Enhancing Part-Load performance of the simple recuperated supercritical carbon dioxide cycle through shaft separation

In this study, the operability of a simple recuperated supercritical carbon dioxide (S-CO₂) cycle under off-design conditions, specifically during part-load operation, was quantitatively analyzed by implementing shaft separation to place a compressor-driving turbine (CDT). For off-design evaluation, both the heat exchanger and turbomachinery were designed in one dimension before being inserted into the off-design platform of the system. To ensure physical consistency, all turbines were designed using the same set of loss models. The analysis results revealed that the efficiency of the single-shaft configuration decreased by about 12 %p at 10 % output, while that of the separated-shaft configuration decreased by < 8 %p under the same conditions. The arrangement of the CDT and power turbine had minimal impacts on off-design performance. The power required to drive the CDT–compressor operating at the optimal Revolution Per Minuate was found to be less than 5 % of the design output. These findings imply that layout modifications can enhance overall off-design efficiency and that the incorporation of a motor that supplies about 5 % of the design output for the CDT–compressor set significantly improves part-load operability. This requirement is practical, as such a motor is typically required for startup procedures. Although these results were obtained from the simplest recuperated S-CO₂ cycle, similar approaches could enhance off-design performance in more complex cycles such as waste heat recovery or S-CO₂ recompression cycles. The findings of this study demonstrate that altering the shaft arrangement while considering off-design operability can significantly enhance the operability of S-CO₂ systems.