Process for increasing low pressure pure nitrogen production by revamping original apparatus for cryogenic air separation

A process of revamping an original apparatus for the separation of air by cryogenic distillation so as to increase the production of low pressure pure nitrogen, the original apparatus for the separation of air by cryogenic distillation comprising:

• a. a first column operated under a first pressure and a second column operated under a relatively lower second pressure, a condensation evaporator disposed on top of the first column and an original pure nitrogen column connected to a top of the second column and having a smaller diameter than the second column,
• b. a main compressor, an air purification and cooling system, a main heat exchanger, an expander and a conduit conveying system for compressing, purifying, and cooling feed air, and transferring said feed air to at least the first column,
• c. a subcooler for indirect heat exchange between fluids to be cooled, which comprise an oxygen enriched liquid air, original waste liquid nitrogen and original pure liquid nitrogen produced from the first column and possibly pure liquid oxygen from the second column, and fluids to be warmed, which comprise the original low pressure pure nitrogen and original waste nitrogen produced from the second column, the subcooler comprising a first group of passages through which the original waste liquid nitrogen is passed and a second group of passages through which the original pure liquid nitrogen is passed, and the total heat exchange area of the first group of passages being greater than the total heat exchange area of the second group of passages,
• d. a first conduit having a diameter D that transfers the original waste liquid nitrogen from the first column to the first group of passages in the subcooler and a second conduit having a diameter D′ that transfers the original waste liquid nitrogen from the first group of passages in the subcooler to an upper part of the second column as well as a third conduit having a diameter d that transfers the original pure liquid nitrogen from the first column to the second group of passages in the subcooler and a fourth conduit having a diameter d′ that transfers the original pure liquid nitrogen from the second group of passages in the subcooler to the top of original pure nitrogen column, wherein D>d, D′>d′,
• wherein the process comprises the steps of:
• substituting the original pure nitrogen column with a revamped pure nitrogen column having an increased diameter and/or height as compared to the original pure nitrogen column to thereby improve the production capacity of the low pressure pure nitrogen in the revamped pure nitrogen column and/or installing an additional pure nitrogen column in parallel to the original pure nitrogen column in order to improve the overall production capacity;
• and
• physically switching the first and third conduits having diameters D and d at a hot end of the subcooler, and physically switching the second and fourth conduits having diameters D′ and d′ at a cold end of the subcooler, thereby allowing the pure liquid nitrogen after revamping to be passed through the first group of passages in the subcooler, and the waste liquid nitrogen after revamping to be passed through the second group of passages in the subcooler.