Problems encountered during evacuation of very fine coals (-0.5mm) from the concrete

We have coal washeries. After processing of raw coal clean coal produced are stored in a concrete overhead bunker of nearly 6000 tonnes capacity. Below the bunker a moving plow feeder is there which moves over rails with the help of electrical drive simultaneously scoops the coal from the slot area of the bunker with the help of circulatory rotating plows. In this way the clean coal from the bunker are extracted and fed to the belt conveyor placed below the plow feeder. Generally this clean coals are having surface moisture of 11-12%. The clean coals are on an average 75% coarse ( 13mm x 0.5mm) & the balance are fines (-0.5mm)

Problem: Normally there is no issue in the operation till the composition of clean coals are around 80:20 or so. In case of some raw coal seams the fines quantity increases which results into very high fines quantities in clean coal. At these circumstances the fines increases beyond 35% and goes up to 50%. . During such instances the extraction from the bunker by plow feeder becomes too difficult and this directly impacts on the productivity of the plant. Normally the plow feeder extracts at the rate of 450-500 tph but whenever the fines quantities increases the feed rate comes down to 300-350 tph.

We are looking for solutions which may be achieved within a shorter period ( short range) without going for longer shutdowns or injecting major investments.

If no workable short range solutions are not found the long range solutions may be advised keeping in mind that such massive concrete bunkers can not be replaced or modified very easily. However option of replacing the extracting device may be thought of if the same are already proven equioment. ■