llE PtODUCIION OC ChAI[COAL
IN 11T! OI4INAiY Il-rIIN
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST PRODUCTS LABORATORY
In Cooperation with the University of Wisconsin
Digitized by the Internet Archive
rTFr, pR.'. ''T.-1:' OF CHARCOAL :: THE ODRINARY PIT IKIL:
Charcoal has been produced since prehistoric times by the
general method of burnin woviod .-iith limited access of
modification although different countries hve slo'.ly developed standard
methods which may vary widely in size and shape of kiln and in the dct7 ils
of construction and operation.
The proper supervision of a charcoal kiln requires considerable
exDerience and it is difficult to furnish directions which r'ill 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 s r-rr.ted by blocks
throughout their entire length. This stay, which should be front one to
two feet in diameter, depending upon the size of the kiln, sCrvers as a
sui: ::rt against which to pile the wood, and forms a flu f-r rormoting a
dr.;u,!]t and for carrying off the smoke and v'rnors. As t-o kiln is built
up this central channel is filled with loose combustible otri' such as
dry grass, twigs or small sticks of dry w1ood. Around this central sta.y the
wood is piled, usually in the form of cordwood, the first r'lwavs being
placed on end and Icr..inK' slightly toward the center and the l'st layers
being laid flat, giving the pile the shape of a circular mound. The ;:ood
should be at least partly air seasoned for the best results. The size of
the kiln depends upon van ous circumstances and may vary from 15 to 45
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 materil in the central o ening
and the supply of air is regulated by means of small openinus around the
bottom of the kiln. The general principle on w-hich the kiln operates is
the admission of air in such amounts that, as the fire sl -ly ': rks back
from the center to the circ-.ference against the draft, there is not no'a*
air left to burn the charc al previously formed. The timc. rquir to
finish the process depends ui .-n the size of the kiln and the moisture in
the wood, etc., and may be as long as two weeks. en the smoke co
from the top of the kiln becomes thin and blue, the process is considcrei to
be complete. All openings are then closed and the kiln is I t'1 od t
cool from one to five d -, depending on the si7. C(nsi, rable sIir l "n l
experience are necessary to obt in the besot yie!d, of charc'al, whichh for
maple, oak, beech, and birch is about 4C bushels r cor The fo in
sa: ost ions 'ill ', found IelpfuIl:
1. The kiln needs constant attention 'At rnd day., and 1oor
turf should always be on han to mver any cracks which m'ay f-rm.
2. The object of the process is to char the ''od withoutt
burnini,- it, and hence after the fire i3s "well started the air supply is
cut down, and is regulated so that the process keeps goin--./uithout
unnecessary combustion of the charcoal.
3. The kiln should become completely cool before it is opened,
since there is always d'.n-.., r1 that the charcoal '-ill ignite when brought
into contact with the air. Have plenty of water on hand to quench '.
fire that m'ay start "'hen the kiln is first or',ned.
A modern modification of this general type of kiln is th, rick
kiln. This, of course, makes a more permanent and (xpensive construction,
but is easier to operate and better yields are obtained.
When very resinous -rood such as liFghtwood or stum- *",'ood from
longleaf pine is 'burned in a kiln as just described there is another
product for:.d and recover, d beside the charcoal. During the burning of
the 'tood, tar is formed largely from the resin in the "'-ood and collects
in the bottom of the kiln. B,-y arrangi',,i- a pr.L rl]'-loped clay floor for
the kiln, the tar may be removed from a single ocening at the lowest point
of the floor.
The price which c?'n be obtained for charcoal] va ries a gre:t deal
since the markets are mostly local; the product is so chear 'and bulky that
ordinarily it can not be profitably shipped for *ny great distance.
Probably the largest single use for charcoal is in blast furn- ces for the
production of charcoal pig iron. Large quantities are used for domestic
fuel especially in the southern and eastern states. There re 'Iso
large number of miscellaneous uses any one of which -mi.-ht se;,m very small
but which in aggregate are important; these include uses in poultry and
stock feeds, in casehardening c-r.t.unds, by tin nd co,,- r smIlters, as n
insulating material, etc. Some ordinary hari ood charcoal m.-y be used for
making black powder but specially prepared charcoals from willow and olderr
are preferred for this -,':r-ose,
Hardwood charcoal weights about 20 pounds per bushel ,and softw:ood
charcoal about 18 pounds.
UNIVERSITY OF FLORIDA
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3 1262 08929 0612