Bottom ash is part of the non-combustible residue of combustion in a power plant, boiler, furnace or incinerator. In an industrial context, it has traditionally referred to coal combustion and comprises traces of combustibles embedded in forming clinkers and sticking to hot side walls of a coal-burning furnace during its operation. The portion of the ash that escapes up the chimney or stack is, however, referred to as 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.
In a conventional water impounded hopper (WIH) system, the clinker lumps get crushed to small sizes by clinker grinders mounted under water and fall down into a trough from where a water ejector takes them out to a sump. From there it is pumped out by suitable rotary pumps. In another arrangement a continuous 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 handlingEdit
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 impactsEdit
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 geomembranes, leachate collection systems, or other flow controls often found in municipal solid waste landfills.[5] Following a 2008 failure that caused the Tennessee Valley Authority’s Kingston Fossil Plant coal fly ash slurry spill, the 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 recyclingEdit
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 road construction and in cement kilns (clinker production). A noticeable other use is as 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]
^McLaren, R.J. & DiGioia, A.M. (1987). "The Typical Engineering Properties of Fly Ash". In Woods, R. D. (ed.). Geotechnical Practice for Waste Disposal '87; Proceedings of a Specialty Conference. Reston, VA: American Society of Civil Engineers. ISBN9780872626041.
^2017 Coal Combustion Product Production & Use Survey Report (PDF) (Report). Farmington Hills, MI: American Coal Ash Association. 2018.
^Schlossberg, Tatiana (2017-04-15). "2 Tennessee Cases Bring Coal's Hidden Hazard to Light". The New York Times.
^Kessler, K. A. (1981). "Wet Disposal of Fossil Plant Waste Case History". Journal of the Energy Division. American Society of Civil Engineers. 107 (2): 199–208. doi:10.1061/JDAEDZ.0000063.
^"EPA Letting Some Hazardous Coal Ash Ponds Stay Open Longer". U.S. News. 2020-10-16.
^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.
^"Revisions to the Coal Combustion Residuals (CCR) Closure Regulations; Fact sheet". EPA. July 2020.
^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
^Smoot, D.E. (2020-12-11). "Groups challenge rollback of coal ash rule". Muskogee Phoenix. Muskogee, OK.
EcoSmart Concrete – Use of fly ash and other supplementary cementing materials in concrete
– How bottom ash is processed to make aggregate
October 19, 2023
bottom, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, 2019, learn, when, . This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Bottom ash news newspapers books scholar JSTOR May 2019 Learn how and when to remove this template message Bottom ash is part of the non combustible residue of combustion in a power plant boiler furnace or incinerator In an industrial context it has traditionally referred to coal combustion and comprises traces of combustibles embedded in forming clinkers and sticking to hot side walls of a coal burning furnace during its operation The portion of the ash that escapes up the chimney or stack is however referred to as 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 A coal fired power plant with ash pondsMost bottom ash generated at U S power plants is stored in ash ponds which can cause serious environmental damage if they experience structural failures Contents 1 Ash handling processes 2 Waste handling 3 Environmental impacts 3 1 Ash recycling 4 See also 5 References 6 External linksAsh handling processes EditIn a conventional water impounded hopper WIH system the clinker lumps get crushed to small sizes by clinker grinders mounted under water and fall down into a trough from where a water ejector takes them out to a sump From there it is pumped out by suitable rotary pumps In another arrangement a continuous 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 EditIn 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 EditIn 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 geomembranes leachate collection systems or other flow controls often found in municipal solid waste landfills 5 Following a 2008 failure that caused the Tennessee Valley Authority s Kingston Fossil Plant coal fly ash slurry spill the 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 Edit 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 road construction and in cement kilns clinker production A noticeable other use is as 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 EditCoal combustion products Fly ash Health effects of coal ash Industrial wastewater treatmentReferences Edit McLaren R J amp DiGioia A M 1987 The Typical Engineering Properties of Fly Ash In Woods R D ed Geotechnical Practice for Waste Disposal 87 Proceedings of a Specialty Conference Reston VA American Society of Civil Engineers ISBN 9780872626041 Coal Ash Basics EPA 2021 01 25 2017 Coal Combustion Product Production amp Use Survey Report PDF Report Farmington Hills MI American Coal Ash Association 2018 Schlossberg Tatiana 2017 04 15 2 Tennessee Cases Bring Coal s Hidden Hazard to Light The New York Times Kessler K A 1981 Wet Disposal of Fossil Plant Waste Case History Journal of the Energy Division American Society of Civil Engineers 107 2 199 208 doi 10 1061 JDAEDZ 0000063 EPA Letting Some Hazardous Coal Ash Ponds Stay Open Longer U S News 2020 10 16 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 Revisions to the Coal Combustion Residuals CCR Closure Regulations Fact sheet EPA July 2020 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 Smoot D E 2020 12 11 Groups challenge rollback of coal ash rule Muskogee Phoenix Muskogee OK Coal Ash Reuse EPA 2021 01 25 External links EditEcoSmart Concrete Use of fly ash and other supplementary cementing materials in concrete LondonWaste How bottom ash is processed to make aggregate Retrieved from https en wikipedia org w index php title Bottom ash amp oldid 1135492264, wikipedia, wiki, book, books, library,
