Coal Combustion Products (CCPs) are produced in coal-fired power stations
which burn either hard or brown coal.
Due to the mineral components of coal and the combustion technique fly ash (FA), bottom ash (BA), boiler slag (BS) and fluidized bed combustion (FBC) ash as combustion products as well as the products from dry or wet flue gas desulphurization, especially semi dry absorption (SDA) product and flue gas desulphurization (FGD) gypsum are produced.
The major CCPs from coal are:
Fly Ash is obtained by electrostatic or mechanical precipitation of dust-like particles from the flue gases of furnaces fired with coal or lignite at 1100 to 1400°C. Fly ash is a fine powder, which is mainly composed of spherical glassy particles. Depending upon the type of boiler and the type of coal siliceous and calcereous fly ashes with pozzolanic and/or latent hydraulic properties are produced.
Pulverized Fuel Ash (PFA) is another term for fly ash in UK and is derived from firing boilers with pulverized coal.
Cenospheres (floaters) are recovered from the surface of ash disposal ponds and are of similar chemical composition to fly ash. They float on water and are essentially composed of thin-walled hard-shelled, hollow, minute spheres with a specific gravity (relative density) less than 1.0 kg/dm3
(Furnace) Bottom Ash (BA) is a granular material removed from the bottom of dry boilers, which is much coarser than FA though also formed during the combustion of coal.
Boiler Slag (BS) is a vitreous grained material deriving from coal combustion in boilers at temperatures of 1500 to 1700°C, followed by wet ash removal of wet bottom furnaces.
Fluidized Bed Combustion (FBC) Ash is produced in fluidized bed combustion boilers. The technique combines coal combustion and flue gas desulphurization in the boiler at temperatures of 800 to 900°C. FBC ash is rich in lime and sulphur.
Semi Dry Absorption (SDA) Product is a fine grained material resulting from dry flue gas desulphurization with lime acting as the sorbent.
Flue Gas Desulphurization (FGD) Gypsum is a natural gypsum like product which is obtained by wet desulphurization of flue gas and special treatment of the adsorbed products.