Abstract
Solution of phase equilibria with flash calculations is central in many processes. During the integrating of the conservation equations in these systems, flash calculations are traditionally solved in inner loops at each integration step. Some of these systems can be solved more efficiently using modern DAE solvers, where the differential equations and the algebraic equations describing the phase equilibrium are solved simultaneously. In this paper we present a framework, called the Thermodynamic Differential Algebraic Equation (TDAE) method, which handles most two-phase flash variants. The phase boundary is tracked, enabling a robust solution also with phase changes. The time consumption of the TDAE method has been compared to the traditional approach in several examples implemented in both Fortran and Matlab. In some cases, the TDAE method is more than 800 times faster, and in other cases the traditional methodology should be used. We will give insight into how and when DAE solvers can be used to speed up phase equilibrium calculations.