Methanol, Glycol injection 1

[DiegoMartinez]

This question might have a simple answer I do not know. Why where there is a high pressure drop across a PSV or PCV, they inject glycol or methanol upstream of the device?

 

[MortenA]

Im sorry but there may be language barrier here. I dont get the question BTW: PSV= saftety valev, PCV: Pressure control valve they are not similar in function.

Hopefully you can eloborate a little.

If it exists a small "java scetch" application would really benefit this site

Best regards

Morten

 

[TD2K]

If there is a high pressure drop across a valve in gas service, there is an accompanying temperature drop. If that temperature drop is sufficient, you can get hydrates downstream of the valve. The glycol or methanol injection is to prevent that.

I also have not seen this for a pressure relief valve (PSV).

 

[DiegoMartinez]

MortenA and TD2K,

Thank you guys for your reply. MortenA, the answer to your question is affirmative. PSV is pressure safety valve and PCV stands for pressure control valve.

TDK2,

I know that the dp accross the PCV creates hydrate downstream of the valve. Why they don't inject MEG or Methanol downstream then?

When I was working in Iran in sour gas compressor station, I ran into a case where a 1" Methanol injection line was connected to upstream of a PSV which was installed on the composite gas K.O.D.

Rgds,
M.E

 

[monaco8774]

The hydrate formation temperature depends also on pressure, downstream of your PSV the pressure is very low (usually less than 5 bar) so the hydrate formation temperature is much lower. For you PCV the flow is continuous and the pressure will usually be higher. This may be the reason in your case.

 

[TD2K]

The advantage I would imagine of adding it upstream of the control valve is that it also makes promotes good contact of the gas with the inhibiting fluid. It's going to get to the downstream side ;-)

The injection rates on a volumetric basis are pretty low typically if you think about it.

 

[DiegoMartinez]

Cheers TD2K. Makes sense.

 

[Monagas]

Hello my friends, at the plants that I´ve worked, the methanol or MEG injection sites, are always upstream of the place that the calculations had predicted the hydrate formation. i.e. PCV`s, Chillers and others heat exchangers.
You can ask for the simulation cases of your plant to the process engineering department, and you would learn more about hydrate formation across PCV`s, Injection rates, temperature and pressure conditions that promotes the hydrate formation

Hope this would help you.

My best regards from Venezuela !!

 

[DiegoMartinez]

Thank you Monagas,

All the best.

 

[weldsv1]

Hi all !
About injection methanol upstream of PCV. Once we had accident with PCV, because of leaking it hydrated. One of possible solution this problem proposed to inject methanol upstream of PCV.
Best regards.

 

[DiegoMartinez]

Weldsv1:

Could you please rephrase "because of leaking it hydrated"?

Do you mean you had a leak upstream of PCV and you had ice formation around it?

Thanks

 

[weldsv1]

MEbrahim:
Yes. It didn't look like ice. We didn't make special analysis for it. That plug looked like hydrate. The 4" outlet pipe was completly blocked that half metre plug.
Best regards.