A dynamic model for level prediction in aerated tanks. (15th August 2018)

• Record Type: Journal Article
• Authors: Shean, B.; Hadler, K.; Neethling, S.; Cilliers, J.J.
• Is Part Of: Minerals engineering. Volume 125(2018)
• Page Start: 140
• Page End: 149
• Publication Date: 2018-08-15
• Subjects: Froth flotation -- Flotation control -- Gas holdup -- Level control -- Bubble size; Mines and mineral resources -- Periodicals; Ressources minérales -- Périodiques; Mines and mineral resources; Periodicals; Electronic journals; 622
• DOI: 10.1016/j.mineng.2018.05.030
• Languages: English
• ISSNs: 0892-6875

Abstract

Graphical abstract: Predicted change in pulp height compared to experimental values for randomised step changes in air rate. Highlights: A model is derived from first principles to predict level changes in aerated tanks. The model is tested against a laboratory flotation system. The model shows good agreement with experimental data. This will enable improved operating stability of industrial flotation systems. 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.