LATEST TECHNOLOGICAL INNOVATIONS IN GRINDING WITH THE VERTICAL ROLLER MILL

D. Strohmeyer, Loesche GmbH, Duesseldorf, Germany

NEUESTE TECHNOLOGISCHE ENTWICKLUNGEN BEI VERTIKAL-ROLLENMÜHLEN

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ZUSAMMENFASSUNG

Die Mahlanlagen von heute sind durch den Einsatz hoch

effizienter Mühlen, ausgerüstet mit Hochleistungssichtern,

gekennzeichnet, die sich durch einen niedrigen spezifischen

Energiebedarf und eine höchst mögliche Dauerverfügbarkeit

auszeichnen. Allerdings reichen diese Merkmale allein nicht

aus, um dem denkbar höchsten Standard zu entsprechen.

Es sind Konzepte gefragt, die nicht nur auf Veränderungen

bestimmter Teile einer Mahlanlage und des Prozesses aus-

gerichtet sind, sondern die generell das Ansinnen verfolgen,

wettbewerbsfähige Produkte zu kreieren. Das ist nur dann

erreicht, wenn solche wichtigen Anforderungen wie niedrige

TCO-Werte, kleinstmögliche Einwirkungen auf die Umwelt

und auch ein hoher Sicherheitsstandard Berücksichtigung fin-

den. Jedes Designdetail einer Mahlanlage muss heute dieser

Philosophie folgen. Mit dem innovativen COPE-Antrieb, den

(4 + 4) Loesche Mühlen für die Zementmahlung und seinen

6-Rollenmühlen für die Rohmaterialmahlung in Kombination

mit einem Gleichteile-Konzept, werden die technischen

wie auch kommerziellen Risiken, die sich aus Ein-Mühlen-

Lösungen ergeben, signifikant herabgesetzt. Unerwartete

und unerwünschte Stillstände einer Mahlanlage können

vermieden werden durch „eingebaute“ Redundanz und ein

kluges Ersatzteilmanagement. Indem ein sehr kompaktes

Anlagendesign zur Anwendung gelangt, das den jeweiligen

Projekterfordernissen anzupassen ist, wird die CAPEX einer

Installation signifikant reduziert bei gleichzeitiger Verbesse-

rung charakteristischer Prozessmerkmale. Ergänzend dazu

erhöht das LM-Master Steuerungssystem die Verfügbarkeit

der Mahlanlage auf hohem Leistungsniveau und sorgt für

die Aufrechterhaltung einer konstanten Produktqualität.

Zahlreiche andere Fragen, wie z.B. die Anlagenflexibilität,

die Vorteile etwa einer separaten oder gemeinsamen Mah-

lung von bestimmten Additiven oder die regelbare oder

konstante Mahlschüsseldrehzahl usw., können erörtert und

auch kontrovers im Hinblick auf ihren Beitrag zur „idealen“

Mahlanlage diskutiert werden. Gute Lösungen sind generell

immer individueller Natur, ausgerichtet auf die Erfordernisse

des Projekts und des Zementmarkts.3

Without any doubt, today´s grinding plants have to feature

highly efficient mills with high efficiency classifiers showing

low specific energy consumption and the highest possible

mechanical durability. However, that alone is not sufficient

to create the highest conceivable standard. Concepts are

required which are not only aimed at certain parts of a grind-

ing plant and its process but which are part of a comprehen-

sive approach to creating competitive projects. This can only

be done by keeping the main goals in mind, which are low

TCO-values, as little as possible environmental impact and

the highest safety standards. Any design detail of a grinding

unit should follow this philosophy. With the innovative COPE

drive and the “4+4” cement mills and 6-roller raw mills in

combination with a common parts concept covering both of

the mill types, the technical and commercial risks derived

from single grinding unit solutions are significantly reduced.

Unexpected and undesirable down-time of the grinding plant

is avoided by built-in redundancy and an optimized spares

management. By employing the compact plant design which

can be adapted to the respective project specifics, the

CAPEX of an installation is significantly reduced whilst improv-

ing on process features at the same time. Supplementary to

this, the LM-Master control system increases the availability

of the grinding plant at high capacity levels and maintains a

constant product quality. Many other issues, such as plant

flexibility, separate versus intergrinding or variable speed ver-

sus fixed speed etc., can be raised and also controversially

discussed with respect to their purpose in contributing to

the “ideal” grinding plant. In any case, clever solutions are

of an individual nature aligned with the requirements of the

project and those of the cement market.3

SUMMARY

4D. Strohmeyer, Loesche GmbH, Duesseldorf, Germany

(English text supplied by the author)

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1 Introduction The cement market is constantly evolving and many factors do have an impact on this. Fluctuating energy prices, cement demand, mergers, political, economic and environmental set-ups – many of them global phenomena – result in scenar-ios which eventually define the regional and local cement market with all its facets and prospects. As part of this sys-tem, product development in the field of grinding techno- logy needs not only to follow trends but also to predict future developments and to lead the way, offering solutions which are not even visible on the horizon today.

Basically, the feasibility of a certain technology and a related project is based upon a multitude of circumstances. More spe-cifically, a lot is about key indicators such as TCO, CAPEX and OPEX which have always been of crucial importance. But fur-ther to that, environmental considerations have gained ground and depending on the region may have a greater effect. Water is a scarce resource in some areas of the world and emission limits have become strict and more constraining to the indus-try. CO2 is held to be responsible for global warming, leav-ing the cement industry in a slightly vulnerable situation with roughly 1 t of CO2 emissions per tonne of cement. In gen-eral, producing a “green” product is beneficial even though that appears to be somewhat contradictory considering the cement production process. Definitely cement producers opt for more tailor-made products with reasons varying from more economically viable – including the reduction of CO2 emis-sions – to application-related ones. Resulting from this, grind-ing technology in the cement industry needs to exhibit low CAPEX and OPEX values and at the same time consume as few resources as possible. Endeavoring to achieve this, it is obviously not sufficient to focus on a single section of a grind-ing plant; probably it is not even enough to focus solely on the technology. A state-of-the-art grinding unit combines all the differing contributory aspects, such as a highly efficient mill, a perfect plant layout, a proper maintenance and spares con-cept as well as a modern control system.

Latest technological innovations in grinding with the vertical roller millNeueste technologische Entwicklungen bei Vertikal-Rollenmühlen

2 Modern state-of-the-art grinding plant

2.1 Large unitsOne of the trends coming with large cement kilns – the largest is in the range of 13 000 tpd – is the demand for large cement, raw and coal mills. The basic question that needs to be answered during the project stage is whether to implement one or two grinding units for the raw ma- terial, the cement or for coal. Playing it safe, one would rather decide in favor of two mills instead of one but after taking the investment costs – about 20 to 30 % higher for two units – the maintenance costs and the staff requirements – less for one unit – into consideration, there are many arguments in favour of one single mill. What is of the greatest concern? High on the list is the availability of the grinding plant which is not necessarily meant in the sense of an average avail- ability. This is usually dominated by the material handling rather than the main equipment. It is basically the fear of experiencing a catastrophic failure with a long period of down-time, in the worst case (e.g. raw mill) of the entire kiln system. As a result, large grinding units need to demonstrate as much in-built safety and redundancy as possible. This is in particular with respect to the long-lead or expensive stock items. Amongst others these involve the mill drive and the roller/hydraulic system.

Figure 1: Loesche Mill type LM 69.6 with 6 rollers for cement raw material grinding

Grinding trackouter diameter

Number of rollers

Mean roller diameter

Roller width

Mill motor capacity kW

m

–

m

m

9600

7.0

4 S + 4 M

˜ 2.7

˜ 0.75

Mill radial bearingMill axial thrust bearingCustom 6-planetoutput stageMotor and input shaftdrive unitOil volume

Figure 2: Loesche MILL LM 70.4+4 CS with technical data

Figure 3: The principle of the COPE drive

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NGLoesche´s approach to this situation are the 6-roller raw (e.g. LM 69.6) (� Fig. 1) and the 4-roller coal mills (e.g. LM 43.4 D) both of which have been on the market since 2006. Since 2014 the (4+4)-roller cement mills have completed the cement mill product range. The Loesche MILL LM 70.4+4 CS (� Fig. 2) has been sold to a cement producer in Nigeria and will be put into operation in 2016.

Today Loesche raw mills as well as the cement mills are available with the COPE (Compact Planetary Electric) drive which has been jointly developed by RENK AG and Loesche GmbH to ensure the utmost reliability and redundancy. The COPE drive system (� Fig. 3) is a 2-stage multi-drive-type gear box with up to 8 individual drive units and a combined installed power of up to 13 MW. The vertically installed elec-trical motors connect to the gear box by means of helical gears, thus rendering the formerly (for large units) critical bevel stage obsolete. The second stage consists of a typi-cal planetary gear. The mill and the drive are able to operate even, if half of the drive units should fail. The gear box can be installed with or without a frequency converter, whichev-er is more appropriate with respect to the number of cement qualities and the range of finenesses to be ground.

Additional in-built redundancy is provided by the 6-roller sys-tem (raw mills) and the (4+4)-system (cement mills) com-prising four master rollers to do the grinding and four sup-port rollers for grinding bed preparation. The machines are equipped with independent hydraulic systems which allow for the swinging out of two of the rollers whilst remaining in operation with four rollers (raw mill) or two rollers (coal or cement mill), the remaining capacities being 80 and 60 %, respectively. Cement and raw mills share many common parts which has a positive impact on the spare part man-agement of a plant. The gear box as well as the roller mod-ules roller with tire, rocker arm and hydro-pneumatic spring system are kept equal for various combinations of raw and cement mills (� Figs. 4a and 4b). These are suitable for all typical cement production line capacities, also when taking different raw material physical properties into consideration.

2.2 LDC classifierThe inherent design of a vertical roller mill includes classi- fiers which are integrated into the machine leading to a vari-ety of positive aspects of the grinding system such as a compact self-supporting structure, high capacity, low spe-cific energy consumption and an excellent drying capabil-

LM 69.6LM 60.6LM 56.4LM 53.6LM 48.4LM 46.4LM 45.4LM 41.4LM 38.4LM 35.4LM 38.3LM 31.3LM 31.2LM 24.2LM 21.2

0 200

~2600 kW~3100 kW

~3600 kW~4200 kW

~5300 kW~6900 kW

400 600

Product throughput [t/h]

Product rate [t/h] as function of the LM size

800 1000 1200 1400

FinenessFine Coarse

Dif�cultGrindability

Easy~450 kW

~600 kW~700 kW

~1200 kW~1400 kW

~1600 kW~1750 kW~1900 kW

~2000 kW

LM 75.4+4LM-CS models with product throughputs and drive power (approx. values)

LM 70.4+4LM 63.3+3LM 59.3+3LM 56.3+3LM 53.3+3LM 56.2+2LM 48.2+2LM 46.2+2LM 41.2+2LM 35.2+2

0

5600 kW6200 kW

7100 kW9600 kW

13000 kW

50 100 150 200 250 300Product throughput [t/h]

350 400 450 500 550 600

FinenessFine

Cement

GGBFS

Coarse

Dif�cultGrindability

Easy1600 kW2700 kW

3450 kW3800 kW

4300 kW4650 kW

Figure 4: a) Sizes of Loesche cement raw material mills; b) Sizes of Loesche cement mills

New features compared to LSKS:• Vortex rectifier• Bearing cartridge• Optimized guide vane• Enlarged classifying gap• Improved velocity profile

GGBFS, �neness 4500 cm2/g (Blaine)

CEM I, �neness 3500 cm2/g (Blaine)

Pres

sure

dro

pPr

essu

re d

rop

6.5

20

16

12

8

4

0

20

16

12

8

4

0

LM 46.2+2 LM 53.3+3 LM 56.3+3

LM 46.2+2 LM 56.3+3

8.4

12.5

14.2

7.5

13.2

7.0

8.2

16.1

14.1

LDC

LSKS

LDC

LSKS

Figure 5: LDC with Vortex Rectifier Figure 6: Pressure drop data of the LDC compared to the LSKS

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Figure 7: Compact plant design as built

advantages of the latest classifier design can be applied with-out changing any of the interfaces, e.g. the duct to the fil-ter/cyclone, the connection to the feed inlet chute and the flange to the mill.

3 Compact plant design

Since the overall investment for a grinding plant is not only defined by the mill itself but rather by the entire grinding plant including the civil, mechanical and electrical engineer-ing as well as the construction, great efforts are made to opti-mize all of these to save costs and time. The compact plant design (� Figs. 7 and 8) represents a stripped-down-to-the-minimum plant combining a small footprint, a low building height and a minimum of steel structure together with excel-lent process efficiency and proper maintenance concepts.

For any new grinding unit the basic compact plant design is adapted to the actual projects specifics. The environmental conditions play a role in the same way as the question of whether the project is a green-field, brown-field, stand-alone or an integrated unit. Is there a need for a building? Where is the product silo located? Are mobile maintenance cranes available? How much space is allocated to the feeding sys-tem? Those factors require thorough consideration, always targeting low CAPEX values and short erection times which may well positively influence the total project realization time.

Figure 7: Figure 7: Compact plant design as builtCompact plant design as built

ity. The design of the classifier has an influence upon the particle size distribution (PSD) of the product and the inter-nal circulation of the machine. The latter is one of the fac-tors determining the pressure drop of the mill and related to this, the specific energy consumption at the fan as well as the grinding efficiency.

Bearing that in mind, Loesche re-designed its LSKS classi-fier in 2008 and the LDC classifier (� Fig. 5), which repre-sents the latest generation of dynamic classifier develop-ment, was introduced to the market in 2009. Compared to the former LSKS, the LDC exhibits enhanced process and mechanical features of which the patented Vortex Rectifier is the most prominent.

By the beginning of 2015 some 35 classifiers of this type have been put into operation in combination with different mills for raw material, slag and cement grinding.

The comparison of delta p-values over the classifier for the old and the new design shows a consistently reduced pres-sure drop for the LDC (� Fig. 6). In terms of product quality the particle size distribution (PSD) is in the same range as before with slopes of n = 0.90 to 1.05.

For the purpose of retrofitting existing LSKS classifiers, the LDC classifier comes in its LSVS-version adapted to the geo-metrical situation in the respective grinding plant. Thus the

24700 mm37305 mm

2895

0 m

m 3842

5 m

m

Maximum limit

Time

Controlled variable

e.g. fineness, outlettemperature

e.g. vibration, motor load

e.g. feed, classifierspeed, grinding

pressure

e.g. feed moisture, grindability, wear

Constraint variable Manipulated variable Disturbance variable

Figure 8: Compact plant design vs. conventional with a Loesche Mill LM 53.3+3 CS

Figure 9: LM-Master control system

4 LM-Master control system

Basically, there is no such thing as a modern grinding plant without a state-of-the-art control system. Loesche´s approach to this is the LM-Master (� Fig. 9) which can be combined with most of the common PLCs and, in its basic version, works with standard instrumentation. The system is aimed at an increased average production rather than at the peak performance. To accomplish this, the LM-Master actively controls parameters such as the grinding pressure, water injection, gas flow and classifier speed. Always main-taining the product quality, the system finds the ideal com-bination of process parameters to increase the availability of the mill at the highest possible throughput. In case the throughput is not of highest priority, the LM-Master is capa-ble of optimizing for specific energy consumption as well. Furthermore the vibration level and the absorbed power of the main drives are kept within the given limits. 3

Loesche – worldwide presenceLoesche is an export-oriented company run by the owner, which was established in 1906 in Berlin. Today the company is inter-nationally active with subsidiaries, representatives and agencies worldwide.Our engineers are constantly developing new ideas and individual concepts for grinding technologies and preparation processes for the benefit of our customers. Their competence is mainly due to our worldwide information management. This ensures that current knowledge and developments can also be used immediately for our own projects.The services of our subsidiaries and agencies are of key importance for analysis, processing and solving specific project problems for our customers.

Loesche GmbHHansaallee 24340549 DüsseldorfTel. +49 - 211 - 53 53 - 0Fax +49 - 211 - 53 53 - 500Email: loesche@loesche.de

Please visit our homepage at www.loesche.com for up-to-date information on our overseas companies.