Coal is ground to the size of a fine grain, mixed with air and burned in the flue gas flow.
This type of boiler dominates coal-fired power stations, providing steam to drive large turbines.
Air for combustion was blown upward through the grate carrying the lighter ash and smaller particles of unburned coal up with it, some of which would adhere to the sides of the firebox.
Those experiments helped Fred L. Dornbrook to develop methods of controlling the pulverized coal's tarry ash residues with boiler feed water tube jackets that served to reduce the surface temperature of the firebox walls and allowed the ash deposits be easily removed.
[citation needed] The Oneida Street power plant near Milwaukee's City Hall was decommissioned and renovated in 1987.
The feeding rate of the pulverized coal is controlled by computers, and is varied according to the boiler demand and the amount of air available for drying and transporting fuel.
According to its report, the boiler heated with pulverized coal on the Mercer ran at 95% of the efficiency of its best oil-fuelled journey.