Stirred Milling 2010 Final LowRes

7/27/2019 Stirred Milling 2010 Final LowRes

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Stirred Mills

VERTIMILL® & Stirred Media Detritor



2 Stirred Milling

Stirred Milling

Metso is the industry leader...Metso has

• The most mature stirred milling technologies • The largest installed base in terms of quantity of units and installed power

• Continuous development program

The stirred milling technologies currently available can be divided into two sub-categories: gravity-induced and uidized.Gravity-induced stirred mills initiate a ball charge motion via rotational movement of a screw to provide a size reduction

mechanism. In contrast, uidized stirred mills use a rotational movement to uidize a media-slurry mixture, resulting ina size reduction mechanism. The type of mill and the circuit con guration are intrinsic to maximizing the grade andrecovery pro le of an ore. Metso has both stirred milling technologies in the Vertimill and the Stirred Media Detritor(SMD), allowing Metso to o er the optimum equipment solution for the circuit.

The Vertimill

• 300+ Units by Metso• 160 MW Installed Power• Standard Unit Sizes from 15 to 3000 HP• Gravity Induced Stirred Mill

• Feed Size from 6 mm• Product Sizes to sub 20 microns• High Density media – steel or ceramic

Vertimills are globally recognized as energye cient grinding machines and have beenproven to grind more e ciently than ballmills with feeds as coarse as 6 mm toproducts ner than 20 microns. In additionto grind e ciency, reduced mediaconsumption, lower installation cost,minimal maintenance, and minimal linerwear make the Metso Vertimill the lowesttotal cost of ownership in many applications,substantially improving the pro tability of

concentrators.

The Vertimill is a unique product o eredexclusively by Metso that has a long historyin the metallic mining industry. Thetechnology was originally developed in the1950’s for industrial applications. Metsosuccessfully developed and implementedthe technology in the rst large scalemetallic operations in 1980. In the thirtyyears since, the Vertimill has built the largestinstalled base of any stirred millingtechnology.

Mechanically, the Vertimill is a very simplemachine with an agitating screw suspendedinto the grinding chamber, supported byspherical roller bearings and driven by a

xed speed motor through a planetarygearbox. The gure above shows theVertimill in its standard arrangement with allof its major components. The capacity of each unit size is relative to the requiredpower input for the intended grind, howevermills have been operated with throughputs

exceeding 500 mtph.



Stirred Milling 3

Stirred Media Detritor

• 149 Units by Metso• 46 MW Installed Power• Standard Units Sizes from 7.5 to 1100 kW• Fluidize Media Mill

• Feed sizes from 250 microns• Product to sub 5 microns• Low density media: Sand or Ceramic

The Stirred Media Detritor (SMD) is a uidized,vertical stirred mill designed for optimumgrinding e ciency for ne and ultra negrinding products. The SMD utilizes therotational energy of the impeller arms toimpart a high-energy motion to the media/ slurry mixture inside the mill. This results inparticle-to-particle shear and compressiveforces which produce the desired grindingmechanism for ne grinding. The verticalarrangement allows the drive train to be

entirely supported by the mill body which

leads to a small foot print and simplefoundation. Also, the vertical arrangementdoes not require any slurry seals or inlet feedpressure. The SMD is a uidized media millwhich means, the stirrer speed is highenough to distribute the media throughoutthe slurry regardless of media density, forcingparticle and media contact.

The SMD power intensity is optimized toachieve e cient grinding, limit wear, and

allow for heat dissipation in the case of ahigh energy grind. The power intensity

(kW/m3) is relatively high compared withother mill types, but is required to generatea vortex of the media and slurry duringoperation and to bring the particles incontact with one another for e cientgrinding. However, the power intensity isnot so high that a cooling system wouldbe required to dissipate the heat generatedduring a high energy grind. Also, limitingpower intensity, limits the sheer force of themedia/slurry on the liners, impellers and

improves wear life.

Lower Capital Cost• Less Floor Space Required• Simple, Smaller Foundation• Faster Installation

Lower Operating Cost• Energy E cient Grinding• Reduced Media Consumption• Lower Maintenance

Additional Advantages:• Quiet Operation• High Availability• Greater Operational Safety• Easy to Control and Optimize

Why Vertical Stirred Mills?With any technology consideration, you want a solution that has the lowest total cost of ownershipwhile meeting the product requirements. Vertically stirred mills have many advantages that makethem the lowest total cost of ownership. These advantages include:



4 Stirred Milling

Materials successfully groundin stirred Mills

Aluminum OxideAragoniteBariteBlast Furnace SlagCalcined Bauxite

CalciteCalcium CarbonateClayCoal – oilCoal – waterCoal Tar SludgeCoke – oilCopper MolybdenumCopper ConcentrateCopper OreCopper SlagCopper-Lead-Zinc OreDecanter Tar SludgeFerriteFerro Alloy

Ferro ManganeseGold OreGold TailingsGraphiteHydrated Alumina

Iron OxideIron SandKaolineLead ConcentrateLead Zinc Ore Lime(slaking)Lime PowderLimestoneMagnesium OxideMagnetite ConcentrateManganese DioxideManganese OreMarbleMolybdeniteMolybdenum Conc.

Oil SludgePetroleum CokePhosphate Rock Pottery StonePyrite

Red PhosphorousRock SaltSaltSand IronSericiteSilicaSilica SandSlagStrontium FerriteSulphur

TalcUraniumZinc ConcentrateZinc Lead Ore

Ball Mill

Vertimill®

SMD

100000 10000 1000

Microns

100 10 1

Typical Grinding Ranges

Ball Mills and stirred mills are applied acrossa wide range of applications, but for eachore there is optimum e cient range. The

gure to the left shows the typicalapplication ranges for ball mills and stirredmill. The Vertimill is always more e cientthan a ball mill with energy savings rangingfrom 30% to greater than 50%. Thetransition point from the Vertimill toan SMD varies depending on the oreproperties but generally is in the range of 20 to 40 microns. A detailed test programcan be carried out to determine theoptimum energy e cient circuit.



Stirred Milling 5

Fewer Moving Parts

Ball Mill SMD Vertimill

Motor

√ √ √

Reducer

√ √ √

Couplings

√ √ √

Hyrostatic Bearing

√

Bearing Lube Unit

√

Gear Lube

√

Trommel

√

• Flexibility in Feed ArrangementMultiple layout options can be optimized for speci c process needs

• Less Noise – Less than 85 dBIf current ball mill acts as standby, building will be much quieter

• Greater Operating SafetyMoving parts are enclosed

Easier, less frequent maintenance

• Operator FriendlyMore forgiving

Easy to control and optimize

Additional Advantages

Energy EfciencyStirred Mills have been proven to provide energy savings comparedwith traditional ball mills. The ner the product required, the moree cient stirred mills will be than a ball mill. The attrition grindingaction, vertical arrangement, and the ner media size distributioncontribute to make stirred mills more energy e cient grindingmachines. The Vertimill energy savings range from 30% to greaterthan 50% compared with traditional ball mills and the SMD energysavings are far greater than 50% of ball mill energy in ne grinds.

Media SavingsMedia consumption is directly related with energy e ciency.At a concentrator in Mexico, they experienced reduced mediaconsumption from a previous average of 821 g/t to 429 g/t, or a 48%reduction by using Vertimills. The savings in media consumption isfor two reasons. First, less energy is being consumed with grinding,so less grinding media will be consumed. Second, since the wastefulimpact breakage of ball-to-ball or ball-to-liner is eliminated, there arefewer ball fractures and the media inside the mill can maintain itsshape and usefulness.

Green TechnologyEnergy e ciency and environmental consciousness is very importanttoday. A savings in energy usage not only means big savings inoperational cost, but also a reduction in carbon emissions. Energyis also used to create grinding media, so a reduction in mediaconsumption is also a reduction in net carbon emissions. Usingenergy e cient technology will not only decrease operating costs,but could also generate a more positive public opinion and ease thepermitting process. In many cases, stirred mills can reduce thecarbon footprint of a grinding circuit by 30 – 50%.



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The Vertimill is typically arranged in closed circuit and fed by thecyclone under ow. The motor power turns the Vertimill screw atconstant speed to stir the grinding balls and slurry. As the particlesare ground, they rise to the top of the mill and over ows into theseparating tank. A change in the rotational direction of the slurrywhen it transitions from the mill to the separating tank causesturbulence which facilitates a settling of the coarser material.Product from the mill exits the tank through a stand pipe and thento the cyclone sump. The slightly coarser portion of the mill over owis recycled back into the bottom of the Vertimill. The recycle systemcan reduce cyclone circulating load by allowing the mill topreferentially grind the coarser material. Also, the uprising velocity inthe mill can be controlled by a recycle pump to a ect the productsize distribution, prevent over grinding, and reduce the circulatingload from the cyclone.

Vertimill Operational Control

Final product size is a factor of applied grinding power, ow rate, andslurry density. The e ective operation of the Vertimill requires theseparameters to be accurately and constantly monitored and adjustedto meet the required product speci cations.

Motor Power/Media Addition - The power drawn by the Vertimillmotor is required to establish the grinding rate. Motor power shouldbe measured using corrected power. Monitoring mill motoramperage is not an accurate method. As the grinding media wears

ne enough to be carried out by the uprising velocity in the mill, thetotal media charge will diminish and the power draw will decrease.Consistent power draw is required in order to achieve the desiredproduct size, so media should be added either manually orautomatically periodically to maintain as consistent a power draw aspossible. The Vertimill has an excellent turndown ratio and can beoperated at lower than installed power with less e ect on grind

e ciency than horizontal ball mills.

Feed Flow-Rate - This parameter is used in conjunction with thefeed density and motor power to establish the grinding rate in kWh/ mt. The Vertimill can easily handle a uctuating ow but it should bemonitored and can be varied to achieve required productrequirement.

Feed Density - The feed density is required, in conjunction withthe feed ow-rate, to establish the feed rate of solids.

Vertimill Functional Description



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SMD Functional Description

The feed slurry enters through a feed spout in the top cover whichdirects the feed into the bottom of the vortex (bottom of the mill)without any inlet head. Grinding media is added either by theautomatic Media Addition System through one of the unused feedports or manually through the media feed chute. Final productleaves the SMD through the media retention screens, situatedaround the top of the body and is collected in an external launderand is then pumped, or ows under gravity, to the next stage in theprocess.

In operating a SMD, there is no set combination of parameters,because the di erent parameters have in uence on each other.Experience and practice usually establish optimum operatingconditions with the lab testing establishing the initial set points. The particle size distribution produced is governed primarily by thethroughput and the amount of media and multiple millarrangement. Primary mill control is by media addition to maintainthe required power draw to achieve the desired product. MultipleSMDs can be arranged in parallel or series depending on the circuitrequirements to a ect the particle size distribution.

SMD Operational Control

The e ective operation of the SMD requires the followingparameters to be accurately and constantly monitored:

Feed Flow-Rate - This parameter is used in conjunction with thefeed density and motor power to establish the grinding rate in kWh/ mt. Flow rate should be as steady as possible. If the whole stream isfeeding direct to the mill, surge tanks should be considered. Feedingthe SMD from a thickener or scalping cyclone regulates the ow verywell and generates a suitable feed density.

Feed Density - The feed density is required, in conjunction with thefeed ow-rate, to establish the feed rate of solids. Typical operationalfeed density range is 30-60% solids. Optimum grinding e ciency isusually in the range of 40-50% solids.

Motor Power/Media Addition - The power drawn by the SMDmotor is required to establish the grinding rate. As the grindingmedia wears ne enough to exit through the mill screens, the totalmedia charge will diminish and the power draw will decrease. Somedia should be added either manually or automatically to maintainas consistent a power draw as possible. The SMD is normallyoperated at 85-100% of full power.

Grinding Media - The grinding media can be varied with a widerange of alternatives, depending on the application and the processrequirements. Grinding media plays an important role in grindinge ciency and millliner wear life so ahigh quality mediais bene cial, butan economicalsolution is also

important.



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B L / P i t t s b u r g h

Metso Minerals ndustries, nc., 2715 Pleasant Valley Road, York PA, 17402 USA, tel +1 717 849 7213, fax +1 717 849 7252, www.metso. com

The information contained herein is a general description only is not guaranteed and contains no warranties of any kind

Stirred Milling 2010 Final LowRes

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