5 replies to this topic

[Supriyo Mukherjee]

Dear All,

 

I have a pipeline of 350mm dia and 3500metres length. The pipeline is at  34 kg/cm2g(gaseous nitrogen).

I want to pressurise the pipeline to 44 kg/cm2g. I am using nitrogen cylinder(jumbo) of 150kg/cm2g each of 65m3. I need to calculate how many number of cylinders are required to perform this operation?

 

Kindly suggest me how to estimate the number of cylinders.

 

Regards,

 

Supriyo Mukherjee

[ankur2061]

Supriyo,

 

Volume of Pipe = pi*0.35²/4*3500 = 336.7 m³

 

Density of N₂ at 34 kg/cm²g = 35.033*28 / 0.0848*(273.15+30)*0.99 = 38.54 kg/m³

 

Density of N₂ at 44 kg/cm²g = 45.033*28 / 0.0848*(273.15+30)*0.99 = 49.54 kg/m³

 

(Note: Temperature assumed constant as 30°C)

 

Mass to be filled in pipeline = 336.7*(49.54-38.54) = 3703 kg

 

Density of N₂ at 150 kg/cm²g = 151.033*28 / 0.0848*(273.15+30)*1.006 = 163.5 kg/m³

 

Mass contained in each cylinder = 65*163.5 = 10627.5 kg

 

No. of cylinders required = 3703 / 10627.5 = 0.35 cylinder

 

Roughly 1/3^rd of a cylinder of 65 m³ at 150 kg/cm2g will be required to fill the pipeline. By the way I have never heard of a 65 m³ cylinder. In my view 65 m³ volume qualifies as a vessel. 

 

You can do the same calculations in moles instead of mass.

 

Regards,

Ankur.

[thorium90]

I think supnit might have been referring to large tube trailers. A few of those would likely have water volumes of around 65m3.

https://www.google.c...iw=1920&bih=863

Attached Files

•  Compressed gas Equipment -April 2008.pdf   1.48MB   272 downloads

Edited by thorium90, 20 June 2013 - 09:23 AM.

[Art Montemayor]

I believe Thorium90 is correct in his suspicions.  I don't understand Supnit's description of his gas cylinder content either.  I strongly suspect that what he is trying to describe is a gas cylinder that contains 65 standard m³ and not 65 m³ of actual volume (water content).  I started to calculate the required volume(s) as Ankur did - but using actual Database densities to see if the results compared well with Ankur's, and they did.

 

Refer to the attached workbook and see the Air Liquide listing of normal, conventional nitrogen compressed gas cylinders to see the available capacities.  If some one is trying to pressurize a 3.5 km pipeline I would also suggest that tube trailers be employed.  This has been the method used in the past - not using normal compressed gas cylinders.  And even then, you are going to require a LOT of tube trailers because you can only transfer the high pressure nitrogen by the cascade system.  This leavea a lot of unused, lower pressure nitrogen behind.   What I would do is obtain a skid-mounted liquid nitrogen vessel complete with a liquid nitrogen pump and pump the liquid through an ambient vaporizer and into the pipeline.  This is much faster, more efficient, and wastes no nitrogen.

   Pressurizing Pipeline with Nitrogen.xlsx   140.96KB   421 downloads

[Supriyo Mukherjee]

Thank you Mr. Montemayor.

 

I have asked my project manager to go for the option with pump, and we are doing it the same way.  About cylinder volume, it was the fault of a sales person in the supplying company who misunderstood the difference between NM³ and actual m³.  So, all your suggestions are being basically proven right.

 

Thanks once again

[Art Montemayor]

Suprit:

 

You are welcome.  One point I would emphasize on this topic is the safety aspect of compressing nitrogen in such a pipeline.  I presume this pipeline is out in the isolated territory and is a transport pipeline - not a distribution pipeline in/close to an infrastructure and residential area.  This being the case, the only process hazard I see here is the possibility of over-pressuring the pipeline beyond its rated level or suffering a pipeline rupture during the pressuring operation.  If this were to occur, you must ensure that the nitrogen supplier is contracted under a binding agreement that a safety plan be submitted by him and approved by you in carrying out the proposed application.  A Hazop certainly would be expected for this operation.  I foresee that a liquid nitrogen supplier would provide cryogenic tanker trucks at the injection site (and this site should be clearly identified by you) together with a positive displacement cryogenic pump and ambient vaporizer.  I would expect that the pump would be fully instrumented by the contractor to shutdown immediately upon a sudden loss of pressure in the pipeline while the pump suction line would be blocked off with an automatic block valve.  The same pump shutdown would be employed as the pump approaches the final, specified pipeline pressure.  I would set this pressure at approximately 95% of fill and do the final pressurization manually with superintendents and engineers present.  Once reached, the pressure in the pipeline should be left to settle down and equalize.  This might take an additional day to monitor the situation.  If the pressure decreases, an additional boost in pressure might be required.

 

Good luck.