principle of cfb boiler , 30 april 2012, presented at scgbkk ,th
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BASIC DESIGN OFCIRCULATING FLUIDIZED BED
BOILER
30 APIRL 2012, Bangkok, Thailand
Pichai Chaibamrung Asset Optimization Engineer
Asset Optimization and Reliability Section
Energy Division
Thai Kraft Paper Industry Co.,Ltd.
By Chakraphong Phurngyai :: Engineer, TKIC
Biography
Name :Pichai Chaibamrung
Education
2009-2011, Ms.c, Thai-German Graduate School of Engineering
2002-2006, B.E, Kasetsart Univesity
Work Experience
Jul 11- present : Asset Optimization Engineer, TKIC
May 11- Jun 11 : Sr. Mechanical Design Engineer, Poyry Energy
Sep 06-May 09 : Engineer, Energy Department, TKIC
Email: pichacha@scg.co.th
By Chakraphong Phurngyai :: Engineer, TKIC
Content
1. Introduction to CFB
2. Hydrodynamic of CFB
3. Combustion in CFB
4. Heat Transfer in CFB
5. Basic design of CFB
6. Cyclone Separator
7. Operation Optimization
By Chakraphong Phurngyai :: Engineer, TKIC
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
• To have awareness on operation optimization
By Chakraphong Phurngyai :: Engineer, TKIC
1. Introduction to CFB
1.1 Development of CFB
1.2 Typical equipment of CFB
1.3 Advantage of CFB
By Chakraphong Phurngyai :: Engineer, TKIC
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
1.2 Typical Arrangement of CFB Boiler
By Chakraphong Phurngyai :: Engineer, TKIC
1.2 Typical Arrangement of CFB Boiler
By Chakraphong Phurngyai :: Engineer, TKIC
1.3 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 recirculation
- Long combustion zone
• In situ sulfur removal
• Low nitrogen oxide emission
By Chakraphong Phurngyai :: Engineer, TKIC
2. Hydrodynamic in CFB
2.1 Regimes of Fluidization
2.2 Fast Fluidized Bed
2.3 Hydrodynamic Regimes in CFB
2.4 Hydrodynamic Structure of Fast Beds
By Chakraphong Phurngyai :: Engineer, TKIC
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
2.1 Regimes of Fluidization
• Particle Classification
<130
<180
<250
<600
Foster
Size (micron)
<590<25025%
>420>100100%
<840<45050%
75%
100%
Distribution
<1190<550
<1680<1000
PB#15HGB
By Chakraphong Phurngyai :: Engineer, TKIC
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 :: Engineer, TKIC
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
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
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
2.1 Regimes of Fluidization
• Turbulent Beds
when the superficial is continually increased through a bubblingfluidization bed, the bed start expanding, then the new regime called turbulent bed is started.
By Chakraphong Phurngyai :: Engineer, TKIC
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 particle is equilibrium
By Chakraphong Phurngyai :: Engineer, TKIC
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
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 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
2.3 Hydrodynamic regimes in a CFB
Lower Furnace below SA: Turbulent or bubbling
fluidized bed
Furnace Upper SA: Fast Fluidized Bed
Cyclone Separator :Swirl Flow
Return leg and lift leg : Pack bed and Bubbling Bed
Back Pass:Pneumatic Transport
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Axial Voidage Profile
Bed Density Profile of 135 MWe CFB Boiler (Zhang et al., 2005)
Secondary air is fed
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Velocity Profile in Fast Fluidized Bed
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Velocity Profile in Fast Fluidized Bed
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Particle Distribution Profile in Fast Fluidized Bed
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Particle Distribution Profile in Fast Fluidized Bed
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Particle Distribution Profile in Fast Fluidized Bed
Effect of SA injection on particle distribution by M.Koksal and F.Hamdullahpur (2004). The experimental CFB is pilot scale CFB. There are three orientations of SA injection; radial, tangential, and mixed
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Particle Distribution Profile in Fast Fluidized Bed
No SA, the suspension density is proportional
l to solid circulation rate
With SA 20% of PA, the solid particle is hold up
when compare to no SA
Increasing SA to 40%does not significant on
suspension density aboveSA injection point but the low zone is
denser than low SA ratio
Increasing solid circulationrate effect to both
lower and upper zoneof SA injection pointwhich both zone is
denser than lowsolid circulation rate
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Effects of Circulation Rate on Voidage Profile
higher solid recirculation rate
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Effects of Circulation Rate on Voidage Profile
higher solid recirculation rate
Pressure drop across the L-valve is proportional to solid recirculation rate
By Chakraphong Phurngyai :: Engineer, TKIC
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
2.4 Hydrodynamic Structure of Fast Beds
• Core-Annulus Model
- the furnace may be spilt into two zones : core and annulus
Core
- Velocity is above superficial velocity
- Solid move upward
Annulus
- Velocity is low to negative
- Solids move downward
core
annulus
By Chakraphong Phurngyai :: Engineer, TKIC
2.4 Hydrodynamic Structure of Fast Beds
• Core-Annulus Model
core
annulus
By Chakraphong Phurngyai :: Engineer, TKIC
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
3. Combustion in CFB
3.1 Stage of Combustion
3.2 Factor Affecting Combustion Efficiency
3.3 Combustion in CFB
3.4 Biomass Combustion
By Chakraphong Phurngyai :: Engineer, TKIC
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
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
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
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
3.1 Stage of Combustion
• Communition Phenomena During Combustion
Volatile release cause the particle swell
Volatile release in non-porous particle cause the high internal pressure result in break a coal particle into fragmentation
Char burn under regime I, II, the pores increases in size àweak bridge connection of carbon until it can’t withstand the hydrodynamic force. It will fragment again call “secondary fragmentation”
Attrition, Fine particles from coarse particles through mechanical contract like abrasion with other particles
Char burn under regime I which is mass transfer is higher than kinetic trasfer. The sudden collapse or other type of second fragmentation call percolative fragmentationoccurs
By Chakraphong Phurngyai :: Engineer, TKIC
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
3.2 Factor Affecting Combustion Efficiency
• Operating condition (Bed Temperature)
- higher combustion temperature --- > high combustion efficiency
High combustion temperature result in high oxidation reaction, then burn out time decrease. So the combustion efficiency increase.
Limit of Bed temp
-Sulfur capture
-Bed melting
-Water tube failure
By Chakraphong Phurngyai :: Engineer, TKIC
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
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
3.2 Factor Affecting Combustion Efficiency
• Operating condition (excess air)
- combustion efficiency improve which excess air < 20%
Excess air >20% less significant improve combustion efficiency.
Combustion loss decrease significantly when excess air < 20%.
By Chakraphong Phurngyai :: Engineer, TKIC
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
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
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
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
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
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
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
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 transfer to tube
By Chakraphong Phurngyai :: Engineer, TKIC
August 2010August 2010PB#11 : Fouling Problem (7 Aug 2010)
3.Front water wall- Add refractory 2 m. (Height) above kick-out
2.Right water wall- Change new tubes (4 Tubes)
5.Roof water wall-Change new tubes (4 Tubes)- Overlay tube - More erosion rate 1.5 mm/2.5 months
4. Screen tube & SH#3 - พบ Slag ทีเ่กาะจาํนวนมาก
1.Front water wall upper opening inlet
- Overlay tube (26Tubes)- Replace refractory
May 2010 Aug 2010
By Chakraphong Phurngyai :: Engineer, TKIC
PB11 Fouling
May20106 months
Aug20102 months
Oct20102 months
Severe 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
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
Foster Wheeler experience Wood/Forest Residual
Straw,Rice husk
Waste Reject
By Chakraphong Phurngyai :: Engineer, TKIC
3.5 Performance Modeling
• Performance of Combustion
- Unburned carbon loss
- Distribution and mixing of volatiles, char and oxygen along theheight 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
4. Heat Transfer in CFB
4.1 Gas to Particle Heat Transfer
4.2 Heat Transfer in CFB
By Chakraphong Phurngyai :: Engineer, TKIC
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
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
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
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 Phurngyai :: Engineer, TKIC
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 :: Engineer, TKIC
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
4.1 Heat Transfer in CFB Boiler
• Circumferential Distribution of Heat Transfer Coefficient
By Chakraphong Phurngyai :: Engineer, TKIC
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
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 properties
Required Data :
- Main steam properties - Flue gas temperature
- Flue gas emission - Boiler efficiency
By Chakraphong Phurngyai :: Engineer, TKIC
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
5.3 Heat and Mass Balance
• Heat Balance
Fuel and sorbent
Unburned in bottom ash
Feed water
Combustion air
Main steam
Blow down
Flue gas
Moisture in fuel and sorbent
Unburned in fly ash
Moisture in combustion air
Radiation
Heat input
Heat output
By Chakraphong Phurngyai :: Engineer, TKIC
5.3 Heat and Mass Balance
• Mass Balance
Fuel and sorbent
bottom ash
Solid Flue gas
Moisture in fuel and sorbent
fly ash
Mass input
Make up bed material
bottom ash
Fuel and sorbent
Make up bed material
Solid in Flue gas
fly ash
Mass output
By Chakraphong Phurngyai :: Engineer, TKIC
5.4 Furnace Design
• The furnace design include:
1. Furnace cross section
2. Furnace height
3. Furnace opening
1. Furnace cross section
Criteria
- moisture in fuel
- ash in fuel
- fluidization velocity
- SA penetration
- maintain fluidization in lower zone at part load
By Chakraphong Phurngyai :: Engineer, TKIC
5.4 Furnace Design
2. Furnace height
Criteria
- Heating surface
- Residual time for sulfur capture
3. Furnace opening
Criteria
- Fuel feed ports
- Sorbent feed ports
- Bed drain ports
- Furnace exit section
By Chakraphong Phurngyai :: Engineer, TKIC
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 as
• Under steady state drag force = centrifugal force
By Chakraphong Phurngyai :: Engineer, TKIC
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
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
6.2 Critical size of particle
Effective number
Ideal and operation efficiency
By Chakraphong Phurngyai :: Engineer, TKIC
7. Operation Optimization
7.1 Maximization vs. Optimization
7.2 Choice for Optimization
7.3 Case Study
By Chakraphong Phurngyai :: Engineer, TKIC
7.1 Maximization vs Optimizaiton
• Maximization
objective is to get the highest performance considering only oneoperating variable
• Optimizationobjective is to get the best performance considering many operating variables. Many of these operating variables have exactly the opposite effect, making it impossible to get the highest performance from each of these variables
By Chakraphong Phurngyai :: Engineer, TKIC
7.2 Choices for Optimization
• Combustion efficiency
• Boiler efficiency
• Unburned carbon content in fly ash
• Wear of tubes as result of erosion and reducing conditions
• Fuel mix (percentage of different fuels) at different operation conditions
• Power consumption (net output of plant)
• SO2 emissions
• NOx emissions
• Air split (split between PA, and SA)
• Sootblowing cycle
• Excess air (related to boiler efficiency)
• Bed inventory
By Chakraphong Phurngyai :: Engineer, TKIC
7.3 Case Study
Case I PB#16 High bed Temperature
Advantage
- higher combustion efficiency.
Concerning parameter
- high bed temp mean higher flue gas volume
- high flue gas volume higher fluidization velocity
- high fluidization velocity, higher erosion
- high bed temp., higher probability for NOx emission
- higher lime stone consumption
- ash Sintering
- materials break up due to over heating
By Chakraphong Phurngyai :: Engineer, TKIC
7.3 Case Study
• Operation Survey
- Average bed temp 920-935 C (some point >970 C)
- Bed pressure 30-40 mbar
- PA/SA ratio 0.68 : 0.32
- Boiler load > 90%
- SA upper / lower ratio 0.75 : 0.25
- O2 4%
- CO 0.04 ppm
By Chakraphong Phurngyai :: Engineer, TKIC
7.3 Case Study
• What we found. What we have done.
Found : Bed pressure is lower when comparing to other unit.Typically, 50 mbar.
Done : increasing bed pressure to 50 mbar.
Result : bed temperature dramatically decrease.
Concerning : power consumption of PA is slightly increased
Learning point ?
By Chakraphong Phurngyai :: Engineer, TKIC
7.3 Case Study
• What we found. What we have done.
Found : ratio of PA/TA is low
Done : increasing PA ratio from 68% to 70-71%
Result : bed temperature dramatically decrease.
Concerning : Power consumption of PA increase, high DP over grid nozzle
Learning point ?
By Chakraphong Phurngyai :: Engineer, TKIC
7.3 Case Study
• What we found. What we have done.
Found : ratio of SA lower/ upper is low
Done : increasing SA flow by partial close SA upper valve
Result : bed temperature dramatically decrease. SA pressure increase
Concerning : SA power consumption is increased
Learning point ?
By Chakraphong Phurngyai :: Engineer, TKIC
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 airinjection, Chemical engineering research and design, 82 (8A), 2004, 979-992
By Chakraphong Phurngyai :: Engineer, TKIC
THANK YOU FOR YOUR ATTENTION
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