CFD-Based Models of Entrained-Flow Coal Gasifiers with...
Transcript of CFD-Based Models of Entrained-Flow Coal Gasifiers with...
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Mike Bockelie, Martin Denison, Zumao Chen, Temi Linjewile, Connie Senior and Adel Sarofim
Reaction Engineering International
Collaboration: N. Holt (EPRI), K.Hein (IVD, Germany)T.Wall, Peter Benyon, David Harris, John Kent (Black Coal CCSD, Australia)
Colloquium on Black Liquor Combustion and GasificationMay 13-16, 2003, Park City Marriott, Park City, Utah
DOE Vision 21 Program Cost Shared Agreement DE-FC26-00NT41047
CFD-Based Models of Entrained-Flow Coal Gasifiers with Emphasis on
Slag Deposition and Flow
Outline• Motivation• Gasifier Model• Slag Submodel• One stage results• Two stage results• Summary
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Carbon Conversion & Syngas Quality
See Gasification Technologies 2001:• Stiegel, Clayton and Wimer• HoltSee Clearwater 2002• Dogan
• Fuel Switching– Coal, Petcoke, Blends
• Fuel Feed System – Dry (N2, CO2); Wet (H2O)– Pre-heat– Oxidant: Air vs O2
• Injector Modifications • L/D ratio (volume)• System pressure
Other Considerations• Slag and Ash Management
– Viscosity, composition, flux mat’l– Carbon content: slag vs flyash
• Refractory Wear– Heat extraction
• Transient Operation – start-up– Shutdown– Switching– Upsets
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Gasifier – Process Model• fast running model to asses
operating conditions• mass & energy balance
– particle burnout + equilibrium chemistry
– heat transfer– critical viscosity
• Includes impacts of:– fuel type, recycled char– ash composition– oxidant conditions– wet vs dry feed– particle size– residence time
• Predicts– carbon conversion, unburned
carbon in slag & flyash– syngas temperature,
composition, carryover– slag flow indicator
CFD Model
• Geometry• Wall Properties• Fuel & Oxidant
– Properties– Composition
• Ultimate, proximate• Ash composition
– Temperature– Particle grind– Splits
• Multiple Injectors• Quench
• Carbon Conversion• Flow Patterns & Velocities• Gas & Surface Temperatures• Gas Species Concentrations
– Major : CO2, CH4, H2, H2O, N2, O2– Minor: H2S, COS, NH3, HCN,….– Reducing vs oxidizing
• Wall Heat Transfer– Incident, net flux– Backside cooling
• Particle / Droplet Trajectories and Reactions– Time temperature histories– Wall deposition– Flyash (Unburned carbon)– Slag
• Temperature, viscosity, thickness• composition
Inputs Outputs = Predicted Values
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Gasifier CFD Model• Computer model represents
– Gasifier geometry – Operating conditions– Gasification processes
• Accuracy depends on– Input accuracy– Numerics– Representation of
physics & chemistry
Turbulence
ParticleReactions
Surface Properties
Gasification & CombustionChemistry
Radiation &Convection
Fuel Conversion
Slag Flow Model• Model accounts
for:– Wall refractory
properties– Back side cooling– Fire side flow field – Fuel ash
properties• Based on work by
– Benyon– Seggiani– Senior
Hot GasS
Liquid Slag
xy
u (x, y)
RefractoryLining
Metal Wall
Coolant
Qradiation
Hot ParticlesSolid Slag Layer
Qconvection
TAmbient
Tw
Ts
TiTw1
Tw2
Hot GasHot GasS
Liquid Slag
xy
u (x, y)
RefractoryLining
Metal Wall
Coolant
Qradiation
Hot ParticlesSolid Slag Layer
Qconvection
TAmbient
Tw
Ts
TiTw1
Tw2 Tw
Ts
TiTw1
Tw2
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CFD model provides• Incident heat flux
– Radiation– Convection
• Particle deposition on wall– Rate– Composition (ash,
carbon)– Burning on wall
Hot GasS
Liquid Slag
xy
u (x, y)
RefractoryLining
Metal Wall
Coolant
Qradiation
Hot ParticlesSolid Slag Layer
Qconvection
TAmbient
Tw
Ts
TiTw1
Tw2
Hot GasHot GasS
Liquid Slag
xy
u (x, y)
RefractoryLining
Metal Wall
Coolant
Qradiation
Hot ParticlesSolid Slag Layer
Qconvection
TAmbient
Tw
Ts
TiTw1
Tw2 Tw
Ts
TiTw1
Tw2
Slag model computes• Ash viscosity (ash
chemistry)
• Tcv = Temperature of critical viscosity (ash chemistry)
• Liquid slag velocity profile
• Slag surface temperature
• Liquid & frozen slag layer thickness
• Heat transfer through wall
Hot GasS
Liquid Slag
xy
u (x, y)
RefractoryLining
Metal Wall
Coolant
Qradiation
Hot ParticlesSolid Slag Layer
Qconvection
TAmbient
Tw
Ts
TiTw1
Tw2
Hot GasHot GasS
Liquid Slag
xy
u (x, y)
RefractoryLining
Metal Wall
Coolant
Qradiation
Hot ParticlesSolid Slag Layer
Qconvection
TAmbient
Tw
Ts
TiTw1
Tw2 Tw
Ts
TiTw1
Tw2TBeTA / = µ
θθ
θ∫
ρ
θd
eA ) - T(
)T,x(q
k g = T) u(x, /BnsT
Tss
2
w
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Slag model computes• Info returned to
CFD model– slag surface
temperature
Hot GasS
Liquid Slag
xy
u (x, y)
RefractoryLining
Metal Wall
Coolant
Qradiation
Hot ParticlesSolid Slag Layer
Qconvection
TAmbient
Tw
Ts
TiTw1
Tw2
Hot GasHot GasS
Liquid Slag
xy
u (x, y)
RefractoryLining
Metal Wall
Coolant
Qradiation
Hot ParticlesSolid Slag Layer
Qconvection
TAmbient
Tw
Ts
TiTw1
Tw2 Tw
Ts
TiTw1
Tw2
Temperature at Critical Viscosity (Tcv)Correlated Fit with Measured Data
Where α = SiO2/Al2O3 and β = Fe2O3 + CaO + MgOSiO2 + Al2O3 + Fe2O3 + CaO + MgO = 100 [weight%]
22cv 860. + 8.67 - 5.74 + 5.519 - 4523 = [K] T ββαα Measured data from
Patterson et al, 2001
1000
1200
1400
1600
1800
2000
1300 1400 1500 1600 1700 1800Measured TCV (K)
Pred
icte
d TC
V (K
)
+15%
-15%
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Example Results
1-stage up flow 2-stage up flow
Single Stage – Up Flow• Firing Conditions
– [Benyon, 2002], [Seggiani, 1998]– Pressure = 25 atm.– 2600 tpd dried bituminous coal
• 22% ash– Dry feed
• N2:Coal (lb) = 0.075– Oxidant
• 76% O2 , 11% H20, 10% N2, 3% Ar• O2:C (molar) = 0.46• Inlet Stoichiometry ~ 0.4
L
0.2 D
0.75 D
D
0.1 D
0.4 D
L/D = 1.75D = 3.7m Injector
Orientation
5.5--Deposition (%)
4642(4248)(4431)HHV (Btu/lb)-
-
--
1.83.2
76.51803
Seggiani
(91.5)
-
--
1.810.070.9
(1650)Benyon
~100Carbon Conversion(%)
83.1Cold-Gas Efficiency (%)
REIExit Conditions
3.0H2O (wt %)10.1N2 (wt %)
1.9H2 (wt %)6.2CO2 (wt %)
76.6CO (wt %)1740Gas Temp (K)
water jacketcooled
(…) = estimated value
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Slag Model Summary
0
1
2
3
4
5
6
7
8
1000 1300 1600 1900 2200
Slag surface temperature, K
Gas
ifier h
eigh
t, m
0
2
3
4
5
6
7
8
0 100000 200000 300000 400000
Heat f lux, W/m2
0 0.005 0.01 0.015 0.02
Liquid slag thickness, m
0 0.02 0.04 0.06 0.08 0.1
Solid slag thickness, m
Slag SurfaceTemperature
Seggiani
Benyon
REI
Heat Flux to Slag
Liquid Slag Thickness
Solid Slag Thickness
Critical Viscosity ~ 1625 K
Slag Model – 2D Wall Plots
Solid Slag Thickness, m Slag Surface Temp., K Wall Heat Flux, kW/m2
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Slag Thickness – Surface Display
• curve = camera path• ball on curve = camera location• gas temperature at ball shown in
bar display
• displayed = frozen slag thickness• surface elevation = slag thickness•surface color
mm
0
100
Gas and Particle Flow FieldVolatiles Mass
FractionChar MassFraction
137 micron
Gas Temperature, K
Axial Velocitym/s
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Two Stage – Up Flow• Vision 21 Firing Conditions
– Pressure = 18 atm.– 3000 tpd Illinois #6
• H2O 11%, Ash 10%– Slurry: 74% solids (wt.)– Slurry Distribution
• 39%, 39%, 22% (upper)– Oxidant
• 95% O2, 5% N2• O2:C (molar) = 0.40• Inlet Stoichiometry ~ 0.47
D
11 D
1.58 D
0.33 D
0.25 D
D
Two Stage, Upflow
Tangentially Fired Gasifier
D
1.58 D
0.33 D
0.25 D
D
Two Stage, Upflow
Tangentially Fired Gasifier
Upper injectors
0.5 D
Jet centerline
0.5 D
Jet centerline
0.5 D
Jet centerline
Lower Injectors
L / D = 11 D = 1.65m
• System– 4 fuel injectors / level– Fuel Injectors ~ pipes
Gas and Particle Flow Field
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Gas Composition at Elevations
H2 CO H2O CO2 O2
Molten Slag Thickness, m Solid Slag Thickness, m Surface Temperature, K
Slag Summary
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ComparisonAverage Wall Temp., K 1705
Exit Temperature, K 1390Carbon Conversion, % 96.1
Exit LOI, % 19.7Deposit LOI, % 47.9Deposition, % 3.3
PFR Residence Time, s 1.797Particle Residence Time, s 0.926
Mole Fraction: CO 42.5%H2 32.3%
H2O 13.8%CO2 8.7%H2S 0.8%
COS 0.0%N2 1.6%
Exit Mass Flow, klb/hr 493HHV of Syngas, Btu/lb 4899
HHV of Syngas, Btu/SCF 247Cold-Gas Efficiency, % 80.9
• V21 “Design” Conditions– DOE flow sheet analysis of
“DESTEC-style” 2 stage gasifier in an IGCC plant
– Syngas:• HHV ~ 250 Btu/SCF• Temp. ~ 1300 K (1900F)• Fuel Flow ~ 499 klb / hr• Composition (after GCU):
– CO = 43.5%– H2 = 32.5%– H2O = 13.6%– CO2 = 8.6%– N2 = 0.9%
• Demonstrated CFD based gasifier models– One stage and two stage designs– Mechanistic based– Can be used to address broad range of operational and design
problems for gasifiers• Comparisons to available information
…getting better …• Next ?
– improve slag (mineral matter) model, gasification kinetics – Petcoke– Scavenger for model verification data– pre-processor to allow defining flows to gasifier based on desired
syngas at gasifier exit• fuel, oxidant, recycled char, fluxing material
– Impact on power production and downstream equipment
Summary