There is increasing talk of the importance of partnership in the value chain. Swedish market pulp producer Södra Cell has put words into action, making the biggest investment in its history to grow with its customers.
Amanda Marcus Carr
At the end of September, Södra inaugurates its Värö mill. This single-line softwood pulp mill has been virtually rebuilt (see box on the next page), enhancing quality and increasing capacity from 425,000 to 700,000 tpy of NBSK pulp. A large factor driving this expansion to create one of the most modern mills of its kind is Södra’s desire to grow with its customers, provide bespoke solutions and premium, consistent quality, especially for tissue. One of the key assets of the rebuilt mill is its woodyard. Peter Carlsson, technical product manager at Södra, explains the importance of wood sorting and fiber control: “Properties which impact papermaking depend on the fiber going into the refiner. Softwood is not homogenous – variations in fiber length and thickness happen not just within the same species but within the same tree. Younger trees have thinner walls and shorter fiber than older trees and an older tree will have a mix of fiber, growing thinner towards the center or pith where the wood from the tree’s young age resides.” Because Södra is owned by a cooperative of some 50,000 forest owners in Southern Sweden, it has tight control and complete chain of custody over its fiber supply, and the knowledge that all its wood is sourced from sustainable forests managed to the highest environmental standards. The company needs to make the most of these assets since they are from its members – its fiber basket is dictated by what grows in southern Sweden.”
SÖDRA CELL RECEIVES THREE MAIN TYPES OF WOOD FROM ITS MEMBERS: Older trees; thinnings, or young trees with thin-walled fiber which have a tendency to collapse more easily during refining, with good binding properties and yielding decent tensile strength without too much refining; and sawmills wood chips, usually the outer part of the tree with long fiber and thick walls. Södra’s Green pulp series has the highest proportion of sawmill chips, thus lower tensile strength but good bulk and stiffness - a good choice for folded napkins. Blue pulps have an average fiber length of 2.3 mm. They are a mix of fiber yielding intermediate properties for high-quality and standard tissue grades such as toilet roll, towel and facial. At the top end of the portfolio is the Black series of pulps with a high proportion of thinnings and a short average fiber length of around 2.1 mm. Black offers the closest to Canadian softwood characteristics. Carlsson: “Many of the fiber end properties are determined by the latitude where the wood is grown, which is out of our control. To get this close to Canadian softwood is a result of good fibre control and a lot of work.”
IT’S ALL IN THE MIX. Södra is working increasingly in partnership with its customers at the specific pulp parameters which affect the final paper product. This includes benchmarking using a Voith LR-40 lab refiner. In addition to specific projects, the refiner is used every few years to compile a database of 15 Södra pulps compared with around 35 competitors’ softwood pulps. The last survey was conducted in 2013 when, as an average grade, Södra compared a theoretically calculated pulp from a typical mix; 26% sawmill chips, 37% thinnings and 37% final cuttings. The ‘Södra Mix’ was then benchmarked against the company’s Black, Green and Blue pulps, as well as those of its competitors, including seven Canadian softwoods, three from continental Europe, 11 from Scandinavia and two from Chile.
THE TESTS looked at properties such as fiber length, where Södra Mix was average. After segregating the wood and introducing a more thinnings to the Södra Black recipe, however, fiber length fell very close to several Northern European softwoods. Green, in contrast, produced one of the longest fiber lengths, as expected, since it contains a higher proportion of sawmill chips. The Blue range was around average. Coarseness, which is closely linked to fiber wall thickness, is also an important parameter for tissue. Here Black pulps performed in the lower range close to Canadian grades while Green pulps were on the high side and Blue in between. “So what? you may ask,” comments Carlsson. “In general, customers don’t care about fiber dimensions. But they do care about sheet tests after refining, which is why we then tested tensile index at 75 kWh/t.” The results here showed considerable variation between countries and while Canadian softwood proved hard to beat, Black pulps were a close match and even exceeded one Canadian grade. The same trends were evidenced in other parameters such as reinforcement potential. This shows the importance of wood segregation and fiber control: Particular pulps within the product portfolio really shone, indicating the importance of fiber mix for paper properties. Tensile of 69 and reinforcement potential of 18 in the average mix were changed to a tensile of 78 for Black pulps for example, while Green’s reinforcement potential was 22.
A NEW PLUS. In addition to Södra’s fibre work, the company also does projects with customers and this is increasing. Södra launched Pulp+ this year, a new service concept which will be driven by the customer rather than from within Södra. In the past, says Marcus Hellberg, Marketing Director, Södra has promoted innovative product ideas to customers, or offered a range of off-the-shelf service options. But now the emphasis will be switched – customers are invited to tell Södra what they want to solve or develop and the companies will work together on bespoke solutions, whether to launch a new product, tweak an existing one or enhance a particular area of the business such as logistics. “Whatever the challenge, we will use our expertise in fiber to add real value for our customers through cooperation. So if they haven’t thought of involving us before in their plans for the future, now is the time to ask.” *