i work in a PTA(Purified Terephthalic Acid for polyester) plant. we are using Nucleonic Level gauges for our Level measurement Requirement for our critical applications eg. reactor,crystalliser etc.. The temp. in most cases is under 250degC and the pressure under 25 bar. we are using berthold level gauges with co-60 rod sources and in some cases caesium-137 point sources with scintillation counters. we are facing lot of problems of interference, wrong level indication, saturation of level indication etc.. inspite of our best efforts and lot of shielding considerations. since this is a slurry application i would like some help on what other types of level measurement can be used for these application. please help.

 

For you kind of service, nucleonic should be the best alternative to use. If you haven't contacted the manufacturer, you should do so. You situation could possibly be interference between gauges dependent on where the levels are. Re-orientation of gauges may resolve the problems you are having.

L.Kolbert
[email protected]

 

It is probably difficult for anyone to recommend alternative methods without more information particularly when nucleonic gauges should work The most common methods of level measurement in vessels are probably diffrential pressure, microwave radar and ultrasonics. The temperature may eliminate some possibilities although most systms can be protected/isolated from the temperatures. Being a slurry doesn't necessarily present a problem for many techniques unless there are agitated abrasive particles or the distribution is not homogeneous. What are the densities of solids and fluids? What solids concentration? What variability is there in the composition and density? Aeration? Size of vessels? Characteristics of fluid?
Scaling? etc.

Noise/high counts in nuclear systems is not necessarily due to background radiation interference so shielding may not help. The discrimination capability of the sensor and circuitry are important in cases where background radiation is an issue. Noise can be due to other causes such as electrical interference, poor connections, vibration, high temperature, static electricity etc depending on the type of scintillator used and the circuitry. What scintillator is being used? Have Berthold offered any advice on the causes or made any recommendations? Is calibration an issue?

Vince Dooley

 

I notice you mention Berthold devices. I am familiar with the products of this company and know that they have recently completed a lot of work to provide interference detection and suppression capabilities. The problems are typically due to unscheduled radiography in the area using very large sources for welded seam inspection or other devices interfering directly. The specific solution depends on the type of problem and consists of a mix of energy discrimination and/or software data manipulation. I suggest you contact the manufacturer who is based in Oak Ridge, Tennessee.

 

There are many ways we can solve this problem, but I will need more information first. There is a system that not only recognizes pipe x-raying but suppress it and allows you to continue your measurement. At this time it does have one limitation, due to the energy of the typical pipe x-ray and Cs-137 being so close we need to use Co-60. There are some other things we can look at with the equipment you have now. If you would like to contact me at (865)483-1488 or e-mail me at [email protected] Thanks

 

we have agitated tanks.so that in effect rules out most of the other non-contact measurement techniques. Most of our problems relating to radiography testing in the vicinity have reduced but we would have definitely loved it if berthold devices had a facility in which they would hold the last valid value in case of rapid drop to zero as in when radiography tests are occurring in the vicinity. inspite of changing over from point sources to rod sources the linearity is not as much as we would love it to be. we are calibrating our instruments with water calibration as recommended by the vendor but theoretical calculations include use of the vaopr density and the liquid density. we dont do that. does that cause a significant problem.

 

There are a couple of inherent problems with level measurement in agitated tanks.

The first is, that while the agitator is "on" there is really no level. What you want to measure is "what the level would be if the agitator is not on" which is an interesting inferential measurement.

Gamma point sources are inherently nonlinear, and rod sources can be either more linear or can be "linearized" by the placement of the gamma sources along the rod. In either case, the linearization is "rough". The more linearization points you can enter into the breakpoint table, or the better the linearization equation you can come up with, the more linear the measurement will be.

Vapor density and liquid density are important. Sometimes, the liquid is volatile and gives off vapor that stratifies in the vessel. This is not likely in an agitated vessel, but can happen. It is important to know what the vapor density is, since the "level" is actually a differential density measurement.

Walt Boyes

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to your below reply, i would suggest that you contact Ohmart Vega their Nucleonic Level gauges are used world wide and is well accepted. Or you can could contact me. Sam Trimo/ Simpex Corporation (USA), 973-244-66363, Fax: 973-244-1319, email: [email protected]