28 replies to this topic

[project eng.]

Hello everybody,

This is my first post in this great forum..

In our site, we are producing polymer using batch reactors

they are ranged between 10 to 40 cubic meter

bursting disc are already installed for all these reactors.They are designed for a max. pressure of 300 KPag.

In addition, PRV are also installed.

The confusing point is that the bursting disc will rapture in 1 bar for all reactors with a PRV set @ MAWP 300 KPag

The diameter of bursting is 20 cm

Now I am asked to do calculations show that our situation is safe so far.

Any guidance please.. I had a look in API 520 and Crane's TP 410 but I am lost there

Thanks

Edited by project eng., 15 October 2012 - 07:40 AM.

[fallah]

project eng.

Lack of information:

Reactors design pressure (or MAWP)?
If bursting disc is installed upstream of the PSV? or installed separately?

Fallah

[project eng.]

Sorry for this lack of info and thanks for reply
max. design pressure is 300 kpa
and the the BD and PRV are separated
PRV is placed in the condenser

[flarenuf]

I am sure fallah has mentioned this before to others but if you have a sketch of the system it helps us asssit you much easier than trying to work out the installation from words.

flare e nuf

[kkala]

In addition to the sketch requested, can you recheck design pressure of the reactors (e.g. through their data sheets) and setting pressure of their PRVs? Design pressure of 300 kPag = 3 Barg, while their PRV set pressure of 72 psig =4.96~5.0 Barg.
All mentioned pressures are considered as gauge pressures (Atmospheric pressure = 0 Barg), as expected, but please also confirm.

[project eng.]

After checking , the design pressure 300 KPag for the reactor vessel
and for PRV it is 300 Kpag

[project eng.]

flarenuf , kkala and Fallah

see the the sketch here:
http://store1.up-00....12/tbT06537.jpg
many thanks

[Lowflo]

Careful with that axe, Eugene! (Pink Floyd)

That song title comes to mind as I read this thread. I'm guessing this is an old installation for which you don't have sizing documentation, thus you're being asked to generate it.

This is a polymerization reactor, so there's likely a credible scenario involving a runaway reaction, If so, that's almost certainly a 2-phase relief scenario, which requires more orifice area than an all-vapor scenario.

it's common to use rupture disks on reactors for the 2-phase reactive relief scenario. Just guessing, i bet the disk is sized for a reactive scenario and the PRVs are sized for other scenarios. Possibly, the PRVs provide additional area for the reactive scenario too.

Rate-of-reaction is a possible explanation for the disks being set at 1 barg while the vessel MAWP = 3 barg. Reaction rates generally increase exponentially with temperature, which often requires the relief flow to start early, before the temperature-of-no-return is reached.

The take-away messages here are the following:

• Pull in the necessary technical expertise to verify whether or not there's a reactive relief scenario.
  
• The required relief flowrate for a reactive relief scenario typically requires special test data and special expertise. Hire that out if you don't have the internal resources, and don't try to do this yourself unless you have that specialized training and expertise.
  
• Until all the fact are known, don't make any changes to the existing installation which might reduce the safety margin.

[breizh]

A comment based on experience :
Make sure there is no "mask" of polymer in front of the BD which could make your equipment unsafe .
my two cents.
Breizh

[project eng.]

Lowflo,

you are right , it is a polymerization reactor and it is old and all your explanations made a sense to me but I am not asked to change what's already existed, |'m asked to show by calculations why 1 barg set to be bursting pressure



breizh, Thanks for this advise but how + again I am looking for calculation


Thanks all

[fallah]

project eng.

I cannot open the link you provide for the sketch. Would you please upload it in PDF format.

Fallah

[project eng.]

yes here is it in pdf format

Attached Files

•  R-reliefe.pdf   45.5KB   69 downloads

[fallah]

project eng.

The sketch you uploaded shows there is superimposed back pressure downstream of the RD. Hence, appears 1 barg to be differential disc pressure at RD burst point. Please recheck and let's know the result.

Fallah

[project eng.]

I checked the BD specs. and I am sure that the set pressure is 1.00-1.04 barg with tolerance of +/- 10%
and this BD is vented to the atmosphere
but i dont get your point fallah backpressure, hence E-1 is a condenser contains PRV set @ 3 barg

[fallah]

project eng.

With lack of adequate information i can submit my viewpoints just as follows:

1- Seems PRV on the condenser protects both reactor and condenser against blocked outlet scenario.
2- Although you stated the RD outlet is routed to the atmosphere, the sketch shows RD tail pip extended a bit such that in presssure spike condition, let say due to fast reaction, the pressure in the reactor itself can built-up even after disc bursting. Hence, this may be the reason of lowering RD burst pressure respect to reactor design pressure; then in one hand there would be adequate margin for pressure built-up and on the other hand prevents installing huge size of RD on the reactor. If you have the relief load of RD in hand it can be checked with more accuracy.

Fallah

Edited by fallah, 16 October 2012 - 06:46 AM.

[project eng.]

Fallah ,
I could not see an more information more than that I gave
Even in the ELFAB web the manufacturer
So, what do you suggest to do regarding calculations

[fallah]

project eng.

Sizing calculation of RD are to be done based on eight edition of API 520 (part 1) sec 5.11.1.2 and sec. 5.11.1.3.

Fallah

[project eng.]

Thanks a lot
I working on it Thank you Fallah

[Adil Akbar]

Dear All,
I have also similar query regarding frequent failure of rupture disc. I am also working in polymerizer plant. I just want to confirm from all of you that can rupture disc fails if there are stresses in the piping?

Best Regards,
Adil Akbar

[fallah]

Adil Akbar,

Yes, improper piping support design or piping configuration might lead to rupture disc failure due to transfer of excessive piping loads to the disc. Misaligned pipe flanges, very tall discharge pipes and long horizontal pipe runs could be among improper piping configurations.

[Adil Akbar]

Thanks Fallah
Tell me one more thing will rupture disc fail in same fashion as it fails on its set pressure or its profile will be different.
Though we are using our rupture disc with holder, so won't holder prevent rupture disc from piping stresses.
How much misalignment/or load can rupture disc bear? In our case we have 8 to 12 mm misalignment in pipes and fittings.

[fallah]

Adil Akbar,

A rupture disc is a differential pressure device. Then it would be failed at specified burst pressure which is the value of the upstream static pressure minus the value of the downstream static pressure prior to disc rupture.
The disc holder nothing to do other than holds the disc in its position and ensures outward tightness. Then appears having no role to prevent piping stress.
As far as i know the piping misalignment which a rupture disc can tolerate is almost equal to half of the gap between relevant flange bolt hole and bolt itself, then appears your piping misalignment to be much more than what a rupture disc can bear.

[Adil Akbar]

Dear Fallah,

What is the source of your information regarding bursting of RD due stresses in the piping? Is it experienced based or you have read it somewhere?

[fallah]

Adil Akbar,

I have found them in some technical references supported by some field experiences.

[Adil Akbar]

Naser Fallah

Can you send me the link of that technical reference, if you have it please.


Regards,
Adil Akbar