API 521 Vapor Discharge Capacity Equation

[anubis512]

Hi all,

I'm in the process of sizing relief valves and I have a question about the equation for vapor discharge capacity (W) found in API RP 521. We have an old copy on file (1990) and the equation for vapor discharge (A-7) is a little complicated.
Looking through our Consolidated book, Crosby Engineering Handbook, and a bulletin put out by Leser, all show W = Q/latent heat of vaporization, which is much simpler. Is this equation in the newer versions of API 521, otherwise where can I find this equation in a standard?


Thanks!

 

[CMA010]

Equation A-7 is for vessels which do not contain liquid while W = Q/dH is for vessels which do. The A-7 equation is still part of the latest version (2008).

 

[anubis512]

I understand that, but I don't see W = Q/dH in the actual standard, at least the version we have. Is it located elsewhere?

 

[CMA010]

From you question you seemed to have the concepts mixed up. I'm sure in the standard a statement is made (or was made) that the vapour relief required is equal to the total rate of heat absorption divided by the latent heat of vapourisation, or W = Q/dH.

 

[anubis512]

After further reading, I found it mentioned in text, but it wasn't in equation form. Thanks for your help