Strategies to improve durability of switchgrass briquettes

Densification of switchgrass into briquettes contributes to efficient handling, transportation, storage, and use in bioenergy applications. The effects of fine grinding of switchgrass, adding biomass-based binders (corn stover, corn distillers dried grains with solubles, and starch), and mixing commercial chemical feed binders (lignin-sulfonate, lime, and sodium bentonite) on durability of switchgrass briquettes (about 19.0 mm diameter) were investigated using a uniaxial, piston-cylinder densification apparatus. At a compression pressure of 150 MPa, preheating of switchgrass grind (geometric mean particle diameter of 0.56 mm) to 100°C without adding any binders improved the briquette durability to 67% compared to the briquette durability of 0% without preheating. In addition to preheating to 100°C, either mixing of 20% (wt.) of corn stover or 5% (wt.) of lime significantly improved the switchgrass briquette durability to 80%. Mixing of 20% (wt.) corn stover with 80% (wt.) switchgrass appears to be the best strategy to improve switchgrass briquette durability because addition of 20% (wt.) corn stover would involve almost no additional cost for densification compared to the addition of 5% (wt.) of lime. Preheating was essential to fully activate the natural binders in the switchgrass as well as the binding agents added to the switchgrass.