Instructables
Picture of Nitrogen gas generator

This instructable will walk you through the basics of making your own nitrogen gas generator. Using pressure swing adsorption with carbon molecular sieve you can make an endless supply from the air without using any consumables. You can use this for filling your tires (nitrogen stays in tires much longer than oxygen, reducing the time you need to refill them), having a non-combustible gas or, in my case, to feed into a liquid nitrogen generator.

I won't go into any theory here. I'll just go over the basic construction. A unit of the size I will describe can go between $6000 to $8000. You can build this for a fraction of the price. If you are interested in this subject in more detail you can go to my nitrogen generator web tutorial. There you will find more pictures, animations and other information. There is also a video going over the nitrogen generator. You can also view my liquid nitrogen generator tutorial.

If you are ready to build this for your shop just click next.

 
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Step 1: Basic theory

Picture of Basic theory

This is a big project and will most likely need to stay in your shop or garage. The generator runs off of compressed air. It has two tower beds, each filled with CMS (carbon molecular sieve). Pneumatic valves control the airflow into one at a time. Under pressure, oxygen is preferentially trapped, while nitrogen passes through and out the bottom. The controller opens the next bed for filling, isolating it from the first one as it opens it to the atmosphere. During decompression, the first bed releases the oxygen back into the atmosphere, regenerating the CMS.

The picture above shows the CMS, which looks like chocolate sprinkles. They are approximately 0.5 x 2mm in size. Let's go over a basic materials list.

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JordanRinke5 months ago

So, the waste gas in this case is pure oxygen?

imsmooth (author)  JordanRinke5 months ago
yes
imsmooth (author)  imsmooth10 days ago
It is not pure oxygen. It is concentrated. I believe I measured 35-40% oxygen on the waste side with one stage.
en2oh imsmooth10 days ago

I would suspect that the waste gas is actually enriched air not pure oxygen. In the zeolite oxygen Concentrators, the waste gas is not pure nitrogen. I don't think PSA conceptually allows for this.

squalyl imsmooth5 months ago

It's a waste to discard pure oxygen! If I made one, I would make sure to also compress this using a second regenerative system! Copenhagen suborbitals (and other amateurs) would be very happy with that :)

en2oh10 days ago

did you ever secure a source for CMS that the rest of us can tap into? I'd like to make a considerably smaller system for my Stirling cooler but don't want to deal with China and their shipping costs. There was a U.S. destributor but they seem to be out of business.

Doug

imsmooth (author)  en2oh10 days ago
The CMS comes in 20kg canisters. If you are seriously interested give me your address and the quantity. I will contact my supplier. I was hoping they would have a website setup to keep me out of the loop, but I will work with you to get the stuff. Once I know your address and quantity I can get you a price quote for having it shipped directly to you.
MMIChris3 months ago

Awesome tutorial! I'm a mechanical engineering (part-time) student and I will definitely be making one of these to have in my shop.

Just a suggestion on your parts list: change the listing of the "(2) 8" ID x 33" long" steel tubes to: (2) 8" schedule 40 pipe at 33" long. On the flanges: change your listing to (2) 8" 150# raised-face slip-on flange and (2) 8" 150# raised-face blind flange. Most people don't have 8" pipe or flanges laying around, so when they go to ask for it at a supply store or search online, it makes for a smoother purchasing experience. It also makes for an easier assembly experience (for either the welder or the one building the entire generator) with those pieces.

My day job is a piping and structural designer, just trying to help.

Cheers!

imsmooth (author)  MMIChris3 months ago

Thanks for the comment. Changes made. Please look at my video on youtube and my liquid nitrogen generator video and tutorial pages on the web.

en2oh5 months ago
No need to recharge. MTBF is outrageously long.
Search "64volks". I know he has a couple more of these.
The one I bought is a pretty stripped down unit. No frills.

http://www.ebay.com/itm/111382303763?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

He sets the auction at $200. The first one went for $501 (the buy now offer was $500) so I just bought the next one outright.

No need to recharge with helium. They're sealed units. Run them with a Variac at 30vAC or so.

Doug
imsmooth (author)  en2oh5 months ago
I just looked at the link
It looks like a filter
Where does it say its a cryo cooler?
en2oh imsmooth5 months ago
Take a look at this link ;)

http://picclick.com/850SLA6F1R-SUPERCONDUCTOR-TECHNOLOGIES-CRYOCOOLER-SUPERLINK-RX-850MHZ-390620686311.html
en2oh imsmooth5 months ago
When it says "Superfilter", it contains a stirling Cryocooler.
I contacted SuperConductor Technologies for that specific model and they confirmed this unit has a 5watt thermal lift at 77K.
He has a couple of these physically smaller units (same size Cryocooler) but said he also has others with stirling engines.
Doug
en2oh5 months ago

you're using a considerably higher pressure for your PSA system, presumably based on the adsorbant your used. Zeolite based oxygen concentrators typically pressurize to less than 30psi. I broke down and grabbed a stirling Cryocooler today but want to couple this with a countercurrent JT cooler to increase production. The Stirling engine has around 5watts thermal lift at 77k. I couldn't see a 3000psi Compressor out in my garage. :). A two pound stirling engine with a 10bar compressor is much lower risk ;)

Doug

imsmooth (author)  en2oh5 months ago
Where did you get it
How much was it?
en2oh imsmooth5 months ago
The Stirling Cryocooler was $500 plus shipping.
Ebay
imsmooth (author)  en2oh5 months ago

Would you send the link from the item listing. I would like to see how it was advertised. I have seen many cryo units on Ebay, but they usually are too expensive or contain more parts than I would have needed. Also, don't you have to charge this with helium every so often?

en2oh imsmooth5 months ago
$500 plush shipping.
Ebay
imsmooth (author) 5 months ago
Cardiac Anesthesia
Nj
That's funny your in the same field
en2oh imsmooth5 months ago

I'm long out of the OR. I spent the last 20 years in Pain Management.

Specialized in high risk opioid management. Still travel a lot but have wound down considerably.

It's a small world! :)

dgateley5 months ago

Wow yet again. What is your background that allows such simple yet sophisticated designs?

imsmooth (author)  dgateley5 months ago
I was an engineering major, but I practice medicine. BTW, they do not teach this in engineering school. I just figured it out and got a little help on specific questions along the way.
en2oh imsmooth5 months ago

imsmooth: what kind of medicine? I'm an anesthesiologist by profession but PChem grad studies prior. :)

Small world!

Sammbo5 months ago

Nice !

any chance this could be modified to generate Argon Gas, for my MIG welder :-)

Robibame Sammbo5 months ago

I am NOT a welder, not by any means, my grandfather was, and to an extent my sister is, but I've not been lucky enough to get the chance to learn...... but I have seen and heard of people using CO2 gas in place of Argon when in places where it was harder to acquire Argon .... I'll bet there is enough CO2 in regular air that you could filter it out in a way like this..... although I'll bet there are cheaper n' easier ways to get some CO2 than using a system like this.... and I'm sure there are variables that make straight CO2 not great or everybody would use it in place of Argon.

imsmooth (author)  Sammbo5 months ago
I don't believe you can separate argon with a sieve. I did not come across this. Industrially, air is liquefied and the other gases are separated with fractionation.
Sammbo imsmooth5 months ago

Oh . Just thought there would be a big market for cheap argon given that its used in manufacturing, welding etc.

Down here (Australia) you have to factor in cylinder rental and all up the cost can come in high.

So for small companies already struggling its another cost to worry about.

Even more so for third world countries.

When you consider that Argon is all around us, its would be nice if someone could come up with a cheap DIY process

Sammbo Sammbo5 months ago

hey I just realised something, Argon is used as a shielding gas because its Inert.

Isn't Nitrogen also Inert? I wonder if it can be used for shielding?

grapenut Sammbo5 months ago

Yes and no, technically nitrogen is pretty darn reactive, however it is so reactive that it loves to bond with itself, forming a nitrogen molecule of 2 nitrogen atoms. This is why industry typically refers to nitrogen as 'N2.' Now this nitrogen molecule is so stable that it is considered to be inert, and often considered to be on par with inert noble gases such as Argon...

(I could add the caveat that many modern day physicists have managed to create unlikely circumstances that change alot of the old rules; but for the overwhelming vast majority of us N2 (and all the noble gases)is inert...)

jj.inc Sammbo5 months ago

It can be

grapenut5 months ago

The question I've been wanting to ask is: Are these CMS grains the same thing used in a 'membrane filter?'

imsmooth (author)  grapenut5 months ago

O2 gets into the grain's pores and binds to them. With a filter the smaller N2 gets through the filaments more than the O2 which exits out a different port. Membranes are very expensive.

grapenut5 months ago

For those who wish to somehow harness the waste gas (Oxygen); (and quite possibly why the author may not have explained it too much) Just be advised that 100% oxygen (particularly pressurized) IS highly reactive (dangerous) and requires a bit more training, preparation, and specifications,etc...

Specifically there are cleanliness standards that need to be striclty adhered to.

Specifically the piping, valves, storage tanks, etc. need to be very clean and free of any oil/grease.

I myself am interested in the O2 harnessing capabilities; mostly as a prepper; I tend to believe the earth once had an atmoshere of 35% Oxygen (currently @ 21%) which supported life of dinosaurs....It was a meteor impact which consumed so much oxygen that most dinosaurs died...Some experts say we are due for another meteor strike; It may someday be necessary to produce a bit of extra O2...

spiderfurby5 months ago

amazing mate - what your technical background?

master53yoda5 months ago

There is a number of mistakes made in the comments based on incomplete understanding of air. Nitrogen and "DRY" have very similiar expansion patterns, this can be verified by looking at the physical properties tables. BUT air coming from a compressor has substantial amounts of water vapor depending on the surrounding realive humidity. water vapor has a substantual difference in expansion from dry air or nitrogen.

The primary reason for using nitrogen in tires is that it is DRY and inert. It doesn't react with the rubber or wheels etc. It has about a 2% per 10 degree expansion ratio which is very close to air, because air is 80% nitrogen anyway, Boyle's law states that the pressure is the sum of the pressures of the combined gases at any given temperature. If you look at the evaporation temps at atmospheric pressure, nitogen and the other components of a dry air mixture are very close but the waters evaportaion temperatures are the surrounding temps of the tire. All you need to look at to see the issues involved is a standard phsycometric chart used in the HVAC industry. The approximate 30 to 50 psi range in tires places the evaporation temp range in the same temp range the tire is operating in. Nitrogeon or DRY air filled tires will vary far less in pressure due to temperature then compressed air filled tires will.

imsmooth (author)  master53yoda5 months ago
I agree with this. Water vapor is why the pressure changes more. Nitrogen, though, stays in the tire longer. Equal molar amounts of N2 and O2 should expand very similarly. PV = nRT says nothing about the type of gas.

indeed, but

does say something about the gas :)

still, that doesn't make a big difference

very nice project by the way... I've made a somewhat similar oxygen generator/concentrator using zeolite as sieve

keep up the good work :)

:)) there was suposed to be an equation there ... the Van der Waals equation of real gases, but it seems that instructables didn't post it so let me try again :

(p+ n2a/V2)(V
- nb) = nRT (this time without equation editor)

this says something about the gas :D

jj.inc5 months ago

This is an impressive device, good job! I am curious as to where one can get some CMS-H as I have yet to find a supplier of it just to get an idea of what the whole thing would cost. Just a thought, the oxygen could be captured and re-compressed for various shop uses, like in a torch. It could also be liquefied to my belief and stored in a small pressurized cryo-tank and last for quite some time.

Halfdead5 months ago

I believe your induction heater tutorial has an error. You asserted heating above the curie point is more efficient when it's actually less efficient due to no more heating from hysteresis loss.

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