WELCOME TO THE TRAINING ON KILN OPERATION & OPTIMISATION

Raw mix characteristics

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 pointin maintaining of quality of cement. The mineral compoundscontaining 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 clinker2. Chemical and mineralogical

composition of raw mix3. Chemical and mineralogical composition

of clinker4. Burning process & cooling process5. 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 cementWhite cement,Oil well cement,Sulfate resistant cement,Slag cementOther cements for special application

Gpsum&fly ash orOther additive quality

Physical charateristicsParticle size & shapeparticle size distributionHomogenity

Characteristics of raw meal

ChemicalcharactericticsChemical composition

MineralogicalMorphology( 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 – 0.3Upto0.2

Upto 0.1Na2O0.2 – 1.4Up to 10.5 - 50.1 - 4Upto 0.3K2O

0.3 - 3Up to 0.5Up to 50.5 -50.5 - 5MgO40 -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+TiO212 -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 distributionAn efficient separator & efifcient grinding system narrow downthe particle distribution. Wide distribution means heterogenity in physical

and chemical characteristics of raw meal.

Optical micrograph and super imposed size analysisof quality audit standards

Calcite-rhombo

Calcite-cubic

quartz Silica sand

Kaolinite

Minerals in a lime stone

Pure lime stoneonly Calcite > 99 % CaCO3

Impure lime stone imbeddedwith 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& inputTo raw mill

time

StdLSF

Outlet of mill

Influence of efficient mining on quality

Std of LSF =1SIM=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 / Fe2O3AlM

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 strengthhigh fuel consumption

< 99 , easy to burn , excess coating , excess liquid phase , possible brick infiltrationreduced cement strength , low free limeacceptable standard deviation = 1.2

Effects :High MsResults in hard burning & high fuel consumption.Causes Unsoundness.Difficulty in coating formation.Deteriorates Kiln Lining.Results in slow setting and hardening of cementLower 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:- 1.7-2.3The Hydraulic Modulus of good quality cements was approximately2. Cement with HM<1.7 showed mostly insufficientstrength and cement with HM>2.3 and more had poorstability of volume. It was found that with an increasingHM, 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 timesthe Hydraulic Modulus is still used. Later fora 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 sieve3. Size distribution of free silica4. Degree of homogeneity (both chemical & mineral)5. Liquid phase of clinkering temperatures.6. Moisture content of raw meals

Effects: Higher MAImparts harder burning & e tails higher fuel consumption.Increases the C3A and reduces C4AF contentsIncreases both C3S and C2S (C3S>C2S)Reduces the liquid phase and kiln outputTends to render quick setting and strong at early ages.Increases viscosity of liquid phase in raw mixMA determines the role of Fluxes in raw mixMA <1.23: - Al2O3 acts as FluxMA >1.23: - Fe2O3 acts as FluxLower MAIf MA is too low and raw mix is without free silica, clinker sticking and balling is high.

1. Mineralogical Make-up2. 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

ni - n

C3S actual = the calculated C3S of one instantaneous daily sample of kiln raw mix feedC3S Target = the C3S target established for the mill productn = 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 calledstandard deviation. The standard deviation of a property can be calculated by taking anumber of measurements on the property (such as LSF, SR etc.), and applying thefollowing formula:-

Where X is the measured variable (e.g. LSF)X is the variable mean (or average)N is the number of measurements or observationsTable 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 likeMoisture , 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

Blending silo

“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 65.4SiO2 22.2Al2O3 5.0Fe2O3 2.8

∼ 5 %

∼ 95 %

Milestones in clinker formation0 200 400 600 800 1000 1200 1400

Dehydration

Decarbonation

Belite formation

Liquid phaseformation

Aliteformation

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

PressureTim

e

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) inthe clinker which can be derived from chemical analysis according Bogue formula. Some other minute phases alsoexist 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 thefollowing composition.

Microphotograph of clinker

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 micronCrystal Morphology:

Alite: prismatic hexagonalBelite: roundC3A: Fine crystals in matrix.

Crystal Distribution:Minimum clustering, total porosity: 25-30%

Litre weight: 1150-1350 g/lGranulometry : 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 +SAt 1340 o C , (AR > 1.38) L.P = 6.1 F + M + N +K + SAt 1400 o C, L.P = 2.95 A+2.20 F+M+N+K+SAt 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 optimumand 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 cWith change in Silica ratio and alumina ratio at 100 % LSF

40% 35% 30 %

25 % 20%

Silica ratio S/ ( A+F)

Alum

ina

ratio

A/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 illustrationOf 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 reducesfree lime due to intense stirring there by improvingbetter heat exchange.It also improves nodulisation.

Lower rpm , high % filling , less activeLayer , high free lime, high radiationlosses

high rpm , low % filling , more activeLayer , low free lime and low radiationlosses

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 flameenvelope. In this case there is a chance of chars trapped inside the charge causinglocalised 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 mostpronounced effect on liquid-phase viscosity. Increasing theburning temperature by 93degrees C (199degrees F), reducesliquid 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 refractorylining, 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 detrimentalto 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 nodulizebetter than low C3A clinkers. Moreover, the liquid phase is considerablyless damaging to the refractory lining when the liquid is viscous.Another important property of the liquid phase is its surface tension, or itsability to "wet" the lining. The surface tension has a direct impacton 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. Sulphurand potassium have the strongest effects, followed by sodiumand 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, therheological 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 flametemperature as steady as possible. Whenever introducingdrastic changes in raw material or fuel properties, therefractory 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

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 kilnbeyond the reaction temperature ?

tem

pera

ture

OC

1100 1200 1300 1400 1500 1600Liter weight, gms/liter

1700

1600

1500

1400

1300

0.5 %

1

1.5

2

2.5

Free lime

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 micronsCalcite : + 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 belitedistribution

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 Performance 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

1chemistry

LSF = 98MS= 2.5CaCO3 125 µ =7.2 %SiO2 = +44 µ =1.2 %17% .4900

LSF = 98MS= 2.5CaCO3 125 µ =5 %SiO2 = +44 µ =1.2 %12% .4900

LSF = 98MS= 2.5CaCO3 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 bothas 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 inIn excess of alkali will combine with calcium to form CaCl2.

• A part of the alkalis in excess of chloride combine with sulphur to formNa2SO4, K2SO4 and double salts such as Ca2K2(SO4)2

• Alkalis not combined with chloride or sulphur will be present as Na2O andK2O 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

εd

bc K a

Ve

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 clinkerε = 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

Evaporation 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

SO3Alk

optimum

SO380

K2O 94

+ 0.5 .Na2O62

= 1.1=

The sulphur and alkalis is the total input. If ratio exceeds 1.1 it is held that anamount of sulphur is present in the kiln material which is not covered b alkalisand as excess sulphur will form CaSO4.

The amount of excess sulfur ( E.S) is expressed in grams SO3 per 100 KgsAnd 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 clinkerFor easy burning raw mix the high value 600 gram SO3 / 100 kg clinker shouldPresent no problems for the kiln opeartion , but for hard burning raw mix the lowerValue is the limit. Above these limits , the sulphur will give rise to coating problemsIn the pre heater tower.

The amount of excess sulphur ( E.S) is expressed in grams per 100 Kg clinkerAnd 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

SO3ClNa2OK2Osympol

Volatile Matter typical values for ε and V

0.5- 0.80.30.70.4Elec precipitatorvalue

-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 preheatervalue

-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 compositionLS

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 representationOf clinker micrograph

• MicroscopicA mixture of different mineral phasesParticle size ≈ 0 – 100 µm

• MacroscopicA gray, granulated, rocky materialGrain 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 portlanditeis 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

4050

60

70

80

90

100

0.0 0.1 1.0 10.0 100.0sieve size / mm

pass

ing

/ %

dust onlyfine, dustynormal, some dustcoarse, no dustvery 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

CoolingOnce 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.

alite

alite

belitebelite

aluminate

aluminate

ferriteferrite

Influence of cooling on clinker phases

Fast coolingWell distributedsmall crystals

Slow cooling Larger crystals

C3S

Clinker when it is quenched in cooler it creates micro cracks whichneeds less energy for comminution during grinding.

C3S

Clinker cooling

C2S

How fast must clinker be cooled ?Clinker cooling takes place in two stages, the firstcooling 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) alitepartially 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 aluminateand 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 phaseassemblages in the system CaO - Al2O3 - SiO2 can be seen.

Minor components have major influence onburnability and cement properties. Many ofthem act as fluxes and mineralisers in burning. They change the course of thereaction , morphology of the clinker andcement 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 andQuality of cement

Setting retarderContardictary

results on strength

In adm amountC3S

0.2 -0.4 % good burbality

If it is > 0.5 % coating in preheater

0.2 – 0.6TiO2

Setting acceleratedEarly strength up

Final strength down

In adm amount C3SC2SC3A

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 acceleartedEarly strength up

Late strength down

C3SC2SC3A

Less the betterMax limit < 0.5 %

If it is > 0.5 % coating in preheater & kiln

0.2 – 0.9 % volatileSO3

Periclasecauses

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 grindabilitymax 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 upFinal strength down

C3SMax = 2%. If >2 % coating in preheaterBurning improved

F

Early strength upLate strength down

C3SC2S

BaO reacts with Silica earlier than Cao. Hence free lime increases

900 ppmSrO,BaO

Cement color change to green 0r blue

Initial strength –upFinal strength - down

C3SC2SC3AC4AF

Good burability as it is flux

Mn

Accelerate setting Initial strength upLate strength undefinite

C3AIf >100 ppm coating in preheater.Goodburnability

50 – 80 ppmCl

Influence on quality of cement

Influence on hydraulic reactivity

Influence on manufacturing process

Content volatile/nonvolatile

element

Thank you for yourkind attention

K.P.Pradeep kumar