Performance Analysis And Optimization Study Of The Novel Combine Power And Cooling System Driven By Low-grade Heat Source

In recent years,in face of world energy shortages and excessive carbon emissions,how to recover and use low-grade heat sources has become a research hotspot in countries all over the world.However,the temperature of low-grade heat source is low,leading to the energy conversion efficiency in the conventional utilization process is low.Effectively improving the low-grade heat source utilization efficiency has become the research’s focus and difficulty.In this paper,two kinds of combined power and cooling systems driven by low-grade heat source are proposed,one of which is a splitter assisted combined power and cooling circulation system(SCCP),and another is extraction based combined power and cooling circulation system(ECCP).And then the system modeling,analysis and optimization are conducted.The influence of different parameter changes on the performance of the two cogeneration systems is analyzed.Besides,a cogeneration system combined SCCP with solar collectors(SCCP-PTSC)is proposed.The main study contents are shown as follows:1)Based on thermodynamic analysis theory,energy cascade utilization principle and thermoeconomic theory,the SCCP and ECCP systems are modeled and calculated.The results show that the cost of system equipment is concentrated in the turbine,the boiler,the regenerator and the condenser;system exergy destruction mainly occurs in the rectifier,the regenerator,the condenser and the boiler.Under given conditions,the thermal efficiency and economic cost of the SCCP is better,while the exergy efficiency of the ECCP is higher.2)The key parameters of heat source temperature,cycle high pressure,cycle medium pressure and split ratio(extraction rate)are selected to study their effects on system output,cooling capacity,thermal efficiency,exergy efficiency and the overall capital cost rate.The results show that the impact of key parameters on the performance changes of the two systems is roughly the same,as the parameters are varied,it is found that a conflict between the thermodynamic performance and the economic cost exists.3)Based on the parameter analysis,the highest thermal efficiency and the lowest overall capital cost rate,the highest combined exergy efficiency and the lowest overall capital cost rate are employed as two sets of objective functions to perform multi-objective optimizations.The cycle high pressure,heat source temperature and cycle medium pressure are selected as decision variables and the system is optimized by using multi-objective genetic algorithm(NSGA-II)in MATLAB optimization toolbox to obtain Pareto frontier solution.The optimal solution is selected using the TOPSIS decision-making method based on entropy weight.4)A power and cooling cogeneration system driven by parabolic trough solar collectors(PTSC-SCCP)is proposed.By system modeling and parameter analysis,the results show that the flow rate of the heat transfer fluid at the outlet of the collector first increases and then decreases with time;it decreases as the temperature of the heat transfer fluid at the outlet of the collector and the temperature of the heat transfer fluid at the boiler outlet increases.The SCCP net power output and cooling capacity output increase with the increase of the heat transfer fluid flow rate at the outlet of the heat tank.