Physicochemical Properties and Thermal Decomposition of Torrefied Woody Biomass and Energy Crop

Abstract

Torrefaction was performed on pine, sweetgum, and switchgrass to determine its effect on the properties and degradation profiles of the biomass, and the influence of feedstock moisture content on the enthalpy of torrefaction was also studied. Torrefaction did improve fuel characteristics of the biomass made it similar to that of coal. The biomass was made less hygroscopic by decreasing the amount of moisture absorbed by up to 50%. The volatile matter concentration of the biomass decreased, while the fixed carbon content increased to levels similar to lignite coal. The elemental composition also improved with lower oxygen levels and higher carbon content, which were increased by nearly 50%. The energy content of the biomass also increased with torrefaction pretreatment. Energy content was found to increase by up to 25%, depending on the intensity of the treatment. Untreated and treated biomass, and treated biomass and coals blends were analyzed using thermogravimetric analysis. Torrefaction had an effect on the degradation profiles of the biomass. Biomass was found to be slightly less reactive at lower temperatures due to the loss of hemicellulose in during torrefaction. Activation energies were found using the isoconversional method. The activation energies were different for untreated and treated biomass samples, but the trends were inconsistent. Torrefaction did not have an effect on the isoconversional reaction kinetics of the biomass. For the biomass and coal blends, activation energies were found to increase with the concentration of biomass in the mixture. Differential scanning calorimetry showed moisture content had a linear effect on the enthalpy of torrefaction.