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Study of Modeling & Analysis of Wind Turbine
1. Introduction:
1.1 General:
Bangladesh is a least developed country. The area of this country is 1,47,570 square kilometer and population is 1.44 million. Bangladesh is mainly an agrarian country. The industrialization process of this country is increasing rapidly in present. There is no alternative of industrialization for the economic development of Bangladesh. Modernization of agricultural sector is necessary for obtaining the food security as such. And for these types of activities continuous supply of good quality electricity is very essential. But the lack of electricity in Bangladesh has come to an alarming state. The expected development in Bangladesh is hampering due to a huge gap between production capacities in response to demand. Bangladesh must have to solve her electricity problem to become a technologically advanced and food secured economically solvent developed country. As a result, besides meeting increasing electricity demand, new employment will be created; unemployment problem will be solved and will turn into an agriculturally self dependent and industrially developed country. By this means economic freedom of our country will be achieved.
The ice in the arctic regions is melting because of temperature rise which is caused by emission of green house gases. As a result, the sea level is also rising and the coastal low lying countries will probably disappear in the sea in future. Besides this due to this climate change the frequency of natural calamities has also increased. The human being has also come under considerable threat of extinction. For the sake of sustainable economic development of agricultural, industrial and other sectors in this aspect, all the activities must be environmental friendly. So, to produce electricity environmental consequences of it must be considered. The power plant of Bangladesh is currently using fossil fuel for generating electricity. Bangladesh is not rich in mineral resources. Although coal and gas mine has been discovered here but these are not plenty. Most of the power plant of Bangladesh use gas. The coal driven power plant is also found in Bangladesh. The petroleum reserve has not been discovered so far in Bangladesh. So, to operate power plant depended on petroleum huge foreign currency is expensed to import those petroleum from abroad. So, the production cost of electricity has increased substantially. The impact of this is felt in our socio-economic life.
Bangladesh has one water driven power plant. This power plant has developed by building a dam in Kaptai Lake. A vast land area has become submerged and biodiversity lost after construction of this plant due to the rise of water level in the lake. Moreover, the power plant is old enough to produce expected amount of electricity. Some of its units have collapsed. Some of it has completely lost its productivity. So, this power plant is not able to produce expected amount of electricity.
It is now essential to establish new power plants to meet the increasing demands. Although, the establishment of contemporary power plant require less time and money, to keep it running and considering the fuel cost high the long term cost for electricity production remain high. The fuel used in this purpose is harmful to environment. So, technologically advanced countries of the world are giving importance to establish wind turbine power plant as an alternative means for producing electricity in an average scale. The advantage of this is to produce average amount of electricity in a average scale.
Although primary establishment cost of this type of power plant is huge but to produce electricity in the long run power production cost is comparatively lower. Environmental pollution is also becomes less. The longevity of this power plant is more than other types of power plants and fuel cost gets zero. The production capacity is average. To take all the things into consideration, the necessity to establish a wind turbine power plant in Bangladesh is very much. This type of power plant can be able to meet the demand for electricity for long time. The safe usage of wind turbine power can play an important role in the socio-economic development of Bangladesh.
1.1 Objectives:
Knowledge about the problem and prospect of the power sector of Bangladesh can be gained through this thesis.
* To get concept on conventional power plants.
* To become aware about the problem of generating power through these conventional power plants.
* To get knowledge of the advantages and disadvantages of conventional power plants.
*To get knowledge on wind turbine power plant.
* To get knowledge of the advantages and disadvantage of wind turbine power plant.
* To get knowledge on the prospect of wind turbine power plant in the context of Bangladesh.
The proposals for solving the power problem in the context of Bangladesh for sustainable environmental friendly development.
2. Power generation:
Electricity generation is the process of generating electric energy from other forms of energy.
The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday. His basic method is still used today: electricity is generated by the movement of a loop of wire, or disc of copper between the poles of a magnet.
For electric utilities, it is the first process in the delivery of electricity to consumers. The other processes, electricity transmission, distribution, and electrical power storage and recovery using pumped storage methods are normally carried out by the electric power industry.
Electricity is most often generated at a power station by electromechanical generators, primarily driven by heat engines fueled by chemical combustion or nuclear fission but also by other means such as the kinetic energy of flowing water and wind. There are many other technologies that can be and are used to generate electricity such as solar photovoltaic’s and geothermal power.
2.1 Methods of generating electricity:
There are seven fundamental methods of directly transforming other forms of energy into electrical energy:
* Static electricity, from the physical separation and transport of charge (examples: turboelectric effect and lightning)
* Electromagnetic induction, where an electrical generator, dynamo or alternator transforms kinetic energy (energy of motion) into electricity, this is most used form for generating electricity, it is based on Faraday’s law, can be experimented by simply rotating a magnet within closed loop of a conducting material (e.g. Copper wire)
* Electrochemistry, the direct transformation of chemical energy into electricity, as in a battery, fuel cell or nerve impulse
* Photoelectric effect, the transformation of light into electrical energy, as in solar cells
* Thermoelectric effect, direct conversion of temperature differences to electricity, as in thermocouples, thermopiles, and Thermionic converters.
* Piezoelectric effect, from the mechanical strain of electrically anisotropic molecules or crystals
* Nuclear transformation, the creation and acceleration of charged particles (examples: beta voltaic or alpha particle emission)
Static electricity was the first form discovered and investigated, and the electrostatic generator is still used even in modern devices such as the Van de Graff generator and MHD generators. Charge carriers are separated and physically transported to a position of increased electric potential.
Almost all commercial electrical generation is done using electromagnetic induction, in which mechanical energy forces an electrical generator to rotate. There are many different methods of developing the mechanical energy, including heat engines, hydro, wind and tidal power.
The direct conversion of nuclear potential energy to electricity by beta decay is used only on a small scale. In a full-size nuclear power plant, the heat of a nuclear reaction is used to run a heat engine. This drives a generator, which converts mechanical energy into electricity by magnetic induction.
Most electric generation is driven by heat engines. The combustion of fossil fuels supplies most of the heat to these engines, with a significant fraction from nuclear fission and some from renewable sources. The modern steam turbine (invented by Sir Charles Parsons in 1884) currently generates about 80 percent of the electric power in the world using a variety of heat sources.
3. Source of energy:
3.1 Renewable energy:
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally replenished). About 16% of global final energy consumption comes from renewable, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from hydroelectricity. New renewable (small hydro, modern biomass, wind, solar, geothermal, and bio fuels) accounted for another 3% and are growing very rapidly. The share of renewable in electricity generation is around 19%, with 16% of global electricity coming from hydroelectricity and 3% from new renewable.
Wind power is growing at over 20% annually, with a worldwide installed capacity of 238,000<href=”#Megawatt” title=”Watt”>megawatts (MW) at the end of 2011, and is widely used in Europe, Asia, and the United.<href=”#cite_note-Glob-4>[5] Since 2004, photovoltaic’s passed wind as the fastest growing energy source and since 2007 has more than doubled every two years. At the end of 2011 the photovoltaic (PV) capacity worldwide was 67,000 MW, and PV power stations are popular in Germany and Italy. Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 MW SEGS power plant in the Mojave Desert. The world’s largest geothermal power installation is the Geysers in California, with a rated capacity of 750 MW. Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugarcane, and ethanol now provides 18% of the country’s automotive fuel. Ethanol fuel is also widely available in the USA.While many renewable energy projects are large-scale, renewable technologies are also suited to rural and remote areas, where energy is often crucial in human development. As of 2011, small solar PV systems provide electricity to a few million households, and micro-hydro configured into mini-grids serves many more. Over 44 million households use biogas ade in household-scale digesters for lighting and/or cooking, and more than 166 million households rely on a new generation of more-efficient biomass cook stoves. United’ Secretary-General Ban Ki-moon has said that renewable energy has the ability to lift the poorest nations to new levels of prosperity.
Climate change concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization. New government spending, regulation and policies helped the industry weather the global financial crisis better than many other sectors. According to a 2011 projection by the International Energy Agency, solar power generators may produce most of the world’s electricity within 50 years, dramatically reducing the emissions of greenhouse gases that harm the environment.
3.2 Main stream from of renewable energy:
3.2.1 Wind power:
Airflows can be used to run wind turbines. Modern wind turbines range from around 600 kW to 5 MW of rated power, although turbines with rated output of 1.5–3 MW have become the most common for commercial use; the power output of a turbine is a function of the cube of the wind speed, so as wind speed increases, power output increases dramatically.<href=”#cite_note-EWEA-19>[20] Areas where winds are stronger and more constant, such as offshore and high altitude sites are preferred locations for wind farms. Typical capacity factors are 20-40%, with values at the upper end of the range in particularly favorable sites.
Globally, the long-term technical potential of wind energy is believed to be five times total current global energy production, or 40 times current electricity demand. This could require wind turbines to be installed over large areas, particularly in areas of higher wind resources. Offshore resources experience average wind speeds of ~90% greater than that of land, so offshore resources could contribute substantially more energy.
Fig: 1.1 Wind Turbine Power Plant
3.2.2 Hydropower:
Energy in water can be harnessed and used. Since water is about 800 times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy. There are many forms of water energy:
* Hydroelectric energy is a term usually reserved for large-scale hydroelectric dams. Examples are the Grand Coulee Dam in Washington State and the Akosombo Dam in Ghana.
* Micro hydro systems are hydroelectric power installations that typically produce up to 100 kW of power. They are often used in water rich areas as a remote-area power supply (RAPS).
* Run-of-the-river hydroelectricity systems derive kinetic energy from rivers and oceans without using a dam.
Fig: 1.2 Hydro Electric Power Plants
3.2.3 Solar energy:
Solar energy is the energy derived from the sun through the form of solar radiation. Solar powered electrical generation relies on photovoltaic’s and heat engines. A partial list of other solar applications includes space heating and cooling through solar architecture, delighting, solar hot water, solar cooking, and high temperature process heat for industrial purposes.
Fig: 1.3 Solar Power Plants
Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.
3.2.4 Biomass:
Biomass (plant material) is a renewable energy source because the energy it contains comes from the sun. Through the process of photosynthesis, plants capture the sun’s energy. When the plants are burnt, they release the sun’s energy they contain. In this way, biomass functions as a sort of natural battery for storing solar energy. As long as biomass is produced sustainably, with only as much used as is grown, the battery will last indefinitely.
In general there are two main approaches to using plants for energy production: growing plants specifically for energy use (known as first and third-generation biomass), and using the residues (known as second-generation biomass) from plants that are used for other things. See biobased economy. The best approaches vary from region to region according to climate, soils and geography.
3.2.5 Biofuel:
Biofuels include a wide range of fuels which are derived from biomass. The term covers <href=”#Solid_biofuels” title=”Biofuels”>solid biomass, liquid fuels and various biogases. liquid biofuels include bioalcohols, such as bioethanol, and oils, such as biodiesel. Gaseous biofuels include biogas, landfill gas andsynthetic gas.
Bioethanol is an alcohol made by fermenting the sugar components of plant materials and it is made mostly from sugar and starch crops. With advanced technology being developed, cellulosic biomass, such as trees and grasses, are also used as feedstock’s for ethanol production. Ethanol can be used as a fuel for vehicles in its pure form, but it is usually used as a gasoline additive to increase octane and improve vehicle emissions. Bioethanol is widely used in the USA and in Brazil.
Biodiesel is made from vegetable oils, animal fats or recycled greases. Biodiesel can be used as a fuel for vehicles in its pure form, but it is usually used as a diesel additive to reduce levels of particulates, carbon monoxide, and hydrocarbons from diesel-powered vehicles. Biodiesel is produced from oils or fats using transesterification and is the most common biofuel in Europe. Biofuels provided 2.7% of the world’s transport fuel in 2010.
3.3 Non-renewable energy:
A non-renewable resource is a natural resource which cannot be reproduced, grown, generated, or used on a scale which can sustain its consumption rate, once depleted there is no more available for future needs. Also considered non-renewable are resources that are consumed much faster than nature can create them. Fossil fuels (such as coal, petroleum, and natural gas), nuclear power(uranium) and certain aquifers are examples. Metals are prime examples of non-renewable resources. In contrast, resources such as timber (when harvested sustainably) are considered renewable resources.
3.4 Main stream from of non-renewable energy:
3.4.1 Fossil fuel:
Natural resources such as coal, petroleum (crude oil) and natural gas take thousands of years to form naturally and cannot be replaced as fast as they are being consumed. Eventually natural resources will become too costly to harvest and humanity will need to find other sources of energy.
At present, the main energy source used by humans are non-renewable fossil fuels, as a result of continual use since the first internal combustion engine in the 17th century, the fuel is still in high demand with conventional infrastructure and transport which are fitted with the combustion engine. The continual use of fossil fuels at the current rate will increase global warming and cause more severe climate change.
Fig: 1.4 Coal Mine
3.4.2 Radioactive fuel:
The use of nuclear technology requires a radioactive fuel. Uranium ore is present in the ground at relatively low concentrations and mined in 19 countries. The uranium resource is used to create plutonium,uranium-238 is fissionable and is transmuted into fissileplutonium-239 in a reactor. Nuclear fuel is used for the production of nuclear weapons and in nuclear power stations to create electricity.
Nuclear power provides about 6% of the world’s energy and 13–14% of the world’s electricity. The expense of the nuclear industry remains predominantly reliant on subsidies and <href=”#Indirect_nuclear_insurance_subsidy” title=”Nuclear power debate”>indirect insurance subsidies to continue. Nuclear technology is a volatile and contaminating source of fuel production, with elements that are unstable and each decays radioactively into other elements. Nuclear power facilities produce about 200,000 metric tons of low and intermediate level waste (LILW) and 10,000 metric tons of high level waste (HLW) (including spent fuel designated as waste) each year worldwide.
The use of nuclear fuel and the radioactive waste the nuclear industry collects is highly hazardous to people and wildlife. Radio contaminants in the environment become bio accumulative by entering the chain, internal or external exposure causesmutagenic DNA breakage, producing teratogenic generational birth defects, cancers and other damages. The United Nations (UNSCEAR) estimated in 2008 that average annual human radiation exposure includes 0.01 mSv (milli-Sievert) from the legacy of past atmospheric nuclear testing plus the Chernobyl disaster and the nuclear fuel cycle, along with 2.0 mSv from natural radioisotopes and 0.4 mSv from cosmic rays; all exposures vary by location. Some radioisotopes in nuclear waste emit harmful radiation for the prolonged period of 4.5 billion years or more, and storage has risks of containment. The storage of waste, health implications and dangers of radioactive fuel continue to be a topic of debate, resulting in a controversial and unresolved industry.
The nuclear fuel cycle, unlike burning fossil fuels, produces carbon dioxide emissions from production, construction and transport, between being mined, milled, enriched, formed into fuel rods, used in the power station, then stored or reprocessed, including nuclear decommissioning and <href=”#Management_of_waste” title=”Nuclear waste”>management of nuclear waste, all these actions produce carbon emissions contributing significantly to global warming.
3.4.3 Reciprocating engines:
Small electricity generators are often powered by reciprocating engines burning diesel, biogas or natural gas. Diesel engines are often used for back up generation, usually at low voltages. However most large power grids also use diesel generators, originally provided as emergency back up for a specific facility such as a hospital, to feed power into the grid during certain circumstances. Biogas is often combusted where it is produced, such as a landfill or wastewater treatment plant, with a reciprocating engine or a micro turbine, which is a small gas turbine.
A coal-fired power plant in Laughlin, Nevada U.S.A. Owners of this plant ceased operations after declining to invest in pollution control equipment to comply with pollution regulations.
3.4.4 Photovoltaic panels:
Unlike the solar heat concentrators mentioned above, photovoltaic panels convert sunlight directly to electricity. Although sunlight is free and abundant, solar electricity is still usually more expensive to produce than large-scale mechanically generated power due to the cost of the panels. Low-efficiency silicon solar cells have been decreasing in cost and multifunction cells with close to 30% conversion efficiency are now commercially available. Over 40% efficiency has been demonstrated in experimental systems.<href=”#cite_note-6″>[7] Until recently, photovoltaics were most commonly used in remote sites where there is no access to a commercial power grid, or as a supplemental electricity source for individual homes and businesses. Recent advances in manufacturing efficiency and photovoltaic technology, combined with subsidies driven by environmental concerns, have dramatically accelerated the deployment of solar panels. Installed capacity is growing by 40% per year led by increases in Germany, Japan, California and New Jersey.
Fig: 1.5 Solar or Photovoltaic Power Plants
3.5 Other generation methods:
Wind-powered turbines usually provide electrical generation in conjunction with other methods of producing power.
Various other technologies have been studied and developed for power generation. Solid-state generation (without moving parts) is of particular interest in portable applications. This area is largely dominated by thermoelectric (TE) devices, though thermionic (TI) and thermo photovoltaic (TPV) systems have been developed as well. Typically, TE devices are used at lower temperatures than TI and TPV systems. Piezoelectric devices are used for power generation from mechanical strain, particularly in power harvesting. Beta voltaic are another type of solid-state power generator which produces electricity from radioactive decay. Fluid-based magneto hydrodynamic (MHD) power generation has been studied as a method for extracting electrical power from nuclear reactors and also from more conventional fuel combustion systems. Osmotic power finally is another possibility at places where salt and sweet water merges (e.g. deltas …). Modern innovation now allows kinetic energy to be generated by simply walking on floor tiles that have energy harvesting sensors embedded within them, thus producing renewable electricity.
Electrochemical electricity generation is also important in portable and mobile applications. Currently, most electrochemical power comes from closed electrochemical cells (“batteries“), which are arguably utilized more as storage systems than generation systems, but open electrochemical systems, known as fuel cells, have been undergoing a great deal of research and development in the last few years. Fuel cells can be used to extract power either from natural fuels or from synthesized fuels (mainly electrolytic hydrogen) and so can be viewed as either generation systems or storage systems depending on their use.
3.6 Other sources of energy:
Other power stations use the energy from wave or tidal motion, wind, sunlight or the energy of falling water, hydroelectricity. These types of energy sources are called renewable energy.
Fig: 1.6 A hydroelectric dam
A hydroelectric dam and plant on the Muskegon river in Michigan, United States.
3.6.1 Hydroelectricity:
Dams built to produce hydroelectricity impound a reservoir of water and release it through one or more water turbines, connected to generators, and generate electricity, from the energy provided by difference in water level upstream and downstream.
3.6.2 Pumped storage:
A pumped-storage hydroelectric power plant is a net consumer of energy but can be used to smooth peaks and troughs in overall electricity demand. Pumped storage plants typically use “spare” electricity during off peak periods to pump water from a lower reservoir or dam to an upper reservoir. Because the electricity is consumed “off peak” it is typically cheaper than power at peak times. This is because the “base load” power stations, which are typically coal fired, cannot be switched on and off quickly so remain in service even when demand is low. During hours of peak demand, when the electricity price is high, the water pumped to the high reservoir is allowed to flow back to the lower reservoir through a water turbine connected to an electricity generator. Unlike coal power stations, which can take more than 12 hours to start up from cold, the hydroelectric plant 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, one to the East of Cape Town (Pelmet) and one in the Frankenberg, Natal.
3.6.3 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, and so 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 airborne animals.
Fig: 1.7 Wind turbines in front of a thermal power station in Amsterdam, the Netherlands.
4. Power station:
A power station (also referred to as a generating station, power plant, or powerhouse) is an industrial facility for the generation of electric power. At the center of nearly all power stations is a generator, a rotating machine that converts mechanical power into <href=”#Electrical_power” title=”Power (physics)”>electrical power by creating relative motion between a magnetic field and a conductor. The energy source harnessed to turn the generator varies widely. It depends chiefly on which fuels are easily available, cheap enough and on the types of technology that the power company has access to.
Central power stations produce AC power, after a brief Battle of Currents in the 19th century demonstrated the advantages of AC distribution.
4.1 History:
The world’s first power station was built by Sigmund Schuckert in the Bavarian town of Etta and went into operation in 1878<href=”#cite_note-3″>[4]. The station consisted of 24 dynamo electric generators which were driven by a steam engine. It was used to illuminate a grotto in the gardens of Linder of Palace.
The first public power station was the Edison Electric Light Station, built in London at 57, Holborn Viaduct, which started operation in January 1882. This was an initiative of Thomas Edison that was organized and managed by his partner, Edward Johnson. A Babcock and Wilcox boiler powered a 125 horsepower steam engine that drove a 27 ton generator called Jumbo, after the celebrated elephant. This supplied electricity to premises in the area that could be reached through the culverts of the viaduct without digging up the road, which was the monopoly of the gas companies. The customers included the City Temple and the Old Bailey.
Another important customer was the Telegraph Office of the <href=”#Headquarters” title=”General Post Office”>General Post Office but this could not be reached though the culverts. Johnson arranged for the supply cable to be run overhead, via Holborn Tavern and New gate.In September 1882 in New York, the Pearl Street Station was established by Edison to provide electric lighting in the lower Manhattan Island area; the station ran until destroyed by fire in 1890. The station used reciprocating steam engines to turn direct-current generators. Because of the DC distribution, the service area was small, limited by voltage drop in the feeders. The War of Currents eventually resolved in favor of AC distribution and utilization, although some DC systems persisted to the end of the 20th century. DC systems with a service radius of a mile (kilometer) or so were necessarily smaller, less efficient of fuel consumption, and more labor intensive to operate than much larger central AC generating stations.
AC systems used a wide range of frequencies depending on the type of load; lighting load using higher frequencies, and traction systems and heavy motor load systems preferring lower frequencies. The economics of central station generation improved greatly when unified light and power systems, operating at a common frequency, were developed. The same generating plant that fed large industrial loads during the day, could feed commuter railway systems during rush hour and then serve lighting load in the evening, thus improving the system load factor and reducing the cost of electrical energy overall. Many exceptions existed, generating stations were dedicated to power or light by the choice of frequency, and rotating frequency changers and rotating converters were particularly common to feed electric railway systems from the general lighting and power network.
Throughout the first few decades of the 20th century central stations became larger, using higher steam pressures to provide greater efficiency, and relying on interconnections of multiple generating stations to improve reliability and cost. High-voltage AC transmission allowed hydroelectric power to be conveniently moved from distant waterfalls to city markets. The advent of the steam turbine in central station service, around 1906, allowed great expansion of generating capacity. Generators were no longer limited by the power transmission of belts or the relatively slow speed of reciprocating engines, and could grow to enormous sizes.
For example, Sebastian Ziani de Ferranti planned what would have been the largest reciprocating steam engine ever built for a proposed new central station, but scrapped the plans when turbines became available in the necessary size. Building power systems out of central stations required combinations of engineering skill and financial acumen in equal measure. Pioneers of central station generation include George Westinghouse and Samuel Insull in the United States, Ferranti and Charles Hester man Merz in UK, and many others.
4.2 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, and these 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.
Fig: 1.8 Rotor of a modern steam turbine
The efficiency of a steam turbine is limited by the maximum temperature of the steam produced and 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).
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. Most commonly, exhaust gases from a gas turbine are used to generate steam for a boiler and steam turbine. The combination of a “top” cycle and a “bottom” cycle produces higher overall efficiency than either cycle can attain alone.
Fig: 1.9 CHP plant in Warsaw, Poland
Fig: 2.1 geothermal power stations in Iceland.
Fig: 2.2 Coal Power Stations in Tampa
Coal Power Station in Tampa, States. Thermal power plants are classified by the type of fuel and the type of prime mover installed.
4.2.1 By fuel:
* Fossil fuelled power plants 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 electricity by burning coal to generate steam, and has the side-effect of producing large amounts of sulfur dioxide which pollutes air and water and carbon dioxide, which contributes to global warming. About 50% of electric generation in the USA is produced by coal-fired power plants
* Nuclear power plantsuse a nuclear reactor‘s heat to operate a steam turbine generator. About 20% of electric generation in the USA is produced by nuclear power plants.
* Geothermal power plants use steam extracted from hot underground rocks.
* <href=”#Biomass_conversion_process_to_useful_energy” title=”Biomass”>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.
4.2.2 Prime Mover:
A machine that transforms energy from thermal, electrical or pressure form to mechanical form, typically an engine or turbine
4.2.3 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% of all electric power produced in the world is by 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 base-loaded plants. These may be comparatively small units, and sometimes completely unmanned, being remotely operated. This type was pioneered by the UK, Prince town being the world’s first, commissioned in 1959.