Effect of turbine shaft cooling on the performance of supercritical carbon dioxide Brayton cycle system

The supercritical carbon dioxide Brayton cycle is a closed system with a turbine that generates CO2 gas leaks when operating at high temperatures, pressures, and rotational speeds. Currently, dry gas seals are primarily used to mitigate these issues at the shaft end of rotating components. However, due to their limited heat resistance in high-temperature turbines and the operational challenges they face in such environments, it becomes necessary to apply active cooling measures to the turbine shaft. However, introducing cooling gas affects turbine performance and alters the state of the working fluid, which significantly impacts the overall system performance. This study evaluates the influence of turbine shaft cooling on real operational performance by using an actual system as the basis for analysis. The results show that as the turbine inlet temperature increases, the efficiency loss due to turbine shaft cooling also rises. When the compressor outlet pressure remains constant, an increase in the mass flow rate of working fluid reduces the efficiency loss caused by turbine shaft cooling. When the mass flow rate of the working fluid in the system remains constant, the efficiency loss due to turbine shaft cooling initially increases and then decreases as the compressor outlet pressure rises. Finally, when the cooling gas inlet temperature rises, the system efficiency loss due to turbine shaft cooling increases.