Slow pyrolysis is a biomass conversion process in which biomass is converted into char with the aim of improcing its solid fuel properties, of to serve in new applications such as biochar (soil amendment). in this project, a CFD reactor model will be developed to simulate these slow pyrolysis processes, as carried out in a screw reactor. Amultistage approach is followed in which, first a single particle pyrolysis model is developed. next, the single particle model is integrated into a population balance model, which will be coupled to the CFD model of the reactor demain.