1.6 mineralisation

7/27/2019 1.6 Mineralisation

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CemNet Training - Course CKPC01 Module 1 Session

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1.6 Mineralisation.

Cement Kiln

ProcessChemistryModule 1. Cement kiln energy efficiency and

productivity.

Cement Kiln Chemistry 1.6 Mineralisation

In the preceding session we discussed the equilibrium of thecombination reaction between C2S and CaO to form C3S.

No C3S will be formed until the temperature rises above1250C as the equilibrium of the reaction:

C2S + CaO C3S

..is predominantly to the left.

..with the formation of a liquid phase significantly

increasing the rate of reaction to form C3S

Above 1250C the equilibrium shifts to the right to favour the

formation of C3S.

C2S + CaO C3S

how can that be explained?

Cement Kiln Chemistry

In the preceding session we discussed the equilibrium of the

combination reaction between C2S and CaO to form C3S.

No C3S will be formed until the temperature rises above1250C as the equilibrium of the reaction:

C2S + CaO C

3S

..is predominantly to the left.

Above 1250C the equilibrium shifts to the right to favour theformation of C3S.

C2S + CaO C3S

The explanation relies on consideration of free energies andchemical potentials of the reactants and products at different

temperatures.

1.6 Mineralisation


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...and C3S unstable.




CaO and C2S are stable...

1.6 Mineralisation

Below 1250C the Gibbs

free energy (chemicalpotential) of C3S is higherthan free CaO or C2S andtherefore C3S will not be

formed from an intimatemixture of CaO and C2S

because it is unstable.CaO C3S C2S

Increasing SiO2

content

Gibbs

Free Energy

C2S + CaO C3S

The equilibrium lies to the left.



1.6 Mineralisation

Above 1250C the Gibbsfree energy (chemical

potential) of C3S is lowerthan free CaO or C2S and

therefore C3S is the moststable compound and will beformed.

CaO C3S C2S

Increasing SiO2 content

Gibbs

Free Energy




Dependent on the SiO2content either CaO and C3S

are stable...

1.6 Mineralisation

Above 1250C the Gibbsfree energy (chemical

potential) of C3S is lower

than free CaO or C2S andtherefore C3S is the most

stable compound and will beformed.

CaO C3S C2S


Gibbs

Free Energy

...or C3S andC2S are stable.

C2S + CaO C3S

The equilibrium lies to the right.


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Dependent on the SiO2content either CaO and C3Sare stable...

1.6 Mineralisation

Above 1250C the Gibbs

free energy (chemicalpotential) of C3S is lowerthan free CaO or C2S andtherefore C3S is the most

stable compound and will beformed.

CaO C3S C2S

Increasing SiO2

content

Gibbs

Free Energy

...or C3S andC2S are stable.

C2S + CaO C3S

C3S will be formed because it is the most stable.



1.6 Mineralisation

Returning to the chemicalpotentials below 1250C.

CaO C3S C2S


Gibbs

Free Energy

.the free energy of anycompound can be reduced byincorporation of minorsubstitutions or impurities.

Most common impurities,

Na2O, K2O, SO3, Al2O3,are incorporated in the

belite, C2S.. ..freeenergy of the C2S is

reduced.




1.6 Mineralisation


CaO C3S C2S


Gibbs

Free Energy

.the free energy of any

compound can be reduced byincorporation of minorsubstitutions or impurities.

Most common impurities,Na2O, K2O, SO3, Al2O3,are incorporated in the

belite, C2S.. ..free

energy of the C2S isreduced. .C2S is stabilised and formation of

C3S becomes more difficult.


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1.6 Mineralisation

Returning to the chemical

potentials below 1250C.

CaO C3S C2S

Increasing SiO2

content

Gibbs

Free Energy


Most common impurities,

Na2O, K2O, SO3, Al2O3,are incorporated in the

belite, C2S.. ..freeenergy of the C2S isreduced. .Na2O, K2O, SO3 and Al2O3 inhibit

the formation of C3S.



1.6 Mineralisation


CaO C3S C2S


Gibbs

Free Energy


Fluorides are an important

exception to the rule thatimpurities are

preferentially incorporatedin C2S, belite fluorides are preferentially

incorporated in the alite, C3S, reducing its free energy.

..fluoridesmineralise the formation of C3S.

the temperature at which C3S becomes themost stable compound is reduced..




1.6 Mineralisation


CaO C3S C2S


Gibbs

Free Energy

.the free energy of any

compound can be reduced byincorporation of minorsubstitutions or impurities.

Fluorides are preferentiallyincorporated in the alite,C3S, reducing its free

energy.


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This does involve theaddition of fluoride to thekiln feed




1.6 Mineralisation

CaO C3S C2S

Increasing SiO2

content

Gibbs

Free Energy

but also in combination with sulphate, SO3, aninhibitor. .the principle aims relate to

clinker and cement quality.

Mineralisation is sometimes

thought to be synonymouswith the production ofmineralised clinker, as

practiced at Aalborg in

Denmark, and promoted byFL Smidth.

We will return to the subjectof the quality related benefitsof mineralised clinker inmodule 2 of the course



1.6 Mineralisation

CaO C3S C2S


Gibbs

Free Energy

in module 1 we arefocusing on the impact on kiln energy efficiency and

productivity.

Mineralisation is sometimesthought to be synonymouswith the production ofmineralised clinker, as

practiced at Aalborg inDenmark, and promoted byFL Smidth.

.the SO3 also reducesthe viscosity of the C4AF and C3A melt when it forms.

clinker mineral formation takes place

through the medium of this SO3 melt..

..SO3forms low temperature meltsfrom ~1100C

SO3 is an inhibitor, but it is

also a fluxing agent




1.6 Mineralisation

CaO C3S C2S


Gibbs

Free EnergyMineralisation is sometimesthought to be synonymouswith the production of

mineralised clinker, aspracticed at Aalborg inDenmark, and promoted byFL Smidth.


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.C3S is not stable atthose temperatures in the absence of fluoride.

however, this low temperature flux isnot useful in the absence of fluoride


SO3 is an inhibitor, but it isalso a fluxing agent




1.6 Mineralisation

CaO C3S C2S

Increasing SiO2

content

Gibbs

Free EnergyMineralisation is sometimes

thought to be synonymouswith the production ofmineralised clinker, as

practiced at Aalborg in

Denmark, and promoted byFL Smidth.

in the presence of fluoride the combinedmineralisation effect of fluoride, and fluxing effect ofSO3 more than overcome the inhibiting effect of SO3.


SO3 is an inhibitor, but it isalso a fluxing agent



1.6 Mineralisation

CaO C3S C2S


Gibbs

Free EnergyMineralisation is sometimesthought to be synonymouswith the production ofmineralised clinker, as

practiced at Aalborg inDenmark, and promoted byFL Smidth.

..with severeblockages of the preheater of the suspension preheater kiln.

and sulphur, aspyrites, FeS2, in shale, were presentin the raw materials.


Mineralisation of the raw mix fed to a cement kiln is not entirely

straight-forward.

1.6 Mineralisation

Aalborgs technology and patent derive from a patent first takenout by Blue Circle in the 1970s.

In part Blue Circles discoveries

arose for experience at their HopeWorks in the UK where fluoride, asCaF2 in limestone,

Trials with mineralised kiln feedwere carried out on long wet, Lepoland suspension preheater kilns..


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and sulphur, aspyrites, FeS2, in shale, were presentin the raw maerials.



straight-forward.

1.6 Mineralisation

Aalborgs technology and patent derive from a patent first taken

out by Blue Circle in the 1970s.

In part Blue Circles discoveriesarose for experience at their HopeWorks in the UK where fluoride, asCaF2 in limestone,

Trials with mineralised kiln feedwere carried out on long wet. Lepoland suspension preheater kilns.. ..this increased

stickiness of the hot feed in the preheater is oftenreported when mineralisation is introduced.

..leading to the hotmeal stickiness and preheater blockages.

.ifnot the additional thermal energy input, over-and-abovethat required for clinker combination, will be absorbed to

volatilise alkalis and sulphates from the kiln charge and aheavy alkali cycle will develop..

Never-the-less this represents a reduction in the combinationtemperature of 125~150C.


Mineralisation of the raw mix fed to a cement kiln is not entirelystraight-forward.

1.6 Mineralisation

Mineralisation with fluoride will stabilise C3S and promote itsformation from CaO and C2S at 1170C. in practice~1350C is required to overcome the inhomogeneities in the kilnfeed we have already discussed.

The kiln burning zone temperature must be reduced in responseto this lower combination temperature requirement..

.kiln operators will need support and coaching to makethe necessary reductions in burning zone temperature.




straight-forward.

1.6 Mineralisation

Mineralisation with fluoride will stabilise C3S and promote itsformation from CaO and C2S at 1170C. in practice~1350C is required to overcome the inhomogeneities in the kiln

feed we have already discussed.

The kiln burning zone temperature must be reduced in responseto this lower combination temperature requirement..


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..kiln exhaust gas

volume is reduced and exhaust fan capacity released toallow kiln output to be increased.

.and therefore the amount of fuel which must be burntper tonne of clinker produced.




straight-forward.

1.6 Mineralisation

Mineralisation with fluoride will stabilise C3S and promote its

formation from CaO and C2S at 1170C. in practice~1350C is required to overcome the inhomogeneities in the kilnfeed we have already discussed.

Provided the kiln burning zone temperature is lowered by thisamount the thermal energy requirement is significantly reduced..

..or less

expensive refractories will be required to the desiredlength of kiln campaign.

.longer kiln campaigns betweenrefractory replacement should follow..




1.6 Mineralisation


Thermal load on the burning zone refractories is alsosignificantly reduced ..

..kiln feed mineralisation is one means to achievethis...

.we are going to spend a couple of sessions talking aboutNOx generation and emissions mitigation in Module 3...




straight-forward.

1.6 Mineralisation

Mineralisation with fluoride will stabilise C3S and promote itsformation from CaO and C2S at 1170C. in practice~1350C is required to overcome the inhomogeneities in the kiln

feed we have already discussed.

The lower temperature in the burning zone can cut NOx levels atthe kiln inlet to 40% of those prior to mineralisation..

...along with better quality clinker,

lower fuel consumption and more output.


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straight-forward.

1.6 Mineralisation

Mineralisation with fluoride will stabilise C3S and promote its

formation from CaO and C2S at 1170C. in practice~1350C is required to overcome the inhomogeneities in the kilnfeed we have already discussed.


...CO2 emissions will also be reduced asa consequence of the lower fuel consumption.






1.6 Mineralisation



...one of the few win-win-win-winoptions provided by cement kiln chemistry!

F.L. Smidth promote the production of mineralised clinker andhave developed methodologies to overcome the difficultieswhich can arise.



straight-forward.

1.6 Mineralisation

The first requirement is to install the equipment to dose thefluoride and sulphate needed for the production of mineralisedclinker.

This might simply be additional feed bins and weigh feeders to

dose the fluoride mineral and gypsum into the raw mill.


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F.L. Smidth promote the production of mineralised clinker and

have developed methodologies to overcome the difficultieswhich can arise.



straight-forward.

1.6 Mineralisation

The first requirement is to install the equipment to dose thefluoride and sulphate needed for the production of mineralisedclinker.

If the additional sulphur is to be provided by a high sulphur fuel,such as petroleum coke, then there are modifications to solid fuelgrinding circuits, precalciners and main burners that may berequired.. ..that is a technology in itself and not

specifically related to mineralisation.




1.6 Mineralisation

As discussed a couple of sessions ago mineralisation might thesolution if the kiln feed is particularly hard to burn

..allowing rotational speed to be increased and kiln output tobe boosted..or if a two support, short rotary kilndoes not provide sufficient residence time for the sinteringreactions to be completed.

.the main burner of thekiln may require modification to avoid these problems.




straight-forward.

1.6 Mineralisation

As previously stated the burning zone temperature must bereduced to prevent the volatilisation of alkalis..sulphate volatilisation is particularly to be avoided with the

Aalborg technology as sulphur loads in the kiln are boosed aspart of the technology.

These issues of volatile cycles in the kiln will be the topic ofthe next sessions of the course.


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1.6 Mineralisation.

Cement Kiln

ProcessChemistryModule 1. Cement kiln energy efficiency and

productivity.

1.6 mineralisation

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