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I would like to know if there are any as reliable instruments available as the Gamma meaurement instruments to determine slurry density. The slurry consists of fly ash (fine ash) and coarse ash from coal boilers and water. Average density varies from 1000 to 1500 kg/m3. I would like to do away with the radiation source to have a nuclear free instrument - if it is available at the same accuracy.

Sure. You can use a coriolis meter.

The problem with this is that the coriolis meter will last about three weeks in a corrosive and abrasive slurry like fly ash.

You could try an ultrasonic density meter, but you won't get the accuracy or the repeatability, and the sensors (if you are correctly using wetted sensors) will be destroyed by the slurry within two or three months.

There are reasons for using nuclear gauges. You just found an application where you can either use a nuclear gauge or keep replacing meters until you learn.

So, unless you want to explain to your management why you screwed up a perfectly good application that might run for another decade without much maintenance in favor of any of several maintenance-heavy solutions, just so you could be 'nuclear free,' I'd stay with the gamma gauges.

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://waltboyes.livejournal.com
_________________

Putman Media Inc.
555 W. Pierce Rd. Suite 301
Itasca, IL 60143
630-467-1301 x368
wboyes@putman.net

Where can I get a nuclear density gauge? I am struggling to find a US supplier. Is there a trade off in accuracy vs. the need for on site radiation trained personnel?

Ohmart/Vega is a good supplier of these devices. Thermo... now Fisher Scientific had TN Technologies devices. They all can provide excellent product. Ronan also is a good supplier.

Radiation training for on-site personnel would be worthwhile. Don't recall any relation to device accuracy.

L.Kolbert

Thermo Fisher Scientific is the manufacturer of what used to be Texas Nuclear and Kay-Ray. OhmartVega makes nuclear density gauges in the US.
Berthold sells nuclear gauges in the US.

There's three.

It is difficult to talk about accuracy with nuclear gauges, because we'd all rather talk about precision. Nuclear gauges are statistically based devices, since gamma energy is statistical as electrons, not continuous. Precision is "compared to the last measurement" while accuracy is "compared to some standard."

Can a nuclear density gauge be very accurate? Absolutely. You can be very accurate indeed.

There is no tradeoff.

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://waltboyes.livejournal.com
_________________

Putman Media Inc.
555 W. Pierce Rd. Suite 301
Itasca, IL 60143
630-467-1301 x368
wboyes@putman.net

I work for Berthold Technologies USA, LLC in Oak Ridge, TN. We provide nuclear density systems for slurry measurements on a regular basis - flyash slurries, limestone, gypsum, bauxite, etc. In many cases, we can provide an accurate solution with our low-activity sources that don't require shutter checks or leak tests, and that can be installed/serviced by plant technicians without special training. You can contact me at 865-483-1488 if you'd like more information. Our website is http://www.berthold-us.com

go to http://www.endress.com
The model is FMG60. Hope this helps.

Unfortunately, Endress+Hauser does not distribute the FMG60 in the United States... at least not at this writing.

There are several suppliers of nuclear slurry density gauges that are available in the United States. The best of them, in my opinion, is Thermo (the old Texas Nuclear AND Kay-Ray brands), followed quickly by Ohmart-Vega (whose nuclear level gauges are better than Thermo's) and Berthold Systems.

There is no trade-off in accuracy. It is all a matter of radiation statistics. The bigger the source, the more precision of measurement.

The problem in slurry density measurement is if you want to measure in "percent solids."

Whether you use a nuclear density gauge, or a coriolis meter, or an ultrasonic or other type of density measuring device, they all measure what we call "bulk density." Actually, they all _infer_ "Bulk density," and that can be a problem in itself.

In order to accurately calculate "percent solids" from bulk density, it requires to know the dry solids density, and the fluid density.

Generally, the fluid density is approximately equal to 1.0 g/cc or 1 SGU, because most slurries are water based. If the slurry isn't water based, again it is a different story.

Where the problem exists is if the dry solids density changes. When you have a variable constant, the Finagle Constant intervenes and makes your mathematics mush.

Other problems for density calculation happen when the measurement is of sludge density in wastewater treatment. Typically, the dry solids density of activated sludge is about 1.6 g/cc. Since the apparent density of water (when measured by a nuclear density gauge, anyway) approaches 1.1 g/cc, you can see that trying to read 5% solids with any real hope of either precision or accuracy is a forlorn hope.

You do not, necessarily, have to have licensed and trained staff on site, but it sure helps, and is way cheaper in the long run.

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://www.controlglobal.com/soundoff _________________

Putman Media Inc.
555 W. Pierce Rd.
Suite 301
Itasca, IL 60143
630-467-1301 x368 wboyes@putman.net

Ultrasonic sensors are available for this application which are very easy to install & handle unlike nuclear ones.

Go to http://www.bestobell.com for further details.

Regards,
MAU

While sonic density may seem to be an alternative to nuclear density, I would caution that the sonic systems are not suitable for heavier solids slurries. Non-linearity of measurement and lack of precision are negatives for this type of measurement.

L.K.

I would have a look at Micro Motion Coriolis for this measurement. An earlier post identifies a potential issue with corrosion. While I do not agree with the "3 week" sensor life statement, I do agree that corrosion/errosion is a concern... but there are ways around the issue. Since density is the req'd measured variable, one option may be to oversize the meter to keep the velocity down or mount in a slip stream configuration and limit the velocity thru the meter. Contact your local Micro Motion representative... they MAY be able to assist you... it would be worth a shot anyways.

Cheers!!

Dear Anonymous,

I have spent over a decade making this measurement. Anyone who would suggest a coriolis meter for this measurement is doing his client or customer a grave disservice. I don't care whose coriolis meter you suggest.

I don't care whether you agree with "3 week" sensor life or not. I have _seen_ this life expectancy personally in this application.

There are some things coriolis meters simply cannot do. Abrasive slurries are a significant part of that.

What part of "really bad application" didn't you get?

Spending upwards of $5000 US on "worth a shot" is bad advice.

Wow, I did NOT recommend running out and spending $5K... I simply stated that it MAY be worth while looking into... as in at least making a freakin' phone call!! So if you call that "bad advice" then that is your choice I guess. BTW, I don't see "really bad application" anywhere...

I see lots of horrible, questionable advice/suggestions on here. Do you always jump in and "Slam" the folks here?

I didn't realize your reply was the "Be all" answer. Isn't that the purpose of this board... to solicit advice??

Have a great day!!

No, I don't jump in and slam the folks here. YOU posted as "anonymous" and provided some very bad advice. That advice might, if the original asker took it, and put the coriolis meter in, have cost him his job. If you had read upthread you would have seen that people had already talked about the highly abrasive conditions in a fly ash slurry.

BTW, I had the occasion to discuss this application and your answer with one of the top experts of one of the largest coriolis meter manufacturers a couple of days ago. After he quit laughing, he said that his company wouldn't consider selling a coriolis meter for fly ash slurry, and he doubted any of his competitors would, either. The subject wasn't even worth
your "freakin' phone call."

He recommended, as did I, a nuclear gauge.

If you want to be taken seriously post with your name and affiliation.

Walt Boyes
www.waltboyes.com
wboyes@ix.netcom.com
630-639-7090

Look at the website from Krohne http://www.krohnemar.com/Mass_Flowmeters.25.0.htm

l. They have got a mass flow meter for abrasive sludge/slurries (Type Optimass 7000). The major advantage of Krohne mass flow meters is that they use a single straight measuring tube. Give them a freakin' phone call and find out what they think.

I'm sorry for the anonymous respond, but if you got comments post them thru this website so others can learn from the discussion.

Ok, Krohne is the ONLY coriolis meter manufacturer that sells something they
say will work in abrasive slurries. I suppose you work for them. I am not
going to argue that they should not. Krohne is a reputable company. In fact,
I was the first Krohne America representative in the United States.

But I still think that the correct technology is nuclear.

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!!
http://waltboyes.livejournal.com
_________________

Putman Media Inc.
555 W. Pierce Rd. Suite 301
Itasca, IL 60143
630-467-1301 x368
wboyes@putman.net

In the mining industry, slurry density is commonly measured by using dual bubbler tubes and pressure transmitters. Very cheap, stable and accurate.

I agree with Walt. In fact, if law of land permits, better to go for nucleonic sensor, which, if carefully selected, will be reliable for years.
As the pipeline diameter/thickness is not known, identifying source strength is difficult, but with a scintillation counter type detector, you may get benefit of selecting lowest source strength.

What needs to be deliberated at your end is:
1. Orientation of sensor in pipeline so that the radiation towards detector is preferably away from common manways, if at all acceptable.

2. Administrative control through:
a. Awareness/training
b. Safety marks
c. pocket dosimeters for operators/technicians working around

3. Periodic inspection of source leakages:
a. Through surveymeters
b. At frequency as guided by statutory bodies
c. Reported by (own) Radiation Safety Officer to statutory bodies

4. Decommissioning:
a. Be careful to choose a source with appreciable halflife.
b. Disposal guidelines

Selection of a fireproof source is a good engineering practice.

I am not aware of bubbler measurement in similar service but technically it appears to be quite feasible except for calibration reference because it may be quite difficult to predict slurry distribution (density) on a horizontal pipeline which may be dependent on flow and other conditions too.

I have been recommending the nuclear solution for density measurement of continuous process of slurries for many years. If anyone has a better solution, please advise. I was given the information on "vibrating tubes" and "coriolis tubes", yet was also instructed these methods were not recommended for longevity in slurries.

The material in the slurry is a polyol blend and wollastonite. There are other, less abrasive materials carried as slurries in polyol blends but the most common is wollastonite.

So, if there is a better idea than nuclear, I am open to it! Thank you.

Michael F. Palmosina II
Senior Technical Service Specialist
Bayer Material Science, Llc.
mf.palmosina@bayerbms.com

How about a compact (20 cm) high energy X-ray machine? Offers nuclear performance but you can turn it off whenever you want to.

This thread makes me laugh! OP suggests removing radiation sources to be nuclear free as long as accuracy isn't lost, suggesting that price is of little object. I'm wondering if I should market $5,000 smoke detectors.

Then Walt responds with a pretentious show of good advice and gets into an arguement with anonymous. He then laughs at anonymous' idea with a top industry expert over a cup of tea and truffles.

Hard to take sides here. If you haven't seen this whole thread, I'd recommend it! Good readin's. You'll know who to direct your next question about nuc gauges to.

----
Nathan Boeger
on behalf of myself

I'm glad you enjoyed the free advice.

I would ask you to tell me why my "show of good advice" was pretentious.

Been there, done that, and the tee-shirt got so raggedy I tossed it.

Walt

This thread is amusing indeed, and if Walt doesn't think he was pretentious just for someone providing alternative advice to his own then he is disillusioned. Is this site not for helping people and giving advice, not to shoot down anyone who doesn't share your opinion?

I think people need to remember this, and that if 100 engineers were given the same problem to solve you'd get 100 different solutions!

More to the point though, I agree with Walt's advice that a gamma source density meter would be the best option, although I am not familiar with the specific coriolis meters mentioned above and so cannot comment. Probably worth investigation though, as it would more than likely be significantly cheaper.

I like you Walt. You're knowledgeable and you know it - and too well written for me to get into a debate with. Lucky for me, I don't know a thing about Slurry Density measurement.

About you coming off as pretentious -

>You just found an application where you can >either use a nuclear gauge or keep replacing >meters until you learn.
>
>So, unless you want to explain to your management >why you screwed up a perfectly good application >that might run for another decade without much >maintenance in favor of any of several >maintenance-heavy solutions, just so you could be >'nuclear free,' I'd stay with the gamma gauges. <

Or was it this one?

>Dear Anonymous,
>
>I have spent over a decade making this >measurement. Anyone who would suggest a coriolis >meter for this measurement is doing his client or >customer a grave disservice. I don't care whose >coriolis meter you suggest.
>
>I don't care whether you agree with "3 week" >sensor life or not. I have _seen_ this life >expectancy personally in this application.
>
>There are some things coriolis meters simply >cannot do. Abrasive slurries are a significant >part of that.
>
>What part of "really bad application" didn't you >get?
>
>Spending upwards of $5000 US on "worth a shot" is >bad advice. <

No, the best one, my personal favorite, was about laughing over anonymous' coriolis meter recommendation with the top expert and how you cleverly ended with it not being worth the "friggin' phone call".

The thread really made my day. Who ever thought that you could learn so much about a technically obscure (well, very specific) topic and get such a good laugh? The really great part was that I constantly shifted who I sympathized with. I don't think I'll every forget that coriolis meters aren't the tool for measuring the density of abrasive substances. At the very least, I'll know where to go when it comes up.

I do feel your pain, though - about forum posters constantly bringing back a technically incorrect/irresponsible application. Can you mow your lawn with tweezers? Maybe. But why? On the other forum guys keep coming back asking how to make a custom data historian using DDE calls in a VBA script from within Excel. I don't mind the first timers who know that Excel can read OPC data, and naturally try to expand it. It's the know it alls who pipe in with poor advice that get me going! They take my advice "that it's clunky and hard to do" as a challenge, disregard "lots of cheap applications already accomplish what you're looking for" and completely ignore numerous strong points about why data logging should occur in a database, not a spreadsheet. Even stubborn HMI vendors figured this one out in the 90s. Somehow the question keeps coming up and "programmers" keep recommending it. Ughh! Dishing out that much pain, frustration, and opportunity cost should be illegal! Enough on that
tangent...

----
Nathan Boeger
"Design Simplicity Cures Engineered Complexity"
http://www.inductiveautomation.com

As one who has significant experience in using nuclear devices to measure slurry densities I can offer the following:

If the device can be calibrated with repeatable and representative sampling, there are no better ways to obtain this measurement. These devices have been in use for many many years and with proper education and handling they are as safe to use as anything else. Two things may add errors to the reading. The first is Compton scatter. As the gamma photons pass between the source and the detector some are scattered out of the direct line of sight to the detector and then are re-directed back to the detector. They do so at a reduced energy. However the detectors cannot discriminate between energies and therefore if this scatter is not exactly the same for all densities there will be a small error for any measured densities that have not been verified by sampling.

The second point is that these instruments respond to three things. The distance between the detector and source (which is constant) the density of the material between the source and the detector, and finally the composite absorption co-effieient of the material. For most elements having a mass number (Z) of about 50 or less this remains constant. This includes iron, carbon and many other elements your meter will be exposed to. The major exception is hydrogen. Hydrogen has twice the absorption rate as do the other elements for Cs137 for example. As the density of your fly ash changes so does the hydrogen content, and so also does the composite absorption co-efficient. The meter however only is set up to respond to density changes and so it will be in error as the ratio of hydrogen to solids changes.

These errors are small, depending on your range, source size and geometry of the installation, but overall there is nothing that can even come close to the reliability and simplicity of these devices.

Use them with confidence!!!!

Guest,

I worked in the mining industry for many years. My favourite Nuclear Density is from Ronan,
see http://www.ronanmeasurement.com Toronto based I think. I haven't used one for a couple of years but I see they claim that the source is now so weak in some cases you don't need a license. A far cry from the 2 Curie source I used 20 years ago (level application). I agree they are very reliable.

Roy

I don't remember whether it was this list or another where someone suggested using a coriolis meter on a trolley as a reference meter to calibrate nuclear density gauges. It is connected to the sample point. The fluid is run through the reference meter to drain during the calibration check. It is then flushed with water and the reference meters calibration checked on the water. It certainly overcomes all the issues with sampling.

Some nuclear density gauges are not affected by forward scatter. An electronic energy discrimination window is set up around the energy of interest to eliminate forward scatter and background. In some cases two windows are set up. One covers a band just below and up to the peak of interest the other just above. Automatic gain control can then be achieved by adjusting the voltage so the count in each window is equal.

Vince Dooley

Well, a visit to the Micromotion site will show you the range of density meters they offer. These are what used to be the Solartron sensors and you will see they have fork type density sensors.
These use the vibrating element principle where the resonant frequency is a function of the density. The fork types give accuracies of around +/-1.0kg/m3. Obviously significantly lower than the tube density meters but popular in a range of applications because they can be installed into the main pipe line, especially now they are available long stem (up to 4 meters long).

The key to erosion is velocity and shielding.
Coriolis meters employ relatively thin walled tubes and often have a complex flow path that leads to erosion spots just after the bends.
With a fork sensor you can use the long stem version and install on an elbow in the pipe or through the side wall at an angle such that the tines the sensitive part of the sensor, are directed upstream or downstream.

The sensor itself is a tuning fork spark eroded from bar stock and the spigot is machined from bar stock. The long stem version is basically a length of 40mm sched 40 pipe with the sensor mounted on the end.

These sensors have a history of use in slurry applications ranging from china clays (not very abrasive at all, originally used the tube type density meters but then moved to the fork type) through to granite washings plant underflow and, as a viscometer, chalk slurry.

The chalk slurry application is worth considering.
Chalk is quarried for the cement industry and in those that use the wet process the chalk is made up into slurry to be pumped to the cement works. The higher the solids content the less energy required during subsequent processing. Solids content is a function of pumpability which is dependent on the viscosity. A viscometer (the self same tuning fork used for density)is used to measure the viscosity and determine the amount of viscosity modifier to be added (ligno-sulphontae, I seem to recall). This reduces the viscosity allowing a higher solids content. % mass solids is a standard inbuilt calculation with these sensors.

The chalk slurry is abrasive. It contains whatever other material is in the chalk, e.g. flints and occasionally small bits of mining machinery. Go to this page and see a short stem fork that was used on this application: http://www.viscoanalyser.co.uk/solids2.html

This is a sensor that was in operation for around five years. The installation was not ideal and the sensor suffered continuous abrasion as can be seen and finally, was evidently struck by a large lump of something moving pretty fast which bent the tine over. The sensor was still functioning when received back at the factory.

Over the years they compensated for the erosion by periodically re-calibrating the sensor (a simple density offset value). With the modern long stem sensor and modern installation methods this type of erosion ca be managed much better.

Yes, Walt is right, any time you put anything into a flowing stream of abrasive slurry you will get erosion if you expose the sensor to high velocities but by angling the sensor downstream the sensor will prove very rugged and durable. It now depends on what life time you can live with, it will be substantially more than three weeks. We are talking many years. The sensor shown in the link was five years in a bad installation (they did not have the long stem version then) so in that same application a long stem could be expected to survive significantly longer than five years.

But if you want to move away from nuclear devices, you can get very long service life with a well designed installation i.e. by carefully choosing where to install and how to install.

Re: Abrasive Slurry

I worked in the mining industry for many years, for abrasive slurry they typically use rubber lined pipes keeping the velocity quite low. I wonder if any coriolis manufacturer has tried the rubber lining approach. A rubber product I have seen 'LINATEX" is very soft and will outlast the hardest metal in severe abrasive applications.
I have also seen differential pressure used to measure density where the slurry is traveling in a vertical line, 2 taps about 3 ft apart flushed with water.

I must agree with Walt however that Nuclear Density is the most reliable method. In my experience it has never been much of an issue getting approval. The manufacturer will be most helpful in this respect. Check out "Ronan" my favorite by far.

In mining the meters typically output %Solids by weight, not density.

Something to be aware of in horizontal service is stratification, you will get a different reading depending on if the beam is vertical or horizontal. It is also difficult to get a representative sample of a slurry for the same reason.

The "Solatron" fork type density sensors sound interesting, perhaps they would also benefit from rubber coating.

"An interesting article I read recently claimed that rubber is non compressible - think about that one".

Regards,

Roy

There is always more than one way to skin a cat! Coriolis can and will work and is the easiest way to do it. You simply need to oversize the meter slightly and pick a suitbale material for it. The manufacturer I work for (E+H) has a range of straight tube meters and we have also supplied 10" models on mud flows from oil wells. The second option is to go for a vibrating level switch optimised for density. These simply sit in a line with a temp probe and go back to a controller. The varying density has a noteable effect on the 'tuned' switch and as such this change in vibrating frequency is detected by the controller - using the temp probe to offset any effects of temp on the product.

An interesting read.

I've had a pilot plant in operation where (for reasons of portability) we avoided installing a nuclear gauge for the measurement of lime slurry densities. Instead installed an E+G coriolis flow meter and a tuning fork. The tuning fork was very unstable but we didn't spend too much time trying to work it out because the coriolis (straight through type) worked reasonably well.

The coriolis meter was installed on a recirculating loop to provide a controlled flow rate through the instrument. We operated the plant for approximatley 100hrs a week for about 9 months with the same flow meter.

It was good enough for our purposes (control of lime dose rate to the process)- although occasionally it would appear to be "out" when copmared to our operational samples (but then again sampling slurries isn't easy--and the analysis was by weight and volume--not by filtering and drying the solids).