Process and apparatus for separating gas mixtures

Claim 1

IN A CYCLE FOR THE LOW TEMPERATURE SEPARATION OF AIR TO PRODUCE OXYGEN OF SUBSTANTIAL PURITY BY PARTIAL LIQUEFRACTION OF COMPRESSED AIR AND LOW TEMPERATURE RECTIFICATION OF LIQUID AND VAPOR FRACTIONS OF THE AIR IN STAGES INCLUDING A STAGE OF RECTIFICATION AT LOW PRESSURE WHEREIN AN UPPER EFFUENT COMPRISING MAINLY NITROGEN AND A LOWER PRODUCT OXYGEN IS PRODUCED, THE IMPROVEMENTS COMPRISING COMPRESSING THE AIR TO BE SEPARATED TO ONLY THAT SUPPLY PRESSURE AT WHICH IT, AFTER COOLING, WILL PARTIALLY CONDENSE BY HEAT EXCHANGE AGAINST BOILING LIQUID PRODUCT OXYGEN OF THE LOW PRESSURE RECTIFICATION, EFFECTING SUCH PARTIAL CONDENSATION OF THE AIR, EXPANDING THE RESULTANT GAS FRACTION AND AT LEAST PART OF THE RESULTANT LIQUID FRACTION TO AN INTERMEDIATE PRESSURE BETWEEN THE SUPPLY PRESSURE AND SAID LOW PRESSURE, EFFECTING A SEPARATION AT INTERMEDIATE PRESSURE OF THE EXPANDED VAPOR FRACTION TO PRODUCE AN INTERMEDIATE NITROGEN PRODUCT, EFFECTING CONDENSATION OF THE INTERMEDIATE NITROGEN PRODUCT BY HEAT EXCHANGE AGAINST A PORTION OF SAID LIQUID FRACTION AFTER EXPANSION OF SAME TO SAID LOW PRESSURE, AND UTILIZING AT LEAST PART OF SUCH CONDENSED NITROGEN FOR TOP REFLUX FEED TO SAID LOW PRESSURE RECTIFICATION.