494 CEMENTS, LIMES, AND PLASTERS. 



tion is immensely greater than that demanded by theory. This is due 

 to the fact that heat is wasted or lost in various ways during the process 

 of burning in the rotary kiln. The more important losses of heat occur 

 from the fact that the stack-gases and clinker are usually discharged 

 at high temperatures; that the air-supply injected into the kiln is always 

 greater, and usually much greater, than that theoretically necessary; 

 and that much heat is lost by radiation from the exposed surface of 

 the kiln. 



Sixty-foot rotary kilns are nominally rated at a production of 

 200 barrels per day per kiln. Even on dry materials and with good 

 coal, however, such an output is rarely attained. Normally a 60-foot 

 kiln working on a dry mixture will produce from 140 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 120 to 140 Ibs. of 

 coal per barrel of cement, though it may range as high as 160 Ibs., and, 

 on the other hand, has fallen as low as 90 Ibs. An output of 160 barrels 

 per day, with a coal consumption of 130 Ibs. per barrel, may therefore 

 be considered as representing the results of fairly good practice on dry 

 materials. With longer kilns, however, much better results are obtained, 

 as will be noted later. 



In dealing with a wet mixture, which may carry anywhere from 

 30 to 70 per cent of water, the results are more variable, though always 

 worse than with dry materials. In working a 60-foot kihi en a wet 

 material, the output may range from 80 to 140 barrels per day, with 

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

 kiln, partly drying the mix, and utilizing waste heat will, of course, 

 improve these figures materially. 



When oil is used for kiln fuel, it may be considered that one gallon 

 of oil is equivalent in the kiln to about 10 Ibs. of coal. The fuel con- 

 sumption, using dry materials, will range between 11 and 14 gallons 

 of oil per barrel of cement; but the output per day is always some- 

 what less with oil fuel than where coal is used. 



Natural gas in the kiln may be compared with good Pennsylvania 

 or West Virginia coal by allowing about 20,000 cubic feet of gas as 

 equivalent to a ton of coal. This estimate is, however, based upon 

 too little data to be as close as those above given for oil. 



The figures given in Table 185, below, are believed to be entirely 

 reliable. They are of interest as showing what can actually be expected 

 from kilns under average management, as distinguished from the 

 expectations which embellish company prospectuses and the reports 

 of "cement experts." With the exception of A, B, and J, the mills 



