26 100 1890 Colchester, s.s. Natural draught — plain furnace tubes. Two double ended — 6 fires and furnaces. 2 Block Fuel, Belgium. 14,390 n 2 31J 60 1892 Ville de. Do/mm, s.s. Forced di-augbt — plain furnace tubes. Four single ended boilers — 3 fires in each boiler. 3 4 5 "West Hartley. 12,760 19 130 1890 Fusiyama, s.s. Forced draught — plain furnace tubes. One boiler with 3 furnaces. Tyne. 14,830 3 22i 130 1891 Steamship lona. Forced draught— Purve tubes. Two single ended boilers — Best efficiency this set. HAND FIRING-ON LAND— NO BRICK SETTING. South Yorkshire. 14,296 24-7 1896 Seaton, Hull — Shop boiler — Steel. Two 24' furnace tubes— 88— 3" smoke tubes— 5' 9" long. Natural draught. Sent from Seaton — No brick setting. Best efficiency this page. 10 EXPERIMENTS ON LOCOMOTIVE AND AGRICULTURAL TYPE OF BOILEE WITH ONE BOILBE EfFIOIBNCIKS PEOM 57 TO 8I4 PER CENT. Pakticclaks of Boilek Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. 73 % St si il Gases. Water Evapokated. Heating Surface TotaL General Dimensions. £■8 i-s ill > 1 ■5 Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler wtien not otlierwise stated}. Lbs. of Water Evapor- ated per Hour per Boiler, from and at 212" F. 1 Lbs. of Water Evapor- ated per sq. ft. Heating Surfaceperliout.Boiler only, from andat213''S'. ^ ° a . H ^ s 1 1 i5 =1 a° 8 S3. W.2 S i At end of Boiler and difference above Steam Temp. U =1 ^ S Percentage by Volume. OOj. 0. 00, Sq. ft. Sq. ft. Ft. Ft. Ins. Sq, ft. % % X Lbs. isq. in. F.° F.= % y. % Lbs. Lbs, Lbs. ; 228 12 3 0'15 10-5 . 57 57 85 328° 565° 328 227 5-3 15-7 390 8-45 17 228 12 3 0-2 10-5 66 66 212" 560° 212 348 7 '9 12-2 800 9-65 3-6 370 10 4-7 0-5 Sm'ke Box. 10'3 59 59 103 340° 1000° 340 660 6-0 13-2 3100 8-55 8-4 285 11-5 3-5 0-25 10-5 65 65 72 318° 575° 318 257 No t tak en. 1090 9-57 3-8 316 11-5 3-5 0-2 9-7 70 70 61 308° 625° 308 317 11-3 7-3 0-2 1290 10 '8 4-0 , 2240 24 7 0-5 37-2 70 70 140 361° 438° 361 77 No t tak en. 4548 9-6 2-0 V-2 1177 197 4-2 0'8 31-4 73 73 90 331° Do. 8520 10-6 265 Feed Water Heater ... ... 79-7 188 383° 304° 11-9 7-3 0-5 447 11-71 17 6-2 37 859 13-6 4-2 1-0 12-4 80-7 80-7 130 356° 12-4 6-2 1-1 5370 12-2 711 12-7 4-5 ... 15-3 81-5 81-5 107 342° No t tak en. 2620 11 as INTERNAL FURNACE, HAND FIRING— NO BRICK SETTING— ALL WITH SMOKE TUBES. No EcoNOMisER— Chimney and Induced Draught. 75 Fdel. Am. Tear of Tost. • +3 g s H o d a 1 Name of Coal or Fuel. =.3 §2 •S3 III S la £1 Excess otAliat End of Boiler in per cent over that required for Com bustion of Coal 1 , LOCO. TYPE— WITH SMOKE TUBES. A^^^^m Coal when not noted. y, -NOT RUNNING. STATIONARY T.U. % Ll)S. X Authority, Reference, Experimenter, Locality, Remarks, &c. Nixon's Nav., Welsh. 15,560 5-5 6-2 328 1887 Two Expts. on same boiler and same coal and stoker. One evaporating at no pressure and one at 85 lbs., but at different rates of evaporation. In last case boiler working too light for good result. Donkin & Kennedy, (Nns. 4 and 5), University College, London. Evaporation at atmos. pressure — Brick chimney. Engineering, Nov. 21, 1890. 6" fii'e- 34 smoke tubes, 3J" ext. diam. 1 2 3 Nixon's Navig. , Welsh. 15,560 8-6 7-9 160 Do. Scotch Steam Coal. 13,930 35-4 200 1895 Barr — Engineering, Dec. 20, 1895 — Dumbarton. Patterson system — induced fan draught. 120 2" smoke tubes. 4% moisture in steam. Nixon's Nav. 15,560 6-8 10-8 1888 Donkin & Kennedy, No. 18 — Portable — Royal Arsenal, Woolwich. Marshall's — iron chimney. Engineering, Dec. 22, 1893. Smoke tubes as in last Expt. , No. 3. 4 Nixon's Nav. 15,560 2-4 12-4 80 Do. Donkin & Kennedy, No. 11 — Marshall's portable— in yard at Bermondsey — ordinary iron chimney. Engineering, March 18, 1892—50 2J" smoke tubes. Fired well— door open very short time — 4J" fires. 5 Pitsburg. 13,226 3 12-7 1894 Belpaire loco. — Dean's Report. Not clean — U. States — Louisville Water Co, Double furnace. 159 smoke tubes, 3" diam. — 16 ft. long. 6 7 Nixon's Nav. 15,560 5-2 25-5 1889 Donkin & Kennedy, No. 21— Fixed large loco, boiler. Steam .iet in chimney to give induced draught. Royal Belgium Testing Fuel Station, Brussels. Engineering, Nov. 2, 1894— 2^" fires— 226 smoke tubes, l^"diam. Powell Duffryn. 14,200 ih. 14-8 35-5 60 1888 Kennedy & Hopkinson — Soe. Arts Journal, 1889. Semi-portable, with feed-water heater — area not given — Paxman boiler — Judge's Electric Lighting Engine tests. 8 Nixon's Nav. 15,560 5-7 60 1887 Donkin & Kennedy, No. \Z— Engineering, Oct. 21, 1892. Loco, boiler — Gt. Eastern Railway— Fixed temporary in yard for trial — steam jet in chimney (iron) for induced draught — copper fire box— 6" fire. 223 tubes, If" diam. 9 13,420 ... 18-3 ... 1886 Kennedy & Rich — Colonial Exhibition, S. Kensington. Semi-portable — Davey Paxman — 40 H.P. Engineer, Nov. 26/86. Best efBciency this page. 10 10 EXPEEIMENTS ON LOCOMOTIVE AND AGRICULTURAL TYPE OF BOILER WITH ONE BoiLEK Efficiencies fkom 74J to 824 per cent. PASUOULAliS Of BOILEK TESTED. Efficiencies or per cent, of Heat Value in Fuel utilised. 1 k Pa ha |l Gases. 1 Watee Etapoeated. Seating Surface Total. General Dimensions. £■8 11 1 6 1 Temperature of Furnace Gases. Analysis of Furnaco Gases (at end of Boiler when not otherwise stated). Lbs. of Water Evapor- ated per Hour per Boiler, from and at 212= F. =3 li Lbs. of Water Evapor- ated per sq. ft. Heating Surface per bour.JBoIler only, from aildat212°i\ O a . o >^ i 1 1 .s Q III Boiler only. Eeono- miser only. ■i At end of Boiler and diflference above Steam Temp. At end of Economlser. Percentage by Volume. 002 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins, Sq. ft. % % % Lts. sq. in. F.' F." z X t tak X Lbs. Lbs. Lbs. 1412 ... 5-3 27-2 |74 6; ... 74-6 95 334° 400° 334 66 No en. 2438 10-9 1-73 1998 31 6-8 0-5 30-0 78 8 78-8 113 346° ■ 469° 346 123 Do. 5997 12-2 3-00 2310 24 7 0-33 48 80 80-0 125 353° 410° 353 57 No t tak en. 3975 11-2 1-7 249 16-7 10-5 ... 2-74 79-7 188 383° 400° 383 17 304 11-8 7-3 0-5 447 Cold. 11-7 1'8 Gold. Do. Do. Do. Do. 82-0 191 884° 355 10-0 9-7 449 Cold. Do. 1-8 Cold. 202 50 11 3 0-2 3-6 ... 80-5 195 385° 587° 385 202 287 No t tak en. 680 11-3 3-4 Do. Do. Do. 0-26 Do. 78-0 197 386° 560° 386 174 285 Do. 710 11-0 3-5 Do. Do. Do. .- 0-35 Do. 78-5 67 313° 466° 313 153 250 Do. 870 11-1 4'3 is Do. Do. Do. 0'44 Do. 81-0 70i 316° 490° 316 174 267 ft Do. 910 11-5 Do. Do. Do. 0-90 Do. 82'5 71 316° 569° 318 253 335 Do. 1260 11-7 6-2 ; ! 78 INTERNAL FURNACE, HAND FIRING— NO BRICK SETTING— ALL WITH SMOKE TUBES. With and Withottt Feed Water Heater— Draught et Chimney and Forced. 77 F0EL. AlK. Tear of Test. 1 B I ■3 6 1 1 1 £U NameofCoal ^eh •Si iM III 3b. •=» 11 r Excess of Air at End of BoUei- in per cent, over that required for Com- bustion of Coal. LOCO. TYPE- STATIONARY. NOT RUNNING— WITH HMnK-F. TTTRlfS 11 ^. loo. W ; 1 =- 1 Coal when not noted. 1 T.TT. X Lbs. X Authority, Reference, Experimenter, Locality, Remarks, &c. George's Creek, Cumber- land. 14,098 8-0 8-2 1894 Belpaire loco. — Dean & Main— U. States. Taunton — 5% moisture in coal. Dry steam. 11 Do. 14,092 5-0 16-0 1893 Belpaire loco. — Dean & Main Report. New Bedford Water Works— U. States. 5% moisture in coal — dry steam. 160 smoke tubes. 12 Cumber- land Coal. 13,452 7-3 7-4 1892 Belpaire loco. — Jour. Franklin Inst. Dean's Report — City Newton, U. States. 170 3" smoke tubes. 13 14 15 Powell Duffryn. 14,200 15-0 60 1888 Kennedy— Soo. Arts tests— Electric lighting, 1889. Paxman boiler — agricul. type. Feed water heater in smoke box — 167 sq. ft. 53 2" smoke tubes — 8 ft. long. Do. Do. 14-5 90 Do. Welsh. 13,600 16-8 1896 Reynolds— Owens College, Manchester. Expts. sent to Author by request. Feed water heater or economiser in smoke flue under boiler — with scrapers. 5 Expts. , gradually increasing rates combustion and evaporation. Boiler efficiency gradually increased with increased evaporation. Steam pressure not same in last 3 Expts. Little doubtful whether heating value of coal same in all these Expts. Chimney 100 ft. high. Smoke tubes 2" —8 ft. long. 16 17 18 19 20 Do. Do. 17-8 Do. .' Do. ;1 Do. ... 22-0 1897 i \ \ Do. Do. 21-8 ... Do. Do. Do. 29-7 ... Do. For drawing of boiler, see Vol. Forced drauglit by fan. 99, P.I. C.E:— Reynold's paper. 9 EXPERIMENTS ON 8 H.P. AGRICULTURAL TYPE OF BOILER WITH ONE INTERNAL FURNACE, BoiLEK Efficiency fkoji 59 to 84 pes cent. Particulaes of BOILE E Tested. Efficiencies or per cent, of Heat Value m Fuel utilised. 1 1 % m Gases. Wateb Evaporated. Heating Surface Total. General Dimensions. .a's W B o >, m > 1 ■s ■5 Temper.aturo of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). Lbs. of Cold "Water eva- porated per sq. ft. Heating Surface per Hour, Eoiler only. Pi- BO O S 1 ^ 1 i5 i« o u 1 At end of Boiler and difference above Steam Temp. Pei'centnge \yj Volume. CO2. 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. 'L 7. % Lbs. sq. in. F.° F,' 7. 7. 7. Lbs. Lbs. ; Lbs. 149 6 2'5 Not given. 6-0 58-9 58-9 Min. 80 324° 700° 324 376 7-7 11-6 0-5 790 Max. ... 5-3 Max. 168 6-2 2-7 4-2 65-6 65-6 85 327° 480° 327 153 12-0 7-4 720 10-16 4-2 125 6-5 2-4 3 '6 696 69-6 125 352° 680° 352 328 10-6 8-9 0-3 600 ... 4-9 1 i 238 11 ax. 7 2-7 47 72-5 72-5 95 334° 38.5° 334 51 8-9 11-0 357 11-21 1-5 j 218 6-5 2-6 ... 3-4 78 6 78-6 125 352° 441° 352 89 7-7 11-3 430 12-27 2-0 1 192 ... 2-5 ... 2 6 79-4, 79-4 250 406° 435° 406 29 14-2 7'5 5-7 307 12-26 1-6 218 6-7 2-6 ... 3-4 81-4 81-4 155 368° 460° 368 92 11-8 415 12-59 1-9 211 6 2-;" ... 2-6 83-9 83-9 120 350° 388° 350 38 15-7 Max. 2-8 1-2 320 Min. 12-96 1-5 Min. 227 7 2-6 4-3 84 84-0 Max. 150 366° 410° 366 44 8-5 11 '3 365 12-99 Max. 1-6 Prizes were awarded for best results, so all boilers were doubtless in first-class condition and very- Arranged in order HAND FIRING— NO BRICK SETTING— ALL WITH SMOKE TUBES. No ECONOMISEES — INDUCED DbAXTGHT. 79 Fuel. AlK. Tear of Test. Newcastle Series Expts., Eoyal Agricultural Society, 9 Special Expts. 8H.P.,WITH SMOKE TUBES. STATIONARY. s s I •A m ■S. 6 Name of Coal or Fuel. III ■"I IS iij 1^^ ■°s Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. ^ r 1" CoEil when not noted. ij^~^^*^ T nnn att. ax^tttt 3 ' SAME COAL. & ANDERSON'S TESTS. BRAMWELL 1 T.rr. % Lbs. % Authority, Reference, Experimenter, Locality, Remarks, &c. Powell Duffryn, Welsh. 14,940 16 145 1887 Boiler and engine, Alnwick Co. — 24 2J" iron smoke tubes. 21 Do. Do. ... 21 60 Do. Humphrey — 30 2i" smoke tubes, iron.' 22 Do. Do. ... 174 80 Do. Cooper — 22 2^^" smoke tubes, iron. 23 Do. Do. ... 9-3 110 ■Do. Paxman — 53 l^f" smoke tubes, steel. 24 Do. Do. 13-5 145 Do. M'Laren — 51 IJ" smoke tubes, iron. 25 26 Do. Do. 13 30 Do. Eoden & Son— 76 IJ" smoke tubes, steel. Do. Do. 30 150 Do. M'Laren — 51 IJ" smoke tubes, iron. 27 28 Do. Do. 12 20 Do. FoJen & Son — 76 IJ" steel smoke tubes. Do. Do. 87 120 Do. Paxman — 53 1^" steel smoke tubes. Best efficiency this page. 29 well stoked. Lbs. air required per lb. coal for perfect combustion = 11 '38 lbs. of boiler efficiency. 5 EXPERIMENTS ON LOCOMOTIVE TYPE OF BOILER WITH ONE INTERNAL FURNACE, Boiler Efficiency fkom 54 to 76 pbb cent. I Pakticulahs of Boileb Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. ■a s g ■ m Gases Water Evaporated. ; Heating Surface 1 Total. General Dimensions. .S'3 n = £• c c ^ m 9> o o < Temperature of Furnace Oases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). 1^ Si -1 la ... " ° « One Boiler only. P i 1 >> .-> §° O ° H.2 m g V. 7. 1 At end of Boiler and difference .above Steam Temp. At end of Economiser. Percentage by Volume CO3. 0. CO. Sq.ft. Sq ft. Ft. Ft. Ins. Sq. ft. Lbs. !;q. in. F." F.° 7. 7. '■• Lbs. Lbs. lbs. 246 12 3-5 ... 8-25 53-7 ... 53-7 88 330° ... ... 10-5 10-6 1158 frpm 212° 8-1 4-7 \ from 212° Do. ... Do. Do. ... 6-0 69-7 ... 69-7 91 332° 655° 332 323 637° 331 306 12-1 4-8 0-45 1120 12-7 4-5 '\ Do. ... Do. Do. Do. 67-8 67-8 90 331° ... No t tak en. 761 10-2 3-1 Do. ... Do. Do. ... Do. 72 9 72-9 91 332° 615° 332 283 ... Do. 1028 11-0 4-2 2849 1660 34 7-7 0-4 68-7 74-7 175-7 378° 502° 378 124 233 9-3 7-2 0-15 About 6000 11-2 Boiler and Econo. 2-1 ''I About, ; Arranged in order of boiler efficiency, 1 EXPERIMENT ON LOCOMOTIVE TYPE OF BOILER WITH ONE INTERNAL FURNACE, 700 16-6 3-4 0-4 11-6 76-2 76-2 64 311° 504° 311 193 12-1 7-0 2105 7-4 3'0 ;[ HAND FIRING— NO BRICK SETTING— WITH SMOKE TUBES. No EcoNOMisER — Chimney Draught. 81 Ifameof Coal or Fuel. Coal when not noted. 1^ •S3 gs Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal, Tear of Test. " — ^ ; % J '" " LOCOMOTIVE TYPE, SEMI- PORTABLE OR FIXED, WITH SMOKE TUBES. Authority, Reference, Experimenter, Locality, Remarlcs, &c. Powell Duffryn. Oil Fuel. Powell Duffryn. Do. George's Creek, Cumber- land, Lump. 14,570 4i 174 18,000 14,570 4| 12-4 Do. Do. 16 14,450 About. 9-8 100 1897 50 Do. Do. Do. 80 1895 Capper— King's College — Boiler not lagged. 4 Expts. on same boiler — 3 same coal — different rates firing, etc. • 1 patent on fuel. Do. do. Lagged. Patent oil fuel. Do. do. Partly lagged. Do. do. Lagged. Arranged in order of boiler efficiency. Chestnut Hill Pumping Station — Boston, U. States. Professor Millar — I'ech. Quarterly. Belpaire type boiler. 30 31 32 33 34 HAND FIRING— NO BRICK SETTING— NO ECONOMISER— CHIMNEY DRAUGHT— FIXED. i Hard. J Brown. 9450 12 28 53 1889 Lewicki Report, 1896 — Loco, external fired — Dresden — inclined grate, 45°- — no brick work. 110 smoke tubes. If". No. 2. Transmission, T.U. per sq. ft. p.m. = 56. 35 11 EXPERIMENTS ON LOCOMOTIVE TYPE OF BOILER WITH ONE INTERNAL FURNACE, Boiler Efficiencies from 65J to 82J pee cent. PARTICDLAE9 OV BOILER TESTED. {1 is IS ai Gases Water Evaporated., Heating , Surface Totol. General Dimensions. U ill 3 s or per cent, of Heat Talue m Fuel utilised. Temperature of Furnace eases. Analysis of Furnace Oases (at end of Boiler wben not otberwise stated). 3 tia oogn S pa >^ i1 o 30 t s 5 ■s" a a 1 At end of Boiler and difference above Steam Temp. Percentage by Volume. CO2. 0. CO. Sq. ft. Sl. ft. Ft. Ft. Ins. Sq. ft. . "'• X 7. Lbs. sq. in. F.* F." 'U 7o 7. Lbs. Lbs. Lbs. 1358i 11 4-3 7 to 15 18-14 66-6 66-6 169 374° 627° 374 253 No t tab en. 11,600 9-3 8-5 Do. Do. Do. 64 to 11 Do. 70-0 70-0 167 373° 494° 373 121 Do. 11,167 10-3 8-2 ■ Do. Do. Do. 6i to 14 Do. 711 71-1 171 376° 604° 376 228 Do. 11,560 10-4 8-5 Do. Do. Do. 4 to 7 Do. 75 5 77-5 75-5 170 374° 575° 374 201 Do. 12,288 10-9 9-0 Do. Do. Do. 5 to 8 Do. 77-5 167 373° 489° 373 116 Do. 11,000 11-3 8-0 1216 10-6 4-2 4 Max. 18-75 65-6 65-6 162 371° Not taken. No t tak en. 9550 9-6 7-8 Do. Do. Do. Do. Do. 733 73-3 160 370° Do. 15-1 2-0 0-8 11,000 10-8 9-0 Do. Do. Do. Do. Do. 73 8 76-7 73-8 158 369° Do. 12-8 4-1 0-8 9620 10-8 7-9 j Do. Do. Do. Do. Do. 76-7 156 369° Do. No t tak en. 9180 11-3 5 7-611 1. 859 15 4-2 1-2 12-4 81 '3 81-3 125 352° 617° 352 265 Abo as ut sa belo me 4800 12-3 6-6 S from 212° Do. Do. Do. VO Do. 82 6 82-6 119 349° 570° 349 221 11-2 7-8 4380 12-6 ^k HAND FIRING— NO BRICK SETTING. With Smoke Tubes — Induced Draught — No Economisek. 83 Fuel. Air. Tear of Test. 3 I ■A ■A d >5 Name of Coal or Fuel. 1^ Is ea O O Sob. I'S SS.I II 3« Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. LOCOMOTIVE BOILER RUNNING ON RAILS. ^^^^'^ , ^ Coal when not noted T.U. % Lbs. % Autliority, Reference, Experimenter, Locality, Remarks, &c. Not given. 12,840 ... 81 1891 Adams & Pettigrew— P.I.C.E., Vol. 125. South-Western Railway (No. 4). Express locomotive— steel boiler. Feed water measured by checked water meter, also gauge on tender tank (No. 2). Inches induced draught represent the means and maxima (No. 3). Draught varies with road or gradients from 2" to 15" water (No. 5). 5 Expts. placed in order of boiler efficiency — all on same boiler. 240— If" smoke tubes — copper fire box (No. 1.) 36 37 38 1 39 1 40 Do. Do. 13,903 70 Do. 13,583 ... 72 Do. Do. 13,477 72i ... Do. Do. 13,903 624 1891 Barnsley Coal. 14,200 23 64 ... 1894 Beare & Donkin— P.I.M.E., 1896. B. Express locomotive — Lane. & Yorkshire Railway, 4 trials. Do. 220—1^" tubes- copper fire box-— steel boiler. D. Do. do. C. 40 to 70 miles p. hr. between Manchester and York. Probably some priming. All on same boiler— placed in order of boiler efficiency. A. 41 42 43 44 Do. Do. 22, 66 15 Do. Do. Do. 13 p7-3 30 Do. Do. Do. 17 52-6 ... Do. Nixon's Nav. 15,560 5i 32 70 1887 Donkin & Kennedy, No. 15— Great Eastern Railway. Heat acot. overbalances in these 2 Expts. Some priming doubtless — Engineering, Oct. 21st, 1892. 45 46 Do. 15,560 Do. 28 70 1887 223 smoke tubes— copper 2 Expts. same coal. Best tire box. efficiency this page. i EXPERIMENTS ON TWO-STOREY TYPE OF BOILER WITH ONE INTERNAL FURNACE. Boiler Eeficienoibs fkom 63| to 754 pee cekt. PARTICULAES op BotLEE TESTED. Eificiencies or per cent, of Heat Yalue in Fuel utilised. 1 si r Gases, Watek Evaporated.-, Heating Surface Total. General Dimensions. ft HI |6^ f a "3 £ < Temperature of Furnace Oases. Analysis of Furnace Gases (at end of Boiler when not othei-wise stated). I! p ■5-2 il Pit .SofflB. 6 1 . i , 1 5 1 Eh At end of JBoiler and difference above Steam Temp. 1 •d ° s < Percentage by Volume. C02. 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. 7. 7. °L Lbs. sq. ia P." F.° °l„ 7^ 7. Lbs. Lbs. Lbs, 8 '6 800 1375 18 4-5 5-0 0-6 63-7 8-8 72-5 118 348° 356° 348 8 247° 2910 8-7 Do. Do. Do. Do. Do. 69-5 9-4 78-9 143 362° 345° 362 264° 9-1 9-5 2870 8-2 3-6 Do. Do. Do. Do. Do. 70-0 8-2 78-2 Do. 328° 362 239° 12-0 5-6 3150 10-9 3'9 Do. Do. Do. Do. Do. 75-4 11-3 86-7 141 361° 436° 361 75 . 271° No t tak en. 4620 11-7 6-8 ■ 5 EXPERIMENTS ON TWO-STOREY TYPE WITH TWO INTERNAL FURNACES, Boiler Efficiencies from 70 to 81 pee cent. 2044 No t giv en. 40-2 70-0 ... 70-0 53 301° 401° 301 100 No t giv en. 4300 8-8 2'1 ... Do. Do. 71-6 71-6 55 303° 365° 303 32 Do. 4090 9-0 n 1 2100 18-0 16-4 6-5 0-25 .53-7 76-7 76-7 130 355° 450° 355 95 13-8 6-7 5900 3'0 1345 Do. 29-4 78-6 78-6 91 332° 577° 332 245 No t giv en. 5280 9-7 3'9' 2464 Do. 34-0 81-1 81-1 114 346° 311° 346 Do. 5200 9-1 •2'l! Si MACHINE FIRING— BRICK SETTING— WITH SMOKE TUBES. With EcoifoMisBR — Chimney Deaught. 85 Name of Coal or Fuel. Coiil when not noted. ■8.3 5 2 til w T.TT. Ill 111 ss AlK. Excesa of Air at End of Boiler In per cent, over that required for Com- bustion of Coal. Year of Test. TWO STOREY, WITH SMOKE TUBES. CORNISH BELOW— STATIONARY. Authority, Reference, Experimenter, Locality, Eemarks, &c. Small Ordinary. 13,300 18-2 Do. Do. Nixon's Nav. 15,100 Do. 15,000 20 15-4 20'l 105 45 1892 Do. Do. Do. Donkiii — Hydraulic Power Co., Wapping, London. Vicar's Stoker — 4 Expts. on same boiler, with increasing quantities coal burnt, and with increasing evaporation. Boiler efficieiicy higher, with greater evaporation. Furnace tube, 3' 9" diara. Expts. classed in order of efficiency. Corni.sh with 65 — 3" smoke tubes, 5 ft. long, below, and plain oyl. above. Gases samfiled, at end boiler and also at end economiser. Best efficiency this set. HAND FIRING— BRICK SETTING. Without Eoonomisbr — Chimney Deaught. TWO-STOREY LANCASHIRE BELOW. SMOKE TUBES ABOVE. Jrussian Coal. Austrian ' Small Coal. Saxon Brown Coal. Silesiau Small Coal. Lower Silesian. 12,130 12,200 4370 11,950 10,875 Ui 13i 36 56 19i 145 152 36 56 155 1897 Do. 1897 Do. Do. Vienna Boiler Association Report, 1897. (16) 2 water lines. 2 Expts. on same boiler at same rate evaporation. Same authority. (14) Frankel— Z.V.D.L, 6th Nov. 1897. Lancashire below — 102 — 3J" smoke tubes above. One water line. Vienna Boiler Association Report, 1897. Do. Best efficiency this set. (38) 10 EXPERIJIENTS ON TWO-STOREY TYPE OF BOILER WITH TWO INTERNAL FURNACES, BoiLEK Efficiencies from 61 to 75 pee cent. Paeticulabs of Boiler Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. -a a i Il ii Gases. Watee Evaporated. Heating Surface Total. General Dimensions, u ill i o ■s •5 Tempevature of Fui-nace Oases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). 1.1 ="3 i in 51II o . 1° .2 o >, 11 a t 3 1 5 1^ |i s 3 o H At end of Boiler and differenco .ibove Steam Temp, ■si 1^ Percentage by Volume, CO2, 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. 7. 7. 7. Lbs. sq. in. F." F.' 7. 7. 7. Lbs. Lbs. Lb., 1400 11-5 19 6-2 6-2 0-7 26-7 61-1 61-1 109 344° 556° 344 212 9-8 9-0 3704 9-1 . 2-62 1991 12-8 19-7 7-2 7-2 0-3 37-5 60-9 67-7 60-9 82 325° 460° 325 135 9-2 7-7 8-5 11-3 ... 3293 6-5 re Do. 1 Do. Do. 0-37 Do. 67-7 80 324° 494° 324 170 12-6 10-6 5-3 7-9 4560 7-7 2-2 1334 13-0 8-5 6-6 6-6 0-4 29 67-9 67-9 66-4 «8 330° 530° 330 200 13-8 13-0 ... ... 4285 6-0 3-1 2150 No t giv en. 37-0 66-4 95 335° 440° 335 105 No t giv en. 3860 8-0 1-8 1347 Do. 19-0 70-6 70'6 147 364° 400° 364 36 Do. 2280 7-7 1-7 2430 Do. , 41-0 73-1 73-1 95 33.'i° 480° 335 146 Do. 4615 8 '9 1'9 1345 Do. 23-5 73-2 73-2 110 344° 530° 344 186 Do. 3500 8-7 2'6 \ 1'6 P 1345 Do. 21 '5 73-8 73-8 168 370° 420° 374 46 Do. 2150 9-1 1866 Do. 25-8 75-0 75 '0 144 363° 455° 363 92 Do. 3700 5-5 2'0 ss HAND FIRING— BRICK SETTING. No EooNOMisEE — Chimney Deauoht. 87 Fuel. Air. Tear of Test. i- 3 ■s i o D5 ' N'ameofCoal or Fuel. 1 it- III "11 Is. y E:u:ess ofAirat End of Boiler In per cent, over that ■ required for Com- bustion ot Coal. ^^^ ^^® WITH SMOKE TUBES. ^^^ / ^ LANCASHIRE BELOW, Coal when not noted. &''~V'^ fe^.y.^g tiMUKJi; TUuiiS ABOVK \^^^ ^^^ STATIONARY. T.tJ. X Lbs. X Authoi-ity, Reference, Experimenter, Locality, Remarks, &c. "West- plialian Coal. 14,560 5 14-7 115 1895 Saxon Boiler Association — Munter — Erfurt. Ordinary horizontal grate — 1% water in coal. Expt. sent to Author — Like drawing above. 9 Washed Coal. 10,340 9 15 100 127 1890 Lewicki Report, 1896— Chemnitz. 98 smoke tubes, 3|". Cario grate — no water tubes. T.U. per sq. ft. p. m. =31. (11) 2 water lines — like drawing above. 2 Expts. on same boiler at very different rates evaporation. T.U. per sq. ft. p. m. =43. (12) 10 11 12 13 ' Do. 11,000 8 17 48 75 Do. Brown Coal. 7054 9 35 33 41 85 Do. Lewicki Report, 1896 — Dresden. Cornish below — smoke tubes above, 78 — SJ". External fire in front Cornish — Step grate, angle 45°. T.U. per sq. ft. p. m. =62. (6) Small Coal and Slack. 11,770 16-1 Do. Vienna Boiler Association — ^Report, 1895. Lancashire boiler below — smoke tubes above. Expts. arranged in order of boiler eflBcienoy from 66 to 75 %. "Washed Small. 10,640 ... 18-7 57 Do. Like drawing above. Do. 14 15 16 Sllesian Coal. 11,800 14-9 157 Do. Do. Washed Small. 11,570 ... 19-7 39 Do. Do. Austrian Coal. 11,900 ... 13-4 180 Do. ( Expts. 14, 16, 17 on same Do. < boiler, with difft. grate ( areas, difft. rates evairt. 17 Brown Coal and Slack. 7192 ... 30-9 107 1895 Do. Highest efficy. this page. IS 11 EXPERIMENTS ON TWO-STOREY TYPE OF BOILER WITH ONE OR TWO INTERNAL FURNACES, BoiLBK Efficiencies from 56 to 73i pek cent. Pahticulaes or Boilek Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. 1 k si i| If IS Gases Watee Evapokated. Heating Surface Total. General Dimensions. .S'S 11 > 1 o 1 Teniper.ature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). 1 Lbs. of Cold Water eva- porated per sq. ft. Heating Surface per Hour, Boiler only. "3 . 1 O >, i§ J 1 5 a 1 At end of Boiler and difference above Steam Temp. 1 11 < Percentage by Volume. COn. CO. SiJ. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. '1. Lbs. sq. in. F.° F.° "/o 7. % Lbs. Lbs. Lbs. . 869 20-0 15-0 3-2 2-5 0-4 19-4 55-9 55-9 70 310° 532° 310 222 7-7 10-7 1-4 2700 9-0 3-1 945 10-0 20-0 5-5 6-0 ... Do. 61-8 61-8 100 338° 470° 338 132 9-7 9-3 1800 5-9 1-9 945 10-0 20-0 5-5 6-0 ... 18-0 64-9 •:64-9 102 339° 440° 339 101 10-7 8-2 ... 2340 5-9 2 '4 160O 12-5 16-5 6-2 7-0 0-3 28-0 66-1 66-1 127 354° 480° 354 126 7-9 ... 3180 7-1 2-0 1520 15-0 13-0 5-5 6-5 0-4 33-4 67-6 67-6 70 310° 514° 310 204 5-9 13-1 0-2 3625 10-9 2-4 1600 12'5 16-5 6'7 7-0 0'35 |Do. 28-0 67-9 67-9 124 352° 640° 352 188 8-4 3450 6-7 2-2 Do. 12-0 15-3 7-0 7-2 Do. 68-9 68-9 71 308° 338° 308 30 11-0 7-5 0-7 4937 11-1 2-3 2142 12-0 15-3 7-0 7-2 0-3 34-7 69-1 69-1 75 312° 368° 312 56 9-0 9-7 0-1 4664 11-1 2-2 1600 12-5 16-5 6-2 7-0 0-45 33-5 69-6 69-6 126 353° 650° 353 297 9-6 5100 8-9 3-2 236 23 20 '5 2-7 2-0 0-4 9-7 71-1 71-1 102 339° ... No Do. 690 9'1 2-9 236 23 20-5 2-7 2-0 0-3 Do. 73-5 73-5 106 342° ... t tak en. 645 7-8 2-7 HAND FIRING— BKICK SETTING— WITH AND WITHOUT SMOKE TUBES. No EooNOMisER — Chimnbt Dkaught 89 Kame of Coal or Fuel. Fuel. Coal when not noted. ^ «0 a .93 9 p. .0 Excess of Air at End of Boilox* in per cent, over that required for Com- bustion of Coal. Year of Test. TWO STOREY— STATIONARY. EXPTS. ON BOTH THESE TYPES. Authority, Reference, Experimenter, Locality, Remarks, &c. Elizabeth Pit, Bohemian Bohemian Bavarian Small. Elizabeth Pit, Essen, Bavarian Small. Elizabeth Pit, Essen. Elizabeth Pit, Essen. Austrian Coal. Slack Bohemian Maria, Slack Bohemian 15,540 9334 8882 4-0 10,360 15,540 9518 Do. 15,540 12,400 12,320 12,185 4-2 18-8 3-2 19 '5 26 9-1 18-5 12-2 21-2 4-0 15-6 37 14-6 3-5 20-5 6-4 90 82 145 95 75 137 220 125 70 110 1880 Do. 1895 1894 1880 Dusseldorf Expt. — Piedboeuf boiler. Cornish below, with smoke tubes. Cyl. above, plain. Boiler cost £463— brick work, £29—912 cub. (0) Lancashire boiler below. 42 smoke tubes above. do. Do. Passau Brewery. 2 Expts. on same boiler — same eoal — greater evaporation — higher efficiency. Munich Association — Gyssling — Electric Station. Same as Nos. 27 and 24' — All three on same boiler. 1894 1880 1880 1894 1895 1895 Dusseldorf Expt.— Cost boiler, £537— brick work, £40. Lancashire below. Cyl. boiler above, with 50 smoke tubes, 3J". Piedboeuf boiler— Cub. ft. brick work, 1873. (a) Munich Boiler Association — Gyssling — Electric Lighting. Lancashire below. Cyl. above. 82 smoke tubes. Do. do. 2 Expts. on same boiler — about same rates— same efficiency. Cub. ft. brick work, 2924. {k) 19 Dusseldorf Exhibition Report — Cost boiler, £652 — brick work, £63 Lancashire below. Cyl. boiler above, with 102 smoke tubes. 2 water lines. (A) Munich Association — Gyssling — Elec. Lighting, Munich. Lancashire boiler below. Cyl. boiler above, with 82 smoke tubes. 2other Expts. on th is boiler — see Nos. 24-25. Water Works, Nuremburg. Munich Boiler Association — Gyssling — Report Tenbrink inclined grate, about 45°, in centre of large water tube. No smoke tubes. 2 Expts. on same boiler. 20 21 22 23 24. 25 26 27 28 29 11 EXPERIMENTS ON RETURN SMOKE TUBE TYPE 01" BOILER WITH EXTERNAL FURNACE, Boiler Effioiencibs fkom 564 to 81 per cent. Particdlars of Boiler Tested. Efficiencies or per cent, of Heat Value in Fuel utili.sed. £ ft H |l 03 Gases. Waidk Evaporated. Heating Surface Total. General Dimensions. .£■3 mi o 1 Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwisa stated). r feWS III ill ■ssj J Si- ll M ; '3 . it o cA B a |1 '5 n 1 At end of Boiler and difference above Steam Temp. At end of Bcono'miser. Percentage by Volume. COj. 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. X % % Lbs. sq. in. F.- F.° X % % Lbs. Lba. Lbs. 939 24 5 0-6 58 56-6 56-6 98 336° 542° 336 206 5-4 9-8 0-43 6840 5-7 7-3 ; Do. Do. Do. 0-8 53 38-6 68-5 68-5 57'5 99 337° 640° 337 203 7-6 9-5 0-14 7610 7-1 8-1 329 20 3-8 0-4 57-5 74 319° 619° 319 300 No t tak en. 2929 6-57 i 8-86 ■ 728 18 4-5 Do. 0-4 25 58-5 58-5 73 318° 645° 318 327 Do. 4412 8 '92 6-1 Do. Do. 0-4 4-4 Two. 70-0 70-0 71 317° 524° 317 207 Do. 5420 10-97 7-6 1755 Not given 0-25 36 68-3 72-0 68-8 68-3 148 365° 372° 366 7 Do. 3769 10-08 . 2-1 1112 ... Do. 214 72-0 85 328° 389° 328 61 Do. 4994 10-71 4-5 1692 20 6 1-0 1-1 64J 68-8 76-4 95-5 335° 566° 335 230 Do. 10,697 7-8 6-2 Do. Do. Do. Do. 76-4 96 336° 439° 336 104 Do. 4876 8-6 2-9 , 2-1 877 16 6 0-14 36 77-5 77-5 69 335° 486° 336 151 Do. 1840 10-7 1260 16 5 0-4 20 22 81-2 81-2 108 343° 491° 343 148 10-6 10-0 4671 11-38 3-7 90 HAND FIRING— BRICK SETTING. No EcoNOMiSBRS— Chimney Draught. 91 Fdel. AlK. Tear of Test, 1^ RETURN LARGE SMOKE TUBES. 1 CYLINDRICAL AMERICAN TYPE. 9 STATIONARY BOILER 4i 1 Name or Coal or ruel. «?■ °.S §1 % Sua ^1 i 111 III is §1 Ms Excess of Air at End of Boiler ta per cent over that required for Cora bustion of Coal. ^^ Coal when not noted. '^^ ( All Expts. on this page made in United States. '■■■■iniimm T.tr. X Lbs. % Authority, Reference, Experimenter, Locality, Kemarks, &c. Gillespie Small. 9722 13-3 414 250 1893 Bryan — St Louis — Dry steam. Much smoke— 18— 6" smoke tubes. Ordinary grate, 6" fires. Bryan— Efficiency higher, 56 to 68% 9" fires — ^practically no smoke. Hawhy down draught — 2 grates — one above other. 1 2 3 i i 5 Do. 9976 14-3 41 155 Do. Mount Olive. 11,100 13 23 ... 1895 Bryan — St Louis. Thomas smokeless furnace — 8" fires. Dry steam. 4—10" smoke tubes. Atlantic Main. 14,700 7-5 20 ... 1896 Whitham — Philadelphia — Quaker City. Ordinary grate — 26 — 4J" smoke tubes. 132 hours' test in both trials. Hawley down draught — 2 grates— one above other. Efficiency improved from 584 to 70. Do. 15,125 5-7 llj ... Do. George's Creek. 14,240 84 10 1894 Dean & Main — Boston. Lowell Water Wks. — Steam dry. 6 Cumber- land Lump Coal. 14,360 7-4 21-7 Do. bo. do. 7 Mount Olive Lump. 10,980 10-8 43-7 1895 Bryan — St Iiouis. 10" fires— 68— 4" smoke tubes. Do. do. 2 Expts. on same boiler, diift. rates — both with Hawley down draught furnace. 7i" fires — lower evap. of 3 lbs. giving higher efficiency. 8 9 Do. 10,965 6-5 18 Do. 1892 New River and Cumber- land. 13,361 8 9-7 Barrus — IT. States — Lowell Pumps. Steam dry. 140—3" smoke tube. 10 11 Pocahon- tas Coal. 13,553 6i 20 9 75 1897 Hale Report — Boston — Gases under boiler, through smoke tubes and over top — Hawley down draught — 2 furnaces — upper grate water tubes— 12" fire upper grate, 9" lower— dry steam. 91 — 3" smoke tubes — Best efficiency this page. 8 EXPERIMENTS ON LANCASHIRE TYPE OF BOILER WITH EXTERNAL FURNACE, BOILEK EmOIENCIES FROM 46 TO 74 PEE CENT. Pakticclahs of Eoilee Tested. Efficienoies or per cent, of Heat Value in Fuel utilised. ■d It Gases. Watek Evapokated. Heating Surface Total. General Dimensions. So fs 1- Pa II > f o •s g Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). is i m li Lbs. of Cold Water eva- porated per sq. ft. Heating Surface per Hour, Boiler only. iS o 11 m 1 1 S |t "3 Eh a mil <1 T3 rt < Percentage by Volume. CO2. 0. CO. Sq. It. Sq,. ft. Ft. Ft. Ins. Sq. ft. % % % Lbs. sq. in. F.' r.° 7. 7, 7. Lbs. Lbs. Lbs. 630 29 5-7 0-7 31 53-0 53-0 58 306° 680° 306 374 14-8 3-9 0-47 2440 2-85 3-87 860 33 6-5 0-8 41 59-1 59-1 85 327° 442° 327 115 13-9 4-1 1830 2-53 2-12 820 32-8 6-5 0-65 34 60-0 60-0 75 320° 566° 320 236 13-1 7-3 0-5 2050 2-64 2-5 415 20 5'6 0-7 26J 74-3 74-3 47 295° 470° 295 175 15-7 3-4 1720 3-0 4-1 409 17-3 5-4 0-2 52 45-9 45-9 60 307° 536° 307 229 No t tak en. 1313 4-0 3-2 613 26-1 6 '2 0-3 14-5 53-9 53-9 61 308° 608° 308 300 7-8 11-4 1311 5-2 2-1 3-1 Do. Do. Do. 0'24 Do. 55-0 ... 55-0 61 308° 681° 308 373 9-6 8-4 1950 5-4 i 522 21-6 5 '9 0-5 21-7 57-4 57-4 76 321° 669° 321 348 10-7 9-9 6'6 8-0 2310 5-1 4-3 92 HAND FIRING— BRICK SETTING. No EcoKOMiSER— Chimney Dkattght. 93 Fuel. AlK. Tear of Test. ^--^ 1 s s; & s ; •s d 1 1 Name of Coal or Fuel. 1^: Pi fic5 Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. &'^4^'~^1 EXTERNAL GRATE IN FRONT 'L J^ JS °^ BOILER. Goal when not noted. !^-^-rjif Lakge % Water in Poor Coal. STATIONARY— NO SMOKE nimimrararai TUBES. T.U. X Lbs. % Authority, Reference, Experimenter, Locality, Remarks, &c. Brown Coal. 5115 5-7 33 25 1881 Saxon Boiler Association — Munter — Halle. 50% water in coal — Horizontal grate. Sent to Author. 1 2 Brown Coal. 4133 8 21 35 1895 Same authority — Zeitz. 52% water in coal — Step grate in front of boUer. Brown Coal. 4345 94 26i 45 Do. Same authority — HaUe. 51J% water in coal — Step grate in front of boiler. 3 4 5 Brovm Coal. 3909 11 25 20 1894 Same authority — Greppin. 56% water in coal — Step grate in front of boiler. Heating value taken in all these oases with water in coal. Best Expt. this page. Brown Coal. 8460 6 7-2 1891 Lewicki Report, 1896 — Gas firing — Siemens. Dresden — No water tubes. Transmission, T.U. p. sq. ft. p. m. =22. (16) * Brown J Hard 9458 13 20-0 128 1889 Same authority — Dresden Railway. No water tubes — inclined grate, 45° T.IT. p. sq. ft. p. m. =40, transmission. (3) Same authority. Gases through furnace flues— sides— bottom. Grate in front of boiler. T.U. p. sq. ft. p. m. =60, transmission. (4) 6 7 8 Do. 9540 9 28 87 Do. Brown Coal. 8630 15 24-0 67 81 1891 Same authority — gas firing. Gases sampled in 2 places — end tube and end boiler. Transmission, T.U. p. sq. ft. p. m. = 84. (17) 10 EXPEKIMENTS ON ELEPHANT TYPE OF BOILER WITH EXTERNAL FURNACE, BOILKR EfFIOIEXCII'^S from 55 TO 65 J PEE CENT. Particulaks op Boiler Tested, EfFiciencies or per cent, of Heat Value in Fuel utilised. ■a 1 SB il Gases. Water Evaporated. Heating Surface Total. General Dimensions. .So ill ill 1 o o 1 Tempevature of Furnace Gases. Analysis of Furnace Gases {at end of Boiler when not otherwise stated). ft Lbs. ""a li Lbs. of Cold Water eva- porated per sq. ft. Heating Surface per Hour. Boiler only. u O U) a 1 5 1 H 7. At end of Boiler and difference abore Steam Temn. < Percentage by Volume. COo. 0. CO. Sq It. Sq. St. Ft. Ft. Ins. Sq. ft. 7. 7. Lbs. sq. in. F.' F.- 7. V. 7. Lbs. Lbs. 450 1280 23 4 24i 55-5 14-8 70-3 60 307° 600° 307 293 222° 9-5 9-2 0'4 1750 7-1 3-8 f ■■I 480 30 25 3-6 2-3 0-35 15i 55-7 55-7 57-5 83 326° 470° 326 144 8-0 8-5 10-9 5-9 11-0 10-5 1050 7'97 2-2 Do. Do. Do. 0-3 Do. 57-5 86 328° 480° 328 152 1130 8 '23 2-36 ; 430 24 21 3'2 2-0 0-2 13 61-7 61-7 84 327° 610° 327 283 6'7 1730 8 '6 4-0 -•1 1 I 418 515 21 4 19 657 85 328° 322° 13'1 7-9 0-1 1320 7-3 3-2 Do. Do. Do. Do. 4 Do. 13 '0 68-7 Do. 280° 10-7 1270 8-2 3-1 430 1033 24 19 65-5 54-9 78-5 45 293° 264° 10-3 8-3 2100 10-0 4-9 t ! 346 23 4'1 0-22 0-27 20-4 54-9 57 305° 818° 651° 305 346 9-5 7-0 10-7 11-0 1373 5-1 ■ 1 1 3-9 -- Do. Do. Do, Do. Do. 55 6 62 55-6 57 305° 606° 305 . 301 9-1 8-7 9-6 9-9 8-4 7-9 ... 1223 5-2 , 1 3-5 ■/ Do. Do. Do. Do. 0-20 Do. 62-0 61 308° 806° 620 308 312 9-9 10-3 ... 1400 7-3 4'0 1 HAND AND MECHANICAL FIRING— BRICK SETTING— NO SMOKE TUBES. With and without Feed Watee Heatek — Chimney Dbaught. 95 Fuel. Am. Excess at Air at End of BoUer in per cent, over that required 'or Com- bustion of Coal. Tear of Test. /— N ! ■3 ! SameofCoal or Fuel. ■Sa III =- hi m II 3d |li57^ fTfm ELEPHANT BOlLKliB. /^Q%^ i^KX ^^ SMOKE TUBES. ^^L^V \,«wwOTf STATIONARY. Coal when not noted. r"™™! '"'■ ' T.U. % Lbs. % Authority, Reference, Experimenter, Locality, Remarks, &c. Small Coal. 10,400 174 114 95 1896 W. Meunier — Boiler Association — Mulhouse, 1896. Hand stoking. 3 tubes below boiler. 1 2 3 4 Ruhr Nuts. 13,840 5-1 10-0 130 1895 Boiler Association — Munich Report, 1895 — Gyssling. Paper mill — Hand stoking. 2 tubes below boiler. 2 Expts. on same boiler, same coal, and about same rates filing and evaporation. Do. Do. Do. 10-5 120 Do. Do. 13,475 4-5 18 70 1896 Same authority— Engineering works at Wurzburg. Grate concave — 2 water tubes below boiler. Hand stoking. North France Coal. Gas Coke. 11,000 114 200 1894 W. Meunier — Boiler Association — Mulhouse, 1895. Colmar — 2 Expts. on same boiler at about same rates of evapora- tion. This Expt. with coal and next with gas coke — 3 tubes below boiler. Hand stoking. 5 6 7 12,600 11 10 110 Do. Nixon's Nav. Welsh. 15,560 7 11 100 1887 Donkin & Kennedy, No. 12 — Engineering, 22nd July 1892. Sch. Kestner. Thann — Alsace — Gases under boiler, round upper boiler to econoraiser (Green). 3 tubes below boiler — Hand stoking — Best Expt. this page. § Hard. J Brown. 8974 2i 15 100 112 1892 Lewicki Report, 1896 — Mechanical stoker. Inclined grate — Sohulz Rbber. Gases under top cyl. — round 2 bottom tubes. Transmission, T.U. p. sq. ft. p. m. =75. (21) Same authority — 3 Expts. on same boiler with less coal burnt and greater eflSciency. T.U. p. sq. ft. p.m. =67. (20) In these 3 Expts. gases and temperature taken at end 1st run and at end boiler. T.U. p. sq. ft. p. m. = 77. (22) 8 9 10 Do. 9082 1 7 13J 97 100 Do. Hard 8330 i 7 104 62 70 Do. 8 EXPERIMENTS ON ELEPHANT TYPE OF BOILER WITH EXTERNAL FURNACE, BoiLBK Efficiencies feom 59 to 70"8 per cent. Paexicdlaes op Boiler Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. g k .ale 1" Gases. "Water Evaporated. Heating Surface Total. General Dimensions. .H'S fl On > f o o rt 1 Temperature of Fui-nace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). 1:. =11 ?1 li ■S-3 Lbs. of Hot Water eva- porated per sq. ft. Heating Surface per Horn-, Boiler only. 'is. Sq.ft. 1° s i 1 c° B 7. ■i At end of Boiler and difference above Steam Temp. i < Percentage by Volume. CO2. 0. CO. Sq. ft. rt. Ft. Ins. Sq. ft. 7. 7. Lbs. sq. in. F.° p." 7. 7. 7. Lbs. Lbs. Lbs. 2033 320 11 7-5 0-9 47 ... 61-4 98 336° 507° 336 171 368° 10-7 7-0 ... ... 5310 8-5 2'6 2-9 1S93 16-5 7-0 33 62-7 62-7 85 325° 379° 325 64 6-5 ... 5495 7 '4 1374 1130 16 6 0-6 34 58-9 4-6 63-5 96 331° 544° 331 213 248° 11-4 3452 8-4 2-63 i^ Do. Do. Do. Do. Do. Do. 66-6 4-6 71-2 Do. 515° 331 184 260° 11-9 4090 9-5 3-0 2050 170 6-6 0-7 28 63-0 63-0 67 310° 473° 310 163 12 ... ... 7410 8-8 3'6 Do. Do, Do. 0-9 Do. 67-4 67-4 60 306° 464° 306 158 11 7568 9-6 3-7 Do. Do. Do. 0-6 Do. 68-2 68-2 67 310° 455° 310 146 10-0 ... ... 6290 10-0 3-1 2-8 Do. Do. Do. 0-75 Do. 70-8 70-8 67 310° 425° 310 115 11-8 ... 5722 9-7 HAND FIRING— BRICK SETTING— WITH SMOKE TUBES. "With and wixHOtTT Feed 'Watee, Heaters — Chimney Draught. 97 Fuel. Aie. Tear ol Test. ^S^ ELEPHANT BOILERS, ^S^^^ WITH RATHER LARGE SMOKE 1 1 n ■s d s a 1 1 Name of Coal or FueL "S.S ill •91 ill i Excess ol Air at End of Boilei- in per cent over that required for Com bustion of Coal. Coal when not noted. [""""""[ STATIONARY. T.U, % Lbs. 7. Authority, Reference, Experimenter, Locahty, Remarks, &c. Mixed. 14,428 Si 12^2 175 1892 Schmidt— Boiler Association, Amiens, France. 54 — 3i" smoke tubes— 2 feed water heaters. Gases taken at end 1st run and at damper. Dust Coal. 12,700 Hi 23 200 1896 Same authority — 84 smoke tubes, 3J" Ferret water grate— J" forced air supply under grate. Gases under boiler — through smoke tubes — split sides. 2 3 4 - Small. 14,260 9 12-3 66 1894 Schmidt — Boiler Association, Amiens, France. 54— 3J" smoke tubes— 2 tubes below. Direction gases — under boiler, through tubes — split sides. Do. Do. Do. 12-8 60 Do. Nuts, N. France. 13,986 9 30-4 57 1896 Same authority — 98 — 3^" smoke tubes. Gases under boiler and through tubes only. Do. do. Do. do. Do. do. 4 Expts. on same boiler — decreasing rates evaporation and increasing efficiency. Best efficiency this page. 5 6 7 8 Anzin Coal. 14,355 7 28-5 72 Do. Anzin CoaL 14,530 6i m 87 Do. Nuts, N.France. 13,930 9 21-3 60 Do. G 9 EXPERIMENTS ON TWO-STOREY TYPE OF BOILEE "WITH EXTERNAL FURNACE, Boiler Efficiencies from 574 to 79 pee cent. PAETICnr.ARfl OP BOILEK TESTED. Efficiencies or per cent, of Heat Value In Fuel utillsecl. li Eg 1" Gases. Watek Evapokated. Heating Surface Total. General Dimensions. II iil 1 Temperature of Furnace Oases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). =13 li Lbs. of Cold Water eva- porated per sq. ft. Heatins Surface per Hour, Boiler only. % . It .1 |t i 1 1 Q ■so ca o § is B 1 At end of Boiler and djflFerence above Steam Temp. 1 ■Si •d Pi !l Percentage by Volume. OOj. 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. V. 7. 7. Lbs. sq. in. P.- F.' 7. 7. 7. Lbs. Lbs. Lbs. 546 10 ih 0-40 7-3 57-6 57-6 105 341° 1520° End furnace. 12-0 9-4 6-6 9-9 0-08 0-03 1350 4-5 2-48 Do. Do. Do. t giv 0-35 Do. 70-2 70-2 118 349° 1500° End furnace. 11-0 9'0 8-5 10-0 0-01 O'Ol 1460 8-85 2-68 1539 No en. 25-8 65-5 65-5 68 315° 580° 315 265 No t tak en. 4617 4-8 3-0 2368 Do. 53-8 70-5 70-5 86 328° 530° 328 202 Do. 9472 7-1 4-0 1948 Do. 31 73-0 73-0 96 335° 640° 335 305 Do. 6005 8-5 3a 2350 Do. 53i 70-5 70-5 88 330° 530° 330 200 Do. 9500 7-1 4-0 1160 16J 13 5 25i 73-2 73-2 66 313° 310° 313 9-5 1720 4-65 3-25 882 20 16 Do. 6i 19 73-0 73-0 136 356° 367° 356 11 15-7 0-05 1740 5 ■ 2-0 Do. Do. Do. 79-0 79-0 138 357° 462° 357 105 14-7 2325 51 2'65 , HAND PIEING— BRICK SETTING— WITH SMOKE TUBES. No EooNOMisERS— Chimney Deattght. 99 Fuel. Ant. Tear of Test. 1 1 Q m ■s d 1 Name ot Coal or Fuel. ■3.a .S*i Mi P II Excess of All- at End of Boiler in per cent, over that required for Com- bustion of Coal. ^^, TWO-STOREY BOILERS— ^^ STATIONARY. Goal whea not uoted. IsjiJ 1 WITH RATHER LARGE SMOKE ' TUBES. T.U. % Lbs. % Authority, Beferenco, Experimenter, Locality, Bemarks, &c. Bohemian Brown Coal. 6700 8-6 50 44 87 1893 Prussian Smoke Commission Report, 1894. Schneider and De Grahl. Ten Brink inclined grate— Mehlis & Behren's boiler. Temp, gases and analysis taken at end furnace flue and at end boiler near damper. Two Expts.— different rates firing and evaporation. Gases under boiler — through smoke tubes, over top boiler to chimney — 2 Expts. on one boiler. 1 2 3 Silesian Nuts. 13,200 Do. 27 66 88 Do. Brown Coal and Slack. 7192 43 113 1895 Vienna Boiler Association Report, 1895. Dii'ection gases — under bottom boiler, through smoke tubes to chimney. Slack. 9742 28 106 Do. Do. do. 4 5 6 7 8 9 Austrian ; Coal. 11,250 24-2 80 Do. Do. do. Local Coal. 9800 Mi 28 200 1895 Boiler Association — Arad — Austria— Made by Nutz. Direction gases as No. 3. Inclined grate. Local Inferior ■ Coal. 6400 32 100 1884 Boiler Association— Zlonitz— Made by Profeld. Three inclined grates. Direction gases — under lower boiler, through tubes and round upper boiler — 84 — 3J" smoke tubes. Turf. 6450 r 23 25 1896 Boiler Association — Salzberg — Bavaria. Elec. Light Station— Experiment made by Pelikan. Direction gases as in No. 7—3 inclined grates. 100 smoke tubes, SJ" and 3J". Do. Do. Do. 28 30 Do. 2 Expts, at 2 different rates firing and evaporation. Greater evaporation p. sq. ft. and greater efficiency. Best efficiency this page. 10 EXPERIMENTS ON WATER TUBE TYPE OF BOILER WITH EXTERNAL FURNACE, BoiLBE Efficiencies from 50 to 724 pek cent. Particulars of Boiler Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. steam Pressure by Gauge and Steam Temperature F. Gases. Water Etapokaied. Heating Surface Total. General Dimensions. u ill > • s ■s £ Teinperature of Furaace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). if 1! 2S. ■s|l =3 Si 'A ? . Bi- gg o 1 is i It ■S«9 n 1 E-i At end of Boiler and difference above Steam Temp. i p o Percentage by Volume. CO2. 0. CO. Sq. ft. Sq. ft. Ft. Ft. Ins. Sq. ft. 7. 7. 7. Lbs. sq. in. I'.' F." 7o 7. 7. libs. Lbs. Lbs. 2756 0-7 45 50 50-0 54 301° 839° 310 538 8-6 9-0 11,604 5-4 4-2 1610 18 25 500 51-0 50-0 98 336° 760° 336 424 9-6 9-5 13-6 5697 6-8 3-i)4 863 18 0-3 lOf 51-0 60 ' 307° 5-6 0-5 1844 7-2 2-14 2756 16 0-8 45 52-7 52-7 50 297° 736° 297 439 8-2 9-0 0-3 11,179 6-0 4'05 840 460 0-5 11 53-0 6-0 59-0 75 320° 549° 320 229 296° 8-5 0-01 2300 7-5 2 '74 r 1667 18 0-5 28 61-6 61-6 148 365° 445° 365 60 No t tak en. 5540 9-4 3 ■23 Do. Do. Do. Do. 62-9 62 '9 142 362° 447° 362 85 Do. 6730 9-4 3-45 Do. Do. Do. Do. 65-8 65-8 140 360° 395° 360 35 Do. 3180 9-1 r9 306 1619 480 16 29 70-5 6-0 76-5 144 362° 562° 362 200 361° 9-9 8-8 9-8 10-9 0-05 0-05 4950 983 0-4 15-5 72-6 72-6 155 368° 519° 368 151 n-7 3-8 0-4 2930 10-8 2'9r j HAND FIRING- BRICK SETTING. With and Withottt Eoonomiser— Chimney and Fokoed Dkaught. 101 FOEI. Air. rear of Test. 1 1 ■3 i 1 1 Name of Coal ov PueL §1 Ml ■31 IS 1ll 3« Excess of Air at End of Boiler in per cent over that required for Com bnstion of Coal. t-^=.:^=^.*-srf 10 EXPTS. ON BABCOCK AND WILCOX. STATIONARY. 1 w Coal when not noted. S!*^\k\^^^^^^^N^^^fS*KJ«^^sssS!^^^ LAKUJi WATJiK JLUCJi. ' T.TJ. X Lbs, X Authority, Reference, Experimenter, Locality, Remarks, &c. Daldowie Triping. 11,738 7-7 474 120 1893 Smoke Report, 1895— Thomson, No. 16. Steel Co., Scotland— 15" fires. Coal spread on grates — alternate stoking. 1 2 3 4 ■ Wigan Slaolf. 13,040 38 100 1888 Longridge Report, 1888—5" fires. 72—4" water tubes. Burgy Coal. 13,360 8-3 25J 240 1888 Same authority — 42 water tubes. Ext. surf. bk. wk.-840 sq. ft. Steam probably superheated a little. Radiation, 13% of total heat. Daldowie Triping. 11,064 11-7 46 30 130 1893 Smoke Report, 1895— Thomson, No. 17. Steel Co., Scotland— 15" fires. ^c:s 13,769 11-5 120 1890 Longridge Annual Report, 1890. 42 — 4" water tubes in boiler. 1 48 — i" do. in economiser. J 5 Gas Coke. 14,656 9-3 24i 1895 Fletcher, tests sent to Author. . 3 tests at different rates firing. | 50—3" water tubes, 17' 9" long. 1 steam jets. J; Blower under grate. Do. do. / Do. do. Without blower. Best efficiency of 3 tests. Decreasing rates evaporation with increasing efficiency. 6 7 8 Do. 14,376 5-7 27 Do. Do. 13,404 11-8 15J Do. Good Gas Coke. 12,800 8i 19 100 Do. Orossland Report to Manchester Corporation. 9 rows of 9 tubes = 81 tubes— 4" — 16 ft. long— clean. Manchester — Gases analysed end boiler and end economiser. 9 Nixon's Nav., : Welsh. 14,400 7 21 60 1894 Robinson — Elec. Station, St Pancras. 4 hrs. test only— Best efficiency this page. 10 6 EXPERIMEjSTTS OlSr WATER TUBE TYPE OF BOILER WITH EXTERNAL FURNACE, Boiler Efficiencies fkom 54i to 74 per cent. Particulaks op Boiler Tested. EfFiciencies or per cent, of Heat Value in Fuel utilised. ■3 g OS If IS Gases. Vatkk Evapoeated. Heating Surface Total. General Dimensions. £■3 II i > o o 1 Temperature of Furaace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). is 4 St =!3 i o'S -! S . Lbs. of Cold Water eva- ppiated per sq. ft. Heatinff Surface per Hour, Soiler only. 1* 1 i "I" a '1. o At end of Boiler and difference above Steam Temp. 1 li Percentage by Volume. CO2. 0. CO. Sq. ft. Sq. ft. Ft Ft. Ins. Sq. ft. 7„ 7. Lbs. sq. In. F.' F.' 7. 7. 7. Lbs. Lbs. Lbs. 1-5 1614 No t giv Do. p.n. 20-4 54-5 54-5 58-6 59-0 155 368° 556° 368 188 No t tak Do. en. 2400 7-2 Do. 21-5 58-6 166 373° 507° 373 134 2250 7-7 7'0 1'4 ■ 731 No t giv en. 12-9 59 112 345° 551° 345 206 Do. 13,900 1-9 1400 Do. en. 29-3 71-2 71-2 128 354° 540° 354 186 411° 368 43 513° 369 144 Do. 2800 7-9 2-0 2727 No t giv 56 72-2 72-2 74-0 154 368° Do. 5310 8-2 1'95 3737 18 0-5 41 46 74 157 369° Do. 10,332 from 212° 11-2 2-76 from 212° 2 EXPERIMENTS ON WATER TUBE BOILERS WITH EXTERNAL FURNACES, 2852 1805 18 ... 0-6 40 57-8 9-4 67-2 85 328° 429° 328 101 ... No t giv en. 5470 8-6 1-9 840 460 10 59 8-0 67-0 75 320° 617° 320 297 297° 7-4 ... 1-0 2231 8-0 2-6 HAND FIRING— BRICK SETTING. With and without Economiser— Chimney Dkaught. 103 Fotbt.. Air. J ! 1 i o P5 Name of Coal orFaeL Si |3» ■33 III S II 1^ Excess of Air a End of Boiler ir per cent over that reqnirec for Com bastion of Coal. 1 1 ^-^*^« BABCOCK & WILCOX AND OTHER STATIONARY BOILERS. LARGE WATER TUBE. t Tear of Test. 1 Coal when not noted. S^^\WN'N>N«^^^}S««S<*iSSN«5Si T.rr. ■ X Lbs. X Authority, Reference, Experimenter, Locality, Remarks, &c. Prussian Coal. 12,700 20 80 1897 Boiler Association Vienna, Report, 1897. With superheater. 2 Expts. on same boiler with same coal — different rates. (10) Do. do. (11) 1 11 12 Do. Do. 17 40 Do. Austrian Coal. 11,475 17-7 180 Do. Boiler Association Vienna, Report, 1897 — Babcock. (28) 13 J Do. ^Coke ' Breeze. 10,800 15 Do. Do. Do. do. (39) 14 Vienna Gas Coke. 11,065 13 54 Do. Do. Diirr, Gehre & Co. — No superheater. (36) 15 New River Coal. 14,559 5 254 Upper 12 Both 1895 Barrus Report — U. States. Boston — Edison Co. — Hawley down-draught furnace— 2 grates- upper and lower — upper with water tubes — 168 water tubes — Babcock. 16 Ip^ "^'^ ^1 MACHINE FIRING— BRICK SETTING. Chimney Drattght — With Economiser — Babcock Boiler. Bamsley Slack. 14,495 10 17-8 1894 Fletcher, test given Author — Halifax. 126 — 4" tubes in boiler. 169—4" ,, economiser. Hodgkinson stoker — reciprocating bars. 17 Not given. 13,769 7-7 29 155 1890 Longiidge Annual Report, 1890. 42 — 4" tubes in boiler. 48 — 4" ,, economiser. Benuis stoker. 18 10 EXPERIMENTS ON WATER TUBE TYPE OF BOILEE WITH EXTERNAL FURNACE BOILEK EfFIOIBNOIES from 55 TO 69 PEE CENT. PAKIIOnLAKS OF BoiLEE TESTED. Efficiencies or per cent, of Heat Value in Fuel utilised. is Gases. Watee Evaporated. Heating Surface Total. General Dimensions. 1" o >> ill m 1 6 ■s 1 Tetoperature of Furnace Oases. Analysis of Furnace Oases (at end of Boiler when not otherwise stated). II 1-^ Lbs. of ColdWater eva- porated per sq. XK Hour, Boiler only. o . s§ o .s S . o >. 11 J 5 1 >-i^ i^ >> II E 1 At end of Boiler and difference above Steam Temp. < Percentage by Volume. COa. 0. CO. Sq. It. Sq. ft. rt. Ft. Ins. Sq. ft. 7. 7. 7. Lbs. sq. in. F.* F." 7. 7. 7. Lbs. Lbs. Lbs. 724 12-5 0-5 32-2 55-3 55-3 71 310° 527° 310 217 87 9-1 1-3 3276 1 8-9 4-6 947 49 0-4 157 55-6 70 310° 392° 3-9 15-5 0-5 2020 8-9 2-1 1945 233 0-5 77i ... 597 58-1 125 348° , 468° 348 120 385° No t giv en. 3370 1 7-6 172 . 710 16 0-35 0-50 1075 58-1 67 313° 490° 313 177 8-5 6-0 11-1 13-4 0-04 0-03 1320 7-9 1-85 Do. Do. 0-15 0-25 Do. 62-4 62-4 79 323° 440° 323 117 107 8-4 7-6 10-1 0-21 oa9 1220 8 '5 17 1 470 470 0-15 14-95 60 1 117 71-8 75 320° 626° 320 306 324° 7-4 12-3 0-1 2013 9-53 4-3 1 Do. Do. Do. Do. 62-5 11-9 74-4 86 328° 646° 328 318 329° 7-1 12-5 0-3 2026 9-9 4-3 201 5-1 66 66-0 160 370° No t talc en. 1220 873 6-1 936 105 0-5 12-5 67-5 71 310° ... 396° 5-6 13-4 0'8 3392 10 '6 3'6 263 10-2 69 69-0 200 3.87° No t tak en. 1650 9-26 6-2 HAND FIRING— BRICK SETTING. With and without Economisbrs— Chimney Dbattght. 105 Fuel. Am. Tear of Test. 1 s- m o I £ 19 Name of Coal or Fuel. li i 1^" 1! II Excess of Air at End of Boiler in per cent, over Ithat required for Com- bustion of Coal. fcaJJl VARIOUS WATER TUBE BOILERS. STATIONARY. LARGE WATER TOBES. Coal when not noted. - ^n' SS5i^W\\SS!^N;^5S«;^K^S5S^'"^ T.U. z Lbs. % Autliority, Reference, Experimenter, Locality, Remarlcs, &c. Queen Elizabeth Pit. 15,540 4 14 115 1880 Dusseldorf Exhibition — Steinmiiller boiler — Report. (/) Boiler cost £455— bk. wk., 912 c.f. = ie24. 96— 2|" water tubes. Do. Do. Do. 17 300 Do. Do. do. Walther boiler. (m) 80 — 5" water tubes, 10 ft. long. Cost boiler, £307— bk. wk., 653 o.f.=.£15. 20 ■ Small French Coal. 13,850 H 11 1894 Schmidt, Amiens — Boiler Association. Feed heater — two long and Large tubes. De Naeyer boiler— 120 — 4" water tubes, 17 ft. long. 21 i Silesian Nuts. 13,200 i 184 120 210 1893 Prussian State Commission — Smoke Report, 1894. Heine boiler— Schomburg grate — inclined — Post Office, Berlin. Direction gases — outside tubes and under top drum to chimney. ■52— 3J" tubes, 13 ft. long. Temp, and analysis gases at end fire and at end boiler. 2 Expts. at same rates firing — ^less evaporation — greater efficy. 22 23 Do. Do. 4 Do. SO 125 Do. Nixon's Nav., Welsh. 15,560 2-9 147 160 1887 Donkin & Kennedy, No. 7 — De Naeyer boiler. 2 Expts. on same boiler at Liige— 3J" fires. Engineering, Feb. 27/91. No. 6— 3J" fires. Same evaporation — about same efficiency. 24 25 Do. Do. 4-1 14-3 165 Do. Nixon's Nav., Welsh 14,858 27-3 1895 Seaton, Hull — Test from Seaton. Yarrow boiler. 26 Queen Elizabeth Pit. Do. 4-2 31 230 1880 Dusseldorf Exhibition — Buttner boiler. {1} Cost boiler, £420— bk. wk., 936 c.f. = £34. 64— 4 J" and 5" water tubes— step grate. 27 28 ■ Nixon's Nav., Welsh. Do. 3i 17-5 1895 Seaton, Hull. Seaton boiler — Best efficiency this page. 5 EXPERIMENTS ON WATER TUBE TYPE OF BOILER "WITH EXTERNAL FURNACE, Boiler Efficiencies from 62 to 73J pbe cent. Pakticulaes of Boiler Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. 1 IS. Gases, Wateb Evapokated. Heating Surface Total. General Dimensions. .So R a a a ill > 1 ■s Teniperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). ^ i 1 Lbs. of Cold Water eva- aeatlns Surface* per Hour, Soller only. o !>■ ID a U S §■3 o o 3 .1 St i! o o rvj M s "3 Eh 7. At end of Boiler and difference abovB Steam Temp. J Percentage by Volume. CO2. 0. CO. Sq. ft. Sq. ft K. Ft. Ins. Sq. ft. % 7. Lbs. sq. in. F.' F.° 7, 7. 7, Lbs. Lbs. Lbs. ' 1307 20 15 0-3 50 62-0 62-0 113 344° 475° 344 131 7-0 11-1 End 6-8 boiler Fire brl'ge 3900 8-6 3-0 1688 20 10 0-3 33 69-9 69-9 117 348° 593° 348 245 8-3 11-4 10-2 ... 560O 9-5 3 '3 ■ 1651 23 9 0-4 31 69-9 69-9 141 361° 551° 361 190 9-7 11-2 7-3 4950 9-9 3-0 1641 34 9 0-25 33 70-9 70-9 105 341° 603° 341 262 9-9 10-3 8-4 ... 4440 10-0 2'7 860 14-7 0-2 22-5 73-3 73-3 134 357° 595° 357 238 10-6 11-6 8-0 ... 2400 10-2 2-8 1 1 2 EXPERIMENTS ON WATER TUBE BOILER— " STERLING "—WITH EXTERNAL FURNACES, ' 2552 i ... 0-2 57 74-5 74-5 123 352° No t tak en. 7144 11-0 2-8 ; 1 3222 0-5 49 76-7 76-7 121 350° 504° 350 154 Do. 9750 10-4 3-0 i HAND FIRING— BRICK SETTING. No EcoNOMisBK — Chimney Draught. 107 Name of Coal or Fuel. Coal when not noted. 3I 111 Air. •93 Excess s. ^1 of Air at End of .^"^ Boiler in Tear of B g^ per cent. Test. r4 over that required for Com- f bustion of Coal X Lbs. X §5^S5 FRANKFORT EXH. TESTS. VARIOUS TYPES WATER TUBE BOILERS— GERMAN. STATIONARY. LARGE WATER TUBES. Authority, Reference, Experimenter, Locality, Remarks, &c. Clean Ruhr. Nuts. Do. Do. Do. Do. George's Creek Coal. 13,712 Do. Do. Do. Do. 6i a n 2U 21 170 80 125 65 184 15-7 12-5 90 70 90 85 80 75 1891 1891 1891 Do. Do. Engineer, June 8, 1894 — Willmann boiler. Report by Gyssling, 1893—5 Expts. on different 'boilers, with same coal, and yarying rates coal and water— analysis gases shows air leakage through brick work, etc. Gases taken after fire bridge and end boiler near damper. For No. 29 test, 66—4" water tubes, 15J ft. long. No. 30 Diirr boiler— 93— 4" water tubes, 14i ft. long. Gbhrig boiler— The decrease of CO2 at end of all boilers shows air leakage through brick work, etc. 95—3" water tubes, 16J ft. long. Herrmann boiler — all tubes vertical— 3 boilers — gases passing horizontally through all tubes. 192 — 4" water tubes, 7J ft. long— not like other water tube boilers. Lowest rate water per sq. ft. heating surface and lowest rate coal per sq. ft. grate per hr. 60—3" water tubes— Best efficiency this set. Kett & Co. boiler. HAND FIRING— NO ECONOMISER-CHIMNEY DRAUGHT— SMALL WATER TUBES. Do. 14,235 14,345 10 14 9 21-7 1894 Sterling boiler — Barrus, Boston, U. States. Portland— 2 grates- 250 H.P. 260 small water tubes — chiefly vertical. Do. Sterling boiler — Cooley Report — U. States. Toledo — Ohio Water Works. 300 H.P. — steam dry — Best efficiency of two Expts, 29 30 31 32 3r4 35 10 EXPERIMENTS ON WATER TUBE TYPE Boiler EFFicrENOiEs from OF BOILER WITH EXTERNAL EUENACE, 52 TO 76| PEE CENT. J*ARTICDLARS OK BOILER TESTED. Efficiencies or per cent, of Heat Value m Fuel utilised. % h si sg. Sa II Gases, Water Evaporated. Heating Surface Total General Dimensions. .H'S §S °.S °|- ill > 1 a ■s 1 Temperature of Furnace Gases. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). °°2 i II ■S-3 Lbs. of Cold Water eva- porated per sq. ft. Heating Surface per Hour, Boiler only. O 1 . o >> 11 t a 2 ■s" ea >> 11 as E ■i At end of Boiler and difference above Steam Temp. ■0 Percentage by Volume 002. 0. CO. Sq ft. Sq. ft. Ft. Ft. Ins. Sq. ft. 7. 7o °L Lbs. sq. in. F." F." 7. 7. 7. Lbs. Lbs. Lbs. 233 7-9 0-35 8-5 51-9 51-9 84 325° 530° 325 205 7-4 11-7 0-07 430 1-91 1-84 2280 50 61-8 61-8 98 336° 600° 336 264 No t giv en. 5000 7-5 2-2 1960 41 62-4 62-4 100 338° 630° 338 192 Do. 3900 4-0 2-0 2450 52 64-7 64-7 156 369° 450° 369 81 Do. 4650 7-6 1-9 573 17 67-4 67-4 55 303° 520° 303 217 Do. 1300 7-5 2-3 2160 76 69-5 69-5 141 361° 440° 361 , 79 Do. 4060 8 '9 1'9 2450 52 72-5 72-5 146 364° 430° 364 66 Do. 7350 8 '4 3-0 474 1-5 11-4 73-0 73 '0 147 364° 473° 364 109 10-7 5-4 2-8 1403 10 '7 S'O 2450 ... 34-5 74-2 74-2 145 363° 430° 363 67 No t giv en. 6850 8-6 2'8 1050 25 76-3 76-3 105 341° 630° 341 189 Do. 4500 8-9 4-3 HAND FIRING— BKICK SETTING. No ECONOMISBRS — CHIMNEY DRAUGHT. 10& Fdii.. 1 AlH. Tear of Test. { VARIOUS WATER TUBE BOILERS— FOREIGN STATIONARY. 1 : ■s d a 1 1 Name of Coal or Fuel. Oh ■3.3 I'S 1- 6< u is. ■°« Excess of Air at End of Boiler in per cent, over that required for Com- bustion of Coal. t-^:^^=_^ Coal when not noted. T.TJ. % Lbs. X Authority, Reference, Experimenter, Locality, Remarks, &c. Brown Coal. 3363 74 30 150 1895 Saxon Boiler Association — Munter — Halle. 60 water tubes, 8' long, 2J" — step grate. 56 % water in coal — heating value taken when wet. Sent to author. 36 37 Silesian Coal. 11,800 15J 120 1895 Boiler Association, Yienna— Report, 1895. Steiumiiller boiler. Turf. 6305 27i 123 Do. Do. do. 38 39 40 41 Gas Coke. 11,3.50 17-8 150 Do. Boiler Association, Vienna — Report, 1895. Diirr & Gehre boiler. Silesian Coal. 10,680 ... 16i 206 Do. Boiler Association, Vienna — Report, 1895. SteinrntiUer boiler. Washed Coal. 12,400 14-5 76 Do. Boiler Association, Vienna — Report, 1893. Dtirr & Gehre boiler. Pea Coal. 11,170 19-6 215 Do. Do. do. 42 George's Creek. 14,168 lOi 14 75 1896 Almy boiler — Barrus, Boston, U. States. Water tubes all round tire, li" tubes. 43 44 Pea Coal. 11,250 ... 27-5 217 1895 Boiler Association, Vienna— Report, 1895. Diirr & Gehre boiler. Steam superheated. Slack. 11,300 21-7 Do. Boiler Association, Vienna — Report, 1895. Steinmuller boiler. Best efficiency this page. 45 3 EXPEEIMElirTS ON WATER TUBE TYPE OF BOILER "WITH EXTERNAL FURNACE, Boiler Efficiencies feom 72 to 73 pee cent. Particulars op Boiler Tested. Efficiencies or per cent, of Heat Value in Fuel utilised. steam Fressm-e by Gauge and Steam Temperature F. Gases. Water Evjiporated. Heating Surface Total. General Dimensions. .a "3 i g d ^ ill > 1 ta •s Temperatui-e oJ! I< urnace Gases. Analysis of Furnace Gases at end of Boiler when not otherwise stated. "Pffl la =1. h1 Lbs. of Cold Water Eva- porated per sq. ft. Heat- mg Suilace per iiour. Boiler only. I« 1. 1- 5 1 .1^ h s At end of Holler and difference above Steam Temp. gi ^1 Percentage by Volume. co^. 0. CO. Sf.ft. Sl. xt. Ft. Ft. Ins. 0-2 Sq. It. % 72-0 Lbs. sq. in. F.- F." % 7. 7. Lbs. Lbs. Lbs. 649 72-0 144 362° 732° 362 370 No 8'8 t tak 10-2 en. 0-3 4100 10'34 '6-3 Do. Do. 73 1 73-1 159 370° 503° 370 133 2160 8-69 3-33 Do. ... Do. 72-9 72-9 158 369° 511° 369 142 9-0 10-1 0-8 2200 8-67 3-4 1 4 EXPERIMENTS ON WATER TUBE TYPE OF BOILER WITH EXTERNAL FURNACES, BOILEE EfFIOIENOIES FKOM 664 TO 86| PER CENT. 1837 10 10 0-4 26-2 66-6 66-6 78-2 180 379° 777° 379 398 12-6 4-4 2-3 15,554 10-3 8'5 1 j Do. Do. Do. 0-12 30-0 78-2 149 365° 610° 365 245 11-r 7-4 t tak 0-6 8583 12-0 47 Do. Do. Do. 0-03 Do. 81-4 81-4 171 375° 540° 375 165 No en. 5852 12-5 3;2 Do Do. Do. 26 '2 868 86-8 182 380° 421° 380 41 11 '7 7-7 0-1 2281 13-4 1-24 no Fuel. Name of Coal or Fuel Coal when not noted. ■sa 33 Powell Duifryn. moisture. Do. Do. 13,860 Do. Do. S&8 67 Do. Do. HAND FIRING— BRICK SETTING. No EooNOMisEE— Chimney and Foecbd Dkatjoht. Ill no 4:>tlj II AlK, of Air at End of Boiler in per cent, over that required for Com bustion of Coal. Tear of Test. 25i 13i 134 115 110 1894 Do. Do. 3 EXPERIMENTS ON NICLAUSSE BOILER— tt STATIONARY. LARGE water' TUBES. Autliorlty, Reference, Experimenter, Locality, Remarks, &c. Kennedy & Unwin — Inst. Naval Architects, 1895. At Willans & Robinson — Thames Ditton. Water tubes, 3^" diam. — 7 ft. long — steam jets below grate- forced draught. Do. Best efficiency this set. do. Do. do. 3 Expts. on same Niclausse boiler, with same coal, at different rates firing and evaporation. 46 47 48 HAND FIRING— BRICK SETTING— NO ECONOMISER. Forced Draught — Small "WATEii Tubes. THORNYCROFT BOILER. Nixon's Navig., "Welsh. 15,Q20 50 1888 4 Expts. on same Thornycroft boiler. On Torpedo — different steam pressures — same coal — different rates firing and evaporation. 2" air pressure in stoke-hole. T.TJ. per sq. ft. heating surface p. m. = 158. 49 Do. Do. 29-8 60 Do. At Chiswick. I" air pressure in stoke-hole. T.U. per sq. ft. surface p. m. = 89. 50 Do. Do. Do. Do. 18-6 Do. Do. do. i" air pressure stoke-hole. T.U. per sq. ft. heating surface p. m. =61. 77 60 Do. Do. do. 0" air pressure stoke-hole. All these Expts. by Kennedy, and of rather short duration— P. /. C. jr.. Vol. 99. T. U. per sq. ft. heating surface p. m. = 24 — Best efficien cy this set. 51 52 3 EXPERIMENTS ON BELLEVILLE TYPE OF BOILER "WITH EXTERNAL FURNACE, Boiler Efficiency fkom 75J to 78i pek cent. PahTICULAES of UOILER TESTED. Elficiencies or per cent, of Heat Value in Fuel utiUsed. Gases. Water Evapoeated. [ Heating Surface TotaL General Dimensions. .S'S u 1! i "o Temperature of Furnace Gases. Analysis of Furnace Gases at end of Boiler wben not otherwise stated. =3 la Lbs. of Cold Water Eva- porated per sq. ft. Heat- ing Surface per hour, -Boiler only. o 1 o " @ Hi 1§ B •3 1 At end of Boiler and difference above Steam Temp. Percentage by Volume. COo. 0. CO. Sq.ft. Sq. ft. Ft. Ft. Ins. Sq. ft. X \'U 7. Lbs. sq. In. F." F.' 7. 7. 7. en. Lbs. Lbs. Lbs. 1450 12-5 4-5 0-60 45-7 75-5 75-5 260 406° 640° 406 234 No t tak 9290 10-4 6 '4 Do. Do. Do. 0-45 Do. 78-6 78-6 Do! 631° 406 225 ... Do. 7230 10-8 5'0 ; 840 430 1-0 43 78'0 224 395° 780° 13-4 4'5 0-56 13,700 10-7 15'5 Hot Feed. 5 EXPERIMENTS ON VARIOUS VERTICAL TYPES OF BOILERS WITH EXTERNAL FUENACES NO ECONOMISER— CHIMNEY AND INDUCED DRAUGHT— BOILER EFFICIENCY FROM m 10 5 2-6 44-2 44-2 119^ 341° 587° 341 246 7-0 13-6 0-0 262 6-2 7-0 Cold. 30 3 2 1-1 45-2 510 45-2 54^ 303° 637° 303 334 5-9 13-9 0-0 146 6-9 4'8 Cold. 102 4-7 2-5 1 5-7 51-0 100 338° ... No t tak en. 1310 212° 7-9 13-1 from 212° 771 13-5 5-5 ■e. 10-5 63-8 63-8 35 280° 392° 280 112 10-3 6-0 2-7 1770 212° 9-6 2'3 from 212° 410 14 4 ... 15 76 5 ... 76-5 127 353° 428° 353 75 8-7 10-8 0-3 652 10-3 1-6 Cold, 112 HAND FIRING— NO BRICK SETTING. With and without Economisbks— Chimney and Induced Dbauqht. 113 Name of Goal or Tuel. Fuel. Coal when not noted. Sfi IS .3 Pi "a ri 9 ? O Air. of Ail- in per cent. Year of Test. BELLEVILLE MARINE TYPE EXPERIMENT ON LAND— STATIONARY. LARGE WATER TUBES. Autliority, Reference, Experimenter, Locality, Remarlts, &e. Peniikz- ber. Do. Cardiff, Welsh. 13,300 Do. 13,150 11 24 18 36 1896 Do. Two tests — brick furnace — ironwork round outside boiler — air delivered under pressure' in jets above fires — feed water de- livered in jets — J" fire bars J" spaces. T.U. per sq. ft. heating surface p.m. = 127 for No. 53. T.TJ. per sq. ft. heating surface p.m. =100 for No. 54. Expts. given to author by Admiralty, and made at a dockyard in England— best Expt. this set. 45 Do. Official tests made at Paris by Government Marine Engineers — boiler pipes 4" ext. diam. — economiser pipes SJ" ext. diam. — induced draught by steam jet — tests given by Belleville — air spaces in grate 39% of total grate area. 53 54 55 —HAND FIRING — BRICK SETTING— 44 TO 76 PER CENT. © STATIONARY— WATER AND SMOKE TUBE. Coke 80%. Coal 20%. 13,688 17 170 1896 Ripper— Sheffield— P.J. C.X, Vol. 128, 1897— Tech. CoUege. Schmidt — probably wet steam, afterwards superheated. Ordinary Coal. 14,900 25 220 1891 Kennedy — Bermondsey — small SerpoUet boiler, superheated steam — gases vertical up to chimney — 295° of superheat — no water line. Do. Do. 34-3 Nixon Navig. 15,560 5-2 17-9 Anthra- cite. 12,970 14 4-9 1888 Fire engine on wheels — Merryweather, London — Donkin & Kennedy, No. 16 — Engineering, January 27, 1893 — cross water tubes above fire — gases straight through tubes to 7 ft. chimney — induced draught — extaust steam in chimney. 85% 1887 Donkin & Kennedy, Bermondsey, London — 14" fires. No. 1 — Engineering, July 1890 — vertical water tubes — gases up through centre boiler, down outside shell, then up to chimney 68 ft. high. 120 1890 Denton — Pawtucket Pumping Engine Works, U.S. — Engineer- ing News, 1890 — 48 3" smoke vertical tubes— steam slightly superheated — best Expt. this set. SUMMARY OF TWO BEST EXPERIMENTS ON EACH OF 6 TYPES OF BOILERS WITH INTERNAL FURNACES. ARRANGED IN ORDER OF HEAT EFFICIENCIES. Boiler Effioienoies fbom 84 to 66 "7 pee cent., excluding Eoonomisees in all Cases, Paetiodlaes op Boiler Tested. Efriciencies or per cent, of Heat Value in Fuel utilised in Evaporating Water. Boiler only. K s 1 Gase,s. Water Evapobated. 1 ■s Heating Surface Total. General Dimensions. 1 ■s 1 i 1 1 at end of Boiler when notothervriae stated. ? u Hi u •S.-3 Lbs. of Cold Water Eva- poratedpersq. ft. Heat- ing Sumce per hour. Better only. Percentage by Volume. !« bO § 1 i3 CO2. 0. CO. Sq. ft. Ft. Ft. Sq. ft. % Lbs. ,sq. in. F.° v. 7. 7. Lbs. Lbs. Lba Locomotive. ■{ 227 7 ' 9-6' ^"- ^ 1 ^'';duced. 4-3 840 150 44° 8-5 11-3 0-0 365 13-0 1-6 859 15 4-2! Do. 12-4 82-6 119 221° 11-2 7-8 0-0 4380 12-5 5-1 from 212° ( Cornish. V 600 28 1 6 '^''™- ney. 16-0 81-7 ' 79 116° No t tak en. 1700 12-4. 2'9 538 ... i ... Do. 8-3 810 77 4° Do. 1020 7-95 1-9 Two Storey. - 2464 1 ... Do. 34-0 81-1 i 114 Do. 5200 9-1 2-1 1345 ] ... Do. 29-4 78-6 91 245° Do. 5280 , 9-7 3-9 Two Flue Lancashire Hand Firing. - No Smoke Tubes. 1070 31 7-5 Do. 22-6 80-3 43 175° 10-5 9-9 0-0 4860 lO'O 4-5 975 i 28 1 7-5 Do. 30-0 78 7 95 6° No t tak en. 2794 12-1 2-86 Dry Back. - 446 14-7 6-0 Forced 7-2 75 7 55 480° Do. 2853 From 10-67 Hot 6-4 Feed. 930 12-0 10-5 Chim- ney, 73-4. 160 214° 9-5 about 8000 9-55 8-6 Two Flue Lancashire .Hand Firing.^ With Smoke Tubes. '1 2350 Do. 38-5 746 88 157° No t giv en. 6800 8-8 2-9 1614 V ... ... Do. 1 26-2 74-3 156 114° Do. 3700 9 '3 2-3 Two Flue Lancashire /i 1 1 8-0 Do. 74-0 40 393° 12-5 8700 7-4 Firing. No Smoke Tubes. ' 935 1 30 \ 7 Do. 30-2 72 89 Nc t tal :en. 5400 10 '2 5-6 Wet Back '\ 502 8-5 8-5 Do. 22 -5 70 70 Do. 4920 8-8 9-8 Marine. 1580 10-0 13-2 r Force 1 i 21-0 69-2 1 165 79° 8-4 11-4 0-0 4308 10-63 2-7 Thi-ee Flue ngg Lancashire. 30 8-2 Cliim ney. ■ 36-0 66 7 100 318° 12-4 2-9 : 0-4 5895 9-3 4-9 For Experiments with air heated for combustion, see pages 71 and 35 ; boiler efficiency, 78 '4% and 72-1%. 114 HAND With Chimney — Foucbd AND MACHINE FIRING— WITH AIR SdPPLY FOR COMBUSTION AT ATMOSPHERIC TEMPERATURE. OB Induced Dbaught. Stationary at Sea and on Rails. 115 Fuel. Air. Year oi Test. Hand or Machine Stoking.' EXPERIMENTER— LOCALITY- REMARKS. For drawing of Type of Boiler, see No. of page next column. [Mostly Brick Setting, except Loco. Type.] o 1 i a ■s 1 1 a Name of Goal or Fuel. "Sb |l pi il 111 7^ Hi Coal when not noted. t.u. 'L Lbs. 7. 1 Powell Duffryu. 14,940 8-7 120 1887 Hand. Royal Agricultural Society — Newcastle. Smoke tubes. Stationary — semi-portable. 79 29 >• 46 J Nixon Navig. 15,560 5-5 28 70 1887 Do. Donkin & Kennedy, No. U— G. E. By. Smoke tubes— Copper fire box. Possibly some priming. On rails. 83 46 Welsh. 14,500 2'2 10 ... 1893 Do. Unwin — West Middlesex Water Works. No smoke tubes. Stationary. 23 21 y 34 J Silesian Nuts. 10,670 19-4 72 1895 Do. Vienna Boiler Association. Smoke tubes. Stationary. 27 « Lower Silesian. 10,875 19-5 155 . 1897 Do. Do. Smoke tubes. Stationary. 85 9 - 30 / -114 J ^ 1 - 33 J Silesian Small. 11,950 21-0 56 Do. Do. Do. Smoke tubes. Stationary. 85 8 Do. 12,000 6 24-5 85 1893 Do. Prussian Smoke Commission. No smoke tubes. Stationary. 53 89 Nixon Navig. 14,878 4 9-3 1896 Do. Unwin— West Middlesex Water Works. No smoke tubes. Stationary. 49 70 Newcastle Nuts. 13,620 - 37-0 1887 Do. Spence — Newcastle. Smoke tubes. Stationary. 69 18 Scotch. 40 to [About 45 ! 100 1895 Machine. Kennedy — Edinboro — steam slightly superhtd. Smoke tubes. Stationary. 63 6 Silesian. 11,385 ... 21 83 1896 Hand. Vienna Boiler Association. Smoke tubes. Stationary. 59 10 ' 10 Prussian. 12,070 17-5 120 Do. Do. Same authority. Smoke Tubes. Stationary. 59 9 Small. 9740 26 30-5 50 1893 Machine. English Smoke Report— Bolton. No smoke tubes. Stationary. 35 42 ^ 42 Yorkshire 13,600 11 19-5 1882 Do. Longridge Report — Blackburn. No smoke tubes. Stationary. 35 40 / Do. 14,296 8 ,24-7 1896 Hand. Seaton. Smoke tubes. Stationary. 73 6 V Newcastle 14,830 3 22-5 130 1891 Do. I. M. Engineers — lona, S.S. Smoke tubes. At sea. 73 5 Burnley. 13,492 9-8 18-8 50 1891 Do. Longridge Report. No smoke tubes. Stationary. 61 5 6 SUMMARY OF ONE OR TWO BEST EXPERIMENTS ON 7 TYPES OF BOILERS WITH EXTERNAL FURNACES. ARRANGED IN ORDER OF HEAT EFFICIENCIES. Boiler Efficiencies from 86 '8 to 65 '5 per cent., bxclttding Economiseks Particulars of Boiler Tested. Effrciencies or per cent, of Heat Value in Fuel utilised in Evaporating Water. Boiler onry. 1 1 1 1 Gases. Water Evaporated. Name of BoUer. Heating Surface Total. General Dimensions. 1 Q s a P l 1 3 r CO2. 0. 7. CO. Sq. ft. i Ft. Ft. 1 Sq. ft. ■% Lbs. sq. in. F." 7o Lbs. Lbs. Lbs. Water Tube. 1837 1450 .1260 10 12-5 10 Chim-lgg.g ney. 86-8 182 41° 11-7 No 10-6 No 14-7 9-6 7-7 0-1 2281 13-4 1-24 5-0 4 '5 Do. 45-7 2 grates 20 22 78-6 260 225' t tak en. 7230 10-8 11-38 Return Smoke Tube. 16 5 Do. Do. Do. 81-2 108 148° 151° 10-0 t tak 0-0 en. 4671 1840 2325 1720 652 1720 3-7 877 882 1160 410 415 16 6-0 4-5 6-2 36 77-5 96 138 10-7 2-1 Two Storey. 20 16 19 79-0 105° ... 5-25 4-65 10-3 2-65 3-25 16-5 13 5 6-2 Do.- 1 25-2 73-2 66 0-3 Vertical. 14 20 4 Do. 15 '0 76-5 127 47 75° 8-7 15-7 10-8 1-6 4-1 2'8 Lancashire, 5-6 Do. 6-6 Do. 1 26-5 74-3 175° 3-4 0-0 3-0 r Elephant. 1 2050 17 28 70-8 67 115° 11-8 10-3 ... 5722 9-7 10-0 1 430 24 4 5-9 Do. 19 65-5 45 8-3 O'O 2100 4-9 i Cornish. 520 23 Do. 12-9 65 9 91 169° 11-9 6-1 1338 5-9 2'5 The mean efficiencies and rates of evaporation per sq. ft. of heating surfect- 116 HAND FIRING— WITH AIR SUPPLY AT ATMOSPHERIC TEMPERATURE. 117 [N ALL Cases — With Chimney Deattsht. Stationak-s AND ON Rivers. Fttel. AlK. Tear of Test. 9> 1 d |2i 1 1 •s ! a SB =■3 1 Name of, Coal 01- Fuel. IS =.5 |5^ ■33 i If II 11 Pi P!. a Hand or Machine Stoking. EXPERIMENTER— LOCALITY- REMARKS. For drawings of each Type of Boiler, see No. of page next column. [Mostly Brick Setting.] Coal when not noted. T.U. 7. Lbs. 7. j Nixon's Navig. 15,020 ... 7-7 60 1888 Hand. Kennedy — Thornyoroft boiler, England. Short experiment — no brick flues. Small water tubes — on torpedo boat. Marine. 111 52 . 55 Penrikz- ber. 13,300 11 18 1896 Do. Admiralty, England — Belleville. No brick flue. Partly induced draught. Water tubes. Stationary. 113 54 Poca- hontas. 13,553 6-5 9 on two grates. 75 1897 Do. Hale— Boston, U.S. Smoke tubes. Stationary. 91 11 . 11 New River and Cumber- land. 13,361 8 9-7 1892 Do. Barrus— U.S. Smoke tubes. Stationary. 91 10 Turf. 6450 7 28 30 1896 Do. Boiler Association — Bavaria. Smoke tubes in top boiler. Stationary. 99 9 - 9 Local Coal. 6400 ... 32 100 1884 Do. Boiler Association — Zlonitz. Smoke tubes in top boiler. Stationary. 99 7 Anthra- cite. 12,970 14 4-9 120 1890 Do. Denton — Pawtucket pumping engine, U.S. Steam little superheated. Smoke tubes, vertical. Stationary. 113 5 5 Brown Coal. 3909 11 25 '20 1894 Do. Boiler Association — Saxony. 56% water in brown coal. No smoke tubes. Stationary. 93 4 8 Niits, N. France. 13,930 9 21-3 60 1896 Do. Boiler Association— Amiens — Schmidt. With smoke tubes. Stationary. 97 8 • 18 Nixon's Navig. 15,560 7 11-0 100 1887 Do. Donkin & Kennedy, No. 12 Experiment. Soheurer Kestner — Alsace. No smoke tubes. Stationary, 95 7 Brown Coal. 8700 ... 20-0 52 1890 Do. Lewicki — Dresden. No smoke tubes. Stationary. 25 28 3 per hour, in these four pages, 114-117, have been plotted ; see fig. 77, page 223 SUMMARY OF 405 BOILER EFFICIENCIES FROM THE TABLES, ARRANGED IN ORDER OF MERIT FOR THE DIFFERENT TYPES OF STEAM BOILERS, AND AT VARIOUS RATES OF EVAPORATION PER SQ. FT. OF HEATING SURFACE PER HOUR. With COLD Aik Supply foe Combtjstion, exoltjding Eoonomisers. I. 11. III. IV. V. VI. VII. VIII. IX. TYPE OF BOILER. Fires External or Internal. Tubes. Stoking. Page in Tables. No. of Experi- ments. Mean Efficiency two best Experi- ments on each Type. Lowest Efficiency of each Type, one Experi- ment only. Mean Effi- ciency of all Experi- ments. Water. Smoke. Water tube, Ext. Small U" None. Hand. 107-111 6 % 84-1 % 66-6 77'4 Locomotive, Int. None. Small. Do. 75-83' 37 83-3 53-7 72 5 Lancashire (2 flue), Do. Do. Do. Do. 59 10 74'4 65'6 72-0 Two storey, Ext. Do. Do. Do. Hand and 99 9 76 '1 57-6 70 '3 Two storey, Int. Do. Do. machine. 85-89 29 79-8 55-9 69-2 Dry back, Do. Do. Do. Hand. 65-71 24 75-7 64-7 69-2 Return smoke tube, . Ext. Do. Do. Do. 91 11 81 -2 56-6 68'7 Cornish, Int. Do. None. Do. 21-25 25 81-7 53-0 680 Cornish, Do. Do. Small. Do. 27 9 81-0 55-0 67-7 Wetback, Do. Do. Do. Do. 73 6 69-6 62-0 66-0 Elephant, Ext. Do. Do. Do. 97 7 70-8 58'9 65 '3 Water tube. Do. Large 4" None. Do. 101-111 49 77-5 50-0 64-9 Lancashire (2 flue). Int. None. Do. Machine. 29-35 40 73 '0 51-9 64-2 Cornish, Ext. Do. Do. Hand. 26 3 65-9 60-0 62 7 Lancashire (2 flue). Int. Do. Do. Do. 37-57 107 79-5 42-1 62-4 Dry back. Do. Do. Small. Do. 63 6 73-4 54-8 61 -0 Lancashire (3 flue), Do. Do. None. Do. Hand and 61 6 66-7 52-0 59-4 Elephant, Ext. Do. Do. machine. 95 8 65-5 54-9 58-5 Lancashire (2 flue). Do. Do. Do. Hand. 93 8 74-3 45-9 57-3 Vertical, Do. With and without. Do. 113 5 76-5 44-2 56-2 405 With HOT Air Suppl^ I FOE COMI iUSTION. i Dry back, Int. None. Small. Do. 71 3 77-2 75-6 76 7 CHAPTEE IV. Fire Grates of Various Types. Grates Externally and Internally Fired — Fire Bars— Excess of Air — Tenbrink — Kuhn — Pellatt — Stepped Grates— Marsilly — Barber — Munich — Seipp — Rinne — Stauss — Donneley — Godillot — Dulao — Waokamie — Belpaire — Kudllcz — Cario — Ferret — II eldrum — Empire — Ferrando^Wilton — American Down-Draught Furnaces — Hawley and others. Grates externally and internally fired. — ! Boiler grates may be classified under two heads, according to their position, whether external to the boUer, or placed within the furnace tube. Both kinds may be stoked by hand or by mechanical means. They are used under all boilers fired with sohd fuel or coal, as fixed land boilers, locomotives, portable and marine boilers, for ships on rivers and lakes, boats, etc. In front of the grate is the dead plate, a small piece of flat cast-iron ; at the opposite end is the fire bridge, to prevent coal from being carried onwards or thrown off the fire bars, and to direct the hot gases against the boiler heating surfaces. Beyond this bridge there is usually a chamber in which the combustion of the gases is com- pleted. This combustion chamber is a desirable feature, as the gases are liable to escape from the grate before much of their heat has been evolved, and imperfect combustion is generally the result, unless further time and space are allowed for chemical combination, and" the thorough mixing of the air and hot gases. Fire bars. — The bars forming the grate vary in many ways. Usually they are fixed, but sometimes movable, sometimes alternately fixed or movable by hand, while occasionally they are arranged in two rows, forming two grates, one above the other, at two difierent levels. Generally, however, the bars are horizontal or slightly inclined, and are of cast-iron ; in a few cases thin wrought-iron is used, and they are so arranged that they can be easily replaced when burnt or worn out. Their "life" depends 119 greatly on the lbs. of fuel burnt per square foot of grate, and this again upon the amount of draught, the kind of coal used, and other circum- stances. The space between the bars to admit air for combustion should vary with the quahty of coal burnt and the draught, but it is too often determined by guess work, of by rule of thumb. Too much small coal or ash should not be allowed to fall through, but if the bars are too close to- gether the arc cannot penetrate between them, the supply wiU be deficient, and the evaporation will suffer. Sometimes the bars' are made thinner in the middle, to allow the air to reach them more freely. Excess of air. — The only right method of testing the efficiency of a given grate with a given coal and draught is to analyse the gases of combustion, and thus to ascertain the percentage of air in excess, or the reverse. If too much air has been admitted to the grate the bars should be arranged nearer together ; if too little, they should be spaced out further apart. The quantity of air should always be slightly in excess of that required for perfect combustion, say from 30 to 50%. To allow too little air to reach the grate is decidedly an error, nor should there be 100% in excess. Both extremes must be avoided, or the evaporation per lb. of fuel will diminish, and the boiler efficiency decrease. As a rule, the tendency is for too great an excess of air to leak in. With all kinds of fuels, types of grate, fire bars, and boiler settings, thickness of fires, position of grate relative to boiler surface, etc., there is plenty of opportunity for an excess 120 HEAT EFFICIENCY OF STEAM BOILERS. of air to penetrate, and analysis of the gases is the only way to rectify any faults in this direc- tion. Care should he taken not to allow the grates and gases to he too near the heating surface of the hoiler, particularly if internally fired. Mr Spence's experiments show that by lowering the grate 3 in. from the furnace crown, a much better boiler efficiency and evaporation were obtained. In some English and foreign grates a second supply of air is admitted, generally behind the fire bridge, and many authorities consider that perfect combustion cannot take place without this supplementary quantity of air. In nearly all the special types of grate described, air is in- troduced at several places, sometimes above as well as below the grate, sometimes at the further end of the furnace chamber. It is perhaps due to the better quality of the coal used in England that ordinary grates with cast-iron bars are the rule, and specially con- structed grates the exception. On the Continent, where coal is generally smaller, and often of lower heating value, there are more varieties of grates. Most of the hand fired grates here described will be found to have a foreign origin. In Germany and elsewhere on the Continent large quantities of lignite or brown coal, as well as other inferior fuels containing much moisture, are often burnt under boilers. In some cases the grate bars are made hollow, with water circulating through them, to keep them cool, and prevent the clinker adhering. Anthracite coal, so much burnt in America, requires more air, and therefore wider spaces are allowed between the bars than with the bituminous coal used in England and abroad. Thus there are endless variations in combustion, corresponding with the many different kinds of fuel burnt in Europe and America, to each of which a special type of grate is suitable. The Tenbrink is a grate much used on the Continent, though not hitherto adopted in England. It is rather costly, and the labour of the stoker is shghtly increased, but it gives better combustion and evaporation than the ordinary type, and is more economical. The grate consists of bars arranged in steps, set in a large furnace tube, and inclined at an angle of about 45°. Air is admitted both above and below the fire, and the supply carefully regu- lated. It enters from below through openings in the usual way, and from above through a slide adjustable at will. Thus the currents of de- scending air meet and mingle with the hot ascending gases of combustion, and by utilising the system of contrary currents the two are thoroughly mixed. The CO generated in the lower layers of combustion, where the fire is thickest, is burnt as it comes in contact with the upper air. There is no fire bridge, but the upper edge or crown of the furnace tube above the fire deflects the gases as they rise, and forces them to pass round a sharp angle before entering the main brick flue under the boiler. Although protected by fire brick, this corner is often de- stroyed by the great heat to which it is exposed. Mechanical stokers cannot be used with the Tenbrink grate. The coal, introduced at the top through a hopper, is fed on to the dead plate, and pushed by hand on to the grate and furnace tube. Combustion is stimulated by the admission of air from below, and as the coal is consumed fresh fuel sinks down by gravity and takes its place. The ashes and clinker fall to the bottom, where they bank up the lower end of the furnace tube, and prevent the entrance of too much air. The circulation of water is maintained by pipes connecting the water round the furnace with the lower part of the boiler. The hot gases are first led off from the top of the furnace tube, pass along the bottom of the cylindrical shell, and are then carried round in different ways to the chimney. In a comparative trial made by M; Burnat in Alsace in 1875 on a Tenbrink and an ordinary grate, both burning the same poor coal, the Tenbrink was found to give 35% more evapora- tion. The special advantages of this grate are that combustion is more perfect, owing to the better supply and regulation of the air, more coal is burnt per square foot of grate than in an ordi- nary grate, and there is a better circulation of water. Some trials will be found at pages 89, Nos. 28, 29, and 99, Nos. 1 and 2. Drawings of the grate are given by many Continental authorities on boilers, and two will be found in Mr D. K. Clark's work on The Steam Engine, vol. i. p. 188. The Kuhn grate resembles the Tenbrink in the arrangement of the bars. The proper direc- tion is imparted to the flames and hot gases by a cross-shaped horizontal tube, which forms part of the boiler. This grate is said to give good results. Three trials on a boiler fitted with it PELLATT AND STEPPED GRATES. 121 were made by the Prussian Smoke Commission, and will be found on page 23, Nos. 15, 16, and 17. Messrs Pellatt & Co. of Nottingham have lately brought out a new form of grate, with fixed horizontal bars, especially intended to consume smoke. It may be applied to internally or externally fired boilers. The hollow cast-iron bars are rather wider than usual, and rectangular in shape. At the front ends, where they open out into the boiler house, they are slightly bell- mouthed, for the in-draught of air. The bars pass through the fire bridge, and deliver the heated air at the rear end into the combustion chamber. The object of this arrangement is to have a continual current of air passing through the bars to cool them, and at the same time to facilitate the mixture of gases and air in the combustion chamber behind the bridge. Hollow grate bars acting as air pipes are not a novelty, but in addition there are a series of vertical openings in each of these bars, through which air is drawn into it from under the grate. The bars are placed longitudinally to the boiler, and form air delivery pipes from the front to the back of the bridge. The quantity of warm air going through is regulated by a kind of flat wrought-iron door, controlled by a lever in front. At page 49 will be found several compara- tive experiments which the author has made with very smoky coal, on ordinary grate bars, and on these hollow bars. The trials were carried out in pairs, one day with the hollow bars open, and all the air passages, both hori- zontal and vertical, free, the next day with all the openings completely blocked. The same boiler and coal were used, and the same stoker was employed. All the working conditions were similar. The flue gases from this boiler passed into a separate chimney, so that accurate observations on the smoke could be made every two or three minutes. The results with very smoky coal were most satisfactory. There was practically no smoke with all the air channels open, and a great deal when they were closed. The makers have also introduced another form of grate with interlocking bars, which can be moved by hand by means of a lever, to break up the clinker. Step grates. — These are very useful, in ex- ternally fired boilers, for burning small and poor coal. In most grates of this type the bars are arranged one below and beyond the other, in a series of small steps, so that the combustible, as it is gradually consumed, falls from one to the other, and is thoroughly burnt before it reaches the bottom. There is always a short, level grate at the foot of the steps, on which the com- bustible, ashes, and refuse rest, when they have completed their descent. The horizontal aic passages are regulated by adjusting the width between the steps. The combustible is charged on to the grate at the top through a hopper, and one advantage claimed for this kind of grate i.s that when small coal is used, it does not fall through the bars, as it would through an ordinary horizontal grate. A high temperature is main- tained, and large surface exposed, and there is said to be little smoke. These grates are used abroad, and very small coal, peats, lignites, tan, and even sawdust can be burnt on them. There are several varieties, as the Chobrzinski, Langen, Barber, etc. A grate in three stages or tiers has been apphed to a Lancashire boiler. Trials on another will be found on page 93, Nos. 2 to 4, and at pages 99 and 109. Although the principle in all is the same, namely, a sloping instead of a horizontal grate surface, the type of construction varies, and the grates are either inclined or stepped, according to the kind of fuel to be burnt. Some even are made without any bars at all, and consist of one large flat iron plate, the admission of air being at the side, and carefully regulated. One of the earliest types was the MarsiUy, in which the usual bars were replaced by iron plates arranged in shelves or ledges, one below and overlapping the other, from the charging door at the top to a short ordinary grate of five or six bars at the bottom. Such combustible as reached this grid was there burnt, the ashes and clinker falling through to the ash-pan. Air for com- bustion was admitted through the vertical spaces between the plates, and through the bars of the lower grate. In the Barber external stepped grate the fuel is stoked on to each stage separately. There are three shelves of varying lengths, arranged one below the other ; the fuel is fed to each in- dependently from below, and care is taken not to break up the sloping fire. The Munich stepped grate has been adopted in Bavaria to burn small coal and lignite nuts. It was originally designed to utilise waste Bavarian coal dust, but will also burn hard coal. The grate is arranged in stages 122 HEAT EFFICIENCY OF STEAM BOILERS. at a moderate incline; the combustible burns and falls gradually down, till it readies tlie flat ash- pan at the bottom. In a recent type of this grate, an arrangement has been made for tipping over the ash-pan to get rid of the cHnker, and the work of the stoker is thus hghtened. Air is admitted from above and from below the bars. It can be previously heated and the quantity regulated, according to the kind of coal burnt. The Seipp apparatus has two grates, both at a considerable incline, one below and beyond, but not, as in the American down-draught system, immediately beneath the other. By shifting the bars in the upper grate, the space between them can be varied. The combustible, as it burns, shps down from one on to the other. The top of the furnace above the grate is at an angle of one in four, and the opening between it and the steeply inclined fire bridge is too small to allow the flames to strike back, but a good combustion is probably secured by the double grate. There is no second provision of air. This grate is used for lignite, but will not burn caking coal. In the Rinne grate the air for combustion is introduced in two separate currents, under the grate and behind the fire bridge, and is previously carried through passages in the outer shell to heat it. To supply the grate it is drawn through a brick flue under the boiler, and is introduced at the fire bridge from the back through two flues. This inclined fire bridge is peculiarly shaped, with interstices to admit the air. The apparatus is said to consume the smoke, but no doubt the fire bridge must soon be injured by the great heat, and require frequent repairs. This grate, made by Sohulz Knaudt of Essen, was used under their boiler at the Frankfort Exhibition of 1891, and gave excellent results. Details of the trial will be found at page 23. The Stauss grate is also fed with a second supply of air previously heated. It is intro- duced behind the fire bridge, and the quantity regulated by an automatic admission valve. In the Adam grate a brick projection over the bars towards the front has been added to the fire bridge. The flames generated in the back part of the grate, where combustion is most perfect, are forced to strike back, and pass over the freshly stoked fuel, before they escape to the combustion chamber. The coal is thus said to be rapidly converted into coke, and the currents of hot gases are thoroughly mixed. Air can also be admitted through openings in the fire doors. The Donneley grate is vertical, with water tubes on the boiler side. On the external side are ordinary vertical grate bars, through which the air passes horizontally to the fire. At the further end, the grate is closed by hollow bars with water circulating through them from the boiler. Beyond these tubes is a chamber where combustion of the gases is completed. The fuel falls down by gravity, and forms a vertical column of burning coal. As combustion proceeds, the coal gradually sinks and is replenished from a hopper above. The ashes and clinker fall to the bottom of the column, where they form a tliick layer, impervious to the air ; thus it is only through the outer vertical cast-iron bars that the air needed for combustion can enter in horizontal streams, instead of vertically, as in an ordinary grate. The author has seen many of these grates on the Continent, and with fairly smoky coal the results are generally satisfactory with regard to smokelessness. They have, however, several disadvantages. The radiation is very consider- able, and with bad water the tubes sometimes burn out. The grate itself is placed at some distance from the heating surface of the boiler, and therefore the boiler efficiency would prob- ably not be high. A good trial on the Donneley with Saxon brown coal, by Professor Lewicki, will be found at page 25, N"o. 28. These grates are best suited to externally fired boilers, but will not burn hard coal. They are a good deal used on the Continent, and form an un- usual but interesting type introduced about ten years ago. The Godillot is another grate intended especially for burning small fuel containing much moisture, such as sawdust, wood shavings, chips, peat, tan, etc. It is a stepped grate, and is formed of tiers of semicircular bars rising one above the other in the shape of a cone. The fuel is fed in at the top through a hopper worked by a screw; the gases are led off over a fire bridge in the usual way. This grate can, it is said, be utilised for burning dust, anthracite, and ordinary coal; the bars are then kept cool by hollow grooves in their lower surfaces, dipping into water troughs. It may be applied to various boilers. The air to supply the grate is drawn through the ash-pit, and circulates round the furnace chamber before it is admitted, in order WACKAKNIE, KUDLICZ, CAEIO, AND FERRET GRATES. 123 to produce a better combustion of the poor coal. In a trial on a boiler fitted with this grate, and fired with tan said to contain 55% moisture, the evaporation was nearly 4 lbs. of steam per lb. of dry fuel. In all cases where poor and small combustibles are burnt, it is desirable to use a mechanical stoker, to save labour and waste in handling. Smoke is said to be diminished with this grate, but in a trial made by the author some years ago, the results were not very satisfactory, and there was a good deal of smoke. It is used with externally fired boilers. Another stepped grate of the same type is the Dulac, in wHch water circulates through the hollow grate bars. By an ingenious arrange- ment, the position of the latter can be shifted by a lever. The Wackarnie and Belpaire are grates partly rocked by hand, much used on the Continent, but seldom in England. The oscillating process is very simple. The bars are about 9 in. long, and a small number running not quite the whole length are hinged to the further end of the fixed grate, and movable hke a shelf. These can be tipped over in a body by the stoker from outside, to throw out and get rid of the clinker. The Wackarnie grate has bars set at a slight incline, to which the rocking motion can be given by the stoker through a lever. Combustion is thus facilitated, and the clinker broken up. In the Belpaire, a Belgian grate, frequently used in locomotive boilers for burning greasy and small coal, the system is the same. These hand rock- ing bars are often useful where a good fire is necessary, as , they help to break up the clinker, and prevent its adherence to the bars. The fire bars are of very thin wrought-iron, bolted together, and arranged in sets of six or eight. Trials on this grate will be found at page 75, No. 6, and page 77, Nos. 11, 12, and 13. Another grate suited to stationary boilers is the Kudlicz, in which perforated plates, having about 100 holes to the square foot, are sub- stituted for ordinary grate bars. The grate is slightly inclined, and the holes are about -^^^ in. diameter. Air previously heated is forced in with steam jets. With this and other systems of grate, in which the draught is produced by a steam jet, too much steam is often used to keep up the supply of air. For the very small dusty coal found in mining districts, the method is, however, useful, and collieries are thereby en- abled to burn their waste fuel, which is often unsalable, and of no value. In the Carlo, one of the best known of the special types, the bars are arranged in thp shape of a double-stepped grate, the layers of com- bustible being parallel to the direction of the flames. The bars' run transversely to the furnace tube, and not longitudinally as in most stepped grates, and there is an arrangement for admitting air at the fire bridge. The steep grate forms a double ridge, like the roof of a house or a V reversed, and the coals are supplied at the top, in the centre of the furnace tube, by means of a long shovel shaped like a cheese scoop. This shovel is filled outside by hand, and then pushed in without lifting, and by turning it sometimes to one side, sometimes to the other, the fresh coal is deposited along the whole length of the ridge. Combustion is com- pleted on the two flat grates at the foot of the stepped grate. The flames pass horizontally along the furnace tube, as in an ordinary grate, but the gases require mixing, because their com- position differs in the upper and lower layers. This grate has the advantage of giving a larger area for combustion than flat grates, since, for the same length, it presents an increased surface to the combustible. There is also no door to open while firing, and the ordinary fire door is thus done away with. It is not suitable for burning caking coal, or coal containing much slack, as the ash-pan underneath is very small, being only the space contained between the two ridges of the bars. Air is admitted in two places, through the fire door in front, and at the back of the bridge. This system can be applied to internally or externally fired boilers. Trials on it, by Professor Lewicki, are given at page 87, Nos. 10, 11. The Perret is a horizontal grate with forced air supply, suitable for very small and cheap dirty fuels, coals, or gas coke. The cast-iron bars are aljout -| in. wide, but are 10 in. deep, and much thinner than usual, and are placed very near together, with -^^ in. air space between. Underneath is a shallow trough of water, kept at a constant level, into which all the bars dip at their lower extremities. The object of this water-cased grate is to keep the bars cool, and to prevent the clinker adhering ; the vertical currents of air between them also help in the same direction. Air is supplied 124 HEAT EFFICIENCY OF STEAM BOILERS. Tinder the grate by a small fan, and between the water in the trough and the coal. The slight evaporation from the trough assists com- bustion. The part of the grate between the water line in the trough and the coal on the top of the bars is under air pressure, and the strength of the forced blast, which is about ^ in., can be varied to suit the quantity of steam required, and regulate the combustion. All kinds of cheap dust fuels can be burnt on this grate. There is considerable economy in using it with every description of small coal, and clinkers are very easily removed. It is largely employed on the Continent, and many grates have been fixed in England. Several trials with different rates of combustion will be found on pages 43, 45, 47, and 97. Meldrum. — This is a grate much used of late years in ordinary horizontal furnaces for burn- ing very smaU dust fuel. The bars are placed close together, and force draught is used under- neath them to stimulate combustion. The under part of the grate is closed in. To give a good air supply one or two small steam jets, surrounded by annular trumpet-shaped inlets, are introduced, which deliver air under pressure beneath the grate. Small dust breeze and coke du,st are often burnt in this grate, especially in gas works, mines, collieries, and other places where this kind of fuel can be cheaply procured. The consumption of steam for the jets, to pro- duce the draught, is said to be small. The Empire Co. has recently introduced a new type of grate, with horizontal cast-iron bars, also well adapted for burning very small dust and poor coal. The bars are indented like teeth, and interlock in zigzag fashion one into the other, the spaces between being very small. In this, as in the last grate, one or two steam jets are introduced under the grate, to produce a pressure of air. The author has made some experiments on this type, the results of which will be found on page 47. Within the last few years a number of Empire grates have been started in England, and many are working in the colhery districts and in Germany. The Ferrando, brought out by Messrs Scott, is another form of grate suitable for burning very small and poor coal. The cast-iron hori- zontal bars are close together, only about ^ in. apart. Like the Ferret it has a closed ash-pit supplied with air from a fan, but instead of the bars dipping into water, they are kept cool by injecting water spray into the ash-pit ; this also prevents the clinker from adhering. This system seems to have had considerable success in the north of England, and for marine boilers. Another kind of furnace introduced and suc- cessfully apphed at Beckton, the South Metro- politan, and other Gas Works, is the Wilton, in which there are no fire bars. Two oast-iron pipes are placed at the bottom of an internal Lancashire boiler tube. A steam jet is intro- duced into the front end of each pipe, and induces a current of air through them, sufficient to maintain combustion. The fuel is piled up over these pipes, and a fire thus formed in the bottom of the tube 10 in. or 12 in. thick. A second supply of air is admitted above the fuel, over a fire-brick slope. The cheapest and poorest kinds of fuel, such as coke breeze, or pieces of coke about ^ in. diameter, can be burned in this furnace, and an economy of fuel and a high evaporative duty are said to be obtained with it. American down-draught furnaces. — A very ingenious method, recently introduced, for pro- curing good combustion without smoke, is that of the American system of down-draught water grates for externally fired boilers. In these there are two grates, one above the other, the lower burning completely the coal that falls through from the upper. The air for combustion is chiefly introduced above the upper grate, and the current is downwards instead of upwards, as usual. There are several varieties of these ingenious grates brought out in America^ though hardly known as yet in England. The most important is the Hawley down-draught furnace, designed about 1888, after several preliminary attempts. The earliest type, used to fire a stationary boiler at St Louis, consisted of a single row of water tubes forming the grate bars. The water circulating in these hollow bars was derived from the boiler above, to which the bars were connected by water boxes and headers at either end of the grate. To increase the circulation, the bars were raised at the rear end, and set at an incline of about 2J to 3 in. per foot length of grate. In the latest type of the Hawley furnace there are two grates, one below the other, a water tube grate above, with one or two rows of hollow bars filled with water, and an ordinary AMEEICAISr TYPES. 125 horizontal grate below, which serves the double purpose of burning any coal falling through from the upper grate, and supplying sufiBcient heat to insure smokeless combustion. The connection of the upper grate with the cylindrical shell above is also greatly improved. The pipes are led both at the rear and in front into two drums or headers communicating with the water above, and a ccmstant circulation is thus kept up. These grates are hand fired, and as the upper door is at an inconvenient height for the stoker, it is now customary to raise the floor a little, about 3 feet in front of the grate. Eor trials, see pages 91, 103. The main feature of aU down-draught furnaces is that the gases are led downwards. The coal is fed in at the top, and nearly all the air enters above the water grate, the aperture below it being extremely small. Carbonic oxide is first generated, but as fresh coal is added from above, the gases and half-consumed fuel are forced downwards over a stratum of greater heat, where they meet more air from below. The heat strikiag up from the lower grate completes their combustion, even before the fuel falls upon the bottom grate. Smoke and unburnt carbon are thus forced downwards, and practically can- not exist. If any additional air is required, it is admitted between the two grates or through the ash door. With this method, however, a very good draught is necessary, as the ordinary direction of the flue gases is reversed, and the chimney should be high, especially if the boilers have to be forced. Under normal conditions it is found that 90% of the combustion takes place on the upper grate, and very Uttle on the lower. To force the boiler, combustion is stimulated by vigorously raking out the bars of the upper grate, thus sending half-burnt coal down on to the lower, where its combustion is completed. In this grate, as in any other, it is necessary that the supply of air should be neither in excess nor deficient. Cheaper and smaller coal can be burnt, and to better advantage, than on a common grate. In a comparative test made at St Louis in 1893 on a water tube and an ordinary grate under similar conditions, the efficiency of the water tube grate was 21% more, but the chimney was nearly half as high again. There was practically no smoke. It is, of course, necessary to have very pure feed water with these tube grates, and much care is required not to injure the bars in stoking. Mechanical stokers cannot be used. In three years these down- draught furnaces have been applied to 1600 boilers in America, but they are not all of the Hawley type. The Baldwin is similar to the Hawley in most respects, except that the air for combustion, in- stead of entering through the charging doors, is led in through channels in the masonry, and is slightly heated before passing to the furnace. The lower grate consists of perforated iron plates instead of the usual solid bars. No trials seem to have been made on this grate, but it is said to give good results. In the Plummer furnace, the breadth of the grate is divided into three sections, of which the two outer are ordinary grates with up-draught, fired in the usual way, and the centre a water tube grate, with connec- tion to the water in the boiler. By means of fire-brick partitions the course of the gases is so directed, that they can only escape downwards through the middle water grate. The disadvan- tage of this type is the great width of grate required, a difficulty partly overcome in the Bosley furnace, in which the two grates, the ordinary and the water tube, are external to the boiler, and on the same level, but placed one behind the other below the cyhndrical boiler shell. Fires are made in both, but the course of the gases is so arranged that they pass upwards from the front ordinary grate, and downwards through the water grate in the rear. The ashes from each grate can be cleared out through separate doors. The system of down-draught furnaces is still in its infancy, and will certainly be much im- proved. The results abeady obtained are si> satisfactory that a higher efficiency may be confidently looked for, when the principles governing their construction are - better under- stood. CHAPTEK V. Mechanical Stokers. Advantages and Disadvantages — Coking and Sprinkler Stokers — Vicars — Bennis— Juckes — M'Dougal — Hodgkinson— Leach — Henderson — Proctor — Cass — Whitaker — Frisbie — -Wilkinson — Coxe — Babcock — Roney — Hale's Report. Advantages and disadvantages. — The use of an apparatus for introducing the combustible on to the grate, instead of stoking by hand, has both advantages and drawbacks. Mechanical stokers have scarcely yet been so largely and continuously used, as to enable engineers to determine in all cases whether their merits or disadvantages preponderate. For large boilers they are undoubtedly desirable. If by using them a cheaper coal can be employed than with hand firing, they wiU be more economical, even if there is no saving in labour. Generally, how- ever, an economy of fuel and combustion are obtained, with better evaporation, while there is little or no smoke, and the labour of the stoker is diminished. The frequent opening of the fire doors is avoided, the fuel is delivered to the boiler with great regularity, and its supply is not contingent on the care and attention of a stoker subject to the inevitable weaknesses of human nature. The furnace is methodically fed, and improved and uniform combustion is the result. In large boiler plants there is sometimes as much as 40% economy of labour; in small plants burning less than 50 tons of coal per week, there is practically no gain, and mechanical stokers are seldom desirable, unless it is especi- ally necessary to avoid all smoke, or to burn a particular class of small poor coal. Mechanical firing is not yet used at sea, where it would be very suitable, as the heat and discomfort to the stoker, with or without forced blast, especially in tropical coimtries, is very great. Some suc- cessful experiments, however, have been made in this direction. On the other hand, certain disadvantages are inseparable from the use of mechanical stokers. There is a difficulty in regulating the feed of coal according to the varying quantities of steam required, and driving gear is necessary, with its rather complicated machinery, while the cost in setting up and wear and tear are sometimes considerable. The coal must also be dry, which is not always easy to obtain. In estimating the saving in fuel, the coal required for the small uneconomical engines to drive the machinery, and to furnish the steam jet when used, must not be overlooked. But in most cases the gain in greatly diminished production of smoke and improved combustion more than compensates for these drawbacks. Por constant work, like pumping water, these stokers are very valuable, and especially for dry and small coal, but they are not suitable for large coal. Arrangements should always be made to revert to hand stoking in case of accident, or if the coal is too wet to pass the machine. Coking and sprinkler stokers. — Mechanical stokers may be divided into two classes, dis- tinguished respectively as coking and sprinkler stokers. In the first, of which the Vicars stoker is a good example, the fuel is fed from a hopper on to the front of the grate, and then carried forward into the furnace by the slowly moving bars, being gradually converted into coke as it advances. In the sprinkler stokers, the fuel is thrown directly on to the grate by means of small fans, shovels, pushers, or beaters. The grate bars sometimes move forward, sometimes they are stationary. With both kinds of stokers 126 VICARS AND BENNIS STOKEES. 127 sufficient air or oxygen must be admitted to insure perfect combustion, otherwise carbonic oxide will be formed. As a rule, the grate bars are kept much more evenly covered with mechanical stokers than when fed by hand. The better the bars are covered, the less air in excess will enter between them, and the higher will be the boiler efficiency. Many experiments will be found in the Tables on boilers with different types of mechanical stokers. They are not, as a rule, much employed on the Continent, but a good deal in England and America. Vicars. — In the Vicars coking stoker (see pages 297, 298, 299) small coal drops automatically from a hopper into two boxes at either side of the front of the furnace flue. The movement for introducing it into the furnace is communicated from a driving shaft, which actuates a dog-shaft, as it is called, running horizontally across the front of the boiler, and imparts to it an inter- mittent motion. Two reciprocating plungers or rams, worked by a bell crank lever and eccentrics from the dog-shaft, push the fuel down from the boxes on to a perforated coking plate, where it ignites, and a second thrust sends it forward on to the fire bars. These are placed alternately at two different levels, and by an ingenious arrange- ^ ment they are connected to the shaft in such a way, that all the bars are sent simultaneously forward about 3 or 4 ins., and the burning mass carried slowly on. The bars are then returned to the front of the fire one by one and successively from each alternate layer. By this method the burning fuel is pushed slowly forward, and gradually transformed into coke, untU it reaches the furthest end of the grate. Here the ashes and clinker fall over into the bottom of the flue, where they form an incline, banking up the end, and thus diminishing the entrance of cold air. Any unburnt coal falling in with the ashes is consumed, but care should be taken in removing the clinker and ash to leave sufficient to shut out the air. An ordinary fire bridge is placed just beyond the grate. Combustion is assisted and the bars kept cool by a small jet of steam under them. There are two motions in this stoker, the travel of the bars, and the action of the rams for feeding in the fuel. Both are automatic, and are produced by the same shaft, but each is independent of the other. The travel or stroke of the bars may be adjusted to suit the kind of coal burnt, and the work required of the boiler. within certain limits. There is little or no smoke, because the fresh fuel is not carried forward into the furnace until it is already ignited and turned into coke, and any smoke formed during this process is more or less consumed. Of coking stokers, the Vicars is one of the most widely adopted in England. It is chiefly used with internally fired boilers. When small coal is burnt, the hoppers are often fed from coal worms and elevators outside the boiler house, and the whole supply and introduction of the combustible is efiected by mechanical means, as shown in fig. 137. A saving of 30 to 40% in labour is said to be thus obtained, but this is only in large plants. In a trial of a Lancashire boiler made by the author on this stoker, 12 '4 lbs. of water from and at 212° F. were evaporated per lb. of best Welsh coal, but a good evaporation can be obtained with much poorer coal. (See page 29, No. 5, and pages 31, 33, 35, and 85, for various trials with Vicars stokers.) From 40 to 50 lbs. of small coal can be burnt per hour per square foot of grate. Jets of steam are generally intro- duced under the bars. fiennis. — The Bennis, also used with internally fired boilers, is an example of mechanical stokers of the sprinkling type. In it the coal is first fed into the hopper above the grate, usually by a conveyor or elevator, and falls on to a horizontal shelf in front of the furnace, carrying a pusher plate. By means of a lever and scroll cam the pusher is periodically drawn back, and the coal deposited in front of it ; the return stroke of the pusher drives the coal before it, over the edge of the shelf. Here it is ' caught by a mechanical shovel and thrown on to the grate. The shovel is attached to a lever, and its action is regulated and adjusted by a tappet with four different sized "throws," driven from a shaft in front. Each time one edge of the tappet catches the lever and shovel they are forced back against a spring, and, on being released, the shovel flings the coal into the furnace to four varying distances. The first throw delivers the coal just in front of the bars, the second to the farthest end of the fur- nace, the third and fourth at intermediate points (depending on the size of the throw in play). The coal can be sent to a distance of 6 feet if desired, and each throw scatters it over about 18 ins. The object of this arrangement is to secure a good combustion by feeding in the fresh fuel at 128 HEAT EFFICIENCY OF STEAM BOILERS. different places on the grate, where the coal is already at a red heat. This method was adopted in the earlier Bennis stokers, but, as the bars were stationary, it was very difficult to remove the ash. A second shaft has therefore now been added, working below the first. This auxiliary shaft carries a cam which acts on the upper and lower edges of the fire bars, and imparts a slight motion to them. Each revolution of the cam shaft carries the fuel 1| in. further forward into the boiler flue, and the cam also acts by displacing one bar in eight at a time, to detach the clinker, and make the ashes fall through. The bars are so arranged with reference to the length of the grate that they first slope downwards, then rise, to facilitate combustion. By the motion given to them the ashes and clinker are carried forward to the further end of the grate, where they fall into the ash-box, having parted with nearly all their heat. The varying throw of the shovel is said to insure good combustion, with little or no smoke. Sometimes a still further diminution of hand labour is obtained, and the small coal fed into the hoppers mechanically by means of a moving tray, worked from the shaft by an endless chain. Where several boilers are fired together this is a good arrangement, and some form of machine for handling the coal is used with most mechanical stokers, to convey it from the adjoining yard or pit. Trials on this stoker will be found at page 29, Nos. 1, 4, and 10, and page 31, Nos. 15, 19, 20. Both the Vicars and the Bennis stokers show the improved and systematic combustion obtained with mechanical firing, because part of the coal fed on to the grate is still fresh and black, while the other part, at an intense red heat, helps to gasify it. A marked economy is also realised, because the cheaper small coal used has some- times as good an evaporative efiiciency as larger coal with hand firing. To regulate the evapora- tion, and force the boiler at times, if necessary, is however always a difiiculty with mechanical stokers. On the other hand much small coal, which was formerly of no value, can now be not only utilised, but turned to excellent account. With some stokers it is even better than large coal, because no crushing is required, but this depends on the size of the coal. If the demand for steam is very intermittent, recourse must be had to hand firing. All mechanical stokers are fitted with charging doors for this purpose. Juckes. — The Juckes is another stoker of the coking type, applied to both Cornish and Lanca- shire boilers, but not now much used, except in America. It is simple in action, and useful for burning coal slack. The fuel is fed from a hopper on to the dead plate, and carried slowly on to the grate. The travelling bars, of which the grate consists, are linked together at either side, to form two series of parallel endless chains. They convey the coal from the front to the back of the furnace, and move onwards upon two pulleys, one at the front, the other at the rear. The coal, as it advances, is gradually transformed into coke, and there is said to be no smoke. The forward and upward movement is from the front of the grate, where the coal is delivered, and iu its slow progress through the furnace it is com- pletely burnt. The ashes and clinker fall into the ash-pan from the chains, as the latter com- plete their return journey under the grate. The frame runs on a tramway, and the whole grate can be drawn out for repairs ; the same arrange- ment will be found in some American grates. This type of endless chain stoker was at work forty or fifty years ago in London ; it is chiefly applied to externally fired boilers. The Juckes original mechanical stoker ' has been improved, and is now made by Messrs Whitworth. A difficulty in the old type was, that the chain bars and brick-work were soon worn out and burnt. Messrs Whitworth have introduced steam jets and water boxes running across the width of the grate, into which the bars dip, and are thus kept cool. No modern trials on this stoker appear to have been made. M'Dougal.— In the M'Dougal coking stoker, made by Messrs Haigh & Co., the fuel is fed by the hopper on to the coking or dead plate, along the whole width of the grate. It is then pushed into the furnace by a ram, which delivers it in larger quantities at the side than in the centre, and is next carried forward upon reciprocating movable fire bars. They are supported at one side on a horizontal transverse shaft, with eccentrics and cams, and each bar is lifted and moved forward one-third of a revolution after the one before it. The other end of the bars rests upon a bridge, which varies the level at which they lie as they move forward ; the fuel is thus effectually broken up, and clinkers do not adhere to the bars. An eccentric on the MECHANICAL STOKERS. 129 transverse or cam shaft works tlie ram. The speed at which this shaft is driven regulates the rate .of combustion, and can be varied to suit most kinds of coal ; the bars are spaced apart, to admit air for combustion. These stokers are ■chiefly applied to internally fired boilers. Many are worldng in London, at the County Council "Works, etc.; steam jets are generally used under them. In a trial made by Mr E. B. Longridge, the gain in evaporation over hand stoking varied from 8% to 12%. Hodgkinson. — The Hodgkinson coking stoker is shown at fig. 136, page 297. Here the fuel is fed into a hopper, sometimes by hand, sometimes l)y mechanical means, and from thence into "two passages at either side of the fire door. A square piston driven from an eccentric delivers it into the fire box at the back of the dead plate, •where it is partly turned into coke, and another ■thrust of the piston sends it on to the grate below. The bars have projecbions on their Tinder side, and are successively raised by a slowly revolving steel cam shaft ; each bar is •driven back separately, but aE. are carried for- ward together. Thus the coal is gradually sent •on till it reaches the end of the grate, where the ashes and clinker fall down on to the bottom of the flue. The rate of motion and of admission of the coal can be adjusted to suit the com- bustible burnt. Care must be taken with both this and the M'Dougal stoker that no unbu.rnt coal passes into the ash-box. In all mechanical stokers the clinker is removed by hand from beneath the grate. The Hodgkinson is chiefly used for Lancashire and Cornish boilers. Trials •on it will be found at page 29, No. 8, and page 103, No. 17. Leach. — In the Leach apparatus the coal is fed from the hopper on to a slowly revolving vertical wheel, divided by spokes into five com- partments. As each of these sections is brought round during one revolution, the- coal in it is emptied into a chamber below, containing a kind of paddle wheel revolving on a fixed axis, which sends it on to the grate. As the coal is swept in, it strikes against a projection, the position of which can be varied with the rest of the mechanism, and the coal is thus scattered ■evenly over the grate. Many of these stokers are used in Germany and elsewhere on the Continent. A trial with one, made by Professor Lewicki, is given at page 35. Henderson. — In the Henderson sprinkler stoker the coal is crushed in the hopper, and a certain quantity, regulated by a screw, is carried down to the furnace, and dropped upon two horizontal fans revolving rapidly on spindles, which deliver it into the grate. One transverse shaft actuates the spindles through eccentrics, and also, by means of two sets of cranks, imparts a rocking motion to every other fire bar, and a longitudinal movement to and fro to the alter- nate bars, thus causing the fuel to travel through the grate. Proctor. — The Proctor stokers are made of both types, sprinkling and stoking. In the sprinkler the coal is fed in front of a ram, which, in a Lancashire boiler, alternately pushes it to the right or left, according to the furnace to be served. From thence it is delivered on to the grate by means of a shovel with three throws, held in place by a spring. This method has now been partly superseded by the coking stoker, in which the coal is also fed on to a ram. The latter is carried forward into the fire, and the coal drops off from the edge on to the furnace beneath. The ram is then withdrawn, the rapid return stroke carrying it out of the heat j the next forward stroke sends on the coal already deposited. Thus it is laid on the glowing fuel, instead of being pushed on to it, and it is also claimed for this stoker that the coal is coked inside the furnace, and not in front of the boiler. The bars are kept cool by a small steam jet play- ing upon them, and are rocked by hand to facihtate combustion, and keep the air spaces free. Each alternate bar is continually lifted and dropped by means of levers and a rocking shaft, driven by worm gearing from the trans- verse shaft. The coal, as it burns, is gradually shifted to the back of the grate. With a range of boilers fired with small coal, it is of advantage to have the coal supplied by mechanical elevators or conveyors. About 7000 Proctor furnaces are said to be now at work. They are chiefly used with Lancashire boilers. In a competitive trial with another stoker the Proctor evaporated 9'64 lbs. of water per lb. of coal, but the heating value of the coal was not given. Trials on it will be found at pages 29, 31, 33, 35. Cass. — The Cass, made by Messrs Bryden & Co. and Messrs Cass, is a mechanical stoker of the coking type, introduced about seven years ago. The hopper, holding about 10 cwt. of small 130 HEAT EFFICIENCY OF STEAM BOILERS. inferior coal, is placed in front of the boiler, just above the grate level. The fuel is fed from it on to the dead plate, from whence it is carried forward by travelling grate bars into the furnace, and enters across the entire section of the furnace tube in a layer about 5 in. thick. The bars carry it forward about 2i in. at a time, the coking of the coal proceeds as it is slowly worked along from bar to bar, and the ashes drop over into the bottom of the flue at the further end. To keep the moving bars cool and prevent the clinkers adhering to them, steam jets are used underneath, but this is not always necessary, and depends upon the amount of fuel burnt, and kind of coal used. The machinery for moving the bars is worked by worm wheels from a shaft in the boiler house. This stoker is independent of the boiler, and is supported in front on pillars, so that it can easily be removed, if required. The action is automatic, and once started the fire requires no attention. Arrangements are made for firing by hand, if necessary. The Cass stoker came out well in the English smoke tests as pro- ducing little smoke, and some hundreds are said to be now at work. Trials on it will be found at page 29, No. 9, and page 35, Nos. 41, 42. Whitaker. — The Whitaker sprinkler stoker, used chiefly in Lancashire boilers, is a new and simple apparatus. The stoking machinery is worked by gearing with worm wheels, driving a lay shaft at the bottom of the hoppers, in front of the boilers, by a strap. The coal is fed from a hopper on to a movable deflecting plate, from whence it is thrown in small regular quantities on to the grate, by means of alternate revolving shovels. The distance of the throw, and quantity of coal delivered into the furnace at a time, are regulated by a screw. The makers claim that there is little smoke, and that very little power is required. The shovels are adjusted to keep the bars covered evenly with fuel, an object which is said to be attained. About 1500 boilers have been fitted with these stokers in England and abroad. FrisMe. — The Frisbie stoker is an American invention, applicable only to underfired boilers. The fuel is fed in from below on to a circular grate by means of elevator machinery. Wilkinson. — Another American apparatus is the Wilkinson, in which there is no pusher or ram, but the coal is fed directly on to the outer end of the coking or dead plate. The grate is in steps, and each bar is hollow, to allow the passage through it of a jet of steam, carrying air with it into the fire, for combustion. The in- clined grates are set at an angle of 25°, and move in sets of two in opposite directions, by means of a toggle motion and gearing, driven from an auxiliary engine. It is the movement of the grate itself which carries the fuel into the furnace, and hence this stoker belongs to the coking type. It is suited especially for anthracite, and is said to burn as much as 45 lbs. of dry coal per hour per square foot of grate surface. It can be worked with natural draught, or with a fan blast, and is applied chiefly to externally fired boilers. Coxe. — In the Coxe stoker, also an American machine, made on the same lines as the Juckes, and introduced about 1894, the fuel is fed from a hopper on to a traveUing endless chain grate, moving at the rate of about 3 to 4J feet per hour. The grate and bars move continuously from front to back and round to the front again, passing underneath in their return journey through a reservoir of water to cool them. The special feature of this grate is that the furnace chamber is divided into four horizontal compartments, to each of which a blast of air, of varying intensity, is delivered. To the first, nearest the entrance, a moderate blast is sent to ignite the coal. In the second compartment the blast is stronger, to intensify combustion, the third receives less air,, and only suificient is delivered into the fourth to carry off the ash. This rather elaborate system of regulating the air blast is sometimes trouble- some to manage. The economy obtained is about the same as with the Wilkinson. Babcock and Wilcox. — A fourth mechanical stoker, introduced in America, but now employed also in England, is the Babcock and Wilcox, which is applied chiefly to the boilers of the same name. There are two types, both coking stokers. In the first the fuel is fed from the hopper, and sent by plungers on to the dead plate. Here it is received and carried forward through the furnace by travelling bars, after coking, or giving off the volatile gases. The fuel parts gradually with all its heat until it reaches the rear end, where the ashes fall into the clinker pit. The plungers and bars are actuated by gearing. English coal, in lumps about 2 in. square, can be burnt with this stoker. The second type has also a travelhng chain grate, coming forward from the furnace to- MECHANICAL STOKERS. 131 receive the coal delivered down a shoot. The endless chain revolves over drums at either end, and is worked by worm gear from an auxiliary engine. It can be used either with forced or chimney draught, but requires a strong draught in either case, because the air openings are only half the size of those of an ordinary grate. Combustion is said to be practically smokeless, and the grate is simple to work. It will burn as much as 33 lbs. of dry coal per hour per square foot of grate, and is applicable to Scotch or American bituminous coal. A special advantage is that the frame of the grate runs on wheels, and the whole can be drawn out from the furnace without taking it to pieces. Roney. — Another form of mechanical stoker and grate combined is the Eoney, in which the fuel is fed on to the top of an inclined stepped grate. The bars do not move separately, but their angle is shifted periodically several times per minute, to facilitate the descent of the com- bustible. They are kept cool by water circula- tion. This apparatus has been applied to sixty grates in Philadelphia. Hale's Beport. — Some excellent remarks on boiler labour and the saving effected by mechanical stokers are given in a report (issued January 1897) by Mr E. S. Hale, late Engmeer to the Steam Users' Association, Boston, U.S. A large number of circulars were sent to owners of boilers and mechanical stokers in America, making various inquiries as to cost, general conditions of work, etc. The replies were syste- matically tabulated and summarised, and from them Mr Hale draws the following useful con- clusions : — "In small boiler plants, having grate areas from 25 to 190 square feet, one man, under average conditions, can run an engine, and fire up to about 10 tons per week ; one man (besides engineer and nightman) can fire up to about 35 tons per week; two men (besides engineer and nightman) can fire up to about 55 tons per week; three men (besides engineer and night- man) can fire up to about 80 tons per week." As regards mechanical stokers they "save 30 to 40% of labour in very large plants, burning over 200 tons per week, 20 to 30% in medium- sized plants (50 to 150 tons per week), and save no labour in small plants." From twelve replies to the circulars sent out, Mr Hale concluded that " these stokers may save a slight amount of coal; they save labour in large plants, provided coal handUng machinery is also installed ; they save smoke in all plants. Lastly, they cut down the capacity for evapo- ration, but not to any great extent, and this may be made up by extra draught." From a financial point of view, the following heads should be considered : — " What is the first cost complete, and how much interest, could be obtained if the money was invested in any other way 1 " How much are the repairs per year on the present furnaces, and how much would they be on mechanical stokers ? " How much money must be laid aside each year to allow for depreciation of the stokers ? "How much labour will they save, and how much is this in £ sterling per year 1 " How much coal per year was burned with hand firing, and how much did it cost ? How much coal, including that for the stoker engine and steam blast, will be used with the stokers, and how much will it cost ? " In a large plant, stokers will be advisable, if they make possible the use of a cheaper fuel than can be fired by hand. But it should be ascertained that cheaper fuel cannot be used without the stoker. ... In such oases there wiU be a savirig in cost of fuel, and a consider- able saving in labour and smoke, which the ex- penses incurred will not be sufficient to counter- balance. If no gain can be made by using a cheaper fuel, stiU stokers may be advisable in large plants burning a poor grade of soft coal. ... In small plants, stokers will be seldom advisable, unless the saving in cost of fuel is quite large, or unless the smoke nuisance is considerable." The author's views coincide more or less with those of Mr Hale, though he has not had the benefit of the useful and practical information collected by means of the circulars. , As against the many advantages of mechanical stokers must be set the wear and tear of the shafts and gear- ing, the extra power required to drive them, and the steam needed for the steam blast when used. If it becomes suddenly necessary to raise the steam pressure, mechanical stokers cannot be relied on to keep it up as well as firing by hand. They are not generally applicable, and do not seem to be much used where the amount of water to be evaporated varies much from hour to hour, as, for instance, in electrical light stations. 132 HEAT EFFICIENCY OF STEAM BOILERS. Where the work is constant, and the evaporation practically always the same, as in water wo][ks, they are very suitable, and much employed. Unfortunately, they are not yet applied to marine hollers. Their two great advantages are that comhustion is practically smokeless, and that a much cheaper and poorer fuel can he used than with hand firing. About 8% of all the boilers in Great Britain are fired with mechani- cal stokers; with one boiler there is little economy of labour, but with many it may be considerable. The quantity of coal burnt varies generally from 20 to 60 lbs. per square foot of grate per hour. CHAPTEE VI. Combustion of Puel in Boilees. Conditions of Oombustion — Admission of Air — Heating Value of Fuel — Formulse — Chemical Process of Combustion-^ Hoadley's Experiments — Analysis of Flue Gases — Quantity of Air rec^uired — Percentage of CO2 — Method of Calculation — Place for Sampling — Spenoe's Experiments — Process of Combustion in Practice — Methods of J regulating Combustion. To produce heat under a boiler all kinds of fuel are used, and the processes by which the chemical combinations are obtained are called combustion, whether they are effected with soHd, liquid, or gaseous combustibles. Fuel contains chiefly carbon and hydrogen, and it is when these combine with the oxygen of the air that they give out heat. The problepa is to generate as much heat as possible from each lb. of fuel, and to utilise it completely under a boiler, whether the heat be evolved from coal, coke, wood, oil, gas, turf, etc. Conditions of Combustion. — To obtain the maximum amount of heat, combustion must be complete. This involves compliance with certain conditions, not always easy to procure with a boiler, and which are very often neglected in industrial applications. In the first place, the requisite quantity of air must be supplied, and this amount varies with the particular fuel used, all coals differing in composition. Air is needed in order that the oxygen' it contains should combine with the carbon and hydrogen in the fuel to produce combustion. The oxygen is present with more than four times its weight of nitrogen, an inert gas which does not burn, but must nevertheless be heated up to the tempera- ture of the flue gases, thus absorbing uselessly some of the heat generated by combustion. This loss of heat is unavoidable, but it can be reduced by carefully regulating the admission of ' Chemical symbols :— = oxygen, ■ H = hydrogen, C = carbon, N = nitrogen, S = sulphur, CO -carbonic oxide, CO., = carbonic acid. air, and some of it is returned to the boiler by the feed water heaters. Admission of air. — The volume of air re- quired for combustion must be introduced when and where it is wanted. It should be divided into a number of small currents, and admitted to the furnace not only through and above the grate bars, but at and above the bridge, in order that all the gases generated during combustion may be thoroughly burnt, with the minimum of smoke. The draught, whether produced by a chimney, forced, or induced, and the distance between the grate bars, both largely affect the quantity of air admitted, as also the method of introducing it. Again, the air may be supplied either hot or cold. It is very important, though too often neglected, that it be properly aiid intimately mixed with the fuel and burning gases. This process depends upon the thickness of fuel on the grate, varying from 2 in. to 12 in., upon the size of the coal, which runs from y\ in. to 2 in. or more, upon its character, whether caking or non-caking, and on many other con- ditions. It is desirable to facilitate the mixture of the air with the hot gases as much as possible, and this is often usefully done by bafQe plates made of fire-brick and other arrangements, to produce contrary currents and agitation. In locomotive boilers a fire-brick arch fixed above the grate is now much used, to deflect the gases and cause them to flow forward, instead of going directly into the smoke tubes. This economical arrangement . has a very important effect informing a chaniber or space, where the combustion of the gases by their union with the 133 134 HEAT EFFICIENCY OF STEAM BOILEES. air can be completed, and tMs is especially necessary with coal containing much hydrogen and carbon. Professor Lewis and others consider it most important that the flames playing along the boUer surfaces should not be unnecessarily cooled, while transmitting their heat to the water through the iron plates. The boiler plates when clean are only a few degrees hotter than the water in the boiler, and seldom higher in temperature than, say, 400° F., while the temperature of the flames is from 1850° F. to 2700° F. The result is that a layer of unburnt gas, or gases escaping combustion is formed, which checks the transmission of heat from the flames to the boiler plates, and this action diminishes the evaporation, and reduces boiler efficiency. To insure fairly complete combustion a high temperature should be aimed at. If the colder boiler plates are placed too near the grate and fire, and the gases are much chilled by contact with them, bad results will follow, and smoke be produced. This question is too often in- sufficiently, considered. The quantity of heat set free by a combustible is independent of the activity or rate of com- bustion. Whether quick or slow, the same quantity of heat is given out if radiation is the same in both cases, but the temperature of com- bustion may be higher or lower. Heating value of fuel. — The heating value of any fuel, that is, the amount of heat generated by it during combustion, can be quickly and accurately determined, and with very little ex- pense or trouble, by an instrument called a fuel calorimeter. In aU exact boiler experi- ments the heat value of the fuel should be thus ascertained. The heat of combustion of the difierent elementary bodies of which the fuel is composed has long been known. If the com- position of the coal is determined by analysis, its heating value may be thence calculated by adding together the heating values of its constituents, and allowing for their heat of combination. The heat required for the combination of the hydrogen with the oxygen and with the carbon is not yet absolutely determined, but, having regard to this slight imcertainty, the results obtained should agree with those found by a calorimeter. Several formulae are used for this purpose. In that drawn up by Didong the heating value of the C and H in the coal are calculated, and the N and S neglected, the quantity of the latter being too small to practically affect the results. It is assumed that the unites with its equivalent weight of H, rendering it inert, and forming water. This quantity is consequently deducted from the H, and the formula is as follows : — 14,650 C + 62,100(H- JO). Heating value of 1 lb. of = 14,650 B.T.U.; 1 lb. of H, 62,100 B.T.U. ; 1 lb. of S (neglected), 4032 B.T.U. Formulae. — The heating value of a Newcastle coal of the following percentage composition, viz. : — C 80-51, H4-24, 8-16, Nl-11, S 0-81, Ash 3-74, "Water 1-43 = 100, is thus calculated : 14,650 C + 62,100(H- J 0) = 14,650 X -8051 + 62,100 (-0424- J-0816) = ll,794 + 62,100x -0322=13,793 B.T.U. Some years ago this formula was much used. Since the introduction of the Berthelot-Mahler calorimeter, M. Mahler has made a large number of experiments to compare the heating values thus obtained with those yielded by the Dulong formula. All his results are carefully plotted on curves. Those who wish to study this interesting branch of the subject are referred to M. Mahler's valuable work on combustion.^ M. Mahler proved that the Dulong formula gave results too little by about 10 or 11%, and drew up an empirical formula deduced from his own experiments, which seems at present accepted as yielding more correct values for certain kinds of coal. If properly worked out, the heating value, as determined by chemical analysis and calculation, and in a calorimeter, should agree within 1% or 2%. M. Scheurer-Kestner, in the Bulletin de la Societe de Mulhouse for 1891, also carefully compares the heating value of coal as calculated with the Dulong formula, and as given by a good form of calorimeter, and considers the Dulong results too low. The Mahler empirical formula is 14,650 C + 62,100 H-5400 (0 + N). Taking the same coal as before, the calculation will be 14,650 X -8051 + 62,100 x -0424 - 5400 (-0816 + -0111) = 11,794+2633-500 = 13,927 T.TJ. per lb. ' Contributions it I'&ude des Combustibles, by P. Mahler, Paris, Baudry et Cie, 1893. CHEMICAL PEOCESS OF COMBUSTION. 135 The quantity of air theoretically required for complete combustion may be determined from the chemical composition of the coal, by sub- stituting for the heating value of the C and H the oxygen required for their combustion. The proportions of N and in atmospheric air are as follows : — ijy weignt, ^ ijitrogen, N, 0768 / Bv volume -f ^^yS^""' 0> O'^OS* l ay vomme, -^ jjitrogen, N, 07906 J Thus, 4J lbs. of air are required for every lb. of oxygen combining with the fuel. is by weight 8 times as heavy as H. As compared with carbon its weight is 16 to 12. But to pro- duce perfect combustion the C and must unite to burn to COg, and therefore their relative weights will be as 12 to 32 = 3 to 8, or 2-66 lbs. O to every lb. of C. (The variations in the composition of coal generally used under a boiler do not greatly affect this theoretical proportion of air.) The Dulong formula now becomes : — = 2-66 C + 8 (H-g) = = 2-66x -8051 + 8 ( -0424 - ^g— j = = 2-1415 + 8 X •0322 = = 2-1415 + •2576 = 2-3991 lbs. ; and the supply of air required for combustion wUl be 2-3991 X 4-33 = 10^38 lbs. of air. Chemical process of combustion. — The chemical processes taking place during combustion may be thus described. When coal is first put on the fire the hydro- carbons are distilled off, that is, the gaseous con- stituents of the fuel are volatilised, and much heat absorbed, being converted from sensible to latent. A high temperature is necessary at this point, because gasification is a very cooling process. The H in the coal, having greater afiinity -with the O of the air, first combines -with it to produce steam. C is liberated, and, unless supplied ivith enough to form COg, it will pass away unburnt, or combine in insufficient quantities as CO. The heat evolved by the combination of part of the with part of the C heats the COj thus formed, and also the remaining free in the gases, and the N. These chemical processes show the importance of a plentiful supply of air, and therefore of oxygen, in the early stages of combustion, and after stoking. High tempera- tures are essential, because hydrogen will not unite with oxygen under 600° F., nor will carbon combine with it at a lower temperature than 800° F. The formation of a certain proportion of CO is unavoidable when coal is first fed on to the grate, but if a proper supply of oxygen is present, the CO will be turned into COg without unduly chilling the fire. Mr Spence is of opinion that CO2 is first formed and reduced to CO as it passes over the unburnt carbon on the bars. The heat generated by the combustion of CO is very much less than that evolved when COj is formed. If carbon be consumed to COg, it pro duces 14,650 B.T.U. per lb., if consumed to CO it produces only 4400 B.T.U. per lb. Therefore, when CO is formed there is great loss of heat. Its presence in a furnace is shown by a blue flame, and is a sign of imperfect combustion. The main object in all boiler firing should be to produce as much COg as possible, and as little CO. Mr Hoadley's experiments. — A series of careful experiments were carried out by Mr Hoadley during one working day, to determine the amount of CO generated by continuous and excessive firing, and the consequent loss of heat. The flue gases were analysed every half hour throughout the day, except at noon. As far as the author is aware, a similar set of interesting experiments has not been made before, and he therefore adds the Table (page 136), showing the principal results obtained. In the original work they are plotted in curves.^ Not only an excessive consumption of fuel, however, but also a deficiency in the air supply to the grate results in the formation of CO, and causes a double loss of heat. There is first a suppression of actual heat, because the C is not burned to COg, and next of heat rendered latent by the process of gasification. If sufficient air is afterwards suppUed to the gases, this CO is transformed into CO,, but if the air is lacking in quantity, or the temperature is not high enough, the CO escapes into the flues, where it often bursts into a beautiful blue flame. To observe this interesting phenomenon, the author has often had the blue flame produced in the flues of ^ In Appendix III., page 254, further notes on Mr Hoadley's experiments will be found, with a dra-wing of the boiler, snowing the way in which the air for com- bustion was previously heated, and a curve giving the fall of temperature of the gases. 136 HEAT EFFICIENCY OF STEAM BOILERS. boilers and watched it through a sight hole. A series of very exact observations of the appear- ance of the flue during 1^ hours of trial No. 1, page 65, were made by Mr Spence, and will be foiind in the Appendix, page 257. The blue or violet flame denoted the combustion of the CO, the red flame that of the other gases which some- times ignite in the flue, if they meet more oxygen. Mr Spence considered that in his experiments the CO flame showed that the gases first burned to COj, and were afterwards reduced to CO, because sufficient air was not supplied to them after they had left the furnace. Table of Carbon Monoxide produced by excessively rapid firing under an externally fired boiler like fig. 11. •SI 1|8 IB .^ o IIS Time »•§ m o ■s's lbs. 7. 7. 11)S. lbs. 6.16 a.m. 200 6.46 „ 200 7.15 „ 200 7.45 „ 200 8.15 ,, 200 8.45 „ 200 9 6-12 2-54 3'3-2 83-81 2'7'-84 9.15 „ 200 9.30 ,, 6-56 2-99 29-5 9'3'-75 29'-14 9.4B „ 200 10 7-79 3-99 21-4 12'9'-24 28-37 10.16 „ 200 10.30 „ 7-70 4-61 20-1 157-60 30-81 10.46 „ 200 11 ,. 7-82 4-70 19-8 139'C8 30-88 11.15 „ 200 11.30 „ 8-01 4-81 48-5 14'3'^30 30-86 12 Noon. 19-3 143-30 12.30 p.m. 16-21 ■■-25 19-8 143-30 1-60 12.45 „ .200 1 2'o'-9 13^94 1.30 „ 14-11 ■'-21 20-8 132^96 'l'-49 2 21-0 137-94 2.30 „ l'3'-62 ■■-33 21^8 129-85 2-31 2.45 „ 200 3 14-50 "-48 19-4 14'2'-56 3-14 3.30 ,, 13-18 -29 22-0 125-34 2-12 3.45 „ 200 4 „ 14-96 '•38 I'o'-s 148-80 ^'•44 4.30 „ 14-18 -41 20-3 136-25 2-76 4.45 „ 200 5 13-01 •41 2'2'-0 12'6'-34 '3-00 The higher the temperature the less surplus air (or 0) will be required, and the more readily will the H and the C unite with the 0. As far as possible all the air should be supplied to the grate, or just beyond it in the chamber where the process of combustion is completed ; none should be allowed to penetrate to the gases afterwards by leakage through the brick-work., As time is required for the process of combus- tion, that is, the perfect union of the C with the 0, and it is rarely completed when the gases leave the furnace, a very high velocity of the gases is not desirable. Time is also needed to transmit the heat to the water from the hot gases through the boiler plates. Analysis of flue gases. — The only way to determine whether combustion is good, bad, or indifi'erent, is to analyse the flue gases. This is now easily done, and the gases are sampled, either at the end of the first passage, or at the boiler side of the damper, or better, at both places. Without this analysis no boiler, experiments are complete, but boiler owners have hitherto not realised its value, and it is seldom carried out, except in trials. (See, page 187 for description of apparatus for analys-, ing gases.) On this point Mr Hoadley says : — "Unless the composition of the escaping gases, is known, nothing is known; this accurately ascertained, -and their weight and temperature, almost everything which it is desirable to know is ascertainable." To obtain complete combus- tion, the fuel should be spread over the grate in a layer of fairly uniform thickness. If the bars are not well covered, too much air will enter, and the greater the excess of air the less will be the intensity of the flame. With most boilers the above conditions are not carefully attended to ; too much or too little air is introduced, the grate badly covered, and the losses of heat are often large. From 10 to 20% increase of bofler efficiency, with the same boUer and coal, has often been realised in experiments by the author and others, after analysis of the gasea , had shown how defective combustion could be remedied. In practical applications there is often a loss by the generation of CO. Taking the weight of gases produced during the process of combustion, the chemical relation is as follows : — One unit by weight of carbon unites with two units of oxygen, giving two units of carbonic acid (COj). The following is the chemical formula :— 1 unit C + 2 units = 2 units COj. When oxide of carbon is produced, 1 unit C-l-l unit = 2 units CO. QUANTITY OF AIR REQUIRED FOR COMBUSTION. 137 Oxide of carbon can again combine with oxygen, yielding 2 units CO + 1 unit = 2 units CO.j. There are other combinations of oxygen with hydrogen, and hydrogen with carbon, but for these and other details we must refer our readers to chemical works on combustion. Herr Ernst considers {JSngineering, April 4, 1893) that the oxidation of the carbon begins at a temperature of only 752° P., and that COj is then formed as the main product, with only a small amount of CO, whether the air be admitted in large or small quantities. When the rate of combustion is increased, and the temperature rises to 1292° F., the chief product is still CO.,, even when the excess of air is such that the exhaust gases contain 20% by volume of COj, which is practically this theoretical maximum limit, proving that all the oxygen has been consumed. Above 1292° F., the proportion of CO to CO2 rapidly increases, until 1823° F. is reached, when CO is exclusively produced. ftuantity of air required. — If the exact theoretical quantity of air necessary for the com- bustion .of the coal, assuming it to be pure carbon, were used, 21% by volume of CO3 would be obtained in the gases of combustion, as the proportion of oxygen in the air is 21% by volume. This theoretical quantity, however, is not sufficient, and a certain excess, usually estimated at from 33% to 55% by volume, is necessary. " Perfect combustion with " the theoretical " quantity of air is only possible," says Mr Spence, " on a very small and experimental scale, where due attention and time can be given for perfect diffusion, and the bringing of each atom of carbon and hydrogen into what may be termed actual mechanical contact with its combining equivalent of oxygen. In practical operations on a large scale, such as steam boiler furnaces, the available time is so short, and the conditions, even when at their best, under which the air can be intro- duced to the sohd carbon and coal gas, are so little calculated to help diffusion, that a greater quantity than is chemically necessary should be supplied, to facilitate the combinations of the atoms. . . . The real practical difficulty in air introduction lies in this : that if each atom of carbon and hydrogen of the coal is not first brought into actual mechanical contact with its combining equivalent of oxygen it cannot com- bine with it, and is lost, or worse than lost, for the production of increased temperature." In most well- worked boUer plants about 100% and more excess of volume of air is often found. The experiments, as seen in the Tables, show even much larger quantities. Enough, we hope, has now been said to show the great importance of regulating the supply of air for combustion. It is not sufficient to determine the requisite quantity by calculation. Care must also be taken that the amount furnished is neither deficient nor excessive, and that it should be introduced in the right place, in the right way, and properly diffused. Analysis of the gases alone can determine these points. Too little attention is paid to this, although provision is sometimes made for a second supply of air, usually at or just beyond the fire bridge ; this is often done on the Continent. Percentage of CO3. — The percentage of COj forms an approximate guide for measuring the excess of air going up the chimney, and estimat- ing the loss of heat caused by it, which can be diminished by careful management of the furnace and good stoking. As it is chiefly occasioned by the air entering the grate which escapes unburnt, or the volume of unused air in 100 volumes of exit gases, the larger this excess of air the greater will be the percentage of COj. By a simple calculation based on the chemical analysis of the gases, or on the composition of the fuel and its heating value, this loss of heat can be determined. But to avoid either of these somewhat laborious methods, it is sometimes calcu- lated from the percentage of COg by the German authorities, according to the following formula, V = c, T-t, 7oCO, in which V is the loss of heat in percentage of the heat value of the fuel, T and t the tempera- tures of the .air in and gases out, and c is a coefficient = 0'65 (Bunte's formula for hard coal). The excess of air in the chimney can also be calculated from the percentage volume of COo in 18'9 the flue gases, thus ^ . = ratio of air in excess . % ^^2 over that theoretically required for combustion. The figure 18"9 is arrived at as follows: — If the whole of the in the air combined with the C to form CO2, its volume, as already said, would be 21%. But as the chemical analysis of the 138 HEAT EFFICIENCY OF STEAM BOILEES. coal always shows an appreciable amount of H and of S, allowance is made for tiie combination of part of the oxygen with them, and the value 18"9 has been determined by Dr Bunte, and is generally used by German writers, to denote the (average) oxygen in the air "admitted which is available to form COj. Methods of calculation. — Table giving the % loss of heat for dilleroiiL % by volume of COj in the flue gases, and of % excess of air in 1S-Q them calculated from the CO, 18-9 (% CO,)-' % % % % % % % % % 9 % % % % % % Percentage CO^in flue gases 1 2 3 4 5' 6 7 8 10 11 12 13 14 15 by volume. Percentage of excess of air 1790 850 530 370 280 220 170 140 110 90 70 60 50 40 30 over that theoretically required for combustion, Percentage loss in coal. 1803 90 60 45 36 30 26 23 20 18 16 15 14 13 12 Exit gases at 518° F.^ ^ Ze^sohrift des Vereines deutscher Inginieure, July 8, 1893. ^ Tne loss is calculated for a temperature of the incoming air of 68° F., and a difference of 482° F. between it and the exit flue gases. ■' If the loss of heat js above 100%, it is at the expense of the heat stored "up in the brick-work. Another method of calculating the excess of air is from the percentage of and N shown in the flue gases. The foUowing formula has been kindly communicated to the author (the percent^e of N is usually calculated by difference) : — N" ¥■ N-lfO Taking flue gases of the following composition by volume : N 81-25% - 4-84% - OO2 13-08%, CO 0-83% ; this formula works out TS 81-25 81-25 N-f!0 81-25-3-7x4-84=63-35' 1 = 28% excess of air. In an experiment on an internally fired elephant boiler, M. Scheurer-Kestner, the great French authority, analysed the gases of combus- tion seven times during the intervals between two firings by hand, and found the following averages by volume: — With 7% excess of air the gases generated contained 14-87% C0„, 1-4% 0, 0-84% CO, 1-35% H. With 119% air in excess he found 7-73% COj, 11-42% 0, and 0-41% CO. The five intermediate analyses. with gradually increasing percentages of air in excess, gave gradually diminishing COj, gradually increasing 0, rather less CO and H. Place for sampling. — The place near the furnace whence the gases are drawn for analysis is another important point. They should first be sampled, if possible, just where they are generated, at the back of the furnace, and before any air has been added except that used for combustion. Beyond this point, in most fire tube boilers, air penetrates into the flues through the brick-work. How great the effect of this after-infiltration of air is upon the dilu- tion of the flue gases is shown by the fact that the percentage of COj is often greatly reduced in the samples of gases taken at the end of the boiler near the damper. Some- times with only 33% excess of air CO is found, because the air supply in the furnace was insuf- ficient, and, although air was afterwards added, the CO already formed could not be burnt to COj, because the temperature was too low. Whether the proper quantity of air to furnish the O required for complete combustion is ad- mitted under or above the grate, or at the bridge, seems to matter little as far as economy is concerned, provided no CO is allowed to escape up the chimney. COMBUSTION OF COAL. 139 Mr Spence's experiments. — On pages 65 to 71 will be found four series of Mr Spence's in- teresting experiments under different conditions, made on the same marine type of boiler, with, the same coal and stoker. The eleven experi- ments on Table 1. are all with chimney- draught, and air at atmospheric temperature. In this series, other conditions being kept constant, the quantity of air admitted was gradually increased from 12J^ lbs. per lb. of coal (10"4 lbs. being the theoretical quantity) to 18J lbs. The boiler efficiency rose steadily from 65% to a maximum of 73%. Very much less' smoke was produced than with ordinary firing, and ' there was much better combustion. The different places above and below the grate, and at the fire bridge, where the admission of air was gradually increased, are fully described in each experiment, page .65. The next set. Table II., page 67, was with forced draught and air at atmospheric temperature as before. Here the quantity of air admitted was again increased by the methods described from 18 J lbs. to 27 lbs. per lb. of coal, and then again diminished. The boiler efficiency first increased in proportion, then decreased. The maximum boiler efficiency ittj^this set was lower than in the first, being only 68%. The third set of eight experiments, page 69, was also made with forced draught and air at atmospheric temperature. . The quantity of air per lb. of coal per hour varied from 17 to 23 lbs., and the maximum boiler efficiency was 75f % with 20 lbs. of air per lb. of coal. In the fourth series, page 71, three experiments were made with forced draught, but in this case the air was heated to 250° F. The quantity of air varied from 17 to 20 lbs. per lb. of coal, and the boiler efficiency from 75^% to 78J%, the latter being the maximum in all the experiments with 20 lbs. air per lb. of coal. The temperature of the flue gases in the up- take immediately below the chimney was con- stantly taken, and it was found that as the supply of air, not to the furnace, but to the gases after leaving the furnace, increased, the tempera- ture of the gases rose, and the smoke greatly diminished. Mr Spence drew the conclusion that good combustion cannot be obtained in an ordinary grate if the air is admitted only through the bars in the usual way, but that it should be introduced above and below, direct to the gases, in the proportion of 4% to 5% of the open spaces betvyeen the bars. By allowing the air to enter in this way, the combustion of the gases after they leave the furnace, and not that of the coal on the grate, is stimulated, and it was found in these experiments to result in an economy of about 10% of coal, with 50% diminu- tion in the smoke. Even then, however, Mr Spence was of opinion that it is difficult to get a sufficient supply of air to the grate. With force blast, less air space between the bars is desirable. A very high rate of combustion does not give the best efficiency, but the consumption of coal with this type of boiler should be about 35 lbs. per square foot of grate per hour. An important point to note, however, is that any apparatus for previously heating the air supplied to the grate must be efficient and not costly, otherwise com- mercially it may be a failure. It will be seen from the Tables that heating the air produced a slightly better efficiency, but the cost must be carefully considered. For further detail' the reader is referred to Mr Spence's original paper,^ and also to Mr Hoadley's experiments, p. 255. With good Welsh coal the quantity of air necessary for perfect combustion is about 11 cubic feet at ordinary temperature and pressure per lb. of coal. As to the temperature of com- bustion, with about 50% excess of air, it may be taken to be between 2730° F. and SCSO" F. with ordinary natural draught and good coal. It will be seen in the Tables of boiler experi- ments how greatly the quantity of fuel burr ; per-square foot of grate surface per hour varies in practice from 5 lbs. to 90 lbs. with different draughts, chimney or forced, different fuels, and many other conditions. The analysis and tem- perature of the gases of combustion are also shown in the Tables in some 400 tests. Process of combustion in practice. — Having examined the subject of combugtion from a theoretical and chemical point of view, the course it follows in practice must now be considered. The author will attempt to describe what he has often seen and observed in a Lancashire boiler, fired by a stoker of average capacity. When fresh fuel is thrown by hand through the open furnace on to the glowing fire, to a thickness of, say, 6 in. to 8 in., the first effect is to cool considerably the whole mass of combustible. 1 " On the Combustion of Coal," by W. G. Spence, Proceedings of the N.M. Coast Institution of Engineers and Shipbuilders, 1888. 140 HEAT EFFICIENCY OF STEAM BOILERS. Tke bars and boiler plates present relatively cold surfaces, and diminisbed evaporation is the result. The black coal and coal dust obstruct the passage of air through the bars of the grate, and reduce the volume entering, and much smoke is generally produced for two or three minutes or more. During the next five minutes combustion is stimulated, and gases are rapidly given off, in quantities greater or less according to the composition of the coal, its size and thick- ness. The coal is often not spread over the grate to a uniform depth, and the quantity of air admitted is thus not always the same. This is the time, immediately after firing, when more air should be supplied, both above and below the grate, but it is seldom admitted in sufficient quantities, and the conditions of combustion are usually decidedly bad. As the fire continues to burn and brighten, more coal is consumed, holes are produced in it, and more air gets through, but the supply is mostly deficient when the maximum quantity is required. Although the temperature of the mass has risen, more or less smoke is still given ofi^, a proof of bad combustion. The smaller pieces of coal are burnt first, some of the finest particles and dust being carried away over the bridge by the draught into the flues. Some of the lightest of all are blown out at the top of the chimney by the current of air, while the heavier particles lodge at the bottom of the furnace tubes and brick flues. After some minutes have elapsed, the stoker stirs up the fire with his long poker, and tries to mix the black and the red coal, but his efforts, as a rule, only produce more smoke. After one or two minutes combustion improves, and becomes more uniformly diffused. As it proceeds, the fire gets hotter and thinner by degrees, coke is produced, and air penetrates the diminished thickness of red-hot coal in the tliinner parts, over the grate. The volume of gases given ofi^ is reduced, no more black coal is visible, and at last the proper conditions for combustion are attained, the air supply is suf- ficient, the fire burns red and white, and there is no smoke. The evaporation of water from the boiler plates above the fire and throughout the boiler wiU, of course, be very much greater with such a good hot fire than before. After a few minutes of combustion under these excellent conditions the fire gets too thin, all the gases have been given ofi^, and most of the coal trans- formed into coke. Again, bad firing and im- perfect combustion foUow. Air is now admitted too freely through the thin Hght fire. Its percentage in excess is much increased for some minutes, and it passes too easily through the fire, under the boiler plates, and through the flues to the chimney, cooling all the surrounding brick flues, etc., and reducing the temperature, the evaporation, and the boiler efficiency, although there is no smoke. The process of stoking has again to be gone through. The fire is replenished with black coal, the doors being opened for the purpose, and the same bad results and production of smoke follow as before. After firing from two to four hours with ordi- nary coal, the process of clinkering becomes neces- sary. The heavy red-hot incombustible re- siduum from the burnt coal must be taken off the top of the grate bars, and raked out on to the iron floor of the stoke hole, the fire doors being open during the whole time of the opera- tion, which lasts from two to four minutes. Cold air is thus let in on to the top of the grate, where it is not wanted, and reduces the tem- perature of the boiler and flues. This un- pleasant process, with its attendant dust and sulphurous vapours, must be performed two or three times in the ten hours, as the clinker adheres to the bars, covers most of the air spaces between them, and diminishes largely the supply of. air. With fuel containing from 15% to 30% of dirt it has to be done more often, with all the multiplied ill effects of coohng the boiler, opening the fire doors, stopping up the fire spaces, etc. These undesirable fluctuations in the intensity of the fire cause much variation in the transmission of heat through the boiler plates to the water, and the evaporation. Methods of regulating combustion.— Thus with hand fired grates, there is only a very short period between two stokings in which combustion is really satisfactory — with closed fire doors and the proper admission of air. The time during which these good conditions of firing prevail depends upon how 'often it is necessary to put fuel on the grate, to evaporate at a given pres- sure the quantity of steam required of the boiler, and this again rests with the stoker. With ordinary hand fired grates, stoking and poking the fires nearly always produce more or less COMBUSTION OP COAL. 141 smoke. To admit the right quantity of air above the grate and at the bridge greatly tends to reduce the smoke and improve combustion. Mechanical coking stokers also help in this direction, and make combustion and evaporation much more regular. "With these variations in the temperature and intensity of the fires, the stoker must not only look after the steam pressure and maintain it fairly uniform, but also alter his damper to give more or less draught on the grate, according to his judgment. Again, the entrance of the feed water into the boiler must be regulated. As this water is generally rather cold, it tends to cool the boiler, and reduce the steam pressure. When this is highest is the time to feed in the water and coal, if it cannot be done continuously, which is preferable. Another fluctuation in the combustion, which afl'ects it more than is generally thought, is the difference of vacuum under and above the grate, caused by the thickness of the burning coal. These variations have been measured by very sensitive water U tubes. With a good fire there is sometimes ^ in. diff'erence, and with less coal on the grate ^ in., the opening of the damper being the same in both cases. Boiler grates are often fired every quarter of an hour to twenty minutes, and sometimes much more frequently; the average time between the stokings depends upon a variety of conditions. Many good authorities consider that, for good combustion, the percentage excess of air in the flue gases, over that required for the proper combustion of the fuel, should not exceed 50%, and not be less than 25%. From these observations the importance of the analysis of the gases will at once be apparent. To insure good combustion on the grate, it is also necessary that the fire bars should not be allowed to remain when burnt, say for not more than two or three years. They should be replaced by new ones as soon as they become old and worn at the top, as their deforma- tion affects the free passage of the air between them. Coals give off more and more hydrocarbons in the gases, according to the greater proportion of hydrogen they contain in excess beyond the quantity necessary to unite with the oxygen. Mr WHson says : — " There is a marked difference observable between different coals containing similar percentages of hydrogen. In some cases the hydrogen appears to be combined with carbon in a form which leads to the immediate liberation of hydrocarbons on heating. In other cases, the hydrogen can be burnt with little or no liberation of hydrocarbons." Analyses of the gases of combustion have been often made by many chemists and engineers, but the results obtained present many anomalies. This want of harmony is explained by the various conditions under which the formation of these gases takes place. The nature of the fuel used, its thickness on the grate, amount of draught, combustion, whether gentle or forced, all affect the gases. Their composition is also influenced by the number of minutes the fire doors are open, leakage of air through the brick- work, extent to which the damper is opened, etc. It is also of importance to specify the place where the gases are sampled, the method adopted in taking them, and whether they are sampled only for a few minutes each hour, or continuously during eight or ten hours. CHAPTEE VII. Transmission of Heat through Boiler Plates, and their Temperature. General Eemarks — Examples of Transmission of Heat— Bleohynden's Experiments — Durston's Experiments — Hirsch's Experiments — Professor Witz's Tests — Dr Kirk's Experiments — Serve Tubes — Hudson on Heat Transmission. General remarks. — The all-important subject of the transmission of heat through the plates of steam boilers, and its effect upon their tempera- ture, is too often lost sight of and. neglected by engineers and boiler owners. A boiler is an apparatus for raising steam by transmitting as much heat as possible from the external fire and hot gases through the boiler plates to the water, producing evaporation and steam as a result. The object is to evaporate the maximum quantity of water into steam per lb. of fuel, but in boilers generally this transmission is retarded instead of facilitated. The outside surfaces of the boiler plates and tubes are often left dirty, and not cleaned at sufficiently frequent intervals. On the inside surfaces grease, mud, and deposit of all kinds are allowed to collect and adhere to the plates, thus defeating the main object aimed at, namely, the transmission of the heat through the metal. The heat-receiving surfaces on the hotter sides of the boiler plates should often be cleaned, to give them a fair chance of performing their proper function. Again, in order that the heat, after penetrating the metal, which is a good conductor, may pass out again quickly to the cooler water, the inter- nal surfaces of the plates should be kept clean. Unfortunately this is seldom the case. Unin- tentionally, though with much pecuniary loss, the heat once generated is very carelessly treated. Through neglect and the accumulation of dirt allowed on the surfaces, it can neither get freely into the plates, nor when in, can it pass out of them rapidly to the water. The heat-absorbing and heat-transmitting surfaces should receive much more attention than they do. The money spent in keeping them clean would be well repaid in the increased boiler efiioiency obtained. Experiments made on the same boiler, with the same stoker and coal, prove that the diiference in efficiency produced by clean or dirty surfaces amounts to 10 or 15%. Too much is now left to the attendants, who cannot be expected to realise the importance of keeping the metallic surfaces of boilers and economiisers clean, and making everything subserve the ultimate object of transmitting the maximum amount of heat. Intelligent young engineers should be sent into the boiler flues, to inspect every square foot of surface, after the dirty and disagreeable task of the nominal cleaners is over. The work is often done on Sundays and holidays, and too fre- quently in a great hurry. A spare steam boiler diminishes all these difficulties considerably. With boiler plates the transmission of heat, although thus often more or less checked, is always in one direction, viz., from the fire and hotter gases to the cooler water. The plates over the fire ought to transmit from sixteen to seventeen times more heat, and evaporate six- teen to seventeen times more water per square foot of heating surface per hour, than those at the end of the boiler, and it is therefore much more important to keep these parts clean. See fig. 36 of results of experiments on a locomotive boiler, showing graphically the difference in evaporation at different parts of the boiler. But as there is much greater evaporation from these -Plotted results of five ex- periments on the Northej-n Rail- way of France on a locomotive boiler, divided into five water- tight compartments, showing the much greater evaporation near the fire box and then gradually Briquettes used as fuel. As the surfaces in contact with the fire and gases are further away from the fire box, the transmission of heat following a geometrical progression. The surfaces increase in arithmetical progression. The quantity of heat transmitted is proportional to the difference of temperature between the gases and the water (with clean surfaces). HEAT TRANSMISSION. 143 ftmpen "r»337'f. boiler plates, there is also generally more dirt on them than elsewhere ; in other words, the direct heating surfaces above the fire and flames become dirtier than those which are only ex- posed to the hot gases. The question may be asked, why boiler plates should transmit heat in such different quantities over the fire and at the end of the boiler 1 The cause lies in the greater difi'erence of tempera- ture between the fire and the cooler water at the one than at the other of these two places. To make our meaning clear, let us take a numerical example. We will assume a tem- perature above the fire of 2500° F., and steam generated at a pressure of 100 lbs. = 338° F. Thus, over the fire we get 2500° - 338° = 2162° F. difference of temperature, or "head of heat," to transmit from the hot fire and flames to the cooler water. Now, if the hot exit gases have a temperature of 800° F. at the end of the boiler, we shall only have 800° - 338° = 462° F. difference of temperature, or "head of heat," to transmit at that spot from the hot gases to the water. The former, 2162° F., is 4f times as much as the latter. Thus the quantity of heat transmitted per square foot of heating surface in a given time is in proportion to the difference of temperature between the hot flames and gases, and the water, on each side of a theoretically clean boiler plate. The transmission also shows the conductivity of the metal, and is inversely in proportion to the square of its thickness. Again, the better the circulation of water inside the boiler, and of gases outside, the better will be the transmission of heat up to a certain limit. It should not be forgotten, however, that the temperature of clean iron plates, even over the fire, is only slightly above the temperature of the water on their other side, and greatly inferior to that of the flames and gases through- out their first run. If the plates are dirty and greasy, they give out the heat received with great difficulty, and become dangerously hot. As we shall see, the heat absorbed cannot get away. Figs. 37, 38, and 39 illustrate these remarks with reference to boiler plates of water tubes and smoke tubes. Examples of transmission of heat. — In the last column of the Table of Tests will be found in several cases the quantity of heat transmitted in thermal units per square foot of heating surface per minute, in the particular boiler 144 HEAT EFFICIENCy OF STEAM BOILERS. Fig. 37.— Boilerplates. Cfats Seei:ryOt^. Fig. 38. — Tubes with water inside and hot gases outside. tit » . C5F — ~ ^^^g^^^^^^g^. ^^^^^^^^^^^^^y ^) V^^^^^'f^^'^l (•/^'!W7V?''S??^3^' l^^^^l Fig. 39.— Smoke tubes, gases inside, water outside. EXAMPLES OF HEAT TRANSMISSION. 145 tested. This is the mean quantity, taking the total heating surface, including the smoke tubes. Over the fire the quantity of heat will be very much greater, perhaps ten to twenty times more than the average amount, depending on many conditions. (The number of T.U. transmitted per square foot of heating surface per minute in any boiler experiment in the Tables can easily be calculated from the number of lbs. of water evaporated from and at 212° per square foot of heating surface per hour. Multiply by 966° (total heat) and divide by 60, or multiply by 16-1). P. 81. Locomotive boiler with smoke tubes, 56T.U. per sq.ft. of heating surface per min. passed through the boilerplates. P. 87. Two-storey boiler (3 boilers), 31—43—62 T.U. P. 93. Lancashire boiler (4 boilers), 22—40 — 60—84 T.TJ. P. 95. Elephant boiler (3 boilers), 67—75—77 T.U. P. 111. Thornvcroft (1 boiler), 24—61—89—158 T.U. P. 113. Belleville (2 boUers), 100—127 T.U. The number of thermal units wUl naturally vary much with the intensity of the fires, rate of evaporation and of stoking, condition of surfaces, whether clean or dirty, etc., etc. This will be seen from the following figures, quoted from the Donkin and Kennedy series of experiments.^ The minimum rate of evaporation was 28 T.U. per square foot of heating surface per minute, and the maximum 211 T.U., with a fire engine boiler, much forced. The experiments gave respectively 28—38—41—42—56—62—65—66—68—69—72—77—79—82—87—91— 101 — 120^ — 126 — 211 T.U. per square foot of heating surface per minute. In these trials there was no doubt every variety of more or less clean or dirty boiler sur- faces, and sometimes the plates were covered with soot and scale. The difierent types of boilers were also worked under various conditions, some forced, some very gently. In the Proceedings of the Institution of Mechanical Engineers, 1884, in the discussion on a paper on "Fuel for Locomotives," Mr Halpin gives a Table of the heat transmission per square foot of heating surface per hour, from which the following is abstracted: — With three Field boilers, fi-om 37 to 73 T.U. per square foot of heating surface per minute were transmitted. With four portable agricultural boilers, from 25 to 57 T.U. ,, ,, ,, ,, With four Lancashire boilers, from 25 to 45 T.U. ,, „ ,, ,, With six locomotive ,, „ 110 to 202 T.U. ,, „ „ ,, With four torpedo „ ,, 202 to 334 T.U. ,, „ ,, „ Another Table, giving examples of the trans- mission of heat from hot boiler gases to steam, for superheating the latter, will be found in Chapter VIII. p. 174. Blechynden's experiments on the transmission of heat through Siemens-Martin steel plates, with furnace gases on one side, and water at 212° on the other. — The object of these trials was to determine the rate of transmission through a boiler plate when (1) the thickness of the plate, and (2) the temperature of the furnace, was varied. About 106 of these interesting and careful experiments, of which the following is a short summary, were made by Mr Blechynden, and published in the Proceedings of the Institii- tion of Naval Architects, 1893. The plates tested were only 10 in. diameter = 0"545 square' feet, but they well represent the transmission of heat taking place above a small boiler furnace. As aU the trials were made in the same way, they can be compared -fogether, and the results form an important addition to our knowledge of the still somewhat obscure subject of heat trans- mission, and help to solve its difiiculties. The quantity of water evaporated with varying dififerences of temperature between the fire and the water was measured, and thus the quantity of heat transmitted per square foot of heating surface known. ' The temperature of the furnace gases was taken, and also that of the water. Five plates, all of Siemens-Martin steel, and of thicknesses varying from 1'187 in. to 0"125 in., ^ See Donkin and Kennedy's Experiments on Steam Boilers, published in book form by Engineering. 146 HEAT EFFICIENCY OF STEAM BOILERS. were used in the experiments. The furnace temperatures varied from 600° F. to 1500° F, af the top, and 1850° F. at the bottom of the furnace. The lbs. of water evaporated per square foot of heating surface per hour varied from a minimum of IJ lbs. to a maximum of 46 lbs., and the transmission per square foot of heat- ing surface per minute from 24 T.U. (min.) to 750 T.U. (max.). Fig. 40 gives a section of the small boiler used, and shows the arrangements. The boiler was open at the top, and the water evaporated at atmospheric pressure. The furnace, as shown, Fig. 40. — Small boiler used in Blechynden's transmis- sion of heat tests, through steel plates of different thicknesses, evaporating water at 212° F. over a furnace. consisted of asbestos balls, with wire gauze above them, into which jets of gas and of air from a blast were introduced, a method of combustion adopted in order to vary quickly and easily the temperature of the fire. The temperature of the water in the boiler was taken by a mercurial thermometer, that of the furnace by balls of copper or iron dropped through holes above the fire as shown, allowance being made for the specific heat of these metals, which varies some- what with their temperature. After the balls had been kept long enough in the furnace to acquire its heat, they were plunged as quickly as possible into a known weight of water, and from the rise in temperature of the latter the tempera- ture of the balls, and that of the furnace, was calculated. There was probably a little loss of heat in removing the balls, so that the real temperature might be taken as slightly above that shown. Five sets of experiments on this boiler, each with a different plate, were made, and marked respectively A, B, C, D, and E. Each set was again divided into a number of subsidiary trials, with different thicknesses of plate, each trial last- ing from one to two hours. With plate A five series of trials were made, in which the tempera- tures were measured at the top of the furnace only. The first series comprised six experiments with the boUer plate 1*187 in. thick, and six different temperatures of the furnace, and con- sequent variations in the heat transmitted through the boiler plate to the water above. See fig. 41, and Table below, giving the details. (The different thicknesses in each figure are shown full size.) In the second series (fig. 42, and Table below) the plate was reduced to 0'75 in., and five trials with increasing furnace temperatures were made. The plate was then thinned to 0'56 in., and four experiments (fig. 43) under similar conditions were carried out; to 0'25 in., with six experi- ments (fig. 44) ; and, lastly, to \ in. (fig. 45), with eight different temperatures of furnace. Plate B was treated in the same way, except that the temperatures were taken both at the top and at the bottom of the furnace. The original thick- ness was 0"468 in., with eight furnace tempera- tures (fig. 46) ; it was then reduced to 0'375 in. (fig. 47), and seven experiments made on it, and then to 0"156 in. (fig. 48), and seven experi- ments with varying furnace temperatures carried out. With plates G and D only one thickness of plate was used, viz., 0'812 in. for C, with both sides of the plate natural mill surface (fig. 49), and \ in. for D (fig. 50), and six and eight experiments made on them respectively. With plate E two thicknesses were tested, 1'187 in. (fig. 51) and 0-187 in. (fig. 52), and four trials made on each, with varying furnace tempera- tures. In both sets, D and E, the temperatures were noted at the top and at the bottom of the furnace. BLECHYNDEN'S EXPERIMENTS, 147 Kg. 41. Temperature of furnace, 1060° 1205° 1225° 1425° 1440° 1490° 'F. Difference of temperature between fur- nace and water, .... 848° 993° 1013° 1213° 1228° 1278° F. Pounds of water evaporated per sq. ft. of heating surface per hour, . 11-21 15-29 16-04 23-65 25-3 27-82 lbs. Transmission per sq. ft. of heating surface per minute, 180 246 258 379 408 446 T.U. Thermal units per sq. ft. per hour per , 1° difference of temperature, . 1278 14-55 15-26 18-73 19-9 20-9 T.U. 6 expts. on Plate A, 1-187 inch (original thickness). ^-ccryc ace *S<-aCe. Eig. 42. Temperature of furnace, .... Difference of temperatures between furnace and water Pounds of water evaporated per sq. ft. of heating surface per hour. Transmission per sq. ft. of heating surface per minute, Thermal units per sq. ft. per hour per 1° difference of temperature. 838° 626° 7-05 114 10-89 1000° 788° 11-4 182 13-9 1125° 913° 15-14 244 16-04 1270° 1445° I 1058° 1233° 21-02 28-1 338 452 19-18 21-92 F. F. lbs. T.U. T.U. 5 expts. Plate A reduced to 0-75 inch thick. 148 HEAT EFFICIENCY OF STEAM BOILERS. :F'CC'y>t-a.ee Temperature of furnace Difference of ten[iperature between furnace and water, Pounds of water evaporated persq. ft. of heating surface per hour, Transmission per sq. ft. of heating surface per minute Thermal units per sq. ft. per hour per 1° difference of temperature, .... 776° 920° 1175° 1360° F. 563° 708° 963° 1148° F. 6-95 10-52 20-18 30-68 lbs. 112 170 324 492 T.U. 11-90 14-37 20-18 25-7 T.U. 4 expts. on Plate A, reduced to 0-562 inch thick. ^l^rrt^^x^z;^^^T!^vf^:MP^4^i^^^^^^3^ ts-^jct e-. — ~T ^^ ie«-7* ^ ^f^isceUtit^, Temperature of furnace, 715° 858° 935° 1040° 1105° 1190° F. Diff'erence of temperature between furnace and water. 503° 646° 723° 828° 893° 978° F. Pounds of water evaporated persq. ft. of heating surface per hour, . 6-15 9-58 12-42 15 96 19-04 23-5 lbs. Transmission per sq. ft. of heating surface per minute, 99 154 198 257 308 377 T.U. T.U. per sq. ft. per hour per 1° difference of temperature, 11-81 14-35 16-55 18-65 20-65 23-15 T.U. 6 expts. on Plate A, reduced to 0-25 inch thick. BLECHYNDEN'S EXPERIMENTS. 149 ^^^^t^t^^e ^^fPi^^T^^^^^^^ ^^t=^^^^^^e4&F^^*tdSb&ti,tj^3^Mir'y^^ sZS^ ^p Kg. 45. Temperature of furnace, . 950° 1120° 1210° 1295° 1335° 1345° 1350° 1530° F. Difference of temperature between furnace and water, 738° 908° 993° 1083° 1123° 1133° 1138° 1318° F. Pounds of water evaporated per sq. ft. of heating surface per tour, . 12-59 19-5 24-8 28-63 31-65 31-96 32-28 46-73 lbs. Transmission per sq. ft. of heating surface per minute, 203 314 400 460 510 515 522 752 T.U. T.ir. per sq. ft. per hour per 1° difference of temperature, . 16-48 20-75 24-1 25-48 27-25 27-27 27-48 34-21 T.TJ. 8 ezpts. on Plate A, reduced to j^ inch thick. ^Pktrtt^ee Fig. 46. Temperature of furnace, . 625° 850° 855° 1205° 1240° 1335° 1340° 1360° F. Difference of temperature between furnace and water, 413° 638° 643° 993° 1028° 1123° 1128° 1148° F. Pounds of water evaporated per sq. ft. of heating surface per hour, . 4-42 9-5 9-63 24-4 26-38 31-6 32-0 33-1 lbs. Transmission per sq. ft. of heating surface per minute. 71 153 156 392 425 507 514 532 T.U. T.U. per sq. ft. per hour per 1° difference of temperature, . 10-32 14-38 14-53 23-70 24-80 27-10 27-34 27-80 T.U. 8 expts. on Plate B, original thickness 0-468 inch. 150 HEAT EFFICIENCY OF STEAM BOILERS. ^Pkt,f9^{3tce Side Fig. 47. Temperature of fiirnaoe, . 862° 868° 1170° 1180° 1320° 1500° 1520° F. Difference of temperature between furnace and water, 650° 656° 958° 968° 1108° 1288° 1308° F. Pounds of water evaporated per sq. ft. of heating surface per hour, . 9-87 10-81 23-56 23-67 31-45 ■ 42-86 44-53 lbs. Transmission per sc[. ft. of heating surface per minute, 159 173 379 381 507 691 719 T.U. T.U. per sq. ft. per hour per 1° difference of temperature, . 14-74 15-87 23-74 23-62 27-40 32-l.'i 33-0 T.U. 7 expts. on Plate B, reduced to 0-375 inch. CTik Fig. 48. Temperature of farnace, . 755° 950° 1185° 1270° 1335° 1460° 1475° . F. Difference of temperature between furnace and water. 543° 738° 973° 1058° 1123° 1248° 1263° F. Pounds of water evaporated per sq. ft. of heating surface per hour, . 7-82 14-01 25-62 29-92 34-06 44-9 43-9 lbs. Transmission per sq. ft. of heating surface per minute. 126 226 411 482 548 723 707 T.U. T.U. per sq. ft. per hour per 1° difference of temperature, . 13-88 18-35 25-3 27-3 29-28 34-8 33-58 T.U. 7 expts. on Plate B, reduced to 0-156 inch thick. BLECHYNDEN S EXPERIMENTS. 151 Fig. 49. Temperature of furnace, 864° 975° 985° 990° 990° 1060° F. Difference of temperature between fur- nace and water 652° 763° 773° 778° 778° 848° F. Pounds of water evaporated per sq. ft. of heating surface per hour, . 8-05 11-24 11-82 10-82 11-33 12-92 lbs. TransBiission per sq. ft. of heating surface per minute, 129 181 190 174 186 208 T.U. T.U. per aq. ft. per hour per 1° difterenoe of temperature, 11-91 14-25 14-80 13-46 14 -.31 14-70 T.U. 6 expts. on Plate C, 0-812 inch thick. ^^j^gggg^Z^/g=^^^^^ ^ ^^^ ^^ ^i/tz^^tef^JhrfiS s4MC£f ■J9TZ3CcS^J^e^ ^^UTTtaeesTote. >M^ Fig.- 50. Temperature of furnace, . 651° 967° 950° 956° 980° 1059° 1091° 1122° F. Difference of temperature between fur- nace and water, .... 439° 755° 738° 744° 768° 847° 879° 910° F. Pounds of water evaporated per sq. ft. of heating surface per hour, . 4-4 13-67 13-57 14-06 14-47 16-77 19-39 21-12 lbs. Transmission per sq. ft. of heating surface per minute, 71 220 218 226 233 270 312 340 T.U. T.U. per sq. ft. per hour per 1° difference of temperature, . 9-66 17-49 17-75 •18-23 18-26 19-13 21-32 22-45 T.U. 8 expts. on Plate D, \ inch thick" 152 HEAT EFFICIENCY OF STEAM BOILERS. Fig. 51. Temperature of furnace Difference of temperature between furnace and water Pounds of water evaporated per sq. ft. of heating surface per hour, Transmission per sq. ft. of heating surface per minute, Thermal units per sq. ft. per hour per 1° difference of temperature, .... 513° 652° 856° 301° 440° 644° 1-47 2-89 5-41 24 46 87 4-72 6-34 8-12 1 1285° ! F. I 1073° ; F. 16-72 '■ lbs. 269 ! T.U. 15-05 ; T.U. 4 expts. on Plate E, original thickness- 1-187 inch. j:^,:.- - j f — j^ — , '~ r r . ■ -n. ^ — ^ — — ■ > • ^£&fit^tz=±tta:^^tcPe.e^=^ V-^ 2^lu.ri^/3tee Strcl^- Fig. 52. Temperature of furnace, Difference of temperature between furnace and water Pounds of water evaporated per sq. ft. of heating surface per hour, Transmission per sq, ft. of heating surface per minute Thermal units per sq. ft. per hour per 1° difference of temperature 534° 771° 955° 1340° F. 322° 559° 743° 1128° F. 2-08 6-22 10-72 25-76 lbs. 33 100 172 415 T.U. 6-22 •10-75 13-94 22-06 T.U. 4 expts. on Plate E, reduced to 0-187 inch thick. DURSTON S EXPERIMENTS. 153 The same boiler plate was used throughout each set of experimeuts, and gradually planed thinner and thinner on the top, that is, the side exposed to the water, the side next the furnace being always left untouched, or " natural," as shown in the drawings. This was found to be the best way of eliminating errors arising from various conditions of the surfaces tested. Before each experiment both surfaces of the plates, above and below, were well cleaned with caustic soda solu- tion, to get rid of any dirt and grease, and were thus in a fairly similar clean condition for each trial. Of course, boiler plates in actual use would not be nearly so clean as these, but are often very dirty, with soot on one side and deposit on the other, both of which affect greatly the transmission of heat. It is well to remember, also, that the capacity of water for absorbing heat from a hotter metal plate is some hundreds of times greater than the capacity of air under similar conditions. As will be seen from the drawing, fig. 40, the boiler plate was always horizontal, and thus all the experiments were made with horizontal surfaces exposed to the hot gases from the furnace, and to the water. Had the plates been placed vertically or at different angles, the results would doubtless have been different. Results. — These are given above in the Tables in some detail, but for full particulars the original paper should be consulted. The broad general fact, as brought out by these experiments, is that the heat transmitted through the plates per degree difference of temperature between the fire and the water, is in proportion to this differ- ence. In other words, the quantity of heat in T.U. is proportional to the square of the difference between the temperatures of the two sides of the plate. This may be reduced to the following formula : — • Heat transmitted per square foot , r..p.,,..^^ foj. each plate. (Ditferenoe in temperature)^ There is a general slight rise in the value of this ratio, with decreasing thicknesses of boiler plate. In Mr Blechynden's original paper all the results are plotted, and they agree well together. It was found that even the very slightest trace of grease caused a great fall in the rate of heat transmission, and merely to wipe the bottom sur- face of the plate with a piece of greasy rag was sufficient to affect the results. If this is so, how much heat must be checked with our sooty external surfaces, and deposit and grease inside the boilers. The surface conditions of these plates, even when clean, was also found to be an important factor, and the efficiency of transmission varied with their degree of smoothness, whether rough from the mill, or planed perfectly smooth, or only roughly planed. The transmission seems also to be slightly influenced by the carbon in the steel, as the plate which contained the smallest percentage of carbon possessed the least conductivity. The experiments point to the conclusion that the thinner the plate forming part of the heating surface of a boiler, the higher should be the efficiency, provided always that the plates are perfectly clean. As this is never the case, the thickness can practically be neglected, as far as its influence on the efficiency is con- cerned. Durston's experiments on the temperature of marine tube plates, etc., at Devonport. — These constitute a very interesting and instructive series of trials, made by Sir A. Durston, and published in the Proceedings of the Institution of Naval. Architects, 1893, of which the following is a brief summary. The chief object of the experiments was to determine the rate of transmission of heat through smoke tubes and plates, and the effect of over- heating, and its bearing on leakage. The important questions were also treated of the temperatures of the tube plates in different parts, especially ia the centre, and the tempera- tures of the furnace under different conditions of fires, forcing, with and without air blast, etc. The great loss in efficiency of heating surface, due to grease and deposit, and the temperatures at different parts of the smoke tubes, were also studied. Other trials, all on marine boilers, and some at sea, were made on different kinds of ferrules fitted into the ends of the smoke tubes, over the fire, to prevent overheating. The temperatures of the plates were taken approxi- mately, by means of pieces of fusible alloys, of different known melting points. The first point examined was the effect of grease in the boiler. Many of Durston's ex- periments show the bearing of this important matter on the boiler efficiency. Although too often neglected, grease and greasy water have a very dangerous influence on boiler plates, because 154 HEAT EFFICIENCY OF STEAM BOILERS. grease, being a bad conductor, greatly checks transmission. If, after a layer of grease, how- ever thin, has collected on the boiler tubes, the fire and gases continue to heat the plates, although the temperature of the furnace may be no higher than before, the heat cannot pass out of the plates at the same rate at which it is received, and overheating ensues. Thus the steam pressure causes the furnace tubes to be pressed out towards the fire, a danger which has often arisen with boilers of aU types, at sea and on land. In tests made on a boiler at Devonport dockyard a furnace "gave out" with greasy water, with steam at only 60 lbs. pressure, no difficulty having been experienced before, when fresh water was used. Durston's experiments show very clearly how greatly the temperature of boiler plates is raised by a very thin layer of grease. With the surface condensers now so much employed, when the same water is used over and over again, and continuously evaporated, condensed, and re-evaporated, if any grease be admitted to the steam cylinders, it soon collects on the boiler plates, with great danger to the latter, and to the safety of the ship. Much trouble has been caused in marine boilers by leaky boiler and smoke tubes, but the same remarks also apply to land boilers. Such of Sir A. Durston's trials as concern our present subject may be divided into — (1) Experi- ments on overheating of boilers by forcing the fires; and (2) on overheating by introducing grease into the boiler. Experiment No. 1 (see figure 53) was niade Fig. 53. — Experiment No. 1 — Durston. With Clean Plate. 210° Water. 240° Bottom plate. Difiference 28° F. 1500° Fire. 1500° -212° = 1288° F. differejice of heat between fire and water. With Grease on Plate — 3*1 inch thick. Difference 118° F., or 90° higher than with clean plate. 1500°F. 212° 330° 1500° -212° = 1288° difference. a, a, eight pieces of fusible solder, melting points varying from 220° to 250° F. No. 1. — To ascertain the temperature of the hot side of a plate through which heat is passing to boiling water. 10-in. circular dish, 3 in. deep. Result — Greasy plate became 90° hotter than clean plate ; other conditions same. on an open 10-in. circular dish, ^ in. thick, 3 iu. deep, with water inside and flame below. When clean, the temperature of the plates was 240° F. ; with ^l. in. layer of grease it rose to 330°, or 90° F. higher, dvie to the grease which checked the transmission of heat. Experiment No. 2 (see figure 54, and plate). — Here a 14-in. circular plate, 4 in. deep and f in. thick, was used, with ten short lengths of steel boiler smoke tubes, rolled in in the usual way. The plate or dish was filled with water, and forced blast applied to the fire underneath. To ascertain the approximate temperature of the centre of the plate, nine f Qsible plugs were placed in holes drilled horizontally round it; and, from those which melted or remained intact, the temperature was estimated to be between 290° F. and 330°, say about 310°. The temperature of the fire was 2000° F. Difierence between tem- perature of the plate and of the water 98° ; between the water and the fire 1788° F. Only one smoke tube is represented in the drawing. Experiment No. 3 was made to determine at what temperature a |-in. tube plate becomes injuriously overheated, and begins to leak. A small boiler was used, 2 feet diameter and 2 feet 7 in. long, with twenty-four vertical 2|-in. smoke tubes, eight of brass, seven of steel, and nine of iron, grouped as far as possible in sets of three. It was filled with as much water as would evaporate to steam at 100 lbs. pressure, placed over a forge fire with blast, and the tubes made red-hot. When raised to a temperature of 1400° F. all the tubes leaked badly. Plugs of lead and zinc were DURSTON'S EXPERIMENTS. 155 then inserted in the fire side of the tube plates, and it was found that for a tube plate to be over- heated sufficiently to make the joints leak to an appreciable extent, its temperature, not that of the water or fire, must be raised at least to 750° F. Uxp&i-iment No. 4. — Tests were made, with a horizontal 2|-in. tube, about 10 in. long and 0'135 in. thick, to ascertain the loss in trans- mission of heat due to a thin coating of grease on the outside, next the water, as compared with perfectly clean tubes. The result showed a decrease in the efficiency of the heating surface, or in the transmission of heat, of from 8% to 15%, a mean of many experiments giving 11%. Hence the great importance of avoiding grease when the maximum quantity of steam is required of a boiler. In Experiment No. 5 (see figure 55) the Fig. 54. — Experiment No. 2 — Durston. Forge Fire with Blast. Water, Plate, Difference = 212° No. 2. Difference of temperature between the water and the fire, 1788° F. a, eight plugs of fusible metal, with various melting points. -To ascertain the temperature, at the centre of its thickness, of a |-in. plate resembling a boiler tube plate, exposed to a forced blast fire. Fig. 55. — Experiment No. 5 — Durston. •A o l|i ill |l Is? Fresh Water with 2 J7. of Methylated Spirit. ■Si |g lis i above 280° 310° 330° 300° 550° Bottom of plate. 2200° 2300° 2100° 2500° 2500° Fire temperature. 1920° 1990° 1770° 2200° 1950° Difference between fire and water. 68° 98° 118° 88° 338° Difference of tempera- ture between plate and water. Temperature of plates when boiling water in an open vessel under various conditions similar to experiment No. 1, in 24-iD. circular dish, 2^ in. deep, J in. thick, placed over a forge fire. Greasy water increased temperature of plate. Greasy film increased temperature greatly. 156 HEAT EFFICIENCY OF STEAM BOILERS. water was evaporated in an open dish 2 feet diameter, 2J in. deep and ^ in. thick, heated over a forge fire. The trials were made with clean water, with grease, etc., added to it, or with a greasy deposit ^ in. thick on the plate. When grease or oil was mixed with the water, the temperature of the plate rose from 280° to 330° F. With a layer of grease it went up to above 550° F., showing again the dangerous nature of even the thinnest layer of grease, and the check given by it to the free transmission of heat. Experiment No. 6 (see figure 56, and Table) was made with a small closed vessel or boiler, under similar conditions to No. 5, and the tem- peratures of the plate, with and without grease, etc., on it, were taken. With clean water and a clean plate there was a difi'erence in tem- perature between the water and the side of the plate next the fire of from 67° to 85° F., but with greasy deposit Jg- in. thick, this difference rose to 151°, and, when thicker grease was used, to 199°. With grease spread on the vertical as well as the horizontal sides of the boiler the difference was 537°. Thus the temperature of the plate was raised from 430° when clean, to 617° when coated with grease, or 187° higher, afibrding a confirmation of former experiments. The thickness of the plate appears to have been about f in. Experiment No. 7. — Smoke tubes of various metals, copper, brass, iron, and mild steel, in a tube plate f in. thick, were tested in a small vertical boiler, 2 feet diameter, 2 feet 7 in. high. Experiment No. 6 — Durston. Fig. 56. Pellets of fusible metal on bottom of small boiler. Tempera- ture of hot side of Plate. Tempera- ture of Water. DtSerence Tempera- ture Water and Plate. 67° 84° Over Bunsen burner, Over blast forge (full blast), . F. 430° 430° F. 363° 344° Over forge fire, grease deposit tV-id., Do. , but using grease of thinner and earthier nature, Do., and spreading the grease also up the sides of the vessel, . 510° 550° 617° 359° 351° 80° 151° 199° 537° Clean water and clean i boiler surfaces. Clean water, but plate coated with grease, etc. Temperature of a boiler plate at a higher temperature than 212° F. with and without grease, etc. The result showed that brass and copper smoke tubes leaked even when the tube plate was below the temperature of melting lead, 617° F., and did not stand so well as iron or steel, which were practically equal in durability. In Experiment No. 8 it was found that higher pressures of steam caused no marked increase in the temperatures of the hot side of the plate, as compared with boiling water at 212° F. Experiments No. 9 were made with a small marine experimental boiler (see figs. 57, 58), to determine the temperature of the centre of a tube plate, with closed ash-pit, and an air pressure of ^0 and -f^ in. of water. The tube plate was pierced with a number of holes. Five of these, f in. long, had each four pieces of fusible aUoy let into the plate in the middle of its thickness. as shown in fig. 58. The pressure of steam was about 143 lbs., the air pressure under the grate A *° TT i^' The temperature in the combustion chamber was 2850° to 3100° F. ; in the centre of the tube 1550° to 1800°; in the smoke box 1400° to 1600° F. An examination of the alloys after the experiment showed that the temperar ture of the tube plate was about 535° F., or about 173° above the temperature of the water in the boiler. About 30 lbs. of coal were burnt per square foot of grate, and 4'6 lbs. water were evaporated per square foot of heating surface per hour. Experiments No. 10 were continued on the same lines, and had for their object to get the approximate temperature on the fire side of a tube plate, as well as that in the middle of its DUESTON'S EXPERIMENTS. 157 thickness (f in.). The same experimental boiler was used as in the last trials, fig. 57, with forced Fig. sure, 0"-3 0"o. .57- -Experiment No. 9 — Durston. Temp. SOlbs.ofooalbumt Tcmp. in per sq. ft. of of Smoke grate. Comb. Temp. Gases Box, 4-62 lbs. of water Ci-., in centre of 1400° evaporated per 2860' Tubes, (mean), bom- per sq. ft. 8100' 1550° 1600° of beating sur- max. 1800°. (max.). face. ^Ma-GttMe Heating surface— 223 sq. ft. Temp, air 30° to 50° F. Experimental boiler with smoke tubes and external fire. draught and closed ash-pit, but the rate of combustion was higher. Additional plugs were placed on the face of the tube plate and around the tubes, as shown at A, fig. 58, and four good experiments were made with the boiler forced. From 12 to 13 lbs. of water were evaporated Fig. 58. — Experiment No. 9 — Durston, AO |-in. tube plate and smoke tube of experimental boiler. per square foot of heating surface per hour, and from 84 to 102 lbs. of coal burnt per square foot of grate per hour. The following Table gives the results : — Table of Dukston's Experiments, No. 10. ForcingTests on Temperature of Tube Plates with Clean and Oily Water. Experimental Boiler used, fig. 57, with sixty-five Smoke Tubes. Heating surface, 223 square feet. Diameter, 4 feet. Length, 5 feet. Forced draught in all the tests, about 3 inches under the bars. Number of Test, Pressure of steam per sq. inch, .... Coal burnt per sq. ft. of grate per hour, "Water evaporated per sq. ft. heating surface per hour, Transmission of heat per sq. ft. heating sur&ce per minute (assuming cold feed) Temperature in combustion chamber, Temperature of middle of tube plate by plugs, approximate, Amount of mineral oil added to feed water, Condition of tubes after test lbs. lbs. lbs. T.U. °F. F. F. F. 145 90 12-6 250 2750° 690° 1060° II. 142 102 13-2 262 2500° 690° 1060° III. 140 84 11-7 232 3100° 750° 1060° 700° 700° 700° clean water, no oil. ' 7% Tubes not leaking at all. IV. 144 12-0 238 3200° 1060° 700° Tubes leak- ing badly. The temperature of the front of the tube plates varied approximately from 690° to 1060° F. In the middle of the same plate the temperature was about 700°, so that the face of the plate may be taken to be some 200° hotter than the middle, in these experiments. In the last experiment, when oil was added to the feed water, nearly all the tubes leaked badly, and the limit of this arrangement seems to have been reached with greasy water. With clean water none, of the tubes leaked. Experiments No. 11 were made on the same boiler as before, with Lowmoor iron and steel smoke tubes placed alternately. The results 158 HEAT EFFICIENCY OF STEAM BOILERS. appear to show that these iron tubes were not superior to steel, and Durston gives the preference to the latter metal. Both kinds were subjected to the test of keeping the fan going after the fires were drawn, thus exposing them to cold currents of air, but no leakage was found. Experiments No. 12 were made to verify the effect of grease in boilers. After using greasy water experimentally at Portsmouth the furnace crown bulged, and the same thing occurred at Devonport, the pressure of steam being only 60 lbs. Usually these boilers were worked with clean water, and no bad effects followed. This serious result was confirmed by many experi- ments on navy boilers. Experiments No. 13, on the temperature at various parts of the smoke tubes in a marine boiler, were carried out on an ordinary boiler with two internal furnaces, and 166 horizontal smoke tubes 2f in. diameter and 6 feet 6 in. long. The temperatures were taken for each foot length of tube when burn- ing 17 lbs. of coal per square foot of grate per hour. Fig. 59 shows the gradual fall of temperature plot- ted to scale, from Fig. 59.— Fall of temperature of 1644° F in the gases through smoke tubes in a combustion cham- marine boiler plotted to scale. T^ ikca" 1 l^t 166 tubes, i in. thick, 23 in. dia. °^'^> 1°^" ^^ ^"^^ outside, 4 in. centres. entrance to the tubes, and 887° at the exit, to 782° in the smoke box, or a fall of 663° in a length of 6 feet 8 in. Hirsch's experiments on the overheating of boilers were made in Paris, and published in 1890 in the Bulletin de la SociitS d' Encourage- ment. The object of the first part of these careful trials was to ascertain, in a small exter- nally fired cylindrical boiler (see fig. 60), the difference between the transmission of heat, or lbs. of water evaporated over the whole surface of the boiler, and the lbs. evaporated in a small carefully isolated portion of it. This separate part was situated exactly over the hottest place in the fire, where overheating generally occurs. About sixteen experiments were carried out with 60 lbs. steam pressure, on a boiler 10 feet long and 2 feet 2 in. diameter, with a heating surface of 35;| square feet, and a grate surface 3'85 square feet. Arrangements were made to increase the induced draught, and intensify the . combustion with a jet of steam. A vertical tube, ' 4 in. diameter, was bolted on to the concave sur- face of the boiler, and the joint made tight, so that the evaporation from this small surface could be separately determined, and compared with that from the rest of the boiler. The tube was fed with water at the same temperature, from a separate pipe. Without much forcing about 9 J lbs. of water were evaporated per square foot of general heating surface, excluding the 4-in. part, where the evaporation was at the fJSi'i-scis 'j m Fig. 60. rate of 20 lbs. per square foot, or, say, about double the average of the whole boiler surface. When forcing the boiler, M. Hirsch obtained 19 lbs. per square foot over the rest of the boiler surface, and 43 lbs. over the 4-in. portion, or rather more than double. In another experi- ment the evaporation in the isolated tube was three times as much, with 50 lbs. water evapo- rated. It is important to note that the part over the fire was only 4 in. The temperature of the fire was not recorded in these experiments, nor the temperature of the boiler plates. The con- sumption of coal per square foot of grate varied from 1 6 to 48 lbs. The force draught was found to increase combustion, but not evaporation. The second part of these experiments relates to the temperature of a f-in. boiler plate, 15'7 in. diameter, exposed to a strong flame on one side, and covered with water on the other. The object was to determine the propagation of heat through the metal, and from the metal to the HIRSCH'S AND WITZ'S EXPERIMENTS. 159 ■water, and for this purpose a small open boiler (see fig. 61) was jointed to the plate. The transmission of heat was measured per unit of boiler plate surface, by measuring the lbs. of water evaporated at 212° and atmos- pheric pressure in a given time. The tem- perature of the plate was approximately de- termined in all cases by about twenty-four plugs of metalhc alloys, fusible at known tem- peratures, which were placed in holes drilled in the bottom of the plate on the fire side. From the melting of some or all of these plugs, the approximate temperatures were ob- tained. These appear to be among the first experiments in which this method was em- ployed. Trials were first made with dis- tilled water and clean surfaces of plate. A ^,a>,^*csc^^^^^fr^^C ^^i^t . 7*1^a.H- a/^^a^/ft-^r- yfeiie^ . Fig. 61. large number were then carried out with various substances, such as starch, plaster, talc, grease, oil,' etc., either mixed with the water, or spread over the water side of the boiler plate. Pieces of iron were also aifixed to the plate, to imitate flaws, cracks, or joins, where the thicknesses are not continuous. The results of all these experiments are in the original paper plotted graphically (see fig. 62), and from them M. Hirsch draws the following conclusions : — If a sound boiler plate be in immediate contact with the water, it will safely bear exposure to the hottest fire, and the viscosity of the water does not prevent its wetting the plate. If the boiler plates overlap, the transmission of heat'is to a certain extent checked. A flaw or bad join, if exposed to a fierce fire, is almost certain to cause a failure of the boiler plate. Any greasy deposit on a boiler plate hinders heat transmission, especially if the fatty sub- stance be readily decomposed by heat. But if a boiler be kept clean, and filled with water, it may be exposed without injury to the strongest fire. *} 50 60 70 ■'ff m r .. ^9 -^yo Fig. 62, Professor Witz {Academie des Sciences, Paris, vol. 113) made a series of experiments in 1892 on a small vertical laboratory boiler with de- tachable bottoms of various thicknesses, in order to test difierent thicknesses of boiler plate. Neither the temperature of the fire nor that of the plate were taken. The object of the trials was to study the spheroidal condition of water, and the maximum rate of evaporation and trans- mission of heat per unit of surface, which might be attained with excessive blast fires. The ex- periments were made on a small boiler having 4:6^ square inches heating surface. The follow- ing Table shows the result with a uniform thick- ness of plate of '47 in. : — With 7 Bunsen burners. 7 7 7 coke and air blast, 7 Bunsen burners, coke with air blast, Table of Evaporation of Watek. 13 lbs. water were evaporated per sq. ft. of heating surfaoe per hour. 37 lbs. no air blast, 1 oxy hydrogen flame, 41 lbs. and 3 blowpipes, ... 54 lbs. 89 lbs. 1 air blast, 1 oxyhydrogen flame, 136 lbs. 204 lbs. Surfaces quite clean. Plate not red-hot. Plate red-hot. 160 HEAT EFFICIENCY OF STEAM BOILERS. Professor Witz concludes that, if the plates of a boiler become red-hot, the water does not assume the spheroidal condition, but the rate of evaporation is increased to an abnormal extent, as shown above. But if the water is in a spheroidal condition, the evaporative power of the same metallic surfaces is thirty- one times less when red-hot than when at 608° F. Dr Kirk's experiments on the temperature of boiler plates.^ — Although these six trials do not give the quantity of water evaporated at 212° to atmosphere, nor the temperature of the fire, they show the importance of not having the tube plates too thick, about f in., accord- ing to Dr Kirk, being the right thickness. He experimented upon a small open malleable iron dish, 11 in. diameter and 6 in. deep, with one central 2J-in. steel tube placed vertically over a forced smith's fire on brick-work, and filled with water. Six tests were made with this tube plate of different thicknesses, from 2| in. to if in. Plugs of tin, lead, and antimony were inserted over the fire, half in the tube and half in the tube plate, to ascertain their approximate tempera- tures. The tube was expanded into the tube plate in the usual way. The following are the results : — Table of Dk Kikk's Expebimbnts, showing importance of thin tube plates. Experiment No 1 2 3 4 5 6 Thickness of tube plates, . . inches Approximate temperature of tube plates, F. Temperature of water, . . F. Difference, . . F. Observations on plate at end of experiment, 2J" 1000° 212° If" 700° 212° 600° 212° li" over 600° 212° 1" 500° 212° H" 440° 212° 788° 488° 388° 388° 288° 228° red-hot. Clean wate surf red-hot. r and clean ices. not red-hot, OU added to water. notred-hot. notred-hot. 'notred-hot. Clean water, clean surfaces. Each experiment lasted three-quarters of an hour. It will be seen how marked, with greater thicknesses of plate, was the difference in tem- perature between the plate and the water, and how greatly this difference was reduced from 790° to 228°, when the tube plate was diminished to ^ in. in thickness. A forced fire was used to play upon the centre of the tube plate, just below the tube. The former was horizontal and the tube vertical, which is not generally the case in marine boilers. Probably the action of the fire was momentarily greater, but less prolonged, and more uniformly applied than in an actual boiler, but the lesson conveyed is obvious, viz., to have the tube plates as thin as practicable. If thick, they become red-hot, and the tubes will soon leak. Doubtless, in these experiments, the water and plates were cleaner than in ordinary work. Serve tubes. — Some interesting experiments have also been made on the relative transmission of heat through ordinary and through Serve ^ See Engineering, July 16, 1892. tubes.^ A couple of small model boUers, 21 in. long by 7| in. diameter, were used, one containing Serve, the other ordinary tubes, both about 2J in. diameter. The tubes of one boiler were coupled to those of the other, and Siemens pyrometers were fitted at the end of each tube. A flame from a blowpipe gas jet was sent through one set of tubes, and the pyrometer temperatures and evaporation were noted. The mean of several experiments showed that, with a difference in temperature of 1000° F. between the gases and the water in the boiler, the Serve tube transmitted 6000 B.T.U. per square foot per hour, and the plain tube 4500 B.T.U. A valuable series of papers, by Mr J. G. Hud- son, M.I.C.E., appeared in The Engineer, December 5, 12, and 26, 1890, on "Heat Trans- mission ill Boilers." Mr Hudson takes as his starting - point the process of heating liquids by steam, the laws of which are rather better understood than those of transmission from a Engineering, October 5, 1894. TRANSMISSION OF HEAT. 161 fire and hot gases. Dealing first with the ques- tion of boiler efficiency, he confines himself to the efficiency of absorption, or the ratio of the heat absorbed by the water to that developed by combustion ; in other words, to the efficiency of transmission. If it be assumed that there is no loss of heat by radiation, all the heat de- veloped by combustion, minus that transmitted to the water, should be found in the exit gases. Of the three efficiencies which make up the boiler efficiency, not one is ever equal to unity, but this must be attributed, not to any inherent impossibility in the boiler plates to transmit heat, but to mechanical defects and errors in construction. These an engineer ought to a great extent to remedy, by diminishing radiation, and reducing the temperature of the exit gases to that of the fuel and air before combustion. It has not hitherto been found possible to frame uniform formulse, showing the rate of heat transmission per degree difference of temperature between the hot gases and the water, and the difference in heat transmitted at "the fire-box and at the end of the flues. As a rule, transmission in feed-water heaters is found to increase, per degree difference between the ■steam and the water, in proportion to this increase in the temperatures, and for a small •difference the amount of heat transferred is relatively large. When steam is condensed in a surface condenser, much more heat is trans- mitted through the metal, per degree difference, than in a boiler plate, the proportion being as 1 to 28. Steam, therefore, parts with its heat much more readily than hot gases to a metal surface in contact with it. Probably the high- •est evaporation obtained with a boiler furnace was in a Thornycroft boOer, viz., 40 lbs. of Tvater per square foot of fire-box surface ; while with a Weir feed- water heater, 140 lbs. of water per square foot of surface were evaporated with- out difficulty by means of steam at 150 lbs. pressure. When water is heated by steam, the temperature of the latter can be accurately known, and furnishes a clue to the probable temperature of the boiler plate. Hence the value of this method of estimating the trans- mission of heat. In any case, the temperature of the metal is much nearer that of the water than of the fire. Thus to obtain the maximum evaporation of 40 lbs. water per square foot of heating surface in a feed-water heater, steam at a temperature of 376° F., say 170 lbs. pressure, would be re- quired, or a difference of only 36° between the steam and the water, while for the same duty a furnace temperature of probably 2500° would be necessary. Of the total heat transmitted, 98% is absorbed in transmission from the gases to the metal, and only 2% from the metal to the water. In the case of a copper tube, the "head of heat " required to overcome the resistance of the metal to transmission is calculated at about 6° ; for iron or steel it is about 55°. The action of steam, as compared with a fire in transmitting heat through a copper tube, is divided approxi- mately between absorption, conduction, and emission in the following Table : — steam. Temp, of heating medium, . Ditferenoe for absorption = Temp, of surface, hotter side, Difference for conduction = Temp, of surface next water. Difference for emission = Temp, of water in boiler, . Total difference = 376° 1 '}6° 340° i 36^ 2500 Fire. '] 366° 360° „-i 2134° I. 360° J 340° \ 20° 2160° Here we see that the quantity of heat required to effect its transfer from the metal to the water is so very small, in proportion to that needed to heat the metal by absorption from the hot gases, that it may practically be neglected. As far as transmission is concerned, there is no gain in having an active circulation of water, though it is indirectly of value, by preventing over-heat- ing. In boilers having a bad water circulation, the difference of temperature between the plate and the water is probably as miich greater as the transmission is less, and in badly designed boilers the temperature of the plate just before ebullition may even be 600° or 700° F. One of the special points treated in Mr Hud- son's paper is that the speed of the gases in- fluences the transmission of heat, and may account for various hitherto unexplained anom- alies. In any formula for calculating transmis- sion it should be taken into account. The trans- mission of heat increases almost as rapidly as the speed of the water on the other side of the metal, and varies from 20 or 30 T.U. to 1000 T.U. per degree difference, according to the speed of the water. If it is affected to this extent, it 162 HEAT EFFICIENCY OF STEAM BOILERS. seems reasonable to infer tliat it is also influenced by the speed of the gases on the other side of the metal, which may vary from 4 to 200 feet per second, over the same surface, for different types of boilers. Various considerations seem to show that the transmission depends upon the speed as well as the temperature of the gases. On the other hand, too high a speed of gases may hinder transmission, by affording them less time to part with their heat. Further experi- ments are needed to determine this point, but Mr Hudson is of opinion that increased speed of gases produces better transmission, while a uniform speed through all the tubes of a boiler is highly desirable. As regards heat transmission in the fire-box, produced chiefly by direct radiation from the furnace and hot gases, Mr Hudson considers that the amount radiated cannot be taken, as is usually assumed, as half the total heat of com- bustion, but depends upon the temperature of the fire, and the area of surface exposed. It is true that the heat radiated from the fire-box is very much more than that transmitted through the tubes, but it cannot be greatly increased by enlarging the fire-box at the expense of the tube surfaces. If the speed of the gases increases transmission up to a certain point, the tube sur- faces may even transmit heat quite as efficiently as the fire-box. Still, the higher the tempera- ture of the gases when they leave the furnace, the more readily must they part with their heat. The rate of transmission from the fire-box would seem to depend on the extent of surface in proportion to fuel burnt. If the surface be very small, the gases will not impart much of their heat to it before they leave the furnace. The transmission varies from 10,000 to 30,000 T.U. per square foot per hour, unless there are no tubes. For fire-box surfaces of 1 foot and 0"05 foot per lb. of coal burnt, the T.TJ. transmitted will be 10,000 and 1500 respectively, and the temperatures of the gases 937° and 2801°, with 18 lbs. of air at 60° F. supplied per lb. of coal. From these considerations the following con- clusions are drawn :— With the fire-box surfaces the transmission of heat takes place principally by radiation, and the absorption is generally greater in proportion to the area of these surfaces, but less per unit of surface. An excessive supply of air, beyond that necessary for combustion, by reducing the temperature of combustion, reduces the absorption of the heat by the metal. With regard to the surfaces in contact with- the hot gases only, the heat is here transmitted chiefly by convection, that is, by direct contact of two bodies, a soUd and a fluid, and the displacement of each fluid molecule, as it becomes heated. The quantity of heat is proportioned to the square root of the speed. The transmission per degree difference is greater the higher the temperature ; a mean between the absolute temperatures of the gases and the water agrees with actual results. In all boiler surfaces the difference in tempera- ture between the water and even the hottest side of the metal, that next the gases, is small. The temperature of the furnace has been found by Mr Blechynden to vary from about 2500° in the centre of the flre to 1200° just beyond it, and 900° where the gases leave the furnace. These remarks and conclusions are embodied in five formulae for calculating in a boiler, (as) Heat units absorbed by the fire-box per lb. of fuel burnt. (6) Heat units remaining in the gases leaving the fire-box. (c) Temperature of these gases, (d) Speed of the gases. (e) T.U. transmitted per degree per square foot of tube surface per hour. Although empirical, Mr Hudson is of opinion that these formulae wiU fairly represent the conditions of heat trans- mission, and give a rate of about 11° or 12° F. per degree difference between the water and the gases leaving the fire-box. A comparative Table shows the results of trials on various Lancashire, Cornish, locomotive, and water tube boilers, and gives in parallel columns the disposal of the heat generated by 1 lb. of fuel, calculated from the formulae and from actual results. The heat is divided between that absorbed by the fire-box and the tubes and wasted in the chimney gases, and the temperature of the exit gases is given in the same way. This Table, the formulae, and a numerical example of their application to a portable engine, will be found in Appendix IL pp. '252 to 254. The results obtained with the formulae for fire- box transmission, for different weights of air and fire-box surfaces, are plotted graphically on curves in the original paper. A s6t of temperature curves are added for various proportions of fire- box surfaces, and area through tubes, and these are plotted separately for the portable boiler. The variations in the rate of heat transmitted, the transmission per degree difference, and the TRANSMISSION OF HEAT. 163 speed of the gases are also plotted graphically in curves from the calculated and actual results, and show that the transmission depends not only upon the difference in temperature and extent of surface, but also upon the speed of the In Cornish and Lancashire boilers the calcu- lated temperatures for the exit gases is always in excess of that actually shown by the thermometer. This is due probably to leakage of air through the brick-work during or after combustion, which reduces the temperature, and causes a loss of heat of 700 to 1000 T.TJ. per lb. of coal in boilers set singly, and 400 to 700 T.U. in a series of boilers side by side. This leakage also affects the calculation of the air supply, from the analysis of the gases, and diminishes trans- mission, and it has a greater effect the smaller the rate at which the boiler is worked. At ordinary rates of combustion, the discrepancy between the calculated and the observed tempera- tures of the exit gases is less. The whole question is summed up as follows : — To obtain a maximum efficiency of transmission the cross-section of the gas passages should be made small, and thus as high a speed obtained as practicable. The fire-box surfaces should be kept within such limits that the transmission per square foot is the same as that of the gases entering the tubes, and a good circulation of water is essential. With forced draught a high speed of the gases is likely to cause overheating, and this is best remedied by enlarging the water spaces, and thus improving the circulation. Some interesting details are added with refer- ence to Serve tubes with internal ribs (see page 205, where a drawing of them is shown). These ribbed tubes were generally found to give 1 lb. more water evaporated per lb. of coal than ordinary tubes, or 10% to 14% economy, thus confirming Mr Hudson's view, that "it is. the efficiency of the heat absorbing surfaces which should be chiefly considered, the heat conducting and emitting surfaces having far less work to do." The comparative results of working with Serve and plain tubes, both burning 750 lbs. coal per hour per total grate area at lower power, and 1300 lbs. at higher power, are shown in a Table. The heat absorption with Serve and plain tubes, calculated from the formulae, exceeds the actual slightly for the lower rate of working, and greatly for the higher. The gain in economy with the former was 12% calculated, and 10% actual, and with the latter 12-3% calculated, and 13-8% actual. Overheating probably accounted for the discrepancies, and checked the passage through the metal of the total heat absorbed, and thus it was not fully transmitted to the water. CHAPTEE VIII. Feed-water Heaters, Superheaters, Feed Pumps, etc. Feed-Water Heaters — ^Efficiency of Eoonomisers — English Type — French Type — Hale's Opinions — Pimbley's Econo- miser — Heating by Exhaust Steam — Eoonomiser Trial — Superheaters — Hicks — M'Phail and Simpson — Schwoerer — Gehre — Sinclair — Serpollet — Schmidt — Longridge's Table — Feed Pumps — Donkey Pumps — Injectors. Wb have now dealt successively with the best methods of securing good combustion in a boiler, and of transmitting the heat thus obtained through the metal to the water. The point to be next considered is how to economise this heat, that is, to procure the maximum evaporation of steam, with the minimum expenditure of heat. For this purpose various appliances are available, having for their object to put some of the waste heat from the boiler into either the water or the steam. Feed-water heaters. — It is well known that water does not begin to evaporate and give off steam until raised to a temperature of 212° F. If it is pumped into the boiler at 32° F., the fuel has to put 180° of heat into it before boiling begins. If, on the contrary, it enters at a tem- perature of 212°, no additional heat is necessary, except for evaporation. In both cases, if 1 lb. of steam, at 150 lbs. pressure, is required, the heat of vaporisation must be supplied. If the water be admitted to the boiler at 32°, 1193 T.U. per lb. of steam will be necessary to evaporate it ; if at 212°, only 1013 T.XJ., or 15% less heat. The hotter the feed water the better, if a boiler is required to evaporate the maximum amount of steam. Thus for real economy and efficiency, the temperature of the water must be at a maximum, with minimum cost. This object is often attained by placing a large number of pipes giving a con- siderable heating surface in the flues or at the end of the boiler, and surrounding them with the hot exit gases, which would otherwise escape to waste at a high temperature. In modern steam condensing plants two systems are utilised for the purpose. The first is employed where the feed water is not used over and over again, as in a jet condenser; the second where it is continuously used, sent to the cylinder, condensed and pumped back into the boiler, to be again evaporated and sent on, and a closed cycle thus obtained. In the first case, the feed water is evaporated into steam, con- densed, and escapes to waste with the water used for the jet condenser. This is what takes place in most mills and factories, and power installations. As fresh water has to be con- tinually pumped into the boiler, the heat in the condensed water, including the feed, is generally lost. In the second case, the steam is condensed in a closed surface condenser, cooled by circulat- ing water, and pumped as water back again into the boiler, at a temperature of, say, between 100° and 120° F. Here we have very different work- ing conditions, as compared with the first case, and with such a surface condenser there will be a considerable economy of heat, although a large cooling surface is required. This method of feeding the boiler is now always employed in modern steamers, and often on land, in water- works and factories. In land boilers where jet condensers are used, the problem is how to pre- vent waste by heating the feed water, and this is chiefly done by utilising the escaping boUer gases. Sometimes in the case of non-condensing engines the feed water is heated by the exhaust steam. Both methods lead to economy if pro- perly carried out. Him designed a feed-water ENGLISH ECONOMISERS. 165 heater in 1845, with" vertical cast-iron pipes 4 in. diameter, in which, with a larger heating surface than that of the boiler, the temperature of the gases was sometimes reduced, to 220° F. A great many careful experiments were made at MuUiouse by Him, Burnat, GrossetSte, and Scheurer-Kestner, and continued till about 1866. We will now consider economisers or feed- water heaters in which the escaping gases are iitilised. (See page 302 for illustrations of economiser.) It wiU be seen, on referring to the Tables of boiler experiments, that the total heat generated by the fuel is divid-ed into two portions, that utilised in the boiler alone in evaporating the water into steam, and that absorbed by the pipes of the economiser in raising the tempera- ture of the water, before it is sent into the boiler. The latter quantity of heat is taken from the escaping gases, which are lowered in tempera- ture. In the tests the gain in economy thus realised is in all cases given separately, and apart from the boiler results, as the economiser forms a distinct apparatus worked for a definite object. The heating surfaces of the economisers alone are also stated, and the temperature of the gases both on entering and leaving them. In experi- ments on economisers it is not difficult to make a balance of heat. So many thermal imits per minute leave the boiler in the exit gases, and enter the economiser flues, and so many T.U. in the gases leave them per minute. The differ- ence to be accounted for is the heat lost by the gases. A certain proportion is absorbed by radiation, and the rest goes to raise the tempera- ture of so many lbs. of water so many degrees per minute, or to put so many thermal units into it. This is the total amount of heat received by the water from the gases, and the proportion of this to the total heat lost by the gases gives the thermal efficiency of the economiser. Efficiency of economiser. — ^This, however, is not the efficiency shown in the column, but the ratio of the percentage of heat received by the water to the total heat in the fuel burnt under the boiler. The heat absorbed by the feed water depends largely upon the extent of heating surface exposed to the gases, or the size of the economiser, and this varies considerably in practice. In some cases the heating surface of the economiser is only one-third that of the boiler surface, or even less ; in other cases, it is actually much larger than the boiler. Much de- pends again upon the temperature of the gases and of the water going into the economiser, and other circumstances, particularly the amount of dirt and soot allowed to collect outside, and of scale inside, the 4-in. vertical economiser pipes. Both the latter conditions greatly check the transmission of heat from the hot gases to the cooler water. Economiser tubes are too often kept very dirty, and air is also allowed to leak in through the numerous chain holes driving the scrapers, and cool the gases. Notwithstand- ing this too frequent want of care and attention, a gain of from 8% to 12% in economy of heat may be realised by the use of economisers, and their cost is not very great. Boilers have often, by the author's advice, been fitted with economisers hav- ing the same heating surface as the boiler, but the suitable area depends upon the temperature of the gases, draught, and other local conditions. Description of English type of economisers. (See p. 300 for illustration.) — There are very few makers of this apparatus, but the type most largely used is that introduced by Messrs Green & Co., which may be taken as the best at present employed. It consists of a nest of cast-iron pipes, 4 in. diameter and 10 feet long, placed vertically and close together, as shown. The whole is surrounded by brick walls, and the exit gases from the boiler or boilers pass outside 30, 50, or 100 of these pipes, whilst the feed water is pumped through them on its way to the boiler, in an opposite direction to that of the gases. As much soot and dirt accumulate on the outside of the 4-in. vertical pipes, it is necessary to clean them automatically and continuously. This is done by means of a particular arrangement of scrapers driven by chain gear, passing slowly vertically up and down each pipe, and thus caus- ing the soot, etc., to fall to the bottom, into a pit provided for the purpose. The chains working the scrapers are driven either by a very small steam engine, or more economically from any available mill shaft, or by water or an electric motor. If the water is very bad, the 4-in. econ- omiser pipes soon scale up, and are hardly applicable. The water should be softened or filtered by some special process, before it is admitted to the economiser and boiler. Scheurer-Kestner's trials. — The advantages of systematically cleaning the external surfaces of pipes from the soot collecting on them was 166 HEAT EFFICIENCY OF STEAM BOILEES. proved in a series of trials made by M. Scheurer- Kestner on a feed-water heater of the usual French type, without scrapers. There were six heaters, each 26 feet long and about 19"7 in. diameter, placed horizontally in three brick flues, two in each. The first day they were worked after cleaning, the temperature of the feed water in the pipe was 147° F., giving an evaporation in the boiler of 6 '4:6 lbs. per lb. of coal. After working for only five days the temperature fell to 127°, or a loss of 20°, and the evaporation was reduced to 6 lbs. A thick coating of soot was found on the pipes. When this was removed, the temperature rose again to 170° and the evaporation to 6^ lbs. These figures show the practical necessity, in order to obtain the best results, of cleaning the pipes of the heaters at least every two or three days. The amount of soot will vary much with the kind of coal used, and with the temperature of the water admitted, and probably more wiU lodge on large horizontal than oh vertical surfaces. A safety-valve should always be added on the top of the economiser, as steam is sometimes generated, as in a boiler. A blow-ofi' valve at the bottom is also required. A brick bye-pass should be arranged, so that the hot gases can go direct to the chimney, should the economiser have to be cleaned or repaired. A brick pit is niade under the economiser, in which the soot accumulates from the scrapers, and this is cleaned out at stated intervals. The brick casing round the economiser should be thick and well built, to diminish radiation. These economisers are much used in America, and sometimes in Germany and Austria, but seldom in France. There are some other well-known English makers of feed- water heaters, namely, Messrs Kircaldy, Kowe, Wheeler, Wright, and Weir (mentioned at page 202). Messrs Maudslay make them for marine boilers. French feed- water heaters. — French engineers seem to prefer heating their feed water in a some- what different way, though they also utiHse the heat from the escaping gases, with about the same economical results. They place two, three, or four large wrought-iron pipes, often 1^ to 2 feet in diameter, and about the same length as the boiler, horizontally along the side of it. These pipes are inclosed in brick-work flues, arranged horizontally one above the other. The feed water is sent through the pipes, the hot gases are conducted round each pipe in succession before they escape up the chimney. The gases are well cooled and the water raised in temperature, but the arrangeinent does not afford such a large surface in proportion to the volume of 4 in. pipes as with vertical pipe economisers, and they are rather more difficult to clean externally. Jets of steam are generally used for the purpose. Inter- nally they give less trouble than the 4-in. pipe economisers, as a small man can get through them to clean them. They are very largely used in France, many thousands being at work. Many water tube boUermakers, both here and on the Continent, have a similar arrangement of a nest of 4-in. horizontal pipes at the back of the boiler, which it almost exactly resembles. The gases escape from the heaters at a low tempera- ture, and the feed water is well heated. The pipes, like those of the boiler itself, are cleaned by jets of steam, and are surrounded by brick- work, in which holes and doors are provided, to admit the steam. In the Tables of tests, details will be found of experiments on all these different ways of heating feed water by the hot boiler gases, giving the temperature of the gases entering and leaving the economiser, T.U. trans- mitted per square foot of surface per hour, and other points. The gases may be much cooled, but within certain limits. If their temperature is reduced below 200° to 250°, the draught is affected, but this depends on the height of the chimney, etc. Hale's opinions. — Mr Hale of Boston, U.S., whose contributions to the study of combustion in steam boilers have been already noticed, gives some sound practical conclusions, in his circulars, on economisers, chiefly those of the Green type, with vertical pipes 4 in. diameter and 10 feet long. Speaking of American economisers, although his remarks apply equally to English, he observes that the cost of keeping their surfaces clean is less than for the same amount of boiler heating surface. The cost of the scrapers and cleaning out the soot chambers he estimates at £10 per year per economiser, and repairs are also less expensive than for similar areas of boiler surface. In the economisers he studied, the ratio between the heating surfaces of the economiser and of the boiler varied from ^ to f , and the decrease in draught from zero to 60%. Economisers always diminish the draught a little. If there is not enough where they are used, it must be arti- ADVANTAGES OF ECONOMISERS. 167 ficially increased, and this, of course, adds to the expense. It should be remembered that the cost of heating surface in the economiser is generally- less per square foot than the same amount of boiler heating surface, and it increases the capacity of the plant and its evaporative power. If the temperature of the water in an economiser is between 100° and 250° F., each unit of surface has a greater capacity for taking up heat than the boiler surface generally, where the water is at; say, from 300° to 400° F. In other words, the difference in temperature between the exit gases at the end of the boiler, and the water in it, is less than the temperature difference between the gases outside the economiser surfaces, and the water inside. Thus the latter should transmit more heat per square foot of heating surface per hour than the former. The following questions should be carefully considered with reference to eoonomisers and boilers in different countries and locaHties : — How much more do 100 square feet of economiser surface cost than 100 square feet of boiler surface ? and if the money were invested, what would it bring in, as compared with the probable saving in fuel? What will the depreciation of boiler and economiser cost per year? What kind of water will be used — hard, soft, or dirty ? What ■wiU be the annual cost per 100 square feet of heating surface for cleaning the boiler and economiser both inside and out, including all flues, and what for repairs? What will the extra draught cost for the economiser, if it has to be provided ? The reserve of hot water in an economiser is of a certain value, in case of a sudden call. The life of a boiler will probably be longer if hot water is always used, and this also increases the value of an economiser. Its total cost, including the brick- work, if added to an existing boiler, is another question. If the boiler is already there, and not forced, and the smoke temperature is low, the economy of fuel may not pay sufficient interest to cover the out- lay on an economiser. In new plants the boiler can be made small and the economiser large, as the latter costs less. As a rule, 100 square feet of economiser surface fixed with brick- work costs, in London, about one-quarter the price of 100 square feet of boiler heating surface. If space allows, therefore, the latter surface may be reduced and the former increased, all other con- ditions being equal. For annual repairs per 100 square feet both surfaces will cost about the same, in large towns in England. General conclusions. — In the event of an accident to a pipe, it can be quickly replaced. A man-hole door in the brick-work is useful, as throagh it the flue can be entered, and the economiser pipes inspected from time to time. The pipes are usually tested up to 500 lbs. per square inch. Thermometers to record the tem- perature of the feed water every few days should be placed under two small cocks at each end of the economiser, where the cooler water enters, and the hot passes out to the boiler. To deter- mine the rise in temperature of the feed water, open the cock and let the water run out on to the thermometer. This is a better plan than to have fixed thermometers in sockets. External corrosion often takes place in econo- miser pipes, and arrangements should be made to prevent it. If the ground is damp and the foundation bad, concrete should always be placed under the economiser. If very cold feed water is used, the outside of the pipes offers a condens- ing surface to any vapour in the gases, and it runs down their external surfaces, and causes the cast-iron to rust badly. To avoid this, warmer feed water should be used, or heated direct by steam. In some cases the pipes have rusted quite through in three or four years, owing to neglect of these precautions. A few years ago Messrs Green published a pamphlet, giving a series of tests on economisers made by the engineers of four Boiler Insurance Companies. There are in all about fourteen detailed tests, and many useful particulars will be found in them, as heat balance sheets, analysis of the gases, temperature, heating sur- face, heating power of the fuel, etc. Messrs Green made their first experiment and took out the patent in 1845. Since then they have sold economisers to all parts of the world, and supplied about 150,000 boilers with them. Pimbley's fixed circulating economiser. — This is another type of feed-water heater. The vertical pipes are made very short, about 4 feet high, of cast-iron, with a rectangular vertical slit right through them for the gases. The scrapers are worked up and down by rods from a rocking beam. Experiments are required to prove if there is any advantage with this system, as com- pared with the ordinary type of economiser, for the same heating surface. 168 HEAT EFFICIENCY OF STEAM BOILERS. Heating feed water by exhaust or boiler steam. — This is now often done, especially on steamers, and there are various ways of carrying out the process. Boiler steam is sometimes used, or steam taken from the low pressure cylinder on its way to the surface condenser. With non- condensing engines in electric light stations, the exhaust steam is often employed to heat the feed water. In nearly all these examples the trans- mission of heat from the hot steam to the feed water is by means of small tubes, the steam passing outside the pipes and the water inside. Many makers supply apparatus of this description. See Chapter XI. p. 203, for an account of Weir's feed-water heaters for marine boilers. Pro- vision should always be made for cleaning both sides of the tubes from oil, grease, deposit, and dirt, which greatly hinder the transmis- sion of heat. Fig. 63 gives an exhaust steam feed-water heater, con- sisting of a number of pipes, as made by Wright. The following ex- ample of a trial on an economiser by Mr M. Longridge in 1894, may be found useful to students. The economiser with which the trial was made was constructed by Messrs Green, and was used at their works in conjunction with two Lancashire boilers 7 feet diameter by 27 feet long. It consisted of 192 vertical pipes in 24 rows of 8 pipes. Of these, however, only the 16 rows next the boUers were used. When working in the ordinary way, the feed water enters the bottom branch or cold feed pipe at the end next the chimney, passes along this pipe into the six- teen bottom boxes in connection with it, rises Fig. 63.— Feed-water Heater by Exhaust Steam. through the vertical pipes into the top boxes, and flows from them into the top branch or hot feed pipe, from whence it is discharged at the end next the boiler. Under this system, therefore, the water has the same distance to travel through the economiser, whether it passes through the section next the chimney, through that next the boiler, or through any other section. The dis- tribution of the flow is regulated by the tem- perature. The feed enters at the initial tem- perature, and is gradually forced up each pipe, being heated as it rises. As soon as the water in any one pipe becomes hotter, and therefore lighter, than in the others, it is forced into the top box and feed pipe by the weight of the water in the remaining pipes. Thus the tem- perature of the water in the bottom of each vertical pipe is the initial temperature of the feed, and the temperature at the top that of the discharge to the boiler. Trial of an Economiser. Date of trial, . . . . April 27, 1894 Duration, . . . 7 "92 hours Weather, . . . . . fine Heating surface in boilers, . . . sq. ft. 1465 ,, ,, eoonomisers (128 pipes), ,, 1370 Grate area, , 68 Temperature of outside air, . . . . 60° F. ,, gases leaving ^ ^7 T boiler flues, I Callender'sJ 702° F. ,, gases leaving j electrical j economiser flues, J pyrometer (^ 406° F. ,, feed to economiser, . . 50° F. ,, feed after passing through 1st group of 32 pipes, ,, feed after passing through 2nd group of 32 pipes, . . V247°F ,, feed after passing through 3rd group of 32 pipes, ,, feed entering boiler after pass- ing through 4th group. Average steam pressure, . . lbs. per sq. in. 61 Feed per hour lbs. 7617 Water heated per sq. ft. of economiser heating surface per hour, 5 '56 Water evaporated per sq. ft. of boiler heating surface per hour, ,, 5'20 Water evaporated per sq. ft. of total heating surface per hour, ,, 2"69 Weight of coal used per hour, . . . ,> 910 Moisture in coal as burnt, . . . . °/o 2"7 Dry coal fired per hour, .... lbs. 885 Weight of water mixed with each lb. of dry coal „ 0-028 Ash and clinker drawn from furnaces per hour, „ 78 Percentage of ash % 8'6 Weight of ash drawn from furnace per lb. of dry coal lbs. 0-088 ECONOMISER TEST. 169 Weight of ash per analysis, . Difference, being unburnt carbon, Calorific value of 1 lb. of dry coal, Carbon value of dry coal. Dry coal fired per sq. ft. of boiler heating surface per hour, Dry coal fired per sq. ft. of total heating surface per hour, Dry coal fired per sq. ft. of grate per hour, . Water evaporated per lb. of coal under actual conditions Equivalent evaporation from and at 212° F., . Water evaporated per lb. of dry coal under actual conditions, Equivalent evaporation from and at 212° F., . Water evaporated per lb. of combustible burnt under actual conditions, Equivalent evaporation from and at 212° F., . Analysis of gases from boiler flues, COj") N , , ." >• >. -*^"^ Analysis of gases from eoonomiser flues, COj N AirJ . lbs. 0'064 . ,, 0-023 T.U. 14,575 1-002 lbs. 0-60 ,, 0-31 „ 13 8-37 10-03 8-61 10-30 9-44 11-31 r 8-65 ■ 41-52 49-83 7o K weight 7-66 36-50 1.55-80 Weight of products of combustion leaving boiler flues per lb. dry coal, . . . lbs. 12-07 Weight of steam leaving boiler flues per lb. of dry coal, ,, 0-028 Weight of unburnt air leaving boiler flues per lb. of dry coal, 10-90 Total weight of air and gases leaving boUer, . ,, 23-0 Weight of products of combustion leaving eoonomiser flue per lb. dry coal, . . ,, 12-0 Weight of steam leaving eoonomiser flue per lb. dry coal, 0-028 Weight of unburnt air leaving eoonomiser flue per lb. dry coal, . . . .,, 13-80 Total weight of air and gases leaving eoono- miser ,, 25-84 Heat capacity of gases and steam from boiler flues per lb. dry coal, ~ . . . . ,, 5-58 Heat capacity of gases and steam from eoono- miser flues per lb. dry coal, . . . ,, 6-25 Efficiency of boiler, °/„ 56 ,, economise!-, . . . . % ^1 , , whole apparatus, . . °/„ 68 Percentage of evaporation produced in the eoonomiser % 16-3 Pressure in feed pipe entering eoonomiser, . lbs. 64 Dr. Heat Balance Sheets. Boilers only. Cr. To calorific value of 1 lb. of dry coal, , , heat contained in fuel and moisture, ,, heat contained in entering air. Total, April 27th, 1S94. Th. Units. 14572 9 147 14728 Per cent. 100-00 April 27th, 1804. Th. Units. Per cent. By heat transmitted to water, . 8271 56-16 ,, heat carried off in products of combustion 1992 -j „ heat carried off in excess air. 1741 , , heat lost in evaporating and super- 25-62 heating steam from water mixed with coal, .... 41 J ,, heat equivalent of unburnt carbon mixed with ashes. 342 2-32 ,, heat unaccounted for, including radiation, 2341 15-90 Total, 14728 100-00 Dr. Economiser only. Or. reed cold. Feed cold. April 27th, 1894. April 27th, 1894. Th. Units. Per cent. \ Th. Units. Per cent. To heat received from boiler in gases By heat transferred to water, . 1637 41-09 and steam per lb. dry coal. 3774 ,, heat carried of in gases and steam ,, heat contained in air entering at received from boiler flues, 2089) chain and damper holes, . 19 ,, heat carried off in air entering at f 58-91 ,, heat unaccounted for, . 192 damper and chain holes, and at 259) cracks in the brick- work, . ,, heat unaccounted for, . Total, — — Total, 3985 100 3985 100-00 170 HEAT EFFICIENCY OF STEAM BOILEES. Dr. Boilers and Economiser together. Or. To calorific value of 1 lb. of dry coal, „ heat contained in fuel and moisture, , , heat contained in entering air, Total, I'eed cold. April 27th, 1894. Th. Units. 14572 9 166 14747 100-00 By heat transmitted to water, . ,, heat carried off in products of combustion, .... , , heat carried off in excess of air, . , , heat lost in evaporating and super- heating steam from water mixed with coal, .... ,, heat equivalent of unburnt carbon mixed with ashes, . „ heat unaccounted for, including radiation, difference of heat con- tained in brick-work at begin- ning and end of trial, and errors of observation, (All from 32° F.) Total, Feed cold. April 27th, 1S94. Th. Units. 10026 1112 > 1230 36 J 342 2001 Per cent. 68-00 16-12 2-32 13-56 14747 100-00 Superheating steam in boiler flues. — As the main object of this book is to treat of combustion in boilers, it is only necessary to touch briefly upon the question of superheating steam, in and around boiler flues. It is impossible, however, ■wholly to pass over the subject, as it has been brought prominently forward, and has assumed special importance in England and on the Con- tinent during the last few years. It is not here proposed to deal with the great advantages of superheated .steam in the cylinders of steam engines, and its important effect in reducing condensation by raising the temperature. Many careful and exhaustive experiments on this point have been published in full, or as a sum- mary, by various writers, including the author, to which the reader is referred for full details. It is the methods of superheating that are here described, and those only are considered in which the steam is superheated inside the boiler flues, and by means of the hot gases. The other system, where the steam, after leaving the boiler, is superheated by a separate furnace, is foreign to our subject. Superheaters may thus be classed under two divisions, namely, direct or separately fired, which are distinct from the boiler, and form in no sense a part of it; and indirectly fired, or superheaters utilising the heat from the gases and in the boiler flues to superheat the steam. These are applied to many types of boilers, both internally and externally fired. There are several varieties of direct fired superheaters, with nests of pipes a few feet from the fire. They are like water-tube boilers, except that, instead of water, saturated steam goes through the tubes, and is dried and superheated by the flames and hot gases surrounding them. In every case the apparatus is quite apart from the boiler. The term superheated steam is appUed to saturated steam raised to a higher temperature than that due to its pressure, by heating it in pipes without allowing the pressure to rise. The steam becomes first dry, then superheated, its volume is considerably increased by the addition of heat, and in this state it resembles a gas. Let us assume that we are deahng with saturated steam at 100 lbs. gauge pressure, and at a temperature corresponding to this pressure of about 338° F., according to the steam Tables. By adding heat, this steam is often raised 100° or 150° in temperature = 438° or 488° F. This is called the temperature of superheat, and the additional heat 100° of superheat. Both methods of superheating steam, either by the hot flue gases or by direct firing, are only applica- tions under another form of the principle of transmission of heat from a hot gas to steam, through steel and cast-iron pipes. Superheating was advocated and used many years ago by Him, but had to be abandoned, STEAM SUPERHEATERS. 171 owing to the poor quality of the lubricating oils then in use, and the consequent burning of the valves, etc., of the cylinders. With the better mineral oils now employed, the subject has again been taken up, and it is found that practically even a high degree of superheat causes, with care, no injury to the internal parts of the engine. As compared with the Continent, the number of applications of superheated steam in England a,re relatively few, and both boiler owners and engineers seem rather afraid of using this highly heated steam. In Germany great strides have been made with it, and it is now used with engines giving, according to an excellent authority, about 200,000 H.P. At the Edinburgh Electric Light "Works, the engines are now regularly worked with superheated instead of saturated steam. "We will now describe briefly the different methods of superheating steam indirectly in boiler flues by the hot gases. The Hicks superheater consists of a series of steel "LT tubes about 1 in. diameter, placed gener- ally at the end of a Lancashire boiler. The gases coming from the two furnace tubes at a tem- perature of probably 1000° F. pass all round the superheating tubes. The latter are suspended in the flues from a tube plate forming a cast- iron box, divided into two parts. The saturated steam from the boiler enters on one side, and, passing through the tubes heated by the flue gases, returns to the other side as superheated steam. The degree of superheat, or amount of heat put into the steam, will, of course, depend on the temperature of the gases, heating surface exposed, percentage of moisture in the saturated steam, weight of steam passing per hour, and other conditions. In the case of a Lancashire boiler 8^ feet by 30 feet, with two 3 feet 3 in. furnace tubes and nine conical water tubes in each, the heating surface of the boiler was 1195 square feet, grate surface 39 square feet, the surface exposed to the hot gases in the super- heating tubes was 120 square feet, or about 10% that of the boiler; steam gauge pressure 100 lbs. An experiment mentioned in Mr Patchell's paper in the Proceedings of the Institution of Mechanical Engineers, April 1896, was made in March 1895, in which the boiler evaporated 5140 lbs. of water per hour. The steam was superheated 55° F., and the engine indicated 311 H.P. Even this small amount of superheat and small apparatus gave 9|% economy in water per I.H.P. and 19% economy of coal, as compared with saturated steam. A drawing of the Hicks superheater will be found in the paper just mentioned. M'Phail and Simpson's superheater and feed-water heater combined. — Drawings of this apparatus, as applied to a Lancashire and to a Babcock arid "Wilcox boiler, are also given in the above paper. It consists of two parts, the steam superheater proper, which is composed of two sets of tubes, and the steam radiating pipes inside the boiler. There are two nests of small vertical steel pipes placed in the flues at the end of the boiler, and thus receiving the full heat from the gases circulating round them from the two furnace tubes. Steam from the anti- priming pipe is first conveyed into the top of one of the two sets of superheating tubes, and from thence into the copper tube running the whole length of the bottom of the boiler, just below the internal flues. This is called the radiating tube, and there are two of them, one above and one below each internal flue. The highly heated steam" passes through the first, radiating heat into the water by which it is surrounded, and is carried round to the front, and back to the rear, into the bottom of the second nest of tubes. Here it is again super- heated, and passes upwards into a second copper radiating tube running along the top of the boiler above the flue, and just below the water line. Having thus heated the water by radia- tion both above and below the flues, the super- heated steam finally passes to the engine. This arrangement is said to improve the circulation of water in the boiler, as well as to put heat into it from the gases. It increases the evaporation, and gives drier steam on leaving the boiler, but, as applied to a Lancashire boiler, the apparatus seems to be more of a water heater than a steam superheater. Some modification of it was required when fitted to a Babcock and "Wilcox boiler, and it was found impossible to have more than one set of steel superheating tubes and one copper radiating tube. The steam is taken, as before, from the anti-priming pipe at the top of the drum, and thence passes through a superheating coil of tubes, arranged horizontally between the drum and the water tubes forming the boiler. 172 HEAT EFFICIENCY OF STEAM BOILEES. Being thus superheated by the heat from the fire below, it is carried into the radiating pipes inside the drum, and thence to the steam valve. This appears an ingenious arrangement for diffus- ing heat throughout the boiler, but probably little superheat can be left in the steam by the time it reaches the engine. In Mr Patchell's paper several tests on this superheater are given, in which the amount of superheat varied from 56° F. to 234° F., accord- ing to the extent of surface exposed. It has been applied to a good many boilers in Lanca- shire and Yorkshire. In 1 8 93 Mr Patchell fitted one to a Babcock boUer of the Strand Electricity Corporation. The apparatus consisted of a nest of small pipes, situated above the tubes of the Babcock boiler, through which the saturated steam passed, and thence through twelve radiating pipes. Total heating surface of the boiler 1827 square feet, of the superheating pipes 355 square feet, of the radiating pipes 174 square feet. The evaporative power of the boiler was greatly increased, and the thermal efficiency rose from 68% without, to 75% with, a superheater. Pressure of steam 135 lbs., amount of superheat about 66° F., saving in fuel 13%. The boiler evaporated 50% more water than before, and this without priming. In subsequent experiments a fan was added to obtain induced draught. The temperature of the gases round the superheating tubes rose to 1058° F., the steam entering them at 362°, and leaving them at 650° F. The application of these superheaters and induced draught increased the capacity of the water tube boiler tested 140%, and raised the evaporation per hour from 3500 lbs. to 8300 lbs. A trial in January 1896 by Mr Patchell gave the above results. The- steam pressure was 145 lbs. ; degree of superheater 37° ; coal burnt per square foot of grate per hour 29 lbs. ; water evaporated per square foot of heating surface per hour 4^ lbs. ; temperature of the gases leaving the boiler 654° ; chimney draught 1*1 in. Schwoerer. — This is another type of super- heater, designed by M. Schwoerer of Alsace, usually placed in the flues of boilers, and heated by the exit gases. It has been applied to many hundreds of boilers, of various types, especially in France and Germany. The author has seen several at work near Mulhouse, and they seem to give very good results. The superheater con- sists of a coil of 4-in. cast-iron pipes, generally placed in an elephant boiler at the end of the first run of gases, and just beyond the grate. They have " gills " or ribs cast on them inside and out. The outside gills are circular discs set a short distance apart, which present a considerable heating surface to the hot gases, and when kept clean afford free transmission of heat from the gases to the cooler saturated steam. Inside, there is the same arrangement of longitudinal radial ribs as in the Serve tubes. The Superheating coils are placed at the further end of the flues in a Lancashire, and between the drum and the water tubes in a Babcock and Wilcox boiler. One disadvantage of the apparatus is the material used, cast-iron not being so suitable as steel for high pressures of steam. Many experiments have been published on this type of superheater, some of the best by Professor Unwin. Steam super- heated up to 200° F. above that due to its pressure has given 20% economy of coal, and 20% economy of feed water, as compared with saturated steam. Gehre superheater. — This is also a German type, and is usually placed either in the top flue of a Lancashire or Cornish boiler, or in the flues between the boiler and the chimney. It consists of an apparatus hke a small surface condenser, about 2 feet diameter, and about the same length as the boiler. The cylinder or drum is made of steel, and fitted with a large number of small tubes, with a tube plate at each end. It ofiers a large heating surface in a small space for the transmission of heat from the hot gases to the cooler steam. The former pass inside the small tubes, and the steam outside them. This super- heater is largely used in Germany, several hundreds being at work with all types of boilers, and a great many have been seen by the author. Various tests and experiments have been made on it with good results. The amount of super- heat depends on the temperature of the gases in the ttues, on the surface allowed for superheating a given weight of steam, the quantity of steam passing through per hour, and also upon the per- centage of water in the saturated steam. The Sinclair superheater is another form, with small steel tubes suitable for high pressures of steam and high temperatures. It consists of a nest of tubes affixed to the upper flue of a boiler, and through which the gases pass before escaping to the chimney. There are twenty-six vertical coils of pipes, IJ in. diameter. Each tube is separately flanged on to the two steam SUPERHEATERS AND FEEDING OF BOILERS. 173 pipes, one conveying the saturated steam from the boiler, through the other the superheated steam passes to the engine. These pipes can expand freely and move easily, and can also be cleaned and replaced quickly. Several boilers in the Electric Light Station at Edinburgh have been provided with these superheaters by Professor Kennedy. Many experiments have been made on them by the chief engineer, and no difficulties ■were found after they were regularly at work. (See page 63 for experiments on a boiler at this station, in which the gain in economy, or saving in steam, was from 10 to 11%, with some 30° F. of superheat, and 22%, with 65° F. of superheat at the engine.) The hot gases can be shut off from the superheating pipes, if necessary, an arrangement which obtains in most of the superheaters described. A drawing of this superheater, as applied to a dry back boiler, is given in Mr Patchell's paper, and an experiment will be found in the Tables. The amount of superheat is often from 60° to 80° F. The SerpoUet boiler and superheater com- bined, of which a drawing is given at page 291, is a special type, having neither water gauge nor safety-valve, and containing very little water indeed. The boiler consists of horizontal coils, forming water tubes. As the feed is sent into the lower pipes, which are surrounded by the hot gases and fire, it is immediately evaporated into saturated steam. The next row of pipes dry the steam, and in the last row it is super- heated 200° or 300°, or even more if required. Hundreds of these little superheating boilers are now used on the Paris tramways, and for shunting purposes at railway stations. In an experiment by Dr Kennedy and the author, at Bermondsey, on a very small 4 or 5 H.P. boiler, the steam was easily superheated 200° F. Schmidt. — This German superheater has been much used for the last few years, chiefly fixed on the top of small vertical boilers. It is also applied at the end of Cornish and other boilers for superheating the steam. The novelty in Herr Schmidt's arrangement is that he generates and uses highly superheated steam for rather small engines, and the degree of superheat is much higher than in most types. The heating surface is therefore, comparatively large, with the gases at a fairly high temperature. With a vertical boiler the gases, after passing upwards through the boiler, impinge on the small horizontal coil of tubes, 1^ in. diameter, forming the super- heater. Very wet steam is first generated, enters the superheater in the contrary direction to the gases, and is dried, then highly superheated before passing to the engine. The coU of pipes forming the superheater is arranged watch- spring fashion, one above the other, and is divided into two, 'the "fore" and the main superheater. The gases pass round and between them on their way to the chimney. The hottest gases play first round the "fore" superheating pipes, containing the most water or wettest steam, then pass around the main pipes. Many trials on this superheater have been published in Germany : the best have perhaps been made by Professor Schroter. The author has also carried out some experiments in Germany on a boiler of about 15 H.P. Professor Ripper, at the Sheffield Technical College, has one of these Schmidt boilers and superheaters combined, and has published experiments in Proc. Inst. Civil Engineers, vol. cxxviii., 1896-97, giving many interesting particulars, and proving the great economy of superheated over saturated steam. At Sheffield the boiler has a surface of 37 "6 square feet, the "fore" superheater of 32^ square feet, and the main 143 square feet ; total, 175|- square feet, or nearly five times the heating surface of the boiler. Steam pressure, nine atmospheres. The degree of superheat was varied f com zero to about 350° above the temperature due to the pressure. The temperature of the steam at the engine was often 670° F. Drawings and all details will be found in Professor Ripper's paper. Longridge's Table. — The quantity of heat passing through superheating tubes has been worked out by Mr Longridge (Proc. Institution Mech. Engineers, April 1896), and is shown on p. 174. The kind of metal, and its thickness for transmitting heat, are unfortunately not given in each case, nor is it stated whether the surfaces were clean or dirty. Supply of feed water to boilers. — Boilers at work under steam pressure require to be con- stantly or intermittently suppHed with hot or cold water, and it is very desirable that this should be done economically, and without risk of accident or trouble. It is so important to keep a boiler well supplied with water that, in any well- appointed boiler-house, there ought always to be two methods available of doing it. If one fails the other can then be applied at once, and the 174 HEAT EFFICIENCY OF STEAM BOILERS. supply must always be equal to the maximum demand. There are generally three ways of forcing the water into the boiler : — 1. By feed pump attached to the large engine, and driven direct from it. 2. By a separate small feed pump in the boiler-house. 3. By injectors. 1. Feedpumps. — This plan is often adopted on land, and is convenient and economical where there are one or two boilers, but as the feed pump always goes at the same speed as the engine, the delivery cannot be varied to suit the demand. 2. Donkey pumps. — For a large number of boilers it is often found convenient to have special feed pumps, worked by the steam in the boiler-house. These pumps, which are made in every possible form and shape, are nearly always very uneconomical, and cannot be recommended for daily use. They are also often worked inter- mittently, with many stoppages, whether by day or by night. Thus the cylinder gets cold, the amount of steam condensed is very great, particularly with long and uncovered steam pipes, and all the exhaust steam goes to waste Superheating Steam by Hot Boilek Gases. Examples of transmission of heat from hotter gases to cooler steam. Arranged in order of heat transmitted per sq. ft. Particulars, etc. M'PhaU's Super- heater. Gelive Super- heater. B. Donkin. M'Phail's Super- heater. Schmidt fore heater. Schroeter. Hlclts Super- heater. Schmidt Super- heater. Schroeter. Gehre Super- heater. B. Donkin. Heat transmitting surface, . Weight of steam passing superheating pipes per hour, .... j- Final, . Steam temperature, J Inlet, . Fahrenheit, J V Superheat, Mean difiference of temperature between gases and inlet steam or head of heat, f per hour. Heat transmission, 1 P"!! ?i°''*f ' 1 ° T.TJ. per sq.ft., P^^^Jof [_ temperature. Metal, Thickness of metal, .... sq. ft. lbs. F°. F°. F°. F°. T.U. T.U. T.U. in. 162 33-5 524° 299° 62-5 38-8 448° 346° 162 34-3 425° 299° 72 9-4 422° 354° 120 22-2 420° 340° 359 1-8 694° 442° 646 3 388° 348° 225°, 102° 126° 68° 80° 252° 40° 424° 3617 60-0 8-53 ■? ? 403° 1900 31-7 4-72 iron. A"t0T:V' 447° 2074 34-5 4-64 ? ? 709° 1931 32-0 2-72 steel. A" 440° 852 14-2 1-94 steel. ? 217° 225 3-7 1-04 steel. A" 187° 57 0-9 0-30 iron. A"toA" Surfaces dirty or clean not mentioned, nor speed of steam or of the gases passing the surfaces. as a rule. Such pumps are certainly to be avoided, and, if used, much more care should be taken in their manufacture. At present the sole object often is to make them as cheaply as possible, and neither seller nor buyer have generally any knowledge of the amount of steam they use per hour for pumping so much water. It would be better on land to drive the feed pumps by gas, oil, or electric motors. In many electric power stations the latter are used, with greatly improved economical results. Sometimes the pumps are driven from a fixed shaft. At sea the boilers are mostly fed by small steam pumps, and the hot water is often twice pumped from the surface condenser. 3. Injectors. — Injectors are frequently a very economical way of feeding all kinds of boilers, as all the steam used goes into the feed water, and therefore into the boiler. Many kinds are made. On locomotives they are almost univer- sally employed for hot or cold water; two are often fitted to the same boiler, and they seem to FEEDING OF BOILERS. 175 give little trouble. They should be more used for land boilers, and the uneconomical donkey pumps only kept in reserve. These injectors should be so fixed with flanges that they can be taken off very quickly for inspection and clean- ing, and easily replaced. Feeding. — Boilers should, if possible, be fed continuously, and not in an intermittent way. The quality of the water admitted is of great importance. If hard, it wiU generally be found that to soften it, and thus avoid the barbarous practice of chipping, so usual in boilers, is the cheapest plan in the end. If there is much sediment or dirt in the water, a large tank should be placed to receive it, and it should on no account be allowed to go direct into the boiler. If it is absolutely necessary to treat the water with some chemical or often dangerous mixture, it should not be put at once into the feed water, but added to it outside the boiler in a tank, and no deposit should be permitted inside the boiler if it can possibly be avoided. The internal surfaces of the boiler should never be chipped, only swept and washed out. When the water contains much carbonate or sulphate of lime, the author has often recommended the method of softening it in tanks, and then pumping it into the boiler. In the case of one donkey steam pump having to feed several boilers, the quantity of water for each should be regulated by the feed valves, and the feed water should go into all the boilers simultaneously. On the position of the feed pipe inside the boiler, the following valuable practical remarks have been kindly communicated to the author by Mr Michael Longridge': — Longridge on feeding boilers. — " In a Lanca- shire boiler the feed delivery should be above the level of the crown of the internal flues, so that the latter may not be left bare, in the event of water escaping from the boiler through the check valve ; and below the bottom of the gauge glass, so that violent disturbances (anal- ogous to water hammer in steam pipes) may not be caused by the careless injection of a large quantity of cold water into the steam space. " The internal feed pipe should be horizontal, so that the feed water may be mixed with the water in the boiler and warmed, before reaching the bottom of the boiler, and it should deliver near the back end, so that the deposit, which is generally greatest near the feed delivery, may not accumulate upon the plates exposed to the first heat of the gases. The feed may be dis- charged entirely from the open end of the inter- nal pipe, or through perforations in the part near the back end of the boiler. " The feed valve may be fixed upon the front end plate at one side above the level of the furnaces, in which case the internal pipe will be straight, but when the pressure is high it is often better to have the internal pipe bent, and put it on the top of the boiler, as the joint to the front end plate is liable to give trouble by leaking." CHAPTEE IX. Smoke and its Prevention. Smoke from Factories — Nature of Smoke — Soot — Chemical Combinations — Methods of Preventing Smoke — Good Combustion — Air — Spenoe's Experiments — Down-Draught Furnaces — Powdered Coal— Various Smoke Scales — Lewicki— Ringelmann — Smoke Abatement Commissions : English, Prussian — Lewicki's Trials. Smoke from factories. — The subject of the prevention of smoke is closely connected with combustion, and the various mechanical appH- ances and devices for improving it, already described. The question has excited much interest of late years, both in England and abroad, because of the increasing density of population in large towns, the much greater quantity of smoke produced, and its injurious effect, both on animal and vegetable life. The public still seems to think that smoke cannot be prevented, but experts generally are not of this opinion. In several countries the production of smoke from factories has been restricted or for- bidden by law, and stringent measures to abolish it, or to make manufacturers "burn their own smoke," have been framed, which it has not been possible hitherto to enforce. The dense pall of smoke covering so many manufacturing towns, and affecting vegetable growth, is usually attri- buted to the chimneys of factory buildings, but the latest reports upon the subject and state- ments of facts seem to show that such is not the case. It is the very large number of domestic fires which causes the most smoke. In London it largely increases between 6 and 8 a.m., when smoke begins to issue from three-quarters to one milhon fireplaces. Nevertheless, it is very necessary that manufacturers should do all in their power to diminish the nuisance, and the subject has not yet received the attention its importance deserves. For convenience in studying the question of smoke, chiefly from factories, it may be divided under the four following heads, namely : — • I. What is smoke? II. Its prevention. III. Determination of the intensity of smoke by different kinds of smoke scales. IV. Eeports of Commissions upon trials, chiefly in England and Germany, on smoke and its abatement by various mechanical appliances. I. Nature of smoke.— Not much has yet been authoritatively published concerning the nature of smoke, though most scientific men are agreed upon the methods to be adopted for its preven- tion. Till quite lately, it seems to have been regarded as a necessary evil, and many people think that to attempt to abolish smoke would impair the efficiency of combustion. This false theory has now been wholly disproved, but the subject is still in the experimental stage, and cannot yet be treated in a positive or dogmatic way. The precise nature of smoke is still rather obscure, and no reliable or recognised standard method of testing it, to determine the degree of intensity, has yet been introduced. Some authorities are of opinion that to get rid of the smoke by admitting a large excess of air causes a greater loss of heat than the imperfect combustion to which smoke is known to be due, because the air carries off so much heat from the boiler up the chimney. It is not a continuous, but a properly regulated, quantity of air, intro- duced at the right moment and in the right places, which is required with most coals and stokers, to prevent smoke or largely diminish it. Notwithstanding all that has been said and 176 NATUKE OF SMOKE. 177 written about the process of combustion, the actual way in which the chemical constituents of the coal separate and recombine is still rather uncertain. It is well known, however, that as soon as a fuel is burnt on a grate, that is, oxygen (in air) is introduced and combustion started, the coal becomes divided into solid and volatile parts. This separation takes place simultaneously with the combination of the carbon and the ■oxygen, which results in the heat-giving chemical process called "combustion." The volatile parts, hydrocarbons or tarry vapours, combine with the oxygen of the atmosphere to form CO,, if eufficient air, at a suitably high temperature, is admitted to the grate ; while, if the air and temperature are deficient, CO only will be pro- duced. If before recombination has taken place, and while the cooling process of volatilisation is proceeding with energy, part of the hydrocarbons escape into a cooler part of the flue, they will not combine and burn at all, but are condensed by contact, and form smoke. The phenomenon may be watched on any domestic fire, when coals are first put on the grate. At the same time, a large number of very fine and light particles of sohd carbon escape as soot. Thus it is both the ■gaseous hydrocarbons and the solid carbon which cause trouble as smoke and soot. When all the hydrocarbons have been driven ofi', and volatilisation is complete, the coal becomes coke. If the temperature of the hydrocarbons or tarry vapours is further raised to, say, 750° F., the H will burn, but not the C, which requires for ■combustion a temperature more than double that of the H, 1470° F. to 1650° F. Thus the lighter and smaller particles of carbon go to increase the volume of soot and smoke. Some authors insist on a distinction between smoke, or the condensed unburnt tarry vapours, and soot, which is practically carbon, forming "the residuum after the hydrogen has been burnt off. The author is of opinion that no such rigid difference between them can be established ; and such a theory does not take sufficient count of the ash, which is also unburnt carbon. This ash is a powder, and very light, and, like soot, it is nearly all carbon. It may often be seen ^coming from the funnel of a locomotive engine ; indeed, the large quantities of smoke, soot, and light ash sent up the chimneys of locomotives by the induced draught are notorious. The pro- duction of soot and ash vary much with the kind of fuel burnt, thickness of the fire, and the draught, every coal giving off different quantities. With anthracite, for instance, very little or no ash escapes up the chimney. M. Ser thinks that the production of smoke and soot can never be attributed to carbon detached in a solid shape from the coal, and carried off by the current of air, but rather to carbon formed on the grate itself, by the partial combustion of the volatilised hydrocarbons. Coke and charcoal give off no hydrocarbons, and anthracite only in small quantities. With these fuels, therefore, little or no flame is produced by the combustion of the volatile gases. Of the gases which escape combustion, it may be said that smoke and soot (condensed tarry vapour and carbon) form the visible portion ; the flue gases, properly so called — COj, O, and CO — are invisible. Chemical combinations. — Another reason is sometimes given to account for the formation of smoke and soot. In the opinion of some writers, dissociation of the carbon and the hydrogen takes place at the high temperatures prevailing in a boiler furnace, and assists in the precipita- tion of the carbon. If this separated carbon finds enough oxygen to combine with, it burns as a clear flame to CO2J ^nd this is the flame usually met with in boiler practice. If the supply of air, and hence of oxygen, fails, CO will be formed, carbon deposited, and waste of heat wiU be the result. Professor Eingelmann advances a similar hypothesis to explain the presence of smoke. He thinks that what is technically known as " cracking " of the hydro- carbons occurs, due to the high temperature of the furnace; that they are split up into, hydrogen and carbon, and escape as smoke, instead of com- bining ; and that this result is not affected in any way by the quantity of air admitted to the grate. In any case, the processes are gradual. The exact nature of the combinations taking place are not accurately known, but according to the character of these combinations between the flue gases, air, nitrogen, and products of com- bustion, the flames are longer or shorter. From these various considerations, it wiU be seen that the production of smoke means, generally speak- ing, a waste of heat, due to imperfect combustion. With our present systems of hand-firing, to force a boiler generally results in smoke, unless great care is taken, but the large volumes of black smoke often seen escaping from factory M 178 HEAT EFFICIENCY OF STEAM BOILEES. chimneys, particularly after stoking, are almost wholly preventable, and a disgrace to our existing methods of combustion. The actual loss of carbon in the shape of soot does not, according to M. Scheurer-Kestner, exceed 1% of the total carbon in the fuel. Payen gives an experiment -with Sarrebruck coal, in which, with combustion greatly forced, only 3"3 lbs. of smoke, actually weighed, were produced per 100 lbs. of coal burnt. Thus the direct loss of heat due to smoke may be taken at not more than 3%, but to this must be added other losses, equally real, though indirect. By covering the boiler plates and flues with a layer of fine, almost impalpable carbon dust, the formation of soot greatly retards the transmission of heat from the hot gases to the boiler plates and the water, and thus the total loss of heat is greatly increased. Both sides of the boiler plates should be cleaned much more often than is usually done. More attention should be given to this important matter, which would well repay any trouble, and should not be left to the mercy of the stoker or cleaner. The excess of air admitted is generally too large, as shown by the analysis of the gases of combustion, and there is considerable loss in undeveloped heat, due to imperfect combustion. From an economic point of view the diminution, or rather the virtual abolition of smoke, is not of such great conseqi.ience, but from the hygienic side its importance cannot be overrated. II. Methods of preventing smoke. — Coming next to consider the methods of preventing smoke, these depend, in the first place, on the combustion, which, as has already been stated, is regulated by two circumstances. (1) The admission of suificient air to insure the complete combination of the oxygen with the carbon, and their combustion to COg ; and (2) the mainten- ance of that part of the furnace, into which the gases of combustion rise after their volatilisation, at a temperature high enough to insure that the carbon, as well as the hydrogen, shall be com- pletely burnt. The conditions to be observed for preventing smoke are laid down with great clearness and accuracy by Herr Eeischle, Chief Engineer of the Bavarian Boiler Association, to whose valuable paper on Smoke Preventing Apphances the writer is much indebted. Eeischle considers that the three requisites for the com- plete combustion of the liberated hydrocarbons are the following : — Conditions for good combustion. — a. To heat them rapidly to a high temperature before they escape. b. To supply them with sufficient air for com- bustion during the whole time they are in the furnace. c. To insure that this air shall not only be present, but thoroughly mixed with the gases. None of these conditions should be neglected.. It is possible, for instance, to have a large excess of air, and yet the presence of smoke may show that combustion is imperfect. This is because the fire burns in clusters of flames, produced by the unequal distribution of air through the layer of combustible. Careless hand-stoking is usually responsible for this violation of one of the essential conditions of good combustion. If the fuel be stoked in layers of unequal thickness, and lumps of coal are left, the air and gases cannot be thoroughly mixed. It also sometimes happens that the tarry vapours, when liberated, expand and force the air aside, so that it cannot reach the coal. A good draught will generally remedy this difiiculty. The process of hand-stoking, poking, and rak- ing fires, on which the admission of air partly depends, is more complicated than appears at. first sight. As a rule, mechanical stokers give better combustion with less smoke than hand- firing, and coking are preferable to sprinkling stokers from a smoke-preventing point of view. The cost of this machinery is sometimes an obstacle, and these stokers are not very suitable- if the quantity of steam varies much from hour to hour, and it is necessary at times to force the boilers. Nor are they economical when appKed' to small boiler plants, and recourse must then be- had to hand-stoking. There are three different methods of hand-firing, the coking, the alternate, . and the spread systems. In the first, the coal is deposited by hand, as in a coking stoker, on the- front of the dead plate, and gradually and gently introduced into the fire, being, slowly pushed- back as combustion proceeds, and its place taken- by fresh coal fed in front of it. In the alternate hand method the coal is stoked first on one side, then on the other, of the grate. Care should be taken never to supply fresh or green coal on one side until the fuel on the other is in a state of incandescence, though this is perhaps rather too much to expect of an average stoker. In hand- stoking on the spread or sprinkhng system, all. METHOD OF INTRODUCING AIR. 179 the coal is put on at once in a thin layer over the whole of the grate, but this method is not generally considered as "desirable as the two former. As a rule, unless hand-firing is very skilfully carried out, it produces more smoke than mechanical stokers. Method of introducing air. — To introduce air to the grate is another rather difficult point. It is necessary, as already indicated in the chapter on combustion, that the air should be admitted under and above the furnace, and also at the fire bridge, before combustion is quite ended. If introduced later, or, rather, if it filters in unintentionally through cracks in the brick-work, it dilutes the flue gases, and retards instead of furthering combustion, by chilling the products. Some boiler furnaces have hollo sv or perforated fire bridges, others contain passages to conduct the air to the furnace above the grate. To raise the temperature of combustion, the air is sometimes previously heated. This is more done at sea than on land, and the gain in economy is said to be considerable. To prevent smoke it is not enough to have plenty of air ; the air must also, according to Reischle's second condition, be at a sufficiently high temperature to insure perfect combustion. No very good system of raising the temperature of the air, in which the economy of combustion obtained more than counterbalances the cost of installation, appears to have been yet really at work on land. Mr Hoadley's experiments, though proving that smoke can be diminished by previously heating and regulating the admission of air, do not appear to have been financially successful. Although a certain excess of air is necessary, and smoke cannot be prevented without an abundant supply, too large an excess results in loss of heat, because, for every cubic foot of' free or uncombined oxygen passing through the furnace, nearly 5 cubic feet of air are admitted, and carry off heat as waste to the chimney. There are numerous varieties of fire bridges, and methods of admitting air to a boiler grate, so as to minimise the production of smoke. At the moment of stoking, the air usually enters freely through the charging doors, but it also passes to the fire, through the bars, if chimney draught is used. Often too large a quantity is allowed to enter, and the fire gets unduly chilled. Sometimes the doors are left slightly open for a certain time after stoking. The admission of a supplementary volume of air, while combustion is proceeding, has, however, been proved, both in England and abroad, to be of great value — indeed, almost essential to insure good combustion. In Sheffield the apparatus most approved for this purpose admits air automatically to the fire bridge every time the furnace is stoked, and the door opened. By this means the production of black smoke is said to be checked. Spence's experiments. — This subject is very fully treated by Mr Spence' in his interesting experiments. He lays special stress upon the method of introducing the air, and the best place for its admission, in order that it should not only be present in sufficient quantities, but also be thoroughly mixed with the gases, according to Reischle's third condition. If combustion is to be smokeless, all the air admitted must be utilised, and none allowed to escape before the oxygen has combined with the carbon on the grate. (See Appendix VI., page 257, for an ac- count of Mr Spence's experiments with CO flames and smoke.) In his trials the main entrance for air was immediately over the door and burning fuel. To stimulate combustion and diminish smoke, it was also introduced at three different places — through holes in the furnace front above the grate, above, and also below the fire bridge. The number and size of the openings in all these places were varied, and the considerable economy obtained by increasing the air supply is shown in the Tables, pages 65 to 71. Newcastle coal was used throughout the trials. "With varying conditions of fire, Mr Spence studied the smoke qu.estion carefully. In the first set of experi- ments, where the air for combustion entered only under the grate, and in the usual quantities, there was a great deal of black smoke. As the supply was gradually increased, and more and more allowed to reach the fuel through the bars, over the top of the firb, and at the fire bridge, the quantity of smoke greatly diminished. In duration and intensity it varied approximately, in proportion to the amount of supplementary air, up to a certain hmit. The conclusions to be drawn from these experiments seem to be that, with air admitted in proper quantities, and at 1 " On the Combustion of Coal," by W. G. Spence,. Excerpt Minutes Proc. Institute N.E. Coast Engineers, vol. iv., 1888. 180 HEAT EFFICIENCy OF STEAM BOILERS. proper places and times, the chimney, with the coal used, was practically smokeless, without recourse being had to any of the hundreds of patented arrangements. In Germany the fire bridges are often made hollow or in sections, to facilitate the introduction of air at the further end of the furnace. To in- crease its temperature, this second supply of air is often passed outside a portion of the boiler flues, before being admitted to the combustion chamber. (See also Chapter IV., on Grates, for description of appliances for diminishing smoke.) Gaseous fuel. — Another way of preventing smoke, the most efficacious of all, though it cannot be universally apphed, is the use of gaseous, instead of solid fuel. With this method, almost perfect immunity from smoke and practi- cally complete combustion are obtained, and whenever it can be used the results are excellent. It is, of course, open to the objection that the gas must previously be distilled, and, except where gas as a waste product from metallurgical fur- naces is available, it has not yet been much utilised with boilers. At the chemical works of Messrs Brunner & Mond, a striking proof is afforded of the value of gaseous fuel. Coal gas is there distilled, the ammonia separated, and the gas utilised in the steam boilers. It is said to be "incapable of causing black smoke," and the residts obtained have been very satisfactory. Combustion is controlled by continual analysis of the furnace gases, and these are now tested by the competent workman in charge, who is often able to judge, to within a very smaU percentage, of the amount of COg, 0, and CO, merely from the appearance of the flame, and thus to regulate the combustion. Gas firing is not apphcable for day work only, and therefore not to factories and mills. For constant work, night and day, it is often used. Down-draught furnaces. — Among methods for preventing smoke, one of the most efficient is said to be the down-draught furnaces (Hawley and others), described at page 124, many of which are working in the United States. These furnaces are especially valuable when applied to boilers doing variable work, and greatly forced, — a class in which it had hitherto been found impossible to adjust combustion so that there should be no smoke. According to Mr W. Bryan, by the use of these furnaces smoke " can now be abated by practical means, without hardship, no matter what the type of boiler, the character of the work required of the plant, or the kind of fuel used," The principles' regulating combustion in these furnaces are twofold. There are two grates, one below the other, and the current of air supplied to them is drawn in downwards instead of upwards. Combustion is started and mainly carried out on the upper grate, which is stoked from above, and is completed on the lower, the fire thus burning downwards. Nearly all the air is also admitted at the top. The fresh coal is charged by hand on to a mass of glowing fuel ; the hydrocarbons as they are Hberated, and the particles of uncombined carbon, are continu- ally forced downwards. Those which escape com- bustion on the upper are wholly consumed on the lower grate, where the coal already coked is burnt. There is practically no smoke with this class of furnace, but it does not seem to have yet been adopted in England. It is not satisfactory where the draught is not good ; about f in. to 1 in. draught gives the best results. Smokeless powdered coal firing. — Between the years 1868 and 1873, Mr Crompton made some interesting experiments in England on this method of combustion for the prevention of smoke, but since then nothing has been done till within the last few years, when pubhc attention has again been turned to the subject. There are now several systems of powdered coal firing in use on the Continent, but the most successful appears to be that of Herr Carl Wegener of Berlin. His apparatus differs from others, because in it a current of air for combustion is induced by means only of the chimney draught, whereas other inventors employ various means, such as fans, for obtaining forced draught. With this finely powdered coal the particles are only about y^ in. in diameter, and less. A much more intimate mixture of the fuel in this powdered condition with the oxygen of the air can be obtained, and therefore combustion is more perfect from a chemical point of view, than when coal of all sizes, from j-\ in. to 2 in. diameter, is burnt in a grate in the ordinary way. The boiler efficiency and the temperature of the fur- nace are higher with this system of firing, but its chief recommendation is the almost complete absence of smoke. There is no grate, and as the powdered coal is introduced continuously and automatically, there are no fire doors to open. As apphed to internally fired boilers, such as SMOKE SCALES. 181 the Lancashire, the furnace tubes are lined with 1 in. fire brick, to form a reservoir of heat for igniting the powdered coal as it is admitted. This is necessary, because there is no store of glowing fuel in the furnace to kindle it, as with an ordinary grate. For a complete description of Herr Wegener's invention, with drawings, the reader is referred to an article in The Engineer, May 15, 1896. In it an experiment is also given, made by the author, in Berlin, in 1895, on a Cornish boiler fired successively in the ordinary way, and with a Wegener apparatus. The chimney-top was constantly watched by a competent observer, and notes made every few minutes as to the degree or intensity of smoke. With the powdered coal firing there was practically no smoke ; with the same coal burnt on an ordinary grate there was a great deal. Many trials on the Wegener system have been made during the last two or three years in Berlin, Paris, Berne, and Brussels. In Germany there are now about fifty or sixty boilers working with this apparatus, one or two at Messrs Krupp's at Essen. In France and Belgium there are six or seven boilers at work, three in Switzerland, about twenty in Chili, and for some time one has been working in London. Fig. 64 gives an example of the intensity of smoke from a boiler furnace fired with one of these apparatus. The scale, as used by the author, is divided into five shades of different degrees of blackness. The percentage of COj in the chimney gases is a good deal higher with the Wegener firing, than with ordinary large coal. III. Smoke scales. — Various methods have been adopted for determining the degree of smoke from a boiler furnace. It is a difficult matter to test the exact shade or intensity, and no very satisfactory arrangement for recording it seems to have been yet proposed. Most authorities on the subject have devised some kind of smoke scale, in which the various degrees of intensity are denoted by numbers on the scale, ranging up to three, five, or ten, according to the different varieties of shades agreed upon. To determine the number for each varying dehcate shade of blackness at the top of the chimney is not an easy task, because it depends wholly on the judgment and eye of the observer. The light varies greatly, from full sunshine to dull at- mosphere or fog. The same intensity of smoke will appear somewhat different in different months of the year. X I \ 1 \ ^ 1 N - V. /- 1 y^ eg C \ 1 1 m v. - J f \ -9 1^ ^ f N o "v^ J / s l;iJi;i,lions.) Nn. :l. X" 1, Xn. M.i;. 6b. — \ eiy Daik (ircy .Sui'jkc I'l;;, G;i. -lUuck Siiiuki I'lj;. 70.-- \ cry Black .Smoke. REPORTS OF SMOKE COMMISSIONS. 1&5 exhaustive report to the Saxon Engineering Association in 1896. In France and America the abatement of smoke is receiving much attention, although no formal committee has been appointed. From whatever side the sub- ject is approached, there are two points to be con- sidered — (1) How far the mechanical appliances tested for diminishing smoke answer that pur- pose ? and (2) To what extent, when there is no smoke, combustion is complete ? Perfect combustion, that is, the approximation of the actual to the theoretical heat eificiency of the coal, is estimated in two ways. It may either be determined from analysis of the gases of com- bustion, showing the excess of air, and the percent- age of oxygen supphed to that actually combining with the carbon. This may be called the chemical test, and its value has already been pointed out. The other way is by measuring the work done by a given quantity of coal in evaporating water, or the evaporative test. The economy is deter- mined by taking the temperature of the gases out, of water into the boiler, the fuel burnt and water evaporated per lb. of carbon value. These data are necessary to know whether the prevention of smoke may not be purchased at the expense of the boiler efficiency. The result of the various investigations undertaken during the last fifteen years tend to show that this is not the case, and that the less smoke there is — in other words, the better the combustion, and the more completely all the carbon is consumed — the higher will be the efficiency of the boiler. First English Commission. — In the two English Smoke Abatement Commissions, a large number of grates and mechanical stokers were tested under ordinary working conditions. The First Commission, to which the late Mr D. K. Clark was Secretary, sat in London in 1881. An Exhibition was held at South Kensington of appHances for preventing smoke, and the following were tested : — The Chubb, Duncan, and Martin grates, and the Sinclair and Proctor stokers, together with many others, both grates and stokers, now obsolete. A voluminous report was drawn up by Mr Clark in 1882, and pubHshed (Smith, Elder & Co., 1883). Second English Commission. — The Second Commission, appointed about 1895, tested a number of appliances for diminishing smoke. Sixty-nine trials were made in all, about one- third of which were on the following mechanical stokers : — -Vicars, Juckes, Bennis, Sinclair, Cass, Hodgkinson, and M'Dougal. This committee sums up the question of smoke and its prevention as follows : — " "While future experiments and in- ventions may be the means of introducing new and better methods of treatment in the combus- tion of fuel, enough is known at present to enable steam users to work their boilers with a fair degree of economy, and practically without smoke." They were of opinion that the smoke from factory chimneys is not so great a cause of pollution of the atmosphere as that from domestic fires, especially in large towns, and they con- sidered that almost, if not quite, all the smoke now issuing from boiler chimneys should be pre- vented, either by employing mechanical stokers, or by more careful hand-firing. The Sheffield branch of the Commission thought it possible to limit the production of smoke in that town to two minutes per hour for one boiler ; three minutes per hour for two boilers; and four minutes per hour for three or more boilers. Prussian Smoke Commission. — In the Prussian Smoke Commission (1894) seven boilers were tested, fitted with different smoke-prevent- ing apphances. The first was a Lancashire, with Galloway tubes, and a Kowitzke hollow cast-iron fire bridge. In the second, a Chubb fire bridge, very similar to the last, was used ; and for the third trial, a Stauss apparatus was fitted to the same boiler. The fourth experiment was made on a Cornish boiler, with Galloway tubes and a Kuhn grate ; the fifth on a tubular boiler, with semi-Tenbrink grate. In the sixth trial, a Heine water-tube boiler, fitted with a Schomberg inclined grate, the lower ends of the bars resting in water, was used ; the seventh was on a Lanca- shire boiler, with Donneley grate. All the grates produced about the same quantity of thin grey smoke ; the Tenbrink gave rather less than any of the others. None of the apparatus were con- sidered by the committee as working better than the rest, though the Tenbrink and Donneley were perhaps the most satisfactory. Lewieki's trials. — In the trials made by Pro- fessor Lewicki, twenty-three boilers were tested, mostly hand-fired, with Carlo, Donneley, and other grates, and Helix, Leach, and Schulz- Rdber mechanical stokers. Although the degree of smoke was determined, this was rather a sub- sidiary question, the trials being made chiefly from a calorimetric point of view. A description 186 HEAT EFFICIENCY OF STEAM BOILERS. of nearly all the grates and stokers enumerated will be found in Chapters IV. and V. The Schulz-Ebber is a coking stoker, conveying the coal by means of worm gear from a hopper above on to the dead plate. The Helix sprinkler stoker scatters the coal over the grate, and it is carried slowly forward on travelling bars to the ash-pit. Not much appears to have been published in America with reference to smoke and its abate- ment. Mr D. K. Clark, in his work on the Steam- Engine, goes into the question of the prevention of smoke in great detail, and gives a large number of excellent drawings, and description of various methods of diminishing smoke, in use since the beginning of the century. Several select committees of the House of Commons have been appointed, and their Eeports 1843-45 have been published. Sir W. Fairbairn also reported on the prevention of smoke to the British Associa- tion in 1844. Various papers on the subject have appeared in the Proceedings of the Institu- tion of Civil Engineers and other societies and institutions, and a Parliamentary Eeport was issued in 1855. Note. — While these pages were passing through the press, the Eeport of a valuable series of trials on the prevention of smoke in steam boilers, made by the Municipahty of Paris, was drawn up and privately circulated. The Author succeeded in obtaining a copy of this report, a complete summary of which, with tables giving an abstract of the details of the trials, will be found in Appendix VIII. p. 260. CHAPTER X. Instruments used in Testing Boilers. Sampling and Analysing Gases— Methods of drawing them off— Oisat— Winkler— Bunte— Elliott— Waller— Dasymeter — Measurement of Temperatures— Pyrometers — Ball and Platinum Thermometers— U AVater Gauge — Fuel Calorimeters — Thomson — Berthelot and Mahler — Carpenter — Steam Calorimeters^ — Him— Carpenter's Separating Calorimeter — Superheating Calorimeter — Barrus— Rateau — Peabody's Throttling Calorimeter- Other Instruments. Like all other subjects connected with steam, the art of making boiler trials, and the know- ledge and methods required, have been much improved and perfected during the last twenty years. The principles governing combustion and evaporation are now more carefully studied and better understood than formerly. Ifothing has contributed more to the increased efl&ciency now obtained in steam boilers, than the various chemical and physical instruments, which have been introduced to test the composition and heating value of the coal, analyses of the gases of combustion, etc. It is proposed to give a short account in this chapter of such of these instruments as are generally used. With delicate laboratory appliances, invaluable to a chemist and physicist, but requiring much patient study before they can be successfully manipulated, the author does not intend to deal. His object is to place before practical men and boiler owners a short and simple description of instruments which can and should be employed, daily or weekly, in testing boilers. Nearly all of them he has himself handled and used in the boiler-house, and most young engineers, and even mechanics of ordinary in- telligence, can easily be taught to apply them. For accuracy, these simple methods cannot be compared with the exact tests of scientific men; but to make combustion, in its essential principles, intelligible to boiler owners and steam engineers, is also a matter of great and increasing importance. It is a mistake to suppose that, because scientific determinations cannot be made every day, therefore the progress of combustion and evaporation under a boiler may, as a rule, be left to chance. The diffi- culties in the way of fairly accurate knowledge are no longer insurmountable. Instruments haye not only been multiplied, but much simpli- fied ; and it is more perhaps due to ignorance of the advantages to be realised, than the trouble of using them, that they are so seldom applied. These instruments may be classed under four divisions, namely : — I. Those used in sampling and analysing the gases of combustion. II. Thermometers and other instruments for measur- ing high and low temperatures. III. Fuel calorimeters for determining the heating value of any combustible. IV. Steam calorimeters for ascertaining the percentage of moisture or water in steam. I. Sampling and analysing gases. — The great importance of the process of sampling and ana- lysing the gases of combustion has already been pointed out in the chapter dealing with combus- tion, but it is equally desirable that it should not be confined to the actual period during which a boiler is tested for efficiency. Simple and rapid analyses of the gases should be made from time to time during the ordinary course of a day's work, because they afford the only accurate method of determining the progress of combustion, and the quantity of air entering, whether in excess or otherwise, of that required for the fuel used. 187 188 HEAT EFFICIENCY OF STEAM BOILERS. It is a difficult and troublesome process to measure the quantity of air passing into boiler furnaces by means of anemometers, and the writer has always found it very unsatisfactory. To measure the air going out, or the quantity contained in the flue gases after combustion, and determine from it the amount of air passing through the furnace over and above what is necessary for the combustion of the coal, is a simple and very practical method, although its importance has scarcely yet been realised. Till lately it was confined to the laboratory. The gases were drawn off from the flue into a tube or bottle under mercury, and sent to a chemist to be analysed. The value of immediate, and, if possible, continuous analysis having been at last recognised, instruments simpler, easier to handle, and giving more expeditious results were re- quired, and are now available. The great advantage of this method is, that the gases can be analysed as well as sampled in the boiler- house, and any deficiency or excess in the quantity of air admitted can be at once remedied by an intelligent fireman, as has often been done by the author and his stoker. The analysis of the gases furnishes a check on the performance of a boUer, and explains anomalies. " Since," as Mr Hales says, " the gas analysis shows the owner of a boiler ivhere his losses are, it is a more important part of the boiler test than the analysis of the coal or the determination of its calorific power, which only shows how much his losses are." Sampling. — The first requisite is to sample the gases from the flue, and for this purpose a pipe of metal or other material is inserted, and the gases drawn off by suction. Some metals, when clean, may absorb part of the gases in contact with them. Prpfessor Thurston prefers porcelain or glass tubes, as subject to least deterioration from the heat ; iron tubes, if clean, become oxidised at high temperatures. The author uses iron tubes for the vertical parts, and very small copper tubes, about \ in. diameter, to convey the gases from the flue to the sampling apparatus. As soon as the tubes are a little dirty, the absorption is prac- tically nil. Care must, of course, be taken to obtain a fair average sample of the gases. Some- times the sampKng tube is surrounded by a circulating water-jacket to prevent the pipe melting when used very near the furnace, and also to cool the gases, that the metal may have less efiect on them. The gases are then drawn into a glass bulb over water, or, better, over mercury. If their composition is to be determined at once, and on the spot, they are passed into a glass burette, about I in. diameter and 18 in. long, previously filled with water, which is allowed to run out at the bottom, as the gas is drawn in at the top. If the samples are not to be analysed at the time, it is best to collect the gases over mercury, but the latter is costly and difficult to handle, and water is best for ordinary work. For analysis of boiler gases, some authorities recommend the use of pumps, either steam or water, to draw the gases from the flue. Water pumps are of two kinds, and act either by the fall or the injection of water. In the apparatus described by M. Scheurer-Kestner, a small tube is inserted to a considerable depth into the brick boiler flue, to obtain a representative sample of the gases. Water discharged down another vertical pipe sucks the gases from the flue, and forces them into a bottle filled with mercury, the latter run- ning out below as the gases enter above. Mercury gives, perhaps, more exact results than when the gases are sampled over water, but it is not so handy for practical purposes. Another method is to connect the boiler flue to a bottle of known capacity, half filled with water, covered with a layer of oU. As the water is slowly run out from a cock, the level of oU in the bottle is reduced, and the gases drawn in. Sometimes a steam jet is used, the force of the steam carrying the air along, and inducing a current of gases behind it. The author often employs a simpler method, which he has found very useful for sampling the gases continuously, namely, the Waller system (see fig. 71). A closed brass vessel, about 1 foot in diameter and 3 feet high, with a cock at the bottom, is connected at the top with a small copper pipe from the flue. The vessel is filled quite full of water, saturated with COj, and has a glass gauge at the side, indicating the water level. The apparatus and pipe having previously been tested for leakage, the water is allowed to trickle out from a cock in the bottom of the vessel, and thus gas is drawn in from the flue by suction to take its place. A disadvantage of this and of any method of sampling over water is, that the water is liable to absorb the GOj. To SAMPLING AND ANALYSING GASES. 189 prevent this, it is either previously saturated ■with GO2 or salt, or a thin layer of oil or glycerine spread over the top. As the same water is used over and over again, it becomes, after a short time so impregnated with COg that it will not take up any more. The same arrangement is used if only a small sample is needed to fill a burette. Special care must be taken that no air is drawn in with the gases from the joints in the pipes, or penetrates into the samphng tube, else the results of the analysis will be vitiated. The best plan is to exhaust all the air from the pipes and sampling apparatus before making an analysis, and fill them with flue gases for some time previously. If the brass vessel is used, this is easUy done by first fiUing the vessel with water and running it all out ; the water draws the gas after it. Hempel recommends the same simple method for drawing off the gases. A kind of siphon may also be arranged with bottles connected by tubes, one of which is filled with water. When the other bottle, which is nearly empty, is lowered, a current of air is induced from the flues. As the composition of the gases varies from hour to hour, samples should be taken continuously, and the average analysed, say, every half hour. If the coal is very smoky, the gases may sometimes be filtered. Analysing. — -Whatever the method em- ployed, it is an invaluable help, when making an experiment, to be able to find out the percentage of COj and for a known condition of fires on the grates. The operation can easily be performed in a quarter of an hour or twenty minutes. If the analysis shows too much 0, the grates should be at once better covered, and the entrance of air checked, or the grate area may be reduced by adding a row or two of fire-bricks at the back of the bars. The gases can be analysed with the damper more or less open, with thin or thick fires, with different fuels and grate bars, etc., and useful information may be thus obtained as to the most economical combustion for the particular fuel, grate, and draught used. The principles upon which the analysis of the flue gases are based are the same, although the methods of sampling them may differ. Gases given off after combustion consist in varying proportions of COg, and free oxygen, that is, the oxygen which has passed through the furnace and combustion chamber with the excess of air, without combining with the carbon in the coal, or has leaked in through the brick- work. There is also a certain quantity, which should be a minimum, of CO ; the residuum is chiefly nitrogen. When about 5% of oxygen by volume is obtained at the end of the boiler flue, about 15% of COj, Fig. 71. — Waller's Gas Sampling and Analysing Apparatus. and very little or no CO, it is a proof of good combustion. Three chemical compounds or re- agents are successively used, which respectively absorb the COj, the 0, and the CO : the balance, after absorption has taken place, gives the nitrogen. The usual plan is to pass the flue gases, by one of the methods already described, into a glass burette of 100 cubic centimetres capacity, with a scale marked in centimetres. Thus the volumes shown in the burette give the 190 HEAT EFFICIENCY OF STEAM BOILERS. percentages of the total gas sampled without any calculation. The reagents employed are potas- sium hydrate for absorbing the COo, potassium pyrogallic for the 0, and cuprous chloride for absorption of the CO. All these can be pur- chased in England of the wholesale chemists. The gases are always treated in the above order, otherwise the several reagents absorb not only the gas on which they ought to act, but also one of the others. The three glass vessels used for absorption vary somewhat in shape. The gases may be collected over water, mercury, or glycerine, but water being the simplest is often used in boiler trials. Orsat. — The Orsat is perhaps the best known apparatus on the Continent for sampling and analysing gases, and the author has often seen it used. It is inclosed in a portable case, and consists of three small glass pipettes or bottles containing the three reagents, namely, caustic potash, pyrogallic acid, and cuprous chloride. Each pipette is connected by a separate tube to a water-jacketed glass burette containing the gas to be analysed. At the side of this collect- ing burette is a bottle connected by rubber tubing, which is raised or lowered by hand, to adjust the level of water, gases, or reagents in the burette and pipettes. The water is slightly acidulated with hydrocliloric acid to prevent absorption of the COj. To make a determination, the air is first drawn out of all the pipes by a little bellows, the levelling bottle is lowered, and the water in it passed over into the burette. A cock at the top is then opened, the levelling bottle carefully raised, and the water passes back into it, being replaced by the gases to be analysed, until they occupy exactly 100 cubic centimetres. By manipulating the levelling bottle, the gases are then forced once or twice into the first pipette to absorb the COg, and back into the burette, after absorption has taken place. The difference in the level of the gas in the burette is then read off, and the loss of volume marks the percentage of COg in the original quantity. The same method is repeated for the absorption of the and of the CO. The gases are generally passed once or twice into each pipette to insure complete absorption, and four or five times when testing for oxygen. The temperature of the room where the apparatus is fixed should be kept fairly constant during an analysis of the gases. Winkler. — The Winkler apparatus is also sometimes used to analyse the gases of combustion. It consists of two vertical glass burettes connected by a tube at the bottom, the one containing the fluid reagent, the other the gas to be analysed. By placing the burettes horizontally, the reagent is allowed to pass from one to the other, and can be well shaken. After a few minutes, to give time for absorption, the burettes are again placed perpendicularly, and the level read off. The increase in volume of the fluid agent shows the percentage of gas absorbed. To analyse for COg, O, and CO, three sets of burettes are used. Bunte. — The Bunte apparatus is an improve- ment on the Winkler. A single glass burette marked to scale is used, terminating at the bottom in a fine tip, and with a cup receiver at the top. It is connected by rubber tubing to a " suction " bottle filled with water. The water is first run into the burette, the gas then drawn in by means of the levelling bottle, and its volume exactly determined by draining water from the cup through the burette. The reagent is then introduced through the tip at the bottom of the burette, the whole well shaken, and, when a diminution in volume is no longer shown, absorption is complete, and the rest of the reagent is washed out with distilled water. Before introducing the cuprous chloride to test for CO, both the two previous reagents must be well washed out. The readings are taken under water, and at the same temperature, and the pressure is practically the same. Each analysis takes about twenty-five minutes. Elliott. — Another gas sampling and analysing apparatus is the "Elliott," used in America. There are two glass burettes, each connected to a separate levelHng bottle, one of them carrying a glass cup on the top. To analyse the gases, they are passed from one burette into the other below the cup, by manipulating the levelling bottles. The cup is then filled with the reagent, which passes into the tube as water is drawn off from the bottom. After allowing sufficieiit time for complete absorption, the gases are passed back into the second burette, and their volume read off; the difference shows the quantity of gas absorbed by the reagent. This apparatus, with mercury, was improved by Mr Wilson, and used by him in the Society of Arts, and many other trials. A drawing of Mr Wilson's appa- GAS SAMPLING AND ANALYSING APPARATUS. 191 ratus is given in the Journal of the Society of Arts, February 15, 1889. The various instruments described above are used to obtain an analysis by volume of the CO2, O, and CO gases. Gravimetric analysis, or sampling the gases by weight, is seldom done, but the volumetric method is open to the objec- tion that it shows only the volume of the actual gas tested, and not that of the other gases, such as sulphur, hydrocarbons, etc. Two instruments have lately been brought out in Germany which give the percentage volume of COg only, by readings on a scale. Some authorities are of opinion that, from the COj, the composition of the exit gases and the percentage of frep oxygen they contain can be deduced with sufficient accuracy for general use. Professor Unwin con- siders that .even the analysis of the gases may not always afford reliable indications of the quantity of air supplied to a boiler, on which its efficiency greatly depends. As the percentage of CO2 varies greatly in very short periods of time, constant readings, even if only approximate, are an excellent guide to the stoker, to check the waste of heat by varying the supply of air to the grate. Hence the value of the " Dasy- meter," invented by MM. Diirr and Siegert. It is based on the principle, usually though not always correct, that the flue gases consist chiefly of COo, 0, and N, the CO being a negligible quantity ; and further, that the difference in weight for the same volume of CO^ and of at- mospheric air can be utilised to indicate the percentage of COj in any given flue gas. Thus, if air be taken as the zero of a scale, the amount of CO2 wUl be shown and read above zero. " Dasymeter." — The instrument consists of an air-tight glass receiver, containing a delicately adjusted scale, carrying on one side a compen- sator, or apparatus to counterbalance the fluctua- tions in barometric pressure and in the tem- perature of the flue gases. On the other side of the scale is a glass globe filled with air, and having a pointer abtached to it, moving along a scale. The pointer is adjusted to read zero when the receiver is filled with pure air. The instru- ment is then connected to the boiler flue by a small pipe, and the gases drawn into it through a filter by an injector. As COg is much heavier than air, the glass globe sinks according to the density of the gases, the pointer shows the ex- tent of the fall, and thus the percentage of CO2 may be read off the scale. The apparatus can be connected to different parts of the boiler flues. It affords a rapid means of estimating the per- centage volume of COg ; and although it has not the accuracy of a chemical determination, it possesses the great advantage of being easily read by the stoker at a glance, and supplying him with a valuable approximate indication of the efficiency of combustion. It should be checked from time to time by the Orsat or other method of analysis. Econometer. — The " Econometer," designed by Herr Arndt, is similar in principle to the dasy- meter, and differs only in the method of taking the weight of the gases. A beam balance carries at one end a small globe or gas-holder with glass sides, through which the gases from the furnace are passed, and at the other end a weight. A finger between them moves to and fro on a scale, and marks the weight of the gas. The apparatus is inclosed in an air-tight chamber, iu which a partial vacuum is formed. The tube conveying the gases is connected tO' the boiler flue, and passes up the centre of the holder. M. Soheurer-Kestner describes a similar apparatus designed by Herr Schumacher. Much depends on the place where the samples of gases are taken. Mr Hale considers that they should be collected and their temperature taken at the same place in the flues, and as soon as possible after they leave the boiler. Before analysing the gases, all the cracks in the brick- work setting, flue doors, etc., should be carefully stopped, and all places closed where air can get in. A good place to sample the gases is after the first run, at the end of the furnace tube. They should also be taken at the boiler side of the damper. At these two places the percen- tages of and of COj will generally be found to differ. Near the damper the volume of COg is usually smaller, and of oxygen greater, because the gases on their way through the flues are diluted with air filtering in through the brick- work, holes of the doors, etc. On the ques- tion of the supply of air to a boiler, Pro- fessor Unwin has some excellent remarks, so- greatly to the point that the author may be pardoned for quoting them : — " The air supply is the one controllable factor in the working of a boiler furnace, and we have trusted far too long to the practical experience of boilermakers, and the common-sense of stokers, to regulate 192 HEAT EFFICIENCY OF STEAM BOILERS. this important factor in boiler management. We do not trust the common-sense of the stoker to regulate the boiler pressure or the water level ; and it is equally necessary, if economy is to be obtained, that he should be supplied with some means of ascertaining definitely whether his management of the fire is good or bad. I believe that in good and large installations, at least, it will come to be considered as necessary to have an instrument of the dasymeter type as to have a pressure gauge, and this, I think, may be re- regarded as a gift of science to the practical engineer." II. Measurement of temperatures. — We pass next to a consideration of the instruments used to determine the temperatures of combustion, gases, etc., in a boiler. Nearly all the scientific authorities have different systems. M. Scheurer- Kestner describes an ingenious and very sensitive Httle instrument, called a metastatic thermometer, in which the mercury is allowed to run out, and the zero itself is shifted, as the temperature rises. For ordinary gas temperatures the author uses special glass mercurial thermometers, 2 or 3 feet long, and ^ in. diameter, with nitrogen gas under pressure at the top of the mercury. The thermometers are protected by brass tubes. They wUl give temperatures up to, say, 800° to 1000° F., and can be put through a hole in any part of a boiler flue not too near the fire. The following simple and fairly efiicacious means of measuring higher temperatures approximately has also often been employed by the author. Five small pieces of metal, of different alloys of zinc, lead, tin, etc., fusible at from 400° to 800° F., are strung on a steel wire, and suspended in the middle of the boiler flue. The melting point of each alloy being known and stamped on it, the fusion of any one or more of them affords an approximate estimate of the maximum tempera- ture. With these metals there is nothing to break, as with mercurial thermometers, they are handy and portable, and can be left in the furnace for a week, and the highest temperatures reached may be thus ascertained. Pyrometers. — For determining temperatures, recourse is also sometimes had to some form of pyrometer, but they are not very rehable, and often go wrong and get out of order. One of the best known is the Le Chateher electrical thermometer. It consists of two thermo-electric wires, inclosed in fire clay to within 4 in. of their junction. They are connected to a very sensitive galvanometer, the deflections of which are marked by a needle on a graduated scale. The zero of the scale corresponds to the junction of the wires at the temperature of the atmosphere. The deflections of the galvanometer, when affected by heat, are determined by plunging the wires -into baths of boiling sulphur, naphthaline, and other substances, to standardise the instrument. It is usual to plot the readings on a curve, the temperatures being given as ordinates, and the readings of the galvanometer as abscissae. The hotter the wires at their junction in the flues, the greater the current, and the more the galvano- meter needle is affected. This instrument may be connected to a boiler flue, but it is delicate and costly, and the galvanometer readings in a dirty boiler-house may differ from those given in a laboratory. Sir A. Durston, Chief Engineer of the British Navy, in his interesting experiments on the temperatures of boiler plates, published by the Institution of Naval Architects, made use of Le Ch^teUer's thermo-electric thermometer. In a marine boiler having smoke tubes 2| inches diameter and 6 feet 8 in. long, he obtained the temperatures of the gases as they passed along the centre of the tubes for each foot in length (see page 153). Ball thermometers. — Another method of measuring temperatures, of which there are several varieties, is the platinum or ball ther- mometer. Mr Hoadley, in his experiments, used a couple of fire-brick crucibles, each containing a platinum ball /^ to ^^ of a lb. in weight, placed in the glowing fire. After a sufficient time the crucibles were removed, and the balls dropped into a well-protected brass calorimetric vessel, filled with a known quantity of water. The calorimeter was then closed, an agitator and a thermometer were passed through the centre of the cover, the water was stirred, and its rise in temperature, due to the heat of the balls, noted. The actual temperatures are usually taken from a table, or calculated. An alloy of equal weights of platinum and iron was found to give results almost as good as pure platinum, at a much lower cost. This method of taking high furnace temperatures with balls plunged in the hot gases from the fire was also used by Dr Slaby in his experiments on gas engines. He exposed a small iron ball to the full stream of the exhaust ANEMOMETERS AND U-GAUGES. 193 gases for half-an-hour ; the ball was then dropped directly into a water calorimeter placed below it. For accuracy, everything with this apparatus depends on rapid manipulation, to get the ball into the water with as little loss of heat as possible. Whatever the method employed, it should be done almost instantaneously, and, according to Dr Slaby, the readings of the ther- mometer should be taken every second. To remove the ball from the furnace and plunge it into the water should be the work of four or five seconds, otherwise it is necessary to allow for loss of heat. Mr Blechynden, in his experiments on the transmission of heat through steel plates, used the hot-ball method for determining the temper- ature of the furnaces. The balls were of copper and iron, and were plunged into a known weight of water. M. Hirsch employed the melting point of metals for obtaining the approximate temperatures of boiler plates. For taking moderate temperatures beyond the furnace, platinum or iron balls are sometimes suspended in the flues. The author has made use of them, but considers electrical thermometers better. Platinum resistance thermometers are also applicable. They indicate the variations in temperature by the electrical resistance of a platinum wire, and are accurate, but delicate to handle. There are several forms of this type of electrical thermometer, the best known of which is the Callender. The instrument used by Professor Burstall with naked wires is a modi- fication. The principle in both is the same, namely, to measure the variations in tempera- ture by the corresponding fluctuations in the electrical resistance of the wire. Anemometers. — The quantity of air entering a boiler furnace is sometimes shown by an ane- mometer, but this instrument does not give results as correct as the method of calculating the air from the percentage of or CO^ in the gases passing out. The error of anemometers must be allowed for. The air, as it comes in, is measured through a pipe of given section, but this shows only the quantity of air admitted in the regular way to the grate, not that filtering in through cracks in the brick-work, etc. U- water-gauge. — A U- water-gauge is a cheap and simple little instrument, often used to indicate the amount of vacuum in a chimney, or •any part of a boiler flue. It consists of a small tube of glass, about | in. diameter, bent into the shape of the letter U, each leg being about 3 in. or 4 in. long. It is attached to a piece of wood, and half filled with water. One end is left open, and the other connected by a rubber pipe to the base of the chimnej'. A f in. hole is made in the brick-work, a small ^ in. gas pipe inserted, the joint made good with cement, and the rubber pipe connected. The vacuum in the chimney raises the water in one leg, and it falls in the other. It is the difl'erence of level between the two water lines in the two legs that measures the vacuum or draught in the chimney or flues. In the Table of results, all draughts are taken with this kind of instrument, of which fig. 72 shows one form. Fig. 72.— U-Water-Gauge. III. Fuel calorimeters. — The third branch of our subject comprises fuel calorimeters, for determining the heating value of any coal or fuel. Two principal methods are used, namely, by calculation from the analysis of the chemical constituents in the fuel, or by burning a very small quantity of fuel with oxygen in a vessel or bomb under water, and determining its heating value, or amount of heat generated, from the rise in temperature of a given weight of water. Neither of these processes can be carried out in a boiler-house, and it is usual, in making an experiment, to take a sample of the coal, and N 194 HEAT EFFICIENCY OF STEAM BOILERS. test it after the trial, either chemically or in a calorimeter. The chemical process of determining the com- position of coal requires delicate manipulation, and is expensive, as it takes two or three days ; it is always done in a laboratory. Great care is necessary to obtain a good representative sample. Supposing 2 or 3 tons of coal are burnt during an eight or ten hours' test, the first question to be considered is the best way of sampling a certain portion, so that it shall really represent the average quality of the coal. If this is care- lessly done, it will affect the boiler efficiency, by making it higher or lower than it ought to be. The usual way is to take a lb. or two of coal from different parts of each sack, so as to have, say, nearly 100 Ibsi. at the end of the day. The quantity thus obtained should be well mixed, laid out on a clean floor, and divided into four parts. One of these fourths should again be well mixed and spread out, and the process con- tinued till the whole is reduced to about 2 or 3 lbs. If properly and carefully done, this final amount may be taken to represent an average sample for estimating the heating value of the coal. It should be labelled and put away in a glass-stoppered bottle if it has to be kept for a few days, after which it is tested in the calori- meter. As a rule, sampling is carelessly done, and the quantities of- coal taken are too small. A httle machine for sampKng coal in the same way as ore has lately been introduced. To obtain the percentage of moisture in any coal or fuel, 50 or 60 lbs. should be weighed, placed on the top of the boiler or some other warm spot to dry, and again weighed. The difference shows the amount of moisture dried out. In Germany it is usual to take the coal as air-dried, that is, exposed to the air for a few days after coming from the pit. No elaborate methods are required to determine the calorific value of coal in a calorimeter. The process occupies only about J to f of an hour, and any one of average skill can be taught to apply it in a short time. When carefully done with a good instrument, it is as accurate in its results as the method by chemical analysis, and has also certain advantages of its own. The two processes should agree witliin 2% or 3%. The calorific value of a given weight of coal is the number of thermal units imparted to a given weight of water by its complete combustion. When coal is tested in a calorimeter, this heat is directly communicated by transmission to the water, the process being similar to that of the evaporation of water in a boiler, though on a very much smaller scale. The calorific values of about 400 varieties of fuel, English, German, French, and American, will be found in the Tables. Calorimeters have been used for nearly half a century, but it is only within the last twenty years that they have been sold at moderate prices, and much employed for testing coal under a boiler. The principle of all modern fuel calori- meters is more or less the same. The fuel is- burnt with oxygen in a closed vessel or bomb under water. The rise in temperature of the water, due to the heat developed by combustion, is noted, and read off on thermometers. Allow- ance is made for the heat absorbed by the instru- ment, which is generally previously determined, and represented by a coefficient. The Favre and Silbermann was long the chief instrument, but has now been generally superseded, except for laboratory work. The Berthelot-Mahler bomb calorimeter and Professor Thomson's apparatus may, at the present time, be considered the two representative types in England and on the Continent, and in America the Barrus and Carpenter. Professor Thomson's calorimeter. — In the Lewis Thompson calorimeter, now no longer used, the fuel to be tested was burnt with a powdered oxygen mixture. A great improve- ment was effected by Professor Thomson, who substituted oxygen gas for powdered oxygen, to obtain combustion. His instrument consists of a glass diving-bell with a cover, through which a brass tube is passed. The diving-bell is placed in a glass vessel containing a known weight of water, and carries a small platinum crucible,, resting upon a support attached to the per- forated base plate. The brass tube is connected by india-rubber tubing to a holder containing oxygen. Two thermometers are inserted in the cover, one for taking the temperature of the surrounding air, the other that of the water. To make a determination, 2 grammes of powdered' fuel are placed on the crucible, and introduced into the diving-bell. The outer glass vessel is filled with 2000 grammes of water, and com- pressed oxygen admitted into the bell. The- sample of coal is then fired by a fuse, the pro- BERTHELOT-MAHLER FUEL CALORIMETER. 195 ducts of combustion escape downwards through the perforated base plate, and pass through the water. The bubbles of gas are broken up by wire gauze as they rise. The oxygen impinging upon the glowing fuel produces "good combustion, and, as all the vessels are of glass, the process is visible the whole time. Berthelot and Mahler. — The calorimeter de- signed by M. Berthelot, and improved and simplified by M. Mahler, is used both here and on the Continent, and is perhaps the best instrument at present in the market, but expensive. The combustible is placed in a strong bomb, oxygen is introduced under pressure, the bomb hermeti- cally closed, and the coal fired. The whole of the heat generated is transmitted to the water contained in an external shell surrounding the bomb, and protected by another outermost vessel, to reduce radiation. Combustion is almost in- stantaneous, and with proper precautions no heat is lost by radiation, or by imperfect com- bination of the oxygen with the carbon. The coal is fired electrically, a method adopted in all modern fuel calorimeters. Thermometers are placed in the water, and there is an agitator to stir it up and diffuse the heat. The bomb is of steel with platinum lining, and the fuel is deposited on a small platinum capsule. This metal makes the Berthelot calorimeter very expensive. To reduce its cost, M. Mahler has devised a cheaper instrument, in which the bomb is of soft steel, nickelled externally, and Hned inside with enamel. It is also much larger than the Berthelot bomb, but similar in other respects. The enamel lining is much cheaper than platinum, but it is apt to scale off, and the steel, being exposed, rusts. In bbth instruments commercial oxygen is used, com- pressed to 25 atmospheres ; the tube containing it is connected by a metal pipe to the bomb. The heating value of coal has also been care- fully and closely studied by M. Mahler, who, in his valuable work. Contributions a I'Mude des Combustibles (Paris, Baudry et Cie, 1893), gives the heating value, as determined by his calori- meter, of more than fifty fuels. He has examined American, French, Belgian,, English, and Tonkin coal, besides wood, peat, and other fuels, and gives in his book a graphic representation of the relation between the heating value and the com- position of various combustibles. The author has designed and uses a modified calorimeter of the Berthelot type, fired by electricity, and burning the fuel under com- pressed oxygen. (See fig. 73.) The bomb is made of a special metal, as strong as steel, gdt inside and non-corrosive, and is adapted to burn exactly one gramme of fuel, coal, or oil. It contains a small platinum crucible, and is sur- rounded by an outer water-jacketed chamber, with three thermometers. Two agitators driven by wheels carrying small paddles are rotated in opposite directions by hand. Before making a determination, the calorimetric vessel is filled with water, carefully agitated, and its tempera- ture taken continuously for several miautes. To avoid correction for radiation, the tempera- ture of the water at starting should be lower Fig. 73. — Fuel Calorimeter. than the temperature of the room by half the expected rise in temperature. The bomb is then fiUed with compressed oxygen, the cover bolted on, and the dried and powdered fuel in the crucible fired electrically from a small battery. For about ten minutes the water is continuously stirred by the agitators, and its temperature again taken. At the end of that time, combus- tion being complete, and the gases having parted with their heat, the bomb is washed out with water, and the heat value calculated, allowance being made for the heat lost by radiation. As the experiment lasts ten or twelve minutes, the gases generated in the closed bomb have time to give up all their heat. 196 HEAT EFFICIENCY OF STEAM BOILEES. Carpenter. — Another fuel calorimeter, designed by Professor Carpenter, is used in the Sibley College laboratories, U.S. In it, as in those already described, the fuel to be tested is burnt in an air-tight chamber under water, with oxygen at a pressure of 2 to 5 lbs. per square in. The products of combustion are led through a spiral coil, immersed like the combustion chamber in a larger vessel full of water. The products pass up the coil to the top of the vessel, and are then led downwards and dis- charged below. The rise in temperature of the water, and thus the heating value of the coal, are noted by the increase in pressure of the water as it rises up the stem of a glass tube at the top of the instrument. The charge of coal is fired electrically. In the Barrus calorimeter the fuel is fired in a small bomb placed inside a vessel fiUed with water, to which the heat generated by combustion is imparted. The bottom of the platinum crucible containing the sample of coal is perforated with holes, through which the products of combustion escape, and bubble up- wards through the water to the open top of the vessel, where they are discharged. Thus the heat of combustion is said to be immediately transmitted to the water. IV. Steam calorimeters.— The fourth class of instruments for boiler trials are steam calori- meters, or apparatus for determining the amount of moisture in steam. These are quite distinct from fuel calorimeters. It is often important to know the quality of the steam, and especially during a boiler and engine trial, but it has hitherto been a difficult process, requiring dehcate manipulation, and no satisfactory instrument for the purpose has appeared till quite recently. Professor Peabody's throttling calorimeter, which the author has lately had the opportunity of seeing at work in America, seems to be one of the best and most easily applied, and one or two other American instruments are very ingenious. The subject has been more studied in America than elsewhere, and drawings and descriptions of many apparatus will be found in the Trans- actions of the American Society of Mecli. Engineers for the last few years. Hirn. — The earliest forms of steam calorimeters may be divided into two kinds — those in which the steam was separated from the water, and those where no separation took place. Both Hirn in Alsace and Joule were among the first to suggest that the steam from a boiler should be tested for moisture. The Hirn calorimeter was formed simply of an iron vessel containing water, into which the steam from a boiler was led and condensed. The water was then thoroughly mixed, its temperature taken with a thermometer, and the amount of steam condensed was weighed. Its temperature and weight were determined, and, when compared with the heat of an equal amount of dry steam, gave approximately the moisture in the steam. Another kind of in- strument, called the "barrel calorimeter," was used by Joule. It consisted of a barrel filled with water, the weight and temperature of which were noted. It was then connected to the boiler, steam was led to the bottom of the water, and condensed until the temperature had risen to about 110° F. The steam valve was shut off, the water stirred, and the temperature and weight again taken ; the proportion of moisture was obtained by calculation. Carpenter's separating calorimeter. — In later steam calorimeters the moisture is deter- mined by separating the water from the steam, superheating the steam, or condensing it con- tinuously. In the separating calorimeter, intro- duced by Professor Carpenter, the boiler steam is taken from the supply pipe, and led into a circular vessel with two concentric divisions, the outer forming a jacket round the inner. As the steam enters through small holes it strikes against the sides of the inner vessel, and the action separates the water from the steam. The latter passes into the outer jacket, and through a very small orifice of known diameter to a condenser below, the water is collected in the inner vessel, and its amount measured by means of a glass water gauge at the side. Sometimes, instead of condensing the steam, the quantity is calculated from the diameter of the orifice and the pressure, but the condenser gives more accurate results. This is a simple and efficient instrument, though it is hardly a calorimeter. In the continuous condensing calorimeter, the steam from the boiler is injected into a small tank, and condensed by mixing with water drawn from another tank. The temperatures of both are taken, and the increase in weight in the condensing tank, less the diminution in weight of water in the supply tank, givesthe weight of steam condensed. In another form of the same instrument used by Mr Barrus, the steam is led into a vessel, through STEAM CALORIMETERS. 19'7 which, a known weight of condensing water circulates continuously. The temperatures of the water in and out and of the steam are taken, allowance made for radiation, and the amount of water in the steam thus calculated. A similar method was used by Mr Hoadley. In these methods of testing steam, its total heat, after condensing and weighing, is compared with the total heat of an equal weight of dry saturated steam. The difference gives the amount of water in the steam. Superheating calorimeter. — Another way of determining the moisture in saturated steam is by the application of superheated steam. The steam to be tested is passed from the boiler throiigh a chamber or heater, jacketed with superheated steam. Heat is withdrawn from the latter to evaporate the moisture contained in the boiler steam, the temperature of which, in and out of the heater, and of the superheated steam before and after it has passed through the jacket, are taken. From these and from the pressures the moisture in the steam is determined. This method demands great care in reading delicate thermometers. Barrus. — In the Barrus wire drawing calori- meter, the steam to be tested is led from the boiler into a separator or drainer, where the bulk of the water it contains is deposited, and drawn off through a pipe at the bottom; its level in the separator should always be the same. The rest of the steam, containing an amount of moisture not exceeding 2% or 3%, is led through an orifice -J of an inch in diameter, and discharged to the atmosphere, or to a condenser, and the water weighed. The pressure and temperature of the steam, before and after passing the orifice, are noted, and the percentage of moisture calcu- lated. In this instrument the separating and superheating tests are combined, as the wire drawing, superheats the steam, and it is one of the best yet produced. Mr Cummins of New- castle proposes to test the steam by admitting it into a number of small horizontal tubes in a jacketed cylindrical vessel, and filling the jacket with superheated steam. The connection between it and the inner cylinder is then cut off, and the rise in pressure of the steam in both carefully noted. As long as the steam contains any moisture, the heat supphed by the jacket will be expended in evaporating it, and the temperature and pressure will rise regularly. As soon as all the water is evaporated, the steam will become superheated, and will not increase, so rapidly in pressure. Bateau. — Asteamcalorimeter, ontheprinciples of the throttling calorimeter, has lately been intro- duced by M. Eateau, and described by him, with drawings, in the Annales des Mines, April 1897. M. Eateau starts with the fact that the heat of vaporisation is always relatively high, and much heat must therefore be added to steam to evaporate the water contained in it. If this quantity of heat be measured, it will give very nearly the proportion of water in the steam. In his apparatus, M. Eateau adds the heat from an external source. The pipe drawing off the steam from the boiler has two branches, of exactly the same diameter, both commimicating with a small vessel below. Through one the saturated steam passes direct to the vessel, the other branch is bent in the shape of a U over a small furnace to superheat the steam, which then passes to the vessel, where both kinds of steam are thoroughly mixed. The temperature of the superheated steam is taken before it enters, and also in the vessel after its mixture with the saturated steam. The difference gives, by calculation, the percentage of water in the steam. The pressure in the boiler is maintained constant, and the pressure of steam in the vessel is taken with a pressure' gauge. M. Eateau has for some months made numerous experiments with this apparatus, and it seems to give correct results, but the pipes require to be carefully covered to prevent radiation, and the steam thoroughly mixed. Peabody's throttling calorimeter. — One of the simplest and most rehable, and perhaps the best American instrument which has yet appeared, in which the pruning in the steam can be cal- culated by a formula, is Professor Peabody's throttling calorimeter. It is based on the principle that " steam which contains a moderate amount of moisture will become superheated if the pressure is reduced by throttling, without loss of heat." A small pipe is introduced into the main steam-supply, and an endeavour made to obtain an average sample of boiler steam, always a difficult matter, and one depending on the particular method adopted of drawing off the steam. This pipe leads through a small conical hole or nozzle, \ in. diameter, into the ' calorimetric vessel, which is carefuUy protected 198 HEAT EFFICIENCY OF STEAM BOILERS. from radiation by felt and asbestos. At the bottom of the calorimeter is a f in. outlet pipe, the valve of which is kept wide open during the experiment. Good delicate pressure gauges Fig. 74. — Peabody's Throttling Steam Calorimeter. should be fixed both on the pipe connecting to the main supply and in the calorimeter (see fig. 74), and the latter also carries a thermometer, as shown. To make a determination, the instru- ment is first brought to a uniform heat by open- ing both valves, below and above. Steam is PEABODY STEAM OALOEIMETER. 199 then allowed to flow tlirougli the nozzle or hole into the calorimeter. The pressure of the holier steam hefore entering, the reduced, pressure of the steam in the calorimeter, and its temperature are noted. The reduced pressure of steam in the instrument being known, the temperature it should have at that pressure is found from the Tables of saturated steam, and compared with the temperature of superheat in the calorimeter, as shown by the thermometer. The pri min g in the steam is then calculated from the following data and formulae, tabulated by Professor Pea- body and Mr Hall: — X = r + q = total heat of one pound of steam, or the amount of heat required to convert one pound of water of the temperature of 32° F. into steam of a given pressure. T = \ q = heat of vaporisation, or the amount of heat required to convert one pound of water of the temperature of steam of a given pressure into steam of this pressure. q = A. - r = heat of the liquid, or the amount of heat, reckoned from 32° F. , contained in one pound of water of a given temperature. \i = total heat of one pound of steam corre- sponding to pressure as shown by gauge on the calorimeter. p = pressure of steam, by gauge, in the main steam pipe. Pc = pressure of steam, by gauge, in the calori- meter. t„ = temperature corresponding to the pressure of steam in the calorimeter, as found from the steam tables. ts = temperature of steam in the calorimeter, as found from the thermometer. X = weight of dry steam contained in one pound of the mixture of steam and water drawn from the main steam pipe. CP = 0'4808 = the specific heat of superheated steam at constant pressure, or the heat required to raise one pound of super- heated steam, under constant pressure, 1° F. in temperature. ts — tc = the amount the steam, of pressure pc, in the calorimeter is superheated. The amount of heat contained in one pound of steam in the calorimeter is therefore Ac -I- cp (ts - tc). The heat in one pound of the mixture of steam and water drawn from the main steam pipe is rx + q. Assuming that no heat is lost, but that all the heat generated in throttling or wire-drawing is expended in evaporating the water in the mixture from the main steam pipe, then xr -t- q = Ac + CP (ts - tc) X = Ac -F CP (ts - tc) - q r and the moisture or priming will be — 1 - X = 1 - Ac + cP (ts - tc) - q Example from Thermodynamics of the Steam Engine, etc., by Cecil H. Peabody. Second edition, page 238. Pressure of the atmosphere, . . . 14 'Bibs. Pressure in main steam pipe, by gauge, . 69 "8 „ =p Pressure in the calorimeter, by gauge, . 12'0 ,, = pc Temperature in the calorimeter, . . 268"2° F. = ts Then r and q corresponding to an absolute pressure of 14-8 + 69-8 = 84-6 lbs. will be, r = 8927 : q = 286-3. And tc, A= corresponding to the absolute pressure of 12 -I- 14-8 = 26-8 lbs. will be tc = 243-9 : Ac = 1156-4. Ac Cp ts . _ 1 156-4-1- 0-48 (268-2 tc 243-9) 1 286-3 92-7 = 0-988. Per cent, of priming = (1 - 0-988) x 100 = 1-2. Notes. — Loss from radiation may be reduced to -f^ of 1 per cent, by running a sufficient quantity of steam per hour. For the above size at least 120 lbs. should be used per hour. To know the amount used it is proposed to admit the steam to the calorimeter through rounded orifice of suitable size, the diameter of which is determined with sufficient accuracy from Napier's formula G = J^ F., in which G = weight in lbs. of flow of steam per second, F = area in square inches, and p is the absolute pressure above the orifice, in lbs. per square inch. For these tests above, the orifice should be about 0-2 of an inch in diameter. The pressures in the boiler and calorimeter must remain constant some minutes before and during the test. All gauges should be compared with a mer- cury column, and great attention should be given to the selection of a thermometer, as the position of the zero point of the latter is liable to change. This must be noticed. The calorimeter can be used in tests where the priming is not excessive, in which latter case wire drawing will fail to superheat the steam. The limit for any pressure may be found by making ts = tc or xr -H q = Ac ; that is, assume steam in calorimeter dry and saturated at that limit. Where a condensing engine is used, the limit may be raised by connecting outlet pipe with the condenser. There is also a method, employed in the boiler trials at the Frankfort Exhibition, 1891, of test- ing the quality of the steam by adding salt to the water in the boiler. The author has used it in some boiler tests, but the best authorities agree that the determinations thus made are not reliable. The main difficulty in aU these methods of estimating the moisture in steam is to obtain a really representative sample from the boiler or steam pipes. Professor Unwin's paper, read before the British Association, gives an excellent account of different steam calorimeters, and the author gratefully acknowledges his indebtedness for much valuable information. Reference should also be made to a paper by the same writer :— " On the Determination of the Dryness 200 HEAT EFFICIENCY OF STEAM BOILEES. of Steam," Institution Meah. Engineers, January 1895, and to tlie works of Professors Peabody and Carpenter and Mr Barrus. Other instruments.^ — There are a few other simple instruments which are useful in making boiler tests. Among them may be mentioned a 50 or 100 lbs. can for measuring the feed water exactly. This should be so gauged that the contents weigh, when full, precisely 50 or 100 lbs. without the weight of the can, and at a given temperature. Tanks for measuring the feed water gauged by the can are also necessary, and accurate scales for weighing the coal, ash, clinker, etc. After weighing the coal, say the previous day, it should be put into sacks, all containing the same net weight, say 100 lbs., numbered and labelled, and the labels kept as tallies as the coal is burnt. A little board behind the glass water gauge to boiler, marked in inches and tenths of inches. to show the level of water at the beginning and end of an experiment, is also advisable. Accurate thermometers for taking the temperatures of the feed water, air, etc., are essential. A recording steam pressure gauge is a very handy instrument for registering continuously with ink and paper the pressure of the steam during a day's trial. All log sheets should be drawn up beforehaiid, and handed to each assistant with instructions (see Chapter XIV.). A U-water-gauge must be placed a,t the bottom of the chimney, for determin- ing the vacuum in tenths of inches of water. It is a good plan to have two, — one in the chimney^ and another on the damper side of the boiler, The latter marks the difference in vacuum pro- duced by partly opening the damper. When the damper is fully open, the two readings should asree. CHAPTER XI. Marine and Locomotive Boilers. Greneral Remarks — Stoking — Draught— Economisers — Weir Feed-Water Heater — Evaporators — Howden's Force Draught— Serve Tubes— Retarders— Comparison of Boilers— Internally Fired Scotch Marine— Gunboat Type — Water Tube Boilers — Belleville— Baboook and Wilcox — Mclausse — Normand—Thornycroft— Yarrow- Various Locomotive Boilers for Ships— Locomotive on Railways — Statistics — Trials. A BOOK on boilers, without a few words con- cerning the chief types of Marine and Locomotive Boilers, would be incomplete. Marine engineer- ing is now a subject of great and increasing importance, and special attention has been devoted to it of late years in England and on the Continent. Owing to the peculiar conditions under which they work, marine boilers form more or less a class by themselves. Locomotive boilers yearly increase in number, as railways are multiplied and fresh countries opened up, though the type is seldom varied. These two important classes practically date from about 1820-1830. A few statistics on them will be found at the end of this chapter. Marine boilers may be separated into two divisions, in the same way as land boilers, namely, internally and externally fired, represented respectively by Scotch smoke tube boilers, and water tube boilers ; the latter have tubes from about f in. to 4 in. diameter. With both kinds of firing, stoking is generally by hand, and machine stoking is very seldom used, although it is most desirable, and more necessary at sea than on land. Chimney, forced, or induced draught, both with hot and cold air, are employed with all kinds of boilers at sea, and on rivers and lakes. Feed-water heaters generally take up heat from the exhaust steam, and the smoke or hot gases are seldom utilised for the purpose. Among internally fired marine boilers the two types here treated are, first, rectangular with smoke tubes; and second, Scotch with smoke tubes. Of externally fired boilers, all with water tubes, only modern types are described, as the Belleville, Babcock, Niclausse, Normand, Du Temple, Thornycroft, Yarrow, and others. A short account is also given of Mr Howden's system of heating air for combustion, Weir's feed- water heaters, and Serve tubes with internal ribs, so often used in marine work. General Kemarks. — In all steamers, whether at sea or on lakes and rivers, the surface of the water is often more or less agitated, and the waves impart this motion to the water in the boiler, the level in which is seldom constant. The size, and particularly the weight, of marine boilers is of much greater importance than on land, as all extra weight diminishes the carrying or cargo power of the ship. It is the lesser relative weight, and greater pressure of steam required, that has directed the attention of marine engineers of late years to water tube boilers. Instead of a boiler shell 10 to 18 feet diameter, with smoke tubes, there are in this type only water tubes, 1 in. to 4 in. diameter. Brick- setting is, of course, inadmissible in a ship, where space and weight must be reduced to a mini- mum. In modern steamships the same feed water is used over and over again through a surface condenser, whatever the type of boiler, and sea water, evaporated by means of steam, is used to make up for slight loss by leakage. As the feed water is evaporated into steam in the boiler, and passes through the cylinders giving power, and thence to the surface condenser, to 201 202 HEAT EFFICIENCY OF STEAM BOILERS. be again pumped back and returned to the boiler, a closed cycle is obtained. The lubrication by oil of the internal parts, cylinders, and pistons must be kept within the smallest limits, or, if possible, wholly omitted, as oily deposit is liable to settle over the boiler furnace tubes, or in the small water tubes. The result is, that the transmission of heat is greatly checked, and the iron plates or tubes sometimes become red hot, with great danger to the men and the ship. Filters are often used to prevent oil or grease getting into the boilers. With water-tube boilers, rapid circulation is the most effective means of diminishing deposit or scale, and keeping the tubes clean. In warships as little smoke should be produced as possible, and aU sparks and flames from the funnels avoided. This, though often difficult, is necessary, that the ship may not be conspicuous. StoMng. — Hitherto nearly all marine boilers have been fired by hand, but it is very desirable, on account of the heat in the stoke-hole, that the best types of mechanical stokers should be tried and adopted. A cheaper and smaller coal could then be used, and the number of stokers, and their now exhausting labour, diminished. The chief argument in favour of mechanical stokers is, that the temperature of the stoke-hole would be less, and there need be no doors to open. Firing at sea is very dirty and trying work, and any relief given to the men, with any type of boiler, is desirable. At present the stokers are exposed to great heat, especially in tropical countries, and to much risk in a closed stoke-hole with forced draught, while, in case of accident, they would escape with difficulty. Marine boiler grates are usually of the ordinary horizontal type. Draught. — Artificial draught is now very general in all types of ship boilers, whether for commercial or war purposes. To a certain ex- tent, the particular fuel used afl'ects the amount of draught. li; is generally produced by large fans, driven by small direct acting steam engines. The first application of a fan for accelerated combustion on a steamship appears to have been made by Mr Stevens, in New Jersey, in 1827, and it was used by Ericsson on a steamer in 1828. Artificial draught is of three kinds, namely : — (1) force blast delivered into a closed stoke-hole; (2) force draught sent under the grates, with closed ash-pits ; and (3) induced draught, the fan drawing the hot gases through the boiler up the chimney. In both the two first, the air is forced under the boiler grate at a certain pressure, 1 in., 2 in., 3 in., or 4 in. With artificial draught the funnel may be shorter than with natural draught, and this is one reason for its adoption in warships. The air required for combustion can also be heated by the waste gases. Water tubes of smaller diameter may be used with induced draught, and, the velocity of the gases being greater, more steam is evaporated with the same heating surface. In fact, the chief object of mechanical draught is to evapo- rate more water, and to produce more steam per unit of heating surface. Care should be taken that the gases are not led off before they have been well divided over all the heating surfaces, or loss of heat will be the result. In the British Navy 2 inches air pressure is allowed, but it is often much higher on other ships. Economisers, or feed- water heaters, are some- times used on steamships, and are likely to be more applied in the future, as they effect a con- siderable saving of heat. They take this avail- able heat either out of the chimney gases, or out of the steam, and transfer it to the feed water, raising it in temperature. Sometimes the water is heated by circulating it, before it is pumped into the boiler, over surfaces of sufficiently large extent, heated by the exit gases from the boiler, or by steam from the engine. In the latter case the steam is often taken from the exhaust of the intermediate or low-pressure cylinders, but it may be drawn from any cylinder, or from the exhaust of the auxiliary engines. The higher the tem- perature of this steam, and the greater its pressure, the more efficiently does it heat the feed water. This is done in two ways — either by passing the feed water on one side of a nest of tubes, and the steam on the other, or by mix- ing the water and steam together. The latter method, introduced by Messrs Weir, gives an important economy of heat. Instead of heating the feed water indirectly by steam, the two are brought into immediate contact by mixing, them. Thus the excess of temperature of the steam over that of the feed water is directly communicated to it. Messrs Weir, who have studied the sub- ject, have also proved by experiment that, to avoid boiler corrosion, air should not be allowed to enter vrith the feed water, because it often contains corrosive acids. Special small pumps, WEIR'S FEED WATER HEATER. 203 freeing the water from the air, are now generally used. Professor Cotterill, E.E.S., in Enr/ineering, 1890, page 527, describes the principle of the Weir system of feed-water heating as follows :■ — The feed-water heater is "supplied with steam from the low-pressure reservoir of a triple- expansion engine. If the steam, instead of being taken from the reservoir, were taken from the boiler, the feed water might be raised to the temperature of the boiler, but the loss of work which might have been done by the condensed steam would exactly compensate for the saving of heat, so that the process on the whole would be neither a gain nor a loss. If, on the other hand, the steam were taken at release from the low-pressure cylinder, the feed would only be raised to the temperature of release, but the saving of heat would be an unmixed gain. It is therefore easily understood that if the steam be taken from the low-pressure reservoir, that is, after it has done two-thirds of its work, there must be, on the whole, a gain of about 7%." The heating steam thus taken from the inter- mediate receiver or the exhaust of an auxUiary engine is led into the heater, and the water pumped through it, being spread out in a thin sheet as it enters, and forced through a circular ring and conical nozzle, to mix the two more thoroughly. The high pressure at which the water is pumped in forces out the air, which escapes through a cock at the top. The advan- tages of the Weir method of heating feed water by direct mixture may be summarised as follows : — It separates the dissolved air and other corrosive gases in ordinary feed water. It effects an economy of from 5% to 8% of the total heat, depending on the kind of engine used, whether compound, triple, or quadruple expansion. Assuming that the steam applied to the feed heating surfaces is taken from the last receiver between the cylinders, it will raise the tempera- ture of the feed water from 100° F. to 220° F. or more, according to the steam pressure in the receiver. Many hundreds of these and other feed-water heaters are in use in steamships, and in the navies of our own and other countries. As mentioned at pages 209, 210, Messrs Belleville, Babcock, and others adopt economisers to heat the feed water by the escaping gases. These usefully reduce the temperature of the gases by absorbing their heat, and thus an exchange is effected from the hot gases to the cooler water. Evaporators. — Another important and necessary adjunct in marine engines is an evaporating apparatus for producing steam from sea water, to make up for the loss by leakage from the stuffing boxes, glands, steam pipes, and other parts. This is required where the feed water and steam are used over and over again with a surface condenser. The steam can be taken direct from the boilers, or from the receivers of one of the engine cylinders. There are many makers of these evaporators for ships, and they are now recognised as a necessary auxiliary of a complete engine-room. They obviate the need for employing sea water in boilers, with its attendant difficulties, and corro- sion and scale in boiler furnaces and other parts are prevented. A large number are now used in steamships, both in the navy and mercantile marine, at home and abroad. One of the leading types is the Weir evaporator, which is, in fact, a miniature boiler. It consists of a large heating surface of copper tubes, 1 J in. diameter and \ in. thick, resembling a surface condenser. Steam is admitted inside the tubes, the sea water on the outside, and is evaporated into pure water by the heat of the steam, instead of the heat of the fuel, as in a steam boiler. Messrs Weir fit these evaporators to work by taking the steam from the intermediate receiver of a triple engine, and evaporating it into the low-pressure receiver. Other evaporators send the fresh water thus obtained into the condenser, and use boiler steam to evaporate it, but this does not give as great an economy of heat. In an experiment made with steam from the inter- mediate receiver, and evaporating into the low- pressure receiver with a Weir evaporator, the heat required was equal to about 68 lbs. of good coal per ton of fresh water produced. About twelve sizes of Weir evaporators with copper tubes are made. To produce 10 tons of fresh water or steam per twenty-four hours, by means of the steam from the intermediate pressure receiver of a triple eugine (50 to 60 lbs. pressure in the tubes), an evaporator of only about 3 feet in diameter by 4^ feet long is required. This gives a steam pressure of 8 lbs. in the shell. With direct boiler steam of 160 lbs., this same evaporator will give 20 tons of steam per twenty-four hours. The weight of 204 HEAT EFFICIENCY OF STEAM BOILERS. water distilled by an evaporator depends upon the extent of heating surface in the tiihes, the cleanness of the surfaces, the temperature of the steam inside them to produce the heat, and temperature of the steam in the shell. In other words, the difference of temperature, or "head of heat," on each side of the tubes constitutes the efficiency of the evaporator. Provision is carefully made for cleaning the outside of the tubes, which become covered with scale from the sea water. This thin scale cracks off the tubes, and collects at the bottom of the shell, from whence it can be removed through a sludge hole door. There is also a blow-off cock, to get rid of the brine once or twice daily. Howden's system of forced draught, with hot air, for steamships. About the year 1860 Mr Howden made some experiments on the economy obtained by using heat which would otherwise be lost in the escaping gases going up the funnel, to heat the air for combustion. In 1880 he designed his method, and his experiments were published in the Proe. Institute of Naval Architects in 1884 and 1886. Fig. 90, p. 276, shows a front and side elevation of the system, as applied to a Scotch three-flue boiler. As will be seen, the gases after leaving the furnaces pass through a large number of smoke tubes to the chimney. In the uptake their temperature is from 500° to 800° F., and here they are conducted through nests of vertical air-heating tubes about 4 feet long, inclosed in an air-tight chamber. These tubes are placed just above the smoke tubes, and in front of the boiler, well out of the way of the stoker. The air for combustion under pressure from a fan is forced into the chamber round the outside of all the air tubes. Entering at a temperature of, say, 50° F., it meets the tubes, which offer a very large heating surface, raised by the hot gases to a temperature of, say, 700° F. The transmission of heat effected is thus due to a difference of temperature of about 650° F. The gases part with this heat to the air, and the latter, raised considerably in temperature, is then used hot above and below all the grates, and its admission carefully regulated. The exchange of heat is between the hot furnace gases and the atmospheric air, which is also a gas. Some of the heat in the gases, as in Mr Hoadley's ex- periments, is returned to the fires by supplying them with hot instead of cold air, and improved results, as regards combustion and economy of coal, are obtained. There is, of course, the extra cost of the fan, the steam and coal required to drive it, the cost of the air-heating pipes, and their wear and tear, but there can be no question of the total gain, because more work can be got out of the boilers per unit of heating surface. The temperature of the air is often raised in practice from 150° to 170° F. The air tubes are of iron, and about 2f in. diameter, and 15 B.W.G. thick. The smoke tubes in the. boiler are about 2|^ in. diameter. Eetarders^ are always used, and sometimes Serve smoke tubes. One great advantage of this system is that neither a closed ash-pit nor closed stoke-hole, with their occasionally objectionable features, are necessary, and the admission of the hot air is carefully regulated by valves. It has hitherto only been used with the Scotch type of boiler. Mr Howden cites the case of a Scotch marine boiler having three furnaces, each 3 feet 7 in. diameter, with grate 5 feet 6 in. long. Worked under the ordinary system, the rates of combus- tion were respectively 12, 16, and 20 lbs. of coal burnt per square foot of grate per hour, and 22, 24, and 28 lbs. of air per lb. of coal. The corresponding temperatures of the escaping gases in the funnel were about 450°, 600°, and 750° F., with chimney draught and a funnel of average height. To allow the gases to escape at this temperature is, of course, very wasteful. It was to utilise a certain part of this heat by making the gases raise the temperature of the air required for combustion, and to economise the fuel, that Mr Howden devised his system of special nests of tubes, and the delivery of the hot air both above and below the grates. It is said to result in a considerable decrease in the consumption of coal, with diminished wear and tear of the boilers, and has been found suitable for burning very small inferior coal, both in America and England. Some of the advan- tages claimed, as compared with natural draught in ordinary mercantile steamers, are : — increased evaporation in the boilers ; economy of fuel ; reduced wear and tear ; and much cooler stoke- holes. An increase in evaporation of from 40% to 50% is said to result. About 22 I.H.P. are obtained per square foot of grate, with a good triple steam engine, in which the temperature of the escaping gases is reduced to about 300° F. 1 See page 206. HOWDEN'S FORCED DRAUGHT SYSTEM. 205 According to Mr Howden, if the air for com- bustion is raised 200° F. by the air heaters in the chimney, the average temperature of the furnace is also raised 200° F. About 20 to 25% less heating surface appears to be required for a given H.P., with the hot force draught arrange- ment, than with natural funnel draught and cold air for combustion. In regard to the pro- portions of the total boiler heating to the air heating surface, the^Jstter-arcrages about J of the former, but it -inay be varied considerably, according to the power reqtiired. With a good triple engine, about 2^ square feet of boiler heat- ing surface per H.P. is sufficient. From the increased furnace temperature several distinct advantages accrue. 1. The evap- orative power of the heating surface is increased, because the rapidity of the evaporation per unit of surface (other things being equal) is in pro- portion to the difference of temperature between the furnace and the water to be evaporated. 2. As the temperature of the fire increases, the gases from the burning fuel combine more readily with the oxygen of the air for combustion, and consequently less excess of air is required per unit of coal. 3. This reduction in the quantity of air required has also an important economic result. The furnace temperature is increased because there is less air to be heated up, and less heat is also carried off by the chimney gases. Further, the volume of gases passing through the boiler being less in a given time, its velocity is less, and thus the hot gases are longer in con- tact with the evaporating surfaces, and impart a greater proportion of heat to the ivater. With this system the space in steamers occupied by the boilers, and their weight, is less than with the natural draught arrangement. Both weight and space in a ship are of great importance, as their reduction affords increased cargo capacity. Mr Howden seems to have been very success- ful in applying his method to a great number of ships in some of the largest and most powerful lines, including thirty-five ships of the Clan line, seventeen of the P. & O., some of the Allan line, the Royal Mail Packet Co., the Ifew Zealand Shipping Co., Alfred Holt's steamers at Liver- pool, and many others. Altogether, it is repre- sented by an I.H.P. of about 1^ millions, or a total of some live hundred ships, but it has not yet been tried by the British Admiralty. The British India Steam Navigation Company o lately made some very practical tests. They built two steamers, the hulls and engines of which were exactly alike, the only difference being in the boilers. Two double-ended Scotch boilers, with eight furnaces, were worked with natural draught in the one ship, and in the other, two single-ended boilers with four furnaces, worked on the Howden forced draught system, with heated air. The result of three years' working of the two ships was found to be, that the one fitted with the forced draught consumed about 20% less fuel, and the speed of the ship was greater. Serve smoke tubes (see fig. 75) are much used in marine cylindrical boilers in France and other countries, and are said to afford 75% more heat absorbing surfaces than ordinary smooth tubes. It is much more difficult to get heat from the hot gases into the 1 I metal of the tubes, than ' " from the same metal into the water surrounding it. In the first case, the trans- mission is from the gases to Fig. 75. the iron ; in the second, from the iron to the water. Gases part with their heat much more slowly to metal, than metal to water. Hence the value of the Serve tubes. They are formed of a number of small radial projections or ribs, presenting a large heat- receiving area to the hot gases as they pass along them. The ribs project into the interior of the tubes about ^ of the radius. As they offer a little more resistance to the passage of the gases than the ordinary tubes, and do not expand so easily, they give good results with forced or induced draught. Ribbed water tubes have also occasionally been tried, but without much success, as the larger heating surface is required for the gases outside, and not for the water inside the tubes. When used in cyhn- drical boilers with smoke tubes. Serve tubes, as compared with plain, give about 10% economy of coal. They are also much employed in traction and railway locomotive boUers, and are made by J. Brown & Co., of the following diameters : — 2^ in., 2| in., 3 in., 3^ in., 3| in., 3f in., 4 in., and with ribs ^ in., ^ in., f in., Y^ in., f in. Trials on boilers fitted with them will be found at the bottom of page 213. In one 206 HEAT EFFICIENCY OF STEAM BOILERS. trial of a Scotch boiler with natural draught and Serve tubes, an economy of 10% was effected. In another trial- a boiler efficiency of 80% is said to have been attained. Retarders. — With Scotch boilers, in some cases, the smoke tubes are provided with thin loose spiral pieces o,f iron, shaped like a cork- screw, called retarders. They are wedged into the tubes, and cause the hot gases to follow a course in spiral fashion, instead of going straight through the tubes. The speed of the gases is diminished, but this is an advantage, because it allows them more time to part with their heat. On the other hand, retarders somewhat impede the draught, and are rather difficult to keep clean. Comparison of Scotch and water tube boilers. — "With large Scotch cylindrical boilers having smoke tubes, a better circulation and mixing of the hot gases is probably obtained than with water tube boilers, but their weight is greater for the same heating surface. It takes a longer time to raise steam in them, but the necessary pressure once produced, it is more easily maintained than in the water tube type. In the latter, the steam pressure rises and falls more quickly according to the intensity of the fire, and, as the volume of water is much smaller, more care is necessary on the part of the stoker, and greater attention to the fires. In a cyhn- drical boiler there is less danger of the water liae falling below the level of the flame surface ; in the water tube boiler this requires constant attention. The steam is generally drier in Scotch, and priming greater in water tube boilers. During the last half century steam pressure in all boilers has been continually increased, and pressures of 200, 250, and 280 lbs. are now not unusual with water tube boilers. In a paper recently read before the Institution of Naval Architects, on the "Progress of Marine Engineering," Sir A. Durston and Mr Milton give some interesting details and comparisons, from which we extract the following: — "The effective H.P. in the Eoyal Navy is now about 2| millions. The steam pressute in 1845 was about 10 lbs. to the square in., it is now 250 to 300 lbs. Piston speeds in 1860 about 450 feet per minute ; in 1897, about 1000 feet per minute. Triple vertical steam engines, often in duplicate, and driving screw shafting, are mostly used in the Navy and mercantile marine. Several ex- periments wUl be found in the Tables of tests on both Scotch and water tube boilers. We pass now to a consideration of Internally fired marine boilers. — Of these, the rectangular form, with smoke tubes, is an old type for very low pressures of about 20 to 30 lbs. It is now seldom made, and practically obsolete. The best known boiler of this class is Cochrane's, a description of which will be found in Seaton's Manual of Marine Engineering. Internally fired Scotch marine boilers, with smoke tubes. (See fig. 82, page 273.) These are made with two, three, or four furnace tubes, grates below, and smoke tubes above, and may be single- ended, viz., fired at one end only, or at both ends. In the latter case, the boiler is double, or like two boUers placed back to back. (See fig. 89.) The diameter of the furnace tubes is usually from 3 to 4 feet. The outer shell is cylindrical, and varies from 12 to 18 feet in diameter, and for high pressures the plates require to be very thick, often from 1 to If in. This type of boiler is largely used iu passenger and mercantile ships, but less in the Navy than formerly. The number and arrangement of the combustion chambers vary. Sometimes there is one chamber to each furnace tube, but more often the gases from two furnace tubes are led into the same combustion chamber. With double-ended boilers there is generally a common combustion chamber to both sets of tubes in the centre of the boUer, serving four, six, or eight grates. Occasionally all the furnaces on one side and on the other have a common combustion chamber, the two chambers being placed back to back. The furnace flues are plain or corrugated. There are several ways of corrugating or ribbing them, such as the Fox tubes, which are much used, the Morrison suspension furnaces, a varia- tion of the Fox, and others. (See page 303.) These corrugations or undulations increase the strength of the furnace tubes, and there seems no difficulty in removing the scale or deposit. Tubes thus ribbed keep their original circular shape better than plain cylindrical tubes, as the ridges have a stiffening effect. Some hundreds of Morrison's furnaces have been fixed in ships of the mercantile marine in England and other countries. Experiments on Scotch marine boilers will be found on page 73. The weight of water is about \ the total weight of the boiler ; the steam pressures are often 160 lbs., and sometimes more. WATER TUBE BOILERS. 207 The smoke tubes in these boilers are about 3 in. diameter. Serve tubes, giving a good economy of heat, are sometimes used, and are easily cleaned inside and out. The smoke tubes should not be too close together, and the circulation is improved if some rows over the furnace are omitted. The Grunboat type of boiler is also internally fired. It has two short Lancashire furnace tubes leading into a common combustion chamber, from whence short smoke tubes run horizontally to the back of the boiler, and so to the chimney. Thus the flue gases pass directly and horizontally from the furnace to the smoke tubes. This type is used only for small steamships, its great length being a disadvantage. Externally fired boilers — Water tube type. — This is a large and important class, and, for the high pressures now usual, it enters much into competition with Scotch smoke tube boilers, having several advantages in regard to weight and space over older forms. The difficulty in all marine boilers is to get the maximum of heating and evaporating surface, with a minimum of space and weight, and higher pressures of steam, and these without risk of burning the tubes. "Water tube boilers seem to offer a more success- ful solution of the problem than Scotch, but, in case of accident, it should be possible to remove and replace the tubes easily at sea in a short time, and without stopping the boiler or engine for long. These tubes consist of a very large number of water tubes, generally of steel, varying from about 1 iu. to 4 in. diameter. A cylindrical drum above, much smaller than the steam space in Scotch boilers, forms a reservoir of steam. There are also two or more drums below, into which the water from the steam space above is sent. The circulation of water, or rather of water and steam, is generally quicker in the small tubes than in boilers 12 to 18 feet diameter, but they are not nearly so easy to clean. Now, however, that pure water is used, and a minimum of oil for the cylinders, they give less trouble in this respect. The better the circulation, the less risk there will be of burning the tubes, and the better the evaporation per square foot of heating surface. Steel tubes, on the whole, seem to stand the heat better than tubes of other metal. These boilers can as easily be used for forced or induced draught as the large cylindrical type, but pitting or corrosion of the tubes sometimes takes place. To prevent this, especially at sea, zinc plates, in the United States and English Navies, are often hung inside the boiler from the stays. Metallic connection being established, the zinc sets up galvanic action on the boiler plates and tubes, which has a beneficial effect, and maintains them intact. The zinc itself gradually wears away, and must be renewed : about ^ lb. is required per square foot of grate surface. Dirt, salt, scale, or grease should be frequently removed from these boilers, or overheating of the tubes will occur. All sea boilers should be carefully examined after each voyage, both internally and externally, as is done on the Liverpool and New York lines. The causes of the circulation of water when exposed to great heat are not yet well under- stood. Many experiments have been made with glass tubes heated by gas jets, but more trials are necessary to determine the laws governing this important question. There are two sets of tubes in a water tube boiler. In the one, the heavier and cooler water descends ; iu the other, the much lighter and hotter mixture of water and steam ascends and rises into the steam drum. It is the varying densities of the water and steam which mainly cause the circulation, but there are many conflicting points to clear up. With pipes of different diameters the speeds vary much, and cannot be uniform in all the small pipes. In some the circulation will be very active, in others sluggish, depending on many conditions of clean or slightly dirty surfaces, distance from the fire, bends, etc. Layers of soot will not adhere equally on the outside of all the tubes. They are generally cleaned externally from soot and dirt by jets of steam, at the end of a rubber pipe, played about them through special doors. On the subject of saving in weight of water tube, as compared with Scotch and other marine boilers, we cannot do better than quote the following abridged Table from Seaton's Marine Engineering. 208 HEAT EFFICIENCY OF STEAM BOILERS. Table of Weights of Diffeeent Marine Boilees. Pressiu'e Weiglit I.H.P. Weight perLH.P. Name of Ship. Type of Boiler. of Steam. Weight. of Water. Natural Forced Natural Forced Draught. Draught. Draught. Draught. lbs. tons. tons. lbs. lbs. H.M.S. Immortalite , 1 Double-ended cylindrical Scotch, 135 188 59 3,490 4,680 118 80 Foreign Cruiser, 1 Do. do. 175 697 206 15,000 17,500 104 89 H.M.S. Majestic, Single-ended cylindrical Scotch, 155 325 86 5,000 6,000 145 121 H.M.S. Magpie, Gunboat type. 145 53 19 1,030 1,340 116 89 H.M.S. Havoc, Locomotive dry bottom, . 180 53 — — 3,600 — 33 H.M.S. Terrible, Belleville water tube. 260 888 66 18,000 25,000 110 80 Foreign Cruiser, , Baboock and Wilcox water tube. 200 594 87 15,000 17,500 89 76 H.M.S. Salmon, Yarrow water tube, . 180 10 n — 1,100 — 20 H.M.S. Decoy, 1 Thoruyoroft water tube. 210 43 6-3 — 4,570 — .' 21 H.M.S. Ferret, Normand water tube. 47 11-5 " 4,500 23 An interesting paper on the same subject was recently read (July 1897) before the Institution of Naval Architects by M. Sigaudy of France. He takes the case of a high speed ocean steamer, with engines developing 23,000 H.P. (effective), and boilers, say, of the Normand and Sigaudy type, with small water tubes and steam pressures of about 220 lbs. Sixteen boilers, each with two furnaces, and a grate surface of 95 square feet, would be required, or 1520 square feet total grate surface, and 74,400 square feet total heat- ing surface. Tubes |- in. thick, 7 feet 8 in. in length, and internal diameter 1^^ in. Each boiler would carry 1700 tubes, or a total of 27,200. Total weightof boiler complete, including water, funnel, floor plates, feed pumps, fans, and engines, feed regulator, spare gear and tools = 938 tons. Taking the consumption of good coal at 1^ lbs. per I.H.P. per hour for triple engines ■of 23,000 H.P., he calculates that 22-7 lbs. of ■coal would be burnt per square foot of grate per hour. If Scotch cylindrical boilers of large diameter were used with the same pressure of steam, the weight would be about 1700 tons. Thus, 1700-938 = 762 tons, representing the saving in weight of water tube boilers. This comparison supposes that combustion per square foot of grate were the same in both types of boilers, and shows that in a water tube boiler of this class, and probably of other classes also, the weight is reduced to nearly one-half. This is a very important matter on board ship, as all the extra weight can be carried as cargo. Belleville water tube boiler — (French. See Frontispiece). — This boiler is used in the French Navy and Mercantile Marine more than any other, and, after many tests and trials, it has, within the last few years, been adopted in the British Navy. Many of the largest warships have been successfully fitted with Belleville boUers,' as the "Powerful" and the "Terrible," each of which carry boilers providing steam for 25,000 H.P. On these two ships there are twenty-eight boilers in all, working at a steam pressure of about 200 to 230 lbs. Messrs Maudsley are the repre- sentatives of the Belleville firm in England. The straight water tubes are of steel, slightly inclined to the horizontal, and about 4 in. in diameter. There is a steam collecting drum at the top, and a lower water collector. They are united by- an external vertical pipe, and connected to a receiver, where the sediment in the water is deposited. The connections between the water tubes were at first a source of much trouble, because the mixture of water and steam in the tubes became " wedged." As the result of much careful study, these ingeniously contrived "headers" now cause little or no difficulty. There is a special baffle or dash-plate arrangement in the upper steam receiver for dividing the priming water from the steam, before the latter passes into the main steam pipes to the engine. By a separate apparatus the boiler is fed con- tinuously and automatically. Each tube is closed at the end with a clamped door, pierced with holes, through which it can be examined and cleaned. The fire and grates have a brick casing all round them, and the boiler is surrounded BABCOCK AND WILCOX MARINE BOILER. 209 externally with light sheet steel, Uned with ^ in. sheets of asbestos, to keep in the heat and diminish radiation, and sometimes only with steel plates and air between. , Like other water tube boilers, the Belleville contains much less water than the Scotch type, the weight of water being only about 8 to 10% of the total weight of the boiler. The water line is about half way up the boiler : half the tubes are nominally full of water, the other half of steam and water, or steam only. The latter act in somewhat the same way as the pipes of a superheater, and the steaan should be fairly dry, but the author has not found any reliable data giving the percentage of moisture in the steam. The pressure of steam in the boiler is generally purposely kept con- siderably above that in the engine, and steam pressures up to 300 lbs. are usual. A nest of horizontal steel tubes, 3 in. diameter, has lately been added to this boiler at the top, to form an economiser, similar to the well-known vertical tube economisers used in this country for the last thirty years on land. For twenty or thirty years the Belleville land Kg. 76. — Babcock Marine Boiler. boilers have been much employed in France. The author has seen the large factory near Paris where they are chiefly manufactured. In England the marine type is made in many shipyards, and, so far, our Admiralty authorities seem well satisfied with the working and tests. Experiments on the Belleville, giving a boiler eificiency of about 78%, will be found in the Tables, page 112. Babcock and Wilcox marine boiler — (see fig. 76). — This type is of American origin, and is much used in the United States and in Eng- land for land purposes. Of late years it has been applied to ships. As seen in fig. 76, the marine somewhat resembles the ordinary land type described at page 12. It consists of some 4 in. water tubes, forming the outer connections, and of a large number of steel tubes 1| in. diameter, placed above the furnace at an angle, as shown. All the parts of this boiler are made of steel, the tubes are straight, and no screwed joints are used. A large steam dome is placed at the top. The tubes are expanded at either end, and connected to malleable steel junction pieces of rectangular section. Stay tubes are not used, but baffles are placed at intervals o 210 HEAT EFFICIENCY OF STEAM BOILERS. across the tubes, to direct the course of the hot gases between them, that all the tubes may be in contact with the heat. There is a hand hole for cleaning and inspection opposite each tube in the headers, the joints being made metal against metal, and all the heating surfaces are easily accessible. A mud drum is fitted below with blow-off cock to get rid of any deposit. As in all other boilers, the tubes become covered with soot, and are cleaned with jets of steam, and defective tubes are said to be easily replaced. The furnaces are lined with fire-brick, and the ' whole of the boiler is inclosed in a light wrought- iron casing. Inside this is a layer of fossil meal and asbestos cloth, and beyond it corrugated iron sheets, forming an air space, to diminish radiation and keep the boiler-room comparatively cool. The boiler can be made double or single ended, with any kind of draught, forced, in- duced, or chimney, but clean, not sea water should be used, and no oil allowed to collect inside. This type is made for the maximum boiler pressure. There are now about eighty • boilers at work, twenty-seven in England, seventeen or more in the United States, and ■about forty-four ships and yachts have been fitted with them, in-cluding three or four ships for the American Navy, and boilers on the " Shel- drake " for the British Admiralty. Messrs Wil- son of Hull have five ships fitted with nine Babcock boilers, and find them much hghter than Scotch boilers. In some of the latest a coil of pipes is added above the boiler, forming a feed- water heater or economiser. This adds, of course, to the economy, but also to the weight, — both matters of great importance on board ship. The Niclausse marine boiler has a battery of tubes arranged as in the Belleville and Babcock, but connecting into a common vertical shaft or " header " at either end, and delivering into a large steam collector at the top. Each tube is formed of two concentric tubes, an inner and an outer, fitted into each other with conical joints. The feed water is pumped into the steam drum, where, if there is any sediment, it is deposited and withdrawn. There are special ingenious arrangements in the steam drum for separating the priming water from the steam. As in the Belleville, the junction of the ends of the tubes is carried out by means of separate headers join- ing every two tubes in sets. These boilers are suited for high pressures, and are said to give very dry steam. Messrs Willans & Eobinson, who are the owners of the patent in England, had one working for some time at their factory, and several now drive their works at Rugby. Experiments on the Niclausse will be found at page 111. Normand water tube boiler, designed by M. Normand of Havre (fig. 130). Here the collec- tion of water tubes is smaller in diameter than those previously described, viz., IJ to 2 in., according to the size of the boiler, and the tubes connecting the upper steam drum to the lower water drum are larger. Some of the small tubes deliver above and some below the water line in the upper steam drum, and they are curved in such a way at the ends connecting with the drums that much of their surface is exposed to the heat of the fire. The circulation is said to be very good, and the heating surface unusually large : some of the middle rows of small tubes, however, are rather difficult to reach for repairs and cleaning. Much care is taken to direct the flames and gases in a zigzag course between the tubes by tire-brick partitions, etc. Air is ad- mitted under and above the grates, and through the fire bridge, and is slightly heated by passing it first through the "outer shell of the boiler. With all these types of water tube boilers the tubes cannot well be cleaned internally ; and if they become dirty, burnt, or damaged, they must be replaced by new. These should be carried in reserve in the ship ; the process of renewal takes time, according to their position. The Thomycroft water tube boiler is one of the class in which the steam and water are delivered into the upper drums, above the water line. The curved shape given to the tubes is said to allow more room for expansion, and to offer a larger heating surface to the fire. The method of construction adopted is also supposed to procure a better circulation of the water, and utihsation of the difference in weight between the two columns, the ascending column of water and steam mixed, and the descending, of water only. Forced or induced draught is chiefly used. This boiler is lighter than some others of the same type, as may be seen by comparing the figures in the Table at page 208. The difficulty of replacing the tubes, if they fail, is sometimes felt, but the heating surface provided is ample. Steel THOHNYCROFT, YARROW, AND OTHER BOILERS. 211 tubes are generally used, f in. external diameter for launch boilers, up to l^ in, for large boilers, as fitted to the " Speedy." In this class of boiler it is essential that the tubes should be capable of resisting very high pressures, and kept clean, to facilitate the transmission of heat. The Thornycroft boilers have been adopted in many ships in the Danish Navy since 1886, and have been found very successful, giving excellent results under trial. They were first used in four boats with engines of 1300 H.P., working with a steam pressure of 200 lbs., and proved so satisfactory that they have been applied' to larger vessels. An interesting series of trials made by Professor Kennedy, with natural and forced draught, will be found at page 111. Boilers representing one million H.P. have, it appears, been made. Yarrow water tube boiler. — This small tube boiler for high steam pressures is of the same class as those already described, and has been largely used since its introduction by Mr Yarrow. Its distinguishing feature is, that all the water tubes are quite straight, whereas, in nearly all other types, they are more or less curved. No difficulty, however, seems to arise from the expansion of the different tubes at diff'erent distances from the fire. There are two sets of water tubes, one on either side of the grate, in the shape of the letter A. (See fig. 124, page 291.) They are generally made 1 inch in diameter, and of galvanised steel for smaller, and 1^ in. steel for larger boilers. There is the usual arrange- ment of an upper large steel drum, and two smaller water drums below, at about the same level as the grate. The water tubes discharge their contents into the bottom of the steam drum, above and below the water line, while the external tubes of larger diameter convey the cooler water to the two lower collectors at the bottom. It is easy to replace the tubes on the outside and inside rows, but in the centre of each set the process, if necessary, seems more difficult, although the boiler can be retubed without being taken out of the ship. The tubes are rolled into the top and bottom collectors by tube expanders driven by power, and a sound and tight joint is the result. In all boilers of this class the tubes are exposed to great diiferences of temperature from time to time, but the circulation in the Yarrow is good. The boilers are surrounded by sheet steel or iron casing, and forced or induced draught is nearly always used. The tubes are accessible externally only for examination, clean- ing, and repair. A large number of these boilers have been made especially for torpedo boats and small ships and launches, and seem to have been successful in very severe tests at sea. For an ex- periment, see page 105, but not many have been published. Various. — There are numerous other water tube boilers, some of them now obsolete, dating from the early part of the century. Among the most important are the boilers introduced by successive members of the Perldns family. The Herreshoff, like the Perkins, has horizontal tubes placed over the grate, but owing to its defective circulation, this ingenious boiler is now seldom made. The Du Temple is a boiler of the Normand type, with curved tubes, \ in. diameter over the grate. Various patents for improving it have been taken out, and it forms a typical French boiler, though not very much in use. The De Naeyer, a Belgian type, is ingenious, but not extensively used at sea. The Heine was one of the earher water tube boilers : a trial on it will be found at page 105. Other boilers having but a limited application, and requiring no detailed notice, are the Oriolle and the Lagrafel and d'AUest in France, and the Reid, White, Blechynden, Seaton, Fleming and Fergusson, Rowan, Root, and Howard in England and America. For a description of these we must refer our readers to works on marine boilers. Number of steamship boilers. — It is difficult to obtain exact statistics of the number of steam- ships used in our own and foreign navies and mercantile marines, but the following figures may be accepted as approximate estimates : — In the Royal Navy, at the present time, the boilers furnish 2J millions effective H.P. In the English Mercantile Marine, the number of vessels registered at Lloyd's above 100 tons burden was 6747 in 1896, and 7530 in 1897. In France, up to 1893, there were about 2200 boilers in the Mercantile Marine alone. Accord- ing to the report of the English Embassy at Berlin, there is now a great advance in the progress of the German Mercantile Marine, and it possesses more ships than France. The tonnage of the ships in the North Sea Fleet in January 1896 was three-quarters of a million, and in the Baltic Fleet in January 1897, 100,000. 212 HEAT EFFICIENCY OF STEAM BOILERS. Locomotive boilers for marine application. — Before passing to consider the large and important class of internally fired locomotive boUers, as used on all railways throughout the world, brief mention must be made of the appli- cation of this economical type of boiler to sea and river purposes. It is practically a locomotive boiler fitted up on board ship, the only difi'erence being that the chimney is higher than is usual on railways. It can be worked with ordinary, induced, or forced draught, and for high pressures of steam. This class of boiler has been a good deal used in our own and other navies for steam launches and torpedo boats, gunboats, and torpedo catchers, and also for launches in the mercantile marine, pleasure-boats on rivers, canals, lakes, etc. It is a comparatively light boiler for the heating surface it aifords, though not so light as a water tube boiler with small tubes, and is usually made with internal rectangular furnace, and a large number of horizontal small smoke tubes. "When the draught is much forced, a difficulty is experienced in keeping the ends of the tubes tight. Sometimes two boilers are placed back to back, forming a double-ended locomotive. This type has now been to a great extent superseded at sea by the lighter water tube boiler, but in South Eussia and a few other countries it is much used when fired with petroleum. In the steamers plying on the Caspian and Volga, liquid petroleum, chiefly in the form of spray, is burnt under the boilers, instead of coal, to evaporate the water. Locomotive boilers on railways, all in- ternally fired. — This large class of boilers is second to none in importance, but the type is very seldom varied, the exigencies of railway locomotion tending to keep it uniform. It is practically similar to the agricultural type (see fig. 12), and is used for high pressures of steam, from 200 to 250 lbs. It is always internally fired, and has a large grate, with rectangular fire box, often of copper. The fire bars are generally of cast-iron, particularly in England, but wrought- iron is sometimes used for this purpose, especi- ally in Belgium, and the bars are rivetted together in sets of six ; the smaller the space left between them, the better for burning very small coal and broken briquettes. The course of the gases and flames is regulated by a fire-brick deflector, and they pass from the furnace through a large number of small horizontal tubes, and thence direct to the chimney. This fire-brick deflector is a modern but great improvement. It forms a combustion chamber, and causes the gases to pass over the fire towards the furnace door, before entering the smoke tubes. Experi- ments in France and elsewhere have proved the practical economical value of this arrangement. The front portion of the boiler, containing the fire-box, is rectangular ; the barrel end, in which the smoke tubes are placed, is cylindrical. The numerous smoke tubes are always small, and are placed as close to one another as possible, to get the maximum heating surface. The material is mostly steel, but sometimes brass. The diameter of the tubes varies from 1^ to 2 in. On the Great Northern Railway they are If in.; on the Great Eastern Railway rather less, and from 100 to 300 are used on a locomotive. Serve smoke tubes are much employed in France (see fig. 75), but little in England ; retarders are scarcely ever placed in the tubes. A very short chimney is of necessity required, as natural draught cannot be relied on to stimulate combustion. Hence the draught is always what is known as 'induced,' and is created by the escape of the exhaust steam from the cylinders up the chimney. It varies from ^ in. to 2 in. on the level, and, going up an incline, is much greater, rising to 4 or 5 in., or even more. In England the fire box is of copper or steel, and nearly always rectangular in all countries. Being built with flat sides, it has to be well stayed on its vertical sides and on the horizontal top. The shell is generally cylin- drical, and of steel, like most other parts of the boiler, except the fire box. The smoke tubes open into the smoke box at the front of the locomotive, below the short chimney. At the bottom of this box the dirt and ashes sometimes accumulate to a consider- able depth, especially after a long run. Here there are large wrought-iron doors, by means of which all the small smoke tubes can be cleaned out, and the ashes removed at the end of each run. Nevertheless, this is a diificult boiler to clean inside, and it is important that soft and clean water be used. Many railway companies soften the water beforehand. This is an excellent plan, and gets rid of the carbonate, sulphate of lime, and other impurities, before the water is sent into the boiler. Injectors to feed in the water are now nearly always used on most STATISTICS OF LOCOaiOTIVE BOILERS. 213 railways, English and. foreign, and often two are fixed on the same hoUer. A thin lagging of wood is generally employed to protect the boiler, but loss by radiation is not nearly as much prevented as it should be, considering that the boiler is exposed to all weathers when at work. The life of the smoke tubes seems to depend on the mileage traversed by the engine, and they wear out after the locomotive has run about 150,000 to 200,000 miles. The barrel of the boUer should be miTch better covered than it is at present. Statistics. — Locomotives may be divided into Express, Ordinary, Goods, and Shunting. The first locomotive engine was run by George Stephenson about 1829. The following list gives an idea of the total heating surface in well built locomotives of modern type : — On four coupled express passenger loco- motives of the Midland Eailway, the total heating surface was about 1260 square feet, and pressure of steam 1 60 lbs. On a passenger locomotive of the Great Northern of Scotland, the heating surface was 1110 square feet; on an express. Great Northern Eailway, 1165 square feet. On an express "newspaper" locomotive of Sharp- Steward's, the heating surface was 1134 square feet; on a goods locomotive (Beyer Peacock), 1071 square feet. On another goods of the Great Eastern Eailway the total heating surface was 1400 square feet ; and on a goods of the Prussian State Eailway, 1050 square feet. It is difficult to get the approximate number of locomotives working on all the railways in the world, but the following figures have been obtained from different sources by applying to the Statistical Departments of the chief countries : — In England up to 1896, about 18,600 locomotives. In the United States up to 1894, ,, 36,000 In Germany up to 1895, , , 16,000 In France up to 1893, , , 11,000 In Austria up to 1890, , , 3,700 In Belgium up to 1895, , , 3,300 In Switzerland up to 1895, , , 1,000 In British Colonies, Canada, India, Australia, etc., up to 1896, about 8,000 „ Thus the approximate number of locomotives in the world (including countries not represented in the above list) is about 124,000. Taking the cost of each locomotive at £3000, this makes a total value of about £372,000,000 for all loco- motive engines. In 1896 the total number of train miles run in Great Britain (that is, the number of trains x number of miles covered by each train) was 350 millions. Taking the average consumption of ooal at 60 lbs. per train mile, and the price at 7s. 3d. per ton, this brings the cost for locomotive fuel alone to three and a half million pounds sterling for that year. In the United States the consumption of coal in locomotives is fifty million tons per year, or one-third the total output of coal from mines in that country. Several tests will be found on page 83 with locomotives running on rails, and at page 75 on locomotives working as stationary boilers. Of locomotives burning petroleum instead of coal under the boilers on the Eussian South-Eastern railways, an interesting account is given by Mr Urquhart, the superintendent of the hne, in the Proc. Medli. Engineers, August 1884 and January 1889. In 1889 about 140 locomotives were burning petroleum refuse, and 50 stationary boilers. The heating value of petroleum refuse may be taken at 19,800 B.T.U. per lb. "With thin copper tubes the boiler efficiency was about 82%, and when burning other crude oils it seems to have been from 82% to 83%. A valuable and. interesting set of trials on the economy to be obtained by varying the length of the smoke tubes in a locomotive boiler, and the effect of this variation on the evaporation, were made by the chief officials of the Paris, Lyons, and Mediterranean Eailway from 1885 to 1890. Ordinary and Tenbrink grates were also tested, and the draught, the area of the grate, and the number and diameter of the smoke tubes were varied within wide limits. Experiments were also carried out, under the same working con- ditions, upon ordinary and Serve tubes (ribbed). The same stationary locomotive boiler, exactly similar to a running locomotive boiler, was used throughout these excellent trials. Smoke tubes of medium length, with a Tenbrink or arched grate, were found to give the highest boiler efficiency, and Serve were preferable to ordinary tubes. The complete report in the Annales des Mines, vol. vi., 1894, should be carefully studied ; a summarised translation was published in The Engineer, July 12th and 26th, and September 6th, 1895. CHAPTER XII. Fuel Testing Stations. Need of Fuel Testing Stations— Difficulties— Advantages— English Trials, 1850, 1857— Wigau Trials— Dantzig, 1863 —Brieg Trials, 1878— Munich Trials, 1879-1880— German Imperial ITavy Trials —Belgian Trials. The importance of testing the evaporative value of fuel when hurnt under a boiler has long been recognised. It is often done by boiler owners, especially when introducing any kind of improvement, but such trials do not tend to advance the sum of our knowledge of the heating and evaporative value of combustibles. System- atic and continuous experiments are needed, in which different kinds of fuel can be tested in the same way, under similar working conditions, and their relative heating power definitely deter- mined. So far as is known to the author, no station with apparatus for this purpose exists in this country or America. On the Continent, where they are often ahead of us, there are several places where coals may be tested for their evaporative power, the gases of combustion analysed, and all the results carefully recorded. Need of coal testing stations. — It is a singular fact that in England, where the pro- duction and utilisation of coal form such impor- tant branches of industry, and hundreds of millions of tons change hands yearly, the sellers of fuel take no trouble to find out how much heat they are offering for sale, nor the purchasers how much they are buying for their money. Colliery owners, coal merchants, and most large consumers know, as a rule, very little about the calorimetry of coal, although the former sell so much heat in the market, and the latter buy and endeavour to utilise it to the best advantage. In mills and factories coal is seldom weighed regularly, and a record kept of the quantities consumed, and of the clinker and ash, though this is the only method of knowing how much worthless dust and incombustible matter has been paid for. To estimate the cost in fuel of evaporating, say, 1000 gallons of water into steam, is one of the best standards for comparing the different coals in a given district, but it is rarely done. Perhaps in the next generation a more common-sense and rational method of controlling the consumption of coal wUl be adopted. Des- ultory experiments are troublesome, and, unless made on a regular system, and with a definite object, are not very advantageous. Various instruments are required, some of them rather costly, and all must be tested for accuracy. The uniform testing of fuel, like many other opera- tions, can only be carried out at a remunerative rate if done systematically in a central station, and on a large scale. The great feature in these stations, and that which distinguishes tests thus made from ordinary coal trials, is that the com- bustible is not only chemically analysed, but burnt under a boiler, and hence its evaporative value is determined in the same way as under ordinary working conditions. Difficulties. — Hitherto many difficulties have prevented the establishment of such a station. It would be expensive to start, and some time must of necessity elapse before its advantages became widely known. Colliery owners would no doubt find it to their credit to have different kinds of coal tested and reported on, and thus be able to offer them to their customers with a guarantee of their ascertained heating value, or evaporative power. Eailway and "Water Com- panies, and other large consumers, ought to know the calorific power of the coal they buy, and the 2U ENGLISH FUEL TESTING TRIALS. 215 percentage of incombustible matter, but these advantages could not be realised all at once. The desirabihty of establishing such a station seems the greater in England, because it is one of the largest coal-producing countries in the world. Coal is still plentiful with us, and perhaps that is the reason why so Uttle trouble is taken to find out the real value of the fuel burnt, and how much is wasted. Considering the amount of coal which changes hands yearly in this country, it is astonishing that people should be so indifferent, and the formation of central coal testing stations still a project of the future. Such stations would be useful as laboratories, and of great value as a standard for comparison and reference. Advantages. — The advantage of this method of testing coal under an experimental boiler has long been recognised, and many temporary trials have been made from time to time. The earliest fuel testing station was established in 1847 at Berhn by Brix. Coal was burnt under a boiler, and the steam allowed to escape at atmospheric pressure, but the trials were naturally conducted in a primitive fashion. English trials, 1850. — The next series of ex- periments were made by Sir Henry de la Beche and Dr Lyon Playfair about 1850, with different coals suitable for the Navy. They were carried out near London, under a small marine boiler, at atmospheric pressure, and for a special purpose. The quantity of air seems to have been measured. As the results were not considered satisfactory, a committee of experts was appointed by the Newcastle Collieries Association in 1857, to test and report upon the evaporative power of Northumbrian coal. This committee consisted of Lord Armstrong, Mr Longridge, and Dr Richardson. The coal was burnt under a marine multi-tubular boiler, 10 feet by 7 feet by 10 feet, with two internal furnace tubes and smoke tubes above. A feed - water heater was afterwards added. Two sizes of grates were used : the larger grate area was 28^ square feet, and the smaller 19|^ square feet. The water was evaporated at atmospheric pressure, and the exit gases were not analysed. A special point studied was the admission of air. During one set of experiments the fire doors were closed, and air entered only through the bars. In the second set, air was admitted through the doors, and a much better combustion consequently obtained. "Welsh coal was also tested under the same boUer, and an interesting series of trials was conducted in 1858, to determine the relative evaporative value of Northumbrian and Welsh steam coal. Another set of experiments was made with the same object in the same year on board a steamer, with a small three-flue marine boiler, having smoke tubes. The superiority of the Welsh coal was proved, but the trials were not carried out with the care that distinguishes later tests. At about the same time various interest- ing experiments were made under small marine boilers by the English Dockyard Authorities. In none of them were the gases of combustion analysed. The author believes that these trials are still continued on coals supplied to the Navy, but the results are not published, as in Germany. Wigan trials. — From 1865 to 1868 a series of important experiments, to test the evaporative value of Lancashire coals, were carried out at Wigan by Messrs Richardson and Lavington Fletcher, first on a small marine, then on three stationary boilers. The marine boiler, on which a large number of trials were made, had two internal flues, with smoke tubes above. Fifteen samples of coal were tested, and 1000 lbs. burnt in each trial. The thickness of the fires was successively 14 in., 12 in., and 9 in. : the pressure of steam was only one atmosphere. Total grate area 10'3 square feet. Of the stationary boUers, two were Lancashire, and the third had conical tubes. A Green's economiser was placed in the back flue, serving the three boilers. All were tested with spreading, coking, and alternate firing, with the above different thicknesses of fuel on the grate, and with various grates and mechanical stokers. Air was admitted below the grate, at the bridge, and also through perforations in a kind of box inside the fire door. The number of perforations was varied, as well as the length of the fire, and the amount of air entering was carefully regulated by sliding grids. Both slack and ordinary Lancashire coal were tested. Two hundred and ninety trials were made on these three boilers, of which sixty were comparative. Those in which an economiser was used showed a considerable increase in water evaporated (9 to 10%). As the steam pressure was so low, supplementary trials were made at a pressure of 40 lbs. per square in. The velocity of the enter- ing air was measured with an anemometer. In the Wigan experiments an analysis of the flue 216 HEAT EFnCIENCY OF STEAM BOILERS. gases was made, though the quantity of air passing through the fire does not seem to have heen deduced from it. A full account of these trials -will be found in Mr D. K. Clark's book, The Steam Engine, vol. i. page 123. Dantzig, 1863. — Tests were also made by Jansen at Dantzig in 1863, upon coal evapo- rating water under a boiler. Brieg trials, 1878. — An important seriesof trials upon the heating value of Lower Silesian coal was carried out during the years 1878 to 1880 by Herr Noeggerath, under the supervision of the Associa- tion for Promoting Mining Industry in Lower Silesia. The object of the experiments was chiefly to estabhshthe excellent qualitiesof Lower Silesian coal, and bring them to the notice of coal consumers in Germany. A station with two boilers was erected at Brieg, and fitted with all necessary instruments and apphances. That nothing might be lacking in the arrangements, Herr Noeggerath visited the Imperial testing station at Wilhelms- haven, then already at work; and was present at a trial made there upon the coal he was about to test. The visit bore fruit in several improve- ments, especially for sifting and sorting the coals. Various kinds of coals from different seams and mines were tested, and, in order to determine the best way in which each could be utilised, a generator was attached to the second boiler, and it was fired with gas instead of solid fuel. Coal from nearly every mine in the district was suc- cessively tested, and sometimes burnt under both boilers at once — solid in the one, and as gaseous fuel in the. other. The evaporative value of the coals from different mines was carefully com- pared, and the arrangements of the gas generator modified to suit them. Lower Silesian being a caking coal, rich in gas, and troublesome to handle in the raw state, it was found that nearly all kinds gave 25% better evaporation under a boiler, when first turned into gas, than when burnt as solid fuel. Quite contrary results were obtained with Upper Silesian coal. The boilers were both of the elephant type, set in masonry, and of the same size. The smoke gases were carried first through the upper boiler, then back through the lower, and so to the chimney. Feed- water heaters on the French system, and of the same diameter as the boilers, were placed along- side them. The total heating surface of each boiler, including the feed- water heater, was 430 square feet. In this testing station the arrangements ap- pear to have been more complete than in any of those previously described. The feed water was measured in gauged iron tanks, the coal and ash caref uUy weighed, and the speed of the air taken with an anemometer, — a method open to the usual objection to such instruments, namely, the diificulty of preventing air from filtering in through cracks in the brick-work. The gases were drawn from the flues by a Bunsen pump, and analysed in an Orsat apparatus. The tem- peratures of the air, feed water, and hot gases were carefully noted. The steam pressure was 100 lbs., but it was found impossible to determine the amount of priming water. The grate surface was varied to suit the kind of coal burnt. This excellent station was closed in April 1880, after all the different kinds of Silesian coal had been tested. Munich trials, 1879 to 1889.— By far the most important of the fuel testing stations which have yet been estabhshed was that opened at Munich under the direction of Dr Bunte, an excellent authority on the combustion of coal, and a dis- tinguished chemist. Work was begun here at about the same time as at the Brieg station, viz., January 1879. At the outset of the experiments the following programme was laid down. The coals were to be tested : — 1. For their theoretical heating value. 2. For their practical heating value, with varying dimensions and different constructions of grate, varying quantities of air, draught, kinds and sizes of fuels, and different stoking. 3. For their caking qualities, and other important characteristics. Two features especially distinguished the Munich testing station. In the first place, the number of trials was much larger than had previously been attempted, as many as seventy- six tests being made in six months. Experience has shown that to make numerous tests, under carefully varied working conditions, on the same boiler, is the best, and indeed the only reliable way of determining scientific data with accuracy. These experiments appear also to have been the first in which the quantity of air required for combustion, and therefore the excess, was calcu- lated from analysis of the products of combustion. The amount of air theoretically needed for the combustion of each particular kind of coal was determined beforehand, and hence the percentage MUNICH FUEL TESTING STATION. 217 of COg, which ought to be found in the flue gases, was known. Before each experiment, a portion of the coal to be tested was burnt, and the amount of COj in the gases noted. The damper was then opened or closed, and the draught varied till the proper amount was obtained. The theoretical heating value was determined from the chemical analysis of the coal, both by Scheurer-Kestner's and Dulong's formulse. The testing station was provided with two boilers, both vertical, and each having seventy- three smoke tubes, and a total heating surface of 258 and 182 square feet respectively. The experiments were divided into two sets. In the first the steam pipes and boilers were purposely not covered, to prevent radiation, and a part of the heat from the combustible and the hot gases was thus lost. Some of this loss was calculated, and the relative heating value of the combustible thus obtained. In the second series, all surfaces were carefully covered, and loss by radiation diminished. The total theoretical heating value of the coal was determined by adding together all the quantities of heat measured directly during the trials, or calculated from observations. This heating value is independent of the method of firing, and of the efficiency of combustion. Both, however, greatly afi'ect the practical heat value of coal, which is also influenced by the particular construction of the grate, amount of air admitted, etc. It was the determination of this practical heating value of the coal tested which formed the chief object of the experi- ments. The horizontal grate and hearth were so arranged that the coal could either be burnt on a small grate with short flames, or on an enlarged grate with long flames. In the first case the grate was immediately below the boiler, the bars were spaced ^ in. apart, and the volume of the combustion chamber varied from 17 to 35 cubic feet. With the second grate the bars were spaced ^ in. apart, the combustion space was 13 feet long, and about 2^ feet wide; the grate surface varied from 3'7 to 8 square feet. Each arrangement was suited to difierent kinds of coal, and one or the other grate was used according to the coal burnt. In all, seventy-six experiments were made on four difi'erent German coals and on peat, — fifty-seven with short flames and small combustion space, and nineteen with long flames. Observations were carried out upon the quantity of coal burnt per square foot of grate per hour, and of unburnt combustible falling through the bars. Special attention was paid to the important effect produced by admitting different quantities of air. On this point Dr Bunte says : — " It is clear that we have here the kernel of the whole question of the economical combustion of fuel, since the air not only contains the indispensable element of oxygen, but the amount of the flue gases, the medium for absorbing the heat of combustion, is directly proportional to the quantity of air admitted." The volume of flue gases is exactly the same as the volume of air entering through the grate, COj being produced by com- bination of the C and the 0, without any change of volume. The amount of flue gases was determined by calorimetric and by chemical methods, chiefly the latter. The temperature was taken and the draught measured at difi'erent places in the flues and in the chimney. The layer of fuel on the grate was generally 4 in. thick, and the fires were stoked at intervals varying from ten to forty-five minutes. The progress of combustion was found to depend, not so much upon the shape and size of the coal, as upon its caking or non-caking qualities. Before beginning an experiment the coal already burning on the grate was removed, weighed, and replaced, all additional coal was weighed, and the level of water in the boiler observed. At the end of the experiment the coal on the grate was again withdrawn and weighed, and the difference between the two quantities noted. The temperatures of the furnace, smoke gases, and feed water were also taken. The gases were sampled continuously, and the chemical analysis of the combustible having been previously made, all the data for calculating the heating value of the coal under the boiler were at hand. In the original report the log sheet for one of the trials is given. The different losses of heat were tabulated under their respective heads. The percentage of air in the flue gases, and the quantity of the latter passing dry through the boiler per unit weight of coal, are given. By dividing the volume of gases per kilogramme of coal by the theoretical quantity of air required, the coefficient of the excess is obtained. The losses of heat are shown graphically in a series of diagrams, a method of illustration now familiar, but unusual in 1879. Coals from the Euhr and Saar districts, 218 HEAT EFFICIENCY OF STEAM BOILERS. Bohemia, and Upper Bavaria, were tested in the various ways described, as well as coke and peat. The Bohemian coke was tested only on the grate with wide bars, and gave a very uniform combustion, with slight variations in the per- centage of COj, the mean being 13|-%. Upon two kinds of peat from two different districts three experiments were made, all with large- combustion space and long flames. Peat con- tains a large proportion of volatile gases, and, when burnt on a coking grate, yields only about one-quarter solid, and three-quarters gasified constituents. This characteristic caused much fluctuation in the composition of the flue gases, the percentage of COg varying from 7% to 18%. The peat burnt completely to ashes, without leaving any other incombustible residuum. 1880. — A new series of trials was begun at this testing station in August 1880, on forty- three difl!erent kinds of German and Austrian coal, lignite, coke, and peat. The coal was first divided, mixed, and sampled in the usu.al Avay, the samples chemically analysed, and the theoretical heating value of the coal thus calcu- lated. A hundred and six experiments were made in all, with long and short flames (large and small combustion chambers), as before. The internal "dimensions of the grates were varied, and thus the amount of heat developed in the furnace was regulated. Seven difl^erent kinds of grates, with wide or narrow spaced bars, stepped grates, and other special types, were tested. The stokers being more skilled, the percentage of CO^ varied less than in the former experiments, although, with Bavarian coal, it was found necessary to stoke every five minutes. In all other respects the working conditions were practically the same as before. The trials ex- tended over a long period, and, in several with Saar coal, the boiler efficiency reached 86%. With Bohemian and other kinds of coal, air was admitted on the following system : — Experiments were first made with a good draught, damper full open, and giving about twice the theoretical quantity of air required. The layer of coal on the grate was then shghtly increased, the damper partly closed, and about 1^ the theoretical quantity of air was admitted. Again, the layer of combustible was raised to 8 in., the damper remained in the same position, and very little more than the theoretical quantity of air entered. With some coals, 84% boiler efficiency was obtained, with 50% excess of air. Of the fuel tested, Euhr coal gave the highest, and lignite and peat the lowest heating value. From the weight of steam evaporated per hour per square foot of heating surface, the efficiency of the latter was calculated. In the end of 1880 the Bavarian Steam Boiler Association took over the Munich fuel testing station, Dr Bunte remaining at the head of it. The station was then utilised to test the evapo- ration of brine in the salt works at Rosenheim. Peat was burnt for this purpose, and the pro- cesses of combustion and the temperatures were tested in the same way as before. These Bava- rian trials are perhaps unique in their way, and very complete. Another valuable series of evaporative trials was made in 1881 on two Lancashire boilers, with economisers and Mehl grates. Each had a heating surface of 936 square feet, and no small smoke tubes. Saar and Upper Bavarian coal were tested. The temperature of the gases leaving the economisers was taken ; the gases were drawn off by a pump, and sampled in a burette, and the distribution of heat was very carefully studied. An interesting set of comparative trials was carried out on two plain cylindrical boilers, with' gas firing, and with an ordiaary horizontal grate. They were intended to determine whether small Bavarian coal could be burnt to better advantage under a boiler if first turned into gas, than if fired in the ordinary way. The same coal was used in both boilers, and each had 559 square feet of heating surface. The trials lasted twenty- four hours, the boilers being worked simul- taneously. The heating value of the coal used was very low, and the draught only one-sixth of an inch. Other experiments were also under- taken to test the effect of forced draught below the grate upon the combustion. The same boiler was worked on two consecutive days, with and without forced blast. The results proved that such a draught was not desirable, but the coal used was very poor. In comparative trials made on a Tenbrink and on an ordinary grate, the two boilers tested were of the same dimensions, each with a heating surface of 242 square feet. Only the Tenbrink had an economiser. The same coal was used, and the Tenbrink grate gave 9% better heat efficiency. A careful test of lignite under six boilers was made in June 1881, and three kinds of brown coal, all of low heating GERMAN IMPERIAL NAVY TRIALS. 219 value, were tested. The steam pressure was 90 lbs. Some years ago it was unfortunately found necessary, through lack of funds, to close this useful fuel testing station. The excellent prac- tical work carried out in it may be seen from the above slight sketch, but the original report ' should be studied by all interested in the question of fuel. The author visited the station a few years after its erection, and was most courteously received by Dr Bunte, who gave him much interesting information. Dr Bunte is now at the Hochschule, Karlsruhe, but he still pursues his valuable investigations. Since the abolition of this station, no centre for testing fuel on a large and commercial scale exists on the Conti- nent, as far as is known to the author. Grerman Imperial Navy trials. — Tests extend- ing over a period of more than twenty years have been made at the Imperial German dock- yards at Kiel, Dantzig, and "Wilhelmshaven. They were begun in 1874, and have, the author believes, been continued up to the present time. The principal object of these trials was, by testing various German coals, to ascertain which mines yield coals suitable to the requirements of the Imperial Navy. Subsidiary evaporative experi- ments were also made on samples of coal deUvered at the dockyards, in quantities of not less than 2000 tons, for use under land and marine boilers. These were in order to determine whether the coals came up to the required standard with respect to heating value, rate of combustion, degree of smoke, consistency, and percentage of incombustible residuum. Trials were also made on various foreign coals, such as might be supplied to German ships in other countries. About 3 tons taken from the total quantity of any coal were used for a test, and no trials were made unless 2000 tons from the same mine had been delivered. For the sake of comparison, each experiment lasted six hours, and all trials were carried out, as far as possible, by the same stoker. The experimental apparatus consisted of a two- flued internally-fired marine boiler of 9 tons water capacity, with smoke tubes above. Each of the three Imperial dockyards at Kiel, Dant- zig, and Wilhelmshaven were provided with a 1 Berioht der Heizversuohstations jMunohen, from the Bayerischen Industrie — wid Gewerbeblait. Also pub- lished separately in three numbers, 1879, 1881, 1882, by Dr C. Wolf und Sohn, Munich. similar boiler. There were 176 brass smoke tubes, each 2 "7 in. internal diameter, in the boilers at Kiel and Wilhelmshaven, and 192 in that at Dantzig. The total heating surface in the first and second boilers was 1083 square feet, and in the last 1119 square feet. Total grate surface of each, 37 "8 square feet. The feed water was run into the boilers from two tanks. Each tank at Kiel and Wilhelmshaven held 3 tons of water, at 15° C. ; one tank at Dantzig heldl'8 tons, the other 3'7 tons. All the tanks were gauged, and fitted with a glass scale. The chimney at each station was 36 feet high above the boiler, 20 in. diameter at the bottom, and 17 in. at the top. The boiler was placed in a house by itself. The coal was first tested for "cohesion" by breaking it into pieces of J to 1 lb., and screen- ing it over a sieve with about 1:^ in. holes; set at an angle of 40°. One hundred lbs. of the coal failing to pass the sieve were then placed in a closed iron cylinder, 3'7 feet long, 2"7 feet in diameter, with three radial divisions, and revolv- ing twenty-five times per minute. After two minutes, or fifty revolutions, the coal was taken out, again screened, and the percentage of large coal gave what is called its " cohesive " value. All the different kinds of coal were thus treated three times : for the Imperial Navy the limit of cohesion might not fall below 40%. The relative weight of the large pieces in a ton of coal was obtained in the same way. The percentage of small coal in the total coal as dehvered was also determined. The limit allowed by the Imperial Naval Authorities was from 15 to 40% for rough sea-borne coal, and from 10 to 30% for coal brought by land. To test the evaporative and heating value of the coal, it was first carefully dried in the warm boiler-house for two or three days, and the larger pieces broken and screened as before. The fire in the grate was then started with wood, and a given weighed quantity of coal put on. The temperatures of the water and of the smoke gases in the chimney were taken. Stoking at regular intervals was then begun, and the tem- peratures noted at the same periods : the thickness of coal on the grate was not allowed to exceed 4 to 5 in. The vacuum in the chimney, time required for heating up, colour of the flame, and progressof combustion, were all carefully observed. The method of stoking was varied to suit the 220 HEAT EFFICIENCY OF STEAM BOILERS. coal tested. The chimney was watched during each trial, and the degree of smoke noted accord- ing to three grades, whether thick black, medium, or hardly visible smoke. All ashes were weighed : in the coal supplied to the Imperial Navy the per- centage of ash might not exceed 8'4%. The heating value of the coal was calculated from the weight of water evaporated and of coal burnt, evaporation being apparently at atmospheric pres- sure. The Imperial Authorities required that the weight of water evaporated should not be less than 8'3 times the weight of coal, or 8'3 lbs. water per lb. of coal, from and at 0° C. These valuable experiments were most care- fully carried out on a large number of different kinds of coal, and an immense mass of useful information thus accumulated. For the object in view, namely, to estimate the value of each coal for marine purposes, they are very complete and useful, but no attempt seems to have been made to analyse the gases, or the chemical com- position of the coals, or to determine their heating value accurately in a calorimeter. The immense number of tests recorded makes them of value, and is excellent for purposes of comparison, and the qualities of the different coals, both German and foreign, were carefully studied, but the trials would have been still more useful had the heat- ing value of the coal been taken. Seven hundred and fifty-two trials were made, in all, upon German coals. WestphaUan coal of four different kinds was tested, namely, gas coal, bituminous or greasy, a mixture of the two, and a mixture of poor and caking coal. Upper and Lower Silesian coals were also tested, and were found rather inferior, of lower heating value, and giving off more smoke. On English, Scotch, and Welsh coals, fifty-one trials were carried out, sis on Japanese, five on Australian, and one on South American coal of very poor quality. Two hundred and five trials were made on briquettes, chiefly of German manufacture, and three on German and English coke. Special attention was paid to the way in which the coal burnt, its fracture or cleavage, the length of flame, and the smoke produced. Full details will be found in the report, " Zusammenstellung der vergleiafienden Versuche, avsgefuhH auf den Kaiserlichen Werften," E. S. Mittler, 68 Kochstrasse, Berlin, 1895. Belgian trials. — Trials of the same kind, but on locomotive instead of marine boilers, have, been made by the Belgian State Eailways De- partment at their testing station near Brussels, for more than twenty years, and are still con- tinued. The coal supplied by various contractors to these State railways must be accompanied by a guarantee that it is of a certain specified evap- orative power, and does not contain more than a given quantity of incombustible substance and moisture. Daily trials are made to test the coal, and prove that it comes up to this stand- ard. Large quantities of coal are sent in as samples by the various colheries and contractors ; all are fired under a locomotive boiler, under strict test conditions, and the coal accepted or rejected according to the results of the trial. The contractor or his representative is allowed to be present. Private firms can also have their coals tested and reported on, and the author has availed himself on one occasion of this permission. As the trials have been going on since 1875, and all results are duly recorded in the books of the station, the authorities must have a very interesting collection of facts relating to the various kinds of Belgian coal, but they are considered the private property of the Government, and thus lost to the world. There is also a fuel testing station at Magde- burgh, maintained by the German Boiler Insur- ance Co., but the author has not succeeded in obtaining any information respecting it. The Donkin and Kennedy experiments, 1887 to 1889, were made on twenty-two boilers, and at various places, all with the same Welsh coal. The particulars of these trials, with both English and metric measurements, can now be obtained in separate book form, published by Engineering. CHAPTEE XIIT. Discussion of the Teials and Conclusions. Tables of Efficiencies — Summary of all the Trials— Value of Tests — Conditions of Boiler Efficiency — Variations in Efficiency, with different rates of Evaporation — Best Evaporation for Maximum Efficiency — Opinions of M. Sauvage — Of Mr Barrus — Graphic Diagram of Loss of Heat due to varying percentages of COj. On page 115 will be found a Table giving the results of the two best experiments on each type of boiler with internal fires, taken from 321 trials, and arranged in order of boiler efficiency. The succeeding Table, at page 117, shows similar results for 109 trials of boilers with external fires. On page 118 is a third Table, showing a summary of all the experiments, together with the maximum efficiency (mean of the two best trials on each type, from the two previous Tables), the minimum, and the mean efficiency of all the trials. These are ranked according to their boiler efficiency (exclusive of economisers), and vary from 77^ to 56^%. Column VI. shows the number of trials forming the basis of the mean in column IX. In column VII., giv- ing the efficiencies of the two best experiments for each type, the maximum is 84% for small water tube boilers, and the minimum 65^% for elephant boilers. The lowest efficiency of each type, shown in column VIII., yields a maximum of 66|^% for small water tube boUers, and a minimum of 42% for Lancashire boilers. In all the three columns of efficiencies, small water tube and locomotive boilers yield about the best results. It wiU be seen in this summary how greatly the efficiencies vary, even in the same type of boiler, owing to very different working condi- tions. Thus, in Cornish internally fired, they ranged from almost the highest, 81-7% to 53%. Again, Lancashire internally fired show, under favourable conditions, an efficiency of nearly 80%, while they als, 37. Nitrogen (iV), 38. Sulphur (S), . . 100 per cent. 39. Moisture in sample of coal as received, ,, Analysis of Ash and Refuse. 40. Carbon, . . . . per cent. 41. Earthy matter, ... ,, Fuel per Howr. 42. Dry coal consumed per hour, . lbs. 43. Combustible consumed per hour, ,, 44. Dry coal per square foot of grate surface per hour, . . . , , 45. Combustible per square foot of water- heating surface per hour, , , Galorifk Value of Fv,el. (Art. XVI., Code.) 46. Calorific value by oxygen calorimeter, B.T.U. per lb. of dry coal, 47. Calorific value by oxygen calorimeter, per lb. of combustible, . . , , 48. Calorific value by analysis, per lb. of dry coal,' . . . . . ,, 49. Calorific value by analysis, per lb. of combustible, •. . ,, ' Including equivalent of wood used in lighting the fire, not including unburnt coal withdrawn from furnace at end of test. 1 lb. of wood is taken to be equal to 0-4 lb. of coal. ^ This is the total moisture in the coal as found by drying it artificially, as described in Art. XIV. of Code. ^ See formula for calorific value under Art. XVI. of Code. Quality of Steam. 50. Percentage of moisture in steam, . per cent. 51. Number of degrees of superheating, deg. 52. Quality of steam (dry steam = unity), . 53. Factor of correction for quality of steam. Water. 54. Total weight of water fed to boiler, lbs. 55. Water actually evaporated, corrected for quality of steam, . . ,, 56. Equivalent water evaporated into dry steam from and at 212 degrees, ,, Water per Sour. 57. Water evaporated per hour, corrected for quality of steam, . . „ 58. Equivalent evaporation per hour from and at 212 degrees, ,, 59. Equivalent evaporation per hour from and at 212 degrees per square foot of water -heating surface, . . , , Horse-Power. 60. Horse-power developed. (34J lbs. erf water evaporated per hour into dry steam from and at 212 degrees, equals one horse-power),' . H.P. 61. Builders' rated horse-power, . ,, 62. Percentage of builders' rated horse-power developed, . . per cent. Fconomic Results. 63. Water apparently evaporated per lb. of coal under actual conditions. (Item 54 4- Item 23) lbs. 64. Equivalent evaporation from and at 212 degrees per lb. of coal (including moisture), . . . . ,, 65. Equivalent evaporation from and at 212 degrees per lb. of dry coal, . ,, 66. Equivalent evaporation from and at 212 degrees per lb. of combustible, . ,, Efficiency. (See Art. XX., Code.) 67. Efficiency of the boiler ; heat absorbed by the boiler per lb. of combustible divided by the heat value of 1 lb. of combustible,^ . per cent. 68. Efficiency of boiler, including the grate ; heat absorbed by the boiler, per lb. of dry coal fired, divided by the heat value of 1 lb. of dry coal,* . . , , ' Held to be the equivalent of 30 lbs. of water per hour evaporated from 100 degrees Fahr. into dry steam at 70 lbs. gauge pressure. (See introduction to Code.) ^ In all cases where the word combustible is used, it means the coal without moisture and ash, but including all other constituents. It is the same as what is called in Europe "coal dry and free from ash." * The heat value of the coal is to be determined either by an oxygen calorimeter, or by calculation from ultimate analysis. When both methods are used the mean value is to be taken. 242 HEAT EFFICIENCY OF STEAM BOILERS. Cost of Evaporation. 69. Cost of coal per ton of 2240 lbs. delivered in boiler-room, .... 70. Cost of fuel for evaporating 1000 lbs. of water under observed conditions, 71. Cost of fuel used for evaporating 1000 lbs. of water from and at 212 degrees, Smoke Observations. 72. Percentage of smoke as observed, 73. Weigbt of soot per hour obtained from smoke meter, 74. Volume of soot obtained from smoke meter per hour. The above data for trials are followed in the original Report of the Committee by copious appendices, of which the following is a short summary : — Goal and loater. — The principal facts to be ascertained in any boiler trial are the weight of water evaporated, and of fuel required. To keep a careful tally of the amount of coal used, both the coal and water should be weighed at regular intervals, and the time noted in every case when a fresh quantity is supphed. Drying aoal. — Two methods for this process have till now been employed. The first, which is most usual in boiler tests, consists in drying 50 lbs. or more on the top of the boiler or flue. It has the drawback that there are no means of knowing whether the temperature is high enough to dry out all the moisture in the coal. In the second method a small sample of crushed coal is dried at a temperature of 212° for an hour, or till the weight becomes constant. The difficulty is to obtain an average sample, and to prevent the moisture from being absorbed by the air, during the process of repeated crushing. It was found that by successive heatings at gradually increasing temperatures, from 212° up to 300° or over, and weighing at intervals of an hour or more, the weight of coal continually de- creased until it became nearly constant, and then a very sKght increase took place, which became greater on further repeated heatings to tempera- tures above 250°. Tests showed that no volatile matter was given off with the moisture, even at a temperature of 350°, and the method proposed in Section XIV. of the Report (see p. 238) was accordingly adopted, and its accuracy carefully checked by other means. The proper range of temperature for drying the coal, to prevent any loss of volatile matter, was previously determined. Analysis and sampling of coal. — In makin^ the proximate analysis of the coal, it is recom- mended that the four constituents determined by heating in a crucible should be given in percentages, instead of subtracting the sulphur from the fixed carbon and volatile matter, as is sometimes done. The proximate analysis fixes the general character of the coal, and shows the amount of volatile matter, ash, moisture, and sulphur it contains. Goal calorimeter. — The instrument recom- mended for use is the Barrus, which is very similar to the Carpenter Coal Calorimeter, de- scribed at page 196. Mr Barrus has made more than 200 tests with it, and the results found have always been substantially consistent with each other. He uses one gram of coal for a test, and 2000 grams of water, and the heating values thus obtained agree within from 1% to 3% with those calculated by the Dulong formula from the chemical analysis of the coal. A draw- back of the calorimetric method is the slightly varying results obtained with the same coal with different calorimeters and by analysis, as shown in the following Table (Coal No. I. is from Ohio ; No. II. from Virginia ; Nos. III. and IV. are two samples of Illinois coal) : — Heating Value per lb. Coal, B.T.U. Heating Value per lb. Combustible, B.T.U. Ratio (2)^-(l) I. II. I. II. (I) m (1) (2) Carpenter Calorimeter, . 13,170 15,200 14,620 16,210 1109 Thompson Calorimeter (Boston), . 11,913 13,066 13,302 13,799 1-037 Thompson Calorimeter (St Louis), 11,894 13,527 Ban-US Calorimeter, 12,706 14,631 13,646 15,320 1-123 Analysis, Williams, 12,328 14,462 13,208 15,197 1-150 Prof. K. C. Carpenter, Cai'penter Calorimeter, Prof. N.W. Lord, Mahler Caloiimeter, ,, E. C. Potter, Tliompson „ Analysis by Ricketts & Banks, . Average, Heating Value per lb. Gafio Combustible, (2)-r(l). B.T.U. III. IV. (1) (2) 13,700 13,800 1-007 13,870 13,968 1-007 13,687 13,787 1-007 14,020 18,955 0-996 13,819 13,878 1-004 The difference appears to lie not in the calorimeters, but in their manipulation. The DETAILS OF AMERICAN STANDARD BOILER TESTS. 243 writers of the report are of opinion that closely agreeing results may be obtained from different calorimeters, when properly handled by expert chemists, and will coincide with those calculated from accurate analysis. The Thompson calori- meter needs specially careful treatment. In esti- mating the heat value by Dulong's formula from the analysis of the coal, it is not necessary to allow for the sulphur, as it is not present in a free condition. Steam Calorimeters. — To determine the moist- ure in the steam by the Peabody, Barrus, or Carpenter calorimeters, care should be taken that an average sample of the steam is obtained, though this is very difficult, especially if the percentage of moisture exceed 2% or 3%. The formula used for calculating the percentage moisture in steam in a throttling calorimeter is given in the original paper. Allowance should be made for radiation from the instrument, which ■slightly reduces the temperature of the wire drawn steam. Formulae are also added for correcting the quality of the steam ; that is, the proportional weight of the steam in a mixture of steam and water, and for showing the equivalent evaporation in superheated steam. Both these formidse are based on the same principle as that for determin- ing the moisture in steam given at page 199. Boiler Efficiency. — The efficiency of the boiler including the grate is the quotient obtained by ■dividing the heat absorbed by the boiler, by the heating value of the total amount of coal suppHed, including that which falls through the grate. The efficiency of the boiler, not including the grate, is the quotient obtained by dividing the heat absorbed by the boiler by the heating value ■of the dry coal burnt, less chnker and ash. The latter (the standard of efficiency adopted in this booki) is the more accurate measure of comparison. It should be used when the object of a boiler test is to determine its efficiency as an absorber of heat, or to compare different boilers, because the results are not so much affected by errors in sampling the coal, as when the efficiency is based on the total coal supplied. The efficiency should be reported as the percentage of the heating value of the coal actually utilised in producing steam, and it is not advisable to make allowance for the latent heat of moisture in the chimney gases. The moisture in the coal should be dried out, by contact with the air, as far as possible. ^ Including clinker and ash. The total heating value of the coal is dis- tributed into : (1). Loss through the grate, de- pending on the space between the grate bars, size of the coal and kind of grate, and rate of working the boiler. (2). Unburnt coal carried over the fire bridge. (3). Heating and evaporating the moisture in the coal. (4). Steam formed by combination of the H in the coal and the of the air. (5). Superheating the moisture in the air supplied for combustion. (6). Heating the gaseous products of combustion to the tempera- ture of the flue. (7). Loss due to imperfect combustion, depending on the character of the coal, and the skill of the fireman. (8). Radiation. (9). The balance is the useful work done. Blank forms. — The observations taken during the test should be recorded on a series of blank forms provided for the purpose. The coal and water measurements should be kept separate from the others, and the first column of both should show the time, and state when a particular barrow, of coal is supplied, or tank of water begun. The temperature of the feed water, and height of water in the .glass gauge, should always be noted at intervals. Cod of evaporation. — As the final result in all boiler tests is to determine the value in money of the work done, it is always necessary to know the average cost of evaporation prior to the test, that is, under ordinary working conditions. For a boiler trial everything is put into perfect order, but these are not the conditions which usually obtain in practice. The cost of the output during a trial is often from -Jth to ^rd less than the ordinary working cost, and it is not always possible to tell what causes the difference, though much of it is generally due to careless stoking. The feed water measurements should be continu- ously checked, and the quantity recorded compared with the total weight of coalpurehased. Preliminary tests, conducted' without notice to the workmen and extending over long periods, will furnish' a basis of comparison with special tests, and show where the losses have occurred, and how best to remedy them. Vacimm in chimney: — For measuring the draught two instruments are described, one a modi- fication of the ordinary U-gauge. In the second the variations in the chimney draught are recorded by a tin can, suspended within another from a hehcal spring, and connected to the flue. The expansion of the spring gives by a formula the 244 HEAT EFFICIENCY OF STEAM BOILERS. pressure of air in the chimney in inches of water. This instrument multiplies the indications of the U-tube about seven times, and readings can be obtained to -Jjy inch. Weight of chimney gases. — The computation of the weight of the chimney gases from the analysis by volume of the dry gas is carried out by means of the formula in the footnote at page 240. It is based on the principle that the den- sity relative to hydrogen of an elementary gas (0 and N) is proportional to its atomic weight, and that of a compound gas (CO and CO2) to half its molecular weight. Another formula, also given, does not take count of the hydrogen, and is inaccurate, unless the fuel burned is pure carbon, — a condition which can never occur in actual boiler practice. Both formulae are illus- trated by a numerical example. Analysis and Sampling of gases. — For analysing the flue gases the preference is given to the Orsat apparatus, as affording a valuable and reliable guide to determine what kind of firing is most advantageous, when the fuel is bitumin- ous coal. The results obtained show in a very , satisfactory way the distribution of the heat. A single unperforated tube, which should extend into the flue to a central point, is best for sampling the gases. Care must be taken that aU the tubes and connections are tight, and the absorbing liquids in good condition. It is recommended that the gas apparatus be placed on the boiler-room, floor near the furnaces, and connected by a small leaden pipe. The taking of the samples should be carefully timed, and cover the whole period between two stokings, if it is desired to work out the heat balance. Smoke observations. — A new method is also described for taking smoke observations. A flat brass plate, 24 inches long, | inch wide, is suspended in the smoke passage between the boiler and the flue, at right angles to the current. Upon it a certain portion of the soot carried along by the waste gases is collected, and furnishes an indirect method of testing the smoke in the flue gases. The plate is inserted through a hole in the flue and hung by a wire ; it can be withdrawn at pleasure, and the soot removed from it and weighed. During a series of trials in 1897 this was done every two hours. The quantity of soot thus collected varied from 9 to 184 milligrammes per hour, according to the type of furnace, kind of coal used, and working con- ditions. The records thus obtained agreed with those based on ocular observation of the smoka from the chimney. Locomotive Boiler Trials. Lastly, we have to consider trials on locomotive boilers and how to conduct them. Unfortunately no recognised system exists in this country. The standard method of conducting locomotive tests in America, taken from the Report of the Committee of the American Society of Mechanical Engineers, is as follows : — those parts only relating to the testing of boilers are extracted, and given in the actual words of the report. A uniform system of making locomotive tests seems to be very desirable. The object of the report is therefore to standardise the methods of testing locomotives, so that the results obtained from different boilers may form a basis of comparison, as far as can be done in loco- motive service. To determine questions of this character, the committee recommends that, wherever possible, resort be had to the uniform conditions of test supplied by this suggested method of trial. The predominant object of a standard method of ' ' road test " is to ascertain the efficiency of a locomotive when engaged in its normal work ; that is, when hauling a train of cars over a route of considerable length. The test should therefore be made on a through train running over a route at least 100 miles long, and, when practicable, on a special train not hampered by an absolutely fixed time table. It may often be desirable to make partial tests of efficiency, to ascertain, for instance, the relative economy of different fuels, requiring simply evaporative tests of the boiler, or the economy of different conditions of work- ing the cylinders, for which feed water tests would suffice. These may also conform as far as necessary to the standard methods recommended. We advise in general that the locomotive test, whether made in the shop or on the road, be conducted with such completeness that all the information relating to the performance of both the boiler and the cylinders be determined. With this object the data to be found em- braces the weight of coal burned, its chemical analysis, heat of combustion, weight of ashes and cinders, weight of water evaporated and that lost by overflow of the in- jector and otherwise, moisture in the steam, temperature of the escaping gases, analysis of the gases, force of the draught, pressure of the steam in the boiler and steam chest, number of revolutions of the driving wheels per minute, indicated horse power of the engine, tightness of the valves and pistons, and pull on the draw-bar. For a road test we advocate starting with a good fire, the actual thickness to be estimated, and burning it down to the same thickness and condition (as near as can be estimated) at the end of the run ; the observations noted for the start being taken just before the time of beginning to run, and those noted for the stop, im- mediately after reaching the end of the trip. We realise that this method applied to the road test is not scientifi- cally accurate, but it must be remembered that the rate of combustion in a locomotive fire-box is exceedingly high, and the error which occurs in estimating the thickness of the fire (should the observations be slightly AMERICAN LOCOMOTIVE BOILER TRIALS. 245 erroneous) is far less serious than in stationary boilers working at their usual slow rate, and, under the circum- stances, this seems to be the best course to pursue. For the measurement of the feed water we advocate the employment of a reliable water-meter, suitably calibrated at the time of use. Observations of the instrument can be made leisurely and at regular inter- vals, whether the locomotive is in motion on the road, or at rest. The familiar method of tank or tender measurement must, on the other hand, be based on observations taken only at stopping places, and these often in great haste. Although a meter is not always accurate, it is believed that for the purpose in view it is much less subject to error than observations made at the tank. The meter observations should, however, be checked by tank measurements made at all water stations. The apparent weight of water fed during a certain period must be corrected for differences in the quantity of water in the boiler at the beginning and end of the period, but in making this correction, which must be done by observing the positions of the water line ift the glass water gauge, it is important that these positions should first be corrected for the inclination of the boiler, and measurements at the tank should likewise be cor- rected for the inclination of the tender. The weight of ashes and cinders found on the road test furnishes little indication of the actual amount of ash and unhurnt matter in the fuel, on account of the great chance of loss through the stack, due to the effect of forced draught. It is desirable, however, to obtain these weights, as they often fiirnish some indication of the character of the fuel. The percentage of ash, from which the quantity of combustible is found, should be obtained from the calorimeter test of the coal. Keoent progress in the determination of the heating value of the coal, by the use of some form of oxygen calorimeter, has been so satisfactory that the relative quality of different coals can now be readily and definitely measured. It is fully as important to know the character of the fuel as to find the number of pounds of coal burned, and no test can be satisfactory that leaves out the heat value of the fuel. Chemical analysis of the ooal is desirable, and it gives much useful information, but it is believed that the heat test is of greater value. The introduction and development of the wire-drawing calorimeter, with or without separating apparatus, has made the determination of moisture in the steam, especially on locomotives, a comparatively simple matter. No reason now exists for omitting the calorimeter test for want of a suitable instrument. We recommend, for a standard basis on which to compare the efficiency of locomotives, the number of pounds of standard coal burned per dynamometer horse-power per hour. The term ' ' standard coal " refers here to coal in which the total heat of combustion, as determined by an oxygen calorimeter, is 12,500 British thermal units per pound. The unit 12,500 B.T.U. is selected, partly on account of its numerical simplicity, and partly because it represents the total heat of the average grades of coal used in the United States. To convert the actual amount of coal used into the equivalent weight of " standard coal," the weight of coal burned is multiplied by the total heat of combustion of the coal, and the product is divided by 12,500. We advocate this unit of standard coal, believing that it is extremely desirable to refer the efficiency of different engines to a coal basis. In view of the practical diffi- culty of always testing the locomotives with the same kind of fuel, the method of correction given above is recommended. This method may be regarded as to some extent approximate, but we believe the compara- tive results obtained by its use will be all that can be desired. The consumption of standard coal is referred to the dynamometer horse-power ; that is, the power obtained from the pull on the draw-bar, — first, because the dynamometer horse-power is a correct average record of the power developed ; and, second, it is the useful work done by the engine. In selecting standard coal and dynamometer horse- power as the leading units of comparison, we do not underrate the desirability of expressing the performance in terms which are commonly used, and in any other terms which may render the results complete, and these should be made a part of the report. Of these we recommend for purposes of comparison the weight of coal and water and the number of heat units of the steam consumed per indicated horse-power per hour ; the same, referred to the dynamometer horse-power ; the weight of actual coal and standard coal referred to the ton mile of total load and the ton mile of train load ; and the number of lbs. of water evaporated per lb. of coal. With these results the performance of the locomotive may be well studied in detail. Preparations for Test and List of Instructions. A locomotive should be put in good condition pre- paratory to the test. The boiler and tubes should be tight, and both the interior and exterior surfaces should be clean, and if possible free from scale. There should be no lost motion in the valve gear, and the valves should be set properly. No change in the engines should be allowed during the progress of a series of tests, unless so ordered for the purposes of the trial. A glass water-gauge should be fitted to the boiler, if not already provided. The following instruments should be verified or cali- brated : — Steam gauges, draught gauge, pyrometer, thermometers for calorimeter and feed water, water meter, tank, revolution counter, indicator springs, and dynamometer recording mechanism. The radiation loss on the steam calorimeter should be determined, or the normal readings ascertained ; and the quantity of steam which passes through the instrument in a given time should be measured. To facilitate the measurement of coal, and the determination of the quantity used during any period of the run, it is desirable to provide a sufficient number of sacks of a size holding a weight of say 100 lbs., and weigh the coal into these sacks pre- paratory to starting the test. If desired, the sacks may be numbered, to facilitate the accuracy of the record. To facilitate the work of operating the indicators and reading the instruments at the front end, the smoke box should be surrounded with a fence, resting on the top of the cowcatcher and extending back far enough to enclose also the sides of the cylinders. This box is floored over, and the enclosure thus provided forms a convenient 246 HEAT EFFICIENCY OF STEAM BOILEES. space for the accommodation of the assistants at this end of the locomotive, and it alfoi"ds.theni some measure of protection against wind and rain, as also the jolting and vibrations due to rapid ti'avel. A special steam gauge with a long syphon is to be used for registering the boiler pressure. It can be best located on the left hand sidS of the cab. A draught gauge, consisting of a U-tube containing water properly graduated in inches, should be connected to the smoke box, and attached to the side of the pilot box. A pyrometer for showing the temperature of the escap- ing gases should be used iii a position below the tip of the exhaust nozzles. The calorimeter should be attached either to the steam dome at a point close to the throttle opening, or to the steam passage in the saddle casting on one side, according as it is desired to obtain the character ■ of the steam at one point or the other. The former location is preferred by the committee. A perforated half-inoh pipe should be: used for sampling and convey- ing the steam to the calorimeter pipe. The water meter should be attached to the suction pipe of the injector, and located at a point where it can be conveniently read when the locomotive is running. It should be provided with a check valve, to prevent the hot water from flowing back through it from the injector, and a strainer to intercept foreign material. To ndeasure the depth of the water in the tank a metallic float should be used, carrying a vertical tube, which slides upon a. graduated rod, the lower end of which rests upon the bottom of the tank. This should be placed at the centre of gravity of the water space. If the desired location cannot be used, provision should be made for ascertaining the level or inclination of the tank. The best device for this purpose is a plumb line of a cer- tain known length, provided at the bottom with a double horizontal scale, having one set of divisions parallel to the side of the tank, and the other set at right angles to it. From the readings on these scales referred to the length of the line, the level of the tank in both directions can be ascertained. A similar- device should be attached to the boiler, to correct for the variation in its inclina- tion. The plumbline may be conveniently attached for this purpose at some point near the front end. It is needless, except for a complete record of directions for preparatory work, to call attention to the desirability of having the test, and especially the road test, made under the supervision of a competent person, who is not only familiar with the details of testing, but also with the proper method of firing and mechanical operation of the locomotive. This is a most important factor, for it is only the clear-headed and able experimenter who is likely to obtain satisfactory work in this most difficult department of engineering tests. In the matter of assistants, the conductor of the test is best able to judge as to the number required, the various duties of the different men, and the manner of taking reooi-ds. A good test can be made with eight assistants, distributed in the manner indicated in the following list which gives their duties : — Two cab assistants, who read the steam gauge, the- position of the throttle valve and reversing lever, the water meter, the height of water in the tank, the height of water in the glass water gauge, the level of the tank, the number of times the whistle is blown, the length of time the safety-valve blows, the length of time the blower is in action, the reading of the counter, the temperature of the feed water in the tank, the time of starting and stopping the injector, the time of opening and closing the throttle valve, and the number of sacks of coal used. These two observers have previously checked the weights of coal placed in the sacks. Three pilot-box assistants, one of whom reads the pyrometer, the draught gauge, the steam chest gauge, the revolution counter, and marks on the indicator diagrams the time, position of reversing lever, steam chest pressure, . and revolutions per minute. He also takes the levels of ■ the boiler, at the stopping places. The other twO'; observers are stationed at the cylinders and manipulate the indicators, one being employed on each side. One calorimeter assistant, who reads the calorimeter, thermo- > meters, and the gauges connected with the instrument, if these are employed. Two dynamometer car assistants, who record time of each start and stop time of passing each station and each mile-post, time of taking each indicator diagram as obtained from signals of the indicator men. All these readings are marked, so far as possible, on the dynamo- meter paper. One of these men also assists the cab observer in read- ing the tank depth and its levels at stopping places. These men also keep a record of the direction and force of the wind, and the temperature of the atmosphere. An additional assistant is required if the gases are sampled and analysed. It is of paramount importance, after the complete pre- paratory work has been accomplished, that the locomo- tive be subjected to a preliminary run of sufficient duration to make a fair trial of the testing apparatus, and to give the various assistants an opportunity of be- coming trained to their duties. Data and Results of Test on Loco. Made 189 Kind of engine, . Heating surface, sq. ft., Grate surface, ,, ,, Diameter of exhaust nozzles, Whole run. Total Duration hrs. Weight of dry coal burned, including -i weight of wood, lbs. Weight of water evaporated corrected for moisture in the steam, .... , , Weight of ashes and refuse from ash pan, . ,, Weight of cinders from smoke box, . . , . Percentage of ash, as found by calorimeter test, . % Total heat of combustion per lb. coal, as found by Calorimeter test in B.T.U,, ■■ . Pull on draw-bar, . ... lbs. Dynamometer horse-power, .... h.p. AMERICAN LOCOMOTIVE BOILER TRIALS. 247 Whole run. Total Quantities — continued. ■ Boiler pressure, Temperature of smoke box, Mean -! draught suction, . Temperature of feed water. Temperature of atmosphere, Percentage of moisture in the steam. Weight of dry coal burned per hour, . Weight of dry coal burned per hour per sq. foot of grate surface, . . . , Weight of dry coal burned per hour per sq. foot of heating surface, . Weight of water evaporated per hour. Equivalent weight of water evaporated per hour, with feed water 100° F. and pres sure at 70 lbs., lbs. deg. F. in. lbs. Whole run. Total Quantities — continued. Equivalent weight of water from 100° F. at 70 lbs., evaporated per sq. foot of heat- ing surface, . . ... Coal consumed per I.H.P. per hour. Coal consumed per dynamometer horse-power per hour, ...... Weight of "standard coal" consumed per I.H.P. per hour Weight of "standard coal" consumed per dynamometer horse-power per hour, Water evaporated per lb. of coal, . Equivalent evaporation per lb. of coal irom and at 212° Equivalent evaporation per lb. of combustible from and at 212°, . lbs. Analysis of Gases if possible. Locomotive Boiler. APPEI^DICES. APPENDIX I. On the Cost of Generating Steam in Factoeibs. Summary of various Experiments extending over Long Periods. These numerous and practical experiments on steam boilers, lasting several years, were made by Herr Jaufs, Director of the Cologne and Kottweil Powder Factory. Their object was, not to advocate any particular type of boiler, nor to reach an abnormally high rate of evapora- tion, but to ascertain the cost of evaporating steam in the ordinary way, and under usual working conditions. The iirst set of trials was carried out in 1892 on thirteen boilers fired with German coal and briquettes at Rottweil, and five at Diineberg burning English coal. A better evaporation was obtained with the latter, and the Diineberg boilers were not so forced. Automatic feed water purifiers were used throughout. The coal was analysed, and the German was found to be of better q^uality, though the English coal, being cheaper, gave more economical results. The experiments were contin- ued throughout the year, the coal and feed water weighed, and the temperature of the latter taken. The gases were also sometimes analysed, and a dasymeter was used in some of the trials, resulting in an increased boOer efficiency. The feed water was measured with a good water meter. The efficiency, or utilisation of the heat in the coal, was higher in the summer than in the winter, varying at Diineberg from 67%. in May to 75% in August. The first table shows the work done in 1892 by the thirteen boilers at KottweO, with a total heating surface of 11,384 square feet. The heating value of the coal varied from 13,507 T.U. to 12,857 T.U. per lb. Steam pressure 7 atmospheres. Water evaporated per lb. of fuel from 32° F. to 212° F.— 7'56 lbs. Mean boiler efficiency 66%. Cost of evaporating 220 gallons of water 3 shillings. The mean result of the year's work at Diine- berg on five boilers, with a total heating surface of 5380 square feet, using English coal of 12,385 T.U. per lb. and with a steam pressure of 7 atmospheres, was a boiler efficiency of 70 '6%, and an evaporation of 7 '62 lbs. of water from 32° F. to 212° F. per lb. of coal. Cost of evaporating 220 gallons of water 2'38 shillings. A table follows, giving 41 experiments on different boilers at Rottweil with different German coals. Each boiler had a heating surface of 1076 square feet, and 28 '4 square feet of grate surface. The best of these trials gave an efficiency of 84"3% with briquettes of 13,892 T.U. heating value. "Water evaporated per sq. foot of heating surface per hour. Coal burnt ,, ,, ,, grate ,, „ Water evaporated from 32° F. to 212° F. per lb. of coal, . Steam pressure 5J atmospheres. Percentage of COg, 3-12 lbs. 11-64 „ 10-18 „ 11-5 % Each of the boilers tested had large water tubes about 24 feet diameter, in two tiers, three in each row, or six in all, running the whole length and forming the boiler, while the hot gases passed outside them. The grate was inclined, of the Tenbrink type, with the furnace in the centre of a tube surrounded by water. Thirteen experiments were also made at Diineberg on boilers of exactly similar type and dimensions, all fired with English coal of 12,151 T.U. heating value per lb., and containing 4 j% ash. The highest efficiency attained was 76%, with a steam pressure of 7-3 atmospheres in chimney. Percentageof COo, 12-3%. Excess of air over that theoretically required for combustion, 54%. Water evaporated per hour per sq. foot of heating surface. Coal burnt „ „ „ „ grate surface, . Water evaporated from 32° F. to 212° F. per lb. of fuel, . 249 3-6 ] 16-4 8-06 250 HEAT EFFICIENCY OF STEAM BOILERS. Another set of eight experiments were carried out at Diineberg on three boilers with the same English coal. Two of the boilers had a heating surface of 516 square feet, and 13 square feet grate surface, the third had 774 square feet heating, and 19 3 square feet grate surface. The highest boiler efficiency was 78'3%. Steam pressure 6 atmospheres. Air in excess, 59%. Percentage of CO,, 11-6%. Water evaporated per hour per sq. foot of heating surface, Coal burnt ,, ,, ,, ,, grate surface, Water evaporated from 32° F. to 212° F. per lb. of fuel, 4-8 lbs. 22 „ 8-3 ,, The coal and the residuum after combustion were chemically analysed. The heating value was calculated from the analysis according to the following formula, drawn up by the Verein Ueutsoher Ingenieure, and the German Association of Boiler Inspectors (C being carbon, H hydrogen, oxygen, S sulphur, W hygroscopic water in the coal). 8000 C + 29000 h[H- °")+2500S-600W in calories per kilogramme. The results of the different experiments are plotted in curves in the original paper. By means of these careful and exhaustive trials, the price of evaporating 220 gallons of water at Eottweil was reduced from 4s. 3d. in 1891 to 3s. in 1892, or an economy of Is. 3d. Of this saving Herr Jaufs attributes only 38% to the lower price of coal, and 62% to the better working methods introduced in the trials, one of which consisted in the purifying of the feed water. , Such a gain in economy rendered it advisable to make further experiments. These were undertaken in 1893 and 1894, and in all of them a dasymeter, draught gauge. pyrometers, and good thermometers were used, the coal was weighed, and feed water measured. As briquettes had been found to give the best results, they were burnt whole, instead of being broken up, as before, but it was more difficult to obtain the full utilisation of the heat from them, and from hard coal, than from coal of lower value. Gaseous coal gave the best results. With bri- quettes the boiler efficiency was from 73% to 75%, with a uniform evaporation of 3 '2 lbs. of water per hour per square foot of heating surface. After many trials, it was found possible to utilise the briquettes to even better advantage than English coal. From January 1893 to June 1894, 86 trials were made at Rottweil, all with German coal and briquettes. Various boilers were tested, all exactly of the same type as those already described. The maximum heating value of the briquettes was 14,627 T.U. per lb. Five experiments were also made at Duneberg on a similar boiler under the same working conditions. The mean results of these trials are summed up in a short Table. The highest efficiency, 79%, was obtained at Rottweil, with a mixture of gaseous coal and briquettes. Water evaporated per sq. foot of heating surface per hour. Coal burnt , , , , , , grate , , , , Lbs. ot water evaporated from 32° F. to 212° F. per lb. of fuel, f , The lowest efficiency, 67 "2%, was with the same mixed fuel. ' Water evaporated per sq. fiiot of heating surface per hour. Coal burnt' ,, ,, „ grate ,, , ,, Water evaporated per lb. of fuel, from 32° F. to'212° F.,' . 3-4 14 9-52 lbs 3-1 14-6 8-13 lbs )1 Thl-ee of the boilers at Duneberg, each ha'vpg 1076 square feet of heating, and 28'4 square feet of gi-ate sur- face, were then tested continuously for a week, day and night. Briquettes and English coal mixed were burnt, and gave a mean evaporation of 8 "45 lbs. water from 32 to 212° F. per lb. of coal, and a mean efficiency of 72%. Water evaporated per sq. foot of heating surface per hour (mean), Fuel-burnt ,, ,, • ,, grate ,, _,, ,, 2-0 lbs. The same boilers were also tested for one week working by day and by night only, saparately, under otherwise similar conditions. By day they gave a mean efficiency of 77 '1%, and , an evaporation of 8 '93 lbs. water per lb. of fuel ; by night, an efficiency of 627%, and an evapora.^ tion'of 7'6 lbs. of water per lb. of fuel. Two Lancashire boilel-s at Duneberg were also tested for a week, under the same conditions, burning briquettes only. They had a' total heating surface of 2119 square feet and a grate surface of 72 "3 square feet. Diameter of the boilers 7 '2 feet. Length 32 '8 feet. Diameter of each furnace tube 27 feet. The highest boiler efficiency was 90%, when evaporaiting 11 lbs. of water per lb. of fuel from 32° F. to 212° F. ; the lowest was 74-4%, with an evaporation of 8 '95 lbs. of water per lb. of fuel. The cost, of evaporating 220 gallons of water at these tempera- tures was reduced to about 1'8 shilling. Lastly, there were 40 experiments made in January and February 1.894, on two of the Diineberg boilers, each having a heating surface of 774 square feet, and ,19:3 square feet 'grate surface. English coal was burnt^ arid the boilers were worked night and d^y. The highest efficiency obtained was 87 •3%, with an evaporation of 9-39 lbs. of .water from 32° to 212° F. per lb. fuel, and the lowest 62%, with an evaporation' of 677 lbs. of water at the same temperatures per lb. of fuel. It was found that in all these trials the efficiency was practically the same ;with all kinds, of German coal, '-puie and mixed, but the briquettes witli a heating value of 14, 627 T. U. per lb. gave the best results, iind an efficiency of 78 '6%. In APPENDICES. 251 some of the weekly trials no special supervision was exercised, and tha ^oilers were stoked as, usual. As much less steam was required at night, the fires were let down towards evening, and vigorously stoked towards moTniug, to raise the steam pressure for beginning the day's work. Hence the value of experiments extending over long periods. The Diineherg boilers gave rather better economy with smaller than with larger heating surfaces : all boilers were hand-fired. The results obtained being so satisfactory, experiments were next made in both factories with the object of using briquettes only as fuel. From January to December 1893 and 1894 the work of all the Rottweil boilers was tabulated monthly. Fired with mixtures of German coal and briquettes, they gave a mean boiler efBlciency for 1893 of 72-2% and for 1894 of 74-1%. Steam pressure 7 atmospheres. In 1893, with a fuel com- posed of about equal parts of coal and briquettes, the mean evaporation per lb. of fuel was 8'53 lbs. water from 32° to 212° F. ; in 1894 it was 8-84 lbs., with a mixture of ^ lb. coal to 5 J lbs. briquettes, showing the greater efBciency obtained when the proportion of briquettes was much increased. At Diineherg the efBciency of the boilers burning 3 lbs. of English coal to J lb. of briquettes was 70%, with an evaporation per lb. of fuel of 7*6 lbs., of water from 32° to 212° F. In 1894 the two kinds of fuel were used in more equal proportions. The heat utilised varied from 71% to 72%, and about 8 lbs. of water from 32° to 212° F. were evaporated per lb. of fuel. Tables are added in. the original paper showing the cost of evaporation, heating value of the coal, and other details, both at Eottweil and Diineherg for 1891, 1892, 1893, and 1894. During these years the boiler efficiency i;ose from 55% to 73% at Rottweil, and from 66% to 72% at Diineherg, with a corresponding increase in the water evaporated, and diminution in the cost of evaporation, which was always lower at Diineherg. The heating value of the coal was calculated from the chemical analysis of " air-dried " fuel according to the formula already given, and also determined in a Berthelot-Mahler bomb calori- meter. The two sets of results agree closely. The com- bustible residuum was also carefully analysed, after free- ing it from water and ash, the C, H,.S, 0, and N separated, and the percentage of coke, water, ash, and volatile substances determined. The author sums up the economy obtained by impi'ov- ing the working conditions as follows : — Duringthese four years the evaporation of water per lb. of coal increased in Eottweil 38%, in the new boilers at Diineherg 14%, and in the old boilers 25%. The cost of evaporation fell 39% in Rottweil, 28% in DUneberg, representing a gain for 1894 alone of nearly £6000. Part of this saving is attribut- able to the better working conditions, by means of which it was possible to substitute briquettes as fuel, instead of the dearer coal. Fourteen per cent, was due to the cheaper combustible itself, and 86% to improved con- ditions, although the latter did not necessitate any change in the grates. The author considers that Lancashire boilers wiU give 78% boiler efficiency, but only on con- dition they are not forced, and are made to evaporate about 2J lbs. of water per square foot of heating sur- face per hour. . This agrees well with the highest curve on p. 223, fig. 77. When forced, the efficiency diminishes, but much less with Tenbrink than with ordinary grates. The greater efficiency of the summer, as compared with the winter, is tabulated from September 1891 to March 1895. The author lays special stress on clean feed water, which greatly contributed to the improved working conditions.^ 1 Summarised from the Zeitschrift dei Vereines deutscher Ing^nieure, March 31st, 1894, December 14th and 2l8t, 1895. This is a valuable collection of practical experiments, and full of instruction. It shows what can be done with careful trials and attention to details, and what large sums of money have been saved in annual cost of evaporation. 252 HEAT EFFICIENCY OF STEAM BOILERS. APPENDIX Table showing Data obtained ekom actual Experiments on Boilers, compaeed with the Results Authority, Name, etc. Per 1 lb. of Coal fired. Heat absorbed per sq. ft. of Firebox per hour. Gases entering the Tubes. Heating surface. Area through Flues. Air at 60 deg. Heat de- veloped. Tem- perar ture of Gases. Speed per second of Gases. Transmission. Fire- box. Tubes. Total. Per deg. dift. Per sq. ft. per hr. Report of the Re- / search Committee, Inst. Mech. Eng.," May 1890. 1, See ante page 73. Fusi Yama, Colchester sq. ft. •5 •15 sq. ft. 1^79 •86 sq. ft. 2^29 1^01 sq. ft. •015 •008 lb. 22^8 18^5 Ther. units. 12,500 13,054 Ther. units. 11,036 21,053 Fah. deg. 1285 2165 ft. 17 63 42^2 Ther. units. 4^2 8^82 ITier. units. 4,120 16,237 Spence's trials Navy- type boiler, N.E.C.- Eng., 1888. See ante pa^e 65. Natural draught, Cold forced do. Hot (261°) forced do. •28 •24 •31 1-34 1-08 1^46 1-62 1^32 1^77 9^0 3^28 2^05 1^05 •010 •009 •012 16^6 20^0 18^0 13,000? 18,453 17,216 17,967 1916 1833 1879 •26^2 35-3 24^3 63 7^26 6^12 10,162 11,108 9,645 Thornyoroft's water tubeboiler,P.I.C.E..<( vol. XCIX. See ante page 111. D Natural draught, . . C -27 in. forced draught B-49in. E 2-00 in. „ •4 •143 ■09 •046 8^6 3^137 1^96 1^004 •064 •02 •012 •006 17^4 17-8? 18^1 W2 14,946 14,500? 14,270 13,622 17,000 24,294 26,089 28,543 1886 2600 2651 2878 6^25 18 •S 31^8 66^4 2^92 65 8^88 136 4,395 13,812 20,299 33,973 Thomycroft'slocomo- tive type torpedo boiler, P.I.C.E.,"^ vol. LXVI. 2 in. forced draught, , . 3 in. 4 in. ,, 6 in. ,, •06 •05 ■04 •031 •61 •477 •38 •309 •67 •527 •42 •34 •003 •002 •001 •001 20- ? W 7 W ? 14- 7 13,900 ? 13,360? 12,750 ? 12,360? 24,683 26,760 29,276 33,097 2624 2694 2898 3206 ]32^5 160 • 189^4 2^26 • 174 20^ 22-8 26-9 37,862 46,920 58,163 76,907 8 H.-P. boiler. / Koyal Agricultural Society, portable engine trials at the.< Newcastle Show, 1887. Report. All with induced draught. See ante page 79. Ahiwick, Foden (single cylinder), ,, (compound) .. M'Laren (single oyl.), „ (compound), D. P. & Co. (single), .. „ (compound), Cooper, . . ■i •68 •56 •8 ■744 •88 •75 •35 1^105 6^12 6^09 41 4^026 4^63 5^29 1^62 1605 6^8 5^66 4^9 4^77 6^41 6^04 1^97 •008 •03 •028 ■014 ■014 •022 •025 ■01 23^2 12^4 W2 26^2 27^4 23-6 24^4 W 13,264 13,964 14,715 14,940 14,880 14,646 14,664 14,644 14,668 14,539 12,666 12,622 14,800 ? 13,900 14,316 12,820 13,628 14,877 9,427 9,468 9,267 9,899 17,014 23,190 24,801 19,483 24,977 20,886 18,160 7,537 1460 1619 1697 1194 1213 1164 1247 1849 2299 2473 2053 2488 2142 1387 1006 36^9 6^68 8^16 20^8 22^7 12- 11^4 30 •S 4 36 10^8 24^4 18^4 3^53 17^11 11^20 657 2^66 3^46 4^61 4^77 3^37 3^42 6-9 7,470 3,104 4,460 3,832 4,031 2,773 3,013 10,307 5,880 10,710 11,271 13,868 4,642 4,899 2,066 HolUday, P.I.C.E., vol. XCII. Donltin • Type with Smoke Tubes. 6-63 1-7 432 385 341 8155 55-6 4303 29-6 12,468 86-1 12,736 87-0 2188 14-9 1911 13-0 10,819 73-9 6-0 1-7 440 410 366 7424 0-6 22 33-6 12,346 84-2 12,629 85-5 2818 16-8 2136 14-5 12,645 85-6 14-2 2-8 615 680 363 5956 41-0 5925 40-7 11,880 81-7 11,568 79-6 2664 18-3 2976 20-4 10,384 71-4 / 1-6 -9 600 399 298 6957 47-8 5775 39-6 12,732 87-4 13,416 92-1 1886 12-6 1162 7-9 9,621 6B-1 4-6 11-9 1-7 2-8 790 770 630 700 304 327 4117 2299 28-4 18-1 7268 6667 50-0 62-7 11,385 8,966 78-4 70-8 1-2,077 9,331 83-1 73-7 3154 3699 21-6 29-2 2462 3334 16-9 26-3 9,679 8,839 66-5 65-7 - Lancashire. > 7-2 2-1 690 648 326 3297 26-2 6831 64-7 10,128 80-9 10,288 82-2 2394 19-1 2234 17-8 9,472 75-6 / 1-4 -8 565 422 307 6067 40-9 6633 44-8 12,690 85-7 13,287 89-8 2110 14-3 1613 10-2 11,464 77-5 max. Cornish. 9-96 7-84 2-2 2-0 615 565 560 565 212 323 ' 4869 5060 35-0 36-3 5226 4396 37-6 30-7 10,095 9,446 72-6 66-0 10,468 9,546 75-3 66-6 3805 4870 27-4 34-0 3432 ,4770 24-7 83-4 9,225 8,163 66-3 57-0 > Locomotive. 254 HEAT EFFIOIENCY OF STEAM BOILERS. FoKMULa;. H,! = heat units developed per 1 lb. fuel, less latent heat of any moisture evaporated from the fiiel. Ha = heat units available above temperature of steam, = B.a-w{Ts-60). A = lbs. air per lb. fuel ; assumed temperature, 60°. s = specific heat of gases, taken as "24. w = heat capacity of gases, = s (A + 1). F = heating surface exposed to radiant heat, in sq. ft. per lb. fuel. S = tube or flue surface, sq. ft. per lb. fuel. C = sectional area through tubes or flues, sq. ft. per lb. , fuel. V = speed of gases in tubes or flues, feet per second. T,, = temperature of gases, Fahrenheit. Ts = temperature of steam, Fahrenheit. B = coefficient of transmission = 1250, when same is calculated step by step for successive intervals, terminating at the following values of S respec- tively : -05, -15, -3, -5, -8, 1-3, 2, 3, iS, 6-5, 9. Then, heat units absorbed in fire-box per 1 lb. fuel = H„x 1 A-(-45F (1) Available heat units remaining in gases leaving fire-box A Temperature of gases leaving fire-box Speed of gases 144,000 C . A \ , A + 45F^ Ax(Tj-H461) (2J (3) (4) Thermal units transmitted per square foot per degree per hour, in tubes or flues _T9 + Ts + 922 V'W 2 "" B" (5) "Alnwick" Portable Engine, Numerical Example. ParticularB — H, sq. ft.= 5,128-7- -4 . . . =12,820 Available T. unitsremammglngases=ll,736-5128 = 6,608 Smoke Tubes. Surface in section, sq. ft. Entering temperature v= -0192 (T5-)-461) Transmission per ]_deg., v Tsr+Ts+922 Vj) f 2 12B0 > Degrees of diff. = Ts - Ts Transmission T.IT. per ) sq. ft. . . )" ,, for section Fall of temperature J. Final „ P. Values of S (see previous column). 0--05J-05--15 •16- -3 •3- -5 •5-^8 •8-1-8 •05 •1 •15 •2 •3 •5 1460° 1396° 1280° 1136°: 989° 827° 36-88 36-65 38-42 130-66 27-84 24-78 6-57 6-30 1 5-84 6-27 4-72 4-12 1137 1073 957 813; 666 604 7470 6760 5688 4284 3143 2076 373 676 838 857: 948 1038 64° 116°, 144° 147°, 162° 179° 1396°i 1280° 1136° 989° 827° 648° Temperature of gases on leaving, ^^^ -1-823 = 1,460° F. APPENDIX III. "Wakm Blast Steam Boilee Fuunaoe." Trials of an Apparatus for transferring Part of the Heat of escaping Flue Gases to the Furnace. — By J. C. HoADLET, Boston, U.S. These carefully conducted trials made by Mr Hoadley extended over nearly a year. They are not described in the text, because they took place about 1881, and because, although they proved a certain economy by the use of heated instead of cold air to the furnace, the method was too costly for general adoption. The trials, however, were so accurate, and carried out with such care, that they should not be wholly overlooked. As much is often learnt by comparative failure as by success ; a brief summary of them is therefore appended. The experiments were made on a boiler at Lawrence, Massachusetts. Their object was to determine what portion of the heat generated escapes up the chimney to waste, how much of this waste could be arrested and re- turned to the boUer, by utilising it to heat the air supplied for combustion, and what kind of apparatus was most suitable for this purpose. A drawing of the externally fired cylindrical boiler used, with return smoke tubes, is given at fig. 79. Two sets of trials were carried out, one with air supplied to the furnace in the usual way, at the temperature of the external air ; in the other the supply of air was previously heated by the chimney gases. The two boilers used were both exactly alike, each being 5 feet in diameter, a,nd 21 feet long. There were 65 smoke tubes, each 34 in. diameter, with 1 in. clear space between them. The air heating tubes were above, on either side of the centre flue, as shown in fig. 79. The fire grates were of the ordinary type, about 5 feet long. Both boilers were set in brick- work, and elaborate precautions taken against loss by radiation and air penetration. But in spite of the ut- most care, it was found that air filtered in, not only through cracks, but through invisible fissures in the APPENDICES. 255 o-J nioz brick- work. To prevent this the smoke flues were coated with desiccated tar, and covered with tarred cotton cloth. The coal, refuse fi-om the grates, feed water, and quan- tity of air entering were all measured, the products of combustion analysed, and the quality and pressure of the steam, temperature of the a fires, and radiation from the =t brick- work determined. The coal used was Boston anthracite and Cumberland bituminous. Samples were continually taken, *®°°' and two independent analyses were made each week. The feed water was measured in tanks. The amount of air in excess was determined by calculation from the analysis of the flue gases, and the temperature of the latter isoo' was taken by mercurial ther- mometers plunged in oil cups set in the flues. The gases were sampled daily ; the quality of ,Qgo the steam was determined in a steam calorimeter, and the tem- perature of the furnace was ^-^^ taken by means of iron and platinum balls, according to the method described at page 192, Chap. X. The temperature of the flue gases was also repeatedly taken. To determine the radiation from the brick - work, it was necessary to ascertain its tem- perature. With this object, various interesting ex- periments were made, which, so far as the author is aware, have not been carried out so perfectly before. Two small closed tin vertical vessels, 1 foot square and 1 in. thick, were fixed against the brick-work, and covered on every side, except that in contact with the masonry, with flannel and eider-down. At the top of each was a small round hole filled in with cork, through which were passed two glass tubes, one for the incoming water, carried down nearly to the bottom of the vessel, the other, ending near the top, for the outflow. The side of the vessel next the briok-work was covered with lamp black, to absorb the heat. The temperature of the water in and out was noted, and the quantity flovring through each vessel in a given time. The two "radiometers" were placed on the smoke-box cover, in front of the boiler, and the difference in temperature of the water in and out was taken every flfteen minutes. The mean increase was found to be 24° F. with one and 30° with the other. The mean radiation over the whole surfeoe was 40 B.T.U. per square foot per hour. Holes were also made for studying the transmission of heat through the brick-work, which of course passed through it from within outwards, by conduction. These holes alternated in depth, some penetrating deeply into the brick-work, and others being very shallow. Ther- mometers were inserted in each, to get the temperatures f the brick-wOrk at diflferent depths. These temperatures are plotted graphically, and show clearly the variations due to the opening of the fire doors, etc. The holes penetrated into the brick-work 4, 8, 12-, 16, 20, 24, and 28 in. respectively from the outside. The extreme and the mean variations of temperature are all plotted and shown in diagrams in the original, and three sets of observations were made. The first series extended HOADLEYS EXPERIMENTS OK HOT AND COLD AIR FOR COMBUSTION FORCED DRAUGHT COLO AIR INLET CURVES, FALL OF TEMPERATURE OF CASES FROM FIRE > TO CHIMNEY. PLOTTED ON BASE OF HEATING SURFACES "^ >s«t*ST .TEM PERATURE OF GASES ESCAPJNCTO 0HlpNEV_AFTER.PA33mG_TUaES. |KeiRitLRI_OF STEAM ( WATER IN BOILElT. .'ilj.1. <-n23SQ.FT.TUBE3 BOILER BOTTOM OFBOILEB -22G2 SQ.FT.FOR COOLING GASES . AND HEATING AIR FOB COMBUSTION. bAsE line square FEET Kg. 79. through the working hours of one week, and were taken every quarter of an hour in the hole 28 in. deep, and 12J feet from the front end of the boiler. Here the tempera- ture fluctuated on the first day from 239° F., when the fire was first started, to 400° F. at closing time. On the other days the fluctuations were not so marked, ranging about 50° from 344° F. to 394° F., whUe on the fifth day the brick-work attained its maximum temperature of 452° F. It cooled down about 30° at night. The next set of observations were taken every fifteen minutes during one day of six hours, in three holes at depths respectively of 24, 16, and 8 in. from the external surface of the brick -work. In the 8-in. hole the tempera- ture rose from 180° F. to 293° F., in the 16-in. hole from 230° to 487° F., in the 24-in. hole (84 feet from the fire) from 294° to 519° F. In the third series thermometer readings were taken in holes 4 in., 16 in., and 28 in. from the outside surface of the brick-work. In the 4-in. hole the temperature rose from 118° to 180° F. ; the other holes gave results similar to those of the former trials, but not quite such high temperatures. A study of these diagrams and tables shows the great importance of thick walls round boilers. For sampling the gases Mr Hoadley used a small steam or elettric pump, about J inch diameter and j in. stroke, to pump the gases from the flues. Such a pump has also been employed by the author for the same purpose, and it forms a convenient substitute for a siphon. The apparatus for heating the air was fitted on the top 256 HEAT EFFICIENCY OF STEAM BOILERS. of the boiler, as seen in fig. 79. It consisted of two sets of tubes placed above the fines, each having 120 tubes, or 240 in all, 2 in. diameter and 20 feet long. The hot gases from the fire were led as shown, first under the boiler, then through the smoke tubes, and thence into the heat-abstracting tubes. These latter were set 3 in. apart in twelve rows, ten tubes in each row. Originally each was encased in a thin iron spiral locked outer tube 3 in. diameter. Through the annular space thus formed the cold air was drawn in to feed the furnace. It entered in the rear through an iron box at the top, and was dis- charged at the front end at the bottom into flues in the brick- work, conveying it to the ash-pit through arches in the side wall. By means of the tubes a large heating surface was provided for the air. The hot flue gases were drawn from the smoke box, and after passing through the heat-abstracting tubes were earned downwards through a brick flue to a Koot's exhauster, creating induced draught, whence they were discharged to the chimney. The currents of gases and incoming air were regulated by dampers. The main difficulty found was with the grates. A water grate was used at first, but had to be abandoned, because it leaked badly. Ordinary long grates were then tried, and after working three weeks showed signs of wear, and were discarded. "Williams' rocking grates were substituted, and gave good results. They obviated to a great extent the necessity for keeping the fire doors open for a long time, and it was only found needful to clean the grate once a day for ten minutes. Mr Hoadley is, however, of opinion that the best type to use with the warm blast would be a water grate, if possible. The drawbacks of this system of heating the air were found to be, first, the cost of the tubes; secondly, that they were apt to become choked with dust and dirt ; and lastly, that the hot gases did not part with enough of their heat, but were discharged at a temperature of about 160° F. above that of the outer air. The external 3-in. tubes were therefore omitted, and only the internal 2-in. tubes retained ; the construction of the latter was simpli- fied and made less costly. The air circulated around and between the tubes containing the hot gases, and its course was directed by deflectors or baffles of sheet-iron, set at intervals of about 1 foot, as shown in the drawing. The total heating surface of the tubes was 2262 square feet, and of the smoke tubes 1123 square feet. The air entered at the top, and passed along and between all the tubes, until it was discharged at the lower end to the ash-pit. The cost of the deflectors was very much less than that of the 3-in. tubes they replaced, and the impact of the air against them and against the surfaces of the heated tubes increased its temperature. The whole heat-ab- stracting apparatus was covered in brick-work, and encased externally in galvanised sheet-iron, and this improved arrangement was added to the boiler previously worked with cold air. Much better results were obtained than before, and the temperature of the escaping gases was reduced 20°. The greater part of this gain was attributed to the increased motion of the air, which circulated freely among the tubes. It is essential, however, with the warm air apparatus, as with ordinary firing, that all cracks in the brick-work should be stopped, and all doors and covers carefully packed. A large number of trials, extending over many weeks, were made, first, on a boiler fitted with the ordinary method of supplying cold air ; secondly, on a similar boiler fitted with the warm air apparatus first described ; and lastly, on a boiler fitted with a warm air apparatus of the improved type, namely, with single tubes for the hot gases, and air circulating outside them. The power required to drive the exhauster for the induced draught was about 1% of the total. A summary under each of these three working conditions is given of the pressures, tem- peratures, consumption of coal and feed water, and efficiencies. The percentage losses at the chimney caused by radiation and imperfect combustion were 22% with the ordinary boiler, and 18% to 19% with the warm air supplied to the furnace. The net gain is from 10% to 12% by the use of the hot blast arrangement for warm- ing the air, as compared with cold air for combustion. A condensed record is shown of results of six weeks' observations. The ratio of heat utilised to heat supplied in the coal, or boiler efliciency, was 77% with cold air to the furnace, and 81% with warm air, or a difiereuce of 4%. Other tables show the analysis of the coal and of the flue gases, with the dampers both open and closed ; the observations of temperature in the warm air apparatus, taken at the bridge wall and in the heart of the fire by methods already described ; these are also plotted on curves. The temperatures found with the ordinary and the warm air boilers are then compared, and it is seen that in the latter the gases were cooled 213° and the temperature of the incoming air raised 300° F. The temperature of the furnace was carefully studied. The comparative temperatures are shown in a diagram, and are reproduced, with the surfaces, at the side of fig. 79. This curve shows the exact course in the two sets of experiments, of the fall of temperature from the furnace, where it was 2750°, down to a temperature of 400° at the end of the boiler, and about 200° F. at the end of the air-heating tubes. The quality of the steam and amount of priming water also formed the object of numerous trials. The flue gases were continuously analysed, and various interesting experiments made. The boiler steam pressure is also given for the different weeks of the trials, and the transmission of heat through the brick-work is gi'aphically shown in a number of curves. These tests afford an excellent collection of facts re- specting combustion in steam boilers, and their effi- ciencies. As such they are valuable for reference, and for studying the effects of hot and cold air for com- bustion. APPENDIX IV. List of Boilbes at the Hydbaulic Powek Com- pant's and the Elbctbio Lighting Company's Stations in London in 1897. The following list of the numbers and types of boilers at the Hydraulic Power Company's Stations in London may be of interest, as they have all been erected during the last few years. At the Falcon Wharf Pumping Station, Blackfriars, there are four Lancashire boilers, 28 ft. by 7 ft., working APPENDICES. 257 at 85 lbs, steam pressure ; at Kensington Court two Cornish, 16 ft. by 4 ft. 6 in., steam pressure 80 lbs. At Millbank Street, Westminster, the Company have three Lancashire boilers, 30 ft. by 7i ft., steam pressure 100 lbs. At Wapping and City Boad Stations there are six Fairbairn Beeley boilers (two storey), twelve in all, each working at 150 lbs. steam pressure ; while at the Mill- bank Street (Extension) Station, four Fairbairn Beeley boilers work at the same pressure. All these nineteen boilers are internally fired, with Vicars' stokers. Green's eoonomisers, and chimney draught. The above list was kindly furnished by the engineers, Messrs Ellington and Woodall. The following is a list of the type and number of steam boilers put in at the different electric lighting stations during the last five or six years, and up to the year 1897. It has been kindly communicated to the author by the chief engineers. At Amberley Road Station there are 5 locomotive boilers. At Westminster Electric Station, 3 dry back boilers. At Netting Hill Station, 1 locomotive, 2 Babcock and Wilcox water- tube boilers. At Metropolitan Electric Station, 12 Babcock and Wilcox water-tube boilers. At Kensington Court Station, 5 dry back, 2 Babcock and Wilcox water-tube boilers. At Chelsea Station, 4 Babcock and Wilcox water-tube boilers. At St James, Pall Mall Station, 5 locomotive boilers. At St Pancras, King's Road Station, 5 Lancashire boilers. At St Pancras, Regent's Park Station, 8 Babcock and Wilcox water-tube boilers. At City of London Station, 28 Babcock and Wilcox boilers with Vicars' stoker. The steam pressure at these various stations ranges from 100 to 160 lbs. APPENDIX Y. Note on the Db Laval Watee-Tube Steam Boilek. (Pressure 3000 lbs. per square inch.) At the Stockholm Exhibition of 1897 several of these novel and interesting boilers were shown, giving an aggregate of 500 H.P. The boilers are vertical, and the usual pressure is about 115 atmospheres, but they have actually been worked up to 300 atmospheres. Twice a day the tubes feeding the coal into the fire-box are refilled, and the feed water and steam pressure are regulated automatically, according to the consumption of steam. The coal is fed into the tire-box from an elevated platform, and the ashes fall through rotary bars into a receptacle beneath. The vertical boilers are of the water-tube type, and consist of a single tube of small diameter, twisted into several spirals or coils. There is no water chamber, because the water is trans- formed into steam as soon as it enters the boiler, as in the SerpoUet system, and is supplied in proportion to the consumption of steam. The fire grate is circular, and has a revolving motion. The air necessary for com- bustion is forced beneath the grate by a fan, coupled direct to the shaft of the Laval steam turbine. The feed water is pumped continuously into one end of the spiral coil, and passes through it with considerable velocity. There is no steam chamber, the boiler consisting entirely of this coil, in which the steam generated is highly superheated before it is led to the engine. The very rapid circulation of water makes the heating surface very effective. A 100 H.P. steam turbine with boiler and condenser only occupies a floor space of 19 feet by 10 feet, and the boiler being self-contained no brick-work is required, except for the foundations. The air for combustion passes through an outer shell, thereby absorbing the radiant heat. At the Stockholm Exhibition these boilers were generally worked at 1700 lbs. pressure per sq. in., equal to a tem- perature of steam of 600° F. This short account has been summarised from Engineer- ing, 26th November 1897. APPENDIX VI. -CoLOUK OF Flames, etc., in a Marine Type Boilee, AND Smoke Tubes. WITH Two Internal Flues The following notes give an account of the appearance of the interior of the uptake, as seen through a sight hole during an hour and a half of Mr Spence's boiler trial, No. 1, page 65. Time. 3.0 3.3 3.4 3.12 3.17 Fires thin and bright, violet flames some 2 feet long, curling upwards towards chimney till When flames disappeared, and interior of uptake became clear, with no smoke, till When loth fires were charged ; uptake black and full of dense smoke. Both fires raked ; slight red blush, soon dying away. Red flame some 9 inches long, issuing firom tubes, and continuing till 258 HEAT EFFICIENCY OP STEAM J30ILERS. I'ime. 3.21 Wlieu uptake again became clear. S.S:2 Both fires charged ; dense black smoke with one or two short Hashes during charging. 3.27 Red iiame from ends of tubes ; light smoke from chimney. 3.33 Flames died away ; no smoke. S.31 Fives raked ; slight red appears, but dies away soon. ■3.35 Red from all tubes ; flames terminate in violet. 3.3,ii Violet i)art of flame considerably increased. 3.36 Flame red for about 6 inches from tube ends, tapering into violet about 3 feet long, curling up into chimney. 3.39 Flames froju one-half of tubes disappear; red and violet flame from other part shortens, and red portion becomes lighter and more yellow. Total length of flame (red and violet) about 12 inches. 3.40 Flame disappears ; a few sparks come through tubes till S.J^l WJien loth fires were charged ; thick black smoke ; a few red flashes for a moment or two. 3.51i Fires raked ; uptake still black and full of smoke. 3. 58 Red blush appears at ends of tubes. 3.59 Red flame, about 9 inches long, coming from tube ends. 4.1 Red flame now extending about 2 feet, and curling up chimney, dull red at tip, but no violet. 4. 2i Flames gradually dying away, coming from only six or seven tubes. 4.4 Uptake black again. 4 8 Fires charged ; uptake full of dense black smoke. 4.15 Red llames beginning to appear, 4. 16 Red flames, 12 inches long, coming from about half the tubes. 4. 17 Fires raked ; while door was open, whole interior of uptake filled with dull red glow. 4.18 Uptake black again. 4.20 Red flames beginning to appear. 4. 2 1 Red flames with violet tips from nearly all the tubes, violet rapidly increasing. 4.22 Whole uptake filled with violet flame, except for small red portion, about 3 inches from tube ends. 4.24 Violet flame, toning into sky-blue, from tubes opposite furnace, and curling up into chimney. 4.25 Flames from about six tubes only, composed of 3 inches red, 6 inches violet, 3 feet sky-blue. Total length of flame, 3 feet 9 inches. 4. 26i Faint greenish-blue from one tube ; short yellowish-green flame from another. 4.28 Uptake black, except yellowish -green flames, about 6 inches long, intermittently from two tubes. 4.29 Uptake black ; sparks through tubes ; fires thin and very bright. 4.29^ Fires raked ; shower of Sparks through tubes, but uptake black. J^.SO Fires charged ; thick black smoke. On one occasion, just before the violet flame began, the uptake temperature registered 750° F. ; a few minutes aftenvards, when filled with blue flame, the temperature was 910° F., the fires not having been touched in the interval. — ("On the Combustion of Coal," by W. G. Spence, pp. 158, 159, Proc. N.E. Coast Inst. Engineers and Shipbuilders.) Violet flame means a good deal of CO gas. APPENDICES. 239 APPENDIX VII, Heating Sttkfaces of Coknish axd Lascashike Steam Boilbks of diffbrbnt Lengths and Diameteks. Without Cross Tubes or Smoke Tubes. Gornisli Boiler. Diameter. Lengtli. Diameter of Tube. Heating Surface. ft. lus. 5 6 ft. 20 ft. ins. 2 9 sq. ft. 363 5 6 25 2 9 462 5 6 30 2 9 562 6 20 3 401 6 25 3 509 6 30 3 G18 6 6 20 3 3 459 6 d 25 3 3 547 6 6 30 3 3 665 7 20 3 6 462 7 25 3 6 ■ 590 7 30 3 6 717 7 6 20 3 9 504 7 6 25 3 9 642 1 6 30 3 9 777 8 25 4 730 8 30 4 875 Lancashire Boiler, Length. ft. Ins. 5 6 5 6 5 6 6 6 6 6 6 6 6 6 6 7 7 7 7 6 7 6 7 6 8 8 ft. 20 25 30 20 25 30 20 25 30 20 25 30 20 25 30 25 30 Diameter of Tube. ft. 2 2 2 2 2 2 o 2 2 2 2 2 3 3 3 3 3 ins. 3 3 3 6 6 6 Heating Surface. sq. ft. 431 561 670 471 605 736 518 664 809 564 723 SSI 611 783 954 925 1110 260 HEAT EFFICIENCY OF STEAM BOILERS. Appendix viii. Paris Smoke Tkials. Trials made by the Municipality of Paris ou various Apparatus for the Prevention of Smoke from Steam Boilers. Summai-y of the Engineers' Report, December 1897. In June 1894, a Commission was formed by the Muni- cipality of Paris, to consider the question of the Preven- tion of Smoke, and to carry out competitive trials of dirt'erent apparatus for that purpose. The labours of this Commission extended over three and a half years, and their Report has just been printed privately. The object of the trials was to examine the different systems entered for competition, to select such as appeared most suitable, to test them by various experiments, and to draw definite and practical conclusions from the results. Three prizes were offered, of £400, £200, and £80, respectively. In all, 110 apparatus for "diminishing smoke" in the furnaces of steam boilers were presented, and these were divided into the following classes : — 16 mechanical stokers. 20 with supplementary injection of hot or cold air. 5 with injection of steam, with or without the ad- dition of air. 7 for thoroughly mixing the products of combustion and smoke. 7 for burning gaseous fuel. 2 fired with powdered coal. 16 smoke washers or soot catchers. 37 miscellaneous. Among these apparatus 76 were French, 19 English, 4 German, 3 American, the remaining 8 from difl'erent countries. After careful examination, the above number, of which a detailed list is given in the original Report, was reduced to 30, the rest being rejected. These were then inspected, as far as possible, at places where they were working, and finally 8 apparatus were admitted to the decisive tests. Trials on these took place from June 1894 to May 1897 at Paris, each of the eight systems being worked for a month. The results aimed at by the engineers' sub-committee of the Commission were essen- tially practical, and comprised the two following condi- tions. Each apparatus was 1. Not to give off an inconvenient amount of smoke, when fired with ordinary fuel. 2. To satisfy the practical requirements of combustion and evaporation in steam boilers. Working conditions. — In order to keep the conditions of the trial as uniform as possible for the diS'erent com- petitors, the following technical programme was drawn up. Each experimental apparatus was to be tested under a boiler of ordinary dimensions, used to generate steam for mills. The points to be specially kept in view during each trial were, the degree of intensity of the smoke produced, evaporation or lbs. of water evaporated per lb. of fuel burnt, and general working conditions, cost, ease in handling, steadiness while running, etc. To ensure uniformity it was decided to test all the apparatus under the same boilers, with the same fuel, and at the same two rates of evaporation. The total duration of the trials was one month in every case, but each system was during this time subjected to an official test of four days, two days with the boiler working ©ncsteami eugiiie onfy, and two days with the same boiler -working two steam engines. In other words, the evaporation per square foot of heating surface per hour was. nearly doubled on the last two days. It is these official tests alone which are here dealt with. During the rest of the time the- apparatus were worked to supply power in the usual way. The two Tables at the end of this summary give- the mean evaporative results for each apparatus, of two- days' tests with one, and two days' with two engines. The steam pressure was the same thi-oughout, and as far as possible the same stoker was employed. The boiler efficiency is not shown in the original Report, as the- heating value of the coal is ne>t given, but it has been worked out by the author from data kindly supplied at his request, and will be found in the Tables. The other columns are filled up as usual. Boilers. — The boiler plant belonged to the Munici- pality, and was in use at the Pumping Station on the Quai de Javel at Paris. There are three elephant boilers- exactly alike, and two water pumjjing steam engines. The boilers are usually very easily worked, and each supplies one engine only, but if forced one boiler will supply the two engines without difficulty. The height to which the water is raised and the speed of the engines- are practically constant. The three boilers are in a line,, and the experiments were all carried out alternately on. one or other of the two end boilers. In each the cylin- drical shell is 4'5 feet diameter, and 11 '5 feet long, with fifty smoke tubes, each 2'9 in. internal, and 3'1 in. ex- ternal diameter, and two "bouilleurs." Total heating, surface, 730 square feet. Total grate surface, 16 '14 square feet. Height of chimney, 98 feet. Diameter at the top, 2 '3 feet ; diameter at the bottom, 4 feet. The boilers throughout the trials were supiJied with cold feed water. Fuel. — ^The combustible was the same throughout, namely, briquettes made from Anzin coal from the North of France, where this combustible is much used. This fairly smoky fuel was selected because the composl; tion of the briquettes was tolerably constant. It con. tained 8 '17% ash, and 17-84% volatile matter. Before the competitive trials, a test was made on one- of the same boilers, with the ordinary horizontal grate and usual bars. It was undertaken to accustom the staff to the conditions of trial, and, to establish a basis of' comparison for the smoke observations, was carried out with the same fuel and stoker, and was again repeated at the close of the regular official tests. Two methods, of observation were employed throughout, — firstly, the measurement of the intensity of the smoke produced, and secondly, the determination of the evaporative power of. the fuel, working one and two engines respectively. Smoke observations. — ^The Commissioners decided that direct observation of the top of the chimney was the best way to estimate the volume and intensity of smoke emitted. Two points of view were therefore chosen in the windows of houses, about 1000 feet from the chimney, and at a good height from the ground. One lay to the north, the other to the south, so that whatever the direction of the wind, the amount of smoke produced might be within the line of sight. A careful watcher was installed in each; and kept a record of the degree of smoke according to the following scale. 1. No smoke. 2. Slight smoke. 3. Medium smoke. 4. Black smoke.. APPENDICES. 261 5. Very thick smoke. These were noted every minute throughout each ten hours' trial on a continuous belt of paper divided into small squares, and fixed round a drum driven by clockwork. A pen above the drum was moved by each observer, and allowed to trace a mark on the re- volving paper. The diameter of the drum was about 3 J in., length about 8^ in. The paper was divided in one direction into spaces of 1 mm. , each representing one minute of time, so that an hour occupied about 2| ins. In the other direction it was marked off into five divisions, representing the five different intensities of smoke, and numbered in columns 1 to 5. When no smoke was emitted from the chimney the observer did not move the pen. With No. 1 degree of smoke he moved it to mark No. 1, while witli intensely black smoke (No. 5) the pen was moved out to record a mark on No. 5 column. The pen rested on the paper for the same length of time as such smoke was produced. In this way, at the end of the ten hours' trial, a certain smoke area could be calculated fi'om the diagi'ams thus produced, and a comparative number worked out, repre- :senting the relative area of the smoke diagi'am ; in other words, the quantity of smoke for each apparatus for the ten hours. For instance, with the ordinary grate, the ill umber representing the quantity of smoke was 8 '9. With apparatus No. II. this same representative number was only 0'25 ; and the quantity of smoke for all the other apparatus was calculated in the same way. The results obtained by the two isolated observers :agreed very well together ; slight differences were due to variations in the light, and in the direction of the wind. As far as the author is aware, this method of observing and recording smoke is good and new. Euaporation. — To determine the evaporation from the boiler, it was necessary to take count of the quantity of feed water used and fuel burnt during the experiments. The water was measured in a gauged tank and by a water meter on the feed pipe, the one forming a check upon the other. A glass water gauge, marked to scale, was, as usual, fixed on the fi'ont of the boiler, to show the level of water in it. Care was taken, at the be- ginning and end of each trial, to bring the steam pressure and' the level of water in the boiler to the same point. The temperature of the feed water was taken, but the amount of primjug in the steam was not deter- mined. As all the trials were made under similar con- ditions, this omission could not affect the comparison of the results. The fael burnt was weighed in small trucks. Fires were lighted at 6 a.m. and the experiment began each day at 8 and ended at 6 p.m., leaving everything, as far as possible, in the same condition as at the beginning. Samples of Hue gases were taken every half hour, and Analysed for COg in an Orsat apparatus, an Arndt "Econometer" not giving sufficiently accurate results. The amount of draught was measured by means of a re- .cording draught gauge in three places, above the grate, in front of the damper, and behind it. Some of the mass of data thus obtained are shown in the accompany- ing Tables. The utmost attention was paid to every detail by the staff of experts, and drawings of all the grates and boilers are given in the original paper. Ko. I.. Apparatus. — Ordinary grate. — The first ex- jperiments, as already stated, were made on an ordinary horizontal grate 3'7 feet long and 4'2 feet wide. Witli one engine the evaporation was 9*6 lbs. of water per lb. of fuel from and at 212°, and 9"1 lbs. with two engines. Boiler efficiency 65'5% and 62'1% respectively. In the final trials made with this gi-ate the evaporation was 10 "5 lbs. of water per lb. fuel with one engine, and 1 "3 lbs. with two. Boiler efficiency respectively 71"6 % and 70'3 %. The boiler worked well, and the pressure of steam was easily maintained, but the smoke was thick and very inconvenient during at least three-quarters of the time. Kepresentative smoke number, 8 "89. This boiler could not have yielded a much higher evaporation, as there was so much resistance to the passage of the gases through the tubes and fines. The following conclusions were drawn from the experiments : — That with a good plant, properly proportioned and carefully stoked, a good evaporative result may be obtained ; but if tlie combustible is smoky, it is im|iossible with such a grate to abolish, or even to diminish the smoke. No. II. Two grates. — The first trials on a special apparatus were made with an American down draught furnace with two grates. In these furnaces combustion proceeds downwards from the upper of the two grates. By regulating the admission of air, the products of com- bustion and smoke are drawn down through the top grate on to the glowing fuel of the second gi-ate below it, and a good combustion is secured. Both grates are about 4 feet square. With one engine the boiler evaporated 11 '2 lbs. of water fi'om and at 212° per lb. of fuel, and with two engines 10 '7 lbs. Boiler efficiency 76"4% and 73 "0% respectively. There were several stoppages during work, because the pressure could not be main- tained when steam was supplied to two engines. On one occasion it fell to 43 lbs., instead of 78 lbs. as required ; this was attributed by the inventor to an error in construction. The writers of the Report consider that in theory this is a very interesting system. The circula- tion of water through the hollow bars of the upper grate prevents overheating, and these bars increase the heating surface, but there was some smoke, the representative smoke number being 2 '34. Mean percentage of CO., in the fine gases 6 •4%, showing a gi-eat excess of air. The delicate part of the apparatus appears to be the tubular grate bars, which are exposed to the hottest flame, although communicating freely with the water in the boiler, and there is some risk of an accident. Probably on e reason of the bad results obtained with a grate which has achieved considerable success in America is tliat briquettes of inferior coal were burnt on it, instead of anthracite or hard coal, for which it is principally intended. No. III. Vertical grate. — The next trial was made on a German grate, the vertical bars of which form a kind of rectangular box, connected to the flues by a brick combustion chamber. The air passes horizontally through the fuel, which is introduced from a hopper above, and burns in a vertical column. The admission of air is regulated by dampers in the charging doors. Some of the bars are movable, to facilitate the passage of the clinker and ash to the bottom of the grate. The boiler evaporated 10 '1 lbs. of water per lb. of fuel, from and at 212^, with one engine, and 10-4 lbs. with two engines. Boiler efficiency 68-9% and 71-0% respectively. The apparatus worked well, and st(?ani of the requisite 262 HEAT EFFICIENCY OF STEAM BOILERS. pressure was generated without difficulty as long as only one engine was supplied, but as soon as the second was connected the pressure fell. Of all the systems tested, this grate proved the best as regards smokeless- ness. Representative smoke uumber 25, or one- thirtieth the smoke emitted by the ordinary grate. This is due to the skilful arrangements to obtain com- plete combustion ; the fresh fuel is fed on to coal already coked and in a state of incandescence ; the hydrocarbons are slowly distilled from the bottom upwards, and the gases, before reaching the heating surfaces, are thoroughly mixed in a hot chamber. The conditions laid down in the Report, as essential to complete and smokeless com- bustion, gradual distillation of the fuel, and thorough mixing of the gases and air at a high temperature, are thus attained. The accumulation of clinker at the bottom of the grate soraewljat checked the draught, but this might easily be remedied. As in most grates of this type, there was one serious difficulty, namely, the close contact of the water tubes and the iijoandescent fuel. Any incrustations, defects in circulation, unequal ex- pansion, or faulty joints, might cause an accident, hence special precautions are required. , iVo. IJ'. Inclined grate. — Experiments were next made on a Fronch inclined grate, in which the combustible is fed in at the top, and descends by gravity. The gases of combustion and the air, heated by passing through coal already coked, are mixed in a fire-brick chamber before coming in contact with the heating surfaces. The grate bars, as well as the fire bridge, are hollow, with water circulating through them, and are connected to the lower part of the boiler. The fuel is first fed in from two automatic hoppers upon a dead plate in front, where it is partially turned into coke. With this gi-ate the boiler evaporated 10'9 lbs. of water from and at 212° per lb. of fuel- when worked with one, and 9'8 lbs. when supplying two engines. Boiler efficiency 74 '4% and 67 '0% respectively. Several of these apparatus are working satisfactorily at Paris. The grate being of good size, the boiler supplied the two engines without difh- . culty, and gave less smoke than when feeding one. Representative smoke number 2 "48. The diminished smoke with greater evaporation was probably due to the increased current of air. The writers of the Report con- sider that this grate is rather complicated, and the water circulating tubes of the bars and fire bridge constitute a difficulty. The flames are in too direct contact with the water in the boiler for absolute safety, No. V. Smoke washer. — The next system tested was a French smoke washer or soot catcher. The gases on leaving the flues wore drawn through a kind of eoonomiser, then upwai-ds through a column containing coke con- stantly moistened. Artificial draught was irsed. The economiser had forty-eight tubes, each affording lOJ square feet of heating surface ; the feed water passed through, and the gases outside them. A fan then delivered the gases into a short cast-iron chimney, 20 I'eet high and 6| feet diameter. The water for washing '.he smoke was supplied by a pump which, with the fan and scrapers, was driven by a small engine. The boiler evaporated 10 '9 lbs. of water from and at 212° per lb. of fuel when worked with one, and 10 -1 lbs. with two engines. Boiler efficiency 74'4% and 68'9% Tospectlvely, excluding the economiser. As the smoke was discharged from the mouth of the short chimney, about 22 feet high, instead of from the tall chimney, the smoke observations were not as complete as usual,. Representative smoke number 8'80. The apparatus was- stopped several times for repairs, and when the boiler was connected to the second engine, the pressure fell too low to continue working. The invention was not found successful during the trial. The purifying column only slightly diminished the intensity of the smoke, while the repairs and constant renewals of the coke were troublesome. As it does not seem possible to abolish the- complicated machinery of the fan, pumps, etc., the writers of the Report do not consider the .systent desirable. No. VI. Special French grate. — These experiments' were made on a new French grate in two parts. The fuel is first fed on to the front, which is divided from-' the back part by a brick arch and wall, \yhen distilla- tion is sufficiently advanced, the half-coked fuel is pushed over to the back, and the residual products are forced on to a third stage, where combustion is completed. This- ledge is rocked by hand from a lever, and the clinker and ash fall into an ash-pit provided with a movable partition, to regulate the admission of air. The total heating surface of the gi'ato is 26^ square feet. The boiler evaporated 9'8 lbs. of water from and at 212° per lb. of fuel with one engine, and 10 '3 lbs. when supplying two- engines. Boiler efficiency 67 '0% and 70'3% respectively.. The apparatus was no sooner set to work than a piece of the brick arch gave way,' and later on one of the grate bars was burnt out. It is, however, an improvement on the ordinary method of stoking smoky coal, the different parts of the grate being ingeniously divided off, in somewhat the same way as in a Tenbrink grate. The apparatus was fairly smokeless, the representative smoke number being 2'10. There was some loss of coal, owing to the necessity of raking it down successively from one stage to the next. .No. VII. Grate with injectimi of steam and air. — This is another French apparatus, in which steam from the- boilei', and air are injected into the furnace after stoking. The -steam jets are arranged round the furnace, converg- ing to the centre, and draw in the air with them. The boiler gave with this gi-ate an evaporation of 1 '4 lbs. of water from and at 212° per lb. of fuel when supplying one engine, and 10 "2 lbs. when supplying two. Boiler- efficiency 71 '0% and 69 '6% respectively. The quantity of steam used for the jets was determined by condensing a small portion separately in a tank. A slight difficulty was found with these injectors, as they did not always^ act properly, in spite of the automatic regulation. Th^ objection to the use of steam jets in a boiler furnace is the large quantity of steam required. The apparatus was fairly smokeless, the representative smoke number being 3'93. The consumption of steam for the injectors was about i% of the total water evaporated, and they were used for twelve hours out of the forty hours' trial'. As they can only act while the boiler is under pressure; they have been given up in many French workshops. No. VIII. Powdered coal firing without grate. — This was a German apparatus with powdered coal firing and no grate. The coal, previously ground to a very fine powder, is drawn into the furnace by the current of air created by the 'chimney. It is delivered from a. hoppcj APPENDICES. 263 above onto a sieve, whicli is tapped at reijeated intervals by a projection on a vertical revolving shaft, attached to an air turbine, and driven by the current of air in the chimney. The current carries the fine powder into the combustion chamber, which is lined with one-inch fire- bricks and kept always at a red heat. Here it is instantly ignited. With this apparatus the boiler gave 10 '5 lbs. of water evaporated from and at 212° per lb. of fuel with one engine, and 10 lbs. when supplying two engines. Boiler efficiency 71-6% and 68-3% respectively. The steam pressure was well maintained but care was re- quired, and a difBculty was found in getting the coal ground fine enough with the coal grinder used. The temperature in the combustion chamber was very high, and there was a considerable accumulation of ashes be- hind the fire bridge. Some smoke was produced, and the representative smoke number was 3 '35. The results ob- tained at Javel were not very favourable. Improvements have been made since. No. IX. F.nglish mechmiical stoker. — The last tests were made on an English mechanical stoker, in which the coal is fed from the hopper above on to a dead plate, where it is pushed into the furnace by two rams worked from an eccentric. The grate is formed of alternate moving and stationary bars ; the former receive a double motion from another eccentric, and the fuel is carried forward through the ^rate. At Javel, the power for driving the rams and the moving bars was provided by a small steam engine. From thirty to eighty throws per hour were delivered by the rams. "With this stoker the boiler evaporated 9*6 lbs. of water from and at 212' per lb. of fuel with one, and 10 lbs. with two engines. Boiler efficiency 65'5% and 68'3% respectively. No difficulties were found, the pressure was well maintained, and the combustion good, but the transmission gear re- quired attention. The apparatus was almost completely smokeless : representative number, 0"63. The authors of the Report commend this stoker from every point of view. Prizes awarded. — No first prize was given, none of the apparatus exhibited being considered worthy of it. The smoke washer was eliminated from the competition, as in it the production of smoke was not sensibly diminished. Of the seven others, jSTos, III. and IX. received the second prize. The first of these was the better, as re- garded the diminution of smoke, but it did not admit of the boiler being forced, while the mechanical stoker, al- though not quite so smokeless, was more practical, easier to work, and less cumbrous. No. II. received the third prize, because it evaporated the largest quantity of water per lb. of fuel of any grate. Nos. IV. and VI., which were equal to it in smokelessness, had honourable mention. These experiments, like those of the Prussian Smoke Commission at Berlin in 1892, served to elucidate the question of smoke production, and clear up many doubt- ful points, but also to show that the subject is still in the ezperimental stage. Some of the apparatus tested were almost smokeless, and gave an excellent evaporation, but much still remains to be done. The following con- clusions may, however, the Commissioners consider, he drawn from these trials. Official conclusions. — The idea that a smoke-consuming apparatus is not necespary to diminish smoke, but that the ordinary grate, if carefully stoked, will burn without smoke, is disproved. In spite of every care, the ordinary type of grate here tested produced more smoke than any of the others. On the other hand, smokelessness and economy do not always go hand in hand. The opinion has long been held that thick smoke carries off a large proportion of the fuel, but from the various trials made it is now known that soot contains much black matter, and that the blackest smoke only carries off an insignifi- cant proportion of carbon. At Javel the apparatus which gave the least smoke was not more economical in evaporation than the ordinary grate, when carefully stoked, and it appears probable that to produce no smoke entails a certain expense. The authors of the Report consider it erroneous to as- sume that every system of combustion which failed in these tests should therefore be condemned. Some of the grates tested at Berlin gave very good results, and in others, which were not admitted to this competition, the fuel was nevertheless burnt practically without smoke in a very satisfactory way. If coke only be used, there will seldom be any smoke, and this method of avoiding smoke is employed on steam-boats and in motor carriages at Paris, but it would be impossible to adopt coke universally as fuel. Poor and non-smoky coals may be successfully used up to a certain point, and this has been done with good results in the municipal workshops at Paris. It might also be possible so to modify the com- bustion chamber that the stoker could see the top of the chimney. It is further suggested that the various apparatus should be subjected to a permanent official test. As there is no economy to be procured by diminishing the smoke, it is evidently not to the interest of the manufacturer to do so; it is the public and the neighbours only who would be benefited. This is the kernel of the whole question. If it is absolutely desirable to avoid smoke, it will be necessary to exercise a certain con- straint over the individual, and his personal interest must be made subservient to that of the general public. The question is. Can this restraint be put in force ? In a town it certainly can and should be, by the local authorities, as soon as the smoke becomes a public nuisance. Pending the solution of this important question, the writers of the Report recommend the following remedial measures : — Practical measures recommended for the future, — The first step towards abolishing is to diminish smoke. All factory chimneys in Paris do not emit black smoke ; it is only a certain number which are in fault, and if the owners are forced to reduce their smoke, by improving the construction of the grates and burning less smoky coal, much would already be achieved. An order perhaps miglitbe passed prohibiting the productionofblacksmoke, not only in factories, but in private houses. Time and patience are needed to overcome so inveterate an evU. To sum up finally the result of the trials, the Commis- sioners are of opinion that, in spite of the severity of the tests carried out, it is doubtful whether the different apparatus experimented on would last, if subjected to hard practical work. It would be advisable to instal them in the different municipal workshops, and make them undergo more prolonged trials. The writers also consider that, as methods for preventing, to a great ex- tent, thick black smoke from factory chimneys already exist, an order should be passed to proAilit its production , and that permanent and efficacious steps should be taken to put the regulations now extant into execution. 264 PAEIS SMOKE 10 EXPERIMENTS ON SAME ELEPHANT BOILER AVITH EXTERNAL FURNACE, Boiler Efficiencies fkom 62 to 76j pek cent., all with same Fuel, " Beiquettbs d'Anzin." PAUTICUI-AKS of ItOILKK Tj-,KTIiI>. -a 9 Gases. i Wateb Evaporatkd. 1 Efficiencies or per cent, of Heat Value in Fuei utilised in Evaporating Water 1 02 Heating Surface Total. General Dimensions. .So II - 1^ a 1 Teniiierature of Furnace Gxses. Analysis of Furnace Gases (at end of Boiler when not otherwise stated). if , p 1 1 rt — it! •0 oS I Percentage by i Is .1 — sA is 1 si tc s s i lis P oilei* only Eeono isep on 1 fig : find of Boiler an differenc above St Temp. ; end of Rconom' \ olume. 1^ g. 1 CO., 0. CO, o a ^ c t* < ca a |.; ^.1 Si Percentage by : S 1 B . : ss 1 s B a ^' II 2 o |1 o s:^ a M 01 ■3 ^1 S|!a|g 1 T3 P gs Volume. 1 ^1 CO.,. 0. CO. ! 1 >J Ft, > ■< fia E Lbs. sq. in. F." < F.° >^ Lbs. Sq. ft. Sq. ft. Ft. Ins. Sq ft. 0/ 1 «/ % X X Lbs. / 1 83-9 470° 730 n-4 4-4 0-22 16 74"4 74-4 5-4 Notg iven. 8-8 10-9 j 2-3 i 326° 1 144° ! : 1 72-5 528° 1 1 1 Do. ' Do. Do. 0-33 IG 68-91 68-9 5-8 D 0. Do. 10-1 3-9 ! 1 317" 211° 1 f 1 i 82-5 529° Do. Do. Do. : 0-o2 26-5 670 1 67-0 8-2 D'o. 2-1 9-8 2-5 - - 325° 78-2 204° i 610° 1 f Do. 1 Do. Do. 0-57 26-5 70-31 70-3 322° 288° 9-7 Do. Do. 10-3 4-5 i 83-9 512° ■ ! Do. Do. Do. 0-53 16 71-0; :71-0 9-1 i Do. 3-9 10-4 j 2-4 326° 186° ! 1 78-2 640° 1 10-^ ' Do. Do. Do. 0-64 16 69-5 1 69-6 10-5 D 0. ; Do. 4-0 No Grate. 322° 83-9 318° 446° - 1 ! 1 1 ! Do. Do. Do. I 0-46 i 71-6 j71-6 i_ 1 326° 82-5 120° 9-8 Do. 3-3 10-5 , 2-3 1 495° 1 Do. Do. Do. 0-48 i Do. 68-3 68-3 325° 170° 10-7 r )o. Do. 10-0 i 1 S-9 /■ 82-5 490° 1 1 ! Do. Do. Do. 0'59 18-2 65-5' 65-5 9 Do. 0-63 9-6 I 2-4 ! 1 325° 165° 1 1 1 1 i i 85-3 639° 1 i Do. Do. Do. 0-62 18-2 68-31 i68-3 9-7 i Do. 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SB OS 's^iBd oAiij o:jui qoiB 3iiO4i-i[0iiq jfq papjAip 'afj^if) •Sui^fjoji saniSua om^ qfjiM. apBHi s^uarauadxa om^ jo nBam'aqi aw sajnSg asaqx 5X-6 •SuiJiioAi. amSua ano qim epBui s^uaniuedxa ojai} jo u^ara; eq; am sainSg asaqx S 61-81 •a^ioras aq^ qs^a. o^ sniiBi'eddv 'Sniiiio^ saaiSna an^ q^m apBui S4.uamuadxa oitj^ jo UBani aq^ ajB sajnSg asaqx os-zi •Sm^iioAi auiSaa uiBa^s auo q;m apBni s^uamuadxa oti.\ jo UEara aqi aiB sajnSg asaqx •oa 9681 585 9S5 IS ^■11 8.Z 8-8 j •oa iSl'^l ■oa asuej^ JO q^jojii 'uizuy.p sa;;anl)ug 7. ■sqi V. ■ 'ii-i I i 1 : 1 JO .TCSi ■juao .i9d m Jiv JO la P SE 1 lit ill i-*o as- If ■ps^on !;ou uoqM iBOf) ■saani axoMS houi-s aism Z:?^ >^^ aaiioa usEvnaaia ^^^ lanj JO lUOOJOQWU^ ■ai^ ■lan^ ^9S •XHOiivHa iaiJKiHO— saasiKONOoa "N ■ojs[ixj,as soma— DKraia hkihovw qniv aK"yH "siNswraadxa BIBLIOGRAPHY. BOOKS AND PAMPHLETS. Barrus. Boiler Trials. Boston, U.S., 1891. Bellens, Charles. Traite des Ohaudieres a Vapeur. Paris, Baudry, 1895. 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Scheurer-Kestner. Pouvoir calorifique des Com- bustibles. Paris, Masson, 1896. (Containing Biblio- graphy of French Authors in detail. ) Schmidt. Various Reports to the "Syndicat des Sucr^ries." Schwackhofer and Bro'wrne. Fuel and Water- London, Griffin, 1884. ■270 HEAT EFFICIENCY OF STEAM BOILEES. Seaton, A. E. Jlanua,! of Marine Engineering. London, Griffin, 1896. Ser, E. Physique Industvielle. Paris, 5Iasson, 1888. Spence, W. Cr. On the Combustion of Coal. Newcastle, A. Reid, 1888. Stohmann, T. Calorimetrische Uutersuchungen. Thorpe, Prof. Coal, its History and Uses. Mao- ■millan, 1878. Thurston , Prof. K. G. Handbook of Engine and Boiler Trials. London, E. Spon, 1890. Thurston, Prof. E.. G. Manual of Steam Boilers. New York, Wiley, 1888. Wilson, R. A Ti'eatise on Steam Boilers. London, ■€. Lookwood, 1879. "Witz, Prof. A. Etudes sur les Explosions des Scheurer-Kestner. ) Annales des Mines. (Rateau, Apijareils a Mesurer I'Humidite d'une Vapeur. ) Bericht der Commission zur Prufuiig von MaucJwer- irennungs Vorrichten. BericMe der deutsehen chemischen Qesellsohaft. ( Alexe- jew, Chaleur de combustion et composition des houilles russes. ) Bulletin de la SocicU chimique de Paris. (Articles ■ by Soheurer-Kestner. ) Bulletin de la SociM^ d' Encouragement pour I' Industrie Nationale. Bulletin de la Sociiti IndustrielU de Mulhouse. Bulletin de la Socidti Industrielle d' Amiens. Der Civil Ingenieur. Contours pour la ^Suppression des Fumies. Rapport . de la Commission Technique. Bingler's polytechnische Journal. (Fischer, Etude ■des gaz de la combustion. Sur la determination de la ■chaleur de combustion. ) Ibid. (Linde, Methode pour determiner la temperature initiale, etc., dans les recherches sur le pouvoir calori- -fique des combustibles.) The Engine, Boiler, and Employers' Liability Insur- ■ anee Company, Manchester. The Engineer. Engineering. Le Genie Civil. Industries. Institution of Saval Architects, Adelphi Terrace, London, Iron and Steel Institute, The Iron Age. Journal of Proceedings of Inst, of Electrical Engineers, Journal of the Franklin Institute. Journal far Oasbeleuchtimg. Journal of the Society of Arts. Manchester Association of Engineers. On the Evapo- ration of Lancashire Boilers (Longridge). Mimoires de la Sooiiti des Inginieurs Civils de France, Philosophical Magazine. The Practical Engineer. (Grover on the Economic Combustion of Fuel. ) Proceedings of the Institution of Civil Engineers. (Donkin and Holliday on Calorimeters. ) Proceedings of the Institution of Mechanical Engineers. Proceedings of the North-East Institution of Engineers and Shipbuilders, Reports of the National Boiler and General Insurance Company, Report of the Louisville Water Company, Report of the Committee for Testing Smoke-Preventing Appliances, Report of the Glasgow and W. of Scotland Smoke Abatement Association. Report of the Sheffield Smoke Abatement Association. Report of the Committee on Methods of Determining the Dryness of Steam (by Professor Unwin, F.R.S.). Revue Industrielle. Revue de Micanique, 1897. Circulation dans les ohaudieres ^ tubes d'eau. Walckenaer. Revue Technique. Steam User's Association, Boston, U.S. Syndicat des Fabricants de Sucre de France. Transactions of the American Society of Mechanical Engineers. Transactions of the American Society of Mining Uutersuchungen von Dampfmaschinen der Ausstellung in Dusseldorf, 1880. Zeitschrift fur angewandte Chemie, (Fischer, Etude sur le gaz produit par un gazogene. ) Zeitschrift des Vereines deutscher IngMeure, Zeitschrift der Dampfkesseluntersuchungs- und Ver- sicherungs- Gesellschaft, Zeitschrift fur Liiftung und Heizung, Zusammenstellung der vergleichenden Versuclie auf den Kaiserliehen Werften, Berlin, 1895, Mittleru. Sohn. PLATES OK STEAM BOILERS-LAjND, MARINE, AND LOCOMOTIVE ILLUSTRATING {A) PROGRESS MADE DURING THE PRESENT CENTURY ; (B) BEST MODERN PRACTICE. 272 HEAT EFFICIENCY OF STEAM BOILERS. ANCIENT AND MODEEN LAND STATIONAEY BOILERS— 1775 and 1897. Fig. 80.— SMEATON'S BOILER, 1775. About 155 sq. ft. heating surface. External fire. ( (- — - — — (1=-'==^ \^=r^~^^-^ Fig. 81.— LANCASHIRE BOILER, 1897. With two internal fires. 30 ft. long by 8 ft. diameter. About 1000 sq. ft. heating surface. 200 lbs. pressure. Both drawn to same scale. 273 ANCIENT AND MODERN MARINE STEAM BOILEES— 1820-1893. Bailers of the S. S. Luaani'a la'-O" diSr ir'O" long. IBS lbs. Eight Furnsces. 828 tubes 3V dia!' 1893. •••••• -•oa«»» -o»*a«« • — o««»***o« •--••••o«*a« • "••••••■•• • — oooo*o«»« • — ••••••••• • — •••o*ao«a •'~o*«*o*o*< • — •••ocoeoa • ~ •00090000 ~~oooooooo« -ooooooooa — oooooooa ooooooo oooooo* oooooo* oo ooooc - OOOOOOOOO— OO00O0OO-- — oooooo-ooo~oooooooo — "OOOOOOOOO — vooooooo ~ OOOOOOOOO — ooooooooo~ -OOOOOO OOO OOOOOOOOO— -OOOOOOOOO — OOOOOOOOO - —OOOOOOOOO — ^OOOOOOOOO— — OOOOOOOOO — OOOOOOOOO - -OOOOOOOOO — OOOOOOOOO— Zooooooooo _OOOOOOOAO -OOOOOOOO— -3- -oooooo*--/' -ooooooo — ' -OOOOOO o^, _ OOOOOO uz[ ■ — y""T» Fig. 82. -BOILER OP S.S. "LUCANIA," 1893. Pressure, 165 lbs. Double ended. 12 Boilers in this S. Ship. Kg. 83.— MARINE BOILER, 1820. 16 ft. long, to 5 lbs. pressure. Both drawn to same scale. 274 HEAT EFFICIENCY OF STEAM BOILERS. >s J^ CO p4 W ;> H ffl n S W O u o p^ l-I o r/1 1?; W ^ pcj Oi XI w |x o U| H ^ s <■! C M m Iz; OS S2 r/1 W >^ is o H " o EH S P "S 6b 275 ANCIENT AND MODERN STEAM SHIPS— 1815-1893. Fig. 86.— S.S. "LTJCANIA," 1893.— 165 lbs. steam pressure, Horse-power 28,000, 620 ft. long, 65 13,000 tons displacement. Twelve large steel boilers (see page 273). Two screws and two engines, miles per hour. Crew, 400 men. No. of passengers, 2000. ft. wide, 25 Fie 87 —MARGATE STEAM YACHT, 1815.— 10 lbs. steam pressure, about 14 Horse-power, 79 ft. long, 14^ ft. wide, 70 tons displacement. One copper boiler. Paddle wheels. Speed. 8 miles per hour. Crew, 6 men. No. of passengers, one or two. Both drawn to same scale. 276 HEAT EFFICIENCY OF STEAM BOILERS. EXAMPLES OF MODEEN MARINE BOILEBS— Internal Fiees. I PRESTON Fig. 88.— THREE ELUE AND THREE FURNACE BOILER, with Smoke Tubes. Fis. 89.— THREE FLUE SCOTCH BOILER, Double ended, with Six Internal Fires. Fig. 90. — Howden's method of Heating the Air for Combustion by the Hot Gases. ■Ill CO CO O O O W u •a? ^ FIX g* ■3 S O 0) 0.& IJ i g-g fi P=< from feed between h valves. i 1 § y ^ PiPj cil PMPLimliiO W^ H-i MhP 0) aj ^ So ' t^ 7. m « fc o ;h -^ n O 1' O O w„ J3 =3 £ S !r:i .,H «*-! H E=3 o „ s « c; oj -.2=S ^; 1 ! O m t«-. td S »H O O J M s s I to so Si 280 HEAT EFFICIENCY OF STEA.M BOILERS. EXAMPLES OF MODEEN COENISH AND LANCASHIEE BOILEES. Internal Eires. CORNISH BOILEE, with Smoke Tubes (Messrs Maeshall & Co.). Kg. 99. —Cross Section. Fig. 100. — Longitudinal Section. jmjiimiiijiiisM LANCASHIRE BOILER, with Cross Water Tubes (Messrs Marshall & Co. ). Fig. 101.— Cross Section. Fig. 102.— Longitudinal Section. 281 EXAMPLES OF MODERN CORNISH AND DRY BACK BOILERS. With Internal Fires. n""T 'to fed to iisw 'b* Wi liisi :te Kg. 103.— CORNISH BOILER (H. Patjcksoh, Landsberg, Germany). Furnace flue in short lengths and different diameters. (Copyright.) Fig. 104.— CORNISH BOILER (Messrs Mabshall). Kg. 105.— DRY BACK BOILER, with smoke tubes (Messrs Paxman). 282 HEAT EFFICIENCY OF STEAM BOILERS. EXAMPLE OF "PEEEET" WATEE-CASED GEATE. FoECED AiE Supply. LONGITUDINAL, SECTION. CROSS SECTION; Fig. 107. 283 EH I E-i I— I w M H t—t O I— I W CO H \^ I— I O Eh o pq w W a 12; P O o M S Eh >5' 03 W iJ o s o ■< ■ (J 6 Eh 285 CO Pi I— I H o w H Hi h- 1 O id ^ 02 O ■< M H p£| « O O X ■H m S « H h-i h-H o ffl f^ M 1— t M r/) <5 O S i pa w ti o o 02 en o O la <1 t o ^ J H P^ W W PS G f1 (■ 5 1— I § pq <1 H M f=H hd O ^ S O Ph [__;] S f^ <1 p M ^ P!? o I an M E 290 HEAT EFFICIENCY OF STEAM BOILERS. EXAMPLES OE MODEEN' WATEE TUBE BOILEES. External Fires. 121 and 122.— WATER TUBE BOILERS with Small Tubes (Messrs Thoknyoroft). Fig. 123.— WATER TUBE BOILER, Larger Type (Messrs Thokntoroft). 291 1— I O 3 f^ ^ O O 1-5 m H E-i X 292 HEAT EFFICIENCY OF STEAM BOILERS. EXAMPLE OF A MODEEN WATER TUBE BOILER— CLIMAX BOILER. External Fire — 500 H.-Power. Fig. 126.— "With small Steel Tubes. Nq Bj.jgjj pj^,g One Circular Grate, with Four Firing Doors. Fig. 127.— Plan. 293 EXAMPLES OF MODERN WATER TUBE BOILERS (with small tubes). External Fires. Kg. 128.— WATER TUBE BOILER (Messrs MiRRLBES, Watson, & Yartan Co.). Fig. 129.— WATER TUBE BOILER, smaU Tubes (Messrs MiRRLEES, Watson, & Yartan Co.). Fig. 130.— WATER TUBE BOILER, with small Tubes (Messrs Normand & Co., Havre). 294 HEAT EFFICIENCY OF STEAM BOILERS. EXAMPLES OF MODEEN WATEE TUBE BOILEES. With External Fire. k^mm \ Fi<^. 131.— WATER TUBE BOILER (Messrs Clabkb Chapman). Eig, 132.— WATER TUBE BOILER (Messrs Hoknsby). 295 EXAMPLE OF MODERN WATER TUBE BOILER. Fig. 133.— WATERjTUBE BOILER (Baboock & Wilcox). 296 HEAT EFFICIENCy OF STEAM BOILERS. EXAMPLE OF MODERN WATEE TUBE BOILER Front View. Sectional View. Fig. 134.— HAYTHORN TUBULOUS BOILER, 2'297 EXAMPLES OF MECHANICAL STOKEES. For Internal Fire Tubes. JFig. 135.— Sectional View (Messrs Vicaes). iff. las.— (Messrs Hodgkinson). 298 HEAT EFFICIENCY OF STEAM BOILERS. U2 o GO < o I— I o o i-:t 299 EXAMPLES OF MECHANICAL STOKEES. Foe Internal Fires. Fig. 138. — Mefsrs Vicakp 300 HEAT EFFICIENCY OP STEAINF BOILERS. ECONOMISEES. Fig. 139.— Messrs Gbeen's ECONOMISER, for Heating Feed Water by Hot Gases. Vertical 4-inch Tubes, with scrapers- Fig. 140.— Plan of Gbeen's ECONOMISER. 301 FEED- WATER HEATEl!. Fio'. 141.— COPPER COIL FEED- WATER HEATER, for Inside of Exhaust Steam Pipe. . EXAMPLES OF JOINTS between FUENACE TUBES AND FEONT PLATE, etc. Fig. U2.— FURXACE TUBE. Fig. Ii3, FURKACE TUBE. JOIN'TS OF FURNACE TUBES. /"N r~\ ■P^ Front. Back. Fig. 144.— FURNACE TUBE. Front. Back. Fig. 145.— FURNACE TUBE. Messrs Yates & Tuom. 302 HEAT EFFICIENCY OF STEAM BOILERS. tD lO H M ^ < r/} S 1 :-P 1 E-( •Ph & w u rH p5 =; w 1 — 1 H^ p-l 3 ,, ,, with short smoke tubes, Trials on, 4 ,. ,, with two furnace tubes, ,, 5 „ „ „ _ . ,, Spenee's experiments, ... 6 ,, ,, with three furnace tubes. Trials on, ..... 4 Leach mechanical stoker, .... 129 ,, ,, Lancashire boiler. Trials on a, . . 35, 129, 185 Lewioki, calculation of amount of soot, . . 183 Cornish boiler experiments, ... 25 elephant ,, ... 95 Lancashire ,, 51, 93 locomotive ,, . .81 two-storey ,, ... 87 Lignite, Tests on, 218 List of boilers at the Hydraulic and Electric Light- ing Companies; 256 Locomotive boilers, 6, 212 ,, ., for marine application. . . 212 „ '., Number of, ... . 213 Trials on, . . . 8,244 ,, ,, Trials on a French railway, . 213 Log sheets for boiler trials, .... 200, 231 Longridge, Cornish boiler experiments, - .23 ,, Lancashire „ 39, 45, 47, 61 ,, on feeding boilers, . . . 175 ,, table of superheating steam by hot gases, 174 Loss of heat due to different percentages of COj, . 226 Lowell Water-works, boiler experiments, . . 91 Magdbbtjbgh fuel testing station, Mahler on heating value of fuel, . . Marine boilers at sea. Trials on, . draught in, . gunboat type, locomotive, . rectangular, Oochrane's, Scotch, . stoking in, . water tube, . . 220 . 134 . 73 . 202 . 207 . 212 . 206 206, 276 . 202 . 207 PAOE Marine boiler trials, suggestions for, . , . 235 Marsilly grate • 121 Maximum boiler efficiency, Calculation of, 224, 239, 243 ,, effioieijcy of transmission, . . . 163 M'Dougal mechanical stoker, .... 128 M'Phail and Simpson's superheater, . . - 171 Measurements of coal and water in boiler trials, 235, 245, 261 , , of temperature, . . . .192 Mechanical stokers, Babcock and Wilcox, . . 130 ,, ,, Bennis, .... 127 „ . Cass, 129 Coxe 130 Frisbie, .... 130 ,, „ Hale's report, . . . 131 ,, ,, Henderson 129 ,, ,, Hodgkinson, . . . 129 Juckes, . . . 128, 185 Leach, . . . .129 M'Dougal 128 Proctor, .... 129 „ „ Roney, . . . .131 Vicars, 127, 233, 297, 298, 299 Whitaker, . . . .130 Wilkinson 130 Meldrum grate, 124 Mercury, sampling gases over, .... 188 Methods of introducing air to grates, . . . 179 ,, regulating combustion, . . . 140 Moisture in coal, estimation of, . . 229, 238, 242 Morrison's furnaces for marine boilers, . . . 206 Mulhouse Boiler Association, Elephant boiler ex- periments ... .95 Munich Boiler Association, Elephant boiler experi- ments, 95 Munich Boiler Association, Lancashire boiler experiments, .... 37, 41, 43, 45, 49 Munich Boiler Association, Two-storey boiler ex- periments, 89 Munich coal testing station, 216 Natttre of smoke, 176 Newcastle coal testing experiments, . . . 215 , , trials on agricultural boilers, . 79 Niclausse water tube boiler, . . . 210 ,, ,, ,, experiments, . 14, 111 Noeggerath's coal testing experiments, . . . 2] 6 Normand water tube boiler, . . . 210, 293 Northern Railway of France, Plotted results of trials on 143 Notes on boiler tests, 229 Number of locomotive boilers in the world, . . 213 . . 211 190 Orsat apparatus for analysing gases. Paris smoke trials 186, 260 Patchell on superheating steam, . . . 171, 172 Patterson system, locomotive boiler experiments, . 75 Paucksch boiler. Trials on a, . . . . 57 Paxman locomotive boiler experiments, . 75, 77 Peabody's throttling steam calorimeter, . . 197 Pellatt fire bars, Lancashire boiler, Trials on a. 49, 121 ,, grate, 121 SIO ii:eA¥ EFFICIElfCY OF STEAM BOILERS. PAGE Percentage of 00.,, ..... 137, 138 ,, ,, graphic diagram of, . .225 Perkins water tube boiler, ... . 211 Ferret grate 123, 282 ,, Lancashire boiler, Trials on a, 43, 45, 47, 124 Pimbley's economiser, 167 Plain cylindrical boiler, 9 Plotted results of Spence's experiments, . . 7 Plummer down-draught iiirnace, .... 125 Powdered coal firing, Wegener, . . .180 ,, ,, ,,■ Trials on, . 262 Prevention of smoke. Practical measures for the, . 263 ,, „ Reischle on, . 178 Priming in steam, ... .18, 230 Process of combustion in practice, . 139 Proctor mechanical stoker, . . . 129 , , , , Lancashire boiler. Trials on a, . . . . 29, 31, 33, 35, 129, 185 Professor Thomson's fuel calorimeter, . . 194 Prussian Smoke Commission, . . 182, 185 „ ,, Cornish boilerexperiments, 23 ,, ,, Lancashire ,, 4, 53 ,, ,, Two-storey ,, 99 Pyrometers, ... . . 192 Quality of steam, .... .238 Quantity of air required for combustion, . 137 Rateau steam calorimeter, . . . 197 Reischle on smoke prevention, . . . 178 Relative cost of fuels. Table of, . . 228 Retarders, .... ... 204, 206 Reynolds locomotive boiler experiments, . 77 Ringelmann's precipitation of soot, . . 183 ,, smoke scale, .... 184 Rinne grate, . . . . 122 Ripper, Professor, Trials on a Schmidt boiler, 173 Roney mechanical stoker, . . . .131 Russian locomotiveboilers. Use of petroleum on, 212, 213 Salt test for quality of steam, .... 199 Sampling coal for an experiment, . . 238, 242 ,, gases over mercury, . . .188 Sauvage on boiler efficiency 224 Saxon Boiler Association, Lancashire boiler ex- periments, 35, 47, 93 Saxon Boiler Association, Two-storey boiler ex- periments, 87 Saxon Boiler Association, Water tube boiler experiments 109 Scheurer-Kestner, analysis of flue gases, . . 138 ,, ,, on heating value of fuel, . . 134 ,, „ on smoke, .... 178 „• ,, trial ofaFrenohfeed- water heater, 166 Schmidt boiler and superheater 173 SchrBter, Professor, Trials of a Schmidt boiler, . 173 Schulz-Knaudt boiler, Trials of a, . . 25, 27 Schulz-Rober stoker, Ti'ials on a, . . . 93, 185 Schwoerer superheater, 172 Scotch and water tube boilers. Comparison of, . 206 , , marine boiler, ... . 206, 276 Seaton's table of comparative weights of marine boilers, 208 I'AOB Seaton water tube boiler. Trials on a, . . . 105 ,, wet back boiler experiments, ... 73 Seipp grate, .... . . 122 Ser, M., on smoke 177 Serpollet superheating boiler, . . . 173, 291 Serve tubes, 205, 207 ,, experiments on, . . 160,163,206,213 Sigaudy on comparative weights of marine boilers, 208 Sinclair stoker, Lancashire boiler. Trials on a, 29, 63, 185 Sinclair superheater 172 Smoke Abatement Committee, English, . 182, 185 Smoke, Chemical composition of, . . . 177 ,, Commission, Prussian, . . .182, 185 ,, Determination of, in Lewicki's trials, . 183 , , observations, American method of taking, 244 ,, ,, French method of taking, . 260 ,, Prevention of, . . . . . . 178 ,, ,, ,, bydown-draughtfurnaces, 180 ,, ,, ,, by use of gaseous fael, . 180 „ D. K. Clark on, , . 186 Smoke scale, . . . . 181 ,, Ringelmann's, . .184 ,, trials at Paris, 186,260 ,, tubes. Serve, . . . . 205 , , washer. Trials on a, . . . .262 Soot, Calculation of, Lewicki, . . . 183 Precipitation of, Ringelmann, . . . 183 Spence's Experiments, 136, 139, 179, 182 53, 196, dry back boiler, . 65, 67, 69, 71 , , , , Lancashire boiler, ,, „ plotted results of, , , • , , on colour of flames, ,, table of carbon monoxide. Standard coal unit of measurement, ,, ■ method for American boiler trials, Stauss grate, .... ,, ,, Lancashire boiler, Trials on a, Steam calorimeters — Barrel, . ,, ,, Barrus, , , , , Carpenter's separating. Him, . ,, ,, Peabody's throttling, ,, ,, Rateau, ,, ,, superheating type, , , gauge for registering boiler pressures, ,, priming in Steinmliller water tube boiler. Trials on a, Stepped grates, Stepped grates. Trials on, . Stirling water tube boiler, . „ ,, ,, ,, Trials on, . Suggestions for marine boiler trials. Summary of efficiencies of boilers. Superheaters— Gehre, .... ,, Hicks ,, M'Phail and Simpson, ,, Schmidt, ,, Schwoerer, ,, Sinclair, Superheating boiler, Serpollet, , , steam by boiler gases. Table of, , , , , in boiler flues, ,, ,, Patohell on, . I 257 136 245 237 122 185 196 197 243 . 196 . 197 . 197 . 197 . 246 . 18 105, 109 . 121 93, 121 . 12 13, 107 . 235 118, 221 . 172 . 171 . 171 . 173 . 172 . 172 173, 291 . 174 . 170 171, 172 PAGK Table of comparative weight? of marine boilers, . 208 , , loss of Keat for different percentages of CO2, 138 ,, relative cost of fuels, . . . 228 Temperature of boiler plates, Kirk's experiments on, 160 , , measurements of, . . . .192 Tenbrink grate, 120, 213, 249 ,, „ Trials on a, . 99, 120, 185, 213, 218 Thermometers, Ball, . . . 146, 154, 159, 192 ,, Le Chatelier's 192 Thornliebank stoker, Lancashire boiler. Trials ona, . . . ... 33, 35 Thornycroft water tube boiler, ... 13, 290 ,, ,, ,, Trials on, . 13, 111 Transmission of heat, Blechynden's experiments on, 145 ,, „ Durston's ,, 153 „ ,, Hirsch's ,, 158 ,, ,, Hudson's table, . . 252 Trial of a Green economiser, .... 168 Two-storey boiler, Cornish, Trials on, . . . 8 ,, „ ,, Cylindrical, . . 9 ,, ,, ,, with smoke tubes. Trials on, 9 Two-storey boiler, Lancashire, Trials on, . . 9 ,, ,, with two water lines. Trials on, 11 U- WATER gauge .193 Unwin, Cornish boiler experiments, . 21, 23 , , Lancashire boiler experiments, 49 on the dasy meter, . . .191 ,, „ dryness of steam, . . 199 Urquhart on Russian locomotive boilers, . . 213 Vacuum, in chimneys, 243 Vertical boilers, Trials on, . . . 14, 15, 113 ,, with inclined water tubes, Trials on 15 ,, with vertical smoke tubes, 287,288 Vicars mechanical stoker, , 127, 233, 297, 298, 299 INDEX. 811 I'AHE Vicars mechanical .stoker, Lancashire boiler. Trials on a, . 29, 31, 33, 35, 85, 127, 185 Vienna Boiler Association, Babooek and Wilcox, Ti-ials, . . 103 ,, ,, ,, Cornish, Trials, . 27 ,, ,, ,, Lancashire, Trials, 43, 45, 57, 69 ,, ,, „ two-storey, Trials, 85, 87, 99 Wackaknie grate, Waller's apparatus for sampling gases, Walther water tube boiler. Trials on a. Warm blast steam boiler furnace. Hoadley, Water tube bo: lers, 123 . 188 . 105 . . 254 12, 207 12, 209, 295 13, 208, 277 . 257 211 211 . 210 13, 210, 290 14, 211, 291 232 180 Babcock and Wilcox Belleville, De Laval, De Naeyer, Heine, Niclausse, Thornycroft, Yarrow, Weekly account of fuel and water for boilers, Wegener's powdered coal firing, . Weight of gases per lb. of carbon, Calculation of, 240, 244 Weir's evaporators, . . . . 203 ,, feed- water heaters, . . . 202 Wet back boiler, Trials on, . .5 Whitaker mechanical stoker, .... 130 ,, ,, ,, Lancashire boiler. Trials on, ' . . . . .61 Wigan coal testing station, . .215 Wilkinson mechanical stoker, . . . 130 Wilson on combustion, 141 Wilton grate . 124 Winkler apparatus for analysing gases, . .190 Witz, experiments on evaporation, . . . 159 Yaerow water tube boiler. Trials on. 14, 211, 291 . 14, 105 PRINTED BY NEILL AND COMPANY, EDINBURQH. STANDAR D WORKS FOR E NGINEERS. nA<^ nil AlSin AIP FNOINP^;* ^ Praetleal Text-Book on Internal U/\0, V^IL,, i^l>L» J^liK L.i'^VJii^u.o . Combustion Motors without Boiler, By BRYAN DONKIN, M.Inst.C.E. Second Edition, Revised tlirougliout ami Enlarged. With numerous additional lUustratipns. Large 8vo. 25s. 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