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MEI Online: Comminution: Latest News: July 2nd 2013

 
 

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:: Power Smart Helps Bring 'Stirred Mill' Technology to B.C.

 

In an industry where the energy-intensive activity of breaking rocks is a key part of the production process, a new technology promises to stir things up by cutting energy, improving quality, and reducing costs. It's called "stirred mill" technology, recently implemented by Taseko Mines Limited in the regrind circuit at its Gibraltar Mine in south central B.C. (For its conservation efforts, Taseko has been selected as a Power Smart Excellence Awards finalist.)

Stirred mills have been shown to use as little as two-thirds of the energy of conventional grinding equipment. The difference lies in the way that the stirred mill agitates the grinding media (steel balls) and rock to reduce the size of the rock particles.

Conventional "ball mills" rotate the mill body, a horizontal cylinder, tumbling the rock with steel balls that break up the rock. In stirred mills, the mill body is stationary. The steel balls and rock are agitated by an internal auger that causes the contents to circulate, reducing the size of the rock particles. Stirred mill technology was developed in Australia and has been in use for a number of years, but had not been adopted in B.C. "It's a commercially available technology that has no market penetration in B.C.," says Markus Zeller, an industrial technology innovation manager with BC Hydro.

That meant that the installation of the stirred mill at Gibraltar qualified for support under Power Smart's Conservation Technology Innovation program. The program also supports near-commercial technologies that are developed in B.C. The program provided technical support and engineering analysis to quantify the energy savings of the installation. "With the technology now being used in B.C., we can get better insights into its performance," says Zeller. "For any mine that's expanding or being built new, we can now offer this as a proven energy-efficient technology, where we have a little more knowledge of how it behaves and how it works. "It lets us validate the energy savings, so we can transfer that knowledge to other sites, or other applications."

It's estimated that the stirred grinding mill at Gibraltar will save 4 gigawatt hours (GWh) of electricity annually. At the Tier 2 rate for BC Hydro's transmission customers, that's a savings of $325,000 per year for the mine. The total provincial potential for energy savings through the use of stirred mills in regrinding (a second stage grinding circuit where minerals collected in the first stages of the process are further reduced in size to allow physical separation into final product) is 18 to 24 GWh per year.

The energy saving potential is impressive, but it is not the only reasons to shift to stirred mill technology. "You get a more consistent product out of a stirred mill than a ball mill," says Zeller. "Further, the stirred mill has the potential to achieve finer grind sizes than a conventional ball mill which can offer downstream benefits to separate out the copper or whatever else you're looking for. The stirred mill also requires less floor space and is simple to install and maintain." "It's almost a no-brainer," he adds. "If a mine is expanding, this technology requires low additional capital, provides annual savings, and gives a better grind."

Capturing all those benefits is important in ensuring the future competitiveness of the B.C. mining industry says BC Hydro industrial marketing manager Steve Quon. Mining is B.C.'s second largest industrial consumer of electricity after the pulp and paper industry, using 15-17% of all purchased industrial electricity. "Efficiency innovation is critical in the mining sector because the products that we produce are cyclical in nature," says Quon. "The market prices will go up and down, but if you have energy efficient processes you're able to weather the ups and downs a lot more capably than your competitors."

 

 

   

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