Improved Pseudo Root for Cubic Equations of State

Abstract An analytical method for calculating a pseudo root for cubic equations of state proposed by Zhao and Saha (1998) has been implemented to perform vapor-liquid equilibrium (VLE) calculations in a commercial simulation software package. In this study, the proposed method is validated by applying it to rigorous blowdown modeling solved through a simultaneous solution method rather than traditional sequential method. Our experience and suggested improvements are also presented in this paper to maintain continuity in the transition between real root and pseudo root. Continuity is very important for VLE calculations, especially for a simultaneous solution approach in which VLE equations are solved simultaneously with other model equations. In this paper, analytical derivatives of the pseudo root are also given to support the continuous results.