The widespread use of powdered coal in industrial furnaces has, since its introduction in the 1930's, produced considerable increases in efficiency for many industrial processes. In its wake, however, it has brought its own unique problems, and chief among these has been the problem of collecting and disposing of the residue which results from the combustion of the powdered or ground coal. This residue, known commonly as fly ash, is a nuisance if it is allowed to be dispersed into the atmosphere; and if collected it presents a difficult disposal problem. In present industrial practice it is almost always collected, either with electrostatic precipitators or cyclone separators, and deposited in ever-growing disposal dumps. A recent estimate (20)* gives the imposing figure of six million tons as the annual U.S. production of this waste product.

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No. 127

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