Mineralisation.pdf

CemNet Training - Course CKPC01

Module 1 – Session 6

Cement Kiln Process Chemistry Module 1. Cement kiln energy efficiency and productivity. 1.6 Mineralisation.

Cement Kiln Chemistry

1.6 Mineralisation

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 above 1250°C as the equilibrium of the reaction: C2S + CaO

↔ ←

C3S

……..is predominantly to the left. Above 1250°C the equilibrium shifts to the right to favour the formation of C3S. C2S + CaO

↔ →

C3S

……..with the formation of a liquid phase significantly increasing the rate of reaction to form C3S…… …how can that be explained?

Cement Kiln Chemistry

1.6 Mineralisation

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 above 1250°C as the equilibrium of the reaction: C2S + CaO

↔ ←

C3S

……..is predominantly to the left. Above 1250°C the equilibrium shifts to the right to favour the formation of C3S. C2S + CaO

↔ →

C3S

The explanation relies on consideration of free energies and chemical potentials of the reactants and products at different temperatures.

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Below 1250°C the Gibbs Gibbs Free Energy free energy (chemical potential) of C3S is higher than free CaO or C2S and therefore C3S will not be formed from an intimate mixture of CaO and C2S because it is unstable. CaO and C2S are stable…... …...and C3S unstable. C2S + CaO

↔ ←

CaO

C3S

C2S

Increasing SiO2 content

C3S

The equilibrium lies to the left.

Cement Kiln Chemistry

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Above 1250°C the Gibbs Gibbs Free Energy free energy (chemical potential) of C3S is lower than free CaO or C2S and therefore C3S is the most stable compound and will be formed. CaO

C3S

C2S

Increasing SiO2 content

Cement Kiln Chemistry

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Above 1250°C the Gibbs Gibbs Free Energy free energy (chemical potential) of C3S is lower than free CaO or C2S and therefore C3S is the most stable compound and will be formed. Dependent on the SiO2 CaO content either CaO and C3S are stable…... ...or C3S and C2S are stable. C2S + CaO ↔ C3S The equilibrium lies to the right.

C3S

C2S

Increasing SiO2 content

→

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Above 1250°C the Gibbs Gibbs Free Energy free energy (chemical potential) of C3S is lower than free CaO or C2S and therefore C3S is the most stable compound and will be formed. Dependent on the SiO2 CaO CS content either CaO and C3S are stable…... ...or C3S and Increasing SiO content C2S are stable. C2S + CaO ↔ C3S C3S will be formed because it is the most stable. 3

C2S

2

→

Cement Kiln Chemistry

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Returning to the chemical Gibbs Free Energy potentials below 1250°C… …. ….the free energy of any compound can be reduced by incorporation of minor substitutions or impurities. Most common impurities, Na2O, K2O, SO3, Al2O3, are incorporated in the belite, C2S….. …..free energy of the C2S is reduced…….

CaO

Cement Kiln Chemistry

C3S

C2S

Increasing SiO2 content

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Returning to the chemical Gibbs Free Energy potentials below 1250°C… …. ….the free energy of any compound can be reduced by incorporation of minor substitutions or impurities. Most common impurities, Na2O, K2O, SO3, Al2O3, CaO CS are incorporated in the belite, C2S….. …..free Increasing SiO content energy of the C2S is reduced……. …….C2S is stabilised and formation of C3S becomes more difficult. 3

C2S

2

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Returning to the chemical Gibbs Free Energy potentials below 1250°C… …. ….the free energy of any compound can be reduced by incorporation of minor substitutions or impurities. Most common impurities, Na2O, K2O, SO3, Al2O3, CaO CS are incorporated in the belite, C2S….. …..free Increasing SiO content energy of the C2S is reduced……. …….Na2O, K2O, SO3 and Al2O3 inhibit the formation of C3S. 3

C2S

2

Cement Kiln Chemistry

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Returning to the chemical Gibbs Free Energy potentials below 1250°C… …. ….the free energy of any compound can be reduced by incorporation of minor substitutions or impurities. Fluorides are an important exception to the rule that CaO CS impurities are preferentially incorporated Increasing SiO content in C2S, belite…… …… fluorides are preferentially incorporated in the alite, C3S, reducing its free energy. 3

C2S

2

Cement Kiln Chemistry

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Returning to the chemical Gibbs Free Energy potentials below 1250°C… …. ….the free energy of any compound can be reduced by incorporation of minor substitutions or impurities. Fluorides are preferentially incorporated in the alite, CaO CS C3S, reducing its free energy.…… Increasing SiO content ……the temperature at which C3S becomes the most stable compound is reduced….. …..fluorides mineralise the formation of C3S. 3

C2S

2

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Mineralisation is sometimesGibbs Free Energy thought to be synonymous with the production of mineralised clinker, as practiced at Aalborg in Denmark, and promoted by FL Smidth. This does involve the CaO CS CS addition of fluoride to the kiln feed……… Increasing SiO content ………but also in combination with sulphate, SO3, an inhibitor……. …….the principle aims relate to clinker and cement quality. 3

2

2

Cement Kiln Chemistry

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Mineralisation is sometimesGibbs Free Energy thought to be synonymous with the production of mineralised clinker, as practiced at Aalborg in Denmark, and promoted by FL Smidth. We will return to the subject CaO CS of the quality related benefits of mineralised clinker in Increasing SiO content module 2 of the course…… ……in module 1 we are focusing on the impact on kiln energy efficiency and productivity. 3

C2S

2

Cement Kiln Chemistry

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Mineralisation is sometimesGibbs Free Energy thought to be synonymous with the production of mineralised clinker, as practiced at Aalborg in Denmark, and promoted by FL Smidth. SO3 is an inhibitor, but it is CaO CS CS also a fluxing agent… ..SO3 forms low temperature melts Increasing SiO content from ~1100°C…………clinker mineral formation takes place through the medium of this SO3 melt….. ….the SO3 also reduces the viscosity of the C4AF and C3A melt when it forms. 3

2

2

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Mineralisation is sometimesGibbs Free Energy thought to be synonymous with the production of mineralised clinker, as practiced at Aalborg in Denmark, and promoted by FL Smidth. SO3 is an inhibitor, but it is CaO CS CS also a fluxing agent… ..SO3 forms low temperature melts Increasing SiO content from ~1100°C…………however, this low temperature flux is not useful in the absence of fluoride…… ….C3S is not stable at those temperatures in the absence of fluoride. 3

2

2

Cement Kiln Chemistry

1.6 Mineralisation

In the preceding session we discussed the equilibrium of the combination reaction between C2S and CaO to form C3S. Mineralisation is sometimesGibbs Free Energy thought to be synonymous with the production of mineralised clinker, as practiced at Aalborg in Denmark, and promoted by FL Smidth. SO3 is an inhibitor, but it is CaO CS CS also a fluxing agent… ..SO3 forms low temperature melts Increasing SiO content from ~1100°C…………in the presence of fluoride the combined mineralisation effect of fluoride, and fluxing effect of SO3 more than overcome the inhibiting effect of SO3. 3

2

2

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Aalborg’s technology and patent derive from a patent first taken out by Blue Circle in the 1970s. In part Blue Circle’s discoveries arose for experience at their Hope Works in the UK where fluoride, as CaF2 in limestone, …and sulphur, as pyrites, FeS2, in shale, were present in the raw materials. Trials with mineralised kiln feed were carried out on long wet, Lepol and suspension preheater kilns….. …..with severe blockages of the preheater of the suspension preheater kiln.

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Aalborg’s technology and patent derive from a patent first taken out by Blue Circle in the 1970s. In part Blue Circle’s discoveries arose for experience at their Hope Works in the UK where fluoride, as CaF2 in limestone, …and sulphur, as pyrites, FeS2, in shale, were present in the raw maerials. Trials with mineralised kiln feed were carried out on long wet. Lepol and suspension preheater kilns….. …..this increased “stickiness” of the hot feed in the preheater is often reported when mineralisation is introduced.

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Mineralisation with fluoride will stabilise C3S and promote its formation from CaO and C2S at 1170°C…. ……in practice ~1350°C is required to overcome the inhomogeneities in the kiln feed we have already discussed. Never-the-less this represents a reduction in the combination temperature of 125~150°C. The kiln burning zone temperature must be reduced in response to this lower combination temperature requirement….. ….if not the additional thermal energy input, over-and-above that required for clinker combination, will be absorbed to volatilise alkalis and sulphates from the kiln charge and a heavy alkali cycle will develop….. …..leading to the hot meal “stickiness” and preheater blockages.

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Mineralisation with fluoride will stabilise C3S and promote its formation from CaO and C2S at 1170°C…. ……in practice ~1350°C is required to overcome the inhomogeneities in the kiln feed we have already discussed. Never-the-less this represents a reduction in the combination temperature of 125~150°C. The kiln burning zone temperature must be reduced in response to this lower combination temperature requirement….. ….kiln operators will need support and coaching to make the necessary reductions in burning zone temperature.

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Mineralisation with fluoride will stabilise C3S and promote its formation from CaO and C2S at 1170°C…. ……in practice ~1350°C is required to overcome the inhomogeneities in the kiln feed we have already discussed. Never-the-less this represents a reduction in the combination temperature of 125~150°C. Provided the kiln burning zone temperature is lowered by this amount the thermal energy requirement is significantly reduced.. ….and therefore the amount of fuel which must be burnt per tonne of clinker produced……. …..kiln exhaust gas volume is reduced and exhaust fan capacity released to allow kiln output to be increased.

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Mineralisation with fluoride will stabilise C3S and promote its formation from CaO and C2S at 1170°C…. ……in practice ~1350°C is required to overcome the inhomogeneities in the kiln feed we have already discussed. Never-the-less this represents a reduction in the combination temperature of 125~150°C. Thermal load on the burning zone refractories is also significantly reduced ….. ….longer kiln campaigns between …..or less refractory replacement should follow….. expensive refractories will be required to the desired length of kiln campaign.

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Mineralisation with fluoride will stabilise C3S and promote its formation from CaO and C2S at 1170°C…. ……in practice ~1350°C is required to overcome the inhomogeneities in the kiln feed we have already discussed. Never-the-less this represents a reduction in the combination temperature of 125~150°C. The lower temperature in the burning zone can cut NOx levels at the kiln inlet to 40% of those prior to mineralisation….. ….we are going to spend a couple of sessions talking about NOx generation and emissions mitigation in Module 3.….. …..kiln feed mineralisation is one means to achieve this……... ……...along with better quality clinker, lower fuel consumption and more output.

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Mineralisation with fluoride will stabilise C3S and promote its formation from CaO and C2S at 1170°C…. ……in practice ~1350°C is required to overcome the inhomogeneities in the kiln feed we have already discussed. Never-the-less this represents a reduction in the combination temperature of 125~150°C. The lower temperature in the burning zone can cut NOx levels at the kiln inlet to 40% of those prior to mineralisation….. ….we are going to spend a couple of sessions talking about NOx generation and emissions mitigation in Module 3.….. …..kiln feed mineralisation is one means to achieve this……... ……...CO2 emissions will also be reduced as a consequence of the lower fuel consumption.

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. Mineralisation with fluoride will stabilise C3S and promote its formation from CaO and C2S at 1170°C…. ……in practice ~1350°C is required to overcome the inhomogeneities in the kiln feed we have already discussed. Never-the-less this represents a reduction in the combination temperature of 125~150°C. The lower temperature in the burning zone can cut NOx levels at the kiln inlet to 40% of those prior to mineralisation….. ….we are going to spend a couple of sessions talking about NOx generation and emissions mitigation in Module 3.….. …..kiln feed mineralisation is one means to achieve this……... ……...one of the few win-win-win-win options provided by cement kiln chemistry!

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. F.L. Smidth promote the production of mineralised clinker and have developed methodologies to overcome the difficulties which can arise. The first requirement is to install the equipment to dose the fluoride and sulphate needed for the production of mineralised clinker. This might simply be additional feed bins and weigh feeders to dose the fluoride mineral and gypsum into the raw mill.

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Cement Kiln Chemistry

Module 1 – Session 6

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. F.L. Smidth promote the production of mineralised clinker and have developed methodologies to overcome the difficulties which can arise. The first requirement is to install the equipment to dose the fluoride and sulphate needed for the production of mineralised clinker. If the additional sulphur is to be provided by a high sulphur fuel, such as petroleum coke, then there are modifications to solid fuel grinding circuits, precalciners and main burners that may be required……….. ………..that is a technology in itself and not specifically related to mineralisation.

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. F.L. Smidth promote the production of mineralised clinker and have developed methodologies to overcome the difficulties which can arise. As discussed a couple of sessions ago mineralisation might the solution if the kiln feed is particularly hard to burn…… ……..allowing rotational speed to be increased and kiln output to be boosted……….……….or if a two support, short rotary kiln does not provide sufficient residence time for the sintering reactions to be completed.

Cement Kiln Chemistry

1.6 Mineralisation

Mineralisation of the raw mix fed to a cement kiln is not entirely straight-forward. F.L. Smidth promote the production of mineralised clinker and have developed methodologies to overcome the difficulties which can arise. As previously stated the burning zone temperature must be reduced 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 as part of the technology………. ……….the main burner of the kiln may require modification to avoid these problems. These issues of volatile cycles in the kiln will be the topic of the next sessions of the course.

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com

CemNet Training - Course CKPC01

Module 1 – Session 6

Cement Kiln Process Chemistry Module 1. Cement kiln energy efficiency and productivity. 1.6 Mineralisation.

This document is for the sole use of students enrolled on course CKPC01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © http://Training.CemNet.com