METHOD AND APPARATUS FOR REMOVING NITROGEN FROM A CRYOGENIC HYDROCARBON COMPOSITION

摘要

Nitrogen is removed from a cryogenic hydrocarbon composition comprising nitrogen and a methane-containing liquid phase. A by-product vapour from the cryogenic hydrocarbon composition, at a low pressure of between and 2 bar absolute, is compressed to a separation pressure in the range of between 2 and 15 bar absolute. The such compressed vapour is partially liquefied by heat exchanging the compressed vapour against an auxiliary refrigerant stream and thereby passing heat from the compressed vapour to the auxiliary refrigerant stream at a cooling duty. The condensed fraction of the partially liquefied compressed vapour is depressurized and at least a portion of it is reinjected into the cryogenic hydrocarbon composition. An off gas consisting of a, non condensed, vapour fraction of the partially liquefied compressed vapour is discharged from the first gas/liquid separator. The cooling duty is adjusted to regulate a heating value of the vapour fraction being discharged.