Flowmeter Specification 1

[sheiko]

Hi,

In my plant, we need to buy a flowmeter and I have difficulties to determine the minimum flowrate in the line. Indeed, data retrieval software always gives "zero" as min flowrate.

So I was wondering:
- Is it mandatory to specify the minimum flowrate in the process data sheet of a flowmeter?
- Is it possible to assume a turndown ratio without knowing which technology will be chosen?

Thanks

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[TD2K]

It's not mandatory to specify the minimum flow but I always like to let my instrumentation engineer know the range I want to be able to measure. It's also a useful piece of information when max meter ranges for devices like orifice meters are set. While orifice meters are commonly designed so that 'normal' flow is about 70% of the meter's maximum, that can be adjusted if the instrument engineer knows the minimum is 1/3 of the 'normal' since a reasonable rule of thumb for orifice meters is only about 3:1.

If you know the current meter and it's turndown, that gives you at least an idea where your current 'zero' (which is more a minimum turndown of the meter than a true flow measurement) may lie. With that information, you have a better chance of the next meter covering your turndown range since different metering technologies have different turndown capabilities.

 

[DRWeig]

As for turndown without knowing the technology, the range is pretty wide. Turbines and ultrasonics can get up to 40:1.

I generally have to consider the need-to-know lowest velocity (and of course, the normal and upper limits) before choosing which technology to employ...


Good on ya,

Goober Dave

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[sheiko]

Thanks,

Do you guys know any minimum velocity criteria for the coriolis flowmeter?

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[DRWeig]

Some manufacturers brag 100:1 on coriolis, but real accuracy is limited (in my opinion) to something a good bit less, maybe 30:1?

See attached for a good discussion.

http://www.cbeng.com/resources/whitepaper/Flow Meter Spec & App.pdf

Good on ya,

Goober Dave

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[zdas04]

I have found 30:1 to be really optimistic in gas (especially below 150 psig). With medium pressure gas (about 50 psig to 150 psig) they struggle to do 10:1. Below 50 psig they struggle to provid any repeatable numbers.

David

 

[sheiko]

I forgot to mention that my fluid is Fuel Oil.

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[DRWeig]

I had assumed a liquid -- coriolis or ultrasonic might be a good choice if turndown is important. Talk to some manufacturers. They cost more, but since non-invasive the maintenance and reliability aspects add value...

Good on ya,

Goober Dave

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[ports394]

What's the viscosity of it? And give us an idea of some flowrates. Are we talking 100 gallons per minute, or 10000 gpm? Pipe size?

Need a little more information to really help you.

 

[knapee]

Dear sheiko

Information required from the Process Engineer to be provided in the flow data,
includes the minimum, normal and maximum flows, pressures, temperatures and alarm set points.


The positive displacement flow meters now are the best flow meters currently
available for fluid flow measurement, particularly for crude oil. They are highly accurate, have a good rangeability (turndown) ratio andcan handle high viscosities.

Turbine flow meters have good precision and turndown for hydrocarbon fluid.
They are suitable for both gas and liquid measurement, they have a wide turn down ratio.

Ultrasonic meters are finding applications for accurate measurement for both liquids and
gasses. Accuracy and turn down make this type of meter attractive to legal metrology flow
applications.

 

[ports394]

Line pressure and allowable backpressure may also make a difference.

 

[sheiko]

Ports394,
Flowrate ranges from 300 to 2000 kg/h
Pipe size ranges from 1 to 2 inches
Viscosity ranges from 6 to 20 cSt
Temperature is around 130 degC



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[FlowGuy]

sheiko-

Your Fuel Oil application would be a good fit for one of our Positive Displacement Gear Meters. Unlike most PD Gear meters, we guarantee an accuracy of ±0.3% of reading over the entire 200:1 operating range of our gear meters.

The flow range and viscosity of your application would work in our 1/2", 3/4" or 1" port gear meters. You will see an increased pressure drop created by the meter as you go to a smaller port, but a smaller port sized meter does have a more economical price.

Let me know if you have any questions.

http://www.maxmachinery.com/content/gear-flow-meters

 

[sheiko]

Thanks,
Apart from price, may I know what are the advantages of PD type in comparison with coriolis type?

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[FlowGuy]

Here are some advantages of a Max PD meter over a Coriolis meter.

1. Lower flow rate capability, able to measure below 1 cc/min

2. Wider operating range allows one Max meter to replace several others

3. Lower pressure drop reduces energy lost through metering

4. Completely immune to vibration

5. Robust designs with pressure ratings to 7250 psi

6. Offers bi-directional capability with a fast response to change in direction

7. Faster response to flow changes with user adjustable dither and damping settings

8. Meter output linearized within 0.2% over a 200:1 range

 

[ports394]

Coriolis can drift with a density change or temperature change. Same if your velocity/flow rate is out of spec.

with a PD meter, 1 turn = 1 fixed volume. That's why you can have such a high turndown ratio...which your application needs.

I converted your flow rates.. and at max you're about 10 GPM. I'd go with a 1/2" or 3/4". The 1" is probably too large.

 

[sheiko]

Thanks all,
FYI, I have just checked my company general spec, and it recommends Coriolis for combustibles.

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