Modeling and Optimization of Reverse Osmosis Desalination: AnIndustrial Case Study

Steven Chao, Sophia Bui, Mingheng Li

Department of Chemical and Materials EngineeringCalifornia State Polytechnic University, Pomona

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Outline

1 Motivation

2 Background

3 Objective

4 Methodology

5 Results

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Motivation

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US Desalination Capacity

1Cooley, Heather, Peter H. Gleick, and Gary Wolff. Desalination, with a Grain of Salt. A California Perspective. (2006): n.pag. Web.

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Economic Considerations

Energy Consumption

Capital Investment

Brine Disposal

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Economic Considerations

Energy Consumption

Capital Investment

Brine Disposal

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Economic Considerations

Energy Consumption

Capital Investment

Brine Disposal

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Background

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What is Reverse Osmosis?

Osmotic pressure is the minimum amountof pressure needed to stop water fromflowing across the membrane

Water flow will be reversed by applyingpressure greater than osmotic pressure

1Benefits of Reverse Osmosis, http://greenbookpages.com/blog/286167/benefits-of-reverse-osmosis/

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Factors Affecting Driving Force in RO Module

J = Lp(∆P −∆π)

Pressure drop

Concentration polarization

2Induceramic, n.d. photograph, http://www.induceramic.com/rsrc/1313636320994/porousceramicsapplication/filtration-separation-application/Cake20filtration20figure.jpg

3Nalco, n.d. photograph, http://image.slidesharecdn.com/reverseosmosismodule-151109040456-lva1-app6892/95/reverse-osmosis-module-21-638.jpg?cb=1447042092

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Objective

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Chino I Desalter

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RO Desalination Plant

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Methodology

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Geometry

Platform: COMSOLTM Multiphysics

FilmtecTM BW30-400 RO element

Fully developed inlet velocity profile

4Johnson and Busch, Engineering Aspects of Reverse Osmosis Module Design, http://www.lenntech.com

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Governing Equations

Navier Stokes Equation (Hydrodynamics)

ρ(u · ∇)u = ∇ ·[−pI + µ(∇u + (∇u)T )

]ρ∇ · u = 0

Diffusion-Convection Equation (Salt transport)

∇ · (D∇c) = u · ∇cn · (−D∇c + cu) = 0

Water Flux (Boundary condition)

Jw = Lp(P − Pp − fosc)

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Results

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Coupled Transport Phenomena

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Pressure Drop

0 0.05 0.1 0.15 0.2 0.25 0.3Avg Interstitial Velocity ū (m/s)

0

5

10

15

20

25

30

35

40

45

50

55Concentrate

Pressure

Drop-dP/dx(kPa/m) Spacer-filled channel

Open channel

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Average Mass Transfer Coefficient

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System Level Model

dQ

dx= −JwA ; Q = Q0 at x = 0

d(∆P)

dx= −kQ1.67 ; ∆P = ∆P0 at x = 0

Jw = Lp[∆P −∆π exp(Jw/(k̄Q0.40))]

∆π = Q0∆π0/Q

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Parameter Fitting and Prediction

0 1 250

100

150

200

250

300

350

RO Stage

Flo

w r

ate

(m3 /

hr)

ModelPlant data

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RO Plant Trial

Production rate kept constant at 1235GPM

Adjusted simultaneously

⇒ Intake Flow⇒ Valve Position

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Transmembrane Pressure

0.75 0.8 0.85 0.9 0.95 1Recovery

12.5

13.5

14.5

15.5

16.5

Transm

embrane∆Pinlet(bar)

Plant dataModel

0.75 0.8 0.85 0.9 0.95 1Recovery

9

10

11

12

13

14

15

16

Transm

embrane∆Poutlet(bar)

Plant dataModel

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Normalized Energy Consumption

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Conclusions

By increasing recovery from 80% to 90% while maintainingproduction rate:

10% electricity reduction ($40k/year in savings)Reduction in waste volume by 50% ($360k/year in savings for disposal)

Making incremental changes so that operating cost is reducedwithout substantially shortening membrane life.

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Acknowledgments

Inland Empire Utility Agency

Special thanks to Brian Noh and Moustafa Aly for plant trials.

Petroleum Research Fund

This work is partially supported by the American Chemical SocietyPetroleum Research Fund (No. 55347-UR9).

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References

Li, M.; Bui, T.; Chao, S. Three-dimensional CFD analysis ofhydrodynamics and concentration polarization in an industrial ROfeed channel, Desalination, 397, 194-204, 2016.

Li, M.; Noh, B. Validation of Model-Based Optimization of BrackishWater Reverse Osmosis (BWRO) Plant Operation, Desalination, 304,20-24, 2012.

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MotivationObjectiveMethodologyResults