PSV Sizing for Water Containing Vessel: two phase flow

[DDP20]

Hello,

Currently working on sizing a PSV for a pressurized water vessel, I would like to consult the members of the community for help and advice.

Fluid = Water
P_op = 22 barg
T_op = 170°C
P_PSV = 28 barg
Accumulation = 10%
Outlet: to ATM
Maximum Back Pressure = 0.1 barg

For the closed outlet case, I have to evacuate 83 tons/h via the PSV. I initially applied the single phase method for Liquids as per API520, 9th Edition, pargraph 5.8. The result was 1.5G3. I then looked at the project's line sizing criteria and found DN100 at inlet and DN600 at outlet (factor of 6!) which brings me to my first question, is it common to have such a configuration in the industry?

I then realized that the water will flash across the PSV hence I am now on the maximum mass flux method (API520, Annex C). The result I obtain once I've applied a discharge coefficient Kd of 0.65 is 5.44 cm2. As per API526, an appropriate size would be at least 2J3 or 3J4. In this case, my upstream line is DN150 and downstream line, still DN600. I would've expected a much greater orifice size with the maximum mass flux method. Perhaps, I am missing something.

Thank you for your time,

Derek

 

[Latexman]

83,000 kg/hr, right? If so, my software confirms a J nozzle.

I am not sure what phase of the project you are in. Now that you are into the detailed design of this PSV, can you check the inlet and outlet line sizes and recommend a change if needed? I'd use HEM on the outlet. The inlet is a subcooled liquid, P_sat'd ~ 7 barg at 170^oC.

Good Luck,
Latexman
Pats' Pub's Proprietor

 

[DDP20]

Hello Latexman,

Thank you for your input! Apologies for the late reply, I was expecting an email alert for the thread. We are in the EPC phase of the project. We have specific criteria for inlet and outlet lines; including rho*v2, Delta P and Mach Number. I simulated the flash across the PSV in Aspen Plus and found only a 13% mass vapor fraction therefore my final values are inlet DN150 (API Flow) and outlet DN400; this configuration seems reasonable.

Thank you for your help.

Cordially,

Derek