Solid phase precipitation can greatly affect thermal effects in isenthalpic expansions; wax precipitation may occur in natural hydrocarbon systems in the range of operating conditions, the wax appearance temperature being significantly higher (as high as 350 K) for hyperbaric fluids. Recently, methods for calculating the Joule-Thomson inversion curve (JTIC) for two-phase mixtures, and for three-phase vapor-liquid-multisolid systems have been proposed.

Phase stability testing is an important subproblem in phase equilibrium calculations. Phase stability analysis consists in finding either all stationary points or only the global minimum of the tangent plane distance (TPD) function. The TPD surface is non-convex and may be highly nonlinear, and many phase stability calculations are rather difficult. In this work we are solving the phase stability problem using the Tunneling global optimization method

An analytical and consistent delumping procedure is implemented for fluids of petroleum interest containing water, non-hydrocarbon gases (such as N2, CO2 and H2S) and hydrocarbon (HC) compounds. Two sorts of difficulties are associated with these fluids: they often exhibit three or more equilibrium phases, and their thermodynamics cannot be described by conventional cubic equation of state (EoS). In this work, the Soreide-Whitson modification of

The Joule-Thomson inversion curve (JTIC) separates regions in which heating and cooling occur upon an isenthalpic expansion. Mixture JTIC calculation is a clear matter for single phase conditions; if the mixture splits in two or more equilibrium phases, derivatives properties are not defined. However, in practice a system may change its state during an isenthalpic expansion (i.e. a phase boundary is crossed between initial and final conditions);

The elegant method proposed by Michelsen [Comput. Chem. Eng. 18 (1994) 545-550] for solving multiphase Rachford-Rice equations as a bound constrained minimization is extended to the negative flash region; this method is definitely much more robust than any method based on equation solving. The problem is reformulated as an unbounded linearly constrained minimization. The feasible domain is limited by (only few of the) hyperplanes defined by equilibrium

Phase stability calculation is a very important topic in phase equilibrium modeling. Usually the phase stability problem is solved by minimization of the tangent plane distance (TPD) function, the sign of the objective function at its global minimum indicating the state of the mixture at given conditions. The TPD function is non-convex and may be highly nonlinear, many phase stability problems being really challenging. The Tunneling global optimization

A reduction method for constructing vapor–liquid equilibrium phase envelopes with cubic equations of state is presented. The paper describes the calculation procedures for saturation (dewpoint/bubblepoint) pressures and temperatures, quality lines (for given mole fraction or volume fraction of one of the equilibrium phases), cricondentherm and cricondenbar points, the critical point, and the spinodal. The phase envelope construction is fully automatic.

Modeling of wax precipitation from hydrocarbon mixtures requires extended compositional data for the heavy fractions; as a result, the number of components in the mixture is usually large and phase equilibrium calculations are computationally expensive and may be prohibitive. A lumping procedure which reduces the dimensionality of phase equilibrium calculations without affecting the location of solid phase transitions is used. By lumping into pseudocomponents,

In this paper, we advocate the use of the Tunnelling global optimization method for phase stability analysis and for multiphase equilibria calculations. The method had been successfully used for solving a variety of phase-equilibrium problems. The Tunnelling method has two steps. First, a minimum (which may not be the putative global minimum) of the objective function is found by a local bounded minimization algorithm. In a second step, the method

The convergence locus (CL) and stability test limit locus (STLL) are important underlying properties of multicomponent system phase diagrams. In the pressure–temperature plane, the CL separates the region where the negative flash has non-trivial solutions. The mathematical domain of flash calculations is significantly wider than the physical domain; if a negative flash is performed, the equilibrium constants are continuously derivable when a phase