The concept of coal pulverization stems from the belief that if the coal is made fine enough, it will burn almost as easily and efficiently as a gas. The raw coal is fed into the pulverizer along with heated air. As the coal gets crushed, the hot air dries it and blows the usable fine coal powder out, which thereafter is transported to coal bunker for storage or directly for use in blast furnace. The exhaust air is then purified by a bag filter.