The Grindability Of Coal is a measure of the ease with which it can be ground fine enough for use as a pulverised fuel, & it also shows the physical properties of coal like hardness, tenacity and fracture. There is a fixed relationship between Grindability and rank of coal in the natural series from brown coal to lignite & anthracite. Coals easier to grind have 14 to 30 percent volatile matter Coals with higher volume matter are more difficult to grind. However petrographic & mineral constituents influence grindability. The hardgroove index of coal is affected by its moisture content and hence on the humidity of the atmosphere in which the test is carried out.

Experimental Procedure

1 kg of coal sample was taken and crushed to pass through 4.73mm sieve. The resulting sample was put in two steve of 1.18mm sieve (upper sieve) and +600 size(kwer sieve). Sieve the materiol for 2 minutes until the entire material pass through 1.18mm sieve* The 1.18mm by 600 size coal was mixed thoroughly and 120 gm of the sample was removed for sample divider The 30gm sample was taken in a ball mill along with 8 iron baits with diameter 234*0 003 mm. The mouth of the ball mill was closed and it was set to rotate for about 60 revolutions, when the rotation is achieved, the machine was stopped. The sample left in the ball mill was then collected along with any powdered substance sticking to the surface of the machine by help of a brush* This sample was then put in a sieve of 73 size and was shaken for about 10 minutes. After sieving for about 3 minutes, the sample which passes through 73 size was weighed on the balance.

Calculation - The hard groove grindobility index of coal is calculated using the following formula. HGI = 13 + 6.93 W. W = weight of the test sample passing through 73 sieve after grinding