Flowability Parameters for Chopped Switchgrass, Wheat

A direct shear cell to measure the shear strength and flow properties of chopped switchgrass, wheat straw and corn stover was designed, fabricated, and tested. The shear strength measured at various normal stresses was found to be significantly different. Shear strength for all three chopped biomass types measured at a particular normal stress was not significantly different. The R value of the experimental yield loci was found to be more than 0.99 for all three chopped biomass, indicating that the chopped biomass followed the Mohr-Coulomb theory for critical state of friction. The experimental yield loci developed at a preconsolidation pressure of 4.92 kPa showed that the cohesive strength of chopped corn stover was the highest. The effect of changing the particle size had a profound effect on the angle of internal friction of chopped switchgrass compared to chopped wheat straw and chopped corn stover. The friction coefficients measured at different normal pressures were always more than 1 for chopped corn stover. But for chopped switchgrass and wheat straw, the friction coefficient was found to be less than 1 for a normal stress of above 2.55 kPa. These results indicate that changing the particle size of chopped biomass will have a profound effect on the flowability of chopped switchgrass compared to chopped wheat straw and corn stover. These results are useful for development of handling, storage and transportation equipments for biomass in biorefineries.