Dry vs wet torrefaction of oxytree biomass
Researchers (dr. Andrii Kostyniuk and dr. Blaž Likozar) from the Department of Catalysis and Chemical Reaction Engineering (D13), together with partners from Lodz University of Technology (Poland), have published a new comparative study evaluating dry and wet torrefaction of oxytree biomass. The work demonstrates that wet torrefaction significantly improves fuel quality, energy yield, and carbon enrichment, positioning it as a highly promising pathway for bioenergy production from rapidly growing oxytree residues. The study was conducted under matched experimental conditions and published in Energy Conversion and Management.
The research focused on pruning residues of oxytree (Paulownia Clone in Vitro 112), a fast-growing energy crop increasingly cultivated across Europe. Using identical temperature ranges (200–260 °C) and residence times (30–60 min), the study compared two torrefaction methods: dry torrefaction (DT) and wet torrefaction (WT). The results showed that WT produced a substantially more carbon-rich and energy-dense solid fuel.
At the most severe conditions (260 °C, 60 min), WT achieved a higher heating value of 27.9 MJ/kg and a carbon content of 68.3%, outperforming DT, which reached 20.5 MJ/kg and 54.2% carbon under the same conditions. WT also preserved over 74% of the original energy yield while reducing oxygen content to levels comparable to low-rank coals, resulting in improved hydrophobicity, combustion stability, and storage behavior.
The study also included detailed thermal and chemical analyses of the aqueous phase produced during WT. GC–MS results revealed the formation of valuable platform chemicals such as acetic acid, furfural, and phenolic compounds, adding circular-economy potential to the process. Ignition experiments further demonstrated that WT chars ignite at lower temperatures and require lower activation energy than DT chars, improving their applicability for bioenergy and co-firing systems.
The findings provide clear, residue-specific operating guidelines for choosing between dry and wet torrefaction processes in decentralized bioenergy systems. Wet torrefaction emerges as the preferred method when maximizing fuel quality, carbon retention, and chemical valorization. Future research will focus on scale-up, reactor optimization, and environmental performance of oxytree-derived biochars in soil and anaerobic digestion applications.
More info: https://www.sciencedirect.com/science/article/pii/S0196890425014980?via%3Dihub
Contact: andrii.kostyniuk(at)ki.si