Power production from seawater and discharge brine of thermal desalination units by reverse electrodialysis

Abstract

Direct discharge of brine with high concentration from desalination plants can deteriorate offshore ecology. Intensive treatment on the brine, such as salt production and precious metals extraction, will consume large amounts of energy and cost. Here, the reverse electrodialysis (RED) method is introduced to harvest the salinity gradient energy (SGE) between brine with high concentration (HS) and seawater (LS) for power production and alleviating the damage to marine ecology. Firstly, natural seawater with different concentrations is injected into a single-stage RED stack to verify the feasibility of harvesting this SGE. Secondly, performances of the stack are analyzed under different feed parameters, including concentration, feed temperature, and flow velocity. Finally, the multi-stage reverse electrodialysis (MS-RED) is proposed to harvest more SGE and make energy conversion more efficient. Experimental results show that the HS-LS combination has higher output power and a wider voltage range than the LS-freshwater combination. Concentration of brine is the most critical factor affecting performances of the RED stack, followed by feed velocity and temperature. Energy conversion efficiency increases to 18.0% with stages number increasing to 22. This study can give some suggestions for the capture of SGE between brine discharged from desalination plants and seawater.