Sub-Product

Coal Bottom Ash is the coarse, granular, incombustible by-product of coal combustion that is collected from the bottom of furnaces. Most bottom ash is produced at coal-fired power plants. When pulverized coal is burned in a bottom boiler, most of the unburned material is caught in the flue gas and captured as fly ash. Only about 10-20% of this ash is bottom ash. This ash is dark grey in colour, and is about the size of sand. This ash is collected in a water-filled hopper at the bottom of the furnace and removed by high-pressure water jets. It is deposited in a collection pond and stored for disposal or later use after recycling.

Source: Energy Education, Bottom ash