Extraction of Helium From Natural Gas. The Diffusion-Through-Glass Process

The conventional low temperature process for extracting' helium from natural gas involves liquefying the whole gas stream in order to remove the relatively small fraction of helium. A process based on the selective diffusion of helium through a semipermeable barrier is, in principle, more economical and flexible, particularly for the treatment of small reserves and low concentrations. The well-known permeability of glass to helium offers the possibility of such a diffusion process and McAfee of the Bell telephone Laboratories showed in 1958 that practical separations could be achieved by passing natural gas over bundles of fine capillary glass tubing. Developmental studies have been carried out involving larger units and more extended field tests than those of McAfee. Fine capillary tubing of Pyrex glass 0.0035 in. diameter was prepared by drawing ordinary 6 mm. laboratory tubing in a furnace. Extraction units were prepared containing about 10,000 such tubes, 4 ft. long and cemented inside a length of %, in. pipe. It was confirmed, using pure helium and also a natural gas stream, that these units perform in accordance with the published permeabilities of helium through glass. Gas phase diffusional resistances outside the tubes and flow resistances inside the tubes were negligible. Brief tests were made up to 1000 psi. and extended field tests with natural gas at 120 psi. and 450 ° C. No deterioration in performance nor breakage of any tubes occurred over a 5-month period. Vycor (96 per cent silica) glass in limited tests was less durable although McAfee has reported that pure silica stands up indefinitely. Finally, an approximate economic assessment appears encouraging for further work
Keywords: flow, Glass, Hydrogen and Helium Survey, natural gas, pyrex, silica, Vycor, Natural gas, Plants, Pressure, Silica, Temperature, Tests, Tubes, Tubing
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