Method and installation for low temperature separation of air

An air separating installation comprising:

• a distillation column system (100) that has a first separating unit (110), a second separating unit (120), a third separating unit (130), and a fourth separating unit (140), wherein the air separating installation is set up to feed compressed and cooled air into the first separating unit (110), to operate the first separating unit (110) at a first pressure level of 4 to 9 bar of absolute pressure, to operate the second separating unit (120), the third separating unit (130), and the fourth separating unit (140) at a second pressure level of 1 to 3 bar of absolute pressure, to form an oxygen-enriched, nitrogen-depleted, argon-containing first sump liquid and a nitrogen-enriched, oxygen-depleted first head gas by means of the first separating unit (110), to transfer the first sump liquid partially or completely into the fourth separating unit (140), to partially or completely liquefy the first head gas and to return it to the first separating unit (110), to form an oxygen-rich second sump liquid and an argon-enriched second head gas by means of the second separating unit (120), to transfer a first fraction of the second head gas into the third separating unit (130) and a second fraction of the second head gas into the fourth separating unit (140), to partially or completely separate off the argon which is contained in a quantity of air supplied overall to the distillation column system (100) by means of the third separating unit (130), to provide a liquid return flow to the second separating unit (120) by means of the third separating unit (130), to form a fourth sump liquid and a fourth head gas by means of the fourth separating unit (140), and to return the fourth sump liquid at least partially to the second separating unit (120), wherein the second separating unit (120) has 10 to 50 theoretical plates, the third separating unit (130) has 10 to 60 theoretical plates, that the third separating unit (130) is arranged above the second separating unit (120), that the fourth separating unit (140) is arranged adjacent to the first separating unit (110), and that the third separating unit (130) opens in a lower region with respect to an upper region of the second separating unit (120), or the third separating unit (130) is connected to the second separating unit (120) via pipelines which run between an upper region of the second separating unit (120) and a lower region of the third separating unit (130).