Method for measuring gas reduction rate, method for operating blast furnace, method for operating direct reduction shaft furnace, and iron raw material

Abstract

Provided are: a method for measuring a gas reduction rate, with which it is a possible to properly measure a gas reduction rate, including influence of the stagnation of a reduction reaction, of an iron raw material for use in an iron production process; a method for operating a blast furnace; a method for operating a direct reduction shaft furnace; and an iron raw material.　The method for measuring a gas reduction rate is for measuring a gas reduction rate of an iron raw material to be used in an iron production process by a gas reducing material. The measurement time t (min) for measuring the gas reduction rate of the iron raw material is set to a time that is equal to or more than 0.9 time a tret value calculated in accordance with formula (1).　(1): tret = 5×d / (XCO-2×XCO2+2×XH2-4×XH2O)×exp(6000 / T) In the formula, T represents a reduction temperature K, d represents an average particle diameter mm of the iron raw material, XCO represents a CO concentration % of the gas reducing material, XCO2 represents a CO2 concentration % in the gas reducing material, XH2 represents a H2 concentration % in the gas reducing material, and XH2O represents a H2O concentration % in the gas reducing material.

Description

Gas reduction rate measurement method, blast furnace operation method, direct reduction shaft furnace operation method, and iron raw materials

[0001] The present invention relates to a method for measuring the gas reduction rate of iron raw materials used in an iron-making process using a blast furnace, a direct reduction shaft furnace, or the like, a method for operating a blast furnace, a method for operating a direct reduction shaft furnace, and the iron raw materials.

[0002] The blast furnace method (a method for producing molten iron using a blast furnace) accounts 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 CO emissions through reductions and conversion to processes other than the blast furnace method ２ Reducing emissions is an urgent issue for the steel industry.

[0003] CO in the blast furnace process ２ There are several ways to reduce emissions, one of which is to use hydrogen as a gas reducing agent. Proposed methods for utilizing hydrogen include simply blowing hydrogen into the tuyere together with the airflow, blowing hydrogen into the tuyere as a specific compound (e.g., a hydrocarbon such as methane), and blowing hydrogen-based reducing gas into the tuyere 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 reasons for the reduction in emissions is the increase in the gas reduction rate of iron oxide in the iron raw material.

[0005] Iron raw materials charged into a blast furnace are reduced mainly by two 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 (iron raw materials and solid reducing agent) descend from the top to the bottom of the blast furnace. After that, the iron raw materials that were not reduced by gas reduction melt and are melt-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] Another option for converting to ironmaking processes other than the blast furnace method is the direct reduction method (a method of producing reduced iron using a direct reduction shaft furnace). Unlike the blast furnace method, the direct reduction method produces reduced iron rather than molten pig iron, but like the blast furnace method, it is an ironmaking process that can produce iron from iron raw materials.

[0008] In the direct reduction method, coke is not required, and the iron raw material is reduced by a preheated gas reducing agent. By using hydrogen as the gas reducing agent, in principle, CO ２ It is possible to create a steelmaking process that does not emit CO2.

[0009] In the direct reduction process, the reduction reaction of the iron raw material proceeds solely through gas reduction. The resulting reduced iron is then melted and refined in a downstream process such as an electric furnace. If the reduction rate (final reduction rate) of the reduced iron is low (iron oxide remains), problems such as a decrease in the yield of molten steel and damage to refractories can occur. The reduction rate of the reduced iron that is required is approximately 80% to 90%.

[0010] In the direct reduction process, the gas reduction rate of iron raw materials can be improved by reducing the passage speed of the iron raw materials through the direct reduction shaft furnace and extending the reduction time. However, reducing the passage speed through the furnace leads to a decrease in production volume.

[0011] As described above, in the blast furnace process and direct reduction process in which a gaseous reducing agent (such as hydrogen gas) is injected, it is important to improve the rate of gaseous reduction of the iron raw material. However, it is known that even when gaseous reduction of agglomerates (pellets or sintered ore) as iron raw material is carried out using a gaseous reducing agent at a temperature (e.g., 900°C) at which the agglomerates do 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 agglomerates contain structures that hinder gaseous reduction, and the influence of these structures causes the gaseous reduction reaction to stagnate. 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).

[0012] Furthermore, a method based on "Iron ore - reducibility test (JIS M 8713:2009)" is known as a method for measuring the gas reduction rate of iron raw materials. However, the evaluation of the reducibility of iron raw materials by this method involves testing a sample with an average particle size of 20 mm with 30% carbon monoxide (CO) gas and 10% nitrogen (N ２ This method involves carrying out a reduction reaction for 180 minutes under conditions of 70% saturation gas and a temperature of 900°C (1173K), and then evaluating the gas reduction rate. The average evaluation value (reduction rate) under these conditions is around 60% because the measurement time is short, and it is not possible to evaluate the gas reduction rate (70% or higher) at which the reduction reaction stagnates.

[0013] Although many methods for improving the gas reduction rate of iron raw materials have been proposed, there have been almost no studies on methods for avoiding stagnation of the reduction reaction or methods for measuring an appropriate gas reduction rate. Patent Document 1 discloses a method for suppressing stagnation of the reduction reaction at high temperatures by adding dolomite or limestone to pellets to raise 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.

[0014] Japanese Patent Publication No. 3-77853 Patent No. 7035869

[0015] 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

[0016] However, the method disclosed in Patent Document 1 is suitable for suppressing stagnation of the reduction reaction when the iron raw materials are in a high-temperature state, but is difficult to apply to stagnation of the reduction reaction at a temperature state where the iron raw materials do not start to melt. Furthermore, while the method disclosed in Patent Document 2 can produce sintered ore with excellent reduction reaction properties, it does not disclose any mention of 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 iron raw materials 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 based on gas reduction is observed. Therefore, Patent Document 2 cannot be said to take into consideration the stagnation of the reduction reaction based on gas reduction.

[0017] The present invention has been made in view of the above circumstances, and aims to provide a gas reduction rate measurement method, a blast furnace operation method, a direct reduction shaft furnace operation method, and iron raw materials, which are capable of properly measuring the gas reduction rate, including the influence of stagnation of the reduction reaction, for iron raw materials used in the iron-making process.

[0018] The present invention provides a method for measuring a gas reduction rate of an iron raw material used in an iron-making process by a gas reducing agent, the method comprising the steps of: determining a measurement time t (min) for measuring the gas reduction rate of the iron raw material by a gas reducing agent; ｒｅｔ × 0.9 or more. ｒｅｔ = 5 × d / (X ＣＯ -2 x X ＣＯ２ +2 x X Ｈ２ -4 x X Ｈ２Ｏ ) × exp(6000 / T) (1) where T is the reduction temperature (K), d is the average particle size (mm) of the iron raw material, and X ＣＯ is the CO concentration % of the gaseous reducing agent, X ＣＯ２ is the CO of the gas reducing agent ２ Concentration%, XＨ２ is the H of the gas reducing agent ２ Concentration%, X Ｈ２Ｏ is the H of the gas reducing agent ２ [2] The measurement time t (min) is the time t ｒｅｔ [3] The gas reduction rate measuring method according to [1], wherein the CO concentration and the H concentration in the gas reducing agent are equal to or less than 1.3. ２ [4] The gas reduction rate measurement method according to [1] or [2], wherein the total concentration of the iron raw material and the concentration of the iron raw material is 30 mass % or more and 100 mass % or less. [4] The gas reduction rate measurement method according to [1] or [2], wherein the average particle size of the iron raw material is 9 mm or more and 21 mm or less. [5] The gas reduction rate measurement method according to [1] or [2], wherein the reduction temperature is 1073 K or more and 1273 K or less. [6] The gas reduction rate measurement method according to [1] or [2], wherein the iron raw material having the measured gas reduction rate of 95% or more is charged into a blast furnace, and 100 Nm of gas reducing agent is added to the blast furnace. ３ [7] A method for operating a direct reduction shaft furnace, comprising measuring a gas reduction rate using the gas reduction rate measurement method according to [1] or [2], charging iron raw materials having the measured gas reduction rate of 95% or more into a direct reduction shaft furnace, and producing reduced iron. [8] A method for operating a direct reduction shaft furnace, comprising measuring a gas reduction rate using the gas reduction rate measurement method according to [1] or [2], charging iron raw materials having the measured gas reduction rate of 95% or more into a direct reduction shaft furnace, and producing reduced iron. [9] A method for operating a direct reduction shaft furnace, comprising measuring a gas reduction rate using the gas reduction rate measurement method according to [1] or [2], charging iron raw materials having the measured gas reduction rate of 95% or more into a direct reduction shaft furnace, ｒｅｔ x 0.9 or more, and the measured gas reduction rate is 95% or more. ｒｅｔ = 5 × d / (X ＣＯ -2 x X ＣＯ２ +2 x X Ｈ２ -4 x X Ｈ２Ｏ ) × exp(6000 / T) (1) where T is the reduction temperature (K), d is the average particle size (mm) of the iron raw material, and X ＣＯ is the CO concentration % of the gaseous reducing agent, X ＣＯ２ is the CO of the gas reducing agent ２ Concentration%, X Ｈ２ is the H of the gas reducing agent ２ Concentration%, X Ｈ２Ｏis the H of the gas reducing agent ２ O concentration %.

[0019] According to the present invention, it is possible to properly measure the gas reduction rate, including the influence of stagnation of the reduction reaction, of an iron raw material used in an iron-making process.

[0020] Fig. 1 is a diagram showing the charging state of gas reducing material and solid reducing material in a blast furnace. Fig. 2 is a diagram showing the relationship between the amount of gas reducing material and the optimum gas reduction rate. Fig. 3 is a diagram showing the test results of gas reduction of a sample (agglomerate ore) under test condition A. Fig. 4 is a diagram showing the test results of gas reduction of a sample (agglomerate ore) under test condition B. Fig. 5 is a diagram showing the results of gas reduction tests on a sample (agglomerate ore 1) under different test conditions.

[0021] Hereinafter, the present invention will be described through embodiments of the present invention.

[0022] The present invention relates to a reduction reaction of iron raw materials including agglomerated ores, lump ores, etc. (hereinafter referred to as "iron raw materials") by a gas reducing agent injected into a furnace in an iron-making process, for example as shown in FIG. 1, and particularly to a method for measuring the gas reduction rate of iron raw materials.

[0023] The present inventors first focused on the relationship between the amount of gaseous reducing agent injected (hereinafter referred to as "amount of gaseous reducing agent") and the gaseous reduction rate. In particular, they focused on the relationship between the amount of gaseous reducing agent and the gaseous reduction rate when the total amount of the solid reducing agent used (hereinafter referred to as "amount of solid reducing agent") and the gaseous reducing agent amount is minimized (hereinafter referred to as "optimum gaseous reduction rate"). Then, the amount of gaseous reducing agent Nm ３ The optimum gas reduction rate % for molten iron / t was calculated based on a heat and mass balance calculation that takes into account 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 gaseous reducing agent) used, as a value for minimizing the total amount of reducing agents (total amount of solid reducing agent and amount of gaseous reducing agent) from the viewpoint of the heat supply in the furnace and the function of the reducing agents.

[0024] Here, the gas reduction rate refers to the proportion of gaseous reduction reactions that occur in the reduction reaction of the iron raw material relative to all reduction reactions. The gaseous reducing agent may include not only gases that function as gaseous reducing agents themselves, such as hydrogen and carbon monoxide (CO), but also gases that function as gaseous reducing agents via oxidation reactions or thermal decomposition reactions, such as methane and ammonia.

[0025] The amount of gas reducing agent is, for example, 1 Nm ３ When methane is blown into the furnace, it reacts with the oxygen in the air, 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 blown into the furnace, the amount of gas reducing agent is 3 Nm ３ and count it.

[0026] Also, for example, 1 Nm ３ When ammonia was blown into the 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 blown into the furnace is 1.5 Nm ３ and count it.

[0027] 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 furnace. Therefore, the gaseous reducing agent may be a mixture of multiple types of gases.

[0028] The temperature of the gas reducing agent is preferably 1,300°C or less, which is the hot air temperature in the 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%).

[0029] Furthermore, the concentration of the gaseous reducing agent that actually contributes to gaseous reduction among the gaseous reducing agents injected into the furnace is preferably 90% by volume or more, and more preferably 95% by volume or more.

[0030] 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 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 material when a gas reducing material (assuming 100% room temperature hydrogen) was blown in. In this case, the shaft efficiency was set to a maximum value of 0.95 [-: dimensionless number].

[0031] 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 stagnates due to the gas reduction of the iron raw material (reduction rate 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.

[0032] In the direct reduction method, the gas reduction rate of the reduced iron product must be 80% to 90%, as described above. Therefore, if the reduction reaction stagnates when the gas reduction rate reaches 70% during the gas reduction of the iron raw material, this will lead to a deterioration in product quality or a decrease in productivity.

[0033] Next, the present inventors prepared various agglomerates as iron raw materials and performed reduction reaction tests on the prepared iron raw materials (agglomerates) under various conditions, thereby investigating an appropriate method for measuring the gas reduction rate in the gas reduction of iron raw materials.

[0034] Specifically, the chemical composition was adjusted by changing the agglomerate ore blend, and the firing time and oxygen concentration of the blast gas were also changed to produce the agglomerates. The agglomerates were produced by mixing the blended raw materials, granulating them, and firing them in a pot test. The agglomerates were also classified by particle size and subjected to reduction tests.

[0035] Then, after heating the prepared iron raw material (agglomerate), a gaseous reducing agent was passed through the raw material while maintaining the temperature at a constant level, and the change in mass was measured to obtain a reduction degree curve based on the change in mass. In this case, the reduction temperature, the composition of the gaseous reducing agent, and the sample particle size were changed, and the change in mass of each agglomerate was measured. Furthermore, tests were also conducted under different test conditions for the same sample (agglomerate).

[0036] Regarding the test conditions for gas reduction using a gas reducing agent, the reduction temperature was changed in the range of 1073 to 1173 K, and the average particle size of the sample (agglomerate ore) was changed in the range of 10 to 20 mm. Here, the average particle size means the harmonic mean diameter. Regarding the composition of the gas reducing agent, the carbon monoxide (CO) was changed in the range of 0 to 95 mass%, and the carbon dioxide (CO ２ ) was changed in the range of 0 to 5 mass%, and hydrogen (H ２ ) was changed in the range of 0 to 100 mass%, and nitrogen (N ２ ) was changed in the range of 0 to 70 mass %.

[0037] Other test conditions for gas reduction using a gas reducing agent included a reduction time of up to 5 hours (300 minutes), a flow rate of the gas reducing agent of 15 L / min, and an initial mass of the sample (agglomerated ore) of 150 g.

[0038] Based on the time-series changes in the mass of the iron raw material (agglomerate) detected during the test, the time-series changes in the gas reduction ratio R during the test were calculated. Specifically, the gas reduction ratio R was calculated by expressing the proportion of oxygen removed from the iron raw material (agglomerate) in mass fraction % and converting the change in mass into the gas reduction ratio R using the following formula (2) based on "JIS M 8713:2021 Iron ore - Measurement method for reducibility."

[0039]

[0040] Here, the reduction rate curve obtained in the gas reduction test 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 "stagnant gas reduction rate"). Specifically, the reduction rate curve obtained as the test result was used to perform fitting of the reduction model, and it was deemed that the reduction reaction began to stagnate at the gas reduction rate at which the value of the reduction rate curve and the value of the reduction model began to diverge.

[0041] Then, based on the time when the gas reduction rate (stagnation gas reduction rate) at which it can be determined that the reduction reaction has started to stagnate is reached, the time at which the influence of the stagnation of the reduction reaction can be evaluated is determined as the time t at which the stagnation of the reduction reaction can be confirmed. ｒｅｔ (min).

[0042] The time t at which the stagnation of the reduction reaction can be confirmed ｒｅｔ (min) can be calculated by the following formula (1) based on the composition of the gaseous reducing material used for gaseous reduction. ＣＯ -2 x X ＣＯ２ +2 x X Ｈ２ -4 x X Ｈ２Ｏ ) is a coefficient and is the ratio of carbon monoxide (CO) and hydrogen (H ２ ) is approximately 1:2, and the CO / CO ratio at the Fe-FeO equilibrium is ２ or H ２ / H ２ The coefficient "5" in 5×d may be determined by conducting multiple reduction experiments (gas components and temperature under predetermined conditions) to determine the test time that is confirmed to exceed the stagnant gas reduction rate under each condition, and then determining the coefficient "5" so as not to exceed that time. ｒｅｔ = 5 × d / (X ＣＯ -2 x X ＣＯ２ +2 x X Ｈ２ -4 x X Ｈ２Ｏ )×exp(6000 / T)...(1)

[0043] In equation (1), T is the reduction temperature (K), d is the average particle size of the iron raw material (mm), and X ＣＯ is the CO concentration of the gas reducing agent, X ＣＯ２ is the gas reducing agent CO ２ Concentration%, X Ｈ２ is the gas reducing agent H ２ Concentration%, X Ｈ２Ｏ is the gas reducing agent H ２ O concentration %.

[0044] The ratio of the component composition of the sample (agglomerate ore) used in the gas reduction test is shown in Table 1. The test conditions for gas reduction are shown in Table 2. As shown in Table 2, the test conditions (A to D) were carried out by changing the ratio of the component composition of the gas reducing material used in the gas reduction, the reduction temperature for gas reduction, and the particle size of the sample (agglomerate ore). ｒｅｔ " is a value calculated by applying the proportions of the component composition of the gaseous reducing material to formula (1). Note that "Test condition D" shown in Table 2 indicates a test condition equivalent to the conventional gaseous reduction test condition "Iron ore - reducibility test (JIS M 8713:2009)."

[0045]

[0046]

[0047] Figure 3 shows the test results of gas reduction of the sample (agglomerate) under test condition A. Test condition A requires that the reduction temperature is 900°C (1173K) and the particle size of the sample (agglomerate) is 12mm. The component composition of the gas reducing agent is hydrogen (H ２ ) was set to 100% by volume. The gas reduction test under test condition A was carried out using agglomerates 1 to 3 shown in Table 1 as samples.

[0048] As shown in FIG. 3, under test condition A, “time t ｒｅｔ " is 50 min. As shown in FIG. 3, "time t ｒｅｔBy setting the "time t" to 50 min, the reduction rate curves of the gas reduction rates of the agglomerates 1 to 3 could be measured including the stagnant gas reduction rate and over the time period when the change in the gas reduction rate had settled down. In other words, the gas reduction rates of the sample agglomerates 1 to 3 could be properly measured including the influence of the stagnation of the reduction reaction. Specifically, the "time t" of 50 min ｒｅｔ The gas reduction rates of agglomerates 1 to 3 could be determined from the values ​​on the reduction rate curve in

[0049] 4 shows the test results of gas reduction of the sample (agglomerate ore) under test condition B. Test condition B is set to a reduction temperature of 900°C (1173K) and a particle size of the sample (agglomerate ore) of 10mm. The gas reduction material is composed of 95% carbon monoxide (CO) and 10% carbon dioxide (CO ２ The gas reduction test under test condition B was carried out using agglomerates 1 and 4 to 6 shown in Table 1 as samples.

[0050] As shown in Table 2, under test condition B, "time t ｒｅｔ " is 98 min. As shown in FIG. 4, "time t ｒｅｔ By setting the "time t" to 98 min, the reduction rate curves of the gas reduction rates of the agglomerates 1 and 4 to 6 could be measured including the stagnant gas reduction rate and over the time when the change in the gas reduction rate subsided. In other words, the gas reduction rates of the sample agglomerates 1 and 4 to 6 could be properly measured including the influence of the stagnation of the reduction reaction. Specifically, the "time t" of 98 min ｒｅｔ The gas reduction rates of agglomerates 1, 4 to 6 could be determined from the values ​​on the reduction rate curve in

[0051] Figure 5 shows the results of gas reduction tests carried out on the sample agglomerate 1 under different test conditions. The upper limit of the test time was set to 180 minutes, which is the measurement time specified in the conventional gas reduction test conditions "Iron ore - Reducibility test (JIS M 8713:2009)." As shown in Figure 5, under test conditions A to C, the "time t ｒｅｔBy measuring the gas reduction rate of the agglomerate 1 based on the time of ", it was possible to measure the reduction rate curve of the gas reduction rate including the stagnant gas reduction rate (85%) of the agglomerate 1 and over the time point when the change in the gas reduction rate subsided. In other words, it was possible to properly measure the gas reduction rate of the sample agglomerate 1, including the influence of the stagnation of the reduction reaction.

[0052] Specifically, it was possible to measure the gas reduction rate of the agglomerated ore 1 when gas reduction was performed using the gas reducing agent used under each of the test conditions A to C. That is, for each of the test conditions A to C, the gas reduction rate of the agglomerated ore 1 was measured at each "time t ｒｅｔ The values ​​on each reduction rate curve in "" could be taken as the gas reduction rate of the agglomerate 1 under each test condition.

[0053] On the other hand, under test condition D, the upper limit of the measurement time was 180 minutes, and therefore, the gas reduction of the agglomerated ore 1 did not proceed until the stagnant gas reduction rate was reached, at which the reduction reaction stagnates. For this reason, the stagnant gas reduction rate could not be included in the reduction rate curve of the gas reduction rate, and further, measurement could not be performed until the point at which the change in the gas reduction rate settled down.

[0054] As shown in Figures 3 to 5, even if the composition and properties of the iron raw material (agglomerate ore) as a sample change and the test conditions are changed, the "time t ｒｅｔ ", the gas reduction test was carried out based on the stagnation gas reduction rate, and the gas reduction rate was measured over the period until the change in the gas reduction rate subsided. Therefore, the "time t ｒｅｔ By conducting a gas reduction test based on ", the gas reduction rate of the iron raw material (agglomerate ore) can be properly measured, including the influence of stagnation of the reduction reaction. ｒｅｔ The value on the reduction rate curve in " was determined to be the gas reduction rate of the iron raw material (agglomerate ore).

[0055] The measurement time t (min) for measuring the gas reduction rate of the iron raw material is t ｒｅｔ It is desirable that the time is t ｒｅｔ -10% time (time t ｒｅｔ× 0.9) as a reference, and for the reduction rate curve of the gas reduction rate at the subsequent measurement time t (min), a value at any point on the reduction rate curve may be taken as the gas reduction rate of the iron raw material. In this case, a more accurate gas reduction rate can be obtained for the test target iron raw material. Then, the measurement time t (min) for measuring the gas reduction rate of the iron raw material is set to time t ｒｅｔ x 0.9 and the value on the reduction rate curve at that time is specified as the gas reduction rate of the iron raw material, it is possible to calculate a gas reduction rate that exceeds the stagnant gas reduction rate of the iron raw material.

[0056] In measuring the gas reduction rate of the iron raw material (agglomerate ore), when a reduction rate curve of the gas reduction rate is used, if the time for measuring the gas reduction rate is too long, the gas reduction rate of the iron raw material will asymptotically approach 100%, making it difficult to accurately detect the gas reduction rate from an operational standpoint. ｒｅｔ It is desirable that the time be 1.3 times or less.

[0057] CO concentration and H in equation (1) ２ The total concentration of the iron ore and the iron raw material is preferably 30% by mass or more as specified in the conventional gas reduction test conditions "Iron ore - Reducibility test (JIS M 8713:2009)", and more preferably 80% by mass or more and 100% by mass or less from the viewpoint of the test time for the gas reduction rate of the iron raw material.

[0058] The reduction temperature in formula (1) is preferably set to 1073 K or more and 1273 K or less, which are the main temperatures used in the blast furnace method and the direct reduction method, and more preferably 1073 K or more and 1173 K or less from the viewpoint of reducing the cost of reduction tests. The average particle size of the iron raw materials in formula (1) is preferably 9 mm or more and 21 mm or less, which is the range of average particle sizes of iron raw materials that can actually be charged in the blast furnace method and the direct reduction method, and more preferably 9 mm or more and 15 mm or less from the viewpoint of the test time for the gas reduction rate of the iron raw materials. Here, the average particle size of the iron raw materials refers to the harmonic mean diameter.

[0059] As mentioned above, at time t ｒｅｔThe value on the reduction degree curve at time t may be specified as the gas reduction degree of the iron raw material, and the iron raw material with the specified gas reduction degree may be applied to the iron making process. ｒｅｔ × 0.9 or more (time t ｒｅｔ A value on the reduction rate curve at a subsequent measurement time t (min) based on a time of −10% relative to the reduction rate of the iron raw material is identified as the gas reduction rate of the iron raw material, and the iron raw material with the identified gas reduction rate may be applied to an iron making process.

[0060] Furthermore, prior to the operation of the iron-making process, an iron raw material with a specified gas reduction rate may be prepared in advance. Specifically, the iron raw material is subjected to gas reduction by a gas reducing agent in the iron-making process, and the measurement time t (min) for measuring the gas reduction rate of the iron raw material by gas reduction is set to the time t calculated by the formula (1). ｒｅｔ The gas reduction rate is measured as above, and an agglomerate ore having the measured gas reduction rate of 95% or more is prepared and may be used in the subsequent operation of the iron-making process.

[0061] As described above, according to the gas reduction rate measurement method, blast furnace operation method, direct reduction shaft furnace operation method, and iron raw material according to the present embodiment, it is possible to properly measure the gas reduction rate of iron raw materials used in iron making processes including the blast furnace method and the direct reduction method, taking into account the influence of stagnation of the reduction reaction. ２ This makes it possible to reduce emissions, suppress declines in productivity in the steelmaking process, and improve the quality of products obtained through the steelmaking process.

[0062] Hereinafter, examples based on the gas reduction rate measuring method according to this embodiment and iron raw materials will be described.

[0063] In the examples, a virtual physical blast furnace and a virtual physical direct reduction shaft furnace implemented in cyberspace were used to confirm whether it was possible to measure an appropriate gas reduction rate when iron raw materials (agglomerates) with different compositions and properties were used.

[0064] The gas reduction rate of the agglomerated ore was measured by two methods: a conventional measurement method (iron ore - reducibility test (JIS M 8713:2009)) and the gas reduction rate measurement method according to the present invention. With regard to the reduction behavior of gas reduction in the virtual physical blast furnace and the virtual physical direct reduction shaft furnace, Non-Patent Document 4 was referenced, and calculation parameters were determined so as to be consistent with the test results (Tables 1 and 2, and Figures 3 to 5). In addition, in Tables 3 and 4, the conventional measurement method (JIS M 8713:2009) is indicated as "gas reduction rate (conventional)," and the gas reduction rate measurement method according to the present invention is indicated as "gas reduction rate (present invention)."

[0065] First, the gas reduction rate in the blast furnace method was measured as follows. ２ For standard operation 1, which is the basis for the reduction rate, the hot air blowing is performed with a blowing temperature of 1100°C, an oxygen concentration of 21%, and a blowing moisture content of 20g / Nm ３ The heat loss was 100 Mcal / t, and the solid reducing agent ratio, which is the sum of the pulverized coal ratio and the coke ratio, was 487 kg / t. In Standard Operations 2 and 3, Comparative Example 1, and Invention Examples 1 to 3, in addition to the operating conditions in Standard Operation 1, a gas reducing agent was injected from the tuyere.

[0066] The measurement of the gas reduction rate (invention) was carried out under the conditions of "Test Condition B" shown in Table 2. Therefore, the time t ｒｅｔ The gas reduction time was set to 98 min, and the gas reduction time was set to 100 min. Specifically, the gas reduction rate at the time of 100 min was taken as the gas reduction rate of each agglomerate. Table 3 shows the results of the measurement of the gas reduction rate in the blast furnace method.

[0067]

[0068] As shown in Table 3, the gas reduction rate of the agglomerate 1 used in the standard operations 1 to 3 was 70% when measured based on the gas reduction rate (conventional) and 90% when measured based on the gas reduction rate (invention). The stagnant gas reduction rates shown in Table 3 indicate the stagnant gas reduction rates determined for the agglomerates used in each example.

[0069] The "Evaluation" in Table 3 is based on a comparison of the gas reduction rates of several agglomerates, and indicates that by using agglomerates with a high gas reduction rate, CO ２ If the reduction rate improved, it was evaluated as "good (○)." If the result was anything other than that, it was evaluated as "bad (×)."

[0070] In the standard operations 1 to 3, the operation mode was hot air blowing, and the amount of gas reducing agent was changed. As shown in Table 3, as the amount of gas reducing agent increased, the CO ２ The reduction rate has improved.

[0071] In Comparative Example 1, the gas reduction rate (conventional) is higher than that in Reference Operation 2, which has the same amount of gas reducing agent. However, the gas reduction rate (conventional) is lower than the stagnant gas reduction rate, and the CO ２ In comparison with standard operation 2, the reduction rate of CO ２ The reduction rate was about the same.

[0072] In Example 1 of the present invention, when compared with Reference Operation 2 in which the amount of gas reducing agent is the same, the gas reduction rate (conventional) is the same, but the gas reduction rate (present invention) is higher. ２ The reduction rate was higher than that of standard operation 2. In invention example 2, when compared with standard operation 3 in which the amount of gas reducing material is the same, the gas reduction rate (conventional) is the same, but the gas reduction rate (present invention) is higher. The gas reduction rate (present invention) exceeds the stagnant gas reduction rate, and the CO ２ The reduction rate was higher than that of standard operation 3. In invention example 3, when compared with standard operation 2 in which the amount of gas reducing material is the same, both the gas reduction rate (conventional) and the gas reduction rate (present invention) are higher. The gas reduction rate (present invention) exceeds the stagnant gas reduction rate, and the CO ２ The reduction rate was higher than that of standard operation 2.

[0073] As described above, the gas reduction rate measurement method according to the present invention can properly measure the gas reduction rate of iron raw material (agglomerate ore) including the influence of stagnation of the reduction reaction. Furthermore, by using the iron raw material (agglomerate ore) whose gas reduction rate has been properly measured by the gas reduction rate measurement method according to the present invention, it is possible to measure the CO ２ This makes it possible to reduce emissions.

[0074] More specifically, the gas reduction rate of the iron raw material (agglomerate ore) can be properly measured up to a range exceeding the stagnant gas reduction rate, and therefore evaluation (measurement) taking into account the influence of stagnation of the reduction reaction in the gas reduction can be performed. When the iron raw material (agglomerate ore) selected based on the gas reduction rate (conventional) is charged into a blast furnace, CO ２ Although the reduction in CO emissions is small, when iron raw materials (agglomerates) selected by the gas reduction rate (this invention) are charged into a blast furnace, ２ For example, as a blast furnace operation method, the gas reduction rate is measured using the gas reduction rate measurement method according to the present invention, and iron raw material (agglomerate ore 5 or 6) having the measured gas reduction rate of 95% or more is charged into the blast furnace, and a gas reducing agent is supplied to the blast furnace at a rate of 100 Nm ３ / t or more to produce molten iron.

[0075] Next, the gas reduction ratio in the direct reduction process was measured as follows. As shown in Table 4, the production amount of reduced iron in the standard operation was set to 1.0. Then, agglomerated ore 1 used in the standard operation was replaced with other agglomerated ores having different gas reduction ratios (conventional) and (present invention). Changes in the product reduction ratio were confirmed, and it was also confirmed whether an appropriate gas reduction ratio could be measured.

[0076] The measurement of the gas reduction rate (invention) was carried out under the conditions of "Test Condition B" shown in Table 2. Therefore, the time t ｒｅｔ The gas reduction time was set to 98 minutes, and the gas reduction time was set to 100 minutes. Specifically, the gas reduction rate at the time of 100 minutes was taken as the gas reduction rate of each agglomerate. Table 4 shows the results of the measurement of the gas reduction rate in the direct reduction method in the examples.

[0077]

[0078] As shown in Table 4, the gas reduction rate of the agglomerate 1 used in the standard operation was 70% when measured based on the gas reduction rate (conventional) and 90% when measured based on the gas reduction rate (invention). The stagnant gas reduction rates shown in Table 4 indicate the stagnant gas reduction rates determined for the agglomerates used in each example.

[0079] In Table 4, the "evaluation" was evaluated as "good (○)" when the value improved compared to the product reduction rate or production volume in the standard operation. Any other results were evaluated as "bad (×)."

[0080] In Comparative Example 1, the gas reduction rate (conventional) was higher than that in the standard operation. However, the gas reduction rate (conventional) was lower than the stagnant gas reduction rate, and the product reduction rate was comparable to that in the standard operation.

[0081] In Invention Example 1, when compared with the standard operation, the gas reduction rate (conventional) was the same, but the gas reduction rate (present invention) was a higher value. Furthermore, as the gas reduction rate (present invention) exceeded the stagnant gas reduction rate, the product reduction rate was higher than that of the standard operation. In Invention Example 2, when compared with the standard operation, the gas reduction rate (conventional) was the same, but the gas reduction rate (present invention) was a higher value. Furthermore, as the gas reduction rate (present invention) exceeded the stagnant gas reduction rate, the product reduction rate became the same as that of the standard operation, resulting in a higher production volume. In Invention Example 3, when compared with the standard operation, both the gas reduction rate (conventional) and the gas reduction rate (present invention) were higher. Furthermore, as the gas reduction rate (present invention) exceeded the stagnant gas reduction rate, the product reduction rate was higher than that of the standard operation.

[0082] As described above, the gas reduction rate measuring method according to the present invention can properly measure the gas reduction rate of iron raw materials (agglomerates) including the influence of stagnation of the reduction reaction. Furthermore, by using iron raw materials (agglomerates) whose gas reduction rate has been properly measured by the gas reduction rate measuring method according to the present invention, it is possible to improve the product reduction rate or production volume.

[0083] More specifically, the gas reduction rate of the iron raw material (agglomerate ore) can be properly measured up to a range exceeding the stagnant gas reduction rate, thereby enabling evaluation (measurement) taking into account the influence of stagnation of the reduction reaction during gas reduction. Furthermore, when iron raw materials (agglomerates) selected based on the gas reduction rate (conventional) are directly charged into a reduction shaft furnace, the effect of improving the product reduction rate cannot be obtained. However, when iron raw materials (agglomerates) selected based on the gas reduction rate (invention) are directly charged into a reduction shaft furnace, the product reduction rate or production volume can be improved. For example, as a method for operating a direct reduction shaft furnace, the gas reduction rate may be measured using the gas reduction rate measurement method according to the present invention, and iron raw materials (agglomerates 5 or 6) having the measured gas reduction rate of 95% or more may be charged into the direct reduction shaft furnace to produce reduced iron.

Claims

1. A method for measuring a gas reduction rate of an iron raw material used in an iron-making process by a gas reducing agent, the method comprising the steps of: a measuring time t (min) for measuring the gas reduction rate of the iron raw material; and a time t calculated by the following formula (1): ｒｅｔ x 0.9 or more. ｒｅｔ = 5 × d / (X ＣＯ -2 x X ＣＯ２ +2 x X Ｈ２ -4 x X Ｈ２Ｏ ) × exp(6000 / T) (1) where T is the reduction temperature (K), d is the average particle size (mm) of the iron raw material, and X ＣＯ is the CO concentration (%) of the gas reducing agent, X ＣＯ２ is the gaseous reducing agent CO ２ Concentration%, X Ｈ２ is the H of the gas reducing agent ２ Concentration%, X Ｈ２Ｏ is the H of the gas reducing agent ２ O concentration %.

2. The measurement time t (min) is the time t ｒｅｔ The gas reduction rate measuring method according to claim 1, wherein the gas reduction rate is 1.3 or less.

3. The CO concentration and the H concentration in the gas reducing agent ２ The gas reduction rate measuring method according to claim 1 or 2, wherein the total concentration of the gas reduction rate and the concentration of the oxidizing agent is 30 mass% or more and 100 mass% or less.

4. A method for measuring a gas reduction rate as described in claim 1 or 2, wherein the average particle size of the iron raw material is 9 mm or more and 21 mm or less.

5. A method for measuring a gas reduction rate according to claim 1 or 2, wherein the reduction temperature is 1073K or higher and 1273K or lower.

6. The gas reduction rate is measured using the gas reduction rate measuring method according to claim 1 or 2, and the iron raw material having the measured gas reduction rate of 95% or more is charged into a blast furnace, and a gas reducing agent is injected into the blast furnace at a rate of 100 Nm ３ A blast furnace operating method in which molten iron is produced by supplying more than 100 t of iron.

7. A method for operating a direct reduction shaft furnace, comprising measuring the gas reduction rate using the gas reduction rate measuring method according to claim 1 or 2, and feeding iron raw material having the measured gas reduction rate of 95% or more into the direct reduction shaft furnace to produce reduced iron.

8. An iron raw material that is gas-reduced by a gas reducing agent in an iron-making process, wherein the measurement time t (min) for measuring the gas reduction rate of the iron raw material by the gas reduction is calculated by the following formula (1): ｒｅｔ x 0.9 or more, and the measured gas reduction rate is 95% or more. ｒｅｔ = 5 × d / (X ＣＯ -2 x X ＣＯ２ +2 x X Ｈ２ -4 x X Ｈ２Ｏ ) × exp(6000 / T) (1) where T is the reduction temperature (K), d is the average particle size (mm) of the iron raw material, and X ＣＯ is the CO concentration (%) of the gas reducing agent, X ＣＯ２ is the gaseous reducing agent CO ２ Concentration%, X Ｈ２ is the H of the gas reducing agent ２ Concentration%, X Ｈ２Ｏ is the H of the gas reducing agent ２ O concentration %.

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