Level of Level Transmitter and Liquid Volume

[C26M13]

Hello Everyone,

I am currently working a process to determine the liquid volume and level of level transmitter in a vessel.
I am looking for some guidance and advice to perform liquid volume in a vessel and level transmitter calculation.

I have two questions below:
1. How can I determine the percentage of the low level alarm of -300 mm (type of fluid: Natural Gas Liquids NGL)?
2. How can I calculate the liquid volume in a vessel if my low alarm point (LL) is at -300 mm?

I am not really sure how to use the low level alarm which is -300 mm ( i am confused with the value of -300 mm) which is below the Bottom Tangent Line to calculate the liquid volume and the percentage of level transmitter.

I have attached a sketch of the system in question for your understanding.


Can you please advice and give any relevant references for me?


Many thanks

 

[LittleInch]

It's a little unusual, but it can be done using negative nos.

no 1 - Not quite sure what you mean, but the TX range appears to be -700 to + 200, so a rnage of 900. Your LL is at -300 so you are 400/900 of the range, i.e 44.4%. Is this what you mean?
no 2 - You need the rest of the vessel dimensions and shape. You seem to have a few hundred mm of a cylinder - volume of that bit is easy. Then some undefined length of a torispherical end.

Try this

https://www.vcalc.com/wiki/vCalc/Torispherical+Head+-+Volume

or just google volume torispherical head.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[danw2]

Your diagram, with the liquid level substantially higher than the upper port is typical of a density measurement using differential pressure, as shown the shots below.

There is no way to get a tank level measurement when the liquid level is above the upper sensing port; the transmitter will report its maximum 20mA value.

Is your question about calculating volume academic for a true level measurement or are you trying to calculate volume based on a density measurement?

 

[LittleInch]

There are many types of level tx.

We can only assume this one measures within that range

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[C26M13]

Hi All,

Thanks for the response. Appreciate it.

What I am doing at the moment is to determine what is the liquid volume left in the vessel if the level in the vessels reached LL and on this LL in millimeter (mm) what percentage of the level would be?

 

[TiCl4]

I assume T.L. = tangent line of the head? If your dP meter impulse line is down into the bottom head (below the tangent line), the volume calculation becomes more complicated.

First, determine what kind of head you have. From your dimensions given, it does not appear that you have a 2:1 elliptical or F&D head - the head height is too large. Is it a hemispherical head? Whatever head type you have, find a calculation that determines the liquid fill volume vs fill height. The reference provided below has calcs for F&D and 2:1 heads, but not hemisph

You'll then need to correlate the dP reading to mm liquid height in the head itself, then run that through the appropriate equation to find total volume.

This reference below gives you the volume of a partially filled F&D or 2:1 head. You just need to know liquid height and total head volume.

https://proquipinc.com/wp-content/uploads/2014/04/vessel_and_head_volumes_reference.pdf

Your PLC/DCS system will have a 2-part equation. The first equation will be
Volume = [Head fill height calculation]

which you will get from a reference. Since your TL is 700 mm above the bottom impulse line and your sensor range appears to be 900 mm, this equation will apply when the 4-20 signal from the transmitter is between 4.0-16.44 mA. From 16.44 to 20.0 mA, the equation
Volume = Total Head Volume + [Cylinder fill height calculation] will be used.

Since the vessel is a cylinder above the head, it should just be a simple matter of figuring out how many m^3/mA (for 1.700m diameter and a span of 0.900m on the transmitter, I get 0.1276 m^3/ mA.