Thermodynamic analysis of cavern and throttle valve in large-scale compressed air energy storage system

The compressed air energy storage system has the potential to enable large-scale implementation of renewable energies. However, the exergy destruction in the throttle valve and cavern is an important factor that affects the overall performance of the system. The conventional diabatic compressed air energy storage system consisted of compressors, heat exchangers, cavern, combustion chambers and turbines was studied and parameters of the Huntorf plant were adopted for calculation. Mathematical models of the components in the compressed air energy storage system were developed based on the equation of state for the real gas and the thermodynamic laws. The models are derived on the basis of assumptions that the inlet and outlet air flow rates of the cavern are negligible and that the system is operated in steady state. The test data of the Huntorf plant during the initial test was used to validate the models. Sensitivity analyses were conducted to identify the domain parameters that affect the exergy destruction in the cavern and throttle valve. The results indicated that 18.85% of the stored exergy was lost in the cavern and throttle valve during a complete cycle. The exergy destruction in the cavern was higher than that in the throttle valve, and the exergy destruction coefficients in the cavern and throttle varied with opposite tendencies when the parameters were changed. The heat transfer coefficient, injected air temperature, and initial temperature of the cavern were found to highly affect the total exergy destruction coefficient. Higher injected air temperature and lower cavern initial temperature reduces the total exergy destruction in the cavern and throttle valve.