.
“For every project, we want to be able to compare apples-to-apples as much as possible when we evaluate quotations.”
Per Strand, Managing Director for the Obbola mill.
“When the capital project was approved, it was a very positive signal for us,” says Fredrik Mellesmo of SCA Packaging. “First, that the company was investing in our future at Obbola, and second that we were getting modern and interesting technology to work with.”
Mellesmo directed the capital investment project that led to a new Andritz High Energy Recovery Boiler (HERB), an Andritz methanol plant, a new Siemens 25 MW turbine-generator, and a water treatment plant being installed at the Obbola mill.
But before Mellesmo became Project Director, he was part of the team that conducted a pre-study for a major rebuild of the mill’s old recovery boiler. The shift in thinking from rebuild to replace makes for an interesting story.
Reduced pressure, reduced capacity“We began in 2004 to investigate the rebuild of our old recovery boiler (installed in 1962) because the boiler had cracks in the water and steam drums,” Mellesmo says. “To run within safe limits, the authorities required us to decrease the pressure in the boiler every year. We knew we could operate until about 2007 without doing anything big, but after that a major rebuild would be required.”
Per Strand, Managing Director for the Obbola mill continues, “Our initial hope was that we could rebuild the old boiler in steps. This way, we could reduce the amount of capital required and spread it over several years. But the age of the boiler, and uncertainties about what surprises we might encounter when we opened the boiler during the rebuild, concerned us.”
“To keep the boiler alive, we would have to replace the drums in a very short period of time, so that meant we would almost have to do everything in one step instead of a phased approach,” Mellesmo says. “We would lose the advantage of spreading out the capital investment, and the shutdown time would be very long – 70-80 days. Plus, we would not gain any electrical power production.
When you build a recovery boiler in Sweden today, you must take into account the electricity generation capacity,” Mellesmo says. “Green Certificates (a tradeable commodity in Sweden) can give us big economic benefits since the power we generate is from renewable energy sources. We look at the boiler from an energy point of view and try to get as high steam data as possible.”
The study team’s conclusion was that it would be a really huge investment just to rebuild the boiler. “Toward the end of that pre-study we began to investigate the possibility of buying a new recovery boiler instead,” Mellesmo says.
Getting what we wantedSo, during 2005, the emphasis shifted to intensive discussions with all the recovery boiler suppliers about a new boiler. “We went into considerable detail and took it to the point of having almost final contracts that were technically acceptable to us. The scope was well-defined.”
With technical solutions and price quotations in hand, the capital request was presented to SCA Packaging’s top management in the autumn of 2005. The project was green-lighted in October. “The decision had to come quickly because we wanted to do the switchover during a planned maintenance stop in 2007,” Mellesmo says. “So, working back from that date, we knew when we needed to start.”
In December 2005, Andritz was awarded the contract. “They had a solution that was most acceptable to us in terms of materials, processes, technologies, and commercial terms,” Strand says. Mellesmo adds, “There is a lot of knowledge and experience within the Andritz organization. It was very easy to discuss process solutions with them. The same people were involved through the entire project from pre-sales to completion so there was real continuity and commitment.”
High energyThe design capacity of the old boiler was 750 tds/d, with 60 bar pressure at 460 ºC. Design capacity for the new boiler would be 1000 tds/d with 110 bar pressure at 505 ºC, which would produce significantly more steam and electrical energy.
It helped that SCA’s Östrand mill in Sweden (see FiberSpectrum Issue 14) had gone through a similar process of installing a high-pressure, high-temperature Andritz recovery boiler in 2006. Åke Westberg, SCA’s Project Director at the time, sat on the steering committee for Obbola’s boiler. “Since we are using basically the same suppliers that Östrand did, we got a lot of experience and information from Åke’s successful project.”
Originally, the Obbola/Andritz team had thoughts of trying to improve upon the steam values that were achieved at Östrand. The cost of the special materials required to achieve a higher temperature than Östrand were prohibitive. “Keep in mind that the Östrand boiler is about three times the size of ours,” Mellesmo says. “We could not justify the investment expense for the little extra energy we might produce. We are a bit lower in steam temperature (10 ºC lower), but higher in pressure (4 bar).”
Smooth projectIn March 2006, site work began. Obbola was responsible for the civil work (foundations, etc.). In July, pressure parts were delivered from Andritz. “There were no real delays throughout the project,” Mellesmo says. “I am quite pleased with our overall safety record. During construction, there were no major safety problems.
By April 2007, commissioning started and the first oil firing began in August. The first black liquor was fired in the new boiler on September 26, 2007 and the switchover from the old boiler to new was done at this time. “We had a provision to be able to switch back to the old boiler if we needed to for any reason,” Mellesmo says, “but we never had to do it. Once we fired the Andritz boiler, we never looked back.”
Basically one month after liquor firing, the Obbola team took over the boiler and has been operating it since. Urban Lundström, a Boiler Operator at Obbola who has worked at the mill for 18 years, agrees the new boiler is “working very nicely.” Was he sad to see the old boiler shut down? “No, not at all,” he says. “There was not much emotion during the start-up of the new boiler; everyone was focused on their work.”
The turbine (25 MW) was also completed in October. “The time schedule followed perfectly what we had planned in the beginning,” Mellesmo says. “The project ran quite smoothly the whole way.”
Simulation and trainingMellesmo attributes part of the smooth start-up to the extensive training program conducted by Obbola, which Andritz supported with technical and maintenance experts. “In the old boiler, we had an old-fashioned panel-based control system,” Mellesmo says. “Many of the operators had worked with that system their whole career. We used the Andritz IDEAS dynamic simulator and the experience was very positive. We had a lot of good training before start-up with that simulator. That was a good investment as I see it.”
Strand agrees. “The simulator was a very good tool,” he says. “We can see a payback on that training investment already. We have had some shuts in the boiler due to faulty instrumentation (black liquor consistency being measured too low so the boiler safely shuts down). But we have had very smooth and quick re-starts every time. The operators had trained for this with the simulator and can do it very well.”
One thing that Obbola is working on now is how to keep the simulator alive so it can be used for new operators or refresher training. “A lot of mills don’t do this and I think we see that as a mistake,” Strand says. “We spent a lot of time and money on training and we want to ensure that we get the most economic payback from it.”
Fine-tuningLars Åke Larson, Boiler Operator and a veteran at the mill with 28 years experience, really likes the new operating environment. “It was very physical work with the old boiler,” Larson says. “Now we are much more automated. But the automation also has more trips and safety logics built-in so that we have to be much more precise to meet all the environmental limits.”
Helena Lindqvist, Production Technician, is relatively new to the recovery area, but has been involved in instrumentation at Obbola for over 20 years. “Coming from outside the chemical recovery area, I have to say that the system is more complex than I thought it would be,” Lindqvist says. “We are very satisfied with the new boiler and with Andritz. We get the help we need.”
Lindqvist says that the main activity at the moment is trimming the air pressures and flows at the different levels (what is known as the “interlace” of air) and also char bed control. “Each boiler has its own personality,” she says. “The operators are moving from the old personality to the new one, and learning how to fine-tune as they go.”
Recovery and green electricity“The system in Sweden is so that if you put energy out into the market, you have to have a certain percentage of green electricity,” Strand says. “If you don’t produce green electricity yourself, you can buy certificates from someone else who is producing it. We purchase about 50% of our power at this mill, but we have already covered the green certificates that SCA needs. That means we can sell the remainder, which is quite a large part of our total electricity production, to other companies.”
To maximize the production of green electricity, Obbola not only has black liquor, but also the pitch oil (residue from the tall oil by-product) that it burns in its recovery boiler. The tall oil is processed by another company and the pitch oil is transported back to the mill. This way, the mill can utilize the full capacity of the boiler even if the black liquor load is not sufficient. In addition, methanol is used to burn the strong gases from the mill in the recovery boiler. Andritz supplied the methanol plant.
“Based upon the materials that are commercially available today, we at SCA are at the limits of extracting the most energy from the recovery boiler,” Mellesmo says.
View from the “helicopter”“Wood prices and recovered paper prices are moving rapidly upwards,” Strand says. “Energy costs are also rising, so we are facing a tight squeeze. The recovery boiler gives us a big positive effect since we can produce more green electrical power.”
Obbola still has to purchase power from the grid because its large paper machine requires more power than the mill can generate. “Still, we are buying much less power than we used to,” Strand says.
“For me, I was not so much involved in the technical detailed discussions,” he continues. “My interest as the MD is in making sure we have the performance levels and guarantees that we want. If I climb into a helicopter to take an overall view, the project was executed very smoothly. My overall impression is that it is a successful project. From the helicopter, it looks very good.”
SCA Packaging and the Obbola millSCA Packaging is Europe’s second largest producer of containerboard paper used for the manufacturing of corrugated board. The Obbola mill can trace its roots back to 1889 as a sawmill, but first began pulp production in 1913.
By the end of the 1960’s, the special pulp produced at Obbola (to produce insulation paper for the inside of electrical cables) was no longer needed. At this juncture, SCA had to come to a decision – either close the mill or convert it to some other production. A major investment was required to continue. SCA formed a joint venture with St. Regis for the production of kraftliner. This included the installation of a paper mill and the conversion of the pulp mill to support the production of kraftliner.
The kraft mill produces about 240,000 t/a and the recycled fiber line produces about 200,000 t/a. Obbola has one of the widest liner machines in the world (9.4 m) and is known for its high productivity in manufacturing low basis weight kraftliner.
The products from the mill are Kraftliner and Eurokraft. Kraftliner is mainly based on virgin fibers.
Eurokraft is based on recycled fibers, but with a virgin top layer. The mill is specialized in the lower grammage range. About 50% of the production is sold to SCA Packaging box plants.
