Comminution is au energy intensive process and methods of producing the required product which result in energy savings are continually being sought. In this paper, the modelling of an air-swept cement grinding mill and air separator which have been undertaken with the objective of plant and circuit optimisation. The simulation models developed predict full size distribution, specific surface area and tonnage for all streams in cement grinding circuit under a particular set of operating condition. The mill model is based on two widely accepted concepts, namely the selection and breakage functions with, in addition a internal classification function to incorporate the air sweeping action. The separator model is based on the concepts of a classifier efficiency curve. The performance of different cement grinding flowsheets is evaluated and discussed on the basis of sampling surveys undertaken in the Asian Cement Plant and Nub Cement Plant in Turkey.