Maintained cathodes ensure refinery’s cost-efficiency

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.

Cathode maintenance is a green choice

Boliden Harjavalta could have hired in-house service personnel for their cathode maintenance, or they could have outsourced it to several small workshops, but according to Jukka Tähkä, Outotec’s solution was the only viable for Boliden Harjavalta. Because Outotec is not only a technology company for minerals and metals processing, but also a manufacturer of cathodes, it has the expertise, equipment and resources to guarantee a full line of service. For the customer, this means cathodes are practically maintenance-free and are always available.

Tähkä also reiterates the importance of cathode assembly straightness, which is ensured during service as well. “If a bent cathode touches an anode, it can cause a short circuit, in which case cathode’s copper production is not maximal even if energy consumption and costs remain. Pure contacts are important for effective cathode performance. In general, Outotec’s cathodes minimize energy consumption thanks to their low resistance,” adds Tähkä.

Outotec’s cathode maintenance service enhances energy efficiency to the cathode process, extend cathode lifetime and lower plant operating costs.

Regular, preventive maintenance is also a green choice. ”We enable sustainable operation with an extended life cycle, efficiency and reliable performance of cathodes. The alternative to our solution – cooperating with a small workshop – would most likely be just a corrective measure, not a preventive one, and the benefits that our approach offers would not be realized,” states Ari Kaartti.

To further fine-tune the service program and strengthen the cooperation, Boliden Harjavalta's Tähkä and Outotec’s Ari Torssonen have established a routine schedule of annual site visits.

“Operators need to meet and see first-hand why cathodes have to be straight and edge strips seamlessly in place,” explains Torssonen, who coordinates cathode manufacturing and maintenance at the Outotec Turula workshop. He continues: “Our cooperation with Boliden Harjavalta has been really fruitful and constructive throughout the process. We receive and provide feedback on a regular basis. This has truly been a joint effort.”

Documentation adds reliability

Each cathode has a unique ID code which is used for tracking production, maintenance, materials and invoicing. Divergence in production compared to other cathodes may be an indication of a need for maintenance and has to be evaluated. Based on the ID code, the history and location of each cathode can be documented.

”Refineries cannot avoid cathode maintenance and Outotec has made this a professional, industrial process which benefits both parties. It allows our customers to focus on their core business, namely copper production,” concludes Kaartti.

Maintenance for all brand cathodes

The Boliden refinery in Pori uses Outotec Edge Strip cathodes. However, cathode maintenance program is not restricted to Outotec’s own cathodes and can also be utilized to service or upgrade cathodes produced by other manufacturers. Outotec’s patented edge strip technology extends the lifespan of the cathode as well.

Cathode maintenance can be arranged either at the customer site, in the Outotec service center – or as Ari Kaartti envisions – even in a specially equipped truck. For Boliden Harjavalta, the best option is the Outotec Turula manufacturing facility, just a few hundred kilometers from Pori.

Depending on the plant location, customers have the option of leasing or buying the necessary equipment. Outotec cathode maintenance service can be customized to meet a customer’s specific needs and based on some pre-configured modules.

*This case study has been written prior to the merger of Metso and Outotec.