Slurry Density Measurement

N

Nathan Boeger

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
 
R
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.
 
N

Nathan Boeger

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
 
G
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
 
D

Dooley, Vince

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
 
D

Danny OConnor

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).
 
A
Hi,

I don’t know more about pumps but I know who can help you. You should contact with the members of the Toyo Pumps at this URL Because Toyo Pumps North America is proud to be the only authorized distributor of Feluwa High Pressure pumps and parts in the Americas; their pumps handle everything from dirty water to the heaviest slurries. Toyo Pumps has different types of pumps and pump sets like horizontal pumps, submersible parts, agitator pumps, submersible pumps, slurry pumping, recessed impeller pumps, industrial pumps, vortex pumps, mining pumps etc.

http://www.toyopumps.com/contact-us.html

I hope they will solve your problem.

Thank you,

John
 
C
I just performed flow loop testing on what I believe is the same material -- FGD -- a power plant by-product--made up of fly ash.

I believe you are looking in the 1.0 to 1.5% Total Solids range. The unit measured based on microwave technology so you would not need any special license, training. Let me know if you are interested. My cell 678-772-9584 or email [email protected].
 
Bully, Walt,

I agree completely. I foresee two problems with this advice.

Government regulations (AEC) require that there is a trained person available for handling these nuclear elements; things are much worse now that people have realized that these elements, made of spent rod material, make good dirty bombs. You can hire help but they must be available 24/7 if you need to work on the LT/LE.

The second problem, though not nearly as bad, is that your slurry may coat the sides of the vessel. I am not sure how this will affect density measurement but it could reduce the LE transmission strength. I know we saw a typical life of 8-10 years with these elements, maybe more; the signal grows weaker. It seems to me that the thicker the wall, or the build-up in the tank, the shorter the useful life.

Another minor issue is the construction. These elements weigh more than gold. I built one that required 6-inch I beams.

Dirk
 
1.00 - 1.50 is easily achievable with a differential pressure transmitter using diaphragm seals, bubble tubes or water purge.

Roy
 
E

Enrique Rengel

We have developed an densimeter for slurry for mining and other applications that not use radiation. The principle of measurement is on line weighing of sample with constant volume. Complete specifications for your application we can offer.
 
All due respect to Walt but the answer to any density problem isn't always coriolis meters.

Slurries are not necessarily a problem for tube type density measurement, many hundreds have been used for china clay slurries, for example, but for abrasive slurries then there can be a problem for tube types, especially twin bent tube coriolis.
The two principle problems would appear to be erosion on the bends and tube plugging where one or other tube might block.

One usually finds that the tube wall thickness leaves something to be desired if erosion is expected.

So at the very least you would need to look at straight single tube designs.

But a good option is the tuning fork sensor.
This is very rugged, the sensor being spark eroded from bar stock and the support structure also being bar stock, and they can take a lot of punishment.

I have seen one returned from a chalk slurry application where it had obviously finally met its end after being hit by something very heavy moving very fast in the pipe line but wit evidence of long term erosion that had been compensated for by periodically applying a simple density offset to the calibration.

The option to look at is the 7828, possibly thee long stem version:

http://www2.emersonprocess.com/en-U...ertion-liquid-density-meters/Pages/index.aspx
or www.viscoanalyser.com.

The key is to choose the right version for the application and install to suit the process conditions.
 
Sorry, Walt, misread your post.

Slurries are not the automatic killers of density meters, however.

The tube type density meters were the standard solution for china clay slurries until replaced by the tuning forks. The reason or replacing them was not erosion but installation cost and maintenance issues. They had to be installed in a bypass and protected against freezing with trace heating.

Tuning fork installs directly in to the pipe.
Of course, china clays are not particularly abrasive.

Chalk slurries are as they contain bits of lint, impurities in the chalk and even bits of excavation equipment.

One unit I witnessed had been in service for years in a side of pipe installation and showed serious erosion on one side. The reason it was replaced was because it had taken a hit from something heavy enough and moving fast enough to bend one tine right over and bend the stem. Since these were 316 stainless bar stock, this took some doing.

It would not today be installed as it was then. The long stem options allows the sensor to be installed much more flexibly.

Because they can be installed in any size pipe, it offers the opportunity to pick a cross-section with lower flow velocity.
All that is needed is to periodically check for calibration drift due to erosion and apply a K0 density offset.
 
Top