Torrefaction of eucalyptus-tree residues: A new method for energy and mass balances of the process with the best torrefaction conditions

Torrefaction of eucalyptus-tree residues was performed in a lab-scale batch reactor, to evaluate the influence of temperature and time on the process. A new response variable, called Energy Gain (EG), was proposed and it was demonstrated that it is better than the response variable Energy Yield (EY) that has been traditionally used to measure the torrefaction efficiency, because it makes a compromise between high HHV and low mass loss. The experiment with the best Energy Gain was subjected to a further analysis and its solid and gaseous effluents were characterized. Differential Scanning Calorimetry (DSC) was used as a new method to estimate the heat involved in the torrefaction process, in a more accurate fashion than other reported estimation methods. The process led to a solid fuel with an energy densification of 29% compared to the raw biomass, and with characteristics close to lignite coal. An integrated process, where the combustion of exhaust gases from the torrefaction is used to generate the necessary heat for drying and torrefaction, allowed providing 72% of the energy needs.