Compression and Relaxation Characteristics of Selected Biomass `Grinds

Abstract

Ongoing densification studies are essential for the logistic and economic improvement of biomass use for chemical and energy production. A heated cylindrical plunger-die apparatus was used to study the effect of process temperature, feedstock particle size, and feedstock moisture content on the quality of flax shive, oat hull, and wheat straw pellets. The three feedstocks were ground in a hammer-mill utilizing screen sizes of 0.8, 1.6, and 3.2 mm. Feedstock moisture contents were adjusted to 9, 12, and 15% wet basis. The grinds were compressed to a pressure of 139 MPa at die (process) temperatures of 60, 80, and 100C. Density, dimensional expansion, and asymptotic modulus values were used as pellet quality determinants. Pellet density was increased by an increase in die temperature, and a decrease in screen size and moisture content. Dimensional expansion (diametral and longitudinal) was reduced by an increase in the die temperature and a decrease in moisture content. Screen size had marginal effects on the dimensional expansion of the pellets. Decreasing the screen size served to significantly increase the asymptotic modulus values of the three grinds. Die temperature had no effect on the asymptotic modulus, and decreasing the moisture content only increased the asymptotic modulus for the wheat straw grinds.