provided by warming or vaporizing any suitable process stream one alternative is for all or a portion of nitrogen reflux stream 111 to be used in this event the nitrogen stream 111 could either be warmed in which case it would have previously been cooled by heat exchange with some other sufficiently cold process stream or could be at least partially vaporized in which case stream 111 would have been previously reduced in pressure another alternative arises when pumped liquid oxygen is employed as a processing option in this event the condensed liquid air stream may be either warmed or vaporized just as previously described for nitrogen stream 111 the selection of the most preferred stream is an optimization exercise the colder the fluid used the higher the nitrogen content of the vapor purge stream and the lower the argon losses thus use of the nitrogen reflux 111 appears the best choice on the other hand this colder fluid also represents the best feed stream for reducing oxygen losses from the lower pressure column hence a trade off exists between increasing oxygen recovery and increasing argon recovery for all the embodiments described an acceptable modification is the removal of the rectifying section 177 in the side arm column the embodiments of fig1.