Industrial methods to measure strong nitric acid

[MrFission]

In industrial settings what process monitoring techniques are used for measuring very strong acids on-line? In particular I am interested in strong (~2 M) nitric acid but I am curious to know of the approaches for acids in general.

Based on your experiences what are the weaknesses of these instruments? For example do they require frequent maintenance or repair or does their calibration drift significantly, etc. How long can these instruments operate in continuous mode before requiring service?

Through my own searching I have found, for example, Foxboro electrochemical sensors, electrodeless conductivity sensors, and ultrasonic sensors. Are these the current state of the art? In a non-abrasive environment how long would you estimate their life (2 M acid strength) prior to the need for service? How well do they work?

Thanks for your wisdom and assistance.

 

[cheute79]

It's been a long time since I've had anyone consider 2M as strong. The time I spent in the nuclear industry, we figured anything in that range as "dilute", and if it was in the pH range, it wasn't anything we bothered ourselves with.

here's a simple concept: Conductivity monitoring is a well-established method. Electrochemical also works, but requires replacement of reference cells or more frequent calibration. If you can assure yourself that there won't be much contaminants, you can also look into density monitoring. We used 2 dip tubes spaced at known and constant height differential, and bubbled nitrogen (or other dry inert gas) thru the 2 tubes, measured the pressure at the point of bubble break-over, and then used the dP divided by the height differential to monitor density. The difference is greater for sulfuric and caustic, but it should be sufficient for nitric, as well.

 

[ash9144]

As cheute mentions, density is very accurate for concentrated acids with no contaminants. Micromotion flow meters are great for density measurement. That would be the high end solution. The other side would be hydrometers and check samples manually.

 

[jmw]

See comments on density measurement and coriolis in the second posting of this question (Measurement and Control Instrumentation Engineering forum).

JMW

http://www.ViscoAnalyser.com