NOVELTY - Carbon dioxide is separated in sewage gas compression filling system by employing the existing reciprocating sewage gas compressor, controlling temperature higher than 31.1 degrees C and partial pressure above the critical pressure of 7.38 MPa during the carbon dioxide separation period of the sewage gas filling system, cooling the carbon dioxide in the sewage gas below 31.1 degrees C, mixing with gaseous methane, separating, and putting the pure methane gas in a filling conduit for filling.    USE - Method for separating carbon dioxide in sewage gas compression filling system (claimed).    ADVANTAGE - The removal ratio of carbon dioxide can reach above 99%. The purified and compressed sewage gas can reach the quality of natural gas. Industrial carbon dioxide is provided, so that natural resource is utilized more sufficiently. The method is convenient in operation, energy-saving, and cost-reducing.    DETAILED DESCRIPTION - Separation of carbon dioxide in sewage gas compression filling system involves:    (A) employing the existing reciprocating sewage gas compressor;    (B) controlling the temperature in a fourth stage cylinder higher than the carbon dioxide critical temperature of 31.1 degrees C and controlling the partial pressure of carbon dioxide above the critical pressure of 7.38 MPa during the carbon dioxide separation period of the sewage gas filling system;    (C) discharging the pressurized sewage gas out of a four-stage cooler and entering an external cooling coil pipe device;    (D) cooling the carbon dioxide in the sewage gas below 31.1 degrees C to be liquefied;    (E) mixing with gaseous methane and entering a high pressure gas/liquid separator for gas liquid separation;    (F) introducing the separated carbon dioxide to a steel bottle and collecting; and    (G) putting the pure methane gas in a filling conduit for filling.    An INDEPENDENT CLAIM is included for a device for separating carbon dioxide in sewage gas compression filling system.    DESCRIPTION OF DRAWING(S) - The drawing is a sectional view of a device for separating carbon dioxide in sewage gas compression filling system.