Presentation Title

Multistage Hybrid RO-PRO for Energy-Efficient Seawater Desalination – A Model-based Optimization Study

Faculty Mentor

Dr. Mingheng Li

Start Date

18-11-2017 11:30 AM

End Date

18-11-2017 11:45 AM

Location

9-245

Session

Engineering/CS 2

Type of Presentation

Oral Talk

Subject Area

engineering_computer_science

Abstract

Normalized specific energy consumption (NSEC) in different reverse osmosis (RO) desalination systems with pressure retarded osmosis (PRO) and energy recovery devices (ERD) are investigated using a mathematical model. The model optimally allocates a fixed total membrane area between the different RO and PRO units, which is solved by a constrained optimization model. The dimensionless area parameter gamma_total = AtotalLp_Pi0/Q0 is varied to compare the NSEC of a two-stage hybrid RO-PRO system to different RO configurations at 30%, 40%, 50%, and 60% water recoveries. The hybrid RO/PRO configuration has a slightly lower NSEC compared to other RO configurations at the current industry standard (gamma = 0:8). Doubling at 1.6 creates a significantly large difference in NSEC of the two-stage hybrid RO-PRO configuration compared to other RO configurations.

Summary of research results to be presented

Matlab simulation was performed in order to investigate NSEC of described hybrid RO/PRO system at different design parameters gamma_total (0.2 to 2) and overall water recoveries Ytotal (30%, 40%, 50%, and 60%). In addition, PRO efficiencies were varied at 70%, 80%, 90%, and 100%.

A consistent trend is observed among different water recoveries that as PRO efficiency increases at a particular gamma_total, NSEC decreases. Furthermore, the impact of PRO efficiency is more significant at gamma_total being greater than unity than when it is less than unity. This is because the efficiency of the PRO is negatively affected by both internal and external concentration polarization, which result in reduced water flux and increased NSEC.

Energy consumption by proposed hybrid RO/PRO system with ERDs was also compared to existing popular systems such as multi-stage RO configuration with installed ERDs. Simulation results were assessed at mentioned water recoveries and PRO efficiencies, if applicable, of 70% and 100% for one-stage RO, two-stage RO, single-stage hybrid RO/PRO, and two-stage hybrid RO/PRO, all with ERDs employed. As total membrane area capital investment increases and/or membrane permeability improves, overall magnitude of NSEC is reduced at any water recoveries.

Ultimately, at current or low values of dimensionless membrane area, the allocation of membrane area is best applied to RO stages. The benefits of the PRO stages are not truly observed in this study until the dimensionless membrane area is significantly improved to values of 1.2 for 30% recovery and beyond for greater water recovery.

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Nov 18th, 11:30 AM Nov 18th, 11:45 AM

Multistage Hybrid RO-PRO for Energy-Efficient Seawater Desalination – A Model-based Optimization Study

9-245

Normalized specific energy consumption (NSEC) in different reverse osmosis (RO) desalination systems with pressure retarded osmosis (PRO) and energy recovery devices (ERD) are investigated using a mathematical model. The model optimally allocates a fixed total membrane area between the different RO and PRO units, which is solved by a constrained optimization model. The dimensionless area parameter gamma_total = AtotalLp_Pi0/Q0 is varied to compare the NSEC of a two-stage hybrid RO-PRO system to different RO configurations at 30%, 40%, 50%, and 60% water recoveries. The hybrid RO/PRO configuration has a slightly lower NSEC compared to other RO configurations at the current industry standard (gamma = 0:8). Doubling at 1.6 creates a significantly large difference in NSEC of the two-stage hybrid RO-PRO configuration compared to other RO configurations.