Abstract: 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.

Abstract: Method for gas liquefaction comprising cooling a feed gas by a first refrigeration system in a first heat exchange zone and withdrawing a substantially liquefied stream therefrom, further cooling the substantially liquefied stream by indirect heat exchange with one or more work-expanded refrigerant streams in a second heat exchange zone, and withdrawing therefrom a further cooled, substantially liquefied stream. At least one of the one or more work-expanded refrigerant streams is provided by compressing one or more refrigerant gases to provide a compressed refrigerant stream, cooling all or a portion of the compressed refrigerant stream in a third heat exchange zone to provide a cooled, compressed refrigerant stream, and work expanding the cooled, compressed refrigerant stream to provide one of the one or more work-expanded refrigerant streams.