KR20200077594A - How to refine molten iron - Google Patents

Abstract

An object of the present invention is to adjust the secondary blown slag basicity with good precision. In the refining method of molten iron of the present invention, when the refining of molten iron is performed using a converter type container, the intermediate exclusion amount of the primary blown slag is set as the target variable, and the primary blown slag basicity and the slag discharge start angle are set in advance. Multiple regression analysis is performed using information including any one or more and the primary blow slag amount as an explanatory variable, and the molten iron is charged into the converter-type container to perform primary blow, followed by slag after the primary blow treatment. After performing the intermediate exclusion for discharging a portion of the product out of the container, the intermediate exclusion amount of the primary blown slag and the residual amount in the furnace of the primary blown slag are calculated using the results of the multiple regression analysis. In performing a second blow by adding a lime-based solvent to the retained molten iron and slag after the first blow, the second blow blow treatment using the residual amount in the furnace of the first blow blow slag and the calculated composition of the first blow blow slag The amount of lime-based solvent to be added in is calculated without extending the purification time.

Description

How to refine molten iron

The present invention relates to a method for refining molten iron in a converter-type container (hereinafter abbreviated as a converter), such as a quench furnace, a quench furnace, a quench furnace, and the like. The present invention relates to a method of refining molten iron in which primary and secondary blows are continuously performed.

As a refining method in a converter, after the slag of a relatively low-salt airway produced by the primary blow of the current charge (for desulfurization only or for desulfurization and dephosphorization) is discharged to a part of the furnace by an intermediate exclusion, the furnace There is a method of reducing the amount of a lime-based solvent or the amount of slag discharged by performing a second blow (at least one of dephosphorization and decarburization) to generate a slag of a relatively high-base airway by adding a lime-based solvent to the remaining slag.

In this method, it is possible to adjust the amount of desorption (at least one of the amount of desorption and the amount of cover slag in the case of decarburization) by adjusting the slag basicity by adding a lime-based solvent during the second blow, but it should be added The appropriate amount of the lime-based solvent is changed according to the amount of residual slag in the furnace immediately after the intermediate exclusion and the amount of basic slag in the furnace, in addition to the target slag basicity. However, since the amount of residual slag in the furnace and the basicity of residual slag in the furnace fluctuate depending on various factors in the operation, it is added at the time of the second blow if the basicity of slag or the amount of intermediate exclusion in each charge is not accurately determined. There is a problem that poor dephosphorization due to insufficient CaO content or excessive dephosphorization caused by excessive addition of CaO.

As a method to solve such a problem, the method of determining the intermediate amount of waste by weighing the amount of slag discharged from the current amount of intermediate waste, or using a large amount of data indicating the state of blow, estimates the slag basicity performance with better precision. How to do this is proposed. That is, the method of adjusting the amount of CaO added in the secondary blow and considering the mass change of the weight value of the exclusion ladle before and after the intermediate exclusion is considered as the intermediate exclusion amount (patent document 1) or similar to the process from the large amount of past data. It is a method (patent document 2) which estimates the slag basicity of the said process from the slag performance value of a process.

Japanese Patent Application Publication No. 2010-126790 Japanese Patent Application Publication No. 2016-188404

However, as in the method of Patent Document 1, as a method of considering the mass change of the weighing machine before and after the intermediate exclusion as the intermediate exclusion amount, the mass of slag contained in the intermediate excreted slag and the amount of slag are distinguished. There is a problem that it is impossible to estimate the excess amount of intermediate waste. In addition, since the amount of iron contained in the slag varies greatly depending on the properties of the slag, the situation of the intermediate waste, etc., it is difficult to constantly evaluate the proportion of the iron contained in the slag discharged by the intermediate waste. In addition, large-scale facility investments such as weighing machines for slag emissions are also required.

Also, as in the method of Patent Document 2, when estimating the slag basicity from the results of the slag component of the past similar treatment, in order to properly adjust the slag basicity of the secondary blow, not only the slag basicity of the primary blow, but also after the intermediate exclusion 2 It is necessary to grasp the amount of slag that flows into the car blow, and, in addition, the prolongation of steelmaking time becomes an obstacle in operation. In the same manner as in Patent Document 1, the exact amount of dephosphorization agent cannot be calculated until the intermediate exclusion is finished and weighing is finished. Since the dephosphorization agent is usually wound up on a hearth hopper or prepared in the form of pressure feeding to a dispenser, the second blow start time is delayed until a predetermined dephosphorization agent can be supplied. Patent Literature 2 does not show how to handle the amount of slag that is passed over, and records the intermediate exclusion which is considered necessary when directly estimating the basicity of the secondary blown slag, and mentions no operating parameters to be referred to. It is not. In addition, in this method, the concentration of each component in the slag is derived based on the similarity of the operating conditions from a large amount of operation data. There was also a problem that it was lacking because it was not.

This invention was made|formed in view of such a problem, and in the refining method including a primary blow process in a converter, an intermediate exclusion process, and a secondary blow process, it is intermediate from the slag property and intermediate exclusion situation of a primary blow. The aim is to adjust the secondary blown slag basicity with good precision by estimating and calculating the amount of waste, and adding the CaO amount necessary for the secondary blowing to be appropriate.

As a result of repeated studies of the inventors in order to solve the above problems, the inventors started to discharge the slag amount after the first blow treatment or the slag basicity and the slag discharge after the first blow treatment, with respect to the intermediate amount of slag after the first blow treatment. It has been found that it can be estimated from an angle (referring to "the angle of tilt of a converter when the slag starts to flow out of the furnace") and the like, and based on this knowledge, the present invention has been completed. Here, the basicity of the slag is generally expressed as "the concentration of CaO in the slag (mass%)/the concentration of SiO _{2 in the} slag (mass%)", but e × the MgO concentration in the slag (mass%) is added to the molecule, or the denominator In addition, an index for adding an Al ₂ O ₃ concentration (mass%) (e and f are coefficients of 1 or less) in f × slag may be used, and may be determined in accordance with the respective operating conditions. When the MgO concentration in the slag is 15% by mass or more, and the operation in which the "CaO concentration in the slag (mass%)/SiO ₂ concentration in the slag (mass%)" is less than 0.8 includes the above MgO concentration in the molecule. It is preferable to use an indicator that adds the term of. When the Al ₂ O ₃ concentration in the slag is 30 mass% or more, and the operation in which the "CaO concentration (mass%) in the slag/SiO ₂ concentration (mass%) in the slag" exceeds 4.0 is included, the denominator is described above. It is preferable to use an index to add the term of the Al ₂ O ₃ concentration. In the slag of the normal primary and secondary blows, the slag composition rarely becomes as described above, and the slag as an index of "CaO concentration (mass %) in slag/SiO ₂ concentration (mass %) in slag" as an index. The basicity can be sufficiently applied. In addition, the unit of slag basicity is dimensionless. In addition, the slag discharge start angle θ is set to an angle at which the slag is started to flow out of the furnace from the furnace port with the converter upright state being 0°.

That is, the present invention makes the gist as follows.

[1] As a method of refining molten iron,

When the refining of molten iron is performed using a converter type container, the intermediate exclusion amount of the primary blown slag is set as a target variable in advance, and at least one of the primary blown slag basicity and the slag discharge start angle, and the primary blown off. A multiple regression analysis is performed using information including the amount of slag as an explanatory variable.

The molten iron is charged into the converter-type container to perform primary blowing for desulfurization only or desulfurization and dephosphorization purposes,

Subsequently, after performing the intermediate exclusion for discharging a part of the slag after the primary blown treatment out of the converter type container, the intermediate exclusion amount of the primary blown slag and the residual amount in the furnace of the primary blown slag using the results of the multiple regression analysis Calculate

Subsequently, in the second blow blowing by adding a lime-based solvent to the molten iron and slag after the first blow blow remaining in the converter-type container, the residual amount in the furnace of the first blow blow slag and the first blow blow slag A method for refining molten iron using a calculated composition to calculate the amount of a lime-based solvent to be added in the secondary blow, and to increase the precision of basicity control of the secondary blow slag without waiting time for the second blow.

[2] The method for refining molten iron according to [1], wherein the intermediate exclusion amount of the primary blown slag is calculated using the following formula (1).

W _D (n) = a1 + b1 × W ₁ (n) × 1000/{W _H (n) + W _SC (n)} – c1 × B _C,1 (n)… (1) Expression

Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)

W ₁ (n): Primary blown slag amount in nth charge (t/ch)

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

W _SC (n): scrap charge in the nth charge (t/ch)

B _C,1 (n): Primary blown slag basicity (dimension number)

a1, b1, c1: integer

[3] The method for refining molten iron according to [1], wherein the intermediate exhaust amount of the primary blown slag is calculated using the following formula (2).

W _D (n) = a2 + b2 × W ₁ (n) × 1000/{W _H (n) + W _SC (n)} – d2 × θ(n)… (2) Expression

Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)

W ₁ (n): Primary blown slag amount in nth charge (t/ch)

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

W _SC (n): scrap charge in the nth charge (t/ch)

θ(n): Slag discharge start angle (°)

a2, b2, d2: integer

[4] A method for refining molten iron according to [1], wherein the intermediate exclusion amount of the primary blown slag is calculated using the following formula (3).

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

Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)

W ₁ (n): Primary blown slag amount in nth charge (t/ch)

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

W _SC (n): scrap charge in the nth charge (t/ch)

B _C,1 (n): Primary blown slag basicity (dimension number)

θ(n): Slag discharge start angle (°)

a3, b3, c3, d3: integer

The refining method of molten iron of the present invention can increase the precision of basicity control of the secondary blown slag without waiting time for the secondary blown. More specifically, according to the present invention, since it is possible to estimate the amount of intermediate exhaust from the slag properties of the primary blow and the intermediate exhaust condition, the primary blow blow slag at the start of the secondary blow without the steelmaking time is prolonged. By adjusting the amount of CaO to be added in the secondary blow based on the residual amount in the furnace and the basicity of the primary blown slag, the basicity of the secondary blown slag can be adjusted with good precision.

1 is a flow chart showing an outline of a method for refining a converter according to the present invention.
2 is a graph showing the transition of the basic blown slag basicity in each example.

EMBODIMENT OF THE INVENTION Hereinafter, the form suitable for implementing this invention is demonstrated, referring an accompanying drawing.

First, Fig. 1 shows an outline of a method for refining a converter according to an embodiment of the present invention and items calculated in each process. In the method of operating the converter for recycling the secondary blown slag of the previous charge to the primary blown of the current charge, the first to fifth steps described below are repeatedly performed. In the following, the current charge to be noted is described as n charge (n is a natural number), the previous charge as (n-1) charge, and the next charge as (n+1) charge.

In the first step (charging) of the nth charge, for example, the molten iron 4 is charged from the molten iron charging ladle 3 to the converter (converter type container) 2 in which the iron scrap 1 is charged. . At this time, there is a (n-1) secondary blown slag 5 in the furnace.

Before performing the second step (primary blow), the charge of the molten iron in the nth charge W _H (n) or the Si concentration in the molten iron M _Si (n) (mass %), the amount of scrap charge W _SC (n), and the heat source of Si Since the input amount and the like are predetermined, when the value of the slag amount W ₂ (n-1) and the slag basicity B _C,2 (n-1) of the secondary blown slag 5 of the (n-1) charge is known, , The amount of lime-based solvent W _SL,1 (n) for adjusting the slag basicity to be input in the first blow of the nth charge is calculated. For example, when the basicity is adjusted by decarburization as in the examples described later, the amount of primary blown slag W ₁ (n) and the primary blown slag basicity B _{C, 1} (n) of the n th charge are each a substance. It calculates as follows (4) Formula and (5) Formula from resin (i). In addition, in the following, the slag basicity _{C B, 1} (n) is, as will be explained to mean a SiO ₂ concentration (% by weight) of the CaO content (% by mass) / slag in slag.

X _W2 is the second, and the sum of the CaO concentration (% by weight) and the SiO ₂ concentration (% by weight) of blown slag varies depending on the ingredient content of the non-CaO and SiO _2, but the average value of the operation (e. G. Example In 50.6), a fixed value may be employed. X _W1 is the sum of the CaO concentration (mass %) and the SiO ₂ concentration (mass %) of the primary blown slag 7 and similarly differs depending on the content of components other than CaO and SiO ₂ , but the average value of operation (eg For example, in the example, 60.0) may be employed as a fixed value. X _SL is the sum of the CaO concentration (mass%) and SiO ₂ concentration (mass%) of the lime-based medium for slag basicity adjustment (decarbonization residue in the example). C _SL is the CaO concentration (mass %) of the lime-based medium for slag basicity adjustment (in the example, decarbonization residue), S _SL is SiO ₂ concentration in the lime-based medium for slag basicity adjustment (in the embodiment, decarbonization residue). (Mass%). When a plurality of materials are used as a lime-based solvent for adjusting slag basicity, W _SL,1 (n) × X _SL /100, W _SL,1 (n) × C _SL /100, and W _{SL in the} above formula. For each term of _,1 (n) × S _SL /100, an integrated value may be used for each of a plurality of materials. In addition, W _CaO,1 (n), W _SiO2,1 (n) are CaO amount and SiO ₂ amount derived from auxiliary materials other than the lime-based solvent for adjusting slag basicity, respectively, which is input in the primary blow. Is SiO ₂ ). In addition, the above calculation formula is premised on the operation of degassing almost all of the silicon in the molten iron during the primary blow, but in the case of an operation in which the primary blow is terminated during degassing, the declining of the molten iron designated empirically from the operating conditions. It is sufficient to substitute M _Si (n) in the formula in the weight (mass%). Here, the target basicity B _C,1 (n) can be obtained by adjusting the amount of the slag basic solvent W _SL,1 (n) for adjusting the slag basicity to be input in the first blow. Moreover, the target basicity B _C,1 (n) can also be obtained by adjusting W _CaO,1 (n), W _SiO2,1 (n) without adding a lime-based medium for adjusting slag basicity. As described above, the composition (calculated composition) of the primary blown slag can be estimated by calculation from estimates of the amount and composition of slag remaining in the furnace, the amount of reaction products, and the amount and composition of additives into the furnace.

In the second step of charging, in the converter (2) in which the molten iron (4) is charged, if necessary, a Si heat source such as ferrosilicon or SiC, or a primary blowing auxiliary material (6) such as CaO or decarbonization residue is added. , The primary blown slag 7 to be produced is adjusted to a target basicity (e.g., a basicity of 1.5 or less), and desulfurization and dephosphorization are only carried out while blowing oxygen for refining from the blowing lance 8 or the like. Conduct a primary blow. At this time, the amount of lime-based solvent for adjusting slag basicity W _SL,1 (n) is determined so that the calculated primary blown slag basicity B _C,1 (n) matches the target basicity.

After the end of the second step, as a third step, intermediate exclusion is performed in which a part of the primary blown slag 7 is discharged out of the converter 2. Here, the inventors estimate the amount of the primary blown slag 10 discharged out of the furnace, that is, the intermediate exclusion amount W _D (n) (hereinafter referred to as "exhaust amount"), which is caused by weighing with a large error. Instead of the method, the idea of using a method to estimate from various operating conditions is conceived, and the performance of the exclusion amount excluding the current (including slag in the slag) is investigated and accumulated, and it is combined with various operating factors. By revealing the relationship quantitatively, the present invention has been completed. That is, in addition to the primary blown slag amount W ₁ (n), the primary blown slag basicity B _C,1 (n), any of the group consisting of the slag discharge start angle θ(n) when the furnace is intermediately discharged By calculating using one or more pieces of information, the amount of waste can be estimated with good precision.

For example, in the example described later, a middle regression analysis is performed in which the intermediate exclusion amount (exclusion amount) of the primary blown slag is a target variable, and the exclusion amount W _D (n) is estimated by the following equation. .

(Iii) Primary blown slag amount W ₁ (n) and primary blown slag basicity calculated from 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) Expression

Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)

W ₁ (n): Primary blown slag amount in nth charge (t/ch)

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

W _SC (n): scrap charge in the nth charge (t/ch)

B _C,1 (n): Primary blown slag basicity (dimension number)

In addition, a1, b1, and c1, which are integers, were obtained by a multiple regression analysis as described later, and were respectively 6.26, 0.143, and 2.86.

(Ii) When calculated from the primary blown slag amount W ₁ (n) and the slag discharge start angle θ(n)

W _D (n) = a2 + b2 × W ₁ (n) × 1000/{W _H (n) + W _SC (n)} – d2 × θ(n)… (2) Expression

Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)

W ₁ (n): Primary blown slag amount in nth charge (t/ch)

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

W _SC (n): scrap charge in the nth charge (t/ch)

θ(n): Slag discharge start angle (°)

In addition, a2, b2, and d2, which are integers, were determined by heavy regression analysis as described later, and were set to 9.19, 0.1592, and 0.0885, respectively.

(I) When calculating from primary blown slag amount W ₁ (n), primary blown slag basicity B _C,1 (n), and slag discharge start angle 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) Expression

Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)

W ₁ (n): Primary blown slag amount in nth charge (t/ch)

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

W _SC (n): scrap charge in the nth charge (t/ch)

B _C,1 (n): Primary blown slag basicity (dimension number)

θ(n): Slag discharge start angle (°)

In addition, a3, b3, c3, and d3, which are integers, were determined by a multiple regression analysis as described later, and were respectively 9.25, 0.146, 1.78, and 0.0650.

Since the coefficient of each term in the estimation formula varies with the volume and shape of the converter, in order to obtain the coefficient applicable to the converter with different shapes, the relationship between the performance value of the amount of exhaust and the operating factor that is a variable It is necessary to perform a multiple regression analysis in advance and evaluate using the obtained multiple regression equation. At this time, as the actual value of the amount of waste, in the discharge by the method of pulverizing and charitable, re-dissolving the specific gravity, or using both of these, from the discharge containing the slag and the ingots interposed in the middle. It is preferable to separate the contained iron and find the amount of slag.

As the explanatory variables of the multiple regression analysis, any one or more of the primary blown slag basicity and the slag discharge start angle was used, and the primary blown slag amount was used, but other explanatory variables can be used. For example, an intermediate exclusion time (sec), a slag discharge end angle (°), a molten iron temperature, a molten iron mixing rate, an alumina input amount, and an estimated value of the (T. Fe) concentration in the slag can be preferably used. In addition, 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 slag, calculating the amount of oxygen consumed for decarburization from the exhaust gas component, and integrating the oxygen substance. It can be estimated by a method obtained from resin or the like. In the above expressions (1) to (3), by setting W ₁ (n) × 1000/{W _H (n) + W _SC (n)} with respect to the primary blown slag amount, substantially the primary blown slag raw unit ( Kg/t-melting), but when operating in a converter of the same or similar type, use of W ₁ (n) (t/ch) does not interfere with the practice of the present invention.

Moreover, although the linearity is used as a multiple regression expression in the said (1)-(3) Formula, it is not limited to linearity, and may be a nonlinearity. As a nonlinear example, as a parameter to determine, for example, α, β, and γ, a result of performing a multiple regression analysis on a functional type such as the following (6) equation can be used, but in addition, an expression model including parameters It goes without saying that various functional types, such as those in the denominator of the expression, the exponent of the power, or the inside of the exponential, logarithmic, trigonometric functions, etc., are likely to be the subject of nonlinear multiple regression.

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

From the estimate of the exhaust discretion W _D (n), move to the secondary blow of the fourth process (referred to as primary blow slag remaining amount) of 1 mass Primary blow slag (9) W _S (n) (7) of or less Can be calculated as

W _S (n) = W ₁ (n)-W _D (n)… (7) Expression

In the fourth step of the nth charge, the secondary blown slag 12, such as CaO and decarbonization residue, is added so that the generated secondary blown slag 12 becomes the target basicity (for example, basicity of 2.0 or more). Adjustment is performed, and secondary blowing is performed for the purpose of dephosphorization or dephosphorization/decarburization while blowing oxygen for refining from the blowing lance 8 or the like. In the secondary blow, the secondary blow blow of the nth charge is performed using the primary blow blow slag residual amount W _S (n) and the calculated composition of the primary blow blow slag (for example, the value of basicity B _C,1 (n)). By adjusting the amount of the lime-based solvent for adjusting the slag basicity W _SL,2 to be added, the target secondary blown slag basicity B _C,2 (n) can be obtained. For example, in the case where the basicity is adjusted by decarburization as in Examples described later, the amount of secondary blown slag W ₂ (n) and the secondary blown slag basicity B _C,2 (n) of the n th charge are each less than or equal to It is calculated as in equations (8) and (9).

When a plurality of materials are used as a lime-based solvent for adjusting slag basicity, W _SL,2 (n) × X _SL /100, W _SL,2 (n) × C _SL /100, and W in the above formula. For each term of _SL,2 (n) × S _SL /100, an integrated value may be used for each of a plurality of materials. W _CaO,2 (n) and W _SiO2,2 (n) are the amount of CaO and the amount of SiO ₂ contained in the auxiliary materials other than the lime-based _medium for slag basicity input in the secondary blow, respectively. Generated SiO ₂ ). Here, the target B _C,2 (n) can be obtained by adjusting the amount of the slag basic solvent W _SL,2 (n) for adjusting the slag basicity to be input in the second blow. Moreover, the target B _C,1 (n) can also be obtained by adjusting W _CaO,2 (n) and W _SiO2,2 (n) without adding a lime-based solvent for adjusting slag basicity.

After the 4th process, the 5th process of pouring molten iron or molten steel is carried out, and the 2nd charge blown slag of the nth charge which remain|survived in a furnace passes to the (n+1) charges, and it is an order from 1st process again Repeat operation.

When the present invention is used as described above, by adjusting the amount of the lime-based solvent for adjusting slag basicity W _SL,2 (n) or W _CaO,2 (n), W _SiO2,2 (n) included in other auxiliary materials, etc. , Secondary blown slag basicity B _C,2 (n) can be adjusted with good precision. For example, even if the slag cannot be sufficiently discharged as an intermediate exhaust material after the primary blow, the primary blown slag basicity of the present charge calculated by the present invention is B _C,1 (n) and the primary blown slag residual amount W _S (n), taking into account the amount of lime-based solvent for dephosphorization to be added in the second blow, the amount of lime-based solvent for adjusting the slag basicity to be added in the second blow, W _SL,2 (n) or other lime-based By adjusting W _CaO,2 (n) and W _SiO2,2 (n) containing a _solvent , the secondary blown slag basicity B _C,2 (n) can be adjusted to a target value with good accuracy. Thereby, it becomes possible to improve the control precision of the phosphorus concentration of molten iron, or to suppress the amount of CaO used to obtain the target phosphorus concentration. The secondary blown slag basicity B _C,2 (n) to be secured varies depending on the phosphorus concentration in the molten iron after the target treatment or the molten iron temperature after treatment, but for example, for the purpose of desulfurization by primary blown, secondary blown blow In the case where the dephosphorization treatment is intended as a pretreatment for decarburization, it is preferable that the secondary blown slag base also has a B _C,2 (n) of 2.1 or higher.

In addition, the basicity of the primary blown slag slag B _C,1 (n) to be secured varies depending on the phosphorus concentration in the molten iron after the target treatment or the molten iron temperature after treatment, but for example, for the purpose of desulfurization in the primary blown, 2 When dephosphorization is used as a preliminary treatment for decarburization in primary blow, it is preferable that the primary blown slag basicity B _C,1 (n) be 0.8 or more and 1.5 or less. When the primary blown slag basicity B _C,1 (n) is lowered than 0.8, the concentration of molten iron from the secondary blown slag of the previous charge to molten iron is large, and the molten iron phosphorus concentration increases after treatment. On the other hand, when the primary blown slag basicity B _C,1 (n) is higher than 1.5, the molten iron phosphorus concentration after treatment is low, but the amount of iron in the discharged primary blown slag increases and the Fe yield after treatment decreases. Will be discarded. Moreover, in order to make molten iron phosphorus concentration low level stability after treatment, it is more preferable to set the primary blown slag basicity B _C,1 (n) to 1.1 or more and 1.5 or less.

Example

Using an upper-lowering converter, a scrap amount of 46.2 t and a molten iron amount of 283.8 t (the Si concentration of the molten iron is 0.4 mass%) are charged, desulfurization treatment is performed in the first blow, and intermediate exclusion is carried out. The dephosphorization treatment was carried out, and the second blown slag was transferred to the next charge. In Comparative Examples and Inventive Examples, this series of treatments was carried out continuously for 10 charges, but for the 1st charge, in the first blow, the treatment was started without residual slag in the furnace. In all of the examples, the slag basicity adjustment in the primary blowing was carried out using decarburization residue, and in the secondary blowing, the slag basicity was adjusted by changing the amount of added lime, which is a lime-based medium for dephosphorization.

In Comparative Example 1, the measured discharge mass W _M (n) during intermediate exclusion was measured using a slag discharge ladle conveyance truck (not shown) equipped with a load cell, and the exclusion amount W _D (n) The following equation (10) using the measured emission mass W _M (n) was used as an estimation equation for.

W _D (n) = 0.85 × W _M (n)… (10) Expression

In the equation (10), since the metal Fe was contained in an average of 15% by mass in the majority of the charges irradiated with respect to the actual emission mass W _M (n), 0.85 excluding the metal Fe component was multiplied. In Comparative Example 2, the following formula (11) using only the primary blown slag amount W ₁ (n) was used as an estimation formula for the amount W _D (n).

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

In Example 1 of the present invention, the equation (1) described above using the primary blown slag amount W ₁ (n) and the primary blown slag basicity B _C,1 (n) as an estimation formula of the amount of waste W _D (n) Was used. In Example 2 of the present invention, the above-described formula (2) using the primary blown slag amount W ₁ (n) and the slag discharge start angle θ(n) was used as an estimation formula for the amount of waste W _D (n). In Example 3 of the present invention, as the estimation formula of the exclusion amount W _D (n), the primary blown slag amount W ₁ (n) and the primary blown slag basicity B _C,1 (n), the slag discharge start angle θ(n) The formula (3) described above was used. Using the amount of excrement W _D (n) calculated according to each estimation formula, the amount of slaked lime added in the secondary blow was adjusted so that the basic blow slag basicity B _C,1 (n) became the target value of 2.40.

Further, the embodiment, the primary sum X _W1 = 60.0 of the CaO content (% by weight) of blown slag and the SiO ₂ concentration (% by weight), the second CaO content (% by weight) of blown slag and the SiO ₂ concentration (% by weight ) And X _W2 = 50.6. In the decarburization furnace residue used in primary blowing as a lime base solvent for slag basicity adjustment, the sum of CaO concentration (mass %) and SiO ₂ concentration (mass %) X _SL = 50, CaO of lime base solvent for slag basicity adjustment Concentration (mass %) C _SL = 40, SiO ₂ concentration of lime-based medium for slag basicity adjustment (mass %) S _SL = 10. , Respectively, X _SL = 95, C _SL = 95, and S _SL = 0. In addition, in the primary blow, only debris was used as a lime-based solvent for adjusting slag basicity, and no auxiliary ingredients other than a lime-based solvent for adjusting slag basicity were used. In the second blow, only slaked lime is used as a lime-based medium for slag basicity adjustment, and the amount of slaked lime (i.e., W _SL, so that the calculated basicity of slag after the second blow is calculated to be 2.40 of the target value) ₂ (n)) was adjusted. In addition, no secondary raw materials other than the lime-based solvent for adjusting slag basicity were used in the second blow.

In Table 1 and Table 2, Comparative Example 1 and Comparative Example 2 and Tables 3 to 5 show the summary of the operating specifications and estimated results in the invention examples 1 to 3 and the performance values of the additives. The secondary blown slag basicity (measured value) of each Example is shown.

In the case of Comparative Example 1 in which the amount of emissions was estimated using the measured emission mass W _M (n), the result was significantly different from the target slag basicity of 2.40, and the standard of the basicity performance value of all 10 charges The deviation (σ) was 0.102, which was the largest among all examples. In short, the secondary blown slag basicity could not be adjusted with great difference or good precision. This is because there is a large variation in the amount of metal Fe contained in the emission, and a large gap arises between the estimated value and the performance value of the amount of waste. In addition, the dephosphorization agent necessary for the second blow was prepared, and the time until supply became possible, that is, the waiting time for the start of the second blow was 0.8 to 3.1 minutes, and on average about 2 minutes.

In the case of Comparative Example 2 in which the amount of excreted was estimated only by the amount of primary blown slag, the amount of blown slag can be known before the start of intermediate exuding, so that the amount of dephosphorization agent of the secondary blown can be calculated from the start of the intermediate exuding. For this reason, the waiting time for the second blow start was 0 minutes. For the target slag basicity of 2.40, a treatment in which the performance value was significantly deviated from the target value was found, and the standard deviation (σ) of the basic performance value of 10 charges was 0.089. That is, there was a deviation, and the secondary blown slag basicity could not be adjusted with good precision. For example, in the fifth charge treatment, since the amount of exhaust is large because the medium is excluded from a relatively small tilt angle, the residual amount in the furnace of the primary blown slag is expected to be small, but since the information of the angle at which the slag is discharged is not used, it is estimated. It can be thought that the amount of waste was estimated to be less than the amount of waste. As a result, compared with the residual amount in the furnace of the primary blown slag, the amount of slaked lime injected in the secondary blown becomes excessive. In the subsequent sixth charge, since the primary blown slag was not discharged until the furnace was significantly hardened, the amount of exhaust was small, and the residual amount of the primary blown slag in the furnace was expected to be large, but the estimated discharge amount was less than the actual flue amount. You can think it was guessed. As a result, compared with the residual amount in the furnace of the primary blown slag, the amount of slaked lime injected in the secondary blown becomes insufficient.

In Example 1 of the present invention, in addition to the primary blown slag amount, the primary blown slag basicity is also considered to estimate the amount of waste. Since these are information to be known before the intermediate exclusion, the waiting time for the second blow start was 0 minutes for the same reason as Comparative Example 2. Since the basicity of the primary blown slag greatly affects the fluidity of the slag during the intermediate exclusion, in the case of a treatment involving a change in the target basicity of the primary blown slag, the secondary blown slag basicity can be adjusted with good precision. I think. The standard deviation (σ) of the basicity performance value of all 10 charges was 0.059, and the secondary blown slag basicity could be adjusted with better precision than the comparative example.

In Example 2 of the present invention, in addition to the primary blown slag amount, the discharge amount is also estimated in consideration of the discharge start angle. Among these, the discharge start angle is information that can be known after starting the intermediate exhaust, but the intermediate exhaust time is longer than the preparation time of the dephosphorization agent required in the second blow, and the waiting time for the start of the second blow was 0 minutes. The parameter reflecting the fluctuation of the direct factor indicating the exclusion situation is thought to affect the excretion amount more than the primary blown slag basicity, and the standard deviation (σ) of the basic performance value of all 10 charges is 0.035, which is the 2nd order. The basicity of the blown slag basicity could be adjusted with better precision.

In Example 3 of the present invention, in addition to the primary blown slag amount, the primary blown slag basicity and discharge start angle are all considered to estimate the amount of exhaust. For the same reason as in Inventive Example 2, the waiting time for the second blow start was 0 minutes. By considering all of these parameters, the secondary blown slag basicity can be adjusted with better precision, and the standard deviation (σ) of the basicity performance value of the total 10 charges has decreased to 0.019.

1: iron scrap
2: converter (converter type container)
3: chartered ladle
4: charter boat
5: (n-1) second blow blow slag
6: 1st Blowing Supplementary Materials
7: Primary blow slag
8: Injured lance
9: 1st blow slag coming to 2nd blow
10: Primary blown slag discharged outside the furnace
11: Secondary Blowing Supplementary Materials
12: 2nd blow slag

Claims (4)

As a method of refining molten iron,
When the refining of molten iron is performed using a converter type container, the intermediate exclusion amount of the primary blown slag is set as a target variable in advance, and at least one of the primary blown slag basicity and the slag discharge start angle, and the primary blown off. A multiple regression analysis is performed using information including the amount of slag as an explanatory variable.
The molten iron is charged into the converter-type container to perform primary blowing for desulfurization only or desulfurization and dephosphorization purposes,
Subsequently, after performing the intermediate exclusion for discharging a part of the slag after the primary blown treatment out of the converter type container, the intermediate exclusion amount of the primary blown slag and the residual amount in the furnace of the primary blown slag using the results of the multiple regression analysis Calculate
Subsequently, in the second blow blowing by adding a lime-based solvent to the molten iron and slag after the first blow blow remaining in the converter-type container, the residual amount in the furnace of the first blow blow slag and the first blow blow slag A method for refining molten iron using a calculated composition to calculate the amount of a lime-based solvent to be added in the secondary blow, and to increase the precision of basicity control of the secondary blow slag without waiting time for the second blow. According to claim 1,
A method for refining molten iron, wherein the intermediate exclusion amount of the primary blown slag is calculated using the following formula (1).
W _D (n) = a1 + b1 × W ₁ (n) × 1000/{W _H (n) + W _SC (n)} – c1 × B _C,1 (n)… (1) Expression
Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)
W ₁ (n): Primary blown slag amount in nth charge (t/ch)
W _H (n): Charge of the molten iron in the nth charge (t/ch)
W _SC (n): scrap charge in the nth charge (t/ch)
B _C,1 (n): Primary blown slag basicity (dimension number)
a1, b1, c1: integer According to claim 1,
A method for refining molten iron, wherein the intermediate exclusion amount of the primary blown slag is calculated using the following formula (2).
W _D (n) = a2 + b2 × W ₁ (n) × 1000/{W _H (n) + W _SC (n)} – d2 × θ(n)… (2) Expression
Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)
W ₁ (n): Primary blown slag amount in nth charge (t/ch)
W _H (n): Charge of the molten iron in the nth charge (t/ch)
W _SC (n): scrap charge in the nth charge (t/ch)
θ(n): Slag discharge start angle (°)
a2, b2, d2: integer According to claim 1,
A method for refining molten iron, wherein the intermediate exclusion amount of the primary blown slag is calculated using the following formula (3).
W _D (n) = a3 + b3 × W ₁ (n) × 1000/{W _H (n) + W _SC (n)}-c3 × B _C,1 (n)-d3 × θ(n)… (3) Expression
Here, W _D (n): Intermediate exclusion amount of primary blown slag at the nth charge (t/ch)
W ₁ (n): Primary blown slag amount in nth charge (t/ch)
W _H (n): Charge of the molten iron in the nth charge (t/ch)
W _SC (n): scrap charge in the nth charge (t/ch)
B _C,1 (n): Primary blown slag basicity (dimension number)
θ(n): Slag discharge start angle (°)
a3, b3, c3, d3: integer

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