Analysis of Various Cement grinding Systems with Respect to Power Consumption keeping same quality Parameters

1. 1
GRINDING SYSTEM ANALYSIS & ITS EFFECT ON POWER CONSUMPTION
Project Report on
“ANALYSIS OF VARIOUS GRINDING SYSTEMS WITH
RESPECT TO POWER CONSUMPTION KEEPING SAME
QUALITY PARAMETERS”
MM ZG628T: Dissertation
By
Karan Walia
2014HT79520
Dissertation work carried out at
Colleagues Consultants Pvt. Ltd., Gurgaon
BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE
PILANI (RAJASTHAN)
November 2016

2. 2
GRINDING SYSTEM ANALYSIS & ITS EFFECT ON POWER CONSUMPTION
“ANALYSIS OF VARIOUS GRINDING SYSTEMS WITH
RESPECT TO POWER CONSUMPTION KEEPING SAME
QUALITY PARAMETERS”
MM ZG628T: Dissertation
by
Karan Walia
2014HT79520
Dissertation work carried out at
Colleagues Consultants Pvt. Ltd., Gurgaon
Submitted in partial fulfillment of M.Tech Manufacturing Management
degree programme
Under the Supervision of
Siddhartha Kumar, VP (Process & Services)
Colleagues Consultants Pvt. Ltd.,
BIRLA INSTITUTE OF TECHNOLOGY & SCIENCE
PILANI (RAJASTHAN)
November, 2016

3. 3
GRINDING SYSTEM ANALYSIS & ITS EFFECT ON POWER CONSUMPTION
November, 2016
CERTIFICATE
This is to certify that the Dissertation entitled “Analysis of Various
Grinding System with respect to power consumption keeping same
quality parameters” submitted by Karan Walia having ID-No.
2014HT79520 for the partial fulfillment of the requirements of M.Tech.in
Manufacturing Management degree of BITS embodies the bonafide work
done by him/her under my supervision.
Place: Gurgaon
Date: 14-10-16
Signature of the Supervisor
Mr. Siddhartha Kumar-VP (Process & Services)

4. 4
Abstract
Birla Institute of Technology & Science, Pilani
Work-Integrated Learning Programmes Division
First Semester 2016-2017
MM ZG628T: Dissertation
ABSTRACT
BITS ID No. : 2014HT79520
NAME OF THE STUDENT : Karan Walia
EMAIL ADDRESS : walia.karan@rocketmail.com
STUDENT’S EMPLOYING : Colleagues Consultants Pvt. Ltd., Gurgaon
ORGANIZATION & LOCATION
SUPERVISOR’S NAME : Siddhartha Kumar
SUPERVISOR’S EMPLOYING : Colleagues Consultants Pvt. Ltd., Gurgaon
ORGANIZATION & LOCATION
SUPERVISOR’S EMAIL ADDRESS: Sid@colleagues.co.in
DISSERTATION TITLE : Analysis of grinding system with respect to
power consumption keeping same quality parameters.
Signature of the Student Signature of the Supervisor
Name: Karan Walia Name-Siddhartha Kumar
Date-14/10/16 Date-14/10/16
Place-Gurgaon Place: Gurgaon

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BITS ID No. : 2014HT79520
NAME OF THE STUDENT : Karan Walia
SUPERVISOR’S NAME : Siddhartha Kumar
DISSERTATION TITLE : Analysis of grinding system with respect to
power consumption keeping same quality parameters.
Abstract-Cement Sub-sector consumes 12-15 % of total industrial energy
use. With grinding section being the largest consumer of energy in cement
industry .Therefore, a state of the art review of energy consumption in
cement sector was needed. This study compiled a Comprehensive &
Calculative approach on industrial power demand (cement grinding section)
as a thesis topic. The most commonly used grinding systems for cement
production have been discussed in brief.
Broad Academic Area of Work: Mechanical Technology
Keywords- Grinding systems, Ball Mill (BM), Vertical Roller mill (VRM), Roller
press (RP), Blaine (cm2/g), Tonnes per hour (TPH), Ordinary Portland
Cement (OPC)
Name-Karan Walia
Date: 14/10/16
Place: Gurgaon

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GRINDING SYSTEM ANALYSIS & ITS EFFECT ON POWER CONSUMPTION
ACKNOWLEDGEMENT
Words are only representations of our regards and gratitude that we have
towards our actions and their inherent associations. As a matter of fact,
without cooperation no thought could be coined into real action. Consistent
motivation and invaluable support throughout any project is an issue that
cannot be quantitatively measured. These acknowledgments are only a
fraction of regards towards their gestures.
My Sincere Thanks to Mr. Siddhartha Kumar, VP (process & services),
Colleagues Consultants Pvt. Ltd. for his cooperation & operational
support throughout my project.
I would like to thank the entire team of draughtsman, project engineers of
Colleagues Consultants Pvt. Limited, Gurgaon for their assistance
throughout my project.

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Contents
Page No.
Abstract 4
Acknowledgement 5
1. Chapter-1 Introduction 9
1.1. Background 9
1.2. General 10
1.3. From Raw Material to cement 11
2. Chapter-2 Objective 12
2.1. Theory Basis 13
3. Chapter-3 Cement Grinding Technologies 14
3.1. Ball Mill System(BM System) 15
3.2. Vertical Roller System(VRM System) 17
3.3. Roller press System-Comflex System(RP in finish mode) 18
3.4. Classification system-Separators 19
3.4.1.Circulating load 20
3.4.2.Calculation of Circulating load 20
3.4.3.Separator Efficiency 20
4. Chapter-4 Analysis of Grinding System-Communition theories22
4.1. Types of Grinding process 24
4.1.1.Closed Circuit Ball Mill System 25
4.1.2.Vertical Roller Mill System(VRM) 28
4.1.3.Roller Press System(Finish Mode) 32
5. Chapter-5 Technical Evaluation of Grinding system 36
6. Chapter-6 Conclusions & recommendations 37
6.1. Maintenance of wear parts 38
6.2. Grinding power comparison 39
6.3. Process Concepts 39
7. Chapter-7 Case Study 40
8. Chapter-8 Bibliography 42
Figures
1. Figure 1. -Lafarge Cement-Value Added Cement (Fibre Reinforced
Cement) Executed by CCPL
2. Figure 2. Reaction chart of a Cement Plant
3. Figure 3. Process Flow chart of a Cement Plant
4. Figure 4. Main Clinker Phases
5. Figure 5. Average Chemical Composition of OPC
6. Figure 6: Ball Mill System
7. Figure 7: Ball Mill operation
8. Figure 8: Vertical Roller Mill
9. Figure 9: Recirculation factor Vs Efficiency of a Separator

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10. Figure 10: Separator
11. Figure 11: Recirculation factor Vs Efficiency of a Separator
12. Figure 12: Zeisel Test Result
13. Figure 13: Machine for Bond Index Determination
14. Figure 14: Typical Flow Sheet of a Ball Mill Grinding Circuit in a Cement
Plant
15. Figure 15: Typical Flow Sheet of a VRM Grinding Circuit in a Cement
Plant
16. Figure 16: Different Roller Configuration
17. Figure 17: Typical Flow Sheet of a RP Grinding Circuit in a Cement Plant
18. Figure 18: Roller Press Working
19. Figure 19: Block Diagram of Roller Press Circuit in Finish Mode
20. Figure 20: Grinding Power Diagram
Tables
1. Table 1: Zeisel Test Result
2. Table 2: Bond Work Index of various materials
3. Table 3: Bond Work Index Method Calculations
4. Table 4: Parameters for VRM Calculations
5. Table 5: Torque factor-Supplier Specific
6. Table 6: Data Available from VRM Supplier
7. Table 7: Roller Press Calculation
8. Table 8: Technical Evaluation of Grinding System
9. Table 9: Bar Chart for Power Comparison
10. Table 10: Case Study @ 150 TPH
Abbreviations
TPH-Tonnes per hour
Blaine(Specific Surface)- Specific surface is expressed as the total
surface area in square centimeters of all the cement particles in one gram of
cement usually expressed as cm2/g.
VRM-Vertical Roller Mill
RP-Roller Press
µ-Micron
mmmm- Torque factor

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1. Chapter -1 Introduction
Cement is a bonding material, vital for a country’s economy like steel, oil &
gas. With technological advancement there is growing demand for finding
better & efficient ways of production. In this context, this literature serves
as a guiding document to choose an efficient grinding system in cement
sector with respect to power consumption in today’s industrial world.
1.1 Background
Colleagues Consultants is a team of dynamic professionals involved in
design, engineering & consultancy of Cement & Coal Handling plants.
However, with course of time Colleagues has ventured into solar & other
engineering field.
Credentials of Colleagues include feasibility studies, conceptual design
preparation as well as complete project execution related to Cement & other
allied industries.
Figure 1.
Lafarge Cement-Value Added Cement (Fibre Reinforced Cement) Executed by
CCPL

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Colleagues strive to continue to provide the highest level of service to both
their working Principals and to their customers relating to:-
Project Engineering & review;
Design Engineering, Project Execution;
Testing & Commissioning Services;
Technical Audits-Environmental & process.
Colleagues Consultants Provides for the Client:-
Strong Consulting Expertise;
Highly qualified and experienced technocrats;
Skilled service team for design, engineering support;
Supply & Erection Support (site supervision).
1.2 General
When limestone, which is composed mainly of calcium carbonate CaCO₃, is
heated to temperatures above 700-800 °C, it will decompose into gaseous
carbon dioxide and solid calcium oxide or burnt lime (CaO), according to the
process. Burnt lime slaked with water will harden when left under
atmospheric conditions by absorbing and thereby reversing the above
process. Slaked lime mixed with sand and used, as a mortar between
building bricks has been known since antiquity.
CaCO₃+ ∆t CaO + CO₂
If a small percentage of clay is burnt together with the limestone, a
different type of binder will develop which will hydrate and harden due to
the direct influence of water. This is the hydraulic building material, which
we know and use today under the name of Cement.
The Romans already more than 2,000 years ago knew cement making, but
the knowledge was lost with the fall of their empire. It was not until the
19th century, starting with the British bricklayer John Aspdin's patent in
1824, that manufacturing of cement was taken up again as an industry.
Cement was originally manufactured in vertical shaft kilns and it was not
until the invention of the rotary kiln and the tube mill that large-scale
industrial exploitation became possible.

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Cement is mainly used in the form of concrete, i.e. cement to which is
added sand or stones as filler during casting. Concrete has high
compression strength but must be rein-forced with iron bars or similar
reinforcements to obtain acceptable tensile strength.
1.3 From Raw Material to Cement
Cement is manufactured from 75-80% limestone and 20-25% clay, or from
raw materials containing the same chemical constituents. The raw materials
are quarried and crushed after which they are mixed in the correct
proportions. The raw mix is then ground in a raw mill and subsequently
burned in a rotary kiln at a temperature around 1,450°C. During the burning
process, the raw materials will undergo a number of very complex chemical
Reactions and will eventually leave the kiln as cement clinker, i.e.
agglomerates of clinker minerals.
The final product - cement - is obtained by grinding the clinker to a fine
powder, in a cement mill together with some 3-5% of gypsum. The gypsum
is a necessary additive in order to retard the setting time of cement.
Without the addition of gypsum, the cement would harden immediately with
the addition of water.
Figure 2: Reaction chart of a cement Plant

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Figure 3. Process Flow chart of a Cement Plant
2. Chapter -2 Objective
The objective of this thesis is to compare different grinding system mainly:-
Ball Mill System(BM System)
Vertical Roller Mill System(VRM)
Roller Press system-Comflex System (RP in finish mode)
with respect to their efficiency in terms of specific power consumption
(kWh/ton) in grinding. Normal Ordinary Portland cement (OPC) @ 3000
Blaine (cm²/g) & 80 Tonnes per hour (TPH) of grinding circuits have been
selected for experimental study.
95%
5%
OrdinaryPortland Cement
Clinker
Gypsum
Pie Chart of OPC

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2.1 Theory Basis
Ordinary Portland Cement (OPC) is the most commonly used cement. This
hydraulic binder was named after the island “Portland” in Great Britain and
was patented by Joseph Aspdin in 1824. Joseph Aspdin gave that name
because the color of the produced cement was the same as the color of the
Portland stone (oolitic limestone) which was commonly used for buildings in
this area. Aspdin crushed a hard limestone and calcined it, and mixed the
lime with clay. He then applied wet grinding to that raw mix, and calcined
the ground component in a kiln, CO₂ was expelled. At the end, main
component of cement was obtained, and called “clinker” which was ground
to get a powdered material, cement.
Figure 4. Main Clinker Phases (courtesy-Stark & Wicht, 2000)
The chemical composition of Ordinary Portland Cement Clinker varies
considerably because it depends upon chemical & mineralogical composition
of the used raw material & combustibles.
The average chemical composition, as illustrated in fig. 5, shows that main
component are CaO & SIO₂ & secondarily are Al₂O₃ & Fe₂O₃.

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Figure 5. Average Chemical Composition of OPC
3. Chapter -3 Cement Grinding Technologies
Cement is an energy intensive field, with average power consumption of a
full fledged cement plant ranging from 90-120 kWh/ton and around 85% of
energy demand being spent on grinding process. Finish grinding process is
one of the basic technical operations of cement production as well as the
concluding process. Present-day design criteria for grinding is cement
fineness, as a rule of specific surface, expressed in cm2
/g, and the residue
on the 25 micron mesh (sieve). Whereas the former stipulates the average
surface, the latter gives a point on the granulometric curve. The two
combined give an idea of the particle size distribution, since for identical 25
micron residues a high specific surface implies large amount of fines and a
flat granulometric curve, while a low specific surface indicates larger
particles and a steeper curve. The ultimate criterion for Cement is the
concrete strength. Strength development is the result of hydration of
particles. The smaller the particles the larger the specific surface & faster
the hydration.
It is useless to grind cement to large specific area, but the ground surface
must obey certain laws relative to particle size distribution. The particle size

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fraction from 3µ to 30µ is conducive to strength development of the
Cement. The particle size fraction below 3µ contributes to initial strength.
This particle fraction hydrates faster & after one day result in higher
compressive & flexural strengths. The fraction above 60µ hydrates slowly &
contributes little to the strength of cement.
Cement Mill Design Considerations:-
• Material Grind ability-dependent upon physical properties,
composition, moisture content, particle shape etc.
• Grinding process-Communition, drying, handling & wear behavior of
fed material.
• Feed Size
• Moisture Content
• Product Fineness
3.1 Ball Mill System
Figure 6: Ball Mill System
Principle
Ball or tube mills are horizontally rotating steel cylinders where size
reduction of mill feed is performed by the motion of grinding media.
Rotation of mill cylinder raises the pile of mill feed & grinding media to the
height of grinding operation. Grinding is performed by impact & friction
between grinding balls, which hit against each other, as well as between the
grinding media & mill lining. Experimental study is carried out on ball mill in

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Closed circuit (with material recirculation) with product output of 80 TPH
@3000 Blaine (cm²/g).
Working
There are two compartments divided by a diaphragm. First compartment is
30-33% of the overall length, & lifting liners with a ball charge from 50 mm
to 90 mm are employed for size reduction. Then material pass into the
second compartment when the size are less than 2-3mm, & grinding
operation is applied with 15 to 50 mm sized balls or cylpebs in the second
compartment. Cascading and cataracting are the main grinding actions in
the ball mill process. When lifted media fall on to the particles, impact and
percussion forces reduce the sizes, and that action is known as cataracting.
Another motion is the cascading which grinds particles by flowing and rolling
rather than falling. Compression and shear forces are effective at cascading
motion. Those motions are used at different zones in the mill. Cataracting is
more effective at first compartment where the coarser particles are broken,
and cascading is used at second compartment to pulverize particles.
Ball mills normally operate about 75% of critical speed (the speed at which
centrifugal force will just hold charge to the shell during rotation), and 25-
35% volumetric charge loading. Circulating load is generally 200-300% with
mechanical separators and 150-200% with high efficiency separators.
Friction between the particles, grinding elements and liners is converted into
heat, noise and electrostatic charge. Moreover, elastic and plastic
deformations of materials and elements, and formation of particle
agglomerations also cause losses.
Figure 7: Ball Mill Operation

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3.2 Vertical Roller Mill System
Figure 8: Vertical Roller Mill
Principle
The working principle of Roller mills is based on two to four grinding rollers
with shafts carried on hinged arm & riding on a horizontal grinding table.
Grinding pressure of the rollers upon the mill feed is affected hydro-
pneumatically. Communition is done by Compressive forces of the rollers
upon the material.
Working
The material (fresh feed, recirculating material and separator tailings)
passes from the table center under the rollers. The material is drawn in-
between roller and grinding track and is comminuted, depending on the
roller diameter, table speed, roller pressure and the material characteristics
(Granulometry and properties) a certain max. Particle size can be drawn
under the rollers (max. size = 5 to 8% of roller diameter). Higher bed
thicknesses require higher grinding pressures and thus absorb more power.
More power is also absorbed with increasing material moistures.

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The ability to form a stable grinding bed is essential for a stable mill
operation. Dam rings are often utilized for adjustment of the grinding bed
thickness. They serve as retention device for the material on the grinding
table. Experimental study is carried out on Vertical mill with 3 roller
arrangement with built-in separator at product output of 80 TPH @3000
Blaine (cm²/g).
3.3 Roller Press System (Comflex Grinding System-Finish
Grinding)
Principle
In recent years, new grinding processes have started to be used as an
alternative to the existing technology, the ball mill. One of the most
commons is the roller press (also defined as high pressure grinding rollers
(HPGR) in literature), which is also a relatively new comminution device that
offers less energy requirements and improved capacities. Comminution in
the roller press is the result of high interparticle stresses which are
generated by compressing a bed of solids between two pressurized rollers.
Finer particle amount after that interparticle stress is much higher than
conventional breaking and crushing techniques.
Roller press has a simple design and working principle. One of the roller
rotates on a fixed axis while the other roller is allowed to move linearly
towards or backwards from the fixed one according to the applied pressure
and pressed material dispersion. The moveable roller is forced to press
materials, which is placed in the gap between two rollers, by a hydraulic oil
cylinder system.
Working
The compressed material forms a cake and agglomerates after passing
between the rollers. Accordingly, disagglomeration is applied by generally V-
separator system, which is mainly a subsequent classifier.
It has a static configuration of stepped plates down which the materials
cascades through a cross flow of air.
General usage of roller press in cement grinding operations is as a pre-
grinding unit prior to conventional ball mill system. Accordingly, efficient

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energy usage of roller press and grinding ability of ball mill are combined to
get high reduction ratios with higher capacities. Roller press weakens the
particles by compression, and micro cracks are formed on the particles.
Therefore, bond index values of materials are reduced after passing through
the roller press, and less effort required at ball mill stage to pulverize the
materials. Increasing feeding rates and dropped specific consumptions
results 10-50% energy savings when compared with closed circuit ball mill
operations. With a pre-grinding operation, large ball charge can be replaced
with 20-25 mm balls at mill, and mill capacity is increased by 20%.
The most common circuits are pregrinding with slab recirculation, semi-
finish grinding & now days as finish grinding.
3.4 Classification System-Separators
Figure 9: Separator
The fineness & particle size distribution of the product leaving a cement
grinding system is of great importance to the cement quality. The target
given for these parameters is achieved by separators. Separation is
performed by mechanical air separators by the division of a given material
stream into two separate streams, using air as a carrying medium. Hereby
one stream should contain only fine particles and other as far as possible
coarse particles. To perform this function, the separator feed must be
evenly distributed inside the separator, & subjected to classifying forces
acting upon the various solid particles of different sizes. The
Main
Feeding
Coarse rejects
Fines
Re circulated
Air

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dispersion separator (also called the mechanical air separator) is the most
commonly used separator in the cement industry. Feed material is
introduced through a chute onto a distributor plate that disperses the
particles in the airflow. Air with dispersed particles flows up and passes the
rotating counter blades. Coarse particles are centrifuged out to the
surrounding wall and fall down into the tailings cone. Air with fines flows
through the fan to the fines chamber. Here the fine material is separated
from the conveying air and collected in the outer cone. Air together with
some amount of fine material is returned to the separating zone through air
vanes.
3.4.1 Circulating load
The Circulating load in closed circuit grinding is defined as the mass of
separator feed (A) divided by the mass of fine fractions (F), or:
Circulating Load U=A/F
The actual value of the circulating load depends on various factors, such as
mill design, grinding efficiency, product fineness, etc., but as a guide the
following values can be given:
Cement Mill Low Fineness u=1.5 to 2
High Fineness u>2
3.4.2 Calculation of Circulating load
If the mass flows of fines & feed (or rejects) are given. Most mills are
equipped with weigh feeders, so M is known, which is equal to F in steady
state operation.
If no weighing equipment for separator feed or rejects is installed, u must
be determined using particle size analysis data & formula (1), (2).
A=F + R (1)
A.a =F.f + R.r (2)
U=A/F
Using above two equations;
U= (f-r)/ (a-r)

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3.4.3 Separator Efficiency
Efficiency takes some account of size distribution, to the extent that it is
defined as the recovery of a feed size class (0 to x µm) into the fines
stream.
η (x) = F.f/ A. a 100 [%]
η (x) = f/u.a 100 [%]
If x is chosen as the maximum particle size present in the feed, η(x) is
equal to 1/u.
Figure 10: Recirculation factor Vs Efficiency of a Separator(Courtesy-Holcim
Guide)
Blaine –Residue Correspondence
Currently, Blaine-Residue Correspondence with respect to high efficiency
separator gave following reference:-
Blaine cm2/g Residue on 90µ
Close Circuit Basis 3000 0.5-1.5%

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4. Chapter -4 Analysis of Grinding System-Communition
Theories
Based on approximations & empirical findings are trying to explain/
describe the relationship b/w the process input & increase in material
fineness commonly known as “Communition laws”, out of which
bond theory is the most commonly used.
Most Common communition forces are: - Impact forces, compression
forces, inter-particle contact forces, friction-shear forces.
Material Grind ability
"Grind ability (kWh/T) is the measure of specific energy consumption
required to reduce a certain mass of material from a given fresh and initial
size up to a defined product size". The grind ability of a material is
dependent upon lot of factors. The Composition of clinker material & the
degree of curing has a bearing on the grind ability. Dusty clinker, often with
a high silica ratio, is easy to coarse-ground but requires high specific power
consumption for fine grinding. Hard-burnt clinker requires higher power
consumption for coarse grinding. Also, the lump size of the clinker feed
influences the grind ability. Therefore, we can say that Clinker grind ability
depends on its chemical composition and the conditions of burning and
cooling. We know that alite (C₃S) cracks much more easily than belite (C₂S),
then a clinker with a high lime saturation will have a better grind ability.
Sample Testing
Clinker Samples from NCC, Egypt were analyzed in a lab in Germany to
determine the grind ability of Clinker using Zeisel test (as per ASTM
D409 standards). Results of Zeisel Grind ability test as per lab report from
Germany is indicated herewith:-

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Figure 11: Zeisel Test Result
Table 1: Zeisel Test Result
Table 2: Standard Bond Work Index of various materials
Material Bauxite Clinker Clay Limestone Slag
Bond Work
Index
9.45 15 7.10 10.18 15.76
Grind ability basis-35.35kWh/t @ 3000 Blaine OPC (Closed Circuit ball mill
basis)
High grind ability can be attributed to hard burnt or over burnt clinker at
NCC, Plant. Usually grind ability is around 27-32 kWh/T @ 3000 Blaine OPC.
The test Report was Cross-verified using Bond’s Work-Index Method of grind
ability Calculation, which states that “energy input is directly proportional to
the new crack length developed by the communition process”.
The test developed by Fred C. Bond in 1952/1961 is widely used worldwide
for doing practical estimation of grinding power.
Specific Surface cm2/g 1500 2000 2500 3000 3500 4000
Specific Power(kWh/T) 13.88 18.95 25.89 35.37 48.31 65.99

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Figure 12: Machine for Bond Index Determination
Mill diameter 305 mm (12") and length 305 mm (12") with rounded corners
and a smooth internal lining is used in the laboratory.
The work index (Wi) is then calculated with the following formula:
where Pf = test sieve product in µ,
Gbp = the mill grind ability in gr/rev,
P80 = sieve with 80% of passing of the product and
F80 = sieve with 80% of passing of the feed.
4.1Types of grinding process
Figure 13: Typical Flow Sheet of a Ball Mill Grinding Circuit in a Cement Plant

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4.1.1 Closed Circuit Ball Mill System
Circuit Explanation
Clinker and gypsum will be ground in a ball mill, where steel balls are used
as grinding media. The discharge from mill will be lifted by a bucket elevator
and fed to a high efficiency separator. Fines from the separator will be
collected in the cyclones and further transported to the cement silo. The
coarse material from the separator shall be fed along with fresh feed to the
mill inlet for further grinding. Partial quantity of separator circulating air is
vented in a bag filter. For mill venting a bag filter or an ESP may be
installed. Fines collected in bag filter/ ESP will be transported to cement
storage silo by a system of air slides and bucket elevator.
Mathematical Analysis:-
Grind ability Calculation based on Clinker bond Work index of
15(Assumption),
Mill Size- ø4m X13m length (two compartment close circuit) (1)
Capacity (to be designed)-80 TPH @ 3000 Blaine (Close Circuit basis),
Mill Speed-16.1/0.2 Rpm, (2)
Ball charge (both compartment)-238 T, (3)
Volume loading- 30-33%, (4)
Grinding charge value of the 1st chamber,
Balls φ 80+40mm-117 Tonnes,
Grinding charge value of the 2nd chamber,
Balls φ 50+30mm
Balls φ 25+15mm-121 Tonnes,
• Feed -OPC
Clinker : 95%, bulk density-1.3kg/dm3
Gypsum: 5%, bulk density-1.25kg/dm3
Clinker Temperature: 100 ºC,
Clinker / gypsum feed: 80% < 30 mm
85% < 50mm
100 %< 80mm
Max. 80 mm
• Moisture: Clinker-0%
Gypsum-<5%
Data
Available
from
supplier

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Table 3: Bond Work Index Method Calculations
Grinding power Calculation @35.35 kWh/T @3000 cm²/g
35.35 X 80(kWh/T x T/H) =2828kW,
Taking 10% design margin, 2828x 1.1=3110 kW or 3200kW (Approx.)
The theoretical power consumption of a Ball Mill is Expressed by the DAWN
formulae:-
CALCULATION OF GRINDABILITY FROM BOND WORK INDEX - CLINKER
PLANT : NCC RUSSIAN MILLS-EGYPT
Grind ability = W*10*1.1023*((1/(P80)^0.5)-(1/(F80)^0.5))*F1*F2*F3*F4*F5*F6*F7
= 35.35 kWh/t @ 3000 Blaine at shaft
W = 15 Bond's work index from laboratory test
P80 = 40 Size in microns where 80% product passes
F80 = 50000 Size in microns where 80% feed passes
F1 = 1.3 Factor for wet or dry grinding - 1.0 for wet and 1.3 for dry
F2 = 1 Factor for open or closed circuit, 1.0 for close and 1.035 for open
F3 = 0.903 Factor for mill diameter
0.903 for mill dia. > 3.9 m Mill dia. = 400 cm
0.914 for mill dia. < 3.9 m
F4 = 1.080 Factor for coarseness of feed
1.080 for F80 > 4000
F5 = 1.098 Factor for Fine grinding
1.098 for P80< 70
F6 = 1 Factor for high efficiency separator
F7 = 1 Factor for mill type and lining type
N=0.2846 D • A • W • N [kW(net)]

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Where,
D=Internal Diameter of Mill (inside lining) (2X50mm lining both sides)
=3.9m
A= 1.073-J (where J= Fractional Volume loading (VL), here VL=30-33%)
W= Mill Charge in Tonnes
N=Mill Speed in RPM
Applying Above mentioned Formulae:-
From Eqns 1, 2, 3 & 4 We get,
N= 0.2846x 3.9 x (1.073-0.33) x 238 x 16.1
N=3160 kW or 3200 kW (Approx.)
Therefore, Mill design has been found satisfactory.

28. 28
4.1.2 Vertical Roller Mill System (VRM)
Figure 14: Typical Flow Sheet of a VRM Grinding Circuit in a Cement Plant
Circuit Explanation
It is envisaged that a VRM with inbuilt high efficiency separator will be
installed for cement grinding. The mix of clinker, gypsum is fed to the
grinding table fitted with hydraulically operated rollers, which apply
pressure on the material bed for grinding purpose. The ground material is
air swept to the high efficiency separator, where coarse materials fall back
on grinding table for further grinding. Fines from separator will be collected
in a bag filter. Fines collected in bag filter will be transported to cement
storage silo by a system of air slides and bucket elevator.
Depending on the supplier`s recommendation, grinding aid may be used to
stabilize the bed.
In order to maintain the required gas flow through mill nozzle ring, hot gas
may be required sometimes like during mill startup after long shutdown,

29. 29
also for removing moisture from gypsum. Moreover, if the input clinker is of
ambient temperature, to maintain the Temperature inside mill is usually
about 100 Deg ºC; continuous hot air will be required.
Mathematical Analysis:-
Calculation based on Vertical Roller Mill with 3 Grinding rollers & built in
separator.
Material Grind-ability - 35.35 kWh/T @3000 Blaine (Close Circuit ball mill
basis). For Converting to Vertical roller mill basis, a conversion factor of 1.6-
1.8 is used in cement industry purely based on experience.
35.35/1.6=22 kWh/T, 22.09375 X 80(kWh/T x T/H) =1760kW;
Taking 10% design margin, 1767.5x 1.1=1944.5 kW or 2000kW (Approx.)
• Feed -OPC
Clinker : 95%, bulk density-1.3kg/dm3
Gypsum: 5%, bulk density-1.25kg/dm3
Clinker Temperature: 100 ºC,
Clinker / gypsum feed: 80% < 30 mm,
85% < 50mm,
100 %< 80mm,
Max. 80 mm,
• Moisture: Clinker-0%
Gypsum-<5%
Figure 15: Different Roller Configuration

30. 30
Table 4: Parameters for VRM Calculations
Table 5: Torque factor-Supplier Specific
Cross checking-The theoretical power consumption of Vertical Roller Mill is
expressed by the formulae:-
Calculations of
Vertical Roller Mill
A Roller projected area, one roller [m2]
A nozzle Nozzle ring area [m2]
Do Grinding table diameter [m]
D cyI Hydraulic cylinder diameter [m]
Dm Grinding track diameter [m]
D piston Hydraulic piston diameter [m]
Droller Roller diameter [m]
F Grinding force [kN]
FH: Hydraulic grinding force [kN]
FR: Roller grinding force [kN]
KT Specific grinding pressure [kN/m2]
MR Roller assembly weight, one roller [kg]
mmmm Torque factor [.1]
N Mill power uptake [kW]
n Grinding table speed [rpm]
P hyd Hydraulic grinding pressure [Bar]
v Grinding track speed [m/s]
W roller Roller width [m]
Z Number of rollers [-]
Torque Factors
VRM Mill Application m - range
Atox Raw mat. Grinding 0.09-0.11
Atox Coal grinding 0.07 - 0.09
OK Cement grinding 0.08-0.10
OK Slag grinding 0.09-0.11

31. 31
N= KT • A • z • v • µ [kW(net)]
Figure 16: Rollers of VRM
F = FR + FH [kN]
Where, FR=MR * 9.81/1000;
FH = P hyd • ((D cyl) 2 - (D piston) 2) • P/4 • 100;
Specific Grinding Pressure Will then be,
KT=F/A
KT: Typically 700 ….1000[kN/m2] (1)
A = D roller • W roller [m2] (2)
z = 3 or 4 (3)
v = n • 1/60 • Dm (m/s) (4)
µ=0.1(Torque Factor for Cement Grinding)
Table 6: Data Available from VRM Supplier
Applying Above Mentioned Formulae:-
From Eqns 1, 2, 3 & 4 we get,
N Net=3 x0.1 x 800x 2 x 0.71 x 4.2x23.3/60 x pie=1745.35 kW
N installed (10% design margin) =1745.35 X 1.1=1919.885 kW or 2000kW
Therefore, Mill design has been found satisfactory.
Z µ KT Dr Wr Dm V
3 0.1 800kN/m² 2 m 0.71m 4.25m 23.3/min

32. 32
4.1.3 Roller Press system (Finish Mode)
Figure 17: Typical Flow Sheet of a RP Grinding Circuit in a Cement Plant
Circuit Explanation
In finish grinding, the cement grinding is carried out in the RP. Fresh feed
along with the RP output is fed to a high efficiency static separator installed
above the RP. Coarse material from this separator is taken as feed to the
RP. Fines from this separator are taken to a high efficiency dynamic
separator. The fines from this separator will be transported to the cement
silo. For improved control of product fineness, a high efficiency dynamic
separator is installed. In that case, the coarse material from the dynamic
separator will be taken to the RP along with the coarse material from the
static separator. For venting a bag filter can also be installed. Fines
collected in bag filter will be transported to cement storage silo by a system
of air slides and bucket elevator. Generally, such types of grinding system
are also preferred for slag grinding to high fineness (around 4000 cm2/g).

33. 33
Mathematical Analysis:-
Figure 18: Roller Press Working
Guide Values for α are:-
• Clinker 6.9 - 9.2 [°]
• Raw material 9.2 - 12.6 [°]
• Slag 5.7 - 7.5 [°](for roller design)
Guide values for ß are:
• Clinker 2.3 - 2.85 [°]
• Raw material 2.85 - 4 [°]
• Slag 1.7 - 2.3 [°](for roller design)
V=1.5m/s-1.6 m/s
The compaction of the material with the density ρo starts at the nip angle
α.The maximum is achieved at the so called attack angle ß (center of
pressure) where the material reaches the slab density.
Between α and ß an interparticle comminution takes place where each
particle transmits the force imposed on it to another particle. Best results
are achieved with materials of wide particle size distribution with a
maximum filling of the voids. In the pressing process a simple size reduction
takes place but also flaws and fissures within the particles are produced
reaching into the micro range.

34. 34
• Feed -OPC
• Clinker : 95%, bulk density-1.3kg/dm3
Gypsum: 5%, bulk density-1.25kg/dm3
Clinker Temperature: 100 ºC,
Clinker / gypsum feed: 80% < 30 mm,
85% < 50mm,
100 %< 80mm,
Max. 80 mm,
• Moisture: Clinker-0%
Gypsum-<5%
Figure 19: Block Diagram of Roller Press Circuit in Finish Mode (Comflex system)
Material Grind-ability - 35.35 kWh/T @3000 Blaine (Close Circuit ball mill
basis). For converting to Roller Press basis, a conversion factor of 1.8-2 is
used in cement industry purely based on experience,
35.35/1.8=19.6388 kWh/T, 19.638 X 80(kWh/T x T/H) =1571 or 1600kW
(2 x800 kW motors), taking 10% design margin) =1600 X 1.1=1760 kW or
1800kW
High Efficiency
Separator
Product
Collection
bag house
Roller Press
Static Separator

35. 35
Table 7: Roller Press Calculation
Calculations of Roller Press
1 Roller Diameter [D] [m] 1.7
2 Roller Width [W] [m] 0.9
3 Roller Speed [n] [rpm] 21.79
4 Roller Peripheral velocity [v] [m/s] 1.94
5 Grinding Bed Thickness [s] [m] 0.04
6 Roller Force [F] [KN] 7963
7 Hydraulic Pressure [B] [bar] 120
8 Piston area [A] [m2] 0.581
9 No of hydraulic cylinders [-] 2
10 Density of pressed material [€] [kg/m3] 2200
11 Torque factor [ ] [-] 0.1035
12 Specific roller force [β] [kN/m2] 5205
13 Roller Press Capacity [M] [t/h] 540
14 Power Consumption [N] [kW] 1599
15 Specific Power Consumption [E] [kWH/t] 19.512
16 Roller Press Circulation Factor [C] [-] 6.75
17 New Feed to roller press [P] [t/h] 80
18 Constant [c] [-] 1.12
19 Total Roller Force [T] c*A*B*102 7963
20 Specific Roller Pressure [β] T/(D*W) 5205
21 Peripheral Velocity [v] P*D*(n/60) 1.940
22 Throughput capacity M [N] 3.6*s*€*W*v 553.0
23 Power Consumption [N] µ*T*v 1599
[N] µ*β*D*w*v 1599
24 Specific Power Consumption [E1] N/M 2.89
25 Roller Press Circulating Factor [C] M/P 6.75
26 Specific Power Consumption [E] c*E1 19.512

36. 36
Cross Checking-Specific Power Consumption=19.512kWh/t x 80
TPH=1717kW or 1800kW (Margin in power already taken). Therefore,
Roller Press design has been found satisfactory.
5. Chapter -5 Technical evaluation of grinding systems
Table 8: Technical Evaluation of Grinding System
S. No Description Ball Mill Vertical
Roller Mill
Roller press Remarks
1. Communition
Technique
Impact &
Attrition in ball mill
Compression Compression
2. Moisture
handling
capacity
Low High can
handle up to
10-15 %
moisture
Less than VRM,
but can handle
up to 10% by
drying in static
Separator.
3. Total Power
requirement
On a higher side Lower than
ball mill
Lowest
4. Ease of
operation
Moderate(high
Moisture problem)
Moderate Moderate(difficult
to handle dry fly
ash)
5. Investment
cost
Moderate(little
less than VRM)
High Low
6. Auxiliary
Equipments
High Low Low
7. Space
Requirement
High Low Low
8. Plant
availability
80-90% 80-90% 80-90%
9. Life of wear
parts
High Low Moderate
10. Particle Size
Distribution
Somewhat
Steep
Steep Steep
11. Capacity in TPH @
3000cm²/g
80 80 80
11. Expected Power
Consumption kWh/t
Cement @
3000Cm²/g
35.35 22 19.6
12. Maintenance Low High High

37. 37
6. Chapter -6 Conclusions & Recommendations
Although the specific power consumption is the least for Roller
press for producing OPC, which is beneficial in long term and points
for its selection, it is evident that the grinding efficiency of the
vertical roller mill combined with an ability to grind, classify and – if
required – dry within a single unit gives the vertical roller mill
system a decided advantage over a ball mill system & roller press.
Power consumption for ball mill circuit is the highest followed by
Vertical Roller Mill & Roller Press.
For Decision on new Cement Grinding, it is essential to not only
consider power requirement, but also equipment reliability,
maintenance requirements, plant availability, operational flexibility,
cement quality & of course investment cost.
Less than 20% of energy is reckoned to be converted to useful
grinding, the bulk is lost as heat, noise, equipment wear & vibration;
for example in Ball mills only 3-6% of absorbed energy is utilized in
surface production, the heat generated can increase mill temperature
to >120º C causes excessive gypsum dehydration & media coating, if
mill ventilation is not proper. This usually attributed to high grinding
power in mill circuits.
Table 9: Bar Chart for Power Comparison
0
500
1000
1500
2000
2500
3000
3500
Power Consumption(kW) @3000 cm2/g OPC Basis
Ball Mill
VRM
RP

38. 38
6.1 Maintenance of wear parts:-
Wear parts for a ball mill, i.e. grinding balls, liner plates and other
mill internals are either very easy to maintain or they have a long
life time. The grinding charge is simply maintained by adding more
grinding balls to the mill as the mill charge becomes worn and the
power consumption and the output capacity decrease.
Liners and mill internals for the first compartment have typical
lifetimes from at least two years (grate plates for the intermediate
diaphragm) to around 5 years (shell liners). Parts for the second
Compartment last even longer, typically from around 4 years
(Outlet grates) to around 9 years (shell liners).
Also, for a vertical roller mill the performance will deteriorate as a
consequence of progressive wear of the grinding parts. This,
however, is not only reflected in a reduced capacity, but also in
higher specific energy consumption and a higher level of mill
vibrations.
Works for remedy of progressive wear of the grinding parts for an
vertical mill may involve reversal of roller segments, hard facing of
roller and table segments and/or eventually replacement of worn
out parts.
These works are obviously more complicated than just adding more
balls to a ball mill. However, the wear rate for grinding parts of an
vertical mill grinding OPC is fairly low and maintenance of wear
parts, i.e. reversal, hard facing or replacement, can usually be
scheduled to take place say once per year to follow the plant’s kiln
maintenance program.
The wear rate measured in gram per ton of cement produced is
much higher for a ball mill than for a vertical roller mill. However,
the unit cost for wear parts for a ball mill is much lower than for a
vertical roller mill.
For a ball mill grinding OPC to a fineness of 3200 to 3600 cm2/g
(Blaine) the cost of wear parts (ball, liners and mill internals) is
typically 0.15-0.20 EUR per ton of cement.

39. 39
For a Vertical mill grinding a similar product, the cost of wear parts
depends on the maintenance procedures, i.e. whether hard facing is
applied. If hard facing is not applied the cost is as for the ball mill,
i.e. 0.15-0.20 EUR per ton of cement. If hard facing is applied, the
corresponding figure will be 0.10-0.15 EUR per ton of cement.
In Case of Roller press, hard facing of rollers usually done as they
rollers deteriorate with respect to time. Stud-lined rollers are
generally used for improved life.
6.2 Grinding Power Comparison
The most significant advantage of a vertical roller mill or Roller
press as compared to a ball mill system is related to the
consumption of electrical energy of the systems. Significant heat &
friction losses occur in ball mill during operation.
It appears from the table that the specific energy consumption of
the Vertical mill system is 25% - 40% lower than for the ball mill
system. The benefit of the vertical mill is in particular pronounced
when grinding to a high fineness and/or when slag is included in the
cement. Same holds for Roller press also.
6.3 Process Concepts
Ball Mill System are suitable for grinding Ordinary Portland
Cement(OPC), Pozzolana Portland Cement(PPC) as a result of low
wear profile of the raw materials, whereas Portland Slag Cement
(PSC) is usually not preferred to grind. Slag is usually separately
grounded to required fineness (3800-4000cm2/g) using vertical mill
System or Roller press & then mixed with Ordinary Portland Cement
to produce Portland Slag Cement. This is because Hardness of slag
is considered 1.2 times to that of clinker.
VRM Circuits are capable of producing almost all combination of
Cements produced worldwide like OPC, PPC, PSC etc.
RP Circuits are usually not preferred to produce PPC as fly ash
mixing does not occur properly in roller press circuits. Fly ash is
usually fed directly to high-efficiency separator for including the
material in the circuit.

40. 40
Figure 20: Grinding Power Diagram
7. Chapter -7 Case Study
Table 10: Case study @ 150 TPH
Basis-3200 cm2/g
(OPC)
Ball Mill Roller Press Vertical Roller
Mill
Mill machinery Ø4.6 x 14.25m RP-13 Type 46
Capacity(TPH) 150 150 150
Main power
absorbed(kW)
4350 2400 2900
Spec. Mill Power
absorbed (kWh/t)
29 16 19.3
Ancillaries
(kWh/t)
5 4 11.6
Plant
Total(kWh/t)
34 20 30.9
The table indicated above shows a comparative result for power
absorbed by cement grinding systems at 150 TPH OPC @ 3200 Blaine.
Ball Mill-3200kW
@ 3000Blaine
VRM -2000kW
@ 3000Blaine
RP -1800kW @
3000Blaine

41. 41
Specific power consumption of roller press is the lowest among ball
mill & vertical roller mill system. However, detail study on project
basis for instance plant layout, project costing, Return on investment
should be carried out to come to a final decision.

42. 42
8. Chapter -8 Bibliography
Holcim Ltd.-Holcim guide. Year of Publication:2003
Duda,W.H.,Cement Data Book-Volume1-International process
engineering in the Cement industry, third Edition, Bauverlag Gmbh,
Wiesbaden-Berlin, Germany Year of Publication:1985

43. 43
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