Study On Power Generation Performance Of Reverse Electrodialysis Stack With Ion-conducting Spacers

The salt difference energy at locations where river water flows into the sea as the energy source with the highest energy density in the ocean,and is less limited by climate conditions.However,it is also the energy source with the lowest utilization rate among many marine energy sources.Reverse electrodialysis(RED),as a kind of salt differential energy generation technology,has become a popular research topic in the field of new energy generation today because of its high energy density,simple device structure,high operability and low investment cost.However,in the traditional RED power generation process,the spacer used as the flow channel is usually made of non-conductive polyvinyl chloride material,which blocks the effective usage area of the membrane and hinders ions transport across the membrane,resulting in a shadow effect of the spacer.This introduces additional resistance,which significantly reduces the actual output power of RED.In order to address the above problems,an ion-conducting spacer type RED stack design is proposed in this paper.An experimental platform for RED power generation was built.Based on this platform,the power generation performance of the ion-conducting spacer type RED stack was analysed,the impact of spacer configuration on the power generation characteristics of stack was evaluated and the economic evaluation of stack has been carried out.Finally,the evolution of concentration polarization phenomenon under different factors and its influence on the power generation performance were studied.The ion-conducting spacer was designed based on the principle of permselective of membranes,and the power generation performance of conventional non-conducting and ion-conducting spacer type RED stacks was analyzed to verify the effectiveness of ion-conducting spacer type RED stack.The influence of spacer configuration on the power generation performance of stack was further studied.The results indicate that compared with traditional spacers,ion-conducting spacers reduce the spacer shadow effect of stack by more than 95%,but also introduce stronger concentration polarization phenomenon.Ultimately,due to the significant reduction in stack resistance,the output power density of ion-conducting spacers type RED stack is significantly increased.Increasing the flow rate and reducing the pore size of the spacer are both effective measures to suppress the spacer shadow effect,and are more conducive to limiting the concentration polarization phenomenon.However,the variation of the flow channel shape has little effect on the shadowing effect and the concentration polarization phenomenon.The highest power density of 0.81 W/m~2 obtained under pore size of 4.5 mm,flow rate of 40 L/h and cell pair of 3 increases by 50%compared with non-conducting spacers.Finally,the economic analysis suggests that the use of ion-conducting spacers is a cost-effective measure to increase the power output of RED when the number of cell pairs is less than 47.The evolution of the concentration polarization phenomenon in ion-conducting spacer type RED stack was studied for different membrane types,solution flow rates,number of cell pairs,solution concentrations and temperatures,and the effects of concentration polarization on the power generation performance of stack were obtained.The results show that the proportion of non-ohmic resistance in the total resistance of stack is less than 50%.The increase in flowrate and solution temperature can effectively suppress the concentration polarization of stack,which is conducive to the improvement of output power.However,the type of membrane,the number of cell pairs,and the concentration of solution hardly affect the concentration polarization.Nevertheless,all these factors have a significant impact on the power generation performance of stack.Among them,increasing the concentration of the concentrated solution alone is most beneficial for improving the power density of stack.Secondly,solution temperature was the second major factor in increasing the power density.Solution feed flow rate and type of membrane did not have a significant effect on power density,while an increase in the number of membrane pairs had a smaller negative effect on power density improvement.