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Optimal design and operation of a Draft Tube Spouted Bed Reactor for a
photocatalytic process
David Follansbee, John Paccione, Lealon Martin
Environmental DivisionFundamentals of Environmental Systems Engineering
Tuesday, November 6, 2007
Outline
• Motivation for process• Process Model• Parameters and Problem statement• Results• Conclusion and Future Work
Traditional photocatalytic Reactors• Photocatalytic slurry reactors
• Batch configuration• Photocatalyst particle separation• Photocatalyst loading limitations
• Photocatalytic fixed bed reactors• Cross sectional area limitations• Longer reactor length for increase throughput• High pressure drops• Mass transfer and kinetics are coupled
• Photocatalyst coating of reactor walls• Cross sectional and mass transfer limitations
Motivation for DTSMB
• Decoupling of mass transfer from kinetics
• Continual degradation of contaminant and regeneration of photocatalyst
• Counter-current design
• Photocatalyst immobilized on large, dense particles
Draft tube
Clean water outlet
Dirty Water inlets
UV
Jet flow
Process block diagram
Photo Reactor
Packed bedreactor
Draft tube
Gfa
yi
Gfa
yo
TargetParameters
DA
εA
Dt
DesignParameters
Gp
Gp
Gp
Gfd
Gfd
HA
Key designvariables
M
εD
WUV
WPump
.
.
Performancevariables
xo
xo
xi
Annular bed Model
V. Manousiouthakis and L. L. Martin. Computers & Chemical Engineering, 28(8):1237–1247, July 2004.
A. Y. Khan. Titanium dioxide coated activated carbon: Masters thesis, University of Florida, 2003.
Gp
GA
Gp
xi
xo
yo
yi
GA
DA
M HA
Mass load :
Mass balance:
Log mean concentration difference:
Height:
Langmuir adsorption:Assumptions:1. Counter current contact2. Constant fluid properties3. Costant particle size and density
H
yi
GA
yi
GA
GA
yo
Gp
xo
Gp
xi
HA
Draft tube model
Gp
Gp
GfD
GfD
Dt
εD
Ht
Z. B. Grbavcic, R. V. Garic, D. V. Vukovic, D. E. Hadzismajlovic, H. Littman, M. H. Morgan, and S. D. Jovanovic. Powder Technology, 72(2):183–191, Oct. 1992.
Slip velocity:
Mass flowrate of fluid:
Mass flow rate of particles:
Fluid-particle interphase drag coefficient:
Pressure Drop
Assumptions•Only non-accelerating portion of bed
UV model (Intensity, Power, and Kinetics)
Gp
Gp
xo
xi
Io
DUV
WUV
.
HUV
Intensity (Lambert-Beer Law):
Adsorption coefficient:
Power required:
• Modeled as a PFR• Pseudo first order reaction• No mass transfer limitations
I
Mass flow rate:
Rate equation:
Operation limitations and specifications • Mass flowrate can not exceed an upper limit where particles will not settle
in annular bed1. Gp<(1-mf)Aapva(max)
• Voidage in the draft tube has to be above a critical collapsing voidage and below 1
1. vc< D<1
1. The fluid velocity has to be great enough to ensure transport of particles1. u1.5vt
Test System
• Reactive Red degradation• 2 mm catalyst particles • TiO2/AC photocatalyst composites
• SiO2 substrate
Design Parameters p 2507 kg/m3
f 1000 kg/m3
f 1.119*10-3 Ns/m2
Dt 1 in
DA 6 in
DUV 2 in
Dp 2 mm
At
AA
AUV
Ht 2.5 m
HUV 1.22 m
vterminal 0.257 m/s
g 9.81 m/s2
Model Constants
Umf 0.0205 m/s
mf 1.74*106 kg/m-4
mf 0.447
vc 0.87
-0.9418
c1 0.9984
c2 -0.06014
Z. B. Grbavcic, R. V. Garic, D. V. Vukovic, D. E. Hadzismajlovic, H. Littman, M. H. Morgan, and S. D. Jovanovic. Hydrodynamic modeling of vertical liquid solids flow. Powder Technology, 72(2):183–191, Oct. 1992.
System Parameters
k 0.00833 s-1 C. ハM. So, M. ハ Y. Cheng, J. ハ C. Yu, and P. ハ K. Wong
I 180 W/m2 C. ハM. So, M. ハ Y. Cheng, J. ハ C. Yu, and P. ハ K. Wong
300 m-1 M. ハ Nazir, J. ハ Takasaki, and H. ハKumazawa
KA 602430 ppm-1 A. ハ Y. Khan. Titanium dioxide coated activated carbon
xt 0.272 kgcon/kgparA. ハ Y. Khan. Titanium dioxide coated activated carbon
Kla 0.00615 s-1
9.24 $/kWh
Problem Statement
Given:• Adsorptive mass transfer rates • Contaminant degradation rates • The annular flowrate and inlet concentration• Target concentration
Minimize
yi 10 ppm
yo 1 ppm
GfA 0.5 GPM
Schematic of Algorithm
Physical Properties
Design Parameters
Operation specs
Interval analysis
Math ModelOptimal design
and operating conditions
Minimizing objective function
SensitivityAnalysis
SensitivityAnalysis
Results
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Results cont.
Results cont.
Optimal Design and Operation
UV
HA 52.65 in
Gp 0.06 kg/s
Gf 5-25 GPM
D 0.922-0.986
0.5-0.9 $/hr
Conclusion
• Height of annular bed is insensitive to change in mass flowrate.
• Operating at a low mass flowrate (<0.1 kg/s) allows for the most robust performance.
• For the test system of TiO2/AC UV cost is high
• Motivates for optimization of catalyst properties i.e. density, UV adsorption, and kinetics
• Model must be experimentally validatedSpecifically the kinetics and mass transfer models
Acknowledgements
• Dr. Howard Littman• Dr. Joel Plawsky• Dr. David Dziewulski (DOH and SUNY school of Public health)• Martin Research Group• RPI funding• Department of Defense
Sedimentation voidage
0
0.1
0.2
0.3
0.4
0.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Voidage
Particle Mass flowrate (kg/s)
Grbavcic
vt
richardson-zaki