WO2025219366A1

WO2025219366A1 - Method of producing a pozzolanic material in a cement manufacturing plant

Info

Publication number: WO2025219366A1
Application number: PCT/EP2025/060326
Authority: WO
Inventors: Giovanni David SANTILLAN; Francisco Navarro Gabaldón; Edelio Bermejo
Original assignee: Holcim Technology Ltd
Current assignee: Holcim Technology Ltd
Priority date: 2024-04-15
Filing date: 2025-04-15
Publication date: 2025-10-23
Anticipated expiration: 2026-10-15
Also published as: MX2024012427A

Abstract

Method of producing a pozzolanic material in a cement manufacturing plant comprising a cement kiln (1) and a clinker cooler (2), a head region (20) of the clinker cooler (2) being connected to an outlet end of the cement kiln (1) for cooling cement clinker coming from the cement kiln, the clinker cooler (2) comprising a recuperation zone (12) adjacent the outlet end, in which incoming cooling air is heated by the cement clinker (4) and heated cooling air is fed into the cement kiln (1) via the head region (20) as secondary air and/or used as tertiary air, and a cooling zone (13) remote from the outlet end, in which incoming cooling air is used to cool the cement clinker (4) and exhaust air is released from the clinker cooler (2) through an exhaust duct (16), the method comprising: - providing a silico-aluminous mineral material susceptible of pozzolanic reactivity upon calcination, - introducing the silico-aluminous mineral material into the cooling zone (13) of the clinker cooler (2) and calcining the silico-aluminous mineral material in the cooling zone (13) at a temperature of 600-900°C, in order to obtain said pozzolanic material.

Description

Method of producing a poz zolanic material in a cement manufacturing plant

The invention refers to a method of producing a poz zolanic material in a cement manufacturing plant .

Further, the invention refers to a method of producing a composite cement containing cement clinker and a poz zolanic material in a cement manufacturing plant .

Various types of mineral components may be added to Portland cement in order to obtain composite cements . In particular, it has become common practice to use poz zolanic and/or latent hydraulic material as supplementary cementitious materials in Portland cement mixtures .

By substituting supplementary cementitious materials for Portland cement the speci fic emission of CO2 in the production of cement will be reduced . During the production of Portland cement clinker a considerable amount of CO2 per ton of Portland cement clinker is emitted by the decarbonation of the raw materials and from the oxidation of the fuels that occur during calcination of the raw materials in rotary kilns .

Supplementary cementitious materials comprise a broad class of siliceous or siliceous and aluminous materials which, in finely divided form and in the presence of water, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties . Examples of supplementary cementitious materials include granulated blast- furnace slag, fly ash, natural poz zolans , burnt oil shale , or calcined clay . Cement is a product that in most cases is used in locations relatively close to where it is manufactured . Therefore , in case of composite cements , its production requires the availability of a source of a supplementary cementitious material , this source being either natural or synthetic . However, the local availability of such sources is not guaranteed in all regions where cement is produced, mainly because of the decreasing availability of some synthetic sources of supplementary cementitious materials . Synthetic supplementary cementitious materials are in most cases a byproduct of various industrial processes , such as fly ash from coal- fired power plants or blast- furnace slag from steel mills . The decreasing supply of fly ash from the power industry is encouraging the search for new sources of supplementary cementitious materials for the cement and concrete production .

Therefore , increasing ef forts are undertaken to use widely available sources for producing supplementary cementitious materials , such as calcined clays . Various types of raw clay can be treated thermally by heating to a temperature high enough to alter the structure of the clay minerals by dehydroxylation, but low enough to avoid recrystalli zation and the formation of chemically inert phases . A particularly useful type of clay is kaolinite that has a layered silicate structure , composed of alternating layers of tetrahedral sheets of silica and octahedral sheets of alumina linked with each other by oxygen atoms . When kaolinite is heated during a calcination process , dehydroxylation and trans formation of the kaolinite into an amorphous material known as metakaolin are occurring . Various methods have been proposed for producing calcined clay . WO 2022 / 106966 Al discloses a method, which comprises adding raw clay into a clinker cooler to obtain a calcined clay cement . Such a method has several advantages as it enables the production of calcined clay cements without the need of building and operating a dedicated device for the calcination of clays . Furthermore , the method takes advantage of the heat in the clinker that is coming out of the rotary kiln where the clinker is calcined, to then calcine the clay, meaning that clay is calcined without needing an additional source of heat .

However, the method disclosed in WO 2022 / 106966 Al is associated with several drawbacks . First , introducing raw clay into a clinker cooler tends to generate high amounts of dust . This dust can circulate back to the cement kiln, leading to the following concerns : it can contaminate the clinker, thereby af fecting the clinker ' s quality and performance ; it can decrease the proportion of calcined clay present in the final cement products ; it reduces the flame temperature in the kiln due to additional dust in the secondary air ; and it increases the speci fic heat consumption caused by the thermal energy absorption of the silico- aluminous mineral material into the rotary kiln . Additionally, the calcination process as described lacks precise control . This lack of control can lead to scenarios where the clay is either overburnt or not suf ficiently calcined, which ultimately compromises the reactivity of the resulting cementitious material .

Therefore , it is an obj ect of the invention to adapt a method of producing poz zolanic material that is integrated into a cement manufacturing plant , but that does not involve the drawbacks described above .

In order to solve this obj ect , the invention provides a method of producing a poz zolanic material in a cement manufacturing plant comprising a cement kiln and a clinker cooler, a head region of the clinker cooler being connected to an outlet end of the cement kiln for cooling cement clinker coming from the cement kiln, the clinker cooler comprising a recuperation zone adj acent the outlet end, in which incoming cooling air is heated by the cement clinker and heated cooling air is fed into the cement kiln via the head region as secondary air and/or used as tertiary air, and a cooling zone remote from the outlet end, in which incoming cooling air is used to cool the cement clinker and exhaust air is released from the clinker cooler through an exhaust duct , the method comprising : providing a silico-aluminous mineral material susceptible of poz zolanic reactivity upon calcination, introducing the silico-aluminous mineral material into the cooling zone of the clinker cooler and calcining the silico-aluminous mineral material in the cooling zone at a temperature of 600- 900 ° C, in order to obtain said poz zolanic material .

Thus , the invention is based on the idea to introduce the silico-aluminous mineral material into the cooling zone of the clinker cooler, rather than the recuperation zone , which signi ficantly reduces the circulation of dust back to the cement kiln due to the di f ferences in air flow between these two zones . In the recuperation zone , which is located closer to the outlet end of the cement kiln, the primary obj ective is to heat the incoming cooling air by direct contact with the hot cement clinker . This heated air is then channeled back into the cement kiln as secondary air or used as tertiary air . Due to the direction and purpose of the air flow in this zone — to capture heat and carry it back to the kiln — the potential for entraining fine particles and dust from added materials is signi ficantly higher . I f the silico-aluminous mineral material were added in this zone , the vigorous air flow designed to maximi ze heat recuperation could easily pick up and transport dust particles back to the kiln, leading to contamination issues and a reduction in the quality of the calcined material in the cement .

On the other hand, the cooling zone , situated further from the kiln ' s outlet end, employs incoming cooling air primarily to lower the temperature of the cement clinker . The air flow in this zone is designed to cool the clinker and then exit through an exhaust duct , rather than being recirculated back into the kiln . By introducing the silico-aluminous mineral material into this zone , the potential for dust to be picked up by the air flow and transported back to the kiln is minimi zed . The air flow here is not directed towards the kiln but towards the exhaust system, which means any dust generated during the calcination of the silico-aluminous material is more likely to be contained within the cooler and then safely expelled through the exhaust system, where a filter may be arranged to capture the suspended particles in the airflow .

The cooling zone of the clinker cooler is usually characteri zed by the so-called zero point of the clinker cooler. The zero point of a cooler is defined as the point in the cooler beyond which no gas flows back to the kiln. It is easily determined by the skilled person by air flow measurements, and is the point where the temperature of the clinker is optimal for the calcination of the silico- aluminous mineral material.

An additional effect of the invention is that, by introducing the silico-aluminous mineral material into the cooling zone, in particular at an upstream end region of the cooling zone, where the zero point is located, the silico-aluminous mineral material can be calcined at a temperature of 600-900°C, in order to obtain the pozzolanic material. At the zero point of a clinker cooler, the clinker is typically at a temperature comprised between 600°C and 900°C. Calcining the silico- aluminous mineral material at a temperature of 600-900°C means that the material is heated to a temperature of 600- 900°C, i.e. to a temperature of at least 600°C and not above 900°C.

By reaching the specific temperature range of 600°C to 900°C, the desired mineralogical change in the silico-aluminous mineral material can be obtained that is characteristic of the mineralogical composition of the material. This change can develop a pozzolanic activity in the material. If the specific activation temperature range of the silico-aluminous mineral material is surpassed, over-burning takes place and crystallization of the silica phase occurs, resulting in a reduction of the pozzolanic reactivity of the material.

In the recuperation zone of a clinker cooler, the finer particles of the material would be transported back into the cement kiln by the air flow necessary to recover thermal energy from the clinker in order to achieve a lower specific heat consumption. Particles that are recirculated into the cement kiln reach temperatures as high as 1450°C, which results in the undesired effect of overturning the silico- aluminous mineral material, as described above.

In order to safely achieve pozzolanic activation of the silico-aluminous mineral material, the method of the invention preferably comprises an initial step of selecting a silico-aluminous mineral material that activates its pozzolanic activity within a temperature range of 600-900°C, preferably 600-700°C. Said selection process preferably comprises the steps of: a) Chemical XRF analysis of the available silico- aluminous mineral material, b) Activation of the material at different temperatures from 500°C to 900°C in progressive steps of, e.g., 100°C, c) Pozzolanic reactivity analysis of the material at each temperature, d) Selection of the material the pozzolanic reactivity of which matches or surpasses the functional properties of the cement clinker.

The step of calcining the silico-aluminous mineral material in the cooling zone of the clinker cooler preferably comprises contacting the silico-aluminous mineral material with the cement clinker that is transported through the cooling zone of the clinker cooler.

Thus, the invention uses waste energy from the cooling of the clinker to calcine the mineralogical phases of the silico- aluminous mineral material that would otherwise have to be produced in a standalone process with an additional thermal power input to achieve the same temperature conditions as described herein .

According to a preferred embodiment of the method of the invention, the silico-aluminous mineral material is introduced into the cooling zone at a vertical distance of 10-20 cm above a bed of cement clinker being conveyed through the clinker cooler . This avoids the suspension of the silico- aluminous mineral material into the air flow .

According to a preferred embodiment of the invention, the clinker cooler is designed as a grate cooler . The structure of a grate cooler is essentially a hori zontal , moving grate by means of which cement clinker travels from the kiln ' s outlet end to the cooler ' s discharge end . Cooling air is blown through the grate from beneath, passing through the hot clinker and facilitating heat exchange . This process not only cools the clinker but also heats the cooling air . Cooling air is typically blown into the clinker cooler from below by means of a plurality of cooling fans that are distributed over the length of the cooler, i . e . in the conveying direction of the grate ( s ) . This allows for separate fans for the recuperation zone and for the cooling zone of the clinker cooler .

Preferably, the clinker cooler is designed as a singlechamber cooler and the silico-aluminous mineral material is introduced into the clinker cooler at the zero point of the clinker cooler .

Alternatively, the clinker cooler may comprise two or more consecutive cooling chambers and the silico-aluminous mineral material is introduced into a second cooling chamber arranged downstream of a first cooling chamber, wherein the silico- aluminous mineral material is preferably introduced at an upstream end of the second cooling chamber . The at least two cooling chambers allow for a two-stage cooling process , wherein the two stages are typically physically separated, each designed for speci fic cooling and heat recovery tasks within the overall clinker cooling process . In particular, the first cooling chamber houses the recuperation zone and the second chamber houses the cooling zone of the clinker cooler . A physical separation of the two stages may be reali zed by, e . g . , separating walls , which help to control the flow of clinker and cooling air between the stages , ensuring that the cooling air in each stage can be managed independently . In particular, the physical separation is designed to allow the clinker to transit from the first stage to the second stage , while keeping the flow of cooling air separate .

According to a preferred embodiment of the invention, the silico-aluminous mineral material is introduced into the cooling zone by means of an air-tight dosing system . The airtight dosing system ensures that the exact required amount of silico-aluminous mineral material is introduced into the cooling zone , thereby eliminating the risk of atmospheric contamination and preventing the escape of fine particulate matter into the surrounding environment .

Preferably, the silico-aluminous mineral material is introduced into the cooling zone at a dosing rate of 5-20 wt . -% , preferably 10-20 wt . -% , of the cement clinker . This ensures an optimal ratio of cement clinker to poz zolanic material in the final product , and achieves a balance that maximi zes the reactivity of the poz zolanic material without compromising the performance of the final product .

In preferred embodiment , the silico-aluminous mineral material is charged onto a bed of cement clinker in the clinker cooler in a continuous manner, preferably by means of a rotary valve or a feeding screw . Rotary valves or feeding screws have the advantage of providing a more continuous supply of material on the hot clinker bed . On the contrary, a feeding device that makes use of a double-inlet valve is not preferred as it delivers materials in a non-continuous manner, resulting in varying thicknesses of silico-aluminous mineral material on the hot clinker, which then does not allow for a homogeneous calcination of the material . In an even more preferred embodiment , the material is discharged onto the hot clinker bed in the clinker cooler by means that do not include a double-inlet valve .

Preferably, a first temperature of the cement clinker is measured upstream of the cooling zone and a second temperature of the cement clinker is measured at a discharge end of the clinker cooler and a feeding rate of the silico- aluminous mineral material introduced into the clinker cooler is controlled as a function of said first and second temperature so that the silico-aluminous mineral material is heated to a temperature of at least 600 ° C and not above 900 ° C . Preferably, the first temperature is measured at the inlet of the clinker cooler . By correlating the feeding rate with real-time temperature readings of the clinker, the method improves the ef ficiency of the heat exchange process , optimi zing the use of residual thermal energy from the clinker for the calcination of the mineral material . Preferably, the raw clay material is used as said silico- aluminous mineral material. The raw clay material may preferably comprise at least 40 wt.-% raw clay. This substantial proportion of raw clay ensures that the final calcined material retains a high content of aluminosilicates, which are essential for the pozzolanic reaction in cementitious applications.

The raw clay material may contain various clay minerals, such as kaolinite, smectite, illite, sepiolite, attapulgite, and vermiculite .

It was also found that the method herein described is suitable for a variety of silico-aluminous mineral materials. This is of particular interest when such materials can develop or increase their pozzolanic reactivity upon calcination at a temperature of 600-900°C. Alternatively, granulated blast furnace slag (GBFS) , basic oxygen furnace (BOF) slag, electric arc furnace (EAF) slag, air-cooled blast furnace slag (ACBF) , mining sludges, bottom ash, incineration ash, refractory residues, foundry sand, waste glass, oil shale, or mixture thereof, can be used as the silico- aluminous mineral material. In particular, natural pozzolan as defined in EN 197-1 published in September 2011, or mixtures of natural pozzolan and raw clay, can be used as the silico-aluminous mineral material.

The suitable particle size for the silico-aluminous mineral material in the calcination process may be selected according to the circumstance of the individual process. A finer particle size is generally preferred as it provides a larger surface area for the heat and chemical reactions to occur, facilitating a more uniform and complete calcination. However, the particle si ze should not be excessively fine as it can lead to operational challenges like dusting or handling di f ficulties . The optimal particle si ze is typically determined through a balance between maximi zing reactivity and practical considerations related to processing and handling in the speci fic calcination system being used . Preferably, the particle si ze of the silico-aluminous mineral material when being subj ected to the calcination step is in the range of 50 micrometers to 1000 micrometers .

Preferably, the silico-aluminous mineral material comprises a water content of 5-25 wt . -% of the total weight of the silico-aluminous mineral material . In case the silico- aluminous mineral material has a humidity above 25 wt . -% , waste heat from the cement process can be used to reduce the amount of water in the material before the material is being introduced into the clinker cooler . Also , the water should preferably be above 5 wt . -% of the amount of the silico- aluminous mineral material to ensure that the occurrence of dust during the process of adding the material onto the hot clinker bed is minimi zed .

Calcining the silico-aluminous mineral material in the clinker cooler of a cement manufacturing plant , in particular by being contacted with the clinker bed, advantageously results in that the poz zolanic material is obtained in combination with the cement clinker . Therefore , a preferred embodiment of the invention provides that a combined material comprising the cement clinker and the poz zolanic material is discharged from a discharge end of the clinker cooler . The combined material results in environmental benefits due to the poz zolanic material ' s ability to substitute a portion of the cement clinker, ef fectively reducing the carbon footprint of the cement .

The combined material may later be ground, with a source of calcium sul fates and other optional mineral components to form a composite Portland cement . Calcium sul fate serves as a setting time regulator for the hydrated cement in a concentration of 1- 10 wt . -% . Since clinker sets quickly, the addition of calcium sul fate lengthens the setting time of the cement in proportion to its increase in the composite cement .

In a preferred embodiment , calcium carbonate may be added as an additional component to the composite cement in an amount of 1-30 wt . -% of the total weight of the composite cement .

According to a second aspect , the present invention provides a method of producing a composite cement containing cement clinker and a poz zolanic material in a cement manufacturing plant comprising a cement kiln and a clinker cooler, a head region of the clinker cooler being connected to an outlet end of the cement kiln for cooling cement clinker coming from the cement kiln, the method comprising : calcining cement clinker in the cement kiln, discharging cement clinker from the cement kiln into the clinker cooler and cooling the cement clinker in the clinker cooler producing a poz zolanic material by a method according to the first aspect of the invention, wherein the poz zolanic material is contacted with the cement clinker present in the clinker cooler, discharging a combined material comprising the cement clinker and the poz zolanic material from the clinker cooler, grinding the mixture in a cement mill together with a source of calcium sul fates in order to obtain said composite cement .

Preferably, the composite cement further comprises calcium carbonate , preferably in an amount of 1-30 wt . -% of the total weight of the composite cement .

Preferably, the composite cement further comprises a supplementary cementitious material , such as a natural poz zolan, fly ash, granulated blast furnace slag and/or a silica-aluminous natural or arti ficial mineral having poz zolanic activity .

The invention will now be described in more detail with reference to an exemplary embodiment shown in Fig 1 .

Fig . 1 shows the outlet end of a cement kiln 1 , such as a rotary kiln, for calcining cement clinker . Cement clinker is discharged from the cement kiln 1 into the clinker cooler 2 , as illustrated by arrow 3 and forms a clinker bed 4 that is conveyed through the clinker cooler 2 by means of moving grates 6 to a discharge end 5 , from where the clinker falls onto a conveyor 7 for being further transported to a storage facility .

A burner for providing thermal energy to the cement kiln 1 is denoted by reference numeral 8 , to which fuel 9 and primary air 10 are fed .

For cooling the cement clinker, ambient air is blown into the clinker cooler 2 by means of a plurality of fans 11 that are distributed over the length of the clinker cooler 2 . Cooling air is blown through the grates 6 from beneath and passes through the clinker bed 4 , thereby cooling the cement clinker and increasing the temperature of the cooling air . The clinker cooler comprises a recuperation zone 12 adj acent the outlet end of the cement kiln 1 , in which incoming cooling air is heated by the cement clinker and heated cooling air is fed into the cement kiln 1 via the head region 20 as secondary air 14 and/or used as tertiary air 15 , and a cooling zone 13 remote from the outlet end, in which incoming cooling air is used to cool the cement clinker and exhaust air 17 is released from the clinker cooler 2 through an exhaust duct 16 . The zero point 18 of the clinker cooler 2 is located at the beginning of the cooling zone 13 . As illustrated by arrows pointing upwards , the flow of cooling air in the recuperation zone 12 is directed to the head region 20 of the cooler, and the flow of cooling air in the cooling zone 13 is directed to the exhaust duct 16 .

A silico-aluminous mineral material susceptible of poz zolanic reactivity upon calcination, such a raw clay material is introduced into the cooling zone 13 of the clinker cooler 2 , as illustrated by the arrow 18 , in order to calcine the silico-aluminous mineral material at a temperature of 600- 900 ° C . The introduction point of the silico-aluminous mineral material 19 is located approximately 10-20 cm above the clinker bed 4 . In this way, the silico-aluminous mineral material 19 gets into contact with the clinker bed 4 and is heated to a temperature of 600- 900 ° C in order to get calcined . The calcined material is entrained by the moving clinker bed 4 and conveyed to the discharge end 5 . Therefore , as a result of the method described, a combined product containing cement clinker and a calcined poz zolanic material is obtained .

Claims

Claims :

1. Method of producing a pozzolanic material in a cement manufacturing plant comprising a cement kiln (1) and a clinker cooler (2) , a head region (20) of the clinker cooler (2) being connected to an outlet end of the cement kiln (1) for cooling cement clinker coming from the cement kiln (1) , the clinker cooler (2) comprising a recuperation zone (12) adjacent the outlet end, in which incoming cooling air is heated by the cement clinker (4) and heated cooling air is fed into the cement kiln (1) via the head region (20) as secondary air (14) and/or used as tertiary air (15) , and a cooling zone (13) remote from the outlet end, in which incoming cooling air is used to cool the cement clinker (4) and exhaust air is released from the clinker cooler (2) through an exhaust duct (16) , the method comprising: providing a silico-aluminous mineral material susceptible of pozzolanic reactivity upon calcination, introducing the silico-aluminous mineral material into the cooling zone (13) of the clinker cooler (2) and calcining the silico-aluminous mineral material in the cooling zone (13) at a temperature of 600-900°C, in order to obtain said pozzolanic material.

2. Method according to claim 1, wherein the silico- aluminous mineral material is introduced into the clinker cooler (2) at an upstream end region of the cooling zone (13) .

3. Method according to claim 1 or 2, wherein the silico- aluminous mineral material is introduced into the cooling zone (13) at a vertical distance of 10-20 cm above a bed (4) of cement clinker (4) being conveyed through the clinker cooler ( 2 ) .

4. Method according to claim 1, 2 or 3, wherein the clinker cooler (2) is designed as a grate cooler.

5. Method according to any one of claims 1 to 4, wherein the clinker cooler (2) is designed as a single-chamber cooler and the silico-aluminous mineral material is introduced into the clinker cooler (2) at the zero point (18) of the clinker cooler ( 2 ) .

6. Method according to any one of claims 1 to 4, wherein the clinker cooler (2) comprises two or more consecutive cooling chambers and the silico-aluminous mineral material is introduced into a second cooling chamber arranged downstream of a first cooling chamber, wherein the silico-aluminous mineral material is preferably introduced at an upstream end of the second cooling chamber.

7. Method according to any one of claims 1 to 6, wherein the silico-aluminous mineral material is introduced into the cooling zone (13) by means of an air-tight dosing system.

8. Method according to any one of claims 1 to 7, wherein the silico-aluminous mineral material is introduced into the cooling zone (13) at a dosing rate of 5-20 wt.-%, preferably 10-20 wt.-%, of the cement clinker (4) .

9. Method according to any one of claims 1 to 8, wherein a first temperature of the cement clinker (4) is measured upstream of the cooling zone (13) and a second temperature of the cement clinker (4) is measured at a discharge end (5) of the clinker cooler (2) and a feeding rate of the silico- aluminous mineral material introduced into the clinker cooler (2) is controlled as a function of said first and second temperature so that the silico-aluminous mineral material is heated to a temperature of at least 600°C and not above 900°C.

10. Method according to any one of claims 1 to 9, wherein a raw clay material or a mixture of raw clay and a natural pozzolan is used as said silico-aluminous mineral material.

11. Method according to any one of claims 1 to 10, wherein granulated blast furnace slag (GBFS) , basic oxygen furnace (BOF) slag, electric arc furnace (EAF) slag, air-cooled blast furnace slag (ACBF) , mining sludge, bottom ash, incineration ash, refractory residues, foundry sand, waste glass, oil shale, natural pozzolans, or mixture thereof, is used as said silico-aluminous mineral material.

12. Method according to any one of claims 1 to 11, wherein the silico-aluminous mineral material comprises a water content of 5-25 wt.-% of the total weight of the silico- aluminous mineral material.

13. Method according to any one of claims 1 to 12, wherein a mixture comprising the cement clinker (4) and the pozzolanic material is discharged from a discharge end (5) of the clinker cooler (2) .

14. Method of producing a composite cement containing cement clinker and a pozzolanic material in a cement manufacturing plant comprising a cement kiln (1) and a clinker cooler (2) , a head region (20) of the clinker cooler (2) being connected to an outlet end of the cement kiln (1) for cooling cement clinker (4) coming from the cement kiln, the method comprising : calcining cement clinker in the cement kiln (1) , discharging cement clinker from the cement kiln (1) into the clinker cooler (2) and cooling the cement clinker (4) in the clinker cooler (2) producing a pozzolanic material by a method according to any one of claims 1 to 12, wherein the pozzolanic material is contacted with the cement clinker (4) present in the clinker cooler ( 2 ) , discharging a combined material comprising the cement clinker (4) and the pozzolanic material from the clinker cooler ( 2 ) , grinding the mixture in a cement mill together with a source of calcium sulfates in order to obtain said composite cement .

15. Method according to claim 14, wherein the composite cement further comprises calcium carbonate, preferably in an amount of 1-30 wt.-% of the total weight of the composite cement .

16. Method according to claim 14 or 15, wherein the composite cement further comprises a supplementary cementitious material, such as a natural pozzolan, fly ash, granulated blast furnace slag and/or a silica-aluminous natural or artificial mineral having pozzolanic activity.