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Coal

Coal

Coal is a naturally occurring combustible material consisting primarily of the element carbon. It also contains low percentages of solid, liquid, and gaseous hydrocarbons and/or other materials, such as compounds of nitrogen and sulfur. Coal is usually classified into subgroups known as anthracite, bituminous, lignite, and peat. The physical, chemical, and other properties of coal vary considerably from sample to sample.

Origins of coal

Coal is often referred to as a fossil fuel. That name comes from the way in which coal was originally formed. When plants and animals die, they normally decay and are converted to carbon dioxide, water, and other products that disappear into the environment. Other than a few bones, little remains of the dead organism.

At some periods in Earth's history, however, conditions existed that made other forms of decay possible. The bodies of dead plants and animals underwent only partial decay. The products remaining from this partial decay are coal, oil, and natural gasthe so-called fossil fuels.

Words to Know

Anthracite: Hard coal; a form of coal with high heat content and a high concentration of pure carbon.

Bituminous: Soft coal; a form of coal with less heat content and pure carbon content than anthracite, but more than lignite.

British thermal unit (Btu): A unit for measuring heat content in the British measuring system.

Coke: A synthetic fuel formed by the heating of soft coal in the absence of air.

Combustion: The process of burning; a form of oxidation (reacting with oxygen) that occurs so rapidly that noticeable heat and light are produced.

Gasification: Any process by which solid coal is converted to a gaseous fuel.

Lignite: Brown coal; a form of coal with less heat content and pure carbon content than either anthracite or bituminous coal.

Liquefaction: Any process by which solid coal is converted to a liquid fuel.

Oxide: An inorganic compound whose only negative part is the element oxygen.

Peat: A primitive form of coal with less heat content and pure carbon content than any form of coal.

Strip mining: A method for removing coal from seams located near Earth's surface.

To imagine how such changes may have occurred, consider the following possibility. A plant dies in a swampy area and is quickly covered with water, silt, sand, and other sediments. These materials prevent the plant debris from reacting with oxygen in the air and decomposing to carbon dioxide and watera process that would occur under normal circumstances. Instead, anaerobic (pronounced an-nuh-ROBE-ik) bacteria (bacteria that do not require oxygen to live) attack the plant debris and convert it to simpler forms: primarily pure carbon and simple compounds of carbon and hydrogen (hydrocarbons).

The initial stage of the decay of a dead plant is a soft, woody material known as peat. In some parts of the world, peat is still collected from boggy areas and used as a fuel. It is not a good fuel, however, as it burns poorly and produces a great deal of smoke.

If peat is allowed to remain in the ground for long periods of time, it eventually becomes compacted. Layers of sediment, known as over-burden, collect above it. The additional pressure and heat of the overburden gradually converts peat into another form of coal known as lignite or brown coal. Continued compaction by overburden then converts lignite into bituminous (or soft) coal and finally, into anthracite (or hard) coal.

Coal has been formed at many times in the past, but most abundantly during the Carboniferous Age (about 300 million years ago) and again during the Upper Cretaceous Age (about 100 million years ago).

Today, coal formed by these processes is often found layered between other layers of sedimentary rock. Sedimentary rock is formed when sand, silt, clay, and similar materials are packed together under heavy pressure. In some cases, the coal layers may lie at or very near Earth's surface. In other cases, they may be buried thousands of feet underground. Coal seams usually range from no more than 3 to 200 feet (1 to 60 meters) in thickness. The location and configuration of a coal seam determines the method by which the coal will be mined.

Composition of coal

Coal is classified according to its heating value and according to the percentage of carbon it contains. For example, anthracite contains the highest proportion of pure carbon (about 86 to 98 percent) and has the highest heat value (13,500 to 15,600 Btu/lb; British thermal units per pound) of all forms of coal. Bituminous coal generally has lower concentrations of pure carbon (from 46 to 86 percent) and lower heat values (8,300 to 15,600 Btu/lb). Bituminous coals are often subdivided on the basis of their heat value, being classified as low, medium, and high volatile bituminous and subbituminous. Lignite, the poorest of the true coals in terms of heat value (5,500 to 8,300 Btu/lb), generally contains about 46 to 60 percent pure carbon. All forms of coal also contain other elements present in living organisms, such as sulfur and nitrogen, that are very low in absolute numbers but that have important environmental consequences when coals are used as fuels.

Properties and reactions

By far the most important property of coal is that it burns. When the pure carbon and hydrocarbons found in coal burn completely, only two products are formed, carbon dioxide and water. During this chemical reaction, a relatively large amount of heat energy is released. For this reason, coal has long been used by humans as a source of energy for heating homes and other buildings, running ships and trains, and in many industrial processes.

Environmental problems associated with burning coal. The complete combustion of carbon and hydrocarbons described above rarely occurs in nature. If the temperature is not high enough or sufficient oxygen is not provided to the fuel, combustion of these materials is usually incomplete. During the incomplete combustion of carbon and hydrocarbons, other products besides carbon dioxide and water are formed. These products include carbon monoxide, hydrogen, and other forms of pure carbon, such as soot.

During the combustion of coal, minor constituents are also oxidized (meaning they burn). Sulfur is converted to sulfur dioxide and sulfur trioxide, and nitrogen compounds are converted to nitrogen oxides. The incomplete combustion of coal and the combustion of these minor constituents results in a number of environmental problems. For example, soot formed during incomplete combustion may settle out of the air and deposit an unattractive coating on homes, cars, buildings, and other structures. Carbon monoxide formed during incomplete combustion is a toxic gas and may cause illness or death in humans and other animals. Oxides of sulfur and nitrogen react with water vapor in the atmosphere and then settle out in the air as acid rain. (Acid rain is thought to be responsible for the destruction of certain forms of plant and animalespecially fishlife.)

In addition to these compounds, coal often contains a small percentage of mineral matter: quartz, calcite, or perhaps clay minerals. These components do not burn readily and so become part of the ash formed during combustion. This ash then either escapes into the atmosphere or is left in the combustion vessel and must be discarded. Sometimes coal ash also contains significant amounts of lead, barium, arsenic, or other elements. Whether airborne or in bulk, coal ash can therefore be a serious environmental hazard.

Coal mining

Coal is extracted from Earth using one of two major methods: sub-surface or surface (strip) mining. Subsurface mining is used when seams of coal are located at significant depths below Earth's surface. The first step in subsurface mining is to dig vertical tunnels into the earth until the coal seam is reached. Horizontal tunnels are then constructed off the vertical tunnel. In many cases, the preferred way of mining coal by this method is called room-and-pillar mining. In room-and-pillar mining, vertical columns of coal (the pillars) are left in place as the coal around them is removed. The pillars hold up the ceiling of the seam, preventing it from collapsing on miners working around them. After the mine has been abandoned, however, those pillars may collapse, bringing down the ceiling of the seam and causing the collapse of land above the old mine.

Surface mining can be used when a coal seam is close enough to Earth's surface to allow the overburden to be removed easily and inexpensively. In such cases, the first step is to strip off all of the overburden in order to reach the coal itself. The coal is then scraped out by huge power shovels, some capable of removing up to 100 cubic meters at a time. Strip mining is a far safer form of coal mining for coal workers, but it presents a number of environmental problems. In most instances, an area that has been strip-mined is terribly scarred. Restoring the area to its

original state can be a long and expensive procedure. In addition, any water that comes in contact with the exposed coal or overburden may become polluted and require treatment.

Resources

Coal is regarded as a nonrenewable resource, meaning it is not replaced easily or readily. Once a nonrenewable resource has been used up, it is gone for a very long time into the future, if not forever. Coal fits that description, since it was formed many millions of years ago but is not being formed in significant amounts any longer. Therefore, the amount of coal that now exists below Earth's surface is, for all practical purposes, all the coal available for the foreseeable future. When this supply of coal is used up, humans will find it necessary to find some other substitute to meet their energy needs.

Large supplies of coal are known to exist (proven reserves) or thought to be available (estimated resources) in North America, Russia and other parts of the former Soviet Union, and parts of Asia, especially China and India. China produces the largest amount of coal each year, about 22 percent of the world's total, with the United States (19 percent), the former members of the Soviet Union (16 percent), Germany (10 percent), and Poland (5 percent) following.

China is also thought to have the world's largest estimated resources of coal, as much as 46 percent of all that exists. In the United States, the largest coal-producing states are Montana, North Dakota, Wyoming, Alaska, Illinois, and Colorado.

Uses

For many centuries, coal was burned in small stoves to produce heat in homes and factories. As the use of natural gas became widespread in the latter part of the twentieth century, coal oil and coal gas quickly became unpopular since they were somewhat smoky and foul smelling. Today, the most important use of coal, both directly and indirectly, is still as a fuel, but the largest single consumer of coal for this purpose is the electrical power industry.

The combustion of coal in power-generating plants is used to make steam, which, in turn, operates turbines and generators. For a period of more than 40 years beginning in 1940, the amount of coal used in the United States for this purpose doubled in every decade. Although coal is no longer widely used to heat homes and buildings, it is still used in industries such as paper production, cement and ceramic manufacture, iron and steel production, and chemical manufacture for heating and for steam generation.

Another use for coal is in the manufacture of coke. Coke is nearly pure carbon produced when soft coal is heated in the absence of air. In most cases, 1 ton of coal will produce 0.7 ton of coke in this process. Coke is valuable in industry because it has a heat value higher than any form of natural coal. It is widely used in steelmaking and in certain chemical processes.

Conversion of coal

A number of processes have been developed by which solid coal can be converted to a liquid or gaseous form for use as a fuel. Conversion has a number of advantages. In a liquid or gaseous form, the fuel may be easier to transport. Also, the conversion process removes a number of impurities from the original coal (such as sulfur) that have environmental disadvantages.

One of these conversion methods is known as gasification. In gasification, crushed coal is forced to react with steam and either air or pure oxygen. The coal is converted into a complex mixture of gaseous hydrocarbons with heat values ranging from 100 Btu to 1000 Btu. One day it may be possible to construct gasification systems within a coal mine, making it much easier to remove the coal (in a gaseous form) from its original seam.

In the process of liquefaction, solid coal is converted to a petroleum-like liquid that can be used as a fuel for motor vehicles and other applications. On the one hand, both liquefaction and gasification are attractive technologies in the United States because of its very large coal resources. On the other hand, the wide availability of raw coal means that expensive new technologies have been unable to compete economically with the natural product.

[See also Carbon family; Petroleum; Pollution ]

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Coal

Coal


Coal, a naturally occurring combustible solid, is one of the world's most important and abundant energy sources. From its introduction 4,000 years ago as a fuel for heating and cooking, to its nineteenth- and twentieth-century use in generating electricity and as a chemical feedstock , coal, along with oil and natural gas, has remained an important source of energy. The United States alone has 1.7 trillion short tons of identified coal resources (natural deposits) and enough recoverable reserves (coal that can be developed for use) to meet its energy needs until the year 2225. Its demonstrated reserves include 274 billion short tons that existing technology can recover, representing 25 percent of the world's 1.08 trillion short tons of recoverable coal, and 508 billion short tons of coal that existing technology can potentially mine economically. Its recoverable reserves contain more than twice the energy of the Middle East's proven oil reserves. About 100 countries have recoverable reserves; 12 countriesamong them Canada, the People's Republic of China, Russia, Poland, Australia, Great Britain, South Africa, Germany, India, Brazil, and Colombiapossess the largest reserves.

Origin, Composition, and Structure of Coal

Geologists believe that underground coal deposits formed about 250300 million years ago, when much of Earth was swamp covered with thick forest and plant growth. As the plants and trees died, they sank under Earth's wet surface, where insufficient oxygen slowed their decay and led to the formation of peat. New forests and plant life replaced the dead vegetation, and when the new forests and plants died, they also sank into the swampy ground. With the passage of time and accompanying heat buildup, underground layers

of dead vegetation began to accumulate, becoming tightly packed and compressed, and gave rise to different kinds of coal, each with a different carbon concentration: anthracite, bituminous coal, subbituminous coal, and lignite. The English geologist William Hutton (17981860) reached this conclusion in 1833 when he found through microscopic examination that all varieties of coal contained plant cells and were of vegetable origin, differing only in the vegetation composing them. Because of its origin in ancient living matter, coal, like oil and gas, is known as a fossil fuel. It occurs in seams or veins in sedimentary rocks; formations vary in thickness, with those in underground mines 0.72.4 meters (2.58 feet) thick and those in surface mines, as in the western United States, sometimes 30.5 meters (100 feet) thick.

Until the twentieth century chemists knew very little about the composition and molecular structure of the different kinds of coal, and as late as the 1920s they still believed that coal consisted of carbon mixed with hydrogen-containing impurities. Their two methods of analyzing or separating coal into its components, destructive distillation (heating out of contact with air) and solvent extraction (reacting with different organic solvents such as tetralin), showed only that coal contained significant carbon, and smaller percentages of the elements hydrogen, oxygen, nitrogen, and sulfur. Inorganic compounds such as aluminum and silicon oxides constitute the ash. Distillation produced tar, water, and gases. Hydrogen was the chief component of the gases liberated, although ammonia, carbon monoxide and dioxide gases, benzene and other hydrocarbon vapors were present. (The composition of a bituminous coal by percentage is roughly: carbon [C], 7590; hydrogen [H], 4.55.5; nitrogen [N], 11.5; sulfur [S], 12; oxygen[O], 520; ash, 210; and moisture, 110.) Beginning in 1910, research teams under the direction of Richard Wheeler at the Imperial College of Science and Technology in London, Friedrich Bergius (18841949) in Mannheim, and Franz Fischer (18771938) in Mülheim made important contributions that indicated the presence of benzenoid (benzenelike) compounds in coal. But confirmation of coal's benzenoid structure came only in 1925, as a result of the coal extraction and oxidation studies of William Bone (18901938) and his research team at Imperial College. The benzene tri-, tetra-, and other higher carboxylic acids they obtained as oxidation products indicated a preponderance of aromatic structures with three-, four-, and five-fused benzene rings, and other structures with a single benzene ring. The simplest structures consisted of eight or ten carbon atoms, the fused-ring structures contained fifteen or twenty carbon atoms.

Classification and Uses of Coal

European and American researchers in the nineteenth and early twentieth centuries proposed several coal classification systems. The earliest, published in Paris in 1837 by Henri-Victor Regnault (18101878), classifies types of coal according to their proximate analysis (determination of component substances, by percentage), that is, by their percentages of moisture, combustible matter, fixed carbon, and ash. It is still favored, in modified form, by many American coal scientists. Another widely adopted system, introduced in 1919 by the British scientist Marie Stopes (18801958), classifies types of coal according to their macroscopic constituents: clarain (ordinary bright coal), vitrain (glossy black coal), durain (dull rough coal), and fusain, also called mineral charcoal (soft powdery coal). Still another system is based on ultimate analysis (determination of component chemical elements, by percentage), classifying types of coal according to their percentages of fixed carbon, hydrogen, oxygen, and nitrogen, exclusive of dry ash and sulfur. (Regnault had also introduced ultimate analysis in his 1837 paper.) The British coal scientist Clarence A. Seyler developed this system in 18991900 and greatly expanded it to include large numbers of British and European coals. Finally, in 1929, with no universal classification system, a group of sixty American and Canadian coal scientists working under guidelines established by the American Standards Association (ASA) and the American Society for Testing Materials (ASTM) developed a classification that became the standard in 1936. It has remained unrevised since 1938.

The ASAASTM system established four coal classes or ranksanthracite, bituminous, subbituminous, and lignitebased on fixed-carbon content and heating value measured in British thermal units per pound (Btu/lb). Anthracite, a hard black coal that burns with little flame and smoke, has the highest fixed-carbon content, 8698 percent, and a heating value of 13,50015,600 Btu/lb (equivalent to 14.216.5 million joules/lb [1 Btu=1,054.6 joules, the energy emitted by a burning wooden match]). It provides fuel for commercial and home heating, for electrical generation, and for the iron, steel, and other industries. Bituminous (low, medium, and high volatile ) coal, a soft coal that produces smoke and ash when burned, has a 4686 percent fixed-carbon content and a heating value of 11,00015,000 Btu/lb (11.615.8 million joules/lb). It is the most abundant economically recoverable coal globally and the main fuel burned in steam turbine-powered electric generating plants. Some bituminous coals, known as metallurgical or coking coals, have properties that make them suitable for conversion to coke used in steelmaking. Subbituminous coal has a 4660

percent fixed-carbon content and a heating value of 8,30013,000 Btu/lb (8.813.7 million joules/lb). The fourth class, lignite, a soft brownish-black coal, also has a 4660 percent fixed-carbon content, but the lowest heating value, 5,5008,300 Btu/lb (5.88.8 million joules/lb). Electrical generation is the main use of both classes. In addition to producing heat and generating electricity, coal is an important source of raw materials for manufacturing. Its destructive distillation (carbonization) produces hydrocarbon gases and coal tar, from which chemists have synthesized drugs, dyes, plastics, solvents, and numerous other organic chemicals. High pressure coal hydrogenation or liquefaction and the indirect liquefaction of coal using FischerTropsch syntheses are also potential sources of clean-burning liquid fuels and lubricants.

Environmental Concerns

The major disadvantage of using coal as a fuel or raw material is its potential to pollute the environment in both production and consumption. This is the reason why many coal-producing countries, such as the United States, have long had laws that regulate coal mining and set minimum standards for both surface and underground mining. Coal production requires mining in either surface (strip) or underground mines. Surface mining leaves pits upon coal removal, and to prevent soil erosion and an unsightly environment, operators must reclaim the land, that is, fill in the pits and replant the soil. Acid mine water is the environmental problem associated with underground mining. Water that seeps into the mines, sometimes flooding them, and atmospheric oxygen react with pyrite (iron sulfide) in the coal, producing acid mine water. When pumped out of the mine and into nearby rivers, streams, or lakes, the mine water acidifies them. Neutralizing the mine water with lime and allowing it to settle, thus reducing the presence of iron pyrite before its release, controls the acid drainage.

Coal combustion emits sulfur dioxide and nitrogen oxides, both of which cause acid rain . Several methods will remove or reduce the amount of sulfur present in many coals or prevent its release into the atmosphere. Washing the coal before combustion removes pyritic sulfur (sulfur combined with iron or other elements). Burning the coal in an advanced-design burner known as a fluidized bed combustor, in which limestone added to coal combines with sulfur in the combustion process, prevents sulfur dioxide from forming. Scrubbing the smoke released in the combustion removes the sulfur dioxide before it passes into the atmosphere. In a scrubber, spraying limestone and water into the smoke enables the limestone to absorb sulfur dioxide and remove it in the form of a wet sludge. Improved clean coal technologies inject dry limestone into the pipes leading from the plant's boiler and remove sulfur dioxide as a dry powder (CaSO3) rather than a wet sludge. Scrubbing does not remove nitrogen oxides, but coal washing and fluidized bed combustors that operate at a lower temperature than older plant boilers reduce the amount of nitrogen oxides produced and hence the amount emitted.

Clean coal technologies and coal-to-liquid conversion processes have led to cleaner burning coals and synthetic liquid fuels, but acid rain remains a serious problem despite society's recognition of its damaging effects since 1852. Global warming resulting from the emission of the greenhouse gases, carbon dioxide, methane, and chlorofluorocarbons , is another coal combustion problem that industry and government have largely ignored since 1896, but it can no longer be avoided without serious long-term consequences.

Conclusion

Coal remains the world's most abundant fossil fuel, and along with petroleum and natural gas, it will continue to provide most of the world's energy. But all three are finite resources, and society should consume them wisely, not wastefully, in order to extend their lifetimes and reduce their harmful emissions. The conservation of fossil fuels and the development of alternative energies, such as solar and wind power, are pathways to a global society's cleaner energy future.

see also Fossil Fuels; Global Warming; Steel.

Anthony N. Stranges

Bibliography

Lowry, H. H., ed. (1945). Chemistry of Coal Utilization, Vols. 1 and 2. New York: Wiley.

Lowry, H. H., ed. (1963). Chemistry of Coal Utilization, Supplementary Vol. New York: Wiley.

Internet Resources

Kentucky Coal Council. "Kentucky Coal Education." Available from <http://www.coaleducation.org>.

U.S. Department of Energy, Office of Fossil Energy. "Home Page." Available from <http://www3.fossil.energy.gov/>.

U.S. Geological Survey, Energy Resources Program. "National Coal Resources Assessment (NCRA)." Available from <http://energy.er.usgs.gov/NCRA/>.

World Coal Institute. "Home Page." Available from <http://www.wci-coal.com>.

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Coal

Coal


Coal is a brown-to-black combustible rock that originated from peat deposits in large swamp environments, through their burial to great depths and over a few hundred thousand to tens of millions of years. During burial peat is converted first into lignite, then subbituminous and bituminous coal, and, uncommonly, anthracite. Due to the loss of moisture during burial (peat has about 90 percent in its natural state, bituminous coal as little as 2 to 3 percent) and the chemical changes in the plant material that are induced by the rising temperature during burial to thousands of feet (increased carbon and decreased oxygen contents in particular), the heating value of coal increases significantly from peat to lignite and on to bituminous coal and anthracite.

The various environments that prevailed in the peat swamps (e.g., forests with large trees; marshes with sedges, grasses, and reeds) produced various kinds of peat and thus coal with significantly different properties. The major coal typesbanded, nonbanded, and impure coalare easily recognizable. Banded coals are most common. In subbituminous and bituminous coal the bands are composed of vitrain (shiny, glassy, brittle), clarain (bright luster, tough), durain (dull luster, hard), and fusain (charcoal-like, soft). Under the microscope, the so-called macerals become visible. Many of these clearly reveal their plant origin (e.g., sporinite, cutinite, resinite, alginite), whereas others have lost much or all of the plants' original cell structure (e.g., vitrinite, collinite, inertinite, semifusinite).


Coal Mining and Pollution

Coal is recovered from the ground either by underground or surface mining. Underground mining creates voids over many square miles. Two basically different methods are used: longwall and room-and-pillar mining. In longwall mining all coal is recovered from the mined panels; hence, subsidence occurs at the surface almost immediately and it is planned for. Room-and-pillar mining leaves about half of the coal in the ground as pillars to support the surface and prevent subsidence. However, subsidence may still occur because coal pillars or the floor strata under them fail, sometimes decades after mining (this sort of unplanned subsidence is a significant problem in major coal-producing states of the past). Subsidence causes damage to structures and interferes with the drainage of surface water; it may also impact aquifers. Coal left in the ground may catch fire, for example, through spontaneous combustion. Mine fires are difficult to control; some have burned for decades, even centuries. They can cause considerable local pollution, as well as other problems. Coal also always contains methane (CH4), most of which is released into the atmosphere during mining. On the average, the deeper a mine, the more methane it generates. Methane is a very potent greenhouse gas and contributes to global warming. Another significant environmental problem is related to underground mines that operated above the local drainage level. The mine workings collect and conduct water that oxidizes the ever-present pyrite (FeS2) in coal-bearing strata and causes acid mine drainage into the local drainage system. This is a common problem in the mountainous Appalachian coal fields where many old mines were operated at shallow depth above valley floors.

For surface mining, large machines are used to remove all rocks and/or soil above the coal bed or beds to gain access to it or them (usually at depths of less than 150 to two hundred feet). Any surface drainage and aquifers in the overburden will be severely impacted within the vicinity of the mine pit. Also, the fertility of agricultural land becomes a concern. Modern mining laws require the careful monitoring of groundwater at mines and the restoration of proper drainage and fertility to farmland, to its premining levels, through reclamation . Contaminated water (e.g., water containing suspended fine solids and/or dissolved minerals) may run off the open pit and must be treated before release into the local drainage system.

Modern mining laws seek to remedy or minimize the above-mentioned environmental and other problems related to the mining and cleaning of coal, as well as many other related concerns. See the table for a listing of the top producers of coal by state.

LEADING COAL-PRODUCING STATES OF THE UNITED STATES
rank state 2001 production
source: adapted from u.s. department of energy.
1 wyoming 365.6
2 west virginia 160.4
3 kentucky 132.6
4 pennsylvania 76.4
5 texas 45.0
6 montana 39.1
7 indiana 37.1
8 illinois 33.8
9 colorado 33.4
10 virginia 32.5
11 north dakota 30.5
12 new mexico 29.6
13 utah 27.0
14 ohio 25.3
15 alabama 19.2
16 arizona 13.4
  other states 20.4
  u.s.a. 1,121.3

Coal Cleaning and Pollution

Many mined coals, especially from eastern and Midwestern coal fields, contain significant mineral matter in their raw mined stateup to about half by weightand they are cleaned before sale. Preparation plants, capable of cleaning or processing several million tons of coal a year, generate large quantities of refuse that must be disposed of locally, safely, and in an environmentally sound manner. The materials rejected by a cleaning plant tend to be enriched in iron sulfides (FeS2: pyrite and marcasite) in particular; these oxidize easily into sulfates, causing the acidification of any water that percolates through and exits from refuse piles; acid water in turn tends to dissolve various other minerals, creating products that are potentially harmful to plants, animals, and humans. Cleaning plants always reject some coal, together with the incombustible material; spontaneous combustion can cause refuse piles to catch fire, which emit pollutants and are difficult to control.


Coal Utilization and Pollution

Coal, due to its origin from plants, is composed primarily of the "organic" elements carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S). Whenever coal is used, it eventually ends up being burned, either through direct combustion in boilers, for example, those in large electric utility power plants, or after conversion into intermediate products like coke . Of all the oxidation products of these elements, carbon dioxide (CO2) has become a major concern because it is a powerful greenhouse gas that accumulates in the atmosphere and is considered the primary cause of global warming. Sulfur and nitrogen oxides (SO2, NOx ), when released into the atmosphere from power plants, become a human health hazard and lead to the formation of acid rain downwind. This has been an important social and political issue for several decades, and various laws have been enacted that force power companies to limit the emission of sulfur and nitrogen oxides. All "new" (since 1970) electric power plants must remove most of the SO2 from their flue gas, using various types of scrubbers . A cost-effective way to control SO2 total emissions has been emissions trading, the federal government's decision to award a limited number of SO2 "pollution allowances" to utilities that they are permitted to trade; this allows industry to decide at which plants it is most cost-effective to add scrubbers. The 1970 Clean Air Act (CAA) exempted existing power plants from this requirement, assuming that they would be shut down in the near future. To close this loophole, the 1977 CAA amendments established the "new source review" process (NSR), which requires a careful review of any changes performed in "old" (pre-1970) plants to determine whether they represent "routine maintenance, repair, and replacement" or a significant upgrading in which the plant would become subject to the same rules as new plants. Over the years these reviews became highly controversial because of the gray area between "routine maintenance" and "significant upgrading." In response, after a multiyear review process, the U.S. Environmental Protection Agency (EPA) proposed revisions of the regulations in late 2002, intending to overcome these widely recognized problems, provide greater flexibility for power companies to improve old plants, lead to increases in energy efficiency, and decrease pollution. However, environmental and political groups have challenged the proposed new regulations. One proposal to resolve the controversy would be to abolish the NSR process entirely and expand the pollution allowances trading system to old power plants. By capping the number of allowances over time, total pollution could be further lowered.

Besides these major elements, coal always contains a large number of other elements in minor and trace amounts. Some of these are highly toxic, for instance, mercury (Hg), arsenic (As), cadmium (Cd), lead (Pb), selenium (Se), and uranium (U). Because coal is burned in such large quantities, primarily to generate electricity (nearly a billion tons in the United States alone!), even trace amounts add up to large quantities being released into the atmosphere. The 1990 Amendments to the Clean Air Act identify 189 hazardous air pollutants (HAPs), eighteen of which are associated with coal. Of particular concern are those elements that form volatile compounds during coal burning and are carried into the atmosphere with the flue gas. The 1990 amendments require the EPA to study the health effects of HAPs and develop appropriate regulations for their control.

Even cleaned coal still contains incombustible minerals (about 5 to 15 percent by weight) that are converted into ash when coal is burned at very high temperatures. Some ash particles are small and light enough to be carried up tall chimneys into the atmosphere with the flue gas (fly ash). Most power plants are required to remove fly ash from flue gas, using bag houses or electric precipitators. Both methods are highly efficient. However, tiny particles (PM-10 ) may still escape. Because of their potential harm to humans, they have been targeted for regulation in recent years. Coarsergrained ash remains at the bottom of boilers (bottom ash); it is removed and disposed of nearby. Fortunately, this material is rather inert and of limited environmental concern.

see also Acid Rain; Air Pollution; Carbon Dioxide; Electric Power; Emissions Trading; Fossil Fuels; Global Warming; Greenhouse Gases; Methane; NOx (Nitrogen Oxides); Particulates; Scrubbers.

Bibliography

ASTM. "Standard Classification of Coals by Rank," Standard D388. In Annual Book of ASTM Standards, Vol. 05.05. New York.

ASTM. "Standard Terminology Relating to Megascopic Description of Coal and Coal Seams and Microscopic Description and Analysis of Coal," Standard D2796. In Annual Book of ASTM Standards, Vol. 05.05. New York.


Internet Resources

U.S. Environmental Protection Agency. "Clean Air Act of 1970" and "1990 Amendments to the Clean Air Act." Available from http://www.epa.gov.

U.S. Office of Surface Mining. Public Law 95-87, "The Surface Mining Control and Reclamation Act of 1977 (SMCRA)." Available from http://www.osmre.gov/smcra.htm.

Heinz H. Damberger

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Coal

COAL

COAL is a major source of energy in the United States. It formed as the legacy of trees and plants that grew in primeval swamps and forests. For millions of years, the debris of these jungles accumulated in shallow water or in boggy soil, decayed, and was converted into peat bogs. The mountain-building era subjected these bogs to extreme pressures as well as to the internal heat of the earth. The combination of these factors transformed the peat into coal. Coal has the same chemical composition as diamonds and is sometimes referred to as "black diamonds."


The conversion of peat into coal is estimated by geologists to have taken hundreds of thousands of years.

Bituminous coal is the most abundant type of coal in the United States and the one most commonly used for power generation, heating, and industrial purposes. Nearly all eastern bituminous coals have "coking" properties. Coking is a heating process that breaks down coal, leaving the relatively pure carbon needed for metallurgy. Many western bituminous coals are noncoking, or "free burning." Bituminous coals used in the coking process are heated in a sealed oven. After the volatile liquids and gases have been driven off, the coke, a porous, dull-gray mass, remains. The by-products driven off during the carbonization process, consisting of gases, light oils, and tar, have many important uses in the chemical industry.

The only source for anthracite coal, which is a clean-burning coal with little volatile matter, is northeastern Pennsylvania, although history records small deposits in Rhode Island during the early nineteenth century. Anthracite production peaked during 1917, when 100 million tons were produced and nearly 150,000 miners toiled to reach that tonnage. Another peak was reached in 1944 when 64 million tons were produced with a workforce of 78,000 men. After that time, the consumption of anthracite coal declined; by 1973 only 6,000 men were employed in the industry. Similar statistics for the bituminous coal industry record the first peak in production in 1918, when 550 million tons were mined with a labor force of 615,000. The maximum production by the industry occurred in 1947, when 630 million tons were produced with a labor force of 420,000 miners. In 1974 approximately 590 million tons of coal were produced with a labor force of only 125,000 miners.

The coal-producing areas of the United States are divided into six large provinces: the Eastern province, the Interior province, the Gulf province, the Northern Plains province, the Rocky Mountain province, and the Pacific Coast province. Coal mining activity migrated west ward from its eighteenth-century beginnings in the Eastern province, and significant production was reported from the Interior province during the 1830s. By the late 1850s the Pacific Coast province was producing significant amounts of coal, as was the Gulf province in the late 1860s. The Rocky Mountain province began producing well into the mid-1870s and the Northern Plains province in the late 1870s.

The Eastern, or Appalachian, field, after its modest beginning as a small mine along the Monongahela River opposite Fort Pitt (now Pittsburgh, Pennsylvania), in 1760, became the most important source of bituminous coal for the nation. Beginning in western Pennsylvania, it extends southwesterly into Alabama and contains large mining operations in the states of Pennsylvania, Ohio, West Virginia, Kentucky, Tennessee, Virginia, and Alabama. Pennsylvania was for many years the largest producer of coal in the province, but after 1946 it was superseded by West Virginia. The Eastern province was responsible for approximately two-thirds of the total coal produced in the United States in the mid-1970s.

West of the Appalachian field is the Interior province, which is subdivided into eastern and western portions. The eastern portion includes deposits through most of Illinois, western Indiana, and western Kentucky; the western portion covers deposits in Iowa, Missouri, eastern Kansas, Oklahoma, and Arkansas. Two isolated fields included in the Interior province are in Texas and central Michigan.

The Eastern and Interior provinces have always furnished most of the coal produced in the United States and contain the largest reserves of coking coals. The coal-fields found in the other provinces contain the largest percentage of reserves on a tonnage basis but consist mainly of subbituminous coals and lignites. With lower-grade coals and locations remote from major consuming industries, they have not been extensively developed, although development is assured in the ever-pressing need for additional energy supplies.


Scientists evaluate a region's coal supply by measuring its reserves and resources. Reserves are the amount of coal that is commercially accessible and can be readily mined. Resources are the total amount of coal in a region, whether or not it is accessible. In 2002, the total U.S. estimated recoverable coal reserves was some 274 billion short tons, while U.S. coal production for 2001 was approximately 1.1 billion short tons. The U.S. Geological Survey estimated in 1997 that the identified resources of U.S. coal were some 1,731 billion short tons. With improved technological innovations and increased efficiency in mining methods, these reserves and resources could be greatly extended.

Coal is mined by two principal methods, underground and surface operations, and both practices are widely used in the United States. Coal seams within two hundred feet of the earth's surface are generally more adaptable to surface mining methods, although attention must also be paid to the content and thickness of the over-burden (rock and other material) on the coal seam and to the thickness of the seam. Strip mining is often used to mine surface coal. In this method, huge earth-moving machines strip away areas of vegetation, and explosives shatter sedimentary rock to access underlying coal deposits. Area and contour mining methods allow for strip mining of hilly areas, as machines move away landscape and slice large cuts into a hillside to access coal. Giant augers that bore into hillsides and throw out buried coal are also used on rough terrain. In the late 1990s, coal mining companies started using global positioning system (GPS) and satellite technology to track mines and machinery and increase their efficiency.

Mechanization of underground mining operations received its greatest impetus with the introduction of Joy loading machines in the early 1920s. Earlier attempts to introduce machinery to the industry proved unsuccessful except for the first successful undercutting machine, introduced in 1877. The introduction of rubber-tired haulage units in 1936 gave further impetus to mechanization, and during the late 1940s total mechanization of underground operations was becoming a reality. Mechanization of mining operations increased significantly after World War II, with a trend toward larger capacity machinery and the elimination of many laborious manual operations. Improved under ground machinery has led to continuous mining. U.S. coal production rose rapidly during the nineteenth century, from an annual production in 1800 of approximately 120,000 tons to approximately 265 million tons by 1900. The average output per man per day exceeded twenty tons, a significant increase over the five ton average prior to extensive mechanization.

The U.S. coal industry has been subjected to labor unrest, loss of important markets, and most importantly, has exposed workers to tremendous dangers. Under-ground coal miners were constantly exposed to dangerous gases such as explosive methane and poisonous carbon monoxide. After a mine explosion in the 1800s, miners took to releasing a canary into mine shafts to test for poisonous gases before entering. If the canary did not return, miners improved ventilation systems down the shaft. The coal dust produced in the blasts and hauling was also extremely flammable and harmful to miners' lungs. Prolonged inhalation of coal dusts produces pneumoconiosis, or black lung disease, as well as a number of other problems, such as heart disease, emphysema, and cancer. Mining protests and labor activism in the 1900s brought about much reform in mining conditions.

The environmental impact of recovering coal increased concern over mining methods during the late twentieth century. Strip mining destroys large areas of vegetation and habitat, leaving them exposed to erosion. The waste products of strip mining create acid drainage that combines with oxygen in water and air to create sulfuric acid, polluting water and contaminating soil. Burning coal produces greenhouse gases that trap heat in the earth's atmosphere and lead to global warming. Sulfur dioxide emissions combine with water and oxygen in air to form acid rain. Since the U.S. Clean Air Act passed in 1970, and was revised in 1990, industries that burn coal are required to reduce emissions of carbon dioxide and sulfur to safer levels. Coal mining companies are required to submit detailed reports of mining plans to ensure minimal destruction of the environment. In 1986 the U.S. government and private industry began working together through the Clean Coal Technology Program to find cleaner, more efficient methods of mining coal and using its energy.

BIBLIOGRAPHY

Blatz, Perry K. Democratic Miners: Work and Labor Relations in the Anthracite Coal Industry, 1875–1925. Albany: State University of New York Press, 1994.

Bowman, John R. Capitalist Collective Action: Competition, Cooperation, and Conflict in the Coal Industry. New York: Cambridge University Press, 1989.

Dix, Keith. What's a Coal Miner to Do?: The Mechanization of Coal Mining. Pittsburg, Pa.: University of Pittsburg Press, 1988.

Fishback, Price V. Soft Coal, Hard Choices: The Economic Welfare of Bituminous Coal Miners, 1890–1930. New York: Oxford University Press, 1992.

Seltzer, Curtis. Fire in the Hole: Miners and Managers in the American Coal Industry. Lexington: University Press of Kentucky, 1985.

J. H.Hoffman/h. s.

See alsoAir Pollution ; Anthracite Strike ; Appalachia ; Coal Mining and Organized Labor ; Conservation ; Energy Industry .

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Coal Chamber

Coal Chamber

Rock group

For the Record

Selected discography

Sources

A self-described spooky core group, Coal Chamber emerged from the Los Angeles music scene in the mid-1990s as part of a wave of gothic- and industrial-inspired metal bands. Although the band shared a love of confrontational lyrics and driving guitars with the grunge bands that dominated the musical landscape at the time, its members also reacted against the down-to-earth image of most Seattle-based groups with theatrical stage shows, costumes, and makeup. As vocalist Dez Fafara told Alternative Press in September of 1999, Were trying to forge ahead with a different kind of style, musically and looks-wise. If people are going to peg us as anything, were the crazy band that says, Be yourself.

Coal Chamber had its origins in 1994 with two Los Angeles musicians, singer Dez Fafara and guitarist Miguel Meegs Rascon, who met through a classified ad in a local newspaper. The roommate of Farfaras girlfriend, Rayna Foss, soon joined the band as a bassist, though she had only six months of experience playing the instrument. Every show that was considered rock music, we were there, Rascon told Guitar One about the bands early days. And eventually we started playing shows, we started hooking up with

For the Record

Members include Mikee Cox, drums; Dez Fafara (born B. Dez Fafara), vocals; Rayna Foss-Rose (born Rayna Foss), bass guitar; Meegs Rascon (born Miguel Rascon), guitar.

Formed in Los Angeles, CA, 1994; gained following on Los Angeles club circuit; released first album, Coal Chamber, 1997; toured on Ozzfest 98; released second album, Chamber Music, 1999.

Addresses: Record company Roadrunner Records, 902 Broadway, 8th Floor, New York, NY 10010; 9229 Sunset Blvd., Suite 705, Los Angeles, CA 90069, website: http://www.roadrun.com. Website Coal Chamber Official Website: http://www.coalchamber.com.

other bands, and before you know it, our shows start-edgetting packed, and we developed a following. After a year of paying its dues on the club circuit and promoting itself with flyers and demo tapes, the band had a promising deal with Roadrunner Records.

Despite the groups optimism, however, the initial run of Coal Chamber was short-lived; after Fafara married his girlfriend, he left the group and it appeared that the deal with Roadrunner Records would be lost. But in 1995, Fafara divorced his wife, rejoined the group, and regained the deal at Roadrunner. The final piece of the Coal Chamber lineup, drummer Mikee Cox, joined the band in 1997, when he was just 19 years old. As Cox later told Drums!, I went straight from high school to being on tour on a bus for two years.

The timing of the group was fortunate. After a heyday in the 1980s with bands such as Mötley Crüe and Poison, the Los Angeles metal scene was making a comeback in the mid-1990s. At a time when Seattle-based grunge ruled the airwaves and record-buyer consciousness was raised across the nation, Los Angeles concert crowds filled the metal clubs that lined the Sunset Strip. Coal Chamber quickly developed a friendly rivalry on the Strip with competing alternative metal band Korn. One of singer Fafaras fondest memories from the bands earliest days was playing a sold-out show at the Whiskey-A-Go-Go while Korn played a sold-out set at the Roxy in 1995. In an effort to differentiate themselves from the rest of the metal bands, however, Coal Chambers members concentrated on creating a distinct image for the band, with outrageous stage makeup, numerous tattoos and piercings, and gothic-oriented costumes. The fact that the band also included a female member on bass guitar helped it gain a unique profile among the new crop of Los Angeles metal bands.

Coal Chamber entered the studio to record its self-titled debut effort, which was released in February of 1997 to generally good reviews in the metal and mainstream press. In a three-star review, a Q magazine critic even anointed the band flag-bearers for the post-slacker, no-hoper generation. Without much radio or video play, however, the band focused on touring as a means to break through to new listeners. The group gained a new manager on one such tour, Ozzfest 98. When the tour began, Coal Chamber was a supporting act on the second stage. Sharon Osbourne, wife of headliner Ozzy Osbourne, decided that the group deserved a spot on the main stage and took on the act as its manager as well. The Osbournes served as informal mentors to the group, even inviting its members to their home in England to celebrate the singers birthday. Meanwhile, the band contributed two songs to soundtracks in 1998: Blisters appeared on the soundtrack to The Bride of Chucky, while Not Living appeared on the soundtrack for Strangeland.

While its debut did not make a significant impact on the sales charts, the large audiences of Ozzfest gave the band greater confidence in its abilities as well as higher aspirations for the music it wanted to make. In the 1999 Alternative Press article written about Coal Chambers second release, Chamber Music, Fafara said, We needed to make a huge departure from the hip-hop-metal thing, so we jumped off the cliff while the train was still moving and came up with a new sound. Were still heavy rock and roll, but I think were giving people a little more in terms of ear candy, something a little more tangible to listen to. In an interview with the MTV website, Rascon echoed the sentiment: I think we definitely created our own sound. This is like our defining album. Weve always wanted to stick to the darker side of music with these elements, and thats what we did with all the new sounds and keyboard sounds.

Fafara also polished his vocals for the groups sophomore effort, taking voice lessons to broaden his vocal range and adapt his style to a greater range of songs. I never became a vocalist before we made this album, he told Metal Edge. I went to a coach, and he helped me hit these lows and highs like never before. I had never gone into those waters in the past. Continuing to serve as the bands primary songwriter, Fafara also concentrated on writing lyrics that turned away from the nihilism of many metal bands. I like to think of myself as a storyteller, rather than a singer or songwriter, he told the magazine. I think that were a dark rock n roll band with a really positive message. One track that showed Fafaras direction on Chamber Music, Tylers Song, was written as a message to his young son to persevere against school bullies.

The effort to diversify its sound was welcomed by critics such as a Washington Post reviewer who noted the bands progress toward a more hospitable brand of musical pillage. A Los Angeles Times critic also approved of Chamber Musics move to thoughtful strains of optimism that muscle their way through the cuts grinding digs and lacerating rhythms, offering fans something more than a soundtrack for partying and destruction. The bands more significant breakthrough, however, came with a remake of the Peter Gabriel song Shock the Monkey with guest vocals by Osbourne. With attention from radio and video outlets for the song, Coal Chamber made further headway with a broader audience; it even gained a higher East Coast profile with a guest appearance on The Howard Stern Show with manager Sharon Osbourne. The troubled character of Mafia son Tony Soprano Jr. from the hit HBO show The Sopranos even sported a Coal Chamber sweatshirt as a sign of his teenage angst.

Married to Sevendust drummer Morgan Rose, Rayna Foss-Rose took a short break from touring in order to have a baby in 1999, making her the third of the bands members to become a parent. Fafara explained the impact of parenthood to the Los Angeles Times, saying, Everybody is bummed and angry. But I try to give them something else lyrically, to base their life around, other than just pure hate. We all grow up, we all learn to hate. You look into a childs eyes and you want to instill something positivesomething that can get them through that.

Hoping for a long career despite the volatility of the music business, Coal Chamber continued to tour almost nonstop and entered the studio for its third effort, Dark Days, planned for a spring 2002 release. As Fafara told Alternative Press in 1999, Two albums, three albums, four albums, thats nothing to me. I think were going to be the best band ever in five years.

Selected discography

Coal Chamber, Roadrunner, 1997.

(Contributor) The Bride of Chucky (soundtrack), BMG/Sanctuary, 1998.

(Contributor) Strangeland (soundtrack), TVT, 1998.

Chamber Music, Roadrunner, 1999.

Sources

Periodicals

Album Network, September 24, 1999.

Alternative Press, September 1999, pp. 6568.

Amusement Business, November 8, 1999, p. 6.

Drum!, September/October 1999, p. 39.

Guitar One, July 1999.

Guitar Player, March 2000, p. 47.

Guitar World, October 1999, pp. 3840.

Los Angeles Times, April 16, 2000, p. E1.

Maxim, July 2000.

Metal Edge, December 1999, p. 2829.

Q, May 1997.

Washington Post, September 17, 1999, N17.

Online

Coal Chamber, MTV.com, http://www.mtv.com/bands/az/coaLchamber/artist.jhtml (November 20, 2001).

Timothy Borden

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Coal

Coal

Coal is a naturally occurring combustible material consisting primarily of the element carbon , but with low percentages of solid, liquid, and gaseous hydrocarbons and other materials, such as compounds of nitrogen and sulfur. Coal is usually classified into the sub-groups known as anthracite, bituminous, lignite, and peat. The physical, chemical, and other properties of coal vary considerably from sample to sample.

Coal forms primarily from ancient plant material that accumulated in surface environments where the complete decay of organic matter was prevented. For example, a plant that died in a swampy area would quickly be covered with water , silt, sand , and other sediments. These materials prevented the plant debris from reacting with oxygen and decomposing to carbon dioxide and water, as would occur under normal circumstances. Instead, anaerobic bacteria (bacteria that do not require oxygen to live) attacked the plant debris and converted it to simpler forms: primarily pure carbon and simple compounds of carbon and hydrogen (hydrocarbons). Because of the way it is formed, coal (along with petroleum and natural gas ) is often referred to as a fossil fuel.

The initial stage of the decay of a dead plant is a soft, woody material known as peat. In some parts of the world, peat is still collected from boggy areas and used as a fuel. It is not a good fuel, however, as it burns poorly and with a great deal of smoke.

If peat is allowed to remain in the ground for long periods of time, it eventually becomes compacted as layers of sediment, known as overburden, collect above it. The additional pressure and heat of the overburden gradually converts peat into another form of coal known as lignite or brown coal. Continued compaction by overburden then converts lignite into bituminous (or soft) coal and finally, anthracite (or hard) coal. Coal has been formed at many times in the past, but most abundantly during the Carboniferous Age (about 300 million years ago) and again during the Upper Cretaceous Age (about 100 million years ago).

Today, coal formed by these processes is often found in layers between layers of sedimentary rock . In some cases, the coal layers may lie at or very near the earth's surface. In other cases, they may be buried thousands of feet or meters under ground. Coal seams range from no more than 3197 ft (160 m) or more in thickness. The location and configuration of a coal seam determines the method by which the coal will be mined.

Coal is classified according to its heating value and according to its relative content of elemental carbon. For example, anthracite contains the highest proportion of pure carbon (about 86%98%), and has the highest heat value (13,50015,600 Btu/lb [British thermal units per pound]) of all forms of coal. Bituminous coal generally has lower concentrations of pure carbon (from 46%86%) and lower heat values (8,30015,600 Btu/lb). Bituminous coals are often sub-divided on the basis of their heat value, and are classified as low, medium, and high volatile bituminous and sub-bituminous. Lignite, the poorest of the true coals in terms of heat value (5,5008,300 Btu/lb) generally contains about 46%60% pure carbon. All forms of coal also contain other elements present in living organisms, such as sulfur and nitrogen, that are very low in absolute numbers, but that have important environmental consequences when coals are used as fuels .

By far the most important property of coal is that it combusts. When the pure carbon and hydrocarbons found in coal burn completely, only two products are formed, carbon dioxide and water. During this chemical reaction, a relatively large amount of energy is released. The release of heat when coal is burned explains the fact that the material has long been used by humans as a source of energy, for the heating of homes and other buildings, to run ships and trains, and in many industrial processes.

The complete combustion of carbon and hydrocarbons described above rarely occurs in nature. If the temperature is not high enough or sufficient oxygen is not provided to the fuel, combustion of these materials is usually incomplete. During the incomplete combustion of carbon and hydrocarbons, other products besides carbon dioxide and water are formed, primarily carbon monoxide, hydrogen, and other forms of pure carbon, such as soot.

During the combustion of coal, minor constituents are also oxidized. Sulfur is converted to sulfur dioxide and sulfur trioxide, and nitrogen compounds are converted to nitrogen oxides. The incomplete combustion of coal and the combustion of these minor constituents result in a number of environmental problems. For example, soot formed during incomplete combustion may settle out of the air and deposit an unattractive coating on homes, cars, buildings, and other structures. Carbon monoxide formed during incomplete combustion is a toxic gas and may cause illness or death in humans and other animals. Oxides of sulfur and nitrogen react with water vapor in the atmosphere and then are precipitated out as acid rain . Acid rain is thought to be responsible for the destruction of certain forms of plant and animal (especially fish) life.

In addition to these compounds, coal often contains a few percent of mineral matter: quartz , calcite, or perhaps clay minerals . These do not readily combust and so become parts of the ash. The ash then either escapes into the atmosphere or is left in the combustion vessel and must be discarded. Sometimes coal ash also contains significant amounts of lead , barium, arsenic, or other compounds. Whether air borne or in bulk, coal ash can therefore be a serious environmental hazard.

Coal is extracted using one of two major techniques, sub-surface or surface (strip) mining. The former method is used when seams of coal are located at significant depths below Earth's surface. The first step in sub-surface mining is to dig vertical tunnels into the earth until the coal seam is reached. Horizontal tunnels are then constructed laterally off the vertical tunnel. In many cases, the preferred method of mining coal by this method is called room-and-pillar mining. In this method, vertical columns of coal (the pillars) are left in place as coal around them is removed. The pillars hold up the ceiling of the seam, preventing it from collapsing on miners working around them. After the mine has been abandoned, however, those pillars may often collapse, bringing down the ceiling of the seam and causing subsidence in land above the old mine.

Surface mining can be used when a coal seam is close enough to the earth's surface to allow the overburden to be removed economically. In such a case, the first step is to strip off all of the overburden in order to reach the coal itself. The coal is then scraped out by huge power shovels, some capable of removing up to 100 cubic meters at a time. Strip mining is a far safer form of coal mining, but it presents a number of environmental problems. In most instances, an area that has been strip-mined is scarred, and restoring the area to its original state is a long and expensive procedure. In addition, any water that comes in contact with the exposed coal or overburden may become polluted and require treatment.

Coal is regarded as a non-renewable resource, meaning that it was formed at times during Earth's history, but significant amounts are no longer forming. Therefore, the amount of coal that now exists below the earth's surface is, for all practical purposes, all the coal that humans have available to them for the foreseeable future. When this supply of coal is used up, humans will find it necessary to find some other substitute to meet their energy needs.

Large supplies of coal are known to exist (proven reserves) or thought to be available (estimated resources) in North America , the former Soviet Union, and parts of Asia , especially China and India. According to the most recent data available, China produces the largest amount of coal each year, about 22% of the world's total. China is also thought to have the world's largest estimated resources of coal, as much as 46% of all that exists.

For many centuries, coal was burned in small stoves to produce heat in homes and factories. Today, the most important use of coal, both directly and indirectly, is still as a fuel. The largest single consumer of coal as a fuel is the electrical power industry. The combustion of coal in power generating plants is used to make steam, which in turn, operates turbines and generators. For a period of more than 40 years, beginning in 1940, the amount of coal used in the United States for this purpose doubled in every decade. Coal is no longer widely used to heat homes and buildings, as was the case a half century ago, but it is still used in industries such as paper production, cement and ceramic manufacture, iron and steel production, and chemical manufacture for heating and for steam generation.

See also Environmental pollution

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coal

coal, fuel substance of plant origin, largely or almost entirely composed of carbon with varying amounts of mineral matter.

Types

There is a complete series of carbonaceous fuels, which differ from each other in the relative amounts of moisture, volatile matter, and fixed carbon they contain. Of the carbonaceous fuels, those containing the largest amounts of fixed carbon and the smallest amounts of moisture and volatile matter are the most useful to humans. The lowest in carbon content, peat, is followed in ascending order by lignite and the various forms of coal—subbituminous coal or black lignite (a slightly higher grade than lignite), bituminous coal, semibituminous (a high-grade bituminous coal), semianthracite (a low-grade anthracite), and anthracite.

Lignite and subbituminous coal, because of the high percentage of moisture they contain, tend to crumble on exposure to the air. Bituminous coal, being more consolidated, does not crumble easily; it is a deep black in color, burns readily, and is used extensively as fuel in industries and on railroads and in making coke. Anthracite, which is nearly pure carbon, is very hard, black, and lustrous and is extensively used as a domestic fuel. Cannel coal, a dull, homogeneous variety of bituminous coal, is composed of pollen grains, spores, and other particles of plant origin. It ignites and burns easily, with a candlelike flame, but its fuel value is low.

Formation

The vegetable origin of coal is supported by the presence in coal of carbonized fibers, stems, leaves, and seeds of plants, which can be detected with the naked eye in the softer varieties and with the microscope in harder coal. Sometimes carbonized tree stumps have been found standing in layers of coal. The general interpretation of these facts is that coal originated in swamps similar to present-day peat bogs and in lagoons, probably partly from plants growing in the area and partly from plant material carried in by water and wind. From the thickness of coal seams, it is assumed that the coal swamps were located near sea level and were subject to repeated submergence, so that a great quantity of vegetable matter accumulated over a long period of time.

The initial processes of disintegration and decomposition of the organic matter were brought about by the action of bacteria and other microorganisms. Peat, the first product formed, is altered to form lignite and coal through metamorphism. The pressure of the accumulated layers of overlying sediments and rock upon the submerged plant matter forced out much of the water and caused some of the volatile substances to escape and the nonvolatile carbon material to form a more compact mass. The greater the stress exerted in the process of metamorphism, the higher was the grade of coal produced. Cannel coal was probably formed in ponds, rather than in lagoons or swamps, as it occurs in lenticular masses and is frequently found to contain fossil fish. Coal was formed chiefly in the Carboniferous period of geologic time, but valuable deposits date also from the Permian, Triassic, Jurassic, Cretaceous, and Tertiary periods.

Natural Occurrence

Coal is found in beds or seams interstratified with shales, clays, sandstones, or (rarely) limestones. It is usually underlaid by an underclay (a layer of clay containing roots of plants). The coal is removed by strip (surface) mining or underground mining methods (see coal mining).

The chief coal fields of the United States are the Appalachian (from N Pennsylvania into Alabama), the Eastern Interior (Illinois, Kentucky, and Indiana), the Northern Interior (Michigan), the Western Interior (Iowa, Kansas, Missouri, Oklahoma, and Arkansas), the Rocky Mountain (Colorado, Wyoming, Utah, New Mexico, Montana, and North Dakota), the Pacific (Washington), and the Gulf Coast (Texas, Arkansas, and Louisiana). In Europe the chief coal-producing countries are Germany, Russia, Ukraine, and Poland. There are valuable coal fields in China, India, Indonesia, Australia, South Africa, and Korea but only a few in South America, mainly in Colombia.

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coal

coal A brown or black carbonaceous deposit derived from the accumulation and alteration of ancient vegetation, which originated largely in swamps or other moist environments. As the vegetation decomposed it formed layers of peat, which were subsequently buried (for example, by marine sediments following a rise in sea level or subsidence of the land). Under the increased pressure and resulting higher temperatures the peat was transformed into coal. Two types of coal are recognized: humic (or woody) coals, derived from plant remains; and sapropelic coals, which are derived from algae, spores, and finely divided plant material.

As the processes of coalification (i.e. the transformation resulting from the high temperatures and pressures) continue, there is a progressive transformation of the deposit: the proportion of carbon relative to oxygen rises and volatile substances and water are driven out. The various stages in this process are referred to as the ranks of the coal. In ascending order, the main ranks of coal are: lignite (or brown coal), which is soft, brown, and has a high moisture content; subbituminous coal, which is used chiefly by generating stations; bituminous coal, which is the most abundant rank of coal; semibituminous coal; semianthracite coal, which has a fixed carbon content of between 86% and 92%; and anthracite coal, which is hard and black with a fixed carbon content of between 92% and 98%.

Most deposits of coal were formed during the Carboniferous and Permian periods. More recent periods of coal formation occurred during the early Jurassic and Tertiary periods. Coal deposits occur in all the major continents; the leading producers include the USA, China, Ukraine, Poland, UK, South Africa, India, Australia, and Germany. Coal is used as a fuel and in the chemical industry; by-products include coke and coal tar.

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coal

coal A carbon-rich mineral deposit formed from the remains of fossil plants. These are deposited initially as peat, but burial and increase in temperatures at depth bring about physical and chemical changes. The process of ‘coalification’ results in the production of coals of different ranks (‘coal series’), from peat, through the bituminous coals and lignite to anthracite. Each rank marks a reduction in the percentage of volatiles and moisture, and an increase in the percentage of carbon. They are termed ‘woody’ or ‘humic’ coals if formed from fragments of trees or bushes. If the major constituents of coal are pollen grains and/or finely divided plant debris, the term ‘sapropelic coal’ is used.

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"coal." A Dictionary of Ecology. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

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coal

coal Carbon-rich mineral deposit formed from the remains of fossil plants. These are deposited initially as peat, but burial and increase in temperatures at depth bring about physical and chemical changes. The process of ‘coalification’ results in the production of coals of different ranks (‘coal series’), from peat, through the bituminous coals and lignite, to anthracite. Each rank marks a reduction in the percentage of volatiles and moisture, and an increase in the percentage of carbon. They are termed ‘woody’ or ‘humic’ coals if formed from fragments of trees or bushes. If the major constituents of coal are pollen grains and/or finely divided plant debris, the term ‘sapropelic coal’ is used.

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coal

coal / kōl/ • n. a combustible black or dark brown rock consisting mainly of carbonized plant matter, found mainly in underground deposits and widely used as fuel: [as adj.] a coal fire. ∎  a red-hot piece of coal or other material in a fire: the glowing coals. • v. [tr.] provide with a supply of coal: [as n.] (coaling) the coaling and watering of the engine. DERIVATIVES: coal·y adj. ORIGIN: Old English col (in the senses ‘glowing ember’ and ‘charred remnant’), of Germanic origin; related to Dutch kool and German Kohle. The sense ‘combustible mineral used as fuel’ dates from Middle English.

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coal

coal Blackish, solid fuel formed from the remains of fossil plants. In the carboniferous and tertiary periods, swamp vegetation subsided to form peat bogs. Sedimentary deposits buried the bogs, and the resultant increase in pressure and heat produced lignite (brown coal), then bituminous coal and finally anthracite if temperature increased sufficiently. This is termed the coal rank series; each rank of coal represents an increase in carbon content and a reduction in the proportion of natural gas and moisture. Lignite is a poorer fuel than anthracite.

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coal

coal †glowing piece of wood OE.; †charcoal XIII; black mineral used for fuel XIII (orig. seacoal). OE. col, corr. to OFris., MLG. kole, MDu. cole (Du. kool), OHG. kol(o) (G. kohle), ON. kol, of uncert. orig.

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"coal." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

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Coal

Coal. A description among Coptic, Ethiopic, and E. Syrian Christians of the sacramental body of Christ. The description is derived from Isaiah 6. 6 f.

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"Coal." The Concise Oxford Dictionary of World Religions. . Encyclopedia.com. 22 Aug. 2017 <http://www.encyclopedia.com>.

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coal

coalbarcarole, bole, bowl, cajole, coal, Cole, condole, console, control, dhole, dole, droll, enrol (US enroll), extol, foal, goal, hole, Joel, knoll, kohl, mol, mole, Nicole, parol, parole, patrol, pole, poll, prole, rôle, roll, scroll, Seoul, shoal, skoal, sole, soul, stole, stroll, thole, Tirol, toad-in-the-hole, toll, troll, vole, whole •Creole •carriole, dariole •cabriole • capriole •aureole, gloriole, oriole •wassail-bowl • fishbowl • dustbowl •punchbowl • rocambole • farandole •girandole • manhole • rathole •armhole • arsehole • hellhole •keyhole, kneehole •peephole •sinkhole • pinhole • cubbyhole •hidey-hole • pigeonhole •eyehole, spyhole •foxhole •knothole, pothole •borehole, Warhol •porthole • soundhole • blowhole •stokehole • bolthole • loophole •lughole, plughole •chuckhole • buttonhole • bunghole •earhole • waterhole • wormhole •charcoal • caracole • Seminole •pinole

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