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The focus to PM2’s rebuild was the finishing section. An operator checks the profiles on the Andritz Küsters PrimeCal ProSoft calender system. Paper widths up to 7.3 m can be calendered at production speeds up to 1600 m/min.
With sales to more than 70 countries, Stora Enso has developed a global production strategy designed to increase efficiency and profit. The strategy is based not only upon an analysis of its competition, but also upon the capabilities of each of its mills around the world. This balance of internal teamwork and internal competition provided the momentum for the Summa mill to move from standard newsprint to value-added SC-A Plus grades to stay one step ahead of the competition – internally and externally.
“Competition is what keeps our mills efficient, our costs low, and our quality high,” says Juha Mäkimattila, Mill Manager for the Summa mill. “The idea is that every mill is measured not only by its results, but also by its prospects for growth and competitiveness.”
The Summa mill was founded in 1953 on the south coast of Finland near Hamina. The first paper machine started production in 1955. PM2 followed three years later, and a third machine was added in 1972. The mill has been producing standard newsprint for years.
Then came LangerbruggeWhen Stora Enso built the new PM4 at Langerbrugge in Belgium, it created a modern and massive newsprint production line. Other mills in the Stora Enso network could not compete with the size, speed, and efficiency of the Langerbrugge machine (10.3 m width and 2000 m/min design speed).
The new machine created a challenge for Summa, as standard newsprint production at the mill was no longer an option for growth. “We had to deal with the cost of three machines, while our production was approximately down to one and a half machines,” Mäkimattila says. “We finally had to shut down PM1 completely.”
Time for new thinkingSince the future was not going to be in standard newsprint, Summa’s Production Manager Antti Outinen reasoned that adding SC-A Plus grades to the product range would add value for the company. With the advantage of the Scandinavian spruce fibers, and his team’s dedication to continuous improvement, the outcome looked promising. Now to convince top management to make the investment.
Stora Enso invested € 90 million to prepare Summa for the new grades – adding a new peroxide bleaching stage, new quality-based tools to regulate a stock fractionation system, and a new PrimeCal ProSoft multi-nip calender to produce machine-finished (MF) papers.
Today, Summa’s PM2 produces SC-A Plus under the brand name MagniPress Bulky, and MF magazine paper under the SilvaPress name. The volume ratio in the paper is decisively improved –
reaching more than 1.0 cm3/g. This, plus a roughness below 1.5 pps and a gloss higher than 45%, create a paper with excellent printability, according to Stora Enso’s key customers.
A dozen customer companies were invited to test the paper in its early stages. The 15% increased bulk, the smoothness that gave the feel of coated paper, and the economic advantage of reduced grammage were quite convincing.
Radical changesMaking that kind of shift in grade structure requires some radical changes. This was not a problem for the team at Summa. They were accustomed to change and willingly looked at ways to continuously improve. The necessary changes to stock preparation, PM2, and paper finishing were planned and executed with precision.
The first changes were to the fiber preparation area. Here, Andritz played a significant part in optimizing the TMP plant with Summa specialists. Andritz also supplied a new peroxide bleaching stage to increase the stock brightness. Consumption of bleaching chemicals and fresh water use was reduced as the brightness of the pulp was increased.
The main changes were to the paper machine itself. PM2, originally built in 1958, had been modernized in the 1990’s and again in 2000. An interesting part of the rebuild was the implementation of the “Firewall Concept,” developed by the Summa team. With it, operators could allocate different feedstock qualities to PM2 and PM3 and optimize the product quality of both machines. If for any reason the stock did not match the quality requirements for SC-A Plus, it would be used for other grades.
The focus of the rebuild was PM2’s finishing section. “We wanted to install the best possible calendering system,” Mäkimattila explains. “That’s why we selected Andritz Küsters. Their calendering system was proven at Langer-brugge. The online calender achieves high temperatures, perfect nip-load, and excellent steam regulation. With that reference, we trusted Andritz Küsters’ competence.”
Once the contract was signed, the work was fulfilled in about 12 months. The PrimeCal ProSoft calender was manufactured in Germany and assembled before it was dismantled and delivered to Finland for final erection.
Design stageRight from the design stage of the project, Andritz Küsters played a significant part in the process. Several test runs at the company’s Technical Center in Krefeld, Germany helped Summa to determine the specifics of SC-A Plus paper and the technical parameters for their machine rebuild.
Andritz Küsters had to redesign its ProSoft concept a little to be able to retrofit it to Summa’s machine. At Langerbrugge, the paper web is transferred to the first calender stack from above. However, at Summa the usual top-to-bottom route was not practical. Significant machine structural changes were avoided by using a rather unusual bottom-to-top route – also making the Summa machine unique.
Impressive machineThe PrimeCal ProSoft calender consists of two pairs of frames, each carrying five rolls. The top and bottom rolls are PrimeRoll MHV zone-controlled rolls. Also in each stack are two heated steel rolls and a conventional roll.
While the conventional rolls must only be manufactured precisely, the thermo roll’s most important qualities are consistency in temperature and resilience. The PrimeRoll MHV (Multi-HV technology) rolls weigh 33 tonnes each, have a product width of 7.3 m, and operate at a production speed of 1600 m/min.
The two-stack construction of the 580-tonne calender system ensures an extraordinary high rigidity of the entire machine.
The whole system is 7.5 m high and has a length of 9.5 m between the feeding system and transfer to the winder. That makes a distance of about 48 m for the paper to travel through the calander – a trip which it completes in only 1.8 seconds.
One other aspect of the design is the MultiMaster control system, which monitors the important components of the calender and regulates the drive of every single roll. The adjustment with MHV technology offers even more possibilities to improve the paper and the machine’s performance.
Smooth start-upAfter a smooth assembly and start-up, the system was handed over to Stora Enso Summa in March 2005. According to the mill, all expectations have been fulfilled. Originally designed at a roll temperature of up to 180°C, the calander today reaches 190°C. Production speed of 1600 m/min, paper width up to 7.3 m, and nip loads to 500 kN/m complete the picture. Approximately 183,000 tonnes of paper (7.6% more than originally calculated) are produced on PM2.
Excellent resultsBesides the capacity figures, the paper specifications are very satisfying to Summa. For the basis weight range produced (48-60 g/m2), D65 brightness is 75% and gloss is 45%.
The smoothness stays at 1.5 µm and the volume is up to 1.1 cm3/g. The rebuild of the PM2 contributes to a positive development in results, according to Summa management.
“The more complex the technology gets, the more important it is to train our operators to monitor the machine’s parameters,” Mäkimattila says. “The project does not end with taking over the delivered systems. We want to maintain a long-term partnership with at least those suppliers who built the core components.”
Stora Enso SummaLocation:
Hamina (southern coast of
Finland – 150 km from Helsinki)
Product range:
SC-A plus, MF magazine,
newsprint and bulky paper
Brand names:
MagniPress Bulky,
SilvaPress, NewsPress,
ExoPress, LibroBook
Raw material: Spruce fiber
Paper machines:
PM2 6720 mm trim, 1200 m/min, 183,000 t/a
PM3 7650 mm trim, 1500 m/min, 230,000 t/a
Personnel: 430 employees
