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Digital gold

Gleaming nuggets in panning screens beside rushing mountain rivers: Modern gold mining has very little in common with such images of the Wild West. But an eye for detail is still important. In the largest gold mine in the eastern USA, ANDRITZ technology is being used to optimize many facets of this industrial process.

It is pitch dark on a country road in South Carolina. At 6:20 in the morning, yellow school buses are already out on the road to collect the children. Brett Schug indicates right and turns onto a narrow road. “This is Gold Road,” says the ANDRITZ business developer. In front of him, a huge industrial site appears out of nowhere: the Haile Gold Mine. Four large towers are visible, enormous metal frameworks everywhere. Conveyor belts throw rubble onto a gray heap several houses high and brightly lit. “That’s the gold ore,” he says. Even though the pile seems gigantic, the gold content is low: It takes more than twenty tons of ore to produce one ounce of gold.

Gold prospecting has been going on for 200 years here, four hundred kilometers east of Atlanta. Captain Benjamin Haile found the precious metal in Kershaw in 1827 and built one of the first ever gold mines in the United States.

Following a break in operations, the Australian company OceanaGold produced its first gold here on January 20, 2017 – with help from ANDRITZ. One of the technologies used is known as the “Digital Twin” and provides “Virtual Instrument” capabilities that enable the plant operators to take measurements very effectively. Thus, the problems some physical instruments have in terms of reliability, and expensive maintenance problems in some casesare avoided.

Drum of the ball mill

The drum of the ball mill is as big as a house. It rotates around its own axis in just a few seconds.

© Jan Philip Welchering

An eye for the bigger picture.

A Digital Twin is a detailed, mathematical model of an industrial process, connected live to the actual operating plant. When applied to create Virtual Instruments, it provides reliable, calculated measurements, helping the operators and the automatic control system to run the processing plant at a higher efficiency. The Virtual Instruments at the Haile Gold Mine are currently mounted on slurry pipes through which a mixture of water and gold ore flows. Physical density measurements at such points are traditionally difficult, use nuclear radiation, and must be recalibrated frequently.

Digital Twin employs a detailed, first-principles, dynamic process simulation model built in the ANDRITZ proprietary IDEAS simulation software. This process model contains information about the plant equipment, including the size of each pipe and the characteristics of the slurry pump, for example. It connects to the process control system, uses values from trusted physical plant measurements, and calculates the slurry density every second. This Digital Twin system provides a reliable density value without the need for nuclear instruments, recalibration, or manual sampling. It can also issue warning messages to the plant operators if it detects operating problems in the process. The Virtual Instrument thus provides reliable, real-time information and helps the processing plant operate with higher stability and efficiency.

The Haile Gold Mine also uses the ANDRITZ-proprietary ACE (Advanced Control Expert)  optimization technology. For the people working there, it is a little like a virtual colleague – but with a great deal of power and responsibility. ACE acts like a specially-trained expert who optimizes processes, makes sure that consumption of resources and energy is as low as possible, and is always fully focused on the task at hand so that the plant operates as efficiently as possible. The Virtual Instrument values from the Digital Twin also provide some of the input values and information for the ACE systems at the mine.

Anderson and Schug at one of the grinding area hydrocyclones where the ore undergoes beneficiation in a physico chemical process.

© Jan Philip Welchering

Simulating and optimizing

As Metallurgical Superintendent, Caelen Anderson supervises a team that is responsible for helping the mine function most efficiently around the clock. “I create value,” is how he first explains his job profile when asked. Although the modern mine around him has nothing more to do with the prospecting romanticism of the Gold Rush, Anderson’s family can still look back on a proud history in this field. His Irish grandfather worked in mining, and the family from Butte, Montana, has spent over 100 years in the industry. He was involved himself in the early planning work for the Haile Gold Mine years before it actually went into operation in 2017. And ANDRITZ was on board as well at that time. “

ANDRITZ has been with us from the very beginning,” he says. “From the start, ANDRITZ and the staff clearly demonstrated their know-how,” Anderson explains and adds that he was especially impressed by the ANDRITZ expertise in the mining sector. And ANDRITZ staff are still on the site regularly, in the meantime there is even a full-time member of staff working entirely on the mine site. “The conditions we had in the beginning at 250 tons per hour (ore feed rate) are different from now, with over 430 tons per hour,” Anderson says.

“The system has grown with us.” Much of Anderson’s work is done in front of computer screens. In a large control room, he discusses mining progress with several colleagues. They are sitting in front of huge monitors watching live camera scenes or computer graphics that show the inside of the rotating mills and what is happening outside on the conveyor belts. A particularly large screen is emblazoned with at least 150 numbers, some are flashing, but only a handful are shown in red. All around, his fellow workers have easily a dozen screens to monitor.

One of these colleagues takes the opportunity to demonstrate some ANDRITZ technologies together with Anderson and Schug. In a small window, the computer shows two values: “SIM Value/Field Value” – where the SIM Value is the value calculated by the new Virtual Instrument tool, based on the Digital Twin technology.
“The system ensures that the processes are predictable and efficient. All this pays off for us,”

Good business with gold

Anderson explains. “The operators can see in real time how changes affect their circuit. The system provides them with more information – the more information we have, the better decisions we can make.” The Digital Twin and other ANDRITZ technologies are helping Haile Gold Mine process more ore and extract more gold from the ore it processes.

This means that more gold is produced without additional effort. And it really could be more in the future: OceanaGold explains on the mine’s website that the original plans were to mine approximately two million ounces of gold annually, and further exploration at Haile has revealed additional ore deposits. So there is justified hope that the final result will be much higher. ANDRITZ is there to help by applying new technologies – technologies the prospectors in the Wild West could never have imagined.

A sizable heap, and not without good reason. More than 20 tons of ore are needed to recover a single ounce of gold.

© Jan Philip Welchering

HOW DOES A DIGITAL TWIN WORK?

The ANDRITZ Digital Twin mirrors the physical process using real equipment characteristics such as physical dimensions and pump curve data.

A Digital Twin is the mathematical model of an industrial process that is linked in real time to a physical plant. This is where the IDEAS software from ANDRITZ comes into play. The Twin generates reliable information and values for optimum operation of the plant. In addition, it issues alerts for the operators or the control software if operating problems start to emerge. The schematic diagram shows a clear and simplified version of the main process steps.

1. Within the industrial process, important and trustworthy measurement equipment is identified.

2. Measurements are taken here in order to collect data, e.g. flow rate or pump speed, and sent to the control system.

3. The data are transferred from the physical control system to the Digital Twin with the aid of an OPC industrial communication protocol.

4. Then the data is uploaded into the IDEAS process model at the heart of the Digital Twin.

5. The Digital Twin calculates process values at desired locations – providing the Virtual Instruments.

6. These process values are sent to the control system, including alerts and fault messages if they are needed.

7. The operators and the control system use all available data, including Digital Twin data, to generate control signals.

8. Actuators adjust and control the physical equipment and parts of the plant on the basis of these control signals.

OceanaGold

The OceanaGold Corporation has its headquarters in Melbourne, Australia, and operated a total of four mines as of December 2018 in New Zealand, the Philippines, and the USA - including the Haile Gold Mine in the state of South Carolina with over 550 employees. OceanaGold had annual sales of 724 million USD in 2017.

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