(110h) Flow Characterization of Fibrous Woody Biomass Using Experiments and Modeling

Critical problems often arise when feeding biomass in large scale processes. Frequently, solid feeding devices, such as screw feeders and hoppers, become blocked, and fail to provide uniform and continuous flow of the feed material. Reliable, efficient, and economical feeding of lignocellulosic biomass into pyrolysis reactors makes biofuels production one step closer to the goal of replacing fossil fuels. In this work, transporting biomass solids in compression-screw feeders is the primary focus. In order to mimic the flow properties of compressed biomass inside a compression-screw feeder, rheological properties of compressed lignocellulosic biomass were investigated. Then, the experimental results were validated by Computational Fluid Dynamics (CFD) simulations using OpenFOAM software package for a simple pipe flow case. To conduct the experiments, woodchips were fed into a twin-screw compounder in order to obtain compression conditions experienced in a compression-screw feeder in an industrial scale process. Then, changes in flow behavior were measured when varying the material and operating conditions, including screw speed, moisture content, and particle size distribution. After solving the equations of continuity and conservation of momentum for the microcompounder, screw speed and force were converted to shear rate and viscosity, respectively. We found that at higher screw speeds and moisture contents, the material flows easier. In addition, the viscosity of biomass in the microcompounder falls within the shear thinning region of a Cross model fit. Moreover, the impact of particle size distribution on the flow behavior of compressed biomass is insignificant. For the modeling and simulation efforts, biomass was modeled as a compressible fluid with a pressure-dependent density and density-dependent yield stress. Density-dependent Bingham and Cross models developed were validated for biomass pipe flow under pressure. Rheological values obtained from pipe flow simulations agreed with experimental data obtained from literature showing that the models developed are able to capture the flow behavior of compressed biomass under pressure. The next phase of this project will focus on performing computational simulations of the industrial scale compression-screw feeder and refining the model parameters and validating the simulation results against pilot-scale experimental data.