Generalized negative-flash method for multiphase multicomponent systems

We describe a generalization of the negative-flash method for computing the equilibrium compositions of systems that can form more than two fluid phases. We show the solution existence and uniqueness of the general Rachford–Rice problem for systems with any number of phases. A bisection based strategy is proposed either as a solution procedure to guarantee convergence, or as a preconditioning step of Newton based methods. A multi-stage negative-flash procedure is developed to identify the state of a multicomponent mixture where the maximum number of phases is arbitrary. The approach should be used in combination with a tie-simplex based modeling framework to provide a general method for phase behavior computations. Challenging numerical examples are presented to demonstrate the accuracy and robustness of the negative-flash approach.