1 1 Development of coal gasifier operation supporting technique Hiroaki WATANABE Hiroaki WATANABE Energy Engineering Research Laboratory Energy Engineering Research Laboratory Central Research Institute of Electric Power Industry Central Research Institute of Electric Power Industry - Evaluation of gasification performance and slag Evaluation of gasification performance and slag discharge characteristics using CFD technique discharge characteristics using CFD technique - 2 250 MW class around 1700 t/d Power Output Feed Rate System, Spec. Coal Gasifier Gas Purification Gas Turbine Target Efficiency LHV (HHV) gross efficiency net efficiency Environmental Target SOx NOx Dust Air Blown, Dry Feed Wet, Sulfur Recovery 1200 degC class 48% (46%) 42% (40.5%) 8 ppm (16%O2 ) 5 ppm (16%O2 ) 4 mg/Nm 3 (16%O2 ) Ref. Clean Coal Power R&D Co., Ltd. (http://www.ccpower.co.jp/index.html) Specification of Specification of IGCC demonstration plant in Japan IGCC demonstration plant in Japan
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Development of coal gasifieroperation supporting technique
Hiroaki WATANABEHiroaki WATANABE
Energy Engineering Research LaboratoryEnergy Engineering Research LaboratoryCentral Research Institute of Electric Power IndustryCentral Research Institute of Electric Power Industry
-- Evaluation of gasification performance and slag Evaluation of gasification performance and slag discharge characteristics using CFD technique discharge characteristics using CFD technique --
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250 MW class
around 1700 t/d
Power Output
Feed Rate
System, Spec.
Coal Gasifier
Gas Purification
Gas Turbine
Target EfficiencyLHV (HHV)
gross efficiency
net efficiency
EnvironmentalTarget
SOx
NOx
Dust
Air Blown, Dry Feed
Wet, Sulfur Recovery
1200 degC class
48% (46%)
42% (40.5%)
8 ppm (16%O2)
5 ppm (16%O2)
4 mg/Nm3 (16%O2)
Ref. Clean Coal Power R&D Co., Ltd.(http://www.ccpower.co.jp/index.html)
Specification ofSpecification ofIGCC demonstration plant in JapanIGCC demonstration plant in Japan
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BackgroundBackground
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Ø To clarify influence of oxygen concentration of
gasifying agents and air ratio on gasification
performance
Ø To discuss relationship between operation range
and variations of gasification performance
²Representative slag viscosity
²Three dimensional slag flow calculation
ObjectiveObjective
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ØØ Three dimensional timeThree dimensional time--mean conservation equationsmean conservation equations
Backward reaction rate constant : Backward reaction rate constant : /b f eqk k K=
,min( )fu ch t uR R R=
[[MagnussenMagnussen, B.E. et al. (1976)], B.E. et al. (1976)]
[ ] [ ]i ix y
ch i i iR k A B= Jones, S.K. et al. (1988)Jones, S.K. et al. (1988)Westbrook, C.K. et al. (1981)Westbrook, C.K. et al. (1981)GururajanGururajan, V.S. et al. (1992), V.S. et al. (1992)
ØCalculation results of gas temperature distribution, per pass carbon conversion and product gas composition are in good agreement with the experimental data.
Comparison of calc. and exp. ResultsComparison of calc. and exp. Results(air ratio = 0.47, X(air ratio = 0.47, XOO22 = 21 = 21 volvol%)%)
Gas temperaturePer pass carbon conversionand product gas composition
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Gasification performance Gasification performance –– Varying air ratio at 21% OVarying air ratio at 21% O22
Temperature H2 CO CO2 H2O
(0.39, 0.41, 0.43, 0.47)(0.39, 0.41, 0.43, 0.47)
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Ø Both combustor and reductor temperature rise, as air ratio increases.
Ø Both carbon conversion in combustor and reductorare improved, as air ratio increases. So per pass carbon conversion is improved, as air ratio increases.
Gasification performance Gasification performance –– Varying air ratio at 21% OVarying air ratio at 21% O22(0.39, 0.41, 0.43, 0.47)(0.39, 0.41, 0.43, 0.47)
(21, 30, 40 (21, 30, 40 volvol%) at air ratio 0.39%) at air ratio 0.39
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Ø Combustor temperature rises and reductortemperature drops, as air ratio increases.
Ø Carbon conversion in combustor is improved but in reductor decreases, as air ratio increases. Totally, per pass carbon conversion is improved, as air ratio increases.
Gasification performance Gasification performance –– Varying OVarying O22 concentrationconcentration(21, 30, 40 (21, 30, 40 volvol%) at air ratio 0.39%) at air ratio 0.39
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Gasification performance Gasification performance –– Oxygen Oxygen vsvs Air ratioAir ratio
Ø Total carbon conversion is 100%.Ø PPCC and char production rate are used for an assessment of gasifier’s capacity.Ø For instance, if ASU facility is included, air ratio can be reduced.
Per pass carbon conversion Char production rate
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Ø HHV increases in higher O2 concentration and lower air ratio conditions.Ø CGE increases in lower O2 concentration and lower air ratio conditions.
Gasification performance Gasification performance –– Oxygen Oxygen vsvs Air ratioAir ratio
HHV of product gas Cold gas efficiency
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Ø Combustor temperature and heat flux on the combustor wall rises in higher O2 concentration and higher air ratio conditions.
Ø Slag properties are obtained from these data.
Gasification performance Gasification performance –– Oxygen Oxygen vsvs Air ratioAir ratio
Combustor temperature Heat flux on combustor wall
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Gasification performance Gasification performance –– Oxygen Oxygen vsvs Air ratioAir ratio
Ø (Representative) Molten slag temperature and slag viscosity canbe obtained from ash feeding rate and heat generated in the combustor (using slag viscosity model).
Slag temperature Slag viscosity
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Viscosity model for molten slagViscosity model for molten slag
Ø T-shift model is employed in slag viscosity estimation from a comparison of the model results with the experimental data.
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Gasification performance Gasification performance –– Oxygen Oxygen vsvs Air ratioAir ratio
Ø Operating range in which stable operation can be done was obtained from slag viscosity data (using slag viscosity model and prefixed critical viscosity).
Ø Evaluation for high efficient and stable operation can be done (using representative slag property) .
Slag viscosity and cold gas efficiency
26unstable dischargeunstable discharge
Stable dischargeStable discharge
Molten slag flowMolten slag flow
Discharge of molten slagDischarge of molten slag
CombustorCombustor
Slag holeSlag hole
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Ø Gas-liquid two phase flow modelØ Gas phase … Combustor gas layerØ Liquid phase … Molten slag layerØ Molten slag viscosity is estimated by the T-shift model.
Ø Solidification modelØ Define a liquid phase fraction as a function of temperature
Ø Vary a drag coefficient in solidification layerØ Take a latent heat release into account
Modeling of molten slag flowModeling of molten slag flow
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GasGas--liquid two phase flow calculationliquid two phase flow calculation
Slag viscosity : empirical model [Browning et al., (2003)] Slag viscosity : empirical model [Browning et al., (2003)]
14788log 10.931
s sT T T Tη
= − − −
Solidification : solidification model [Solidification : solidification model [BennonBennon et al., (1987)]et al., (1987)]
( ) 0i i iα ρ∇ ⋅ =u
( ) ( ){ } ( )Ti i i i i i s g
iPα ρ αµ α β ∇ ⋅ − ∇ ⋅ ∇ + ∇ = − ∇ + − u u u u u u
ii = = gg (gas), (gas), ll (liquid)(liquid)
( ) 0Lρ∇⋅ =u L l l s sf f= +u u u
( ) ( ) ( ) ( )L L L L sP Kρ µ µ∇ ⋅ − ∇ ⋅ ∇ =−∇ − −u u u u u
( ){ }230 1l lK K f f= − ( ) ( )l s l sf T T T T= − −
Modeling of molten slag flowModeling of molten slag flow
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Heat from Combustor
Cooling
Cooling Tube
SlagTap
Analysis Area
Com
bust
or W
all
Cen
tral
Axi
s of
Gas
ifie
r Gas Layer
Molten Slag Layer
Heating Boundary
Cooling Boundary
Solidification Layer
Schematic drawing of slag holeSchematic drawing of slag hole
Slag flow vectors & temperatureSlag flow vectors & temperature
Model resultsModel results
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Model results Model results –– Air ratio = 0.47, OAir ratio = 0.47, O22 = 21 = 21 volvol%%
Ø Slag flows toward the gate.Ø Slag is cooled down by the bottom boundary (cooling water).Ø Slag viscosity rises, as slag temperature drops.
Temperature Ts Kand velocity vectors
Slag viscosity µs Pa*s
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Model results Model results –– Air ratio = 0.47, OAir ratio = 0.47, O22 = 21 = 21 volvol%%
Ø Slag solid layer develops on the bottom of combustor.Ø Highest point of slag surface is located at 90 deg. from the gate.Ø Slag overflow might be observed at the points.
Solid layer on the bottom Slag surface height ys m
overflow location
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Model results Model results –– solidification characteristicssolidification characteristics
Solid layerSolid layer
Air ratio = 0.47, O2 = 30 vol%
Air ratio = 0.47, O2 = 21 vol%
Air ratio = 0.43, O2 = 30 vol%
Solid layerSolid layer
Ø Thickness of solid layer develops thicker, as temperature drops.
Ø Total thickness of slag layer develops thicker, as the thickness of solid layer develops.
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Gasification performance Gasification performance –– Oxygen Oxygen vsvs Air ratioAir ratio
Slag overflow region and cold gas efficiency
Ø Operating range in which it is possible to avoid slag overflow was obtained by 3-D slag flow calculation.
Ø Evaluation for high efficient and stable operation can be done.
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SummarySummaryØ Influence of air ratio and oxygen concentration in gasifying agent on gasification performance and slag discharge was investigated by 3-D gas-particle reacting flow calculation. Representative slag viscosity was obtained by the calculation in order to discuss slag discharge characteristics.
Ø Slag behavior such as slag overflow over inner wall, which is caused by slag solidification, can be predicted by 3-D gas-liquid-solid free surface calculation in detail.
Ø Presented technique is useful to assess gasification performance and slag discharge.