Analysis And Optimization Of Energy System Based On Stirling Cycle And Water-salt Separation Process

Stirling power cycle,which has been successfully applied to energy cascade utilization and renewable energy exploitation,has the advantages of wide range of suitable heat sources,no emission in the closed cycle and high theoretical thermal efficiency.Thus,this dissertation mainly focuses on the Stirling power cycle and its application in the water-salt separation process,to conduct the following work.In view of the dynamic power output of dish solar Stirling engine affected by the fluctuating intensity of sunlight,the energy conservation between internal cycle and external solar receiver and cooling system is further considered,to propose a modified theoretical model which can reflect the direct relationship between external operating parameters and cycle performance.Based on this model,the influence of operating parameters in internal cycle,external heat source and sink on cycle performance was studied,and the influence mechanism from the perspective of temperature variance at hot and cold ends was analyzed as well.The mass of charged cycle gas was optimized to maximize the total energy output during a characteristic operating period,thus to clarify the theoretical dynamic cycle performance under the optimal condition.Stirling engine is adopted as the conversion unit of moderate temperature heat and solar energy to power the reverse osmosis process for clean and low-carbon fresh water production.For the brackish water reverse osmosis system powered by moderate temperature Stirling engine,the influence of hot end temperature,hydraulic pressure difference,energy recovery efficiency and membrane area on the performance of water production and energy consumption was studied,corresponding mechanism was analyzed as well.For the seawater desalination system driven by dish solar Stirling engine,it is proposed to store solar energy as stable salinity gradient energy while producing fresh water.To improve the separation limitation under the maximal bearable pressure difference for achieving better water production and energy storage performance,a self-diluted 2-stage reverse osmosis configuration was proposed.After evaluating the fundamental performance and analyzing the corresponding mechanism,the theoretical maximal water production and energy storage performance was evaluated by optimization.Based on dish solar Stirling engine,reverse osmosis and pressure retarded osmosis,cascade and complementary systems are proposed to achieve synergetic utilization of solar energy and salinity gradient energy.In the cascade energy system,reverse osmosis was adopted to consume the unstable power output of dish solar Stirling engine to generate concentration difference,then pressure retarded osmosis converts the stored salinity gradient energy to power output to achieve clean and stable utilization of solar energy.By comparing and analyzing the system performance under ideal and non-ideal conditions,the main direction to improve the efficiency of cascade energy system was clarified.In comparison,complementary energy system aims at the complementary utilization of solar energy,natural salinity gradient energy and low temperature waste heat.It uses the power of dish solar Stirling engine and low temperature waste heat to increase the concentration difference and temperature of natural river and sea water respectively,to achieve the stable utilization of solar energy,power generation by low temperature waste heat and power enhancement of natural salinity gradient simultaneously.According to the analysis,it is found that through the enhancement of osmotic pressure difference by solar energy and low temperature waste heat,the total power output is about twice as high as the power output from natural salinity gradient energy.The function of available potential is adopted to the power cycle of ideal gas.It is believed that the working fluid undergoes an iso-available potential process without exergy destruction while exchanging heat with external cold and heat sources,thus to achieve the complete conversion of technical work and thermal exergy.Then combining this process with isochoric heat regeneration,a novel thermodynamic cycle named iso-available potential and isochoric cycle is established.To reveal the influence of realistic internal and external heat transfer process on energy conversion performance of this cycle,finite-time thermodynamics was used to analyze the performance of this novel cycle under endoreversible conditions with perfect and imperfect heat regeneration.Results indicate that improving heat transfer performance can enhance the energy conversion efficiency,and there exists optimal heat transfer performance to maximize the power output.Based on this,external temperature difference for heat transfer at hot and cold ends were optimized to achieve the maximal power output of endoreversible cycle,and the corresponding theoretical cycle performance was evaluated as well.