Apparatus and method for purifying natural gas via cryogenic separation

Abstract

An apparatus for separating CO.sub.2 from a mixture of gases includes CO.sub.2 and a second gas, the apparatus includes an active heat exchanger and a regenerating heat exchanger. The active heat exchanger includes a heat exchange surface in contact with the mixture of gases. The mixture of gases is present in the active heat exchanger at a predetermined pressure which is chosen such that CO.sub.2 freezes on the heat exchange surface when the surface is cooled by a refrigerant having a temperature below that at which CO.sub.2 freezes at the predetermined pressure. The regenerating heat exchanger includes a heat exchange surface in contact with the refrigerant and also in contact with a layer of frozen CO.sub.2. The refrigerant enters the regenerating heat exchanger at a temperature above that at which the CO.sub.2 in the frozen layer of CO.sub.2 sublimates. The sublimation of the solid CO.sub.2 cools the refrigerant prior to the refrigerant being expanded through an expansion valve, which reduces the temperature of the refrigerant to a point below the freezing point of CO.sub.2 at the predetermined pressure. The refrigerant is re-compressed by a compressor after leaving the active heat exchanger. In the preferred embodiment of the present invention, the gaseous CO.sub.2 released by the regenerating heat exchanger is used to precool the incoming gas mixture. A second precooling heat exchanger precools the compressed refrigerant by providing thermal contact with the refrigerant leaving the active heat exchanger.

Dependencies are inferred from the claim text.