A method for producing a C3+ hydrocarbon-rich cut and a methane- and ethane-rich stream, from a feed stream containing hydrocarbons, the method comprising the following steps:
- partially cooling and condensing a first fraction of the feed stream in a first heat exchanger;
- injecting the first cooled fraction into a first separating flask to form a first gas headstream and a first liquid bottoms stream;
- injecting at least part of the first headstream into a first dynamic expansion turbine;
- forming a first feed stream of a first column from the first expanded fraction coming from the first dynamic expansion turbine and injecting the first feed stream into the lower part of a first column to recover a first headstream and a first bottoms stream;
- heating at least part of the first headstream in a second heat exchanger, then in the first heat exchanger, and compressing at least part of the heated headstream in a first compressor coupled to the first turbine, then in a second compressor to form the methane- and ethane-rich stream;
- injecting the first bottoms stream into a second fractionating column to recover a second headstream and a second bottoms stream;
- forming the C3+ hydrocarbon-rich cut from the second bottoms stream;
- at least partially cooling and condensing the second headstream, advantageously in the first heat exchanger, and injecting the second partially condensed headstream into a head separating flask to form a second gas headstream and a second liquid bottoms stream;
- injecting the second liquid bottoms stream in reflux into the second fractionating column;
- at least partially cooling and condensing the second gas headstream, advantageously in the second heat exchanger;
- expanding the second partially condensed headstream and injecting into the first column;
- injecting at least part of the first bottoms stream into the first column and/or into the second fractionating column;
- separating the feed stream into the first fraction of the feed stream and a second fraction of the feed stream;
- injecting at least part of the second fraction of the feed stream into a second dynamic expansion turbine to form a second expanded fraction;
- cooling at least part of the second expanded fraction by heat exchange with at least part of the first headstream coming from the first column;
- forming a second feed stream of the first column from the second cooled expanded fraction;
- and
- injecting the second feed stream into the first column.