Stillwater Mining opts for electric hauling as it goes deeper underground
Monday, June 8th, 2009
Stillwater Mining has opted for electric ‘trolley’ haulage for its future deep mine production following an order for two Kiruna K635ED’s – its first electric vehicles and intended to comply with diesel particulate matter (dpm) legislation in North American underground mines.
Stillwater Mining’s Curt Jacobs, Chief Engineer, Rick Collins, Electrical Maintenance Superintendent and Karl Haumberger, General Foreman – Maintenance, were recent visitors to Sweden’s mining and tunnel equipment manufacturer GIA, to witness the factory acceptance certification for two Kiruna K635ED electric trucks, prior to their delivery.
Both trucks were ordered when Stillwater opted for electric haulage as the mining company opens deeper production tunnels at its palladium and platinum operations in Southern Montana, USA, later this year.
The mine has been producing 400,000 oz annually in the only known significant source of platinum group metals in the United States.
The operation occupies over a 6 mile segment along the eastern end of the 28 mile long JM Reef, located in the Beartooth Mountain Range. It is accessed by a 1950 ft vertical shaft – collared at an elevation of 5000 ft – and a system of horizontal adits and drifts.
In four development phases over the next three years Stillwater plans to deepen its electric truck haulage operation by a further 1050 ft taking it to an elevation of 2000 ft median.
In addition to the two 35 short ton Kirunas, ABB will also be supplying 5400 ft of overhead trolley line in phase 1, increasing to approximately 12,000 ft over phase 1-4 by 2012.
The mining company undertook a feasibility study into all of its options in deepening the mine which included: extending the existing shaft, stepping off, using conveyors, expanding its current fleet of diesel trucks as well as the electric ‘trolley’ trucks.
Produced in Sweden in cooperation between GIA Industri and ABB, the Kiruna trucks operate via a 3-phase a.c. 690 V overhead trolley line secured to the back of the truck. Kiruna electric trucks are engineered (electrically), sold and serviced by ABB in Canada for the North American market.
The complete design incorporates an all AC electric system with one motor for each axle, making it a true 4-wheel drive truck.
Two electric traction motors drive all four wheels allowing it to maintain a high speed, particularly on steep ramps compared with diesel trucks; resulting in a higher productivity per truck unit.
A single Kiruna is able to provide the same work as several diesel trucks. Faster speeds up steeper ramps result in a much smaller total truck fleet size of electric trucks for the same ore haulage as a larger fleet of diesel trucks.
The Kiruna truck also offers reduced noise levels in the confined underground workings. The measured outside noise level at maximum output is 85-90 dBA in the mine – appreciated not only by the operator but also by the miners working in the vicinity.
Electric power also allows easy and smooth stop/start operations with less strain on the operator and truck components.
A 75 kW Tier 3 diesel engine automatically starts up for off line duties such as, for example, loading, dumping and turning sites.
In passing areas no complicated overhead trolley lines are required. The operator simply drops the power collector which starts the diesel engine, allowing the oncoming vehicle to pass.
Whilst the study indicated that initial costs were comparable, according to Curt Jacobs all options, other than the electric trolley operation, meant a capital costs outlay with no payback for some years.
“We therefore opted in favour of the Kiruna trucks as a ‘pay as we go’ option,” he said.
Also favoring the electric truck option was the difficulty in reducing diesel particulate matter (dpm) concentrations below the statutory limit of 160 µgm/m3 with additional diesel trucks and without additional ventilation fans and corridors.
Tony DiGrappa, Project Director, ABB in Canada also indicated that ventilation legislation in North American mines is expected to be an issue in the coming months. “The reduction in ventilation required with the Kirunas will provide a ‘real’ significant cost saving.”
He added, “The combination of both the dpm and ventilation requirements means that there is considerable interest around North America in the Stillwater operation.”
In placing the order for the Kiruna trucks, Stillwater had used the haulage operation at Canada’s Inco mines as a model.
After a number of visits to Inco’s two operations featuring six 50 t capacity Kiruna trucks, the company was able to witness the quiet operation and speed of the trucks.
Rick Collins confirmed that they had also been very impressed with the operating and low maintenance costs of the six 50 t Kirunas at both operations.
“We were also able to use the Inco operations as a resource of information and, in fact based our proposed ramp designs on Inco’s experience,” he said.
Stillwater is pursuing final road surface using Emulsified Asphalt and compacted gravel similar to Inco’s installations.
The ramps in the new phases below 2000 ft will be laid in this format at a maximum grade of 15% allowing the Kirunas to reach uphill speeds of up to 18 km/h.
Electric vs diesel (Summary)
• Operational costs are reduced by approximately 50% using electric trucks
• Reduction in the number of electric trucks for the same t/h.
• Longer life – 7 years compared with diesels 5 years
• Environmentally friendly – reduced fumes/less noise
• Fewer operators/drivers needed
• Reduced energy costs
• Reduced maintenance
• Electric trucks can use steeper ramps at faster speeds
• Reduced need for ventilation
Photo caption: Left to right: Leif Bergstrand, responsible for Kiruna assembly, GIA; Curt Jacobs – Chief Engineer, Stillwater Mining; Karl Haumberger – General Foreman Maintenance, Stillwater Mining; Rick Collins – Electrical Maintenance Superintendent, Stillwater Mining; Tony DiGrappa – Project Director, ABB in Canada.