| 摘要 |
PROBLEM TO BE SOLVED: To secure product purity and a recovery ratio by simple constitution even when the flow rate of raw material gas is decreased. SOLUTION: The raw material gas g1 of a mixed gas containing a gas which can easily pass through a gas separation membrane 1 and a gas which can hardly pass through the membrane 1 is pressurized by a compressor 2 and supplied to a membrane separation part 3 equipped with the gas separation membrane 1. The gas g2 which passed through the membrane 1 is recovered to obtain a cleaned gas g3 of a high gas g2 concentration. For this purpose, a part of the gas g2 is circulated to the raw material gas side, the mixed gas and a part of the circulated gas g2 are supplied to the membrane separation part 3, and the residue of the gas g2 is obtained as the purified gas g3.
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