EP4628599A1 - Process control method, blast furnace operation method, molten-iron manufacturing method, and process control device and program - Google Patents

Abstract

A process control method including: a response prediction step of determining a predicted value of future hot metal temperature using a physical model; and an operation amount determination step of, when an absolute value of a difference between the predicted value of the hot metal temperature determined in the response prediction step and a target value is a defined threshold value or greater, determining a deviation between the predicted value of the hot metal temperature and the target value, and determining operation amounts of pulverized coal rate and blast moisture so that an evaluation function comprising a term corresponding to the deviation and a term for decreasing the reducing agent rate or blast moisture is minimized or maximized, and when the absolute value is less than the defined threshold value, determining the operation amounts of a combination of two of the pulverized coal rate, the blast moisture, and blast temperature.

Description

TECHNICAL FIELD
• The present disclosure relates to a process control method, a blast furnace operation method, a hot metal production method, a process control device, and a program.
BACKGROUND
• Hot metal temperature (HMT) is an important management index in a blast furnace process of the steel industry, and is controlled mainly by adjusting pulverized coal rate and blast moisture. In recent years, blast furnace operations have been carried out under low coke rate and high pulverized coal rate conditions in order to rationalize raw fuel costs, which can easily lead to furnace instability. Therefore, suppressing variation in hot metal temperature is necessary.
• Further, the blast furnace process is an operation carried out in a solid-filled state, and is therefore characterized by a large heat capacity for the entire process and a long time constant for response to action. Further, it may take several hours, for example, for raw material charged at the top of the furnace to descend to the lower part of the furnace. Therefore, appropriate operation based on prediction of future furnace heat is necessary to control hot metal temperature.
• In order to account for delayed response derived from the long time constant of blast furnaces, some methods of controlling blast furnaces based on predictions use physical models, such as described in Patent Literature (PTL) 1.
CITATION LIST Patent Literature
• PTL 1: JP H11-335710 A
SUMMARY (Technical Problem)
• Recent social demand for reducing CO₂ emissions has led to demand for a decrease in reducing agent rate (the sum of the coke rate and the pulverized coal rate) in the blast furnace process. To decrease the reducing agent rate, it is effective to decrease the blast moisture blown into the furnace and to decrease furnace heat loss, so that excess heat source is not consumed. Further, there may be situations in which, due to external requirements, it is desirable to temporarily increase blast furnace exhaust gas, regardless of the reducing agent rate. On the other hand, the reducing agent rate also greatly affects gas permeability (permeability) inside the furnace, and careful operation is required to maintain stable operation. However, PTL 1 describes a technique to predict and calculate hot metal temperature, and not a technique of proposing a control method that takes into account the reducing agent rate that depends on an intention while continuing stable operation.
• In view of the above, it would be helpful to provide a process control method, a blast furnace operation method, a hot metal production method, a process control device, and a program to realize proposing a reducing agent rate that depends on an intention that also suppresses variation of hot metal temperature and continues stable operation in a blast furnace.
(Solution to Problem)
1. (1) A process control method according to an embodiment of the present disclosure, comprising:
   • a response prediction step of determining a predicted value of future hot metal temperature using a physical model capable of calculating an internal state of a blast furnace; and
   • an operation amount determination step of,
   • when an absolute value of a difference between the predicted value of the hot metal temperature determined in the response prediction step and a target value is a defined threshold value or greater, determining a deviation between the predicted value of the hot metal temperature and the target value, and determining operation amounts of pulverized coal rate and blast moisture so that an evaluation function comprising a term corresponding to the deviation and a term for decreasing the reducing agent rate or blast moisture is minimized or maximized, and
   • when the absolute value is less than the defined threshold value, determining, depending on an intention, the operation amounts of a combination of two of the pulverized coal rate, the blast moisture, and blast temperature, to maintain the predicted value.
2. (2) The process control method according to (1), as an embodiment of the present disclosure, wherein
   the intention includes a first intention of prioritizing decreasing the reducing agent rate and a second intention of temporarily increasing exhaust gas from the blast furnace.
3. (3) The process control method according to (2), as an embodiment of the present disclosure, wherein
   the operation amount determination step,
   • when the intention is the first intention, determines the operation amounts of a combination of an operation decreasing the pulverized coal rate and an operation decreasing the blast moisture, a combination of an operation decreasing the pulverized coal rate and an operation increasing the blast temperature, or a combination of an operation decreasing the blast temperature and an operation decreasing the blast moisture, and
   • when the intention is the second intention, determines the operation amounts of a combination of an operation increasing the pulverized coal rate and an operation increasing the blast moisture, a combination of an operation increasing the pulverized coal rate and an operation decreasing the blast temperature, or a combination of an operation increasing the blast temperature and an operation increasing the blast moisture.
4. (4) The process control method according to (3), as an embodiment of the present disclosure, wherein
   the operation amounts in the combination of two of the pulverized coal rate, the blast moisture, and the blast temperature are determined so that a theoretical combustion temperature is within a predetermined defined range of temperature.
5. (5) The process control method according to any one of (1) to (4), as an embodiment of the present disclosure, wherein
   the response prediction step determines the predicted value of the future hot metal temperature using the physical model, based on the predicted value of the future hot metal temperature when current operating variables are held unchanged and the predicted value of the future hot metal temperature when the current operating variables are changed.
6. (6) The process control method according to any one of (1) to (5), as an embodiment of the present disclosure, wherein
   the operation amount determination step determines unknown variables by using the evaluation function, which is a quadratic function regarding the unknown variables, under a constraint of a linear equation regarding the unknown variables, with the operation amounts of the pulverized coal rate and the blast moisture as the unknown variables.
7. (7) The process control method according to any one of (1) to (6), as an embodiment of the present disclosure, further comprising
   a step of manipulating blast volume so that the predicted value of production rate matches a target value and manipulating coke rate so that the predicted value of permeability is an upper limit or less.
8. (8) A blast furnace operation method according to an embodiment of the present disclosure, the method comprising
   changing operational conditions using the operating variables manipulated by the process control method according to any one of (1) to (7).
9. (9) A hot metal production method according to an embodiment of the present disclosure, the method comprising
   producing hot metal using the blast furnace operated according to the blast furnace operation method according to (8).
10. (10) A process control device according to an embodiment of the present disclosure, comprising:
    • a storage configured to store a physical model capable of calculating internal conditions of a blast furnace; and
    • a hot metal temperature controller configured to acquire a target hot metal temperature that is a target value of hot metal temperature and calculate operation amounts of pulverized coal rate and blast moisture at which the hot metal temperature becomes the target hot metal temperature, wherein
    • the hot metal temperature controller is further configured to:
      • determine a predicted value of future hot metal temperature using the physical model;
      • when an absolute value of a difference between the predicted value of the hot metal temperature and a target value is a defined threshold value or greater, determine a deviation between the predicted value of the hot metal temperature and the target value, and determine operation amounts of pulverized coal rate and blast moisture so that an evaluation function comprising a term corresponding to the deviation and a term for decreasing the reducing agent rate or blast moisture is minimized or maximized; and
      • when the absolute value is less than the defined threshold value, determine, depending on an intention, the operation amounts of a combination of two of the pulverized coal rate, the blast moisture, and blast temperature, to maintain the predicted value.
11. (11) A program according to an embodiment of the present disclosure is configured to
    cause a computer to execute:
    • a response prediction step of determining a predicted value of future hot metal temperature using a physical model capable of calculating an internal state of a blast furnace; and
    • an operation amount determination step of,
      • when an absolute value of a difference between the predicted value of the hot metal temperature determined in the response prediction step and a target value is a defined threshold value or greater, determining a deviation between the predicted value of the hot metal temperature and the target value, and determining operation amounts of pulverized coal rate and blast moisture so that an evaluation function comprising a term corresponding to the deviation and a term for decreasing the reducing agent rate or blast moisture is minimized or maximized, and
      • when the absolute value is less than the defined threshold value, determining, depending on an intention, the operation amounts of a combination of two of the pulverized coal rate, the blast moisture, and blast temperature, to maintain the predicted value.
(Advantageous Effect)
• The present disclosure provides a process control method, a blast furnace operation method, a hot metal production method, a process control device, and a program to realize proposing a reducing agent rate that depends on an intention that also continues stable operation and suppresses variation of hot metal temperature in a blast furnace.
BRIEF DESCRIPTION OF THE DRAWINGS
• In the accompanying drawings:
• FIG. 1 is a diagram illustrating operating variables and control variables in a blast furnace process;
• FIG. 2 is a diagram illustrating a process control method according to an embodiment of the present disclosure;
• FIG. 3 is a diagram illustrating effects of pulverized coal rate, blast moisture, and blast temperature on a furnace;
• FIG. 4 is a diagram illustrating input/output information of a physical model used according to the present disclosure;
• FIG. 5 is a diagram illustrating results of a control simulation of simultaneous manipulation of pulverized coal rate and blast moisture;
• FIG. 6 is a diagram illustrating results of a control simulation of manipulation of only pulverized coal rate (comparative example);
• FIG. 7 is a diagram illustrating a case in which operation amounts of a combination of two operating variables are determined; and
• FIG. 8 is a diagram illustrating an example configuration of a process control device according to an embodiment of the present disclosure.
DETAILED DESCRIPTION
• The following describes, with reference to the drawings, a process control method, a blast furnace operation method, a hot metal production method, a process control device, and a program according to an embodiment of the present disclosure.
• FIG. 1 illustrates basic operating variables and control variables in a blast furnace process (a process in operation of a blast furnace). Control variables are variables that should be controlled during operation but cannot be manipulated directly or are difficult to manipulate directly, and are changed via correlated operating variables. In the operation of a blast furnace, to achieve a target value of hot metal temperature, pulverized coal rate, blast moisture, and the like are mainly manipulated. To maintain good blast furnace gas permeability (permeability), the pulverized coal rate, the blast moisture, coke rate, blast volume, and the like are mainly manipulated. Further, to achieve a target value of production rate, blast volume is mainly manipulated. Here, as permeability, in-furnace pressure drop, which has a direct effect on gas channeling, is used in the present embodiment. The in-furnace pressure drop is a difference between blast pressure and top gas pressure (pressure at the top of the furnace). In addition to the in-furnace pressure drop, there are various other indicators of gas permeability, such as ventilation resistance and facing shaft differential pressure. Therefore, another indicator of gas permeability may be used instead of the in-furnace pressure drop as the permeability, or a combination of multiple measures of gas permeability may be used. The process control method according to the present embodiment focuses on the pulverized coal rate and the blast moisture, which are operating variables for controlling hot metal temperature, and determines optimal operation amounts of the pulverized coal rate and the blast moisture so that the reducing agent rate is decreased while suppressing the hot metal temperature. Further, the relationship between the pulverized coal rate, the blast moisture, and the blast temperature is also focused on, and the operation amounts are determined for a combination of these factors.
• FIG. 2 is a diagram illustrating processing of the process control method according to the present embodiment. In the process control method according to the present embodiment, the cascade control described in Reference Literature 1 ( JP 7107444 B2 ) is used, for example. In the cascade control, a control to calculate the target pulverized coal rate (PCR) (hot metal temperature control in FIG. 2) and a control to calculate the pulverized coal injection rate required for the target PCR (PCR tracking control in FIG. 2) are carried out continuously. For the hot metal temperature control, the target hot metal temperature (HMT), that is, the target value of the hot metal temperature, may be obtained and the target PCR may be calculated using the physical model described below. Further, the hot metal temperature control not only calculates the target PCR (not only determines the operation amount of the pulverized coal rate), but also calculates the operation amount of the blast moisture.
• The process control method according to the present embodiment also includes production rate control and permeability control. In the production rate control, the target production rate (Prod), that is, the target value of the production rate, is obtained, and the operation amount of the blast volume (BV) is calculated using the physical model described below. The permeability control obtains an in-furnace pressure drop (ΔP) upper limit, which is an upper limit of pressure drop in the furnace, and calculates the operation amounts of the blast volume and the coke rate using the physical model described below. Here, actual performance values (which may be observed or calculated) at the plant including the blast furnace, may be fed back to update the physical model used in each control. In the example in FIG. 2, the actual performance values of the pulverized coal rate (PCR), the hot metal temperature (HMT), the in-furnace pressure drop (ΔP), and the production rate (Prod) are indicated as actual PCR, actual HMT, actual ΔP and actual Prod, respectively. Further, mapping between the control variables and correlated operating variables in the blast furnace process is not limited to that illustrated in FIG. 1 and FIG. 2. For example, in the production rate control, blast volume oxygen may be manipulated instead of the blast volume.
• In construction of the multi-variable control system illustrated in FIG. 2, separate controllers (hot metal temperature control, permeability control, and production rate control) are constructed to control the hot metal temperature (HMT), the in-furnace pressure drop (ΔP), and the production rate (Prod). The hot metal temperature is controlled by manipulation of the blast moisture and by the cascade control that manipulates the pulverized coal rate (PCR) and the pulverized coal injection rate. The permeability is controlled by manipulating the blast volume and the coke rate. The production rate is controlled by manipulating the blast volume. Here, for example, when the blast volume is manipulated in the production rate control, changes in the blast volume have an effect on the hot metal temperature. This effect is reflected by the physical model in the hot metal temperature control and calculated as the operation amount of the pulverized coal rate or the blast moisture, and the hot metal temperature is kept near the target value by reflecting the calculated operation amount of the pulverized coal rate or the blast moisture. Although separate controllers are constructed in the present embodiment as described above, control that takes into account interference between the respective operating variables is also possible to achieve. That is, for example, although the hot metal temperature control and the production rate control interfere, the system is constructed as a control system with disturbance cancellation properties in which variation based on manipulation of another operating variable is absorbed by manipulation of the operating variable itself, thereby decreasing the effects of interference. The same is also true for the permeability control.
• In the process control method according to the present embodiment, the physical model of the blast furnace based on reaction kinetics is used to predict future hot metal temperature and production rate. When the absolute value of a difference between the predicted value and the target value is a defined threshold value or more, the process control method according to the present embodiment determines change amounts of the pulverized coal rate and blast moisture so that the predicted value approaches the target value. By using quadratic programming that minimizes an evaluation function that takes the reducing agent rate into account when determining the operation amount, it is possible to both increase or decrease the reducing agent rate and suppress variation in the hot metal temperature. Here, the reducing agent rate can be increased or decreased depending on an intention. The intention is operation policy. When a low reducing agent rate is used for environmental considerations, the reducing agent rate may be decreased. Further, the reducing agent rate may be increased when external requirements require a temporary increase in blast furnace exhaust gas. External requests include, for example, requests resulting from limited electrical power supply or limited raw material inventories. According to the present embodiment, the intention includes a first intention of prioritizing decreasing the reducing agent rate and a second intention of temporarily increasing the blast furnace exhaust gas. In the following, the description assumes the first intention (low reducing agent rate intention), but is not limited to this and the methods of the present disclosure can be applied to the second intention (temporary exhaust gas increase intention), for example.
• Further, in the process control method according to the present embodiment, when the absolute value of the difference between the predicted value and the target value is less than the defined threshold value, the predicted value is determined to be near the target value, and therefore the operation amounts of the two parameters that depend on the intention are determined while maintaining the predicted value. An outline of the processing flow in the process control method according to the present embodiment is illustrated in steps 1 to 4 below.
• First, as step 1, future hot metal temperature is predicted using the physical model. Step 1 is the response prediction step. The response prediction step determines the predicted value of the future hot metal temperature using the physical model, based on the predicted value of the future hot metal temperature when current operating variables are held unchanged and the predicted value of the future hot metal temperature when the current operating variables are changed. The predicted value of the future hot metal temperature when the current operating variables are held unchanged is the free response, which is discussed below. The predicted value of the hot metal temperature when the current operating variables are changed is the step response described below according to the present embodiment, but is not limited to this example.
• Next, as step 2, manipulation of the operating variables is carried out 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 operation amount determination step, in which deviation between the predicted value and the target value is determined, the operation amount is determined to eliminate the deviation, and the operating variables are adjusted. According to the present embodiment, the operating variables are the pulverized coal rate and the blast moisture.
• Further, as step 3, to simulate actual operation of the blast furnace, the blast volume may be manipulated so that the predicted value of the production rate matches the target value, and at least the coke rate may be manipulated so that the predicted value of the blast volume becomes an upper limit or less. According to the present embodiment, the permeability is the in-furnace pressure drop, and when the predicted value of the in-furnace pressure drop exceeds a set upper limit, the permeability state is determined to be abnormal. When the permeability state is determined to be abnormal, an operation to increase the coke rate may be carried out. When the permeability state is determined to be not abnormal, that is, the predicted value of the in-furnace pressure drop is the upper limit or less, an operation to decrease the coke rate may be carried out. Manipulation of the blast volume and the coke rate according to step 3 is a disturbance to the hot metal temperature control.
• As step 4, when the predicted value of the hot metal temperature in step 1 approximately matches the target value, amounts that can maintain the predicted value are determined as the operation amounts, which are a set of two parameters from among the pulverized coal rate, the blast moisture, and the blast temperature, depending on the intention. The blast temperature is the temperature of the blast and is one of the operating variables. The predicted value of the hot metal temperature approximately matching 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 defined threshold value. The defined threshold value may be determined in advance based on past actual performance data or the like. Here, as above, the intention includes, for example, the first intention (low reducing agent rate intention) and the second intention (temporary exhaust gas increase intention). For example, in the case of the first intention, decreasing the pulverized coal rate makes the operation more suitable for the purpose. Carrying out the operation to decrease the pulverized coal rate will improve (decrease) the permeability but decrease the predicted hot metal temperature. Therefore, in the control method according to the present embodiment, the operation amounts are determined so that an operation to decrease the blast moisture is treated as a set (in combination) with the operation to decrease the pulverized coal rate. The operation to decrease the pulverized coal rate decreases the hot metal temperature and the permeability. On the other hand, the operation to decrease the blast moisture increases the hot metal temperature and the permeability, so the effects of the two operations cancel each other out.
• FIG. 3 is a diagram illustrating effects of the pulverized coal rate, the blast moisture, and the blast temperature on a furnace. An increase operation is an operation that increases the value of the operating variable. Further, a decrease operation is an operation that decreases the value of the operating variable. As described above, for example, by simultaneously lowering the pulverized coal rate and the blast moisture content, the predicted hot metal temperature may be maintained and stable operation may continue.
• As illustrated in FIG. 3, when the intention is the first intention (low reducing agent rate intention), the operation amounts may be determined to be a combination of a pulverized coal rate decrease operation and a blast moisture decrease operation. In this case, the effects on the hot metal temperature and the permeability cancel each other out. The combination is not limited to this, and when the intention is the first intention, the operation amounts may be determined to be a combination of a pulverized coal rate decrease operation and a blast temperature increase operation or a blast temperature decrease operation and a blast moisture decrease operation.
• On the other hand, in the case of the second intention (temporary exhaust gas increase intention), the operation amounts may be determined to be a combination of a pulverized coal rate increase operation and a blast moisture increase operation. The combination is not limited to this, and when the intention is the second intention, the operation amounts may be determined to be a combination of a pulverized coal rate increase operation and a blast temperature decrease operation or a blast temperature increase operation and a blast moisture increase operation. By combining two of the pulverized coal rate, the blast moisture, and the blast temperature, and determining the operation amounts in a way that cancels each other out so that the predicted values are maintained, the hot metal temperature may be maintained and stable operation may continue. Verification is described below.
• Whether the intention of operation is the first intention or the second intention may be predetermined, or the controller 13, described below, may accept input to specify the intention.
• Here, the operating variables are changed to maintain the predicted value of the hot metal temperature (to cancel out effects) when the predicted value of the hot metal temperature approximately matches the target value, but the amount of change is not unlimited. For example, when the intention is the first intention and the predicted value of the hot metal temperature approximately matches the target value, the pulverized coal rate and the blast moisture cannot be decreased without limit. Further, for example, when the intention is the second intention and the predicted value of the hot metal temperature approximately matches the target value, the pulverized coal rate and the blast moisture cannot be increased without limit. In a blast furnace, the theoretical combustion temperature (calculated combustion temperature) at the point where the pulverized coal and the blast moisture are blown in needs to be within a predetermined defined range (control value). When the theoretical combustion temperature deviates from the control value, various operational problems may occur. The control value of the theoretical combustion temperature may be determined using various known calculation formulas, but as an example, may be from 2000 °C to 2500 °C. The theoretical combustion temperature is preferably taken into account when determining the operation amount.
• Details of calculations in steps 1 to 4 are described below. The physical model used in the present disclosure is the same as the method described in Reference Literature 2 (Michiharu Hatano et al., "Investigation of Blow-in Operation through the Blast Furnace Dynamic Model", Tetsu-to-Hagane, vol. 68, p. 2369). That is, a physical model is used that can calculate the conditions inside the blast furnace (in-furnace) in a transient state, consisting of a set 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 is hereinafter sometimes referred to as a dynamic model.
• As illustrated in FIG. 4, the main input variables provided to the dynamic model that vary over time are the blast volume, the blast volume oxygen, the pulverized coal injection rate, the blast moisture, the blast temperature, the coke rate, and top gas pressure. These input variables are the operating variables or operating factors of the blast furnace. The blast volume, the blast volume oxygen, and the pulverized coal injection rate are the flow rates of air, oxygen, and pulverized coal delivered to the blast furnace, respectively. The blast moisture is the humidity of the air delivered to the blast furnace. The blast temperature is the temperature of the air delivered to the blast furnace. The coke rate is the coke rate at the furnace top and is the weight of coke used per tonne of hot metal produced.
• The main output variables of the dynamic model are gas utilization rate, solution loss carbon amount, the reducing agent rate, the production rate, the hot metal temperature, and the in-furnace pressure drop. The dynamic model may be used to calculate the hot metal temperature, the production rate, and the in-furnace pressure drop, which are ever-changing. The time interval for this calculation is not particularly limited, but is 30 minutes according to the present embodiment. The time difference between "t+1" and "t" in the dynamic model expressions described below is 30 minutes according to the present embodiment.
• The dynamic model may be expressed by the following expressions (1) and (2). $$\begin{array}{l}x\left(t+1\right)=f\left(x\left(t\right),u\left(t\right)\right)\\ y\left(t\right)=C\left(x\left(t\right)\right)\end{array}\begin{array}{c}\left(1\right)\\ \left(2\right)\end{array}$$
• Here, x(t) is state variables calculated within the dynamic model. The state variables are, for example, the temperature of the coke, the temperature of the iron, the oxidation degree of the ore, and the descent speed of raw material. y(t) is the control variables, the hot metal temperature, the production rate, and the permeability (the in-furnace pressure drop). u(t) is the input variables described above, which may be manipulated by an operator of the blast furnace. That is, the input variables are: blast volume BV (t), blast volume oxygen BVO (t), pulverized coal injection rate PCI (t), blast moisture BM (t), blast temperature BT (t), coke rate CR (t), and top gas pressure TGP (t). The input variables can be expressed as u(t) = (BV(t), BVO(t), PCI(t), BM(t), BT(t), CR(t), TGP(t))^T.
• First, a predictive calculation of the future control variable is executed, assuming that the current values of the input variables are held constant. Using the current time step, t₀, as 0, the following expressions (3) and (4) are used to predict future control variables. The response y_f(t) of the control variable obtained in this way is called the free response. $$\begin{array}{l}x\left(t+1\right)=f\left(x\left(t\right),u\left(0\right)\right)\\ y_f\left(t\right)=C\left(x\left(t\right)\right)\end{array}\begin{array}{c}\left(3\right)\\ \left(4\right)\end{array}$$
• The following describes a method for determining current and future operation amounts of the pulverized coal rate (PCR) and the blast moisture (BM). An example of predicting two hours ahead is explained. By introducing unknown variables θ = (ΔPCR₀, ΔBM₀, ΔPCR₁, ΔBM₁), the operation amounts of the pulverized coal rate (PCR) and the blast moisture (BM) are determined by quadratic programming. The subscript 0 indicates a current value. Further, the subscript 1 indicates 2 hours later.
• As an assumption for predictive control using the physical model, it may be assumed that the future hot metal temperature can be approximated by superposition of the free response, response y_f(t), and the step response. y_pre(t), which is the predicted value of the hot metal temperature every 2 hours up to 10 hours ahead, is as in expression (5) below.
• [Math. 3] $$\left(\begin{array}{c}{y}_{\mathit{pre}}\left(4\right)\\ y_{\mathit{pre}}\left(8\right)\\ y_{\mathit{pre}}\left(12\right)\\ y_{\mathit{pre}}\left(16\right)\\ y_{\mathit{pre}}\left(20\right)\end{array}\right)=\left(\begin{array}{cccc}{S}_{\mathit{PCR}}\left(4\right)& S_{\mathit{BM}}\left(4\right)& 0& 0\\ S_{\mathit{PCR}}\left(8\right)& S_{\mathit{BM}}\left(8\right)& S_{\mathit{PCR}}\left(4\right)& S_{\mathit{BM}}\left(4\right)\\ S_{\mathit{PCR}}\left(12\right)& S_{\mathit{BM}}\left(12\right)& S_{\mathit{PCR}}\left(8\right)& S_{\mathit{BM}}\left(8\right)\\ S_{\mathit{PCR}}\left(16\right)& S_{\mathit{BM}}\left(16\right)& S_{\mathit{PCR}}\left(12\right)& S_{\mathit{BM}}\left(12\right)\\ S_{\mathit{PCR}}\left(20\right)& S_{\mathit{BM}}\left(20\right)& S_{\mathit{PCR}}\left(16\right)& S_{\mathit{BM}}\left(16\right)\end{array}\right)\left(\begin{array}{c}\mathrm{\Delta }{\mathit{PCR}}_0\\ \mathrm{\Delta }{\mathit{BM}}_0\\ \mathrm{\Delta }{\mathit{PCR}}_1\\ \mathrm{\Delta }{\mathit{BM}}_1\end{array}\right)+\left(\begin{array}{c}{y}_f\left(4\right)\\ y_f\left(8\right)\\ y_f\left(12\right)\\ y_f\left(16\right)\\ y_f\left(20\right)\end{array}\right)$$
• Here, S_PCR(t) is the change in hot metal temperature when the pulverized coal rate (PCR) is manipulated by a unit amount (1 [kg/t]). Further, S_BM(t) is the change in the blast moisture when the blast moisture (BM) is manipulated by a unit amount (1 [g/Nm³]). S_PCR and S_BM may be determined, for example, by another physical model or step response tests in actual operations. In the calculations in the present disclosure, Reference Literature 3 (Y. Hashimoto, Online prediction of hot metal temperature using transient model and moving horizon estimation. ISIJ Int. 2019, vol. 59, p. 1534) was used in the simulation results.
• In the following, when expression (5) is expressed as in expression (6) below using the step response matrix S, the deviation of the predicted value of the hot metal temperature from the target value y_pre(t) is as in expression (7). $$\begin{array}{l}{y}_{\mathit{pre}}=\mathit{S\theta }+y_f\\ y_{\mathit{pre}}-y_{\mathit{ref}}=\mathit{S\theta }+\left(y_f-y_{\mathit{ref}}\right)=\mathit{S\theta }+\mathit{\delta y}\end{array}\begin{array}{c}\left(6\right)\\ \left(7\right)\end{array}$$
• The deviation of the free response, y_f(t), from the target value, y_pre(t), is denoted as δy. The square of the deviation between the predicted value of the hot metal temperature and the target value y_pre(t) is indicated in expression (8) below.
• [Math. 5] $${\left|y_{\mathit{pre}}-y_{\mathit{ref}}\right|}^2=\left({\theta }^T{S}^T+{\mathit{\delta y}}^T\right)\left(\mathit{S\theta }+\mathit{\delta y}\right)={\theta }^T{S}^T\mathit{S\theta }+2{\mathit{\delta y}}^T\mathit{S\theta }+\mathit{const}$$
• In order to achieve both a decrease in variation of the hot metal temperature and minimize the reducing agent rate, an evaluation function J used in the quadratic programming includes, in addition to a first term and a second term in expression (8), a term to decrease the blast moisture (third term), as indicated in expression (9). The evaluation function J also includes a fourth term to control excessive manipulation.
• [Math. 6] $$J={\theta }^T{S}^T\mathit{S\theta }+2{\mathit{\delta y}}^T\mathit{S\theta }+a^T\theta +{\theta }^T\mathit{R\theta }$$
• Here, a and R are coefficients. Comparing the responsiveness of the hot metal temperature to changes in the pulverized coal rate (PCR) and the blast moisture (BM), respectively, it is known that the blast moisture has a more immediate response. However, increasing an average value of the blast moisture to ensure operable ranges in the increasing and decreasing directions is necessary so that the blast moisture can be increased or decreased. Increasing the average value of the blast moisture causes heat absorption due to the water vapor decomposition reaction of the blast moisture, and therefore more reducing agent needs to be added to compensate for the decreased heat due to the heat absorption. Therefore, a third term is introduced to limit the operation amount of the blast moisture, and the weighting of ΔPCR and ΔBM in the vector θ can be changed according to the size of the elements of the coefficient vector a to adjust the distribution of the two operations.
• Further, θ is determined using expression (9) under the constraints of expressions (10) through (13) below. $$\begin{array}{l}{\mathit{PCR}}_{\mathit{min}}<{\mathit{PCR}}_{\mathit{now}}+\mathrm{\Delta }{\mathit{PCR}}_i<{\mathit{PCR}}_{\mathit{max}}\\ -\mathrm{\Delta }{\mathit{PCR}}_{\mathit{max}}<\mathrm{\Delta }{\mathit{PCR}}_i<\mathrm{\Delta }{\mathit{PCR}}_{\mathit{max}}\\ {\mathit{BM}}_{\mathit{min}}<{\mathit{BM}}_{\mathit{now}}+\mathrm{\Delta }{\mathit{BM}}_i<{\mathit{BM}}_{\mathit{max}}\\ -\mathrm{\Delta }{\mathit{BM}}_{\mathit{max}}<\mathrm{\Delta }{\mathit{BM}}_i<\mathrm{\Delta }{\mathit{BM}}_{\mathit{max}}\end{array}\begin{array}{c}\left(10\right)\\ \left(11\right)\\ \left(12\right)\\ \left(13\right)\end{array}$$
• Here, the subscript i in expressions (10) through (13) is 0 or 1. Further, the subscript now means the current value of the pulverized coal rate (PCR) or the blast moisture (BM). PCR_max and PCR_min are upper and lower limits of the target range of the pulverized coal rate (PCR), respectively. ΔPCR_max is an upper limit of the magnitude of allowable change in the pulverized coal rate (PCR). BM_max and BM_min are upper and lower limits of the target range of the blast moisture (BM), respectively. ΔBM_max is an upper limit of the magnitude of allowable change in the blast moisture (BM). The unknown variable θ is determined using quadratic programming so that the evaluation function J, which is a quadratic function regarding the unknown variable θ, is minimized under the constraints of the linear equations for the unknown variable θ indicated in expressions (10) through (13). The control to determine the unknown variable θ using expression (9) corresponds to the hot metal temperature control in FIG. 2.
• Here, according to the present embodiment, the evaluation function J was designed to decrease the blast moisture to decrease the reducing agent rate, but the same effect is obtainable by using the evaluation function J that directly decreases the reducing agent rate, for example, by penalizing an increase in the pulverized coal rate. Further, although the unknown variable θ was determined for the case of minimizing the evaluation function J according to the present embodiment, the evaluation function J may be designed so that the minimization of the deviation of the predicted value of the hot metal temperature from the target value and the reducing agent rate (or the blast moisture) corresponds to the maximization of the evaluation function J. That is, the operation amounts of the pulverized coal rate and the blast moisture may be determined so that the evaluation function J is minimized or maximized.
• In order to verify by simulation the effects of the present disclosure on decreasing the reducing agent rate under operational conditions close to those of actual operations, the operating variables (the blast volume and the coke rate) are also manipulated for control variables other than the hot metal temperature (the production rate and the in-furnace pressure drop) using the following method.
• The following expression (14) is used to determine ΔBV, the operation amount of the blast volume (BV) [Nm³/min], so that the deviation between the target value and the predicted value is eliminated for the production rate.
• [Math. 8] $$\mathrm{\Delta }\mathit{BV}=\frac{-b\left(\mathit{Prod}\left(t+T\right)-{\mathit{Prod}}_{\mathit{ref}}\right)}{S_{\mathit{BV}}}$$
• Here, Prod (t + T) is the predicted value of the production rate T steps ahead. As an example, T may be 4, which means a predicted value 2 hours (30 minutes × 4) ahead. Prod_rcf is the target production rate (the target value of the production rate). Further, S_BV is the change in the production rate when the blast volume (BV) is manipulated by a unit amount (1 [Nm³/min]). S_BV can be determined by another physical model or by step response tests in actual operations. Further, b is a coefficient and a positive number. The control to determine ΔBV according to expression (14) corresponds to the production rate control in FIG. 2.
• Further, the operation amounts of the coke rate (CR) and the blast volume (BV) are determined by comparison with the upper limit (threshold) for the in-furnace pressure drop (ΔP). When the in-furnace pressure drop (ΔP) exceeds the upper limit, the operation amount is determined so that the coke rate is increased and the blast volume is decreased at the same time. This corresponds to the operation of stabilizing the unloading of raw materials in a blast furnace operation. Further, the operation amount is determined so that the coke rate is gradually reduced when the in-furnace pressure drop is the upper limit or less. In principle, the in-furnace pressure drop is controlled to not exceed the upper limit, but when the in-furnace pressure drop is the upper limit or less, the cost of operation can be decreased by gradually decreasing the coke rate. When such control is carried out, the value of the in-furnace pressure drop remains near the upper limit. The control that determines the operation amounts of the coke rate (CR) and the blast volume (BV) by comparison with the upper limit of the in-furnace pressure drop corresponds to the permeability control in FIG. 2.
• FIG. 5 is a diagram illustrating simulation results from the process control described above, assuming that the absolute value of the difference between the predicted value of the hot metal temperature determined in the response prediction step and the target value is a defined threshold value or more. That is, the simulation in FIG. 5 is of manipulation of the blast moisture (BM), the pulverized coal rate (PCR), the blast volume (BV), and the coke rate (CR) based on predicted values using the dynamic model of the hot metal temperature (HMT), the production rate (Prod), and the in-furnace pressure drop (ΔP) as an example of permeability. The target hot metal temperature is 1500 °C. The target production rate is 7 [t/min]. The upper limit of the in-furnace pressure drop is 100 [kPa].
• FIG. 5 illustrates that the hot metal temperature (HMT) is operated near the target value, and based on the evaluation function J indicated in expression (9), the hot metal temperature variation is suppressed while the blast moisture (BM) is kept near the lower limit. The blast moisture being near the lower limit means that heat absorption by the water vapor decomposition reaction, which requires the input of reducing agent, is less likely to occur, and therefore leads to a decrease in the reducing agent rate. Further, the production rate (Prod) is controlled near the target value, and the in-furnace pressure drop (ΔP) is also kept at the upper limit or less.
• For comparative verification, a simulation was carried out for a comparative example in which only the pulverized coal rate (PCR) is manipulated and the blast moisture (BM) is not. FIG. 6 is a diagram illustrating simulation results according to the comparative example control. In the simulation illustrated in FIG. 6, the pulverized coal rate (PCR), the blast volume (BV), and the coke rate (CR) are manipulated based on the predicted values using a dynamic model of the hot metal temperature (HMT), the production rate (Prod), and the in-furnace pressure drop (ΔP) as an example of permeability. The conditions of the simulation are the same as in FIG. 5, except for the blast moisture (BM). The blast moisture is set at a constant value of 15.5 [g/Nm³]. The average value of the reducing agent rate in the process control method according to the present embodiment is decreased from the average value of the reducing agent rate in the comparative example. The decrease in the reducing agent rate decreases the amount of oxygen (oxygen unit consumption) [Nm³/t] blown in through the tuyere that is required to produce 1 tonne of hot metal. Therefore, the target production rate can be reached with a smaller blast volume. As a result, there is a greater margin for pressure drop, and therefore the coke rate can also be decreased (see CR in FIG. 5 and FIG. 6).
• FIG. 7 illustrates results when the operation amounts are determined by combining two of the operating variables, assuming that the absolute value of the difference between the predicted value of the hot metal temperature determined in the response prediction step and the target value is less than the defined threshold value. BV, Prod, and the like are the same as in FIG. 5. Further, the horizontal axes are a common time axis. The example in FIG. 7 illustrates changes over 12 hours. As indicated by the dashed circles in the pulverized coal rate (PCR) and the blast moisture (BM), the operation amounts are changed by the combination of the operation to decrease the pulverized coal rate and the operation to decrease the blast moisture. However, this change does not result in a significant change in the hot metal temperature (HMT). That is, while changing the reducing agent rate according to the intention, the hot metal temperature is maintained and stable operation is continued.
• FIG. 8 is a diagram illustrating an example configuration of a process control device 10 according to an embodiment. As illustrated in FIG. 8, the process control device 10 according to the present embodiment includes a communicator 11, a storage 12, and the controller 13. The controller 13 includes a hot metal temperature control unit 14, a production rate control unit 15, a permeability control unit 16, and a PCR tracking control unit 17. The process control device 10 executes the process control method described above. Here, the process control device 10 may display information such as the operation amount on a display such as a liquid crystal display when manipulating the blast moisture, the blast volume, the coke rate, or the pulverized coal rate, for example.
• The communicator 11 comprises a communication module for communicating with a higher-level system. The higher-level system includes a process computer that manages the processes at the plant, including the blast furnace. The communicator 11 may include, for example, a communication module compatible with a mobile communication standard such as 4G (fourth generation) or 5G (fifth generation). The communicator 11 may include a communication module compatible with a wired or wireless LAN standard, for example. The controller 13 can acquire information such as the target hot metal temperature, the target production rate, and the in-furnace pressure drop upper limit from the higher-level system via the communicator 11. Further, the controller 13 can also, via the communicator 11, output to the higher-level system information on the operating variables that were manipulated, that is, the operating variables that reflect the calculated operation amounts.
• The storage 12 stores the physical model described above. Further, the storage 12 stores programs and data related to the control of the blast furnace process. The storage 12 may include any storage device, such as a semiconductor storage device, an optical storage device, and a magnetic storage device. Semiconductor storage devices may include, for example, semiconductor memory. The storage 12 may include a plurality of types of storage devices.
• The controller 13 controls and manages each functional unit of the process control device 10 and the process control device 10 overall. The controller 13 may also execute acquisition of data used for control. That is, the controller 13 may acquire the hot metal temperature, the production rate, and the permeability of the blast furnace by observed or calculated values. The controller 13 includes at least one processor, such as a central processing unit (CPU), for controlling and managing various functions. The controller 13 may include a single processor or a plurality of processors. The processor of the controller 13 may function as the hot metal temperature control unit 14, the production rate control unit 15, the permeability control unit 16, and the PCR tracking control unit 17 by reading and executing programs from the storage 12.
• The hot metal temperature control unit 14 acquires the target hot metal temperature, which is the target value of the hot metal temperature, and when the absolute value of the difference between the predicted value of the hot metal temperature and the target value is the defined threshold value or more, calculates the operation amounts of the blast moisture and the pulverized coal rate at which the hot metal temperature becomes the target hot metal temperature. The hot metal temperature control unit 14 is the functional unit that executes the "hot metal temperature control" illustrated in FIG. 2. Further, when the absolute value of the difference between the predicted value of the hot metal temperature and the target value is less than the defined threshold value, the hot metal temperature control unit 14 combines two of the pulverized coal rate, the blast moisture, and the blast temperature to determine the operation amounts to maintain the predicted value.
• The production rate control unit 15 acquires the target production rate, which is the target value of the production rate, and calculates the operation amount of the blast volume so that the production rate becomes the target production rate. The production rate control unit 15 is a functional unit that executes the "production rate control" illustrated in FIG. 2.
• The permeability control unit 16 acquires the upper limit of the permeability (in-furnace pressure drop according to the present embodiment) and calculates at least the operation amount of the coke rate so that the permeability does not exceed the upper limit. The permeability control unit 16 may further calculate the operation amount of the blast volume, as in the present embodiment. The permeability control unit 16 is the functional unit that executes the "permeability control" illustrated in FIG. 2.
• The PCR tracking control unit 17 acquires the target value of the pulverized coal rate (target PCR) determined by the hot metal temperature control unit 14 and calculates the operation amount of the pulverized coal injection (PCI) rate to follow the target PCR by PCR tracking control. The PCR tracking control unit 17 is a functional unit that executes the "PCR tracking control" illustrated in FIG. 2.
• The hot metal temperature control unit 14, the production rate control unit 15, and the permeability control unit 16 are individual controllers for controlling the hot metal temperature (HMT), the production rate (Prod), and the in-furnace pressure drop (ΔP), respectively. To explain using steps 1 to 3 described above, the hot metal temperature control unit 14 executes step 1 (response prediction step) using the physical model to determine the predicted value of the hot metal temperature. The hot metal temperature control unit 14 executes step 2 (part of the operation amount determination step) to determine the operation amounts of the pulverized coal rate and the blast moisture. The production rate control unit 15 executes step 3 to determine the operation amount of the blast volume to cancel out the deviation of the production rate between the target value and the predicted value. Further, the permeability control unit 16 executes step 3 to determine the operation amounts of the blast volume and the coke rate so that the predicted value of the in-furnace pressure drop does not exceed the upper limit. Further, when the predicted value of the hot metal temperature is near the target value, the hot metal temperature control unit 14 executes step 4 (part of the operation amount determination step) to determine the operation amounts for an appropriate combination, depending on the intention, of two of the pulverized coal rate, the blast moisture, and the blast temperature. Here, the hot metal temperature control unit 14, the production rate control unit 15, and the permeability control unit 16, which are constructed as individual controllers as described above, are control systems that have disturbance cancellation properties that absorb fluctuations that are due to the manipulation of operating variables by other control units through their own manipulation of operating variables. Therefore, the hot metal temperature control unit 14, the production rate control unit 15, and the permeability control unit 16 can decrease the effects of interference of operating variables from other control units.
• As part of the blast furnace operation method, a process control method may be used that is executed by the process control device 10. For example, the operating variables manipulated in the process control method described above may be used to change the operational conditions in the operation of the blast furnace. Further, such a blast furnace operation method can also be carried out as part of a production method of producing hot metal. In a blast furnace, the raw material of iron ore is melted and reduced to pig iron, which is then tapped as hot metal, and the blast furnace may be operated according to this operation method. The operation amount determined by the hot metal temperature control unit 14, for example, may be displayed on a display device or the like to inform an operator as a proposal of a reducing agent rate that depends on the intention of the operation.
• The process control device 10 may be realized, for example, as a separate computer from the process computer that controls the operation of the blast furnace, or as the process computer. The computer includes, for example, memory and a hard disk drive (storage device), a CPU (processing device), and a display device such as a display. Various functions may be realized by organic cooperation between hardware, such as CPU and memory, and programs. The storage 12 may be realized, for example, by a storage device. The controller 13 may be realized, for example, by a CPU.
• As described above, the process control method, the blast furnace operation method, the hot metal production method, the process control device 10, and the program according to the present embodiment realize, through the configuration described above, proposing a reducing agent rate that depends on the intention that also suppresses variation of the hot metal temperature and continues stable operation.
• Although an embodiment of the present disclosure has been described based on the drawings and examples, it should be noted that a person skilled in the art may make variations and modifications based on the present disclosure. Therefore, it should be noted that such variations and modifications are included within the scope of the present disclosure. For example, functions and the like included in each component and step may be rearranged, and a plurality of components and steps may be combined into one or divided, as long as no logical inconsistency results. The embodiments according to the present disclosure may be realized as a storage medium on which a program executed by a processor provided to a device is stored. The scope of the present disclosure should be understood to include these examples.
• The process control device 10 configuration illustrated in FIG. 8 is an example. The process control device 10 need not include all of the components illustrated in FIG. 8. The process control device 10 may include components other than those illustrated in FIG. 8. For example, the process control device 10 may further include a display.
REFERENCE SIGNS LIST

10

process control device

11

communicator

12

storage

13

controller

14

hot metal temperature control unit

15

production rate control unit

16

permeability control unit

17

PCR tracking control unit

Claims (11)

1. A process control method comprising:

   a response prediction step of determining a predicted value of future hot metal temperature using a physical model capable of calculating an internal state of a blast furnace; and

   an operation amount determination step of,

   when an absolute value of a difference between the predicted value of the hot metal temperature determined in the response prediction step and a target value is a defined threshold value or greater, determining a deviation between the predicted value of the hot metal temperature and the target value, and determining operation amounts of pulverized coal rate and blast moisture so that an evaluation function comprising a term corresponding to the deviation and a term for decreasing the reducing agent rate or blast moisture is minimized or maximized, and

   when the absolute value is less than the defined threshold value, determining, depending on an intention, the operation amounts of a combination of two of the pulverized coal rate, the blast moisture, and blast temperature, to maintain the predicted value.
2. The process control method according to claim 1, wherein the intention includes a first intention of prioritizing decreasing the reducing agent rate and a second intention of temporarily increasing exhaust gas from the blast furnace.
3. The process control method according to claim 2, wherein
   the operation amount determination step,

   when the intention is the first intention, determines the operation amounts of a combination of an operation decreasing the pulverized coal rate and an operation decreasing the blast moisture, a combination of an operation decreasing the pulverized coal rate and an operation increasing the blast temperature, or a combination of an operation decreasing the blast temperature and an operation decreasing the blast moisture, and

   when the intention is the second intention, determines the operation amounts of a combination of an operation increasing the pulverized coal rate and an operation increasing the blast moisture, a combination of an operation increasing the pulverized coal rate and an operation decreasing the blast temperature, or a combination of an operation increasing the blast temperature and an operation increasing the blast moisture.
4. The process control method according to claim 3, wherein the operation amounts in the combination of two of the pulverized coal rate, the blast moisture, and the blast temperature are determined so that a theoretical combustion temperature is within a predetermined defined range of temperature.
5. The process control method according to any one of claims 1 to 4, wherein the response prediction step determines the predicted value of the future hot metal temperature using the physical model, based on the predicted value of the future hot metal temperature when current operating variables are held unchanged and the predicted value of the future hot metal temperature when the current operating variables are changed.
6. The process control method according to any one of claims 1 to 5, wherein the operation amount determination step determines unknown variables by using the evaluation function, which is a quadratic function regarding the unknown variables, under a constraint of a linear equation regarding the unknown variables, with the operation amounts of the pulverized coal rate and the blast moisture as the unknown variables.
7. The process control method according to any one of claims 1 to 6, further comprising a step of manipulating blast volume so that the predicted value of production rate matches a target value and manipulating coke rate so that the predicted value of permeability is an upper limit or less.
8. A blast furnace operation method comprising changing operational conditions using the operating variables manipulated by the process control method according to any one of claims 1 to 7.
9. A hot metal production method comprising producing hot metal using the blast furnace operated according to the blast furnace operation method according to claim 8.
10. A process control device comprising:

    a storage configured to store a physical model capable of calculating internal conditions of a blast furnace; and

    a hot metal temperature controller configured to acquire a target hot metal temperature that is a target value of hot metal temperature and calculate operation amounts of pulverized coal rate and blast moisture at which the hot metal temperature becomes the target hot metal temperature, wherein

    the hot metal temperature controller is further configured to:

    determine a predicted value of future hot metal temperature using the physical model;

    when an absolute value of a difference between the predicted value of the hot metal temperature and a target value is a defined threshold value or greater, determine a deviation between the predicted value of the hot metal temperature and the target value, and determine operation amounts of pulverized coal rate and blast moisture so that an evaluation function comprising a term corresponding to the deviation and a term for decreasing the reducing agent rate or blast moisture is minimized or maximized; and

    when the absolute value is less than the defined threshold value, determine, depending on an intention, the operation amounts of a combination of two of the pulverized coal rate, the blast moisture, and blast temperature, to maintain the predicted value.
11. A program configured to cause a computer to execute:

    a response prediction step of determining a predicted value of future hot metal temperature using a physical model capable of calculating an internal state of a blast furnace; and

    an operation amount determination step of,

    when an absolute value of a difference between the predicted value of the hot metal temperature determined in the response prediction step and a target value is a defined threshold value or greater, determining a deviation between the predicted value of the hot metal temperature and the target value, and determining operation amounts of pulverized coal rate and blast moisture so that an evaluation function comprising a term corresponding to the deviation and a term for decreasing the reducing agent rate or blast moisture is minimized or maximized, and

    when the absolute value is less than the defined threshold value, determining, depending on an intention, the operation amounts of a combination of two of the pulverized coal rate, the blast moisture, and blast temperature, to maintain the predicted value.