Influence of residual loadings on mass transfer and efficiency in sorption cycles

The axial residual loading profile of an activated carbon column during a sorption cycle has been determined experimentally. The sorption cycle contains the steps adsorption, steam desorption, drying/cooling and a following adsorption. For the system toluene/SORBONORIT 4 the drying parameters have been varied to examine the influence of the residual loading profile on the breakthrough time and the exit concentration on the adsorption step. At higher drying temperatures toluene is being desorbed from the coal and is readsorbed in the following layers. This shift of the loading profile results in a shortening of the breakthrough time as well as in an increase of the exit concentrations. To achieve low emissions, a longer part of the bed must be regenerated to reduce the residual loading. A heterogeneous model has been developed to simulate this behaviour. The transport effects in a particle are thereby combined with the transport phenomena in the bed. The simulation of adsorption considering the preloading profile caused by different drying conditions reveal different governing transport mechanism leading to significant differences in the breakthrough behaviour.