This work is done within the research group NewDeP (New Development for Pellet Technology), located at Karlstad University, Sweden. The NewDeP focus area is additive use, energy analyzes and bonding mechanisms. The research group manages test bed lab equipment including a single pellet press unit and a full pilot scale production unit, with the possibility to measure and analyze the pellet process from wet raw material to stored pellets.

There is a need to increase the utilization of biomass and thus be part of the transformation towards a circular bio-economy, and also to do it with high energy-efficiency. When industries process biomasses, it is often done through multiple operations where drying is the most energy demanding step, since large quantities of thermal energy are used. The Drinor Continuous Dewatering Press (CDP) is a new Swedish compression press technology for dewatering of biomass. The CDP reduces the water content by 50% and reduces energy costs by 95%. Energy-efficient dewatering of biomasses increases the possibilities to use more by-products from the forest, and it could also be used in the creation of completely new process chains while refining raw materials. Including the CDP press in the pellet production chain creates new prerequisites for making pellets.

In the literature are presented that the fibrous cell walls collapse under high pressure, resulting in the elimination of hemicellulose and lignin as well as affects further drying and internal diffusion of water. The fact that hemicellulosan's flexible polysaccharides strongly link to pelletability have been demonstrated in a recent study at Karlstad University and that lignin has positive bonding properties while high proportion of extractants is negative for pelletability. This is well described in the literature.

This initial study had the aim to investigate how the CDP affects the drying and pelleting processes. The sawdust used was dewatered by the CDP from 55% down to 40 % (wb). The thermal drying tests was carried out in a pneumatic dryer with an inlet air temperature of 150°C from 40 % down to 10 % (wb). The pelltizing tests where done in both single pellet press unit and continous pilot scale production.

Early results show that the change in material structures on the basis of the CDP have a positive effect on the drying efficiency (SMER) compared to non-pressed sawdust. Further, the CDP as a complement to thermal drying and its affection on the structure of sawdust and its porosity is favorable to the pellet density and hardness as well as the decrease in friction work during production (in a single pellet unit). The CDP could also reduce the energy needed for grinding since the results show that the lowest friction force in the press and highest pellet density and hardness was created from non-grinded material. The lower friction work could mean that the production rate could be increased producing good quality pellets. The results indicate that the pellet production chain can be redesigned using CDP but further research is needed.