02 cement production2011 - SGTK · clinker: around 1.0 ... At 1450°C and above the liquid content depends on the silica modulus Klinker production 15 20 25 30 ... 02_cement_production2011

Technical Mineralogy Department of Geosciences

Technische Mineralogie ETHZ IMP 2010



Alite

Ca3SiO5 = C3S

Polymorphic transformations: T1 T2 T3 M1 M2 M3 R T: triclinic M: monoclinic R: rhombohedral

620°C 920°C 980°C 990°C 1060°C 1070°C

Max. concentration of impurities: 1.0 wt% Al2O3, 1.2% Fe2O3, 1.5 % MgO impurities stabilize the M1 and or M3 in klinkers, rarely T2 is found

orthosilicate 0.71nm!

R- C3S projected along the c-axis

SiO4

Ca

O

Klinker production




Belite

Ca2SiO4 = C2S

Polymorphic transformations: O1(g) M1(b) M2(aL ’) O2(aH’) H1(a) O: orthorhombic M: monoclinic H: hexagonal

<500°C 630°C 1160°C 1425°

Max. concentration of impurities: 4.0-6.0wt% Al2O3+ Fe2O3 impurities stabilize the b-phase

orthosilicate

0.55nm!a - C2S proj. down c-axis

Klinker production




Aluminates and ferrites

Ca3Al2O6 = C3A (cubic) impurities: up to 4wt% NaO up to 16% Fe2O3+ SiO2 imputirities stabilize an orthorhombic polymorph

Ca2AlxFe1-xO10 = C4AF xclinker: around 1.0

impurities: up to 10 wt% MgO +TiO2 + SiO2

Klinker production




Polymorphs and composition of phases present in clinker

C3A polymorphs is coupled with substitution. Clinker aluminate phases are cubic (fine grained) or orthorhombic (lath shapedand twinned) 13% to 20% of substituting elements: Mg, Al, Fe, Si

C3S early crystallized small crystals rich in substitutes: M3 late crystallized large crystals: M2 (single twins), rarely T1 (polysynthetic twins) 3-4% of substituting elements, mainly Mg, Al and Fe!

C2S usually only in the M1(b) polymorph with parallel twin lamellae. M2(aL ’) has typical crossed twin lamellae. The transformation M2(b) !M(g) should be avoided, because the accompanying drastic volume increase leads to excessive dusting. 4-6% of substituing elements, mainly Al and Fe

C3AF Main exchange vector Fe-2 SiMg !

Klinker production




Microstructures

Alite crystals with both single and polysynthetic twins !

Klinker production

Belite crystals with complex twin lamellae (M2(aL ’) polymorph)

Belite crystals with paralllel twin lamellae (M(b) polymorph)

Belite crystals with crack formation along lamellae boundaries (M(b) !(M(b) transf.)




Rotary kiln Without preheater/precalciner the kiln aspect ratio is about 30

Klinker production




Rotary kiln with precalciner unit

Klinker production




énergie



Klinker reactions below 1300°C

Decomposition of calcite (calcining): 500 - 900°C free lime (CaO)

Decomposition of phyllosilicates: 300 - 900°C dehydroxilated, amorphous material

Temp. range products

Formation of first clinker phases: > 800°C belite, aluminates (different phases), ferrites

Formation of first melt phases: > 1000°C

Drying 100°C free water evaporates 100 - 300°C release of adsorbed and crystal water

Klinker production




Decomposition of carbonate phases I

Decomposition reaction: CaCO3 = CaO + CO2

K =CaO[ ] CO2[ ]CaCO3[ ]

= pCO2

Equilibrium constant

Rate of decarbonation is influenced by:

- gas temperature (heat transfer)

- material temperature (=> K)!

- external partial pressure of CO2

- size and purity of the calcite particles

Klinker production

Calcite decomposition temperature as function of CO2 partial pressure

0.0

0.25

0.5

0.75

1.0

750 800 850 900

890!C

T(!C)

P(CO2)




Belite formation

1. Formation of belite through solid state reaction

quartz amorphous material

belite

2. Transformation of the belite shells to belite crystal clusters

lime

Klinker production




Klinker reactions between 1300°C and 1450°C

1. Melting reactions - Melting of primary aluminates and ferrites phases - Melting of part of the early formed belite

2. Formation of new phases Reaction of melt, free lime, unreacted silica and remaining belite to alite

3. Polymorphic transformation of belite

4. Recrystallization of alite and belite

5. Nodulization (clinkering)

Klinker production




Appearance of first melt

1. Alkali and sulfate melts

Klinker production


2. C-S-A for cement compositionmelts: lowest eutecticum 1455°



P: typical bulk composition of Portland cement klinkers First melt appearance: 1455°C

Phase diagram

Klinker production


see excercise 2



Klinker production


CaO - SiO2 - Al2O3 phase diagram: section at 1500°C

A typical Portland cement composition at 1500° C (section shown on the right) is in a three phase field i.e. with alite, belite and an aluminium rich melt. The grey shaded areas are two phase fields



Amount of melt and the silica module

At 1450°C and above the liquid content depends on the silica modulus

Klinker production

15

20

25

30

35

1.5 2.0 2.5 3.0 SM

Liqu

id p

hase

(wt

%)

3.5




Formation and recrystallization of alite

amorphous material

lime

belite

alite

1. Formation of melt around lime crystals

2. Crystallization of alite walls at the contacts between belite cluster and lime

3. Recrystallized and new formed alite replaces lime crystals

Klinker production




Klinker production




Microtextures I (all pictures FL Smidth review 25)

0.05mm!

Alite wall separating CaO and a belite cluster

alite melt phase (aluminates,ferrites) belite lime

Belite clusters replacing previous quartz grains.

0.1mm!

Klinker production




Alite crystallizing at the expense of lime and belite

0.3mm!

Microtextures II

lime belite

alite

Well crystallized, homogeneous clinker. The raw mix contained few quartz grains and a well controlled carbonate grain size.

pores

0.2mm!

Klinker production




Klinker reactions during cooling

1. Crystallization of the restitic melt. Products: aluminates (C3A) and ferrites (C4AF)

2. Polymorphic transformations of alite and belite

3. Backreaction of alite to belite + lime

4. Recrystallization aluminates and ferrites

If cooling is too slow

Klinker production




Microtextures III

Backreaction of alite rims to belite plus lime in a belite poor clinker (fast cooling).

0.04mm!

belite rims

Klinker production


Fast cooled clinker with euhedral alite and rounded belite crystals.

0.05mm!



CU500898 0305.raw:1

6564636261605958575655545352515049484746454443424140393837363534333231302928272625242322212019181716151413121110

1'600

1'500

1'400

1'300

1'200

1'1001'000

900

800

700

600

500

400

300200

100

0

-100

-200

-300

-400

-500

C2S beta (MUMME) 22.64 %C3S monoclinic (NISHI) 55.50 %C4AF 4.13 %Periclase 3.76 %Lime 0.54 %C3A cubic 12.59 %Arcanite K2SO4 0.84 %

Klinker production


Quantitative determination of the klinker mineralogy

X-ray powder diffraction patterns are used for the quantitative determination of the klinker mineralogy. The technique, which allows to extract the quantity of each phase present is called Rietveld refinement.



Normative mineralogy of clinker

Klinker production




Energy balance in clinker production

Temp range 20-450°C wet 100°C ca. 450°C 450-900°C ca. 900°C ca. 900°C 900-1400°C 900-1400°C ca. 1300°C 1400-20°C 900-20°C 450-20°C !

Process Heating of the material Evaporation of free H2O Removal of H2O from clay heating of the material Dissociation of calcite Crystallisation of dehydrated clay Heating of the decarbonated material Heat of formation of clinker minerals Melting of liquid phases Cooling of clinker Cooling of CO2 Cooling of H2O Total

Heat exchange kJ/kg clinker 710 (1800) 170 820 2000 -40 525

-420 100

-1510 -500

-85 4325 -2555 !

Klinker production



Energy costs of cement production

Process Quarry Crushers Prehomoginizing and transport Raw mill Raw meal silo Kiln feeder Kiln and cooler Coal mill Cement mill Packing plant Other total

Fuel Electricity Cost($/day) kcal/kg cement kwh/ton cement

0 0 2.5 600

1.5 360 0-100 27.0 9813 1.5 360 1.5 360 700 23.0 28853

2.5 600 30.0 7200

1.0 240 4.5 1080 700-800 95.0 49467 !

Klinker production

Dry process cement plant 5000t/day

Documents

02 cement production2011 - SGTK · clinker: around 1.0 ... At 1450°C and above the liquid content depends on the silica modulus Klinker production 15 20 25 30 ... 02_cement_production2011