Short Torrefaction Process: A New Alternative Way for Biomass Pellet Upgrading

Ordinary torrefaction process has objectives on the increase of higher heating value and energy density. Because of these expectations, the torrefaction of biomass pellet is facing many limitations. The other interest way to upgrade biomass pellet is short torrefaction which focuses on improvement of hydrophobic property and maintain energy density at the similar level to untreated biomass pellet. This work studied variations of equilibrium moisture content (EMC), durability index, and energy density of cassava rhizome pellet when it was torrefied at short residence times of 0-15 min. The normal residence times of 30 and 60 min were also conducted to identify the suitable residence time for short torrefaction process. The mathematical model was also developed to predict properties of cassava rhizome pellet after torrefaction. It was found that EMC and durability index drastically decreased for short residence times (0-15 min). There was insignificant difference in EMC and durability index for residence times of 30 and 60 minutes. Slight difference in energy density was found for residence time and torrefied temperature range of 0-60 min and 230-270 degrees C, respectively. Therefore, the suitable residence time was dependent on EMC and durability index. The suitable residence time for short torrefaction at torrefied temperature of 230, 250, and 270 degrees C was 30, 15, and 10 min, respectively. Short torrefaction contributed to improvement of hydrophobic property. However, it was impossible to increase energy density by short torrefaction. In addition, the prediction results obtained from developed model displayed relationship between pellet properties and thermal degradation rate. The average absolute error (AAE) for prediction of EMC and durability index was 11.60 and 0.25%, respectively.