Steam torrefaction of Eucalyptus globulus for producing black pellets: A pilot-scale experience

- Pilot-scale steam torrefaction of Eucalyptus globulus was performed for first time.
- Torrefaction severity linearly correlates to combustion behavior and process yields.
- Pellets from steam torrefied Eucalyptus globulus are energy dense and durable.
- PCA demonstrated correlation among structural changes and torrefaction temperatures.
- Combustion behavior of Eucalyptus globulus was evaluated by Coats-Redfern's model.

Steam torrefaction of Eucalyptus globulus was performed at temperatures between 245 °C and 265 °C in a 100 kg/h pilot plant. Torrefied biomass was then pelletized in a 300 kg/h unit and the pellets were subject to durability, density and combustion tests. The structural changes measured with FTIR were studied along with the combustion behavior of the materials. Compositional analysis showed that increasing the torrefaction temperature reduced both hemicellulose fraction and overall mass yield (MY). Furthermore, there was a linear relationship between the energy yield (EY) and mass yield (EY = [1.04−0.9(1−MY)]) for these samples. The ignition and comprehensive indexes confirmed that the stability of the torrefied biomass in a combustion environment was higher than for untreated biomass. Finally, pellets showed high durability (98%), and had an energy density (13-14 GJ/m3), which is comparable to low-rank coals.