(380at) Computational Study on Biomass Fast Pyrolysis: Hydrodynamic Effects in a Laboratory-Scale Fluidized Bed

Authors: 
Ramirez, E., Oak Ridge National Laboratory
Li, T., National Energy Technology Laboratory
Finney, C. E. A., Oak Ridge National Laboratory
Shahnam, M., National Energy Technology Laboratory
Daw, C. S., Oak Ridge National Laboratory
Fast pyrolysis is a leading candidate process for converting biomass to liquid fuels and high value chemicals. During fast pyrolysis in bubbling bed or circulating bed reactors, biomass particles are rapidly heated through contacting with hot gases and solids, and their constituent components decompose into volatiles, ash, and char. The product vapor/gas composition, which determines the yield of fuel and/or chemical feedstock-compatible molecules, is highly dependent on the bubbling intensity which promotes heat and mass transfer and also controls the particle residence time. As with other energy-intensive processes, accurate characterization of biomass pyrolysis reactors at smaller lab and pilot scales is a vital first step in developing successful commercial versions.

In this study, we simulate a lab-scale bubbling fluidized bed biomass fast pyrolysis reactor to explore the effects of hydrodynamics on biomass conversion as the gas flow is increased through the bubbling-to-slugging transition, with all the other operating variables held constant. We employ a 3D implementation of MFiX, which is an open-source software package supported by DOE that utilizes a continuum (two-fluid) approach for modeling the fluidzed reactor hydrodynamics. Bubbling intensity and dynamics and the resulting impact on pressure measurements have been reported for a similar reactor set up previously[http://dx.doi.org/10.1016/j.cej.2016.08.113].

We compare mixing and elutriation predictions from our computational model to experimental studies in the literature, as well as experimental pyrolysis yield measurements when reaction chemistry is coupled to the hydrodynamics. We also discuss implications from the results of this study for future numerical and experimental studies of similar reactors.