The modelling of biomass gasification enables the optimization of the process designs, but it is a challenge due to its high complexity. Here a model for prediction of the performance of a 100-kW dual bed fluidized biomass gasifier is derived and implemented in the ASPEN plus environment. Detailed pyrolysis modelling is properly addressed, and this is believed to be a key factor of this approach and enables more accurate results. The proposed model and its basic assumptions were extensively validated on a range of operating temperature by conducting experiments using softwood pellets as fuel and fresh olivine sand as bed material. The impact of the gasifier temperature variation on the final product gas composition is measured in the experiments and used to tune the model to have a better insight on the pyrolysis process, the char heterogeneous reactions as well as the deviation from equilibrium of the water gas shift reaction. After the assessment phase, the model was applied to to the simulation of a real case experiments and measured gas yields. The results can be considered appropriate and the difference between prediction and measurement of H-2, CO and CO2 are lower than 10%, while CH4/C2H4 show values that are slightly higher than 10%. (C) 2019 Elsevier Ltd. All rights reserved.