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Tank PVV Setting Different Product API

  • 1.  Tank PVV Setting Different Product API

    Posted 09-14-2020 10:50
    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.
    Marlon H. Guerra Mutis

  • 2.  RE: Tank PVV Setting Different Product API

    Posted 09-15-2020 00:06


    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.

    Shantal Ramdeo PE
    Senior Process Engineer
    Heritage Petroleum Company Limited
    Princes Town

  • 3.  RE: Tank PVV Setting Different Product API

    Posted 09-15-2020 10:21
    Marlon, the PVV settings are set to protect the tank.  So the settings depend on the design pressure ratings of the tank and not what is inside.  You also need to consider an emergency vent which usually takes the form of an emergency manway and is seized for fire relief.  Both the PVV and the emergency vent need to fit within the  pressure rating of the tank.  If this is an API 650 tank, be aware that the relieving pressure should not exceed the design pressure.  If it does on a regular basis, the roof seam will fail, and it will make its own vent relief path.  I witnessed this behavior on a large atmospheric tank used for storing ethanol (a by-product) in one chemical plant.  After making the settings, you must make sure that the storage conditions are compatible for the fluids inside, even if it means cooling the contents.  I hope this helps.
    Bob Clay