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Krupp PolysiusA companyof ThyssenKrupp

Tube mills for dry grinding.

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Contents.

4 Two-com-partmentseparator mill

6 DOUBLEROTATOR®

7 AEROFALLmill

8 Air-sweptmill

9 Single-com-partment mill

10 Mill bearingarrangementsand driveconcepts

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A 6.2 m x 20 mmill shell on itsway from Franceto Malaysia.

With an extensive range of grinding systems,consisting of x tube mills,x rod mills,x autogenous and semi-autogenous mills,x AEROFALL mills,x roller mills and x POLYCOM® high-pressure grinding rolls

including x separators,x cement coolers,x dryers and x expert systems for automatic process control, Krupp Polysius offers need-specific solutions for economical, reliable and energy-efficientgrinding and drying of diverse materials, such as minerals, cement clinker, ores and coal.

Having successfully designed and built grind-ing plants since 1880, Polysius possesses thenecessary comprehensive process and plantknowhow. Moreover, the company’s Researchand Development Centre provides back-upservices, such as application-specific test grind-ing, to ensure optimum system design in everycase. The all-embracing range of Polysius acti-vities also includes the optimisation and up-grading of existing plants and the full spectrumof services.

Grinding and drying systems meet everyrequirement

For grinding and drying, Krupp Polysius suppliesa variety of tube mills. Selection of the appro-priate system depends on various parameters,such as feed size, grindability, moisture contentand drying properties of the raw material.

Welding a mill shellon site.

High-performancesystems for dry grinding.

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The first compartment, linedwith lifter plates, is for coarsegrinding and therefore has acharge of large balls.

The second compartment hasa classifying plate lining and acharge of smaller balls for finegrinding.

Adjustable lifter scoops in theintermediate diaphragm ensurean optimum flow of materialfrom the first compartment intothe second compartment.

The ground material is dis-charged mechanically by a dis-charge diaphragm at the end of the second grinding com-partment.

The two-compartment mill issuitable for grinding dry, brittlematerials, such as cement clin-ker, granulated blast furnaceslag, ore etc.. It can be oper-ated most economically if aseparator is included in the millcircuit. This particularly appliesif the mill product has to bevery fine or without stray over-size grains that could have anegative effect on the down-stream process stages.

The heat from the feed materialand the grinding action can bedissipated by injecting waterinto the first and second com-partments.

Two-compartment separator mill.

Two-compartmentseparator mill for

cement clinkergrinding in

Florida, USA.

Sliding shoebearing assemblyof a two-compart-ment separatormill.

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Flowsheet of a grinding plant withtwo-compartment separator mill.

6 DOUBLE ROTATOR®.

The DOUBLE ROTATOR® grind-ing process involves drying,primary grinding, separating,fine grinding and renewedseparating, all in one system.

The material components aredried in a drying chamber,primary ground in the coarsegrinding compartment andthen conveyed to the high-effi-ciency separator via the centraldischarge, airslides and abucket elevator. The coarsematerial from the separator ismostly fed into the fine grind-ing compartment, but approx.25 % is returned to the coarsegrinding compartment to im-prove the flow properties of thematerial being ground. Theground product from the finegrinding compartment alsoleaves the mill through thecentral discharge and is carriedto the separator.

The hot gases required for dry-ing the material, as well as thegas quantity needed for venti-lating the mill, are extracted viathe central discharge and rou-ted to a static separator (tail-ings separator). This collectsthe entrained material, which isthen supplied to the high-effi-ciency separator for secondaryseparation. The finished mate-rial contained in the gas streamis collected in a cyclone / filtercombination or directly in thefilter. Even if a large flow vol-ume of gas is needed for dryingvery moist materials, this hasno negative effect on the grind-ing process, as it is drawnthrough the coarse grindingcompartment.

As large balls are used in thecoarse grinding compartment,the mill can handle lumpy feedmaterial. Depending on thetype of material, the feed sizecan range up to 50 mm – in

special cases even more. TheDOUBLE ROTATOR® is not sen-sitive to feed size fluctuationsand is suitable for grinding eventhe hardest and most abrasivematerials.

The mill’s division into twogrinding compartments and theintermediate material separa-tion permit optimum adaptationto the coarse and fine grindingrequirements of the respectivefeed material. The DOUBLEROTATOR®

therefore hasthe lowestspecific energyrequirementwhen com-pared withother tube mill systems.

5.8 m x 20.5 mDOUBLE ROTATOR®

equipped with7,500 kW ring

motor for gold orecomminution in

the USA.

Flowsheet of agrinding plant withDOUBLE ROTATOR®.

7AEROFALL mill.

View into the drying chamberof a DOUBLE ROTATOR®.

Flowsheet of a grinding plantwith AEROFALL mill.

6.2 m x 25.5 m DOUBLE ROTATOR®

equipped with 11,200 kW ring motorfor gold ore comminution in the USA.

Semi-autogenous millfor ore grinding.

Krupp Polysius offers AEROFALLmills as autogenous or semi-autogenous mills for drying andgrinding.

A large diameter:length ratio ischaracteristic for these mills.Units with up to 10.5 m dia-meter, 4,500 kW drive powerand 1,200 tph throughput havealready been installed. The feedmaterial can have a lump size ofup to 500 mm. One fundamen-tal advantage of this mill is thatit even accepts materials thattend to form incrustations andhave moisture contents of up to20 %. If this mill is used, secon-dary and tertiary crushers arenot required.

The mill lining is fitted with lifterbars and guide rings, the so-called deflectors. As the millshell rotates, the material is lift-ed by the bars to a point where it cataracts to the floor of themill. The comminution processis thus performed autogenouslyby material impacting on ma-terial. The deflectors guide thefalling material to the middle ofthe mill, improving the auto-genous comminution effect. Theseparator and the cyclones in-stalled in the grinding circuit se-parate the fine and coarse ma-terial. In semi-autogenousmills the com-minution pro-cess is assistedby adding asmall charge ofgrinding media.

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5.8 m x 10 m air-swept mill with 4,900 kWCOMBIFLEX® driveunit in Egypt.

The air-swept mill only has onegrinding compartment. Theground material is dischargedpneumatically from the mill andcarried in the gas stream to thehigh-efficiency separator.

Air-swept mills are used forgrinding very moist materials,which requires a large flow rateof low-temperature gas throughthe drying chamber.

Grinding plants using air-sweptmills have the advantage ofsimple design and low capitalexpenditure.

Air-swept mill.

Flowsheet of agrinding plant with

air-swept mill.

9Single-compartment mill.

The pre-reduced material com-ponents are supplied at a regu-lated rate to the single-com-partment mill for drying andgrinding. In contrast to the air-swept mill, the ground materialis not discharged pneumati-cally, but mechanically via adischarge diaphragm at theend of the mill. It is then con-veyed to a dynamic separatorfor classification into fines andcoarse material. The coarsematerial is returned to the millfor regrinding. The single-com-partment mill can be equippedwith a pre-drying compartmentfor drying the feed material.

As the material is dischargedmechanically from the mill, the power consumption for ma-terial handling is minimised.

The mill is particularly suitablefor grinding fine material and is therefore often used for the secondary grinding of a high-pressure grinding roll product.

Flowsheet of agrinding plant with

single-compartmentmill preceded by

a POLYCOM®.

10 Sliding shoe bearing arrangement and reliabledrive systems for individual requirement profiles.

Sliding shoe bearingarrangement

Depending on the size of mill, it runs in two, four or six slidingshoes per bearing assembly.As the bearing shoes are pivot-mounted, they compen-sate any out-of-true running of the mill slide rings causedby sagging, thermal defor-mation and manufacturingtolerances. Depending on theexpected load, the mill isequipped with either hydro-dynamic or hydrostatic slidingshoes.

Hydraulic cylinders installed in the base of the bearing allowlifting and positioning of theentire mill in order to compen-sate for foundation subsidenceor to install or remove bearingshoes without complicatedsupporting of the mill shell.Load cells in the base of thebearing record the weight ofthe mill.

Well-tried seals prevent dirt or splash water from enteringthe bearing housing. The millshell is of welded constructionand has no heavy and com-plicated cast end walls.

Straight mill end walls offerthe advantage that the

mill liner plates have a simple shape and

are easy to replace. Also, the design principle providestotal freedom for mill inlet andoutlet dimensioning.

COMBIFLEX® drive unit

The COMBIFLEX® drive systemcombines the advantages ofthe ring motor drive, such aslow maintenance requirementand good availability, with the advantages of a normalgirth gear drive unit, such asfavourable capital cost. Thesystem integrates the drivepinion, girth gear, sliding shoebearing, slide ring and axialguide into a single unit. EveryCOMBIFLEX® drive unit isequipped with its own auxiliarydrive unit.

High operating reliability:Thanks to its self-centring,hardened and ground pinionand simple oil supply system,the drive unit provides optimumoperating conditions.

Minimum maintenancerequirement and low oper-ating costs:The drive unit requires no re-adjustment. A central oil supplysystem serves both the girthgear and the pinion, greatlyreducing the amount of oil required and the subsequentdisposal costs.

Standardised design: Just four models cover a powerrange from around 1,200 kW to8,000 kW. If a dual drive isemployed, drive powers of upto 16,000 kW can be transmit-ted. Thanks to the use of iden-tical components, the spareparts inventory is minimised.

Quality control: The manufacturing quality of

the drive toothing is checkedusing special, portable toothmeasuring devices.

Tube mill withCOMBIFLEX® drive unit.

Self-aligning drive pinionscompensate wobblingand faulty alignmentof the girth gear.

A mountedsliding shoe.

Installation ofa sliding shoe

bearing.

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Direct drive

The direct drive is intendedespecially for smaller mills.Similar to the COMBIFLEX®

drive system, the direct drivealso integrates the drive pinion,girth gear, sliding shoe bear-ing, and slide ring into a singleunit.

Ring motor drive

The ring motor is particularlysuitable for mills requiring veryhigh drive powers.

This gearless system transmitsthe driving torque by means of magnetic forces in the airgap between rotor (mill shell)and stator. The lifting cylindersincorporated in the sliding shoe bearing enable perfectrotor / stator centring.

Compared with other drivesystems, the ring motor hasthe lowest maintenance re-quirement and highest avail-ability.

Girth gear and pinion drive

In this drive variant the millshell is driven via one or twopinions and a girth gear boltedonto the mill shell.

Fast-running slip ring motorswith interposed gear units orslow-running synchronousmotors can be used.

Central drive

Tube mill central drives connect-ed to a mill trunnion are time-tested systems with a very lowmaintenance requirement.

Spur gear units or planetarygear units with multiple powertransmission paths are used.Mills with low drive powers areequipped with shaft-mountedplanetary gear units and motorsdirectly mounted on the gear-box.

Tube mill withring motor.

Tube mill with direct drive.