Raw mix characteristics final

WELCOME TO THE TRAINING
ON KILN OPERATION &
OPTIMISATION

Cement is a substance (often a ceramic) that by a chemical
reaction binds particulates aggregates into a cohesive structure.
( hydraulic binder). The quality of raw material is the main point
in maintaining of quality of cement. The mineral compounds
containing the main components of cement: lime, silica, alumina
and iron oxide are used in cement manufacturing process.
Therefore it is usually necessary to select a measured mixture of a
high lime component with a component which is lower in lime,
containing however more silica, alumina and iron oxide
(clay component). The purpose of calculating the composition
of the raw mix is to determine the quantitative proportions of the
raw components, in order to give the clinker the desired chemical
and mineralogical composition
What is cement ?

quality
Factors influencing the cement quality
1. Mechanical handling of clinker
2. Chemical and mineralogical
composition of raw mix
3. Chemical and mineralogical composition
of clinker
4. Burning process & cooling process
5. Chemical composition of fuels (ash)
6. Circulation phenomena (volatiles)

Process flow sheet
CBA analyzer
CBA analyzer
X ray
analyzer

Cement quality – type of cement
Clinker quality
Fuel chemistry
Raw mix design
OPC, PPC, WC, OWC, SRC,SC
Ordinary portland cement,
Pozalona portland cement
White cement,
Oil well cement,
Sulfate resistant cement,
Slag cement
Other cements for special application
Gpsum&fly ash or
Other additive quality

Physical charateristics
Particle size & shape
particle size distribution
Homogenity
Characteristics of raw meal
Chemical
characterictics
Chemical composition
Mineralogical
Morphology
( crystal size of
minerals &
Cystal distribution)

Up to 1.2Upto 0.5Up to 30.1 -
0.4
Up to 0.1SO3
0.01 – 0.1Cl
Up to 0.3Up to 0.50.1 – 0.3Upto
0.2
Upto 0.1Na2O
0.2 – 1.4Up to 10.5 - 50.1 - 4Upto 0.3K2O
0.3 - 3Up to 0.5Up to 50.5 -50.5 - 5MgO
40 -450.1-30.5 – 2.55 - 5252 - 55CaO
Up to 20.5 - 22 -150.5 -100.1 -0.5Fe2O3
+Mn2O3
2 -50.5 - 37 -301 - 200.1 - 1Al2O3+TiO2
12 -1680 - 9937 -783 - 500.5 - 3SiO2
32 - 36Up to 5
%
1 - 202 -4240-44Ig loss
rawmixsandclaymarllime
stone
Weight loss %
Chemical composition of cement raw materials and mix

Physical characteristics
of Raw meal

Particle size & Particle size distribution
An efficient separator & efifcient grinding system narrow down
the particle distribution. Wide distribution means heterogenity in physical
and chemical characteristics of
raw meal.

Optical micrograph and super imposed size analysis
of quality audit standards

Calcite-rhombo
Calcite-cubic
quartz Silica sand
Kaolinite
Minerals in a lime stone

Pure lime stone
only Calcite > 99 % CaCO3
Impure lime stone imbedded
with silicates and other minerals
Lime stone

time
temperature
Impure calcite
pure calcite
heat
CO2

Well developed quarry
In a well developed mine, the mines manager knows where what and how much is
available?
If quality is controlled in mines then the quality variation is minimised to a great
extent through mines blend program through griging or geostatics
Benches (10 M height)

From mines
(input to stacker)
Output of
blending
System& input
To raw mill
time
Std
LSF
Outlet of mill
Influence of efficient mining on quality

Std of LSF =1
SIM=0.2
Std of ,CaO < 0.2
Control on chemistry

Main parameters for raw mix design
Lime saturation factor = CaO / (2.8 SiO2+1.65Al2O3 + 0.65 Fe2O3)
( LSF)
Silica modulus = SiO2 / ( Al2O3+Fe2O3)
Alumina modulus = Al2O3 / Fe2O3
AlM
Here we have apply the formula (as per British Standard)
LSF = CaO-0.7SO3
(2.8*SiO2 + 1.2* Al2O3 + 0.65*Fe2O3)
(SIM)

Lime saturation factor on clinker basis
If MgO is below 2 %
LSF = 100( CaO – free CaO+0.75 MgO)
(2.85 SiO2) + ( 1.18 Al2O3) +(0.65 Fe2O3)
If MgO is above 2 %
LSF = 100( CaO – free CaO+1.5 MgO)
(2.85 SiO2) + ( 1.18 Al2O3) +(0.65 Fe2O3)
> 99 –hard to burn, tendency to high free lime & C3S clinker , high early strength
high fuel consumption
< 99 , easy to burn , excess coating , excess liquid phase , possible brick infiltration
reduced cement strength , low free lime
acceptable standard deviation = 1.2

Effects :High Ms
Results in hard burning & high fuel consumption.
Causes Unsoundness.
Difficulty in coating formation.
Deteriorates Kiln Lining.
Results in slow setting and hardening of cement
Lower Ms:
Increases liquid phase.
This improves burnability of the clinker and the formation of coating in kiln
Effect of modulie
Effects: Higher LSF
Imparts harder burning & entails higher fuel consumption.
Tends to produce unsound cement.
Increases C3S content, reduces C2S content.
Causes slow setting with high strengths of cement.
Improves the grind ability characteristics of clinker.
Lower LSF:
Low lime contents, lower will be strength

HM= CaO/(SiO2 + Al2O3 + Fe2O3)
Limiting Range:- 1.7-2.3
The Hydraulic Modulus of good quality cements was approximately
2. Cement with HM<1.7 showed mostly insufficient
strength and cement with HM>2.3 and more had poor
stability of volume. It was found that with an increasing
HM, more heat is required for clinker burning.
The strengths, especially initial strengths step up and also the
heat of hydration rises. Simultaneously the
resistance to chemical attack decreases. At times
the Hydraulic Modulus is still used. Later for
a better evaluation of the cement, the Silica ratio,
Alumina ratio were introduced; to certain degree these
ratios supplement the hydraulic modulus.
Hydraulic modulus

Parameters influencing the burnability:
1. Residue on 212-micron sieve.
2. Residue on 90 micron sieve
3. Size distribution of free silica
4. Degree of homogeneity (both chemical & mineral)
5. Liquid phase of clinkering temperatures.
6. Moisture content of raw meals
Effects: Higher MA
Imparts harder burning & e tails higher fuel
consumption.
Increases the C3A and reduces C4AF contents
Increases both C3S and C2S (C3S>C2S)
Reduces the liquid phase and kiln output
Tends to render quick setting and strong at early ages.
Increases viscosity of liquid phase in raw mix
MA determines the role of Fluxes in raw mix
MA <1.23: - Al2O3 acts as Flux
MA >1.23: - Fe2O3 acts as Flux
Lower MA
If MA is too low and raw mix is without free silica,
clinker sticking and balling is high.

1. Mineralogical Make-up
2. Reactivity and Burnability.
3. Volatility.
4. Optimum fineness & specific surface for effective burning.
6 Level of free quartz , calcite and its size distribution.
7 Sensitivity of free quartz content & size with KF burnability.
8 Minor elements level (Mg, Na ,K, S, P) & their effect on
kiln feed burn ability and volatility.
Characterization of kiln feed

In homogeneous homogeneous
Kiln feed uniformity index (KFUI)
KFUI= n ( C3S actual - C3S target )2
n
i - n
C3S actual = the calculated C3S of one instantaneous daily sample of kiln raw mix feed
C3S Target = the C3S target established for the mill product
n = number of samples ( calculation of average C3S is done monthly)
Target for KFUI is < 10
( an instantaneous sample is one made up of 5 consecutive increments taken at short intervals)

Homogenising systems
3.1 Variabilitv and standard deviation
The normally accepted method of measuring variability is in the form of a term called
standard deviation. The standard deviation of a property can be calculated by taking a
number of measurements on the property (such as LSF, SR etc.), and applying the
following formula:-
Where X is the measured variable (e.g. LSF)
X is the variable mean (or average)
N is the number of measurements or observations
Table 1 illustrates a worked example using actual kiln feed LSF data:-
Blending ratio = Std in/ Std out , = 1 for an ideal blending system.
σ=
Σ ( X - X ) 2
N - 1

Different stacking system
Stacking and reclaiming sytem is selected on the basis of material characteristics like
Moisture , variability in mines, size and size distribution of particles.

Circular stock pile
Reclaiming zone
Stacking zone
Blended zone

Longitudinal stock pile
End cone problem

Well blended slice without end cone
End cone problems Linear stock pile
Blending ratio = S in / S out
More variation, high std
Less variation, low std

“Average” clinker composition
MgO 1.80
SO3 0.54
K2O 0.63
Na2O 0.25
TiO2 0.27
Mn2O3 0.09
P2O5 0.14
Cl- 0.01
F- 0.08
LOI: 0.3 %
CaO 65.4
SiO2 22.2
Al2O3 5.0
Fe2O3 2.8
∼ 5 %
∼ 95 %

Milestones in clinker formation
0 200 400 600 800 1000 1200 1400
Dehydration
Decarbonation
Belite formation
Liquid phase
formation
Alite
formation
Temperature [°C]

Clinker manufacture
• Calcite – CaCO3
• Dolomite –
CaMg(CO3)2
• Quartz – SiO2
• Clay minerals
• Micas
• Feldspars
• Aluminum oxide
• Pyrite
• Iron oxide
• Gypsum / anhydrite
• Alite
• Belite
• Aluminate
• Ferrite
• Free lime(un wanted)
• Periclase(un wanted)
• Alkali
sulfates(unwanted)
Mineral phases in raw meal Mineral phases in clinker
Temperature
Pressure
Time

Potential clinker composition
The chemical analysis presents a picture of the composition of
the oxides in the clinker. There are four mineralogical phases
are C3S (alite), C2S (belite), C3A (Aluminate), C4AF (Ferrite) in
the clinker which can be derived from chemical analysis
according Bogue formula. Some other minute phases also
exist in clinker C2(A,F), Free lime, MgO (periclase)
(Note: C3S- gives initial strength, C2S- final strength,
C3A- setting time, C4AF- some setting property & color)
the clinker of Portland cement approximately contains the
following composition.

Parameters for good clinker:
<0.5<1.2<2.0<1.564-66
%SO3%(K2O,
Na2O)
% MgO% Free-
CaO%
T.CaO
MINEROLOGY:
Alite 45-55%, C3A 9-11%, C4AF 12%
Phase Stabilisation:
β/ α / ά only for belite and not significant for others.
Average Crystal size: 35-40 micron
Crystal Morphology:
Alite: prismatic hexagonal
Belite: round
C3A: Fine crystals in matrix.
Crystal Distribution:
Minimum clustering, total porosity: 25-30%
Litre weight: 1150-1350 g/l
Granulometry : not more than 15% below 0.5mm

To achieve the goal of smooth kiln operation it is necessary to know
• which parameters in the raw mix influence kiln operation
• How and why they influence operation
• What can be done about it
Three concepts in the reation between raw meal characteristics and
Kiln operation is treated , namely.
• the burnability of raw mix
• the clinker formation treated as a physical agglomeration process and
•The circulation phenomenon of volatile matter in a kiln system

Required burning zone temperature
RBT = 1300 OF+4.51C3S – (3.74C3A +12.64 C4AF )
Clinker liquid phase ( % L.P)
At 1340 OC ,( AR< 1.38 ) L.P = 8.2 A – 5.22 F + M + K + N +S
At 1340 o C , (AR > 1.38) L.P = 6.1 F + M + N +K + S
At 1400 o C, L.P = 2.95 A+2.20 F+M+N+K+S
At 1450 O C L.P = 3.0 A +2.25 F+M+N+K+S
Potential free lime ( PFL)
PFL = ( 6.77+(0.05C3S))-((0.15C3A)+(0.56C4AF)
To make a good clinker the liquid content must be optimum
and with right viscosity.

1 1.5 2 2.5 3
3
2.5
2
1.5
1
0.5
Variation in % liquid phase at 1338 deg c
With change in Silica ratio and alumina ratio at 100 % LSF
40% 35%
30 %
25 %
20%
Silica ratio S/ ( A+F)
AluminaratioA/F
15 %
15 %

Influence of minor components on liquid properties
Can either increase or decrease both liquid viscosity
and surface tension depending upon the
electronegativity of the ions and alumina ratio .
Trace metals
Lowers the liquid viscosityCl, F
Behaves similarly to Fe2O3 in increasing the level of
flux and reducing its viscosity
Mn2O3
Forms a separate liquid to the main oxide flux at
around 1250 deg c . At higher temperatures it is partially
miscible and results in both a higher viscosity and
higher surface tension. Overall effect is to accelerate
the formation nodules at a lower temperature but restrict
their growth resulting in dustier clinker.
K2O , Na2O
and SO3
Can increase the liquid phase present at burning zone
temperature
MgO
Influence on liquid formationMinor
components

Raw material particles
Before the reaction
Raw material particles
during the reaction

Schematic illustration
Of clinker at 1400 deg C

Active layer
Passive layer
Free board
Radial cross section of rotary kiln
Higher the rpm more the area of active layer which reduces
free lime due to intense stirring there by improving
better heat exchange.It also improves nodulisation.

Lower rpm , high % filling , less active
Layer , high free lime, high radiation
losses
high rpm , low % filling , more active
Layer , low free lime and low radiation
losses
Influence of revolutions / minute on kiln operation
Optimum % filling = 9 – 11 with raw meal retention time of 20 -25 minutes
unfavorable favorable

Influence of revolutions / minute on kiln operation
unfavorable favorable
High degee of filling brings the surface of the charge closer to the flame
envelope. In this case there is a chance of chars trapped inside the charge causing
localised reduced conditions and increases volatile cycle.

Sequence of chemical reactions in cement rotary kiln,
temperature and energy input

Properties of the liquid phase Temperature has the most
pronounced effect on liquid-phase viscosity. Increasing the
burning temperature by 93degrees C (199degrees F), reduces
liquid viscosity by 70% for a regular Type 1 clinker. This simple fact
explains why hotter-than-normal temperatures are beneficial
to clinkering yet potentially harmful to the refractory
lining, as shown in Photo 1.MgO, alkali sulphates, fluorides,
and chlorides also reduce liquid-phase viscosity. Extreme caution
should be exerted when insufflating calcium chloride into the burning
zone as a way to reduce alkali in the clinker. The injection
of sodium carbonate into the burning zone also is detrimental
to the refractory lining.Free alkali and phosphorus increase
liquid-phase viscosity, but this effect is offset by MgO and SO3. Only
Clinkers with sulphate-alkali ratio lower than 0.83 and low MgO would
experience the negative effects of high liquid viscosity.
Properties of liquid

The liquid-phase viscosity increases linearly with the alumina-iron ratio.
For a given burning temperature, high C3A clinkers tend to nodulize
better than low C3A clinkers. Moreover, the liquid phase is considerably
less damaging to the refractory lining when the liquid is viscous.
Another important property of the liquid phase is its surface tension, or its
ability to "wet" the lining. The surface tension has a direct impact
on clinker fineness, coating adherence to the lining and clinker quality.
High surface tension values favor nodule formation and liquid penetration through
the nodules. The resulting clinker contains less dust
(fraction below 32 mesh) and lower free lime content. A liquid phase
with high surface tension has less tendency to wet the brick surface,
therefore reducing clinker coatability or adherence to the lining.
Alkali, MgO, and SO3 reduce liquid surface tension, as does temperature. Sulphur
and potassium have the strongest effects, followed by sodium
and magnesium. Therefore, MgO, SO3, and K2O are good coating promoters.
Conclusions Although the amount of liquid phase in the burning and transition zones of the kiln
is important to clinker formation and brick performance, the
rheological properties of the melt are even more important.
The rheological properties of the clinker melt control parameters,
such as clinker mineral formation, clinker coatability, clinker fineness,
cement strength, and refractory depth of infiltration.
It is then very important to keep fuel and raw materials properties and flame
temperature as steady as possible. Whenever introducing
drastic changes in raw material or fuel properties, the
refractory lining must be changed accordingly to meet the differences
in clinker coatability and burnability. This proves particularly true
when adding slags, kiln dust, or solid wastes to the kiln.

Milestones in clinker formation (2)
• Belite formation (700 – 1200 °C)
– 2 CaO + SiO2 Ca2SiO4
– Solid state reaction
– Reaction rate depends on contact surface between reactants
(diffusion of Ca2+)
Marl Limestone, sand
SiO2
CaO
Fast Slow
Raw material
Reaction rate
Raw meal fineness: 15 % R90&1.5% R212
Ratio of 90 µ / 212µ = 8 −9 must never be distributed

Milestones in clinker formation (3)
• Alite formation (1250 – 1450 °C)
– Ca2SiO4 + CaO Ca3SiO4
– Reaction rate depending on:
• Quantity and viscosity of the melt
• Diffusion distance between the reactants
• Formation of liquid phase (1250 °C)
– Pure system Al2O3 – CaO eutectic point at 1338 °C
– In clinker system other elements (e.g. MgO, Na2O) 1250 °C

Relevance of the liquid phase
• Significance for
– Clinker granulation
– Coating (but also formation of rings)
– Rate of alite formation
• Typical amount 20 –30 %
– Dry: ≤ 23 %
– Normal: 23 – 27 %
– Wet ≥ 27%
• Viscosity:
– Decreases with increasing temperature
– Depending on composition and minor elements
• Reduced by Na2O, CaO, MgO, Fe2O3, MnO
• Increased by SiO2, Al2O3

What is free lime ?
Have you seen a clinker with 0 % free lime ?
Free lime exists ,Is it because mis match of stoichiometry ?
Or is it because of unreacted calcite ?
Is it possible to reduce the free lime by increasing the liquid % ?
Or by reducing the LSF ?
Is it possible to reduce the free lime by overburning or heating the kiln
beyond the reaction temperature ?
temperatureOC
1100 1200 1300 1400 1500 1600
Liter weight, gms/liter
1700
1600
1500
1400
1300
0.5 %
1
1.5
2
2.5
Freelime
γ C3S formation

How to determine what constitutes a coarse grain?
The following particle sizes have been found critical for residual free lime
Quartz and silicates : + 45 microns
Calcite : + 125 microns
It has been found that at 1400 deg C an increase in the amount of coarse
Particles results in the following increase in free lime
+ 1 % quartz + 45 microns leads to + 0.93 % free lime
+ 1 % Calcite + 125 microns leads to + 0.56% free CaO
The following formula may be used for estimating the free CaO at 1400 Deg C
CaO 1400
0
C = 0.33.( LSF – 95)+1.8.(Ms -2) + 0.93.SiO2(+45 mic) +0.56.caCO3(+125 mic)

• increased water demand
• decreased early strength and
increased
• admixture incompatibility later
strength during periods where
alkalis
• abnormalities in setting
behavior are decreasing
• pack set due to static charge
(large alites)
• possible erratic
expansion
results due to
free lime
Cement
Performance
Possible
Effects:
• decrease in free lime
• low porosity, difficult grindability
• large alite
• possible poor nodulization
• variation in alkali sulfate
content
• kiln on the hot side
• increase in alkalis and sulfate in
kiln internal cycle, possible
surges, potential for buildups
• low porosity makes it hard to
cool
• lower clinker reactivity
• color differences, brown clinker
center
• large variations
in free lime
• poor belite
distribution
Clinker/Kiln
Operation
Possible
Effects:
AFTER — burning harderBEFORE

• less variability, more
uniformity
• smaller alite crystals,
enhanced reactivity,
possibly allowing lower
cement fineness.
• possible
erratic
expansion
results due to
free lime
Cement
Performan
ce
Potential
Effects:
• good distribution of free
lime
• good distribution of belite
• better clinker uniformity
• kiln is easier to control
• poor
distribution of
free lime and
belite
Clinker
Potential
Effects:
After — burning harderBefore

Effect of raw mix changes on resulting free lime
8
7
6
5
4
3
2
1
chemistry
LSF = 98
MS= 2.5
CaCO3 125 µ =7.2 %
SiO2 = +44 µ =1.2 %
17% .4900
LSF = 98
MS= 2.5
CaCO3 125 µ =5 %
SiO2 = +44 µ =1.2 %
12% .4900
LSF = 98
MS= 2.5
CaCO3 125 µ =5 %
SiO2 = +44 µ =1.2 %
12% .4900
CaCO3 125 µ =0.56 %
SiO2 = +44 µ =0.93 %
% estimated
1400 1450 1500 1550
O C

Burnability index = C3 S/ ( C3A + C4AF)
15
20
30
1300 1400 1500 Deg C
% liquid

Formation and size of nodules and formation of C3S at various temperatures both
as a function of time.
Dmm
T1 T2 T3
T1> T2> T3
Amount of C3S
time
D max
time

Behaviour of volatiles
• Chloride reacts primarily with alkalis forming NaCl and KCl . Any chloride in
In excess of alkali will combine with calcium to form CaCl2.
• A part of the alkalis in excess of chloride combine with sulphur to form
Na2SO4, K2SO4 and double salts such as Ca2K2(SO4)2
• Alkalis not combined with chloride or sulphur will be present as Na2O and
K2O embedded in the clinker minerals
• Sulphur in excess of alklis combine with CaO to form CaSO4

Kiln process
Volatile matter
Burning zone Back end etc
R
ε
d
bc K a
V
e
1.Evaporation factor ε = d/b = (b-c) / b = 1- c/b
2.Valve V = e / d = (a-c) / ( b-c)
3.Circulation factor K = b / a
4 .Residual component R = c / a

Evoporation n factor = 1 - % within clinker
% at kiln inlet ( LOI free basis)
ε = 1 means all evoporates and nothing leaves with the clinker
ε = 0 means nothing evaporates and all leave with the clinker
Average evaporation factors of various compounds
0.800 -0.200 – 0.100 – 0.150 – 0.100 –
0.10
Filter
value
0.420.05 –
0.25
0.050.05 –
0.2
0.150.05Pre heater
value
0.750.30 –
0.90
0.990 –
0.996
0.10 –
0.25
0.10 –
0.40
0.990 -
0.996
Evaporatio
n factor
Excess
SO3
Alkali
SO3
ClNa2OCl-free
K2O
KCl

Melting points and boiling points
13903281320360- hdroxide
14408011411768- chloride
-88416891074- sulphate
Decomp.850Decomp.894- carbonate
1275sublime350Decomp.- oxide
Boiling point
( O C)
Melting point
( O C)
Boiling point
( O C)
Melting point
( O C)
compound
K Na

ASR – Alkali-Sulfur ratio
SO3
Alk
optimum
SO3
80
K2O
94
+ 0.5 .
Na2O
62
= 1.1=
The sulphur and alkalis is the total input. If ratio exceeds 1.1 it is held that an
amount of sulphur is present in the kiln material which is not covered b alkalis
and as excess sulphur will form CaSO4.
The amount of excess sulfur ( E.S) is expressed in grams SO3 per 100 Kgs
And calculated according to the equation
E.S = 1000 .SO3 – 850 .K2O – 650 . Na2O ( gr SO3/ 100 kg clinker)
The limit on excess sulfur is given to be in the range of 250 – 600 g / 100 Kg clinker
For easy burning raw mix the high value 600 gram SO3 / 100 kg clinker should
Present no problems for the kiln opeartion , but for hard burning raw mix the lower
Value is the limit. Above these limits , the sulphur will give rise to coating problems
In the pre heater tower.

The amount of excess sulphur ( E.S) is expressed in grams per 100 Kg clinker
And calculated according to the equation
E.S = 1000.SO3 - 850.K2O – 650 .Na2O ( gr SO3/ 100 Kg clinker)
The limit on excess sulphur is given to be in the range of 250 – 600 g / 100 Kg clinker

-1-1-1-1Vo4-stages kiln
0.60.850.850.7Vo2-stages kiln
0.350.80.80.55Vo1-stage kiln
0.40.60.50.2VoLong dry kiln
0.40.60.60.4Vo-Wet dust –op-kiln
0.60.70.70.5VoWet module-op-kiln
Kiln Value
0.35 – 0.800.990-
0.996
0.10 -
0.25
0.20 -
0.4
εEvaporation factor
SO3ClNa2OK2Osymp
ol
Volatile Matter typical values for ε and V

0.5- 0.80.30.70.4Elec precipitator
value
-1-1-1-1Cooling tower value
0.30.70.80.6VtRaw mill value
0.550.50.70.6VktDedusting cyclone
Value
0.15-0.50.050.40.15Vm-4 stages
0.30.20.450.2Vc-2 stages
0.450.350.50.5Vc-1 stage
VcCyclone preheater
value
-1-1-1-1Precalciner kiln
SO3ClNa2OK2Osympol

Hard-burnt clinker limits the early strength
potential and promotes the late strength
potential.
This clinker does not need microscopy to
state a very hard burning regime, a bad
grindability and a modest early strength
potential. The clinker had been sent to be
investigated because of client complaints
about long setting times: Initial setting
time 200 min, final setting time 450 min.

How to assess and understand burnability (cont.)
• Characteristics considered to influence burnability:
– Chemical composition
LS
SR (quantity of liquid phase)
AR (viscosity of liquid phase)
Other influences: F, P2O5, MgO, SO3, alkalis
– Micro-homogeneity
Size and distribution of minerals in kiln feed
– Mineralogical composition
Clay Mica Feldspar Quartz “refractory” minerals
(mullite, corundum)
Easy to
react
difficult to
react

C4AF
C3S
C2S
Mgo
CaO
C3A
Pictoral representation
Of clinker micrograph

• Microscopic
A mixture of different mineral phases
Particle size ≈ 0 – 100 µm
• Macroscopic
A gray, granulated, rocky material
Grain size ≈ 0 – 50 mm
What is portland cement clinker

Uniform Nodule Sizes
Rather uniform-sized nodules are ingeneral an
advantage regarding burning efforts and uniform
degree of burning.

Quickly cooled clinkers are favourable for the early strength potential; no
alite is lost. The fine crystalline liquid phase prevents aluminate from an early
hydration. The influence of aluminate on the setting time is limited in quickly
cooled clinker.

Dusty Clinker
Elevated amount of clinker fines are especially common in high LS or
high SR clinkers. A low AR and high S content can also contribute to
clinker fines. These fines are a heat carrier in the kiln atmosphere and
contribute to a flat temperature profile.

The setting time is in tendency shortened by elevated amounts of coarse
crystalline aluminate and extended by high burning efforts; compensating
influences are possible. Decomposition effects due to slow cooling impair both
early and late strength potential.

Dusty clinker impairs the clinker grindability in tube mills
above Blaine values of > 2000.

Increasing free lime contents ( ) which are still below the expansion
risk level lead to shortened setting times, to slightly elevated early
strength potentials and to a decrease of the late strength potential.

Free lime contents above 2% can create an expansion risk in concrete. Here we see crack
formations due to free lime hydration which are filled with portlandite. The volume increase
which accompanies the density change from 3.33 g/ccm of lime to 2.41g/ccm of portlandite
is visible.

Clinker Granulometry
The clinker portion < 1mm is in general taken as an indicator of the dust load in
the burning process. Large kilns are more likely to have dusty clinkers. High-
grade corrective components or in general corrective components that are
difficult to grind or homogenize tend to contribute to elevated amounts of clinker
fines.
Graph: Stefan Gross
Clinker granulometry
0
10
20
30
40
50
60
70
80
90
100
0.0 0.1 1.0 10.0 100.0
sieve size / mm
passing/%
dust only
fine, dusty
normal, some dust
coarse, no dust
very coarse, no dust

Reactions during clinker cooling
• Resorption of alite
– Liquid phase + C3S ⌫ C2S + C3A + C2(A,F)
• Decomposition of alite
– very slow cooling
– reducing conditions
– C3S ⌫ C2S + CaO
• Crystallization of liquid phase
– Slow cooling: large crystals – improved reactivity

Cooling
Once the formation of the
C3S is complete,
there is no further value in
prolonging the process at
this elevated temperature.
This final process is called
cooling, not just to reduce
the temperature, but to
freeze the crystal growth
and to convert the liquid
phase back to a solid for
easier transport.
At this point, C3A and C4AF
cool to form solids.
The objective
now is to halt
further growth of
the C3S crystals
and to trap any
dis-solved MgO
present in the
amorphous
stage.
alit
e
alit
e
belitebelite
aluminat
e
aluminat
e
ferriteferrite

Influence of cooling on clinker phases
Fast cooling
Well distributed
small crystals
Slow cooling
Larger crystals

C3S
Clinker when it is quenched in cooler it creates micro cracks which
needs less energy for comminution during grinding.
C3S
Clinker cooling
C2S

How fast must clinker be cooled ?
Clinker cooling takes place in two stages, the first
cooling stage occurring within the kiln, the second in the clinker cooler.
The rate of cooling within the kiln depends upon the flame length, the position
in the kiln and the throughput and speed of the kiln charge. The temperature
of clinker at the outlet of the kiln is around between 1350 oC and 1200 oC.
If the flame is long, this part of the cooling process will be very slow and alite
and belite can grow into an excessive crystal size. In some cases,
(when the cooler efficiency is low) alite
partially decomposes into belite and free lime (see fig. 1).
Fig.1: Alite decomposition into
belite and free lime. 250 X
The texture of the solidified liquid phase is quite dependent on the cooling
rate. During slow cooling, the crystals have time to grow. Ferrite and
aluminate form a coarsely grained matrix (see fig. 2). Alternatively, if the
cooling process proceeds quickly, the opposite is true - the crystals are fine
grained (see fig. 3).
Fig.2: Differentiated aluminate (grey) and ferrite (white)
caused by slow cooling. 640 X Fig.3: Finely grained aluminate
and ferrite duCooling can also proceed so quickly that the crystals can
only form in the submicroscopic range. Distinction between aluminate and
ferrite is no longer possible by microscopy but can be effected by X-ray
methods.
Why raw meals must be homogeneous?
If the raw meal is homogeneous enough, units of varying sizes will exist
which do not have the required chemical composition. It can be easily
deduced from the phase diagram for the system CaO - Al2O3 - Fe2O3 -
SiO2 the
phase compositions which can coexist assuming different volumes to have
different chemical composition. In figure A the different phase
assemblages in the system CaO - Al2O3 - SiO2 can be seen.

Minor components have major influence on
burnability and cement properties. Many of
them act as fluxes and mineralisers in
burning. They change the course of the
reaction , morphology of the clinker and
cement properties.

Mineraliser accelerates the C3S formation , increases rate of
conversion from C2S to C3S
Mineralisers

Influence of minor components on the burnability of rawmeal , process and
Quality of cement
Setting retarder
Contardictary
results on strength
In adm amount
C3S
0.2 -0.4 % good
burbality
If it is > 0.5 % coating
in preheater
0.2 – 0.6TiO2
Setting accelerated
Early strength up
Final strength down
In adm amount
C3S
C2S
C3A
0.2 – 0.4 % good
burnability.If it is >1%
coating in preheater
0.1 – 0.5 %
0.4 – 1.2 %
volatile
Na2O,
K2O
Early strength
remarkably up if <
0.5%
Early and late
strength down if >
0.5%
C3S0.1 – 0.3
Max=0.5. If more
than 0.5% coating in
preheater
0.1 – 0.34 % volatileP2O5
Alkali
sulfate is
easily
formed
Setting accelearted
Early strength up
Late strength down
C3S
C2S
C3A
Less the better
Max limit < 0.5 %
If it is > 0.5 % coating
in preheater & kiln
0.2 – 0.9 % volatileSO3
Periclase
causes
expansion
early sterngth up if
< 2.0%
late strength down
if > 2.0
C3S if it is less
than 2.0%
1 – 1.5 % good
burability
good grindability
max limit -2.0%
0.8 – 2.5 , non -volatileMgO
Influence on quality
of cement, strength
Early late
Influence on
hydraulic
reactivity
Influence on
manufacturing
process
Content volatile/nonvolatileelement

Initial strength up
Final strength down
C3SMax = 2%. If >2 %
coating in preheater
Burning improved
F
Early strength up
Late strength down
C3S
C2S
BaO reacts with Silica
earlier than Cao.
Hence free lime
increases
900 ppmSrO,
BaO
Cemen
t color
change
to
green
0r blue
Initial strength –up
Final strength - down
C3S
C2S
C3A
C4AF
Good burability as it
is flux
Mn
Accelerate setting
Initial strength up
Late strength
undefinite
C3AIf >100 ppm coating
in preheater.Good
burnability
50 – 80 ppmCl
Influence on quality of
cement
Influence on
hydraulic
reactivity
Influence on
manufacturing
process
Content
volatile/nonvolatile
element

Thank you for your
kind attention
K.P.Pradeep kumar

Raw mix characteristics final

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