JP7740490B2 - 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 - Google Patents

Description

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

In the steelmaking industry, blast furnaces are the most upstream process, and technology to stabilize their operation is therefore highly valued. Ensuring good ventilation within the furnace is crucial for stable blast furnace operation. One factor impairing ventilation within the furnace is the rise in the liquid level of the molten iron and molten slag (hereinafter collectively referred to as the "molten material") remaining 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 contribute to an increase in blast pressure. Furthermore, if the molten material 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 ensure stable blast furnace operation, it is essential to ensure that the molten material level does not reach the blast tuyere level.

Against this background, methods have been proposed for evaluating the amount of molten material remaining in a blast furnace based on material balance, taking into account various operational parameters of the furnace. Specifically, Patent Document 1 describes a method for estimating the amount of molten material remaining in the furnace by calculating the theoretical amount of molten material to be discharged from the blast furnace using the actual volume of the material charged in the furnace and a theoretical volume calculated from operational parameters, and comparing this with the amount of molten material actually discharged. Furthermore, Patent Document 2 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, applying parameters representing the properties of the blast furnace's constituent materials, including the molten material level, to a general equation for continuous ambient strain.

Patent Document 3 describes a method utilizing Bernoulli's theorem to calculate the discharge rate of molten material from the discharge distance, discharge angle, and discharge height of the molten material discharged from the taphole of a blast furnace, and use this to estimate the molten material level within the furnace. The accuracy of this method depends on the accuracy of the calculation of the discharge rate of molten material discharged from the taphole, and this method estimates the discharge rate through image analysis of images taken with a camera. Patent Document 4 describes a method for measuring the vibration intensity of the furnace wall at the bottom of the furnace and estimating the molten material level within the furnace from the correspondence between the vibration intensity in a specific frequency band determined in advance and the molten material level.

Japanese Patent Application Laid-Open No. 2002-302709 Special Publication No. 2015-528905 Patent No. 7056813 International Publication No. 2022/201717

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 with estimating the liquid level of the molten material, which is important for stable blast furnace operation. Furthermore, because it is affected by various weighing errors, there is a concern that estimation errors will accumulate in blast furnace processes that handle large volumes, and estimation accuracy will decrease over time.

The method described in Patent Document 2 also has the following problems. It is known that in addition to the steel shell and cooling staves on the surface of the blast furnace, the lower furnace also contains refractory bricks and a solidified layer of cooled and solidified molten material inside the furnace. 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. This makes it 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.

Furthermore, with the method described in Patent Document 3, a large amount of dust is generated as high-temperature molten material is discharged during the tapping operation, 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, because the opening shape differs for each tap, it is difficult to quantify the frictional force the molten material experiences on its 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.

The method described in Patent Document 4 also has the following issues: The vibration intensity of an actual furnace body is more strongly affected by fluctuations in the blast air volume 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 operational 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 only effective in extremely ideal situations 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.

The present invention was made to solve the above-mentioned problems, and its purpose is to provide a method and device for measuring the molten material level in a blast furnace that can accurately measure the molten material level in the blast furnace regardless of the blast furnace's operating conditions. Another purpose of the present invention is to provide a blast furnace operating method that enables stable, eco-friendly blast furnace operation.

The method for measuring the molten material level in a blast furnace according to the present invention includes 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; and a molten material level calculation step of calculating discontinuities in the change in vibration intensity in the height direction of the furnace body and determining the positions corresponding to the discontinuities as the position of the molten material level in the blast furnace.

The molten material level calculation step may include the steps of: classifying vibration intensity data at each measurement position into first vibration intensity data at a measurement position higher than the measurement position and second vibration intensity data at a measurement position lower than the measurement position; constructing a first linear approximation equation and a second linear approximation equation at each measurement position from the first vibration intensity data and the second vibration intensity data, respectively, which indicate the relationship between the vertical position of the furnace body and vibration intensity; calculating the difference in vibration intensity at each measurement position between the first linear approximation equation and the second linear approximation equation as a discontinuity; and determining the measurement position among all measurement positions at which the discontinuity is greatest as the molten material level.

The vibration meter should be installed between the taphole level and the tuyere level of the furnace body.

The frequency range derived from the air blowing should preferably be within the range of 700 to 900 Hz.

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 to 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 discontinuities in the change in vibration intensity in the height direction of the furnace body, and determines the positions corresponding to the discontinuities as the position of the molten material level in the blast furnace.

The 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.

The method and device for measuring the molten material level inside a blast furnace according to the present invention can measure the molten material level inside a blast furnace with high accuracy regardless of the operating conditions of the blast furnace. Furthermore, the blast furnace operating method according to the present invention can ensure stable, eco-friendly blast furnace operation.

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 inside a blast furnace according to one embodiment of the present invention is applied. FIG. 2 shows the intensity of the air-blast-induced vibration measured by multiple vibration meters when the melt level was changed, plotted against the height of the measurement position relative to the melt level. FIG. 3 is a diagram showing an outline of a method for measuring the molten material level in a blast furnace according to one embodiment of the present invention. FIG. 4 is a diagram showing the change over time in the measured value of the molten material level from the early stage to the end of tapping.

Below, with reference to the drawings, we will explain one embodiment of the present invention, which is a method for measuring the molten material level in a blast furnace, a device for measuring the molten material level in a blast furnace, and a method for operating a blast furnace.

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

Figure 1 is a schematic cross-sectional view showing the configuration of a blast furnace to which a device for measuring the molten material level within a blast furnace, which is one embodiment of the present invention, is applied. As shown in Figure 1, the blast furnace 1, which is one embodiment of the present invention, comprises a substantially cylindrical furnace body 2, a blower 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 wall bricks 6, and the inner and outer wall surfaces of the hearth wall bricks 6 are covered by a cooling sleeve 7 and a steel shell 8, respectively.

Furthermore, the blast furnace 1, which is one embodiment of the present invention, is equipped with multiple vibration meters 9, data loggers 10, and information processing devices 11 as devices for measuring the molten material level within the blast furnace. Each vibration meter 9 is set at equal intervals along a straight line that is perpendicular to the circumferential tangent of the furnace body 2 and that follows the surface of the steel shell 8, from the height of the tap hole 4 to the height of the tuyere 3. Each vibration meter 9 measures the vibration value of the furnace body 2 as a current value and outputs an electrical signal indicating the measured current value to the data logger 10.

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-lapse data of the vibration values at the installation position (measurement position) of each vibration meter 9 generated by the data logger 10. The information processing device 11 then calculates the molten material level in the blast furnace by using the calculated vibration intensity and executing the method for measuring the molten material level in the blast furnace shown below.

Measurements using an actual furnace revealed that vibrations of the furnace body 2 span a wide range of vibration frequencies, with the 700-900 Hz frequency band showing particularly high peak values and peaks at all measurement positions. Because it was confirmed that vibrations in the 700-900 Hz frequency band generally tend to be higher near the tuyere 3, they are thought to be vibrations caused by the air blast 23 from the tuyere 3 (air blast-derived vibrations). Therefore, in this invention, the molten material level is measured using the vibration intensity observed in the 700-900 Hz frequency range, which corresponds to air blast-derived vibrations. However, the frequency band in which air blast-derived 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. For this reason, when applying this invention to other blast furnaces, it is advisable to analyze the basic vibration frequency bands each time.

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

[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.

Figure 2 shows the results of plotting the blast-induced vibration intensity measured by multiple vibration meters 9 against the relative height of the measurement position of the vibration meters 9 relative to the molten material level (vibration meter height based on the liquid level) using a cold model simulating the lower furnace of a blast furnace 1 when the molten material level was changed. As shown in Figure 2, the blast-induced vibration intensity changes discontinuously at the surface of the molten material. This experiment also included results for multiple cases simulating factors that may vary in an actual blast furnace, such as the physical properties of the molten material, the blast volume, the packing particle diameter, and the packing particle size distribution. None of the cases overturned the trend shown in Figure 2. Furthermore, the trend shown in Figure 2 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 ratio, 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 discontinuous fluctuations in vibration intensity at the surface layer of the molten material are a phenomenon that is consistently observed under all operating conditions. Therefore, if the discontinuous point in the change in vibration intensity along the height of the furnace body can be calculated, the molten material level within the blast furnace can be measured with high accuracy regardless of the blast furnace's operating conditions, since the molten material surface will be located near that discontinuous point. Furthermore, this allows for early detection of a rise in the molten material level and prevents an increase in the reducing agent ratio caused by an increase in air flow resistance due to a rise in the molten material level, thereby enabling stable, eco-friendly blast furnace operation. The technical concept of this invention is based on the above logic.

FIG. 3 is a diagram illustrating an overview of a method for measuring the molten material level in a blast furnace according to one embodiment of the present invention. In this method for measuring the molten material level in a blast furnace according to one embodiment of the present invention, first, vibration intensity in the frequency band caused by the air blowing is measured using vibration meters 9 installed at equal intervals at multiple locations on a line perpendicular to a tangent line in the circumferential direction of the furnace body 2 from the tap hole 4 to the height of the tuyere 3. In this embodiment, n (≧2) vibration meters 9 are installed. Next, the information processing device 11 classifies the vibration intensity data at each measurement position (vibration measurement point) i (=1 to n) into first vibration intensity data at a measurement position higher than the measurement position and second vibration intensity data at a measurement position lower than the measurement position. Next, the information processing device 11 constructs, at each measurement position i, a first linear approximation equation and a second linear approximation equation, respectively, from the first vibration intensity data and the second vibration intensity data, which respectively indicate the relationship between the vertical position of the furnace body 2 and the vibration intensity. Next, as shown in FIG. 3, the information processing device 11 calculates, at each measurement position i, the vibration intensity difference between the two linear approximations as the discontinuity Δe(i). Finally, the information processing device 11 determines the measurement position i showing the maximum value max[Δe(i)] _i=1,n among the n discontinuities Δe(i) as the melt level.

In this example, a large blast furnace with a capacity of approximately 5,000 ^m3 was used, and 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 circumferential direction of the furnace body from the tap hole level (height 2 m) to the tuyere level, and the molten material level in the blast furnace was measured. Table 1 shows the operating conditions for Examples 1 and 2. Figure 4 shows the time change in the measured molten material level from the beginning to the end of tapping. As shown in Figure 4, in both Examples 1 and 2, the molten material level ultimately reached the same level as the tap hole level. This confirmed that the present invention allows for highly accurate measurement of the molten material level.

The above describes an embodiment of the invention developed by the inventors, but the present invention is not limited to the descriptions and drawings that form part of the disclosure of the present invention according to this embodiment. In other words, all other embodiments, examples, and operational techniques, etc., developed by those skilled in the art based on this embodiment are included in the scope of the present invention.

The present invention provides a method and device for measuring the molten material level in a blast furnace, which can accurately measure the molten material level in the blast furnace regardless of the operating conditions of the blast furnace. Furthermore, the present invention provides a method for operating a blast furnace, which enables stable, eco-friendly blast furnace operation.

REFERENCE SIGNS LIST 1 blast furnace 2 furnace body 3 blast tuyere, tuyere 4 tap hole 5 hearth brick 6 furnace wall brick 7 cooling sleeve 8 iron shell 9 vibration meter 10 data logger 11 information processing device 21 iron ore 22 coke 23 blast 24 molten material 25 tapping slag

Claims (4)

a measuring step of measuring a vibration frequency distribution in the height direction of the furnace body using a plurality of vibrometers 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 a frequency range caused by air blowing at each measurement position by performing a Fourier transform on the vibration frequency distribution;
A molten material level calculation step of calculating a discontinuous point in the change in vibration intensity in the height direction of the furnace body and determining the position corresponding to the discontinuous point as the position of the molten material level in the blast furnace;
Including ,
The vibration meter is installed between the tap hole level and the tuyere level of the furnace body,
The frequency range from the air blowing is within the range of 700 to 900 Hz.
A method for measuring the molten material level inside a blast furnace. The melt level calculation step includes:
classifying vibration intensity data at each measurement position into first vibration intensity data at a measurement position higher than the measurement position and second vibration intensity data at a measurement position lower than the measurement position;
At each of the measurement positions, a first linear approximation formula and a second linear approximation formula are constructed from the first vibration intensity data and the second vibration intensity data, respectively, which represent the relationship between the height direction position of the furnace body and the vibration intensity;
calculating a vibration intensity difference between the first linear approximation formula and the second linear approximation formula at each measurement position as a discontinuity;
determining the measurement position at which the discontinuity is greatest among all measurement positions as the melt level;
2. The method for measuring the melt level in a blast furnace according to claim 1, comprising: a plurality of vibrometers arranged at predetermined intervals along the height direction of the furnace body of the blast furnace, for measuring the vibration frequency distribution in the height direction of the furnace body;
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 discontinuities in the change in vibration intensity in the height direction of the furnace body, and determines the position corresponding to the discontinuity as the position of the molten material level in the blast furnace;
Equipped with
The vibration meter is installed between the tap hole level and the tuyere level of the furnace body,
The frequency range from the air blowing is within the range of 700 to 900 Hz.
A device for measuring the molten material level inside a blast furnace. A method for operating a blast furnace, comprising the step of operating the blast furnace according to the smelt level measured using the method for measuring the smelt level within the blast furnace according to claim 1 or 2.