Fly ash or flue ash, also known as pulverized fuel ash in the United Kingdom, is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired boilers together with the flue gases. Ash that falls to the bottom of the boiler’s combustion chamber (commonly called a firebox) is called bottom ash. In modern coal-fired power plants, fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys. Together with bottom ash removed from the bottom of the boiler, it is known as coal ash. Depending upon the source and composition of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline), aluminium oxide (Al2O3) and calcium oxide (CaO), the main mineral compounds in coal-bearing rock strata.
The minor constituents of fly ash depend upon the specific coal bed composition but may include one or more of the following elements or compounds found in trace concentrations (up to hundreds ppm): arsenic, beryllium, boron, cadmium, chromium, hexavalent chromium, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium, along with very small concentrations of dioxins and PAH compounds. It also has unburnt carbon.
SPECIFICATION OF FLY ASH
Blaine 2000 cm2/gm
45 micron residue 35% Max
|03.||Calcium Oxide (CaO)||2% Max|
|04.||Silicon di Oxide (SiO2)||52-60%|
|05.||Aluminum Oxide (Al2O3)||24-30%|
|06.||Ferric Oxide (Fe2O3)||6% Max|
|07.||Magnesium Oxide (MgO)||1% Max|
|08.||Sulphuric Anhydride (SO3)||1% Max|
|09.||Sulphide Sulpher||0.5% Max|
|10.||Sodium Oxide (Na2O)||0.5% Max|
|11.||Potassium Oxide (K2O)||0.5% Max|
|12.||Loss of Ignition (LOI)||4% Max|