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 THE PRODUCTION Of CHARCOAL 
 IN THE ORDINARY PIT-KIEN 
 
 June 1932 
 
 AGt 
 
 m . u 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE 
 
 FOREST SERVICE 
 FOREST PRODUCTS LABORATORY 
 Madison, Wisconsin 
 
 In Cooperation with the University of Wisconsin 
 
Digitized by the Internet Archive 
 
 in 2013 
 
 http://archive.org/details/producOOfore 
 
THE PRODUCTION OF CHARCOAL IN THE ORDINARY PIT KILN 
 
 Charcoal has "been produced since prehistoric times "by the 
 general method of "burning v/ood with limited access of air. The simple 
 primitive methods used many years ago are still in use with slight 
 modification although different countries have slowly developed standard 
 methods which may vary widely in size and shape of kiln and in the details 
 of construction and operation. 
 
 The proper supervision of a charcoal kiln requires considerable 
 experience and it is difficult to furnish directions which will make it 
 possible for an inexperienced person to operate a kiln successfully. 
 Following is a "brief description of the operation as usually practiced in 
 this country. The kiln is "built up around a central stay formed "by driving 
 three or more poles into the ground and keeping them separated "by "blocks 
 throughout their entire length. This stay, which should "be from one to 
 two feet in diameter, depending upon the size of the kiln, serves as a 
 support against which to pile the v/ood, and forms a flue for promoting a 
 draught and for carrying off the smoke and vapors. As the kiln is "built 
 up this central channel is filled with loose combustible material such as 
 dry grass, twigs or small sticks of dry wood. Around this central stay the 
 wood is piled, usually in the form of cordwood, the first always being 
 placed on end and leaning slightly toward the center and the last layers 
 being laid flat, giving the pile the shape of a circular mound. The wood 
 should be at least partly air seasoned for the best results. The size of 
 the kiln depends upon various circumstances and may vary from 15 to ty-5 
 cords. 
 
 This entire mound, with the exception of the central opening is 
 covered with sod or turf thick enough to exclude the air, the charring 
 process is then started by kindling the dry material in the central opening 
 and the supply of air is regulated by means of small openings around the 
 bottom of the kiln. The general principle on which the kiln operates is 
 the admission of air in such amounts that, as the fire slowly works back 
 from the center to the circumference against the draft, there is not enough 
 air left to burn the charcoal previously formed. The time required to 
 finish the process depends upon the size of the kiln and the moisture in 
 the wood, etc., and may be as long as two weeks. When the smoke coming 
 from the top of the kiln becomes thin and blue, the process is considered to 
 be complete. All openings are then closed and the kiln is allowed to 
 cool from one to five days, depending on the size. Considerable skill and 
 experience are necessary to obtain the best yield of charcoal, which for 
 maple, oak, beech, and birch is about UO bushels per cord. The following 
 suggestions will be found helpful: 
 
 1. The kiln needs constant attention night and day, and loose 
 turf should always be on hand to cover any cracks which may form. 
 

2. The object of the process is to char the wood without 
 burning it, and hence after the fire is well started the air supply is 
 cut down, and is regulated so that the process keeps going without 
 unnecessary combustion of the charcoal. 
 
 3. The kiln should become completely cool before it is opened, 
 since there is always danger that the charcoal "'ill ignite when brought 
 into contact with the air. Have plenty of water on hand to quench any 
 fire that may start when the kiln is first opened. 
 
 A modern modification of this general type of kiln is the brick 
 kiln. This, of course, makes a more permanent and expensive construction, 
 but is easier to operate and better yields are obtained. 
 
 When very resinous wood such as lightwood or stump wood from 
 longleaf pine is burned in a kiln as just described there is another 
 product formed and recovered beside the charcoal. During the burning of 
 the wood, tar is formed largely from the resin in the wood and collects 
 in the bottom of the kiln. By arranging a properly-sloped clay floor for 
 the kiln, the tar may be removed from a single opening at the lowest point 
 of the floor. 
 
 The price which can be obtained for charcoal varies a great deal 
 since the markets are mostly local; the product is so cheap and bulky that 
 ordinarily it can not be profitably shipped for any great distance. 
 Probably the largest single use for charcoal is in blast furnaces for the 
 production of charcoal pig iron. Large quantities are used for domestic 
 fuel especially in the southern and eastern states. There are also a 
 large number of miscellaneous uses any one of which might seem very small 
 but which in aggregate are important; these include uses in poultry and 
 stock feeds, in casehardening compounds, by tin and copper smelters, as an 
 insulating material, etc. Some ordinary hardwood charcoal mpy be used for 
 making black pov/der but specially prepared charcoals from willow and alder 
 are preferred for this purpose. 
 
 Hardwood charcoal weights about 20 pounds per bushel and softwood 
 charcoal about 18 pounds. 
 
 RU66 -2- 
 
JNIVERSITY OF Fl ORIDA 
 
 3 1262 08929 0612