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Psv On The Vapor Line

psv

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#1 August

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Posted 18 July 2017 - 03:08 AM

There is a vapor return line from LPG storage tank to the loading ship. On this line, two relief valves are installed. (normal operating P is 4 barg, line design P is 22 barg) People on site indicate that these two valves are installed for ESD valves blocking this line. (one ESD valve is at the tank outlet, one is at middle of the line, the other one is near the loading station ) So they call them thermal relief valves.  My point of view, TRV only release liquid for thermal expansion. But they say LPG gas also expanses when temperature rises. Based on my calculation, if these valves opens (24.2 barg), it must be the fire case, even higher than material melt down temperature. There is no other case which can lead such high pressure.

 

The way they size the valves is that taking the normal flow times 1.5, that is the relief load to the valve. To me this is not a meaningful approach.

 

Is that necessary to have these RV's ? if yes, they have to be sized based on the fire case.

 

Thanks.

 

 


Edited by August, 19 July 2017 - 02:28 AM.


#2 fallah

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Posted 18 July 2017 - 03:33 AM

There is a vapor return line from LPG storage tank to the loading ship. On this line there are two relief valves installed. (normal operating P is 4 barg, line design P is 22 barg) People on site indicate that these two valves are installed for ESD valves blocking this line. (one ESD valve is at the tank outlet, one is at middle of the line, the other one is near the loading station ) So they call them thermal relief valves.  My point of view, TRV only release liquid for thermal expansion. But they say LPG gas also expanses when temperature rises. Based on my calculation, if these valves opens (24.2 barg), it must be the fire case, even higher than material melt down temperature. There is no other case which can lead such high pressure.

 

The way they size the valves is take the normal flow times 1.5, that is the relief load to the valve. To me this is not a meaningful approach.

 

Is that necessary to have these RV's ? if yes, it has to be sized based on the fire case.

 

 

August,

 

With such description of your query, seems a schematic drawing is to be highly helpful... 
 



#3 breizh

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Posted 18 July 2017 - 04:36 AM

August ,

Check in the technical dossier (file) the reason for those equipment  .What about Hazop study related to this project?

 

 

my 2 cents

Breizh



#4 August

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Posted 18 July 2017 - 07:11 AM

 

There is a vapor return line from LPG storage tank to the loading ship. On this line there are two relief valves installed. (normal operating P is 4 barg, line design P is 22 barg) People on site indicate that these two valves are installed for ESD valves blocking this line. (one ESD valve is at the tank outlet, one is at middle of the line, the other one is near the loading station ) So they call them thermal relief valves.  My point of view, TRV only release liquid for thermal expansion. But they say LPG gas also expanses when temperature rises. Based on my calculation, if these valves opens (24.2 barg), it must be the fire case, even higher than material melt down temperature. There is no other case which can lead such high pressure.

 

The way they size the valves is take the normal flow times 1.5, that is the relief load to the valve. To me this is not a meaningful approach.

 

Is that necessary to have these RV's ? if yes, it has to be sized based on the fire case.

 

 

August,

 

With such description of your query, seems a schematic drawing is to be highly helpful... 
 

 

 

The sketch is up loaded
 

Attached Files

  • Attached File  pic2.pdf   15.85KB   25 downloads

Edited by August, 18 July 2017 - 07:12 AM.


#5 August

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Posted 18 July 2017 - 07:19 AM

August ,

Check in the technical dossier (file) the reason for those equipment  .What about Hazop study related to this project?

 

 

my 2 cents

Breizh

 

There is no Hazop performed. And no failure cases study.  And site engineer says if I can't size the valve for vapor, just imagin there is liquid in the pipe. Because in the fire case, there can be some liquid pushed into the line.

 

My opinion is, there is a ESD valve at the outlet of the tank. This line would have been blocked when fire is able to heat the liquid in the tank hot enough. Tank is vacuum insulated.



#6 breizh

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Posted 18 July 2017 - 09:52 PM

Hi August ,

 

How the liquid is tranfered , it seems to me that a piece of equipment is missing ( pump  or compressor) ? I don't understand the purpose of the manual valve between the 2 SVs.

 

Breizh

 



#7 August

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Posted 19 July 2017 - 02:24 AM

There is a pump. 

 

I don't really know why a valve sitting in the middle. What I have been told "truck and tank are from different maintenance parties".


Edited by August, 19 July 2017 - 02:32 AM.


#8 fallah

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Posted 19 July 2017 - 06:20 AM

There is a vapor return line from LPG storage tank to the loading ship. On this line, two relief valves are installed. (normal operating P is 4 barg, line design P is 22 barg) People on site indicate that these two valves are installed for ESD valves blocking this line. (one ESD valve is at the tank outlet, one is at middle of the line, the other one is near the loading station ) So they call them thermal relief valves.  My point of view, TRV only release liquid for thermal expansion. But they say LPG gas also expanses when temperature rises. Based on my calculation, if these valves opens (24.2 barg), it must be the fire case, even higher than material melt down temperature. There is no other case which can lead such high pressure.

 

The way they size the valves is that taking the normal flow times 1.5, that is the relief load to the valve. To me this is not a meaningful approach.

 

Is that necessary to have these RV's ? if yes, they have to be sized based on the fire case.

 

 

August,

 

As far as the vapor return line can never become liquid full and the pressure rise from thermal expansion due to solar radiation in blocked-in condition is within the design limit of the relevant piping system; there is no need to consider such TSV's on mentioned line...
 






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