Method for detecting fluctuation of solidified layer and method for operating blast furnace

Abstract

Provided are: a method for detecting fluctuations in a solidified layer, whereby fluctuations in the solidified layer can be detected at an early stage; and a method for operating a blast furnace using the method. The method for detecting the variation of the solidified layer includes detecting the variation of the solidified layer at the lower part of the blast furnace by using the heat of the molten iron supplied to the lower part of the blast furnace and the heat of the molten iron discharged during a predetermined period.

Description

[0001] This application is a divisional application of an application with an application date of April 7, 2021, application number 202180030929.7, and invention name “Method for detecting changes in solidified layer and blast furnace operation method”. Technical Field

[0002] The present invention relates to a solidified layer variation detection method for detecting variation of a solidified layer at the bottom of a blast furnace and a blast furnace operating method using the variation detection method. Background Art

[0003] For the purpose of extending the life of a blast furnace and stabilizing its operation, it is very important to quantitatively grasp the solidified layer at the bottom of the blast furnace. For example, Non-Patent Document 1 discloses that one factor limiting the life of a blast furnace is the erosion of the blast furnace bottom bricks. The blast furnace bottom bricks are corroded due to contact with molten iron. The presence of a solidified layer on the surface of the bottom bricks can suppress the erosion, and therefore, it is preferred that a solidified layer of appropriate thickness be present on the surface of the bottom bricks.

[0004] On the other hand, if the solidified layer grows excessively, the volume of the lower part of the blast furnace that can store molten iron will decrease. If the volume that can store molten iron decreases, when the discharge of the molten material from the blast furnace is hindered due to some reasons, the molten material will easily accumulate to the height of the blast furnace's air supply tuyere. If the molten material contacts the air supply tuyere, it will melt at the air supply tuyere. If it melts at the air supply tuyere, the operation of the blast furnace must be interrupted and the air supply tuyere must be repaired, so the blast furnace operation cannot be continued stably.

[0005] If a large solidified layer is formed at the bottom of a blast furnace, an operation is performed to melt the solidified layer, and it is necessary to understand whether the melting of the solidified layer in the furnace is properly performed during the operation. Therefore, it is very important to understand the changes in the solidified layer in the blast furnace. Non-patent document 1 discloses a method for estimating the thickness of the solidified layer in the furnace by performing heat transfer calculations based on the temperature measured by a thermometer set around the blast furnace floor bricks. Patent document 1 discloses a method for performing image analysis on the amount of molten iron slag discharged from a blast furnace for the purpose of detecting the amount of molten iron slag discharged from the blast furnace.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2016-6221

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2-115311

[0010] Non-patent literature

[0011] Non-patent document 1: Fumiaki Yoshikawa et al., "Application of blast furnace hearth to estimation and operation of refractory erosion and solidified layer distribution", Iron and Steel ( ), Year 73 (1987), No. 15, P2068-P2075 Summary of the invention

[0012] Problems to be solved by the invention

[0013] In the method disclosed in non-patent document 1, a thermometer installed in the blast furnace bottom bricks is used to perform heat transfer calculations assuming stable heat transfer in the solidified layer and the bottom bricks. Therefore, the thickness of the solidified layer cannot be estimated unless the change in the solidified layer thickness ends and the heat transfer reaches a stable state. Therefore, for the method disclosed in non-patent document 1, there is a problem that the change in the solidified layer cannot be grasped at an early stage. Although the method disclosed in patent document 1 can estimate the amount of slag discharged from the molten iron, it is impossible to distinguish the newly generated molten iron in the blast furnace from the molten iron formed by the melting of the solidified material in the molten iron after the iron is tapped, and therefore, it is difficult to grasp the change in the solidified layer. The present invention is made in view of such problems in the prior art, and its purpose is to provide a method for detecting the change of the solidified layer that can detect the change of the solidified layer at an early stage and a blast furnace operation method using this method.

[0014] Solutions to the problem

[0015] A method for solving the above-mentioned problems is as follows.

[0016] [1] A method for detecting changes in a solidified layer, the method comprising:

[0017] The fluctuation of the solidified layer in the lower part of the blast furnace is detected by using the heat of molten iron supplied to the lower part of the blast furnace and the heat of the molten iron tapped during a given period.

[0018] [2] The method for detecting changes in a solidified layer according to [1], wherein:

[0019] When the following formula (1) is satisfied, it is determined that the solidified layer is growing, and when the following formula (2) is satisfied, it is determined that the solidified layer is decreasing.

[0020] α×T Q >a×T pig +b・・・(1)

[0021] α×T Q <a×T pig +b・・・(2)

[0022] In the above formulas (1) and (2), α is the ratio of heat supplied to the lower part of the blast furnace to the molten iron in a stable state where the solidified layer does not increase or decrease,

[0023] T Q The furnace heat index (MJ / t-pig) is an indicator of the amount of heat supplied to the lower part of the blast furnace.

[0024] T pig is the temperature of the molten iron (°C)

[0025] a and b are constants determined by the concentration of components of the molten iron being tapped.

[0026] [3] The method for detecting changes in a solidified layer according to [1] or [2], wherein:

[0027] The above-mentioned given period is a period from the completion of the last molten iron tapping to the completion of the current molten iron tapping.

[0028] [4] A blast furnace operating method, the method comprising:

[0029] The solidified layer variation at the bottom of the blast furnace is detected by using the solidified layer variation detection method described in any one of [1] to [3],

[0030] When the solidified layer grows, melting of the solidified layer is promoted, and when the solidified layer decreases, growth of the solidified layer is promoted.

[0031] Effects of the Invention

[0032] By implementing the variation detection method of the solidified layer of the present invention, the increase or decrease of the solidified layer can be detected at an early stage. Moreover, by means of the variation detection method, when it is determined that the solidified layer at the lower part of the blast furnace is growing, the melting of the solidified layer is promoted, and when the solidified layer is reduced, the growth of the solidified layer is promoted. Thus, the variation of the solidified layer at the lower part of the blast furnace can be suppressed, and the stabilization of the blast furnace operation can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It shows the molten iron temperature and furnace heat index T during stable operation Q of the relationship between .

[0034] Figure 2 It shows W x / W prod Graph of changes relative to elapsed days.

[0035] Figure 3 This is a graph showing the change in furnace bottom temperature with respect to the elapsed days. DETAILED DESCRIPTION

[0036] Hereinafter, the present invention will be described through the embodiments of the present invention. The molten iron produced in the blast furnace is mainly heated by the sensible heat of the hot air in the lower part of the blast furnace and the heat generated by the combustion of carbon materials. On the other hand, in the lower part of the blast furnace, endothermic reactions such as dissolution reaction and reduction reaction of water contained in the air supply at the front end of the tuyere will also occur. As heat is discharged from the furnace wall in the lower part of the furnace, heat loss caused by heat discharge from the stave in the lower part of the furnace will also occur. These heats are not helpful for heating the molten iron. Therefore, it can be considered that in a stable state where the solidification layer does not change, there is a certain relationship between the thermal balance of the lower part of the blast furnace and the molten iron temperature.

[0037] One of the indices of the amount of heat supplied to the lower portion of the blast furnace is the furnace heat index T disclosed in Patent Document 2. Q (MJ / t-pig). Q It is represented by the following formula (3).

[0038] T Q =Q 1 +Q 2 -(Q 3 +Q 4 +Q 5 +Q 6 )・・・(3)

[0039] In the above formula (3), Q 1 Q is the heat of combustion of coke at the front end of the tuyere (MJ / t-pig). 1 It can be calculated by dividing the calorific value generated by the combustion of coke, which is calculated based on the amount of oxygen blown from the tuyere to the blast furnace per unit time, by the amount of molten iron produced per unit time.

[0040] Q 2 It is the sensible heat of the air supplied to the blast furnace through the air outlet (MJ / t-pig). 2 The heat input to the blast furnace by air supply per unit time can be calculated by determining the amount of heat input to the blast furnace by air supply per unit time from the measured values ​​of the air supply volume and air supply temperature per unit time, and dividing the value by the amount of molten iron produced per unit time.

[0041] Q 3 The heat of reaction is calculated based on the amount of carbon burned by air supply per unit time and the CO gas from the top of the blast furnace, CO 2 The difference in the amount of carbon discharged from the gas concentration analysis value can be used to calculate the amount of carbon consumed by the reaction in the furnace per unit time, and the heat of the dissolution reaction can be calculated based on the amount of carbon consumed. 3 It can be calculated by dividing the reaction heat by the amount of molten iron produced per unit time.

[0042] Q 4 It is the decomposition heat of moisture mainly contained in the supply air (MJ / t-pig). 4 It can be calculated by dividing the decomposition heat per unit time obtained from the measured value of the air moisture content by the amount of molten iron produced per unit time. 5 It is based on the heat rejection of cooling water (MJ / t-pig). 5 It can be calculated as follows: the amount of heat discharged from the cooling water per unit time is calculated based on the amount of cooling water and the temperature difference between the inlet and outlet sides of the cooling water in the blast furnace body, and the heat discharged is divided by the amount of molten iron produced in the unit time. 6 It is the decomposition heat of the reducing material blown in through the tuyere per unit time. 6 It can be calculated by dividing the decomposition heat by the amount of molten iron produced per unit time.

[0043] As an indicator of the amount of heat supplied to the lower part of the blast furnace, the following heat can be used instead of T calculated by equation (3): Q , the heat is: from T Q The heat supplied to the molten iron is calculated by subtracting the sensible heat brought by the gas moving from the lower part of the blast furnace to the upper part, and on the other hand, the heat obtained by adding the sensible heat brought by the coke and ore raw materials supplied from the upper part of the blast furnace to the lower part of the blast furnace is proportionally distributed to the molten iron and the molten slag. The sensible heat brought by the gas can be calculated by multiplying the specific heat of the gas in the blast furnace by the temperature difference between the estimated temperature of the gas burning in front of the tuyere and the reference temperature representing the upper end of the lower part of the blast furnace. The sensible heat of the raw material supplied to the lower part of the blast furnace can be calculated by multiplying the specific heat of the raw material by the temperature difference between 1450~1500℃, which is estimated to be the temperature of the lower end of the cohesive zone, and the above-mentioned reference temperature. The values ​​obtained by performing these treatments are distributed to the melt present in the lower part of the blast furnace, and therefore, the value obtained by multiplying the ratio of the specific heat of the molten iron by the sum after considering the mass ratio of the specific heat of the molten iron and the slag is regarded as the heat supplied to the molten iron. The reference temperature is 800 to 1200°C, preferably 900 to 1000°C.

[0044] Figure 1 It shows the temperature of molten iron and the furnace heat index T under steady state Q of the relationship between . Figure 1 The horizontal axis is the furnace heat index T Q (with reference T QThe vertical axis is the molten iron temperature (the difference from the reference molten iron temperature) (°C). The steady state refers to the state of blast furnace operation when the difference between the calculated amount of molten iron slag calculated based on the average amount of raw materials charged to the blast furnace per day and the actual amount of molten iron slag discharged from the blast furnace on that day is within 5% by mass. In the following, blast furnace operation in a steady state is sometimes described as stable operation. The molten iron temperature in the following description is set to the average value of the molten iron temperature on that day. Figure 1 In the process, the middle value of the molten iron temperature is taken as the reference molten iron temperature (in Figure 1 In the example shown, it is 1500°C) and is expressed as the difference from this reference molten iron temperature.

[0045] like Figure 1 As shown in the figure, under stable conditions, the furnace heat index T Q Therefore, when α is defined as the ratio of heat supplied to the lower part of the blast furnace to be transferred to the molten iron in a steady state, the relationship of the following equation (4) holds.

[0046] α×T Q ×W prod =Q pig ×W drain ・・・(4)

[0047] In the above formula (4), W prod (t-pig) is the amount of molten iron produced in the blast furnace during the period t from the end of the previous tapping to the end of this tapping, W drain Q is the amount of molten iron (t) discharged from the blast furnace this time. pig (MJ / t-pig) is the molten iron temperature T pig The heat capacity of molten iron at (°C) can be calculated by the following formula (5).

[0048] Q pig =a×T pig +b・・・(5)

[0049] In the above formula (5), a and b are constants determined by the concentration of the components of the molten iron to be tapped. The values ​​of the constants "a, b" corresponding to molten iron of various component concentrations are known in advance. For example, for molten iron with a carbon concentration of 4 to 5 mass%, a = 0.84, b = 84.

[0050] When the amount of molten iron melted or solidified in the blast furnace during time t is defined as Wx(t-pig), W drain It can be calculated by the following formula (6).

[0051] W drain =W prod +W x・・・(6)

[0052] In the above formula (6), W x is the amount of solidified matter (t-pig), which is a positive value when the solidified matter is melted, and a negative value when the solidified matter is solidified. When equations (5) and (6) are substituted into equation (4), equation (4) is expressed as equation (7).

[0053] α×T Q ×W prod =(a×T pig +b)×(W prod +W x )・・・(7)

[0054] By transforming the above equation (7), the following equation (8) is derived.

[0055] W x / W prod =[α×T Q / (a×T pig +b)]-1・・・(8)

[0056] Here, during stable operation, the heat supplied to the lower portion of the furnace is transferred to the molten iron at a constant ratio α, and therefore the relationship of the following equation (9) holds.

[0057] α×T Q =Q pig =a×T pig +b・・・(9)

[0058] When the relationship of equation (9) is substituted into the above equation (8), it can be expanded as equation (10). That is, in stable operation, W x =0.

[0059] W x / W prod =[α×T Q / (a×T pig +b)]-1=1-1=0・・・(10)

[0060] In this assumption, the solidified layer does not increase or decrease during stable operation. Therefore, the molten iron temperature and T when the expected molten iron production amount based on the charged raw material amount is substantially the same as the actual molten iron production amount are calculated. Q By substituting the value into equation (9), we can find the ratio of heat supplied to the lower part of the blast furnace to the molten iron under steady state, i.e., the value α.

[0061] When the solidified layer melts and decreases, the right side of the equation (8) becomes a positive value, and therefore the equation (8) is expressed by the following equation (1).

[0062] α×T Q>a×T pig +b・・・(1)

[0063] The above formula (1) indicates that, when the solidified layer is melted and reduced, the molten iron with a lower tapping temperature is obtained relative to the heat supplied to the lower part of the blast furnace compared to the stable operation. In the solidified layer variation detection method of the present embodiment, this relationship is used to calculate the heat (α×T Q ) than the heat of the molten iron (a×T pig +b) is large, it is judged that the heat of the difference is used to melt the solidified layer, and the solidified layer in the lower part of the blast furnace is reduced.

[0064] On the other hand, when the solidified layer grows, the equation (8) becomes a negative value, and therefore the equation (8) is expressed by the following equation (2).

[0065] α×T Q <a×T pig +b・・・(2)

[0066] The above formula (2) indicates that, when the solidified layer grows, the hot iron with a higher heat value is tapped relative to the heat value supplied to the lower part of the blast furnace than when the blast furnace is in stable operation. In the method for detecting the variation of the solidified layer of the present embodiment, this relationship is used to calculate the heat value (α×T Q ) than the heat of the molten iron (a×T pig +b) is small, it is judged that the heat of the difference is used for solidification of the solidified layer, and the solidified layer in the lower part of the blast furnace grows.

[0067] Therefore, in the solidified layer variation detection method of the present embodiment, the heat amount (α×T Q ), and the heat of the molten iron (a×T pig +b) to detect the change of the solidified layer in the lower part of the blast furnace. Specifically, the heat amount (α×T Q ), and the heat of the molten iron (a×T pig +b), in (α×T Q ) and (a×T pig +b) When the above formula (1) is satisfied, it is determined that the solidified layer has decreased within the given period. On the other hand, in (α×T Q ) and (a×T pig + b) When the above formula (2) is satisfied, it is determined that the solidified layer grows within the given period. Thus, the change of the solidified layer during the blast furnace operation can be detected at an early stage, and the blast furnace operation can be performed in a manner that the solidified layer at the bottom of the blast furnace is kept in an appropriate state.

[0068] Calculate (α×T Q ) and (a×T pig The given period of +b) is preferably the period from the last time the molten iron was tapped to the current time the molten iron was tapped. Each time the molten iron is tapped, the temperature and composition of the molten iron are measured, and thus, T can be obtained by using these values. pig (℃), and use the component values ​​to find constants a and b. Q ” and “a×T pig + b" and is not limited to the period from the end of the last molten iron tapping to the end of this molten iron tapping. For example, the amount of molten iron at each tapping can be used to calculate the T of each tapping from the end of any molten iron tapping to the end of any molten iron tapping. pig The weighted average of the values ​​is calculated. Similarly, the T Q The values ​​are weighted averaged and the obtained values ​​are used to obtain the values ​​in an arbitrary period.

[0069] When the solidified layer is judged to be growing by the solidified layer variation detection method, the following blast furnace operation method is implemented: by increasing the target input heat, the heat supplied to the lower part of the blast furnace is increased, thereby promoting the melting of the solidified layer. As an operation to increase the heat supplied to the lower part of the blast furnace, as long as the above Q 1 The average coke combustion heat per 1 ton of hot metal shown in the figure is increased, or the above Q 2 The operation can be carried out by increasing the average sensible heat of the air per 1 t of molten iron as shown.

[0070] When it is determined by the solidified layer variation detection method that the solidified layer is reduced, the following blast furnace operation method is implemented: by reducing the target input heat to reduce the heat supplied to the lower part of the blast furnace, or by increasing the heat discharged from the lower part of the blast furnace, the growth of the solidified layer is promoted. As a method for reducing the heat supplied to the lower part of the blast furnace, as long as the above Q 5 Thus, the fluctuation of the solidified layer in the lower part of the blast furnace can be suppressed, and the blast furnace operation can be stabilized.

[0071] Example

[0072] Next, for the use of the content volume 5000m 3 The W was confirmed in the blast furnace operation of the blast furnace x / W prod The following is an example of the changes in the temperature of the furnace bottom. Figure 2 It shows W x / W prod Graph of changes relative to elapsed days. Figure 2 The horizontal axis is the number of days (days), and the vertical axis is W x / W prod .

[0073] like Figure 2 As shown, W x / W prod It decreased on the 5th day. x / W prod The decrease in W x / W prod It becomes a negative value, thus satisfying the above formula (2). Therefore, it can be detected that the solidified layer in the lower part of the blast furnace has grown on the fifth day.

[0074] W x / W prod It increased on the 8th day. x / W prod The increase in W x / W prod It becomes a positive value, and thus satisfies the above-mentioned formula (1). Therefore, it can be detected that the solidified layer in the lower part of the blast furnace has decreased on the 8th day.

[0075] Figure 3 This is a graph showing the change in furnace bottom temperature with respect to the number of days that have passed in the same blast furnace operation. Figure 3 The horizontal axis of is the number of days (days), and the vertical axis is the furnace bottom temperature (° C.) The furnace bottom temperature is the value of a thermometer installed in the center of the bottom plate of the blast furnace bottom.

[0076] like Figure 3 As shown, the furnace bottom temperature decreased on the 6th day after the number of days. It can be considered that the decrease in the furnace bottom temperature is due to the growth of the solidified layer at the furnace bottom, and therefore, the heat transfer from the furnace to the furnace bottom is reduced. That is, it can be seen that the detection of the change of the solidified layer based on the furnace bottom temperature is slower than the detection using the heat supplied to the lower part of the blast furnace and the temperature of the molten iron of the iron tapping. According to the result, it is confirmed that by implementing the change detection method of the solidified layer of the present embodiment, the increase or decrease of the solidified layer at the lower part of the blast furnace can be detected at an early stage. Then, based on the detection, when it is judged that the solidified layer at the lower part of the blast furnace is growing, an operation to promote the melting of the solidified layer is implemented, and when it is judged that the solidified layer at the lower part of the blast furnace is reduced, a blast furnace operation to promote the growth of the solidified layer is implemented. It can be seen that the change of the solidified layer at the lower part of the blast furnace can be suppressed, and the stabilization of the blast furnace operation can be achieved.

Claims

1. A method for detecting changes in a solidified layer, the method comprising: The difference between the heat of the molten iron supplied to the lower part of the blast furnace and the heat of the molten iron discharged during a given period is used to detect the change of the solidified layer in the lower part of the blast furnace. When the following formula (1) is satisfied, it is determined that the solidified layer is reduced, and when the following formula (2) is satisfied, it is determined that the solidified layer is grown. α×T Q >a×T pig +b・・・(1) α×T Q <a×T pig +b・・・(2) In the above formula (1) and formula (2), α is the ratio of heat supplied to the lower part of the blast furnace to the molten iron in a stable state where the solidified layer does not increase or decrease, T Q It is the furnace heat index which is an index of the amount of heat supplied to the lower part of the blast furnace. The unit of the furnace heat index is MJ / t-pig. T pig is the temperature of the molten iron, the unit of temperature is °C, a and b are constants determined by the concentration of components of the molten iron being tapped.

2. The method for detecting changes in a solidified layer according to claim 1, wherein: The given period is a period from the completion of the last molten iron tapping to the completion of the current molten iron tapping.

3. A blast furnace operating method, the method comprising: The method for detecting the change of the solidified layer according to claim 1 or 2 is used to detect the change of the solidified layer at the bottom of the blast furnace. When the solidified layer grows, melting of the solidified layer is promoted, and when the solidified layer decreases, growth of the solidified layer is promoted.

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