Patent ID: 7520143
Filing Date: 2009-04-21
Classification: F25J,Y10S

Abstract:
1. A method of preparing a nitrogen-freed liquefied natural gas stream comprising liquefying a nitrogen-containing natural gas, using work provided by a gas turbine, to provide a nitrogen-containing liquified natural gas stream and subjecting said liquefied gas stream to a first fractionation in a distillation column to provide a first nitrogen-enriched overhead vapor stream and a nitrogen-containing bottoms liquid stream; sub-cooling, using refrigeration duty provided by a refrigerant fluid not derived from the liquefied natural gas feed, and pressure reducing at least a portion of said bottoms liquid stream; subjecting said sub-cooled, pressure reduced portion to a second fractionation in a flash drum to provide a second nitrogen-enriched overhead vapor stream that is of lower purity than said first overhead vapor stream and a purified liquefied natural gas stream; condensing a portion of the first nitrogen-enriched overhead vapor stream in said flash drum to provide heat duty therein and produce a condensed nitrogen-enriched overhead stream; and returning at least a portion of said condensed nitrogen-enriched overhead stream as reflux to the distillation column, and the second, but not the first of said nitrogen-enriched overhead vapor streams is used as, or added to, a fuel gas used in said gas turbine providing work for use in connection with liquefaction of the natural gas feed.