Separation of air

Claim 1

A PROCESS FOR THE LOW TEMPERATURE SEPARATION OF AIR TO PRODUCE AT LEAST THE MAJOR PART OF THE OXYGEN PRODUCT AS A COMPRESSED GASEOUS OXYGEN FRACTION AND A PART OF THE NITROGEN PRODUCT AS A DRY GASEOUS NITROGEN FRACTION UNCONTAMINATED BY CARBON DIOXIDE, COMPRISING THE STEPS OF COMPRESSING THE AIR TO A RELATIVELY LOW PRESSURE, DIVIDING THE COMPRESSED AIR INTO TWO STREAMS, NAMELY A MAJOR STREAM AND A MINOR STREAM, COOLING SAID MAJOR STREAM WITH REMOVAL OF CONDENSIBLE IMPURITIES BY HEAT EXCHANGE WITH A FIRST COLD GASEOUS NITROGEN FRACTION OF A MASS FLOW GREATER THAN THAT OF SAID MAJOR STREAM IN A REVERSING HEAT EXCHANNGE ZONE, FURTHER COMPRISING SAID MINOR STREAM TO A SUBSTANTIALLY HIGHER PRESSURE WITH REMOVAL OF CONDENSIBLE IMPURITIES THEREFROM, DIVIDING SAID FURTHER COMPRESSED MINOR STREAM INTO A FIRST AND A SECOND SUB-STREAM, BOTH AT SAID SUBSTANTIALLY HIGHER PRESSURE, COOLING SAID FIRST SUB-STREAM BY HEAT EXCHANGE WITH A PRESSURIZED LIQUID OXYGEN FRACTION WITH STIMULATEOUS VAPORISATION OF SAID LIQUID OXYGEN FRACTION TO PRODUCE A COMPRESSED GASEOUS OXYGEN FRACTION, COOLING SAID SECOND SUB-STREAM BY HEAT EXCHANGE WITH A SECOND COLD GASEOUS NITROGEN FRACTION, WITHDRAWING SAID SECOND GASEOUS NITROGEN FRACTION AFTER SUCH HEAT EXCHANGE AS A DRY GASEOUS NITROGEN PRODUCT UNCONTAMINATED BY CARBON DIOXIDE, DIVIDING FROM SAID COOLED SECOND SUB-STREAM A THIRD SUB-STREAM EXPANDING SAID THIRD SUB-STREAM WITH THE PERFORMANCE OF EXTERNAL WORK, AND COMBINING SAID EXPANDED THIRD SUB-STREAM WITH THE MAJOR STREAM LEAVING SAID REVERSING HEAT EXCHANGE ZONE, FURTHER COOLING THE REMAINDER OF SAID SECOND SUBSTREAM BY HEAT EXCHANGE WITH SAID SECOND GASEOUS NITROGEN FRACTION, EXPANDING SAID FIRST SUB-STREAM AND THE REMAINDER OF SAID SECOND SUB-STREAM AND SAID COMBINED MAJOR STREAM AND THIRD SUB-STREAM AND SAID EXPANDED FIRST AND SECOND SUB-STREAMS TO RECTIFICATION IN A RECTIFICATION ZONE, WITHDRAWING A LIQUID OXYGEN FRACTION FROM SAID RECTIFICATION ZONE AND PUMPING AT LEAST A MAJOR PART OF SAID LIQUID OXYGEN FRACTION UNDER PRESSURE TO PROVIDE SAID PRESSURIZED OXYGEN LIQUID OXYGEN FRACTION VAPORIZED BY HEAT EXCHANGE WITH SAID FIRST SUB-STREAM.