Process control method, blast furnace operation method, molten iron manufacturing method, 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

[Technical Field]

[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. [Background technology]

[0002] In the blast furnace process in the steel 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 fuel costs, which makes the furnace condition prone to instability. 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, there is a method for controlling the blast furnace based on prediction, such as that described in Patent Document 1, which uses a physical model. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-335710 Summary of the Invention [Problem to be solved by the invention]

[0006] In response to recent societal demands for CO2 reduction, a reduction in the reducing agent rate (the sum of the coke rate and pulverized coal rate) is required in the blast furnace process. To reduce the reducing agent rate, it is effective to reduce the blast moisture injected into the furnace or reduce the heat loss of the furnace body, thereby avoiding the consumption of excess heat sources. Furthermore, external demands may necessitate a temporary increase in the exhaust gas volume of the blast furnace, regardless of the reducing agent rate. Meanwhile, the magnitude of the reducing agent rate significantly affects the permeability (air permeability) within the furnace, and careful operation is required 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 reducing agent rate in accordance with 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. [Means for solving the problem]

[0008] (1) A process control method according to an embodiment of the present disclosure includes: 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 of the molten pig iron temperature and a target value obtained in the response prediction step is equal to or greater than a predetermined threshold value, a deviation between the predicted value of the molten pig iron temperature and the target value is obtained, and manipulated variables for the pulverized coal rate and the 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 the reducing agent rate or the blast moisture; and an operation amount determination step of 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 preference when the absolute value is less than the predetermined threshold 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 manipulated variable determination step includes: When the inclination is the first inclination, an operation amount is calculated so as 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, When the inclination is the second inclination, the operation amount is determined so as to be a combination of an operation to increase the pulverized coal ratio and an operation to increase the blast moisture content, an operation to increase the pulverized coal ratio and an operation to decrease the blast temperature, or an operation to increase the blast temperature and an operation to increase the blast moisture content.

[0011] (4) As an 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 determined 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), In the operation variable determination step, the operation variables of the pulverized coal ratio and the blast moisture to be determined are set as unknown variables, and the unknown variables are determined using the evaluation function, which is a quadratic function of the unknown variables, under the constraint condition of a linear equation regarding the 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 coincides with 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 includes: The operating conditions are changed using the manipulated variables manipulated by any of the process control methods (1) to (7).

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

[0017] (10) A process control device according to an embodiment of the present disclosure includes: a storage unit that stores a physical model that can calculate 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 the pulverized coal ratio and the 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 value of future hot metal temperature using the physical model; when the absolute value of the difference between the predicted value and the target value of the molten pig iron temperature is equal to or greater than a predetermined threshold value, a deviation between the predicted value and the target value of the molten pig iron temperature is calculated, and manipulated variables for the pulverized coal rate 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 rate or the blast moisture; If the absolute value is less than the predetermined threshold, an operation amount is determined to maintain the predicted value by combining two of the pulverized coal ratio, the blast moisture, and the blast temperature according to preference.

[0018] (11) A program according to an embodiment of the present disclosure includes: 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 of the molten pig iron temperature and a target value obtained in the response prediction step is equal to or greater than a predetermined threshold value, a deviation between the predicted value of the molten pig iron temperature and the target value is obtained, and manipulated variables for the pulverized coal rate and the 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 the reducing agent rate or the blast moisture; If the absolute value is less than the predetermined threshold, an operation amount determination step is executed in which an operation amount is determined so as to maintain the predicted value by combining two of the pulverized coal ratio, the blast moisture, and the blast temperature according to preference. [Effects of the Invention]

[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. [Brief explanation of the drawings]

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

[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 the blast furnace process (steps 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, the furnace pressure drop, which directly affects blow-through, is used as the permeability. The furnace pressure drop is the difference between the blast pressure and the furnace top pressure (pressure at the furnace top). In addition to furnace pressure drop, various other permeability indicators exist, such as airflow resistance and shaft pressure difference. 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 showing the processing 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 Document 1 (Japanese Patent No. 7107444). In the cascade control, control for calculating a target pulverized coal ratio (PCR) (hot metal temperature control in FIG. 2) and control for calculating the 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 described below. 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 humidity.

[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. The correspondence between the control variables and the correlated manipulated variables in the blast furnace process is not limited to those shown in FIGS. 1 and 2 . For example, in controlling the ironmaking speed, 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 of the two parameters are determined according to the intention while maintaining the predicted value. The process flow in the process control method according to this embodiment is outlined in the following 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 adjusted so that the predicted value of the iron-making rate matches the target value, and at least the coke rate may be adjusted 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 adjustment of the blast flow rate and coke rate in step 3 is 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 operation, and which can maintain the predicted value. The blast temperature is the temperature of the blast 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 operation may include, for example, a first desired operation (a desired low reducing agent ratio) and a second desired operation (a desired temporary increase in flue gas). For example, in the case of the first desired operation, 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 rate inclination), the manipulated variables may be determined so as to combine the operation of decreasing the pulverized coal rate and the operation of decreasing the blast moisture content. At this time, the influences of the two on 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 so as to combine the operation of decreasing the pulverized coal rate and the operation of increasing the blast temperature, or the operation of decreasing the blast temperature and the operation of 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, which will be described later, may receive an input for specifying the orientation.

[0036] Here, when the predicted molten iron temperature is approximately equal to the target value, the manipulated variables are varied to maintain the predicted molten iron temperature (to offset the effect), but the amount of variation is not unlimited. For example, when the first-order trend is selected and the predicted molten 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-order trend is selected and the predicted molten 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 as an example, it may be set to 2000°C to 2500°C. When calculating the manipulated variables, 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 on Blast Furnace Burn-in Operation Using a Non-Steady-State Model," Tetsu-to-Hagané, 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 below.

[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 the 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, which 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]

number

[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 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. 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 input variable values ​​are kept constant and calculate the future control variables. The current time step, t0, is set to 0, and the future control variables are predicted using the following equations (3) and (4). The response of the control variables obtained in this way, y f (t) is called the free response.

[0044]

number

[0045] Below, we will explain how to determine the current and future operation amounts for pulverized coal ratio (PCR) and blast moisture (BM). An example of predicting two hours into the future will be explained. Introducing unknown variables θ = (ΔPCR0, ΔBM0, ΔPCR1, ΔBM1), the operation amounts for pulverized coal ratio (PCR) and blast moisture (BM) are determined using quadratic programming. The subscript 0 indicates the present, and the subscript 1 indicates two hours into the future.

[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 (t) and the step response. The predicted value of the hot metal temperature every two hours for the next 10 hours, y pre (t) is as shown in the following equation (5).

[0047]

number

[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 when only S PCR and S BM can be obtained, for example, by using another physical model or a step response test in actual operation. The calculations in this disclosure used 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).

[0049] In the following, if we express equation (5) as equation (6) using the step response matrix S, the predicted value of the hot metal temperature and the target value y pre The deviation from (t) is as shown in equation (7).

[0050]

number

[0051] where y is the free response f (t) target value y pre The deviation from (t) is δy. The predicted value of the hot metal temperature and the target value y pre The square of the deviation from (t) is as shown in the following equation (8).

[0052]

number

[0053] In order to simultaneously reduce the variation in hot metal temperature and minimize the reducing agent rate, the evaluation function J used in the quadratic programming method includes a term to reduce 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 to suppress excessive operation.

[0054]

number

[0055] where a and R are coefficients. Comparing the responsiveness of hot metal temperature to changes in pulverized coal ratio (PCR) and blast moisture (BM), it is known that blast moisture has a more immediate response. However, to ensure a controllable range for both increasing and decreasing blast moisture, the average blast moisture must be increased. Increasing the average blast moisture causes 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 by changing the magnitude of 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 equations (10) to (13) below.

[0057]

number

[0058] Here, the subscript i in 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 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 of the unknown variable θ, under the linear constraint conditions for 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], which is the operating amount ΔBV, is calculated.

[0062]

number

[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 for 2 hours (30 minutes x 4) ahead.ref is the target iron making speed (target value of iron making speed). BV is the unit volume of the air flow rate (BV) (1 [Nm 3 / min]. BV can be obtained using another physical model or a step response test in actual operation. b is a coefficient and is a positive number. The control that obtains ΔBV according to equation (14) corresponds to the ironmaking speed control in Figure 2.

[0064] In addition, the coke rate (CR) and blast volume (BV) control variables are determined by comparing the furnace pressure drop (ΔP) with an upper limit (threshold). When the furnace pressure drop (ΔP) exceeds the upper limit, the control variables are determined to increase the coke rate and simultaneously decrease the blast volume. This corresponds to the operation of stabilizing the material unloading in blast furnace operation. Furthermore, when the furnace pressure drop is below the upper limit, the control variables are determined to gradually decrease the coke rate. In principle, control is performed to prevent the furnace pressure drop from exceeding the upper limit. However, when the furnace pressure drop is below the upper limit, gradually decreasing the coke rate can reduce operating costs. When this control is performed, the value of the furnace pressure drop remains near the upper limit. The control that determines the coke rate (CR) and blast volume (BV) control variables by comparing the furnace pressure drop with the upper limit corresponds to the permeability control shown in Figure 2.

[0065] Figure 5 shows the results of a simulation performed using the process control described above, assuming that the absolute difference between the predicted and target hot metal temperature values ​​obtained in the response prediction step 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 the 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 content (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 content 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 for the comparative example. In the simulation of Figure 6, the pulverized coal ratio (PCR), blast volume (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, which allows for a reduction in the coke rate (see CR in Figures 5 and 6).

[0068] Figure 7 shows an example of the results when the manipulated variable is calculated 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. The items such as BV and Prod are the same as in Figure 5. The horizontal axis also represents the 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 the combination of decreasing the pulverized coal ratio and decreasing the blast moisture. However, even with these changes, no significant change is observed in the hot metal temperature (HMT). In other words, the hot metal temperature can be maintained and stable operation can be continued while changing the reducing agent rate according to the demand.

[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 memory 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 host system. The host 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 host 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 host 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 calculates manipulated variables for the blast moisture and pulverized coal ratio so that the molten iron temperature becomes the target molten iron temperature when the absolute value of the difference between the predicted molten iron temperature and the target value is equal to or greater than a predetermined threshold. 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 molten iron temperature and the target value is less than a predetermined threshold, the molten iron temperature control unit 14 calculates 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 the target iron-making speed, which is the 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 Figure 2.

[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 ratio 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 the target value determined by the molten iron temperature control unit 14, and calculates the manipulated variable of the pulverized coal flow rate (PCI) so as to follow the target PCR through PCR tracking control. 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 of 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 of the furnace pressure drop from exceeding the upper limit. Furthermore, when the predicted value of the hot metal temperature approaches the target value, the hot metal 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 hot metal temperature control unit 14, the ironmaking speed control unit 15, and the 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 hot metal temperature control unit 14, the ironmaking speed control unit 15, and the 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 rate 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 configurations, realize the proposal of a reducing agent ratio according to the customer's preference while maintaining stable operation and suppressing variation in the molten iron temperature.

[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 one 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. [Explanation of symbols]

[0083] 10 Process control devices 11 Communications Department 12 Storage section 13 Control Unit 14 Molten iron temperature control unit 15 Ironmaking speed control section 16 Air permeability control section 17 PCR tracking control section

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 the absolute value of the difference between the predicted value of the molten pig iron temperature and the target value obtained in the response prediction step is equal to or greater than a predetermined threshold value, a deviation between the predicted value of the molten pig iron temperature and the target value is obtained, and operation amounts for the pulverized coal ratio and the blast moisture are determined so as to minimize or maximize an evaluation function having a term corresponding to the deviation and further including a term for reducing the blast moisture and a term for suppressing excessive operation; and a manipulated variable determination step of determining, when the absolute value is less than the predetermined threshold, a manipulated variable that maintains 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 process control method according to claim 1, wherein the preferences include a first preference for reducing the reducing agent rate and a second preference for temporarily increasing exhaust gas from the blast furnace.

3. The manipulated variable determination step includes: When the inclination is the first inclination, an operation amount is calculated so as 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, 3. A 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 to increase the pulverized coal ratio and an operation to increase the blast moisture content, an operation to increase the pulverized coal ratio and an operation to decrease the blast temperature, or an operation to increase the blast temperature and an operation to increase the blast moisture content.

4. The process control method according to claim 3, wherein the manipulated variables for two combinations of the pulverized coal ratio, the blast moisture, and the blast temperature are determined 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 predicted value of the future molten iron temperature based on a predicted value of the future molten iron temperature when a current operating variable is maintained and a predicted 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 on the unknown variables, with the pulverized coal ratio and the blast moisture to be determined as unknown variables.

7. 5. The method for controlling a process according to claim 1, further comprising the steps of manipulating the blast flow rate so that a predicted value of the iron-making rate matches 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 that can calculate 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 the pulverized coal ratio and the 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 value of future hot metal temperature using the physical model; When the absolute value of the difference between the predicted value and the target value of the molten iron temperature is equal to or greater than a predetermined threshold value, a deviation between the predicted value and the target value of the molten iron temperature is calculated, and operation amounts 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 further including a term for reducing the blast moisture and a term for suppressing excessive operation; A process control device that, when the absolute value is less than the predetermined threshold, determines an operation amount by combining two of the pulverized coal ratio, the blast moisture, and the blast temperature according to a preference so as to maintain the predicted value.

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 the absolute value of the difference between the predicted value of the molten pig iron temperature and the target value obtained in the response prediction step is equal to or greater than a predetermined threshold value, a deviation between the predicted value of the molten pig iron temperature and the target value is obtained, and operation amounts for the pulverized coal ratio and the blast moisture are determined so as to minimize or maximize an evaluation function having a term corresponding to the deviation and further including a term for reducing the blast moisture and a term for suppressing excessive operation; and an operation amount determination step of 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 preference when the absolute value is less than the predetermined threshold value.

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