Swedish roller coaster ride
October 2009
Spherical iron ore pellets start their up-and-down journey north of the Arctic Circle and, thanks to hydraulic drives, never stray from their appointed course.
It’s cold and wet in Sweden’s northernmost town. The weather here in Kiruna, above the Arctic Circle, is so utterly inhospitable that it wasn’t until the start of the twentieth century that the company Luosavaara & Kiirunavaara AB (LKAB) began developing the gigantic iron ore deposits found there. Given the fact that Luleå, the nearest port, is 340 kilometers away, the mining company started off by setting up its own railroad. That railway transports these metallic spheres right down to this very day. But before the pellets can be loaded into railroad cars and sent off to the smelters, they take a hilly ride on a conveyor belt 1.8 kilometers long.
The extreme weather wasn’t the only challenge to be overcome when engineering this link between the new KK4 pelletization plant and the loading depot. The course first descends and then climbs at a 6 per cent grade. What’s more, the material being transported comprises many tiny spheres that, if at all possible, are not to shift and move relative to each other during acceleration and deceleration. Thus the drive has to be powerful enough to start the heavily laden belt from a standstill and gradually accelerate it to maximum speed.
Even more efficient
The basic requirements here are high torque values and sophisticated controls. “With the hydraulic drive made by Hägglunds we are able to move up to 9,000 tons per hour. We now have a flexible conveyor system that can be stopped and started as needed, without the pellets rolling around,” raves Kurt Hansson of PROing, consultants to LKAB for this project. And Jan Lundgren, project manager at LKAB, concurs: “A hydraulic drive system appears to be the most dependable option, since it can apply full torque at virtually any loading level.”
The drive system selected for the conveyor belt was one dubbed “Gemini”. This concept features multiple rugged, high-performance modules, each fitted with tandem pumps. These modules are not only tough enough to withstand the frigid environment. They also apply a gentle touch in their work. Should a disruption loom in one of the modules, the integral monitoring system will detect and report it well in advance. If repairs are needed, then the unit affected can be shut down with no impact on production operations. And the Hägglunds CBP hydraulic motor used here is a true energy miser, as Lundgren is happy to testify. “We’re always concerned about making our production operations even more energy-efficient and that’s why we are so enthusiastic about the motor’s 95 per cent efficiency.”
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