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Photomicrograph made with a scanning electron microscope and back-scatter detector: cross section of fly ash particles. Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK)—plurale tantum: coal combustion residuals (CCRs)—is a coal combustion product that is composed of the particulates that are driven out of coal-fired boilers together with the flue gases.
Fly ash brick (FAB) is a building material, specifically masonry units, containing class C or class F fly ash and water. Compressed at 28 MPa (272 atm) and cured for 24 hours in a 66 °C steam bath, then toughened with an air entrainment agent, the bricks can last for more than 100 freeze-thaw cycles.
The Kingston Fossil Plant 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 (4.2 million cubic metres) of coal fly ash slurry.
In addition, when coal ash is recycled, costs related to coal ash disposal sites are avoided. [5] [15] There are two forms of coal ash recycling: “encapsulated” and “unencapsulated." [5] [15] When coal ash is bound to other materials it is encapsulated. [5] For example, coal ash can be reused in making concrete, bricks and wallboards. [15]
Fly ash sample containing ceramic cenospheres, magnified 40×. The process of burning coal in thermal power plants produces fly ash containing ceramic particles made largely of alumina and silica. They are produced at temperatures of 1,500 to 1,750 °C (2,730 to 3,180 °F) through complicated chemical and physical transformation.
The total amount of ash produced by waste-to-energy plants ranges from 15% to 25% by weight of the original quantity of waste, and the fly ash amounts to about 10% to 20% of the total ash. [1] The fly ash, by far, constitutes more of a potential health hazard than does the bottom ash because the fly ash contains toxic metals such as lead ...
Coal is ground to the size of a fine grain, mixed with air and burned in the flue gas flow. Biomass and other materials can also be added to the mixture. Coal contains mineral matter which is converted to ash during combustion. The ash is removed as bottom ash and fly ash. The bottom ash is removed at the furnace bottom.
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]