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High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
High Pressure Boilers
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High Pressure Boilers
High Pressure Boilers
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High Pressure Boilers

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  • 1. HIGH PRESSURE BOILERS VANITA THAKKAR ASSOCIATE PROFESSOR, MECHANICAL ENGINEERING DEPARTMENT, BABARIA INSTITUTE OF TECHNOLOGY, VARNAMA, VADODARA
  • 2. INTRODUCTION  A Power Plant / Power Station is an industrial facility for generation of Electric Power.  It is a set-up consisting of systems and sub-systems, equipments and auxiliaries required for the generation of Electricity, which involves conversion of energy forms like chemical energy, heat energy or gravitational potential energy into Electrical Energy. 2VANITA N THAKKAR BIT, VARNAMA
  • 3. ENERGY CONVERSION PROCESS IN POWER PLANT The energy content in a primary source of energy, like  Chemical Energy of a Fossil Fuel,  Potential Energy of water stored at a height,  Renewable / Non-conventional sources, like Solar Thermal Energy, Wind energy, Geothermal Energy, Tidal Energy, Wave Energy, etc. is converted stage-wise to Mechanical Energy (Rotational Energy) to obtain Electricity by creating relative motion between a magnetic field and a conductor. 3VANITA N THAKKAR BIT, VARNAMA
  • 4. THERMAL POWER PLANTS  In Thermal Power Plants, 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 Plants / 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 distinct heating, the power plant is referred to as a Cogeneration Power plant or CHP (combined heat-and-power) plant. 4VANITA N THAKKAR BIT, VARNAMA
  • 5. RANKINE CYCLE  A Thermal Power Plant is a power plant in which the prime mover is steam driven.  Water is heated, turns into steam in Boiler 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 – as shown in the figure. 5VANITA N THAKKAR BIT, VARNAMA G2 G3 G1
  • 6. Slide 5 G2 A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884. Guest, 01-01-2002 G3 Electrical Generator is a device that converts mechanical energy to electrical energy, generally using electromagnetic induction. Guest, 01-01-2002 G1 A machine that transforms energy from thermal or pressure form to mechanical form; typically an engine (A mechanical device used to produce rotation to move vehicle or otherwise provide the force needed to generate kinetic energy.) or turbine (any of various rotary machines that use the kinetic energy of a continuous stream of fluid - a liquid or a gas - to turn a shaft). Guest, 01-01-2002
  • 7. MORE ABOUT RANKINE CYCLE  The Rankine cycle is a thermodynamic cycle which converts heat into work.  The heat is supplied externally to a closed loop, which usually uses water as the working fluid.  This cycle generates about 80% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants.  It is named after William John Macquorn Rankine, a Scottish polymath. 6VANITA N THAKKAR BIT, VARNAMA G4
  • 8. Slide 6 G4 A polymath (Greek polymathēs, πολυμαθής, "having learned much") is a person whose expertise fills a significant number of subject areas. In less formal terms, a polymath (or polymathic person) may simply refer to someone who is very knowledgeable. Guest, 01-01-2002
  • 9. WILLIAM RANKINE  The Rankine Cycle is named after William Rankine. Trained as a civil engineer, William Rankine was appointed to the chair of civil engineering and mechanics at Glasgow in 1855. He developed methods to solve the force distribution in frame structures.  He worked on heat, and attempted to derive Sadi Carnot's law from his own hypothesis. His work was extended by Maxwell.  Rankine also wrote on fatigue in the metal of railway axles, on Earth pressures in soil mechanics and the stability of walls. He was elected a Fellow of the Royal Society in 1853.  Among his most important works are Manual of Applied Mechanics (1858), Manual of the Steam Engine and Other Prime Movers (1859) and On the Thermodynamic Theory of Waves of Finite Longitudinal Disturbance. 7VANITA N THAKKAR BIT, VARNAMA
  • 10. PROCESSES IN RANKINE CYCLEThere are Four processes in the Rankine cycle, each changing the state of the working fluid.  Process 1-2: Working fluid is PUMPED from low to high pressure, as the fluid is a liquid at this stage the pump requires little input energy.  Process 2-3: The high pressure liquid enters a BOILER where it is heated at constant pressure by an external heat source to become a dry saturated vapour (or wet vapour).  Process 3-4: The dry saturated vapour expands through a TURBINE, generating power. Due to decrease in temperature and pressure of the vapour, and some condensation may occur.  Process 4-1: The wet vapour then enters a CONDENSER where it is condensed at a constant pressure and temperature to become a saturated liquid. The pressure and temperature of the condenser is fixed by the temperature of the cooling coils as the fluid is undergoing a phase-change. 8VANITA N THAKKAR BIT, VARNAMA
  • 11. RANKINE CYCLE : PRACTICAL CARNOT CYCLE  The Rankine cycle is sometimes referred to as a Practical Carnot cycle as, when an efficient turbine is used, the TS diagram begins to resemble the Carnot cycle.  The main difference is that a pump is used to pressurize liquid instead of gas. This requires about 1/100th (1%) as much energy than that in compressing a gas in a compressor (as in the Carnot cycle). 9VANITA N THAKKAR BIT, VARNAMA
  • 12. Thus, BASIC COMPONENTS OF THERMAL POWER PLANT  BOILER  STEAM TURBINE : The Prime Mover  CONDENSER  FEED PUMP Supported by various sub-systems / accessories / equipments required for their proper, efficient working and to ensure their proper working in co- ordination with each other. 10VANITA N THAKKAR BIT, VARNAMA
  • 13. SCHEMATIC DIAGRAM OF A STEAM POWER PLANT 11VANITA N THAKKAR BIT, VARNAMA
  • 14. BOILER  A boiler is a closed vessel in which water or other fluid is heated.  The heated or vaporized fluid exits the boiler for use in various Processes or Heating applications or for Power generation.  In a Steam Power Plant, typically called Thermal Power Plant, Water is heated to get Steam for Power Generation. 12VANITA N THAKKAR BIT, VARNAMA
  • 15. STEAM PRODUCTION 13VANITA N THAKKAR BIT, VARNAMA
  • 16. STEAM PRODUCTION (contd.) 14VANITA N THAKKAR BIT, VARNAMA
  • 17. STEAM PRODUCTION (contd.) 15VANITA N THAKKAR BIT, VARNAMA
  • 18. STEAM PRODUCTION (contd.) : From Steam Tables …. 16VANITA N THAKKAR BIT, VARNAMA
  • 19. STEAM PRODUCTION (contd.) 17VANITA N THAKKAR BIT, VARNAMA
  • 20. STEAM PRODUCTION (contd.) : From Steam Tables …. Boiling point 18VANITA N THAKKAR BIT, VARNAMA
  • 21. STEAM PURITY 19VANITA N THAKKAR BIT, VARNAMA
  • 22. STEAM QUALITY 20VANITA N THAKKAR BIT, VARNAMA
  • 23. BASIC COMPONENTS OF BOILER In a conventional steam power plant, a boiler consists of : BOILER FURNACE : FUEL IS BURNT Fuel : Fossil Fuel / Waste Fuel / Nuclear Fuel SURFACES : TO TRANSMIT HEAT FROM COMBUSTION PRODUCTS TO WATER. SPACE (DRUM) : WHERE STEAM CAN FORM AND COLLECT 21VANITA N THAKKAR BIT, VARNAMA
  • 24. HISTORICAL BACKGROUND  Boilers were built as early as the 1st century AD by Hero of Alexandria but were used only as toys.  Not until the 17th century was serious consideration given to the potential of steam power for practical work.  Denis Papin of France designed the first boiler with a safety valve in 1679;  Earlier Boilers were made of wrought iron.  As the advantages of high pressure and temperature were realized, manufactures turned to steel.  Modern boilers are made of alloy steel to withstand high pressures and extremely high temperatures. 22VANITA N THAKKAR BIT, VARNAMA
  • 25. TYPES OF BOILERS 23VANITA N THAKKAR BIT, VARNAMA
  • 26. FIRE-TUBE BOILERS  Water surrounds the steel tubes through which hot gases from the furnace flow.  The steam generated collects above the water level in a cylindrically shaped drum.  A safety valve is set to allow escape of steam at pressures above normal operating pressure; this device is necessary on all boilers, because continued addition of heat to water in a closed vessel without means of steam escape result in a rise in pressure and ultimately, in explosion of the boiler.  Fire-tube boilers have the advantage of being easy to install and operate.  They are widely used in small installations to heat buildings and to provide power for factory processes and in steam locomotives. 24VANITA N THAKKAR BIT, VARNAMA
  • 27. FIRE-TUBE BOILERS (contd.) 25VANITA N THAKKAR BIT, VARNAMA
  • 28. WATER-TUBE BOILERS  Water is inside tubes with the hot furnace gases circulating outside the tubes.  When the steam turbo generator was developed early in the 20th century, modern water tube boilers were developed in response to the demand for large quantities of steam at high pressures and temperatures, far exceeding those possible with fire-tube boilers.  The tubes are outside the steam drum, which has no heating surface and is much smaller than that in the fire-tube boiler.  So, drum of water tube boiler is better able to withstand higher pressures and temperatures.  A wide variety of sizes and designs of water tube boilers are used in ships and factories. 26VANITA N THAKKAR BIT, VARNAMA
  • 29. WATER-TUBE BOILERS (contd.)  The Express Boiler is designed with small water tubes for quick generation of steam.  The Flash Boiler may not require a steam drum, because the tubes operate at such high temperatures that the feed water flashes into steam and superheats before leaving the tubes.  The largest units are found in the central-station power plants of public utilities.  Units of substantial size are used in steel mills, paper mils, oil refineries, chemical plants, and other large manufacturing plants. 27VANITA N THAKKAR BIT, VARNAMA
  • 30. HIGH PRESSURE BOILERS Boilers used for : Steam capacities – 30 tons/hr. to 650 tons/hr. and above, Pressure – up to 160 bar (can be more), Maximum steam temperatures – typically about 540oC (can be more). 28VANITA N THAKKAR BIT, VARNAMA
  • 31. UNIQUE FEATURES OF HIGH PRESSURE BOILERS  Method of water circulation : Forced circulation, using pump.  Type of Tubing : Water Tube Boilers, with flow through several sets of parallel system of tubing – to reduce pressure loss occurring in single tube system and to have better control over quality of steam. 29VANITA N THAKKAR BIT, VARNAMA
  • 32. UNIQUE FEATURES OF HIGH PRESSURE BOILERS (contd.)  Improved Method of Heating :  Saving of heat by evaporation of water above critical pressure of steam.  Heating of water by mixing with superheated steam, to give high heat transfer coefficients.  Increase in overall heat transfer coefficient by increasing water velocity inside the tubes and increasing gas velocity above sonic velocity. 30VANITA N THAKKAR BIT, VARNAMA
  • 33. LA MONT BOILER 31VANITA N THAKKAR BIT, VARNAMA
  • 34. LA MONT BOILER (contd.) 45 – 50 Tons of superheated steam at a pressure of about 160 bar and a temperature of 500oC. 32VANITA N THAKKAR BIT, VARNAMA
  • 35. BENSON BOILER One of the main difficulties in La Mont Boiler : Formation and attachment of bubbles on inner surfaces of heating tubes, which reduce heat flow and steam generation due to high thermal resistance than water film. If boiler pressure is raised to critical pressure (225 atm.), density of steam and water would be the same, hence bubble formation would be prevented. Benson got this idea in 1922 and the first Benson Boiler became operational in West Germany in 1927. 33VANITA N THAKKAR BIT, VARNAMA
  • 36. BENSON BOILER (contd.) 34VANITA N THAKKAR BIT, VARNAMA
  • 37. BENSON BOILER (contd.) Typical Parameters : Temperature Range : upto 650oC Pressure : upto 500 atm Steam Generating Capacity : 150 tons/hr. 35VANITA N THAKKAR BIT, VARNAMA
  • 38. BENSON BOILER (contd.) First Benson Boiler - 1927 36VANITA N THAKKAR BIT, VARNAMA
  • 39. 37VANITA N THAKKAR BIT, VARNAMA
  • 40. VELOX BOILER  Uses Pressurized Combustion, i.e. When gas velocity exceeds sound velocity, heat is transferred from the gas at much higher rates than those achieved with sub-sonic flow. This fact is made use of to obtain large heat transfer rates from smaller surface area in Velox boilers. 38VANITA N THAKKAR BIT, VARNAMA
  • 41. VELOX BOILER Gas Turbine runs Axial Compressor : raises pr. of incoming air from atmospheric pr. to furnace pr. Feed Water Steam separated here flows to superheater and then to prime mover 39 VANITA N THAKKAR BIT, VARNAMA
  • 42. VELOX BOILER (contd.) 40VANITA N THAKKAR BIT, VARNAMA
  • 43. LOEFFLER BOILER One of the main difficulties in La Mont Boiler : Deposition of sand and sediment on inner surfaces of heating tubes, which reduce heat transfer and steam generation due to high thermal resistance than water film. This difficulty is solved in Loeffler Boiler by preventing flow of water in boiler tubes. Principle : Evaporation of feed water by means of Superheated steam from Superheater, hot gases from furnace being primarily used for superheating purposes. 41VANITA N THAKKAR BIT, VARNAMA
  • 44. LOEFFLER BOILER (contd.) Loeffler boiler can manage higher concentrations of salt than any other type. It is more compact than indirectly heated boilers having natural circulation. Hence it is very useful for land and sea transport power generation. Typical specifications : 100 tons/hour generating capacity, 140 bar pr. 42VANITA N THAKKAR BIT, VARNAMA
  • 45. LOEFFLER BOILER (contd.) 43VANITA N THAKKAR BIT, VARNAMA
  • 46. LOEFFLER BOILER (contd.) This boiler can carry higher salt concentrations than any other boiler. Hence more compact than indirectly heated boilers having natural circulation. So, it is useful for land and sea transport power generation. 44VANITA N THAKKAR BIT, VARNAMA
  • 47. SCHMIDT HARTMANN BOILER Working similar to that of a transformer. Two pressures are used to effect interchange of energy. 45VANITA N THAKKAR BIT, VARNAMA
  • 48. SCHMIDT HARTMANN BOILER (contd.) 46VANITA N THAKKAR BIT, VARNAMA
  • 49. SCHMIDT HARTMANN BOILER (contd.) 47VANITA N THAKKAR BIT, VARNAMA
  • 50. SCHMIDT HARTMANN BOILER (contd.) 48VANITA N THAKKAR BIT, VARNAMA
  • 51. SUPER-CRITICAL BOILERS 49VANITA N THAKKAR BIT, VARNAMA
  • 52. SUPER-CRITICAL BOILERS (contd.) Advantages of Super-ciritical Boilers (contd.) : 50VANITA N THAKKAR BIT, VARNAMA
  • 53. SUPER-CHARGED BOILER 51VANITA N THAKKAR BIT, VARNAMA
  • 54. SUPER-CHARGED BOILER (contd.) 52VANITA N THAKKAR BIT, VARNAMA
  • 55. SUPER-CHARGED BOILER (contd.) ADVANTAGES : 53VANITA N THAKKAR BIT, VARNAMA
  • 56. SUPER-CHARGED BOILER (contd.) DISADVANTAGES : 54VANITA N THAKKAR BIT, VARNAMA
  • 57. FLUIDIZED BED COMBUSTION BOILERS 55VANITA N THAKKAR BIT, VARNAMA
  • 58. PRINCIPLE : FBC BOILERS 56VANITA N THAKKAR BIT, VARNAMA
  • 59. PRINCIPLE : FBC BOILERS (CONTD.)  When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity.  As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream – the bed is called “fluidised”. 57VANITA N THAKKAR BIT, VARNAMA
  • 60. PRINCIPLE : FBC BOILERS (CONTD.)  With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface.  The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized bed”. 58VANITA N THAKKAR BIT, VARNAMA
  • 61. PRINCIPLE : FBC BOILERS (CONTD.)  At higher velocities, bubbles disappear, and particles are blown out of the bed. Therefore, some amounts of particles have to be recirculated to maintain a stable system - "circulating fluidised bed".  Fluidization depends largely on :  particle size  air velocity. 59VANITA N THAKKAR BIT, VARNAMA
  • 62. PRINCIPLE : FBC BOILERS (CONTD.)  The mean solids velocity increases at a slower rate than does the gas velocity (Refer Fig 2.).  Mean Gas Velocity – Mean Solid Velocity = Slip velocity.  Maximum slip velocity is desirable for good heat transfer and intimate contact. 60VANITA N THAKKAR BIT, VARNAMA
  • 63. PRINCIPLE : FBC BOILERS (CONTD.)  Sand particles in a fluidised state heated to ignition temperatures of coal + coal injected continuously into the bed  coal will burn rapidly + bed attains a uniform temperature.  The F B combustion (FBC) takes place at about 840°C to 950°C – much below the ash fusion temperature  melting of ash and associated problems are avoided. 61VANITA N THAKKAR BIT, VARNAMA
  • 64. PRINCIPLE : FBC BOILERS (CONTD.)  Lower combustion temperature is achieved due to high coefficient of heat transfer by :  rapid mixing in the fluidised bed  effective extraction of heat from the bed through in- bed heat transfer tubes and walls of the bed.  Gas velocity is maintained between minimum fluidisation velocity and particle entrainment velocity to ensures stable operation of bed and to avoid particle entrainment in gas stream. 62VANITA N THAKKAR BIT, VARNAMA
  • 65. PRINCIPLE : FBC BOILERS (CONTD.)  Combustion process requires the three “T”s : Time, Temperature and Turbulence.  In FBC, turbulence is promoted by fluidisation. Improved mixing generates evenly distributed heat at lower temperature.  Residence time is many times greater than conventional grate firing. Thus an FBC system releases heat more efficiently at lower temperatures. 63VANITA N THAKKAR BIT, VARNAMA
  • 66. PRINCIPLE : FBC BOILERS (CONTD.)  Since limestone is used as particle bed, control of sulfur dioxide and nitrogen oxide emissions in the combustion chamber is achieved without any additional control equipment.  This is one of the major advantages over conventional boilers. 64VANITA N THAKKAR BIT, VARNAMA
  • 67. AFBC / BUBBLING BED FBC BOILER 65VANITA N THAKKAR BIT, VARNAMA
  • 68. CFBC BOILER 66VANITA N THAKKAR BIT, VARNAMA
  • 69. PFBC BOILER 67VANITA N THAKKAR BIT, VARNAMA
  • 70. SUPER-HEATERS  A super-heater is a device used to convert saturated steam or wet steam into dry steam used for power generation or processes.  There are three types of super-heaters namely: radiant, convection, and separately fired.  A super-heater can vary in size from a few tens of feet to several hundred feet (a few meters or some hundred meters). 68VANITA N THAKKAR BIT, VARNAMA
  • 71. TYPES OF SUPERHEATERS Based on mode of heat transfer :  A Radiant Super-heater is placed directly in the combustion chamber.  A Convective Super-heater is located in the path of the hot gases, before economizer.  A Separately-fired Super-heater, as its name implies, is totally separated from the boiler.  Combined Radiant-Convective Superheater (Pendant Superheater.) 69VANITA N THAKKAR BIT, VARNAMA
  • 72. TYPES OF SUPERHEATERS (contd.) Based on position in furnace with respect to water tubes :  Over-deck Superheater.  Inner-deck Superheater.  Inner tube Superheater.  Inner bank Superheater. 70VANITA N THAKKAR BIT, VARNAMA
  • 73. SUPERHEATER : IMAGES 71VANITA N THAKKAR BIT, VARNAMA
  • 74. SUPER-HEATERS (contd.) The Super-heater :  Increases capacity of the plant.  Eliminates corrosion of the steam turbine.  Reduces steam consumption of the steam turbine.  To resist metal temperatures above 600oC different types of materials are used for the tubes : M.S., seamless carbon steel tubes to chromium molybdenum seamless alloy steel tubes to Stainless Steel Tubes. 72VANITA N THAKKAR BIT, VARNAMA
  • 75. RE-HEATERS For reheating steam going to lower turbine stages to :  To improve efficiency of the plant.  To prevent steam in the lower stages from becoming wet – so, erosion and maintenance problems can be reduced. 73VANITA N THAKKAR BIT, VARNAMA
  • 76. RE-HEATERS (contd.) 74 VANITA N THAKKAR BIT, VARNAMA
  • 77. ECONOMIZERS Feed-water heaters in which heat from waste gases is recovered to raise the temperature of feed-water supplied to the boiler. Advantages :  Fuel economy.  Longer life of the boiler.  Increase in steaming capacity. 75VANITA N THAKKAR BIT, VARNAMA
  • 78. ECONOMIZERS (contd.) Types :  Based on construction :  Finned / Gilled Tube Economizers : C.I. Gilled Tube Economizers.  Plain Tube Coil Economizers.  Based on part of steam generation :  Steaming type Economizers (5-7% feed water is converted into steam; used in large steam power plants.).  Non-steaming type Economizers.  Based on location :  Independent Economizers  Integral Economizers. 76VANITA N THAKKAR BIT, VARNAMA
  • 79. AIR PRE-HEATERS  Device designed to heat air before another process (for example, combustion in a boiler) with the primary objective of increasing thermal efficiency of the process.  Air preheater recovers heat from boiler flue gases which increases thermal efficiency of the boiler by reducing useful heat lost in flue gases.  Flue gases are sent to the flue gas stack (or chimney) at a lower temperature, allowing simplified design of the ducting and the flue gas stack.  It also allows control over the temperature of gases leaving the stack (to meet emissions regulations, for example). Types : Recuperative : Tubular Type and Plate Type Regenerative : Storage Type77VANITA N THAKKAR BIT, VARNAMA
  • 80. TYPICAL PLANT LAYOUT SHOWING DIFFERENT ACCESSORIES 78VANITA N THAKKAR BIT, VARNAMA
  • 81. METHODS OF SUPERHEAT CONTROL  Dampers in the flue gas circuit : operated manually.  Instrumentation for monitoring and controlling Boiler superheat.  Combined Radiant-Convective Superheaters.  Desuperheating.  Pre-condensing the steam.  By-passing furnace gas around superheater.  Gas recirculation.  Tilting burners in furnace  Auxiliary burners.  Twin furnace. 79VANITA N THAKKAR BIT, VARNAMA
  • 82. CORROSION IN BOILERS CORROSION : Conversion of metal into oxides and salts, causing loss of material, which if not prevented, leads to failure of metal parts. In boilers, corrosion occurs in :  Inner surfaces (water / steam side) : due to –  Acidity of water (low pH)  Presence of O2 (enters through leakages – condenser, condenser pump, etc.), CO2 (released by heating of bicarbonates) and chlorides dissolved in feed water.  External surfaces (flue gases side) : due to coal ash. 80VANITA N THAKKAR BIT, VARNAMA
  • 83. PREVENTION OF CORROSION IN BOILERS INNER SURFACE CORROSION PREVENTION : 1. Addition of adequate amount of scavengers like hydrazine sodium sulphite – to remove dissolved oxygen for protection against pitting of inner tube surface. 2. Deaerator in water treatment plant to remove dissolved O2 and CO2. 3. Addition of ammonia for neutralizing amines in water and lowering pH value of water  Effect of CO2 gets neutralized. 4. Addition of alkali salts in water  neutralizing acids. 5. Addition of ammonium hydroxide in water  reacts with CO2 to form ammonium carbonate and water  Effect of CO2 gets neutralized. 6. Applying protective coating of amines on boiler tube inner surfaces. 81VANITA N THAKKAR BIT, VARNAMA
  • 84. PREVENTION OF CORROSION IN BOILERS (contd.) OUTER SURFACE CORROSION PREVENTION : 1. For Air Preheater – Flue gases should not be cooled below dew point of corrosion species by : 1. Passing some air around preheaters. 2. Recirculating air from preheater outlet to forced draught fan inlet. 2. Removing deposits of soot regularly from surfaces of economizer, superheater, evaporator tubes, air preheaters, reheaters, etc. 3. Heating feed water with steam from boiler in shell and tube heat exchanger to prevent low temperature corrosion by feed water. 82 VANITA N THAKKAR BIT, VARNAMA
  • 85. PREVENTION OF CORROSION IN BOILERS (contd.) OUTER SURFACE CORROSION PREVENTION : 4. Using low sulphur coal – to enable use of low temperature feed water, as chances of carrying sulphur trioxide with flue gases is less, leading to acid formation (feed water temperature has to be maintained above acid dew point temperature). 5. High temperature corrosion in superheaters, reheaters, etc. can be prevented by : 1. Using good quality coal. 2. Providing stainless steel tube shields. 3. Replacing damaged / old tubes with tubes containing high chromium content. 83VANITA N THAKKAR BIT, VARNAMA
  • 86. THANKS !!! VANITA THAKKAR ASSOCIATE PROFESSOR, MECHANICAL ENGINEERING DEPARTMENT, BABARIA INSTITUTE OF TECHNOLOGY, VARNAMA, VADODARA 84VANITA N THAKKAR BIT, VARNAMA

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