Master’s Dissertation Defense

Carlos M. Teixeira

Supervisors:

Prof. José Carlos LopesEng. Matthieu Rolland

Direct Numerical Simulation of Fixed-Bed Reactors:

Effect of Random Packing

17th July 2013

2

Outline

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

IntroductionObjectivesState of the ArtMethodologyResults and DiscussionConclusions

3

Introduction

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Catalysts performance evaluation Performed in units at pilot scale The trend is to reduce the size of testing units

(economic and safety reasons) Catalyst size remains constant (customer

demands)

ConsequenceReactors with low tube-to-particle diameter ratio

)

4

Introduction

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Reactors with low tube-to-particle diameter ratio

Pseudo Homogeneous Models may not be valid Local Phenomena are dominant

Wall Effect Packing Effect

5

Introduction

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Example of Packing Effect

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

C out

/Csu

rface

Parti

cles i

n co

ntac

t

Problem Description Packing of eight cylinders with

different arrangements Fluid with zero concentration at

the inlet flows through the packing

Laminar regime Cylinders with constant

concentration in their surface Transfer solute to the fluid

Normalized outlet concentration for the different arrangements

6

Outline

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

IntroductionObjectivesState of the ArtMethodologyResults and DiscussionConclusions

7

Objectives

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Study the phenomena of single phase fluid flow through fixed-bed reactors at low particle Reynolds number

Understand how the packing structure affects the flow

8

Outline

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

IntroductionObjectivesState of the ArtMethodologyResults and DiscussionConclusions

9

State of the Art

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Benchmark Method: Lattice Boltzmann

Finite Volume method has been successfully used

by many authors

In most published works, the ratio of tube-to-

particle diameter is low

CFD Simulation of Fixed-Bed Reactors

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State of the Art

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Coupling between Hydrodynamics, Heat Transfer and Chemical Reaction:

Less works on the literature

Applied in small size problems (dozens of

particles)

Particle shape: mostly spheres

CFD Simulation of Fixed-Bed Reactors

11

Outline

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

IntroductionObjectivesState of the ArtMethodologyResults and DiscussionConclusions

12

Methodology

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Coupling between DEM and CFD GRAINS3D (Packing

Simulation) PeliGRIFF (Fluid Flow Simulation)

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Methodology

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Grid Refinement Studies1

10-1

10-2

10-3

10 100 1000dp/ h

Relat

ive E

rror i

n Uinl

et

0° Re=0.01 0° Re=50

45° Re=0.01 45° Re=50

90° Re=0.01 90° Re=50

Relative error in the inlet velocity as a function of the grid resolution (ε=0.799, l/dp=1)

14

Outline

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

IntroductionObjectivesState of the ArtMethodologyResults and DiscussionConclusions

15

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Structured Packed Beds

Unit cell approach

A packed bed of simple cubic arrangement of spheres. a) Unit cell b) Alternative representation of a simple cubic unit cell.

(a)

(b)

16

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Structured Packed Beds of SpheresValidation Case

Comparison between the simulated dimensionless pressure drop and results from Hill et al. (2001) for a dilute array of spheres (ε=0.799)

17

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Effect of cylinder orientation

0.1

1

10

100

1 10 100 1000Redp

Dime

nsion

less P

ressu

re D

rop,

ϕ

0°

45°

90°

Effect of cylinders orientation on dimensionless pressure drop (ε=0.799, l/dp=1)

Flow through Structured Packed Beds of Cylinders

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Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Transition from laminar regime to unsteady and chaotic flow

Flow through Structured Packed Beds of Cylinders

Particle Reynolds number as a function of time for 45º orientation (ΔP=10 Pa)

19

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds of Cylinders

Case ID FBR1 FBR2 FBR3Nº of particles 540 200 100Porosity, ε 0.451 0.444 0.467

20

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds of CylindersSimulated Packed Beds

Grid parameters and computing times on 128 processors

21

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds of CylindersPressure Drop

Dimensionless pressure drop as a function of porosity. Comparison between simulations and Ergun correlation predictions (Redp=1).

22

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds of CylindersSpatial Velocity Distribution

Three different zones are identified:

Recirculation zones in the packing top and bottom and in the wake of the particles (with negative velocities)

High velocity zones where the void fraction is small and the velocity increases up to a factor of 15

Low velocity zones near the particles surfaces

23

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds of CylindersStatistical Velocity Distribution

0

0.2

0.4

0.6

0.8

1

1.2

1.4

-2 0 2 4 6 8 10U z/ U inlet

P(U

z/U

inlet)

InletZ2Z3Z4Z5Z6Z7Z8Z9Z10Z11Z12Z13Z14Z15OutletEntire Domain

Probability density functions of normalized z-velocity in different zones of the fixed-bed.

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Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds of CylindersStatistical Velocity Distribution (link with porosity)

0.35

0.45

0.55

0.65

0.75

0.85

0 0.2 0.4 0.6 0.8 1z/ L

Poro

sity,

ε

Inlet OutletAxial average porosity profile

25

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds of CylindersStatistical Velocity Distribution (link with porosity)

Probability density functions of normalized z-velocity for different porosities

26

Results and Discussion

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds of CylindersStatistical Velocity Distribution

Probability density functions of normalized x-velocity for different porosities

27

Outline

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

IntroductionObjectivesState of the ArtMethodologyResults and DiscussionConclusions

28

Conclusions

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Structured Packed Beds The methodology was validated with well-established cases from

the literature

Dependence of Pressure Drop across Packed Beds of cylinders on its orientation was studied

Transition from steady laminar flow to time oscillatory and chaotic flow was observed at

29

Conclusions

FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Flow through Randomly Packed Beds Good agreement between Ergun’s pressure drop predictions and

simulation results were found

Velocity distributions were analyzed and three different zones were identified

Velocity distributions appear to follow the average local porosity: the length to establish the flow is identical to the length to establish the porosity

30FEUP/IFPEN

Direct Numerical Simulation of Fixed-Bed Reactors:Effect of Random Packing

Thank you for your attention

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