RELIABLE PHASE-STABILITY ANALYSIS FOR CUBIC EQUATION OF STATE MODELS

The reliable prediction of phase stability is a challenging computatio nal problem in chemical process simulation, optimization and design. T he phase stability problem can be formulated either as a minimization problem or as an equivalent nonlinear equation solving problem. Conven tional solution methods are initialization dependent, and may fail by converging to trivial or nonphysical solutions or to a point that is a local but not global minimum. Thus there has been considerable recent interest in developing more reliable techniques for stability analysi s. In this paper we demonstrate, using cubic equation of state models, a technique that can solve the phase stability problem with complete reliability. The technique, which is based on interval analysis, is in itialization independent, and if properly implemented provides a mathe matical guarantee that the correct solution to the phase stability pro blem has been found.