New and accurate thermodynamic property data of CO2-EGS relevant working fluids with data fitted to existing thermodynamic models

The article presents a new setup for the accurate measurements of the phase behaviour of CO₂ mixtures relevant to CCS as well as a CO₂-H₂O working fluid for EGS, designed to cover the temperature range from -60 to 200 °C and up to 100 MPa in pressure. Included in the article are a description of the experimental setup, methodology, and results of the experimental campaign conducted in the SINTEF Energy Research labs for the EnerGizerS project. Phase equilibrium of the CO₂-water system has been investigated at the temperature of 50 °C and pressures between 1 and 17.5 MPa, using the analytical isothermal technique. These measurements are compared and verified against the existing data, followed by a presentation of the fit of GERG-2008/EOS-CG for CO₂ and H₂O. The maximum mole fraction of water in the CO₂[sbnd]H₂O mixture at measured conditions should not exceed 0.35 % and even less than 0.3481 % at 7.8 MPa to maintain the vapour phase of the mixture. The accuracy with respect to GERG-2008/EOS-CG varies from 1.044 % to 10.683 % near the critical values of sCO2. The estimated uncertainty of the setup is 31 mK for temperature measurements, from 0.4 to 2.5 kPa for pressure measurements and from 0.2 to 2.1 % of total combined relative uncertainty as regards the mole fraction. Despite the fact that the EGS reservoir could reach conditions above 150 °C and 50 MPa, lower values were adopted to validate the setup at 50 °C. Knowledge gaps at higher pressure and temperature values are still in dire need of filling. © 2024