A computational fluid dynamic simulation for CO2/CH4 membrane separation process

چکیده مقاله

Hollow fiber membrane contactors have several advantages that make them a good alternative to conventional absorption processes in the gas industry and have attracted the attention of many researchers. However, important issues such as wetting prevent the use of membranes on a large scale. Humidification is the penetration of liquid absorbent through the membrane pores, reducing the mass transfer and thus affecting the efficiency of CO_2absorption and reducing the effectiveness of the separation process. Investigating the wetting phenomenon and simulating it in hollow fiber membranes and the effects of this phenomenon is the main goal of this research. For this purpose, Computational Fluid Dynamics (CFD) technique and Comsol software are used. The physical and chemical absorption of carbon dioxide in two different solvents, MEA and distilled water, was evaluated through mathematical modeling and its comparison with experimental results. A polypropylene hollow fiber membrane was used to investigate the effect of different operating conditions on CO_2 removal from a binary mixture containing 10% CO_2 in methane. A general two-dimensional mathematical model was developed to determine the effect of liquid and gas flow rates on membrane wettability and CO_2 removal using hollow fiber membrane (HFM) contactors. This model considers complete wetting, partial wetting and dry conditions. Also, axial and radial diffusion in the tube, membrane and side of the contact shell are considered. A laminar parabolic velocity profile was used for flow on the pipe side. Meanwhile, the flow on the shell side is calculated approximately with the Hoppel free surface model. The effect of gas and liquid flow rate was investigated for these two solvents. The model predictions were in good agreement with 6.8% deviation from the experimental data on average and showed that the membrane wettability mostly depends on the gas and solvent flow rates. At high solvent flow rates and low gas flow rates, membranes with large pores may exhibit wettability even under dry conditions.