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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
Just an update. I am on my 3rd modification. I have increased the cooling tower size and modified the collection system. I may have to make another change to improve the cool-down rate. I just tested it and I can cool 20 deg F every 7 minutes. At this rate I can get to -321 in under two hours. If I change my collection chamber the way I envision I should be able to shave another 30 minutes.
I also got an RTD probe that accurately measures down to -321F. I already tested in some liquid N2.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
So here is my update:
I am at an impasse. I have successfully cooled to liquifying temperature in 1:45, averaging about 3.5 degrees farenheit / minute. When I opened my collecting valve I could see the mist of liquified air escaping the tube. However, I do not seem to be able to collect enough to see actual liquid; I just see the mist of the liquid as it evaporates. I am not able to liquify enough in my collecting chamber.
I believe the problem is two-fold. Despite my efforts to pack the chamber in insulation, it is not as good as a vacuum. When I pour liquid nitrogen into a dewar the bubbles from boiling almost completely stop. When I pour some into my collecting chamber there is still some bubbling at the drain, which goes to my metal valve. I have packed this valve in closed-cell polyisocyanurate. Second, I believe the throttle is blowing over the liquid and dispersing it into my regenerative stream.
I am not sure how to deal with these issues. I certainly don't have the equipment to make a vacuum chamber, and I still need to have a means of emptying the chamber. Any suggestions?
I found a company that sells small cyrogenic throttle systems. Maybe they will be kind enough to give me some advice.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Well, I finally got to a point where I could collect a small amount of liquid air. At the end you can hear it working its way through the tubing, and you can see it at the bottom of the dewar. I have a few modifications I want to try to increase the yield.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I have re-started working on my project as the outside temperature is a little cooler now. I am almost done with my second phase, which is the construction of a pressure swing absorber. I have gotten almost 99% pure nitrogen out using my home depot air compressor. Because it only puts out 4 cfm I can only run my PSA pressure near 50-70psi. I would love to get it over 110psi, but I will need a bigger compressor.
If anyone is interested in how I constructed the PSA just let me know and I'll put together a tutorial and schematic of the construction. Otherwise, I won't bother.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615
I'd be extremely interested to see your PSA design - in particular details of your absorber material. I confess to being more interested in getting an oxygen stream, rather than nitrogen.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Here is a picture of the pressure swing absorber. I am also including a video link to it being used (I temporarily turned off the compressors). I plan to store the N2 in a tank for the liquid nitrogen generator.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I have gotten my N2 purity from the PSA down to 99.1% pure N2. The O2 analyzer shows 0.9% O2. Since I scrubbed the water vapor and CO2 only N2 is left. This is the best I'm going to get. I have read that to get the pure N2 I would need towers over 15 feet tall to provide enough CMS to remove the O2. Another choice is to use a two-stage PSA. The 95% plus pure N2 from the first stage goes through a second PSA tower system, removing the remaining O2. This is overkill for me.
I have retrofitted a 30 gallon tank that I got off Craig's list to store the N2 product. I will feed this into my refrigeration unit once it gets a little cooler outside. I hope you all find this as interesting as I do. I just don't know if there is enough "internet" interest out there for me to spend the time writing up plans so others can build this.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I tested the unit again. Close to being done. I ran 98.3% nitrogen through the compressor with my PSA device. I was able to achieve -320 in 1 hr 10 minutes starting from 39F. I think that is pretty good. I was able to collect about 20cc of liquid nitrogen after running the unit for another 20-30 minutes after the target temperature. I will have to run better measurement next time.
I modified my compressor and had a loose screw so I had to end the run. Once I am satisfied everything is safe I will let it run on its own for a few hours and see what I get.
I am curious if anyone is interested in this or am I just nuts doing this? Does anyone think there would be an interest for plans how to build your own with the parts, sizes and sources?
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Condesation/Fractional distillation of air
