Cogeneration

Cogeneration or combined heat and power (CHP) is the use of a heat engine[1] or power station to generate electricity and useful heat at the same time. Trigeneration or combined cooling, heat and power (CCHP) refers to the simultaneous generation of electricity and useful heating and cooling from the combustion of a fuel or a solar heat collector. The terms cogeneration and trigeneration can be also applied to the power systems generating simultaneously electricity, heat, and industrial chemicals – e.g., syngas or pure hydrogen (article: combined cycles, chapter: natural gas integrated power & syngas (hydrogen) generation cycle).

Cogeneration is a more efficient use of fuel because otherwise wasted heat from electricity generation is put to some productive use. Combined heat and power (CHP) plants recover otherwise wasted thermal energy for heating. This is also called combined heat and power district heating. Small CHP plants are an example of decentralized energy.[2] By-product heat at moderate temperatures (100–180 °C, 212–356 °F) can also be used in absorption refrigerators for cooling.

The supply of high-temperature heat first drives a gas or steam turbine-powered generator. The resulting low-temperature waste heat is then used for water or space heating. At smaller scales (typically below 1 MW) a gas engine or diesel engine may be used. Trigeneration differs from cogeneration in that the waste heat is used for both heating and cooling, typically in an absorption refrigerator. Combined cooling, heat and power systems can attain higher overall efficiencies than cogeneration or traditional power plants. In the United States, the application of trigeneration in buildings is called building cooling, heating and power. Heating and cooling output may operate concurrently or alternately depending on need and system construction.

Cogeneration was practiced in some of the earliest installations of electrical generation. Before central stations distributed power, industries generating their own power used exhaust steam for process heating. Large office and apartment buildings, hotels and stores commonly generated their own power and used waste steam for building heat. Due to the high cost of early purchased power, these CHP operations continued for many years after utility electricity became available.[3]

Overview

Masnedø CHP power station in Denmark. This station burns straw as fuel. The adjacent greenhouses are heated by district heating from the plant.

Many process industries, such as chemical plants, oil refineries and pulp and paper mills, require large amounts of process heat for such operations as chemical reactors, distillation columns, steam driers and other uses. This heat, which is usually used in the form of steam, can be generated at the typically low pressures used in heating, or can be generated at much higher pressure and passed through a turbine first to generate electricity. In the turbine the steam pressure and temperature is lowered as the internal energy of the steam is converted to work. The lower pressure steam leaving the turbine can then be used for process heat.

Steam turbines at thermal power stations are normally designed to be fed high pressure steam, which exits the turbine at a condenser operating a few degrees above ambient temperature and at a few millimeters of mercury absolute pressure. (This is called a condensing turbine.) For all practical purposes this steam has negligible useful energy before it is condensed. Steam turbines for cogeneration are designed either for extraction of some steam at lower pressures after it has passed through a number of turbine stages, with the un-extracted steam going on through the turbine to a condenser. In this case, the extracted steam causes a mechanical power loss in the downstream stages of the turbine. Or they are designed, with or without extraction, for final exhaust at back pressure (non-condensing).[4][5] The extracted or exhaust steam is used for process heating. Steam at ordinary process heating conditions still has a considerable amount of enthalpy that could be used for power generation, so cogeneration has an opportunity cost.

A typical power generation turbine in a paper mill may have extraction pressures of 160 psig (1.103 MPa) and 60 psig (0.41 MPa). A typical back pressure may be 60 psig (0.41 MPa). In practice these pressures are custom designed for each facility. Conversely, simply generating process steam for industrial purposes instead of high enough pressure to generate power at the top end also has an opportunity cost (See: Steam supply and exhaust conditions). The capital and operating cost of high pressure boilers, turbines and generators are substantial. This equipment is normally operated continuously, which usually limits self-generated power to large-scale operations.

A cogeneration plant in Metz, France. The 45MW boiler uses waste wood biomass as energy source, and provides electricity and heat for 30,000 dwellings.

A combined cycle (in which several thermodynamic cycles produce electricity), may also be used to extract heat using a heating system as condenser of the power plant's bottoming cycle. For example, the RU-25 MHD generator in Moscow heated a boiler for a conventional steam powerplant, whose condensate was then used for space heat. A more modern system might use a gas turbine powered by natural gas, whose exhaust powers a steam plant, whose condensate provides heat. Cogeneration plants based on a combined cycle power unit can have thermal efficiencies above 80%.

The viability of CHP (sometimes termed utilisation factor), especially in smaller CHP installations, depends on a good baseload of operation, both in terms of an on-site (or near site) electrical demand and heat demand. In practice, an exact match between the heat and electricity needs rarely exists. A CHP plant can either meet the need for heat (heat driven operation) or be run as a power plant with some use of its waste heat, the latter being less advantageous in terms of its utilisation factor and thus its overall efficiency. The viability can be greatly increased where opportunities for trigeneration exist. In such cases, the heat from the CHP plant is also used as a primary energy source to deliver cooling by means of an absorption chiller.

CHP is most efficient when heat can be used on-site or very close to it. Overall efficiency is reduced when the heat must be transported over longer distances. This requires heavily insulated pipes, which are expensive and inefficient; whereas electricity can be transmitted along a comparatively simple wire, and over much longer distances for the same energy loss.

A car engine becomes a CHP plant in winter when the reject heat is useful for warming the interior of the vehicle. The example illustrates the point that deployment of CHP depends on heat uses in the vicinity of the heat engine.

Thermally enhanced oil recovery (TEOR) plants often produce a substantial amount of excess electricity. After generating electricity, these plants pump leftover steam into heavy oil wells so that the oil will flow more easily, increasing production. TEOR cogeneration plants in Kern County, California produce so much electricity that it cannot all be used locally and is transmitted to Los Angeles.

CHP is one of the most cost-efficient methods of reducing carbon emissions from heating systems in cold climates [6] and is recognized to be the most energy efficient method of transforming energy from fossil fuels or biomass into electric power.[7] Cogeneration plants are commonly found in district heating systems of cities, central heating systems of larger buildings (e.g. hospitals, hotels, prisons) and are commonly used in the industry in thermal production processes for process water, cooling, steam production or CO2 fertilization.

Types of plants

Topping cycle plants primarily produce electricity from a steam turbine. Partly expanded steam is then condensed in a heating condensor at a temperature level that is suitable e.g. district heating or water desalination.

Bottoming cycle plants produce high temperature heat for industrial processes, then a waste heat recovery boiler feeds an electrical plant. Bottoming cycle plants are only used in industrial processes that require very high temperatures such as furnaces for glass and metal manufacturing, so they are less common.

Large cogeneration systems provide heating water and power for an industrial site or an entire town. Common CHP plant types are:

• Gas turbine CHP plants using the waste heat in the flue gas of gas turbines. The fuel used is typically natural gas.
• Gas engine CHP plants use a reciprocating gas engine which is generally more competitive than a gas turbine up to about 5 MW. The gaseous fuel used is normally natural gas. These plants are generally manufactured as fully packaged units that can be installed within a plantroom or external plant compound with simple connections to the site's gas supply, electrical distribution network and heating systems. Typical outputs and efficiences see [8] Typical large example see [9]
• Biofuel engine CHP plants use an adapted reciprocating gas engine or diesel engine, depending upon which biofuel is being used, and are otherwise very similar in design to a Gas engine CHP plant. The advantage of using a biofuel is one of reduced hydrocarbon fuel consumption and thus reduced carbon emissions. These plants are generally manufactured as fully packaged units that can be installed within a plantroom or external plant compound with simple connections to the site's electrical distribution and heating systems. Another variant is the wood gasifier CHP plant whereby a wood pellet or wood chip biofuel is gasified in a zero oxygen high temperature environment; the resulting gas is then used to power the gas engine. Typical smaller size biogas plant see [10]
• Combined cycle power plants adapted for CHP
• Molten-carbonate fuel cells and solid oxide fuel cells have a hot exhaust, very suitable for heating.
• Steam turbine CHP plants that use the heating system as the steam condenser for the steam turbine.
• Nuclear power plants, similar to other steam turbine power plants, can be fitted with extractions in the turbines to bleed partially expanded steam to a heating system. With a heating system temperature of 95 °C it is possible to extract about 10 MW heat for every MW electricity lost. With a temperature of 130 °C the gain is slightly smaller, about 7 MW for every MWe lost.[11] A review of cogeneration options is in [12]

Smaller cogeneration units may use a reciprocating engine or Stirling engine. The heat is removed from the exhaust and radiator. The systems are popular in small sizes because small gas and diesel engines are less expensive than small gas- or oil-fired steam-electric plants.

Some cogeneration plants are fired by biomass,[13] or industrial and municipal solid waste (see incineration). Some CHP plants utilize waste gas as the fuel for electricity and heat generation. Waste gases can be gas from animal waste, landfill gas, gas from coal mines, sewage gas, and combustible industrial waste gas.[14]

Some cogeneration plants combine gas and solar photovoltaic generation to further improve technical and environmental performance.[15] Such hybrid systems can be scaled down to the building level[16] and even individual homes.[17]

MicroCHP

Micro combined heat and power or 'Micro cogeneration" is a so-called distributed energy resource (DER). The installation is usually less than 5 kWe in a house or small business. Instead of burning fuel to merely heat space or water, some of the energy is converted to electricity in addition to heat. This electricity can be used within the home or business or, if permitted by the grid management, sold back into the electric power grid.

History

Cogeneration in Europe

A cogeneration thermal power plant in Ferrera Erbognone (PV), Italy

The EU has actively incorporated cogeneration into its energy policy via the CHP Directive. In September 2008 at a hearing of the European Parliament’s Urban Lodgment Intergroup, Energy Commissioner Andris Piebalgs is quoted as saying, “security of supply really starts with energy efficiency.”[37] Energy efficiency and cogeneration are recognized in the opening paragraphs of the European Union’s Cogeneration Directive 2004/08/EC. This directive intends to support cogeneration and establish a method for calculating cogeneration abilities per country. The development of cogeneration has been very uneven over the years and has been dominated throughout the last decades by national circumstances.

The European Union generates 11% of its electricity using cogeneration.[38] However, there is large difference between Member States with variations of the energy savings between 2% and 60%. Europe has the three countries with the world’s most intensive cogeneration economies: Denmark, the Netherlands and Finland.[39] Of the 28.46 TWh of electrical power generated by conventional thermal power plants in Finland in 2012, 81.80% was cogeneration.[40]

Other European countries are also making great efforts to increase efficiency. Germany reported that at present, over 50% of the country’s total electricity demand could be provided through cogeneration. So far, Germany has set the target to double its electricity cogeneration from 12.5% of the country’s electricity to 25% of the country’s electricity by 2020 and has passed supporting legislation accordingly.[41] The UK is also actively supporting combined heat and power. In light of UK’s goal to achieve a 60% reduction in carbon dioxide emissions by 2050, the government has set the target to source at least 15% of its government electricity use from CHP by 2010.[42] Other UK measures to encourage CHP growth are financial incentives, grant support, a greater regulatory framework, and government leadership and partnership.

According to the IEA 2008 modeling of cogeneration expansion for the G8 countries, the expansion of cogeneration in France, Germany, Italy and the UK alone would effectively double the existing primary fuel savings by 2030. This would increase Europe’s savings from today’s 155.69 Twh to 465 Twh in 2030. It would also result in a 16% to 29% increase in each country’s total cogenerated electricity by 2030.

Governments are being assisted in their CHP endeavors by organizations like COGEN Europe who serve as an information hub for the most recent updates within Europe’s energy policy. COGEN is Europe’s umbrella organization representing the interests of the cogeneration industry.

The European public–private partnership Fuel Cells and Hydrogen Joint Undertaking Seventh Framework Programme project ene.field deploys in 2017[43] up 1,000 residential fuel cell Combined Heat and Power (micro-CHP) installations in 12 states. Per 2012 the first 2 installations have taken place.[44][45][46]

Cogeneration in the United Kingdom

In the United Kingdom, the Combined Heat and Power Quality Assurance scheme regulates the combined production of heat and power. It was introduced in 1996. It defines, through calculation of inputs and outputs, "Good Quality CHP" in terms of the achievement of primary energy savings against conventional separate generation of heat and electricity. Compliance with Combined Heat and Power Quality Assurance is required for cogeneration installations to be eligible for government subsidies and tax incentives.[47]

Cogeneration in the United States

Perhaps the first modern use of energy recycling was done by Thomas Edison. His 1882 Pearl Street Station, the world’s first commercial power plant, was a combined heat and power plant, producing both electricity and thermal energy while using waste heat to warm neighboring buildings.[48] Recycling allowed Edison’s plant to achieve approximately 50 percent efficiency.

By the early 1900s, regulations emerged to promote rural electrification through the construction of centralized plants managed by regional utilities. These regulations not only promoted electrification throughout the countryside, but they also discouraged decentralized power generation, such as cogeneration.

By 1978, Congress recognized that efficiency at central power plants had stagnated and sought to encourage improved efficiency with the Public Utility Regulatory Policies Act (PURPA), which encouraged utilities to buy power from other energy producers.

Cogeneration plants proliferated, soon producing about 8% of all energy in the United States.[49] However, the bill left implementation and enforcement up to individual states, resulting in little or nothing being done in many parts of the country.

The United States Department of Energy has an aggressive goal of having CHP constitute 20% of generation capacity by the year 2030. Eight Clean Energy Application Centers[50] have been established across the nation whose mission is to develop the required technology application knowledge and educational infrastructure necessary to lead "clean energy" (combined heat and power, waste heat recovery and district energy) technologies as viable energy options and reduce any perceived risks associated with their implementation. The focus of the Application Centers is to provide an outreach and technology deployment program for end users, policy makers, utilities, and industry stakeholders.

High electric rates in New England and the Middle Atlantic make these areas of the United States the most beneficial for cogeneration.[51][52]

Applications in power generation systems

Non-renewable

Any of the following conventional power plants may be converted to a combined cooling, heat and power system:[53]

Renewable

• Steam, Its Generation and Use (35 ed.). Babcock & Wilson Company. 1913.

References

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CHP Directive

This refers to the Directive on the promotion of cogeneration based on a useful heat demand in the internal energy market and amending Directive 92/42/EEC, officially 2004/8/EC and popularly better known as the 'Combined Heat and Power (CHP) Directive'.

It is a European Union directive for promoting the use of cogeneration in order to increase the energy efficiency and improve the security of supply of energy. This is intended to be achieved by creating a framework for the promotion and development of high efficiency cogeneration.

The directive entered into force in February 2004 and member states have been obliged to begin its implementation since 2006. (however due to delays resulting out of the comitology process, member states had to adopt the first obligations of the directive by 6 August 2007.)

It is intended that the directive will have a significant impact on the legislation and the diffusion of CHP/cogeneration and district heating within the member states of the European Union.

In summary, the Member States are obliged to produce reports covering their analysis of the state of CHP in their own countries, to promote CHP and show what is being done to promote it, to report on and remove barriers, and to track progress of high-efficiency cogeneration within the energy market.

Capitol Power Plant

The Capitol Power Plant is a fossil-fuel burning power plant which provides steam and chilled water for the United States Capitol, the Supreme Court, the Library of Congress and 19 other buildings in the Capitol Complex. Located at 25 E St SE in southeast Washington, D.C., it is the only coal-burning power plant in the District of Columbia, though it mostly uses natural gas. The plant has been serving the Capitol since 1910, and is under the administration of the Architect of the Capitol (see 2 U.S.C. § 2162). Though it was originally built to supply the Capitol complex with electricity as well, the plant has not produced electricity for the Capitol since 1952. Electricity generation is now handled by the same power grid and local electrical utility (Pepco) that serves the rest of metropolitan Washington.According to the U.S. Department of Energy, the facility released 118,851 tons of carbon dioxide in 2007. In 2009 it switched to using natural gas, unless coal was needed for backup capacity. In 2013, it was announced that the Capitol Power Plant would add a Cogeneration Plant to the CPP that will use natural gas in a combustion turbine in order to efficiently generate both electricity and heat for steam, thus further reducing emissions.

Copper–chlorine cycle

The copper–chlorine cycle (Cu–Cl cycle) is a four-step thermochemical cycle for the production of hydrogen. The Cu–Cl cycle is a hybrid process that employs both thermochemical and electrolysis steps.

It has a maximum temperature requirement of about 530 degrees Celsius.The Cu–Cl cycle involves four chemical reactions for water splitting, whose net reaction decomposes water into hydrogen and oxygen. All other chemicals are recycled. The Cu–Cl process can be linked with nuclear plants or other heat sources such as solar and industrial waste heat to potentially achieve higher efficiencies, lower environmental impact and lower costs of hydrogen production than any other conventional technology.

The Cu–Cl cycle is one of the prominent thermochemical cycles under development within the Generation IV International Forum (GIF). Through GIF, over a dozen countries around the world are developing the next generation of nuclear reactors for highly efficient production of both electricity and hydrogen.

District heating

District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating and water heating. The heat is often obtained from a cogeneration plant burning fossil fuels or biomass, but heat-only boiler stations, geothermal heating, heat pumps and central solar heating are also used, as well as heat waste from nuclear power electricity generation. District heating plants can provide higher efficiencies and better pollution control than localized boilers. According to some research, district heating with combined heat and power (CHPDH) is the cheapest method of cutting carbon emissions, and has one of the lowest carbon footprints of all fossil generation plants. Fifth generation district heat networks do not use combustion on-site and have zero emissions of CO2 and NO2 on-site; they employ heat transfer which uses electricity which may be generated from renewable energy, or from remote fossil fuelled power stations. A combination of CHP and centralized heat pumps are used in the Stockholm multi energy system. This allows the production of heat through electricity when there is an abundance of intermittent power production and cogeneration of electric power and district heating when the availability of intermittent power production is low.

Energy recycling

Energy recycling is the energy recovery process of utilizing energy that would normally be wasted, usually by converting it into electricity or thermal energy. Undertaken at manufacturing facilities, power plants, and large institutions such as hospitals and universities, it significantly increases efficiency, thereby reducing energy costs and greenhouse gas pollution simultaneously. The process is noted for its potential to mitigate global warming profitably. This work is usually done in the form of combined heat and power (also called cogeneration) or waste heat recovery.

Kwinana Cogeneration Plant

Kwinana Cogeneration Plant is located 40 kilometres south of Perth, Western Australia. It provides steam and electrical power to the BP Australia Kwinana Oil Refinery and electricity only to Synergy, the State owned generator/retailer.

As a cogeneration plant, Kwinana supplies both steam and electrical power to its two customers. Steam production from the plant comes predominantly from the waste heat from the gas turbine exhausts and is supported by burning refinery fuel gas from the BP Refinery using 'Duct Burners' inside the Heat Recovery Steam Generators (HRSG). The steam produced drives a steam turbine, further enhancing the plant's efficiency, with BP's steam supply coming from the extraction port on the steam turbine after some pressure and temperature has been lost.

Kwinana produces 120MW of electricity, or approximately 6% of Western Australia's requirements. It is primarily fueled by natural gas from Western Australia's North West Shelf gas fields and delivered to the plant by the Dampier to Bunbury Natural Gas pipeline. The plant is certified for its environmental practices (ISO 14001), quality assurance (ISO 9001) and health and safety (AS4801 & BS18001).

List of generating stations in Ontario

This is a list of electrical generating stations in Ontario, Canada.

List of power stations in Latvia

List of power stations in Portugal

The following page lists some power stations in Portugal.

Micro combined heat and power

Micro combined heat and power or micro-CHP or mCHP is an extension of the idea of cogeneration to the single/multi family home or small office building in the range of up to 50 kW. Local generation has the potential for a higher efficiency than traditional grid-level generators since it lacks the 8-10% energy losses from transporting electricity over long distances. It also lacks the 10–15% energy losses from heat transfer in district heating networks due to the difference between the thermal energy carrier (hot water) and the colder external environment. The most common systems use natural gas as their primary energy source and emit carbon dioxide.

Midland Cogeneration Venture

The Midland Cogeneration Venture (MCV) is a natural gas-fired electrical and steam co-generation plant in Midland, Michigan owned by Midland Cogeneration Venture Limited Partnership. When it began operation in 1991, it was the largest gas-fired steam recovery power plant in the world.Originally designed as the Midland Nuclear Power Plant, the initial design called for two Babcock & Wilcox pressurized water reactors. Reactor one was designed with a 460 MWe rating, and reactor two with an 808 MWe rating. The design called for once-through steam generators (OTSGs) similar to those at Oconee. Consumers Power abandoned the project, which was 85% complete, in 1984 citing numerous construction problems, most notably a sinking foundation. These problems included sinking and cracking of some buildings on the site due to poor soil compaction prior to construction, as well as shifting regulatory requirements following the 1979 accident at Three Mile Island. Construction was also opposed by environmentalists, led by Midland resident, Mary P. Sinclair.By then, 17 years and US$4.3 billion had been invested in the project. Consumers Power, nearly bankrupted by the project, formed a holding company, CMS Energy for it to be a subsidiary of and eventually changed its name to Consumers Energy. Conversion of the plant began in 1986 and was completed at a cost of$500 million, almost twice the original estimate of the nuclear facility. First electrical production occurred in 1990. The plant produces 1,560 Megawatts of electricity for Consumers and 1.35 million pounds per hour of industrial steam for Dow Chemical. The electrical capacity is approximately 10% of the power consumption for the lower peninsula of Michigan. Over time the plant capacity was further up-rated to 1,633 Megawatts and 1.5 million pounds per hour steam.

On July 17, 2002, one of the unused 84-ton nuclear reactor vessel heads was removed from its containment building for transportation to Davis-Besse Nuclear Power Station near Toledo, Ohio, where it replaced a damaged vessel head on a reactor built by the same contractor as the Midland units, B&W.

Consumers owned a 49 percent share in MCV until 2006. Eight other companies owned the remaining 51 percent. In mid-December 2012 Midland Cogeneration Venture was purchased by Borealis Infrastructure. In 2013 the Global Strategic Investment Alliance (GSIA) became a 33% investor. In 2017, Borealis Infrastructure was renamed OMERS Infrastructure Management Inc. Peter (Pete) Milojevic, MCV President and CEO since August 2013, has indicated the company is ready to further expand the electricity capacity of the facility by approximately 800 Megawatts to help replace permanent shutdowns of other generating facilities in the state of Michigan. This would increase MCV's total electricity capacity to about 2,400 Megawatts.

Pearl Street Station

Pearl Street Station was the first commercial central power plant in the US. It was located at 255-257 Pearl Street in Manhattan on a site measuring 50 by 100 feet (15 by 30 m), just south of Fulton Street and fired by coal. It began with six dynamos, and it started generating electricity on September 4, 1882, serving an initial load of 400 lamps at 82 customers. By 1884, Pearl Street Station was serving 508 customers with 10,164 lamps. The station was built by the Edison Illuminating Company, which was headed by Thomas Edison. The station was originally powered by custom-made Porter-Allen high-speed steam engines designed to provide 175 horsepower at 700 rpm, but these proved to be unreliable with their sensitive governors. They were removed and replaced with new engines from Armington & Sims that proved to be much more suitable for Edison's dynamos.Pearl Street Station was also the world's first cogeneration plant. While the steam engines provided grid electricity, Edison made use of the thermal byproduct by distributing steam to local manufacturers, and warming nearby buildings on the same Manhattan block.

The station burned down in 1890, destroying all but one dynamo that is now kept in the Greenfield Village Museum in Dearborn, Michigan.

Photovoltaic thermal hybrid solar collector

Photovoltaic thermal hybrid solar collectors, also known as hybrid PV/T (PVT) or solar cogeneration systems, are power generation technologies that convert solar radiation into usable thermal and electrical energy. Such systems combine a solar cell, which converts sunlight into electricity, with a solar thermal collector, which captures the remaining energy and removes waste heat from the PV module. These technologies can be more energy efficient overall than solar photovoltaic (PV) or solar thermal alone.Significant research has gone into developing a diverse range of PV/T technologies since the 1970s.. While many collector types have been developed for small-scale residential or specific process use, powerful and highly-efficient systems for industrial and utility-scale applications are also beginning to enter the market. Collectors co-generating up to 250kW electricity plus 400kW heat, and operating with 80% conversion efficiency, are commercially available as of 2017.

Public Utility Regulatory Policies Act

The Public Utility Regulatory Policies Act (PURPA, Pub.L. 95–617, 92 Stat. 3117, enacted November 9, 1978) is a United States Act passed as part of the National Energy Act. It was meant to promote energy conservation (reduce demand) and promote greater use of domestic energy and renewable energy (increase supply). The law was created in response to the 1973 energy crisis, and one year in advance of a second energy crisis.

Upon entering the White House, President Jimmy Carter made energy policy a top priority. The law started the energy industry on the road to restructuring.

Sarnia Regional Cogeneration Plant

Sarnia Regional Cogeneration Plant is a natural gas power station owned by TransAlta Energy, in Sarnia, Ontario. The plant is primarily used to supply steam to Arlanxeo, Styrolution, Suncor and Nova Chemicals and power onto the Ontario Grid.

Steam

Steam is water in the gas phase, which is formed when water boils or evaporates. Steam is invisible; however, "steam" often refers to wet steam, the visible mist or aerosol of water droplets formed as this water vapour condenses. At lower pressures, such as in the upper atmosphere or at the top of high mountains, water boils at a lower temperature than the nominal 100 °C (212 °F) at standard pressure. If heated further it becomes superheated steam.

The enthalpy of vaporization is the energy required to turn water into the gaseous form when it increases in volume by 1,700 times at standard temperature and pressure; this change in volume can be converted into mechanical work by steam engines such as reciprocating piston type engines and steam turbines, which are a sub-group of steam engines. Piston type steam engines played a central role to the Industrial Revolution and modern steam turbines are used to generate more than 80% of the world's electricity. If liquid water comes in contact with a very hot surface or depressurizes quickly below its vapor pressure, it can create a steam explosion.

Te Rapa cogeneration

The Te Rapa cogeneration plant is a 45 MW cogeneration plant owned and operated by Contact Energy. It is located at the Fonterra dairy factory at Te Rapa near Hamilton in New Zealand.

The plant is based on a gas turbine (a GE frame 6B) which can produce up to 45 MW of electricity. Hot exhaust gases from this gas turbine are ducted to a HRSG to raise steam. This HRSG has duct burners to increase steam output, which can be up to 180 tons of steam per hour. The plant was commissioned in 1999.

The cogeneration plant is designed for flexible operation, and can provide electricity to the dairy factory, export electricity to the local network or import electricity for use in the dairy factory. A common operating mode is 30 MW of electricity exported and 15 MW plus 120 tons per hour of steam provided to the dairy factory.

Thor Cogeneration Power Station

Thor Cogeneration is a planned gas-fired cogeneration plant, which is to be built on Seal Sands near Billingham, in County Durham, North East England.

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