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Pipeline Depressurization


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#1 Butterfly

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Posted 25 February 2015 - 12:51 PM

I know there are some related topics here, but my problem is that I don't know where should I start from.

 

I have a 8 km-8" gas pipeline operating at 2000 psig. I want to depressurize it to atm, no matter if time is more tan 15 min. I have been asked to fix a depresurizing rate of 2 ton/h (and check the time it takes).

 

I have neve done these kind of calcualtions. I was trying to use hysys depressurizing utility, but I cannot put a time higher tan 16 min. I think this utility is not the way I shoul do it...

 

 

Can you guide me a little?

 

Thank you!



#2 Zauberberg

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Posted 25 February 2015 - 12:56 PM

If it is that simple (just to limit the max flow rate), you can start by designing a restriction orifice which will pass maximum 2,000 kg/hr at differential pressure of 2,000 psig.

 

Refer to an excellent article/FAQ written by Dave Simpson at Eng-Tips. It shows almost about everything on pipeline depressurization: http://www.eng-tips....qs.cfm?fid=1864



#3 Ajay S. Satpute

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Posted 01 March 2015 - 07:44 AM

Hi,

 

1. There are 2 options available in Hysys Depressuring utility in "Design/Operating Conditions/Vapor outlet solving option"

    a. Calculate (RO) area for given final pressure or

    b. Calculate final pressure for given RO area

   

    And for both the options, you can change the Depressuring time. 

 

2. Please make sure the initial mass flow rate is 2 tph. It seems to be very less for the given system.

 

 

 

Regards.

 

Ajay S. Satpute


Edited by Ajay S. Satpute, 01 March 2015 - 11:39 PM.


#4 Butterfly

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Posted 02 March 2015 - 06:21 AM

Thank you for your answers

 

The problema I am having with the depressurization utility is that it does the calculation for 960 seconds (16 min), no matter how I fixed the time.

 

For example, I put a small hole, and I got the pressure profile for the first 16 minutes, even setting the time to 30 minutes (or more).

 

With a time higher tan 16 minutes, the only way I get the pressure profile till the end is when the hole is big enough to get the complete depressurization in that time. But then, I get a mass flowrate higher than I what I want.



#5 Ajay S. Satpute

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Posted 02 March 2015 - 07:19 AM

Butterfly,

 

Can you share the hysys file?

 

 

Regards.

 

Ajay S. Satpute



#6 Butterfly

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Posted 02 March 2015 - 09:03 AM

Sorry,I think I can't...

 

Maybe I used wrong parameters... I chose General vapor flow equation, with Cd= 0.7. Then, calculate pressure (vapor outlet solving option), and trying with different áreas to get between 2-10 ton/h flowrate.

 

I will also study the info sent by Zauberberg, to get a better undestanding.

 

Thanks for your help



#7 shan

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Posted 02 March 2015 - 12:02 PM

Your system is totally depressured at 16 min (system pressure = back pressure).  You may specify smaller RO to extend the depressuring process beyond 16 min.



#8 Butterfly

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Posted 02 March 2015 - 12:03 PM

I think there was something wrong with my hysys file. I created a new one, and it works now :)



#9 S.Chittibabu

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Posted 14 March 2015 - 04:43 AM

Grote Equation gives de-pressurization time. Attached spread sheet gives approximate time required for depressurization

Attached Files



#10 Manan_Joshi

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Posted 15 March 2015 - 12:58 AM

I had a simillar problem.  We have a flowline (well flow line) and we need to design system for manual depressrisation.  The utility in HYSYS does the flash calculations and if your system is two phase it fails to provide the results.  In such situration you need OLGA. I am still looking for the alternative how to perfoem such two phase depressrisation in HYSYS.






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