Comprehensive performance investigation of an ejector-assisted adiabatic compressed air energy storage: From numerical analysis of ejector to multi-objective optimization of the whole system

Compressed air energy storage (CAES) can provide dispatchable balancing capacity to support the stable and efficient operation of energy system with high-penetration of renewable energy sources. However, the employment of throttling valve to maintain constant-pressure operation of the turbine inevitably causes substantial exergy destruction, thereby constraining further improvements in CAES performance. Accordingly, an innovative ejector assisted CAES (EA-CAES) system is proposed in this study to enhance the system efficiency by recovering substantial fraction of throttling loss. To address the limitations of thermodynamic ejector model cannot resolve the internal flow mechanisms governing ejector behavior, an integrated computational framework that combines thermo-economic modeling with computational fluid dynamics simulation of the ejector is proposed to mechanistically evaluate the effects of geometry and operating conditions of ejector on the performance and to reveal the reliability implications for system performance improvements. Sensitivity analysis results show that the ejector parameters control the flow rate and entrainment ratio of the ejector by influencing the existing flow oscillations, the starting position and intensity of fluid mixing as well as the shock wave strength. The sensitivity analysis results from thermodynamic analysis of the system show a negative correlation between specific exergoeconomic factor and RTE. Among these parameters, rstar[jls-end-space/], rmix[jls-end-space/], and Pp have the most significant impact on thermo-economic performance of the system. To further improve system comprehensive performance, multi-objective optimization is employed to obtain the best trade-off solution. On the Pareto front, the maximum RTE can reach 55.79%, and the minimum specific exergoeconomic factor can achieve 238.22 $/MWh. The solution selected by the TOPSIS method results in the RTE of 55.14% and specific exergoeconomic factor of 294.41 $/MWh, attributed to the reduction in exergy destruction due to shock wave in the optimized ejector. This paper achieves efficient optimization of the ejector in the CAES system through a combination of thermodynamic analysis, exergoeconomic analysis and numerical simulation.