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BASIC DESIGN OF   CIRCULATING FLUIDIZED BED            BOILER                    8 FEBRUARY 2012               Pichai Chai...
BiographyName :Pichai ChaibamrungEducation2009-2011, Ms.c, Thai-German Graduate School of Engineering2002-2006, B.E, Kaset...
Content1. Introduction to CFB2. Hydrodynamic of CFB3. Combustion in CFB4. Heat Transfer in CFB5. Basic design of CFB6. Cyc...
Objective•   To understand the typical arrangement in CFB•   To understand the basic hydrodynamic of CFB•   To understand ...
1. Introduction to CFB1.1 Development of CFB1.2 Typical equipment of CFB1.3 Advantage of CFB           By Chakraphong Phur...
1.1 Development of CFB• 1921, Fritz Winkler, Germany, Coal Gasification• 1938, Waren Lewis and Edwin Gilliland, USA, Fluid...
1.2 Typical Arrangement of CFB Boiler• CFB Loop  - Furnace or Riser  - Gas – Solid Separation (Cyclone)  - Solid Recycle S...
1.2 Typical Arrangement of CFB Boiler       By Chakraphong Phurngyai :: Engineer, TKIC
1.2 Typical Arrangement of CFB Boiler       By Chakraphong Phurngyai :: Engineer, TKIC
1.2 Typical Arrangement of CFB Boiler• Air System  - Primary air fan (PA. Fan)  - Secondary air fan (SA. Fan)  - Loop seal...
1.2 Typical Arrangement of CFB Boiler• Flue Gas Stream  - Induced draft fan (ID. Fan)                By Chakraphong Phurng...
1.2 Typical Arrangement of CFB Boiler• Solid Stream  - Fuel Bunker                 Feed  - Bed Bunker  - Sorbent Bunker   ...
1.2 Typical Arrangement of CFB Boiler• Water- Steam Circuit  - Economizer  - Steam drum  - Evaporator  - Superheater      ...
1.3 Advantage of CFB Boiler• Fuel Flexibility                 By Chakraphong Phurngyai :: Engineer, TKIC
1.3 Advantage of CFB Boiler• High Combustion Efficiency  - Good solid mixing  - Low unburned loss by cyclone, fly ash reci...
1.3 Advantage of CFB Boiler • In Situ Sulfur RemovalCalcination  Sulfation                 By Chakraphong Phurngyai :: Eng...
1.3 Advantage of CFB Boiler• Low Nitrogen Oxide Emissions              By Chakraphong Phurngyai :: Engineer, TKIC
2. Hydrodynamic in CFB2.1 Regimes of Fluidization2.2 Fast Fluidized Bed2.3 Hydrodynamic Regimes in CFB2.4 Hydrodynamic Str...
2.1 Regimes of Fluidization• Fluidization is defined as the operation through which fine solid are  transformed into a flu...
2.1 Regimes of Fluidization• Particle Classification   Distribution             Size (micron)                  Foster     ...
2.1 Regimes of Fluidization• Particle Classification                By Chakraphong Phurngyai :: Engineer, TKIC
2.1 Regimes of Fluidization• Comparison of Principal Gas-Solid Contacting Processes               By Chakraphong Phurngyai...
2.1 Regimes of Fluidization• Packed Bed  The pressure drop per unit height of a packed beds of a uniformly  size particles...
2.1 Regimes of Fluidization• Bubbling Fluidization Beds  Minimum fluidization velocity is velocity where the fluid drag is...
2.1 Regimes of Fluidization• Bubbling Fluidization Beds  For B and D particle, the bubble is started when superficial gas ...
2.1 Regimes of Fluidization• Turbulent Beds  when the superficial is continually increased through a bubbling  fluidizatio...
2.1 Regimes of Fluidization        By Chakraphong Phurngyai :: Engineer, TKIC
2.1 Regimes of Fluidization• Terminal Velocity   Terminal velocity is the particle velocity when the   forces acting on pa...
2.1 Regimes of Fluidization• Freeboard and Furnace Height  - considered for design heating-surface area  - considered for ...
2.2 Fast Fluidization• Definition               By Chakraphong Phurngyai :: Engineer, TKIC
2.2 Fast Fluidization• Characteristics of Fast Beds  - non-uniform suspension of slender particle agglomerates or  cluster...
2.3 Hydrodynamic regimes in a CFB  Cyclone Separator :      Swirl Flow                                                    ...
2.4 Hydrodynamic Structure of Fast Beds• Axial Voidage Profile                                                            ...
2.4 Hydrodynamic Structure of Fast Beds• Velocity Profile in Fast Fluidized Bed                By Chakraphong Phurngyai ::...
2.4 Hydrodynamic Structure of Fast Beds• Velocity Profile in Fast Fluidized Bed                By Chakraphong Phurngyai ::...
2.4 Hydrodynamic Structure of Fast Beds• Particle Distribution Profile in Fast Fluidized Bed                 By Chakraphon...
2.4 Hydrodynamic Structure of Fast Beds• Particle Distribution Profile in Fast Fluidized Bed                 By Chakraphon...
2.4 Hydrodynamic Structure of Fast Beds• Particle Distribution Profile in Fast Fluidized BedEffect of SA injection on part...
2.4 Hydrodynamic Structure of Fast Beds• Particle Distribution Profile in Fast Fluidized Bed                              ...
2.4 Hydrodynamic Structure of Fast Beds• Effects of Circulation Rate on Voidage Profile                                   ...
2.4 Hydrodynamic Structure of Fast Beds• Effects of Circulation Rate on Voidage Profile                                   ...
2.4 Hydrodynamic Structure of Fast Beds• Effect of Particle Size on Suspension Density Profile  - Fine particle - - > high...
2.4 Hydrodynamic Structure of Fast Beds• Effect of Bed Inventory on Suspension Density Profile                By Chakrapho...
2.4 Hydrodynamic Structure of Fast Beds• Core-Annulus Model  - the furnace may be spilt into two zones : core and annulusC...
2.4 Hydrodynamic Structure of Fast Beds• Core-Annulus Model                                                               ...
2.4 Hydrodynamic Structure of Fast Beds• Core Annulus Model  - the up-and-down movement solids in the core and annulus set...
3. Combustion in CFB3.1 Stage of Combustion3.2 Factor Affecting Combustion Efficiency3.3 Combustion in CFB3.4 Biomass Comb...
3.1 Stage of Combustion• A particle of solid fuel injected into an FB undergoes the following  sequence of events:  - Heat...
3.1 Stages of Combustion• Heating and Drying  - Combustible materials constitutes around 0.5-5.0% by weight    of total so...
3.1 Stages of Combustion• Devolatilization and volatile combustion  - first steady release 500-600 C  - second release 800...
3.1 Stages of Combustion• Char Combustion  2 step of char combustion       1. transportation of oxygen to carbon surface  ...
3.1 Stage of Combustion• Communition Phenomena During Combustion                                                          ...
3.2 Factor Affecting Combustion Efficiency• Fuel Characteristics  the lower ratio of FC/VM result in higher combustion eff...
3.2 Factor Affecting Combustion Efficiency• Operating condition (Bed Temperature)  - higher combustion temperature --- > h...
3.2 Factor Affecting Combustion Efficiency• Fuel Characteristic (Particle size)  -The effect of this particle size is not ...
3.2 Factor Affecting Combustion Efficiency• Operating condition (superficial velocity)  - high fluidizing velocity decreas...
3.2 Factor Affecting Combustion Efficiency• Operating condition (excess air)  - combustion efficiency improve which excess...
3.2 Factor Affecting Combustion Efficiency• Operating Condition  The highest loss of combustion result from elutriation of...
3.3 Combustion in CFB Boiler• Lower Zone Properties  - This zone is fluidized by primary air constituting about 40-80% of ...
3.3 Combustion in CFB Boiler• Upper Zone Properties  - Secondary is added at interface between lower and upper zone  - Oxy...
3.3 Combustion in CFB Boiler• Cyclone Zone Properties  - Normally, the combustion is small when compare to in furnace  - S...
3.4 Biomass Combustion• Fuel Characteristics  - high volatile content (60-80%)  - high alkali content à sintering, slaggin...
3.4 Biomass Combustion• Agglomeration  SiO2 melts at 1450 C  Eutectic Mixture melts at 874 C  Sintering tendency of fuel i...
3.4 Biomass Combustion• Options for Avoiding the Agglomeration Problem  - Use of additives       - china clay, dolomite, k...
3.4 Biomass Combustion• Agglomeration             By Chakraphong Phurngyai :: Engineer, TKIC
3.4 Biomass Combustion• Fouling  - is sticky deposition of ash due to evaporation of alkali salt  - result in low heat tra...
PB#11 : Fouling Problem (7 Aug 2010)                                               August 2010 1.Front water wall upper   ...
PB11 Fouling  May2010     Aug2010               Oct2010  6 months    2 months              2 monthsSevere problem in Super...
3.4 Biomass Combustion• Corrosion Potential in Biomass Firing  - hot corrosion  - chlorine reacts with alkali metal à from...
Foster Wheeler experience                                      Wood/Forest Residual                                       ...
3.5 Performance Modeling• Performance of Combustion  - Unburned carbon loss  - Distribution and mixing of volatiles, char ...
4. Heat Transfer in CFB4.1 Gas to Particle Heat Transfer4.2 Heat Transfer in CFB            By Chakraphong Phurngyai :: En...
4.1 Heat Transfer in CFB Boiler• Mechanism of Heat Transfer     In a CFB boiler, fine solid particles     agglomerate and ...
4.1 Heat Transfer in CFB Boiler• Effect of Suspension Density and particle size        Heat transfer coefficient is propor...
4.1 Heat Transfer in CFB Boiler• Effect of Fluidization Velocity      No effect from fluidization velocity when leave the ...
4.1 Heat Transfer in CFB Boiler• Effect of Fluidization Velocity                By Chakraphong Phurngyai :: Engineer, TKIC
4.1 Heat Transfer in CFB Boiler• Effect of Fluidization Velocity                By Chakraphong Phurngyai :: Engineer, TKIC
4.1 Heat Transfer in CFB Boiler• Effect of Vertical Length of Heat Transfer Surface                By Chakraphong Phurngya...
4.1 Heat Transfer in CFB Boiler• Effect of Bed Temperature              By Chakraphong Phurngyai :: Engineer, TKIC
4.1 Heat Transfer in CFB Boiler• Heat Flux on 300 MW CFB Boiler (Z. Man, et. al)                By Chakraphong Phurngyai :...
4.1 Heat Transfer in CFB Boiler• Heat transfer to the walls of commercial-size                                            ...
4.1 Heat Transfer in CFB Boiler• Circumferential Distribution of Heat Transfer Coefficient                By Chakraphong P...
5 Design of CFB Boiler•   5.1 Design and Required Data•   5.2 Combustion Calculation•   5.3 Heat and Mass Balance•   5.4 F...
5.1 Design and Required Data• The design and required data normally will be specify by owner or  client. The basic design ...
5.2 Combustion Calculation• Base on the design and required data the following data can be  calculated in this stage :  - ...
5.3 Heat and Mass Balance                                                                                            Heat ...
5.3 Heat and Mass Balance                                                                                              Mas...
5.4 Furnace Design•    The furnace design include:                           1. Furnace cross section1.   Furnace cross se...
5.4 Furnace Design2. Furnace height                                          3. Furnace opening    Criteria               ...
6. Cyclone Separator• 6.1 Theory• 6.2 Critical size of particle                 By Chakraphong Phurngyai :: Engineer, TKIC
6.1 Theory• The centrifugal force on the particle entering the cyclone is• The drag force on the particle can be written a...
6.1 Theory• Vr can be considered as index of cyclone efficiency, from above  equation the cyclone efficiency will increase...
6.2 Critical size of particle• The particle with a diameter larger than theoretical cut-size of  cyclone will be collected...
6.2 Critical size of particle   Effective number                                                        Ideal and operatio...
References•   Prabir Basu , Combustion and gasification in fluidized bed, 2006•   Fluidized bed combustion, Simeon N. Oka,...
THANK YOU FOR YOUR ATTENTION  By Chakraphong Phurngyai :: Engineer, TKIC
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Circulating fluidized bed boiler (cfb boiler) how does it work and its principle

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  • need a document on the calculations involving voidage,boiler height,change in preassure..etc..please share with me
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Circulating fluidized bed boiler (cfb boiler) how does it work and its principle

  1. 1. BASIC DESIGN OF CIRCULATING FLUIDIZED BED BOILER 8 FEBRUARY 2012 Pichai Chaibamrung Asset Optimization EngineerReliability Maintenance Asset Optimization Section Energy Division Thai Kraft Paper Industry Co.,Ltd.
  2. 2. BiographyName :Pichai ChaibamrungEducation2009-2011, Ms.c, Thai-German Graduate School of Engineering2002-2006, B.E, Kasetsart UnivesityWork ExperienceJul 11- present : Asset Optimization Engineer, TKICMay 11- Jun 11 : Sr. Mechanical Design Engineer, Poyry EnergySep 06-May 09 : Engineer, Energy Department, TKICEmail: ty_giuly@hotmail.com, pichacha@scg.co.th By Chakraphong Phurngyai :: Engineer, TKIC
  3. 3. Content1. Introduction to CFB2. Hydrodynamic of CFB3. Combustion in CFB4. Heat Transfer in CFB5. Basic design of CFB6. Cyclone Separator By Chakraphong Phurngyai :: Engineer, TKIC
  4. 4. Objective• 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 separator By Chakraphong Phurngyai :: Engineer, TKIC
  5. 5. 1. Introduction to CFB1.1 Development of CFB1.2 Typical equipment of CFB1.3 Advantage of CFB By Chakraphong Phurngyai :: Engineer, TKIC
  6. 6. 1.1 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, 15 MWth, Peat By Chakraphong Phurngyai :: Engineer, TKIC
  7. 7. 1.2 Typical Arrangement of CFB Boiler• CFB Loop - Furnace or Riser - Gas – Solid Separation (Cyclone) - Solid Recycle System (Loop Seal)• Convective or Back-Pass - Superheater - Reheater - Economizer - Air Heater By Chakraphong Phurngyai :: Engineer, TKIC
  8. 8. 1.2 Typical Arrangement of CFB Boiler By Chakraphong Phurngyai :: Engineer, TKIC
  9. 9. 1.2 Typical Arrangement of CFB Boiler By Chakraphong Phurngyai :: Engineer, TKIC
  10. 10. 1.2 Typical Arrangement of CFB Boiler• Air System - Primary air fan (PA. Fan) - Secondary air fan (SA. Fan) - Loop seal air fan or Blower By Chakraphong Phurngyai :: Engineer, TKIC
  11. 11. 1.2 Typical Arrangement of CFB Boiler• Flue Gas Stream - Induced draft fan (ID. Fan) By Chakraphong Phurngyai :: Engineer, TKIC
  12. 12. 1.2 Typical Arrangement of CFB Boiler• Solid Stream - Fuel Bunker Feed - Bed Bunker - Sorbent Bunker Drain - Bottom ash Bunker - Fly ash Bunker By Chakraphong Phurngyai :: Engineer, TKIC
  13. 13. 1.2 Typical Arrangement of CFB Boiler• Water- Steam Circuit - Economizer - Steam drum - Evaporator - Superheater By Chakraphong Phurngyai :: Engineer, TKIC
  14. 14. 1.3 Advantage of CFB Boiler• Fuel Flexibility By Chakraphong Phurngyai :: Engineer, TKIC
  15. 15. 1.3 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 By Chakraphong Phurngyai :: Engineer, TKIC
  16. 16. 1.3 Advantage of CFB Boiler • In Situ Sulfur RemovalCalcination Sulfation By Chakraphong Phurngyai :: Engineer, TKIC
  17. 17. 1.3 Advantage of CFB Boiler• Low Nitrogen Oxide Emissions By Chakraphong Phurngyai :: Engineer, TKIC
  18. 18. 2. Hydrodynamic in CFB2.1 Regimes of Fluidization2.2 Fast Fluidized Bed2.3 Hydrodynamic Regimes in CFB2.4 Hydrodynamic Structure of Fast Beds By Chakraphong Phurngyai :: Engineer, TKIC
  19. 19. 2.1 Regimes of Fluidization• Fluidization is defined as the operation through which fine solid are transformed into a fluid like state through contact with a gas or liquid. By Chakraphong Phurngyai :: Engineer, TKIC
  20. 20. 2.1 Regimes of Fluidization• Particle Classification Distribution Size (micron) Foster HGB PB#15 100% <600 <1000 <1680 75% <250 <550 <1190 50% <180 <450 <840 25% <130 <250 <590 100% >100 >420 By Chakraphong Phurngyai :: Engineer, TKIC
  21. 21. 2.1 Regimes of Fluidization• Particle Classification By Chakraphong Phurngyai :: Engineer, TKIC
  22. 22. 2.1 Regimes of Fluidization• Comparison of Principal Gas-Solid Contacting Processes By Chakraphong Phurngyai :: Engineer, TKIC
  23. 23. 2.1 Regimes of Fluidization• Packed Bed The pressure drop per unit height of a packed beds of a uniformly size particles is correlated as (Ergun,1952) Where U is gas flow rate per unit cross section of the bed called Superficial Gas Velocity By Chakraphong Phurngyai :: Engineer, TKIC
  24. 24. 2.1 Regimes of Fluidization• Bubbling Fluidization Beds Minimum fluidization velocity is velocity where the fluid drag is equal to a particle’s weight less its buoyancy. By Chakraphong Phurngyai :: Engineer, TKIC
  25. 25. 2.1 Regimes of Fluidization• Bubbling Fluidization Beds For B and D particle, the bubble is started when superficial gas is higher than minimum fluidization velocity But for group A particle the bubble is started when superficial velocity is higher than minimum bubbling velocity By Chakraphong Phurngyai :: Engineer, TKIC
  26. 26. 2.1 Regimes of Fluidization• Turbulent Beds when the superficial is continually increased through a bubbling fluidization bed, the bed start expanding, then the new regime called turbulent bed is started. By Chakraphong Phurngyai :: Engineer, TKIC
  27. 27. 2.1 Regimes of Fluidization By Chakraphong Phurngyai :: Engineer, TKIC
  28. 28. 2.1 Regimes of Fluidization• Terminal Velocity Terminal velocity is the particle velocity when the forces acting on particle is equilibrium By Chakraphong Phurngyai :: Engineer, TKIC
  29. 29. 2.1 Regimes of Fluidization• Freeboard and Furnace Height - considered for design heating-surface area - considered for design furnace height - to minimize unburned carbon in bubbling bed the freeboard heights should be exceed or closed to the transport disengaging heights By Chakraphong Phurngyai :: Engineer, TKIC
  30. 30. 2.2 Fast Fluidization• Definition By Chakraphong Phurngyai :: Engineer, TKIC
  31. 31. 2.2 Fast Fluidization• Characteristics of Fast Beds - non-uniform suspension of slender particle agglomerates or clusters moving up 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 leading particle decrease, fall under the gravity until it drops on to trailing particle By Chakraphong Phurngyai :: Engineer, TKIC
  32. 32. 2.3 Hydrodynamic regimes in a CFB Cyclone Separator : Swirl Flow Back Pass: Pneumatic Transport Furnace Upper SA: Fast Fluidized Bed Lower Furnace below SA: Turbulent or bubbling fluidized bed Return leg and lift leg :Pack bed and Bubbling Bed By Chakraphong Phurngyai :: Engineer, TKIC
  33. 33. 2.4 Hydrodynamic Structure of Fast Beds• Axial Voidage Profile Secondary air is fed Bed Density Profile of 135 MWe CFB Boiler (Zhang et al., 2005) By Chakraphong Phurngyai :: Engineer, TKIC
  34. 34. 2.4 Hydrodynamic Structure of Fast Beds• Velocity Profile in Fast Fluidized Bed By Chakraphong Phurngyai :: Engineer, TKIC
  35. 35. 2.4 Hydrodynamic Structure of Fast Beds• Velocity Profile in Fast Fluidized Bed By Chakraphong Phurngyai :: Engineer, TKIC
  36. 36. 2.4 Hydrodynamic Structure of Fast Beds• Particle Distribution Profile in Fast Fluidized Bed By Chakraphong Phurngyai :: Engineer, TKIC
  37. 37. 2.4 Hydrodynamic Structure of Fast Beds• Particle Distribution Profile in Fast Fluidized Bed By Chakraphong Phurngyai :: Engineer, TKIC
  38. 38. 2.4 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 By Chakraphong Phurngyai :: Engineer, TKIC
  39. 39. 2.4 Hydrodynamic Structure of Fast Beds• Particle Distribution Profile in Fast Fluidized Bed Increasing solid circulation Increasing SA to 40% rate effect to both does not significant on lower and upper zone suspension density above of SA injection point SA injection point which both zone is but the low zone is denser than low denser than low SA ratio solid circulation rate No SA, the suspension With SA 20% of PA, density is proportional the solid particle is hold up l to solid circulation rate when compare to no SA By Chakraphong Phurngyai :: Engineer, TKIC
  40. 40. 2.4 Hydrodynamic Structure of Fast Beds• Effects of Circulation Rate on Voidage Profile higher solid recirculation rate By Chakraphong Phurngyai :: Engineer, TKIC
  41. 41. 2.4 Hydrodynamic Structure of Fast Beds• Effects of Circulation Rate on Voidage Profile Pressure drop across the L-valve is proportional to solid recirculation rate higher solid recirculation rate By Chakraphong Phurngyai :: Engineer, TKIC
  42. 42. 2.4 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 By Chakraphong Phurngyai :: Engineer, TKIC
  43. 43. 2.4 Hydrodynamic Structure of Fast Beds• Effect of Bed Inventory on Suspension Density Profile By Chakraphong Phurngyai :: Engineer, TKIC
  44. 44. 2.4 Hydrodynamic Structure of Fast Beds• Core-Annulus Model - the furnace may be spilt into two zones : core and annulusCore- Velocity is above superficial velocity core- Solid move upwardAnnulus- Velocity is low to negative annulus- Solids move downward By Chakraphong Phurngyai :: Engineer, TKIC
  45. 45. 2.4 Hydrodynamic Structure of Fast Beds• Core-Annulus Model core annulus By Chakraphong Phurngyai :: Engineer, TKIC
  46. 46. 2.4 Hydrodynamic Structure of Fast Beds• Core Annulus Model - the up-and-down movement solids in the core and annulus sets up an internal circulation - the uniform bed temperature is a direct result of internal circulation By Chakraphong Phurngyai :: Engineer, TKIC
  47. 47. 3. Combustion in CFB3.1 Stage of Combustion3.2 Factor Affecting Combustion Efficiency3.3 Combustion in CFB3.4 Biomass Combustion By Chakraphong Phurngyai :: Engineer, TKIC
  48. 48. 3.1 Stage of Combustion• A particle of solid fuel injected into an FB undergoes the following 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 By Chakraphong Phurngyai :: Engineer, TKIC
  49. 49. 3.1 Stages of Combustion• Heating and Drying - Combustible materials constitutes around 0.5-5.0% by weight of total solids in combustor - Rate of heating 100 °C/sec – 1000 °C/sec - Heat transfer to a fuel particle (Halder 1989) By Chakraphong Phurngyai :: Engineer, TKIC
  50. 50. 3.1 Stages of Combustion• Devolatilization 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 devolatilze at 850 C (Basu and Fraser, 1991) By Chakraphong Phurngyai :: Engineer, TKIC
  51. 51. 3.1 Stages of Combustion• Char Combustion 2 step of char combustion 1. transportation of oxygen to carbon surface 2. Reaction of carbon with oxygen on the carbon surface 3 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 By Chakraphong Phurngyai :: Engineer, TKIC
  52. 52. 3.1 Stage of Combustion• Communition Phenomena During Combustion Attrition, Fine particles from coarse particles through mechanical contract like Volatile release in non-porous abrasion with other particles particle cause the high internal pressure result in break a coal particle into fragmentation Char burn under regime I which is mass transfer is higher than kinetic trasfer. The sudden collapse or other Volatile release cause the type of second fragmentation particle swell call percolative fragmentation occurs Char burn under regime I, II, the pores increases in size à weak bridge connection of carbon until it can’t withstand the hydrodynamic force. It will fragment again call “ secondary fragmentation” By Chakraphong Phurngyai :: Engineer, TKIC
  53. 53. 3.2 Factor Affecting Combustion Efficiency• Fuel Characteristics the lower ratio of FC/VM result in higher combustion efficiency (Makansi, 1990), (Yoshioka and Ikeda,1990), (Oka, 2004) but the improper mixing could result in lower combustion efficiency due to prompting escape of volatile gas from furnace. By Chakraphong Phurngyai :: Engineer, TKIC
  54. 54. 3.2 Factor Affecting Combustion Efficiency• Operating condition (Bed Temperature) - higher combustion temperature --- > high combustion efficiency Limit of Bed temp -Sulfur capture -Bed melting -Water tube failure High combustion temperature result in high oxidation reaction, then burn out time decrease. So the combustion efficiency increase. By Chakraphong Phurngyai :: Engineer, TKIC
  55. 55. 3.2 Factor Affecting Combustion Efficiency• Fuel Characteristic (Particle size) -The effect of this particle size is not clear -Fine particle, low burn out time but the probability to be dispersed from cyclone the high -Coarse size, need long time to burn out. -Both increases and decreases are possible when particle size decrease By Chakraphong Phurngyai :: Engineer, TKIC
  56. 56. 3.2 Factor Affecting Combustion Efficiency• Operating condition (superficial velocity) - high fluidizing velocity decrease combustion efficiency because Increasing probability of small char particle be elutriated from circulation loop - low fluidizing velocity cause defluidization, hot spot and sintering By Chakraphong Phurngyai :: Engineer, TKIC
  57. 57. 3.2 Factor Affecting Combustion Efficiency• Operating condition (excess air) - combustion efficiency improve which excess air < 20% Combustion loss decrease significantly when excess air < 20%. Excess air >20% less significant improve combustion efficiency. By Chakraphong Phurngyai :: Engineer, TKIC
  58. 58. 3.2 Factor Affecting Combustion Efficiency• Operating Condition The highest loss of combustion result from elutriation of char particle from circulation loop. Especially, low reactive coal size smaller than 1 mm it can not achieve complete combustion efficiency with out fly ash recirculation system. However, the significant efficiency improve is in range 0.0-2.0 fly ash recirculation ratio. By Chakraphong Phurngyai :: Engineer, TKIC
  59. 59. 3.3 Combustion in CFB Boiler• Lower Zone Properties - This zone is fluidized by primary air constituting about 40-80% of total air. - This zone receives fresh coal from coal feeder and unburned coal from cyclone though return valve - Oxygen deficient zone, lined with refractory to protect corrosion - Denser than upper zone By Chakraphong Phurngyai :: Engineer, TKIC
  60. 60. 3.3 Combustion in CFB Boiler• Upper Zone Properties - Secondary is added at interface between lower and upper zone - Oxygen-rich zone - Most of char combustion occurs - Char particle could make many trips around the furnace before they are finally entrained out through the top of furnace By Chakraphong Phurngyai :: Engineer, TKIC
  61. 61. 3.3 Combustion in CFB Boiler• Cyclone Zone Properties - Normally, the combustion is small when compare to in furnace - Some boiler may experience the strong combustion in this zone which can be observe by rising temperature in the cyclone exit and loop seal By Chakraphong Phurngyai :: Engineer, TKIC
  62. 62. 3.4 Biomass Combustion• Fuel Characteristics - high volatile content (60-80%) - high alkali content à sintering, slagging, and fouling - high chlorine content à corrosion By Chakraphong Phurngyai :: Engineer, TKIC
  63. 63. 3.4 Biomass Combustion• Agglomeration SiO2 melts at 1450 C Eutectic Mixture melts at 874 C Sintering tendency of fuel is indicated by the following (Hulkkonen et al., 2003) By Chakraphong Phurngyai :: Engineer, TKIC
  64. 64. 3.4 Biomass Combustion• Options 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 By Chakraphong Phurngyai :: Engineer, TKIC
  65. 65. 3.4 Biomass Combustion• Agglomeration By Chakraphong Phurngyai :: Engineer, TKIC
  66. 66. 3.4 Biomass Combustion• Fouling - is sticky deposition of ash due to evaporation of alkali salt - result in low heat transfer to tube By Chakraphong Phurngyai :: Engineer, TKIC
  67. 67. PB#11 : Fouling Problem (7 Aug 2010) August 2010 1.Front water wall upper opening inlet 4. Screen tube & SH#3 - Overlay tube (26Tubes) - Slag - Replace refractory 2.Right water wall - Change new tubes (4 Tubes) May 2010 Aug 2010 5.Roof water wall -Change new tubes (4 Tubes) - Overlay tube - More erosion rate 1.5 mm/2.5 months 3.Front water wall - Add refractory 2 m. (Height) above kick-out By Chakraphong Phurngyai :: Engineer, TKIC
  68. 68. PB11 Fouling May2010 Aug2010 Oct2010 6 months 2 months 2 monthsSevere problem in Superheat tube fouling•Waste reject fuel (Hi Chloride content)•Only PB11 has this problems •this problems also found on PB15 (SD for Cleaning every 3 months) By Chakraphong Phurngyai :: Engineer, TKIC
  69. 69. 3.4 Biomass Combustion• Corrosion Potential in Biomass Firing - hot corrosion - chlorine reacts with alkali metal à from low temperature melting alkali chlorides - reduce heat transfer and causing high temperature corrosion By Chakraphong Phurngyai :: Engineer, TKIC
  70. 70. Foster Wheeler experience Wood/Forest Residual Straw,Rice husk Waste Reject By Chakraphong Phurngyai :: Engineer, TKIC
  71. 71. 3.5 Performance Modeling• Performance of Combustion - Unburned carbon loss - Distribution and mixing of volatiles, char and oxygen along the height and cross section of furnace - Flue gas composition at the exit of the cyclone separator (NOx,SOx) - Heat release and absoption pattern in the furnace - Solid waste generation By Chakraphong Phurngyai :: Engineer, TKIC
  72. 72. 4. Heat Transfer in CFB4.1 Gas to Particle Heat Transfer4.2 Heat Transfer in CFB By Chakraphong Phurngyai :: Engineer, TKIC
  73. 73. 4.1 Heat Transfer in CFB Boiler• Mechanism of Heat Transfer In a CFB boiler, fine solid particles agglomerate and form clusters or stand in a continuum of generally up-flowing gas containing sparsely dispersed solids. The continuum is called the dispersed phase, while the agglomerates are called the cluster phase. The heat transfer to furnace wall occurs through conduction from particle clusters, convection from dispersed phase, and radiation from both phase. By Chakraphong Phurngyai :: Engineer, TKIC
  74. 74. 4.1 Heat Transfer in CFB Boiler• Effect of Suspension Density and particle size Heat transfer coefficient is proportional to the square root of suspension density By Chakraphong Phurngyai :: Engineer, TKIC
  75. 75. 4.1 Heat Transfer in CFB Boiler• Effect of Fluidization Velocity No effect from fluidization velocity when leave the suspension density constant By Chakraphong Phurngyai :: Engineer, TKIC
  76. 76. 4.1 Heat Transfer in CFB Boiler• Effect of Fluidization Velocity By Chakraphong Phurngyai :: Engineer, TKIC
  77. 77. 4.1 Heat Transfer in CFB Boiler• Effect of Fluidization Velocity By Chakraphong Phurngyai :: Engineer, TKIC
  78. 78. 4.1 Heat Transfer in CFB Boiler• Effect of Vertical Length of Heat Transfer Surface By Chakraphong Phurngyai :: Engineer, TKIC
  79. 79. 4.1 Heat Transfer in CFB Boiler• Effect of Bed Temperature By Chakraphong Phurngyai :: Engineer, TKIC
  80. 80. 4.1 Heat Transfer in CFB Boiler• Heat Flux on 300 MW CFB Boiler (Z. Man, et. al) By Chakraphong Phurngyai :: Engineer, TKIC
  81. 81. 4.1 Heat Transfer in CFB Boiler• Heat transfer to the walls of commercial-size Low suspension density low heat transfer to the wall. By Chakraphong Phurngyai :: Engineer, TKIC
  82. 82. 4.1 Heat Transfer in CFB Boiler• Circumferential Distribution of Heat Transfer Coefficient By Chakraphong Phurngyai :: Engineer, TKIC
  83. 83. 5 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 Heat Absorption By Chakraphong Phurngyai :: Engineer, TKIC
  84. 84. 5.1 Design and Required Data• The design and required data normally will be specify by owner or 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 By Chakraphong Phurngyai :: Engineer, TKIC
  85. 85. 5.2 Combustion Calculation• Base on the design and required data the following data can be calculated in this stage : - Fuel flow rate - Combustion air flow rate - Fan capacity - Fuel and ash handling capacity - Sorbent flow rate By Chakraphong Phurngyai :: Engineer, TKIC
  86. 86. 5.3 Heat and Mass Balance Heat input• Heat Balance Main steam Heat output Radiation Feed water Blow down Flue gas Moisture in fuel Unburned in fly ash and sorbent Fuel and sorbent Combustion air Unburned in Moisture in bottom ash combustion air By Chakraphong Phurngyai :: Engineer, TKIC
  87. 87. 5.3 Heat and Mass Balance Mass input• Mass Balance Mass output Solid Flue in Flue gas Solid gas Make up bed material Fuel and sorbent Moisture in fuel fly ash and sorbent Fuel and sorbent Make up bed material fly ash bottom ash bottom ash By Chakraphong Phurngyai :: Engineer, TKIC
  88. 88. 5.4 Furnace Design• The furnace design include: 1. Furnace cross section1. Furnace cross section Criteria2. Furnace height - moisture in fuel3. Furnace opening - ash in fuel - fluidization velocity - SA penetration - maintain fluidization in lower zone at part load By Chakraphong Phurngyai :: Engineer, TKIC
  89. 89. 5.4 Furnace Design2. Furnace height 3. Furnace opening Criteria Criteria - Heating surface - Fuel feed ports - Residual time for sulfur capture - Sorbent feed ports - Bed drain ports - Furnace exit section By Chakraphong Phurngyai :: Engineer, TKIC
  90. 90. 6. Cyclone Separator• 6.1 Theory• 6.2 Critical size of particle By Chakraphong Phurngyai :: Engineer, TKIC
  91. 91. 6.1 Theory• The centrifugal force on the particle entering the cyclone is• The drag force on the particle can be written as• Under steady state drag force = centrifugal force By Chakraphong Phurngyai :: Engineer, TKIC
  92. 92. 6.1 Theory• Vr can be considered as index of cyclone efficiency, from above equation the cyclone efficiency will increase for : - Higher entry velocity - Large size of solid - Higher density of particle - Small radius of cyclone - Higher value of viscosity of gas By Chakraphong Phurngyai :: Engineer, TKIC
  93. 93. 6.2 Critical size of particle• The particle with a diameter larger than theoretical cut-size of cyclone will be collected or trapped by cyclone while the small size will be entrained or leave a cyclone• Actual operation, the cut-off size diameter will be defined as d50 that mean 50% of the particle which have a diameter more than d50 will be collected or captured. By Chakraphong Phurngyai :: Engineer, TKIC
  94. 94. 6.2 Critical size of particle Effective number Ideal and operation efficiency By Chakraphong Phurngyai :: Engineer, TKIC
  95. 95. References• 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 bed boiler, Chemical Engineering Journal, 162, 2010, 821-828• Zhang M., et al, Heat Flux profile of the furnace wall of 300 MWe CFB Boiler, powder technology, 203, 2010, 548-554• Foster Wheeler, TKIC refresh training, 2008• M. Koksal and F. Humdullahper , Gas Mixing in circulating fluidized beds with secondary air injection, Chemical engineering research and design, 82 (8A), 2004, 979-992 By Chakraphong Phurngyai :: Engineer, TKIC
  96. 96. THANK YOU FOR YOUR ATTENTION By Chakraphong Phurngyai :: Engineer, TKIC

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