Power plant. The types of power plants
The efficiency of a thermal power cycle. Use of waste heat for process or central heating. Ways to increase the overall efficiency of the power plant. A combination of different thermodynamic cycles in a combined cycle. Once-through cooling systems.
| Рубрика | Физика и энергетика |
| Вид | статья |
| Язык | английский |
| Дата добавления | 20.02.2019 |
| Размер файла | 37,1 K |
Отправить свою хорошую работу в базу знаний просто. Используйте форму, расположенную ниже
Студенты, аспиранты, молодые ученые, использующие базу знаний в своей учебе и работе, будут вам очень благодарны.
Размещено на http://www.allbest.ru/
Vladimir state university named after the Stoletov brothers
Power plant. The types of power plants
Rassolov A.P.
Power plant. The types of power plants
A power station, also referred to as a power plant or powerhouse and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Most power stations contain one or more generators, a rotating machine that converts mechanical power into electrical power. The relative motion between a magnetic field and a conductor creates an electrical current. The energy source harnessed to turn the generator varies widely. Most power stations in the world burn fossil fuels such as coal, oil, and natural gas to generate electricity. Others use nuclear power, but there is an increasing use of cleaner renewable sourcessuch as solar, wind, wave and hydroelectric.
Classification
• Thermal power stations
• Power from renewable energy
• Storage power stations
Thermal power stations
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 stations. 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 gases 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.
By heat source
• Fossil-fuel power stations may also use a steam turbine generator or in the case of natural gas-fired plants may use a combustion turbine. A coal-fired power station produces heat by burning coal in a steam boiler. The steam drives a steam turbine and generator that then produces electricity. The waste products of combustion include ash, sulphur dioxide, nitrogen oxides and carbon dioxide. Some of the gases can be removed from the waste stream to reduce pollution.
• Nuclear power plants use the heat generated in a nuclear reactor's core (by the fissionprocess) to create steam which then operates a steam turbine and generator. About 20 percent of electric generation in the USA 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 crust.
• Biomass-fuelled power plants may be fuelled by waste from sugar cane, municipal solid waste, landfill methane, or other forms of biomass.
• In integrated steel mills, blast furnace exhaust gas is a low-cost, although low-energy-density, fuel.
• Waste heat from industrial processes is occasionally concentrated enough to use for power generation, usually in a steam boiler and turbine.
• Solar thermal electric plants use sunlight to boil water and produce steam which turns the generator.
By prime mover
• Waste heat from industrial processes is occasionally concentrated enough to use for power generation, usually in a steam boiler and turbine.
• Solar thermal electric plants use sunlight to boil water and produce steam which turns the generator.
By prime mover
• 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.
• 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 baseloaded plants. These may be comparatively small units, and sometimes completely unmanned, being remotely operated. This type was pioneered by the UK, Princetown 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 engines 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.
• 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.
By duty
• Base load power plants run nearly continually to provide that component of system load that doesn't 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 plants 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 sometimes 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 plants 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.
Cooling towers
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. Gas-fired power plants can achieve as much as 65 percent conversion efficiency, while coal and oil plants achieve around 30 to 49 percent. The waste heat produces a temperature rise in the atmosphere, which is small compared to that produced by greenhousegas emissions from the same power plant. Natural draft wet cooling towers at many nuclear power plants and large fossil fuel-fired power plants use large 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, petroleum refineries, petrochemical plants, geothermal, biomass and wasteto-energy plants use fans to provide air movement upward through downcoming water, and are not hyperboloid chimney-like structures. The induced or forceddraft cooling towers are typically rectangular, box-like structures filled with a material that enhances the mixing of the upflowing air and the downflowing water.[8][9]
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.
thermal power thermodynamic cycle
Once-through cooling systems
Electric companies often prefer to use cooling water from the ocean, a lake, or a river, or a 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 exchangers.
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 screens, 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.[10][11] For example, the cooling system at the Indian Point Energy Center in New York kills over a billion fish eggs and larvae annually.[12]
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.
Water consumption by power stations is a developing issue.[13]
In recent years, recycled wastewater, or 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.
Power from renewable energy. Hydroelectric power station
In a hydroelectric power station water flows through turbines using hydropower to generate hydroelectricity. Power is captured from the gravitational force of water falling through penstocks to water turbines connected to generators. The amount of power available is a combination of height and flow. A wide range of Dams may be built to raise the water level, and create a lake for storing water. Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest hydroelectricity producer, with 721 terawatt-hours of production in 2010, representing around 17 percent of domestic electricity use.
Solar
Solar energy can be turned into electricity either directly in solar cells, or in a concentrating solar power plant by focusing the light to run a heat engine.
A solar photovoltaic power plant converts sunlight into direct current electricity using the photoelectric effect. Inverters change the direct current into alternating current for connection to the electrical grid. This type of plant does not use rotating machines for energy conversion.
Solar thermal power plants are another type of solar power plant. They use either parabolic troughs or heliostats to direct sunlight onto a pipe containing a heat transfer fluid, such as oil. The heated oil is then used to boil water into steam, which turns a turbine that drives an electrical generator. The central tower type of solar thermal power plant uses hundreds or thousands of mirrors, depending on size, to direct sunlight onto a receiver on top of a tower. Again, the heat is used to produce steam to turn turbines that drive electrical generators.
Wind
Wind turbines can be used to generate electricity in areas with strong, steady winds, sometimes offshore. Many different designs have been used in the past, but almost all modern turbines being produced today use a three-bladed, upwind design. Grid-connected wind turbines now being built are much larger than the units installed during the 1970s. They thus produce power more cheaply and reliably than earlier models. With larger turbines (on the order of one megawatt), the blades move more slowly than older, smaller, units, which makes them less visually distracting and safer for birds.
Marine
Marine energy or marine power (also sometimes referred to as ocean energy or ocean power) refers to the energy carried by ocean waves, tides, salinity, and ocean temperature differences. The movement of water in the world's oceans creates a vast store of kinetic energy, or energy in motion. This energy can be harnessed to generate electricity to power homes, transport and industries.
The term marine energy encompasses both wave power -- power from surface waves, and tidal power -- obtained from the kinetic energy of large bodies of moving water. Offshore wind power is not a form of marine energy, as wind power is derived from the wind, even if the wind turbines are placed over water.
The oceans have a tremendous amount of energy and are close to many if not most concentrated populations. Ocean energy has the potential of providing a substantial amount of new renewable energy around the world.
Osmosis
Salinity gradient energy is called pressure-retarded osmosis. In this method, seawater is pumped into a pressure chamber that is at a pressure lower than the difference between the pressures of saline water and fresh water. Freshwater is also pumped into the pressure chamber through a membrane, which increases both the volume and pressure of the chamber. As the pressure differences are compensated, a turbine is spun creating energy. This method is being specifically studied by the Norwegian utility Statkraft, which has calculated that up to 25 TWh/yr would be available from this process in Norway. Statkraft has built the world's first prototype osmotic power plant on the Oslo fiord which was opened on November 24, 2009.
Biomass
Biomass energy can be produced from combustion of waste green material to heat water into steam and drive a steam turbine. Bioenergy can also be processed through a range of temperatures and pressures in gasification, pyrolysis or torrefaction reactions. Depending on the desired end product, these reactions create more energy-dense products (syngas, wood pellets, biocoal) that can then be fed into an accompanying engine to produce electricity at a much lower emission rate when compared with open burning.
Storage power stations
t is possible to store energy and produce the electricity at a later time like in Pumped-storage hydroelectricity, Thermal energy storage, Flywheel energy storage, Battery storage power station and so on.
Pumped storage
The worlds largest form of storage for excess electricity, pumped-storage is a reversible hydroelectric plant. They are a net consumer of energy but provide storage for any source of electricity, effectively smoothing peaks and troughs in electricity supply and demand. Pumped storage plants typically use "spare" electricity during off peak periods to pump water from a lower reservoir to an upper reservoir. Because the pumping takes place "off peak", electricity is less valuable than at peak times. This less valuable "spare" electricity comes from uncontrolled wind power and base load power plants such as coal, nuclear and geothermal, which still produce power at night even though demand is very low.
During daytime peak demand, when electricity prices are high, the storage is used for peaking power, where water in the upper reservoir is allowed to flow back to a lower reservoir through a turbine and generator. Unlike coal power stations, which can take more than 12 hours to start up from cold, a hydroelectric generator can be brought into service in a few minutes, ideal to meet a peak load demand. Two substantial pumped storage schemes are in South Africa, Palmiet Pumped Storage Scheme and another in the Drakensberg, Ingula Pumped Storage Scheme.
References
1. "Hydro-electricity restored to historic Northumberland home". BBC News.
2. Nuclear Power Plants Information, by International Atomic Energy Agency.
3. Wiser, Wendell H. (2000). Energy resources: occurrence, production, conversion, use.
4. Nuclear Power Plants Information, by International Atomic Energy Agency.
5. https://en.wikipedia.org/wiki/Power_station#Thermal_power_stations.
Размещено на Allbest.ru
...Подобные документы
The basic principles and the protection of power lines patterns used in this process methods. Physical basics of high-power transformers in substations. Justification of the information received. Diagram illustrating the operation of the protection.
презентация [628,0 K], добавлен 18.02.2016Угловая скорость вращения магнитного поля. Математическая модель асинхронного двигателя в форме Коши, а также блок-схема его прямого пуска с использованием Power System Blockset. Зависимость угловой скорости ротора от величины электромагнитного момента.
реферат [672,5 K], добавлен 03.01.2010Definition the certain latent high temperature of evaporation of the liquid using capital equipment and calculations. The accepted value of the latent high temperature of evaporation. The uncertainty for the specific latent heat of vaporization.
лабораторная работа [247,8 K], добавлен 29.12.2010The overall architecture of radio frequency identification systems. The working principle of RFID: the reader sends out radio waves of specific frequency energy to the electronic tags, tag receives the radio waves. Benefits of contactless identification.
курсовая работа [179,1 K], добавлен 05.10.2014The principles of nonlinear multi-mode coupling. Consider a natural quasi-linear mechanical system with distributed parameters. Parametric approach, the theory of normal forms, according to a method of normal forms. Resonance in multi-frequency systems.
реферат [234,3 K], добавлен 14.02.2010The Chernobyl disaster is a huge global problem of 21st century. Current status of Chernobyl NPP. The most suitable decision of solving problem of wastes is a reburial in the repository "Buryakovka". The process of the Arch assembling and sliding.
реферат [396,5 K], добавлен 19.04.2011Political power as one of the most important of its kind. The main types of political power. The functional analysis in the context of the theory of social action community. Means of political activity related to the significant material cost-us.
реферат [11,8 K], добавлен 10.05.2011Power Point программа для создания презентаций, которые необходимы во многих сферах профессиональной деятельности. Возможности и настройка программы Power Point. Запуск программы, мастер автосодержания. Способ вывода презентации и шаблоны оформления.
реферат [635,5 K], добавлен 13.09.2010The Structure of Ukrainian Government. Rights and Duties of the Ukrainian Citizens. The Constitution of Ukraine. The state language. The Verkhovna Rada's main function is making laws. The Cabinet of Ministers is the highest body of the executive power.
контрольная работа [15,3 K], добавлен 13.11.2010Спеціальні ефекти переходу між слайдами в Microsoft Power Point. Розробка ефектів при зміні слайдів. Анімація тексту на слайді. Видалення ефекту зміни кадрів. Додавання кнопок до презентації. Створення та видалення гіперпосилань на інші слайди.
реферат [538,2 K], добавлен 09.08.2011Использование программы подготовки презентаций Power Point в повседневности. Подготовка и демонстрация слайдов для печати на прозрачных плёнках и бумаге. Создание новой презентации с помощью мастера автосодержания, шаблона оформления, пустой презентации.
контрольная работа [695,8 K], добавлен 16.04.2011Розгляд soft power як компоненту сучасних міжнародних відносин. Надання послуг вищої освіти, розвиток наук, завдання яких полягає у виробництві теорій, легітимізуючих позицію і погляди держави. Формування світогляду через добровільних агентів впливу.
доклад [13,8 K], добавлен 27.11.2014Сферы применения компьютерных презентаций. Разработка технологии обучения созданию презентации в Power Point с различным интерфейсом. Структура, основные элементы электронного учебного пособия, его текстовая основа. Тестовая проверка результатов обучения.
презентация [6,4 M], добавлен 10.10.2010Призначення та переваги використання автоматизованих робочих місць (АРМ). Огляд нових функцій програмного продукту Microsoft Power Point. Створення і публікація HTML-документів, показ презентацій, співпраця в реальному часі за допомогою програми.
контрольная работа [45,3 K], добавлен 26.12.2012Преимущества использования мультимедиа в проведении лекции, использование Power Point для её создания. Визуализация процесса обучения и особенности психологии восприятия, лекция-визуализация. Отношение студентов к проблематике обычной вузовской лекции.
курсовая работа [70,0 K], добавлен 26.08.2011История профессии - оператор ЭВМ. Общая характеристика и история развития пакета программ Microsoft Office. Основные возможности Microsoft Power Point, ее преимущества. Порядок создания презентаций, обоснованное использование эффектов мультимедиа.
реферат [127,7 K], добавлен 04.09.2013The Keynesian concept in economic of endogenous cycles seems to require non-linear structures. One of the theories of business cycles in the Keynesian vein is that expounded in a pioneering article by N. Kaldor. Non-linear dynamics of the Kaldor's cycle.
контрольная работа [233,8 K], добавлен 18.07.2009Навчальні дисципліни, що складають план підготовки кваліфікованого робітника. Характеристики навчальної теми підготовки кваліфікованого робітника за спеціальністю "Робота зі шрифтами, стилями, кольором в Power Point". Зміст, методи та засоби навчання.
курсовая работа [1,6 M], добавлен 26.06.2013Description the introductions between man and nature, polluting of the air, oceans. Analyzes problems of cities: the wastes from factories, chemical plants, electric and atomic power stations. Studying the antipollution campaigns of car corporation’s.
эссе [10,1 K], добавлен 21.03.2012Рассмотрение принципов компьютерного моделирования. Изучение программных методов числового интегрирования и дифференцирования. Ознакомление с правилами создания и оформления презентации в Power Point, преимуществами ее использования на уроках физики.
дипломная работа [2,5 M], добавлен 27.06.2010
