The air tightness model of compressed air storage energy caverns is then established. In the model, the permeability coefficient and air density of sealing layer vary with air pressure, and the effectiveness of the model is verified by field data in two test caverns.
An air tightness test is defined as a procedure to determine the air tightness of a given pipeline at air tight joints and U traps. In order to maintain the pressure in the pipeline, a certain amount of air has to escape. Thus, an air tightness test also determines the percentage of lost air over a certain time period.
During the operation of compressed air storage energy system, the rapid change of air pressure in a cavern will cause drastic changes in air density and permeability coefficient of sealing layer. To calculate and properly evaluate air tightness of polymer sealing caverns, the air-pressure-related air density and permeability must be considered.
Finally, a compressed air storage energy cavern is taken as an example to understand the air tightness. The air leakage rate in the caverns is larger than that using air-pressure-independent permeability coefficient and air density, which is constant and small in the previous leakage rate calculation.
In this context, the high-pressure air penetration in the polymer sealing layer is studied in consideration of thermodynamic change of the cavern structure during the system operation. The air tightness model of compressed air storage energy caverns is then established.
The model is validated using field measurement data, numerical simulations, and analytical solutions. Subsequent simulations were conducted to analyze air leakage, pore pressure, and leakage range under various operating conditions. Finally, the impacts of different parameters on air tightness were assessed.