30 replies to this topic

[Dilu]

Hi

 

I am working on decanting vessel placed in a pit having rupture disc. Stabilized condensate is coming from PSVs and tank drains. Operating pressure of decanting vessel is atm and design is 50 psig. Kindly guide what should be the operating ratio and what brust pressure i should consider, also what could be the possible scinerios for the sizing of rupture disc.

[fallah]

Hi,

 

Please upload a simple sketch of the system...

[fallah]

Dilu,

 

Please specify if you are at the stage of preparing the RD data sheet and sending an order to vendor...If so please specify MAWP of the vessel and operating/design temperature of the vessel... 

 

Also be informed the burst pressure will be specified by customer but it would be finalized by vendor as marked set pressure. It would be equal to an average value of test values of disc lot qualification...In general, final marked set pressure should be equal to or lower than vessel MAWP... 

 

For operating ratio maximum operating pressure should be specified...

Edited by fallah, 22 November 2013 - 03:36 AM.

[Dilu]

Yeah m at the stage of preparing. Operating Temperature 30-55 C and operating pressure is 0 psig(atm). Design pressure is taken as 50 psig, Design temperature 72 C. Kindly guide what burst pressure i should consider, according to my understanding for fire case scinerio (21 %) it will be (60.5 psig).

 

Also kindly tell me how to calculate relieving rate from rupture disc.

Edited by Dilu, 22 November 2013 - 04:51 AM.

[fallah]

Dilu,

 

You fail to specify maximum operating temperature and MAWP...

 

Anyway, you can specify the burst pressure equal to design pressure i.e. 50 psig and also ask vendor to specify manufacturing design range. Obviously, marked burst pressure must fall within this range and not to be exceeded to MAWP...

[breizh]

Hi,

 

You may consider this paper to support your work  .

 

Breizh

[Dilu]

Thanx Fallah and Breizh

[Dilu]

Breizh

 

From the article I have considered fire case for rupture disc sizing (liquid case as condensate is stablized). From API 521 equation Q=21000FA^.82 I have calculated heat rate and then deviding by latent heat of vaporization i can get W. BY using eq 5 of API 520 for critical flow I can find A. Is this method correct.???

 

If so how can i calculate latent heat of vapourization using hysys?

Edited by Dilu, 25 November 2013 - 01:35 AM.

[breizh]

Additional resource from Ankur's spreadsheet to calculate the rate of emission .

 

Sorry I have no clue about Hysys.

 

Breizh

[fallah]

breizh,

 

 

Additional resource from Ankur's spreadsheet to calculate the rate of emission .

 

Sorry I have no clue about Hysys.

 

Breizh

 

Breizh,

 

Your attached spread sheet is applicable for emergency venting calculation of atmospheric and low pressure storage tanks and cannot be applicable for calculation of the fire relief load of pressure vessel with design pressure of 50psig as per OP query...

 

API 521 is applicable for such fire case...

[fallah]

 

From the article I have considered fire case for rupture disc sizing (liquid case as condensate is stablized). From API 521 equation Q=21000FA^.82 I have calculated heat rate and then deviding by latent heat of vaporization i can get W. BY using eq 5 of API 520 for critical flow I can find A. Is this method correct.???

 

If so how can i calculate latent heat of vapourization using hysys?

 

 Dilu,

 

You will have vapor relief in fire case and yes, you should use Eq. (5) of API 520 Eight Ed. with K_d equal to 0.62.

 

To find the latent heat of vaporaization you can simulate the relieving vapor in HYSYS at relieving condition; i.e. relieving pressure/temperature.. But it might the complete/exact data for multicomponent inventory wouldn't be available then you can use 50 Btu/lb as an conservative approximation...

Edited by fallah, 25 November 2013 - 04:18 AM.

[breizh]

Yes Fallah you are right !

Breizh

[Dilu]

Thanx Fallah and Breizh...... Using P1/T1=P2/T2 relieving temp. comes out about 280 C (For fire case). But using figure 1 of API 521 (After 15 min of fire wall temperature will become 1400 F for 1/2 inch thick plate for fire case). Kindly tell which relief temperature can i use for fire case.

 

In any way the selected temperature in both cases exceeds Design temperature i.e. 72 C so the vessel will rupture, considering much higher temperatures i..e. 280 C or 1400 F for rupture sizing seems inappropriate. Kindly Clarify..?

[fallah]

Dilu,

 

Because the vessel contains both liquid and vapor at initial relieving condition, then the initial relieving temperature would be none of above mentioned temperatures (280 C, 1400 F). In fact, supposing vessel content is a multi-component liquid, the initial relieving temperature would be the initial bubble point corresponding to relieving pressure. It might be lower or higher than 72 C.

As a general point, relieving temperature being higher than vessel design pressure in fire case isn't an important issue because basically the relieving temperature in fire case wouldn't be considered in vessel's design temperature evaluation...

Edited by fallah, 26 November 2013 - 02:41 AM.

[Dilu]

Thanx Fallah ....

[staffel]

Fallah is correct,
however when gas density is high (as when PSV opens) gas fraction must be taken in account
(as the two phases are in equilibria) and, for that,
you can solve a specific flash operation,
see for example

"http://prodesoftware...onditions.html"

possibly you can use the same procedure with your simulator,
that should return accurate estimates

Edited by staffel, 26 November 2013 - 06:09 AM.

[Dilu]

In case of fire if pressure reaches brusting pressure of rupture disc on decanting vessel the gas comes out and it may be more hazardous and can cause explosion if reielved in atmosphere . Any solution ???? We dont have any flare system installed because facility is designed for liquid service only.....

Edited by Dilu, 27 November 2013 - 04:09 AM.

[fallah]

In case of fire if temperature reaches brusting pressure of decanting vessel the gas comes out and it may be more hazardous and can cause explosion if reielved in atmosphere . Any solution ???? We dont have any flare system installed because facility is designed for liquid service only.....

 

Dilu,

 

Appears a post of yours included the sketch has been deleted...!

 

Anyway please specify you really mean "bursting pressure of decanting vessel" or "bursting pressure of rupture disc"...

Edited by fallah, 27 November 2013 - 03:59 AM.

[Dilu]

In case of fire if pressure reaches brusting pressure of rupture disc on decanting vessel the gas comes out and it may be more hazardous and can cause explosion if reielved in atmosphere . Any solution ???? We dont have any flare system installed because facility is designed for liquid service only.....

[fallah]

Dilu,

 

You deleted the sketch and i don't remember which safety facilities were located on it...

 

Anyway, are you certain the fire case can be a credible scenario for such a vessel located inside a pit? If so, considering rupture disc routed to atmosphere for such reletively low pressure vessel/tank and high inventory which will act as an emergency relieving facility isn't an uncommon practice, because the consequences of not considering such emergency relieving facility would normally be more severe than those of atmospheric relieving through a rupture disc...!

Edited by fallah, 27 November 2013 - 05:46 AM.

[curious_cat]

In case of fire if pressure reaches brusting pressure of rupture disc on decanting vessel the gas comes out and it may be more hazardous and can cause explosion if reielved in atmosphere . Any solution ???? We dont have any flare system installed because facility is designed for liquid service only.....

 

What are the gases? If not a flare can they be scrubbed? 

[Dilu]

Fallah .. Please find the attached image ....

Attached Files

•  Rupture Disk.JPG   24.1KB   3 downloads

[fallah]

Dilu,

 

Please specify if the clearances between the vessel wall and pit walls have been filled, let say, with sand or something like this...If so, then external pool fire case wouldn't be an applicable scenario for this vessel...

[Dilu]

Fallah

 

Clearance is empty.

[fallah]

 

Clearance is empty.

 

Dilu,

 

Then fire case and gas blow by case could be applicable scenarios for rupture disc sizing...

Edited by fallah, 28 November 2013 - 01:01 AM.