Hydrothermal pretreatments to make durable pellets from herbaceous biomass

Crop residues (straw) as the alternative feedstocks for the pellet industry could reduce the dependence on woody biomass, the price of which is increasing. Yet, the lack of natural binders (such as lignin) and high ash content are impediments to produce durable pellets from herbaceous biomass feedstocks. This research aimed at improving the durability of agri-pellets using mild hydrothermal treatment of biomass prior to pelletization. Different ways of steam generation were explored at a mild-to-high temperature range (80-220 °C) to determine the effects on pellet quality improvement. The relationships between treatment severity factor and the main properties of the pellets were then developed. Results indicated that the pellet durability first increased but subsequently decreased as the severity factor increased. Energy consumption showed positive correlation while equilibrium moisture content showed negative correlation with the severity factor. The optimal treatment temperature was found to be 140 ℃ for biomass with 50% moisture content (wb), and 180 ℃ was able to produce high quality pellets with lower ash content. Pellet durability, energy consumption during pelletization, and water sorption were all affected by an increase in lignin content due to the decomposition of hemicellulose together with the change of particle size distribution. Overall, this study has explored a relatively wide range of hydrothermal treatment conditions, which includes low to high biomass moisture content, treatment temperature, and treatment time. It not only considers the potential for commercial-scale agri-pellet production, but also detects the potential of lower treatment severity for the biomass, utilizing less water and energy for pelletization. Moreover, from the biomass quality perspective, this study also detects the best conditions for producing the pellets with greater durability, higher calorific value, and lower ash content.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat