| 摘要 |
Nitrogen is rejected from a pressurised feed gas stream comprising methane and nitrogen by cooling the feed gas stream in a main heat exchanger 10 and rectifying the cooled feed gas stream in a double rectification column 20 comprising a higher pressure rectification column 22, a lower pressure rectification column 24 , and a condenser-reboiler 25 placing the higher pressure column 22 in heat exchange relationship with the lower pressure column 24. A pump 50 withdraws a methane product stream from the column 24. The methane product stream is pressurised by the pump 50 and is vaporised in the main heat exchanger 10. The pressurised feed gas stream is expanded with the performance of external work in an expansion turbine 6 upstream of the main heat exchanger 10.
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