Influence of pollutants in seawater on performance of reverse electrodialysis stacks
Salinity gradient energy,existing in electrolyte solutions with different concentration,can be harnessed for power production cleanly.The concentrated brine discharged from the seawater desalination device will cause a waste of salt difference energy.The reverse electrodialysis(RED)stack can effectively recover this salt difference energy and directly convert it into electrical energy.However,the performance of the RED stack using seawater and concentrated brine as the working solution is affected by insoluble substances in the working solution,which may cause performance decrease of the RED.Here,experiments were conducted on a RED stack to investigate the degradation phenomenon caused by the pollutants in concentrated brine and seawater.The experiments aimed to assess the impact on the performance of the RED stack,as well as the types of contaminants and elements in the RED stack.First,the performance of the RED stack was periodically tested to monitor changes in open-circuit voltage,maximum power density,energy conversion efficiency,internal resistance,and pressure drop.These measurements were recorded to analyze the causes of the performance degradation.Subsequently,scanning electron microscope and energy dispersive spectrometer were used to analyze the types of contaminants and elements present on the ion-exchange membranes and the spacers.Experimental results show that the open-circuit voltage,maximum power density,and energy conversion efficiency of the power reactor decrease rapidly,and there is a noticeable increase in internal resistance at the early stage of operation(0-20 d),and in the later stage of operation(20-45 d),the pressure drop increases on both the concentrated brine and seawater sides,with the concentrated brine side showing a particularly rapid growth rate.The decline in the performance of the RED stack is primarily attributed to the accumulation of pollutants on the ion exchange membrane and spacer pads.Additionally,due to their different charges,the anion exchange membrane and spacer pads exhibit different behaviors.The main reason for the decline in performance of the RED stack is the buildup of contaminants on the ion exchange membrane and spacer.The types of contaminants on the anion exchange membrane and cation exchange membrane differ because of their distinct charges.This study provides theoretical support for cleaning strategy of the RED stack.
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