A generalized flash algorithm to bridge stability analysis and phase split calculations

Abstract

Phase split and phase stability algorithms traditionally have been the backbone of all phase behavior calculations in the presence of an Equation of State model. Phase stability examines whether a feed composition at given specifications is stable, or if it will split in two or more phases. In the latter case, phase split will further provide the composition and molar fraction of all equilibrating compositions.Despite the extension and improvement of the original algorithms developed by Michelsen as far as both speed and robustness are concerned, those two calculations are still treated as independent. In this work, we explore the relationship between them and develop a new algorithm called “the generalized flash” which acts as a bridge between stability and phase split. By utilizing suitable values of its parameters, namely, the stability distance θ and the molar fraction β, it is shown that the generalized algorithm can reduce to any of the two basic ones. Additionally, it can offer intermediate results between stability and phase split which also guarantee minimum Gibbs energy. The algebraic, geometric and computational aspects of the proposed algorithm are investigated. Finally, applications of the new algorithm with emphasis to negative flash calculations are discussed.