Methods for detecting molten material height and operating methods of smelting furnaces

Abstract

A method for detecting the height of molten material in a smelting furnace having a furnace body with a furnace belly and two or more tuyeres for blowing hot air into the lower part of the furnace body, wherein the height of molten material accumulated at the bottom of the smelting furnace is detected by using the correspondence between the rate of increase of pressure loss in the furnace belly relative to the pressure in front of the tuyeres and the height of the molten material.

Description

TECHNICAL FIELD

[0001] The present application relates to a molten material height detecting method for detecting the height of molten material in the bottom portion of a smelting furnace, and a smelting furnace operation method. BACKGROUND

[0002] One of the smelting furnaces having a tuyere for blowing in gas is a blast furnace. The blast furnace is a smelting furnace in which iron is smelted by charging ore containing a large amount of iron component and coke from the top of the furnace and blowing in a mixed gas of air or pure oxygen and the like from the lower portion of the furnace. Molten pig iron slag generated by the above method is accumulated in the bottom portion of the blast furnace, and the iron slag is discharged from a hole called a tap hole at a certain cycle. In the production of pig iron using the blast furnace as described above, it is required to operate the blast furnace without failure and stably in order to achieve the planned production amount of pig iron.

[0003] However, the molten pig iron slag is excessively accumulated in the bottom portion of the blast furnace due to failure of the equipment leaving the tap hole or deterioration of the flowability of the molten pig iron slag in the furnace, and the like. Then, deterioration of gas permeability, clogging of the tuyere by the molten slag, and the worst case of production stoppage occur. In order to avoid such failure, it is preferable to grasp the height of the molten material accumulated in the bottom portion of the smelting furnace in the operation of the smelting furnace.

[0004] There is a technology for measuring the height of the molten material accumulated in the bottom portion of the smelting furnace. For example, in Patent Literature 1, three rod-shaped electrodes are inserted into the lower portion of the furnace, a voltage is applied to these electrodes, and the current flowing therethrough is measured, whereby the height of the molten material is grasped. Further, in Patent Literature 2, it is disclosed that the void fraction in the furnace and the height of the molten material can be measured from a value obtained by dividing the difference between the blast pressure at the lower portion of the furnace and the pressure at the lower portion of the furnace body by the variation of the gas volume in the bosh. Both of the technologies disclosed in these Patent Literatures 1, 2 are technologies for measuring the height of the molten material accumulated in the bottom portion of the smelting furnace.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Laid-Open No. 2011-158206

[0008] Patent Literature 2: Japanese Patent Application Laid-Open No. 51-27809

[0009] NON-PATENT LITERATURE

[0010] Non-Patent Literature 1: Michio Haneda, other two persons, "Influence of charging method, furnace body shape, and liquid surface shape on gas flow in a blast furnace" (Iron and Steel), Vol. 63 (1977), No. 2, pp. 217-226

[0011] Non-patent literature 2: Masakazu Iida and 2 others, “Analysis of the molten material discharge rate from the blast furnace”, Iron and Steel, Vol. 95 (2009), No. 4, pp. 331-339.

[0012] Non-patent literature 3: Yusuke Kashiwabara and 4 others, “The Influence of Undisappeared Mixed Small Pieces of Coke on the Ventilation of the Lower Part of the Blast Furnace,” Iron and Steel, Vol. 102 (2016), No. 12, pp. 661-668. Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] However, in order to measure the molten height using the method disclosed in Patent Document 1, a rod-shaped electrode for generating voltage in the furnace, a voltage generating device, a current detection device for measuring the current generated by the voltage, and cables connecting them are required. Therefore, the method disclosed in Patent Document 1 has the problem of increasing the cost of pig iron production due to the addition of these devices.

[0015] In the method disclosed in Patent Document 2, the furnace porosity and molten material height are measured by dividing the difference between the furnace lower blast pressure and the furnace lower pressure by the change in the furnace belly gas volume. However, the furnace lower blast pressure and the furnace lower pressure vary significantly depending on the particle size and particle size distribution within the furnace. Consequently, the furnace porosity, calculated from the difference between the furnace lower blast pressure and the furnace lower pressure and the change in the furnace belly gas volume, also varies significantly depending on the furnace pressure caused by the particle size and particle size distribution within the furnace.

[0016] Thus, the air pressure at the bottom of the furnace, the pressure at the bottom of the furnace body, and the void ratio inside the furnace are greatly affected by the particle size and particle size of the particles inside the furnace. However, Patent Document 2 does not consider the influence of the particle size and particle size inside the furnace. Therefore, the method disclosed in Patent Document 2 has the problem of not being able to accurately determine the height of the molten material accumulated at the bottom of the smelting furnace. The present invention was made in view of such problems of the prior art, and its object is to provide a method for detecting the height of molten material that can control the increase in the manufacturing cost of pig iron and accurately determine the height of molten material, as well as an operating method of the smelting furnace using the detected height of molten material.

[0017] Methods for solving problems

[0018] The methods used to solve the above problems are as follows.

[0019] (1) A method for detecting the height of molten material in a smelting furnace having a furnace body having a furnace belly and having two or more tuyeres for blowing hot air at the lower part of the furnace body, wherein the height of molten material accumulated at the bottom of the smelting furnace is detected by using the correspondence between the rate of increase of pressure loss in the furnace belly relative to the pressure in front of the tuyeres and the height of the molten material.

[0020] (2) An operating method for a molten metal furnace, wherein, when the height of the molten metal detected by the molten metal height detection method described in (1) exceeds a predetermined threshold, at least one of an operation to reduce the manufacturing speed of the molten metal and an operation to increase the discharge speed of the molten metal is performed.

[0021] Invention Effects

[0022] The rate of increase in pressure loss within the furnace belly relative to the pressure before the tuyere, in relation to the height of the molten material, is constant and independent of the raw material particle size, porosity, and furnace belly gas volume. Therefore, by implementing the molten material height detection method of the present invention using this correlation, it is possible to control the increase in pig iron manufacturing costs and detect the molten material height with high precision. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view of blast furnace 10.

[0024] Figure 2 This is a graph showing the relationship between melt height and pressure loss.

[0025] Figure 3 This is a graph showing the relationship between the rate of increase in pressure loss and the height of the melt. Detailed Implementation

[0026] The present invention will be described through embodiments thereof. In this embodiment, a blast furnace is used as the ore melting furnace, and an embodiment of the method for detecting the height of the molten material in the blast furnace will be described. However, the method for detecting the height of the molten material of the present invention is not limited to a blast furnace, and can be applied to any ore melting furnace having two or more tuyeres at the bottom of the furnace body and having a furnace belly.

[0027] Figure 1 (a) is a cross-sectional schematic diagram of blast furnace 10. Figure 1 (b) is Figure 1(a) Enlarged view of part A. The blast furnace 10 has a furnace body 20, a pressure sensor 12, and two or more temperature sensors 14. The furnace body 20 is a bottomed cylindrical furnace body composed of a furnace shaft 22, a furnace waist 24, a furnace belly 26, and a hearth 28. The pressure sensor 12 is located at the upper end of the furnace belly 26. In addition, two or more temperature sensors 14 are located at different positions along the height of the furnace belly 26.

[0028] Additionally, in the hearth section 28, two or more tuyeres 16 are provided on the circumference of the blast furnace to blow high-temperature hot air into the blast furnace. The number of tuyeres 16 is, for example, 40. Furthermore, in the hearth section 28, two or more tapping holes 18 are provided on the circumference of the blast furnace to tap molten pig iron 32 and molten slag 34. The number of tapping holes 18 is, for example, 4.

[0029] In such a blast furnace 10, ore and coke are alternately and layered into the blast furnace from the top, forming an ore layer 36 and a coke layer 38. Hot air and reducing materials such as finely powdered coke are blown in from the tuyeres 16 located at the bottom of the blast furnace to produce molten pig iron 32. The produced molten pig iron 32 and the slag 34 generated during the production of molten pig iron 32 accumulate at the bottom of the furnace and are tapped from the tap hole 18 at predetermined intervals. In this embodiment, the molten pig iron 32 and the slag 34 are collectively referred to as melt 30.

[0030] In such blast furnace operation, when excessive molten material 30 accumulates at the bottom of the furnace, problems arise such as deterioration of gas permeability and blockage of the tuyeres 16 due to molten slag 34. Therefore, to suppress such problems, it is preferable to detect the height of the molten material 30 accumulated at the bottom of the furnace with higher precision. Figure 1 (h).

[0031] As the height of the molten material 30 accumulated at the bottom of the blast furnace 10 increases, the volume from the surface of the molten material 30 to the furnace belly 26 decreases. Therefore, the pressure loss within the furnace belly relative to the pressure before the tuyeres immediately after hot blast is blown in from the tuyeres 16 changes. Therefore, in order to understand the relationship between this pressure loss and the height of the molten material 30, this relationship needs to be confirmed.

[0032] Figure 2 This is a graph showing the relationship between melt height and pressure loss. In Figure 2 In the diagram, the horizontal axis represents the molten material height (m), which is the height with the tuyeres 16 as the reference (0.0m). The vertical axis represents the pressure loss (kPa / m), which is the pressure loss between the internal pressure P1 at the upper end of the furnace belly 26 and the pressure P2 in front of the tuyeres. Figure 1 As shown in (b), when the height from the air vent 16 to the pressure sensor 12 is set to L, the pressure loss is calculated as (P2-P1) / L.

[0033] Pressure loss and molten material height are obtained through simulation using a two-dimensional numerical model of the gas flow in the lower part of the blast furnace. Specifically, the gas flow analysis and molten material surface shape analysis in the lower part of the blast furnace described in Non-Patent Document 1 are repeatedly performed until a specified convergence condition is met (the relative error between the surface shape obtained by the analysis and the surface shape obtained in the previous analysis is less than 0.001%), and the molten material surface shape and pressure distribution in the lower part of the blast furnace that meet this convergence condition are obtained. The pressure loss is calculated based on this pressure distribution, and the molten material height is calculated based on the molten material surface shape.

[0034] The gas flow analysis at the bottom of the blast furnace is performed using equations (1) to (3) described in Non-Patent Document 1. Equation (1) is derived from the equation of motion of the gas in the blast furnace packing layer. Equation (2) and equation (3) are derived from the equation of state of the gas.

[0035]

[0036] div(ρ g ×ε×r×q)=0…(2)

[0037] p = K × ρ g ×T…(3)

[0038] When solving equations (1) to (3) above, firstly, cylindrical coordinates (r, z) are used to define the stream function ψ that satisfies mathematical equation (2), and the distribution of the stream function ψ is obtained by solving equations (1) and (3) above. Then, based on the distribution of the stream function ψ, the gas velocity vector and gas pressure distribution in the furnace are calculated.

[0039] The analysis of the liquid surface shape of the molten material is also performed using the following equation (4) described in Non-Patent Document 1. Equation (4) is a formula derived from the liquid surface shape of the molten material, and equation (4) provides boundary conditions for gas flow analysis. In addition, Table 1 below shows the calculation and measurement methods for each variable in equations (1) to (3) above and equation (4) below.

[0040] p+ρ l ×g×h=const…(4)

[0041] [Table 1]

[0042]

[0043]

[0044] In equation (5) above, μ (T)It is the viscosity (Pa·s) at the average furnace temperature.

[0045] The amount of gas in the furnace belly used in the calculation of gas density can be calculated using the following formula (6).

[0046] V bosh =BV×1·21…·(6)

[0047] In equation (6) above, V bosh The gas volume in the furnace belly (Nm³) 3 / minute), BV is the air volume (Nm³) from vent 16. 3 / minute).

[0048] The average furnace pressure can be obtained by using the pressure value (P1) measured by pressure sensor 12. Furthermore, the average furnace temperature can be obtained by using the average of the temperatures measured by two or more temperature sensors 14. The corrected gas density ρ is calculated using these values ​​and equation (7) below. g .

[0049]

[0050] In equation (7) above, ρ g This is the corrected gas density (kg / m³) 3 V bosh The gas volume in the furnace belly (Nm³) 3 / minute), P is pressure (Pa), and T is temperature (K). When explaining the constants in equation (7), 28 is the molecular weight of the gas in the furnace belly (N2:CO = 79:42), 101325 is the atmospheric pressure under standard conditions (Pa), and 273 is the temperature under standard conditions (K).

[0051] Regarding the porosity within the furnace, for example in a blast furnace where the height of the molten material is measured, one can... Figure 1 (b) The values ​​of P1, P2, and L shown are substituted into the Ergun formula (the flow equation for gas flowing through the voids in the filled layer) for calculation. Alternatively, the porosity value described in Non-Patent Document 2 can also be used. Furthermore, regarding the melt density (kg / m³)... 3 For example, the slag 34 tapped from the tap hole 18 can be air-cooled and its density can be measured. Regarding the coke particle size, the measured value of the average particle size of the coke charged from the top of the furnace can be used, or the measured value can be corrected for the height of the blast furnace as described in Non-Patent Document 3.

[0052] Furthermore, by altering the raw material particle size, porosity, or furnace belly gas volume relative to the basic conditions, the aforementioned airflow analysis and liquid surface shape analysis were performed to determine the relationship between pressure loss and the height of the molten material 30 under each condition. It should be noted that... Figure 2As shown, low porosity is a condition that reduces porosity relative to the basic conditions, while high porosity is a condition that increases porosity relative to the basic conditions. Similarly, small particle size and small furnace gas volume are conditions that reduce particle size or furnace gas volume relative to the basic conditions, while large particle size and large furnace gas volume are conditions that increase particle size or furnace gas volume relative to the basic conditions.

[0053] like Figure 2 As shown, a prescribed correspondence was confirmed between pressure loss and the height of the melt 30. Furthermore, when the porosity, particle size, and furnace gas volume are changed relative to the basic conditions, these curves become curves that are horizontally shifted upwards or downwards relative to the curves under the basic conditions.

[0054] Thus, even if the porosity, particle size, and furnace gas volume are changed, the curve becomes the curve after the basic conditions are shifted parallel to each other in the vertical direction. Therefore, it can be seen that if the slope of the tangent at any point on the curve, that is, the correspondence between the increase in pressure loss at any molten height and the height of the molten material 30, is used to detect the height of the molten material 30, the height of the molten material 30 can be detected without being affected by the porosity, particle size, and furnace gas volume.

[0055] As mentioned above, the pressure loss is calculated by (P2-P1) / L. Therefore, when P2-P1 is set as ΔP, the increase in pressure loss at any melt height can be expressed by the following equation (8). It should be noted that in equation (8), h is the height of the melt 30.

[0056]

[0057] On the other hand, assuming that the height of the melt 30 is linearly related to time t and rises at a certain fixed speed, the following equation (9) holds. It should be noted that in the following equation (9), a and b are arbitrary constants.

[0058] h = a × t + b…(9)

[0059] When differentiating and rearranging both sides of equation (9) with the height h of the melt 30, we obtain equation (10) below.

[0060]

[0061] When using equation (10) above, equation (8) above can be modified as shown in equation (11) below.

[0062]

[0063] Equation (11) above indicates that confirming the increase in pressure loss at any melt height has the same meaning as confirming the rate of increase in pressure loss calculated by equation (12) below. It should be noted that in equation (12) below, ΔP = P2 - P1.

[0064]

[0065] Thus, confirming the increase in pressure loss at any melt height has the same meaning as confirming the rate of increase in pressure loss calculated by equation (12) above. Therefore, it can be seen that even if the relationship between the rate of increase in pressure loss and the melt height is used instead... Figure 2 The increase in pressure loss at any melt height shown can also be used to detect the melt height regardless of porosity, particle size, and the amount of gas in the furnace belly.

[0066] Next, the method for calculating the rate of increase in pressure loss will be explained. Regarding the internal pressure of the furnace belly 26, the pressure value P1 measured by the pressure sensor 12 installed at the upper end of the furnace belly 26 is used. Regarding the pressure in front of the tuyeres, the pressure value P2 in front of the tuyeres is calculated by analyzing the gas velocity vector and gas pressure distribution in the furnace using the above-described (1) to (3) formulas, and obtained from the gas pressure distribution.

[0067] Then, using the internal pressure P1 of the furnace belly 26 at time t1 and time t2, the pressure P2 in front of the tuyere, the height L from the tuyere 16 to the pressure sensor 12, and the above equation (12), the rate of increase of the pressure loss of the internal pressure of the furnace belly 26 relative to the pressure in front of the tuyere is calculated.

[0068] Next, the method for calculating the relationship between the rate of increase in pressure loss and the height of the melt will be explained. Figure 3 This is a graph showing the relationship between the rate of increase in pressure loss and the height of the melt. Figure 3 The horizontal axis represents the height of the melt (m), which is the height of the melt when the vent height is taken as the reference (0.0m). Figure 3 The vertical axis represents the rate of increase in pressure loss (kPa / (m×min)).

[0069] Figure 3 The diagram shown uses an internal volume of 5000m. 3 The blast furnace is constructed using operating parameters from periods without operational failures. The rising rate of the molten material accumulated at the bottom of the blast furnace is calculated by dividing the amount of molten pig iron produced per unit time (iron-to-feed ratio: 2) by the effective bottom area of ​​the blast furnace hearth. Here, the effective bottom area of ​​the hearth is the value obtained by multiplying the hearth bottom area by the porosity.

[0070] The initial height of the molten material was set 4.0m below the vent height. Pressure loss was calculated for every 0.5m increase in molten material height. Then, the rate of increase in pressure loss was calculated based on the time required for the molten material to rise from -4.0m to each height and the corresponding pressure loss value. This yielded the relationship between the rate of increase in pressure loss and the molten material height (m). Figure 3 The curve shown.

[0071] In the method for detecting the height of melt in this embodiment, the information is known in advance. Figure 3 The relationship between the rate of increase in pressure loss and the height of the molten material is shown. Then, with the height of the molten material detected, the internal pressure in the furnace belly and the pressure in front of the tuyeres at times t1 and t2 are calculated. Using these values, L, and the above equation (12), the rate of increase in pressure loss is calculated. The height of the molten material accumulated at the bottom of the blast furnace is detected using this rate of increase and the above relationship. Figure 3 In the example shown, with the calculated rate of increase in pressure loss being 0.15 (kPa / (m×min)), molten material was detected accumulating from the height of the vent to -1.0m.

[0072] As described above, the relationship between the rate of increase in pressure loss and the height of the molten material is unaffected by porosity, particle size, and the amount of gas in the furnace belly. Therefore, the molten material height detection method of this embodiment, which uses the relationship between the rate of increase in pressure loss and the height of the molten material to detect the height of the molten material, can be said to be a method that can detect the height of the molten material accumulated at the bottom of the furnace with higher accuracy than existing technologies. Furthermore, since the height of the molten material can be detected without using equipment such as electrodes, the molten material height detection method of this embodiment becomes a method that can suppress the increase in pig iron manufacturing costs and detect the height of the molten material with high accuracy.

[0073] Furthermore, if the height of the molten material detected by the aforementioned molten material height detection method exceeds a preset threshold, it is preferable to perform an operation that reduces the molten material production rate. This prevents excessive accumulation of molten material at the bottom of the blast furnace, thereby avoiding deterioration of gas permeability and tuyeres blockage caused by slag. Reducing the molten material production rate, for example, refers to reducing the air supply from tuyeres 16. Alternatively, an operation that increases the molten material discharge rate can be performed instead of reducing the molten material production rate, or the operation that increases the molten material discharge rate can be performed simultaneously with the operation that reduces the molten material production rate. This again prevents excessive accumulation of molten material at the bottom of the blast furnace, thereby avoiding deterioration of gas permeability and tuyeres blockage caused by slag.

[0074] In this embodiment, an example is shown where the pressure sensor 12 is disposed at the upper end of the furnace belly 26, but this is not a limitation. The pressure sensor 12 is not limited to being disposed at the upper end of the furnace belly 26; it can be disposed at any position within the range of the furnace belly 26.

[0075] Symbol Explanation

[0076] 10 Blast Furnaces

[0077] 12 Pressure Sensors

[0078] 14 Temperature Sensor

[0079] 16. Opportunities

[0080] 18 Iron outlet holes

[0081] 20 furnace main bodies

[0082] 22 Furnace body

[0083] 24. Furnace waist section

[0084] 26 Furnaces (belly section)

[0085] 28. Furnace Hearth Section

[0086] 30 Molten material

[0087] 32 Molten pig iron

[0088] 34 Slag

[0089] 36 Ore Layers

[0090] 38. Coke layer.

Claims

1. A method of detecting a molten material level in a molten ore furnace provided with a furnace body having a furnace bosh portion and two or more tuyeres for blowing hot air into a lower portion of the furnace body, wherein a correspondence relationship between an increase rate of a pressure loss in the furnace bosh portion with respect to a pressure before the tuyeres and a level of the molten material is previously obtained based on a change in the pressure loss in the furnace bosh portion with respect to a pressure before the tuyeres and a change in the level of the molten material based on the level of the tuyeres as a reference, the increase rate of the pressure loss in the furnace bosh portion with respect to the pressure before the tuyeres is obtained using an internal pressure of the furnace bosh portion and the pressure before the tuyeres at a time tl and a time t2, the increase rate of the pressure loss in the furnace bosh portion with respect to the pressure before the tuyeres is obtained using the internal pressure of the furnace bosh portion and the pressure before the tuyeres obtained, and a level of the molten material accumulated at a bottom portion of the molten ore furnace is detected using the increase rate of the pressure loss in the furnace bosh portion with respect to the pressure before the tuyeres obtained and the correspondence relationship between the increase rate of the pressure loss and the level of the molten material.

2. A method of operating a smelting furnace wherein, at least one of an operation of decreasing a production rate of the molten material and an operation of increasing a discharge rate of the molten material is performed when the level of the molten material detected by the method of detecting a molten material level according to claim 1 exceeds a predetermined threshold value.

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