1997 脉冲筛板萃取柱的一简化水力学模型

Swati Mohanty
Imtitut fiir Therm&he ?/erfflhiensteclzrzi,
*l Alfons
TU Claustlznl,
Vogelpohl
0-3367s Clmstlml, Gerr!xq
Received 10 January 1997; received in revised form 5 March 1997; accepted 6 March 1997
Abstract
A simplified stage-wise hydrodynamic model for simulation of a pulsed sieve-plate extraction column has been presented. The
model is based on a drop population balance which takes into account drop breakage and coalescence in each stage. Each stage is represented by the actual column compartment between two sieve plates. Although experimental break-up parameters have been used in the model, the coalescencecoefficients have been taken as the fitting parameters and the values which gave the best fit with the experimental data have been used. The predicted values have been compared with data from two different diameter pilot plant columns and the agreement is found to be quite satisfactory for the system butylacetate-water, The model can be used for coalescence parameter estimation of different drop sizes, which will be taken up as part of the extension of the present work. 0 1997 Elsevier Science S.A.
Keywords:
Liquid-liquid
extraction; Modeling; Pulsed sieve-plate
1. Introduction Although liquid-liquid extraction is the second most important unit operation in the chemical industry, next only to distillation, the literature is not so exhaustive as in the case of distillation. In order to design an optimum extractor, the hydrodynamic and the mass transfer behavior of the system should be well understood. The dispersed phase in the case of liquid-liquid extraction undergoes changes and loses its identity continuously as the drops break and coalesce. This makes the study of hydrodynamics quite complex. The pulsed sieve-plate extractor (PSE), which has been found to have high throughput, high separation efficiency and insensitivity towards contamination of the interface, has led to its wide applicability, particularly in the extraction of radioactive materials. An empirical model for predicting the hydrodynamics in a PSE has been proposed by Kumar and Hartland [l] and several population balance models have been pro* Corresponding author. Current address: Regional Research Lab-
Chemical Engine ring 8 Gessing
ELSEVIER
Chemical Engineering and Processing 36 (1997) 385-395
A simplified hydrodynamic model for a pulsed sieve-plate extraction column
Table 1 Break-up parameters for the butylacetate-water mm Apf’ (m s-‘) Break-up parameters 4isiab (mm) 0.015 0.0175 0.020 2.63 2.28 2.32 km (mm) 6.62 6.35 6.04 WlZ 1.00 0.94 nry,
A. Vogelpohl;‘Ci~erwicai
Engineering
and Processing
36 (1997)
385-395
basic model for the dynamic simulation of a pneumatically pulsed liquid-liquid extraction column. assuming that the drop breaks into two drops of identical size and the coalescence frequency between two drops follows the equation proposed by Delichatsios and Probstein 1’71.Haverland et al. [8] have applied the model for steady-state simulation of a pulsed sieve-plate extraction column. Although they have taken into account drop breakage, drop coalescence has been assumed to be negligible in the operation range considered. The daughter drop size distribution has been represented by a Beta function. Later studies [9>10] also show that the daughter drop size distribution of a drop when it undergoes breakage fits well with the beta function. Haverland [ll] has also used a simplified stagewise model to predict the hold-up and Sauter mean diameter for a pulsed sieve-plate column and has found it to fit well with experimental data. He has, however, neglected drop coalescence. In this study, a simplified stagewise model has been proposed for simulation of a pulsed sieve-plate extrac-
oratory [CSIR), BhubanesLvar 751013,India.
0255-2701/97~$17.00 Q 1997 Elsevier Science S.A. All rights reserved. PUSO255-2701(97)00010-X
posed by various authors. A stagewise model for the transient behavior of a sieve-plate extraction column, taking into account the back flow and assuming constant hold-up, has been developed by Blass and Zimmerman [2]. Garg and Pratt [3] have developed a population balance-model for a pulsed sieve-plate extraction taking into account experimentally determined values for drop breakage and coalescence. For drop breakage, the assumption made by them is that a drop breaks into two equal size daughter drops, and for drop coalescence, the assumption is that the drop coalesces with drops of the same and adjacent size intervals. Major work on the population balance model has been carried out by Casamatta and co-workers who applied the model to various types of extraction columns, a good review of which is presented by Gourdon et al. [4]. Dimitrova Al Khani et al. [5] have applied this model for d.ynamic and steady-state simulations of a pulsed sieve-plate extraction column with the assumption that the drop breaks into three equal sized drops and taking the coefficients accounting for drop coalescence as the fitting parameters. Milot et al. [6] have used the same