Boilerintroduction 130518020407-phpapp01

• 1. BURNER WATER SOURCE SOFTENERS CHEMICAL FEED FUEL BLOW DOWN SEPARATOR VENT STACK DEAERATOR PUMPS BOILER ECO- NOMI- ZER VENTEXHAUST GAS STEAM TO PROCESS

2. SOFTENERS By- Mukesh Jha Sr.Engineer -Projects, a2z Powercom Pvt.Ltd. 3. Boiler- A Boiler means a pressure vessel in which steam is generated for use external to itself by application of heat which is wholly or partly under pressure when steam is shut off but does not include a pressure vessel (1) With Capacity less than 25 ltrs (such capacity being measured from the feed check valve to the main steam stop valve); (2) With less than 1 kilogram per centimeter square design gauge pressure & working gauge pressure; or (3) In which water is heated below one hundred degree centigrade . 4. Boiler component means Steam piping , Feed water piping, Economizer ,Super heater, any mounting or other fitting and any other external or internal part of a Boiler which is subjected to pressure exceeding one kilogram per centimeter square gauge. 5. Steam Pipe "means any pipe through which steam passes if- (1)The pressure at which the steam passes through such pipe exceeds 3.5kg/cm^2 above atmospheric pressure, or (2)Such pipe exceeds 254 mm in internal diameter and pressure of steam exceeds 1kg/cm^2.above the atmospheric pressure. and includes in either case any connected fitting of a steam pipe. 6. At atmospheric pressure water volume increases 1,600 times BURNER WATER SOURCE SOFTENERS CHEMICAL FEED FUEL BLOW DOWN SEPARATOR VENT STACK DEAERATOR PUMPS BOILER ECO- NOMI- ZER VENTEXHAUST GAS STEAM TO PROCESS Figure: Schematic overview of a boiler room 7. Boiler Systems Flue gas system Water treatment system Feed water system Steam System Blow down system Fuel supply system Air Supply system 8. Fuels used in Boiler S.No Solid Liquid Gaseous AgroWaste 1 Coal HSD NGas Baggase 2 Lignite LDO Bio Gas Pith 3 Charcoal Fur.Oil Rice Husk 4 LSHS Paddy Straw 5 Coconut shell 6 Groundnutshell MSW/RDF 9. Types of Boilers 1. Fire Tube Boiler 2. Water Tube Boiler 3. Packaged Boiler 4. Stoker Fired Boiler 5. Pulverized Fuel Boiler 6. Waste Heat Boiler 7. Fluidized Bed (FBC) Boiler 10. Type of Boilers (Light Rail Transit Association) 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 11. Type of Boilers 2. Water Tube Boiler (Your Dictionary.com) 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 12. Type of Boilers (BIB Cochran, 2003) 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 13. Type of Boilers 4. Stoke Fired Boilers a) Spreader stokers Uses both suspension and grate burning Coal fed continuously over burning coal bed Coal fines burn in suspension and larger coal pieces burn on grate Good flexibility to meet changing load requirements Preferred over other type of stokers in industrial application 14. Type of Boilers 4. Stoke Fired Boilers b) Chain-grate or traveling- grate stoker (University of Missouri, 2004) Uses both suspension and grate burning Coal fed continuously over burning coal bed Coal fines burn in suspension and larger coal pieces burn on grate Good flexibility to meet changing load requirements Preferred over other type of stokers in industrial application 15. Type of Boilers Tangential firing 5. Pulverized Fuel Boiler Pulverized coal powder blown with combustion air into boiler through burner nozzles Combustion temperature at 1300 -1700 C Benefits: varying coal quality coal, quick response to load changes and high pre-heat air temperatures Coal is pulverized to a fine powder, so that less than 2% is +300 microns, and 70-75% is below 75 microns. Coal is blown with part of the combustion air into the boiler plant through a series of burner nozzles. 16. Advantages Its ability to burn all ranks of coal from anthracitic to lignitic, and it permits combination firing (i.e., can use coal, oil and gas in same burner). Because of these advantages, there is widespread use of pulverized coal furnaces. Disadvantages High power demand for pulverizing Requires more maintenance, flyash erosion and pollution complicate unit operation Pulverized Fuel Boiler (Contd..) 17. Type of Boilers Agriculture and Agri-Food Canada, 2001 6. Waste Heat Boiler Used when waste heat available at medium/high temp Auxiliary fuel burners used if steam demand is more than the waste heat can generate Used in heat recovery from exhaust gases from gas turbines and diesel engines 18. 7.Fluidized Bed (FBC) Boiler An Overview- Fluidized bed combustion has emerged as a viable alternative and has significant advantages over conventional firing system and offers multiple benefits compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse & other agricultural wastes. The fluidized bed boilers have a wide capacity range. 19. Mechanism of Fluidised Bed Combustion 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 fluidized. 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. 20. 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 the particle size and the air velocity. If sand particles in a fluidized state is heated to the ignition temperatures of coal, and coal is injected continuously into the bed, the coal will burn rapidly and bed attains a uniform temperature. The fluidized bed combustion (FBC) takes place at about 840OC to 950OC. 21. Since this temperature is much below the ash fusion temperature, melting of ash and associated problems are avoided. The lower combustion temperature is achieved because of high coefficient of heat transfer due to rapid mixing in the fluidized bed and effective extraction of heat from the bed through in-bed heat transfer tubes and walls of the bed. The gas velocity is maintained between minimum fluidisation velocity and particle entrainment velocity. This ensures stable operation of the bed and avoids particle entrainment in the gas stream. Combustion process requires the three Ts that is 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. 22. Fixing, bubbling and fast fluidized beds As the velocity of a gas flowing through a bed of particles increases, a value is reaches when the bed fluidises and bubbles form as in a boiling liquid. At higher velocities the bubbles disappear; and the solids are rapidly blown out of the bed and must be recycled to maintain a stable system. principle of fluidisation 23. 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. Types of Fluidised Bed Combustion Boilers There are three basic types of fluidised bed combustion boilers: 1. Atmospheric classic Fluidised Bed Combustion System (AFBC) 2. Pressurised Fluidised Bed Combustion System (PFBC). 3. Circulating (fast) Fluidised Bed Combustion system(CFBC) 24. AFBC / Bubbling Bed In AFBC, coal is crushed to a size of 1 10 mm depending on the rank of coal, type of fuel feed and fed into the combustion chamber. The atmospheric air, which acts as both the fluidization air and combustion air, is delivered at a pressure and flows through the bed after being preheated by the exhaust flue gases. The velocity of fluidising air is in the range of 1.2 to 3.7 m /sec. The rate at which air is blown through the bed determines the amount of fuel that can be reacted. Almost all AFBC/ bubbling bed boilers use in-bed evaporator tubes in the bed of limestone, sand and fuel for extracting the heat from the bed to maintain the bed temperature. The bed depth is usually 0.9 m to 1.5 m deep and the pressure drop averages about 1 inch of water per inch of bed depth. Very little material leaves the bubbling bed only about 2 to 4 kg of solids are recycled per ton of fuel burned. 25. Bubbling Bed Boilers In the bubbling bed type boiler, a layer of solid particles (mostly limestone, sand, ash and calcium sulfate) is contained on a grid near the bottom of the boiler. This layer is maintained in a turbulent state as low velocity air is forced into the bed from a plenum chamber beneath the grid. Fuel is added to this bed and combustion takes place. Normally, raw fuel in the bed does not exceed 2% of the total bed inventory. Velocity of the combustion air is kept at a minimum, yet high enough to maintain turbulence in the bed. Velocity is not high enough to carry significant quantities of solid particles out of the furnace. 26. This turbulent mixing of air and fuel results in a residence time of up to five seconds. The combination of turbulent mixing and residence time permits bubbling bed boilers to operate at a furnace temperature below 1650F. At this temperature, the presence of limestone mixed with fuel in the furnace achieves greater than 90% sulfur removal. Boiler efficiency is the percentage of total energy in the fuel that is used to produce steam. Combustion efficiency is the percentage of complete combustion of carbon in the fuel. Incomplete combustion results in the formation of carbon monoxide (CO) plus unburned carbon in the solid particles leaving the furnace. In a typical bubbling bed fluidized boiler, combustion efficiency can be as high as 92%. This is a good figure, but is lower than that achieved by pulverized coal or cyclone-fired boilers. In addition, some fuels that are very low in volatile matter cannot be completely burned within the available residence time in bubbling bed-type boilers. 27. Features of bubbling bed boiler Fluidised bed boiler can operate at near atmospheric or elevated pressure and have these essential features: Distribution plate through which air is blown for fluidizing. Immersed steam-raising or water heating tubes which extract heat directly from the bed. Tubes above the bed which extract heat from hot combustion gas before it enters the flue duct. 28. Bubbling Bed Boiler-1 29. Bubbling Bed Boiler-2 30. 2. Pressurised Fluidised Bed Combustion System (PFBC). Pressurised Fluidised Bed Combustion (PFBC) is a variation of fluid bed technology that is meant for large-scale coal burning applications. In PFBC, the bed vessel is operated at pressure up to 16 ata ( 16 kg/cm2). The off-gas from the fluidized bed combustor drives the gas turbine. The steam turbine is driven by steam raised in tubes immersed in the fluidized bed. The condensate from the steam turbine is pre-heated using waste heat from gas turbine exhaust and is then taken as feed water for steam generation. The PFBC system can be used for cogeneration or combined cycle power generation. By combining the gas and steam turbines in this way, electricity is generated more efficiently than in conventional system. The overall conversion efficiency is higher by 5% to 8%. . At elevated pressure, the potential reduction in boiler size is considerable due to increased amount of combustion in pressurized mode and high heat flux through in-bed tubes. 31. PFBC Boiler for Cogeneration 32. 3. Circulating (fast) Fluidised Bed Combustion system(CFBC) The need to improve combustion efficiency (which also increases overall boiler efficiency and reduces operating costs) and the desire to burn a much wider range of fuels has led to the development and application of the CFB boiler. Through the years, boiler suppliers have been increasing the size of these high-efficiency steam generators. This CFBC technology utilizes the fluidized bed principle in which crushed (6 12 mm size) fuel and limestone are injected into the furnace or combustor. The particles are suspended in a stream of upwardly flowing air (60-70% of the total air), which enters the bottom of the furnace through air distribution nozzles. The fluidising velocity in circulating beds ranges from 3.7 to 9 m/sec. The balance of combustion air is admitted above the bottom of the furnace as secondary air. 33. The combustion takes place at 840-900oC, and the fine particles (200C then recover waste heat Energy Efficiency Opportunities 2. Feed Water Preheating Economizers Potential to recover heat from 200 300 oC flue gases leaving a modern 3-pass shell boiler 3. Combustion Air Preheating If combustion air raised by 20C = 1% improve thermal efficiency 75. 4. Minimize Incomplete Combustion Symptoms: Smoke, high CO levels in exit flue gas Causes: Air shortage, fuel surplus, poor fuel distribution Poor mixing of fuel and air Oil-fired boiler: Improper viscosity, worn tops, cabonization on dips, deterioration of diffusers or spinner plates Coal-fired boiler: non-uniform coal size Energy Efficiency Opportunities 76. 84 Energy Efficiency Opportunities 5. Excess Air Control Excess air required for complete combustion Optimum excess air levels varies 1% excess air reduction = 0.6% efficiency rise Portable or continuous oxygen analyzers Fuel Kg air req./kg fuel %CO2 in flue gas in practice Solid Fuels Bagasse Coal (bituminous) Lignite Paddy Husk Wood 3.3 10.7 8.5 4.5 5.7 10-12 10-13 9 -13 14-15 11.13 Liquid Fuels Furnace Oil LSHS 13.8 14.1 9-14 9-14 77. Energy Efficiency Opportunities 7. Automatic Blow Down Control 6. Radiation and Convection Heat Loss Minimization Fixed heat loss from boiler shell, regardless of boiler output Repairing insulation can reduce loss Sense and respond to boiler water conductivity and pH 78. Energy Efficiency Opportunities 9. Reduced Boiler Steam Pressure 8. Scaling and Soot Loss Reduction Every 22oC increase in stack temperature = 1% efficiency loss 3 mm of soot = 2.5% fuel increase Lower steam pressure = lower saturated steam temperature = lower flue gas temperature Steam generation pressure dictated by process 79. Energy Efficiency Opportunities 11. Control Boiler Loading 10. Variable Speed Control for Fans, Blowers and Pumps Suited for fans, blowers, pumps Should be considered if boiler loads are variable Maximum boiler efficiency: 65-85% of rated load Significant efficiency loss: < 25% of rated load 80. Energy Efficiency Opportunities 13. Boiler Replacement 12. Proper Boiler Scheduling Optimum efficiency: 65-85% of full load Few boilers at high loads is more efficient than large number at low loads Financially attractive if existing boiler is Old and inefficient Not capable of firing cheaper substitution fuel Over or under-sized for present requirements Not designed for ideal loading conditions 81. Boilers THANK YOU FOR YOUR ATTENTION