Effect of production conditions on self-heating propensity of torrefied sawmill residues

• Self-heating screening of bio-chars torrefied under different conditions.
• Bio-char properties affecting self-heating propensity based on a coal self-heating review.
• Higher self-heating propensity on bio-chars compared to un-treaded materials.

In this work, a screening of the self-heating propensity of bio-char produced from softwood bark and sawdust under different torrefaction conditions was performed. As there is an abundance of information regarding coal self-heating behavior, the bio-char evaluation was based on a review of coal self-heating and the tests used to evaluate the behavior. Bio-char physical and chemical properties, such as; proximate analysis, heating value, porosity, ash composition, and mineral composition, were determined and analyzed for impact on self-heating. Bio-char had a higher susceptibility for self-heating when compared to the feedstock as torrefaction increases carbon content and depletes volatile compounds resulting in an increase in available oxidation sites. The bio-char self-heating propensity increased with torrefaction temperatures under the range studied. This increase is likely not due to an increase in porosity as there is little difference in the porosity between chars studied from different feedstocks or temperatures and residence times. The self-heating propensity increases with fixed carbon content.