Coriolis flow and density measurement of mixed sulhpide slurry


Thread Starter


We have been having problems with our E&H coriolis flow meters and i would appreciated any pointers. There are set up to measure both density and volumetric flow - 2 current outputs- of a mixed sulphide feed into an autoclave. The slurry has a pH of about 2.0 and density is about 1300kg/m³ and a flow range of 0 to 100m³/h. the flow and density readings are all over the place with either or both disappearing and we get Fluid inhomogeneos, Oscillating tube current limit and tube not oscillating errors. Is this a case of wrong application or are we doing something wrong?
You are using a coriolis mass flow meter to determine both density and volume.
Mass flow and density are primary measurements.
Volume is a secondary derived function of the mass flow and density so if the density is disturbed so to will be the volume flow.

How is the mass flow responding?
If it is reasonably stable it might be that the slurry is non-homogeneous giving unbalanced flow which will upset the density measurement, and hence also the volume, but not necessarily the mass flow.

If the mass flow is unstable also possibly you have air in the flow?

Is there a reason you coriolis when you obviously want volume flow?
Why not a magnetic flow meter?
I perhaps didn't focus on the error message you reported.

Almost certainly, re-reading your post, you have a lot of air in the flow. Air tends to be much more mobile than liquid and compressible.
It sounds like a lot of air, more than coriolis can handle even with entrained air capability.

If these are horizontal lines, even more reason to ask why coriolis and not magnetic meters. Some of these are designed to handle partially filled lines i.e. with air flow along the top and liquid along the bottom. This assumes air is an expected and intrinsic part of the process and not easily prevented.
I would guess, without any data, that your pipe is not full. It sounds like you are getting entrained air bubbles in the line that have a very large difference in density.

Dick Caro
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Joshua Mhora

I am guessing you are correct about the entrained air. my question is how can we make the best out of the situation as we have about 20 of these meter in 1 process area, all of them measuring slurry feeds? Would an increase in pressure help?
Increasing back pressure might help if you have some bubbles or cavitation.
The amount of air you have is very high and will not be cured by back pressure.

I think the first thing to do is find the source of the air and stop it getting in. It may be that some simple (and inexpensive) solution will be found.

I don't know enough about the application but I would have to guess that there is a lot of air getting in via the mixing process.
Adding dry powders to liquids will result in some air.
But how is the mixing being performed? Do you use air mixing?
Do you use mechanical mixing such that air can be drawn into the slurry an then into the discharge? e.g. paddles and a partially filled tank.

If this is a relatively new installation then if you have 20 off these installed then at some point someone is going to have to explain why you have coriolis meters in a process where you want volume and density (presumably to get the mass flow of solids?) and where there is a lot of air present.

And if all 20 show the same problem, did not some one buy one to start and see how it went before buying all 20? Was entrained air included in the original specification for the meters?

Or is this an existing installation and they all worked at one time and now they don't? - in which case you look for what changed.

I would also be concerned that this is exactly the sort of problem that will come from the single source supplier way of doing business.

PS I assume these are Profimass single tube.

You might take a look at a couple of the current threads on density measurement of slurries.
(this goes back to 2007) and this one which is more recent:
unlikely that air entrainment is involved in this application,

with slurries such as this, inhomogeneous flows are common with solids build up, partially plugged piping, and as in this case meters, all leading to non-stationary flow process, i.e. fluid properties and flow rates constantly changing in erratic fashion.

most such systems, have a minimum flow velocity the reduce sedimentation and to keep the slurry more or less well mixed and the lines flushed, tough process design to work with.

increasing fluid velocities might help

with heavy slurries where velocity increases are not an option, weigh systems described in your responses are the best bet
You cannot correct the air bubble problem without a piping change to make sure that the line is filled. You must examine the piping upstream of each meter to determine why air is flowing in the line. There may be other piping fixes to be made to solve this problem, but we have no data here - you do.

Gerald Beaudoin

Air getting into the system can be as simple as a loose pipe fitting or clamp connection on the suction side of the pump.....can give you all sorts of headaches...and everyone screams "instrumentation problem"....been there...tightened the pipe more "instrumentation problem"! Good luck.

Gerald Beaudoin

Jerry Stevens

I would like to talk with you directly.

As the manufacturer, we should discuss operation conditions, experience and application to help you resolve your problem

I can be reached at: 1-888-ENDRESS or at my desk at 1-317-535-2133.

Jerry Stevens
Senior Product Business Manager - Flow
Endress+Hauser, Inc
United States

While it is always desirable to approach the manufacturer to obtain help resolving issues, it would be helpful, having raised the issue here, to publish an outcome as a courtesy to those who have attempted to assist and to help further the understanding of how to optimise meter performance.

I hope someone can keep us informed.