Performance analysis of supercritical carbon dioxide Brayton cycle with leakage reinjection system

Rotating machinery in supercritical power cycles typically employs dry gas seals or labyrinth seals, and the leakage gas needs to be reinjected to maintain long-term operation. This paper focuses on a MW-scale supercritical CO₂ power generation system. State of leakage gas after passing through the dry gas seals and labyrinth seals were estimated. The impact of reinjecting the leakage gas on system performance was evaluated through simulations. The effects of different leakage reinjection locations on the performance of the supercritical CO₂ Brayton cycle were analyzed, and the performance impacts of using dry gas seals versus labyrinth seals were compared. The results demonstrated that using a dry gas seal and reinjecting the leakage gas back into the hot-end inlet of the high-temperature regenerator led to the smallest reduction in system efficiency, with a decrease of 1.013 %. For the labyrinth seal, reinjecting the leakage gas from the compressor into the turbine inlet, and from the turbine into the hot-end inlet of the high-temperature regenerator minimized the reduction in system efficiency. When the outlet pressure of leakage gas after the labyrinth seal ranged from 5 to 9 MPa, system efficiency improved as the outlet pressure increased, and the heat exchanger area per unit of power output decreased, enhancing the overall compactness of the power plant. These findings provide valuable insights for the design and optimization of supercritical CO₂ Brayton cycle leakage reinjection systems.