Fly Ash

Fly ash is one of the residues generated in combustion, and comprises the fine particles that rise with the flue gases. Ash which does not rise is termed bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of coal. Fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys of coal-fired power plants, and together with bottom ash removed from the bottom of the furnace is in this case jointly known as coal ash. Depending upon the source and makeup of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO), both being endemic ingredients in many coal-bearing rock strata.

Toxic constituents depend upon the specific coal bed makeup, but may include one or more of the following elements or substances in quantities from trace amounts to several percent: arsenic, beryllium, boron, cadmium, chromium, chromium VI, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium, along with dioxins and PAH compounds.

In the past, fly ash was generally released into the atmosphere, but pollution control equipment mandated in recent decades now require that it be captured prior to release. In the US, fly ash is generally stored at coal power plants or placed in landfills. About 43% is recycled, often used to supplement Portland cement in concrete production. Some have expressed health concerns about this.

In some cases, such as the burning of solid waste to create electricity ("resource recovery" facilities a.k.a. waste-to-energy facilities), the fly ash may contain higher levels of contaminants than the bottom ash and mixing the fly and bottom ash together brings the proportional levels of contaminants within the range to qualify as nonhazardous waste in a given state, whereas, unmixed, the fly ash would be within the range to qualify as hazardous waste.

Read more about Fly AshChemical Composition and Classification, Disposal and Market Sources, Fly Ash Reuse, Exposure Concerns

Other articles related to "fly ash, ash, fly":

Coal Combustion Products
... coal combustion methods and emission controls Fly ash is captured after coal combustion by filters (bag houses), electrostatic precipitators and other air pollution control devices ... Cements blended with fly ash are becoming more common ... Many asphaltic concrete pavements contain fly ash ...
Stella Power Stations - Environmental Impact
... From the start, the power stations' fly ash was dumped in the North Sea, and 800,000 tonnes of fly ash were dumped between the Stella and Blyth stations in 1976 ... been restricted to dumping only 50,000 tonnes of ash a year from the Stella power stations ... By this point the North East coast was the only place in Europe to dump fly ash at sea ...
Fly Ash - Exposure Concerns
... Although industry has claimed that fly ash is "neither toxic nor poisonous," this is disputed ... Exposure to fly ash through skin contact, inhalation of fine particle dust and drinking water may well present health risks ... Fine crystalline silica present in fly ash has been linked with lung damage, in particular silicosis ...
Henry Liu (civil Engineer)
... In 2001, after his retirement, Liu founded FPC, the company which developed a new type of fly ash brick, a building brick made from a waste by-product of ... In 1999, he was given some fly ash by a client, and decided to compress it "just to see what would come out." Liu mixed the fly ash with water and applied 4,000 psi (28 MPa) of pressure ... Owing to the high concentration of calcium oxide in fly ash, the bricks can be described as "self-cementing" ...
Geopolymers - Geopolymer Cements - Geopolymer Cement Categories - Fly Ash-based Geopolymer Cement
... cements, on the one hand and on the synthesis of zeolites from fly ashes on the other hand, Silverstrim et al ... and van Jaarsveld and van Deventer developed geopolymeric fly ash-based cements ... US Patent 5,601,643 was titled 'Fly ash cementitious material and method of making a product' ...

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