Study On The Dynamic Characteristics Of S-CO₂ Recompression Brayton Cycle

Human beings are always faced with the problem of energy sustainability and environmental protection.It is the only way to realize the sustainable development of energy and environment to develop and utilize new energy,change the diversified energy structure and improve the conversion efficiency of energy system.The Brayton cycle energy conversion technology of supercritical carbon dioxide（S-CO₂）has high thermoelectric conversion rate and is expected to bring revolutionary changes in the field of energy and power technology.Firstly,the REFPROP is used to calculate the physical Properties of CO₂ and the variation characteristics of CO₂ in the pseudo-critical region are analyzed.The mathematical model of S-CO₂ recompression Brayton cycle system is established,and the calculation program is compiled with MATLAB software.The accuracy of the calculation program is verified by comparing with experimental data in literature.The influences of key parameters such as shunt coefficient,inlet and outlet pressure of the main compressor,inlet temperature of the main compressor,the inlet temperature of turbine and isentropy-efficiency on the thermal efficiency of the cycle were calculated and analyzed.Simulink software was used to build the dynamic simulation model of S-CO₂recompression Brayton cycle.According to the idea of modular modeling,the circulation system was divided into a series of modules for processing.Based on the basic theories of thermodynamics,fluid mechanics and heat transfer,the Brayton cycle mathematical model of S-CO₂ recompression was established,mainly including compressor,heater,turbine,regenerator,precooler and other modules.Each module is compiled and implanted into the simulation platform through the module library and toolbox of software.On the simulation platform,according to the corresponding relationship of each component in the S-CO₂circulation system,the modules of each component are coupled and connected,so that the dynamic simulation system can be established.By comparing the simulation results under the same input conditions with the experimental results in the literature,it is proved that the simulation system has high precision and can meet the requirements of dynamic analysis.Finally,the dynamic simulation model was subjected to disturbance test to analyze the response curves of parameters such as temperature,pressure,heat exchanger heat exchange and turbo mechanical power in the S-CO₂ recompression Brayton cycle system under disturbance of heat source heating power,turbine mechanical speed and system mass flow.The results show that the model has high accuracy and fast simulation speed,and can truly reflect the dynamic response of system performance under parameter perturbation.When the system operates stably at the design point of working condition,the parameters of the circulation system are more sensitive to the decrease of heat source power,the increase of turbine speed,and the change of flow.The temperature change at the outlet of the precooler is small and the pressure change is relatively large under various disturbances,but this has a significant impact on the whole system.According to the dynamic characteristics of the perturbation,the control strategy of the S-CO₂recompression Brayton cycle system was proposed.The research results can provide basic design parameters and theoretical basis for the design of components in the S-CO₂ Brayton cycle system,and provide technical basis for advanced energy conversion technology and promote the early implementation of engineering applications.