Using Air Compressor for Nitrogen Service

[KenRad]

I have an application for compressing a mixture of 6% oxygen and 94% nitrogen to about 45 psig. The mixture is being pulled from a process that has nitrogen inerting for explosive hazard reasons. The gas will be clean, since it will pass through a dust collector with fairly high efficiency bag filters, and the dewpoint will be very low.

I don't see why I couldn't use a conventional air compressor for this service. My local compressor reps didn't exactly give me an overwhelming endorsement, but they didn't have any reason why it wouldn't work. I suppose that it just isn't something they run into everyday.

Any thoughts on this?

---KenRad

 

[quark]

I agree with your idea. There shouldn't be any problem but manufacturers never suggest it. One reason may be that they don't have any data with them.

Sometime back, I required a pressure booster for nitrogen (5 bar to 10 bar) and asked quotation from FESTO. They were apprehensive about using the air pressure booster for nitrogen service. Still I purchased it and used for almost 4 years without trouble.

 

[Montemayor]

Like most engineers today that post on these forums you have failed to state WHAT TYPE of compressor you are talking about - centrifugal or reciprocating. I'll assume you mean reciprocating.

There is absolutely no reason why a conventional reciprocating air compressor can't be used as a nitrogen compressor. I've done it on more than one occasion - and the fact that I've done it sucessfully for years is not really the reason I say this. I did it on the advice and consultation of compressor manufacturers - like Ingersoll-Rand, Worthington, Norwalk, Chicago-Pneumatic, etc. most of which were the main designer/manufacturers of compressors in the USA for many years. Normal cast iron construction and oil lubrication will do very well.

I say this without reservations about the type or model of reciprocating machine you are debating. HOWEVER, if you are talking about a centrifugal, you may have problems meeting your head/capacity needs. That's why you should be specific about the type of compressor you are talking about. A reciprocating machine simply displaces the gas that it is given and if the gas is not corrosive, reactive, or gums up then it can be handled. A centrifugal machine is a dynamic model and produces different P/V characteristics with different molecular weight gases. I've yet to see a conventional centrifugal handling Hydrogen.

 

[KenRad]

I stand corrected for my breach of protocol, Montemayor.

I'm acutally talking about an oil-free screw compressor of about 125 CFM capacity. Discharge pressure of about 50 psig.

---KenRad

 

[zdas04]

KenRad,
A dry screw is (like a recip) a positive displacement machine. Your windage losses might be a bit higher with an extra 14% nitrogen, but it shouldn't be a problem.

David

 

[unclesyd]

We have two rotary screw compressors in a service that changes from 100% air, 100% N, 100% NOX, with any combination of the preceding on the fly.
These compressors operate either in parallel or series depending on process demands.
We see no change in performance using the normal process control instruments, though the electrical people say there are some change in load as the inlet gas composition changes.

 

[StoneCold]

Tell us more about where the gas comes from? "Explosive hazards reasons". Are you interting liquids or powders?
Do you have a way to positively not drag solids into the compressor. Screw compressors do not like solids at all, especially wet ones. (experience talking)

Regards
StoneCold