Multi-stage ejector based low-pressure leaking gas recirculation system for supercritical CO2 Brayton cycle

The supercritical carbon dioxide Brayton cycle (SCBC) is an appealing power system for its high compactness and efficiency. The ultra-high rotational speeds of mechanical components and the large pressure difference in turbomachinery lead to the supercritical CO2 (S-CO2) leakage affecting overall efficiency and stability. This study presents a four-stage ejector based leakage gas recovery system to reuse the leaking S-CO2 and enhance the system performance. This work proposes a design methodology for the four-stage ejector and then investigates its operating characteristics under different working conditions through a verified numerical simulation model. The findings indicate that the working conditions of the multi-stage ejector affect the number of ejectors in critical mode and then its entrainment performance. Increasing primary flow pressure improves the pressure lift performance of the multi-stage ejector, while variations in secondary fluid pressure have minimal impact. Besides, the final-stage ejector design is critical for maximizing pressure lift capacity of multi-stage ejectors, while the first-stage design highly influences their entrainment performance. Finally, compared to the compressor-based SCBC and the single-ejector-based SCBC, the proposed system can recycle 5.0 g/s of leaking S-CO2 and achieve a pressure lift of 7.5 MPa with a more compact geometric structure, thereby facilitating the miniaturization of SCBCs.