WO2023218914A1

WO2023218914A1 - Control device for vacuum degassing equipment, control method for vacuum degassing equipment, operation method, and manufacturing method for molten steel

Info

Publication number: WO2023218914A1
Application number: PCT/JP2023/016017
Authority: WO
Inventors: 祐汰大東; 伸司富山; 拓幸島本
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2022-05-09
Filing date: 2023-04-21
Publication date: 2023-11-16
Also published as: JP2023166207A; TW202407108A

Abstract

Provided is a control device, etc., for vacuum degassing equipment in which the carbon concentration in molten steel is estimated with high precision and a decarburization treatment is to be ended at an appropriate timing. The control device (10) for vacuum degassing equipment comprises: an operational information input unit (11) into which are input information about the weight of the molten steel and the component concentration therein prior to the decarburization treatment, and information about operational result values and auxiliary raw materials during execution of the decarburization treatment; a component calculation unit (12) which estimates the carbon concentration in the molten steel; a correction calculation unit (13) which computes correction parameters for correcting the estimated carbon concentration in the molten steel and the estimated value of the amount of carbon emitted from the vacuum degassing equipment; and a decarburization treatment control unit (14) which ends the decarburization treatment when the carbon concentration, in the molten steel, corrected using the correction parameters, has reached a target value.

Description

Control device for vacuum degassing equipment, control method for vacuum degassing equipment, operating method, and method for producing molten steel

The present disclosure relates to a control device for vacuum degassing equipment, a method for controlling vacuum degassing equipment, an operating method, and a method for manufacturing molten steel.

In the steelmaking process, impurities in hot metal such as carbon are removed and the composition of molten steel is adjusted by adding useful alloying components. In particular, regarding carbon, decarburization is promoted by placing molten steel in a vacuum environment using vacuum degassing equipment, and it is possible to produce ultra-low carbon steel in which the carbon concentration in the molten steel is less than 10 ppm.

Here, in the vacuum degassing process, the carbon concentration in molten steel is not directly measured, but 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 decarburize for too long due to concerns that the carbon concentration will be out of specification.

In order to solve the problem of prolonged processing time due to excessive decarburization, it is effective to estimate the carbon concentration in molten steel with high accuracy, and various methods have been proposed so far. . Methods for estimating the carbon concentration in molten steel can be roughly divided into two. One method is to physically consider the details of the decarburization reaction in vacuum degassing equipment and construct a decarburization reaction model (for example, Non-Patent Document 1). The other method is to estimate the carbon concentration in molten steel by calculating the amount of decarburization from the flow rate and measured values (for example, measured values of component concentrations) of exhaust gas discharged from vacuum degassing equipment during processing. In addition, as a combination of the two, a method has been proposed in which the parameters of a decarburization reaction model are determined from the exhaust gas measurement values, and the carbon concentration in molten steel is estimated using the decarburization reaction model with the determined parameters (for example, Patent Document 1 and Patent Document 2).

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

Japanese Patent Application Publication No. 2005-330512 Japanese Patent Application Publication No. 2015-101742 Japanese Patent Application Publication No. 2006-104521

When building a decarburization reaction model from physical considerations, it is often difficult to determine model parameters when trying 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 from the results of basic experiments. There is. As Non-Patent Document 2 points out, it has not been verified that there is no problem in using the same value of the additional pressure parameter in an actual vacuum degassing facility. In addition, vacuum degassing equipment differs in equipment shape and operating conditions, and model parameters are also expected to vary. Therefore, even if the decarburization reaction model proposed in Non-Patent Document 1 is introduced, the carbon concentration in molten steel cannot be estimated with high precision if the device shape or operating conditions are different.

As mentioned above, the technologies of Patent Document 1 and Patent Document 2 determine the parameters of the decarburization reaction model from the exhaust gas measurement values that reflect the decarburization performance, so that, for example, the model parameters that match the equipment shape and operating conditions are determined. can be set. However, since the errors included in the exhaust gas measurements are directly reflected in the model parameters, there is a need for a method to further improve the accuracy of the estimated value of the carbon concentration in molten steel.

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. , it is assumed that the decarburization reaction model is accurate. Therefore, since errors in the decarburization reaction model are reflected in the estimation results, a method is required to further improve the accuracy of the estimated value of the carbon concentration in molten steel.

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

The purpose of the present disclosure, which was made in view of the above circumstances, is to provide a control device for vacuum degassing equipment, a method for controlling vacuum degassing equipment, and a method for controlling vacuum degassing equipment that accurately estimates the carbon concentration in molten steel and ends decarburization treatment at an appropriate timing. The object of the present invention is to provide an operating method and a method for producing molten steel.

(1) A control device for vacuum degassing equipment 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,
Information regarding the weight and component concentration of the molten steel before the decarburization treatment, operational performance values including measurement results of the flow rate and component concentration of the exhaust gas discharged from the vacuum degassing equipment during the execution of the decarburization treatment; an operation information input section into which information regarding auxiliary materials input during execution of decarburization processing is input;
a component calculation unit that estimates a carbon concentration in molten steel of the molten steel based on information regarding the weight and component concentration of the molten steel before the decarburization treatment and the operation performance value;
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 carbon balance calculation results, an estimated value of the carbon amount discharged from the vacuum degassing equipment and the estimated carbon content of the molten steel. a correction calculation unit that calculates a correction parameter for correcting the carbon concentration in molten steel;
The method further includes a decarburization process control unit that terminates the decarburization process when the carbon concentration in the molten steel corrected by the correction parameter reaches a target value.

(2) As an embodiment of the present disclosure, in (1),
The correction calculation unit calculates the correction parameter based on an evaluation function based on the difference between the amount of decrease in the amount of carbon in molten steel and the amount of carbon in exhaust gas.

(3) As an embodiment of the present disclosure, in (2),
The evaluation function is based on the carbon content in the molten steel, a square value term calculated by subtracting the carbon content in the exhaust gas from the carbon content in the auxiliary raw material, the carbon content in the exhaust gas per unit time, and decarburization. Contains the term of the square value of the difference from the speed.

(4) As an embodiment of the present disclosure, in (2) or (3),
The evaluation function includes the correction parameter of the exhaust gas measurement value, which is set as a correction coefficient by which the value before correction is multiplied.

(5) A method for controlling vacuum degassing equipment according to an embodiment of the present disclosure includes:
A method for controlling vacuum degassing equipment, which is executed by 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, the method comprising:
Information regarding the weight and component concentration of the molten steel before the decarburization treatment, operational performance values including measurement results of the flow rate and component concentration of the exhaust gas discharged from the vacuum degassing equipment during the execution of the decarburization treatment; an input step in which information regarding auxiliary materials input during execution of decarburization processing is input;
a component calculation step of estimating the carbon concentration in the molten steel based on the information regarding the weight and component concentration of the molten steel before the decarburization treatment and the operation performance value;
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 carbon balance calculation results, an estimated value of the carbon amount discharged from the vacuum degassing equipment and the estimated carbon content of the molten steel. a correction calculation step of calculating a correction parameter for correcting the carbon concentration in the molten steel;
and a decarburization treatment termination step of terminating the decarburization treatment when the molten steel carbon concentration of the molten steel corrected by the correction parameter reaches a target value.

(6) As an embodiment of the present disclosure, in (5),
The correction calculation step calculates the correction parameter based on an evaluation function based on the difference between the amount of decrease in the amount of carbon in molten steel and the amount of carbon in exhaust gas.

(7) As an embodiment of the present disclosure, in (6),
The evaluation function is based on the carbon content in the molten steel, a square value term calculated by subtracting the carbon content in the exhaust gas from the carbon content in the auxiliary raw material, the carbon content in the exhaust gas per unit time, and decarburization. Contains the term of the square value of the difference from the speed.

(8) As an embodiment of the present disclosure, in (6) or (7),
The evaluation function includes the correction parameter of the exhaust gas measurement value, which is set as a correction coefficient by which the value before correction is multiplied.

(9) The operating method according to an embodiment of the present disclosure includes:
The vacuum degassing equipment is operated by executing the vacuum degassing equipment control method according to any one of (5) to (7).

(10) A method for manufacturing molten steel according to an embodiment of the present disclosure,
The molten steel is refined in a vacuum degassing facility operated by the operating method of (9) to produce the refined molten steel.

According to the method of the present disclosure, it is possible to simultaneously correct errors included in the decarburization reaction model, the exhaust gas measurement value, and the amount of carbon in the exhaust gas calculated from the decarburization reaction model. Therefore, it is possible to estimate the carbon concentration in molten steel with high accuracy, finish the decarburization process at an appropriate timing according to the carbon concentration standard, and shorten the decarburization process time. A method for controlling gas equipment, a method for operating it, and a method for producing molten steel can be provided.

FIG. 1 is a block diagram showing the configuration of a control device for vacuum degassing equipment, which is an embodiment of the present disclosure. FIG. 2 is a flowchart showing the flow of decarburization control processing according to an embodiment of the present disclosure. FIG. 3 is a time series calculation result of the exhaust gas carbon amount correction coefficient α, which is a correction parameter in the embodiment of the present disclosure. FIG. 4 is a time-series calculation result of a correction value _ΔCV of carbon concentration in molten steel in a vacuum chamber, which is a correction parameter in an example of the present disclosure.

Hereinafter, a control device and control method for vacuum degassing equipment according to an embodiment of the present disclosure will be described with reference to the drawings. In this embodiment, the vacuum degassing equipment will be described as an RH vacuum degassing equipment, but it is not limited to the RH vacuum degassing equipment. The control method described below also applies to equipment that has only one immersion pipe that is immersed in a vacuum tank and a ladle and sucks up the molten steel into the vacuum tank, or equipment (equipment) that does not have a vacuum tank and puts the surface of the molten steel in the ladle in a vacuum state. can be carried out.

[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 the control device 10 of the vacuum degassing equipment 100, and controls the operation of the vacuum degassing equipment 100. The vacuum degassing facility 100 performs decarburization treatment by placing at least molten steel in a reduced pressure environment. In this embodiment, the vacuum degassing facility 100 is operated by the control device 10 executing a control method for the vacuum degassing facility 100 described later. That is, as a method of operating the vacuum degassing facility 100, control of the vacuum degassing facility 100 is executed. Further, in this embodiment, the vacuum degassing equipment 100 constitutes a part of molten steel manufacturing equipment. A method for producing molten steel is executed in a molten steel production facility, and includes refining molten steel in a vacuum degassing facility 100 to produce refined molten steel.

As shown in FIG. 1, the control device 10 includes an operation information input section 11, a component calculation section 12, a correction calculation section 13, and a decarburization processing control section 14.

The operation information input unit 11 acquires information regarding operations using the vacuum degassing equipment 100. In the present embodiment, the operation information input unit 11 includes information regarding the weight and component concentration of molten steel before decarburization, and the flow rate and component concentration of exhaust gas discharged from the vacuum degassing equipment 100 during the decarburization process. Operational performance values, including measurement results, and information regarding auxiliary materials input during the decarburization process are input.

The component calculation unit 12 estimates the carbon concentration in molten steel based on the operation information acquired by the operation information input unit 11. In the present embodiment, the component calculation unit 12 estimates the carbon concentration in the molten steel based on information regarding the weight and component concentration of the molten steel before decarburization treatment, and operational performance values.

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

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

The control device 10 is configured by, for example, an information processing device such as a computer. The control device 10 has an operation information input section 11, a component calculation section 12, a correction calculation section 13, and a decarburization processing control section 14 by executing a program by an arithmetic processing device such as a CPU (Central Processing Unit) of an information processing device. It may be configured to function as a.

The vacuum degassing equipment 100 may have a known configuration. As mentioned above, an RH vacuum degassing facility is used in this embodiment. The RH vacuum degassing equipment includes, for example, a vacuum tank and a ladle, which are connected by two immersion tubes. The vacuum chamber is connected to an exhaust duct, through which the gas inside the vacuum chamber is exhausted to reduce the pressure in the vacuum chamber and suck up the molten steel in the ladle. Then, by blowing inert gas through piping from one side of the immersion tube, the molten steel flows back between the vacuum tank and the ladle. Further, in order to accelerate the decarburization process, oxygen may be blown from a blowing lance installed in the vacuum chamber.

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. By performing highly accurate estimation, it is possible to avoid performing the decarburization process for an excessively long time due to concerns that the carbon concentration may deviate from the standard, and as a result, the decarburization process time can be shortened. The flow of the decarburization control process, which is an embodiment of the present disclosure, will be described below with reference to FIG. 2.

[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 at the timing when a command to execute the decarburization process is input, and the process of step S1 is performed.

In the process of step S1, the operation information input unit 11 acquires the weight of molten steel measured before the start of the decarburization process and the component concentration obtained by component analysis. Examples of the components whose concentration is to be measured include C, Si, Mn, P, S, Al, Cu, Nb, and Ti. Further, if necessary for the calculation in the component 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, temperature is also acquired. Thereby, the process of step S1 is completed, and the decarburization control process proceeds to the process of step S2.

In the process of step S2, the operation information input unit 11 acquires the operation performance value during the decarburization process. Items necessary for calculation in the component calculation section 12 and correction calculation section 13 are acquired as the operation performance value. In this embodiment, the operation information input unit 11 acquires the measurement results of the flow rate and component concentration of exhaust gas discharged from the vacuum degassing equipment 100 as operation performance values. Further, in this embodiment, the operation information input unit 11 acquires information regarding auxiliary raw materials that are input during execution of the decarburization process. The information regarding the auxiliary raw materials is, for example, the type and input amount of the auxiliary raw materials. Further, information such as the pressure of the vacuum chamber, the flow rate of inert gas for reflux, and the flow rate of oxygen from the top blowing lance during the decarburization process may be input to the operation information input section 11. When the process of step S2 is executed after step S6, which will be described later, the operation information input unit 11 may also acquire estimated values of molten steel components including an estimated value of carbon concentration in molten steel. Thereby, the process of step S2 is completed, and the decarburization control process proceeds to the processes of step S3 and step S4. Here, step S1 and step S2 correspond to input steps.

In the process of step S3, the component calculation unit 12 calculates (estimates) the carbon concentration in molten steel according to a preset decarburization reaction model. In the present embodiment, the component calculation unit 12 acquires input information such as operational performance values every predetermined period or continuously, and estimates the carbon concentration in molten steel every predetermined period or continuously. The requirements for the decarburization reaction model used by the component calculation unit 12 are that the carbon concentration in the molten steel can be estimated at predetermined intervals or continuously, and that the decarburization rate, that is, the rate of change of the carbon concentration in the molten steel, is such that the decarburization rate in the portion where the decarburization reaction occurs There are two points that can be expressed as a function of carbon concentration in molten steel. The part where the decarburization reaction occurs corresponds to a vacuum chamber in the RH vacuum degassing equipment. These two points are conditions that a general decarburization reaction model naturally satisfies.

In this embodiment, during the decarburization process in the RH vacuum degassing equipment, the decarburization reaction model of the following equations (1) and (2) is assumed, assuming that the molten steel concentrations in the vacuum tank and the ladle are in a completely mixed state, respectively. is used.

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]. _CE is the equilibrium value [ppm] of the carbon concentration in molten steel in the vacuum chamber. C _alloy is the carbon concentration conversion value [ppm] in molten steel of the weight of carbon in the input auxiliary raw material. Equation (2) explicitly indicates that the decarburization reaction capacity coefficient depends on the carbon concentration in the molten steel in the vacuum chamber. Moreover, the subscript L indicates the physical quantity of molten steel in the ladle. The subscript V indicates the physical quantity of molten steel in the vacuum chamber. For example, C _V indicates the carbon concentration [ppm] in molten steel in a vacuum chamber. The subscript i is used to identify a specific decarburization reaction site. Specific examples of the decarburization reaction site include the surface of molten steel and bubbles of inert gas for reflux.

The amount of carbon emitted as exhaust gas is calculated using the second term of equation (2). Further, by calculating the amount of change in the carbon concentration in molten steel per minute time from equations (1) and (2) and subtracting it from the current carbon concentration in molten steel, the carbon concentration in molten steel after a minute time is calculated. Thereby, the process of step S3 is completed. Here, step S3 corresponds to a component calculation step.

In the process 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 exhaust gas per unit time is expressed by the following formula (3). Further, the cumulative total of the amount of emitted carbon from the start of the process (time 0) to time t is expressed by the following formula (4).

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]. V _off (t) is the volumetric flow rate [Nm ³ /s] of exhaust gas at time t. r _CO (t) is the CO concentration [vol%] in the exhaust gas at time t. r _CO2 (t) is the CO ₂ concentration [vol%] in the exhaust gas at time t. Q _C,OG (t) is the cumulative amount of carbon emissions [kg] from time 0 to t.

Here, when a known error is included in the measurement results of the exhaust gas flow rate and component concentration, it is preferable that the correction calculation unit 13 performs the calculation of equation (3) after removing or reducing the known error. For example, if the CO concentration measurement value and CO ₂ concentration measurement value take a non-zero value even when measurement is not performed (if the zero point is shifted), calculate the shift of the zero point from the measured value. The subtracted value may be used in the calculation. This completes the process of step S4. When Step S3 and Step S4 are completed, the decarburization control process proceeds to Step S5. Here, the process of step S4 can be executed independently from the process of step S3, and step S3 and step S4 may be executed in parallel as in this embodiment. However, the process is not limited to parallel processing, and step S3 and step S4 may be executed in order, and in this case, there is no limitation on which one comes first (the order of execution).

According to the law of conservation of mass, the cumulative total of the amount of carbon in molten steel and the amount of carbon emitted from molten steel is the sum of the amount of carbon in molten steel before decarburization and the amount of carbon contained in auxiliary materials input during treatment. be equivalent to. However, in general, the calculation using the cumulative amount of carbon in molten steel based on the carbon concentration in molten steel estimated in step S3 and the amount of emitted carbon estimated in step S4 does not satisfy the law of conservation of mass. In this embodiment, the correction calculation unit 13 calculates the deviation from the mass conservation law as a carbon balance calculation, and assumes that this deviation is due to errors included in both the decarburization reaction model and the exhaust gas measurement value. Set parameters to correct each error.

In the process of step S5, the correction calculation unit 13 determines the correction parameters of the calculation results in the processes of step S3 and step S4 so that the law of conservation of mass is satisfied. The vacuum tank molten steel carbon concentration correction value ΔC _V [ppm] is a correction parameter of the decarburization reaction model. Further, 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 processes of step S3 and step S4 are corrected as follows.

First, the carbon concentration in the vacuum tank molten steel is corrected to C _V +ΔC _V by adding a correction value ΔC _V for the carbon concentration in the vacuum tank molten steel. The amount of carbon in the exhaust gas per unit time is multiplied by the amount of carbon in the exhaust gas correction coefficient α to be corrected to αq _C,OG (t). Further, the cumulative total of the exhaust carbon amount is multiplied by the exhaust gas carbon amount correction coefficient α to be corrected to αQ _C,OG (t). The correction parameters α and correction value ΔC _V for carbon concentration in exhaust gas are determined as a solution to the optimization problem shown in equation (5) below.

Here, Q _C,IN is the total [kg] of the amount of carbon in the molten steel before decarburization treatment and the amount of carbon contained in the auxiliary raw materials input during the treatment. Q _{C, ST} is the amount of carbon in molten steel [kg]. The difference between QC _,IN and QC _,ST includes the amount of decrease in the amount of carbon in the molten steel. Furthermore, taking the difference from αQ _C,OG (t) corresponds to evaluating the difference between the amount of decrease and the amount of carbon in the exhaust gas (cumulative amount of emitted carbon). deC (ΔC _V ) is the decarburization rate [kg/s] calculated by the component calculation unit 12 from the decarburization reaction model. α _ave is a standard value of α based on operational performance values. σ ₁ , σ ₂ , σ ₃ and σ ₄ are weighting coefficients, which are set by the user, for example. Q _C,ST (ΔC _V ) is defined by equation (6). Further, deC(ΔC _V ) is defined by equation (7).

The first term in equation (5) represents 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 discrepancy 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 terms for preventing the correction parameter from taking an extreme value. First, regarding the carbon content correction coefficient α in exhaust gas, since deterioration of the exhaust gas measuring device and deterioration of the measurement environment progress on a sufficiently longer time scale than the time of one vacuum degassing treatment, continuous vacuum degassing treatment is expected to continue taking approximately the same value as the standard value (α _ave ). Therefore, the third term is the sum of the square value of the difference between α and α _ave . The standard value α _ave can be determined, for example, by calculating the average of the exhaust gas carbon amount correction coefficient α for a predetermined charge that has been processed most recently. The predetermined number of times is preferably a plurality of times, and is not limited to a specific value. Furthermore, the error of the decarburization reaction model is expected to be small regarding the correction value ΔC _V of carbon concentration in molten steel in a vacuum chamber. Therefore, the fourth term is the sum of the square value of _ΔCV . In this embodiment, the correction calculation unit 13 calculates the correction parameters by minimizing the evaluation function, which is Equation (5), but an evaluation function that maximizes it may be used. In other words, the correction calculation unit 13 may obtain correction parameters that minimize or maximize the evaluation function.

Here, the exhaust gas carbon content correction coefficient α is different from the vacuum tank molten steel carbon concentration correction value ΔC _V to be added, and is preferably set as a correction coefficient by which the value before correction is multiplied. For example, the amount of carbon in the exhaust gas per unit time can be calculated by using the correction value Δq _C,OG [kg/s] for the amount of carbon in the exhaust gas per unit time instead of the correction coefficient α for the amount of carbon in the exhaust gas as a correction parameter for the measured value of the exhaust gas. Even if q _C,OG (t)+Δq _C,OG is processed, the accuracy of carbon concentration estimation cannot be improved. It is known that the error width of the exhaust gas measurement value fluctuates greatly as time passes during the decarburization process. Therefore, when the exhaust gas carbon amount correction coefficient α is used as the added correction value (Δq _C,OG ), error removal may be insufficient depending on the timing of progress of the applied decarburization process. Furthermore, it is difficult to change the correction value in accordance with the timing of the progress of the decarburization process. Therefore, as in the present 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.

Further, the evaluation function is not limited to the above equation (5), and for example, a correction coefficient a _V for the carbon concentration in the vacuum tank molten steel can be used instead of the correction value ΔC _V for the carbon concentration in the vacuum tank molten steel. At this time, the carbon concentration in the vacuum tank molten steel is multiplied by the vacuum tank molten steel carbon concentration correction coefficient a _V and corrected to a _V ·C _V. Then, the correction parameters α, which are the correction coefficient α for carbon content in exhaust gas and the correction coefficient _αV for carbon concentration in molten steel in the vacuum chamber, are determined as a solution to the optimization problem shown in the following equation (8).

_aV is 1 when there is no need to correct the estimated value of carbon concentration in molten steel based on the decarburization reaction model. The fourth term in equation (8) is the sum of the square value of the difference between a _V and 1. Q _C,ST ′(a _V ) is defined by equation (9). Further, deC'(a _V ) is defined by equation (10).

The minimization problem using the evaluation functions of equations (5) and (8) can be solved using a known nonlinear optimization method. In the following description, it will be assumed that the evaluation function of equation (5) is used. The correction calculation unit 13 determines the correction parameters (the carbon content correction coefficient α in the exhaust gas and the carbon concentration correction value ΔC _V in the vacuum tank molten steel) by solving the minimization problem of Equation (5). Thereby, the process of step S5 is completed, and the decarburization control process proceeds to the process of step S6. Here, step S5 corresponds to a correction calculation step.

In the process of step S6, the carbon concentration in molten steel is updated by adding the correction value ΔC _V for the carbon concentration in the vacuum tank molten steel obtained in step S5 to the estimated value of the carbon concentration in molten steel obtained in step S3. Thereby, the process of step S6 is completed, and the decarburization control process proceeds to the process of step S7.

In the process of step S7, the decarburization process control unit 14 determines whether the carbon concentration in molten steel determined in step S6 has reached a predetermined target value (below the target value). If the corrected carbon concentration in molten steel is higher than the target value, the process returns to step S2, and the processes from step S2 onwards are repeated using the newly input operation performance value. On the other hand, when the corrected carbon concentration in molten steel becomes equal to or lower than the target value, the decarburization process ends. Here, step S7 corresponds to the step of terminating the decarburization process.

As described above, the control device 10 of the vacuum degassing facility 100, the control method, the operating method, and the method of manufacturing molten steel of the vacuum degassing facility 100 according to the present embodiment are based on the decarburization reaction model and the steps described above. It is possible to assume both errors in the exhaust gas measurement value and to correct these errors simultaneously. Therefore, the control device 10 of the vacuum degassing equipment 100 is capable of estimating the carbon concentration in molten steel with high accuracy, completing the decarburization process at an appropriate timing according to the carbon concentration standard, and shortening the decarburization process time. A method for controlling the vacuum degassing facility 100, a method for operating it, and a method for producing molten steel can be provided.

(Example)
Hereinafter, the effects of the present disclosure will be specifically explained based on Examples, but the present disclosure is not limited to the contents of the Examples.

In this example, decarburization treatment was performed using RH vacuum degassing equipment to produce ultra-low carbon molten steel with a standard upper limit of carbon concentration of 25 ppm. At the end of the decarburization process, a portion of the molten steel was taken as a sample, and the carbon concentration in the molten steel of this sample was actually measured. Termination of decarburization is at the operator's discretion. Furthermore, the carbon concentration in molten steel was estimated using the invention method and the comparative method. In the invention method, the carbon concentration in molten steel was estimated as in the above embodiment. Table 1 shows the results of comparing the estimated values at the end of the decarburization treatment with the actual values. Here, the carbon concentration in molten steel was estimated using two different methods for comparison. One method is to calculate the decarburization amount from the exhaust gas measurement value and estimate the carbon concentration (exhaust gas model in Table 1). However, the amount of decarburization calculated from the exhaust gas measurement value is multiplied by α _ave , which is the average value of the correction coefficient α for the amount of carbon in the exhaust gas determined from the operational results of the verification charge and the charges processed at the same time. It is being done. Another method is to estimate the carbon concentration in molten steel using only the decarburization reaction model (decarburization reaction model in Table 1). The latter decarburization reaction model is also used in the calculation for estimating the carbon concentration in molten steel using the invented method.

FIG. 3 shows the change over time of the exhaust gas carbon amount correction coefficient α, which is the correction parameter calculated using the verification charge A in Table 1. Further, FIG. 4 shows the change over time of the correction value _ΔCV of carbon concentration in molten steel in a vacuum chamber, which is a correction parameter calculated using verification charge A in Table 1.

As shown in Table 1, the invention method estimates a value closer to the actually measured value of the carbon concentration in molten steel than the comparative method. From this, it was confirmed that the invented method, which assumes errors in both the decarburization reaction model and the exhaust gas measurement values and corrects them, is effective in improving the accuracy of estimating the carbon concentration in molten steel.

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 can easily make various changes or modifications based on the present disclosure. It should therefore be noted that these variations or modifications are included within the scope of this disclosure. For example, the functions included in each component or each step can be rearranged to avoid logical contradictions, and multiple components or steps can be combined or divided into one. It is. Embodiments according to the present disclosure can also be realized as a storage medium recording a program executed by a processor included in the device. It is to be understood that these are also encompassed within the scope of the present disclosure.

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

Claims

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,
Information regarding the weight and component concentration of the molten steel before the decarburization treatment, operational performance values including measurement results of the flow rate and component concentration of the exhaust gas discharged from the vacuum degassing equipment during the execution of the decarburization treatment; an operation information input section into which information regarding auxiliary materials input during execution of decarburization processing is input;
a component calculation unit that estimates a carbon concentration in molten steel of the molten steel based on information regarding the weight and component concentration of the molten steel before the decarburization treatment and the operation performance value;
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 carbon balance calculation results, an estimated value of the carbon amount discharged from the vacuum degassing equipment and the estimated carbon content of the molten steel. a correction calculation unit that calculates a correction parameter for correcting the carbon concentration in molten steel;
A control device for vacuum degassing equipment, comprising: a decarburization processing control unit that terminates the decarburization processing when the carbon concentration in the molten steel corrected by the correction parameter reaches a target value.
The control device for vacuum degassing equipment according to claim 1, wherein the correction calculation unit calculates the correction parameter based on an evaluation function based on a difference between the amount of decrease in the amount of carbon in molten steel and the amount of carbon in exhaust gas.
The evaluation function is based on the carbon content in the molten steel, a square value term calculated by subtracting the carbon content in the exhaust gas from the carbon content in the auxiliary raw material, the carbon content in the exhaust gas per unit time, and decarburization. 3. The control device for vacuum degassing equipment according to claim 2, comprising a term for the square value of the difference with the speed.
The control device for vacuum degassing equipment according to claim 2 or 3, wherein the evaluation function has the correction parameter of the exhaust gas measurement value set as a correction coefficient by which the value before correction is multiplied.
A method for controlling vacuum degassing equipment, which is executed by 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, the method comprising:
Information regarding the weight and component concentration of the molten steel before the decarburization treatment, operational performance values including measurement results of the flow rate and component concentration of the exhaust gas discharged from the vacuum degassing equipment during the execution of the decarburization treatment; an input step in which information regarding auxiliary materials input during execution of decarburization processing is input;
a component calculation step of estimating the carbon concentration in the molten steel based on the information regarding the weight and component concentration of the molten steel before the decarburization treatment and the operation performance value;
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 carbon balance calculation results, an estimated value of the carbon amount discharged from the vacuum degassing equipment and the estimated carbon content of the molten steel. a correction calculation step of calculating a correction parameter for correcting the carbon concentration in the molten steel;
A method for controlling vacuum degassing equipment, comprising: a decarburization treatment termination step of terminating the decarburization treatment when the molten steel carbon concentration of the molten steel corrected by the correction parameter reaches a target value.
The method for controlling vacuum degassing equipment according to claim 5, wherein the correction calculation step calculates the correction parameter based on an evaluation function based on the difference between the amount of decrease in the amount of carbon in molten steel and the amount of carbon in exhaust gas.
The evaluation function is based on the carbon content in the molten steel, a square value term calculated by subtracting the carbon content in the exhaust gas from the carbon content in the auxiliary raw material, the carbon content in the exhaust gas per unit time, and decarburization. 7. The method of controlling vacuum degassing equipment according to claim 6, comprising a term of the square value of the difference between the speed and the speed.
The method for controlling vacuum degassing equipment according to claim 6 or 7, wherein the evaluation function has the correction parameter of the exhaust gas measurement value set as a correction coefficient by which the value before correction is multiplied.
An operating method for operating the vacuum degassing facility by executing the method for controlling the vacuum degassing facility according to any one of claims 5 to 7.
A method for producing molten steel, comprising refining the molten steel in a vacuum degassing facility operated by the operating method according to claim 9 to produce the refined molten steel.