Airtightness evaluation of rubber sealing layers for compressed air energy storage cavern using the solution-diffusion model

Accurate calculation of air leakage in compressed air energy storage (CAES) caverns during operation is essential for designing rubber sealing layers. However, current airtightness calculations for rubber sealing layers rely more on the pore-flow model rather than the solution-diffusion model. Compared with the pore-flow model, the solution-diffusion model can more accurately characterize the air permeation mechanism in rubber, therefore, the airtightness of cavern cannot be accurately assessed using previous method. In this study, we developed a modified airtightness calculation model of rubber sealed CAES cavern based on solution-diffusion model and the cavern air leakage was calculated. Furthermore, we investigated the air permeation characteristics in butyl rubber by pressure testing, from which the key parameters governing air permeation behavior were determined. Finally, a numerical model of the CAES cavern was developed and the long-term operation process of CAES was numerically simulated. The comparative analysis was conducted between the air leakage rates calculated by the pore-flow model and those predicted by the solution-diffusion model. The pore-flow model used both the permeability parameters from testing and the equivalently processed permeability parameters. It was illustrated that the pore-flow model using tested permeability parameters overestimates sealing layer leakage by 225 % compared to the solution-diffusion model, with 24-h air loss rates of 0.13 % and 0.04 %, respectively. The pore-flow model using equivalent permeability parameters gives close air loss rates to the solution-diffusion model. However, there is still a 34.5 % difference in result due to different fundamental mechanistic. The parameter analysis indicates that the air loss rate exhibits nonlinear growth with decreasing rubber sealing layer thickness, while higher air injection rates can result in reduced air loss.