A structure or machine designed for drying substances by the application of heat. Their forms are as various as the substances or manufacture for which they are designed; for, although it may be said that a certain kiln will answer several purposes, yet for one single purpose we often find a variety of kilns employed. The requisite qualities in a good kiln are cheapness and durability of construction; effectiveness in producing the required result with the utmost economy of fuel; a perfect command of the temperature, and facility of working. Ovens must be regarded as of the same class of apparatus as kilns; indeed, the terms kiln and oven are often indiscriminately applied to the same structure, as may be noticed under several articles in this work. Under the head of Lime the usual form of lime-kilns is described;' and under Coal and Iron, several forms of coke ovens. In this place we shall notice an admirable combination of both, which was the subject of a patent granted to Mr. Charles Heathorn about seven years ago, since which time it has been in successful operation at Maidstone and other places.
The object of this invention, as expressed in the specification of the patent, is the preparation of quick-lime and coke in the same kiln at one operation. The economy of this process must be evident from the circumstance, that the inflammable part of the coal which is separated to form it into coke, is the only fuel employed to burn the lime; and as the coke is in many places as valuable as the coal from which it is prepared, the cost, if any, of making lime, must be reduced so the most trifling amount. The engraving on the following page represents a vertical section of the lime shaft and coke ovens: a a are the side walls, 4 feet thick, of a rectangular tower, the internal space being filled with lime-stone from the top to the iron bars b b at bottom, whereon the whole column rests. The lime-stone is raised in a box d, or other proper receptacle, to the top of the building, by means of a jib and crane e or other tackle which is fixed at the back of the tower, together will, a platform projecting beyond the walls for affording security and convenience for - landing the line-stone; he raised as represented, the jib is swung round, and the lime-box tilted, by which the whole contents are thrown down the shaft.
The coke ovens, of which there may be two, or a greater or lesser number, according to the magnitude of the works, are constructed and arranged in connexion with the lime shaft m the same manner as the two represented in the diagram at ff. These ovens are supplied with coal through iron doors in the front wall (not seen in the section); the doors have a long and narrow horizontal opening in the upper part of them to admit sufficient atmospheric air to cause the combustion of the bituminous or inflammable part of the coal; the flames proceeding from thence pass into the lime shaft through a series of lateral flues (two of which are brought into view at g g), and the draft is prevented from deranging the process in the opposite oven by the interposition of the partition wall h, which directs the course of the heat and flames throughout the whole mass of the lime, the lowermost and principal portion of which attains a white heat, the upper a red heat, and the intervening portions the intermediate gradations of temperature.
When the kiln is completely charged with lime, the openings in front and beneath the iron bars at i i are closed and barricaded by bricks and an iron-cased door, which is internally filled with sand to effectually exclude the air, and prevent the loss of heat by radiation; therefore, when the kiln is at work, no atmospheric air is admitted but through the narrow apertures before mentioned in the coke oven doors. When the calcination of the lime is completed, the barricades at i i are removed, the iron bars at b b are drawn out, by which the lime falls down and is taken out by barrows. It sometimes happens, however, that the lime does not readily fall, having caked or arched itself over the area that encloses it, in which case a hooked iron rod is employed to bring it down. To facilitate this operation in every part of the shaft where it may be necessary, a series of five or six apertures, closed by iron doors, is made at convenient distances from the top to near the bottom of the shaft; two of these are brought into view at k k. Two similar apertures are shown in section in the coke ovens at b b, whicn are for the convenience of stoking and clearing out the lateral flues g g from any matter that might obstruct the free passage of the heated air.
When the coals have been reduced to coke, the oven doors in front (not shown) are opened, and the coke taken out by a peel iron, the long handle of which is supported upon a swinging jib that acts as a movable fulcrum to the lever or handle of the peel, and facilitates the labour of taking out the contents of the oven. The operation of this kiln is continuous, the lime being taken from the bottom whenever it is sufficiently burned, and fresh additions of raw lime-stone being constantly made at the top.