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Indiana University Studies 



powdered coal the coal must be dried, then crushed. The average 

 moisture content of coals is about 8 per cent, and under favorable 

 conditions it takes about a pound of fuel to dry 100 pounds of 

 coal. The best type of dryer now in use is the rotary dryer. 

 At the above figures the cost of drying fuel will be about 3 to 4 

 cents per ton of dried product. Coal, to give the best results, 

 when powdered for cement burning, must be very fine, and the 

 usual practice is to reduce it to such a size that from 85 to 95 

 per cent will pass a 100-mesh sieve. The poorer the grade of 

 coal used the finer it must be powdered. The coal is usually 

 powdered by two operations. It is first reduced to about 30- 

 mesh by means of ball mills and then fed thru a tube mill. This 

 process may be varied to fit the conditions in any mill altho the 

 cost will total about the same. 



The total cost of crushing (provided fine slack is not obtain- 

 able), drying, and pulverizing the coal, together with the cost 

 of elevating and conveying the coal to the kilns, will amount 

 to as much as 30 cents per ton, which is equivalent to from 1 to 2 

 cents per barrel on the cost of the cement. 



Power cost in a cement plant is also a large item since the 

 power consumption is put as high as a horse-power per barrel 

 of output per day, while the figure of 1 cent per horse-power hour 

 is low except in the very large plants. Of course many plants are 

 saving a part of the heat from the kilns and using it in the form 

 of power, but it will be seen that the power cost will in any case 

 be fairty heavy. 



The cost of labor varies so in different localities that any 

 figures given will be only approximations. Professor Grimsley 

 gives the relative cost of production as follows: fuel 35 per cent 

 of total cost, labor 45 per cent of total cost, and other expenses 

 as 20 per cent of the total (West Virgiana Geological Survey, 

 Vol. Ill, p. 440). 



The following figures are given for the cost of production 

 per barrel of cement in Bulletin 3 of the Ohio Geological Survey 

 (p. 330) : 



LABOR 



Quarrying $0,050 



Crushing and drying 0 . 005 



Grinding . . . 0 . 015 



Burning 0 . 015 



Power generation 0.011 



Coal grinding 0 . 010 



Yard work 0.015 



Machine shop. . . . : 0.0225 ' 



Miscellaneous 0.0025 



. $.15 



