Hi,
The setting of the pressure vacuum valve is a bit more complicated than that. Although the physical properties play a role, and the higher API indicates a higher evaporative loss during out breathing, the following shall also be undertaken when sizing the PVV (also refer to API 2000):
normal inbreathing: pumping out of tank as well as thermal inbreathing (to account for condensation of fluid)
normal outbreathing: pumping into tank as well as thermal outbreathing (to account for evaporation of fluid)
emergency venting: for example when the tank is on fire, an overpressure scenario arises
The above will indicate the capacity of the PVV(s). For the pressure and vacuum settings:
Pressure: the failure pressure of the tank shall be used as a guide to set the pressure, refer API 650 annex F
Vacuum: reference can be made to API 650 to determine any vacuum pressure limitations
To clearly answer your question, however, I would use the higher API as this is the more volatile liquid and will result in more evaporative losses. Hope this helps.
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Shantal Ramdeo PE
Senior Process Engineer
Heritage Petroleum Company Limited
Princes Town
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Original Message:
Sent: 09-14-2020 10:50
From: Marlon Guerra Mutis
Subject: Tank PVV Setting Different Product API
Dear friends
I would like to know your opinion about how to approach the setting of a PVV for a 15000 bbls atmospheric tank which operates with a different product API from 60 to 80. Is it recommended to set it for the higher density/API? Is it that technically enough for this condition?
Thanks in advance for your responses.
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Marlon H. Guerra Mutis