Chlorine in ClinkerA. Pisch – Lafarge LCRGTT workshop 2015

Table of contents

The cement making process

Origin of Chlorine in clinker Alternative fuels

Chlorine cycling in a cement kiln Kiln inlet

Sintering zone

cooling

Conclusions

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The cement making process

3

Sokhna plant

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The cement making process

4

Process scheme

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Origine of Chlorine in clinker

Two potential inputs for chlorine

Raw materials

Fuels

Raw materials

Input from raw materials is small (few ppm)

Alternative raw materials (mineral sludge…) may have higher levels

Fuels

Input from classical fuels is low (coke, petcoke, gas…)

Input from alternative fuels is high (% range)

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Alternative fuels

6

Biomass

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Coffee husk

PKS: Palm Kernel Shells

Sunflower seed shells

Alternative fuels

7

Plastics

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Plastic pieces

Shredded municipal waste

Shredded tyres

Alternative fuels

8

Burning

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Chlorine cycling in a rotary kiln

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1800°C – 2000°C

800°C – 900°C

Chlorine cycling in a rotary kiln

10

Kiln inlet

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1% of Cl

=

1.9% of liquid

pHCl = 4.3 mbar

@900°C

Chlorine cycling in a rotary kiln

11

Kiln inlet

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.10.20.30.40.50.60.70.80.9

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

KCl

CaCl2 CaOmass fraction

Liquid

CaO - CaCl2 - KCl

900oC, 1 atm

Solubility of CaO decreases

with KCl

pHCl for KCl-CaO mixture

=

0.014 mbar @ 900°C

Chlorine cycling in a rotary kiln

12

Kiln inlet

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.10.20.30.40.50.60.70.80.9

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

CaSO4

CaCl2 CaOmass fraction

Liquid + CaO(s) + CaSO4(s)

Liquid

CaO - CaCl2 - CaSO4

1000oC, 1 atm

pHCl for CaCl2-CaSO4-CaO mixture

=

3.1 mbar @ 900°C

Chlorine cycling in a rotary kiln

13

Kiln inlet

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0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.5 1 1.5

Cl m

ea

su

red

by X

RF

Cl calculated from KCl, NaCl (Rietveld)

• No CaCl2 detected in XRD analyses

• Main contribution from alkali chlorides

• Other Cl-bearing species

• Ca12Al14O32Cl2

• Ca10(SiO4)3(SO4)3(OH,Cl)l2

Chlorine cycling in a rotary kiln

14

Kiln inlet

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0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5

Cl m

ea

su

red

[%]

Cl calculated from Rietveld (NaCl, KCl, 0.5*Ellestadite) [%]

Chlorine cycling in a rotary kiln

Main contribution at kiln inlet are alkali chlorides

All chlorides are liquid initially and form a salt melt

Some CaO can be dissolved if CaCl2 is present

CaSO4 dissolves and increases the amount of liquid phase

CaCl2 and CaSO4 in the salt melt react with Alumina and Silica to form

solid compounds (Mayenite, Ellestadite) with high sticking potential

Ring formation + blockages

Ball formation

15

Kiln inlet

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Chlorine cycling in a rotary kiln

16

Sintering zone

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Vaporization zone

Limited gas-solid interaction

Congruent vaporization of alkali-chlorides

KCl(l) = KCl(g)

The reaction is independent of HCl in the gas

Decomposition for other chlorides

CaCl2(l) + H2O(g) = CaO (s,l) + 2 HCl (g)

The reaction depends on H2O(g) and HCl(g) in the combustion gas

Typical chlorine levels in clinker : 300 to 1500 ppm (0.03% to 0.15%)

Regulatory level in final cement: 0.1%

Chlorine cycling in a rotary kiln

17

Sintering zone

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0

200

400

600

800

1000

1200

1400

1600

0.00 0.02 0.04 0.06 0.08 0.10

Ch

lori

ne

in

cli

nk

er

[pp

m]

%HCl in gas phase

• Simulation with FTOxid +

diluted sulfate / chloride

• Main Cl-bearing species• 75% ”CaCl2”

• 15% “FeCl3”

• 5% “MgCl2”

• 4% “KCl”

• 1% “NaCl”

Chlorine cycling in a rotary kiln

18

Clinker cooling

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• High level of CaO

• 0.19 – 0.54% of Cl

• some K, S

Conclusions

There are two different chlorine cycles in a cement kiln

Alkali-chlorides

CaCl2 with HCl as vector

Chlorides lead to liquid phase formation with high sticking potential at

kiln inlet

The alkali chlorides accumulate in the kiln if no by-pass is present

Some chlorine leaves with the clinker (up to 0.15%), mainly as CaCl2

It is difficult to simulate chlorine cycling

Missing thermodynamic data

Highly process dependant : residence time (inclination, bed height, rotation speed),

kiln geometry, temperature profile

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