A 1-dimensional model for an atmospheric circulating fluidized bed biomass gasifier (CFBBG) under stationary state is presented in this paper. The model is based on the kinetic equations for the reaction network solved together with mass and heat balances and with several hydrodynamic considerations. Kinetics used include both our own kinetic data and published equations with some corrective factors. The reaction network used involves twelve different reactions. A sub-model for the tar generation-elimination in the CFBBG is included in the whole model. The model has an academic structure, but several assumptions were made because of lack of accurate data in some areas. The overall model has some empirical aspects and can therefore be considered as semi-rigorous. Hydrodynamics in the model were checked with a survey carried out worldwide among the existing pilot and commercial CFBBGs. The axial profiles of concentration of ten different species (H-2, CO, CO2, tar, char,...) and temperature can be calculated with this model which was conceived to optimize both design and operation of CFBBGs. (c) 2004 Elsevier B.V. All rights reserved.