Dry vs wet torrefaction of oxytree biomass: A comparative study on fuel properties and energy yield

This study evaluates the performance of dry torrefaction and wet torrefaction processes applied to oxytree (Paulownia Clone in Vitro 112) biomass, focusing on their effects on fuel quality and energy efficiency. Experiments were conducted at 200–260 °C for 30 and 60 min. Dry torrefaction increased the higher heating value from 16.3 to 20.5 MJ/kg, with notable carbon enrichment but at the expense of mass and energy yields. Wet torrefaction achieved a higher heating value (up to 27.9 MJ/kg) and better preservation of energy yield (>90 %), alongside favorable reductions in atomic O/C and H/C. GC–MS analysis of the wet torrefaction liquids revealed acetic acid, furfural, and phenolic compounds, highlighting value-added potential. Differential scanning calorimetry analysis showed that both the ignition temperature and activation energy (E a ) decrease with increasing torrefaction temperatures. Wet torrefaction samples consistently ignited at lower temperatures (272–302 °C) and exhibited lower activation energy (39.5–45.3 kJ/mol) than dry torrefaction samples (287–299 °C; 43.6–52.9 kJ/mol), indicating superior combustion readiness. The findings suggest that wet torrefaction offers superior carbon retention and energy densification for oxytree biomass, positioning it as a promising method for bioenergy production and biorefinery applications. By integrating solid-fuel quality, ignition behaviour, and dissolved organic content in the aquatic phase, the study provides residue-specific operating windows that support the practical choice between dry and wet torrefaction for oxytree pruning residues.