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Autori: Alexandre Lapene , Dan Vladimir Nichita, Gérald Debenest and Michel Quintard
Editorial: Elsevier, Fluid Phase Equilibria, 297 (1), p.121-128, 2010.
A novel Modified Rachford-Rice equation is developed for three-phase equilibrium calculations in hydrocarbon-water systems, based on the free-water assumption, i.e., the water-rich liquid phase consists of pure water only. In the inner loop of the flash algorithm, the three-phase problem (consisting in a system of two non-linear equations) is replaced by a pseudo two-phase problem (consisting in a non-linear equation). Unlike previous formulations, the new Modified Rachford-Rice function is guaranteed to monotonically decrease between two adjacent asymptotes. The negative flash concept is used, and a search window is proposed for the vapor fraction. The new free-water flash method proved to be robust, and excellent agreement between full three-phase flash and pseudo two-phase free-water flash was obtained for various test problems. The proposed method is very useful in compositional reservoir simulation of certain oil recovery methods and in process simulation.
Cuvinte cheie: flash calculations; three-phase equilibrium; water; free-water flash; Rachford-Rice; equation of state