Jz. Hua et al., ENHANCED INTERVAL-ANALYSIS FOR PHASE-STABILITY - CUBIC EQUATION OF STATE MODELS, Industrial & engineering chemistry research, 37(4), 1998, pp. 1519-1527
The reliable prediction of phase stability is a challenging computatio
nal problem in chemical process simulation, optimization, and design.
The phase stability problem can be formulated either as a minimization
problem or as an equivalent nonlinear equation-solving problem. Conve
ntional 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 a global minimum. Thus, there has been considerable rec
ent interest in developing more reliable techniques for stability anal
ysis. Recently, we have demonstrated, using cubic equation of state mo
dels, a technique that can solve the phase stability problem with comp
lete reliability. The technique, which is based on interval analysis,
is initialization independent and, if properly implemented, provides a
mathematical guarantee that the correct solution to the phase stabili
ty problem has been found. However, there is much room for improvement
in the computational efficiency of the technique. In this paper we co
nsider two means of enhancing the efficiency of the method, both based
on sharpening the range of interval function evaluations. Results ind
icate that, by using the enhanced method, computation times can be red
uced by nearly an order of magnitude in some cases.