Patent ID: 6945075

Claim:
In a process for liquefying a natural gas stream containing methane and heavier hydrocarbon components wherein (a) said natural gas stream is cooled under pressure to condense at least a portion of it and form a condensed stream; and (b) said condensed stream is expanded to lower pressure to form said liquefied natural gas stream; the improvement wherein (1) said natural gas stream is treated in one or more cooling steps; (2) said cooled natural gas stream is divided into at least a first gaseous stream and a second gaseous stream; (3) said first gaseous stream is cooled to condense substantially all of it and thereafter expanded to an intermediate pressure; (4) said expanded substantially condensed first gaseous stream is directed in heat exchange relation with a more volatile vapor distillation stream which rises from fractionation stages of a distillation column and is thereby warmed; (5) said second gaseous stream is expanded to said intermediate pressure; (6) said warmed expanded first gaseous stream and said expanded second gaseous stream are directed into said distillation column wherein said streams are separated into said more volatile vapor distillation stream and a relatively less volatile fraction containing a major portion of said heavier hydrocarbon components; (7) said more volatile vapor distillation stream is cooled by said expanded substantially condensed first gaseous stream sufficiently to partially condense it and is thereafter separated to form a volatile residue gas fraction containing a major portion of said methane and lighter components and a reflux stream; (8) said reflux stream is directed into said distillation column as a top feed thereto; and (9) said volatile residue gas fraction is cooled under pressure to condense at least a portion of it and form thereby said condensed stream.