Ash is present in two forms: 1) Fly-ash, a lighter material that exits the boiler in the flue-gas stream at the top of the boiler. 2) Bottom ash, a heavy, sometimes molten material that falls to the bottom of the boiler. It ranges from small, sand-like material to large masses that form on the superstructure of the boiler and fall violently to the bottom.
Water impounded bottom ash collection systems
Ash is a by-product of the combustion process in power generating stations that burn coal as a primary fuel. Combustion takes place in a boiler that is actually a large open furnace. The walls of the furnace are lined with pipes that carry water to produce steam that powers a turbine generator.