Relief Valve Calculation on Vessel Jacket

[Tonylmiller]

I'm calculating the relief valve requirement of a fire case for a water-filled jacket on a vessel. I'm planning to calculate the heat from the fire, calculate the vapor generation, and then convert it to the same volume of liquid (at relief pressure) since liquid will be pushed out the relief valve first, and should be the worst case. So the actual orifice calculation would be based on the liquid flow. The relief valve is on the piping coming out of the top of the jacket.

Are these fair assumptions? I've never done calculations on just the liquid filled jacket before. Any recommendations would be appreciated.

Thanks,

Tony

 

[Zapster]

You may want to reconsider your assumptions. Run a quick calc for both liquid expansion with the large delta T and when liquid is boiling. I don’t know which the worst case is; however, the calculations are fairly straight forward for the comparison. I assume that this is a life-safety issue and as such, I strongly recommend you have someone with experience with this type of heat transfer calculation review your work.

 

[Tonylmiller]

Thank you for your reply. I have done many thermal expansion relief scenarios, and the flow for liquid thermal expansion has always been very small compared to a fire case boiling scenario. Nevertheless, I will check into it. The calculation is easy enough, as you said.

 

[JAlton]

If the RV is mounted at the top of the Jacket, how do you arrive at the liquid being pushed out first? You will more likely have Vapor escaping first in a boiling scenario.

J. Alton Cox

http://www.delucatest.com

 

[JimCasey]

Most states recognize ASME section VIII as having force of law. Get a copy of section VIII, or at least the excerpts of it from a safety-relief valve catalog, and be sure you are in compliance. This will protect both you and your company. Fire-case flows are calculated at 21% overpressure.

 

[vzeos]

This handbook may be of some help.

http://www.tycovalves-na.com/getlit.asp?lit=ld/CROMC-0296-US.pdf

 

[GL431]

The DIERS methodology was formulated especially to size relief valves and systems for cases like these. Bubbling systems with two phase reliefs. The effect here is vapor relief with entrained liquid, because of the narrow jacket. The formulas are quite complicated.

In the pre-DIERS days one would calculate the relief area required for vapor relief (vapors calculated by heat input from fire). Then one would assume (or calculate) the liquid entrainment and calculate the area required for that flow. The two areas would be added and a generous factor multiplied in to account for choking by the two flows.

You might want to google DIERS to see whether you get any formulas for this case. I have not looked into the API RP 521 for a long time, but does DIERS not get a mention there?

 

[JAlton]

Try this website. They have connections with DIERS.

http://www.digitalsolutions.org/

J. Alton Cox

http://www.delucatest.com

 

[PVRV]

I dont understand your acertions hope the following
helps


1. Heat Absorbed From The fire

qin = 34,500 F(A^0.82) <------NFPA 58

2. Vapor Flow Rate

Qrv = qin / hfg

where;
qin = is the total heat absorbed (Btu/hr.),
F= (insulation factor)
A is the total surface area (ft^2)
Qrv is the gas discharge rate (kg/s)
qin is the total heat absorbed (kJ/s)
hfg is the latent heat of vaporization at release Temp.


Let me know if you need sizing calculations and for what type of flow.

Cheers