Sunila makes the most out of lignin

Stora Enso’s Sunila softwood pulp mill is one of the company’s mid-range production units in Finland. Its annual production capacity of 370,000 tonnes is not among the industry giants, but it has an agile and flexible technological setup that meets the market demand. Over its 80-year history, the mill has always had a special role in taking new technologies into use.

“Everything that is made out of fossil-based materials today can be made out of wood tomorrow. It’s Stora Enso’s strategy and aim for the future,” says Jarmo Rinne, Development Director at the Sunila Mill. “We are moving away from being a bulk kraft pulp producer into more specific product segments. All of our Nordic pulp mills have their own roles and product segments that they focus on. Sunila’s specialties include strong Nordic kraft pulp and kraft lignin, together with turpentine and tall oil”.

The Sunila Mill’s lignin production is based on Valmet’s LignoBoost™ technology. The lignin is extracted and washed, then dried to a fine powder. Stora Enso constructed an automated big bag filling system to facilitate transport for further use of the lignin in high-value products.

Project with a strong R&D nature

Stora Enso had been involved in lignin research work for years, and the planning of this lignin extraction investment started in 2011. In 2013, Stora Enso and Valmet agreed on a LignoBoost plant delivery to Sunila, and production began in January 2015. Today, Sunila’s annual kraft lignin production capacity is 50,000 tonnes, making it the largest in the world.

Jarmo Rinne says that Valmet was really the only true provider for the technological solution they were looking for. The key elements in Stora Enso’s decision-making process were Valmet’s R&D knowledge and the LignoBoost plant it delivered to the Domtar Plymouth mill in USA.

“I was impressed by the professionalism of Valmet’s project team. Even though Valmet had already built a similar industrial plant in the past, both parties knew from the beginning that this project would have a strong R&D nature,” says Jarmo Rinne.

Lignin for valuable end products

Stora Enso is the first company to produce kraft lignin with an extremely high dry content – up to 97 percent. The lignin produced at the Sunila Mill is both sold to other users as a raw material and used as a biofuel in the lime kiln, which has significantly decreased the mill’s CO2 emissions. 

Stora Enso’s LineoTM lignin product was launched in early 2018 and was named “Bio-Based Product of the Year” at the Bio-Based World News Innovation Awards in March 2018. Lineo™ by Stora Enso is the first wood-based product that can replace oil-based phenolic adhesives, which are used for example in plywood, oriented strand board, laminated veneer lumber, paper lamination and insulation materials.

Stora Enso produces kraft lignin at its Sunila Mill.

 “We have achieved the the targeted product quality”

“Throughout the entire Sunila Mill LignoBoost project, Valmet and Stora Enso have been working very closely together, in a solution oriented way on optimizing the process design and on identifying potential problem areas. Working with Stora Enso has challenged and helped us to develop our technology even further, and we are continuing to work closely together in various development activities,” says Hanna Karlsson, head of Valmet’s LignoBoost team.

“All in all, the project has gone really well, and it was a pleasure working with Valmet. The quality of the product has reached the specifications that we were promised. Naturally, we are continuing to develop the parameters based on end-product needs. Our staff are also gaining more experience in running the plant as we go forward. But we have already achieved the target in product quality we were aiming for,” Rinne concludes.

Lignin is future

Lignin is a renewable, wood-based, non-toxic alternative to fossil-based materials. Lignin is a complex macromolecule, and it is the most abundant natural aromatic polymer. In nature, lignin acts as the glue that binds cellulose and hemicellulose together. Lignin can be separated during the kraft pulping process and then utilized in various applications as an alternative to fossil-based raw materials. For example, refined lignin can be used as a replacement for phenols, which are used in resins for adhesives in, for example, plywood and veneer applications.

Working together towards the common goal

“In this project, we utilized the learnings from our first LignoBoost delivery to Domtar, but we had also areas that were done for the first time ever. It was a pleasure to work with Stora Enso’s team, as they were very professional and experienced, and showed true commitment towards the common goal. All in all, the project went well and the start-up was successful, but the R&D nature of the project is visible in the fact that the process still needs some finetuning,” explains Jari-Pekka Johansson, who was Valmet’s Project Manager in this project.

"Naturally, there were challenges along the way. For example, installing the equipment inside an existing, Alvar Aalto designed, building was not easy, but with 3D laser scanning and careful layout planning, we were able to achieve a good end result," Johansson concludes.

TEXT Antti Ratia PHOTOS Antti Ratia, Stora Enso and Valmet