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N2 purge and Reduced Husa method

N2 purge and Reduced Husa method

N2 purge and Reduced Husa method

(OP)
I am trying to get to a min purge rate in our vent header to keep the O2 conc below the LEL. As I understand, Reduced Husa allows a flammable mixture to exist for some distance in the vent stack from the tip. I guess the assumption is that, if an ignition were to occur then the flame would only propagate for a short distance. I am used to flared rather than non-flared systems, however I don't know if it is good practice to use Reduced Husa on a flared system as the likelihood of a flame existing in the stack at low flow rates must be great?

I received some useful articles from Flareman on the subject (thanks Flareman). I am trying now to evaluate the effect of adding nitrogen to the purge gas stream. Part of the purge gas is fuel gas, and part is N2 (approx. 70% by vol. of required purge rate is made up of fuel gas). There are a couple of things which I would like to clear up and would appreciate feedback on:

1) It seems that N2 is better than fuel gas (Mr=18) at keeping air from entering the stack but I haven't seen a method for quantifying this. I have included the N2 as an equivalent quantity of fuel gas and assumed it to be conservative.

2) Small amounts of O2 are present in the N2 (it comes from a PSA unit). Can you use Reduced Husa directly in this case, or will the presence of O2 increase the purge rate? What is the latest thinking on this?

Thanks
Mark

RE: N2 purge and Reduced Husa method

Mark
I responded to this at Thread798-66873.


David

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