Installing Chemical Storage Tank: Pressure of Liquid or Gas?

[NewEngineer]

Hello Forum,

I'm looking to install a new chemical storage tank at my site. The tank itself is not rated for vacuum. We will have proper ventilation and nitrogen pumping into the tank to compensate when we are pumping out of the bottom.

However, I do want to include a pressure transmitter on the tank that will turn off the outlet pump in case pressure in the tank continues to drop to a dangerous level that may implode the tank. My question is should I be more concerned about the pressure of the liquid in the tank or the pressure of the gas (in this case nitrogen) of the tank?

 

[.Scott]

You will have the least pressure at the top of the tank, so that is where the pressure measurement should be made.
The answer seems too simple - I am suspecting I do not understand the full question.

 

[CWatters]

Worn pumps can allow liquid to pass even when off. I would suggest you also want a spring loaded motorised valve as well (the spring is to turn off the valve if there is a power cut).

Should also have a pressure relief valve to stop too much nitrogen being injected.

Also some sort of expansion vessel? What happens if the tank is filled with cold chemical from a delivery tanker in winter and then warms up. Could it burst the tank?

 

[NewEngineer]

it is a new pump we will be using. We will also include a automated block valve on the tank's outlet line, so when we are pumping out material the tank's outlet will be closed off.

THe tank is not expandable, but we will be fitting it with a breathing ventilation line equipped with a conservation vent as well as an emergency ventilation line with a rupture disk to burst in case psi in the tank continues to grow.My main concern that I just wanted to validate is that I want to measure the pressure of the "air" in the tank, not the liquid itself.
(i put "air" in quotes because we want to replace the O2 with N2 to remove a source of combustion from inside the tank.

 

[CWatters]

Yes I agree with what Scott said. The lowest pressure will be at the top.