43535602 Thermal Power Plant | Steam Engine | Boiler

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A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which either drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because such facilities
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  A thermal power station is a  power plantin which the prime mover  issteam driven. Water  is heated, turns into steam and spins asteam turbine which either drives an electrical generator .After it passes through the turbine, the steam is condensed in acondenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to usethe term energy center  because such facilities convert forms of  heat energyinto electrical energy. Some thermal power plants also deliver heat energy for industrial purposes, for district heating, or for desalinationof water as well as delivering electrical power. Introductory overview Almost all coal, nuclear ,geothermal,solar thermal electric, andwaste incineration plants, as well as many natural gas power plants are thermal.  Natural gasis frequentlycombustedingas turbinesas well as boilers. The waste heat from a gas turbine can be used to raise steam, in a combined cycleplant that improves overall efficiency. Power plants burning coal,oil, or  natural gas are often referred to collectively as  fossil-fuel power plants . Some biomass-fueledthermal power plants have appeared also. Non-nuclear thermal power plants, particularlyfossil-fueled plants, which do not usecogeneration are sometimes referred to as conventional  power plants .Commercialelectric utility  power stations are most usually constructed on a very large scale and designed for continuous operation. Electric power plants typically usethree-phase or  individual-phaseelectrical generatorsto produce alternating current (AC) electric power at afrequency of 50 Hz or 60 Hz (hertz, which is an AC sine wave per second) depending on itslocation in the world. Other large companies or institutions may have their own usuallysmaller power plants to supplyheatingor electricity to their facilities, especially if heat or steam is created anyway for other purposes. Shipboard steam-driven power plants have beenused in various large ships in the past, but these days are used most often in large navalships. Such shipboard power plants are general lower power capacity than full-size electriccompany plants, but otherwise have many similarities except that typically the main steamturbines mechanically turn the propulsion propellers, either through reduction gears or  directly by the same shaft. The steam power plants in such ships also provide steam toseparate smaller turbines driving electric generators to supply electricity in the ship.Shipboard steam power plants can be either conventional or nuclear; the shipboard nuclear  plants are mostly in the navy. There have been perhaps about a dozen turbo-electric ships in which a steam-driven turbine drives an electric generator which powers anelectric motor for  propulsion.In some industrial, large institutional facilities, or other populated areas, there are  combined heat and power  (CHP) plants   , often called cogeneration plants , which produce both power and heat for facility or district heatingor industrial applications. AC electrical power can bestepped up to very highvoltagesfor long distancetransmissionwith minimal loss of power. Steam and hot water lose energy when piped over substantial distance, so carrying heatenergy by steam or hot water is often only worthwhile within a local area or facility, such assteam distribution for a ship or industrial facility or hot water distribution in a localmunicipality. [edit] History Reciprocating steam engines have been used for mechanical power sources since the 18thCentury, with notable improvements being made by James Watt.The very first commercial central electrical generating stations in thePearl Street Station, New York and theHolborn Viaduct power station, London, in 1882, also used reciprocating steam engines. Thedevelopment of thesteam turbineallowed larger and more efficient central generating  stations to be built. By 1892 it was considered as an alternative to reciprocating engines [1] Turbines offered higher speeds, more compact machinery, and stable speed regulationallowing for parallel synchronous operation of genrators on a common bus. Turbines entirelyreplaced reciprocating engines in large central stations after about 1905. The largestreciprocating engine-generator sets ever built were completed in 1901 for the ManhattanElevated Railway. Each of seventeen units weighed about 500 tons and was rated 6000kilowatts; a contemparary turbine-set of similar rating would have weighed about 20% asmuch. [2] [edit] Efficiency The energy efficiency of a conventional thermal power station, considered as saleable energy(in MWe) produced at the plant busbars as a percent of the heating value of the fuelconsumed, is typically 33% to 48% efficient. This efficiency is limited as all heat engines aregoverned by the laws of thermodynamics (See:Carnot cycle). The rest of the energy must leave the plant in the form of heat. This waste heatcan go through acondenser and be disposed of with cooling water or incooling towers. If the waste heat is instead utilized for  district heating, it is calledcogeneration. An important class of thermal power station are associated withdesalinationfacilities; these are typically found in desert countries with largesupplies of  natural gasand in these plants, freshwater production and electricity are equally important co-products.ARankine cyclewith a two-stagesteam turbine and a single feedwater heater. Since the efficiency of the plant isfundamentally limited  by the ratio of the absolute temperatures of the steam at turbine input and output, efficiency improvements require use of   higher temperature, and therefore higher pressure, steam. Historically, other working fluidssuch asmercuryhave been experimentally used in amercury vapour turbine power plant, since these can attain higher temperatures than water at lower working pressures. However,the obvious hazards of toxicity, and poor heat transfer properties, have ruled out mercury as aworking fluid.Above thecritical pointfor water  of 705 °F (374 °C) and 3,212 psi (22.15 MPa), there is no  phase transitionfrom water to steam, but only a gradual decrease in density. Boiling does not occur and it is not possible to remove impurities via steam separation. In this case asupercritical steam plant is required to utilise the increasedthermodynamic efficiency  by operating at higher temperatures. These plants, also called once-through plants because boiler water does not circulate multiple times, require additional water purification steps to ensurethat any impurities picked up during the cycle will be removed. This purification takes theform of high pressure ion exchange units calledcondensate polishersbetween the steamcondenser and the feedwater heaters. Subcritical fossil fuel power plants can achieve 36–40%efficiency.Supercritical designs have efficiencies in the low to mid 40% range, with new ultra critical designs using pressures of 4,400 psi (30 MPa) and dual stage reheat reachingabout 48% efficiency.Currentnuclear power plantsoperate below the temperatures and pressures that coal-fired plants do. This limits their thermodynamic efficiency to on the order of 30–32%. Someadvanced reactor designs being studied, such as the Very high temperature reactor , Advanced gas-cooled reactor  andSupercritical water reactor , would operate at temperatures and  pressures similar to current coal plants, producing comparable thermodynamic efficiency. [edit] Cost of electricity See also: Relative cost of electricity generated by different sources The direct cost of electric energy produced by a thermal power station is the result of cost of fuel, capital cost for the plant, operator labor, maintenance, and such factors as ash handlingand disposal. Indirect, social or environmental costs such as the economic value of environmental impacts, or environmental and health effects of the complete fuel cycle and plant decommissioning, are not usually assigned to generation costs for thermal stations inutility practice, but may form part of an environmental impact assessment. [edit] Diagram of a typical coal-fired thermal powerstation  Typical diagram of a coal-fired thermal power station  1.Cooling tower 10. SteamControl valve19.Superheater  2.Cooling water pump11. High pressuresteamturbine20. Forced draught (draft)fan3.transmission line(3-phase)12.Deaerator 21. Reheater  4. Step-up transformer (3-phase)13.Feedwater heater 22.Combustionair intake 5.Electrical generator  (3-phase)14.Coal conveyor 23.Economiser  6. Low pressuresteam turbine15.Coalhopper24.Air preheater  7.Condensate pump16.Coal pulverizer 25.Precipitator  8.Surface condenser 17.Boiler steam drum 26. Induced draught (draft)fan9. Intermediate pressure steamturbine18.Bottom ashhopper27.Flue gas stack  For units over about 200MWcapacity, redundancy of key components is provided byinstalling duplicates of the forced and induced draft fans, air preheaters, and fly ashcollectors. On some units of about 60 MW, two boilers per unit may instead be provided. [edit] Boiler and steam cycle In fossil-fueled power plants,  steam generator  refers to a furnace that burns the fossil fuel to boil water to generate steam.In thenuclear plantfield,  steam generator   refers to a specific type of largeheat exchanger   used in a pressurized water reactor  (PWR) to thermally connect the primary (reactor plant) and secondary (steam plant) systems, which generates steam. In a nuclear reactor called a boiling water reactor (BWR), water is boiled to generate steam directly in the reactor itself and there are no units called steam generators.
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