Grindability Studies on Blended Coals of High-Ash Indian Coals with Low-Ash Imported Coals

Abstract

ABSTRACTThe study investigates the Hardgrove Grindability Index (HGI) values for binary blends of high-ash Indian coals and low-ash imported coals. The coals were selected in such a way that their grindability values were not closely spaced for studying the effect of blending in the HGI of coal blends. In addition, the coals were selected with the proximate analysis values being close to each other, where the proximate-based predictions of grindability values differ greatly for individual coal samples. It was observed that when the difference between the HGI values of the parent coals was less than 25% from the softer coal, then the grindability of coal blends closely followed the linear weighted average of the parent coals; otherwise a nonlinear relationship was observed. The nonlinear relationship between blending proportion and HGI was due to the preferential grinding of softer coal, which was confirmed by the increased ash content in the fines corresponding to a different blending ratio. A practical approach has been discussed to arrive at a suitable blending ratio to achieve the desired coal properties in the final product during the comminution process in pulverized fuel-fired boilers.