Process for purifying gaseous streams by rectification

Claim 1

A PROCESS FOR UPGRADING A CONTAMINATED, IMPURITYCONTAINING NITROGEN GAS MIXTURE HAVING MOISTURE AND CARBON DIOXIDE CONTAMINANTS AND OXYGEN AND ARGON IMPURITIES BY LOW TEPERATURE RECTIFICATION INCLUDING THE STEPS OF PROVIDING A CONTAMINATED, IMPURE NITROGEN GAS MIXTURE STREAM AT A PRESSURE BELOW ABOUT 75 P.S.I.G.; PASSING SAID MIXTURE TO A REVERSIBLE HEAT EXCHANGE ZONE; COOLING SAID IMPURITY-CONTAINING NITROGEN GAS MIXTURE IN SAID REVERSIBLE HEAT EXCHANGE ZONE TO ABOUT ITS DEW POINT THEREBY CONDENSING SAID MOISTURE AND CARBON DIOXIDE CONTAMINANTS IN SAID REVERSIBLE HEAT EXCHANGE ZONE; WITHDRAWING THE COOLED IMPURITY-CONTAINING NITROGEN GAS MIXTURE; DI VERTING A PORTION OF SAID IMPURITY-CONTAINING NITROGEN GAS MIXTURE TO A NON-REVERSING HEAT EXCHANGE ZONE FOR FURTHER COOLING OF SAID DIVERTED PORTION; RECOMBINING SAID DIVERTED POTION WITH SAID IMPURITY-CONTAINING NITROGEN GAS MIXTURE FOR PASSAGE TO A RECIFICATION ZONE; CONTACTING THE IMPURITY-CONTAINING NITROGEN GAS MIXTURE IN SAID RECTIFICATION ZONE WITH A NITROGEN REFLUX LIQUID THEREBY TRANSFERRING SUBSTANTIALLY ALL OF THE OXYGEN AND ARGON IMPURITIES IN SAID GAS MIXTURE TO SAID REFLUX LIQUID AND PRODUCING A HIGH-PURITY NITROGEN EFFLUENT VAPOR; DIVIDING SAID HIGHPURITY NITROGEN EFFLUENT VAPOR INTO A PRODUCT STREAM AND A VAPOR STREAM; PASSING SAID HIGH-PURITY PRODUCT STREAM TO SAID NON-REVERSING HEAT EXCHANGE ZONE FOR PARTIAL WARMING; PASSING THE PARTIALLY WARMED HIGH-PURITY PRODUCT STREAM TO SAID REVERSING HEAT EXCHANGE ZONE FOR FURTHER WARMING; WITHDRAWING A PORTION OF THE FURTHER WARMED HIGH-PURITY PRODUCT STREAM FROM SAID REVERSING HEAT EXCHANGE ZONE FROM AN INTERMEDIATE THERMAL LEVEL THEREIN AND COMBINING SAID WITHDRAWN PORTION WITH SAID HIGH-PURITY VAPOR STREAM; REMOVING THE IMPURITY-CONTAINING REFLUX LIQUID FROM SAID RECTIFICATION ZONE; HEAT EXCHANGING SAID HIGH-PURITY NITROGEN VAPOR STREAM AND SAID WITHDRAWN PORTION OF THE PRODUCT STREAM WITH SAID IMPURITY-CONTAINING REFLUX LIQUID IN A CONDENSING ZONE THEREBY LIQUEFYING SAID HIGH-PURITY NITROGEN VAPOR STREAM AND SAID WITHDRAWN PORTION OF THE HIGH-PURITY PRODUCT AND EVAPORATING SAID IMPURE REFLUX LIQUID; AND RETURNING SAID LIQUEFIED HIGH-PURITY VAPOR AND WITHDRAWN PRODUCT TO SAID RECTIFICATION ZONE AS AT LEAST PART OF SAID NITROGEN REFLUX LIQUID.