Influencing parameters on mechanical–physical properties of pellet fuel made from corn harvest residues
Herbaceous biomass can be used as an alternative for wood to produce fuel pellets, but obtaining the appropriate properties for these pellets is a challenge. Worldwide, corn harvest residues have significant potential as a herbaceous biomass. The objective was to investigate influences on the mechanical properties of corn stover and corn cob pellets. The parameters varied included particle size and the moisture content of raw material, the shares of wood and additives, and pressing intensity. Corn cob pellets had better properties with bulk densities of 547.7–719.5 kg/m3, a mechanical durability of 88.0–98.8%, and pellet yields of 98.2–100.0%. When corn stover was used, these properties were 510.1–644.3 kg/m3, 77.9–99.2%, and 41.1–100.0%. Pressing intensity and blending with wood had a very strong significance (p < 0.001) in terms of improving the properties of corn stover pellets. These pellets reached quality thresholds when the extrusion ratio was raised to 5, when blended with 40% of wood, or when an admixture with 1% of pressing aid was used. To keep the pellets’ moisture content under a limit of 15%, corn stover should be conditioned to a moisture content no higher than 17%. When corn cobs were used, particle size and pressing intensity showed a very strong significance (p < 0.001). Thresholds for corn cob pellets were achieved by either raising the extrusion ratio to 4 or reducing the particle size using sieve mesh size larger than the pellet press die openings.