Liquid-phase mass-transfer processes in packings with a segregated flow model

Abstract

Liquid back mixing behavior has significant influences on the liquid-side mass-transfer coefficient in packed columns and rotating packed beds(RPBs). And the liquid-side mass-transfer coefficient without the liquid back mixing behavior is called a liquid-side intrinsic mass-transfer coefficient. A ratio of the liquid-side mass-transfer coefficient to the liquid-side intrinsic mass-transfer coefficient is defined as a liquid-side mass-transfer coefficient factor. The lower coefficient factor means the bigger reduction in the liquid-side mass-transfer coefficient. A segregated flow model in packings is developed. From the model, the liquid back mixing effect is first separated from the liquid-side mass-transfer coefficient and is then involved in the coefficient factor, and equations of the liquid-side intrinsic mass-transfer coefficient and coefficient factor are derived. Values of the liquid-side intrinsic mass-transfer coefficient and coefficient factor of oxygen desorption from water in Flexipac 2 structure packing in a packed column were calculated. The values of the intrinsic mass-transfer coefficient were in good agreement of a deviation of 0.58 % with the predictions by theoretical mass-transfer model. Values of the coefficient factor of oxygen desorption from water in a RPB with wire mesh packing were also obtained. Values of the coefficient factor in the RPB rotor were much lower than those in the packed column due to a highly intensified mass-transfer and a higher liquid back mixing in the RPB rotor as compared with those in the packed column. The best method to increase the coefficient factor is to reduce the liquid back mixing and to increase the liquid flow rates in packed columns and RPBs.