Design And Performance Analysis Of S-CO₂ Brayton Cycle Solar Thermal Power Generation System

Concentrated Solar Power（CSP）technology is a clean and efficient way which can convert solar energy into electrical energy.The development of CSP will help reduce the dependence on fossil energy and accelerate the transformation of the current energy structure.As one of the thermal power generation cycles,the supercritical CO₂（S-CO₂）Brayton cycle can be well integrated with the CSP station,and it plays a key role of converting thermal energy into electrical energy.Its Research and optimization can effectively improve the total efficiency of the CSP.Based on the existing layout of S-CO₂ Brayton cycle,a split-recompression Brayton combined cycle system model was established in this paper with Ebsilon software.The system performance was compared and analyzed when a variety of organic working fluids and transcritical CO₂ were used as working fluids in the bottom cycle.Then the influence of the coupling parameters of the combined cycle on the overall system was explored,and the coupling parameters were optimized based on genetic algorithm.The simulation results show that the efficiency of the combined cycle is higher than that of other organic working fluids when transcritical CO₂ is used as the bottom cycle working fluid;and there is an optimal combination of parameters that makes the Brayton combined cycle power generation efficiency reach the highest,the corresponding efficiency is 50.4%.In view of the energy storage requirements in tower solar power station,this paper designed the conventional molten salt heat storage scheme and two new types of compressed CO₂ energy storage scheme.The equipment selection,structure layout and parameter design of the energy storage system are carried out respectively,and the corresponding simulation model is established.Solar PILOT software was used to study the heat collecting system and simulate the optimal arrangement of heliostat field to explore the optical performance of the field and the performance of receiver under different energy storage schemes.The thermo-economic and techno-economic indexes of the three energy storage schemes were calculated under the operating conditions of the typical day.The influence of different heat storage hours on the system cost and the cost structure of different energy storage schemes was analyzed.The results show that the integrated scheme of compressed CO₂ energy storage and auxiliary combustion has the highest average daily efficiency（26.62%on summer solstice and 23.04%on winter solstice,respectively）and the lowest initial equipment investment.However,due to the additional cost of natural gas,the scheme has the highest levelized cost of energy（LCOE）at 0.1168（?）/k W·h.The LCOE of the integrated scheme of compressed CO₂ energy storage and molten salt heat storage was the lowest at 0.1048（?）/k W·h,which is slightly lower than that of the molten salt heat storage scheme.The two new tower solar thermal energy storage schemes and the method for performance analysis of power generation systems proposed in this paper have a certain guiding significance for the selection of working medium,parameter optimization and energy storage design of supercritical CO₂ Brayton cycle solar power generation system.