Brown Clinker

8/17/2019 Brown Clinker

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Gerold Gerold Schnedl /Schnedl / Ingo Ingo Leth Leth

CTECCTEC Quality Quality Days Days 2003 2003

Brown clinkerBrown clinker

BrownBrown cementcement

BrownBrown concreteconcrete



Brown clinker Sötenich

2Feb 03G. Schnedl

CENTRE TECHNIQUE EUROPE CENTRALE

TheThe problemproblem::BrownBrown concreteconcrete




3Feb 03G. Schnedl


TheThe reasonreason: Brown clinker: Brown clinker




4Feb 03G. Schnedl


Situation 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+)

Fuels:

Lignite, presently animal meal

Old burner, old grate cooler

Distinguish between:Colour of cementBrown stainings due to Fe2+




5Feb 03G. Schnedl


Study: Find levers to get “black cores”and grey cement

Several industrial tests: Not successful

Higher amount of animal meal causes higher amount of Fe2+

Brown clinker cores even without animal meal

September 2002: Start of systematic clinker sampling

Fuels, kiln conditions, clinker chemistry, granulometry Study in CTEC-Lab

Literature study, microscopy, process data, lab burnedclinker granules

2003: Investment in new burner




6Feb 03G. Schnedl


Summary of findings

What causes dark / light clinker ? C4AF is the only dark component in clinker

Incorporation of Mg leads to dark C4AF - changes latticeparameters – semi conductive properties leads to darkcolour

This electrical properties can be disturbed by even smallamounts 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

Literature




7Feb 03G. Schnedl


What bleaches C4AF in brown cores?

Fe2+ seems to be the main reason in Sötenich but:

Fe2+, Mn2+, Ti, Si in clinker cores: no significant differencesdetectable, but:

No Fe2+ in clinker after cooler does not necessarily meanthat no Fe2+ in liquid phase in sinter zone

Fe2+normally re-oxidised after sinter zone

but needs time and oxygen

Fe2+ appears not only due to reducing conditions:

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




8Feb 03G. Schnedl


What bleaches C4AF in brown cores?

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 ofFe2+

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




9Feb 03G. Schnedl


Confirmation of hypothesisPlant and lab tests

Analysis of plant clinker samples and process data Fuel mix / fuel rates

burner positions

Extensive microscopic investigation in CTEC-Lab Lab burned clinker with Sötenich raw material

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)




1Feb 03G. Schnedl


Analysis of plant clinker samples

Influence on animal meal on clinker colour

59,00

60,0061,00

62,00

63,00

64,0065,00

66,00

67,00

68,00

0 0,2 0,4 0,6 0,8 1 1,2

tons / hour animal meal

b r i g h t

n e s s L * c l i n k e r m e a l

No significantimpact of animal

meal on colour, buton FeO content




1Feb 03G. Schnedl



Brightness vs fineness

100

150

200

250

300

350

400

58 60 62 64 66 68

Brightness L*

f i n e n e s s k - v a l u e

k-value (fineness)Coarse clinker hasbrighter (browner)

cores




1Feb 03G. Schnedl



Brightness (L*) vs Literweight

1,00

1,10

1,20

1,30

1,40

1,50

1,60

1,70

55,00 60,00 65,00 70,00

Brightness L*

l i t e r w e i g h t

fraction 11,2-16 mm

fraction 4-8 mm

Dense clinkergranules (higherliter weight) havebrighter cores




1Feb 03G. Schnedl


Microscopic examination

Fast cooling

Partly reducing conditions No difference between brown and black cores

High amounts of Alkali Aluminate Fast stiffening




1Feb 03G. Schnedl


Lab clinker tests




1Feb 03G. Schnedl


Different cooling conditions




1Feb 03G. Schnedl


Lab tests to check cooling conditions

Check of different cooling rates > 1250 °C in lab furnace

a1 a2 a3 b c




1Feb 03G. Schnedl


Comparison of different conditions

CIZ clinkerReference

5 % MgO 1 % MnO 5 % MgO +1 % MnO

Slowcooled

quickcooled




1Feb 03G. Schnedl


Results of process data an lab test study:

Brown cores appear, even only very little FeO is

detectable, nevertheless FeO is the cause

Microscopy investigation – confirms lab burning tests

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 tooxygen diffusion barrier into the core




1Feb 03G. Schnedl


Recommendations

Shorter flame – shorter sinter zone

With old burner not possible

Convergent flame – not touching the clinker

With old burner not possible

Move burner into the kiln in order to lengthen cooling zone Detrimental to clinker reactivity

Finer fuels

No coal mill in Sötenich

Finer raw mix decrease coarse Quartz content (raw millimprovement)

Increase SO3 in clinker in order to improve burnability and

produce smaller clinker granules (+ increase workability)




2Feb 03G. Schnedl


Industrialisation: A new burner for Sötenich

Not only due to brown cores,also to increase waste fuelrate

Start: 21.05.2003

Shorter, convergent flame

Controllable




2Feb 03G. Schnedl


Other plant actions

Manual estimation of clinker colour separation Only black clinker for precast cement

Target: Implement automatic colour measurement of presstablets in auto-lab – result triggers separation of clinker

Implement FeO quick test

Separate clinker

Change fuel mix (reduce

animal meal)

Result: No claims in 2003

Documents

Brown Clinker