Optimization And Analysis Of Supercritical Carbon Dioxide Brayton Cycle Based On Tower Solar Power Generation System

Improving the utilization of renewable energy is one of the effective solutions to the energy and environmental problems.The solar thermal power generation can easily equip with the thermal storage system to realize continuous power generation for a long time and improve the stability of the power grid,which is not available in photovoltaics power generation.But the weakness of the conventional solar thermal power generation technology is the higher power generation cost,compared with the photovoltaics power generation and wind power generation.Therefore,to enhance the competitiveness of solar thermal power generation technology in renewable energy technologies,it is necessary to develop more cost-effective novel solar thermal power generation technologies.The SCO₂（Supercritical Carbon Dioxide）Brayton cycle is a power cycle that can be used in a solar thermal power generation system.This paper systematically analyzes and optimizes the SCO₂ Brayton cycle based on the tower solar power generation system.Firstly,the pinch point problem of regenerators on supercritical carbon dioxide Brayton recompression cycle was studied.And the position of the pinch point with the spilt ratio changing and the effects of spilt ratio on the performance of supercritical carbon dioxide Brayton recompression cycle were analyzed.In addition,the performance of simple regenerative cycle and the recompression cycle was compared.Secondly,Organic Rankine Cycle and Supercirtical Rankine Cycle were used as the bottoming cycles to recycle the waste heat of supercritical carbon dioxide Brayton recompression cycle.The effects of working fluid types and parameters of the bottoming cycle on the recovery of supercritical carbon dioxide recompression cycle and the optimization of waste heat recovery combined cycle were studied.Finally,the model of tower solar power generation system based on the SCO₂recompression Brayton cycle is established.The influence of the thermal storage temperature on the tower solar power generation system is studied and optimized.Then,the conventional Rankine cycle system of previous research was thermodynamically compared.The results show that:（1）As the split ratio increases,the pinch point of the recompression cycle regenerator first appears at the outlet of the low temperature regenerator on the low temperature side,and then appears in the low-temperature regenerator.Finally,it appears at the inlet of the low-temperature regenerator on the low temperature side.（2）At the same heat source temperature,SCO₂/SRC combined cycle is more efficient than SCO₂/ORC combined cycle.（3）The thermal efficiency of recompression cycle is not necessarily higher than that of a simple regenerative cycle for the split ratio.When the split ratio is greater than 0.408,the recompression cycle is more efficient than that of a simple regenerative cycle;The recompression cycle is more suitable for the waste heat recovery cycle with a smaller split ratio.While at a larger split ratio,the performance of the waste heat recovery cycle is almost the same between the recompression cycle and the simple heat recovery cycle.（4）The thermal efficiency and exergy efficiency of the solar thermal power generation system based on SCO₂ recompression cycle are 25.95%and 28.42%,respectively,which are 13.37%and 16.09%higher than the conventional solar thermal power generation system based on Rankine cycle,respectively.