(252a) Discrete Element Modeling of Granular Flow of Flexible Woody Biomass Particles

Biomass source materials such as pine chips, corn stover and chopped switchgrass are all irregular-shaped, deformable particles. Unlike traditional granular materials that are usually hard, biomass particles exhibit significant deformability in feeding and handling processes even under low-pressure compression. Such deformability has a profound impact on bulk flow behavior of biomass materials and makes it difficult for design of feeding and handling equipment. This work presents a bonded-sphere Discrete Element Method (DEM) approach for simulating and studying the flow behavior of irregular-shaped, deformable particles. In this approach, an individual particle is modeled by a cluster of elastically bonded spheres. The model is designed to simultaneously capture irregular particle shapes and particle-level deformations such as compression, deflection, and distortion. This approach is applied to simulate and study the behavior of a woody biomass source material of interest (i.e., fine chips) in a cyclic compression and hopper flow test. With calibration, the bulk densities and bulk moduli of elasticity calculated from the DEM simulations agree reasonably with those measured in the physical test. A sensitivity study of the impact of particle shapes and deformability on bulk flowability is conducted through simulations of a hopper test. Results show that hard particles have higher change to suffer from clogging issues, whereas deformable particles have less chance to. This indicates that particle deformation reduces the critical bridging width in hopper. Overall, this work has demonstrated the necessity to take into account of the particle deformability for the simulations of biomass particles in working conditions.