Bottom ash refers to the non-combustible constituents of coal with traces of combustibles embedded in forming clinkers and sticking to hot side walls of a coal-burning furnace during its operation. The portion of the ash that escapes up the chimney or stack is, however, referred to as fly ash. The clinkers fall by themselves into the water or sometimes by poking manually, and get cooled.

The clinker lumps get crushed to small sizes by clinker grinders mounted under water and fall down into a trough from where a water ejector takes them out to a sump. From there it is pumped out by suitable rotary pumps to dumping yard far away. In another arrangement a continuous link chain scrapes out the clinkers from under water and feeds them to clinker grinders outside the bottom ash hopper.

An alternative bottom ash handling system is the MAC (Magaldi Ash Cooler) system; the MAC Dry Bottom Ash System is a unique system for dry extraction, cooling and handling of bottom ash from pulverized coal-fired boilers. It eliminates water usage in the cooling and conveying of bottom ash. This system cools ash using only a small controlled amount of ambient air.

Bottom ash may be used as an aggregate in road construction and concrete, where it is known as furnace bottom ash (FBA), to distinguish it from incinerator bottom ash (IBA), the non-combustible elements remaining after incineration. It was also used in the making of the concrete blocks used to construct many high-rise flats in London in the 1960s

[edit] See also

• Fly-ash

[edit] External links

• EcoSmart Concrete : A site dedicated to the use of Fly ash and other supplementary cementing materials in concrete.
• London Waste: London waste website where you can see how bottom ash is processed to make aggregate.