486 CEMENTS, LIMES, AND PLASTERS. 



ing kilns, and at present kilns of 80 feet in length are common, while 

 several of the best plants have installed kilns respectively 100, 107, and 

 110 feet long. 



In the writer's opinion, however, the most remarkable development 

 of recent years has been in an entirely different direction. Several 

 plants in the United States are at present forcing their 60-foot kilns in 

 such a way as to give over 300 barrels per day of good cement. This 

 remarkable performance is not accompanied, it is true, by any saving in 

 the amount of coal used per barrel ; but even so, the production is worthy 

 of note. The above statements as to production may be taken as ac- 

 curate. 



Feeding coal to the kiln. In Fig3. 121 and 122 is shown a typical 

 coal-feeding installation, being one supplied by the B. F. Sturtevant Co. 

 for the plant of the International Portland Cement Co., at Durham, 

 Ontario. For the following description of this installation I am indebted 

 to the manufacturers. 



The coal is crushed, dried, and pulverized in the coal-house, located 

 independently of kiln-room. It is very essential to the proper burn- 

 ing of the coal that it be well dried and pulverized. At least 88 per 

 cent of the coal should pass a 100-mesh screen. The finer the coal is 

 pulverized, the more advantageously can it be burned. 



Pulverized coal is transferred from coal-house to storage-bins A, 

 located directly in front of kiins, by means of an overhead-screw con- 

 veyor B, which discharges the pulverized coal into top of storage- 

 bins. Each kiln has an independent storage-hopper which holds from 

 ten to eighteen hours supply of pulverized coal. 



Pulverized coal is fed from the storage-hoppers into the injectors 

 H by means of a small screw conveyor C, located at bottom of storage- 

 bin, amount of coal handled by each injector being dependent upon the 

 speed of the corresponding screw conveyor. The screw conveyor C 

 is driven by a variable-speed machine D through a series of gears, so 

 that the speed of the conveyor can be regulated according to operating 

 conditions of plant, which vary to a great extent in most plants. The 

 variable-speed machine is driven from a light-line shaft E, usually located 

 on front of coal-hoppers . Pulley F on variable-speed machine is pro- 

 vided with a friction-clutch so that any unit consisting of kiln, storage- 

 hopper, etc., can be shut down for repairs without interfering with the 

 remainder of the plant. 



For furnishing blast, two special gas-exhausters G are provided, 

 each exhauster being of sufficient capacity to operate all injectors, 

 the other exhauster being held in reserve in case of accident to the first. 



