Process for producing oxygen

Claim 1

A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR, WHICH COMPRISES PASSING A STREAM OF RECTIFICATION PRODUCT THROUGH A PATH IN A HEAT EXCHANGE ZONE, PASSING A STREAM OF AIR THROUGH ANOTHER PATH IN SAID HEAT EXCHANGE ZONE, COOLING THE AIR TO A TEMPERATURE CLOSE TO ITS CONDENSATION POINT AT THE PRESSURE PREVAILING IN THE AIR FLOW PATH IN SAID HEAT EXCHANGE ZONE AND EFFECTING SUBSTANTIALLY COMPLETE REMOVAL OF CARBON DIOXIDE FROM THE AIR IN ITS PASSAGE THROUGH SAID HEAT EXCHANGE ZONE, SUBJECTING THE THUS COOLED AIR TO RECTIFICATION TO PRODUCE SAID RECTIFICATION PRODUCT STREAM, PERIODICALLY REVERSING THE FLOW OF THE AIR STREAM AND THE SAID RECTIFICATION PRODUCT STREAM THROUGH THEIR RESPECTIVE FLOW PATHS IN SAID ZONE, PASSING A SECOND STREAM OF RECTIFICATION PRODUCT THROUGH A PATH EXTENDING THROUGH AT LEAST THE COLDER END OF SAID HEAT EXCHANGE ZONE IN HEAT EXCHANGE RELATION WITH THE AIR AND THE FIRST-MENTIONED STREAM OF RECTIFICATION PRODUCT PASSING THERETHROUGH, RECIRCULATING A PORTION OF SAID SECOND STREAM OF RECTIFICATION PRODUCT LEAVING SAID LASTMENTIONED PATH THROUGH SAID LAST-MENTIONED PATH, AND WITHDRAWING A PORTION OF THE RECIRCULATED STREAM OF RECTIFICATION PRODUCT AS PRODUCT UNCONTAMINATED BY CARBON DIOXIDE REMOVED FROM THE AIR STREAM.