Clinker Manufacture - Clinker Formation .docx

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Clinker Manufacture Formation of

Clinker

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Kiln

April 5, 2013

Clinker ManufactureFormation of Clinker- By Mark from

Linkedin

please concentrate with me , this lecture is easy if you concentrate

the lectures for advanced Engineers and beginners and students

fi rst I wi ll give you small in troduction , then we wil l talk about the reaction dur ing cli nker

formation

then we wil l talk about the reaction mechanism , and the kinetics of cli nker burning

then we will talk about the thermo dynamics of cli nker formation

1.I ntroduction

2.Reaction Pathways Encountered Dur ing Clinker F ormation

Basic Sequence of Reactions

Mineralogical and Chemical Characteri stics of Raw M ixes

I ntermediate Products

L iqui d Phase

The Overall Reaction Sequence

3.Reaction M echanisms

4.Kinetics of Cli nker Burning

Practical Considerations

Assessment of Raw Meal Burnabi li ty

5.Thermodynamics of Cl inker Formation

==================================================================

=====================================================

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Introduction:

Why study clinker burning?

To understand the influence of changes in kiln operation

conditions

Normal ki ln operation

I nf luence of chemistry, f ineness, mineralogy changes

I nf luence of new mix components (pozzolan, AFR, sand,

etc.)

Abnormal ki ln operation

know causes of badly burnt clinker

understand why r ings and deposits form

be able to suggest counter measures

Synthetic Hydraulic Minerals

Analogy to transformation of igneous and sedimentary rocks

into metamorphic rocks

Difference in T, p, t

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=========================================================

==================================

Two principal steps during transformation into clinker

Disintegration of original structure

Mechanical crushing and grinding

Thermal decomposition

Structural rearrangement on heating (e.g. polymorphism

Formation of new structures

Occurrence of intermediate products

Genesis and growth of final clinker minerals

Crystallization of liquid phase

=========================================================

============================

Features characterising the clinker formation process

-Complex system (series of diverse mechanisms)!

-Requires mechanical, thermal and electrical energy

-Reaction rate is slow (necessity of high temperatures, finely dispersed material)

-Clinker minerals are not stable at normal temperature!

-Quality of product is determined by:

Clinker chemistry

Clinker microstructure

====================================================================================

Control of burning process

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Material technological aspects

-Raw meal burning behaviour

Burnability

Dust formation

Coating behaviour

Granulation of clinker

etc.

-Quantity and properties of liquid phase

Process technological aspects

-Temperature profile

-Kiln atmosphere

-Fuel type

-Flame characteristics

===================================================================================

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Reaction pathway

indicates the intermediate products occurring between reactants and products

Reaction mechanism

type(s) and reaction(s) taking place

Reaction kinetics

indicates rate at which the final products are produced

Reaction thermodynamics dictates whether reaction will be at all possible, and what the heat

and

temperature requirements will be

===================================================================

=====================================================

Now to my linkedin colleges I fi nished the fi rst part of my lecture if you have

any question contact me here or in my linkedin account

Or contact me by Email :[email protected]

========================================================

=========================================

Reaction Pathways Encountered During Clinker Formation

Basic Sequence of Reactions

Mineralogical and Chemical Characteristics of Raw Mixes

Intermediate Products

Liquid Phase

The Overall Reaction Sequence

To fully describe the pathway of clinkering, it is necessary to consider the following

aspects:

-the chemical and mineralogical content of the raw mix

-the overall sequence of reactions

-the chemical and mineralogical nature of the intermediate products

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Heating (C)

20100 Evaporation of H2O

100300 Loss of physically adsorbed water

400900 Removal of structural H2O (H2O and OH groups) from clay minerals

>500 Structural changes in silicate minerals

600900 Dissociation of carbonates

>800 Formation of belite, intermediate products, aluminate and ferrite

>1250 Formation of liquid phase (aluminate and ferrite melt)

~1450 Completion of reaction and re-crystallization of alite and belite

Cooling (C)

13001240Crystallization of liquid phase into mainly aluminate and ferrite

===================================================================

=========================================================

Mineralogical characteristics of raw mixes

Carbonates

calcite CaCO3, dolomite CaCO3 MgCO3, ankerite CaCO3 (Mg,Fe)CO3 magnesite MgCO3,

siderite FeCO3

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Simple Oxides

quartz SiO2, hematite Fe2O3, magnetite Fe3O4

Feldspars

potassium feldspars (Na,K)Si3O8 and

plagioclase series (Na,Ca)(Si,Al)Al2Si2O8

Sheet si l icates

minerals of the mica and chlorite groups

(e.g. biotite, muscovite, chlorite),

clay minerals (e.g. kaolinite, montomorillonite, illite, palygorskite)

Hydroxides

Al-hydroxides (e.g. boehmite),

Fe-hydroxides (e.g. goethite, limonite)

Sul fi des / sulf ates

pyrites FeS2, anhydrite CaSO4, gypsum CaSO4H2O

Fluorides

fluorspar CaF2

===================================================================

=========================

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===================================================================

==========================

Intermediate products encountered during clinker production

Type Mineral Name Formula

Simple Sulfates anhydrite CaSO4

arcanite K2SO4

Compound Sulfates sulfate-spurrite 2(C2S) Ca SO4

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calcium-langbeinite K2Ca2 (SO4)3

Compound Carbonates spurrite 2(C2S) CaCO3

Simple Chlorides sylvite KCl

Calcium Aluminates mayenite 12 CaO 7 Al2O3CaO Al2O3

Calcium Ferrites 2 CaO Fe2O3

Calcium Alumino-Silicates gehlenite 2 CaO Al2O3 SiO2

=========================================================================================================================================

Reasons for the formation of intermediate products

-Intermediate products are preferentially formed by kinetically faster reaction rates

-Intermediate products are the reaction products of localised zones in the meal charge,

i.e. local equilibrium but not overall equilibrium was reached (e.g. gehlenite formation)

-Intermediate products are really the equilibrium products at the given temperature and gas

atmosphere,

but not at the final clinkering temperature (e.g. spurrite formation)

=======================================================================================================

Liquid Phase

basically created by early melting compounds such as Fe2O3 and Al2O3 and some minor

compounds such as MgO and Alkalis

The compositi on of the raw mix determines

-temperature at which liquid will first be formed

-amount of liquid formed at any given temperature

-the physical properties of the liquid at any particular temperature, especially its viscosity

-Although most raw mixes show about the same minimum temperature of liquid formation

(eutectic point),

the quantity of liquid formed at this and progressively higher temperatures varies according tothe raw mix chemistry.

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-In the Portland cement relevant parts of the system C SAF, in which melting begins at

1338 C, the composition of the liquid is:

CaO - 55 %

SiO2 - 6 % Alumina ratio

Al2O3 - 23 % (AR) = 1.38

Fe2O3 - 16 %

Quantity calculation formulae acc. to LEA, considering different temperature:

1338 oC = 6.1 Fe2O3 + MgO + Na2O + K2O if AR 1.38

8.2 Al2O35.22 Fe2O3 + MgO + Na2O + K2O if AR1.38

1400oC = 2.95 Al2O3 + 2.2 Fe2O3 + MgO + Na2O + K2O for MgO 2 %

1450 oC = 3.0 Al2O3 + 2.25 Fe2O3 + MgO + Na2O + K2O for MgO 2 %

Quanti tative change of l iqu id phase with temperatu re in several group plants (in fl uence of

MgO, Na2O and K2O included)

I nf luence of Al2O3 and Fe2O3 alone on the quanti ty of li quid formed at 1338 C.

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The most effective use of A l2O3 and Fe2O3with respect to l iquid formation at 1338 C

occur s when the two are used in the weight ratio of 1.38

Viscosity of l iquid phase

-The viscosity of the liquid phase diminishes exponentially with increasing temperature and at

1400 C is reduced by addition of fluxing components in the following order:

Na2O < CaO < MgO < Fe2O3 < MnO

-With increasing SiO2 content of the melt and to a lesser extent with increasing Al2O3,

appreciable increases in viscosity occur.

======================================================================================================================================

=====

The overall reaction sequence, displayed based on qualitative change of minerals from

samples taken from an operational kiln

Minerals identified at different locations (long wet kiln)

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Sequence of compound formation according to chemical compositi on

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==================================================================

==================================================================

==============

Now to my li nkedin coll eges I finished the second part of my lecture if you

have any question contact me here or in my linkedin account

Or contact me by Email :[email protected]

========================================================

========================================================

=====

Reaction Mechanisms

Definitions

State of matter

solid: definitive volume and definite shape

liquid: definitive volume, assumes shape of container

gaseous: neither definitive volume nor definite shape

Classification of reactions

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1. according to their type:

structural change high quartz low quartz

decomposition CaCO3 CaO + CO2

combination 2CaO + SiO2 C2S

2. according to the state of matter:

solidsolid quartz and free CaO belite

solidliquid liquid phase crystallisation of aluminate + ferrite

solidgas CaCO3 CaO + CO2

liquidliquid -

liquidgas drying process, volatilisation of alkalis

gasgas CO + 1/2 O2 CO2

3. according to rate controlling step (kinetics of reaction)

diffusion formation of alite

phase boundary quartz + free CaO belite (initial reaction)

nucleation liquid phase crystallisation of aluminate + ferrite; alite formation

Examples

Structural changes: Arrangement of the atoms in low and high quartz

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Structural changes: CalciteAragonite transition

Decomposition reactions (during clinker production)

-solid / gas type

De-hydroxylation of the clay minerals (kaolinite, etc.)

De-carbonation of the carbonate minerals (magnesite, dolomite, calcite, spurrite)

-solid / solid type

decomposition of alite

Characteristic of this reaction type is that the single reactant is transformed into two products.

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===================================================================

===================================================================

===

Decomposition reaction: Equilibrium dissociation pressure of calcite and spurrite with

temperature

Decomposition reaction: Decomposition of C3S at 1175 C

In the case of impure C3S, i.e. clinker alite, the rate of decomposition is appreciablyaccelerated by:

the presence of lime and C2S nuclei the presence of Fe2+ , H2O and K2SO4 / CaSO4 melts

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Combination reaction: Formation of Belite

Belite formation is the result of a combination between the calcite and silica components of

the raw mix.

The rate limiting mechanism by which belite is formed (after an initial phase boundary

controlled reaction) depends on the diffusion of ions through the solid state.

The rate of this reaction is thus dependent on:

the path distance that the diffusing species have to travel

defects in the reactants crystal lattices.

Combination reaction: Formation of Alite

Formation of alite only at T > 1250 C (lower stability limit). At that temperature, the liquid

phase is also starting to form: The formation of alite is a liquidsolid reaction

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The formation of alite and its stabilisation depends on the presence of the liquid phase.

The rate of reaction is dependent on:

the path distance that the diffusing species have to travel

quantity and viscosity of liquid phase

==================================================================================================================================================

Now to my linkedin colleges I f in ished the thi rd part of my lecture if youhave any question contact me here or in my linkedin account

Or contact me by Email :[email protected] ====================================================

====================================================

=============

4. Kinetics of Clinker Burning

Theoretical consequences:

Rate increases with higher temperature (but also costs!)

Rate decreases with higher activation energy (different raw mix mineralogy)

Rate increases with higher frequency factor (larger contact surface, i.e. finer mix)

The rate of reaction

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increases with temperature and contact surface between raw mix components(frequency factor A)

decreases with higher activation energy Ea for raw mix components.To compensate for the slow reactivity of the less reactive minerals, a higher burning

temperature and / or longer burning period (longer clinkering zone) is required.

Practical considerations:

development of suspension preheater

In practice, the most convenient method of following the reaction is by measuring therate of decrease of non-combined lime (i.e. free lime).

This technique is illustrated in the following figures that show two raw mixes, I and II,ofidentical chemistry (LS = 95, SR = 3.2 and AR = 2.2) and similar fineness (R200m

= 0.5 %, R90m = 7 % and R60m = 15 %).

It is evident that the difference in mineralogy and actual particle size of theindividual crystals influence both the mechanism and rate of reaction, especially at

start of the clinker formation.

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Limestone

Calcite 97 %

Dolomite ~ 2 %

Quartz traces

Chlorite -

Illite and Micas -

Pyrite traces

Feldspars -

Shale A

Calcite ~ 40 %

Dolomite -

Quartz ~ 25 %

Chlorite ~ 20 %

Illite and Micas ~ 10 %

Pyrite ~ 2 %

Feldspars ~ 2 %

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Shale S

Calcite ~ 10 %

Dolomite -

Quartz ~ 55 %

Chlorite ~ 10 %

Illite and Micas ~ 20 %

Pyrite traces

Feldspars traces

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==================================================================

==================================================================

===========

Assessment of Raw Meal Burnabi li ty

In practice, simple methods are mostly applied to asses the burnability of a mix, i.e. the ease

of formation of the clinker minerals. Three distinct methods are practiced at HGRS:

Statistical burning modelin which ten material parameters influence the rate of clinker

formation. The non-combined CaO value, of any raw mix, relative to that of a standard raw

mix is calculated.

Physicochemical burning modelrequires no standard raw mix. Only 4 parameters need to be

considered.

===================================================================

===================================================================

===========

Statistical Burnability Model

Quantitative evaluation of the data obtained by the Mark burnability testo The 1350, 1400 and 1450 free lime values of other raw mixes from the same

raw material components can be determined based on one single burnability

test of one mix

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o Chemical Parameters: lime saturation, silica ratio, alumina ratio, K2O +Na2O, MgO

o Physical Parameters: residue on 200 m and 90 m sieves, quantity of mica,quartz and iron minerals

NOTE : The burnability model can be used as an instrument for optimization of raw mixes

===================================================================

===================================================================

==============

Physiochemical Burnability Model

the amount of uncombined lime depends ono Specific reaction area (area of contact between grains)o Local oversaturation (grain size of individual minerals)o Ambient conditions (pressure, temperature, burning time)o Diffusion coefficient of CaO through the liquid phase (composition of the

liquid phase)

o Amount of liquid phase formed during burningo Supply and demand of CaO

all these influencing factors may be incorporated in four parameters: SR, LS, amountof oversized quartz grains, amount of oversized calcite grains.

(Pressure, temperature and burning time are considered to be constant.)

Silica ratio (SR) and lime saturation (LS) The formation of C3S from C2S and CaO is governed by the diffusion of CaO through

the melt. The silica modules and lime saturation are sufficient to describe this

chemical reaction quantitatively.

The amount of CaO which can be accommodated within the liquid phase and in whichit can diffuse and thus react, is inversely proportional to the silica ratio. A linear

relationship exists between max. lime saturation and silica ratio values at which no

free lime can be observed.

Quartz and calcite grains Whether a grain of material reacts fully under given burning conditions depends on its

diameter, structure and chemical composition.

Too large calcite grains result in CaO not being completely combined as also resultsfrom grains whose lime saturation is over 100 %.

For the Holderbank burnability test conditions the following grain diameters werefound to be critical limits:

o quartz 32 mcalcite 90 m

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==================================================================================================================================================

Now to my li nkedin colleges I f in ished the Fourth part of my lecture ifyou have any question contact me here or in my l inkedin account

Or contact me by Email :[email protected] ====================================================

====================================================

=============

Thermodynamics of Clinker Formation

During clinker production, heat is both absorbed (endothermic heat changes) and produced

(exothermic heat changes)

Temp. (C) Type of Reaction Heat Change

20100 Evaporation of free H2 O Endothermic

100300 Loss of physically adsorbed H2O Endothermic

400900 Removal of structural H2O (H2O, OH groups from

clay minerals) Endothermic

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600900 Dissociation of CO2 from carbonate Endothermic

> 800 Formation of intermediate products, belite, aluminate and ferrite Exothermic

> 1250 Formation of liquid phase (aluminate and ferrite melt) EndothermicFormation

of alite Exothermic

13001240 Crystallization of liquid phase into mainly (cooling cycle) aluminate and

ferrite Exothermic

Examples forexothermic reactions (heat liberated)o Coal (C) + O2 CO2o Lime (CaO) + H2O Ca(OH)2o Cement + H2O Cement Hydrateso Liquid K2SO4 Solid K2SO4

Examples forendothermic reactions (heat absorbed)o H2O (liquid) H2O (steam)o CaCO3 CaO + CO2

===================================================================

===================================================================

=====================

DTA curves of typical cement raw meals

The greatest heat requirement occurs between 850900 C, i.e. for the decomposition

of the carbonate minerals.The total heat requirements for dehydration, decarbonisationand melting exceed the heat liberated by the formation of belite and the intermediate

and final products.

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Endothermic processes kJ/kg clinker

dehydration of clays 170

decarbonisation of calcite 1990

heat of melting 105

heating of raw materials 01450 C 2050

Total endothermic 4315

Exothermic processes kJ/kg clinker

crystallization of dehydrated clay -40

heat of formation of clinker minerals -420

crystallization of melt -105

cooling of clinker -1400

cooling of CO2 (ex calcite) -500

cooling of H2O (ex clays) -85

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Total exothermic -2550

Net theoretical heat of clinker formation + 1765

=============================================================

=====================================================

Heat balance of wet and dry kiln, kJ/kg clinker

( HFW Taylor: Cement Chemistry, 1998 )

Dry kiln Wet kiln

Evaporation of H2O 13 (0.4%) 2,364 (41.5%)

Heat of reaction 1,807 (54.6%) 1,741 (30.5%)

Heat losses through 711 (21.5%) 812 (12.3%)

gas, clinker, dust, etc.

Heat lost in air from cooler 427 (13.0%) 100 (1.7%)

Heat losses by radiation 348 (10.5%) 682 (12.0%)

and convection

3,306 kJ/kg 5,699 kJ/kg

======================================================================================================================

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NOW I am finished , I hope you understood

everything

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Related posts:

1. Raw Mix Optimization2. Production of fused corundum refractories3.

Burners and FlamesFLS , Pillard , KHD , Calculation of Burner Momentum4. Refractory performance indicators

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