Nitrogen Purity - Is 98 % too low?

Question

Nitrogen Purity - Is 98 % too low?

cougarfan (Mechanical)

(OP)

23 Apr 03 14:45

We are a batch chemical facility and purge and blanket with nitrogen. The nitrogen is generated with a nitorgen generator putting out a 99.5% purity with liquid nitrogen backup. Has anyone out there ventured to use a lower purity -say 98 % nitrogen.. We have a couple of proudcts that chemically will degrade so we will bring pure nitrogen to these tanks but we are looking at the safety aspects and it scares a lot of people to lower the purity.

quark (Mechanical) · Answer 1 · 2003-04-24 00:27:14

Infact 99.5% is low purity. I have seen applications (for PET) where the purity is maintained at 99.999% (actually it is 10ppm oxygen) As a pharma company we use 99.995% purity.

What is your concern? Do you want to increase the capacity of plant by reducing purity?

Generally there should not be any problem upto 7.5% oxygen (as far as ignition problems are concerned) But for oxidation, well it is your judgement.

Is it a PSA Nitrogen Generator?

25362 (Chemical) · Answer 2 · 2003-04-24 01:42:22

There are chemical plants, for example, dealing with reactive aldehydes, that ask for inert gas having less than 80 ppm oxygen.

tmc1 (Chemical) · Answer 3 · 2003-04-24 02:00:12

In general, 99.5% is commonly used in industry and is considered low in purity. Our O2 content is 10 ppm or lower.
It depends on your application.

dcguffey (Chemical) · Answer 4 · 2003-05-21 23:41:04

As previously stated, oxygen concentration depends on the purpose of the blanket. For chemicals that are flammable/explosive, it would be best to contact NFPA or other agency for data on MOC (minimum oxygen for combustion) and ensure that your N2 has no more than ½ of that value. If your facility has hydrogen and is trying to inert vessels, then the 98% N2 would be a very bad choice.

If your N2 is coming off a PSA, then check flow very carefully. My experience with PSA (pressure swing absorption) units is that the rating of 98% N2 will be at a specific flowrate. As the flow goes up, the purity goes down.

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Nitrogen Purity - Is 98 % too low?