502 



CEMENTS, LIMES, AND PLASTERS. 



Heat Losses in Practice. 



In practice with the rotary kiln, there are a number of distinct sources 

 of loss of heat, which result in a fuel consumption immensely greater 

 than the theoretical requirements given above. The more important 

 of these sources of loss are the following: 



(1) The kiln gases are discharged at a temperature much above 

 that of the atmosphere, ranging from 300 F. to 2000 F., according 

 to the type of materials used and the length of the kiln. 



(2) The clinker is discharged at a temperature varying from 200 F. 

 to 2500 F., the range depending as before on materials and length 

 of the kiln. 



(3) The air-supply injected into the kiln is always greater, and 

 usually very much greater, than that required for the perfect combus- 

 tion of the fuel, and the available heating power of the fuel is thereby 

 reduced. 



(4) Heat is lost by radiation from the ends and exposed surfaces 

 of the kiln. 



(5) The mixture in plants using a wet process carries a high per- 

 centage of water, which must be driven off. 



It is evident, therefore, that present-day working conditions serve 

 to increase greatly the amount of fuel actually necessary for the pro- 

 duction of a barrel of cement above that required by theory. 



The extent of these losses, compared with the amount of heat ac- 

 tually used, can be seen from the following comparison of various 

 estimates and tests, all relating to a 60-foot kiln on dry material: 



TABLE 190. 

 UTILIZATION AND LOSSES OF HEAT IN ROTARY KILNS. 



Heat carried out in flue-dust. A considerable amount of fine dust 

 is carried out of the kiln by the hot gases. This flue dust, deposited 

 wherever the air current is checked, may amount to from to 3 per 

 cent of the total amount of mix charged to the kiln. 



