Wear of refractories, particularly when using waste fuels and their influence on the brick life Dr. Johannes Södje
Influences on the part of the cement producer Refractory installation
thermal
storage Lifetime of refractories
chemical kiln burning conditions mechanical
Refractory selection
Installation draw
Productionquality
Raw material quality 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 impact coating 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 compound SO2, SO3, S2Potassium oxide K2O Sodium oxide Na2O Chlorine Cl2, 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
Calculation of the alkali-sulphate modulus (ASM) in the cement clinker
K 2O Na2O Cl + − 62 71 ASM = 94 SO3 80
<1
KCl + K2SO4 + SO3 free
1
KCl + K2SO4
>1
KCl + K2SO4 + K2O free
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 together with 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 refractoriness and 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 by incomplete combustion of fuels (coarse coal, ashes on the lining’s surface) Basic brick grades with alpine magnesia (crystalline magnesia) are sensitive to 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 bricks forming alkali alumina silicates (feldspar, feldspathoids). This formation is accompanied by volume increase.
wear by alkalis
alkali spalling due to the formation of new minerals
ng palli s i l alka
alumina content, refractoriness, mechanical resistance
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 leads to 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 marks on 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 other brickwork is intact (spallings of 2 - 3 brickwork width) Brickwork rings are closed too tightly, damage of the key bricks using a wrong hammer 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 tensions occur within the brickwork leading to cracks and spallings of brick parts. Instable, deformed kiln shell or ovality increase this wear.
Wear influences onto the monolitic lining vapour explosion
mechanical influences
monolithic wear
thermal influences
chemical influences
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
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
Lining and coating zone of kilns using fuel oil and gas
outlet zone
burning zone
safety zone
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
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
Lining and coating zone of kilns using coal and fuel oil
outlet zone
lower transition zone
burning zone
upper transition zone
safety zone
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)
Salt infiltrations, alkali chromate formation and reducing burning conditions in case of magnesia-chromite bricks
Development of magnesia-spinel and magnesia-zirconia bricks
MAGPURE®93/95
ALMAG®A1
ALMAG SLC®
REFRAMAG®85
ALMAG®85 FERROMAG®90 MAGNUM®95
MAGNUM®S
Main properties: high resistance to alkali attack (no corrosion of the MA spinel or the zirconia) insensitive to reducing or redox conditions
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
Lining and coating zone using fuels with 50 % usual fuels and 50 % alternative fuels
outlet zone
lower transition zone
burning zone I
transition zone
burning zone II
transition zone
safety zone
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)
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 by salt infiltrations (alone or in combination with other attacks)
23 % thermochemical influences and salts 23 % mechanical/thermomechanical influences and salts 17 % salts 23 % overheating 8 % mechanical/thermomechanical influences 1 % redox conditions 5 % 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))
Silicate corrosion, surplus of sulphur in kiln atmosphere (ASM <1) refractoriness and the structural flexibility are reduced 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
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 conditions carbon disintegration, Boudouard reaction (CO2 + C <-> 2CO)
carbon horizon 16
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 under formation 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 installation in 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 cement kiln system including a flexible and fast installation of high grade refractory concretes and bricks Innovative insulating and protection options for the anchoring system and steel shell 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 material brick grades established concept new development refractory concretes high grades high grade and fast application Installation technology
AR-series: KRONAL 50 AR, KRONAL 63 AR KRONAL 60 AR LCC, and LCC-AR product range JC- and MCG-technology AR-lining concept with integrated refractory design including wear lining, insulating concept, and anchor system
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