Thesis for the Degree of Master of Science


Year 1998
Tatu Kuitunen

High level control system for the HGM- separator

The object of this thesis was to develop a high level control system for the high-gradient magnetic (HGM) separator and to implement and test it at the slime circuit of Outokumpu Chrome OY, Kemi mine concentrator.

Changes in the feed type, grade and tonnage cause considerable variations in the concentrating results at the Kemi mine slime circuit. The choice of the operating parameters is difficult without a measurement of the concentrate grade. This has caused strong variations in the concentrate grade and consequently there have been losses in recovery due to a too high grade.

The object of the control system was to reduce the variation of the concentrate grade due to variations in the feed, and to maximize the recovery. The desired concentrate grade was set at 43%.

For the control system a grade-measurement of the slime circuit concentrate was programmed into the Courier-analyser. The aim of this thesis was to benefit this measurement in controlling the HGM- separator. The measurement enabled the use of a feedback control system to compensate the effect of feed variations on concentrating results.

In the literature survey the theory of the high-gradient magnetic separation, experimental models found in literature and high level control systems were studied. The different types of continuous HGM- separators were also briefly presented.

In the experimental part the Kemi mine was described shortly, and a more detailed description was given of the slime circuit and its automation system. The previously used control strategy was also presented. Based on earlier tests a high level control strategy was selected and the use of control variables was decided. The programming of the control system into the PLC was done by Siemens OY. In the implementation phase the control system was tuned and tested. The results were compared with the results of the old system. The function of the control in exceptional conditions was tested and the stability and speed of control action was also considered.

The implemented control strategy could significantly reduce variations in the concentrate grade. Also the variation in recovery was reduced. The recovery was increased approximately seven in percentage units, despite the low feed grade during the testing period. The control is fast enough to compensate changes in the feed ore type, and it also operates reliably even if the grade measurement fails momentarily.

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