Customised liner solution boosts SAG mill throughput and mine profits

by Philippine Resources - March 08, 2022

Photo: The existing grates within the SAG Mill were pegging. Critical size grinding media were blocking apertures, reducing throughput

A gold and copper mine in South East Asia was experiencing a range of challenges with its SAG mill that were hitting productivity. Facing a significant increase in ore hardness that would have exacerbated the problems, the mine turned to us to provide a solution for a safer and more productive grinding operation.

A multifaceted mill challenge 

A remote copper and gold mine in South East Asia had a problem: its 34 ft SAG mill was experiencing a range of performance issues that were limiting its production performance:

  • Pulp dischargers of many parts. The steel dischargers on the SAG mill comprised 187 pieces. Not unsurprisingly, this led to lengthy downtimes for component replacement. Making the situation worse: the discharger service life was a relatively short 12 months.
  • Inadequate liner service life. The SAG mill’s steel liners were failing to meet the required service life. To remedy the problem, the supplier had added more material to the liner design. But this created its own challenges, reducing the effective grinding volume and adding weight to the mill that was pushing bearing pressures dangerously close to limitations.
  • Peening liners. The steel used to make the liners produced a significant amount of peening. This made liner removal a time-consuming activity and more hazardous activity, as a heat lance is needed to remove peened liners. It also increases the risk of structurally damaging the mill’s shell. 
  • Pegging of the grate plates. There was excessive pegging of the grate plates by worn metal grinding media, reducing flow. As temporary measure, the mine was cutting out the pegged media every few weeks. Which only increased the time and cost spent on mill maintenance.

To solve these challenges, the mine issued a request for quote to three companies with the challenge to improve the safety of mill maintenance and increase mill discharge. In practice, this meant reducing the number and length of maintenance interventions, as well the need for hazardous installation manoeuvres, lowering mill weight and eliminating flow constraints, such as clogging and pegging.

The beginning of the solution is understanding the problem

The journey to our solution began with a thorough review of operating conditions and liner design. Through this, we determined the first course of action should be to tackle the problems associated with the discharge system. This would allow us to increase throughput and reduce weight – and would also lead to other objectives being met.

With some key improvements in mind, we created sophisticated DEM simulations to help evaluate what discharge design would best meet the mine’s objectives. These simulations allowed us to beat the mine’s throughput target of 2,100 tpd and forecast a maximum possible throughput of 2,300 tpd. The new simulated design also showed a significant increase in service life, meeting the need to reduce maintenance interventions.

DEM simulations were conducted to help evaluate the discharge design and meet mine’s objectives

After initial onsite discussions, mine personnel were invited to review the design adjustments and define the final scope. This made sure customer knowledge was also incorporated into the solution, as well as those of our engineering team.’

Exceeding expectations 

Our solution centred on our PulpMax™ composite mill liners, which were combined with material and design modifications to the steel lining system to promote increased efficiency and service life. The new liners boast 27% fewer parts (136 vs 187) and 45% lower weight (106,130 kg vs 191,962 kg).

  • Made from material that is up to 50% LIGHTER. This makes the liners easier to handle and improves worker safety. Lighter materials allow us to engineer larger components at reduced weight. It also results in less parts.
  • They typically have 50% FEWER PARTS. This results in a faster reline speed and quicker installation, and this adds up to workers spending less time in a confined space performing hazardous work.


Along the journey, we were also able to provide solutions to other challenges – for example, pegging of the grates and peening of the discharge steel. The result was a solution that exceeded original expectations:

  • Improved safety. Fewer pieces and lower weight make maintenance simpler and quicker. This reduces the amount of time that workers spend on the mill – improving safety. It also lowers the total cost of ownership. Compounding these benefits, PulpMax composite wear liners last much longer than previous liners – through some 25 million tonnes of production. Liner service life has therefore been extended from 12 months to 15 months and based on wear measurements, could extend to 18 months.
  • Improved throughput. The new system consistently achieves throughput of 2,250-2,300 tpd, exceeding the target of 2,100 tpd. This results from:
    • Reduced liner mass (>100 tonnes)
    • Improved shell design
    • Improved discharge efficiency
    • Less clogging and pegging

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Philippine Resources - June 30, 2021

Gold mine in Indonesia installing KREBS® UMD™ Pumps to increase safety

Article by Rachel Johnson A large gold mine in Indonesia set a goal to increase safety. As part of the goal, they evaluated the frequency and risk of site maintenance procedures to find areas where they could make changes. They found that their mill discharge pumps had shorter periods between maintenance events than planned, and researched further to find that the wet end components were not reaching the target wear life. Every maintenance shutdown carried a low level of risk, but in a facility that processes 240,000 tons of ore per day, the frequent maintenance tasks added up to be significant. Site management decided that the time had come to investigate other pump options. The conditions the pumps were operating under were highly abrasive and severe, but management was hopeful that a safer and longer-lasting solution was possible. Safety would remain the top priority in any pump conversion plan, but if the downtime caused by pump maintenance could safely be reduced, the increase in production would be welcome. The mine reached out to FLSmidth to ask if they had any solutions. FLSmidth responded with a proposal for a side by side comparison between the existing pumps and the KREBS Ultimate Mill Discharge (UMD) pump. For the comparison, FLSmidth would install a UMD pump at the discharge of one ball mill. The remaining mills would continue to operate with the existing pumps. During this same period, FLSmidth would set up a trial of different material combinations for the suction liner and wear ring in the UMD pump to make sure that the final recommendation would minimize maintenance events as much as possible. The gold mine agreed to the proposal and FLSmidth installed a UMD 650×550 mm (26×22 in) pump at the ball mill discharge. The pump fed the highly abrasive discharge to a cyclone but it was designed for severe duty applications such as this. A trial was planned in phases to test different combinations of the suction liner and wear ring, with the materials for the impeller and casing remaining constant. At the same time as these materials were to be tested, all components would be compared with the wear experienced by the remaining discharge pumps. Before starting the first phase of the trial, FLSmidth established targets that the life of the suction liner assembly would be 200% of the competitor pump, the life of the impeller would be 220% and the life of the casing would be 102%. At the end of the first phase of the trial, the UMD pump was stopped to evaluate wear. Even wear was seen across the wear ring, but the suction liner showed little wear and could have been used longer. At this point, the suction liner assembly (which includes the wear ring) had already run 306% of the competitor’s suction liner life and with a new wear ring the suction liner could have lasted significantly longer. Regardless of remaining wear life for the suction liner, it was decommissioned to prepare for the second phase with a new wear ring and suction liner material. After the first phase, the impeller and casing had significant life remaining, as expected. These parts had not reached the end of their wear life for the UMD or competitor pumps. New materials would not be tested in the trial so they were left in the pump to continue the comparison. Component Wear Life (%)  Competitor pump 24×20  Target Wear Life (%)                      UMD 26×22               Run 1 & 2 Wear Life (%)         UMD 26×22            Run 1 Wear Life (%)            UMD 26×22            Run 2 *Suction Liner Assembly 100% 200% 306% 233% Impeller 100% 220% (still running) **see note 270% (still running) **see note Casing 100% 102% (still running) **see note 90% (still running) **see note * KREBS® suction liner assembly contains the wear ring ** Note that the impeller and casing operated in both Run 1 and 2 and are still running. The current wear life percentages are shown in Run 2. At the end of the second phase of the trial, the UMD pump was stopped again to evaluate wear. Significant uniform wear was seen on the suction liner, but the wear ring showed no signs of wear and could be used longer. The suction liner assembly had run 233% of the competitor’s suction liner life and the wear ring could last longer with a new suction liner. The suction liner assembly was decommissioned to prepare for the third phase with a new wear ring and suction liner material. After the second phase, the impeller and casing still had significant life remaining so they were left in the pump to continue the comparison. At this point, the impeller had already lasted 270% of the life of the competitor’s impeller. The casing had so far lasted 90% of the life of the competitor’s casing, and with the wear seen it was anticipated that it also would reach or surpass the target wear life. Phase three of the trial is ongoing and a fourth phase is planned, so the successes presented here will be surpassed as the best material combination for the UMD wear components is determined. Yet, the existing data shows that the UMD suction liner assembly lasts more than three times the life of the competitor’s liner and the impeller lasts more than 2.7 times the life of the competitor’s impeller. The gold mine is pleased with the results they have already seen from the pump comparison and the added safety that they can expect when the trial is complete and they can proceed with converting the remaining discharge pumps. The added financial benefit of an increase in production due to the decrease in maintenance is also appreciated.


Philippine Resources - August 26, 2021

Advanced froth phase control: the key to higher recovery

​  Considered a mix of science and art, flotation is the most widely used process for extracting vital minerals in the modern mining operation. As the amount and type of froth changes from cell to cell, the best recovery systems must be able to accommodate variable froth conditions, otherwise valuable materials end up being lost to tailings. Newer technologies eliminate the guesswork previously associated with flotation, and the latest advancements allow for adapting to the unique conditions within each cell. This improves control of the froth phase and directly affects the mine’s ability to recover either higher volumes or higher grades. As a leading innovator in froth recovery, FLSmidth has created a Froth Recovery Upgrade package that provides customers with more control, resulting in better overall metallurgical performance. 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The mine’s existing equipment for monitoring slurry levels and controlling dart valves lacked consistency, which caused large deviations in level control. The lack of control and stability reduced overall copper recovery and had a significant impact to the bottom line. Left: Multisense Level Sesnor. Right: Festo Actuator160 Every large fluctuation in level control resulted in two scenarios: First, the cell level would become too high, and pulp would overflow into the launders, resulting in unacceptable grade. Then the level would drop too low and result in little to no recovery of the froth phase, impacting overall recovery. Data from the condition monitoring system revealed an opportunity for improvement, as shown in Figure 1. Sporadic movement of the actuator (blue) caused unstable deviations to the slurry level (green), causing it to fall short of the target level (yellow) needed for optimal performance. Actuator Figure 1 FLSmidth engineers recommended installation of new level sensors and FESTO actuators. The customer agreed to replace its current equipment, and the upgrade yielded immediate improvements. Following the retrofit, slurry levels showed significantly higher stability and remained consistent within the target level, shown in Figure 2. Actuator Figure 2 After a month with the new equipment, slurry levels consistently remained on target. As a result, the customer recovered 0.5% to 0.8% more copper than previously possible with the older equipment. Based on the short-term results, the customer anticipated replacing the remaining flotation cells in the entire plant with new level control. The mine’s return on investment was less than three months. Customer 2 – Adjustable Radial Froth Crowders Another copper mine in Peru consulted with the FLSmidth Flotation team to improve its froth phase control and improve performance of its rougher flotation circuit. The customer was seeking a low-capital solution using its existing equipment and opted to install FLSmidth’s Adjustable Radial Froth Crowders. Radial Froth Crowders Installation of the crowders required no cutting or welding and was completed during a scheduled downtime. With no required permanent structural changes to the cell, modifications could easily be reversed if the customer chose. After installation of the package on just one row of its rougher flotation cells, the customer noticed significant improvements to its operation. Operators were able to decrease reagent consumption, increase the froth phase depth by 3 to 10 cm, and ultimately improve the downstream operations by stabilising concentrate mass flows. With the economic gains seen from the retrofit’s improved performance, the mine retrofitted the remaining two concentrator plants with the same type of adjustable radial froth crowders. Customer 3 – Froth Camera A mine in western Canada contacted FLSmidth with concerns about frequent variations in its copper grade, along with low recovery numbers in its flotation circuit. FLSmidth determined that the frequent variations were caused by poor setpoint control and selection, and that a software solution would provide immediate benefits without a large capital investment.  The three-part solution utilised a combination of Model Predictive Control (MPC), fuzzy logic and FLSmidth’s newest technology in froth vision systems, to improve recovery by 4% at the desired grade with less variation. The first step was to ensure stabile level control throughout the flotation circuit. This was accomplished by controlling the dart valve positions directly using an MPC controller which greatly reduces setpoint error and variation. This process ensures that when a level setpoint is sent to a cell, that the dart valve position will be adjusted to reach the desired level set point in a quick and efficient manner. A mine in western Canada contacted FLSmidth with concerns about frequent variations in its copper grade, along with low recovery numbers in its flotation circuit. FLSmidth determined that the frequent variations were caused by poor setpoint control and selection, and that a software solution would provide immediate benefits without a large capital investment.  The three-part solution utilised a combination of Model Predictive Control (MPC), fuzzy logic and FLSmidth’s newest technology in froth vision systems, to improve recovery by 4% at the desired grade with less variation. The first step was to ensure stabile level control throughout the flotation circuit. This was accomplished by controlling the dart valve positions directly using an MPC controller which greatly reduces setpoint error and variation. 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Philippine Resources - November 28, 2021

Optimum froth recovery floats into view

Froth Recovery Upgrade package The flotation process can be divided into two stages: formation of the bubble-particle aggregates in the slurry and recovery of these aggregates in the froth. Historically, most attention – both from the theoretical and practical point of view – has been given to the first part of this process. But due to a newly developed instrumentation package, optimising froth recovery rates is now set to deliver real dividends. “It is probably no exaggeration to say that the potential from augmenting froth recovery rates – in terms of what more efficient control of the level, residence time in froth and pulling rates could deliver – was only recognized a few years ago by the industry,” commented Dr. Dariusz Lelinski, Global Product Manager for Flotation, FLSmidth. “This is because it was assumed that there are no losses during transport from slurry to the launder. It was only a few years ago it was measured that the loses are typically 50% and can reach as high as 90% for coarse particles. What it means is that 50% (averaging over all sizes) of particles must be captured again after detachment in froth phase.” “Our goal was to increase the probability of recovery of particles in the froth phase, especially coarse ones. There is no simple way to achieve it, because of it we came up with combination of instruments and devices flexible enough to achieve our goal in majority of flotation applications,” explains Lelinski. Equally applicable to sites operating with either self-aerating WEMCO® flotation cells or externally aerated nextSTEP™ machine, the newly developed froth-recovery instrumentation package could be a game-changer in flotation recovery. The solution comes from the recognition that the combination of exact slurry level measurement, accurate control of flow using redesigned dart valves and new Festo actuators (designed specifically for FLSmidth) allows for superior control of the froth phase. This in turn results in quicker reactions to flow and slurry density changes, which will dramatically improve performance of flotation machines. The conventional way to influence froth recovery is a combination of changes to froth height (improved by new actuators and dart valves), froth crowding (in the middle of the cell without the possibility of adjustment after installation and not influencing the most active part of the froth surface), and number of radial launders. “All these changes are still possible while using FLSmidth froth recovery package,” says Lelinski. “The most difficult part is froth recovery at the end of the row; there is not enough of hydrophobic particles to form stable, deep froth and a large percentage of these particles is left unrecovered.” “Our package allows not only to recover these particles, but to control required balance between recovery and grade in this part of flotation circuit. So overall, you get better results, but it also gives you another degree of process control, not only during difficulties of froth formation, but during normal operation allowing to more flexibility in selecting grade-recovery relationship.” Adjustable Radial Froth Crowders (ARFC) Central to the froth recovery package are Adjustable Radial Froth Crowders (ARFC) that were recently developed in-house by FLSmidth. The ARFCs are mechanical devices enabling increase of either recovery or grade regardless of amount of froth formed at the top of the machine. They allow for much higher pulling rates (recovery) or much deeper froth (grade) which is currently hindered by top of the flotation machine geometry. Froth Camera Froth cameras are a flotation instrument of central importance, as they allow precise monitoring of the froth phase. Our froth camera systems utilize a combination of Model Predictive Control (MPC), fuzzy logic, and the newest technology in froth vision systems to provide optimised set point selection in real-time. This system combines Deep Neural Networks (DNN) technology and object detection with traditional froth measurements such as velocity and stability to create a cutting-edge system which will optimize each individual flotation cell with the most comprehensive information available. Multisense level sensor (left) and Festo actuator (right) Alongside these elements are improved and redesigned actuators, developed in cooperation with Festo, and a new and improved level sensor, which monitors both the slurry and froth positions with the MultiSense probe, provided in cooperation with HyControl. The final piece of the package are redesigned dart valves (typically in a hinged dart valve configuration), which are the result of an in-house, value engineering project. “We are excited to deliver this complete package to our customers. All the elements working together in combination with radial froth crowders, means this package will deliver better recovery at the same grade or increased grade at the same recovery, making this package better that the sum of all parts.”

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Philippine Resources - May 26, 2022

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Philippine Resources - May 26, 2022

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