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

Abstract

To provide a control device for a vacuum degassing facility, a control method for the vacuum degassing facility, an operation method, and a molten steel production method for estimating carbon concentration in the molten steel with high accuracy and terminating a decarburization treatment at an appropriate timing.SOLUTION: A control device (10) for a vacuum degassing facility includes: an operation information input part (11) for inputting information on the weight and component concentration of molten steel before decarburization, an operation result value during execution of the decarburization, and information on an auxiliary raw material; a component calculation part (12) for estimating the carbon concentration in the molten steel; a correction calculation part (13) for calculating the estimated amount of carbon discharged from the vacuum degassing facility and a correction parameter for correcting the estimated carbon concentration in molten steel; and a decarburization treatment control part (14) for terminating the decarburization treatment when the carbon concentration in molten steel corrected by the correction parameter reaches a target value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a control device for vacuum degassing equipment, a control method for vacuum degassing equipment, an operation method, and a method for producing molten steel. [Background technology]

[0002] In the steelmaking process, the molten steel composition is adjusted by removing impurities such as carbon from the molten iron and adding useful alloying elements. Regarding carbon in particular, vacuum degassing equipment is used to place the molten steel in a vacuum environment, accelerating decarburization and making it possible to produce ultra-low carbon steel with a carbon concentration of less than 10 ppm in the molten steel.

[0003] In the vacuum degassing process, the carbon concentration in the molten steel is not measured directly, 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 the decarburization process for an excessively long time due to concerns about the carbon concentration not being within specifications.

[0004] To solve the problem of excessive decarburization treatment resulting in prolonged treatment times, it is effective to estimate the carbon concentration in molten steel with high accuracy during treatment, and various methods have been proposed to date. Methods for estimating the carbon concentration in molten steel can be broadly divided into two. One method involves physically considering the details of the decarburization reaction in a vacuum degassing system and constructing a decarburization reaction model (e.g., Non-Patent Document 1). The other method involves calculating the amount of decarburization from the flow rate and measurement values (e.g., measured values of component concentrations) of the exhaust gas discharged from the vacuum degassing system during treatment, and estimating the carbon concentration in molten steel. Furthermore, as a combination of these two methods, a method has been proposed in which parameters of a decarburization reaction model are determined from exhaust gas measurement values, and the carbon concentration in molten steel is estimated using a decarburization reaction model having the determined parameters (e.g., Patent Documents 1 and 2).

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

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-330512 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-101742 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-104521 [Non-patent literature]

[0007] [Non-Patent Document 1] Shinya Kitamura and three others, "Decarburization Reaction Model in Vacuum Degassing Furnace", Iron and Steel Vol.80(1994) No.3, pp.213-218 [Non-patent document 2] Yoshihiko Higuchi and two others, "Effects of [C], [O] and Vacuum Level on RH Vacuum Decarburization," Tetsu-to-Hagané Vol. 84 (1998) No. 10, pp. 709-714 Summary of the Invention [Problem to be solved by the invention]

[0008] When constructing a decarburization reaction model based on physical considerations, it is often difficult to determine the model parameters when attempting to express the details of the decarburization reaction. For example, the decarburization reaction model proposed in Non-Patent Document 1 introduces an additional pressure parameter to formulate CO bubble generation inside molten steel, but this value is determined based on the results of basic experiments. As Non-Patent Document 2 points out, there is no verification that using the same additional pressure parameter value in an actual vacuum degassing equipment is problem-free. Furthermore, vacuum degassing equipment varies in equipment configuration and operating conditions, and it is thought that the model parameters also vary. Therefore, even if the decarburization reaction model proposed in Non-Patent Document 1 is introduced, if the equipment configuration or operating conditions are different, it is not possible to accurately estimate the carbon concentration in molten steel.

[0009] As described above, the techniques of Patent Documents 1 and 2 determine the parameters of a decarburization reaction model from exhaust gas measurement values that reflect the actual decarburization results, thereby making it possible to set model parameters that suit, for example, the equipment shape and operating conditions. However, since errors contained in the exhaust gas measurement values are directly reflected in the model parameters, there is a need for a method that further improves the accuracy of the estimated value of the carbon concentration in molten steel.

[0010] As described above, the technology of Patent Document 3 corrects the estimated value of the carbon concentration in molten steel based on the difference between the decarburization rate calculated from the decarburization reaction model and the decarburization rate calculated from the exhaust gas measurement value, but this is premised on the accuracy of the decarburization reaction model. Therefore, errors in the decarburization reaction model are reflected in the estimation result, and therefore a method for further improving the accuracy of the estimated value of the carbon concentration in molten steel is desired.

[0011] As described above, in the conventional technology, although there may be errors in the decarburization reaction model and errors in the exhaust gas measurement values, calculations are performed on the assumption that at least one of them is accurate. Since the conventional technology estimates the carbon concentration in molten steel while ignoring either of the errors, there is a problem in that the accuracy of the estimation of the carbon concentration in molten steel is insufficient.

[0012] In view of the above circumstances, an object of the present disclosure is to provide a vacuum degassing equipment control device, a vacuum degassing equipment control method, an operation method, and a molten steel manufacturing method that can estimate the carbon concentration in molten steel with high accuracy and terminate the decarburization treatment at an appropriate timing. [Means for solving the problem]

[0013] A control device for a vacuum degassing facility according to an embodiment of the present disclosure includes: A control device for vacuum degassing equipment that controls the operation of vacuum degassing equipment that performs decarburization treatment by placing molten steel in a reduced pressure environment, an operation information input unit into which information regarding the weight and component concentrations of the molten steel before the decarburization treatment, operation performance values including measurement results of the flow rate and component concentrations of exhaust gas discharged from the vacuum degassing equipment during the execution of the decarburization treatment, and information regarding auxiliary materials to be added during the execution of the decarburization treatment are input; a component calculation unit that estimates a carbon concentration in the molten steel based on information about the weight and component concentrations of the molten steel before the decarburization treatment and the operational performance values; a correction calculation unit that calculates an estimated value of the amount of carbon discharged from the vacuum degassing equipment and a correction parameter for correcting the estimated carbon concentration in the molten steel, based on the estimated carbon concentration in the molten steel, measurement results of the flow rate and component concentrations of the exhaust gas, and carbon balance calculation results; and a decarburization treatment control unit that terminates the decarburization treatment when the carbon concentration in the molten steel corrected by the correction parameter reaches a target value.

[0014] A method for controlling a vacuum degassing facility according to an embodiment of the present disclosure includes: 1. A control method for vacuum degassing equipment, executed by a control device for vacuum degassing equipment that performs decarburization treatment by placing molten steel in a reduced pressure environment, comprising: an input step in which information about the weight and component concentrations of the molten steel before the decarburization treatment, operational performance values including measurement results of the flow rate and component concentrations of exhaust gas discharged from the vacuum degassing equipment during the execution of the decarburization treatment, and information about auxiliary materials to be added during the execution of the decarburization treatment are input; a component calculation step of estimating a carbon concentration in the molten steel based on information on the weight and component concentrations of the molten steel before the decarburization treatment and the operational performance values; a correction calculation step of calculating an estimated value of the amount of carbon discharged from the vacuum degassing equipment and a correction parameter for correcting the estimated carbon concentration in the molten steel, based on the estimated carbon concentration in the molten steel, measurement results of the flow rate and component concentrations of the exhaust gas, and carbon balance calculation results; 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.

[0015] An operating method according to one embodiment of the present disclosure includes: The vacuum degassing facility is operated by carrying out the above-described method for controlling the vacuum degassing facility.

[0016] A method for producing molten steel according to an embodiment of the present disclosure includes: The molten steel is refined in a vacuum degassing facility operated by the above-described operating method to produce the refined molten steel. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to simultaneously correct errors contained in the decarburization reaction model, exhaust gas measurement values, and the amount of carbon in the exhaust gas calculated from them, thereby making it possible to estimate the carbon concentration in molten steel with high accuracy, and to provide a control device for vacuum degassing equipment, a control method for vacuum degassing equipment, an operation method, and a manufacturing method of molten steel that can terminate the decarburization process at an appropriate timing relative to the carbon concentration standard and shorten the decarburization process time. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a block diagram showing the configuration of a control device of a vacuum degassing facility according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a flowchart showing the flow of the decarburization control process according to one embodiment of the present disclosure. [Figure 3] FIG. 3 shows the time series calculation results of the exhaust gas carbon amount correction coefficient α, which is a correction parameter in the embodiment of the present disclosure. [Figure 4] FIG. 4 shows the time series calculation results of the vacuum vessel molten steel carbon concentration correction value ΔCV, which is a correction parameter in the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a control device and a control method for a vacuum degassing system according to an embodiment of the present disclosure will be described with reference to the drawings. In this embodiment, the vacuum degassing system will be described as an RH vacuum degassing system, but the system is not limited to an RH vacuum degassing system. The control method described below can also be applied to a system having only a vacuum vessel and a single immersion tube immersed in a ladle for sucking up molten steel into a vacuum vessel, or to a system (apparatus) that does not have a vacuum vessel and creates a vacuum on the surface of molten steel in a ladle.

[0020] [composition] FIG. 1 is a block diagram showing the configuration of a control device 10 according to an embodiment of the present disclosure. The control device 10 is a control device 10 for a vacuum degassing equipment 100 and controls the operation of the vacuum degassing equipment 100. The vacuum degassing equipment 100 performs decarburization by placing at least molten steel in a reduced-pressure environment. In this embodiment, the vacuum degassing equipment 100 is operated by the control device 10 executing a control method for the vacuum degassing equipment 100, which will be described later. That is, the method for operating the vacuum degassing equipment 100 involves controlling the vacuum degassing equipment 100. In addition, in this embodiment, the vacuum degassing equipment 100 constitutes part of a molten steel manufacturing facility. A molten steel manufacturing method is performed in the molten steel manufacturing facility, and the molten steel manufacturing method includes refining molten steel in the vacuum degassing equipment 100 to manufacture refined molten steel.

[0021] As shown in FIG. 1, 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.

[0022] The operation information input unit 11 acquires information about operations using the vacuum degassing equipment 100. In this embodiment, the operation information input unit 11 receives inputs of information about the weight and component concentrations of the molten steel before the decarburization treatment, actual operation results including measurement results of the flow rate and component concentrations of the exhaust gas discharged from the vacuum degassing equipment 100 during the decarburization treatment, and information about auxiliary materials to be added during the decarburization treatment.

[0023] 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 weight of the molten steel before decarburization treatment, information on the component concentrations, and actual operation values.

[0024] The correction calculation unit 13 calculates correction parameters for correcting the estimated value of the amount of carbon discharged from the vacuum degassing equipment 100 and the estimated carbon concentration in the molten steel. In this embodiment, the correction calculation unit 13 calculates correction parameters for correcting the estimated value of the amount of carbon discharged from the vacuum degassing equipment 100 and the estimated carbon concentration in the molten steel, based on the estimated carbon concentration in the molten steel, measurement results of the flow rate and component concentrations of the exhaust gas, and carbon balance calculation results.

[0025] The decarburization process control unit 14 terminates the decarburization process when the carbon concentration in the molten steel corrected by the correction parameter reaches the target value.

[0026] The control device 10 is configured by an information processing device such as a computer, etc. The control device 10 may be configured to function as an operation information input unit 11, a component calculation unit 12, a correction calculation unit 13, and a decarburization treatment control unit 14 by an arithmetic processing device such as a CPU (Central Processing Unit) of the information processing device executing a program.

[0027] The vacuum degassing equipment 100 may have a known configuration. As described above, an RH vacuum degassing equipment is used in this embodiment. The RH vacuum degassing equipment includes, for example, a vacuum vessel and a ladle, which are connected by two immersion pipes. The vacuum vessel is connected to an exhaust duct, through which gas inside the vacuum vessel is evacuated to reduce the pressure inside the vacuum vessel and suck up the molten steel in the ladle. Then, an inert gas is blown into one end of the immersion pipe through a pipe, causing the molten steel to circulate between the vacuum vessel and the ladle. Furthermore, oxygen may be blown into the vacuum vessel from an injection lance installed in the vacuum vessel to promote the decarburization process.

[0028] The control device 10 having such a configuration estimates the carbon concentration in molten steel with high accuracy by executing the decarburization control process described below. Highly accurate estimation makes it possible to avoid performing an excessively long decarburization process due to concerns about the carbon concentration not conforming to specifications, and as a result, it is possible to shorten the decarburization process time. Hereinafter, the flow of the decarburization control process according to one embodiment of the present disclosure will be described with reference to FIG. 2.

[0029] [Decarburization control treatment] Fig. 2 is a flowchart showing the flow of the decarburization control process executed by the control device 10. The flowchart shown in Fig. 2 starts when a command to execute the decarburization process is input, and the process of step S1 is performed.

[0030] In the processing of step S1, the operation information input unit 11 acquires the weight of molten steel measured before the start of decarburization treatment and the concentrations of elements obtained by elemental analysis. Examples of elements whose concentrations are to be measured include C, Si, Mn, P, S, Al, Cu, Nb, and Ti. Furthermore, if necessary for the calculation in the element calculation unit 12, the operation information input unit 11 may also acquire the measurement results of the molten steel temperature. In the example of FIG. 2, the temperature is also acquired. This completes the processing of step S1, and the decarburization control processing proceeds to the processing of step S2.

[0031] In the processing of step S2, the operation information input unit 11 acquires operational performance values during the decarburization treatment. The operational performance values include items necessary for calculations by the component calculation unit 12 and the correction calculation unit 13. In this embodiment, the operation information input unit 11 acquires, as operational performance values, measurement results of the flow rate and component concentrations of the exhaust gas discharged from the vacuum degassing equipment 100. In this embodiment, the operation information input unit 11 also acquires information about the auxiliary materials added during the decarburization treatment. Specific examples of the information about the auxiliary materials include the type and amount of the auxiliary materials added. Furthermore, information about the vacuum chamber pressure, the flow rate of the reflux inert gas, and the oxygen flow rate from the top lance during the decarburization treatment may be input to the operation information input unit 11. When the processing of step S2 is performed after step S6 (described later), the operation information input unit 11 may also acquire estimated values of the molten steel components, including an estimated carbon concentration in the molten steel. This completes the processing of step S2, and the decarburization control process proceeds to steps S3 and S4. Here, steps S1 and S2 correspond to input steps.

[0032] In the processing of step S3, the composition calculation unit 12 calculates (estimates) the carbon concentration in the molten steel in accordance with a predetermined decarburization reaction model. In this embodiment, the composition calculation unit 12 acquires input information such as actual operational results at predetermined intervals or continuously, and estimates the carbon concentration in the molten steel at predetermined intervals or continuously. The decarburization reaction model used by the composition calculation unit 12 has two requirements: the carbon concentration in the molten steel can be estimated at predetermined intervals or continuously, and the decarburization rate, i.e., the rate of change in the carbon concentration in the molten steel, can be expressed as a function of the carbon concentration in the molten steel in the portion where the decarburization reaction occurs. In an RH vacuum degassing system, the portion where the decarburization reaction occurs corresponds to the vacuum tank. These two requirements are conditions that a general decarburization reaction model naturally satisfies.

[0033] In this embodiment, the decarburization reaction models of the following formulas (1) and (2) are used, assuming that the molten steel concentrations in the vacuum vessel and ladle are in a completely mixed state during the decarburization treatment in the RH vacuum degassing equipment.

[0034]

number

[0035] where w is the mass of molten steel [kg], C is the carbon concentration in molten steel [ppm], Q is the reflux rate of molten steel [kg / s], and ak is the decarburization reaction capacity coefficient [kg / s]. E is the equilibrium carbon concentration in the molten steel in the vacuum vessel [ppm]. alloy is the carbon concentration in molten steel converted from the weight of carbon in the added auxiliary materials [ppm]. Equation (2) explicitly shows that the decarburization reaction capacity coefficient depends on the carbon concentration in the molten steel in the vacuum vessel. Also, the subscript L indicates the physical quantity of the molten steel in the ladle. The subscript V indicates the physical quantity of the molten steel in the vacuum vessel. For example, C V indicates the carbon concentration [ppm] in the vacuum vessel molten steel. The subscript i is used to identify specific decarburization reaction sites. Specific decarburization reaction sites include the surface of molten steel and reflux inert gas bubbles.

[0036] The amount of carbon emitted as exhaust gas is calculated by the second term of formula (2). Furthermore, the amount of change in the carbon concentration in the molten steel per minute time is calculated from formulas (1) and (2), and the carbon concentration in the molten steel after the minute time is calculated by subtracting this from the current carbon concentration in the molten steel. This completes the processing of step S3. Here, step S3 corresponds to the component calculation step.

[0037] In the processing of step S4, the correction calculation unit 13 calculates the amount of carbon in the exhaust gas from the measurement results of the flow rate and component concentration of the exhaust gas. Considering that carbon emitted from molten steel takes the form of CO or CO2, the amount of carbon in the exhaust gas per unit time is given by the following formula (3). In addition, the cumulative amount of emitted carbon from the start of processing (time 0) to time t is given by the following formula (4).

[0038]

number

[0039] where 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]. V off (t) is the volumetric flow rate of exhaust gas at time t [Nm 3 / s]. r 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%]. Q C,OG (t) is the cumulative carbon emissions [kg] from time 0 to time t.

[0040] Here, if the measurement results of the flow rate and component concentrations of the exhaust gas contain known errors, it is preferable that the correction calculation unit 13 remove or reduce the known errors before performing the calculation of equation (3). For example, if the CO concentration measurement value and the CO2 concentration measurement value are non-zero even when measurements are not being taken (if the zero point is shifted), the value obtained by subtracting the zero point shift from the measurement value may be used in the calculation. This completes the processing of step S4. After steps S3 and S4 are completed, the decarburization control process proceeds to step S5. Here, the processing of step S4 can be executed independently of the processing of step S3, and steps S3 and S4 may be executed in parallel as in this embodiment. However, parallel processing is not limited, and steps S3 and S4 may be executed sequentially, and the order in which they are executed first (the order of execution) is not limited.

[0041] According to the law of conservation of mass, the total of the amount of carbon in the molten steel and the cumulative amount of carbon released from the molten steel is equal to the total of the amount of carbon in the molten steel before the decarburization process and the amount of carbon contained in the auxiliary materials added during the process. However, in general, a 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 cumulative amount of released carbon estimated in step S4 does not satisfy the law of conservation of mass. In this embodiment, the correction calculation unit 13 determines this deviation from the law of conservation of mass as a carbon balance calculation, and, assuming that this deviation is due to errors in both the decarburization reaction model and the exhaust gas measurement values, sets parameters to correct each error.

[0042] In the process of step S5, the correction calculation unit 13 determines correction parameters for the calculation results in the processes of steps S3 and S4 so that the law of conservation of mass is satisfied. V [ppm] is a correction parameter for the decarburization reaction model. Furthermore, the exhaust gas carbon amount correction coefficient α is a correction parameter for the exhaust gas measurement value. Using these correction parameters, the calculation results in the processing of steps S3 and S4 are corrected as follows:

[0043] First, the carbon concentration in the molten steel in the vacuum vessel is calculated by the corrected carbon concentration in the molten steel in the vacuum vessel ΔC V Add C V +ΔC V The amount of carbon in the exhaust gas per unit time is multiplied by the exhaust gas carbon amount correction coefficient α to obtain αq C、OG (t). The cumulative amount of carbon emissions is multiplied by the exhaust gas carbon correction coefficient α to obtain αQ C、OG The correction parameters are the exhaust gas carbon correction coefficient α and the vacuum vessel molten steel carbon concentration correction value ΔC V is determined as a solution to the optimization problem shown in the following equation (5).

[0044]

number

[0045] Here, Q C,IN is the total amount of carbon in the molten steel before decarburization and the amount of carbon contained in the auxiliary materials added during the process [kg]. C,ST is the amount of carbon in the molten steel [kg]. Q C,IN and Q C,ST The difference between these two includes the reduction in the carbon content in the molten steel. C、OG Taking the difference from (t) corresponds to evaluating the difference between the reduction and the amount of carbon in the exhaust gas (cumulative amount of carbon emitted). deC(ΔC V ) is the decarburization rate [kg / s] calculated by the component calculation unit 12 from the decarburization reaction model. aveis the standard value of α based on the actual operation 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). Also, deC(ΔC V ) is defined by equation (7).

[0046]

number

[0047] The first term in equation (5) represents the deviation from the law of conservation of mass for carbon. When the law of conservation of mass is completely satisfied, the first term becomes 0. The second term in equation (5) represents the deviation between the amount of carbon in the exhaust gas per unit time and the decarburization rate calculated from the decarburization reaction model. When the amount of carbon in the exhaust gas per unit time and the decarburization rate calculated from the decarburization reaction model match, the second term becomes 0. The third and fourth terms in equation (5) are used to prevent the correction parameters from taking extreme values. First, regarding the exhaust gas carbon amount correction coefficient α, since the deterioration of the exhaust gas measuring device and the measurement environment progresses on a time scale that is sufficiently longer than the time for one vacuum degassing process, the standard value (α ave ) is expected to remain roughly the same value. Therefore, the third term is ave The standard value is α ave can be determined by, for example, calculating the average of the exhaust gas carbon correction coefficient α for a predetermined number of charges that have been processed most recently. The predetermined number of charges is preferably a plurality of times, and is not limited to a specific value. In addition, the carbon concentration correction value ΔC in the vacuum vessel molten steel V The error of the decarburization reaction model is expected to be small. Therefore, the fourth term is ΔC V In this embodiment, the correction calculation unit 13 calculates the correction parameters by minimizing the evaluation function of equation (5), but an evaluation function that maximizes the evaluation function may also be used. In other words, the correction calculation unit 13 may calculate correction parameters that minimize or maximize the evaluation function.

[0048] Here, the exhaust gas carbon correction coefficient α is the added correction value ΔC V For example, instead of the exhaust gas carbon amount correction coefficient α, the exhaust gas carbon amount correction value Δq per unit time is used as a correction parameter for the exhaust gas measurement value. C,OG [kg / s], the amount of carbon in the exhaust gas per unit time is q C,OG (t)+Δq C,OG Even if the process of carbon concentration estimation is performed, the accuracy of carbon concentration estimation cannot be improved. It is known that the error in the exhaust gas measurement value varies greatly with the time of decarbonization process. Therefore, the correction value (Δq C,OG ), error removal may be insufficient depending on the timing of the progress of the applied decarburization treatment. In addition, it is difficult to change the correction value in accordance with the timing of the progress of the decarburization treatment. Therefore, as in this embodiment, it is preferable that the exhaust gas carbon amount correction coefficient α is set as a correction coefficient by which the value before correction is multiplied.

[0049] The evaluation function is not limited to the above formula (5), and may be, for example, the correction value ΔC V Instead of the carbon concentration correction coefficient a in the molten steel in the vacuum vessel, V In this case, the carbon concentration in the molten steel in the vacuum vessel can be calculated by the correction coefficient a V Multiply by a V C V Then, the correction parameters, the exhaust gas carbon correction coefficient α and the vacuum vessel molten steel carbon concentration correction coefficient a V is determined as a solution to the optimization problem shown in the following equation (8).

[0050]

number

[0051] When there is no need to correct the carbon concentration in molten steel estimated by the decarburization reaction model, Vbecomes 1. The fourth term of equation (8) is a V It is the sum of the square of the difference between Q and 1. C,ST ´(a V ) is defined by equation (9). Also, deC´(a V ) is defined by equation (10).

[0052]

number

[0053] The minimization problem using the evaluation functions of Equation (5) and Equation (8) can be solved using a known nonlinear optimization method. In the following, it is assumed that the evaluation function of Equation (5) is used. The correction calculation unit 13 solves the minimization problem of Equation (5) to obtain the correction parameters (exhaust gas carbon amount correction coefficient α and vacuum vessel molten steel carbon concentration correction value ΔC V ) is determined. This completes the process of step S5, and the decarburization control process proceeds to the process of step S6. Here, step S5 corresponds to a correction calculation step.

[0054] In the process of step S6, the estimated carbon concentration in molten steel obtained in step S3 is corrected by the carbon concentration correction value ΔC in the vacuum vessel molten steel obtained in step S5. V This completes the process of step S6, and the decarburization control process proceeds to step S7.

[0055] In the processing of step S7, the decarburization treatment control unit 14 determines whether the carbon concentration in the molten steel calculated in step S6 has reached a predetermined target value (whether it is equal to or less than the target value). If the corrected carbon concentration in the molten steel is higher than the target value, the processing returns to step S2, and the processing from step S2 onwards is repeated using the newly input operational performance value. On the other hand, if the corrected carbon concentration in the molten steel is equal to or less than the target value, the decarburization treatment is terminated. Here, step S7 corresponds to the decarburization treatment termination step.

[0056] As described above, the control device 10 for vacuum degassing equipment 100, the control method for vacuum degassing equipment 100, the operation method, and the method for producing molten steel according to this embodiment can assume errors in both the decarburization reaction model and the exhaust gas measurement values and correct these errors simultaneously using the above-mentioned configuration and processes. Therefore, it is possible to provide the control device 10 for vacuum degassing equipment 100, the control method for vacuum degassing equipment 100, the operation method, and the method for producing molten steel that can estimate the carbon concentration in molten steel with high accuracy, terminate the decarburization treatment at an appropriate timing relative to the carbon concentration standard, and shorten the decarburization treatment time.

[0057] (Example) The effects of the present disclosure will be specifically described below based on examples, but the present disclosure is not limited to the contents of the examples.

[0058] In this example, decarburization was performed using RH vacuum degassing equipment to produce ultra-low carbon molten steel with a carbon concentration of 25 ppm, the upper limit of which is specified. At the end of the decarburization process, a portion of the molten steel was taken as a sample, and the carbon concentration in this sample was measured. The decision to end the decarburization process was made by the operator. The carbon concentration in the molten steel was also estimated using the inventive method and the comparative method. The inventive method estimated the carbon concentration in the molten steel as in the above embodiment. Table 1 shows the results of comparing the estimated value at the end of the decarburization process with the actual measured value. Here, the carbon concentration in the molten steel was estimated using two comparative methods. One is a method in which the amount of decarburization is calculated from the measured exhaust gas values and the carbon concentration is estimated (exhaust gas model in Table 1). However, α, which is the average value of the exhaust gas carbon correction coefficient α obtained from the operational results of the verification charge and charges processed at the same time, was used. ave The amount of decarburization calculated from the exhaust gas measurement values is multiplied by this. The other method is to estimate the carbon concentration in molten steel using only the decarburization reaction model (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 estimation in the invention method.

[0059] Figure 3 shows the time variation of the exhaust gas carbon correction coefficient α, which is a correction parameter calculated for verification charge A in Table 1. Also, Figure 4 shows the time variation of the vacuum vessel molten steel carbon concentration correction value ΔC, which is a correction parameter calculated for verification charge A in Table 1. V The time change of is shown.

[0060] [Table 1]

[0061] As shown in Table 1, the inventive method estimates values closer to the actually measured values of the carbon concentration in molten steel than the comparative method. This confirms that the inventive method, which assumes and corrects errors in both the decarburization reaction model and the exhaust gas measurement values, is effective in improving the accuracy of estimating the carbon concentration in molten steel.

[0062] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art would easily be able to make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure. For example, the functions included in each component or step can be rearranged so as not to cause logical inconsistencies, and multiple components or steps can be combined or divided into one. The embodiments of the present disclosure can also be realized as a storage medium on which a program executed by a processor included in an apparatus is recorded. It should be understood that these are also included within the scope of the present disclosure. [Explanation of symbols]

[0063] 10 Control device 11 Operation information input section 12 Component calculation part 13 Correction calculation section 14 Decarburization processing control unit 100 Vacuum degassing equipment

Claims

1. A control device for vacuum degassing equipment that controls the operation of vacuum degassing equipment that performs decarburization treatment by placing molten steel in a reduced pressure environment, an operation information input unit into which information regarding the weight and component concentrations of the molten steel before the decarburization treatment, operation performance values including measurement results of the flow rate and component concentrations of exhaust gas discharged from the vacuum degassing equipment during the execution of the decarburization treatment, and information regarding auxiliary materials to be added during the execution of the decarburization treatment are input; a component calculation unit that estimates a carbon concentration in the molten steel based on information about the weight and component concentrations of the molten steel before the decarburization treatment and the operational performance values; a correction calculation unit that calculates a correction parameter for correcting the estimated value of the amount of carbon discharged from the vacuum degassing equipment based on the estimated carbon concentration in the molten steel, the measurement results of the flow rate and component concentrations of the exhaust gas, and the carbon balance calculation results, and also calculates a correction parameter for correcting the estimated carbon concentration in the molten steel; a decarburization treatment control unit that terminates the decarburization treatment when the corrected carbon concentration in the molten steel reaches a target value.

2. 2. The control device for vacuum degassing equipment according to claim 1, wherein the correction calculation unit calculates a correction parameter for correcting the estimated value of the amount of carbon discharged from the vacuum degassing equipment and a correction parameter for correcting the estimated carbon concentration in the molten steel, based on an evaluation function based on a difference between an amount of reduction in the amount of carbon in the molten steel and an amount of carbon in the exhaust gas.

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

4. 4. The vacuum degassing facility control device according to claim 2, wherein the evaluation function has a correction parameter that corrects the estimated value of the amount of carbon emitted from the vacuum degassing facility and is set as a correction coefficient by which the value before correction is multiplied.

5. 1. A control method for vacuum degassing equipment, executed by a control device for vacuum degassing equipment that performs decarburization treatment by placing molten steel in a reduced pressure environment, comprising: an input step in which information about the weight and component concentrations of the molten steel before the decarburization treatment, operational performance values including measurement results of the flow rate and component concentrations of exhaust gas discharged from the vacuum degassing equipment during the execution of the decarburization treatment, and information about auxiliary materials to be added during the execution of the decarburization treatment are input; a component calculation step of estimating a carbon concentration in the molten steel based on information on the weight and component concentrations of the molten steel before the decarburization treatment and the operational performance values; a correction calculation step of calculating a correction parameter for correcting the estimated value of the amount of carbon discharged from the vacuum degassing equipment based on the estimated carbon concentration in the molten steel, the measurement results of the flow rate and component concentrations of the exhaust gas, and the carbon balance calculation results, and calculating a correction parameter for correcting the estimated carbon concentration in the molten steel; and a decarburization treatment termination step of terminating the decarburization treatment when the corrected carbon concentration in the molten steel reaches a target value.

6. 6. The method for controlling vacuum degassing equipment according to claim 5, wherein the correction calculation step calculates a correction parameter for correcting the estimated value of the amount of carbon discharged from the vacuum degassing equipment and a correction parameter for correcting the estimated carbon concentration in the molten steel, based on an evaluation function based on a difference between an amount of reduction in the amount of carbon in the molten steel and an amount of carbon in the exhaust gas.

7. 7. The method for controlling vacuum degassing equipment according to claim 6, wherein the evaluation function includes a term for a square value calculated by subtracting the amount of carbon in the exhaust gas from the amount of carbon contained in the auxiliary raw materials, and a term for a square value of a difference between the amount of carbon in the exhaust gas per unit time and a decarburization rate.

8. 8. The method for controlling a vacuum degassing facility according to claim 6, wherein the evaluation function has a correction parameter that corrects the estimated value of the amount of carbon emitted from the vacuum degassing facility, the correction parameter being set as a correction coefficient to be multiplied by the value before correction.

9. An operating method for operating a vacuum degassing facility by carrying out the control method for a vacuum degassing facility according to any one of claims 5 to 7.

10. A method for producing molten steel, comprising: refining the molten steel in vacuum degassing equipment operated by the operating method according to claim 9 to produce refined molten steel.

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