19 replies to this topic

[Anshul619]

Dear all,

 

I was studying the sizing of PSV in the oil gas separator.

 

And came across the terminology;"LP & HP Flare Header".

 

I want to know how to size these headers.

I know the concept of erosion velocity but I am not able to grasp the concept of Flare header sizing.

 

Can any one pls direct me in right direction & help me in sizing of Flare headers.

 

I am working in the vendor company.

Edited by Anshul619, 10 July 2013 - 04:20 AM.

[fallah]

Hi,

 

Reading he API 521 is a good starting point toward the target...

[Anshul619]

Hi,

 

Reading he API 521 is a good starting point toward the target...

 

Hello Naser,

 

Thanks for reply.

 

Can tell me the specific pages in it which only deal with sizing of LP/HP Header.

I do not want to size flare stack or KOD,Just Headers.

 

Moreover,I have studied the API 521, 5th Ed but can not find the topics on LP/HP Header.

 

Please direct me accordingly.

 

And again thanks for your assistace.
 

Edited by Anshul619, 10 July 2013 - 07:11 AM.

[Shivshankar]

HI ANshul,

 

Here are some links might be helpful.

 

http://knowledgelovi...are-system.html

 

http://kolmetz.com/p...lare Rev1.1.pdf

 

http://www.tech-trad...laring 2010.pdf

 

http://people.clarks...gn/FlareSel.pdf

 

http://academia.edu/...41/flare_system

 

Regards

Shivshankar

[Anshul619]

HI ANshul,

 

Here are some links might be helpful.

 

http://knowledgelovi...are-system.html

 

http://kolmetz.com/p...lare Rev1.1.pdf

 

http://www.tech-trad...laring 2010.pdf

 

http://people.clarks...gn/FlareSel.pdf

 

http://academia.edu/...41/flare_system

 

Regards

Shivsha

 

 

Thank You Shivshankar Sir

 

These are very good links.

 

But I need to size the HP/LP flare headers.....in which PSV lines are connected from the compressor skid.

The headers are in the compressor skid(which is supplied by vendor) and they are converging in the main flare header(which is in scope of client).

 

So,my basic question is : "HOW TO SIZE FLARE HEADERS FOR BOTH LP & HP WHICH ARE GIVEN BY VENDOR"

 

What should be my Initial Parameters for starting the sizing??

What should be the approch??

And where can I find the texts or articles or books regarding  my problem???

 

Once again thank you sir;I hope you can reply to my problem and try helping me solve it.

[fallah]

Hi,

 

The link in below might be helpful:

 

http://www.cheresour...-header-design/

 

But you should strongly note to below statement from Joe Wong included in it: 

 

"Designing flare system is NOT easy stuff. Certain years of experiences and exposures is required... Moreover this is SAFETY related issue. I think you need a competence and experience people to guide you personally and look through in details on your design to avoid any mistake."

 

[Anshul619]

Hi,

 

The link in below might be helpful:

 

http://www.cheresour...-header-design/

 

But you should strongly note to below statement from Joe Wong included in it: 

 

"Designing flare system is NOT easy stuff. Certain years of experiences and exposures is required... Moreover this is SAFETY related issue. I think you need a competence and experience people to guide you personally and look through in details on your design to avoid any mistake."

 

Thank you sir for the reference link...it has been helpful.

 

Maybe I can ask you more questions after understanding the basics.

[Shivshankar]

Anshul,

 

I recommed you to reasearch before desigining flare system, as it important from safety point of view. Please go through this thesis which will give you idea about Flare system.

 

On last page there are numerous references. Once you read and understand, you can always come back and ask questions on forum. 

 

http://www.argoflare...-and-operation/

http://www.tceq.stat...nDiscussion.pdf

http://www.chemkb.co...nd-vent-systems

http://www.slideshar...culations-flare

 

Regards

Shivshankar

Attached Files

•  Thesis.pdf   2.98MB   624 downloads

Edited by Shivshankar, 11 July 2013 - 07:07 AM.

[Anshul619]

Anshul,

 

I recommed you to reasearch before desigining flare system, as it important from safety point of view. Please go through this thesis which will give you idea about Flare system.

 

On last page there are numerous references. Once you read and understand, you can always come back and ask questions on forum. 

 

http://www.argoflare...-and-operation/

http://www.tceq.stat...nDiscussion.pdf

http://www.chemkb.co...nd-vent-systems

http://www.slideshar...culations-flare

 

Regards

Shivshankar

 

THANK YOU SIR

[flarenuf]

anshul

 

I am not sure what you are really trying to do here

you say you are the vendor company and therefore will have sized the PSv's i guess on the skid

these PSV's then need to go into a short headers which will be connected to the main flare headers in the plant.

Without any knowledge of the Plant relief scenarios you cannot size the skid part of the headers, these will depend on the backpressures at the tie in point to the main headers, these backpressures will be calculated by the client/EPC company.

Once you know the max BP at the tie in point then you can size the skid headers to give you the required BP at the PSV outlet.
You may find that thr tie in BP is in fact too high for your PSV's  in which case you will have to liase with the client on line size increases or respecify your PSV's as balanced/pilot type.
In reality the client should advise you of the header sizes as , i assume he has the complete Flare System model and therefore can calculate BP's back to your PSVs.

 

 

flarenuf

[Anshul619]

anshul

 

I am not sure what you are really trying to do here

you say you are the vendor company and therefore will have sized the PSv's i guess on the skid

these PSV's then need to go into a short headers which will be connected to the main flare headers in the plant.

Without any knowledge of the Plant relief scenarios you cannot size the skid part of the headers, these will depend on the backpressures at the tie in point to the main headers, these backpressures will be calculated by the client/EPC company.

Once you know the max BP at the tie in point then you can size the skid headers to give you the required BP at the PSV outlet.
You may find that thr tie in BP is in fact too high for your PSV's  in which case you will have to liase with the client on line size increases or respecify your PSV's as balanced/pilot type.
In reality the client should advise you of the header sizes as , i assume he has the complete Flare System model and therefore can calculate BP's back to your PSVs.

 

 

flarenuf

 

Flarenuf,

 

You right on everything you have said on how to decide the back pressure.

 

But my query is not about PSV's in my skid.

 

What I want is to size my flare headers.

 

My client has given me the back pressure of 4 bar(g).

 

What I dont know is "how to calculate the size of flare header in my skid which is consequently connected to clients flare system"??

 

I feel I may have cleared something of question...

 

Hoping for your reply soon..............

[flarenuf]

hi

ah ha now you didn't mention you had a tie in backpressure provided .!

you also say " But my query is not about PSV's in my skid."    unfortunately it is Anshul.

 

two things here .

1) the client has told you max 4 barg BP, is that with your PSV's venting or another scenario where they are not contributing?
    if the 4 barg is for the relief scenario that includes your PSV load then you need to size the line from the tie in back to your PSV outlet flange such that the pressure drop gives a  bp  less than 10% of the PSV set pressure, if conventional valve , or ~ 40% if balanced bellows.
If the set point of your PSV is less than 40barg then you are looking at balanced.

2) if the 4 barg bp is not caused by a scenario with your PSV passing gas then you must ensure that 10% or 40% rule are still met. ie the bp at PSV flange doesnt exceed the limits.

 

remember the relief loads result in a backpressure through out the system , the calculated backpressure will/could dictate the type of PSV you need to install  conventional- balanced bellows- pilot

 

hope this helps

flarenuf

[Erwin APRIANDI]

Hi Anshul619,

 

I hope I understand what you are trying to know here

 

HP and/or LP Flare Header sizing is not like doing a normal line sizing, where you size a line based on maximum allowable criteria.

Yes there is a max. allowable criteria for mach no, momentum and sound limit in sizing the HP and LP header

 

However, the most important in sizing the HP and LP header is to ensure that the header is capable to be use

safely for any flaring scenarios, more than that you also have to try to reduce the back pressure in all PSV, PCV, or BDV

which connected to HP and/or LP header to as low as possible In order to minimized the used of Ballanced or Pilot operating PSV,

and also to limit the Flare System design pressure.

 

Common software tools that widely used for flare network analysis and sizing is by using Aspen Flare System Analyzer,

this software will enable you to run several flaring scenario and to analyze the flare system back pressure, momentum, mach number, sound limit in each HP and/or LP flare Header and Sub Header.

 

But as what has Fallah highlighted

 

"Designing flare system is NOT easy stuff. Certain years of experiences and exposures is required... Moreover this is SAFETY related issue. I think you need a competence and experience people to guide you personally and look through in details on your design to avoid any mistake."
 

Because making the scenarios of flaring is not easy and also there will be numberous of scenarios to be considered, where to list it. Its requires people who really has years of experience and know what will be the credible scenarios of flaring.

 

Hope This Help

 

 

[Anshul619]

hi

ah ha now you didn't mention you had a tie in backpressure provided .!

you also say " But my query is not about PSV's in my skid."    unfortunately it is Anshul.

 

two things here .

1) the client has told you max 4 barg BP, is that with your PSV's venting or another scenario where they are not contributing?
    if the 4 barg is for the relief scenario that includes your PSV load then you need to size the line from the tie in back to your PSV outlet flange such that the pressure drop gives a  bp  less than 10% of the PSV set pressure, if conventional valve , or ~ 40% if balanced bellows.
If the set point of your PSV is less than 40barg then you are looking at balanced.

2) if the 4 barg bp is not caused by a scenario with your PSV passing gas then you must ensure that 10% or 40% rule are still met. ie the bp at PSV flange doesnt exceed the limits.

 

remember the relief loads result in a backpressure through out the system , the calculated backpressure will/could dictate the type of PSV you need to install  conventional- balanced bellows- pilot

 

hope this helps

flarenuf

Flarenuf,

 

Sorry for the late reply,

 

The PSV types are conventional type.

 

The set pressure I have taken is 10 barg in one set of PSVs and 14.8 barg in another set of PSVs.

 

So governing would be 14.8 barg. and hence limit of back pressure is limiting.

 

My client has told me when our flare header is to connected to their system, it will have back pressure of 4 barg.Nothing else is said.

 

Now flow rate is varying in both sets as 668 kg/hr in 10 barg PSVs and 185 kg/hr in 14.8 barg PSVs.

 

Now what should I do to size the flare header after sizing all the PSVs.

 

I am a process Engineer not instrumentation engg.

 

Please help me.........

[gegio1960]

Anshul,

please carefully consider the recommendations that the Members have been already made to you.

I just repeat some items for you....

1) If you have PSV sets of 10 and 14.8 barg and a back pressure of 4 barg, you cannot (and mustn't) use conventional PSV.

Above BP > 0.1 Pset you need balanced (or else pilot operated) PSVs.

2) a back pressure of 4 barg is very high... and cannot be the same for two different flare systems (ie LP and HP)

3) you're a Process Engineer. You have the responsibility on the selection of both the downstream system (ie HP or LP) and the PSV type.

Anyway, you shall be guided in this kind of work by more expert people.... other than asking on a website.

Good luck

Edited by gegio1960, 03 August 2013 - 09:36 AM.

[Root]

Ask your client the lowest operating vessel and PSV set value, take 10% of lowest operating PSV vlaue in account for back pressure which can affect the Lowest operating vessel and then size the  PSVs for other vessels, (those have high pressure and select PSV types).

Toor

[Jome128]

Dear Sir:

 

The procedure for sizing of flare header is below :

 

1. Start at the flare tip, where outlet pressure is atm and estimated the pressure drop arocss the flare tip for the relief design flow. typical tip drop is 2 psi.

2. Starting point is B/L pressure are provdied in the ITB design basis.

3. Determinge the relief contingencies produced the maximum loads.

4. Calculate the relevant fluid properties in case of failure contingencies.

5. Assume a measured siz for flare header/sub header/PSV oulet line.

6. Estimate the equivalent pipe length between flare tip or B/L position.

7. Limit the Mach no. of 0.2 at the flare header.

8. Calculate the inlet pressure for each section of the line by adding the calculated pressure drop for thtat section to the known oulet pressure.

9. Contine calculations, working towards the relief valve.

10.Check calculated backpressure at relief valve against the max. allowable backpressure.

11. Limit the MABP to about 10% of the set pressure for Coventional relief valve and 40% of the set pressure for balance bellow relief valve.

 

 

Please  correct me if anything wrong.

Thank you.
 

[Mach21]

Dear Sir:

 

The procedure for sizing of flare header is below :

 

1. Start at the flare tip, where outlet pressure is atm and estimated the pressure drop arocss the flare tip for the relief design flow. typical tip drop is 2 psi.

2. Starting point is B/L pressure are provdied in the ITB design basis.

3. Determinge the relief contingencies produced the maximum loads.

4. Calculate the relevant fluid properties in case of failure contingencies.

5. Assume a measured siz for flare header/sub header/PSV oulet line.

6. Estimate the equivalent pipe length between flare tip or B/L position.

7. Limit the Mach no. of 0.2 at the flare header.

8. Calculate the inlet pressure for each section of the line by adding the calculated pressure drop for thtat section to the known oulet pressure.

9. Contine calculations, working towards the relief valve.

10.Check calculated backpressure at relief valve against the max. allowable backpressure.

11. Limit the MABP to about 10% of the set pressure for Coventional relief valve and 40% of the set pressure for balance bellow relief valve.

 

 

Please  correct me if anything wrong.

Thank you.
 

 

hi there,,

Mind explain more about how the basic of Mach 0.2 coming from and which project is typically involved i.e. FPSO , LNG , Compresser Module

 

Would it be seems like too stringent?

[demank]

Dear Mach21,

mach 0.2 is coming from API STD 521. Here I attached the paragraph from 7.3.3.2:

 

" Flare stack diameter is generally sized on a velocity basis, although pressure drop should be checked. It can be desirable to permit a velocity of up to 0.5 Mach for a peak, short term, infrequentl flow, with 0.2 Mach maintained for more normal and possibly more frequent conditions for low pressure flares."

[Mattd]

Hi,

 

 

Not sure if this has been finalised yet but I thought I would add some information.

 

Anshul from what you have mentioned so far you should be able to size your sub-header(s) to the main header.

 

Firstly, we need to understand what are the tie-in back pressure for both the LP and HP system.

 

Firstly, at said 4 barg back-pressure is there a relieving scenario occurring from any of your relieving points (i.e. PSV's, BDV's, etc.)?

 

 If yes, then you will not be able to use conventional PSVs (should the PSV set pressures be 10 barg & 14.8 barg) as the back pressure will be 4 barg plus the addition of any pressure drop within the sub-header and the PSV tailpipe. Hence greater than 4 barg and therefore higher than the 10% allowable back pressure guideline (API 521 Section 7.3.1.3.1) for conventional PSVs. As such you will need to use Balanced type PSVs which allow 30-50% back pressure (will vary depending on the specific vendor).

 

The sizing of the flare header is not solely dependent on the relieving sources but you must size the header such that the following are taken into consideration:

 

1. Back pressure at the relieving source is such that the PSV will not be affected. i.e. back pressure is not higher than 10% of the set pressure for Conventional PSVs and is not higher than 30-50% for Balanced PSVs.

 

2. Mach No. within the header and tail pipe. Consider a Mach No. limit of 0.5-0.6 for headers and up to 0.7-0.8 for tailpipes. This will depend of the Clients requirements but these are some standard guidelines to go with.

 

3. Headers should be sized based on REQUIRED flowrates, while tailpipes should be sized based on RATED flowrates.

 

4. Rho.V2 criteria is important to observe for vibration problems amongst others. I would suggest that anything below 100,000 kg/m/s2 is acceptable without the requirement for AIV studies. Anything above 150,000 kg/m/s2 is probably excessive. Again these figures will depend on the Client requirements, and what theory you read.

 

Now should your relieving sources not be opening at 4 barg, and no other source is attached to your header then there is no requirement from your side. You need to size your headers for when your PSVs are "popping". If this is not occurring at the case which gives a tie-in back pressure of 4 barg then you must obtain a tie-in pressure at the time that your PSVs are "popping".

 

Hope this helps and that anything i have mentioned is not incorrect. I'm sure it will be corrected if that is the case.

 

Matt

Edited by Mattd, 29 January 2014 - 01:57 AM.