Dynamic multiple-phase flash simulation: Global stability analysis versus quick phase determination

Abstract Both, a method for global stability analysis based on a necessary and sufficient equilibrium criterion and a simplified method for quick phase determination based on necessary equilibrium conditions have been included into dynamic multiphase flash models. The potential and limitations of both methods in dynamic process simulation are discussed and illustrated for binary and multicomponent systems. It is shown that the quick method provides correct results for a large class of technically relevant systems. In complex cases, however, the method fails to converge or converges to incorrect results. Global stability analysis improves reliability and robustness at the expense of a high computational demand. As a reliable and reasonably fast method is needed for dynamic simulation in design and control of chemical processes, these results motivate the development of a hybrid dynamic flash model which combines the advantages of both methods. A first step towards hybrid modelling is presented.