Customer story

Expert control for high pressure grinding rolls (HPGR) improves productivity for South American copper miner

The main challenge for the customer, a South American copper miner, at the initial stage was to keep a healthy level of inventory in the feeders to ensure a consistent feed between the rolls.

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A shift in copper mining practices

HPGRs are steadily becoming ubiquitous in the copper mining industry, replacing the SAG mill grinding stage.

The HPGR exposes feed material to very high pressure for a short amount of time. The compression typically causes the rock to crack and cleave along the grain boundaries, weakening the rock structure. This high pressure also creates a large amount of fines and causes the formation of microcracks in the larger particles, lowering the Bond work index of the ore which, in turn, reduces both ball mill loading and power consumption. The higher the pressure, the more fines (“final product”) are produced.

Explore HPGR / HPGR Pro

The customer challenge

The main challenge for the customer, a South American copper miner, at the initial stage was to keep a healthy level of inventory in the feeders to ensure a consistent feed between the rolls. A layer of ore between the rolls helps the compression forces to break the particles more effectively and consequently a softer ore will be fed to the next stage.

To keep this layer of material at its desired level the operator must constantly monitor the level of the four discharge bins, making sure they don’t get too full (this can cause the feeder to get stuck between the discharge bins) or too empty (causing the rolls to stop resulting in a decrease in overall throughput). The process to fill the bins happens relatively quickly and the operator must monitor other equipment in the area at the same time, making the task of keeping everything at an optimal operation daunting.

Another challenge with the HPGRs is to maximise the comminution energy by increasing the power in the rolls. With hardness changes it is necessary to adjust the pressure dynamically to produce a softer ore for the ball mills.

Controlling the HPGRs with Expert Control

Our expert control software has the ability to capture the human knowledge with ease, distilling the expertise of metallurgists and operators and expressing this knowledge in rules that use fuzzy logic. By being a multivariable control system, it can monitor all of the components of a process and take the best decisions, in a matter of seconds.

The customer had great knowledge of this area, obtained from theory and practice. Expert control was the best tool to capture this mastery and automate the tertiary crushing 24/7/365.

Expert control strategy

The following objectives were pursued with the Expert Control for the HPGRs:

Increase the operational continuity and reduce the variability in the production
Manipulate and stabilise the inventory level in the bins
Increase the power in the HPGR rolls
Increase the tonnage downstream
Protect the conveyor belt against high current, speed deviation and excessive tonnage

Benefits achieved

Increase in tonnage

The attached graph shows the benefits obtained when implementing Expert Control for the HPGRs. The analysis shows an increase of 1745 t/h in throughput when Expert Control in turned on, this accounts for an increase of around 21%. The increase in tonnage for the HPGRs can be attributed to the tight control over the bin levels, by manipulating the moving bin and the feeders. These actions are taken every minute and have a significant impact on operational continuity and overall tonnage delivered to the grinding stage.

Conclusion

By implementing expert control in the HPGR’s we can achieve operational continuity by constantly monitoring the bin levels. Two benefits are immediately presented:

Higher throughput by reducing load disruptions
Optimum layer of ore between the rolls to achieve the best rupture

Once the inventory for each HPGR has been stabilised, the Expert System increases power in the rolls to enhance its breakage capabilities and provides a softer ore downstream. This in turn decreases the work done by the ball mills and increases overall throughput.

This strategy also influences the circulating load in crushing, lowering it by a noticeable margin, and increasing the fresh feed to the equipment.