Abstract:

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.

Key words: recycle, salinity gradient energy, reverse electrodialysis, sustainability, membrane contamination

摘要：

海水淡化装置排出的浓缩卤水会造成盐差能的浪费，逆电渗析电堆可以有效回收这种盐差能，并直接转换为电能。但是以海水和浓缩卤水为工作溶液的电堆性能易受工作溶液中不溶性物质的影响。为揭示这种影响规律，对逆电渗析电堆进行了定期的污染物附着实验研究。首先定期测试逆电渗析电堆的输出性能，获得了电堆性能衰减的规律；进而采用扫描电镜和能谱分析仪对离子交换膜和隔垫上的污染物种类进行分析，探究各附着物引起电堆性能下降的原因。结果表明：运行初期（0～20 d），电堆的开路电压、最大功率密度、能量转换效率，以及内阻变化速度快；运行后期（20～45 d），浓缩卤水侧的压降增速较快。本研究可为逆电渗析电堆的清洗策略提供一定的理论支持。

关键词: 回收, 盐差能, 逆电渗析, 可持续性, 膜污染