A new equation of state for CCS pipeline transport: Calibration of mixing rules for binary mixtures of CO₂ with N₂, O₂ and H₂

Highlights: • We develop a general framework for pressure-explicit equations of state for impure CO₂. • For CCS modelling, we consider mixture data around the CO₂ critical point. • We generalise a pure CO₂ equation of state to mixtures with N₂, O₂ and H₂. • For N₂ and H₂ our model captures coexistence data more accurately than the GERG. - Abstract: One of the aspects currently holding back commercial scale deployment of carbon capture and storage (CCS) is an accurate understanding of the thermodynamic behaviour of carbon dioxide and relevant impurities during the pipeline transport stage. In this article we develop a general framework for deriving pressure-explicit EoS for impure CO₂. This flexible framework facilitates ongoing development of custom EoS in response to new data and computational applications. We use our method to generalise a recent EoS for pure CO₂ (Demetriades et al., 2013) to binary mixtures with N₂, O₂ and H₂, obtaining model parameters by fitting to experiments made under conditions relevant to CCS-pipeline transport. Our model pertains to pressures up to 16 MPa and temperatures between 273 K and the critical temperature of pure CO₂. In this region, we achieve close agreement with experimental data. When compared to the GERG EoS, our EoS has a comparable level of agreement with (CO₂ + N₂) VLE experiments and demonstrably superior agreement with the O₂ and H₂ VLE data. Finally, we discuss future options to improve the calibration of EoS and to deal with the sparsity of data for some impurities.