Sawdust as an effective binder for making torrefied pellets

In this study, torrefied sawdust produced from pine sawdust in a fixed bed reactor was mixed with different binders in a ratio of 5-30 wt.%, and then compressed into pellets in a single die press to explore the feasibility of making torrefied pellets from torrefied powders. The quality of torrefied pellets was examined based on pellet density, higher heating value, hardness, saturated moisture uptake, and energy density. Results showed that torrefied sawdust particles prepared under typical torrefaction conditions (280-300 °C for 10-30 min) could be made into strong pellets by compression at a die temperature higher than 220 °C or by introducing biomass binders such as untreated sawdust, starch or lignin at a lower die temperature. The pellets density and bulk density made at a low die temperature with binders were slightly lower than those made at a die temperature of 220 °C or higher without the binder, and the energy density of torrefied pellets was similar to the control pellets made from untreated sawdust. Since the raw sawdust is abundantly available and much cheaper than lignin and starch, it is recommended as a low-cost and effective binder for densifying torrefied sawdust into torrefied pellets.