THE CRUSHING OF ANTHRACITE

Special Research Report SR-1

The research project on the crushing of anthracite was incorporated as a part of an over-all project on the grindability of anthracite. This phase of the over-all project was originally initiated because several members of the advisory committee and many anthracite engineers are vitally interested in economical methods of crushing the stove and nut sizes of anthracite to the more popular buck, rice, and barley sizes. At the present time the larger sizes are crushed to the smaller sizes in stages, i.e. the stove size is crushed in a toothed roll crusher to nut size, the nut is reduced to pea, and the pea is reduced to buck. This requires three crushers for the complete job, and, in addition, requires three screens for scalping each size prior to crushing. Each crushing operation is performed with a small reduction ratio. With the recent developments made in crushing equipment it appeared quite possible that a single crusher with a high reduction ~atio could be substituted in the present plant flow arrangements to obtain the same goal. Naturally, this idea is not new but the difficulty in the past with this type of operation has been the over-production of the extreme fine sizes of No. 4 and No. 5 buck. Certain engineers representing anthracite companies thought that the newly developed aerofall mill should be investigated as a possible crushing method. Along with the decision to conduct tests with this mill it was also decided to conduct a thorough investigation of all types of conunercial crushers and to show the behavior of the stove and nut sizes in the various types of crushing equipment available on the market today. Thus the object of this investigation was to study the characteristics of all types of industrial crushers with the hope of being able to recommend the best single stage crusher to be used for reducing the larger sizes of anthracite to the more popular smaller sizes without the production of excessive amounts of fines. Research to date indicates this to be feasible. Such an arrangement would reduce capital and maintenance cost and permit flexibility to better meet market requirements.