Preliminary Research On Capacitive Deionization Regeneration Method Used For Absorption Air-conditioning System

At present,the building sector becomes one main part of the total energy consumption,while the air-conditioning system is the leading consumer in buildings.The vapor compression air-conditioning system is efficient,but the refrigerant brings some environmental problems.Absorption air-conditioning system is environmental friendly,however,it lacks attraction because of the energy waste in the thermal regeneration process.To improve the performance,the membrane regeneration absorption air-conditioning system based on electrodialysis(ED)method was proposed.The system is driven by electric power,which avoids the harmful heat in the regeneration.It has been proved to be feasible on the treatment of absorbent solution.Nevertheless,the mass transfer resistance and the cost of the ion exchange membrane restrict the system's development.To solve this problem,this paper proposed capacitive deionizaition(CDI)to replace ED method used for absorption system.Instead of membranes,the electrode pairs is installed in the new system,which improves the performance and reduces the cost.Besides,as a capacitor,the energy recovery makes the system more promising.However,CDI method is mainly used to regenerate electrolyte with low concentration,there is no experiment about absorbent solution.We have designed a experiment device to solve absorbent solution from the aspect of the voltages,the concentrations,and the kinds.Based on the experimental results,the feasibility of its engineering application is analyzed.We established the model of the CDI regeneration absorption system.Based on the energy and mass balance,the COP of the system is given.On this basis,the influences of the average voltage,solute concentration and energy recovery was researched.The comparison has been made between the new system,the thermal system,the membrane system and compression system.In addition,the concept of multistage CDI system was proposed to further improve the performance.According to the preliminary analysis,CDI method has shown good adsorption characteristics by treating with LiCl and LiBr solution,and the adsorption capacity,the charge efficiency increase as the concentration increases,which is quite useful for engineering application.The COP of the new system can approach 5 in theory,but the practical value could be 2-2.5 by considering the restrict of the engineering structure.The CDI regeneration system shows the superiority on the performance compared with the thermal regeneration and membrane regeneration system.Under some conditions,it is even efficient than compression system.We also verified the energy storage capacity of the equipment.The results implied the energy can be reused although the equipment was designed without considering the energy storage.Double-stage CDI units betters the performance with optimized parameters,which indicates multistage units could be more efficient.Consequently,CDI regeneration system could be promising for future application.