CFD Modelling of Biomass Pyrolysis in a Fixed Bed Reactor Using an Eulerian-Eulerian Multiphase Approach

Greencorn, M. J., Jackson, D. , Hargreaves, J. S.J. , Datta, S. and Paul, M. C. (2021) CFD Modelling of Biomass Pyrolysis in a Fixed Bed Reactor Using an Eulerian-Eulerian Multiphase Approach. 7th International Symposium on Gasification and its Applications (ISGA 7), 27-30 Sept. 2021.

Abstract

Thermochemical conversion of solid biomass to char and volatile chemical species is an important process for many renewable technologies. Whether as an initial stage for further combustion or gasification reactions or directly used to produce biochar and/or bio-oils, pyrolysis is a critical step that is sensitive to hydrodynamic temperature and velocity fields within a reactor. In this work we present a CFD model to analyse the pyrolytic conversion of solid biomass to simple gasses in a fixed bed reactor. Flow conditions inside the reactor volume use a multiphase, Eulerian-Eulerian CFD model to represent the solid biomass phase, the gaseous mixture phase, and the solid char phase produced. Kinetic devolatilization reactions are modelled to calculate the solid to vapour transition while heterogenous gas phase reactions model volatile species interactions. Solid, granular phases are constrained to maintain zero-velocities and thus be representative of fixed bed conditions within a reactor. One key model input is the kinetic parameters for the biomass devolatilization which can be sourced from available literature or determined from TGA/DTG analysis. Proximate and ultimate analysis of the biomass feedstock provides a basis for the process mass balance to determine the pyrolysis product chemical species. Stoichiometry and kinetic parameters for the key heterogeneous gas phase reactions are also known in the literature. The reaction energy balance is completed from Hess’ law using the heat of formation for the biomass feedstock calculated from either a known heating value or from a correlation based on its elemental composition. Applicable calculations of the mass, momentum, energy, and closure equations are completed in the ANSYS Fluent CFD environment. Transient simulations show the temperature and velocity fields inside the reactor volume over the reaction time. Key outputs of interest are the flow rates of the evolved pyrolysis gas and the molar ratios of constituent chemical species in the pyrolysis gas. These results are assessed over time and across a range of pyrolysis temperatures.

• Item Type: Conference or Workshop Item
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Hargreaves, Professor Justin and Greencorn, Mr Michael and Paul, Professor Manosh and Jackson, Professor David and Datta, Souvik
• Authors: Greencorn, M. J., Jackson, D., Hargreaves, J. S.J., Datta, S., and Paul, M. C.
• College/School: College of Science and Engineering > School of Chemistry; College of Science and Engineering > School of Engineering > Systems Power and Energy
• Copyright Holders: Copyright © 2021 The Authors
• Publisher Policy: Reproduced with the permission of the Author

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