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A dynamic model for level prediction in aerated tanks

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Title: A dynamic model for level prediction in aerated tanks
Authors: Shean, B
Hadler, K
Neethling, S
Cilliers, JJ
Item Type: Journal Article
Abstract: Stirred aerated tanks are a key unit operation in many industries, including froth flotation. Reliable and robust level control is of great importance in maintaining steady operation for successful implementation of higher level optimising control strategies, particularly when such tanks are arranged in series. When changes are made to the rate of aeration, there is a corresponding change in the pulp bubble size and gas holdup (the volume fraction of air in the tank), and consequently the pulp height. Stable operation of flotation tanks must, therefore, include the effect of air rate on pulp height in level control systems, especially if air rate is being actively controlled. In this paper, a model is developed from first principles to link the change in gas holdup with variation in air rate under dynamic conditions, accounting for the variability in gas holdup with height that results from differences in gas compressibility. This is validated experimentally. In order to test the model, experiments were carried out using a 70 L laboratory tank comprising water and reagent systems. For both simple and complex changes in air rate, the model showed good agreement with the experimental results when predicting the change in pulp height at steady state. Under dynamic conditions, the experimental system exhibited a slightly slower response than is predicted by the model; this is likely to be due to the well mixed assumption not being adequately met. This model provides a method to improve the operating stability of aerated tanks through better modelling of the dynamic pulp height changes that result from changes in air flowrate. In flotation tanks, this will enable greater control over froth height, which has been found to affect significantly mass pull, froth stability and flotation performance.
Issue Date: 15-Aug-2018
Date of Acceptance: 26-May-2018
URI: http://hdl.handle.net/10044/1/60902
DOI: 10.1016/j.mineng.2018.05.030
ISSN: 0892-6875
Publisher: Elsevier
Start Page: 140
End Page: 149
Journal / Book Title: Minerals Engineering
Volume: 125
Issue: 1
Copyright Statement: © 2018 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/
Sponsor/Funder: Technological Resources PTY Ltd
Funder's Grant Number: Project EF
Keywords: Science & Technology
Physical Sciences
Engineering, Chemical
Mining & Mineral Processing
Froth flotation
Flotation control
Gas holdup
Level control
Bubble size
0306 Physical Chemistry (incl. Structural)
0904 Chemical Engineering
0914 Resources Engineering and Extractive Metallurgy
Mining & Metallurgy
Publication Status: Published
Online Publication Date: 2018-06-15
Appears in Collections:Earth Science and Engineering
Faculty of Engineering