Use of salt caverns in the energy transition: Application to Power-to-Gas–Oxyfuel

Abstract

Power-to-Gas–Oxyfuel, or Electrolysis-Methanation-Oxyfuel, is an advanced concept that addresses some concerns of conventional Power-to-Gas: supply of high-purity CO2, release of greenhouse gases to the atmosphere and fate of the O2 from electrolysis. Due to the intermittent nature of several renewable energy sources, massive storage is needed to balance supply and demand. This paper focuses on the storage phase required for Electrolysis-Methanation-Oxyfuel. Synthetic CH4, O2 and CO2 have to be stored at different times. Due to the high fluid rates and volumes required, salt caverns are potential candidates. While salt caverns have been used for decades to store CH4, storage of CO2 and O2 has not been implemented to date. A generic seasonal scenario with a 200 MW oxyfuel unit is investigated. Numerical modelling that couples cavern thermodynamics with the thermomechanical response of the surrounding rock salt has been performed. The results, although exploratory, show that the caverns would be stable as they respect the criteria commonly used for cavern design. Moreover, combined storage of CO2 and O2 in the same cavern, rather than independent storage, would reduce the number of caverns needed and the likelihood of phase changes, but it would require separation of the two substances at the ground surface.