| abstract |
For the method, air (103, 104) is fractionated in a medium-pressure column (6) and a low-pressure column (5). The sump heating (3) of the low-pressure column (5) is carried out with a second airflow (204), which is liquefied at the same time. An intermediate fraction (18) is taken from the low-pressure column (5) and evaporated in the head condenser (10) of the medium-pressure column (6). The thereby resulting vapor (19) is returned to the low-pressure column. In the event that impure oxygen is obtained, the second airflow (203, 204) is recompressed (202) upstream from the sump heating (3), external energy being supplied, to a pressure above that of the medium-pressure column, the pressure being relieved downstream from the sump heating (3) in a first pressure relief valve (208) to the pressure of the medium-pressure column (6). If pure oxygen is recovered, the sump heating of the low-pressure column is operated with an airflow, which at the same time is condensed at least partially and is under a pressure, which is less than the pressure of the medium-pressure column. If oxygen of high and low purity is to be recovered, a portion of the evaporated first intermediate fraction and/or a fraction obtained below the second intermediate site are recovered from the low-pressure column as oxygen product of lower purity. |