The determination of pressure drops is of major interest in the design of most air treatment processes, which often use activated carbon granules, beads in packing columns, or carbon cloths, for the removal of Volatile organic compounds or odorous molecules charged in the air. In this paper, numerical simulations of flows occurring in air treatment devices are performed using computational fluid dynamics (CFD), in order to assess the reliability of such a tool relatively to the prediction of pressure drops in these systems. The calculation of pressure drops is compared to experimental measurements in typical industrial configurations of air treatment devices using activated carbon cloths modules. This comparison between numerical predictions and experimental measurements of pressure drops reveals a very good agreement. The use of CFD tools also provides spacial distributions of the flow variables, that can be analysed in order to improve such treatment systems, from the aerodynamic behaviour point of view.