Dynamic response characteristics of sCO2 mixtures under variable conditions

Using CO2-mixed working fluids in power cycle devices can enhance the thermal conversion efficiency of solar thermal power plants without altering the system layout. However, the dynamic characteristics of CO2-mixed working fluids in solar thermal systems remain unclear. The present study employs binary CO2 mixtures as alternative working fluids to construct a dynamic power generation system that integrates the Brayton cycle with parabolic solar energy. Based upon multi-objective optimization, the design operating parameters for the system were determined. The study also explored the dynamic characteristics of the system under mass and speed step change. The results indicated that CO2-propane achieved the highest cycle efficiency, though it was limited by a 25-s adjustment time and significant parameter oscillations, affecting its stability. In contrast, CO2-H2S demonstrated better dynamic characteristics due to its moderate thermal efficiency, excellent stability, and rapid response time. Furthermore, CO2-propane was sensitive to the compressor inlet pressure (CIP) and exhibited considerable fluctuations. When the CIP deviated from the design value, CO2-H2S experienced a temperature overshoot of up to 52 K, while CO2-propane exhibited delays in temperature and pressure due to the interactions of its physical properties, resulting in significant oscillations and a slower pressure response.