Process for the production of nitrogen by cryogenic distillation of atmospheric air
AssigneesL'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des Procedes George Claude, Liquid Air Engineering Corporation, Teisan Kabushiki Kaisha
InventorsSophie Gastinne, Francois Venet, Bao Ha, Naohiko Yamashita
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Abstract
An air separation process wherein a nitrogen enriched fraction is withdrawn from the distillation column, a portion of which is compressed and recycled through the lowest positioned reboiler in the column and directed to an upper portion of the column as reflux.
Claims23
A process for producing gaseous nitrogen from a mixture to be treated in a distillation column, said mixture comprising nitrogen and oxygen, said process comprising the steps of:
- a) compressing the mixture to be treated to a pressure at least equal to the column pressure;
- b) cooling the compressed gas mixture and expanding a first portion of said cooled mixture in a turbine to produce an expanded feed gas mixture for refrigeration and fractionated distillation in the column to obtain, at a lower portion of the column, an oxygen-enriched fraction and, at the top of the column, a nitrogen-enriched fraction;
- c) drawing off at least a portion of the nitrogen-enriched fraction as nitrogen product;
- d) compressing the remaining portion of the nitrogen-enriched product;
- e) recycling at least a portion of the compressed remaining portion of the nitrogen-enriched fraction to a lowest-positioned reboiler of the column where it condenses to provide reboil for the column;
- f) introducing at least a portion of the condensed nitrogen stream of step e) to the column as reflux;
- and
- g) drawing off an oxygen-enriched fraction in liquid form from the bottom of the column and expanding at least a portion of said fraction to a pressure less than the column pressure and vaporizing this portion by heat exchange with nitrogen-enriched fraction condensing at the top of the column.
A process for producing gaseous nitrogen from a mixture to be treated in a distillation column, said mixture comprising nitrogen and oxygen, said process comprising the steps of:
- a) compressing the mixture to be treated to a pressure at least equal to the column pressure;
- b) further compressing a first portion of said compressed gas mixture into a compressor driven by a turbine, cooling said further compressed gas mixture and expanding it in said turbine and thereafter fractionating by distillation said expanded gas mixture in the column to obtain, at a lower portion of the column, an oxygen-enriched fraction and, at the top of the column, a nitrogen-enriched fraction;
- c) drawing off at least a portion of the nitrogen-enriched fraction as nitrogen product;
- d) compressing the remaining portion of the nitrogen-enriched fraction;
- e) recycling at least a portion of the compressed remaining portion of the nitrogen-enriched fraction to a lowest-positioned reboiler of the column where it condenses to provide reboil for the column;
- f) introducing at least a portion of the condensed nitrogen stream of step e) to the column as reflux;
- and
- g) drawing off an oxygen-enriched fraction in liquid form from the bottom of the column and expanding at least a portion of said fraction to a pressure less than the column pressure and vaporizing this portion by heat exchange with nitrogen-enriched fraction condensing at the top of the column.
A process for producing gaseous nitrogen from a mixture to be treated in a distillation system comprising a low pressure distillation column and a high pressure distillation column, said mixture comprising nitrogen, oxygen and light impurities, said process comprising the steps of:
- a) compressing the mixture to be treated to a pressure at least equal to the low pressure column pressure,
- b) cooling the compressed gas mixture and expanding a first portion of said cooled mixture in a turbine to produce an expanded gas mixture for refrigeration and fractionated distillation in the low pressure distillation column to obtain, at the bottom of the low pressure distillation column, an oxygen-enriched fraction and, at the top of the low pressure distillation column, a nitrogen-enriched fraction;
- c) compressing at least a portion of the nitrogen-enriched fraction;
- d) recycling at least a portion of the compressed portion of the nitrogen-enriched fraction to a lowest positioned reboiler of the high pressure distillation column where it at least partially condenses to provide reboil for the distillation system;
- e) introducing at least a portion of the at least partially condensed nitrogen stream of step e) into the high pressure distillation column at an intermediate stage;
- f) recovering a nitrogen product substantially free of light impurities from the high pressure distillation column, and;
- g) drawing off an oxygen-enriched fraction from the bottom of the low pressure distillation column and expanding at least a portion of said oxygen-enriched fraction to a pressure less than the low pressure column pressure and condensing at least a portion of the nitrogen-enriched fraction near the top of the low pressure column by heat exchange with the expanded oxygen-enriched fraction.
Dependencies are inferred from the claim text.