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Kiruna, a tiny mining town 200 km north of the Arctic Circle in the northern Sweden is today known also as a town that is sinking. Therefore, Kiruna is in the process of being moved to another location as a result of the cracks that have been developed in the mine wall under the town during its 100- year long history in mining.
The move of the town does not frighten the Kiruna people or LKAB, an international high-tech minerals group operating a more than 100 years in the region. To save the town and to provide LKAB with access to the iron ore lying under Kiruna and worth a fortune, the town officials have made extensive plans for relocating the town centre. LKAB, in turn, has started a major investment program of more than €1.1 billion to increase production capacity for iron ore products in the region from the current 23 million tonnes to 25 Mt by 2007 and to 30 Mt by 2008. These investments are LKAB’s response to the globally increasing demand for iron ore products needed for making steel.
Reliability and fast service are the keys
High production goals cannot be reached without reliable and smoothly operating rocesses. When LKAB was selecting a drives supplier for their new concentrating and pelletizing plants in Kiruna, a vital part of their major investment program, they knew whom to turn to. During a period of several years, Vacon has supplied roughly 100 AC drives to control pumps and fans at LKAB’s concentration plant (KA2) in Kiruna, and the ventilation system in the tunnels of the mining caves in Malmberget, 75 km from Kiruna. In Malmberget, some of the Vacon AC drives are located almost 1,000 meters under ground. This depth poses many risk factors to electrical equipment.
Consequently, for the essential task of pump, fan, conveyor and feeder control at LKAB’s new concentrating plant (KA3) and pelletizing plant (KK4) under construction in
Kiruna, LKAB has chosen Vacon AC drives. About 200 air- and liquid-cooled NXP drives of 690 V will be controlled via Profibus. CANbus will be used for communication with the maintenance system. Commissioning of the plants will take place during the winter 2007, and the plants are expected to be operational in April 2008.
In mining processes where a downtime can raise to hundreds of thousands of euros per day, the reliability of the equipment is of utmost importance. The other fundamental is-sue is fast service. With Vacon’s subsidiary located in Sweden, support and service are available at short notice when needed.
Liquid cooling for demanding environments
Liquid cooling enables the use of cabinets with a high protection class - this is why the liquid-cooled AC drives are ideal for the underground excavation industry, where dust and humidity are major risk factors. Liquidcooled Vacon AC drives are well suited for locations where air cooling would be difficult, expensive or impractical, or where the installation space is at a premium. Vacon’s liquid-cooled units, which use normal drinking water as coolant, have a very compact construction and a low noise level as no large fans, additional air conditioning or filtered ventilation systems are needed. A low noise level also means a better working environment.
An additional factor that contributed to the choice of these AC drives was their heat loss transportation. In concentrating and pelletizing plants, the air is filled with coal and iron ore dust. The liquid-cooled drives make it possible to transport the heat losses outside the electrical room without ventilating the room and cabinets with the surrounding air.
A town driven to a new location
With an ore body of about 4 km long and an estimated depth of more than 2 km, LKAB Kiruna mine is the world’s largest, most modern underground iron ore mine. To date, more than one billion tonnes have been mined, and the present main level is at a depth of 1,045 meters. Mining towns elsewhere in the world have struggled with the problem of sinking earth, but in most
cases, the approach has been to prop up sinking buildings rather than move them. This massive and expensive move operation of Kiruna, a city of 23,000 persons, will take a few tens of years, maybe even more than one hundred years. Photographs: Courtesy of LKAB.
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