Investigation of the reduced specific energy consumption of the RO-PRO hybrid system based on temperature-enhanced pressure retarded osmosis

• Published in: Journal of membrane science Vol. 581; pp. 439 - 452
• Main Authors: Wang, Qun, Zhou, Zongyao, Li, Jinqiang, Tang, Qingchen, Hu, Yunxia
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2019
• Subjects: artificial membranes; Desalination; energy; energy recovery; freshwater; mathematical models; Operating temperature; Pressure retarded osmosis; Reverse osmosis; seawater; sodium chloride; specific energy; Specific energy consumption; temperature; Reverse osmosis; Specific energy consumption; Pressure retarded osmosis; Desalination; Operating temperature
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2019.03.079

Reverse osmosis (RO) has been widely used as a dominant desalination technology to produce fresh water from seawater (SW), but still consumes huge energy. To reduce the energy consumption of RO, pressure retarded osmosis (PRO) has been developed to extract osmotic energy from RO brine. In this study, the PRO process is optimized for efficient energy recovery from RO brine via one system/module-level mathematic model in RO-PRO hybrid system. The system-level model illustrates that the specific energy consumption (SEC) of the hybrid system can be significantly reduced when achieving a high permeate flow under high operating pressure in PRO. However, the specific PRO membrane configuration has to sacrifice a high permeate flow under high operating pressure. The module-level model finds that the increase of PRO operating temperature facilitates to achieve a high permeate flow under a high optimal operating pressure. Furthermore, results present that the SEC at a kiloton-scale SWRO desalination capacity can be reduced by 14.41% (0.6 M NaCl as a draw solution) and 17.93% (1.2 M NaCl as a draw solution) when the PRO operating temperature increases from 25 °C to 50 °C, confirming the great potential of temperature-enhanced PRO to further reduce the SEC of seawater desalination. [Display omitted] •RO-PRO system was analyzed via system/module-level mathematic model.•Flow-dependent pump efficiency was mathematically introduced.•Optimal operation criteria with high ΔQPRO and ΔPPRO were obtained.•High temperature was theoretically validated to efficiently operate the PRO.•Temperature-enhanced PRO could further reduce the SEC of the RO-PRO system.