1/50 mfix overview m. syamlal, fluent, inc. federal energy technology center morgantown, wv...

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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


M

m( ) ( )

1

Momentum Equation

Interaction between phases interphase forces

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Momentum Equation

t


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


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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


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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


0.0 - 0.05 g/cc

• Coal conversion to char completes in the pyrolyzer

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CO Mass Fraction


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


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

1/50 mfix overview m. syamlal, fluent, inc. federal energy technology center morgantown, wv...

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