An air separation unit and associated method for separating air by cryogenic distillation using a distillation column system including a higher pressure column, a lower pressure column, an intermediate pressure kettle column, and an argon column arrangement is provided. The disclosed air separation unit and method is particularly suited for production of an argon product as well as several nitrogen products wherein a portion of the nitrogen overhead intermediate pressure kettle column is taken as an intermediate or elevated pressure nitrogen product. The present air separation unit and associated method employs a once-through kettle column reboiler, a once-through kettle column condenser while the argon condenser condenses an argon-rich vapor stream against a pumped oxygen stream from the bottom of the lower pressure column.