Thesis for the Degree of Master of Science


Year 2002
Otso Tiili

Development and Implementation of Control Strategy for Pulp Levels in a Series of Flotation Cells

The aim of this thesis was to develop and implement a control strategy for pulp levels in a series of flotation cells.

Flotation is a very complex separation process for minerals. Pulp level in a cell is one of variables affecting the process. An industrial scale concentrator usually has cells connected in series. This leads to problematic level control due to interactions between control loops. The control performance of widely used separate PI-controllers has been noticed to be insufficient for this task.

In the literature part of the thesis, the flotation process and the principles of the flotation control were studied. Also the most commonly used control strategies and their applications to level control reported in the literature are presented.

In the experimental part, different level control strategies were evaluated by means of value analysis. Control performance as well as aspects of usability, cost, marketing and hardware requirements were taken into consideration in the value analysis. On the basis of the results of the value analysis, a decoupling controller with on-line parameter estimation was chosen to the implementation. The prototype was implemented in the automation system of Outokumpu Mintec and was tested in simulations.

The simulations showed that the performance of the new decoupling controller was substantially better than the performance of the traditional PI-controller.

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