Bottom ash

Last updated
A coal-fired power plant with ash ponds Intermountain Power Plant, Utah.jpg
A coal-fired power plant with ash ponds

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 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.

Contents

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 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, 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.

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.

Health impacts

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 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. The 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 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

Related Research Articles

<span class="mw-page-title-main">Ash</span> Waste product of fires

Ash or ashes are the solid remnants of fires. Specifically, ash refers to all non-aqueous, non-gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash is the non-gaseous, non-liquid residue after complete combustion.

<span class="mw-page-title-main">Hazardous waste</span> Ignitable, reactive, corrosive and/or toxic unwanted or unusable materials

Hazardous waste is waste that must be handled properly to avoid damaging human health or the environment. Waste can be hazardous because it is toxic, reacts violently with other chemicals, or is corrosive, among other traits. As of 2022, humanity produces 300-500 million metric tons of hazardous waste annually. Some common examples are electronics, batteries, and paints. An important aspect of managing hazardous waste is safe disposal. Hazardous waste can be stored in hazardous waste landfills, burned, or recycled into something new. Managing hazardous waste is important to achieve worldwide sustainability. Hazardous waste is regulated on national scale by national governments as well as on an international scale by the United Nations (UN) and international treaties.

<span class="mw-page-title-main">Incineration</span> Waste treatment process

Incineration is a waste treatment process that involves the combustion of substances contained in waste materials. Industrial plants for waste incineration are commonly referred to as waste-to-energy facilities. Incineration and other high-temperature waste treatment systems are described as "thermal treatment". Incineration of waste materials converts the waste into ash, flue gas and heat. The ash is mostly formed by the inorganic constituents of the waste and may take the form of solid lumps or particulates carried by the flue gas. The flue gases must be cleaned of gaseous and particulate pollutants before they are dispersed into the atmosphere. In some cases, the heat that is generated by incineration can be used to generate electric power.

<span class="mw-page-title-main">Tailings</span> Materials left over from the separation of valuable minerals from ore

In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material that overlies an ore or mineral body and is displaced during mining without being processed.

<span class="mw-page-title-main">Resource Conservation and Recovery Act</span> Federal law in the United States

The Resource Conservation and Recovery Act (RCRA), enacted in 1976, is the principal federal law in the United States governing the disposal of solid waste and hazardous waste.

<span class="mw-page-title-main">Waste-to-energy plant</span> Building that incinerates unusable garbage

A waste-to-energy plant is a waste management facility that combusts wastes to produce electricity. This type of power plant is sometimes called a trash-to-energy, municipal waste incineration, energy recovery, or resource recovery plant.

<span class="mw-page-title-main">Fossil fuel power station</span> Facility that burns fossil fuels to produce electricity

A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal, oil, or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical generator. The prime mover may be a steam turbine, a gas turbine or, in small plants, a reciprocating gas engine. All plants use the energy extracted from the expansion of a hot gas, either steam or combustion gases. Although different energy conversion methods exist, all thermal power station conversion methods have their efficiency limited by the Carnot efficiency and therefore produce waste heat.

<span class="mw-page-title-main">Thermal power station</span> Power plant that generates electricity from heat energy

A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam turbine connected to an electrical generator. The low-pressure exhaust from the turbine enters a steam condenser where it is cooled to produce hot condensate which is recycled to the heating process to generate more high pressure steam. This is known as a Rankine cycle.

<span class="mw-page-title-main">Waste-to-energy</span> Process of generating energy from the primary treatment of waste

Waste-to-energy (WtE) or energy-from-waste (EfW) is the process of generating energy in the form of electricity and/or heat from the primary treatment of waste, or the processing of waste into a fuel source. WtE is a form of energy recovery. Most WtE processes generate electricity and/or heat directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or synthetic fuels, often derived from the product syngas.

<span class="mw-page-title-main">Coal combustion products</span> By-products of coal combustion

Coal combustion products (CCPs), also called coal combustion wastes (CCWs) or coal combustion residuals (CCRs), are categorized in four groups, each based on physical and chemical forms derived from coal combustion methods and emission controls:

<span class="mw-page-title-main">Coal-fired power station</span> Type of thermal power station

A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide there are over 2,400 coal-fired power stations, totaling over 2,130 gigawatts capacity. They generate about a third of the world's electricity, but cause many illnesses and the most early deaths, mainly from air pollution. World installed capacity doubled from 2000 to 2023 and increased 2% in 2023.

<span class="mw-page-title-main">Health and environmental impact of the coal industry</span>

The health and environmental impact of the coal industry includes issues such as land use, waste management, water and air pollution, caused by the coal mining, processing and the use of its products. In addition to atmospheric pollution, coal burning produces hundreds of millions of tons of solid waste products annually, including fly ash, bottom ash, and flue-gas desulfurization sludge, that contain mercury, uranium, thorium, arsenic, and other heavy metals. Coal is the largest contributor to the human-made increase of carbon dioxide in Earth's atmosphere.

<span class="mw-page-title-main">Teesside EfW</span> Power station in Billingham, UK

Teesside Energy from Waste plant is a municipal waste incinerator and waste-to-energy power station, which provides 29.2 megawatts (MW) of electricity for the National Grid by burning 390,000 tonnes of household and commercial waste a year. It is located on the River Tees at Haverton Hill, east of Billingham in North East England. Developed and built by NEM, a subsidiary of Northumbrian Water, the initial plant replaced the Portrack Incinerator and opened in 1998. Subsequently, the facility became part of SITA, now Suez.

<span class="mw-page-title-main">Kingston Fossil Plant coal fly ash slurry spill</span> 2008 environmental disaster in Tennessee, US

The Kingston Fossil Plant coal fly ash slurry spill was an environmental and industrial disaster that occurred on December 22, 2008, when a dike ruptured at a coal ash pond at the Tennessee Valley Authority's Kingston Fossil Plant in Roane County, Tennessee, releasing 1.1 billion US gallons of coal fly ash slurry. The coal-fired power plant, located across the Clinch River from the city of Kingston, used a series of ponds to store and dewater the fly ash, a byproduct of coal combustion. The spill released a slurry of fly ash and water which traveled across the Emory River and its Swan Pond embayment onto the opposite shore, covering up to 300 acres (1.2 km2) of the surrounding land. The spill damaged multiple homes and flowed into nearby waterways including the Emory River and Clinch River, both tributaries of the Tennessee River. It was the largest industrial spill in United States history.

<span class="mw-page-title-main">Ash pond</span> Coal plant disposal structure

An ash pond, also called a coal ash basin or surface impoundment, is an engineered structure used at coal-fired power stations for the disposal of two types of coal combustion products: bottom ash and fly ash. The pond is used as a landfill to prevent the release of ash into the atmosphere. Although the use of ash ponds in combination with air pollution controls decreases the amount of airborne pollutants, the structures pose serious health risks for the surrounding environment.

<span class="mw-page-title-main">Big Sandy Power Plant</span>

The Big Sandy Power Plant is a 268 megawatt (MW), natural gas power plant owned and operated by Kentucky Power Company, a subsidiary of American Electric Power (AEP), on the shores of the Big Sandy River near Louisa, Kentucky. It was established in 1963. It was formerly a coal-fired power plant, but was converted to natural gas in 2016.

Solid waste policy in the United States is aimed at developing and implementing proper mechanisms to effectively manage solid waste. For solid waste policy to be effective, inputs should come from stakeholders, including citizens, businesses, community-based organizations, non-governmental organizations, government agencies, universities, and other research organizations. These inputs form the basis of policy frameworks that influence solid waste management decisions. In the United States, the Environmental Protection Agency (EPA) regulates household, industrial, manufacturing, and commercial solid and hazardous wastes under the 1976 Resource Conservation and Recovery Act (RCRA). Effective solid waste management is a cooperative effort involving federal, state, regional, and local entities. Thus, the RCRA's Solid Waste program section D encourages the environmental departments of each state to develop comprehensive plans to manage nonhazardous industrial and municipal solid waste.

<span class="mw-page-title-main">Health effects of coal ash</span>

Coal ash, also known as coal combustion residuals (CCRs), is the mineral residue that remains from burning coal. Exposure to coal ash and to the toxic substances it contains may pose a health risk to workers in coal-fired power plants and residents living near coal ash disposal sites.

<span class="mw-page-title-main">2014 Dan River coal ash spill</span> Ecological disaster in North Carolina

In February 2014, an Eden, North Carolina facility owned by Duke Energy spilled 39,000 tons of coal ash into the Dan River. The company later pled guilty to criminal negligence in their handling of coal ash at Eden and elsewhere and paid fines of over $5 million. The U.S. Environmental Protection Agency (EPA) has since been responsible for overseeing cleanup of the waste. EPA and Duke Energy signed an administrative order for the site cleanup.

<span class="mw-page-title-main">Allen Fossil Plant</span>

The Allen Fossil Plant was a 741-megawatt (MW), coal power plant located south of Memphis, Tennessee. It generated electricity from 1959 to 2018. At the time of its closure, the plant was operated by Tennessee Valley Authority (TVA).

References

  1. 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. ISBN   9780872626041.
  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. Kessler, K. A. (1981). "Wet Disposal of Fossil Plant Waste Case History". Journal of the Energy Division. 107 (2). American Society of Civil Engineers: 199–208. doi:10.1061/JDAEDZ.0000063.
  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.