CO2 vs Nitrogen in LPG Systems

[Saint1968]

Hi
In a new LPG-cylinder it helps 1. time lighting of gas if the cylinder is charged with CO2 instead of air prefilling of LPG.

Will Nitrogen have same effect?

 

[berkeman]

Hi
In a new LPG-cylinder it helps 1. time lighting of gas if the cylinder is charged with CO2 instead of air prefilling of LPG.

Will Nitrogen have same effect?

Welcome to the PF.

Sorry, but your post is not very clear. Can you post links to the types of LPG cylinder systems you are referring to? Something like this?

http://www.venusgas.com/images/airmix.jpg

 

[anorlunda]

Is the idea to increase the pressure in the tank with CO2?

 

[Averagesupernova]

There is no need to put anything in an LPG cylinder besides the fuel itself. It will boil until it pressurizes itself and reaches an equilibrium. I have worked a fair amount with propane.

 

[Saint1968]

The kind of cylinders I talk about is this: http://www.ppsolutions.com.tw/plasticnotes/lpg-cylinders-technical-specification

Manufacturer deliever the cylinder with atmosfære of CO2 insteed of air. This make the lpg Easy to ignite the forst time after filled with lpg.

If air inside the air comes out first and can't be ignited. CO2 mix with log and ignite easy.

Will Nitrogen mix with log? Or will IT come out of cylinder first, like air?

Is the idea to increase the pressure in the tank with CO2?

No. Idea is to easy ignition by avoiding air trapped inside the cylinder to come our first. Co2 mix with lpg or are more heavy than lpg.

 

[CWatters]

Edited: most likely they put in CO2 to stop an explosion or corrosion of the cylinder by displacing the oxygen in air?

If that's the reason then I think nitrogen will also work.

 

[anorlunda]

This make the lpg Easy to ignite the forst time after filled with lpg.

I'm sorry but we do not understand this part. How does it make it easier to ignite?

 

[NascentOxygen]

My guess is that N₂ should function the same as CO₂ but not for the reason you think. Note, I am just guessing, but I think it might be the O₂ premixed with the LPG that is hindering the gas sustaining a flame. You may have noticed how a Bunsen burner can be nigh impossible to light if you premix an abundance of air with the gas; the mixture can certainly be burnt but you have to keep the lighted match held in the gas stream.

It may seem that your ignition difficulty is due to a non-combustible fraction first issuing from your freshly filled LPG cylinder, but I think the gaseous component above the liquid in the tank will be uniformly mixed. If there is appreciable air then I think it's contributing too much O₂ to the gas coming off, making a LPG:O₂ mixture that is too lean for its combustion flame front to advance against the flow and set up a self-sustaining flame. The gas stream is blowing its own flame away.

It's a good question, but probably a better fit in the chemistry section, so I'll move it there.

 

[OldYat47]

Oxygen or air and LPG inside a sealed cylinder sounds like a recipe for disaster. Reference NPGA safety bulletin 133-89 (a). It will also reduce cylinder capacity.

 

[berkeman]

Oxygen and LPG inside a sealed cylinder sounds like a recipe for disaster.

Depends on pressure and temperature. Have you heard of BLEVEs?

 

[Saint1968]

I'm sorry but we do not understand this part. How does it make it easier to ignite?

It seems like if it is Oxygene inside the cylinder that oxygene come out before the LPG. If you replace oxygene with Co2 it seems like eighter; CO2 mix with LPG or are more heavy than LPG.

 

[Saint1968]

Depends on pressure and temperature. Have you heard of BLEVEs?

No pressure. Air or CO2 is only the volume trapped inside the cylinder mounting the valve.

 

[NascentOxygen]

No pressure. Air or CO2 is only the volume trapped inside the cylinder mounting the valve.

Isn't the LPG vapour exerting pressure?

 

[Saint1968]

Isn't the LPG vapour exerting pressure?

Yes. LPG is building pressure as normal, but somehow the air/oxygen comes out first. (Only some seconds).

I think its related to the weight of oxygene.(lighter than lpg)?

 

[anorlunda]

It sounds like you are describing a "purge" of the tanks for the first use.

They ship new with no LPG. When they are filled the first time, some air (or CO2 or N2) remains in the tank. The first time you use it, the air will be "purged" . When the tank is empty, only LPG gas remains, waiting to be filled again.

So the answer to your question is yes, N2 would work as well as CO2.

 

[jim mcnamara]

CO₂ is soluble in alkanes, N₂ is not - apparently. So when you open the ignite the very first time N₂ is not liquid at the pressure inside the lpg tank. So N₂ comes out first because one keeps the valve/tank upright so liquid propane does not come out of the valve and cause a disaster.

N₂ is on top, because pressure at room temp in the tank is not sufficient to liquify the nitrogen.

I assume CO₂ leads to better "first ignition".

https://srdata.nist.gov/solubility/IUPAC/SDS-50/SDS-50.pdf This is a long paper, so I just skimmed the alkanes chapter. Any corrections are welcome.
I cannot get to the ACS site for what seems to be a more concise resource. Perhaps @DrClaude or @Borek are able to do so.

 

[Saint1968]

It sounds like you are describing a "purge" of the tanks for the first use.

They ship new with no LPG. When they are filled the first time, some air (or CO2 or N2) remains in the tank. The first time you use it, the air will be "purged" . When the tank is empty, only LPG gas remains, waiting to be filled again.

So the answer to your question is yes, N2 would work as well as CO2.

You are right. It is some remains of air or Co2 inside the cylinders the first time. If you purge the cylinder i doesn't matter if it is air or CO2 inside. If you purge only lpg remains and ignition is easy.
Co2 is a way to avoid to purge and still be able to ignite easy.

 

[Tom.G]

does'nt matter if it is air or CO2 inside.

Are you sure you want a pressurized air (Oxygen) - Flammable Gas mixture in the plumbing when you ignite? Seems like a set-up for an explosion in the plumbing.

 

[Saint1968]

Are you sure you want a pressurized air (Oxygen) - Flammable Gas mixture in the plumbing when you ignite? Seems like a set-up for an explosion in the plumbing.

No pressure. Air or CO2 is only the volume trapped inside the cylinder when mounting the valve.

 

[NascentOxygen]

CO2 is soluble in alkanes, N2 is not - apparently.

Solubility is a good explanation. So it follows that for ease of first ignition, nitrogen would give no significant improvement over air.