Swirl flow is a simple mixing (agitation) technology that creates a tornado-like flow pattern inside mixing tanks to lift settling solids from the bottom. It was developed using world-class science and is saving the mineral processing industry time and money.
Many mineral processing procedures rely on keeping solids in suspension. Under gravity, solids will naturally form sediment at the bottom of mixing tanks. Stirrers and mixers are then used to resuspend the solids in solution.
Suspension mixing is usually achieved using massive impellers (rotors used to increase the pressure and flow of a fluid) 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
Although stirrers and mixers have been used in the industry for many years some challenges persist, such as scale build-up in tanks leading to production downtime for cleaning, and high power consumption at high solid concentrations.
Harnessing the power of a tornado in a tank
We developed swirl flow technology with our partners at Queensland Alumina. The technology uses a radial agitator located just below the liquid surface to create a tornado-like flow pattern.
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.
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 for the impellers used in traditional systems.
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.
Taking the industry by storm
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.
Swirl flow can be applied throughout the minerals industry for a wide variety of mixing. We have done work for both the gold and zinc industries. For example, 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.
Swirl flow is effective for all applications where the prime need is to ensure no solids settle to the bottom of the tank. It 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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