Pressure Swing Absorption, 95% O2?

Dawktah

Hello!

I haven't taken a CCR course as of yet but was doing more research. I am currently taking a gas blender course. I am trying to schedule some CCR introductions in the near future.

I just needed to know if Oxygen obtained by a Pressure Swing Absorption unit is satisfactory for diving CCR at a max concentration of 95%? The unit has a flat cost over time versus the cost of buying oxygen from a supplier when its not readily available or is locally expensive.

Thanks,

Chris

EBT

Its ok at a push, but be aware that you'll tend to concentrate argon in the output too (which is very narcotic).

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jradomski

I don't agree totally..

The concentration of Argon and its effect depends on multiple factors

Time Between loop flushes
Work rate (frequency of injections)
and
Depth

The deeper you go the less effect the argon from oxygen has on the loop.. In many places Oxygen from PSA systems is the only way to get oxygen..

There always will be some additional narcotic potential in the gas, but luckily where its the most critical the effect is the smallest.. Unless the work loads are REALLY high a simple loop flush every 15 minuets will keep the amount of argon in the loop quite small (at any depth), on deep dives it could be extended quite alot more..


I do a long presentation on this in my Tech and Trimix rebreather proggrams..

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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.

jradomski

Yes it is acceptable, although 100% is preferred.. On several electronics systems, the calibration requires 100% oxygen so you either need a small supply of 100% o2, dela with the calibration error, or use some tricks to get a proper calibration (see my article about accurate po2 calibration on this site)


Several PSA systems can be fitted with an additional stage that absorbs the argon and results in 99.9% purity.. its bascally another PSA system designed to absorb Argon instead of Nitrogen..

__________________
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.

iain-hsm

PSA units are of great interest but just a word of caution. IMHO there are three methods of producing oxygen with the pressure swing absorption PSA or VPSA method being the only practical end user option.
There are however liabilities and huge responsibilities in self generation for breathing purposes that should be investigated before going down this route.

The practical method using a synthetic zeolite mixture (molecular sieve) for breathing purposes would require an adequate method of analysis before I would be happy and would suggest a paramagnetic means and not a galvanic fuel cell as means of analysis at the very least. Further a minimum double rack system for >99% purity and not allow the industrial <95% PSA plants that are not 100% effective, and go off purity surprisingly often. Frankly they are not suitable for diving and should not be used if at all possible.

In remote areas military field hospitals for example there is a case for use, then the supplier responsibility comes into play. For medical oxygen use of 95% has been deemed adequate for use but this is more for production capability than patient.

The process gas needs to be analyzed accurately, there is no scope for variance or error here. When I pay for a product I expect it to be what it says on the label. Oxygen for breathing purposes is spectrographically analyses for purity and certified. The PSA produced oxygen is not.

Secondly PSA produce oxygen is produced at a very low pressure <2 barg (25psig) So in addition to the huge amount of electrical power wasted in producing the product in the first place you then have to compress the low pressure oxygen up to high pressure with all the associated risk and concerns involved in compressing high pressure oxygen. The risk for example on a live aboard storing high pressure oxygen is less than that of oxygen generation but practicalities may preclude storage.

Jpeg is a 11,000l/min (400scfm) PSA plant (we built earlier) 700Kw of low pressure air is used to generate the oxygen. Iain Middlebrook.

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