PREPARING THE MIXTURE FOR THE KILN. 



403 



T 



o 



upper sections of the stack are arranged to 

 slide longitudinally in their slots, reciproca- 

 ting motion being provided by a motor- 

 driven system of rocker arms sliding suc- 

 cessive rows of plates in opposite directions 

 at the rate of 20 cycles per minute. By this 

 action clogging of possibly damp rock is pre- 

 vented until it has fallen far enough to be 

 dried sufficiently to have no such tendency. 

 The shear-pin principle, used at this plant 

 for driving the crushing rolls, is also applied 

 in a modified form to the baffle-shakers. The 

 rock-dryer is 8X8 feet in plan section, 40 

 feet high, and has a capacity of 3000 tons 

 per day, the same as the crusher plant. 

 The performance of the dryer stack is 

 very efficient; the fuel consumption 

 is small, the percentage of moisture in 

 the crushed rock is reduced from 3 or 

 4 per cent to within 1 per cent, and 

 the gases leave at a temperature scarcely 

 above 212. A blower equipment is pro- 

 vided for increasing the furnace draft when 

 necessary. 



The cost of drying raw materials will 

 depend on the cost of fuels, the percentage of 

 water present in the wet material, and the 

 efficiency of the dryer. Dryers are usually 

 arranged and located so as to require little 

 attention, and the labor costs of drying are 

 therefore slight. Even under the most un- 

 favorable conditions 5 Ibs. of water can 

 be expected to be evaporated for each 

 pound of coal used, while a good dryer 

 will usually evaporate 7 or 8 Ibs. of water 

 per pound of coal. Marls containing much 

 organic matter are notably more reten- 

 tive of moisture than any other raw 

 material, and a marl-drying proposition ^^~ io-'o ^j 



is therefore apt to be expensive. For a FIG. 83. Elevation of stack 

 f ,, , . ,. . drier, Edison plant. (En- 



iull description of a most elaborate and gineering News ) 



