Analytical models for adiabatic compressed air energy storage (A-CAES) systems in lined tunnels

Abstract

Adiabatic compressed air energy storage (A-CAES) systems consist of an underground reservoir where compressed air is stored at high pressures. The ambient air is compressed by compressors located at the surface and the thermal energy is stored using thermal energy storage (TES) systems. The compressed air is stored in the subsurface reservoir (charge). Then, when the electricity is needed, the compressed air is released and expanded in gas turbines to produce electricity (discharge). In this paper, an analytical model has been developed to investigate the thermodynamic behaviour during air charge and discharge processes. Operating pressures from 4.5 to 7.5 MPa has been employed in lined tunnels in the compression and decompression stages. The model considers a 20 mm thick sealing layer, a 0.4 m thick concrete lining and a 1 m thick rock mass around the air. Air mass flow rates of 0.19 and 0.27 kg s−1 have been used in the charge processes for polymer material and steel, respectively. Finally, in the discharge processes the mass flow rate increases up to -0.38 and -0.45 kg s−1 for polymer and steel. The air temperature and pressure and the temperature and heat transfer in the sealing layer, concrete lining and rock mass have been analyzed for 100 cycles considering polymer material and steel as sealing layers. The heat transfer through the sealing layer reaches -150 and -95 W m-2 for steel and polymer, respectively. The results obtained show that the storage capacity increases when the heat transfer through the sealing layer increases.