The efficiency of columns for fluid separation can be increased by the application of sandwich packings. During the operation, different load-dependent regimes with peculiar separation performance arise. In order to account for the effects of the individual flow regimes in a single model, both separation performance measurements and tomographic imaging are applied. A rate-based model is presented, which takes the heterogeneous regimes in sandwich packings into account by means of appropriate correlations. The model is tested with experimental data for CO₂ absorption.