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

Abstract

Dry torrefaction (DT) and wet torrefaction (WT) as pretreatment methods to prepare sawdust pellets show 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°C–280°C) and WT (180°C–240°C) on the physicochemical properties of sawdust and sawdust pellets were investigated. The results showed that both pretreatment methods reduced the mass yield (92.67–84.33% for DT, 93.42–90.39% for WT) and energy yield (94.78–90.78% for DT, 93.42–92.20% for WT) of sawdust while increasing the higher heating value (17.79–18.73 MJ/kg for DT, 17.44–17.79 MJ/kg for WT). Fourier-transform infrared spectroscopy 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, 10.22–10.91% for WT) and improved the stability of sawdust compared with untreated sawdust (13.70%). Sawdust pellets prepared by WT-180 and WT-200 exhibited enhanced hydrophobicity and pressure resistance. The WT-200 had the superior effect on the performance improvement of sawdust and sawdust pellets. This work offers insights into selecting appropriate pretreatment techniques to enhance the quality of biomass pellets and tackle logistics and transport challenges.