Sub-Product

Description

Boiler slag is a coarse, granular, incombustible by-product of coal combustion.^[1,2]

It is angular, dense, and very hard, with particles between 0.5 and 5.0 mm in size and a smooth surface. Boiler slag is only produced in a wet-bottom boiler, which has a special design that keeps bottom ash in a molten state until it is removed.^[1]

Wet bottom boilers are preferred for low volatile coals that produce a lot of ash, but they have higher investment and maintenance costs, so they are built less often. The resulting boiler slag is a coarse, hard, black, angular, glassy material that is washed from the hopper pit into a sluiceway which is then conveyed to a collection basin for dewatering, possible crushing or screening, and either disposal or reuse.^[3]

Boiler slag can be included in roofing shingles and structural fill.^[4]

References

1. Energy Education, Boiler Slag, accessed 15th Apr 2024.
2. Recycled Materials Ressource Center, Coal Bottom Ash/Boiler Slag - Material Description, accessed 14^th Apr 2024.
3. Wikipedia, Web bottom furnace, accessed 15th Apr 2024.
4. NRDC, 9^th Jan 2015, Coal Ash, Fly Ash, Bottom Ash, and Boiler Slag.