08. Thermal & Chemical Kilb 2006

Chemical and thermal requirements for optimal refractory lining lifetime Dr. Lothar Kilb

Cyclone

Critical areas in stationary and rotating units of a modern cement kiln

Precalciner

Inlet chamber & Riser duct

Safety & Upper Transition main burning zone

Lower Transition Zone/Outlet/Nosering Burner, Kiln hood, Hot parts of cooler

Types of stress conditions in rotary cement kilns

Lower transition zone

Sintering zone

Upper transition zone

• Unstable coating

• Protection by stable coating

• Unstable coating

• High thermal shock

• Infiltration by liquid phase of clinker is possible

• Increased alkali, chlorine and sulphur attack

• High abrasion by clinker • Alkali attack • High thermal load • Redox load • Mechanical load due to ovality in tire area

• Thermal shock • Redox load • Mechanical load due to ovality in tire area

Critical areas in stationary and rotating units of a modern cement kiln thermal load thermal shock clinker infiltration salt infiltration redox mechanical stress ring formation

7 3 10

4 6 5 3 4

• Cyclone • Calciner • Inlet housing

2 5 5

• Safety zone • Upper transition zone

3 2 5

6

4 2 3

9

• Main burning zone

3

2

• Lower transition zone • Kiln outlet • Nose ring

7

• Cooler side walls • bull nose • Kiln hood

Refractory life time determining aspects • Chemical aspects Composition of raw material Composition of fuel • Thermal aspects Thermal shock Specific heat load • Mechanical aspects Ovality Kiln alignment

Chemical aspects by feed and fuel: variations in cement raw material production of different cement types frequent change of fuel or alternative fuels use of high ash, high sulfur coal disturbance of the SO3/ (K2O+Na2O) equilibrium by the kiln atmosphere: change between reducing and oxidizing conditions condensation or deposition of volatile components in the brick lining

Secondary phases introduced by alternative fuels and raw mixes

S03 / SO2

Cl H2O Cl

O2

Na2O Na2O K2O

S03 / SO2

Secondary phases entering the kiln firing unit by alternative fuels and or raw mixes

K2 O

Tools

Tools – determining chemical conditions cement moduli cement modulus

typical values

statement

Lime standards (KSt III)

85-95 95-100

content of CaO, which can technically be bond to SiO2, Al2O3 and Fe2O3

Hydraulic Modulus (HM)

1.7 – 2.3

ratio of CaO to the hydraulic factors SiO2, Al2O3 and Fe2O3

Silica Ratio (SR)

1.9 – 3.2 (opt.: 2.2 – 2.6 !)

characterizes the ratio solid/liquid, i.e. the amount of liquid phases in the clinker

Alumina Ratio (AR)

1.5 – 2.5 (possibly: < 1.5; >2.5)

characterizes the composition of the melt and ist viscosity

Alkali-Sulphate-Ratio (ASR)

0.8 – 1.2

characterizes the ratio alkali versus sulphate

(Portland cement) (high-grade cem.)

Tools – determining chemical conditions cement moduli cement modulus

formula

Lime standards (KSt III)

KSZ III =

Hydraulic Modulus (HM)

HM =

CaO SiO2+Al2O3+Fe2O3

Silica Ratio (SR)

SR =

SiO2 Al2O3+Fe2O3

Alumina Ratio (AR)

AR =

Al2O3 Fe2O3

Alkali-Sulphate-Ratio (ASR)

Na 2 O + K 2 O - Cl 94 71 ASR = 62 SO 3 80

100 (CaO+0,75 MgO) 2,8SiO2+1,18Al2O3+0,65Fe2O3

Silica modulus versus content of liquid phases at 1450°C

Liquid phase at 1450 °C in % by weight

AM =

Al2O3 = 2.2 Fe 2O3

Lime standard = 96

35

30

25

20

15 1,5

2

2,5

SM =

3

SiO2 Al2O3 + Fe 2O3

3,5

4

Coating

Coating – liquid phase

20 %

28 %

Liquid phase

Calculation of the Alkali-Sulphate-Ratio (ASR) in Cement Clinker Na 2O K2O Cl + − Alkali / Chlorides ASR ASR = = 62 SO94 71 Sulphates 3 80

<1

1.0

>1

KCl / NaCl + K2SO4 / Na2SO4 + SO3 free

KCl / NaCl + K2SO4 / Na2SO4

KCl / NaCl + K2SO4 / Na2SO4 + K2O free / Na2Ofree

ASR < 1 ASR > 1 ASR = 1

ASR < 1

Corrosion, surplus of sulphur in kiln atmosphere

Corrosion reduces the refractoriness and the structural flexibility 2C2S + MgO + SO3

CaSO4 + C3MS

C3MS2 + MgO + SO3

CaSO4 + 2CMS

CMS + MgO + SO3

CaSO4 + M2S

ASR < 1 ASR > 1 ASR = 1

Corrosion of basic Mg-Chrome bricks ASR > 1

Na2, K2 (CrO4)

Na2, K2 (CrO4) MgCr2O4 III MgCr2O4 + Na, K

VI Na2, K2 (CrO4)

Deposit of alkali-chromate

ASR > 1

Corrosion of chrome ore

Alkali attack on alumina bricks and concretes unaffected microstructure

destruction of grains

Formation of new minerals i.e. feldspar, leucite, calsilite Volume expansion of up to 30% causes: “alkali-bursting”

Al2O3 + K2O + SiO2 3Al2O32SiO2 + 3K2O + 4 SiO2

K2O Al2O 32 SiO2 + ( 2,5 % Vol ) 3K2OAl2O32SiO2 + ( 29 % Vol )

Reaction path / formation of salt compounds affinities salts

formula

NaCl, KCl

I.

Na,K

+

Cl2

II.

Na,K

+

SO3 SO2

K2SO4 Na2SO4 double salts

III.

Na,K

+

CO

K2CO3 Na2CO3

IV.

SO3 SO2

+

CaO

CaSO4

Build - up Problems

Sulphur Reactions in the Calcining Zone – Ring Formation

50 40

adhesion strength of alkali-sulphate melt in kp/cm²

30 20 10 800

1000

1200

1400 Temperature °C

adhesion strength of clogging on refractory lining

ASR < 1 ASR > 1 ASR = 1

• Bulk density

ρ

g/cm³

• Apparent porosity

Φ

%

• Cold chrushing strength σ N/mm² • Thermal expansion

α

lin. %

• Thermal conductivity

λ

W/mK

• Elasticity

E

N/mm²

Physical Properties

ρ1 , %1 , N/m²1 , lin. % 1 , W/mK 1 ρ2 , %2 , N/m²2 , lin. % 2 , W/mK 2

ρ3 , %3 , N/m²3 , lin. % 3 , W/mK 3

Infiltration of alkali/sulphate melts

Salt infiltration, mechanical load

AR

0.4

1.6

2.0

2.4

2.8

SR

1.4

2.2

2.4

2.6

3.8

HM

1.4

1.7

2.0

2.3

2.6

ASR

0.6

0.8

1.0

1.2

1.4

LSF

85

90

94

98

103

LP

19

22

25

28

31

Acceptable Range

AR = Alumina Ratio SR = Silica Ratio

Favourable Range

HM = Hydraulic Modul ASR = Alkali-Sulphate-Ratio

The favourable Ranges of Modules

Acceptable Range

LSF = Lime Saturation Factor LP = Liquid Phase

Cement Clinker

Plant A

Plant B

Plant C

SiO2 Fe2O3 Al2O3 CaO MgO K2O Na2O SO3 Cl

20.33 3.03 5.05 65.14 4.07 0.26 0.38 1.49 0.02

22.34 3.44 5.01 67.20 0.83 0.54 0.24 0.34 0.20

22.68 5.65 4.33 63.07 1.34 0.27 0.31 1.04 0.00

AR SR ASR

1.64 2.50 0.33

1.45 2.65 1.40

0.72 2.27 0.61

K2O+Na2O free SO3 free LP

0,00 1,00 27,00

0,37 0,00 25,10

0,00 0,41 29,10

Caution:

sulphate surplus spurrite clogging PX 83, AG 85 AG AF

alkali surplus corrosion of Mg.Cr. FM 90, AG 85, RG AF, TG AF

Clinker analysis reports

sulphate surplus aggressive LP chem. therm. attack , MN , AG AF

ASR in rotary kiln

ASR clinker

ASR raw mix

Thermal aspects • Flame shape • Overheating • Secondary or incomplete combustion • By temp. changes: - loss of coating - interruptions of production • By changes in burner control - variation in dosing, particle size • Fuel inhomogenities • Flame momentum, pulsation • Burner position

Burning zone heat input net burning zone cross section

Max. thermal burning zone load: 5.8 x 106 kcal/m2h

max. specific burning zone load

Concave melting pits due to overheating

1. SP preheater system: Plant production:

1000 tpd 41tph

Heat consumptionn

800 kcal/kg clinker

Kiln diameter

3,8 m inside shell

Brick thickness Cross section:

200 mm ( 3,4/2 )2 x π = 9,07 m2

Heat load: Specific Heat load:

41000 kg x 800 kcal = 33 x 106 kcal h 33 x 10 6 / 9,07 = 3,66 x 106 kcal / m2 h

2. SP preheater system: Plant production:

3000 tpd 125 tph

Heat consumption

800 kcal/kg clinker

Kiln diameter

5,4 m inside shell

Brick thickness Cross section:

250 mm ( 4,9/2 )2 x π = 18,85 m2

Heat load: Specific Heat load:

125000 kg x 800 kcal = 100 x 106 kcal h 100 x 10 6 / 18,85 = 5,3 x 106 kcal / m2 h

KRONEX 85 high alumina

2 - 3 G cal./m2 h

PERILEX 83 magnesia-chromite

3 - 4 G cal./m2 h

ALMAG 85 magnesia-spinel

4 - 5 G cal./m2 h

ALMAG AF premium spinel

> 5 G cal / m2 h

MAGNUM

> 6 G cal./m2 h

premium magnesia

Limiting specific heat load for refractory material

2000 °C Δ 600 °C

1450 °C

Temperatures in kiln cross section of unstable coating area

Heating up in 8 hours up to 1000°C

1. Control your chemical parameters

2. Observe your specific heat load 3. Control your mechanical conditions

Essential control steps for optimal kiln operation