Ground softwood Douglas fir (Pseudotsuga menziesii) was treated with pressurized saturated steam at 200−220 °C (1.6−2.4 MPa) for 5−10 min in a sealed container. The contents of the container were released to the atmosphere for a sudden decompression. The steam-exploded wood particles were dried to 10% moisture content and pelletized in a single-piston−cylinder system. The pellets were characterized for their mechanical strength, chemical composition, and moisture sorption. The steam-treated wood required 12−81% more energy to compact into pellets than the untreated wood. Pellets made from steam-treated wood had a breaking strength 1.4−3.3 times the strength of pellets made from untreated wood. Steam-treated pellets had a reduced equilibrium moisture content of 2−4% and a reduced expansion after pelletization. There was a slight increase in the high heating value from 18.94 to 20.09 MJ/kg for the treated samples. Steam-treated pellets exhibited a higher lengthwise rigidity compared to untreated pellets.
The effect of steam explosion pretreatment on the physical and mechanical properties of the pellets made from empty fruit bunch (EFB) and palm kernel shell (PKS) was investigated and compared to that of softwood Douglas fir (DF). It was found that the high heating value of the empty fruit bunch was increased by 21% after steam explosion
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