1 refa1 clinker burning , coating form , flame

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Clinker chemistry(related to Refractory)

Burning mechanism

Mechanism of clinker coating formation

and

Flame

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Clinker chemistrySilica ratio = SiO2 / Al2O3+ Fe2O3 normally 1.9 - 3.2

(optimum: 2.2 - 2.6)Silica ratio characterizes the ratio solid / liquid i.e., Theamount of liquid phases in the clinker.

Alumina ratio = Al2O3 / Fe2O3 , normally 1.5 - 2.5

Alumina ratio characterizes the composition of the melt and itsviscosity in the clinker.

Low AR ( < 1.5 ) increases the Fe2O3 content, decreases the viscosityand increases the infiltration of liquid, deep into the brick

Silicic acid ratio, SAR = SiO2 / Al2O3, normally 2.5 -3.5



1

1.5

2 2.5

3

4 5

8

4 3 2.5 2 1.5 1 0.75 0.5

Silic

ic ac

id ra

tio(S

iO2/A

l2O3

Incre

asing

form

ation

of co

ating

Increasing formation of coatingAlumina ratio = Al2O3 / ( Fe,Mn)2O3

Silica ratio SiO2 /(Al2 O

3 + (Fe,Mn)2 O

3

Increasing formation coating

6 4

3 2 1.5 1

Al2O3(Fe,Mn)2O3

SiO2Optimization of rawmealmoduli for betterrefractory life .



Phase CaO-Al2O3-SiO2

C3S

C2S

C3A



Al2O3

SiO2CaO

Fe2O3

CASF -Phase diagram



Liquid content

According to Lea and Parker the % of liquid formed (S)

S = 3 Al2O3 + 2.25 ( Fe2O3 + Mn2O3) +MgO + K2O + Na2O

( % by weight at 1450 deg) If S = 30 % dense and firm coating

S = 25 % good coating conditionsS = 20 % loose and porous coating



Burnablity and coating indexBurnability index = C3S /( C3A + C4AF)

Minimum burning zone temp=13000C +4.51C3S+ 3.74C2S -12.64 C4AFCoating index , AWAR > 0.64,AW = C3A + C4AF + 0.2 C2S + 2F ( = normally 27 - 32 )AR < 0.64,AW = C3A + C4AF + 0.2 C2S + 2F

When AW < 20 , No coating or very less coatingWhen AW > 30, Excessive but unstable coating with tendency to form thick ring formation.

Liquid percentage ( by Weight)

If AR > 1.38 , % L.P = 6.1 F+ M + K+ SO3If AR < 1.38 , % L.P = 8.2 A - 5.22F+M+K+N+SO3 at 1338 deg CIf AR< or = 0.64, L.P = 3.0A+2.25F+M+K+N+SO3 at 1450 deg C

Viscosity Al2O3,K2O and Na2O increases the viscosityFe2O3 and SO3 decreases the viscosity



Liqu

id c

ont e

nt b

y w

eigh

t in

%at

145

0 de

g C

1.5 2 2.5 3. 3.5 4.0

AM= Al2O3/ Fe2O3

LSF= 96, AM=2

35

30

25

20

15

SM= S/ (A=F)

Silica modulus vs liquid content



Mechanism of clinker reaction

Liquid silicate lime

1) At 1200 deg c the material consists of C2S, CaO, C3Aand C2A all as small crystal grains

2) Viscosity and surface tension of liquid decreases withincreasing temperature

3) C2S and CaO continue to undergo size enlargementwith prolonged soaking in the absence of contact with the liquid.

P.t.o



4) Prolonged tumbling of material with droplets of clinker liquid with high surface tension will promote the coalescence of these droplets among themselves rather than reaching and wetting of silicate and lime grains

with slow drop in the viscosity and surface tension thetiny droplets get enough to meet one another andenlarge their own size leaving most of the silicates and lime

away.5) With rapid drop in the viscosity and surface tension

of clinker most of the silicates and lime grains aredrawn into the liquid even the liquid droplets get enoughopportunities to meet one another and grow.



Clinker nodule





Model of clinker reactionsThe clinker reactions proceed in the following ways

up to 700deg C : dehydration of the clay minerals withthe associated lattice formations and increase in surfacereactivity700 - 900 deg c: calcination of CaCO3 ,partial reaction ofthe release of CaO with Al2O3 and Fe2O3 to C2(A,F) and C12A17 and with the active part of the silica to belite (C2S)

900 - 1200 deg c: Transformation of the calcium ferrites into liquid state and commencement of the formation ofthe alite (C3S) from the belite and the uncombined CaO ( free lime)

Above 1350 deg c : almost complete reaction of thefree lime to alite , together with further decomposition ofthe belite content.



Phase transformation

1. Evaporation of free water from the feed 100 deg c2.Evolution of the chemically combined

water 550 deg c 500 deg c( required 363 Kcal / kg cl )

3. Evolution of CO2 from CaCO3 and MgCO3 805 deg c4. Formation of interim phase C2F 800 deg c5. Formation of interim phase CF 900 deg c6. Formation of interim phase C2S+C2AS+CF

+C2F 1000 deg c7. Formation of interim phase C2S+C5A3+

C5A+ CF + C2F 1100 deg c8. Formation of interim phase C2S+C3A+

C5A3+C2F+C3S 1200 deg c

9. Formation of C3A + C3S + C2S + C2F 1300 deg c ( required 511 Kcal / Kg cl )



AliteCaO

Belite

Liquid

CaCO3

Beta quartz

Gammaquartz C3A

Calcining zone Transition zone Burning zone coolingzone

1400

1200

1000

800

600

400

200

1450 OCDeg C

Pre heating zone

C12A7 C2(A, F)C4AF

Clinkering process



Clinker moduli and their influence on the burningproperties of clinker



Chemical and minerologica processes during clinkerburning



Quasi-quantitative variation of minerals with temperature



Reactions in preheaterStage-1 Evaporation of free water0.3% H2O = - 3 kcal / kg .cl

Stage-2 Evaporation of chemicallycombined water0.7 % H2O = - 18 kcal / Kg clOxidation of sulfides ( pyrites)

Stage-3 Oxidation of sulfides, partialDecarbonation of CaCO3 and combustionof coal in the rawmix( organic matter)

Stage-4 Oxidation of sulfides, partialDecarbonation and recarbonation

Stage-5 Decarbonation or CaCO3 ( 30 -40 %)CalcinerDecarbonation(90 - 95 % ).Lime reacts with reactive silica

310 deg c

490 deg c640deg c

750 deg c

820 deg c900 deg c

1400 deg c 1100 deg c



Heat

1350 deg c

1400 deg c

1450 ded c

1500 deg

Clinker burning

Higher rpm improves the thermal distribution,better heat exchange between refractory and raw meal bed and soreduces the radiation losses

1900

1)Radiation of heatfrom flame torefractory

2)Conduction ofheat fromrefractoryto charge

3)Convection ofheat fromparticle toparticle while rotating.Higher rpmincreases the rateof convection



Heat

1350 deg c

1400 deg c

1450 ded c

1500 deg

Clinker burning

Higher rpm improves the thermal distribution,better heat

1900

Ideal flame

Short,intense and convergent flame is favourable forburning, favorable coating formation improves therefractory life.Burner pipe at center - this flame radiates the heat to the the refractory surface(evenly) in well distributed manner



Short and divergent flame

Short and divergent flame is favorable for burning,unfavourable for coating formation and deterioratesthe refractory life. This flame radiates intense heat on the refractory surface and causes more thermal stresses on the brick. Some times it impinges the refractory.

Heat1550 degcc

Clinker burning

Higher rpm improves the thermal distribution,better heat

1500 deg c1600 deg c

1650 deg c

1900



Long flame is neither good for burning nor for favorablecoating. It releases heat over a long distance and hencerelieve some thermal stresses on the refractory.It formsunstable long coating and so if coating dislodgesrefractory has thermal shocks.

Long and loose flame



Coating formation on magnesite bricks in cement rotary kilns

coating

falling off formation

adhesion

1

4

5

6

3

2

Chemisorptionand adsorptionon the bricksurface

Infiltration ofliquid phases

of the clinkerand the reaction

with the brick

Stress formation(increase coatingweight,differences in contraction

Mechanical anchoring ofthe coating inthe brick(max 1200 deg c

Solidifying ofthe infiltrated

material in the brick at furtherformation of coating

Coating dropsoff(too high stresses,irregularities in operation.Moving of kiln,C2S disintegration)



Pores on the bricks

Open pores

Closed pores



Coating formation on the brick

• Penetration of the liquid into the pores of the brick• Mixing of the liquid with the liquid of the brick• Reaction or dissolution the solid phase by the new liquid



Clinker coatingoptimum coating

Thick coating

Thin coating

500 mm

300 mm

100 mm



Coating formation

Alumina brickDicalcium silicate (C2S)Anorthite(CAS2) Gehlenite(C2AS)

Magchrome brickMerwinite(C3MAS)

Dolomite brickCaO - C3S

Merwinite(C3MAS)Monticellite(MCS) Forsterite(MS2)

Spinel brick



Micro structure of clinker coating on dolomite



Clinker coating on magchrome bricks



Clinker coating on dolomite brick



Contact zone between clinker and spinel brick



Typical burning conditionsGood coating formation



in R-63 brick



Constriction of the free cross sectiondue to coating ring formation



Heavy and unwanted coating



Firm and optimum coating for good refractory life



Thank you for yourkind attention



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1 refa1 clinker burning , coating form , flame