A comprehensive mine plant audit, or an audit focused on one particular circuit within a flowsheet, can identify multiple opportunities to improve process performance.
And the benefits don’t just extend to increased recovery… a good audit can also help ensure optimal energy consumption and resource usage and drive down operating costs.
Think of it like giving your car a winter check (assuming you live somewhere temperate). You know cold weather’s coming, so you put your snow tyres on, you check the antifreeze, make sure you have a snow shovel in the trunk… Maybe your car’s an older model and doesn’t like the cold so you schedule an engine service at a garage.
Conditions are changing, and you prepare to the best of your abilities. But, sometimes, life throws you a curveball and the car doesn’t operate as expected. You need the help of an expert.
At a mine, things are a little (ok, a lot) more complex. There’s no such thing as a homogenous orebody and, while sampling, testing and modelling techniques are improving, it’s still difficult to know exactly how different ore types will react under certain conditions with specific combinations of equipment.
And ore properties aren’t the only variable input, fuel prices change constantly, water supplies aren’t always reliable… things can change on a dime.
While mines generally know their plants inside out, sometimes an unbiased opinion can be really valuable in achieving optimal process performance. If that expert eye also comes with analytics technology to pinpoint where settings can be tweaked, parts replaced or upgraded, or circuits rejigged to ensure sustainable outcomes, then so much the better.
It’s important to understand that an audit isn’t just about staying on top of process inputs and outputs; it’s about making sure plant performance stays aligned with your short and long-term business goals too.
“We typically refer to audits as surveys when we go to customer’s sites,” Siwale began by correcting me. “Some personnel see an audit as a check and report on their performance – which it’s not – so, to lighten the process, we refer to the scope of work as a ‘survey’.”
What, why, how?
“What does a plant survey typically involve?” I asked.
“No two plants or orebodies are the same, and so each customer faces unique challenges,” she replied. “Typically, it’s best to focus on a specific issue up and downstream within the flowsheet to best address the customer’s concerns and keep the scope focused. Once the main concerns are addressed the scope can be adjusted to focus on other activities.”
“What does the process look like and how long would it usually last?” I said.
“First, we look at plant site information, and review process data related to the unit operation(s),” said Siwale. “We then do a historical data analysis to identify potential bottlenecks. And then the plant survey scope and breadth must be discussed with the customer before execution.”
Plant survey scopes can vary greatly, and the turnaround time is dependent on the size of the survey, the number of samples collected, and analytical methods selected for samples.
Lab metallurgical testing is often recommended as these data points will help to show the technical personnel the absolute maximum recoveries, grades etc. that can be achieved. These data will also feed into the process simulations to show what is actually achievable.
“Metallurgical balances and process simulations utilise data from all three of the sections listed above,” Siwale explained. “The project time depends upon the complexity of the plant issues and scope. It can vary from three days at site to 1-2 months, or more.”
Setting objectives & measuring outcomes
As part of a survey, digital tools are used to measure and estimate best practice and define goals to achieve the best outcomes. Examples include residence time distribution (RTD) probes, statistical analysis software and state-of-the-art simulation models.
“The initial review of the process data and a potential baseline process survey will help mines to understand their baseline performance,” said Siwale. “Metallurgical balances and process simulations will show the customer how best to address the process issues and what process changes are required.”
The customer must then perform an economic evaluation to determine the cost/benefit to implement the required process changes (i.e., piping changes to change process flow directions within the process). An additional process survey or process data review, metallurgical balance and simulations may also be required to validate and show the benefits of the process changes.
“Improvements in the efficiency of each equipment or process circuit can translate into better recoveries and grades, higher throughputs, improved safety and efficiency,” Siwale added.
“Improvements in throughput, grade and recoveries will certainly payback the cost of spare parts, equipment adjustments and improvements in the process that might be suggested. Payback periods are typically short.”
Aligning process & business goals
“How often would you recommend that mines perform a survey? I asked. “Are there any key indicators operators should look for?”
“Any sustained drop in recovery, throughput, or ore mineralogy changes should trigger, at minimum, a process data analysis to understand what’s causing the process change,” said Siwale.
“The benefit of having completed a previous survey with FLSmidth is that the new process data can be fed into the process simulator to identify the required process changes to get back on track.”
As mentioned earlier, surveys or audits can play a key role in helping mines to meet their business goals, and that extends to the growing focus on ESG and decarbonisation too.
“For example, the benefits of a grinding circuit audit coupled with metallurgical testing could allow for a better understanding of the operational parameters provided to technical plant personnel,” explained Siwale.
“They also provide guidance that allow mines to operate at their maximum efficiency to get the most out of their ore and valuable resources such as water and power.”