500 



CEMENTS, LIMES, AND PLASTERS. 



TABLE 188. 

 HEAT USED IN DISSOCIATION OF CARBONATES PER BARREL CEMENT. 



the kiln temperature by optical methods. The temperature in the 

 kiln when working under best conditions, as determined by the Noel 

 optical pyrometer, varied from 2250 F. near the discharge end to 2950 

 F. about 20 feet from the lower end, and about 1800 F. at the upper 

 end. The temperature in the burning zone seemed to average about 

 2850 F., and the temperature of the entire kiln on the inside seemed 

 to average nearly 2500 F. 



For ordinary purposes of calculation, it may be assumed that 1400- 

 1500 C., or 2500-2700 F., is about the necessary temperature in rotary 

 kilns under present conditions for an average mixture. Variations 

 in the composition of the mixture would, of course, change the clinker- 

 ing point for a low-limed high-alumina mix will clinker at a consider- 

 ably lower temperature than will a mix high in lime and silica. 



It is also true that to a certain degree longer exposure to the heat 

 will be equivalent in effects to higher temperature. In stationary 

 kilns, for example, where the charge may be exposed for days to the 

 heat, the requisite temperature is much less than in the modern rapid 

 practice with the rotary kiln. 



Heat utilized in heating the mix. One of the important uses of 

 the kiln heat is in simply heating the mix up to the point at which it 

 will clinker. Fortunately, this can be determined with sufficient ac- 

 curacy for all practical purposes. 



Whatever the percentage of the water present, the dry portion of 

 the mix will be about 600 Ibs. for each barrel of cement. This 600 Ibs. 

 of material must be raised from the temperature of the air say 60 F. 

 to about 1300 F. At this latter temperature the carbon dioxide, 

 sulphur trioxide, etc., will have been driven off; and this will reduce 

 the weight to 380 Ibs. This 380 Ibs. of quicklime and clay must now 

 be raised to a temperature of about 2600 F., at which clinkering will 

 take place. 



