Method for blowing molten iron and method for producing molten steel

Abstract

To provide a method for blowing molten iron and a method for producing molten steel by which operation conditions capable of reducing the amount of CaO to be used can be obtained in refining treatment in a converter type refining furnace for performing multi-stage refining treatment.SOLUTION: A blowing method for molten iron includes: a CaO charge amount determination step of determining a charge amount of CaO in blowing treatment; a first step of performing desiliconization and dephosphorization treatment by charging molten iron, or molten iron and a cold iron source into a converter-type refining furnace 1, charging a refining agent 6 comprising CaO, and performing oxygen blowing; a second step of discharging a part of slag 3 generated in the first step from the converter-type refining furnace 1 while holding the molten iron in the furnace; and a third step of obtaining molten steel by performing a decarburization treatment and a finishing dephosphorization treatment by charging the refining agent 6 comprising CaO and performing oxygen blowing. In the CaO charge amount determination step, the charge amount of CaO to be charged in the first step and the third step is determined based on a first P concentration, which is the P concentration in the molten iron after the first step, and the basicity of the slag after the first step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for blowing molten iron and a method for producing molten steel.

Background Art

[0002] In the refining process of molten steel, a method is known in which the refining treatment over multiple steps is concentrated in a converter-type refining furnace. For example, Patent Document 1 discloses a method capable of minimizing the total cost of the refining treatment by performing desiliconization and dephosphorization treatments in a converter-type refining furnace, discharging a part of the generated dephosphorization slag, and performing decarburization and finish dephosphorization to obtain molten steel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 discloses a technique for maintaining a high dephosphorization oxygen efficiency in the dephosphorization step by setting the slag basicity to 0.8 to 1.8, (T·Fe) to 8 to 19% by mass percentage, and (S) to 0.1% or less in order to achieve a highly efficient dephosphorization treatment.

[0005] However, the basicity of the slag is determined only after slag analysis is performed after the completion of the desiliconization and dephosphorization treatment (the first step), and it is difficult to accurately estimate the amount of CaO required for the first step before the treatment.

[0006] In Patent Document 1, in order to minimize the amount of CaO used for cost minimization, it is necessary to perform the treatment in the range of 0.8 to 1.3 on the low basicity side within the basicity range of 0.8 to 1.8. However, in such a low basicity region, it has been reported that there is a positive correlation between the slag basicity and the dephosphorization efficiency in the first step, and the same relationship can also be recognized in FIG. 2 of Patent Document 1 actually. The required amount of CaO in the decarburization and finishing dephosphorization step (the third step) is the larger amount of CaO among the amount of CaO required for dephosphorization and the amount of CaO required to suppress slopping. When this required amount of CaO is determined by slopping suppression, the total CaO usage in the first step and the third step can be minimized by reducing the basicity of the first step and suppressing the required amount of CaO in the first step to a low level. On the other hand, when the required amount of CaO in the third step is determined by de-P, by increasing the basicity of the first step and reducing P after the first step treatment, the required amount of CaO in the third step can be reduced, and the total CaO usage can be minimized. That is, in order to minimize the total amount of CaO used, it is necessary to determine the basicity of the first step in consideration of the de-P load in the third step. However, in Patent Document 1, no consideration is given to the de-P in the third step at all, and since the operating conditions of the first step where the CaO usage is minimized cannot be determined, it has been difficult to reduce the unit consumption.

[0007] Therefore, the present invention has been made paying attention to the above problems, and in the refining process of a converter-type refining furnace that performs multi-step refining treatment, it aims to provide a blowing method for molten iron and a method for manufacturing molten steel that can be operating conditions capable of reducing the amount of CaO used.

Means for Solving the Problems

[0008] (1) According to one aspect of the present invention, in a method for blowing molten iron to produce molten steel by performing a blowing treatment in a converter-type refining furnace, a CaO input amount determination step for determining the input amount of CaO in the blowing treatment, charging hot metal or a mixture of hot metal and a cold iron source into the converter-type refining furnace, charging a refining agent containing CaO, and performing oxygen blowing to perform desiliconization and dephosphorization treatment in a first step; after the first step, while holding the hot metal in the furnace, discharging a part of the slag generated in the first step from the converter-type refining furnace in a second step; and after the second step, charging a refining agent containing CaO and performing oxygen blowing to perform decarburization treatment and finish dephosphorization treatment to obtain molten steel in a third step. In the CaO input amount determination step, based on a first P concentration which is the P concentration in the hot metal after the first step and the basicity of the slag after the first step, the input amount of CaO to be input in the first step and the third step is determined, and a method for blowing molten iron is provided.

[0009] (2) In the method for blowing molten iron according to (1) above, in the CaO input amount determination step, for a plurality of the basicities, the total input amount of CaO to be input in the first step and the third step is calculated, and the basicity with the smallest total input amount is set as the target basicity of the slag after the first step. The input amount of CaO in the first step is calculated according to the basicity of the slag and the slag conversion rate estimated according to the basicity. The input amount of CaO in the third step is calculated based on the first P concentration estimated based on the basicity of the slag after the first step and the intermediate slag discharge rate of the slag in the second step.

[0010] (3) In the method for blowing molten iron according to (2) above, the conversion rate is calculated based on the calculated slag amount in the furnace and the cumulative number of uses since the brick replacement of the furnace body. The first P concentration is the equilibrium P concentration calculated from the P distribution ratio based on the basicity of the slag after the first step.

[0011] (4) In the method for blowing molten iron as described in (3) above, the slag formation rate is calculated using a multiple regression equation with variables being the calculated slag amount in the furnace, the cumulative number of uses, and the input Si amount which is the amount of Si component charged into the furnace, all obtained from past performance.

[0012] (5) In the method for blowing molten iron as described in (4) above, the slag formation rate is calculated from equation (1). S = α0 + α1×W S +α2×N + α3×I Si ···(1) Here, α0 = 61.46 α1 = -0.3230 α2 = -0.006132 α3 = 6.759 W S : Calculated slag amount in the furnace (kg / t) N: Number of furnace operations (-) I Si : Input Si amount (kg / t)

[0013] (6) In the method for blowing molten iron as described in (3) above, the de - Si external oxygen amount in the first step is calculated from the equilibrium P concentration and the de - P reaction rate equation obtained from past performance.

[0014] (7) In the method for blowing molten iron as described in (6) above, the first - order reaction volume coefficient of the de - P reaction rate equation is calculated using a multiple regression equation with variables being the basicity of the slag after the first step and the calculated slag amount in the furnace, both obtained from past performance.

[0015] (8) In the method for blowing molten iron as described in (6) above, the first - order reaction volume coefficient is calculated from equation (4).

[0016]

Equation

[0017] (9) According to one aspect of the present invention, there is provided a method for producing molten steel using the method for blowing molten iron described in any one of the above (1) to (8).

Effects of the Invention

[0018] According to one aspect of the present invention, there are provided a method for blowing molten iron and a method for producing molten steel, which can adopt operating conditions capable of reducing the amount of CaO used in the refining process of a converter-type refining furnace that performs multi-step refining treatment.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

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Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0020] In the following detailed description, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals, and redundant descriptions are omitted. Each drawing is schematic and may include cases where it is different from the actual one. Further, the embodiments shown below illustrate apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the materials, structures, arrangements, etc. of the components as the following. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

[0021] <Apparatus Configuration> Referring to FIG. 1, the apparatus configuration of the converter-type refining furnace 1 in an embodiment of the present invention will be described. The converter-type refining furnace 1 is a converter facility for producing molten steel by blowing and refining using hot metal or hot metal and scrap as raw materials. As shown in FIG. 1, it includes a furnace body 10, an oxygen lance 11, a hopper 12, and a control device 13. In this embodiment, hot metal and molten steel are collectively referred to as molten iron 2.

[0022] The furnace body 10 is provided with a tapping hole 100 at the upper side and a plurality of bottom blowing tuyeres 101 at the bottom. The upper opening of the furnace body 10 is also referred to as a furnace mouth 102. From the bottom blowing tuyere 101, bottom blowing gas 5 composed of an inert gas is blown in to stir the molten iron 2. The oxygen lance 11 is a lance that injects an oxygen-containing gas 4 from the lower tip, and supplies oxygen to the molten iron 2 by injecting the oxygen-containing gas 4 in a state of being inserted into the furnace body 10 from above. The hopper 12 is a container for storing auxiliary raw materials, cuts out the stored auxiliary raw materials from the bottom, and inputs the auxiliary raw materials into the molten iron 2 through the connected chute 120. In the example shown in FIG. 1, the hopper 12 stores a refining agent 6 containing CaO, which is one of the auxiliary raw materials. Note that the converter-type refining furnace 1 is provided with a plurality of hoppers 12, and each hopper 12 stores a refining agent or auxiliary raw material different from the refining agent 6.

[0023] The control device 13 is an electronic computer that controls the blowing process of the converter-type smelting furnace 1, and includes a control unit 130 and a CaO input amount calculation unit 131. The control unit 130 controls a series of operations of the converter-type smelting furnace 1 related to the blowing process, such as the tilting of the furnace body 10, the lifting and lowering operation of the oxygen lance 11, the adjustment of the injection amount (oxygen supply amount) of the oxygen-containing gas 4, and the cutting and input operations of auxiliary materials such as the refining agent 6. The CaO input amount calculation unit 131 calculates the CaO input amount (input amount of the refining agent 6) in the first and third steps described later. Details of the method for calculating the CaO input amount will be described later.

[0024] <Method for Blowing Molten Iron> In the molten iron refining method according to this embodiment, molten steel is produced from hot metal by performing a multi-step refining process consisting of the first to third steps.

[0025] In this embodiment, first, hot metal as a raw material or hot metal and a cold iron source are charged into the furnace body 10 (inside the furnace) of the converter-type smelting furnace 1, and a desiliconization treatment and a dephosphorization treatment (desiliconization and dephosphorization treatment) are performed (the first step). In the first step, after charging the raw materials into the furnace, the refining agent 6 corresponding to the CaO input amount determined by the method described later is charged into the furnace of the converter-type smelting furnace 1, and oxygen gas is supplied from the oxygen lance 11 to the raw materials to perform oxygen blowing, thereby removing Si and P in the hot metal.

[0026] The charging of the refining agent 6 is performed by cutting out a predetermined amount of the refining agent 6 from the hopper 12 and charging it into the molten iron 2 in the furnace body 10 through the chute 120. The charged refining agent 6 forms slag 3 by slagging. In addition, refining agents or auxiliary materials other than the refining agent 6 (for example, auxiliary materials containing Si and Mg) may be charged into the molten iron 2 as necessary. Further, in oxygen blowing, the molten iron 2 is agitated by blowing the bottom blowing gas 5 from the bottom blowing tuyere 101. The CaO input amount in the first step is also referred to as the first input amount. That is, in the first step, the refining agent 6 with a CaO pure content of the first input amount is charged.

[0027] After the first step, while holding the hot metal in the furnace, a part of the slag 3 (desiliconization slag) generated in the first step is discharged from the converter-type refining furnace 1 (second step). In the second step, by tilting the furnace body 10 (in the case of FIG. 1, tilting the furnace body 10 counterclockwise), the desiliconization slag is discharged from the furnace mouth 102 by a predetermined discharge amount. The ratio of the discharge amount of the slag 3 in the second step to the amount of slag in the furnace before the second step is referred to as the slag discharge rate. The discharged desiliconization slag is a part of the desiliconization slag in the furnace, and the slag discharge rate is adjusted by adjusting the tilting angle of the furnace body 10.

[0028] After the second step, a refining agent 6 is added to the hot metal held in the furnace, and decarburization treatment and finish desiliconization treatment are performed by oxygen blowing (third step). In the third step, the refining agent 6 corresponding to the amount of CaO input determined by the method described later is added to the furnace. The oxygen blowing and the method of adding the refining agent 6 in the third step can be the same as those in the first step. In the third step, by oxygen blowing, C and P in the hot metal are removed, so that the hot metal becomes molten steel with a low carbon concentration. The amount of the refining agent 6 input in the third step is also referred to as the second input amount. The slag 3 generated in the third step is also referred to as decarburization slag. That is, in the third step, a refining agent 6 with an input amount such that the pure CaO content is the second input amount is added.

[0029] After the third step, by tilting the furnace body 10 to the side opposite to the second step (in the case of FIG. 1, tilting the furnace body 10 clockwise), the molten steel is discharged from the tapping hole 100 provided in the upper part of the side surface of the furnace body 10 (fourth step). At this time, the decarburization slag is in a floating state on the molten steel. By returning the tilting of the furnace body 10 immediately before or immediately after the decarburization slag is discharged from the tapping hole 100, after the molten steel is discharged, mainly the decarburization slag remains in the furnace. Further, by tilting the furnace body 10 to the same side as the second step, the decarburization slag remaining in the furnace body 10 is discharged from the furnace mouth 102. Thereby, the molten steel and the decarburization slag in the furnace are discharged and recovered respectively.

[0030] In addition, in this embodiment, before the first step to the third step, a CaO input amount determination step is performed to determine the first input amount and the second input amount in the first step and the third step, that is, the CaO input amount in the refining process. Details of the method for determining the CaO input amount in the CaO input amount determination step will be described later.

[0031] Through the above steps, the blowing treatment of the molten iron 2 in the converter-type refining furnace 1 is completed. Note that the series of blowing treatments from the first step to the fourth step are performed by the control device 13. In addition, by repeatedly performing the series of blowing treatments from the first step to the fourth step, the blowing treatment is continuously performed. Here, the unit of the blowing treatment in the converter-type refining furnace 1 is also referred to as a charge. Furthermore, the charge for which the blowing treatment will be performed next and for which the CaO input amount is calculated is referred to as the current charge, and the charge that was blown immediately before the current charge is referred to as the previous charge.

[0032] <Method for Determining CaO Input Amount> In the CaO input amount determination step, the CaO input amount calculation unit 131 determines the first input amount and the second input amount, which are the CaO input amounts in the first step and the second step, in consideration of the refining conditions in the first step, the second step, and the third step.

[0033] First, the relationship between the refining process in the first step and the first input amount will be described. The first input amount is determined based on the basicity (target basicity) of the slag 3 after the first step, which is the target.

[0034] The basicity of slag 3 is the ratio of the CaO concentration (%CaO) to the SiO2 concentration (%SiO2) in slag 3, and is expressed as (%CaO) / (%SiO2). Also, the actual basicity value of slag 3, which is obtained by analyzing the components of the granulated slag 3, is called the actual basicity. Furthermore, the basicity estimated based on the input amount of the refining agent 6, etc. and the amount of SiO2 generated by oxygen blowing, etc. with respect to the actual basicity is also called the design basicity. The design basicity can be calculated based on the input amount of the auxiliary raw material (set value), the components and weight of the hot metal, the injection amount of oxygen gas (set value), etc. Also, the ratio of the actual basicity to the design basicity of slag 3 is also called the granulation rate S (%).

[0035] The granulation rate S is an index indicating the solubility of the input refining agent 6, and can be obtained by a multiple regression equation with the operating conditions related to the dissolution of the refining agent 6 as variables. As these variables, the calculated slag amount in the furnace, the number of furnace cycles, and the amount of Si component charged into the furnace can be used. The calculated slag amount in the furnace is the weight of slag 3 in the furnace calculated, and is calculated according to the components of the hot metal and the input amount of the refining agent 6. When the calculated slag amount in the furnace is large, that is, when the input amount of the refining agent 6 is large, it becomes difficult for the auxiliary raw material to dissolve, so the granulation rate decreases. The number of furnace cycles is the cumulative number of uses (cumulative number of charges) since the brick renewal of the furnace body 10. When the number of furnace cycles is large, the wear of the furnace body bricks progresses, so the steel bath becomes shallow, and the stirring power density supplied to the steel bath by the bottom blowing gas during blowing decreases. For this reason, the more the number of furnace cycles, the more difficult it is for the auxiliary raw material to dissolve, and the granulation rate decreases. The amount of Si component charged into the furnace is also called the input Si amount, and is the amount of Si component burned by oxygen blowing. The input Si amount is, for example, the total amount of Si in the hot metal and Si in the auxiliary raw material. Such Si burns and generates heat by oxygen blowing, so it promotes the dissolution of the auxiliary raw material. Therefore, the higher the input Si amount, the higher the granulation rate.

[0036] The multiple regression equation for the slag formation rate S can be obtained, for example, using the following equation (1) from the results of multiple past charges (past results). In this embodiment, the unit of t (ton) is the metric ton, and the unit of kg / t is the weight (kg) per ton of converter charge of the main raw materials such as the calculated slag amount and input Si, etc. (hot metal + cold iron source).

[0037] S = α0 + α1×W S + α2×N + α3×I Si ···(1) Here,[[]]END]] α0, α1, α2, α3: Constants W S : Calculated slag amount in the furnace (kg / t) N: Number of furnace heats (-) I Si : Input Si amount (kg / t)

[0038] Regarding the multiple regression equation for the slag formation rate S in (1), the results calculated from the actual performance in the first step of the actual converter-type refining furnace 1 are shown in FIGS. 2 and 3. FIG. 2 shows the results of multiple regression. Further, FIG. 3 shows a graph with the horizontal axis as the estimated basicity (estimated basicity) obtained by multiple regression of equation (1) and the vertical axis as the measured basicity (measured basicity). As shown in FIGS. 2 and 3, the constants α0, α1, α2, and α3 are 61.46, -0.3230, -0.006132, and 6.759, respectively, and it can be seen that a good correlation is obtained.

[0039] Also, in the desiliconization and dephosphorization treatment in the first step, as the dephosphorization behavior during the treatment, a model as shown in FIG. 4 can be assumed. In this model, the dephosphorization of hot metal proceeds in a first-order reaction form with respect to the amount of deoxidation outside silicon from the P concentration (input P (P I )) of the hot metal before the desiliconization and dephosphorization treatment. Then, when the P in the hot metal reaches the equilibrium P concentration, it becomes constant at the equilibrium P concentration. The amount of deoxidation outside silicon is the amount obtained by subtracting the amount of oxygen source used for the desiliconization reaction from the supply amount of the oxygen source such as oxygen gas supplied in the first step, and can be obtained according to the Si concentration in the hot metal.

[0040] The equilibrium P concentration can be estimated using the P distribution ratio L P obtained from the basicity, composition, and temperature of the slag 3. The P distribution ratio L P is the ratio (%P) / [%P] of the P concentration (%P) in the slag 3 to the P concentration [%P] in the hot metal in a state where it has reached near apparent equilibrium. In the desiliconization and dephosphorization treatment, the P distribution ratio L P can be estimated using the following equation (2). For the values of (%T.Fe) and (MgO, MnO, P2O5, Al2O3) in equation (2), the average value of the composition analysis results of the slag 3 in past performance may be used, or the calculated slag composition value calculated from the composition of the auxiliary materials charged into the converter may be used. Also, a model equation for estimating the slag composition from other operating factors may be created, and the calculation of L P may be performed using the estimated value.

[0041]

Equation

[0042] The behavior of the P concentration until the P concentration in the hot metal reaches the equilibrium P concentration can be estimated using the dephosphorization reaction rate equation of the following equation (3). [%P]=[%P i ×exp(-k×O Si ) ···(3) Here, [%P]: P concentration (mass%) of the hot metal [%P i : P concentration (mass%) of the hot metal before desiliconization and dephosphorization treatment k: Volume coefficient O Si : Amount of external oxygen for desiliconization (kg / t)

[0043] (3) The volumetric coefficient (primary reaction volumetric coefficient) k in the primary reaction formula indicates the ease of progress of the de-P reaction and can be estimated using a multiple regression formula created from the P concentration results in the hot metal after the desiliconization and dephosphorization treatment (after the first step) in a plurality of past charges. As explanatory variables for this multiple regression formula, operating conditions related to de-P can be selected. For example, the larger the amount of slag 3, the more the amount of granular iron suspended in the slag 3 increases, and the de-P reaction interface area increases. Therefore, there is a correlation between the slag amount and the de-P rate. Also, as shown in formula (2), when the basicity of slag 3 is high, the equilibrium P concentration decreases, the driving force of the reaction increases, and de-P is promoted. Therefore, there is a correlation between the basicity of slag 3 and the de-P rate. Note that the driving force of this reaction is obtained as the value obtained by subtracting the equilibrium P concentration P e from the P concentration P in the hot metal (P - P e ).

[0044] The volumetric coefficient k can be obtained, for example, from the following formula (4).

[0045] [Number] Here, β0, β1, β2: Constants

[0046] Regarding the multiple regression formula of the volumetric coefficient k in (4), the results calculated from the actual performance in the first step of the actual converter-type refining furnace 1 are shown in FIGS. 5 and 6. FIG. 5 shows the result of multiple regression. Also, FIG. 6 shows a graph with the horizontal axis as the first P concentration (estimated P concentration) calculated using the volumetric coefficient k obtained by multiple regression of formula (4) and the vertical axis as the measured first P concentration (actual P concentration). As shown in FIGS. 5 and 6, it can be seen that the constants β0, β1, and β2 are -0.9567, -0.2474, and 24.5733, respectively, and a good correlation is obtained.

[0047] That is, in the first step, the first input amount is determined according to the set target basicity. Also, since the first P concentration is preferably as low as possible to the equilibrium P concentration or about the equilibrium P concentration, it is set according to the target basicity. Furthermore, the supply amount of an oxygen source such as oxygen gas is set according to the first P concentration. That is, in the first step, when the target basicity is set, the first input amount, the first P concentration, etc. are also set. For example, when the first P concentration is the equilibrium P concentration, the amount of de-Si external oxygen is set so as to be the value shown at the intersection position of the curve shown by the formula (3) shown in FIG. 4 and the equilibrium P concentration (the P concentration after the first step shown in FIG. 4). Then, by adding the amount of oxygen required for de-Si determined from the Si concentration in the hot metal to the amount of de-Si external oxygen, the supply amount of the oxygen source in the first step is set. That is, in the present embodiment, according to the present embodiment, a kinetic analysis is performed based on past results, and a prediction formula for the volume coefficient k of the de-P reaction rate formula is obtained, so that the transition of the P concentration before the P concentration in the hot metal reaches the equilibrium concentration can be accurately estimated. Therefore, the amount of de-Si external oxygen required for the P concentration to reach the equilibrium concentration can be accurately estimated, and the P concentration of the hot metal after the first step can be accurately estimated. The finally determined target basicity is set so that the total amount of the CaO input amounts in the first step and the third step is minimized in relation to the input amount of CaO in the third step described later.

[0048] Next, the relationship between the refining process in the third step and the second input amount will be described. In determining the second input amount, first, the amount of P in the furnace (the total amount of the amount of P in the hot metal and the amount of P in the slag 3) is calculated from the slag discharge rate (intermediate slag discharge rate) in the second step and the estimated P concentrations in the slag 3 and the hot metal after the first step. The intermediate slag discharge rate corresponds to the tilting angle of the furnace body 10 at which slag discharge is started, the slag discharge start angle, and is estimated according to the set slag discharge start angle. FIG. 7 shows, as an example, the relationship between the slag discharge start angle and the intermediate slag discharge rate.

[0049] The second input amount, which is the amount of CaO required in the refining process in the third step, is the larger of the amount of CaO required for dephosphorization and the amount of CaO required for suppressing slopping.

[0050] In the third step, the amount of CaO input required for dephosphorization can be calculated using the P distribution ratio in the decarburization process. Specifically, using the P distribution ratio, the P concentration and weight of the hot metal, and the components (P concentration, basicity) and weight of the slag 3 in the furnace after the second step, the P concentration of the molten steel after the third step (the second P concentration) can be calculated so as to reach the target value. Here, the P distribution ratio can be estimated by using the existing estimation formula of the P distribution ratio in the decarburization process.

[0051] The amount of CaO input required to suppress splashing is determined according to the basicity of the slag 3 in the third step. A range of basicity (at least the lower limit) where splashing does not occur is set based on actual results, etc., and the target basicity is set so as to be within this range. Also, basically, since no SiO2 source is added after the second step, the amount of CaO input required to suppress splashing is determined according to the amount of SiO2 in the furnace after the second step. Note that the lower limit of the basicity is preferably set appropriately according to the converter-type refining furnace 1 because stirring conditions, furnace body shape, etc. have an impact.

[0052] As described above, in this embodiment, the input amount of the refining agent 6 is determined so that the total amount (total input amount) of the first input amount and the second input amount is minimized or minimized. In this case, for the target basicity in the first step, the total input amount is calculated with a plurality of target basicities, and the basicity with the minimum total input amount among them may be set as the final target basicity.

[0053] Here, in the first step, if the basicity is too low, the basicity of the slag after the second step will also be low, and the dephosphorization load in the third step will increase, so the second input amount will increase. In such a case, the amount of CaO input required for dephosphorization becomes the second input amount. On the other hand, in the first step, if the basicity is too high, the amount of SiO2 in the furnace after the second step will increase, so the second input amount will increase. In such a case, the amount of CaO input required to suppress splashing becomes the second input amount. Note that the target basicity may be the designed basicity or the actual basicity in the first step.

[0054] Figure 8 shows an example in which, with the design basicity in the first step as the target basicity, the first input amount and the second input amount are calculated under a plurality of conditions where the target basicity is in the range of 1.5 to 2.0. In Figure 8, the vertical axis indicates the new lime usage amount (CaO input amount) when lime is used as the refining agent 6. In this case, it can be seen that the total input amount is minimized under the condition that the target basicity is 1.7. When the target basicity is 1.6 or less, although the first input amount decreases, the dephosphorization load in the third step increases, so the second input amount increases, and as a result, the total input amount increases. On the other hand, when the target basicity is 1.8 or more, in order to suppress slopping, the decrease amount of the second input amount becomes smaller than the increase amount of the first input amount, and as a result, the total input amount increases. Therefore, in the case of Figure 8, the first input amount and the second input amount are determined under the condition that the target basicity is 1.7.

[0055] In the blowing method of hot metal 2 according to this embodiment, in the CaO input amount determination step, the first input amount and the second input amount are determined based on the first P concentration and the target basicity. Further, in the CaO input amount determination step, the total input amount of CaO is calculated for a plurality of target basicities, and among them, the basicity with the smallest total input amount is set as the target basicity after the first step. Furthermore, the first input amount is calculated according to the basicity of slag 3 and the slagging rate of slag 3 estimated according to the basicity, and the second input amount is calculated based on the first P concentration estimated based on the basicity of slag 3 and the intermediate slag discharge rate. According to such a configuration, since the CaO input amount in the third step is determined in consideration of the influence of the refining treatment in the first step, the total input amount of CaO in the entire multi-step refining treatment can be considered. Therefore, when performing the multi-step refining treatment in the converter-type refining furnace 1, the CaO usage amount can be reduced.

[0056] <Modification Example> Although the present invention has been described above with reference to specific embodiments, it is not intended to limit the invention by these descriptions. By referring to the description of the present invention, those skilled in the art will also understand other embodiments of the present invention including various modifications together with the disclosed embodiments. Therefore, the embodiments of the invention described in the claims should be construed as covering embodiments including these modifications alone or in combination described herein.

[0057] For example, in the above embodiment, although the refining agent 6 is introduced into the furnace body 10 through the chute 120, the present invention is not limited to such an example. The refining agent 6 may be configured to be injected together with the carrier gas from the acid injection lance 11 or the bottom blowing tuyere 101 in addition to the top addition from the chute 120. Further, the supply method of the refining agent 6 may be a combination of these plurality of supply methods.

[0058] Also, in the above embodiment, although the CaO input amount calculation unit 131 is one of the functions of the control device 13, the present invention is not limited to such an example. For example, the CaO input amount calculation unit 131 may be configured as a device (such as an electronic computer) independent of the control device 13.

[0059] Furthermore, in the above embodiment, when determining the second input amount in the third step, although the existing estimation formula of the P distribution ratio is used, the present invention is not limited to such an example. For example, the second input amount may be determined by the following method.

[0060] (Modification example of the method for determining the second input amount) When obtaining the second input amount, the CaO input amount calculation unit 131 first calculates the P distribution ratio L from the P distribution formula using the estimated FeO concentration, CaO concentration, and MgO concentration in the slag, which are parameters affecting P removal, and the set end-point molten steel temperature (P distribution ratio calculation step). Specifically, the CaO input amount calculation unit 131 calculates the P distribution ratio L from the P distribution formula of the following formula (5). P is calculated (P distribution ratio calculation step). Specifically, the CaO input amount calculation unit 131 calculates the P distribution ratio L from the P distribution formula of the following formula (5). P is calculated.

[0061] [Number] Here, L P : P distribution ratio (%T.Fe): FeO concentration in slag 3 (mass%) (%CaO): CaO concentration in slag 3 (mass%) (%MgO): MgO concentration in slag 3 (mass%) T2: End-point molten steel temperature (°C) a0, a1, a2, a3: Constants

[0062] In formula (5), the FeO concentration, CaO concentration, and MgO concentration in slag 3 are estimated by the following estimation method.

[0063] (FeO concentration in slag) The FeO concentration in slag 3 has a strong correlation with the tapping oxygen (end-point molten steel O concentration), the end-point molten steel temperature T, and the calculated basicity. Therefore, by using the preset tapping oxygen, the end-point molten steel temperature T, the calculated basicity, and the following formula (6), the FeO concentration in the slag can be estimated. Note that the tapping oxygen and the end-point molten steel temperature are preset according to the steel type, the treatment process, etc. Also, the calculated basicity is the basicity preset in consideration of the de-P reaction, etc.

[0064] [Number] Here, [O]: Tapping oxygen (mass%) B cal : Calculated basicity b0, b1, b2, b3: Constants

[0065] The constants b0, b1, b2, b3 can be determined by performing a multiple regression analysis using formula (6) based on past actual operation data (actual values). For example, in the case of a general upper-bottom blown converter-type refining furnace 1 with a charge of about 300 t as in this embodiment, the following formula (7) can be used.

[0066]

Number

[0067] (CaO concentration in slag) The CaO concentration in slag 3 can be estimated using the estimated FeO concentration in slag 3 and the calculated basicity. Specifically, the CaO concentration in slag 3 can be estimated using the following formula (8).

[0068]

Number

[0069] (MgO concentration in slag) The MgO concentration in slag has a strong correlation with the estimated FeO concentration in slag 3 and the end-point molten steel temperature T. Therefore, the MgO concentration in slag can be estimated by using the estimated FeO concentration in slag 3, the preset end-point molten steel temperature T, and the following formula (9).

[0070]

Number

[0071] The constants c0, c1, c2 can be determined by performing a multiple regression analysis using formula (9) based on past actual operation data (actual values). For example, in the case of a general top-bottom blown converter-type refining furnace 1 with a charge of about 300 t as in this embodiment, the following formula (10) can be used.

[0072]

Number

[0073] In addition, in this modified example, the constants a0, a1, a2, and a3 in equation (5) can be determined by performing multiple regression analysis using equation (5) based on past actual operation data (actual values). In this case, as the results of chemical analysis of the actual slag 3, the FeO concentration, CaO concentration, and MgO concentration in the slag 3 may be used, or estimated values as described above may be used.

[0074] Furthermore, due to the endpoint molten steel P concentration, the mass balance between the P concentration in the slag 3 and the P concentration in the hot metal 2 is different, and this difference in the mass balance also affects the P distribution ratio. For this reason, it is preferable that a plurality of constants a0, a1, a2, and a3 are respectively set according to the target endpoint molten steel P concentration. Also, the target endpoint molten steel P concentration is 10×10 -3 mass% or less, 10×10 -3 mass% over 20×10 -3 mass% or less, and 20×10 -3 mass% over, and it is preferable to set the constants a0, a1, a2, and a3 respectively in three cases. In this way, by dividing the target endpoint molten steel P concentration into three ranges and providing a P distribution formula for each range, the behavior of the actual P distribution ratio can be accurately reproduced.

[0075] When using a general top-bottom blown converter-type refining furnace 1 with a charge of about 300 t as in this modified example and setting the P distribution formula by dividing the target endpoint molten steel P concentration into three as described above, the P distribution formula can be the following equations (11) to (13). When the target endpoint molten steel P concentration is 10×10 -3 mass% or less, equation (11) is used; when it is 10×10 -3 mass% over 20×10 -3 mass% or less, equation (12) is used; when the endpoint molten steel P concentration is 20×10 -3 mass% over, equation (13) is used respectively.

[0076]

Equation

[0077] After the P distribution ratio calculation step, the CaO addition amount calculation unit 131 determines the CaO addition amount at the initial stage of the blowing in the second step (CaO addition amount determination step) based on the calculated P distribution ratio, the P concentration in the hot metal (the P concentration in the molten iron 2 before the blowing treatment), and the target final molten steel P concentration. In the CaO addition amount determination step, specifically, the CaO addition amount is calculated according to the formula (14).

[0078]

Equation

[0079] Note that the unidentified P in the formula (14) is a numerical value indicating the influence of the P contained in the slag 3 of the previous charge remaining in the furnace body 10 before the charging process of this charge. The unidentified P can be calculated by the following formula (11) based on the amount of the residual slag, which is the slag 3 of the previous charge remaining in the furnace body 10, and the P concentration of the residual slag. Note that the P concentration (%P)1 in the slag 3 of the previous charge may be a measured value obtained by analyzing the slag 3 of the previous charge or an estimated value estimated from the P distribution ratio. The P concentration (%P)2 in the slag 3 of this charge is obtained from the P distribution ratio L P and the CaO addition amount W T.CaO and the P concentration P in the hot metal before the blowing treatment HM and the final molten steel P concentration P f and. Note that the unidentified P and the CaO addition amount W T.CaO are mutually related, that is, the formula (14) and the formula (15) are mutually related. Therefore, the unidentified P and the CaO addition amount W T.CaO converge or the CaO addition amount W T.CaOIt is preferable to repeat the calculations according to formulas (14) and (15) so that it becomes smaller.

[0080] [Number] Here, (%P)1: P concentration in the slag of the previous charge (mass%) (%P)2: P concentration in the slag of this charge (mass%) W S1 : Amount of residual slag (t)

[0081] According to the blowing method according to this modification example, by determining the amount of CaO input using the estimated P distribution ratio, the optimal amount of CaO input can be determined in the static control of the blowing process.

Example

[0082] Next, the examples conducted by the inventors will be described. In the examples, in the multi-step refining process in the converter-type refining furnace 1 composed of the first step, the second step, and the third step, using the method of the above embodiment, the first input amount and the second input amount were determined so that the total input amount of lime, which is the refining agent 6, was minimized, and molten steel was produced. Further, as a comparative example, molten steel was also produced under the condition that the first input amount and the second input amount were set individually in the same manner as in the prior art.

[0083] In FIG. 9, as the results of the examples and the comparative examples, the first input amount and the second input amount, that is, the results of the amount of new lime used in the first step and the third step are shown. As shown in FIG. 9, it was confirmed that by setting the target basicity so that the total amount was minimized and determining the CaO input amount as in the above embodiment, the amount of new lime used was reduced by 3.9 kg / t.

Explanation of Signs

[0084] 1 Converter-type refining furnace 10 Furnace body 100 Tap hole 101 Bottom blowing tuyere 102 Furnace mouth 11 Acid lance 12 Hopper 120 Shoot 13 Control device 130 Control unit 131 CaO input amount calculation unit 2 Molten iron 3 Slag 4 Oxygen-containing gas 5 Bottom-blowing gas 6 Refining agent

Claims

1. In a hot metal blowing method for producing molten steel by performing blowing treatment in a converter-type refining furnace, a CaO input amount determination step for determining the input amount of CaO in the blowing treatment; a first step of charging hot metal or a mixture of hot metal and a cold iron source into the converter-type refining furnace, charging a refining agent containing CaO, and performing desiliconization and dephosphorization treatment by performing oxygen blowing; after the first step, while holding the hot metal in the furnace, a second step of discharging a part of the slag generated in the first step from the converter-type refining furnace; after the second step, charging a refining agent containing CaO and performing oxygen blowing to perform decarburization treatment and finish dephosphorization treatment to obtain molten steel, a third step; comprising In the CaO input amount determination step, based on a first P concentration which is the P concentration in the hot metal after the first step and the basicity of the slag after the first step, the input amount of CaO to be input in the first step and the third step is determined. A hot metal blowing method.

2. In the CaO input amount determination step, for a plurality of the basicities, the total input amount of CaO to be input in the first step and the third step is calculated, and the basicity with the smallest total input amount is set as the target basicity of the slag after the first step. The input amount of CaO in the first step is calculated according to the basicity of the slag and the slag conversion rate estimated according to the basicity. The input amount of CaO in the third step is calculated based on the first P concentration estimated based on the basicity of the slag after the first step and the intermediate slag discharge rate of the slag in the second step. The hot metal blowing method according to claim 1.

3. The conversion rate is calculated based on the calculated slag amount in the furnace and the cumulative number of uses since the brick renewal of the furnace body. The first P concentration is an equilibrium P concentration calculated from a P distribution ratio based on the basicity of the slag after the first step. The hot metal blowing method according to claim 2.

4. The slag formation rate is calculated using a multiple regression equation with the calculated slag amount in the furnace, the cumulative number of uses, and the input Si amount, which is the amount of Si component charged into the furnace, obtained from past performance as variables, in the hot metal blowing method according to claim 3.

5. The slag formation rate is calculated from equation (1), in the hot metal blowing method according to claim 4. S = α ０ + α １ × W Ｓ + α ２ × N + α ３ × I Ｓｉ ... (1) Here, α ０ = 61.46 α １ = -0.3230 α ２ = -0.006132 α ３ = 6.759 W Ｓ : Calculated slag amount in the furnace (kg / t) N: Number of furnace runs (-) I Ｓｉ : Input Si amount (kg / t)

6. The de - Si external oxygen amount in the first step is calculated from the equilibrium P concentration and the de - P reaction rate equation obtained from past performance, in the hot metal blowing method according to claim 3.

7. The first - order reaction capacity coefficient of the de - P reaction rate equation is calculated using a multiple regression equation with the basicity of the slag after the first step and the calculated slag amount in the furnace, obtained from past performance, as variables, in the hot metal blowing method according to claim 6.

8. The first - order reaction capacity coefficient is calculated from equation (4), in the hot metal blowing method according to claim 6. 【Equation 1】 Here, k: First - order reaction capacity coefficient β ０ ,β １ ,β ２ : Constant W Ｓ : Calculated slag amount in the furnace B: Basicity of slag

9. A method for producing molten steel using the method for blowing molten iron according to any one of Claims 1 to 8.

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