Going deeper, Stillwater orders a third Kiruna electric hauler
Published 2012-01-04 00:00:00
Stillwater Mining Co has tentatively placed an order for a third Kiruna K635ED electric hauler to meet increased production as the company initiates its next development phase – extending its underground electric truck hoisting system from 3500 ft above sea level (asl) down to 2500 ft (asl).
The Stillwater Mining Company (SMC) has tentatively ordered a third Kiruna K635ED electric hauler – and is negotiating a possible fourth unit – for its palladium/platinum mine in Montana, USA; as it initiates its next development phase to extract ore at lower levels.
The company took delivery of the first two units early last year when it opted for a dedicated ramp below the mine’s shaft bottom.
Located in Nye, Southern Montana, SMC undertakes development, extraction, processing, smelting and refining of palladium, platinum and associated metals. It is the only known significant resource outside Russia and South Africa.
With proven reserves of approximately 4.5 million tons of ore, the mine is producing 400,000 oz annually.
The operation occupies more than 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.
Deeper production
In four development phases over the next five years Stillwater plans to deepen its electric truck haulage operation by a further 1500 ft taking it to an elevation of 2000 ft (asl).
In addition to the two 35 metric ton Kirunas, ABB also supplied plans and specifications for 5600 ft of overhead trolley line in phase 1, which will increase to approximately 12,000 ft over phases 1-4 by 2015.
The mining company undertook a feasibility study into all of its options in deepening the mine which included: extending the existing shaft using conveyors, expanding its current fleet of diesel trucks as well as the electric ‘trolley’ trucks.
Kiruna 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 excavation. 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.
Feasibility study
Factors studied in assessing the efficiency and cost benefits per hoisted ton of these alternatives included the MSHA limits on airborne diesel exhaust particulate levels, the relative costs per hauled ton of diesel fuel and electric power, effects on ventilation demand and capital costs.
The result of this exercise was the decision not to extend the shaft but rather to utilise the trolley electric truck hoisting system.
“While the study indicated that initial costs were comparable,” said SMC Chief Engineer, Curt Jacobs, all of the options, except using the electric trolley system, meant a capital cost outlay with no pay-back for some years.
“We therefore opted in favour of the Kiruna trucks as a ‘pay as we go’ option,” he said.
Diesel particulate matter
Also favouring the electric truck option was the difficulty in reducing diesel particulate matter (dpm) concentrations below the statutory limit of 160 µg/m3 if additional diesel trucks were to be used without additional ventilation fans and corridors.
“In contrast,” said Tony DiGrappa, Project Director for ABB in Canada, “Ventilation legislation in North American mines is expected to be an issue in the future.”
“The reduction in ventilation required with the Kirunas will provide a ‘real’ significant cost savings.” He added, “The combination of both the dpm and ventilation requirements means that there is considerable interest around North America in the Stillwater operation.”
Ramp extension
The ramp has been operating since March 2010 at between 3500 – 2800 ft levels (1067 – 853 m) and is 5600 ft (1707 m) long.
Next year, according to Joel DeBruycker, Stillwater Project Engineer, the ramp will be extended to the 2500 ft level and “the long term plan is to eventually go down to 1400 ft (asl).”
The ramp is 16 – 17 ft wide x 16 ft high and generally has a gradient of between 13 – 17%. The final haul road surface has been prepared with an emulsified asphalt and compacted gravel, allowing the trucks to reach pre-set uphill speeds of 10 miles (16 km/h) – but capable of reaching 14 miles/h (22.5 km/h) and ensuring a quiet and smooth ride.
Throughout the remainder of the mine, hauling is undertaken by a fleet of underground diesel powered mining trucks.
These travel at 4 – 5 mph (6.4 – 8 km/h) compared with the Kiruna’s 18 km/h. They are also considerably noisier than the Kiruna trucks.
As one of Kiruna drivers, Pat Wilson, commented, “Having driven the Caterpillar AD30 for most of my working life it is great to drive the much quieter Kiruna.”
“Today I go home much less tired after a shift,” he said, adding, “Whilst it initially looked so much larger it is so easy to drive and very quiet.”
Currently the round trip is approximately 18 – 20 minutes for the 11,200 ft journey.
“When all goes well, we can move around 1000 t/shift, working two 12 hour shifts,” said David Crabtree, General Foreman of Haulage.
Once again this compares favourably against the Caterpillar AD30 carrying 23 t compared with the 35 t capacity of the Kiruna; resulting in fewer journeys.
Today 43% of the mines production is from the lower levels below the shaft bottom.
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
