Patent ID: 7152429

Claim:
A method of separating a dry feed gas, which mainly includes methane, ethane and propane, into a first, relatively more volatile treated gas, and into a second, relatively less volatile product, called C2 plus fraction, said method comprising: (i) cooling said dry feed gas, for turning said dry feed gas into a cooled gas; (ii) separating and treating said cooled gas produced by said cooling step, by separating said cooled gas into a first, essentially liquid, bottom stream and a first, essentially gaseous, top stream; then at least partially expanding said first bottom stream in order to form a first cooled bottom stream; and separating said first top stream into a main stream and a secondary stream, expanding said main stream in a turbine in order to form an expanded main stream, and cooling said secondary stream in an exchanger and then expanding said secondary stream in order to form an expanded secondary stream; and (iii) producing in a distillation device a second top stream and a second bottom stream, feeding said distillation device by at least part of said expanded main stream, by at least part of said first cooled bottom stream, and by at least part of said expanded secondary stream wherein said distillation device comprises a first distillation column operating at pressure P 1 ; said first cooled bottom stream being at a relatively less cold temperature than said expanded main stream and said expanded secondary stream being at a relatively colder temperature than said expanded main stream; said second top stream cooling said secondary stream in said exchanger and then, after reheating and a plurality of compression and cooling stages, forming said first product; said second bottom stream, after compression and reheating, forming said second product; wherein said distillation device further comprises at least a second distillation column operating at pressure P 2 , a difference between P 1 and P 2 being between 5 and 25 bar; wherein said second distillation column produces a fourth top stream and a fourth bottom stream, said fourth bottom stream forming the said second bottom stream produced by said distillation device, at least part of said fourth top stream feeding, after compression and at least partial liquefaction, a top stage of said first distillation column; and wherein said first distillation column produces a third top stream and a third bottom stream, said third top stream forming said second top stream produced by said distillation device, said first distillation column being fed at a lower stage by at least part of said expanded main stream and at an intermediary stage by at least part of said expanded secondary stream.