Production of nitrogen

Claim 1

A PROCESS FOR PRODUCING HIGHLY PURE NITROGEN AT A SUBSTANTIAL SUPERATMOSPHERIC PRESSURE FROM AIR WHICH HAS BEEN COMPRESSED TO ABOUT SAID SUPERATMOSPHERIC PRESSURE AND FROM WHICH CO2 AND MOISTURE HAVE BEEN REMOVED, COMPRISING THE STEPS OF: (A) COOLING SAID AIR AT ABOUT SAID SUPERATMOSPHERIC PRESSURE TO A TEMPERATURE AT WHICH A MINOR PART OF SAID AIR IS LIQUEFIED; (B) SUPPLYING THE RESULTING PARTIALLY LIQUEFIED AIR TO THE BASE OF A SINGLE FRACTIONING COLUMN HAVING A CONDENSER FOR PROVIDING REFLUX AT THE UPPER END THEREOF AND OPERATING AT ABOUT SAID SUPERATMOSPHERIC PRESSURE; (C) SEPARATING SAID SUPPLIED AIR IN SAID COLUMN INTO A HIGHLY PURE NITROGEN GAS AS OVERHEAD PRODUCT AND AN OXYGEN-ENRICHED LIQUID AIR AS BOTTOMS PRODUCT; (D) WITHDRAWING SAID OXYGEN-ENRICHED LIQUID AIR FROM THE BOTTOM OF SAID COLUMN AND EXPANDING THE SAME TO A PRESSURE INTERMEDIATE SAID SUPERATMOSPHERIC PRESSURE AND ATMOSPHERIC PRESSURE; (E) PASSING SAID EXPANDED OXYGEN-ENRICHED LIQUID AIR THROUGH SAID CONDENSER IN INDIRECT HEAT EXCHANGE WITH THE NITROGEN GAS SEPARATED IN THE UPPER END OF SAID COLUMN WHEREBY SAID OXYGEN-ENRICHED LIQUID AIR IS EVAPORATED IN SAID CONDENSER INCONDENSING NITROGEN GAS TO PROVIDE REFLUX FOR SAID COLUMN; (F) WITHDRAWING SAID EVAPORATED OXYGEN-ENRICHED LIQUID AIR FROM SAID CONDENSER AND PASSIGN THE SAME IN INDIRECT HEAT EXCHANGE WITH INCOMING AIR TO COOL SAID INCOMING AIR AND WARM SAID EVAPORATED OXYGENENRICHED LIQUID AIR; (G) THEN EXPANDING AT LEAST A PART OF SAID WARMED OXYGEN-ENRICHED AIR TO A PRESSURE CLOSE TO ATMOSPHERIC PRESSURE IN AN EXPANSION TURBINE THEREBY TO PRODUCE COLD FOR USE IN SAID PROCESS; (H) UTILIZING THE OXYGEN-ENRICHED AIR AT CLOSE TO ATMOSPHERIC PRESSURE TO COOL INCOMING AIR BY INDIRECT HEAT EXCHANGE AND THEN VENTING IT FROM THE PROCESS; (I) WITHDRAWING GASEOUS NITROGEN PRODUCT FROM THE TOP OF SAID COLUMN; (J) PASSING AT LEAST A PART OF SAID WITHDRAWN GASEOUS NITROGEN PRODUCT IN INDIRECT HEAT EXCHANGE WITH INCOMING AIR TO COL SAID INCOMING AIR; AND (K) THEN COLLECTING AT LEAST SAID PART OF SAID WITHDRAWN GASEOUS NTIROGEN PRODUCT AT SUBSTANTIALLY SAID SUPERATMOSPHERIC PRESSURE.