Vacating Tedlar Bags Containing Explosive Gases

Hoffer in the Lab,

What does the other 10% of the gas in the tedlar bag consist of?

How large are the tedlar bags you are evacuating? (0.5 l, 1.0 l, 10 l, 100 l)

What kind of vacuum pump is being used?

Into what does the vacuum pump discharge?

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As you are probably aware, Hydrogen will burn/explode when it's "atmospheric" concentration is between 4% and 75% (the lower and upper explosive limits, respectively), with "air" making up the balance of the atmosphere.

The key ingredient from the "balance of the atmosphere" that will support combustion is of course oxygen...

Can you set up the vacuum pump so that it is bathed in nitrogen gas, and discharges into a nitrogen enriched atmosphere, which then vents to the ambient air through a metal screened flame arrestor...

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Just my $0.02...

The other 10% is CH4, C2H2, C2H4, CO, N2, CO2, C2H6. The size is 1 litre. The vacuum pump is a dry piston type which discharges into the lab atmosphere. We are going to vent this outside.

Dennis

Except for the N₂ & CO₂ gases, all the others are flammable. Since N₂ is inert and CO₂ will not normally support combustion, the mixture should be safe as long as it does not come into contact with any oxidizing agent. Ensure that your venting system is equipped with a flashback arrestor to prevent any unpleasant mishaps.

Hi,

this is an application that should be designed fail-safe!

So if one part of the system fails the rest shall not explode or make other hazards.

1. Any leaks - either the total vacuum system enclosed in a separate housing and venting, or a platinum "self igniting" catalytic pill near any possible leak. This will start a flame as soon as there is a sufficient amount of gas.

2. Ask the vacuum pump supplier - they have a lot of experience with any gas. We once used a nonburnable oil in a pump as this is very inert. (Fomblin or Krytox).

3. Can you change the pump to a non-mechanical suction pump?

4. What is the source of the hydrogen? Is this safe?

Let an expert look at the total installation. This will suffice in most cases.

RHABE

Hi RHAGE

I don't believe we have any leaks as the pump will hold a good vacuum even though it is around 30 years old. It is a dry pump so no oil. A non-mechanical pump is a possible option I didn't think of. The hydrogen is waste gas from our process and is what we sample to see how our methane is cracking.

Thanks

Hi,

depending on the principle of analysis may be you can circumvent any dangerous amount of hydrogen?

Gas-chromatography? Mass spectrometer? Else?

mm³ to cm³ would be sufficient.

RHABE

Purge the bag with nitrogen, venting the purged hydrogen as you do now, then pump out the nitrogen.

Hi Jaguar,

Do you know if there are dual port tedlar bags so you can feed N2 in and allow flow through to exit?

Dennis

Why not use a copper or stainless steel tube run to outside. Flare the gas and let the resulting convection draw the gas out of the bag?