Last month at the 16th AusIMM Mill Operators Conference in Perth, Hans Liang from the Mipac Optimisation team took to the main stage to present a technical paper titled “The Journey of Process Improvement – Ok Tedi’s vision” which he co-authored with Ok Tedi’s, Lyndah Brown and Bevin Wong, Operations Manager from JKTech.
Liang, H, Brown, L, and Wong, B, 2024. The journey of process improvement – Ok Tedi’s vision, in Proceedings of the Sixteenth Mill Operators Conference, pp 81-94 (The Australasian Institute of Mining and Metallurgy: Melbourne).
For those who want a quick update, we’ve got the abstract below followed by some of the meaty questions Hans has answered about Ok Tedi journey to operational excellence.
The abstract
The Ok Tedi mine has been operating since 1984, and is the longest running open-pit copper, gold, and silver mine located in the Western Provinces of Papua New Guinea. When it first went into production the original Life-of-Mine was expected to be 25 to 30 years. Since then, multiple extensions to Life-of-Mine have been announced with current plans up to 2050.
To reach this plan, plant processes must be continuously reviewed and developed in line with new technologies. In 2015, more than 30 years since the first operations commenced, Ok Tedi conducted an internal gap analysis on the state of their existing data network and control systems to identify priority work fronts. They needed to de-risk the operation to achieve the production targets through the extended Life-of- Mine
Between 2015 and 2017 various improvement projects were executed to mitigate the identified business risks such as upgrading of the network infrastructure and improving reliability of instrumentation and equipment on site.
However, declining ore grades and various production challenges leading into 2018 culminated in Ok Tedi experiencing low gold and copper recoveries. The plant’s unstable operation was resulting in operations teams reverting to manual control of the processing plant. They had lost trust in the process control system.
During this period the operating norm became one of reacting and firefighting. Making the situation even worse was the lack of visibility and transparency of underperformance root cause – bringing to the fore gaps identified in the 2015 review relating to insufficient digital maturity for business intelligence.
The Processing Improvement department at Ok Tedi was established in 2018 as part of the overall business improvement strategy. The group initiated various engagements with subject matter experts and concurrent improvement projects to address the poor performance and mitigate future business risks based on the previous gaps identified.
The technical paper presented at the 2024 Mill Operators Conference discussed the process improvement journey Ok Tedi embarked on from 2017. To address the challenges they were facing, Ok Tedi initiated several concurrent projects focussed on:
- optimising the existing plant,
- undertaking capital projects to upgrade capacity,
- and investment in upskilling their workforce.
Successful and systematic execution of the project initiatives by the Ok Tedi Process Improvement department, in partnership with external domain experts like Mipac and JKTech resulted in significant improvements to process stability, which were transformative to the increased copper recovery by 2.4 per cent and gold recovery by 7.4 per cent achieved.
Key Themes in the Technical Paper
- Declining plant performance and operational technology risk:
- Declining ore feed grades, increasing ore hardness, and plant reliability from an ageing asset contributed to declining throughput and recovery performance leading into 2015 (shortly after extension announced to Life of Mine).
- Various work fronts identified to de-risk business to deliver on Life-of-Mine production plans. Significant gaps associated with the existing process control system and network infrastructure.
- Control system had evolved into a hybrid of programmable logic controllers (PLC), Expert systems, and a distributed control system (DCS) – almost 40 per cent of the existing automation was bypassed or redundant.
- Manual control of the processing plant became the norm, leading to reactive firefighting.
- Production monitoring systems lacked visibility into the root causes of underperformance.
- Understanding the value drivers
- Main lever to address production shortfall leading into 2015 was to maximise mill throughput. Recovery projects were in the context of maintaining recovery while ramping up tonnages.
- Operating at high mill throughput rates was an unsustainable long-term solution without addressing recovery.
- A recovery improvement plan was initiated in 2017, highlighting multiple priority projects to address plant stability and process variability for increasing recovery, particularly gold.
- Strategic focus, collaboration, and drive towards stability:
- A Process Improvements Team was established in 2018 to triage the priority projects under the recovery improvement plan.
- Two significant automation projects implemented that were foundational to realising the value of multiple concurrent projects: primary hydrocyclone control and flotation level control.
- Leveraging automation and operating data led to reduced downtime events, improved plant stability, and facilitated data-driven operational insights.
- Only through stability, can you optimise:
-
- Foundational to realising the value of the parallel work fronts was minimising process variability through the automation projects.
- Successful and systematic execution of the improvement projects resulted in significant increases in both gold and copper recoveries.
- Gold recovery improved by 7.4% between 2017 and 2021, from 59.5% to 66.9%, while increasing gold in copper concentrate by 5.4 g/t from 16.8 g/t to 22.2 g/t.
- Copper recovery improved by 2.4% during the same period, from 84.5% to 86.9%, while increasing copper grade in concentrate by 0.4% from 24.5% to 24.9%.
- These improvements were achieved despite a continued decline in ore feed grades.
Key Takeaways:
Prioritising process stability and mitigating variability
Ok Tedi Mining Limited’s success highlights the importance of focusing on the fundamentals – achieving stable plant operation and minimising process variability to improve overall recovery.
Data-driven decision-making
Investing in data infrastructure and leveraging data analytics to identify and prioritise improvement opportunities was crucial for effective decision-making.
Embracing automation
Implementing targeted automation projects, such as the primary hydrocyclone and flotation level control, played a significant role in driving operational stability and efficiency.
Cultural shift and building internal capability
Upskilling and empowering site personnel to maintain and improve the control systems, rather than relying solely on external vendors, facilitated long-term sustainability of the process improvements.
Conclusion:
Ok Tedi Mining Limited’s process improvement journey serves as a valuable case study for demonstrating the benefits of addressing foundational issues to achieve sustainable improvements in operational performance.
The commitment and focus on mitigating process variability and leveraging automation and data-driven insights were key enablers in achieving the recovery improvements in the backdrop of declining ore feed grades and ageing infrastructure.
So, let’s look at some of the key questions that were raised from this paper.
How did Ok Tedi address the challenges related to primary hydrocyclone control?
The material discharged from the grinding mills combine into a common hydrocyclone feed sump. There is no dedicated conditioning tank prior to the copper flotation cells, and the hydrocyclone feed sump serves as an intermediate “buffer” for transferring milled material to the flotation circuit. Addressing process stability issues upstream often alleviates many of the perceived downstream variability challenges.
On top of this, there are also several ore types that are presented to the mill, each with different hardness characteristics which directly impact throughput rates. Minimising flow variations to the hydrocyclones would also assist in flotation control.
The revised control strategy utilised the capacity of the hydrocyclone feed sump for surge protection (configured for “averaging level” control rather than tight level control) and aimed to distribute the total flow output across the operating hydrocyclone clusters. Stabilising the level within the hydrocyclone feed sump then enabled additional pressure and density control loops to build upon the operating strategy.
The implemented hydrocyclone control strategy had flow on benefits of mitigating pump cavitation risks and historical downtime events related to poor level and pressure control, as well as minimising flow disturbances into the flotation circuit.
What actions were taken to improve flotation level control at Ok Tedi
Stability upstream (hydrocyclone controls) reduced the flow variations reporting to flotation. Flotation level control was achieved by a vendor APC and performed well, though a risk identified from Mipac’s review in 2018 was the APC server did not have any redundancy (operated from standalone computer).
When the system unfortunately fell over in 2019, Mipac along with the site controls team implemented changes to the existing DCS based PID controllers to incorporate feedforward capabilities. The updated DCS controllers reduced both the error (deviation from set-point) and standard deviation by more than 40% compared to the previous APC system!
Figure 1. Updated DCS controllers compared to APC on flotation level error
Developing the in-house capability to manage and update the existing DCS controllers also benefited site by eliminating costs associated with additional hardware, software, and on-going licensing.
Why is minimising process variability important?
Reducing process variability, aside from enabling systems to push towards operating limits, also allows for more definitive evaluation of other process improvement opportunities.
Take the common scenario of a concentrator conducting a plant trial of a new reagent claiming to improve flotation recovery, most recovery improvement projects kick off in the noble goal of demonstrating real 1-2% uplift.
A common method to statistically assess the trials is using a paired t-test to determine if the result is real or come about by chance from experimental error. If the the normal operating state of the plant sees a standard deviation of 4% in recovery, the number of paired tests required to minimise the uncertainty in a 1% real improvement is in the order of 75 pairs (almost 3 months of operating days if comparing shift-by-shift data)!
If the standard deviation can be reduced to 3%, this shrinks the number of test sets significantly (almost halving the required pairs).
What improvements were made to the operational performance monitoring?
As with many of Mipac’s customers embarking on their modernisation journey, there are a plethora of opportunities where digitising and leveraging operational information can be used for data driven insights and improved decision making. An audit of the site PI System from Mipac’s in-house PI system specialists often uncovers multiple avenues to improve the PI system performance (system architecture, data integrity, PI point optimisation, PI Asset Framework configuration).
Mipac’s MPA software was deployed to consolidate the various data sources to streamline the Processing department’s daily production and short interval control meetings. Additional tags were created to monitor controller performances with tailored reports built to provide critical production insights for effective decision-making.
Figure 2. Example MPA report highlighting milling throughput constraint states
Figure 3. Example MPA report for flotation level control monitoring
Figure 4. Example MPA report for vibration monitoring of equipment
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