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

[Technical Field]

[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. [Background technology]

[0002] The blast furnace method (a method of 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, because the blast furnace method consumes large amounts of coal as a reducing agent to melt and reduce the iron oxide in the iron ore, it also has the aspect of being a process that emits a lot of CO2. In light of the current social situation regarding environmental issues, reducing CO2 emissions from the blast furnace method is an urgent issue for the steel industry.

[0003] There are several ways to reduce CO2 emissions in the blast furnace process, one of which is to use hydrogen as a gas reducing agent.Methods that have been proposed for utilizing hydrogen include simply injecting hydrogen into the tuyere together with the blast air, injecting hydrogen into the tuyere as a specific compound (for example, a hydrocarbon such as methane), or injecting a hydrogen-based reducing gas from a location other than the tuyere.

[0004] Here, one of the main reasons why CO2 emissions from a blast furnace can be reduced by injecting a gas reducing agent such as hydrogen into the furnace is that the gas reduction rate of iron oxide in the agglomerated ore increases.

[0005] Agglomerates charged into a blast furnace are reduced in two main ways. The first is gas reduction using gaseous reducing agents such as CO or hydrogen. The second is smelting reduction using carbon (C) in coke, a solid reducing agent. In the blast furnace method, gas reduction progresses as the raw materials (agglomerates and solid reducing agents) 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 lies in the amount of heat generated by the reduction reaction. Gas reduction is a reduction reaction that generates a small amount of heat (or endotherm). In contrast, smelting reduction is a reduction reaction that generates a large amount of heat (endotherm). Increasing the proportion of gas reduction using a gas reducing agent (such as hydrogen gas) can reduce the proportion of smelting reduction using a solid reducing agent. 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 lowering CO2 emissions.

[0007] As described above, in the 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, 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 is known to stagnate when the reduction reaction reaches a predetermined state (reduction rate of 70%). Specifically, the presence of a structure within the agglomerated ore that inhibits gaseous reduction causes the gaseous reduction reaction to stagnate due to the influence of this structure. Furthermore, 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 structure of sintered ore with a high SiO2 content that is excellent in the reduction reaction at high temperatures while maintaining the strength of the sintered ore. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 3-77853 [Patent Document 2] Patent No. 7035869 [Non-patent literature]

[0010] [Non-Patent Document 1] Iron and Steel, Vol.79(1993)9, N618 [Non-patent document 2] Iron and Steel, Vol.79(1993)10, N711 [Non-patent document 3] Iron and Steel, Vol.73(1987)15, p.1956 [Non-patent document 4] Iron and Steel, Vol.69(1983)3, p.363 Summary of the Invention [Problem to be solved by the invention]

[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 the 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 mention the 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, and has an object to provide a blast furnace operation method that can reduce CO2 emissions. [Means for solving the problem]

[0013] The gist and configuration of the present invention to solve the above problems are as follows. [1] A blast furnace operating method in which agglomerated ore 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, wherein the supply amount of the gas reducing agent is 100 Nm 3 / t or more, and the FeO concentration of the agglomerate ore is 10 mass% or less. [2] The method for operating a blast furnace according to [1], wherein the FeO concentration of the agglomerates is set to 5 mass% or less. [Effects of the Invention]

[0014] According to the present invention, CO2 emissions can be reduced. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the charging state of a gas reducing agent and a solid reducing agent in blast furnace operation. [Figure 2] FIG. 2 is a diagram showing the relationship between the amount of gas reducing agent and the optimum gas reduction rate. [Figure 3] FIG. 3 is a graph showing the relationship between the FeO concentration of the agglomerates and the stagnant gas reduction rate. DETAILED DESCRIPTION OF THE INVENTION

[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 agent (coke, pulverized coal) charged from the top and the tuyere of the blast furnace and a gas reducing agent 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 the 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 molten iron / t was calculated based on a heat and mass 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 refers to the rate at which gas reduction 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 1Nm 3 of carbon monoxide and 2Nm 3 In this case, the total amount of gas reducing material is 3 Nm 3 The amount of 1Nm 3 The amount of gas reducing agent when methane is injected into a blast furnace is 3 Nm 3 and count it.

[0021] Also, for example, 1 Nm 3 When ammonia is injected into the blast furnace, the ammonia 3 of hydrogen and 0.5Nm 3Nitrogen does not function as a reducing agent, so it is 3 The amount of gas reducing agent when injecting ammonia 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 1300°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: thermal reserve zone temperature 1000°C, blast temperature 1100°C, blast moisture 20g / 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 agent when gas reducing agent (assuming 100% by volume of room temperature hydrogen) was injected. In this case, the maximum shaft efficiency was set to 0.95 [-: dimensionless number].

[0026] Figure 2 shows the gas reducing agent amount Nm 3 As shown in Figure 2, the relationship between the gas reducing agent and the optimum gas reduction rate is shown. 3 It can be seen that the optimum gas reduction rate exceeds 75% when the gas reducing agent amount exceeds 100 Nm 3It can be confirmed that when the gas reduction rate exceeds 800 Nm / t, the optimum gas reduction rate exceeds the state where the reduction reaction due to the gas reduction of the agglomerate ore stagnates (reduction rate of 70%). In addition, although the amount of CO2 reduction in blast furnace operation increases with an increase in the amount of gas reducing agent, taking into account the point at which no change in the amount of CO2 reduction is observed, the gas reducing agent amount is set to 800 Nm 3 / t or less, and 600 Nm 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 concentration 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 refers to 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 ferrous iron (Fe ions) analyzed by titration. 2+ ) and magnetite (Fe3O4 = Fe +2 O Fe +3 The concentration of the FeO portion in the FeO phase was evaluated.

[0029] The agglomerates were produced by mixing the 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 raw materials. Other adjustments include changing the oxygen concentration in the blast gas and changing the firing time.

[0030] Although the analytical results of the prepared agglomerates varied from sample to sample, the iron content (T.Fe) was in the range of 55-60 mass%, the open porosity was 5-15%, and the basicity (CaO concentration / SiO2 concentration) was in the range of 1.8-2.2%. The open porosity was measured using the mercury porosimetry method. All other measurements were made by chemical analysis. The iron content and basicity were measured by the 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: 10-15 mm, and gas reduction time: 2 hours. The composition of the gas reducing agent was 95% by volume of carbon monoxide (CO) and 5% by volume of carbon dioxide (CO2).

[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 based on "JIS M 8713:2021 Iron ore - Measurement method for reducibility," 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):

[0033]

number

[0034] Based on the reduction curves obtained in gas reduction experiments, it was revealed that the lower the FeO concentration of the agglomerated ore, the less likely the reduction reaction stagnation caused by 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 form from secondary hematite and magnetite phases. This is consistent with the experimental results that show that agglomerates with a lower FeO concentration, i.e., less magnetite, are less likely to experience stagnation in the reduction reaction.

[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 from the experiment, and it was considered 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 agglomerates and the stagnant gas reduction rate. As shown in Figure 3, the FeO concentration of the agglomerates 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 agglomerates, 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 agglomerates 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 of the agglomerates to 5% by mass or less.

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

[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 reducing agent 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 stagnant gas reduction rate at which the reduction reaction begins to stagnate can be increased by adjusting (reducing) the FeO concentration of the agglomerated ore. Furthermore, in a blast furnace process using a gas reducing agent, the usage rate of the gas reduction of the agglomerated ore is increased and the usage rate of the smelting reducing agent is reduced, thereby reducing CO2 emissions. [Example]

[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 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 with different injection rates into the blast furnace 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 gas reduction reaction. Regarding the reduction behavior after the stagnation of the gas reduction reaction, Non-Patent Document 4 was referred to, and calculation parameters were determined to be consistent with the experimental results, assuming that the reduction rate of the agglomerates is determined by the diffusion rate of oxygen ions in the metallic iron covering them.

[0045] The standard operation that serves as the basis for the CO2 reduction rate is hot air operation (air temperature 1100°C, oxygen concentration 21 mass%, air humidity 20 g / Nm 3 Two types of operation were confirmed: standard operation 1 (blast temperature 25°C, oxygen concentration 100 mass%, heat loss 100 Mcal / t, coke rate 487 kg / t), and standard operation 2 (oxygen blast operation) (blast temperature 25°C, oxygen concentration 100 mass%, heat loss 100 Mcal / t, coke rate 585 kg / t). The FeO concentration of the agglomerates in each standard operation was 10 mass%. The ratio of agglomerates to the main raw materials was 70%. The results of the examples are shown in Table 1.

[0046] [Table 1]

[0047] In Table 1, for the "stagnation gas reduction rate", a result of 72% or more was evaluated as "good (○)", and a result of 80% or more was evaluated as "even better (◎)". Note that for Comparative Examples 1 and 2, the CO2 reduction rate was 0%, so they were evaluated as "poor (×)".

[0048] As shown in Table 1, in Comparative Examples 1 and 2, the amount of gas reducing agent was 0 Nm 3 / t, and because the rate of gas reduction of the agglomerated ore could not be increased, the CO2 reduction rate was also 0%.

[0049] In contrast, in Examples 1 to 4, the FeO concentration of the agglomerated ore 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 was increased to 72%, thereby improving the CO2 reduction rate.

[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, which further improved the CO2 reduction rate.

Claims

1. A blast furnace operating method for producing molten iron by charging agglomerated ore, which is produced by mixing raw materials, granulating the mixed ore, and firing the mixed ore into the top of the blast furnace, and supplying a gas reducing agent into the lower part of the blast furnace, The supply amount of the gas reducing agent was 100 Nm ３ / t or more, and the FeO concentration of the agglomerate ore is 10 mass% or less.

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

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