Study On Membrane Absorption Of H₂S In The Biogas

This paper summarized the research status of removing acid gas by membrane absorption at home and abroad, the principle of membrane absorption and mass transfer process. The existing theoretical knowledge was used as the basisfor carrying out study of removing H2 S in the biogas by membrane absorption.Firstly, selecting hollow polypropylene fiber membrane contactor as absorber,the influence of single factor on desulfurization efficiency and its reason were studied. The results show that the desulfurization efficiencies of positive process and countercurrent flow are better than that of opposite process and current flow. When the liquid flow is less than 0.3m/min, the desulfurization efficiency of upright slightly larger than that horizontal, while the liquid flow rate is greater than 0.3m/min, the change trend goes in the other direction. With same concentration of NaOH, Na2CO3 and MDEA solution, thedesulfurization efficiency of NaOH is the biggest. The desulfurization efficiencies increase along with the increase of liquid flow, which is over 90% at least, but decrease with the increase of gas flow. Considering the energy consumption and the heat resistance of membrane, the temperature is usually set to 25 ℃, although desulfurization efficiencies increase with the increase of temperature, it. The desulfurization efficiency increases with the increase of inlet pressure, and 0.08 MPa is seted as the inlet pressure to prevent too much gas hydraulic differential.With alkaline as absorbent, the repeated stability of membrane absorber is better than that of long term stability. The desulfurization efficiency could reach more than 99% under the best conditions,Secondly, Absorbent concentration 0.2 mol/L, gas flow 0.6m/min liquid flow 0.95m/min are the favorable process parameters obtained by orthogonal experiment, and H2 S removal efficiency could reach 99.94% in the preferential conditions. Meanwhile, influence of each factor on the H2 S removal is decreased in the order: gas flow, liquid flow, and absorber concentration.Finally, the influence of single factor on total mass transfer coefficient was studied and it was analysed quantitatively and qualitatively by mass transfer theory of gas membrane separation. The results show that when the liquid flow is less than 0.54m/min, the total mass transfer coefficient increases with the increase of alkali liquor flow, and when the liquid flow is greater than 0.54m/min, the total mass transfer coefficient then keep stable with increasing of liquid flow. The total mass transfer coefficient increases with the increase of gas flow and the concentration of alkali liquor.when the concentration increased from 0.02mol/L to 0.25 mol/L, the total mass transfer coefficient is improved significantly. The total mass transfer coefficient increases with the increase of inlet pressure and temperature, which should not be ignored.To sum up, the influence of liquid concentration and flow on the total mass transfer coefficient is same to that of the desulfurization efficiency, but the influence of the inlet flow is opposite.