Pelletization of torrefied canola residue: Effects of microwave power, residence time and bio-additives on fuel pellet quality

Abstract

This study involves a sequential torrefaction and pelletization process to produce high-quality fuel pellets from canola residue. Firstly, canola residue was torrefied via microwave irradiation at 250–450 W for 10–20 min with 70–110 g feed load and further pelletized under 3500 N load for a relaxation time of 15 s. The Box-Behnken design was employed to understand the interactions between torrefaction operating conditions for optimal relaxed density, durability, and hardness of the pellets. The optimal torrefaction as determined at 250 W for 10 min with 90 g feed load having the highest relaxed density (1090 kg/m3), durability (83%) and mechanical strength (0.55 MPa) of fuel pellets. The results show that torrefaction significantly improved the energy content as well as hydrophobicity due to the degradation of the lignocellulosic structure. The goal of this study was to investigate the effects of bio-additives (i.e., lignin, sawdust, mustard meal and pyrolysis-derived bio-oil) to further improve the relaxed density, durability, tensile strength, energy density and hydrophobicity of fuel pellets. The combination of the mustard meal, lignin with bio-oil improved the density, durability, tensile strength by 21%, 20% and 123%, respectively. The energy densities of raw, torrefied pellets and torrefied pellets with additives were found to be 15.6, 19.4 and 21.2 GJ/m3, respectively.