Robust Dynamic Simulation of Three-Phase Reactive Batch Distillation Columns

Abstract

The dynamic simulation of heterogeneous distillation columns is a demanding task because the number of liquid phases can vary over time on each tray. The success of the simulation depends on the rapid, reliable, and robust assessment of the number of phases and the correct initialization of the compositions of the liquid phases. In this work, a flexible simulation strategy is presented that decouples the phase split and flash algorithms from the process model. Therefore, no discontinuous model switching occurs in the process model, and the column can easily be simulated using standard tools employing a simultaneous equation-oriented simulation strategy. The phase state is assessed with a rapid and reliable homotopy−continuation algorithm that is well-suited for dynamic simulation because it decomposes the phase stability problem into two steps to minimize the necessary computational effort. The simulation strategy is applied to the production of butyl acetate from butanol and acetic acid in a three-phase reactive batch distillation column as an illustrative example.

Conceptual Design of Azeotropic Distillation Processes

“…In addition, the model discontinuities stemming from switching between heterogeneous and homogeneous trays may complicate or even impede the optimization. The solution of the equilibrium problem including a phase stability test as a subproblem has been shown to improve the robustness of the solution algorithms in dynamic simulation [128]. This computational strategy has been shown to improve robustness also in rigorous design optimization [129].…”

Dynamic simulation of fluids in vessels via entropy maximization

“…Interval analysis [24], for example, gives mathematical guarantee of finding the global minimum, but with a computational effort that currently makes it unsuitable for dynamic simulations. The use of homotopy to test phase stability has also been considered in the context of dynamic simulations [25]. Another way of handling the possible appearance and disappearance of phases during a dynamic simulation is to execute calculations with the maximum number of phases expected during a simulation (typically two or three) [26].…”

New processes for recovery of acetic acid from waste water

“…However, for some systems, significant differences between states in the pseudo-homogeneous regime (no liquid phase splitting) and heterogeneous regime (with phase splitting) can be revealed (Bausa and Marquardt 2000;Brüggemann et al 2004). As consequence, an appropriate model has to be used in order to better reflect the real system behavior.…”

“…On the left, the simulation time SIM_TIME is expressed in (s · 10 4 ), on the right, t is in (h). The right hand side picture is taken from Brüggemann et al (2004).…”

“…To reliably predict the liquid-liquid phase split on the column trays in the course of a simulation run, an extra routine for the phase split calculations is required. The routine is based on homotopy continuation methods (Bausa and Marquardt 2000;Brüggemann et al 2004;Steyer et al 2005). The complexity introduced by the liquid-liquid phase split besides the existing complexity of a reaction-separation interaction makes the analysis of this process very challenging.…”