Thermal power generation.docx (Size: 221.88 KB / Downloads: 1621)
A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which either drives an electrical generator or does some other work, like ship propulsion. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle.
Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as many natural gas power plants are thermal. Natural gas is frequently combusted in gas turbines as well as boilers.
Commercial electric utility power stations are most usually constructed on a very large scale and designed for continuous operation. Electric power plants typically use three-phase or individual-phase electrical generators to produce alternating current (AC) electric power at a frequency of 50 Hz or 60 Hz (hertz, which is an AC sine wave per second) depending on its location in the world.
2. Need For thermal power generationÂ¦Â¦..04
4. Basic definitionsÂ¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦.07
5. Functioning of thermal power plantÂ¦Â¦...11
8. Future ProspectsÂ¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦19
Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as many natural gas power plants are thermal. Natural gas is frequently combusted in gas turbines as well as boilers. The waste heat from a gas turbine can be used to raise steam, in a combined cycle plant that improves overall efficiency. Power plants burning coal, oil, or natural gas are often referred to collectively as fossil-fuel power plants. Some biomass-fueled thermal power plants have appeared also. Non-nuclear thermal power plants, particularly fossil-fueled plants, which do not use cogeneration, are sometimes referred to as conventional power plants.
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.
Commercial electric utility power stations are most usually constructed on a very large scale and designed for continuous operation. Electric power plants typically use three-phase or individual-phase electrical generators to produce alternating current (AC) electric power at a frequency of 50 Hz or 60 Hz (hertz, which is an AC sine wave per second) depending on its location in the world. Other large companies or institutions may have their own usually smaller power plants to supply heating or electricity to their facilities, especially if heat or steam is created anyway for other purposes. Shipboard steam-driven power plants have been used in various large ships in the past, but these days are used most often in large naval ships. Such shipboard power plants are general lower power capacity than full-size electric company plants, but otherwise have many similarities except that typically the main steam turbines mechanically turn the propulsion propellers, either through reduction gears or directly by the same shaft. The steam power plants in such ships also provide steam to separate smaller turbines driving electric generators to supply electricity in the ship. Shipboard steam power plants can be either conventional or nuclear; the shipboard nuclear plants are mostly in the navy. There have been perhaps about a dozen turbo-electric ships in which a steam-driven turbine drives an electric generator which powers an electric motor for propulsion.
Thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which either drives an electrical generator or does some other work, like ship propulsion. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy.
Reciprocating steam engines have been used for mechanical power sources since the 18th Century, with notable improvements being made by James Watt. The very first commercial central electrical generating stations in New York and London, in 1882, also used reciprocating steam engines. As generator sizes increased, eventually turbines took over they encres the hose power.
NEED FOR THERMAL POWER GENERATION
Scarcity of water resources: Water resources are not abundantly available and are geographically unevenly distributed. Thus hydel power plants cannot be installed with ease and are limited to certain locations.
Widely available alternate flues: Many alternate fuels such as coal, diesel, nuclear fuels, geo-thermal energy sources, solar-energy, biomass fuels can be used to generate power using steam cycles.
Maintenance and lubrication cost is lower: Once installed, these require less maintenance costs and on repairs. Lubrication is not a major problem compared to hydel power plant.
Coal is abundant: Coal is available in excess quantities in India and is rich form of energy available at relatively lower cost.
Working fluid remains within the system, and need not be replaced every time thus simplifies the process.
Thermal power plants are classified by the type of fuel and the type of prime mover Installed.
Nuclear power plants use a nuclear reactor's heat to operate a steam turbine generator.
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 a large amount of carbon dioxide, which is released from burning coal and contributes to global warming
Geothermal power plants use steam extracted from hot underground rocks.
Biomass Fuelled Power Plants may be fuelled by waste from sugar cane, municipal solid waste, landfill methane, or other forms of biomass.
Solar thermal electric plants use sunlight to boil water, 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
Gas turbine plants use the dynamic pressure from flowing gases (air and combustion products) to directly operate the turbine.
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
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
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
Power is energy per unit time. The power output or capacity of an electric plant can be expressed in units of megawatts electric (MWe). The electric efficiency of a conventional thermal power station, considered as saleable energy (in MWe) produced at the plant busbars as a percent of the heating value of the fuel consumed, is typically 33% to 48% efficient. This efficiency is limited as all heat engines are governed by the laws of thermodynamics (See: Carnot cycle). The rest of the energy must leave the plant in the form of heat. This waste heat can go through a condenser and be disposed of with cooling water or in cooling towers. If the waste heat is instead utilized for district heating, it is called cogeneration. An important class of thermal power station is associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas and in these plants, freshwater production and electricity are equally important co-products.
Since the efficiency of the plant is fundamentally limited by the ratio of the absolute temperatures of the steam at turbine input and output, efficiency improvements require use of higher temperature, and therefore higher pressure, steam. Historically, other working fluids such as mercury have been experimentally used in a mercury vapor turbine power plant, since these can attain higher temperatures than water at lower working pressures. However, the obvious hazards of toxicity, and poor heat transfer properties, have ruled out mercury as a working fluid.
Steam is vaporized water and can be produced at 100â„¢C at standard atmosphere.
In common speech, steam most often refers to the visible white mist that condenses above boiling water as the hot vapor mixes with the cooler air.
Turbine A turbine is a rotary engine that extracts energy from a fluid or air flow and converts it into useful work.
The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum, with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor. Early turbine exare windmills and waterwheels.
Fig Typical turbine
Electric generator An electric generator is a device that converts mechanical energy to electrical energy. A generator forces electrons in the windings to flow through the external electrical circuit. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside.
Fig Typical Generator
A boiler or steam generator is a device used to create steam by applyingheat energy to water. Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers and worked at low to medium pressure
(1â€œ300 psi/0.069â€œ20.684 bar; 6.895â€œ2,068.427 kPa), but at pressures above this it is more usual to speak of a steam generator.
A boiler or steam generator is used wherever a source of steam is required. The form and size depends on the application: mobile steam engines such as steam locomotives, portable engines and steam-powered road vehicles typically use a smaller boiler that forms an integral part of the vehicle;
Second law of thermodynamics The second law of thermodynamics is an expression of the universal principle of entropy, stating that the entropy of anisolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium; and that the entropy change dSof a system undergoing any infinitesimal reversible process is given by dq / T, where dq is the heat supplied to the system and T is the absolute temperature of the system.
FUNCTIONING OF THERMAL POWER PLANT:
In a thermal power plant, one of coal, oil or natural gas is used to heat the boiler to convert the water into steam. The steam is used to turn a turbine, which is connected to a generator. When the turbine turns, electricity is generated and given as output by the generator, which is then supplied to the consumers through high-voltage power lines.
Fig steam power generation â€œ
Typical diagram of a coal-fired thermal power station
1. Cooling tower
10. Steam Control valve
2. Cooling water pump
11. High pressure steam turbine
20.Forced draught (draft) fan
3. transmission line (3-phase)
4. Step-up transformer (3-phase)
13. Feed water heater
22. Combustion air intake
5. Electrical generator (3-phase)
14. Coal conveyor
6.Low pressure steam turbine
15. Coal hopper
24. Air preheater
7. Condensate pump
16. Coal pulverizer
8. Surface condenser
17. Boiler steam drum
26.Induced draught (draft) fan
9.Intermediate pressure steam turbine
18. Bottom ash hopper
27. Flue gas stack
Detailed process of power generation in a thermal power plant:
Water intake: Firstly, water is taken into the boiler through a water source. If water is available in a plenty in the region, then the source is an open pond or river. If water is scarce, then it is recycled and the same water is used over and over again.
Boiler heating: The boiler is heated with the help of oil, coal or natural gas. A furnace is used to heat the fuel and supply the heat produced to the boiler. The increase in temperature helps in the transformation of water into steam.
Steam Turbine: The steam generated in the boiler is sent through a steam turbine. The turbine has blades that rotate when high velocity steam flows across them. This rotation of turbine blades is used to generate electricity.
Generator: A generator is connected to the steam turbine. When the turbine rotates, the generator produces electricity which is then passed on to the power distribution systems.
Special mountings: There is some other equipment like the economizer and air pre-heater. An economizer uses the heat from the exhaust gases to heat the feed water. An air pre-heater heats the air sent into the combustion chamber to improve the efficiency of the combustion process.
Ash collection system: There is a separate residue and ash collection system in place to collect all the waste materials from the combustion process and to prevent them from escaping into the atmosphere.
Apart from this, there are various other monitoring systems and instruments in place to keep track of the functioning of all the devices. This prevents any hazards from taking place in the plant.
A Rankine cycle with a two-stage steam turbine and a single feedwater heater.
The second law of thermodynamics states that any closed-loop cycle can only convert a fraction of the heat produced during combustion into mechanical work. The rest of the heat, called waste heat, must be released into a cooler environment during the return portion of the cycle. The fraction of heat released into a cooler medium must be equal or larger than the ratio ofabsolute temperatures of the cooling system (environment) and the heat source (combustion furnace). Raising the furnace temperature improves the efficiency but also increases the steam pressure, complicates the design and makes the furnace more expensive. The waste heat cannot be converted into mechanical energy without an even cooler cooling system. However, it may be used in cogeneration plants to heat buildings, produce hot water, or to heat materials on an industrial scale, such as in some oil refineries, cement plants, and chemical synthesis plants.
Typical thermal efficiency for electrical generators in the electricity industry is around 33% for coal and oil-fired plants, and up to 50% for combined-cycle gas-fired plants
The fuel used is quite cheap.
Less initial cost as compared to other generating plants.
It can be installed at any place irrespective of the existence of coal. The coal can be transported to the site of the plant by rail or road.
It requires less space as compared to Hydro power plants.
Cost of generation is less than that of diesel power plants.
This plants can be quickly installed and commissioned and can be loaded when compare to hydel power plant
It can meet sudden changes in the load without much difficulty controlling operation to increase steam generation
Coal is less costlier than diesel
Maintenance and lubrication cost is lower
It pollutes the atmosphere due to production of large amount of smoke and fumes.
It is costlier in running cost as compared to Hydro electric plants.
well, stations always take up room for the environment which could be cultivated for the use of growing food etc. which is a great disadvantage is our day and age, as food is necessary to live.
However, this could create more jobs for a lot of people thus increasing in a good way our current economic situation which by is failing miserably.
Over all capital investment is very high on account of turbines, condensers, boilers reheaters etc .maintenance cost is also high on lubrication, fuel handling, fuel processing.
It requires comparatively more space and more skilled operating staff as the operations are complex and required precise execution
A large number of circuits makes the design complex
Starting of a thermal power plant takes fairly long time as the boiler operation and steam generation process are not rapid and instantaneous
Effective Use of Fossil Fuels and Reduction in CO2 Emissions by Improving the Efficiency of Thermal Power Generation
At present, thermal power generation accounts for approximately 70% of the total amount of electricity produced around the world. However, thermal power generation, which uses fossil fuels, causes more CO2 emissions than other power generation methods. In order to reduce CO2emissions per unit power produced, Toshiba Group is developing next-generation thermal power technologies aimed at improving plant efficiency and commercializing the CCS*1 (CO2 capture and storage) system.
To improve the efficiency of thermal power generation, it is of vital importance that the temperature of the steam or gas used to rotate the turbines is raised. Toshiba Group is working on the development of ultra-high-temperature materials and cooling technologies in order to commercialize an A-USC*2 system (Advanced Ultra-Super Critical steam turbine system) more efficient than previous models, which is designed to increase steam temperature from 600Ã‚Â°C to above the 700Ã‚Â°C mark. In the area of combined cycle power generation using a combination of gas and steam turbines, we are also engaged in jointly developing a power generation system designed to increase gas temperature to the level of 1,500Ã‚Â°C with the U.S. Company General Electric, which is starting commercial operation in July 2008 in Japan.
Accelerating the Development of CO2 Capture and Storage Technology
The Key to Realizing Next-generation Power Generation System
Toshiba Group is engaged in the development of CO2 capture and storage (CCS) technology designed to separate and capture CO2 emitted from thermal power plants and other such facilities and then store it underground. More specifically, this development is aimed at commercializing CCS technology. In order to commercialize this technology, it is essential that we develop a system that makes it possible to separate and capture CO2 without reducing the economic performance of a power plant. In the course of its basic research, Toshiba Group has developed a high-performance absorbent that minimizes the energy consumption required for the CO2 capture process. Experiments conducted using small-scale test equipment have confirmed that its level of performance is the best in the industry.
Preventive Maintenance Technologies That Support the Long-term, Stable Operation of Facilities and Extension of the Service Life of High-temperature Gas Turbine Parts
The use of combined cycle power generation facilities using gas turbines is increasing year by year for the purpose of achieving the reduction in CO2 emissions required to create a low-carbon society, increasing energy use efficiency and improving economic performance. Toshiba Group is developing various technologies that support the long-term, stable operation of facilities.
In order to analyze and assess high-temperature gas turbine parts, which are used in harsh environments and to determine their remaining service lives based on the level of degradation, we developed a technology for making highly accurate diagnoses by combining a number of methods, including the finite element method (FEM) and methods for testing cleavage strength, tensile strength, durability and fatigue strength. We are also working to commercialize service life extension and repair technologies aimed at recycling gas turbine rotor/stator blades and extending their service lives. Based on the BLE (Blade Life Extensionâ€žÂ¢) concept unique to our company group, we repeatedly reuse old rotor blades that meet our repair standards instead of simply discarding them. The repair and recycling of these parts not only reduces running costs and improves economic performance, but also effectively minimize the environmental impact.
Fig- Concept of the BLE Process
1. British Electricity International (1991).Modern Power Station Practice: incorporating modern power system practice (3rd Edition (12 volume set) ed.). Pergamon. ISBN 0-08-040510-X.
2. Babcock & Wilcox Co. (2005).Steam: Its Generation and Use (41st edition ed.). ISBN 0-9634570-0-4.
3. Thomas C. Elliott, Kao Chen, Robert Swanekamp (coauthors) (1997).Standard Handbook of Powerplant Engineering (2nd edition ed.). McGraw-Hill Professional.ISBN 0-07-019435-1.
4. Air Pollution Control Orientation Coursefrom website of the Air Pollution Training InstituteAir Pollution Control Orientation Coursefrom website of the Air Pollution Training Institute
5. Fundamentals of Steam Power by Kenneth Weston,
6. First and second lectures by S. Banerjee on "Thermal Power Plants"
8. cleantechnica.com/.. -thermal-electricity
9. http://www.britannica.com/. -Thermal-Power-Generation-Technology