Help understanding diagram for differential pressure measurement n 1

[VPbris]

Hi Guys,

I'm a junior engineer

I need some help understanding some principles on the aplication of a differential pressure gauge to measure liquid level on a CO2 tank. (the tanks operates at 16 - 24 bar for co2 storage). Probably is a very easy question, but I could not figure out myself.

Attached is a diagram from the DP supplier of how it should be installed. My initial guess was that I just needed to take a measurement from the top and one from the bottom, making sure the bottom is levelled with the input of the DP to get a correct liquid height. However, I saw some pieces I could not quite figure out their reason to be.

Could someone please explain the need for a inverted U (I know it says it is for gas trapping), but why trap the gas? Then there is a vapor generator, that I do not understand what it is and its use, first guess would be that it vaporizes the liquid so that only gas gets in contact with the DP, but did not understand it properly. And finally, with this mounting apparently I do not need to level the bottom of the tank with the DP.

Could someone please give me some hints on this?

 

[Compositepro]

You need to understand the properties of CO2 to understand the system design. It does not say this on your drawing, but it appears that this is a refrigerated storage tank so that it does not have to be made to withstand the high pressure that liquid CO2 has at room temperature. All of the lines shown in your drawing are uninsulated and therefore will contain only vapor. Any liquid that gets past the gas trap will vaporize and prevent anymore liquid from getting past the gas trap. As long as all the lines only contain gas, the DP instrument will accurately read the liquid level in the tank, regardless of the height at which the DP instrument is mounted.

 

[VPbris]

Hi Compositepro

Yes you guessed correctly, this is a refrigerated unit. Thanks for the reply, makes sense to me now.

Just one more question, just to check, it appears to me that the reference height for my DP gauge will be at the tip of the inverted U (gas trap) inside the tank, hence in order to know the correct liquid level I should take into consideration this distance, I know it sounds pretty basic stuff, but just to make sure I understood the process.

Best Regards

 

[Compositepro]

You are correct, but the u-tube is probably designed to curve back down close to the bottom of the tank, and the storage volume below this point is very small.