An improved process for liquid nitrogen production by cryogenic air separation using a distillation column system to enhance the product recovery.

A method for low-temperature air separation, in which an air-separation system having a column system is used that has a first column, a second column, a third column, and a fourth column, wherein fluid from the first column is fed at least into the second column, fluid from the second column is fed at least into the third column, fluid from the third column is fed at least into the fourth column, and fluid from the fourth column is fed at least into the third column, and wherein the fluid fed from the third column into the fourth column includes at least a portion of a side flow, which is withdrawn from the third column and has a lower oxygen content and a higher argon content than the third sump liquid. The present invention also relates to a corresponding system.

The invention relates to a method for a low-temperature air separation in which an air separation unit is used comprising a first rectification column and a second rectification column. The first rectification column is operated at a first pressure level, and the second rectification column is operated at a second pressure level below the first pressure level. Fluid which is oxygen-enriched compared to atmospheric air is drawn from the first rectification column in the form of one or more first material flows. At least one fraction of the fluid which has been drawn from the first rectification column in the form of the one or more first material flows is heated in a heat exchanger; a fraction of the fluid which has been heated in the heat exchanger is compressed using a compressor and is returned to the first rectification column.

Enhancements to a dual column, nitrogen producing cryogenic air separation unit are provided. Such enhancements include an improved air separation cycle that uses multiple condenser-reboilers and recycles a portion of the vapor from one or more of the condenser-reboilers to the incoming feed stream and or the compressed purified air streams to yield improvements in such dual column, nitrogen producing cryogenic air separation units. The multiple condenser-reboilers preferably include an integrated condenser-reboiler arrangement comprising a heat exchanger having a set of nitrogen condensing passages, a first set and second set of boiling passages, and a phase separator.

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.

Enhancements to a dual column, nitrogen producing cryogenic air separation unit are provided. Such enhancements include an improved air separation cycle that uses three condenser-reboilers and recycles a portion of the vapor from one or more of the condenser-reboilers to the incoming feed stream and or the compressed purified air streams to yield improvements in the performance of such dual column, nitrogen producing cryogenic air separation units in terms of overall nitrogen recovery as well as power consumption.

Enhancements to a dual column, nitrogen producing cryogenic air separation unit with waste expansion are provided. Such enhancements include an improved air separation cycle 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; and (iii) a recycle stream of a portion of the vapor from one or more of the condenser-reboilers that is recycled back to the incoming feed stream and or the compressed purified air streams to yield improvements in the performance of such dual column, nitrogen producing cryogenic air separation units in terms of overall nitrogen recovery as well as power consumption compared to conventional dual column, nitrogen producing cryogenic air separation units employing waste expansion.

A portion of feed air is expanded and cooled in front of a main heat exchanger, and is used as cold for precooling the remaining unexpanded feed air inside the main heat exchanger. A portion of the feed air precooled inside the main heat exchanger is removed to outside the main heat exchanger, expanded and cooled, and used as cold to cool the remaining unexpanded precooled feed air inside the main heat exchanger.

A gas production system that can supply liquefied gas obtained by rectifying source gas as product gas continuously with high heat efficiency without using a machine that has a risk of contamination like a pump. A gas production system includes a single pressure device having a single pressurized container to which liquefied gas extracted from a rectification unit is supplied, a pressure line for extracting and vaporizing a part of the liquefied gas in the pressurized container and returning the part of the liquefied gas to the pressurized container, and a second heat exchange unit that is disposed in the pressure line, and a liquefied gas storage unit that stores liquefied gas which is led out from the pressurized container.

Enhancements to a dual column, nitrogen producing cryogenic air separation unit are provided. Such enhancements include an improved air separation cycle that uses multiple condenser-reboilers and recycles a portion of the vapor from one or more of the condenser-reboilers to the incoming feed stream and or the compressed purified air streams to yield improvements in such dual column, nitrogen producing cryogenic air separation units. The multiple condenser-reboilers preferably include an integrated condenser-reboiler arrangement comprising a heat exchanger having a set of nitrogen condensing passages, a first set and second set of boiling passages, and a phase separator.