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Indiana University Studies 



It consists of an arched circular room divided by moveable partitions into 

 sections (usually 12 in number). The limestone is placed in these 

 sections and fired through openings in the roof into the first section, and 

 when the lime is burned the fire is added to the next section and so on around 

 the circle. The air enters the section in which the lime is being removed and 

 cools the burned lime, becoming heated in the section where the full fire is 

 maintained and then reaches the sections charged but not burned giving 

 off its heat and passes from the last section out through a chimney at the 

 center of the kiln. Dampers serve to regulate the air current and sections 

 not in use can be shut off, as all are connected with the central chimney by 

 openings which can be readily closed. 



In England, according to Frasch, the Hoffman kiln produces daily 1,200 

 to 1,500 cubic feet of lime with a consumption of only 5 pounds of slack coal 

 per cubic foot of lime. In Germany the saving of fuel in the Hoffman kiln 

 is almost 75 per cent over the old methods. The lime is said to slake more 

 easily and cannot be stored for so long a time as that made in other kilns. 

 The saving in fuel in Hoffman kiln over the best constructed draw kilns is 

 said to be about 40 per cent. This form of kiln could be used with economy 

 where the lime is hydrated before being placed on the market. 



Rotary kilns are in use in a few instances, but not enough 

 data are available to determine their economic value. The 

 figures on the cost of lime burning with oil fuel, and a rotary 

 kiln are as follows: 



Average output 25 tons per day. 



Fuel consumption 40 barrels (42 gallons). 



Stone 98.5 per cent CaCOs. 



Labor cost $22 per day. 



Oil consumption per 100 pounds of lime 26.2 pounds. 



This represents a total cost of about 9 cents per bushel. 



The cost of lime manufacture diffsrs markedly in different 

 sections of the country. Some of the most important factors 

 in the cost of lime, or the factors which chiefly cause variations 

 in cost of production, are different labor costs, variations in fuel 

 cost, and the cost of quarrying the rock. 



The following figures are given as the average cost with a two- 

 kiln plant having a daily capacity of 500 bushels. The expenses 

 run as follows: 



Interest on plant and land . $1 .60 



Repairs, taxes, etc 1.30 



Quarry cost of quarrying 30 tons of rock 7.00 



Fuel cost (coal $1.25 per ton) 5.00 



Additional labor cost 12.00 



Total cost of 500 bushels. 26.90 



Cost per bushel 5.4 cents. 



