Optimizing operations efficiency with Metso Outotec’s stirred mill technology

Ideal for grinding finer products, stirred mills are known for their energy efficiency and compact design, resulting in reduced floor space requirements. 

These mills are based on gravity-induced and fluidized technologies, allowing for the optimal equipment solution for all comminution circuits covering secondary, tertiary, fine, ultrafine, regrind, and lime slaking applications.

Metso Outotec has a wide portfolio of stirred milling technologies: Vertimill, HIGmill, and Stirred Media Detritor (SMD) all designed for a large range of product sizes. We speak with two of Metso Outotec’s top mill experts.

Graham Davey, Metso Outotec’s Director, Stirred Mills, discusses the design and functionality of the brands:

MDC: Can you give a quick overview of what stirred mills are and why they are beneficial in minerals processing?

Davey: Stirred mills are quite similar to horizontal grinding mills as they have the same goal: Liberate the minerals. So both horizontal mills and stirred mills have their place in minerals processing, but stirred mills may be a preferred option for different operations.

Davey: Typically, compared to horizontal mills the stirred mills find benefits such as lower energy and media consumption with a lower plant footprint due to the design. This also leads to a reduced foundation requirement,  minimizing concrete usage. All of these features lead to a large reduction in the carbon footprint for a stirred mill, compared to a conventional horizontal mill.

MDC: Can you describe the Metso Outotec Stirred mills portfolio and its suite of products?

Davey: The Metso Outotec stirred mills are suitable for a large range of product sizes. The standardized range includes chamber units of up to 50,000 liters and the world’s largest industry units with up to 6,500 kW of installed power. Floor space use is optimized, which reduces investment costs, and installation is easy. All our stirred mills are part of the Planet Positive product portfolio, thanks to the sustainability benefits they deliver.

The Vertimill is globally recognized as the leading energy-efficient stirred grinding mill. Through a low total cost of ownership due to its simple and robust design, it brings substantial improvement to the profitability of concentrators. Over the years, Vertimill technology has proven to be efficient – especially in fine secondary and tertiary grinding, regrinding, and lime slaking applications.

The HIGmill is an advanced, energy-efficient fine and ultra-fine grinding solution that relies on proven technology. With the tall, narrow, vertical body arrangement, grinding media is evenly distributed and mineral particles remain in constant contact, significantly increasing grinding efficiency. It takes advantage of gravitational forces and GrindForce rotor technology to produce a finer grind for mineral liberation.

The Stirred Media Detritor (SMD) is a fluidized, vertical stirred mill designed for optimum grinding efficiency for fine and ultrafine grinding products. Due to its small footprint and height the SMD is especially suitable for retrofitting into existing concentrators requiring a high efficiency stirred regrind mill.

MDC: Where have you seen success for the portfolio?

Davey: We prove performance leadership through our successful, global installation base and the results our customers receive. The Metso Outotec installed base includes references from a wide range of different applications such as Poltava, Cote Gold and Malmyzh. These are a mix of greenfield and brownfield projects highlighting the flexibilty of the Metso Outotec stirred mill range.

Common benefits have been increased recovery and grades for concentrator products, increased energy efficiency, increased wear life of components and reduced downtime from less required maintenance. One that might get missed is the reduction of CO2 emissions and costs from reduced media consumption and foundation requirements.

MDC: You mentioned the entire portfolio is part ‘Planet Positive’. Could you give some examples on how?

Davey: Planet Positive is our all-encompassing approach to sustainability. It covers the environmental, social and financial aspects of sustainability. Planet Positive efforts enforce our purpose to enable sustainable modern life.

All of our products in the Stirred mills portfolio are Planet Positive examples. They provide up to 45% higher energy efficiency compared to horizontal ball mills. Reduction in media consumption is up to 40%, which helps reduce the energy consumption in manufacturing the media and shipping to potentially remote sites. Reduction in the foundation requirements means less concrete for those foundations. This lowers CO2 emissions through reduced cement production requirements & shipping volumes to the site.

Rodrigo Rizzoli, Metso Outotec’s Stirred Milling product line director highlights energy and cost savings efficiencies:

MDC: How are energy consumption and costs affected?

Rizzoli: Stirred Mills have been proven to provide energy savings compared with traditional ball mills. The finer the product required, the more efficient stirred mills will be. The attrition grinding action, vertical arrangement, and the finer media size distribution contribute to make stirred mills more energy efficient grinding machines. The Vertimill energy savings range from 30% to greater than 50% compared with ball mills. Energy and grinding media costs are very significant in mining operations.

MDC: Can you cite some examples where you are working on delivering significant improvements?

Rizzoli:  Some very positive results have been achieved through partnerships with various mining companies and Metso Outotec.

The most relevant case we are currently working on is with an iron ore producer where they needed to increase production by 50% between 2017 and 2021. The new wear components we have offered have an estimated average service life of 5,5 thousand operating hours, meaning an increase of up to 40% lifetime in comparison to the wear parts the miner previously employed.

MDC: In terms of wear and spares for stirred mills, how does the particular application impact the lifespan of the components? What should the client take into consideration?

Rizzoli: In the past years, we have developed new designs and alloys to improve the performance  of wear parts. The new generations of screw liners grant longer wear life, up to 50% compared to the first version depending on the application. Moreover, it was designed with a wear cap to efficiently protect the screw shaft.

Improvements also occurred in the method of replacing parts. The new process enables replacement in 7 minutes instead of the previous 25 minutes. The new installation practice eliminated the use of straps and chains around the components, replacing them by a lifting eyebolt appropriate for the loads, which can be threaded into an insert installed on the component. These new practices help to ensure greater safety.

MDC: What other parts and services can help in maintaining a stirred mills performance and longevity?

Rizzoli: Our solutions aim for safe operation and help to increase the availability, production efficiency and reliability of a plant.

Parts wear out over time and need replacement to ensure increased safety and production levels. Some examples of parts and services to improve overall process performance are: special lifting tool devices for wear parts; screw maintenance solutions for faster liner replacement, a hydraulic arm for the mill door; screw transport, draining media systems and automation solutions.

Other offers include performance contracts, training, equipment upgrades and refurbishments as well as field services, plant diagnostics and upgrades.  Depending on their exact needs, there is really a wide range of offers that can help make a difference for our customers.

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