| Torrefaction is a thermal pretreatment for biomass to improve its performance as a solid fuel. The main benefits of torrefaction include higher energy density and hydrophobicity, improved grindability and reactivity. As cellulose and lignin in biomass show high thermal stability, the effects of milling methods on the torrefaction process were studied. Ball- and hammer-milled (screen size 1 mm) pine sawdust samples were torrefied at three temperatures (230,260, and 290 ℃) and two durations (30 and 60 min) to investigate into their torrefaction behavior and physicochemical properties.The results showed that, under identical torrefaction conditions, torrefied ball-milled pine sawdust had a higher carbon content and fixed carbon, and lower hydrogen and oxygen contents than torrefied hammer-milled pine sawdust. Torrefied ball-milled pine sawdust produced lower mass and energy yields, but higher heating values than torrefied hammer-milled pine sawdust. The HHV of torrefied BMP (290℃,60 min) was 26.02 MJ/kg, while that of torrefied HMP was 23.94 MJ/kg under the same condition. Ball milling destroyed the structure of pine sawdust into irregular and agglomerate granules, destroyed the crystalline structure of cellulose, and reduced the thermal stability of hemicellulose, cellulose, and lignin, causing them to degrade at relatively lower temperatures. In conclusion, biomass pretreated with a combination of ball milling and torrefaction has the potential to produce an alternative fuel to coal. |
