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Blowdown Valve Restriction Orifice Sizing

ro depressurisation hysys peak flow fire case adiabatic case restriction orifice blowdown

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#1 Messery

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Posted 22 May 2017 - 10:11 PM

Dears,

I would like to check the size of an installed RO downstream blowdown valve in a gas processing plant as it didn't meet the blowdown criteria during last plant ESD (final pressure of 7 bars within 15 mins)

The plant is old & the blowdown time wasn't checked before.

 

Given:

Operating pressure=88 bars

Operating temperature varies through the section (55 C before contactor , 60 C in the contactor, 30 C after gas gas exchanger)

Composition (varies also)

blowdown valve  whose downstrean orifice to be resized installed on gas gas exchanger outlet

Volumes of piping & vessels are known.(40 m3)

 

Hysys depressurisation utility to be used for peak flow & low temperature check then RO sizing would be completed with another software, but I have the following queries:

 

1-Which temperature & composition to use

2- Which case to use (fire cases or adiabatic)

3- start from design or operating pressure

4-Concerning valve parameter tab, which vapor flow equation to use

5-Heat flux tab, which heat loss model to use.

& what if heat loss is ignored, How would the calculated area be affected

6-Isentropic efficiency, what is the proper value to use in my case

 

 

I know I am asking for a lot of things, but this is my first assignment & I want to return back with reasonable value.

 



#2 Bobby Strain

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Posted 22 May 2017 - 10:38 PM

Well, you have a real dilemma. What you really should do is to have a frank discussion with your supervisor. And ask for some guidance. The worst thing you can do is get advice from people you don't know, and fumble in the dark. This is serious business and should be properly addressed. Your supervisor will be understanding and offer proper support. If not, you should seek other employment where you have an opportunity to develop your engineering skills.

 

Bobby

 

.



#3 serra

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Posted 23 May 2017 - 02:06 AM

I agree with Bobby,

as first step all potentially hazardous conditions should be identified and evaluated

then you can use a software to simulate blowdown and/or calculate Valve / Orifice parameters,

nowadays most simulators include procedures to simulate vessel depressurization

depending from the software parameters such as isentropic efficiency may have large impact on final results,

other applications can include procedures for estimating heat transfer (vapor/liquid/walls) or simulate valves / orifices with HEM or similar methods,

as result you can get very different results depending from settings...



#4 Messery

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Posted 23 May 2017 - 12:53 PM

Well, you have a real dilemma. What you really should do is to have a frank discussion with your supervisor. And ask for some guidance. The worst thing you can do is get advice from people you don't know, and fumble in the dark. This is serious business and should be properly addressed. Your supervisor will be understanding and offer proper support. If not, you should seek other employment where you have an opportunity to develop your engineering skills.

 

Bobby

 

.

Thanks Bobby, you are right it's my first step to engineering work.

Actually no real decision will be taken according to my preliminary calculations.

It's just an exercise for my self.

Also I want to discuss the issue with my supervisor with a reasonable background & this why I have started the thread.

 

Please pick one of my questions & enlighten me.



#5 Messery

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Posted 23 May 2017 - 12:56 PM

I agree with Bobby,

as first step all potentially hazardous conditions should be identified and evaluated

then you can use a software to simulate blowdown and/or calculate Valve / Orifice parameters,

nowadays most simulators include procedures to simulate vessel depressurization

depending from the software parameters such as isentropic efficiency may have large impact on final results,

other applications can include procedures for estimating heat transfer (vapor/liquid/walls) or simulate valves / orifices with HEM or similar methods,

as result you can get very different results depending from settings...

As I mentioned in my reply to Bobby this just an exercise for my self.

Many questions arise & having guidance & answers from professionals would be great.



#6 Messery

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Posted 23 May 2017 - 01:35 PM

Lets make it more specific,

I need a reply to the second query (which case to use, fire cases or adiabatic)



#7 serra

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Posted 24 May 2017 - 02:29 AM

the student's forum is a good place for generic questions,

anyway, you may find answers in this forum and publications as,

for example, API 521 (pressure relieving and depressuring systems),

for the settings of a software it depends from specific application,

as said nowadays most simulators include specific procedures but

the details change from software to software and results may differ.



#8 flarenuf

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Posted 07 June 2017 - 05:49 AM   Best Answer

hi

attached are two good articles from Saeid that may help you with your initial introduction into depressuring topics

There are many others on the web so i suggest a google search and some spare time reading.
Read what different people say and if you are then still unsure talk to your supervisor to clarify.

 

as Bobby says
  "The worst thing you can do is get advice from people you don't know, and fumble in the dark. This is serious business and should be properly addressed."
look at API 520 521 to get an idea of the Industry standards and recommendations.

good luck

Attached Files



#9 Messery

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Posted 17 June 2017 - 04:27 AM

hi

attached are two good articles from Saeid that may help you with your initial introduction into depressuring topics

There are many others on the web so i suggest a google search and some spare time reading.
Read what different people say and if you are then still unsure talk to your supervisor to clarify.

 

as Bobby says
  "The worst thing you can do is get advice from people you don't know, and fumble in the dark. This is serious business and should be properly addressed."
look at API 520 521 to get an idea of the Industry standards and recommendations.

good luck

Many Thanks flarenuf,

Really helpful articles






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