Search

Highlights: [•] The impact of impurities on the phase diagram of CO2 was studied and the capabilities of three mixture models were assessed. [•] An expansion in the phase transition envelope was observed in all mixtures compared to pure CO2. [•] The phase transition zone for CO2-impurities mixtures is located at higher pressures in comparison with pure CO2. [•] Looking to the models predictions, simulation deviations were observed close to the critical point. [•] Transporting liquid CO2 in pipelines with the presence of impurities requires higher pipeline pressure. [Copyright &y& Elsevier]

Abstract: Carbon capture and storage (CCS) technologies result in demands on thermodynamic-property models that were previously unknown in energy technologies. This article summarises recent developments allowing for an accurate description of thermodynamic properties of mixtures that are typical for oxyfuel processes and for compression and transport of separated CO2. It addresses homogeneous fluid state as well as phase equilibria of fluid and solid phases. However, phase equilibria with scrubbing agents, as they are common for post combustion processes, are out of the scope of this article. [Copyright &y& Elsevier]

Abstract: Formation of gas hydrates is an important feature of the water–carbon dioxide system. An accurate description of thermodynamic properties of this system requires a consistent description of both fluid (liquid, vapor, and supercritical fluid) and solid states (ice, dry ice, and hydrates) and of their respective phase equilibria. In this study, we slightly modified and refitted the gas hydrate model by A.L. Ballard, E.D. Sloan [Fluid Phase Equilib. 194 (2002) 371–383] to combine it with highly accurate equations of state (EoS) in form of the Helmholtz energy and Gibbs energy for other phases formed in the water–carbon dioxide system. The mixture model describing the fluid phases is based on the IAPWS-95 formulation for thermodynamic properties of water by W. Wagner, A. Pruß [J. Phys. Chem. Ref. Data 31 (2002) 387–535] and on the reference EoS for CO2 by R. Span, W. Wagner [J. Phys. Chem. Ref. Data 25 (1996) 1509–1596]. Both pure-fluid equations are combined using newly developed mixing rules and an excess function explicit in the Helmholtz energy. Pure-component solid phases were modeled with the IAPWS formulation for water ice Ih by R. Feistel, W. Wagner [J. Phys. Chem. Ref. Data 35 (2006) 1021–1047] and with the dry ice EoS by A. Jäger, R. Span [J. Chem. Eng. Data 57 (2012) 590–597]. Alternatively, the hydrate model was combined with the GERG-2004 EoS [O. Kunz, R. Klimeck, W. Wagner, M. Jaeschke, GERG technical monograph 15, VDI Verlag GmbH, Düsseldorf, 2007]. Since the gas hydrate model uses the fugacity of the gas component in the coexisting phase as an input variable, the accuracy of the predicted phase equilibria was significantly improved by using highly accurate EoSs for coexisting phases. The new hydrate model can be used in a temperature range of 150–295K and at pressures up to 500MPa. Together with the models describing the fluid and pure solid phases it allows for the desired accurate and consistent description of all phases and phase equilibria including, e.g., flash calculations into two and three phase regions. [Copyright &y& Elsevier]