Feasibility analysis of the comprehensive utilization of coupling salt cavern CAES and insoluble sediment thermal storage

The cavern constructed in the layered inter-bedded salt rock contains significant insoluble sediment, whose heat storage and utilization potential remains underexplored. To investigate the feasibility of integrating compressed gas energy storage in salt caverns with heat storage in the sediment, a thermo-hydro-mechanical numerical model was developed using Comsol Multiphysics, accounting for the porous medium characteristics of the sediment layer. Firstly, the thermal response of the cavern was analyzed under varying sediment contents during conventional compressed gas storage. The specific heat capacity of the sediment was found to mitigate the thermal impact of hot air on the cavern wall. Temperature fluctuations in the surrounding rock decreased when the sediment layer’s vertical thickness exceeded 30 m. During the gas production stage, temperature fluctuations were restricted to below 0.5 ℃, while during the gas injection stage, they were less than 1 ℃. Subsequently, a dual-cavern model with connected channels was constructed to study the temperature field changes under short-term heat storage, respectively. Simulations showed that temperature fluctuations at the outflow interface during operation ranged from 45 ℃ to 55 ℃, which is 66% lower than at the injection interface, ranging from 30 ℃ to 60 ℃. After three operation cycles, sediment temperature was observed to vary periodically between 49 ℃ and 53 ℃, validating the feasibility of using sediment as an underground heat storage module for compressed air energy storage systems. Results demonstrate that the sediment’s heat capacity contributes to cave wall stability and offers a reference for developing a comprehensive system for utilizing compressed air and heat energy storage in sediment-filled salt caverns.