Integration of the torrefaction and briquetting of eucalyptus sawdust to produce a high-quality solid biofuel

This study investigates the integration of torrefaction and briquetting to produce a high-quality solid biofuel from eucalyptus sawdust, a lignocellulosic residue abundantly available in Brazil. Eucalyptus sawdust samples were torrefied at temperatures of 200, 225, 250, 275, and 300 °C for 30 min under nitrogen atmosphere, then mechanically densified into briquettes (18 MPa and 120 °C). The integration of these technologies resulted in torrefied eucalyptus sawdust briquettes with significantly enhanced energy density, compressive resistance, and hydrophobicity compared to raw material briquettes. Torrefaction increased the carbon content (from 46.3% to 55.6%) and HHV value (from 19.06 MJ kg⁻¹ to 24.32 MJ kg⁻¹), while reducing the O/C and H/C atomic ratios. Both mass and energy yields remained above 80% and 90%, respectively, up to 275 °C, while the highest enhancement factor (1.28) was achieved at 300 °C. However, torrefaction at 250 °C provided the best balance between fuel quality and mechanical performance of briquettes, with an energy density of 25.35 GJ.m− 3, compressive strength of 4.68 MPa, and the highest contact angle (116.2°), indicating superior hydrophobicity. These findings confirm that integrating torrefaction and briquetting under inert conditions is an effective pathway for converting eucalyptus sawdust into high-quality solid biofuels. Torrefaction and briquetting of eucalyptus sawdust to produce briquettes was studied. Torrefaction at 250 °C enhances eucalyptus sawdust for high-quality briquette production. Torrefied eucalyptus sawdust briquettes show significantly enhanced mechanical strength, energy density and hydrophobicity. Torrefied eucalyptus sawdust self-bonds into stable briquettes without binders.