Fly ash is the solid, dispersed ( particulate, particulate, dust-like ) residue of burns, which due to its high dispersity ( fineness ) is discharged with the flue gases. Fly ash is produced in large quantities in thermal power plants and waste incinerators and there must be separated by filter from the flue gases. The particle size ranges from about 1 micron to 1 mm. At particle shapes occur in both smooth, solid spheres and hollow spheres (called cenospheres ), platelets, fibers and agglomerates. The density is 2.2 to 2.4 kilograms per cubic decimeter, the bulk density is between 0.9 to 1.1 kilograms per cubic decimeter.
The composition of the fly ash depends strongly on the fuel ( lignite or hard coal) and extends from residual carbon and minerals ( quartz, aluminum silicate ) to toxic substances such as heavy metals (arsenic and zinc) and dioxins. The fly ash also acts as a carrier of adsorbed pollutants. While pure, uniform, consistent fuels such as coal yield a good usable fly ash, the lignite fly ash sets ( BFA) from many different fabrics together.
Previously, the exhaust gases from the stationary combustion of fossil fuels were unfiltered emitted into the atmosphere - including the combustion in large installations such as power plants and industrial furnaces. For gas to do this even today ( gas burns less polluting than other fabrics, because the fuel has less impurities). This was just in densely populated and heavily industrialized regions visible pollution result: the chimneys met gray smoke; hung up to dry laundry was dirty after a short time; depending on weather and distance to the issuers visible dust layers were deposited. In 1964 the first Clean Air Act in force; In 1974, the Federal Pollution Control Act; In 1988, the First Regulation implementing the Federal Pollution Control Act.
The filtering of exhaust gases on a commercial scale has been advanced. In the 1980s, forest dieback caused an intensification of efforts; the first known dioxin contamination in the vicinity of incinerators was another opportunity to improve the filtering technique further. The higher the efficiency of the filter and the higher their degree distribution, the higher was the amount of particulate matter collected annually. Not usable in industry or in construction fly ash is landfilled.
Lignite yields per kilowatt hour about three times more ash ( ie, about 63 grams) than coal (20 grams).
Accumulate annually in the United States 61 million tonnes, 10 million tonnes of it are in Turkey
Due to their chemical and physical properties such as the pozzolanic reactivity of the spherical particle shape and the particle distribution is in particular coal fly ash (SFA) is a high-quality secondary raw material and in the construction industry, a wide variety of applications.
Non-toxic fly ash is used in the construction industry in accordance with DIN EN 450 as an additive in cement and concrete. In addition, the fly ash can be used for the production of bricks from calcium or aerated concrete. In road construction and earthworks, the fly ash is used in conjunction with aggregate as a building material for unbound base.
Meanwhile, the method for separating fly ash in its components and therefore to higher value products are used commercially. The spheres and hollow spheres of aluminum silicate are used as fillers in the rubber and plastics industry use, the residual carbon as fuel in power plants.
Emission of radioactive metals
Naturally occurring, radioactive metals can be emitted from the power plant in the coal over the fly ash. The combustion of the combustible constituents, another important factor to a concentration of the metals. This means a higher specific radioactivity of fly ash in comparison to the fuel used. The BUND demands to consider the emitted radioactivity in immission control approval process.