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OPERATING EXPERIENCE WITH IMPROVED PRECIPITATION AGITATION SYSTEM

Stegink, D., Davis, T. and Wu, J.

CSIRO and Queensland Alumina Ltd have jointly developed patented Swirl Flow agitation technology, which uses high slurry velocity to minimise scale formation in precipitation tanks. The objectives of Swirl Flow agitation are to increase yield, reduce cost and safety risks, and improve operational security.
In a Swirl Flow precipitation tank, a radial flow rotor near the top of the tank draws in slurry along the vertical axis of the tank and discharges the slurry radially with a large tangential velocity component. The resulting high slurry velocities along the tank wall result in a reduced scaling rate, which improves performance through its impact on tank volume and operating factor.

The agitator can be installed and removed by working on the agitator access platform, and as there are no tank internals, there is no need for personnel to enter the tank for agitation system maintenance. This eliminates a high risk activity from the tank’s safety risk profile.

To date, 16 cone-bottom precipitation tanks have been converted to Swirl Flow agitation.  Based on over a decade of operating experience, the performance of the technology is assessed and compared to conventional agitation technology. Swirl Flow precipitation increases yield through increased operating factor and tank volume, and the low conversion cost makes it the preferred option over replacement of a damaged draft tube. The agitator has superior re-suspension capability, which allows easy recovery from an interruption of power supply; care must be taken to optimise cycle duration.