Dynamic behaviour and simulation of a liquid‐liquid extraction column

Abstract

Dynamic behaviour of a stirred liquid-liquid extraction column was studied experimentally. Various input variables of the column were varied stepwise and the resulting variations in the system and output variables were measured. In addition to experimental work, a computer model was developed on the basis of the dispersion model to simulate the dynamic behaviour of the extractor. This model forms a component program of the dynamic process simulator DIVA, developed at the TU Stuttgart. The experiments showed that the hydrodynamic parameters exhibit no significant dynamic behaviour of their own. Therefore, changes occurring in these parameters closely follow variations in input and system variables. As a result, steady-state relationships for the calculation of flow parameters could be used in the simulation program. The simulator satisfactorily reproduced the experimental results for a number of disturbances. However, this was not always the case. As shown in the following, the model did not take into account the column level controller which, under certain conditions, exerts a very strong influence on the column's dynamic behaviour. As a result, larger differences occurred between experimental and simulated data. This influence on the extractor's dynamic behaviour can, however, be eliminated by a simple modification of the level controller arrangement.

LLECMOD: A Bivariate Population Balance Simulation Tool for Liquid- Liquid Extraction Columns

“…In this control scheme the outlet continuous flow rate is manipulated to control the position of the interface at the top of the column. The velocity model corresponding to this scheme shows an oscillatory behaviour in the dispersed phase hold-up as reported both experimentally by Hufnagl et al [56] and theoretically by Weinstein et al [14] and Attarakih et al [19]. Fig.…”

Numerical solution of the spatially distributed population balance equation describing the hydrodynamics of interacting liquid–liquid dispersions

“…Hufnagl et al (1991) tried to improve the prediction of their lumped hydrodynamic model, which was unable to follow the oscillatory experimental hold-up behavior by suggesting an elegant interface level control scheme that proved experimentally to eliminate the transient oscillatory behavior of the dispersed phase hold up. However, their idea was not mathematically formulated until 1998 when Weinstein et al (1998) included this idea in their lumped hydrodynamic model for a Kuhni LLEC.…”

“…For comprehensive review of the slip velocity, as well as a simple guide for choosing the terminal droplet velocity, the reader could refer to Gourdon and Casamatta (1994). Nevertheless, we will assume a quite general form of the relative velocity so that it could be simply adapted to the type (Hufnagl et al, 1991).…”

“…Accordingly, we present below an improved nonoscillatory continuous velocity model based on the control scheme of Hufnagl et al (1991). The idea of these authors is to manipulate the inlet continuous feed ow rate rather than the traditional manipulation of the outlet continuous ow rate (see Fig.…”

LLECMOD: A Bivariate Population Balance Simulation Tool for Pulsed Liquid-Liquid Extraction Columns

“…The population of droplets is modelled by a multivariate number concentration function, which takes into account the dynamic evolution of droplet size and solute concentrations. The understanding of liquid-liquid extraction columns dynamic behavior can be notably used in the design of process control strategy or the start-up and shutdown procedures [8][9][10][11]. In attempting to model this dynamic behavior, one has to consider the macroscopic dispersed phase interactions (droplet breakage and coalescence) as well as the microscopic interaction (interphase mass transfer) occurring in the continuously turbulent flow field, which results in a distributed population of droplets.…”