Effects of Moisture and Coal Blending on the Hardgrove Grindability Index of Pakistani Coals

The Hardgrove Grindibility Index (HGI) of coal is an indicator of its grindibility characteristics to determine the energy required for its pulverization. The present study is aimed at investigating the effect of inherent moisture and the blending behavior on HGIs of indigenous coals. Experiments were carried out using the standard Hardgrove Grindibility Machine to determine HGIs of three indigenous coals belonging to the Lakhra, Degari, and Chamalang coal deposits. In addition, the blending effect of six binary and six ternary blends of parent coals with different blending ratios were also tested for their HGIs. The Lakhra coal has shown the highest HGI value of 66 against 23% of inherent moisture, whereas the Degari and Chamalang coals respectively indicated HGI values of 53 and 32 against 10% and 6.95% of inherent moisture content. It was found that as the inherent moisture in coal increased the HGI values also increased. Lakhra coal, having the highest HGI value, was found to be easy to grind as compared to the Degari and Chamalang coals that have lower HGI values. The HGI values of the binary and ternary blends of parent coals, in various proportions, were found to be the proportionally average values of the parent coals.