Dissertation Defense
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Transcript Dissertation Defense
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Master’s Dissertation Defense
Carlos M. Teixeira
Supervisors:
Prof. José Carlos Lopes
Eng. Matthieu Rolland
17th July 2013
Outline
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Introduction
Objectives
State of the Art
Methodology
Results and Discussion
Conclusions
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Introduction
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)
Consequence
Reactors with low tube-to-particle diameter ratio
(1 < 𝐷/𝑑𝑝 < 5)
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Introduction
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
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Introduction
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Example of Packing Effect
Problem Description
0.8
Packing of eight cylinders with
0.7
different arrangements
Laminar regime
Cylinders with constant
concentration in their surface
Transfer solute to the fluid
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0.5
0.4
0.3
0.2
Particles in contact
the inlet flows through the packing
Cout/Csurface
Fluid with zero concentration at
0.6
0.1
0
Normalized outlet concentration for the different arrangements
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Outline
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Introduction
Objectives
State of the Art
Methodology
Results and Discussion
Conclusions
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Objectives
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
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Outline
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Introduction
Objectives
State of the Art
Methodology
Results and Discussion
Conclusions
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State of the Art
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
CFD Simulation of Fixed-Bed Reactors
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 (𝐷/𝑑𝑝 < 10)
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State of the Art
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
CFD Simulation of Fixed-Bed Reactors
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
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Outline
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Introduction
Objectives
State of the Art
Methodology
Results and Discussion
Conclusions
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Methodology
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Coupling between DEM and CFD
GRAINS3D (Packing Simulation)
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PeliGRIFF (Fluid Flow Simulation)
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Methodology
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Grid Refinement Studies
Relative Error in U inlet
1
10-1
0° Re=0.01
0° Re=50
45° Re=0.01
45° Re=50
90° Re=0.01
90° Re=50
10-2
-3
10
10
100
d p/h
1000
Relative error in the inlet velocity as a function of the grid resolution
(ε=0.799, l/dp=1)
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Outline
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Introduction
Objectives
State of the Art
Methodology
Results and Discussion
Conclusions
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Structured Packed Beds
Unit cell approach
(a)
(b)
A packed bed of simple cubic arrangement of spheres. a) Unit cell b) Alternative
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representation of a simple cubic unit cell.
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Structured Packed Beds of Spheres
Validation Case
Comparison between the simulated dimensionless pressure drop and results from
Hill et al. (2001) for a dilute array of spheres (ε=0.799)
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Direct Numerical Simulation of Fixed-Bed Reactors:
Results and Discussion
Effect of Random Packing
Flow through Structured Packed Beds of Cylinders
Effect of cylinder orientation
100
0°
Dimensionless Pressure Drop, ϕ
45°
90°
10
1
0.1
1
10
100
1000
Redp
Effect of cylinders orientation on dimensionless pressure drop
(ε=0.799, l/dp=1)
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Structured Packed Beds of Cylinders
Transition from laminar regime to unsteady and chaotic flow
Particle Reynolds number as a function of time for 45º
orientation (ΔP=10 Pa)
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Randomly Packed Beds of Cylinders
Case ID
FBR1
FBR2
FBR3
Nº of particles
540
200
100
0.451
0.444
0.467
Porosity, ε
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Randomly Packed Beds of Cylinders
Simulated Packed Beds
Grid parameters and computing times on 128 processors (𝑅𝑒𝑑𝑝 = 1)
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Randomly Packed Beds of Cylinders
Pressure 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
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Randomly Packed Beds of Cylinders
Spatial 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
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Randomly Packed Beds of Cylinders
Statistical Velocity Distribution
1.4
Inlet
Z2
Z3
Z4
Z5
Z6
Z7
Z8
Z9
Z10
Z11
Z12
Z13
Z14
Z15
Outlet
Entire Domain
1.2
P (U z /U inlet)
1
0.8
0.6
0.4
0.2
0
-2
0
2
4
U z/U inlet
6
8
10
Probability density functions of normalized z-velocity in different zones of
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the fixed-bed.
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Direct Numerical Simulation of Fixed-Bed Reactors:
Results and Discussion
Effect of Random Packing
Flow through Randomly Packed Beds of Cylinders
Statistical Velocity Distribution (link with porosity)
0.85
Porosity, ε
0.75
0.65
0.55
0.45
0.35
0
Inlet
0.2
0.4
z/L
0.6
0.8
1
Outlet
Axial average porosity profile
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Randomly Packed Beds of Cylinders
Statistical Velocity Distribution (link with porosity)
Probability density functions of normalized z-velocity for different porosities
(𝑅𝑒𝑑𝑝 = 1)
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Results and Discussion
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Flow through Randomly Packed Beds of Cylinders
Statistical Velocity Distribution
Probability density functions of normalized x-velocity for different porosities
(𝑅𝑒𝑑𝑝 = 1)
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Outline
Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Introduction
Objectives
State of the Art
Methodology
Results and Discussion
Conclusions
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Conclusions
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 𝑅𝑒𝑑𝑝 ≥ 60
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Conclusions
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
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Direct Numerical Simulation of Fixed-Bed Reactors:
Effect of Random Packing
Thank you for your attention
www.ifpenergiesnouvelles.com
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