(215f) Continuum-Mechanics-Based Flow Modeling of Particulate Milled Biomass

Biomass material is one of the most promising energy resources because of its natural abundance and easy-to-access. However, the commercialization of biomass energy is prohibited by severe material handling issues manifested as clogging of particulate biomass materials in handling equipment (e.g., hopper arching and screw feeder jamming). Fundamentally, these issues are caused by the poor flowability of milled biomass. In comparison to conventional granular materials (e.g., sand, bean, pill), milled biomass at the macro-scale exhibit high internal friction with high compressibility resulting from the low particle density, the high angularity large aspect ratio, and the high particle compressibility at the micro-scale. In this study, we attempt to elucidate the flow behavior of pine chips, one of the most widely used bioenergy resources, using multi-scale experiments and continuum-mechanics-based simulations. We first present the mechanical behavior of the pine chips characterized by the physical experiments (e.g., Schulze ring shear test, cyclic axial compression test). We then establish a workflow to calibrate a shear rate-independent hypoplastic model based on the critical state soil mechanics and a shear rate dependent rheology model based on shear thickening. After validating the model, the hypoplastic model is used to simulate pine chips flow in a wedge-shaped hopper with variable geometry and initial conditions. The qualitative comparison of flow pattern (i.e., mass flow: first-in-first-out and funnel flow: first-in-last-out) and the quantitative comparison of flow metrics (mass flow rate, clogging) between the numerical prediction and experimental characterization shows the shear rate-independent constitutive model is capable of capturing the flow physics at a low shear rate. To accurately capture flow behavior at a high shear rate, we demonstrate that the shear rate dependent rheology model is needed as it is capable of predicting plane flow pattern along the inclined plane at a high inclination angle, while the hypoplastic model predicts a heap flow, in contrast to the physical observation. This work not only promotes the understanding of the flow physics of compressible particulate materials but also provides an advanced flow characterization scheme and insights on the application of soil mechanics constitutive model for novel granular flow. This study sheds light on the design of bioenergy material handling equipment.