Separation and purification system and method for carbon dioxide-containing produced gas in oil field

The invention discloses a separation and purification system and method for oilfield produced gas containing carbon dioxide, and belongs to the field of oilfield produced gas recovery, the system comprises a compressor, a desulfurizer, a dryer, a precooler, a dealkylation tower, a multi-stage alkane separation and purification tower, a condenser, a multi-stage carbon dioxide purification tower, a subcooler and a pressure swing adsorber; the method comprises the following steps: compressing, desulfurizing and drying produced gas rich in carbon dioxide and separated from oil extraction in an oil field, feeding into a precooler for cooling, then feeding into a dealkylation tower, and feeding the removed hydrocarbon into a multi-stage alkane separation and purification tower to obtain high-purity light components and heavy components. Carbon dioxide liquid obtained through multi-stage rectification of gas from the dealkylation tower can be reinjected into an oil field for oil displacement, carbon dioxide is remov