Non-Nuclear Density Meter for Mining Slurries

[londnbob]

Can anybody advise on a non-nuclear technique for continuous in-line density metering. Nuclear is too costly, with safety officers, reporting, wipe tests, separate nuclear source delivery and disposal all contributing to those high dollars.
I've tried ultrasonic density sensors, but above 10% solids, they are so noisy the signal needs damping so much that errors ensue. The damped signal is not the true average of the truth. The ultrasonic signal senses just one thin diameter of the pipe cross section and ignores the rest of the cross section.
I went to microwave sensor manufacturers who admit they are not suitable for dredging and mining slurries on account of the large variation of dielectric constant and high conductivity.

 

[Thealanator]

Coriolis? One usually thinks of flow meters, but I believe a coriolis meter can directly measure density.

They are expensive, and I'm not sure about maximum line size. Perhaps you could make a "sample" line off the main line and measure density of the sample.

 

[londnbob]

Thank you Thealanator. Yes, I've looked at Coriolis. Fantastic accuracy, but they embody thin wall metal tubing. Because of the very abrasive nature of mining or dredging slurries they would not last a week.
I have heard of a continuous weighing technique, which continuously and in-line measures the mass per unit volume of a good representative volume in a thick wall rubber flow tube. That sounds interesting.
Anybody ?

 

[micalbrch]

What if you install the coriolis meter in a separate piece of pipe like an abandoned channel of a river? Do you understand what I mean? The meter will be in contact with the slurry but will not be affected that much by the pipe velocity. Just an idea. I do not know if that will work. It just comes to my might when I think about the abrasive nature of the slurry.

 

[londnbob]

Thank you Micalbrch, but we have found once you sample media at a lower velocity, it is not a continuous and representative sample of what is coming out of good old mother earth.
I still like the sound of continuous in line weighing. In principle it sounds just right. I just have to find it.

 

[jmw]

Yes, I think the coriolis comment hits on the right technique - resonant frequency - but wrong instrument.
Coriolis meters can, but don't all of them, give good density and have good signal processing but for slurries you need to think twice.
Not only are they thin walled but they usually have too many other worries. The best bet would be the single straight tube but by then you might just as well look at dedicated density.

However, insertion tuning fork may be a good way to go.

This image is included to show a viscometer (measures density and viscosity) after 5 years of abuse on a chalk slurry application and a bad installation.

This is in the cement industry where they quarry the chalk, add water and chemicals to up the solids content and then pump a considerable distance to the cement works.

Though this doesn't look like a good advert it is. The installation was poor and the slurry contained not just chalk but bits of flint and, it seems, bits of quarry machine.
The sensor is spark eroded from bar stock.
Over the years they did encounter erosion and would simple make a density offset correction and a similar correction for viscosity. However, one tine can be seen to be bent over and he stem (also bar stock) was also bent. It evidently had been hit by something very heavy going pretty fast.
It was still working when returned, just way out of calibration.

With the long stem version you can install in pretty much any pipe size and make much better installations than this one.

This is available from Emerson/Micromotion or from distributors. (But do note: the accuracy is only 1kg/m3. On the plus side it is a smart sensor with all the calculations, including %mass, in the on node amplifier).

Another option might be the Cidra ultrasound sensor. This isn't ultrasonics but uses a different technique to measure density.
If you look for the SOntrac you will find a lot of good data on coal tailings and other slurries.

JMW

http://www.ViscoAnalyser.com

 

[stanier]

A vertical loop equipped with pressure transmitters on both legs. This device is shown in Slurry Transport Using Centrifugal Pumps by Wilson Addie & Clift. These guys worked for Georgia Iron Works.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[Compositepro]

I agree with stanier. Differential pressure transmitter measuring between two points at different elevations, using water purged sensing lines.

 

[StoneCold]

You might look into a Densitrol Meter.
I have seen that work in heavy oil applications.
Here is the link of applications.
I could not find a link for the actual units.
Maybe they don't make them anymore??

http://www.princoinstruments.com/applications.htm

Regards
Stonecold

 

[londnbob]

Gentlemen,
May be I didn't make myself clear. I need continuous, long term reliable density measurement of highly abrasive mining and dredging slurries, which measures a good representation of what is really coming our of good old mother earth, in pipes for 3" to 40". The noble suggestions we have to date are:
JMW : a tuning fork principle : With a lot of luck this will last a while, but common sense will tell us the forks will quickly become eroded and bent out of shape. Furthermore the fine fork senses at just one part of the diameter, ignoring the complete cross section. Sorry, that is not a solution.
Stanier and Compositepro: A pressure transmitter on both legs of a vertical loop: The pressure tappings will quickly become blocked. If diaphragm sealed units are embodied, differential pressures are limited to typically a minimum of 1/5 of the maximum static, resulting in bad resolution, and in any case, the thin diaphragm seals would last not last more than a week. Sorry, no joy here.
StoneCold: A Densitrol density meter is suitable for liquids only, and I could accept clay slurry. But for mining and dredging slurries it would be another poor bet.
I really appreciate the suggestions but my search prevails.

 

[londnbob]

Compositepro: I take your point about purged water tappings on the dp transmitters suitably placed on a vertical pipe, but nobody wants water injected into the mining slurry. To keep those tappings from blocking up, there would have to be some nice flow of pressurized water. The other problem is, the tappings are at the ID of the pipe, which hardly measures a representative volume of the variation in density over the cross section.

 

[jmw]

Variation in density over the cross section?
Forget tuning fork.
Investigate Cidra.

JMW

http://www.ViscoAnalyser.com

 

[Compositepro]

Purge flow in sensing lines is typically less than 50 ml/min. Is'nt your slurry water based? DP transmitters can measure a fraction of an inch of water with a static pressure of hundreds of psi. DP would be measuring the average density between the two ports. Purged impulse lines for measurement of fouling streams has been very succesfully used for a hundred years. Diaphagms can work well too.

 

[londnbob]

Compositepro,
Thank you for your suggestions.
I accept your point about low rate purged flow being a viable consideration, and the ability of today's dp cells, provided they are not sealed with diaphragms, having the ability to measure inches of water with static pressures of hundreds of psig. I also accept that for homogeneous liquids,the average density would be measured between the pressure tappings. But the problem is, mining and dredging slurries are far from homogeneous, and, as such, I am advised by that the average density would not be measured at all. Also the dp is a measure of density and square of the flow rate. So for a simple dp measurement would have to have accurate mean velocity compensation.
As for diaphragm seals, they would last about a week.

 

[stanier]

Compositepro,

The suggestion of air or water purged dp cells on a vertical loop isn't some crazy notion It has been used in industry for decades for measuring average density of heterogenous slurries of the type you describe. The coal and metalliferrous mining industry use such techniques rather than nucleonic for the very reason you give.

Suggest you get in touch with GIW and get their book Slurry Transport Using Centrifugal pumps and their technical papers. Also check out the myriad of technical papers by BHRA on measuring slurries.

One concern with such slurries is measuring the density going into a pipeline does not represent the density of the solids loading within the pipeline itself. The solids do not travel at the same velocity as the fluid. If there is saltation the carrier fluid will travel significantly faster than the solids. If the pipeline is sloping there will more changes in density.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/