1. By- Mukesh Jha Sr.Engineer -Projects,a2z Powercom Pvt.Ltd.

2. Boiler-As per THE INDIAN BOILERS(AMENDMENT ) ACT2007A Boiler means a pressure vessel in which steam is generatedfor use external to itself by application of heat which is whollyor partly under pressure when steam is shut off but does notinclude a pressure vessel(1) With Capacity less than 25 ltrs (such capacity beingmeasured from the feed check valve to the main steam stopvalve);(2) With less than 1 kilogram per centimeter square designgauge pressure & working gauge pressure; or(3) In which water is heated below one hundred degreecentigrade . 3. Boiler component means Steam piping , Feed waterpiping, Economizer ,Super heater, any mounting or other fittingand any other external or internal part of a Boiler which issubjected to pressure exceeding one kilogram per centimetersquare gauge. 4. Steam Pipe "means any pipe through which steam passes if-(1)The pressure at which the steam passes through such pipeexceeds 3.5kg/cm^2 above atmospheric pressure, or(2)Such pipe exceeds 254 mm in internal diameter and pressureof steam exceeds 1kg/cm^2.above the atmospheric pressure.and includes in either case any connected fitting of asteam pipe. 5. At atmospheric pressure water volume increases 1,600 times STEAM TO EXHAUST GAS VENT PROCESS STACKDEAERATORPUMPS ECO- NOMI-ZER VENT BOILERBURNERWATERSOURCE BLOW DOWN SEPARATORFUELCHEMICAL FEED SOFTENERSFigure: Schematic overview of a boiler room 6. Boiler Systems Water treatment system Feed water system Steam System Blow down system Fuel supply system Air Supply system Flue gas system 7. Fuels used in Boiler S.NoSolidLiquid Gaseous AgroWaste 1Coal HSD NGasBaggase 2Lignite LDOBio Gas Pith 3Charcoal Fur.Oil Rice Husk 4 LSHSPaddy Straw 5 Coconut shell 6 Groundnutshell MSW/RDF 8. Types of Boilers1. Fire Tube Boiler2. Water Tube Boiler3. Packaged Boiler4. Stoker Fired Boiler5. Pulverized Fuel Boiler6. Waste Heat Boiler7. Fluidized Bed (FBC) Boiler 9. Type of Boilers Relatively small steam capacities (12,000 kg/hour)1. Fire Tube Boiler Low to medium steam pressures (18 kg/cm2) Operates with oil, gas or solid fuels(Light Rail Transit Association) 10. Type of Boilers2. 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 (Your Dictionary.com) 11. Type of Boilers3. Packaged BoilerTo Chimney Comes in complete package Features High heat transfer Faster evaporation Good convectiveheat transfer Good combustionefficiencyOil Burner High thermalefficiency(BIB Cochran, 2003) Classified based on number of passes 12. Type of Boilers4. Stoke Fired Boilersa) Spreader stokers Uses both suspension andgrate burning Coal fed continuously overburning coal bed Coal fines burn in suspensionand larger coal pieces burn ongrate Good flexibility to meetchanging load requirements Preferred over other type ofstokers in industrialapplication 13. Type of Boilers Uses both suspension and4. Stoke Fired Boilers grate burningb) Chain-grate or traveling- Coal fed continuously overgrate stoker 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(University of Missouri, 2004) application 14. Type of Boilers 5. Pulverized Fuel BoilerCoal is pulverized to a fine powder, so that less than 2% is +300microns, and 70-75% is below 75 microns.Coal is blown with part of the combustion air into the boiler plantthrough a series of burner nozzles. Pulverized coal powder blown withcombustion air into boiler throughburner nozzles Combustion temperature at 1300 -1700C Benefits: varying coal quality coal,quick response to load changes andhigh pre-heat air temperatures Tangential firing 15. Pulverized Fuel Boiler (Contd..)Advantages Its ability to burn all ranks of coal from anthracitic tolignitic, and it permits combination firing (i.e., canuse coal, oil and gas in same burner). Because ofthese advantages, there is widespread use ofpulverized coal furnaces.Disadvantages High power demand for pulverizing Requires more maintenance, flyash erosion andpollution complicate unit operation 16. Type of Boilers6. Waste Heat Boiler Used when waste heatavailable at medium/hightemp Auxiliary fuel burnersused if steam demand ismore than the waste heatcan generate Used in heat recoveryfrom exhaust gases fromgas turbines and dieselAgriculture and Agri-Food enginesCanada, 2001 17. 7.Fluidized Bed (FBC) BoilerAn Overview-Fluidized bed combustion has emerged as a viablealternative and has significant advantages overconventional firing system and offers multiple benefits compact boiler design, fuel flexibility, higher combustionefficiency and reduced emission of noxious pollutantssuch as SOx and NOx. The fuels burnt in these boilersinclude coal, washery rejects, rice husk, bagasse & otheragricultural wastes. The fluidized bed boilers have a widecapacity range. 18. Mechanism of Fluidised Bed CombustionWhen an evenly distributed air or gas is passed upwardthrough a finely divided bed of solid particles such as sandsupported on a fine mesh, the particles are undisturbed at lowvelocity. As air velocity is gradually increased, a stage isreached when the individual particles are suspended in the airstream 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. 19. At higher velocities, bubbles disappear, and particles areblown out of the bed. Therefore, some amounts of particleshave 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 ignitiontemperatures of coal, and coal is injected continuously intothe bed, the coal will burn rapidly and bed attains a uniformtemperature. The fluidized bed combustion (FBC) takesplace at about 840OC to 950OC. 20. Since this temperature is much below the ash fusiontemperature, melting of ash and associated problems are avoided.The lower combustion temperature is achieved because of highcoefficient of heat transfer due to rapid mixing in the fluidized bedand effective extraction of heat from the bed through in-bed heattransfer tubes and walls of the bed. The gas velocity is maintainedbetween minimum fluidisation velocity and particle entrainmentvelocity. This ensures stable operation of the bed and avoids particleentrainment in the gas stream.Combustion process requires the three Ts that is Time, Temperature andTurbulence. In FBC, turbulence is promoted by fluidisation. Improvedmixing generates evenly distributed heat at lower temperature. Residencetime is many times greater than conventional gratefiring. Thus an FBC system releases heat more efficiently at lowertemperatures. 21. Fixing, bubblingand fast fluidizedbedsAs the velocity of agas flowing througha bed of particlesincreases, a value isreaches when thebed fluidises andbubbles form as in aboiling liquid. Athigher velocities thebubbles disappear;and the solids arerapidly blown out ofthe bed and must berecycled to maintainprinciple of fluidisationa stable system. 22. Since limestone is used as particle bed, control of sulfur dioxide and nitrogenoxide emissions in the combustion chamber is achieved without any additionalcontrol equipment. This is one of the major advantages over conventionalboilers.Types of Fluidised Bed Combustion BoilersThere 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) 23. AFBC / Bubbling BedIn AFBC, coal is crushed to a size of 1 10 mm depending on the rank ofcoal, type of fuel feed and fed into the combustion chamber. Theatmospheric air, which acts as both the fluidization air and combustionair, is delivered at a pressure and flows through the bed after beingpreheated by the exhaust flue gases. The velocity of fluidising air is in therange of 1.2 to 3.7 m /sec. The rate at which air is blown through the beddetermines the amount of fuel that can be reacted.Almost all AFBC/ bubbling bed boilers use in-bed evaporator tubesin the bed of limestone, sand and fuel for extracting the heat fromthe bed to maintain the bed temperature. The bed depth is usually 0.9m to 1.5 m deep and the pressure drop averages about 1 inch of water perinch of bed depth. Very little material leaves the bubbling bed only about2 to 4 kg of solids are recycled per ton of fuel burned. 24. Bubbling Bed BoilersIn the bubbling bed type boiler, a layer of solid particles(mostly limestone, sand, ash and calcium sulfate) iscontained on a grid near the bottom of the boiler. This layeris maintained in a turbulent state as low velocity air is forcedinto the bed from a plenum chamber beneath the grid. Fuelis added to this bed and combustion takes place. Normally,raw fuel in the bed does not exceed 2% of the total bedinventory. Velocity of the combustion air is kept at aminimum, yet high enough to maintain turbulence in thebed. Velocity is not high enough to carry significantquantities of solid particles out of the furnace. 25. This turbulent mixing of air and fuel results in a residence time of up to fiveseconds. The combination of turbulent mixing and residence time permitsbubbling bed boilers to operate at a furnace temperature below 1650F. Atthis temperature, the presence of limestone mixed with fuel in the furnaceachieves greater than 90% sulfur removal. Boiler efficiency is the percentageof total energy in the fuel that is used to produce steam. Combustionefficiency 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 typicalbubbling bed fluidized boiler, combustion efficiency can be as high as92%. This is a good figure, but is lower than that achieved bypulverized coal or cyclone-fired boilers. In addition, some fuels that arevery low in volatile matter cannot be completely burned within theavailable residence time in bubbling bed-type boilers. 26. Features of bubbling bed boilerFluidised bed boiler can operate at near atmospheric or elevatedpressure and have these essential features: Distribution plate through which air is blown for fluidizing. Immersed steam-raising or water heating tubes which extract heatdirectly from the bed. Tubes above the bed which extract heat from hot combustion gasbefore it enters the flue duct. 27. Bubbling Bed Boiler-1 28. Bubbling Bed Boiler-2 29. 2. Pressurised Fluidised Bed CombustionSystem (PFBC).Pressurised Fluidised Bed Combustion (PFBC) is a variation of fluid bedtechnology that is meant for large-scale coal burning applications. InPFBC, 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. Thesteam turbine is driven by steam raised in tubes immersed in the fluidizedbed. The condensate from the steam turbine is pre-heated using wasteheat from gas turbine exhaust and is then taken as feed water for steamgeneration.The PFBC system can be used for cogeneration or combined cycle powergeneration. By combining the gas and steam turbines in this way,electricity is generated more efficiently than in conventional system. Theoverall conversion efficiency is higher by 5% to 8%. .At elevated pressure, the potential reduction in boiler size is considerabledue to increased amount of combustion in pressurized mode and highheat flux through in-bed tubes. 30. PFBC Boiler for Cogeneration 31. 3. Circulating (fast) Fluidised Bed Combustionsystem(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 whichcrushed (6 12 mm size) fuel and limestone are injected into the furnaceor combustor. The particles are suspended in a stream of upwardlyflowing air (60-70% of the total air), which enters the bottom of thefurnace through air distribution nozzles. The fluidising velocity incirculating beds ranges from 3.7 to 9 m/sec. The balance of combustionair is admitted above the bottom of the furnace as secondary air. 32. The combustion takes place at 840-900oC, and the fine particles (200C then recover waste heat2. Feed Water PreheatingEconomizers Potential to recover heat from 200 300 oC fluegases leaving a modern 3-pass shell boiler3. Combustion Air Preheating If combustion air raised by 20C = 1% improvethermal efficiency 74. Energy Efficiency Opportunities4. 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 ondips, deterioration of diffusers or spinner plates Coal-fired boiler: non-uniform coal size 75. Energy Efficiency Opportunities5. 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 analyzersFuelKg air req./kg fuel %CO2 in flue gas in practiceSolid FuelsBagasse 3.310-12Coal (bituminous)10.710-13Lignite 8.59 -13Paddy Husk4.514-15Wood5.711.13Liquid FuelsFurnace Oil13.8 9-14LSHS 14.1 9-14 83 76. Energy Efficiency Opportunities6. Radiation and Convection HeatLoss Minimization Fixed heat loss from boiler shell, regardless ofboiler output Repairing insulation can reduce loss7. Automatic Blow Down Control Sense and respond to boiler water conductivityand pH 77. Energy Efficiency Opportunities8. Scaling and Soot Loss Reduction Every 22oC increase in stack temperature = 1%efficiency loss 3 mm of soot = 2.5% fuel increase9. Reduced Boiler Steam Pressure Lower steam pressure= lower saturated steam temperature= lower flue gas temperature Steam generation pressure dictated by process 78. Energy Efficiency Opportunities10. Variable Speed Control forFans, Blowers and Pumps Suited for fans, blowers, pumps Should be considered if boiler loads arevariable11. Control Boiler Loading Maximum boiler efficiency: 65-85% of rated load Significant efficiency loss: < 25% of rated load 79. Energy Efficiency Opportunities12. Proper Boiler Scheduling Optimum efficiency: 65-85% of full load Few boilers at high loads is more efficient thanlarge number at low loads13. Boiler ReplacementFinancially 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 80. BoilersTHANK YOUFOR YOUR ATTENTION