Torrefaction of Forest Residues Using a Lab-Scale Reactor

Abstract

Forest residues have been gaining interest as a source of renewable fuels due to their availability and the risks they represent for increasing forest fires. A major drawback for their removal and processing is the cost of transportation, which can be overcome through densification procedures, e.g., torrefaction. To optimize the torrefaction parameters, Cistus ladanifer residues from the Portuguese forest were torrefied for 30 min in a lab-scale reactor at 250 and 350 °C. The quality of the torrefied material was assessed, and its energy and mass yields were determined through thermal analysis. The changes in morphological structure occurring during torrefaction were analysed through scanning electron microscopy. When compared to the original biomass, the charcoal obtained at 350 °C had a substantial increase in energy density accompanied by a significant mass reduction. Increasing the mass in the reactor had a positive effect on the energy yield. For the highest mass tested, a mass reduction of around 30% was obtained and a char with no loss in energy content (with a cumulative heat flow (CHF) of 9.0 MJ/kg compared to 5.8 MJ/kg of the original biomass). Modelling of the reactor allowed the analysis of the heat profile required for torrefaction.