Cfb boiler basic design, operation and maintenance
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This material provides the basic of design, operation and maintenance so that you can use this as guide line to operation, to inspect your boiler. Hope this will be benefit you.

This material provides the basic of design, operation and maintenance so that you can use this as guide line to operation, to inspect your boiler. Hope this will be benefit you.

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  • 1. 1CFB Boiler Design, Operation andMaintenanceBy Pichai Chaibamrung
  • 2. 2Content Day11. Introduction to CFB2. Hydrodynamic of CFB3. Combustion in CFB4. Heat Transfer in CFB5. Basic design of CFB6. Operation7. Maintenance8. Basic Boiler Safety9. Basic CFB control
  • 3. 3Objective— To understand the typical arrangement in CFB— To understand the basic hydrodynamic of CFB— To understand the basic combustion in CFB— To understand the basic heat transfer in CFB— To understand basic design of CFB— To understand theory of cyclone separatorKnow Principle Solve Everything
  • 4. 41. Introduction to CFB1.1 Development of CFB1.2 Typical equipment of CFB1.3 Advantage of CFB
  • 5. 51.1 Development of CFB— 1921, Fritz Winkler, Germany, Coal Gasification— 1938, Waren Lewis and Edwin Gilliland, USA, Fluid Catalytic Cracking,Fast Fluidized Bed— 1960, Douglas Elliott, England, Coal Combustion, BFB— 1960s, Ahlstrom Group, Finland, First commercial CFB boiler, 15MWth, Peat
  • 6. 61.2 Typical Component of CFB Boiler
  • 7. 71.2 Typical Component of CFB BoilerWind box and grid nozzleprimary air is fed into wind box.Air is equally distributed onfurnace cross section by passingthrough the grid nozzle. This willhelp mixing of air and fuel forcompleted combustion
  • 8. 81.2 Typical Component of CFB BoilerBottom ash draincoarse size of ash that is nottake away from furnace byfluidizing air will be drainat bottom ash drain portlocating on grid nozzlefloor by gravity.bottom ash will be cooledand conveyed to silo bycooling conveyor.
  • 9. 91.2 Typical Component of CFB BoilerHP Blowersupply high pressure air tofluidize bed material in loopseal so that it can overflow tofurnaceRotameterSupplying of HPblower to loop seal
  • 10. 101.2 Typical Component of CFB BoilerCyclone separatorlocated after furnace exit andbefore convective part.use to provide circulation bytrapping coarse particle back tothe furnaceFluidized boiler without thiswould be BFB not CFB
  • 11. 111.2 Typical Component of CFB BoilerEvaporative or Superheat Wing Walllocated on upper zone of furnaceit can be both of evaporative or SHpanellower portion covered by erosionresistant materials
  • 12. 121.2 Typical Component of CFB BoilerFuel Feeding systemsolid fuel is fed into the lowerzone of furnace through thescrew conveyor cooling withcombustion air. Number offeeding port depend on thesize of boiler
  • 13. 131.2 Typical Component of CFB BoilerRefractoryrefractory is used to protectthe pressure part fromserious erosion zone such aslower bed, cyclone separator
  • 14. 141.2 Typical Component of CFB BoilerSolid recycle system (Loop seal)loop seal is located betweendip leg of separator andfurnace. Its design physical issimilar to furnace which haveair box and nozzle todistribute air. Distributed airfrom HP blower initiatefluidization. Solid behave likea fluid then over flow back tothe furnace.
  • 15. 151.2 Typical Component of CFB BoilerKick outkick out is referred tointerface zone betweenthe end of lower zonerefractory and water tube.It is design to protect theerosion by by-passing theinterface from fallingdown bed materials
  • 16. 161.2 Typical Component of CFB BoilerLime stone and sand systemlime stone is pneumatically feed or gravitational feed intothe furnace slightly above fuel feed port. the objective is toreduce SOx emission.Sand is normally fed by gravitation from silo in order tomaintain bed pressure. Its flow control by speed of rotaryscrew.
  • 17. 171.2 Typical Arrangement of CFB Boiler
  • 18. 181.3 Advantage of CFB Boiler— Fuel Flexibility
  • 19. 191.3 Advantage of CFB Boiler— High Combustion Efficiency- Good solid mixing- Low unburned loss by cyclone, fly ash recirculation- Long combustion zone— In situ sulfur removal— Low nitrogen oxide emission
  • 20. 202. Hydrodynamic in CFB2.1 Regimes of Fluidization2.2 Fast Fluidized Bed2.3 Hydrodynamic Regimes in CFB2.4 Hydrodynamic Structure of Fast Beds
  • 21. 212.1 Regimes of Fluidization— Fluidization is defined as the operation through which finesolid are transformed into a fluid like state throughcontact with a gas or liquid.
  • 22. 222.1 Regimes of Fluidization— Particle Classification<130<180<250<600CFB1Size (micron)<590<25025%>420>100100%<840<45050%75%100%Distribution<1190<550<1680<1000BFBCFB2
  • 23. 232.1 Regimes of Fluidization— Particle Classification
  • 24. 242.1 Regimes of Fluidization— Comparison of Principal Gas-Solid Contacting Processes
  • 25. 252.1 Regimes of Fluidization— Packed BedThe pressure drop per unit height of a packed beds of a uniformly sizeparticles is correlated as (Ergun,1952)Where U is gas flow rate per unit cross section of the bed calledSuperficial Gas Velocity
  • 26. 262.1 Regimes of Fluidization— Bubbling Fluidization BedsMinimum fluidization velocity is velocity where the fluiddrag is equal to a particle’s weight less its buoyancy.
  • 27. 272.1 Regimes of Fluidization— Bubbling Fluidization BedsFor B and D particle, the bubble is started when superficialgas is higher than minimum fluidization velocityBut for group A particle the bubble is started whensuperficial velocity is higher than minimum bubblingvelocity
  • 28. 282.1 Regimes of Fluidization— Turbulent Bedswhen the superficial is continually increased through abubbling fluidization bed, the bed start expanding, thenthe new regime called turbulent bed is started.
  • 29. 292.1 Regimes of Fluidization
  • 30. 302.1 Regimes of Fluidization— Terminal VelocityTerminal velocity is the particle velocity when theforces acting on particle is equilibrium
  • 31. 312.1 Regimes of Fluidization— Freeboard and Furnace Height- considered for design heating-surface area- considered for design furnace height- to minimize unburned carbon in bubblingbed- the freeboard heights should be exceed orclosed to the transport disengaging heights
  • 32. 322.2 Fast Fluidization— Definition
  • 33. 332.2 Fast Fluidization— Characteristics of Fast Beds- non-uniform suspension of slender particle agglomerates or clusters movingup and down in a dilute- excellent mixing are major characteristic- low feed rate, particles are uniformly dispersed in gas stream- high feed rate, particles enter the wake of the other, fluid drag on the leadingparticle decrease, fall under the gravity until it drops on to trailing particle
  • 34. 342.3 Hydrodynamic regimes in a CFBLower Furnace below SA:Turbulent or bubblingfluidized bedFurnace Upper SA:Fast Fluidized BedCyclone Separator :Swirl FlowReturn leg and lift leg :Pack bed and Bubbling BedBack Pass:Pneumatic Transport
  • 35. 352.4 Hydrodynamic Structure of Fast Beds— Axial Voidage ProfileBed Density Profile of 135 MWe CFB Boiler (Zhang et al., 2005)Secondary air is fed
  • 36. 362.4 Hydrodynamic Structure of Fast Beds— Velocity Profile in Fast Fluidized Bed
  • 37. 372.4 Hydrodynamic Structure of Fast Beds— Velocity Profile in Fast Fluidized Bed
  • 38. 382.4 Hydrodynamic Structure of Fast Beds— Particle Distribution Profile in Fast Fluidized Bed
  • 39. 392.4 Hydrodynamic Structure of Fast Beds— Particle Distribution Profile in Fast Fluidized Bed
  • 40. 402.4 Hydrodynamic Structure of Fast Beds— Particle Distribution Profile in Fast Fluidized BedEffect of SA injection on particledistribution by M.Koksal andF.Hamdullahpur (2004). Theexperimental CFB is pilot scale CFB.There are three orientations of SAinjection; radial, tangential, and mixed
  • 41. 412.4 Hydrodynamic Structure of Fast Beds— Particle Distribution Profile in Fast Fluidized BedNo SA, the suspensiondensity is proportionall to solid circulation rateWith SA 20% of PA,the solid particle is hold upwhen compare to no SAIncreasing SA to 40%does not significant onsuspension density aboveSA injection pointbut the low zone isdenser than low SA ratioIncreasing solid circulationrate effect to bothlower and upper zoneof SA injection pointwhich both zone isdenser than lowsolid circulation rate
  • 42. 422.4 Hydrodynamic Structure of Fast Beds— Effects of Circulation Rate on Voidage Profilehigher solid recirculation rate
  • 43. 432.4 Hydrodynamic Structure of Fast Beds— Effects of Circulation Rate on Voidage Profilehigher solid recirculation ratePressure drop across the L-valve isproportional to solid recirculation rate
  • 44. 442.4 Hydrodynamic Structure of Fast Beds— Effect of Particle Size on Suspension Density Profile- Fine particle - - > higher suspension density- Higher suspension density - - > higher heat transfer- Higher suspension density - - > lower bed temperature
  • 45. 452.4 Hydrodynamic Structure of Fast Beds— Core-Annulus Model- the furnace may be spilt into two zones : core andannulusCore- Velocity is above superficial velocity- Solid move upwardAnnulus- Velocity is low to negative- Solids move downwardcoreannulus
  • 46. 462.4 Hydrodynamic Structure of Fast Beds— Core-Annulus Modelcoreannulus
  • 47. 472.4 Hydrodynamic Structure of Fast Beds— Core Annulus Model- the up-and-down movement solids in the core andannulus sets up an internal circulation- the uniform bed temperature is a direct result of internalcirculation
  • 48. 483. Combustion in CFB3.1 Coal properties for CFB boiler3.2 Stage of Combustion3.3 Factor Affecting Combustion Efficiency3.4 Combustion in CFB3.5 Biomass Combustion
  • 49. 493.1 Coal properties for CFB BoilerProperties- coarse size coal shall be crushed by coal crusher- sizing is an importance parameter for CFB boiler improper size mightresult in combustion loss- normal size shall be < 8 mm
  • 50. 503.2 Stage of CombustionA particle of solid fuel is injected into an FB undergoes thefollowing sequence of events:- Heating and drying- Devolatilization and volatile combustion- Swelling and primary fragmentation (for some types of coal)- Combustion of char with secondary fragmentation and attrition
  • 51. 513.2 Stages of Combustion— Heating and Drying- Combustible materials constitutes around 0.5-5.0% byweightof total solids in combustor- Rate of heating 100 °C/sec – 1000 °C/sec- Heat transfer to a fuel particle (Halder 1989)
  • 52. 523.2 Stages of CombustionDevolatilization and volatile combustion- first steady release 500-600 C- second release 800-1000C- slowest species is CO (Keairns et al., 1984)- 3 mm coal take 14 sec to devolatilzeat 850 C (Basu and Fraser, 1991)
  • 53. 533.2 Stages of Combustion— Char Combustion2 step of char combustion1. transportation of oxygen to carbon surface2. Reaction of carbon with oxygen on the carbon surface3 regimes of char combustion- Regime I: mass transfer is higher than kinetic rate- Regime II: mass transfer is comparable to kinetic rate- Regime III: mass transfer is very slow compared to kinetic rate
  • 54. 543.2 Stage of Combustion— Communition Phenomena During CombustionVolatile release cause theparticle swellVolatile release in non-porousparticle cause the highinternal pressure result inbreak a coal particle intofragmentationChar burn under regime I, II,the pores increases in size àweak bridge connection ofcarbon until it can’t withstandthe hydrodynamic force. It willfragment again call “secondary fragmentation”Attrition, Fine particles fromcoarse particles throughmechanical contract likeabrasion with other particlesChar burn under regime Iwhich is mass transfer ishigher than kinetic trasfer.The sudden collapse or othertype of second fragmentationcall percolative fragmentationoccurs
  • 55. 553.3 Factor Affecting Combustion Efficiency— Fuel Characteristicsthe lower ratio of FC/VM result in higher combustionefficiency (Makansi, 1990), (Yoshioka and Ikeda,1990),(Oka, 2004) but the improper mixing could result in lowercombustion efficiency due to prompting escape of volatilegas from furnace.
  • 56. 563.3 Factor Affecting Combustion Efficiency— Operating condition (Bed Temperature)- higher combustion temperature --- > high combustionefficiencyHigh combustion temperature result in highoxidation reaction, then burn out timedecrease. So the combustion efficiencyincrease.Limit of Bed temp-Sulfur capture-Bed melting-Water tube failure
  • 57. 573.3 Factor Affecting Combustion Efficiency— Fuel Characteristic (Particle size)-The effect of this particle size is not clear-Fine particle, low burn out time but theprobability to be dispersed from cyclonethe high-Coarse size, need long time to burn out.-Both increases and decreases arepossible when particle size decrease
  • 58. 583.3 Factor Affecting Combustion Efficiency— Operating condition (superficial velocity)- high fluidizing velocity decrease combustion efficiency becauseIncreasing probability of small char particle be elutriated fromcirculation loop- low fluidizing velocity cause defluidization, hot spot and sintering
  • 59. 593.3 Factor Affecting Combustion Efficiency— Operating condition (excess air)- combustion efficiency improve which excess air < 20%Excess air >20% lesssignificant improvecombustion efficiency.Combustion lossdecreasesignificantly whenexcess air < 20%.
  • 60. 603.3 Factor Affecting Combustion EfficiencyOperating ConditionThe highest loss of combustion result from elutriation of char particlefrom circulation loop. Especially, low reactive coal size smaller than 1mm it can not achieve complete combustion efficiency with out flyash recirculation system.However, the significant efficiency improve is in range 0.0-2.0 fly ashrecirculation ratio.
  • 61. 613.4 Combustion in CFB Boiler— Lower Zone Properties- This zone is fluidized by primary air constituting about40-80% of total air.- This zone receives fresh coal from coal feeder andunburned coal from cyclone though return valve- Oxygen deficient zone, lined with refractory to protectcorrosion- Denser than upper zone
  • 62. 623.4 Combustion in CFB Boiler— Upper Zone Properties- Secondary is added at interface between lower and upperzone- Oxygen-rich zone- Most of char combustion occurs- Char particle could make many trips around the furnacebefore they are finally entrained out through the top offurnace
  • 63. 633.4 Combustion in CFB Boiler— Cyclone Zone Properties- Normally, the combustion is small when compare to infurnace- Some boiler may experience the strong combustion inthis zone which can be observe by rising temperature inthe cyclone exit and loop seal
  • 64. 643.5 Biomass Combustion— Fuel Characteristics- high volatile content (60-80%)- high alkali content à sintering, slagging, and fouling- high chlorine content à corrosion
  • 65. 653.5 Biomass Combustion— AgglomerationSiO2 melts at 1450 CEutectic Mixture melts at 874 CSintering tendency of fuel is indicated by the following(Hulkkonen et al., 2003)
  • 66. 663.5 Biomass CombustionOptions for Avoiding the Agglomeration Problem- Use of additives- china clay, dolomite, kaolin soil- Preprocessing of fuels- water leaching- Use of alternative bed materials- dolomite, magnesite, and alumina- Reduction in bed temperature
  • 67. 673.5 Biomass Combustion— Agglomeration
  • 68. 683.5 Biomass Combustion— Fouling- is sticky deposition of ash due to evaporation of alkali salt- result in low heat transfer to tube
  • 69. 693.5 Biomass Combustion— Corrosion Potential in Biomass Firing- hot corrosion- chlorine reacts with alkali metal à from lowtemperature melting alkali chlorides- reduce heat transfer and causing high temperaturecorrosion
  • 70. 704. Heat Transfer in CFB4.1 Gas to Particle Heat Transfer4.2 Heat Transfer in CFB
  • 71. 714.1 Gas to Particle Heat Transfer— Mechanism of Heat TransferIn a CFB boiler, fine solid particlesagglomerate and form clusters orstand in a continuum of generallyup-flowing gas containing sparselydispersed solids. The continuum iscalled the dispersed phase, whilethe agglomerates are called thecluster phase.The heat transfer to furnace walloccurs through conduction fromparticle clusters, convection fromdispersed phase, and radiationfrom both phase.
  • 72. 724.1 Heat Transfer in CFB Boiler— Effect of Suspension Density and particle sizeHeat transfer coefficient is proportional to the square root of suspension density
  • 73. 734.1 Heat Transfer in CFB Boiler— Effect of Fluidization VelocityNo effect from fluidization velocity when leave the suspension density constant
  • 74. 744.1 Heat Transfer in CFB Boiler— Effect of Fluidization Velocity
  • 75. 754.1 Heat Transfer in CFB Boiler— Effect of Fluidization Velocity
  • 76. 764.1 Heat Transfer in CFB Boiler— Effect of Vertical Length of Heat Transfer Surface
  • 77. 774.1 Heat Transfer in CFB Boiler— Effect of Bed Temperature
  • 78. 784.1 Heat Transfer in CFB Boiler— Heat Flux on 300 MW CFB Boiler (Z. Man, et. al)
  • 79. 794.1 Heat Transfer in CFB Boiler— Heat transfer to the walls of commercial-sizeLow suspension density lowheat transfer to the wall.
  • 80. 804.1 Heat Transfer in CFB Boiler— Circumferential Distribution of Heat Transfer Coefficient
  • 81. 815 Design of CFB Boiler— 5.1 Design and Required Data— 5.2 Combustion Calculation— 5.3 Heat and Mass Balance— 5.4 Furnace Design— 5.5 Cyclone Separator
  • 82. 825.1 Design and Required DataThe design and required data normally will be specify by owneror client. The basic design data and required data are;Design Data :- Fuel ultimate analysis - Weather condition- Feed water quality - Feed water propertiesRequired Data :- Main steam properties - Flue gas temperature- Flue gas emission - Boiler efficiency
  • 83. 835.2 Combustion Calculation— Base on the design and required data the following datacan be calculated in this stage :- Fuel flow rate - Combustion air flow rate- Fan capacity - Fuel and ash handling capacity- Sorbent flow rate
  • 84. 845.3 Heat and Mass BalanceFuel andsorbentUnburned inbottom ashFeed waterCombustion airMain steamBlow downFlue gasMoisture in fueland sorbentUnburned in fly ashMoisture incombustion airRadiationHeat inputHeat output
  • 85. 855.3 Heat and Mass Balance— Mass BalanceFuel andsorbentbottom ashSolid Flue gasMoisture in fueland sorbentfly ashMake upbed materialbottom ashFuel andsorbentMake upbed materialSolid in Flue gasfly ashMass outputMass input
  • 86. 865.4 Furnace Design— The furnace design include:1. Furnace cross section2. Furnace height3. Furnace opening1. Furnace cross sectionCriteria- moisture in fuel- ash in fuel- fluidization velocity- SA penetration- maintain fluidization in lowerzone at part load
  • 87. 875.4 Furnace Design2. Furnace heightCriteria- Heating surface- Residual time for sulfurcapture3. Furnace openingCriteria- Fuel feed ports- Sorbent feed ports- Bed drain ports- Furnace exit section
  • 88. 885.5 Cyclone Separator— 6.1 Theory— 6.2 Critical size of particle
  • 89. 895.5 Cyclone Separator— The centrifugal force on the particle entering the cycloneis— The drag force on the particle can be written as— Under steady state drag force = centrifugal force
  • 90. 905.5 Cyclone Separator— Vr can be considered as index of cyclone efficiency, fromabove equation the cyclone efficiency will increase for :- Higher entry velocity- Large size of solid- Higher density of particle- Small radius of cyclone- low value of viscosity of gas
  • 91. 915.5 Cyclone Separator— The particle with a diameter larger than theoretical cut-size of cyclone will be collected or trapped by cyclonewhile the small size will be entrained or leave a cyclone— Actual operation, the cut-off size diameter will be definedas d50 that mean 50% of the particle which have adiameter more than d50 will be collected or captured.
  • 92. 926. Operation
  • 93. 93Content6.1 Before start6.2 Grid pressure drop test6.3 Cold Start6.4 Normal Operation6.5 Normal Shutdown6.6 Hot Shutdown6.7 Hot Restart6.8 Malfunction and Emergency
  • 94. 946.1 Before Start— all maintenance work have been completely done— All function test have been checked— cooling water system is operating— compressed air system is operating— Make up water system— Deaerator system— Boiler feed water pump— Condensate system— Oil and gas system— Drain and vent valves— Air duct, flue gas duct system
  • 95. 956.1 Before Start— Blow down system— Sand feeding system— Lime stone feeding system— Solid fuel system— Ash drainage system— Control and safety interlock system
  • 96. 966.2 Grid Pressure Drop Test— For check blockage of gridnozzle— Furnace set point = 0— Test at every PA. load— Compare to clean data or designdata— Shall not exceed 10% fromdesign data— Perform in cold conditionPwPbFIPf= 0
  • 97. 976.3 Cold StartFill boilerBoiler InterlockStart up BurnerFeed Solid FuelBoiler Warm UpPurgeStart FanFeed Bed MaterialRaise to MCR-100 mm normal levelID,HP,SA,PALow level cut off300 STb 150-200 C30-50 mbar, Tb 550-600 C
  • 98. 98Fill Boiler-Close all water side drain valve-Open all air vent valve at drum andsuperheat-Open start up vent valve 10-15%-Slowly feed water to drum until level 1/3 ofsigh glass
  • 99. 99Start Fan1.Start ID.Fan2.Start HP Blower3.Start SA.Fan4.Start PA.Fan
  • 100. 100Boiler InterlockEmergency stop in orderFurnace P. < Max (2/3)ID. Fan runningHP Blower startDrum level > min (2/3)SA. Fan runningPA. Fan runningHP. Blower P. > minPA. Flow to grid > minTrip Solid FuelFlue gas T after Furnace < maxTrip Soot BlowerTrip OilTrip SandTrip Lime StoneTrip Bottom Ash
  • 101. 101Purge— To carry out combustible gases— To assure all fuel are isolatedfrom furnace— Before starting first burner forcold start— If bed temp < 600 C or OEMrecommend and no burner inservice— Total air flow > 50%— 300 sec for purging time
  • 102. 102PurgeNFPA85: CFB Boiler purge logic
  • 103. 103Start up burner— Help to heat up bed temp to allowable temperature forfeeding solid fuel— Will be stopped if bed temp > 850 C— Before starting, all interlock have to passed— Main interlock— Oil pressure > minimum— Control air pressure > minimum— Atomizing air pressure > minimum
  • 104. 104Start up burnerNFPA85 - Typical burner safety for CFB boiler
  • 105. 105Drum and DA low level cut-off— Test for safety— During burner are operating— Open drain until low level— Signal feeding are not allow— Steam drum low level = chanceto overheating of water tube— DA low level = danger for BFWP
  • 106. 106Boiler warm up— Gradually heating the boiler to reduce the effect ofthermal stress on pressure part, refractory and drum swell— Increase bed temp 60-80 C/hr by adjusting SUB— Control flue gas temperature <470 C until steam flow >10% MCR— Close vent valves at drum and SH when pressure > 2 bar— Continue to increase firing rate according torecommended start up curve— Operate desuperheater when steam temperature are within 30 C of design point— Slowly close start up and drain valve while maintain steamflow > 10% MCR
  • 107. 107Feed bed material— Bed material should be sand which size is according torecommended size— Start feed sand when bed temp >150 C— Do not exceed firing rate >30% if bed pressure <20 mbarotherwise overheating may occur for refractory and nozzle— Continue feed bed material unit it reach 30 mbar
  • 108. 108Feed solid fuel— Must have enough bed material— Bed temperature > 600 C or manufacturerrecommendation or refer to NFPA85 Appendix H— Pulse feed every 90 s— Placing lime stone feeding, ash removal systemsimultaneously— Slowly decrease SUB firing rate while increasing solid fuelfeed rate— Stop SUB one by one, observe bed temperature increasing— Turn to auto mode control
  • 109. 109Rise to MCR— Continue rise pressure and temperature according torecommended curve until reach design point— Drain bottom ash when bed pressure >45-55 mbar— Slowly close start up valve— Monitor concerning parameters
  • 110. 1106.4 Normal Operation— Increasing- manual increase air flow- manual increase fuel flow- monitor excess oxygen- monitor steam pressure— Decreasing- manual decrease air flow- manual decrease fuel flow- monitor excess oxygen- monitor steam pressureChanging Boiler load (manual)
  • 111. 1116.4 Normal Operation— Furnace and emssion- monitor fluidization in hotloop- monitor gas side pressure drop- monitor bed pressure- monitor bed temperature-monitor wind box pressure- monitor SOx, Nox, COFurnace and Emission Monitoring
  • 112. 1126.4 Normal Operation— Bottom ash drain- automatic or manual drainingof bottom ash shall be judged bycommissioning engineer for thedesign fuel.- when fuel is deviated from thedesign, operator can be judge bythemselves that draining needto perform or not.- bed pressure is the mainparameter to start draining— Soot blower- initiate soot blower to cleanthe heat exchanger surface inconvective part- frequent of soot blowingdepend on the degradation ofheat transfer coefficient.- normally 10 C higher thannormal value of exhausttemperatureBottom ash and Soot Blower
  • 113. 1136.4 Normal Operation— Boiler Walk Down- boiler expansion joint- Boiler steam drum- Boiler penthouse- Safety valve- Boiler lagging- Spring hanger- Valve and piping- Damper position- Loop seal- Bottom screw- Combustion chamber- Fuel conveyor
  • 114. 1146.4 Normal Operation— Sizing Quality- crushed coal, bed material, lime stone and bottom ashsizing shall be periodically checked by the operator- sieve sizing shall be performed regularly to make surethat their sizing is in range of recommendation
  • 115. 1156.5 Normal Shut Down1. Reduce boiler load to 50% MCR2. Place O2 control in manual mode3. Monitor bed temperature4. Continue reducing load according to shut down curve5. Maintain SH steam >20 C of saturation temperature6. Start burner when bed temperature <750 C7. Empty solid fuel and lime stone with bed material >650 C8. Decrease SUB firing rate according to suggestion curve9. Maintain drum level in manual mode10. Stop solid fuel, line stone, sand feeding system
  • 116. 1166.5 Normal Shut Down11. Maintain drum level near upper limit12. Continue fluidizing the bed to cool down the system at 2C/min by reducing SUB firing rate13. Stop SUB at bed temperature 350 C14. Continue fluidizing until bed temperature reach 300 C15. Slowly close inlet damper of PAF and SAF so that IDFcan control furnace pressure in automatic mode16. Stop all fan after damper completely closed17. Stop HP blower 30 S after IDF stopped18. Stop chemical feeding system when BFWP stop19. Continue operate ash removal system until it empty
  • 117. 1176.5 Normal Shut Down20. Open vent valve at drum and SH when drum pressurereach 1.5-2 bar21. Open manhole around furnace when bed temp < 300 C
  • 118. 1186.6 Emergency Shut down— Boiler can be held in hot stand by condition about 8 hrs— Hot condition is bed temp >650 C otherwise follow coldstar up procedure— Boiler load should be brought to minimum— Stop fuel feeding— Wait O2 increase 2 time of normal operation— Stop air to combustion chamber to minimize heat loss
  • 119. 1196.7 Hot restart— Purge boiler if bed temperature < 600 C— Start SUBs if bed temperature > 500 C— Monitor bed temperature rise— If bed temperature does not rise after pulse feeding solidfuel. stop feeding and start purge
  • 120. 1206.8 Malfunction and Emergency— Bed pressure— Bed temperature— Circulation— Tube leak— Drum level
  • 121. 121Bed PressureBed pressure is an one of importanceparameter that effect on boiler efficiencyand reliability.Measured above grid nozzle about 20 cm.PwPbFIPf= 0
  • 122. 122Bed Pressure— Effect of low bed pressure- poor heat transfer- boiler responds- high bed temperature- damage of air nozzle and refractory— Effect of high bed pressure- increase heat transfer- more efficient sulfur capture- more power consumption of fan
  • 123. 123Bed Pressure— Cause of low bed pressure- loss of bed material- too fine of bed materials- high bed temperature— Cause of high bed pressure- agglomeration- too coarse of bed material
  • 124. 124Bed Temperature— Measured above grid nozzle about20 cm— Measured around the furnace crosssection— It is the significant parameter tooperate CFB boiler
  • 125. 125Bed temperature— Effect of high bed temperature- ineffective sulfur capture- chance of ash melting- chance of agglomeration- chance to damage of air nozzle
  • 126. 126Bed temperature— Cause of high bed temperature- low bed pressure- too coarse bed material- too coarse solid fuel- improper drain bed material- low volatile fuel- improper air flow adjustment
  • 127. 127Circulation— Circulation is particularphenomena of CFB boiler.— Bed material and fuel arecollected at cyclone separator— Return to the furnace via loopseal— HP blower supply HP air tofluidize collected materials toreturn to furnace
  • 128. 128Circulation— Effect of malfunction circulation- No circulation result in forced shut down- high rate of circulation- high circulation rate need more power of blower- low rate of circulation
  • 129. 129Circulation— Cause of malfunction circulation- insufficiency air flow to loop seal nozzle- insufficient air pressure to loop seal- plugging of HP blower inlet filter- blocking or plugging of loop seal nozzle-
  • 130. 130Tube leak— Water tube leak- furnace pressure rise- bed temperature reduce- stop fuel feeding- open start up valve- don’t left low level of drum- continue feed water until flue gas temp < 400 C- continue combustion until complete- small leak follow normal shut down
  • 131. 131Drum levelSudden loss of drum level- when the cause is known and immediately correctablebefore level reach minimum allowable. Reestablish steamdrum level to its normal value and continue boileroperation-if the cause is not known. Start immediate shut downaccording to emergency shut down procedure
  • 132. 132Drum levelGradual loss of drum level- boiler load shall be reduced to low load- find out and correct the problem as soon as possible- if can not maintain level and correct the problem, boilermust be taken out of service and normal shut downprocedure shall be applied.
  • 133. 1337. Maintenance
  • 134. 134Before maintenance work— Make sure that all staff are understand about safetyinstruction for doing CFB boiler maintenance work— Make sure that all maintenance and safety equipmentsshall be a first class
  • 135. 135Overview Boiler MaintenanceRefractory and tube are the mainarea that need to be checked
  • 136. 1366.1 Windbox Inspection— Inspect sand inside windboxafter shutdown— Drain pipe— Crack— Air gun pipe— Refractory— Crack, wear and fall down inspectby hammer(knocking) if burner isunder bed designDrain pipe
  • 137. 1376.2 Furnace Inspection— Nozzle :— Wear— Fall-off— Refractory— Crack, wear and fall down inspectby hammer knocking if burner isunder bed design— Feed fuel port— Wear— Crack— BurnerRefractoryBurner Feed FuelNozzle
  • 138. 1386.2 Furnace Inspection— Limestone port— Crack— Deform— Refractory damage at connectionbetween port and refractory— Secondary & Recirculation Airport— Crack— Deform— Refractory damage at connectionbetween port and refractory— Bed Temperature— Check thermo well deformation— Check wearSecondary & Recirculation Air port
  • 139. 1396.3 Kick-Out Inspection— Refractory— Wear— Crack and fall down byhammer(knocking)— Water tube— Wear— Thickness
  • 140. 1406.3 Kick-Out Inspection— Water Tube:— Thickness measuring— Erosion at corner— CO Corrosion due to incompletecombustion at fuel feed side.— Defect from weld build up— Water tube sampling for internalcheck every 3 yearsInside water tube inspect by borescopewelded build up excessive metal because use welding rodsize bigger than tube thickness
  • 141. 1416.4 Superheat I (Wingwall)— Water Tube:— Thickness measuring— Erosion at tube connection— Refractory— Crack and fall down byhammer(knocking)— Guard— Crack— fall down
  • 142. 1426.4 Superheat I (Omega Tube)— Offset Water Tube:— Thickness measuring— Erosion at offset tube— SH tube— Thickness measuring— Omega Guard— Crack— fall downOmega GuardOffset WaterTube
  • 143. 1436.5 Roof— Water Tube:— Thickness measuring— Erosion— Refractory— Crack, wear and fall down byhammer(knocking)
  • 144. 1446.6 Inlet Separator— Water Tube:— Thickness measuring near openinghave more erosion than anothertube because of high velocity of fluegas— Refractory— Crack, wear and fall down byhammer(knocking)
  • 145. 1456.7 Steam Drum— Surface :— Surface were black by magnetite— Deposits— Deposits at bottom drum need tocheck chemical analysis— Cyclone Separator— Loose— Demister— Blowdown hole— Plugging— U-Clamp— LooseDeposits at bottom drum
  • 146. 1466.8 Separator— Central Pipe:— Deformation— Crack— Refractory— Wear at impact zone due to highimpact velocity— Crack and fall down byhammer(knocking)
  • 147. 1476.9 Outlet Separator— Water Tube— Tube Thickness— Erosion— Outlet Central Pipe:—Support or Hook— Refractory—Crack and fall down byhammer(knocking)
  • 148. 1486.10 Screen Tube— Water Tube— Thickness measuring upper part ofscreen tube at corner have moreerosion than another area becauseof high velocity of flue gas— Guard— Loose— Refractory— Crack and fall down byhammer(knocking)Weld build up or install guard to prevent tube erosionupper part of screen tube at corner have more erosion
  • 149. 1496.11 Superheat Tube— Tube— Thickness measuring— High erosion between SH tube andwall— Steam erosion due to improper sootblower— Guard— Fall down— Crack
  • 150. 1506.12 Economizer— Water Tube— Thickness measuring— High erosion between economizertube and wall— Steam erosion due to improper sootblower— Guard— Fall down— CrackGuardInstall guard toprevent tube erosion
  • 151. 1516.13 Air Heater— Tube— Cold end corrosion due to highconcentrate SO3 in flue gas— Steam erosion due to improper sootblowerInlet air heaterCold end corrosion due to SO3 in fluegas
  • 152. 1528. Basic Boiler Safety
  • 153. 153WarningOperating or maintenance procedure which, ifnot as described could result in injured deathor damage of equipment
  • 154. 154General safety precaution— Electrical power shall be turned off before performinginstallation or maintenance work. Lock out, tag out shallbe indicated— All personal safety equipment shall be suit for each work— Never direct air water stream into accumulation bedmaterial or fly ash. This will become breathing hazard— Always provide safe access to all equipment ( plant from,ladders, stair way, hand rail— Post appropriate caution, warning or danger sign andbarrier for alerting non-working person— Only qualify and authorized person should serviceequipment or maintenance work
  • 155. 155General safety precaution— Do not by-pass any boiler interlocks— Use an filtering dust mask when entering dust zone— Do not disconnect hoist unless you have made sure thatthe source is isolated
  • 156. 156Equipment entry— Never entry confine space until is has been cooled, purgedand properly vented— When entering confine space such as separator, loop sealfurnace be prepared for falling material— Always lock the damper, gate or door before passingthrough them— Never step on accumulation of bottom ash or fly ash. Itsunderneath still hot— Never use toxic fluid in confine space— Use only appropriate lifting equipment when lift or moveequipment
  • 157. 157Equipment entry— Stand by personnel shall be positioned outside a confinespace to help inside person incase of emergency— Be carefully aware the chance of falling down when entercyclone inlet or outlet.— Don not wear contact lens with out protective eye nearboiler, fuel handing, ash handing system. Airborne particlecan cause eye damage— Don not enter loop seal with out installing of cover overloop seal downcomer to prevent falling material fromcyclone
  • 158. 158Operating precautionsCFB boiler process— Use planks on top of bed materials after boiler is cooleddown. This will prevent the chance of nozzle plugging— Do not open any water valve when boiler is in service— Do not operate boiler with out O2 analyzer— Do not use downcomer blown donw when pressure > 7bar otherwise loss of circulation may occure— Do not operate CFB boiler without bed material— When PA is started. PA flow to grid must be increase toabove minimum limit to fully fluidized bed maerial— Do not operate CFB boiler with bed pressure > 80mbar.This might be grid nozzle plugging
  • 159. 159Operating precautions— on cold start up the rate of chance in saturated steam shallnot exceed 2 C/min— On cold start up the change of flue gas temp at cycloneinlet shall not exceed 70 C/min— Do not add feed water to empty steam drum withdifferent temperature between drum metal and feed watergreater than 50 C— All fan must be operated when add bed material
  • 160. 160Operating precautionsRefractory— When entering cyclone be aware a chance of falling down— Refractory retain heat for long period. Be prepared for hotsurface when enter this area— An excessive thermal cycle will reduce the life cycle ofrefractory— After refractory repair, air cure need to apply about 24 hror depend on manufacturer before heating cure— Heating cure shall be done carefully otherwise refractorylife will be reduced
  • 161. 161Operating precautionsSolid Fuel— Chemical analysis of all solid fuel shall be determined forfirst time and compared with OEM standard— Sizing is important— Burp feeding shall be performed during starting feedingsolid fuel instead of continuous feeding
  • 162. 1629. Basic CFB Boiler Control
  • 163. 163— Basic control— Furnace control— Main pressure control— Main steam pressure control— Drum level control— Feed tank control— Solid fuel control— Primary air control— Secondary air control— Oxygen control
  • 164. 164Basic control— Simple feedback controlPRIMARY VARIABLEXTKA T Af(x)SET POINTPROCESSMANIPULATED VARIABLE
  • 165. 165Basic control— Simple feed forward plus feedback controlPR IM ARY VARIABLEXTYTSECO NDARYVARIABLEA T Af(x)MANIPULATED VARIABLEPROCESSSET POINTK
  • 166. 166Basic control— Simple cascade controlPRIMARY VARIABLEXTZTKKSET POINTA ATPROCESSf(x)MANIPULATED VARIABLESECONDARYVARIABLE
  • 167. 167Basic controlCOSPPVPIDControl Mode of PID-MAN (Manual)-AUT (Automatic)-CAS (Cascade)Signal to open0-15 m3/h0-100% (closed à open)4-20 mAElectrical signal 4-20 mAEng. Unit 0-15 m3/hPercent 0-100 % 0-100%
  • 168. 168Feed water controlLTPTPIDPIDMake up waterHeating steamPressure-Manual mode 0-100% heating steam valveposition-Auto mode, specify pressure set point-Temperature compensationLevel-Manual mode 0-100% make up water valve-Auto mode, specify level set point-Temperature compensation-Protection, high level over flow
  • 169. 169Drum Level controlDP feedwater pumpControl valveA, SPM, 0-100%Main steam flowMain steam PressureManual mode, 0-100%control valveAuto mode, specify drumlevel. Automatically adjustvalveProtection-lower limit-2/3 principle- 10 s delay-Close steam valve for low level
  • 170. 170Main steam pressure controlSPPVFFCO
  • 171. 171CombustionCalculationSA SPPA SPTotal air SP Total Fuel SPFuel1 SP Fuel3 SPFuel2 SPPA.Fan Conveyor1 Conveyor2 Conveyor3SA.FanX -Main steamPressure
  • 172. 172Solid Fuel ControlMWTPIDCascadeAutoManualManual : speed of coal conveyor isspecified by operatorAuto : operator specify fuel flow loadCascade: fuel flow set point calculated bymain steam pressure control
  • 173. 173Primary air controlMPIDFTAutoCascadePVManualManual: position of damper isspecifiedAuto: desired air flow is specified byoperatorCascade: set point is calculated frommaster combustionFlow (interlock) > minimumPA wind box P > minimumPA running
  • 174. 174Secondary air controlMPIDAutoCascadeManualFTFTPTManualManualPID AutoCascadeLower SAUpper SAFTPV
  • 175. 175HP Blower Control— Pressure is controlled by control valve— Control valve is connected to primary air— It will release the air to primary air duct if pressure higherthan set point— If operating unit stop due to disturbance or pressure falldown, stand by unit shall be automatically started— Pressure should be higher than 300 mbar, boiler interlock— Pressure < 350 mbar parallel operation start
  • 176. 176Furnace Pressure controlMPIDPTAutoFurnacepressureManualPIDManualAuto2/3 furnace P < max (35 mbar)
  • 177. 177Lime stone control— Lime stone can be control by— lime stone/ fuel flow ratio— SO2 feed back control— Manual feed rate
  • 178. 178Fuel oil controlMAPressure controlPressurecontrol valveFlow controlvalveAutoManual
  • 179. 179Referenced• Prabir Basu , Combustion and gasification in fluidized bed, 2006• Fluidized bed combustion, Simeon N. Oka, 2004• Nan Zh., et al, 3D CFD simulation of hydrodynamics of a 150 MWe circulating fluidized bedboiler, Chemical Engineering Journal, 162, 2010, 821-828• Zhang M., et al, Heat Flux profile of the furnace wall of 300 MWe CFB Boiler, powdertechnology, 203, 2010, 548-554• Foster Wheeler, TKIC refresh training, 2008• M. Koksal and F. Humdullahper , Gas Mixing in circulating fluidized beds with secondaryair injection, Chemical engineering research and design, 82 (8A), 2004, 979-992