optimal design and operation of a draft tube spouted bed reactor for a photocatalytic process david...

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

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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