Tar removal in biomass gasification systems is one of the key challenges to overcome for the successful commercialization of this technology. This study focused on tar conversion over the active char particle besides the simultaneous carbon conversion of the char particle. In the presented model, the char particle was assumed a sphere surrounded by a gas film in a bulk gas composition of naphthalene, nitrogen, steam, hydrogen, carbon monoxide, carbon dioxide and methane. The model treated the heterogeneous gasification reaction kinetics, external and internal mass transfer and changing particle properties during gasification. In addition, the effect of different parameters on naphthalene and carbon conversion was investigated. The investigated parameters were particle size, temperature and time on stream. The gas and solid mass balance equations besides the energy balance equation were solved in the radial direction using a set of initial and boundary conditions. The model results show that the naphthalene and carbon conversion reactions were kinetically limited at the reference conditions of 850 degrees C bulk gas temperature and 600 mu m char particle size. Further, the model calculations show that isothermal char particle can be assumed up to a bulk temperature of about 1160 degrees C. The variation of the physical properties and pore structure of the char particle with carbon conversion affects the active surface area of the particle. Finally, the results of the single particle model will be extended to a fixed bed reactor model and will be validated with experiments. (C) 2014 Elsevier Ltd. All rights reserved.