Study on Factors Influencing Energy Storage Efficiency in Long-Narrow Roadway of Abandoned Mines for Compressed Air Energy Storage

The use of abandoned mine roadways for compressed air energy storage (CAES) presents a viable solution for the large-scale integration of renewable energy. However, the intricate thermodynamic interactions between compressed air and surrounding rock in long, narrow roadways significantly affect energy storage efficiency. This study investigates the thermodynamic evolution and energy conversion characteristics of the CAES in such environments, identifying key efficiency-influencing factors. A three-dimensional computational fluid dynamics (CFD) model was developed, incorporating a horseshoe-shaped roadway geometry and conjugate heat transfer at the air-rock interface. Multicycle simulations were conducted under varied operational conditions (charging/discharging mass flow rates, temperature, and pressure) and structural parameters (roadway length and cross-sectional area). Exergy analysis was applied to quantify the energy storage efficiency and thermodynamic losses. Results show that temperature and pressure exhibit cyclic fluctuations, with heat transfer to surrounding rock, leading to a cumulative temperature rise of 0.74 K over seven cycles. Energy storage efficiency decreases by 3.2% per cycle due to thermal losses. Optimizing the charging-to-discharging flow ratio (e.g., from 1.75 to 2.13) enhances energy conversion efficiency by 12-18%, whereas increasing roadway length reduces efficiency by 8% per 100 m extension, thus it is recommended not to exceed 500 m. Thermal properties of the surrounding rock have negligible short-term effects but become critical in long-term operations. This research offers essential insights for optimizing CAES design in abandoned mines, emphasizing operational strategies to minimize thermal losses and criteria for selecting structural parameters.