Effect of Plum Seeds and Rosin Adding to Sawdust on the Pelletisation Process and Fuel Pellet Quality

This study investigates the influence of crushed plum stones and rosin (colophony) as additives in the pelletisation of pine sawdust, with a focus on energy consumption, pellet quality, and combustion performance. The addition of crushed plum stones combined with 10% rosin reduced the energy demand of the process. Incorporating 10–20% plum stones with 10% rosin decreased the pelletiser power demand by 18% and 25%, respectively, compared to pure sawdust. Plum stone addition significantly improved the energetic parameters of pellets. At a 20% share, the calorific value increased to 18.02 MJ·kg−1 and the heat of combustion to 20.04 MJ·kg−1, while 10% rosin further enhanced these values by 1.67 MJ·kg−1 (8.4%). Although bulk and particle density slightly decreased, a 10% plum stone share raised the kinetic strength to 97.24%, indicating improved mechanical durability. Combustion tests confirmed favourable properties of the modified pellets, including lower air excess coefficients (λ) and reduced emissions of CO, NO, and SO2. However, a 10% rosin content slightly exceeded CO emission limits set by the Ecodesign Directive, suggesting that its share should be reduced to ~5%. The results confirm that crushed plum stones and rosin are effective modifiers in sawdust pelletisation, enhancing both process efficiency and fuel quality. This approach supports circular economy principles by converting plant-based residues into high-quality biofuels.