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Power Generation-10n.ppt
- 1. Power Plant SteamGenerators : Introduction By P M V Subbarao Professor Mechanical Engineering Department I I T Delhi A Two in One – Combustor and Heat Exchan
- 2. The Steam PowerPlant Executes a Thermodynamic Cycle using an assembly of CVs
- 3. Cause – EffectAnalysis of A Steam Generator • Combustion is a primary cause. • Steam Generation is an ultimate effect. • Heat transfer is a mediation. • Combustion caused the generation of heat in side furnace volume. • Heat generation caused the production of high temperature gases. • These high temperature gases caused the Radiation and convection heat transfer processes. • Heat Transfer processes carried the thermal energy to furnace wall & steam tubes. • Conduction through the tubes and walls caused the convection inside the tubes. • Convection Caused the generation of steam. • Few hundred years of ingenious trials lead to a Scientific technologty.
- 4. Historical Development inSteam Generators
- 5. 1720 Haycock :Shell-type boiler made of copper plates
- 6. Water Tube Boilers:The Steam Generators • As industry developed during 19th century, so the use of boilers for raising steam became widespread. • Disastrous explosions sometimes occurred. • Boilers of that period consisted of heated pressure vessels of large diameter. • These are subject to internal pressure which is tensile stresses in the walls of the enclosure. • The value of stress, known as ‘hoop stress’ is given by T D p f 2
- 7. Historical Development inSteam Generators
- 8. Steam generator versussteam boiler • Opposite the principle of the steam boilers, the water in the steam generators evaporates inside the tube winded up into serial connected tube coils. • The feed water is heated up to the evaporation temperature and then evaporated. • The intensity of the heat, the feed water flow and the size/length of the tube are adapted, so that the water is exactly fully evaporated at the exit of the tube. • This ensures a very small water and steam volume (content of the pressure vessel). • Thus there are no buffer in a steam generator, and is it temporary overloaded.
- 9. Steam generator versussteam boiler • The advantages using a steam generator compare to conventional steam boilers: • Easy to operate - normally no requirement for boiler authorization. • Rapid start-up and establishing full steam pressure Compact and easy to adapt in the existing machinery arrangement • Price attractive - especially at low steam rates.
- 10. Bird View ofPower Plant Steam Generator
- 11. DPNL SH Platen SHTR R H T R LTSH Economiser APH ESPID Fan drum Furnace BCW pump Bottom ash stack screen tubes Thermal Structure of A Subcritical SG
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- 18. The Steam Generator: The water tube boiler • As you can see, the Water Tube Boiler (below) looks very complicated. • Thousands of tubes are placed in strategic location to optimize the exchange of energy from the heat to the water in the tubes. • These types of boilers are most common because of their ability to deliver large quantities of steam. • The large tube like structure at the top of the boiler is called the steam drum. • The hundreds of tube start and eventually end up at the steam drum.
- 19. Steam Generator Theory •Within the boiler, fuel and air are force into the furnace by the burner. • There, it burns to produce heat. • From there, the heat (flue gases) travel throughout the boiler. • The water absorbs the heat, and eventually absorb enough to change into a gaseous state - steam. • To the left is the basic theoretical design of a modern boiler. • Boiler makers have developed various designs to squeeze the most energy out of fuel and to maximized its transfer to the water.
- 20. Steam Generator Theory •Water enters the boiler, preheated, at the top. • The hot water naturally circulates through the tubes down to the lower area where it is hot. • The water heats up and flows back to the steam drum where the steam collects. • Not all the water gets turn to steam, so the process starts again. • Water keeps on circulating until it becomes steam. • Meanwhile, the control system is taking the temperature of the steam drum, along with numerous other readings, to determine if it should keep the burner burning, or shut it down.
- 21. Steam Generator Theory: Water Side • As well, sensors control the amount of water entering the boiler, this water is know as feedwater. • Feedwater is not your regular drinking water. • It is treated with chemicals to neutralize various minerals in the water, which untreated, would cling to the tubes clogging or worst, rusting them. • This would make the boiler expensive to operate because it would not be very efficient.
- 22. Steam Generator Theory: Fire Side • On the fire side of the boiler, carbon deposit resulting from improper combustion or impurities in the fuel can accumulate on the outer surface of the water tube. • This creates an insulation which quickly decrease the energy transfer from the heat to the water. • To remedy this problem the engineer will carry out soot blowing. At a specified time the engineer uses a long tool and insert it into the fire side of the boiler.. • This device, which looks like a lance, has a tip at the end which "blows" steam. • This blowing action of the steam "scrubs" the outside of the water tubes, cleaning the carbon build up.
- 23. Scaling of SteamGenerators • This blowing action of the steam "scrubs" the outside of the water tubes, cleaning the carbon build up. • Water tube boilers can have pressures from 7 bar to as high as 350 bar. • The steam temperature's can vary between saturated steam, 100 degrees Celsius steam with particle of water, or be as high as 600 - 650 degrees Celsius, know as superheated steam or dry steam • The performance of boiler is generally referred to as tons of steam produced in one hour. • In water tube boilers that could be as low as 1.5 t/hr to as high as 2500 t/hr.
- 24. Classification of SteamGenerators
- 25. Role of SGin Rankine Cycle Perform Using Natural resources of energy …….
- 26. Economics of FlowSteam generation Subcritical Flow Boiling Pump Exit
- 27. Natural Circulation Boiler HotWater Dry Steam to Super heaters Pump Exit
- 28. Forced Circulation Boiler HotWater Dry Steam to Super heaters Recirculation Pump Pump Exit
- 29. Once Through Boiler HotWater Dry Steam to Super heaters Pump
- 30. Once Through SubcriticalSteam Generator Once-through tangential fired Max. continuous rating: 520 kg/s Max.Steam temperature outlet: 540°C Live steam pressure outlet: > 18.3 MPa
- 31. Major Components ofCoal Fired Steam Generator Offline Online ~600mm Crushed to small pieces of about 20 mm diameter
- 32. Design Steps forSteam Generators • Thermodynamic Design – Air/fuel ratio – Specific Size/Output. – Efficiency • Thermodynamic Parameters. • Heats Transfer based Design – Surface area of various parts. – Materials used for various parts. – Geometry of various parts. • Detailed Temperature distribution. • Constructional details.
- 33. Design Steps forSteam Generators • Hydraulic Design. – Pressure distribution/drop in various parts – Velocity distribution. • Hydraulic parameters. • Design Optimization. • Mechanical Design.
- 34. Steam Generator Specifications •Steam – Flow rate , Pressure & Temperature • Feed Water – Economizer inlet temperature • Fuel – Type, Ultimate Analysis, Heating value & Physical Properties • Sorbent • Emissions – SO2 , Nox & Particulate
- 35. Steam Generator Specifications •Pressure Drop • Solid Waste – Ash Deposit system • Auxiliaries • Site • Personnel • Evaluation Criteria • Special Parameters – Heat Recovery SG • Flue gas amount composition • Gas temperature at inlet • Back pressure of Turbine Pinch point.
- 36. Steam Generator DesignMethodology • Preliminary Design – Useful for estimation of budget price • Detailed proposal Design – Essential for making a detailed competitive bid. • Final Design – Used in preparation of manufacturing drawings
- 37. Preliminary Design • PrimitiveFirst Law Analysis of various controls volumes. • INPUT: Steam conditions and Fuel Analysis • Database: Design data of previous plants. • Procedure: Interpolation or Extrapolation of past data. – Overall size – Weight – Cost of the plant • Commercial Software Packages available – CFBCAD for Fluidized Bed Boilers.
- 38. Detailed Proposal Design •Detailed study and Review of parameters of SG w.r.t. – Steam – Fuel – Environment • Thermodynamic Design • Heats Transfer based Design • Hydraulic Design. • Design Optimization. • Mechanical Design.
- 39. Combustion Safeguards andControls • Furnace Explosion : The ignition and almost instantaneous combustion of highly inflammable gas or vapour or dust accumulated in furnace. • Conditions leading to Furnace Explosion: – Accumulation of unburned fuel. – Air and fuel in an explosive mixture. – Source of ignition. -- hot furnace walls, improper ignition timing, faulty torch etc. • Types of Furnace Explosions: – Gas explosions and coal dust explosions. – Primary and Secondary. • Reasons for increased number of furnace explosions: – Large Boilers -- higher burner capacity – Compact furnaces. – Low fire box temperatures in water tube boilers. – New fuels.
- 40. Causes of FireExplosions • Flame failure due to liquids or inert gases entering the boiler fuel system. • Insufficient purge before lighting the first burner. • Human error. • Faulty automatic fuel regulating controls. • Fuel shutoff valve leakage. • Unbalanced fuel/air ratio. • Faulty fuel supply systems. • Loss of furnace draft. • Faulty pilot igniters.
- 41. Furnace Controls • ManualControl • Remote Manual Sequence Control • Automatic Sequence Control System. • Degree of Automation: – Manual – Supervised manual – Automatic nonrecycling – Automatic recycling.
- 42. Burner Flame SafeguardSystem • An arrangement of flame detector, interlocks and relays – to sense the presence of a proper flame – cause fuel to be shut of to the furnace during hazardous conditions. • Prevent Boiler and Furnace explosions.