unstabilized crude flow measurement

[compo]

ultrasonic have no chance with boiling fluids like unstabilized crude, or crudes with small gas bubbles mechanically entrained exiting the primary separators--- as most oil facilities operate with at 2 to 3 stages of separation I am curious why more often of not US have been applied and get bad feedback. Good old fashioned meters work however can anyone point in direction of successful meter technology that you have had reliable and consistent readings with for measurement of crude and crude/water mixture with entrained gas bubbles i.e. for liquid lines from primary separation stages, and manufacturers?

 

[jmw]

The problem with entrained air is to know if the meter performance is disturbed by the entrained gas.
For example, a Positive displacement meter is likely to be virtually immune to the gas bubbles. That is to say, if 1 litre flows through the meter then 1 litre is registered whether it is 1 litre of liquid or 1 litre of liquid plus air.
Some corolis meters will measure 1 kg of liquid but suffer an error when that 1kg is a mix of liquid plus air.
Of course, the problem is to know how much of the fluid is crude and how much is air.

Some US meters are said to be quite good with entrained bubbles. Hence, if they, like the positive displacement meters can report the volume accurately then it only remains to use an Entrained Gas Density meter (+/-1.0% accurate fro fluids of from 0-100% air) to determine the mass flow of crude (actually the mass flow of liquid plus air; but while the volume of air is significant, the mass isn't and hence the mass measured can be accepted as the mass of crude.)

Work has been going on with Coriolis meters. The results are said to be promising. I think, so far, some 10" meters have been tested and found to be 3% accurate with entrained air.

JMW

http://www.ViscoAnalyser.com

 

[dcasto]

you cannot measure two phase flow, period. try this place for reseach on the topic.

http://www.ceesi.com/.

The coriolis meters can tell you the total mass that goes through them, but they have no way of saying what is water, oil, or gas. try this link to see how they can be used.

http://www.documentation.emersonpro...blic_mmisami/documents/brochures/gi-00713.pdf

 

[Cat3347]

While you may not be able to actually read percentages of two phase flows, you can get accurate mass flow readings in two phase flow. Foxboro has a coriolis meter that does this. Please see:

http://www.foxboro.com/us/eng/products/instrumentation/flow/massflowmeters/digitalcoriolis.htm

 

[jmw]

The real problem with multiphase flow is to know the relative proportions of the various components.

In a system where you have crude oil plus air mass flow measurement is achievable with accuracies of 1.0-1.2%.

A volumetric meter will record the volume flow total and rate accurately. Of course, what you don't know is what fraction of that volume is air and what is crude but if you want mass flow, no problem, you don't care about the volume fraction.

Note that a brooks style meter is used for liquids and for gases, same principle.

The problem is to measure the density since you need density and volume to get mass. Most density meters have a problem with entrained gases and that includes most coriolis.

The "give-away" is that while a liquids only density meter will return 0.03% accuracy, an entrained gas density meter will return <1.0% accuracy and this is the dominant error in mass flow.

So, by combining a pD meter with an EGA density meter the mass accuracy is 1.0-1.2%. Not ideal, but pretty good considering that in trials of one coriolis meter the mass accuracy with entrained air is 3.0%.

But "you cannot measure two phase flow, period..." No, you can.

Of course, if one of those phases is a mix of two or more different liquids then you have a problem. Thus, if the crude has a variable water content then establishing the mass flow of crude from the mass flow of crude plus water is more difficult if there is air also.


JMW

http://www.ViscoAnalyser.com

 

[glowing]

You can measure 2 stage flow very accurately...its all a matter of how much you want to spend. You must install an anaylzer. I have seen it done, it just doesn't make a lot of financial sense.

BTW...US flow meters are not very accurate. Go with a MAG tube...uber results.

 

[Oldliar]

MAG for crude? -It must be quite some special MAG tube.

 

[JLSeagull]

Don't confuse the Mag-Tube with a Magnetic flow meter.

http://www.usbr.gov/pmts/hydraulics_lab/pubs/pap/PAP-0904.pdf

 

[Oldliar]

Hey, it's what I would call a pitot. So is this considered to give better accuracy compared to a us flowmeter? Btw, what does 'Mag' actually mean?

 

[JLSeagull]

Henry Magallanez according to the site previously noted. Don't let a little flame bait get to you. US flow meters and similar international technologies exist world-wide. Flow measurement technologies improve continuously. This pitot technology is neither revolutionary nor evolutionary. A Coriolis flow meter might work if the flashing is minimal. Even orifice meter could work with some noise dampening; or by keeping the fluid pressurized to reduce the flash.

 

[jmw]

Trials so far suggest that severely aerated fluids cause coriolis meter errors of around 3% or less.
Of course, I haven't been able to establish if this is a % reading error or a cumulative error nor to what extent the fluid is aerated nor if it is a fine dispersion of bubbles or a chaotic mix of bubbles and pockets, but those involved in the tests seem persuaded they can do better. I think Invensys has an article out claiming success for these trials.

JMW

http://www.ViscoAnalyser.com

 

[dcasto]

i can't get to the link, but I'll stack up an orifice meter to anything else when it comes to measuring mass. Oh, well, that off my chest, the problem I had with two phase through coriolis is how the flashing escalates, more gas, more presure drop, more drop, more gas, BINGO, the meter can't seperate the base signal from the "meter" signal and it just fails.

 

[JLSeagull]

Emerson and others claim to accommodate liquid measurement with entrained gas. See the link.

http://www.emersonprocess.com/micromotion/products/sensors_ELITE_transientflow.html

In the early seventies I used to observe local circular chart recorders on steam condensate using an orifice plate. The flashing caused the ink to paint the chart like it was air-brushed instead of draw a line. You could still see an average that could be interpreted as the flow rate. An electronic signal could dampen that same signal to provide a steady reading. Others can comment on the precision of such a measurement. I suspect that a similar noisy signal would occur on liquid with entrained gas. The orifice and dp transmitter could measure the flow. The precision could be questioned.

 

[JLSeagull]

Here is a link to the multiple phase white paper found at the previous link.

http://www.documentation.emersonpro...ments/articles_articlesreprints/mc-001022.pdf

 

[engineeringguy]

I was lucky enough to visit the Micro Motion factory and play around with one of their demonstration devices. Essentially it had a reference meter with water running through it, a line where air was pumped into the line at adjustable flow rates and 'test' meter. For mass measurement, the meter read dead on until there were significant air bubbles in the line. Mass flow with entrained gas is easy. Volumetric flow is the tricky part.

What we've done in the past is install a Micro Motion with a GVF (Gas Void Fraction) meter (Cidra Sonatrac) downstream of the Micromotion and have been able to back out a relatively accurate volumetric flow rate.





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