A two-stage macro-TGA experiment on pyrolysis and gasification of a thermally thick wood cylinder showed that during pyrolysis at 400 degrees C particle shrinkage and cracking take place, but there is no fragmentation. The fragmentation became noticeable during wood char gasification at high temperature (930 degrees C). The experiment showed that wood char particles begin to break down shortly after gasification is initiated. A three-dimensional, transient model of biomass pyrolysis and gasification was proposed and implemented in the ANSYS Fluent CFD package. The results of simulations, corresponding to the macro-TGA experiment show that the effect of particle cracking and shrinkage may be neglected. However, the results also show that for successful modelling of gasification wood char fragmentation must be taken into account. (c) 2014 Elsevier Ltd. All rights reserved.