Contenido

En las centrales térmicas, la potencia mecánica es producida por un motor térmico que transforma la energía térmica, a menudo de la combustión de un combustible, en energía de rotación. La mayoría de las centrales térmicas producen vapor, por lo que a veces se las denomina centrales de vapor. No toda la energía térmica se puede transformar en potencia mecánica, de acuerdo con la segunda ley de la termodinámica; por lo tanto, siempre hay calor perdido al medio ambiente. Si esta pérdida se emplea como calor útil, para procesos industriales o calefacción urbana, la planta de energía se denomina planta de energía de cogeneración o planta de cogeneración (central de energía y calor combinada). En los países donde la calefacción urbana es común, existen plantas de calor dedicadas que se llaman estaciones de calderas"). Una importante clase de centrales eléctricas en el Medio Oriente utiliza el subproducto de calor para la desalinización del agua.

La eficiencia de un ciclo de energía térmica está limitada por la temperatura máxima del fluido de trabajo producido. La eficiencia no es directamente una función del combustible utilizado. Para las mismas condiciones de vapor, las centrales eléctricas de carbón, nucleares y de gas tienen todas la misma eficiencia teórica. En general, si un sistema está encendido constantemente (carga base) será más eficiente que uno que se use de forma intermitente (carga máxima). Las turbinas de vapor generalmente funcionan con mayor eficiencia cuando funcionan a plena capacidad.

Además del uso del calor rechazado para el proceso o la calefacción urbana, una forma de mejorar la eficiencia general de una central eléctrica es combinar dos ciclos termodinámicos diferentes en una central de ciclo combinado. Más comúnmente, los gases de escape de una turbina de gas se utilizan para generar vapor para una caldera y una turbina de vapor. La combinación de un ciclo "superior" y un ciclo "inferior" produce una eficiencia general más alta de lo que cualquiera de los dos ciclos puede lograr solo.

Classification

Power plants that can be arranged (scheduled) to provide on-demand electricity to a system include:

Non-programmable plants include sources such as wind and solar energy; While its long-term contribution to the system's energy supply is predictable, on a short-term (daily or hourly) basis, its energy must be used as available since generation cannot be deferred. Contractual ("take or pay") arrangements with independent power producers or interconnections of systems to other networks may be effectively non-dispatchable.

cooling towers

All thermal power plants produce waste heat as a byproduct of the useful electrical energy produced. The amount of waste heat is equal to or greater than the amount of energy converted into useful electricity. Gas plants can achieve up to 65 percent conversion efficiency, while coal and oil plants reach around 30 to 49 percent. The waste heat produces a temperature increase in the atmosphere, which is small compared to that produced by greenhouse gas emissions from the same power plant. Natural draft wet cooling towers at many nuclear power plants and large fossil fuel power plants use large hyperboloid chimney-like structures (as seen in the image to the right) that release waste heat to the ambient atmosphere by the evaporation of water.

However, mechanically induced draft or forced draft wet cooling towers at many large thermal power plants, nuclear power plants, fossil fuel plants, oil refineries, petrochemical plants, geothermal plants, biomass, and waste-to-energy plants use fans to provide upward air movement through approaching water, and are not hyperboloid chimney-type structures. Induced or forced draft cooling towers are typically rectangular, box-shaped structures filled with a material that improves the mixing of air flowing upward and water flowing downward.[8]​[9]​.

In areas with restricted water use, a dry cooling tower or directly air-cooled radiators may be necessary, as the cost or environmental consequences of obtaining water for evaporative cooling would be prohibitive. These chillers have lower efficiency and higher energy consumption to drive the fans, compared to a typical wet evaporative cooling tower.

One-Step Cooling Systems

Power companies often prefer to use cooling water from the ocean, a lake or river, or a cooling pond, rather than from a cooling tower. This one-pass cooling system can save the cost of a cooling tower and can have lower energy costs for pumping cooling water through the plant's heat exchangers. However, waste heat can cause thermal pollution when water is discharged. Power plants that use natural bodies of water for cooling are designed with mechanisms such as "fish screens" to limit the ingestion 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 each year by power plants.[10][11] For example, the cooling system at the Indian Point Energy Center in New York annually kills more than one billion eggs and larvae fish.[12]​.

An additional environmental impact is that aquatic organisms that adapt to warmer discharge water may be injured if the plant is stopped in cold weather.

Water consumption by power plants is a developing problem.[13]​.

In recent years, recycled wastewater, or gray water, has been used in cooling towers. The Calpine Riverside and Calpine Fox power plants in Wisconsin, as well as the Calpine Mankato power plant in Minnesota are among these facilities.

Las centrales eléctricas también pueden generar energía eléctrica a partir de fuentes de energía renovables.

Hydroelectric power station

In a hydroelectric power plant, water flows through turbines that use hydroelectric energy to generate hydroelectricity. Energy is captured from the gravitational force of water falling through gates to turbines connected to generators. The amount of power available is a combination of head and flow. A wide range of dams can be built to raise the water level and create a lake to store water. Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest producer of hydropower, with 721 terawatt-hours of production in 2010, accounting for about 17 percent of domestic electricity use.

Solar

Solar energy can be converted into electricity, either directly in solar cells, or in a concentrating solar power plant by focusing light to drive a heat engine.

A photovoltaic solar power plant converts sunlight into direct current electricity using the photoelectric effect. "Inverter (electronics)") inverters change 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 parabolic troughs or heliostats to direct sunlight into a pipe containing a heat transfer fluid, such as oil. The hot oil is then used to boil water into steam, which spins 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 toward a receiver at the top of a tower. Again, the heat is used to produce steam to spin the turbines that drive electrical generators.

Wind

Wind turbines can be used to generate electricity in areas with strong, constant winds, sometimes offshore. Many different designs have been used in the past, but almost all modern turbines produced today use a three-blade upwind design. The grid-tied wind turbines being built now are much larger than the units installed during the 1970s. Thus, they produce energy more economically and reliably than previous models. With larger turbines (on the order of one megawatt), the blades move more slowly than older, smaller units, making them less visually distracting and safer for birds.

Marine

Marine energy or ocean energy refers to the energy transported by waves, tides, salinity and temperature differences in the ocean. The movement of water in the world's oceans creates a vast reserve of kinetic energy. This energy can be harnessed to generate electricity to power homes, transportation and industries.

The term marine energy encompasses both wave energy (power of surface waves and tidal energy) obtained from the kinetic energy of large bodies of moving water. Offshore wind energy is not a form of marine energy, as wind energy is derived from wind, even if the wind turbines are placed over water.

The oceans have an enormous amount of energy and are close to many, if not the most concentrated populations. Ocean energy has the potential to provide a substantial amount of new renewable energy worldwide.[14]​.

Osmosis

The energy of the salinity gradient 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. Fresh water is also pumped into the pressure chamber through a membrane, increasing both the volume and pressure of the chamber. As pressure differences are equalized, 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/year would be obtained in this process in Norway. Statkraft has built the world's first prototype osmotic power plant in the Oslo Fjord, which opened on November 24, 2009.

Biomass

Biomass energy can be produced from the combustion of waste green material to heat water into steam and drive a steam turbine. Bioenergy can also be processed over 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 to an accompanying engine to produce electricity at a much lower emission rate compared to open burning.

Es posible almacenar energía y producir la electricidad en un momento posterior, como en la hidroelectricidad de almacenamiento por bombeo, el almacenamiento de energía térmica, el almacenamiento de energía del volante, la central eléctrica de almacenamiento de baterías, etc.

Pumped storage

The world's largest form of storage for excess electricity is pumped storage in a reversible hydroelectric plant. It is a net consumer of energy, but provides storage for any source of electricity, effectively smoothing out peaks and troughs in electricity supply and demand. Pumped storage plants typically use "spare" electricity during peak periods to pump water from a lower reservoir to an upper reservoir. Because pumping takes place "off-peak," electricity is less valuable than during peak hours. This less valuable, "spare" electricity comes from uncontrolled wind power and baseload power plants, such as coal, nuclear and geothermal, which still produce power at night, although demand is very low. During peak demand during the day, when electricity prices are high, storage is used to achieve peak power, where water in the upper reservoir can return to a lower reservoir via a turbine and generator. Unlike coal-fired power plants, which can Taking more than 12 hours to start from cold, a hydroelectric generator can be commissioned in a few minutes, ideal for meeting peak load demand. Two substantial pumped storage schemes are found in South Africa, Palmiet Pumped Storage Scheme and another in Drakensberg, Ingula Pumped Storage Scheme.

The power generated by a power plant is measured in multiples of watts, typically "Mega (prefix)" megawatts (10 watts) or gigawatts (10 watts). Power plants vary greatly in capacity depending on the type of power plant and historical, geographic and economic factors. The following examples offer a sense of scale.

Many of the largest operating onshore wind farms are located in the United States. As of 2011, the Roscoe Wind Farm is the second largest onshore wind farm in the world, with 781.5 MW of power, followed by the Horse Hollow Wind Energy Center (735.5 MW). As of July 2013, the London Array in the United Kingdom is the world's largest offshore wind farm at 630 MW, followed by the Thanet Offshore Wind Project in the United Kingdom at 300 MW.

By 2015 the largest photovoltaic (PV) power plants in the world were led by the Longyangxia Dam solar park in China, with 850 megawatts.

Solar thermal power plants in the United States have the following output:.

Large coal plants, nuclear plants and hydroelectric plants can generate hundreds of megawatts to multiple gigawatts. Some examples:

Gas turbine power plants can generate tens to hundreds of megawatts. Some examples:

The rated capacity of a power plant is almost the maximum electrical power that that power plant can produce. Some power plants run at almost exactly their rated capacity all the time, such as a base load power plant that does not follow load except at times of scheduled or unscheduled maintenance.

However, many power plants typically produce much less power than their rated capacity.

In some cases, a power plant produces much less power than its rated capacity because it uses an intermittent power source. Operators try to extract the maximum available power" from such power plants, because their marginal cost is virtually zero, but the available power varies widely - it can be zero during strong overnight storms.

In some cases, operators deliberately produce less power for economic reasons. The cost of fuel to run a baseload auxiliary plant") can be relatively high, and the cost of fuel to run a peaking power plant is even higher: they have relatively high marginal costs. Operators keep power plants off ("operating reserve") or running at minimum fuel consumption ("spinning reserve") most of the time. Operators supply more fuel to baseload power plants only when demand increases above what the lowest-cost plants (i.e., baseload plants) can produce. intermittent), and then supply more fuel to peak power plants when demand increases faster than base load plants can keep up.

The operating personnel of a power plant have several tasks. Operators are responsible for the safety of work crews who frequently perform repairs on mechanical and electrical equipment. They maintain the equipment with periodic inspections and record temperatures, pressures and other important information at regular intervals. Operators are responsible for starting and stopping the generators as needed. They are able to synchronize and adjust the voltage output of the added generation with the operating electrical system, without disturbing the system. They must understand the electrical and mechanical systems to troubleshoot the facility and increase the reliability of the facility. Operators must be able to respond to an emergency and know the procedures established to deal with it.

Contenido

En las centrales térmicas, la potencia mecánica es producida por un motor térmico que transforma la energía térmica, a menudo de la combustión de un combustible, en energía de rotación. La mayoría de las centrales térmicas producen vapor, por lo que a veces se las denomina centrales de vapor. No toda la energía térmica se puede transformar en potencia mecánica, de acuerdo con la segunda ley de la termodinámica; por lo tanto, siempre hay calor perdido al medio ambiente. Si esta pérdida se emplea como calor útil, para procesos industriales o calefacción urbana, la planta de energía se denomina planta de energía de cogeneración o planta de cogeneración (central de energía y calor combinada). En los países donde la calefacción urbana es común, existen plantas de calor dedicadas que se llaman estaciones de calderas"). Una importante clase de centrales eléctricas en el Medio Oriente utiliza el subproducto de calor para la desalinización del agua.

La eficiencia de un ciclo de energía térmica está limitada por la temperatura máxima del fluido de trabajo producido. La eficiencia no es directamente una función del combustible utilizado. Para las mismas condiciones de vapor, las centrales eléctricas de carbón, nucleares y de gas tienen todas la misma eficiencia teórica. En general, si un sistema está encendido constantemente (carga base) será más eficiente que uno que se use de forma intermitente (carga máxima). Las turbinas de vapor generalmente funcionan con mayor eficiencia cuando funcionan a plena capacidad.

Además del uso del calor rechazado para el proceso o la calefacción urbana, una forma de mejorar la eficiencia general de una central eléctrica es combinar dos ciclos termodinámicos diferentes en una central de ciclo combinado. Más comúnmente, los gases de escape de una turbina de gas se utilizan para generar vapor para una caldera y una turbina de vapor. La combinación de un ciclo "superior" y un ciclo "inferior" produce una eficiencia general más alta de lo que cualquiera de los dos ciclos puede lograr solo.

Classification

Power plants that can be arranged (scheduled) to provide on-demand electricity to a system include:

Non-programmable plants include sources such as wind and solar energy; While its long-term contribution to the system's energy supply is predictable, on a short-term (daily or hourly) basis, its energy must be used as available since generation cannot be deferred. Contractual ("take or pay") arrangements with independent power producers or interconnections of systems to other networks may be effectively non-dispatchable.

cooling towers

All thermal power plants produce waste heat as a byproduct of the useful electrical energy produced. The amount of waste heat is equal to or greater than the amount of energy converted into useful electricity. Gas plants can achieve up to 65 percent conversion efficiency, while coal and oil plants reach around 30 to 49 percent. The waste heat produces a temperature increase in the atmosphere, which is small compared to that produced by greenhouse gas emissions from the same power plant. Natural draft wet cooling towers at many nuclear power plants and large fossil fuel power plants use large hyperboloid chimney-like structures (as seen in the image to the right) that release waste heat to the ambient atmosphere by the evaporation of water.

However, mechanically induced draft or forced draft wet cooling towers at many large thermal power plants, nuclear power plants, fossil fuel plants, oil refineries, petrochemical plants, geothermal plants, biomass, and waste-to-energy plants use fans to provide upward air movement through approaching water, and are not hyperboloid chimney-type structures. Induced or forced draft cooling towers are typically rectangular, box-shaped structures filled with a material that improves the mixing of air flowing upward and water flowing downward.[8]​[9]​.

In areas with restricted water use, a dry cooling tower or directly air-cooled radiators may be necessary, as the cost or environmental consequences of obtaining water for evaporative cooling would be prohibitive. These chillers have lower efficiency and higher energy consumption to drive the fans, compared to a typical wet evaporative cooling tower.

One-Step Cooling Systems

Power companies often prefer to use cooling water from the ocean, a lake or river, or a cooling pond, rather than from a cooling tower. This one-pass cooling system can save the cost of a cooling tower and can have lower energy costs for pumping cooling water through the plant's heat exchangers. However, waste heat can cause thermal pollution when water is discharged. Power plants that use natural bodies of water for cooling are designed with mechanisms such as "fish screens" to limit the ingestion 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 each year by power plants.[10][11] For example, the cooling system at the Indian Point Energy Center in New York annually kills more than one billion eggs and larvae fish.[12]​.

An additional environmental impact is that aquatic organisms that adapt to warmer discharge water may be injured if the plant is stopped in cold weather.

Water consumption by power plants is a developing problem.[13]​.

In recent years, recycled wastewater, or gray water, has been used in cooling towers. The Calpine Riverside and Calpine Fox power plants in Wisconsin, as well as the Calpine Mankato power plant in Minnesota are among these facilities.

Las centrales eléctricas también pueden generar energía eléctrica a partir de fuentes de energía renovables.

Hydroelectric power station

In a hydroelectric power plant, water flows through turbines that use hydroelectric energy to generate hydroelectricity. Energy is captured from the gravitational force of water falling through gates to turbines connected to generators. The amount of power available is a combination of head and flow. A wide range of dams can be built to raise the water level and create a lake to store water. Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest producer of hydropower, with 721 terawatt-hours of production in 2010, accounting for about 17 percent of domestic electricity use.

Solar

Solar energy can be converted into electricity, either directly in solar cells, or in a concentrating solar power plant by focusing light to drive a heat engine.

A photovoltaic solar power plant converts sunlight into direct current electricity using the photoelectric effect. "Inverter (electronics)") inverters change 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 parabolic troughs or heliostats to direct sunlight into a pipe containing a heat transfer fluid, such as oil. The hot oil is then used to boil water into steam, which spins 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 toward a receiver at the top of a tower. Again, the heat is used to produce steam to spin the turbines that drive electrical generators.

Wind

Wind turbines can be used to generate electricity in areas with strong, constant winds, sometimes offshore. Many different designs have been used in the past, but almost all modern turbines produced today use a three-blade upwind design. The grid-tied wind turbines being built now are much larger than the units installed during the 1970s. Thus, they produce energy more economically and reliably than previous models. With larger turbines (on the order of one megawatt), the blades move more slowly than older, smaller units, making them less visually distracting and safer for birds.

Marine

Marine energy or ocean energy refers to the energy transported by waves, tides, salinity and temperature differences in the ocean. The movement of water in the world's oceans creates a vast reserve of kinetic energy. This energy can be harnessed to generate electricity to power homes, transportation and industries.

The term marine energy encompasses both wave energy (power of surface waves and tidal energy) obtained from the kinetic energy of large bodies of moving water. Offshore wind energy is not a form of marine energy, as wind energy is derived from wind, even if the wind turbines are placed over water.

The oceans have an enormous amount of energy and are close to many, if not the most concentrated populations. Ocean energy has the potential to provide a substantial amount of new renewable energy worldwide.[14]​.

Osmosis

The energy of the salinity gradient 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. Fresh water is also pumped into the pressure chamber through a membrane, increasing both the volume and pressure of the chamber. As pressure differences are equalized, 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/year would be obtained in this process in Norway. Statkraft has built the world's first prototype osmotic power plant in the Oslo Fjord, which opened on November 24, 2009.

Biomass

Biomass energy can be produced from the combustion of waste green material to heat water into steam and drive a steam turbine. Bioenergy can also be processed over 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 to an accompanying engine to produce electricity at a much lower emission rate compared to open burning.

Es posible almacenar energía y producir la electricidad en un momento posterior, como en la hidroelectricidad de almacenamiento por bombeo, el almacenamiento de energía térmica, el almacenamiento de energía del volante, la central eléctrica de almacenamiento de baterías, etc.

Pumped storage

The world's largest form of storage for excess electricity is pumped storage in a reversible hydroelectric plant. It is a net consumer of energy, but provides storage for any source of electricity, effectively smoothing out peaks and troughs in electricity supply and demand. Pumped storage plants typically use "spare" electricity during peak periods to pump water from a lower reservoir to an upper reservoir. Because pumping takes place "off-peak," electricity is less valuable than during peak hours. This less valuable, "spare" electricity comes from uncontrolled wind power and baseload power plants, such as coal, nuclear and geothermal, which still produce power at night, although demand is very low. During peak demand during the day, when electricity prices are high, storage is used to achieve peak power, where water in the upper reservoir can return to a lower reservoir via a turbine and generator. Unlike coal-fired power plants, which can Taking more than 12 hours to start from cold, a hydroelectric generator can be commissioned in a few minutes, ideal for meeting peak load demand. Two substantial pumped storage schemes are found in South Africa, Palmiet Pumped Storage Scheme and another in Drakensberg, Ingula Pumped Storage Scheme.

The power generated by a power plant is measured in multiples of watts, typically "Mega (prefix)" megawatts (10 watts) or gigawatts (10 watts). Power plants vary greatly in capacity depending on the type of power plant and historical, geographic and economic factors. The following examples offer a sense of scale.

Many of the largest operating onshore wind farms are located in the United States. As of 2011, the Roscoe Wind Farm is the second largest onshore wind farm in the world, with 781.5 MW of power, followed by the Horse Hollow Wind Energy Center (735.5 MW). As of July 2013, the London Array in the United Kingdom is the world's largest offshore wind farm at 630 MW, followed by the Thanet Offshore Wind Project in the United Kingdom at 300 MW.

By 2015 the largest photovoltaic (PV) power plants in the world were led by the Longyangxia Dam solar park in China, with 850 megawatts.

Solar thermal power plants in the United States have the following output:.

Large coal plants, nuclear plants and hydroelectric plants can generate hundreds of megawatts to multiple gigawatts. Some examples:

Gas turbine power plants can generate tens to hundreds of megawatts. Some examples:

The rated capacity of a power plant is almost the maximum electrical power that that power plant can produce. Some power plants run at almost exactly their rated capacity all the time, such as a base load power plant that does not follow load except at times of scheduled or unscheduled maintenance.

However, many power plants typically produce much less power than their rated capacity.

In some cases, a power plant produces much less power than its rated capacity because it uses an intermittent power source. Operators try to extract the maximum available power" from such power plants, because their marginal cost is virtually zero, but the available power varies widely - it can be zero during strong overnight storms.

In some cases, operators deliberately produce less power for economic reasons. The cost of fuel to run a baseload auxiliary plant") can be relatively high, and the cost of fuel to run a peaking power plant is even higher: they have relatively high marginal costs. Operators keep power plants off ("operating reserve") or running at minimum fuel consumption ("spinning reserve") most of the time. Operators supply more fuel to baseload power plants only when demand increases above what the lowest-cost plants (i.e., baseload plants) can produce. intermittent), and then supply more fuel to peak power plants when demand increases faster than base load plants can keep up.

The operating personnel of a power plant have several tasks. Operators are responsible for the safety of work crews who frequently perform repairs on mechanical and electrical equipment. They maintain the equipment with periodic inspections and record temperatures, pressures and other important information at regular intervals. Operators are responsible for starting and stopping the generators as needed. They are able to synchronize and adjust the voltage output of the added generation with the operating electrical system, without disturbing the system. They must understand the electrical and mechanical systems to troubleshoot the facility and increase the reliability of the facility. Operators must be able to respond to an emergency and know the procedures established to deal with it.