Clinker Burning

Lime saturation factor

LSF is the amount of calcium oxide required to react with the entire available
oxides in the KF.
Therefore, when LSF = 100, it represents the optimum CaO content in the
raw mix which will react with the entire acidic oxides in the raw mix.
In theory a clinker with LSF of 100% can be burned to 0 % FCaO, practically
when LSF equals 100% the ordinary clinker will always contain FCaO “LSF
input is between 90 and 102, but value of LSF over 97 is considered high
and will result in very high quality clinker which means higher heat input
and “or” higher free lime rates”.
When firing a kiln with coal or other fuels containing ash, the LSF of the
raw meal to be increased according to the ash content to compensate the
acidic oxide content in the coal ash.
For every 1 % increase in FCaO in the clinker the setting time of the cement
will be shorten by 55 min and also concrete expansion.

The Silica ratio

At the clinkering temperature in the sintering zone, the silicon dioxide will
mostly exist as the solid phases “C2s or C3S”, while the other two acidic
oxides will exist as liquid phase.

In case of SR is less than 2 %

1. The raw mix will be easy to burn but the kiln operator will face excessive
liquid phase in the burning zone which eventually will lead to higher
torque, kiln motor over load and snow man formation on cooler static
grates.
2. Severe attack on kiln bricks where the coating will be washed out.
3. The clinker will start balling in the burning zone and may lead to
operational problems in the grate cooler.
4. The cement produce by such raw mix will have lower strength
Silica ratio higher than 3
1. This raw mix will be hard to be burnt due to low liquid phase content.
2. Elevated kiln thermal load.
3. There will be scarce or no coating formation in the burning zone.
4. Dusty clinker due to low melt leading to mechanical troubles in cooler
parts and also hard to grind in clinker.
5. High to very high free lime content leading to low kiln productivity.
6. The cement made by the clinker produced by such raw mix will have high
compressive strength but slow in hardening.
7. The increase of silica ratio will lead to poor clinker reactivity.
8. The increase of silica ratio will lead to poor cement workability.
Free silica
Since quartz is very hard it is much more difficult to be ground than
limestone and is therefore concentrated mostly in the coarse fractions of the
kiln feed.
The quartz in clays “combined silica” is already very fine and normally
poses no problem, however the limestone component can sometimes
contain thick pure quartz which has been deposited over long periods of time
in cracks in the limestone by silica-rich ground waters.
Such large quartz is very difficult to be ground and the resultant particle size
of quartz grains in the raw meal produced from such material is therefore
increased significantly.
During reaction in the kiln, large quartz grains react at their surface
with nearby CaO grains to form C2S. In the burning zone, the reaction
occurs by diffusion of the CaO dissolved in the liquid phase. If the quartz
particle is big enough, a barrier of C2S is formed around the remaining
quartz, isolating it from the liquid phase and preventing any more diffusion
of CaO. i.e. the reaction SiO2 + 2CaO → C2S becomes stalled at this point
and, no matter how hard the clinker is burned, this free silica can never
 all react in time. This leaves unreacted equivalents of CaO lime behind
which increases FCaO content of the clinker.
A similar situation occurs if the large quartz grains are just small enough to
completely react into C2S. The next step is for this C2S to react with further
CaO to form C3S. Again, if the C2S cluster resulting from a coarse quartz
particle is large enough, a wall of C3S will form around the cluster
preventing CaO diffusion through to the centre of the cluster. This results
in unreacted equivalents of free lime being left behind.
It was found that 1% increase in the quartz “ > 45 μ” for raw mill mix which
is burned for 30 minutes at 1400 °C will increase free lime by nearly 1% in
the sample if compared to a sample without this increase in quartz coarse
particles, while in a similar sample of 1% increase in the calcite “ > 125 μ “
and burned for 30 minutes at 1400 °C will increase the free lime by nearly
0.5 % in the sample if compared to a sample without this increase of calcite
coarse particles .

The alumina ratio

It is the ratio of alumina to iron in the raw mix, at clinkering temperature the
Al2O3 and Fe2O3 are predominantly exist as liquid phase portion. Therefore,
this ratio expresses the composition of this form, it also expresses the nature
of the liquid phase where the higher its value, the more viscous the melt
phase, the lower its value the more fluent is the melt phase.
The temperature by which the melt forms depends on the AR, the lowest
temperature is obtained when the AR is approximately 1.6 which is the
optimum regarding to the formation of clinker minerals and nodulization.
The AR also affects the colour of the clinker and cement, the higher the AR
the lighter the colour of the cement. AR is not always a directly controlled
parameter

Alumina Ratio 1.3 < A.R > 2.5

 1. When alumina ratio is higher than 2.5, the kiln will produce a high viscous
melt while the cement produced by such raw mix will have high early
strength due to higher C3A content.
2. When alumina ratio in the raw mix is less than 1.3 the kiln will produce a
high fluent melt while the cement of such clinker will have low early
strength and low heat of hydration, and kiln productivity will suffer.
3. The reduction of alumina ratio will assist the formation of the liquid phase
at lower temperature, this means that the raw mix will have a longer time
with enough liquid phase to improve nodulizing and forming better
clinker, easy to be cooled and easy to be ground.
4. The iron in the reduced state “kiln reducing conditions” will not form the
C4AF but other products such as FeO, Fe2S or even Fe. The aluminum
that would have formed C4AF is now available to form more C3A.

Reaction mechanism

States of the matter

Solid Definitive volume and shape

Liquid Definitive volume, shape of container

Gaseous Neither definitive volume nor shape

Under specific circumstances of pressure and temperature it is possible for

more than one state to coexist.

Classification of reactions
1. According to chemical type
1.1. Structural change
This type occurring within single minerals in the solid state is also
known as "polymorphic transition". In this reaction the chemical
composition remains constant but the arrangement of atoms changes
usually upon reaching a specific temperature.
Low quartz to high quartz "both have SiO2"
 Aragonite to calcite "Both have CaCO3"

1.2. Decomposition "calcination reaction"

1.3. Combination "formation of belite".
2. According to state of matter
2.1. Solis-solid "belite formation reaction"
2.2. Solid-liquid "alumino-ferrite formation".
2.3. Solid-gas "Calcination reaction"
2.4. Liquid-gas " alkali voltization"
2.5. Gas-gas "CO + 1/2 O2 → CO2”.
3. According to controlling step "reaction kinetics"
3.1. Diffusion "alite formation"
3.2. Phase boundary "belite formation"
3.3. Nucleation "alite formation"

Kinetics of clinker burning

General Aspects
The burning of clinker consists of a series of reactions taking place between
finely divided solids, only at temperatures above 1250 °C that a liquid is
formed and becomes the medium through which reaction occurs. When
liquids or solutions react together, the actions usually occur rapidly and the
products depend only on the composition of the reaction mixture and the
 temperature. With reactions between solids the conditions are very different.
Reaction takes place at the surface of grains, and diffusion of fresh solid to
the surface proceeds but slowly. If a particle of clay is imagined surrounded
by particles of lime, the reaction will commence at the surface of the clay
particle. This in turn will react with further clay inside. If complete
combination is not attained, the stage to which the reaction has progressed
depends not only on the temperature, but also on the time, or rate of heating
and the general physical and chemical condition of the reacting materials.
Experience demonstrates that a raw mix composed of non-reactive minerals
(high activation energy EA) such as quartz, forms clinker more slowly than
a raw mix incorporating more reactive components such as clay minerals or
amorphous silica. The lower activation energy required for the reaction with
lime results in a high rate of clinker formation. To compensate for the slow
reactivity of the less reactive minerals, a higher burning temperature and / or
longer burning period “longer clinkering zone” is required.

Litre weight
The litre weight of a selected fraction of the clinker product is measured. It
is usually the fraction of 5 – 10 mm or 6 –12 mm particles that are sieved
and weighed in a cup with fixed volume. The measurement in g/l is generally
between 1100 –1300. The litre weight of a clinker type at a specific plant
correlates to free lime when burnability remains constant. Higher
temperature generally gives higher litre weight but very high temperatures
can lower the liter weight because of dust agglomerates “higher melt
formation causes the formation of agglomerates”.

Liquid phase
Clinker liquid phase or clinker melt is the fraction of the kiln feed that melts
between the upper transition and the burning zone. The liquid has a critical
role in clinker nodulization and clinker mineral development and properties.
In the absence of liquid, the conversion of C2S and free lime to C3S would
be almost impossible.
Importance of liquid phase
1. Assists the diffusion of the CaO and C2S and accelerates the formation
of the C3S.
2. Filling out most of the voids between the particles “15 up to 20 % wt”
leading to reducing dust content and enhancing the clinker granulation.
3. Prevents or reduces the dust formation by forming strong agglomerates
In clinker nodules solid raw material particles as well as formed crystal
phases are held together by the liquid phase. Further crystal phase formations
are accelerated due to the diffusion of Ca2+ through the melt, which is faster
than diffusion through solids. Strong agglomerates are formed, when melt is
present, around 15 - 20 wt. % filling out most of the void space between
particles. The amount of ungranulated material increases with a decrease of
liquid, since less particles are moistened by the liquid.
To understand why alite “C3S” formation requires liquid phase, one must
first understand the alite formation mechanism:
1. C2S and free CaO dissolve in the clinker melt.
2. Calcium ions migrate towards C2S through chemical diffusion.
3. C3S is formed and crystallized out of the liquid.
Without liquid phase the diffusion of Ca ions towards C2S would be
extremely slow, and that of C2S almost impossible, at commercial clinkering
temperatures. It is important to mention that Na2O and K2O decrease the
mobility of Ca ions, whereas MgO and sulphates considerably increase it.
This is why the addition of gypsum to the raw mix promotes alite formation.
Similarly, the addition of metallurgical slags to the raw mix promotes clinker
formation. Fluxes, such as calcium chloride, feldspars and slags should not
be confused with mineralizers, although both promote clinker formation.
Mineralizers are usually transition metals such as copper, lead and zinc that
reduce the amount of energy required for clinker silicate formation.
 Low calcination degree will delay the LP formation and vice versa, where
the calcining zone inside the kiln has to be longer which will shift the
remaining zone to the kiln outlet.

Liquid Phase Formation

The liquid phase of clinker mass is composed mainly from calcium-ferrites
and aluminates and small quantity of silicates. The quantity of this liquid
silicate is a function of burning zone temperature i.e. the higher the
temperature the higher will be its percent in the liquid phase.
In systems consisting of only CaO, SiO2, Al2O3 and Fe2O3, with typical
portland cement compositions, melting C3A and C4AF crystal phases
commences at the eutectic at 1338 ºC.
This is only valid in an absolutely homogeneous mixture, where
inhomogeneities “minor elements” in the raw meal mixture cause a shift of
the eutectic toward lower temperatures “Earlier formation of the melt”.
The liquid phase fulfills two important tasks in the clinker burning process:
1. Acceleration of the clinker phase formation and
2. Prevention of clinker dust formation.
The granulation proceeds in three steps:
1. Agglomeration and re-grouping of the particles,
2. Granule growth, and
3. Solidification and crystallization of the melt.
The first step occurs rapidly. Primary particles are moistened by droplets of
liquid, which are then quickly drawn and held together to form porous
granules. Small granules have an excess of liquid at their outer boundaries,
so more particles can be incorporated in the granule. Denser agglomerates
are formed by re-grouping grains. The melt enters the pores in and between
the agglomerated particles, and carries weakly bound particles into the
interior which is accommodated by particle shrinkage. This process is
strongly dependent on the surface tension and viscosity of the liquid, but
independent of rotational speed of the kiln, retention time in the kiln or
material loading. A high surface tension is required to ensure sufficient
adhesion of the particles to each other and a lower viscosity supports particle
transport. It was found by Timiashev, that the final size of clinker nodules is
directly proportional to the surface tension of the melt. In this context the
effect adding minor compounds is of great importance. Pure cement clinkers
exhibit surface tensions of ca. 0.5 N/m (comparable with the surface tension
of Hg) and a viscosity of 0.1 - 0.2 (similar to the viscosity of olive oil).
The second stage of the nodulization is characterized by granule growth and
the formation of the crystal phases C2S and C3S. Therefore alite is
surrounded by more melt than belite, since it develops a less dense crystal
packing. This stage becomes dependent on time, rotational velocity and
loading, while inertial and gravitational forces become important with the
tendency for granules to break down, counteracting growth. In the third stage
the liquid crystallizes to form the aluminate and ferrite phase at a temp of
~1250 ºC 15 or, if the liquid cools down too rapidly, it forms a glass residue.
Early melt formation causes the formation of agglomerates, which are
separated from the gases in the cyclone system and enter kiln feed as
particles above the critical size.
It is possible, though, that melt formation starts already at lower
temperatures due to minor compounds and local inhomogeneities, causing
early agglomeration and solid-liquid phase formation even for the belite,
aluminate and ferrite phases. Whether this is the case and if early melt
formation is beneficial on an industrial level, should be the subject of further
investigations and might also be exploited in future applications
 Plant chemists and kiln operators are usually more concerned with the
amount of liquid rather than with the rheological properties of the liquid. The
latter is much more important during clinkering reactions than the former
The most important clinker mineral C3S (alite) requires the presence of
liquid for its formation. In the absence of liquid, alite formation is extremely
slow and it would render commercial clinkering impossible. This fact also
explains why alite is formed essentially in the burning zone, where the
amount of liquid is at a maximum.
Influence of modules on liquid phase
1. Lime saturation factor
Reduction of LSF slightly increases the quantity of liquid phase. The
influence of a reduction of LSF on the burnability may have a positive
effect on nodulization.
2. Silica ratio
Reduction of SR will increase the quantity of A and F, effectively
increasing the quantity of liquid phase. The length of the melting zone
will remain the same but the formation of nodules will be more rapid
and increase the nodule size and coating thickness.
3. Alumina ratio
Influences the temperature at which the melt forms. The lowest
temperature of melt formation is with an AR of 1.6. If the melt occurs
at higher temperatures the heating zone will lengthen and the melting
zone “coating” will shorten.
Liquid phase nature
First what are the causes that led to changing the melt viscosity “from
viscous to fluent and vice versa” was the iron ore increased or aluminum
oxide decreased?
The increase of the iron ore with decreasing the aluminum while maintain
the same LSF can lead to the following: -
1. More fluent melt phase
 2. Early formation of the liquid phase.
3. The calcined raw materials will have more retention with the early
formed liquid phase leading to better granulation
4. Moving the reaction to the KBE side that may lead to severe
problems, ball formation.
5. The shifting in the zones due to early formation of liquid phase may
have little bit effect on the formation of the C3S.
6. Early melt formation causes the formation of agglomerates, which are
separated from the gases in the cyclone system and enter kiln feed as
particles above the critical size.
The increase of the alumina with decreasing the iron content while maintain
the same LSF will lead to the following:-
1. More viscous melt phase.
2. Stable coating with the probability of balls and ring formation.
3. The melt phase formation may be delayed due to higher temp
requirement.
4. The delay formation of the liquid phase will lead to poor granulation
and dust formation.
5. Due to delayed liquid phase formation, the burnability may suffer
Al2O3, K2O and Na2O increases the viscosity while Fe2O3 and SO3 decreases
the viscosity
Viscosity and surface tension of liquid decreases with increasing temp.
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.
Fluent liquid phase attacks brick, it infiltrates the refractory lining faster,
leading to its premature failure.
Liquid percent = 30 % dense firm coating
Liquid percent = 25 % good coating conditions
Liquid percent = 20 % loose porous coating
 Effect of volatiles on liquid phase
1. Sodium and potassium oxides
1.1. Viscosity increases
1.2. Surface tension decreases
1.3. Clinker formation rate reduces
Therefore the rate of brick attacks will be decreased and also rate
of coat formation will decrease.
2. Na, K in presence of high amount of MgO
2.1. Viscosity decreases
2.2. Surface tension stays nearly the same without substantial increase
2.3. Clinker formation rate increases
Therefore rate of brick attack will increase and coat thickness will
increase.
3. Sulfates
3.1. Surface tension and viscosity decrease
3.2. Clinker formation increases
Therefore rate of brick attack will increase and coat thickness will
increase

Belite formation
The formation of C2S starts at more than 800 °C and is mainly formed by
solid-state reaction. In many raw mixes it is formed in quantities exceeding
those found in the final clinker and then further reacts with FCaO “via the
melt” to yield alite, the quantity of belite thus falling back to that finally
observed. During the solid state reaction of silica and calcite “or CaO” the
first reaction product is always C2S.
CaO + SiO2 → CaO + C2S + SiO2 → CaO + C2S + CS + SiO2
Sequence of appearance of phases in the solid state reaction of CaO and SiO2
showing the order of appearance of phases at a CaO / SiO2 interface. Only
later does the most silica rich phase CS appear as a result of reaction s
between C2S and SiO2. This demonstrates the remarkably strong nature of
 the belite formation reaction. At temperatures at which solid state reactions
occur, the formation of C3S does not take place due to its thermal instability.
The rate limiting mechanism by which belite is formed “after an initial phase
boundary controlled reaction” depends on the diffusion of ions through the
solid state. The rate of this reaction is thus dependent on
1. The path distance that the diffusing species have to travel.
2. Defects in the reactant’s crystal lattices.
The former factor is dependent on both the size of the CaO and SiO2
particles, and the effective contact area between them. It is this easy to
understand why finely milled and/or densely intergrown powder mixtures
react faster than large-grained coarse ones, and thus, why cement raw meals
must be finely ground and intimately mixed.
From the results of many studies, the main diffusion species is known to be
the Ca2+ ion which migrates into the solid SiO2; although evidence does exist
to indicate that the diffusion of Si4+ into CaO can occur to a lesser extent.
That the Ca2+ ion is the major diffusing species is confirmed by the well-
known fact in clinker formation that the quartz must be finer ground than the
limestone if complete reaction is to take place

Alite formation
The content is 50 up to 65 % hardens faster than C2S and contributes to early
strength formation. C3S has a high heat of hydration (500 kj/kg). It is
resistant to sulphur attack. Higher C3S value increases strength at all ages.
The formation of alite commences only when the temperature is above its
lower stability limit of more than 1250 °C. At that temperature, the liquid
phase is also starting to form. Consequently the formation of alite is a liquid
- solid reaction, as reaction via a liquid medium is faster than by solid state
processes. In the laboratory, C3S can be formed by the solid state reaction
of CaO and SiO2, but this requires many hours at temperatures above those
encountered during clinker formation. The resulting finely crystalline
 product must be rapidly quenched, at much faster rate than can be achieved
in a production kiln, to prevent its decomposition at normal temperatures.
In the industrial production of clinker, the formation of alite and its
stabilization is thus wholly dependent on the presence of the melt.
At the temperature at which alite formation begins “more than 1250 °C”, the
material consists mainly of free lime, belite and liquid phase.
Belite C2S
The content is 10 up to 25 % hardens slowly and contributes more to late
strength development. It is resistant to sulphur attack. It has a low heat of
hydration “250 kJ/kg”. The content of C2S in low heat cement used for the
castings of large foundations is high.
C3A Calcium aluminate
The content is 4 up to 10 % sets quickly and contributes to the early strength
but minimally to the final strength. C3A also has a high heat of hydration
where it liberates a large amount of heat during the first few days of
hardening “900 kj/kg”. Cements with low percent of C3A are resistant to soil
and water containing sulphates. Higher concentrations of C3A can react with
sulphate causing expansion and crack formation exposing more C3A leading
to further penetration of sulphates.
C4AF Calcium alumino ferrite
The content is 2 up to 10 % has a minimal effect on the strength of cement,
contributing only to the final strengths. C4AF gives a dark colour to cement
and is avoided in the manufacture of white cement.

C3S and C2S make up the main part 75 – 85 % of the clinker and responsible
for most of the strength properties of the cement. C3A and C4AF act as melt
in the clinker formation process constituting 10 – 20 % of the clinker.

Any free lime which has not reacted with silica, alumina, or iron will be left
as free CaO. The free oxides of CaO and MgO usually represent less than 5%
of the clinker. They are generally unwanted components indicating
 insufficient burning of the clinker “CaO”, decomposition of C3S in the
clinker or too high lime saturation “LSF” of the clinker.

Kiln coating tendency

1. Low AR indicates low viscosity melt, low SR indicates high coating
tendency which may shift the flame to the kiln inlet that may produce
free lime due to ball formation "the material is very easy to be brunt".
2. High AR with high SR gives very thin coating due to little viscous melt.
3. High AR with low SR leads to thick coating or sintering ring formation
due to plenty viscous liquid phase.
4. Low AR with low SR leads to thin coating due to plenty fluid melt.
5. Low AR with high SR leads to thin coating due to little fluid liquid
 MgO can increase liquid phase at burning zone temp by around 1.5%
 MgO can give rise to cracking in concrete if present as periclase
 Mn2O3 increases level of flux and reduces viscosity
 Cl, F lowers the liquid viscosity
 Cl can accelerate strengths but can also cause corrosion in steel
reinforcing bars
 Alkalies as alkali sulphates enhance early strength and concrete slump but
depress late strengths
 Alkalies in solid solution can enhance the reactivity of belite and C3A.
With its high reactivity, the C3S mainly determines the strength
development, while the C3A is responsible for the stiffening and setting
of the cement and thus for its workability
 Alkalies can lead to durability problems and ASR
Durability is the ability of concrete to resist weathering action, chemical
attack, and abrasion while maintaining its desired engineering properties
or the longevity of the material against various environmental conditions.
 SO3 excess SO3 over alkalies will form Ca langbeinite and free CaSO 4,
which can result in larger, less reactive alite crystals
 SO3 in clinker limits the gypsum addition in cement mill
 SO3 major influence on formation of lumps in cement
 + 1% SO3 lower the combination temperature by 60 C.
 K2SO4 improves the burnability but the clinker will have poor
nodulization.
 If the alkali sulfate ratio is more than unity this leads to increasing the
SPC for cement grinding.
 If the alkali sulfate ratio equals unity this leads to increasing the early
strength
 If the alkali sulfate ratio is less than unity this leads to poor clinker
burnability, and poor cement workability and durability.
  For every 0.1% increase in total alkalis in clinker the 28 days strength will
decrease by 0.5 – 1 MPa at 28 days.
 + 1% K2O increases the combination temperature by 35 C.
 Uncombined alkali takes up atmospheric water upon exposure, leading to
air-setting of cement in silo and poor workability.
 Too coarse coal leads to late deposition and formation of of coal ash rings
 C3S contributes to strength development up to 28 days.
 C2S continues to contribute to strength after 28 days “slower reaction”.
 C3A hydration reaction very fast if not controlled - flash set, paste loses
its workability very quickly but does not develop strength

PC kiln relative zones length with respect to kiln diameter

 Calcining zone 2D
 Transition zone 7D
 Burning zones 6D
 Cooling zone 1D
Hood pressure
Kiln hood is the separation point between kiln and cooler and should always
have constant slight negative draught to ensure stable cooler operation.
Pressure should be close to zero as much as possible "Just to prevent the over
pressure"

Kiln cycling
This is an unstable condition when the kiln loads decreases causing the BZ
temp to rise and forcing the operator to reduce fuel rate, then BZ starts to
cool down that in turn forcing the operator to increase fuel rate.
Some cases the temp continues to drop even though the fuel rate is at max
and it is necessary to reduce kiln speed. Cycling may be due:
 Physical or chemical changes of kiln feed.
 Variation in dust re-introduction to the kiln.
 Variation of hood pressure.
 Poor cooler setting which promote sec and tertiary air variation.
 Bad kiln operating practices especially over kiln speed.
 Volatile materials circulation inside the kiln.
How to break a cycle in a kiln?
 Reduce feed and speed by 10 % in order to regulate the feed flow
and load in the kiln burning zone.
 Increase fuel rate by 5 % above the normal setting.
 Keep the KBE oxygen level at 2 % and control the KBET as much
as possible “Feed and speed reduction and also fuel increase may
lead to sharp increase in the KBET”
 Changes in the operation parameters should be carefully and slowly.
Material flush
Heavy rush of feed might end up too far under the flame.
Here the operator must decide if he can control the heavy feed flow only
using fuel rate or he needs to reduce kiln speed.
 In this case the factors to be considered are
 Oxygen content at kiln inlet
 Back end temperature
 Movement of the feed rush.
 Conditions of the cooler.
The following rules must be applied:
 When in doubt the kiln speed reduction should be greater than
required.
 Never allow the raw material to enter the cooler even if the kiln
stopped and rotated ¼ turn on the auxiliary drive.
 Cut down the feed, fuel flow, draught and maintain the oxygen
content in the kiln inlet at 2.0 % ± 0.5
Snow man

 Actually, the snowman is localized only in one side of the cooler because
of the aerodynamics created by the kiln rotation and the secondary air
preferentially flow in that direction.
 When the deposits formation are associated with dusty clinker normally
are due to a result of larger crystal size and presence of clinker dust in the
cooler. Larger silicate crystals mainly alites cause the segregation of
liquid phase to the surface of clinker particles. The presence of large
particles means deficient nodulization of clinker and of course dusty
clinker formation. When the dust enter in the cooler the melt solidifies the
clinker particles and resulting in a formation of deposit.
 The problem can be particularly acute when dust formation is so severe
that is blown back into the kiln from the cooler due to the air pressure in
first chamber of cooler. so, crystals can undergo further growth on
reheating and the melt can be more concentrated on the particle surface.
 Not only the flame shape but also its position can influence the tendency
of snowman formation. It is necessary to avoid flames very short or very
long or impinging on the clinker load. Impinging flames can lead to
reducing conditions in the clinker which greatly change the liquid phase
viscosity and surface tension. The reduction of the melt viscosity and
surface tension cause the formation of large clinker balls.
practical measures against the snow men formation
1. To change of the inclination of side ramp “inclined static grates
and horse shoe” where the deposits are formed.
2. To decrease the clinker temperature at the kiln nose ring by
lengthening the pre cooling zone and/or increasing the air/clinker
ratio at the first cooling chamber.
3. To improve the clinker nodulization avoiding the formation of
dusty clinker or ball clinker.
4. To avoid segregations in raw meal. For example, if the finest
fraction of the mix is disproportionnately rich in clay or iron ore,
the bulk of the melt will be associated with the materials easiest to
nodulize. Such situation can lead to the simultaneous formation of
clinker dust and large clinker balls.
5. To reduce the size of C3S and C2S crystals by modification of the
temperature profile of the kiln and improvement of the clinker
nodulization condition.
6. Flame alignment and adjusting to avoid impinging the flame on the
kiln load and very long, lazy flames or very short, sharp flames