Comparing severity of continuous torrefaction for five biomass with a wide range of bulk density and particle size. (October 2019)

• Record Type: Journal Article
• Authors: Campbell, William A.; Coller, Amy; Evitts, Richard W.
• Is Part Of: Renewable energy. Volume 141(2019)
• Page Start: 964
• Page End: 972
• Publication Date: 2019-10
• Subjects: Continuous torrefaction -- Particle size effect -- Bulk density -- Horizontal moving bed -- Mass yield; Renewable energy sources -- Periodicals; Power resources -- Periodicals; Énergies renouvelables -- Périodiques; Ressources énergétiques -- Périodiques; 333.794
• DOI: 10.1016/j.renene.2019.04.057
• Languages: English
• ISSNs: 0960-1481

Abstract

Abstract: This study presents five continuous torrefaction experiments using five lignocellulosic biomass feedstocks: coppiced willow, wheat straw, cattail ( typha ), moringa leaf, and spruce pellets. Experiments were conducted in a horizontal moving bed pilot plant operating at 250 °C and 6.8–10 min residence time to evaluate the flexibility of this torrefaction reactor. Differences in particle mass, bulk density, and physical form were examined as to how they affect the severity of torrefaction. Torrefaction mass yield for these experiments ranged from 73.7 wt% (moringa) to 91.2 wt% (spruce pellets), increasing with particle mass and bulk density. Individual particle mass had the most direct linear correlation to mass yield, while the bulk density correlated indirectly to mass yield through mass feed rate for 4/5 biomass; Ym = 0.35Q+0.7 (R 2 = 0.98). Wheat straw was the outlier in both correlations, having significantly higher mass yield than expected. The long, slender shape and resulting low sphericity are thought to limit heating and mass loss for this feedstock. These and other experiments along with the correlations presented illustrate the flexibility of the horizontal moving bed pilot plant; a wide range of biomass particle size, and form can be accommodated; however some shapes/forms of biomass may limit mass loss. Highlights: Willow, wheat straw, cattail, moringa & spruce pellets were torrefied in a horizontal moving bed. Average particle mass and mass flowrate were predictive of torrefaction mass yield for 4/5 types. Mass flow correlated to mass yield at 250 °C by Ym = 0.35Q+0.7, validated by additional datapoints. The long, cylindrical shape of wheat straw seemed to limit torrefaction. Horizontal moving bed should be concluded to be a feedstock-flexible design for torrefaction.