Design and thermodynamic performance analysis of a novel adiabatic compressed air energy storage system based on liquid piston re-pressurization

Compressed air energy storage (CAES) is a crucial technology for integrating renewable energy into the grid and supporting the “dual carbon” goals. To further utilize compressed heat and reduce throttling losses, this paper proposes a novel A-CAES energy storage system with liquid piston re-pressurization (LP-A-CAES). During the energy release process, the air in the air storage tank enters the liquid piston directly without passing through the throttle valve, then undergoes further pressurization and expansion. This approach avoids throttling losses while increasing the expansion ratio of the expander, facilitating the efficient use of compressed heat. By establishing thermodynamic models for both the proposed re-pressurized A-CAES and the traditional A-CAES systems, we compare their performance variations with changes in key parameters. Results indicate that under design conditions, the system's energy efficiency is 70.74 %, a 5.07 % improvement over traditional throttle-based A-CAES systems. The total exergy loss of the system is 1.42 × 10¹⁰ J, with the compressor and expander units accounting for the largest exergy losses, at 32 % and 31.6 %, respectively. The liquid piston exhibits excellent isothermal performance, maintaining air and water temperature rises within 20 K and 2.5 K, respectively. Reducing the maximum pressure difference in the air storage tank enhances system performance, although the performance improvement of the re-pressurized A-CAES system compared to the traditional A-CAES system diminishes. Increasing the height of the thermal energy storage and reducing the diameter of the thermal storage material both contribute to higher system energy efficiency. When the height of the thermal energy storage increases from 4 m to 8 m, the system's efficiency rises from 70.04 % to 70.74 %. Similarly, reducing the diameter of the thermal storage material from 0.05 m to 0.01 m increases the system's efficiency from 68.85 % to 71.47 %.