A CFD model for biomass fast pyrolysis in fluidized-bed reactors

Abstract

In this work, an Euler–Euler multiphase CFD model is proposed for continuous fast pyrolysis of biomass in a fluidized-bed reactor. In the model, a lumped, multi-component, multi-stage kinetic model is applied to describe the pyrolysis of a biomass particle. Variable particle porosity is used to account for the evolution of the particle's physical properties. Biomass is modeled as a composite of three reference components: cellulose, hemicellulose, and lignin. Pyrolysis products are categorized into three groups: gas, tar vapor (bio-oil), and solid char. The particle kinetic processes and their interactions with the reactive gas phase are modeled with a multi-fluid description derived from the kinetic theory of granular flows. A time-splitting approach is applied to decouple the convection and reaction calculations using a synchronized time step. The CFD model is employed to study the fast pyrolysis of both cellulose and bagasse in a lab-scale fluidized-bed reactor. The dynamics, particle heating, reaction of the biomass phase, char formation, elutriation, and spatial distribution of tar and gas inside the reactor are investigated. The yields of tar, gas, and char are also discussed.