Ash Fusion
During combustion of coal, the remaining noncombustible material becomes an ash or liquid slag. Understanding how ash or slag will behave in a furnace or boiler is important because both may cause clogging or fouling of equipment (van Krevelen, 1993). Ash fusion, also called fusibility, is a test to determine how the ash residue remaining from combustion of a coal will react in a furnace or boiler. In this test, coal ash is put into conical molds as specified in ASTM method D1857-04 guidelines and procedures (American Society for Testing and Materials, 2013, p. 431–435). The molds are heated in a furnace in a reducing atmosphere (air lacking oxygen). The ash cones change shape in response to increasing heat. Temperatures are recorded for different stages in the shape changes, which, in order of increasing heat, are called the:
- Initial deformation temperature (IT)
- Softening temperature (ST)
- Hemisphere temperature (HT)
- Fluid temperature (FT)