# Presentation: 140160

## MFIX Overview

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

## Outline

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

## Multiphase Theory

## Multiphase Formulation

- Two Phases
- Three phases

- Fluid

- Solids

- Solids - 1

- Solids - 2

- Fluid

- Coal

- Char

## 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)

**Notes:**
Ergun (1952)

## Continuity Equation

## Momentum Equation

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

## Momentum Equation

- Interaction between phases interphase forces

## Momentum Equation

- Interactions with rest of the universe  body forces

## Drag -- MFIX

- Cd from a Richardson and Zaki correlation

- MFIX manual p.10

**Notes:**
Single sphere drag coefficient -- Dalla Valle (1948)
Velocity voidage correlation -- Garside and Al-Dibouni (1977)

## 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 buoyancy;e.g., doesn’t 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)

## 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

## Energy Balance

- originates from a work term for  changes

## Energy Balance

- Viscous dissipation

## Energy Balance

- Energy sources; e.g..., radiation

## Energy Balance

- heat conduction

## Energy Balance

- Interphase heat transfer

## Energy Balance

- Energy transfer with mass transfer

## Fluid-Particle Heat Transfer

- - The interphase heat transfer coefficient is given by

- where the Nusselt number is given by1

- 1. Gunn (1978)

## Species Mass Balance

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

## Fluid Catalytic Cracking

- Ten-lump model1

- Aromatic Side chains

- Naphthenes

- paraffins

- Aromatic Carbon

- Gasoline

- Coke

- 1. Mobil/Sundaresan

## Validation Studies

## 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)

- a

## Bubble Size and Shape

- Gidaspow (1994)  Fig. 7.10

**Notes:**
Photograph from Gidaspow (1994) p.

## Bubble Size and Shape

- Gidaspow (1994)  Fig. 7.11

**Notes:**
Photograph from Gidaspow (1994) p. 

## Voidage Contourstime average

- 3.55 m/s

- 5.77 m/s

- Data - Gidaspow, Lin, and Seo (1983)

**Notes:**
Experimental data from Gidaspow, Lin, and Seo (1983).

## Centerline Voidagetime average

- Data -- Gidaspow and Ettehadieh (1983)

**Notes:**
Experimental data from Gidaspow and Ettehadieh (1983).

## Bubble Rise Velocity

- Rowe and Partridge (1962), Davidson and Harrison (1963), Syamlal and O’Brien (1989)

**Notes:**
Experimental data from Rowe and Partridge ( 1962).
Davies-Taylor formula Ub = 0.711 Sqrt(g*db), where Ub is the bubble rise velocity, g is the acceleration due to gravity, and db is the bubble diameter (Davidson and Harrison 1963).

## 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)

## Jet Velocity Profile

- Boyle and Sams (1997)

**Notes:**
Boyle and Sams (1997)

## 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

- a

## Bubble PropertiesAverage of 9 bubbles 

- Data -- Halow and Nicoletti (1992)

**Notes:**
Data from Halow and Nicoletti (1992).

## Bubble Rise Velocity

- Data -- Halow and Nicoletti (1992)

**Notes:**
Data from Halow and Nicoletti (1992).

## Circulating Fluidized Bed

- Bader, Findlay, and Knowlton (1988)
- 76 m 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

- O’Brien and Syamlal (1993)

**Notes:**
See O’Brien and Syamlal (1993) for details.

## Pressure Drop Across CFB

- Data --  Bader et al.  (1988)

**Notes:**
Data from Bader, Findley, and Knowlton (1988).

## Solids Distribution in Riser

- Data --  Bader et al.  (1988)

**Notes:**
Data from Bader, Findley, and Knowlton (1988).

## Turbulent Gas-Solids Jet

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

## Gas and Solids Velocities Centerline

- Data -- Tsuji et al. (1988)

**Notes:**
Data from Tsuji et al. (1988).

## 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)

- a

**Notes:**
See Syamlal, Venkatesan, and Cho (1996) for details.

## Carbonizer Chemistry

- Ash

- Moisture

- Volatile Matter

- Fixed Carbon

- CaO

- CaCO3

- 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

## Temperature Distribution

- Syamlal  et al. (1996)

**Notes:**
See Syamlal, Venkatesan, and Cho (1996) for details. Data from private communications with Foster Wheeler.

## SynGas Composition

- Syamlal  et al. (1996)

**Notes:**
See Syamlal, Venkatesan, and Cho (1996) for details. Data from private communications with Foster Wheeler.

## Gasifier Application

## 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

- a

**Notes:**
See Syamlal, Venkatesan, and Cho (1996) for details.

## Gas Temperature

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

## Coal Mass Fraction

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

## 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

## 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

## 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

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

- - Henri Poincare

- <date/time>