| 摘要 |
Nitrogen is removed from a liquefied natural gas feed ( 41 ) by a two stage separation in which the liquefied natural gas ( 41 ) is first fractionated ( 23 ) to provide a first nitrogen-enriched overhead vapour stream ( 46 ) and a nitrogen-containing bottoms liquid stream ( 19 ) and then at least a portion of said bottoms liquid stream ( 19 ) is fractionated ( 25 ) to provide a second nitrogen-enriched overhead vapour stream ( 36 ) that is of lower purity than said first overhead vapour stream ( 46 ) and a purified liquefied natural gas stream ( 50 ). Preferably, the first fractionation is conducted in a distillation column ( 23 ) refluxed ( 45 ) with nitrogen overhead ( 43 ) condensed in a condenser ( 24 ) located in a flash drum ( 25 ) in which the second fractionation is conducted. The provision of two nitrogen-containing streams ( 26, 36 ) of different concentration permits control of the nitrogen content of fuel gas for use in the natural gas liquefaction plant.
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