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)
13
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)
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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)
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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 Cylinders
Case ID FBR1 FBR2 FBR3Nº of particles 540 200 100Porosity, ε 0.451 0.444 0.467
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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 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).
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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 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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