Nitrogen generator

I think a low-flow nitrogen generator would be a useful darkroom piece of equipment. It could be used to purge cabinets holding developers to keep them from becoming oxidized. There may be other uses as well.

I found a home-made nitrogen generator.

https://www.instructables.com/id/Nitrogen-gas-generator/

It uses a technique known as pressure swing adsorption. I think this design could probably be scaled down to a low-flow configuration. Note that with this device there is negligible risk of asphyxiation from oxygen displacement from a room. Homework quiz: why does this design not present a risk of asphyxiation? Hint: this assumes the nitrogen generator is in the same room as where the nitrogen is used.

What do you think?

Why not just rent a bottle with pressurized nitrogen? Saves you several thousand $ ...

AgX said:

Why not just rent a bottle with pressurized nitrogen? Saves you several thousand $ ...

Click to expand...

Good question. According to the article, the cost of the home-made device is a fraction of the cost of a commercially available device, which would put it in the range of hundreds of dollars rather than thousands of dollars. (Also, scaled down version would likely cost quite a bit less.)

A system based on nitrogen bottles would also cost a few hundred dollars to set up, just for the equipment. (The cylinder alone would cost about $200 for an 80 CF size cylinder.) Plus there would be the recurring cost and inconvenience for nitrogen refills for long-term use.

No way. To justify this you would need to be using a huge amount of nitrogen. I've looked at these things for laboratories . Still hard to justify . I suppose if you had a junkyard full,of free parts and liked these kind of projects, sure. You would need access to cheap power and a darn good compressor.

Keeping it dry, that's a whole big problem on it's own.

mshchem said:

No way. To justify this you would need to be using a huge amount of nitrogen. I've looked at these things for laboratories . Still hard to justify . I suppose if you had a junkyard full,of free parts and liked these kind of projects, sure. You would need access to cheap power and a darn good compressor.

Keeping it dry, that's a whole big problem on it's own.

Click to expand...

Did you look at the link and also consider my comment about scaling down the system?

Here's another link with more details about the system he built.

http://homemadeliquidnitrogen.com/PSA/index.html

He used a 6hp compressor at a flow rate of 6 to 9 scfm. In his device he pressurized the adsorption beds to 110-120 psi. A lower-flow system with enough flow to continuously purge a box would need only a tiny fraction of that power and flow capacity. I assume that 90 psi would probably be enough to operate the adsorption beds. This is easily achievable with a small 100psi compressor for under $60, such as a 1/3 hp unit from Harbor freight that is rated at 0.6 cfm at 90psi, which already is far more flow than would be needed to purge an enclosed cabinet to prevent oxygen infiltration. For example, if one only used 0.06 cfm then the system could run at about 10% duty cycle. Assuming an efficiency factor of 50% for sake of discussion, that would be enough to supply an average of 0.8 Liter/minute. One could probably get away with an order of magnitude less flow than that, which would bring the duty cycle of even that small compressor down to 1%.

Since this is a non-critical application, I think one could make most of the device from mild steel parts rather than stainless, which would drastically reduce the cost.

The person who built this device also included measures to remove moisture and particulates. I think a first stage of moisture removal could probably apply at the compressor air storage tank by adding a small bleed valve at the bottom of the tank. This could bleed off condensation of much of the atmospheric water that would occur when compressing the gas.

By the way, I have also looked into nitrogen generators in the past, in this case to supply nitrogen for tandem mass spectrometers. I no longer work at that facility, but as far as I know they never adopted nitrogen generators and are still using liquid nitrogen boil-off from a huge liquid nitrogen tank to supply nitrogen for dozens of tandem mass spectrometers.

I worked for a huge manufacturing plant, we used nitrogen blankets on chemical tanks. Always had issues keeping things dry. I use a little butane for color developer concentrates, but I usually just keep working solutions in absolutely full bottles.
I am not knocking your idea. I just wouldn't use enough. I go to Costco they give away nitrogen.
I remember sparging liquids with Helium in the good old days. I wasn't paying for any of that.

mshchem said:

I worked for a huge manufacturing plant, we used nitrogen blankets on chemical tanks. Always had issues keeping things dry. I use a little butane for color developer concentrates, but I usually just keep working solutions in absolutely full bottles.
I am not knocking your idea. I just wouldn't use enough. I go to Costco they give away nitrogen.
I remember sparging liquids with Helium in the good old days. I wasn't paying for any of that.

Click to expand...

A question about using nitrogen blankets. Nitrogen is lighter than air, so depending on the geometry of the tanks it could be more easily lost than if a heavier gas were used. What about Argon? It's heavier than air, but is it too expensive?

alanrockwood said:

A question about using nitrogen blankets. Nitrogen is lighter than air, so depending on the geometry of the tanks it could be more easily lost than if a heavier gas were used. What about Argon? It's heavier than air, but is it too expensive?

Click to expand...

Way to expensive, these were huge tanks held polyurethane chemicals, blended polyols in some isocyanates in the others . We would use 100,000 lbs a day. Dry air was used when it could be kept dry. We received liquid Nitrogen in the 5 foot tall Tanks. The nitrogen wasn't used much, when the dry air wasn't dry.
We used He mass specs for leak detection. Pain in the butt, if you contaminated the assembly areas with Helium, all 5he leak detectors would go nuts.
I retired a year back, no longer my problem .

I never heard of such system used at any plant or laboratory over here. That alone raises doubts. But I admit that in the professional world there may by system-blindness and people tend to do things as the ever did.

Concerning costs the term "fraction" in that article is if course a vague one... Also concerning the alternative one must differ between buying and renting bottles (with buying haven hidden costs). Furthermore one would have to be more critical on what really is needed, what may be needed in both cases. Whereas in the bottled sytem one likely would try to keep consumation of gas as low a possible, in the generator system one likely would be less concerned and thus may save resp. devices.
On the other hand the costs of payed labour should not be overlooked. I typically advise DIY solutions, but this likely is beyond the scope of most fellows here.

Needed space is also an issue.

First of all, I would like to say that I think the project is very cool. Putting something like this together would be satisfying in and of itself. Having said that, there is virtually no reason to have such a thing, particularly not for making developers last longer. If your developers are failing due to oxidation, you are simply not making enough photographs. A bottle of mixed D-76 will easily last a year in full glass bottles and I have found the same for Xtol even in accordion style bottles. I keep Rodinal, T-Max and PMK around just for fun and after years of sitting around they always work.

I would love to see the results if anyone builds one of these. It would be quite impressive (to me at least).