1/50 mfix overview m. syamlal, fluent, inc. federal energy technology center morgantown, wv...
TRANSCRIPT
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MFIX Overview
M. Syamlal, Fluent, Inc.
Federal Energy Technology Center
Morgantown , WV 26507-0880
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Outline
• Multiphase Theory
• Validation Studies– Bubbling Fluidized Bed– Circulating Fluidized Bed– Turbulent Gas-solids Jet– Carbonizer
• Gasifier Application
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Multiphase Theory
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Multiphase Formulation
• Two Phases
• Three phases
Fluid
Solids
Solids - 1
Solids - 2
Fluid
Coal
Char
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Multiphase Formulation
• Details of flow field and particle interaction have been averaged out.
• Account for the information lost due to averaging constitutive equations
• Constitutive equations specify how the phases interact with themselves and with each other1
1. Drew and Lahey (1993)
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Continuity Equation
t
v Rm m m m m mll
M
( ) ( )
1
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Momentum Equation
t
v v v S I fm m m m m m m m mll
M
m( ) ( )
1
Interaction within the phase stresses–collisions, sliding or rolling friction–electrostatic, van der Waals, capillary
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t
v v v S I fm m m m m m m m mll
M
m( ) ( )
1
Momentum Equation
Interaction between phases interphase forces
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Momentum Equation
t
v v v S I fm m m m m m m m mll
M
m( ) ( )
1
Interactions with rest of the universe body forces
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Energy Balanceoriginates from a work term for changes
th h u
p
tu p S u S
q T T R h
m m m m m m m mm
m m m m
m ml l m ml mll
M
( ) ( ) :
( )
1
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Energy Balance
Viscous dissipation
th h u
p
tu p S u S
q T T R h
m m m m m m m mm
m m m m
m ml l m ml mll
M
( ) ( ) :
( )
1
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Energy BalanceEnergy sources; e.g..., radiation
th h u
p
tu p S u S
q T T R h
m m m m m m m mm
m m m m
m ml l m ml mll
M
( ) ( ) :
( )
1
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Energy Balance
heat conduction
th h u
p
tu p S u S
q T T R h
m m m m m m m mm
m m m m
m ml l m ml mll
M
( ) ( ) :
( )
1
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Energy Balance
Interphase heat transfer
th h u
p
tu p S u S
q T T R h
m m m m m m m mm
m m m m
m ml l m ml mll
M
( ) ( ) :
( )
1
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Energy Balance
th h u
p
tu p S u S
q T T R h
m m m m m m m mm
m m m m
m ml l m ml mll
M
( ) ( ) :
( )
1
Energy transfer with mass transfer
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Species Mass Balance
• Multiphase chemical reactions are described by tracking chemical species in each of the phases
t
X X u D X
R
m m mn m m mn m m m mn mn
mn
( ) ( ) ( )
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Validation Studies
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Fluidized Bed with Jet
• Gidaspow (1994)1
• 500 & 800 m sand (2610 kg/m3)
• Jet velocities: 3.5, 5.77, 9.88 m/s
• 2D bed with a central jet
• 0.39 m width x 0.58 m height
• 124 x 108 cells
1. Sec.7.8.1; Syamlal (1997)
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Bubble Size and Shape
Gidaspow (1994) Fig. 7.10
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Bubble Size and Shape
Gidaspow (1994) Fig. 7.11
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Voidage Contourstime average
3.55 m/s 5.77 m/s
Data - Gidaspow, Lin, and Seo (1983)
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Centerline Voidagetime average
0.45
0.55
0.65
0.75
0.85
0 10 20 30
Ht. above jet inlet, cm
Vo
id f
rac
tio
n Mfix 3.55 m/s
Mfix 5.77 m/s
Data 3.55 m/s
Data 5.77 m/s
Data -- Gidaspow and Ettehadieh (1983)
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Bubble Rise Velocity
0
50
100
0 5 10
Bubble diameter, cm
Ris
e v
el.
, c
m/s
Davies-TaylorRowe-PartridgeFLUENTMFIX
Rowe and Partridge (1962), Davidson and Harrison (1963), Syamlal and O’Brien (1989)
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Uniform Fluidization
• Halow and Nicoletti (1992)• 700 m plastic (1460 kg/m3)
• Uniform flow 1.04 Umf -air
• 3D cylindrical bed• 0.15 m diameter x 0.25 m
height• 30 x 100 x 16 cells
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Bubble PropertiesAverage of 9 bubbles
Data MFIX
Frequency, s-1 4.2 5.3
Diameter, cm 5.2 2.5
range, cm (3.4 - 6.9) (1.5 - 4.0)
Spacing, cm 10.7 4.4
range, cm (2.4 - 23.) (2.3 - 9.4)Data -- Halow and Nicoletti (1992)
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Bubble Rise Velocity
0
20
40
60
80
1 3 5 7
Bubble diameter, cm
Ur,
cm
/s
Data
Davies-Taylor
MFIX
Data -- Halow and Nicoletti (1992)
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Circulating Fluidized Bed
• Bader, Findlay, and Knowlton (1988)
• 76 m FCC catalyst (1714 kg/m3)• Solids flux: 98 and 147 kg/m2s• Vg0 : 3.7 - 9.1 m/s
• 0.305 m dia x 12.20 m height• 2-D, cyl., 12 x 240 cells Gas
Solids
Gas + solids
O’Brien and Syamlal (1993)
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Pressure Drop Across CFB
0
1
2
3
4
2 4 6 8 10
Gas velocity, m/s
P/L
, k
Pa
/mData: 98 kg/m2.s
Data: 147 kg/m2.s
MFIX: 98 kg/m2.s
MFIX: 147 kg/m2.s
Data -- Bader et al. (1988)
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Solids Distribution in Riser
Data -- Bader et al. (1988)
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Carbonizer Model
• Froehlich et al. (1994)• 550 m coal and sorbent particles• 1207 K, 1034 kPa• axisymmetric cylindrical coordinates• Flows (kg/s): coal- 0.044; sorb- 0.01;
air - 0.1; N2- 0.028; Steam - 0.007
• 0.36 max dia x 10.36 m height• 16 x 132 cells
Coal, sorbent, air and steam
Product gas
Syamlal et al. (1996)
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Carbonizer Chemistry
AshMoisture
Volatile Matter
Fixed Carbon
CaOCaCO3
CaMg(CO3)2
MgO
CO2 + H2O + CO
+ CH4 + H2
+Tar
CO2 + H2O + CO +
CH4 + H2 + Fixed Carbon
CO2 + H2O
O2
O2
coal sorbent
H2O CO + H2O CO2 + H2
CO2
O2
CO2 CO2
CO
H2O H2 + CO
H2
CH4
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Temperature Distribution
0
1000
2000
3000
0 10 20 30Height above nozzle, ft
Tem
p.,
oF Gas
CoalCarbonizer data
Char
Syamlal et al. (1996)
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SynGas CompositionDry Mole %
Species Experiment MFIX
CO 9.0 5.7
CO2 9.2 9.2
CH4 1.9 5.5
H2 7.9 5.8
N2 68.7 73.8
Syamlal et al. (1996)
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Gasifier Application
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PyGAS Gasifier
• Novel gasifier1;1200 K, 4130 kPa• 2120 m coal and sorbent • axisymmetric cylindrical
coordinates• Flows (kg/s): coal+sorb- 1.8; air:
pyro - 2.6, top - 0.9, grate- 2.9• 2.0 max dia x 8.2 m height• 39 x 165 cells
1. Sadowski (1992)
air + Steam
air+coal
air
fuel gas
ash
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Gas Temperature
• Scale: Red - Blue
300 - 1500 K
• Upper Zone Flame (~1800 K)
• Stable flame at the riser bottom (~1600 K)
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Coal Mass Fraction
• Scale: Red - Blue
0.0 - 0.05 g/cc
• Coal conversion to char completes in the pyrolyzer
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CO Mass Fraction
• Scale: Red - Blue
0.0 - 0.2
• CO and CH4
concentrations are low in hot regions
• Nonuniform CO distribution in the packed bed
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Tar Mass Fraction
• Scale: Red - Blue
0.0 - 0.003
• Coal devolatilization is completed 20 ft above the inlet
• Tar cracking is completed in the pyrolyzer
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Other Results
• Information on gas and solids flow patterns
• Cannot maintain a tall coflow bed
• No regions where coal agglomerate
Sticky coal particle
(350-500o C)
Char particles
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It is far better to foresee even without certainty than not to foresee at all.
- Henri Poincare
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