A method for producing a methane-rich stream and a C2+ hydrocarbon-rich fraction from a dehydrated feed natural-gas stream, consisting of hydrocarbons, nitrogen and of CO2, having a C2+ hydrocarbon molar content of more than 10%, the method comprising:
- cooling the feed natural-gas stream at a pressure of more than 40 bars in a first heat exchanger, and introducing the cooled feed natural-gas stream into a separator flask;
- separating the cooled natural gas stream in the separator flask and recovering a gaseous light fraction and a liquid heavy fraction;
- forming a turbine input flow from the light fraction;
- dynamically expanding the turbine input flow in a first expansion turbine, and introducing the expanded flow into an intermediate portion of a splitter column;
- expanding the heavy fraction and introducing the heavy fraction into the splitter column, the heavy fraction recovered in the separator flask being introduced into the splitter column without passing through the first heat exchanger;
- recovering, at the foot of the splitter column, a C2+ hydrocarbon-rich bottom stream to form the C2+ hydrocarbon-rich fraction;
- taking at the head of the splitter column a methane-rich head stream;
- heating up the methane-rich head stream in a second heat exchanger and in the first heat exchanger to form a heated methane-rich head stream and compressing the heated methane-rich head stream in at least one first compressor coupled with the first expansion turbine and in a second compressor in order to form a compressed methane-rich head stream, the methane-rich stream being formed from the compressed methane-rich head stream;
- taking from the methane-rich head stream a first recirculation stream;
- passing the first recirculation stream into the first heat exchanger and into the second heat exchanger in order to cool down the first recirculation stream, and then introducing at least one first portion of the cooled recirculation stream into the upper portion of the splitter column;
- forming at least one second recirculation stream obtained from the methane-rich head stream downstream from the splitter column;
- forming a dynamic expansion stream from the second recirculation stream and introducing the dynamic expansion stream into the first dynamic expansion turbine or into a second expansion turbine in order to produce frigories;
- and
- introducing the frigories into the separation column,
- wherein the second recirculation stream is mixed with the cooled feed natural-gas stream before the cooled feed natural-gas stream is introduced into the separator flask, the dynamic expansion stream being formed by the turbine input flow formed from the separator flask.