Can Nitrogen Replace CO2 for First Ignition in LPG Systems?

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Discussion Overview

The discussion revolves around the potential use of nitrogen as a replacement for carbon dioxide (CO2) in LPG (liquefied petroleum gas) cylinders to facilitate easier ignition during the first use. Participants explore the implications of using different gases in the cylinder, focusing on ignition characteristics and safety concerns.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that CO2 helps with the first ignition of LPG by displacing air, which may contain oxygen that hinders ignition.
  • Others question whether nitrogen would have a similar effect as CO2, with some proposing that nitrogen might not mix well with LPG due to its solubility characteristics.
  • One participant notes that the presence of air or oxygen in the cylinder could lead to difficulties in ignition, as it may create a mixture that is too lean for combustion.
  • There are claims that CO2 might be used to prevent explosions or corrosion by displacing oxygen, and some participants speculate that nitrogen could serve a similar purpose.
  • Concerns are raised about the safety of having a pressurized air and flammable gas mixture in the plumbing during ignition.
  • Some participants discuss the concept of "purging" the tank, suggesting that the first use involves removing residual air or CO2 before ignition.
  • One participant mentions that CO2 is soluble in alkanes while nitrogen is not, which could affect the ignition process.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the effectiveness of nitrogen compared to CO2 for ignition in LPG systems. The discussion remains unresolved, with no consensus on whether nitrogen would provide the same benefits as CO2.

Contextual Notes

Participants highlight various assumptions regarding gas behavior, solubility, and the physical properties of the gases involved. The discussion does not resolve the complexities of gas mixtures and their implications for ignition.

Saint1968
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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?
 
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Saint1968 said:
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

airmix.jpg
 

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Is the idea to increase the pressure in the tank with CO2?
 
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.
 
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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?
anorlunda said:
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.
 
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.
 
Last edited:
Saint1968 said:
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?
 
Last edited:
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.
 
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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.
 
  • #10
OldYat47 said:
Oxygen and LPG inside a sealed cylinder sounds like a recipe for disaster.
Depends on pressure and temperature. Have you heard of BLEVEs? :smile:
 
  • #11
anorlunda said:
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.
 
  • #12
berkeman said:
Depends on pressure and temperature. Have you heard of BLEVEs? :smile:
No pressure. Air or CO2 is only the volume trapped inside the cylinder mounting the valve.
 
  • #13
Saint1968 said:
No pressure. Air or CO2 is only the volume trapped inside the cylinder mounting the valve.
Isn't the LPG vapour exerting pressure?
 
  • #14
NascentOxygen said:
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)?
 
  • #15
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.
 
  • #16
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.
 
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  • #17
anorlunda said:
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.
 
  • #18
Saint1968 said:
does'nt matter if it is air[/color] 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.
 
  • #19
Tom.G said:
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.
 
  • #20
jim mcnamara said:
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.
 
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