Process for the low-temperature separation of air in an air separation plant and air separation plant

摘要

The invention relates to a process for the separation of air (AIR), in which cooled air (AIR) at a first separation pressure is separated in a first separation column (S1) at least into a nitrogen-enriched top fraction and an oxygen-enriched bottom fraction, and in which further cooled air (AIR) in a mixing column (M) is liquefied at a mixing column pressure by means of direct heat exchange against a liquid oxygen-enriched stream, which is at least partly obtained from the oxygen-enriched bottom fraction from the first separation column (S1), to form a mixing column bottom fraction. According to the invention further cooled air (AIR) at a second separation pressure is likewise separated in a second separation column (S2) into a nitrogen-enriched top fraction and an oxygen-enriched bottom fraction, wherein the nitrogen-enriched top fraction from the second separation column (S2) is at least partly cooled by using the mixing column bottom fraction from the mixing column (M). To this end, the nitrogen-enriched top fraction from the second separation column (S2) is at least partly guided through the liquefaction chamber of a top condenser (E2) of the second separation column (S2), which is constructed as a condenser evaporator and the evaporation chamber of which is operated at an evaporation chamber pressure which lies between the mixing column pressure and a third separation pressure, at which the liquid oxygen-rich stream is obtained in a third separation column (S3), and in which at least part of the mixing column bottom fraction from the mixing column (M) is fed in in liquid form at the evaporation chamber pressure. The invention further relates to a corresponding air separation plant.