PSV design question

[TheDruid]

Hi folks,

we have the following problem:

existing tank has inlet line DN65 with a CV. Before this CV there is saturated steam with 22 bar@theoretical 14 t/h. The tank is designed for 12 bar.

We are designing now the PSV for the tank. Failure case is broken CV.

regarding the inlet pressure drop, is it correct, that only the part from tank to PSV is important (and not the line from boiler to tank to PSV) ?

Are there any regulations about the flow rate. 14 t/h is the theoretical flow rate of the boiler (which is approx. 150 m away, with several bends and valves --> pressure drop). Could this be a problem, regarding vibrations ?

For our calculations we get a DN65 valve (14.5 t/h).

Is this the correct choice ?

thanks very much &
best regards

Alex.

 

[Latexman]

Yes, only the part from tank to PSV is important.

Assuming an ideal gas and k = 1.3, I calculated an ideal nozzle of about 47 mm diameter is needed. I know this is not too rigorous, but how does this compare to the real nozzle in your 65 mm PSV? What's the flow coefficient of your PSV?

Good luck,
Latexman

 

[TheDruid]

Hi Latexman,

thank you for your answer.

This compares very well. The (so far) selected nozzle has a diameter of 60 mm at the narrowest point. alpha is 0.7.

Follow-up question:

Boiler spec is 14000 kg/h. Piping is about 150 m with several bends and so on to the VC. what mass flow is the correct one for the PSV ? The theoretical flow (14t/h) or the practical possible flow (approx. 9-10 t/h) ? Are there any regulations ?

thank you.

Alex.

 

[Latexman]

I assume the boiler has it's own PSV that handles 14 t/hr, so the basis for the tank PSV should be the expected flow thru the line for the scenario. I know of no regulation that would specify a basis other than good engineering practice (i.e. the expected flow for the scenario).

Good luck,
Latexman