Modified RAND Framework for Phase Split Calculations

  • Duncan PatersonEmail author
Part of the Springer Theses book series (Springer Theses)


The classical example of the phase equilibrium problem is isothermal flash, with the temperature, pressure and molar feed specified. This is at the heart of many processes and reservoir simulation tools. The conventional approach to solve the isothermal flash problem involves alternating use of stability analysis (Baker et al. 1982) and phase split calculation, as described in Sect.  1.3. Stability analysis based on the tangent plane distance criterion can in principle be used to determine if the current state is a global minimum in the Gibbs energy. The method proposed by Michelsen (1982a) and its variants are widely used for stability analysis in practical calculations. The problem is essentially a global search over all possible trial compositions, and one can resort to global optimisation methods (McDonald and Floudas 1995; Hua et al. 1996). Such methods are generally too expensive to use for multicomponent systems. The phase split calculation solves the equilibrium equations given a number of phases, the solution to the problem corresponds to the local minimum in the Gibbs energy (Michelsen 1982b). If there is no advance knowledge about the maximum number of phases in a system, it is necessary to check the local minimum from the phase split calculation with stability analysis to ensure the Gibbs energy cannot be reduced further by the introduction of a new phase.


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© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of ChemistryTechnical University of DenmarkKongens LyngbyDenmark

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