Patent ID: 6898949

Claim:
A method for refrigerating a pressurized liquefied natural gas, wherein the gas contains methane, C 2 and higher hydrocarbons, the method comprising: (Ia) expanding the pressurized liquefied natural gas to provide an expanded liquefied natural gas stream; (Ib) splitting the expanded liquefied natural gas stream into a relatively more volatile first top fraction and a relatively less volatile first bottom fraction comprised of refrigerated liquefied natural gas; (Ic) collecting the first bottom fraction comprised of refrigerated liquefied natural gas; (Id) heating the first top fraction, compressing the heated first top fraction by a first compression step and then cooling the compressed top fraction for providing a first fuel gas compressed fraction, and collecting the first fuel gas compressed fraction; (Ie) tapping off a second compressed fraction from the first compressed fraction, cooling the second compressed fraction and then mixing the cooled second compressed fraction with the expanded liquefied natural gas stream; (IIa) compressing the second compressed fraction in a second compression step which is coupled to an expansion turbine for providing a third compressed fraction; (IIb) cooling the third compressed fraction; splitting the third compressed fraction into a fourth compressed fraction and a fifth compressed fraction; (IIc) cooling the fourth compressed fraction and expanding the fourth compressed fraction in the expansion turbine coupled to the second compression step for providing an expanded fraction, and heating the expanded fraction; introducing the expanded fraction into a medium-pressure first stage of the first compression; and (IId) cooling the fifth compressed fraction and then mixing the cooled fifth compressed fraction with the expanded liquefied natural gas stream.