(222a) The Hopper Flow of Biomass Pellets: Experiments, Simulations, and Economics

The efficient utilization of lignocellulosic biomass for biofuel and biochemical production is hindered by material handling issues such as clogging, segregation, and downtime, among other challenges. Current preprocessing methods such as drying, screening, and milling have de-risked feedstock variabilities to improve conversion yield but have not sufficiently improved flowability, especially herbaceous biomass. The poor flowability of herbaceous biomass is rooted in some particle attributes (irregular particle shape, high surface roughness, high bulk compressibility, high friction angle under stress consolidation, etc.) that remain less altered by those preprocessing methods, making the materials hard to flow to deliver scale-up throughput. Applying additional preprocessing such as pelletization (densification) to fundamentally alter those particle attributes is possible to improve feedstock flowability, which though have not been comprehensively investigated. This work aims to unveil the relationships between the biomass attributes, flowability, and economics resulting from using two feedstock preprocessing workflows for an herbaceous energy crop: 1) a baseline method of fine comminution to generate loose particulate feedstock with a nominal sieve screen size at 2 mm, and 2) an exploratory method of coarse comminution with a nominal sieve screen size at 6 mm and then densification to generate biomass pellets. Experimental measurement will be conducted, and smoothed particle hydrodynamics (SPH) and discrete element method (DEM) based flow models will used to examine the flow characteristics (i.e., critical arching distance and throughput mass rate) of the two physical forms of the feedstock, respectively, in a hopper discharge test and assist in the techno-economic analysis (TEA) case studies. In addition, particular attention will be paid to a DEM simulation-based parametric study focusing on the influence of pellet geometries (i.e., aspect ratio of length and diameter) and material properties (i.e., Young’s modulus and friction coefficient) on the resultant hopper flow characteristics. While biomass pellets are expected to yield higher mass throughput than loose particulate biomass for feeding and transport such as the representative hopper discharge unit operation, the economic viability of the proposed exploratory preprocessing pathway will be reported based on the result of the TEA case studies.