Argon and Oxygen

deanc

Håkan,

The PSA (pressure swing adsorption) method for producing oxygen is a *cheap* industrial process for very very large plants.

Specifically its a novel process, cheap because lots of energy is not required, so it might be used by an industry that doesn't need purity - it might be to support combustion or for a reaction etc where other gases mix and react and produce before more seperation processes anyway. Energy like cryogenic distillation is big dollars running costs. Even a waste gas from the reactor might run a gas turbine and generator to get back some electricity in a big plant.

Since air is the feed gas, and the zeolite molecular sieve ZMS 9 is best for oxygen production if I could remember rightly.

It is a matter of packing 3 columns with ZMS 9 much like the Rebreather scrubber, just bigger stronger steel pressure vessels a few metres in diameter and a few metres tall. And a bunch of pipework, valves and compressors.

Now the vessel is compressed say to 10 atm with air. The nitrogen is adsorbed into the ZMS because of the specific molecule size of nitrogen and the chosen chemistry of the zeolite - like a sponge small molecular pore spaces. The oxygen isn't adsorbed, so what comes out of the top of the vessel is quite good oxygen content. The compressor keeps running and oxygen can be vented into the process. i.e. it wouldn't be stored, purified or anything, just fed say into a reactor just like that.

Since the ZMS will only hold a certain mass of nitrogen, break through will occur (sensors measure the produced gas) and nitrogen will come out the top, and the oxygen quality would drop. At this time, now its just a matter of a 2 to 3 minutes, valves are closed and others opened to run into and out of a 2nd fresh vessel. In fact a 3rd vessel really makes a perfect process, because the breakthrough gas from the first will be used to pressure the 3rd (because it might be 90% oxygen when the switch is made - perfect for pressuring another vessel with, rather than starting with fresh air -- that would be a waste of zeolite capacity)

Now comes the pressure swing (and 1 reason why the process is at 10 atm) -- drop the pressure in the first column to 1 atmosphere and the nitrogen that was adsorbed is vented to atmosphere as a waste gas. Wait for breakthrough in the second vessel and switch to the 3rd, filling the first with breakthrough gas from the 2nd.

That process goes all day every 2-3 minutes swinging vessels, 3 way ball valves etc. all automated producing bulk cheap oxygen say 90-95 % at 10 atm or whatever the process was designed and operated for.

Contamination from oils etc. is a big factor to keep a long life of the molecular sieve.

So why is argon there? It exists in a ratio 0.93 : 20.9 in the feed air from atmosphere. If you only remove the nitrogen, then argon/ oxygen ratio doesn't change, the new gas composition might be something like argon/oxygen/co2/nitrogen 4.2/95/0.17/0.6 %.

For the industrial reactor nobody would really care too much about the 5 % impurity. For breathing its another story.

Hope that helps with PSA oxygen production and argon from air.

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jradomski

I agree its adsorbtion.. The definitions are clouded some times, and I didn;t feel like looking up the definitions up to decide if it was a B or a d (I always forget)... But I got the idea across.. my explanation indicates its adsorbtion..

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Joe Radomski
CCR Trimix Instructor Trainer
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All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

jradomski

Take a look at this link..

OGSI: Oxygen generator manufacturer: Oxygen generators, oxygen tanks, pressure swing adsorption, og 15 portable oxygen generators equipment

I have used products by this company in the past..

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Joe Radomski
CCR Trimix Instructor Trainer
ANDI Instructor Trainer Director #10

All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

Abbo

Apologies: I didn't mean to sound like I was trying to win points.

Using 94% O2 made by PSA, there's 4.2% Ar in the oxygen you are injecting. For an 8 litre loop, if you metabolize 1 lpm of O2, at the end of one hour there's an Argon partial pressure of 0.32 bars (independent of depth). If you take Argon to be 2.33x as narcotic as nitrogen, then you are adding to your narcosis the equivalent of another 1.33 x 0.32 = 0.42 bars of PN2. That is equivalent to another 4.3m of END per hour, or 0.4 martinis on an empty stomach. That's worth considering, but not worth losing sleep over.

Sten

So is humidity also "concentrated", as it is in membrane systems?

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