Method for fractionating a stream of cracked gas, using an intermediate recirculation current, and related plant

A fractionating plant for a first stream of cracked gas coming from a hydrocarbon pyrolysis plant to obtain an ethylene-rich cut and a C2+ hydrocarbon-lean fuel stream, the fractionating plant comprising:

• a cooling and compression stage for the stream of raw cracked gas comprising at least one compressor, to form a stream of compressed cracked gas;
• an upstream cooling and partial condensation stage for an upstream stream of cracked gas, obtained from the stream of compressed cracked gas, the upstream stage comprising at least one upstream heat exchanger, and at least one upstream separator balloon for an upstream liquid to form an intermediate stream of cracked gas pre-cooled to a first temperature;
• an intermediate cooling and partial condensation stage for the intermediate stream of cracked gas, the intermediate stage comprising an intermediate heat exchanger and an intermediate separating balloon for an intermediate liquid to form a downstream stream of cracked gas cooled to a second temperature below the first temperature;
• a downstream cooling and partial condensation stage for the downstream stream of cracked gas to cool the downstream stream of cracked gas to a third temperature below the second temperature, the downstream stage comprising at least one downstream heat exchanger;
• a downstream separator and an introducer for introducing the downstream stream of partially condensed cracked gas coming from the downstream heat exchanger into the downstream separator;
• a recovery stage, at the head of the downstream separator, for recovering a gaseous stream of high-pressure fuel, lean in C2+ hydrocarbons, and recovering, at the bottom of the downstream separator, a downstream liquid, rich in C2+ hydrocarbons;
• a passage assembly for the stream of high-pressure fuel through the downstream exchanger and the intermediate exchanger to form a stream of reheated high-pressure fuel;
• at least first one dynamic expansion device for the stream of reheated high-pressure fuel to obtain a partially expanded fuel stream;
• a passage for the stream of partially expanded fuel through the downstream exchanger and the intermediate exchanger to reheat the stream of partially expanded fuel;
• a treatment stage for at least one liquid stream obtained in at least one of the upstream cooling, intermediate cooling, and downstream cooling stages to form the ethylene-rich cut;
• a former for forming an expanded intermediate recirculation stream from a liquid obtained in at least one of the upstream cooling and/or intermediate cooling stages, upstream from the downstream cooling stage;
• a circulator for circulating the intermediate recirculation stream at least in the upstream heat exchanger to cool the upstream stream of cracked gas;
• a reintroducer for reintroducing the heated intermediate recirculation stream into the raw cracked gas upstream from at least one compressor of the cooling and compression stage,
• the upstream, intermediate and downstream stages assemblies being configured to respectively cool the upstream stream of cracked gas, the intermediate stream of cracked gas and the downstream stream of cracked gas without heat exchange with an outside refrigeration cycle.