Blog: Measuring density in grinding circuits 2/3

Posted on Thursday, 26 March 2020 at 13:45

In the previous 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. Also, we explained the possible installation points for density meters in the grinding circuit.

In this second blog you can read how real-time density measurement contributes to effective grinding and optimal classification. First, we will explain why control over parameters, such as the particle size and slurry density, is important to reach an efficient classification process.

The cyclone utilizes centrifugal force to accelerate the settling rate of slurry particles and separate them according to size, shape, and specific gravity.

Due to centrifugal forces, faster settling particles (coarse) move to the wall of the cyclone, where the velocity is lowest, and migrate to the underflow. Slower-settling particles (fines) move toward the zone of low pressure along the axis and are carried upward to the overflow.

A certain slurry density is needed for optimal (re)classification of particles in the cyclone. The cyclone has proved extremely efficient at fine separation sizes. However, for middle size particles this process is less efficient.

Example of a (hydro) cyclone

When too much water is added to the process, more middle size particles are produced by the ball mill, so the cyclone overflow allows a lot of these middle size particles to escape the grinding circuit. This results in a decrease of material that the ball mill would have to grind, which lowers its efficiency. Also, unwanted particle sizes are leaving the grinding circuit to next process stages.

For optimal classification of particles, it is important to detect changes in real-time in the cyclone feed. An optimal control of the cyclone can be achieved by controlling the % solids in the feed flow to a desired target, which is done through the use of a density meter. The cyclone overflow and underflow can also be monitored by density meters. Other crucial parameters to be monitored are the pressure and particle size.

Example of the Rhosonics SDM installed in the cyclone feed

Too much solids content (overloading the grinding circuit) can result in poor grinding. Therefore, the slurry density should be kept within the targets and parameters defined by the process personnel. Water can be used to dilute the slurry and control the density in the process. Adding water could help to reduce the amount of middle sized particles in the grinding circuit. In this way, poor grinding caused by an overload of solids could be prevented. Continuous (real-time) measurement is needed in the grinding circuit to check if the density is kept within the optimal conditions.

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

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