In a typical secondary aluminium process, the scrap feed is charged into a rotary furnace, melting and mixing under a salt layer in the furnace. The complexity in such a pyrometallurgical process is due not only to the high temperature effect and the complex chemical reactions, but also to the highly complex scrap feed with a distributed nature of aluminium types, compositions, sizes, shapes, paintings and other contaminations. In this study, user sub-models, which represent the distributed nature of the scrap feed, were developed and integrated into a computational fluid dynamics (CFD) based process model of a rotary furnace. Aluminium scrap was classified into several groups depending on their properties, e.g., size, establishing a discretized Population balance model (PBM). The melting behaviour of aluminium scrap was simulated with the exchange of information between the melting sub-model and the CFD calculations. In addition, the sub-model for scrap burn-off was also developed and integrated in the CFD framework providing distributed burn-off rates. Simulations of the melting process were made to model the flow and thermal phenomena ill such a furnace, and the influence of the scrap size, shape and quality, as well as burn-off rate were studied. (c) 2005 Elsevier Ltd. All rights reserved.