Multiphase modeling of anisotropic biomass particle pyrolysis accounting for particle deformation and coupled gas-phase dynamics
Numerical models of biomass particle pyrolysis focus on either the solid particle evolution or on the surrounding gas-phase dynamics, neglecting the coupled interactions between the two. This work addresses this limitation by proposing a single-grid model that fully resolves both phases without relying on sub-grid-scale correlations. The model adopts an Eulerian representation of the two-phase system, using a Volume-Of-Fluid (VOF) method to track the interface between the biomass and the surrounding gas phase. Solid-phase pyrolysis reactions are included, and a novel approach is proposed to capture the coupling between the evolution of biomass porosity and the particle shrinkage, combining different biomass conversion models into one unique framework. The anisotropic nature of the biomass particle is accounted for in this multidimensional framework. The resulting model is independent of the number and shape of the particle, and demonstrates mass conservation and numerical convergence. Extensive validation with experimental data, collected from wood particles in the centimetre scale and operating temperature between 400-700°C, shows excellent agreement in terms of mass and temperature profiles and correct volatiles trends. Predicted char yields fall within 2% error range. Shrinking profiles reveal correct trends, with a 10% average error in the final particle shape, but they also highlight the need for a better fundamental understanding of the evolution of the biomass structure. Overall, the model takes a step forward in aiding the development of sustainable pyrolysis processes. The code and simulation setups, developed within the open-source Basilisk framework, are made publicly available.