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2013edusat lecture on steam plant(2)

  1. steam power plant By :- Rakesh kumar Assistant professor Electrical Engineering Department. BABA HIRA SINGH BHATTAL INSTITUTE OF ENGINEERING AND TECHNOLOGY LEHRAGAGA- 148031 DISTT.SANGRUR (Pb.)
  2. Essentials of Steam Power Plant Equipment A steam power plant must have following equipment : (a) A furnace to burn the fuel. (b) Steam generator or boiler containing water. Heat generated in the furnace is utilized to convert water into steam. (c) Main power unit such as an engine or turbine to use the heat energy of steam and perform work. (d) Piping system to convey steam and water.
  3. The flow sheet of a thermal power plant consists of the following four main circuits : (a) Feed water and steam flow circuit. (b) Coal and ash circuit. (c) Air and gas circuit. (d) Cooling water circuit.
  4. A steam power plant using steam as working substance works basically on Rankine cycle. Steam is generated in a boiler, expanded in the prime mover and condensed in the condenser and fed into the boiler again.
  5. The different types of components used in steam power plant (a) High pressure boiler. (b) Prime mover . (c) Condensers and cooling towers . (d) Coal handling system . (e) Ash and dust handling system . (f) Draught system . (g) Feed water purification plant . (h) Pumping system . (i) Air preheater, economizer, super heater, feed heaters.
  6. Types of steam Generators  Horizontal vertical or inclined.  Fire tube or water tube.  Externally fired or internally fired.  Forced circulation and natural circulation.  High pressure or low pressure boiler.
  7. Dalton’s law  The partial pressure pressure of each constituent is that pressure which the gas would exert if it occupied alone that volume occupied by the mixture at the same temperature.
  8. Factors that should be considered while selecting the boiler  Working pressure and quality of steam required.  Steam generation rate.  Floor area available.  The portable load factor.  Erection facilities.
  9. Properties of good steam generators  It should be absolutely reliable.  It should occupy minimum space.  It should be light in weight.  Capable of quick starting.  Erection of boiler should be simple.
  10. Steam Power Plants are Classified as 1. By fuel. 2. By prime mover. 3. By cooling tower.
  11. Steam Power Plants are also Classified as; Central stations; the electrical energy available from these stations is meant for sale to the consumers who wish to purchase it. Industrial/ captive power stations; this type of power station is run by the manufacturing company for its own use and its output is not available for general sale.
  12. Jet condenser; low manufacturing cost. Low upkeeps, requires small floor space and more auxiliary power required. surface condenser; high manufacturing cost. high upkeeps, requires large floor space and less auxiliary power required.
  13. Feed water heating improves overall plant efficiency. Quantity of steam produced by the boiler is increase. Thermal stress due to cold water entering the boiler drum are avoided. Chance of boiler corrosion are decrease.
  14. Dust collectors are Classified as; Mechanical dust collectors; (a)Wet type(scrubbers). Spray type, packed type and impingement type. (b) Dry type. Gravitational separators, cyclone separators, electrical dust collectors; Rod type and plate type.
  15. DIFFERENT TYPES OF BOILERS USED IN STEAM POWER PLANTS  horizontal, vertical or inclined.  fire tube and water tube .  Externally or internally fired.  Forced or natural circulation.  High pressure or low pressure.  Stationary or portable.  Single-tube and multi-tube.
  16. Working diagram Thermal power station.
  17. C saturated water Steam Turbine Power Plant hot gases Steam Turbine Gen compressed water superheated steam Condenser Pump cooling water saturated steam Steam Generator (Boiler / Furnace)
  18. Schematic arrangement of equipment of a steam power station.  Coal received in coal storage yard of power station is transferred in the furnace by coal handling unit. Heat produced due to burning of coal is utilized in converting water contained in boiler drum into steam at suitable pressure and temperature. The steam generated is passed through the superheater.
  19.  Superheated steam then flows through the turbine. After doing work in the turbine the pressure of steam is reduced. Steam leaving the turbine passes through the condenser which is maintained the low pressure of steam at the exhaust of turbine.
  20.  Steam pressure in the condenser depends upon flow rate and temperature of cooling water and on effectiveness of air removal equipment. Water circulating through the condenser may be taken from the various sources such as river, lake or sea. If sufficient quantity of water is not available the hot water coming out of the condenser may be cooled in cooling towers and circulated again through the condenser.  Bled steam taken from the turbine at suitable extraction points is sent to low pressure and high pressure water heaters.
  21.  Air taken from the atmosphere is first passed through the air pre-heater, where it is heated by flue gases. The hot air then passes through the furnace.  The flue gases after passing over boiler and superheater tubes, flow through the dust collector and then through economiser, air pre-heater and finally they are exhausted to the atmosphere through the chimney.
  22. Disadvantage of steam power plant  Maintenance and operating cost are high.  Long time required for erection and putting into action .  Large quantity of water is required.  Great difficulty experienced in coal handling .  Efficiency decreases rapidly below about 75 percent load.
  23. Mechanical equipment in Thermal power station. BOILER ECONOMISER TURBINE SUPER HEATER AIR PREHEATER CONDENSER
  24. Superheater The superheater consists of a superheater header and superheater elements. Steam from the main steam pipe arrives at the saturated steam chamber of the superheater header and is fed into the superheater elements. Superheated steam arrives back at the superheated steam chamber of the superheater header and is fed into the steam pipe to the cylinders. Superheated steam is more expansive.
  25. Advantages of superheated steam  Capacity to do work is increased without increasing its pressure.  High temperature of super heated steam results in an increase in thermal efficiency.  Heat losses due to condensation of stem on cylinder walls are avoided to a great extent.  Does not produce corrosion effect on turbine.
  26. Superheater  It is a heating device.  It is used to raise temp of steam at const pressure.  It removes even last traces of moisture.
  27. Classification of super heater  Convection.  Radiation.  Combination of convection and radiation.
  28. Reheater  The function of reheater is similar to the superheater in that it serves to elevate the steam temperature. Primary steam is supplied to the high pressure turbine.  After passing through the high pressure turbine, the steam is returned to the steam generator for reheating (in a reheater) after which it is sent to the low pressure turbine. A second reheat cycle may also be provided.
  29. Soot Blowers  The fuel used in thermal power plants causes soot and this is deposited on the boiler tubes, economizer tubes, air pre heaters, etc.  This drastically reduces the amount of heat transfer of the heat exchangers. Soot blowers control the formation of soot and reduce its corrosive effects.  The types of soot blowers are fixed type, which may be further classified into lane type and mass type depending upon the type of spray and nozzle used.
  30. Condenser  The use of a condenser in a power plant is to improve the efficiency of the power plant by decreasing the exhaust pressure of the steam below atmosphere.  Another advantage of the condenser is that the steam condensed may be recovered to provide a source of good pure feed water to the boiler and reduce the water softening capacity to a considerable extent. A condenser is one of the essential components of a power plant.
  31. Functions of Condensers  The main purposes of the condenser are to condense the exhaust steam from the turbine for reuse in the cycle and to maximize turbine efficiency by maintaining proper vacuum.  As the operating pressure of the condenser is lowered (vacuum is increased), the enthalpy drop of the expanding steam in the turbine will also increase. This will increase the amount of available work from the turbine (electrical output).
  32. Cooling Tower  The importance of the cooling tower is felt when the cooling water from the condenser has to be cooled.  The cooling water after condensing the steam becomes hot and it has to be cooled as it belongs to a closed system. The Cooling towers do the job of decreasing the temperature of the cooling water after condensing the steam in the condenser.
  33. Cooling Towers have one function :  Remove heat from the water discharged from the condenser so that the water can be discharged to the river or re-circulated and reused.
  34. A cooling tower extracts heat from water by evaporation. In an evaporative cooling tower, a small portion of the water being cooled is allowed to evaporate into a moving air stream to provide significant cooling to the rest of that water stream.
  35.  Cooling Towers are commonly used to provide lower than ambient water temperatures and are more cost effective and energy efficient than most other alternatives.  The smallest cooling towers are structured for only a few litres of water per minute while the largest cooling towers may handle upwards of thousands of litres per minute. The pipes are obviously much larger to accommodate this much water in the larger towers and can range up to 12 inches in diameter.
  36. Advantages of regenerative cycle  Improve overall plant efficiency.  Protect boiler corrosion.  Avoid the thermal stresses due to cold water entering the boiler .  Increased the quantity of steam produced by boiler.
  37. Function of economizer  To extract a part of heat from the fuel gas coming out of the boiler. To use heat for heating feed water to the boiler.  To increases the efficiency of boiler.
  38.  The economizer is a feed water heater, deriving heat from the flue gases. The justifiable cost of the economizer depends on the total gain in efficiency. In turn this depends on the flue gas temperature leaving the boiler and the feed water inlet temperature.
  39. Air Pre-heater  The flue gases coming out of the economizer is used to preheat the air before supplying it to the combustion chamber. An increase in air temperature of 20 degrees can be achieved by this method. The pre heated air is used for combustion and also to dry the crushed coal before pulverizing.
  40. Advantages of mechanical handling  Higher reliability.  Less labour required.  Operation is easy and smooth.  Economical for large capacity plant.  Losses in transport are minimised.  Easily started.
  41. Disadvantages of mechanical handling  Need continuous maintenance and repair.  Capital cost of plant is increased.
  42. Working diagram Thermal power station.
  43. Side view Thermal power station.
  44. C Total Heat saturated water Steam Turbine Power Plant Gen compressed water superheated steam in Steam Generator Loss??? Where??? cooling water Pump Total Steam Turbine Condenser saturated steam hot gases Workout Workin
  45. R. Shanthini 15 Aug 2010 According to the 2nd Law of Thermodynamics when heat is converted into work, part of the heat energy must be wasted Power generation type Unit size (MW) Energy wasted (MW) Diesel engine 10 - 30 7 – 22 Gas Turbine 50 - 100 36 – 78 Steam Turbine 200 - 800 120 – 560 Combined (ST & GT) 300 - 600 150 – 380 Nuclear (BWR & PWR) 500 - 1100 330 – 760
  46. The Simple Ideal Rankine Cycle 9-1 © The McGraw-Hill Companies, Inc.,1998
  47. How can We Increase the Efficiency of the Rankine cycle?  Rankine cycle efficiency can be increased by increasing average temperature at which heat is transferred to the working fluid in the boiler or decreasing the average temperature at which heat is rejected from the working fluid in the condenser. That is, the average fluid temperature should be as high as possible during heat addition and as low as possible during heat rejection.
  48. The three ways by which efficiency of the Rankine cycle can be increased are : (a) Lowering the condenser pressure. (b) Superheating the steam to high temperatures. (c) Increasing the boiler pressure.
  49. • The thermal efficiency of the Rankine cycle can be increased by increasing the average temperature at which heat is added to the working fluid and/or by decreasing the average temperature at which heat is rejected to the cooling medium. The average temperature during heat rejection can be decreased by lowering the turbine exit pressure.
  50. Consequently, the condenser pressure of most vapor power plants is well below the atmospheric pressure. The average temperature during heat addition can be increased by raising the boiler pressure or by superheating the fluid to high temperatures. There is a limit to the degree of superheating, however, since the fluid temperature is not allowed to exceed a metallurgically safe value.
  51. • Superheating has the added advantage of decreasing the moisture content of the steam at the turbine exit. Lowering the exhaust pressure or raising the boiler pressure, however, increases the moisture content. To take advantage of the improved efficiencies at higher boiler pressures and lower condenser pressures, steam is usually reheated after expanding partially in the high-pressure turbine.
  52.  This is done by extracting the steam after partial extraction in the high-pressure turbine, sending it back to the boiler where it is reheated at constant pressure, and returning it to the low-pressure turbine for complete expansion to the condenser pressure.
  53.  The average temperature during the reheat process, and thus the thermal efficiency of the cycle, can be increased by increasing the number of expansion and reheat stages. As the number of stages is increased, the expansion and reheat processes approach an isothermal process at maximum temperature. Reheating also decreases the moisture content at the turbine exit.
  54. • Another way of increasing the thermal efficiency of the Rankine cycle is by regeneration. During a regeneration process, liquid water (feed water) leaving the pump is heated by some steam bled off the turbine at some intermediate pressure in devices called feed water heaters.
  55. The two streams are mixed in open feed water heaters, and the mixture leaves as a saturated liquid at the heater pressure. In closed feed water heaters, heat is transferred from the steam to the feed water without mixing.
  56. • The production of more than one useful form of energy (such as process heat and electric power) from the same energy source is called cogeneration. Cogeneration plants produce electric power while meeting the process heat requirements of certain industrial processes.
  57. This way, more of the energy transferred to the fluid in the boiler is utilized for a useful purpose. The faction of energy that is used for either process heat or power generation is called the utilization factor of the cogeneration plant.
  58. • The overall thermal efficiency of a power plant can be increased by using binary cycles or combined cycles. A binary cycle is composed of two separate cycles, one at high temperatures (topping cycle) and the other at relatively low temperatures.
  59.  The most common combined cycle is the gas-steam combined cycle where a gas-turbine cycle operates at the high-temperature range and a steam-turbine cycle at the low-temperature range. Steam is heated by the high-temperature exhaust gases leaving the gas turbine. Combined cycles have a higher thermal efficiency than the steam- or gas-turbine cycles operating alone.
  60. Selection of plant site  The selection of plant site for thermal power plant compared with hydro-power plant is more difficult as it involves number of factors to be considered for its economic justification. A few important factors to be considered for the selection of thermal power plants.
  61. Selection of plant site AVAILABILITY OF COAL. Huge quantity of coal is required for large thermal plants. ASH DISPOSAL FACILITIES. SPACE REQUIREMENT. NATURE OF LAND. AVAILABILITY OF WATER.
  63. ABOUT ELECTROSTATIC PRECIPITATOR Nowadays, the environment protection has become a crucial problem and the authorities are requested to set increasingly more stringent limits , one of which is the emissions from the industrial plants of solid particulate and other gaseous pollutants.
  64. ABOUT ELECTROSTATIC PRECIPITATOR What is ESP Electrostatic precipitator (ESP) is a widely used device in so many different domains to remove the pollutant particulates, especially in industrial plants.
  65. HOW ESP WORKS Main process of ESP Generally, the processes of electrostatic precipitator are known as three main stages: particle charging, transport and collection.
  66. Schematic of wire-plate ESP Schematic of wire-plate electrostatic precipitator
  67. Mechanism of ESP Mechanism of electrostatic precipitator
  68. PROCESS OF Particle charging Particle charging is the first and foremost beginning in processes. As the voltage applied on precipitator reach threshold value, the space inside divided into ionization region and drift region.
  69. The electric field magnitude around the negative electrode is so strong that the electrons escape from molecule. Under the influence of electric field, the positive ions move towards the corona, while the negative ions and electrons towards the collecting plates.
  70. Particle transport In the moving way, under the influence of electric field, negative ions cohere and charge the particles, make the particles be forced towards collecting-plate.
  71. Particle collection As soon as the particles reach the plate, they will be neutralized and packed by the succeeded ones subsequently. The continuous process happens, as a result, particles are collected on the collecting plate.
  72. 72 Introduction What is a Boiler? • Vessel that heats water to become hot water or steam • At atmospheric pressure water volume increases 1,600 times • Hot water or steam used to transfer heat to a process
  73. The boiler is a rectangular furnace about 50 feet (15 m) on a side and 130 feet (40 m) tall. Its walls are made of a web of high pressure steel tubes about 2.3 inches (58 mm) in diameter.
  74. A boiler should fulfill the following requirements (a)Safety : The boiler should be safe under operating conditions. (b) Accessibility : The various parts of the boiler should be accessible for repair and maintenance. (c) Capacity : The boiler should be capable of supplying steam according to the requirements.
  75. (d) Efficiency : To permit efficient operation, the boiler should be able to absorb a maximum amount of heat produced due to burning of fuel in the furnace. (e) It should be simple in construction and its maintenance cost should be low. (f) Its initial cost should be low. (g) The boiler should have no joints exposed to flames. (h) The boiler should be capable of quick starting and loading.
  77. Types of Boilers What Type of Boilers Are There? 1. Fire Tube Boiler 2. Water Tube Boiler 3. Packaged Boiler 4. Fluidized Bed (FBC) Boiler 5. Stoker Fired Boiler 6. Pulverized Fuel Boiler 7. Waste Heat Boiler 8. Thermic Fluid Heater (not a boiler!)
  78. The boilers can be classified according to the following criteria. According to flow of water and hot gases : (a) Water tube (b) Fire tube.
  79. Type of Boilers 1. Fire Tube Boiler • Relatively small steam capacities (12,000 kg/hour) • Low to medium steam pressures (18 kg/cm2) • Operates with oil, gas or solid fuels
  80. Type of Boilers 2. Water Tube Boiler • Used for high steam demand and pressure requirements • Capacity range of 4,500 – 120,000 kg/hour • Combustion efficiency enhanced by induced draft provisions • Lower tolerance for water quality and needs water treatment plant
  81. 3. Packaged Boiler Oil Burner To Chimney • Comes in complete package • Features • High heat transfer • Faster evaporation • Good convective heat transfer • Good combustion efficiency • High thermal efficiency • Classified based on number of passes
  82. Working of power plant Pulverized coal is air-blown into the furnace from fuel nozzles at the four corners and it rapidly burns, forming a large fireball at the center. The thermal radiation of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter.
  83. The water circulation rate in the boiler is three to four times the throughput and is typically driven by pumps. As the water in the boiler circulates it absorbs heat and changes into steam at 700 °F (371 °C) and 3,200 psi
  84. The water enters the boiler through a section in the convection pass called the economizer. From the economizer it passes to the steam drum. Once the water enters the steam drum it goes down to the lower inlet water wall headers.
  85. From the inlet headers the water rises through the water walls and is eventually turned into steam due to the heat being generated by the burners located on the front and rear water walls (typically). As the water is turned into steam/vapor in the water walls, the steam/vapor once again enters the steam drum.
  86. The steam/vapor is passed through a series of steam and water separators and then dryers inside the steam drum. The steam separators and dryers remove water droplets from the steam and the cycle through the water walls is repeated. This process is known as natural circulation.
  87. super heater Fossil fuel power plants can have a super heater and/or re-heater section in the steam generating furnace. In a fossil fuel plant, after the steam is conditioned by the drying equipment inside the steam drum, it is piped from the upper drum area into tubes inside an area of the furnace known as the super heater,
  88. which has an elaborate set up of tubing where the steam vapor picks up more energy from hot flue gases outside the tubing and its temperature is now superheated above the saturation temperature. The superheated steam is then piped through the main steam lines to the valves before the high pressure turbine.
  89. Condenser  The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases.
  90. For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam.
  91. Since the condenser temperature can almost always be kept significantly below 100 °C where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensible air into the closed loop must be prevented.
  92. The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.
  93. The condenser tubes are made of brass or stainless steel to resist corrosion from either side. Nevertheless they may become internally fouled during operation by bacteria or algae in the cooling water or by mineral scaling, all of which inhibit heat transfer and reduce thermodynamic efficiency.
  94. Many plants include an automatic cleaning system that circulates sponge rubber balls through the tubes to scrub them clean without the need to take the system off-line.
  95. Re heater Power plant furnaces may have a re heater section containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the re heater tubes to pickup more energy to go drive intermediate or lower pressure turbines.
  96. Main pollutants from a power system Non –toxic dust  Sulphurous anhydride Carbon monoxide  Nitrogen dioxide  Soot (fly ash) Hydrogen sulphide  Pollution can be define as the contamination of soil, air and water with undesirable amount of material and heat.
  97. Acid rain; the rain which contain acid as its constituents, brings all the acid down from high above the environment. Contaminant; it is the another name of pollution. It is undesirable substances which may be physical, chemical or biological.  Pollutant; these are undesirable substances present in the environment these can be NO2, SO2, CO2,smoke,salt, bacteria.
  98. Bad effects of thermal pollution  Lot of heat is injected into biosphere from thermal power plant, through exhaust gases and waste water. The major problem is the effect of discharge of large quantity of heated wasted water into natural water basins. Hot water raises the temperature and disturbs the natural ecological balance
  99. Advantages of combined operation of plants Greater reliability of supply to the consumers. Avoid complete shut down.  The overall cost of energy per unit of an interconnected system is less.  There is a more effective use of transmission line facilities.  Less capital investment required.  Less expenses on supervision, operation and maintenance.
  100.  Due to limited generating capacity diesel power stations is not suitable for base load plants.  Nuclear power stations is not suitable for peak load plants. Incremental rate curve shows that as output power increases, cost of plant also increases.