Pelleting characteristics of torrefied forest biomass
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Forest biomass (pine wood chips) was torrefied at different temperature (225 to 300oC) to generate energy dense and hydrophobic biomass suitable for producing pellets. It was found that torrefaction of forest biomass improved the energy density of biomass close to bituminous coal. Energy required for grinding of torrefied biomass was significantly reduced to 23 kWh/t compared to 238 kWh/t for raw pine chips. Feed and flow properties of torrefied wood powders also improved, as roundness (0.48 to 0.62), specific surface area (14 mm-1 to 64 mm-1), and flowability increased, while, cohesiveness decreased. Pelleting of torrefied biomass required significantly more applied pressure to achieve high pellet density compared to that of untreated biomass resulted in increased compressive energy consumption. Pellets made from torrefied biomass were found in dimensionally stability, high strength and durability, and absorbed less water compared to that of untreated biomass pellets.