Process and apparatus for producing high-purity nitrogen by low-temperature fractionation of air

An apparatus for producing nitrogen by low-temperature fractionation of air in a rectification system comprising:

• a high-pressure column (4) and a low-pressure column (5);
• a feed line (1, 3) for introducing air into the high-pressure column (4);
• a line (11) for introducing an oxygen-containing liquid fraction from the high-pressure column (4) into the low-pressure column (5);
• a top condenser (17), the liquefaction side of which is connected to a region of the low-pressure column (5) above a mass transfer section (25), said mass transfer section having at least one theoretical or practical plate;
• a nitrogen product line (26, 27, 30) for removing high-purity nitrogen, which is connected to the low-pressure column (5) below the mass transfer section (25);
• and
• a refrigeration-supply system, which has a refrigeration-fluid line (31, 32, 34;
• 38) connected to the low-pressure column (5) above the mass transfer section (25),
• wherein said refrigeration-supply system has an expansion machine (33), the inlet of which is connected to the high-pressure column (4) and the outlet of which is directly connected (34) to low-pressure column (5), or said refrigeration-fluid line is a liquid line (38) for feeding into the refrigeration-supply system a cryogenic liquid produced outside the rectification system.

A process for producing high-purity nitrogen by low-temperature fractionation of air in a rectification system which comprises a high-pressure column (4) and a low-pressure column (5), said process comprising:

• introducing feed air (1, 3) into the high-pressure column (4),
• removing an oxygen-containing liquid fraction (11) from the high-pressure column (4) and feeding at least a portion of said oxygen-containing liquid fraction into the low-pressure column (5),
• extracting gaseous nitrogen (18) from the low-pressure column (5) above a mass transfer section (25) which has at least one theoretical or practical plate, and at least partially condensing said gaseous nitrogen in a top condenser (17) by indirect heat exchange with a refrigerant (13), and
• removing high-purity nitrogen (26, 27, 30) from the low-pressure column (5) below the mass transfer section (25),
• wherein said process further comprises a refrigeration-supply system, within which a refrigeration fluid (31, 32, 34, 38) flows and at least part of the refrigeration fluid from the refrigeration-supply system is introduced (34, 38) into the low-pressure column (5) above the mass transfer section (25) or into the upper region of the high-pressure column (4),
• wherein said refrigeration fluid is removed from the high-pressure column (4), expanded (33) in a work-performing manner in said refrigeration-supply system, and introduced (34) into the low-pressure column (5), or said refrigeration fluid is formed by a cryogenic liquid (38) produced outside the rectification system, and
• wherein said refrigerant (13) for the top condenser (17) is removed from the lower region of the low-pressure column (5).

A process for producing high-purity nitrogen by low-temperature fractionation of air in a rectification system which comprises a high-pressure column (4) and a low-pressure column (5), said process comprising:

• introducing feed air (1, 3) into the high-pressure column (4),
• removing an oxygen-containing liquid fraction (11) from the high-pressure column (4) and feeding at least a portion of said oxygen-containing liquid fraction into the low-pressure column (5),
• extracting gaseous nitrogen (18) from the low-pressure column (5) above a mass transfer section (25) which has at least one theoretical or practical plate, and at least partially condensing said gaseous nitrogen in a top condenser (17) by indirect heat exchange with a refrigerant (13), and
• removing high-purity nitrogen (26, 27, 30) from the low-pressure column (5) below the mass transfer section (25),
• wherein said process further comprises a refrigeration-supply system, within which a refrigeration fluid (31, 32, 34, 38) flows and at least part of the refrigeration fluid from the refrigeration-supply system is introduced (34, 38) into the low-pressure column (5) above the mass transfer section (25) or into the upper region of the high-pressure column (4),
• wherein said refrigeration fluid is removed from the high-pressure column (4), expanded (33) in a work-performing manner in said refrigeration-supply system, and introduced (34) into the low-pressure column (5), or said refrigeration fluid is formed by a cryogenic liquid (38) produced outside the rectification system, and
• wherein bottom liquid removed from said high-pressure column is supercooled, throttled, and introduced into a lower region of said low-pressure column.