Blast furnace operation method

Abstract

To provide a blast furnace operation method by which a blast furnace may stably be operated when shifting from a base operation to a hydrogen gas blowing operation.SOLUTION: The gist of the present invention is as follows: (1) a blast furnace operation method during transition from a base operation to a hydrogen gas blowing operation in which a hydrogen-based reducing gas is blown into a blast furnace, wherein a tuyere tip combustion temperature and a furnace top exhaust gas temperature are maintained constant by adjusting at least a blowing air moisture content, an oxygen enrichment ratio, and a pulverized coal ratio; and (2) in the blast furnace operation method according to (1), the tuyere tip combustion temperature and the furnace top exhaust gas temperature are monitored until a predetermined time elapses from the start of the transition from the base operation to the hydrogen gas blowing operation.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace. [Background technology]

[0002] In the steel industry, the blast furnace process is the mainstream method for producing pig iron. In this process, iron-based raw materials (raw materials containing iron oxide, mainly sintered ore, hereinafter simply referred to as "iron-based raw materials") and coke are alternately and in layers charged into the blast furnace from the top of the furnace, while hot air is blown into the blast furnace from tuyeres 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). In other words, 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. As the iron-based raw materials descend within the blast furnace, they are heated and reduced by the reducing gas. The iron-based raw materials then melt and drip down the blast furnace, where they are further reduced by the coke. The iron-based raw materials are eventually stored in the hearth as molten pig iron (pig iron) containing just under 5% by mass of carbon. The molten pig iron in the hearth is removed from the taphole and used in the subsequent steelmaking process. Therefore, in the blast furnace process, carbonaceous materials such as coke and pulverized coal are used as reducing agents.

[0003] In recent years, there has been a growing call to prevent global warming, and reducing emissions of carbon dioxide (CO2 gas), a greenhouse gas, has become a social issue. As mentioned above, the blast furnace process uses carbonaceous material as a reducing agent, which generates large amounts of CO2 gas. Therefore, the steel industry is one of the major industries in terms of CO2 gas emissions, and it must respond to this social demand. 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] The reducing agent serves two purposes: to generate heat in the furnace, raising the temperature of the charge, and to reduce the iron-based raw materials in the furnace. In order to reduce the reducing agent rate, it is necessary to increase the reduction efficiency in the furnace. The reduction reactions in the furnace can be expressed by various reaction equations. Among these reduction reactions, the direct reduction reaction with coke (reaction equation: FeO + C ⇒ Fe + CO) is an endothermic reaction that involves a large heat absorption. Therefore, minimizing this reaction is important in reducing the reducing agent rate. Because this direct reduction reaction occurs in the lower part of the blast furnace, if the iron-based raw materials can be sufficiently reduced with reducing gases such as CO and H2 before they reach the lower part of the furnace, the amount of iron-based raw materials subject to the direct reduction reaction can be reduced.

[0005] As a conventional technique for solving the above problems, a technique for increasing the reducing gas potential in the furnace by blowing hydrogen gas together with hot air from the tuyere is known, as disclosed in Patent Document 1. In this technique, hydrogen gas is used as a reducing gas for the iron-based raw materials, thereby reducing the reducing agent ratio. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2021 / 107091 Summary of the Invention [Problem to be solved by the invention]

[0007] However, after studying the technology disclosed in Patent Document 1, the inventors discovered that the conditions inside the blast furnace change significantly when switching from base operation to hydrogen gas injection operation, in which hydrogen gas is injected into the blast furnace, making stable operation of the blast furnace difficult. Specifically, when switching from base operation to hydrogen gas injection operation, the tuyere combustion temperature and the top flue gas temperature decrease significantly. To ensure stable blast furnace operation, it is necessary to maintain the tuyere combustion temperature and the top flue gas temperature as constant as possible. For example, as will be described in detail later, a decrease in the tuyere combustion temperature decreases the molten iron temperature. Furthermore, a decrease in the top flue gas temperature may cause moisture adhering to the iron-based raw materials and coke to enter the blast furnace without evaporating, potentially worsening the conditions inside the furnace. This makes stable blast furnace operation difficult.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for operating a blast furnace that enables stable operation of the blast furnace when transitioning from base operation to hydrogen gas injection operation. [Means for solving the problem]

[0009] The gist of the present invention is as follows. (1) A method for operating a blast furnace carried out when transitioning from base operation to hydrogen gas injection operation in which a hydrogen-based reducing gas is injected into the blast furnace, characterized in that the tuyere combustion temperature and the furnace top exhaust gas temperature are maintained constant by adjusting at least the blast moisture, the oxygen enrichment rate, and the pulverized coal ratio. (2) The method for operating a blast furnace according to (1), characterized in that the tuyere tip combustion temperature and the furnace top exhaust gas temperature are monitored until a predetermined time has elapsed from the time when the transition from the base operation to the hydrogen gas injection operation is started. [Effects of the Invention]

[0010] According to the present invention, the blast furnace can be operated stably when shifting from base operation to hydrogen gas injection operation. [Brief explanation of the drawings]

[0011] [Figure 1] 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 amount of hydrogen gas injected (kg / t-pig). [Figure 2] 1 is a graph showing the correlation between the oxygen enrichment rate (%) and the time (h) elapsed since the start of the transition from base operation to hydrogen gas injection operation. [Figure 3] 1 is a graph showing the correlation between the elapsed time (h) from the start of the transition from base operation to hydrogen gas injection operation and the blast moisture (g / Nm3). [Figure 4] 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 furnace top exhaust gas temperature (° C.). [Figure 5] 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 tuyere tip combustion temperature (°C). DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0013] <1. Investigation by the Inventor> First, the inventor's investigation will be described. First, the inventor performed base operation (operation without hydrogen gas injection) and investigated the correlation between the molten iron temperature and the tuyere combustion temperature during this operation. Here, the base operation is operation according to the above-mentioned blast furnace method, without hydrogen gas injection. Specifically, iron-based raw materials and coke are alternately and layeredly charged into the blast furnace from the top of the blast furnace, 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). In other words, 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. As the iron-based raw materials descend within the blast furnace, they are heated and reduced by the reducing gas. The iron-based raw materials then melt and drip down the blast furnace while being further reduced by the coke. The iron-based raw materials are ultimately deposited in the hearth as molten pig iron (pig iron) containing slightly less than 5% carbon by mass. The molten pig iron temperature was measured. The tuyere combustion temperature, the temperature at the tip of the tuyere (gas outlet), was determined by simulating blast furnace operation. The simulation model used was the so-called "blast furnace mathematical model" described, for example, by Kouji Takatani, Takanobu Inada, and Yutaka Ujisawa, "Three-dimensional Dynamic Simulator for Blast Furnace," ISIJ International, Vol. 39 (1999), No. 1, pp. 15-22. This blast furnace mathematical model roughly divides the internal region of the blast furnace into multiple meshes (small regions) in the vertical, radial, and circumferential directions, and simulates the behavior of each mesh. The results revealed a strong correlation between the molten pig iron temperature (°C) and the tuyere combustion temperature (°C). Therefore, in order to operate a blast furnace stably, it is necessary to maintain the tuyere combustion temperature (℃) as constant as possible, because if the tuyere combustion temperature fluctuates, the molten iron temperature will also fluctuate.It may seem that the tuyere tip combustion temperature (°C) can be monitored by monitoring the molten iron temperature (°C), but because the molten iron temperature (°C) fluctuates due to various factors, the tuyere tip combustion temperature (°C) cannot be accurately monitored simply by monitoring the molten iron temperature (°C).

[0014] On the other hand, maintaining a constant furnace top exhaust gas temperature is also a necessary condition for stable blast furnace operation. Iron-based raw materials and coke are charged from the furnace top, and these materials often contain moisture from rain and other sources. Therefore, if the furnace top exhaust gas temperature is low, this moisture will not evaporate and will enter the blast furnace, potentially worsening the condition inside the furnace. This makes it difficult to operate the blast furnace stably.

[0015] Next, the inventors studied the change in the state inside the furnace when transitioning from base operation to hydrogen gas injection operation (when hydrogen gas injection is started). Specifically, the above-mentioned blast furnace operation was simulated to study the change in the state inside the furnace when transitioning from base operation to hydrogen gas injection operation. Here, the specifications of the base operation were as follows. In Table 1, CR is the coke rate, and PCR is the pulverized coal rate.

[0016] [Table 1]

[0017] In this embodiment, "constant" means that the rate of change of the value per unit time is 1.0% or less.

[0018] The results are shown in Figures 1 to 5. The horizontal axes of Figures 1 to 5 show the elapsed time (h) when the transition from base operation to hydrogen gas injection operation (the start of hydrogen gas injection) is set to 0. The vertical axis of Figure 1 shows the amount of hydrogen gas injected per ton of molten pig iron (kg / t-pig). The vertical axis of Figure 2 shows the oxygen enrichment rate (%). Here, the oxygen enrichment rate is the volume percentage of oxygen gas injected into the blast furnace other than hot air (volume percentage relative to hot air). The vertical axis of Figure 3 shows the delivered moisture (g / Nm 3) indicates the moisture content (moisture) per unit flow rate of hot air (g / Nm 3 The vertical axis of Fig. 4 shows the furnace top exhaust gas temperature (°C). The vertical axis of Fig. 5 shows the tuyere tip combustion temperature (°C).

[0019] Graph L1 shows the correlation between the elapsed time and the amount of hydrogen gas injected. As is clear from Figure 1, in this study, 10 kg / t-pig of hydrogen gas was injected into the blast furnace at time 0.

[0020] Graphs L2 to L4 show the correlation between elapsed time and the oxygen enrichment rate. In all graphs, the oxygen enrichment rate is adjusted simultaneously with the injection of hydrogen gas, but the amount of adjustment is different. Graphs L5 to L7 show the correlation between elapsed time and blast humidity. In graph L5, the blast humidity is reduced simultaneously with the injection of hydrogen gas, while in graphs L6 and L7, the blast humidity is not changed. Therefore, graphs L6 and L7 overlap.

[0021] Graphs L8 to L10 show the correlation between elapsed time and the top exhaust gas temperature. In graph L8, the top exhaust gas temperature remains constant even when hydrogen gas is injected into the blast furnace. In graph L9, the top exhaust gas temperature fluctuates significantly before and after hydrogen gas injection. Specifically, the injection of hydrogen gas significantly reduces the top exhaust gas temperature. In graph L10, although there is some variation in the top exhaust gas temperature immediately after hydrogen gas injection, results are almost the same as those in graph L8.

[0022] Graphs L11 to L13 show the correlation between elapsed time and tuyere tip combustion temperature. In graphs L11 and L12, the furnace top exhaust gas temperature remains constant even when hydrogen gas is injected into the blast furnace. In graph L13, the tuyere tip combustion temperature fluctuates significantly before and after hydrogen gas injection. Specifically, the tuyere tip combustion temperature decreases significantly due to the injection of hydrogen gas.

[0023] Here, when the operations of graphs L1, L2, and L5 were performed, the results of graphs L8 and L11 were obtained. In other words, when transitioning from base operation to hydrogen gas injection operation, the tuyere tip combustion temperature and furnace top exhaust gas temperature can be maintained constant by adjusting at least the blast moisture, oxygen enrichment rate, and pulverized coal ratio. The specific adjustment amounts may vary depending on the base operating conditions, the amount of hydrogen gas injection, etc., but appropriate blast moisture, oxygen enrichment rate, and pulverized coal ratio can be identified by performing a simulation of blast furnace operation.

[0024] On the other hand, when the operations of graphs L1, L3, and L6 were performed, the results of graphs L9 and L12 were obtained. In other words, when switching from base operation to hydrogen gas injection operation, if only the oxygen enrichment rate was adjusted, the tuyere tip combustion temperature could be kept constant, but the furnace top temperature decreased. In this case, there is a possibility that the moisture adhering to the iron-based raw materials and coke cannot be sufficiently removed.

[0025] On the other hand, when the operations of graphs L1, L4, and L7 were performed, the results of graphs L10 and L13 were obtained. In other words, when switching from base operation to hydrogen gas injection operation, if only the oxygen enrichment rate was slightly adjusted, the furnace top exhaust gas temperature could be kept constant, but the tuyere combustion temperature decreased. In this case, the molten iron temperature may decrease.

[0026] From the above, it has become clear that when transitioning from base operation to hydrogen gas injection operation, the tuyere tip combustion temperature and furnace top exhaust gas temperature can be maintained constant by adjusting at least the blast moisture, oxygen enrichment rate, and pulverized coal ratio. Note that the specific adjustment amounts may vary depending on the base operating conditions, the amount of hydrogen gas injection, etc., but it is sufficient to perform a simulation of blast furnace operation and identify the appropriate blast moisture, oxygen enrichment rate, and pulverized coal ratio.

[0027] <2. Blast furnace operation method> Next, a method for operating a blast furnace according to this embodiment will be described. First, a base operation is performed using a blast furnace. That is, iron-based raw materials and coke are alternately and layeredly charged into the blast furnace from the top of the blast furnace, while hot air is blown into the blast furnace from tuyere holes at the bottom of the blast furnace. 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 in this case). That is, the hot air gasifies the coke and pulverized coal. The reducing gas rises within the blast furnace and reduces the iron-based raw materials while heating them. While descending within the blast furnace, the iron-based raw materials are heated and reduced by the reducing gas. The iron-based raw materials are then melted and dripped down the blast furnace while being further reduced by the coke. The iron-based raw materials are ultimately accumulated in the hearth as molten pig iron (pig iron) containing slightly less than 5% by mass of carbon. The molten iron in the hearth is taken out through a tap hole and is used in the next steelmaking process.

[0028] Meanwhile, a hydrogen-based reducing gas is prepared. Here, the hydrogen-based reducing gas is a concept that includes not only hydrogen gas but also a mixed gas of hydrogen gas and another gas (such as nitrogen gas) (which does not impair the effects of this embodiment).

[0029] Furthermore, a simulation of blast furnace operation is performed based on the above-mentioned specifications of the base operation and specifications related to hydrogen gas injection operation, such as the injection amount of hydrogen-based reducing gas, etc. At this time, the blast moisture, oxygen enrichment rate, and pulverized coal ratio are adjusted, and the blast moisture, oxygen enrichment rate, and pulverized coal ratio at which the tuyere combustion temperature and furnace top exhaust gas temperature become constant when transitioning from base operation to hydrogen gas injection operation are specified.

[0030] Next, the base operation is switched to hydrogen gas injection operation. At this time, the hydrogen gas-related parameters, such as the injection rate of hydrogen-based reducing gas, are set to the values ​​used in the blast furnace operation simulation. Furthermore, the blast moisture, oxygen enrichment rate, and pulverized coal ratio are adjusted to the values ​​specified by the blast furnace operation simulation. This allows the tuyere tip combustion temperature and furnace top exhaust gas temperature to be kept constant when switching from base operation to hydrogen gas injection operation.

[0031] Here, the tuyere through which the hydrogen-based reducing gas is injected is assumed to be a tuyere provided at the lower end of the blast furnace, a so-called normal tuyere, but a shaft tuyere may be provided in the shaft portion of the blast furnace, and the hydrogen-based reducing gas may be injected from this shaft tuyere.

[0032] In actual operation, even if the blast moisture, oxygen enrichment rate, and pulverized coal ratio are adjusted, the tuyere combustion temperature and the furnace top exhaust gas temperature may fluctuate slightly. Therefore, it is preferable to monitor the tuyere combustion temperature and the furnace top exhaust gas temperature from the time when the transition from base operation to hydrogen gas injection operation begins until a predetermined time has elapsed. The predetermined time is the time until the tuyere combustion temperature and the furnace top exhaust gas temperature become constant, and may be approximately 8 to 10 hours.

[0033] According to this operating method, when switching from base operation to hydrogen gas injection operation, the tuyere combustion temperature and top exhaust gas can be maintained constant, thereby enabling stable hydrogen gas injection operation. For example, the tapping temperature and tapping rate can be maintained constant. Furthermore, since the top exhaust gas can be maintained constant, moisture adhering to the iron-based raw materials and coke can be sufficiently removed.

[0034] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

Claims

1. A method for operating a blast furnace carried out when transitioning from base operation to hydrogen gas injection operation in which a hydrogen-based reducing gas is injected into the blast furnace, characterized in that the tuyere combustion temperature and the furnace top exhaust gas temperature are maintained constant by adjusting at least the blast moisture, the oxygen enrichment rate, and the pulverized coal ratio.

2. 2. The method for operating a blast furnace according to claim 1, wherein the tuyere combustion temperature and the furnace top exhaust gas temperature are monitored until a predetermined time has elapsed from the time when the transition from the base operation to the hydrogen gas injection operation is started.

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