Experiments on a pilot-scale 150-litre forced circulation crystallizer with external circulation flow rates of 2 and 3 l/s revealed a hi,oh sensitivity of the product crystal size distribution for this operational variable. It is believed that a change in the circulation How rate influences (1) the nucleation rate, which is mainly caused by the mechanical action of the pomp, (2) the degree of internal dissolution in the heat exchanger and (3) the settling of the larger crystals in the crystallizer body, This paper presents a modelling framework which allows for a mechanistic description of growth and dissolution, attrition and secondary nucleation and settling, Such a description is seen as a prerequisite for the development of crystallization models with a predictive value for different operational conditions or fur another scale of operation. Growth, attrition and nucleation kinetics are modelled using relationships from both Eek [1] and O Meadhra [2] whereas a diffusion-controlled model is applied to describe size-dependent dissolution kinetics. The settling behaviour of crystals is described using Stokes law combined with Richardson-Zaki＇s equation for hindered settling. From the simulation results it can be concluded that the modelling framework presented here is capable of qualitatively predicting the effects of a change in the circulation Row rate. The quantitative predictions of the median crystal size are within 15% of the experimental values, whereas the oscillations predicted during start-up show a far larger deviation from the experimental results.