The Effect of Cherry Stone Addition to Sawdust on the Pelletization Process and Fuel Pellet Quality

This study presents the results of research on the pelleting process of pine sawdust with the addition of cherry stone waste, which was carried out using a flat-die pellet press in the context of fuel pellet production. The findings indicate that increasing the proportion of crushed cherry stones in the sawdust mixture from 10% to 20% reduced the pelletizer’s power demand by approximately 14% (from 3.35 to 2.86 kW) and by around 24% (from 3.79 to 2.86 kW), compared with the compaction of sawdust alone. The incorporation of 10% crushed cherry stone waste into pine sawdust slightly improved the kinetic strength of the pellets, increasing it by about 2% (from 94.6 to 96.60%). However, raising the cherry stone content further to 20% resulted in a moderate decrease in kinetic strength, by approximately 5% (from 96.60 to 91.37%). A similar trend was observed for pellet density: the addition of cherry stones (10–20%) slightly reduced the density by about 5.5% (from 1312.02 to 1241.65 kg·m−3), accompanied by a small decrease in bulk density. This study also confirmed the high calorific potential of crushed cherry stones, with a heat of combustion of 24.418 MJ·kg−1 (dry basis) and a net calorific value of 22.326 MJ·kg−1. Their incorporation at levels of 10–20% into sawdust mixtures increased the heat of combustion of the pellets by 0.42–0.84% (from 19.959 MJ·kg−1 for sawdust alone at 15% moisture content to 20.042 MJ·kg−1 with a 10% addition and 20.126 MJ·kg−1 with a 20% addition). Moreover, the inclusion of cherry stone waste in the mixture had a beneficial effect on combustion performance, lowering emissions of harmful compounds such as CO, NO, and SO2, due to the higher combustion temperature achieved. Consequently, the use of cherry stone waste as an additive to sawdust not only enhances the energetic and environmental performance of pellets but also provides an effective pathway for the management of large quantities of fruit industry residues.