70-463: Homer City Generating Station is a decommissioned 2- GW coal-burning power station near Homer City , in Indiana County, Pennsylvania , USA. It is owned by hedge funds and private equity firms and is operated by NRG Energy . Units 1 and 2, rated at 660 MWe , began operation in 1969. Unit 3, rated at 692 MWe nameplate capacity, was launched in 1977. It employed about 124 people. During
140-558: A light bulb with a power rating of 100 W is turned on for one hour, the energy used is 100 watt hours (W·h), 0.1 kilowatt hour, or 360 kJ . This same amount of energy would light a 40-watt bulb for 2.5 hours, or a 50-watt bulb for 2 hours. Power stations are rated using units of power, typically megawatts or gigawatts (for example, the Three Gorges Dam in China is rated at approximately 22 gigawatts). This reflects
210-687: A semiconductor and is used in photocells . Applications in electronics , once important, have been mostly replaced with silicon semiconductor devices. Selenium is still used in a few types of DC power surge protectors and one type of fluorescent quantum dot . Although trace amounts of selenium are necessary for cellular function in many animals, including humans, both elemental selenium and (especially) selenium salts are toxic in even small doses, causing selenosis . Symptoms include (in decreasing order of frequency): diarrhea, fatigue, hair loss, joint pain, nail brittleness or discoloration, nausea, headache, tingling, vomiting, and fever. Selenium
280-567: A $ 1 billion impairment charge related to the Homer City plant and several other coal-fired power plants. At the end of 2012 full control of the plant was transferred back to General Electric, which hired an NRG affiliate to operate it. In early 2017, the plant filed for bankruptcy protection. In early 2022 the facility's owners announced that they were considering deactivating some of its units. The owners initially decided to continue operation, but on April 3, 2023 Homer City Generation announced
350-470: A byproduct, obtained from the anode mud of copper refineries. Another source was the mud from the lead chambers of sulfuric acid plants, a process that is no longer used. Selenium can be refined from these muds by a number of methods. However, most elemental selenium comes as a byproduct of refining copper or producing sulfuric acid . Since its invention, solvent extraction and electrowinning (SX/EW) production of copper produces an increasing share of
420-494: A chemistry plant near Gripsholm , Sweden, producing sulfuric acid by the lead chamber process . Pyrite samples from the Falun Mine produced a red solid precipitate in the lead chambers, which was presumed to be an arsenic compound, so the use of pyrite to make acid was discontinued. Berzelius and Gahn, who wanted to use the pyrite, observed that the red precipitate gave off an odor like horseradish when burned. This smell
490-633: A decision to shut down the power plant and be offline by June 2, 2023. The power plant was permanently decommissioned on July 1, 2023. The plant was a major polluter , ranking highly both nationally and within the state, recently releasing 8,500,000 pounds (3,900 metric tons) of toxic chemicals according to the Pittsburgh Post-Gazette . Pennsylvania has ranked it the #2 polluter in the state. Homer City Generating Station released huge amounts of mercury , sulfur dioxide , carbon dioxide , and other toxic or damaging chemicals. A scrubber
560-475: A glass dye, and a reducing agent in fireworks . Selenium trioxide may be synthesized by dehydrating selenic acid , H 2 SeO 4 , which is itself produced by the oxidation of selenium dioxide with hydrogen peroxide : Hot, concentrated selenic acid reacts with gold to form gold(III) selenate. Selenium reacts with fluorine to form selenium hexafluoride : In comparison with its sulfur counterpart ( sulfur hexafluoride ), selenium hexafluoride (SeF 6 )
630-408: A period of one year: equivalent to approximately 114 megawatts of constant power output. The watt-second is a unit of energy, equal to the joule . One kilowatt hour is 3,600,000 watt seconds. While a watt per hour is a unit of rate of change of power with time, it is not correct to refer to a watt (or watt-hour) as a watt per hour. Selenium Selenium is a chemical element ; it has
700-468: A product of nuclear fission . Selenium also has numerous unstable synthetic isotopes ranging from Se to Se; the most stable are Se with a half-life of 119.78 days and Se with a half-life of 8.4 days. Isotopes lighter than the stable isotopes primarily undergo beta plus decay to isotopes of arsenic , and isotopes heavier than the stable isotopes undergo beta minus decay to isotopes of bromine , with some minor neutron emission branches in
770-496: A ring are not equivalent (i.e. they are not mapped one onto another by any symmetry operation), and in fact in the γ-monoclinic form, half the rings are in one configuration (and its mirror image) and half in another. The packing is most dense in the α form. In the Se 8 rings, the Se–Se distance varies depending on where the pair of atoms is in the ring, but the average is 233.5 pm, and
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#1732797929597840-488: A role analogous to that of sulfur. Another naturally occurring organoselenium compound is dimethyl selenide . Certain soils are selenium-rich, and selenium can be bioconcentrated by some plants. In soils, selenium most often occurs in soluble forms such as selenate (analogous to sulfate), which are leached into rivers very easily by runoff. Ocean water contains significant amounts of selenium. Typical background concentrations of selenium do not exceed 1 ng/m in
910-541: A turbine, which generates 648 MW e (i.e. electricity). Other SI prefixes are sometimes used, for example gigawatt electrical (GW e ). The International Bureau of Weights and Measures , which maintains the SI-standard, states that further information about a quantity should not be attached to the unit symbol but instead to the quantity symbol (e.g., P th = 270 W rather than P = 270 W th ) and so these unit symbols are non-SI. In compliance with SI,
980-495: A unit of time, namely 1 J/s. In this new definition, 1 absolute watt = 1.00019 international watts. Texts written before 1948 are likely to be using the international watt, which implies caution when comparing numerical values from this period with the post-1948 watt. In 1960, the 11th General Conference on Weights and Measures adopted the absolute watt into the International System of Units (SI) as
1050-557: Is 343.6 pm. Gray selenium is formed by mild heating of other allotropes, by slow cooling of molten selenium, or by condensing selenium vapor just below the melting point. Whereas other selenium forms are insulators , gray selenium is a semiconductor showing appreciable photoconductivity . Unlike the other allotropes, it is insoluble in CS 2 . It resists oxidation by air and is not attacked by nonoxidizing acids . With strong reducing agents, it forms polyselenides. Selenium does not exhibit
1120-407: Is a rare mineral, which does not usually form good crystals, but, when it does, they are steep rhombohedra or tiny acicular (hair-like) crystals. Isolation of selenium is often complicated by the presence of other compounds and elements. Selenium occurs naturally in a number of inorganic forms, including selenide , selenate , and selenite , but these minerals are rare. The common mineral selenite
1190-1045: Is a strongly odiferous , toxic, and colorless gas. It is more acidic than H 2 S. In solution it ionizes to HSe . The selenide dianion Se forms a variety of compounds, including the minerals from which selenium is obtained commercially. Illustrative selenides include mercury selenide (HgSe), lead selenide (PbSe), zinc selenide (ZnSe), and copper indium gallium diselenide (Cu(Ga,In)Se 2 ). These materials are semiconductors . With highly electropositive metals, such as aluminium , these selenides are prone to hydrolysis, which may be described by this idealized equation: Al 2 Se 3 + 6 H 2 O ⟶ 2 Al ( OH ) 3 + 3 H 2 Se {\displaystyle {\ce {Al2Se3 + 6 H2O -> 2 Al(OH)3 + 3 H2Se}}} Alkali metal selenides react with selenium to form polyselenides, Se n , which exist as chains and rings. Tetraselenium tetranitride, Se 4 N 4 ,
1260-469: Is an explosive orange compound analogous to tetrasulfur tetranitride (S 4 N 4 ). It can be synthesized by the reaction of selenium tetrachloride (SeCl 4 ) with [((CH 3 ) 3 Si) 2 N] 2 Se . Selenium reacts with cyanides to yield selenocyanates : 8 KCN + Se 8 ⟶ 8 KSeCN {\displaystyle {\ce {8 KCN + Se8 -> 8 KSeCN}}} Selenium, especially in
1330-482: Is for the production of glass. Selenium compounds confer a red color to glass. This color cancels out the green or yellow tints that arise from iron impurities typical for most glass. For this purpose, various selenite and selenate salts are added. For other applications, a red color may be desired, produced by mixtures of CdSe and CdS. Selenium is used with bismuth in brasses to replace more toxic lead . The regulation of lead in drinking water applications such as in
1400-405: Is formed by combustion of elemental selenium: It is a polymeric solid that forms monomeric SeO 2 molecules in the gas phase. It dissolves in water to form selenous acid , H 2 SeO 3 . Selenous acid can also be made directly by oxidizing elemental selenium with nitric acid : Unlike sulfur, which forms a stable trioxide , selenium trioxide is thermodynamically unstable and decomposes to
1470-585: Is listed as an ingredient in many multivitamins and other dietary supplements, as well as in infant formula , and is a component of the antioxidant enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants) as well as in three deiodinase enzymes. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts and others apparently not requiring any. Selenium forms several allotropes that interconvert with temperature changes, depending somewhat on
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#17327979295971540-501: Is mixed with water and acidified to form selenous acid ( oxidation step). Selenous acid is bubbled with sulfur dioxide ( reduction step) to give elemental selenium. About 2,000 tonnes of selenium were produced in 2011 worldwide, mostly in Germany (650 t), Japan (630 t), Belgium (200 t), and Russia (140 t), and the total reserves were estimated at 93,000 tonnes. These data exclude two major producers:
1610-461: Is more reactive and is a toxic pulmonary irritant. Selenium tetrafluoride is a laboratory-scale fluorinating agent . The only stable chlorides are selenium tetrachloride (SeCl 4 ) and selenium monochloride (Se 2 Cl 2 ), which might be better known as selenium(I) chloride and is structurally analogous to disulfur dichloride . Metastable solutions of selenium dichloride can be prepared from sulfuryl chloride and selenium (reaction of
1680-733: Is named after the Scottish inventor James Watt . The unit name was proposed by C. William Siemens in August 1882 in his President's Address to the Fifty-Second Congress of the British Association for the Advancement of Science . Noting that units in the practical system of units were named after leading physicists, Siemens proposed that watt might be an appropriate name for a unit of power. Siemens defined
1750-467: Is not a selenium mineral, and contains no selenite ion , but is rather a type of gypsum (calcium sulfate hydrate) named like selenium for the moon well before the discovery of selenium. Selenium is most commonly found as an impurity, replacing a small part of the sulfur in sulfide ores of many metals. In living systems, selenium is found in the amino acids selenomethionine , selenocysteine , and methylselenocysteine . In these compounds, selenium plays
1820-732: Is operated by the station. From there, the Black Lick enters the Conemaugh River , which goes on to meet the Loyalhanna River , creating the Kiskiminetas River , before entering the Allegheny River . With diminishing local coal and mines to support it, the train track that ran through Indiana University of Pennsylvania had reopened and supplies were brought in by train. Until its construction in
1890-465: Is represented in selenium chemistry by the selenoxides (formula RSe(O)R), which are intermediates in organic synthesis, as illustrated by the selenoxide elimination reaction. Consistent with trends indicated by the double bond rule , selenoketones, R(C=Se)R, and selenaldehydes, R(C=Se)H, are rarely observed. Selenium ( Greek σελήνη selene meaning "Moon") was discovered in 1817 by Jöns Jacob Berzelius and Johan Gottlieb Gahn . Both chemists owned
1960-445: Is the dominant consumer of selenium at 1,500–2,000 tonnes/year. During the electrowinning of manganese, the addition of selenium dioxide decreases the power necessary to operate the electrolysis cells . China is the largest consumer of selenium dioxide for this purpose. For every tonne of manganese, an average 2 kg selenium oxide is used. The largest commercial use of selenium, accounting for about 50% of consumption,
2030-523: Is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V), meaning the watt is equivalent to the volt-ampere (the latter unit, however, is used for a different quantity from the real power of an electrical circuit). 1 W = 1 V ⋅ A . {\displaystyle \mathrm {1~W=1~V{\cdot }A} .} Two additional unit conversions for watt can be found using
2100-472: Is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m ⋅s . It is used to quantify the rate of energy transfer . The watt is named in honor of James Watt (1736–1819), an 18th-century Scottish inventor , mechanical engineer , and chemist who improved the Newcomen engine with his own steam engine in 1776. Watt's invention
2170-626: The Western Pennsylvania Hospital burn center, and three were treated locally. The incident was investigated by the Occupational Safety and Health Administration . In 2001, affiliates of General Electric bought the plant from Edison International , and subsequently leased it back to them. In 2011, Edison failed to secure financing to add pollution-control devices and announced plans to transfer full control to General Electric. On February 29, 2012, Edison took
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2240-496: The carrier lifetime . As of now, the only defect-engineering strategy that has been investigated for selenium thin-film solar cells involves crystallizing selenium using a laser . Amorphous selenium (α-Se) thin films have found application as photoconductors in flat-panel X-ray detectors . These detectors use amorphous selenium to capture and convert incident X-ray photons directly into electric charge. Selenium has been chosen for this application among other semiconductors owing to
2310-467: The symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elemental state or as pure ore compounds in Earth's crust . Selenium (from Ancient Greek σελήνη ( selḗnē ) 'moon') was discovered in 1817 by Jöns Jacob Berzelius , who noted the similarity of
2380-417: The 1950s, research on selenium thin-film solar cells declined. As a result, the record efficiency of 5.0% demonstrated by Tokio Nakada and Akio Kunioka in 1985 remained unchanged for more than 30 years. In 2017, researchers from IBM achieved a new record efficiency of 6.5% by redesigning the device structure. Following this achievement, selenium has gained renewed interest as a wide bandgap photoabsorber with
2450-583: The 1960s by the Pennsylvania Electric Co. (PenElec) and others, much of the property was owned by the George family. In 1969, Units #1 and #2 began operation, while Unit #3 began operating in 1977. Six workers were injured on February 10, 2011, when a six-inch, high-pressure steam pipe in Unit 1 ruptured and caused an explosion on the sixth floor of a building. Three of the men were airlifted to
2520-466: The 1970s, following which they were replaced with less expensive and even more efficient silicon rectifiers . Selenium came to medical notice later because of its toxicity to industrial workers. Selenium was also recognized as an important veterinary toxin, which is seen in animals that have eaten high-selenium plants. In 1954, the first hints of specific biological functions of selenium were discovered in microorganisms by biochemist, Jane Pinsent . It
2590-481: The 2010s, it underwent two bankruptcies within five years. On April 3, 2023, Homer City Generation announced a decision to shut down the power plant and be offline by June 2, 2023. The station is located in Center Township, Indiana County, Pennsylvania , occupying approximately 2,400 acres (9.7 km). The site also includes the 1,800-acre (7.3 km) Two Lick Reservoir, a water conservation facility which
2660-403: The 2013 summer ozone season, this trend in rising emission rates continued resulting in over 6,300 tons of NO x emissions in excess of what could have been achieved had the plant operated at its previously demonstrated optimum rates seen in 2005-06. The plant's Unit 3 has a 371 m (1,217 ft) tall chimney , which was built in 1977. This chimney is currently the third-tallest chimney in
2730-572: The Earth, Berzelius named the new element after the Moon . In 1873, Willoughby Smith found that the electrical conductivity of grey selenium was affected by light. This led to its use as a cell for sensing light. The first commercial products using selenium were developed by Werner Siemens in the mid-1870s. The selenium cell was used in the photophone developed by Alexander Graham Bell in 1879. Selenium transmits an electric current proportional to
2800-540: The II oxidation state, forms a variety of organic derivatives. They are structurally analogous to the corresponding organosulfur compounds . Especially common are selenides (R 2 Se, analogues of thioethers ), diselenides (R 2 Se 2 , analogues of disulfides ), and selenols (RSeH, analogues of thiols ). Representatives of selenides, diselenides, and selenols include respectively selenomethionine , diphenyldiselenide , and benzeneselenol . The sulfoxide in sulfur chemistry
2870-457: The Se–Se–Se angle is on average 105.7°. Other selenium allotropes may contain Se 6 or Se 7 rings. The most stable and dense form of selenium is gray and has a chiral hexagonal crystal lattice (space group 152 or 154 depending on the chirality) consisting of helical polymeric chains, where the Se–Se distance is 237.3 pm and Se–Se–Se angle is 103.1°. The minimum distance between chains
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2940-522: The US with the Safe Drinking Water Act of 1974, made a reduction of lead in brass necessary. The new brass is marketed under the name EnviroBrass. Like lead and sulfur, selenium improves the machinability of steel at concentrations around 0.15%. Selenium produces the same machinability improvement in copper alloys. The lithium–selenium (Li–Se) battery was considered for energy storage in
3010-468: The United States and China. A previous sharp increase was observed in 2004 from $ 4–$ 5 to $ 27/lb. The price was relatively stable during 2004–2010 at about US$ 30 per pound (in 100 pound lots) but increased to $ 65/lb in 2011. The consumption in 2010 was divided as follows: metallurgy – 30%, glass manufacturing – 30%, agriculture – 10%, chemicals and pigments – 10%, and electronics – 10%. China
3080-470: The above equation and Ohm's law . 1 W = 1 V 2 / Ω = 1 A 2 ⋅ Ω , {\displaystyle \mathrm {1~W=1~V^{2}/\Omega =1~A^{2}{\cdot }\Omega } ,} where ohm ( Ω {\displaystyle \Omega } ) is the SI derived unit of electrical resistance . The watt
3150-409: The amount of light falling on its surface. This phenomenon was used in the design of light meters and similar devices. Selenium's semiconductor properties found numerous other applications in electronics. The development of selenium rectifiers began during the early 1930s, and these replaced copper oxide rectifiers because they were more efficient. These lasted in commercial applications until
3220-399: The atmosphere; 1 mg/kg in soil and vegetation and 0.5 μg/L in freshwater and seawater. Anthropogenic sources of selenium include coal burning, and the mining and smelting of sulfide ores. Selenium is most commonly produced from selenide in many sulfide ores , such as those of copper , nickel , or lead . Electrolytic metal refining is particularly productive of selenium as
3290-441: The changes in viscosity that sulfur undergoes when gradually heated. Selenium has seven naturally occurring isotopes . Five of these, Se, Se, Se, Se, Se, are stable, with Se being the most abundant (49.6% natural abundance). Also naturally occurring is the long-lived primordial radionuclide Se, with a half-life of 8.76×10 years. The non-primordial radioisotope Se also occurs in minute quantities in uranium ores as
3360-703: The dioxide above 185 °C: Selenium trioxide is produced in the laboratory by the reaction of anhydrous potassium selenate (K 2 SeO 4 ) and sulfur trioxide (SO 3 ). Salts of selenous acid are called selenites. These include silver selenite (Ag 2 SeO 3 ) and sodium selenite (Na 2 SeO 3 ). Hydrogen sulfide reacts with aqueous selenous acid to produce selenium disulfide : Selenium disulfide consists of 8-membered rings. It has an approximate composition of SeS 2 , with individual rings varying in composition, such as Se 4 S 4 and Se 2 S 6 . Selenium disulfide has been used in shampoo as an anti dandruff agent, an inhibitor in polymer chemistry,
3430-402: The elements generates the tetrachloride instead), and constitute an important reagent in the preparation of selenium compounds (e.g. Se 7 ). The corresponding bromides are all known, and recapitulate the same stability and structure as the chlorides. The iodides of selenium are not well known, and for a long time were believed not to exist. There is limited spectroscopic evidence that
3500-515: The energy company Ørsted A/S uses the unit megawatt for produced electrical power and the equivalent unit megajoule per second for delivered heating power in a combined heat and power station such as Avedøre Power Station . When describing alternating current (AC) electricity, another distinction is made between the watt and the volt-ampere . While these units are equivalent for simple resistive circuits , they differ when loads exhibit electrical reactance . Radio stations usually report
3570-1002: The facility as 33rd largest CO 2 emitter in the United States. In 2007, the Pennsylvania Department of Environmental Protection (DEP) fined the owners of the Homer City electricity generating station, EME Homer City Generation LP, $ 200,000 for violating the Pennsylvania Clean Streams Law. The station exceeded its permitted effluent standards for selenium , total suspended solids, and biochemical oxygen demand in its wastewater discharges, and allowed unpermitted discharges of stormwater associated with its flue-gas desulfurization scrubbers. Homer City's three coal boilers installed Selective Catalytic Reduction to reduce ozone-forming NO x emissions in 2000 and 2001. This technology produced up to an 83% reduction in NO x emissions in subsequent years. Since
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#17327979295973640-481: The family of lithium batteries in the 2010s. Selenium was used as the photoabsorbing layer in the first solid-state solar cell, which was demonstrated by the English physicist William Grylls Adams and his student Richard Evans Day in 1876. Only a few years layer, Charles Fritts fabricated the first thin-film solar cell, also using selenium as the photoabsorber. However, with the emergence of silicon solar cells in
3710-449: The heaviest known isotopes. Selenium compounds commonly exist in the oxidation states −2, +2, +4, and +6. It is a nonmetal (more rarely considered a metalloid ) with properties that are intermediate between the elements above and below in the periodic table , sulfur and tellurium , and also has similarities to arsenic . Selenium forms two oxides : selenium dioxide (SeO 2 ) and selenium trioxide (SeO 3 ). Selenium dioxide
3780-428: The lower iodides may form in bi-elemental solutions with nonpolar solvents, such as carbon disulfide and carbon tetrachloride ; but even these appear to decompose under illumination . Some selenium oxyhalides— seleninyl fluoride (SeOF 2 ) and selenium oxychloride (SeOCl 2 )—have been used as specialty solvents. Analogous to the behavior of other chalcogens, selenium forms hydrogen selenide , H 2 Se. It
3850-460: The maximum power output it can achieve at any point in time. A power station's annual energy output, however, would be recorded using units of energy (not power), typically gigawatt hours. Major energy production or consumption is often expressed as terawatt hours for a given period; often a calendar year or financial year. One terawatt hour of energy is equal to a sustained power delivery of one terawatt for one hour, or approximately 114 megawatts for
3920-451: The new element to the previously discovered tellurium (named for the Earth). Selenium is found in metal sulfide ores , where it substitutes for sulfur. Commercially, selenium is produced as a byproduct in the refining of these ores. Minerals that are pure selenide or selenate compounds are rare. The chief commercial uses for selenium today are glassmaking and pigments . Selenium is
3990-436: The optimum years of 2005-06, emissions have begun to creep back up towards what they were before the installation of this technology. During the summer of 2012 plant emissions of NO x doubled over the 2005-06 period from 2,300 tons to 4,500 tons, even as electrical generation fell by 30%. Through this same period, the price of natural gas, which competes with coal as a fuel for electrical generation, fell by some 60%. Through
4060-450: The potential of being integrated in tandem with lower bandgap photoabsorbers. In 2024, the first selenium-based tandem solar cell was demonstrated, showcasing a selenium top cell monolithically integrated with a silicon bottom cell. However, a significant deficit in the open-circuit voltage is currently the main limiting factor to further improve the efficiency, necessitating defect-engineering strategies for selenium thin-films to enhance
4130-488: The power of their transmitters in units of watts, referring to the effective radiated power . This refers to the power that a half-wave dipole antenna would need to radiate to match the intensity of the transmitter's main lobe . The terms power and energy are closely related but distinct physical quantities. Power is the rate at which energy is generated or consumed and hence is measured in units (e.g. watts) that represent energy per unit time . For example, when
4200-558: The rate of temperature change. When prepared in chemical reactions, selenium is usually an amorphous , brick-red powder. When rapidly melted, it forms the black, vitreous form, usually sold commercially as beads. The structure of black selenium is irregular and complex and consists of polymeric rings with up to 1000 atoms per ring. Black selenium is a brittle, lustrous solid that is slightly soluble in CS 2 . Upon heating, it softens at 50 °C and converts to gray selenium at 180 °C;
4270-413: The transformation temperature is reduced by presence of halogens and amines . The red α, β, and γ forms are produced from solutions of black selenium by varying the evaporation rate of the solvent (usually CS 2 ). They all have a relatively low, monoclinic crystal symmetry ( space group 14) and contain nearly identical puckered cyclooctaselenium (Se 8 ) rings as in sulfur . The eight atoms of
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#17327979295974340-569: The unit of power. In the electric power industry , megawatt electrical ( MWe or MW e ) refers by convention to the electric power produced by a generator, while megawatt thermal or thermal megawatt (MWt, MW t , or MWth, MW th ) refers to thermal power produced by the plant. For example, the Embalse nuclear power plant in Argentina uses a fission reactor to generate 2,109 MW t (i.e. heat), which creates steam to drive
4410-570: The unit within the existing system of practical units as "the power conveyed by a current of an Ampère through the difference of potential of a Volt". In October 1908, at the International Conference on Electric Units and Standards in London, so-called international definitions were established for practical electrical units. Siemens' definition was adopted as the international watt. (Also used: 1 A × 1 Ω.) The watt
4480-479: The world, the second-tallest in North America, and the tallest in the United States. On clear days, it is possible to spot the chimney from as far south as Greensburg, Pennsylvania , and as far east as Ebensburg, Pennsylvania . The chimney is no longer in use, as the gas flow from Unit 3 has been bypassed through a newer flue gas treatment system installed in 2002. Gigawatt The watt (symbol: W )
4550-431: The worldwide copper supply. This changes the availability of selenium because only a comparably small part of the selenium in the ore is leached with the copper. Industrial production of selenium usually involves the extraction of selenium dioxide from residues obtained during the purification of copper. Common production from the residue then begins by oxidation with sodium carbonate to produce selenium dioxide, which
4620-553: Was added in 1998 which reduced mercury output. In 2012, General Electric, through contractors, began construction of anti-pollution control equipment known as "scrubbers" to further reduce the plant's emissions. According to Public Citizen: "The plant ranks #33 in the nation for total CO 2 emissions, contributing 13,745,174 tons of the pollutant primarily responsible for global warming to our atmosphere." The organization Carbon Monitoring for Action (CARMA) reported in 2007 that this plant emitted 12,800,000 tons of CO 2 and also ranked
4690-420: Was defined as equal to 10 units of power in the practical system of units. The "international units" were dominant from 1909 until 1948. After the 9th General Conference on Weights and Measures in 1948, the international watt was redefined from practical units to absolute units (i.e., using only length, mass, and time). Concretely, this meant that 1 watt was defined as the quantity of energy transferred in
4760-424: Was discovered to be essential for mammalian life in 1957. In the 1970s, it was shown to be present in two independent sets of enzymes . This was followed by the discovery of selenocysteine in proteins. During the 1980s, selenocysteine was shown to be encoded by the codon UGA . The recoding mechanism was worked out first in bacteria and then in mammals (see SECIS element ). Native (i.e., elemental) selenium
4830-694: Was fundamental for the Industrial Revolution . When an object's velocity is held constant at one meter per second against a constant opposing force of one newton , the rate at which work is done is one watt. 1 W = 1 J / s = 1 N ⋅ m / s = 1 k g ⋅ m 2 ⋅ s − 3 . {\displaystyle \mathrm {1~W=1~J{/}s=1~N{\cdot }m{/}s=1~kg{\cdot }m^{2}{\cdot }s^{-3}} .} In terms of electromagnetism , one watt
4900-475: Was not typical of arsenic, but a similar odor was known from tellurium compounds. Hence, Berzelius's first letter to Alexander Marcet stated that this was a tellurium compound. However, the lack of tellurium compounds in the Falun Mine minerals eventually led Berzelius to reanalyze the red precipitate, and in 1818 he wrote a second letter to Marcet describing a newly found element similar to sulfur and tellurium. Because of its similarity to tellurium, named for
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