Problems and remedies of cement kiln bricks

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 02, February 2019, pp. 1010-1019, Article ID: IJCIET_10_02_098
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=02
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
THE PROBLEMS OF ROTARY KILN OF
CEMENT AND THEIR REMEDIES
Prof. Dr. Mohammed Mosleh Salman and Asmaa Mahdi Ali
Civil Engineering Department, College of Engineering,
University of Mustansiriayah, Baghdad, Iraq
ABSTRACT
This research aims to study the problems of the rotary kiln of al Kufa cement plant.
The heating process of the furnace starts by burning a certain amount of wood near the
fuel outlet inside the rotary kiln to provide the initial combustion process of the heating
oil at (80-100°C). Then the front fan of the furnace is operated while the heating
process is continuing for 24 hours. The most important problems that appear during
the use of the rotary kiln were: mechanical wear, thermal wear and chemical wear.
These problems have been diagnosed and taking the necessary treatments to reduce
them, whereas the operational limits must e observed during the operation. When
mechanical, thermal or chemical problems occur they will result high torque furnace
that causes the risk of the main vehicles of the rotary kiln.
Keywords: portland cement, Rotary kiln, magnesia bricks, Kiln shell.
Cite this Article: Prof. Dr. Mohammed Mosleh Salman and Asmaa Mahdi Ali, the
Problems of Rotary Kiln of Cement and Their Remedies, International Journal of Civil
Engineering and Technology, 10(02), 2019, pp. 1010–1019
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=02
1. INTRODUCTION
Portland cement is essentially calcium silicate cement, which is produced by firing to partial
fusion, at a temperature of approximately 1500°C, a well-homogenized and finely ground
mixture of limestone or chalk (calcium carbonate) and an appropriate quantity of clay or shale.
The composition is commonly fine-tuned by the addition of sand and/or iron oxide [1].
The cement manufacturing process basically includes quarry, raw meal preparation,
preheating of raw meal, kiln, clinker cooling, grinding, storage, and dispatch, which is
illustrated in Figure 1. The chemical reaction within the cement manufacturing process starts
with the decomposition of calcium carbonate (CaCO3) at about 900°C to leave calcium oxide
(CaO) and liberatesCO2; this process is known as calcination. Then the clinkerization occurs
inside the kiln at high temperature (typically 1400 -1500°C) [2].

Inside the kiln,calcium oxide reacts with silica, alumina, and ferrous oxide to form the
silicates (C3S, C2S), aluminates (C3A), and ferrites (C4AF) respectively, which are the main
constituent of the clinker. This clinker is then ground in a ball mill together with gypsum and
other additives to produce cement. Fuels are required to generate thermal energy during the
process of calcination in the preheater-precalciner tower and during the clinkerization process
in the kiln [3-4].
Figure 1 Cement Manufacturing Process
Magnesia bricks must be stored in ventilated and dry rooms with protection against weather
conditions as they are sensitive to hydration and can be damaged if stored improperly. The
lining failed due to the hydration of magnesia caused by an unexpected source of water.
Hydration of magnesia (MgO) in refractory material occurs when the material comes into
contact with humid air, water, or steam. This exposure can occur during storage, construction,
or operation. The optimal conditions for this hydration occur when water is present at 40°C to
120°C. This process is characterized by the transformation of magnesia into magnesia
hydroxide according to this reaction [5-6]:
MgO + H2O Mg (OH)2 (1)
The rate of the reaction depends on temperature, the magnesia content of the brick, and
pressure (if water is present in the vapor phase). The hydration rate with liquid water is slow,
but as soon as the water penetrates as steam the hydration becomes faster. Hydration of
magnesia to magnesium hydroxide (consist of powder) results in an increase in volume of the
bricks due to density change up to 115% [7]. Figure 2 shows how extensive hydration leads to
crack formation in the bricks and can subsequently lead to disintegration of the whole brick.

The Problems of Rotary Kiln of Cement and Their Remedies
Figure 2 Hydrated Magnesite Bricks After One Month Of Service.
Magnesia hydroxide decomposes thermally at approximately 330°C, and the last traces of
water are expelled at higher temperatures to yield MgO as shownin the reaction [5]:
Mg (OH)2 MgO + H2O (2)
Although the reaction is reversible, the damage to the bricks in the form of cracks has
already taken place. Reversing this reaction will therefore result in more porous bricks, which
will lead to an increased and deeper molten material penetration.The most important steps need
to be considered to avoid or reduce the possibility of magnesia bricks hydration are [8]:
1) Magnesia bricks must be transported in a container to protect the material against
moisture.
2) Magnesia bricks should be stored inside storage rooms where it is dry, free of frost,
ventilated, and with a temperature between 10°C and 30°C.
3) Bricks may not be stored for more than four weeks prior to installation and preheating.
4) Lining should be protected against moisture during installation and preheating.
Corrosion of the rotary kiln shell behind the refractory lining has become an increasingly
serious problem for cement industry as it acts silently and reduces the shell thickness to below
critical structural and mechanical limits of stability of kiln shell. Understanding the factors
influencing the kiln shell corrosion and its formation mechanism is the best way to inhibit it.
Corrosion of kiln shell behind the refractory is influenced by a number of factors such as
composition of the metallic shell and its environment, temperature of the shell, cleanliness or
roughness of the shell surface, its contact with other materials and severe process conditions.
The main reason of shell corrosion can be attributed to alternate oxidation at high temperature
and acidic reaction at low temperatures when the kiln is stopped for repairs [9, 10].
The corrosion phenomenon takes place mainly due to presence of oxides, chlorides and
sulphide at high temperature. The reactions inside the kiln are different from reactions on the
kiln shell surface since both the temperature and atmosphere are different. One of the most
important reactions in the lining is the oxygen consumption where SO2 consumes oxygen and
condenses as SO3 :
2SO2 (g) + O2 = 2SO3 (↓) (3)

The SO3 formed condenses as calcium or magnesium salts. The result can be that an
oxidizing environment inside the kiln turns into a reducing environmentat the kiln shell [11].
2. EXPERIMENTAL WORK:
2.1. Factors Affecting the Performance of Brick in Rotary Kiln:
This research aims to study the problems of Al- Kufa Cement Plant in Iraq, where field visits
were implemented during 2016 to Al-Kufa Cement plant in Iraq to view the rotary kiln of
cement manufacturing. One of the problems identified in Cement Rotary Kiln is bricks that
must be used in buildings. Where there are two purposes for the use of bricks:
1. For the purpose of protecting the kiln structure from high heat.
2. Reduce the amount of heat lost through the furnace body.
As the areas of the kiln are divided according to the temperature of the furnace and areas
of chemical reactions.
One of the problems identified in cement rotary kiln is bricks that must be used in buildings
according to a particular specification. The most impottant problems that appear during the use
of the rotary kiln were
2.1.1. Mechanical Wear
1. Convex spalling
a. Phenomena: Convex spalling in longitudinal direction of bricks, so called cobble-
stones.
b. Reasons: 1- Insufficient clearance in the expansion joints. 2-No installation of
cardboard spacers
3- Frequent stoppages of operation after cardboard spacers burnt off.
c. Symptoms: Axial pressure produced by dilation causing spalling.
2. Concentric Stress Cracks
a. Phenomena: Concentric stress cracks in 3-5cm depth around the circumference.
b.Reasons: Steel plates oxidize and react with the bricks forming a monolithic horizon of
magnesioferrite with volume increase.
c. Symptoms: Cracks in reaction zone of steel plate-lined bricks and key bricks.
3. Spiralling:
a. Phenomena: Spiralling , tilting and edging. Cold face wear from rubbing against the
kiln shell
b.Reasons: 1- Loose installation 2- Increased kiln shell ovality 3-Expansion and
contraction due to frequent kiln stoppages. 4- Changing coating formation 5-Deformations in
the kiln shell
c.Symptoms: Lining displacements due to relative movements.
4. Ovality:
a. Phenomena: Deep outbreaks of single bricks.Spallings here and there in between
completely perfect brick sections.

b. Reasons: 1- Used tyre shoes increase the clearance leading to excessive ovality.
2-Limit for Ω-value maximum 1/10 of kiln diameter, e.g. 0.5% for 5m diameter kiln.
c. Symptoms: Kiln shell ovality in tyre area (squeeze and release) during each rotation
shear stressing the brick heads.
5. Formation of Grooves
a. Phenomena: Parallel grooves 2-4 bricks wide of deep spalling appearing along the kiln
axis.
b. Reasons: 1- Keyline with excessive tightness. 2-Damage to the key bricks by jack
hammer.
3- More than one metal shim per joint.
c. Symptoms: Orientated premature wear channels within sound lining.
6. Pinch at Retaining Rings:
a. Phenomena: Collapse of bricks rings against retaining ring and outlet segment from
pinch spalling.
b. Reasons: 1-Thrust and oscillations generate shear cracks and grinding
2- Flexing kiln outlet or ovality accelerate the damage.
c. Symptoms: Horizontal cuts and cracks of bricks at the upper edge of retaining rings and
Trans passing nose ring segment.
2.1.2. Thermal Wear:
1. Concave Melting Pits:
a. Phenomena: Concave wear, so-called duck nesting (looking like eutectic melting of
alumina bricks).
b. Reasons: 1-Coating-free operation of standard grade bricks with moderate
refractoriness.
2- Flame impingement on the lining.
c. Symptoms: Overheating of bricks weakens the brick structure at hot face.
2. Lava-Like Coating:
a. Phenomena: Lava-like coating solidly connected with the bricks and cracks behind the
densified surface. Falling coating takes off densified brick heads.
b. Reasons: Overheating of clinker with formation of increased liquid clinker phase
infiltrating the hot face, e.g. peaks of ferritic phase during production of SRC.
c.Symptoms: Overheating of clinker with densification at the hot face of bricks and change
of mechanical properties.
3. Excessive Thermal Load:
a. Phenomena: Change from uniform brick matrix with round grain to periclase needles
of a brittle structure.
b. Reasons: 1- Overheating above 1700°C without liquid phase.
2- Thermotacticrecrystallisation.

c. Symptoms: Structural fatigue of high quality bricks at coating free operation due to high
temperature.
4. Thermal Shock:
a. Phenomena: Spilt –like spallings in 2-3cm layers.
b. Reasons: 1- Quick heating up. 2- Sudden cooling down. 3-Coating losses.
c. Symptoms: Sudden changes in temperature produce thermal tensions causing horizontal
cracks.
2.1.3. Chemical Wear:
1. Infiltration Of Alkali Salts:
a. Phenomena: A cut through the brick shows infilitration horizons and the inner kiln shell
is attacked by corrosion.
b. Reasons: Deposits of mainly K2SO4 in lower transition zone and burning zone, along
with KCI in the upper transition zone.
c. Symptoms: Gaseous alkali salt compounds migrate into the bricks, filling the brick
pores, condensating and solidifying them.
2. Corrosion of Chrome Ore:
a. Phenomena: Yellow-green discoloration and brittle surface with crack
b. Reasons: 1-With free (K, Na)2O formation of (K, Na)2CrO4
2- Loosening of the brick structure by dissolving of the chrome ore
c. Symptoms: With excessive alkalis the chrome ore attacked and corroded and toxic
hexavalent alkali chromates are formed.
3. Redox Bursting:
a. Phenomena: Bleaching of dark brown magnesia-chromite bricks to cappuccino colour
and bursting of the structure. Carbon deposits in the joints and on the kiln shell.
b. Reasons: Temporarily reducing atmosphere due to:
1-Insufficient combustion. 2-Use of fuels rich in ashes 3-Course grain coal or petcoke
4- Use of substitute fuels
c. Symptoms: Repeated change from oxidizing to reducing atmosphere, so-called Redox
causes voloume change between trivalent (red) and bivalent (green) iron.
4. Hydration Cracks:
a. Phenomena: Spider web cracks from the surface into the bricks and in extreme cases,
disintegration.
b. Reasons: MgO reacts with water to Brucite Mg (OH)2 under volume increase.
c. Symptoms: CaO and MgO are sensitive to humidity. Magnetite bricks are by far less
sensitive than dolomite bricks but should be protected against seawater, rain and humid air.
3. RESULTS AND DISCUSSION
If such types of damage below are recognized, the kiln must be shut down. Kiln problems have
to be avoided by taking appropriate measures of improvement:

3.1. Mechanical Wear
a. Convex Spalling:
Improvements:
1- Insertion of cardboard spacers according to installation drawings.
2- Use of bricks with preattached cardboard.
b. Concentric Stress Cracks:
Improvements:
Lining without steel plates:
Mortar lining 2-Clench lining of PERILEX, ALMAG and REFRAMAG
c. Spiralling:
Improvements:
1- Uniform kiln operation 2-Repair of bulged kiln shell
3- Ovality control 4-Proper and tight installation with staggered joints
d. Ovality:
Improvements:
1-Permanent monitoring of migration. 2- REFFRA shell test control
3- Insertion of new spacers. 4-Beast flexible lining with PERILEX 80 mortar
e. Formation of Grooves:
Improvements:
1-Correct insertion of key bricks 2-Insert liners uniformly in the whole joint.
3- Only one steel plate per joint. 4- Use REFRA shim driver with jack hammer.
f. Pinch At Retaining Rings:
Improvements:
1- Stiff kiln shell. 2-No nose-shaped bricks.
3- Use retaining rings 50x180mm with full brick on top KRONEX 87, ALMAG 85.
3.2. Thermal Wear:
a. Concave Melting Pits:
Improvements:
1-Adjustment of burner. 2-Limits for silica modulus SM< 2.6
3- Bricks with coating ability PERILE or FERROMAG.
4- Premium grade ALMAG for coating –free operation.
b. Lava-Like Coating:
Improvements:
1-Avoid burning conditions with increased liquid phase LPh <26%

2-Uniform operation conditions
3-Best possible homogeneity
4-Use refractories with high flexibility PERILEX or high thermo-chemical resistance
MAGNUM, ALMAGSLC
c. Excessive Thermal Load
Improvements:
1-Uniform and continuous operation conditions
2. Use of magnesia-zirconium bricks with balanced elastification: MAGNUM or
ALMAGSLC with large crystals and fused spinel.
d. Thermal shock
Improvements:
1-Rational heating-up with 50°C/h 2-Slowly cooling down
3-Uniform operating conditions 4-Stable coating
5-Use optimally elastified brick with thermal shock resistance of minimum 80.
3.3. Chemical Wear:
a. Infiltration of Alkali Salts:
Improvements:
1-Reduce alkali salt content 2-Balance alkali/ sulphate ratio in a range of 0.8-1.2
3-Use bricks with improved flexibility REFRAMAG 85, ALMAG A1
4-Use REFRACOAT for protection of kiln shell.
b. Corrosion of Chrome Ore:
Improvements:
1-Reduce alkali or balance alkali/ sulphate ratio
2-Use chrome ore-free bricks: FERROMAG 90 or REFRAMAG 85.
c. Redox Bursting:
Improvements:
1-Minimum of 1.5% of O2 for complete combustion.
2-coal fineness (maximum reside 50% on 90 micron mesh of volatile content)
3-Use chrome ore-free bricks with low iron content: REFRMAG 85 or ALMAG.
d. Hydration Cracks:
Improvements:
1-Dry storage under roof
2-Recommended storage time 6 months in subtropical climate. 3-Ventilated storage of wet
package 4- Maximum ignition loss of humid bricks 0.3% 5- Use REFRACK seaworthy packing
double pre-shrunk plastic covering.

4. CONCLUSIONS
Based on the above findings and discussion, the following conclusions can be drawn:
1. The main variables that affect the performance of bricks are:
a. The nature of the primary materials involved in the process of production.
b. Type and specifications of cement to be produced.
2. Corrosive wear as a result of chemical reaction of charge reagents with refractory
materials during operation.
3. Stable kiln operation such as uniform feed rate, chemical composition and fineness of
raw meal and a well-designed combustion system.
4. Lower kiln system velocities and dust loads
5. Lower volatile cycles attained by:
a. Choice of raw materials
b. Minimize < 20 µ material in raw meal.
6. The coating can protect the refractories and prolong its service life. Therefore, it is
essential for the refractories used in the burning zone to form coating. An acceptable coating
thickness from the viewpoint of solid flow along the kiln and refractory protection.
7. The flame should not be let to flatten in the lining of the rotary kiln even for a short
peried of time, due to its destructive effect on the lining.
8. No procedures taken on the flame unless the burning zone is stable; neither hot nor should
cold that means the production of clinker not be brittle due to a high temperature or a yellow
clinker at a low temperature.
REFERENCES
[1] Soumaya Ibrahimi and Mohamed Bagané “The Effect Of Raw Material’s Fineness And
Lime Saturation Factor On Clinker’s Grindability And Energy Effeciency In The Gabes
Cement Industry, Journal of Multidisciplinary Engineering Science and , Technology
(JMEST) ISSN: 3159-0040 Vol. 2, No. 11, 2015 , PP.25-30.
[2] Jacek Szczerba, “Chemical corrosion of basic refractories by cement kiln materials”
Journal of Ceramics International Vol.18, 2010 pp1877–1885.
[3] Azad Rahman, M.G. Rasul, and S. Sharma" Cement Kiln Process Modeling to Achieve
Energy Efficiency by Utilizing Agricultural Biomass as Alternative Fuels"
[4] School of Engineering and Technology, Australia, chapter 9, 2016, pp.197-225.
[5] Fasil Alemayehu and Omprakash Sahu “Minimization of variation in clinker
quality”Journal of Advances in Materials. Vol. 2, No. 2, 2013, pp. 23-28.
[6] TRL Krosaki , "Development Of Magnesia-Spinel Brick For Transition Zone In Cement"
INDIA,Proceedings of the Unified International Technical Conference on Refractories
(UNITECR 2013), pp.1-7.
[7] Guoxiang Yin"High Performance Iron-Rich Magnesia-Spinel Composite For Burning
Zone Of Cement Rotary Kiln" School of materials Science and Engineering, University of
Science and Technology Beijing,China, Advanced Materials Research , ISSN: 1662-8985,
Vols. 476, 2012,, pp 1915-1919.
[8] Makoto Ohno, Hitoshi Toda, Kozo Tokunaga and Yoshio Mizuno, “Development Of
Magnesia-Spinel Brick For Transition Zone In Cement Rotary Kilns Under The Vastly
Increasing Use Of Waste” Japan, the Unified International Technical Conference on
Refractories, American Ceramic Society,2014 , PP.1-3.

[9] B.Gerald, M.T.Homas,"Magnesia-BricksAn InnovativeBurnt Basic Refractory",
inProceedingsofUNITECR’99, Osaka, Japan, 2009, pp. 201–203.
[10] Recio Dominguez and J. Gómez-Millán “Build-up formation and corrosion of monolithic
refractories in cement kiln” Journal of the European Ceramic Society 27 February 2010,
pp.1879–1885.
[11] Sara Serena, M. Antonia Sainz and Angel Caballero, “Corrosion Behavior Of
MgO/CaZrO3 Refractory Matrix By Clinker” Spain, Journal of the European Ceramic
Society, Vol 24, 2004, pp. 2399–2406.
[12] Fasil Alemayehu and Omprakash Sahu “Minimization of variation in clinker
quality”Journal of Advances in Materials. Vol. 2, No. 2, 2013, pp. 23-28.

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