Optimizing Supercritical Carbon Dioxide Cycles Performance With Respect to Split Ratio and Intermediate Pressure

Abstract

Supercritical carbon dioxide power cycles are getting more attention every day due to their high efficiencies. This study has examined determination of split ratio and intermediate pressure for maximum efficiency in various supercritical carbon dioxide recompression cycle configurations. Five cycle variants have been analyzed: reheating, partial cooling, partial cooling with reheating, intercooling, and intercooling with reheating. Partial derivatives of efficiency with respect to split ratio and intermediate pressure have been determined and set equal to zero to find optimum split ratio and intermediate pressure. This process has isolated the system's response to these two key parameters while keeping other cycle variables constant. Across all configurations, following parameters have been fixed: inlet temperatures of 550 °C and 32 °C for turbine and compressor components, an energy source temperature of 600 °C, an ambient temperature of 27 °C, and pressure limits of 75 bar and 200 bar. Optimization results show that recompression–reheating cycle achieves the highest efficiency of 39.62% at an optimum intermediate pressure of 139.43 bar and a split ratio of 71.1%. Recompression–partial cooling cycle exhibits the lowest maximum efficiency at 37.35%, with an optimum intermediate pressure of 85.87 bar and a split ratio of 62.6%. Recompression–partial cooling with reheating cycle reaches a maximum efficiency of 37.98% at an optimum intermediate pressure of 123.94 bar and a split ratio of 67.2%, while the intercooling cycle and intercooling with reheating cycle attain 39.57% at an optimum intermediate pressure of 80.03 bar and a split ratio of 66.4% and 39.59% at an optimum intermediate pressure of 116.1 bar and a split ratio of 69.2%, respectively. Additionally, exergy destruction has been calculated for all components of the system and it is related to thermal efficiency of the cycle.