Research On Membrane Separation-Cryogenic Hybrid Process For Helium Extraction From Natural Gas

As a rare resources, Helium(He) has been used in semiconductor manufacturing, special welding, magnetic levitation train, magnetic resonance imaging(MRI), thermal imaging, medical treatment, aerospace and other fields. The nature gas contained He is the main source of He, So the nature gas has been focused on in extracting He industrial field.However, in our country, due to the He resources’s rare reserves and low concentration, the development of He-extracted in industry has been limited. The process of He extracted from natural gas(NG) in cryogenic conditions aimed at extracting He, with high energy consumption, complex equipment and low production of LNG, isn’t competitive in terms of economic efficiency. And along with the increasing sales of LNG, the He-extracted process based on the NG liquefaction process has a higher competitive advantage, which is worth considering.Based on the liquefaction process of the mixed refrigerant including pre-cooled propane, the process of He extracted from LNG was studied in this paper. The membrane-cryogenic hybrid process, used to extract He from NG, made the He recovery be70%after a step-wise enrichment processes, these processes were condensation, membrane treatment and Pressure Swing Adsorption(PSA), in that order. And at the same time, the optimum operation parameters were also obtained through studying the influencing factors of process conditions.In allusion to the disadvantage of membrane-cryogenic integrated, the low yield of He, the membrane-cryogenic coupling process of He extracted from NG was proposed, and the coupling effects of the cryogenic temperature, the flash pressure and the membrane separation process were in consideration. A two-stage membrane separation was coupled with the liquefaction process in the process, making the yield of He be96%and increasing the rate of NG liquefaction by1.4t/h. The proposed process has many advantages, such as simple equipment, easy operation, without liquid nitrogen refrigeration and higher economic effectiveness.Some researches on mixed refrigerant refrigeration were also studied in this paper, the quaternary-refrigerant component’s influence on the cooling curve was considered, and the refrigerant’s component was simulated and optimized. The better refrigerant component which could get better economic benefit, was obtained through analysing the optimization process and explaining the optimization process from the point that the transfer temperature difference and the heat capacity of refrigerant have relate to component.