Finding the flaw in the flow

RESEARCHERS using computational fluid dynamics (CFD) have identified a large recirculating vortex as the cause of performance variations in precipitation tanks being used at an alumina refinery.

Researchers using computational fluid dynamics (CFD) have identified a large recirculating vortex as the cause of performance variations in precipitation tanks being used at an alumina refinery.

At Worsley Alumina, tanks of different designs were showing variations in their performance. Ideally, the bulk of the particle-laden solution remains within the tank and only solution with a low particle concentration enters the overflow. But in some tanks, the particle concentration in the overflow was too high. Enter Dr Graeme Lane, CFD modeller at CSIRO Minerals.

Dr Lane used advanced computer modelling methods to simulate the flow in tanks of different sizes. These tanks shared many similarities in their design, but there was a significant difference in overall height.

“The simulated flow pattern revealed a large recirculating vortex,” Dr Lane says. “This was creating a flow instability, which resulted in surges of particle-laden solution being sent to the top of the tank.

“These surges were particularly problematic in the shorter tanks due to the proximity of the vortex to the overflow. When a surge occurred, solution with a higher solids loading was being forced into the overflow.”

Having identified the problem and developed a greater understanding of flow patterns within the tanks, Dr Lane has suggested a possible remedy may be the installation of internal baffling plates.

This article first appeared in Process (October 2007) – a publication of CSIRO’s Minerals Resources sector.

Key contact:

Dr Graeme Lane, CSIRO Minerals

Graeme.Lane@csiro.au

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