Clinker burning , coating formation , flame

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seminar

K.P.Pradeep kumar
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Clinker chemistry(related to Refractory)

Burning mechanism

Mechanism of clinker coating formation

and

Flame


Clinker chemistry
Silica ratio = SiO2 / Al2O3+ Fe2O3 normally 1.9 - 3.2
(optimum: 2.2 - 2.6)
Silica ratio characterizes the ratio solid / liquid i.e., The
amount of liquid phases in the clinker.

Alumina ratio = Al2O3 / Fe2O3 , normally 1.5 - 2.5

Alumina ratio characterizes the composition of the melt and its
viscosity in the clinker.

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

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


Optimization of rawmeal SiO2

Si l
moduli for better

ica
refractory life .

rat Incre
6
8
tin 3

io
2.5 coa O
g
of Al2

5

4

SiO sing
4
on 2/

2
3

a
ati iO

/(A ma
3
S

l 2O tion
fo tio(

for
2
ing ra
rm

3
+ ( coa 1
2
as id

Fe ting
c

1.5
a

,M
ic
lic

n) 2
re
1.5
Inc
Si

O3
1

Al2O3 4 3 2.5 2 1.5 1 0.75 0.5 (Fe,Mn)2O3
Increasing formation of coating
Alumina ratio = Al2O3 / ( Fe,Mn)2O3

Phase CaO-Al2O3-SiO2

C2S

C3S

C3 A

CASF -Phase diagram

Fe2O3

SiO2
CaO

Al2O3


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 conditions
S = 20 % loose and porous coating


Burnablity and coating index
Burnability index = C3S /( C3A + C4AF)
Minimum burning zone temp=13000C +4.51C3S+ 3.74C2S -12.64 C4AF
Coating index , AW
AR > 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 coating
When 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+ SO3
If AR < 1.38 , % L.P = 8.2 A - 5.22F+M+K+N+SO3 at 1338 deg C
If 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 viscosity
Fe2O3 and SO3 decreases the viscosity

Silica modulus vs liquid content
AM= Al2O3/ Fe2O3
LSF= 96, AM=2

35
Liquid content by weight in %

30

25
at 1450 deg C

20

15

1.5 2 2.5 3. 3.5 4.0
SM= S/ (A=F)


Mechanism of clinker reaction

Liquid silicate lime

1) At 1200 deg c the material consists of C2S, CaO, C3A
and C2A all as small crystal grains
2) Viscosity and surface tension of liquid decreases with
increasing temperature
3) C2S and CaO continue to undergo size enlargement
with 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 the
tiny droplets get enough to meet one another and
enlarge 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 are
drawn into the liquid even the liquid droplets get enough
opportunities to meet one another and grow.


Clinker nodule


Model of clinker reactions
The clinker reactions proceed in the following ways

up to 700deg C : dehydration of the clay minerals with
the associated lattice formations and increase in surface
reactivity
700 - 900 deg c: calcination of CaCO3 ,partial reaction of
the 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 of
the alite (C3S) from the belite and the uncombined CaO
( free lime)

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


Phase transformation
1. Evaporation of free water from the feed 100 deg c
2.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 c
4. Formation of interim phase C2F 800 deg c
5. Formation of interim phase CF 900 deg c
6. Formation of interim phase C2S+C2AS+CF
+C2F 1000 deg c
7. Formation of interim phase C2S+C5A3+
C5A+ CF + C2F 1100 deg c
8. 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 )


Clinkering process Deg C
1450 OC
1400

1200

CaCO3 1000
CaO
Alite 800

Belite 600

Beta Gamma
400
quartz quartz C3A
C12A7 C2(A, F) Liquid
Pre heating C4AF
200
zone
Calcining zone Transition zone Burning zone cooling
zone


Clinker moduli and their influence on the burning
properties of clinker


Chemical and minerologica processes during clinker
burning


Quasi-quantitative variation of minerals with temperature


Reactions in preheater
Stage-1 Evaporation of free water 310 deg c
0.3% H2O = - 3 kcal / kg .cl

Stage-2 Evaporation of chemically
combined water 490 deg c
0.7 % H2O = - 18 kcal / Kg cl 640deg c
Oxidation of sulfides ( pyrites)

Stage-3 Oxidation of sulfides, partial 750 deg c
Decarbonation of CaCO3 and combustion
of coal in the rawmix( organic matter) 820 deg c
900 deg c
Stage-4 Oxidation of sulfides, partial
Decarbonation and recarbonation

Stage-5 Decarbonation or CaCO3 ( 30 -40 %)
Calciner
Decarbonation(90 - 95 % ).
Lime reacts with 1100 deg c
1400 deg c
reactive silica

Clinker burning
1)Radiation of heat
from flame to
refractory Heat
2)Conduction of 1400 deg c
heat from
refractory
to charge
3)Convection of 1900
1350 deg c
heat from 1450 ded c
particle to
particle while
rotating.Higher rpm 1500 deg
increases the rate
of convection
Higher rpm improves the thermal distribution,better heat
exchange between refractory and raw meal bed and so
reduces the radiation losses

Ideal flame
Clinker burning

1400 deg c
Heat

1900
1450 ded c 1350 deg c

1500 deg


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


Short and divergent flame burning
Clinker

Heat
1550 degcc

1600 deg c
1500 deg c
1900

1650 deg c


Short and divergent flame is favorable for burning,
unfavourable for coating formation and deteriorates
the 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.


Long and loose flame

Long flame is neither good for burning nor for favorable
coating. It releases heat over a long distance and hence
relieve some thermal stresses on the refractory.It forms
unstable long coating and so if coating dislodges
refractory has thermal shocks.


Coating formation on magnesite bricks in cement rotary kilns
6 1
Coating drops
off(too high stresses, Chemisorption
irregularities in and adsorption
operation. on the brick
Moving of kiln, surface
C2S disintegration)
2
5
Infiltration of
Solidifying of falling off formation
liquid phases
the infiltrated
coating of the clinker
material in the
and the reaction
brick at further
adhesion with the brick
formation of
coating 4 3
Mechanical
anchoring of Stress formation
the coating in (increase coating
the brick weight,differences
(max 1200 deg c in contraction


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 coating
Thick coating
optimum coating
500 mm

300 mm

Thin coating

100 mm


Coating formation

Dicalcium silicate (C2S)
Alumina brick Anorthite(CAS2)
Gehlenite(C2AS)

Merwinite
Magchrome brick (C3MAS)

CaO - C3S
Dolomite brick

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


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 conditions
Good coating formation


in R-63 brick


Constriction of the free cross section
due to coating ring formation


Heavy and unwanted
coating


Firm and optimum coating for good refractory life


Thank you for your
kind attention


Clinker burning , coating formation , flame

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Clinker burning , coating formation , flame