Effects of particle size, distribution, and morphology on bulk shear behavior of milled loblolly pine

Abstract

Due to the anisotropic, non-uniform, and highly compressible nature of biomass granular materials it is challenging to accurately characterize bulk shear and flow performance. This work investigates these complexities by connecting shear behavior of milled loblolly pine with its particle size and morphology. Samples with incremental sizes, and ranges of size distributions were characterized to elucidate the impacts of overall particle scale, and the competing factors of size distribution. A Schulze rotary shear tester was used to perform tests at different consolidation stresses that are typically experienced in industrial scale equipment. Experimental data was then statistically analyzed using multidimensional linear regression, and empirical relationships for apparent cohesion and unconfined yield strength were developed. The results show that both increase with decreasing average particle size. Regression analysis revealed that cohesion for the incrementally classified particles was well described by accounting for the preshear normal stress as well as the ratio of particle surface area to the cross-sectional area (a generalized parameter that captures gross differences in particle morphology and surface roughness). Comparatively, the cumulatively distributed samples were explained by the preshear normal stress, the size of the relatively small particles (10 % cumulative passing size), and the span of the sieve size distribution (90 %–10 % cumulative passing sizes). Combining these parameters to estimate all the measured data resulted in good prediction (R² = 0.95, RMSE = 0.07) of the collected data. The established correlations between material properties and bulk shear response provide a mechanistic interpretation of biomass variability in flow performance. The developed correlations eliminate the need for extensive testing in specialized equipment and provide a method to qualitatively interpret the impacts of changing material attributes on resultant shear properties.