Loose-filled and Tapped Densities of Chopped Switchgrass, Corn Stover and Wheat Straw

Bulk density is one of the important engineering property of biomass having significant impact on the supply logistics and processing in ethanol production facilities using lignocellulosic materials. Bulk density of most of the comminuted biomass significantly increased by tapping. Switchgrass, wheat straw and corn stover were chopped in a knife mill at different operating conditions including four different screens having 50, 25, 19, 12 mm diameter. Mean loose-filled bulk densities were 67.5 ± 18.4 kg/m for switchgrass, 36.1 ± 8.6 kg/m for wheat straw, and 52.1± 10.8 kg/m for corn stover. Mean tapped bulk densities were 81.8 ± 26.2 kg/m for switchgrass, 42.8 ± 11.7 kg/m for wheat straw, and 58.9 ± 13.4 kg/m for corn stover. The maximum volume reduction ratio observed for switchgrass, wheat straw and corn stover was 0.159, 0.165, and 0.154, respectively for fine-chopped samples and 0.107, 0.117, and 0.098, respectively for coarse-chopped samples. By tapping, the infinite compressibility was highest for chopped switchgrass followed by chopped wheat straw and corn stover as indicated by the ‘a’ values in Sone’s model. Degree of difficulty in packing was minimum for chopped wheat straw followed by chopped switchgrass and corn stover. This indicated that the chopped wheat straw particle compacts very rapidly by tapping compared to chopped switchgrass and corn stover. Hausner ratio, a measure of internal friction, determined after 50 taps ranged from 1.114 to 1.321 for chopped switchgrass, 1.105 to 1.309 for chopped wheat straw and 1.060 to 1.239 for chopped corn stover.