Performance Analysis And Optimization Of Solar Organic Rankine Cycle Cogeneration System

In areas not covered by China’s border defense,island and other power grids and municipal heat supply networks,the local areas are remote,and generally adopt diesel power supply and coal-fired heating,which is costly and poor in environmental protection.Solar-driven cogeneration system has the advantages of small structure,small investment,output of two products of power supply and heating,which reduces the dependence on fossil energy.In this paper,a solar driven organic Rankine cycle cogeneration system is proposed,and its performance is analyzed and optimized.Firstly,the composition of the solar organic Rankine cycle cogeneration system is introduced,that is,the heat transfer oil absorbs heat through the solar collector and transfers the heat to the organic Rankine cycle through the evaporator for power generation.The heat transfer oil of the waste heat after heat exchange in the evaporator enters the heat exchanger for heat supply,and the power generation and heating system can operate independently.According to the fluctuation characteristics of solar energy,heat storage device and supplementary combustion device are added.The physical and mathematical models of each component of the system are established.As important components of the system,the efficiency and heat transfer model of collector and evaporator are carefully analyzed and calculated.According to the selection standard of organic working medium and considering the characteristics of safety,stability,environmental protection and economy,the working medium R245 fa most suitable for the system is determined.Then,based on the mathematical model of components,the simulation program is written with MATLAB.Given the electric load,three design parameters,evaporation temperature,superheat and pinch point temperature difference,as well as the operating parameters,thermal efficiency,rake efficiency and RSC（thermal cost rate of the system）are simulated.The simulation results show that with the increase of evaporation temperature,thermal efficiency increases,RSC decreases and raking efficiency decreases.With the increase of superheat,both thermal efficiency and raking efficiency will decrease,while RSC will increase.So the selection of superheat should be as small as possible.The thermal efficiency and raking efficiency both decrease with the increase of temperature difference between pinch points,but the area of heat exchanger decreases,which makes RSC smaller.The increase of thermal-electric ratio is beneficial to both thermodynamic and economic indexes,but the excessive thermal-electric ratio means that excessive heat collection is used for heating,which does not conform to the principle of energy step utilization.Then,through sensitivity analysis of design parameters,it is found that for thermal efficiency,the thermal-electrical ratio has the greatest influence and the pinch point temperature difference has little effect.In terms of raking efficiency,both the thermoelectric ratio and the temperature difference between the pinch points have a great influence.For RSC,the effects of thermal-electric ratio,evaporation temperature,superheat and temperature difference between pinch point are very great,of which the thermal-electric ratio is the largest and the temperature difference between pinch point is the smallest.Finally,in order to determine the optimal system design parameters,according to the above simulation results,the equation between design parameters and performance parameters is established by response surface method,and then the Pareto optimal solution set is obtained by multi-objective optimization using NSGA-II algorithm.According to ideal point method,the optimal design parameters are evaporation temperature 147.5℃,superheat 2℃,pinch point temperature difference 6℃.At this time,the system thermal efficiency is 13.60%,and the optimal solution set is determined by ideal point method.The raking efficiency is 32.88% and RSC is 0.64.At the same time,the storage time and solar multiple are optimized.Finally,the real climatic conditions are selected for the whole year simulation.Under the optimum conditions,the generation power is about 122.07 MWh and the heating power is 255.7 MWh.Compared with the same power and heat energy for diesel power generation and coal-fired heating,the carbon dioxide can be saved 178300 kg a year and the cost can be reduced by 0.92 times,which proves the environmental protection and economy of the system.