Metso Full portfolio Stirred Media Detritors (SMD)
Stirred Media Detritor (SMD) is a fluidized, vertical stirred mill designed for optimum grinding efficiency for fine and ultrafine grinding products. SMDs have the capacity to operate continuously at full load power draw with no steel contamination of the product. They are suitable for both open- and closed-circuit operation.

Lower capital cost

Faster installation. Less floor space required.

Lower operating cost

Energy efficient. Reduced media consumption.

Easy to maintain

High availability. Less required maintenance.

Improved safety

Easy to control and optimize. Quiet operation.

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Stirred Media Detritors for efficient fine and ultrafine grinding

Stirred Media Detritor (SMD) is a fluidized media grinding mill. It utilizes the rotational energy of the impeller arms to impart a high-energy motion to the media and slurry mixture inside the mill. This results in particle-to-particle shear and compressive forces that produce the desired grinding mechanism for fine grinding.

Lower capital cost

SMD has a modular design ensuring faster installation and reducing installation costs.

The vertical arrangement, on the other hand, allows the drive train to be entirely supported by the mill body which leads to a small footprint and simple foundation.

Furthermore, the vertical arrangement does not require any slurry seals or inlet feed pressure.

Lower operating cost

SMD’s power intensity is optimized to achieve efficient grinding, limit wear, and allow for heat dissipation in the case of a high energy grind.

Optimizing power intensity limits the sheer force of the media and slurry on the liners and impellers to improve wear life. SMD also operates with a small carbon footprint.

Easy to maintain

Thanks to having fewer moving parts than traditional grinding mills, SMD requires less frequent maintenance.   

The mechanically simple design and the ability to change all wear parts through access doors means that SMD is easy, safe and cost-effect to maintain when needed.

Improved safety

Easier and less frequent maintenance also results in better operational safety. Simple control and optimization, in turn, allow friendlier operation.

In addition, all the moving parts of SMD are enclosed, and it generates notably less noise when in operation than traditional grinding mills.


How does Stirred Media Detritor (SMD) work?

The feed slurry enters through a feed spout in the top cover which directs the feed into the bottom of the vortex (bottom of the mill) without any inlet head. Grinding media is added either by the automatic Media Addition System through one of the unused feed ports, or manually through the media feed chute.

Final product leaves SMD through the media retention screens, situated around the top of the body and is collected in an external launder and is then pumped, or flows under gravity, to the next stage in the process.

In operating SMD, there is no set combination of parameters, because the different parameters have influence on each other. Experience and practice usually establish optimum operating conditions with the lab testing indicating the initial set points.

The particle size distribution produced is governed primarily by the throughput and the amount of media and multiple mill arrangement. Primary mill control is by media addition to maintain the required power draw to achieve the desired product. Multiple SMDs can be arranged in parallel or series depending on the circuit requirements to affect the particle size distribution.

SMD Operational Control

The effective operation of the SMD requires the following parameters to be accurately and constantly monitored.

Feed Flow-Rate

This parameter is used in conjunction with the feed density and motor power to establish the grinding rate in kWh/mt. Flow rate should be as steady as possible. If the whole stream is feeding direct to the mill, surge tanks should be considered. Feeding SMD from a thickener or scalping cyclone regulates the flow very well and generates a suitable feed density.

Feed Density

The feed density is required, in conjunction with the feed flow-rate, to establish the feed rate of solids. Typical operational feed density range is 30-60% solids. Optimum grinding efficiency is usually in the range of 40-50% solids.

Motor Power/Media Addition

The power drawn by the SMD motor is required to establish the grinding rate. As the grinding media wears fine enough to exit through the mill screens, the total media charge will diminish, and the power draw will decrease.

Media should be added either manually or automatically to maintain as consistent a power draw as possible. SMD is normally operated at 80-100% of full power.

Grinding Media

The grinding media can be varied with a wide range of alternatives, depending on the application and the process requirements. Grinding media plays an important role in grinding efficiency and mill liner wear life so a high-quality media is beneficial, but an economical solution is also important.

Stirred mill plants units
Metso concentrator plant units bring flexibility & certainty to the forefront with industry leading plant configurations that seamlessly integrate operational performance and assure profitability with optimum risk management.


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