A system and method for separating air in an air separation plant is provided. The disclosed systems and methods divert a portion of the compressed, purified air stream to a bypass system configured to selectively produce a higher pressure compressed output stream or a lower pressure compressed output stream. The higher pressure and/or lower pressure compressed output streams are cooled in a main heat exchanger by indirect heat transfer with a plurality of product streams from the air separation plant and then rectified in the distillation column system. A second portion of the compressed, purified air stream is partially cooled in the main heat exchanger and expanding in a turbo-expander to produce power and an exhaust stream which is directed to the distillation column system of the air separation plant where it imparts additional refrigeration generated by the expansion of the compressed air stream in the turbo-expander.

An apparatus for the production of low pressure gaseous oxygen includes a heat exchanger and a system of columns comprised of an auxiliary column, a higher pressure column and a lower pressure column. The LP column and the HP column are thermally integrated via a top reboiler/condenser disposed on top of the HP column. The system of columns is configured to separate a cooled air stream into oxygen and nitrogen. The auxiliary column comprises a distillation section and a first and second reboiler. One of the reboilers is driven by the cooled air stream and the other reboiler is driven by a pressurized nitrogen stream. The first and second reboilers boil their fluids at the same pressure as the auxiliary column.

A method for the production of low pressure gaseous oxygen includes providing a system of distillation columns and a heat exchanger, wherein the system of columns comprises a lower pressure column, a higher pressure column, an auxiliary column, the auxiliary column having a distillation section, a first reboiler, and a second reboiler, wherein the LP column and the HP column are thermally integrated via a top reboiler/condenser disposed on top of the HP column. A cooled air stream is rectified within the system of columns such that the auxiliary column produces a cold oxygen fluid that is then warmed in the heat exchanger to produce a low pressure oxygen product. The cooled air stream provides reboiling duty for the first reboiler prior to rectification within the system of columns, and a compressed nitrogen stream received from a cold end of the heat exchanger provides reboiling duty for the second reboiler.