Torrefaction of Pinus radiata and Eucalyptus globulus: A combined experimental and modeling approach to process synthesis

The use of wood as feedstock for the production of energy and chemicals is a strategy used by both developing and developed countries because it increases the sustainability of their energy infrastructure. Torrefaction of forest resources for co-firing and densification of biomass energy is among the most prominent alternatives. This study is focused on technical aspects of torrefaction technology by analyzing both energy and exergy changes through a comprehensive physico-chemical model (Aspen One v8.6 software) of a plant operating in mild (250 °C) and severe (280 °C) regimes. The main wood species in Chilean plantations, Eucalyptus globulus and Pinus radiata, were processed in a lab-scale apparatus to obtain the data for model calibration. We found that xylan composition in hemicelluloses has a considerable effect on global thermal efficiency, volatiles energy content, energy density, and exergy yield of torrefied product. The highest efficiency (96%) is obtained for Eucalyptus at 250 °C when moisture in the feedstock is ≤ 20%. Combustion of volatile products (torgas) for drying does not result in substantial technical benefits for the overall process; however, their post-combustion does lead to lower exergy losses.