(92f) Modeling Intensification of Biomass Fast Pyrolysis through Autothermal Operation

Biomass fast pyrolysis has been identified as a viable method to produce bio-oil, a renewable alternative to petroleum-derived sources of fixed carbon. Fluidized beds are commonly used for pyrolysis due to their precise temperature control and high solid-to-solid heat transfer rates, but the largest barrier to scale-up is the difficulty of heat transfer into the pyrolysis reactor. Autothermal operation has been proven to overcome these heat transfer limitations by allowing a limited amount of oxygen within the bed, combusting a portion of the contents to supply the heat of pyrolysis. Current fluidized bed reactor models are focused on fluid-phase or heterogeneous reactions, and so are not conducive to the modeling of solid-phase reactions within a mostly inert bed.

This work presents a novel approach to the modeling of a fluidized bed reactor, focusing on the experience of small particles that make up a minority of the bed mass. Due to the decoupling of solid- and vapor-phase reactions, the group of reactive particles can be modeled as a series of open control volumes surrounded by a uniform temperature heat source. The phenomena of heat transfer, chemical reaction, density loss, and elutriation are all captured in a format applicable within commercially available process simulators. The addition of oxidation reactions to the solid and vapor phases allows the reactor model to operate autothermally. Simulation results are used to estimate the performance enhancement derived from autothermal operation.