6 replies to this topic

[Corwin]

How can I calculate vent size to atmosphere for PSV installed on a hydrogen compressor knock-out drum? PSV set to 150 bar.

What is maximum allowable velocity for hydrogen in vent lines to atmosphere?

[Lowflo]

When you ask, what is the max velocity for releasing H2 to the atmosphere, I assume you're asking for the max allowable velocity to prevent the H2 from igniting.

Unless the H2 is very dilute, it's unrealistic to expect it not to ignite when released from a PSV. When dealing with PSVs in H2 service, assume it will ignite (it usually will) and connect a snuffing steam line to the tailpipe so the flame can be extinguished. The steam flow can be opened manually or automatically. Also, be aware that you'll only see a H2 flame at night. During the daytime, a flame won't be detected unless you have instrumentation for doing so.

[fallah]

Corwin,

At a glance seems it needs to be tied to relevant flare network.Why don't you consider this possibility for mentioned PSV vent line?

Fallah

[Corwin]

Fallah, it's very problematic to connect this vent to flare system, so only possible solution is relief to atmosphere. I think to use several restriction orifices to decrease pressure and velocity. Will it help in your opinion?

[fallah]

Corwin,

Accidentally in such situation when you have to discharge the gas to the atmosphere,you should increase the gas velocity in order to create acceptable dispersion.Sec 6.3.2.2 of API 521 (FIFTH EDITION) may help you out in this regard.

Fallah

[Corwin]

Thank you, Fallah.

I've decided to make 16 inch vent (hydrogen velocity about 230 m/s) with automatic steam injection in pipe.

[saeed.s]

Fallah, it's very problematic to connect this vent to flare system, so only possible solution is relief to atmosphere. I think to use several restriction orifices to decrease pressure and velocity. Will it help in your opinion?

I can not understand why using flare network is problematic? for example, in hydrocracking unit all the hydrogen compressor psv ( set press=203 barg , 105barg , 42.7 barg ) are connected to flare ( HP flare) network.