Sciencemadness Discussion Board

Compressor for CO2, oxygen

vmelkon - 12-5-2016 at 18:54

I looked for threads about compressors but there isn't much.
The commercial compressors (Canadian Tire, Home Dept, Reno, Rona), do they have an input hose?
We have a large compressor but there is no way to put a hose on and the air tank is large, maybe 100 L.

Can a vacuum pump be used as a compressor?
I don't have a vacuum pump but I built something with a cheap 20$ tire compressor.

Twospoons - 12-5-2016 at 19:47

Whatever you do don't run pure O2 into a compressor that is not specifically designed for it. Bad things are likely to happen.

gsd - 12-5-2016 at 21:54

If you use air compressor for any other gas then the principal issue is the Molecular Weight (and hence the density) of the gas.

Avg MW of air is 28.9. If you use the compressor for CO2 (MW = 44) which is about 1.5 times that of air. Which means for the same volumetric compression the motor needs to deliver 1.5 times the power required for air which in all probability it is not likely to handle for sustained operation (unless it is grossly over designed). For O2 (MW=32) this ratio is only 1.1 - about 10 % extra power which it might deliver.

I don't think there is any problem in using air compressor for these two gases. For other gases you need to look into the Material of Construction of your compressor head, pistion, sealing rings, valves, tubing, gauges, tanks etc for compatibility. Also safety issues like gas flammability etc must be taken into account.

gsd

vmelkon - 13-5-2016 at 02:30

Quote: Originally posted by Twospoons  
Whatever you do don't run pure O2 into a compressor that is not specifically designed for it. Bad things are likely to happen.


YES!

Long ago, I had used one of these cheap 20$ for oxygen. Since I can't attach a hose to it, I build a box with a input hose and output hose. The entire compressor was in the box.

Since it sucks oxygen from the input hose, the entire box was filled with O2. The heat/spark from the electric motor of the compressor caused a fire. The compressor motor and plastic body burned.

There was no way to stop it.
The box was made with 2 cm thick glass :)

unionised - 13-5-2016 at 02:57

Quote: Originally posted by gsd  
If you use air compressor for any other gas then the principal issue is the Molecular Weight (and hence the density) of the gas.

Avg MW of air is 28.9. If you use the compressor for CO2 (MW = 44) which is about 1.5 times that of air. Which means for the same volumetric compression the motor needs to deliver 1.5 times the power required for air which in all probability it is not likely to handle for sustained operation (unless it is grossly over designed). For O2 (MW=32) this ratio is only 1.1 - about 10 % extra power which it might deliver.



gsd


Are you sure about that?
The molecules of CO2 are heavier, but they are also moving more slowly.
The energy needed to compress a gas is pretty much independent of the gas.

And there is- as has been pointed out- a very good reason not to use a pump for oxygen unless it was designed for it (and uses the right grade of oil etc.)

gsd - 13-5-2016 at 03:11

Quote: Originally posted by unionised  
Are you sure about that?
The molecules of CO2 are heavier, but they are also moving more slowly.
The energy needed to compress a gas is pretty much independent of the gas.

And there is- as has been pointed out- a very good reason not to use a pump for oxygen unless it was designed for it (and uses the right grade of oil etc.)


Power consumption is proportional to the mass displaced.

For a compressor, volume displaced is independent of gas but mass displaced = V*Density of gas

Hence higher power is required for higher MW gas.

BTW it is hilarious to read in a science forum that "Oxygen Caught Fire".

gsd

unionised - 13-5-2016 at 04:08

Quote: Originally posted by gsd  
Quote: Originally posted by unionised  
Are you sure about that?
The molecules of CO2 are heavier, but they are also moving more slowly.
The energy needed to compress a gas is pretty much independent of the gas.

And there is- as has been pointed out- a very good reason not to use a pump for oxygen unless it was designed for it (and uses the right grade of oil etc.)


Power consumption is proportional to the mass displaced.


BTW it is hilarious to read in a science forum that "Oxygen Caught Fire".

gsd

No it isn't
http://physics.stackexchange.com/questions/37634/how-much-wo...
and the only instance of that phrase on this page is in your post- which is amusing.

If you were pumping a liquid up hill you would have a point. We aren't: you don't.

Fegie - 13-5-2016 at 06:00

Quote: Originally posted by Twospoons  
Whatever you do don't run pure O2 into a compressor that is not specifically designed for it. Bad things are likely to happen.


Good old grease and oxygen....

XeonTheMGPony - 13-5-2016 at 06:43

you need to use the jouls Thompson process with a natural gas compressor.


http://homemadeliquidnitrogen.com/

Read that, you can make a system using a more conventional compressor but it will take longer and be a bit more complicated due to need of an inter cooler and oil scrubbing.

Then to isolate your target gasses fractional distillation.

[Edited on 13-5-2016 by XeonTheMGPony]

vmelkon - 13-5-2016 at 06:49

Quote: Originally posted by gsd  
Quote: Originally posted by unionised  


BTW it is hilarious to read in a science forum that "Oxygen Caught Fire".

gsd


I didn't write "Oxygen Caught Fire".

Dr.Bob - 13-5-2016 at 07:35

Seriously, making pure oxygen for anything is dangerous, I know of a history of those types of fires, need to be very careful, use oxygen safe regulators, compressors, no oil or grease, etc. But for either gas, the cost of a cylinder of the gas is comically cheap, so just go buy or rent a cylinder of the gas from a welding company, they cost about $20 to refill and that will last a long time, and get the right regulator.

unionised - 13-5-2016 at 08:36

Quote: Originally posted by vmelkon  
Quote: Originally posted by gsd  
Quote: Originally posted by unionised  


BTW it is hilarious to read in a science forum that "Oxygen Caught Fire".

gsd


I didn't write "Oxygen Caught Fire".

And nor did I.
The only person who wrote it- rather than quoting it- is GSD when he said it was hilarious to see it, which is ironically amusing

gsd - 13-5-2016 at 17:29

Sorry. My bad.

@ vmelkon - you didn't say oxygen caught fire. But your post gave me an impression that in effect you are saying that. I should have quoted you verbatim.

@ unionised - power is not proportional to mass displaced but moles displaced. So equal volume of hydrogen and say Chlorine will need roughly equal power to compress to same pressure.

gsd

unionised - 14-5-2016 at 05:02

You also said "I don't think there is any problem in using air compressor for these two gases."
Given that one of the gases is O2 and just about everyone has said you need a special compressor for that, do you accept you were wrong about that too?

gsd - 14-5-2016 at 07:03

No. I don't retract that statement.
It is expected that machine used is mechanically and electrically sound.

Quote: Originally posted by vmelkon  
YES!

Long ago, I had used one of these cheap 20$ for oxygen. Since I can't attach a hose to it, I build a box with a input hose and output hose. The entire compressor was in the box.

Since it sucks oxygen from the input hose, the entire box was filled with O2. The heat/spark from the electric motor of the compressor caused a fire. The compressor motor and plastic body burned.

There was no way to stop it.
The box was made with 2 cm thick glass :)


With this kind of contraption I bet it would have caught fire even with normal air.

gsd

unionised - 14-5-2016 at 11:36

Quote: Originally posted by gsd  
No. I don't retract that statement.
It is expected that machine used is mechanically and electrically sound.

Quote: Originally posted by vmelkon  
YES!

Long ago, I had used one of these cheap 20$ for oxygen. Since I can't attach a hose to it, I build a box with a input hose and output hose. The entire compressor was in the box.

Since it sucks oxygen from the input hose, the entire box was filled with O2. The heat/spark from the electric motor of the compressor caused a fire. The compressor motor and plastic body burned.

There was no way to stop it.
The box was made with 2 cm thick glass :)


With this kind of contraption I bet it would have caught fire even with normal air.

gsd

So, you think everyone else is wrong.Including whole booklets of stuff like this .
https://www.eiga.eu/index.php?id=172&tx_abdownloads_pi1%...

Interesting point of view- especially from someone who got a bunch of other things wrong.


[Edited on 14-5-16 by unionised]

[Edited on 14-5-16 by unionised]

[Edited on 14-5-16 by unionised]

j_sum1 - 14-5-2016 at 15:26

Hey, unionised. You got a partial retraction and a gracious one at that. The warning is out there for the OP. If gsd persists in the idea that running a highly oxidising gas through an unmodified compressor is a good idea, then that is pretty much on him. I would not labour the point.

gsd - 14-5-2016 at 16:52

Quote: Originally posted by unionised  

So, you think everyone else is wrong.Including whole booklets of stuff like this .
https://www.eiga.eu/index.php?id=172&tx_abdownloads_pi1%...

Interesting point of view- especially from someone who got a bunch of other things wrong.


Yes I do.

If I start following every safety information available on the net to the letter, then all I will be able to do in my lab/workshop is to sit in front of a computer and read reports. (And learn at some point of time that even that -excessive reading on computer - is a very hazardous thing to do).
Hell I would be hard pressed to even drink "Dihydrogen Monoxide" out of tap.

If I got "bunch of other things" wrong then so be it.

@j_sum1 - Nicely put.

gsd

PS: One thing just stuck me, OP has not specified from where s/he is going to get the "pure" CO2 and O2.

gsd

[Edited on 15-5-2016 by gsd]

XeonTheMGPony - 14-5-2016 at 20:47

Quote: Originally posted by gsd  
Quote: Originally posted by unionised  

So, you think everyone else is wrong.Including whole booklets of stuff like this .
https://www.eiga.eu/index.php?id=172&tx_abdownloads_pi1%...

Interesting point of view- especially from someone who got a bunch of other things wrong.


Yes I do.

If I start following every safety information available on the net to the letter, then all I will be able to do in my lab/workshop is to sit in front of a computer and read reports. (And learn at some point of time that even that -excessive reading on computer - is a very hazardous thing to do).
Hell I would be hard pressed to even drink "Dihydrogen Monoxide" out of tap.

If I got "bunch of other things" wrong then so be it.

@j_sum1 - Nicely put.

gsd

PS: One thing just stuck me, OP has not specified from where s/he is going to get the "pure" CO2 and O2.

gsd

[Edited on 15-5-2016 by gsd]


With oxygen in high concentrations things end very badly, ask the early Apollo astronauts.

There are very well lined out procedures to dealing with oxygen, being I work with oxygen I know them well.

What you don't know can and will kill you. Hot compressed oxygen makes nearly any thing flammable, inside a compressor where the gasses can not escape = ?

We did this once with a fridge compressor, as an experiment based off historical accidents in refrigeration work, where systems where accidentally charged with both O2 and N2

O2 = Boom
N2 = Boom, both cases people died (Not in our practical experiment)

SO to ignore safety, please jump off a bridge, so you do not give this hobby a bad name!

Or use your brain! Learn,plan, acquire materials to execute plan properly and safely.

[Edited on 15-5-2016 by XeonTheMGPony]

unionised - 15-5-2016 at 01:21

Quote: Originally posted by j_sum1  
Hey, unionised. You got a partial retraction and a gracious one at that. The warning is out there for the OP. If gsd persists in the idea that running a highly oxidising gas through an unmodified compressor is a good idea, then that is pretty much on him. I would not labour the point.

If I thought he'd only kill himself, I'd leave it. But the problem is that he might convince others that safety rules written in the light of previous accidents aren't a good thing.
Some people won't realise it's better to learn from other people's mistakes and they will repeat those mistakes and get hurt.

And it doesn't matter where he gets the gases from- the gases won't know either.

j_sum1 - 15-5-2016 at 01:37

Reading this thread in its entirity, it is pretty clear that O2 through a standard compressor is inviting disaster. gsd is not acknowledging that.I don't think hammering the point helps. I would think the few anecdotes given will be pretty convincing for the OP. And if not, slamming another SMer won't help.

vmelkon - 15-5-2016 at 03:09

Quote: Originally posted by XeonTheMGPony  

O2 = Boom
N2 = Boom, both cases people died (Not in our practical experiment)
[Edited on 15-5-2016 by XeonTheMGPony]


Why would the nitrogen one blow up?
I'm assuming you are talking about these home refrigerator compressors, which are weak.

In my case, I would be producing the oxygen with electrolysis. I guess I could store it in a inflatable polyethylene bag and avoid the compressor.

Yes, I understand how dangerous these things are. I have watched some OSHA videos on youtube.

XeonTheMGPony - 15-5-2016 at 08:12

Quote: Originally posted by vmelkon  
Quote: Originally posted by XeonTheMGPony  

O2 = Boom
N2 = Boom, both cases people died (Not in our practical experiment)
[Edited on 15-5-2016 by XeonTheMGPony]


Why would the nitrogen one blow up?
I'm assuming you are talking about these home refrigerator compressors, which are weak.

In my case, I would be producing the oxygen with electrolysis. I guess I could store it in a inflatable polyethylene bag and avoid the compressor.

Yes, I understand how dangerous these things are. I have watched some OSHA videos on youtube.


Because it is a high compression gas, in a refrigeration system not designed for a trans critical process the pressure builds and blows the head plate off the compressor, during test procedures, and no I am talking about big industrial compressors, doesn't matter though flying metal and flesh, bad things happen.


I should have clarified that. both cases high light the dangers of playing with such systems.

The point of the Jules Thompson process is it keeps the pressures low (Low being upwards of 3k + PSI) it is a fractional system by nature.

The lower the pressure delta the longer it takes but point being it can be don safely with more conventional compressors and some proper scrubbing gear.

Once dealing with pure O2 is when all the large danger starts, LO2 can cause some materials to spontaneously combust if they have sufficient temp!

O2 is nothing to dick around with in large amounts, but follow good safety protocols and be alert and mind full of the system as a whole it is just as safe as any thing ells!

[Edited on 15-5-2016 by XeonTheMGPony]

[Edited on 15-5-2016 by XeonTheMGPony]

[Edited on 15-5-2016 by XeonTheMGPony]

XeonTheMGPony - 15-5-2016 at 08:28

FYI those "weak" fridge pots will exceed 500 psi with out blinking! Ignorance can and WILL kill you!