492 CEMENTS, LIMES, AND PLASTERS. 



TABLE 183. 

 ANALYSES OF LOW-ALUMINA CLAYS USED FOR KILN BRICK. 



Silica (SiO 2 ) 



Alumina (A1 2 O 3 ) 



Iron oxide (Fe 2 3 ) . . . 



Lime (CaO) 



Magnesia (MgO) 



Alkalies (K 2 O,Na 2 O). 

 Carbon dioxide (CO 2 ). 

 Water. . . 



55.0 

 30.0 

 tr. 

 tr. 

 tr. 

 2.0 



13.0 



56.02 

 28.26 

 2.18 

 2.04 

 0.95 

 n. d. 



10.50 



TABLE 184. 

 ANALYSES OF LOW-ALUMINA BRICK, FURNISHED AS KILN BRICK. 



The manner in which these bricks are set in lining kilns is shown 

 in Figs. 125 and 126. 



Actual fuel consumption and output. In the following chapter 

 the question of heat requirements and heat distribution in the rotary 

 kiln will be discussed in considerable detail. At present it is only 

 necessary to state that in burning a dry mixture to a clinker, practi- 

 cally all of the heat consumed in the operation will be that required 

 for the dissociation of the lime carbonate present into lime oxide and 

 carbon dioxide. Driving off the water of combination that is chem- 

 ically held by the clay or shale, and decomposing any calcium sulphate 

 (gypsum) that may be present in the raw materials, will require a small 

 additional amount of heat. The amount required for these purposes 

 is not accurately known, however, but is probably so small that it will 

 be more or less entirely offset by the heat which will be liberated during 

 the combination of the lime with the silica and alumina. We may, 

 therefore, without sensible error regard the total heat theoretically 

 required for the production of a barrel of Portland cement as being 

 that which is necessary for the dissociation of 450 Ibs. of lime carbonate. 

 With coal of a thermal value of 13,500 B.T.U. per pound, burned with 

 only the air-supply demanded by theory, this dissociation would require 

 about 25^ Ibs. of coal per barrel of cement, a fuel consumption of only 

 6 per cent on the weight of cement produced. 



In actual practice, however, the heat required for cement produc- 



