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.