(133b) Influences of Biomass Compositions, Particle Sizes, and Fluidization Gases on Fast Pyrolysis
This research investigated the influence of biomass chemical compositions, particle sizes, and fluidization gases on fast pyrolysis in a bubbling fluidized bed. A multistep biomass pyrolysis kinetic was validated using two different experimental data set with detailed yields of bio-char, bio-oil, and bio-gas. The predicted C/H/O compositions in these products also compared well with the available experimental data. The validated kinetics was then used to investigate the influence of feedstock compositions on the pyrolysis yields using systematic MFIX-based simulation campaigns using UQ features in Nodeworks toolkit. The sampling simulations were generated by the Latin hypercube sampling method to leverage space-filling property for the targeted parameter space. A data-fitted surrogate model was then constructed to be used as a fast evaluation tool to quickly estimate the pyrolysis products based on different biomass input compositions without solving stiff and complex chemical reactions with MFIX. The adequacy of the surrogate model was assessed with cross-validation errors to minimize the uncertainty introduced due to surrogate model in lieu of actual MFIX simulations. At last, it was coupled with a coarse-grained discrete element method to model the fast pyrolysis in a bubbling fluidized bed. To accurately capture the residence time of biomass particles, a hybrid drag model which couples the Syamlal-OâBrien drag and a filtered drag was proposed and validated using a cold flow experiment. The predicted biomass particle residence time varied from 3.8 s to 10.8 s when its size increased from 130 micros to 400 micros. The change of particle size also leads to an increase of oil yields and a decrease of bio-char yields. The particle temperatures are uniformly distributed around 738 K in all the tested cases. This CFD model was then utilized to investigate the influence of fluidization gases such as pure Nitrogen and a mixture of Nitrogen and Hydrogen.