JP7732147B2 - Slag mass estimation method, slag mass estimation device, refining system, auxiliary raw material addition method, molten iron refining method, and molten steel manufacturing method - Google Patents

Description

This disclosure relates to an estimation method, estimation device, and refining system for estimating the bulk density of slag that occurs during settling of foamed slag containing CO gas after blowing processes such as desiliconization or dephosphorization in a converter, in order to estimate the settling behavior of refining foamed slag. This disclosure also relates to a method for adding auxiliary materials, a method for refining molten iron, and a method for producing molten steel, all of which use the method for estimating slag bulk density.

In recent years, advances have been made in molten iron pretreatment technology, and various molten iron pretreatment methods using converter-type refining furnaces have been developed. For example, Patent Document 1 discloses a method in which, when performing desiliconization, dephosphorization, and decarburization processes using a converter, the next charge of molten iron is charged into the converter without discharging the decarburization slag from the previous charge, and when the silicon (Si) in the molten iron falls to 0.2% or less, some of the slag is discharged from the furnace, followed by the subsequent dephosphorization and decarburization processes.

As mentioned above, in refining methods that involve removing slag, increasing the slag volume through slag foaming is important for ensuring the amount of slag that can be removed. Slag foaming occurs when carbon monoxide (CO), generated by the reaction between carbon (C) in the molten iron and iron oxide (FeO) in the slag, is trapped in the slag.

When refining is carried out following the slag removal process, the amount of auxiliary materials added is determined based on the mass of slag remaining in the furnace. If there is a discrepancy between the calculated mass of slag remaining in the furnace and the actual mass of slag, and too much auxiliary material is added, this will result in increased costs or heat loss. Conversely, if too little auxiliary material is added, components such as phosphorus will be removed. Therefore, in order to minimize costs, it is necessary to accurately estimate the mass of slag remaining in the furnace after the slag removal process.

Conventionally, the mass of slag remaining in the furnace has been estimated by operators visually checking the slag discharge status. However, the volume of slag changes from moment to moment due to the slag settling phenomenon that occurs during slag discharge. Therefore, it is extremely difficult for operators to estimate the mass of slag remaining in the furnace. In particular, in actual operation, variations in settling behavior are likely to occur due to differences in slag composition, temperature, or blowing conditions. Variations in settling behavior make it even more difficult to accurately estimate the mass of slag remaining in the furnace.

To solve this problem, methods have been proposed for estimating the mass of slag remaining in the furnace from measurement data. For example, Patent Document 2 discloses a method for estimating the mass of slag remaining in the furnace from the final tilting angle of the converter. Furthermore, Patent Document 3 proposes a method for estimating the density of the slag after slag removal and the mass of slag remaining in the furnace by continuously measuring the slag height before slag removal.

Japanese Patent Application Publication No. 11-323420 Japanese Patent Application Laid-Open No. 2007-308773 International Publication No. 2020/129887

Here, in the process of discharging slag from a converter, predicting the mass of the slag after discharging is extremely important in order to determine the amount of lime to be added as an auxiliary raw material in the next process. Previously, methods have been proposed, such as one shown in Patent Document 2, which estimates the mass of slag remaining in the converter from the final tilting angle, and one shown in Patent Document 3, which estimates the density of the slag after discharging and the mass of slag remaining in the converter from the history of the slag height before discharging.

However, the method of Patent Document 2 assumes that the bulk density of the slag is constant, making it impossible to estimate the mass of the slag during settling. Furthermore, while the method of Patent Document 3 takes into account the effects of settling behavior, it is necessary to continuously measure the slag height for a certain period of time for each charge. There is a risk that productivity will decrease due to the time lost in measuring the slag height.

As mentioned above, differences in actual operating conditions cause variations in settling behavior. This variation in settling behavior makes it difficult to estimate the bulk density of the slag after slag removal and the mass of slag remaining in the furnace. It is necessary to easily predict the impact of slag settling behavior based on operating conditions and improve the accuracy of estimating the mass of slag remaining in the furnace. Furthermore, by improving the accuracy of estimating the mass of slag remaining in the furnace, it is desirable to reduce the amount of lime added in the next process, reduce heat loss, and prevent component loss.

The present disclosure aims to provide a slag mass estimation method, a slag mass estimation device, and a refining system that can estimate the mass of slag remaining in a furnace, as well as a method for adding auxiliary materials, a method for refining molten pig iron, and a method for producing molten steel that can efficiently produce molten steel based on the results of slag mass estimation.

A slag mass estimation method according to an embodiment of the present disclosure includes:
A slag mass estimation method for estimating a mass of slag remaining in a furnace after slag removal from a furnace for treating molten iron, comprising:
an information acquisition step of acquiring information that identifies a relationship between the physical properties of the slag and the settling behavior of the slag;
a physical property determination step of determining the physical properties of the slag based on the operating conditions of the treatment of the molten iron in the furnace;
a density estimation step of predicting the settling behavior of the slag based on the information acquired in the information acquisition step and the physical properties of the slag determined in the physical property determination step, and estimating the density of the slag remaining in the furnace after the slag is discharged;
a volume estimation step of estimating the volume of the slag remaining in the furnace by measuring the height of the slag in the furnace and the volume of the furnace body;
and a mass estimation step of estimating the mass of the slag remaining in the furnace based on the density of the slag estimated in the density estimation step and the volume of the slag estimated in the volume estimation step.

A method for adding an auxiliary material according to one embodiment of the present disclosure includes a step of adding an auxiliary material to a furnace based on the mass of slag remaining in the furnace, estimated by performing the slag mass estimation method described above.

A method for refining molten iron according to one embodiment of the present disclosure includes a step of performing blowing in a furnace to which auxiliary materials have been added by carrying out the auxiliary material addition method described above.

A method for producing molten steel according to one embodiment of the present disclosure includes a step of pouring molten iron treated by carrying out the above-described molten iron refining method from a furnace.

A slag mass estimation device according to one embodiment of the present disclosure includes a processor that executes the above-described slag mass estimation method.

A refining system according to one embodiment of the present disclosure includes the above-described slag mass estimation device and a refining device that processes molten iron.

This disclosure provides a slag mass estimation method, a slag mass estimation device, and a refining system that can estimate the mass of slag remaining in a furnace, as well as a method for adding auxiliary materials, a method for refining molten pig iron, and a method for producing molten steel that can efficiently produce molten steel based on the results of slag mass estimation.

1 is a block diagram illustrating an example configuration of a refining system according to the present disclosure. FIG. 1 is a cross-sectional view showing an example of a process for foaming slag in a refining furnace. FIG. 1 is a cross-sectional view showing an example of a process for removing slag from a refining furnace. FIG. 1 is a cross-sectional view showing an example of the change in foam height of slag over time. 1 is a graph showing an example of a change in foam height of slag over time. 1 is a graph showing an example of a change in slag density over time. 1 is a flowchart illustrating an example of a procedure of an information processing method according to the present disclosure.

The following describes embodiments of a refining system 100 (see Figure 1, etc.), an estimation device 50 (see Figure 1, etc.), and an estimation method according to the present disclosure, with reference to the drawings. The drawings are schematic and may differ from the actual product. Furthermore, the following embodiments exemplify devices or methods that embody the technical concepts of the present disclosure, and are not intended to limit the configuration to those described below. In other words, the technical concepts of the present disclosure may be modified in various ways within the technical scope set forth in the claims.

The refining system 100, estimation device 50, and estimation method disclosed herein investigate the relationship between the physical properties of slag and the settling behavior of slag in advance through preliminary experiments, etc. By predicting the settling behavior during operation based on the relationship between the physical properties of slag and the settling behavior of slag, the bulk density of slag and the mass of slag remaining in the furnace can be estimated with high accuracy.

(Configuration example of refining system 100)
As shown in FIG. 1 , a refining system 100 according to one embodiment includes an estimation device 50 and a refining device 40 .

<Refining device 40>
As illustrated in Fig. 2, the refining apparatus 40 includes a refining furnace 1 and a top-blowing lance 42. In this embodiment, the refining furnace 1 is of a converter type. The refining furnace 1 is not limited to a converter type and may be of various other types. The refining furnace 1 is also simply referred to as a furnace. The refining apparatus 40 according to this embodiment is configured to perform desiliconization treatment on the molten pig iron 3 contained in the refining furnace 1. The refining apparatus 40 is not limited to desiliconization treatment, and may be configured to perform various other treatments such as dephosphorization treatment.

In the refining apparatus 40, desiliconization is performed on the molten pig iron 3 in the refining furnace 1. During the desiliconization process, an oxygen-containing gas is supplied to the molten pig iron 3 from the top lance 42. The oxygen-containing gas supplied from the top lance 42 reacts with the silicon (Si) in the molten pig iron 3 to produce slag 2. Slag 2 is also called desiliconization slag. Because the density of slag 2 is lower than that of the molten pig iron 3, slag 2 floats above the molten pig iron 3.

Oxygen-containing gas supplied from the top lance 42 reacts with carbon in the molten iron 3 to generate carbon monoxide (CO) gas. The slag 2 becomes foamy due to the inclusion of CO gas bubbles. The apparent volume of the slag 2 increases by several times or more due to the inclusion of CO gas bubbles. This state is also referred to as a foaming state.

As illustrated in Figure 3, the refining apparatus 40 controls the tilting angle of the refining furnace 1 to discharge at least a portion of the slag 2 from the refining furnace 1 without causing the molten iron 3 to flow out of the refining furnace 1. The process of discharging the slag 2 is also called slag removal processing.

The refining apparatus 40 may further include an input device for inputting auxiliary materials into the refining furnace 1. The auxiliary materials may include, for example, lime. The input device may be configured to control the type or amount of auxiliary materials input into the refining furnace 1.

The refining device 40 may be equipped with a process computer that controls the flow rate of gas supplied from the top-blowing lance 42, the type or amount of additives added to the refining furnace 1, or the tilting angle of the refining furnace 1. The process computer may be equipped with, for example, a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). The process computer may be equipped with a storage device such as a semiconductor memory or an electromagnetic recording medium. The process computer may be equipped with a communication interface for communicating with other devices such as the estimation device 50.

<Estimation device 50>
The estimation device 50 estimates the mass of the slag 2 remaining in the refining furnace 1 after the slag 2 is discharged from the refining furnace 1. The estimation device 50 is also referred to as a slag mass estimation device. The estimation device 50 includes a processor 52, a memory unit 54, and an interface 56.

The processor 52 may be configured to include, for example, a CPU or GPU in order to control and manage various functions of the estimation device 50. The processor 52 may implement the functions of the estimation device 50 by reading and executing programs stored in the memory unit 54.

The memory unit 54 stores various information or data used by the estimation device 50. The memory unit 54 may store, for example, a program executed by the processor 52, or data or processing results used in processing executed by the processor 52. The memory unit 54 may function as a work memory for the processor 52. The memory unit 54 may be configured to include, for example, semiconductor memory, but is not limited to this. The memory unit 54 may be configured as, for example, internal memory of the processor 52, or as an electromagnetic recording medium such as a hard disk drive (HDD) accessible from the processor 52. The memory unit 54 may be configured as a non-transitory readable medium. The memory unit 54 may be configured integrally with the processor 52 or as a separate entity from the processor 52.

The interface 56 may be configured to include a communication interface for communicating with other devices, such as the refining device 40, via a wired or wireless connection. The communication interface may be configured to be able to communicate with other devices via a network. The interface 56 may be configured to include an input/output port for inputting and outputting data to and from other devices. The interface 56 transmits and receives necessary data and signals to and from a process computer or a higher-level system. The interface 56 may communicate based on a wired communication standard or a wireless communication standard. For example, wireless communication standards may include cellular phone communication standards such as 3G, 4G, and 5G. Furthermore, for example, wireless communication standards may include IEEE 802.11, Bluetooth (registered trademark), and the like. The interface 56 may support one or more of these communication standards. The interface 56 is not limited to these examples and may communicate with other devices or input/output data based on various standards.

The interface 56 may be configured to output information obtained from the processor 52. The interface 56 may notify the user of information by outputting visual information such as text, figures, or images, either directly or via an external device. The interface 56 may include a display device or may be connected to a display device via a wired or wireless connection. The display device may include various displays such as an LCD display. The interface 56 may notify the user of information by outputting auditory information such as sound, either directly or via an external device. The interface 56 may include an audio output device such as a speaker or may be connected to an audio output device via a wired or wireless connection. The interface 56 may include a vibration device. The interface 56 may notify the user of information by outputting not only visual, auditory, or tactile information, but also information that the user can perceive with other senses, either directly or via an external device.

The interface 56 may include an input device that accepts input from a user. The input device may include, for example, a keyboard or physical keys, a touch panel or touch sensor, or a pointing device such as a mouse. The input device is not limited to these examples and may include various other devices.

(Example of operation of refining system 100)
Below, an example of operation in the refining system 100 of this embodiment is described, in which the estimation device 50 estimates the mass of slag 2 remaining in the refining furnace 1 after the refining device 40 discharges the slag 2 from the refining furnace 1.

<Basic procedure example for estimating the mass of slug 2>
In the information acquisition step (A), the processor 52 of the estimation device 50 acquires information that identifies the relationship between the physical properties of the slag 2 and the settling behavior of the slag 2. The physical properties of the slag 2 may include, for example, the viscosity, solid fraction, or surface tension of the slag 2. The physical properties of the slag 2 may include the rate of CO gas generation that occurs along with the slag 2. The settling behavior of the slag 2 is the behavior in which the volume of the slag 2 decreases as the CO gas contained in the slag 2 is released when the slag 2 enters a foaming state. The settling behavior of the slag 2 may be identified by the relationship between the elapsed time and the volume of the slag 2 as the volume of the slag 2 decreases.

As shown in Figure 4, the settling behavior of slag 2 may be expressed as the change over time in the height of slag 2 from the hearth 11 of the refining furnace 1, which has become foamed inside the refining furnace 1. The height of slag 2 to the molten metal surface 21 after blowing is represented by H1. The height of slag 2 decreases over time. The height of slag 2 to the molten metal surface 22 after a predetermined time has elapsed is represented by H2.

The settling behavior of slag 2 may be expressed as the relationship between the time elapsed since the end of blowing and the height of slag 2, as shown in the graph of Figure 5, for example. In the graph of Figure 5, the horizontal axis represents the time elapsed since the end of blowing. The vertical axis represents the height of slag 2 that has reached a foamed state. The height of slag 2 that has reached a foamed state is also referred to as the foam height of slag 2. The points plotted as circles (○) on the graph of Figure 5 represent the measured values of the foam height of slag 2 at each elapsed time. The solid line on the graph of Figure 5 represents a function, such as an exponential function, that approximates the measured value of the foam height of slag 2.

The processor 52 may acquire data on the change in foam height over time in an actual refining furnace 1 as information identifying the relationship between the physical properties of slag 2 and the settling behavior of slag 2. However, it is difficult to measure the change in foam height over time in an actual refining furnace 1. Therefore, the processor 52 may acquire data acquired by conducting a preliminary experiment that reproduces the internal state of the refining furnace 1 immediately after blowing, for example, as information identifying the relationship between the physical properties of slag 2 and the settling behavior of slag 2. The preliminary experiment may be conducted using an aqueous solution that simulates the physical properties of slag 2 in order to investigate the effect of the physical properties of slag 2, such as the viscosity or solid fraction, on the settling behavior of slag 2.

In a preliminary experiment, gas is sprayed onto an aqueous solution simulating the physical properties of slag 2. The change over time in the volume of the aqueous solution, which is foamed by the gas spray and enters a foaming state, is measured. The height of the aqueous solution in the foaming state may be measured as the volume of the aqueous solution in the foaming state. The height of the aqueous solution in the foaming state is also referred to as the foam height of the aqueous solution. The measurement results of the change over time in the foam height of the aqueous solution represent the change over time in the foam height of slag 2 when slag 2, whose physical properties are simulated by the aqueous solution, enters a foaming state in the refining furnace 1.

The physical properties of slag 2 are determined by a combination of various parameter values that determine the physical properties. A preliminary experiment may be conducted using aqueous solutions that simulate each of multiple combinations of parameter values that determine the physical properties of slag 2. In other words, a preliminary experiment may be conducted using aqueous solutions that simulate each of slag 2 exhibiting different physical properties. Through the preliminary experiment, data on the change in foam height over time for slag 2 exhibiting different physical properties is obtained as measured values of the change in foam height over time for aqueous solutions that simulate each of slag 2 exhibiting different physical properties. Processor 52 may obtain information that associates combinations of parameter values that determine the physical properties of slag 2 with measured values of the change in foam height over time for aqueous solutions that simulate the physical properties of slag 2, as information that determines the relationship between the physical properties of slag 2 and the settling behavior of slag 2.

Information associating combinations of parameter values specifying the physical properties of slag 2 with measured values of the change in foam height over time of an aqueous solution simulating the physical properties of slag 2 may be prepared in advance as a database. The database may be stored in the memory unit 54 of the estimation device 50 or in an external storage device. The processor 52 may acquire information specifying the association between the physical properties of slag 2 and the settling behavior of slag 2 from the database.

In the physical property determination step (B), the processor 52 determines the physical properties of the slag 2 based on the operating conditions when the molten iron 3 is treated in the refining furnace 1. The operating conditions may include the amount of impurities such as silicon (Si) contained in the molten iron 3, the amount of lime added as an auxiliary material to the molten iron 3, or the estimated temperature of the slag 2. The operating conditions may include, for example, the amount of molten iron 3 in the refining furnace 1, the carryover amount of slag 2 (the amount of slag 2 remaining after slag 2 is drained), the estimated foaming height of the slag 2, or the estimated amount of iron oxide (FeO). The processor 52 may also derive physical properties of the slag 2 that affect the settling behavior of the slag 2, such as the viscosity, solid fraction, or surface tension of the slag 2, based on a thermodynamic database or the like.

In the density estimation step (C), the processor 52 predicts the settling behavior of the slag 2 based on the information acquired in the information acquisition step (A) and the physical properties of the slag 2 determined in the physical property determination step (B), and estimates the density of the slag 2 remaining in the refining furnace 1 after the slag 2 has been removed.

Specifically, the processor 52 extracts measurement data of the change over time in the foam height of an aqueous solution simulating the physical properties of slag 2 from the information acquired in the information acquisition step (A) that identifies the relationship between the physical properties of slag 2 and the settling behavior of slag 2, and acquires this as predicted data for the settling behavior of slag 2.

Furthermore, processor 52 estimates the bulk density of slag 2 when the slag discharge of slag 2 is completed based on predicted data on the settling behavior of slag 2. The bulk density of slag 2 increases over time as the CO gas contained in slag 2 in a foaming state escapes over time, reducing the foam height of slag 2. The bulk density of slag 2 increases over time, for example, as shown in the graph of Figure 6. In the graph of Figure 6, the horizontal axis represents the elapsed time after the end of blowing. The vertical axis represents the bulk density of slag 2 at each time. The elapsed time from the end of blowing to the end of slag discharge of slag 2 is represented by T0. Processor 52 estimates the bulk density of slag 2 when the elapsed time is T0 in the graph of Figure 6 as the bulk density of slag 2 when the slag discharge of slag 2 is completed.

In the volume estimation step (D), the processor 52 estimates the volume of the slag 2 remaining in the refining furnace 1 by measuring the height of the slag 2 in the refining furnace 1 and the volume of the furnace body of the refining furnace 1. The processor 52 may obtain a measurement value of the height of the slag 2 when the refining furnace 1, which had been tilted to discharge the slag 2, is returned to its original position. The processor 52 may estimate the volume of the slag 2 remaining in the refining furnace 1 based on the measurement value of the height of the slag 2 and the volume of the furnace body of the refining furnace 1.

In the mass estimation step (E), the processor 52 estimates the mass of the slag 2 remaining in the refining furnace 1 based on the density of the slag 2 estimated in the density estimation step (C) and the volume of the slag 2 remaining in the refining furnace 1 after slag removal estimated in the volume estimation step (D).

<<Flowchart example>>
The processor 52 of the estimation device 50 may execute a slag mass estimation method including the steps of the flowchart illustrated in Fig. 7. The slag mass estimation method may be realized as a slag mass estimation program executed by the processor 52. The slag mass estimation program may be stored in a non-transitory computer-readable medium.

In the information acquisition step (A), the processor 52 acquires the results of a preliminary experiment as information identifying the relationship between the physical properties of the slag 2 and the settling behavior of the slag 2 (step S1). In the physical property determination step (B), the processor 52 derives the physical properties of the slag 2 whose mass is to be estimated (step S2). In the density estimation step (C), the processor 52 estimates the bulk density of the slag 2 after the slag 2 has been discharged from the refining furnace 1 (step S3). In the volume estimation step (D), the processor 52 estimates the volume of the slag 2 remaining in the refining furnace 1 after the slag 2 has been discharged (step S4). In the mass estimation step (E), the processor 52 estimates the mass of the slag 2 remaining in the refining furnace 1 (step S5). After executing the procedure of step S5, the processor 52 terminates execution of the procedure of the flowchart in FIG. 7.

＜＜Summary＞＞
By executing the above-described example of the basic procedure, the estimation device 50 can estimate the mass of the slag 2 remaining in the refining furnace 1 after the slag 2 has been removed, without measuring the state of the slag 2 from immediately after blowing until the completion of the slag removal. Being able to estimate the mass of the slag 2 without measuring the state of the slag 2 avoids interrupting the process for measurement. As a result, work efficiency is improved.

In the refining system 100, the refining device 40 can determine the amount of auxiliary materials to be added in the next stage of refining processing based on the estimated mass of slag 2 remaining in the refining furnace 1. By accurately estimating the mass of slag 2 remaining in the refining furnace 1, the amount of auxiliary materials required in the next stage of processing can be estimated with high accuracy. By accurately estimating the amount of auxiliary materials, there is no excess auxiliary material in the refining furnace 1. In other words, the amount of auxiliary materials added is kept appropriate. As a result, the amount of auxiliary materials added is reduced. Furthermore, by accurately estimating the amount of auxiliary materials, heat loss in the refining process is reduced. Furthermore, by accurately estimating the amount of auxiliary materials, the composition of the refined molten pig iron 3 is less likely to deviate from the target. In other words, the quality of the molten pig iron 3 produced is improved.

<Example of information acquisition process>
The information acquisition step (A) may include a data acquisition step (F), a mathematical formulation step (G), and a stability derivation step (H). In the data acquisition step (F), the processor 52 acquires data on the settling behavior of the slag 2, obtained through an experiment that reproduces the settling phenomenon under operation, taking into account similarity conditions of dimensionless numbers related to the physical properties of the slag 2, as information specifying the relationship between the physical properties of the slag 2 and the settling behavior of the slag 2. In the mathematical formulation step (G), the processor 52 mathematically formulates the data on the settling behavior of the slag 2 acquired in the data acquisition step (F) by function approximation. In the stability derivation step (H), the processor 52 derives the forming stability from the approximate function obtained in the mathematical formulation step (G).

Regarding the data acquisition process (F), the specific method for investigating in advance the relationship between the physical properties of slag 2 and the settling behavior of slag 2 is not limited. For example, the relationship between the physical properties of slag 2 and the settling behavior of slag 2 may be investigated by conducting a cold model experiment that simulates the settling behavior of slag 2 using an aqueous solution.

In order to reproduce the influence of the physical properties of the slag in the cold model experiment, the physical properties of the aqueous solution are adjusted so that at least one of the following two properties matches the physical properties of the slag 2: Morton's number Mo, which is a dimensionless number related to the stability of bubbles and is expressed by the following formula (1), or the solid fraction _Φs, which is a dimensionless number representing the influence of particle precipitation in the slag 2 and is expressed by the following formula (2).

In formula (1), μ is the viscosity of the liquid [Pa·s]. g is the acceleration of gravity [m/s ² ]. ρ is the density of the liquid [kg/m ³ ]. σ is the surface tension of the liquid [N/m]. In formula (2), V _s is the solid phase volume [m ³ ] contained in the solid-liquid coexistence material. _{V l} is the liquid volume [m ³ ] contained in the solid-liquid coexistence material.

An aqueous solution prepared based on the above-mentioned formula (1) or (2) is foamed by gas blowing. From the time gas generation is stopped, the settling phenomenon is reproduced in the foamed aqueous solution. The change in the foam height of the aqueous solution over time is recorded. In this experiment, experiments may be conducted for multiple combinations of parameter values specifying the physical properties of slag 2 expected in an actual machine and values of the gas velocity blown onto the molten iron 3. By conducting experiments for multiple combinations, data on the settling behavior of slag 2 under various operating conditions can be obtained.

With regard to the mathematical formulation process (G) and the stability derivation process (H), the function used to mathematically formulate the settling behavior of slag 2 (the change in the foam height of slag 2 over time as slag 2 settles) is not limited. For example, the following formula (3) may be used as an approximate function.

In equation (3), v(t) is the gas generation rate [m/s] at t seconds (-∞<t<0) after the current time is 0 seconds. τ is the time constant [s ^-1 ] representing the foaming stability. _h∞ is the height of slag 2 when slag 2 has completely settled (the height of the liquid phase of slag 2). Here, the gas generation rate v(t) is known because it is specified by the experimental conditions. The change in the foaming height h over time is measured in advance. The time constant τ representing the foaming stability is derived based on the change in v(t) and h over time.

<Example of operation of physical property determination process>
The physical property determination step (B) may include an operating condition extraction step (I) and a slag physical property estimation step (J). In the operating condition extraction step (I), the processor 52 extracts the operating conditions of the refining furnace 1 from data of a process computer that controls the operation of the refining furnace 1. In the slag physical property estimation step (J), the processor 52 estimates the physical properties of the slag 2 using a thermodynamic database and the operating conditions of the refining furnace 1 extracted in the operating condition extraction step (I).

In the operating condition extraction step (I), the operating conditions required to derive the physical properties of slag 2 are extracted. For example, the amount of molten pig iron 3 required to derive the viscosity, solid fraction, and surface tension of slag 2, the amount of slag 2 carried over (the amount of slag 2 remaining after slag removal), the amount of auxiliary raw materials added, or the estimated temperature of slag 2 may be extracted. Furthermore, the estimated foam height immediately after the end of blowing or the estimated amount of iron oxide (FeO), which are required to derive the gas generation rate, may be extracted.

With regard to the slag property estimation process (J), the viscosity or solid fraction of slag 2 may be obtained from a thermodynamic database such as FactSage. The surface tension may be calculated based on Butler's model formula. Furthermore, the CO gas generation rate v(t) may be expressed, for example, as the following formula (4):

In equation (4), _VCO is the CO gas generation rate [m/s] just before the end of blowing, _T0 is the elapsed time [s] from the end of blowing, and _τCO is the decay coefficient [s ^-1 ] of the CO gas generation rate after the end of blowing.

It is difficult to measure or calculate the CO gas generation rate V _(t) during operation and the CO gas generation rate decay coefficient τ( _t) after the end of blowing in real time. Therefore, these values may be analytically derived from past operational results. The analytically derived values may be linked to the CO gas generation rate v(t) and the estimated amount of iron oxide (FeO) on the assumption that there is a correlation between them.

First, the foaming height h(T ₀ ) at the CO gas generation rate v(t) assumed in equation (4) and the gas phase ratio Φ(T ₀ ) representing the gas phase ratio contained in the foamed slag 2 are expressed by the following equations (5) and (6).

That is, the foaming height h(t ₀ ) and the gas phase fraction Φ(T ₀ ) when T ₀ seconds have elapsed since the end of blowing are expressed as functions of the CO gas generation rate V _CO , the time constant τ representing foaming stability, and the damping coefficient τ _CO of the CO gas generation rate after the end of blowing. Of the variables included in equations (5) and (6), V _CO is estimated based on the foaming height immediately after blowing (T ₀ =0 seconds). τ is known in the stability derivation step (H). Therefore, the only unknown variables are Φ(T ₀ ) and τ _CO . The gas phase fraction Φ(T ₀ ) is estimated by the following equation (7):

In equation (7), ρ _air is the density of air [kg/m ³ ]. ρ _slag is the density of pure solid-liquid slag [kg/m ³ ]. Here, the bulk density ρ (T ₀ ) of the slag 2 when T ₀ seconds have elapsed since the end of blowing is estimated based on operational records. For example, the bulk density of the slag 2 at the start of slag discharge is derived by dividing the mass of the slag 2 estimated from the amount of auxiliary raw materials charged by the volume of the slag 2 estimated based on the tilting angle of the refining furnace 1.

Finally, the damping coefficient _τCO is derived by simultaneously applying Equations (5) to (7) and the estimated slag density ρ( _T0 ) when _T0 seconds have elapsed since the end of blowing. By performing a series of operations on multiple charges, a correlation between the estimated amount of iron oxide (FeO) and the CO gas generation rate _VCO and damping coefficient _τCO can be obtained. Online, a method of estimating the CO gas generation rate by allocating the CO gas generation rate _VCO and damping coefficient _τCO corresponding to the estimated amount of iron oxide (FeO) may be employed.

<Example of operation of density estimation process>
The density estimation step (C) may include a dimensionless number calculation step (K), a settling behavior allocation step (L), and a bulk density determination step (M). In the dimensionless number calculation step (K), the processor 52 calculates dimensionless numbers related to the physical properties of the slag 2 estimated in the slag physical property estimation step (J). In the settling behavior allocation step (L), the processor 52 allocates a settling behavior corresponding to the operating conditions of the refining furnace 1 based on the foaming stability derived in the stability derivation step (H) and the dimensionless number calculated in the dimensionless number calculation step (K). In the bulk density determination step (M), the processor 52 determines the bulk density of the slag 2 based on the elapsed time since the end of blowing in the refining furnace 1 and the settling behavior allocated in the settling behavior allocation step (L).

In the dimensionless calculation step (K), the physical property values of the slag 2 calculated in the slag property estimation step (J) are substituted into the above-described formulas (1) and (2), whereby the Morton number Mo and the solid fraction Φ _s are derived.

In the settling behavior allocating step (L), a time constant τ representing forming stability corresponding to the Morton number Mo and the solid fraction Φ _s derived in the dimensionless number calculation step (K) is allocated.

Regarding the bulk density determination step (M), the gas phase fraction Φ(T 0 ) of the slag 2 remaining in the refining furnace 1 after the end of slag removal (when T ₀ seconds have elapsed since the end of blowing) is calculated using the above-mentioned formula ( ₆ ). Then, the bulk density of the slag 2 remaining in the refining furnace 1 is estimated using the following formula (8).

<Example of operation of volume estimation process>
The volume estimation step (D) may include a slag height measurement step (N) and a slag volume estimation step (O). In the slag height measurement step (N), the height from the hearth 11 to the melt surface 21 or 22 of the slag 2 (see FIG. 4) after the slag removal is measured, for example, by a method using microwaves. In the slag volume estimation step (O), the volume V _slag of the slag 2 remaining in the refining furnace 1 after the slag removal is calculated using the following equation (9).

In equation (9), S(h) is the cross-sectional area [m ² ] of the furnace body of the refining furnace 1 when the height from the hearth 11 is h. V _metal is the volume [m ³ ] of the introduced molten iron.

<Example of mass estimation process>
Regarding the mass estimation step (E), the slag mass M slag remaining in the refining furnace 1 is estimated using the following formula (10) based on the slag density ρ (T ₀ ) remaining in the refining furnace 1 after the completion of slag removal calculated in the bulk density determination step (M) and the volume V _slag of _the slag 2 calculated in the slag volume estimation step (O).

(Example)
Examples carried out by the inventors of the present disclosure are described below. In the examples, the mass of the slag 2 remaining in the refining furnace 1 is estimated from the bulk density and volume of the slag 2 after the completion of slag removal (300 seconds after the end of blowing) in the refining process of a charge (molten pig iron 3 containing impurities to be refined) specified by the following parameters:
Basicity C / S: 1.8
Estimated amount of iron oxide (FeO) contained in slag 2: 30%
Estimated slag temperature: 1400°C

To reproduce the physical properties of slag 2 under the above-mentioned operating conditions at room temperature, the inventors prepared an aqueous solution by adding glycerol and glass beads to pure water, and then foamed the prepared solution by blowing gas into it, thereby reproducing the sedation phenomenon by stopping the gas generation. The data obtained by measuring the change in the foam height of the aqueous solution over time is represented by the points plotted with circles (○) on the graph in Figure 5. The curve approximating the plotted points corresponds to the graph of equation (3) above. Based on this approximation curve, the time constant τ was calculated to be 130 seconds.

The values of the CO gas generation rate _VCO and the CO gas generation rate decay coefficient _τCO after the end of blowing when the estimated amount of iron oxide (FeO) contained in slag 2 is 40% were estimated in advance based on the results of another charge. By substituting these values and the time constant τ representing foaming stability into the above-mentioned equation (5), the time history h( _T0 ) of the height of slag 2 was obtained.

From the time history h(T ₀ ) of the height of the slag 2 and the above-mentioned equations (6) and (8), the time history ρ(T ₀ ) of the bulk density of the slag 2 was obtained as shown in the graph in Figure 6. Then, by substituting the elapsed time of 300 seconds from the end of blowing to the end of slag discharging into T ₀ , the bulk density ρ(T ₀ ) of the slag 2 after the end of slag discharging was estimated to be 246 kg/m ³ .

By substituting the bulk density ρ(T ₀ ) of the slag 2 after the completion of slag removal estimated as described above and the volume V _slag = 20 m ³ of the slag 2 remaining in the refining furnace 1 after the completion of slag removal estimated by the microwave method into the above-mentioned formula (10), the mass M _slag of the slag 2 remaining in the refining furnace 1 was calculated to be 4.9 tons.

Here, as a comparative example, the mass of slag 2 remaining in the refining furnace 1 was estimated assuming that the bulk density ρ (T ₀ ) of the slag 2 after the completion of slag removal was equal to the bulk density of the slag 2 immediately after the completion of blowing (ρ = 100 kg/m ³ ). The estimated value of the residual slag mass in the comparative example was 2.0 tons. On the other hand, the value of the mass of slag 2 remaining in the refining furnace 1 derived from the weighing value of the slag rolling cart to which the slag 2 was removed was 6.0 tons. In other words, the estimated value of the residual slag mass in this example is closer to the actual value of the residual slag mass than the estimated value of the residual slag mass in the comparative example. From the above, it can be seen that the accuracy of estimating the mass of slag 2 remaining in the refining furnace 1 is improved by executing a slag mass estimation method that takes into account settling behavior.

As described above, the slag mass estimation method disclosed herein allows for highly accurate and simple estimation of the mass of slag 2 remaining in the refining furnace 1 after slag removal is complete.

(Other embodiments)
By executing the above-described slag mass estimation method, the mass of the slag 2 remaining in the refining furnace 1 is estimated. The process computer of the refining device 40 may control the amount of auxiliary materials to be charged into the refining furnace 1 based on the estimated remaining slag mass. The process computer of the refining system 100 or the refining device 40 may execute an auxiliary material addition method including a step of adding auxiliary materials to the refining furnace 1 based on the mass of the slag 2 remaining in the refining furnace 1.

The process computer of the refining apparatus 40 may perform blowing in the refining furnace 1 to which the auxiliary material has been added by executing the auxiliary material addition method described above. The process computer of the refining system 100 or the refining apparatus 40 may perform a refining method that includes the step of performing blowing in the refining furnace 1 to which the auxiliary material has been added by executing the auxiliary material addition method described above.

The process computer of the refining apparatus 40 may produce molten steel by pouring the molten iron 3 processed by executing the refining method described above from the refining furnace 1. The process computer of the refining system 100 or the refining apparatus 40 may execute a method for producing molten steel, which includes the step of pouring out the molten iron 3 refined by executing the refining method described above.

Although embodiments of the present disclosure have been described based on various drawings and examples, it should be noted that those skilled in the art would 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 may be rearranged so as not to cause logical inconsistencies, and multiple components or steps may be combined into one or divided. Embodiments of the present disclosure may also be realized as a program executed by a processor provided in an apparatus, or as a storage medium on which a program is recorded. It should be understood that these are also included within the scope of the present disclosure.

100 Refining system 40 Refining apparatus (1: refining furnace, 11: hearth, 2: slag, 21: slag surface immediately after blowing, 22: slag surface after a predetermined time has elapsed, 3: molten iron, 42: top blowing lance)
50 Estimation device (52: processor, 54: memory unit, 56: interface)

Claims (10)

A slag mass estimation method for estimating a mass of slag remaining in a furnace after slag removal from a furnace for treating molten iron, comprising:
an information acquisition step of acquiring information that identifies a relationship between the physical properties of the slag and the settling behavior of the slag;
a physical property determination step of determining the physical properties of the slag based on the operating conditions of the treatment of the molten iron in the furnace;
a density estimation step of predicting the settling behavior of the slag based on the information acquired in the information acquisition step and the physical properties of the slag determined in the physical property determination step, and estimating the density of the slag remaining in the furnace after the slag is discharged;
a volume estimation step of measuring the height of the slag in the furnace after the slag has been removed and estimating the volume of the slag remaining in the furnace using the cross-sectional area of the furnace body for each height of the furnace body;
A slag mass estimation method including a mass estimation step of estimating the mass of the slag remaining in the furnace based on the density of the slag estimated in the density estimation step and the volume of the slag estimated in the volume estimation step. 2. The slag mass estimation method according to claim 1, wherein in the volume estimation step, the height of the slag in the furnace after completion of the slag removal is measured only once. A slag mass estimation method for estimating a mass of slag remaining in a furnace after slag removal from a furnace for treating molten iron, comprising:
an information acquisition step of acquiring information that identifies a relationship between the physical properties of the slag and the settling behavior of the slag;
a physical property determination step of determining the physical properties of the slag based on the operating conditions of the treatment of the molten iron in the furnace;
a density estimation step of predicting the settling behavior of the slag based on the information acquired in the information acquisition step and the physical properties of the slag determined in the physical property determination step, and estimating the density of the slag remaining in the furnace after the slag is discharged;
a volume estimation step of estimating the volume of the slag remaining in the furnace by measuring the height of the slag in the furnace and the volume of the furnace body;
a mass estimation step of estimating the mass of the slag remaining in the furnace based on the density of the slag estimated in the density estimation step and the volume of the slag estimated in the volume estimation step;
The information acquisition step includes a data acquisition step of acquiring data on the settling behavior of the slag, the data being obtained by an experiment that reproduces the settling phenomenon under operation, taking into account similarity conditions of dimensionless numbers related to the physical properties of the slag, as information specifying the relationship between the physical properties of the slag and the settling behavior of the slag;
The density estimation step includes a mathematical formulation step of formulating data on the settling behavior of the slag acquired in the data acquisition step by function approximation, and a stability derivation step of deriving forming stability from the approximate function obtained in the mathematical formulation step .
Slag mass estimation method. The slag mass estimation method according to claim 3, wherein the physical property determination step includes an operating condition extraction step of extracting operating conditions of the furnace from data of a process computer that controls the operation of the furnace, and a slag physical property estimation step of estimating the physical properties of the slag using a thermodynamic database and the operating conditions of the furnace extracted in the operating condition extraction step . 5. The slag mass estimation method according to claim 4, wherein the density estimation step includes a dimensionless number calculation step of calculating dimensionless numbers related to the physical properties of the slag estimated in the slag physical property estimation step, a settling behavior allocation step of allocating a settling behavior corresponding to the operating conditions of the furnace based on the foaming stability derived in the stability derivation step and the dimensionless number calculated in the dimensionless number calculation step, and a bulk density determination step of determining a bulk density of the slag based on the elapsed time since the end of blowing in the furnace and the settling behavior allocated in the settling behavior allocation step . A method for adding auxiliary materials to a furnace, the method comprising: adding an auxiliary material to the furnace based on the mass of slag remaining in the furnace, the mass of slag being estimated by executing the slag mass estimation method according to any one of claims 1 to 5. A method for refining molten iron, comprising the step of carrying out blowing in a furnace to which auxiliary materials have been added by carrying out the method for adding auxiliary materials according to claim 6 . A method for producing molten steel, comprising the step of pouring from a furnace molten iron that has been treated by carrying out the method for refining molten iron according to claim 7 . A slag mass estimation device comprising a processor that executes the slag mass estimation method according to any one of claims 1 to 5 . A refining system comprising the slag mass estimation device according to claim 9 and a refining device that processes molten iron.