Method and apparatus for argon rejection and recovery

A method of producing an impure argon-rich stream in a cryogenic air separation plant, the method comprising the steps of:

• (a) directing a flow of compressed and purified feed air into a higher pressure column configured to produce an oxygen-enriched liquid and a nitrogen-rich stream by cryogenic rectification within the higher pressure column;
• (b) withdrawing the nitrogen rich stream from the higher pressure column and directing it to a lower pressure column configured to produce an oxygen product stream and a nitrogen waste stream and optionally a nitrogen-rich product stream by cryogenic rectification within the lower pressure column;
• (c) directing an argon-oxygen containing vapor stream from the lower pressure column to an argon rectification column disposed within the lower pressure column, the argon rectification column configured to produce an impure argon-rich vapor stream having oxygen impurities and an oxygen-rich bottoms liquid by cryogenic rectification within the argon rectification column;
• (d) directing the oxygen-rich bottoms liquid from the argon rectification column to the lower pressure column;
• (e) directing a portion of the impure argon rich vapor stream to an argon condensing assembly disposed within the lower pressure column at a location above the argon rectification column;
• (f) withdrawing the oxygen-enriched liquid from the higher pressure column and directing it to the argon condensing assembly, the argon condensing assembly configured to condense the impure argon-rich vapor stream against the oxygen-enriched liquid from the higher pressure column to produce an impure argon-rich liquid stream and a partially vaporized oxygen-rich stream;
• (g) passing the partially vaporized oxygen-rich stream from the argon condensing assembly into the lower pressure column;
• and
• (h) removing an argon rejection stream consisting essentially of a portion of the impure argon-rich liquid stream from the argon condensing assembly disposed within the lower pressure column or a portion of the impure argon-rich vapor stream from the argon rectification column;
• wherein the an argon rejection stream contains between about 4% and 25% of oxygen impurities.