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Brown clinker Brown cement Brown concrete Gerold Schnedl / Ingo Leth CTEC Quality Days 2003
Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
The problem: Brown concrete G. Schnedl
Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
The reason: Brown clinker
G. Schnedl
Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Situation
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Sötenich plant: ❏ Brown cored clinker caused brown cement and brownish concrete surfaces ❏ Market focus: pre-cast cement ❏ Colour of cement / concrete important ❏ Cement less competitive Problems with brown cored clinker is not new (since years, but increased in 2002) ❏ but does not always appear ❏ Sometimes problems with brown stainings (Fe2+) Distinguish between: Fuels: Colour of cement ❏ Lignite, presently animal meal Brown stainings due to Fe2+ Old burner, old grate cooler
G. Schnedl
Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Study: Find levers to get “black cores” and grey cement
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Several industrial tests: Not successful ❏ ❏
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September 2002: Start of systematic clinker sampling ❏
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G. Schnedl
Fuels, kiln conditions, clinker chemistry, granulometry
Study in CTEC-Lab ❏
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Higher amount of animal meal causes higher amount of Fe2+ Brown clinker cores even without animal meal
Literature study, microscopy, process data, lab burned clinker granules
2003: Investment in new burner
Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Summary of findings Literature ■
What causes dark / light clinker ? ❏ ❏
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G. Schnedl
C4AF is the only dark component in clinker Incorporation of Mg leads to dark C4AF - changes lattice parameters – semi conductive properties leads to dark colour This electrical properties can be disturbed by even small amounts of other ions. e.g. Fe2+ Mn2+ , Ti4+ or Si4+ Incorporation only when C4AF crystallizes: > 1250 °C
Colour depending on condition in sinter zone and pre-cooling condition (crystallisation) in kiln Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
What bleaches C4AF in brown cores? ■
Fe2+ seems to be the main reason in Sötenich but: ❏
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No Fe2+ in clinker after cooler does not necessarily mean that no Fe2+ in liquid phase in sinter zone ❏ ❏
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Fe2+normally re-oxidised after sinter zone but needs time and oxygen
Fe2+ appears not only due to reducing conditions: ❏ ❏ ❏
G. Schnedl
Fe2+, Mn2+, Ti, Si in clinker cores: no significant differences detectable, but:
a) reducing atmosphere or flame touching the lining b) fuel in clinker (too coarse material – solid fuels..) c) thermal dissociation of Fe3+ in hot sintering zone Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
What bleaches C4AF in brown cores? ■
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Experience of plants: ❏ The core is brown and never the surface ❏ Bigger clinker granules have more often brown cores ❏ More often when kiln is operated at full capacity Hypothesis, resulting from literature study: Brown clinker cores seems to be caused by an diffusion effect: Balance of crystallisation speed of C4AF and re-oxidation of Fe2+ ❏ Cooling speed > 1250 °C (pre-cooling in kiln) ❏ O2 content in atmosphere / flame ❏ Porosity of clinker ❏ Liquid phase content Even when only very few FeO is detectable < 0,04 %) – meaning that the not incorporated FeO oxidised afterwards Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Confirmation of hypothesis Plant and lab tests
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Analysis of plant clinker samples and process data ❏ ❏
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Extensive microscopic investigation in CTEC-Lab Lab burned clinker with Sötenich raw material ❏ ❏ ❏ ❏
G. Schnedl
Fuel mix / fuel rates burner positions
Different cooling conditions over and below 1250 °C Comparison with other raw meals Impact of atmosphere Impact of Manganese (Sötenich: 0,2 % MnO in clinker)
Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Analysis of plant clinker samples
brightness L* clinker meal
Influence on animal meal on clinker colour 68,00 67,00 66,00 65,00 64,00 63,00 62,00 61,00 60,00 59,00
No significant impact of animal meal on colour, but on FeO content 0
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tons / hour animal meal G. Schnedl
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Analysis of plant clinker samples Brightness vs fineness 400
fineness k-value
350 300 250
(fineness) Coarse k-value clinker has brighter (browner) cores
200 150 100 58
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Brightness L* G. Schnedl
Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Analysis of plant clinker samples Brightness (L*) vs Literweight 1,70 1,60
literweight
1,50 1,40
fraction 11,2-16 mm fraction 4-8 mm
1,30 1,20 1,10 1,00 55,00
60,00
65,00
Dense clinker granules (higher liter weight) have brighter cores 70,00
Brightness L* G. Schnedl
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Microscopic examination ■ ■ ■ ■
G. Schnedl
Fast cooling Partly reducing conditions No difference between brown and black cores High amounts of Alkali Aluminate Fast stiffening
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Lab clinker tests
G. Schnedl
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Different cooling conditions
G. Schnedl
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Lab tests to check cooling conditions Check of different cooling rates > 1250 °C in lab furnace
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G. Schnedl
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Comparison of different conditions CIZ clinker Reference
5 % MgO
1 % MnO
5 % MgO +1 % MnO
Slow cooled
quick cooled
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Results of process data an lab test study: ■
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Brown cores appear, even only very little FeO is detectable, nevertheless FeO is the cause Microscopy investigation – confirms lab burning tests ❏
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G. Schnedl
Partly reducing conditions due to coarse fuel (lignite + animal meal) + divergent flame + sometimes thermal overheating Too rapid cooling: No pre-cooling zone in kiln caused by burner position Rather coarse raw mix causes “overheating”
High Manganese content might boost the effect Coarse clinker granules favour brown cores – due to oxygen diffusion barrier into the core Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Recommendations ■
Shorter flame – shorter sinter zone ❏
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Convergent flame – not touching the clinker ❏
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Detrimental to clinker reactivity
Finer fuels ❏
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With old burner not possible
Move burner into the kiln in order to lengthen cooling zone ❏
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With old burner not possible
No coal mill in Sötenich
Finer raw mix decrease coarse Quartz content (raw mill improvement) Increase SO3 in clinker in order to improve burnability and produce smaller clinker granules (+ increase workability) Feb 03
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Industrialisation: A new burner for Sötenich
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Not only due to brown cores, also to increase waste fuel rate Start: 21.05.2003 Shorter, convergent flame Controllable
G. Schnedl
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Brown clinker Sötenich CENTRE TECHNIQUE EUROPE CENTRALE
Other plant actions ■
Manual estimation of clinker colour ❏ ❏
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Only black clinker for precast cement Target: Implement automatic colour measurement of press tablets in auto-lab – result triggers separation of clinker
Implement FeO quick test ❏
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separation
Separate clinker Change fuel mix (reduce animal meal)
Result: No claims in 2003 Feb 03
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