Analysis of the washability characteristics of low-volatile Indian coking coal with crushing at different top sizes - a case study

The effect of comminution on liberation characteristics has been studied for a low volatile coking coal of Indian origin through washability studies. Two parameters, namely "Index of Washability" (IW) and "Near Gravity Material Index" (NGMI), are used to describe the ease of washability. The ROM Coal is crushed to four different top sizes namely, 75 mm,
25 mm, 13 mm and 6mm. On the basis of calculated IW it is observed that relative ease of washabiltiy increases with decrease in top size. The value of IW at -6 mm crushing size is 41.4 which confirm the ease of washing of this coal at this feed size. From the calculated NGMI values the critical specific gravities have bee n estimated. Critical specific gravity suggests that the separation at this specific gravity range is most difficult task using gravity methods. NGMI analysis reveals that the critical specific gravities for crushing to -75 mm, -25 mm, -13 mm and -6mm are 1.65, 1.68, 1.53 and 1.58 respectively.