calculating Liquid & Vapour volume


Thread Starter

Hesham Anwer

We are installing 37 LPG Bullets of different capacity & size. we require to know the quantity of LPG Liquid & Vapours in term of M.Tons in each vessel through some transmitter/instrument in our control room. Also the pressure & Temperature of the vessels.

hesham [at]
Hi there,

Your best bet might be the RTG3920 radar (or their latest version)from Saab-Rosemount. It can also give press and temp readings incorporated in the same instrument but measured at a different point on the vessel. We used similar type SAAB radars to measure our crude storage tank level, pressures and temp. All these L,P,T readings are then send to a PLC and compensations are being done there before it is send to a small SCADA system in the CCR. Very simple, reliable and accurate system.
[email protected]

or to have a quick overview,

On a more personal note from my own personal experiences and ideas, I would not throw out the Guide Wave Radars either, since even with a low Dielectric constant of 1.6 to 1,9 the GWR should still be able to give you accurate readings.

The distance is not a problem either since you can use the cable type that can be up to sixty meter long. I have used these GWR to measure crude interfaces on various applications and I found them to be extremely accurate and reliable. To measure only one product will be even easier and better. The dielectric constant of crude is also quite low, 1,8 to 4. On these GW radars the temp and pressure also needs to be measured separately.

Might be worth speaking to Khrone (BM100) or Emerson about them as well to see which type will be most suited for your application.

The radars from SAAB are the Frequency modulation radars(cone non contact type) and the ones from Krone and Emerson are the Guide wave type although I think both companies will be able to supply both types.
Hi again,

As you already have the inside diameter of the vessel and you have the LPG level (as per suggestions in my previous reply) you will be able to calculate the volume of the product inside the vessel in M3, but since the bullet is not a symmetrical vessel, volume is not directly related to level and you need to calculate and work out a conversion table to convert the volume at different levels into liters. 1m3 = 1000L

Something like this:
10% level = 200m3 = 200000liters

To convert that into weight you need the density as well but since the density of LPG changes all the time it might be better to do a measurement of the density with a permanently installed DP transmitter at the bottom of the vessel. You can then use that density measurement and calculate the metric tons in the vessel based on the simple formula for water.

1 liter of clean water = 1kg since the density of water is 1, so 1 liter of LPG = 0,550Kg if the density at that point is 0,55. Then just convert the kg into metric tons.