Effect of Fine Particles on the Breakage Behavior of Coarse Coal in the Hardgrove Mill

It is well known that fine particles have a negative influence on the energy size reduction of other materials in the grinding chamber. But a quantitative evaluation about it is relatively less. In this article, a Hardgrove mill was used to investigate the effect of fine coal on the grinding energy, specific rate of breakage of the top size, and the production of fine coal in -0.074 mm size fraction. A qualitative description of the friction coefficient between coal and grinding media demonstrates that this index drops with more fines added in the particle bed. The decreasing degree of grinding energy increases 2.5 times if added level of fine coal changes from 2.5 g to 10 g. Breakage of the top size at different added levels of fine coal still follows the first-order law. But due to the decrease of grinding energy and the cushion effect of added fine coal, the breakage rate of coarse particles decreases 2% to 25% if compared with the single breakage. Decreases of grinding energy and breakage rate finally result in a lower yield of fines (-0.074 mm). Hence, added fines decrease the grinding energy efficiency and make the breakage time consuming.