■ Compact design

■ Suitable for grinding any raw material

■Outstanding performance record

ATOX Raw Mill

Continuous improvement

IntroductionVertical roller mills are widely accepted as the most efficient means of preparing kiln feed for the production of cement clinker. They are capable of preparing a wide range of feed materials to the required fineness in an energy efficient process. Although cement raw materials vary considerably in grindability, drying requirement and abrasion, the roller mill has the flexibility to be adapted to these variations, as well as other specific requirements.

FLSmidth commenced the development of the ATOX mill around 1980. Continuous improvement of the ATOX raw mill has resulted in today’s compact construction featuring a unique design concept entailing a number of advantages enhancing the reliability and performance of the ATOX raw mill.

Working principleThe ATOX mill uses pressure and shear generated between the rollers and the rotating table to crush and grind raw materials.

Feed material is directed onto the grinding table by the feed chute. The rotation of the grinding table accelerates the material towards the grinding track and passes it under the rollers. Partially ground material passes over the dam ring encircl-ing the grinding table and into the hot gas stream coming from the nozzle ring.

The moisture in the materials is evaporated almost immediately while the finer portion of material is carried by the gas stream to the separator and the coarser portion is deflected directly back to the table. The separator allows mate-rial that has reached the required fineness to leave the mill, while it rejects oversized

material and sends it back to the table for further grinding.

The coarsest fraction of the material that spills over the dam ring may fall through the nozzle ring and be con-veyed back to the feed material inlet by a mechanical recirculation system.

MAIN FEATURES

• High-efficiencymillgrinding all types of raw materials

• High-performanceseparator and opti-mized airflow ensure highseparation efficiency and low pressure loss.

• Compactdesign minimizes space requirements

• Noauxiliarymilldriverequired

• Largerollersper-mit coarse feed and ensureathick grinding bed

• Easyadaptabletohighairflowrequiredby specially wet or easy to grind materials

• Lowvibrationsduetoall impact forces and dynamic reactions being small and verticalandthuseasyto accommodate

• Segmentedwear parts for table and rollers allow use ofthemostwearresistant materials. Further,thesegment-ed wear parts are suitable for hardfacing

• Reversibleroller segmentsensurehighmaterial utilization

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Internal and external material circulation.

The ATOX raw mill has demonstrated to be suitable for grinding virtually all types of raw materials.

• Grindability varying from very easy to grind to very hard to grind, say from less than 3 kWh/t to more than 11 kWh/t for the mill drive

• Moisture in feed material varying from less than 1 % to more than 20 %

• Materials varying from being non- abrasive to very abrasive

• Feed materials varying from being non-sticky to very sticky

Raw materials that are easy to grind, i.e. high capacity for the specific mill size, or with high moisture content may require an increased air flow through the mill. The ATOX mill is simply adapted to this situation being provided with an oversize nozzle ring and an oversize separator.

Basic design conceptThe grinding table of the ATOX raw mill has a flat horizontal grinding track encircled by

an adjustable dam ring and an adjustable nozzle ring equipped with an air guide cone.

The dam ring is made of stacked bolted on segmented rings and is simply adjusted by adding or removing one or more segmented rings. The height of the dam ring determines the depth of the grinding bed on the table.

The roller assembly is kept centered on the grinding table and prevented from rotating by three torque rods attached to the mill housing. The grinding pressure is exerted hydraulically through three pull rods attached to the outer ends of each roller shaft. By this unique ATOX roller suspension the grinding forces are transmitted by the tension rods directly into the foundation

Design advantagesWith grinding track being horizontal and the center of gravity of the roller system only moving vertically all impact forces and dynamic reactions are mainly vertical and thus easy to accommodate.

The extremely low mass of the roller suspension system means low total inertia and thereby low dynamic forces. In case of excessive vibrations of the roller system the lower inertia also limits the dynamic loads on the grinding table and trust bearing in the gear box as well on the surroundings.

During grinding the force of reaction on the roller is located in front of the vertical line below the roller shaft, see a). In that position, however, the velocities of the roller and the table have different directions, see b), if the roller is placed traditionally, result-ing in large axial loads on the roller bearing.

Due to a patented toe-in of the rollers of the ATOX mill, the axial load is eliminated, see c), and the roller bearings are thus only exposed to well defined radial load ensur-ing significantly longer life of the spherical bearings.The three cylindrical rollers are rigidly connected

to a common centerpiece.

Applications and adaptability

b) Traditional design Roller tangential to grinding table.Significant axial force on roller bearings.

c) Patented toe-in of grinding roller.Axial force on roller bearings eliminated.

Toe-inofgrindingroller

a) Reaction force from grinding bed

Segmentation of wear parts means low risk of cracking, therefore extremely wear resistant wear parts for both roller and table can be used. Further, the segmented wear parts are suitable for hardfacing.

Roller segments can be reversed enabling high material utilization to be achieved also in case of uneven wear.

The ATOX mill has rollers with larger diameter compared to the diameter of the table than most other vertical roller mills. Larger roller diameter permits operation with a proportionally thicker grinding bed being less critical as re gards uneven wear and foreign bodies in the mill feed.

The rollers of large diameter further allow a pro-portionally coarser mill feed, which reduces the requirements on pre-crushing.

The rollers of the ATOX mill are lifted hydraulically before start, so no auxiliary mill drive is required. Requirement to the mill motor as regards starting torque is modest since it starts unloaded.The roller suspension system of the ATOX mill permits the hot gas inlet section to be designed virtually without restrictions to

the airflow below the grinding table and, further, to be fitted with an oversize nozzle ring. In consequence the standard ATOX mill can operate with the extra amount of gas required by specially wet or easy to grind materials. It is not necessary to involve a larger mill size just to accommodate the air-flow – only the nozzle ring and the separator must be adapted to the higher airflow.

The ATOX raw mill is of a very compact design involving a space-saving arrangement of inlet ducts and, further, crane access for service is required in only one position. The ATOX mill is thus easy to fit into a con-stricted space.

The very compact and efficient design of the ATOX mill offers a correspondingly low cost of foundation and mill building in case of clients demand for the latter.

Features and Components

Feed sluiceCompared to other types of sluices the simple rotary sluice effectively keeps the ingress of false air to a minimum and

furthermore provides a virtually constant

material flow to the mill. To prevent build up of

sticky material the sluice can be supplied in a design having the

option of heating of the rotor by hot gas passing horizontally through the sluice hub. The sluice is provided with a circular outlet flange, so it can always be aligned with an incoming belt conveyor. Further, the sluice is provided with removable side-walls for ease of maintenance.

Atox mill easy to fit into a constricted space.

Rotary sluice with removable walls for ease of maintenance.

Optimized separation processThe ATOX raw mill is provided with various mill inserts to achieve the most appropriate gas and material flow through mill.

Thereby is achieved an optimum utilization of the built-in high-performance separator and a correspondingly high efficiency of the combined grinding and separation process.

High performance gear unitThe standard main gear unit for an ATOX raw mill is the compact bevel-planetary type supplied by MAAG Gear.

The axial thrust bearing supporting the grinding table and the grinding force is a reliable hydrodynamic/semi-hydrostatic bearing of segmented design. All the thrust pads are immersed in an oil bath.

The lubricant for the thrust pads and for the internal gearings/bearings is conditioned and filtered in a separate pump station.

Reversing or replacement of roller wear segments.

Reversing and replacement of roller wear segmentsThe roller wear segments can easily be reversed or replaced inside the mill, i.e. without taking the rollers out of the mill. The separator reject cone is provided with rail and trolley for that purpose.

Bevel- planetary gear type

There is a number of arrangements for raw material grinding systems involving vertical roller mills. The various systems are different as regards placing of gas conditioning tower and dedusting of the mill vent gas. However, they can all be categorized as either three-fan systems or two-fan systems.

A three-fan system uses cyclones to dedust the mill vent gas. This arrangement reduces the operating suction and usually

also the gas volume for the filter, which may be either an electrostatic precipitator or a filter of the baghouse type.

The two-fan system uses a dust collector – an electrostatic precipitator or a baghouse filter – which takes the mill exhaust gases directly, reducing the number of drives and simplifying the system.

The type of system is selected based on specific plant conditions. However, the three-fan system is the most common of the two systems, providing better operational control with less interaction between operation of mill and kiln respectively. For the two fan system, the required size of filter must be foreseen for the total mill air flow, which is normally significantly higher than the kiln gas flow.

Mill feed arrangements: Either of the two systems shown can be provided with basically two different arrangements for feeding of the raw materials to the mill.

The most simple arrangement is the one that is shown in the flow sheet for the three fan system. When the metal detector for the mill feed material activates the change over gate at the mill inlet the feed material containing metallic objects will be rejected to a reject container, or simply to a reject pile.

When a high amount of metal parts is foreseen in the mill feed, a refinery material system as shown in b) will be advantageous. This improved system comprises a reject bin, a small conveyor system and an additional metal detector. Material is extracted from this bin at a very low rate to a conveyor belt provided with a second metal detector. When metallic objects in the extracted material are detected a sec-ond change over gate will be activated to reject a small amount of material contain-ing the metallic objects to a reject container or to a reject pile. Due to the low extrac-tion rate from the reject bin the amount of material rejected to container or pile will thus be reduced to a minimum.

Material flow Mill air flow Material + air flow

Flowsheet

Layout of a) three-fan system and b) two-fan system.System b) is provided with feature to minimise handling of rejected material with metallic objects.

Three-fansystem (a)

Two-fansystem (b)

20

25

2122

24

23

9

8

7

12

13

15

1117

14

10

18

5

3

2

1

19

6

4

16

1 Mill motor

2 Gear box

3 Grinding table Grinding parts in wear resistant high chromium white cast iron

4 Scrapers for external circulation Wear protected with Hardox 400 plate

5 Bottom plate for mill Repairable Densit Wearflex 2000 lining

6 Outlet for external material circulation

7 Rotary feed sluice

8 Feed chute Equipped with low friction stainless steel plates

9 Mill house Weldable mild steel lining

10 Nozzle ring

11 Air guide cone Chromium carbide composite plate

12 Segmented grinding roller assembly Grinding parts in wear resistant high chromium white cast iron

13 Roller body Protection in chromium carbide composite plate

14 Joint head Protection in chromium carbide composite plate

15 Torque rod Protected with mild steel plate

16 Buffer house for torque rod

17 Air and material seal for tension rod

18 Tension rod

19 Hydraulic cylinder with accumulators

20 Variable speed drive for separator

21 Cage rotor

22 Guide vanes Chromium carbide composite plate

23 Reject cone

24 Area in cone below separation zone protected with Chromium carbide composite plate

25 Mill and separator outlet

ATOX Raw Mill

Size A B C D E Power F G H Power, mm mm mm mm mm minimum mm mm mm minimum installed, installed, kW kW 25 7115 Ø3550 6000 9200 3000 665 4030 4100 3220 45 27.5 7415 Ø3900 6000 10000 3500 844 4490 4600 3620 56 30 7380 Ø4360 6600 10500 3500 1048 4950 5100 4040 69 32.5 8420 Ø4694 7600 11300 3800 1280 5440 5500 4460 83 35 8920 Ø5050 8600 12400 4300 1541 5960 6100 4930 99 37.5 9855 Ø5380 9600 13400 4800 1832 6460 6600 5380 116 40 9885 Ø5700 9700 14050 4850 2152 6970 7100 5850 136 42.5 11450 Ø5960 10300 15000 5150 2505 7490 7600 6330 156 45 11915 Ø6324 10900 15900 5450 2889 8020 8200 6790 179 47.5 12500 Ø6694 11500 16200 5750 3307 8570 8700 7250 204 50 13000 Ø7070 12000 17150 6000 3760 9130 9200 7780 232 52.5 13800 Ø7440 12700 17860 6350 4248 9690 9800 8290 260 55 14505 Ø7810 13300 18600 6650 4772 10260 10400 8270 292 57.5 15190 Ø8190 13900 19330 6950 5333 10830 11000 9310 326 60 15875 Ø8570 14500 20070 7250 5931 11450 11368 9650 361

ATOX Raw Mill Separator

Dimensionsandcharacteristicsof ATOX raw mill and separator

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DENMARKFLSmidth A/SVigerslev Allé 77 DK-2500 ValbyCopenhagenTel: +45 36 18 10 00Fax: +45 36 30 18 20E-mail: info@flsmidth.com

USAFLSmidth Inc.2040 Avenue CBethlehem, PA 18017-2188Tel: +1 610-264-6011Tel: +1 800-523-9482Fax: +1 610-264-6170E-mail: info-us@flsmidth.com

INDIAFLSmidth Ltd.Capital Towers180, Kodambakkam High RoadNungambakkamChennai 600 034Tel: +91 – 44-52 191234Fax: +91 – 44-2827 9393E-mail: indiainfo@flsmidth.com

www.flsmidth.com

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