Analysis And Optimization Of Thermal Economic Performance Of Supercritical CO₂ Recompression Tower Solar Thermal Power Generation System

In recent years,due to the world’s emphasis on renewable energy power generation,tower solar thermal power（CSP）has ushered in great development.The cycle efficiency of the tower CSP system using the steam Rankine cycle is 35%-45%,the tower CSP system based on the supercritical CO₂（S-CO₂）Brayton cycle can achieve a cycle efficiency of more than 50%when the temperature reaches 700°C.This can greatly improve the thermal economic performance of tower solar thermal power generation system.The key parameters such as initial parameters have an important impact on the thermal economic performance of the tower CSP system.Therefore,based on the key parameters of the system,it is very necessary to analyze the thermal economic performance of the S-CO₂Brayton cycle combined with the tower CSP system.The main research contents of this paper are as follows:Firstly,the model of direct S-CO₂ recompression tower photothermal（SPT）power generation system was established.Under different radiant intensity,the key parameters impacting the exergy efficiency of different equipment,subsystems and SPT power generation system as well as the heat loss of the heat absorber are studied.The results show that the exergy loss of the heat absorber is the maximum and thermal loss is the minimum,exergy loss of power cycle subsystem is minimum and thermal loss is maximum under the design condition.Under variable condition,the maximum point of the exergy efficiency of the heat collection subsystem and SPT power generation system moves to the direction of higher turbine inlet temperature and higher exergy efficiency.The turbine inlet pressure has a smaller effect on the heat loss of the heat absorber,while the turbine inlet temperature has a larger effect on it.Secondly,based on the SPT power generation system model,the impact of key parameters on the system performance were studied and analyzed.The system’s total exergy loss rate（SPT power generation system）is minimized as the target,and based on the orthogonal array,genetic algorithm（GA）is utilized to optimize the parameters to obtain the smallest total exergy loss rate of the system.Meanwhile,under the optimal parameter conditions,the system is calculated in time series at different times during the summer solstice day and day.The results show that the best turbine inlet pressure reaches the upper limitation of the given range,the optimal cycle low pressure does not necessarily have to be close to the critical pressure,and the optimal cycle high temperature does not necessarily have to be as high as possible.At different times,the total exergy loss rate of the SPT generation system depends on the exergy loss rate of the heat collection subsystem.Finally,based on the SPT power generation system model,the preliminary economic analysis and optimization of the system are carried out.The economic evaluation of the system is carried out from the influence of turbine/main compressor inlet temperature and turbine/main compressor inlet pressure on annual total cost,annual profit rate and investment payback period.The results show that when turbine inlet temperature rises and turbine/main compressor pressure increases,the annual profit rate and investment payback period are optimal.When the inlet temperature of the main compressor increases,the main economic indicators such as the annual profit rate and investment payback period of the system change greatly.The main performance indexes of the system after parameter optimization are greatly improved compared with those before optimization.Among them,the annual profit margin increased by 21.63 percentage points and the payback period decreased by 58.44 percent.