Energy Storage Science and Technology ›› 2021, Vol. 10 ›› Issue (5): 1503-1513.doi: 10.19799/j.cnki.2095-4239.2021.0235

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Using an ejector to intensify the charging process of a compressed air energy storage system

Shenghui ZHOU1(), Yang HE1, Haisheng CHEN2, Yujie XU2, Jianqiang DENG1()   

  1. 1.Xi'an Jiaotong University, Xi'an 710049, Shaanxi, China
    2.Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China
  • Received:2021-05-29 Revised:2021-07-03 Online:2021-09-05 Published:2021-09-08
  • Contact: Jianqiang DENG E-mail:zhoushenghui8019@stu.xjtu.edu.cn;dengjq@xjtu.edu.cn

Abstract:

An ejector can be applied in an adiabatic compressed air energy storage (A-CAES) system to intensify the charging process and improve its overall system performance. In this instance, the ejector will employ high-pressure air from the outlet of a compressor and use it as a primary fluid for entraining low-pressure air from ambient or outlet of earlier stage compressor. The use of an ejector can increase air charging speed and reduce thermodynamic loss of the throttle valve. In this work, the presence of a multiple ejector A-CAES (MEA-CAES) and a single ejector A-CAES (SEA-CAES) in the charging process was researched, respectively, and thermodynamic models of the two systems were constructed. The simulation results showed improved round-trip efficiency of an MEA-CAES under a constant-pressure operation mode and a SEA-CAES under a sliding-pressure operation mode compared with an A-CAES with a constant-pressure operation mode; the maximum increase of the two systems was 2.34%, and 2.73%, respectively. For the MEA-CAES, the work-time of ejectors and the cumulative mass of the ambient air entrained by ejectors both decreased when the entrainment ratio increased. The improvement in the round-trip efficiency of the MEA-CAES was larger in the lower initial storage pressure. It reflected a smaller entrainment ratio and a smaller heat-transfer temperature difference in the heating/cooling exchangers condition. At a fixed initial storage pressure, the SEA-CAES jam margin was larger than the A-CAES when using a sliding-pressure operational mode, and the jam margin decreased when the entrainment ratio increased. The improvement of round-trip efficiency for the SEA-CAES was larger in the higher initial storage pressure and the larger entrainment ratio condition. The study results provide a reference for the further optimization of compressed air energy storage.

Key words: ejectors, compressed air energy storage, in charging process, system performance, entrainment ratio, roundtrip efficiency

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