Steam Generators - SNIST (M.Tech)
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This document discusses steam generators and feedwater heaters used in thermal and nuclear power plants. It provides definitions of boilers and steam generators, describing their main components like drums, superheaters, and economizers. It compares firetube and watertube boilers, listing advantages and disadvantages of each. The document also describes types of feedwater heaters like open and closed, and their purposes in preheating feedwater to improve thermodynamic efficiency.
Steam Generators - SNIST (M.Tech)
- 1. Dr. S. VIJAYA BHASKAR PROFESSORINMECHANICALENGINEERING SREENIDHIINSTITUTEOF SCIENCE& TECHNNOLOGY GHATKESAR,HYDERABAD,TS, INDIA
- 2. Steam Generators - Types, Accessories. - Feed water heaters M.Tech. (THERMAL ENGINEERING) I Year – I Semester THERMAL AND NUCLEAR POWER PLANTS CODE: 6M111
- 3. ‘A closed vessel in which steam is produced from water by combustion of fuel.’ A boiler is defined as "a closed vessel in which water or other liquid is heated, steam or vapor is generated under pressure for external use to do mechanical work.“
- 4. Water is pumped into the boiler at operating pressure Heat of flue gases vaporises water to form steam Steam formed is passed into steam space above the water space This steam is always wet. Superheated steam is obtained by passing wet steam through super-heater, where it is dried and then superheated To increase efficiency, water is passed through an economiser where its temp. is increased and then it is pumped into the boiler. This way less heat is required to heat the steam.
- 5. ‘A combination of apparatus for producing, furnishing or recovering heat together with the apparatus for transferring the heat so made available to the fluid being heated and vapourised.’ Components of a steam generator ◦ Boiler drum ◦ Superheater ◦ Economiser ◦ Air Preheater
- 6. Controlled release of heat in the fuel. Efficient transfer of heat to the feed water to produce steam at desired Pressure (P), Temperature (T) and quality. Steam to be supplied from boiler at constant Pressure by maintaining the steam generation rate and steam flow rate equal. Water must be contained safely.
- 7. 1. Operating Pressure 2. Steam Generating Rate 3. Quality of steam required 4. Availability of floor space 5. Fuel to be used 6. Nature of the load on the boiler 7. Initial cost 8. Operating and maintenance cost 9. Availability of water 10. Accessibility for repair and inspection
- 8. 1. Capable of producing maximum amount of steam with minimum fuel consumption. 2. It should occupy less space and be light in weight. 3. Capable of quick starting and should rapidly meet the fluctuation in load. 4. Safe in working. 5. Economical and should require very little attention during operation. 6. All parts should be easily accessible for inspection and repairs. 7. Components should be transported without difficulty.
- 9. 8. Installation should be simple. 9. Tubes should not accumulate soot or water deposits and should be sufficiently strong to allow for wear and corrosion. 10. Water and gas circuits should be such as to allow minimum fluid velocity for low frictional losses. 11. Should have as less joints as possible to avoid leaks, which may occur due to expansion and contraction. 12. Velocities should be high for high heat transfer rates with minimum pressure drop through the system. 13. Should confirm to safety regulations laid down in Boiler Act.
- 10. HRSH->Heat Recovery Steam Generator
- 11. 1. Position of flue gases and water Fire tube, water tube 2. Axis of shell Horizontal, vertical, inclined 3. Location of furnace Externally fired, internally fired 4. Method of circulation Natural, Forced
- 12. 5. Mobility Stationary, Portable 6. Usage Packaged, Unpackaged 7. Pressure High, Low 8. Tubes Single, Multi
- 13. In the fire tube boiler the hot gases are inside the tubes & the water surrounds in the tube. Ex.
- 14. In the water tube boiler the water is inside the tube & the hot gases are surround them.
- 17. Furnace is located inside the Boiler Drum or shell. Hot flue gases are fed through the tubes. Tubes are surrounded by water. Boiler shell contains water and steam under pressure. Tube contains grate. Air for combustion of fuel, flowing beneath the grate moves upwards through the fire bars. Superheater tubes placed at exit of the flue gases. Used generally for up to 10000 kg/hr and low pressures upto 20 bar
- 18. Low initial cost Large water content provides safety in operation, during failure of feed water supply Suitable for fluctuating loads Low Space occupied
- 19. Rate of evaporation is low and reaches operating pressures slowly Suitable only for low capacities. Shell size 2.4m, shell thickness 3 cm, stress considerations limit generation pressure to 20kg/cm2 Lower efficiency Explosion is very dangerous due to large water content Transportation is difficult due to large shell size Useless for steam power plants due to slow rate of steam generation Difficult design Less accessible to repairs
- 22. Furnace is outside the drum Small parallel tubes contain water connected to drum with the header Gases pass outside tubes containing water Flow of water is downward Steam returns to drum through uptake header
- 24. High pressures and capacity Operating temps and pressures reached faster due to smaller water to steam content Hot gases travel at right angles to water flow so heating surfaces are effective Combustion space is larger so complete combustion possible with better efficiency Thermal stresses low as all parts are at uniform temp due to quick circulation Less serious damage compared to others due to lesser water content. Furnace area can be altered Higher Efficiency Suitable for power plant Parts easily accessible for cleaning Easily transported Simple design
- 25. High initial cost Impure and dirty water not suitable as a small deposit can cause explosion Failure in feed water supply can cause boiler overheat
- 28. Shell Furnace Grate Setting Foaming Scale Blowing Off Lagging (Insulation outside boiler shell or steam piping) Refractory (Fire proof in side combustion chamber by fire brick) Water flow path Steam flow path Gas flow path Water space Steam space Water level Fittings/mountings Accessories
- 30. An economizer is a heat exchanger, used for heating the feed water before it enters the boiler. The economizer recovers some of waste heat of hot flue gases going to chimney. It helps in improving the boiler efficiency. It is placed in the path of flue gases at the rear end of the boiler just before air pre-heater. ECONOMIZER
- 33. A steam injector lifts and forces the feed water into the boiler. It is usually used for vertical and locomotive boilers and can be accommodated in small space. It is less costly. It does not have any moving parts thus operation is salient. It is compact Can achieve high thermal efficiency Easy of operation
- 36. The function of an air pre-heater is similar to that of an economizer. It recovers some portion of the waste heat of hot flue gases going to chimney, and transfers same to the fresh air before it enters the combustion chamber. Due to preheating of air, the furnace temperature increases. It results in rapid combustion of fuel with less soot, smoke and ash. The high furnace temperature can permit low grade fuel with less atmospheric pollution. The air pre-heater is placed between economizer and chimney.
- 41. It is used to feed the water at a high pressure against the high pressure of steam already existing inside the boiler. Reciprocating and Rotary pumps
- 43. STEAM SEPARATOR
- 45. A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. In a steam power plant,feed water heaters allow the feedwater to be brought up to the saturation temperatur very gradually improves the thermodynamic efficiency of the reducing plant operating costs and also helps to avoid thermal shock to the boiler metal.
- 47. Open FeedWater Heater TYPES OF FEEDWATER HEATERS Closed FeedWater Heater An open heat exchanger is one in which extracted steam is allowed to mix with the feed water. This kind of heater will normally require a feed pump at both the feed inlet and outlet since the pressure in the heater is between the boiler pressure and the condenser pressure. A deaerator is a special case of the open feedwater heater which is specifically designed to remove non-condensable gases from the feedwater. Closed feedwater heaters are typically shell and tube heat exchangers where the feedwater passes throughout the tubes and is heated by turbine extraction steam. These do not require separate pumps before and after the heater to boost the feedwater to the pressure of the extracted steam as with an open heater. Many power plants incorporate a number of feedwater heaters and may use both open and closed components. Feedwater heaters are used in both fossil- and nuclear-fueled power plants.
- 48. OPEN FEEDWATER HEATERS An open heat exchanger is one in which extracted steam is allowed to mix with the feedwater. This kind of heater will normally require a feed pump at both the feed inlet and outlet since the pressure in the heater is between the boiler pressure and the condenser pressure. A deaerator is a special case of the open feedwater heater which is specifically designed to remove non-condensable gases from the feedwater.
- 50. CLOSED FEEDWATER HEATERS Closed feedwater heaters are typically shell and tube heat exchangers where the feedwater passes throughout the tubes and is heated by turbine extraction steam. These do not require separate pumps before and after the heater to boost the feedwater to the pressure of the extracted steam as with an open heater. Many power plants incorporate a number of feedwater heaters and may use both open and closed components. Feedwater heaters are used in both fossil- and nuclear-fueled power plants.