Clinker Reactivity Presentation_sept 2012_lafarge

Clinker Reactivity 7th Sept 2012 1

Clinker Reactivity AN OPPORTUNITY Improve Product Quality Improve Financial Return

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Clinker Reactivity How to burn a good clinker?

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The 10 basic facts on clinker Objective Put together basic and widely accepted rules which are easy to apply in all operating units with a view to producing good clinker at low cost.

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First Rule Decreasing raw mix rejects – especially if they are siliceous rejects • helps reduce burning temperature • helps reduce cement grinding energy • is rather beneficial to strength properties Key Figures : Reducing the 100µm raw mix reject from 20 % to 10 % lowers energy consumption by 4 kWh per tonne of cement at a 350 m2/kg fineness. Target value:

1 % at 200 um 10 % at 100 um 5

Mineralogy and Fineness Type of mineralogy in the coarse reject fraction affects the combinability temperature of this material in the kiln Effects of % 100 µm rejects Quartz type raw mix

% free CaO 6 5

5

25 %

4

4

3

3

2

10 %

2

1 0 1350

1 5% 1400

Effects of % 100 µm rejects Marl type raw mix

% free CaO 6

1450

1500 1550 temperature °C

25 % 10 %

0 1350

1400

1450

1500 1550 temperature °C

In summary Finenesss  Influences the ‘combinability’ temperature  Chemistry of Rejects Calcereous rejects - free lime and belite Siliceous rejects - poor combinability 6

Second Rule Maintain the burning zone length as short as possible Advantages • Improvement of clinker grindability • Impact on mechanical strengths Means • Raw material burnability • Type of fuel and its preparation • Burner and its settings • Secondary air temperature • Kiln operation 7

BURNING ZONE PROFILE

SHORT ZONE

LONG ZONE Key Figures : The optimum is achieved when the kiln torque is at the minimum value compatible with stable kiln operation. • Quick rise to maximum temperature - Small crystal sizes • Short burning zone - Maximum reactivity • Flame shape and position correct - Oxidizing conditions/coal ash combination 8

Third Rule Maintain an oxidising atmosphere in the kiln

Consequences of a non-oxidising atmosphere:

• increased sulphur volatilisation • Cyclic operation • Irregular clinker mineral formation

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 Reducing conditions  C3S formation is hampered in a reduced atmosphere resulting in lower C3S content

 Presence of FeO increase C3S instability - alite degrades to belite and free lime with slow cooling

 The iron in the reduced state will not form the C4AF but other products such as FeO. The aluminium that would have formed C4AF is now available to form more C3A.  the actual mineralogical content will be drastically different from those calculated by Bogue and the chemist will be unaware.

Very important not to have Reducing conditions ! 10

Fourth Rule Increasing the clinker free lime content reduces initial and final setting times.

Key figures : When free CaO increases from 0.5 to 1.5%, initial set decreases by about 40 to 50 minutes. This impact may vary greatly from clinker to clinker (-10 to -100 minutes).

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FREE LIME AND SETTING TIME REDUCTION Initial set (mortar)

( min. )

180 160 140 120 100

%

0.2

0.4

1 1.2 0.6 0.8 Free lime clinker

1.4

1.6

St Constant

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Fifth Rule Increase the clinker C3S content

improves strength at 1, 2, 3 and 7 days. After 28 days, the gain may be less because of the C2S contribution. Key figures : +10% C3S => strengths

+2 to +5 MPa

for early

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Sixth Rule For a given Blaine specific surface (SSB), grinding energy increases with C2S content. Key figures : +10% C2S, (or -10% C3S) => +5 kWh/t (@ 3500 cm2/g). Aim at 60 % C3S in the clinker and maintain its regularity.

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Seventh Rule Alkalies are never favorable to 28-day compressive strength 1. 0.1 % eq Na2O total => - 1 MPA at 28 days 2. Alkalies occur in two forms • Soluble alkalies (alkali sulfates) •Alkalies in solid solution, included in the crystalline structure of the aluminates and silicates.

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Influence of Alkalis on Strengths Compressive strength (MPa)

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28 days 40 30

7 days

20

3 days

10 0

0.5 1 total alkali as eq. Na2O (%)

1.5 16

Sulfates & Alkalies in Clinker Na

K

K Na

Na

K K

K

SO4

Clinker burning process

SO4 K

K and Na in C3A crystals

K Na K SO4 K SO4 SO4 Na Na K Na SO4 SO4 K K SO4 K SO4 SO4 Na

Alkali-Sulfates (K2SO4, Na2SO4) and C3A C3A

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Soluble Alkalies  Soluble alkalis (alkali sulphates):  usually improves rheology (some exceptions)  increase early strength ( =f{C3A} )  sensitive to lumping and glueing  reduced 28 day strengths

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Insoluble Alkalies  Insoluble alkalis (in clinker structure):  alkalis occur as Na2O and K2O in C3A crystal structure which becomes orthorhombic

 difficulty in controlling rheology  workability problems  plastic shrinkage  reduced 28 day strength

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Eighth Rule At optimum sulfate addition, soluble alkalies in the form of alkali sulfates improve early strength. Key figures : + 0.1 % Eq. Na2O soluble --> + 0.5 à 1.5 N/mm2 @1 day • Increase sulphate content by adding gypsum to the raw mix • Increase fuel sulphur content • Increase raw mix alkali content

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ALKALIES

SULFATES

Moles 1 K2O + 1 SO3

1 K2SO4 SOLUBLE

1 Na2O + 1 SO3

1 Na2SO4 SOLUBLE

These Soluble alkalies are

Beneficial for à 1, 2 day strength 21

Ninth Rule The molar saturation of alkalies by SO3 in the clinker facilitates workability control. Key figures: The molar ratio SO3/Alkalies should be > 1

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Why Molar saturation is important ? Saturation of Alkalies with Sulphates (Raw meal+fuel)

Alkalies > Sulphate

Sulphate > Alkalies

Burnability, Workability in the Concrete & Durability bad

Clinker finer, dusty burning conditions, bad grindability of clinker 1%  +5 kWh/t 10th rule

Alkalies = Sulphate Increase of early strength + 0.1% Na2O sol. to 1.5 MPa more after 1 day 23

Tenth Rule Increasing clinker SO3 beyond the molar saturation of alkalies results in: • an increase in clinker fineness • an increase in grinding energy Key figures : +1% excess SO3 --> + 5 kWh/t @ 350 m2/kg [excess SO3 will combine with CaO to form CaSO4 anhyride. This results less C3S formation and more C2S formation]

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Conclusions 

Raw Mix The extra cost incurred by the raw mix preparation (composition, fineness) is usually compensated by a decrease in clinker kW and an improvement of cement properties.



Burning A short burning zone and oxidising atmosphere result in a decrease in clinker kW and an improvement of cement properties.



Product A good SO3/alkalies ratio allows optimization of product characteristics and results in a decrease in heat consumption an improvement of cement workability 25

Clinker reactivity improvement Project

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Content  Why a clinker reactivity improvement program in our region ?  Main impacts on clinker reactivity – a statistical evaluation of TCEA zone clinkers  Typical Clinker reactivity program

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Clinker reactivity is a main issue for progress  Increase Cementitious Content (CO2, output, costs…)  One global main objective of the group

 Clinker is the only source of early strength  When we want to increase cementitious and keeping competitive cements we need to increase clinker reactivity

 28 day strength can be “delivered” by cementitious

 On the other side: Alternative fuels have the tendency to decrease the clinker reactivity  Sinter zone temperature profile  Increase P2O5, Lower SO3 28

What are the main drivers for clinker reactivity? Results from a multivariant regression  Lab grindings under controlled conditions, 3100 Blaine, 3,5 % SO3   measurement of setting time, 1day, 2 days 28 days strength

 + all relevant physical / chemical / mineralogical relevant parameters

 Correlation of “phenomena” with clinker and kiln feed parameters  Chemistry, mineralogy (all what can be measured…)  Single and multivariate Regression to determine influences 29

Results of Multivariate Regression Parameters influencing 1 day strength 1D CS [MPA] = a+b*X1+b*X2+c*X3 + … 

%Alite:

+1%



+0,2 MPa



% SO3 in clinker:

+1%



+5 MPa



% MgO:

+1%



- 1 MPa



% Aluminates total:

+1%



+0,2 MPa



µm Alite d50:+10µm 

-0,7 MPa



% Free lime:





Soluble Alkalies: Impact not quantified in the model (overhelmed by sulphur) ( usually 1 % sol Na2Oequ  10 MPa)

+1%

+6 MPa

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Parameters influencing 28 days strength 28D CS [MPA] = a+b*X1+b*X2+c*X3 + … 

% Alite:

+1%



+0,35 MPa



% SO3:

+1%



+1,9 MPa



% MgO:

+1%



-3 Mpa



µm Belite d50:

+1µm



-0,5 Mpa



% Na2Oeq:

+1%



-9 Mpa



Increase of strength with inrease of 1 % Alite is rather low,

as C3S is balanced with C2S which also contributes to strength.

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9 main parameters the explain 90 % of clinker reactivity  These parameters needs to be optimised  Constraint: Each parameter is already “optimised” in regards of plants constraints: Quarry reserves, burnability of raw mix. kiln layout, process specific, fuel mix etc.

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Clinker Reactivity improvement Program: 1. Evaluate the current reactivity and the potential  By plant team and TC experts

2. Improvement plans and improvement actions  Focus on plants with highest need and potential  Individual improvement plans, aligned with plant PIPs -

Quick wins Medium term targets

3. Evaluation of progress  Documentation of activities  Regular measurement of clinker reactivity in ARL - Lab

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