Lecture Slides by Prof. Imitaz Ali at Ghulam Ishaq Khan Institute for Engineering Sciences and Technology (GIKI).

1. 13/12/2013
1
Cement Industries
Introduction
• Cement
– inorganic material
– having adhesive and cohesive properties
– sets and hardens when mixed with water (hydrolysis and
hydration)
• Uses
– buildings, roads, bridges, dam etc
• Types
– hydraulic (Portland cement)
• harden because of hydration, can harden underwater or when
constantlyexposed to wet weather
– non hydraulic (Lime and gypsum plaster)
• slaked limes harden by reaction with atmospheric carbon dioxide

2. 13/12/2013
2
Installed Production Capacity (Mt/yr)
Sr. No. Name and location Capacity 2012/2013
1 Lucky Cement Limited - Pezu 3.91 3.73
2 Lucky Cement Limited - Indus Highway Karachi 3.60 3.43
3 Bestway Cement Limited - Chakwal 3.60 3.43
4 Fauji Cement Company Limited - Fateh Jang 3.43 3.27
5 Maple Leaf Cement Factory Limited - Daudkhel 3.37 3.21
6 Kohat Cement Company Limited - Kohat 2.68 2.55
7 D. G. Khan Cement Limited - D. G. Khan 2.11 2.01
8 D. G. Khan Cement Limited - Chakwal 2.11 2.01
9 GharibWal Cement Limited - Jehlum 2.11 2.01
10 Lafarge Pakistan Cement Company Limited - Chakwal 2.05 1.95
11 Pioneer Cement Limited - Khushab 2.03 1.93
12 Attock Cement Pakistan - Hub Chowki Lasbela 1.80 1.71
13 Askari Cement - Nizampur 1.58 1.50
14 Bestway Cement Limited - Hattar 1.23 1.17
15 Flying Cement Limited - Lilla 1.20 1.14
16 Dewan Hattar Cement Limited - Hattar 1.13 1.08
17 Askari Cement Limited - Wah 1.10 1.05
18 Cherat Cement Company Limited-Nowshera 1.10 1.05
19 Bestway - Mustehkum Cement Limited - Hattar 1.09 1.04
20 Al-Abbas Cement Limited - Nooriabad Dadu 0.95 0.90
21 Fecto Cement Limited - Sangjani 0.82 0.78
22 Dewan Hattar Cement Limited - Dhabeji 0.79 0.75
23 Dandot Cement Limited - Jehlum 0.50 0.48
24 Thatta Cement Limited - Thatta 0.49 0.47
0
5
10
15
20
25
30
35
40
45
50
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Milliontons
Production Consumption Exports Surplus
45 Mt45 Mt
23 Mt23 Mt
10 Mt10 Mt
8 Mt8 Mt
Mt %
Pakistan 45 1.25
India 239 6.64
China 2 137 59.36
Europe 156.3 4.34
USA 73 2.03
World 3600 100

3. 13/12/2013
3
History
• 1796 Roman cement James Parker
– natural cement made by burning certain clay deposits (containing
minerals and calcium carbonate)
• 1817 Artificial cement Louis Vicat
– by burning chalk and clay mixture
• 1822 British cement James Frost
– similar
• 1824 Portland cement Joseph Aspdin
• 1841 Modern Portland cement William Aspdin
Introduction
• Types
– Natural cement : Hydraulic lime
• burning of 20-40% clay, carbonate of lime and small
amount of magnesium carbonate
– Artificial cement :
• Calcination of calcareous (Ca) material followed by the
clinkering process with argillaceous (Al + Si) material at
high temperature

4. 13/12/2013
4
Based on the application, appearance
and constituents
• Acid resistance cement
• Blast furnace cement
• Coloured cement
• White cement
• Rapid hardening cement
• High alumina cement
• Puzzolana cement
• Hydrophobic cement
• Expanding cement
• Low heat cement
• Quick setting cement
• Sulfate resisting cement
Chemical composition of grey cement
Nomenclature Molecular
formula
Cement
chemists
notation
Concentratio
n range (w/w
%)
Tricalcium silicate 3CaO•SiO2 C3S 40-80
Dicalcium silicate 2CaO•SiO2 C2S 10-50
Tricalcium aluminate 3CaO•Al2O3 C3A 0-15
Tetracalcium aluminoferite 4CaO•Al2O3•Fe2O3 C4AF 0-20
Calcium oxide CaO 0-3
Magnesium oxide MgO 0-5
Potassium sulphate K2SO4 0-2
Sodium sulphate Na2SO4 0-1

5. 13/12/2013
5
Compounds
• Tricalcium Silicate (C3S)
– Hardens rapidly and is largely responsible for initial set and early
strength
• Dicalcium Silicate (C2S)
– Hardens slowly and contributes largely to strength increases at
ages beyond 7 days
• Tricalcium Aluminate (C3A)
– Liberates a large amount of heat during the first few days of
hardening and together with C3S and C2S may somewhat
increase the early strength of the hardening cement
• Tetracalcium Aluminoferrite (C4AF)
– acts as a flux during manufacturing. Contributes to the colour
effects that makes cement gray.
Chemical composition of white cement
Characteristics Molecular formula Typicalconcentration(w/w %)
Chemicalcomposition (%) SiO2 22.5-23.8
Al2O3 2.3-6.2
Fe2O3 0.19-0.4
CaO 66.3-68.0
MgO 0.48-1.0
SO3 0.65 – 2.8
F 0.24 – 0.85
K2O 0.12-0.14
Na2O 0.17
Potential compound
composition (%)
3CaO•SiO2 70
2CaO•SiO2 19
3CaO•Al2O3 8
4CaO•Al2O3•Fe2O3 1
Except for colour, white cement has the same properties as grey cement.
highly pure limestone,
white clays, kaolin, quartz
sand, feldspar,
diatomaceousearth, low
contentsof metals such
as iron and manganese.

6. 13/12/2013
6
Principle constituents
• Lime
– calcining the lime stone (CaCO3) at temperature that it will slake, when brought in contact with water. It is
principal constituent of cement. Proper amount of lime is important as excess of it reduces the strength as
well as lesser amount also reduces the strength and makes its quick setting.
• Silica
– It imparts strength to cement.
• Alumina
– It works as an accelerator and makes the cement quick settling.
• Gypsum (Calcium sulfate)
– It retards the setting action of cement but enhances the initial setting time.
• Iron oxide
– It provides colour, strength and hardness of cement.
• Magnesia
– If present in small amount impart hardness and colour to cement
• Sulfur trioxide
– If present in small amount it imparts soundness to cement but excess of it is undesirable
• Alkalis
– Most of the alkalis present in raw materials are carried away by the flue gases during heating and cement
contains only a small amount of alkalis. If present in excess causes the dehydration in cement.
Manufacturing process
• The basic chemistry of the cement manufacturing
process begins with the decomposition of calcium
carbonate (CaCO3) at about 900 °C to calcium oxide
(CaO, lime) and liberated gaseous carbon dioxide (CO2);
this process is known as calcination.
• This is followed by the clinkering process in which the
calcium oxide reacts at a high temperature (typically
1400 – 1500 °C) with silica, alumina, and ferrous oxide
to form the silicates, aluminates, and ferrites of
calcium which comprise the clinker.
• The clinker is then ground or milled together with
gypsum and other additives to produce cement.

7. 13/12/2013
7
Manufacturing process
• It involves the following steps
– Storage and preparation of raw materials
– Burning
– Grinding
– Storage and packaging
Process routes
• The choice of process is, to a large extent, determined by the state
of the raw materials (dry or wet).
– The dry process, in which the raw materials are ground and dried to
raw meal in the form of a flowable powder. The dry raw meal is fed to
the preheater or precalciner kiln or, more rarely, to a long dry kiln.
– The semi-dry process, in which the dry raw meal is pelletised with
water and fed into a preheater before the kiln or to a long kiln
equipped with crosses.
– The semi-wet process, in which the slurry is first dewateredin filter
presses. The resulting filter cake is extruded into pellets and then fed
either to a preheater or directly to a filter cake dryer for raw meal
production.
– The wet process, in which the raw materials (often with a high
moisture content) are ground in water to form a pumpable slurry. The
slurry then is either fed directly into the kiln or first to a slurry dryer.
* Wet processes are more energy consuming, and thus more expensive.

8. 13/12/2013
8
Raw materials
– Clay
– Limestone
– Gypsum
– Water
Dry process
• Lime stone or chalk and clay are crushed into gyratory crusher to get 2-5
cm size pieces.
• Crushed material is ground to get fine particle in ball mill or tube mill.
Materialsafter screening stored in a separate hopper.
• Typical dry grinding systems used are:
– Tube/ballmill, centre discharge
– Tube/ballmill, airswept
– verticalroller mill
• Classification of the powder is carried out using air separators.
• The powder is mixed in require proportions to get dry raw meal which is
stored in silos and kept ready to be fed into the rotary kiln. Raw materials
are mixed in required proportions so that average composition of the final
product is maintained properly.
• For raw meal transport to storage silos, pneumatic and mechanical
conveyor systems are used.

9. 13/12/2013
9
Wet process
• Calcareous raw material is crushed, powdered and stored in silos.
• Clay is washed with water in wash mills to remove adhering organic
matter. The washed clay is stored separately.
• Powdered lime stone and wet clay are allowed to flow in channel
and transfer to grinding mills (closed circuit milling systems) where
they are intimately mixed and paste is formed known as slurry.
• Grinding may be done either in ball mill or tube mill or both. When
sufficiently fine, the material passes through screens in the wall of
the wash mill and is pumped to storage.
• Then slurry is led to correcting basin where chemical composition
may be adjusted. The slurry contains 38-40% water stored in
storage tank and kept ready for feeding to a rotary kiln.
Clinker burning
• This part of the process is the most important in terms
of emissions potential and of product quality and cost.
In clinker burning, the raw meal/slurry is fed to the
rotary kiln system where it is dried, preheated, calcined
and sintered to produce cement clinker.
• Cyclone preheater
– The raw materials are preheated or calcined in preheater
or series of cyclones before entering to the rotary kiln. A
preheater, also called as suspension preheater is a heat
exchanger in which the moving crushed powder is
dispersed in a stream of hot gas coming from the rotary
kiln. Common arrangement of series of cyclones is shown
in figure.

10. 13/12/2013
10
Preheater/Precalciner
• The heat transfer of hot kiln gases to raw meal takes place in co-current.The raw
materialsare heated upto 800 °C within a less than a minutes.About 40% of the
calciteis decarbonatedduring the heat transfer.
• The quality and quantity of fuel used in the kiln can be reduced by introducing a
proportion of the fuel into preheater.50 – 65 % of the total amount of fuel is
introducedinto preheater or precalciner which is often carried out by hot air
ducted from cooler.
• The fuel in the precaliner is burnt at relativelylow temperature,there so heat
transfer to the raw meal is very efficient.The material has residence time in the
hottestzone of a few seconds and its exit temperature is about 900 °C, 90 – 95% of
calciteis decomposed.Ash from the fuel burn in the precalcineris effectively
incorporatedinto mix.
• Advantagesof precalination
– Decrease the size of kiln
– Decrease in capital cost
– Increase in rate of material passes to the kiln.
– Decrease in rate of heat provided which ultimately lengthens the life of refractory lining
– Less NOx is formed, since much of the fuel is burnt at a low temperature, and with some
designs NOx formed in the kiln may be reduced to nitrogen.
Clinker burning
• It is essential to maintain kiln charge temperatures in the sintering
zone of the rotary kilns at between 1400 and 1500 °C, and the
flame temperature at about 2000 °C. Also, the clinker needs to be
burned under oxidising conditions. Therefore, an excess of air is
required in the sintering zone of a cement clinker kiln.
• The rotary kiln consists of a steel tube with a length to diameter
ratio of between 10 : 1 and 38 : 1. The tube is supported by two to
seven (or more) support stations (roller bearings), has an inclination
of 2.5 to 4.5 % and a drive rotates the kiln about its axis at 0.5 to 5.0
revolutions per minute.
• The combination of the tube’s slope and rotation causes material to
be transported slowly along it. In order to withstand the very high
peak temperatures, the entire rotary kiln is lined with heat resistant
bricks (refractories). All long and some short kilns are equipped
with internals (chains, crosses, lifters) to improve heat transfer.

11. 13/12/2013
11
Clinker burning
• Due to inclined position and slow rotation of the kiln,
the material charged from upper end is moving
towards lower end (hottest zone) at a speed of 15m/h.
In the upper part, water or moisture in the material is
evaporated at 400 °C, so it is known as drying zone.
• In the central part (calcination zone), temperature is
around 1000 °C, where decomposition of lime stone
takes place. After escapes of CO2, the remaining
material in the forms small lumps called nodules.
– CaCO3  CaO + CO2
Clinker burning
• The lower part (clinkeringzone) have temperature in between 1500-1700
°C where lime and clay reacts to yielding calcium aluminates and calcium
silicates. The aluminates and silicates of calcium fuse togather to form
small and hard stones are known as clinkers. The size of the clinker is
varies from 5-10 mm.
– 2CaO + SiO2  Ca2SiO4
– 3CaO + SiO2  Ca3SiO5
– 3CaO + Al2O3  Ca3Al2O6
– 4CaO + Al2O3 + Fe2O3  Ca4Al2Fe2O10
• The hot clinkers coming from burning zone are cooled down by air
admitting counter current direction at the base of rotary kiln. Resulting
hot air is used for burning powdered coal or oil.

12. 13/12/2013
12
Clinker coolers
• The clinker cooler is an integral part of the kiln system and has a decisive
influenceon performance and economy of the pyroprocessing plant. The
cooler has two tasks: to recover as much heat as possible from the hot
(1450 °C) clinker so as to return it to the process; and to reduce the clinker
temperatureto a level suitable for the equipment downstream.
• Heat is recovered by preheating the air used for combustion in the main
and secondary firing as close to the thermodynamic limit as possible.
• Rapid cooling fixes the mineralogical compositionof the clinker to improve
the grindability and optimise cement reactivity.
• Typical problems with clinker coolers are thermal expansion, wear,
incorrectairflows and poor availability
• There are three types of coolers: rotary, grate and verticle/gravitycoolers.
– Rotary coolers : tube and planetary coolers
– Grate coolers : travelling, reciprocating,third generationgrate coolers
Clinker grinding
• Portland cement is produced by intergrinding cement
clinker with sulphates such as gypsum and anhydrite.
• Grinding plants may be at separate locations from
clinker production plants.
• Commonly used finish grinding systems are:
– Tube/ball mills, closed circuit (mineral addition is rather
limited, if not dry or pre-dried)
– vertical roller mills (best suited for high mineral additions
due to its drying capacity, best suited for separate grinding
of mineral addition)
– roller presses (mineral addition is rather limited, if not dry
or pre-dried).

13. 13/12/2013
13
Typical process flow diagram
Comparison of dry and wet process
Criteria Dry process Wet process
Hardness of raw material Quite hard Any type of raw material
Fuel consumption Low High
Time of process Lesser Higher
Quality Inferior quality Superior quality
Cost of production High Low
Overall cost Costly Cheaper
Physical state Raw meal (solid) Slurry (liquid)

14. 13/12/2013
14
Ordinary Portland cement
Chemical Analysis Typical EN 197-1 52.N & BS 12-1996 IS 12269
Loss on Ignition % 3.3 5.0% Max. 4.0% Max.
Insoluble residue % 0.95 0.95% Max. 2.0% Max.
Sulphate as SO3 % 2.5 4.0% Max. 3.0% Max.
Chloride % 0.05 0.1% Max. 0.1% Max.
MgO % 2.25 --- 6.0% Max.
LimeSaturation Factor % 0.93 --- 0.8Min - 1.02% Max.
Alkali Equivalent % 0.57 0.60% Max. --
Physical Properties
Fineness by Blaine cm2/g 3200-3000 --- 2250
Setting & Soundness Behaviour
Initial Setting Time (minutes) 180 45 min (Min.) 30 min (Min.)
Final Setting Time (hours) 4:30 h:m -- 600 min (Max.)
Lechatlier's Expansion 1:00 mm 10 (Max.) 10 mm (Max.)
Autoclave Expansion 0.05% -- 0.80% (Max.)
Compressive StrengthPerformance Mortar EN 196-1 Testing Method
Typical Results EN 197-1 52.5 N & BS 12-1996
Earlystrength – 2days (N/mm2) 22.5 20.0 Min.
Standard Strength – 28days (N/mm2) 56 52.5 Min.
Typical Results IS 12269 53 grad
3days (N/mm2) 38 27.0 Min
7days (N/mm2) 47 37.0 Min.
Standard Strength - 8days (N/mm2) 56 53.0 Min.