System and method for introducing low pressure reflux to a high pressure column without a pump

This invention relates generally to air separation and more specifically to cryogenic air separation and nitrogen and/or oxygen production. A method and system for producing nitrogen and/or oxygen by air separation. The system includes at least one high pressure column, at least one low pressure column, and a reboiler-condenser. The method includes generating a high pressure nitrogen stream from the high pressure column and using energy from the high pressure nitrogen stream to provide nitrogen reflux to the high pressure column.