Method for measuring level of molten material inside blast furnace, device for measuring level of molten material inside blast furnace, and method for operating blast furnace

Abstract

This method for measuring the level of molten material inside a blast furnace comprises: a measurement step for measuring a vibrational frequency distribution in the height direction of a furnace body of the blast furnace using multiple vibration indicators disposed at predetermined intervals along the height direction of the furnace body; a vibrational intensity calculation step for calculating a vibrational intensity within a frequency range originating from a blast at each measurement position through Fourier transformation of the vibrational frequency distribution; a numerical value analysis step for calculating a maximum vibrational intensity distribution in a lower part of the blast furnace, which includes a furnace body iron shell, a packed bed in the blast furnace, a furnace floor brick, and a coagulation layer of the molten material in the blast furnace, using a numerical value analysis model with the blast amount and the level of molten material inside the blast furnace as variables; and a molten material level calculation step for calculating the level of molten material at which the difference between the vibrational intensity calculated in the vibrational intensity calculation step and the maximum vibrational intensity distribution calculated in the numerical value analysis step is minimized, and setting the calculated molten material level as the position of the level of molten material inside the blast furnace.

Description

METHOD FOR MEASURING MOLTEN MATERIAL LEVEL IN A BLAST FURNACE, MEASURING DEVICE FOR MOLTEN MATERIAL LEVEL IN A BLAST FURNACE, AND METHOD FOR OPERATING A BLAST FURNACE

[0001] The present invention relates to a method for measuring a molten material level in a blast furnace, a device for measuring a molten material level in a blast furnace, and a method for operating a blast furnace.

[0002] In the steelmaking industry, blast furnaces are located at the most upstream stage, and therefore technologies for stabilizing their operation are highly valued. Ensuring good permeability within the furnace is crucial for stable blast furnace operation. One of the factors impairing permeability within the furnace is the rise in the liquid level of molten pig iron and molten slag (hereinafter collectively referred to as the "molten material") accumulated in the packed bed at the bottom of the furnace. A rise in the liquid level of the molten material (hereinafter abbreviated as the "molten material level") narrows the gas flow path within the furnace and can directly cause an increase in blast pressure. Furthermore, if the liquid level reaches the blast tuyere level, it can cause serious problems such as blast tuyere melting, blockage of the blast tuyere, and slag backflow (a phenomenon in which molten material flows back from the blast tuyere). Therefore, to achieve stable blast furnace operation, it is essential to ensure that the liquid level does not reach the blast tuyere level.

[0003] Against this background, a method for evaluating the amount of molten material remaining in a blast furnace based on material balance has been proposed. Specifically, Patent Document 1 describes a method for estimating the amount of molten material remaining in a blast furnace by calculating a theoretical amount of molten material discharged from the blast furnace using the actual volume value of the charge material in the furnace and a theoretical volume value calculated from the operational parameters, and comparing this with the amount of molten material actually discharged. Patent Document 2 also describes a method for estimating the molten material level in a furnace by solving variables measured by multiple strain gauges installed in the furnace body by providing parameters representing the properties of the constituent materials of the blast furnace, including the molten material level, to a general equation for continuous ambient strain.

[0004] Furthermore, Patent Document 3 describes a method utilizing the so-called Bernoulli's theorem, in which the discharge rate of the molten material discharged from the taphole of a blast furnace is calculated from the discharge distance, discharge angle, and discharge height, and the molten material level in the furnace is estimated using this. The estimation accuracy of this method depends on the accuracy of the calculation of the discharge rate of the molten material discharged from the taphole, and this method estimates the discharge rate by image analysis of images taken with a camera. Furthermore, Patent Document 4 describes a method for estimating the molten material level in the furnace by measuring the vibration intensity of the furnace wall in the lower part of the furnace and using a correspondence relationship between the vibration intensity in a specific frequency band that has been determined in advance and the molten material level.

[0005] Japanese Patent Publication No. 2002-302709 Japanese Patent Publication No. 2015-528905 Japanese Patent No. 7056813 International Publication No. 2022 / 201717

[0006] However, the method described in Patent Document 1 does not take into account the void ratio of the packed bed in the lower part of the furnace or the shape of the solidified layer. Therefore, even if it is possible to estimate the amount of molten material remaining in the furnace, there remains a problem in estimating the liquid level of the molten material, which is important for stable operation of the blast furnace. In addition, because it is affected by various weighing errors, there is a concern that estimation errors will accumulate in blast furnace processes that handle large masses, and estimation accuracy will decrease over time.

[0007] Furthermore, the method described in Patent Document 2 has the following problems. It is known that in the lower furnace, in addition to the steel shell and cooling staves on the surface of the blast furnace, refractory bricks and a solidified layer formed by the cooled and solidified molten material in the furnace are present. The refractory bricks deteriorate over time due to wear and thermal stress, and the extent of the solidified layer changes daily depending on the thermal conditions in the lower furnace. For this reason, it is extremely difficult to grasp the state of these constituent materials. Therefore, with the method described in Patent Document 2, it is virtually impossible to exclude unknown parameters other than the molten material level, which represents the constituent materials of the blast furnace, from the general equation. Therefore, the accuracy of the molten material level estimated from the general equation cannot be said to be satisfactory.

[0008] Furthermore, with the method described in Patent Document 3, a large amount of dust is generated during the tapping operation due to the discharge of high-temperature molten material, making it unlikely that a clear image of the molten material's discharge behavior can be captured using a camera. Furthermore, tapping operations inevitably involve opening errors, such as with horizontal holes, which also contributes to a decrease in the frequency of estimating the molten material's discharge behavior. Furthermore, since the opening shape varies for each tap, it is difficult to quantify the frictional force that the molten material experiences along the path from the furnace to the discharge port. Taking all of these factors into consideration, it can be said that the method described in Patent Document 3 makes it extremely difficult to accurately measure the molten material level.

[0009] Furthermore, the method described in Patent Document 4 has the following problems: The vibration intensity of an actual furnace body is more strongly affected by fluctuations in the blast rate and changes in the shape of furnace fillers and structures such as hearth bricks and the solidified layer than by the molten material level. For this reason, in a blast furnace process where the operating conditions change from moment to moment, it is impossible to establish a one-to-one correlation between the vibration intensity of the furnace body and the molten material level. For this reason, the method described in Patent Document 4 is effective only under extremely ideal conditions where the conditions inside the furnace other than the molten material level are steady, making it difficult to measure the molten material level stably over the long term.

[0010] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method and device for measuring the molten material level in a blast furnace that can measure the molten material level in the blast furnace with high accuracy regardless of the operating conditions of the blast furnace. Another object of the present invention is to provide a method for operating a blast furnace that can perform stable, eco-friendly blast furnace operation.

[0011] The method for measuring the molten material level in a blast furnace according to the present invention includes the following steps: a measurement step of measuring the vibration frequency distribution in the height direction of the furnace body using a plurality of vibration meters arranged at predetermined intervals along the height direction of the furnace body of the blast furnace; a vibration intensity calculation step of calculating the vibration intensity in the frequency range caused by the air blowing at each measurement position by Fourier transforming the vibration frequency distribution; a numerical analysis step of calculating the maximum vibration intensity distribution in the lower part of the blast furnace, including the furnace body shell, the furnace packed layer, the hearth bricks, and the solidified layer of the molten material in the furnace, using a numerical analysis model with the molten material level in the blast furnace and the air blowing volume as variables; and a molten material level calculation step of calculating the molten material level at which the difference between the vibration intensity calculated in the vibration intensity calculation step and the maximum vibration intensity distribution calculated in the numerical analysis step is minimized, and setting the calculated molten material level as the position of the molten material level in the blast furnace.

[0012] The vibration meter may be installed between the taphole level and the tuyere level of the furnace body.

[0013] The frequency range derived from the air blowing is preferably within the range of 700 to 900 Hz.

[0014] The device for measuring the molten material level in a blast furnace according to the present invention comprises a plurality of vibration meters arranged at predetermined intervals along the height direction of the blast furnace body, which measure the vibration frequency distribution in the height direction of the furnace body; and an information processing device that calculates the vibration intensity in the frequency range caused by the air blowing at each measurement position by Fourier transforming the vibration frequency distribution, calculates the maximum vibration intensity distribution in the lower part of the blast furnace, including the furnace body shell, the furnace packed layer, the hearth bricks, and the solidified layer of the molten material in the furnace, using a numerical analysis model with the molten material level and the air blowing volume in the blast furnace as variables, calculates the molten material level at which the difference between the vibration intensity and the maximum vibration intensity distribution is minimized, and sets the calculated molten material level as the position of the molten material level in the blast furnace.

[0015] A method for operating a blast furnace according to the present invention includes a step of operating the blast furnace according to the smelt level measured using the method for measuring the smelt level in a blast furnace according to the present invention.

[0016] According to the method and device for measuring the molten material level in a blast furnace of the present invention, the molten material level in a blast furnace can be measured with high accuracy regardless of the operating conditions of the blast furnace. Furthermore, according to the method for operating a blast furnace of the present invention, it is possible to stably perform eco-friendly blast furnace operation.

[0017] FIG. 1 is a schematic cross-sectional view showing the configuration of a blast furnace to which a smelt level measurement device in a blast furnace according to one embodiment of the present invention is applied. FIG. 2 is a diagram showing the calculation flow of a numerical analysis model related to vibration. FIG. 3 is a diagram showing the configuration of a computational grid. FIG. 4 is a diagram showing an example of analysis using a two-dimensional vibration model. FIG. 5 is a diagram showing the results of plotting the blast-induced vibration intensity measured by multiple vibration meters when the smelt level is changed against the height of the measurement position relative to the smelt level. FIG. 6 is a diagram showing the time change in the measured value of the smelt level from the early stage to the end of tapping. FIG. 7 is a diagram showing the results of fitting the vibration intensity measured in an actual furnace and the maximum vibration intensity predicted by the numerical analysis model using the smelt level.

[0018] Hereinafter, a method for measuring a molten material level in a blast furnace, a device for measuring a molten material level in a blast furnace, and a method for operating a blast furnace according to one embodiment of the present invention will be described with reference to the drawings.

[0019] [Configuration] First, with reference to FIG. 1, the configuration of a device for measuring the level of molten material in a blast furnace according to one embodiment of the present invention will be described.

[0020] Fig. 1 is a schematic cross-sectional view showing the configuration of a blast furnace to which a device for measuring the level of molten material within a blast furnace according to one embodiment of the present invention is applied. As shown in Fig. 1, the blast furnace 1 according to one embodiment of the present invention includes a substantially cylindrical furnace body 2, a blast tuyere (hereinafter abbreviated as tuyere) 3 provided below the furnace body 2, and a tap hole 4 provided in the furnace body 2 below the tuyere 3. The hearth of the blast furnace 1 is composed of hearth bricks 5 and hearth bricks 6, and the inner and outer wall surfaces of the hearth bricks 6 are covered with a cooling sleeve 7 and a steel shell 8, respectively.

[0021] The blast furnace 1, which is one embodiment of the present invention, is equipped with a plurality of vibration meters 9, a data logger 10, and an information processing device 11 as devices for measuring the molten material level inside the blast furnace. The vibration meters 9 are set at equal intervals along a straight line perpendicular to a tangent in the circumferential direction of the furnace body 2 and along the surface of the steel shell 8, from the height position of the tap hole 4 to the height position of the tuyere 3. Each vibration meter 9 measures the vibration value of the furnace body 2 as a current value and outputs an electric signal indicating the measured current value to the data logger 10.

[0022] The data logger 10 converts the current values ​​measured by each vibration meter 9 into vibration values ​​based on the electrical signals output from each vibration meter 9. The information processing device 11 calculates the vibration intensity of the furnace body 2 at the installation position of each vibration meter 9 by performing a Fourier transform on the time-varying data of the vibration values ​​at the installation position (measurement position) of each vibration meter 9 generated by the data logger 10. Then, the information processing device 11 calculates the molten material level in the blast furnace by executing the method for measuring the molten material level in the blast furnace shown below using the calculated vibration intensity.

[0023] Measurements using an actual furnace revealed that the vibration of the furnace body 2 spans a wide range of vibration frequencies, with the highest peaks observed at all measurement positions in the 700-900 Hz frequency band. It was confirmed that vibrations in the 700-900 Hz frequency band tended to exhibit higher values ​​near the tuyere 3, suggesting that these vibrations were caused by the blast 23 from the tuyere 3 (blast-induced vibrations). Therefore, in the present invention, the molten material level was measured using the vibration intensity observed in the 700-900 Hz frequency range, which corresponds to blast-induced vibrations. However, the frequency band in which blast-induced vibrations are observed may vary depending on the shape of the furnace body 2, the influence of the ground, etc., and there is no certainty that this frequency band can be used to evaluate all blast furnaces in the same way. Therefore, when applying the present invention to other blast furnaces, it is desirable to analyze the basic vibration frequency bands each time.

[0024] In a blast furnace 1 shown in Figure 1, raw materials, iron ore 21 and coke 22, are charged in layers into a furnace body 2 from the furnace top and reduced to form a molten material 24 by blown air (hot air) 23 sent under pressure from tuyere 3. The molten material 24 is then stored in the furnace bottom and discharged as tapping slag 25 from a tap hole 4 by drilling the tap hole 4 at predetermined intervals. An apparatus for measuring the molten material level in a blast furnace, which is one embodiment of the present invention, measures the liquid level of the molten material 24 in the lower part of the furnace as the molten material level.

[0025] [Measurement Method] Next, a method for measuring the molten material level in a blast furnace according to one embodiment of the present invention will be described with reference to FIGS.

[0026] In one embodiment of the present invention, a method for measuring the molten material level in a blast furnace is performed by an information processing device 11. The information processing device 11 first measures the vibration intensity in the height direction, which is perpendicular to the tangent line in the circumferential direction of the furnace body 2, and estimates the maximum vibration intensity distribution of the furnace body 2 by executing a numerical analysis model related to vibration. The numerical analysis model related to vibration requires the molten material level and the blast volume as input information. In this embodiment, the former is treated as a variable for fitting the measured data of the vibration intensity distribution to the results of the numerical analysis, and the latter is obtained by sequentially importing operational data of the blast furnace. This allows the molten material level to be determined by fitting the measured data of the vibration intensity distribution to the results of the numerical analysis.

[0027] A numerical analysis model for vibration will now be described. The numerical analysis model for vibration is a physical model that estimates the maximum vibration intensity distribution in the lower furnace section, which is composed of the furnace shell region, the furnace packed bed region, the hearth bricks, and the solidified layer of molten material in the furnace. Figure 2 shows the calculation flow for the numerical analysis model for vibration. As shown in Figure 2, when executing the numerical analysis model for vibration, first, mesh conditions required for setting the computational grid, the analysis time step, and the density and Young's modulus as physical properties of the shell and packed bed are set. In addition, the amount of air blown to the blast furnace 1, which is considered as a vibration source, is input as an operational parameter (step S1).

[0028] Next, the information processing device 11 divides an axisymmetric two-dimensional region 31, which includes the central axis of the furnace body 2 and one of the multiple tuyere ports 3 installed around the furnace body 2 in the lower furnace section of the blast furnace 1, as shown in Figure 3, into multiple elemental regions 32 to set a computational grid (step S2). In this model, each elemental region 32 is connected by a spring 33 and a dash pod 34. Acceleration applied to a certain elemental region 32 propagates to neighboring elemental regions 32 via the spring 33 and the dash pod 34. The spring 33 represents a restoring force that describes the vibration phenomenon, and the dash pod 34 represents a damping force that causes the loss of vibration energy through various energy conversions during the vibration propagation process. Furthermore, in this model, the molten material level (L) is taken into account, and buoyancy and resistance due to the molten material are applied to the motion of elemental regions 32 whose centers of gravity are below the liquid level L.

[0029] 2 , the information processing device 11 then calculates the spring constant k of each element region 32 using the following formula (1) (step S3). In formula (1), E is Young's modulus, A is the cross-sectional area of ​​the element region 32 in a direction perpendicular to the spring 33, and L is the length of the element region 32 in the same direction as the spring 33. In this embodiment, since the numerical analysis model is a two-dimensional analysis model, A is set to the square of the length of the element region 32 perpendicular to the spring 33. Furthermore, since the spring constant k is determined as a material property of each element region 32, the average value of the spring constants k of the two element regions 32 to be connected is used as the spring constant of the spring 33 connecting each element region 32.

[0030]

[0031] Next, the information processing device 11 calculates the viscosity coefficient c of each element region 32 using the following formula (2) (step S4). In formula (2), m represents the mass of each element region 32. The volume of each element region 32 is given as the product of A and L. In addition, since the viscosity coefficient c is determined as a material property of each element region 32, the average value of the viscosity coefficients c of the two element regions 32 to be connected is given as the viscosity coefficient of the dash pod 34 that connects each element region 32.

[0032]

[0033] Next, the information processing device 11 uses the processing results of steps S2 and S3 to formulate a vibration equation for each element region 32 based on vibration engineering theory as shown in the following formula (3) (step S5). In formula (3), x is the displacement of each element region 32, t is time, C ｄ 3, the radial position of the two-dimensional area 31 is represented by a subscript I, and the height position is represented by a subscript J.

[0034]

[0035] The above formula (3) is based on Newton's equation of motion, and the left side takes into account the inertial force of each element area 32, while the right side takes into account the restoring force, damping force, liquid resistance force, buoyancy force, and external airflow force acting on each element area 32. The formula is also based on the assumption that the restoring force is proportional to the magnitude of the displacement of each element area 32, and the damping force is proportional to the velocity of each element area 32. Furthermore, the liquid resistance force C ｄ was calculated using the Kozeny-Carman formula, and the external blowing force was calculated as the product of the pressure loss in front of the tuyere calculated using the Ergun formula and the surface area of ​​the raceway calculated using the raceway depth estimation formula.

[0036] It is known that the general solution of the differential equation of the above formula (3) can be expressed by the following formula (4): where a represents the maximum acceleration of each element region 32, i represents the imaginary unit, and ω represents the vibration frequency.

[0037]

[0038] Therefore, when equation (4) is substituted into equation (3) and rearranged for the maximum acceleration a, equation (5) shown below is obtained.

[0039]

[0040] The above equation (5) relates to the maximum acceleration of the element region 32 represented by the coordinates (I, J) of interest and the four surrounding element regions 32. Formulating the above equation (5) for all element regions 32 results in a simultaneous equation relating to the maximum acceleration a of all element regions 32. Solving this equation using the BiCG-Stab method allows the maximum acceleration a of each element region 32 to be calculated. Therefore, the information processing device 11 calculates the maximum acceleration a of each element region 32 and calculates the maximum vibration intensity distribution of the furnace body 2 by substituting the calculated maximum acceleration a into equation (4) (step S6). The information processing device 11 then repeatedly executes this process until the maximum vibration intensity distribution of the furnace body 2 reaches a steady state (step S7). In this embodiment, the vibration frequency ω is set to 800 Hz, which is the average value of the actually measured vibration frequencies resulting from the air blowing, 700 to 900 Hz.

[0041] As described above, the maximum vibration intensity distribution of the lower furnace section, which is composed of the furnace shell region, the furnace packed bed region, the hearth bricks, and the solidified layer of molten material in the furnace, can be estimated based on vibration engineering theory. However, the molten material level remains an unknown parameter. The range of the liquid resistance and buoyancy forces in Equation (3) changes depending on the molten material level, and the molten material level also affects the calculation result of the maximum vibration intensity distribution. Therefore, the information processing device 11 next determines the molten material level as a variable so as to minimize the error between the vibration intensity distribution measured multiple times in the height direction of the furnace body 2 and the maximum vibration intensity distribution estimated by this numerical analysis model. This allows for highly accurate measurement of the molten material level in the blast furnace regardless of the operating conditions of the blast furnace. Furthermore, early detection of a rise in the molten material level and prevention of an increase in the reducing agent rate caused by an increase in the molten material level can ensure stable, eco-friendly blast furnace operation.

[0042] Figure 4 shows an example of an analysis using a two-dimensional vibration model. As shown in Figure 4, the blast vibration generated in the raceway space, where coke burns vigorously and swirls due to the blast pressure before the tuyere 3, gradually dissipates energy and decays as it propagates to the surrounding area. In the analysis example shown in Figure 4, it was assumed that the molten material surface was present in a region two-thirds of the distance from the hearth to the tuyere 3, and it was possible to confirm that the vibration intensity decayed discontinuously at that interface. Meanwhile, Figure 5 shows the blast-induced vibration intensity measured by multiple vibration meters 9 when the molten material level was changed using a cold model simulating the lower furnace of a blast furnace 1, plotted against the relative measurement position height of the vibration meters 9 relative to the molten material level (vibration meter height based on the liquid level). As shown in Figure 5, the blast-induced vibration intensity had an inflection point at the surface layer of the molten material, and this result qualitatively agreed with the predicted results of the numerical analysis model shown in Figure 4. Furthermore, this experiment included results for multiple cases simulating factors that may vary in an actual blast furnace, such as the physical properties of the molten material, blast rate, packing particle size, and packing particle size distribution, but none of the cases overturned the trend shown in Figure 5. Furthermore, the trend shown in Figure 5 was also confirmed in experiments simulating factors that are thought to be caused by external disturbances, such as vibration during raw material charging, changes in the total weight of the furnace charge due to changes in the blast furnace reducing agent rate, structural changes due to aging deterioration of the hearth bricks due to wear, and the installation conditions of the furnace body. From the above, it is believed that the fluctuations in vibration intensity with an inflection point on the molten material surface confirmed in Figure 5 are a phenomenon that is consistently observed under all operating conditions.

[0043] In this example, the capacity is approximately 5000 m ３In a large blast furnace (1999), pulverized coal was injected through the tuyere using normal charging materials. The vibration of the furnace body was measured using vibration meters installed at equal intervals on a line perpendicular to the tangent line of the furnace body in the circumferential direction from the tap hole level (height 2 m) to the tuyere level, and the molten material level in the blast furnace was measured. In Example 1, the coke rate was 333 (kg / t), the pulverized coal rate was 207 (kg / t), the reducing agent rate was 540 (kg / t), the iron production rate was 10,000 (t / d), and the tapping temperature was 1,495°C. In Example 2, the coke rate was 335 (kg / t), the pulverized coal rate was 198 (kg / t), the reducing agent rate was 533 (kg / t), the iron production rate was 9,950 (t / d), and the tapping temperature was 1,500°C. Figure 6 shows the time course of the measured molten material level from the beginning to the end of tapping. Figure 7 shows the results of fitting the vibration intensity measured in an actual furnace and the maximum vibration intensity estimated by the numerical analysis model with the smelt level. As shown in Figure 6, in both Examples 1 and 2, the smelt level ultimately reached the same level as the taphole level. This confirmed that the present invention can measure the smelt level with high accuracy. Furthermore, as shown in Figure 7(a), at the beginning of tapping, the difference between the actual and estimated values ​​was minimized by setting the smelt level to approximately 4.0 m. Furthermore, as shown in Figure 7(b), at the end of tapping, the difference between the actual and estimated values ​​was minimized by setting the residual iron and slag level to 2.0 m.

[0044] Although the present invention has been described above as an embodiment, the present invention is not limited to the descriptions and drawings that form part of the disclosure of the present invention. In other words, other embodiments, examples, and operational techniques that can be made by those skilled in the art based on the present invention are all included in the scope of the present invention.

[0045] According to the present invention, it is possible to provide a method and an apparatus for measuring the molten material level in a blast furnace, which are capable of measuring the molten material level in the blast furnace with high accuracy regardless of the operating conditions of the blast furnace. Furthermore, according to the present invention, it is possible to provide a method for operating a blast furnace, which is capable of stably performing eco-friendly blast furnace operation.

[0046] DESCRIPTION OF SYMBOLS 1 Blast furnace 2 Furnace body 3 Blast tuyere, tuyere 4 Tap hole 5 Hearth brick 6 Furnace wall brick 7 Cooling sleeve 8 Steel shell 9 Vibration meter 10 Data logger 11 Information processing device 21 Iron ore 22 Coke 23 Blast 24 Melt 25 Tap slag 31 Two-dimensional area 32 Element area 33 Spring 34 Dash pod

Claims

1. A method for measuring the molten material level in a blast furnace, comprising: a measurement step of measuring the vibration frequency distribution in the height direction of the furnace body using a plurality of vibration meters arranged at predetermined intervals along the height direction of the furnace body of the blast furnace; a vibration intensity calculation step of calculating the vibration intensity in the frequency range caused by the air blowing at each measurement position by Fourier transforming the vibration frequency distribution; a numerical analysis step of calculating the maximum vibration intensity distribution in the lower part of the blast furnace, including the furnace body steel shell, the furnace packed layer, the hearth bricks, and the solidified layer of the molten material in the furnace, using a numerical analysis model with the molten material level in the blast furnace and the air blowing volume as variables; and a molten material level calculation step of calculating the molten material level at which the difference between the vibration intensity calculated in the vibration intensity calculation step and the maximum vibration intensity distribution calculated in the numerical analysis step is minimized, and setting the calculated molten material level as the position of the molten material level in the blast furnace.

2. The method for measuring the molten material level in a blast furnace according to claim 1, wherein the vibration meter is installed between the tap hole level and the tuyere level of the furnace body.

3. A method for measuring the molten material level in a blast furnace according to claim 1 or 2, wherein the frequency range derived from the airflow is within the range of 700 to 900 Hz.

4. A device for measuring the level of molten material in a blast furnace, comprising: a plurality of vibration meters arranged at predetermined intervals along the height direction of the blast furnace body, for measuring the vibration frequency distribution in the height direction of the furnace body; and an information processing device that calculates the vibration intensity in the frequency range caused by the air blowing at each measurement position by Fourier transforming the vibration frequency distribution, calculates the maximum vibration intensity distribution in the lower part of the blast furnace, including the furnace body steel shell, the furnace packed layer, the hearth bricks, and the solidified layer of molten material in the furnace, using a numerical analysis model with the molten material level in the blast furnace and the air blowing volume as variables, calculates the molten material level at which the difference between the vibration intensity and the maximum vibration intensity distribution is minimum, and sets the calculated molten material level as the position of the molten material level in the blast furnace.

5. A method for operating a blast furnace, comprising the step of operating the blast furnace in accordance with the smelt level measured using the method for measuring the smelt level in a blast furnace according to claim 1 or 2.

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