Pyrolysis kinetics of wet-torrefied forest residues

Abstract

Forest residues left after forest harvesting are relatively low-cost feedstocks for bioenergy applications in Norway. However, they have low bulk density and contain relatively high moisture and ash contents, which make the energy utilization of these feedstocks challenging. Wet torrefaction, a hydrothermal pretreatment of biomass at temperatures within 180-260 °C, is a promising method to improve the fuel properties of forest residues prior to further applications. Nevertheless, the behaviors of intermediate products from wet-torrefied fuels in subsequent thermal conversion processes are not fully investigated. This work aims to examine the pyrolysis kinetics of raw and wet-torrefied forest residues as well as influence of wet torrefaction conditions on the kinetics. Freshly cut branches from Norway spruce and birch trees were selected as the feedstocks. The branches were first torrefied at 175, 200, or 225 °C for 30 min. The pyrolysis of the raw and wet-torrefied forest residues were studied in a thermogravimetric analysis (TGA) reactor under a continuous nitrogen flow. TGA data was used to evaluate the kinetic behaviors of the raw and wet-torrefied fuels, using a three independent parallel reaction model to extract kinetic parameters. © 2017, ETA-Florence Renewable Energies. All rights reserved.