LIME-BURNING. 



103 



will use 220 to 260 pounds of coal per ton of quicklime burned, equiva- 

 lent to a fuel consumption of 10 to 12 per cent on the weight of the 

 product, which is very close to the theoretical minimum. 



(3) Vertical kilns with separate feed. Kilns of this type, which are 

 now used at most of the larger lime-burning plants, are equipped with 

 separate fireplaces to carry the fuel, distinct from the body of the kiln. 



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FIG. 21. Aalborg kiln for lime-burning. 



These fireplaces may be set either in the wall of the kiln, the usual posi- 

 tion when a stone-walled kiln is used, or outside of the kiln-shell. The 

 kiln body proper contains the charge of limestone, while the fuel is fed 

 and burned in these fireplaces or furnaces. The limestone, therefore, 

 does not come into direct contact with the fuel, but only with the hot 

 fuel gases. Other things being equal, kilns of this type could not show 

 quite as high a fuel efficiency as kilns in which the limestone and fuel 



