steam dispersion at atmospheric discharge

[Lasuen]

Hi,

I would like to know if it's any code which covers how to evaluate the necesary flow of steam to have a proper dispersion at an atmospheric discharge of a safety valve in LPG systems.

Thanks

 

[ajs1972]

According to EPA regulations you need to calculate the dispersion of released chemicals for some possible scenarios. There are some commercial simulators for this. Please read this EPA document regards.

 

[Lasuen]

Thank yoy very much for your answer, and the tecnical chapter attached.

IT is a very dificult method, and it must be analized for a spezialized engineering company.

I was looking for a more practical method, like standarized tables.Somebody told me about NFPA publicated practical tables.

anyway, thank you

 

[don1980]

Is this a liquid filled vessel? In other words, is liquid LPG entering the relief valve?

If this is an LPG drum, and only LPG vapor is entering the relief valve, then there's an easy way to do this hazard analysis. If this is a pop-acting safety valve, and the discharge is pointed upward into an open area, then there's no significant risk of creating an explosive gas cloud. That's because the jet velocity naturally induces large amounts of air into the flammable vapor, diluting it below the lower flammability limit (LFL). Regardless of the temperature or mass-flow, a dispersion analysis will reveal a predictable pattern to the flammable gas cloud. That flammable cloud is very narrow, and the height is a function of release rate. The concentration below the release point is well below the LFL. I have done a number of rigorous gas dispersion analyses and I haven't seen any cases in which a vapor cloud explosion cound be created due to the release of flammable vapor from a pop-acting PSV.

This is the basis for equation 22 in API 521. Do this simple calculation to document your analysis.

Note that this is only for flammable vapor releases - not liquid releases.

 

[Lasuen]

Hi again,

Safety service is a topping tower, atmosferic destilaton tower, with 40.000 NM3 gas release.

equation 22?? could you please tell me which page of new code, I can't see it.

It's a vey nice notice that dilucion with air, and not to be a problem

Regards

 

[don1980]

You might be looking at an old version of API 521. I'm referring to the 5th edition, which is the most recent edition and many paragraph number have changed.

Eq 22 is a Reynolds Number calculation. Do a word search for "Reynolds".