June/July 2008

Improving haulage performance while lowering environmental impact

Stillwater mine implements fleet of Kiruna electric trucks


Kiruna K635ED electric truck

How does an operation simultaneously address lower limits on underground airborne diesel particulate and rising production, without increasing ventilation? This was the challenge faced by Stillwater Mining Company — the only U.S. producer of palladium and platinum and the largest primary producer of platinum group metals outside of South Africa and the Russian Federation — at their Stillwater mine located in Nye, Montana.

In their quest for cleaner air, Stillwater evaluated different technology and ore transport mechanisms, considering factors such as:

  • new lower MSHA underground limits on airborne diesel particulate;
  • the difference in cost between diesel fuel and electrical power;
  • speed of ore transport; 
  • effects on ventilation demand; and
  • the total cost of shaft deepening.

When all factors were considered, their evaluation led them to select the Kiruna electric truck system for underground ore haulage. Part of Stillwater’s evaluation included a reference site visit to Canada, where the trucks have been running very successfully for several years in similar underground mines. The company subsequently purchased a fleet of 35-tonne K635ED electric trucks and power system infrastructure from ABB Inc. (Canada).

The Kiruna truck system was developed in Sweden in 1958 by the Kiruna Truck Company, with the electrical design and system supplied by ABB.  In 1998, the mechanical design was acquired by GIA Industries located in Grängesberg, Sweden. Since that time, ABB and GIA have continued research and development on the Kiruna truck products. The original models supplied in Canada were DC (direct current), many of which are still in operation. However, the current models are all AC (alternating current), and are available in 35-tonne or 50-tonne ore haulage capacity.

With extensive production and development areas below the existing production shaft of the Stillwater mine, the fleet of 35-tonne AC electric trucks will serve as primary movers to transport material from the deeper mine workings to the shaft loading facility. Development and construction is underway on a dedicated ramp haulage system and underground maintenance facilities, designed specifically for the AC Kiruna electric truck and its special attributes. For example, these trucks regenerate power back to the overhead electrical power trolley line while travelling down the ramp. This dynamic braking feature provides an additional energy efficiency benefit. The first 5,300 foot ramp segment will be commissioned for use in mid-2009. Subsequent ramp segments will be completed in future years.

Stanford T. Foy, Stillwater’s technical services manager, said, “Implementation of the Kiruna system at Stillwater will allow us to reach our long-term production goals and provide a flexible operating system that is within our current operating and capital constraints.”

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