snowman

Snowman Formation and Prevention
Thesis
at the Institute of Non-Metallic Materials
Cements and Building Materials
in cooperation
with
HeidelbergCement AG
presented by
cand. Ing. Thomas Rüddenklau
August 2006
HC-Tutor: Ulrich Mrowald First examiner: Prof. Dr. A. Wolter
Second examiner: Prof. Dr. R. Weber

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I declare herewith that the presented thesis is made single-handed and that only the
mentioned sources and utilities were used.
Clausthal-Zellerfeld, 10.08.2006

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Table of contents
0. Abstract...............................................................................................................................7
1. Introduction ........................................................................................................................8
2. Principles ............................................................................................................................9
2.1. Clinker phases ............................................................................................................9
2.2. Calculations of the phase composition..................................................................10
2.3. Calculation of the melting phase ............................................................................11
2.4. Other important moduli............................................................................................11
2.4.1. Lime saturation factor (LSF)................................................................................11
2.4.2. Silica ratio (SR) ...................................................................................................12
2.4.3. Alumina ratio (AR)...............................................................................................12
2.4.4. Degree of sulfatization (DS)................................................................................12
2.5. Burning process .......................................................................................................12
2.6. Vaporizable constituents and its recirculating system.........................................14
2.7. Operation control measurements ...........................................................................16
2.8. Clinker cooling..........................................................................................................17
2.9. Clinker cooler types .................................................................................................18
2.10. Principle design and process technology features of modern grate coolers ..20
2.10.1. Fixed inlet areas................................................................................................20
2.10.2. Grate plate development...................................................................................20
2.10.3. Side sealing.......................................................................................................20
2.10.4. Cooler drive.......................................................................................................20
2.10.5. Clinker crusher..................................................................................................20
2.10.6. Improvement of thermal efficiency ....................................................................21
2.10.7. Material discharge system ................................................................................21
2.10.8. Grate support system........................................................................................21
2.10.9. Cooler control system .......................................................................................21
2.10.10. Cooling air fans ...............................................................................................22
2.11. Process interrelationships – trend curves...........................................................22
2.12. Red River.................................................................................................................28

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2.13. Snowman.................................................................................................................29
3. Checklist ...........................................................................................................................31
3.1. Part 1 (Material data) ................................................................................................31
3.1.1. Chemical Compositions ......................................................................................31
3.1.2. Clinker Mineralogy ..............................................................................................31
3.1.3. Moduli .................................................................................................................31
3.1.4. Clinker.................................................................................................................31
3.2. Part 2 (Process data)................................................................................................32
3.2.1. Feeding system...................................................................................................32
3.2.2. Kiln ......................................................................................................................32
3.2.3. Cooler .................................................................................................................32
3.3. Part 3 (Other data) ....................................................................................................33
3.3.1. Snowman type ....................................................................................................33
3.3.2. Visual checks ......................................................................................................33
4. The cement plant in Brevik, Norway...............................................................................34
4.1. Introduction...............................................................................................................34
4.2. Flow sheet .................................................................................................................34
4.3. Kiln system modification .........................................................................................35
4.4. Actual Cooler at Brevik ............................................................................................38
4.5. Kiln stop list caused by Snowmen..........................................................................39
4.6. Chemical Compositions...........................................................................................40
4.6.1. Raw meal (kiln feed) ...........................................................................................41
4.6.2. Clinker.................................................................................................................41
4.6.3. By-pass dust .......................................................................................................41
4.6.4. Secondary and primary fuels and ash.................................................................41
4.7. Clinker mineralogy ...................................................................................................42
4.8. Moduli ........................................................................................................................42
4.9. Clinker analyses .......................................................................................................42
4.10. Burning system (Process Data) ............................................................................42
4.10.1. Feeding system.................................................................................................43

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4.10.2. Kiln ....................................................................................................................44
4.10.3. Cooler ...............................................................................................................46
4.11. Snowman type ........................................................................................................51
4.12. Visual checks..........................................................................................................52
4.13. Other noticeable features ......................................................................................52
5. The cement plant Burglengenfeld in Germany..............................................................53
5.1. Introduction...............................................................................................................53
5.2. Collected Data...........................................................................................................53
5.3. The two different cooler systems in operation......................................................53
5.4. Specific cooling air calculations.............................................................................54
5.5. Chemical analyses....................................................................................................54
5.5.1. Raw meal ............................................................................................................54
5.5.2. Clinker.................................................................................................................55
5.5.3. Bypass dust.........................................................................................................55
5.5.4. Clinker Mineralogy ..............................................................................................55
5.5.5. Moduli .................................................................................................................55
5.6. Process data .............................................................................................................56
5.7. CARDOX-procedure .................................................................................................56
6. Snowman-Analyses .........................................................................................................57
6.1. Introduction...............................................................................................................57
6.2. Analyses....................................................................................................................57
6.2.1. Preparation of the Snowman samples ................................................................57
6.2.2. XRF – free lime – water soluble salts..................................................................58
6.2.3. XRD – Rietveld....................................................................................................59
6.2.4. Water soluble salts..............................................................................................60
6.2.5. Reflected light microscopy ..................................................................................60
6.2.6. Hot stage microscopy..........................................................................................61
6.2.7. SEM ....................................................................................................................61
7. Conclusions......................................................................................................................63
7.1. Snowman...................................................................................................................63

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7.2. Hypothesis of Snowman formation ........................................................................63
7.3. Comparable natural phenomenon ..........................................................................65
7.4. Emphasis of the important items of the Checklist ................................................67
8. Outlook..............................................................................................................................68
8.1. In general...................................................................................................................68
8.2. Tasks of Brevik .........................................................................................................68
9. List of literature ................................................................................................................71
10. Table of figures...............................................................................................................72
11. List of tables ...................................................................................................................74
12. Appendix.........................................................................................................................76

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0. Abstract
The following thesis is the first step to approach the subject of Snowman formation. In
literature there cannot be found a lot of detailed analyses and coherences of those build-ups
at the static cooler inlet. In general build-ups in the cement production often cause kiln shut
downs with the result of additional cost. Fact is that every identification of a possible problem
leading to loss of production means a prevention to reduce cost. Along a developed checklist
a cement plant with Snowman formation was checked. Influences like e.g. the content of
melting phase of the clinker, the air distribution at the static cooler inlet or the steadiness of
raw meal and fuels feeding, which lead to this kind of production breakdown, are presented
and discussed. Additionally, some analyses of a Snowman are presented and the relevant
consequences for the checked plant have been drawn. These analyses show that the
investigated Snowman is built by fritted clinker dust. Besides this some preventions are
presented like a general chemical analysis of raw meal fed into the kiln, an improvement of
air distribution at the static cooler inlet as well as an additional independent control cycle with
a clinker-level measurement. These actions can help to improve the situation at the
investigated cement plant and other cement plants with Snowman formation problems.

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1. Introduction
Build ups are often the reason for kiln shut downs. Increased pressure losses or the different
chemical compositions of intermediate products, give first indications. Very often salt
compositions (e.g. alkali chlorides and sulfates) cause those undesired build ups, which can
be found from the kiln inlet up to the cyclones of the preheater tower. A bypass system
decreases those emissions by extracting parts of the gas streams from the kiln inlet. Those
extracted gas streams are cooled and dedusted separately.
Another disturbing build up can be found at the discontinuous operating connection between
kiln and cooler. There, especially at the static cooler inlet, build ups are formed which are
called Snowmen because of there design. Apparently the causes are not indicated in
sufficient time. These build ups cannot be predicted because of a lack of information about
the reasons of formation. On the one hand chemical and mineralogical composition, grain
size distribution and temperature of the burned material affect the physical clinker properties.
From this point of view some evidences are desired for the behaviour of clinker at the grate
coolers. On the other hand the cooler construction and the distribution of cooling air at the
cooler inlet affect the clinker transport.
In this thesis the cement plant in Brevik, Norway, which had great problems with Snowman
formations, was checked. For that, a useful checklist is developed and will be presented
along the found facts of this cement plant. It will be shown that several influences combined
with each other lead to Snowman formation. Luckily there was a chance to save a piece of
an indicated Snowman formation. This Snowman sample will be analysed and discussed in
detail. These information will show that this Snowman in particular is built by fritted clinker
dust. For comparable reasons another cement plant, which is located at Burglengenfeld,
Germany, was investigated. This cement plant is selected as one with almost no Snowman
formations. The specific cooling air quantities in particular give useful information for
comparisons.
This thesis is made at the HeidelbergCement Group in cooperation with the Clausthal
University of Technology. Special thanks applies to the people from the cement plant in
Brevik, Norway, the people from Heidelberg Technology Center (HTC-Germany) and the
cooler manufacturers IKN Neustadt and Claudius Peters.

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2. Principles
2.1. Clinker phases
Essentially cement clinker consists of tricalcium silicate (Alite), dicalcium silicate (Belite),
tricalcium aluminate (Aluminate) and calcium aluminoferrite (Aluminoferrite). It is produced
from a raw material mix which contains mainly calcium oxide (CaO), silicon dioxide (SiO2),
aluminium oxide (Al2O3) and iron oxide (Fe2O3). A summary of the potential phase
composition are shown in Table 1.
Table 1: Potential phase composition of German cement clinker [1].
Clinker phases
Chemical
formula
Abbreviated
formula
Content in % by mass
max 85
av 65
Tricalcium silicate
Alite
3CaO*SiO2 C3S
min 52
max 27
av 13
Dicalcium silicate
Belite
2Cao*SiO2 C2S
min 0.2
max 16
av 8
Calcium aluminoferrite
(Aluminoferrite)
2CaO*(Al2O3,
Fe2O3)
C2(A,F)
min 4
max 16
av 11
Tricalcium aluminate
(Aluminate)
3CaO*Al2O3 C3A
min 7
max 5.6
av 1.2Free CaO CaO
min 0.1
max 4.5
av 1.5MgO, total MgO
min 0.7
The raw material mix is fed into the kiln (see chapter Burning process). By increasing the
temperature during the process the following reactions take place to form clinker phases
(Figure 1) [2]:
100°C Evaporation of free water
>500°C Evolution of combined water
>860°C CaCO3 CaO + CO2
>900°C Reactions between CaO and Al2O3, Fe2O3 and SiO2
>1200°C Melting phase formation
>1250°C Formation of C3S and finished reaction of CaO

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Figure 1: Clinker phases formation [3].
2.2. Calculations of the phase composition
The phase composition of a cement clinker can be calculated from the values of the chemical
analyses according to R.H. Bogue. For a cement clinker of usual composition, which
contains C3S, C2S, C3A and C4AF and has the AR >0.638, the following formulae can be
used:
C3S = 4.071*CaO – 7.600*SiO2 – 6.718*Al2O3 – 1.430*Fe2O3
C2S = 2.867*SiO2 – 0.754* C3S
C3A = 2.670*Al2O3 – 1.692*Fe2O3
C4AF = 3.043 Fe2O3
These calculations do not reflect the reality but give a potential composition, which is used in
practice. However the phase composition given by the calculation is only valid if the clinker
melt is always in thermodynamic equilibrium with the solid clinker phases Alite and Belite. In

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practice this precondition is never fulfilled. Therefore the calculation of Bogue always gives
too low values for the Alite and too high values for Belite content. But the difference between
the calculated and the actual clinker composition can be determined by quantitative
microscopic methods or by X-ray diffraction analysis. [1]
2.3. Calculation of the melting phase
The clinker contains 15 % to 25 % by mass of melt at the sintering temperature. The quantity
of melt (S) at 1400 °C can be calculated as follows [1]:
3232 2.295.2 OFeOAlS %mass
2.4. Other important moduli
The calculation of the Bogue potential clinker composition is descriptive but it does not give
any impression of the contents of CaO in the clinker. Therefore the raw material and the
clinker compositions are generally characterized by moduli in practice. These are called the
lime saturation factor (LSF), the silica ratio (SR) and the alumina ratio (AR). Additionally, the
degree of sulfatization (DS) is used. Table 2 shows potential values of German cement
clinker for those moduli. [1]
Table 2: Moduli of German cement clinker [1].
max av min
Lime saturation factor LSF 104 97 90
Silica ratio SR 4.1 2.5 1.6
Alumina ratio AR 3.7 2.3 1.4
Degree of sulfatization DS 109 77 35
2.4.1. Lime saturation factor (LSF)
The lime saturation factor shows the actual CaO content in the raw material mix or in cement
clinker relative to the maximum CaO amount, which can be combined with the SiO2, Al2O3
and Fe2O3 under industrial burning and cooling conditions. It can be calculated as follows [1]:
32322 65.018.180.2
100
OFeOAlSiO
CaO
LSF
%
%
mass
mass

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2.4.2. Silica ratio (SR)
The silica ratio is the mass ratio of the silicon dioxide content relatively to the total of the
aluminum and iron oxide contents. It describes the solid/liquid ratio in the sintering zone of
the cement kiln. The following formula shows the mentioned relation [1]:
3232
2
OFeOAl
SiO
SR
%
%
mass
mass
2.4.3. Alumina ratio (AR)
The alumina ratio gives information about the quantity of calcium aluminate to calcium
aluminoferrite. It reflects the behaviour of the clinker melt. The following formula can be used
for calculation [1]:
32
32
OFe
OAl
AR
%
%
mass
mass
2.4.4. Degree of sulfatization (DS)
The degree of sulfatization shows the percentage of the alkalis, which are presented as alkali
sulfates. It can be calculated as follows:
ClONaOK
SO
DS
13.129.185.0
100
22
3
%
%
mass
mass
(* The chloride content will be considered if Cl (loI-free) is higher than 0.015 % by-mass.)[3]
A degree of sulfatization of 100 % means that all the alkalis in the clinker are totally
combined to alkali sulfate. If the degree of sulfatization is higher than 100 %, then there is a
sulfur excess, which forms Ca-langbeinite (K2SO4*2CaSO4) and/or anhydrite (CaSO4) [1].
2.5. Burning process
At present there are two different techniques of clinker manufacturing; one is the dry and the
other the wet process. For this thesis, only the dry process is relevant and will be described.
In the fifties and early sixties two types of external preheaters were developed; a preheater

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with Lepol grate and a suspension preheater. Progressively the suspension preheaters
predominate and are only important for this thesis [4].
Figure 2: Diagram of cyclone
preheater [1].
Figure 3: Diagram of cyclone preheater with
precalcination [1].
The suspension preheaters, also called cyclone preheaters, have a simple layout and
several designs. The first system of this type was developed by Klöckner-Humboldt-Deutz.
Several cyclones are arranged superposed and displaced sideways. They are connected
and form the preheater tower. The first one consists of four cyclone stages (Figure 2), but
newer kiln systems have up to six stages. The main task is to preheat the raw material. The
exhaust gases from the rotary kiln pass through the cyclones from bottom to top. The dry raw
material is added to the exhaust gases before the top cyclone stage, is separated from the
gas and then drops back into the gas flow before the next cyclone stage. This process is
repeated up to five times until the material is discharged from the last cyclone stage into the
kiln.
Since 1970 those kiln systems got a new development, which is called precalcination. This
means that the supply of fuel energy is divided into two firing systems. The new additional
firing system takes place at the preheater (Figure 3). This means that the calcium carbonate

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in the kiln feed is dissociated over 90 %, when it enters the kiln. The degree of dissociation of
the kiln feed is between 40 – 50 % at conventional burning processes.
Figure 4: Different combustion air supply systems for
precalcination [1].
In the precalcining process the combustion air required for the firing system can be taken
from two different ways (Figure 4). On the one hand, through the rotary kiln (a) and on the
other hand directly from the clinker cooler through a special duct, which is called tertiary air
duct (b). The connection of this duct can be located in two different positions. The first one is
on top of the kiln head (connection between kiln and cooler) and the second is directly after
the kiln head on top of the cooler enclosure.
2.6. Vaporizable constituents and its recirculating system
The hot kiln gas, which heats the kiln feed by counter-current flow, contains various gaseous
or vapour compounds. These are formed from vaporized or disassociated constituents of the

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kiln feed and the fuel. These are mostly alkali, sulphur and chloride compounds as well as
some trace elements like zinc, lead, chromium, cadmium, thallium, mercury and fluoride.
The vapour compounds condense in the cooler parts of the kiln or in the preheater or in the
downstream installations and deposit on the kiln feed and dust. If the fraction deposited on
the kiln feed passes the hot zone of the kiln again and vaporizes, then internal circulations
can be formed. The constituents are often carried out of the kiln and preheater area and
collected in the gas cleaning system. These constituents are added to the raw meal again
with the dust and go back to the kiln. This creates an external recirculating system (e.g. the
green line in Figure 5). The internal and external recirculation can be reduced by removing
part of the recirculating substances from the system e.g. by a bypass system.
Figure 5: Recirculating system [3].
The most important recirculating substances are alkali sulphates and alkali chlorides, which
can affect the operation of a cement kiln system. This recirculation system can be found at
the high temperature part of the kiln system (red line). They can form an additional melt in
the clinker, which influences the flow characteristics of the material in the kiln. [1]

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2.7. Operation control measurements
The kiln operation is mostly monitored by several measurements:
Production rate [t/h]
Operating hours
Involuntary downtime hours
Total fuel rate [t/h]
Specific heat consumption [kcal/kg]
Proportion of fuel to precalciner / riser [%]
Secondary air temperature [°C]
ID fan draft [mmH2O]
Preheater exhaust gas temperature [°C]
O2 Kiln feed-end and exhaust gas [Vol.-%]
Downcomer O2 [%]
Kiln feed-end material: - LoI [%]
- SO3 [%]
Kiln drive power [kW]
There are also numerous other process parameters which should be logged. Those data are
needed to observe trends, which may indicate problems and to provide necessary mean data
for process analyses. Those factors are [2]:
Primary air tip velocity [m/sec]
Specific kiln volume loading [%]
Gas velocity in burning zone [m/sec]
Specific heat loading of burning zone [kcal/h per m² of effective burning zone cross-
section area]
Cooler air [Nm³/h per m² grate area]
Cooler + primary air [Nm³ per kg clinker]
Temperature, pressure and oxygen profile of preheater
NOx and CO in the waste gas

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2.8. Clinker cooling
The cooling process influences the structure of the clinker, its mineralogical composition as
well as the grind ability and in consequence the quality of the produced cement.
The speed of clinker cooling has an influence on the ratio of crystalline and melting phases in
the clinker. During slow cooling almost all clinker components are formed of crystals,
whereas fast cooling delays the formation of crystals and avoids the generation of the
melting phase. A typical value of melting phase in clinkers from rotary kilns is in the range
from 20 – 25 mass-%. Additional fast cooling prevents the crystal growing and has also an
influence on the formation of the periclase crystals (MgOfree). The faster the cooling of clinker,
the smaller the periclase crystals grow, which emerge by crystallization of the melting phase.
A typical size of fast cooled clinker is in the range from 5 – 8 µm. Slow cooled ones have up
to 60 µm large crystals [5].
It is reported that the best clinker is obtained by cooling slowly to 1250 °C followed by rapid
cooling [4]. A summary of the effects of cooling rate on the clinker phase and their properties
can be seen in Figure 6.
Figure 6: Effect of cooling rate on cement properties and phases [4].

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2.9. Clinker cooler types
Clinker coolers can be found basically in three different types. They are built as grate, rotary
or planetary coolers (Figure 7). The coolers differ mainly in the type of heat transfer, the
length and the design of pre-cooling zone (see the dot and dash line in Figure 7), the clinker
inlet temperature and the controllability.
Figure 7: Conventional cooler types [6].
The rotary coolers (Rohrkühler) are the older ones. The heat transfer of the hot clinker to the
cooling air occurs by counter current flow. The pre-cooling zone is longer than the one from
the grate coolers (Rostkühler), which decreases the clinker inlet temperature (1400 –> 1200
°C). The rotary cooler has an independent adjustable rotation speed from the rotary kiln. A
summary of essential technology data of rotary coolers can be found in Table 3.

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Table 3: Essential technical data of rotary coolers [6].
Technical terms Unit Value
Throughputs t/d <2,000 – 4,500
L/D-relation - approx. 10:1
Rotation speed min-1 1 – 3
Incline % 3 – 5
Specific cooling air quantity m3N/kgCli. 0.8 – 1.1
Clinker inlet temperature °C 1,200 – 1,400
Clinker outlet temperature °C 200 – 400
Coolant efficiency ratio % 56 – 70
The planetary coolers (Satellitenkühler) consist of nine to eleven cooling tubes attached
around the perimeter of the kiln tube. The heat transfer also takes place by counter current
flow like the rotary coolers. This cooler cannot be adjusted. The specific cooling air quantity
is identical with the amount of combustion air. Caused by a longer pre-cooling zone the
clinker inlet temperature is lower compared to rotary coolers. Table 4 shows essential
technology data for this type of cooler.
Table 4: Essential technical data of planetary coolers [6].
Throughputs t/d <3,000 – 4,000
L/D-relation - 9 – 11
Specific cooling air quantity m3N/kgCli. 0.8 – 1.0
A grate cooler is nowadays the usual cooler type. In this cooler the clinker bed is transported
on a grate, which is cooled by transverse flow of air. This type of cooler requires more
cooling air than is needed for the combustion. The cooler exhaust air can be used e.g. for
drying the raw material. Table 5 presents the relevant information about the technology of
grate coolers.
Table 5: Essential technical data of grate coolers [6].
Throughputs t/d 700 – >10,000
Grate area loading t/m2d 26 – 55 (100)
Grate incline degree up to 10
Specific cooling air quantity m3N/kgCli. (1.4) 1.6 – 2.6

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2.10. Principle design and process technology features of modern grate
coolers
2.10.1. Fixed inlet areas
The fixed inlet of a cooler is the most important interface between the rotary kiln discharge
and the clinker cooler. Almost all cooler manufacturers use a fixed inlet area with direct
aeration to improve the thermal efficiency of the cooler system and to increase the availability
of the grate plates in the hot zone. But the static inlet also increases the risk of the formation
of a “Snowman”, which is further strengthened by using more and more secondary fuels [7].
2.10.2. Grate plate development
Modern grate plates and their systems enhance the grate resistance for improving the air
distribution and its thermal efficiency of both aeration systems (air beam and chamber). The
new developed plates raise the service life of mechanical parts and minimize their wear.
Additionally they achieve a constant grate resistance over a longer operating time and
reduce the grate riddling by having constant, narrow gaps and slots [7].
2.10.3. Side sealing
New developments of grate seals minimize the gaps during thermal expansion of the grate
surface. Very long service lives are achieved by hardening the surface of the moving parts of
a plate. This prevents air channelling at the edges of a clinker cooler [7].
2.10.4. Cooler drive
The hydraulic cylinder drive is developed continuously. The stroke lengths and the cylinder
speeds are optimized to an effective conveying and minimization of wear (fewer thrusts) [7].
2.10.5. Clinker crusher
A modern cooler requires a roll crusher. This type of crusher is in fact more expensive than a
hammer crusher but the maintenance and spare-parts costs are very low. The dust load at
the end of a cooler is lower by using a roll crusher. This type of crusher deals with very large
pieces of coating from the kiln, which avoids unplanned kiln shut downs [7].

21
2.10.6. Improvement of thermal efficiency
By using a specific and controlled direct aeration of the static inlet, the efficiency of a cooler
can be improved significantly. The air and material distribution play a decisive role. The main
goals are that the clinker is optimally cooled down and gets the best heat recuperation. In
other words a good material distribution at the start of the grate, maintains a constant clinker
bed with a depth of about 500 to 900 mm over the entire grate area. This is achieved by a
static grate or special distribution grates for large widths. Additionally, a partition wall
between the recuperation zone and the cooling area minimizes the heat radiation loss and
assists the heat exchange [7].
2.10.7. Material discharge system
The discharge of grate riddling can be solved in different ways. One is the traditional hopper
arrangement with double flap valves or the other the level-controlled slides with a drag chain
to remove the material. Furthermore coolers with small gaps reduce the grate riddling.
The newest development is a cooler design without grate riddling. At this type of cooler,
known as a reciprocating beam cooler, the transport mechanism is separated from the
cooling mechanism. This means that the aeration base has no moving parts and is protected
by a stationary layer of clinker [7].
2.10.8. Grate support system
The internal roller or axle support systems are used for supporting the grate or moving frame.
The design and material of these systems is improved to reduce the wear [7].
2.10.9. Cooler control system
The following measuring and control loops can be used for an automatic process control of a
clinker cooler:
Cooling air volume flow
Chamber pressure / grate thrust rate
Kiln hood pressure
Grate plate temperature
Secondary / tertiary air temperature
Exhaust air temperature

22
Normally the grate speed is controlled by the pressure in the first air chamber or by a
combination of several initial air chambers. New developments like level radar, which
measures the clinker bed depth at the inlet of the cooler directly, can be very useful for the
control of the grate speed [7].
2.10.10. Cooling air fans
In general the cooling air comes from radial fans with double bearings. By using fans
operating at constant speed with small changes in air quantity the air volume is controlled by
a vane controller with an actuating mechanism. Only fans with large control reserves (e.g. at
the inlet area) are operating with frequency-controlled motors. The first fans indicate a
rotational speed of over 2000 rpm due to the high pressures of 80 – 130 mbar [7].
2.11. Process interrelationships – trend curves
The following trend curves show the qualitative coherence between the described process
parameters. The quantitative coherence and the wave shape are not taken into account. For
simplification all curves are drawn linear to get an impression for the existing
interdependency [8].

23
Table 6: Clinker capacity - clinker exit temperature - cooling air quantity [8].
Higher clinker capacity Higher clinker exit temperature
Constant: Thrust rate, cooling air
quantity
Increasing the capacity means a rise
of the specific grate area load
(capacity / grate area). If the cooler
is operating with the same cooling
air quantity and thrust rate after an
increase of capacity then the clinker
exit temperature will rise.
Higher cooling air quantity Lower clinker exit temperature
Constant: Clinker capacity, thrust
rate
It is significant, for the coherence
between clinker exit temperature
and cooling air quantity, that an
enhanced air volume leads to a
lower clinker exit temperature by
constant capacity.
Lower thrust rate Lower clinker exit temperature
Constant: Clinker capacity, cooling
air quantity
A lower thrust rate supports the heat
transfer between cooling air and
clinker and therewith it produces a
lower clinker exit temperature.
Higher clinker capacity Higher cooling air quantity
Constant: Clinker exit temperature
The clinker exit temperature will be
constant if the clinker capacity and
the cooling air is increased at the
same time and / or the thrust rate is
dropped. The cooling air quantity
and the thrust rate have to be
adjusted to reach an optimum.
The main statement is that an optimal adjustment of cooling air quantity and thrust rate is
preconditioned for a low clinker exit temperature.

24
Table 7:Specific cooling air quantity - secondary air temperature - cooler efficiency [8].
Lower cooling air admission Higher secondary air temperature
Constant: --
A change from an conventional grate plate
arrangement to a direct aeration in the first
chamber enables the reducing of specific
cooling air admission. A lower specific
cooling air admission accords with a lower
air speed and therewith an increasing of the
air stay in the cooler. The result is a better
heat transfer and a higher secondary air
temperature.
The specific cooling air admission at the
beginning of the cooler has to be high
enough to prevent clinker agglomeration.
Higher secondary air temperature Higher cooler efficiency
Constant: --
A higher secondary air temperature (higher
heat content of the secondary air) increases
the cooler efficiency.
Higher cooler efficiency Lower kiln heat requirement
Constant: --
A higher heat recuperation of the clinker
accords with a reduction of fuel in the kiln.
Therewith the kiln heat requirement and the
production cost of the kiln system decrease.
The main statement is that the cooling air admission at the beginning of a cooler affects
essentially the recuperation efficiency of the cooler.

25
Table 8: Clinker bed level - thrust rate/time of stay - clinker exit temperature - wear [8].
Lower thrust rate Higher clinker bed level
Constant: Clinker capacity
If the pressure-set point for the thrust
rate controlling is increased (higher
clinker bed level) than the grate thrust
rate will be lower and the time of stay of
the clinker in the cooler will be
enhanced.
Higher time of stay
Lower clinker exit temperature
The time of stay of the clinker per row or
rather chamber is higher with a lower
speed of the clinker. This means that
there is more time for heat transfer
between hot clinker and cold air. The
result is a lower clinker exit temperature
at the end of the cooler.
Lower thrust rate Less wear
A decreasing of the thrust rate means a
lower friction between the clinker and
the grate plate surface. The result is a
reducing of the wear.
The main statement is that a lower thrust rate affects a higher clinker bed level and a higher
time of stay of the clinker in the cooler. Furthermore the grate plate wear is lower by having a
lower thrust rate standard.

26
Table 9:Clinker bed level - clinker exit temperature - cooler efficiency - power requirement[8].
Higher clinker bed level Lower clinker exit temperature *
By increasing the clinker bed level
the time of stay of cooling air in the
clinker bed is enhanced. Therefore
the heat transfer is better and leads
to a lower clinker exit temperature.
This is confirmed when the clinker
bed level limit is not reached. At this
limit the cooling air starts to blow
through and causes a worser
cooling with higher exit
temperatures.
Higher clinker bed level Higher cooler efficiency *
A good heat transfer during a higher
clinker bed level causes an
increasing recuperation air
temperature. This leads to an
enhanced cooler efficiency. To pass
the clinker bed level limit has the
result of a worse heat transfer and
efficiency.
Higher clinker bed level
Higher fan pressure *
A high clinker bed level means a
higher resistance, which has to be
overcome by the fan. Until reaching
the clinker bed level limit, the fan
pressure will increase. After passing
this limit the pressure will decrease
because the air blows through.
The available fan pressure (by
definition of the cooling air quantity)
limits the maximum of the clinker
bed level.
Higher clinker bed level Higher power requirement
The rise of the clinker bed level and
the fan pressure effect an increasing
of the specific power requirement of
the fans by reducing the kiln heat
requirement.
* It is only essential until reaching the optimal clinker bed level.
The main statement is that clinker bed level optimizing decreases the operating expenses.

27
Table 10: Cooling air quantity - thrust rate - exhaust air quantity - exhaust air temperature [8].
Higher cooling air quantity Higher exhaust air quantity
If the cooling air quantity is increased in the
cooler (especially at the after-cooling-zone)
then the exhaust air quantity rises.
Higher thrust rate Higher exhaust air and clinker exit temperature
Constant: Clinker capacity, cooling air
quantity
If the cooler operates with a higher thrust
rate, then the time of recuperation will be
lower to achieve a sufficient heat transfer.
The result is that an enhanced amount of
heat will be transferred to the after-cooling-
zone. This leads to an increasing of the
exhaust air and clinker exit temperature.
Lower cooling air quantity Higher exhaust air temperature
Constant: Amount of combustion air, clinker
exit temperature
If the total cooling air quantity is reduced at
constant combustion terms, then the amount
of exhaust air will be decreased. The result
is a higher exhaust air temperature.
Higher exhaust air temperature Higher potential heat recovery
An efficient heat recovery leads to a higher
exhaust air temperature. This can be mainly
found at stage coolers because of their
intermediate cooling.
The main statement is that a higher thrust rate standard increases the heat losses of the
cooler, which means that clinker exit and cooler exhaust air temperature rises.

28
2.12. Red River
The “Red River” is a phenomenon in the cooler. Distinctive for it is a narrow stream of fine
clinker which appears far down in the cooler at higher temperatures than the neighboured
clinker. This narrow stream is often red hot (hence the name). Fine and coarse clinker will be
partly segregated in the kiln and fall separated to the right/left side of the static inlet. The fine
clinker falls on the kiln load side and the coarse clinker on the other one. If, additional to the
segregation, a clinker bed with unilateral or bilateral slope is formed on the static inlet, the
fine clinker slides down the slope to the side (Figure 8).
Figure 8: Formation of Red River [9].
The segregation and slope, not inclined in clinker flow direction, are the reasons for “Red
River”. Furthermore a “Red River” can be caused by a “Snowman” because of the
disturbance of aeration at the static inlet in the cooler. A fine clinker has a higher resistance
to the airflow than the coarse clinker, so the cooling air takes the path of least resistance,
which intensifies the “Red River” formation. Figure 9 shows the pressure losses of various
clinker sizes as a function of free air velocity. It can be seen that the particle size has a great
influence on air distribution, which can be described by pressure losses [10].

29
Figure 9: Pressure losses of various clinker sizes as a function of free air velocity [10].
2.13. Snowman
Another phenomenon in the cooler is the formation of a “Snowman”. A Snowman (SM) is a
type of build up formed in the static inlet. In general a snowman is caused by [9]:
fine and sticky clinker
fall of coating from the kiln.
A sticky clinker occurs when the content of the melting phase or the kiln temperature is too
high. In the one case the melting phase works as a binder and bonds the clinker together. In
the other case, fall of coating, a big lump stays in the cooler inlet without transport. The
surface of the big lump means an additional free area. Those formed platforms are the base
where a snowman can grow (Figure 10).

30
Figure 10: Formation of Snowman [9].
These big lumps cannot be cooled down. They store a lot of heat and disturb the aeration.
Figure 11 presents the non-steady state cooling of clinker for a number of different clinker
sizes as a function of time. It shows that it is physically impossible to cool large clinker
particles (> 100 mm) to an acceptable temperature within a reasonable retention time of 20
min, which is typical for grate coolers [10].
Figure 11: Effect of clinker size on needed retention time [10].
Clinker build ups at the static inlet of the cooler are mainly formed at clinker temperatures
over 1250 °C in the kiln outlet [11].
The following checklist was made before visiting the cement plant Brevik in Norway. It was
the first step to approach the Snowman phenomenon.

31
3. Checklist
This general checklist is written in keywords to shorten the thesis. A detailed explanation is
given with the example of the cement plant in Brevik, Norway. The checklist is divided into
three parts. The first one takes a look into the material data, the second one describes the
process data and the last one shows other available data. All data show possible reasons for
Snowman formation. Later on this checklist will be introduced by means of visiting the
cement plant in Brevik, Norway.
3.1. Part 1 (Material data)
3.1.1. Chemical Compositions
To be analyzed: a) Raw meal (kiln feed)
b) Clinker
c) By-pass dust
d) Secondary and primary fuels
e) Ash
Main components and in particular the contents of: sulfates; chlorides; alkalis
mineralizer like CaF2; SnO2
3.1.2. Clinker Mineralogy
Focusing on: liquid phase; CaOfree; MgOfree; oxidizing vs. reducing burning conditions,
homogeneity
3.1.3. Moduli
LSF; AR; SR; SD; Melt content; Sodium equivalent
3.1.4. Clinker
Grain size distribution (from cooler inlet; in front of the crusher)
Segregation of the falling clinker into the cooler inlet
(Stickiness-check)
Liter-weight / density / porosity
Mechanical properties

32
Size distribution
Hot stage microscope liquid phase vs. adhesion
3.2. Part 2 (Process data)
3.2.1. Feeding system
Dosages and amount of: - fuels (primary and secondary)
- kiln feed
- dust
Homogeneity / fineness
Steadiness of feed and fineness
3.2.2. Kiln
Type of fuels
Temperature of: - flame (especially peaks)
- secondary and tertiary air
Design of the flame
Coal fineness
NOx-values (Over-burning)
Zone length (especially pre-cooling and sintering zone)
Electrical power consumption (peaks?)
Rotary kiln speed
Places of Build-ups caused by dust
Dust content in the secondary air and handling system
Gas velocity at the kiln outlet
3.2.3. Cooler
Airflows: - amount
- distribution
- pressure losses
- reserves
Operation: - grate speed
- fan flows
- blasters
- pressures

33
- exhaust temperature
- intensity and frequency of control adjustments
Integrity: - plates
- aeration
- refractories
Clinker level at the inlet (especially free areas at plates and horse shoe)
Slope of the inlet module
Dust content in the air and handling system
Installed crusher type
“RedRiver”-formation
Temperatures of: - clinker (inlet & outlet)
- plates
3.3. Part 3 (Other data)
3.3.1. Snowman type
“mushroom”-formation (fast growing on a small area, not moveable)
“sugar loaf”-formation (fritted dust, moveable)
“bridges”-formation (connection between each side or corner of refractory walls)
3.3.2. Visual checks
- Glowing clinker after cooler outlet amount of crushed clinker (extreme grain sizes)
- “Bubbling” at the surface of the clinker bed in the cooler (“BlowThrough” indication at high
clinker levels)
- Surface colour of the clinker flow

34
4. The cement plant in Brevik, Norway
4.1. Introduction
The investigated cement plant in Brevik is one of two plants of Norcem AS. It has been part
of HeidelbergCement AG since 1999, in Norway. Three different types of clinker, a standard-
(OPC), a low alkali- (LA) and an oil well clinker (LA-SR) are produced in one rotary kiln and
seven types of cement are manufactured in three cement mills. The clinker and cement
production capacities are 1 million and 1.3 million tons per year.
At Brevik there are a lot of problems with snowman formation, which often occur after
changing the clinker type during the production. The first time of mentioning a snowman was
in February 2002 after the cooler modification in November 2001. Before that day no
snowman appeared. During the modification in November 2001 a moveable inlet was
changed to a static one.
The purpose of the visit was to collect data which could give some hints for snowman
formation and information about the kiln and cooler system.
4.2. Flow sheet
Figure 12: Simplified flow sheet of the clinker production at Brevik, Norway.

35
Bauxite, Iron ore, Oxiton, Quartz and limestone of two different qualities are the raw
materials for the production in Brevik. They are fed over a cross belt analyzer to the raw meal
production. The material is milled first with an aero fall mill followed by a roll mill and a
hammer mill. After this the coarse and fine material is separated in the separator. The
finished raw meal is stored in an 25,000 tons raw meal silo. This silo stores the material up to
100 hours. After that the raw meal is fed into the kiln at the second cyclone stage. It goes
through the cyclones of the preheater tower into the kiln and leaves the burning process at
the cooler end. The clinker is also stored in a silo. Typical mass flows can be found in Table
30 in the appendix.
The two red arrows, which can be seen in Figure 12 show the two regular checkpoints of raw
material and raw meal (see also paragraph “4.6 Chemical Compositions”).
4.3. Kiln system modification
A summary of the various tasks of the kiln system modification in Brevik during 2003 and
2004 and the purpose of each task can be found in Table 11.
Table 11: Overview of the kiln system modification items [12].
Part Item Purpose
Installation of a “hot-spot”
combustion chamber (down-draft
type) with high-temperature zone,
high-O2 zone, increased residence
time and increased turbulence level
Improve burnout of lumpy fuels in
the calciner system
Installation of mixing chamber Mixing kiln gas and gas from the
new combustion chamber
Installation of a KHD Pyrotop swirl
chamber at the top of the loop duct
of the calciner
Improve burnout of lumpy fuels
fed to the calciner system
Installation of an orifice in the riser
duct
Balance kiln gas and tertiary air,
as well as ensure sufficient gas
velocity in the riser duct to avoid
drop-through of fuel fragments
Re-routing and extension of the
tertiary air duct
Adapt the tertiary air duct to the
new combustion chamber
Modification of lower cyclone stage
on string 1
Make space for the new
combustion chamber
Re-routing of meal pipes Make space for the new
combustion chamber
Calciner/preheater
system
Modification of the kiln inlet chamber Ensure sufficient inclination of the
re-routed meal pipes
Installation of new 70 m³ cylindrical
silo, equipped with a rotary
discharge feeder
Provide intermediate storage and
waste buffer, with a trouble-free
discharge, in front of weigh feeder
Waste feeding
system
Installation of weight feeder with a
waste feeding capacity of 25 tph
Provide accurate and sufficient
feeding of waste fuels to the new

36
combustion chamber
Extension of existing pocket
conveyor and modification of screw
conveying system for RDF and
SHW
Convey RDF and SHW from
reception bins to new waste silo
and from new waste silo to new
combustion chamber
Installation of mass flow
measurement equipment based on
gamma radiation; mounted outside
screw conveyors
Control discharge rate and mixture
of different waste fuel types from
reception bins
Installation of air-cooled bypass
quenching chamber, designed for
10 % kiln gas extraction
Relieve the kiln system of
chlorine, and hence reduce or
avoid chlorine related operational,
environmental and quality
challenges
Refurbishment of an existing ESP
(previously used on another, closed
kiln line)
Extraction of chlorine rich bypass
dust from the bypass gas
Routing of the de-dusted bypass
gas to the front part of the clinker,
and re-use of the oxygen-rich (19 –
20 % O2) cooled bypass gas as
combustion air in the rotary kiln and
the precalciner
Avoid a new emission point, and
hence avoid additional emissions
of NOx, Sox and dust, and
possible dioxins
Bypass system
Installation of fans and ductwork for
the bypass gas, including re-use of
two existing in-series arranged MRD
blowers
Route the bypass gas from the
kiln inlet, via the ESP to the cooler
In 2003 and 2004 the calciner/preheater modifications took place. The bypass installation
(Figure 14) was commissioned in June 2004, thus completing the new kiln system (Figure
13).
The latest modifications take place during the maintenance shut down in 2006. During this
production stop the kiln head is modified to a bigger one. The area is increased from 7.6 m²
to 12.8 m². The reason for this modification is the high gas velocity at the static cooler and
kiln outlet area. The calculations of the gas velocity before the reconstruction show values of
8 – 10 m/s. The calculation of the new kiln hood indicates a gas velocity of around 4 – 6 m/s,
which can be seen as a normal condition.

37
Figure 13: The modified kiln system [12].
These bypass installation features are an environmentally friendly concept for re-cycling the
bypass gas in the system and avoid new emissions. The hot gas is bled stream at the rotary
kiln inlet, cleaned by an ESP and taken back into the second and third chamber of grate
number one from the cooler.
Figure 14: The new bypass system [12].

38
The cleaning of the bypass gas is sometimes not good enough, which leads to a high dust
concentration in chamber two and three. This causes some problems like clogging of the
cooler grate plates, which reduces the cooler efficiency. Additionally, it is reported that
sometimes Snowman formation in front of the cooler can be seen. It is suggested that this
Snowman formation is caused by insufficient cooling. To prevent this effect, the bypass filter
system has to be improved. At the moment the hot bypass gas is rerouted to the exhaust air
stream of the cooler.
Some characteristics of the modified kiln system are given in the following Table 12.
Table 12: Kiln system characteristics [12].
Parameter Value Unit
Rotary kiln length 68 m
Rotary kiln (outer) diameter 4.4 m
Clinker production capacity 3,300 tpd
Typical specific fuel consumption 3,400 kJ/kgCli
Representative temperature interval in rotary kiln 1,100 – 2,000 °C
Representative temperature interval in the precaliner 840 – 1,300 °C
Typical gas residence time in the rotary kiln 5 s
Typical gas residence time in the precalciner 5 s
Typical O2 concentration in rotary kiln exhaust gas 3.5 %
Typical O2 concentration in precalciner exhaust gas 4 %
4.4. Actual Cooler at Brevik
The following cooler type is used in Brevik (Figure 15). It is a rebuilt Claudius Peters (CP)
cooler with a static inlet. The tertiary air is extracted from the cooler roof directly after the kiln
hood. A hammer crusher is located at the end. Additional this cooler has a so called
“Fishbone aeration” with stoppers, which intensify the cooling of fine clinker at side to prevent
the Red River formation [10].

39
Figure 15: The used clinker cooler system at Brevik, Norway.
4.5. Kiln stop list caused by Snowmen
The following stop list was made from the monthly reports of kiln operating control (1999 -
2006):
Table 13: Kiln stops caused by Snowman formation (1999 - 2006).
Year Dates Comments
Clinker
type
produced
Clinker
type
before
Date of type
change
19.02.2002 Snowman in clinker crusher OPC LA-SR 09.02.2002; 11:002002
19.05.2002 Snowman before crusher LA OPC 13.05.2002; 13:00
25.01.2003 Snowman in cooler & grate 2
stopped
OPC LA-SR 24.01.2003; 13:00
18.08.2003 Snowman in cooler & grate 2
stopped
OPC LA 17.08.2003; 22:00
14.10.2003 Snowman in cooler (&
shooting a ring)
LA OPC 11.10.2003; 15:00
05.11.2003 Snowman in cooler OPC LA-SR 04.11.2003; 0:00
04.12.2003 Snowman in cooler LA OPC 02.12.2003; 17:00
2003

40
07.08.2004 Snowman in cooler LA-SR LA 05.08.2004; 19:00
07.09.2004 Snowman in cooler OPC LA 28.08.2004; 1:00
2004
13.10.2004 Snowman before crusher LA OPC 08.10.2004; 20:00
24.04.2005 Snowman in cooler OPC LA-SR 22.04.2005; 15:00
23.05.2005 Snowman in cooler &
welding after tire slap
OPC LA-SR 22.05.2005; 13:00
22.06.2005 Snowman removed with
dynamite
LA OPC 19.05.2005; 2:00
23.06.2005 Snowman OPC LA 23.06.2005; 10:00
blocked grate from bypass
dust
OPC LA 27.07.2005; 7:00
14.08.2005 Snowman OPC LA-SR 13.08.2005; 16:00
20.08.2005 Snowman LA OPC 19.08.2005; 22:00
22.08.2005 Snowman LA OPC 19.08.2005; 22:00
29.08.2005 Snowman & inlet plates LA OPC 27.08.2005; 19:00
2005
problems with ignition device
of dynamite
LA LA-SR 14.12.2005; 21:00
21.02.2006 Snowman in cooler LA-SR OPC 20.02.2006; 6:002006
07.03.2006 Snowman almost every
day/night until 11.03.06
LA OPC 06.03.2006; 10:00
In total there were 28 Snowman formations in the last five years which led to stops of the
clinker production. Especially in 2005 the Snowman formation became a general problem. In
that year 50 % of the Snowman formations occured and this tendency did not stop in 2006.
Furthermore it is conspicuous that almost all Snowman formations took place within 24 hours
after switching from one type of clinker to another. Unfortunately there is no tendency visible
which would show at what kind of clinker type switch the danger of Snowman formation is
highest. It is also shown that the change of bypass way on 25.08.2005 has no influence on
this kind of build up in the cooler inlet.
For the following investigation of the chemical and process data the last Snowmen (period:
06.03.06 – 11.03.06) will be observed. Other important data like calculated annual average
values can be found in the appendix.
4.6. Chemical Compositions
The following analyses are calculated from the laboratory data, which are averages of the
period from 06.03.06 to 11.03.06.

41
4.6.1. Raw meal (kiln feed)
The raw material is only analysed with the full stream analyzer in this viewed period. This
analyser is operating before the raw mill. There are no comparable analysed values for the
raw meal, which is fed into the kiln. See also part “4.13 Other noticeable features”.
Table 14 shows the raw meal analyses of the full stream analyser.
Table 14: Raw meal chemistry of LA-clinker (06.03.06 - 11.03.06) *FSA.
CaO SiO2 Al2O3 Fe2O3 Na2O K2O SO3 Alkali xSO3
66.10 21.84 4.26 3.28 0.44 0.40 0.80 0.68 1.21
It can be seen that a small content of alkalis and sulfates are coming from the raw mix into
the production process.
4.6.2. Clinker
The low alkali clinker chemistry can be seen in Table 15. Those values shall be the standard
values for the following observations.
Table 15: LA-Clinker chemistry (06.03.06 - 11.03.06).
CaO SiO2 Al2O3 Fe2O3 Na2O K2O MgO Alkali SO3
65.01 21.47 4.37 3.46 0.31 0.45 2.08 0.60 1.10
4.6.3. By-pass dust
For the considered period there are only two measurements of the By-pass dust. See the
Table 16.
Table 16: Bypass dust chemistry (06.03.06 - 11.03.06).
CaO SiO2 Al2O3 Fe2O3 Na2O K2O MgO Cl SO3
56.90 17.21 3.66 2.65 1.06 4.51 1.76 4.13 5.70
It can be found that alkali and sulfate rich bypass dust is extracted. Furthermore this dust
contains a lot of chlorides.
4.6.4. Secondary and primary fuels and ash
In Brevik there are no general analyses made during operation. Caused by this fact those
values are not comparable for the viewed period.

42
4.7. Clinker mineralogy
Table 17 shows the calculated values by Bogue. Furthermore it gives the content of the
melting phase, calculated by Lea and the average analyzed content of free lime.
Table 17: Clinker mineralogy calculated by Bogue and Lea (06.03.06 - 11.03.06).
C3S C2S C3A C4AF CaOfree (analyzed) Melting phase
67.16 10.93 5.81 10.52 1.30 20.49
Demonstrative is the value of melting phase. It stays by 20.49 %. This value can be seen as
having a very low content, which can be depicted as a preventive measure, suggested in a
dissertation by Dr. D. Optiz [11]. Besides this, the free lime lays at 1.3 and can be considered
as a middle value.
4.8. Moduli
In Table 18 the calculated moduli from the LA-clinker values (Table 15) can be found. The
most demonstrative value is the degree of sulfatization which lies over 100.
Table 18: Calculated Moduli (06.03.06 - 11.03.06).
LSF SR AR SD
96.27 2.74 1.26 141.15
4.9. Clinker analyses
No analyses of clinker are made at the cement plant in Brevik. Even the Liter-weight, which
is a very fast and easy way to check the density of a clinker, is not used.
To analyze the grain size distribution from the cooler inlet a lot of time is required and this
means an intervention into the process. Because of safety reasons the segregation analyses
of the falling clinker into the cooler inlet is impossible today. Maybe a system with a CCD-
Camera which is used for particle analyses can help to make this analysis possible in the
future.
4.10. Burning system (Process Data)
There are a lot of influences which can affect the measurement of the process data, and
which cause difficulties in analyzing such data. This has to be remembered by taking a look
into the process data. It must also been taken in consideration, that other problems also

43
occurred besides Snowman formation, during that period of time. So the given values should
be handled with care. They only give suggestions about what might be the reason of having
Snowman formations.
For the following observation of process data it shall be mentioned that only comparable data
of the Snowman analyses will be presented. The viewed period is marked with a red spotted
rectangle in the diagrams. Furthermore the rectangle with lines going from bottom left to top
right shows the period of the first kiln shut down caused by Snowman formation. The other
rectangle with lines going from top left to bottom right indicates the second kiln shut down
caused by Snowman formation. The measurements of process data end with the
maintenances shut down in the morning of March 11, 2006. It was reported that there was
another Snowman indicated.
4.10.1. Feeding system
Figure 16 shows the feed amount of the primary and secondary fuels of the main burner.
Figure 16: Diagram of fuels feeding (06.03.06 - 11.03.06).
The blue line presents the coal, the red one the oil, the green one the animal meal and the
yellow one the feeding of liquid hazardous waste. The first demonstrative subject is, that the
feeding of animal meal makes a lot of problems during the whole period. During the time
period when the second Snowman appeared (marked with the red rectangle), it can be seen,
that there is no measurement of animal meal amount. So it cannot be excluded that there is

44
a possible feeding of animal meal. Besides this there are some regulations of coal feeding,
which show that the operator regulates the heat in the kiln system. After the animal feeding is
shut down the amount of liquid hazardous waste and coal gets higher values to compensate
the missing animal meal. Overall there seems to be too much energy in the kiln system
which may lead to overburning.
Additionally, the feeding of secondary fuels to the calciner seem to be very unstable,
although the process measurements show a steady feeding. The secondary fuels, especially
the RDF contains big pieces of wood. These pieces are bigger than a fist, which also lead to
other problems at the bypass filter system. So it can be mentioned that the steadiness of
feed is affected.
4.10.2. Kiln
Figure 17 shows the temperatures of secondary air (blue line), tertiary air (red line), clinker
exit (yellow line) and the exhaust air from the cooler (green line). These measurements can
only show tendencies and do not represent the real values. The other important values of kiln
amp (red line) and raw meal feeding (blue line) can be found in Figure 18.
Figure 17: Diagram of temperatures (06.03.06 - 11.03.06).
It can be seen that the secondary air temperature contains two significant peaks. These
peaks are the results of the fuel feeding and underline the suggested overburning. The

45
tertiary air temperature indicates a tendency to a lower value which means a worse heat
recuperation. This fact correlates to a Snowman formation. If a Snowman is formed then the
clinker flow is disturbed in the cooler. Furthermore it can be seen that the measurement of
the clinker end temperature shows a high peak followed by a low value. This behavior also
stays in correlation with the clinker flow. A higher clinker end temperature means a higher
amount of clinker flow in the cooler. The best coherence of this correlation can be seen
before the first Snowman formation. There are three peaks in a short time period followed by
a result Snowman formation.
The measurement of the exhaust air temperature is affected by cooling with water and
cannot be used for finding hints of Snowmen formations.
In Figure 18 a sharp peak in the kiln amp can be found. This peak supports the thesis of a
possible fall of coating and underlines the Snowman formation during that time. Besides this
the raw meal feeding shows a regulation. This is explained in the paragraph about the cooler
findings.
Figure 18: Diagram of kiln amp and raw meal feeding (06.03.06 - 11.03.06).
Another interesting point can be seen in the following pictures. Figure 19 shows the used
burner pipe in new condition and Figure 20 directly after removal. The burner pipe is a low-
NOx burner and is built as followes. Twenty jet air openings (a) are arrange outside. Then
the installed opening for the pulverized coal and conveying air (b), followed by the swirl air

46
output (c). The output tubes of waste oil (d), liquid hazardous waste (e) and solid alternative
fuels (f) are arranged in the middle of the burner.
Figure 19: Burner in new condition. Figure 20: Burner in used condition.
The burning pipe in used condition seems to be in a bad shape. By taking a look at the end
of the burning pipe (Figure 20) a broken spacer can be found (see the arrow). The task of the
spacer is to secure a steady entrance gap for the coal. This refers to an uneven entry of
energy into the sintering zone of the kiln, which influences the nodulization of the clinker and
can lead to inhomogeneities in chemistry.
Additionally it should be mentioned that the dust content in the burning process is extremely
high. Especially burning the low-alkali clinker types the dust content is so high, that the flame
of the main burner can not be seen clearly. This is the reason why the flame temperature is
not measured by a pyrometer in Brevik and no statement about the design of the flame can
be made.
The gas velocity at the kiln outlet plays a separate role. As mentioned before the kiln head
enlarged to decrease the gas velocity at the cooler inlet. The calculated high gas velocity in
this area of the cooler can also lead to the high dust content in the process. Additionally, it is
reported that this modification also increases the clinker production.
4.10.3. Cooler
The speed of grate one (yellow line) and grate two (green line) can be seen in Figure 21.
There the two sharp peaks, especially from grate 2, are prominent. They underline the
Snowman formation. The Snowman disturb, is known as, the aeration which leads to
pressure losses. The control cycle which controls the grate speed by measuring the chamber
pressure reacts as seen in Figure 21. The operator notices those regulations of the system

47
and takes corrective action by regulating the raw meal dosage, which correspond to the peak
in Figure 18. The almost periodically grate 1 speed is accelerated significantly for short
periods. This behaviour cannot be explained.
Figure 21: Diagram of fuels feeding into kiln (06.03.06 - 11.03.06).
Table 19 shows the used cooling air volume. By checking the reserves of the operating fans,
it is conspicuous that the fan HE-2 is operating at almost maximum air flow. Furthermore this
fan is working with a steady amount of cooling air flow. There is no regulation module. The
task of this fan is to supply the twelve center plates of the static inlet with cooling air. This fan
in particular is operating in the potential area where a Snowman could be formed.
Table 19: The used cooling air volume calculated from process data (06.03.06 - 11.03.06).
Fan No. HE-1 HE-2 3 4 5 6 7 8 9 10
Process
data ( )
[Bm³/h]
22000 10500 22000 29279 52398 4900 4900 30808 34698 75648
Process
data ( )
[Nm³/h]
21223 10129 21223 28245 50548 4727 4727 29721 33474 72977
Installed air
quantity
[Nm³/h]
23300 10500 22900 38900 69100 12500 12500 36100 39300 92000
Working
load [%]
91.09 96.47 92.68 72.61 73.15 37.82 37.82 82.33 85.18 79.32
Reserves
[%]
8.91 3.53 7.32 27.39 26.85 62.18 62.18 17.67 14.82 20.68

48
The calculation of specific cooling air quantity from the process data of the cooler fans can
be seen at Table 38 in the appendix. The calculated values show that the plates of the static
inlet are supported with a very high amount of cooling air (923 & 844 Nm³/h*plate). This fact
indicates a possible method to prevent a Snowman formation by better cooling.
The time cycle of the blaster seems to be in normal operation. At Brevik there are 12 Blasters
in operation. They are connected into three groups, which operate every 10 minutes. The
break between each group takes 8 seconds and each blaster is switched with a 0.8 second
break. It was reported that any change of the blaster arrangements and their control were not
successful to prevent a snowman.
Figure 22: Static cooler inlet after shut down.
The plates and the refractory in the static inlet are in bad shape. Figure 22 gives an
impression of the static inlet directly after cleaning the grate plates. During cleaning there
was no residue of a potential Snowman on the plates, although a snowman appeared 3
times over the viewed period (06.03.06 - 11.03.06) as mentioned before.

49
Figure 23: One plate of the second row. Figure 24: Plates of the first row.
Figure 23 shows the surface integrity of one plate of the second row on the right side. This
plate is located in the area, where the hot clinker is falling directly from the kiln into the
cooler. Some spotty wear and a blink surface can be detected. There could be several
reasons for it. On the one hand this plate does not get enough cooling air from fan HE-1,
which is supplying that area with cooling air. In the area of the static inlet there are a lot of
gaps between the plates. For example Figure 24 shows a ca. 1 cm gap between two plates,
a ca. 2 cm gap between the steel plate and the refractory-wall, where the air can go through
with the result of a handicapped distribution. On the other hand the pipe of one blaster (arrow
in Figure 22) points on that plate. This may also lead to spotty wear by blasting into the
clinker bed. The fine clinker particularly has an abrasive effect, which gets a great impact
from this blaster. Those two effects blasting and bad aeration lead to the bad shape of this
plate.
Figure 25: Plates 2 & 3 of row five. Figure 26: Plates 4 & 5 of row five.

50
Furthermore some other plates also show a bad surface. The plates 2; 3; 4 and 5 in row 5
(counted from left) indicate spotty wear, too (Figure 25 & Figure 26). These are in the cooling
area of fan HE-1 and HE-2. One reason may be the gaps, which lead to a bad cooling air
distribution.
Figure 27: Overview of the plates of row five on the left side.
Figure 27 shows these plates from a different position. It can be seen that additional to the
gaps at the sides the plates form some other gaps caused by plastic deformation. These
gaps disturb the aeration of the static inlet.
The measuring of four grate plate temperatures at Brevik does nor give the desired result.
The thermo elements, welded under four plates of grate one, are in a bad shape. So the
measurement probably provides wrong values and is not useful.

51
Figure 28: Cooler wall of one side.
Figure 28 shows one side of the refractory wall of the cooler. The clinker level during
operation can only be estimated. The value lies around 600 mm. There is no clinker-level
measurement installed, which would give independent important information for operation.
4.11. Snowman type
Figure 29: Piece of a collected Snowman (09.03.06).

52
During the visit of the plant, Snowmen could be indicated almost every night until the
maintenance shutdown. There was a chance to save a piece of one Snowman, which was
formed in the night from 9.3.06 to 10.3.06 (Figure 29). This piece of Snowman is analysed
(see chapter “6. Snowman-Analyses”).
It was reported that this Snowman was growing on a small area in the middle of the static
inlet, at which point a “mushroom”-formed. This type of a Snowman is built by fritted dust
(see chapter “6. Snowman-Analyses”).
4.12. Visual checks
During the stay in Brevik there could be no distinctive features indicated. “Bubbling” at the
surface of the clinker bed in the cooler could not be seen. Even the content of glowing clinker
after the cooler outlet, which could be seen, seems to be normal.
4.13. Other noticeable features
The main noticeable problem, which can be checked, is the way of carrying out raw meal
analyses at the plant. Samples are only taken before the 25,000 tons raw meal silo, which
contains raw meal for about 100 hours. There are no regular analyses of the raw meal, which
is fed to the kiln. The goal of production is to produce a steady raw meal quality, which is
realized with a full stream analyser (Crossbeltanalyser), located in front of the raw mill. This
arrangement is not acceptable and will be discussed in chapter 7 Conclusions.
Another noticeable thing is the small kiln head with the result of high gas velocities at the
cooler inlet area (see also chapter 4.3 Kiln system modification).

53
5. The cement plant Burglengenfeld in Germany
5.1. Introduction
The cement plant Burglengenfeld in Germany has almost no problems with Snowman
formations. For this reason it was chosen for comparative data collection. There are two
almost identical kiln lines working side by side. Both kiln lines (WT2 & WT3) operate with
three stations rotary kilns with a Preheater tower, but without a calciner. The daily outputs
add up to 2000 tons each system. The main difference are the installed cooler systems. One
cooler is from IKN and the other one from Claudius Peters. It is reported that there have
been no Snowmen indicated for the last two years. If a Snowman did form then it occurred
on kiln line 2, where the Claudius Peters cooler is in operation.
5.2. Collected Data
The following data are collected:
Drawings about the two different cooler systems
Chemical analyses from 2005 about: - Raw meal fed to the kiln
- Clinker
- Bypass dust
Current Process data
Information about the CARDOX-procedure
5.3. The two different cooler systems in operation
The IKN cooler operates at kiln line WT3. This cooler type is equipped with a roll crusher at
the cooler end. The static inlet of an IKN cooler is called KIDS. At this static inlet two fans
support the grate plates with cooling air. Fan No.1 supports the first three rows and fan No.2
the last four rows of the KIDS.
The Claudius Peters cooler operates at kiln line WT2. This cooler type is equipped with a
hammer crusher. Furthermore the aeration of the static inlet, so called HE-Module, has a
different configuration. There the first fan supports the first four rows and the second one
only the last two rows.

54
In total both operating systems for aeration of the static inlet differ to the configuration in
Brevik, Norway. But the calculations of the specific cooling air quantities are conspicuous, as
can be seen in the next chapter “5.4 Specific cooling air calculations”.
5.4. Specific cooling air calculations
For the calculations of the specific cooling air quantities the collected process data are used.
Table 39 and Table 40 show these calculations, which can be found in the appendix. Both
cooler systems (IKN & CP) operate in total with very high specific cooling air quantities. The
Claudius Peters cooler indicates a value of 2.35 Nm³/kgcli and the IKN cooler a value of 2.33
Nm³/kgcli. It is obvious, that the cooling air quantity per cooling plate is much lower at the
IKN cooler (291 & 244 Nm³/plate) than the one at the CP cooler (973 & 754 Nm³/plate).
Comparable values of the CP cooler can be also found at the cooler in Brevik, which is
mentioned in chapter “4.10.3 Cooler”. Maybe these adjustments are preventive actions as a
result from history, where Snowman formations appeared. It is reported that these
adjustment will be changed in the future.
5.5. Chemical analyses
The following analyses are calculated from the laboratory data, which are annual averages
from 2005. Several values are 0.00. Such values are not measured continuously.
5.5.1. Raw meal
Table 20: Raw meal chemistry from kiln WT2 (2005).
CaO SiO2 Al2O3 Fe2O3 K2O SO3 MgO Cl F Na2O MnO
44.08 13.32 3.58 1.99 0.56 0.21 0.00 0.00 0.00 0.00 0.00 63.73
Table 21: Raw meal chemistry from kiln WT3 (2005).
44.18 13.37 3.55 1.97 0.54 0.21 0.00 0.00 0.00 0.00 0.00 63.82
Table 20 and Table 21 shows the measured control analyses of the cement plant in
Burglengenfeld. The most obvious fact is that in Burglengenfeld the raw meal indicates a
much lower content of sulfates. Unfortunately the sodium oxide is not measured.
Furthermore these analyses show that the potassium oxide content is higher than at Brevik.

55
5.5.2. Clinker
Table 22: Clinker chemistry of both lines (WT2 & WT3) from 2005.
CaO SiO2 Al2O3 Fe2O3 MgO K2O SO3 Na2O MnO
WT2 67.46 21.32 5.57 3.26 1.21 0.40 0.28 0.00 0.00
WT3 67.41 21.15 5.62 3.31 1.19 0.38 0.25 0.00 0.00
Table 22 shows the measured Clinker chemistry from 2005. Here the content of sulfates is
very low. This fact can be also seen at the calculated moduli in Table 25.
5.5.3. Bypass dust
Table 23: Bypass chemistry of both lines (2005).
WT2 0.00 0.00 0.00 0.00 19.20 8.72 0.00 9.09 0.00 0.47 0.00
WT3 0.00 0.00 0.00 0.00 23.91 12.53 0.00 9.99 0.00 0.61 0.00
In Table 23 it can be seen that the bypass dust is rich on sulfates and chlorides. In addition it
can be found that only a low content of sodium oxide is in the production process. The
extracted bypass dust indicates a high content of potassium oxide.
5.5.4. Clinker Mineralogy
Table 24: Clinker mineralogy from laboratory data and calculated
melting phase (2005).
C3S C2S C3A C4AF CaOfree Melting phase
WT2 66.50 10.98 9.25 9.91 1.00 23.61
WT3 67.78 9.53 9.29 10.06 0.83 23.87
Table 24 shows the values of the clinker mineralogy of Burglengenfeld. It can be seen that
the content of the melting phase is higher than the value at Brevik. Furthermore, the free lime
content is lower, but it can also be seen as a middle value. It is conspicuous that the free
lime value of kiln WT3 is lower than the one of kiln WT2.
5.5.5. Moduli
Table 25: Calculated Moduli of clinker (2005).
LSF SR AR DS
WT2 98.65 2.41 1.71 82.31
WT3 99.13 2.37 1.70 76.63

56
An obvious fact of the calculated moduli, which are mentioned in Table 25, is that the clinker
from both kiln lines indicates a degree of sulfatization lower than 100. The main reason is the
low content of sulfates in the raw meal and fuels.
5.6. Process data
At Burglengenfeld the employed control system allows only to save data for one week. It is
impossible to see the process data digitally during the time period where a Snowman
formation is indicated. But the current process data is used to calculate the specific cooling
air quantities.
5.7. CARDOX-procedure
Besides the calculated specific cooling air quantities the procedure to destroy build ups at
refractory walls, is very interesting. This method, called CARDOX, is often used at rotary kiln
and at cyclones of the preheater tower (Figure 30 & Figure 31). This system is installed at
the inlet area of the CP cooler at Burglengenfeld.
Figure 30: CARDOX system at rotary kiln
[13].
Figure 31: CARDOX system at cyclones of the
preheater tower [13].
The mode of action is simple. A pressure pipe with different screwable tops is filled up with
CO2-gas. A priming charge and a pressure gas generator are also placed in the pipe. By
igniting the pressure gas generator produced additional 50 litres CO2 gas. This expansion
takes places at 20 milliseconds and has a around 15 tonnes of shear force. This shear force
moves to the top and breaks the build ups.

57
6. Snowman-Analyses
6.1. Introduction
The following samples are collected during the visit of the cement plant Brevik:
One piece of Snowman (from 09.03.06)
LA Clinker from the cooler after shut down
Clinker dust from the tertiary air pipe
The purpose of the analyses is to have the chemistry (main components; sulfates; chlorides;
alkalis; CaOfree; MgOfree), the content of mineral phases, the content of liquid phase and the
porosity. The Snowman sample will be compared to the LA clinker samples and especially to
the laboratory data from Brevik of clinker chemistry (2002-2006).
The Clinker dust from the tertiary air pipe shows a great LOI value (over 5%). This fact
shows that the collected tertiary air pipe dust is very old and cannot be used for comparable
analyses.
6.2. Analyses
The following analyses were made:
XRF (to get the chemistry) + free lime, water soluble salts
XRD + Rietveld (to get the composition and content of mineral phases)
Reflected light microscopy
Hot stage microscope (liquid phase)
SEM
6.2.1. Preparation of the Snowman samples
The piece of the Snowman is cut in the middle. One piece is served and stored under
vacuum. A plate is cut from the other one and from this piece five strips are analysed by XRF
& XRD (Figure 32). The samples for the hot stage microscope are also from these strips.

58
Figure 32: Prepared piece of the found Snowman.
The samples for the reflected light microscope and SEM are located inside of the cut plate. It
is important that these samples consist of different layers.
The last sample is taken from the surface of the Snowman and contains the indicated big
white particles (marked by the arrow in Figure 29), which are analysed in the SEM.
6.2.2. XRF – free lime – water soluble salts
In Table 26 the XRF analyses of the Snowman and the collected clinker can be found. Those
analyses are made with a Bruker-AXS S4 Pionier X-ray system.
Table 26: XRF & free lime analyses of the Snowman sample (rows 1 - 5) and the clinker.
Row 1 Row 2 Row 3 Row 4 Row 5 average Clinker
CaO 66.2 66.0 66.2 66.2 66.3 66.2 64.97
SiO2 22.0 22.4 22.3 21.6 21.7 22.0 20.92
Al2O3 4.39 4.29 4.36 4.45 4.38 4.37 4.55
Fe2O3 3.33 3.28 3.36 3.45 3.35 3.35 3.37
MgO 2.59 2.57 2.59 2.60 2.58 2.59 2.64
SO3 0.807 0.909 0.855 0.946 0.986 0.901 2.01
K2O 0.265 0.288 0.271 0.320 0.340 0.297 0.768
Na2O 0.0406 0.0611 0.0435 0.0611 0.0434 0.0499 0.160
TiO2 0.337 0.332 0.339 0.348 0.341 0.339 0.365
P2O5 0.0614 0.0599 0.0594 0.0615 0.0620 0.0608 0.0920

59
MnO 0.0987 0.0972 0.0992 0.1020 0.0989 0.0992 0.0848
SrO 0.0693 0.0693 0.0700 0.0708 0.0703 0.0699 0.0730
Cl 0.00 0.00 0.00 0.00 0.00 0.00 0.13
CaOfree 0.17 0.10 0.14 0.18 0.14 0.15 5.26
It is an obvious fact that the Snowman has a lower content of sulfates and alkalis than the
collected clinker samples. This coherence can also be found by comparing with the LA-
clinker chemistry from the laboratory data of the cement plant in Brevik. Furthermore this
Snowman indicates a very low free lime value and holds no chlorides.
The free lime value of the collected clinker shows an extreme value of 5.26 %. So this clinker
is burnt weakly. This fact is also underlined by the XRD analyses, see chapter 6.2.3 XRD –
Rietveld and appendix.
The XRF calculated moduli and melting phase value are shown in Table 27. Those are
calculated from values of Table 26. For detailed values of each row see Table 42 in the
appendix.
Table 27: Calculated values (LSF, SR, AR, DS, S).
LSF SR AR DS Melting phase
Snowman 96.01 2.85 1.30 285.01 20.28
Clinker 98.24 2.64 1.35 233.86 22.40
The most interesting fact is the very low content of melting phase of the Snowman. This
value lays at 20.28 % and is a surprise because it is in contradiction to the proposed
hypothesis, which assumed a high content of melt.
6.2.3. XRD – Rietveld
For the XRD analyses a Siemens D 5000 is used. This system operates with an CuK -
radiation. Table 28 shows the average data of the XRD-analyses. These values will be
compared to the calculated values of phases, which can be found in Table 17 in chapter “4.7
Clinker mineralogy”. For detailed values of each row see Table 43 in the appendix.
Table 28: XRD - Snowman sample corresponding to the LA-clinker.
C2S C3S C3A C4AF Anhydrite Periclase
Snowman [%-by mass] 15.0 67.5 2.6 14.1 0.2 0.7
The Snowman has high contents of the C2S and C4AF phases. Beside this the content of the
aluminates phase has quite low value.
The XRD analyses of the clinker sample can be found at Table 44 in the appendix. It shows
very low contents of C3S and C3A phases. Furthermore the C2S phase is increased. This fact

60
also indicates a weak burning. This piece of a clinker was collected directly after the shut
down of the kiln. The rotary kiln was emptied for maintenance. An explanation for this weak
burnt clinker is that some residual material in the kiln is burnt with insufficient sintering
temperature. This configuration leads to a weak burnt clinker.
6.2.4. Water soluble salts
The water soluble salts, tested by the DEV-S4-procedure (a leaching test), of the Snowman,
lay at 1.39 %. The composition of these can be seen in Table 29. These values indicate that
the salts exist mainly of sodium and potassium sulfates. The rest are carbonates, which
explain the content of calcium. The compositions are analysed with an Atom Absorbing
Spectrometer (AAS).
Table 29: Water soluble salts.
Weight
[mg]
[%]
SO4 21 29.62
Na 10 14.10
K 16 22.57
Ca 6 8.46
Rest 17.9 25.25
Total 70.9 100.00
6.2.5. Reflected light microscopy
The reflected light microscopy from Axio Phot Zeiss, Germany is used to make the following
micrographs.
Figure 33: Clinker 2.5x polished surface. Figure 34: Snowman 2.5x polished surface.

61
Figure 33 and Figure 34 show the polished samples of one Snowman and one clinker. The
first visible feature is the porosity. The Snowman has a porosity of 46.28 % in contradiction to
the clinker with a porosity of 8.35 %. The calculations of the porosity are made with a particle
analysing program. The different layers of the Snowman (Figure 29), have different
porosities. The black layer has a higher porosity than the area between two of them. This can
be also seen at the SEM analyses (Figure 36).
Unfortunately the etching with hydrofluoric acid, which will make the different phases visual,
was not successful. Only parts of the samples are etch. But the SEM with the EDX-analyses
show the different clinker phases, which can be found in the appendix. It should be remarked
that the Snowman contains ordinary clinker phases, as analysed with XRD.
6.2.6. Hot stage microscopy
The hot stage microscope, which is used for the analyses, is a self-construction after DIN
51730 [14]. These analyses do not present the correlation, which can be found in literature
[15]. Because of the low content of liquid phase the temperature, which indicates the
softening point, is located at 1560 °C calculated from the following formula [15].
xTEB 1.171907
TEB: Temperature of the softening point
X: Melting phase content in %
The temperature limit of the used hot stage microscope is 1450 °C. Because of this only a
slumping down of the samples can be seen.
6.2.7. SEM
The scanning electron microscope (SEM) CamScan CS4 is used for the following
micrographs. Additionally for the chemical compositions an EDX-detector from Tracor
Northern 5502 is used, which can be found at the appendix.

62
Figure 35: Snowman 20x polished surface. Figure 36: Snowman 20x fractured surface.
The two figures show SEM micrographs of the Snowman. One is a polished surface (Figure
35) the other a fractured surface (Figure 36). At the polished surface small clinker particles
and a high porosity are visible. These particles are smaller than 800 µm. The micrograph of
the fractured surface shows that there are differences in porosities of the Snowman. This is
correlated to the darker layers (marked with arrows in Figure 36), as mentioned before.
Figure 37: Snowman 2000x fractured surface. Figure 38: Snowman 2000x fractured surface.
Figure 37 and Figure 38 show the fractured surface with a higher magnification. Two different
criteria are obvious. On the one hand sintering necks (Figure 37) and on the other hand a
triple point (Figure 38) can be seen. Both are marked with arrows. This criteria is typical for
sintering processes.
Furthermore the analyses with an EDX detector shows that the Snowman is built by clinker.
Additionally the white particles on the surface of the Snowman consists of sodium and
potassium sulfates (appendix). The origin is unknown. Maybe those white particles are the
results of decomposition.

63
7. Conclusions
7.1. Snowman
The Snowman analyses show that the investigated Snowman of Brevik is built by fritted
clinker dust and small clinker particles < 800 µm. The clinker phases have no content of
chlorides and a low content of sulfates. This fact is caused by passing the sintering zone. In
the sintering zone the chlorides vaporize totally. The duration of dwell was not long enough
to vaporize the sulfates completely, so a lower content of sulfates can be found in the
Snowman than in the clinker. The very low free lime content shows that the material of the
Snowman is burnt under higher temperatures as usual. This fact is also underlined by the
measured secondary air temperature from the process data. It is found that the secondary air
temperature has two peaks to higher temperatures, caused by too much fuel feeding.
Furthermore the clinker phases of the Snowman have higher contents of C2S and C4AF and
also a lower content of the C3A phase. This fact can be the result of fluctuations in the raw
meal composition or caused by the uneven energy input which also leads to
inhomogeneities. Possible fluctuations in the raw meal chemistry cannot be checked. As
mentioned the two raw meal checkpoints for the plant analyses are both before the 25,000
tons raw meal silo. There are no general analyses of the kiln feed which can help to prevent
those potential fluctuations. Besides this the most surprising fact is that the content of liquid
phase is lower than expected. Because of a very high temperature in the process and a very
high dust content, which can be seen at the kiln head, this type of Snowman is formed. This
shows that a Snowman formation can be formed although the melting phase content is very
low. A possible formation of this type of Snowman is described in the next paragraph.
7.2. Hypothesis of Snowman formation
During the time period when the analysed Snowman occurred, there seemed to be a coating
fall according to examination of the process data. Big lumps fall from the kiln into the cooler
inlet and stay at the plates of the static part. As mentioned before this leads to a platform
where a Snowman can grow. In Figure 39 the proposed clinker dust cycle is shown.

64
Figure 39: Potential clinker dust circulation at the cooler inlet.
Dust from the cooler streams into the kiln with the secondary air, marked by yellow arrows.
This air is rich on clinker dust and streams under the flame. With additional clinker dust from
the kiln and the jet air pressure differences under the flame, the clinker dust air is deflected,
which is marked by the blue arrows. Furthermore this deflection is probably intensified by the
broken spacer of the burner pipe. The air under the flame streams back to the cooler, passes
the surface of the static inlet and streams back into the kiln with the secondary air. On the
free area as a result of coating fall, the clinker dust can deposit on this lump especially during
the deflection at the cooler inlet. With the indicated high temperature combined with the very
bad aeration in the area of the static inlet this Snowman is formed. Additionally, this type of
Snowman formation is also underlined by the fact that high gas velocities (8 m/s) exist at the
static inlet. These high gas velocities are caused by the small kiln head. Moreover the high
dust content in the secondary air comes from the high sulfate content. The calculation of the
moduli shows a degree of sulfatization over 100, which means a sulfur excess. Free sulfates
makes the clinker granules porous and brittle. These dust particles are easily carried away
from the clinker surface with the high gas velocity.
In addition those glowing dust clouds are well known from nature and can be compared to
the phenomenon at the cooler inlet (see the next paragraph “7.3 Comparable natural
phenomenon”).

65
7.3. Comparable natural phenomenon
In nature glowing dust clouds are called Ignimbrite. Geologists also call them pyroclastic flow
deposits. They are formed during volcanic eruptions. Generally, three different ways of
formations can be found in nature (Figure 40).
Figure 40: Some ways the pyroclastic flows can
originate [16].
The first one is a vertical eruption and column collapse, the second one a low pressure
boiling over and the third one a directed blast or dome collapse. All of them produce a lava
stream combined with glowing dust clouds. The glowing dust clouds consist of particles with
a size of < 2 mm. Those streams have high velocities from 14 up to 230 km/h under
temperatures around 500 - 650 °C and up to 850 °C. The dust content of those clouds varies
around 1 g/cm³. Figure 41 shows such an ignimbrite in detail.

66
Figure 41: Diagram showing development of block and ash flow [16].
It can be seen that the structure of a Ignimbrite is caused by dense segregation. The
particles with a higher density and a bigger size can be found after cooling down at the
bottom layers. In contrast to the particles with a lower density, they deposit more at the top of
the rock. This segregation leads to the typical structure of an Ignimbrite. Furthermore under
high temperatures a plastic deformation affects the structure. Some dust particles are welded
together which can be seen in Figure 42. Lines separate the different layers in this Ignimbrite
from Gran Canaria.
Figure 42: Strongly welded pantelleritic ignimbrite
from Gran Canaria [16].
The affinity to the investigated Snowman is obvious (see Figure 42).

67
7.4. Emphasis of the important items of the Checklist
At Brevik several influences are detected. The fuel feeding, especially of animal meal,
indicates some problems which leads to an uneven energy input. In addition the burner was
in bad shape because of a broken spacer and closed air jet pipes. The process data
indicates a periodical over heating of the kiln. Furthermore the fans of the static cooler inlet
operate almost on maximum air volume to prevent a potential Snowman formation, but with
an extremely disturbed distribution of cooling air this prevention has no effect. Some plates of
the static inlet are overheated and show plastic deformation. Possibly the high gas velocity
and the high dust content in the area of the kiln hood are the basic conditions of the
Snowman formation. The high content of sulfates from the raw meal leads to porous clinker.
Combined with the overheating and high gas velocity the recuperation air becomes rich on
dust. Finally, several influences make a Snowman formation possible. A suggested
emphasis of the important items of the developed checklist are mentioned below.
Figure 43: Emphasis of the important items of the checklist.

68
8. Outlook
8.1. In general
This thesis is a step to take a more systematic look at Snowman formations. It is known that
several Snowman types can be formed. This thesis deals with a mushroom type of a
Snowman. Because of high temperatures in the cooler inlet area it is very difficult to take
direct analyses at the point. Furthermore the measured temperatures and other process data
can only indicate tendencies. These are only indirect ones which give hints of a potential
Snowman formation scheme. Maybe in the future the measurement of the secondary air
temperature for example can be more exactly determined.
Generally, several items can be done to prevent Snowman formations. Besides checking the
chemistry and mineralogy of the produced clinker and its raw material, the aeration at the
static cooler inlet has to be investigated and improved. Furthermore the kiln shall be
operated at lower temperatures or the length of the pre-cooling zone can be increased to get
a lower clinker temperature at the kiln outlet. Additionally, an independent clinker-level
measurement can help to improve the situation of the cooler.
Some important indications can be also seen at the cement plant in Brevik, Norway. To solve
the problem of Snowman formation in Brevik, improvements have to be carried out.
The tasks to prevent Snowman formation in Brevik are presented in the next chapter.
8.2. Tasks of Brevik
The following tasks should be done at the cement plant in Brevik:
1. Chemical analysis of the kiln feed
2. Checking the cooler fans HE-1 & HE-2
3. Improving the air distribution
4. Improving the refractory arrangement at the cooler inlet
5. Improving the secondary fuels measuring and control
6. Saving always pieces of Snowmen
7. Increasing the length of the pre-cooling zone
8. Installing a clinker-level measurement
9. Changeover to the CARDOX system

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