Cement is produced by heating a mixture of clay or shale plus chalk or lime in a rotary kiln up to 250 m long per 8 m diameter rotating at 1 rpm. The process can be wet, semi-dry or dry and the fuel can be pulverized coal, oil or gas. As the coal ash is similar in composition to the clay or shale, it can stay in the cement clinker. As one of the kiln operator's major costs is fuel and even a modest sized kiln can consume 8-10 tons of coal per hour, the cement kiln could, therefore, solve a disposal problem and also benefit the cement manufacturer by reducing fuel costs.
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