Application of near critical behavior of equilibrium ratios to phase equilibrium calculations

Dan Vladimir Nichita (1) , Daniel Broseta (1) , François Montel (2, 1)

1 LFCR - Laboratoire des Fluides Complexes et leurs Réservoirs
2 CSTJF - Centre scientifique et Technique Jean Feger

We examine the asymptotic behavior of the equilibrium ratios (Ki) near the convergence locus in the pressure-temperature plane. When the Equation of State (EoS) is analytical, which is the case of most EoS of engineering purpose, Ki tends towards unity or, equivalently, its logarithm lnKi tends to zero, according to a power ½ of the distance to this locus. As a consequence, if lnKi is expressed as a linear combination of pure component parameters with coefficients only depending on mixture phase properties (i.e., reduction parameters), these coefficients obey a similar power law. Deviations from the ½ power law are thus fairly limited for lnKi and for the reduction parameters (at least in the negative flash window between the convergence locus and the phase boundaries), which can be exploited to speed up flash calculations and for quickly determining approximate saturation points and convergence pressures and temperatures. The chosen examples are representative synthetic and natural hydrocarbon mixtures, as well as various injection gas-hydrocarbon systems.

Mots clés: critical point; asymptotic behavior; convergence pressure; negative flash; reduction method; equation of state; Binary Interaction Parameters (BIPs)

Domaines: Physique [physics]

Dan Vladimir Nichita, Daniel Broseta, François Montel. Application of near critical behavior of equilibrium ratios to phase equilibrium calculations. Oil & Gas Science and Technology - Revue d'IFP Energies nouvelles, 2019, 74, pp.77. ⟨10.2516/ogst/2019049⟩. ⟨hal-02334280⟩