Computational Modelling

Granular Flow - Application

Size segregation by a vibrating screen

Contact personnel:  P.W. Cleary

Vibrating screens are commonly used to separate particles according to their size. Separation is a critical step in most mineral processing operations and the efficiency of this separation has direct implications for both mineral recovery levels and costs.

Particle segregation by one level of a screen is presented here. We consider a 800 mm square screen, 10 mm thick, containing a 12x12 array of 40 mm square holes. The screen is covered by a mixture of 8,000 spherical particles, with sizes uniformly distributed between 10 and 60 mm, to a depth of 400 mm. Periodic boundaries have been applied at each of the sides of the screen to simulate a screen having a much larger area. The screen is oscillated upwards and to one side with a frequency of 190 rpm, a vertical amplitude of 50 mm, and a sideways amplitude of 20 mm. The oscillations in the two directions are in phase so that the screen moves sinusoidal in a straight line inclined at 22 degrees to the vertical.

The figures shows the screen at two times during the vibration cycle. As it moves upwards, smaller particles (shaded blue through to green) move freely through the holes in the screen. The flow of small particles continues throughout the screen’s upward movement, although the rate declines slightly. As the screen moves down, the particles lag behind and loose contact with the screen. The flow of small particles through the screen abates until the screen reaches its lowest point and the particles crash back into the screen producing a surge of smaller particles through the screen. This behaviour leads to a regular pulsing flow of fines from the screen. Also observed in the figures is the well-defined size segregation of the material on top of the screen, with the larger (red) particles being dominant near the upper surface. The progressive percolation of small particles from the upper regions to the region adjacent to the screen ensures a continual supply of fines to flow through the screen.

Particle locations (coloured by size) at two different times during the vibration cycle of the screen.

The ability of DEM to simulate this type of flow demonstrates the method’s potential for use as a design tool for such industrial particle handling equipment.

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last updated July 18, 2007 05:23 PM

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