Parametric analysis of biomass fast pyrolysis in a downer fluidized bed reactor

This study presents a theoretical parametric analysis of biomass fast pyrolysis in a downer reactor, as part of a dual fluidized bed system. The model framework uses a Eulerian-Eulerian CFD approach and incorporates a user-defined function (UDF) for the thermochemical conversion of biomass. The downer reactor consists of a novel gas-solid separator, which is employed to control the gas residence time within the reactor. The parameters investigated included the reactor temperature, the particle (heat carrier and biomass) size and the gas residence time. The product yield was found to be strongly dependent on the reactor temperature (varied through changing the heat carrier flow rate), intermediately dependent on the sweeping gas (N₂) flow rate and the sand particle size, and much less dependent on the biomass particle size (within the range of 1 mm diameter). The developed model and the results demonstrate the advantage and robustness of employing the model for parameters optimization and sensitivity investigation when dealing with complex multiphase flow reactive system. This conclusion will benefit future development and scale-up studies of downer reactors for biomass fast pyrolysis.