Control device for vacuum degassing equipment, control method for vacuum degassing equipment, operation method, and method for manufacturing molten steel

Abstract

The present invention provides a control device for a vacuum degassing facility, which estimates the carbon concentration in molten steel with high precision and terminates decarburization at an appropriate timing. A control device (10) for a vacuum degassing facility is provided with: an operation information input unit (11) for inputting information relating to the weight and component concentration of molten steel before decarburization, an operation performance value during execution of the decarburization, and information relating to auxiliary raw materials; a component calculation unit (12) that estimates the carbon concentration in the molten steel; a correction calculation unit (13) that calculates a correction parameter for correcting the estimated value of the amount of carbon discharged from the vacuum degassing facility and the estimated carbon concentration in the molten steel; and a decarburization process control unit (14) that terminates the decarburization process when the carbon concentration in the molten steel corrected by the correction parameter reaches a target value.

Description

Technical Field

[0001] The present invention relates to a control device of vacuum degassing equipment, a control method and an operation method of vacuum degassing equipment, and a method for manufacturing molten steel. Background Art

[0002] In the steelmaking process, impurities such as carbon are removed from molten iron and useful alloying components are added to adjust the composition of molten steel. In particular, for carbon, vacuum degassing equipment is used to place molten steel in a vacuum environment in advance to promote decarburization, which can produce extremely low carbon steel with a carbon concentration of less than 10ppm in molten steel.

[0003] Here, in vacuum degassing, the carbon concentration in molten steel is not directly measured but is only indirectly estimated from the concentrations of carbon monoxide and carbon dioxide in the exhaust gas. In the production of ultra-low carbon steel, operators tend to perform decarburization for too long because they are worried that the carbon concentration may deviate from the standard.

[0004] In order to solve the problem of prolonged treatment time caused by excessive decarburization treatment, it is effective to estimate the carbon concentration in the molten steel during treatment with high accuracy, and various methods have been proposed so far. The methods for estimating the carbon concentration in the molten steel can be roughly divided into two types. One is a method of physically examining the details of the decarburization reaction in the vacuum degassing equipment and constructing a decarburization reaction model (for example, non-patent document 1). The other is a method of calculating the decarburization amount based on the flow rate and measured value of the exhaust gas discharged from the vacuum degassing equipment during the treatment (for example, the measured value of the component concentration) to estimate the carbon concentration in the molten steel. In addition, as a combination of the two, the following method has been proposed: the parameters of the decarburization reaction model are determined based on the exhaust gas measurement values, and the decarburization reaction model with the determined parameters is used to estimate the carbon concentration in the molten steel (for example, patent document 1 and patent document 2).

[0005] For example, Patent Document 3 discloses a method for correcting an estimated value of carbon concentration in molten steel using a difference between a decarburization rate calculated from a decarburization reaction model and a decarburization rate calculated from exhaust gas measurement values ​​based on observer theory.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-330512

[0007] Patent Document 2: Japanese Patent Application Publication No. 2015-101742

[0008] Patent Document 3: Japanese Patent Application Publication No. 2006-104521

[0009] Non-patent document 1: Shinya Kitamura, the remaining three, "Vacuum Degassing Furnace Decarburization Reaction Model (Decarburization Reaction Model in Vacuum Degassing Furnace)", Iron and Steel (Iron and Steel) Vol. 80 (1994) No. 3, p. 213-218

[0010] Non-patent document 2: Yoshihiko Higuchi and two others, "Effects of [C], [O] and vacuum degree on RH vacuum decarburization", Iron and Steel Vol. 84 (1998) No. 10, p. 709-714

[0011] In the case of constructing a decarburization reaction model based on physical observation, if you want to express the details of the decarburization reaction, it is often difficult to determine the model parameters. For example, the decarburization reaction model proposed in non-patent document 1 is introduced with an additional pressure parameter for formulating the generation of CO bubbles inside the molten steel, but this value is determined by the results of basic experiments. As pointed out in non-patent document 2, there is no verification that there is no problem using the same additional pressure parameter value in the actual vacuum degassing equipment. In addition, it is believed that the device shape and operating conditions of the vacuum degassing equipment are different, so the model parameters also change. Therefore, even if the decarburization reaction model proposed in non-patent document 1 is introduced, if the device shape or operating conditions are different, it is impossible to make a high-precision inference of the carbon concentration in the molten steel.

[0012] As described above, the techniques of Patent Documents 1 and 2 determine the parameters of the decarburization reaction model based on the exhaust gas measurement values ​​reflecting the actual decarburization performance, thereby, for example, being able to set the model parameters that match the device shape and operating conditions. However, since the error included in the exhaust gas measurement values ​​is directly reflected in the model parameters, a method for further improving the accuracy of the estimated value of the carbon concentration in molten steel is required.

[0013] As described above, the technology of Patent Document 3 corrects the estimated value of carbon concentration in molten steel based on the difference between the decarburization rate calculated by the decarburization reaction model and the decarburization rate calculated from the exhaust gas measurement value, but it is based on the premise that the decarburization reaction model is accurate. Therefore, since the error of the decarburization reaction model is reflected in the estimated result, a method for further improving the accuracy of the estimated value of carbon concentration in molten steel is required.

[0014] As described above, in the prior art, when there may be errors in the decarburization reaction model and errors in the exhaust gas measurement value, calculation is performed on the premise that at least one of them is accurate. The prior art ignores one of the errors and estimates the carbon concentration in the molten steel, so there is a problem that the accuracy of estimating the carbon concentration in the molten steel is insufficient. Summary of the invention

[0015] The present disclosure, which was completed in view of the above circumstances, aims to provide a control device for vacuum degassing equipment, a control method for vacuum degassing equipment, an operating method, and a method for producing molten steel, which can estimate the carbon concentration in molten steel with high accuracy and terminate the decarburization treatment at an appropriate timing.

[0016] (1) A control device for vacuum degassing equipment according to an embodiment of the present disclosure controls the operation of the vacuum degassing equipment for decarburizing molten steel by placing the molten steel under a reduced pressure environment, and includes:

[0017] an operation information input unit for inputting information related to the weight and component concentration of the molten steel before the decarburization treatment, operation performance values ​​including measurement results of the flow rate and component concentration of exhaust gas discharged from the vacuum degassing equipment during the decarburization treatment, and information related to auxiliary raw materials added during the decarburization treatment;

[0018] a component calculation unit that estimates the carbon concentration in the molten steel based on information on the weight and component concentration of the molten steel before the decarburization treatment and the operation performance value;

[0019] a correction calculation unit that calculates a correction parameter for correcting an estimated value of the amount of carbon discharged from the vacuum degassing equipment and the estimated carbon concentration in the molten steel based on the estimated carbon concentration in the molten steel, the measurement results of the flow rate and component concentration of the exhaust gas, and the calculation result of the carbon balance; and

[0020] A decarburization control unit is configured to terminate the decarburization process when the carbon concentration in the molten steel corrected by the correction parameter reaches a target value.

[0021] (2) As an embodiment of the present disclosure, based on (1), wherein:

[0022] The correction calculation unit calculates the correction parameter based on an evaluation function based on a difference between a reduction in the amount of carbon in molten steel and an amount of carbon in exhaust gas.

[0023] (3) As an embodiment of the present disclosure, based on (2), wherein:

[0024] The evaluation function includes a term of a square value calculated by subtracting the carbon content in the exhaust gas from the carbon content in the molten steel and the carbon content contained in the auxiliary raw materials, and a term of a square value of a difference between the carbon content in the exhaust gas and a decarburization rate per unit time.

[0025] (4) As an embodiment of the present disclosure, based on (2) or (3), wherein:

[0026] The evaluation function includes the correction parameter of the exhaust gas measurement value set as a correction coefficient to be multiplied by the value before correction.

[0027] (5) A control method for vacuum degassing equipment according to an embodiment of the present disclosure is performed by a control device for vacuum degassing equipment for controlling the operation of the vacuum degassing equipment for placing molten steel under a reduced pressure environment to perform decarburization, and includes:

[0028] An input step, in which information related to the weight and component concentration of the molten steel before the decarburization treatment, operation performance values ​​including measurement results of the flow rate and component concentration of exhaust gas discharged from the vacuum degassing equipment during the decarburization treatment, and information related to auxiliary raw materials added during the decarburization treatment are input;

[0029] a composition calculation step of estimating the carbon concentration in the molten steel based on the information on the weight and composition concentration of the molten steel before the decarburization treatment and the operation performance value;

[0030] a correction calculation step, in which a correction parameter for correcting an estimated value of the amount of carbon discharged from the vacuum degassing equipment and the estimated carbon concentration in the molten steel is calculated based on the estimated carbon concentration in the molten steel, the measurement results of the flow rate and component concentration of the exhaust gas, and the calculation result of the carbon balance; and

[0031] and a decarburization treatment terminating step of terminating the decarburization treatment when the carbon concentration in the molten steel corrected by the correction parameter reaches a target value.

[0032] (6) As an embodiment of the present disclosure, based on (5), wherein:

[0033] The correction calculation step calculates the correction parameter based on an evaluation function based on a difference between a reduction in the amount of carbon in the molten steel and an amount of carbon in the exhaust gas.

[0034] (7) As an embodiment of the present disclosure, based on (6), wherein:

[0035] The evaluation function includes a term of a square value calculated by subtracting the carbon content in the exhaust gas from the carbon content in the molten steel and the carbon content contained in the auxiliary raw materials, and a term of a square value of a difference between the carbon content in the exhaust gas and a decarburization rate per unit time.

[0036] (8) As an embodiment of the present disclosure, based on (6) or (7), wherein:

[0037] The evaluation function includes the correction parameter of the exhaust gas measurement value set as a correction coefficient to be multiplied by the value before correction.

[0038] (9) An operating method according to an embodiment of the present disclosure performs the control method of the vacuum degassing equipment according to any one of (5) to (7) to operate the vacuum degassing equipment.

[0039] (10) A method for producing molten steel according to an embodiment of the present disclosure produces the refined molten steel by refining the molten steel in a vacuum degassing facility operated by the operation method of (9).

[0040] According to the method disclosed in the present invention, the decarburization reaction model, the exhaust gas measurement value, and the error contained in the carbon content in the exhaust gas calculated based on the exhaust gas measurement value can be corrected simultaneously. Therefore, it is possible to provide a control device for a vacuum degassing device, a control method for a vacuum degassing device, an operating method, and a method for manufacturing molten steel, which can estimate the carbon concentration in molten steel with high accuracy, end the decarburization treatment at an appropriate time relative to the carbon concentration standard, and shorten the decarburization treatment time. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a block diagram showing the structure of a control device of a vacuum degassing facility as one embodiment of the present disclosure.

[0042] Figure 2 This is a flowchart showing the flow of the decarburization control process as one embodiment of the present disclosure.

[0043] Figure 3 It is a time-series calculation result of the correction coefficient α of the amount of carbon in the exhaust gas which is a correction parameter in the embodiment of the present disclosure.

[0044] Figure 4 is the carbon concentration correction value ΔC in the vacuum tank molten steel as the correction parameter in the embodiment of the present disclosure V The timing calculation results. DETAILED DESCRIPTION

[0045] Hereinafter, the control device and control method of the vacuum degassing equipment of the embodiment of the present disclosure will be described with reference to the accompanying drawings. In the present embodiment, the vacuum degassing equipment is described as the RH vacuum degassing equipment, but it is not limited to the RH vacuum degassing equipment. The control method described below can also be implemented for an equipment having only one dipping pipe immersed in the vacuum tank and the ladle and sucking into the molten steel vacuum tank, or an equipment (device) having no vacuum tank but making the surface of the molten steel in the ladle in a vacuum state.

[0046] [structure]

[0047] Figure 11 is a block diagram showing the structure of a control device 10 of an embodiment of the present disclosure. The control device 10 is a control device 10 of a vacuum degassing device 100, and controls the operation of the vacuum degassing device 100. In the vacuum degassing device 100, at least molten steel is placed in a reduced pressure environment to thereby perform a decarburization treatment. In the present embodiment, the control device 10 executes a control method of the vacuum degassing device 100 described later, thereby operating the vacuum degassing device 100. That is, as an operation method of the vacuum degassing device 100, the control of the vacuum degassing device 100 is performed. In addition, in the present embodiment, the vacuum degassing device 100 constitutes a part of a molten steel manufacturing device. A method for manufacturing molten steel is executed in the molten steel manufacturing device, and the method for manufacturing molten steel includes refining molten steel in the vacuum degassing device 100, thereby manufacturing refined molten steel.

[0048] like Figure 1 As shown, the control device 10 includes an operation information input unit 11 , a component calculation unit 12 , a correction calculation unit 13 , and a decarburization treatment control unit 14 .

[0049] The operation information input unit 11 acquires information about the operation using the vacuum degassing equipment 100. In the present embodiment, the operation information input unit 11 inputs information related to the weight and component concentration of the molten steel before decarburization treatment, operation performance values ​​including the measurement results of the flow rate and component concentration of the exhaust gas discharged from the vacuum degassing equipment 100 during the decarburization treatment, and information related to the auxiliary raw materials fed during the decarburization treatment.

[0050] The component calculation unit 12 estimates the carbon concentration in the molten steel based on the operation information acquired by the operation information input unit 11. In this embodiment, the component calculation unit 12 estimates the carbon concentration in the molten steel based on the information related to the weight and component concentration of the molten steel before decarburization and the operation performance value.

[0051] The correction calculation unit 13 calculates a correction parameter for correcting the estimated value of the carbon amount discharged from the vacuum degassing equipment 100 and the estimated carbon concentration in the molten steel of the molten steel. In the present embodiment, the correction calculation unit 13 calculates the correction parameter for correcting the estimated value of the carbon amount discharged from the vacuum degassing equipment 100 and the estimated carbon concentration in the molten steel of the molten steel based on the estimated carbon concentration in the molten steel of the molten steel, the measurement results of the flow rate and component concentration of the exhaust gas, and the calculation results of the carbon balance.

[0052] The decarburization control unit 14 ends the decarburization when the carbon concentration in the molten steel corrected by the correction parameter reaches the target value.

[0053] The control device 10 is constituted by, for example, an information processing device such as a computer. The control device 10 may also be constituted so that a program is executed by an arithmetic processing device such as a CPU (Central Processing Unit) of the information processing device, and functions as an operation information input unit 11, a component calculation unit 12, a correction calculation unit 13, and a decarburization control unit 14.

[0054] The vacuum degassing equipment 100 may also be a known structure. As described above, the RH vacuum degassing equipment is used in the present embodiment. The RH vacuum degassing equipment, for example, includes a vacuum tank and a ladle, which are connected by two immersion pipes. The vacuum tank is connected to an exhaust gas pipe, through which the gas inside the vacuum tank is discharged, thereby reducing the pressure on the vacuum tank and sucking the molten steel in the ladle. Then, an inert gas is blown in through a pipe from one side of the immersion pipe, so that the molten steel refluxes between the vacuum tank and the ladle. In addition, in order to promote the decarburization treatment, there is a case where oxygen is blown in from a blowing gun arranged in the vacuum tank.

[0055] The control device 10 having such a structure can estimate the carbon concentration in the molten steel with high accuracy by executing the decarburization control process shown below. By making a high-precision estimate, it is possible to avoid the decarburization process being performed too long due to the concern that the carbon concentration deviates from the standard, and as a result, the decarburization process time can be shortened. Figure 2 , a flow of a decarburization control process as one embodiment of the present disclosure is described.

[0056] [Decarburization control treatment]

[0057] Figure 2 : is a flowchart showing the flow of the decarburization control process executed by the control device 10 . Figure 2 The flowchart shown starts when a command to execute the decarburization process is input, and the process of step S1 is performed.

[0058] In the process of step S1, the operation information input unit 11 obtains the weight of the molten steel measured before the decarburization process begins and the component concentration obtained by component analysis. Examples of components for which concentrations are measured include C, Si, Mn, P, S, Al, Cu, Nb, Ti, etc. In addition, if the calculation of the component calculation unit 12 requires it, the operation information input unit 11 may also obtain the measurement result of the molten steel temperature. Figure 2 In the example of , the temperature is also acquired. Thus, the process of step S1 is completed, and the decarburization control process enters the process of step S2.

[0059] In the process of step S2, the operation information input unit 11 obtains the operation performance value in the decarburization process. The operation performance value obtains the items required for calculation in the component calculation unit 12 and the correction calculation unit 13. In the present embodiment, the operation information input unit 11 obtains the measurement results of the flow rate and component concentration of the exhaust gas discharged from the vacuum degassing equipment 100 as the operation performance value. In addition, in the present embodiment, the operation information input unit 11 obtains information related to the auxiliary raw materials added during the execution of the decarburization process. As a specific example, the information related to the auxiliary raw materials is the type and amount of the auxiliary raw materials. In addition, information such as the pressure of the vacuum tank in the decarburization process, the flow rate of the inert gas for reflux, and the oxygen flow rate from the top blowing lance can also be input by the operation information input unit 11. When the process of step S2 is performed after step S6 described later, the operation information input unit 11 can also obtain the estimated value of the molten steel component headed by the estimated value of the carbon concentration in the molten steel. Thus, the process of step S2 is completed, and the decarburization control process enters the process of step S3 and step S4. Here, step S1 and step S2 correspond to the input step.

[0060] In the process of step S3, the component calculation unit 12 calculates (estimates) the carbon concentration in the molten steel based on the pre-set decarburization reaction model. In the present embodiment, the component calculation unit 12 obtains input information such as the operation performance value at predetermined intervals or continuously, and estimates the carbon concentration in the molten steel of the molten steel at predetermined intervals or continuously. The decarburization reaction model used by the component calculation unit 12 has two requirements: the ability to estimate the carbon concentration in the molten steel at predetermined intervals or continuously, and the decarburization rate, that is, the rate of change of the carbon concentration in the molten steel, is expressed as a function of the carbon concentration in the molten steel in the portion where the decarburization reaction occurs. The portion where the decarburization reaction occurs corresponds to the vacuum tank in the RH vacuum degassing equipment. These two points are conditions that a general decarburization reaction model naturally satisfies.

[0061] In the present embodiment, in the decarburization treatment in the RH vacuum degassing equipment, the molten steel concentrations in the vacuum tank and the ladle are respectively set to be in a completely mixed state, and the decarburization reaction models of the following equations (1) and (2) are used.

[0062] [Formula 1]

[0063]

[0064] Here, w is the mass of molten steel [kg]. C is the carbon concentration in molten steel [ppm]. Q is the molten steel reflux rate [kg / s]. ak is the decarburization reaction capacity coefficient [kg / s]. E It is the equilibrium value of carbon concentration in molten steel in the vacuum tank [ppm]. alloyis the carbon concentration in the molten steel converted to the weight of carbon in the auxiliary raw material [ppm]. Formula (2) clearly shows that the decarburization reaction capacity coefficient depends on the carbon concentration in the molten steel in the vacuum tank. In addition, the subscript L represents the physical quantity of the molten steel in the ladle. The subscript V represents the physical quantity of the molten steel in the vacuum tank. For example, C V represents the carbon concentration in the molten steel in the vacuum tank [ppm]. The subscript i is used to identify the specific decarburization reaction site. Examples of the specific decarburization reaction site include the molten steel surface, reflux inert gas bubbles, etc.

[0065] The amount of carbon discharged as exhaust gas is calculated by the second term of formula (2). In addition, the change in carbon concentration in molten steel per microsecond is calculated using formula (1) and formula (2), and the carbon concentration in molten steel after a microsecond is calculated by subtracting the change from the current carbon concentration in molten steel. Thus, the processing of step S3 is completed. Here, step S3 corresponds to the component calculation step.

[0066] In the process of step S4, the correction calculation unit 13 calculates the amount of carbon in the exhaust gas based on the measurement results of the exhaust gas flow rate and component concentration. The carbon discharged from the molten steel takes the form of CO or CO2, and based on this, the amount of carbon in the exhaust gas per unit time is expressed as the following formula (3). In addition, the cumulative amount of discharged carbon from the start of the process (time 0) to time t is expressed as the following formula (4).

[0067] [Formula 2]

[0068]

[0069] Here, q C，OG (t) is the amount of carbon in the exhaust gas per unit time at time t [kg / s]. m C is the molar mass of carbon [g / mol]. off (t) is the volume flow rate of exhaust gas at time t [Nm 3 / s]. CO (t) is the CO concentration in the exhaust gas at time t [vol %]. CO2 (t) is the CO2 concentration in the exhaust gas at time t [vol %]. C，OG (t) is the cumulative amount of carbon discharged from time 0 to time t [kg].

[0070] Here, in the case where the measurement results of the flow rate and component concentration of the exhaust gas include known errors, it is preferred that the correction calculation unit 13 performs the calculation of formula (3) after removing or reducing the known errors. For example, in the case where the CO concentration measurement value and the CO2 concentration measurement value also take non-zero values ​​when no measurement is performed (in the case of zero point offset), the value obtained by subtracting the zero point deviation from the measured value can also be used for calculation. Thus, the processing of step S4 is completed. If steps S3 and S4 are completed, the decarbonization control processing enters the processing of step S5. Here, the processing of step S4 can be executed independently from the processing of step S3, or step S3 and step S4 can be executed in parallel as in the present embodiment. However, it is not limited to parallel processing, and step S3 and step S4 can also be executed sequentially. At this time, there is no limitation on which one is executed first (execution order).

[0071] Here, according to the law of conservation of mass, the total of the amount of carbon in the molten steel and the amount of carbon discharged from the molten steel is equal to the total of the amount of carbon in the molten steel before the decarburization treatment and the amount of carbon contained in the auxiliary raw materials fed during the treatment. However, in general, the calculation using the amount of carbon in the molten steel based on the carbon concentration in the molten steel estimated in step S3 and the amount of carbon discharged estimated in step S4 does not satisfy the law of conservation of mass. In this embodiment, the correction calculation unit 13 obtains the deviation from the law of conservation of mass as the carbon balance calculation, assuming that the deviation is caused by an error in either the decarburization reaction model or the exhaust gas measurement value, and sets parameters for correcting the respective errors.

[0072] In the process of step S5, the correction calculation unit 13 determines the correction parameter of the calculation results in the processes of steps S3 and S4 in order to satisfy the law of conservation of mass. V [ppm] is a correction parameter of the decarbonization reaction model. In addition, the correction coefficient α of the amount of carbon in the exhaust gas is a correction parameter of the exhaust gas measurement value. Using the above correction parameters, the calculation results in the processing of step S3 and step S4 are corrected as follows.

[0073] First, the carbon concentration in the vacuum tank steel water is added with the carbon concentration correction value ΔC in the vacuum tank steel water. V , and was corrected to C V +ΔC V The amount of carbon in the exhaust gas per unit time is multiplied by the correction coefficient α, and is corrected to αq C，OG (t). In addition, the accumulated amount of carbon discharged is multiplied by the carbon amount correction coefficient α in the exhaust gas and corrected to αQ C，OG (t). The correction coefficient α of the carbon content in the exhaust gas and the correction value ΔC of the carbon concentration in the molten steel in the vacuum tank as correction parameters V It is determined as the solution to the optimization problem represented by the following equation (5).

[0074] [Formula 3]

[0075]

[0076] Here, Q C，IN It is the total amount of carbon in the molten steel before decarburization and the amount of carbon contained in the auxiliary raw materials added during the decarburization process [kg]. C，ST Q is the amount of carbon in molten steel [kg]. C，IN With Q C，ST The difference includes the reduction in carbon content in molten steel. C，OG The difference in (t) corresponds to the difference between the reduction amount and the amount of carbon in the exhaust gas (the cumulative amount of carbon discharged). deC (ΔC V ) is the decarburization rate [kg / s] calculated by the component calculation unit 12 based on the decarburization reaction model. ave is a standard value of α based on the actual operation performance value. σ1, σ2, σ3, and σ4 are weighting coefficients, which are set by the user, for example. Q C , ST (ΔC V ) is defined by equation (6). In addition, deC(ΔC V ) is defined using formula (7).

[0077] [Formula 4]

[0078] Q C，ST (ΔC V )=w L C L +w V (C V +ΔC V )…Formula (6)

[0079] deC(ΔC V )=∑ i ak i (C v +ΔC V ){(C V +ΔC V )-C E,i}…Formula (7)

[0080] The first term of formula (5) represents the deviation from the law of conservation of mass with respect to carbon. When the law of conservation of mass is fully satisfied, the first term is 0. The second term of formula (5) represents the deviation from the amount of carbon in the exhaust gas per unit time and the decarburization rate calculated based on the decarburization reaction model. When the amount of carbon in the exhaust gas per unit time is consistent with the decarburization rate calculated based on the decarburization reaction model, the second term is 0. The third and fourth terms of formula (5) are terms used to prevent the correction parameters from taking extreme values. First, regarding the correction coefficient α for the amount of carbon in the exhaust gas, since the deterioration of the exhaust gas measuring device and the deterioration of the measurement environment are carried out on a time scale that is sufficiently longer than the time for one vacuum degassing treatment, it is expected that the correction coefficient α that is consistent with the standard value (α) will be continuously taken during the continuous vacuum degassing treatment. ave ) has approximately the same value. Therefore, the third term adds α and α ave The square of the difference of . ave For example, it can be determined by calculating the average value of the carbon content correction coefficient α in the exhaust gas for the most recently processed predetermined number of charges. The predetermined number of times is preferably multiple and is not limited to a specific value. In addition, regarding the carbon concentration correction value ΔC in the vacuum tank molten steel V , we expect the decarbonization reaction model to have a smaller error. Therefore, the fourth term adds ΔC V In the present embodiment, the correction calculation unit 13 calculates the correction parameter by minimizing the evaluation function of equation (5), but a maximized evaluation function may be used. That is, the correction calculation unit 13 may also obtain the correction parameter that minimizes or maximizes the evaluation function.

[0081] Here, the carbon content correction factor α in the exhaust gas is added to the carbon concentration correction value ΔC in the vacuum tank molten steel. V For example, even if the correction value Δq of the amount of carbon in the exhaust gas per unit time is used as the correction parameter of the exhaust gas measurement value instead of the correction coefficient α of the amount of carbon in the exhaust gas, C , OG [kg / s], and the amount of carbon in the exhaust gas per unit time is q C , OG (t)+Δq C , OG The processing of the carbon concentration cannot improve the accuracy of carbon concentration estimation. It is known that the error of the exhaust gas measurement value varies greatly with the time of decarbonization treatment. Therefore, when the correction coefficient α of the carbon content in the exhaust gas is set to the added correction value (Δq C , OG), the error removal may become insufficient depending on the timing of the decarburization treatment applied. In addition, it is difficult to change the correction value according to the timing of the decarburization treatment. Therefore, as in the present embodiment, the correction coefficient α of the carbon content in the exhaust gas is preferably set to a correction coefficient multiplied by the value before correction.

[0082] The evaluation function is not limited to the above-mentioned formula (5), and can be replaced by, for example, the carbon concentration correction value ΔC in the vacuum tank molten steel V The carbon concentration correction factor a in vacuum tank steel is used. V At this time, the carbon concentration in the vacuum tank steel water is multiplied by the carbon concentration correction factor a in the vacuum tank steel water. V , and was modified to a V ·C V In addition, the correction coefficient α of the carbon content in the exhaust gas and the correction coefficient a of the carbon concentration in the molten steel in the vacuum tank are used as correction parameters. V It is determined as the solution to the optimization problem represented by the following equation (8).

[0083] [Formula 5]

[0084]

[0085] In the absence of the need to correct the estimated carbon concentration in molten steel based on the decarburization reaction model, a V is 1. The fourth term of formula (8) adds a V The square of the difference from 1. Q C , ST ′(a V ) is defined by formula (9). In addition, deC′(a V ) is defined using formula (10).

[0086] [Formula 6]

[0087] Q C，ST′ (a V )=w L C L +w V a V C V …Formula (9)

[0088] deC′(a V )=∑ i ak i (a V C V )(a V C V -C E，i )…Formula (10)

[0089] The minimization problem of the evaluation function using equations (5) and (8) can be solved using a known nonlinear optimization method. The following is an explanation using the evaluation function of equation (5). The correction calculation unit 13 determines the correction parameters (the correction coefficient α of the carbon content in the exhaust gas and the correction value ΔC of the carbon concentration in the vacuum tank molten steel) by solving the minimization problem of equation (5). V ). Thus, the process of step S5 is completed, and the decarburization control process enters the process of step S6. Here, step S5 corresponds to the correction calculation step.

[0090] In the process of step S6, the estimated value of carbon concentration in molten steel obtained in step S3 is added with the correction value ΔC of carbon concentration in molten steel in the vacuum tank obtained in step S5. V To update the carbon concentration in the molten steel. Thus, the process of step S6 is completed, and the decarburization control process enters the process of step S7.

[0091] In the process of step S7, the decarburization control unit 14 determines whether the carbon concentration in the molten steel obtained in step S6 has reached a predetermined target value (whether it has become below the target value). If the carbon concentration in the molten steel after correction is higher than the target value, the process returns to step S2, and the process of step S2 and thereafter is repeated using the newly input operation performance value. On the other hand, if the carbon concentration in the molten steel after correction becomes below the target value, the decarburization process ends. Here, step S7 corresponds to the decarburization process end step.

[0092] As described above, the control device 10 of the vacuum degassing equipment 100, the control method and the operating method of the vacuum degassing equipment 100, and the method for producing molten steel of the present embodiment can assume the errors of both the decarburization reaction model and the exhaust gas measurement value through the above-mentioned structure and process, and correct these errors at the same time. Therefore, it is possible to provide a control device 10 of the vacuum degassing equipment 100, the control method and the operating method of the vacuum degassing equipment 100, and the method for producing molten steel, which can estimate the carbon concentration in the molten steel with high accuracy, end the decarburization treatment at an appropriate time relative to the carbon concentration standard, and shorten the decarburization treatment time.

[0093] (Example)

[0094] Hereinafter, the effects of the present disclosure will be specifically described based on examples, but the present disclosure is not limited to the contents of the examples.

[0095] As this embodiment, RH vacuum degassing equipment was used to carry out decarburization treatment, and an extremely low carbon molten steel having a standard upper limit of carbon concentration of 25ppm was produced. At the end of the decarburization treatment, a portion of the molten steel was collected as a sample, and the carbon concentration in the molten steel of the sample was measured. The end of the decarburization treatment depends on the judgment of the operator. In addition, the carbon concentration in the molten steel was estimated according to the method of the present invention and the comparison method. The method of the present invention estimates the carbon concentration in the molten steel as in the above-mentioned embodiment. Table 1 shows the results of comparing the estimated value at the end of the decarburization treatment with the measured value. Here, as a comparison method, two methods were used to estimate the carbon concentration in the molten steel. One is a method of calculating the decarburization amount based on the exhaust gas measurement value to estimate the carbon concentration (exhaust gas model in Table 1). However, the average value of the carbon correction coefficient α in the exhaust gas, that is, α, which was obtained based on the operating performance of the verification charge and the charge processed at the same time as them, was calculated. ave The decarburization amount is multiplied by the decarburization amount calculated from the exhaust gas measurement value. Another method is to use only the decarburization reaction model to infer the carbon concentration in molten steel (the decarburization reaction model in Table 1). The latter decarburization reaction model is also used in the calculation of the carbon concentration in molten steel in the method of the present invention.

[0096] Figure 3 The time variation of the correction coefficient α of the amount of carbon in the exhaust gas as a correction parameter calculated using the verification charge A in Table 1 is shown. Figure 4 The carbon concentration correction value ΔC in the vacuum tank molten steel calculated as the correction parameter using the verification charge A in Table 1 is shown as follows: V time changes.

[0097] [Table 1]

[0098] (Table 1)

[0099]

[0100] As shown in Table 1, the method of the present invention estimates a value close to the actual measured value of carbon concentration in molten steel compared to the comparative method. Therefore, the method of the present invention, which confirms the errors of both the assumed decarburization reaction model and the exhaust gas measurement value and corrects them, is effective in improving the accuracy of carbon concentration estimation in molten steel.

[0101] The embodiments of the present disclosure are described based on the drawings and examples, but it should be noted that it is easy for those skilled in the art to make various deformations or modifications based on the present disclosure. Therefore, it should be noted that these deformations or modifications are also included in the scope of the present disclosure. For example, the functions included in each structural part or each step can be reconfigured without logical contradiction, and multiple structural parts or steps can be combined into one, or divided. The embodiments of the present disclosure can also be implemented as a storage medium that records a program executed by a processor possessed by the device. It should be understood that these are also included in the scope of the present disclosure.

[0102] Description of Reference Numerals

[0103] 10 ... control device; 11 ... operation information input unit; 12 ... component calculation unit; 13 ... correction calculation unit; 14 ... decarburization treatment control unit; 100 ... vacuum degassing equipment.

Claims

1. A control device for vacuum degassing equipment, which controls the operation of the vacuum degassing equipment for placing molten steel under a reduced pressure environment to perform decarburization treatment, The control device of the vacuum degassing equipment is characterized by comprising: an operation information input unit for inputting information related to the weight and component concentration of the molten steel before the decarburization treatment, operation performance values ​​including measurement results of the flow rate and component concentration of exhaust gas discharged from the vacuum degassing equipment during the decarburization treatment, and information related to auxiliary raw materials added during the decarburization treatment; a component calculation unit that estimates the carbon concentration in the molten steel based on information on the weight and component concentration of the molten steel before the decarburization treatment and the actual operation performance value; a correction calculation unit that calculates a correction parameter for correcting an estimated value of the amount of carbon discharged from the vacuum degassing equipment and the estimated carbon concentration in the molten steel based on the estimated carbon concentration in the molten steel, the measurement results of the flow rate and component concentration of the exhaust gas, and the calculation result of the carbon balance; as well as A decarburization treatment control unit is configured to terminate the decarburization treatment when the carbon concentration in the molten steel corrected by the correction parameter reaches a target value.

2. The control device of the vacuum degassing equipment according to claim 1, characterized in that: The correction calculation unit calculates the correction parameter based on an evaluation function based on a difference between a reduction amount of carbon in molten steel and a carbon amount in exhaust gas.

3. The control device of the vacuum degassing equipment according to claim 2, characterized in that: The evaluation function includes a term of a square value calculated by subtracting the carbon amount in the exhaust gas from the carbon amount in the molten steel and the carbon amount contained in the auxiliary raw material, and a term of a square value of a difference between the carbon amount in the exhaust gas and a decarburization rate per unit time.

4. The control device of the vacuum degassing equipment according to claim 2 or 3, characterized in that: The evaluation function includes the correction parameter of the exhaust gas measurement value set as a correction coefficient to be multiplied by a value before correction.

5. A method for controlling a vacuum degassing device, the method being performed by a control device for controlling the operation of the vacuum degassing device for placing molten steel under a reduced pressure environment to thereby perform a decarburization treatment, The control method of the vacuum degassing equipment is characterized by comprising: An input step, in which information related to the weight and component concentration of the molten steel before the decarburization treatment, operation performance values ​​including measurement results of the flow rate and component concentration of exhaust gas discharged from the vacuum degassing equipment during the decarburization treatment, and information related to auxiliary raw materials added during the decarburization treatment are input; a composition calculation step of estimating the carbon concentration in the molten steel based on the information on the weight and composition concentration of the molten steel before the decarburization treatment and the actual operation performance value; a correction calculation step, in which a correction parameter for correcting an estimated value of the amount of carbon discharged from the vacuum degassing equipment and the estimated carbon concentration in the molten steel is calculated based on the estimated carbon concentration in the molten steel, the measurement results of the flow rate and component concentration of the exhaust gas, and the calculation result of the carbon balance; as well as and a decarburization treatment terminating step of terminating the decarburization treatment when the carbon concentration in the molten steel corrected by the correction parameter reaches a target value.

6. The control method of vacuum degassing equipment according to claim 5, characterized in that: The correction calculation step calculates the correction parameter according to an evaluation function based on the difference between the reduction amount of the carbon amount in the molten steel and the carbon amount in the exhaust gas.

7. The control method of vacuum degassing equipment according to claim 6, characterized in that: The evaluation function includes a term of a square value calculated by subtracting the carbon amount in the exhaust gas from the carbon amount in the molten steel and the carbon amount contained in the auxiliary raw material, and a term of a square value of a difference between the carbon amount in the exhaust gas and a decarburization rate per unit time.

8. The control method of the vacuum degassing equipment according to claim 6 or 7, characterized in that: The evaluation function includes the correction parameter of the exhaust gas measurement value set as a correction coefficient to be multiplied by a value before correction.

9. An operating method, characterized in that: The control method for the vacuum degassing equipment according to any one of claims 5 to 7 is executed to operate the vacuum degassing equipment.

10. A method for producing molten steel, characterized in that: In the vacuum degassing equipment operated by the operating method according to claim 9, the molten steel is refined, thereby producing the refined molten steel.

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