REFRATECHNIK

Wear Phenomena of Refractory

Linings in Cement Rotary Kilns

G&W Training Program:

Refractories in the Portland Cement Industry
Cairo, June 9-14, 2007

Lars Vieten, REFRATECHNIK Cement GmbH

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Lifetime and consumption of basic refractories

Current situation (global average):

Average consumption of burning zone refractories = 600g/mt

Average lifetime of burning zone refractories = 8 - 10 months

Target:

Average consumption to be less than 500g/mt

Average lifetime to be at least 12 months (or even more)
User‘s responsibility or influence REFRATECHNIK

Refractory thermal
installation load chemical
load

Storing Lifetime Service

conditions
of conditions
Refractories
mechanical
load
Selection of
Refractories

Quality
Installation Product
of raw
drawings quality
materials Producer‘s responsibility
or influence
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Stresses on the Refractory Lining in Rotary Cement Kilns
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Service conditions

Thermal

by the flame:
- temperature influence
- overheating

by temperature changes:
- loss of coating
- interruptions of production
- fuel inhomogenities
- variation in dosing
- changes in burner control
- secondary or incomplete combustion
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Service conditions

Chemical

by kiln feed and fuel:

- use of high sulfur, high chlorine fuel
- use of high ash coal
- frequent change of fuel
- use of alternativ fuels and raw materials (AFR)
- disturbance of the SO3 / (K2O+Na2O) equil.
- variations in raw meal
- grain size of SiO2

by the kiln atmosphere:

- change between reducing and oxidizing conditions
- changes of pO2
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Service conditions

Mechanical

by the kiln shell:

- deformation of shell
- ovality
- axial distortion

by feed and coating fragments:

- erosion
- impact ( falling coating, clinker balls )
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Mechanical wear

• Thermal expansion
• Concentric stress cracks
• Formation of grooves
• Displacements
• Ovality in tire sections
• Retaining rings
Thermal expansion REFRATECHNIK

Phenomena:
- Axial pressure produced by dilatation
exeeding brick resistance causing spalling

Characteristic symptoms:
- Convex spallings in longitudinal direction of brick

Reasons:
- Insufficient clearance in the expansion joints.
- No installation of cardboard spacers
- Frequent stoppages of operation after cardboard
spacers burn off

Correcting measures:
- Insertion of cardboard spacers according to installation
- Use of bricks with preattached cardboard spacers
Thermal expansion REFRATECHNIK
Concentric stress cracks REFRATECHNIK

Phenomena:
- Cracks in reaction zone of
steel plate lined bricks

Characteristic symptoms:
- Concentric stress cracks in 3 - 5 cm
depth around the circumference

Reasons:
- Steel plates oxidize and react with the bricks forming a
monolithic horizon of Magnesioferrite with volume increase

Correcting measures:
- Lining without steel plates
- Mortar lining
- Clench lining of suitable bricks
Concentric stress cracks REFRATECHNIK
Formation of grooves REFRATECHNIK

Phenomena:
- Premature wear from
structural defects in horizontal layers

Characteristic symptoms:
- Parallel grooves 2-4 bricks wide along the kiln axis

Reasons:
- Exessive tightness along keyline
- Too much keying shims in one joint
- Damage of keybricks by closing (jack hammer)

Correcting measures:
- Correct insertion of key bricks
- One steel shim per joint only
Formation of grooves REFRATECHNIK
Displacements REFRATECHNIK

Phenomena:
- Lining displacements due to
extreme relative movements
Characteristic symptoms:
- Spiralling, tilting and edging
Cold face wear due to rubbing against the kiln shell
Reasons:
- Loose installation
- Increased kiln shell ovality – deformation of the shell
- Expansion and contractions due to frequent kiln stoppages
- Changing coating formation
Correcting measures:
- Uniform kiln operation conditions
- Repair of bulged kiln shell
- Tight installation
Displacements REFRATECHNIK
Displacements REFRATECHNIK
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REFRA-Rig

Assure a proper installation of the

refractory lining !
Ovality REFRATECHNIK

Phenomena:
- Ovality in tire area: squeeze and release bricks
during each rotation – shear stressing the brick heads

Characteristic symptoms:
- Deep spalling of bricks in completely perfect brick areas

Reasons:
- Overused tireshoes lead to exessive ovality
- Limit for ovality: 1/10 of diameter

Correcting measures:
- Yearly shelltest and permanent control of the creep
- Shimming of tireshoes
- Mortar lining
- High elastified bricks like ALMAG® A1
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Ovality
Retaining rings REFRATECHNIK

Phenomena:
- Thrust exerted against the retaining
ring can cause collapse of bricks
Characteristic symptoms:
- Diagonal or horizontal cracks at
the upper edge of retainer and
transpassing nosering
Reasons:
- Thrust and bending generate
shear cracks and grinding
- Flexing kiln outlet or ovality increase
the forces
Correcting measures:
- Retaining ring of min. 50 mm with
full brick on top
- Avoid use of cut/special-shaped bricks
Retaining rings REFRATECHNIK
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Thermal wear

• Concave melting pits

• Infiltration of liquid phase
• Excessive thermal load
• Thermal shocks
Thermal wear REFRATECHNIK
Concave melting pits REFRATECHNIK

Phenomena:
- Overheating weakening the brickstructure at hot face

Characteristic symptoms:
- Concave wear, duck nesting

Reasons:
- Coating free operation of bricks with moderate refractoriness
- Flame impingement

Correcting measures:
- Adjustment of burner
- Limits for clincer moduli: SM < 2.5, Coating value: 30 - 36
- Installation of MAGNUM® 95 or ALMAG® AF
Concave melting pits REFRATECHNIK
Concave melting pits REFRATECHNIK
Infiltration of liquid phase REFRATECHNIK
Phenomena:
- Overheating of clincer with infiltration at the hot face
- Densification and change of mechanical properties

Characteristic symptoms:
- Lava-like coating, solidly connected with the bricks
- Falling coating takes off densified brick heads

Reasons:
- Overheating of clinker with formation of increased liquid clinker
phase infiltrating the brick‘s hot face

Correcting measures:
- Avoid burning conditions increased liquid phase
- Uniform operation conditions
- Best possible homogenity
- Use refractories with high thermo-chemical resistance
Infiltration of liquid phase REFRATECHNIK
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Liquid Phase Attack

35
Liquid phase content

Alumina modulus = 2.2

at 1450°C in wt %

30
1 Lime Standard = 96

25

20

15
1.5 2 2.5 3 3.5 4
Silica modulus
Infiltration of liquid phase REFRATECHNIK

Clinker

Corrosion
hole
Infiltration of liquid phase REFRATECHNIK
Quality of the raw materials REFRATECHNIK
Quality of the raw materials REFRATECHNIK
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Exessive thermal load

Phenomena:
- Structural fatigue and coating-free operation
due to high temperature
- Porous and brittle hot face

Characteristic symptoms:
- Change from uniform brick matrix with round
grain to periclas needles of brittle structure

Reasons:
- Overheating above 1700 °C with coating
- Thermotactic recristallisation

Correcting measures:
- Uniform and continous operation of the kiln
- Use of purest bricks with balanced eleastification
Thermal shock REFRATECHNIK

Phenomena:
- Sudden changes in temperature produce thermal
tensions contributing to a breakage of bricks
when exceeding the structural flexibility

Characteristic symptoms:
- Split-like spallings

Reasons:
- Quick heating up
- Sudden cooling down
- Coating losses
Correcting measures:
- Stable coating
- Reasonable heating up with 50°C/h
- Slowly cooling down of kiln
- Uniform operation conditions
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Chemical wear

• Infiltration of alkali salts

• Corrosion of chrome ore
• Redox effects
• Hydration cracks
Infiltration of alkali salts REFRATECHNIK
Phenomena:
- Gaseous alkali salt compounds migrate into the bricks,
filling the pores, condensating and solidifying them

Characteristic symptoms:
- Horizontal infiltration layers
- Corrosion of kiln shell

Reasons:
- Deposits of mainly K2SO4 in lower transition zone and
burning zone, along with KCl in the upper transition zone

Correcting measures:
- Reduction of alkali salt content
- Protection of kiln shell with REFRACOAT
- Use bricks with best flexibility
Infiltration of alkali salts REFRATECHNIK
Unused magnesia spinel brick REFRATECHNIK
Magnesia spinel brick – slightly infiltrated REFRATECHNIK
Magnesia spinel brick – heavily infiltrated REFRATECHNIK
Corrosion of chrome ore REFRATECHNIK

Phenomena:
- Easily detectable deposits of alkali chromates

Characteristic symptoms:
- Densification of brick in the middle zone, reduced structural flexibility
- Alkali chromates are highly soluble and toxic !

Reasons:
- High Alkali in the kiln atmosphere:
K2O > SO3 : alkali chromate volatilises at higher temperatures in
burning zone

Correcting measures:
- Use of chromefree qualities
- Installation of bypass system to reduce alkalies
Redox effects REFRATECHNIK

Phenomena:
- Clearly visible bleaching of brick zone close to hot face

Characteristic symptoms:
- Decrease of structural strength due to repeated volume effects
- Spalling or increased erosion

Reasons:
- Lack of oxygen, reducing atmosphere
- Inhomogenous coal composition
- Secondary combustion if coarse high volatile coal is used

Correcting measures:
- Stable coating means best protection
- Flame control and fine grinding of coal to be improved
- Chrome free bricks with iron oxide content less than 1%
Redox effects REFRATECHNIK
Hydration cracks REFRATECHNIK

Phenomena:
- Cracks after long period of storage

Characteristic symptoms:
- Deep cracks all over the brick
- Significant decrease in strength

Reasons:
- Reaction of MgO with H2O to
Mg(OH)2 under significant volume
increase
- Improper storage conditions
- Damage of packing during transport

Correcting measures:
- „First in first out“ management
- Improve storage facilities
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Recommendations

Optimize uniformity of kiln feed

Try to obtain and maintain stable coating

Control ovality and make kiln alignments

Balance thermal load with suitable burner systems

Avoid frequent kiln stoppages

Train your permanent installation team

Optimize your storage system, avoid use of special shapes

For heating up and cooling down follow supplier‘s recommendations

Select carefully the right brick quality ...

... from REFRATECHNIK

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Cement moduli

cement modulus typical values statement

Lime Standard 85 – 95 (Portland cement) content of CaO, which can technically be

(KSt III) 95 – 100 (high-grade cement) bond to SiO2, AL2O3 and Fe2O3

Hydraulic modulus 1.7 – 2.3 ratio of CaO to the hydraulic factors SiO2,
(HM) AL2O3 and Fe2O3

Silica ratio 1.9 – 3.2 characterizes the ratio solid/liquid, i.e. the
(SR) (optimum: 2.2 – 2.6 !) amount of liquid phase in the clinker

Alumina ratio 1.5 – 2.5 characterizes the composition of the melt

(AR) (possibly: <1.5; >2.5) and its viscosity

Alkali-sulphate-ratio 0.8 – 1.2 characterizes the ratio alkali versus

(ASR) sulphate
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Favourable ranges of cement clinker moduli

AR 0.4 1.6 2.0 2.4 2.8

SR 1.4 2.2 2.4 2.6 3.8

HM 1.4 1.7 2.0 2.3 2.6

ASR 0.6 0.8 1.0 1.2 1.4

LSF 85 90 94 98 103

LP 19 22 25 28 31

Critical Range Favourable Range Critical Range

AR = Alumina Ratio HM = Hydraulic Modulus LSF = Lime Saturation Factor

SR = Silica Ratio ASR = Alkali-Sulphate-Ratio LP = Liquid Phase
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Cement moduli – silica ratio (SR)

SiO 2
SR = Characterizes the solid / liquid ratio, i.e. the
Al2O3 + Fe 2O 3 amount of liquid phase in the clinker

1.9 2.2 2.6 3.2

1
low silica content - low liquid phase content
improves burnability - hard burning conditions
- high kiln load
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C/S-ratio – CaO : SiO2

C/S = 1.87 Formation of highly refractory phases

( C2S )

C/S << 1.87 Formation of low melting phases

( monticellite, CMS )

C/S >> 1.87 Corrosion of the spinel phase

2MgO·SiO2 + 2CaO·SiO2 Î 2(CaO·MgO·SiO2)
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