Hard Groove Index for Coking Coals

Source of coal Imported coal Munidih coal Dugda coal Raw coal

(size fraction)

+80mm 70.6

80-40mm 69.4 66.4

40-25mm 71.1 67.3 70.1 75.3

25-10mm 73.3 69.2 69.9 73.4

10-3.2mm 81.9 74.3 71.8 78.4

3.2-0.6mm 87.9 84.3 76.0 85.5

Avg: 81.2 73.9 72.1 73.3

Significance: The grindibility index is very important when coal is to be pulverized. Coals, which are easy to grind, have got grindibility index near about 60-100. The higher the number the softer the coal or the easier it is to grind. Generally the rank of a coal may be indicated by HGI.

Note: HGI tests are necessary for the coals used in TPP. It gives an advance indication about functioning of a pulveriser i.e. the bowl mills. The HGI also gives an indication about the ash content or grade of the non coking coal.

Thank you Satyanarayan Sir for your valuable input.