RELIABLE COMPUTATION OF PHASE-STABILITY USING INTERVAL-ANALYSIS - 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 non-physical solutions or to a point that is a local but not global minimum. Thus there has been considerable recen t interest in developing more reliable techniques for stability analys is. 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 i nitialization independent, and if properly implemented provides a math ematical guarantee that the correct solution to the phase stability pr oblem has been found. (C) 1998 Elsevier Science Ltd. All rights reserv ed.