Method for the optimised loading of old concrete with carbon dioxide

Abstract

The present invention relates to a method for binding carbon dioxide to an old construction material (10), wherein: the reaction is carried out in a carbonation reactor (20); an old construction material (10) is supplied to the carbonation reactor (20); a carbon-dioxide-containing gas (30) is supplied to the carbonation reactor (20); a carbonation product (50) is discharged from the carbonation reactor (20), characterised in that the alkaline earth content of the old construction material (10) supplied to the carbonation reactor (20) and / or of the carbonation product (50) discharged from the carbonation reactor (20) is determined by means of elemental analysis (60), wherein: the degree of carbonation C of the carbonation product (50) is determined by IR spectroscopy; a degree-of-carbonation limit value Cmax is defined; if the degree-of-carbonation limit value Cmax is not reached, the supply of the old construction material (10) to the carbonation reactor (20) is reduced and / or the supply of the carbon-dioxide-containing gas (30) to the carbonation reactor (20) is increased, wherein, if the degree-of-carbonation limit value Cmax is exceeded, the supply of the old construction material (10) to the carbonation reactor (20) is increased and / or the supply of the carbon-dioxide-containing gas (30) to the carbonation reactor (20) is reduced.

Description

[0001] Method for the optimized loading of old concrete with carbon dioxide

[0002] The invention relates to a method for optimized control of the recarbonation of old concrete.

[0003] As part of the green transformation, the capture and storage of carbon dioxide generated during processes is increasingly being discussed and implemented. However, this also requires the long-term, reliable integration or storage of this captured carbon dioxide to prevent unwanted subsequent emissions into the atmosphere. One possibility is to bind the carbon dioxide to old concrete. Even during the lifespan of a concrete structure, up to 20% of the carbon dioxide released during its production is reabsorbed. After demolition and crushing, there is therefore significant potential for carbon dioxide absorption, which is thus chemically bound in a very stable manner, enabling secure long-term storage.

[0004] From DE 10 2022 132 073 A1 a method and a device for the efficient reduction of carbon dioxide emissions are known.

[0005] From DE 10 2023 133 490 a method and a device for the efficient reduction of carbon dioxide emissions are known.

[0006] From EP 4 108 316 A 1 a process for desulfurization and decarbonation of a gas is known.

[0007] The article by WANG ZHIQIANG ET AL: "High-efficiency CO2 sequestration through direct aqueous carbonation of carbide slag: determination of carbonation reaction and optimization of operation parameters", FRONTIERS OF ENVIRONMENTAL SCIENCE, HIGHER EDUCATION PRESS, BEIJING, Vol. 18, No. 1, September 4, 2023 (2023-09-04), XP038075802, ISSN: 2095-2201, DOI: 10.1007 / S11783-024-1772-Y [accessed on 2023-09-04] addresses CO2 sequestration. One challenge is to optimally utilize the potential, while also considering that excessive loading requires unnecessary energy and thus becomes a potential emission source itself. The challenge, therefore, lies in achieving the optimal loading rate in the process.

[0008] To make matters worse, old concrete or even recycled old concrete does not have a clearly defined initial property, so dynamic process control to adapt to fluctuations in the starting material is advisable.

[0009] The object of the invention is to create a process control for the known processes, so that optimal binding of carbon dioxide is enabled with efficient energy use.

[0010] This problem is solved by the method with the features specified in claim 1. Advantageous further developments are described in the dependent claims, the following description, and the drawings.

[0011] The process according to the invention serves to bind carbon dioxide to a waste building material. Waste building materials are, in particular, waste concrete and its reprocessing products. Waste concrete is typically upgraded—for example, by crushing—in such a way that silicon dioxide in the form of quartz, i.e., the inert sand and rock component, is separated and thus enriched with the waste cement, which has a high proportion of bound calcium oxide. Carbon dioxide can then be rebound to this, forming calcium carbonate. The higher the proportion of waste cement, the easier the recarbonation process. Therefore, many waste building materials are used in varying degrees of reprocessing to find a balance between the energy expenditure for upgrading and the energy savings during recarbonation. Therefore, combining them as waste building materials is advantageous. The reaction is carried out in a carbonation reactor.Such reactors are known in various forms from the prior art and can be designed, in particular, as slurry reactors, fluidized bed reactors, or entrained flow reactors. A certain moisture content of at least a few percent by weight, i.e., freely available water, is necessary for the reaction. The carbonation reactor itself can be designed in any known manner for carrying out the process according to the invention. A waste material is fed into the carbonation reactor. Furthermore, a carbon dioxide-containing gas, for example, exhaust gas to be cleaned, preferably enriched with carbon dioxide, is fed into the carbonation reactor. This enables recarbonation in the carbonation reactor. A carbonation product is then discharged from the carbonation reactor. This product is known to those skilled in the art and can be implemented in any possible embodiment.

[0012] According to the invention, the alkaline earth content of the waste building material fed into the carbonation reactor and / or of the carbonation product discharged from the carbonation reactor is determined by means of elemental analysis. This defines the baseline value, i.e., the maximum amount of material that can be carbonated. Since, as already explained, the composition of waste building material can vary considerably depending on the type of waste concrete used as a starting material, as well as the degree of processing and the enrichment of recycled cement aggregate, elemental analysis is the most suitable method for determining a measure of the theoretically possible carbonation, i.e., for determining the 100% value. Elemental analysis can be performed before the material is introduced into the carbonation reactor or after the conversion and discharge from the carbonation reactor, as the same baseline value can be determined from both measurements. Of course, elemental analysis can also be performed at both points.The degree of carbonation of the carbonation product is determined by IR spectroscopy. While the use of IR spectroscopy in the cement industry is rather unusual, it has proven particularly suitable for the quantitative determination of carbonate. Crucially, for effective control, both the alkaline earth content and the degree of carbonation of the carbonation product can be determined directly, i.e., without any time lag due to sampling, transport, and preparation. Therefore, it is necessary to combine two measurement methods that allow for such direct and immediate measurement. This is achieved by combining elemental analysis for the alkaline earth content with IR spectroscopy for the determination of the carbonate.Elemental analysis, for example using X-ray diffraction, X-ray fluorescence, or atomic absorption spectroscopy, is ideally suited to directly measuring the alkaline earth content during the process, as components such as silicon dioxide do not need to be separated beforehand. Similarly, carbonate content can be determined using infrared spectroscopy within the entire matrix of the recycled building material, preferably directly in the material stream. This combination enables effective measurement of the degree of carbonation of the carbonation product, which can then be used for process control.

[0013] A carbonation degree limit is defined. This limit, for example 80%, represents the ecological and economic optimum. Achieving a higher carbonation degree, while allowing for better utilization of storage capacity, also increases energy demand and thus potentially generates another source of emissions. The precise carbonation degree limit depends particularly on the specific carbonation reactor. If the carbonation degree limit is undershot, the feed of waste material to the carbonation reactor is reduced, and / or the feed of carbon dioxide-containing gas to the carbonation reactor is increased, and / or the feed fineness is increased, and / or the operating parameters of the carbonation reactor are adjusted.Preferably, if the carbonation degree falls below the limit value, the feed of waste material to the carbonation reactor is reduced and / or the feed of carbon dioxide-containing gas to the carbonation reactor is increased and / or the feed fineness is increased. This increases the degree of carbonation. Preferably, reducing the feed of waste material to the carbonation reactor simply increases the residence time in the carbonation reactor. Increasing the feed of carbon dioxide-containing gas to the carbonation reactor also includes increasing the carbon dioxide concentration of the gas. Since different carbonation reactors can be used, the adjustment of the operating parameters depends on the specific carbonation reactor.If, for example, this is a plowshare mixer, the residence time can be influenced by the rotational speed; if the carbonation reactor is a fluidized bed reactor, the residence time is set directly by the flow velocity. If the carbonation degree limit is exceeded, however, the feed of waste material to the carbonation reactor is increased and / or the feed of carbon dioxide-containing gas to the carbonation reactor is reduced and / or the feed fineness is decreased and / or operating parameters of the carbonation reactor are adjusted. Preferably, if the carbonation degree limit is exceeded, the feed of waste material to the carbonation reactor is increased and / or the feed of carbon dioxide-containing gas to the carbonation reactor is decreased and / or the feed fineness is decreased.

[0014] The key is the combination of two different analytical methods. Elemental analysis determines the amount of calcium and, optionally, magnesium. This allows the determination of the maximum potential for carbon dioxide uptake. While elemental analysis can theoretically be performed using wet chemical methods, fast and automatable techniques are preferred, particularly X-ray fluorescence analysis and neutron activation analysis, as these methods do not require further sample preparation. Of course, atomic absorption or atomic emission spectroscopy, preferably with an inductively coupled plasma, can also be used for elemental analysis. A second, very different technique is IR spectroscopy. While rather uncommon in the mineral industry, it is particularly suitable for determining the carbonate content.

[0015] In this way, the fluctuating proportion of alkaline earth metals, particularly calcium, is determined and thus taken into account via elemental analysis. Furthermore, the precise measurement of the carbonate content from both measurements allows for a highly reliable determination of the degree of carbonation, which in turn makes it possible to compare this with the defined limit value for carbonation and identify any deviations. This allows the entire process to be optimized and to respond very dynamically to fluctuations, particularly in the existing building material. This enables the optimal utilization of the existing building material as a carbon dioxide storage medium without unnecessarily expending energy in the process. In a further embodiment of the invention, the elemental analysis and the IR spectroscopic investigation are carried out directly in the product stream, i.e., online and therefore without sampling.Both measurements were chosen so that, in particular, another component, such as silicon dioxide (for example from the sand), would not interfere.

[0016] In a further embodiment of the invention, the degree of carbonation of the carbonation product is determined IR-spectroscopically in the range of 1250 to 1600 cm⁻¹. -1 (wave number) and / or 825 to 890 cm -1 These two areas have proven to be particularly characteristic, and the band appearing in the carbonated old concrete is almost exclusively attributable to carbonate, making determination very simple even in the highly complex composition. The degree of carbonation of the carbonation product is particularly preferred when determined by IR spectroscopy in the range of 825 to 890 cm⁻¹. -1 identified. This gang is particularly sharp and stands out especially well against the background.

[0017] In a further embodiment of the invention, elemental analysis is carried out using X-ray fluorescence analysis. This, like neutron activation analysis as an alternative, can be performed directly on the material without digestion or other preparation, especially when performed inline, i.e., in the actual process without sampling, and is therefore particularly suitable for automation of the process.

[0018] In a further embodiment of the invention, the degree of carbonation of the carbonation product is determined from the IR spectroscopic data using a calibration curve. For this purpose, different degrees of carbonation are first generated in a calibration step and then analyzed, for example, by wet chemical methods. In this way, a degree of carbonation can be assigned to the peak height or peak area via a calibration curve in a very simple manner, without having to perform an absolute analysis regularly.

[0019] The method according to the invention is explained in more detail below with reference to an embodiment illustrated in the drawings. Fig. 1 first example

[0020] Fig. 2 second example

[0021] Fig. 3 Calibration curve

[0022] Figure 1 shows a first example of a device for carrying out the process according to the invention. As is known from the prior art, the waste building material 10 is fed into a carbonation reactor 20. Likewise, a carbon dioxide-containing gas 30 is fed into the carbonation reactor 20. This results in the recarbonation of the waste building material 10, and the gas releases carbon dioxide accordingly and is discharged again as a low-carbon gas 40. The carbonation product 40 is removed from the carbonation reactor 20. The carbonation reactor 20, and thus the process, can be designed as desired, for example as a slurry reactor, a fluidized bed reactor, or an entrained flow reactor.

[0023] It is essential that in the first example shown, the alkaline earth content is determined upstream of the carbonation reactor 20 by means of an elemental analysis 60, thus determining the total amount available for recarbonation. For example, and preferably, the elemental analysis 60 is carried out by means of X-ray fluorescence analysis. Downstream of the carbonation reactor 20, the degree of carbonation C is determined by an IR spectrometer 70 by recording and evaluating the peak in the range of 825 to 890 cm⁻¹. -1The data from the elemental analysis 60 and the IR spectrometer 70 are transmitted to the control unit 80, which, based on a predefined carbonation degree limit Cmax and the current carbonation degree C, then controls the supply of the waste building material 10, the supply of the carbon dioxide-containing gas 30, and the carbonation reactor in order to enable operation as close as possible to the carbonation degree limit Cmax. This is easily achieved by changing the residence time of the waste building material 10 in the carbonation reactor 20.

[0024] Fig. 2 shows a second example, which differs from the first example by an additional IR spectrometer 70 upstream of the carbonation reactor 20, allowing the degree of carbonation C in the old building material to be determined. Due to varying lifespans and material thicknesses, the degrees of carbonation C in the old building material 10 can vary considerably. Therefore, this information can be advantageous, particularly to ensure consistent decarbonation of the carbon dioxide-containing gas 30.

[0025] Figure 3 shows a schematic calibration curve. It has been shown that the intensity is in the range of 825 to 890 cm⁻¹. -1 exhibits good linearity between the peak intensity I and the degree of carbonation C, which can be easily determined for each specific system via simple calibration measurements. This also applies to the broader peak in the range of 1250 to 1600 cm⁻¹. -1, although this peak is broader. The defined carbonation degree limit Cmax represents the economic and therefore also the ecological optimum for the operation.

[0026] Reference sign

[0027] 10 Old building materials

[0028] 20 Carbonation reactor

[0029] 30 Carbon dioxide-containing gas

[0030] 40 Low-carbon gas

[0031] 50 Carbonation product

[0032] 60 Elementary Analysis

[0033] 70 IR spectrometers

[0034] 80 Control unit

[0035] C Degree of carbonation

[0036] Cmax carbonation degree limit

[0037] I Intensity

Claims

Patent claims 1. A process for binding carbon dioxide to a waste building material (10), wherein the reaction is carried out in a carbonation reactor (20), wherein a waste building material (10) is fed to the carbonation reactor (20), wherein a carbon dioxide-containing gas (30) is fed to the carbonation reactor (20), wherein a carbonation product (50) is discharged from the carbonation reactor (20), characterized in that the alkaline earth content of the waste building material (10) fed to the carbonation reactor (20) and / or of the carbonation product (50) discharged from the carbonation reactor (20) is determined by means of elemental analysis (60), wherein the degree of carbonation (C) of the carbonation product (50) is determined by IR spectroscopy, and wherein a carbonation degree limit (Cmax) is established.wherein, if the carbonation degree limit (Cmax) is undershot, the feed of the waste material (10) to the carbonation reactor (20) is reduced and / or the feed of the carbon dioxide-containing gas (30) to the carbonation reactor (20) is increased and / or the feed fineness is increased and / or operating parameters of the carbonation reactor (20) are adjusted, wherein, if the carbonation degree limit (Cmax) is exceeded, the feed of the waste material (10) to the carbonation reactor (20) is increased and / or the feed of the carbon dioxide-containing gas (30) to the carbonation reactor (20) is reduced and / or the feed fineness is decreased and / or operating parameters of the carbonation reactor (20) are adjusted.

2. Method according to claim 1, characterized in that the Degree of carbonation (C) of the carbonation product (50) IR spectroscopically in the range of 1250 to 1600 cm' 1and / or 825 to 890 cm' 1 is determined.

3. Method according to claim 2, characterized in that the Degree of carbonation (C) of the carbonation product (50) IR spectroscopically in the range of 825 to 890 cm' 1 is determined.

4. A method according to any one of the preceding claims, characterized in that the elemental analysis (60) is carried out by means of X-ray fluorescence analysis.

5. A method according to any one of the preceding claims, characterized in that the degree of carbonation (C) of the carbonation product (50) is determined by means of a calibration curve from the IR spectroscopic data.

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