Blast furnace operation method

Abstract

Provided is a blast furnace operation method capable of securing ventilation in a furnace, even in a blast furnace using a large amount of H2 as a reducing material, by suppressing reduction degradation occurrence by using multiple kinds of sintered ores having adjusted components. In the present invention, an operation is performed by using sintered ores which are a mixture of at least two kinds of sintered ore: a high reduction degradation sintered ore; and a low reduction degradation sintered ore which tends to have a lower degree of reduction degradation than the high reduction degradation sintered ore. As a preferred embodiment, the present invention can be applied to a blast furnace operation method in which an operation is performed using a large amount of H2 as a reducing material.

Description

Blast furnace operation method

[0001] The present invention preferably uses a large amount of H as a reducing agent. ２ The present invention relates to a blast furnace operation method that improves the reduction disintegration resistance of sintered ore and ensures permeability inside the furnace in blast furnace operation using a sintered ore.

[0002] CO in the steel industry ２ There is a strong demand for reducing CO emissions. ２ It accounts for approximately 80% of the total emissions. ２ Attempts to use H as a reducing agent for iron oxide are being considered. ２ If you use ２ O, and CO ２ It is possible to reduce emissions. ２ When using H ２ Since the reduction of iron oxide by H is an endothermic reaction, it is expected that the temperature inside the furnace will decrease. Therefore, the low-temperature region of 400 to 550°C, where reduction and disintegration of sintered ore occurs significantly, will increase, accelerating reduction and disintegration of sintered ore, raising concerns about a decrease in production efficiency due to a deterioration in permeability inside the blast furnace (see, for example, Patent Document 1). Reduction and disintegration of sintered ore is caused by the generation of cracks inside the sintered ore due to volume expansion that occurs when hematite is reduced to magnetite at low temperatures, and H ２ It is believed that the reduction rate is high, which increases reduction disintegration.

[0003] Generally, techniques for suppressing reduction disintegration of sintered ore include increasing FeO and adjusting basicity (CaO / SiO ２ In the former case, there is a problem that the reducibility is significantly deteriorated when FeO is increased. In the latter case, the reduction of basicity can be achieved by reducing CaO or SiO ２ However, reducing the CaO content reduces the amount of melt produced during the sintering process, which reduces sintering productivity. ２ From the viewpoint of reducing the reducing agent rate and reducing slag treatment costs, an increase in SiO in sintered ore leads to an increase in the slag ratio in the blast furnace. ２ is required to be reduced as much as possible.

[0004] Low SiO ２ The technology disclosed in Patent Document 1 is known as a technology for achieving both high reducibility and resistance to reduction disintegration in sintered ore. ２ to 4.2 to 4.9 mass%, and the FeO content is increased to a range of 7.0 to 9.0 mass%. Alternatively, the basicity is increased to a range of 1.8 to 2.2, and dolomite of a predetermined particle size is blended as an MgO source to further improve resistance to reduction disintegration, thereby increasing the MgO content to a range of 1.5 to 3.0 mass%. Furthermore, Patent Document 2 proposes a technology in which sintered ores are grouped based on their resistance to reduction disintegration, and the positions at which they are charged into a blast furnace are changed for use.

[0005] JP-A No. 11-131151 JP-A No. 1-188610

[0006] On the other hand, blast furnaces produce approximately 300 kg of blast furnace slag as a by-product per ton of molten iron, which is used for civil engineering and construction materials, etc. To ensure the proper properties of blast furnace slag, the slag basicity must be controlled between 1.0 and 1.35. Therefore, once the operating conditions are determined, the components required for sintered ore are largely determined, so the technology disclosed in Patent Document 1 had a limited range of adjustment. Furthermore, the technology disclosed in Patent Document 2 did not propose a method for adjusting the components to improve reduction disintegration properties.

[0007] The object of the present invention is to solve the problems of the conventional technology and to suppress reduction disintegration by using a plurality of sintered ores with adjusted compositions, and to use a large amount of H as a reducing agent. ２ The present invention aims to propose a blast furnace operation method capable of ensuring permeability inside the furnace even in a blast furnace using a blast furnace.

[0008] The blast furnace operating method of the present invention is a method for operating a blast furnace, characterized in that the blast furnace is operated using sintered ore obtained by mixing at least two or more types of sintered ore, the sintered ore including sintered ore having a high reduction disintegration property and sintered ore having a lower reduction disintegration property than the sintered ore having a high reduction disintegration property.

[0009] In the blast furnace operation method of the present invention, (1) a large amount of H is used as a reducing agent.２ (2) The sintered ore with low reduction disintegration property is blended so that it accounts for 25 to 75 mass% of the total sintered ore mixture; (3) The reduction disintegration property is measured by subjecting 500 g of sintered ore to a temperature of 550°C for 40 minutes in a CO gas concentration of 31 vol%, H ２ Gas concentration 19 vol%, N ２ After reduction in an atmosphere of a predetermined gas composition such that the gas concentration is 50 vol%, it is pulverized using a rolling device specified in JIS M 9720, and evaluated by a reduction disintegration index expressed as the percentage of particles of 2.8 mm or less. (4) The sintered ore with high reduction disintegration properties is obtained by reducing 500 g of sintered ore at 550 ° C for 40 minutes in an atmosphere of a CO gas concentration of 31 vol %, H ２ Gas concentration 19 vol%, N ２ (4) The sintered ore has a reduction rate of 11% or more when reduced in an atmosphere having a predetermined gas composition such that the gas concentration is 50 vol%, and the sintered ore with low reduction disintegration property has a reduction rate of less than 11% when reduced under the same conditions; and (5) the reduction rate of the sintered ore with high reduction disintegration property and the reduction rate of the sintered ore with low reduction disintegration property are different by 6 points or more.

[0010] According to the blast furnace operation method of the present invention, a blast furnace is operated using sintered ore that is a mixture of at least two types of sintered ore, including sintered ore with high reduction disintegration property and sintered ore with lower reduction disintegration property than the high reduction disintegration property. This makes it possible to reduce reduction disintegration property while maintaining the same reducibility (reduction rate) as when a single raw material is used. Furthermore, since blast furnaces must maintain a slag basicity of 1.0 to 1.25, there are compositional restrictions when using a single sintered ore. By operating using different sintered ores based on the present invention, it is possible to alleviate the restrictions on each sintered ore component.

[0011] 1 is a graph showing the relationship between the reduction rate and the reduction disintegration index obtained as prior knowledge of the present invention. FIG. 2 is a graph for explaining an outline of the present invention. FIG. 3 is a graph showing Example 3 of the present invention.

[0012] The following describes in detail the embodiments of the present invention. Note that the following embodiments are intended to exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to that described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope defined in the claims.

[0013] <Background to the invention> The reduction and disintegration mechanism of sintered ore was investigated using the following method. First, sintered ore before reduction was mixed with 30% CO-70% N. ２ Sintered ore reduced under an atmosphere of 19% CO-11% H ２ -70%N ２ The relationship between the reduction index (%) and the reduction rate (%) was investigated for sintered ore reduced under an atmosphere of H. The results are shown in Figure 1. From the results in Figure 1, it was found that the reduction degradation index of sintered ore increases linearly up to a reduction rate of 11%, but the rate of increase of the reduction degradation index stagnates above a reduction rate of 11%. If the reduction rate above 11% is considered to be the reduction degradation stagnation region, then ２ It was found that reduction was rapid in a gas atmosphere containing CO / N and that the reduction was likely to reach the reduction stagnation region. ２ When reduced with CO / H ２ / N ２ The same is true when reducing with a gas containing Fe, and we have newly discovered that the final reduction disintegration amount is determined by the reduction rate at that time. ２ O ３ is Fe ３ O ４ Since this coincides with the region where Fe is reduced to Fe, the main cause of reduction disintegration is Fe. ２ O ３ From Fe ３ O ４ It was found to be a reduction to

[0014] Here, the reduction disintegration index and reduction rate were used as methods for evaluating low-temperature reduction disintegration. The reduction disintegration index was determined as follows: First, 500 g of sintered ore was heated at 550°C for 40 minutes in a CO gas concentration of 31 vol%, H ２ Gas concentration 19 vol%, N ２The sintered ore was reduced with a predetermined gas composition so that the gas concentration was 50 vol%. Then, the sintered ore was pulverized using a rolling device specified in JIS M 8720, and the percentage of particles of 2.8 mm or less was taken as the reduction pulverization index. The reduction rate at this time was calculated by calculating the weight change (g) before and after the reduction test, based on the condition that all the iron in the sintered ore was converted to Fe. ２ O ３ The value was divided by the amount of oxygen (g) to be reduced when it was assumed that the oxygen exists as a carbon dioxide gas, and the result was expressed as a percentage.

[0015] Fig. 2 is a graph illustrating the concept of the present invention, which was obtained based on the above findings. As shown in Fig. 2, in the present invention, by mixing sintered ore with high reduction disintegration (high disintegration sintered ore) and sintered ore with low reduction disintegration (low disintegration sintered ore), reduction disintegration of the entire sintered ore is suppressed while maintaining a certain degree of reduction rate. Note that in the present invention, as long as the sintered ore contains at least one type of sintered ore with high reduction disintegration and one type of sintered ore with low reduction disintegration, two or more types of sintered ore can be mixed, for example, two types of sintered ore with high reduction disintegration and one type of sintered ore with low reduction disintegration.

[0016] The blast furnace operation method of the present invention is effective in a normal blast furnace, but it is not suitable for a furnace containing a large amount of H as a reducing agent. ２ When applied to blast furnace operation using a sintered ore having a low reduction disintegration property, the reduction disintegration property of the sintered ore can be reduced and the gas permeability inside the furnace during operation can be ensured, which is a preferred embodiment. Furthermore, in the blast furnace operation method of the present invention, by blending the sintered ore having a low reduction disintegration property so that it accounts for 25 to 75 mass% of the total sintered ore, the object of the present invention of reducing the reduction disintegration property of the sintered ore can be more effectively achieved, which is a preferred embodiment.

[0017] In a preferred embodiment of the present invention, the reduction disintegration property is measured by subjecting 500 g of sintered ore to a temperature of 550° C. for 40 minutes in a CO gas concentration of 31 vol.% and H ２ Gas concentration 19 vol%, N ２ After reduction in an atmosphere of a predetermined gas composition such that the gas concentration is 50 vol%, the material is pulverized using a rolling device specified in JIS M 9720, and evaluated by a reduction pulverization index expressed as the percentage of particles of 2.8 mm or less.

[0018] In a preferred embodiment of the present invention, sintered ore with high reduction disintegration property and sintered ore with low reduction disintegration property are defined as follows: 500 g of sintered ore is sintered at 550° C. for 40 minutes in a CO gas concentration of 31 vol.%, H ２ Gas concentration 19 vol%, N ２ The sintered ore has a reduction rate of 11% or more when reduced in an atmosphere of a predetermined gas composition such that the gas concentration is 50 vol%. The sintered ore with low reduction disintegration property has a reduction rate of less than 11% when reduced under the same conditions. Furthermore, it is preferable that the reduction rate of the sintered ore with high reduction disintegration property and the reduction rate of the sintered ore with low reduction disintegration property are different by 6 points or more.

[0019] Sintered ore ２ When reduced, the reduction reaction proceeds faster than when CO is reduced, and reduction proceeds at a lower temperature. Therefore, compared to conventional CO reduction, the reduction rate easily reaches 11% even at 550°C, and the reduction degradation stagnates. ２ In the case of an atmosphere containing H, by mixing sintered ores with different reduction rates at 550°C, the effect of reducing reduction disintegration while maintaining a certain degree of reduction rate is significantly exhibited. According to the present invention, by charging a plurality of sintered ores with different reduction rates at 550°C into a blast furnace, a large amount of H is used as a reducing agent. ２ In blast furnace operation using this method, it becomes possible to improve the resistance to reduction disintegration of sintered ore and ensure gas permeability inside the furnace.

[0020] Based on the above findings, in the following examples, high-reducibility sintered ore, low-reducibility sintered ore, and a sintered ore mixture of the two were prepared, and reduction disintegration properties were evaluated.

[0021] As a highly reducible sintered ore having a reduction rate of 15% or more at 550 ° C, a sintered ore with a reduced FeO content of 9.0 to 1.0 mass% was prepared by lowering the blending ratio of coke fines as an agglomeration agent and increasing the oxygen enrichment rate during firing (Sintered ores A to E in Example 1 below). Furthermore, as a low-reducible sintered ore having a reduction rate of 11% or less at 550 ° C, a sintered ore with a blending ratio of coke fines as an agglomeration agent increased to 6.5 mass% (Sintered ore F in Example 1 below) and a sintered ore with a basicity increased to 2.5 or more (Sintered ores H to I in Example 2 below) were prepared. Furthermore, the sintered ores actually prepared were mixed and evaluated for low-temperature reduction disintegration properties, confirming the reduction disintegration index (Example 3 below).

[0022] Example 1 Sintered ores with different reduction rates at 550°C were prepared by adjusting the blending ratio of coke fines, which is an agglomerating agent, and by enriching the sintered ores with oxygen during firing. Table 1 below shows the results of a low-temperature reduction disintegration test of the prepared sintered ores. Under oxygen enrichment conditions, highly reducible sintered ores with a reduction rate of 15% or more at 550°C were obtained with a blending ratio of coke fines of 5.5% or less.

[0023]

[0024] <Example 2> By increasing the basicity from 2.0 to 2.8, a low-reducibility sinter was prepared so that the reduction rate at 550°C was 11% or less. Table 2 below shows the results of a low-temperature reduction degradation test of the prepared sinter, and when the basicity was 2.5 or more, the reduction rate at 550°C was 11% or less, and the reduction degradation index was also low at 30% or less.

[0025]

[0026] Example 3: The sinter A (highly reducible sinter) prepared in Examples 1 and 2 was mixed with either sinter F (lowly reducible sinter) or sinter I (lowly reducible sinter) at a 1:1 ratio to prepare a mixed sinter, and a low-temperature reduction degradation test was performed on the mixed sinter. The results are shown in Figure 3 below. The reduction rate and reduction degradation index of the mixed sinter at 550°C were approximately the average values ​​of the two sinters alone. The reduction degradation index of each mixed sinter was reduced by approximately 5 points from the quadratic approximation of the reduction rate and reduction degradation index at 550°C. This demonstrates that the reduction degradation index can be reduced by using a mixed sinter.

[0027] According to the blast furnace operation method of the present invention, not only normal blast furnace operation but also a large amount of H is preferably used as a reducing agent. ２ Even in a blast furnace using the above, reduction disintegration can be suppressed and gas permeability inside the furnace can be ensured.

Claims

1. A method for operating a blast furnace, characterized in that the blast furnace is operated using sintered ore obtained by mixing at least two types of sintered ore, the sintered ore including sintered ore having a high reduction disintegration property and sintered ore having a lower reduction disintegration property than the sintered ore having a high reduction disintegration property.

2. A large amount of H as a reducing agent ２ The method for operating a blast furnace according to claim 1, characterized in that the operation is carried out using 3. A method for operating a blast furnace as described in claim 1, characterized in that the sintered ore with low reduction disintegration tendency is blended so as to account for 25 to 75 mass % of the total sintered ore mixture.

4. The reduction disintegration property was measured by subjecting 500 g of sintered ore to a temperature of 550° C. for 40 minutes in a CO gas concentration of 31 vol.% and H ２ Gas concentration 19 vol%, N ２ The blast furnace operation method according to claim 1, characterized in that after reduction in an atmosphere having a predetermined gas composition such that the gas concentration is 50 vol%, the sintered material is pulverized by a rolling device specified in JIS M 9720, and evaluated by a reduction powderization index represented by a powder rate of 2.8 mm or less.

5. The sintered ore with high reduction disintegration property was prepared by subjecting 500 g of sintered ore to a CO gas concentration of 31 vol.% and H ２ Gas concentration 19 vol%, N ２ 2. The blast furnace operating method according to claim 1, wherein the sintered ore has a reduction rate of 11% or more when reduced in an atmosphere having a predetermined gas composition such that the gas concentration is 50 vol%, and the sintered ore with low reduction disintegration tendency is a sintered ore with a reduction rate of less than 11% when reduced under the same conditions.

6. A method for operating a blast furnace as set forth in claim 5, characterized in that the reduction rate of the sintered ore having high reduction disintegration property and the reduction rate of the sintered ore having low reduction disintegration property differ from each other by 6 points or more.

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