RELATIONSHIP BETWEEN IN SITU COAL STRATIGRAPHY AND PARTICLE SIZE AND COMPOSITION AFTER BREAKAGE IN BITUMINOUS COALS

Abstract

The hypothesis that the parent stratigraphy of a coal seam, i.e. its lithotype and band distribution, can be used to estimate the input and output size distributions of broken coal for a fragmentation event(s) was tested using the drop-shatter process for core. Coal breakage is a function of the inherent strength of the material, its particle size, and the amount of impact energy imparted. Coal is composed of a heterogeneous mixture of bright and dull bands, and stone, which generate different daughter particle size distributions in response to impact energy. Lithotypes and bands also exhibit an in situ thickness distribution that can be related to input and output size distributions. The results demonstrate that dull coal that is massive and strong requires more energy to break relative to brighter, more friable coals. As a result, brighter and banded coal lithotypes break into finer band components, resulting in the concentration of bright (vitrinite-rich) coal in the finer progeny fractions. Dull coal and stone concentrate in the coarse fractions, except where stone consists of soft claystones or shales. The frequency distributions of the lithotypes' thickness estimate the feed size, and that of the component bright, dull and stone bands of the daughter particle size distribution at the end of the fragmentation process. This has implications for the prediction of size, and composition of size fractions, resulting from fragmentation events that occur during mining and handling, both of which will impact on the downstream processing behaviour of coal.