Analysis of wall temperature change rate limiting supercritical CO₂ power system flexibility

The sCO₂ Brayton cycle has gained interest because of its flexibility and ability to provide higher thermomechanical conversion efficiency. However, considering the constraints imposed by the current heat-resistant material, it is imperative to maintain the wall temperature change rate within the permissible limits of the material to ensure secure system operation. This paper establishes a high-precision system dynamic model, which is calibrated and validated against experimental data. Based on this, the wall temperature change rate of high-temperature heat exchange components within the system under various boundary conditions are explored, highlighting crucial locations where attention should be paid to these changes. Building upon this, a methodology is proposed for determining the load limit of the system based on constraints imposed by wall temperature change rates. The results demonstrate that the temperature change rate is influenced by the thermal inertia of the fluid and the boundary condition. The maximum value is observed at the outlet of the HTR for the cold fluid when there is a variation in working fluid flow rate, breaking the traditional understanding that only the temperature of the boiler outlet should be concerned. Moreover, the load change limit is determined by the maximum wall temperature change rate of in the HTR under continuous high load conditions.