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ELECTRICAL DEPARTMENTA PRESENTATION ONTHERMAL POWER PLANT www.studygalaxy.com
CONTENTS Introductory overview Efficiency Electricity cost Diagram of a typical coal-fired thermal power station Boiler and steam cycle Steam turbine generator Stack gas path and cleanup Transport of coal fuel to site and to storage Major Thermal Power Plants in India Advantages &Disadvantages
Introductory overviewA thermal power station is apower plant in which theprime mover is steam driven.Water is heated, turns into steamand spins a steam turbine whichdrives an electrical generator.After it passes through theturbine, the steam is condensed ina condenser and recycled towhere it was heated; this isknown as a Rankine cycle. Thegreatest variation in the design ofthermal power stations is due tothe different fuel sources. Someprefer to use the term energycenter because such facilitiesconvert forms of heat energy intoelectricity.
Efficiency The energy efficiency of a conventional thermal power station, considered as salable energy as a percent of the heating value of the fuel consumed, is typically 33% to 48%. This efficiency is limited as all heat engines are governed by the laws of thermodynamics. 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 co-generation. An important class of thermal power station are 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.
Electricity cost The direct cost of electric energy produced by a thermal power station is the result of cost of fuel, capital cost for the plant, operator labour, maintenance, and such factors as ash handling and disposal. Indirect, social or environmental costs such as the economic value of environmental impacts, or environmental and health effects of the complete fuel cycle and plant decommissioning, are not usually assigned to generation costs for thermal stations in utility practice, but may form part of an environmental impact assessment.
Diagram of a typical coal-fired thermal powerstation
Key 1. Cooling tower 2. Cooling water pump 3. Transmission line 4. Unit transformer (3-phase) 5. Electric generator (3-phase) 6. Low pressure turbine 7. Boiler feed pump 8. Condenser 9. Intermediate pressure turbine 10. Steam governor valve 11. High pressure turbine 12. Deaerator 13. Feed heater 14. Coal conveyor hopper 15. Coal 16. Pulverized fuel mill 17. Boiler drum 18. Ash hopper 19. Superheater 20. Forced draught fan (3-phase) 21. Reheater 22. Air intake 23. Economizer 24. Air preheater 25. Precipitator 26. Induced draught fan 27. Chimney Stack
Boiler and steam cycle In fossil-fueled power plants, steam generator refers to a furnace that burns the fossil fuel to boil water to generate steam. In some industrial settings, there can also be steam-producing heat exchangers called heat recovery steam generators (HRSG) which utilize heat from some industrial process. The steam generating boiler has to produce steam at the high purity, pressure and temperature required for the steam turbine that drives the electrical generator.
Steam turbine generator The turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft. There is a high pressure turbine at one end, followed by an intermediate pressure turbine, two low pressure turbines, and the generator. As steam moves through the system and loses pressure and thermal energy it expands in volume, requiring increasing diameter and longer blades at each succeeding stage to extract the remaining energy. The entire rotating mass may be over 200 metric tons and 100 feet (30 m) long.
Stack gas path and cleanup As the combustion flue gas exits the boiler it is routed through a rotating flat basket of metal mesh which picks up heat and returns it to incoming fresh air as the basket rotates, This is called the air preheater. The gas exiting the boiler is laden with fly ash, which are tiny spherical ash particles. The flue gas contains nitrogen along with combustion products carbon dioxide, sulfur dioxide, and nitrogen oxides. The fly ash is removed by fabric bag filters or electrostatic precipitators. Once removed, the fly ash byproduct can sometimes be used in the manufacturing of concrete. Fly ash collection Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (or sometimes both) located at the outlet of the furnace and before the induced draft fan.
Transport of coal fuel to site and tostorage Most thermal stations use coal as the main fuel. Raw coal is transported from coal mines to a power station site by trucks, barges, bulk cargo ships or railway cars. Generally, when shipped by railways, the coal cars are sent as a full train of cars.
Major Thermal Power Plants in India Super thermal power plants in India are the solutions the government of India found to overcome the power deficit faced by the country during a period. Maharastra stands first in production of thermal power in India and NTPC leads in the thermal power generating sector with total capacity of 24,395 MW. Maharastra has plenty of coal mines encouraging the inception of coal operated thermal power plants. The entire super thermal power plants in India are coal run. Gujarat with many prominent power plants stands second in the power production sector of India.
Advantages The fuel used is quite cheap. Less initial cost as compared to other generating plants. It can be installed at any place irespective of the existence of coal. The coal can be transported to the site of the plant by rail or road. It require less space as compared to Hydro power plants. Cost of generation is less than that of diesel power plants. Disadvantages 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.