Thermodynamic analysis of a typical compressed air energy storage system coupled with a fully automatic ejector under slip pressure conditions

Abstract

To solve the problem of energy loss caused by the use of conventional ejector with fixed geometry parameters when releasing energy under sliding pressure conditions in compressed air energy storage (CAES) system, a fully automatic ejector capable of adjusting key geometric parameters to maintain the maximum ejection coefficient by an automatic control device according to the running parameters is proposed in this paper. By establishing a thermodynamic model of a typical CAES system coupled with a fully automatic ejector, the effect of the fully automatic ejector on the system performance is studied under sliding pressure conditions. The results show that the fully automatic ejector has the most sensitive ejection coefficient with the variation of high-pressure gas pressure. The cycle efficiency and exergy efficiency of the proposed system were 56.91% and 52.64%, respectively. Compared with the coupled conventional ejector, the cycle efficiency, exergy efficiency, and output power of the system were increased by 0.93%, 0.81%, and 4.59%, respectively. The exergy loss of the combustion chamber is the largest among the components within the system, accounting for 65.2% of the total exergy loss, followed by the heat exchanger, which accounts for 13.8% of the exergy loss, while the fully automatic ejector has the smallest exergy loss, accounting for only 0.8% of the total exergy loss. When the extraction point is at the first stage of the turbine, the system cycle efficiency and external energy efficiency vary parabolically with the extraction pressure, but the system performance will change abruptly when the pressure at the extraction point approaches 1.5 MPa. The system performance index is more sensitive to the change of turbine inlet temperature than other variables. Reducing the heat exchanger heat transfer temperature difference and increasing the fully automatic ejector outlet pressure are the effective ways to improve system performance.