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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.
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
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.
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of thecombination reaction between C2S and CaO to form C3S.
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
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
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
Increasing SiO2 content
Gibbs
Free Energy
...or C3S andC2S are stable.
C2S + CaO C3S
The equilibrium lies to the right.
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Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
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.
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of thecombination reaction between C2S and CaO to form C3S.
1.6 Mineralisation
Returning to the chemicalpotentials below 1250C.
CaO C3S C2S
Increasing SiO2 content
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.
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
1.6 Mineralisation
Returning to the chemicalpotentials below 1250C.
CaO C3S C2S
Increasing SiO2 content
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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Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
1.6 Mineralisation
Returning to the chemical
potentials below 1250C.
CaO C3S C2S
Increasing SiO2
content
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 isreduced. .Na2O, K2O, SO3 and Al2O3 inhibit
the formation of C3S.
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of thecombination reaction between C2S and CaO to form C3S.
1.6 Mineralisation
Returning to the chemicalpotentials below 1250C.
CaO C3S C2S
Increasing SiO2 content
Gibbs
Free Energy
.the free energy of anycompound can be reduced byincorporation of minorsubstitutions or impurities.
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..
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
1.6 Mineralisation
Returning to the chemicalpotentials below 1250C.
CaO C3S C2S
Increasing SiO2 content
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
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
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
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of thecombination reaction between C2S and CaO to form C3S.
1.6 Mineralisation
CaO C3S C2S
Increasing SiO2 content
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
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
1.6 Mineralisation
CaO C3S C2S
Increasing SiO2 content
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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CemNet Training - Course CKPC01 Module 1 Session
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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
..SO3forms low temperature meltsfrom ~1100C
SO3 is an inhibitor, but it isalso a fluxing agent
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of the
combination reaction between C2S and CaO to form C3S.
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.
..SO3forms low temperature meltsfrom ~1100C
SO3 is an inhibitor, but it isalso a fluxing agent
Cement Kiln Chemistry
In the preceding session we discussed the equilibrium of thecombination reaction between C2S and CaO to form C3S.
1.6 Mineralisation
CaO C3S C2S
Increasing SiO2 content
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.
Cement Kiln Chemistry
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.
Cement Kiln Chemistry
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 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.
Cement Kiln Chemistry
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.
Never-the-less this represents a reduction in the combinationtemperature of 125~150C.
Cement Kiln Chemistry
Mineralisation of the raw mix fed to a cement kiln is not entirely
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.
Never-the-less this represents a reduction in the combinationtemperature of 125~150C.
Cement Kiln Chemistry
Mineralisation of the raw mix fed to a cement kiln is not entirely
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..
Never-the-less this represents a reduction in the combinationtemperature of 125~150C.
Cement Kiln Chemistry
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.
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...
Never-the-less this represents a reduction in the combinationtemperature of 125~150C.
Cement Kiln Chemistry
Mineralisation of the raw mix fed to a cement kiln is not entirely
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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..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...
Never-the-less this represents a reduction in the combinationtemperature of 125~150C.
Cement Kiln Chemistry
Mineralisation of the raw mix fed to a cement kiln is not entirely
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.
The lower temperature in the burning zone can cut NOx levels atthe kiln inlet to 40% of those prior to mineralisation..
...CO2 emissions will also be reduced asa consequence of the lower fuel consumption.
..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...
Never-the-less this represents a reduction in the combinationtemperature of 125~150C.
Cement Kiln Chemistry
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 lower temperature in the burning zone can cut NOx levels atthe kiln inlet to 40% of those prior to 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.
Cement Kiln Chemistry
Mineralisation of the raw mix fed to a cement kiln is not entirely
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.
Cement Kiln Chemistry
Mineralisation of the raw mix fed to a cement kiln is not entirely
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.
F.L. Smidth promote the production of mineralised clinker andhave developed methodologies to overcome the difficultieswhich can arise.
Cement Kiln Chemistry
Mineralisation of the raw mix fed to a cement kiln is not entirelystraight-forward.
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.
F.L. Smidth promote the production of mineralised clinker andhave developed methodologies to overcome the difficultieswhich can arise.
Cement Kiln Chemistry
Mineralisation of the raw mix fed to a cement kiln is not entirely
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.