Patent ID: 6227005
Filing Date: 2001-05-08
Classification: F25J

Abstract:
A process for separating air to produce oxygen and nitrogen, said process using a distillation column system having at least three distillation columns, including a first distillation column, a second distillation column, and a third distillation column, wherein each distillation column has a top and a bottom, comprising the steps of:providing a stream of compressed air having a first nitrogen content;feeding at least a first portion of the stream of compressed air to the first distillation column;withdrawing a first oxygen-enriched liquid stream from the bottom of the first distillation column and feeding at least a portion of the first oxygen-enriched liquid stream to the second distillation column and/or the third distillation column;withdrawing a first oxygen-lean vapor stream from or near the top of the first distillation column, feeding at least a first portion of the first oxygen-lean vapor stream to a first reboiler-condenser of the second distillation column or of the third distillation column, and at least partially condensing the at least a first portion of the first oxygen-lean vapor stream, thereby forming a first nitrogen-enriched liquid;feeding at least a first portion of the first nitrogen-enriched liquid to the top of the first distillation column;feeding a second nitrogen-enriched liquid and/or at least a second portion of the first nitrogen-enriched liquid to the top of the second distillation column;withdrawing a second oxygen-enriched liquid stream from the bottom of the second distillation column and feeding the second oxygen-enriched liquid stream to the third distillation column;withdrawing a first nitrogen-rich vapor stream from the top of the second distillation column;withdrawing a second nitrogen-rich vapor stream from the top of the third distillation column;withdrawing a liquid oxygen stream from the bottom of the third distillation column, wherein said liquid oxygen stream is elevated in pressure before being warmed at least in part by indirect heat exchange with a pressurized stream having a nitrogen content at least equal to the first nitrogen content, said pressurized stream being cooled without being subjected to distillation; andfeeding at least a portion of the cooled pressurized stream eventually to any or all of the first distillation column, the second distillation column, or the third distillation column.