The mixology of slurry

by Dr Mark Cooksey

Are baffles necessary for slurry mixing in large tanks?

Large slurry mixing tanks are ubiquitous in minerals processing, with most operations accepting that it is required to implement baffles to achieve the required mixing performance.

While solid suspension is vital to mineral processing operations, the concept of using baffles to accomplish this has been adopted from chemical processing – which typically require much more turbulence to achieve the required reaction rates.

The routine use of baffles may seem normal, but in reality, they can present several challenges for your operation. The high-power requirements, increased difficulty of cleaning, and weaknesses they can introduce to rubber-lined tanks means they may become a liability.

Because of these high risk challenges, investigating options to remove them from your operations can be a safe and worthwhile investment.

Using fluid technology advances and expertise, you can optimise your operation to maintain your current solids suspension and slurry mixing efficiency while reducing costs and mitigating risks.

Hidden inefficiencies of baffle utilisation

Increased power consumption of agitator systems

The localised agitation baffles produce inhibits the larger scale motion around the tank, increasing the energy required for mixing.

High energy costs are therefore unavoidable – and while many operations have accepted this as part of production, growing community and stakeholder concern around environmental harm and overreliance on natural resources can raise presumptions that you’re ignoring serious environmental issues. This can present damaging reputational costs on top of already inflated economic ones.

Tank weaknesses that can lead to failure

Tanks that are used to mix acidic slurries are often internally lined with rubber, as acidic slurries corrode the steel. However, the rubber has to fit around the baffles. This can introduce gaps or points of weakness in the rubber lining and therefore the tank itself, meaning tanks have to be closely monitored in order to avoid tank failure.

Since 2013, there have been reports of three major tank failures resulting in the leak of acidic materials. The operations that experienced these failures faced plant shutdowns, independent reviews and tens of thousands of dollars in fines.

Operational impacts of premature faults

The costs of energy, shutdowns and potential fines are compounded by the cost of damage to tanks and operational machinery. The weaknesses caused by baffles can prematurely age or wear your equipment. This increases the frequency and cost of maintenance and replacement of your rubber lining, shortening the lifespan of your tanks and increasing operational downtime.

Removing baffles and maintaining optimal slurry mixing is possible

While it’s previously been believed that the necessity for baffles means having to live with the risks or pains associated with them, this is no longer the case.

Progress in fluid technology has introduced new ways of maintaining solids suspension, slurry mixing efficiency and operation of agitator systems that don’t require the use of baffles.

Optimising your impellers through modification of design and operation can achieve the same solids suspension previously obtained with baffles – but without the risk to production and high operation costs.

Upgrading your operation to non-baffle operation allows for:

• improved performance, attaining the same mixing outcomes as you experience with baffles
• lower energy needs, usage and cost
• significantly lower environmental and economic risk associated with tank failure
• reduced maintenance time and cost, and
• increased tank lifetime.

These same results can be achieved by replacing, rather than modifying, your existing impellers with the CSIRO developed impeller alternative, Swirl Flow.

Ensure optimisation success through expert engagement with CSIRO

CSIRO’s expertise in fluids engineering allows us to assist and consult on the optimisation of slurry mixing tanks through impeller modification or the introduction of new flow technology.

Our expertise can be applied to existing or new operations, and we don’t need to view your operation to begin the optimisation process – our team will simply:

• review the design and operation of your existing tank and impellers
• create a superior impeller design that would allow for baffles to be removed
• undertake in-house laboratory and pilot scale tank testing of both new and existing designs to refine and confirm design, and
• assist with the installation of new impellers and the removal of baffles, and verify the performance.

Seeking expert fluid engineering assistance while investigating new options for your operation can help decrease costs, risks and operational downtime while ensuring the efficiency of your production remains constant.

Our Fluids Engineering team at CSIRO, through our research and breakthrough science, is uniquely positioned to add value to your operation. Through process improvement assessment, modelling, designing and deploying new technology, we can help you solve your mixing challenges to optimise your operations.

Contact the team on +61 3 9545 8865 or email me, Mark.Cooksey@csiro.au, to discuss how our expertise and experience can help you.

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