LU103142B1 - Climate-friendly pozzolana production - Google Patents

Abstract

The present invention relates to a device for producing a thermally activated clay, wherein the device comprises a rotary kiln 10 and a hot gas generating device 20 separate from the rotary kiln 10, wherein the hot gas generating device 20 and the rotary kiln 10 are connected via a gas line 23 for transferring hot gases generated in the hot gas generating device.

Description

thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 1/14

Climate-friendly pozzolana production

The invention relates to a device and a method for producing a thermally activated clay, an artificial pozzolan, in a rotary kiln.

Since the burning process of limestone produces mineral-bound

Carbon dioxide is released, will lead to reduction of carbon dioxide emissions in

The cement sector is increasingly turning to activated clays, also known as artificial pozzolans, because when activated, no such carbon dioxide is released from the clay. When clays are activated, the energy source and thus the fuel used is the main source of carbon dioxide emissions. In order to reduce these, alternative fuels are increasingly being used, although these are more demanding to burn.

Originally, the production of artificial pozzolans was carried out by thermal

Activation of clays in a rotary kiln. Since in a rotary kiln the

However, the use of substitute fuels is not without problems, currently

Entrained flow processes are used, whereby the use of alternative fuels is much easier. Two aspects are important when using alternative fuels.

On the one hand, a safe and complete burnout must be ensured. This requires sufficiently high temperatures and sufficiently long burning times with a sufficiently high oxygen supply. In a rotary kiln, however, it is not possible to simultaneously optimize the activation of the clay and the burnout of the

alternative fuel is possible.

WO 2018 / 195 642 A2 describes a process for producing pozzolans with

color change known.

Energy recovery during the cooling of color-optimized clays is known from WO 2022/058 206 A1.

thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 2/14

A plant for the production of cement clinker is known from DE 10 2004 009 689 A1.

From DE 10 2012 108 295 A1 a device and a method for processing substitute fuels are known.

It would be desirable to activate a clay in a rotary kiln under

Avoiding emissions, in particular by using as much energy as possible

to enable the use of alternative fuels, such as biomass.

The object of the invention is to provide a device with a rotary kiln for the thermal

To provide a process for the activation of clays that does not require the firing of primary raw materials such as oil or gas in a rotary kiln and can therefore be operated in a particularly climate-friendly manner.

This object is achieved by the device with the features specified in claim 1

Features and by the method having the features specified in claim 28.

Advantageous further developments result from the subclaims, the following

description and drawings.

The device according to the invention serves to generate a thermally activated

Tones. The device comprises a rotary kiln and a hot gas generating device separated from the rotary kiln. The separation enables the separation of the

Process conditions are possible, so that, for example, substitute fuel in the

Hot gas generation device can be carried out under optimal conditions for the combustion of the substitute fuel, while the process conditions in the

Rotary kiln can be optimized for the activation of the clay. The

The hot gas generating device and the rotary kiln are connected via a gas line to the

Transfer of hot gases generated in the hot gas generation device.

Since only the hot gas is thus transferred through the gas line, on the one hand

On the one hand, there is the advantage of separating the two thermal processes. On the other hand, it is disadvantageous that the energy is no longer generated directly in the rotary kiln thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 3/14 and the heat transfer from the gas to the clay is therefore limited. This makes thermal activation more difficult without direct heat generation in a rotary kiln.

In a further embodiment of the invention, the device comprises a first

temperature sensor. The first temperature sensor is an infrared sensor. The first

Temperature sensor is located in the outlet area below the rotary kiln. This special arrangement enables contactless (wear-free) measurement of the

Temperature of the activated clay. With the usual measurement from above, it is not possible to measure the temperature as reliably as dust affects the measurement.

Measuring the escaping material from the bottom, however, has proven to be very reliable.

In a further embodiment of the invention, the device has a second

temperature sensor. The second temperature sensor is arranged in or on the rotary kiln. For example, the second temperature sensor can be on the outside of the

Here, of course, only the outside temperature of the

rotary kiln. The advantage is that it is low-maintenance and wear-free.

The disadvantage is that the measurement is relatively inaccurate. Alternatively, the second

Temperature sensor can be arranged in a fireproof protective tube inside the rotary kiln. This allows the material in the rotary kiln to be measured. The second temperature sensor can be surrounded on three sides by a metallic

To be surrounded and protected by protection.

In a further embodiment of the invention, the gas line has a length such that the gas within the gas line has a residence time of between 0 and 10s, preferably between 0.5 and 10 s. Thus, the gas line can be shorter, for example, but with a larger inner diameter, or longer and with a smaller inner diameter. Preferably, the gas line has a

Length such that the gas within the gas line has a residence time of between 1 and 5 s. Preferably, the gas line has a length such that the gas within the gas line has a residence time of between 1.5 and 2.5 s. This

A safe burnout can be ensured by a long residence time in the gas line, provided this has not already taken place in the hot gas generation device. This enables the use of a hot gas generation device which itself does not, for example, meet the legal requirements for safe burnout. In addition, other measures can be used, such as the addition of ammonia or urea to remove possible nitrogen oxides. Appropriate reaction times are also useful for this.

In a further embodiment of the invention, the device comprises a

The rotary kiln is connected to the material cooler for transferring the thermally treated clay. The material cooler is connected to the

Hot gas generation device for transferring the material preheated in the material cooler

Gas. This cools the finished product and also

Heat is fed back into the process. A dust filter is preferably arranged between the material cooler and the hot gas generation device. The dust separated in this way is preferably fed into the finished product.

In a further embodiment of the invention, the material cooler is a

Drum cooler. Preferably, the gas flow in the drum cooler is countercurrent to the

The advantage of the drum cooler is that the particle size of the activated clay is less important compared to entrained flow heat exchangers. Therefore, the requirements for the clay and the energy required for crushing are correspondingly low.

In a further alternative embodiment of the invention, the material cooler is a walking floor, two-layer cooler or grate cooler.

In a further alternative embodiment of the invention, the material cooler is a

Cyclone or fluidized bed cooler. The advantage is that cooling can be achieved much more quickly. The disadvantage, however, is that the maximum particle size of the activated clay is limited to a particle size that can fly (for example, less than 2 mm).

thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 5/14

In a further embodiment of the invention, a crushing device is arranged between the rotary kiln and the material cooler. The

A crushing device is, for example, a roller crusher.

The comminution device can in particular be cooled, preferably air-cooled.

This is particularly preferred if the material cooler is a cyclone or

fluidized bed cooler.

In a further embodiment of the invention, a screen, in particular a drum screen, is arranged between the rotary kiln and the material cooler. Particularly preferably, behind the coarse outlet of the screen, in particular the drum screen, a

crusher. This allows the amount of hot material to be crushed that is applied to the crusher to be significantly reduced, so that heat is less of an issue.

The sieve can also be designed as a static sieve, in particular as a sieve with an inclination of 30° to 60°. This enables purely gravity-driven transport and thus active conveying can be dispensed with.

Preferably, the sieve has a mesh size of 2 mm so that particles smaller than 2 mm can pass through and particles larger than 2 mm are retained.

In a further embodiment of the invention, the device has a

Product return is used to return products in the

Material cooler cooled product is formed between the rotary kiln and the material cooler. This is particularly preferred if between the rotary kiln and the

A crushing device is arranged in the material cooler, since in this way, by mixing hot activated clay coming from the rotary kiln with cold activated clay that is returned, rapid cooling and thus lower thermal load for the crushing device can be achieved. For further information, please refer to DE 10 2020 211 750 A1.

thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 6/14

In a further embodiment of the invention, the device has a pre-cooler. The pre-cooler is arranged between the rotary kiln and the material cooler.

The pre-cooler has direct or indirect water cooling. With direct

Water cooling involves applying water directly to the activated clay, particularly by spraying it on. This enables extremely fast and efficient cooling, which is particularly advantageous in order to avoid a change in the colour of the activated clay after thermal treatment, where the activated clay is exposed to high temperatures.

temperatures. With indirect water cooling, the water is sprayed onto the outside of the pre-cooler, thus significantly cooling the pre-cooler itself. The disadvantage of the process is the low efficiency in recovering the heat.

In a further embodiment of the invention, the rotary kiln has internals for vertically conveying the clay. The internals for vertically conveying the clay serve to lift the clay, causing it to fall through the gas flow inside the rotary kiln, optimizing the heat transfer from the gas flow to the clay. The internals can be straight, angled or curved.

They can be honeycomb or cross structures or they can be chain elements.

It is essential that the sound is at least partially raised by the built-in elements and thus at least partially falls back down again through the gas flow.

Since wear of the internals is strongly temperature-dependent, these internals are preferably only installed in the side of the rotary kiln facing away from the hot gas generation device, i.e. in areas of the rotary kiln where the temperature of the clay is below 650 °C, possibly below 500 °C.

In a further embodiment of the invention, the rotary kiln has retaining rings.

This increases the filling level in the rotary kiln, increases the residence time and thus improves the heat transfer from the gas phase to the clay to be activated.

Preferably, the rotary kiln has one or more baffle rings.

In a further embodiment of the invention, the gas line has a

Nitrogen supply for the removal of nitrogen oxides. For example, ammonia, aqueous ammonia solution, urea solution or the like can be supplied via the nitrogen supply thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 7/14 so that the supplied nitrogen synproportionates with nitrogen oxides and the nitrogen oxides are thus removed. Further

Possible designs can be found in particular in DE 10 2022 209 826.

In a further embodiment of the invention, in the gas flow direction behind the

Due to the high temperatures in the gas line between the hot gas generating device and the rotary kiln, no fan can be arranged there, so that the conveying capacity is preferably completely dependent on the

This in turn leads to the pressure in the

The pressure in the hot gas generating device is higher than the pressure in the rotary kiln. Due to the usually very low negative pressure in the rotary kiln, this means that the hot gas generating device has practically no negative pressure, and may even have a small positive pressure. Such an operation is suitable for the combustion of

Alternative fuels are unusual.

In a further embodiment of the invention, in the gas flow direction behind the

A dust filter is installed in the rotary kiln. The dust filter is connected to the rotary kiln to return the separated dust. Due to the indirect

Heating and the associated higher gas flow through the rotary kiln means a higher dust development and thus a discharge of very fine material with the

Gas flow from the rotary kiln is expected.

In a further embodiment of the invention, the rotary kiln has in the middle

area has a larger diameter. In particular, the middle area between the first race and the second race is widened. The middle area also contains the middle temperature range. The widening increases the

Flow velocity in this area is reduced, which in turn reduces the discharge of fine material and the heat exchange between gas and clay in this

area improved.

thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 8/14

In a further embodiment of the invention, the device has a preheater and/or a dryer. The preheater or dryer is arranged behind the rotary kiln in terms of gas flow and in front of the rotary kiln in terms of material flow. Although drying and heating can also take place completely and exclusively in the rotary kiln, due to the larger gas flow caused by the external generation of the hot gas flow, it is advantageous if the

Heat transfer takes place in an additional dryer and/or preheater. The

Preheater can be used as a cascade of cyclone preheaters or as

Riser tube heat exchanger with longer residence time and a separating cyclone. A drum dryer is preferably used as the dryer. The

The advantage of the drum dryer is that it can also work with very coarse particles (down to the cm range). A mill or a crusher with a subsequent riser dryer with a separation cyclone can also be used as a dryer.

In a further embodiment of the invention, the hot gas generating device is a combustion device for a substitute fuel. Particularly preferred is the

Combustion device designed to burn biomass. Alternatively, it can be an electrically operated superheater, which would also be climate-neutral when operated with electricity generated from renewable sources.

In a further embodiment of the invention, the combustion device has a gas-tight solids discharge. This enables operation of the

Combustion device also possible at overpressure.

In a further embodiment of the invention, the combustion device is a

Reverse-acting grate, a rotary kiln, a direct-current grate or a rotary kiln.

In a further embodiment of the invention, the rotary kiln has a

Auxiliary combustion device. When using substitute fuels, for example

Biomass, there are usually fluctuations in the calorific value and the

Humidity, so that the temperature generated in the combustion device

These can be mitigated by the supply of substitute fuel, but this is often slow. It can therefore be useful to provide an auxiliary combustion device that works with a fuel that is easy to dose and burns quickly and easily. Typically, this can be a gas burner, in order to avoid these carbon dioxide emissions as well.

Example for biogas. This allows a very quick response to these fluctuations and the temperature in the rotary kiln can be kept particularly constant.

In a further embodiment of the invention, the device has a

The mixing device is used to mix the clay with a

The mixing device is located in the material flow direction in front of the

The mixing device can be arranged, for example, between a

The dryer and the rotary kiln can be arranged. Coal can be used as a reducing agent. Unburned

Carbon residues from the combustion device are used.

Mixing creates a locally reducing atmosphere around the tone to be activated in the

Rotary kiln, which in turn prevents the clay from taking on an undesirable colour, for example due to the oxidation of iron. However, it is essential that only as little reducing agent is used so that in the end there is no and not disturbing

reducing agent ends up in the finished product.

In a further embodiment of the invention, the rotary kiln has at least one laterally arranged feed device for a reducing agent. The laterally arranged feed device can be, for example, a so-called scoop feeder. This allows the reducing agent to be fed into the correct

temperature range can be supplied directly.

In a further embodiment of the invention, the rotary kiln has at least one air supply arranged laterally. In particular, oxygen-containing gas can be supplied through the air supply. This enables complete combustion of, for example, a reducing agent or its gaseous reaction products thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 10/14. At the same time, an extremely oxygen-poor environment can be maintained, particularly in the area of the highest temperature.

In a further aspect, the invention relates to a method for operating a device according to the invention. The clay is thermally activated in a rotary kiln by means of hot gas generated outside the rotary kiln. As already stated, the spatial separation of hot gas generation and thermal

Activation, which allows both to be optimized separately.

In particular, the hot gas generating device can be operated using a substitute fuel at sufficiently high temperatures with sufficient oxygen for a sufficiently long time.

Time, whereas thermal activation takes place especially at lower

temperatures and preferably very low oxygen content.

In a further embodiment of the invention, the pressure in the

combustion device is higher than the pressure in the rotary kiln. This mode of operation is preferred in order to be able to work behind the rotary kiln in terms of gas flow using only an induced draft fan. The pressure in the

Hot gas generation device can be selected at or above ambient pressure.

In a further embodiment of the invention, the temperature in the

Combustion device selected higher than the temperature in the rotary kiln.

This enables safe combustion of substitute fuels, for example

Biomass, without this having a negative impact on the product quality, since too high a temperature leads to a deactivation of the clay.

In a further embodiment of the invention, the temperature in the rotary kiln is regulated by supplying substitute fuel to the combustion device.

The advantage is that no additional, mostly primary, fuels need to be used, thus minimizing carbon dioxide emissions from non-renewable fuels.

thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 11/14

In a further embodiment of the invention, the clay is used together with a

Reducing agent is fed into the rotary kiln. The reducing agent can, for example,

Coal, wood or other biogenic materials, preferably not completely burned

Residues from the combustion of a substitute fuel. Through the joint introduction, a local reducing atmosphere is created in the area of the clay to be activated in the rotary kiln, which prevents, for example,

Iron in the clay is oxidized and the clay, when activated, takes on a

Product takes on an undesirable color. This further supports the separation between the conditions of hot gas generation and activation, as this also

Oxygen concentration can be chosen more freely.

In a further embodiment of the invention, the rotary kiln is filled with

Temperature range of the process gas from 400 to 850 °C, preferably 500 to 650 °C

Oxygen or an oxygen-containing gas mixture is introduced. This is preferably done to ensure complete burnout of incompletely converted

combustion products of the organic components of the feed material (clay) and/or the incompletely converted reaction products of a reducing agent.

In a further embodiment of the invention, after the

In the hot gas generating device in the gas line, the oxygen content is selected to be below 2 vol.%, preferably below 1 vol.%. This minimizes the oxidation of a clay and thus an unwanted color change.

In a further embodiment of the invention, the hot gas generating device is heated electrically. The use of green electricity also enables

Avoidance of carbon dioxide emissions possible.

The device according to the invention is explained in more detail below using an embodiment shown in the drawings.

Fig. 1 first example thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 12/14

Fig. 2 second example

Fig. 3 third example

Fig. 4 fourth example

A first example of a device according to the invention is shown in Fig. 1. The clay to be activated is fed via a clay feed into a dryer 40, for example a

Drum dryer. From there, the clay is transferred to a rotary kiln 10 and thermally treated there. The activated clay is transferred from the rotary kiln 10 to a

Material cooler 30 and cooled there. During the transfer, the

The temperature of the clay is measured by a temperature sensor 11, which is arranged below the rotary kiln 10 and thus contactlessly by means of infrared and without strong

Dust pollution can measure the temperature without wear. The cooled activated

Product is removed from the material cooler 30 via the product outlet 32. This is the

Material flow through the device. The gas flow runs in countercurrent. The cold

Gas is fed via the gas supply 31 to the material cooler 30 and heated there. The heated gas is fed into a dust filter 50. The separated dust is fed to the

Product is fed to the product outlet 32. The dust-free heated gas is fed to the

A substitute fuel, for example biomass, is introduced into the substitute fuel supply 21 and is burned there safely and completely, for example at 1100 °C for at least 20s. Residues of the substitute fuel are discharged via a lock 22 so that the hot gas generating device 21 can be operated under a slight

Overpressure can be operated. The hot gas generated in the hot gas generating device 21 is fed into the rotary kiln 10 via a gas line 23, which has a length such that hot gas remains in the gas line 23 for about 5s. There the

Heat transfer to the clay to be activated and thus the activation of the clay. Since the heat generation does not take place within the rotary kiln 10, it can be assumed that part of the heat is transferred indirectly, i.e. first from the gas to the rotary kiln 10 and then from the

Rotary kiln 10 is used to apply pressure to the clay, since the surface of rotary kiln 10 is larger than the surface of the clay in rotary kiln 10. The gas, which has been cooled significantly in rotary kiln 10, is led from rotary kiln 10 into dryer 40. Dryer 40 is designed as a drum dryer. The gas is then discharged from dryer 40 via exhaust gas 42.

Fig. 2 shows a second example of a device according to the invention. The sound is

Via the clay supply 41 into a preheater 43, which is a cascaded

The preheated air in the preheater 43 is

Material is transferred to the rotary kiln 10 and thermally activated there. The

The material activated in the rotary kiln 10 is passed past the temperature sensor 11 onto a screen 60. For example, particles with more than 2 mm are passed into a crusher 61, and the free material with less than 2 mm from the screen 60 together with the material crushed in the crusher 61 is fed into a mixer 62 and mixed there with cold, returned material and then cooled in a material cooler 30 in the form of an entrained flow heat exchanger. The activated and cooled material leaving the material cooler 30 is divided and partly via the

Product return 33 is returned to the mixer 62 and the other part via the 32

Product outlet 32. The gas flow is guided analogously to the first example, only a dust filter 50 is arranged after the preheater 43 in order to transfer the finest material via the preheater 43 back into the rotary kiln 10 and thus ultimately into the finished product.

The third example shown in Fig. 3 differs from the one shown in Fig. 2

Example in that the temperature sensor 11 is arranged below the sieve 60.

The fourth example shown in Fig. 4 differs from the second example shown in Fig. 2 in that the screen 60 is designed as a drum screen and is mounted on a

Level with the rotary kiln 10. Therefore, the gas line 23 of the

The hot gas generating device 20 is connected to the screen 60 so that the hot gas is fed through the drum screen to the rotary kiln 60. Therefore, the

Temperature sensor 11 arranged behind the sieve 60.

Reference number thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 14/14 10 Rotary kiln 11 Temperature sensor 20 Medicinal gas generation device 21 Alternative fuel supply 22 Lock 23 Gas line 30 Material cooler 31 Gas supply 32 Product outlet 33 Product recirculation 40 Dryer 41 Clay supply 42 Exhaust gas 43 Preheater

Dust filter 60 Sieve 61 Crusher 62 Mixer

Claims (34)

thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 1/5 Patent claims 1. Device for producing a thermally activated clay, the device comprising a rotary kiln (10) and a hot gas generating device (20) separate from the rotary kiln (10), the hot gas generating device (20) and the rotary kiln (10) being connected via a gas line (23) for transferring hot gases generated in the hot gas generating device (20). 2. Device according to claim 1, characterized in that the device has a first temperature sensor (11), wherein the first temperature sensor (11) is an infrared sensor, wherein the first temperature sensor (11) is arranged in the outlet region below the rotary kiln (10). 3. Device according to one of the preceding claims, characterized in that the device has a second temperature sensor, wherein the second temperature sensor is arranged in or on the rotary kiln (10). 4. Device according to one of the preceding claims, characterized in that the gas line (23) has a length such that the gas within the gas line (23) has a residence time of between 0.5 and 10 s. 5. Device according to one of the preceding claims, characterized in that the device has a material cooler (30), wherein the rotary kiln (10) is connected to the material cooler (30) for transferring the thermally treated clay, wherein the material cooler (30) is connected to the hot gas generating device (20) for transferring gas preheated in the material cooler (30). 6. Device according to claim 5, characterized in that a dust filter (50) is arranged between the material cooler (30) and the hot gas generating device (20). thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 2/5 7. Device according to one of claims 5 to 6, characterized in that the material cooler (30) is a drum cooler. 8. Device according to one of claims 5 to 6, characterized in that the material cooler (30) is a cyclone or fluidized bed cooler. 9. Device according to claim 8, characterized in that a comminution device is arranged between the rotary kiln (10) and the material cooler (30). 10. Device according to claim 8, characterized in that a drum screen is arranged between the rotary kiln (10) and the material cooler (30). 11. Device according to claim 10, characterized in that a crusher (61) is arranged behind the coarse outlet of the drum screen. 12. Device according to one of claims 8 to 11, characterized in that the device has a product return, wherein the product return is designed for returning product cooled in the material cooler (30) between the rotary kiln (10) and the material cooler (30). 13. Device according to one of claims 5 to 12, characterized in that the device has a pre-cooler, wherein the pre-cooler is arranged between the rotary kiln (10) and the material cooler (30), wherein the pre-cooler has a direct or indirect water cooling. 14. Device according to one of the preceding claims, characterized in that the rotary kiln (10) has internals for the vertical conveyance of the clay. 15. Device according to one of the preceding claims, characterized in that the rotary kiln (10) has baffle rings. thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 3/5 16. Device according to one of the preceding claims, characterized in that the gas line (23) has a nitrogen supply for removing nitrogen oxides. 17. Device according to one of the preceding claims, characterized in that an induced draft fan is arranged behind the rotary kiln (10) in the gas flow direction. 18. Device according to one of the preceding claims, characterized in that a dust filter (50) is arranged behind the rotary kiln (10) in the gas flow direction, wherein the dust filter (50) is connected to the rotary kiln (10) or to one of the upstream units for material pretreatment, for example (40) or (43), for returning the separated dust. 19. Device according to one of the preceding claims, characterized in that the rotary kiln (10) has a larger diameter in the middle region. 20. Device according to one of the preceding claims, characterized in that the device has a preheater (43) and/or a dryer (40), wherein the preheater (43) or the dryer (40) is arranged behind the rotary kiln (10) in terms of gas flow and upstream of the rotary kiln (10) in terms of material flow. 21. Device according to one of the preceding claims, characterized in that the hot gas generating device (20) is a combustion device for a substitute fuel. 22. Device according to claim 21, characterized in that the combustion device has a gas-tight solids discharge. 23. Device according to one of claims 21 to 22, characterized in that the combustion device is a reverse-acting grate, a rotary kiln, a direct-current grate or a rotary hearth. thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 4/5 24 Device according to one of the preceding claims, characterized in that the rotary kiln (10) has an auxiliary combustion device. 25. Device according to one of the preceding claims, characterized in that the device has a mixing device, wherein the mixing device is designed to mix the clay with a reducing agent, wherein the mixing device is arranged in front of the rotary kiln (10) in the direction of material flow. 26. Device according to one of the preceding claims, characterized in that the rotary kiln (10) has at least one laterally arranged supply device for a reducing agent. 27.Device according to one of the preceding claims, characterized in that the rotary kiln (10) has at least one laterally arranged air supply. 28. Method for operating a device according to one of the preceding claims, characterized in that the clay is thermally activated in a rotary kiln (10) by means of hot gas generated outside the rotary kiln (10). 29. Method according to claim 28, characterized in that the pressure in the combustion device is higher than the pressure in the rotary kiln (10). 30. Method according to one of claims 28 to 29, characterized in that the temperature in the combustion device is higher than the temperature in the rotary kiln (10). 31. Method according to one of claims 28 to 30, characterized in that the temperature in the rotary kiln (10) is regulated by the supply of substitute fuel to the combustion device. thyssenkrupp Polysius GmbH 222380P00LU thyssenkrupp AG LU103142 5/5 32. Method according to one of claims 28 to 31, characterized in that the clay is fed to the rotary kiln (10) together with a reducing agent. 33. Method according to one of claims 28 to 32, characterized in that oxygen or an oxygen-containing gas mixture is introduced into the rotary kiln (10) in a temperature range from 400 to 850 °C, preferably from 500 to 650 °C. 34. Method according to one of claims 28 to 33, characterized in that after the hot gas generating device (20) in the gas line (23) the oxygen content is below 2 vol.%, preferably below 1 vol.%.