Mance: Quarry Industry of Southern Indiana 155 



After a charge has been calcined, the periodic kiln is allowed 

 to cool before it is emptied and recharged. With the continuous 

 kiln this delay is not necessary. The calcined material can be 

 withdrawn and fresh material can be added without loss of time 

 or the great waste of heat, which are necessitated by the periodic 

 kilns. 



Kilns are fired by two general methods. In the first case, 

 with what is known as "short fiame burning", the material 

 to be calcined is charged in alternate layers with the fuel. In 

 this method the limestone is in close contact with the fuel, and is, 

 of course, more or less contaminated with ashes after burning. 

 In what is known as the ''long flame" method of burning, the 

 fuel is burned on a separate grate and only the flames and hot 

 gases pass into the shaft of the kiln. With this method no ashes 

 are left in the product and a purer lime is produced. With the 

 long flame method there is a materially greater loss of heat but 

 the purity of the product more than counterbalances the extra 

 loss. With any of the various forms of kilns other fuels than coal 

 can be used such as natural gas, producer gas, or oil. Any one 

 of these fuels has the advantage over coal, of cleanliness and 

 regularity. The fact is becoming generally recognized that 

 producer gas as a fuel for lime burning is the ideal fuel because the 

 heat can be applied more closely to the charge than is the case 

 with any other fuel and the product will be more even and cleaner 

 than with any other fuel. 



Continuous kilns are preferred where fuel is expensive, and 

 and where regular output is desired. Where close figures are 

 necessary on the cost of fuel the periodic kiln is out of the question. 

 The continuous kiln is a tall, narrow furnace or shaft, built of 

 brick or iron plates, and varies in size. Such kilns are usuallj^ 

 35 to 45 feet high by 6 to 8 feet in diameter. The limestone is 

 fed in at the top and is calcined as it passes down thru the kiln, 

 the lime being taken out at the bottom. The burning goes on 

 without interruption even during the process of charging or re- 

 moving the lime. 



In this country a great many long-flame periodic kilns 

 are now in use, the main reason for their installation being their 

 cheapness and simplicity of construction, but they are very 

 expensive in their use of fuel. With these kilns an arch of large 

 blocks of limestone is built about 3 feet from the bottom of the 

 kiln, openings being left for the flames to pass thru. On top of 

 this arch small lumps varying in size from a cocoanut to an orange 



