Blog: Measuring density in grinding circuits 3/3

Posted on Friday, 3 April 2020 at 16:35

In the first blog 'measuring density in grinding circuits 1/3' we introduced the grinding circuit and explained the importance of in-line measurements and automatic process control. In the second blog you can read how real-time density measurement contributes to effective grinding and optimal classification. In this third blog we describe the use of density to prevent problems with circulating load and as variable in a back-up system for the particle size analyzer (PSA).

If the cyclone keeps returning ore to the ball mill, the total volume of ore will be increasing in the grinding circuit, as is the density of the slurry. The recirculating ore is also called circulating load. If the grinding process becomes less efficient, the circuit load will climb until its volume is greater than can be handled.

The density meter can be applied in the grinding circuit as a warning system. Thanks to real-time density measurement, an increase of circulating load can be detected on-time, to be able to control the process before problems become unmanageable.

Measuring points in the grinding circuit

The particle size is an important indicator of the performances of the grinding circuit. Therefore, this is normally measured by on-line particle size analysers (PSA). When the value from the particle size analyser is not available, it affects the control loop. In an automation project at a grinding circuit in South Africa, a self-correcting particle size predictor has been developed to overcome this problem.

The predicted value was based on the slurry feed density, volumetric flow rate and pressure drop over the cyclone. Using these variables in a model, they were able to calculate the predicted value, which was done every five minutes.

At a certain moment the PSA's value was lost, when it came back, the predicted value was still in close agreement with the actual value. This eliminated problems associated with periods of unavailability of the particle size analyser. This was described by Mr. B.J. du Plessis in a paper about control strategies at the Palabora Mining Company and was published in the Journal of The South African Institute of Mining and Metallurgy.

Nuclear vs. ultrasonic density meter

Density measurement is usually done by radiation-based measuring devices. This technology has been used in the mineral processing industry for decades. However, nowadays governmental regulations are getting stricter and associated costs are increasing. More nuclear density meters are being replaced by alternatives. These alternatives can do the same job, without administration costs and health and safety risks related to the nuclear source.

The eco-friendly Rhosonics Slurry Density Meter (SDM) has been introduced in 2016 and is the first real alternative to substitute nuclear density meters, reaching hundreds installations worldwide in just a few years.

Please contact Rhosonics if you want to have more information about our density meter (SDM).

Source: https://www.saimm.co.za/Journal/v101n04p165.pdf

More information?

You can also read our other blogs or request our whitepapers to learn more about density measurement. We have written several blogs about the grinding circuit and thickening process:

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Tags: Ball Mill, Density meters, Non Nuclear Density Meter, Densimetro no nuclear para pulpa, Molino de bolas