Harnessing the power of a tornado in a tank

A simple mixing technology, developed using world-class science, proves the best option for the mineral processing industry. resourceful investigates how the technology is saving the industry time and money.

Process productivity

Close up of swirl flow mixing rotar

article from resourceful: Issue 6, March 2014

It does not always follow that the more complicated the technology and the more advanced the system, the better the outcome.

A smart mixing technology called swirl flow, developed by CSIRO and Queensland Alumina, greatly simplifies the mixing of solids in suspension in mineral processing. It works by creating a novel fluid flow that mimics a tornado, within large-scale tanks.

Suspension mixing is usually achieved using massive impellers attached to long shafts, at times 20 metres or more in length, resulting in the mixing equipment being heavy, unwieldy and costly. The mixing is not entirely efficient using this approach and the equipment can be costly to maintain.

Dr John Farrow, CSIRO’s Commercial Manager of swirl flow, says its unique mixing offers many advantages over traditional systems.

'Swirl flow uses a radial agitator located just below the liquid’s surface to create a tornado-like flow pattern,’ Dr Farrow says.

The tornado effect extends all the way from the bottom of the tank, sometimes 30 metres or more, to lift any settling solids to the top of the tank. The fluid and solids then swirl downwards and repeat the process.

Swirl flow technology is mixing up a tornado in a tank to keep solids suspended

‘The capital cost of swirl flow is around 50 per cent less than traditional technologies and likewise the maintenance costs are also much lower, in part due to the lower wear rates than the impellers used in traditional systems.

‘Maintenance can also be done without entering the tank, creating significant health and safety advantages.’

Swirl flow has been successfully used for more than 15 years by Queensland Alumina at their Gladstone refinery. Currently, 21 large tanks are operating with the technology, and the company has plans to convert more tanks to swirl flow.

Conversion to swirl flow is not only a major capital cost saving, but also provides long-term operating advantages such as a significant reduction in the tank scaling rate. This allows the tank to stay in operation for much longer periods, increasing production and reducing costs.‘

'A particularly important feature of swirl flow is the ease at which remixing of the suspension can commence after a power failure, since the agitator is close to the liquid’s surface and away from the settled solids,’ Dr Farrow says.

This is unlike traditional systems in which the settled solids may cause the impeller to get stuck.

Swirl flow can be applied throughout the minerals industry for a wide variety of mixing.

‘We’re doing work for both the gold and zinc industries,’ Dr Farrow says.

‘Gold production also has a crystallisation issue and like the aluminium mixing, the process needs the best form of agitation to make sure particles are kept in suspension with no scale.

‘For all applications the prime need is to ensure no solids settle to the bottom of the tank, but swirl flow can also address the need to avoid particle attrition (for example, when resins are used to absorb valuable metals), to provide effective oxygen transfer or to minimise scale formation.’


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