Cement raw mix characteristics

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Cement raw mix characteristics

  1. 1. WELCOME TO THE TRAININGON KILN OPERATION &OPTIMISATION
  2. 2. Raw mix characteristics
  3. 3. Cement is a substance (often a ceramic) that by a chemicalreaction 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, aluminaand iron oxide are used in cement manufacturing process.Therefore it is usually necessary to select a measured mixture of ahigh 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 compositionof the raw mix is to determine the quantitative proportions of theraw components, in order to give the clinker the desired chemicaland mineralogical compositionWhat is cement ?
  4. 4. qualityFactors influencing the cement quality1. Mechanical handling of clinker2. Chemical and mineralogicalcomposition of raw mix3. Chemical and mineralogical compositionof clinker4. Burning process & cooling process5. Chemical composition of fuels (ash)6. Circulation phenomena (volatiles)
  5. 5. Process flow sheetCBA analyzerCBA analyzerX rayanalyzer
  6. 6. Cement quality – type of cementClinker qualityFuel chemistryRaw mix designOPC, PPC, WC, OWC, SRC,SCOrdinary portland cement,Pozalona portland cementWhite cement,Oil well cement,Sulfate resistant cement,Slag cementOther cements for special applicationGpsum&fly ash orOther additive quality
  7. 7. Physical charateristicsParticle size & shapeparticle size distributionHomogenityCharacteristics of raw mealChemicalcharactericticsChemical compositionMineralogicalMorphology( crystal size ofminerals &Cystal distribution)
  8. 8. Up to 1.2Upto 0.5Up to 30.1 -0.4Up to 0.1SO30.01 – 0.1ClUp to 0.3Up to 0.50.1 – 0.3Upto0.2Upto 0.1Na2O0.2 – 1.4Up to 10.5 - 50.1 - 4Upto 0.3K2O0.3 - 3Up to 0.5Up to 50.5 -50.5 - 5MgO40 -450.1-30.5 – 2.55 - 5252 - 55CaOUp to 20.5 - 22 -150.5 -100.1 -0.5Fe2O3+Mn2O32 -50.5 - 37 -301 - 200.1 - 1Al2O3+TiO212 -1680 - 9937 -783 - 500.5 - 3SiO232 - 36Up to 5%1 - 202 -4240-44Ig lossrawmixsandclaymarllimestoneWeight loss %Chemical composition of cement raw materials and mix
  9. 9. Physical characteristicsof Raw meal
  10. 10. Particle size & Particle size distributionAn efficient separator & efifcient grinding system narrow downthe particle distribution. Wide distribution means heterogenity in physicaland chemical characteristics ofraw meal.
  11. 11. Optical micrograph and super imposed size analysisof quality audit standards
  12. 12. Calcite-rhomboCalcite-cubicquartz Silica sandKaoliniteMinerals in a lime stone
  13. 13. Pure lime stoneonly Calcite > 99 % CaCO3Impure lime stone imbeddedwith silicates and other mineralsLime stone
  14. 14. timetemperatureImpure calcitepure calciteheatCO2
  15. 15. Well developed quarryIn a well developed mine, the mines manager knows where what and how much isavailable?If quality is controlled in mines then the quality variation is minimised to a greatextent through mines blend program through griging or geostaticsBenches (10 M height)
  16. 16. From mines(input to stacker)Output ofblendingSystem& inputTo raw milltimeStdLSFOutlet of millInfluence of efficient mining on quality
  17. 17. Std of LSF =1SIM=0.2Std of ,CaO < 0.2Control on chemistry
  18. 18. Main parameters for raw mix designLime saturation factor = CaO / (2.8 SiO2+1.65Al2O3 + 0.65 Fe2O3)( LSF)Silica modulus = SiO2 / ( Al2O3+Fe2O3)Alumina modulus = Al2O3 / Fe2O3AlMHere we have apply the formula (as per British Standard)LSF = CaO-0.7SO3(2.8*SiO2 + 1.2* Al2O3 + 0.65*Fe2O3)(SIM)
  19. 19. Lime saturation factor on clinker basisIf 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
  20. 20. 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 kilnEffect of modulieEffects: Higher LSFImparts 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
  21. 21. 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 theheat of hydration rises. Simultaneously theresistance 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 theseratios supplement the hydraulic modulus.Hydraulic modulus
  22. 22. 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 mealsEffects: Higher MAImparts harder burning & e tails higher fuelconsumption.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.
  23. 23. 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 onkiln feed burn ability and volatility.Characterization of kiln feed
  24. 24. In homogeneous homogeneousKiln feed uniformity index (KFUI)KFUI= n ( C3S actual - C3S target )2ni - nC3S 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)
  25. 25. Homogenising systems3.1 Variabilitv and standard deviationThe 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 ) 2N - 1
  26. 26. Different stacking systemStacking and reclaiming sytem is selected on the basis of material characteristics likeMoisture , variability in mines, size and size distribution of particles.
  27. 27. Circular stock pileReclaiming zoneStacking zoneBlended zone
  28. 28. Longitudinal stock pileEnd cone problem
  29. 29. Well blended slice without end coneEnd cone problems Linear stock pileBlending ratio = S in / S outMore variation, high stdLess variation, low std
  30. 30. Blending silo
  31. 31. “Average” clinker compositionMgO 1.80SO3 0.54K2O 0.63Na2O 0.25TiO2 0.27Mn2O3 0.09P2O5 0.14Cl- 0.01F- 0.08LOI: 0.3 %CaO 65.4SiO2 22.2Al2O3 5.0Fe2O3 2.8∼ 5 %∼ 95 %
  32. 32. Milestones in clinker formation0 200 400 600 800 1000 1200 1400DehydrationDecarbonationBelite formationLiquid phaseformationAliteformationTemperature [°C]
  33. 33. 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)• Alkalisulfates(unwanted)Mineral phases in raw meal Mineral phases in clinkerTemperaturePressureTime
  34. 34. Potential clinker compositionThe chemical analysis presents a picture of the composition ofthe oxides in the clinker. There are four mineralogical phasesare C3S (alite), C2S (belite), C3A (Aluminate), C4AF (Ferrite) inthe clinker which can be derived from chemical analysisaccording 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.
  35. 35. Microphotograph of clinker
  36. 36. Parameters for good clinker:<0.5<1.2<2.0<1.564-66%SO3%(K2O,Na2O)% MgO% Free-CaO%T.CaOMINEROLOGY: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
  37. 37. 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 itThree concepts in the reation between raw meal characteristics andKiln 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
  38. 38. Required burning zone temperatureRBT = 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+SPotential 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.
  39. 39. 1 1.5 2 2.5 332.521.510.5Variation in % liquid phase at 1338 deg cWith change in Silica ratio and alumina ratio at 100 % LSF40% 35%30 %25 %20%Silica ratio S/ ( A+F)AluminaratioA/F15 %15 %
  40. 40. Influence of minor components on liquid propertiesCan either increase or decrease both liquid viscosityand surface tension depending upon theelectronegativity of the ions and alumina ratio .Trace metalsLowers the liquid viscosityCl, FBehaves similarly to Fe2O3 in increasing the level offlux and reducing its viscosityMn2O3Forms a separate liquid to the main oxide flux ataround 1250 deg c . At higher temperatures it is partiallymiscible and results in both a higher viscosity andhigher surface tension. Overall effect is to acceleratethe formation nodules at a lower temperature but restricttheir growth resulting in dustier clinker.K2O , Na2Oand SO3Can increase the liquid phase present at burning zonetemperatureMgOInfluence on liquid formationMinorcomponents
  41. 41. Raw material particlesBefore the reactionRaw material particlesduring the reaction
  42. 42. Schematic illustrationOf clinker at 1400 deg C
  43. 43. Active layerPassive layerFree boardRadial cross section of rotary kilnHigher the rpm more the area of active layer which reducesfree lime due to intense stirring there by improvingbetter heat exchange.It also improves nodulisation.
  44. 44. Lower rpm , high % filling , less activeLayer , high free lime, high radiationlosseshigh rpm , low % filling , more activeLayer , low free lime and low radiationlossesInfluence of revolutions / minute on kiln operationOptimum % filling = 9 – 11 with raw meal retention time of 20 -25 minutesunfavorable favorable
  45. 45. Influence of revolutions / minute on kiln operationunfavorable favorableHigh 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.
  46. 46. Sequence of chemical reactions in cement rotary kiln,temperature and energy input
  47. 47. 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 factexplains why hotter-than-normal temperatures are beneficialto clinkering yet potentially harmful to the refractorylining, as shown in Photo 1.MgO, alkali sulphates, fluorides,and chlorides also reduce liquid-phase viscosity. Extreme cautionshould be exerted when insufflating calcium chloride into the burningzone as a way to reduce alkali in the clinker. The injectionof sodium carbonate into the burning zone also is detrimentalto the refractory lining.Free alkali and phosphorus increaseliquid-phase viscosity, but this effect is offset by MgO and SO3. OnlyClinkers with sulphate-alkali ratio lower than 0.83 and low MgO wouldexperience the negative effects of high liquid viscosity.Properties of liquid
  48. 48. 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 throughthe nodules. The resulting clinker contains less dust(fraction below 32 mesh) and lower free lime content. A liquid phasewith 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 kilnis 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 differencesin clinker coatability and burnability. This proves particularly truewhen adding slags, kiln dust, or solid wastes to the kiln.
  49. 49. 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, sandSiO2CaOFast SlowRaw materialReaction rateRaw meal fineness: 15 % R90&1.5% R212Ratio of 90 µ / 212µ = 8 −9 must never be distributed
  50. 50. 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
  51. 51. 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
  52. 52. 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
  53. 53. 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 ?temperatureOC1100 1200 1300 1400 1500 1600Liter weight, gms/liter170016001500140013000.5 %11.522.5Freelimeγ C3S formation
  54. 54. How to determine what constitutes a coarse grain?The following particle sizes have been found critical for residual free limeQuartz and silicates : + 45 micronsCalcite : + 125 micronsIt has been found that at 1400 deg C an increase in the amount of coarseParticles 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 CaOThe following formula may be used for estimating the free CaO at 1400 Deg CCaO 14000C = 0.33.( LSF – 95)+1.8.(Ms -2) + 0.93.SiO2(+45 mic) +0.56.caCO3(+125 mic)
  55. 55. • increased water demand• decreased early strength andincreased• admixture incompatibility laterstrength during periods wherealkalis• abnormalities in settingbehavior are decreasing• pack set due to static charge(large alites)• possible erraticexpansionresults due tofree limeCementPerformancePossibleEffects:• decrease in free lime• low porosity, difficult grindability• large alite• possible poor nodulization• variation in alkali sulfatecontent• kiln on the hot side• increase in alkalis and sulfate inkiln internal cycle, possiblesurges, potential for buildups• low porosity makes it hard tocool• lower clinker reactivity• color differences, brown clinkercenter• large variationsin free lime• poor belitedistributionClinker/KilnOperationPossibleEffects:AFTER — burning harderBEFORE
  56. 56. • less variability, moreuniformity• smaller alite crystals,enhanced reactivity,possibly allowing lowercement fineness.• possibleerraticexpansionresults due tofree limeCementPerformancePotentialEffects:• good distribution of freelime• good distribution of belite• better clinker uniformity• kiln is easier to control• poordistribution offree lime andbeliteClinkerPotentialEffects:After — burning harderBefore
  57. 57. Effect of raw mix changes on resulting free lime87654321chemistryLSF = 98MS= 2.5CaCO3 125 µ =7.2 %SiO2 = +44 µ =1.2 %17% .4900LSF = 98MS= 2.5CaCO3 125 µ =5 %SiO2 = +44 µ =1.2 %12% .4900LSF = 98MS= 2.5CaCO3 125 µ =5 %SiO2 = +44 µ =1.2 %12% .4900CaCO3 125 µ =0.56 %SiO2 = +44 µ =0.93 %% estimated1400 1450 1500 1550O C
  58. 58. Burnability index = C3 S/ ( C3A + C4AF)1520301300 1400 1500 Deg C% liquid
  59. 59. Formation and size of nodules and formation of C3S at various temperatures bothas a function of time.DmmT1 T2 T3T1> T2> T3Amount of C3StimeD maxtime
  60. 60. 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
  61. 61. Kiln processVolatile matterBurning zone Back end etcRεdbc K aVe1.Evaporation factor ε = d/b = (b-c) / b = 1- c/b2.Valve V = e / d = (a-c) / ( b-c)3.Circulation factor K = b / a4 .Residual component R = c / a
  62. 62. 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 clinkerAverage evaporation factors of various compounds0.800 -0.200 – 0.100 – 0.150 – 0.100 –0.10Filtervalue0.420.05 –0.250.050.05 –0.20.150.05Pre heatervalue0.750.30 –0.900.990 –0.9960.10 –0.250.10 –0.400.990 -0.996Evaporation factorExcessSO3AlkaliSO3ClNa2OCl-freeK2OKCl
  63. 63. Melting points and boiling points13903281320360- hdroxide14408011411768- chloride-88416891074- sulphateDecomp.850Decomp.894- carbonate1275sublime350Decomp.- oxideBoiling point( O C)Melting point( O C)Boiling point( O C)Melting point( O C)compoundK Na
  64. 64. ASR – Alkali-Sulfur ratioSO3AlkoptimumSO380K2O94+ 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 equationE.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.
  65. 65. The amount of excess sulphur ( E.S) is expressed in grams per 100 Kg clinkerAnd calculated according to the equationE.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
  66. 66. -1-1-1-1Vo4-stages kiln0.60.850.850.7Vo2-stages kiln0.350.80.80.55Vo1-stage kiln0.40.60.50.2VoLong dry kiln0.40.60.60.4Vo-Wet dust –op-kiln0.60.70.70.5VoWet module-op-kilnKiln Value0.35 – 0.800.990-0.9960.10 -0.250.20 -0.4εEvaporation factorSO3ClNa2OK2OsympolVolatile Matter typical values for ε and V
  67. 67. 0.5- 0.80.30.70.4Elec precipitatorvalue-1-1-1-1Cooling tower value0.30.70.80.6VtRaw mill value0.550.50.70.6VktDedusting cycloneValue0.15-0.50.050.40.15Vm-4 stages0.30.20.450.2Vc-2 stages0.450.350.50.5Vc-1 stageVcCyclone preheatervalue-1-1-1-1Precalciner kilnSO3ClNa2OK2Osympol
  68. 68. Hard-burnt clinker limits the early strengthpotential and promotes the late strengthpotential.This clinker does not need microscopy tostate a very hard burning regime, a badgrindability and a modest early strengthpotential. The clinker had been sent to beinvestigated because of client complaintsabout long setting times: Initial settingtime 200 min, final setting time 450 min.
  69. 69. How to assess and understand burnability (cont.)• Characteristics considered to influence burnability:– Chemical compositionLSSR (quantity of liquid phase)AR (viscosity of liquid phase)Other influences: F, P2O5, MgO, SO3, alkalis– Micro-homogeneitySize and distribution of minerals in kiln feed– Mineralogical compositionClay Mica Feldspar Quartz “refractory” minerals(mullite, corundum)Easy toreactdifficult toreact
  70. 70. C4AFC3SC2SMgoCaOC3APictoral representationOf clinker micrograph
  71. 71. • MicroscopicA mixture of different mineral phasesParticle size ≈ 0 – 100 µm• MacroscopicA gray, granulated, rocky materialGrain size ≈ 0 – 50 mmWhat is portland cement clinker
  72. 72. Uniform Nodule SizesRather uniform-sized nodules are ingeneral anadvantage regarding burning efforts and uniformdegree of burning.
  73. 73. Quickly cooled clinkers are favourable for the early strength potential; noalite is lost. The fine crystalline liquid phase prevents aluminate from an earlyhydration. The influence of aluminate on the setting time is limited in quicklycooled clinker.
  74. 74. Dusty ClinkerElevated amount of clinker fines are especially common in high LS orhigh SR clinkers. A low AR and high S content can also contribute toclinker fines. These fines are a heat carrier in the kiln atmosphere andcontribute to a flat temperature profile.
  75. 75. The setting time is in tendency shortened by elevated amounts of coarsecrystalline aluminate and extended by high burning efforts; compensatinginfluences are possible. Decomposition effects due to slow cooling impair bothearly and late strength potential.
  76. 76. Dusty clinker impairs the clinker grindability in tube millsabove Blaine values of > 2000.
  77. 77. Increasing free lime contents ( ) which are still below the expansionrisk level lead to shortened setting times, to slightly elevated earlystrength potentials and to a decrease of the late strength potential.
  78. 78. Free lime contents above 2% can create an expansion risk in concrete. Here we see crackformations due to free lime hydration which are filled with portlandite. The volume increasewhich accompanies the density change from 3.33 g/ccm of lime to 2.41g/ccm of portlanditeis visible.
  79. 79. Clinker GranulometryThe clinker portion < 1mm is in general taken as an indicator of the dust load inthe burning process. Large kilns are more likely to have dusty clinkers. High-grade corrective components or in general corrective components that aredifficult to grind or homogenize tend to contribute to elevated amounts of clinkerfines.Graph: Stefan GrossClinker granulometry01020304050607080901000.0 0.1 1.0 10.0 100.0sieve size / mmpassing/%dust onlyfine, dustynormal, some dustcoarse, no dustvery coarse, no dust
  80. 80. 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
  81. 81. CoolingOnce the formation of theC3S is complete,there is no further value inprolonging the process atthis elevated temperature.This final process is calledcooling, not just to reducethe temperature, but tofreeze the crystal growthand to convert the liquidphase back to a solid foreasier transport.At this point, C3A and C4AFcool to form solids.The objectivenow is to haltfurther growth ofthe C3S crystalsand to trap anydis-solved MgOpresent in theamorphousstage.alitealitebelitebelitealuminatealuminateferriteferrite
  82. 82. Influence of cooling on clinker phasesFast coolingWell distributedsmall crystalsSlow coolingLarger crystals
  83. 83. C3SClinker when it is quenched in cooler it creates micro cracks whichneeds less energy for comminution during grinding.C3SClinker coolingC2S
  84. 84. 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 positionin the kiln and the throughput and speed of the kiln charge. The temperatureof 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 aliteand 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 intobelite and free lime. 250 XThe texture of the solidified liquid phase is quite dependent on the coolingrate. During slow cooling, the crystals have time to grow. Ferrite andaluminate form a coarsely grained matrix (see fig. 2). Alternatively, if thecooling process proceeds quickly, the opposite is true - the crystals are finegrained (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 canonly form in the submicroscopic range. Distinction between aluminate andferrite is no longer possible by microscopy but can be effected by X-raymethods.Why raw meals must be homogeneous?If the raw meal is homogeneous enough, units of varying sizes will existwhich do not have the required chemical composition. It can be easilydeduced from the phase diagram for the system CaO - Al2O3 - Fe2O3 -SiO2 thephase compositions which can coexist assuming different volumes to havedifferent chemical composition. In figure A the different phaseassemblages in the system CaO - Al2O3 - SiO2 can be seen.
  85. 85. Minor components have major influence onburnability and cement properties. Many ofthem act as fluxes and mineralisers inburning. They change the course of thereaction , morphology of the clinker andcement properties.
  86. 86. Mineraliser accelerates the C3S formation , increases rate ofconversion from C2S to C3SMineralisers
  87. 87. Influence of minor components on the burnability of rawmeal , process andQuality of cementSetting retarderContardictaryresults on strengthIn adm amountC3S0.2 -0.4 % goodburbalityIf it is > 0.5 % coatingin preheater0.2 – 0.6TiO2Setting acceleratedEarly strength upFinal strength downIn adm amountC3SC2SC3A0.2 – 0.4 % goodburnability.If it is >1%coating in preheater0.1 – 0.5 %0.4 – 1.2 %volatileNa2O,K2OEarly strengthremarkably up if <0.5%Early and latestrength down if >0.5%C3S0.1 – 0.3Max=0.5. If morethan 0.5% coating inpreheater0.1 – 0.34 % volatileP2O5Alkalisulfate iseasilyformedSetting acceleartedEarly strength upLate strength downC3SC2SC3ALess the betterMax limit < 0.5 %If it is > 0.5 % coatingin preheater & kiln0.2 – 0.9 % volatileSO3Periclasecausesexpansionearly sterngth up if< 2.0%late strength downif > 2.0C3S if it is lessthan 2.0%1 – 1.5 % goodburabilitygood grindabilitymax limit -2.0%0.8 – 2.5 , non -volatileMgOInfluence on qualityof cement, strengthEarly lateInfluence onhydraulicreactivityInfluence onmanufacturingprocessContent volatile/nonvolatileelement
  88. 88. Initial strength upFinal strength downC3SMax = 2%. If >2 %coating in preheaterBurning improvedFEarly strength upLate strength downC3SC2SBaO reacts with Silicaearlier than Cao.Hence free limeincreases900 ppmSrO,BaOCement colorchangetogreen0r blueInitial strength –upFinal strength - downC3SC2SC3AC4AFGood burability as itis fluxMnAccelerate settingInitial strength upLate strengthundefiniteC3AIf >100 ppm coatingin preheater.Goodburnability50 – 80 ppmClInfluence on quality ofcementInfluence onhydraulicreactivityInfluence onmanufacturingprocessContentvolatile/nonvolatileelement
  89. 89. Thank you for yourkind attentionK.P.Pradeep kumar

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