3 replies to this topic

[Finchh]

Hi everyone,

 

I'm seeking advice on drying a 56-inch diameter, 20 km long carbon steel sales gas pipeline for pre-commissioning. The required dryness level is exceptionally low, with a water content target of less than 0.1 ppmV.

 

We typically use nitrogen purging for drying, achieving a dew point of around -10°C. However, this method might not reach the ultra-low water content necessary in this case.

 

My questions are:

1. Drying Techniques: What drying techniques and methodologies would be most suitable for achieving a water content below 0.1 ppmV?

2. Dew Point Correlation: Considering the target water content, what dew point temperature would be necessary?

3. Nitrogen Purging Optimization: If nitrogen purging remains a viable option,

   • What amount of nitrogen would be required for purging the pipeline?
   • How long would the purge cycle need to last?
   • Are there specific equations for calculating these parameters?
   • What pressure would be recommended for the nitrogen purge?

Any insights or experience with similar ultra-low water content drying projects in pipelines would be greatly appreciated.

 

Thanks in advance,

[breizh]

Hi,

If I was in your shoes, I will use Hot dry compressed air to remove the maximum quantity of water from your system. You need to take periodic sample of your gas outlet to measure the water content. When you reach a plateau, you may switch to Nitrogen to remove traces of water, you will also check the water content regularly to optimize the N2 Consumption. 

Your system is big, the reason why I will use air first. 

Calculation cannot help much in reality, analysis is key. You need to find a lab (inhouse or outsourcing) to measure H2O content in air stream or Nitrogen stream.

I've attached calculators to support.

EDIT: You may want to consult for pigging your pipe prior to use N2

https://www.dexon-te...ustries/oil-gas

http://marineman.ir/...ndbook-2003.pdf

Good luck

Breizh 

Attached Files

•  inerting & blanketing.pdf   180.8KB   2 downloads
•  Nitrogen Purge D.Crowl.xls   86KB   3 downloads

[shvet1]

1. Drying Techniques: What drying techniques and methodologies would be most suitable for achieving a water content below 0.1 ppmV?

 

Consider pig train with methanol, glycols (mainly MEG), or a proprietary drying gel

https://www.gate.ene...-drying-methods

https://nigen.com/pi...fter-hydrotest/

 

 

update

 

Attached Files

•  Mcallister Pipeline Rules of Thumb Handbook 2001.pdf   73.12KB   7 downloads

Edited by shvet1, 21 August 2024 - 11:35 PM.

[Dacs]

What drying techniques and methodologies would be most suitable for achieving a water content below 0.1 ppmV?

 

 

Desiccant-based dryers can work as long as -40°C dew point (or even lower)

 

Considering the target water content, what dew point temperature would be necessary?

 

 

My rough estimate would be between -40 to -60°C

 

 

If nitrogen purging remains a viable option,

• What amount of nitrogen would be required for purging the pipeline?
• How long would the purge cycle need to last?
• Are there specific equations for calculating these parameters?
• What pressure would be recommended for the nitrogen purge?

 

The challenges are:

1. Volume of purge media
2. Accessibility (I presume this pipeline is at remote location)

You can (as order of magnitude) estimate the requirement by considering displacing 2 to 4 times the pipeline volume, but the main challenge is how to ensure proper purging.

 

You may have to deal with low pockets in your pipeline where water can settle. Also you may be needing an active measurement of purge quality to ensure the dryness is achieved.

 

For the purge source, there are mobile N2 generator skids available, though I'm sure if it does achieve that dew point you require. Alternatively, you can use liquid N2 vaporizers

 

Are you in the position to do pigging/scraping operation? If so, consider that approach before doing the purge to at least remove all settled liquids inside the pipeline. Use the N2 to push the pig/scraper.

Edited by Dacs, 22 August 2024 - 12:10 AM.