Modeling intensification of biomass fast pyrolysis in a fluidized bed reactor with autothermal operation

A complete methodology is presented for modeling the intensification of biomass fast pyrolysis with autothermal operation. First, a base-case entrained-flow reactor model is used to validate the latest thermophysical properties and pyrolysis kinetics. With a rigorous energy balance, the entrained-flow model shows good agreement with observed trends in product distribution. The resulting model can be used for the design and optimization of biomass fast pyrolysis processes, and comparison with the proposed intensified design. Next, a novel reactor model is developed to simulate biomass fast pyrolysis in a fluidized bed. This model decouples reactions and hydrodynamics, allowing for efficient modeling of solid-phase decomposition independent of the vapor phase. The results are validated against pilot-scale experiments, closely matching the observed product distribution and the elemental composition of the product streams. The novel fluidized bed model is expanded with the implementation of oxidation reactions, allowing the enthalpy of pyrolysis to be supplied by partial combustion of the pyrolysis products. Running the pyrolysis reactor under autothermal conditions removes the bottleneck of transferring heat into the bed, greatly increasing throughput and allowing biomass conversion to scale with reactor volume rather than heat transfer area. The autothermal fluidized bed model is validated against the same pilot-scale reactor as the non-autothermal model. The increase in throughput, product distribution, and product elemental composition are in good agreement with experimental observations. Finally, ongoing efforts to produce thermodynamic models for pyrolysis products are discussed. Once complete, these models will provide the foundation for detailed phase equilibrium calculations for downstream separations. In whole, this work brings together the latest experimental measurements, reaction kinetics, and thermophysical properties, implementing them in a novel reactor model. This model is able to match the operation of the pilot-scale reactor with limited modification, but its modular nature allows it to be constantly improved as new properties, pyrolysis and oxidation kinetics become available.

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