Multi-region modeling of conversion of a thick biomass particle and the surrounding gas phase reactions

Abstract

In this paper, a novel multi-region Eulerian model is presented to study the conversion of thermally thick biomass particles. In the present model, the particle and the surrounding fluid are treated as two separate regions that are coupled through an interface. There are some benefits for using a multi-region approach, including a more realistic radiation modeling, flexibility to define the flow boundary conditions at the surface of the particle, and also the possibility to use different governing equations for each region. Furthermore, the multi-region approach provides a solution to the stiff problem of coupling the particle to the surrounding fluid which can be used to significantly reduce the computational cost. In the current model, sub-models for drying, pyrolysis, gasification, combustion, and shrinkage are included. The local effect of shrinkage is considered through porosity change and the global effect of shrinkage is modeled using a dynamic mesh approach. The particle surface and center temperature and particle mass loss during pyrolysis and combustion are compared to different sets of experimental data. The model is used to study the shrinkage and anisotropic heat transfer on particle conversion, and also the pyrolysis in cases with and without the gas phase reactions.