Last month, ABB used the opening of the new Boliden Group facilities at the Aitik open-pit copper mine in northern Sweden, just inside the Arctic circle, to present its total mining capabilities to 35 mineral and processing industry journalists. For this project, ABB supplied the electricity substation, conveyors, drives and motors, plus concentrator plant automation, all controlled by System 800xA, at a total value of $84 million. The plant is effectively the ideal installation for demonstrating the ABB product profile and is also the first installation that uses IEC61850 substation automation communications, which link the electrical protection, switchgear, transmission and distribution equipment with the process control and automation data from Profibus and HART systems on the mineral flotation plant into one single control system and screens.
Mining is a major industry for ABB
The ABB mining business employs 1760 people spread across 26 countries, supported by four centers of excellence, with overall revenues quoted at $1.2 billion in 2009. Mining is an energy intensive activity, and with a typical metal ore concentration of less than 1%, the energy consumed in grinding the rock before any ore concentration can start is 50% to 70% of the total energy used in the process.
ABB was proud to show the gearless mill drives (GMDs) that are used to rotate the two Skega Poly-Met lined autogenous grinding mills, specially designed and supplied by Metso Minerals from Ersmark in Sweden. An autogenous mill is one that uses the larger pieces of ore to grind down smaller pieces by impact in a large rotating drum. These 45-ft. long and 38-ft. diameter mills are used to grind 2200 tons of ore per hour, reducing 16-in. size rocks down to 3 mm (0.1 inches), and then to 0.3 mm after secondary grinding in Metso rubber lined pebble mills. The ABB motors driving the two primary mills are rated at 22.5MW, powerful enough to start the mill smoothly without any mechanical stress, plus they provide speed control and energy efficiency. The GMDs and mills supplied to Aitik are the most powerful and largest mills by volume that have been supplied anywhere in the world: ABB actually delivered the first GMD ever supplied, to Lafarge cement in 1969, and it is still in operation today. Overall ABB claims a world market share for such drives in excess of 50%.
Switchgear protected from Arctic weather
The power consumed by the Aitik mine is significant, at around 1.5% of the total Swedish power demand. Two supply lines are now installed, both linked to power stations around 100 km distant. The ABB SF6 gas insulated 170kV switchgear is small enough to be installed indoors, protected from the Arctic weather, with three 80 MVA power transformers, each linked to a branch of a 3-step harmonic filter, to provide power conditioning and power factor correction, both to protect and improve the site equipment performance, and to ensure that consumers in the local area are not affected by plant operations. In fact, the local power network quality has improved significantly since Aitik switched the system on, and since then the site power factor has been better than 0.99.
The ore from the grinding mills emerges as a water-based slurry, and continues into the concentration plant, which uses two streams of 26 flotation and separation tanks, supplied by Outotec of Finland. The entire site process, including the electrical power supplies, conveyor systems, crushers and mills, concentrators, pumping stations and even the on-site sewage plant, are controlled by the ABB 800xA Extended Automation system: a specific Boliden requirement, according to Patrick Westerlund, ABB project manager for the System 800xA at Aitik was to "avoid islands of automation."
First site to use IEC61850
Aitik is one of the first major industrial sites to use IEC61850 to link the electrical equipment into the same system as the process control and automation data from Profibus and HART systems. In addition the System 800xA is integrated with the Boliden IBM Maximo maintenance system, and with its document management system, enabling instant control room display and access for operators to the maintenance status of all equipment. Asset optimization alert signals from the plant sensors are fed into Maximo to provide maintenance alerts. It is anticipated that this will significantly improve site efficiency and reduce interruptions. ABB claims this is the first industrial installation that includes the integration of all these elements into a single control room interface.
The Boliden Aitik site, with the major emphasis on power supplies, energy efficiency, motors and drives, seems to be exactly suited to the ABB capabilities. In addition, Kjell Svahn, ABB strategic account manager for Boliden, commented, "Boliden took the decision to use System 800xA as its group-wide process automation platform after testing some others."
The Boliden viewpoint
Sales from the Boliden Group mineral mining are split approx 33% copper, 33% zinc and 33% silver, gold and lead, from mines in Sweden and Ireland. At Aitik, mining operations for copper, silver and gold started in 1968, and by 2005 the concentrated ore shipped out by rail to the Rönnskär smelter was 27% copper, significantly higher than the 0.44% in the original rock. A business review conducted then by Jan Moström, now president of the Boliden mines business area, suggested that a further expansion of the plant then in operation would not be viable when treating the lower grades of ore anticipated to be available, against other competing producers, for example from Chile, where the ore grade was around 1%. "The problem we have here in Sweden is ice," said Moström, referring not only to the processing difficulties, but also to the way the ice tore away the richer surface deposits of mineral ore.
Investment of $780m
Surprisingly the Boliden board told Moström to take a new look, talk to his suppliers and come up with a new infrastructure plan that would make Aitik the lowest-cost producer of ore, even able to consider reprocessing previously discarded low-grade ore. Analysis showed that placing the grinding and concentration plants close to the tailings pond reduced the water and slurry pumping energy and costs by significantly more than the conveyor costs introduced in transporting the crushed rock 7 km to the new grinding plant. While the crusher 285 m down in the existing pit crushes the mined rock from the lower levels, a second crusher planned on the surface could also deal with rock from satellite ore bodies, and rock mined from the surface levels. Already a new open-pit mine is planned on the same site at Salmijärvi.
"Mining is a logistics problem," says Moström: With 99% of the mined rock being rejected to the tailings pond, efficiency and productivity are the main drivers. Moström also explained that Boliden "Establishes who will work with us, which suppliers have the technology to help develop our mining techniques," and who will apply a high level of engineering skill alongside Boliden engineers.
Major suppliers are long established
The main suppliers to Aitik were not chosen because of local links, but because they have these capabilities and have demonstrated the use of best available technology: Moström mentioned in this context Sandvik, Atlas Copco, Metso and Outotec, all having a good track record of working with Boliden: ABB in fact worked with them since the 1930s.
The Tara mines in Ireland and the Boliden Odda and Kokkola zinc refineries were acquired in 2004 from Outokumpu, the Finnish group where Outotec (or Outokumpu Technology) had its origins. Similarly the Boliden group is one of Metso's biggest customers for mill linings, Metso having supplied all the mills at the Garpenberg mine and in the Boliden geographic area in Sweden, and achieving a historic production availability rate of over 96%. Undoubtedly the careful planning that went into this three-year, $780-million Aitik investment was reflected in equally careful purchasing arrangements, so the logic behind choosing ABB for the major electrical partner was summed up by Moström as "Best available technology at the lowest price. "
Drive to improve productivity.
When the mined Aitik ore is 0.25% copper, 1.7ppm silver and 0.1ppm gold, any process improvement to the concentrators that increases the relative yield of these precious metal ores has a significant impact on the overall mine profit and productivity. This is a possible area for optimization on the new Aitik flotation plant, and Boliden engineers are applying advanced instrumentation to understand and enable such control. They are using on-line radiation attenuation monitoring to characterize and measure the different metals in the final mineral slurry, and laser ranging techniques to monitor the level of the foam or 'floc' blanket in the flotation separators, above the outflow.
Previous investments were in FF
The Boliden Odda investment in an Emerson DeltaV system using Foundation fieldbus (FF) to automate the zinc direct extraction process in Norway was reported back in 2005, which at the time added "best available" control system technology onto the newly acquired Outokumpu refinery operation, by adding advanced control and asset management onto the Outotec direct leaching extraction process. This was expected to deliver both plant efficiency improvements and better environmental performance. The FF infrastructure used 55 segments and around 400 instruments, plus 25 Profibus DP segments controlling 400 motors. The Emerson control system engineering project cost $4 million, within the whole Boliden Odda refurbishment project cost of $120 million. After an investment in refurbishing the Harjavalta copper smelter in Finland, also acquired from Outokumpu, the Aitik mine expansion was the next major Boliden investment since 2005.
