Publication: Continuous inclined-screw torrefaction with off-gas heat integration: pilot-scale residence-time impacts on severity and fuel quality
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Issued Date
2026-06-01
Resource Type
eISSN
26660164
Scopus ID
2-s2.0-105029116688
Journal Title
Case Studies in Chemical and Environmental Engineering
Volume
13
Rights Holder(s)
SCOPUS
Bibliographic Citation
Case Studies in Chemical and Environmental Engineering Vol.13 (2026)
Suggested Citation
Unsomsri N., Vimolsutr N., Manchit P., Wiriyasart S., Kaewluan S. Continuous inclined-screw torrefaction with off-gas heat integration: pilot-scale residence-time impacts on severity and fuel quality. Case Studies in Chemical and Environmental Engineering Vol.13 (2026). doi:10.1016/j.cscee.2026.101339 Retrieved from: https://hdl.handle.net/20.500.14740/55271
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Abstract
Continuous torrefaction can upgrade biomass pellets, but pilot-scale evidence on how residence time governs thermal zoning, off-gas heat integration, and fuel upgrading in screw reactors remains limited; therefore, this study evaluates a pilot-scale inclined-screw torrefaction system to quantify these effects. Experiments were conducted at two feed rates (17.5 and 20 kg h<sup>−1</sup>) by varying residence time through screw-speed control, covering 20-35 min in Condition 1 and 30-45 min in Condition 2. Temperature monitoring confirmed stable zones: 33-96 °C (drying) and 96-238 °C (torrefaction). Heat supply shifted from LPG (Liquefied Petroleum Gas) start-up to torrefaction off-gas combustion, demonstrating heat integration. At 40 min residence time, the off-gas contained CO<inf>2</inf> 48.8 vol%, CO 22.04 vol%, H<inf>2</inf> 12.7 vol%, and CH<inf>4</inf> 16.2 vol% (LHV 8.7 MJ kg<sup>−1</sup>), indicating potential to reduce LPG use through co-firing. Increasing residence time increased the mass-fraction-weighted LHV up to 24.03 MJ kg<sup>−1</sup> but decreased mass yield (80.2-55.1% and 81.29-46.48%) and energy yield (93.17-81.58% and 92.78-68.94%) because devolatilization and deoxygenation intensified solid mass loss faster than the incremental LHV gain. Longer residence times produced predominantly black material (higher severity), and increasing the feed rate required ∼10 min longer residence time to reach comparable severity.