Flow characterization of compressible biomass particles using multiscale experiments and a hypoplastic model

Abstract

Poor flowability of compressible biomass particles poses severe handling challenges in all processes of biorefineries, which results in poor energy-yielding in conversion. This paper presents the characterization of the flow behavior of a widely used compressible biomass material (ground loblolly pine) using a combination of physical characterization and numerical simulation. An advanced hypoplastic model with implementation and validation in Abaqus VUMAT is adopted. A workflow is established to calibrate material parameters directly from index tests, an oedometer test, and a Schulze ring shear test, and indirectly from numerical simulations of those tests. The finite element simulation of axial shear tests and hopper flow tests using the calibrated hypoplastic model is shown to capture key flow attributes, such as the maximum shear stress in shear tests, as well as the mass flow rate and flow pattern in hopper. The results demonstrate that a subset of the laboratory tests needs to allow large strains for adequate characterization of compressible granular flow, and numerical models developed for non-compressible materials can accurately predict the flow behavior of compressible biomass material, even though strain magnitudes are not scaled correctly. This study provides a potent tool to decipher and resolve material handling upsets in biorefineries and other energy industries that utilize forest products.