Pelletization properties of raw and torrefied pine sawdust: Effect of co-pelletization, temperature, moisture content and glycerol addition

Biomass shows characteristics that makes it a promising feedstock for complementing traditional fossil fuels as main energy source. It is somewhat limited by its generally poor physical properties, but these can be enhanced by densification processes like torrefaction and pelletization. The aim of the present work is to evaluate the influence of different solid biomass additives (almond shell, cocoa shell, grape pomace, Miscanthus, olive pomace and olive stone), and parameters such as temperature, moisture content and glycerol addition upon pine sawdust, PIN, and its torrefied counterpart, PINT, pelletization performance, paying special attention to their abrasion index, higher heating value and energy density. It was observed that the addition of small quantities of lignin-rich solid additives, like grape pomace, enhances the natural binding properties of both PIN and PINT during pelletization using a bench-scale device. It was also found that a 13% overall moisture content and a glycerol addition of between 10 and 20% improve the pelletization properties of PIN and PINT, respectively, and increase their energy density when compared to the raw samples.