For obtaining gaseous nitrogen by low-temperature separation from air, a distillation column system has a single column (4). Compressed air (1) is cooled in a main heat exchanger (2) and fed (3) to single column (4). A nitrogen-rich fraction (5, 7, 8) is drawn off from the distillation column system and compressed at least in part in a circulation compressor (9, 1063). A first part (12, 13) of nitrogen-rich fraction (5, 7, 8) is fed downstream from circulation compressor (9) to the liquefaction chamber of a condenser-evaporator (14) and is condensed under a pressure higher than the operating pressure of single column (4), so to form nitrogen-rich liquid (15, 16). A liquid oxygen-enriched fraction (231) from the distillation column system is at least partially evaporated in the evaporation chamber of condenser-evaporator (14). A first oxygen-enriched gas (234, 533) formed in the evaporation chamber of condenser-evaporator (14), is introduced into single column (4). A second portion (19, 20, 1064) of the nitrogen-rich fraction (5, 7, 8) is drawn off at least at times as gaseous nitrogen product. A second oxygen-enriched gas (221, 521) is removed from the evaporation chamber of condenser-evaporator (14), work expanded (23), and heated in main heat exchanger (2).