all about coal Coal I INTRODUCTION Coal Miners A coal train leaves a mine in Scranton, Pennsylvania, in 1919. United States President William Howard Taft created a federal Bureau of Mines with the objective of reducing mine accidents and fatalities. CORBIS-BETTMANN Coal, a combustible organic rock composed primarily of carbon, hydrogen, and oxygen. Coal is burned to produce energy and is used to manufacture steel. It is also an important source of chemicals used to make medicine, fertilizers, p
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  all about coalCoalIINTRODUCTIONCoal MinersA coal train leaves a mine in Scranton, Pennsylvania, in 1919. United States President William HowardTaft created a federal Bureau of Mines with the objective of reducing mine accidents and fatalities.CORBIS-BETTMANNCoal, a combustible organic rock composed primarily of carbon, hydrogen, and oxygen. Coal is burnedto produce energy and is used to manufacture steel. It is also an important source of chemicals used tomake medicine, fertilizers, pesticides, and other products. Coal comes from ancient plants buried over millions of years in Earth’s crust, its outermost layer. Coal, petroleum, natural gas, and oil shale are allknown as fossil fuels because they come from the remains of ancient life buried deep in the crust.Coal is rich in hydrocarbons (compounds made up of the elements hydrogen and carbon). All life formscontain hydrocarbons, and in general, material that contains hydrocarbons is called organic material.Coal srcinally formed from ancient plants that died, decomposed, and were buried under layers of sediment during the Carboniferous Period, about 360 million to 290 million years ago. As more andmore layers of sediment formed over this decomposed plant material, the overburden exertedincreasing heat and weight on the organic matter. Over millions of years, these physical conditionscaused coal to form from the carbon, hydrogen, oxygen, nitrogen, sulfur, and inorganic mineralcompounds in the plant matter. The coal formed in layers known as seams.Plant matter changes into coal in stages. In each successive stage, higher pressure and heat from theaccumulating overburden increase the carbon content of the plant matter and drive out more of itsmoisture content. Scientists classify coal according to its fixed carbon content, or the amount of carbonthe coal produces when heated under controlled conditions. Higher grades of coal have a higher fixedcarbon content.IIMODERN USES OF COALEighty-six percent of the coal used in the United States is burned by electric power plants to produceelectricity. When burned, coal generates energy in the form of heat. In a power plant that uses coal asfuel, this heat converts water into steam, which is pressurized to spin the shaft of a turbine. Thisspinning shaft drives a generator that converts the mechanical energy of the rotation into electric power (see Electric Motors and Generators; Steam Engine).  Coal is also used in the steel industry. The steel industry uses coal by first heating it and converting itinto coke, a hard substance consisting of nearly pure carbon. The coke is combined with iron ore andlimestone. Then the mixture is heated to produce iron (see Iron and Steel Industry). Other industries usedifferent coal gases given off during the coke-forming process to make fertilizers, solvents, medicine, pesticides, and other products.Fuel companies convert coal into easily transportable gas or liquid fuels (see Synthetic Fuels). Coal- based vapor fuels are produced through the process of gasification. Gasification may be accomplishedeither at the site of the coalmine or in processing plants. In processing plants, the coal is heated in the presence of steam and oxygen to produce synthesis gas, a mixture of carbon monoxide, hydrogen, andmethane used directly as fuel or refined into cleaner-burning gas.On-site gasification is accomplished by controlled, incomplete burning of an underground coal bedwhile adding air and steam. To do this, workers ignite the coal bed, pump air and steam undergroundinto the burning coal, and then pump the resulting gases from the ground. Once the gases arewithdrawn, they may be burned to produce heat or generate electricity. Or they may be used insynthetic gases to produce chemicals or to help create liquid fuels.Liquefaction processes convert coal into a liquid fuel that has a composition similar to that of crude petroleum. Coal can be liquefied either by direct or indirect processes. However, because coal is ahydrogen-deficient hydrocarbon, any process used to convert coal to liquid or other alternative fuelsmust add hydrogen. Four general methods are used for liquefaction: (1) pyrolysis andhydrocarbonization, in which coal is heated in the absence of air or in a stream of hydrogen; (2) solventextraction, in which coal hydrocarbons are selectively dissolved and hydrogen is added to produce thedesired liquids; (3) catalytic liquefaction, in which hydrogenation takes place in the presence of acatalyst; and (4) indirect liquefaction, in which carbon monoxide and hydrogen are combined in the presence of a catalyst.IIICOAL FORMATIONHow Coal FormsThe coal we find today formed from generations of plants that died in ancient tropical swamps andaccumulated on the swamp bottoms. The plant material first formed a compact organic material called peat. As layers of sediment gradually accumulated over the peat, the pressure and heat exerted by thethickening layers gradually drove out the moisture and increased the carbon content of the peat,forming coal.© Microsoft Corporation. All Rights Reserved.Coal is a sedimentary rock formed from plants that flourished millions of years ago when tropicalswamps covered large areas of the world. Lush vegetation, such as early club mosses, horsetails, andenormous ferns, thrived in these swamps. Generations of this vegetation died and settled to the swamp bottom, and over time the organic material lost oxygen and hydrogen, leaving the material with a high percentage of carbon. Layers of mud and sand accumulated over the decomposed plant matter,compressing and hardening the organic material as the sediments deepened. Over millions of years,  deepening sediment layers, known as overburden, exerted tremendous heat and pressure on theunderlying plant matter, which eventually became coal.Cutting PeatA worker cuts peat from lush peatland in Ireland. Peat is the first stage in the transformation of vegetation into coal. For hundreds of years, people have cut, dried, and burned it for heating andcooking. This compact, dark-brown material contains about one third less heating value than coal.Farrell Grenan/Photo Researchers, Inc.Before decayed plant material forms coal, the plant material forms a dark brown, compact organicmaterial known as peat. Although peat will burn when dried, it has a low carbon and high moisturecontent relative to coal. Most of coal’s heating value comes from carbon, whereas inorganic materials,such as moisture and minerals, detract from its heating value. For this reason, peat is a less efficientfuel source than coal. Over time, as layers of sediment accumulate over the peat, this organic materialforms lignite, the lowest grade of coal. As the thickening geologic overburden gradually drivesmoisture from the coal and increases its fixed carbon content, coal evolves from lignite intosuccessively higher-graded coals: subbituminous coal, bituminous coal, and anthracite. Anthracite, thehighest rank of coal, has nearly twice the heating value of lignite (see Heat).Coal formation began during the Carboniferous Period (known as the first coal age), which spanned360 million to 290 million years ago. Coal formation continued throughout the Permian, Triassic,Jurassic, Cretaceous, and Tertiary Periods (known collectively as the second coal age), which spanned290 million to 1.6 million years ago. Coals formed during the first coal age are older, so they aregenerally located deeper in Earth’s crust. The greater heat and pressures at these depths produce higher-grade coals such as anthracite and bituminous coals. Conversely, coals formed during the second coalage under less intense heat and pressure are generally located at shallower depths. Consequently, thesecoals tend to be lower-grade subbituminous and lignite coals.IVCOMPONENTS OF COALCoal contains organic (carbon-containing) compounds transformed from ancient plant material. Thesrcinal plant material was composed of cellulose, the reinforcing material in plant cell walls; lignin,the substance that cements plant cells together; tannins, a class of compounds in leaves and stems; andother organic compounds, such as fats and waxes. In addition to carbon, these organic compoundscontain hydrogen, oxygen, nitrogen, and sulfur. After a plant dies and begins to decay on a swamp bottom, hydrogen and oxygen (and smaller amounts of other elements) gradually dissociate from the plant matter, increasing its relative carbon content.Coal also contains inorganic components, known as ash. Ash includes minerals such as pyrite andmarcasite formed from metals that accumulated in the living tissues of the ancient plants. Quartz, clay,and other minerals are also added to coal deposits by wind and groundwater. Ash lowers the fixedcarbon content of coal, decreasing its heating value.V  COAL DEPOSITS AND RESERVESCoal Production and ConsumptionA comparison of the top ten coal-producing countries and the top ten coal-consuming countries showsthat China is both the leading producer and the leading consumer of coal. Coal is burned in power  plants to produce electricity and in steel mills to make coke for the production of steel.© Microsoft Corporation. All Rights Reserved.Although coal deposits exist in nearly every region of the world, commercially significant coalresources occur only in Europe, Asia, Australia, and North America. Commercially significant coaldeposits occur in sedimentary rock basins, typically sandwiched as layers called beds or seams betweenlayers of sandstone and shale.When experts develop estimates of the world’s coal supply, they distinguish between coal reserves andresources. Reserves are coal deposits that can be mined profitably with existing technology—that is,with current equipment and methods. Resources are an estimate of the world’s total coal deposits,regardless of whether the deposits are commercially accessible. Exploration geologists have found andmapped the world’s most extensive coal beds. At the beginning of 2001, global coal reserves wereestimated at 984.2 billion metric tons, in which 1 metric ton equals 1,016 kg (2,240 lb). These reservesoccurred in the following regions by order of importance: the Asia Pacific, including Australia, 29.7 percent; North America, 26.1 percent; Russia and the countries of the former Union of Soviet SocialistRepublics (USSR), 23.4 percent; Europe, excluding the former USSR, 12.4 percent; Africa and theMiddle East, 6.2 percent; and South and Central America, 2.2 percent.Coal deposits in the United Kingdom, which led the world in coal production until the 20th century,extend throughout parts of England, Wales, and southern Scotland. Coalfields in western Europeunderlie the Saar and Ruhr valleys in Germany, the Alsace region of France, and areas of Belgium.Coalfields in central Europe extend throughout parts of Poland, the Czech Republic, and Hungary. Themost extensive and valuable coalfield in eastern Europe is the Donets Basin, between the Dnieper andDon rivers (in parts of Russia and Ukraine). Large coal deposits in Russia are being mined in theKuznetsk Basin in southern Siberia. Coalfields underlying northwestern China are among the largest inthe world. Mining of these fields began in the 20th century.United States coal reserves are located in six major regions, three of which produce the majority of domestically mined coal. The most productive region in the United States is the Appalachian Basin,covering parts of Pennsylvania, West Virginia, Kentucky, Tennessee, Ohio, and Alabama. Largequantities of coal have also been produced by both the Illinois Basin—extending through Illinois,Indiana, and Kentucky—and the Western Interior Region—extending through Missouri, Kansas, andOklahoma. Other commercially important U.S. coal regions include the Powder River Basin,underlying parts of Montana and Wyoming; the Green River Basin in Wyoming; the Uinta Basin,covering areas of Utah and Colorado; and the San Juan Basin, underlying parts of Utah, New Mexicoand Colorado.In 2002 estimates of total U.S. coal reserves were approximately 246 billion metric tons. At the


Nov 3, 2017


Nov 3, 2017
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