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Weekly UpdatesAt the Greens Creek Mine on Admiralty Island, a steel cylinder larger than an H1 Hummer grinds basketball-sized rocks to small pebbles. A second, smaller mill grinds the pebbles down to a powder before the gold, zinc, lead and silver can be extracted. Meanwhile a ventilation system continuously supplies fresh air to miners working underground.
With grinding circuits, ventilation systems, and other large equipment and machinery running around the clock, mining is an energy-intensive industry. The two mills alone each consume about 15,000 kilowatts per day at Greens Creek Mine, and these are smaller than the grinding circuits found at larger mining operations. Including all of the mine's power needs, the average demand at Greens Creek is about 7 megawatts, while the Fort Knox gold mine northeast of Fairbanks draws about 35 megawatts, and the proposed Pebble Mine in the Bristol Bay watershed is expected to require upward of 250 megawatts. Accessing those amounts of power in the remote areas of Alaska that hold rich ore deposits is no easy task.
"The immediate big challenge is there is no power distribution system except along the Railbelt," said Steve Borell, executive director of the Alaska Miners Association. "The biggest issue of all is that mines typically have to plan for their own power. It's not just talking to the power provider and adding a mile of overhead line, which is the case in the Lower 48 in most cases."
BRINGING POWER IN
While bringing in power from the local utility is not always possible, some lengthy transmission lines have been built for mines. When Fort Knox started up in the late 1990s, they worked with Fairbanks-based Golden Valley Electric Association to build a 26-mile power line to the site.
Even with utility power coming in, a mine must have its own backup system, as Fort Knox demonstrated during its first winter in operation, just a few months after the mine started operating, a heavy snowstorm took down a power pole, knocking out power to the mine. Not only is a powerless mine unable to operate, but also the crushed ore can solidify in mill pipes, making for a difficult cleanup job. Fortunately, the backup diesel generators at Fort Knox worked and GVEA restored power within 24 hours, so the outage ended up being a surprise test of the system rather than a disaster.
Another lengthy transmission line was built recently to allow Greens Creek Mine to switch part of its power supply from on-site diesel generators to hydroelectricity from Alaska Electric Light and Power. With funding from federal grants, the utility built a new 9.5-mile underwater cable from the Juneau power grid to the mine. The line allows Greens Creek to purchase AEL&P's surplus power from its existing hydroelectric facilities, which currently amounts to about 25 percent of the mine's needs. On-site diesel generators will continue to meet the rest of Greens Creek's power demand.
Having the mine buy the excess power allows AEL&P to move forward on building the new Lake Dorothy hydroelectric project, which they say will be needed to fill Juneau's electricity demand in the future. Once the Lake Dorothy project is built, AEL&P should be able to fully supply Greens Creek Mine.
The advantages to the mine are both economic and environmental. "The costs for Greens Creek are lower in using hydropower than using diesel for generating power in most cases," said General Manager Rich Heig. "It also provides a large reduction in greenhouse gases associated with Greens Creek operations because we switch our power generation from diesel generation to clean hydropower."
A larger submarine transmission project is in the plans for the proposed Pebble copper and gold mine in the Bristol Bay watershed. With an expected demand of 250 megawatts, the current plan involves bringing power generated at a natural gas facility in Nikiski across Cook Inlet via an underwater cable. In comparing the feasibility of onsite diesel generation to building a long-distance transmission line, Northern Dynasty Minerals Ltd. Chief Operating Officer Bruce Jenkins said, "The simple answer is it is cheaper and safer to transfer electrons over distance than it is to transfer fuel." Northern Dynasty and Homer Electric Association also considered other options, including wind, nuclear, geothermal and tidal generation, but none of them fit the mine's demands for reliability and cost.
With natural gas prices on the rise, Jenkins said contingencies are in place, should natural gas prices rise too high. If that happens, existing infrastructure at the Nikiski site should allow for other generation alternatives, such as bringing in liquefied natural gas from Asia or local coal if the Beluga mine is approved.
NEW IDEAS FOR ONSITE GENERATION
Diesel has been the fuel of choice for onsite power generation, whether the intention is a backup as in the Fort Knox example, or providing all the power for a more remote mine without access to utility lines. Mines also need to bring in diesel to run equipment, such as large trucks and hydraulic shovels; but with the cost to purchase and transport fuel rising, other alternatives are getting more serious consideration.
For example, NovaGold studied several different alternatives for bringing power in from afar for the proposed Donlin Creek Mine near the Kuskokwim River in Southwestern Alaska. One option was to build a coal-fired power plant in Bethel, connected to the mine by a transmission line almost 200 miles long. However, all of the off-site options proved to be too expensive and too risky to rely on for providing the mine's anticipated 60-megawatt average demand.
"We're looking at a 365-dayper-year, 24/7 operation, and the thought of a power line going down in middle of winter in some of these remote stretches ... the risk was more than our engineering team felt was acceptable for this type of project," said Stan Foo of Barrick Gold Corp., NovaGold's joint venture partner on the Donlin proposal.
In contrast to Northern Dynasty, the Donlin Creek team is turning to wind power as a reliable and cost-effective way to meet part of its electricity needs. The team has proposed a mixture of 25 percent to 30 percent wind power, supplemented with diesel for the remainder. Wind provides environmental advantages by reducing barging on the Kuskokwim River and generating less greenhouse gases, but economics are the driving factor.
"The largest part of the decision is cost-driven, to get affordable power that meets our cost requirements to make this project feasible," Foo said.
A thoroughly different approach to rural power generation may soon get a trial in Interior Alaska. The city of Galena has applied for a permit to install a 10-megawatt nuclear reactor. The unit would be the first of its kind installed worldwide, but former city manager Marvin Yoder says the technology has been under development for more than three decades.
"It runs for 30 years and is buried underground. You almost don't know it's there," said Yoder, who is working through the permit process. "It's estimated that a 50-megawatt unit can sell electricity for 6 cents a kilowatt. That makes it real attractive if you're off the grid and don't have access to other sources." At the end of 30 years, Yoder said the reactor, which is made by Toshiba in Japan, will have about one gallon of nuclear waste left, which will be shipped out in the sealed container for reprocessing or storage.
With Nuclear Regulatory Commission approval likely four years off, Yoder says the nuclear option is still too distant to attract mining companies now, but he expects quite a bit of interest for all types of rural applications worldwide once the unit has proven itself.
REDUCING DEMAND
With energy making up one of the largest expenses for a mine, reducing the demand could create big savings. "We're always looking for ways to save in power costs and that means conserving energy," Foo said.
One strategy mines use is to capture waste heat from generators and use it to heat buildings or underground operations in the winter. This has created an interesting twist for Greens Creek Mine, as they look forward to meeting all of their power needs from hydroelectricity.
"In our case, we use waste heat off of our own generators to heat buildings and the air that goes into our underground system during the wintertime," Heig said. "Presently we will continue to use our generators to do that, but in the future, when the power company is capable of providing all of our power needs, we will have to look at another method of providing heat for our buildings and underground."
Rising energy costs are one factor motivating Fort Knox officials to consider adding heap leach to their operations. The heap-leach method of processing is less efficient at extracting gold, but it also requires much less energy than the grinding circuit currently in use.
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