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Use of air bypass for low purity N2 from cryogenic N2 plant

IP.com Disclosure Number: IPCOM000032923D
Publication Date: 2004-Nov-18
Document File: 1 page(s) / 9K

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Use of air bypass for low purity N2 from cryogenic N2 plant

When gaseous N2 at low purity e.g. 2% O2 in N2 is required it can be advantageous to produce it from a plant designed for high purity e.g. 5 ppm O2 in N2 by bypassing part of the air around the cold box and mixing with high purity N2 from the plant to make the final low purity N2 product. This is shown in the Figure below:

By simple mass balance it can be shown that for 2% O2 in N2  the air flow and air compressor power required is 95% of that for 5ppm O2. Additionally the air bypass flow reduces the air flow to cold box by about 9.5%.

It is possible to operate the cryogenic N2 plant to produce low purity N2 directly. Again at 2% O2 in N2 the air compressor power is about 95% of that required to produce N2 with 5 ppm O2.

Thus the main benefit of the air bypass option is that it can increase the production of low purity N2 from a cold box of a given recovery.