flow metering of LNG

[globalgas]

I was wondering if pressure and temperature has to be taken in account while metering volume flow of LNG? Are there other important factors to take in account? My experiences basically lays in the custody metering of natural gas.

 

[davefitz]

LNG per se is a liquid, so there may be a small temp correction; if you are referring to re-gasified LNG, then you would need to apply P + T corrections to the indication of flow as mesured by conventional flow elements.

I would guess that since there is a range in LNG constituents depending on source of LNG ( rich vs lean), you would also need to apply a correction based on C1-C2-C3-C4 constituents.

 

[globalgas]

Thanks Dave, re-gasified LNG can be treated as natural gas, and P and T as well as the composition of the gas is required for calculation of normalized flow. What LNG concernces, I wondered if -for flow measurment- it cuold be treated as a liquid? I tried to search the internet for a example PID or sketch, however did not found much about LNG measurement.

 

[dcasto]

here how we measure LNG. LNG is measured in a coriolis meter by mass or as it is loaded onto trucks and the trucks are on scales.

Then the density is either contractually stated in either tables or the density is arrived at or samples are taken and the NIST REFPROP program (or othe EOS as set out in contracts) are used to derive the gallons or energy content based on the compostion and the loading conditions (typically the loaded temperature is used to set the conditions to calculate the density). The reason you only need the temperature is because the LNG is at bubble point, so composition plus either temperature or pressure automatically sets the the missing value of press or temp..

 

[globalgas]

Thanks, does anyone of you have already experiences with Ultrasonic metering of LNG.
As we were informed, US metering can handle much more flow and as such requires minimum installation space compared with coriolis. In case of coriolis meters several units has to be put in parallel, however, coriolis measure mass (density incl.) US measures volume and requires the density for calculation mass flow.

 

[dcasto]

a 24" ultra sonic can measure 175,000 lbs/hour. A 10" micromotion measures 75,000 lbs/hr.

The problem is I have not found an ultrasonic that has a design temp of -250F

 

[globalgas]

The internet guided me to GESensing who appeared to have a cyrogenic US meter for this kind of applications. This clarifies why we are taking in account US meters.

 

[dcasto]

yes, I didn't see the panaflow series rated to -310F.

 

[globalgas]

We had in mind to use the BWT (Panametrics Waveguide Technology).

 

[dcasto]

You'll know the gallons, but you'll still need to compensate for T&P. You could do it with an EOS or tables. Or you could put in a micromotion densitometer, thats the same insturment as their direct mass meter.

I've seen LNG contracts that have a fixed density value.