Air separation with medium pressure enrichment

A cryogenic air separation process is disclosed wherein the low pressure column section of a doubler is caused to operate closer to equilibrium and, hence, more efficiently by incorporating a medium pressure column which further enriches HP column enriched oxygen liquid before introduction into the LP column. The MP column is reboiled by indirect heat exchange with condensing HP column nitrogen, and is refluxed by direct injection of condensed nitrogen. A second improvement to cryogenic air separation is disclosed which can be advantageously combined with the above improvement, in which pressurized oxygen up to 10 ATA is efficiently produced from pumped LOX by using the pumped LOX to reflux an auxiliary higher pressure column in which a fraction of the supply air compressed to higher pressure is separated into liquid N2 which is subsequently used as reflux and into oxygen enriched liquid which is further separated