Bottom ash

Source: Wikipedia, the free encyclopedia.
A coal-fired power plant with ash ponds

Bottom ash is part of the non-

fly ash
. The clinkers fall by themselves into the bottom hopper of a coal-burning furnace and are cooled. The above portion of the ash is also referred to as bottom ash.

Most bottom ash generated at U.S. power plants is stored in ash ponds, which can cause serious environmental damage if they experience structural failures.

Ash handling processes

In a conventional

link chain
scrapes out the clinkers from under water and feeds them to clinker grinders outside the bottom ash hopper.

More modern systems adopt a continuous removal philosophy. Essentially, a heavy duty chain conveyor submerged in a water bath below the furnace which quenches hot ash as it falls from the combustion chamber and removes the wet ash continuously up to a de-watering slope before onward discharge into mechanical conveyors or directly to storage silos.

Modern municipal waste incinerators reduce the production of

dioxins by incinerating at 850 to 950 degrees Celsius for at least two seconds, forming incinerator bottom ash
as byproduct.

Waste handling

In United States facilities, the ash waste is typically pumped to ash ponds, the most common disposal method.[1] Some power plants operate a dry disposal system with landfills.

Environmental impacts

In the United States, coal ash is a major component of the nation's industrial waste stream.[2] In 2017, 38.2 million short tons (34.7×10^6 t) of fly ash, and 9.7 million short tons (8.8×10^6 t) of bottom ash were generated.[3] Coal contains trace levels of arsenic, barium, beryllium, boron, cadmium, chromium, thallium, selenium, molybdenum and mercury, many of which are highly toxic to humans and other life. Coal ash, a product of combustion, concentrates these elements and can contaminate groundwater or surface waters if there are leaks from an ash pond.[4]

Most U.S. power plants do not use

U.S. Environmental Protection Agency (EPA) began developing regulations that would apply to all ash ponds in the U.S. EPA published its "Part A" final rule for Coal Combustion Residuals (CCR) on August 28, 2020, requiring all unlined ash ponds to retrofit with liners or close by April 11, 2021. Some facilities may apply to obtain additional time—up to 2028—to find alternatives for managing ash wastes before closing their surface impoundments.[6][7][8] EPA published its ""CCR Part B" rule on November 12, 2020, which allows certain facilities to use an alternative liner, based on a demonstration that human health and the environment will not be affected.[9] Further litigation on the CCR regulation is pending as of 2021.[10]

Ash recycling

Bottom ash can be extracted, cooled and conveyed using dry ash handling technology. When left dry the ash can be used to make concrete, bricks and other useful materials. There are also several environmental benefits.[11]

Bottom ash may be used as raw alternative material, replacing earth or sand or aggregates, for example in

growing medium in horticulture (usually after sieving). In the United Kingdom it is known as furnace bottom ash (FBA), to distinguish it from incinerator bottom ash (IBA), the non-combustible elements remaining after incineration. A pioneer use of bottom ash was in the production of concrete blocks used to construct many high-rise flats in London in the 1960s.[citation needed
]

See also

References

  1. .
  2. ^ "Coal Ash Basics". EPA. 2021-01-25.
  3. ^ 2017 Coal Combustion Product Production & Use Survey Report (PDF) (Report). Farmington Hills, MI: American Coal Ash Association. 2018. Archived from the original (PDF) on 2019-05-07. Retrieved 2019-06-17.
  4. ^ Schlossberg, Tatiana (2017-04-15). "2 Tennessee Cases Bring Coal's Hidden Hazard to Light". The New York Times.
  5. .
  6. ^ "EPA Letting Some Hazardous Coal Ash Ponds Stay Open Longer". U.S. News. 2020-10-16.
  7. ^ EPA. "Hazardous and Solid Waste Management System: Disposal of Coal Combustion Residuals From Electric Utilities; A Holistic Approach to Closure Part A: Deadline To Initiate Closure." Federal Register, 85 FR 53516. 2020-08-28.
  8. ^ "Revisions to the Coal Combustion Residuals (CCR) Closure Regulations; Fact sheet". EPA. July 2020.
  9. ^ EPA (2020-11-12). "Hazardous and Solid Waste Management System: Disposal of CCR; A Holistic Approach to Closure Part B: Alternate Demonstration for Unlined Surface Impoundments." Final rule. 85 FR 72506
  10. ^ Smoot, D.E. (2020-12-11). "Groups challenge rollback of coal ash rule". Muskogee Phoenix. Muskogee, OK.
  11. ^ "Coal Ash Reuse". EPA. 2021-01-25.

External links

  • EcoSmart Concrete – Use of fly ash and other supplementary cementing materials in concrete
  • LondonWaste – How bottom ash is processed to make aggregate