Effect of compressive load and particle size on compression characteristics of selected varieties of wheat straw grinds

• Applied pressure and particle size of biomass affect the pellet density.
• Higher compressive load result in higher stability during storage.
• Pellet durability is a function of applied pressure and biomass particle size.

In this study, the effect of compressive load and particle size on compression characteristics of four varieties (Strongfield, Blackbird, DT773 and DT818) of wheat straw grown at two different fields was investigated. Particle size, bulk and particle densities of all wheat straw samples were determined after grinding. Ground wheat straw samples were densified in a cylindrical die at 90 °C using an Instron testing machine. The wheat straw samples with 9% moisture content were compressed at five levels of compressive pressures (31.6, 63.2, 94.7, 126.4 and 138.9 MPa) and two levels of particle sizes (1.6 and 3.2 mm). Dimensions and mass of all compressed samples were measured to calculate the pellet density. The specific energy required to compress and eject the pellets was calculated from force-displacement data. Applied compressive force and particle size significantly affected the pellet density of wheat straw samples. The pellet density was in the range of 699–1064 kg m−3 increasing with pressure and particle size. The total specific energy required for compression and ejection of pellets varied from 4.35 to 33.64 MJ t−1 that increased with compressive load and particle size. Higher compressive forces and particle size increased the durability of pellets to more than 95%. Blackbird variety was the most compressible of the four varieties of wheat straw.