Pressure retarded osmosis (PRO) is a promising technology to reduce the specific energy consumption of a seawater reverse osmosis (SWRO) plant. In this study, it is projected that 25.6-40.7millionkWh/day of energy can be recovered globally, if the brines from SWRO are used as the draw solution and diluted to the seawater level in a PRO system. Detailed integrated SWRO-PRO processes are developed in this study with the option to form a closed-loop SWRO-PRO process that can substantially reduce the pretreatment cost of desalination. The governing mathematical models that describe both the transport phenomena on a module level and the energy flow on a system level are developed to evaluate the performances of the SWRO-PRO processes. The model aims to investigate the performance of the hollow fibers as dilution occurs and provides guidelines on hollow fiber module design and process operation. Determining the dilution factor and the corresponding operating pressure of PRO is the key to optimize the integrated process. The specific energy consumptions of three SWRO-involved processes; namely, (1) SWRO without a pressure exchanger, (2) SWRO with a pressure exchanger, and (3) SWRO with pressure exchangers and PRO are compared. The results show that the specific energy consumptions for the above three processes are 5.51, 1.79 and 1.08kWh/(m of desalinated water) for a 25% recovery SWRO plant; and 4.13, 2.27 and 1.14kWh/(m of desalinated water) for a 50% recovery SWRO plant, using either freshwater or wastewater as the feed solution in PRO.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This research is supported by the Singapore National Research Foundation, Prime Minister's Office, Singapore, under its Environmental & Water Technologies Strategic Research Programme, administered by the Environment & Water Industry Programme Office (EWI) of the PUB under the project titled "Membrane Development for Osmotic Power Generation, Part 1. Materials Development and Membrane Fabrication" (1102-IRIS-11-01) and NUS Grant No. R-279-000-381-279. The special thanks are due to Dr. Han Gang, Dr. Zhang Sui, Dr. Li Xue, Dr. Xiong Junying and Mr. Cheng Zhenglei for their kind help.