GRINDING BEHAVIOR OF COAL BLENDS IN A STANDARD BALL-AND-RACE MILL

An investigation was carried out to predict the size-composition make- up of the product of a coal blend ground in a ball-and-race mill using the breakage characteristics of the individual components determined by separate grinding. Sometimes a pseudolinearity can be observed when the changes in the grinding rate for the components in the mixture oc cur in a compensated manner. In this case, the HGI of the blend appear s to be additive. However, the composition of the product size interva ls is different from the weighted sum of the two products from separat e grinding. An empirical equation was used to predict; the change in t he breakage parameters as a function of the blending ratio and the dif ference between the relative strength of the two materials. The grindi ng of the individual coals in the Hardgrove mill exhibited non-first-o rder grinding kinetics. Consequently, the false time concept fdr fines accumulation was used to predict the grinding behavior of the coal bl ends with reasonable accuracy. The locked-cycle simulation for grindin g a binary mixture shows that the content of the mill charge becomes r icher in the stronger component. The system attains steady state when the absolute production rates of both materials are the same, although the ratio of materials in the mill charge is not necessarily the same as the ratio in the feed. As a result, the production rate can be low er than expected based on the ratio of the feed.