Load-Following Operation of Supercritical Co2 Power Cycles Under Turbine Speed Control with Different Shaft Configurations

Abstract

The supercritical CO2 power cycle offers high thermal efficiency and wide load-regulation capabilities, making it a promising technology for thermal power generation. Ensuring stable load-following operation requires an effective control strategy to regulate power output while maintaining key system parameters. This study establishes and validates a dynamic model for a recompression supercritical CO2 power cycle based on an existing test bench, incorporating turbine speed control for system output regulation. Both coaxial and split-shaft configurations of turbines and compressors are considered, providing different degrees of freedom for independent turbine speed control. The feasibility of turbine speed control for load-following operation is analyzed across various shaft configurations, including split-shaft arrangements, coaxial coupling of the main compressor and turbine, and a parallel two-turbine configuration with coaxial layouts for either the main compressor or recompressor (2-TAC). The results indicate that the 2-TAC configuration achieves the highest part-load thermal efficiency and operational stability while maintaining a compact shaft design, making it well suited for space-constrained applications such as transportation systems. Additionally, compared to bypass and inventory control methods, turbine speed control improves efficiency and stability while requiring fewer control valves, which reduces potential leakage points and enhances system integration. However, turbine speed control introduces overheating risks in the high-temperature recuperator, potentially affecting material integrity over prolonged operation. To mitigate these risks, a modified control strategy is implemented to maintain a constant turbine outlet temperature through heat source power regulation. While this approach reduces thermal efficiency by 0.77% and increases recovery time by 221.2 seconds at 50% load, it effectively enables stable operation down to 50% load. Overall, the findings demonstrate the potential of turbine speed control under the 2-TAC design to enhance load-following performance and efficiency in supercritical CO2 power cycles, particularly for applications with spatial constraints.

Keywords: Supercritical CO2 power cycles, Dynamic analysis, Shaft configuration, Turbine speed control, Load-following operation, Control strategies