5 replies to this topic

[cea]

A subsea pipeline transporting rich gas typically has a water dew point requirement of around -12°C to -18°C @ 70Bara, even though the seawater temperature outside the subsea pipeline usually is around 0°C to 4°C.
If we only talk about transport from an offshore field to an onshore terminal, where further dehydration usually takes place, why is the water dew point requirement so much lower than the ambient temperature?

[PingPong]

Water content in gas must be low enough to avoid hydrate formation at seawater temperature.

[Profe]

Hi Cea

 

For your question, attached you find a copy of 2 pages of "Handbook Natural Gas Engineering" by Dr Boyun Guo - GPC- 2005

 

I think that answer you.

 

Good luck

 

Fausto

Attached Files

•  Dehydration.pdf   138.98KB   38 downloads

Edited by Profe, 19 September 2014 - 09:57 AM.

[cea]

Hi profe,

Thanks for your share.

Let me reword my query.

If sea water bed temp is in range of 0 to 4 deg C & water dew point temp is -12 to -18 deg c @70 bara, what is need of drying the gas upto water dew point if that temp is not going to achieve.

Hope, I made my query more clear.

[benabed]

Hi cea,

 

May be the operating pressure of the pipeline is less than 70bara.

[ankur2061]

Cea,

 

Hydrate formation in gas pipelines is favored by high gas pressure and low gas temperatures. Free water is not essential for hydrate formation but presence of free water enhances the hydrate formation rate.

 

Hydrate formation temperature corresponding to a given gas pressure can be easily obtianed through process simulator such as HYSYS or others. A free software (CSMHYD) based on gas composition for determining hydrate formation temperature given the gas pressure, is available at the following link:

 

http://hydrates.mine...R/Software.html

 

If you are operating your subsea pipeline at temperatures well above the hydrate formation temperature at the operating pressure along the pipeline route, you don't need to provide any preventivive or mitigative measures due to hydrate formation.

 

Regards,

Ankur.

Edited by ankur2061, 20 September 2014 - 04:34 AM.