Effects of moisture and coal blending on Hardgrove Grindability Index of Western Australian coal

Abstract

Investigations into the effects of moisture and coal blending on Hardgrove Grindability Index (HGI) were carried out on Collie coal of Western Australia. Experiments were conducted in a standard Hardgrove apparatus on four individual Premier seam coals (namely P2, P3, P4 and Hebe) and several blends (namely Hebe/P2, Hebe/P3, Hebe/P4, Hebe/P2/P4) prepared at various blending ratios. The experiments comprised of 5 days of air-drying followed by oven drying. Among the coal seams tested, Hebe showed the highest HGI (58) whereas P4 was the lowest (47). HGI was found to correlate well with residual moisture, with correlation coefficients ranging from 0.5 to 0.9 depending on the type of coal seam or blend. In contrast, moisture measurements on the samples loaded into the HGI apparatus (size 0.600 to 1.180 mm), referred to as the “coarse fraction” showed erratic trends with HGI. The experimental results suggest that no relationship exist between the coarse fraction moisture and HGI. Measured HGI values of binary and ternary blends were found to correspond well with the weighted average values of HGI within ±2 HGI units. This effect was confirmed by a further investigation with a range of 11 binary (P3/Hebe) blends of various proportions.