Significance of gas velocity change during the transport of CO 2 through hollow fiber membrane contactors

Abstract

A comprehensive 2D mathematical model was developed for the physical and chemical absorption of CO 2 from natural gas containing high percentage of CO 2. Unlike previous mathematical models, the model considers change in the axial gas velocity as CO 2 is being absorbed from the gas mixture. The model was validated with the experimental data and compared with previous model results for a gas mixture containing 10% CO 2, and then was expanded to account for higher percentages of CO 2. For 10% CO 2, the model predictions showed a slight difference between the previous model and the experimental data for the physical absorption of CO 2. However, there was a much improved agreement between the model predictions and the experimental data for the case of chemical absorption using 0.005 M MEA. Although this difference might be small for low content of CO 2 in gas mixtures, the model results showed that the decrease in gas velocity becomes significant for higher content of CO 2, particularly if high absorption rate of CO 2 was achieved and thus, maintaining a high percent of removal of CO 2 due to the increase in residence time. This is a major contrast with the previous model behavior where the percent removal of CO 2 continuously decreased with the introduction of more CO 2 in the gas mixture. Furthermore, the model results showed that the effect of bulk flow contribution for gas mixtures containing high content of CO 2 is insignificant for systems where the gas phase mass transfer resistance is small when compared to that of the liquid phase.