A 3D Packed Bed Model for Biomass Pyrolysis: Mathematical Formulation and Experimental Validation

A mathematical CFD model of a biomass packed porous bed system was developed to predict the volatiles in terms of tar and light gas as well as char fraction released during the pyrolysis process. In particular, phenol was considered as tar representative while for gas the single species were considered (in particular H2, CO, CO2, CH4 and steam). The model was implemented in a commercial CFD code through several original User Defined Functions (UDFs) to reproduce the source terms in the continuity, energy and chemical species mass fraction equations. Furthermore, both inertial and viscous resistances within the packed bed were modelled and coded to assess the pressure drop in the porous media. Code validation was achieved by comparing the numerical results against experimental data obtained in a small-scale biomass reactor using N2 as carrier gas. To assess the kinetic parameters of the pyrolysis model at different operating conditions, the experiments were carried out by varying, in a wide range, the temperature of both the N2 flux and reactor walls.