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Thermal Relief Valve In Lng Service


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#1 J_Leo

J_Leo

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Posted 25 November 2019 - 10:40 AM

Hi Fellow Engineers,

 

I want to verify the thermal relief valve capacity in LNG transfer line (thousands of feet, 24"). The line is cold insulated

 

The bubble point is -157F at relieving pressure 297 psig

 

(1) When T<-157F, I use the thermal relief equation in API 521

In this case, the required relief area is only a small fraction of a 3/4" valve

 

(2) When T>-157F, LNG will vaporize. I calculated the vapor relief rate base on heat transfer rate divided by latent heat of LNG

For this case, the required is much larger.

 

My question: is the method I used in (2) when T>-157F correct?

 

Thank you.

Leo



#2 Bobby Strain

Bobby Strain

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Posted 29 November 2019 - 10:24 AM

When sizing the device you must be certain that it is located such that it will relieve vapor. Otherwise it must be sized to relieve liquid volume equal to the vapor volume.

 

Bobby






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