CHAPTER XXXIV. 

 HEAT CONSUMPTION AND HEAT UTILIZATION. 



AN investigation of the ways in which the heat supplied to the kiln 

 is utilized and wasted is a matter of both theoretical and practical 

 importance. It can readily be seen that until some idea can be gained 

 of the relative importance of the different causes of loss of heat, little 

 can be done to prevent this waste or to utilize the heat so dispersed. 

 An exact knowledge of the distribution of the total heat supplied to 

 the kiln would therefore be of great service to the manufacturer. 



In the present chapter the writer has attempted to present such 

 data on this subject as are available, and to discuss them in such a 

 way as to bring out the relations of the various factors in the problem 

 of heat distribution. Attention is drawn, whenever necessary, to any 

 doubts as to the accuracy of the data employed. 



Theoretical Heat Requirements. 



In order that a raw mixture shall be converted into cement clinker 

 in the kiln, sufficient heat must be applied to bring about the necessary 

 physical and chemical changes. The purposes for which this heat is 

 required are: 



(1) Evaporation of the water of the mix. 



(2) Decomposition of the clay. 



(3) Dissociation of sulphates. 



(4) Dissociation of carbonates. 



(5) Heating the mix to clinkering point. 



Of these five requirements, it is to be noted that the first four are 

 for accomplishing chemical changes, and that the heat supplied for 

 these purposes is entirely absorbed in doing chemical work. This is 

 not true with regard to the fifth requirement -the heating of the mix 

 for the heat used for this purpose, after it has once served its purpose, 

 still remains as sensible and therefore utilizable heat. Most of it, in fact, 

 passes out in the clinker. 



In a perfect kiln the only heat required would be that sufficient 

 to accomplish the first four operations in the above list, for in a theo- 

 retically perfect burning device there would be no loss by radiation, 



497 



