KILN, kil (AS, eiin, calenc, from Lat. eft, ino. kitchen). A furnace, oven, or other device for burning, baking, or drying brick, charcoal, pottery, or other materials, generally at a high uniform heat. They are made of stone. brick. or iron. They may be divided into intermittent and continuous kilns. An iatermittent kiln is one in which the fire is permitted to go out after the charge is burned; a Con 1i/111011S kiln is one which is so arranged that the charge may be removed and a fresh one put in v pile the is kept burning. and the furnace kept at its re ducing beat. This mav be effected either by an independent fire, or by placing the fuel and the to be tested in alternate lai,ers. removing the finished charge from the bottom, and adding fuel and charge at the top. A preferable form of continuous kiln is one in which the kiln cylin der is changed only with the material to he burned. and a current (.11 flame or heated gas is introduced at the ;ids near the bottom. The heat thus passing up through the Material reduce it to the proper condition without adding a ny of the ashes of tl,e fuel to it. Kilns are also in aceordance with the course of the draught. into up-draught and down-draught and by shapes, into bd-hire, «la-shaped, bell-shaped, and annular chamber, the latter having a series of cells around a central comliartment.
CEMENT-KU-Ns may be divided somewhat. arbi trarily into: (1) Intermittent dome or bottle kilns; (21 chamber kilns. or kilns with chambers attached for drying the raw mixture by the waste gases front the kilns. may be either intermittent or continuous; (.3) continuous or stage kilns; and (4) rotary kilns. Dome kilns consist of a ealeining chamber. -nrinonnted by a chimney, which together form a structure re a loire bottle in shape At the bottom of the kiln is a set of removable grate-bars. and a door for admitting air to the tire and for with d•awing the burned clinker. Near the top of the calcining ehamber are one or more openings called charging eyes. through which' the new mix ture fuel are fed into the kiln. The top part f the kiln is a ehimnev-like structure, which serves to provide the necessary draught for the fire and to carry away the gases of conihnstion. Dome kilns are built of rough stone. brick, or concrete masonry, lined with tire-brick. the lining eo constructed that it can be removed and re built without disturbing the kiln structure proper. The kilns are charged by placing kin on the grate-bars and tilling above to the level of the charging eyes with alternate layers of fuel and raw mixture. When ealeina don is complete the kiln is allowed to cool down and the clinker is withdrawn. The operation of
the kiln is thus intermittent.
Chamber kilns may be roughly defined as dome kilns in which the chimney-like superstrn•ture is repined] by a long horizontal chamber opening into a stack. The raw material is plaeed in the horizontal chamber to be dried by the hot gases escaping from the kiln proper. The construetion. method of chargim% etc., of ehamber kilns are the same as for dome kilns. Chamber kilns are employed chiefly in England. They are ordinarily intermittent in operation, but by having two or more drying chambers attached to a single kiln, so that some are receiving the hot gases while others are being stripped of the dry mixture and re charged with fresh wet mixture, they may be made to operate continuously. Continuous cham ber kilns are employed only in a few works in Fro nee.
Continuous kilns are made in two general forms., which may be defined as vertical chamber kilns aim ring kilns. The Dietzsch kiln is a well known example of the vertical chamber type. It consists internally of three eonneeting chambers. At the top is the heating chamber, into which the ra AV is led by one or more charging eyes. This heating elmmber connects by means of a horizontal passage with a second vertical elm umber, which is called the crucible, and in which the calcination of the clinker takes place. Below the crucible is the cooling chamber in which the burned clinker from the crucible is cooled by the current of air which passes up through it from the drawing eye below. The ring kiln or Hoffman kiln consists of a ring-shaped chamber surrounding a central shaft connecting with a chimney. This ring-shaped chamber has flues at regular intervals. which connect with the chimney, and doors are placed in the outer walls at corresponding regular intervals. This arrange ment of flues and doors makes it possible to divide the large annular chamber into several— generally from 15 to compartments, each of which has a flue connecting with the chimney, and a door opening to the outside. The horning proceeds progressively from one chamber to another around the ring. Continuous kilns of the vertical chamber and ring types are used chiefly in Continental Europe.
Rotary kilns for burning cement are distinctly an American development, although the device was invented in England. A rotary kiln consists of a steel or iron cylinder lined with fire-brick or some other refractory substance to resist the heat, and mounted on roller bearings, generally and the operation is continuous instead of inter mittent. See CEMENT.