Batch for the production of carbon-bonded products and method for producing carbon-bonded bricks

Abstract

The present invention relates to a batch for the production of carbon-bonded products and a method for producing carbon-bonded products.

Description

Technical Field

[0001] The present invention relates to batches for the production of carbon-bonded products and methods for producing carbon-bonded products.

Background Art

[0002] Carbon-bonded products are known, especially in the form of carbon-bonded refractory bricks, i.e., bricks having a carbon bond and being exposed to high temperatures during application. A typical application of such carbon-bonded refractory bricks is, for example, use in metallurgical plants for the production and treatment of molten steel.

[0003] Batches containing a refractory component, a carbon component, and an organic binder are typically used in the production of carbon-bonded refractory products. The refractory component includes one or more refractory raw materials, such as magnesia-based raw materials or alumina-based raw materials. The carbon component is a carrier of free carbon and serves to form a carbon bond. A typical carbon component is based on graphite. The organic binder, on the one hand, gives the batch green strength. On the other hand, the organic binder can also be involved in the formation of the carbon bond.

[0004] The batch containing the above components is heated to a temperature at which the carbon bond is formed from the carbon component and the organic binder. After firing, a carbon-bonded refractory product is obtained.

[0005] The production of refractory raw materials constituting the refractory component is energy-intensive. In particular, these raw materials are usually produced with a high heat energy input. On the one hand, this high heat energy input is disadvantageous for economic reasons, especially since it is associated with particularly high costs. On the other hand, the high heat energy input is also disadvantageous for ecological reasons, especially since it is inevitably associated with a significant formation of carbon dioxide. However, this carbon dioxide is released into the atmosphere and contributes to the greenhouse effect.

[0006] Typical refractory raw materials for refractory components are magnesia, i.e., raw materials mainly composed of magnesium oxide (MgO). The main supply source for the production of magnesia is magnesite, i.e., magnesium carbonate (MgCO3). In order to produce magnesia from magnesite, calcination must be carried out, and it is necessary to heat magnesite to a temperature exceeding 1,700 °C, which requires a significant input of thermal energy.

[0007] Therefore, for ecological and economic reasons, attempts have been made so far to reduce the thermal energy input required to provide batches for the production of carbon-bonded refractories.

[0008] For example, attempts have been made to recycle used carbon-bonded refractory materials or reuse them in the production of new carbon-bonded refractory products. The advantage of using used refractory materials with carbon bonding as refractory components in this way is, in particular, that this material can be made available with a much lower input of thermal energy. This is because it is not necessary to reuse a number of thermal processes that require a significant energy input such as the calcination of magnesite shown above to provide such used refractory materials.

[0009] However, it has been found that using used refractory materials with carbon bonding as raw materials for the production of new carbon-bonded refractory products is extremely problematic. This is because the properties of carbon-bonded refractory products manufactured with such used refractory materials with carbon bonding as the basic component are significantly deteriorated compared to the properties of carbon-bonded refractory products manufactured without using such used refractory materials. In some cases, the properties were insufficient, so the manufactured products could not be put to useful use. Summary of the Invention Problems to be Solved by the Invention

[0010] The object of the present invention is to provide a batch for the production of carbon-bonded refractory products, the components of which can be provided with a low energy input, in particular a thermal energy input. In particular, the components should be provided with an energy input lower than that possible with batches known from the prior art.

[0011] In particular, the object of the present invention is to provide a batch comprising used refractory materials having carbon bonds, from which carbon-bonded refractory products having good refractory properties can be produced.

[0012] In particular, the object of the present invention is to provide a batch comprising used refractory materials having carbon bonds in a relatively high proportion, from which carbon-bonded refractory products having good or at least still acceptable refractory properties can be produced.

Means for Solving the Problems

[0013] To solve this problem, according to the present invention, there is provided a batch for the production of carbon-bonded refractory products, comprising the following components: Refractory components, and Organic binders wherein the refractory components include at least one used refractory material having carbon bonds and at least one used refractory material having no carbon bonds, the at least one used refractory material having carbon bonds has a particle size distribution having a first d50 value, the at least one used refractory material having no carbon bonds has a particle size distribution having a second d50 value, the first d50 value is higher than the second d50 value, a batch is provided.

[0014] The present invention is based, inter alia, on the finding according to the invention that the refractory properties of carbon-bonded refractory products can deteriorate, especially when the batch used in the production of the products exclusively comprises used refractory materials having a carbon bond in the fines fraction. According to the present invention, it has now been recognized that the properties of carbon-bonded refractory products produced from used refractory materials can be improved when the fines fraction of the batch comprises a part of used refractory materials having no carbon bond. Furthermore, according to the present invention, it has been found that in the production of carbon-bonded refractory products, the use of used materials having no carbon bond in the fines results in properties similar to those obtained by using natural (i.e., unused) materials having no carbon bond in the fines.

[0015] The basic refractory components of the batch according to the present invention comprise at least one used refractory material having a carbon bond and at least one used refractory material having no carbon bond. The at least one used refractory material having a carbon bond has a particle size distribution having a first d50 value, and the at least one used refractory material having no carbon bond has a particle size distribution having a second d50 value. Therefore, the first d50 value according to the present invention is higher than the second d50 value according to the present invention. Thus, the used refractory material having a carbon bond is "coarser" with respect to its particle size distribution, and thus the used refractory material having no carbon bond is "finer".

[0016] As is known from the prior art, the d50 value indicates the particle size of a granular mixture in which 50% by mass of the granular mixture has a particle size that coincides with or is below the d50 value and 50% by mass of the granular mixture has a particle size that exceeds the d50 value.

[0017] Therefore, the first d50 value indicates that 50% by mass of the at least one used refractory material having a carbon bond has a particle size that coincides with or is below the first d50 value and 50% by mass of the at least one used refractory material having a carbon bond has a particle size that exceeds the first d50 value, the mass fractions in both cases being relative to the total mass of the at least one used refractory material having a carbon bond.

[0018] Therefore, the second d50 value indicates that 50% by mass of the used refractory material having no at least one carbon bond has a particle size that matches or is less than the second d50 value, and 50% by mass of the used refractory material having no at least one carbon bond has a particle size that exceeds the second d50 value, and the mass fraction is in each case relative to the total mass of the used refractory material having no at least one carbon bond.

[0019] The criterion used for determining the d50 value depends on the particle size of the particulate matter for which the d50 value is determined. When the particulate matter does not contain particles having a particle size exceeding 1,000 μm, the d50 value is determined by laser diffraction in accordance with Standard ISO 13320:2020-1, "Particle Size Analysis - Laser Diffraction Method". When the particulate matter contains particles having a particle size exceeding 1,000 μm, the d50 value is determined by sieving in accordance with Standard DIN EN 1402-3. Naturally, when the particulate matter contains particles having a particle size around 1,000 μm, both standards can be combined with each other to determine the d50 value.

[0020] Preferably, the d50 value of the used refractory material having at least one carbon bond is determined by sieving in accordance with Standard DIN EN 1402-3, and the d50 value of the used refractory material having no at least one carbon bond is determined by laser diffraction in accordance with Standard ISO 13320:2020-1.

[0021] Surprisingly, according to the present invention, it has been found that carbon-bonded refractory products can be produced using the batch according to the present invention as a basic component, and their refractory properties are good and still acceptable for use in most standard applications of carbon-bonded refractory products. In particular, the density and cold crushing strength of such carbon-bonded refractory products are good and acceptable. In particular, the density and cold crushing strength of such carbon-bonded refractory products produced using the batch according to the present invention as a basic component can be improved compared to products produced solely from used materials having a carbon bond.

[0022] The carbon-bonded refractory products that can be produced batchwise according to the present invention can in principle represent any carbon-bonded refractory products, preferably shaped carbon-bonded refractory products, and particularly preferably carbon-bonded refractory bricks.

[0023] Using the batch according to the present invention, carbon-bonded refractory products are produced. This carbon bond can be formed from the carbon contained in the batch according to the present invention. One source of this carbon is the carbon content of the used refractory material having a carbon bond. Another source of carbon can be an organic binder. Another source of carbon can be another carbon-based component that the batch can further contain, as will be further described below.

[0024] In the sense of the present invention, "used" refractory materials are refractory materials as secondary raw materials, that is, refractory materials that have already been used for their original purpose and are now reused for another purpose, namely to provide the batch according to the present invention. In this regard, the batch according to the present invention is a recyclate. Therefore, the provision of the batch according to the present invention or the production method of the batch according to the present invention is recycling. This is especially true because the used refractory products provided for the batch according to the present invention represent waste without using them in the context of the present invention and are now used for a new purpose within the context of the recycling according to the present invention.

[0025] The original purpose of used refractory materials, with or without carbon bonding, may have been their use in industrial high-temperature aggregates, particularly in industrial high-temperature aggregates for the treatment of metal or glass melts. Industrial high-temperature aggregates for the treatment of molten metals can be, in particular, metallurgical plants. Industrial high-temperature aggregates for the treatment of molten glass can be, in particular, glass tanks. Used refractory materials with carbon bonding can be, in particular, preferably materials that have already been used in metallurgical plants. Used refractory materials without carbon bonding can preferably be materials that have already been used, preferably in a steelworks, preferably, for example, in a safety lining for a converter, a ladle or an electric arc furnace.

[0026] According to the present invention, it has been found that the refractory properties of carbon-bonded refractory products that can be produced from a batch according to the present invention can be improved when a first d50 value is significantly higher than a second d50 value. According to a preferred embodiment, the first d50 value is defined as being at least 4 times higher, more preferably at least 10 times higher, more preferably at least 20 times higher, and even more preferably at least 30 times higher than the second d50 value. According to another development of the inventive concept, the first d50 value is defined as being in the range of 4 to 150 times higher, more preferably in the range of 10 to 150 times higher, more preferably in the range of 20 to 150 times higher, and even more preferably in the range of 30 to 100 times higher than the second d50 value.

[0027] Preferably, it is defined that at least one refractory material having a carbon bond is present in a relatively coarse particle size. According to a preferred embodiment, the first d50 value is defined as being at least 500 μm, particularly preferably in the range of 500 μm to 3,000 μm. Preferably, at least one refractory material without a carbon bond is defined as being present in a small or fine particle size, respectively. According to a preferred embodiment, the second d50 value does not exceed 400 μm, and according to another development of the present invention, it is defined as being in the range of 10 μm to 400 μm, and even more preferably in the range of 30 μm to 100 μm.

[0028] According to an embodiment of the present invention, the mass percentage of the particles of the used refractory material having at least one carbon bond and having a particle size below the second d50 value with respect to the total mass of the refractory components is defined to be lower than the mass percentage of the particles of the used refractory material having no at least one carbon bond and having a particle size below the second d50 value with respect to the total mass of the refractory components.

[0029] Preferably, the refractory material having at least one carbon bond is present in a higher mass percentage in the refractory components than the used refractory material having no at least one carbon bond.

[0030] According to one embodiment, the used refractory material having at least one carbon bond is present in a proportion in the range of 80 to 99% by mass with respect to the total mass of the refractory components, and the used refractory material having no at least one carbon bond is defined to be present in a proportion in the range of 1 to 20% by mass with respect to the total mass of the refractory components. More preferably, the used refractory material having at least one carbon bond is present in a proportion in the range of 85 to 95% by mass with respect to the total mass of the refractory components, and the used refractory material having no at least one carbon bond is defined to be present in a proportion in the range of 5 to 15% by mass with respect to the total mass of the refractory components.

[0031] The used refractory material having at least one carbon bond can, in principle, exist in any form of used refractory material having a carbon bond known from the prior art.

[0032] According to a preferred embodiment, the used refractory material having at least one carbon bond is defined to consist of at least one of the following materials: used carbon-bonded magnesia-based refractory material and used carbon-bonded alumina-magnesia-based refractory material.

[0033] The used carbon-bonded magnesia-based refractory material is a used carbon-bonded refractory material with magnesia as the basic component. Carbon-bonded magnesia bricks, that is, so-called MgO-C bricks, are particularly preferred. Preferably, the used carbon-bonded magnesia-based refractory material has a chemical composition of at least 50% by mass of MgO, more preferably at least 80% by mass of MgO, and even more preferably at least 90% by mass of MgO. Preferably, the proportion of other oxides is less than 50% by mass, more preferably less than 20% by mass, and even more preferably less than 10% by mass. Preferably, the proportion of MgO is in the range of 50 to 99% by mass, and the proportion of other oxides is in the range of 1 to 50% by mass. More preferably, the proportion of MgO is in the range of 80 to 99% by mass, and the proportion of other oxides is in the range of 1 to 20% by mass. Even more preferably, the proportion of MgO is in the range of 90 to 99% by mass, and the proportion of other oxides is in the range of 1 to 10% by mass. The other oxides are preferably at least one of the following oxides: Al2O3, CaO, and SiO2. The above data (unit: mass%) are based on the total mass of the used carbon-bonded magnesia-based refractory material.

[0034] The used carbon-bonded alumina-magnesia refractory is a used carbon-bonded refractory with magnesia and alumina as the basic components. Further or alternatively, the used carbon-bonded alumina-magnesia refractory can be a used carbon-bonded refractory with magnesia, alumina and spinel (i.e., MgO·Al2O3 or MgAl2O4) as the basic components. Carbon-bonded alumina-magnesia-carbon bricks, i.e., so-called AMC bricks are particularly preferred. Preferably, the used carbon-bonded alumina-magnesia refractory has a chemical composition of at least 50% by mass of MgO and Al2O3, more preferably at least 80% by mass of MgO and Al2O3, still more preferably at least 90% by mass of MgO and Al2O3. Preferably, the proportion of other oxides is less than 50% by mass, more preferably less than 20% by mass, still more preferably less than 10% by mass. Preferably, the proportion of MgO and Al2O3 is in the range of 50 to 99% by mass, and the proportion of other oxides is in the range of 1 to 50% by mass. More preferably, the proportion of MgO and Al2O3 is in the range of 80 to 99% by mass, and the proportion of other oxides is in the range of 1 to 20% by mass. Still more preferably, the proportion of MgO and Al2O3 is in the range of 90 to 99% by mass, and the proportion of other oxides is in the range of 1 to 10% by mass. The other oxides are preferably at least one of the following oxides: CaO and SiO2. The above data (unit: mass%) are based on the total mass of the used carbon-bonded alumina-magnesia refractory.

[0035] At least one kind of used carbon-bonded refractory, particularly the above-mentioned used carbon-bonded refractory, can have a proportion of carbon in the range of 1 to 15% by mass based on the total mass of the used carbon-bonded refractory, which is a normal proportion known from the prior art. These carbon contents represent the loss on ignition when determining the oxide content and are not included in the oxides with the above mass fractions.

[0036] According to a preferred embodiment, the at least one used refractory material having no carbon bond consists of at least one of the following materials: used magnesia-based refractory material and used alumina-magnesia-based refractory material.

[0037] The used magnesia-based refractory material may generally be any used magnesia-based refractory material having no carbon bond known from the prior art. Preferably, it is a sintered used magnesia-based refractory material. Particularly preferably, the used magnesia-based refractory material is a sintered used magnesia refractory brick. Preferably, the chemical composition of the used magnesia-based refractory material can be consistent with the above chemical composition of the used carbon-bonded magnesia-based refractory material.

[0038] The used alumina-magnesia-based refractory material may generally be any used alumina-magnesia-based refractory material having no carbon bond known in the prior art, such as spinel (MgAl2O4). Preferably, it is a sintered used alumina-magnesia-based refractory material. Particularly preferably, the used alumina-magnesia-based refractory material is a sintered used alumina-magnesia refractory brick. Preferably, the chemical composition of the used alumina-magnesia-based refractory material can be consistent with the above chemical composition of the used carbon-bonded alumina-magnesia-based refractory material.

[0039] According to a preferred embodiment, the at least one used refractory material having a carbon bond consists of at least one of the following materials: magnesia-based refractory material having a carbon bond and alumina-magnesia-based refractory material having a carbon bond, and the at least one used refractory material having no carbon bond consists of magnesia-based refractory material having no carbon bond and alumina-magnesia-based refractory material having no carbon bond.

[0040] According to a particularly preferred embodiment, the used refractory material having at least one carbon bond is a magnesia-based refractory material having a carbon bond, and the used refractory material having no carbon bond is a magnesia-based refractory material having no carbon bond.

[0041] According to one embodiment, the used refractory material having at least one carbon bond is a droma-based refractory material having a carbon bond, and the used refractory material having no carbon bond is at least one of the following materials: a droma-based refractory material having no carbon bond and a magnesia-based refractory material having no carbon bond.

[0042] According to one embodiment, the batch of refractory components according to the present invention consists only of a used refractory material having at least one carbon bond and a used refractory material having no carbon bond.

[0043] Regarding its chemical composition, the batch according to the present invention is preferably magnesia-based, that is, substantially based on MgO. According to one embodiment, the batch is defined to contain at least 50% by mass of MgO, more preferably at least 80% by mass of MgO, and even more preferably at least 90% by mass of MgO. Even more preferably, the batch is defined to contain at most 50% by mass of other oxides, more preferably at most 20% by mass, and even more preferably at most 10% by mass of other oxides. According to one embodiment, the batch contains 50 to 99% by mass of MgO and 1 to 50% by mass of other oxides, more preferably 80 to 99% by mass of MgO and 1 to 20% by mass of other oxides, and even more preferably 90 to 99% by mass of MgO and 1 to 10% by mass of other oxides, in each case based on the total mass of the batch. The other oxides are preferably at least one of Al2O3, CaO, and SiO2.

[0044] When the chemical composition is described in this application, it is determined by XRF in accordance with standard ISO 12677.

[0045] According to the present invention, surprisingly, batches according to the present invention can contain a relatively high proportion of used refractory materials having carbon bonds, whereby it has been found that carbon-bonded refractory products having acceptable refractory properties can be manufactured from the batches. Thus, batches according to the present invention can be defined as containing at least one used refractory material having at least one carbon bond in a proportion of at least 80% by mass, or even more preferably at least 90% by mass, based on the total mass of the refractory components.

[0046] Batches according to the present invention can more preferably contain carbon-based components as known from the prior art for batches for the production of carbon-bonded refractory products. The carbon-based components can include at least one carbon-based raw material. Preferably, the carbon-based components include a carbon-based raw material in the form of graphite, particularly preferably in the form of flake graphite.

[0047] According to one embodiment, the batch contains the carbon-based component in a proportion of 1 to 15% by mass, more preferably in a proportion of 2 to 10% by mass, based on the total mass of the batch.

[0048] The organic binder can take the form of at least one binder known in the prior art for batches for the production of carbon-bonded refractory products. Preferably, the organic binder takes the form of at least one of the following organic binders: pitch or synthetic resin. Most preferably, the organic binder in the form of a synthetic resin takes the form of a phenolic resin.

[0049] Preferably, the organic binder is present in a proportion in the range of 1 to 10% by mass, more preferably in the range of 2 to 7% by mass, based on the total mass of the batch that does not contain any organic binder in any case.

[0050] According to a preferred embodiment, the organic binder takes the form of a synthetic resin and is defined as containing lignin. Surprisingly, according to the present invention, it has been found that carbon-bonded refractory products can be produced from batches containing the organic binder in the form of lignin. The binder containing lignin is known as a primary binder for refractory batches, but is not known as a primary binder for refractory batches for the production of carbon-bonded products. Surprisingly, it has now been found that according to the present invention, batches for the production of carbon-bonded refractory products can also contain the binder in the form of lignin. The advantage of the organic binder containing lignin is that the energy balance of the batch according to the present invention can be further improved. This is because lignin can be made available as a waste from paper production or as a renewable raw material. In this regard, the organic binder of the batch according to the present invention can be partially replaced by lignin. To that extent, it must be considered that the binder used in the batch for the production of carbon-bonded refractory products, in particular phenolic resins, has to be produced with a high energy input as the main raw material. By having an organic binder containing lignin, the energy input of the batch according to the present invention can be further improved.

[0051] Preferably, the organic binder contains at least 10% by mass of lignin based on the total mass of the organic binder. It has been found that the organic binder cannot be completely replaced by lignin. This is because the carbon-bonded refractory products made from such batches deteriorate in terms of their properties when the batch contains the organic binder exclusively in the form of lignin. According to a preferred embodiment, therefore, the organic binder is defined as containing lignin in a proportion in the range of 10 to 50% by mass based on the total mass of the organic binder. Preferably, the organic binder contains 10 to 50% by mass of lignin based on the total mass of the organic binder and 50 to 90% by mass of a phenolic resin based on the total mass of the organic binder.

[0052] As is well known in the art, the batch according to the present invention can further contain any antioxidant, for example powders of metallic aluminum, silicon or their alloys.

[0053] The object of the present invention is a method for manufacturing a carbon-bonded refractory product, comprising the following steps: providing a batch according to the present invention, subjecting the batch to a temperature to produce a carbon-bonded refractory product and providing a method including the above.

[0054] Preferably, the batch is subjected to a temperature at which the carbon component in the batch becomes coke, thereby forming a carbon bond. Preferably, the batch is subjected to a temperature in the range of 200 to 350 °C. At this temperature range, the carbon component in the batch can become coke, thereby forming a carbon bond. The temperature can be derived from the process heat used.

[0055] Before subjecting the batch to a temperature, it is preferable that the batch can be preferably formed by pressing. Preferably, the batch is formed into a green body, particularly by pressing. Subsequently, by subjecting the green body to a temperature, a carbon-bonded refractory brick is produced from the green body.

[0056] Before subjecting the batch to a temperature and before the batch is formed to the extent that it should be formed and before pressing, the batch is preferably mixed to homogenize the batch. Preferably, the batch can be mixed in a mixer.

[0057] In all other respects, the carbon-bonded refractory product can be produced from the batch according to the present invention by techniques known in the prior art.

[0058] As described above, the used refractory material having at least one carbon bond represents a refractory material that has already been used, particularly as an aggregate for treating molten metal. According to one embodiment, therefore, prior to the process step of providing a batch, the following process steps: Removing a used refractory material having a carbon bond from at least one aggregate for treating molten metal, and then providing the removed used refractory material to provide the at least one used refractory material having a carbon bond can be defined as being carried out.

[0059] Furthermore, as described above, a used refractory material having no carbon bond can represent a refractory material that has already been used in an aggregate for treating molten metal or molten glass. According to one embodiment, therefore, prior to the process step of providing a batch, the following process step: Removing a used refractory material having no carbon bond from at least one aggregate for treating molten metal or treating a glass melt, and then providing the removed used refractory material to provide the at least one used refractory material having no carbon bond can be defined as being carried out.

[0060] As described above, surprisingly, it has been found that carbon-bonded refractory products having acceptable refractory properties can be produced from a batch according to the present invention, especially even when the batch contains a relatively high proportion of used refractory materials having a carbon bond. To that extent, it has been found that carbon-bonded refractory products having an acceptable density and an acceptable cold compressive strength can be produced. The density is considered acceptable if it is at least 2.70 g / cm 3 after the batch has been coked at 1,000 °C. The cold compressive strength is considered acceptable if it is at least 20 MPa after the batch has been coked at 1,000 °C.

[0061] The carbon-bonded refractory products according to the present invention can be applied, for example, in steel ladles or electric arc furnaces.

[0062] Another feature of the present invention is apparent from the claims of the present invention and the following exemplary embodiments.

[0063] All features of the present invention can be combined in any desired form, individually or in combination.

Embodiments for Carrying Out the Invention

[0064] The present invention will be described in more detail with reference to the following exemplary embodiments.

[0065] Exemplary Embodiments In the first step, used refractory materials having a carbon bond and used refractory materials having no carbon bond were taken out from the furnace of the metallurgical plant.

[0066] The used refractory material having a carbon bond was present in the form of used carbon-bonded magnesia bricks, i.e., so-called MgO-C bricks having a chemical composition of 94.0% by mass of MgO and 6.0% by mass of another oxide, particularly Al2O3, CaO, and SiO2.

[0067] The used carbon-bonded magnesia bricks further contained carbon in an amount of 14.0% by mass based on the total mass of the used carbon-bonded refractory material. Since these carbon contents represent the loss on ignition when determining the oxide content, they are not included in the oxides of the above mass fractions.

[0068] The used refractory material having no carbon bond was a sintered used magnesia refractory brick having a chemical composition of 94.0% by mass of MgO and 6.0% by mass of another oxide, particularly Al2O3, CaO, and SiO2.

[0069] All of the above chemical compositions (i.e., oxides) were determined by XRF in accordance with standard ISO 12677 (with reference to the fired sample, i.e., without reference to the carbon content).

[0070] The used refractory material having a carbon bond was crushed to a particle size in the range of >0 to 5 mm and provided as a particle fraction of >0 to 2 mm and a particle fraction of >2 to 5 mm. Further, the sintered used magnesia refractory brick was crushed and provided with a particle size of >0 to 1 mm.

[0071] In the following, batches for the production of carbon-bonded magnesia bricks were provided.

[0072] Therefore, the used carbon-bonded magnesia bricks identified above were crushed to the particle sizes described above and provided as used refractory materials having carbon bonds within the scope of the present invention. In Table 1 below, this material is represented as "used refractory with C bond".

[0073] Furthermore, the sintered used magnesia refractory bricks identified above were crushed to the particle sizes described above and provided as used refractory materials having no carbon bonds within the scope of the present invention. In Table 1 below, this material is represented as "used refractory without C bond".

[0074] In Table 1 below, the formulations of two batches are described. One is designated as A and the other as B. For batches A and B, as shown in the first row of Table 1, the proportions of the components are described in units of mass% with respect to the total mass of each batch.

[0075] [Table 1]

[0076] Batch A represents an exemplary embodiment of a batch according to the present invention. The refractory components consisted of used carbon-bonded magnesia bricks (used refractory with C bond) as particle fractions of >0 - 2 and 2 - 5 mm, and sintered used magnesia refractory bricks (used refractory without C bond) as particle fractions of >0 - 1 mm. Pitch was used as the organic binder. Furthermore, the batch contained a carbon-based component in the form of graphite (flake graphite).

[0077] Batch B was essentially the same as Batch A. The main difference was that Batch B did not contain a component in the form of sintered used magnesia refractory bricks ( "used refractory without C-bond" ). Instead, Batch B contained used carbon-bonded magnesia bricks ( "used refractory with C-bond" ) at a higher ratio in finer granule fractions of >0 to 2 mm.

[0078] For the granule fraction of >2 to 5 mm, the d50 value of the used carbon-bonded magnesia bricks ( "used refractory with C-bond" ) was measured by sieving according to the standard DIN EN 1402-3 and determined to be 3,150 μm.

[0079] For the granule fraction of >0 to 2 mm, the d50 value of the used carbon-bonded magnesia bricks ( "used refractory with C-bond" ) was measured by sieving according to the standard DIN EN 1402-3 and determined to be 700 μm.

[0080] For the entire granule fraction of >0 to 5 mm, the d50 value of the used carbon-bonded magnesia bricks ( "used refractory with C-bond" ) was measured by sieving according to the standard DIN EN 1402-3 and determined to be 2,000 μm.

[0081] The d50 value of the sintered used magnesia refractory bricks ( "used refractory without C-bond" ) was measured by laser diffraction according to the standard ISO 13320:2020-1 and determined to be 500 μm.

[0082] Thus, the refractory components of Batch A and B each had an essentially matching particle size distribution.

[0083] The chemical compositions of Batch A and B were determined by XRF according to the standard ISO 12677 and determined to be as shown in Table 2.

[0084]

Table 2

[0085] In the production of carbon-bonded magnesia bricks from batches A and B, each batch was mixed in a mixer, pressed into a green body, and finally the green body was coked by subjecting it to a temperature of 200 °C from the process heat used for 6 hours. Thereafter, carbon-bonded magnesia bricks were provided.

[0086] To determine whether the carbon-bonded magnesia bricks obtained from batches A and B had acceptable refractory properties, the density in accordance with DIN EN 993-1 and the cold compressive strength in accordance with DIN EN 993-5 were measured after coking at 1,000 °C. The values of the bricks obtained from batch A ("brick A") and the bricks obtained from batch B ("brick B") are shown in Table 3 below.

[0087] [Table 3]

[0088] Accordingly, it can be seen that brick A has a higher density and a significantly higher cold compressive strength than brick B.

[0089] Overall, brick A even had a higher percentage of used refractory material than brick B, but its refractoriness was still an acceptable value in contrast to the value of brick B.

Claims

1. A batch for the production of a carbon-bonded refractory product, comprising the following components: 1.1 A refractory component, and 1.2 An organic binder wherein 1.3 The refractory component comprises 1.3.1 At least one used refractory material having at least one carbon bond, and 1.3.2 At least one used refractory material having no carbon bond wherein 1.4 The at least one used refractory material having at least one carbon bond has a particle size distribution with a first d50 value, 1.5 The at least one used refractory material having no carbon bond has a particle size distribution with a second d50 value, 1.6 The first d50 value is higher than the second d50 value, 1.7 The at least one used refractory material having at least one carbon bond is present in a proportion in the range of 80 to 99% by mass based on the total mass of the refractory component, and the at least one used refractory material having no carbon bond is present in a proportion in the range of 1 to 20% by mass based on the total mass of the refractory component, a batch.

2. The batch according to claim 1, wherein the first d50 value is at least four times higher than the second d50 value.

3. The batch according to claim 1 or 2, wherein the first d50 value is at least 500 μm.

4. The batch according to any one of claims 1 to 3, wherein the second d50 value does not exceed 400 μm.

5. The batch according to any one of claims 1 to 4, wherein the at least one used refractory material having at least one carbon bond consists of at least one of a used carbon-bonded magnesia-based refractory material and a used carbon-bonded alumina-magnesia-based refractory material.

6. The batch according to any one of claims 1 to 5, wherein the at least one used refractory material having no carbon bond consists of at least one of a used magnesia-based refractory material and a used alumina-magnesia-based refractory material.

7. The at least one used refractory material having at least one carbon bond consists of at least one of a magnesia-based refractory material having a carbon bond and an alumina-magnesia-based refractory material having a carbon bond, The at least one used refractory material having no carbon bond consists of a magnesia-based refractory material having no carbon bond and an alumina-magnesia-based refractory material having no carbon bond, The batch according to any one of claims 1 to 6.

8. A batch according to any one of claims 1 to 7, further comprising a carbon-based component.

9. A batch according to claim 8, comprising a carbon-based component in the form of graphite.

10. A batch according to any one of claims 1 to 9, wherein the organic binder is pitch.

11. A batch according to any one of claims 1 to 9, wherein the organic binder contains lignin.

12. A batch according to claim 11, wherein the organic binder contains at least 10% by mass of lignin based on the total mass of the organic binder.

13. A method for manufacturing a carbon-bonded refractory product, comprising: A. providing a batch according to any one of claims 1 to 12; and B. subjecting the batch to a temperature to produce a carbon-bonded refractory product. A method comprising the above steps.

14. The method according to claim 13, further comprising the step of removing a used refractory material having a carbon bond from at least one aggregate for treating molten metal, and then providing the removed used refractory material to provide the at least one used refractory material having a carbon bond.

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