THERMAL POWER PLANT

1. THERMAL POWER PLANT PREPARED BY: PROF.DEEPTI PATNE

2. SYLLABUS • Method of power generation, • layout and energy conversion process. • Types of Turbines & their control. • Types of Boilers and their control. • Types of Generators and their control, Condensers. • Types of Pumps and Fans, variable speed pumps and Fans, Material handling system, study of all loops-water, steam, fuel etc. • Schematics of Gas turbine and Diesel power plant. Application of DCS in power plants.

5. Installed Power Station Capacity in India as of June 30, 2016

6. Method of power generation

7. A steam power plant converts the chemical energy of the fossil fuels (coal, oil, gas) into mechanical/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 to electrical energy as shown in Fig

8. The following two purposes can be served by a steam power plant: a. To produce electric power. b. To produce steam for industrial purposes besides producing electric power. The steam may be used for varying purposes in the industries such as textiles, food manufacture, paper mills, sugar mills and refineries etc.

9. Classification of Steam Power Plants • 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.

10. Classification of Steam Power Plants b. 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 a large quantity of steam (low pressure) is required for different manufacturing operations.

11. Layout of Thermal Power plant

12. Main Components • Coal and ASH circuit • Air and gas circuit • Feed water and steam flow circuit. • Cooling water circuit.

13. Coal and ASH circuit • Coal arrives at the storage yard and after necessary handling, passes on to the furnaces through the fuel feeding device. Ash resulting from combustion of coal collects at the back of the boiler and is removed to the ash storage yard through ash handling equipment.

14. 2. Air and Gas Circuit: • Air is taken in from atmosphere through the action of a forced or induced draught fan and passes on to the furnace through the air preheater, where it has been heated by the heat of flue gases which pass to the chimney via the preheater. • The flue gases after passing around boiler tubes and super-heater tubes in the furnace pass through a dust catching device or precipitator, then through the economises and finally through the air preheater before being exhausted to the atmosphere.

15. 3. Feed Water and Steam Flow Circuit: • In the water and steam circuit condensate leaving the condenser is first heated in a closed feed water heater through extracted steam from the lowest pressure extraction point of the turbine. • It then passes through the deaerator and a few more water heaters before going into the boiler through economiser.

16. In the boiler drum and tubes, water circulates due to the difference between the density of water in the lower temperature and the higher temperature sections of the boiler. Wet steam from the drum is further heated up in the superheater before being supplied to the primemover.

17. After expanding in high pressure turbine steam is taken to the reheat boiler and brought to its original dryness or superheat, before being passed on to the low pressure turbine. From there it is exhausted through the condenser into the hot well. The condensate is heated in the feed heaters using the steam trapped (bled steam) from different points of turbine. • A part of steam and water is lost while passing through different components and this is compensated by supplying additional feed water. This feed water should be purified before hand, to avoid the scaling of the tubes of the boiler.

18. 4. Cooling Water Circuit: • The cooling water supply to the condenser helps in maintaining a low pressure in it. The water may be taken from a natural source such as river, lake or sea or the same water may be cooled and circulated over again. In the latter case the cooling arrangement is made through spray pond or cooling tower.

19. A modern steam power plant consists of the following components: • (i) Superheater • (ii) Reaheater • (iii) Economiser • (iv) Air-heater • 2. Steam turbine • 3. Generator • 4. Condenser • 5. Cooling towers • 6. Circulating water pump • 7. Boiler feed pump • 8. Wagon tippler • 9. Crusher house • 10. Coal mill • 11. Induced draught fans • 12. Ash precipitators • 13. Boiler chimney • 14. Forced draught fans • 15. Water treatment plant • 16. Control room • 17. Switch yard.

20. Types of Turbines & their control. • Steam: • Steam is a vapour used as a working substance in the operation of steam turbine. • Is steam a perfect gas? • Steam possess properties like those of gases: namely pressure, volume, temperature, internal energy, enthalpy and entropy. • But the pressure volume and temperature of steam as a vapour are not connected by any simple relationship such as is expressed by the characteristic equation for a perfect gas.

21. Steam • Sensible heat – The heat absorbed by water in attaining its boiling point. • Latent heat – The heat absorbed to convert boiling water into steam. • Wet steam – Steam containing some quantity of moisture. • Dry steam – Steam that has no moisture content Steam that has no moisture content. • Superheated steam – Dry steam, when heated at constant pressure, attains superheat The properties of steam are dependent on its pressure

22. Steam turbine • PotentialEnergy • Kinetic energy • MechanicalEnergy

23. HIGH HIGH

24. Steam Turbine • Steam turbine convert a part of the energy of the steam evidenced by high temperature and pressure into mechanical power-in turn electrical power • The steam from the boiler is expanded in a nozzle, resulting in the emission of a high velocity jet. • This jet of steam impinges on the moving vanes or blades, mounted on a shaft. • Here it undergoes a change of direction of motion which gives rise to a change in momentum and therefore a force.

25. Steam Turbine • The motive power in a steam turbine is obtained by the rate of change in momentum of a high velocity jet of steam impinging on a curved blade which is free to rotate. • The conversion of energy in the blades takes place by impulse, reaction or impulse reaction principle. • Steam turbines are available in a few kW (as prime mover) to 1500 MW

26. Steam Turbine Classification • Steam turbines can be classified in several different ways: • 1. By details of stage design • Impulse or reaction. • 2. By steam supply and exhaust conditions • Condensing, or Non-condensing (back pressure), • Automatic or controlled extraction, • Mixed pressure Mixed pressure • Reheat

27. Steam Turbine Classification • 3. By casing or shaft arrangement • Single casing Tandem compound or Cross compound • 4. By number of exhaust stages in parallel: • Two flow, Four flow or Six flow. 5. By direction of steam flow: • Axial flow, Radial flow or Tangential flow 6. Single or multi-stage. 7. By steam supply • Superheat or Saturated

28. Impulse Turbine • In the impulse turbine, the steam expands in the nozzles and it's pressure does not alter as it moves over theblades.

29. IMPULSE TURBINE • In an impulse turbine, a fast-moving fluid is fired through a narrow nozzle at the turbine blades to make them spin around. • The blades of an impulse turbine are usually bucket-shaped so they catch the fluid and direct it off at an angle or sometimes even back the way it came (because that gives the most efficient transfer of energy from the fluid to the turbine). • In an impulse turbine, the fluid is forced to hit the turbine at high speed.

30. IMPULSE TURBINE

31. IMPULSE TURBINE • Imagine trying to make a wheel like this turn around by kicking soccer balls into its paddles. You'd need the balls to hit hard and bounce back well to get the wheel spinning—and those constant energy impulses are the key to how it works. • The law of conservation of energy tells us that the energy the wheel gains, each time a ball strikes it, is equal to the energy that the ball loses—so the balls will be traveling more slowly when they bounce back. • Also, Newton's second law of motion tells us that the momentum gained by the wheel when a ball hits it is equal to the momentum lost by the ball itself; the longer a ball touches the wheel, and the harder (more forcefully) it hits, the more momentum it will transfer. • Water turbines are often based around an impulse turbine (though some do work using reaction turbines). They're simple in design, easy to build, and cheap to maintain, not least because they don't need to be contained inside a pipe or housing (unlike reaction turbines).

32. IMPULSE TURBINE • In a reaction turbine, the blades sit in a much larger volume of fluid and turn around as the fluid flows past them. • A reaction turbine doesn't change the direction of the fluid flow as drastically as an impulse turbine: it simply spins as the fluid pushes through and past its blades. Wind turbines are perhaps the most familiar examples of reaction turbines.

35. DIFFERENCE BETWEEN IMPULSE AND REACTIVE TURBINE

37. TURBINE SPEED CONTROL • The main function of the governing is to maintain the speed constant irrespective of load on the turbine. • The different methods which are commonly used for governing the steam turbines are listed below: • Throttle governing • Nozzel control governing • Combination of throttle and nozzel governing • Combination of throttle and by-pass governing.

38. THROTTLE GOVERNING

39. NOZZLE CONTROL GOVERNING

40. NOZZEL • In nozzle governing the flow rate of steam is regulated by opening and shutting of sets of nozzles rather than regulating its pressure.[ • In this method groups of two, three or more nozzles form a set and each set is controlled by a separate valve. • The actuation of individual valve closes the corresponding set of nozzle thereby controlling the flow rate. • In actual turbine, nozzle governing is applied only to the first stage whereas the subsequent stages remain unaffected. • Since no regulation to the pressure is applied, the advantage of this method lies in the exploitation of full boiler pressure and temperature.

41. BY PASS GOVERNOR

42. Types of Boilers and their control • 1. According to Relative Passage of water and hot gases: • Water Tube Boiler: A boiler in which the water flows through some small tubes which are surrounded by hot combustion gases, e.g., Babcock and Wilcox, Stirling, Benson boilers, etc. • Fire-tube Boiler: The hot combustion gases pass through the boiler tubes, which are surrounded by water, e.g., Lancashire, Cochran, locomotive boilers, etc.

43. 2. According to Water Circulation Arrangement: • Natural Circulation: Water circulates in the boiler due to density difference of hot and water, e.g., Babcock and Wilcox boilers, Lancashire boilers, Cochran, locomotive boilers, etc. • Forced Circulation: A water pump forces the water along its path, therefore, the steam generation rate increases, Eg: Benson, La Mont, Velox boilers, etc.

44. According to the Use: • Stationary Boiler: These boilers are used for power plants or processes steam in plants. • Portable Boiler: These are small units of mobile and are used for temporary uses at the sites. • Locomotive: These are specially designed boilers. They produce steam to drive railway engines. • Marine Boiler: These are used on ships.

45. According to Position of the Boilers: • Horizontal, inclined or vertical boilers • According to the Position of Furnace • Internally fired: The furnace is located inside the shell, e.g., Cochran, Lancashire boilers, etc. • Externally fired: The furnace is located outside the boiler shell, e.g., Babcock and Wilcox, Stirling boilers, etc.

46. According to Pressure of steam generated • Low-pressure boiler: a boiler which produces steam at a pressure of 15-20 bar is called a low-pressure boiler. This steam is used for process heating. • Medium-pressure boiler: It has a working pressure of steam from 20 bars to 80 bars and is used for power generation or combined use of power generation and process heating. • High-pressure boiler: It produces steam at a pressure of more than 80 bars. • Sub-critical boiler: If a boiler produces steam at a pressure which is less than the critical pressure, it is called as a subcritical boiler. • Supercritical boiler: These boilers provide steam at a pressure greater than the critical pressure. These boilers do not have an evaporator and the water directly flashes into steam, and thus they are called once through boilers.

47. According to charge in the furnace. • Pulverized fuel, • Supercharged fuel and • Fluidized bed combustion boilers.

48. LA MONT BOILER

49. BENSON BOILER

50. ONCE THROUGH BOILER