Thermophysical Properties of CO2 Rich and Natural Gas Mixtures

Captured CO2 for CCS purposes contains impurities (e.g. H2, N2, Ar, CO, etc.). These impurities can affect thermophysical properties of the stream. From the technical and safety points of view, knowledge of the thermophysical properties of the fluid is essential for efficient and safe transportation and processing. Different predictive models have been suggested to determine the thermodynamic properties of fluids. However, capabilities of these models for accurate estimation of the thermodynamic properties of CO2 natural gas mixtures need to be evaluated.
In this study, density, speed of sound and solid-fluid equilibria of different experimental samples were investigated. The speed of sound and the density were measured simultaneously to provide enough data for determining other derived properties of the fluids. Finally, the obtained results were compared with predictions of the GERG equation of state (EoS).
Density measurements were carried out using a vibrating tube densitometer (VTD) and an isochoric setup. Using the VDT, densities were measured at five isotherms at temperatures and pressures up to 423 K and 65 MPa, respectively. This densitometer was calibrated using water, methane and nitrogen. Moreover, employing the isochoric setup, density measurements were carried out at low temperatures down to 210 K. The validity of the isochoric measurements were tested by conducting isochoric density measurements for nitrogen.
The speed of sound in the experimental fluids was obtained using a high-pressure high-temperature acoustic cell equipped with two ultrasonic transducers. This setup was calibrated using water and nitrogen.
Using the measured densities and sound velocities, derived properties of three samples were calculated from different methods. In the first approach, the SBWR-EoS was matched on the measured densities. Then, the tuned SBWR-EoS was used to determine other derived properties of the fluid. In the second approach, numerical integration method was used to quantify other derived properties.
In addition, solid-fluid equilibrium measurements were conducted using a BT2.15 Calvet type DSC calorimeter. In this apparatus, the solid-fluid equilibrium temperatures of some of the experimental samples were determined at various pressures.