The particle-laden flow in the separator of a laboratory beater wheel mill is computationally and experimentally investigated. The main aim of the present study has been the identification of convenient modelling approaches and the assessment of the modelling predictive capability for this class of problems. For the particulate phase a Lagrangian formulation is adopted. Particle computations are carried out as post-processing, assuming different size class distributions. A modulation of the gas turbulence by the particulate phase is neglected. Different turbulent models are used. The turbulent particle dispersion is modelled by a stochastic approach. Different geometric configurations of the separator are investigated. With the results of the simulation study it became possible to predict the trends correctly.