Blast furnace operation method

Abstract

This blast furnace operation method comprises, in relation to an operation in which a hydrogen-based reducing gas blown into the furnace is increased from a first blowing-in amount: a first step for determining a target blowing-in amount TA of the hydrogen-based reducing gas to be increased; a second step for preliminarily calculating each of the pulverized coal ratio, the air blowing amount, and the oxygen enrichment amount at which it is possible to maintain a constant molten iron tapping amount, a constant molten iron temperature, and a constant furnace top exhaust gas temperature and / or tuyere tip combustion temperature between before the hydrogen-based reducing gas starts to be increased so as to reach the target blowing-in amount TA and after the target blowing-in amount TA is reached; and a third step for starting operation at the pulverized coal ratio, the air blowing amount, and the oxygen enrichment amount calculated in the second step, when starting the blowing-in of the hydrogen-based reducing gas so as to reach the target blowing-in amount TA.

Description

Blast furnace operation method

[0001] This application claims priority to Japanese Patent Application No. 2024-028360, filed February 28, 2024, the contents of which are incorporated herein by reference.

[0002] In the steel industry, the blast furnace process is the mainstream of pig iron production. In the blast furnace process, iron-based raw materials (mainly sintered ore) containing iron oxide and coke are alternately and layeredly charged into the blast furnace from the top, while hot air is blown into the blast furnace from tuyere holes at the bottom. The hot air reacts with the pulverized coal blown in together with the hot air and the coke in the blast furnace to generate high-temperature reducing gas (mainly CO gas). That is, the hot air gasifies the coke and pulverized coal. The reducing gas rises within the blast furnace, heating and reducing the iron-based raw materials. That is, the iron-based raw materials charged from the top are heated and reduced by the reducing gas as they descend within the blast furnace. The iron-based raw materials are then melted and further reduced by the coke as they drip down the blast furnace. The iron-based raw materials are reduced to produce molten pig iron (pig iron) containing just under 5% by mass of carbon, which is then collected in the hearth. The molten pig iron collected in the hearth is then removed from a taphole at the bottom of the blast furnace and used in the subsequent steelmaking process. As described above, the blast furnace process uses carbonaceous materials such as coke and pulverized coal as reducing agents.

[0003] Recently, there has been a growing demand to prevent global warming, and carbon dioxide (CO ２ However, as mentioned above, the blast furnace method uses carbonaceous material as a reducing agent, which results in a large amount of CO ２ Therefore, the steel industry produces a large amount of CO ２ It is one of the industries that emits CO ２ We must respond to the social demand for reducing gas emissions. Specifically, there is an urgent need to further reduce the reducing agent ratio (amount of reducing agent used per ton of molten iron) in blast furnace operation.

[0004] Here, the reducing agent has the role of generating heat in the furnace to raise the temperature of the charge material, and the role of reducing the iron-based raw materials in the furnace. Therefore, in order to reduce the reducing agent ratio, it is necessary to increase the reduction efficiency in the furnace. The reduction reactions in the furnace can be expressed by various reaction formulas. Among these reduction reactions, the direct reduction reaction by coke (reaction formula: FeO + C ⇒ Fe + CO) is an endothermic reaction that involves a large heat absorption. Therefore, it is important to prevent this reaction from occurring as much as possible in order to reduce the reducing agent ratio. This direct reduction reaction occurs in the lower part of the blast furnace. Therefore, CO, H ２ If the iron-based raw material can be sufficiently reduced with a reducing gas such as the above, the amount of the iron-based raw material that is the target of the direct reduction reaction can be reduced.

[0005] As a conventional technique for reducing the reducing agent ratio, for example, a technique for increasing the reducing gas potential in the furnace by blowing hydrogen gas together with hot air from the tuyere, as disclosed in Patent Document 1, is known. In this technique, the reducing agent ratio is reduced by using hydrogen gas as a reducing gas for the iron-based raw materials.

[0006] International Publication No. 2021 / 107091

[0007] Incidentally, when the present inventors studied the technology disclosed in Patent Document 1, they found that during the switching stage (i.e., when the amount of hydrogen-based reducing gas is gradually increased) of transitioning from conventional normal operation (base operation) in which hydrogen gas is not used as a reducing gas to hydrogen-based reducing gas injection operation in which a hydrogen-based reducing gas is injected into the blast furnace (hereinafter also referred to as hydrogen gas injection operation), the state inside the furnace (particularly the reducing environment inside the furnace) changes significantly, and various indicators such as the tuyere tip combustion temperature and the furnace top exhaust gas temperature are also likely to change significantly, resulting in a problem in which it becomes difficult to operate the blast furnace stably.

[0008] Specifically, when switching from base operation to hydrogen gas injection operation, and when increasing the injection rate of hydrogen-based reducing gas during hydrogen gas injection operation, at least one of the tuyere combustion temperature and the furnace top exhaust gas temperature significantly decreases. To ensure stable blast furnace operation, it is necessary to maintain the tuyere combustion temperature and the furnace top exhaust gas temperature as constant as possible. For example, as will be described in detail later, a decrease in the tuyere combustion temperature reduces the molten iron temperature. Furthermore, a decrease in the furnace top exhaust gas temperature may cause moisture adhering to the iron-based raw materials and coke to enter the blast furnace without evaporating, potentially worsening the furnace conditions. As a result, it becomes difficult to operate the blast furnace stably.

[0009] Furthermore, in recent years, CO generated in steelworks has ２ Therefore, there is a need for hydrogen-based reducing gas as a reducing gas. However, as the amount of hydrogen-based reducing gas injected increases, the heat balance inside the furnace deteriorates further, as described above, and the tuyere combustion temperature and the furnace top exhaust gas temperature decrease significantly, which can cause unstable operation.

[0010] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a method for operating a blast furnace that can stably operate the blast furnace even when the amount of hydrogen-based reducing gas injected is increased.

[0011] The gist of the present disclosure is as follows: (1) A method for operating a blast furnace according to one embodiment of the present disclosure is a method for operating a blast furnace injecting a hydrogen-based reducing gas into the furnace, wherein, in an operation in which the hydrogen-based reducing gas is increased from a first injection rate, the method includes: a first step of determining a target injection rate TA of the hydrogen-based reducing gas to be increased; a second step of calculating in advance a pulverized coal ratio, a blast rate, and an oxygen enrichment amount that can maintain constant a pig iron tapping rate, a molten iron temperature, and a furnace top exhaust gas temperature before starting to increase the hydrogen-based reducing gas to reach the target injection rate TA and after the target injection rate TA is reached; and a third step of starting operation at the pulverized coal ratio, the blast rate, and the oxygen enrichment amount calculated in the second step when starting to inject the hydrogen-based reducing gas to reach the target injection rate TA. (2) In the method for operating a blast furnace described in (1) above, after the third step, while monitoring the amount of pig iron tapped, the molten iron temperature, and the top exhaust gas temperature, at least one of the pulverized coal ratio, the blast rate, and the amount of oxygen enrichment may be adjusted so that the amount of pig iron tapped, the molten iron temperature, and the top exhaust gas temperature are constant before and after the third step. (3) A method for operating a blast furnace according to another aspect of the present disclosure is a method for operating a blast furnace injecting a hydrogen-based reducing gas into the furnace, the method comprising: a first step of determining a target injection amount TA of the hydrogen-based reducing gas to be increased in an operation in which the hydrogen-based reducing gas is increased from a first injection amount; a second step of calculating in advance a pulverized coal ratio, a blast rate, and an oxygen enrichment amount that can maintain constant the pig iron output, molten iron temperature, and tuyere combustion temperature before starting to increase the hydrogen-based reducing gas to the target injection amount TA and after the target injection amount TA is reached; and a third step of starting operation with the pulverized coal ratio, the blast rate, and the oxygen enrichment amount calculated in the second step when starting to inject the hydrogen-based reducing gas to achieve the target injection amount TA. (4) In the method of operating a blast furnace described in (3) above, after the third step, while monitoring the pig iron tapping rate, the molten iron temperature, and the tuyere tip combustion temperature, at least one of the pulverized coal ratio, the blast rate, and the oxygen enrichment amount may be adjusted so that the pig iron tapping rate, the molten iron temperature, and the tuyere tip combustion temperature are constant before and after the third step.(5) A method for operating a blast furnace according to yet another aspect of the present disclosure is a method for operating a blast furnace injecting a hydrogen-based reducing gas into the furnace, the method comprising: a first step of determining a target injection amount TA of the hydrogen-based reducing gas to be increased in an operation in which the hydrogen-based reducing gas is increased from a first injection amount; a second step of calculating in advance a pulverized coal ratio, a blast rate, an oxygen enrichment amount, a blast moisture content, and a blast temperature that can maintain constant the pig iron output, the molten iron temperature, the top exhaust gas temperature, and the tuyere combustion temperature before starting to increase the hydrogen-based reducing gas to the target injection amount TA and after the target injection amount TA is reached; and a third step of starting operation at the pulverized coal ratio, the blast rate, the oxygen enrichment amount, the blast moisture content, and at least one of the blast temperature and the blast temperature calculated in the second step when starting to inject the hydrogen-based reducing gas to the target injection amount TA. (6) In the method of operating a blast furnace described in (5) above, after the third step, while monitoring the pig iron tapping rate, the molten iron temperature, the top exhaust gas temperature, and the tuyere combustion temperature, at least one of the pulverized coal ratio, the blast rate, the oxygen enrichment amount, the blast moisture, and the blast temperature may be adjusted so that the pig iron tapping rate, the molten iron temperature, the top exhaust gas temperature, and the tuyere combustion temperature are constant before and after the third step.

[0012] According to the present disclosure, even when the injection amount of hydrogen-based reducing gas is increased, the blast furnace can be operated stably.

[0013] 1 is a graph showing the correlation between the time (h) elapsed since the start of the transition from base operation to hydrogen gas injection operation and the injection rate of hydrogen-based reducing gas (kg / t-pig). 2 is a graph showing the correlation between the time (h) elapsed since the start of the transition from base operation to hydrogen-based reducing gas injection operation and the pig iron production rate (t / g). 3 is a graph showing the correlation between the time (h) elapsed since the start of the transition from base operation to hydrogen-based reducing gas injection operation and the molten iron temperature T ｐｉｇ 1 is a graph showing the correlation between the elapsed time (h) from the start of the transition from base operation to hydrogen-based reducing gas injection operation and the tuyere tip combustion temperature T ｆ 1 is a graph showing the correlation between the time (h) elapsed since the start of the transition from base operation to hydrogen-based reducing gas injection operation and the furnace top exhaust gas temperature T ｔоｐ1 is a graph showing the correlation between the elapsed time (h) from the start of the transition from base operation to hydrogen-based reducing gas injection operation, the amount of hot metal tapped, and the molten iron temperature T ｐｉｇ , tuyere tip combustion temperature T ｆ and the furnace top exhaust gas temperature T ｔоｐ Graphs showing the correlation between each of them.

[0014] A blast furnace operating method according to one embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. However, the present disclosure is not limited to the configuration disclosed in this embodiment, and various modifications are possible within the scope of the present disclosure. Furthermore, the numerical ranges described below with "to" include the lower and upper limits. Numerical values ​​indicated as "less than" or "greater than" do not include the numerical range.

[0015] <1. Investigation by the Inventor> First, the investigation by the inventor will be described. First, the inventor performed base operation, which is operation without injection of a hydrogen-based reducing gas, and investigated the correlations between the pig iron production rate, molten iron temperature, and top exhaust gas temperature and the blast rate, oxygen enrichment amount, and pulverized coal ratio. Here, the "base operation" is operation according to the above-mentioned blast furnace method, without injection of a hydrogen-based reducing gas. The molten iron temperature and the top exhaust gas temperature were actually measured.

[0016] As a result of the above-mentioned investigations by the present inventors, it was found that when switching from base operation to hydrogen gas injection operation in which a hydrogen-based reducing gas is injected into the furnace, the furnace top exhaust gas temperature significantly decreases. When the furnace top exhaust gas temperature decreases, moisture adhering to the iron-based raw materials and coke may enter the blast furnace without evaporating, potentially worsening the condition inside the furnace. This makes it difficult to perform stable blast furnace operation. Therefore, it is clear that in order to perform stable blast furnace operation, it is necessary to maintain the furnace top exhaust gas temperature as constant as possible. Specifically, in order to achieve stable blast furnace operation, it is effective to suppress the decrease in the furnace top exhaust gas temperature.

[0017] Furthermore, the present inventors investigated the correlations between the pig iron production rate, molten pig iron temperature, and tuyere combustion temperature during base operation and the blast rate, oxygen enrichment amount, and pulverized coal ratio. The tuyere combustion temperature is the temperature at the tip of the tuyere (gas outlet), and was determined by simulating blast furnace operation. The simulation model used was a so-called "blast furnace mathematical model" as shown, for example, in "Three-dimensional Dynamic Simulator for Blast Furnace" by Kouji Takatani, Takanobu Inada, and Yutaka Ujisawa, ISIJ International, Vol. 39 (1999), No. 1, pp. 15-22. This blast furnace mathematical model roughly defines multiple meshes (small regions) by dividing the internal region of the blast furnace in the height, radial, and circumferential directions, and simulates the behavior of each mesh. Ｆ , Q Ｂ , Q Ｃ , C ｇ and V Ｔ That is, the combustion temperature at the tip of the tuyere is calculated using Q Ｆ , Q Ｂ , Q Ｃ , C ｇ and V Ｔ The gas temperature at the tip of the tuyere is calculated from

[0018] "Q Ｆ ": Fuel and CO blown into the furnace together with the air ２ , H ２ Reaction heat at the tip of the tuyere (kcal / kg C ｃ ) (where Cc means the C in the coke burning at the tip of the tuyere.) "Q Ｂ ": Sensible heat (kcal / kg C) brought in by the air blown from the tuyere ｃ ). "Q Ｃ ": Sensible heat of coke entering the combustion zone (kcal / kg C ｃ ). "C ｇ ": Constant pressure specific heat of combustion product gas (kcal / Nm ３ ・℃). "V Ｔ ": Amount of combustion gas (Nm ３ / kg C ｃ ).

[0019] As a result, it was found that there is a strong correlation between the molten pig iron temperature and the tuyere combustion temperature. Therefore, in order to operate a blast furnace stably without reducing the pig iron production rate, it is necessary to maintain the tuyere combustion temperature (°C) as constant as possible during the transition. Specifically, in order to achieve stable blast furnace operation, it is effective to suppress the decrease in the tuyere combustion temperature and prevent a decrease in the molten pig iron temperature.

[0020] Next, the inventors studied changes in the state inside the furnace when switching from base operation to hydrogen gas injection operation, in which a hydrogen-based reducing gas is injected into the furnace. Specifically, a simulation of blast furnace operation before and after the start of injection of a hydrogen-based reducing gas was carried out in the same manner as above to study changes in the state inside the furnace. Here, the specifications for the base operation were as follows. In Table 1, "CR" is the coke ratio and "PCR" is the pulverized coal ratio.

[0021]

[0022] The results are shown in Figures 1 to 5. Note that the conditions used in this study are merely examples of conditions adopted to investigate and confirm the feasibility and effectiveness of the present disclosure, and the present disclosure is not limited to the study results and conditions described below. In other words, the present disclosure may adopt various conditions as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

[0023] The horizontal axis in each of Figures 1 to 5 represents the elapsed time (h) from the time when the transition from base operation to hydrogen-based reducing gas injection operation (the time when injection of hydrogen-based reducing gas started) was set as "0". In other words, "0 (h)" on the horizontal axis represents the time when injection of hydrogen-based reducing gas started. The vertical axis in Figure 1 represents the amount of hydrogen-based reducing gas injected per ton of molten iron (kg / t-pig). The graph shown in Figure 1 shows an operation in which injection of 20 kg / t-pig of hydrogen-based reducing gas into the blast furnace started at time 0 (h).

[0024] The vertical axis of Fig. 2 represents the iron production rate (t / d), the vertical axis of Fig. 3 represents the molten iron temperature (°C), the vertical axis of Fig. 4 represents the tuyere combustion temperature (°C), and the vertical axis of Fig. 5 represents the furnace top exhaust gas temperature (°C).

[0025] In this study, in order to examine the changes in the state inside the furnace when switching from base operation to hydrogen gas injection operation, we investigated the relationship between the iron production rate, molten iron temperature, and tuyere combustion temperature or top exhaust gas temperature and various parameters that affect them.

[0026] Therefore, when transitioning to hydrogen gas injection operation, the behavior of the iron production rate (t / d), molten iron temperature (°C), tuyere combustion temperature (°C), and furnace top exhaust gas temperature (°C) was investigated for each of the following cases: Case 1: Injection of hydrogen-based reducing gas (no control of other parameters), Case 2: Control of blast rate only, Case 3: Control of blast rate and pulverized coal ratio only, and Case 4: Control of blast rate, pulverized coal ratio, and oxygen enrichment amount.

[0027] Furthermore, when switching to hydrogen gas injection operation, in order to maintain constant the iron production rate, molten iron temperature, tuyere combustion temperature, and furnace top exhaust gas temperature, the relationship with the various parameters that affect these was investigated in the following cases.

[0028] Case 5: Controlling the blast volume, pulverized coal ratio, oxygen enrichment amount, and blast moisture

[0029] The graph in Figure 2 shows the correlation between elapsed time (h) and iron production (t / d) for each of Cases 1 to 4. When simply injecting a hydrogen-based reducing gas without controlling the blast rate, pulverized coal ratio, or oxygen enrichment rate (Case 1), iron production significantly decreased. Furthermore, when only the blast rate was controlled during the transition to hydrogen gas injection operation (Case 2), the iron production fluctuations were smaller than in Case 1, but the iron production increased sharply immediately after the transition to hydrogen gas injection operation. On the other hand, when the blast rate and pulverized coal ratio were both controlled (Case 3), the iron production did not increase sharply compared to Case 2, and the fluctuations in iron production before and after the transition were also smaller, resulting in stable blast furnace operation. This behavior was also observed in Case 4.

[0030] The graph shown in FIG. 3 shows the relationship between the elapsed time (h) and the molten iron temperature T ｐｉｇIn case 1, the hot metal temperature T ｐｉｇ The temperature of the hot metal T ｐｉｇ rises, and the molten iron temperature T ｐｉｇ In addition, when only the blast rate was controlled when switching to hydrogen gas injection operation (Case 2), the molten iron temperature T ｐｉｇ Although the fluctuation of the molten iron temperature T ｐｉｇ rises, and the molten iron temperature T ｐｉｇ On the other hand, when the pulverized coal ratio was controlled in addition to the blast rate (Case 3), the hot metal temperature T ｐｉｇ There is no sudden drop in the molten iron temperature T ｐｉｇ The fluctuations before and after the transition were small, and it can be seen that stable blast furnace operation was achieved. This behavior was also the same in Case 4.

[0031] The graph shown in FIG. 4 shows the relationship between the elapsed time (h) and the tuyere combustion temperature T ｆ In the cases of Case 1 and Case 2, the tuyere tip combustion temperature T ｆ The combustion temperature T ｆ The combustion temperature T ｆ On the other hand, when the pulverized coal ratio and the oxygen enrichment amount were controlled in addition to the blast rate (Case 4), the tuyere combustion temperature T ｆ There was no sudden drop in the tuyere tip combustion temperature T ｆ It can be seen that the fluctuations before and after the transition are small, and stable blast furnace operation can be achieved.

[0032] The graph shown in FIG. 5 shows the relationship between the elapsed time (h) and the furnace top exhaust gas temperature T ｔоｐ In the cases of Case 1 and Case 2, the furnace top exhaust gas temperature T ｔоｐ The furnace top exhaust gas temperature T ｔоｐ The furnace top exhaust gas temperature T ｔоｐOn the other hand, when the pulverized coal ratio and the oxygen enrichment amount were controlled in addition to the blast rate (Case 4), the furnace top exhaust gas temperature T ｔоｐ There is no sudden increase in the furnace top exhaust gas temperature T ｔоｐ It can be seen that the fluctuation before and after the transition is small, and stable blast furnace operation can be achieved.

[0033] The graph shown in FIG. 6 shows the relationship between the amount of tapped iron and the molten iron temperature T ｐｉｇ , tuyere tip combustion temperature T ｆ and the furnace top exhaust gas temperature T ｔоｐ As is clear from Figure 6, when switching to hydrogen gas injection operation, by controlling the blast moisture content in addition to the blast rate, pulverized coal ratio, and oxygen enrichment amount, the amount of hot metal tapped and the hot metal temperature T ｐｉｇ , tuyere tip combustion temperature T ｆ and the furnace top exhaust gas temperature T ｔоｐ In both cases, it can be seen that there is little fluctuation before and after the transition, resulting in stable blast furnace operation.

[0034] From the above, it was revealed that when transitioning from base operation to hydrogen gas injection operation, adjusting the blast rate, pulverized coal ratio, and oxygen enrichment amount can maintain constant the pig iron production rate, molten pig iron temperature, tuyere combustion temperature, and top exhaust gas temperature. It was also revealed that when transitioning from base operation to hydrogen gas injection operation, adjusting the blast moisture content in addition to the blast rate, pulverized coal ratio, and oxygen enrichment amount can maintain constant the pig iron production rate, molten pig iron temperature, tuyere combustion temperature, and top exhaust gas temperature. While the specific adjustment amounts may vary depending on the base operating conditions and the amount of hydrogen-based reducing gas injected, an appropriate blast rate, pulverized coal ratio, and oxygen enrichment amount can be determined by performing a simulation of blast furnace operation.

[0035] 2. Blast Furnace Operating Method Next, a blast furnace operating method according to this embodiment will be described. The blast furnace operating method according to this embodiment is a blast furnace operating method in which a hydrogen-based reducing gas is injected into the furnace. Note that the "hydrogen-based reducing gas" referred to here refers to a gas containing 30 mol % or more of H as an elemental composition ratio, and exists as a gas under standard conditions (0°C, 1 atmosphere). For example, H２ Gas, unsaturated hydrocarbon gas (C ２ H ４ , C ２ H ２ , C ３ H ６ etc.), saturated hydrocarbon gases (CH ４ , C ２ H ６ , etc.), NH ３ Gas, coke oven gas, city gas, natural gas, etc., and mixtures thereof are particularly preferred. ２ Gas, unsaturated hydrocarbon gas (C ２ H ４ , C ２ H ２ , C ３ H ６ etc.) H ２ The gas does not contain carbon and does not cause a thermal decomposition reaction at the tuyere tip, so it is preferable from the viewpoint of reducing the carbon consumption unit. In addition, the gas has low viscosity and density, so it is also preferable from the viewpoint of gas permeability inside the blast furnace. Unsaturated hydrocarbon gases contain double bonds and triple bonds in the gas molecules, so the combustion heat per 1 mol of oxygen is relatively large and they are preferable because they serve as a heat source at the tuyere tip. It is more preferable that the elemental composition ratio of H in the hydrogen-based reducing gas is 50 mol % or more. In addition, the hydrogen-based reducing gas may be replaced with other gases (e.g., N) that do not impair the effect of this embodiment. ２ A mixed gas with a gas) may also be used.

[0036] In this embodiment, the tuyere for injecting the hydrogen-based reducing gas into the furnace is not limited. For example, the hydrogen-based reducing gas may be injected from a tuyere provided at the lower end of the blast furnace, i.e., a so-called normal tuyere, or from a shaft tuyere provided at a higher position than the normal tuyere (for example, in the shaft).

[0037] The method for operating a blast furnace according to this embodiment includes, in an operation in which the hydrogen-based reducing gas is increased from a first injection rate, a first step of determining a target injection rate TA of the hydrogen-based reducing gas to be increased, a second step of calculating in advance a pulverized coal ratio, a blast rate, and an oxygen enrichment amount that can maintain constant the pig iron production rate, molten iron temperature, and top exhaust gas temperature before the hydrogen-based reducing gas starts to increase and after the target injection rate TA is reached, and a third step of starting operation at the pulverized coal ratio, blast rate, and oxygen enrichment amount calculated in step 2 when starting to inject the hydrogen-based reducing gas to achieve the target injection rate TA. Note that in step 2, the pulverized coal ratio, blast rate, and oxygen enrichment amount may be calculated in advance so that the tuyere combustion temperature can be maintained constant instead of the top exhaust gas temperature. The following explanation of steps 1 to 3 will be given using the furnace top exhaust gas temperature as an example, but the blast furnace operating method of this embodiment may also be in a form in which the "furnace top exhaust gas temperature" below is replaced with "tuyere tip combustion temperature."

[0038] (First step) First, a target injection amount TA of the hydrogen-based reducing gas, which is a target increase value from the first injection amount, is determined. The specific value of the target injection amount TA is not limited, and may be determined appropriately depending on various circumstances in the operation of the blast furnace, such as a desired CO2 reduction target.

[0039] The "first injection amount" here refers to the injection amount of the hydrogen-based reducing gas before the hydrogen-based reducing gas is increased. In other words, the "first injection amount" is naturally smaller than the "target injection amount TA." Furthermore, if the operation before the hydrogen-based reducing gas is increased is a so-called base operation in which no hydrogen-based reducing gas is used, the first injection amount is 0 (kg / t-pig).

[0040] (Second step) Next, the pulverized coal ratio, blast rate, and oxygen enrichment amount that can maintain the pig iron tapping rate, molten iron temperature, and furnace top exhaust gas temperature (or tuyere tip combustion temperature) constant before the hydrogen-based reducing gas starts to increase and after it reaches the target injection amount TA are calculated in advance.

[0041] Specifically, a simulation of blast furnace operation is first performed based on parameters for operation before the hydrogen-containing reducing gas injection rate begins to be increased to the target injection rate TA and operation after the hydrogen-containing reducing gas injection rate reaches the target injection rate TA. The pulverized coal ratio, blast rate, and oxygen enrichment rate are adjusted, and the pulverized coal ratio, blast rate, and oxygen enrichment rate that can maintain constant the iron production rate, molten iron temperature, and top exhaust gas temperature are calculated between the operation before the hydrogen-containing reducing gas injection rate begins to be increased and the operation after the target injection rate TA is reached. That is, in the second step, the simulation of blast furnace operation is used to calculate parameters that can maintain constant the iron production rate, molten iron temperature, and top exhaust gas temperature under ideal conditions.

[0042] In this embodiment, "constant iron production rate" means that the rate of change in the iron production rate is 1.0% or less. "Constant molten iron temperature" means that the rate of change in the molten iron temperature is 1.0% or less. "Constant furnace top exhaust gas temperature" means that the rate of change in the furnace top exhaust gas temperature is 10.0% or less. "Constant tuyere tip combustion temperature" means that the rate of change in the tuyere tip combustion temperature is 1.0% or less.

[0043] Fluctuations in the pig iron production rate and the top exhaust gas temperature before and after the start of increasing the hydrogen-based reducing gas are easily affected by the blast rate and the oxygen enrichment amount. Therefore, in order to further suppress fluctuations in the pig iron production rate and the top exhaust gas temperature and maintain them constant, it is more effective to use the blast rate and the oxygen enrichment amount as adjustment indicators. On the other hand, fluctuations in the molten iron temperature before and after the start of increasing the hydrogen-based reducing gas are easily affected by the pulverized coal ratio. Therefore, in order to further suppress fluctuations in the molten iron temperature and maintain it constant, it is more effective to adjust the pulverized coal ratio as an adjustment indicator. In this embodiment, "adjusting the pulverized coal ratio" means maintaining the pig iron production rate constant and adjusting the amount of pulverized coal injection.

[0044] In this embodiment, the pulverized coal ratio, blast rate, and oxygen enrichment amount are each adjusted so that the furnace top exhaust gas temperature or tuyere tip combustion temperature can be maintained constant, but it is preferable to control each condition so that both the furnace top exhaust gas temperature and tuyere tip combustion temperature can be maintained constant.

[0045] A decrease in the top exhaust gas temperature affects the temperatures of the iron-based raw materials and coke charged from the furnace top, which in turn affects the stable operation of the blast furnace. Therefore, it is preferable to adjust each condition so that both the top exhaust gas temperature and the tuyere combustion temperature are constant before and after starting to increase the hydrogen-based reducing gas.

[0046] In order to keep both the furnace top exhaust gas temperature and the tuyere tip combustion temperature constant before and after the hydrogen-based reducing gas starts to increase, specifically, in the second step, the pulverized coal ratio, blast volume, oxygen enrichment amount, blast moisture, and blast temperature are each calculated in advance so that both temperatures can be maintained constant before the hydrogen-based reducing gas starts to increase and after it reaches the target injection amount TA.

[0047] The changes in the furnace top exhaust gas temperature and the tuyere tip combustion temperature before and after the start of increasing the hydrogen-based reducing gas are also easily affected by the blast humidity and the blast temperature. Therefore, in order to further suppress fluctuations in both temperatures and maintain them constant, it is more effective to use the blast humidity and the blast temperature as adjustment indicators. Note that, in some cases, the furnace top exhaust gas temperature and the tuyere tip combustion temperature can be kept constant by adjusting only either the blast humidity or the blast temperature. Therefore, the value calculated in the second step may be either the blast humidity or the blast temperature.

[0048] (Third Step) Next, the hydrogen-based reducing gas starts to be increased from the first injection rate to the target injection rate TA calculated in the first step. At this time, operation is performed at the pulverized coal ratio, blast rate, and oxygen enrichment amount calculated in the second step. That is, by switching the pulverized coal ratio, blast rate, and oxygen enrichment amount to the target values ​​calculated in the second step at the timing when the hydrogen-based reducing gas injection rate is increased from the first injection rate to the target injection rate TA, the heat balance in the furnace can be maintained, and the iron production rate, molten iron temperature, and furnace top exhaust gas temperature can be maintained constant, even if the injection rate of the hydrogen-based reducing gas is increased. As a result, stable blast furnace operation can be performed.

[0049] In the second step, when the target values ​​of the blast moisture and the blast temperature are calculated, it is advisable to switch at least one of the blast moisture and the blast temperature so as to satisfy the target values ​​together with the switching of the pulverized coal ratio, the blast flow rate, and the oxygen enrichment amount, thereby making it possible to maintain both the furnace top exhaust gas temperature and the tuyere combustion temperature constant, and to carry out more stable blast furnace operation.

[0050] In this embodiment, after the third step, that is, during operation in which the hydrogen-based reducing gas injection amount has been increased to the target injection amount TA, at least one of the pulverized coal ratio, the blast rate, and the oxygen enrichment amount may be further adjusted while monitoring the iron output, molten iron temperature, and tuyere combustion temperature or furnace top exhaust gas temperature, so that these are constant before and after increasing the hydrogen-based reducing gas injection amount to the target injection amount TA.

[0051] In actual operation of a blast furnace, even if the pulverized coal ratio, blast rate, and oxygen enrichment rate are switched to the target values ​​calculated in step 2, the iron production rate, molten iron temperature, tuyere combustion temperature, and top exhaust gas temperature may vary. Therefore, even after increasing the hydrogen-based reducing gas injection rate to the target TA, these may be monitored and, if the values ​​vary from before switching, the pulverized coal ratio, blast rate, and oxygen enrichment rate may be further adjusted. That is, after increasing the hydrogen-based reducing gas injection rate to the target TA in step 3, it is preferable to adjust each parameter so that the iron production rate, molten iron temperature, and top exhaust gas temperature can be maintained constant during actual operation of the blast furnace.

[0052] Here, the actual monitoring of the pig iron tapping rate, molten iron temperature, top exhaust gas temperature, and tuyere combustion temperature may be carried out in the following manner. The pig iron tapping rate can be measured, for example, by measuring the weight of the pig iron tapped by a torpedo car. The molten iron temperature can be measured by inserting a thermometer directly into the molten iron discharged from the tap hole and flowing in the molten iron launder. The molten iron temperature may also be calculated by photographing the molten iron discharged from the tap hole with an imaging device such as a high-speed camera and analyzing the resulting image. The tuyere combustion temperature may be calculated as needed according to the conditions inside the furnace using the above-mentioned formula. The top exhaust gas temperature can be measured by actual measurement. Note that "monitoring" each of the above indicators means measuring the values ​​of each indicator intermittently from moment to moment.

[0053] The monitored values ​​of the iron tapping rate, molten iron temperature, and furnace top exhaust gas temperature may be actual measured values ​​or calculated values.

[0054] According to the blast furnace operation method of the present embodiment described above, even when the injection rate of the hydrogen-based reducing gas to be injected is increased, the pig iron production rate, molten iron temperature, and tuyere combustion temperature and / or furnace top exhaust gas temperature can be maintained constant, so that hydrogen gas injection operation using a hydrogen-based reducing gas can be carried out stably.

[0055] Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications or alterations within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0056] According to the present disclosure, even when the injection rate of hydrogen-based reducing gas is increased, the tuyere combustion temperature and the furnace top exhaust gas can be maintained constant, thereby enabling stable operation of the blast furnace. For example, the molten iron temperature and the iron production rate can be maintained constant. Furthermore, since the furnace top exhaust gas can be maintained constant, moisture adhering to the iron-based raw materials and coke can be sufficiently removed. Therefore, the present disclosure has high industrial applicability.

Claims

1. A method for operating a blast furnace in which a hydrogen-based reducing gas is injected into the furnace, comprising: a first step of determining a target injection amount TA of the hydrogen-based reducing gas to be increased in an operation in which the hydrogen-based reducing gas is increased from a first injection amount; a second step of calculating in advance a pulverized coal ratio, a blast rate, and an oxygen enrichment amount that can maintain constant the pig iron output, molten iron temperature, and furnace top exhaust gas temperature before starting to increase the hydrogen-based reducing gas to reach the target injection amount TA and after the target injection amount TA has been reached; and a third step of starting operation with the pulverized coal ratio, blast rate, and oxygen enrichment amount calculated in the second step when starting to inject the hydrogen-based reducing gas to reach the target injection amount TA.

2. A method for operating a blast furnace as described in claim 1, wherein after the third step, while monitoring the pig iron tapping rate, the molten iron temperature, and the top exhaust gas temperature, at least one of the pulverized coal ratio, the blast rate, and the oxygen enrichment amount is adjusted so that the pig iron tapping rate, the molten iron temperature, and the top exhaust gas temperature are constant before and after the third step.

3. A method for operating a blast furnace in which a hydrogen-based reducing gas is injected into the furnace, comprising: a first step of determining a target injection amount TA of the hydrogen-based reducing gas to be increased in an operation in which the hydrogen-based reducing gas is increased from a first injection amount; a second step of calculating in advance a pulverized coal ratio, a blast rate, and an oxygen enrichment amount that can maintain constant the pig iron output, molten iron temperature, and tuyere combustion temperature before starting to increase the hydrogen-based reducing gas to reach the target injection amount TA and after the target injection amount TA has been reached; and a third step of starting operation with the pulverized coal ratio, blast rate, and oxygen enrichment amount calculated in the second step when starting to inject the hydrogen-based reducing gas to reach the target injection amount TA.

4. A method for operating a blast furnace as described in claim 3, wherein after the third step, while monitoring the pig iron output, the molten iron temperature, and the tuyere tip combustion temperature, at least one of the pulverized coal ratio, the blast rate, and the oxygen enrichment amount is adjusted so that the pig iron output, the molten iron temperature, and the tuyere tip combustion temperature are constant before and after the third step.

5. A method for operating a blast furnace in which a hydrogen-based reducing gas is injected into the furnace, comprising: a first step of determining a target injection amount TA of the hydrogen-based reducing gas to be increased in an operation in which the hydrogen-based reducing gas is increased from a first injection amount; a second step of calculating in advance a pulverized coal ratio, blast rate, oxygen enrichment amount, blast moisture, and blast temperature that can maintain constant the pig iron output, molten pig iron temperature, furnace top exhaust gas temperature, and tuyere tip combustion temperature before starting to increase the hydrogen-based reducing gas to reach the target injection amount TA and after the target injection amount TA has been reached; and a third step of starting operation under the conditions of at least one of the blast moisture and the blast temperature, and the pulverized coal ratio, the blast rate, and the oxygen enrichment amount calculated in the second step when starting to inject the hydrogen-based reducing gas to reach the target injection amount TA.

6. A method for operating a blast furnace as described in claim 5, wherein after the third step, while monitoring the pig iron output rate, the molten iron temperature, the furnace top exhaust gas temperature, and the tuyere tip combustion temperature, at least one of the pulverized coal ratio, the blast rate, the oxygen enrichment amount, the blast moisture content, and the blast temperature is adjusted so that the pig iron output rate, the molten iron temperature, the furnace top exhaust gas temperature, and the tuyere tip combustion temperature are constant before and after the third step.

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