A customer requires to measure flow of oil crude and they typically uses positive displacement and turbine technology, but those shows some problems when the flows contains some gas, because it affects the accuracy or the instrument.

I want to know, in your experience, which would be the possible best technology solutions to handle this kind of flow. The price would be important to decide.

Thank you in advance for your help.

 

I had a Foxboro rep in the office recently, he spoke about their new coreolis meter that supposedly works on two phase flow. You might want to check that out.

I have no affiliation with that brand

Roy

 

If you want to measure the flow/totalization of a liquid/gas combo, and you want to look at the volume of liquid only (basically ignoring the gas content), then you'll probably want to use a "mass flow meter".

There are many brands available, but I unfortunately don't have experience using any of them. Hopefully, some others here on the forum will have more insight to add.

Hope this helps!

 

There are two methods possible will give good results.

The INvensys Coriolis Meter is capable of giving good mass flow measurement of eir entrained fluids. A lot of work done on this at Cambridge University.

Microcmotion have also been busy solving this problem and both manufacturers claim excellent results.

One supposes this relates to work done over the last decade or so to try and develop corilis for well head metering but they have been addressing heavy fuel oil applications successfully and Micomotion carried out trials in SIngapore.

The other way is to use a positive displacement meter such as Petrolinstruments, (very robust) with an entrained gas density meter.
Positive displacement meters accurately measure the volume flow of fluid. What they can't do is give you the volume flow of the oil distinct from the gas content. An entrained gas density meter will give the density of the fluid (0-100% gas) and the two combined give the mass flow with very good accuracy.

This is good over a very wide range of gas contents.
visit www.viscoanalyser.com and go to the contacts page to send an email asking for info on two phase flow for this solution.

 

You need to quantify the amount of gas in the flow stream which will determine the exact solution. If gas is high then you should look at AGAR dual phase flow meter though expensive but a good product on such difficult application. PD Meter is another good solution where in air eliminator valve/vent can be provided in strainer or upstream of the flow meter. This will reduce the amount of gas being driven to flow meter. I liked the solution described to do correction with density meter using a PD Meter. Petrol Instrument really has a rugged PD Meter and a perfect solution on such application. So far I have not heard or got positive inputs on Mass Flow Meter (Coriolis) doing good on liquids with entrapped gas. I would like to have feedback from end users. Coriolis is an excellent product and if they offer solution on such dual phase metering than its an ideal product. Also look at Ultrasonic (Hybrid I.e transit time & Doppler); they could offer a good solution too but installation or placement of insertion probes would be the most important factor.

 

Air eliminators work best with thin fluids and in combination with a filter (primary separation takes place on the screen) and you will see them used with LPG and domestic fuel oil truck meter systems.
However, if there are significant amounts of gas these may not be suitable. If there is a lot of gas then it may be difficult to vent fast enough and then you need a pressure regulator valve downstream of the meter which will close down when gas is being vented.

I only know what the mass meter guys claim and I too would like to hear some first hand experience.

Most multiphase flowmeter solutions are complex and not as accurate as could be desired. The key applications would appear to be well head monitoring where it is necessary to account for the mass of gas and oil. The usual procedure would be to run the stream through a separator and independently measure the gas and liquid flows then recombine the flow streams and pump into the pipeline. Multiphase flow meters a re a lot less cumbersome and expensive than separators but are usually quite complex, some form of flowmeter (several use PD meters, some use oriface plates) and some sort of density meter to determine the gas fraction, often gamma ray types.

There is an obvious attraction to using coriolis in that the solution is much less complex and potentially much more accurate. Work on solving the problems has been ongoing for some time but more recently the coriolis manufacturers have turned their attention to a simpler applications, fuel oil metering. This is because fuel oil is often heavily entrained with air. So Micromotion, invensys and E&H have all been working on solutions for high volume (but what do they consider high? 6%? 10%? 50%?).

BP sponsored trials in SIngapore and the results are said to be very good.

Note that in fuel oil applications no one is interested in the air, just in the mass of fuel delivered. In crude oil applications there is often an interest in separately accounting for the gas which is also a commercial commodity. SO it does require determining the gas volume fraction and the net gas flow and net oil flow. With crudes you should have a good handle o n the density so this shouldn't be a major problem... with fuels oils the oil density has to be considered unknown.

 

Dear All,

i have had experience with coriolis flowmeters and so far I know that the best coriolis flowmeters are Endress+Hauser and Micromotion. Endress+Hauser is cheaper than Micromotion. However, every coriolis will have problems with entrained gases. Coriolis working principle is based on the vibrating frequency of their internal tubes. The thing is that the entrained gases will attenuate the resonance frequency and cause a deviation which will cause measuring errors. The higher the entrained gas the bigger the error. Coriolis form these 2 brands have "adaptative gain circuits" that control the current that they provide to the circuit that makes the tubes vibrate. Coriolis generally can handle 2% - 5% of gas with no problem. In case you have bigger rates of gas then you can change the gain of the circuit and make the coriolis less sensitive to the spikes the gas can cause in the flow signal (similar to a low pass filter). however, the greater you make this value the slower the flowemeter in case flow changes (just to make clear that it's not a damping in the current output. it's totally different). So you can of course not have 60% gas or something like that. Which gas percentage you have in this fluid? This is the key factor to choose the best technology and confirm if Coriolis can work.

Measuring at the output of a wellhead is very complicated (some people mentioned that) since is a multiphase fluid and it not only has crude oil, gas but also has some sand in it. that's why they use separators and that way can separate the sand form the crude oil and the gas. At the output of the separator they measure gas (with a orifice plate for example or a vortex) and on other pipe they measure oil flow with a coriolis or PD meter for example.

I hope this helps.

 

Foxboro has a coriolis meter reputed to be able to handle significant amounts of entrained gases. CiDRA Corporation produces a device that can measure void fraction and compensate the reading of a coriolis meter in that way.

Walt Boyes
Editor in Chief
Control and ControlGlobal.com
555 W. Pierce Rd Suite 301
Itasca, IL 60143

[email protected]
www.controlglobal.com

 

Hello!

Have you some books or articles about measurement errors separator units. Where author(s) tells about hydrostatic method and scheme mass meter and watercut sensor.