Power harvesting from concentrated seawater and seawater by reverse electrodialysis

Abstract

The concentrated seawater discharged from desalination plants has high salinity and temperature, and the direct discharge not only deteriorates offshore ecology but also energy waste. Here, the reverse electrodialysis (RED) approach is introduced to capture the salinity gradient energy (SGE) between the concentrated seawater and seawater for power production. The feasibility of this approach is verified by experimental and simulation studies on a RED stack. The influence factors including concentration, flow rate, and temperature, are analyzed to evaluate its performances. Aimed to harvest more SGE and improve energy conversion efficiency, a preferred independent loop control strategy of multi-stages RED stacks is proposed and studied. The maximum gross power density of concentrated seawater (3.0 mol/L)/seawater (0.60 mol/L) can reach 0.49 W/m2, which is slightly lower than 0.50 W/m2 of seawater/freshwater (0.050 mol/L) under the same experimental conditions. Meantime the reliability of the model is well verified by experiment, and the maximum error is lower than 7%. A modest increase in numbers of multi-stages RED stacks not only decreases the discharge concentration but also harvests more power and higher energy conversion efficiency. In addition, performances of multi-stages stacks are more sensitive to feed concentration and flow velocity.