Stora Enso's new mixer saves energy
The Skoghall Mill is satisfied with the new pulp mixer. Persons in photo from left: Pär Eriksson of Stora Enso, Johan Ahlstrand of Metso, and Mikael Forseryd of Stora Enso.
A number of development and refurbishment projects are carried out at Skoghall Mill every year. Mikael Forseryd, Project Manager for the fiber line tells: “The projects range from minor modifications to major replacements and refurbishments. Our old O2 mixer was from 1992. That may not seem very old, but it was inefficient by modern standards. Development is fast, especially when it comes to energy-efficiency.”
Part of the energy-efficiency program
Stora Enso takes part in PFE – the Swedish Energy Agency’s Program for Improving energy efficiency in energy-intensive Industries. To date the program has made progress far beyond expectations. The energy saving during the first five years of the program was more than twice the Energy Agency’s target.
Planning for the replacement of the O2mixer began in 2009, when a concept and a demand specification were drawn up, with commitments partly based on the PFE program.
Fast installation necessary
Mixing is a vital stage of production, and all sulfate pulp produced at Skoghall Mill goes through the machine. In other words the mill needed a machine that is highly efficient and easy to install.
“We have a production target of 46 tonnes an hour,” says Mikael Forseryd. The mill operates about 8,400 hours and we produce about 320,000 tonnes of pulp ayear. The mill normally has one production shutdown a year which gives us a refurbishment window of around seven days, no more. For this project, it meant that everything – taking down the old machine, casting new foundations, re-drawing the pipes and performing a checkout – had to be done in a week, after which the mixer had to be up and running.”
Better pulp quality
The new Metso SMF mixer came into service in November 2011, and the effects are already evident.
“We’ve reduced energy consumption by this mixer by 37% on average,” says Mikael Forseryd. “At our production rate that means an excellent payoff time. And we’ve had no loss of production or problems with it either.” |  |
 | Metso’s new, energy-efficient SMF mixer has been in service at the Skoghall Mill since November 2011. |
Another unexpected effect of the replacement is improved pulp quality, as
Pär Eriksson explains, “The new mixer allows the fiber to keep its straightness. The old mixer had an output of 270 kW, while the new one has 70 kW. A mixer that uses less energy treats the fiber more gently.
That was what we hoped for, and we now realize that is exactly what has happened. We have also noticed that the new mixer is very stable and has minimal vibrations, which is good for the machine itself and for the pipework.”
Delivery on time
“The cooperation with Metso has gone well,” says Mikael Forseryd. “We had a tight schedule and everything went very fast once we had reached a decision – but Metso delivered on time. The installation also went smoothly, despite the fact that the re-drawing of the pipes was more extensive than we had planned.”
Skoghall Mill is part of Stora Enso’s Renewable Packaging business area, and it produces cartonboard products primarily for food packaging. The raw material used is mainly round timber and sawmill chips (spruce and pine) for two types of pulp: sulfate pulp and CTMP (Chemi Thermo Mechanical Pulp). The mill employs just over 820 people and will celebrate its 100th anniversary in 2017.
