Optimization And Research Of A Closed Brayton Cycle Using Supercritical Carbon Dioxide

Since the development of the fourth-generation nuclear energy system,a closed Brayton cycle using supercritical carbon dioxide?S-CO2?has been extensively concerned.In this paper,the effects of various parameters on S-CO₂ Brayton cycles were studied.The thermodynamic properties of S-CO₂ Brayton cycles with different layouts and S-CO₂ combined cycles with different layouts were analyzed and compared,and the system optimizations were carried out to find the best operating conditions.The S-CO₂ Brayton cycles with different layouts were established by using Ebsilon software,and the performances of different cycles were compared and analyzed in this paper.The cycle maximum temperature,outlet pressure of main compressor,shunt coefficient of compressor,and the efficiency of each component,etc.on the cycle efficiency were studied by using the recompression S-CO₂ Brayton cycle system as the research object.The S-CO₂ Brayton cycles with different layouts were taken as Top Configurations,which were combined with organic rankine cycle?ORC?system or transcritical carbon dioxide?T-CO₂?cycle system by using Ebsilon software,and the combined cycles with different layouts were established and compared.Then the effects of ORC turbine inlet temperature,ORC condensation outlet temperature,and different organic working substances in ORC and T-CO₂ cycle conditions,etc.on the performances of the recompression S-CO₂/ORC combined cycle or the recompression S-CO₂/T-CO₂ combined cycle were studied in order to obtain the optimal directions of the systems.Finally,taking the recompression S-CO₂/ORC combined cycle as an example,the variations of exergy loss and exergy efficiency of each component in the process of changing cycle parameters were studied,and the optimum working conditions of the combined cycles were determined from exergy angle.By comparing and analyzing the cyclic models,it can be concluded that the simulation results based on Ebsilon are in good agreement with the experimental values,the cyclic models meet the simulation requirements and the research of this paper has reliability.The performance of combined cycle is improved relative to its independent S-CO₂ Brayton cycle.The study of combined cycle has important practical significance and is one of the optimization direction of the system.In the recompression S-CO₂/ORC combined cycle,when isoalkane is used as the working substance of ORC,the cycle performance of the system is optimal,and it is suggested that isoalkane should be used as the ORC working substance to optimize the combined cycle.In the process of changing cycle parameters,the exergy loss caused by heater is always the biggest,and the exergy efficiency of heater is always the lowest,which is due to the irreversibility of the heat exchange process.It is better to identify the components with lower performance in the system and to develop the potential of energy saving by using exergy analysis.