Maximizing profitability in ultra fine grinding
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| The new Stirred Media Detritor (SMD) model, SMD-1100-E, offers an optimum solution for fine grinding when requiring large-scale throughputs. |
In the mining industry, the need for efficient fine grinding processes is increasing rapidly. As demand for ores with finer mineral intergrowth rises, grinding technology is being developed to keep up.
Jon Allen, Metso’s Project Manager for Stirred Milling Technologies, notes the shift in the industry: “All the high-grade, easy ore bodies are already being developed,” he says. “What we’re seeing now are deposits that have more finely disseminated valuable mineral. The fact is, those deposits require finer grinding to achieve adequate liberation.”
The challenge in fine and ultra fine grinding applications, however, is the increasing energy requirements and the diminishing returns that occur as operations approach smaller product sizes. The solution: energy-efficient stirred milling machinery that maximizes wear life and availability – all while achieving the desired product size and maintaining profitability. This solution has evolved into the most cost-effective fine grinding technology – from the VERTIMILL® to the latest Stirred Media Detritor (SMD) E-Series, featuring the SMD-1100-E, Metso’s largest-scale SMD.
Allen notes that the VERTIMILL® and the SMD are not competitors, but were “developed as complimentary products. They each have their niche and can work together to offer an optimum equipment solution for fine grinding.” (The VERTIMILL® from six mm to 20 microns, and the SMD from 100 to five-micron feed size).
And now, the SMD-1100-E is bringing efficient ultra fine grinding to large-scale throughput. This machine is the future of fine grinding because its efficiency and specialization enable it to provide the lowest total cost of ownership to operators who need to achieve fine grinds.
Debunking the myth of consumption
Manufacturers and marketers of stirred milling equipment often tout lowest total media consumption as a major influencer of lowest total cost. However, if a machine requires less media – but at a higher cost per ton (sometimes up to $5,000) – the “savings” afforded by lower media consumption are eclipsed by the material cost. In fact, the high-intensity grinding implemented with many of these machines requires frequent replacement of liners and the expensive media itself. “Just because something doesn’t use a lot of media doesn’t mean it’s the most economical,” says Allen. “The value of the consumables is a big part of what drives total cost.”
And it’s the consumables – the grinding media – that is the number-one operating cost in a mill. The entire SMD-E-Series, including the SMD-1100-E, offers the lowest cost per ton processed (between USD 300–1,300 from recommended suppliers). By employing this lower-cost, low specific gravity media, the cost of consumables is decreased significantly, and any slight increase in consumption doesn’t affect your bottom line.
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| A close-up of an impeller of a Stirred Media Detritor. |
Lower intensity, longer wear life
High-energy intensity (a claim that is often used to support efficient stirred milling technology) “doesn’t necessarily mean efficient grinding,” says Allen. “It’s just the result of operating in a smaller vessel. You need to have a certain intensity to get fluidization, but beyond that point, it’s not beneficial to operate at a higher intensity.”
Higher intensity does have an effect on one aspect of operating cost: wear life. High-intensity grinding results in the frequent replacement of high-cost media and liners. And with lower energy inside the SMD-E-Series mills, the wear life is extended. Allen observes, “The wear life of the SMD-1100-E, for example, is about twice as long (in similar applications) compared to our closest competitor.”
The increased volume of the SMD-1100-E is key to maximizing the cost-saving potential of lower-intensity grinding. But space is also an important consideration in a plant, and the solution, says Allen, was to “go vertical. By doing this, we can make use of a larger volume without worrying about affecting the footprint of the unit.”
An additional benefit of a vertically configured machine, when compared with the horizontal unit, is a simpler mechanical design. Because the vessels are pressurized, horizontal stirred milling machines require shaft seams, feed pumps for slurry and media, plus additional shaft bearings, and more concrete for the foundation. The SMD-1100-E is a streamlined unit that can achieve higher availability.
Reach the highest availability with simplified maintenance
“Nine times out of 10, the most energy-efficient system is the lowest total cost of ownership,” says Allen. And while the SMD-E-Series offers the highest energy efficiency in ultra fine grinding applications, maintenance factors – because they’re directly correlated to mill uptime – have also been optimized. Maintenance of the SMD-E-Series is the simplest in the marketplace, with several mechanical improvements from the standard SMD.
Access is the most important concern with regard to maintenance, and every wear component of the SMD-1100-E can be changed with the mill in place – without removing or disassembling the shell. Additionally, the top plate can be rotated in 45-degree increments, and side plates are interchangeable for multiple feed arrangements. The payoff, Allen notes, is significant: “By making these improvements, we’re able to maintain the highest level of efficiency and further decrease total ownership cost through improved availability and maintainability.”
Metso also kept ancillary equipment to a minimum with the SMD-E-Series. “Pumps are a maintenance nightmare,” says Allen. “Feed the mill by gravity – and then you only need one pump per SMD – not five or six like other stirred mill designs. Maintaining one pump is much simpler and less expensive.”
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| 3D drawing of Metso’s SMD-355-E Stirred Media Detritor. |
The right application: the SMD-1100-E brings efficient fine grinding to Anglo Platinum
Major platinum producer Anglo American is always looking for ways to improve recovery in their large-scale mining operation. And as it is for many in the industry, fine and ultra fine grinding is becoming a priority. So after installing an SMD-355-E at Mototolo Platinum Mine in South Africa and seeing the operational benefits of the SMD (including significantly increased energy efficiency and long wear life), Anglo American knew they wanted to scale up.
“The SMD allows us to achieve fine grinds at a high level of efficiency,” says Chris Rule, Head of Concentrator Technology at Anglo Platinum, “and the mechanical improvements with the E-series result in more uptime. In any operation, that’s how you achieve long-term success: the more tons we get through, the more revenue we’ll see, and the SMD-1100-E is going to help us do that. It always comes back to our bottom line.”
Anglo Platinum expects the SMD-1100-E to provide the longest wear life and highest uptime of any fine grinding technology they have trialed. The unit is schedule for startup in September 2012 at the Anglo Platinum Union Mortimer concentrator.
The most cost-effective balance of grinding efficiency, cost, durability and wear
The SMD-1100-E was developed to meet growing demands now and in the future, as ultra fine grinding applications become more vital to large-scale mining operations around the world.
This machinery changes the way miners approach applications that have not been economical in the past. “Our customers are looking at the grind recovery curve,” observes Allen. “They know that in most cases the finer you go, the more recovery you get. But the diminishing returns are a problem.
“Now, with this SMD, we’re ready to supply larger-scale machines that meet greater throughput needs,” says Allen, “and that’s what we’re doing with Anglo. We’re shifting that recovery curve and allowing them to get more valuable minerals out of the ore without decreasing profitability. Our technology continues to deliver the highest energy efficiency, but total cost of ownership is even lower now.”
Allen knows that not every mine currently needs an SMD. But, he says, “The way things are going, you probably will in the future.” And even if the answer isn’t an SMD now, Metso has a full grinding product portfolio to objectively offer the right solution to customers and, Jon says, “That’s something we’re very proud of.”
