Design optimization and off-design performance analysis of one-dimensional supercritical CO2 Brayton cycle

• Turbine inlet pressure control improves cycle efficiency with minimal net power output change. • Inventory control strategies excel at adjusting a wide range, from 10% to 110% of net power output. • Developed models enable cycle design that prevents CO 2 condensation at the compressor inlet. • Stall margin of main compressor is better than re-compressor, whereas the choke margin is reversed. Supercritical carbon dioxide (SCO 2 ) recompression Brayton cycle (RBC) is an encouraging technology for thermal power conversion and heat harvest for a wide range of heat sources due to its high efficiency, low auxiliary power consumption, and compact size. However, most studies on its design and off-design performance analysis are limited to the simple zero-dimensional component models without considering aerothermodynamics and ambient conditions. In this study, we developed a set of fully one-dimensional components models for SCO 2 compressors, turbines, and heat exchangers and, then, applied them to the multi-objective design optimization of a SCO 2 cycle targeting a 50 MW net power output. The cycle off-design performance analysis methods and the control strategies were developed to countermeasure the performance degradation against varying cooling water temperatures and part loads. The multi-objective cycle design optimization demonstrates that the cycle thermal efficiency and total product unit cost can be 0.476 and 11.652$/GJ, respectively, for the 50 MW SCO 2 RBC cycle. The choke margin of the main compressor is 0.136 less than that of the re-compressor, and condensation can lead to a sharp decline in efficiency under high-flow conditions, causing the earlier onset of choking. The off-design performance analysis shows that the turbine inlet pressure control improves cycle efficiency below the design point of 317 K but does otherwise above the point. In contrast, the inventory control strategies can maintain stable cycle efficiency and achieve adjustable net power output between 10 % and 110 %. The findings have the potential to advance further commercial application of SCO 2 cycles in high-temperature thermal energy systems.