Multi-Sloped Screening Efficiency with Changing Strokes, Frequencies, Feed Solids and Feed Rates-Pilot Plant Study

Optimising multi-sloped screens is often described as an art and there is very little data in the open literature describing the role of the control variables. Several variables affect the screening process and these include the screen machine variables such as stroke and frequency of operation, which together make up the g-force, screen aperture, open area and screening area. For these series of experiments the latter three control variables were kept constant while the former were varied. The feed also has properties which will affect the efficiency of screen operation and these include, feed flow rate, feed solids, and the amount of near sized material in the feed.

This project examined the effect of varying the control variables of near size material, frequency, stroke, feed solids and flow rate on the efficiency of the screening process. Near size material changed naturally during the course of the experiments as some breakage occurred.

The efficiency of the screen operation was determined from the response variables which include, the cut point (d50), the amount of water reporting to the overflow (Rf), Alpha which is a Whiten classification model function, (Equation 2), describing how sharp the separation is based on the slope of the partition curve, the amount of minus 1 mm material in the oversize and the Specific Drain Rate (SDR) which is the rate of flow to the screen undersize in m3/h/m2. Over 60 experiments were carried out by varying the frequency of operation, the stroke, the feed flow rate, and the feed solids. Multiple regression analysis was carried out on the results and models produced for each of the response variables. From these models the effects of varying one of the control variables while holding the others constant were observed. The full models and the effects are discussed in the body of the report.