OK vertical roller mill

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Application advantagesProven commercially, the OK mill is the premier roller mill for finish grinding of portland cement, slag and blended cements. With a 30-45% reduction in the energy requirements for cement grinding and 40-50% for slag as com-pared with traditional ball mill opera-tions, the OK mill can contribute signif-icantly to your profitability and com-petitiveness.

The design combines the drying, grind-ing and separation processes into just one unit, thus simplifying the plant lay-

out. A low noise level makes outdoor installation feasible, substantially reducing civil construction costs and improving the working environment.

Because of its highly effective drying performance, the OK mill is a natural choice for grinding blended cements with one or more wet components.

Design advantagesThe OK mill uses a hydro-pneumatic system to press its grinding rollers against the material bed on the rotat-ing grinding table.

Main features- OK vertical roller mills use

30-50% less energy than ball mill systems

- Simple layout and fewer machines in the mill circuit ensure high run-factor and low maintenance costs

- Excellent drying capability when grinding blast furnace slag or blended cements with wet components

- Roller and table profile improve operating stability and reliability

- Consistent cement quality with easy to adjust quality parameters

- Special design features for iron removal during slag grinding minimise wear

- Optimal wear-protection on all internal surfaces

- Space-saving design reduces civil construction costs

- Flexibility to operate with two or four rollers guarantees long term availability

Quality & profit improving features

OK 36-4 mill under erection

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The grooved roller profile has two grind- ing zones, an inner and an outer. This creates a high and concentrated grind-ing pressure on the outer path, allowing air to escape into the grooved centre. The inner path serves to prepare the grinding bed, by compressing the feed material as it moves under the rollers into the high pressure grinding zone.

Segmented roller wear parts are made of the hardest possible material without risk of cracking and are very well suited for hard facing. Re-positioning of roll-ers is possible for evening out wear. These features ensure maximum lon-gevity.

Operating advantagesThe rollers are in a lifted position when the mill is started, ensuring trouble-free start-up. This eliminates the need for an auxiliary drive. A control system monitors the machinery and facilitates operation.

Grinding roller

Nozzle ring

Grinding table

Roller stopper

Product

Feed inlet

Rotaryfeed sluice

Main hydraulicloading system

Roller shape & curved table profile

Swing-out system forroller replacement

Main hydraulicloading system

Separator

Mill design for versatile applications, simple operation and long life

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Mill arrangementThis schematic illustrates a typical grinding installation. The arrangement is very simple and the operation is correspondingly flexible and reliable. To maintain the appropriate tempera-ture in the mill circuit – for example to ensure adequate dehydration of the gypsum when grinding cement – the layout is prepared with provisions for recirculation of hot exit gas to the mill inlet. In case the mill feed is wet slag or includes a significant portion of wet additives, additional heat must be pro-vided, for instance from a heat gener-ator. Otherwise, if the mill feed is very hot, the mill exit temperature controls a damper for cold air intake.

Nozzle ring bypass systemFor slag grinding, a specially designed nozzle ring bypass allows the iron particles to segregate through nozzles without airflow and subsequently be removed by a magnetic separator to minimise wear of the mill internals.

One mill, many productsThe OK mill efficiently grinds blended cements, with a wide range of additives such as slag, puzzolana, limestone and fly ash. Its versatility is demonstrated by the ability to switch between a wide variety of mixes, and to vary the particle size to meet individual needs.

Particle size distributionExamples of adjustments of particle size distribution when grinding to the same Blaine surface. The required steepness of the particle size distribution curve is attained by adjustment of the separator rotor speed, the mill airflow rate and the grinding pressure, in combination with the appropriate height of the dam ring.

Hotair fordrying

Cold airintake

Clinker, gypsum,slag, additive

Finished product

1

2

4

5

3

Nozzle

Table

Discharge chutefor iron particles

To magnetic separator

Air inlet

1 OK mill

2 Dynamic separator

3 Bag filter

4 Fan

5 Magnetic separator

Mill arrangement and nozzle ring bypass system

OK mill feed composition

100908070605040302010

0A+B C D D E E F F F

Plant

(%)

Clinker

Gypsum

Pozzolana

Limestone

PFA

Slag

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Optimisation of operationAdjustment of mill airflow and grinding pressure for optimisation of the opera-tion, including adjustment of particle size distribution, can be made imme-diately. Adjustment of the dam ring, however, requires a mill stop, but only for a few hours. Switching between different types of products, for example from portland cement to slag, only requires easily made operating adjust-ments. Adjustment of the dam ring is not required. However, if the mill is to operate for a long time with one spe-cific product only it may be expedient to adjust the dam ring to optimise the mill for operation with this specific product.

Wear linersThe wear liners of the grinding table and the rollers are of the segmented type and are therefore easy to replace when worn out.

For mills grinding very abrasive materials, like slag, hardfacing is an interesting and viable means of achieving a high availability of the grinding system, optimising the grinding process and saving refurbishment costs.

Hardfacing is an economical alternative to changing wear parts and is very suitable for the high chrome cast iron grinding parts used in the OK mill. Being of the segmented type the wear liners can be hardfaced numerous times throughout their life.

Seal between housing and roller. Hardfaced segments

OK mill steep PSD Typical ball mill PSD OK mill flat PSD

Resi

du

e (

%)

99

97

96

95

98

90

80

70

60

50

40

5

30

20

10

1

0.1

Particle size (µm)

100101

Performance and experience

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Portland cement Slag*

Blaine (cm2/g) 3,300 4,000 4,000 5,000

OK mill Ball mill OK mill Ball mill OK mill Ball mill OK mill Ball mill

Mill 17.6 34.2 21.3 44.9 25.7 51.8 32.2 71.1

Fan etc. 6.9 3.2 8.3 4.9 9.4 7.6 13.0 12.3

Total 24.5 37.4 29.6 49.8 35.1 59.4 45.2 83.4

*Slag with 8% moisture

Portland cement Blended cement Slag cement*

Blaine (cm2/g) 3,300 3,700 4,000 3,800

OK mill Ball mill OK mill Ball mill OK mill Ball mill

3 days 155 145 225 220 115 110

7 days 255 245 275 260 195 190

28 days 430 420 350 330 425 425

*50/50 clinker and slag mixture

Portland cement Slag*

Roller Table Roller Table

Without hardfacing 1 1 5 6

With hardfacing 0.5 0.5 2.5 3.0

*50/50 clinker and slag mixture

Typical specific energy consumption (kWh/t) motor input

Examples of compressive strength (kgf/cm2)

Typical wear rates (g/t cement) of wear parts

Twin mill installation OK 30-4 Installation

Dimensions and characteristics

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OK mill size 25-3 27-4 30-4 33-4 36-4 39-4 42-4 45-4

A m 13.7 13.9 15.5 17.3 19.0 20.6 23.7 26.7

B m 12.1 12.2 13.5 15.3 16.8 18.4 21.2 23.1

C m 5.2 6.0 6.7 7.6 8.4 9.2 11.0 12.1

D m 8.2 7.0 7.8 8.5 9.4 10.2 10.9 11.7

The capacity range depends on fineness, grindability and additives (types and proportion of mill feed)

Dimensions

27-430-433-436-439-442-445-4

OK mill number represents mean grinding track diameter

AB

C

D D

25-3

OK 33-4 for slag

OK mill size 25-3 27-4 30-4 33-4 36-4 39-4 42-4 45-4

Mill motor, installed kW 1350 1800 2350 3000 3750 4600 5500 6500

Airflow, approx., mill outlet Nm3/s 30 40 50 65 80 100 120 145

Cement, capacity range t/h 45-90 60-125 80-165 105-210 130-260 160-315 190-380 225-450

Slag at 420 m2/kg

Gear kW 1544 2161 2829 3590 4446 5412 6488 7763

Output t/h 51 72 94 119 148 180 216 258

Project Centre Denmark FLSmidth A/SVigerslev Allé 77DK-2500 ValbyCopenhagenTel: +45 3618 1000Fax: +45 3630 1820 E-mail: info@flsmidth.com

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

Project Centre IndiaFLSmidth Private LimitedFLSmidth House34, Egatoor, Kelambakkam(Rajiv Gandhi Salai, Chennai)Tamil Nadu – 603 103Tel: +91-44-4748 1000Fax: +91-44-2747 0301E-mail: indiainfo@flsmidth.com

View of rollers inside an OK mill.

Slag mill inspection.

- Proven technology

- Flexible operation

- Designed for grinding blended cements or slag

- Excellent drying capacity

- Easy maintenance and optimum utilisation of wear parts

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The OK mill is manufactured by FLSmidth under patent & license from Earthtechnica Co., Ltd & Taiheiyo Cement Corp.

Copyright © 2010 FLSmidth A/S. ALL RIGHTS RESERVED. FLSmidth is a (registered) trademark of FLSmidth A/S. This brochure makes no offers, representations or warranties (express or implied), and information and data contained in this brochure are for general reference only and may change at any time.