This study describes a computational modeling study of a full-scale rotary kiln using the commercial CFD-code PHOENICS. A steady-state mode is assumed in which solid waste (a mixture of cellulose and toluene) is volatilized and burned. The focus of the model is on the gas phase fluid dynamics. Buoyancy is accounted for, turbulence is modeled with the K-ε model, radiative transfer is in a first step modeled with the composite flux model of radiation and combustion is modeled using the simple chemical reaction scheme (SCRS) model for diffusive, mixing limited reacting flows. The volatilization model makes use of a first-order Arrhenius-type reaction rate that takes the volatilization properties of both toluene and cellulose into account. The goal of this study is to screen various air inlet designs for their mixing characteristics and residence time distribution. This is translated in the destruction efficiency of selected compounds. The actual air inlet configuration in an existing full-scale incinerator is chosen as a reference for comparison. Alternative designs are analysed. The methodology and usefulness of the approach is fully demonstrated and typical design results are reported.