On the Phase Behaviour of the Carbon Dioxide - Water Systems at Low Temperatures (original) (raw)
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Fluid Phase Equilibria, 2013
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 and E.D. Sloan [Fluid Phase Equil. 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 and A. Pruß [J. Phys. Chem. Ref. Data 31 (2002) 387-535] and on the reference EoS for CO 2 by R. Span and 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 and W. Wagner [J. Phys. Chem. Ref. Data 35 (2006) 1021-1047] and with the dry ice EoS by A. Jäger and R. Span [J. Chem. Eng. Data 57 (2012) 590-597]. Alternatively, the hydrate model was combined with the GERG-2004 EoS [O. Kunz, R. * Corresponding author, email: vins.vaclav@seznam.cz, telephone: +420 266 053 152, fax: + 420 286 584 695 2 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 ÷ 295 K and at pressures up to 500 MPa. 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.
Effect of impurities on thermophysical properties and phase behaviour of a CO2-rich system in CCS
International Journal of Greenhouse Gas Control, 2013
a b s t r a c t CO 2 captured from flue gases may contain impurities such as O 2 , Ar, N 2 and water. The presence of such impurities in the CO 2 stream can lead to challenging flow assurance and processing issues. The aim of this communication is to present experimental results on the phase behaviour and thermophysical properties of carbon dioxide in the presence of O 2 , Ar, N 2 and water. The effect of these impurities on density and viscosity was experimentally and theoretically investigated over the range of temperature from 243.15 K to 423.15 K up to 150 MPa. A corresponding-state viscosity model was developed to predict the viscosity of the stream and a volume corrected equation of state approach was used to calculate densities. Saturation pressures and hydrate stability (in water saturated and undersaturated conditions) of the CCS stream were also experimentally determined and modelled. This work shows that the thermodynamic models and approaches adopted were able to satisfactorily describe the thermophysical properties and phase behaviour of a typical CO 2 -rich stream resulting from flue gases.
Effect of Common Impurities on the Hydrate Stability of Carbon Dioxide Rich Systems
CO 2 produced by carbon capture processes is generally not pure and can contain impurities such as N 2 , H 2 , CO, CH 4 and water. The presence of these impurities could lead to challenging flow assurance issues. The presence of water may result in ice and/or gas hydrate formation and cause blockage. The aim of this communication is to evaluate the risk of hydrate formation in a rich carbon dioxide stream. The three phases HLV equilibria of the ternary CO 2 + (N 2 or CH 4 or O 2 or Ar or H 2 or CO) + water systems were determined at a constant composition (4.56% N 2 , 7.09% H 2 , 5.85% CH 4 , 5.87% CO, 5.03% Ar, and 5.34% O 2 in dry basis). The tests were determined by standard constant-volume isochoric equilibrium step-heating techniques. A thermodynamic approach was employed to model the phase equilibria. The thermodynamic model was used to predict the hydrate dissociation conditions of CO 2 and CO 2 rich streams in the presence of free water. Subscript Cal Calculated property exp...
Fluid Phase Equilibria, 2018
This paper deals with the modeling of the phase behavior of CO 2 in water, methanol, ethanol and acetone. The phase equilibria of pure substances and binary mixtures are correlated using different equations of state: PC-SAFT, PCP-SAFT, CPA and GEOS. The adjustable specific coefficients of pure fluids are determined by regression of vapor pressure and saturated liquid and vapor densities data. For binary mixtures, the binary cross-interaction parameters are deduced by regression of the vapor-liquid equilibrium data for wide ranges of temperature and pressure. The obtained results show that the GEOS equation of state appears to be the most adequate in the modeling and prediction of the isothermal vaporliquid phase behavior in the vicinity of the critical region. Moreover, the GEOS model is most adequate in the prediction of the three-phase liquid-liquid-vapor equilibria of CO 2 /water system at temperatures around and below the critical temperature of CO 2 and a formation of a second rich-CO 2 liquid phase. In addition, the dew curves of the water/CO 2 system were most accurately predicted by the GEOS model. The isothermal-isobaric vapor-liquid equilibria of CO 2 /methanol/water and CO 2 /ethanol/water were predicted and the comparison with the literature data demonstrated some advantages to the GEOS equation of state.
The Journal of Supercritical Fluids, 2008
Vapor-liquid equilibria (VLE) data for the carbon dioxide + ethanol system at 293.15, 303.15, 313.15, 333.15, and 353.15 K up to 11.08 MPa are reported. The experimental method used in this work was a staticanalytical method with liquid and vapor phase sampling. The new experimental results are discussed and compared with available literature data. Measured VLE data and literature data for carbon dioxide + ethanol system were modeled with a general cubic equation of state (GEOS) using classical van der Waals (two parameters conventional mixing rule-2PCMR) mixing rules. A single set of interaction parameters was used to calculate the global phase behavior in the binary mixture carbon dioxide + ethanol in a wide range of temperatures (283.3-453.15 K).
Industrial & Engineering Chemistry Research, 2012
Accurate knowledge of the compositions of the equilibrium phases in the systems containing gas hydrates is essential for many hydrate-based separation processes. Unfortunately, there are limited sets of such experimental data available in the literature partly due to the difficulties in measurements of the compositions of the phases in equilibrium with gas hydrate. Consequently, satisfactory accuracy of the measurements may not be obvious. Therefore, reliability of the corresponding data should be checked prior to their further applications. In this article, we present a thermodynamic assessment test (consistency test) based on the area test approach for the experimental compositional data of vapor phase in equilibrium with gas hydrate + liquid water for the carbon dioxide + methane or nitrogen + water system. The van der Waals and Platteeuw (vdW-P) solid solution theory is used to model the hydrate phase, and the Valderrama−Patel−Teja equation of state (VPT-EoS) along with the nondensity dependent (NDD) mixing rule is applied to deal with the fluid phases. The results show that only one of the studied experimental data sets seems to be thermodynamically consistent, and the rest of the data seem to be either not fully consistent or inconsistent.
Energy Procedia, 2012
The accuracy of the extended corresponding state equation SPUNG is preliminary evaluated for the density, and Vapor Liquid Equilibrium (VLE) calculations of the CO 2-water mixtures. The evaluation is done by comparing the behavior of SPUNG to experimental data whenever possible, and three other state-of-the-art equations of state (EoS) of different classes. The three EoS are; the cubic equation Soave-Redlich-Kwong (SRK) with the van der Waals mixing rules, SRK with Huron Vidal mixing rules (SRK-HV), and the multi-parameter approach GERG-2004. The latter is used as a reference in the single phase region. The single phase studies for both liquid and vapor state are conducted at a mixture of 98% CO 2 and 2% H 2 O. Recommendation for future work is highlighted.