MFIX Overview

1
MFIX Overview

• M. Syamlal, Fluent, Inc.
• Federal Energy Technology Center
• Morgantown , WV 26507-0880

2
Outline

• Multiphase Theory
• Validation Studies
• Bubbling Fluidized Bed
• Circulating Fluidized Bed
• Turbulent Gas-solids Jet
• Carbonizer
• Gasifier Application

3
Multiphase Theory
4
Multiphase Formulation

• Two Phases
• Three phases

Fluid
Solids
Fluid
Solids - 1
Char
Solids - 2
Coal
5
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)
6
Continuity Equation
7
Momentum Equation

• Interaction within the phase - stresses
• collisions, sliding or rolling friction
• electrostatic, van der Waals, capillary

8
Momentum Equation
Interaction between phases - interphase forces
9
Momentum Equation
Interactions with rest of the universe - body
forces
10
Drag -- MFIX

• Cd from a Richardson and Zaki correlation

MFIX manual p.10
11
Buoyancy

• Model A
• full description of buoyancy
• 1-D model has imaginary characteristics leads
  to ill-posed initial value problem1
• Model B
• describes only Archimedean buoyancye.g., doesnt
  describe buoyancy in rotating flow
• 1-D model leads to well-posed problem2

1. Gidaspow (1994 p. 191) 2. p.134 Also see
Enwald et al. (1996)
12
Granular Flow Regimes
Elastic Regime Plastic Regime Viscous
Regime Stagnant Slow flow Rapid flow Stress is
strain Strain rate Strain rate
dependent independent dependent Elasticity Soil
mechanics Kinetic theory
13
Energy Balance
originates from a work term for e changes
14
Energy Balance
Viscous dissipation
15
Energy Balance
Energy sources e.g..., radiation
16
Energy Balance
heat conduction
17
Energy Balance
Interphase heat transfer
18
Energy Balance
Energy transfer with mass transfer
19
Fluid-Particle Heat Transfer
- The interphase heat transfer coefficient is
given by
where the Nusselt number is given by1
1. Gunn (1978)
20
Species Mass Balance

• Multiphase chemical reactions are described by
  tracking chemical species in each of the phases

21
Fluid Catalytic Cracking
Ten-lump model1
Aromatic Side chains
Naphthenes
Gasoline
paraffins
Aromatic Carbon
Coke
1. Mobil/Sundaresan
22
Validation Studies
23
Fluidized Bed with Jet

• Gidaspow (1994)1
• 500 800 mm 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

a
1. Sec.7.8.1 Syamlal (1997)
24
Bubble Size and Shape
Gidaspow (1994) Fig. 7.10
25
Bubble Size and Shape
Gidaspow (1994) Fig. 7.11
26
Voidage Contourstime average
3.55 m/s
5.77 m/s
Data - Gidaspow, Lin, and Seo (1983)
27
Centerline Voidagetime average
Data -- Gidaspow and Ettehadieh (1983)
28
Bubble Rise Velocity
Rowe and Partridge (1962), Davidson and Harrison
(1963), Syamlal and OBrien (1989)
29
Jetting Fluidized Bed

• Yang and Keairns (1980)
• 0.28 cm Polyethylene (901 kg/m3)
• Jet velocity 62 m/s, grid velocity 0.96 m/s
• 0.28 m dia x 2.1 m height
• 20x77 cells

Boyle and Sams (1997)
30
Jet Velocity Profile
Boyle and Sams (1997)
31
Uniform Fluidization

• Halow and Nicoletti (1992)
• 700 mm 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

a
32
Bubble PropertiesAverage of 9 bubbles
Data -- Halow and Nicoletti (1992)
33
Bubble Rise Velocity
Data -- Halow and Nicoletti (1992)
34
Circulating Fluidized Bed

• Bader, Findlay, and Knowlton (1988)
• 76 mm FCC catalyst (1714 kg/m3)
• Solids flux 98 and 147 kg/m2.s
• Vg0 3.7 - 9.1 m/s
• 0.305 m dia x 12.20 m height
• 2-D, cyl., 12 x 240 cells

OBrien and Syamlal (1993)
35
Pressure Drop Across CFB
Data -- Bader et al. (1988)
36
Solids Distribution in Riser
Data -- Bader et al. (1988)
37
Turbulent Gas-Solids Jet

• Tsuji et al. (1988)
• 2D Axisymmetric cylindrical
• 500 mm polystyrene (1020 kg/m3) - air
• 24 m/s gas-solids jet
• 20 mm nozzle in 0.3 m dia chamber
• 49 x 259 cells

38
Gas and Solids Velocities Centerline
Data -- Tsuji et al. (1988)
39
Carbonizer Model

• Froehlich et al. (1994)
• 550 mm 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

Product gas
Coal, sorbent, air and steam
a
Syamlal et al. (1996)
40
Carbonizer Chemistry
H2O
CO H2O W CO2 H2
Ash
coal
CO2 H2O CO CH4 H2 Tar
sorbent
Moisture
CaO
CaCO3
CO2
Volatile Matter
CaMg(CO3)2
O2
MgO
Fixed Carbon
CO2 H2O
H2
O2
O2
CO
CH4
CO2 H2O CO CH4 H2 Fixed Carbon
CO2
CO2
H2O
H2 CO
41
Temperature Distribution
Syamlal et al. (1996)
42
SynGas Composition
Syamlal et al. (1996)
43
Gasifier Application
44
PyGASJ Gasifier
air

• Novel gasifier11200 K, 4130 kPa
• 2120 mm coal and sorbent
• axisymmetric cylindrical coordinates
• Flows (kg/s) coalsorb- 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

fuel gas
ash
air Steam
aircoal
a
1. Sadowski (1992)
45
Gas Temperature

• Scale Red - Blue
• 300 - 1500 K
• Upper Zone Flame (1800 K)
• Stable flame at the riser bottom (1600 K)

46
Coal Mass Fraction

• Scale Red - Blue
• 0.0 - 0.05 g/cc
• Coal conversion to char completes in the pyrolyzer

47
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

48
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

49
Other Results

• Information on gas and solids flow patterns
• Cannot maintain a tall coflow bed
• No regions where coal agglomerate

Char particles
Sticky coal particle (350-500o C)
50

• It is far better to foresee even without
  certainty than not to foresee at all.
• - Henri Poincare

51
(No Transcript)