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MEI Online: Control & Instrumentation: Latest News: October 17th 2011

 
 

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:: Ultrasonic View Through Murky Hydromet Water

The ability to accurately measure fluid flow is crucial to the success of a hydrometallurgical mineral extraction process. However, it can be difficult for processing operators to see these flows through the murky solution that results when water, organic solvent and assorted chemicals are mixed in large solvent extraction (SX) tanks.

Over the past few years CSIRO has developed a way to 'see' the different flow patterns in full-scale SX facilities more clearly. The technique uses ultrasound or to be more specific, an instrument called an ultrasonic velocity profiler (UVP).

Dr William Yang, who leads the physical measurement team for CSIRO's multi-sponsor Solvent Extraction Technology (SXT2) project, says UVP is a powerful tool in helping the minerals industry optimise their SX circuits. "SX is widely used in minerals processing, but there are a number of issues in fluid flows that require greater understanding. These include how to increase the separation efficiency between organic and aqueous phases and minimise the loss of organic entrainment into the aqueous phase of the SX process," Dr Yang says.

Laser-based measuring tools - the favourite measuring devices in clear fluids - have their limitations in the opaque fluids of an SX circuit. In effect, lasers cannot 'see' what is going on. UVP solves this problem in much the same way that ultrasound is used to see through human tissue in medical applications.

Dr Yang and his team initially set out to prove in laboratory conditions what had been predicted using computational fluid dynamics (CFD). They set up tests using a simple model system that contains a mix of water and kerosene to closely mimic a real process plant. "By measuring the flow patterns, velocity profiles and even droplet-size distributions, we were able to validate the CFD model of the laboratory-scale mixer­settler," he says. "The next step was to scale up the work using UVP in full-sized mineral processing applications."

Dr Dave Robinson, who leads the SXT2 project, says many of the nine companies supporting this research have gained considerable benefits from using UVP measurements. "By optimising the use of settler volume and the increased opportunity for droplet coalescence, the entrainment losses are reduced and plant operations are improved," Dr Robinson says. This use of the UVP in SX is an effective and practical adaptation of a technique widely used in fluid mechanics.

"We're using an ultrasound probe because it can measure fluid velocity whether the fluid is clear or opaque," Dr Yang says. "SX plant operators are able to use data gathered to manage problems such as local flow circulations and blockages in the tanks."

UVP technology provides a picture of what is happening in the different phases of the SX process - aqueous and organic - where operators cannot otherwise see. More recent work has enabled Dr Yang to use the same probe to map the dispersion band and crud layers in full-scale, operating SX units without disrupting production. "By putting a UVP probe into the solution and measuring all flow movements an operator can learn a lot more about the process and consider modifying the 'furniture' inside the settler to achieve greater process efficiency," Dr Yang says.

 

 

   

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