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Coal Combustion By-Products (CCBs)


CCB-Related Terms

  • Admixtures* - material other than water, aggregates, hydraulic cement and fiber reinforcement, used as an ingredient of concrete or mortar, and added to the batch immediately before or during its mixing. Fly ash is used as an admixture in concrete.

  • Anthracite Coal - a type of coal that has the highest carbon content and the lowest moisture and ash content. Anthracite burns slowly and makes a good heating fuel for homes. The United States has about 7.3 billion tons of anthracite, most of which can be found in Pennsylvania. - See Photo

  • Ash Hopper - a collection chamber, usually in the shape of an inverted tapered cone or pyramid, where collected ash is temporarily stored. As the ash is collected from the flue gas, it drops into the large end of the ash hopper and accumulates. The small end of the hopper is closed with a valve that is periodically opened to remove ash when the hopper is full. - See Photo

  • Ash Impoundment Pond* - an impoundment or surface impoundment used to store or dispose of ash primarily from the combustion of coal. A type of waste management facility consisting of an excavated, a dammed or diked reservoir in which coal ashes are stored for future removal or disposed of as a slurry or sludge. The coal ash solids settle out and leave relatively clear water at the surface that is discharged through a designed and managed outlet structure to a nearby stream, surface water or plant process water system. Ash pond designs reflect local site conditions, federal and state regulations and whether fly ash, bottom ash, boiler slag or a combination of coal ashes are disposed in the ash pond. While some electric utility generating power companies combine the ashes during storage or disposal, other power companies use separate ash ponds for fly ash, bottom ash and boiler slag. The ash pond is referred to as a bottom ash pond, fly ash pond, boiler slag pond when it receives one type of ash. Also a large ash pond is referred to as an ash impoundment, ash reservoir, or surface impoundment.

  • ASTM - ASTM International, as a standards development body, provides technical standards which include metals, petroleum, construction, environment and many other related standards, test methods, specifications, and guides.

  • Beneficiation* - improvement of the chemical or physical properties of a raw material or intermediate product by the removal or modification of undesirable components or impurities. The removal of unburned carbon in fly ash is an example of beneficiation of the raw fly ash.

  • Bituminous Coal - the most common type of coal in the U.S. Bituminous is a term that refers to the "rank" of the coal which is classified based on its content of fixed carbon, volatile matter and heating value. There are several groups of bituminous coal: high-volatile A, B, and C, medium-volatile, and low-volatile bituminous. Bituminous coal generally has a high heating value and low moisture content. It is mainly burned to produce electricity, but is also used to produce metallurgical coke. - See Photo

  • Carbon Injection - See Mercury Removal

  • Calcined - heating of a substance to a temperature until it decomposes.

  • Cement - finely powdered mixtures of inorganic compounds which when combined with water will set and harden.

  • Class C Fly Ash* - fly ash, which meets criteria defined in ASTM C 618 for use in concrete. - See Photo

  • Class F Fly Ash* - fly ash, which meets criteria defined in ASTM C 618 for use in concrete. - See Photo

  • Coal* - a brown to black combustible sedimentary rock (in the geologic sense) composed principally of consolidated and chemically altered plant remains; solid hydrocarbon fuel formed by ancient decomposition of woody substance under conditions of heat and pressure. All solid fuels are classified as anthracite, bituminous, sub-bituminous or lignite by ASTM and in ASTM D388-77.

  • Coke - a hard, porous material produced by heating bituminous coal to a high temperature in the absence of air. It is used in the steel industry to melt and reduce iron ore to metallic iron, which is the main ingredient in steel. (Metallurgical Coke)

  • Concrete - a hard compact building material formed when a mixture of cement, sand, gravel, and water undergoes hydration.

  • Cyclone Boiler* - a type of coal-fired boiler. The coarsely pulverized coal undergoes slagging combustion in a cylindrical (cyclone) burner. Some wet-bottom boilers are not cyclone-fired. The primary byproduct is a glassy slag referred to as boiler slag, which is in great demand for beneficial use, but the supplies are declining.

  • Electrostatic Precipitator (ESP)* - a facility that removes fly ash from the flue gas by producing an electric charge on the fly ash and collecting it electrostatically.

  • Flowable Fill - also termed "controlled low-strength material" or "CLSM", flowable fills are mainly used for trench filling, but may also be used in other applications such as backfilling bridge abutments and retaining walls. Flowable fill contains much less cement and higher proportions of fly ash and water than concrete. Sand is generally the only aggregate used. The fills are designed to have relatively low strength so that they can be excavated if necessary.

  • Flue Gas Desulfurization (FGD)* - removal of gaseous sulfur dioxide from boiler exhaust gas. Primary types of FGD processes are wet scrubbers, dry scrubbers, and sorbent injection. Sorbents include lime, limestone, sodium-based compounds, and high-calcium coal fly ash.

  • Landfill* - a disposal facility where waste is placed in or on land; a facility where “dry” (actually moistened) coal combustion or flue gas cleaning byproducts (CCBs) are placed for disposal in or on land. CCBs are transported to this facility directly from the coal-fired plant after they are produced or after they are dredged from storage impoundments that are used as interim facilities. The disposed CCBs remain in the landfill after closure. Also these CCBs are dry (moistened) and have the consistency of soil. As a result dikes are not required to provide stability. Most large landfills are divided into sections or cells and the CCBs are placed in layers that are referred to as lifts that can vary in thickness. Typically captive CCBs landfills are designed and permitted to receive only CCBs and are classified as mono-fills. - Average Size

  • Lignite - this is the lowest rank coal in the U.S. and thus has a low heating value and a high moisture content. If the lignite is of a sufficiently low rank it might be termed "brown coal." Lignite is fairly soft and can be brown or black in color. It is burned to generate electricity. - See Photo

  • Low-NOx Burners - a component of coal fired boilers which are used to generate electricity. These burners are designed to lower the combustion temperature to generate lower NOx emissions.

  • Pozzolan* - primarily siliceous or siliceous and aluminous materials that will, in finely divided form and in the presence of moisture, chemically react with calcium oxide at ordinary temperatures to form compounds possessing cementitious properties. - See Photo

  • Pozzolanic*(activity/reactivity) - the phenomenon of strength development that occurs when lime and certain aluminosilicates react at ambient temperatures in the presence of water.

  • Pulverized Coal (PCC) Combustion* - refers to any combustion process that uses very finely ground (pulverized) coal in the process. Pulverized coal combustion processes usually result in the production of bottom and fly ashes.

  • Rank - the classification of coal relative to other coals, according to their degree of metamorphism, or progressive alteration, in the natural series from lignite to anthracite (Standard Classification of Coal by Rank, 1992, American Society for Testing and Materials, ASTM Designation D-388-91a). (defintion courtesy of IEA DOE).

  • Scanning Electron Microscope (SEM) - is an electron-beam-based microscope that uses electrons to produce high-resolution three dimensional images of specimens and allows magnifications of hundreds of times greater than a light microscope. An SEM scan is taken by scanning a focused probe across the surface of the sample to be studied. It can focus on both the "hills" and the "valleys" of an object at the same time, so that sharp images of very fine details are produced. The more electrons a particular region emits, the brighter the image at that point. SEM images typically contain a good deal of topographical detail.

  • SEM - See Scanning Electron Microscope

  • Scrubbers* - See Flue Gas Desulfurization

  • Slag Tap - a term used for a coal-fired boiler wherein the ash is kept in a molten state and is removed or "tapped" from the bottom of the boiler. The molten slag is quenched in water to form a glassy solid. Slag tapping is also done in blast furnaces. In this case, molten slag floats on top of the molten iron and is tapped from the surface of the iron.

  • Sorbent - the material within a scrubber that is used to remove sulfur oxides (SOx) from flue gas during coal combustion. In most systems the sorbent is limestone or lime mixed with water.

  • Subbituminous Coal - as the name implies, subbituminous coal is intermediate in rank between bituminous coal and lignite. It thus has an intermediate heating value, volatile matter content and moisture content. It is burned to generate electricity.

  • Wet Bottom Boiler/Furnace* - a pulverized fuel fired furnace in which the ash particles are deposited and retained on the floor thereof and molten ash is removed by tapping either continuously or intermittently.

*Definition courtesy of American Coal Ash Association's - "Glossary of Terms"

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