Level measurement using a bubbler system

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Thread Starter

Garry Pitman

I would like to know the technical calibration details of a D/P cell measuring acid (HCL) in a atompheric tank using an air regulated bubbler system. The height of the tank is 6 metres. The range of the dry leg D/P cell is approx 60 kpa. How do I calculate the air pressure and air flow rate.
 
The calibration for the transmitter is based on the level above the bottom of the bubbler tube end. You have to adjust for the specific gravity of the fluid you're measuring. As an example, if you were measuring water and the maximum level you wanted to measure was 10 feet abve the bottom of the tube, the transmitter would be calibrated for 0-120 inches water column. For fluids other than water, you need to multiply the height by the specific gravity of the fluid. Commercial HCl typically has a specific gravity of 1.16. Therefore, using the previous example, you'd calibrate the transmitter for 120 x 1.16 = 139.2 inches of water column for a 10 foot height measurement.
 
In my previous post, I forgot to mention the airflow rate. This needs to be just enough to keep the tube evacuated with air. Bubblers are generally supplied with air at a pressure roughly 15 psi above the highest measurement height (in psi). Then a rotameter with integral needle valve is adjusted to give a flowrate of 1 scfm. If you want to hold that flowrate constant, install a differential regulator across the rotameter. They're made specifically for bubbler purge control.
 
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Ken Lionarons

I agree with all of the above, but be aware of the problems using a bubbler to measure level in acid. ENtrained moisture will cause deposit buildups at the air exit and maintenance is a headache. Also be aware of the elevation changes of the tubing into the tank so that a siphon is not inadvertantly started.

Regards
 
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