nitrogen depading with vapor equalization line 1

[00000000000001]

I need to know what is vent rate during the liquid tranfer from the tank truck. There would be vapor equalization line between the tank truck and the storage tank during the transfer. I would think that because of this vapor equalization line, there would be no or small vent to the VGO. But I need to know how to calculate it regarless how small it is. Please help me on this. Thanks

 

[Unotec]

You unload 1m3, you displace 1m3. The pump will determine that.
Is this what you're after?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[Latexman]

The liquid going into the tank displaces the vapor space, compressing it. If you have a large equalization line, the pressure will not build much before the vapor volumetric flow = the liquid volumetric flow. If you have a small equalization line, the pressure can build significantly before the vapor volumetric flow = the liquid volumetric flow. I have a tank that pressures up from 0.25 psig to 3-5 psig before the railcar is empty, then we have to wait until the pressures equalize before we disconnect the railcar. The tank PSV is set much higher than 3-5 psig, so it is a zero discharge process.

Good luck,
Latexman

 

[Unotec]

So, Latexman, the vent rate is determined by the pressure losses in the vent header. Am I reading you correct?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[Latexman]

Yep. Imagine the two theoretical limiting conditions. Infinitely small (no) equalization line is strictly a compression problem, and infinitely large (open vent) equalization line has no pressure build-up. In the real world, we are somewhere in the middle.

Good luck,
Latexman

 

[Unotec]

That's why my vent lines are 6". The pump determines the flowrate (about 1m3/min).
Did we answer your question many-zeroes-1?

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[00000000000001]

Thank you so much for all the helps. the bottom line is if I design correctly, then the vent flow rate should be neglectible.

 

[jwysmooth]

Everything everyone has said is true, but many zeros-1 needs to understand that under ideal conditions the liquid to vapor displacement rate is 1:1. However, in practice, there can be a vapor growth rate associated with the transfer. The vapor growth rate will depend on the vapor pressure of the product transfered, temperature differences between the two tanks and the configuration of the liquid fill connection in the recieving tank.

If the liquid product is gasoline and there is some moderate aggitation (submerged fill) in the liquid recieving tank, then the vapor growth factor (GF) will be around 1.1 to 1.15. This is a rule of thumb, developed years ago in the gasoline vapor control industry. If the loading is splash loading from the top of the top of the receiving tank, the GF can equal as much as 1.5, so be careful.

Also, if your original question arises out of a concern for the necessity of the a vapor control system, then a vapor control end device will likely be necessary because of breathing vapor losses from the tank from diurnal heating and cooling of the storage tank.

If the vapor pressure of your liquid product is low, then you can ignore everything in this post.
jwy