Steam explosion of oil palm residues for the production of durable pellets

• Steam exploded empty fruit bunch and palm kernel shell pellets were characterized.
• High extractives content of PKS results in high pressure during steam explosion.
• Steam explosion increases the pellet density of PKS only, but not on EFB and fir.
• Steam explosion improves mechanical strength of steam exploded EFB and PKS pellet.
• The energy input to make steam exploded EFB pellet is higher than untreated one.

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 pretreatment. The pellet density of EFB and Douglas fir pellets did not change while the pellet density of PKS increased from 1.13 to 1.21 g/cm3 after steam explosion. That may be attributed to the rapid volatilization of high mass fraction extractives during high pressure steaming and lead to the shrinkage of micropores of the PKS fibers. The maximum breaking strength of steam exploded EFB and PKS were increased by 63% and 45%, respectively. The required compaction energy for the steam exploded EFB pellet is 44.50 J/g while that of the untreated EFB pellet is 30.15 J/g. Similar to Douglas fir, the required extrusion energy for the steam exploded EFB pellet was about 6 times than that of the untreated EFB pellet. The increased extrusion energy is mainly contributed by the increase in mono-saccharides by auto-hydrolysis during steam explosion pretreatment.

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