Flammability of gas with multiple inerts+flammables

[Jobst]

Hi Everyone,

I'm trying to estimate the flammability ranges of a number of gases, all containing various amounts of two flammable gases (CO and H2) and several inerts (H2O, N2, CO2).

From thread (

http://www.eng-tips.com/viewthread.cfm?qid=33615)

I have dug up the US Bureau of Mines Bulletin 503 and found the chart on page 7.

Is it legitimate to split the gas into two components, say H2+N2 and CO+CO2, find the flammable limits from the chart (ignoring for now the water content), then use Le Chatelier's law to calculate the flamambility range of the mixture of the two mixtures?

I would of course be wary and use a big safety margin before designing anything based on these numbers...

I have also in the past used ISO 10156 for determining flammability of gases, but not too keen on applying this one as it is just for when to apply flammable cylinder standards to a compressed gas...

Any pointers appreciated!

 

[Flareman]

Jobst
Your approach will work. pro-rating the values from the charts and then using Le Chatelier is a good technique.
Essentially you will find that the volumetric dilution of inerts works roughly in proportion to the specific heat of th diluent at flame temperature. I call it Nitrogen Equivalent. Nitrogen=1, H2O=1.35, CO2=1.82 so you have it for water too. I suggest a FOS of at least 1.5. Err on the safe side to ensure you are flammable (if you wish) or not flammable if you don't.
David