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Hydrogen limits

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cryotechnic

Chemical
Dec 20, 2003
92
Known is that the LEL/UEL of hydrogen in air is: 4.1%-76%

In our plant we have the following mixture:
2,0% Oxygen
4,5% Hydrogen
0,5% Nitrogen
93% Argon
Pressure and temperature of this gas mixture: 400dgrC, 4,5barg

What is the LEL/UEL in this mixture?
Does the temperature and the pressure have any influence on the LEL/UEL?

Thanks
Cryotechnic

"Math is the ruler of your potential succes...."
 
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I believe (rather than know) that oxygen activity is very pressure dependent, with the activity of 5 atm air almost equivilent to 1 atm O2.

I would try this on the occupational health and safety board.

Dave Hasse
dave.hasse@Air Liquide.com
 
I have to explain my original post a little. Now I realize that it's not complete.

In our proces we start with the following mixture:
2,0% Oxygen
0,5% Nitrogen
97,5% Argon
temperature and pressure of this mixture: 20dgr C and 4,5barg

Than we supply 4,5% hydrogen to this mixture. The mixture runs through a catalyst. Here the Oxygen and Hydrogen reacts to water. Heat is formed with thes proces
After the catalyst the mixture has a temperature of 400dgrC.

So in the proces before the catalyst, we have oxygen, hydrogen, argon, nitrogen. The LEL/UEL I'm looking for are related to that part.

@EdStainless,
Do you have the data you are talking about? Or do you know where to find it?

Cryotechnic




"Math is the ruler of your potential succes...."
 
Hydrogen auto ignition temp. is 580 dgr C. so even if you exceeded the lel/Uel it shouldn't ignite at 400 dgr C. provided you don't have any other ignition source present. I guess it comes down to how confident you are temp will remain there.

also the lel and uel stand for lower explosive limit and upper respectively. the lower and upper flamability limits are what you have stated before. the explosive limits for hydrogen LEL 15.9% and the UEL 59% in air. these limits change with the temperature of air. I don't have any data for hydrogen you can use sorry. but my opinion is you wont have a problem at that temp anyway
 
@hydroscope,

Thank you Hydro. Your right when you say that when exceeding the LEL/UEL at 400dgrC the hydrogen will not auto ignite... BUT your only an ignition source away of big problems.[bigglasses]

The LEL 15,9% and the UEL 59% for hydrogen in air, is that at 400dgrC?

Cryotechnic

"Math is the ruler of your potential succes...."
 
The LEL and the UEL do change with the increase in temperature, but you also have to have a source of 21% O2. Given that the concentration of O2 is 2% and the H2 concentration is 0.5% at the start of the process, the LEL and UEL will not even be close to being approached even at 400 C. The bigger concerns should be for the storage and delivery system of the H2 depending on the amount you have stored.
 
no the LEL and UEL are both at STP in air % vol. safetydan is correct to point out what I overviewed to quick your oxygen content will also effect the LEL UEL LFL UFL, the more oxygen the wider they become.
 
ok
thank you for your help

Cryotechnic

"Math is the ruler of your potential succes...."
 
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