Consistent delumping of multiphase flash results

An analytical and consistent delumping method, recently formulated and implemented for processes involving two-phase flash calculations, is extended to flash calculations involving any number of coexisting phases. The equation of state considered is a two-parameter cubic equation of state (EoS) with van der Waals mixing rules and non-zero binary interaction parameters (BIPs). The method is used for calculating three- and four-phase equilibria in a series of hydrocarbon mixtures containing different amounts of carbon dioxide, nitrogen, hydrogen sulphide and water. In all examples, the location, compositions and proportions of the coexisting phases obtained by the delumping procedure are extremely close to those obtained from calculations with the detailed fluid, even in cases where the multi-phase region is very tiny. To the best of our knowledge, this is the first time that a delumping procedure is formulated and successfully used for multiphase equilibria.