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Civil-Comp Proceedings
ISSN 1759-3433 CCP: 80
PROCEEDINGS OF THE FOURTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY Edited by: B.H.V. Topping and C.A. Mota Soares
Paper 59
Numerical Modelling of a Gravity Settler in Dynamic Conditions E.F. Gomes+, C.M.N. Madureira*, M.M.L. Guimarães+ and L.M. Ribeiro*
+Superior Institute of Engineering, Porto, Portugal
Full Bibliographic Reference for this paper
, "Numerical Modelling of a Gravity Settler in Dynamic Conditions", in B.H.V. Topping, C.A. Mota Soares, (Editors), "Proceedings of the Fourth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 59, 2004. doi:10.4203/ccp.80.59
Keywords: simulation of liquid-liquid systems, mixer-settler system.
Summary
The study of liquid-liquid extraction and mass transfer processes is of great
importance in many industrial fields. The most used equipments are the extraction
columns and mixer-settler batteries. Direct experimentation with such equipments is
not feasible, due to their high complexity and cost. The possible alternative is
computer simulation. Algorithms for fast and reliable simulation of single stirred
vessels and extraction columns have already been published by some of the present
authors, both for steady state and dynamic conditions [1,5,7].
Recent investigation of the present authors is concerned with the dynamic
simulation of mixer-settlers in mass transfer conditions.
Mixers can be simulated with homogeneous stirred vessels [7]. More complex
equipments, such as extraction columns, may be simulated by combining those
simpler structures [4]. In general, the knowledge about the settler behaviour is
scarcer than the knowledge about the mixers and extraction columns, both in the
steady state and in the transient state. Existing models for the settler apply to
specific physical equipments of a laboratory scale [6,2]. More recently, an
approach based on the population balance equation has been used [3,9].
In this paper we describe a direct numerical technique for the study of the wedge
formed in a settler of an extraction system for the steady and transient states. The
technique is an extension for the settler of the one used on the stirred vessel by
Ribeiro [7]. In this study we used the mathematical model proposed by Ruiz for the
steady state operation of a settler with a wedge-shaped dispersion band [8].
The aim of the method is to model the shape of the formed dispersion band: its
length and thickness The results obtained with the developed simulation model for the transient state of the mixer-settler were compared with the values of Ruiz [8]. The predicted values for the wedge of the dispersion band compared every 10 cm are in excellent agreement with those of Ruiz. The new numerical algorithm here presented has the advantage of adding little complexity for the calculations, being an iterative application of the steady state algorithm. It must be noticed that Ruiz's model was developed for a settler that is fed through a slot, the height of which defines the initial thickness of the dispersion band. Ruiz's calculation of an initial velocity depending on the initial thickness of the inlet slot of the settler of the dispersion band is also a limitation of her model. To overcome these problems, we are currently working on a new dynamic model using a kinetic formulation in which the movement of the dispersion is modelled as caused by gravity. References
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