Following along its path of innovation, Metsa-Botnia's Joutseno Mill in eastern Finland recently started up the world's largest continuous digester, 10.3 m diameter, with a capacity of 2,000 tonnes/ day. The mill was built in 1908 to produce sulphate pulp and among its achievements is the world's first mill scale continuous digester, started up in 1958. A commemorative plaque in the mill says that "excellent pulp" was made using this digester. Until the 1970s, the pulp was unbleached. The mill went fully bleached in the 1980s.
| Risto Joronen: values have been reached |
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The new digester is part of a Euro 250 million project - Pulp 2000 - that started up in June 2001 and brought capacity to 600,000 tonnes/yr of bleached softwood (100% pine) kraft pulp.
Pulp 2000 was the natural successor to the mill's Pulp 1998 project that saw the installation of a complete new recovery island: recovery boiler, recausticizing unit, lime kiln and turbine.
The decision to go ahead with Pulp 2000 was made in October 1999, a year after startup of the new recovery island. "Pulp 1998 was the precursor to the decision to build the new fiber line," explains Joutseno's vice president Risto Joronen. "Perhaps the decision for the new fiber line came sooner than thought."
Joronen was project manager for Pulp 2000 and has been mill manager/vice president since startup. He says that careful planning in the design of the new pulp line was critical to a successful startup. Extensive research and laboratory work were done to ensure the right choices about equipment and processes were taken.
In show business they say that timing is everything. A parallel can be drawn with most industries. Unfortunately, for Joutseno Mill, the timing of the start-up coincided with the severe downturn that the softwood pulp industry is still suffering through. Still, looking at the bright side, Joronen says that starting up in a downturn may be easier because it can give a mill extra time to fine tune and debug the equipment.
| Project 2000 increased pulp capacity at Joutseno Mill to 600,000 tonnes/yr from 400,000 |
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The mill enjoyed quite a good startup and Joronen says it could reach design capacity in 2002 but probably will not because of the poor markets. "Our target for this year is 500,000 tonnes, depending upon the market. We run off the market."
The mill started in tough times in 2001 and they have continued. "This was impossible to know when the project was started," Joronen says. Along with the three week shutdown at startup, there have been other market related stoppages.
All the time the new fiber line was being built, production continued on the old line. It was shut three weeks prior to startup so the mill could make all the final connections.
Perhaps old line is a bit of a misnomer. The mill's equipment was only 15 to 20 years old, but some parts were not in good shape "for the times", according to Joronen. "The old line gave good quality but we chose Compact Cooking® (Kvaerner). It was always clear that quality had to be equal to or better than with our old cooking system."
The old equipment is for sale and once it is sold, the buildings will be demolished. As Joronen says, Joutseno is really a new mill.
A mountain of wood
Joutseno Mill uses 3.5 million m3/yr of wood. If M-real's adjoining BCTMP mill is added to the mix, more than 4 million m3/yr of wood are consumed. The woodroom belongs to Metsa-Botnia, although the two mills share it. Metsa- Botnia makes chips for the BCTMP mill (PPI, April 2002).
Most of the wood comes from eastern Finland, but 10 to 15% comes from Russia. One-third of the total arrives as chips from local sawmills; the rest is roundwood that is chipped on site. Joutseno buys its wood from Metsaliito, one of the mill's owners.
Joronen explains that a lot of money was spent on wood handling and the woodroom to ensure that the highest quality chips would reach the pulping process. "This is the foundation for everything," Joronen adds.
The mill makes four grades:
• Botnia JNO Pine Arm: A special reinforcement pulp for thin supercalendered (SC) and lightweight coated (LWC) papers;
• Botnia JNO Pine 85: For conventional SC and LWC papers;
• Botnia JNO Pine 88: For release/fine papers;
• Botnia JNO Pine 90: For fine papers and tissue.
The mill's biggest customers come from inside the Metsa-Botnia family. Besides Metsaliito, Metsa-Botnia's other owners are UPM-Kymmene and M- real, each owning 47%. The latter two are Joutseno's biggest customers and, prior to expansion, took most of the pulp for their mills in Finland and Germany. Now, with capacity increased, it sells more on the market than it used to. Customers come from a range of countries, including most of western Europe.
Pulp destined for domestic mills goes by rail or truck. For offshore customers, most is sent to the port of Kotka for transfer to ship. In the summer, some goes through the Saimaa Channel, which connects to the Baltic Sea.
The successful completion of the project meant another change, not only for the mill, but company wide. As of March, the company logo was changed to Botnia although the official company name remains Metsa-Botnia.
The technology
As described in the April article about M-real, the woodroom has two debarking lines and uses Andritz's new HHQ-Chippers with a horizontal feed. As noted the digester is the world's largest and uses Kvaerner's Compact Cooking process. Kvaerner also supplied the diffusion washer.
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| The Kvaerner digester is the world’s largest. |
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Along with the wood handling equipment, Andritz supplied the bulk of the fiber line including oxygen delignification, deknotting, screening, washing and the elemental chlorine-free (ECF) bleaching system.
The screening system from Andritz has a primary knotter, two secondary knotters, single primary, secondary and tertiary fine screens, sand removal and fines rejects handling. Accepts from the primary screen pass through two parallel pre-thickeners to ensure acceptable feed consistency to the final stage of the post-oxygen washing system.
The two-stage oxygen bleaching system is unusual for Finland for softwood bleaching, according to Joronen. The sequence is ODEopD and adequately meets Joutseno's needs. Pulp brightness ranges from 85-90 ISO. Full brightness can be reached "easily", Joronen adds.
The pulp dryer was installed in 1990 and rebuilt for Pulp 2000, bringing its capacity up to 2,200 tonnes/day. Metso handled this end of the project. Joronen estimates that 70% of the pulp machine is new. Metso Paper installed the world's largest horizontal pulper, its OptiSlushTM concept, 2,200 tonnes/day capacity, ahead of the former. The former and shoe press are also new. In the finishing area, a new cutter and a third pulp baler were added. All these changes were done during the three week shutdown.
Metso Automation supplied the distributed control system (DCS) for the entire mill. The ultra-modern control room is located near the offices of the mill complex. The one DCS replaces two older systems that were used - one for the old fiber line and one for the dryer.
The new system controls most of the process including the effluent treatment plant and chlorine dioxide generator. The control room has two sides: one for the fiber line, one for the recovery island. There are six large screens hanging on the wall on each side of the room. Each of these can be combined into one giant screen or split into four images to give 24 separate views of the process.
Due to their remote locations, the woodroom and dryer have their own control rooms, but use the same technology. Joronen says that the woodroom operators also have more "field" work.
Rated capacity of the Andritz recovery boiler is 3,150 tonnes/day of dry solids, but Joronen adds, it is really up to 3,500 tonnes/day now. The mill is self- sufficient in energy and can sell 35 MW back to the national grid at any time.
The recovery boiler has 12 liquor guns and five levels of air are used (one primary, two secondary and two tertiary). Primary air is used on all four walls. Secondary and tertiary air openings are only on the front and back walls. The boiler has equipment to burn non-condensible gases.
| Andritz supplied most of the fiber line including these DD washers |
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Joutseno sells all the bark it has from the woodroom as it does not have a power boiler. Its heat recovery system sends steam to the M-real BCTMP mill and receives evaporator liquor in return.
The Andritz evaporation plant is a nine-body, six-effect system able to evaporate all the mill's black liquor to 80% dry solids concentration for firing in the recovery boiler. The evaporator is now rated to remove 18,840 tonnes/day of water. The concentrator design incorporates Andritz's crystallization technology, which minimizes the need for boil-outs.
The recausticizing plant produces 7,000 m3/day of white liquor, sufficient to support the mill's cooking process and to produce oxidized white liquor for oxygen delignification. Raw green liquor is stored in the agitated raw green liquor tank before being filtered by three Andritz cross-flow X-filters. Filtered green liquor is pumped to storage and thickened dregs are dewatered and washed by two DreX presses. The dregs are discharged in a compact cake. The white liquor is filtered and the lime mud is washed by the CD-Filter.
After further treatment, the lime mud is heated and calcined in the lime kiln, which produces 575 tonnes/day to support white liquor production.
Everything about the mill is ultra-modern. It uses the most advanced technology and automation equipment. Part of that came from the start with the use of 3D modeling technology from Cadmatic. The 3D modeling allowed safe and easy installation of all the piping.
Heavy load
Another justification for the new fiber line was environmental. The effluent load to the treatment system was quite large, says Joronen. The added pressure from the new BCTMP mill meant some changes to the activated sludge system were necessary. A neutralization system was installed as was a new pumping system and aerators were added to the basins.
Influent water is taken from the adjacent Lake Saimaa. It is very clean so little treatment is needed. There are three large kraft pulp mills in the area - Imatra, Kaukas and Joutseno - and the lake is a popular recreational area so the mills must be very careful about what they return to the lake. Joronen notes that residents have said how much cleaner the water is now compared with a few years earlier, despite the pulp mills, all of which have expanded. Joutseno returns about 25 m3 of water per tonne of pulp to Lake Saimaa. When the mill reaches design capacity, he adds that this will drop to 20 m3/tonne.
Similar but different
To have the staff gear up for the new equipment, a lot of training was needed. "They had experience producing kraft pulp, but the equipment is not the same," Joronen points out. The training was a mix of classroom and visits to mills using similar equipment. The suppliers also helped bring the staff up to speed.
Joronen noted that he had worked on the pulp project at Rauma where many people with no pulp and paper experience were hired. At Joutseno, he notes, the training did not need to be so "extreme".
There are 250 employees at Joutseno Mill now but the number is dropping. Joronen expects it to stabilize at 215. Every month, he adds, there are fewer and fewer, but the drop is due to attrition. However, Joronen says, the industry in Finland, as in many other countries with a mature pulp and paper industry, has a rapidly ageing workforce. "In five years in Finland, the pulp and paper industry will need more people."
As with the M-real pulp mill, maintenance at Joutseno is handled by Botnia Mill Services (BMS). "This is the company's philosophy," Joronen explains. "We concentrate on making pulp."
BMS started up at about the same time as the mill came online. Many of its staff previously worked for Metsa-Botnia. BMS can use the same personnel in both mills.
The proof
Sometimes pleasing one's self is the toughest task of all. So with most of Joutseno's pulp destined for Metsa-Botnia's owners' paper machines, the mill has some demanding customers. Joronen is pleased for the time being. "We have done a lot of work. We can say that the main values we had with the old line have been reached. Of course, we always need better quality. We still have the potential to improve. There are quite a lot of small things to do."
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