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

Fast pyrolysis is a leading candidate process for converting biomass to liquid fuels. 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-compatible molecules, is highly dependent on the bubbling intensity which promotes heat and mass transfer within the biomass particles and at the particle surfaces as they transit through the reactor. Fluidized bed hydrodynamic characterization at smaller scales is a vital first step in reactor scale-up.

In this study, we simulate a 3D 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 MFiX, an open-source software package supported by DOE, which utilizes a continuum (two-fluid) approach for modeling the reactor hydrodynamics. Bubbling intensity and dynamic characteristics were evaluated utilizing pressure-based measurements [ http://dx.doi.org/10.1016/j.cej.2016.08.113]. Bubble and flow statistics of the bubbles, emulsion, and through flow (gas bypassing) were evaluated using MS3DATA [ http://dx.doi.org/10.1016/j.cej.2016.02.058].

For verification, we compare mixing and elutriation of our computational model to experimental studies in literature. For validation, we compare our computational results with an experimental laboratory biomass pyrolysis fluidized bed using Geldart Group B particles. Lab measurements include oil, gas, and char yield at the reactor exit. We will discuss implications on future numerical simulations and experiments based on our observations.