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CFD modeling of gas

liquid

solidmechanically agitated

contactor

Panneerselvam et al. (2008). In: ChemicalEngineering Research and Design. 86. 1331

1344.

Presented by: Daniel Casas OrozcoComputational Fluid Dynamics (CFD)

August 2nd, 2012

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Outline

1. Introduction2. Problem statement

3. Experimental section

4. CFD Modeling

4.1 Utilized model

4.2 Governing equations4.2.1 Conservation equations

4.2.2 Momentum equations

4.2.3 Constitutive turbulence equations

5. Representative results

5.1 General aspects

5.2 Solid liquid simulations

5.3 Gas liquid simulations

5.4 Three phases simulations

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1. Introduction

Mechanically agitated reactors

Liquid phase

Solid phase

Gas phase

Required suspension of dispersed phases: noparticles remain at the tanks bottom for a long

time

Complete suspension: < 1 2 sec

Homogeneous suspension

Incomplete suspension

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Applications:

Hydrogenations Catalytic oxidations

Chlorination processes

Catalytic oxidation

Solid catalyst: large effective area (Criticalagitation velocity to successfully suspend solid

phase)

Oxidizing agent: injected air (Disperse gas

homogeneously as bubbles)

1. Introduction

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Scaling up determinant aspects

Particle settling velocity

Impeller type

Impeller diameter

Spurger diffuser device and location

1. Introduction

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2. Problem Statement

Analyze the effect of the variables:

Impeller type

Solid loading

Dispersed phases present in the system

on the critical impeller speed

CFD simulation and validation for critical

impeller speed and cloud height distribution

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3. Experimental section

Elliptical shaped bottom tank Two types of impeller:

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Phases

Liquid phase: Water

Solid phase: ilmenite particles (Titanium iron

oxide)(150 230 m)

Gas phase: air

3. Experimental section

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4. CFD Modeling

4.1 Utilized model

MFR: Multiple Frame of Reference

Rotating frame for impeller and neighboring fluid

Stationary frame for tank, baffles and fluid outside

impeller frame

Eulerian Eulerian Multiphase Multifluid

Model: Each phase is treated as a continua

interacting among each other

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4.2.1 Continuity equations for all phases

0

kkkkk u

t

4.2 Governing equations

4. CFD Modeling

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ggggggg uuu

t

lg,, Dgg

T

gggeffgg FguuP

4.2.2 Momentum equations

Conventional terms

Gas phase

lllllll uuu

t

lsDDll

T

llleffll FFguuP ,lg,,

Liquid phase

sssssss uuu

t

lsDss

T

ssseffsss FguuPP ,,

Solid phase

4. CFD Modeling

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4.2.2 Momentum equations Drag force terms

3

4

0

0,

,,

1067.8

4

3

p

D

DlsD

lsls

p

sllsDlsD

d

xC

CC

uuuud

CF

687.00 Re15.01Re

24pDC

Liquid solid interaction

43

8,Re15.01

Re

24

105.6

4

3

687.0

3

6lg,

lg,lg,

Eo

EoMaxC

d

xC

CC

uuuud

CF

bD

p

D

DD

lglg

b

g

lDD

Liquid gas interaction

4. CFD Modeling

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lllllk

tlllll

ll Pkkutk

llll

lll

tlllll

lll CPCk

ut

21

4.2.3 Constitutive equations for turbulence

4. CFD Modeling

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5. Representative results

5.1 General aspects

ANSYS CFX-11

One half simulated

Meshing: graded mesh with further hexagonal

meshing (ICEM option)

MFR model: Interaction between phases

synchronized by continuity Boundary conditions: non slip at surfaces and free

surface as degassing boundary

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5. Representative results

5.1 General aspects

Mean bubble size: 4 mm

Finite Volume Method (FVM) Pressure Velocity Coupling: Rhie Chow Algorithm

Variables: type of impeller, agitation speed,

particle diameter, solid charge, superficial gas

velocity

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5.2 Solid liquid simulation5.2.1 Solid velocity (7% solids, 1200 RPM)

5. Representative results

Rushton turbine4 bladed turbine

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5.2.2 Solid velocity profiles (r/R = 0.5, 1200 RPM, solidcharge = 7 %)

5. Representative results

Radial velocityTangential velocityAxial velocity

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5.3 Gas liquid simulationAxial liquid velocity (300 rpm, upward gas feed)

5. Representative results

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5.4 Three phases simulation

5. Representative results

Impeller effect on solid distribution (30 % solid charge,230 m size, 0.5 vvm air flow)

Rushton Turbine 4 blade turbine

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5.4 Three phases simulation

5. Representative results

Particle size effect on solid distribution (30 % solidcharge, Rushton turbine, 0.5 vvm air flow)

125 m 180 m 230 m

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THANKS FOR YOUR ATTENTION