Dual column process to remove nitrogen from natural gas

摘要

Nitrogen is removed from a natural gas feed stream by a cryogenic distillation process in which said feed stream (1) is fed to a primary column (10) of a distillation column system having a primary column (10) and a secondary column (22) fed (17) from and operating at substantially the same pressure as the primary column (10); at least a portion of a primary column methane-rich bottoms liquid (14) is expanded (29,30) and at least partially vaporized in heat exchange (26) with a condensing primary column nitrogen-enriched vapor (25). The at least partially condensed primary column nitrogen-enriched vapor (24) is returned to the primary column (10) to provide higher temperature reflux to the distillation column system. A secondary column methane-rich bottoms liquid (27) is at least partially vaporized in heat exchange (18) with a condensing nitrogen-rich overhead vapor (15,16) to produce a further methane-rich product (34). At least a portion (20) of the at least partially condensed nitrogen-rich overhead vapor portion is returned to the primary or secondary column (10, 22) to provide lower temperature reflux to the distillation column system.