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    • Abstract: VERTICAL ROLLER MILL TECHNOLOGYI Making vertical stridesby M Keyssner (Dipl-Ing), Due to Asian cement manufacturers’ willingness to innovate, it has beenLoesche GmbH, Germany possible to make great strides in the development of Loesche mills during

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I Making vertical strides
by M Keyssner (Dipl-Ing), Due to Asian cement manufacturers’ willingness to innovate, it has been
Loesche GmbH, Germany possible to make great strides in the development of Loesche mills during
the last 20 years. Powered by the continually increasing Asian requirement
for cement, the cooperation between customers in this part of the world
and Loesche GmbH in Düsseldorf, Germany, has enabled the development
of various concepts to increase the effective and cost-efficient production
of cement raw meal (CRM) and clinker/slag (C/S) in vertical mills (see
Figure 1).
Figure 1: world map with special innovations on Loesche mills of 750tph. This capacity was necessary
in order to realize the customer’s
requirement for a single large vertical mill
to feed a 7000tpd kiln (one-kiln-one-
mill system), instead of the usual parallel
arrangement involving two smaller mills.
This concept reduced the cost of the raw
material transport, the mill foundations,
the steel structure, the mechanical and
electrical equipment installation and
the maintenance by a double-digit
percentage (see Figure 2).
This, at the time, largest vertical mill in
the world was successfully commissioned
in 1998. The successful innovation
convinced customers in other parts of
the world to follow the trend and thus
in 2000 and again in 2005 two further
Figure 2: Loesche mill LM 63.4
ollowing the introduction of a mills of this type, now with larger rollers
Loesche LM 43.4 (4.3m table to increase the production rate to 840tph
diameter, four conical rollers CRM (related to 15 per cent R0.090)
and throughput of 425tph related to were installed in Argentina and Turkey.
medium grade limestone) to Greece for Motivated by the positive experience
CRM grinding during the early 1970s, with large vertical mills, it was again
a demand for large mills was not to be the Asian sector that first demonstrated
found in Europe. interest in installing single mills to feed
Only the strong economic growth kilns of more than 10,000tpd. Taking an
in Asia and the willingness to use new average operational time of 20h/d and
technology to optimise the grinding poor CRM grindability, the mill must have
plants made it possible to develop, line) to cover the CRM requirements of a nominal capacity of 1000tph.
install and commission mills with higher their huge rotary kilns. In order to meet the customer’s
capacities. Of particular note here were, Confidence in Loesche’s proven demand for high reliability with this
between 1981 and 1994, the Loesche technology, especially that related to the single-mill system, Loesche developed a
mills of size: construction of large mills, led in 1994 to “redundancy concept”. This allows, for
• LM 50.4 with a table diameter of 5m, the decision of one of the largest cement instance, in the event of damage to a
an increased capacity of over 500tph producers in Thailand
(CRM) and installed power of 4100kW to order an even larger Figure 3: Loesche-module-system
• LM 56.4 with a table diameter of 5.6m, Loesche mill.
a production rate of ca.40 per cent more This mill, an LM 63.4
than that of the LM 43.4 and an installed with a table diameter
power of 4400kW. of 6.3m and installed
Mills of this size were primarily installed power of 5400kW has
in Thailand in a parallel-concept (double- a nominal throughput
roller, that the mill still produces sufficient Figure 4: roller module of Loesche mill Figure 5: Loesche mills with two-, three- four-
and six-rollers of identical size
product to keep the kiln adequately fed
and avoid a total stoppage of the plant.
The problem was solved by the
development of a six-roller Loesche mill.
Instead of increasing the size of the four
normal rollers, Loesche decided within the
framework of their patented, 30-year-old
modular system of mill design, to use
existing rollers and increase the quantity - depending on capacity requirements – in
from four to six (see Figure 3). the past (Figure 5 shows Loesche mills
This arrangement allows an with two- three- four- and six-rollers of
improvement in the throughput during identical size). Grinding roller modules of
partial-load operation of the mill, when different sizes have been in use for many
four of the six rollers are working. With years, and have repeatedly delivered
a four-roller mill, only two of the rollers proof of the operational reliability of their
can operate under these conditions. In a design.
three-roller arrangement no compromise The newly developed six-roller Loesche
can be made due to the imbalanced roller mills are equipped with these proven
loads subsequently acting on the mill modules. A comparison of the roller
gearbox, so that the mill and possibly also system and pressed onto the grinding masses and guide systems of a four-roller
the kiln must be stopped. bed with a hydraulic cylinder in order to mill with those of a six-roller mill with the
The prerequisite for the development of generate the required grinding force. The same capacity reveals that the individual
the six-roller Loesche mill was the proven advantage of individual grinding rollers roller module in the latter weighs around
Loesche modular system (Figure 4 shows guided in rocker arms is that there is no 40 per cent less. A comparison of roller
the roller module of Loesche mill) need for an additional support frame mass between four- and six-roller mill
Each grinding roller is individually in the grinding area to ensure sufficient is shown in Figure 6. This has a positive
guided and carried in its own rocker arm stability and prevent the rollers from impact on the vibration of the mill during
toppling over or operation and also allows the installation
being derailed on of mill foundations that weigh around
the grinding track. 10 per cent less. Component handling in
This individual maintenance and repair work is also safer
support and and easier because the individual elements
bearing system are lighter.
for each grinding Since the beginning of 2006, six of
roller has also these newly developed large Loesche
enabled Loesche mills with a table diameter of 6.9m have
to supply mills been ordered by Asian cement factory
with a two-, operators. Commissioning is scheduled
three- or four- from 2007 onwards.
Figure 6: comparison of roller mass between
four- and six-roller mill roller arrangement Customers from Asia have shown
similar readiness to adopt innovations in
Figure 7: working principle of support and master roller the area of clinker and slag grinding.
As early as 1993, the first LM 46.2+2
CS was ordered by Lucky Cement
Corporation in Taiwan for grinding
OPC (138tph; 3300cm²/g). Taking the
advantages of the modular system as a
platform, Loesche developed a grinding
concept to meet the finer grinding
requirements of OPC and clinker. To
stabilise the grinding bed, two support
rollers were arranged between the two
master rollers instead of two standard
rollers in a four-roller mill. This makes
the mill run much more quietly and
significantly reduces the dynamic load
on the individual components during
operation (Figure 7 shows the working
principle of support and master roller). Figure 10: Loesche mill for coal grinding
In subsequent years, a large number
of mills of this size for capacities of up to
130tph of OPC (3300cm²/g) and up to
110tph of slag (4200cm²/g) were installed
in different Asian countries. For higher
production levels, the LM 56.2+2 CS
was developed on the basis of the 2+2
concept and using proven CRM grinding
modules. Mills of this size have been
installed in a number of cement factories
in Asia and achieve throughput rates of
more than 170tph of OPC or 220tph of
PPC (with up to 30 per cent fly ash) or
135tph of slag.
The demand for even higher grinding
performance and Orrisa the Asian continent content of up to 40 per cent. This results
Cement Ltd.’s willingness Figure 8: Loesche mill LM 56.3+3 CS Figure 9 shows in high rates of wear. To fire kiln lines
to innovate led in 2003 references of Loesche with a capacity of 8000 to 10,000tpd
to the decision to put clinker/slag mills in with this Indian coal, Loesche developed
the world’s largest Asia. new four-roller coal grinding mills with
vertical clinker and slag Customers from a nominal capacity (based on hard coal
grinding mill in place at Asia have also played and a fineness of 15 per cent R0.09) of
the company’s factory in a considerable part approximately 200tph with an installed
Rajgangpur, India, where in the development power of up to 1450kW. There was no
two LM 46.2+2 CS of large vertical mills development risk with this new vertical
mills had already been for coal grinding. coal grinding mill – the largest in the
in operation for many For many years world – because the roller modules used
years. now, pressure- had already been in successful practical
Here too, Loesche’s proof Loesche mills use in two- and three-roller coal grinding
experience in developing with two or three mills for many years. In 2006, Grasim
large mills with the grinding rollers have Industries Ltd, India ordered three type
modular system was been successfully in LM 43.4D mills for use in different
used to good effect. Instead of increasing operation in that region. A Loesche mill factories in India. The advantages of
the size of the grinding rollers, which for coal grinding is shown in Figure 10. these large coal grinding mills include
would result in increased individual masses The use of lignite with a high moisture lower investment cost and space savings
and higher dynamic loads, the number of content as a fuel for the rotary kilns in compared with lower-capacity double-
rollers was increased for the new, larger cement factories, with the associated line mills. These coal grinding mills are
mill. The new 3+3 arrangement with need for dry-grinding, led in the 1990s to scheduled for commissioning in 2007.
rollers two module sizes smaller than the development of mills with a nominal
those of the LM 56.2+2 CS resulted in a capacity of over 100tph and installed Outlook:
performance increase of over 20 per cent power of up to 800kW. To be able to meet the constantly
with the same table diameter. This LM Large Loesche coal grinding mills were increasing demand for cement in Asia
56.3+3 CS was commissioned in 2005 also needed for the anthracite used in effectively and cost-efficiently, local
(Figure 8: Loesche mill LM 56.3+3 CS). some cement factories in Vietnam, since cement factory operators have been
A total of 19 mills of this size have now the grindability is poor and the coal has willing to support and to use innovations
been ordered worldwide, 14 of them for to be ground finer to achieve complete in the area of large vertical mills.
combustion. Grinding mills of Experience with the operation of these
Figure 9: references of Loesche clinker/slag mills in Asia type LM 35.3D with a table large systems has confirmed that this was
diameter of 3.5m and installed the right approach and the right design,
power of up to 1250kW are and has strengthened the operators’
used here to grind over 40tph confidence in large mill technology based
of anthracite to a fineness of on Loesche’s proven modular concept.
one to two per cent R0.09. Good collaborative relationships
Special requirements are between the mill operators and builders
placed on coal grinding plants will continue to produce further
by cement factory operators innovations in the future, reducing
in India. They often use the production costs for construction
Indian coal, which has an ash materials. __________________________ I

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