Dynamic Modeling and Characteristic Analysis of sCO2 Brayton Cycle System

Abstract The supercritical carbon dioxide Brayton cycle has advantages such as high thermal efficiency, inherent safety, simple structure, and compact space at medium to high heat source temperatures. Being able to cooperate with nuclear energy, solar energy, fossil energy or other heat sources for power generation has enormous development prospects. The FUSTAR system proposed by Xi'an Jiaotong University, utilizing the high core outlet temperature of the fluoride salt reactor and the supercritical carbon dioxide Brayton cycle system, has the characteristics of high efficiency, high safety, compact structure, and anhydrous cooling. It proposes a new solution for power supply in remote areas. However, the SCO2 Brayton cycle system is a highly integrated system, and its dynamic characteristics are very complex. There is an urgent need to establish a dynamic model of the SCO2 Brayton cycle system to lay the foundation for subsequent control system design. Based on the conservation equations of mass, momentum, and energy and the thermal hydraulic model, heat exchangers, regenerators, and coolers were established. A lumped parameter calculation model for turbine compressors has been established. A SCO2 Brayton cycle system model was built based on the MATLAB/Simulink platform, and the dynamic response of each device under disturbance was calculated. The results indicate that there are significant challenges in the stable operation of the SCO2 Brayton cycle under the most efficient operating strategy. The inlet parameters of compressors and turbines are highly sensitive to the outlet fluid pressure and temperature, and other auxiliary equipment is needed to ensure relatively stable inlet conditions for turbomachinery. The thermal inertia of the heat exchanger is relatively large, and the control response of the SCO2 Brayton cycle system requires a long time. The system responds slowly to changes in turbine and compressor speed and cannot be quickly adjusted. Rapid adjustment devices such as turbine throttle valves are required to respond quickly to changes in system load. The modeling and analysis method of SCO2 system can also be used for other configurations.