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Wear Phenomena of Refractories
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Dr. Johannes Södje
Wear of refractories, particularly when using waste fuels and their influence on the brick life
Lifetimeof
refractories
Refractoryinstallation
mechanical
Production-quality
Installationdraw
Raw materialquality
chemicalthermal
storagekiln
burningconditions
Refractoryselection
Influences on the part of the cement producer
Influences on the part of the producer
Stresses on the Refractory Lining in Rotary Cement Kilns
loads on refractory linings
Thermal influences
Typical burning conditions
Clinker melt infiltrations
Concave/sloping erosion
Thermal shocks
Typical burning conditions
Clinker melt infiltration
Densification of the brick‘s hot face caused by clinker melt infiltration
- increased thermal influences
- variations of the kiln feed composition
Concave/sloping erosion (brickwork erosion)
constant thermal overloading of the brickwork
direct flame impactcoating free operating conditions with standard bricks with low refractoriness
Thermal shock influences
Too fast heating up or cooling down
Loss of coating
Optimizing:
Taking heating procedure into consideration/cooling down slowly
Chemical influences
Salt infiltration
Corrosion of chrome spinel
Silicate corrosion
Redox burning conditions
“Alkali Spalling“
Corrosion of the kiln shell
Hydration of basic bricks
Salt infiltration:Volatile elements and their principal compounds(without heavy metals)
Sulphur compoundSO2, SO3, S2-
Potassium oxideK2O
Sodium oxideNa2O
ChlorineCl2, Cl-
Salt infiltration: alkali sources
Kiln feed raw material
Clay and mica minerals
Feldspar (Na,K)AlSi3O8
Plagioclase (Na,Ca) (Si,Al) Al2Si2O8
Additives (ashes, bentonite, etc.)
Alternative combustibles
Salt infiltration: chlorine sources
Coal 0.01 - 0.3 % Cl
Lignite 0.1 - 0.13 % Cl
Animal meal 0.6 - 1.6 % Cl
Plastics »PVC«
20 % of the worldwide production of»plastics«
CH2=CHCl 30 % Cl
Salt infiltration: sulphur sources
Kiln feed raw material: FeS2, PbS, ZnS, CaSO4, CaSO4·H2O
Oil 0.2 - 2.5 %
Pitch/Tar 1 - 6 %
Coal 0.1 - 12 % SO3 in the ash
Petrol coke 5 - 8 %
Lignite 0.2 - 15 % SO3 in the ash
Concentrations of salts in the cement kiln system Circulation of volatile compounds
alkalis + Cl- alkalis + SO2/SO3
80
7162943
22
SO
ClONaOK
ASM−+
=
1
KCl + K2SO4
<1
KCl + K2SO4 + SO3 free
>1
KCl + K2SO4 + K2O free
Calculation of the alkali-sulphate modulus (ASM) in the cement clinker
Salt infiltration, balanced alkali-sulphate modulus (ASM ~1)
Densification of different brick horizons
Infiltration of gaseous alkali chloride and/or sulfate components, condensation and densification of the brick texture
Sulfate salts mostly in the lower transition zone and burning zone togetherwith alkali chlorides in the upper transition zone
Salt infiltration, balanced alkali-sulphate modulus (ASM ~1)
Chrome spinel corrosion, surplus of alkalis in kiln atmosphere (ASM >1)
Corrosion of chrome spinel in the presence of free alkalis at higher temperature Formation of toxic, hexavalent alkali chromate sulfate(yellow efflorescences = water soluble)
Contamination of ground water, mason eczema
Silicate corrosion, surplus of sulphur in kiln atmosphere (ASM <1)
Silicate corrosion reduces the refractorinessand the structural flexibility
2 C2S + MgO + SO3 CaSO4 + C3MS2
C3MS2 + MgO + SO3 CaSO4 + 2 CMS
CMS + MgO + SO3 CaSO4 + M2S
Possibly operational difficulties in the kiln system and to the clinker composition caused by the high sulphur content in the kiln gas atmosphere and/or surplus of sulphur in kiln atmosphere (ASM <1)
Formation of coating rings
and/or build-ups in the calcining
zone, inlet section, cyclones etc.
caused by the formation of
anhydrite (CaSO4), double sulfate salts
(calcium langbeinite, syngenite),
and spurrite phases (sulfate spurrite).
Possibly operational difficulties in the kiln system and to the clinker composition caused by the high sulphur content in the kiln gas atmosphere and/or surplus of sulphur in kiln atmosphere (ASM <1)
Sulphur will be retained as sulfates in the clinker (approach or exceed 2 %),
reducing the add of gypsum at the clinker grinding stage. The retarding of
hydration and setting of cement will be changed.
Formation of dusty clinker
Excess of sulphur in the clinker reduces the viscosity of clinker melt and the surface
tension of the liquid phases, which results in clinker structure loosening, and a
greater proportion of clinker dust is formed.
Redox burning conditions
Local reduction and/or redox burning conditions caused byincomplete combustion of fuels (coarse coal, ashes on the lining’s surface)
Basic brick grades with alpine magnesia (crystalline magnesia) are sensitiveto the high Fe2O3 content
“Alkali Spalling“
Thin hot face spallings due to brittleness of the brick texture
Alkalis react with the brick components from fireclay and high alumina bricksforming alkali alumina silicates (feldspar, feldspathoids). This formation isaccompanied by volume increase.
alkali spalling
alumina content, refractoriness, mechanical resistance
alkali spalling due to the formationof new minerals
wea
r by
alka
lis
Kiln shell corrosion
Migration and efflorescences of salts between brickwork and kiln shell
Chemical attack of salts under kiln operating conditions (high thermal corrosion)
Depending on the alkali-SO3-ratio and oxygen partial pressure bi- and trivalent iron oxides and/or iron sulphides are formed.
Hydration
Cracks from the brick surface into the brick‘s internal texture
Basic bricks are sensitive to humidity and must be stored and protected against humidity, rain and sea water.
MgO reacts with water to brucite (Mg(OH)2) which is accompanied by volume increase (~ 53%).
Tropical/sub-tropical climate conditions accelerate this reaction.
Hydration
Mechanical influences
Thermal expansion
Loosenings of the lining
Kiln shell deformation (ovality)
Grooves in the lining
Pressure loads on the kiln retaining ring
Thermal expansion
Convex spallings on the longitudinal joints
Too little allowance for expansion leadsto higher pressure within the brickwork.Convex spallings finally occur.
Insufficient expansion space
Frequent kiln stops after the burnout of the cardboards
Loosenings of the lining
Loosenings of the brickwork due to brickwork movements
Spiral twisting, tilting of bricks, shearing cracks, abrasion markson the brick‘s cold face
Wrong installation, frequent kiln stoppages, kiln shell deformations and ovalities
Kiln shell deformation (ovality)
Local strong spallings in the tire section, the surrounding brickwork is intact.
Increased ovality in the tire section causes tensions and loosenings of the lining.
The brick‘s hot face is more loaded (spallings).
Groove formation
Increased wear parallel to the kiln axis caused by groove formation, the otherbrickwork is intact (spallings of 2 - 3 brickwork width)
Brickwork rings are closed too tightly, damage of the key bricks using a wronghammer
More than one iron plate within the brickwork rings
High pressure on the retaining ring section
Increased pressure of the brickwork onto the retaining ring. Shearing tensionsoccur within the brickwork leading to cracks and spallings of brick parts.
Instable, deformed kiln shell or ovality increase this wear.
mechanicalinfluences
chemicalinfluences
thermalinfluences
vapour explosion
monolithicwear
Wear influences onto the monolitic lining
Vapour explosion (100 °C to ~600 °C)
Too fast heating up during setting/hardening and after heating up of the monolithic lining
Thermal influences
Thermal shocks, thermal overloading, thermal spots
Chemical influences
Reaction with the kiln feed (clinker dust), thermochemical attack by harmful components (alkali and sulfur compounds)
Mechanical influences
Abrasion, dust erosion (clinker dust), influences due to anchor, kiln shell and metallic construction
Wear influences onto the monolitic lining
Vapour explosion (100 °C to ~600 °C)
Riser shaft to calcinator/inlet chamber Cooler banks
Thermal influences
Cooler banks (tension cracks caused by thermal shock)
Chemical influence
Kiln hood back wall (alkali attack -> alkali spalling)
Chemical influence
Corrosion of metallic anchors
Mechanical influence
Damper in the tertiary air duct (high abrasion caused by strong air stream)
Thermal, chemical and mechanical influence
Burner lance
A change of refractory wear, particularly when using alternative or waste fuels in the cement rotary kiln
A change of refractory wear, particularly when using alternative or waste fuels in the cement rotary kiln
Fuel oil and gas as primary energy since approx. 1960
Changeover to coal after the petroleum crisis in 1973/74
Use of alternative fuels since mid eighties
Coating in the burning zone
The magnesia-chromite bricks used in the hot zones and the high alumina and fireclay bricks in the other sections perform good regarding lifetime and wear resistance
outlet zone burning zone safety zone
Lining and coating zone of kilns using fuel oil and gas
A change of refractory wear, particularly when using alternative or waste fuels in the cement rotary kiln
Fuel oil and gas as primary energy since approx. 1960
Changeover to coal after the petroleum crisis in 1973/74
Use of alternative fuels since mid eighties
Coating in the burning zone and particularly in the transition zones
Magnesia-chromite bricks in the burning zone showing a usual wear
Reduced service life of the magnesia-chromite lining in the transition zones (salt infiltration, formation of alkali chromates, redox burning conditions)
uppertransition zone
burning zonelower transition zone
outlet zone
safety zone
Lining and coating zone of kilns using coal and fuel oil
Salt infiltrations, alkali chromate formation and reducing burning conditions in case of magnesia-chromite bricks
MAGPURE®93/95 ALMAG®A1 ALMAG SLC®
ALMAG®85
REFRAMAG®85
FERROMAG®90
Development of magnesia-spinel and magnesia-zirconia bricks
Main properties:
high resistance to alkali attack (no corrosion of the MA spinel or the zirconia)
insensitive to reducing or redox conditions
MAGNUM®SMAGNUM®95
A change of refractory wear, particularly when using alternative or waste fuels in the cement rotary kiln
Fuel oil and gas as primary energy since approx. 1960
Changeover to coal after the petroleum crisis in 1973/74
Use of alternative fuels since mid eighties
Complex and instable coating situation and various flames
Lining lifetime clearly reduced, particularly in the transition zones(massive salt infiltrations, local overheating, local redox burning conditions)
outlet zone
lower transitionzone
burningzone I
burningzone II
transitionzone
transitionzone
safetyzone
Lining and coating zone using fuels with 50 % usual fuels and 50 % alternative fuels
Influence of secondary fuels on the refractory lining and kiln system
Stronger chemical and physical attack against the basic bricks
Risk of irregular temperature profile in the kiln (local thermal overload)
Risk of formation of local reducing atmosphere
Stronger chemical attack against the aluminous and fireclay bricks
Stronger attack against the kiln/cyclone shell and the anchor system
Percentage of the different wear types
Up-to-date studies show that more than 60 % of the wear cases are caused bysalt infiltrations (alone or in combination with other attacks)
23 % mechanical/thermomechanical influences and salts
23 % thermochemical influences and salts
23 % overheating
17 % salts
8 % mechanical/thermomechanical influences1 % redox conditions5 % other
> 60 %
Increase of salt infiltrations and accumulation of other harmful substances in the structure, balanced alkali-sulphate modulus (ASM ~1)
Increase of salt infiltrations and accumulation of other harmful substances in the structure, balanced alkali-sulphate modulus (ASM ~1)
Use of alternative additives with the kiln feed(e. g.: condensation of lead sulfide (PbS))
2 C2S + MgO + SO3 CaSO4 + C3MS2
C3MS2 + MgO + SO3 CaSO4 + 2 CMS
CMS + MgO + SO3 CaSO4 + M2S
K2O + 3 SO3 + 2 MgO K2Mg2[SO4]3
Silicate corrosion, surplus of sulphur in kiln atmosphere (ASM <1)
refractoriness and the structural flexibilityare reduced
Influence of secondary fuels on the refractory lining and kiln system
Stronger chemical and physical attack against the basic bricks
Risk of irregular temperature profile in the kiln (local thermal overload)
Risk of formation of local reducing atmosphere
Stronger chemical attack against the aluminous and fireclay bricks
Stronger attack against the kiln/cyclone shell and the anchor system
Local overheating and redox burning conditions
Redox burning conditions and salt infiltrations
Formation of oldhamite (CaS), K2S, K2S3, KFeS2 under reducing atmosphere
Sulfate salts reform in oxidizing atmosphere, and lead to the brick‘s destruction.
Typical smell of H2S during kiln stop (smell of foul eggs)
Strong reducing and redox burning conditionscarbon disintegration, Boudouard reaction (CO2 + C <-> 2CO)
16
carbon horizon
Influence of secondary fuels on the refractory lining and kiln system
Stronger chemical and physical attack against the basic bricks
Risk of irregular temperature profile in the kiln (local thermal overload)
Risk of formation of local reducing atmosphere
Stronger chemical attack against the aluminous and fireclay bricks
Stronger attack against the kiln/cyclone shell and the anchor system
“Alkali Spalling“ in the aluminous bricks
Structural embrittlement and spalling of thin layers.
The alkalis react with the components of fireclay and aluminous bricks underformation of alkali containing alumina silicates (feldspars, feldspathoids).This formation is accompanied by a volume increase.
Influence of secondary fuels on the refractory lining and kiln system
Stronger chemical and physical attack against the basic bricks
Risk of irregular temperature profile in the kiln (local thermal overload)
Risk of formation of local reducing atmosphere
Stronger chemical attack against the aluminous and fireclay bricks
Stronger attack against the kiln/cylcone shell and the anchor system
Effect of kiln shell corrosion and cyclone steel shell
Corrosion of metallic anchors (refractory areas installed with castables), formation of alkali chromate (K2CrO4), surplus of alkalis in kiln atmosphere (ASM >1)
Alkali chromate condensation in magnesia spinel lining
arcanite (blue efflorescences)
arcanite (green efflorescences)
alkali chromate
Requirements to refractory material and its installationin Cement Rotary Kilns fired with secondary fuels
Minimization of infiltration and corrosion of refractory components
Optimization of the structural texture by higher flexibility and high structural strength
Renewable sealing of the refractory’s hot face
Optimization of installation technology, especially in the static area of cementkiln system including a flexible and fast installation of high grade refractory concretes and bricks
Innovative insulating and protection options for the anchoring system and steelshell to reduce or even prevent different corrosion mechanism of shell and anchor
19
Refratechnik Cement’s refractory solution
Basic refractory brick grades established concept AF-series: ALMAG AF, REFRAMAG AF, TOPMAG AF new developments TOPMAG A1, FERROMAG F1, FORMAG 88
Non-basic materialbrick gradesestablished concept AR-series: KRONAL 50 AR, KRONAL 63 ARnew development KRONAL 60 AR
refractory concreteshigh grades LCC, and LCC-AR product rangehigh grade and fast application JC- and MCG-technology
Installation technology AR-lining concept with integrated refractory design including wear lining, insulating concept, and anchor system
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