LU103046B1 - Method and device for the efficient reduction of carbon dioxide emissions - Google Patents

Abstract

The present invention relates to a carbon dioxide separation plant, wherein the carbon dioxide separation plant has a gas supply 80, a treatment device 40 fluidically downstream of the gas supply 80, a separation device fluidically downstream of the treatment device 40 and a gas outlet 56 fluidically downstream of the separation device, wherein the carbon dioxide separation plant has a waste material supply 10 10, wherein the waste material supply 10 is connected to a humidification device 30 for transferring the waste material, wherein the humidification device 30 is connected to the treatment device 40, wherein the separation device is connected to a waste material outlet.

Description

thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 1/19

Method and device for the efficient reduction of carbon dioxide emissions

The invention relates to a method for using old building materials, for example cement stone,

To safely bind carbon dioxide and thus ensure safe long-term storage.

It is becoming increasingly necessary to conserve natural resources and to use recycled materials. Likewise, emissions of carbon dioxide as

The cause of global warming is critical. Therefore, the separation of carbon dioxide from the exhaust gas and its permanent storage or use is becoming increasingly important. One possible form is the introduction of liquefied carbon dioxide into the

Soil. However, this process is not without controversy, as permanent retention is not necessarily guaranteed and if it were to escape, the greenhouse effect would be intensified again, especially since further energy is required for separation and storage, potentially producing carbon dioxide again.

One of the carbon dioxide-intensive industries is the cement industry. On the one hand, the process requires a lot of energy, which leads to carbon dioxide emissions when using conventional fossil fuels. On the other hand, carbon dioxide is released from the raw material, such as limestone, as part of the process.

On the other hand, large quantities of old concrete are produced when concrete structures are demolished. Therefore, there is currently discussion about recycling concrete, for example to make new

Cement is produced. However, the problem here is that sand and the hardened cement are mixed and bonded together in a way that is difficult to separate. The sand-free or at least sand-poor component of the old concrete is also known as

It is known that concrete during its lifetime

carbon dioxide, but only a fraction of the carbon dioxide released from the limestone during production. After a long time, for example in very old

In buildings, this value can be around 20% based on the calcium content of the concrete, so it is reabsorbed very slowly and therefore over long periods of time in about 1/5 of the carbon dioxide originally released.

thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 2/19

WO 2020 / 058 247 A1 describes a process and a plant for the processing of

Material containing cement stone is known.

The use of carbon dioxide from and for cement is known from EP 3656 750 A2.

The object of the invention is to provide a safe and permanent method for the separation and final storage of carbon dioxide without requiring a complex, particularly energy-intensive process, which itself would require a new

represents a source of emissions.

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

Features and by the carbon dioxide separation system with the features specified in claim 13. Advantageous further developments result from the

Subclaims, the following description and the drawings.

The process according to the invention serves to bind carbon dioxide to a

Old building material. The process comprises the following steps: a) providing the old building material, b) moistening the old building material to a moisture content of 5 to 25 wt.%, c) introducing the old building material into a gas stream containing carbon dioxide and

Transport of the old building material in the gas stream for at least 1 s, d) Separation of the old building material from the gas stream.

The procedure is therefore fundamentally different from previous procedures.

Treatment takes place during transport in the gas stream. It is therefore not carried out in an aqueous environment as before, but in a comparatively semi-dry

gas flow. This makes the process particularly gentle. This allows the

Conversion directly from the gas phase, which contains carbon dioxide, with the old building material.

This allows for a very fast conversion of relatively small particles. At the same time, the transport in the gas phase also allows for easy

The ability to separate even the smallest particles is given, so that different

Residence times for different particle sizes can be realized. It is essential that the old building material is dry enough on the one hand to be transported in a gas stream and moist enough on the other hand so that the conversion can take place quickly enough. Therefore, for example, the semi-dry formulation can be chosen here. Preferably, for example, a thin film of water can form on the

particle surface or water penetrating the particle pores. At the same time, however, the formation of sludge should be prevented, which is no longer in the

Gas flow can be transported and treated. This optimum is achieved for old building materials, especially old cement brick, at 5 to 25 wt.% water content (moisture).

Old building material in the sense of the invention includes in particular building rubble, broken concrete,

Cement stone and the like in various processing stages.

In a further embodiment of the invention, comminution takes place before or after introduction in step c). The comminution also includes, in particular,

Deagglomeration of particles adhering together, in particular by

Moistening in step b) can cause particles to stick together.

For example, the transport and thus the implementation in step c) takes place in a

Riser pipe. Below this riser pipe, for example, a hammer mill is arranged. In this embodiment, the old building material can be fed directly into the

Hammer mill. Alternatively, the old building material can be introduced into the riser pipe. In this case, excessively large particles not carried by the gas flow sink

Particles fall into the hammer mill, are crushed there and are taken up and transported by the gas stream. The crushing leads to two positive

effects. On the one hand, large particles become smaller, so that they are easier to

On the other hand, the smaller size of the

Particle size reduces the diffusion length for carbon dioxide and thus the

Reaction time shortened.

In a further embodiment of the invention, during transport in

Step c) re-moistening. This can be done, for example, by spraying

Water. Alternatively or additionally, steam can also be used.

This prevents excessive drying during transport in the gas stream thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 11/30/2022 LU103046 4/19. This means that the moisture content in step b) in particular can be set lower, so that improved transport in the gas stream in step c) is possible.

In a further embodiment of the invention, the separation in step d) takes place in two stages. First, in a first sub-step, the larger particles are separated and then in a second sub-step, the smaller

Particles are separated. The first sub-step can be carried out, for example, in a

Separation cyclone or a classifier. The gas flow is then passed through a filter. In the separation cyclone or classifier, the larger

Particles are separated, the small particles in the filter. The first sub-step and the second sub-step can run simultaneously. Alternatively, the first sub-step and the second sub-step can be carried out one after the other, with either the first

Sub-step occurs before the second sub-step or the second sub-step occurs before the first

Sub-step is completed.

In a further embodiment of the invention, after step d), the old building material is returned so that steps b) to d) are repeated. This allows the

The capacity of the old building material to absorb carbon dioxide, which usually corresponds to about 80% to 90% of the amount of CaO, for example, must be fully exploited.

If the separation is carried out in two stages, so that two different fractions of the

old building material, for example, only the fraction from the first step of separation, i.e. the larger particles, can be recycled. In this case, the finer particles separated in the second step of separation are discharged.

This is preferred if the fraction of the smallest particles is already present in a simple

Complete run (in the sense of what is technically possible, i.e. in particular in the

Range of about 80% to 95% of the theoretical maximum possible conversion) with

carbon dioxide. Alternatively, the second fraction can be partially or completely recycled.

In a further embodiment of the invention, a determination of the CO, content of the old building material is carried out. The old building material is returned and steps b) to d) are repeated until a predetermined threshold value of the CO--

content is exceeded. Usually, a maximum loading of thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 5/19 about 95% is assumed, based, for example, on the theoretical CaO content of the

This corresponds to the value that concrete can achieve under normal

circumstances is able to absorb. The threshold value can therefore be set to 60%, 80%, 85%, 90% or 95%, for example, so that the absorption capacity of the old building material is used as far as possible without entering a kinetically disadvantageous range. If the threshold value is exceeded, the

Old building material is removed and new old building material is preferably added. While a maximum of 20% is bound back into the concrete naturally, the invention binds significantly more carbon dioxide in a permanent manner.

In a further embodiment of the invention, the threshold value of the CO,-

Content to 60%, preferably 70%, more preferably 80%, more preferably 85%, more preferably 90%, more preferably 85%, of the sum of calcium, magnesium and/or

Iron. As already mentioned, the limit is about 20%, which without further support already in the building due to loading with carbon dioxide in simple

way over a very long period of time, so that the old building material supplied has a

load between 0% and 20%. The threshold value is intended to prevent a residual absorption capacity that is too low (to the hypothetical / mathematically possible 100%) from leading to practically no further carbon dioxide being released from the

The threshold value thus ensures the balance between maximum utilization of the absorption capacity of the old building material and the

Kinetics of carbon dioxide capture.

In a further embodiment of the invention, the separation in step d) is carried out in a size-selective manner in at least two fractions. This can be done, for example, as already explained, with a separating cyclone or sifter and a filter. The coarser fraction is recycled and the finer fraction is discharged from the process. Due to the significantly shorter diffusion paths for the carbon dioxide from the gas stream, the reaction in small particles is significantly faster than in large

particles. Therefore, the removal of very fine particles, for example after separation from a filter, is sensible and effective.

thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 6/19

In a further embodiment of the invention, after step d), the gas stream is at least partially recycled before step c). This allows the carbon dioxide

content of the gas stream can be reduced. For example, the gas stream can be completely recycled until the carbon dioxide concentration falls below a certain predetermined level. This has the advantage that particularly low carbon dioxide

concentrations are achievable, but the disadvantage is that the treatment of the

gas flow is only discontinuous, which is the case for most exhaust gas producing

systems. Alternatively, only partial recirculation is possible. This allows a lower carbon dioxide concentration than with a simple run-through.

At the same time, a continuous supply and removal of gas is possible, which

Treatment of an exhaust gas stream is simplified. However, it should be noted that the gas flow conveyed by the process increases in the amount of recirculation.

If, for example, 80% of the gas flow is recycled, the gas flow in the

Step c) five times as large as the supplied exhaust gas stream to be cleaned.

In a further embodiment of the invention, the carbon dioxide concentration in the gas stream after transport in step c) is measured. The proportion of the

The amount of gas flow returned in step c) is determined depending on the determined

carbon dioxide concentration is selected. This active control enables, for example,

Compliance with emission values. In addition, this can also be used to detect when the material can no longer absorb carbon dioxide, i.e. after

reaction the absorption capacity for carbon dioxide is exhausted.

In a further embodiment of the invention, a measurement of the moisture content is carried out before and/or after moistening in step b). The measurement of the

Moisture content is preferably measured using a NIR sensor. The preferred sensor is the

Humidification in step b) is regulated depending on the measured moisture content.

It is important to keep the humidity level high enough so that the absorption of the

carbon dioxide is well absorbed. On the other hand, the moisture content should remain low enough to enable transport in the gas stream. Active control is therefore advantageous.

thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 7/19

In a further embodiment of the invention, the gas stream in step c) is a

Exhaust gas flow is selected. For example, the exhaust gas flow can come from a cement plant. For example, the exhaust gas flow has a temperature between 80 °C and 200 °C. It is particularly preferred that the exhaust gas flow is not heated. The

The advantage of this process is the low energy consumption for a safe and long-term binding of the carbon dioxide from the exhaust gas. However, an exhaust gas stream from a waste incineration plant, for example, can also be used.

In a further aspect, the invention relates to a carbon dioxide separation plant.

In particular, the carbon dioxide separation plant is designed to carry out the method according to the invention. The carbon dioxide separation plant has a gas supply, a downstream gas supply

Treatment device, a separation device downstream of the treatment device and a gas outlet downstream of the separation device. Furthermore, the

Carbon dioxide separation plant has a waste material feed. The waste material feed is connected to a humidification device for transferring the waste material. The

The connection can be made either directly or, for example, via an old building material storage facility arranged in between. The old building material is moistened in the humidification device. The humidification device is connected to the

Treatment device. In the treatment device, the moistened waste material stream meets the gas stream. Here, a transition from

Carbon dioxide from the gas stream into the waste material stream. The separation device is connected to a waste material outlet. The waste material outlet can be used to

Old building materials loaded with carbon dioxide can be removed and, for example, permanently stored or used for further purposes.

The humidification device can be, for example, a humidification screw or a

be a mixer.

Thus, from the treatment device to the separation device, the

Gas flow and the old building material flow are led in parallel and thus the old building material flow in thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 8/19

Gas flow. This makes the device different from conventional systems that work with a liquid-solid phase in the treatment device, so that separation already takes place in the treatment device and therefore no downstream separation device is present. This also means that only a significantly lower water requirement is required and thus the product (old building material with bound carbon dioxide) is already much drier and therefore without further

Energy supply can be used, for example to store it permanently, which can also be done by reusing it in the construction industry.

In a further embodiment of the invention, the

carbon dioxide separation plant, a first waste building material storage facility.

The old building material storage is arranged between the old building material supply and the humidification device. The old building material storage is particularly preferred if the old building material is to be returned.

In a further embodiment of the invention, the

carbon dioxide separation plant, a second waste material storage facility. The second

The old building material storage facility is preferably arranged parallel to the first old building material storage facility.

This means that either the first waste building material storage facility or the second

Old building material storage Old building material can be fed to the humidification device. Old building material can also be fed from the old building material supply either to the first old building material storage or to the second old building material storage. If a return is available, the return can also be fed to the first old building material storage or to the second old building material storage. In this case, it is preferred that, for example, old building material is fed to the humidification device from the first old building material storage and that the old building material is fed back to the first old building material storage via the return. In parallel, the second old building material storage can, for example, be fed from the

If the old building material that is being recycled is sufficiently loaded with carbon dioxide, this old building material can be removed from the

carbon dioxide separation plant. The second

Old building material storage Old building material is fed to the humidification device and

Return of the old building material is fed back into the second old building material storage facility. The now emptied first old building material storage facility can then be refilled via the old building material feed system.

In a further embodiment of the invention, the

Carbon dioxide separation plant has a recirculation device. The

The recycling device is designed to collect old building material from the

Separation device connected to the separation device. The

The recycling device is designed to return the old building material to the

Humidification device, in particular in the first old building material storage and/or an optional second old building material storage. The return ensures optimal loading and thus utilization of the old building material for separation and

Binding of carbon dioxide is possible in a simple manner. This also makes it possible to use a very broad particle size distribution, which therefore has very different kinetics.

The use of a recycling device with a first waste material storage and a second waste material storage enables yet another variant of the

For example, the supply of fresh old building material from the

Waste material feed only into the first waste material storage facility and the return from the

Return device only in the second waste building material storage facility. Here, after the

Only a part of the waste material is recycled after separation. According to the proportion discharged here, the waste material from the first waste material storage and from the second

Old building material storage Old building material is fed to the humidification device. If, for example, 80 % of the old building material is returned, the first

Old building material storage 1/5 and from the second old building material storage 4/5 of the

Humidification device supplied old building material.

In a further embodiment of the invention, the separation device comprises a first partial separation device and a second partial separation device. In particular, the first partial separation device is a sifter or a separating cyclone, the second

Partial separation device is a filter. This has two advantages. In addition to separating a very fine fraction that is usually already saturated with carbon dioxide after the first pass, the exhaust gas stream is also freed of old building material to such an extent that it can be released into the environment.

In a further embodiment of the invention, the first partial separation device is connected to the return device. The second partial separation device is connected to the

In this embodiment, a direct connection is made

The fine fraction is discharged while the coarse fraction is returned. Another advantage is that the cycle is not interrupted by the carbon dioxide-saturated

Fine fraction is loaded.

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

Re-humidification device. The re-humidification device can be, for example, a water injection or the supply of steam.

This will prevent the old building material from drying out too much in the

treatment device and at the same time a very low moisture content can be set in the humidification device, which in turn provides very good

This makes the old building material able to fly.

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

Humidification screw.

In a further embodiment of the invention, the

Carbon dioxide separation plant has a shredding device. The

The comminution device is arranged in gas flow terms upstream of the treatment device. For example and preferably, the comminution device is a

Hammer mill. Further exemplary and preferred is the treatment device as

riser pipe and the crushing device under the

This arrangement has the advantage that especially large particles, which are not carried upwards in the riser pipe by the gas flow, but are carried downwards by gravity into the crushing device and are crushed there and thus ultimately become airworthy and can be released through the

The advantage is that even small, airworthy particles are not further crushed, which saves energy. Of course, it is also possible to separate the old building material from the

Humidification device must be completely inserted into the shredding device.

This is particularly preferred if the fine fraction is discharged from the circuit after a filter, while the larger fraction is discharged after a

Separation cyclone or sifter. The constant reintroduction into the shredding device increases the proportion of fine material discharged.

In a further embodiment of the invention, the comminution device is arranged below the treatment device. As already stated, this is preferred if the treatment device is designed as a riser pipe.

In a further embodiment of the invention, the treatment device is designed as

Riser pipe executed.

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

Hammer mill.

In a further embodiment of the invention, the

The carbon dioxide separation plant has a gas recirculation system. The gas recirculation is

Return of at least one partial gas stream from the separation device to the

treatment device. This enables a particularly high reduction of carbon dioxide in the gas stream.

In a further embodiment of the invention, the

Carbon dioxide separation plant a sensor to measure the

carbon dioxide concentration in the gas stream. The sensor is designed to measure the

Carbon dioxide concentration is arranged after the treatment device. This makes it possible to either cyclically release the gas that has been sufficiently freed of carbon dioxide or to adjust the ratio between recirculation and release, for example in order to be able to comply with a maximum permissible emission requirement.

The carbon dioxide separation plant according to the invention is explained in more detail below using an embodiment shown in the drawings.

thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 12/19

Fig. 1 first embodiment

Fig. 2 second embodiment

Fig. 3 third embodiment

A first embodiment is shown in Fig. 1. A waste material feed 10 is used to

Old building material, for example cement stone, is introduced into the system. For example, the old building material is first introduced into the first old building material storage 21. From the first old building material storage 21, the old building material is led to the humidification device 30 past a moisture sensor 32. According to the

The moisture content of the old building material determined by the moisture sensor 32 is

Humidification device 30 Water is added to a content of, for example,

% by weight of water. For example, the humidification device 30 is

This enables a quick and thorough mixing 15. The old building material is fed from the humidification device 30 into the

Treatment device 40 in the form of a riser pipe. The

Treatment device 40 in the form of a riser pipe is supplied with an exhaust gas from a

Gas supply 80 flows through. The gas flow removes the small particles of the

old building material is carried upwards, large particles sink to the bottom. Below the

Treatment device 40 is a crushing device 42 in the form of a

Hammer mill. There, the large particles are crushed until they are carried away by the gas flow and transferred to the treatment device 40. In the treatment device 40, the reaction takes place between the carbon dioxide from the

Gas flow and, for example, CaO from the old building material to CaCO;. This makes the

Carbon dioxide is removed from the gas stream and permanently bound. In a subsequent separation cyclone 44, the majority of the old building material is removed from the

Gas stream removed. The gas stream is passed through a filter for further cleaning, in which even very fine old building material particles are separated. Then a sensor for measuring the carbon dioxide concentration 52 records the carbon dioxide concentration in the gas stream. The gas flow divider 54, for example, is regulated depending on the measured carbon dioxide concentration. There are three fundamentally different procedures here. On the one hand, the gas flow divider 54 can completely recirculate the gas stream until the recorded carbon dioxide concentration falls below a specified value thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 11/30/2022 LU103046 13/19 (for example <2 vol.%). The gas flow divider 54 is then switched over and the gas flow is completely led to the gas outlet 56, for example a chimney. At the same time, new gas is supplied from the gas supply 80. Secondly, the gas flow divider 54 can be variably controlled, whereby the quantity fed to the gas outlet 56 is selected to be larger, the lower the detected

carbon dioxide concentration. In a third variant, a sensor can be used to measure the

carbon dioxide concentration 52 and the gas flow divider 54 can be dispensed with, the

The gas flow is completely led to the gas outlet 56. This is preferred if only a small part of the carbon dioxide is to be removed, for example in a cement plant operated entirely with renewable energy sources, in order to only remove the

Carbon dioxide content from the exhaust gas, which comes from the mineral reactants. However, since such an application is probably not suitable for complete removal of the

Since there is probably not enough old building material available to produce carbon dioxide and therefore only partial separation is possible, a direct discharge of the gas stream can be advantageous.

The waste material from the separating cyclone 44 and the filter 50 is combined and fed to a waste material flow divider 70. This can also be operated in different ways. Either the waste material is recycled cyclically and only temporarily or preferably completely discharged, for example when the carbonate content in the

old building material is so high that further recycling is not advisable. Alternatively, a partial flow can be continuously separated and discharged, whereas a second

This second partial flow is fed back to the second

Old building material storage facility.

Fig. 2 shows a second embodiment. This differs from the first

The advantage of this embodiment is that the waste material separated from the filter 50 is discharged directly and not recycled. Secondly, the system has a

Carbonate Sensor 72, which measures the carbonate content in the old building material after

Separation in the separation cyclone 44. Preferably, the

Waste material flow divider 70 completely reverses the waste material flow until the carbonate

Carbonate content detected by sensor 72 exceeds a threshold value. Then the

Old building material stream is completely discharged. At the same time, the supply of thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 14/19

Old building material from the first old building material storage and the second old building storage are switched, thus exchanging their tasks. The third difference is the

Old building material is introduced directly into the shredding device 42 after the moistening device 30, thus increasing the proportion of small and therefore very quickly reacting particles and at the same time the discharge of the old building material after separation in the filter 50.

A third embodiment is shown in Fig. 3. The third embodiment differs from the second embodiment in that at the end of the

A sifter 43 is arranged in the treatment device 40, which is located in the riser pipe. Very coarse particles of the old building material are separated there and completely returned.

The waste material separated in the separator cyclone 44 and the filter 50 is removed from the

system removed.

Reference numerals 10 Waste material feed 21 First waste material storage 22 Second waste material storage 30 Humidification device 32 Humidity sensor 40 Treatment device 42 Shredding device 43 Sifter 44 Separation cyclone 50 Filter 52 Sensor for measuring the carbon dioxide concentration 54 Gas flow divider 56 Gas outlet 70 Waste material flow divider 72 Carbonate sensor 80 Gas feed

Claims (26)

thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 15/19 Patent claims 1. Process for binding carbon dioxide to an old building material, the process comprising the following steps: a) providing the old building material, b) moistening the old building material to a moisture content of 5 to 25 wt. %, c) introducing the old building material into a carbon dioxide-containing gas stream and transporting the old building material in the gas stream for at least 1 s, d) separating the old building material from the gas stream. 2. Process according to claim 1, characterized in that comminution takes place before or after the introduction in step c). 3. Method according to one of the preceding claims, characterized in that re-moistening takes place during the transport in step c). 4. Method according to one of the preceding claims, characterized in that the separation in step d) takes place in two stages and firstly the larger particles are separated in a first sub-step and the smaller particles are separated in a second sub-step. 5. Method according to one of the preceding claims, characterized in that after step d) the old building material is returned, so that steps b) to d) are repeated. 6. Method according to claim 5, characterized in that a determination of the CO2 content of the old building material is carried out, wherein the return of the old building material and repetition of steps b) to d) are carried out until a predetermined threshold value of the CO2 content is exceeded. 7. Method according to claim 6, characterized in that the threshold value of the CO2 content is set at 60%, preferably 70%, more preferably 80%, more preferably 85%, more preferably 90%, more preferably 85%, of the sum of calcium, magnesium and/or iron. thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 16/19 8. Process according to one of claims 5 to 7, characterized in that the separation in step d) is carried out in a size-selective manner in at least two fractions, the coarser fraction being recycled and the finer fraction being discharged from the process. 9. Method according to one of the preceding claims, characterized in that a measurement of the moisture content is carried out before and/or after the moistening in step b), wherein the measurement of the moisture content is preferably carried out by means of an NIR sensor. 10. Process according to one of the preceding claims, characterized in that an exhaust gas stream is selected as the gas stream in step c). 11. Process according to one of the preceding claims, characterized in that after step d) the gas stream is at least partially recycled before step c). 12. Method according to claim 11, characterized in that the carbon dioxide concentration in the gas stream is determined after the transport in step c), wherein the proportion of the amount of the gas stream returned before step c) is selected as a function of the determined carbon dioxide concentration. 13. Carbon dioxide separation system, wherein the carbon dioxide separation system has a gas supply (80), a treatment device (40) fluidically downstream of the gas supply (80), a separation device fluidically downstream of the treatment device (40) and a gas outlet (56) fluidically downstream of the separation device, wherein the carbon dioxide separation system has a waste material supply (10), wherein the waste material supply (10) is connected to a humidification device (30) for transferring the waste material, wherein the humidification device (30) is connected to the treatment device (40), wherein the separation device is connected to a waste material outlet. thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 17/19 14. Carbon dioxide separation plant according to claim 13, characterized in that the carbon dioxide separation plant has a first waste building material storage (21), wherein the first waste building material storage (21) is arranged between the waste building material supply (10) and the humidification device (30). 15. Carbon dioxide separation plant according to one of claims 13 to 14, characterized in that the carbon dioxide separation plant has a return device, wherein the return device for receiving old building material from the separation device is connected to the separation device, wherein the return device is designed to return the old building material in front of the humidification device (30), in particular into the first old building material storage device (21). 16. Carbon dioxide separation plant according to one of claims 13 to 15, characterized in that the separation device has a first partial separation device and a second partial separation device. 17. Carbon dioxide separation plant according to claim 16, characterized in that the first partial separation device is a sifter (43) or a separation cyclone (44), wherein the second partial separation device is a filter (50). 18. Carbon dioxide separation plant according to one of claims 16 to 17, characterized in that the first partial separation device is connected to the recirculation device and the second partial separation device is connected to the old building material outlet. 19. Carbon dioxide separation plant according to one of claims 13 to 18, characterized in that the treatment device (40) has a re-humidification device. 20. Carbon dioxide separation plant according to one of claims 13 to 19, characterized in that the humidification device (30) is a humidification screw. thyssenkrupp Industrial Solutions AG 221539P00LU thyssenkrupp AG 30.11.2022 LU103046 18/19 21. Carbon dioxide separation plant according to one of claims 13 to 20, characterized in that the carbon dioxide separation plant has a comminution device (42), wherein the comminution device (42) is arranged in gas flow upstream of the treatment device (40). ) 22. Carbon dioxide separation plant according to claim 21, characterized in that the comminution device (42) is arranged below the treatment device (40). 23. Carbon dioxide separation plant according to claim 22, characterized in that the treatment device (40) is designed as a riser pipe. 24. Carbon dioxide separation plant according to one of claims 21 to 23, characterized in that the crushing device (42) is a hammer mill. 25. Carbon dioxide separation plant according to one of claims 13 to 24, characterized in that the carbon dioxide separation plant has a gas return, wherein the gas return is designed to return at least a partial gas flow from the separation device to the treatment device (40). 26. Carbon dioxide separation plant according to claim 25, characterized in that the carbon dioxide separation plant has a sensor for measuring the carbon dioxide concentration (52) in the gas stream, wherein the sensor for measuring the carbon dioxide concentration (52) is arranged downstream of the treatment device (40).