The effect of moisture content on the Hardgrove grindability index of coal from the Kolubara basin

In order to obtain data on the effect of moisture content on the grindability of coals, experimental research was conducted. The experiment included six samples of coal from the Kolubara basin. The samples were selected based on experimentally obtained values of their Hardgrove grindability index (HGI), in order to cover the entire range of experimental HGI values. In addition to determining the HGI, proximate, and petrographic analyses were performed on all samples. Lignites are naturally tough, soft, and greasy when in a moist state. By reducing the moisture content, lignites become more brittle. For this reason, Hardgrove grindability index values have different values depending on the moisture content at which they are determined. The HGI has a non-linear dependence on the moisture content of the coal. All curves have two inflection points, one minimum and one maximum value of Hardgrove grindability index in the tested range. The minimum values of HGI are in the range of 15-22% of the mass fraction of total moisture in coal, while the maximum values of HGI are for a total moisture content of 5-13%. In the case of high moisture content in coal, the obtained high values of HGI may not reflect the true grindability of the coal. These values could be misleading and not necessarily indicative of the coal inherent characteristics. Instead, they could be a result of the imperfections in the Hardgrove method used to determine the grindability index of coal with high moisture content.