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MEI Online: Environmental Issues: Latest News: February 9th 2011


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:: New Injection Technique Reduces Water and Energy Use

CSIRO has developed a new fluid injection technology that promises to help mineral processors reduce their water and energy use by improving the transport of concentrated tailings suspensions.

Efforts to reduce water use and to stabilise mineral processing slurries are demanding the formation of increasingly dense mineral slurries. CSIRO mechanical engineer Dr Lachlan Graham says the thicker the slurry the more likely it is to require expensive high-pressure pumps, and more energy will be needed to transport it to its final destination.

“Some operations dilute concentrated suspensions, or avoid their formation, to reduce pumping pressures. But this makes ‘wetter’ tailings, which are more difficult to manage in storage," says Dr Graham, who is part of the Minerals Down Under Flagship slurry transport team.

The new CSIRO technology uses a small proportion of lubricating fluid to reduce the friction between the flowing slurry and the pipe wall. While liquid injection has been tried in the past, previous approaches have required excessive amounts of the lubricant - usually water - (say 10 per cent) to achieve any meaningful reduction (say 30 per cent) in the total drag of slurry against the pipe.

“This defeats the original purpose of producing concentrated tailings suspensions," Dr Graham says. The new technique uses a liquid injection method that requires significantly lower injection rates to reduce drag by 50 per cent or more.

The essence of this technique, for which a patent has been lodged, is a design configuration that distributes the injected liquid uniformly across the pipe wall. The even distribution allows less liquid to achieve more significant results. For example, in laboratory tests using highly viscous materials, drag was reduced by 50–90 per cent over a practical pipe distance, using approximately one per cent liquid injection.

Dr Graham says the technology has the potential to reduce capital costs by allowing processors to use lower pressure pumps than they might otherwise need, as well as reducing operating costs in operations transporting slurries with a high concentration of solids.

Installing the device into the pipeline immediately before the inlet of a centrifugal pump may further improve pumping efficiency. “Centrifugal pumps used in transporting tailings sometimes don’t have very good suction conditions at their inlet points, although once the slurry is in the pump there’s often no problem. This could make it easier to get the slurry into the pump.

“Oils or polymer solutions could also be used as lubricants, although both would be more expensive than water and would only be used in special circumstances," says Dr Graham.

Other potential uses for the fluid injection device include providing an anticorrosive film along the inside of a pipe wall, or the injection of chemical reagents in the chemical, gas or oil industries.

The new fluid injection technology has been developed through CSIRO’s Minerals Down Under Flagship and they are now seeking partners to commercialise the device.




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