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from the Automation department...
Real time measurement of Specific Gravity
Continuous process industries, DCS questions. topic
Posted by Sankey on 18 January, 2008 - 1:47 am
The mines depends on S.G. values to allow copper and cobalt mixtures to run through the underflow of the roaster and thickener (tanks). At the moment, these readings are done manually on an hourly basis, meaning that any fluctuations in the S.G. values during the interval will go unnoticed.

The current practice results in about 2-5% of Cu and Cobalt losses in the roaster and 1-5% losses in the thickener. At times, technicians cheat various ways for fear of repercussions. This also goes unnoticed. There is absolutely no trending of the S.G. values, which is another big challenge.

Do you know of any solutions that have been implemented to get real time S.G. values on SCADA? What would you suggest could be a feasible approach to this challenge, and what type of sensors should be used?

I look forward to hearing from you.


Posted by Roy Matson on 19 January, 2008 - 12:05 am
Sankey,

I assume you have ruled out nuclear.

We use 2 methods with equal success:
Differential bubble tube for tanks, Coreolis for lines. The MM F series have both Mass flow and SG outputs and are very accurate.

Hope this helps,

Roy


Posted by George Buckbee on 19 January, 2008 - 12:21 am
The most likely candidate for an on-line measurement is a Radiation Densitometer, also known as a "Gamma Guage". A Radiation emitter is placed on one side of the pipe or trough, and a receiver is placed on the other. You can guage the density of the material by seeing how much gamma radiation passes through.

There are many manufacturers:
Endress + Hauser, Kay-Ray/Sensall, Ohmart

One complication: You may be required to have special certification and inspections to handle and account for the radioactive source materials.

-George


Posted by almshouse on 19 January, 2008 - 12:24 am
I have successfully used "bubble tube" to measure specific gravity of a magnatite slurry in coal mines. http://resource.invensys.com/instrumentation/documentation/eib/mi/mi02 0328.pdf


Posted by JMW on 27 February, 2008 - 11:02 pm
Can I suggest you visit the slurry density thread, which essentially considers the same problem and where I have posted a comment on using insertion density meters of the vibrating element type? These have a history of success with slurries.

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