The finer ash produced in a coal fired power station, which is collected using electro-static precipatators. Sometimes spelt as 'fly ash'. This is also know as Pulverised Fuel Ash (PFA) is some countries. About 85% of the ash produced is fly ash.
Furnace Bottom Ash (FBA)
The coarse ash that falls to the bottom of a furnace. The molten ash adheres to the boiler tubes, eventually falling to the base of the furnace. In many furnaces there is a water system that rapdily cools this ash, so called 'wet bottomed' furnace. Usually <15% of the ash produced is FBA.
Hollow ash particles that form in the furnace gas stream. Sometime these particles will contain smaller ash spheres. They float on water and are usually collected from lagoons, where ash/water disposal systems are being used. Only 1 to 2% of the ash produced are cenospheres and with the reduction in ash/water transportation, fewer are collected/available.
Where fly ash is mixed with a proportion of water (10 to 20% by dry mass typically) in order that it can be transported in normal tipping vehicles without problems with dust for sale or disposal.
Flue Gas De-sulfurisation
Where a source of Calcium is injected into the furnace gas stream to remove sulfur compounds. A typical system may consist of ground limestone in water being passed through the gas stream. The sulfur compounds convert the calcium carbonate to calcium sulfate, or gypsum, which is used in the wallboard industry for general construction.