It's Not as Easy as it Looks: Revisiting Peng—Robinson Equation of State Convergence Issues for Dew Point,Bubble Point and Flash Calculations

Abstract

The use of equations of state (EOS) is a ‘modern’ method of physical property prediction and here we present a detailed exposition of the use of the Peng–Robinson EOS for mixtures. This EOS can be used to determine whether a stream is in the vapor phase or liquid phase. However, for two-phase systems the approaches presented in standard textbooks for the calculation of the state frequently will not converge. We provide modifications to standard dew point, bubble point and flash algorithms to help improve the convergence of any EOS. Commercial software can show different values for stream energetic properties (entropy values) and here we utilize species formation from its elements as well as species ideal gas capacities and mixture departure functions to explain observed differences.

Keywords

Peng–Robinson equation of state cubic equations of state cubic equations of state convergence issues enthalpy and entropy determination from equations of state

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