Pressure safety valve in supercritical service

Asked by odadmin 5 years, 12 months ago | 1 Answers

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?

1 Answer

odadmin 5 years, 12 months ago

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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