In a beneficiation plant, during steady operation the products from a hydrocyclone has a definite cut point. However due to variations in the feed slurry characteristics and changes in the hydrocyclone geometry, especially the diameter of the apex due to abrasion, the cut point changes during operation. It is necessary to hold the performance at the desired dsoc value for down stream operations.

The control strategy could be to monitor the deviation of the cut point. The alteration in cut point was obviously due to change in feed characteristics and additionally to changes in cyclone geometry due to abrasion.

An important factor in designing control loops is the instrumental and programmable time delays, the case of hydrocyclone automation, the sources of time delays is given in Table1.

Each instrument has to have a separate time delay factor which could be up to 3 seconds Programmable time delays introduced during iteration could be greater than instrumental time delays

Table1. Source of time delays in a hydrocyclone circuit.

Fig. 1 shows the set up and instrumentation for automatic control of a hydrocyclones.

The apex of the cyclone was fitted with a rubber sleeve which could be pneumatically squeezed to alter its diameter. The vortex finder was specially designed to travel up and down. The centrifugal pump was fitted with a fiequency controller. The control strategy is illustrated in Fig.2.

Fig 1.Basic instrumentation for automatic control of hydrocyclone

Fig2. Strategy for automatic control of d5Oc in a hydrocyclone

Laboratory trials suggested that when a hydrocyclone variable was subjected to a step change and the dsoc value deviated, the operation of the hydrocyclone could be restored such that the dsoc could be maintained to within ± 5 % of the calculated value. The mathematical model used for calculations was derived to suit specific slurry conditions. The conclusion was that such techniques could be developed for automatic control of the cut point of hydrocyclones.