Circularity, everyone is talking about it today, but Stora Enso has been closing the loop for paper for years. With sustainable materials and with sustainable processes. Without water treatment, for example, production comes to a standstill. In order to continue to guarantee reliable operation, a retrofit for the drives was then imminent. Stora Enso approached Danfoss, which put ATS forward as the main contractor, because there was only one day to switch from the old to a new future-proof concept for water treatment.
Finnish-Swedish Group Stora Enso is a leading supplier of sustainable solutions for packaging, biomaterials and wood structures. It does so based on the philosophy that everything made today with materials of fossil origin can come from trees tomorrow. At the Langerbrugge site, 540,000 tons of newsprint and magazine paper are produced annually, entirely from waste paper. Circularity at its best, an approach that it also extends into its own processes.
"At the site, we have two power plants and three wind turbines. This allows us to fully meet our needs for steam and largely for electricity," says Philip Mechelinck, Drives Technician at Stora Enso.
200 liters of wastewater per second
A second important element in that story is water. "Water serves as a carrier for the pulp and for the production of steam, so it plays an essential role here. We pump the water from the New Bald and, after thorough treatment, discharge it into the canal. To give an idea of the flow rate, 200 liters of wastewater per second pass through," said Stora Enso Project Engineer Wanne Verstraeten. In the flotation cells of both "de-inking" plants, the sludge from ink and paper fibers is washed out and removed as much as possible. The reject (ink etc.) coming from those flotation cells is thickened and incinerated at EC1. The other fraction is effluent and is treated by the wastewater treatment plant. "This one has two lines, one dating from the 1950s, the second from 1978. The drive of the motors was already frequency-controlled. But we kept running into the age of the system. Moreover, the system operates at 500 V. That made it even less obvious to get spare parts ."
One day time for transposition
What the new solution was supposed to look like? The same. "Process-wise, no changes were actually necessary. Everything was working as it should. However, we did want a system that increased the availability of the water treatment plant and was ready to make the transition to a fiber network in the future," says Stora Enso Supervisor-planner Gerd Vanrenterghem. The timing was clear: the five-year shutdown scheduled for June 2023. "There is an annual maintenance shutdown for the water treatment plant, but in order to make these changes, everything had to be without power." So it was a project that demanded careful preparation, as there would be as little as one day for the transfer of the drives.
Choice of VLT® AutomationDrive FC 302 variable speed drives
The original drives in water treatment were VACON CX® drives from Danfoss. At the heart of the new solution are VLT® AutomationDrive FC 302 variable speed drives. Koen Schiettekat explains why: "An IT network and a 500 V network can be quite challenging . But this type can handle both. In addition, it can communicate via Profinet S2, also one of Stora Enso's requests. A third reason why they are such a good match here is the combination of standard STO and the VLT® Safety Option MCB 152, which provides two configurable safe digital inputs. Everything is also equipped with circuit boards coated with 3C3." State-of-the-art, in other words, and today that also calls for a digital coating. "Condition monitoring, in other words. At Stora Enso, this works on two levels. On the one hand, the motor's stator windings are checked to detect any aging. On the other hand, we look at the load curve (envelope curve). In this way, the frequency regulator is used as a smart sensor to monitor the state of the motor and application, identify problems early and find solutions even before they have an effect on the process. If there are deviations, an alarm is generated so that the maintenance crew can start looking at what actions are needed to avoid downtime."
Redundant network
A total of 39 drives had to be replaced. All were the same type in terms of intelligence and control. However, three were equipped with sine output filters, because of the very long motor cables. But the work went further than that. The entire network around it was also rebuilt. Mechelinck: "Just to create that redundant structure. Problems on line 1 of the water treatment plant should have no impact on line 2 in the future and vice versa. There was also a switch from Profibus to Profinet S2." ATS was in charge of everything from design, to engineering and implementation on site. "To realize this compartmentalization between the two lines, some signs were replaced and new signs were added. Okken signs from Schneider, Stora Enso was already familiar with the technology, so a logical choice," said Danny Feliers, key account manager ATS.
Very thorough preparation
The process began in September 2022, but proved quite exciting due to long delivery times and the June 2023 deadline. Project leader ATS Kevin Mortier: "Right from the design stage, a number of component choices were made according to availability." At the beginning of May, ATS' team panel building was able to start work. The FAT followed two weeks later in Kruisem. In early June, the conversion of the first line began, two weeks before D-Day. There was a new room for the new cabinets, the cabling was pulled there, the data transfer from the variable speed drive to the DCS system was looked at ... In short, everything was prepared down to the last detail so that the pumps of the first line could be released again as soon as possible. "That was possible because of that new approach. And then quickly resume work on line 2."
Strength of ATS
Still, getting all those steps to follow one another without any delays anywhere remained a feat . "It was crucial to rely on a partner like ATS for this, who could keep the whole project on track," Verstraeten explains. In the end, each pump got its own cabinet. For a number of large drives (110 kW and above), a cabinet model from Rittal was chosen with a specific system for cooling. "Here, optional ventilation kits ("Cooling Duct kits") from Danfoss were used for installation in a standard Rittal cabinet. Thanks to the "Back Channel Cooling" of the FC 302 in combination with the airducts, which are mounted at the top and bottom of the inverter, an efficient cooling is achieved (the drive's own heatsink fan provides the forced airflow into this ventilation channel). 90% of the heat is immediately gone by drawing air through the pedestal. A very efficient heat dissipation that does not require additional cooling ," Feliers clarified. The schematics were worked out in Eplan, but then adapted and integrated within Stora Enso's own structure. "A mix of our standard and their game rules," summarizes Mortier.
Also energy efficiency up
Stora Enso was particularly satisfied afterwards. " A very decently finished installation, in terms of assembly, cabling and panel building. The implementation was done completely without incident and there was clear communication at all times. A pleasant first acquaintance with ATS," Mechelinck is clear. No significant problems have occurred since the conversion in June. "Because the operational picture is simply better together now," Vanrenterghem adds. The same goes for energy management, by the way.
"The new AC drives have a much higher efficiency. They also develop less heat, so the cooling also has to work less hard. The energy efficiency factor, by the way, was decisive in getting this project through. We look very hard at that with every investment," Verstraeten concludes.
Danfoss - ATS: partners in variable speed control
For ATS and Danfoss, this project was not the first tango they danced together. The many years of cooperation culminated in 2023 when ATS was recognized as a Danfoss Drives Authorized Partner. The pooling of both experiences will primarily benefit customers. They can count on both commercial and technical support in their immediate vicinity for all their drive technology needs. Also Stora Enso. This project received an extension in the form of a service level agreement (DrivePro® Response agreement). Together, ATS and Danfoss provide 24/7 support so that when problems arise, there is an immediate response and a support engineer on site within four hours.
