In this system, the raw coal from the coal bunker drops on to the feeder. Hot air is passed through coal in the factor to dry the coal. The coal is then transferred to the pulverising mill where it is pulverised. Primary air is supplied to the mill, by the fan.

The mixture of pulverised coal and primary air then flows to burner where secondary air is added. The unit system is so called from the fact that each burner or a burner group and pulverizer constitute a unit.