The operation and performance of Grinding Mills - especially SAG Mills - are significantly influenced by the density of the mill charge. The decision of what feed dilution ratio to target on its feed - or how much water to feed into the mill compared to the solids feed - is very important.

The problem is that most Operators do not have live feedback on whether their water flow rate (or dilution ratio) is producing the right density in the Mill. They often only get feedback on this when they take a sample, after which they adjust their water feed rate or dilution ratio setpoint.

This uncertainty means that mills long at wrong densities for a long time, limiting the Grinding Circuit's throughput, negatively impacting grind size and/or unnecessarily driving up the cost of production ($/t).

Our Solution's solution to this challenge is the Mill Charge Density Virtual Sensor, with its accompanying Alert.
The Grinding Application's Mill Charge and Material Transport Models track the flow of ore, water and slurry through the mill in real-time - taking into account how the ore breaks to mix into the slurry. It uses a combination of first-principle and empirical modelling to provide Virtual Sensors of both the Density and %Solids in the mill's charge, as well as in the discharge. These give Operators immediate feedback on whether their dilution ratio or water flow rate is correct for the current ore type.

These real-time Virtual Sensors are delivered in as Alerts, which compares the Virtual Sensors with desired/optimal operating bands (minimum & maximum limits) for the particular mill. Whenever the Mill Charge Density moves outside of these ranges, Operators are alerted to correct their mill feed dilution by adjusting their control system setpoint (or changing the mill feed water directly).

The below image shows the SAG Discharge %Solids Alert being triggered, because the Virtual Sensor shows that this %Solids value has decreased below its minimum value.

Figure 1: An Operator Dashboard showing the Mill Charge Density Virtual Sensor being activated.

This Virtual Sensor can also be used historically by Metallurgists to do root-cause analysis, and see which operating regions/strategies gave the best performance over a given period or for a given ore type.


This direct feedback on mill feed dilution allows Operators to:

  • Make immediate corrections, instead of waiting for the next sample before they are able to change the dilution

  • Run at more stable mill charge densities, leading to increased throughput, a more stable P80 and reduced specific power usage

  • Prevent unnecessary mill stoppages (caused by Mill Overloads)

For more info, please do reach out to us via Intercom. We'd be happy to help!

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