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7/31/2019 Cfd Modelling of TBR 2
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CFD MODELING OF TRICKLE BEDREACTORS: Hydro-processing Reactor
Prashant R. Gunjal, Amit Arora and
Vivek V. RanadeIndustrial Flow Modeling Group
National Chemical Laboratory
Pune 411008
Email: vvranade@ifmg.ncl.res.in
mailto:vvranade@ifmg.ncl.res.inmailto:vvranade@ifmg.ncl.res.in7/31/2019 Cfd Modelling of TBR 2
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CFD Modeling of Trickle Bed Reactors
OUTLINE
Trickle Bed Reactors
Applications/ flow regimes Experiments
CFD Modeling of Trickle Bed Reactors Inter-phase momentum exchange/ capillary terms
Estimation of fraction of liquid suspended in gas phase
Simulating Hydro-processing Reactor Reaction kinetics/ other sub-models Influence of reactor scale
Concluding Remarks
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CFD Modeling of Trickle Bed Reactors
TRICKLE BED REACTORS
Wide Applications
Hydro-de-sulfurization Hydro-cracking/ hydro-treating
Hydrogenation/ oxidation
Waste water treatment
Key Characteristics Close to plug flow/ Low liquid hold-up
Suitable for slow reactions
Poor heat transfer/ possibility of mal-distribution
Difficult scale-up
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CFD Modeling of Trickle Bed Reactors
TRICKLE BED REACTORS
Gas & Liquid Flow through Void Space
= 26-48 %
GasLiquid
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CFD Modeling of Trickle Bed Reactors
FLUID DYNAMICS OF TBR
Characterizationof Packed Bed
Wetting of SolidSurface by
Liquid
Flow Regimes &Global FlowCharacteristics
Mal-distribution,Channeling &Mixing
, P, L, ,RTD
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CFD Modeling of Trickle Bed Reactors
FLOW REGIMES
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CFD Modeling of Trickle Bed Reactors
EXPERIMENTS AT NCL
Hydrodynamics
Pressure Drop
Liquid Hold-up
Conductivity Probes
Residence Time Distribution
Liquid Distribution at Inlet Uniform
Non-uniform
Experimental Parameters Bed Diameter: 0.1 & 0.2 m
Particle Diameter: 3 & 6 mm
Liquid Velocity: < 24 mm/ s
Gas Velocity: < 0.50 m/ s
Tracer : NaCl
Data
Acquisition
From CompressorLiquid Tank
Column with
3mm or 6mm
Glass Beads
SeparatorConductivity
Probe
101
PressureIndicator
Pump
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CFD Modeling of Trickle Bed Reactors
TYPICAL PRESSURE DROP DATA
0
5
10
15
20
25
30
35
0 10 20 30
Liquid Flow Rate, Kg/m 2s
Pressuregradie
nt,KPa/m
Trickle f low regime
Pulse flow regime
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CFD Modeling of Trickle Bed Reactors
PUBLISHED EXPERIMENTAL DATA
0
0.2
0.4
0.6
0.81
1.2
1.4
1.6
1.8
2
0 5 10 15 20 25
Liquid Velocity VL, (Kg/m2s)
Sup
erficialGasV
elocityVg,(m
/s)
L= ?
Trickle Flow
1
3
1. Szady and Sundersan (1991)
2. Rao et. al (1983)
3. Specchia and Baldi (1977)
Pulse Flow
Spray Flow
Bubbly Flow
L=L
L=?
L L
2
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CFD Modeling of Trickle Bed Reactors
MODELING OF MACROSCOPIC FLOW
Bed Porosity: Scale of Scrutiny
Bed diameter/ length: overall
Intermediate scale: Gaussian distribution
Smaller than particle diameter: Bi-modal distribution
Approach Used:
Experimentally measured or estimated radial variation ofaxially averaged bed porosity
Specify porosity by drawing a sample assuming Gaussiandistribution with specified variance
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CFD Modeling of Trickle Bed Reactors
CHARACTERIZATION OF PACKED BED
Radial Variation of Porosity: Mueller (1991)
( )
( )
( )
FunctionBesselorderzeroisJandr/Dr
D/d0.724-0.304b
D/d13.0for9.864D/d
2.932-7.383a
13.0D/d2.61for
3.156D/d
12.98-8.243a
)e(ar)J(1r
th
o
*
P
P
P
P
P
br*
oBB
=
=
=
=
+=
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CFD Modeling of Trickle Bed Reactors
CHARACTERIZATION OF PACKED BED
Muellers Correlation
Three data sets from literature Our experiments
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.2 0.4 0.6 0.8 1
Dimensionless Radius
Porosity
D=0.194m, dp=3mm
D=0.194m, dp=6mm
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.2 0.4 0.6 0.8 1
Dimensionless Radius
Porosity
Szady and Sundersan (1991)
Rao et.al. (1983)
Spacchia and Baldi (1977)
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CFD Modeling of Trickle Bed Reactors
VARIATION OF BED POROSITY
Selection of appropriate value is not straight forward: RTD may help
r/R
0.70
0.56 With std dev=0
With std dev=5%
With std dev=10%
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CFD Modeling of Trickle Bed Reactors
CFD MODEL
Multi-fluid Model (Eulerian-Eulerian)
Continuity Equation
0=+
KKK
KK Ut
Momentum Balance Equation
( ) ( )RkRKKKK
KKKKK
KKK
UUFgU
PUUt
U
++
+=+
,
)()(
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CFD Modeling of Trickle Bed Reactors
CFD MODEL
Inter-phase Coupling Terms (Attou & Ferschneider, 2000)
( )
+
=333.0
2
667.0
22
2
1
)1(
)1(
)1(
)1(
G
L
pG
GLGP
G
L
pG
GGGL
d
UUE
d
EF
+
=333.0
2
667.0
22
2
1
)1(
)1(
)1(
)1(
G
S
pG
GGP
G
S
pG
GGGS
d
UE
d
EF
+=
pL
SGP
pL
sLLS
d
UE
d
EF
2
22
2
1
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CFD Modeling of Trickle Bed Reactors
CFD MODEL
Capillary Terms
Attou and Ferschneider (2000)
=
21
112
ddPP
LG
=L
G
PG
LG Fd
PP
5416.0
1
12
333.0
( )
+
=
L
GG
G
ss
G
/
G
s
p
LG
F
z
z
d
.
z
P
z
P2
32
11
1
1
4165
3
2
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CFD Modeling of Trickle Bed Reactors
CFD MODEL
Capillary Terms
Extent of Wetting, f (Jiang et al., 2002)
Scalar Transport
iimiKKiKKKiKK SCDCU
t
C+=+
)( .
cLG PfPP )1( =
025.01.881
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS
0
5
10
15
20
25
3035
40
45
0 0.02 0.04 0.06 0.08 0.1Velocity M agnitude, m/ sec
Non-prewetted Bed
Prewetted B ed
0
5
10
15
20
25
30
35
0 0.1 0.2 0.3Liquid Holdup
Non-prewetted Bed
Prewetted Bed
Pre-wetted Un-wetted
VL= 6 mm/ s, VG=0.22 m/ s, D=0.114 m, dP= 3 mm, =5%
ContoursofL
iquidHold-up
Distributions within the bed
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS
Column Diameter = 0.114 m Particle Diameter = 3 mm, VG=0.22 m/ s
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS
VG= 0.22 m /s, D = 0.114 m VG= 0.22 m /s, D = 0.194 m
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CFD Modeling of Trickle Bed Reactors
GAS-LIQUID FLOW IN TBR
Estimation of Frictional Pressure Drop & Fraction ofLiquid Supported by Gas
Simulate at two values of g (9.7, 9.9 m/s2)
21
1
2
2
1
gg
L
Pg
L
Pg
L
Pf
=
( )21L12
Lgg
L
P
L
P
=
Fraction of Liquid Hold-upSupported by Gas Phase < 1
Solid
Liquid
Gas
( )
LL
L
f
=
Q
gL
P
L
PL
GLGL
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.00 0.20 0.40 0.60 0.80 1.00
Liquid Flow Rate x10-1
, kg/m2s
LiquidSaturation
and
L
Holub et. al. (1993) -Experimental data
Szady and Sundersan (1991)-Exp. Data
CFD Results
Supported Liquid Saturation
Calibrate Model
Parameters from P
Can Predict Total andSupported LiquidVolume Fraction
0
2
4
6
8
10
12
14
0.00 0.20 0.40 0.60 0.80 1.00
Liquid Flow Rate x10-1, Kg/m2s
PressureGradient
KPa/m
Saez and Corbonell (1985)-Exp. dataSzady and Sundersan (1991)-Increase in liquidSzady and Sundersan (1991)-decrease in liquidCFD Simulations w ithout Capillary ForceCFD Simulations
Operating conditions:VG=0.22m/s, D/dp =55, dp=3mm, Std. Dev.=5%, E1=215, E2=1.75
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS
0
10
20
30
40
50
0 0.2 0.4 0.6 0.8 1
Gas Flow Rate, (Kg/m2s)
PressureDrop,
(KPa/m)
CFD ResultsExperimental Data
0
0.1
0.2
0.3
0.4
0.5
0 0.2 0.4 0.6 0.8 1Gas Mass Velocity, kg/m2s
LiquidSaturationand
L
Liquid Saturation- CFD ResultsSupported Liquid SaturationLiquid Saturation- Exp. Data
Data of Spachio & Baldi (1977)
As gas velocity increases,
more & more liquid issupported by gas
Operating conditions: VL=2.8x10-3 m/s, dp=3mm, D/dp=30, Std. Dev.=5%, E1=500, E2=3
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS
0
0.04
0.08
0.12
0.16
0.2
0 2 4 6 8
Gas mass velocity, Kg/m2s
LiquidSaturationa
nd
L
Liquid Saturation- CFD ResultsSupported Liquid SaturationLiquid Saturation Exp. Data
0
40
80
120
160
200
0 2 4 6 8
Gas Mass Velocity, (kg/m2s)
PressureDrop,
(KPa/m) Experimental Data
CFD Results Data of Rao et al. (1983)
As gas velocity increases,
more & more liquid issupported by gas
Operating conditions:VL=1x10-3m/s, D/dp =15.4, dp=3mm, Std. Dev.=5%, E1=215, E2=3.4
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CFD Modeling of Trickle Bed Reactors
RESIDENCE TIME DISTRIBUTION
0
0.02
0.04
0.06
0.08
0.1
0.12
0 20 40 60 80 100 120
Time, (sec)
E(t),sec
-1
Pre-wetted Bed
Non Pre-wett ed Bed
Simulation Results
1
1
1
Ex erimental Results2
2
2
Operating conditions: VL=2.06x10-3m/s VG=0.22m/s, D/dp =18, dp=6mm, Std. Dev.=5%, E1=180, E2=1.75
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CFD Modeling of Trickle Bed Reactors
MODELING OF HYDRO-PROCESSING REACTOR
Reaction and Kinetics (Chowdhury et al. 2002)
Hydro-desulfurisation (HDS)
SH,LAd
6.1S,L
56.0H,L
HDS
2
2
cK1
cckr
+=SHArH2SAr 22 ++
De-aromatisation of Mono-, Di- and Poly- Aromatics
NaphMono_MonoMonoMono CkCkr +=NapthenesH3ArMono 2 +
MonoDi_DiDiDi CkCkr +=ArMonoH2ArDi 2 +
DiPoly_PolyPolyPoly CkCkr +=ArDiHArTri 2 +
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CFD Modeling of Trickle Bed Reactors
SIMPLIFICATIONS/ ASSUMPTIONS
Pressure drop is insignificant compared to the operating
pressure
Trickle bed reactor is operated isothermally (efficient heat
transfer)
Ideal gas law is applicable
Liquid phase reactants are non-volatile (negligible vapor
pressure) Gas-liquid mass transfer is the limiting resistance.
The catalyst particles are completely wetted
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CFD Modeling of Trickle Bed Reactors
MODEL EQUATIONS
Mass Balance of Species i
Source Terms for Gas Phase
Source Terms for Liquid Phase
( ) ( ) kikkikmikkikkkkikkk
SCDCUt
C
,,,.,
,
+=+
= Lii
Gi
GLGLii CH
C
aKS
=
=+
=
nrj
1j
ijB rLii
GiGLGLii CH
C
aKS
=
=
=nrj
1j
ijB riS
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CFD Modeling of Trickle Bed Reactors
MODEL EQUATIONS
Mass Transfer Coefficient (From Goto & Smith, 1975)
Solubility of Hydrogen/ H2S (Korsten et al. 1996)
2/1
1
2
= L
iL
L
L
LL
i
L
L
i
DG
Dak
Li
NiH
.=
220
4
2
320
210H
1
.aTa
T
aTaa2 ++++=
).008470.03670.3exp(2
TSH =835783.0a
1094593.1a
1007539.3a
1042947.0a
559729.0a
4
63
32
3
1
0
=
=
==
=
: molar gas volumeN
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CFD Modeling of Trickle Bed Reactors
CASE STUDIES
Gas and Liquid Superficial Velocities Increase with
Scale Wetting gets Better with Scale
Parameters Laboratory Scale Reactor
(Chowdhury et al. 2002)
Commercial Scale Reactor
(Bhaskar et al. 2004)
Reactor Diameter, mBed Length
Particle Diameter, mBed Porosity
LHSV, h-1Operating Pressure, MpaOperating Temperature, K
Initial H2S Conc., v/v %
0.0190.5 m0.00240.50
1-520-28
573-6930.5-8
3.816 m
0.00150.36
1-520-80
573-6930.5-8
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CFD Modeling of Trickle Bed Reactors
KINETICS/ OIL COMPOSITION
From Chowdhury et al. (2002)
AdKKinetic Constants Values
, m3/kmol 50000
K, Dimensionless 2.5 X 1012 exp(-19384/T)
k*mono, m3/kg.s 6.04 X 102 exp(-12414/T)
k*Di, m
3
/kg.s 8.5 X 10
2
exp(-12140/T)k*poly, m3/kg.s 2.66 X 105 exp(-15170/T)
Component Percentage
Ar-S % 1.67
Poly-Ar % 2.59
Di-Ar % 8.77
Mono-Ar % 17.96
Naphthenes % 19.25
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS-1
Temperature Initial Concentration of H2S
0
25
50
75
100
573 583 593 603 613 623 633 643 653
Temp, K
Con
version,
Ar-S%
Varying Porosity
Uniform Porosity
Ar-S Exp
0
30
60
90
0 2 4 6 8
Initial H2S Conc Gas Phase ( %, V/V)
Conversion,x
(P=4 MPa, LHSV=2.0 h-1, QGNTP/QL=200 m3/m3, TR=320
oC, yH2S=1.4% )Symbols denote experimental data of Chowdhury et al. (2002)
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS-2
(P=4 MPa, LHSV=2.0 h-1, QGNTP/QL=200 m3/m3, yH2S=1.4%)
Symbols denote experimental data of Chowdhury et al. (2002)
0
10
20
30
40
50
60
70
80
90
573 593 613 633 653
Temperature, K
Conversion,
Ar-P
totaltotal
poly
0
10
20
30
40
50
60
573 593 613 633 653
Temperature, K
C
onversion,
%
Ar-D
Ar-M
Ar-Di-Expt
Ar-Mono-Exp
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CFD Modeling of Trickle Bed Reactors
SIMULATED RESULTS-3
0
10
20
30
40
50
60
2 2.4 2.8 3.2 3.6 4
LHSV, h-1
Conversion,
%
Total-Ar
Ar-Poly
Ar-DiAr-Mono
(P=4 MPa, TR=320 oC, QGNTP/QL=200 m3/m3, yH2S=1.4%, filled symbols
are for experimental data of Chowdhury et al., 2002)
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CFD Modeling of Trickle Bed Reactors
INFLUENCE OF REACTOR SCALE
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 0.2 0.4 0.6 0.8 1
Dimensionless Radius
Dim
ensionlessSolidHold-up
0
5
10
15
20
25
30
35
DimensionlessLocalAxialVelocity
Solid hold-up
Local Axial Velocity
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 0.2 0.4 0.6 0.8 1
Dimensionless Radius
DimensionlessSolidHold-up
0
1
2
3
4
5
6
7
DimensionlessLocalAxialVelocity
Solid hold-up
Local Axial Velocity
Industrial (LHSV=2)Laboratory (LHSV=3)
(P=4 MPa, TR=320oC, QGNTP/QL=300 m
3/m3)
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CFD Modeling of Trickle Bed Reactors
INFLUENCE OF REACTOR SCALE
25
50
75
100
573 593 613 633 653
Temperature, K
Conversion,
%Lab-scale Reactor
Commercial Reactor
0
2000
4000
6000
8000
10000
12000
573 593 613 633 653
Temperature, K
Ou
tletConc.
Ar-S,ppm
Lab Scale Reactor
Commercial Reactor
(Plab & com=4 & 4.4 MPa, LHSVlab=2.0 h-1, QGNTP/QL=200 m
3/m3, yH2S=1.4%)
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CFD Modeling of Trickle Bed Reactors
INFLUENCE OF REACTOR SCALE
-20
0
20
40
60
80
100
573 593 613 633 653
Temperature, K
Conversion,
%
Poly-Ar
TotalPoly-Ar-Commercial
Total-Commercial
50
55
60
65
70
75
80
85
90
95
100
2 2.5 3 3.5 4
LHSV, h-1
Conversion,
%
Ar-S-Lab Scale
Ar-S-Commercial
(Plab & com=4 & 4.4 MPa, LHSVlab & com=2.0 & 3.0 h-1,
(QGNTP/QL)lab & com= 200 & 300 m3/m3, yH2S=1.4%)
(Plab & com=4 & 4.4 MPa, Temperature= 593 K,(QGNTP/QL)lab & com= 200 & 300 m
3/m3, yH2S=1.4%)
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CFD Modeling of Trickle Bed Reactors
INFLUENCE OF REACTOR SCALE
0
20
40
60
80
100
120
2 3 4 5 6 7 8
Pressure, MPa
Conversion,
Poly-Ar
Di-Ar
Mono-Ar
Total
0
10
20
30
40
50
60
70
80
90
100
2 2.5 3 3.5 4
LHSV, h-1
Conversion,
%
Poly-Ar
Di-Ar
Mono-Ar
Total
(QGNTP/QL)lab & com= 200 & 300 m3/m3 T=593 K
LHSVlab & com=2.0 & 3.0 h-1 ,yH2S=1.4%
Plab & com=4 & 4.4 Mpa, T=593 K yH2S=1.4%(QGNTP/QL)lab & com= 200 & 300 m
3/m3
Continuous lines: commercial; Dotted lines: laboratory scale
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CFD Modeling of Trickle Bed Reactors
CONCLUDING REMARKS
Macroscopic CFD Model Reasonably Simulates Gas-liquid Flow in Trickle Beds
Liquid hold-up
Residence time distribution
May be used to estimate fraction of suspended liquid
Further Work is Needed for Understanding Wetting/Hysteresis to Make Further Progress
Despite Limitations, CFD Models can be Used toUnderstand Key Issues in Reactor EngineeringIncluding Scale-up & Scale-down
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CFD Modeling of Trickle Bed Reactors
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CFD Modeling of Trickle Bed Reactors
MODELING OF MESO-SCALE FLOWS
Single Phase Flow through Packed Bed
Unit cell approach
Simple cubic, FCC, rhombohedral ..
Inertial flow structures, pressure drop, heat transfer
Interaction of Liquid Drop/ Film with Solid Surface
Regimes of interaction
Dynamic contact angle/ surface characteristics
VOF simulations
Insight into capillary forces???
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CFD Modeling of Trickle Bed Reactors
SINGLE PHASE FLOW
Single Phase Flow through Packed Bed
Periodic Flow
Wall
Wall
Periodic Flow
Wall
Operating Parameters Cell Length 28mm, 3mm Fluid Water Particle Reynolds Number 12-6000
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CFD Modeling of Trickle Bed Reactors
SINGLE PHASE FLOW
Experiments:
Suekane et al.AIChE J., 49, 1
Simulations
0
5
0
4.5
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CFD Modeling of Trickle Bed Reactors
SINGLE PHASE FLOW
0
1
2
3
-1 -0.5 0 0.5 1
x/r
Vz/Vm
ean
Experimental
Simulation-28mm
Simulation-3mm
-1
0
1
2
3
4
-1 -0.5 0 0.5 1
x/r
Vz/Vm
ean
Experimental
Simulation-28mm
Simulation-3mm
-1
0
1
2
3
4
5
-1 -0.5 0 0.5 1x/r
Vz/Vm
ean
Experimental
Simulation-28mm
Simulation-3mm
-1
0
1
2
3
4
5
-1 -0.5 0 0.5 1x/r
Vz/V
mean
Experimental
Simulation-28mm
Simulation-3mm
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CFD Modeling of Trickle Bed Reactors
SINGLE PHASE FLOW
E
S
Vz=8.66mm
/s
Max arrow
length :
A=0.26 mm/s
B=0.29 mm/s
C=0.44 mm/s
A: z/r=0.14 (experimental) B: z/r=0.28 (experimental) C: z/r=0.42 (experimental)A: z/r=0.14 (experimental) B: z/r=0.28 (experimental) C: z/r=0.42 (experimental)A: z/r=0.14 (experimental)A: z/r=0.14 (experimental) B: z/r=0.28 (experimental)B: z/r=0.28 (experimental) C: z/r=0.42 (experimental)C: z/r=0.42 (experimental)
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CFD Modeling of Trickle Bed Reactors
SINGLE PHASE FLOW
Inertial Flow Structures were Captured Accurately byCFD Models
Velocity Distribution in Unit Cells Resembles that in aPacked Bed
Ergun Parameters may be Obtained through Unit CellApproach for Semi-structured Packed Bed
Unit Cell Approach may be Extended to SimulateTwo Phase Flows to Understand Wetting
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CFD Modeling of Trickle Bed Reactors
LIQUID SPREADING ON SOLID SURFACES
Computer
CCD Camera
Monitor
Light Diffuser
Light
Drop Flow Over Pellet
Drop Rest on Flat Plate
8.79mm
1mm
10.4mm
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CFD Modeling of Trickle Bed Reactors
DROP IMPACT ON SOLID SURFACE
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CFD Modeling of Trickle Bed Reactors
DROP IMPACT ON SOLID SURFACE
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CFD Modeling of Trickle Bed Reactors
FLAT SURFACE
(f)
(c)
(d)
(e)
(b)
(a)
t=0ms
t=16ms
t=20ms
t=36ms
t=48ms
t=240ms
t=0ms
t=10ms
t=210mst=25ms
t=45ms
t=45ms
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CFD Modeling of Trickle Bed Reactors
DYNAMICS OF DROP IMPACT
MODELS FOR INTERPHASE COUPLING?
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CFD Modeling of Trickle Bed Reactors
MODELS FOR INTERPHASE COUPLING?
Wall Shear Stress onSolid Surface, red~100 Pa
Drop Shape at 12 ms
ShearStrain onGas-liquidInterface
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