Air separation process employing work expansion of high and low pressure nitrogen

Claim 1

IN THE METHOD OF PRODUCING OXYGEN AT AN ELEVATED PRESSURE FROM FEED AIR AT A SUBSTANTIAL SUPERATMOSPHERIC PRESSURE WHEREIN THE AIR IS COOLED IN REVERSING EXCHANGERS WHICH ARE PERIODICALLY PURGED OF CARBON DIOXIDE AND MOISTURE, TO A TEMPERATURE AT WHICH A MINOR PORTION THEREOF IS LIQUEFIED, AND THE RESULTING COLD AIR IS PASSED TO THE BASE OF THE FIRST COLUMN OF A DOUBLE FRACTIONATING COLUMN, SAID FIRST COLUMN BEING MAINTAINED AT A SUBSTANTIAL SUPERATMOSPHERIC PRESSURE, AND WHEREIN OXYGEN-ENRICHED LIQUID AIR FROM THE BASE OF SAID FIRST COLUMN IS WITHDRAWN AND EXPANDED INTO AN INTERMEDIATE POINT OF THE SECOND COLUMN OF SAID DOUBLE COLUMN, SAID SECOND COLUMN BEING MAINTAINED AT A SUPERATMOSPHERIC PRESSURE BUT LESS THAN THE PRESSURE OF THE FIRST COLUMN, AND WHEREIN HIGH PRESSURE NITROGEN IS REMOVED FROM THE TOP OF SAID FIRST COLUMN; THE IMPROVEMENT WHICH COMPRISES SUPPLYING REFRIGERATION TO THE FEED AIR BY PASSING SAID HIGH PRESSURE NITROGEN IN INDIRECT HEAT EXCHANGE RELATIONSHIP WITH THE FEED AIR AND THEREAFTER EXPANDING SAID HIGH PRESSURE NITROGEN WITH WORK THROUGH A HIGH SPEED TURBINE TO A SLIGHTLY SUPERATMOSPHERIC PRESSURE AND REMOVING SAID EXPANDED NITROGEN AS A FIRST VAPOR PRODUCT, WITHDRAWING GASEOUS OXYGEN PRODUCT AT THE PRESSURE OF SAID SECOND COLUMN FROM THE LOWER END OF SAID SECOND COLUMN, PASSING SAID WITHDRAWN GASEOUS OXYGEN AND SAID EXPANDED GASEOUS HIGH PRESSURE NITROGEN PRODUCT IN INDIRECT HEAT EXCHANGE RELATIONSHIP WITH SAID FEED AIR TO COOL SAID FEED AIR IN SAID AIR COOLING STEP, AND THEREAFTER COLLECTING SAID GASEOUS OXYGEN PRODUCT AT AMBIENT TEMPERATURE AND AT SAID ELEVATED PRESSURE AS A SECOND VAPOR PRODUCT, REMOVING A NITROGEN RICH VAPOR FROM THE TOP OF THE SECOND COLUMN, EXPANDING SAID NITROGEN RICH VAPOR FROM THE SECOND COLUMN THROUGH A SECOND HIGH SPEED TURBINE DOING WORK, PASSING SAID EXPANDED NITROGEN RICH VAPOR FROM THE SECOND COLUMN IN INDIRECT HEAT EXCHANGE WITH THE OXYGEN ENRICHED LIQUID AIR TO COOL SAID OXYGEN ENRICHED LIQUID AIR, AND REMOVING SAID EXPANDED NITROGEN RICH VAPOR FROM THE SECOND COLUMN AS WASTE.