High-pressure gas fractionating process and system

A system for performing fractionation of a gas comprising constituents referred to as light constituents and constituents referred to as heavy constituents, comprising in combination:

• gas refrigeration means and a separation device, at the outlet of which a first gas phase and a first liquid phase are obtained,
• first expansion means for expanding said first gas phase, at the outlet of which a first mixed phase at a temperature T2 is obtained, said first expansion means being connected by a line to a heat exchange and distillation device allowing to perform heat exchange and distillation, said first mixed phase circulating through a first pass,
• first separation means for separating the first mixed phase after passage through the heat exchange and distillation device,
• second expansion means for expanding the first liquid phase, said second expansion means being connected to the separation means, in order to obtain a gas phase mixed with the gas phase resulting from separation of the mixed phase, all of the gas phases circulating through a second pass P2, the gas phases in the first and second passes circulating in a countercurrent flow,
• a discharge line intended for the liquid phases obtained by separation in the separation means
• at least one discharge line intended for the higher constituents in the gas form, obtained by heat exchange and distillation in the heat exchange and distillation device.