Effect of temperature on sawdust and sawdust pellets during dry and wet torrefaction

Dry torrefaction (DT) and wet torrefaction (WT) as pretreatment methods to prepare sawdust pellets shows great potential for enhancing the quality of biomass pellets. However, few studies have focused on the comprehensive comparison and evaluation of DT and WT. Herein, the effects of DT (200-280 degree celsius) and WT (180-240 degree celsius) on the physicochemical properties of sawdust and sawdust pellets were comprehensively investigated. The results showed that both pretreatment methods reduced the mass yield (92.67%-84.33% for DT and 93.42%-90.39% for WT) and energy yield (94.78%-90.78% for DT and 93.42%-92.20% for WT) of sawdust while increasing the higher heating value (17.79-18.73 MJ/kg for DT and 17.44-17.79 MJ/kg for WT). FT-IR indicated that WT had a significant effect on the degradation of cellulose and hemicellulose compared with DT samples. Thermogravimetric analysis revealed that DT and WT efficiently reduced the residue (9.16%-13.63% for DT and 10.22%-10.91% for WT) and improved the stability of sawdust compared with untreated sawdust (13.70%). Furthermore, sawdust pellets prepared by WT-180 and WT-200 exhibited enhanced hydrophobicity and pressure resistance. Comprehensive evaluation showed that WT-200 had the superior effect on the performance improvement of sawdust and sawdust pellets. Through the comparative analysis between DT and WT alongside the introduction of preliminary evaluation system proposed, this work offers insights into selecting appropriate pretreatment techniques to enhance the quality of biomass pellets and tackle logistics and transport challenges.