Hydrogen ignition modes 2

[viridor]

Dear all,

I am investigating modes of hydrogen ignition from a pipline leak.

Some suggested modes are:

1) Self ignition
2) Ignition via Electro-static Discharge (ESD) from clothes
3) Ignition via ESD caused by near by steam leak
4) Sparks from tools/chains from nearby work
5) Pyrophoric deposits in main
6) Smoking!
7) Non spark safe/intrinsically safe electronic equipment
8) Lightening

Questions:

1) I have received mixed messages about H2 self ignition; is there any experience or a theoretical case for this?

2) For ESD from People's clothes and Steam leaks; I have not found quantitative data for this - can anyone help?

3) Can anyone suggest any other modes of ignition that has not been considered?

I would appreciate any help on these,

Regards

 

[owg]

1) Hydrogen self ignition is not a sufficient definition. A hydrogen release can ignite due to a static discharge generated by the velocity of the release itself. Hydrogen has a very low ignition energy requirement. An interesting special case is whether a cloud of hydrogen can gather and then cause a really big unconfined vapour cloud explosion. In the early sixties it was thought that this could not happen. Then it happened during an intentional hydrogen release which was part of rocket motor development.
2) NFPA68 I think lists Minimum Energies for Ignition. It may list energies generated by various events. Good sources are Lees, Bodurtha, and some of the CCPS books. Trevor Kletz is also a good source of this type of data. Sorry I do not have the exact references at hand.
3) The most popular way to make pipeline explosions is to dig them up with a back hoe. This provides the leak and the source of ignition. Welding on the line will also do the job.

 

[Rich2001]

Hydrogen in the ordinary temperature and pressure range has an negative Joule-Thompson coefficient so as it expands (i.e. a leak) from a high preesure source it heats up. Temperature can rise to the auto-ignition range quite quickly. (note this is not unique to hydrogen all gases will heat up upon expansion above some temperature - called the inversion temperature, it just happens that ambient temperatures are above the inversion temperature of hydrogen.)

 

[owg]

Hydrogen auto igntion temperature is 500°C. Would hydrogen really heat up to 500 deg C from moderate temperature and pressure on release to atmosphere. It would also have to heat up the diluting air to 500 deg C for auto ignition.

 

[owg]

There is a T, P, H, calculator for hydrogen at

http://www.inspi.ufl.edu/data/h_prop_package.html

For isenthalpic expansion from 500 psia to 15 psia, starting at 200 deg F, the hydrogen would only pick up 2 deg F. I would certainly welcome a second opinion on this.

 

[kolya]

An explosive concentration of hydrogen in ambient air may be ignited upon contact with platinum metal, most easily with finely divided or powdered platinum metal. These metals are used as catalysts for hydrogenations and other reactions. Maybe also rhodium and palladium might work, I'm not sure.

 

[25362]

Some info. I could gather from literature: flammability % limits in air (LFL-HFL) for hydrogen are among the widest known (4-75) exceeded by acetylene (2.5-90), diborane(1-90), ethylene oxide(3-100), hydrazine on iron rust (5-100) and propyl nitrate (2-100). Published autoignition temperatures for hydrogen run from 400C to 560C. Impact of steel tools may ignite hydrogen clouds.

As always I hope the above may be of help to Viridor.