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Power Generation Steam Power Plants

Salahaddin University – Erbil College of Engineering Electrical Engineering Department 2018-2019. Class: 3 rd Year ( P/ E ) B.SC Degree in Power Engineering. Power Generation Steam Power Plants.  Asst. Prof. Aree Akram. Introduction:

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Power Generation Steam Power Plants

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  1. Salahaddin University – Erbil College of Engineering Electrical Engineering Department 2018-2019 Class: 3rd Year (P/ E) B.SC Degree in Power Engineering Power Generation Steam Power Plants  Asst. Prof. Aree Akram

  2. Introduction: • Steam is an important medium of producing mechanical energy. • A steam power plant converts the chemical energy of fossil fuels (coal, oil, gas) into electrical energy. • This is achieved by raising the steam in the boilers, expanding it through the turbines and coupling the turbines to the generators which convert mechanical energy into electrical energy. • Steam has the advantage that, it can be raised from water which is available in abundance it does not react much with the materials of the equipment of power plant and is stable at the temperature required in the plant. • For a thermal power plant the range of pressure may vary from 10 kg/cm2to super critical pressures and the range of temperature may be from: 250°C to 650°C.

  3. Production of electric energy by steam power plant

  4. Some advantage and dis advantage of steam power plants: Advantages 1. The fuel used is quite cheap,less initial cost as compared to other generating plants. 2. 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. 3. It require less space as compared to Hydro power plants. 4. Cost of generation is less than that of diesel power plants. Disadvantages: 1. It pollutes the atmosphere due to production of large amount of smoke and fumes. 2. It is costlier in running cost as compared to Hydro electric plants.

  5. Essentials of steam power plant equipment A steam power plant must have following equipments: 1. A furnace to burn the fuel. 2. Steam generator or boiler containing water. Heat generated in the furnace is utilized to convert water in steam. 3. Main power unit such as an engine or turbine to use the heat energy of steam and perform work. 4. Piping system to convey steam and water. Classification of steam power plants: The steam power plants may be classified as follows: • Central stations. • Industrial power stations or captive power stations.

  6. 1- Central stations: The electrical energy available from these stations is meant for general sale to the customers who wish to purchase it. Generally these stations are condensing type where the exhaust steam is discharged into a condenser instead of into the atmosphere. In the condenser the pressure is maintained below the atmospheric pressure and the exhaust steam is condensed. 2- Industrial power stations or captive power stations: This type of power station is run by a manufacturing company for its own use and its output is not available for general sale. Normally these plants are non-condensing because large quantity of steam (low pressure) is required for different manufacturing operating.

  7. Component of modern steam power plant: A modern steam power plant consists of the following components: • Boiler :( Superheater, Reheater, Economies and Air- heater). • Steam turbine. • Generator. Condenser. • Cooling tower. • Circulating water pump. • Boiler feed pump. • Wagon tippler. • Crusher house. • Coal mill. • Induced draught fans. • Ash precipitators. • Boiler chimney. • Forced draught fans. • Water treatment plant. • Control room. • Switch yard.

  8. Steam Power Plant

  9. Power station design: Power station design requires wide experience. A satisfactory design consists of the following steps: • Selection of site. • Estimation of capacity of power station. • Selection of turbines and their auxiliaries. • Selection of boilers, and their auxiliaries. • Design of fuel handling system. • Selection of condensers. • Design of cooling system. • Design of piping system to carry steam and water. • Selection of electrical generator. • Design and control of instruments. • Design of layout of power station.

  10. Quality of coal used in steam power station plays an important role in the design of power plant. • The ranks of coal (from most to least carbon content) are as follows: anthracite, bituminous coal, subbituminous coal, and lignite. The coal with the highest carbon content is the best and cleanest type of coal to use. The various factors to be considered while designing the boilers and coal handling units are as follows: • Slugging and erosion properties of ash. • Moisture in the coal. Excessive moisture creates additional problems particularly in case of pulverized fuel power plants. • Burning characteristic of coal. • Corrosive nature of ash.

  11. Characteristics of steam power plant: The desirable characteristic for a steam power plant are as follows: • Higher efficiency. • Lower cost. • Ability to burn coal especially of high ash content, and inferior coals. • Reduced environmental impact in terms of air pollution. • Reduced water requirement. • Higher reliability and availability.

  12. Basic Operation • A simple steam plant works on Rankine cycle. In the first step, water is feed into a boiler at a very high pressure by BFP (boiler feed pump). This high pressurized water is heated into a boiler which converts it into high pressurized super heated steam. This high energized steam passes through steam turbineand rotate it. • Three stage turbines is used which is known as LPT (Low pressure turbine), IPT (intermediate pressure turbine) and HPT (High pressure turbine). The turbine shaft is connected to the generator rotor shaft which makes rotate the generator shaft and produce electricity. • In this process the steam loses its energy. This low pressurized saturated steam further passes through condenser where it converts into water. This water further passes through BFP and boiler and completes the cycle. This cycle continuously run to produce electricity.

  13. Construction of steam power plant Any steam power plant can be grouped into following section: 1-Coal Handling Plant: Coal Storage: The place at which coal stored is known as coal storage. The coal initially received by mines is stored in proper place. Bunker: Coal from coal storage sends to bunkers. It is a container which is upper side of mill and used to continuously provide coal for mill machine. The minimum capacity of bunker is around 10 times of mill capacity. Feeder: Coal from the bunkers send to the feeder which provide coal to mill machine. The main reason to use feeder between bunkers and mill machine is that if we directly send coal to mill, it can damage the internal part of machine due to tones of pressure applied by the coal. Mill Machine: Coal does not directly used into boiler. The place where the coal is converted into pulverized form is known as mill machine. This pulverized coal sends to classifier from it. Classifier: Classifiers are used to separate pulverized and non-pulverized forms of coal. It sends pulverized coal to furnace and non-pulverized coal to mill machine.

  14. 2-Air Handling Plant: PA Fan: PA fan is primary air fan. This is used to transport pulverized coal to furnace. It also used to remove moisture content from pulverized coal. ID Fan: ID fan means induced draft fan. This fan is used to suck the exhausted flue gases from the boiler and send it to atmosphere through chimney. FD Fan: FD means forced draft fan. It is used to provide air i.e. oxygen for proper burning of coal into the furnace. It provides hot air into the furnace. Air Preheater: It is a heat exchanger which transfer heat from exhausted flue gases to incoming PA and FD air. ESP (Electrostatic Precipitator): This device is situated between Id fan and boiler exhaust and used to detect and block ash particles from flue gases and control the pollution being created by it. Chimney: Chimney is used to create natural draft for exhausted flue gases. One chimney is used for two units.

  15. 3-Boiler Section Economizer: Economizer is the first component of boiler section. As the name implies, economizer is used to increase the efficiency of steam power plant. It is used to heat water up to saturation temperature. It extracts heat from exhausted flue gases and used it to heat water. It sends water to the boiler drum. Boiler: Economizer sends water to the Boiler. Boiler is the main part of any thermal power plant. It is used to convert water into steam. In any steam power plant water tube boiler is used. It contains furnace inside the boiler shell. The Coal burns into this section. Drum is major part of steam power plant boiler. It is situated top of the boiler and used to separate water from steam. Steam from boiler section sends to super heaters. Super heater: The efficiency of thermal power plant is directly connected to the temperature of the steam. The boiler creates low temperature steam which is not so economical for any power plant. So a super heater is used to heat the steam again. The temperature of the steam is limited at 550 C because the turbine material can’t sustain temperature above 600 C. The steam from the super heater sends to high pressure turbine. Re heater: When the steam expands into high pressure turbine, both its temperature and pressure get down. If this low temperature steam directly sends to IP turbine, it creates less power. To increase the power of the plant there is an arrangement  to send exhausted steam from HP turbine to Re-heater where it heated and get the initial temperature which is about 550 degree centigrade.

  16. 4-Turbine Section: High Pressure Turbine HPT: The steam from the super heater sends to HP turbine. All the three turbines are connected to same shaft which is further connected to the generator shaft. The HP turbine works around 150 Kg/cm2pressure and 550 Ctemperature. It is smallest among all turbines. Intermediate Pressure Turbine IPT: As the name implies it works at intermediate pressure which is around 70 Kg/cm2. The steam from the Re-heater sends to the IP turbine at around 550 C where it expands and generates power. Low Pressure Turbine LPT: This is the main power generator. It generates around 40 percent of whole power. The steam from IP turbine directly sends to LP turbine where it expand and rotate the turbine. It is biggest part of turbine section. Extractor: To increase the efficiency, some amount of steam is extracted from both HP section exhaust and LP section exhaust. This extracted steam is used to heat water before send to economizer.

  17. 5-Condenser Section: Condenser: To complete the cyclic operation, its need to send water again to the economizer at high pressure. Steam exhausted from LP turbine is not in condensed form and it is not economical to compress the steam at a very high pressure around 150 Kg/cm2. So a device is needed which can condense the steam into water. This device is called Condenser. Condenser is also a heat exchanger in which the cold water runs into tubes and steam flow from shell. The cold water extracts heat from steam and convert it into water.

  18. Condensed Extractor Pumps (CEPs): The condensed water extracted by the pumps and send to LPH. LPH (Low Pressure Heater): The water collected from the condenser is at low pressure. To increase the efficiency of the plant this water is heated by the extracted steam from LP turbine. Deaerator: The water collected from condenser has some dissolved gases like oxygen. This water can’t directly send to boiler and turbines. it can cause of corrosion. To decrease the possibility of corrosion these dissolved gases should be removed from this water before converted it into steam. This work is done by Deaerator. Deaerator heat the water at some extant at which the dissolved gases converted into gases form and removed from water. Feed Water Pump or Boiler Feed Pump: BFP are centrifugal pumps which are used to increase the water pressure up to 150 Kg/cm2 and also send this water at economizer. HPH (High Pressure Heater): The pressurized water forced by BFP passes through high pressure heater which heats this water at some extent to increase the efficiency of plant. The steam extracted from HP exhaust is used to heat this water. Cooling Tower: Cooling tower is used to provide cold water for condenser tp condense steam into water.

  19. 6-Generator Section: • The turbine shaft is connected to the generator which rotates the rotor of the generator and produce electricity. • Exciter: • For the cold starting, the turbine does not rotate due to high inertia.  Exciter is used to rotate the turbine inthe initial run.

  20. Internet links • https://www.youtube.com/watch?v=is5wdVgPOkI • https://www.youtube.com/watch?v=nL-J5tT1E1k • https://www.youtube.com/watch?v=IdPTuwKEfmA

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