NOVELTY - The process comprises separating carbon dioxide from a crude gas by supplying to a physically active washing solution in a counter-current pressure system, dissolving biogas such as methane gas in the washing solution and regenerating the washing solution by carbon dioxide desorption, treating the washing solution in a desorption stage by stripping in a separate stripping stage (K1) using a stripping gas a to separate the carbon dioxide and to obtain completely regenerated washing solution, and supplying a gas mixture obtained in the desorption stage to a washing stage.    USE - The process is useful for separating carbon dioxide from methane-containing crude gas such as biogas.    ADVANTAGE - The process allows separation of carbon dioxide from the methane-containing crude gas with less power consumption.    DETAILED DESCRIPTION - The process comprises separating carbon dioxide from a crude gas by supplying to a physically active washing solution in a counter-current pressure system, dissolving biogas such as methane gas in the washing solution and regenerating the washing solution by carbon dioxide desorption, treating the washing solution in a desorption stage by stripping in a separate stripping stage (K1) using a stripping gas a to separate the carbon dioxide and to obtain completely regenerated washing solution, supplying a gas mixture obtained in the desorption stage to a washing stage, where a head of a wash column is configured for removing methane, and supplying the washing solution obtained in the washing stage to the separate stripping stage for separation of the carbon dioxide. The regenerated washing solution obtained in the separate stripping stage is further supplied to the two washing stages. An expansion of the washing solution is carried out in the desorption stage, and a system pressure is lowered to 0.5-5 bars. The oxygen-containing biomethane obtained in the washing stage is fed back into a fermenter, and is used for biological desulfurization of biogas produced in the fermenter. An INDEPENDENT CLAIM is included for a system for separating carbon dioxide from methane-containing crude gas.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a system for separating carbon dioxide from methane-containing crude gas.    First washing stage (K1)    Desorption stage (K2)    Second washing stage (K3)    Separate stripping stage (K4)    Second compressor. (V2)