TWI685569B - Refining method of molten iron - Google Patents

Abstract

The subject of the present invention is to adjust the alkalinity of the secondary blowing slag with high accuracy.

The method for refining molten iron of the present invention is that when a converter-type vessel is used for refining molten iron, the intermediate slag removal amount of the primary blowing slag is set as a target variable, and the basicity and discharge of the primary blowing slag are included. Any one or more of the slag starting angle and the information of the amount of slag blown at one time are set as the complex regression analysis to explain the variables, and the molten iron is put into the converter-type container for one blow, and then, after one blow processing After a part of the slag is discharged to the intermediate slag removal outside the container, the results of the above-mentioned multiple regression analysis are used to calculate the intermediate slag removal amount of the slag blowing once and the residual amount in the furnace of the slag blowing once. When the molten iron and slag remaining in the container after the first blowing are added with lime-based medium melting material for the second blowing, the residual amount in the furnace using the above-mentioned first blowing slag and the calculation of the above-mentioned first blowing slag For the composition, the amount of lime-based medium fusion material added in the secondary blowing treatment is calculated without extending the steel-making time.

Description

Refining method of molten iron

The present invention relates to a method for refining molten iron in converter-type vessels (hereinafter, collectively referred to as converters) such as top-blown converters, bottom-blown converters, top-bottom-blown converters, and the like, and relates to a continuous blowing process through intermediate slag removal The refining method of molten iron with secondary blowing.

As the refining method in the converter, there are the following methods: the slag with relatively low alkalinity generated by one blowing of the current charge (only for the purpose of desilication, or for the purpose of desilication and dephosphorization) is passed through the middle After a part of the slag is discharged outside the furnace, a secondary blowing (at least one of dephosphorization and decarburization) is carried out by adding a lime-based medium to the slag remaining in the furnace to generate a slag with a relatively high basicity In order to reduce the amount of lime-based medium melting material or slag discharge.

In this method, the amount of dephosphorization can be adjusted by adjusting the alkalinity of the slag by adding a lime-based medium melt during the second blowing (in the case of decarburization blowing, the amount of dephosphorization and the amount of slag on the surface layer At least one), but the appropriate amount of lime-based medium melting material to be added is not only changed according to the target slag basicity, but also based on the amount of residual slag in the furnace immediately after intermediate slag removal and the residual slag in the furnace The alkalinity varies. However, because the amount of residual slag in the furnace and the basicity of the residual slag in the furnace vary according to various factors in the operation, if there is no accurate grasp of the basicity of the slag in each charge or the amount of intermediate slag removal, there are The problem of poor dephosphorization caused by the insufficient amount of CaO added during the second blowing or excessive dephosphorization caused by excessive addition of CaO.

As a method for solving such problems, it is proposed that: by weighing the current charge The method of grasping the amount of slag in the intermediate slag removal and the method of grasping the amount of the intermediate slag, or the method of estimating the actual performance of the slag basicity with a large amount of data indicating the blowing situation. That is, the mass change of the weighing value of the slag removing pot before and after the intermediate slag removal is regarded as the intermediate slag removal amount, and the method of adjusting the amount of CaO added in the secondary blowing (Patent Document 1), or from a large number of past documents A method of estimating the slag basicity of the treatment similar to this treatment (Patent Document 2).

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2010-126790

[Patent Document 2] Japanese Patent Laid-Open No. 2016-188404

However, as in the method of Patent Document 1, in the method of treating the mass change of the weighing machine before and after intermediate slag removal as the intermediate slag removal amount, there is no way to distinguish the iron particles contained in the molten slag that has undergone intermediate slag removal The quality and the amount of slag lead to the problem of overestimating the amount of intermediate slag removal. In addition, since the amount of iron particles contained in the slag varies greatly depending on the properties of the slag and the condition of intermediate slag removal, it is also difficult to set the content ratio of iron particles in the slag discharged from the intermediate slag to a fixed level Evaluation. In addition, investment in large-scale equipment such as weighing devices for slag discharge is also required.

In addition, in the case of estimating the basicity of the slag from the actual performance of the similarly processed slag components as in the method of Patent Document 2, in order to properly adjust the slag basicity of the second blowing, it is not only necessary to grasp the first blowing The basicity of the molten slag also needs to be grasped after the intermediate slag removal and the amount of slag that is left until the second blowing, but then becomes a bottleneck in operation and delays the steelmaking time long. In the method such as Patent Document 1, until the intermediate slag removal is completed and the weighing is completed, the accurate dephosphorization dose cannot be calculated. Since the dephosphorization agent is usually prepared in the form of being wound into a furnace hopper or being pressure-fed to a distributor, the start time of secondary blowing is delayed until a specific dephosphorization agent can be supplied. In Patent Document 2, there is no disclosure of the treatment method of the amount of slag left, and there is no mention of the operations that should be recorded and referred to regarding intermediate slag removal when directly inferring the basicity of the secondary blowing slag parameter. In addition, in this method, there are also a large number of operating data. Based on the similarity of operating conditions, only the concentration of each component in the slag can be derived. The information about the amount of slag that is one of the important information in blowing control The problem of lack of intermediate slag removal is unknown.

The present invention was made in view of such problems, and its purpose is to: from the slag properties or intermediate in the slag of the primary blowing in the refining method including the primary blowing step, the intermediate slag removing step and the secondary blowing step in the converter The slag removal condition is estimated, the intermediate slag removal amount is calculated, and the amount of CaO required for the secondary blowing is appropriately added to thereby adjust the alkalinity of the secondary blowing slag with high accuracy.

The present inventors have repeatedly and keenly studied in order to solve the above-mentioned problems, and found that the intermediate slag removal amount of the slag after one-time blowing treatment can be determined by the amount of slag after one-time blowing treatment or the alkali after the first slag blowing treatment Degree, slag discharge start angle (referred to as "the slag angle of the converter when the slag starts to flow out of the furnace"), etc., and the present invention was completed based on this knowledge. Here, the slag basicity is generally expressed as "CaO concentration in the slag (mass %)/SiO ₂ concentration in the slag (mass %)", but it is also possible to add e× to the slag The MgO concentration (mass %) is added to the denominator with an index of f × Al ₂ O ₃ concentration (mass %) in the slag (e and f are coefficients of 1 or less), as long as it is determined according to each operating condition. When the MgO concentration in the slag is 15% by mass or more and the "CaO concentration in the slag (mass %)/SiO ₂ concentration in the slag (mass %)" is less than 0.8, it is better to use The molecule is added with the index of the above MgO concentration item. When the operation including the Al ₂ O ₃ concentration in the slag is 30% by mass or more and the “CaO concentration in the slag (mass %)/SiO ₂ concentration in the slag (mass %)” exceeds 4.0, it is preferably Use the index to add the above Al ₂ O ₃ concentration to the denominator. In the usual slag of primary blowing and secondary blowing, the slag composition hardly becomes the above-mentioned slag composition, and can be fully applied as "CaO concentration in the slag (mass %)/SiO ₂ concentration in the slag (mass% )” is the index of slag basicity. Furthermore, the unit of slag basicity is dimensionless quantity. In addition, the slag discharge starting angle θ is set to an angle where the upright state of the converter is set to 0°, and the slag starts to flow out of the furnace mouth to the outside of the furnace.

That is, the part of the present invention as its gist is as follows:

[1] A method for refining molten iron, which is a method for refining molten iron. When a converter-type vessel is used for refining molten iron, the intermediate slag removal amount of the primary blowing slag is set as the target variable in advance, including Any one or more of the basicity of the primary slag blowing and the starting angle of the slag discharge and the information of the amount of slag once blown are set as the complex regression analysis to explain the variables, and the molten iron is loaded into the above-mentioned converter-type container For the purpose of desilication or one-time blowing for desiliconization and dephosphorization purposes, then, after the intermediate slag removal that discharges a part of the molten slag after one-time blowing treatment to the outside of the converter-type vessel, use the above-mentioned multiple regression analysis As a result, the intermediate slag removal amount of the primary blowing slag and the residual amount of the furnace in the primary blowing slag are calculated, and then, a lime system is added to the molten iron and slag after the primary blowing remaining in the converter-type container When the medium melting material is subjected to secondary blowing, the amount of lime-based medium melting material added in the above-mentioned secondary blowing is calculated using the calculated amount of the residual amount in the furnace of the primary blowing slag and the calculated composition of the primary blowing slag. The waiting time of the secondary blowing improves the accuracy of the alkalinity control of the secondary blowing slag.

[2] The method for refining molten iron according to [1], wherein the following formula (1) is used to calculate the intermediate slag removal amount of the above-mentioned primary blowing slag, W _D (n)=a1+b1×W ₁ (n )×1000/{W _H (n)+W _SC (n)}-c1×B _C,1 (n). . . (1) formula

Here, W _D (n): the intermediate slag removal amount of the first blowing slag of the n-th charge (t/ch)

W ₁ (n): the amount of molten slag once blown by the nth charge (t/ch)

W _H (n): the molten iron loading of the nth charge (t/ch)

W _SC (n): the amount of broken iron loading in the nth charge (t/ch)

B _C,1 (n): basicity of one-time blowing slag (times without cause)

a1, b1, c1: constant.

[3] The method for refining molten iron according to [1], wherein the following formula (2) is used to calculate the intermediate slag removal amount of the above-mentioned primary blowing slag, W _D (n)=a2+b2×W ₁ (n )×1000/{W _H (n)+W _SC (n)}-d2×θ(n). . . (2) formula

Here, W _D (n): the intermediate slag removal amount of the first blowing slag of the n-th charge (t/ch)

W ₁ (n): the amount of molten slag once blown by the nth charge (t/ch)

W _H (n): the molten iron loading of the nth charge (t/ch)

W _SC (n): the amount of broken iron loading in the nth charge (t/ch)

θ(n): starting angle of slag discharge (°)

a2, b2, d2: constants.

[4] The method for refining molten iron as described in [1], where the following formula (3) is used to calculate the intermediate slag removal amount of the above-mentioned primary blowing slag, W _D (n)=a3+b3×W ₁ (n )×1000/{W _H (n)+W _SC (n)}-c3×B _C,1 (n)-d3×θ(n). . . (3) formula

Here, W _D (n): the intermediate slag removal amount of the first blowing slag of the n-th charge (t/ch)

W ₁ (n): the amount of molten slag once blown by the nth charge (t/ch)

W _H (n): the molten iron loading of the nth charge (t/ch)

W _SC (n): the amount of broken iron loading in the nth charge (t/ch)

B _C,1 (n): basicity of one-time blowing slag (times without cause)

θ(n): starting angle of slag discharge (°)

a3, b3, c3, d3: constant.

The method for refining molten iron of the present invention can improve the accuracy of the alkalinity control of the secondary blowing slag without waiting time for secondary blowing. In more detail, according to the present invention, the amount of intermediate slag removal can be estimated from the slag properties and intermediate slag removal in one blow, so it can be based on the amount of residual slag in the furnace and the first Blowing slag alkalinity, adjust the amount of CaO to be added in the secondary blowing without prolonging the steel making time, and adjust the alkalinity of the secondary blowing slag with high precision.

1‧‧‧ iron filings

2‧‧‧Converter (converter type container)

3‧‧‧Putting molten iron into the pot

4‧‧‧ molten iron

5‧‧‧The second blown slag of (n-1) charge

6‧‧‧Auxiliary materials

7‧‧‧smelting slag once

8‧‧‧top blowing spray gun

9‧‧‧Wait for the first blowing of the molten slag

10‧‧‧smelting slag once discharged outside the furnace

11‧‧‧ Secondary blowing accessories

12‧‧‧second blowing slag

FIG. 1 is a flowchart showing the outline of the refining method of the converter of the present invention.

Fig. 2 is a graph showing the transition of the basicity of the secondary blowing slag in each example.

Hereinafter, with reference to the accompanying drawings, description will be given of a form suitable for implementing the present invention.

First, FIG. 1 shows an outline of a converter refining method according to an embodiment of the present invention and items calculated in each step. In the operation method of using the second blowing slag of the previous charge for the converter of the current charge, the steps 1 to 5 described below are repeated. Hereinafter, it will be described that the current charge of interest is n charge (n is a natural number), the previous charge is (n-1) charge, and the latter charge is (n+1) charge.

In the first step (loading) of the n-th charge, for example, the molten iron 4 is charged from the molten iron loading pot 3 to the converter (converter-type vessel) 2 into which the iron filings 1 are loaded. At this time, the second blown slag 5 of the (n-1)th charge is present in the furnace.

Before the second step (primary blowing), due to the n-th charge of molten iron loading W _H (n) or the concentration of Si in molten iron M _Si (n) (mass %), broken iron loading W _SC ( n), the input amount of Si heat source, etc. is determined in advance, so if the amount of slag W ₂ (n-1) and the basicity of the slag B _C of the second blowing slag 5 of the (n-1) charge are known _{, 2} (n-1) value, then calculate the amount of lime-based medium melting material W _SL,1 (n) for adjusting the basicity of the slag that should be input in the first blowing of the n-th charge. For example, in the case where the decarburized slag is used for alkalinity adjustment as in the following embodiments, the amount of slag in the first blow of the n-th charge W ₁ (n) and the alkalinity of the slag in the first blow B _C,1 (n ) Calculated according to the following equations (4) and (5) due to material revenue and expenditure, respectively. In addition, in the following, slag basicity B _C,1 (n) means that CaO concentration (mass %) in the slag/SiO ₂ concentration (mass %) in the slag.

X _W2 is the sum of the CaO concentration (mass %) and SiO ₂ concentration (mass %) of the secondary blowing slag, and it varies according to the content of components other than CaO and SiO ₂ as long as the average value of the operation is used (for example, in the implementation In the example, 50.6) can be used as a fixed value. X _W1 is the sum of the CaO concentration (mass %) and SiO ₂ concentration (mass %) of the slag 7 once blown, and similarly differs according to the content of components other than CaO and SiO ₂ as long as the average value of the operation (for example In the embodiment, it is 60.0) as a fixed value. The sum of the CaO concentration (mass %) and the SiO ₂ concentration (mass %) of the lime-based medium melting material (in the example, the decarburized slag in the examples) for adjusting the _{SL SL} basicity. C _SL adjust the basicity of slag-lime-based medium with the molten material (slag in the embodiment of the decarburization embodiment) of CaO concentrations (mass%), S _SL adjust the basicity of slag-lime-based medium with the molten material (in The SiO ₂ concentration (mass%) in the examples is decarburized slag. When several materials are used as the lime-based medium melting material for slag basicity adjustment, for W _SL in the above formula _{, 1} (n)×X _SL /100, W _SL,1 (n)×C _SL /100, and W _SL,1 (n)×S _SL /100, as long as the accumulated value of several materials is used. In addition, W _CaO,1 (n) and W _SiO2,1 (n) are the amount of CaO and the amount of SiO ₂ (including SiO ₂ produced by the combustion of Si). In addition, the above calculation formula is based on the premise that almost all the silicon in the molten iron is desiliconized in one blowing, but when the operation of one blowing is ended in the middle of desilication, as long as the operation is performed by The condition is based on M _Si (n) in the substitution formula according to the desiliconization amount (mass %) of molten iron specified by experience. Here, the target alkalinity B _C,1 (n) can be obtained by adjusting the amount of lime-based medium melting material W _SL,1 (n) for adjusting the alkalinity of the slag alkalinity to be input in the first blowing. In addition, especially in the case of not adding a lime-based medium melting material for slag alkalinity adjustment, the target alkalinity B can also be obtained by adjusting W _CaO,1 (n), W _SiO2,1 (n) _C,1 (n). As described above, the composition (calculated composition) of the primary slag blowing can be calculated by calculating the estimated value of the amount and composition of the slag remaining in the furnace and the amount of the reaction product to the amount and composition of additives in the furnace Make a guess.

In the second step of the n-th charge, add Si heat source such as ferrosilicon or SiC or primary blowing auxiliary materials such as CaO and decarburized slag to the converter 2 loaded with molten iron 4 as needed The slag 7 is adjusted so as to become the target alkalinity (for example, alkalinity 1.5 or less), while the oxygen for refining is blown from the top-blowing spray gun 8 and the like, while the purpose of desilication or desilication and dephosphorization is carried out One time refinement. At this time, the amount of lime-based medium melt _WSL,1 (n) for adjusting the slag basicity is determined in such a way that the calculated primary blowing slag basicity B _C,1 (n) matches the target basicity .

After the second step is completed, intermediate slag removal that discharges a part of the molten slag 7 once out of the converter 2 is performed as the third step. Here, the inventors thought that the method of estimating the amount of slag 10 that is discharged to the outside of the furnace at one time, that is, the intermediate slag removal amount W _D (n) (hereinafter referred to as the “slag removal amount”), is used The method of inferring various operating conditions replaces the method of weighing with large errors, and investigates and accumulates the actual results of the amount of slag removed except for the raw metal (including iron particles in the slag) to quantitatively clarify the relationship with various operating factors Thus, the present invention has been completed. That is, in addition to a blowing amount of slag than W ₁ (n), is also used by the row when a basicity of slag blowing B _{C, 1 (n),} for tilting the converter intermediate deslagging the slag start angle θ (n ) Calculate any one or more of the information in the group, which can estimate the amount of slag removal with high accuracy.

For example, in the following examples, a complex regression analysis is performed in which the intermediate slag removal amount (slag removal amount) of the primary molten slag is set as the target variable, and the slag discharge amount W _D (n) is estimated by the following formula .

(i) When calculated from the amount of slag once blown W ₁ (n) and the basicity of slag once blown B _C,1 (n)

W _D (n)=a1+b1×W ₁ (n)×1000/{W _H (n)+W _SC (n)}-c1×B _C,1 (n). . . (1) formula

Here, W _D (n): the intermediate slag removal amount of the first blowing slag of the n-th charge (t/ch)

W ₁ (n): the amount of molten slag once blown by the nth charge (t/ch)

W _H (n): the molten iron loading of the nth charge (t/ch)

W _SC (n): the amount of broken iron loading in the nth charge (t/ch)

B _C,1 (n): basicity of one-time blowing slag (times without cause)

In addition, the constants a1, b1, and c1 are obtained by complex regression analysis as follows, respectively: 6.26, 0.143, 2.86.

(ii) When calculated from the amount of slag blowing W ₁ (n) and the slag discharge starting angle θ(n)

W _D (n)=a2+b2×W ₁ (n)×1000/{W _H (n)+W _SC (n)}-d2×θ(n). . . (2) formula

Here, W _D (n): the intermediate slag removal amount of the first blowing slag of the n-th charge (t/ch)

W ₁ (n): the amount of molten slag once blown by the nth charge (t/ch)

W _H (n): the molten iron loading of the nth charge (t/ch)

W _SC (n): the amount of broken iron loading in the nth charge (t/ch)

θ(n): starting angle of slag discharge (°)

In addition, the constants a2, b2, and d2 were obtained by complex regression analysis as follows, and were 9.19, 0.1592, and 0.0885, respectively.

(iii) When calculated from the amount of slag blown in one blow W ₁ (n), the basicity of slag blown in one blow B _C,1 (n) and the starting angle of slag discharge θ(n)

W _D (n)=a3+b3×W ₁ (n)×1000/{W _H (n)+W _SC (n)}-c3×B _C,1 (n)-d3×θ(n). . . (3) formula

Here, W _D (n): the intermediate slag removal amount of the first blowing slag of the n-th charge (t/ch)

W ₁ (n): the amount of molten slag once blown by the nth charge (t/ch)

W _H (n): the molten iron loading of the nth charge (t/ch)

W _SC (n): the amount of broken iron loading in the nth charge (t/ch)

B _C,1 (n): basicity of one-time blowing slag (times without cause)

θ(n): starting angle of slag discharge (°)

In addition, the constants a3, b3, c3, and d3 were obtained by complex regression analysis as follows, and were 9.25, 0.146, 1.78, and 0.0650, respectively.

Regarding the coefficients of each item in the speculation formula, due to the volume or shape of the converter In order to obtain the applicable coefficients in converters with different shapes, it is necessary to perform a multiple regression analysis on the relationship between the actual value of the slag removal amount and the operating factors that become variables, and use the obtained multiple regression to evaluate. At this time, as the actual value of the slag removal amount, it is preferable to include the slag from the intermediate slag removal method by crushing and magnetic separation, re-melting and performing specific gravity separation, or a method using both. The iron particles contained in the exhaust are separated from the discharge of iron particles and the amount of slag is determined.

The above system uses one or more of the basicity of the primary blowing slag and the starting angle of the slag discharge and the amount of primary blowing slag as the explanatory variables of the multiple regression analysis. In addition, any explanatory variable may be used. For example, the intermediate slag removal time (sec), the slag discharge end angle (°), the molten iron temperature, the molten iron blending ratio, the amount of alumina input, and the estimated value of the concentration of (T.Fe) in the slag can be suitably used. Furthermore, the (T.Fe) concentration in the slag (=total Fe concentration) is obtained by dividing the iron content contained in the iron oxide present in the slag by the amount of the slag, which can be obtained from the exhaust gas composition The amount of oxygen consumed for decarburization is accumulated, and it is estimated based on the method of calculating the oxygen revenue and expenditure. In the above formulas (1) to (3), regarding the amount of slag to be blown at one time, it is actually set to W ₁ (n)×1000/W _H (n)+W _SC (n)} The basic unit of slag blowing (kg/t-melted iron) at one time can also be used to implement the present invention using W ₁ (n)(t/ch) in the case of using a converter of the same or similar form for operation.

In addition, in the above formulas (1) to (3), linear is used as the complex regression formula, but it is not limited to linear and may be nonlinear. As an example of non-linearity, for example, as the parameters that should determine α, β, and γ, the results obtained by performing a complex regression analysis on the functional form like (6) below, in addition The denominator or exponent of the power entered into the model formula, or the diversified functional forms brought into the interior of the exponent, logarithm, trigonometric functions, etc., of course, may also become the object of nonlinear complex regression.

W _D (n)=(α+β×W ₁ (n)×1000/{W _H (n)+W _SC (n)})×exp(-γ×B _C,1 (n)). . . (6)

According to the estimation of the amount of slag removal W _D (n), the mass W _S (n) (referred to as the amount of residual slag in the first blow) of the first blow slag 9 which is left to the second blow in the fourth step can also be borrowed Calculate from the following formula (7).

W _S (n)=W ₁ (n)-W _D (n). . . (7)

In the fourth step of the nth charge, secondary blowing auxiliary materials 11 such as CaO and decarburized slag are added, and the generated secondary blowing slag 12 is adjusted so as to become the target alkalinity (eg, alkalinity 2.0 or more) , While blowing oxygen for refining from the top-blowing lance 8 and the like, on the other hand, secondary blowing for dephosphorization or dephosphorization and decarbonization is performed. In the secondary blowing, use the primary blowing slag residual amount W _S (n) and the calculated composition of the primary blowing slag (for example _, the value of alkalinity B _C,1 (n)), adjust the second charge n The amount of lime-based medium molten material used for the adjustment of the basicity of the slag input in the secondary blowing is W _SL,2 , whereby the target secondary blowing slag basicity B _C,2 (n) can be obtained. For example, in the case where the decarburized slag is used to adjust the alkalinity as in the following examples, the amount of the second blown slag W ₂ (n) of the nth charge and the basicity of the second blown slag B _C,2 (n) Calculated according to the following equations (8) and (9), respectively.

When several materials are used as the lime-based medium melting material for slag alkalinity adjustment, for W _SL in the above formula _{, 2} (n)×X _SL /100, W _SL,2 (n)×C _{For each item of SL} /100 and W _SL,2 (n)×S _SL /100, as long as the accumulated value of several materials is used. _{W CaO, 2 (n),} W SiO2,2 (n) , respectively, for secondary blowing by adjusting the basicity of slag into the amount of CaO contained in the materials other than the molten material in the lime-based medium, SiO ₂ amount (in The case of Si includes SiO ₂ produced by combustion). Here, the target B _C,2 (n) can be obtained by adjusting the lime-based medium molten material used for the adjustment of the slag basicity to be input in the secondary blowing _, W _{SL ,2} (n). And, in particular, without adding adjusting the basicity of slag with the molten medium where the lime-based material, also by adjusting _{W CaO, 2 (n),} W SiO2,2 (n) obtained as a target of _{C B, 1} (n).

After the end of the fourth step, the fifth step of flowing out molten iron or molten steel is carried out, and the second blowing slag of the nth charge remaining in the furnace is left until the (n+1)th charge, and the sequence from the first step again Repeat the operation.

As described above, if the present invention is used, the W _{CaO, 2} (n) contained in the slag alkalinity adjustment lime amount medium solvent material W _{SL, 2} (n) or other auxiliary materials can be appropriately adjusted , W _SiO2 , ₂ (n), and adjust the basicity of secondary blowing slag B _C,2 (n) with high precision. For example, even if the slag cannot be sufficiently discharged in the intermediate slag removal after one-time blowing, the basicity of the first-time blowing slag calculated by the present invention, B _C,1 (n), and the first time blowing Slag residual amount W _S (n), the amount of lime-based medium melt material for dephosphorization added in the second blowing, and the amount of lime-type medium melt material for adjusting the alkalinity of the slag that should be input in the second blowing is adjusted W _{SL, 2} (n) with or include other dephosphorization of molten lime-based material W medium of _{CaO, 2 (n), W} SiO2,2 (n), the secondary blowing basicity of slag B _{C, 2} (n ) Adjust to the target value with high accuracy. By this, the control accuracy of the phosphorus concentration of molten iron can be improved, or the amount of CaO used to obtain the target phosphorus concentration of molten iron can be suppressed. The alkalinity B _C,2 (n) of the secondary blowing slag that should be ensured varies according to the target phosphorus concentration in the molten iron after treatment or the molten iron temperature after treatment. For the purpose of desiliconization, when the pre-treatment for decarburization and blow-off in the secondary blowing is for the purpose of dephosphorization, the alkalinity B _C,2 (n) of the secondary blown slag is preferably set to 2.1 the above.

In addition, the alkalinity B _C,1 (n) of the molten slag should be ensured in one time, which is changed according to the target phosphorus concentration in the molten iron after treatment or the temperature of the molten iron after treatment. For the purpose of desiliconization, as the pretreatment of decarburization and blowing in the secondary blowing and the dephosphorization treatment, it is preferable to set the basicity of the primary blowing slag B _C,1 (n) to 0.8 Above and below 1.5. If the basicity of primary blowing slag B _C,1 (n) is lower than 0.8, the secondary phosphorus from the previous blowing slag to the molten iron will become larger, and the concentration of molten iron and phosphorus will increase after the treatment. On the other hand, if the basicity of primary blowing slag B _C,1 (n) is higher than 1.5, the concentration of molten iron and phosphorus after treatment is low, but the amount of iron particles in the discharged primary blowing slag increases , Fe yield decreased after treatment. In addition, in order to stabilize the molten iron-phosphorus concentration at a low level after the treatment, it is more preferable to set the primary slag basicity B _C,1 (n) to 1.1 or more and 1.5 or less.

[Example]

Using the top-bottom blowing converter, the amount of crushed iron is 46.2t and the amount of molten iron is 283.8t (the Si concentration of the molten iron is 0.4% by mass), desiliconization is carried out in one blowing, after intermediate slag removal, the second The dephosphorization treatment is carried out during the blowing, and the second blowing slag is all left to the next charge. In the comparative example and the inventive example, these series of treatments were continuously performed on 10 charges, and the first charge was processed with no slag remaining in the furnace during one blow. In any of the embodiments, the basicity adjustment of the slag during the primary blowing is performed using decarburized slag, and the amount of bulk lime added as the lime-based medium melting material for dephosphorization is changed during the secondary blowing and implemented Adjustment of slag basicity.

In Comparative Example 1, a slag discharge pot transport trolley (not shown) equipped with a load cell was used to measure the measured discharge mass W _M (n) during intermediate slag removal, and it was assumed to be the slag removal amount W _D (n). Use the following formula (10 formula) using the measured discharge mass W _M (n).

W _D (n)=0.85×W _M (n). . . (10)

In equation (10), with respect to the measured effluent mass W _M (n), the majority of the investigated charge contains an average of 15% by mass of metallic Fe, so it is multiplied by 0.85 excluding the metallic Fe component. In Comparative Example 2, as the estimated formula for the slag removal amount W _D (n), the following formula (11) using only one blow of the molten slag amount W ₁ (n) was used.

W _D (n)=3.76+0.126×W ₁ (n)×1000/{W _H (n)+W _SC (n)}. . . (11)

In Example 1 of the present invention, as the estimation formula for the amount of slag removal W _D (n), the above-mentioned method using the amount of slag once blown W ₁ (n) and the basicity of slag once blown B _C,1 (n) was used (1) Formula. In Example 2 of the present invention, as the estimation formula for the amount of slag removal W _D (n), the above formula (2) using the amount of molten slag W ₁ (n) and the slag discharge starting angle θ(n) was used. In Example 3 of the present invention, as an estimation formula for the amount of slag removal W _D (n), the amount of slag used for one-time blowing W ₁ (n) and the basicity of slag for one time of blowing B _C,1 (n), discharge The above formula (3) of the slag start angle θ(n). Using the slag removal amount W _D (n) calculated according to the various estimation formulas, adjust the bulk lime input in the secondary blowing so that the alkalinity of the secondary blowing slag B _C,1 (n) becomes the target value of 2.40 the amount.

Furthermore, in the embodiment, the sum of the CaO concentration (mass %) and the SiO ₂ concentration (mass %) of the primary blowing slag X _W1 =60.0, and the CaO concentration (mass %) of the secondary blowing slag and The sum of SiO ₂ concentration (mass %) X _W2 =50.6. Calculate the sum of CaO concentration (mass %) and SiO ₂ concentration (mass %) X _SL =50 in the decarburized slag used as the lime-based medium melting material for slag basicity adjustment in one-time blowing. Melt CaO concentration (mass %) of lime-based medium melting material for slag alkalinity adjustment C _SL = 40, SiO ₂ concentration (mass %) of lime-based medium melting material for slag alkalinity adjustment S _SL = 10, as The lime-based medium melting material for slag basicity adjustment is used in the bulk lime used in the secondary blowing, and X _SL = 95, C _SL = 95, and S _SL =0 are calculated respectively. In addition, in the primary blowing, only decarburized slag is used as the lime-based medium molten material for slag basicity adjustment, and auxiliary materials other than the lime-based medium molten material for slag basicity adjustment are not used. In the secondary blowing, only block lime is used as the lime-based medium melting material for slag basicity adjustment, and the calculated basicity of the slag after the secondary blowing calculated based on the estimated slag removal amount becomes the target value The amount of block lime is adjusted by 2.40 (ie W _{SL, 2} (n)). In addition, in the secondary blowing, auxiliary materials other than the lime-based medium melting material for slag basicity adjustment are not used.

Tables 1 and 2 show the comparison of the operating specifications and the estimated results and the actual results of the additives in Comparative Example 1 and Comparative Example 2. Tables 3 to 5 show the operating specifications and the estimated results of Examples 1 to 3 of the present invention. The summary of the actual value of the additive is shown in FIG. 2 as the transition of the alkalinity (measured value) of the secondary blowing slag of each example.

In the case of Comparative Example 1 where the measured effluent quality W _M (n) was used to estimate the amount of slag removal, it resulted in a large deviation from the actual value of the target slag basicity 2.40, the basicity of the entire 10 charge The standard deviation (σ) of the actual results is 0.102, which is the largest among all the examples. That is, there is a large deviation, and the alkalinity of the secondary blowing slag cannot be adjusted with high accuracy. The reason for this is that the deviation of the amount of metallic Fe contained in the discharge is large, which results in a large deviation between the estimated value of the slag removal amount and the actual performance value. In addition, prepare the dephosphorization agent required for the second blowing, and the time until it can be supplied, that is, the waiting time for the start of the second blowing is 0.8 to 3.1 minutes, an average of about 2 minutes.

In the case of Comparative Example 2 in which the amount of molten slag is estimated by using the amount of slag blown only once, the amount of slag blown in is known before the start of intermediate slag removal. Dephosphorization dose. Therefore, the waiting time for the start of the second blowing is 0 minutes. It can be seen that the actual value of the slag basicity is 2.40 and the actual value is greatly deviated from the target value. The standard deviation (σ) of the basic performance value of the entire 10 charge is 0.089. That is, there is a deviation, and the alkalinity of the secondary blowing slag cannot be adjusted with high accuracy. For example, in the treatment of the fifth charge, the intermediate slag removal is performed from a relatively small tilt angle, so it is expected that the amount of slag removal is large, and the residual amount in the furnace for melting slag at a time is small, but it is considered that due to the unused discharge Information on the starting angle of slag, so the estimated slag removal amount is estimated to be less than the actual slag removal amount. As a result, the amount of lumped lime charged in the second blowing is excessive with respect to the remaining amount in the furnace for the first blow of slag. In the subsequent 6th charge, the blowing slag was not discharged once before the furnace was tilted greatly, so it is expected that the amount of slag removal will be small, and the amount of residue in the furnace will be large, but it is thought that the amount of slag removal is estimated It is estimated to be less than the actual slag removal amount. As a result, the amount of lumped lime charged in the second blowing is insufficient with respect to the amount of residual slag in the furnace.

In Example 1 of the present invention, in addition to the amount of slag once blown, the alkalinity of the slag once blown was also taken into consideration to estimate the amount of slag removed. Since these are known information before intermediate slag removal, the waiting time for the start of the second blowing is 0 minutes for the same reason as in Comparative Example 2. Because the intermediate removal of slag basicity during slag blowing has a great influence on the fluidity of the slag, it is considered that it can be adjusted with high accuracy when it is treated with a change in the target basicity of the slag blowing once Secondary blowing slag basicity. The standard deviation (σ) of the actual value of the alkalinity of the entire 10 batches is 0.059. Compared with the comparative example, the alkalinity of the secondary blowing slag can be adjusted with high precision.

In Example 2 of the present invention, in addition to the amount of molten slag blown at one time, the amount of slag removed was estimated in consideration of the angle at which discharge started. Here, the starting discharge angle is information that has been known since the intermediate slag removal is started, but the intermediate slag removal time is longer than the preparation time of the dephosphorizing agent required for the secondary blowing, so the waiting time for the secondary blowing start is 0 minutes. It is considered that the parameters reflecting the changes in the direct factors indicating the slag removal condition have a greater impact on the slag discharge than the basicity of the slag blowing in one blow. The standard deviation (σ) of the actual value of the alkalinity of the entire 10 charge is 0.035, which can be more Adjust the alkalinity of secondary blowing slag with high precision.

In Example 3 of the present invention, in addition to the amount of slag blown in one blow, the basicity of the slag blown in one blow and the start discharge angle are all taken into consideration to estimate the amount of slag removed. For the same reason as in Invention Example 2, the waiting time for the start of secondary blowing is 0 minutes. By taking all these parameters into consideration, the alkalinity of the secondary blowing slag can be further adjusted with high precision, and the standard deviation (σ) of the actual value of alkalinity for the entire 10 batches is reduced to 0.019.

Claims (4)

A method for refining molten iron, which is: when a converter-type vessel is used for refining molten iron, the intermediate slag removal amount of the primary blowing slag is set as the target variable in advance, and the basicity and discharge of the primary blowing slag are included The information of any one or more of the slag starting angle and the amount of slag blown at one time is set as a complex regression analysis to explain the variables, and the molten iron is put into the above-mentioned converter-type container for desilication only or for desilication and One-time blowing for the purpose of dephosphorization, and then, after a part of the slag after the one-time blowing treatment is discharged to the outside of the converter-type container, the intermediate slag is removed, and the result of the above-mentioned multiple regression analysis is used to calculate the The amount of intermediate slag removal and the amount of residual slag blowing in the furnace, and then, when adding the lime-based medium molten material to the molten iron and slag remaining after the primary blowing in the converter-type container for secondary blowing , Using the residual amount of the primary blowing slag in the furnace and the calculated composition of the primary blowing slag to calculate the amount of lime-based medium molten material added in the secondary blowing, without waiting time for secondary blowing The accuracy of the alkalinity control of the secondary melting slag. As in the method for refining molten iron of claim 1, wherein the following formula (1) is used to calculate the intermediate slag removal amount of the above-mentioned primary blowing slag, W _D (n)=a1+b1×W ₁ (n)× 1000/{W _H (n)+W _SC (n)}-c1×B _C,1 (n)…(1) Here, W _D (n): in the middle of the first blowing slag of the nth charge Slag removal amount (t/ch) W ₁ (n): The first blown molten slag amount of the nth charge (t/ch) W _H (n): The molten iron loading amount of the nth charge (t/ch)W _SC (n): Broken iron loading of the nth charge (t/ch) B _C,1 (n): Alkalinity of the slag once blown (causeless number) a1, b1, c1: constant. As in the refining method of molten iron of claim 1, wherein the following formula (2) is used to calculate the intermediate slag removal amount of the above-mentioned primary blowing slag, W _D (n)=a2+b2×W ₁ (n)× 1000/{W _H (n)+W _SC (n)}-d2×θ(n)…(2) Here, W _D (n): the intermediate slag removal amount of the first blowing slag of the n-th charge (t/ch)W ₁ (n): the amount of molten slag once blown at the n-th charge (t/ch) W _H (n): the amount of molten iron charged at the n-th charge (t/ch) W _SC (n ): Broken iron loading of the nth charge (t/ch) θ (n): Starting angle of slag discharge (°) a2, b2, d2: constant. As in the refining method of molten iron of claim 1, wherein the following formula (3) is used to calculate the intermediate slag removal amount of the above-mentioned primary blowing slag, W _D (n)=a3+b3×W ₁ (n)× 1000/{W _H (n)+W _SC (n)}-c3×B _C,1 (n)-d3×θ(n)… (3) Here, W _D (n): the nth charge Intermediate slag removal volume for one-time blowing slag (t/ch) W ₁ (n): First-time blowing slag amount for the nth charge (t/ch) W _H (n): molten iron loading for the nth charge Amount (t/ch) W _SC (n): The amount of broken iron loading in the n-th charge (t/ch) B _C,1 (n): Alkalinity of the slag once blown (causeless number) θ(n) : Starting angle of slag discharge (°) a3, b3, c3, d3: constant.

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