Oxygen concentrators and nitrox sticks

[estresao]

BTW, using "weak" concetrators, maybe, instead of using two of them, maybe enriching the mIx twice would also work. Let say first time we get Nx27 (just a ramdom example) and them use it as gas input to increase it to Nx32.

 

[broncobowsher]

@broncobowsher throttling the compressor can only be done within a very narrow range since most of the small pumps are splash lubricated. You definitely can't slow them to 50% RPM, 60-70 bare minimum on most of them. Definitely better to get a second concentrator than risk causing issues with the lubrication system.

I never said slow the compressor down. I said to divert some output back into the input. Very inefficient, but will cut the throughput to a level that can work.

 

[tbone1004]

My compressoor doesn't have any option to slow it down... probably hacking it, buy I don't want to tink with a brand new compressor which is sill under guaranty.

I was thinking as well about using two concentrators but, even if I get two used ones, they could reach the price of one ablenro refill tanks.

Here there are also many of them on sales second hand (for some reason ) but nlmost of them produce under 5 L/m.

The perfect solution I think is one of those which can refill tanks. These ones are not very popular in Spain (I think) and they are no easy to find 2nd hand.

I'll keep searching alternatives.

BTW, it's for OC... mainly Nx32 and, in a future, trimix also on OC.

BTW, using "weak" concetrators, maybe, instead of using two of them, maybe enriching the mIx twice would also work. Let say first time we get Nx27 (just a ramdom example) and them use it as gas input to increase it to Nx32.

From an operational cost perspective you really don't want to do what @broncobowsher was talking about which will obviously work but the cost of running that compressor essentially twice would be an expensive pill to swallow. A HP compressor uses about 1kwh to produce 1500L/60cf of gas give or take not including consumables in terms of filters/oil. The oxygen concentrators are very low pressure compressors and use about 0.2kwh to move the same quantity of gas because of the lower pressure but it's about 1kwh to produce 1500L/60cf of concentrated O2 because it dumps ~75% of the volume in waste nitrogen.
The concentrators concentration efficiency is determined by dwell time in the zeolite filter towers, no different than any other filter hence lowering the output flow increases the pressure inside of the filter before the valve cycles, increases the dwell time in that filter and traps more of the N2.

For this case you need to figure out how to add in ~10lpm of O2 which is ~12lpm output from the concentrators *since it is ~10% Argon*. The most efficient way to do this from a cost perspective is with a pair of concentrators running simultaneously with the compressor. Running them at their max flow is actually probably the cheapest in terms of kwh/L because they are building less pressure but if I were you I would find a 10lpm unit and just figure out what nitrox mix you end up getting out of it. You will probably get around EAN30 and will most likely determine that EAN32 is not worth the hassle. If you get EAN28 then you may decide to go look for a 5lpm unit or another 10lpm unit and then you can always turn the back.

Granted, you can also just DIY the concentrator, they're not terribly difficult to make and the zeolite is readily available. Of note, I would really recommend going with a diaphragm pump for the LP pump vs. an oiled pump unless you have an air chilled dryer because the zeolite is super sensitive to moisture and other contaminants but if you have a large shop compressor you can get a refrigerated air dryer for it and use the compressor you've already got.

A Simple But Effective High-Flow Oxygen Concentrator From Hardware Store Parts

To say that a lot has happened in the year since the COVID-19 pandemic started is an understatement of epic proportions, so much so that it may be hard to remember how the hardware hacking communit…

hackaday.com

 

[estresao]

From an operational cost perspective you really don't want to do what @broncobowsher was talking about which will obviously work but the cost of running that compressor essentially twice would be an expensive pill to swallow. A HP compressor uses about 1kwh to produce 1500L/60cf of gas give or take not including consumables in terms of filters/oil. The oxygen concentrators are very low pressure compressors and use about 0.2kwh to move the same quantity of gas because of the lower pressure but it's about 1kwh to produce 1500L/60cf of concentrated O2 because it dumps ~75% of the volume in waste nitrogen.
The concentrators concentration efficiency is determined by dwell time in the zeolite filter towers, no different than any other filter hence lowering the output flow increases the pressure inside of the filter before the valve cycles, increases the dwell time in that filter and traps more of the N2.

For this case you need to figure out how to add in ~10lpm of O2 which is ~12lpm output from the concentrators *since it is ~10% Argon*. The most efficient way to do this from a cost perspective is with a pair of concentrators running simultaneously with the compressor. Running them at their max flow is actually probably the cheapest in terms of kwh/L because they are building less pressure but if I were you I would find a 10lpm unit and just figure out what nitrox mix you end up getting out of it. You will probably get around EAN30 and will most likely determine that EAN32 is not worth the hassle. If you get EAN28 then you may decide to go look for a 5lpm unit or another 10lpm unit and then you can always turn the back.

Granted, you can also just DIY the concentrator, they're not terribly difficult to make and the zeolite is readily available. Of note, I would really recommend going with a diaphragm pump for the LP pump vs. an oiled pump unless you have an air chilled dryer because the zeolite is super sensitive to moisture and other contaminants but if you have a large shop compressor you can get a refrigerated air dryer for it and use the compressor you've already got.

A Simple But Effective High-Flow Oxygen Concentrator From Hardware Store Parts

To say that a lot has happened in the year since the COVID-19 pandemic started is an understatement of epic proportions, so much so that it may be hard to remember how the hardware hacking communit…

hackaday.com

I've started to investigate the zeolite path and, so far, I'm havikg some (stupid?) ideas. For example, having the chance to compress air into a scuba tank, we don't need another pump/compressor... a scuba tank could be used ro feed the zeolite.

I've just started to investigate this and I've whatched some video explaining how the O2 generation usingnzeolite works and it seems around 6 bars is enought for the incoming air..... so seems a normal diving regulator xould work (if we connect the BCD hose to the thingy we provide around 9 bars using the stuff we already have.

Some thing else is the zeolite cilinders and the solenoids controlled using arduinos (which is something I'm used to do).

By using a scubabyank I'm nor sure wherther we can soit with no cooling thing.

I'll keep investigating.

 

[estresao]

Having a look to the OxiKit it seems to need no more than 30psi... which are 2 bars, interesting and very promising

 

[tbone1004]

@estresao please see the comments I made above about the cost/cf of running a scuba compressor vs. a low pressure compressor. You will be spending more than 5x to run an oxygen concentrator off of a scuba tank vs. running a low pressure compressor. If you are going to be running any serious volume of gas that will become an enormous expense. Comparable to what happens when people finally realize how expensive running a Haskel is so @Garth should pay attention.... Completely ignoring the fact that you would have to run your scuba compressor roughly 2x as long to fill the tanks with air that you're going to use to create nitrox. Sure it saves you $1k in buying a proper compressor and filter to do the job but the time and direct running costs of the scuba compressor are so high that it's penny wise and pound foolish.

The extra electricity cost alone of doing it from the scuba compressor vs. a diaphragm compressor with a refrigerated dryer system is going to be roughly .08 Euro/cf. Now the ROI on a $1500 compressor and dryer is going to be roughly 18kcf or 500k liters of gas ish. Doesn't sound like a ton but that's only 250 tank fills. This is also assuming that you have no other use for this compressor which is perfectly suitable for any other low pressure system you have, and you certainly don't need a refrigerated dryer but if you are running a Haskel it pays for itself very quickly, and does not include the extra costs of filters and oil on the scuba compressor so if you can justify it on 250 tank fills then you'll just be pleasantly surprised.

In the US we have inexpensive compressors that are usually labeled as "ultra-quiet" which are diaphragm pump type compressors and these do not need the same kind of filtration as an oiled or traditional "oil-less" compressor would.

 

[happy-diver]

If I remove the legs from my horse will it be easier to mount

 

[estresao]

@estresao please see the comments I made above about the cost/cf of running a scuba compressor vs. a low pressure compressor. You will be spending more than 5x to run an oxygen concentrator off of a scuba tank vs. running a low pressure compressor. If you are going to be running any serious volume of gas that will become an enormous expense. Comparable to what happens when people finally realize how expensive running a Haskel is so @Garth should pay attention.... Completely ignoring the fact that you would have to run your scuba compressor roughly 2x as long to fill the tanks with air that you're going to use to create nitrox. Sure it saves you $1k in buying a proper compressor and filter to do the job but the time and direct running costs of the scuba compressor are so high that it's penny wise and pound foolish.

The extra electricity cost alone of doing it from the scuba compressor vs. a diaphragm compressor with a refrigerated dryer system is going to be roughly .08 Euro/cf. Now the ROI on a $1500 compressor and dryer is going to be roughly 18kcf or 500k liters of gas ish. Doesn't sound like a ton but that's only 250 tank fills. This is also assuming that you have no other use for this compressor which is perfectly suitable for any other low pressure system you have, and you certainly don't need a refrigerated dryer but if you are running a Haskel it pays for itself very quickly, and does not include the extra costs of filters and oil on the scuba compressor so if you can justify it on 250 tank fills then you'll just be pleasantly surprised.

In the US we have inexpensive compressors that are usually labeled as "ultra-quiet" which are diaphragm pump type compressors and these do not need the same kind of filtration as an oiled or traditional "oil-less" compressor would.

You're right, I've had a look to those diaphragm compressor and they seems to be "cheap" and low comsuption.

Despite I have solar panels in my house, this approach will reduce maintenance costs of my Bauer.... more stuff to investigate.

 

[estresao]

Finally I've got a provider of oxygen and helium, so no need for a home made concentrator. I'll park the idea, but I have to say the project it's really appealing: OxiKit, LLC

Thanks everyone for the ideas.

 

[happy-diver]

and had I installed a crystal set in my car perhaps my tinnitus may not have become so encompassing