Research Of Seawater To Enhance SO₂ Removal Through Microporous Hollow Fiber Membrane Contactor

Sulfur dioxide is one of the main acid gas sources of air pollution, which is reported to cause serious damange to ecological environment, human heath and cultural ashes. Enormous researches have been carried out in past years and hydro-desulfurization technics is proved to be the most efficient and reliable method. However these conventional systems can not avoid the disadvantages caused by the direct gas-liquid contact in scrubber contactors, such as foaming, emulsions, flooding or channeling and huge space requirement, related high caital costs, additional operatonal limitations and loading limitations, which make it necessary to develop a new technology which not only can be stalled conveniently but also can be operated efficiently and flexibly to meet special demands of vious cases.Comparatively, membrane contactors carry out gas-liquid contacting operation through hollow fiber membrane contactor, in which the absorbent liquid flows on one side and the gas flows on the other side of the membrane through a careful control of gas-liquid pressure drop. Such fluid offers several advantages including higher interfacial area per unit volume, absence of emulsion, no flooding at high flow rates and no unloading at low ones.In this paper, the status quo of desulfurization technology was summarized and then the basic theory and reseach trend of membrane contactors' applicaton in desulfurization process was introduced. Basic on the foregone mass transfer theory and reseach experience, hydrophobic polypropylene hollow fibre membrane was used as membrane contactor in this experiment as membrane contactor.Firstly, the microporous polypropylene hollow fiber membrane was characterized by SEM. According to the pore size andλvalue of sulfur dioxide molecular, the diffusion model of the absorbed momentum SO₂ through the microporous membrane was considered as a transition diffusion which consist of three steps: transition diffusion through the pore channel, Stephen diffusion in the pore edge, and the pore interaction in the membrane surface.The actural fluidness and mass transfer in the shell side and lumen side is very complex in a randomly packed hollow fiber module, which is discussed after the diffusion model of SO₂ through the microporous membrane was determinate. Then the mass transfer coefficient of gas phase, membrane phase and liquid phase was quantitative and qualitative analysised and the different influence factors of mass transfer coefficient and desulfurization efficiency were discussed. In order to verify the application prospective of seawater on SO₂ removal by hollow fiber membrane contactor, tap water, aqueous NaOH solution with a pH value of 8.35 and seawater were used as absorbent respectively. The impacts of various factors such as three different absorbents, pressure gradient between gas and liquid, flow rate of absorbents, flow rate and concentration of feed gas on the overall mass transfer coefficient and desulfurization efficeiency were investigated. The experimental results indicated that seawater can obviously improve the overall mass transfer coefficient compared with tap water and NaOH solution. When the pressure gradient between gas and liquid kept under the Penetration Pressure and the volume ratio of SO₂ kept below 2000×10^-6, seawater could obtain higher absorption rate of above 90% with lower flux. Therefore, membrane contactor coupled seawater absorption is a prospective technology for sulfur dioxide removal in seaside area.