We are having an air swept mill for coal grinding. we are getting washed coal in rakes whichis unloaded in the raw coal hopper in the gantry.This hopper is covered by railing to screen big lumps of rock. The size of rocks vary between 30mm-150mm.The majority size of washed coal is around 3mm with a volatile matter of 28-30 %.
The problem is that the mill gets oftenly jammed bcoz of the large rocks entering the mill and as a result the grinding capacity is low. Can someone suggest any cheap and very effective way of separating the large lumps of rocks from the washed coal.The railings over raw washed coal hopper is not that effective in separating the large rocks.