Effect of the size distribution of granular top coal on the drawing mechanism in LTCC

Abstract

The size distribution of granular top coal holds great influence on the drawing mechanism in longwall top coal caving (LTCC) panel. In this paper, based on the data observed from the Ruilong mine in Shanxi province, China, the effect of the size distribution of granular top coal on the drawing mechanism was investigated using theoretical analysis, 3D physical simulation and discrete element numerical calculation. The results show that the volume of the drawing body increases linearly with increasing weighted average size of granular top coal, while the maximum width of the drawing body increases nonlinearly; with increasing length of the opening, the drawing volume also increases nonlinearly at a gradually decreasing rate. With the increasing weighted average size of granular top coal, the top coal recovery ratio of the panel increases first and then decreases, and when the weighted average size of granular top coal is in the range of 150–250 mm, the recovery ratio is higher. A situation in which the size distribution of granular top coal is relatively dispersed and the standard deviation is larger is more conducive to the granular top coal drawing in the working face. When the percent of small particle is larger, the top coal recovery ratio decreases with increasing length of the opening, and it is suggested to use a single opening; in contrast, when the percent of large size particles is larger, the top coal recovery ratio increases first and then remains at a certain level, and it is suggested to use a double opening. Suggested measurements are proposed to improve top coal recovery in LTCC panel based on the research results.