GB1175688A - Diffusion Systems for Separating Fluid Mixtures - Google Patents

Abstract

1,175,688. Diffusion separation system. E. I. DU PONT DE NEMOURS & CO. 13 Dec., 1966 [22 Dec., 1965], No. 23139/69. Divided out of 1,175,687. Heading D1L. A plurality of diffusion units of the type disclosed in the original Specification 55708/66 (see also Figs. 1, 2, 2A, not shown) are employed in high efficiency systems to separate gaseous mixtures, e.g. He of 99.99+ % purity from natural gas containing <1% He, or from N 2 containing 0.47% He. In Fig. 3, feed passes by lines 201 203 to first diffusion unit 100 and through hollow filamentary mem branes (111) (see Figs. 1, 2, 2A, not shown), depleted effluent leaving by lines 204, 205. Part of the feed stream is diverted by line 210 to act as a sweep medium for the permeate fraction; permeate and sweep medium is then passed by lines 211 and 213 (having been compressed by compressor 212) to second diffusion unit 100. Effluent therefrom is recycled by lines 214-216 to feed line 203, permeate product which passes through the hollow filamentary membranes leaving by line 219. The process is controlled automatically, analyzer units 207, and 217 and 220 in conjunction, respectively controlling the amounts of sweep medium and recycle flow through valves 208, 218. In Figs. 4 and 6 (not shown), 3- and 4-unit systems are respectively described. In Fig. 5, feed passes by lines 430, 431, 432 to the hollow filamentary membranes of two first-stage diffusion units 100, depleted effluent leaving by line 433. Part of the effluent is however returned by line 434 as sweep medium, the swept permeate leaving by line 435 and part thereof being passed by line 436 to sweep the first unit. The combined swept permeate stream is passed through a "deoxo" unit and then dried before being passed by lines 441, 443, 444 to points at both ends of second-stage unit 100 external to the hollow filaments, unpermeated effluent being recycled by line 442. The permeate into the filaments is collected from both ends thereof by lines 448, 449 and passed by lines 450, 451 to both ends of a similar third-stage unit 100, unpermeated effluent therefrom being recycled by line 445 to the input of the second-stage unit, and permeate product leaving the system through line 456. In order to avoid variations in unit performance from unavoidable constructional factors, it is preferred that each unit, whatever the mode of operation, be substituted by three units operating in parallel. By judicious control of the various flow, sweep and effluent rates (see Fig. 6A, not shown), the effluent and permeate compositions from each may thereby be kept constant, and the disturbing effect of these factors on the overall throughput of the three units in parallel greatly minimized.