Vapor/liquid equilibrium calculations by constrained free-energy minimization

A method is presented for approximate vapor/liquid equilibrium calculations using an equation of state. The method reduces the number of variables in the free-energy minimization problem by the introduction of suitably chosen additional constraints. It is based on a representation of a multicomponent fluid as a mixture of a small number of weakly polydisperse components. The approximation method can be used to accelerate sequences of vapor/liquid equilibrium calculations, such as are encountered in many engineering applications [plant design, hydrocarbon (oil/gas) reservoir simulation]. In realistic cases computing time has been reduced by up to 65%.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.