Separation of air into nitrogen

Claim 1

AN AIR RECTIFICATION PROCESS HIGHLY EFFECTIVE FOR THE PRODUCTION OF RELATIVELY HIGH PROPORTIONS OF LIQUID NITROGEN AND HIGH ARGON RECOVERY, COMPRISING THE STEPS OF SEPARATING AN AIR FEED STREAM IN A FIRST STAGE RECTIFICATION COLUMN INTO A NITROGEN-RICH FRACTION, AVAILABLE AS A RELATIVELY PURE NITROGEN LIQUID PRODUCT AND AS LIQUID REFLUX FOR A SECOND STAGE RECTIFICATION COLUMN, AND AN OXYGEN-AARGONRICH LIQUID FRACTION, WITHDRAWING SAID OXYGEN-ARGON-RICH LIQUID FRACTION FROM SAID FIRST COLUMN, AT LEAST PARTIALLY VAPORIZING SAID WITHDRAWN OXYGEN-ARGON-RICH LIQUID FRACTION, DELIVERING AT LEAST A PORTION OF SAID PARTIALLY VAPORIZED OXYGEN-ARGON-RICH FRACTION AS FEED TO SAID SECOND STAGE RECTIFICATION AT AN INTERMEDIATE POINT BELOW THE TOP OF SAID SECOND STAGE RECTIFICATION COLUMN, WITHDRAWING A PORTION OF SAID NITROGEN-RICH FRACTION AS LIQUID NITROGEN PRODUCT, AND EXCLUDING A PORTION OF THE VAPOR PHASE OF SAID PARTIALLY VAPORIZED OXYGEN-ARGON-RICH FEED FROM ANY CONTACT IN ANY OF ITS PHASES WITH SAID LIQUID REFLUX IN A ZONE OF SAID SECOND STEP RECTIFICATION COLUMN ABOVE SAID DELIVERY POINT OF THE SAID OXYGEN-ARGON-RICH FEED AND BELOW THE INPUT OF A NITROGEN-RICH LIQUID FRACTION, THEREBY MAINTAINING A DESIRED BALANCE OF LIQUID REFLUX TO RISING VAPOR IN SAID ZONE OF THE SECOND STAGE RECTIFICATION COLUMN, WHEREBY A DESIRED HIGH RECOVERY OF ARGON IS EFFECTED TOGETHER WITH SUBSTANTIAL PRODUCTION AND WITHDRAWAL OF LIQUID NITROGEN, AND REMOVING AN ARGON ENRICHED FRACTION FROM SAID SECOND STAGE RECTIFICATION COLUMN FOR FURTHER PURIFICATION.