There are many potential markets for lignin. Refined lignin can be used for replacement of phenols that are used in resins for adhesives in, for example, plywood and veneer applications. Stora Enso’s Sunila Mill in Finland is the world’s first integrated lignin extraction plant to produce dry kraft lignin and fire it directly in the mill’s lime kiln and replace fossil-based fuel.
Additionally, Sunila’s lignin can be packed for sales to external customers. The pulp-based biorefinery allows for replacing fossil products with renewable products, made in industrial processes that use biomass as an energy source.
By utilising a greater part of wood, lignin contributes to resource efficiency. So far Sunila Mill is replacing 70% of the natural gas in the lime kilns with lignin, meaning that we reduce our fossil CO2 emission by 27 000 tonnes per year. The target is to increase this, which will most likely be possible after some modifications have been made at the mill.
“The technology was totally new to us and we had to solve several process-related challenges during the project,” says Olli-Pekka Reunanen, Mill Director at Sunila. “Despite that, our operations have reached a smooth production level. Safety has been a high priority”, Reunanen says.
Since the main part of the Sunila equipment is placed indoors, a proper design for the gas collection system was crucial to ensure safety. The atmosphere in the dryer area is kept inert and non-explosive by utilising flue gases from the lime kiln with low oxygen content together with nitrogen as purge gas. The safety systems developed in the project have proven to be effective and there have been no safety-related incidents. The plant is now operating at a high production level.
The lignin is made of sustainably sourced wood. Stora Enso’s Sunila Mill has both FSC and PEFC chain-of-custody certification.