New grinders improve efficiency

There has been an influx of new grinding equipment and technology to hit the market in recent times and it can sometimes be difficult for mining producers to keep up with the developments.

To remove some of the confusion, four mining experts from Metso told National Mining Chronicle how the new advancements might impact the industry and how to overcome potential issues.

Metso Director, Process Engineering Development, Sales Alan Boylston said the main challenge for mining companies in today’s market was in knowing how to balance the increased production needed to meet rising demand for metals with the fact ore grades around the world were continuing to fall.

“What this means is that to even maintain current levels of production mines need to process more and more raw ore, which requires additional energy as they ramp up production,” Mr Boylston said.

“It also translates in many cases to higher investments in equipment and higher operating costs. In order to be pro table, mines have to really zero in on ways to improve operational efficiency.”

In order to meet this challenge Mr Boylston said the trends he had noticed related to options that could lower energy costs as production demands increased. It was important, he said, to find opportunities to drive costs down across the entire process.

One area Mr Boylston had noticed this could happen was in equipment as he said there was more openness to looking at new applications for older technology.

“For example, High Pressure Grinding Rolls (HPGR) have been around a long time in limestone, cement and kimberlite operations, but applications involving hard ores are relatively new,” he said. “With their higher energy efficiency, HPGRs are getting a second look as an alternative to more traditional grinding in certain applications.”

Metso Global Application Support Manager, Mill Linings Håkan Ståhlbröst said another trend he had noticed for driving down costs while improving efficiency was to replace small and medium-sized mills with fewer but much larger mills to handle higher capacity loads.

Technical improvements

One of the biggest issues with traditional horizontal mills was they were not very energy efficient, according to Mr Ståhlbröst. He said only a very small part of the energy was transformed into efficient grinding with the remaining energy channelled into liner and media wear, heat and noise.

In terms of the technology around this, Mr Ståhlbröst said there was not much that could be done with the mill itself, but improvements could be made in controlling the process.

“New and faster simulation tools also allow us to ensure that the mill feed contributes to increased grinding efficiency,” he said.

“Previously, simulations took a long time, but now we simulate almost all designs for larger mills. If the grinding is as efficient as possible, you consume less energy per tonne.”

Metso Global Consulting and Labs Manager Suzy Lynch-Watson said the company was always looking to make improvements in the grinding process.

“One recent advance in mill lining that has received a lot of attention is the Metso Megaliner made from polymet and steel,” she said. “The liners can use less material than previously since we use a ‘skip row’ design, where the liners now have only two-thirds of the number of lifters as before.

“Using this design, we can still achieve the same lift and charge trajectory but with less liner weight. The lower weight can make it possible to load more in the mill and together with an optimised design, you can produce more tonnes and in some cases, increase efficiency.”

Equipment designs and uses

Another way of making improvements throughout the process was to look at how each of the different pieces of equipment worked together in order to discover the most energy efficient combination.

Recent research by Malcolm Powell and Sam Palandiandy at the Julius Kruttschnitt Mineral Research Centre (JKMRC) led Ms Lynch-Watson to this conclusion. She said a great option for this was the Metso Vertimill stirred milling technology, especially in cases where a plant needed extra milling capacity.

“In the past, plants would invest in a second ball mill to run in parallel with their current one to add the additional capacity, but this is not always an energy efficient way of tackling the problem,” she said.

Poor grinding practices

Metso Principal Process Engineer André Vien said even if companies installed the most modern and up-to-date equipment, the overall performance and efficiency generated was dependent on how the equipment was operated.

He said Metso’s global Process Optimisation group had visited hundreds of concentrator plants, looking at the comminution circuits, assessing how things were set up and looking for improvements in energy efficiency or throughput.

“Most of the process bottlenecks we run into are not caused by the machines themselves but rather have resulted from the way the comminution equipment has been configured or is operated,” he said.

“The four most common issues encountered revolve around the grinding media used in the mill, how the mill speed and liner angles are paired, relying too heavily on rules of thumb related to production, and finally, a lack of communication between the mine and the plant.

“As an example, when looking at grinding media we run into situations where the media is too large for the expected grind. The result ends up being high wear rates to both the liners and the media and a very inefficient use of energy.

“The solution to this would be to conduct ongoing calculations to ensure the optimal size of grinding media is used and to keep a close eye on media quality.”

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