These are vitreous, grainy materials from the wet ash removal of wet bottom furnaces. In a wet bottom furnace the ash collects in a molten state on the furnace floor and flows over a water-cooled weir into a quenching tank filled with water. In Australia, quenched and crushed boiler slag is also commonly described as FBA.
This is a coarse substance similar to bottom ash, which collects within the economiser section of the boiler. It is usually handled together with the bottom ash as a combustion product.
This material is produced in power stations where sulfur is removed from the flue gas stream using Flue Gas Desulfurisation (FGD) technology. At this stage there are no utility boilers in Australia equipped with FGD systems.
