Robust algorithms for the calculation of phase equilibrium

摘要

An algorithm for the solution of the phase equilibrium problem at constant pressure andrntemperature (P,T flash) is presented. The approach is based on the formulation of thernphase stability problem as a dual optimisation problem that results from thernminimisation of the Helmholtz free energy. The problem is solved in composition andrnvolume space, which is especially suited to complex equations of state (EOS) that arernhigher than cubic functions in volume, and formulated in the Helmholtz free energy,rnsuch as SAFT (statistical associating fluid theory) [Chapman, W.G., Gubbins, K.E., Jackson, G.rnand Radosz, M. Ind. Eng. Chem. Res., 29 (1990), pp. 1709.]. With the proposed method, one isrnmathematically guaranteed to find all stable phases for multi-component systems withrnany number of fluid phases. Results are presented for the case of liquid-liquid equilibriarnin an asymmetric ternary system, modelled with a SAFT EOS.