Process for the production of nitrogen by cryogenic distillation of atmospheric air

摘要

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 subjecting at least a first portion of said cooled mixture to expansion through a turbine to produce the required refrigeration and thereafter fractionated distillation in the column to obtain at the bottom 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 the bottom 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 top of the column as additional 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 the condensing nitrogen-enriched fraction at the top of the column.