Blast furnace operation method

Abstract

Provided is a blast furnace operation method that is capable of reducing CO2 emissions.　This blast furnace operation method comprises charging agglomerated ore from the top of a blast furnace and feeding gas-reducing material from the bottom part of the blast furnace to produce a hot metal. The amount of the gas-reducing material that is fed is set to 100 Nm3 / t or greater and the FeO concentration of this agglomerated ore is set to 10% or less.

Description

Blast furnace operation method

[0001] The present invention relates to a method for operating a blast furnace in which agglomerated ore as an iron raw material is charged from the top of the blast furnace and a gas reducing agent is supplied from the lower part of the blast furnace to produce molten iron.

[0002] The blast furnace method (a method for producing molten iron using a blast furnace) is a highly efficient steelmaking process suitable for mass production, accounting for more than 70% of crude steel production in Japan. However, the blast furnace method consumes a large amount of coal as a reducing agent to melt and reduce iron oxide in iron ore, which results in CO ２ It also has the aspect of being a high-emission process. In light of the current social situation regarding environmental issues, the CO ２ Reducing emissions is an urgent issue for the steel industry.

[0003] CO in the blast furnace process ２ There are several possible methods for reducing emissions, one of which is to use hydrogen as a gas reducing agent. Proposed methods for utilizing hydrogen include simply injecting hydrogen into the tuyere together with the air blast, injecting hydrogen into the tuyere as a specific compound (e.g., a hydrocarbon such as methane), or injecting a hydrogen-based reducing gas from a location other than the tuyere.

[0004] Here, by injecting a gas reducing agent such as hydrogen into the blast furnace, the CO ２ One of the main reasons for the reduction in emissions is the increase in the gas reduction rate of iron oxide in the agglomerates.

[0005] The agglomerates charged into a blast furnace are reduced by two main methods. The first is gas reduction using gas reducing agents such as CO and hydrogen. The second is smelting reduction using carbon (C) in coke, which is a solid reducing agent. In the blast furnace method, gas reduction progresses as the raw materials (agglomerates and solid reducing agent) descend from the top to the bottom of the blast furnace. After that, the agglomerates that were not reduced by gas reduction melt and are melted and reduced by the solid reducing agent, completing the reduction reaction.

[0006] The difference between gas reduction and smelting reduction is the amount of heat generated by the reduction reaction. Gas reduction is a reduction reaction that generates a small amount of heat (or heat absorption). In contrast, smelting reduction is a reduction reaction that generates a large amount of heat. Increasing the proportion of gas reduction by injecting a gas reducing agent (hydrogen gas, etc.) can reduce the proportion of smelting reduction by solid reducing agents. This makes it possible to reduce the amount of heat required per ton of molten iron in a blast furnace, reducing the amount of solid reducing agent (carbon) used, and reducing CO ２ Emissions can be reduced.

[0007] As described above, in a blast furnace process in which a gaseous reducing agent (such as hydrogen gas) is injected, improving the rate of gaseous reduction of agglomerated ore is essential to reducing the amount of solid reducing agent (carbon). However, it is known that even when gaseous reduction of agglomerated ore (pellets or sintered ore) using a gaseous reducing agent is carried out at a temperature (e.g., 900°C) at which the agglomerated ore does not begin to melt, the reduction reaction based on the gaseous reduction stagnates when the reduction reaction reaches a predetermined state (reduction rate of 70%). Specifically, the agglomerated ore contains a structure that hinders gaseous reduction, and the gaseous reduction reaction stagnates due to the influence of this structure. Furthermore, the stagnation of the reduction reaction refers to a sudden decrease in the rate of change of the reduction rate per hour (reduction rate).

[0008] For this reason, methods have been proposed for improving the rate of gas reduction in agglomerates by adjusting the properties of the agglomerates. Patent Document 1 discloses a method for suppressing stagnation of the reduction reaction at high temperatures by adding dolomite or limestone to pellets to increase the melting point of the pellets. Patent Document 2 discloses a method for suppressing stagnation of the reduction reaction at high temperatures by adding SiO ２ This publication discloses a sintered ore structure that is excellent in reduction reaction at high temperatures while maintaining the strength of the sintered ore, with the sintered ore having a high content of Cr being the target.

[0009] Japanese Patent Publication No. 3-77853 Patent No. 7035869

[0010] Iron and Steel, Vol. 79 (1993) 9, N618 Iron and Steel, Vol. 79 (1993) 10, N711 Iron and Steel, Vol. 73 (1987) 15, p. 1956 Iron and Steel, Vol. 69 (1983) 3, p. 363

[0011] However, the method disclosed in Patent Document 1 is suitable for suppressing stagnation of the reduction reaction when the agglomerates are in a high-temperature state, but is difficult to apply to stagnation of the reduction reaction at a temperature state where the agglomerates do not start to melt. Furthermore, Patent Document 2 sets the target reduction rate at a high temperature state at 71%, which is similar to the reduction rate (70%) at which stagnation of the reduction reaction due to gas reduction is observed. Therefore, Patent Document 2 does not take into consideration the stagnation of the reduction reaction due to gas reduction. Furthermore, although the method disclosed in Patent Document 2 can produce sintered ore with excellent reduction reaction properties, it does not describe stagnation of the reduction reaction related to temperature conditions, making it difficult to apply to stagnation of the reduction reaction at a temperature state where the agglomerates do not start to melt.

[0012] The present invention has been made in view of the above circumstances, ２ The object of the present invention is to provide a blast furnace operation method that can reduce emissions.

[0013] The gist of the present invention for solving the above problems is as follows: [1] A blast furnace operating method for producing molten iron by charging agglomerated ore from the top of the blast furnace and supplying a gas reducing agent from the lower part of the blast furnace, wherein the supply amount of the gas reducing agent is 100 Nm ３ [2] The method for operating a blast furnace according to [1], wherein the FeO concentration of the agglomerates is 5% by mass or less while the FeO concentration of the agglomerates is 10% by mass or less.

[0014] According to the present invention, CO ２ It can reduce emissions.

[0015] Fig. 1 is a diagram showing the charging state of gas reducing agents and solid reducing agents in blast furnace operation. Fig. 2 is a diagram showing the relationship between the amount of gas reducing agent and the optimum gas reduction rate. Fig. 3 is a diagram showing the relationship between the FeO concentration of agglomerates and the stagnant gas reduction rate.

[0016] Hereinafter, the present invention will be described through embodiments of the present invention.

[0017] As shown in FIG. 1 , the present invention relates to a blast furnace operation method in which a reduction reaction of agglomerated ore and lump ore (hereinafter referred to as “agglomerated ore”), which are iron raw materials, is carried out in the furnace using a solid reducing material (coke, pulverized coal) charged from the top and tuyere of the blast furnace and a gas reducing material charged from the lower part of the furnace, and molten iron is obtained from a tap hole located in the lower part of the blast furnace.

[0018] The present inventors first focused on the relationship between the amount of gas reducing agent (hereinafter referred to as "gas reducing agent amount") injected into a blast furnace and the gas reduction rate. In particular, they focused on the relationship between the amount of gas reducing agent and the gas reduction rate when the total amount of the solid reducing agent (hereinafter referred to as "solid reducing agent amount") and the gas reducing agent amount is minimized (hereinafter referred to as "optimum gas reduction rate"). Then, the amount of gas reducing agent Nm ３ The optimum gas reduction rate % for slag / t was calculated based on a heat and material balance calculation for a blast furnace, taking into consideration the reduction equilibrium of wüstite with carbon monoxide (CO) and hydrogen gas (see Non-Patent Documents 1 and 2). Here, the optimum gas reduction rate refers to a value calculated each time based on the amount of each reducing agent (amount of solid reducing agent and amount of gas reducing agent) used, as a value for minimizing the total amount of reducing agent (total amount of solid reducing agent and amount of gas reducing agent) from the viewpoint of the function of heat supply and reducing agents in the furnace.

[0019] Here, the gas reduction rate means the proportion of gas reduction that occurs among all reduction reactions (gas reduction and smelting reduction) of the agglomerate ore charged into the blast furnace. The gas reducing agent may include not only gases that function as gas reducing agents themselves, such as hydrogen and carbon monoxide (CO), but also gases that function as gas reducing agents via oxidation reactions or thermal decomposition reactions in the blast furnace, such as methane and ammonia.

[0020] The amount of gas reducing agent is, for example, 1 Nm ３ When methane is blown into the blast furnace, it reacts with the oxygen in the blast, resulting in a reaction of 1 Nm ３ of carbon monoxide and 2Nm ３ In this case, the total amount of gas reducing material is 3 Nm ３ Since the amount of ３ When methane is injected into a blast furnace, the amount of gas reducing agent is 3 Nm３ and count it.

[0021] Also, for example, 1 Nm ３ When ammonia is injected into the blast furnace, the ammonia ３ of hydrogen and 0.5 Nm ３ Nitrogen does not function as a reducing agent, so ３ The amount of gas reducing agent when ammonia is injected into a blast furnace is 1.5 Nm ３ and count it.

[0022] Similarly, when the gaseous reducing agent contains impurities such as nitrogen, the amount of the gaseous reducing agent is counted based on the amount of the gaseous reducing agent generated in the blast furnace. Therefore, the gaseous reducing agent may be a mixture of multiple types of gases.

[0023] The temperature of the gas reducing agent is preferably 1,300°C or less, which is the hot air temperature in a blast furnace, and is more preferably 500°C or less, and even more preferably 100°C or less, in order to increase the optimum gas reduction rate above the state where stagnation of the reduction reaction occurs due to gas reduction (reduction rate of 70%).

[0024] Furthermore, the concentration of the gaseous reducing agent that actually contributes to gaseous reduction among the gaseous reducing agents injected into the blast furnace is preferably 90% by volume or more, and more preferably 95% by volume or more.

[0025] The optimum gas reduction rate for the amount of gas reducing material was calculated using the following conditions: the thermal reserve zone temperature was 1000°C, the blast temperature was 1100°C, and the blast moisture content was 20 g / Nm ３ In a blast furnace with a heat loss of 100 Mcal / t, the gas reduction ratio was calculated to minimize the amount of solid reducing material when a gas reducing material (assuming 100% by volume of room temperature hydrogen) was blown in. In this case, the shaft efficiency was set to a maximum value of 0.95 [-: dimensionless number].

[0026] FIG. 2 shows the gas reducing agent amount Nm ３ 2 shows the relationship between the gas reducing agent amount and the optimum gas reduction rate (%). ３ It can be seen that the optimum gas reduction rate exceeds 75% when the amount of gas reducing agent exceeds 100 Nm / t.３ It can be confirmed that when the amount of gas reducing agent exceeds 70%, the optimum gas reduction rate exceeds the state where the reduction reaction of the agglomerate ore stagnates (reduction rate of 70%). ２ Although the reduction amount also increases, CO ２ Considering the point at which no change in the reduction amount is observed, the amount of gas reducing agent is set to 800 Nm ３ / t or less, and ３ It is more preferable that the ratio is 1 / t or less.

[0027] Next, the present inventors prepared various agglomerates and closely observed the changes in the reduction reaction of the prepared agglomerates during gas reduction, thereby clarifying the state of the texture in the agglomerates that causes the stagnation of the reduction reaction, and also investigated a method for adjusting the agglomerates that can suppress the stagnation of the reduction reaction.

[0028] Specifically, agglomerates with adjusted FeO concentrations were prepared, and gas reduction was carried out using a gas reducing agent with a fixed composition at a fixed temperature, and the change in mass during gas reduction was detected. Here, the FeO concentration means the value of FeO measured by chemical analysis, and more precisely, ２＋ The FeO concentration calculated from the concentration of ions is the FeO concentration calculated from the concentration of ions. The FeO concentration calculated from chemical analysis is the FeO concentration calculated from the concentration of ferrous iron (Fe ２＋ ) oxides by weight percent, and magnetite (Fe ３ O ４ =Fe ＋２ O.Fe ＋３ ２ O ３ The concentration of the FeO portion in the SiO2 solution was evaluated.

[0029] The agglomerates were produced by mixing the blended raw materials, granulating them, and firing them in a pot test. The FeO concentration in the agglomerates was adjusted by adjusting the amount of coking agent (coke breeze) in the blended raw materials. Other adjustments include changing the oxygen concentration in the blast gas and changing the firing time.

[0030] The analysis results of the prepared agglomerates showed that, although there was some variation between samples, the iron content (T.Fe) was 55 to 60 mass%, the open porosity was 5 to 15%, and the basicity (CaO concentration / SiO ２ The concentration of porosity (sintered body) was in the range of 1.8-2.2%. The open porosity was measured by mercury porosimetry. The rest were measured by chemical analysis. The iron content and basicity were measured by titration method.

[0031] The gas reduction conditions using the gas reducing agent were as follows: reduction temperature: 900°C, gas reducing agent flow rate: 10 L / min, agglomerate mass: 150 g, agglomerate particle size: 10 to 15 mm, and gas reduction time: 2 hours. The gas reducing agent had a composition of 95% by volume of carbon monoxide (CO), 10% by volume of carbon dioxide (CO ２ ) was 5% by volume.

[0032] Based on the time-series changes in the mass of the agglomerates detected during the experiment, the time-series changes in the gas reduction rate R during the experiment were calculated. Specifically, the gas reduction rate R was calculated by expressing the proportion of oxygen removed from iron oxide (agglomerates) as a mass fraction % and converting the change in mass into the reduction rate R using the following formula (1) based on "JIS M 8713:2021 Iron ore - Measurement method for reducibility."

[0033]

[0034] Based on the reduction curves obtained in the gas reduction experiments, it was revealed that the lower the FeO concentration of the agglomerated ore, the less likely the reduction reaction stagnation due to gas reduction occurs, and the higher the final reduction rate after gas reduction is carried out. Here, the reduction curve refers to a curve on a graph showing the time-series change in the gas reduction rate R, with the horizontal axis representing time and the vertical axis representing the gas reduction rate R.

[0035] Observation of agglomerates during gas reduction experiments revealed that the cause of the stagnation of the reduction reaction during gas reduction in agglomerates is the formation of iron oxide surrounded by dense metallic iron within the agglomerate structure. Furthermore, since the iron oxide surrounded by dense metallic iron is prevented from contacting the gas reducing agent, the rate of the reduction reaction is thought to be limited by the diffusion rate of oxygen ions within the agglomerates, slowing down the rate of the reduction reaction.

[0036] Furthermore, observations of the agglomerates before and after gas reduction revealed that iron oxide surrounded by dense metallic iron is likely to be generated from secondary hematite phases or magnetite phases. This is consistent with the experimental results that show that the lower the FeO concentration, i.e., the less magnetite there is in the agglomerates, the less likely the reduction reaction to stagnate.

[0037] Next, the reduction curve obtained in the gas reduction experiment was analyzed using a reduction model that does not consider stagnation of the reduction reaction (unreacted nucleus model: see Non-Patent Document 3), to calculate the gas reduction rate at which the reduction reaction begins to stagnate (hereinafter referred to as the "stagnation gas reduction rate"). That is, fitting of the reduction model was performed using the reduction curve obtained as the experimental result, and it was deemed that the reduction began to stagnate at the reduction rate at which the reduction curve and the value of the reduction model began to diverge.

[0038] Figure 3 shows the relationship between the FeO concentration of the agglomerate and the stagnant gas reduction rate. As shown in Figure 3, the FeO concentration of the agglomerate and the stagnant gas reduction rate are inversely proportional to each other. That is, it can be seen that the lower the FeO concentration of the agglomerate, the higher the stagnant gas reduction rate. Specifically, when adjusting the stagnant gas reduction rate to exceed 70%, it is preferable to set the FeO concentration of the agglomerate to 10% by mass or less. Furthermore, when adjusting the stagnant gas reduction rate to exceed 80%, it is more preferable to set the FeO concentration in the agglomerate to 5% by mass or less.

[0039] Although the gas reduction experiment of the agglomerates described in this embodiment was carried out under the conditions described above, it is not necessary to limit the conditions to these. That is, other reduction test methods (e.g., "JIS M 8713:2021 Iron Ore - Measurement Method of Reducibility") may be used. Then, the relationship between the FeO concentration of the agglomerates and the stagnant gas reduction rate may be calculated to find the FeO concentration that can suppress stagnation of the reduction reaction in the gas reduction.

[0040] Based on the experimental results shown in Fig. 3, the FeO concentration of the agglomerates charged into the blast furnace may be adjusted to increase the stagnation gas reduction rate of the gas reduction in the blast furnace. That is, in a blast furnace operation method in which agglomerates are charged from the top of the blast furnace and a gas reducing agent is supplied from the lower part of the blast furnace to produce molten pig iron, the FeO concentration of the agglomerates may be adjusted to increase the stagnation gas reduction rate of the gas reduction in the blast furnace. ３ / t or more, and the FeO concentration of the agglomerate ore may be adjusted to 10 mass % or less.

[0041] As described above, according to the blast furnace operation method of this embodiment, the stagnation gas reduction rate at which the reduction reaction begins to stagnate can be increased by adjusting (reducing) the FeO concentration of the agglomerated ore. In the blast furnace method using a gas reducing agent, the use rate of the gas reduction of the agglomerated ore is increased and the use rate of the smelting reducing agent is reduced, thereby reducing the CO ２ Emissions can be reduced.

[0042] Hereinafter, examples carried out based on the blast furnace operation method according to this embodiment will be described.

[0043] In the examples, a virtual physical blast furnace implemented in cyberspace was used to confirm the change in coke ratio when a room-temperature gas reducing agent (hydrogen gas) was injected from the bottom of the shaft. Here, the coke ratio refers to the amount of coke charged from the top of the blast furnace to produce 1 ton of molten pig iron. Furthermore, the change in coke ratio when agglomerated ores with different FeO concentrations were used for the gas reducing agent whose injection rate into the blast furnace was changed was also confirmed.

[0044] The reduction reaction of the agglomerates was modeled assuming that the FeO concentration of the agglomerates only affects the stagnation of the reduction reaction of gas reduction. Regarding the reduction behavior after the stagnation of the reduction reaction of gas reduction, Non-Patent Document 4 was referenced, and calculation parameters were determined to be consistent with the experimental results on the assumption that the reduction rate of the agglomerates is determined by the diffusion rate of oxygen ions in the metallic iron covering them.

[0045] CO ２ The standard operation used as the basis for the reduction rate was hot air operation as standard operation 1 (air temperature 1100°C, oxygen concentration 21 mass%, air moisture 20 g / Nm ３Two types of operation were confirmed: a standard operation (blast temperature of 25°C, oxygen concentration of 100 mass%, heat loss of 100 Mcal / t, coke rate of 487 kg / t) and a standard operation 2 (blast temperature of 25°C, oxygen concentration of 100 mass%, heat loss of 100 Mcal / t, coke rate of 585 kg / t). The FeO concentration of the agglomerates in each standard operation was 10 mass%. The ratio of the agglomerates to the main raw materials was 70%. The results of the examples are shown in Table 1.

[0046]

[0047] In Table 1, the "stagnation gas reduction rate" was evaluated as "good (○)" when the result was 72% or more, and as "even better (◎)" when the result was 80% or more. ２ Since the reduction rate was 0%, it was evaluated as "poor (x)."

[0048] As shown in Table 1, in Comparative Examples 1 and 2, the amount of gas reducing agent was 0 Nm ３ / t, and the rate of gas reduction of the agglomerated ore could not be increased. ２ The reduction rate was also 0%.

[0049] In contrast, in Examples 1 to 4, the FeO concentration of the agglomerate was 10 mass % and the amount of gas reducing agent was 200 Nm ３ / t or more, the stagnation gas reduction rate of the gas reduction in the agglomerated ore could be increased to 72%. ２ The reduction rate could be improved.

[0050] Furthermore, in Examples 5 to 10, the FeO concentration of the agglomerated ore was set to 5 mass% or less, and the amount of gas reducing agent was set to 200 Nm ３ / t or more, the stagnation gas reduction rate of the gas reduction in the agglomerated ore could be increased to 80% or more. ２ The reduction rate could be further improved.

Claims

1. A blast furnace operation method for producing molten iron by charging agglomerated ore from the top of a blast furnace and supplying a gas reducing agent from the lower part of the blast furnace, wherein the supply amount of the gas reducing agent is 100 Nm ３ / t or more, and the FeO concentration of the agglomerate is 10 mass% or less.

2. The method for operating a blast furnace according to claim 1, wherein the FeO concentration of the agglomerate is 5 mass% or less.

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