Production of nitrogen gas by low temperature rectification of liquefied air using high and low pressure fractionating columns

摘要

The industrial process for is used for the production of pressurized nitrogen gas. It operates using both high and low pressure columns (14,15). Atmospheric air (1) is compressed (3), purified (6) and cooled in a heat exchanger (12) against low temperature fractions before feeding (13) into the bottom of the high pressure fractionating column (14), and pressurized nitrogen product (22-24) is taken off from the top of the column (14). A nitrogen gas fraction (38) from the top and an oxygen-rich liquid stream from the bottom of the low pressure column (15) are run against each other through a heat exchanger (33) to effect partial condensation of the nitrogen (38), which is then at least partly returned (39) into the upper end of low pressure column (15). The low pressure column has a reboiler (18) which is fed with part of the air feed (16,17) causing partial condensation; at least part of this condensate then being supplied to the head condenser (20) in the high pressure column; the reboiler (18;218) may be internal or external. A plant for operating the process is CLAIMED. The feed air cleaning unit may be a molecular sieve bed for absorbing moisture and carbon dioxide.