Fossil fuel power plant 1560443 226093268 2008-07-16T20:09:56Z Mbeychok 800193 Phanly, if you insist on adding redundant material, then it should at least worked into the "Environmental Impact" section. [[Image:Mohave Generating Station 1.jpg|thumb|300px|right|Mohave Generating Station, a 1,580&nbsp;MW coal power plant near [[Laughlin, Nevada]]]] {{portal|Energy}} A '''fossil fuel power plant''' burns [[fossil fuel]]s such as [[coal]], [[natural gas]] or [[petroleum]] (oil) to produce [[electricity]]. 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. A fossil fuel power plant always has some kind of rotating machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical [[generator]]. The [[Wiktionary:prime mover|prime mover]] may be a [[steam turbine]], a [[gas turbine]] or in small isolated plants, a reciprocating [[internal combustion]] engine. Byproducts of power plant operation must be considered in the design and operation. Waste heat due to the [[Carnot cycle|finite efficiency]] of the turbines must be released to the atmosphere, often using a [[cooling tower]], or river or lake water as a cooling medium. The [[flue gas]] from combustion of the fossil fuels is discharged to the air; this contains [[carbon dioxide]] and water vapour, as well as other substances such as nitrous oxides, sulfur oxides, and (in the case of coal-fired plants) fly ash and [[mercury (element)|mercury]]. Solid waste ash from coal-fired boilers must also be removed, although some coal ash can be recycled for building materials. ==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]] is converted successively into [[thermal energy]], [[mechanical energy]] and, finally, [[electrical energy]] for continuous use and distribution across a wide geographic area. Almost all large fossil fuel [[power plant]]s are [[thermal power station]]s, except for [[gas turbine]]s and [[Electrical_generator#Engine-generator|utility-sized generators]] that may run on natural gas or [[diesel]]. The [[Combustion#Complete|complete combustion]] of fossil fuel using air as the oxygen source is summarized in the following chemical reaction: <math>C_xH_y + (x + \frac{y}{4})O_2 + 3.76 (x+ \frac{y}{4}) N_2 \rightarrow \; xCO_2 + (\frac{y}{2})H_2O + 3.76 (x+ \frac{y}{4}) N_2</math> and the simple word equation for this chemical reaction is: <math>\textrm{Fuel} + \textrm{Air} \rightarrow \; \textrm{Heat} + \textrm{Carbon\ dioxide} + \textrm{Water} + \textrm{Nitrogen}</math> All fossil fuels generate [[carbon dioxide]] when burned. Other products of [[Combustion#Incomplete|''incomplete'' combustion]] are [[sulfur dioxide]] (predominantly in coal) and [[oxides]] of [[nitrogen]]; since no fossil fuel power plant is able to burn the fuel perfectly as seen in complete combustion, such products are always produced in some quantity. Each fossil fuel power plant is a highly complex, custom-designed system. Present construction costs, [[as of 2004]], run to [[United States dollar|US$]]1,300 per [[kilowatt]], or $650 million for a 500 [[megawatt|MW]] unit. Multiple generating units may be built at a single site for more efficient use of [[land use|land]], [[natural resource]]s and [[labor (economics)|labor]]. ==Fuel transport and delivery== [[Image:SSPX0347.jpg|thumb|250px|Coal Power Station in Tampa FL]] Coal is delivered by highway [[truck]], [[railroad|rail]], [[barge]] or [[Collier (ship type)|collier]] ship. Some plants are even built near coal mines and coal is delivered by conveyors. A large coal [[train]] called a "unit train" may be two kilometers (over a mile) long, containing 100 cars with 100 [[ton]]s of coal in each one, for a total load of 10,000 tons. A large plant under full load requires at least one coal delivery this size every day. Plants may get as many as three to five trains a day, especially in "peak season", during the summer months when power consumption is high. A large thermal power plant such as the one in [[Nanticoke Generating Station|Nanticoke]], Ontario stores several million tons of coal for winter use when the lakes are frozen. Modern unloaders use rotary dump devices, which eliminate problems with coal freezing in bottom dump cars. The unloader includes a train positioner arm that pulls the entire train to position each car over a coal hopper. The dumper clamps an individual car against a platform that swivels the car upside down to dump the coal. Swiveling couplers enable the entire operation to occur while the cars are still coupled together. Unloading a unit train takes about three hours. Shorter trains may use railcars with an "air-dump", which relies on air pressure from the engine plus a "hot shoe" on each car. This "hot shoe" when it comes into contact with a "hot rail" at the unloading trestle, shoots an electric charge through the air dump apparatus and causes the doors on the bottom of the car to open, dumping the coal through the opening in the trestle. Unloading one of these trains takes anywhere from an hour to an hour and a half. Older unloaders may still use manually operated bottom-dump rail cars and a "shaker" attached to dump the coal. Generating stations adjacent to a mine may receive coal by [[conveyor belt]] or massive [[diesel-electric]]-drive trucks. A collier (cargo ship carrying coal) may hold 40,000 tons of coal and takes several days to unload. Some colliers carry their own conveying equipment to unload their own bunkers; others depend on equipment at the plant. Colliers are large, seaworthy, self-powered ships. For transporting coal in calmer waters, such as rivers and lakes, flat-bottomed vessels called [[barge]]s are often used. Barges are usually unpowered and must be moved by [[tugboat]]s or [[towboat]]s. For startup or auxiliary purposes, the plant may use [[fuel oil]] as well. Fuel oil can be delivered to plants by [[Pipeline transport|pipeline]], [[Tanker (ship)|tanker]], [[tank car]] or truck. Oil is stored in vertical cylindrical steel tanks with capacities as high as 90,000 barrels' worth (14,000 m³, or about 5 million US gallons). The [[viscosity|heavier]] no. 5 "bunker" and no. 6 fuels are typically steam-heated before pumping in cold climates. Plants fuelled by natural gas are usually built adjacent to gas transport pipelines or have dedicated gas pipelines extended to them. ==Fuel processing== Coal is prepared for use by crushing the rough coal to pieces less than 2 inches (50 mm) in size. The coal is then transported from the storage yard to in-plant storage silos by rubberized [[conveyor belt]]s at rates up to 4,000 tons/hour. In plants that burn pulverized coal, silos feed coal [[pulverizer]]s (coal mill) that take the larger 2 inch pieces grind them into the consistency of [[talcum powder|face powder]], classify them, and mixes them with primary combustion air which transports the coal to the furnace and preheats the coal to drive off excess moisture content. A 500 MWe plant will have six such pulverizers, five of which can supply coal to the furnace at 250 tons per hour under full load. In plants that do not burn pulverized coal, the larger 2 inch pieces may be directly fed into the silos which then feed the [[Cyclone furnace|cyclone]] burners, a specific kind of combustor that can efficiently burn larger pieces of fuel. ==Feedwater heating and deaeration== The feedwater used in the [[steam]] boiler is a means of transferring heat energy from the burning fuel to the mechanical energy of the spinning [[steam turbine]]. The total feedwater consists of recirculated ''condensate'' water and purified ''makeup water''. Because the metallic materials it contacts are subject to [[corrosion]] at high temperatures and pressures, the makeup water is highly purified before use. A system of [[water softener]]s and [[ion exchange]] demineralizers produces water so pure that it coincidentally becomes an electrical [[Electrical insulation|insulator]], with [[electrical conductivity|conductivity]] in the range of 0.3&ndash;1.0 microsiemens per centimeter. The makeup water in a 500 MWe plant amounts to perhaps 20 US gallons per minute (1.25 L/s) to offset the small losses from steam leaks in the system. The feedwater cycle begins with condensate water being pumped out of the [[Surface condenser|condenser]] after traveling through the steam turbines. The condensate flow rate at full load in a 500 MWe plant is about 6,000 US gallons per minute (0.38 m³/s). [[Image:Deaerator.png|thumb|391 px|right|Diagram of boiler feed water deaerator (with vertical, domed aeration section and horizontal water storage section]] The water flows through a series of six or seven intermediate [[feedwater heater]]s, heated up at each point with steam extracted from an appropriate duct on the turbines and gaining temperature at each stage. Typically, the condensate plus the makeup water then flows through a [[deaerator]]<ref name=Spirax>[http://www.spiraxsarco.com/resources/steam-engineering-tutorials/the-boiler-house/pressurised-deaerators.asp#head5 Pressurized deaerators]</ref><ref>[http://www.usfilter.com/NR/rdonlyres/27278F1E-8378-404B-B0F2-1C9CDCAABB20/0/trey_deaerator_brochure.pdf Tray deaerating heaters]</ref> that removes dissolved air from the water, further purifying and reducing its corrosivity. The water may be dosed following this point with [[hydrazine]], a chemical that removes the remaining [[oxygen]] in the water to below 5 parts per billion (ppb). It is also dosed with [[pH]] control agents such as [[ammonia]] or [[morpholine]] to keep the residual [[acid]]ity low and thus non-corrosive. ==Boiler operation== The boiler is a rectangular [[furnace]] about 50 ft (15 m) on a side and 130 ft (40 m) tall. Its walls are made of a web of high pressure steel tubes about 2.3 inches (60 mm) in diameter. [[Coal dust|Pulverized coal]] is air-blown into the furnace from fuel nozzles at the four corners and it rapidly burns, forming a large fireball at the center. The [[thermal radiation]] of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter. The water circulation rate in the boiler is three to four times the throughput and is typically driven by pumps. As the water in the [[boiler]] circulates it absorbs heat and changes into steam at 700 °F (370 °C) and 3,200 psi (22.1 [[Pascal (unit)|MPa]]). It is separated from the water inside a drum at the top of the furnace. The saturated steam is introduced into [[superheat]] pendant tubes that hang in the hottest part of the combustion gases as they exit the furnace. Here the steam is superheated to 1,000 °F (540 °C) to prepare it for the turbine. Plants designed for [[lignite]] (brown coal) are increasingly used in locations as varied as [[Germany]], [[Victoria (Australia)|Victoria]], and [[North Dakota]]. Lignite is a much younger form of coal than black coal. It has a lower energy density than black coal and requires a much larger furnace for equivalent heat output. Such coals may contain up to 70% water and ash, yielding lower furnace temperatures and requiring larger induced-draft fans. The firing systems also differ from black coal and typically draw hot gas from the furnace-exit level and mix it with the incoming coal in fan-type mills that exhaust the pulverized coal and hot gas mixture into the boiler. Plants that use gas turbines to heat the water for conversion into steam use boilers known as HRSGs, Heat Recovery Steam Generators. The exhaust (waste) heat from the gas turbines is used to make superheated steam that is then used in a conventional water-steam generation cycle. ==Steam turbine generator== [[Image:Dampfturbine Laeufer01.jpg|thumb|right|250px|Rotor of a modern steam turbine, used in a power station]] The turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft. There is a high pressure turbine at one end, followed by an intermediate pressure turbine, two low pressure turbines, and the generator. As steam moves through the system and loses pressure and thermal energy it expands in volume, requiring increasing diameter and longer blades at each succeeding stage to extract the remaining energy. The entire rotating mass may be over 200 tons and 100 ft (30 m) long. It is so heavy that it must be kept turning slowly even when shut down (at 3 rpm) so that the shaft will not bow even slightly and become unbalanced. This is so important that it is one of only five functions of blackout emergency power batteries on site. Other functions are [[emergency lighting]], [[communication]], station alarms and turbogenerator lube oil. Superheated steam from the boiler is delivered through 14&ndash;16 inch (350&ndash;400 mm) diameter piping to the high pressure turbine where it falls in pressure to 600 psi (4 MPa) and to 600 °F (315 °C) through the stage. It exits via 24&ndash;26 inch (600&ndash;650 mm) diameter cold reheat lines and passes back into the boiler where the steam is reheated in special reheat pendant tubes back to 1,000 °F (540 °C). The hot reheat steam is conducted to the intermediate pressure turbine where it falls in both [[temperature]] and [[pressure]] and exits directly to the long-bladed low pressure turbines and finally exits to the condenser. The generator, 30 ft (9 m) long and 12 ft (3.7 m) diameter, contains a stationary [[stator]] and a spinning [[Rotor (electric)|rotor]], each containing miles of heavy [[copper]] conductor&mdash;no permanent [[magnet]]s here. In operation it generates up to 21,000 [[ampere|amps]] at 24,000 [[volts]] [[Alternating current|AC]] (504 MWe) as it spins at either 3,000 or 3,600 RPM, synchronized to the [[power grid]]. The rotor spins in a sealed chamber cooled with [[hydrogen]] gas, selected because it has the highest known [[heat transfer coefficient]] of any gas and for its low [[viscosity]] which reduces [[windage]] losses. This system requires special handling during startup, with air in the chamber first displaced by [[carbon dioxide]] before filling with hydrogen. This ensures that the highly [[flammable]] hydrogen-[[oxygen]] environment is not created. The [[utility frequency|power grid frequency]] is 60 [[Hertz|Hz]] across [[North America]] and 50 Hz in [[Europe]], [[Oceania]], [[Asia]] ([[Korea]] and parts of [[Japan]] are notable exceptions) and parts of [[Africa]]. The electricity flows to a distribution yard where [[transformer]]s step the voltage up to 115, 230, 500 or 765 kV AC as needed for transmission to its destination. ==Steam condensing== [[Image:Surface Condenser.png|thumb|right|354 px|Diagram of a typical water-cooled surface condenser]] The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the [[Rankine cycle|cycle]] increases. The condenser is usually a [[shell and tube heat exchanger]] commonly referred to as a [[surface condenser]]. Cooling water circulates through the tubes in the condenser's shell and the low pressure exhaust steam is condensed by flowing over the tubes as shown in the adjacent diagram. The tubing is designed to reduce the exhaust pressure, avoid subcooling the condensate and provide adequate air extraction. Typically the cooling water causes the steam to condense at a temperature of about 32&ndash;38 °C (90&ndash;100 °F) and that creates an absolute pressure in the condenser of about 5&ndash;7 kPa (1.5&ndash;2.0 in Hg), a vacuum of about 95 kPa (28 in Hg) relative to atmospheric pressure. The condenser, in effect, creates the low pressure required to drag steam through and increase the efficiency of the turbines. The limiting factor is the temperature of the cooling water and that, in turn, is limited by the prevailing average climatic conditions at the power plant's location (it may be possible to lower the temperature beyond the turbine limits during winter, causing excessive condensation in the turbine). From the bottom of the condenser, powerful [[condensate pump]]s recycle the condensed steam (water) back to the water/steam cycle. [[Image:A Marley industrial cooling tower.jpg|thumb|150px|right|A Marley mechanical induced draft cooling tower]]The heat absorbed by the circulating cooling water in the condenser tubes must also be removed to maintain the ability of the water to cool as it circulates. This is done by pumping the warm water from the condenser through either natural draft, forced draft or induced draft [[cooling tower]]s (as seen in the image to the right) that reduce the temperature of the water by evaporation, about 11&ndash;17 °C (20&ndash;30 °F) - expelling [[waste heat]] to the atmosphere. The circulation flow rate of the cooling water in a 500 [[MWe]] unit is about 14.2 m³/s (225,000 US gal/minute) at full load.<ref>[http://www.epa.gov/ostwater/presentations/maulbetsch.pdf EPA Workshop on Cooling Water Intake Technologies Arlington, Virginia] John Maulbetsch, Maulbetsch Consulting Kent Zammit, EPRI. [[6 May]] [[2003]]. Retrieved [[10 September]] [[2006]]. </ref> The condenser tubes are made of [[brass]] or [[stainless steel]] to resist corrosion from either side. Nevertheless they may become internally fouled during operation by bacteria or algae in the cooling water or by mineral scaling, all of which inhibit heat transfer and reduce [[thermodynamic efficiency]]. Many plants include an automatic cleaning system that circulates [[sponge rubber ball]]s through the tubes to scrub them clean without the need to take the system off-line. The cooling water used to condense the steam in the condenser returns to its source without having been changed other than having been warmed. If the water returns to a local water body (rather than a circulating cooling tower), it is tempered with cool 'raw' water to prevent thermal shock when discharged into that body of water. Another form of condensing system is the air-cooled condenser. The process is similar to that of a [[radiator]] and fan. Exhaust heat from the low pressure section of a steam turbine runs through the condensing tubes, the tubes are usually finned and ambient air is pushed through the fins with the help of a large fan. The steam condenses to water to be reused in the water-steam cycle. Air-cooled condensers typically operate at a higher temperature than water cooled versions. Whilst saving water, the efficiency of the cycle is reduced (resulting in more carbon dioxide per MW of electricity). == Diagram== [[Image:PowerStation2.svg|thumb|center|595px|'''Simplified thermal power station''' {| |style="width:250px" | 1. [[Cooling tower]] |style="width:250px" | 10. [[Control valve|Steam control valve]] |style="width:250px" | 19. [[Superheater]] |- | 2. [[Cooling tower system|Cooling water pump]] | 11. High pressure [[steam]] turbine | 20. Forced draught (draft) [[Centrifugal fan|fan]] |- | 3. [[Three-phase]] [[Electrical power transmission|transmission line]] | 12. [[Deaerator]] | 21. Reheater |- | 4. Step-up [[Transformer]] | 13. [[Feedwater heater]] | 22. [[Combustion]] air intake |- | 5. [[Electrical generator]] | 14. [[Coal]] [[conveyor]] | 23. [[Economiser]] |- | 6. Low pressure [[steam turbine]] | 15. [[Coal]] hopper | 24. [[Air preheater]] |- | 7. [[Boiler feedwater pump]] | 16. [[Pulverizer|Coal pulverizer]] | 25. [[Electrostatic precipitator|Precipitator]] |- | 8. [[Surface condenser]] | 17. [[Steam drum|Boiler steam drum]] | 26. Induced draught (draft) [[Centrifugal fan|fan]] |- | 9. Intermediate pressure [[steam turbine]] | 18. [[Bottom ash]] hopper | 27. [[Flue gas stack]] |} ]] ==Stack gas path and cleanup== :''see [[Flue gas emissions from fossil fuel combustion]] and [[Flue gas desulfurization]] for more details'' As the combustion [[flue gas]] exits the boiler it is routed through a rotating flat basket of metal mesh which picks up heat and returns it to incoming fresh air as the basket rotates, This is called the [[air preheater]]. The gas exiting the boiler is laden with [[fly ash]], which are tiny spherical ash particles. The flue gas contains [[nitrogen]] along with combustion products [[carbon dioxide]], [[sulfur dioxide]], and [[nitrogen oxide]]s. The fly ash is removed by [[Dust collector#Types of Baghouses|fabric bag filter]]s or [[electrostatic precipitator]]s. Once removed, the fly ash byproduct can sometimes be used in the manufacturing of [[concrete]]. This cleaning up of flue gases, however, only occurs in plants that are fitted with the appropriate technology. Still, the majority of coal fired power plants in the world do not have these facilities.{{Fact|date=February 2007}} Legislation in Europe has been efficient to reduce flue gas pollution. Japan has been using flue gas cleaning technology for over 30 years and the US has been doing the same for over 25 years. China is now beginning to grapple with the pollution caused by coal fired power plants. [[Image:PowerPlantEkibastus.jpg|thumb|right|280px|Flue gas stack at [[GRES-2 Power Station]] in Ekibastus, Kazakhstan]] Where required by law, the sulfur and nitrogen oxide [[pollutant]]s are removed by [[flue gas desulfurization|stack gas scrubber]]s which use a pulverized [[limestone]] or other [[alkaline]] wet slurry to remove those pollutants from the exit stack gas. The gas travelling up the [[flue gas stack]] may by this time have dropped to about 50 °C (120 °F). A typical flue gas stack may be 150–180 m (500–600 ft) tall to disperse the remaining flue gas components in the atmosphere. The tallest flue gas stack in the world is 420 m (1,375 ft) tall at the [[GRES-2 Power Station|GRES-2]] power plant in [[Ekibastusz]], [[Kazakhstan]]. In the United States and a number of other countries, [[atmospheric dispersion modeling]]<ref>{{cite book|author=Beychok, Milton R.|title=[[Fundamentals Of Stack Gas Dispersion]]|edition=4th Edition|publisher=author-published|year=2005|id=ISBN 0-9644588-0-2}} [http://www.air-dispersion.com www.air-dispersion.com]</ref> studies are required to determine the flue gas stack height needed to comply with the local [[air pollution]] regulations. The United State also limits the maximum height of a flue gas stack to what is known as the "[[Good Engineering Practice]] (GEP)" stack height.<ref>''Guideline for Determination of Good Engineering Practice Stack Height (Technical Support Document for the Stack Height Regulations), Revised'', 1985, EPA Publication No. EPA–450/4–80–023R, U.S. Environmental Protection Agency (NTIS No. PB 85–225241)</ref><ref>Lawson, Jr., R.E. and W.H. Snyder, 1983. ''Determination of Good Engineering Practice Stack Height: A Demonstration Study for a Power Plant'', 1983, EPA Publication No. EPA–600/3–83–024. U.S. Environmental Protection Agency (NTIS No. PB 83–207407)</ref> In the case of existing flue gas stacks that exceed the GEP stack height, any air pollution dispersion modeling studies for such stacks must use the GEP stack height rather than the actual stack height. ==Supercritical steam plants== Above the [[critical point (thermodynamics)|critical point]] for water of 705 °F (374 °C) and 3,212 psia (22.1 MPa), there is no [[phase transition]] from 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 a new type of design is required for plants wishing to take advantage of increased [[thermodynamic efficiency]] available at the higher temperatures. These plants, also called ''once-through'' plants because boiler water does not circulate multiple times, require additional water purification steps to ensure that any impurities picked up during the cycle will be removed. This takes the form of high pressure ion exchange units called [[condensate polisher]]s between the steam condenser and the feedwater heaters. Subcritical fossil fuel power plants can achieve 36–38% efficiency. [[Supercritical fluid|Supercritical]] designs have efficiencies in the low to mid 40% range, with new "ultra critical" designs using pressures of 4,400 psia (30 MPa) and dual stage reheat reaching about 48% efficiency. Older [[nuclear power plant]]s must operate below the temperatures and pressures that coal fired plants do. This limits their thermodynamic efficiency to the order of 34–37%. Advanced designs, such as the [[Advanced gas-cooled reactor]] and the [[Supercritical water reactor]], operate at temperatures and pressures similar to current coal plants, producing comparable efficiency. ==Gas turbine combined-cycle plants== [[Image:GE H series Gas Turbine.jpg|thumb|right|300px|480 [[megawatt]] GE H series power generation gas turbine]] [[Image:Misc3 046.jpg|thumb|300px|Currant Creek Power Plant near [[Mona, Utah]] is a natural gas fired combined cycle electrical plant.]] One type of fossil fuel power plant uses a [[gas turbine]] in conjunction with a [[heat recovery steam generator]] (HRSG). It is referred to as a [[combined cycle]] power plant because it combines the [[Brayton cycle]] of the gas turbine with the [[Rankine cycle]] of the HRSG. The thermal efficiency of these plants has reached a record [[thermal efficiency|heat rate]] of 5690 Btu/kWh, or just under 60%, at a facility in Baglan Bay, Wales. <ref>[http://www.ge-energy.com/prod_serv/products/gas_turbines_cc/en/h_system/index.htm GE Power’s H Series Turbine]</ref> The turbines are fueled either with [[natural gas]] or [[fuel oil]]. While more efficient and faster to construct (a 1,000 MW plant may be completed in as little as 18 months from start of construction), the economics of such plants is heavily influenced by the volatile cost of natural gas. The combined cycle plants are designed in a variety of configurations composed of the number of gas turbines followed by the steam turbine. For example, a 3-1 combined cycle facility has three gas turbines tied to one steam turbine. The configurations range from (1-1),(2-1),(3-1),(4-1), (5-1), to (6-1) Simple-cycle gas turbine plants, without a steam cycle, are sometimes installed as emergency or [[peaking power plant|peaking]] capacity; their thermal efficiency is much lower. The high running cost per hour is offset by the low capital cost and the intention to run such units only a few hundred hours per year. ==Environmental impacts== The [[World energy resources and consumption|world's power demands]] are expected to rise 60% by 2030.<ref name=WorldOutlook2004> {{Citation | title = World Outlook 2004 | publisher = [[International Energy Agency|IEA]] | date = [[2004-10-26]] | url = http://www.iea.org/textbase/nppdf/free/2004/weo2004.pdf | accessdate = [[2006-06-13]] | pages = p. 31 | location = Paris | isbn = 92-64-1081-73 }}</ref> With the world-wide total of active coal plants over 50,000 and rising,<ref>{{cite news | title = Carbon Dioxide Emissions From Power Plants Rated Worldwide | work = | pages = | language = English | publisher = Science News | date = 2007-11-15 | url = http://www.sciencedaily.com/releases/2007/11/071114163448.htm | accessdate = 2008-01-29}}</ref> the [[International Energy Agency|IEA]] estimates that fossil fuels will still account for 85% of the energy market by 2030.<ref name=WorldOutlook2004/> World organizations, and international agencies like the IEA are concerned about the environmental impact of burning fossil fuels. According to a 2005 report from the WWF, coal power stations are at the top of the [[List of least carbon efficient power stations]] in terms of the level of carbon dioxide produced per unit of electricity generated. The combustion of fossil fuels contributes to [[acid rain]], [[global warming]], and [[air pollution]] due to the impurities and chemical composition of the fuel (electricity generation is responsible for 41 percent of US manmade carbon dioxide emissions).<ref>[http://www.epa.gov/climatechange/emissions/co2_human.html Human-Related Sources and Sinks of Carbon Dioxide] 2005 figures</ref> Acid rain is caused by the emission of nitrogen oxides and sulfur dioxide into the air. These themselves may be only mildly acidic, yet when it reacts with the atmosphere, it creates acidic compounds such as [[sulfurous acid]], [[nitric acid]] and [[sulfuric acid]] that fall as rain, hence the term acid rain. In Europe and the USA, stricter emission laws have reduced the environmental hazards associated with this problem.{{Fact|date=January 2008}} Another danger related to coal combustion is the emission of [[particulates]] that are dangerous for public health. Natural gas plants emit virtually no particulates. Power plants remove particulate from the flue gas with the use of a [[Dust collector#Fabric_filters|bag house]] or [[electrostatic precipitator]]. Several newer plants that burn coal use a different process, [[Combined cycle#Integrated Gasification Combined Cycle (IGCC)|Integrated Gasification Combined Cycle]] in which [[synthesis gas]] is made out of a reaction between coal and water. This is purified of most pollutants and then used initially to power gas turbines, then the residual heat is used for a steam turbine. The pollution levels of such plants are drastically lower than those of "classical" coal power plants.{{Fact|date=January 2008}} However, all fossil fuel burning power plants emit [[carbon dioxide]]. Research has shown that increased concentration of carbon dioxide in the atmosphere is positively correlated with a rise in mean global temperature, also known as [[climate change]].{{Fact|date=January 2008}} Fossil fueled power stations are major emitters of [[greenhouse gases]](GHG) such as [[carbon dioxide]] which cause [[climate change]], [[global warming]] and associated [[sea level rise]]. Brown coal emits 3 times as much GHG as natural gas, black coal emits twice as much. The [[International Panel on Climate Change]] ([[IPCC]]) says that to avoid dangerous climate change Annexe 1 (developed) countries must reduce GHG emissions by between 25 and 40% by 2020. If emissions are to be reduced coal fired power stations must close as [[carbon capture and storage]] of emissions from coal fired power stations is not expected to be available on a commercial scale and economically viable basis by 2020, if at all. Coal also contains low levels of [[uranium]], [[thorium]], and other naturally-occurring [[radioactive isotopes]] whose release into the environment leads to radioactive contamination. While these substances are present as very small trace impurities, enough coal is burned that significant amounts of these substances are released. A 1,000 MW coal-burning power plant could release as much as 5.2 tons/year of uranium (containing 74 pounds of [[uranium-235]]) and 12.8 tons/year of thorium. The radioactive emission from this coal power plant is 100 times greater than a comparable nuclear power plant with the same electrical output; including processing output, the coal power plant's radiation output is over 3 times greater.<ref>[http://www.ornl.gov/info/ornlreview/rev26-34/text/colmain.html Coal Combustion: Nuclear Resource or Danger?] by Alex Gabbard, [[ORNL]] Review, Summer/Fall 1993, Vol.26, Nos.3 and 4.</ref> Trace amounts of mercury exist in coal and other fossil fuels.<ref name=DOE>{{cite web |url=http://www.fossil.energy.gov/programs/powersystems/pollutioncontrols/overview_mercurycontrols.html |title= Mercury emissions control R&D |publisher= U.S. Dept. of Energy |date=2006-01-18 |accessdate=2008-01-27}}</ref> When these fuels burn, toxic mercury is released which accumulates in food chains and is especially harmful to aquatic ecosystems. The worldwide emission of mercury from both natural and human sources was an estimated 5,500 tons in 1995.<ref name=DOE/> U.S. coal-fired plants emit an estimated 48 tons annually, which is approximately 1/3 of all mercury emitted into the air by human activity in the U.S.<ref name=DOE/> In contrast, China's coal-fired power plants emitted an estimated 68 tons of mercury in 1999, which was about 38% of Chinese human-generated mercury emissions.<ref>{{cite journal |journal= Atmos Environ |date=2005 |volume=39 |issue=40 |pages=7789–806 |title= Anthropogenic mercury emissions in China |author= Streets DG, Hao J, Wu Y ''et al.'' |doi=10.1016/j.atmosenv.2005.08.029}}</ref> Alternatives to fossil fuel power plants include [[nuclear power]], [[solar power]] and other [[renewable energy|renewable energies]] (see [[non-carbon economy]]). ==Clean coal== {{main|clean coal}} [[Image:Grand Junction Trip 92007 098.JPG|thumb|300px|right|Coal fired power plants provide more than 50% of consumed electricity in the United States. This is the Castle Gate Plant near [[Helper, Utah]].]] '''Clean coal''' is the name attributed to [[coal]] chemically washed of [[mineral]]s and impurities, sometimes [[Gasification|gasified]], burned and the resulting flue gases treated with steam, with the purpose of removing sulfur dioxide, and reburned so as to make the carbon dioxide in the flue gas economically recoverable. The coal industry uses the term "clean coal" to describe technologies designed to enhance both the efficiency and the environmental acceptability of coal extraction, preparation and use<ref>[http://www.australiancoal.com.au/cleanoview.htm AustralianCoal.com.au] - Clean Coal Overview</ref>, with no specific quantitative limits on any emissions, particularly carbon dioxide. ==See also== *[[Boiler]] *[[Combined heat and power]] *[[Cooling tower system]] *[[Flue gas stacks]] *[[Geothermal power]] *[[Global warming]] *[[Greenhouse gas]] *[[Power station]] *[[Thermal power station]] *[[Water-tube boiler]] *[[Mercury vapour turbine]] {{commons|Category:Coal power plants|Category:Coal power plants}} ==References== <!-- ---------------------------------------------------------- See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for a discussion of different citation methods and how to generate footnotes using the <ref>, </ref> and <reference /> tags ----------------------------------------------------------- --> {{reflist}} ==Bibliography== *''Steam: Its Generation and Use'' (2005). 41st edition, Babcock & Wilcox Company, ISBN 0-9634570-0-4 *''Steam Plant Operation'' (2005). 8th edition, Everett B. Woodruff, Herbert B. Lammers, Thomas F. Lammers (coauthors), McGraw-Hill Professional, ISBN 0-07-141846-6 *''Power Generation Handbook: Selection, Applications, Operation, Maintenance'' (2003). Philip Kiameh, McGraw-Hill Professional, ISBN 0-07-139604-7 *''Standard Handbook of Powerplant Engineering'' (1997). 2nd edition, Thomas C. Elliott, Kao Chen, Robert Swanekamp (coauthors), McGraw-Hill Professional, ISBN 0-07-019435-1 ==External links== *[http://www.tva.gov/power/coalart.htm Power plant diagram] *[http://www.processassociates.com/bookshelf/units/power_plant_1.htm Power Plant Reference Books] *[http://www.marleyct.com/wet/ Large industrial cooling towers] *[http://www.coinalbum.org/page-us-historic-electricity-463.html Historic Production of Electricity by Fossil Fuels] * [http://www.nytimes.com/2008/07/01/business/01coal.html?_r=1&ref=business&oref=slogin Georgia Judge Cites Carbon Dioxide in Denying Coal Plant Permit]. {{DEFAULTSORT: }} [[Category:Chemical engineering]] [[Category:Power station technology]] [[Category:Coal-fired power stations]] [[Category:Oil-fueled power stations]] [[Category:Oil shale-fired power stations]] [[es:central térmica]] [[fa:نیروگاه سوخت فسیلی]] [[id:PLTU Batubara]] [[pt:Usina termelétrica]]