IN A BLAST FURNACE

Technical field

[0001 ] The present invention generally relates to a device and a method for determining the material distribution in the burden inside a blast furnace. The present invention more specifically relates to a device and a method for determining the material distribution in the burden of a blast furnace based on its electrical conductivity without direct contact to the measuring device.

Background Art

[0002] Different methods and devices for determining the material distribution in a blast furnace are known in the art. The determining of the material distribution in a blast furnace is a quantitative analysis of the radial distribution of various burden materials, e.g. coke and iron-ore materials. As the blast furnace is a counter- current reactor, the gas permeability is important for the process. To influence it, not a homogeneous mix of the burden is charged, but a well-defined scheme of different layers of coke and iron-ore materials. Thanks to the material distribution determinations, the shape and thickness of the material layers in a blast furnace can be determined and if necessary adjusted and optimized to improve the blast furnace performance.

[0003] Several methods for determining the structure of layers in a blast furnace are known. The most common method is a radar profilometer, which measures the shape of the burden surface after the charging of each material layer. The measurement is limited to the burden surface and therefore the dynamic effects that happen below the burden surface and during charging are not recorded. An alternative method to supervise the burden gas permeability is the measurement of the radial temperature and gas distribution profile, either above or below the surface of the burden. Although this method leads directly to the final result, which is the radial gas permeability distribution and the size of the central chimney, the charging optimization based on this measurement is difficult as the detailed structure of the different layers is not determined. [0004] A different approach is proposed by JP2007-155570. In view of the difficulties to measure the distribution of the material inside the blast furnace, JP2007-155570 proposes to determine the relative quantities of the charging material during the charging of the material from the hopper into the blast furnace. The measurement method is characterized by placing the mixture of substances that differ by electromagnetic properties at the inner side of a hollow coil that is applied with alternating current, or by causing the mixture to pass through the axial direction of the coil. The output voltage generated by the coil is measured and the mixture rate of the substances within the mixture is determined based on that output voltage.

[0005] An excitation coil and a measurement coil are disposed in the same axial direction, the mixture is then placed at the inner side of the coils or causing it to pass through the axial direction of the coils, the output voltage generated by the measurement coil is measured. A calibration curve is obtained by measuring in advance the relationship between the mass of the substances and the output voltage generated by the coil, the mixture rate of the substances within the mixture is computed based on the calibration curve.

[0006] Although such a method and device may be helpful to determine the relative quantities of the different material during charging of the material into the blast furnace, it is however not useful to determine exactly how the material is distributed inside the burden of the blast furnace after it has been charged. Indeed, since the material has different densities and/or granulometry, it may segregate during the charging operation. The physical phenomena that interact during the formation of the burden layers are the rolling of material on the burden surface, the penetration of material in lower layers caused by the impact forces, the churn-up of the material caused by the ascending process gas, and the mixing with previously charged materials. Furthermore, since the burden inside a blast furnace is not stationary but moves downwards and is consumed partly, its surface profile and the shape of the formed layers change with time.

[0007] A more appropriate solution to determine the structure of layers in a blast furnace has been proposed in EP 1 029 085. A probe is repeatedly inserted horizontally and into the blast furnace below the burden surface. A material detection sensor arranged at the tip of the probe indicates the presence of either coke or iron-ore materials. With the combination of the fast horizontal movement of the probe, and the slower vertical burden descent speed, an image of the material distribution is obtained.

[0008] The material detection sensor indicates the type of the burden material based on a measurable physical property of the burden material. A multitude of methods are available in the art for blast furnaces.

[0009] A first example is the magnetic permeability. The magnetic permeability of ore-like material is high, whereas coke has a low magnetic permeability similar to the magnetic permeability of air. Several methods have been developed to determine the magnetic permeability of the material in the blast furnace to draw conclusions on the material distribution. In GB 2 205 162, a single coil is moved through a tube inside the blast furnace to measure the magnetic permeability of the material. The auto-inductance of the coil is measured in the sensor coil. This value increases under the presence of magnetically permeable material within the magnetic field lines of said coil and, if this value is increased, ore is detected. In DE 26 55 297, a permanent magnet is aligned to a magnetic field sensor and installed into a blast furnace. The magnetic flux increases if a magnetically permeable material is within the field lines of the permanent magnet. If the magnetic field sensor indicates this increase of the magnetic flux, ore is detected.

[0010] The problem with the magnetic permeability in a material distribution measurement such as DE 26 55 297 is that a large temperature range is present, normally ranging from 100°C near the blast furnace wall to 900°C or more in the blast furnace center. At this temperature, the magnetic permeability of iron ore disappears as the material temperature is beyond the Curie-Point. For Iron-ore III (Fe ₂ O ₃ ) the Curie-Point is at 675°C and for Iron-ore ll-lll (Fe ₃ O ₄ ) the Curie-Point is at 585°C. The property to distinguish the materials is therefore disappearing. The magnetic permeability cannot be used for measuring the material distribution in blast furnaces in a temperature range around the Curie-Point and in particular above the Curie-Point.

[001 1 ] A second example of a property to determine the burden type is the remaining magnetism of iron ores. In DE 26 37 275, a strong magnetic field is generated to excite the self-magnetism of ores. This field is then switched off and a sensing device can detect ore via the remaining magnetic field. However, the same problem as before appears, as above the Curie-Point, the self-magnetism of ores also disappears.

[0012] A third example is the radar wave absorption of ore, as proposed in EP 0 101 219. The radar wave absorption of ores is higher than that of coke. Radar wave antennas for emitting and receiving radar waves are arranged inside the blast furnace. The material situated between the radar wave antennas is identified based on the reflection and absorption of the radar waves. The disadvantage of the radar based measurement is that radar devices are rather fragile, especially the waveguide and antenna components, and an installation in a below-burden probe is technically very problematic.

[0013] A fourth example is based on the electrical conductivity of coke and iron ore as described in EP 1 029 085 and in DE 31 05 380. The electrical conductivity is the preferable method as the conductivity of coke is known to persist to temperatures of 1300°C and more.

[0014] Currently, the material distribution is measured by inserting a probe horizontally into the blast furnace as described in EP 1 029 085. Two electrodes are arranged on or near the tip of the probe, separated from each other by an isolator and connected to each other by means of an electric measuring circuit. The electric measuring circuit determines the signal quantity of the electric circuit when the tip of the sensor is inserted into the blast furnace. The signal quantity depends on the electric conductivity of the burden material around the sensor in the blast furnace. The electric circuit closes when the electrodes connect through a layer of conductive materials. When the tip of the sensor passes through a layer of non-conductive material the electrodes do not connect. Due to the difference between the measurement of a conductive material and a non-conductive material, the probe is capable of determining which materials are present nearby.

[0015] However, when the probe is inserted into the blast furnace, dust deposits are inevitably formed on the isolators. These dust deposits are electrically conductive and form a short circuit between the electrodes and make an accurate measurement impossible. As dust is always present in a blast furnace due to the high amount of coke, the high gas speed and possibly due to additional fuel particle injection, a solution is to use soft ceramics as an isolator. These ceramic isolators have a certain abrasion rate, such that no dust deposits are formed when a measurement is taken. Indeed, as the burden in the blast furnace is hot and abrasive, the friction of the isolator against the burden on the introduction and retrieval of the probe wears down the isolators each time a measurement is taken and thus no dust deposit is formed. After a certain number of measurements, at least the isolators have to be replaced. This results in higher costs and a requirement for regular maintenance.

[0016] A more efficient method or device is thus required for measuring the material distribution inside the burden of a blast furnace, after the materials have been charged into the blast furnace.

Technical problem

[0017] It is an object of the present invention to provide a method and a probe for determining the material distribution of the charged material in the burden in a blast furnace at any temperature.

[0018] This object is achieved by a method as claimed in claim 1 and by a probe as claimed in claim 1 1 .

General Description of the Invention

[0019] To achieve this object, the present invention proposes a measuring probe for determining a material distribution in a burden in a blast furnace without direct contact by inserting the probe into the burden inside the blast furnace.

[0020] The measuring probe comprises:

- At least one sensor, which comprises: o A transmitter coil that has a transmitting surface. o A receiver coil that has a receiving surface.

A protective shell, in which the sensor is housed and which protects the transmitter coil and the receiver coil against heat and abrasion. An alternating current power source, which applies an alternating current to the transmitter coil.

The transmitter coil emits a primary alternating magnetic field, which induces eddy currents in any electrically conductive material of the burden. The eddy currents generate a secondary alternating magnetic field and a receiver coil measures an electrical current, which is generated by the primary alternating magnetic field and the secondary alternating magnetic field.

A control and evaluation unit for evaluating the measured electric current, wherein the electrical current is indicative of the material distribution of the burden in a blast furnace.

[0021 ] Because the measurement is based on the electrical conductivity, the probe can determine, in real-time so to say, the material distribution inside the burden of the blast furnace at any temperature of the material above, beneath or at the Curie-Point. Contrary to the magnetic permeability of the material, the electrical conductivity is a suitable characteristic that is reliable throughout the range of temperatures in the blast furnace.

[0022] Thanks to the detection of an induced eddy current, the sensor can determine the material distribution without directly contacting the burden. Since the sensor is placed inside a protective shell, it is protected against heat and abrasion. The sensor is thus not directly submitted to the harsh blast furnace conditions and thus lasts longer. The main factors that affect lifetime are massive dust, a chemically reactive and corrosive atmosphere, extreme heat, and forces from the burden leading to abrasion or destruction. The lifetime of the measuring probe is thus increased compared to the prior art sensors as described i.e. in EP 1 029 085.

[0023] The measuring probe according to the invention is insensitive to dust, especially towards dust deposits on the protective shell in front of the sensor. Dust particles cause only a very weak, hardly detectable eddy current, which does not perturb the measurement results. The solution of abrasion to remove dust deposits, necessary to put EP 1 029 085 in practice, is not required anymore. [0024] Furthermore, contrary to JP2007-155570, the material does not pass through the inner side of a hollow coil. According to a preferred embodiment of the invention, the sensor can be applied directly onto the inside of the protective shell. Alternatively, the sensor can be applied on a support or a supporting layer, which is applied onto the inner side of the protective shell. In this case, the sensor is arranged between the protective shell and the supporting layer.. The support has to be temperature resistant and has to be non-conductive such as e.g. soapstone or Mica.

[0025] According to a preferred embodiment of the invention, said protective shell comprises a ceramic material that is not electrically conductive. The sensor is thereby sufficiently well protected against the heat and abrasion inside the blast furnace. Good measurement results are obtained with a protective shell with a thickness in the range between 10 to 25 mm. The shell is preferably an annular cylinder.

[0026] The transmitter coil and the receiver coil are preferably arranged such, that the magnetic flux of the transmitter coil is concentric with the magnetic flux of the receiver coil.

[0027] It is possible to arrange multiple sensors at the tip of the probe. In a preferred embodiment, the coils are designed such that their magnetic fields interfere only marginally. Several independent sensors can then be arranged at the tip of the probe inside the same protective shell. This considerably increases the resolution of the material distribution determination. Furthermore, such an arrangement of multiple sensors decreases the requirements of the fast horizontal speed of the probe as is required in the prior art.

[0028] The contacting electrodes as used in EP 1 029 085 have to be sufficiently strong to support the blast furnace burden forces. Consequently, the electrodes on the probe are massive steel rings, which are exposed to the hot burden. Only one measuring sensor can be placed at the probe tip. As only one measurement signal is available, this leads to a limitation of the measurement resolution and the requirement for a high horizontal speed of the probe.

[0029] Advantageously, the transmitter coil has a transmitting surface in the range of 1 to 20 cm ² . The size of the transmitting surface determines the measuring spot by shaping the magnetic field that shall excite the eddy current in the burden. The larger the transmitting surface, the larger will be the measuring spot.

[0030] Preferably, the receiver coil has a receiver surface in the range of 5 to 50 cm ² . A larger size will increase the signal strength, as the received signal is influenced less by the primary magnetic field, but more by the secondary magnetic field from the eddy currents.

[0031 ] Advantageously, an alternating current with a frequency between 0.5 to 5 MHz and a magnitude between 1 to 10 mA is applied to the transmitter coil. The frequency is selected high enough such that sufficient eddy currents are created in the coke, which is known to have a resistivity of 2-6 Ω-cm at 300°C, and of 0.5-2 Ω-cm at 1300°C. In this frequency range, rather long cables can be used to transmit the signal of the transmitter coil to the control unit. For frequencies higher than 5 MHz, the signal generated by the transmitter coil may not be reliably transmitted to the electronic control unit through the rather long cables.

[0032] The magnitude is selected high enough for a reasonable signal-to-noise ratio. A magnitude higher than 10 mA could be seen as a safety risk as it might theoretically cause electric sparks in case of a sensor malfunction.

[0033] The transmitter coil and the receiver coil are preferably of a circular or rectangular shape. The skilled person is however capable of shaping the transmitter coil and the receiver coil according to his needs.

[0034] The probe can be arranged movably in a horizontal direction with regard to the blast furnace shell, such that the probe is inserted into the blast furnace for determining the material distribution therein. Due to the movable arrangement, the material distribution can be determined at different horizontal locations in the blast furnace by changing the position of the probe arranged therein, as described in EP 1 029 085. The horizontal traveling speed is preferably superior to the burden descent speed so that the composition of the burden (i.e. the radial material distribution) can be measured by collecting the data during the repeated movements. [0035] In a further embodiment, the probe is arranged fixedly inside the blast furnace on the blast furnace shell, below the top surface of the burden. The probe is preferably in short distance from the blast furnace wall, and the probe setup can be similar as in the "citoblock" system described in DE 31 05 380. Such a probe can then measure the timely evolution of the material at a fixed radius inside the blast furnace. The goal is to obtain the quantity and the material type (i.e. the material distribution) at one radial location as a function of time.

[0036] According to another aspect, the present invention also concerns a method for determining a material distribution inside a burden in a blast furnace. The method comprises the following steps:

- Inserting a measuring probe into the burden of the blast furnace. The measuring probe has a sensor with a receiver coil and a transmitter coil, said sensor being housed inside a protective shell,

- Applying an alternating current to the transmitter coil such that a primary alternating magnetic field is produced by the transmitter coil. The primary alternating magnetic field induces eddy currents in the material of the burden. The eddy currents generate a secondary alternating magnetic field.

- Measuring an electrical current generated by the primary alternating magnetic field and the secondary alternating magnetic field with a receiver coil.

- Evaluating the material distribution of the burden based on the electrical current in the receiver coil.

[0037] Preferably, the evaluation of the electrical current is used for controlling a distributor chute of the blast furnace. In result, the charging of the material may be adapted based on the measurements carried out by a method or device according to the invention.

[0038] The probe and the method allows thus to determine the radial material distribution and/or the shape, the size and the composition of the burden layers.

[0039] The signal (i.e. the electrical current generated by the primary alternating magnetic field and the secondary alternating magnetic field with a receiver coil) .that indicates the material type is preferably processed using a model. By collecting the data over the radius (x-axis by the horizontal movement of the probe, or one fixed x-point for a low-cost fixed probe) as well as over time (y- axis by the burden descent that moves vertically downwards), the burden distribution (in the sense of the material positioning inside the burden column) is measured. The model result such as described below in more detail is used to understand and optimize the blast furnace process and, if necessary, to adjust the material distribution program of the charging chute.

Brief Description of the Drawings

[0040] Further details and advantages of the present invention will be apparent from the following detailed description of a not limiting embodiment with reference to the attached drawings, wherein:

Fig. 1 is a schematic view of a measuring probe according to a preferred embodiment of the invention,

Fig. 2 is a schematic view of an arrangement of multiple sensors (side cut view) according to a preferred embodiment of the invention,

Fig. 3 is a schematic view of the magnetic flux of a measurement according to a preferred embodiment of the invention,

Fig. 4 is a schematic view of a modified magnetic flux of a measurement according to a preferred embodiment of the invention, when a conductive object approaches the probe,

Fig. 5 is the receiver signal magnitude of the sensor under the presence of several typical blast furnace materials at room temperature,

Fig. 6 is a schematic view of a blast furnace with two probes, one movable probe and one fixed probe, each equipped with sensors to determine the material distribution,

Fig. 7 is a schematic representation of a determined material distribution in a blast furnace. Description of Preferred Embodiments

[0041 ] A schematic arrangement of a measuring probe 2 according to a particularly preferred embodiment of the invention is represented in fig. 1 . The measuring probe 2 can measure the material type of the burden material in a blast furnace via its electrical conductivity without direct contact between the sensor i.e. the transmitter coil 4 and the receiver coil 6 and the burden material 14. A number of measurements in a horizontal and / or vertical dimension allows to determine the material distribution in the burden of a blast furnace.

[0042] The protective shell 8 is made of a ceramic material that withstands extreme conditions, especially the temperature variations and the forces from the burden and friction in the blast furnace. The protective shell 8 has a thickness in the range between 10 and 25 mm. As the ceramic material is harder than the blast furnace burden, it can withstand abrasion during a long operation time. As the measurements are carried out while the blast furnace is operated, the ceramic protective shell 8 protects the transmitter coil 4 and the receiver coil 6 from being damaged when the probe is inserted into or moved through the burden.

[0043] The measuring probe 2 comprises a transmitter coil 4 and a receiver coil 6. In operation, the transmitter coil 4 generates a primary alternating magnetic field and the receiver coil 6 receives an alternating magnetic field. The transmitter coil 4 and the receiver coil 6 are directly arranged on the protective shell 8. The probe has a length of about 5 m in the case of a movable probe, and a length of about 1 m in the case of a fixed probe. The sensor is arranged near the tip of the probe, such that the sensor can be inserted into the blast furnace. The transmitter coil 4 and the receiver coil 6 are electrically connected to the evaluation and control unit 10, which is situated outside of the blast furnace by electrically conductive wires (not shown).

[0044] When the measuring probe 2 in fig. 1 is viewed from above, the transmitter coil 4 and the receiver coil 6 have a circular shape and are separated from the burden material 14 by the protective shell 8. The transmitter coil 4 and the receiver coil 6 are arranged such that their magnetic fields are concentric. The surface of the transmitter coil 4 is between 1 to 20 cm ² and the surface of the receiver coil 6 is between 5 to 50 cm ² . The ratio of the surfaces of the two coils is thus between 1 :1 and 1 :50 (transmitter surface: receiver surface).

[0045] The measurement range, i.e. the volume of the material to be measured can be adapted by changing some of the parameters for generating and receiving the alternating magnetic fields. The frequency of the signal applied to the transmitter coil 4 can be increased or reduced and/or the surface of the transmitter coil 4 and/or the receiver coil 6 can be increased or reduced. The measurement volume of the alternating magnetic fields can be reduced, enlarged or shaped accordingly. In this particular preferred embodiment of the invention, the volume to be measured roughly corresponds to an elliptical hemisphere.

[0046] The surface of the receiver coil 6 is chosen such that it is possible to determine the material distribution of the burden through the protective shell arranged between the burden material 14 and the measurement sensor. The minimal distance between the burden material 14 and the coils 4, 6 is determined by the thickness of the protective shell. If the sensitivity is not satisfactory, the surface of the receiver coil 6 has to be enlarged or the shell thickness reduced.

[0047] To improve the determination of the material distribution in the blast furnace, multiple sensors can be arranged side by side near the tip of the probe. Since eddy currents are only local effects, they do not interfere with eddy currents induced by other coils 104a, 104b, 104c or 104d if the system is designed properly. The material type is detected at several positions simultaneously, so as to increase the local resolution. In result, the number of measurement signals and the measurement resolution can be increased and designed as desired. In fig. 2, the protective shell 8 is an annular cylinder, in which four sensors are arranged. The measuring volume of each individual sensor covers about one quarter of the cylinder circumference. In this particular embodiment, if the annular cylinder is installed on the tip of a horizontal probe, there is one measuring spot on the top, two in the center, and one at the bottom. The material type is detected at three different vertical positions, contributing to a three times higher vertical resolution of the measurement compared to a probe with only one measuring sensor.

[0048] The transmitter coils 104a, 104b, 104c and 104d in fig. 2 and the transmitter coil 4 in fig. 1 are operatively connected to an alternating current power source 12 as illustrated in fig. 1 . In operation, an alternating current applied to the transmitter coil as shown in figs. 3 and 4 emits the primary alternating magnetic field 16. To obtain accurate measurements and good results, alternating currents with a frequency of about 2MHz and a magnitude of 5mA are applied.

[0049] In fig. 3, no conductive material is brought in the range of the primary alternating magnetic field 16, no eddy currents are induced in the conductive material and no secondary alternating magnetic field is generated. Before the resistance of a conductive material can be measured, the conductive object has to be in range of the primary alternating magnetic field 16. The primary alternating magnetic field 16 is limited amongst others by the size and shape of the transmitter coil 4.

[0050] In fig. 4, the burden material 14 is brought into the primary alternating magnetic field 16. The primary alternating magnetic field 16 in fig. 5 induces eddy currents 18 in the burden material 14. The induced eddy currents 18 generate a secondary alternating magnetic field 20. The control and evaluation unit 10 evaluates the measurements based on the primary alternating magnetic field 16 and the secondary alternating magnetic field 20 measured by the receiver coil 6. The magnitude of the electrical current in the receiver coil 6 is indicative of the electrical resistance of the burden material 14.

[0051 ] In fig. 5 an electrical current output of a receiver coil is represented. If the burden material 14 is ore, or if there is no burden material, the measured electrical current in the receiver coil 6 is higher than or equal to 5 mA. When coke is within the primary alternating magnetic field, the electrical current in the receiver coil is inferior to 5 mA, typically about 10% lower than the value if there is no material, thereby as low as 4.5 mA.

[0052] To detect the material type, the current of the receiver coil is compared to a threshold value 24. In this particularly preferred embodiment of the invention, the threshold value 24 is set to 4.9 mA. The person skilled in the art is capable of adjusting the threshold value 24 according to his needs. This is usually done during calibration. For calibrating the measuring probe, an AC current is applied to the alternating transmitter coil 4 when no conductive object but coke dust is in the primary alternating magnetic field 16. This leads to the calibration value 22. The threshold value 24 is defined a bit lower to account for measurement noise and to prevent dust influence. Each change in electrical current in the receiver coil below the threshold value 24 is indicative of the presence of electrically conductive burden material 14 in the primary alternating magnetic field 16.

[0053] The current of the receiver coil 6 is amongst others a function of electrical conductivity of the burden material 14. The electrical conductivity is a characteristic that is reliable throughout the entire range of temperatures in the blast furnace. It is therefore suitable as a characteristic for determining the material distribution. The system is designed to have a good response towards conductivity. To a lesser extend, the secondary alternating magnetic field 20 depends on the magnetic permeability of the burden material 14 at temperatures below the Curie-Point. The influence of magnetic permeability is approximately equal to or less than +2% different from the calibration value 22. This influence is not relevant as the measurement signal for the presence of coke is between 0 to - 10% different from the calibration value 22. Changes in temperature or a constant magnetic flux do not influence the measurement. Small coke and dust particles do not have a notable influence on the measurement.

[0054] To carry out a measurement, the probe as illustrated in fig. 6 is inserted into the blast furnace. A movable probe as well as a fixed probe are used in this blast furnace for determining the material distribution therein. In the following, only the principle of a movable probe is described. At least one sensor 2 is arranged near the tip of a horizontally movable measuring probe. The probe is inserted into a blast furnace that has a diameter of approximately 10 m. The measurements are taken at about 4 m beneath the surface of the burden, typically in a region before the material starts to soften. A travel from the blast furnace shell to the blast furnace center and back to the blast furnace shell takes about 50 seconds. This fast horizontal movement is repeated sequentially. Simultaneously, the burden is descending slowly but constantly with a speed of approximately 12 cm/min.

[0055] The measurement signal is recorded continuously at every point and compared to the threshold value 24. In this way, an image of the material distribution as illustrated in fig. 7 is obtained. The data received from the sensor 2 is arranged in a x-y plot, with the x-axis representing the radius of the blast furnace and the y-axis representing the height of the blast furnace. The pixels in fig. 7 correspond to the measured material distribution in the blast furnace. Each pixel represents about 10 cm x 10 cm of burden. One can clearly recognize that up to a radius of 1 .3 m from the blast furnace center, there is only coke 26. The process gas can basically pass upwards through the coke 26 along this central chimney, but hardly through the layers of ore-like burden 28. This is the central chimney for the process gas that escapes upwards. Furthermore, the layers are arranged such that the process gas can get in contact with the bottom parts of the ore-like material layers.

[0056] It is further possible to apply signal processing methods to extract more information from the raw measurement signal. For instance, instead of a mere differentiation between coke and ore-like materials, material mix values can be obtained during rastering to the pixels. Furthermore, information on the coke particle size can be extracted from the fluctuations of the receiver current magnitude signal.

[0057] The temperature at which the material distribution is measured according to this particularly preferred embodiment of the invention, ranges from about 100°C near the blast furnace wall to 900°C or more in the blast furnace center. Especially in the central chimney of the blast furnace, which is the inner radius up to 1 m, the temperature reaches extreme peaks. On the other hand, the size of this chimney is one of the major information that should result from the measurement. For the typical iron ores used in blast furnaces, the Curie-Point is well below these temperatures. The magnetic properties that differ ore-like material from coke disappear. However, as the measurement is based on the electrical conductivity, and as the conductivity of coke remains intact at the present temperatures, the material distribution is determined at a temperature above, at or beneath the Curie-Point and beneath the melting point of the material.

[0058] Finally, the material distribution program of the charging chute of the blast furnace is adjusted according to the desired material distribution. If an undesired material distribution is determined, the material distribution program of the charging chute is corrected. The target is to improve the efficiency, the productivity and the lifetime of the blast furnace by optimizing the charging. Legend:

2 probe

4 transmitter coil

6 receiver coil

8 protective shell

10 evaluation and control unit

12 alternating current power source 14 conductive burden material

16 primary alternating magnetic field 18 eddy current

20 secondary alternating magnetic field 22 signal level without any object

24 signal level threshold for coke detection 26 coke material

28 ore-like material

108 protective shell

104a, 104b, 104c, 104d transmitter coils

106a, 106b, 106c, 106d receiver coils