Method for separating off acid gases from natural gas

A method for separating off acid gases comprising CO2 from a hydrocarbon-rich fraction, said method comprising:

• cooling and partially condensing (E1-E4) said hydrocarbon-rich fraction to a temperature of at least −45° C. but not below a temperature of −55° C. by a closed multistage refrigeration circuit in which a refrigerant is circulated, said refrigerant having a CO2 fraction of greater than 99.5% by volume,
• wherein, after each stage of the multi-stage heat exchanger, a gaseous refrigerant fraction is fed back to a compressor unit of said refrigeration cycle, and, after each stage of the multi-stage heat exchanger except for the last stage, a liquid refrigerant fraction is fed to the next stage of the multi-stage heat exchanger;
• separating (D1) the partially condensed hydrocarbon-rich fraction into a CO2-depleted gas fraction (3) and a CO2-enriched liquid fraction (5),
• separating the CO2-enriched liquid fraction (5) in a rectification column into a further CO2-depleted gas fraction (6) and a further CO2-rich liquid fraction (7), wherein said rectification column is operated at a pressure between 40 and 65 bar, and
• heating a reboiler of said rectification column by a condensing refrigerant substream of the refrigeration circuit that is at a pressure which is between 1 and 15 bar above the operating pressure;
• wherein said multi-stage heat exchanger has four stages, said condensing refrigerant substream of the refrigeration circuit which is used to heat said reboiler of the rectification column is removed from the reboiler and combined with the liquid refrigerant fraction removed from the first stage of the multi-stage heat exchanger and then fed to the next stage of the multi-stage heat exchanger, said CO2-reduced gas fraction is warmed in a heat exchanger against a substream of said hydrocarbon-rich fraction, and said substream of said hydrocarbon-rich fraction is thereafter combined with the hydrocarbon-rich fraction at a point between the third and fourth stages of said multi-stage heat exchanger, and the CO2 depleted gas fraction from said rectification column is combined with the hydrocarbon-rich fraction at a point between the third and fourth stages of said multi-stage heat exchanger.