This time we're talking about Pressure Swing Adsorption and how we can use fancy sand to pull pure oxygen out of thin air.
Errata and Clarifications:
- If you are going to use PVC pipe to store pressurized gas of any kind at any pressure, you MUST use pressure rated pipe and not "thinwall" or "DWV" pipe. I chose Schedule 40 pipe, which is the thinnest walled pipe that has a pressure rating, but there are such things as Schedule 80 and 120 pipe. Using pressure rated pipe does not make it safe to do, it just makes it safer. (Cheers, @Spirit532)
- Some concern has been raised about material fatigue caused by pressure cycling. I'm not convinced that a 30 psi pressure swing meets the threshold to cause this kind of failure, but the concern is probably well-founded. A failure of this kind at 30 psi could be scary, but probably not lethal. The chances are good that a failure would be unexciting, if it ever occurred. PVC is not a brittle material and is also very resistant to oxidative reactions. I will be sheathing my cannisters in something to prevent shrapnel just in case. (Cheers, @NicolasBana)
- Sieve is pronounced /sɪv/ and I _know_ that in any other context (I pronounce it correctly in the idiom "leaks like a sieve") but I learned to pronounce "molecular sieve" from @NurdRage, for better or worse, and his incorrect pronunciation has stuck with me. (Cheers, @nilo70)
- My description of the PSA cycle is not entirely accurate. I state that the equalizing valve is mostly responsible for purging the nitrogen from one tank to another, but that's not exactly true. Most of the purge actually happens via the orifices in the output junction. The equalizing valve theoretically "primes" the unpressurized canister with the last bits of pressurized O2 from its counterpart (because the tank will adsorb nitrogen better under pressure, so if you already have some O2 pressure in there when you start pumping in air, you'll pass less nitrogen as the pressure ramps up) I may address this in a follow-up video, but this is still not a bad introduction to the PSA cycle.
- Some of the PSA cycle diagrams show out of order, mostly when I cycle through them quickly. What I'm describing is still correct and any diagram that is discussed for any length of time is correct, it's just some of the quick ones. This section is a Google Slides stack that I recorded with a screen recorder and at times I advanced the slides in the wrong direction without noticing.
- If it is working properly, the oil in an oil-filled pressure gauge will never contact the process gas. What I describe as a hazard is absolutely still true, however. Please do not use oil-filled gauges in oxygen service. In fact, if I were building this machine for someone else to operate, I would take apart the cheap pneumatic valves, wash them in degreaser, and re-oil them with a fluorinated oil for reactive gas service. Take care to look into the oxygen compatibility of anything that has to carry pressurized O2 (Cheers, @AdvancedTinkering)
- When describing the tool used to agitate the sieves in the OxiKit video, I call it a "pneumatic vibrator." In my head, they used a concrete vibrator. Watching the footage back, they're clearly using an air hammer. If you go looking for that tool, it's called an air hammer. I don't necessarily recommend using it for this, however. They make a point to run it at low pressure and to only contact the fittings with it and not the pipe wall directly, but it still seems easy to damage your PVC this way. Buy a muscle massager instead, you deserve it.
- I describe the gas separation mechanism as "having to do with the relative size of the molecules" which is sometimes the case with molecular sieves but in this case, the mechanism is actually electrostatic and ion exchange interactions! This is why the metal cation (Li vs Na) bound to the zeolite affects the selectivity. (Cheers, @justliberty4072)
Check out the Oxikit project here:
https://oxikit.com/
You can stay up to date and support me on Patreon here:
https://www.patreon.com/integratedtherm
And if you want more info on my build, you can read the blogposts here:
https://www.nickpoole.me/
And check out the Github Repository:
https://github.com/NPoole/PSA_Oxygen_Concentrator