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# Calculate mass of vapor above liquid level within a Propane Storage Tank.

## Calculate mass of vapor above liquid level within a Propane Storage Tank.

(OP)
Referencing thread481-282609: Total LPG Mass in tank, a calculation was proposed to find the true mass of Propane but I am having a hard time either understanding the calculation or putting it in practice.
Here is what I have, Horizontal Bullet Tank with a capacity of 9361 cu feet, which holds 70,021 Gallons of Propane if filled to the top. Assuming 0.0765 SPGR and 0.55 SGGR at a temperature of 80F with 22% of volume, and an absolute pressure of 173Psi. Based on these numbers, I should have 15,405 Gallons uncompensated to 60F, how do I calculate the 78% of pressurized propane back into gallons compensated gallons at 60F. HELP!!!

### RE: Calculate mass of vapor above liquid level within a Propane Storage Tank.

I'm not sure what you are trying to do but I would try to stick with mass units.

The 173 psia pressure should be the vapor pressure at 80F, I'm going to assume that's correct.

22% of the bullet's total volume (or 15,405 gal) is liquid propane at 80F/173 psia if I'm understanding your post. Therefore the actual vapor volume is the difference or 70,021 gal - 15,405 gal.

Get some thermodynamic tables for propane at 60F and 80F so you know the densities of liquid and vapor.

If you simply want the total liquid and vapor mass of propane in the tank, use the liquid density of propane at 80F * the volume of liquid propane + the vapor density of propane at 80F * the volume of propane vapor.

If you want to convert the vapor portion into liquid, calculate the mass as above. Calculate the volume of liquid using either the liquid propane density at 60F or 80F depending at what temperature you want the equivalent volume of liquid at . You can use the liquid density at 60F and 80F to convert also the volume of propane liquid at 80F to propane liquid at 60F.

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