Patent ID: 7155931

Claim:
In a process for the separation of liquefied natural gas containing methane and heavier hydrocarbon components, in which process (a) said liquefied natural gas stream is supplied to a fractionation column in one or more feed streams; and (b) said liquefied natural gas is fractionated into a more volatile fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said heavier hydrocarbon components; the improvement wherein (1) a distillation stream is withdrawn from an upper region of said fractionation column, is cooled sufficiently to partially condense it, and is thereafter separated to form said more volatile fraction containing a major portion of said methane and a reflux stream; (2) said reflux stream is supplied to said fractionation column at a top column feed position; (3) said liquefied natural gas stream is heated to supply at least a portion of said cooling of said distillation stream and thereafter divided into at least a first stream and a second stream; (4) said first stream is supplied to said fractionation column at an upper mid-column feed position; (5) said second stream is heated sufficiently to vaporize at least a portion of it and thereafter supplied to said fractionation column at a lower mid-colunm feed position; and (6) the quantity and temperature of said reflux stream and the temperatures of said feeds to said fractionation column are effective to maintain the overhead temperature of said fractionation colunm at a temperature whereby the major portion of said heavier hydrocarbon components is recovered in said relatively less volatile fraction.