Process control method, blast furnace operation method, molten-iron manufacturing method, and process control device and program

Abstract

This process control method includes: a response prediction step of finding a predicted value for a prospective molten-iron temperature by utilizing a physical model with which the state of the interior of a blast furnace can be calculated; and an operational-control-level determination step of, if the absolute value of the difference between the predicted value for the molten-iron temperature found in the response prediction step and a target value is greater than or equal to a prescribed threshold value, finding a deviation between the predicted value for the molten-iron temperature and the target value, to find a pulverized coal ratio and an operational-control level for blown-air moisture content such that an evaluation function having a term corresponding to the deviation and a term for decreasing a reducing-material ratio or the blown-air moisture content is minimized or maximized, and if the absolute value is less than the prescribed threshold value, combining, in accordance with intention, two among pulverized coal ratio, blown-air moisture content, and blown-air temperature, to find an operational-control level such that the predicted value is maintained.

Description

Process control method, blast furnace operation method, molten iron manufacturing method, process control device and program

[0001] The present disclosure relates to a process control method, a blast furnace operation method, a molten iron production method, a process control device, and a program.

[0002] In the blast furnace process of the steelmaking industry, hot metal temperature (HMT) is an important control index and is mainly controlled by adjusting the pulverized coal ratio and blast moisture. In recent years, blast furnace operation has been carried out under conditions of low coke rate and high pulverized coal rate in order to pursue rationalization of raw material and fuel costs, which tends to make the furnace condition unstable. Therefore, it is necessary to suppress the variation in hot metal temperature.

[0003] In addition, the blast furnace process is characterized by a large heat capacity for the entire process because it operates in a solid-filled state, resulting in a long time constant for response to actions. Furthermore, it can take several hours for the materials charged at the top of the furnace to descend to the bottom. Therefore, appropriate operation based on future furnace heat predictions is required to control the molten iron temperature.

[0004] In order to take into account the response delay resulting from the long time constant of the blast furnace, a method for controlling the blast furnace based on predictions has been proposed, which uses a physical model, as disclosed in, for example, Patent Document 1.

[0005] Japanese Patent Application Publication No. 11-335710

[0006] Here, recent CO ２Due to social demand for reduction, a reduction in the reducing agent rate (RAR) (the sum of the coke rate and pulverized coal rate) is required in the blast furnace process. To reduce the RAR, it is effective to reduce the blast moisture injected into the furnace or reduce the furnace body heat loss, thereby avoiding the consumption of excess heat sources. Furthermore, external requirements may necessitate a temporary increase in the exhaust gas volume of the blast furnace, regardless of the RAR. Meanwhile, the RAR significantly affects the permeability (air permeability) within the furnace, requiring careful operation to maintain stable operation. However, Patent Document 1 discloses a technology for predicting and calculating the molten iron temperature, but does not propose a control method that takes into account the RAR according to the desired conditions while maintaining stable operation.

[0007] An object of the present disclosure, which has been made to solve the above problems, is to provide a process control method, a blast furnace operation method, a molten iron production method, a process control device, and a program that suppress variation in molten iron temperature in a blast furnace, while maintaining stable operation and proposing a reducing agent ratio in accordance with the user's wishes.

[0008] (1) A process control method according to an embodiment of the present disclosure includes: a response prediction step of determining a predicted value of a future molten pig iron temperature using a physical model capable of calculating the internal state of a blast furnace; and a manipulated variable determination step of determining a deviation between the predicted value of the molten pig iron temperature and a target value when the absolute value of the difference between the predicted value and a target value of the molten pig iron temperature determined in the response prediction step is equal to or greater than a predetermined threshold, and determining manipulated variables for a pulverized coal ratio and a blast humidity so as to minimize or maximize an evaluation function having a term corresponding to the deviation and a term for reducing an reducing agent ratio or a blast humidity; and, when the absolute value is less than the predetermined threshold, determining manipulated variables by combining two of the pulverized coal ratio, the blast humidity, and the blast temperature according to a preference so as to maintain the predicted value.

[0009] (2) As one embodiment of the present disclosure, in (1), the inclinations include a first inclination that prioritizes reducing the reducing agent rate and a second inclination that temporarily increases exhaust gas from the blast furnace.

[0010] (3) As one embodiment of the present disclosure, in (2), the operation amount determination step, when the inclination is the first inclination, determines the operation amount to be a combination of the pulverized coal ratio decreasing operation and the blast moisture decreasing operation, the pulverized coal ratio decreasing operation and the blast temperature increasing operation, or the blast temperature decreasing operation and the blast moisture decreasing operation, and when the inclination is the second inclination, determines the operation amount to be a combination of the pulverized coal ratio increasing operation and the blast moisture increasing operation, the pulverized coal ratio increasing operation and the blast temperature decreasing operation, or the blast temperature increasing operation and the blast moisture increasing operation.

[0011] (4) As one embodiment of the present disclosure, in (3), an operation amount for a combination of two of the pulverized coal ratio, the blast moisture, and the blast temperature is calculated so that the theoretical combustion temperature falls within a predetermined range.

[0012] (5) As an embodiment of the present disclosure, in any one of (1) to (4), the response prediction step uses the physical model to obtain a predicted value of the future molten iron temperature based on a predicted value of the future molten iron temperature when the current operating variables are maintained and a predicted value of the molten iron temperature when the current operating variables are changed.

[0013] (6) As an embodiment of the present disclosure, in any one of (1) to (5), the operation variable determination step determines the unknown variables by using the evaluation function, which is a quadratic function of the unknown variables, under the constraint condition of a linear expression for the unknown variables, with the pulverized coal ratio and the blast moisture to be sought as unknown variables.

[0014] (7) As an embodiment of the present disclosure, in any one of (1) to (6), the method further includes the steps of manipulating the blast flow rate so that the predicted value of the iron-making rate matches the target value, and manipulating the coke rate so that the predicted value of the permeability is equal to or lower than the upper limit.

[0015] (8) A method for operating a blast furnace according to an embodiment of the present disclosure changes operating conditions using an operating variable manipulated by the process control method according to any one of (1) to (7).

[0016] (9) A method for producing molten iron according to an embodiment of the present disclosure produces molten iron using the blast furnace operated by the blast furnace operating method of (8).

[0017] (10) A process control device according to an embodiment of the present disclosure includes: a storage unit that stores a physical model capable of calculating the internal state of a blast furnace; and a molten iron temperature control unit that acquires a target molten iron temperature, which is a target value for the molten iron temperature, and calculates manipulated variables for a pulverized coal ratio and a blast moisture content so that the molten iron temperature becomes the target molten iron temperature. The molten iron temperature control unit: obtains a predicted value of a future molten iron temperature using the physical model; and, when an absolute value of a difference between the predicted value and the target value of the molten iron temperature is equal to or greater than a predetermined threshold, obtains a deviation between the predicted value and the target value of the molten iron temperature, and calculates manipulated variables for the pulverized coal ratio and the blast moisture content so as to minimize or maximize an evaluation function having a term corresponding to the deviation and a term for reducing an agent ratio or a blast moisture content; and, when the absolute value is less than the predetermined threshold, calculates manipulated variables by combining two of the pulverized coal ratio, the blast moisture content, and the blast temperature in accordance with a preference so as to maintain the predicted value.

[0018] (11) A program according to an embodiment of the present disclosure causes a computer to execute: a response prediction step of determining a predicted value of a future molten iron temperature using a physical model capable of calculating the internal state of a blast furnace; and a manipulated variable determination step of determining a deviation between the predicted value of the molten iron temperature and a target value when the absolute value of the difference between the predicted value and a target value of the molten iron temperature determined in the response prediction step is equal to or greater than a predetermined threshold, and determining manipulated variables for the pulverized coal ratio and the blast humidity so as to minimize or maximize an evaluation function having a term corresponding to the deviation and a term for reducing an reducing agent ratio or a blast humidity; and, when the absolute value is less than the predetermined threshold, determining manipulated variables by combining two of the pulverized coal ratio, the blast humidity, and the blast temperature according to a preference so as to maintain the predicted value.

[0019] According to the present disclosure, it is possible to provide a process control method, a blast furnace operation method, a molten iron production method, a process control device, and a program that suppress variations in molten iron temperature in a blast furnace, while maintaining stable operation and proposing a reducing agent ratio according to the user's preferences.

[0020] FIG. 1 is a diagram showing manipulated variables and controlled variables in a blast furnace process. FIG. 2 is a diagram showing a process control method according to an embodiment of the present disclosure. FIG. 3 is a diagram showing the influence of the pulverized coal ratio, blast moisture, and blast temperature on the inside of the furnace. FIG. 4 is a diagram showing input / output information of a physical model used in the present disclosure. FIG. 5 is a diagram showing the results of a control simulation in which the pulverized coal ratio and blast moisture are simultaneously manipulated. FIG. 6 is a diagram showing the results of a control simulation in which only the pulverized coal ratio is manipulated (comparative example). FIG. 7 is a diagram illustrating a case in which a manipulated variable is determined by combining two manipulated variables. FIG. 8 is a diagram showing an example configuration of a process control device according to an embodiment of the present disclosure.

[0021] Hereinafter, a process control method, a blast furnace operation method, a molten iron production method, a process control device, and a program according to an embodiment of the present disclosure will be described with reference to the drawings.

[0022] FIG. 1 shows basic operational variables and control variables in a blast furnace process (a step in blast furnace operation). Control variables are variables that must be controlled during operation, but cannot or are difficult to manipulate directly. They are changed via correlated operational variables. In blast furnace operation, the pulverized coal ratio, blast moisture content, etc. are primarily manipulated to achieve a target molten iron temperature. To maintain good permeability (air permeability), the pulverized coal ratio, blast moisture content, coke rate, and blast flow rate are primarily manipulated. Furthermore, to achieve a target iron-making rate, the blast flow rate is primarily manipulated. Here, in this embodiment, furnace pressure loss, which directly affects blow-through, is used as the permeability. Furnace pressure loss is the difference between the blast pressure and the furnace top pressure (pressure at the furnace top). In addition to furnace pressure loss, various other indicators of permeability exist, such as airflow resistance and shaft pressure differential. Therefore, instead of the furnace pressure drop, another index of permeability may be used as the permeability, or a combination of multiple indexes of permeability may be used. In the process control method according to this embodiment, attention is paid to the pulverized coal ratio and blast moisture, which are manipulated variables for controlling the molten pig iron temperature, and optimal manipulated variables for the pulverized coal ratio and blast moisture are determined so as to reduce the reducing agent rate while controlling the molten pig iron temperature. Furthermore, attention is paid to the relationship between the pulverized coal ratio, blast moisture, and blast temperature, and manipulated variables are determined for the combination of these.

[0023] FIG. 2 is a diagram illustrating the process of the process control method according to this embodiment. The process control method according to this embodiment uses cascade control, as described in, for example, Reference 1 (Japanese Patent No. 7107444). In the cascade control, a control for calculating a target pulverized coal ratio (PCR) (hot metal temperature control in FIG. 2 ) and a control for calculating a pulverized coal flow rate required for the target PCR (PCR tracking control in FIG. 2 ) are performed consecutively. The hot metal temperature control acquires a target hot metal temperature, which is a target value for the hot metal temperature (HMT), and can calculate the target PCR using a physical model, which will be described later. Furthermore, the hot metal temperature control not only calculates the target PCR (i.e., determines the manipulated variable for the pulverized coal ratio), but also calculates the manipulated variable for the blast moisture.

[0024] The process control method according to this embodiment also includes ironmaking rate control and permeability control. Ironmaking rate control involves obtaining a target ironmaking rate (Prod), which is a target value for the ironmaking rate, and calculating the manipulated variable for the blast volume (BV) using a physical model (described later). Permeability control involves obtaining an upper limit for the furnace pressure drop (ΔP), which is an upper limit for the furnace pressure drop (ΔP), and calculating the manipulated variables for the blast volume and coke rate using a physical model (described later). Actual values ​​(which may be observed or calculated) from the plant, including the blast furnace, may be fed back to update the physical models used in each control. In the example of FIG. 2 , the actual values ​​of the pulverized coal ratio (PCR), molten iron temperature (HMT), furnace pressure drop (ΔP), and ironmaking rate (Prod) are shown as actual PCR, actual HMT, actual ΔP, and actual Prod, respectively. Furthermore, the correspondence between control variables and correlated manipulated variables in a blast furnace process is not limited to that shown in Figures 1 and 2. For example, in ironmaking speed control, it is possible to manipulate the blast oxygen flow rate instead of the blast flow rate.

[0025] In this embodiment, a multivariable control system as shown in Figure 2 is constructed, with individual controllers (hot metal temperature control, permeability control, and ironmaking speed control) for controlling the hot metal temperature (HMT), furnace pressure drop (ΔP), and ironmaking speed (Prod). The hot metal temperature is controlled by cascade control, which manipulates the blast moisture content and the pulverized coal ratio (PCR) and pulverized coal flow rate. The permeability is controlled by manipulating the blast flow rate and coke rate. The ironmaking speed is controlled by manipulating the blast flow rate. Here, for example, when the blast flow rate is manipulated in the ironmaking speed control, changes in the blast flow rate affect the hot metal temperature. This effect is reflected by a physical model in the hot metal temperature control, and is calculated as the manipulated variable for the pulverized coal ratio or blast moisture. The calculated manipulated variable for the pulverized coal ratio or blast moisture is reflected, thereby maintaining the hot metal temperature near the target value. In this embodiment, although individual controllers are constructed as described above, it is possible to realize control that takes into account the interference between the respective manipulated variables. That is, for example, although the hot metal temperature control and the ironmaking speed control interfere with each other, the control system is constructed with a disturbance rejection characteristic that absorbs fluctuations due to the manipulation of the other manipulated variable by manipulating the manipulated variable itself, thereby reducing the influence of the interference. The same applies to the gas permeability control.

[0026] The process control method according to this embodiment predicts future hot metal temperature and ironmaking rate using a physical model of the blast furnace based on chemical kinetics. When the absolute value of the difference between the predicted value and the target value is equal to or greater than a predetermined threshold, the process control method determines the amount of change in the pulverized coal ratio and blast moisture content so that the predicted value approaches the target value. By using quadratic programming to minimize an evaluation function that takes the reducing agent rate into account when determining these manipulated variables, it is possible to achieve both an increase or decrease in the reducing agent rate and suppression of hot metal temperature variation. The increase or decrease in the reducing agent rate can be determined based on the desired outcome. The desired outcome is an operational policy. When a low reducing agent rate is required for environmental considerations, the reducing agent rate may be reduced. Furthermore, the reducing agent rate may be increased when external requirements require a temporary increase in blast furnace flue gas. Examples of external requirements include restrictions on the power supply and raw material inventory. In this embodiment, the orientation includes a first orientation that prioritizes reducing the reducing agent ratio and a second orientation that temporarily increases exhaust gas from the blast furnace. In the following, the first orientation (orientation toward a low reducing agent ratio) will be described as a premise, but the present disclosure is not limited thereto, and the method of the present disclosure can also be applied to, for example, the second orientation (orientation toward a temporary increase in exhaust gas).

[0027] Furthermore, in the process control method according to this embodiment, if the absolute value of the difference between the predicted value and the target value is less than a predetermined threshold, the predicted value is determined to be close to the target value, and therefore the manipulated variables for the two parameters are determined according to the inclination while maintaining the predicted value. The process flow in the process control method according to this embodiment can be summarized as follows: Steps 1 to 4.

[0028] First, in step 1, a future molten iron temperature is predicted using a physical model. Step 1 is a response prediction step. In the response prediction step, a predicted value of the future molten iron temperature is calculated using a physical model based on a predicted value of the future molten iron temperature when the current operating variables are maintained and a predicted value of the molten iron temperature when the current operating variables are changed. The predicted value of the future molten iron temperature when the current operating variables are maintained is a free response, which will be described later. In this embodiment, the predicted value of the molten iron temperature when the current operating variables are changed is a step response, which will be described later, but is not limited to this.

[0029] Next, in step 2, the manipulated variables are manipulated using quadratic programming so that the predicted value of the hot metal temperature in step 1 matches the target value and the reducing agent rate is minimized. Step 2 is part of the manipulated variable determination step, in which the deviation between the predicted value and the target value is calculated, the manipulated variables for eliminating the deviation are determined, and the manipulated variables are adjusted. In this embodiment, the manipulated variables are the pulverized coal rate and the blast moisture.

[0030] In addition, in step 3, in order to simulate actual operation of a blast furnace, the blast flow rate may be manipulated so that the predicted value of the iron-making rate matches the target value, and at least the coke rate may be manipulated so that the predicted value of the permeability is equal to or less than an upper limit. In this embodiment, the permeability is the pressure loss in the furnace, and if the predicted value of the pressure loss in the furnace exceeds a set upper limit, the permeability state is determined to be abnormal. If the permeability state is determined to be abnormal, an operation to increase the coke rate may be performed. If the permeability state is determined not to be abnormal, that is, if the predicted value of the pressure loss in the furnace is equal to or less than the upper limit, an operation to decrease the coke rate may be performed. The manipulation of the blast flow rate and the coke rate in step 3 constitutes a disturbance to the molten iron temperature control.

[0031] In step 4, when the predicted value of the hot metal temperature in step 1 substantially matches the target value, a manipulated variable is determined, which is a set of two parameters among the pulverized coal ratio, blast moisture, and blast temperature according to the desired direction, and which can maintain the predicted value. The blast temperature is the temperature of the blast air and is one of the manipulated variables. The near-matching of the predicted value of the hot metal temperature with the target value may be determined by the absolute value of the difference between the predicted value of the hot metal temperature and the target value being less than a predetermined threshold. The predetermined threshold may be determined in advance based on past performance data, etc. As described above, the desired direction includes, for example, a first direction (a direction toward a low reducing agent ratio) and a second direction (a direction toward a temporary increase in flue gas). For example, in the case of the first direction, reducing the pulverized coal ratio can achieve more effective operation. Reducing the pulverized coal ratio improves (decreases) the permeability, but the predicted hot metal temperature decreases. Therefore, in the control method of this embodiment, the operation amount is determined so that the blast moisture is also reduced in combination with the pulverized coal ratio reduction operation. The pulverized coal ratio reduction operation reduces the molten iron temperature and permeability. On the other hand, the blast moisture reduction operation increases the molten iron temperature and permeability, so the effects of these two operations cancel each other out.

[0032] Figure 3 shows the influence of the pulverized coal ratio, blast moisture, and blast temperature on the furnace interior. An increase operation is an operation to increase the value of the manipulated variable. A decrease operation is an operation to decrease the value of the manipulated variable. As described above, for example, by simultaneously performing decrease operations on the pulverized coal ratio and blast moisture, it is possible to maintain the predicted molten iron temperature and continue stable operation.

[0033] As shown in Fig. 3, when the inclination is the first inclination (low reducing agent ratio inclination), the manipulated variables may be determined to achieve a combination of decreasing the pulverized coal ratio and decreasing the blast moisture content. At this time, the influences of the molten pig iron temperature and the permeability are offset. The combination is not limited to this, and when the inclination is the first inclination, the manipulated variables may be determined to achieve a combination of decreasing the pulverized coal ratio and increasing the blast temperature, or decreasing the blast temperature and decreasing the blast moisture content.

[0034] On the other hand, in the case of the second tendency (tending toward a temporary increase in exhaust gas), the operation variables may be determined to be a combination of increasing the pulverized coal ratio and increasing the blast moisture content. The combination is not limited to this, and in the case of the second tendency, the operation variables may be determined to be a combination of increasing the pulverized coal ratio and decreasing the blast temperature, or increasing the blast temperature and increasing the blast moisture content. By combining two of the pulverized coal ratio, blast moisture, and blast temperature and determining the operation variables in a direction that cancels out each other's changes so as to maintain the predicted values, it is possible to maintain the molten iron temperature and continue stable operation. Verification will be described later.

[0035] Whether the operation orientation is the first orientation or the second orientation may be determined in advance, or the control unit 13 described later may receive an input for specifying the orientation.

[0036] Here, when the predicted value of the molten pig iron temperature is approximately equal to the target value, the manipulated variables are varied to maintain the predicted value of the molten pig iron temperature (to offset the influence), but the amount of variation is not unlimited. For example, when the first trend is selected and the predicted value of the molten pig iron temperature is approximately equal to the target value, the pulverized coal ratio and blast moisture content cannot be decreased indefinitely. Similarly, when the second trend is selected and the predicted value of the molten pig iron temperature is approximately equal to the target value, the pulverized coal ratio and blast moisture content cannot be increased indefinitely. In a blast furnace, the theoretical combustion temperature (calculated combustion temperature) at which pulverized coal and blast moisture are injected must be within a predetermined range (control value). If the theoretical combustion temperature deviates from the control value, various operational problems may occur. The control value of the theoretical combustion temperature can be calculated using various known calculation formulas, but may be set to 2000°C to 2500°C, for example. When calculating the manipulated variable, it is preferable to consider the theoretical combustion temperature.

[0037] The calculations of steps 1 to 4 are described in detail below. The physical model used in the present disclosure is similar to the method described in Reference 2 (Hadano Michiharu et al., "Study of Blast Furnace Burn-in Operation Using a Non-Steady-State Model," Iron and Steel, Vol. 68, p. 2369). That is, a physical model is used that is capable of calculating the state inside (inside) a blast furnace in a non-steady state, and is composed of a group of partial differential equations that take into account physical phenomena such as ore reduction, heat exchange between ore and coke, and ore melting. This physical model may be referred to as a non-steady-state model hereinafter.

[0038] As shown in Figure 4, the main time-varying input variables given to the unsteady model are the blast flow rate, blast oxygen flow rate, pulverized coal flow rate, blast moisture, blast temperature, coke rate, and furnace top pressure. These input variables are operational variables or operating factors of the blast furnace. The blast flow rate, blast oxygen flow rate, and pulverized coal flow rate are the flow rates of air, oxygen, and pulverized coal sent to the blast furnace, respectively. The blast moisture is the humidity of the air sent to the blast furnace. The blast temperature is the temperature of the air sent to the blast furnace. The coke rate is the coke rate at the furnace top, and is the weight of coke used per ton of molten iron produced.

[0039] The main output variables of the unsteady-state model are the gas utilization rate, the amount of solution loss carbon (sol-loss carbon), the reducing agent ratio, the iron-making rate, the hot metal temperature, and the furnace pressure drop. The unsteady-state model can be used to calculate the ever-changing hot metal temperature, the iron-making rate, and the furnace pressure drop. The calculation time interval is not particularly limited, but is 30 minutes in this embodiment. The time difference between "t+1" and "t" in the equation for the unsteady-state model, which will be described later, is 30 minutes in this embodiment.

[0040] The unsteady model can be expressed by the following equations (1) and (2).

[0041]

[0042] Here, x(t) is a state variable calculated within the unsteady model. Examples of state variables include the coke temperature, iron temperature, ore oxidation degree, and raw material descending speed. y(t) is the control variable, which is the hot metal temperature, ironmaking rate, and permeability (inner furnace pressure loss). u(t) is the input variable, which can be manipulated by the operator operating the blast furnace. That is, the input variables are the blast flow rate BV(t), blast oxygen flow rate BVO(t), pulverized coal flow rate PCI(t), blast moisture BM(t), blast temperature BT(t), coke ratio CR(t), and furnace top pressure TGP(t). u(t) = (BV(t), BVO(t), PCI(t), BM(t), BT(t), CR(t), TGP(t)). Ｔ It can be expressed as:

[0043] First, we assume that the current values ​​of the input variables are kept constant and calculate the future control variables. ０ The response y of the control variable obtained in this way is predicted using the following equations (3) and (4), with y being set to 0. ｆ (t) is called the free response.

[0044]

[0045] A method for determining the current and future operation amounts of the pulverized coal ratio (PCR) and blast moisture (BM) will be described below. An example of predicting the future for two hours will be described. The unknown variables θ = (ΔPCR ０ , ΔB ０ , ΔPCR １ , ΔB １ ) are introduced, and the operation amounts of the pulverized coal ratio (PCR) and blast moisture (BM) are determined by quadratic programming. The subscript 0 indicates the present time, and the subscript 1 indicates two hours later.

[0046] As a prerequisite for predictive control using this physical model, the future hot metal temperature is calculated based on the free response y ｆ It can be approximated by superposing the step response on the predicted value of the hot metal temperature every two hours up to 10 hours ahead. ｐｒｅ (t) is as shown in the following equation (5).

[0047]

[0048] Here, S ＰＣＲ (t) is the change in the hot metal temperature when the pulverized coal ratio (PCR) is changed by a unit amount (1 [kg / t]). ＢＭ (t) is the unit amount of blast moisture (BM) (1 [g / Nm ３ ]) is the change in the humidity of the air blown when only ＰＣＲ and S ＢＭ can be obtained, for example, by another physical model or a step response test in actual operation. In the calculations in this disclosure, the simulation results described in Reference 3 (Y. Hashimoto, Online prediction of hot metal temperature using transient model and moving horizon estimation. ISIJ Int. 2019, vol. 59, p. 1534) were used.

[0049] In the following, when Equation (5) is expressed as Equation (6) using the step response matrix S, the predicted value of the molten iron temperature and the target value y ｐｒｅ The deviation from (t) is as shown in equation (7).

[0050]

[0051] where y is the free response ｆ (t) target value y ｐｒｅ The deviation from (t) is δy. The predicted value of the molten iron temperature and the target value y ｐｒｅ The square of the deviation from (t) is given by the following equation (8).

[0052]

[0053] In order to simultaneously reduce the variation in the hot metal temperature and minimize the reducing agent rate, the evaluation function J used in the quadratic programming method includes a term for reducing blast moisture (third term) in addition to the first and second terms in equation (8), as shown in equation (9). The evaluation function J also includes a fourth term for suppressing excessive operation.

[0054]

[0055] where a and R are coefficients. Comparing the responsiveness of the hot metal temperature to changes in the pulverized coal ratio (PCR) and the blast moisture content (BM), it is known that the blast moisture content has a more immediate response. However, in order to ensure an operable range for both increasing and decreasing the blast moisture content, it is necessary to increase the average blast moisture content. Increasing the average blast moisture content results in heat absorption due to the steam decomposition reaction of the blast moisture, which necessitates the addition of more reducing material to compensate for the heat loss. Therefore, a third term is introduced to limit the amount of blast moisture manipulation. The weighting of ΔPCR and ΔBM in the vector θ can be adjusted depending on the magnitude of the element in the coefficient vector a, thereby adjusting the distribution of manipulation between the two.

[0056] Moreover, θ is determined using equation (9) under the constraints of the following equations (10) to (13).

[0057]

[0058] Here, the subscript i in the formulas (10) to (13) is 0 or 1. The subscript now means the value of the pulverized coal ratio (PCR) or blast moisture (BM) at the current time. PCR ｍａｘ , PCR ｍｉｎ are the upper and lower limits of the target range of the pulverized coal ratio (PCR), respectively. ｍａｘ is the upper limit of the allowable change in the pulverized coal ratio (PCR). ｍａｘ , B.M. ｍｉｎ are the upper and lower limits of the target range of blast moisture (BM), respectively. ｍａｘ is the upper limit of the magnitude of the allowable change in blast moisture (BM). The unknown variable θ is determined using quadratic programming so as to minimize the evaluation function J, which is a quadratic function related to the unknown variable θ, under the constraint conditions of a linear equation related to the unknown variable θ shown in equations (10) to (13). The control to determine the unknown variable θ using equation (9) corresponds to the molten iron temperature control in Figure 2.

[0059] In this embodiment, the evaluation function J is designed to reduce the blast moisture content in order to reduce the reducing agent rate, but the same effect can be obtained by using an evaluation function J that directly reduces the reducing agent rate, for example, by imposing a penalty on an increase in the pulverized coal rate. Furthermore, in this embodiment, the unknown variable θ is determined when the evaluation function J is minimized, but the evaluation function J may be designed so that minimization of the deviation between the predicted value and the target value of the molten iron temperature and the reducing agent rate (or blast moisture) corresponds to maximization of the evaluation function J. In other words, the manipulated variables for the pulverized coal rate and the blast moisture may be determined so as to minimize or maximize the evaluation function J.

[0060] In order to verify the effect of reducing agent rate reduction according to the present disclosure through simulation under operating conditions close to those of actual operation, the manipulated variables (blast flow rate and coke rate) are manipulated using the following method in addition to the control variables (iron-making rate and furnace pressure drop) other than the molten iron temperature.

[0061] The blast flow rate (BV) [Nm ３ / min] is calculated.

[0062]

[0063] Here, Prod(t+T) is the predicted value of the ironmaking rate T steps ahead. For example, T may be 4, which means the predicted value 2 hours (30 minutes x 4) ahead. ｒｅｆ is the target iron-making speed (target value of the iron-making speed). ＢＶ is the air flow rate (BV) in units of 1 [Nm ３ / min]). ＢＶ can be obtained by another physical model or a step response test in actual operation. b is a coefficient and is a positive number. The control for obtaining ΔBV according to equation (14) corresponds to the ironmaking speed control in FIG. 2.

[0064] Furthermore, the operation amounts of the coke rate (CR) and the blast flow rate (BV) are determined by comparing the furnace pressure drop (ΔP) with an upper limit (threshold value). When the furnace pressure drop (ΔP) exceeds the upper limit, the operation amounts are determined to increase the coke rate and simultaneously decrease the blast flow rate. This corresponds to the operation of stabilizing the unloading of raw materials in blast furnace operation. Furthermore, when the furnace pressure drop is equal to or less than the upper limit, the operation amount is determined to gradually decrease the coke rate. In principle, control is performed so that the furnace pressure drop does not exceed the upper limit. However, when the furnace pressure drop is equal to or less than the upper limit, gradually decreasing the coke rate can reduce operation costs. When such control is performed, the value of the furnace pressure drop remains near the upper limit. The control that determines the operation amounts of the coke rate (CR) and the blast flow rate (BV) by comparing the furnace pressure drop with the upper limit corresponds to the permeability control in Figure 2.

[0065] Figure 5 shows the results of a simulation performed using the process control described above, assuming that the absolute value of the difference between the predicted value of the hot metal temperature obtained in the response prediction step and the target value is equal to or greater than a predetermined threshold. In other words, in the simulation shown in Figure 5, the blast moisture content (BM), pulverized coal ratio (PCR), blast flow rate (BV), and coke rate (CR) were controlled based on predicted values ​​using a transient model of the hot metal temperature (HMT), ironmaking rate (Prod), and furnace pressure drop (ΔP), which is an example of permeability. The target hot metal temperature was 1500°C. The target ironmaking rate was 7 t / min. The upper limit of furnace pressure drop was 100 kPa.

[0066] As shown in Figure 5, the hot metal temperature (HMT) is controlled near the target value, and the blast moisture (BM) is maintained near the lower limit while suppressing the variation in the hot metal temperature based on the evaluation function J shown in Equation (9). Keeping the blast moisture near the lower limit reduces the heat absorption caused by the steam decomposition reaction, which requires the addition of reducing agent, leading to a reduction in the reducing agent rate. Furthermore, the ironmaking rate (Prod) is controlled near the target value, and the furnace pressure drop (ΔP) is also kept below the upper limit.

[0067] For comparative verification, a simulation was carried out for a comparative example in which only the pulverized coal ratio (PCR) was manipulated without manipulating the blast moisture (BM). Figure 6 shows the simulation results under the control of the comparative example. In the simulation of Figure 6, the pulverized coal ratio (PCR), blast flow rate (BV), and coke rate (CR) were manipulated based on predicted values ​​using a non-steady-state model of the hot metal temperature (HMT), the ironmaking rate (Prod), and the furnace pressure drop (ΔP), which is an example of permeability. The simulation conditions were the same as those in Figure 5, except for the blast moisture (BM). The blast moisture was 15.5 [g / Nm ３ The average value of the reducing agent ratio in the process control method according to this embodiment was reduced compared to the average value of the reducing agent ratio in the comparative example. By reducing the reducing agent ratio, the amount of oxygen (oxygen consumption unit) [Nm ３ / t] is reduced. Therefore, the target iron-making speed can be achieved with a smaller blast flow rate. As a result, there is a margin for pressure loss, and the coke rate can also be reduced (see CR in Figures 5 and 6).

[0068] Figure 7 illustrates the results of determining manipulated variables by combining two manipulated variables, assuming that the absolute value of the difference between the predicted value of the hot metal temperature obtained in the response prediction step and the target value is less than a predetermined threshold. Items such as BV and Prod are the same as in Figure 5. The horizontal axis is also a common time axis. The example in Figure 7 shows changes over a 12-hour period. As indicated by the dashed circles for the pulverized coal ratio (PCR) and blast moisture (BM), the manipulated variables change with a combination of decreasing the pulverized coal ratio and decreasing the blast moisture. However, even with this change, no significant change is observed in the hot metal temperature (HMT). In other words, stable operation can be continued by maintaining the hot metal temperature while changing the reducing agent ratio according to the desired condition.

[0069] Fig. 8 is a diagram showing an example of the configuration of a process control device 10 according to an embodiment. As shown in Fig. 8, the process control device 10 according to this embodiment includes a communication unit 11, a storage unit 12, and a control unit 13. The control unit 13 includes a molten iron temperature control unit 14, an ironmaking speed control unit 15, a permeability control unit 16, and a PCR tracking control unit 17. The process control device 10 executes the above-described process control method. Here, when manipulating the blast moisture, blast flow rate, coke rate, or pulverized coal rate, the process control device 10 may display information such as manipulated variables on a display unit such as a liquid crystal display.

[0070] The communication unit 11 includes a communication module for communicating with a higher-level system. The higher-level system includes a process computer that manages processes in a plant including a blast furnace. The communication unit 11 may include a communication module compatible with mobile communication standards such as 4G (4th Generation) and 5G (5th Generation). The communication unit 11 may include a communication module compatible with wired or wireless LAN standards. The control unit 13 can acquire information such as the target molten iron temperature, the target iron-making speed, and the upper limit of pressure drop in the furnace from the higher-level system via the communication unit 11. The control unit 13 can also output information on the manipulated variables that have been operated, i.e., the manipulated variables that reflect the calculated manipulated variables, to the higher-level system via the communication unit 11.

[0071] The storage unit 12 stores the above-described physical model. The storage unit 12 also stores programs and data related to the control of the blast furnace process. The storage unit 12 may include any storage device, such as a semiconductor storage device, an optical storage device, or a magnetic storage device. The semiconductor storage device may include, for example, a semiconductor memory. The storage unit 12 may include multiple types of storage devices.

[0072] The control unit 13 controls and manages each functional unit constituting the process control device 10 and the entire process control device 10. The control unit 13 may also acquire data used for control. That is, the control unit 13 may acquire the molten iron temperature, iron-making rate, and permeability of the blast furnace as observed or calculated values. The control unit 13 includes at least one processor, such as a CPU (Central Processing Unit), to control and manage various functions. The control unit 13 may be composed of one processor or multiple processors. The processor constituting the control unit 13 may function as the molten iron temperature control unit 14, iron-making rate control unit 15, permeability control unit 16, and PCR tracking control unit 17 by reading and executing programs from the memory unit 12.

[0073] The molten iron temperature control unit 14 acquires a target molten iron temperature, which is a target value for the molten iron temperature, and, when the absolute value of the difference between the predicted value of the molten iron temperature and the target value is equal to or greater than a predetermined threshold, calculates manipulated variables for the blast moisture and the pulverized coal ratio so that the molten iron temperature becomes the target molten iron temperature. The molten iron temperature control unit 14 is a functional unit that executes the "molten iron temperature control" in Fig. 2. Furthermore, when the absolute value of the difference between the predicted value of the molten iron temperature and the target value is less than a predetermined threshold, the molten iron temperature control unit 14 determines manipulated variables by combining two of the pulverized coal ratio, blast moisture, and blast temperature so as to maintain the predicted value.

[0074] The iron-making speed control unit 15 acquires a target iron-making speed, which is a target value of the iron-making speed, and calculates the manipulated variable for the blast flow rate so that the iron-making speed becomes the target iron-making speed. The iron-making speed control unit 15 is a functional unit that executes the "iron-making speed control" in FIG.

[0075] The air permeability control unit 16 acquires an upper limit of the air permeability (in-furnace pressure loss in this embodiment) and calculates at least an manipulated variable for the coke rate so that the air permeability does not exceed the upper limit. The air permeability control unit 16 may further calculate an manipulated variable for the blast flow rate, as in this embodiment. The air permeability control unit 16 is a functional unit that executes the "air permeability control" in FIG. 2.

[0076] The PCR tracking control unit 17 acquires the pulverized coal ratio (target PCR), which is a target value determined by the hot metal temperature control unit 14, and calculates the manipulated variable of the pulverized coal flow rate (PCI) by PCR tracking control so as to follow the target PCR. The PCR tracking control unit 17 is a functional unit that executes the "PCR tracking control" in FIG. 2.

[0077] The hot metal temperature control unit 14, the ironmaking speed control unit 15, and the permeability control unit 16 are individual controllers for controlling the hot metal temperature (HMT), the ironmaking speed (Prod), and the furnace pressure drop (ΔP), respectively. Using the above steps 1 to 3, the hot metal temperature control unit 14 executes step 1 (a response prediction step) using a physical model to obtain a predicted value for the hot metal temperature. The hot metal temperature control unit 14 executes step 2 (part of the manipulated variable determination step) to obtain manipulated variables for the pulverized coal ratio and the blast moisture content. The hot metal temperature control unit 14 executes step 3 to obtain manipulated variables for the blast flow rate so as to eliminate the deviation between the target value and the predicted value for the ironmaking speed. The permeability control unit 16 executes step 3 to obtain manipulated variables for the blast flow rate and the coke rate so as to prevent the predicted value for the furnace pressure drop from exceeding the upper limit. Furthermore, when the predicted value of the molten iron temperature approaches the target value, the molten iron temperature control unit 14 executes step 4 (part of the manipulated variable determination step) to determine manipulated variables for an appropriate combination of two of the pulverized coal ratio, blast moisture, and blast temperature according to the preference. As described above, the molten iron temperature control unit 14, ironmaking speed control unit 15, and permeability control unit 16, which are constructed as individual controllers, are control systems with disturbance rejection characteristics that absorb fluctuations based on the manipulation of manipulated variables by other control units by manipulating their own manipulated variables. Therefore, the molten iron temperature control unit 14, ironmaking speed control unit 15, and permeability control unit 16 can reduce the influence of interference of manipulated variables from other control units.

[0078] The process control method executed by the process control device 10 may be used as part of a blast furnace operation method. For example, the manipulated variables manipulated in the above-described process control method may be used to change the operating conditions in the operation of the blast furnace. Furthermore, such a blast furnace operation method may be executed as part of a production method for producing molten pig iron. In the blast furnace, raw iron ore is melted and reduced to produce pig iron, which is then tapped as molten pig iron, and the blast furnace may be operated according to this operation method. Furthermore, for example, the manipulated variable determined by the molten pig iron temperature control unit 14 may be displayed on a display device or the like as a proposal of a reducing agent ratio according to the operation preference, and communicated to an operator.

[0079] The process control device 10 may be realized, for example, by a computer separate from the process computer that controls the operation of the blast furnace, or may be realized by the process computer. The computer includes, for example, a memory, a hard disk drive (storage device), a CPU (processing device), and a display device such as a display. Various functions can be realized by organic cooperation between hardware such as the CPU and memory and programs. The memory unit 12 may be realized, for example, by a storage device. The control unit 13 may be realized, for example, by a CPU.

[0080] As described above, the process control method, blast furnace operation method, molten iron production method, process control device 10, and program according to the present embodiment, by virtue of the above-described configuration, realize the proposal of a reducing agent ratio according to the customer's preference while suppressing the variation in molten iron temperature and maintaining stable operation.

[0081] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art would easily be able to make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure. For example, the functions included in each component or step can be rearranged so as not to cause logical inconsistencies, and multiple components or steps can be combined or divided into one. The embodiments of the present disclosure can also be realized as a storage medium on which a program executed by a processor included in an apparatus is recorded. It should be understood that these are also included within the scope of the present disclosure.

[0082] The configuration of the process control device 10 shown in Figure 8 is an example. The process control device 10 does not need to include all of the components shown in Figure 8. Furthermore, the process control device 10 may include components other than those shown in Figure 8. For example, the process control device 10 may be configured to further include a display unit.

[0083] REFERENCE SIGNS LIST 10 Process control device 11 Communication unit 12 Memory unit 13 Control unit 14 Molten iron temperature control unit 15 Iron-making speed control unit 16 Permeability control unit 17 PCR tracking control unit

Claims

1. a response prediction step of obtaining a predicted value of the future molten iron temperature using a physical model capable of calculating the internal state of the blast furnace; When an absolute value of a difference between the predicted value and a target value of the molten iron temperature obtained in the response prediction step is equal to or greater than a predetermined threshold value, a deviation between the predicted value and a target value of the molten iron temperature is obtained, and manipulated variables for a pulverized coal ratio and a blast moisture are obtained so as to minimize or maximize an evaluation function having a term corresponding to the deviation and a term for reducing an reducing agent ratio or a blast moisture; and when the absolute value is less than the predetermined threshold, determining an operation amount to maintain the predicted value by combining two of the pulverized coal ratio, the blast moisture, and the blast temperature according to a preference.

2. 2. The method of claim 1, wherein the preferences include a first preference for prioritizing a reduction in the reducing agent rate and a second preference for temporarily increasing exhaust gas from the blast furnace.

3. The operation amount determination step includes: When the inclination is the first inclination, a combination of the pulverized coal ratio reducing operation and the blast moisture reducing operation, the pulverized coal ratio reducing operation and the blast temperature increasing operation, or the blast temperature reducing operation and the blast moisture reducing operation is obtained; The process control method according to claim 2, wherein when the inclination is the second inclination, the operation amount is determined to be a combination of an operation of increasing the pulverized coal ratio and an operation of increasing the blast moisture, an operation of increasing the pulverized coal ratio and an operation of decreasing the blast temperature, or an operation of increasing the blast temperature and an operation of increasing the blast moisture.

4. The method for controlling a process according to claim 3, further comprising determining operation amounts for a combination of two of the pulverized coal ratio, the blast moisture and the blast temperature so that the theoretical combustion temperature is within a predetermined range.

5. 5. The process control method according to claim 1, wherein the response prediction step uses the physical model to obtain a prediction value of the future molten iron temperature based on a prediction value of the future molten iron temperature when a current operating variable is held and a prediction value of the molten iron temperature when the current operating variable is changed.

6. 5. A process control method according to claim 1, wherein the operation variable determination step determines the unknown variables by using the evaluation function, which is a quadratic function of the unknown variables, under a linear constraint condition for the unknown variables, the operation variables of the pulverized coal ratio and the blast moisture to be determined as unknown variables.

7. 5. The method of claim 1, further comprising the steps of manipulating the blast flow rate so that a predicted value of the iron-making rate coincides with a target value, and manipulating the coke rate so that a predicted value of the permeability is equal to or lower than an upper limit.

8. A method for operating a blast furnace, comprising changing operating conditions using an operating variable manipulated by the process control method according to any one of claims 1 to 4.

9. A method for producing molten iron, comprising producing molten iron using the blast furnace operated by the method for operating a blast furnace according to claim 8.

10. A storage unit that stores a physical model capable of calculating the internal state of a blast furnace; a molten iron temperature control unit that acquires a target molten iron temperature, which is a target value of the molten iron temperature, and calculates manipulated variables for a pulverized coal ratio and a blast moisture content so that the molten iron temperature becomes the target molten iron temperature; The molten iron temperature control unit includes: determining a predicted future molten iron temperature using the physical model; When an absolute value of a difference between the predicted value and a target value of the molten iron temperature is equal to or greater than a predetermined threshold value, a deviation between the predicted value and a target value of the molten iron temperature is calculated, and manipulated variables for the pulverized coal ratio and the blast moisture are calculated so as to minimize or maximize an evaluation function having a term corresponding to the deviation and a term for reducing the reducing agent ratio or the blast moisture; A process control device that, when the absolute value is less than the predetermined threshold, determines an operation amount to maintain the predicted value by combining two of the pulverized coal ratio, the blast moisture, and the blast temperature according to a preference.

11. On the computer, a response prediction step of obtaining a predicted value of the future molten iron temperature using a physical model capable of calculating the internal state of the blast furnace; When an absolute value of a difference between the predicted value and a target value of the molten iron temperature obtained in the response prediction step is equal to or greater than a predetermined threshold value, a deviation between the predicted value and a target value of the molten iron temperature is obtained, and manipulated variables for a pulverized coal ratio and a blast moisture are obtained so as to minimize or maximize an evaluation function having a term corresponding to the deviation and a term for reducing an reducing agent ratio or a blast moisture; and an operation amount determination step of determining an operation amount so as to maintain the predicted value by combining two of the pulverized coal ratio, the blast moisture, and the blast temperature according to a preference when the absolute value is less than the predetermined threshold value.