Thermo-physical characterization of torrefied fuel pellet from co-pelletization of canola hulls and meal

Abstract

Agricultural processing residues, as renewable sources of energy, can be converted to value-added products such as fuel pellets with the wide applications in the production of heat and power. In this research, densification/torrefaction of canola meal and canola hull was investigated. A bench-scale extruder was used for densification of canola hull and canola meal. Then, to increase the hydrophobicity and heating value of pellets, they were torrefied. For pelletization of canola meal, an increase in canola meal to water mass ratio resulted in an increase in the mechanical strength of pellets. Canola meal was also used to facilitate pelletization of canola hull. Co-pelletization of canola hull with canola meal was successful for canola hull mass percentage up to 60 wt% in the feedstock. In general, torrefied pellets showed lower moisture adsorption (up to 59%), higher carbon content (in the range of 21–25%), lower oxygen content (35–46%), and higher heating value (up to 22%) compared with their respective precursors. To study the effects of operating conditions and additives, different characterization techniques were used to evaluate the thermal, chemical, mechanical, and physical properties of pellets. Synchrotron-based computed tomography showed that after torrefaction, porosity increased by 10% for pellets from canola meal and increased by 22–30% for pellets prepared by co-pelletization. Addition of alkali lignin to canola meal precursor helped to increase the mechanical strength of torrefied pellet produced from canola meal. The use of binders such as alkali lignin and crude glycerol had no effect on the relaxed density of torrefied pellets and resulted in higher moisture adsorption.