Upgrading of physical and elemental quality of wheat straw pellets using additive blends

Abstract

Abstract Densification of biomass is typically done by pelletising to produce clean fuel from renewable resources. This study investigated the impact of additive blends for wheat straw pellet making and upgrading the physiochemical properties. Five additives, including sawdust (SD), bentonite clay (BC), corn starch (S), crude glycerol (CG), and biochar (BioC) were chosen for this study. Pellets were made from seven different combinations using a laboratory-scale pellet mill. The pellets' physical and elemental quality was evaluated and compared with ISO 17225-8 standards. The pellet’s mechanical durability, tensile strength and bulk density increased from 80 to 99%, 0.36 to 2.09 MPa, and 244 to 665.21 kg/m3, respectively, which met the requirements of the ISO standards. The additive blend pellets (T3 ~ T7) had a fines content of less than 2%, also meeting the ISO standard. Further, all pellets showed a water absorption capacity under 2%, except T1 and T5. Finally, the fixed carbon contents increased from 11.1–30.90% and energy contents from 17.02 to 20.36 MJ/kg, which showed a significant synergistic effect of blending additives. Overall, pellets with additives mixed met the pellet ISO standard specification requirements, except for inorganic ash content. The study demonstrated that wheat straw is a good biomass source for pellet-making for energy applications, but further research on suitable additive mixing is still needed.