Free Vent + Gas reaction 1

[Lijantropo]

Dear all colleagues,

I am evaluating the required size of a free vent to be installed in a new atmospheric tank.

Normally I would follow the API STD 2000 to determine inbreathing/out breathing (including thermal in/out breathing) requirements, and then proceed with a hydraulic calculation to estimate the minimum size. However, this tank must be provided with two gas inlet nozzles: The first one is for "process air" and the second one is for a chemical in gas phase. The objective is to make both gases reacting with certain elements present in the liquid to be stored.

My first approach was to calculate the actual volume flow of those gases. Then, estimate the air flow (at tank operating temperature and atmospheric pressure) that represents the same actual volume and add this amount to my out-breathing calculations. However, considering both gases are actually reacting inside the tank, I think I probably should determine the extent of the reaction, use the product density to calculate the volume increase after the reaction and add this volume to the out breathing flow. Finally, subtract the amount of gas consumed from the reaction.

Does anybody have experience in a similar situation? I will appreciate any comment regarding my approach and/or standards I can verify.

Thank you in advance,
Lij

 

[IFRs]

If the process affects the pressure or vacuum inside the tank, by all means take it into account. Since this is just a free vent, don't get too tied up in detailed calculations or worry about the accuracy of the numbers. Presuming that the vent is not part of the process and it just protects the tank from damage due to excess pressure or vacuum, double the size of the vent when you are done, and make sure it can not be blocked by snow build-up on the roof.