Boliden is one of Europe’s leading mining and smelting companies with operations in Sweden, Finland, Norway and Ireland. Boliden Harjavalta Oy, which copper refinery operates in Pori, Finland updated its copper refining process with Outotec’s Tankhouse technology and permanent cathodes in 2007. Related to the technology upgrade project Boliden Harjavalta realized very early on the need for regular cathode maintenance to ensure process reliability as well as maximum production for minimal use of costly energy.
”It is a huge mistake to think of a cathode as merely a simple steel plate. In fact, cathode performance is essential for the refinery’s profitability. Its straightness has to be just right; otherwise copper production is not optimal but energy costs stay. Also, it goes without saying that the cathode’s most important feature, the edge strip, needs constant attention,” states Jukka Tähkä, Manager at Boliden Harjavalta's copper refinery.
Outotec and Boliden jointly develop a cathode maintenance service
Since 2009 Outotec has been responsible for the refinery’s cathode maintenance. Outotec provides Boliden Harjavalta with a full service preventive care concept with the goal of improving tankhouse efficiency, reducing operation and maintenance costs and extending cathode lifetime.
Outotec’s proprietary edge strip technology along with turnkey customer service and dedicated service equipment has taken the maintenance concept for cathodes to a new level in the tankhouse business. With both companies having a common interest in the approach, the two have teamed up to carry out R&D efforts with Boliden Harjavalta having an active role in developing and testing the improved edge strip materials.
“Boliden Harjavalta tested several alternatives and finally selected the material that best suits their copper electro (ER) refining process. This customized process for selecting the right material is just one example of how this full-service concept and cooperation benefits refineries,” explains Outotec sales director Ari Kaartti.
Boliden Harjavalta uses Outotec's edge strip technology that is designed to withstand the high stress and impact caused by mechanical stripping. The edge strip’s seamless attachment to the plate prevents copper from growing around and under the edge strip, thus extending the maintenance interval – and eventually the lifespan of the entire cathode. Boliden Harjavalta's Tähkä estimates the lifetime of the cathodes used in Pori to now be at least ten years, if not longer.
Automation detects cathodes for service
Boliden Harjavalta's 28,000 permanent cathodes produce 155,000 tonnes of cathode copper annually, which translates to a little less than 4,000 kg of gold and 80,000 kg of silver.
In Boliden Harjavalta's case approximately 300 cathodes come back weekly to their origin, Outotec’s Turula workshop, for a maintenance check. “Thanks to the improved edge strip material, we now expect the cathodes to require maintenance on average only once every three years,” says Tähkä.
Boliden Harjavalta is taking the full advantage of the service approach and facilitates efficiency by using automation designed to determine cathode maintenance: a machine vision detects the cathode’s edge strip and straightness and based on pre-defined tolerance levels, directs cathodes either back to production or for maintenance and to the stripping machine’s reject conveyor.
”The stripping machine operator would generally only have a few seconds for this task, which is not enough to evaluate cathode plate condition. The human eye is not as precise as computer-based automation and we have found this automated selection to be highly beneficial to our operations,” states Tähkä.
Boliden Harjavalta's scope of responsibility in terms of maintenance has been scaled down to loading and unloading an Outotec truck which transports the cathodes to and from the Turula workshop. Special transport racks have been designed specifically for this purpose.
The workshop has a dedicated area and equipment for maintenance: a semi-automated edge strip detachment machine, polishing tools and a measuring device for cathode assembly straightness measuring and edge strip replacement.