Process for manufacturing liquefied methane

A liquefaction process for liquefying a natural gas feed stream comprising the steps of:

• a. supplying said natural gas feed stream at a pressure at or above 860 psia,
• b. cooling said feed stream in a plurality of heat exchange zones in indirect heat exchange with a refrigerant in a separate, closed loop refrigeration system,
• c. isentropically expanding said feed stream to a first pressure which is below the critical pressures of both the overhead and bottom streams found in subsequent step (d) and thereby obtaining mechanical energy,
• d. fractionating the expanded feed stream in a scrub column to form an overhead stream rich in methane and a bottom stream rich in heavy hydrocarbons,
• e. cooling and partially condensing said overhead stream in indirect heat exchange with a multi-component refrigerant in a separate, closed loop refrigeration system,
• f. phase separating said partially condensed overhead stream into a liquid fraction rich in heavy hydrocarbons and a methane-rich vapor stream,
• g. supplying said liquid fraction to said scrub column as reflux,
• h. supplying said methane-rich vapor stream at a temperature below -100.degree. F directly to a compressor, and compressing said stream to a pressure of at least 680 psia to form a high pressure methane-rich stream using the mechanical energy recovered in step (c),
• i. supplying said high pressure methane-rich stream to a heat exchange zone,
• j. cooling, liquefying and sub-cooling said high pressure methane-rich stream in said cooling zone in indirect heat exchange with said same multi-component refrigerant recited in clause (e), and
• k. withdrawing said liquefied and sub-cooled methane stream as an LNG product stream.