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Provision Of Thermal Relieving Valve


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#1 vanlt

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Posted 27 October 2016 - 01:34 AM

Dear All,

 

Please kindly help me with one question regarding provision of thermal expansion.

 

According to API 521, 5th edition, part 5.14.1, one of the causes of thermal expansion is “an exchanger is blocked in on the cold side with flow in the hot side”. I understand that thermal expansion is only considered when there is a case that exchanger is not operated and cold side is blocked in.

 

When I study one TRV from our previous PJ (please kindly refer to attached sketch for more details), it is found out that:

 Case 1: TRV was provided for cold side (process flow) of reboiler.

 Case 2: TRV was provided for cold side (utility flow) of cooler.

I don’t understand why TRV should be provided for these cases because the exchanger is always on flow. Please kindly tell me what point I am wrong.

 

Thank you very much.

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#2 latexman

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Posted 27 October 2016 - 07:08 AM

You have to consider non-normal conditions too.  Like, the exchanger is shutdown, valves are closed, and the trapped fluid warms up.



#3 senthil13

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Posted 27 October 2016 - 07:42 AM

Agreed with Latexman. Seems like the thermal reliefs are installed based on experience in that specific plant. It also depends on the characteristic or properties of the fluid involved. such as expansion coefficient and also the length of piping involved during a blocked in case.



#4 shan

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Posted 27 October 2016 - 01:43 PM

The relief valves (TRV's in your sketches) are not necessary for the protection of the scenarios of thermal expansion.  They may be primary for the tube rapture scenarios if they are in lower pressure sides of the heat exchangers.



#5 fallah

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Posted 28 October 2016 - 01:15 AM

 

Please kindly help me with one question regarding provision of thermal expansion.

 

According to API 521, 5th edition, part 5.14.1, one of the causes of thermal expansion is “an exchanger is blocked in on the cold side with flow in the hot side”. I understand that thermal expansion is only considered when there is a case that exchanger is not operated and cold side is blocked in.

 

When I study one TRV from our previous PJ (please kindly refer to attached sketch for more details), it is found out that:

 Case 1: TRV was provided for cold side (process flow) of reboiler.

 Case 2: TRV was provided for cold side (utility flow) of cooler.

I don’t understand why TRV should be provided for these cases because the exchanger is always on flow. Please kindly tell me what point I am wrong.

 

 

vanlt,

 

If there would be the possibility of Cold Side Blocked-In condition, TRV's might be required for mentioned cases. Then you should carefully evaluate such possibility and prove the credibility of overpressure scenario due to thermal expansion in referred locations.

 

Indeed, in CWS/CWR case, the TRV has normally to be located in return part after the HX.... 
 


Edited by fallah, 28 October 2016 - 01:16 AM.


#6 vanlt

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Posted 28 October 2016 - 02:32 AM

Thanks all,

 

Therefore, in case the exchanger is shutdown without drawing out fluid, thermal expansion should be considered. As that consideration, duty of hot side causes to overpressure at cold side in case 1 and the solar radiation causes to overpressure at cold side in case 2.

 

Dear Shans,

 

Tube rupture has been already checked; now I would like to review possibility of thermal expansion. My concern point is that whether the exchanger is shutdown without drawing out fluid or not because I have no experience for shutdown procedure. For safety review, I think we should consider it. Can you advise me if it is not correct? 






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