Mass flow meters on sulfuric acid stream

  • Thread starter Hart, Brett, CA NAR/US
  • Start date
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Thread Starter

Hart, Brett, CA NAR/US

We are experiencing calibration drift on Micromotion mass flow meters in sulfuric acid service. The system is batch metering and the meters stay full between batches. We believe the problem is due to tube deterioration. We are currently using stainless steel tubes but are considering some different alternatives, such as hastelloy. The factory has given us several
different (unsatisfactory) answers. Has anyone else had this type of experience using Micromotions in sulfuric acid, or some suggestions?

Thanks
Brett Hart
 
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Hrvoje Zelenka

Dear Sirs,

We have alot of experience with the Coriolis force meter, and have experienced some problems.

Most of them are already solved.

here are some questions that you should answer:

1. Are You using only the totalizer value (batch) or the Flow signal as well.

2. Are you using the Micro-Motion totalizer for Batch process?

Probably problems:

1. There is a parameter in the RFT Transmitter called Damping ( unit - seconds ) and gives the time of floating averaging.

In case You are calibrating the unit (or authorized laboratory) You have to ask them to calibrate the unit with minimal damping (0.2 sec)-set damping to 0.2 seconds.

In case of long damping ( 15 seconds), and flow rate of 1500 lit / minute the meter will at the start-up loose (1500/4)/2 litres = 187.5 litres. ( due to averaging from 0 lit/min to 1500 lit/min for 15 seconds, although the flow rate raised to max 1500 lit/min within 2-3 seconds.

In case the same signal is used for control, the 0.2 sec. damping could make the signal unstabile, and you could have a problem with control. In such
case make the gain of the controller lower, or the PB higher.

If you give me the Damping that was set before, and the max. flow rate we can theoretically calculate the total error.

In case of small batch, the error in % is higher.

This type of error is systematical and looks that it could be your problem.

Anyway, you should from time to time (1 or 2 times a year ) calibrate the meter.

Please be free to contact me and inform me about the damping parameter you found in the transmitter. The Micro-Motion Coriolis Meter is one of the best, but one shall know the
characteristics, and apply it as requested.
INENCO d.o.o.
Instrumentation Engineering and Consulting
Fiscal Metering Specialists ( custody transfer )

Hrvoje Zelenka
 
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Hi,

What kind of calibration? Density or flow total. In case of density calibration, you could do it with distilled water, because sulfuric acid is
too dangerous such calibration.

Some issues could cause the calibration drift:
Not perform density calibration before flow calibration.
Zero calibration when the meter is not full of liquid.
Improper ground
Batch flow time is less than 45 seconds.
Pipe length from shutdown valve to calibration tank is too long or improper installation.
General calibration factor or calibration factor from MicroMotion software (Prolink) is not always good for specify flowmeter.

If you could give more detailed information about MicroMotion model, batch weight, flowrate, etc., I may have more idea about it.

Hung Lam
 
I faced a problem once which we concluded to be due to some "Multiphase" fluid in the tubes.
Tube deterioration could be one reason, but then the supplier should be able to verify that.
Anand
 
We also had a procedure for zeroing the meter before change in fluid with different density.

We followed the following logic due to several problems in zero drift and accounting problems:
1. For density calculation, you are required to fill the flowmeter and zero it with tubes full and no flow condition.
2. When the density changes the tube is required to calculate the mass, but it could be using the density calculated previously.
3. IF the density changes then the flow reading might be affected.

Anand
 
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Anand wrote:
> 2. When the density changes the tube is required to calculate the mass, but it could be using the density calculated previously.
> 3. IF the density changes then the flow reading might be affected.

A bent tube coriolis meter measure mass flow directly from tube twist/detlta time of the pick off coil sine wave phase shift. The density factor is used to charcterize the tube period. The density calibration should have no effect on the mass flow output. The old 7 wire D series sensor with the RUE transmitters didn't even have a density cal factor.

The drift in calibration may be caused by the sulfuric changing the tube stiffness over time, but the manufacturer should be able to check that out.
 
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Hrvoje Zelenka

Dear sir,

1. The Micromotion Coriolis force meter does not calculate the mass flow from density, but directly measures mass flow.

2. In case you wish to have a flow in volume units ( m3/h or quantity in volume units m3) then the transmitter devides mass by density. The density accuracy is not so good as the mass flow.

3. Zeroing the meter must be done. In case you did it in accordance with the procedure from the manual it is OK.

4. You have also a low flow CUT OFF parameter. Check it. It is a flow at which the transmitter cuts it and makes the output 0 t/h or kg/min . Usually it is a small quantity that never flows. This can cut the noise signal at no flow. It shall be set much lower then the expected flow rate.

5. I mentioned the damping parameter in seconds. check it. In case you wish me to help you provide by e-mail following data:


1. Low flow CUT-OFF _____________ kg/min (t/h)
2. Damping _________________seconds
3. Flow rate at the begining of the Batch (t/h or kg/min)
4. Usual Total batch quantity (if any) ...Batch is how much of sulfuric acid you are measuring in one measuring sequence (if not continuous flow)

Regards,

Hrvoje Zelenka
 
C
Anand wrote:
> 2. When the density changes the tube is required to calculate the mass,
but it could be using the density calculated previously.
> 3. IF the density changes then the flow reading might be affected.

A bent tube coriolis meter measure mass flow directly from tube twist/delta time of the pick off coil sine wave phase shift. The density factor is used to charcterize the tube period. The density calibration should have no effect on the mass flow output. The old 7 wire D series sensor with the RUE transmitters didn't even have a density cal factor.

The drift in calibration may be caused by the sulfuric changing the tube stiffness over time, but the manufacturer should be able to check that
out.
 
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Hakan Ozevin

Dear Brett,
I think stainless steel is not the right material for transfer of sulphuric acid (what is the concentration?).
Did you already check this with the supplier?

Hakan Ozevin
 
I believe that Hastelloy C is the material to be used. But mass flowmeter
supplier may have the correct material list

Anand

 
Hey mate,

You say that you believe the problem exists with the material of the pipe. I work at an alumina refinery and we have sulphuric acid to settle out conc of caustic. We have also experienced your problem and we changed the pipe from just stainless to stainless exterior with a 5.5mm hastelloy c interior. This has been in line for a good while now ans has worked quite well. Hope this notion can be of help.
 
This is standard, Micro Motion has done lab testing on Sulfuric acid on the tubes. The meter was probably sold to you with the understanding that the meter could see corrosion. The Meter should be Hast. or a tefzel lined meter. Both would be better suitable for this application. Also, when measuring Sulfuric you have to look at temperature to determine what the corrosion rate will be.
 
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