JP7722255B2 - Vacuum degassing equipment control device, vacuum degassing equipment control method, operation method, and molten steel manufacturing method - Google Patents

Description

This 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.

In the steelmaking process, impurities such as carbon are removed from the molten iron, and useful alloying elements are added to adjust the composition of the molten steel. With regard to carbon in particular, decarburization is promoted by placing the molten steel in a vacuum environment using vacuum degassing equipment, making it possible to produce ultra-low carbon steel with a carbon concentration of less than 10 ppm in the molten steel.

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 run the decarburization process for an excessively long time due to concerns about the carbon concentration not being within specifications.

To solve the problem of excessive decarburization processes resulting in longer processing times, it is effective to accurately estimate the carbon concentration in molten steel during processing, and various methods have been proposed to date. Methods for estimating the carbon concentration in molten steel can be broadly divided into two categories. One method involves physically considering the details of the decarburization reaction in vacuum degassing equipment 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 emitted from the vacuum degassing equipment during processing, and then estimating the carbon concentration in molten steel. Furthermore, as a combination of these two methods, a method has been proposed in which the 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).

Furthermore, for example, Patent Document 3 discloses a method for correcting the estimated 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.

Japanese Patent Application Laid-Open No. 2005-330512 JP 2015-101742 A Japanese Patent Application Laid-Open No. 2006-104521

Shinya Kitamura and three others, "Decarburization Reaction Model in Vacuum Degassing Furnace," Iron and Steel, Vol. 80 (1994) No. 3, pp. 213-218 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

When building 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 from 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 actual vacuum degassing equipment is problem-free. Furthermore, vacuum degassing equipment varies in equipment shape and operating conditions, and it is thought that the model parameters will also vary. Therefore, even if the decarburization reaction model proposed in Non-Patent Document 1 is introduced, if the equipment shape or operating conditions are different, it will not be possible to accurately estimate the carbon concentration in molten steel.

As described above, the technologies of Patent Documents 1 and 2 determine the parameters of a decarburization reaction model from exhaust gas measurement values that reflect the actual decarburization performance, making it possible to set model parameters that suit, for example, the equipment shape and operating conditions. However, because errors contained in the exhaust gas measurement values are directly reflected in the model parameters, there is a need for a method to further improve the accuracy of estimated values for 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 exhaust gas measurement values, but this assumes that the decarburization reaction model is accurate. Therefore, errors in the decarburization reaction model are reflected in the estimation results, so there is a need for a method to further improve the accuracy of the estimated value of the carbon concentration in molten steel.

As such, in conventional technology, although there can be errors in the decarburization reaction model and errors in the exhaust gas measurement values, calculations are performed under the assumption that at least one of these is accurate. Because conventional technology estimates the carbon concentration in molten steel while ignoring either of these errors, there is an issue with insufficient accuracy in estimating the carbon concentration in molten steel.

The purpose of this disclosure, made in light of these circumstances, 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 accurately estimate the carbon concentration in molten steel and terminate the decarburization process at the appropriate time.

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.

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.

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.

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.

This disclosure makes it 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 enabling the carbon concentration in molten steel to be estimated with high accuracy, and providing a vacuum degassing equipment control device, vacuum degassing equipment control method, operation method, and molten steel manufacturing method that can terminate the decarburization process at an appropriate time relative to the carbon concentration standard and shorten the decarburization process time.

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. FIG. 2 is a flowchart showing the flow of the decarburization control process according to one embodiment of the present disclosure. 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. FIG. 4 shows the time series calculation results of the correction value _ΔCV of the carbon concentration in molten steel in the vacuum vessel, which is a correction parameter in the embodiment of the present disclosure.

The following describes a control device and control method for a vacuum degassing system according to an embodiment of the present disclosure, with reference to the drawings. In this embodiment, the vacuum degassing system is described as an RH vacuum degassing system, but this is not limited to an RH vacuum degassing system. The control method described below can also be implemented for systems that have only a vacuum tank and a single immersion tube that is immersed in a ladle and draws up molten steel into a vacuum tank, or systems (apparatuses) that do not have a vacuum tank and create a vacuum on the surface of molten steel in a ladle.

[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 control device 10 executes a control method for the vacuum degassing equipment 100, which will be described later, to operate the vacuum degassing equipment 100. That is, the control of the vacuum degassing equipment 100 is executed as the operating method of the vacuum degassing equipment 100. Furthermore, in this embodiment, the vacuum degassing equipment 100 constitutes part of a molten steel manufacturing facility. A molten steel manufacturing method is executed 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.

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 process control unit 14.

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 input information about the weight and component concentrations of the molten steel before the decarburization process, actual operation values including measurement results of the flow rate and component concentrations of the exhaust gas discharged from the vacuum degassing equipment 100 during the decarburization process, and information about auxiliary materials added during the decarburization process.

The component calculation unit 12 estimates the carbon concentration in the molten steel based on the operational information acquired by the operational 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 operational results.

The correction calculation unit 13 calculates correction parameters for correcting the estimated 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 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, the measurement results of the exhaust gas flow rate and component concentrations, and the carbon balance calculation results.

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

The control device 10 is configured, for example, by an information processing device such as a computer. 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 executing a program using an arithmetic processing unit such as a CPU (Central Processing Unit) of the information processing device.

The vacuum degassing equipment 100 may have a known configuration. As described above, this embodiment uses an RH vacuum degassing equipment. The RH vacuum degassing equipment comprises, for example, a vacuum vessel and a ladle, 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 inside the ladle. Then, by injecting an inert gas through a pipe from one end of the immersion pipe, the molten steel circulates between the vacuum vessel and the ladle. Furthermore, oxygen may be injected from an injection lance installed in the vacuum vessel to promote decarburization.

The control device 10 configured as described above 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, thereby shortening the decarburization process time. The flow of the decarburization control process, which is one embodiment of the present disclosure, will be described below with reference to Figure 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 when a command to execute the decarburization process is input, and the process of step S1 is performed.

In the processing of step S1, the operation information input unit 11 acquires the molten steel weight measured before the start of decarburization processing and the component concentrations obtained by component analysis. Examples of components whose concentrations are measured include C, Si, Mn, P, S, Al, Cu, Nb, and Ti. In addition, if required for calculations 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 Figure 2, the temperature is also acquired. This completes the processing of step S1, and the decarburization control processing proceeds to processing of step S2.

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

In the processing of step S3, the component calculation unit 12 calculates (estimates) the carbon concentration in the molten steel according to a predetermined decarburization reaction model. In this embodiment, the component 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 component calculation unit 12 has two requirements: it must be able to estimate the carbon concentration in the molten steel at predetermined intervals or continuously, and the decarburization rate, i.e., the rate of change in the carbon concentration in the molten steel, must be expressed as a function of the carbon concentration in the molten steel where the decarburization reaction occurs. In RH vacuum degassing equipment, the area where the decarburization reaction occurs corresponds to the vacuum tank. These two requirements are conditions that a general decarburization reaction model naturally satisfies.

In this embodiment, the decarburization reaction models shown in the following equations (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 process in the RH vacuum degassing equipment.

Here, 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]. ak is the decarburization reaction capacity coefficient [kg/s]. _CE is the equilibrium value of the carbon concentration in molten steel in the vacuum vessel [ppm]. C _alloy is the carbon weight of the added auxiliary materials converted to the carbon concentration in molten steel [ppm]. Equation (2) explicitly indicates that the decarburization reaction capacity coefficient depends on the carbon concentration in molten steel in the vacuum vessel. Furthermore, 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 vessel. For example, CV indicates the carbon concentration in molten steel in the vacuum vessel [ppm]. 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.

The amount of carbon emitted as exhaust gas is calculated using the second term in equation (2). Furthermore, the change in carbon concentration in the molten steel per minute of time is calculated using equations (1) and (2), and the carbon concentration in the molten steel after the minute of 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.

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).

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 of the exhaust gas at time t [Nm ³ /s]. _{r CO} (t) is the CO concentration in the exhaust gas at time t [vol%]. _{r CO2} (t) is the _CO2 concentration in the exhaust gas at time t [vol%]. _{Q C,OG} (t) is the cumulative amount of carbon emitted from time 0 to t [kg].

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 performed (if the zero point is shifted), a 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. Upon completion of steps S3 and S4, the decarbonization 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.

Here, according to the law of conservation of mass, the total amount of carbon in the molten steel and the cumulative amount of carbon emitted from the molten steel is equal to 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. However, calculations 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 emitted carbon estimated in step S4 generally do 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 for each error.

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. The vacuum vessel molten steel carbon concentration correction value ΔC _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 processes of steps S3 and S4 are corrected as follows:

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

Here, Q _C,IN is the sum [kg] of the carbon amount in the molten steel before decarburization and the carbon amount contained in the auxiliary materials added during the process. Q _C,ST is the carbon amount in the molten steel [kg]. The difference between _{Q C,IN} and Q _C,ST includes the amount of carbon reduction in the molten steel. Furthermore, taking the difference from αQ _C,OG (t) corresponds to evaluating the difference between that 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. α _ave is the standard value of α based on actual operating results. σ ₁ , σ ₂ , σ ₃ , and σ ₄ are weighting coefficients, and are set, for example, by the user. _{Q C,ST} (ΔC _V ) is defined by equation (6). Furthermore, deC (ΔC _V ) is defined by equation (7).

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 fully satisfied, the first term is zero. 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 is zero. The third and fourth terms in equation (5) are used to prevent the correction parameter from taking extreme values. First, regarding the exhaust gas carbon amount correction coefficient α, because the deterioration of the exhaust gas measurement device and the measurement environment progresses on a time scale significantly longer than the time required for a single vacuum degassing treatment, it is expected that the value will remain roughly the same as the standard value (α _ave ) during consecutive vacuum degassing treatments. Therefore, the third term is the sum of the squared 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 number of charges most recently processed. The predetermined number of charges is preferably a plurality of times and is not limited to a specific value. Furthermore, the error of the decarburization reaction model for the vacuum chamber molten steel carbon concentration correction value _ΔCV is expected to be small. Therefore, the fourth term is calculated by adding the square of _ΔCV . In this embodiment, the correction calculation unit 13 calculates the correction parameter by minimizing the evaluation function, 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 the correction parameter that minimizes or maximizes the evaluation function.

Here, the exhaust gas carbon amount correction coefficient α is preferably set as a correction coefficient by which the pre-correction value is multiplied, unlike the vacuum vessel molten steel carbon concentration correction value _ΔCV to be added. For example, even if the exhaust gas carbon amount correction value per unit time ΔqC _,OG [kg/s] is used instead of the exhaust gas carbon amount correction coefficient α as the correction parameter for the exhaust gas measurement value and the process is performed to calculate the exhaust gas carbon amount per unit time as qC _,OG (t)+ΔqC _{, OG, the accuracy of the carbon concentration estimation cannot be improved. It is known that the error in the exhaust gas measurement value varies greatly over time during the decarburization process. Therefore, when the exhaust gas carbon amount correction coefficient α is used as the correction value (ΔqC,OG} ) to be added, error elimination may be insufficient depending on the timing of the decarburization process. Furthermore, it is difficult to change the correction value in accordance with the timing of the decarburization process. Therefore, as in this embodiment, the exhaust gas carbon amount correction coefficient α is preferably set as a correction coefficient by which the pre-correction value is multiplied.

Furthermore, the evaluation function is not limited to the above formula (5), and for example, a correction coefficient aV for the carbon concentration in molten steel in a vacuum tank can be used instead of the correction value ΔC _{V for} the carbon concentration in molten steel in a vacuum tank. In this case, the carbon concentration in molten steel in a vacuum tank is corrected to _aV ·C _V by multiplying it by the correction coefficient _aV for the carbon concentration in molten steel in a vacuum tank. Then, the correction coefficients α for the carbon amount in exhaust gas and _aV for the carbon concentration in molten steel in a vacuum tank, which are correction parameters, are determined as a solution to an optimization problem shown in the following formula (8):

When there is no need to correct the carbon concentration estimated in molten steel by the decarburization reaction model, _aV becomes 1. The fourth term in equation (8) is the sum of the square of the difference between _aV and 1. _QC,ST '( _aV ) is defined by equation (9). Also, deC'( _aV ) is defined by equation (10).

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 determines the correction parameters (exhaust gas carbon amount correction coefficient α and vacuum tank molten steel carbon concentration correction value ΔC _V ) by solving the minimization problem of Equation (5). This completes the processing of step S5, and the decarburization control processing proceeds to processing of step S6. Here, step S5 corresponds to the correction calculation step.

In the process of step S6, the carbon concentration in molten steel is updated by adding the correction value _ΔCV of 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. This completes the process of step S6, and the decarburization control process proceeds to the process of step S7.

In step S7, the decarburization process control unit 14 determines whether the carbon concentration in the molten steel determined in step S6 has reached a predetermined target value (whether it is below the target value). If the corrected carbon concentration in the molten steel is higher than the target value, the process returns to step S2, and steps S2 and subsequent steps are repeated using the newly input operational performance value. On the other hand, if the corrected carbon concentration in the molten steel is below the target value, the decarburization process ends. Here, step S7 corresponds to the decarburization process ending step.

As described above, the control device 10 for the vacuum degassing equipment 100, the control method for the vacuum degassing equipment 100, the operation method, and the method for producing molten steel according to this embodiment use the above-described configuration and processes to assume errors in both the decarburization reaction model and the exhaust gas measurement values, and simultaneously correct these errors. As a result, it is possible to provide a control device 10 for the vacuum degassing equipment 100, the control method for the 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 process at an appropriate timing relative to the carbon concentration standard, and shorten the decarburization process time.

(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.

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 the specification. At the end of the decarburization process, a portion of the molten steel was sampled, and the carbon concentration of this sample was measured. The decision to terminate the decarburization process was made at the discretion of the operator. The carbon concentration of the molten steel was also estimated using the inventive method and the comparative method. The inventive method estimated the carbon concentration of the molten steel as in the above-described 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 comparative method estimated the carbon concentration of the molten steel using two different methods. One method calculates the amount of decarburization from flue gas measurement values and estimates the carbon concentration (the flue gas model in Table 1). However, the decarburization amount calculated from the flue gas measurement values was multiplied by α _ave , which is the average value of the flue gas carbon correction coefficient α obtained from the operational performance of the verification charge and charges processed during the same period. 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 carbon concentration estimation in molten steel in the invention method.

Fig. 3 shows the time variation of the exhaust gas carbon amount correction coefficient α, which is a correction parameter calculated for the verification charge A in Table 1. Fig. 4 shows the time variation of the vacuum vessel molten steel carbon concentration correction value _ΔCV , which is a correction parameter calculated for the verification charge A in Table 1.

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

Embodiments of the present disclosure have been described based on various drawings and examples. However, it should be noted that those skilled in the art would easily be able to make various modifications or alterations based on this 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 into one or divided. Embodiments of the present disclosure can also be realized as a storage medium on which a program executed by a processor provided in an apparatus is recorded. It should be understood that these are also included within the scope of the present disclosure.

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

Claims (10)

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. 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. A vacuum degassing equipment control device as described in claim 2, wherein the evaluation function includes a term for the square of the difference between the amount of carbon in the molten steel, the amount of carbon contained in the auxiliary materials, and the amount of carbon in the exhaust gas per unit time, and the decarburization rate. 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. 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. 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. A method for controlling vacuum degassing equipment according to claim 6, wherein the evaluation function includes a term for the square of the carbon amount in the molten steel, calculated by subtracting the carbon amount in the exhaust gas from the carbon amount contained in the auxiliary raw materials, and a term for the square of the difference between the carbon amount in the exhaust gas per unit time and the decarburization rate. 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. An operating method for operating a vacuum degassing equipment by carrying out the control method for a vacuum degassing equipment described in 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 described in claim 9 to produce the refined molten steel.