NOVELTY - The method involves cooling to-be-treated fluid (40), and separating cooled fluid (42) into carbon dioxide rich gas and carbon dioxide poor gas. A portion of the cooled fluid is cooled in a regenerative heat exchanger (112) by exchange of heat with a fraction of the carbon dioxide poor gas. The to-be-treated fluid is divided into fluid flows (140, 240). The fluid flows are respectively cooled in the regenerative exchanger and a multi fluid heat exchanger (109) to produce cooled flows. The cooled flows are joined for forming a third cooled flow.    USE - Method for producing carbon dioxide poor gas and carbon dioxide rich gas from a to-be-treated fluid containing carbon-di-oxide and a volatile compound such as methane, oxygen, argon, nitrogen, carbon monoxide, helium and/or hydrogen, in a production installation that produces electricity from carbon fuels such as coal, hydrocarbons e.g. natural gas, fuel and petroleum residues, household garbage, biomass, refinery gas, chemical plant, steel or cement plants and from exhaust gas of transport vehicles or smokes from a boiler used for heating a building.    ADVANTAGE - The method enables improving the production of carbon dioxide poor gas and carbon dioxide rich gas from the fluid containing the carbon dioxide and the volatile compound by implementing the regenerative exchangers. The method enables cooling the portion of the fluid in the regenerative exchangers by the exchange of heat with the fraction of the carbon dioxide poor gas, so as to reduce head loss and energy consumption, and to save cost.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for an installation for producing carbon dioxide poor gas and carbon dioxide rich gas from to-be-treated fluid containing carbon dioxide and a volatile compound, comprising heat exchangers.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a compression and purification unit of electricity production installation.    To-be-treated fluid (40)    Cooled fluid (42)    Carbon dioxide poor fluid (44)    Multi-fluid heat exchanger (109)    Regenerative heat exchanger (112)    Fluid flows (140, 240)