The Swedish city of Kiruna, 145 kilometres above the Arctic Circle, is literally on the move. In a few years’ time its centre will be moved three kilometres east. Utilities have already been diverted and new roads built. Last year the railway line to the south was abandoned after a new 17 kilometre diversionary route was opened. All because the city is about to be undermined by subsidence from the iron ore mine to which it owes its existence.
This is because surface deformation occurs above the ore face which slopes downwards at around 60° so as the mining gets deeper this ground disturbance approaches the city. A sign at the Mine City Park states that it is a buffer zone between city and mine during urban transformation and that “the appearances of the park will change as a result of the deformations from the mine”.
The biggest mine gets deeper
The opening in May of a the new mining level 1365 metres below the mine reference level, and 320 metres below the previous level, secures the mine’s future for a further 20 to 25 years. In doing so it secures the local economy but also seals the fate of the existing city.
Underground mining at Kiruna started in 1957, since then there have been seven mining levels and it is now the world’s largest underground iron ore mine. The levels are measured from the old summit of Mount Kiirunavaara which was blown up in 1910. The new level is 1.2 kilometres below the surface and just over 12km from the mine’s office above ground.
The mine is operated by the Swedish company Luossavaara-Kiirunavaara AB (LKAB) which, in 2008, decided to invest £1.2 billion in this new level. This was its largest ever investment and required the removal of 4.3 million cubic metres of rock and the construction of 87 kilometres of new tunnels. When fully operational in 2017, it will be able to produce 35 million tonnes
(Mt) per annum. This is done by depositing ore from night-time blasting operations into loading chutes for transport to a crushing plant that evenly grades for hoisting to the surface.
The ore is lifted a total of 1.4 kilometres in two stages at 17 metres per second in skips that carry 34 tonnes. People and equipment, however, do not descend in mine shafts. Instead they are transported in vehicles that take around 20 minutes to drive down the mine’s 10° slopeways.
Rails above and below the surface
Since iron ore mining started in 1890, almost a billion tonnes of ore has been extracted. However, large scale mining operations required the opening of the railway to Lulea, on the Baltic, in 1899. In 1903, this line was extended to the ice-free port of Narvik in Norway. Clearly this railway is essential to the mine. What is not so visible is the railway network down the mine which is also an essential part of the mine’s production process.
When fully operational, the new mine level will have ten loading chute galleries for newly extracted ore, and one kilometre away in stable rock, four crushing plants. Speaking to The Rail Engineer, Hans Engberg, LKAB’s project manager for the new level, explained that a detailed study had shown that a railway was the most cost effective way to transport ore underground as it offered a high degree of automation and, unlike conveyors, can handle unevenly-graded extracted ore.
The underground network
Thus the new mining level has a rail network to transport ore between loading chutes and crushing plants. Loading chutes drop ore into the wagons. During unloading the entire train is supported on rollers as the full- size wagon bottom doors open to dump around 700 tonnes of ore into the crusher in two and a half minutes. To maximise capacity and minimise spillage the new level is a standard gauge (1435 mm) railway compared with the 891 mm gauge railway on the 1045 metre level above.
When fully operational in 2017, there will be a 15 kilometre network with ten loading chute galleries and four crushing plants with a daily haulage capacity of 140,000 tonnes per day. However the mine’s seven trains will carry a typical total of 100,000 tonnes a day in 125 train movements. Currently two trains operate on a 12 kilometre network which connects three loading chutes, one crusher and the workshop.
Each train consists of 21 unbraked wagons and carries between 600 and 800 tonnes of ore. The locomotives produced by Shalke are 108-tonne Bo-Bo locomotives. They have four 225 kW AC traction motors powered from an overhead 750 volt DC supply or their own batteries and have a maximum speed of 25 km per hour.
Hans Engberg explains that Kiruna’s underground mine has to compete with open cast mines on the quality of its ore and efficient mining operations. Hence the underground railway has to be fully automated leading to the selection of Bombardier’s INTERFLO 150 system to control the mine’s driverless trains. This is a Communications Based Train Control (CBTC) system which maximises throughput by variable moving blocks.
The INTERFLO 150 system provides safety through automatic train protection (ATP) and traffic automation through automatic train operation (ATO). The ATP ensures adherence to the railway speed profile and provides safe train separation and junction control. The ATO is an automatic driver that commands the locomotive to drive according to given authorities and perform precision stops where needed.
Train location is determined from tagged balises and axle-driven tachometers. A traffic control centre (TCC) provides centralised traffic control, manages the interlocking and a radio block centre for train communication, issuing movement authorities to the train.
INTERFLO 150 is suitable for both regional and industrial lines. In 1999 it was first used in Chile’s El Teniente mine. It works in the same way as the CITYFLO 650 system to be installed on London Underground’s (LU) Sub Surface lines as described in issue 102 of The Rail Engineer (April 2013) but is adapted for mining operations with automatic route setting, derailment detection, integration with loading and unloading systems, and compatibility with whatever radio system is used in the mine. The Kiruna installation includes 57 point machines and 180 balises. Bombardier is also supplying on-board ATO and ATP equipment for nine production and four service locomotives.
The head of industrial mining for Bombardier Rail Control Solutions, Valentine Paramasivam, considers that there is great potential for increased use of automated railways in mines. To this end, Bombardier have partnering agreements with companies such as ABB, Schalke, Midroc Automation and Nordic Mining Technology to further exploit this market. As an example they were recently awarded a train control systems contract for the Grasberg copper and gold mine on Papua, Indonesia, 2,700 metres above sea level, which will have a 28 kilometre rail network.
The iron ore line
Kiruna’s mine currently has a licence to extract 30 Mt per annum, 37% of which is waste. Iron ore waste is good aggregate material but is too expensive to transport. On the surface a processing plant produces iron ore products, mainly pellets. Kiruna and adjacent mines produce 27 Mt of such products for dispatch by rail to the ports of Lulea on the Baltic or Narvik in Norway which, being ice-free all year, takes 60% of this traffic.
The 473 kilometre Lulea to Narvik railway is single track line and electrified at 15kV 162/3 Hz AC. Trains travelling the 170 kilometres from Kiruna to Narvik first descend to Lake Torneträsk at 400 metres before climbing at a 1 in 91 gradient to reach the 523 metre summit on the Swedish / Norwegian border. The railway then clings to the side of a fjord as it descends to Narvik, 42 kilometres away with a maximum gradient of 1 in 60. At 68° north this is the most northerly point of the European rail network.
Since 1995, the line has been operated by Malmtrafik (MTAB), a subsidiary of LKAB. In 2007 it was upgraded to increase the axle load limit from 25 to 30 tonnes and passing loops were increased to 790 metres to accommodate longer trains. Every year, the line now carries around 4000 ore trains of 8,600 tonnes that are 740 metres long with 68 wagons, each carrying 100 tonnes of ore.
Most powerful locomotives
Hauling these trains are Bombardier’s I-ORE (Iron Ore) two unit locomotives which at 10,800 kW (14,500 hp) are the world’s most powerful. At 2 x 180 tonnes they are also amongst the world’s heaviest locomotives with steel body panels 4 cm thick. They have a maximum speed of 80 km/h but are limited to 60 km/h hauling loaded trains.
They first entered service 2001 and were ordered in three batches; nine in 1999 and four each in 2007 and 2011. Due to their weight the locomotives were delivered on light bogies and were then fitted with the correct bogies and fully assembled at MTAB’s Kiruna depot. This included adding ballast weights of 30 tonnes per unit.
The I-OREs exert a drawbar force of 1200 kN which is controlled in 41 power stages to enable drivers to select the optimum power setting for the line’s many curves and changes of gradient. AC traction motors on each bogie are controlled by a water cooled gate turn-off (GTO) thyristor. I-OREs can haul a loaded train with the motors on one bogie isolated. The control system also provides for slow speed control during shunting and loading. They have buckeye couplers. Screw couplings are also fitted for use in an emergency when the trailing load is restricted to 1000 tonnes.
The locomotives have regenerative braking that exerts a retardation of up to 750 kN and regenerates around 25% of energy consumed. During the descent to Narvik the regenerated energy is sufficient to power empty trains back up to the national border. The locomotive’s tread brakes are isolated above 5 km/h during regenerative braking.
A CATO (Computer Aided Train Operation) system is being installed on the locomotives and throughout the route. This provides the driver with an advisory speed for the optimum speed profile to reach a passing loop at the correct time. This is expected to give further energy savings of around 20%.
I-OREs are designed to operate at temperatures down to -40°C and in heavy snow. To minimise snow accumulation its body has clean lines with minimal roof and underframe equipment. Plastic covers over bogie recesses allow some snow to accumulate before its weight snaps the cover down to release it.
Lessons from the mine
For most rail engineers, a kilometre deep mine is an unfamiliar environment that raises many questions. How to get a 108 ton standard gauge locomotive to the bottom of the mine is an obvious one, to which the answer is down the slopeway. However what is familiar is the use of modern control systems and bespoke rolling stock to save energy and maximise throughput, whether this be iron ore or London’s commuters.
LKAB’s mining operations are applying this concept both underground and on the surface. The result is a railway that is optimised to transport ore from the mine face to the port by the use of systems such as CATO and Bombardier’s INTERFLO. This must surely provide lessons for more conventional railways.