Valorization of eucalyptus branch residues using a mobile charcoal kiln: effect of holding time on the yield and quality of charcoal and wood vinegar

Eucalyptus branch residues are generated in large quantities, yet their decentralized conversion into useful products remains insufficiently studied. This study evaluated the production of charcoal and crude wood vinegar from eucalyptus branch residues using a mobile kiln integrated with a downdraft biomass gasifier–burner. The off-grid system was operated at 600 °C with holding times of 30, 60, and 90 min. Kiln temperatures remained at 610–620 °C, while burner temperatures averaged 1011–1022 °C. Increasing holding time reduced charcoal yield from 24.8 to 21.5 wt.% and energy recovery from 43.51 to 38.68%. Carbon recovery decreased relative to 30 min and remained similar at 60–90 min. Although 30 min gave the highest charcoal yield and recoveries, 60 min was recommended as the shortest tested condition that met the grilling-charcoal standard while retaining slightly more energy than at 90 min. At 60 min, the charcoal contained 3.5 wt.% moisture, 7.5 wt.% volatile matter, and 86.6 wt.% fixed carbon, with a heating value of 31.5 MJ kg -1 . The crude wood vinegar yield reached 41.6 wt.%, and its pH and specific gravity met the relevant Thai standards. The system supports on-site residue valorization; future work should assess long-term operation, emissions, and economic feasibility.