Editing Power station (section)

==Thermal power stations==
{{Main|Thermal power station}}
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In thermal power stations, mechanical power is produced by a [[heat engine]] that transforms [[thermal energy]], often from [[combustion]] of a [[fuel]], into rotational energy. Most thermal power stations produce steam, so they are sometimes called steam power stations. Not all thermal energy can be transformed into mechanical power, according to the [[second law of thermodynamics]]; therefore, there is always heat lost to the environment. If this loss is employed as useful heat, for industrial processes or [[district heating]], the power plant is referred to as a [[cogeneration]] power plant or CHP (combined heat-and-power) plant. In countries where district heating is common, there are dedicated heat plants called [[heat-only boiler station]]s. An important class of power stations in the Middle East uses by-product heat for the [[desalination]] of water.

The efficiency of a thermal power cycle is limited by the maximum working fluid temperature produced. The efficiency is not directly a function of the fuel used. For the same steam conditions, coal-, nuclear- and gas power plants all have the same theoretical efficiency. Overall, if a system is on constantly (base load) it will be more efficient than one that is used intermittently (peak load). Steam turbines generally operate at higher efficiency when operated at full capacity.

Besides use of reject heat for process or district heating, one way to improve overall efficiency of a power plant is to combine two different thermodynamic cycles in a [[combined cycle]] plant. Most commonly, [[exhaust gas]]es from a gas turbine are used to generate steam for a boiler and a steam turbine. The combination of a "top" cycle and a "bottom" cycle produces higher overall efficiency than either cycle can attain alone.

In 2018, [[Inter RAO UES]] and [https://g.esgcc.com.cn/ State Grid] {{Webarchive|url=https://web.archive.org/web/20211221190902/https://g.esgcc.com.cn/ |date=21 December 2021 }} planned to build an 8-GW thermal power plant, <ref>{{cite news|url=http://www.mofcom.gov.cn/article/i/jyjl/e/201807/20180702769118.shtml|title=China and Russia accelerate pace of power cooperation|date=2018-07-24|publisher=[[Ministry of Commerce (China)|Ministry of Commerce]]|access-date=29 July 2020|archive-date=4 February 2023|archive-url=https://web.archive.org/web/20230204142009/http://www.mofcom.gov.cn/404.shtml|url-status=live}}</ref> which's the largest [[coal-fired power plant]] construction project in [[Russia]].<ref>{{cite news|url=http://www.cankaoxiaoxi.com/finance/20180604/2276134.shtml|title=Inter RAO UES cooperates with State Grid Corporation of China|date=2018-06-04|publisher=[[Reference News]]|access-date=29 July 2020|archive-date=4 February 2023|archive-url=https://web.archive.org/web/20230204142011/http://www.cankaoxiaoxi.com/finance/20180604/2276134.shtml|url-status=live}}</ref>
===Classification===
[[File:Ikata Nuclear Powerplant.JPG|thumb|[[Ikata Nuclear Power Plant]], [[Japan]]]]
[[File:Martinlaakson voimalaitos.JPG|thumb|A large gas and coal power plant in [[Martinlaakso]], [[Vantaa]], Finland]]
[[File:NesjavellirPowerPlant edit2.jpg|thumb|[[Nesjavellir Geothermal Power Station]], [[Iceland]]]]

====By heat source====
* [[Fossil-fuel power station]]s may also use a steam turbine generator or in the case of natural [[gas-fired power plant]]s may use a [[gas turbine|combustion turbine]]. A coal-fired power station produces heat by burning coal in a steam boiler. The steam drives a [[steam turbine]] and [[electric generator|generator]] that then produces [[electricity]]. The waste products of combustion include ash, [[sulfur dioxide]], [[nitrogen oxides]], and [[carbon dioxide]]. Some of the gases can be removed from the waste stream to reduce pollution. 
* [[Nuclear power plant]]s<ref>[http://www.iaea.org/cgi-bin/db.page.pl/pris.oprconst.htm Nuclear Power Plants Information] {{Webarchive|url=https://web.archive.org/web/20050213081431/http://www.iaea.org/cgi-bin/db.page.pl/pris.oprconst.htm |date=13 February 2005 }}, by [[International Atomic Energy Agency]]</ref> use the heat generated in a [[nuclear reactor]]'s core (by the [[Nuclear fission|fission]] process) to create steam which then operates a steam turbine and generator. About 20 percent of electric generation in the US is produced by nuclear power plants.
* [[Geothermal power]] plants use steam extracted from hot underground rocks. These rocks are heated by the decay of radioactive material in the Earth's core.<ref>{{Cite web |last=Roberts |first=David |date=2020-10-21 |title=Geothermal energy is poised for a big breakout |url=https://www.vox.com/energy-and-environment/2020/10/21/21515461/renewable-energy-geothermal-egs-ags-supercritical |access-date=2022-04-13 |website=Vox |language=en |archive-date=4 February 2023 |archive-url=https://web.archive.org/web/20230204142009/https://www.vox.com/energy-and-environment/2020/10/21/21515461/renewable-energy-geothermal-egs-ags-supercritical |url-status=live }}</ref>
* [[Biomass#Energy|Biomass-fuelled power plants]] may be fuelled by [[bagasse|waste from sugar cane]], [[Incineration|municipal solid waste]], landfill [[methane]], or other forms of [[biomass]].
* In integrated [[steel mill]]s, [[Blast furnace gas|blast furnace exhaust gas]] is a low-cost, although low-energy-density, fuel.
* [[Cogeneration|Waste heat from industrial processes]] is occasionally concentrated enough to use for power generation, usually in a steam boiler and turbine.
* [[Solar thermal energy|Solar thermal]] electric plants use sunlight to boil water and produce steam which turns the generator.
* [[Combined cycle hydrogen power plant|Hydrogen power plant]]s can use [[green hydrogen]] from [[Electrolysis of water|electrolysis]] to help balance supply and demand from [[Variable renewable energy]] sources.<ref>{{cite magazine|url=https://www.powermag.com/ready-for-the-energy-transition-hydrogen-considerations-for-combined-cycle-power-plants/|title=Ready for the Energy Transition: Hydrogen Considerations for Combined Cycle Power Plants|first=Sebastian|last=Mulder|date=Oct 29, 2021|magazine=Power}}</ref>

====By prime mover====
A prime mover is a machine that converts energy of various forms into energy of motion.
* [[Steam turbine]] plants use the dynamic pressure generated by expanding steam to turn the blades of a turbine. Almost all large non-hydro plants use this system. About 90 percent of all electric power produced in the world is through use of steam turbines.<ref name="Wiser">{{Cite book |last=Wiser |first=Wendell H. |url=https://books.google.com/books?id=UmMx9ixu90kC&pg=PA190 |title=Energy resources: occurrence, production, conversion, use |publisher=Birkhäuser |year=2000 |isbn=978-0-387-98744-6 |page=190 |access-date=21 November 2015 |archive-date=23 January 2023 |archive-url=https://web.archive.org/web/20230123202054/https://books.google.com/books?id=UmMx9ixu90kC&pg=PA190 |url-status=live }}</ref>
* [[Gas turbine]] plants use the dynamic pressure from flowing gases (air and combustion products) to directly operate the turbine. Natural-gas fuelled (and oil fueled) combustion turbine plants can start rapidly and so are used to supply "peak" energy during periods of high demand, though at higher cost than base-loaded plants. These may be comparatively small units, and sometimes completely unmanned, being remotely operated. This type was pioneered by the UK, [[Pocket Power Stations|Princetown]]<ref>[http://www.swehs.co.uk/docs/news13su.html SWEB's Pocket Power Stations<!-- Bot generated title -->] {{webarchive|url=https://web.archive.org/web/20060504055822/http://www.swehs.co.uk/docs/news13su.html |date=4 May 2006 }}</ref> being the world's first, commissioned in 1959.
* [[Combined cycle]] plants have both a gas turbine fired by natural gas, and a steam boiler and steam turbine which use the hot exhaust gas from the gas turbine to produce electricity. This greatly increases the overall efficiency of the plant, and many new baseload power plants are combined cycle plants fired by natural gas.
* Internal combustion [[reciprocating engine]]s are used to provide power for isolated communities and are frequently used for small cogeneration plants. Hospitals, office buildings, industrial plants, and other critical facilities also use them to provide backup power in case of a power outage. These are usually fuelled by diesel oil, heavy oil, [[natural gas]], and [[landfill gas]].
* [[Gas turbine#Microturbines|Microturbines]], [[Stirling engine]] and internal combustion reciprocating engines are low-cost solutions for using opportunity fuels, such as [[landfill gas]], digester gas from water treatment plants and waste gas from oil production.{{Citation needed|date=July 2021}}

====By duty====
Power plants that can be dispatched (scheduled) to provide energy to a system include:
* [[Base load power plant]]s run nearly continually to provide that component of system load that does not vary during a day or week. Baseload plants can be highly optimized for low fuel cost, but may not start or stop quickly during changes in system load. Examples of base-load plants would include large modern coal-fired and nuclear generating stations, or hydro plants with a predictable supply of water.
* [[Peaking power plant]]s meet the daily peak load, which may only be for one or two hours each day. While their incremental operating cost is always higher than base load plants, they are required to ensure security of the system during load peaks. Peaking plants include simple cycle gas turbines and reciprocating internal combustion engines, which can be started up rapidly when system peaks are predicted. Hydroelectric plants may also be designed for peaking use.  
* [[Load following power plant]]s can economically follow the variations in the daily and weekly load, at lower cost than peaking plants and with more flexibility than baseload plants.

Non-dispatchable plants include such sources as wind and solar energy; while their long-term contribution to system energy supply is predictable, on a short-term (daily or hourly) base their energy must be used as available since generation cannot be deferred. Contractual arrangements ("take or pay") with independent power producers or system interconnections to other networks may be effectively non-dispatchable.{{Citation needed|date=July 2021}}

===Cooling towers===
{{main|Cooling tower}}
[[File:RatcliffePowerPlantBlackAndWhite.jpg|thumb|[[Cooling tower]]s showing evaporating water at [[Ratcliffe-on-Soar Power Station]], [[United Kingdom]]]]
[[File:Cooling tower power station Dresden.jpg|thumb|"[[Camouflaged]]" natural draft wet [[cooling tower]]]]

All thermal power plants produce [[waste heat]] energy as a byproduct of the useful electrical energy produced. The amount of waste heat energy equals or exceeds the amount of energy converted into useful electricity{{Clarify|date=October 2021}}. Gas-fired power plants can achieve as much as 65% conversion efficiency, while coal and oil plants achieve around 30–49%. The waste heat produces a temperature rise in the atmosphere, which is small compared to that produced by [[greenhouse-gas]] emissions from the same power plant. Natural draft wet [[cooling tower]]s at many nuclear power plants and large fossil-fuel-fired power plants use large [[hyperboloid structure|hyperboloid]] [[chimney]]-like structures (as seen in the image at the right) that release the waste heat to the ambient atmosphere by the [[evaporation]] of water.

However, the mechanical induced-draft or forced-draft wet cooling towers in many large thermal power plants, nuclear power plants, fossil-fired power plants, [[Oil refinery|petroleum refineries]], [[petrochemical|petrochemical plants]], [[Geothermal power|geothermal]], [[biomass]] and [[trash-to-energy plant|waste-to-energy plants]] use [[Fan (mechanical)|fans]] to provide air movement upward through down coming water and are not hyperboloid chimney-like structures. The induced or forced-draft cooling towers are typically rectangular, box-like structures filled with a material that enhances the mixing of the upflowing air and the down-flowing water.<ref>{{Cite book |editor=J. C. Hensley |url=http://spxcooling.com/en/library/detail/cooling-tower-fundamentals/ |title=Cooling Tower Fundamentals |publisher=SPX Cooling Technologies |year=2006 |edition=2nd |access-date=13 September 2007 |archive-date=18 June 2013 |archive-url=https://web.archive.org/web/20130618074805/http://spxcooling.com/en/library/detail/cooling-tower-fundamentals |url-status=live }}</ref><ref name="Beychok">{{Cite book |last=Beychok, Milton R. |title=[[Aqueous Wastes from Petroleum and Petrochemical Plants]] |publisher=John Wiley and Sons |year=1967 |edition=4th |lccn= 67019834}} (Includes cooling tower material balance for evaporation emissions and blowdown effluents. Available in many university libraries)</ref>

In areas with restricted water use, a dry cooling tower or directly air-cooled radiators may be necessary, since the cost or environmental consequences of obtaining make-up water for evaporative cooling would be prohibitive. These coolers have lower efficiency and higher energy consumption to drive fans, compared to a typical wet, evaporative cooling tower.{{Citation needed|date=July 2021}}

=== Air-cooled condenser (ACC) ===
Power plants can use an air-cooled condenser, traditionally in areas with a limited or expensive water supply. Air-cooled condensers serve the same purpose as a cooling tower (heat dissipation) without using water. They consume additional auxiliary power and thus may have a higher carbon footprint compared to a traditional cooling tower.{{Citation needed|date=July 2021}}

===Once-through cooling systems===
Electric companies often prefer to use cooling water from the ocean or a lake, river, or cooling pond instead of a cooling tower. This single pass or [[once-through cooling]] system can save the cost of a cooling tower and may have lower energy costs for pumping cooling water through the plant's [[heat exchanger]]s. However, the waste heat can cause [[thermal pollution]] as the water is discharged. Power plants using natural bodies of water for cooling are designed with mechanisms such as [[fish screen]]s, to limit intake of organisms into the cooling machinery. These screens are only partially effective and as a result billions of fish and other aquatic organisms are killed by power plants each year.<ref>{{cite court |litigants=Riverkeeper, Inc. v. U.S. EPA |vol=358 |reporter=F.3d |opinion=174 |pinpoint=181 |court=2d Cir. |date=2004 |url=http://openjurist.org/358/f3d/174/riverkeeper-inc-llc-v-united-states-environmental-protection-agency |access-date=2015-08-22 |quote=A single power plant might impinge a million adult fish in just a three-week period, or entrain some 3 to 4 billion smaller fish and shellfish in a year, destabilizing wildlife populations in the surrounding ecosystem.}}</ref><ref>U.S. Environmental Protection Agency, Washington, DC (May 2014). [http://www2.epa.gov/sites/production/files/2015-04/documents/final-regulations-cooling-water-intake-structures-at-existing-facilities_fact-sheet_may-2014.pdf "Final Regulations to Establish Requirements for Cooling Water Intake Structures at Existing Facilities."] {{Webarchive|url=https://web.archive.org/web/20200619180853/https://www.epa.gov/sites/production/files/2015-04/documents/final-regulations-cooling-water-intake-structures-at-existing-facilities_fact-sheet_may-2014.pdf |date=19 June 2020 }} Fact sheet. Document no. EPA-821-F-14-001.</ref> For example, the cooling system at the [[Indian Point Energy Center]] in New York kills over a billion fish eggs and larvae annually.<ref>{{Cite news |last=McGeehan |first=Patrick |date=2015-05-12 |title=Fire Prompts Renewed Calls to Close the Indian Point Nuclear Plant |work=The New York Times |url=https://www.nytimes.com/2015/05/13/nyregion/fire-prompts-renewed-calls-to-close-the-indian-point-nuclear-plant.html |access-date=3 March 2017 |archive-date=11 September 2019 |archive-url=https://web.archive.org/web/20190911085219/https://www.nytimes.com/2015/05/13/nyregion/fire-prompts-renewed-calls-to-close-the-indian-point-nuclear-plant.html |url-status=live }}</ref>  A further environmental impact is that aquatic organisms which adapt to the warmer discharge water may be injured if the plant shuts down in cold weather{{Citation Needed|date=October 2021}}.

Water consumption by power stations is a developing issue.<ref>American Association for the Advancement of Science. AAAS Annual Meeting 17 - 21 Feb 2011, Washington DC. "Sustainable or Not? Impacts and Uncertainties of Low-Carbon Energy Technologies on Water." Dr Evangelos Tzimas, European Commission, JRC Institute for Energy, Petten, Netherlands.</ref>

In recent years, recycled wastewater, or [[greywater|grey water]], has been used in cooling towers. The Calpine Riverside and the Calpine Fox power stations in [[Wisconsin]] as well as the Calpine Mankato power station in [[Minnesota]] are among these facilities.{{Citation needed|date=July 2021}}