(149a) Improving the Flowability of Lignocellulosic Biomass in Wedge-Shaped Hoppers Via External Vibrational Forcing: A DEM Study

The handling and transport of lignocellulosic biomass has emerged as a central topic in the production of biofuel because the low bulk density, polydispersity, and highly non-linear flowability (e.g. arching, ratholing in hoppers) of feedstock particles can impede downstream biorefinery processes and limit overall operations. Vibrational forcing has been utilized as a method for initializing and maintaining flow in hoppers, however, studies on this topic have mostly been limited to uniform granular materials. In this work, we use an in-house developed high-performance computing (HPC) compatible discrete element method solver to simulate the discharge of corn stover from a wedge hopper with and without the influence of external spatiotemporal forcing. The solver (BDEM, https://github.com/NREL/BDEM) includes models for representing complex particle shapes (glued and bonded-sphere models) and particle cohesion (liquid bridge and SJKR models), and has shown excellent strong-scaling performance on state-of-the-art CPU and GPU architectures for large problem sizes (> 100 M particles). Sinusoidal forcing is applied to the feedstock in both the vertical and horizontal directions, and the impacts of force amplitude and angular frequency are both explored. When amplitude and frequency were held constant, it was found that vertical and horizontal vibrations lead to similar average discharge rates, while the horizontal vibrations lead to lower variation in the discharge rate, reducing the intermittency that characterizes the vertical vibrations. In contrast with previous studies, the vibrational forcing amplitude is found to have a stronger impact on flow rate as compared with the angular frequency, as stronger vibrational forces are more effective in breaking the cohesive bonds that impede biomass feedstock flow. Finally, the hopper flow is visualized to show the flow patterns observed, providing deeper insight into the mechanisms by which vibrations help induce hopper flow. The horizontal vibrations induce flow near the walls of the hopper, resulting in an inverted funnel flow pattern, while the vertical vibrations result in funnel flow with a V-shaped valley characterizing the surface of the feedstock.