Process and equipment for producing liquid nitrogen

摘要

The process and equipment are used for producing liquid nitrogen. Air (1) is separated by a two-stage low-temperature rectification in a rectification system which contains a pressure column (4) and a low-pressure column (5). At the top of the low-pressure column (5), a gaseous nitrogen fraction (11, 12) is obtained and warmed in a main heat exchanger system (2). In addition, a liquid nitrogen fraction (20) is taken off from the rectification system essentially under the pressure of the low-pressure column (5) or under a higher pressure and passed to a storage tank (24). This storage tank is under a lower pressure than the low-pressure column (5). The liquid nitrogen fraction (20) is expanded upstream of the storage tank into an interposed separator (21) which is operated under a pressure which is lower than the pressure of the low-pressure column (5) and slightly higher than the pressure in the storage tank (24). The flash gas (22) formed during the expansion is warmed by indirect heat exchange (2). The fraction (23) which has remained liquid during the expansion is passed into the storage tank (24).