Nitrogen removal from natural gas

Claim 1

THE PROCESS THAT INCLUDES COOLING A FEED STREAM OF COMPRESSED NATURAL OR OTHER GAS CONTAINING METHANE AND NITROGEN IN A REFRIGERATION ZONE BELOW THE BOILING TEMPERATURE OF METHANE, PASSING AND EXPENDING THE COOLED EFFLUENT FROM SAID ZONE INTO A SEPARATING ZONE, WITHDRAWING LIQUID METHANE FROM SAID SEPARATING ZONE AND FURTHER COOLING THE WITHDRAWN METHANE, WITHDRAWING FROM THE LAST MENTIONED ZONE A SEPARATED NITROGEN AND METHANE GAS STREAM, COMPRESSING AND RETURNING A PORTION OF SAID SEPARATED GAS STREAM TO THE FEED STREAM IN SAID REFRIGERATION ZONE THROUGH PASSAGE MEANS LEADING FROM THE SEPARATING ZONE TO THE REFRIGERATION ZONE, PASSING THE REMAINDER OF SAID GAS STREAM AT REDUCED PRESSURE INTO A COOLING AND EXPANSION ZONE WHEREIN THE COMPONENTS OF SAID GAS STREAM EXIT AS NITROGEN-METHANE GAS AND ESSENTIALLY METHANE CONDENSATE, COOLING SAID SEPARATED GAS STREAM GOING TO SAID COOLING AND EXPANSION ZONE BY PASSAGE THROUGH AN EXCHANGE ZONE, SEPARATELY WITHDRAWING METHANE CONDENSATE AND NITROGEN-METHANE GAS FROM SAID COOLING AND EXPANSION ZONE, REMOVING A STREAM OF THE WITHDRAWN NITROGEN-METHANE GAS AS PURGE GAS FROM THE SYSTEM, AND VARIABLY RESTRICTING THE LAST MENTIONED STREAM TO IMPOSE BACK PRESSURE IN SAID COOLING AND EXPANSION ZONE VARYING IN ACCORDANCE WITH VARIATIONS IN SAID RESTRICTION OF THE LAST MENTIONED STREAM TO THEREBY VARY METHANE VAPORIZATION IN THE COOLING AND EXPANSION ZONE AND THEREBY THE METHANE CONTENT IN THE PURGE GAS STREAM.