Numerical study on adiabatic compressed air energy storage system with only one ejector alongside final stage compression

Abstract

Sliding-pressure operation of the centrifugal compressor in the charging process makes adiabatic compressed air energy storage (A-CAES) system maintain high roundtrip efficiency. However, the final stage compressor may produce choke at low backpressure. This paper proposes an A-CAES system with one ejector alongside the final stage compressor to alleviate the choke. Dividing outlet air of the third stage compressor into two parts, one part goes into the fourth stage compressor and flows into the ejector as primary fluid. Another goes into the ejector as secondary fluid. The charging process includes two periods. A thermodynamic model of the proposed system is built for simulation study. Simulation results show that the backpressure variation range of sliding-pressure compression reduces by 39.87% with adding ejector. The maximum mass flow rate of A-CAES with sliding-pressure operation is closer to the choke margin. Increasing initial storage pressure benefits to decrease energy consumption and improve exergy efficiency of proposed system. Compared with the A-CAES with constant-pressure operation, the proposed system’s roundtrip and exergy efficiency increase with increasing entrainment ratio and initial storage pressure. For A-CAES with ejector, sliding-pressure operation, and constant-pressure operation, their maximum roundtrip efficiencies reach 57.94%, 58.32% and 55.31%, respectively, under different initial storage pressures.