Phase Equilibrium Computational Algorithhs of Continuous Kixtures

Two continuous mixture phase equilibrium algorithms which can be used for vapor-liquid equilibrium calculation involving verymany-component fluid mixtures are proposed. The algorithms are applied to the case of simulated gas-condensate systems with analytical results. The proposed continuous mixture techniques reduce the required computer time significantly While they retain accuracy of the predictions. In addition, the proposed continuous mixture algorithms are applicable to varieties of multicomponent mixtures, equations of state, and mixing rules. INTRODUCTION There have been a number of new development in the theory of continuous mixtures: Blum and Stell (1979) have introduced a diameter distribution to characterize a hard-sphere continuous mixture, they also have extended the Percus-Yevick approximation for hard-sphere mixture to the continuous fluids of hard-spheres. Aris and Gavalas (1966) have introduced functional analysis into the thermodynamic description of polydisperse system and into the kinetics of continuous reactions such as polymerization or cracking. Concerning petroleum distillation, Hoffman (1968) have presented a numerical integration method in which he adopts an integrated form of the Clausius-Clapeyron equation and Raoult's law to compute vapor pressures of petroleum fluids. He uses a Gaussian distribution, with the normal boiling temperature as the independent variable, to describe the vapor and liquid phases. Similar procedures as Hoffman's have been presented by Kehlen et al. (1985) whose treatment is based on Raoult's law and compositions described by normal density function to derive thermodynamic properties of continuous mixturesAn approach using an equation of state for solving phase equilibrium problems in continuous mixtures, has been developed by Gualtieri et al. (1982). They use the van der Waals equation of state to solve the fractionation of a polydisperse impurity dissolved in a solvent and the shift of the critical point due t0 the presence of a polydisperse impurity. Similar results for flash calculation of continuous mixtures which are based on the Redlich-Kwong equation of state have been reported by Brian0 (1983). Cotterman and Prausnitz (1985) have introduced tvo techniques for phase equilibrium calculation of reservoir fluids, one of which is a continuous model and the other is a semi0378-3812/86/$03.50