Quartz Calcite
Posted in Uncategorized on 06/13/2011 01:01 am by admin
Environmental problems associated with coal combustion
Anthrax is a naturally occurring combustible material consisting primarily of the element carbon. It also contains small percentages of hydrocarbon solids, liquids and gases and / or other materials, such The compounds of nitrogen and sulfur. The physical, chemical and other properties of coal vary considerably sample to sample. Coal is usually classified into sub-groups called anthracite, bituminous coal, lignite and peat. In some periods of Earth history, however, conditions exist that have made other forms of degradation possible. The bodies of dead plants and animals have undergone only partial decomposition. Other products of this partial decomposition are coal, oil and natural gas called fuels fossils. To see how these changes may have occurred, we can consider the following possibility. A plant dies in a marshy area and is quickly covered water, silt, sand and other sediments. These materials prevent debris from reacting with oxygen from the air and decomposition of carbon dioxide and water, a process that occurs under normal circumstances. Instead, anaerobic bacteria attack the plant debris and convert it to simpler forms: carbon and hydrocarbons mainly pure, simple compounds of carbon and hydrogen. The first stage of the decay of plant death is a sweet, woody material known as peat. In some parts of the world, peat is still taken in swampy areas and used as fuel. This is not a good fuel, though, because it burns poorly and produces a large smoke. If peat is allowed to remain in soil for long periods of time, it eventually becomes compacted. The layers of sediment, known as name overloading, collecting above. The additional pressure and heat of the overburden is gradually transformed into another form of peat coal known as the lignite or brown. Following compaction of overburden then converts lignite into bituminous coal, and finally anthracite. Coal was formed several times in In the past, but most abundantly in the Carboniferous age (about 300 million years) and again during the Upper Cretaceous (about 100 million years). Today, coal formed by these processes is often found in layers between other layers of sedimentary rocks. sedimentary rocks form when the sand silt, clay and similar materials are piled up under pressure. In some cases, the layers of coal can be found on or very near the surface. In other cases, they may be buried thousands of meters underground. Coal seams typically range from the absence of more than 3 200 feet (1-60 meters) thick. The location and configuration of a coal seam determines the method by which the coal will be extracted. Coal is classified according to its calorific value and according to the percentage of carbon it contains. For example, anthracite contains the highest proportion of pure carbon (about 86 to 98 per cent) and has the highest heat value of all forms of coal. Bituminous coal is generally lower concentrations of pure carbon (46 to 86 per cent) and lower heat values. bituminous coals are often divided on the basis of their heat value, be classified as low, medium and high volatile bituminous and subbituminous. Lignite, the poorest of the true coals in terms of heat value, usually 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, which are very small in absolute terms, but which have significant environmental consequences when coals are used as fuels. By far the most important property of coal is the harsh reality that it burns. When pure carbon and hydrocarbons in coal burn completely, only two products: carbon dioxide and water are formed. During this chemical reaction, a relatively significant thermal energy is released. For this reason, coal has long been used by humans as an energy source for heating houses and other buildings, ships and trains running, and in many industrial processes. However, the complete combustion of carbon and hydrocarbons occurs rarely in nature. If the temperature is not high enough or is not provided sufficient oxygen to gasoline, Burning these materials is generally incomplete. During the incomplete combustion of carbon and hydrocarbons, products other than carbon dioxide and water are formed. These products include carbon monoxide, hydrogen, and other forms of pure carbon, like soot. During the combustion of coal, minor constituents are also oxidized. For example, sulfur dioxide is converted to sulfur trioxide and sulfur and nitrogen compounds are converted into oxides nitrogen. Incomplete combustion of coal and combustion of these minor constituents results in a number of environmental problems. For example, soot formed during the incomplete combustion may settle out of air and depositing a coating on the attractive homes, cars, buildings and other structures. The carbon monoxide formed during the incomplete combustion gas is toxic and can cause illness or death in humans and other animals. Sulfur oxides and nitrogen react with water vapor in the atmosphere and deposited in the air like acid rain that is thought to be responsible for the destruction of certain types of plants and animals, especially fish and life. In addition to these compounds, coal often contains a small percentage of mineral matter (quartz, calcite, or perhaps clay minerals). Because these components do not burn easily, they Part of the ash formed during combustion. These ashes then either escapes into the atmosphere or is left in the tank and combustion is eliminated. Sometimes the coal ash also contains significant amounts of other elements such as lead, barium, arsenic, etc., whether Embedded or in bulk, coal ash can therefore constitute a serious hazard to the environment. Coal is extracted from the Earth using one of two main methods: underground or surface (strip) mining. mining sub-soil is used when coal seams are located at depths important below the surface of the Earth. The first step in the mining sub-soil is to dig vertical tunnels in the ground until the coal seam is reached. horizontal tunnels were then constructed outside the vertical tunnel. In many cases, the best way to mine coal by this method is called operating room and pillar. Operating room and pillar, carbon columns (pillars) are left in place as coal around them is removed. The pillars supporting the ceiling of the seam, it prevents collapse on miners who work around them. After the mine was abandoned, however, these pillars may collapse, bringing the ceiling of the seam and causing the collapse of ground above the old mine. Surface mining may be used when a coal seam is close enough to the Earth's surface to allow the overburden must be removed easily and cheaply. In such cases, the first step is to remove all overburden to reach the coal itself. Coal is then scraped by huge shovels, some capable of removing up to 100 cubic meters at a time. open pit mining is a much safer form of coal mining for coal workers, but it has a number of environmental problems. In most cases, area that was looted was deeply bruised. Restoring the area to its original condition may be a long and costly procedure. In addition, any Water that comes into contact with the exposed coal or overburden may be contaminated and require treatment. Coal is considered a resource non-renewable, which means it is not replaced easily or quickly. Once a nonrenewable resource has been used, it is left for very long time in the future, if not forever. Coal fits this description, since it was formed several million years ago, but is not formed in significant amounts over time. Therefore, the amount of coal that now exists under the surface of the earth is for all purposes practices, all the coal available for the foreseeable future. When this supply of coal is used, the man may be necessary to find another solution to meet their energy needs. Large amounts of coal are known or thought to be available in many parts of the world. During many centuries, coal was burned in small stoves to produce heat in homes and factories. As the use of natural gas spread in the late twentieth century, coal oil and gas, coal quickly became unpopular because they were a little smoke and the stench. Today the largest use of coal, both directly and indirectly, is still as fuel, but more largest consumer of coal for this purpose is the electricity industry. The combustion of coal in power generation energy is used to produce steam, which in turn operates turbines and generators. The seriousness of the situation can be realized that for a period more than 40 years after 1940, the amount of coal used in the United States for this purpose is said to be doubling every decade. Although coal is more widely used to heat homes and buildings, it is still used in industries like paper manufacturing, cement and ceramic manufacturing, production of iron and steel and chemical production for heating and steam production. Another use of coal is the manufacture of coke. Coke is nearly pure carbon produced when coal is heated in the absence of fresh air. In most cases, 1 ton of coal will produce 0.7 tons of coke in this process. Coke is valuable in the industry because it has a calorific value of any form of natural charcoal. It is widely used in the steel and certain chemical processes. A number of methods have been developed by the solid coal can be converted into liquid or gaseous form for use as fuel. The conversion has a number of advantages. In a liquid or gaseous fuel may be easier to carry. In addition, the process Conversion removes some impurities from the coal origin that have environmental drawbacks. One method of conversion is known such as gasification. In gasification, coal is crushed forced to react with steam and air or pure oxygen. Coal is transformed in a complex mixture of gaseous hydrocarbons, with values of sensible heat. One day it may be possible to construct gasification systems in a mine coal, making it easier to remove the coal, gaseous form, its original vein. In the liquefaction process, coal is converted to solid in a liquid such as oil that can be used as fuel for motor vehicles and other applications. On the one hand, two liquefaction and gasification technologies are attractive because of its huge coal resources. On the other hand, the availability of raw coal means that expensive new technologies have not been able to compete economically with the natural product. About the Author
Dr.Badruddin Khan teaches chemistry in the University of Kashmir, Srinagar, India.
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