53 > 



3. The air supply injected into the kiln is always greater, 

 and usually very much greater, than that required for the per- 

 fect combusion of the fuel ; and the available heating power of 

 the fuel is thereby reduced. 



4. Heat is lest by radiation from the ends and exposed sur- 

 faces of the kiln. 



5. The mixture, in plants using a wet process, carries a high 

 percentage 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 production of a barrel of cement above that required by 

 theory. 



Actual fuel requirements and output. Rotary kilns are nom- 

 inally rated at a production of 200 barrels per day per kiln. 

 Even on dry and easily clinkered materials and with good coal, 

 however, such an output is not commonly attained with a 

 6o-foot kiln, except in the Lehigh) district. Normally 

 a kiln working on a dry mixture will produce from 160 to 180 

 barrels of cement per day of twenty-four hours. In doing this, 

 if good coal is used, its fuel consumption will commonly be 

 from 1 20 to 140 pounds of coal per barrel of cement, though it 

 may range as high as 160 pounds, and, on the other hand, has 

 fallen as low as 90 pounds. An output of 175 barrels per day, 

 with a coal consumption of 130 pounds per barrel, may there- 

 fore be considered 1 as representing the results of fairly good 

 practice on dry materials with a oo-fcot kiln. In dealing with a 

 wet mixture, which may carry anywhere from 30 to 70 per cent, 

 of w r ater, the results are more variable, though always worse 

 than with dry materials. In working a 6o-foot kiln on wet ma- 

 terial, the output may range from 80 to 120 barrels per day, with 

 a fuel consumption of from 150 to 230 pounds per barrel. Using 

 a longer kiln, partly drying the mixture, and utilizing waste 

 heat, will of course improve these figures materially. 



When the heavy Western oils are used for kiln fuel, it may 

 be considered that one gallon of oil is equivalent in the kiln to 

 about ten pounds of coal. The fuel consumption, using dry 

 materials, will range between 1 1 and 14 gallons of oil per bar- 

 rel of cement ; but the* output per day is always somewhat less 

 with oil fuel than where coal is used. 



Natural gas in the kiln may be compared with good Pennsyl- 

 vania coal by allowing about 20,000 to 30,000 cubic feet of gas 



