Читать книгу Coal-Fired Power Generation Handbook - James Speight G., James G. Speight - Страница 62

The hammer mill is a device in which the feed coal is contacted (impacted) by rotating hammers and then further impacted by contact with grid breaker plates. The grinding that occurs in the hammer mill results from the rubbing action of feed material between two hardened surfaces i.e., the hammers and the grid or screen plates. The hammer mill usually produces a relatively high proportion of fine material (Roman, 1967). The fineness obtained can be varied by adjustments of revolutions per minute or the spacing between the hammer tips and the grate bars.

The ring-type hammer mill is a modification of the hammer mill which was developed to help minimize the amount of fines in the product. In these units, the hammers have been replaced by rings (alternately toothed and plain) which revolve and cause size reduction by a rolling compression action rather than by a grinding action (Roman, 1967). The unit emphasizes nipping particles between the hammer and the grate bars. The hammer mill is a versatile unit and has a capacity up to 2,500 tons/hour for industrial units.