The breakage of a coal in compression tests has been studied with the aim of obtaining an appearance function giving the distribution resulting from the breakage of each particle type, which can be used in the simulation of vertical spindle mills that are commonly used in coal fired power plants. The appearance functions from the compression tests were found to take a linear form on logit axes (log(x/(xm − x))), thus giving a simpler description than is available on other axes. In common with other breakage analysis methods the lines can be identified by the percent passing one tenth of the initial size, the t10 parameter. An exponential relation between t10 and specific energy was found for each particle group defined by size and density and the parameters of the exponential relation were related to the particle size and density. It was found for this particular coal that breakage did not preferentially concentrate either coal or mineral matter.
The relations developed allow the generation of a three dimensional breakage-appearance function for the breakage of both size and density components which can be used in the simulation of a pulveriser for the coal tested. The paper also demonstrates the type of test work required for the generation of appearance functions for other types of coal.