Solvent counter-diffusion in gas absorption

The usual design equations for absorption towers are based on the assumption that only one component is diffusing in the gas phase: the counter-diffusion of the solvent is ignored. A correction factor has been developed, based on a solution of the Stefan-Maxwell diffusion equations for the case of two gases diffusing through a stagnant third one. The special case of equimolal counter-diffusion is also considered. The correction factor is obtained by simultaneously solving two non-linear equations. The system ammonia-water-air is used to illustrate the order of magnitude of the error the factor is intended to correct. Le calcul des tours d'absorption comporte generalement l'hypothese qu'un seul composant diffuse dans la phase gazeuse et la contre-diffusion du solvant est negligee. On propose un facteur de correction, etabli a partir d'une solution des equations de Stefan-Maxwell dans le cas de la diffusion de deux gaz a travers un troisieme gaz immobile. Le cas special de contre-diffusion equimolaire est aussi etudie. Le facteur provient de la solution de deux equations non lineaires. On indique, par l'exemple du systeme ammoniac-eau-air, l'ordre de grandeur de l'erreur qu'il sert a corriger.