+1 vote

Pressure safety valve in supercritical service

asked Feb 28, 2014 in Safety by RichS29 (4,320 points)
I have a pressure safety valves (PSVs) located on a vassel containing liquid hydrocarbon. In blocked flow case during a fire makes the conditions inside vessel supercritical fluid.

Can someone suggest a calculation procedure for PSV sizing for supercritical service?
commented Feb 28, 2014 by odadmin (21,030 points)
Could you please provide information about your typical fluid composition?
commented Feb 28, 2014 by RichS29 (4,320 points)
PSV is located on a LPG bullet tank.

1 Answer

+1 vote
answered Feb 28, 2014 by odadmin (21,030 points)

You can use API RP-521 conventional method for sizing the PSV in supercritical service but it is conservative, producing larger orifice areas than required. API RP-521 treats all “un-wetted” vessels the same, whether the fluid contained is supercritical, a vapor or a gas. It also does not account for the change in fluid temperature. 

Furthermore, an over-sized valve has two potential problems: there is a potential for destructive valve “chatter” and larger PSVs are more expensive. Following reference details a procedure for calculatingt the PSV in supercritical service:

Designing for pressure safety valves in supercritical service
Use this rigorous method to prevent over-sizing
R. C. DOANE, S&B Engineers and Constructors Inc., Houston, Texas

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