1 reply to this topic

[neel_avi]

Dear Experts

I request some advice and guidance from the forum regarding typical venting scenario in natural gas pipelines that I will be describing in this topic.

The natural gas pipeline I am going to talk about will be about 1000km in length, with sectionalising valves (isolation valves) at every 30km of the entire pipeline. The vent lines for 24, 30 and 36” sectionalising valves will be 8”, 10” and 12” respectively. 3-4 Compressors will be located strategically on the pipeline.
 schematic.png   480.85KB   17 downloads
Operating parameters

a.      Flow – 50 MMSCMD
b.      Pressure – 95 barg
c.      Temperature – 55 DegC
d.      Ambient Temp ~35 DegC
 

Design Parameters

a.       Pressure – 98 barg
b.      Temperature – 60/(-)20 DegC

 

Please refer to the attached schematic in conjunction to the description. In case of a pipe rupture or leak, the immediate upstream and downstream sectionalising valves (SV-1 and SV-2) for the affected segment are closed consecutively. The operator intervenes later and the two vent valves (VV1 and VV2) are opened to atmosphere to an extent that the lower design margin remains within safe limit (joule Thomson effect) and the velocity of the gas through the vent line (sound basically). After depressurisation the line is handed over for repair after following standard procedures for inertisation.

In this case I am required to calculate the time required to vent out the entire line pack. While doing so I arrived at a situation where pressure shoots upto 145 barg, immediately after closing the SV1&2 and opening the vent valve (VV1&2). It remains above the design pressure for 12-18 seconds for different

scenarios of vent opening and flow coefficient of the vent valves. I have done this simulation TGNET and obtained such results. 

I have tried to find out the minimum closing time required for the valves by using Joukowsky equation, after the lapse of which the transient simulation was started. Howev  schematic.png   480.85KB   17 downloads  schematic.png   480.85KB   17 downloadser, as I interpreted from Perry and in one of the earlier forums, Joukowsky equation is valid for liquids and steam.

My queries

1. Is such surge possible practically in the line between the two valves to such extents?

2. Is joukowsky equation valid for gases?

 

I request all to enlighten me on the subject and eradicate my ignorance.

Apologise for the longish mail. Would be happy to provide any further information if required. 

 

Regards

 

Avijit

[neel_avi]

Dear Experts,

 

requesting some suggestions. Please let me know if I have missed some information which is not providing enough clarity. 

 

regards

 

Avijit