Thermo-economic analysis of regenerative supercritical CO₂ Brayton cycle considering turbomachinery leakage flow

The regenerative supercritical CO₂ Brayton cycle (RSCBC) has great potential to improve the energy utilization efficiency and reduce greenhouse gas emissions. The leakage of supercritical CO₂ into rotor cavity through labyrinth seals in turbomachinery including turbine and compressor inevitably reduces the cycle efficiency. Here, we propose a numerical method coupling the thermodynamic model with the labyrinth seal leakage model. The variations of turbomachinery leakage flow with cycle parameters and its effect on cycle thermo-economic performance are investigated. The optimal cycle parameters and thermo-economic performance are obtained by the multi-objective optimization. We find the cycle maximum pressure benefits the thermo-economic performance, while penalizes the sealing performance of turbomachinery labyrinth seal. Compared with ignoring the turbomachinery leakage, the optimal inlet state of the compressor vicinity of the pseudo-critical point that is adjacent to critical point when considering turbomachinery leakage. Furthermore, the turbomachinery leakage flow accounted for 2.5 % of the total flow under the optimized working condition, causing the thermal efficiency and exergy efficiency decrease 1.38 % and 3.52 % respectively, the heat exchanger area per unit power output and levelized energy cost increase 3.8 % and 3.83 % respectively. The proposed method and obtained results can provide some guidance for the optimal design of RSCBC system.