Water and energy are precious resources and without them life would not be as we know it today.

1. Standalone
Vertical Roller Mills
without
Hot Gas Generator

2. OPTIMISED GRINDING
I Standalone VRMs without HGG
by Dr Daniel Strohmeyer, Water and energy are precious resources and without them life would not
Loesche GmbH, Germany be as we know it today. Both commodities will become more expensive
and scarcer in the future. Consequently, saving energy and water is
essential for ecologically- and economically-viable production, particularly
in the cement industry.
F
or vertical roller mills (VRM), water
injection on the grinding table is a Figure 1: Loesche vertical roller mill for cement grinding
common way to stabilise the grinding – material flow, feed materials and products
bed and gives a smoother mill operation
with lower vibration levels. However,
there are some drawbacks to water use
in a VRM. The feed moisture for OPC is
commonly very low and in case water is
added to the grinding process it has to
be evaporated requiring thermal energy.
If cooler exhaust gases are available in a
cement plant this will not pose a major
problem, but for a standalone grinding
this source of hot gases is not available to
drive-off any additional water. In this case
a hot gas generator is needed to dry the
material and to provide sufficient energy
for the grinding system. This solution not
only wastes fuel, it also creates further
expenses.
In some parts of the world the cement what is the centre of the rotating grinding the grinding table. Lumps, which escape
industry is not permitted to utilise water table. The product is then driven outwards the rollers and are too heavy to rise with
or its use is limited. Loesche has been by centrifugal forces, underneath the the gas flow drop through the louvre ring
working on a system that can provide rollers where the grinding takes place. to a reject system and are then fed back
grinding without the need for any water Ground material moves over the dam via the reject system.
injection. Even if some water is available ring and goes up with the gas flow to the Raw mills or coal mills operate using
the main aim is a grinding system that can classifier. The material has either reached the same size of rollers. What is particular
be run without the need for permanent the required fineness and leaves the mill for Loesche cement mills is the 2+2 or
operation of a hot gas generator. towards the bag filter or is sent back for 3+3 system, which features a combination
further grinding, via the grid cone onto of different sizes of rollers. In cement
VRMs
A vertical roller mill can process many Figure 2: grinding plant flowsheet
materials such as clinker, slag, gypsum,
fly ash or limestone to produce various
cement types of various finesse. The mill
is part of a process that begins at the
quarry. Only after the initial material has
been through the raw material grinding,
preheater, kiln and the cooler it reaches
the finish mill where additives are added
and the final product is obtained. Both
Loesche and its customers are essentially
concerned with this final product and
its properties which are influenced by all
stages of the cement making process.
Material enters the VRM via a rotary
feeder that poses as an air lock (see Figure
1), then moves down the feed chute to
INTERNATIONAL CEMENT REVIEW JUNE 2011

3. OPTIMISED GRINDING
Figure 3: assumed grindability for Ambuja Cement´s Dadri and Nalagarh projects
A system fan provides the draft through
the machine and different sources of
hot gases can be utilized if required.
Furthermore a wide range of feed
materials are tolerated and conveyed to
the mill via the feeding system.
Ambuja Cement’s Dadri and
Nalagarh grinding stations
In 2007, Loesche received an enquiry
for two grinding stations in India. Both
would have a cement capacity of 1.6Mta
and each would be supplied with a
Loesche VRM with 250tph of grinding
capacity. The Dadri project is situated
near New Delhi and the Nalagarh mill
mills, Loesche has a ‘S’ support roller and internal friction within the material layer is located further to the north, close to
a ‘M’ master roller. The ‘S’ roller is solely making it difficult to efficiently apply the the Himalayas. It became apparent that
to prepare and stabilise the grinding bed. grinding forces. So the ‘S’ roller removes the grinding stations would need to be
The most difficult thing to achieve when the air from the grinding bed and operated without a hot gas generator
producing cement is to keep the grinding prepares the material for the master roller and consequently water injection for
bed stable. In comparison to raw material to carry out the grinding. the purpose of grinding bed stabilisation
grinding, with cement milling there are The flowsheet for a grinding system was not permitted. Loesche looked at
more fines and some parts of the grinding with a VRM (see Figure 2) shows that, the customer’s requirements before
bed tend to become partly fluidised, after the classifier, product is precipitated deciding on the best solution. The main
caused by entrapped air. This reduces the and then recovered from the bag filter. constituents to be ground were clinker, fly
Ambuja Cement‘s grinding station Nalagarh, India
JUNE 2011 INTERNATIONAL CEMENT REVIEW

4. OPTIMISED GRINDING OPTIMISED GRINDING
Figure 3: assumed grindability for Ambuja Cement´s Dadri and Nalagarh projects
A system fan provides the draft through
Table 1: key data for Dadri and Nalagarh Table 2: Dadri performance different sources of
the machine and data
grinding stations hot gases can be utilized if required.
Dadri Furthermore a wide range of feed
PPC
PPC capacity (tph) 250 LM 56.3+3 materials are tolerated and conveyed to
Guarantee Achieved
Gearbox power (kW) 5400 (Flender) the mill via the feeding system.
Classifier LSKS 102 CS (kW) 560 Mill throughput (tph) 250 253
Fan motor power (kW) 3000 Fineness Ambuja Cement’s Dadri and
4000 3920
Mill diameter (m) 13.5 Feed moisture (%) Nalagarh grinding stations – 1.1
Height (m) 20 Product moisture (%) 2007, Loesche received an enquiry
In – 0.3
Grinding table diameter (m)  5.6 Specific power consumption grinding stations in India. Both
for two (kWh/t) 30.75 25.60
Grinding table weight (t) 109 (mill, fan, classifier, aux) have a cement capacity of 1.6Mta
would
Master roller (mm) 3 x2450 and each would be supplied with a
Support roller (mm) 3 x 1600 Loesche VRM with 250tph of grinding
capacity. The Dadri project is situated
ash or clinker sources would be sourced.
near New Delhi and had Nalagarh mill
Therefore, Loesche the to assume a
mills, and gypsum (up to five per cent) all
ash Loesche has a ‘S’ support roller and internal friction within theto carry out a
Standard procedure is material layer iscertain ‘grindability the north, close to
located further to factor‘ and specific
aof which have different‘S’ roller is solely
‘M’ master roller. The physical properties making it test to establish a proper sizing
grinding difficult to efficiently apply the the Himalayas. It becamethe feed mix (see
power consumption for apparent that
to prepareleading to different grindabilities
basically and stabilise the grinding bed. grinding mill andSo the ‘S’ box. However,
for the forces. the gear roller removes the grinding stations would need to be
Figure 3). The assumptions were based
The most difficultindividualachieve when
and a particular thing to behaviour the the from theboth of the projects it
at air start of grinding bed and operated without a hot gas generator
on Loesche’s experience and knowledge
producing cement is to keep the grinding
inside the mill. was not known where the different fly
prepares the material for the master roller and other fly ash cement injection for
of consequently water grinding plants
bed stable. In comparison to raw material to carry out the grinding. the purpose of grinding bed concluded
operating in India. Loesche stabilisation
grinding, with cement milling there are The flowsheet for a grinding system was notwould need Loesche looked at
that it permitted. a 56.3+3 mill with
more fines and some parts of the grinding with a VRM (see Figure 2) shows that, thetable diameter of 5.6m. The selected
a customer’s requirements before
bed tend to become partly fluidised, after the classifier, product is precipitated deciding on the best solution. The main
Flender gear box would have a power
caused by entrapped air. This reduces the and then recovered from the bag filter. constituents toof 5400kW,were clinker, fly
consumption be ground a Loesche
dynamic classifier LSKS 102CS and a fan
motor of 3000kW would form the other
main parts of the system (see Table 1).
Loesche’s scope of supply for the
two Indian projects was not for the
whole grinding plants, but for the mills,
classifiers, sampling stations and the air
slides for the product transport. Loesche’s
product targets were PPC of 4000Blaine
at 250tph using a specific power
consumption of 30.75kWh/t for all the
Loesche equipment and the fan supply
Figure 4: erection of gear box (see Table 2).
The PPC product would consist of 60
per cent clinker, five per cent gypsum and
35 per cent fly ash (2500 Blaine). If the
plant receives clinker that is high in C3S
then the fly ash content can be increased
to the maximum permissible according to
Indian standards. If the clinker exhibits a
low C3S value, the plant can increase the
clinker content and reduce the amount
of fly ash to obtain the same required
cement strength development.
Construction of the mill foundation
and the base frame. This is followed by
the erection of the pedestals, which are
a critical part of the construction phase
as correct alignment is essential. The
mill gear box is mounted by applying an
orange ‘Chockfast’ (see Figure 4) which
provides good connection of the gear box
Figure 5: height of Loesche LM 56.3+3 when installed base plate and the foundation. The mill
INTERNATIONAL CEMENT REVIEW JUNE 2011 JUNE 2011 INTERNATIONAL CEMENT REVIEW

5. OPTIMISED GRINDING
OPTIMISED GRINDING
housing is preassembled on the ground
along with the classifier, before being
lifted into place.
The fly ash feeding system (see Figure
6) conveys design feeds dry fly ash
directly to the classifier as part of the fly
ash already has product fineness and does
not need to be ground. Due to that, the
capacity of the mill is increased. In the
two Indian grinding stations, the fly ash
is fed to the machine via two air slides.
However, other setups allow for at least
four inlets giving a more even distribution
of the fly ash over the circumference of
the classifier.
Summary
Loesche received the order for the two Figure 6: gypsum and fly ash feed system to the mill
grinding systems in April 2007 and the
FOB delivery was in November 2008. Figure 7: Nalagarh grinding plant
Erection started in December 2008 and
commissioning commenced in December
2009 with the first feed in February 2010.
By April 2010, 250tph of PPC had been
reached and in September 2010 further
optimisation was done leading to a stable
mill operation without any water injection
for grinding bed stabilisation.
As a result no hot gas generator
was required. The specific power
consumption achieved was 5kWh lower
than expected. That was in part due
to the easier-to-grind clinker and fly
ash compared to the assumed values,
both of which had an impact on the
grindability of the feed mix and the
related specific energy consumption.
______________________________ I
LOESCHE Mill Type LM 56.3+3, Nalagarh, India
Loesche GmbH
Hansaallee 243
40549 Düsseldorf
Tel. +49 - 211 - 53 53 - 0
Fax +49 - 211 - 53 53 - 500
E-Mail: loesche@loesche.de
www.loesche.com
JUNE 2011 INTERNATIONAL CEMENT REVIEW