CEMENT BURNING: FIXED KILNS. 471 



a cylinder, 9 to 12 feet wide and 25 to 30 feet high. This is surmounted 

 by a truncated-cone chimney, often high so that the total height of 

 the kiln may be 35 to 75 feet. Candlot states that at some German 

 plants kilns 22 feet in diameter and 100 feet in height were used, each 

 of which kilns would turn out 400 tons (metric) of cement for each run. 

 Dome kilns are charged with fuel and mix, the latter in the form of 

 bricks, in alternate layers, the proportions varying principally with 

 the height of the kiln and the wetness of the bricks of mix. When 

 the kiln is full the charging doors are closed and luted with fire-clay, 

 and the lowest layer of fuel is ignited. As the burning progresses the 

 entire mass settles, owing to the loss in fuel and carbon dioxide. The 

 kiln may now be refilled to its former level, but nothing is drawn from 

 it until the burning is complete, which may take from one to two weeks. 

 Candlot states that the production of a dome kiln varies from \ to 1 ton 

 of clinker for each cubic meter of burning space, and that from 23 to 

 30 Ibs. of fuel are required per 100 Ibs. of clinker, the latter quantity 

 varying according to whether anthracite, gas-coke, or oven-coke is 

 employed. The labor cost of charging, drawing, and picking clinker 

 from the dome kiln may vary from 30 to 50 cents per ton of cement, 

 equivalent to about 5 to 10 cents per barrel. 



2. Dome Kilns With Drying Accessories. 



The first and simplest improvement on the primitive dome kiln 

 was to provide each kiln with a drying tunnel. The kiln thus improved 

 was still intermittent, but the drying tunnel gave a certain fuel economy, 

 particularly when very wet mixes were employed. The principal type 

 of this class of kiln is the Johnson kiln. 



Johnson kiln. The Johnson or chamber kiln was apparently the 

 first English improvement on the simple dome kiln. It consists essen- 

 tially of a dome kiln roofed over at the top, and with a long horizontal 

 passage, semi-circular in section, opening into the kiln near the top 

 and leading to a stack. The wet slurry is placed in the horizontal 

 passage and dried by the hot gases passing through it from the kiln 

 to the stack. The slurry when dry must be shovelled up and charged 

 into the kiln by hand. 



Various modifications of the Johnson kiln have been suggested 

 and used in English plants,* most of them depending for extra economy 

 on passing the hot gases under as well as over the slurry to be dried. 



The Johnson kim ; with its different modifications, may be considered 



Proc. Institution Civil Engineers, vol. 62, pp. 74-76. 1880. 



