Intensification of G/L absorption in microstructured falling film. Application to the treatment of chlorinated VOC's - part II: Modeling and geometric optimization
Résumé
The falling film microabsorber developed by the Institut für Mikrotechnik Mainz is used to study its performance for the treatment of VOC-containing gases. The technique used is the gas/liquid absorption. The gas (mixture of air and tetrachloroethylene) and the solvent (Di(ethyl-2-hexyl) adipate, DEHA) flow counter-currently in the microabsorber. The solvent streams by gravity on a plate structured by microchannels. This technique makes it possible to miniaturize the process by increasing the mass transfer flow per volume unit as explained in Part I. Experiments are presented and a model is developed from equations of mass and momentum transfers. Results show a competition between two transport phenomena: diffusion and convection. The mass transfer rate is also studied with respect to the structure of microabsorber. It is also shown that it is possible "to optimize" the geometry of the apparatus in order to intensify the transfer so as to miniaturize the process. In the case of physical absorption, mass transfer intensification ( Murphree Efficiency) increases when the number of transfer unit NTU G (= τ/ t transfer) increases too. It is mainly due to the small volume of the apparatus where the gas phase residence time must be taken into account in the study of the mass transport towards the gas/liquid interface: the radial and the axial distances for the mass transfer and the mass transport have the same order of magnitude.