| 摘要 |
A method of rejecting nitrogen from a feed gas stream comprising methane a nd nitrogen so as to form a methane product comprises cooling the feed gas stre am in a main heat exchanger 4 and rectifying the cooled feed gas stream in a doubl e rectification column 12 comprising a higher pressure rectification column 14 and a lower pressure rectification column 16. A flow of gas is recycled from the lower pressure rectification column 16 to the higher pressure rectification column 14. A first part of the recycle flow is compressed in a compressor 48, is cooled, is liquefied in a condenser-reboiler and is introduced into the higher pressure rectificator column 14. A second part of the recycle flow is also compressed in the compressor 48, is cooled, is liquefied in the main heat exchanger 4 or by expansion, an d is introduced into the double rectification column 12 in liquid state. At leas t part of the cooling of both parts of the recycle gas is performed in the main heat exchanger 4. A methane product is withdrawn in liquid state from the lower pressure rectification column 16 by a pump 42.
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