Having problems with a mass flow meter - Coriolis

[cdcosta]

We have installed a Coriolis mass flow meter on a 2" process line. The Unit has been calibrated and is operational. Our problem is we have air bubbles entrained in the liquid. This is causing the density and hence the flowrate to be erratic.

I am looking for ideas on how to minimize the fluctations in the readings. The liquid is Maleic acid and has a high freeze point ~52°C.

 

[jmw]

It may be a bit late to suggest that the choice of mass flowmeter may in question, not all mass meters are as sensitive to entrained air as others. Not much point to that argument, however, since i assume the entrained air was not discovered until after the instrument was installed.
Indeed, the mass meter may be a contributor to the problem. Mass flowmeters usually have quite a high presure drop and this may be leading to gas breakout. Increasing the back pressure, provided that it is safe to do so, may give just enough improvement to get you stable readings by either preventing bubble formation or compressing the bubbles enough not to be a problem. It is not simply that the bubbles are in the fluid as they often do not exist is sufficient quantity to give a seriou error to the measured mass and density. However, bubbles can do two things, they can collect on the tube walls which can lead to serious error and instability; and they can introduce what are thought to be "velocity of sound effects". In vibrating density meters the answer is to operate at the first harmonic, instead of the second, where the velocity of sound effects are insignificant. You do lose some density accuracy but will still be well within 1%. I am not sure that mass meters can easily do this.
If not, I can only suggest waiting for other suggestions before you take it out and start again.

 

[cdcosta]

jmw,

We do have this Mass flow meter on a trial basis. The Rep thought this was a good application for for the Coriolis flow meter. Could you suggest a different type of Meter?
Density measurement is an important parameter, that is why we chose to look at this unit.

 

[jsummerfield]

Depending upon the application, there may be installation issues to address. Before you completely surrender, consider modifying the installation to minimize the flashing issue. This could include a vertical run of pipe flowing the flowmeter for additional head and to assure a liquid full line.

John

 

[hacksaw]

Sounds like you have not installed the meter properly.

Not only do you require liquid filled pipe, you also require adequate liquid/vapor dis-engagement, and adequate line pressure to prevent formation of gas bubbles and or cavitation.

Your operating manual for that meter will contain specific installation advice, and probably is even available on the internet as a pdf file and free.

 

[CARF]

Hi,

Yes, correct installation would be in a VERTICAL pipe with UPWARD flow. Be sure you have no vibrations in the pipe.

see also: thread698-69545

MVD