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Nicole ReedDepartment of Energy and Mineral EngineeringEGEE 520Penn State University
April 29, 2008
COMSOL Modeling of Liquid Flow Through a Fixed-Bed Packed Reactorfor Adsorptive Desulfurization
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Desulfurization approaches require severe conditions and are not suitable for fuel cell applications
Selective Adsorption (SARS) is achieved at ambient pressure and temperature without hydrogen
HydrodesulfurizationHydrodesulfurization (HDS) (HDS)
– High Temp (300-350 °C)High Temp (300-350 °C)
– High Pressure of HHigh Pressure of H22 (30-40 bar) (30-40 bar)
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A fixed-bed continuous flow system measures the performance of adsorbents for various fuels
HPLCPump
(X ppm S)
Fixed-bed reactor
2 3
Fuel samples collected at regular intervals
1
0.2513 g
Samples weighed
1
Amount of Treated Fuel
C = C0
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This study focuses on liquid fuel flow through a packed bed
Fuel
Diesel Fuel
Density = 800 kg/m3
Flow Rate = 0.05 ml/min 0.0005 m/s
Fixed-bed reactor
Volume = 2.49 mLLength = 0.15 mWidth = 0.0025 m
Packed Bed: Activated Carbon
Porosity(ε) = 0.6 (experimental)Permeability(κ) = 1.88x10-11 m2
22
3
)1( vSK
pv DS
6
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Darcy’s Law describes flow through porous medium in terms of head gradients
Darcy’s Law:
kggk
x
hK
A
Term Meaning Units
q Darcy Flux m/s
Q Discharge m3/s
K Hydraulic conductivity m/s
k Permeability m2
µ Absolute viscosity Ns/m2
ρ Density kg/m3
h head m
ν Kinematic viscosity m2/s
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Boundary Conditions
r = 0.0025 m
Insulation BC h = 0.15 m
2-D Axial Symmetry
Inflow/Outflow = 0.005 m/s
Quantity Value Unit Description
ρ 0.8 kg/m3 Density
κ 1.88x10-11 m2 Permeability
µ .0024 Pa·s Dynamic Viscosity
f 0 kg/(m3·s) Source Term
sPasm
kg
m
kg
s
cmx
0024.00024.08.0103
3
22
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Solution
Inflow = 0.0005 m/sΔP = 1.069 atm
Outflow = 0.0005 m/sΔP = 0.975 atm
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Validation
qdx
h
p
32
2)1(180
sm
kg
s
m
mxsm
kg
x
h
2326
2
640000005.06.0)1050(
)6.01(1800024.0
atmPasm
kgm
sm
kg
sm
kgxh 095.9600960015.6400064000
22
Darcy’s Law
Column Length
From COMSOL Solution:
Maximum Pressure - Minimum Pressure = Pressure Drop1.069 – 0.974 = 0.095 atm
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Parametric Study
How does particle size and fuel flow rate affect the pressure drop?
Particle Size Permeabilityq
dx
h
p
32
2)1(180
Fuel flow rate Velocity
Case Flow Rate Velocity Particle Size Permeability Max Min P DROP1 0.05 0.0005 5E-05 1.875E-11 1.069 0.974 0.0952 0.20 0.002 5E-05 1.875E-11 1.278 0.9 0.3783 1.00 0.04 5E-05 1.875E-11 6.56 -0.999 7.5594 0.05 0.0005 5E-06 1.875E-13 8.095 -1.34 9.4355 0.20 0.002 5E-06 1.875E-13 29 -8.4 37.46 1.00 0.04 5E-06 1.875E-13 569 -187 7567 0.05 0.0005 5E-07 1.875E-15 770 -174 9448 0.20 0.002 5E-07 1.875E-15 2736 -1042 3778
9 1.00 0.04 5E-07 1.875E-15 5470 -20890 26360
0.05, 0.20, and 1.0 ml/min
50, 5, and 0.5 microns
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Summary
COMSOL can effectively model packed bed reactors
with the following parameters:– Adsorbent: porosity, particle size, density– Fuel: flow rate, density
Particle size and fuel flow rate affect pressure drop across small reactors
COMSOL can be used to find limits for scale-up models and other reactor designs
THANK YOU!THANK YOU!