Measuring system and method for measuring

Abstract

The invention relates to a method for measuring a degree of metallization of material (12) processable by a direct reduction plant (10) using a measuring system (29), and to a measuring system, wherein the direct reduction plant comprises a shaft furnace (11) in which an iron ore product is reduced to metallic iron by means of a reducing gas, wherein a permeability of the material is measured in situ by means of an inductive sensor (23) of a measuring device (21) of the measuring system, and wherein a processing device (22) of the measuring system determines a degree of metallization of the material from a measured value of the measuring device.

Description

[0001] January 28, 2025

[0002] TMT Tapping Measuring Technology Säri SI / TMT-035-WO Luxembourg Scu / saa

[0003] Measuring system and method for measuring

[0004] The invention relates to a measuring system and a method for measuring the degree of metallization of material processable with a direct reduction plant, wherein the direct reduction plant comprises a shaft furnace in which an iron ore product is reduced to metallic iron by means of a reducing gas.

[0005] Direct reduction plants are well-established and regularly used to produce so-called sponge iron from iron ore. Sponge iron can then be further processed into steel or cast iron, for example. One advantage of direct reduction is that hydrogen can be used as a reducing agent in a shaft furnace. The iron ore is heated to temperatures of up to 900°C to 1080°C using electrical energy, natural gas, and / or hydrogen. A product of the reduction process is lumpy or powdered metallic iron, or sponge iron, with a metallization of up to 95% to over 99% by weight. In direct reduction, it is possible to gradually replace natural gas with hydrogen to reduce CO2 emissions during steel production. Direct reduction plants are therefore becoming increasingly important in steelmaking.

[0006] A shaft furnace in a direct reduction plant is designed so that it is filled at its upper end with input material, i.e., iron ore, which is present in lumpy or powdered form as an iron ore product. Within a reduction zone, the iron ore is heated, and a bed of this material in the furnace is subjected to the flow of reduction gas. At a lower end of the shaft furnace, which may also be tapered, there may be a cooling zone where the sponge iron or powder formed from the iron ore through reduction can cool. A discharge opening is provided at this lower end of the shaft furnace, allowing the sponge iron or powder to be removed. The sponge iron or powder can then be transported as an intermediate product for steel production or, for example, fed directly into an electric arc furnace. Furnaces operated with powder or fine iron ore...Shaft furnaces are also regularly referred to as fluidized bed reactors and can be designed as a multi-stage fluidized bed cascade.

[0007] A disadvantage of such a direct reduction plant is that the shaft furnace, and in particular the reduction process, is only partially controllable due to a lack of knowledge about the processes within the furnace. While the oxygen content of the fed iron ore can be determined in the laboratory, the metallization degree of the output material from the shaft furnace is essentially determined through empirical operation of the furnace. Furthermore, it is a disadvantage that the metallization degree of the output material must be determined in the laboratory using samples, for example, by laser spectroscopy or X-ray diffraction. These measurement methods essentially involve point measurements.Since the degree of metallization varies depending on the location in the shaft furnace and the penetration depth of a given piece of material during hydrogen reduction, a series of measurements must be performed to reliably determine the average degree of metallization of the output material. Furthermore, such measurements are time-consuming, meaning the results are only available long after a batch of material has been produced using the direct reduction system.

[0008] The present invention is therefore based on the objective of proposing a method for measuring the degree of metallization of material that can be processed with a direct reduction plant, a measuring system and a direct reduction plant with a measuring system that enables improved operation of the direct reduction plant.

[0009] This problem is solved by a method having the features of claim 1, a measuring system having the features of claim 14 and a direct reduction plant having the features of claim 21.

[0010] In the inventive method for measuring the degree of metallization of material processable with a direct reduction plant using a measuring system, wherein the direct reduction plant comprises a shaft furnace in which an iron ore product is reduced to metallic iron by means of a reducing gas, a permeability of the material is measured in situ by means of an inductive sensor of a measuring device of the measuring system, wherein a processing device of the measuring system determines a degree of metallization of the material from a measured value of the measuring device.

[0011] In the process according to the invention, lumpy or powdered iron ore is successively fed into the shaft furnace as input material and then reduced in a reduction zone of the shaft furnace with a reducing gas, preferably hydrogen, to metallic iron or sponge iron as output material of the shaft furnace. The reduction proceeds essentially according to the reduction equation: Fe₂Os + 3H₂ → 2Fe + 3H₂O. Besides Fe₂Os, the iron ore can also be present as Fe₂Ch. During the reduction, the degree of metallization of the material is increased, and the output material is predominantly Fe, FeO, and Fe₂C. To increase a potentially desired carbon content of the output material, natural gas or a mixture of hydrogen and natural gas can also be used as the reducing gas.

[0012] Furthermore, according to the invention, the permeability or magnetic permeability of the material is measured in situ at the direct reduction plant or the shaft furnace. This allows the degree of metallization of the material to be determined directly at the shaft furnace, without the need for lengthy waiting times that would be required for laboratory analysis. Any necessary adjustments to the operating parameters of the shaft furnace can then also be made very quickly, for example, if the degree of metallization changes undesirably during operation of the shaft furnace. In particular, the measuring device is intended to measure the magnetic permeability of the material, or of the iron ore, sponge iron, and / or intermediate stages of this material.The processing device is preferably a data processing device, for example, a computer with software running on it, a PLC controller, or the like. Furthermore, in the inventive method for measuring the degree of metallization, it is advantageous that the permeability of the material is not determined only at a single point. The measurement of the magnetic permeability can be carried out, for example, using an inductive sensor, such as a coil or the like. Here, at least a portion or quantity of the material is measured completely, for example, by placing the portion or quantity of material in an inductive field. Any metallization gradient that may have formed in the portion of the material then has no effect on the measurement result, as would be the case with a point-by-point surface measurement. Overall, a more accurate measurement result of the degree of metallization can thus be obtained.

[0013] This method allows for the measurement of ferromagnetic permeability, with the processing device enabling the determination of the iron content of the material. Since iron is a ferromagnetic substance, the permeability, or magnetic permeability, of the material can be easily determined, and the iron content, and thus the degree of metallization, can be readily derived using the processing device. In addition to iron, cobalt and nickel may also be present as ferromagnetic elements in the material, although these are negligible in the production of sponge iron.

[0014] It is advantageous if the material is used in pellet or powder form. The pellets are then essentially of a uniform size and shape, ensuring a comparable penetration depth of the reducing gas across each pellet. This allows for the production of a comparatively homogeneous quantity of metallized output material in the shaft furnace. The powder, fine iron ore, or iron oxide can be advantageously processed in a shaft furnace designed as a fluidized bed reactor.

[0015] The measuring device allows for the measurement of a defined quantity of material. Specifically, the device can determine the volume of the material using a measuring container, the weight of the material using a weighing sensor, and / or the temperature of the material using a temperature sensor. This ensures consistently comparable measurement results. The measuring container can be either closed or open, such as a section of pipe or a conveyor section of a material transport system. The measuring container can define the volume of the material, allowing for easy determination. The weighing sensor determines the weight of the material contained within the measuring container.This is advantageous because the volume of the measuring container can never be completely filled with material. Thus, there are always empty spaces between pieces of material. Furthermore, the temperature of the material in the measuring container can be easily measured using the temperature sensor. The temperature can be used to adjust the amount of material in the measuring container and / or to determine the material composition using the processing device.

[0016] The processing device can take into account the average geometric shape and / or size of the material particles when determining the degree of metallization. If the material is in pellet form, the device can determine the volume of the measuring container filled with a specific number of pellets. The geometric shape and size of the material particles always result in a space between them within the volume, which can also be predetermined or calculated by the processing device. This allows the actual volume of material in the measuring container to be determined. Furthermore, the processing device can consider whether the material is reduced or unreduced. Reducing the material decreases its volume and thus the size of the material particles.Overall, by including these variables using the processing device, an even more accurate measurement of the degree of metallization can be achieved.

[0017] The measurement can be performed above or below the Curie temperature of a specific iron compound in the material. If the measurement is performed above the Curie temperature of the iron compound, this compound cannot be detected by the inductive sensor. However, it then becomes possible to determine the proportion of this iron compound in the total amount of the material using a process of elimination. In this way, the respective proportions of the iron compounds can be determined completely or partially, successively, by performing individual measurements above the Curie temperature of each compound to be determined.

[0018] The measurement can be carried out at a material temperature of < 770°C, preferably < 218°C. The temperature of 770°C essentially corresponds to a Curie temperature of Fe, and the temperature of 218°C essentially corresponds to a Curie temperature of FesC.

[0019] If the measurement is performed at < 770°C, at least the degree of metallization with respect to iron can be determined. If the measurement is performed at < 218°C, all ferromagnetic metal components of the material can be determined.

[0020] Furthermore, the measurement can be performed at a material temperature of

[0021] Measurements are carried out at temperatures above 675°C and below 585°C, preferably above 675°C and below 675°C or above 585°C and below 585°C, wherein the processing device can determine the degree of reduction of the material from the measured values ​​at the specified temperatures. The temperature of 585°C corresponds to a Curie temperature of Fe₂Ch and the temperature of 675°C corresponds to a Curie temperature of Fe₂O₅. From the resulting differences in the permeability measurements of the material at the temperatures specified above, the proportions of Fe, Fe₂C, Fe₂Ch, and Fe₂O₅ present in the material can be determined. The magnetic permeability of the material above the respective Curie temperature, and thus the corresponding material fraction, cannot be determined. This makes it possible to determine the material composition relatively accurately and quickly.The degree of reduction then results from the respective material composition, in particular the proportions of Fe20s and FesCh present and to what extent the reduction of the material to Fe or FesC has progressed.

[0022] The material can be cooled to the required temperature using a cooling gas in a cooling device of the direct reduction plant. The cooling gas can be, for example, a protective gas that prevents oxidation of the material. A reducing gas can also be used as the cooling gas. It is essential that the cooling device cools the material sufficiently to allow the Curie temperature of the material fraction to be measured to be undercut, thus enabling a measurement at all. Furthermore, the cooling device can be designed to maintain a specific material temperature for measurement. The cooling device of the direct reduction plant can also be implemented as a cooling zone within the shaft furnace.

[0023] The measuring system enables continuous measurement. It can be integrated into or positioned within a material flow of the shaft furnace. Measurements can be taken continuously or at regular intervals. The result of measuring the metallization degree of the material is then available essentially immediately after a sample of the material is measured. This allows for timely adjustments to the shaft furnace's operating parameters, should the need arise.

[0024] The measuring system can include at least one second measuring device, which may have a second inductive sensor for measuring the material's permeability in situ. A second metallization degree can then be determined from this second measurement by the processing device. The measuring device and the second measuring device can then be used to measure the material in or at the shaft furnace in various processing states. For example, the first measuring device can measure the output material, and the second measuring device can measure the input material of the shaft furnace. In principle, it is also possible to measure material within the shaft furnace. This allows for even more precise control and regulation of the shaft furnace to achieve the desired metallization degree.

[0025] Depending on the degree of metallization and the secondary metallization level, the processing device can output a status message and / or control the operating state of the shaft furnace. A relative measurement can then be performed using the measuring device and the secondary measuring device, for example, between the input and output material of the shaft furnace, to determine the extent to which metallization of the material has occurred in the shaft furnace. For example, input material can be used that has at least 67% iron by mass and 29% iron-bound oxygen by mass, as well as a residual slag. Since the composition of the input material is subject to fluctuations depending on the batch, the processing device and / or the secondary measuring device can be used to determine the specific composition of the input material.whose data output reacts to a changing composition of input and / or output material, for example by the processing device adjusting or regulating the operating state of the shaft furnace. This can be achieved by changing the temperature in the shaft furnace, the amount of reducing gas, the processing time, or the like.

[0026] Calibration of the measuring system can be performed using an input material and / or an output material from the shaft furnace. Multiple measurements can be taken at different temperatures, and correction values ​​for the degree of metallization measured at each temperature can be stored in the processing device. The composition of the input material and / or the output material can be determined in the laboratory using a suitable measurement method as a reference. It is essential that measurements are taken with the measuring system at different temperatures to correct for the influence of temperature on the measurement result. This can be done, for example, using correction values ​​stored in the processing device. For instance, a lookup table or...A conversion table, correction matrix, or similar data can be stored for a number of temperature values. This allows for a more precise and faster determination of the metallization degree.

[0027] The measuring system according to the invention for measuring the degree of metallization of material processable with a direct reduction plant, wherein the direct reduction plant comprises a shaft furnace in which an iron ore product can be reduced to metallic iron by means of a reducing gas, comprises a measuring device, wherein the measuring device has an inductive sensor by means of which the permeability of the material can be measured in situ, and wherein the measuring system has a processing device by means of which a degree of metallization of the material can be determined from a measured value of the measuring device. For the advantages of the measuring system according to the invention, reference is made to the description of the advantages of the method according to the invention.

[0028] The measuring device can comprise a measuring container for determining the volume of a quantity of material, a weighing sensor for determining the weight of the quantity of material, and / or a temperature sensor for determining the temperature of the quantity of material. The weighing sensor and the temperature sensor can be arranged on the measuring container so that the weight and temperature of the quantity of material in the measuring container can be recorded and processed by the processing device to determine the degree of metallization. The volume can be determined simply by the measuring container defining the volume to be measured. The inductive sensor or a plurality of inductive sensors of the measuring device can be arranged to surround a material flow from the shaft furnace or measuring container of the measuring device, at least partially, preferably completely.For example, the inductive sensor can be ring-shaped and surround a pipe through which the material flow is guided. Alternatively, the material flow from the shaft furnace can be divided into several material flows, one of which is fed to the measuring device. The inductive sensor can be a single coil or multiple coils. The coil can also, for example, surround the material flow in a ring shape. Furthermore, the measuring device can also have multiple inductive sensors, each consisting of coils, which together surround the material flow. In particular, this makes it possible to continuously determine the degree of metallization of the material.

[0029] The measuring device can include a conveying system by means of which material can be extracted from a material stream of the shaft furnace, fed into a measuring container of the measuring device, and preferably returned to the material stream. The conveying system can be the measuring container itself, a second container, a gripper, a chute, a conveyor belt, or the like. The essential feature is that a quantity of material can be extracted from the material stream and filled into the measuring container. After the metallization degree of the material in the measuring container has been measured, this material can then be returned to the material stream by means of the conveying system or other suitable means. The measuring device can then be designed so that it can be positioned along a material stream and perform successive measurements.

[0030] The conveying device can be equipped with a lance by means of which a material sample can be taken from at least one area of ​​the shaft furnace. It is essential that the lance can be inserted into the material flow within the shaft furnace and a quantity of material extracted from this flow. After the material has been extracted, the degree of metallization can be measured. In principle, material samples can then be taken from any area of ​​the shaft furnace, regardless of the temperature in those areas.

[0031] The inductive sensor or a plurality of inductive sensors of the measuring device can form a measuring probe that can be arranged in a material flow of the shaft furnace, preferably in a cooling zone of the shaft furnace. The inductive sensor or the plurality of inductive sensors can, for example, be attached to one end of a lance, the lance being positioned in the material flow. If the lance is positioned in the cooling zone of the shaft furnace, the degree of metallization of the already reduced material can be determined directly. In principle, however, the lance can also be positioned in the area of ​​an inlet or outlet of the shaft furnace or have its own cooling device.

[0032] The measuring system can include a cooling unit downstream of a cooling zone in the shaft furnace, whereby the output material from the shaft furnace can be cooled by means of a protective gas in the cooling unit. Depending on the temperature of the output material leaving the shaft furnace at a discharge opening, only a limited measurement of the degree of metallization may be possible, for example, due to the Curie temperature of FeS-C. It may therefore be necessary to cool the output material further. This can be achieved by feeding the output material completely or partially into the cooling unit, where it can be easily cooled by means of a protective gas flowing through it. For example, nitrogen (N2) or an inert gas can be used as the protective gas. This prevents unwanted oxidation of the output material.At the same time, it is possible to temper the output material to a desired temperature with relative accuracy.

[0033] Further advantageous embodiments of the measuring system result from the feature descriptions of the dependent claims relating back to claim 1.

[0034] The direct reduction plant according to the invention comprises a measuring system according to the invention. The direct reduction plant can operate according to the so-called Midrex process or be configured as a Midrex direct reduction plant. Furthermore, the direct reduction plant can also be, or be configured as, a so-called HyRex, HYL, Ternova, Hybrit Posco, or Finex plant, depending on the manufacturer's designation. The measuring device can be arranged in or on a conveying section of a material flow in a shaft furnace of the direct reduction plant, preferably at an outlet opening, an inlet opening, and / or in a cooling zone of the shaft furnace. This enables a direct measurement of the metallization degree of the material at the outlet opening, the inlet opening, and / or the cooling zone.

[0035] Further advantageous embodiments of a direct reduction plant result from the feature descriptions of the dependent claims relating to the measuring system according to the invention.

[0036] The invention is explained in more detail below with reference to the accompanying drawings.

[0037] They show:

[0038] Fig. 1: a schematic representation of a direct reduction plant;

[0039] Fig. 2: A schematic representation of another direct reduction plant. Fig. 1 shows a schematic representation of a direct reduction plant 10 according to an embodiment of the invention. The direct reduction plant 10 comprises a shaft furnace 11 in which material 12 is arranged in the form of pellets 13. The shaft furnace 11 is designed such that iron ore as pellets 13 is filled into an inlet opening 14 and conveyed downwards within the shaft furnace 11 to an outlet opening 15. The material 12 passes through a reduction zone 16 with a heating device 17 and subsequently a cooling zone 18 with a cooling device 19. In the reduction zone 16, the iron ore is reduced to the form of Fe. 2Os or FeSCH to FeO and Fe, and optionally FeSC. Hydrogen is preferably used as a reducing gas; if a proportion of FeSC is desired, natural gas is also used. The pellets 13 then reach a temperature of, for example, approximately 700°C in the cooling zone 18 and exit the shaft furnace 11 as sponge iron or metallic iron via the discharge opening 15. This sponge iron can then be directly processed metallurgically or further cooled, stored, and transported to another location for further processing.

[0040] The direct reduction plant 10 further comprises a measuring system 20 with a measuring device 21 and a processing device 22. The processing device 22 is designed as a data processing unit, for example, a computer. The measuring device 21 is equipped with an inductive sensor 23, which in this case is a coil 24. The measuring device 21 also includes a tubular measuring container 25, which is surrounded by the coil 24, a weighing sensor (not shown in detail here), and a temperature sensor (also not shown). The material 12 or a number of pellets 13 contained in the measuring container 25 fills a volume of the measuring container 25, so that a quantity of material can be determined. Furthermore, it is possible to determine the weight of this quantity of material with the weighing sensor and to determine the temperature of the quantity of material with the temperature sensor.These respective measured values ​​are processed by the processing device 22, which determines the degree of metallization of the material 12 from the measured values. This is done in particular by measuring the magnetic permeability of the material 12 in situ with the inductive sensor 23.

[0041] The measuring system 20 further comprises a second measuring device 26, which is essentially designed like the measuring device 21. The second measuring device 26 is also connected to the processing device 22, so that the processing device 22 can determine the degree of metallization of the material 12 or the iron ore before it is fed into the shaft furnace 11. The processing device 22 can thus also perform a comparative measurement between the input material and the output material with regard to the degree of metallization.

[0042] The measuring system 20 can further include a cooling device 27, which is located directly downstream of the dispensing opening 15. The cooling device 27 is designed to cool the dispensing material using a protective gas. This makes it possible to lower the temperature of the material 12 below the Curie temperature of FeS₂C. The cooling device 27 can be configured such that the material 12 is selectively cooled to below the respective Curie temperatures of Fe, FeO, FeS₂CH₄, Fe₂O₅, and FeS₂C. The processing device 22 can then determine the respective proportions of these substances in the material 12.

[0043] Figure 2 shows a schematic representation of a direct reduction plant 30 according to a further embodiment. In contrast to the direct reduction plant shown in Figure 1, the direct reduction plant 30 here is configured with a measuring system 31, a measuring device 32, a measuring probe 33, and an inductive sensor 34 inside a shaft furnace 35. Alternatively or additionally, a movable lance 37 is provided as a conveying device 36 for the measuring system 31, by means of which material 12 can be taken from the shaft furnace 35 as a material sample. The conveying device 36 can supply the material 12 to an inductive sensor 38 of the measuring device 32 for measurement. The measuring system 31 can additionally include measuring devices 21 and / or 26.

Claims

January 28, 2025 TMT Tapping Measuring Technology Säri SI / TMT-035-WO Luxembourg Scu / saa Patent claims 1. Method for measuring the degree of metallization of material (12) processable with a direct reduction plant (10, 30) using a measuring system (20, 31), wherein the direct reduction plant comprises a shaft furnace (11, 35) in which an iron ore product is reduced to metallic iron by means of a reducing gas, wherein it comprises characterized by , that a permeability of the material is measured in situ by means of an inductive sensor (23 , 34, 38) of a measuring device (21 , 32) of the measuring system, wherein a processing device (22) of the measuring system determines a metallization degree of the material from a measured value of the measuring device.

2. Method according to claim 1 , characterized by , that a ferromagnetic permeability is measured, wherein the processing device (22) determines an iron content of the material (12).

3. Method according to claim 1 or 2, characterized by , that material ( 12) is used in the form of pellets ( 13) or powder.

4. Method according to any of the preceding claims, characterized by , that a defined quantity of material is measured by means of the measuring device (21 , 32), wherein a volume of the quantity of material is determined by means of a measuring container (25) of the measuring device, a weight of the quantity of material is determined by means of a weighing sensor of the measuring device, and / or a temperature of the quantity of material is determined by means of a temperature sensor of the measuring device.

5. Method according to claim 4, characterized by , that the processing device (22) takes into account an average geometric shape and / or size of material pieces in the quantity of material when determining the degree of metallization.

6. Method according to any of the preceding claims, characterized by , that the measurement is carried out above or below a Curie temperature of a chemical compound of the iron of the material ( 12).

7. Method according to any of the preceding claims, characterized by , that the measurement is carried out at a temperature of the material (12) of < 770°C, preferably of < 218°C.

8. Method according to claim 7, characterized by , that the measurement is carried out at a temperature of the material ( 12) of > 675°C and of < 585°C, preferably of > 675°C and of < 675°C or of > 585°C and of < 585°C, wherein the processing device (22) determines a degree of reduction of the material from the respective measured values ​​of the measuring device (21 , 32) at the temperatures.

9. Method according to any of the preceding claims, characterized by , that the material ( 12) is cooled to the temperature by means of a cooling device ( 19) of the direct reduction plant ( 10, 30) with a cooling gas.

10. Method according to any of the preceding claims, characterized by , that a continuous measurement is carried out with the measuring system (20, 3 1 ).

1. Method according to one of the preceding claims, characterized by , that the measuring system (20, 3 1 ) comprises at least a second measuring device (26, 32), wherein the second measuring device has a second inductive sensor by means of which a permeability of the material ( 12) can be measured in situ, wherein a second metallization degree of the material can be determined from a second measured value of the second measuring device by means of the processing device (22).

12. Method according to claim 1 1 , characterized in that the processing device (22) outputs a status message depending on the metallization degree and the second metallization degree and / or regulates an operating state of the shaft furnace (1 1 , 35).

13. Method according to any of the preceding claims, characterized by , that a calibration of the measuring system (20, 3 1 ) is carried out with an input material and / or an output material of the shaft furnace ( 1 1 , 35 ), wherein a plurality of measurements are carried out at different temperatures, wherein correction values ​​for a degree of metallization measured at the respective temperature are stored in the processing device (22 ).

14. Measuring system (20, 3 1 ) for measuring a degree of metallization of material (12) processable with a direct reduction plant ( 10, 30), wherein the direct reduction plant comprises a shaft furnace ( 1 1 , 35) in which an iron ore product can be reduced to metallic iron by means of a reducing gas, wherein the measuring system comprises a measuring device (21 , 32), characterized by , that the measuring device has an inductive sensor (23 , 34, 38) by means of which a permeability of the material can be measured in situ, wherein the measuring system has a processing device (22) by means of which a metallization degree of the material can be determined from a measured value of the measuring device.

15. Measuring system according to claim 14, characterized by , that the measuring device (21 , 32) comprises a measuring container (25) for determining a volume of a quantity of material, a weighing sensor for determining a weight of the quantity of material and / or a temperature sensor for determining a temperature of the quantity of material.

16. Measuring system according to claim 14 or 15, characterized by , that the inductive sensor (23 , 34, 38) or a plurality of inductive sensors of the measuring device (21 , 32) can be arranged to at least partially, preferably completely, surround a material flow of the shaft furnace (1 1 , 35) or measuring container (25) of the measuring device.

17. Measuring system according to one of claims 14 to 16, characterized by , that the measuring device (21 , 32) comprises a conveying device by means of which material can be extracted from a material stream of the shaft furnace ( 1 1 , 35 ), fed to a measuring container (25) of the measuring device and preferably returned to the material stream.

18. Measuring system according to claim 17, characterized by , that the conveying device is equipped with a lance by means of which a material sample can be taken from at least one area of ​​the shaft furnace ( 1 1 , 35 ).

19. Measuring system according to one of claims 14 to 18, characterized by , that the inductive sensor (23, 34) or a plurality of inductive sensors of the measuring device forms a measuring probe which can be arranged in a material flow of the shaft furnace (11, 35), preferably in a cooling zone (18) of the shaft furnace.

20. Measuring system according to one of claims 14 to 19, characterized in that that the measuring system (20, 30) comprises a cooling device (27) downstream of a cooling zone (18) of the shaft furnace (11, 35), wherein output material of the shaft furnace can be cooled by means of protective gas of the cooling device.

21. Direct reduction plant ( 10, 30) with a measuring system (20, 3 1 ) according to one of claims 14 to 20.

22. Direct reduction plant according to claim 21 , characterized by , that the measuring device (21 , 32) is arranged in or on a conveying section of a material flow of the shaft furnace ( 1 1 , 35 ), preferably at an output opening ( 15 ), an input opening ( 14 ) and / or in a cooling zone ( 18 ) of the shaft furnace.

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