Application advantages
Proven 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 advantages
The OK mill uses a hydro-pneumatic system to press its grinding rollers against the material bed on the rotat-ing grindrotat-ing 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
OK 36-4 mill under erection
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, allowgrind-ing 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 advantages
The 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 Rotary feed sluice Main hydraulic loading system
Roller shape & curved table profile
Swing-out system for roller replacement Main hydraulic
loading system
Mill arrangement
This 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 system
For 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 products
The 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 distribution
Examples 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. Hot air for drying Cold air intake Clinker, gypsum, slag, additive Finished product 1 2 4 5 3 Nozzle Table Discharge chute for 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
100 90 80 70 60 50 40 30 20 10 0 A+B C D D E E F F F Plant (%) Clinker Gypsum Pozzolana Limestone PFA Slag
Optimisation of operation
Adjustment 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 liners
The 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
Residue (%) 99 97 96 95 98 90 80 70 60 50 40 5 30 20 10 1 0.1 Particle size (µm) 100 10 1
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
Dimensions and
characteristics
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 11.7The capacity range depends on fineness, grindability and additives (types and proportion of mill feed)
Dimensions 27-4 30-4 33-4 36-4 39-4 42-4 45-4 OK mill number represents
mean grinding track diameter
A B 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
Project Centre Denmark FLSmidth A/S Vigerslev Allé 77 DK-2500 Valby Copenhagen Tel: +45 3618 1000 Fax: +45 3630 1820 E-mail: [email protected]
Project Centre USA
FLSmidth Inc. 2040 Avenue C Bethlehem, PA 18017-2188 Tel: +1 610-264-6011 Fax: +1 610-264-6170 E-mail: [email protected]
Project Centre India
FLSmidth Private Limited FLSmidth House 34, Egatoor, Kelambakkam (Rajiv Gandhi Salai, Chennai) Tamil Nadu – 603 103 Tel: +91-44-4748 1000 Fax: +91-44-2747 0301 E-mail: [email protected] View of rollers inside an OK mill.
Slag mill inspection.
www.flsmidth.com
C 12-10 300-2-ENG V2 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.
