Enhancements to a dual column, nitrogen producing cryogenic air separation unit with waste expansion are provided. Such enhancements include an improved air separation unit arrangement that uses: (i) three condenser-reboilers; (ii) a reverse reflux stream from the condenser-reboiler associated with the lower pressure column to the higher pressure column; (iii) a waste expansion cycle, and (iv) a recycle stream of a portion of the boil off vapor from one or more of the condenser-reboilers. The improved air separation cycle minimizes the backpressure of the lower pressure column and yields improvements in the nitrogen recovery as well as reductions in unit power consumption compared to conventional dual column, nitrogen producing cryogenic air separation units employing waste expansion.

A distillation column system and a plant are for production of oxygen by cryogenic fractionation of air. The distillation column system has a high-pressure column and a low-pressure column, a main condenser, and an argon column with an argon column top condenser. The low-pressure column comprises an upper mass transfer region, a lower mass transfer region and a middle mass transfer region. The argon column top condenser is arranged within the low-pressure column between the upper and middle mass transfer regions and is configured as a forced-flow evaporator.

A distillation column system and a plant are for production of oxygen by cryogenic fractionation of air. The distillation column system has a high-pressure column and a low-pressure column, a main condenser, and an argon column with an argon column top condenser. The low-pressure column comprises an upper mass transfer region, a lower mass transfer region and a middle mass transfer region. The argon column top condenser is arranged within the low-pressure column between the upper and middle mass transfer regions and is configured as a forced-flow evaporator.