Coal-Fired Power Plant

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A fossil-fuel power station is a type of power station that burns fossil fuels such as coal,natural gas or petroleum (oil) to produce electricity. Central station fossil-fuel power plants are designed on a large scale for continuous operation. In many countries, such plants provide most of the electrical energy used. Fossil fuel power stations have rotating machinery to convert the heat energy of combustioninto mechanical energy, which then operates an electrical generator. The prime mover may be a steam turbine, a gas turbine or, in small plants, a reciprocating internal combustionengine. All plants use the energy extracted from expanding gas - steam or combustion gases. A very few MHD generators have been built which directly convert the energy of moving hot gas into electricity.[citation needed] Byproducts of thermal power plant operation must be considered in their design and operation. Waste heat energy, which remains due to the finite efficiency of the Carnot,Rankine, or Diesel power cycle, is released directly to the atmosphere, directly to river or lake water, or indirectly to the atmosphere using a cooling tower with river or lake water used as a cooling medium. The flue gas from combustion of the fossil fuels is discharged to the air. This gas contains carbon dioxide, water vapour, as well as substances such as nitrogen oxides (NOx), sulfur oxides (SOx), mercury, traces of other metals, and, for coal-fired plants,fly ash. Solid waste ash from coal-fired boilers must also be removed. Some coal ash can be recycled for building materials. [2] Fossil fueled power stations are major emitters of CO2, a greenhouse gas (GHG) which according to a consensus opinion of scientific organisations is a contributor to global warming as it has been observed over the last 100 years. Brown coal emits about 3 times as much CO2 as natural gas, and black coal emits about twice as much CO2 per unit of electric energy. Carbon capture and storage of emissions is not expected to be available on a commercial economically viable basis until government supported legislation is enacted. -------------------------------------------------

Basic concepts
In a fossil fuel power plant the chemical energy stored in fossil fuels such as coal, fuel oil, natural gas or oil shale and oxygen of the airis converted successively into thermal energy, mechanical energy and, finally, electrical energy. Each fossil fuel power plant is a complex, custom-designed system. Construction costs, as of 2004, run to US$1,300 per kilowatt, or $650 million for a 500 MWeunit[citation needed]. Multiple generating units may be built at a single site for more efficient use of land, natural resources and labour. Most thermal power stations in the world use fossil fuel, outnumbering nuclear, geothermal, biomass, or solar thermal plants. [edit]Heat into mechanical energy

The second law of thermodynamics states that any closed-loop cycle can only convert a fraction of the heat produced during combustion into mechanical work. The rest of the heat, called waste heat, must be released into a cooler environment during the return portion of the cycle. The fraction of heat released into a cooler medium must be equal or larger than the ratio of absolute temperaturesof the cooling system (environment) and the heat source (combustion furnace). Raising the furnace temperature improves the efficiency but complicates the design, primarily by the selection of alloys used for construction, making the furnace more expensive. The waste heat cannot be converted into mechanical energy without an even cooler cooling system. However, it may be used in cogenerationplants to heat buildings, produce hot water, or to heat materials on an industrial scale, such as in some oil refineries, plants, andchemical synthesis plants. Typical thermal efficiency for electrical generators in the industry is around 33% for coal and oil-fired plants, and 56 – 60% (LHV) forcombined-cycle gas-fired plants. Plants...
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