In the present study, the impact of shrinking and non-shrinking biomass particles on pyrolysis is studied employing a kinetic model coupled with a heat transfer model using a practically significant kinetic scheme consisting of physically measurable parameters. The numerical model is used to predict the effects of the most important physical and thermal properties (thermal conductivity, heat transfer coefficient, emissivity, reactor temperature and heat of reaction number) considering cylindrical geometry. A finite difference pure implicit scheme utilizing the tri-diagonal matrix algorithm (TDMA) is employed for solving the heat transfer model equation. The Runge-Kutta 4th order method is used for the chemical kinetics model equations. The computer simulations are performed for wide ranges of particle size and temperatures. The results obtained are in excellent agreement with many experimental studies, much better than the agreement with earlier models reported in the literature. The most dominant design variable is reactor temperature and exothermic reaction. The applications of these findings are important and useful for optimum design of biomass gasifiers and pyrolysis reactors. (c) 2006 Elsevier Ltd. All rights reserved.