A mathematical CFD model of pyrolysis process was developed to predict the volatiles in terms of tar and light gas as well as char fraction released in a biomass packed porous bed system. In particular, phenol was considered as tar representative while the main gas species were individually considered (in particular H-2, 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 modeled 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 N-2 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 N-2 flux and reactor walls. (C) 2015 Elsevier Ltd. All rights reserved.