Significance of gas velocity change during the transport of CO2 through hollow fiber membrane contactors

A comprehensive 2D mathematical model was developed for the physical and chemical absorption of CO2 from natural gas containing high percentage of CO2. Unlike previous mathematical models, the model considers change in the axial gas velocity as CO2 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% CO2, and then was expanded to account for higher percentages of CO2. For 10% CO2, the model predictions showed a slight difference between the previous model and the experimental data for the physical absorption of CO2. 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 CO2 in gas mixtures, the model results showed that the decrease in gas velocity becomes significant for higher content of CO2, particularly if high absorption rate of CO2 was achieved and thus, maintaining a high percent of removal of CO2 due to the increase in residence time. This is a major contrast with the previous model behavior where the percent removal of CO2 continuously decreased with the introduction of more CO2 in the gas mixture. Furthermore, the model results showed that the effect of bulk flow contribution for gas mixtures containing high content of CO2 is insignificant for systems where the gas phase mass transfer resistance is small when compared to that of the liquid phase.