Patent ID: 6257020
Filing Date: 2001-07-10
Classification: F25J

Abstract:
Process for the cryogenic separation of gas from air by air distillation in a system of columns comprising at least one column, comprising the steps of:compressing all of the air to an intermediate pressure between a medium pressure and a high pressure;compressing air from the intermediate pressure to the high pressure;dividing the compressed air at the high pressure into a first and a second fraction;cooling the first fraction in a heat exchanger and at least partly expanding the cooled first fraction in a first turboexpander to the medium pressure;cooling the second fraction in the heat exchanger and at least partly expanding the cooled second fraction to the intermediate pressure in a second turboexpander;warming at least one portion of the expanded part of the second fraction in the heat exchanger and recycling at least one part thereof into the air stream at the intermediate pressure;sending the first fraction of air at the medium pressure to a first column, where it becomes enriched with nitrogen at the top of the column and enriched with oxygen at the bottom; andwithdrawing a liquid from one column of the system and vaporizing the liquid at the cold end of the heat exchanger,wherein the feed pressure of the first turboexpander is not less than the feed pressure of the second turboexpander.