Efficient and accurate calculation of critical points is an important aspect of general phase equilibrium calculations. When calculating critical points, the computationally expensive part is to solve the spinodal equation. For Heidemann and Khalil formulation the dimensionality of the problem is equal to the number of components (nc). In this paper we describe a new procedure enabling the reduction of problem dimensionality. The reduction is effectively

The Joule–Thomson inversion curve (JTIC), defined as the locus in the p–T plane where the adiabatic Joule–Thomson (JT) coefficient is zero, separates regions for which heating and cooling occur upon an isenthalpic expansion. JTIC calculation for mixtures is a clear matter for single-phase conditions. For two-phase mixtures, an apparent JT coefficient can be defined, which incorporates: (i) JT effects and (ii) phase distribution changes effects.

For mixtures with many components, some or most of the components are grouped into pseudo-components in order to reduce the dimensionality of the problem for phase equilibrium calculations, and therefore the computational effort. However, knowing the detailed fluid phase split may be important for a variety of applications. The detailed phase compositions resulting from a flash calculation performed on a lumped mixture can be predicted using a delumping

An analytical and consistent delumping method, recently formulated and implemented for processes involving two-phase flash calculations, is extended to flash calculations involving any number of coexisting phases. The equation of state considered is a two-parameter cubic equation of state (EoS) with van der Waals mixing rules and non-zero binary interaction parameters (BIPs). The method is used for calculating three- and four-phase equilibria in

A new method for multiphase equilibrium calculations with cubic equations of state (EoS) has been developed. The minimum of the Gibbs free energy and of the tangent plane distance function should be found in a space with a significantly reduced number of dimensions. The number of independent variables for phase equilibrium calculations does not depend on the number of components in the mixture and non-zero binary interaction coefficients (BICs) are

Development of accurate and efficient methods for direct calculation of critical points is valuable for phase equilibrium calculations in chemical and petroleum engineering. A new method for critical points calculation is developed. For critical point calculation methods, the spinodal equation is given by setting to zero a determinant of nc (number of components) or nc-1 order, containing second-order derivatives of thermodynamic potentials. In this