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5

Required Relieving Capacity For Fire Case.


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#1 shahidulislam48

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Posted 03 January 2017 - 01:38 AM

Hello,

 

I have to size a PSV for Fire Case. The phase of the medium that passes through the PSV is liquid. It is clear that liquid medium through PSV is an indication of the expansion of liquid in vessel from normal volume due to rise of temperature.

 

In that case is it worthwhile to evaluate required relieving capacity by using "Hydraulic Expansion" equation in stead of the equation that is frequently used for Fire Case?

 

Any suggestion is highly appreciated.

 

Many Thanks,

shahidulislam48



#2 breizh

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Posted 03 January 2017 - 05:47 AM

Hi ,

Consider these resources to support your work.

 

Good luck.

 

Breizh

Attached Files


Edited by breizh, 03 January 2017 - 06:20 AM.


#3 fallah

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Posted 04 January 2017 - 04:27 AM

 

I have to size a PSV for Fire Case. The phase of the medium that passes through the PSV is liquid. It is clear that liquid medium through PSV is an indication of the expansion of liquid in vessel from normal volume due to rise of temperature.

 

In that case is it worthwhile to evaluate required relieving capacity by using "Hydraulic Expansion" equation in stead of the equation that is frequently used for Fire Case?

 

Any suggestion is highly appreciated.

 

 

Hi,

 

If the vessel is full of liquid, mostly no, because after a few moments of liquid (or two phase) relief there would be just vapor relief based on which you should evaluate as worst conditions...
 



#4 shahidulislam48

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Posted 04 January 2017 - 06:18 AM

Dear Breizh & fallah ,

 

Thanks for your reply.

 

In the case of my vessel it is not full during operating condition.

Vessel contains a mixture of Dicalite (3.33 wt%, solid) and polyether polyol (96.67 wt%, liquid).

Polyether polyol has a molecular weight of 3000-3600 and boiling point of >150 deg. C.

Is there any possibility for Polyether polyol of being vapor after few moments of liquid relief at set P=3.5barg and Relief T=150 deg. C?

 

Many Thanks.

shahidulislam48



#5 fallah

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Posted 04 January 2017 - 06:43 AM

 

In the case of my vessel it is not full during operating condition.

 

 

Hi,

 

Please clarify how the vessel isn't full of liquid and there is liquid relief? Is the PSV connected to vessel from the wetted shell area instead the top?



#6 shahidulislam48

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Posted 04 January 2017 - 11:20 AM

Dear fallah,

 

About your query in last reply.

 

The mentioned vessel takes all the inputs at the top portion of the vessel and PSV is also set at the top of the vessel above input line as usual. 

 

Datasheet for the PSV of the vessel specify that "Process Fluid State is liquid" and "Required Capacity", that hass to be determined, is in liquid phase. From that point I have come up to liquid relief. Even at the relief pressure and relief temperature the process fluid remains in liquid state.

 

Of course, we will not operate our vessel in normal operation with full of liquid. We will maintain liquid level up to some desired level.

 

Many Thanks.



#7 fallah

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Posted 04 January 2017 - 12:59 PM

Hi,

Then the data sheet might be for another PSV, or if not, the inlet line of the PSV is extended inside the vessel as a dip pipe!

#8 shahidulislam48

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Posted 04 January 2017 - 10:26 PM

Dear fallah,

 

The data sheet is for that PSV and there is no extended dip pipe of PSV in the vessel.

 

For the sake of sizing, could we assume that the vessel is full of liquid mixture?



#9 fallah

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Posted 05 January 2017 - 12:50 AM

Hi,

To know the possibility of that assumption you can check and review the process data sheet of the vessel.

#10 Pan Nainggolan

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Posted 05 January 2017 - 02:45 AM

Hello Shahid,

 

better if you could provide us sketch of boundary system protected by that psv

 

rgds,

 

-PN-



#11 shahidulislam48

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Posted 05 January 2017 - 03:31 AM

Hi,

 

Here goes the vessel that has to be protected by PSV.

Attached File  Drawing1.pdf   3.27KB   20 downloads

 

Liquid height is 1.5 m and vessel height is 2 m from the bottom of the vessel.

 

In liquid relief, is it mandatory to have vapor phase after few moments of liquid relief?

 

In the mentioned case, I don't think polyether polyol will go in vapor phase after liquid relief at set P=3.5barg and Relief T=150 deg. C.

 

Many thanks.

shahidul islam



#12 mirandomka

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Posted 05 January 2017 - 02:40 PM

Liquid fire expansion seems to be unreasonable. What is polyol boiling point at relieving pressure? And is the latent heat very high?

Btw, I wonder how you got 150C relieving temp? Isochoric temp?

I would also consider the following for design PSV like this:

1. Thermal cracking can be possible, molecular weight seems big;

2. Formy behaviour may be possible during fire relief;

3. Solid content can lead to uneven heat distribution, your vessel may subjected to localized overheat and fail.

Most probably vapour generation either due to thermal cracking or vapourization will lead to a bigger PSV. Not liquid expansion..

#13 christopherchoa

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Posted 05 January 2017 - 06:31 PM

Or maybe on the PSV datasheet; it maybe written "Fire Case - Exposed Liquid (Wetted) Area"; and not liquid relief. I agree that liquid expansion is unreasonable.

 

On another note, Mirandomka have good considerations. I checked on your raw material and found out that it is used in making urethane. Maybe its foamy.



#14 shahidulislam48

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Posted 05 January 2017 - 11:53 PM

Hi,

 

I appreciate your consideration about this topic.

 

Polyol has boiling point around 150-290 deg C at 1 bar. At relieving P, it must have very high boiling point. I had not found any specific value of boiling T. But it was roughly around 150-290 deg C.

Latent heat data is not available. I have searched for that but have not got. It is probably rare to have latent heat for polymer.

 

Relief temperature of 150 deg C and Fire Case both are mentioned in data sheet.

 

Process Fluid Phase and Required Capacity Phase both are in Liquid.

 

Many Thanks.



#15 mirandomka

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Posted 06 January 2017 - 07:39 AM

You need to consult with polymer experts or proceed with conservative and generic assumptions for thermal properties. If you do not have original PSV calc, it is always hard to know what was the basis.

Liquid relief in this case is not reasonable. Liquid is incompressible fluid meaning do not expand or compress much. Unless your initial liquid level is very high, overpressure due to liquid thermal expansion and have liquid release is unlikely.

However, Fire thermal expansion and vapour release is always possible. Reliving fluid will be same vapour in the vessel vap space not liquid. Relief load is the volume Change rate due to fire heat input.

#16 shahidulislam48

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Posted 06 January 2017 - 10:20 PM

You need to consult with polymer experts or proceed with conservative and generic assumptions for thermal properties. If you do not have original PSV calc, it is always hard to know what was the basis.

Liquid relief in this case is not reasonable. Liquid is incompressible fluid meaning do not expand or compress much. Unless your initial liquid level is very high, overpressure due to liquid thermal expansion and have liquid release is unlikely.

However, Fire thermal expansion and vapour release is always possible. Reliving fluid will be same vapour in the vessel vap space not liquid. Relief load is the volume Change rate due to fire heat input.

Hi,

 

If liquid relief is not possible then Is it reasonable, in this polymer case, to consider vapor formation (Vapor relief) due to fire case despite having very high boiling point than operating temperature for this polymer while at relieving condition the fluid is still below it's boiling condition?


Edited by shahidulislam48, 06 January 2017 - 10:45 PM.


#17 mirandomka

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Posted 07 January 2017 - 12:02 AM

I suppose you are wondering why the original relieving temperature is 150C?

For that you have to dig out from the original PSV calc to find out the original basis.

However, what I am suspecting is that the original relieving temperature and the relieving fluid phase seems unreasonable.

It's necessary to review the original basis and check for the above mentioned possible phenomenon during a fire and the adequacy of your PSV design.

#18 mirandomka

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Posted 07 January 2017 - 12:37 AM

Again, the problem is lack of thermal dynamic data of your fluid content.

1. What is the BP at relieving pressure and latent heat?
2. What is the thermal decomposition temperature of the polymer? What is the product from decomposition? What is the heat required for thermal decomposition?
3. What is the vapour content in the vapour space at the initial state? What is the expansion rate of this vapour under fire?
4. Is the fluid content reactive and will have foamy behaviour and results in two phase relief?

If you can find answer on the above, then you can analyze which phenomenon will likely to govern your fire case required relief load. Of course, it can still be possible that liquid expansion is the governing condition. It can be because your liquid content is supercritical like, or expand quickly as you add heat to it. However, based on normally what I have seen it is unlikely.

You have to find why it's been considered in the original calc.

#19 shahidulislam48

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Posted 07 January 2017 - 06:55 AM

Thanks mirandomka for your information.



#20 Prabhat123

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Posted 17 January 2017 - 11:29 AM

What are the exact guideline for providing a PSV for Fire case. If an equipment height from grade is more than 8 meter (as recommended by API) PSV installation pertaining to fire case is not required. Is it valid in all the cases ?

 

Reply is highly appreciated.



#21 mirandomka

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Posted 17 January 2017 - 09:55 PM

API521 fire height definition is 7.6 m from "fire sustainable surface".

#22 Prabhat123

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Posted 18 January 2017 - 04:01 AM

Thanks for the reply.

 

In one of new grass root distillation column we are looking to remove PSV by applying HIPPS guidelines. We are already installing the column with the help of raising the elevation till 8 meter from grade.

 

Kindly share the information and experience relateded to this.



#23 mirandomka

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Posted 18 January 2017 - 10:05 PM

Thanks for the reply.

In one of new grass root distillation column we are looking to remove PSV by applying HIPPS guidelines. We are already installing the column with the help of raising the elevation till 8 meter from grade.

Kindly share the information and experience relateded to this.


HIPP system requires certain SIL level which is most likely to be more costly than PSV. :(

Good luck and all the best!




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