Upgrading of biomass by torrefaction and densification process

Biomass is an important source of renewable energy. Due to the lower contents of sulfur and nitrogen in the biomass, its energy utilization also emits less environmental pollution and health risk than fossil fuel. However, biomass utilization as a solid fuel still has many drawbacks from its undesirable properties. Torrefaction is a pre- treatment technique to increase the calorific value and the grindability. It is operated at temperatures below 300 °C in an inert atmosphere under atmospheric pressure. Densification is also another pre-treatment technique aimed to increase the density of biomass. In this study, the effects of torrefaction and densification process on the properties and combustion behaviors of biomass have been investigated. Eucalyptus was torrefied at 225, 250 and 275°C in a fixed bed reactor. Then, the torrefied eucalyptus was densified with a pellet mill. It was found that the yields of the torrefied biomass were decreased while the heating values of the torrefied biomass were increased with increasing the torrefaction temperatures. The heating value of eucalyptus, for example, increased up to 21.8 % when torrefy at 275°C. It was also found that the volumetric energy density of the torrefied pellet was increased as high as 399.3 % when comparing to that of the raw biomass.