Blast furnace operation methods

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

Technical Field

[0001] The present invention relates to a blast furnace operating method that improves the reduction degradation resistance of sintered ore and secures gas permeability in the furnace, preferably in blast furnace operation using a large amount of H2 as a reducing agent.

Background Art

[0002] In the iron and steel industry, there is a strong demand for reduction of CO2 emissions. Among the production processes, the ironmaking process accounts for about 80% of total CO2 emissions. Accordingly, attempts to use H2 as a reducing agent for iron oxide in blast furnaces are currently being investigated. When H2 is used as a reducing agent for iron oxide, the by-product is H2O, which allows a corresponding reduction in CO2 emissions. When H2 is used as the reducing agent, since the reduction of iron oxide by H2 is an endothermic reaction, it is predicted that the temperature inside the furnace will decrease. Accordingly, the low-temperature region of 400 to 550°C where reduction degradation of sintered ore significantly occurs increases, which promotes reduction degradation of sintered ore, and there is concern about a decrease in production efficiency due to deteriorated gas permeability inside the blast furnace (see, for example, Patent Document 1). Reduction degradation 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. It is thought that H2 reduction has a faster reduction rate, which leads to increased reduction degradation.

[0003] Generally, it is known that increasing FeO content and reducing basicity (CaO / SiO2) are effective as techniques for suppressing the reduction degradation property of sintered ore. In the former case, there is a problem that when FeO increases, the reducibility of the sintered ore significantly deteriorates. In the latter case, reducing basicity can be achieved by reducing CaO or increasing SiO2. However, reducing CaO decreases the amount of melt generated during the sintered ore production process, which degrades sintering productivity. Additionally, increasing SiO2 leads to an increase in the slag ratio in the blast furnace. From the perspective of reducing the reducing agent ratio and cutting slag treatment costs, it is required to reduce SiO2 content in sintered ore as much as possible.

[0004] In low-SiO2 sintered ore, the technology disclosed in Patent Document 1 is known as a technique that achieves both high reducibility and resistance to reduction and pulverization. In the technology disclosed in Patent Document 1, the SiO2 content is reduced to 4.2-4.9 mass%, and the FeO content is increased to within the range of 7.0-9.0 mass%. Alternatively, the basicity is increased to within the range of 1.8-2.2, and dolomite of a predetermined particle size is blended as an MgO source to further improve resistance to reduction and pulverization, increasing the MgO content to within the range of 1.5-3.0 mass%. Furthermore, Patent Document 2 proposes a technique in which sintered ore is grouped based on its reducibility and pulverization properties, and used at different charging positions in the blast furnace. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-131151 [Patent Document 2] Japanese Unexamined Patent Publication No. 1-188610 [Overview of the project] [Problems that the invention aims to solve]

[0006] On the other hand, blast furnaces produce approximately 300 kg of blast furnace slag per ton of molten iron, which is used in civil engineering and construction materials. To ensure the appropriate 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 required components of the sintered ore are almost entirely determined, and the range of adjustment in the technology disclosed in Patent Document 1 was limited. Furthermore, the technology disclosed in Patent Document 2 did not propose a method for adjusting the quality of the reductive pulverization properties through component adjustment.

[0007] The objective of the present invention is to solve the problems of the conventional technology and propose a blast furnace operation method that suppresses reductive pulverization by using multiple sintered ores with adjusted compositions, thereby ensuring furnace permeability even in blast furnaces using a large amount of H2 as a reducing agent. [Means for solving the problem]

[0008] The present invention relates to a blast furnace operation method characterized by using a blast furnace that is prepared by mixing at least two types of sintered ores, including a sintered ore with high reductive pulverization properties and a sintered ore with lower reductive pulverization properties than the sintered ore with high reductive pulverization properties.

[0009] Furthermore, in the blast furnace operation method of the present invention, (1) Operating using a large amount of H2 as a reducing agent, (2) The sintered ore with low reductive powdering properties was blended to make up 25 to 75 mass% of the total sintered ore mixture. (3) The reduction pulverization property is evaluated by reducing 500g of sintered ore at 550°C for 40 minutes in an atmosphere with a predetermined gas composition such that the CO gas concentration is 31 vol%, the H2 gas concentration is 19 vol%, and the N2 gas concentration is 50 vol%, and then pulverizing it using a rolling device specified in JIS M 9720, and evaluating it with a reduction pulverization index expressed as a powder content of 2.8 mm or less. (4) The sintered ore with high reducibility to pulverization is a sintered ore in which the reduction rate is 11% or more when 500g of the sintered ore is reduced at 550°C for 40 minutes in an atmosphere with a predetermined gas composition such that the CO gas concentration is 31 vol%, the H2 gas concentration is 19 vol%, and the N2 gas concentration is 50 vol%, and the sintered ore with low reducibility to pulverization is a sintered ore in which the reduction rate is less than 11% when reduced under the same conditions. (5) The reduction rate of the sintered ore with high reductive pulverization properties and the reduction rate of the sintered ore with low reductive pulverization properties are separated by 6 points or more. These are considered to be desirable embodiments. [Effects of the Invention]

[0010] According to the blast furnace operation method of the present invention, the blast furnace is operated using a sintered ore mixture comprising at least two types of sintered ore, including a sintered ore with high reductive pulverization properties and a sintered ore with lower reductive pulverization properties than the sintered ore with high reductive pulverization properties. This makes it possible to reduce reductive pulverization properties while maintaining the same level of reductiveness (reduction rate) as when using a single raw material. Furthermore, since the blast furnace needs to maintain a slag basicity of 1.0 to 1.25, there are constraints on the components when using a single sintered ore. By operating with different types of sintered ore based on the present invention, it is possible to alleviate these constraints on the components of each sintered ore. [Brief explanation of the drawing]

[0011] [Figure 1] This graph shows the relationship between the reduction rate and the reduction powdering index, which was obtained as prior knowledge for the present invention. [Figure 2] This is a graph illustrating the outline of the present invention. [Figure 3] This is a graph showing Example 3 of the present invention. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described in detail below. The following embodiments are illustrative examples of devices and methods for realizing the technical concept of the present invention, and do not limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0013] <Background leading to the invention> The reduction and pulverization mechanism of sintered ore was investigated using the following method. First, the relationship between the reduction index (%) and the reduction rate (%) was examined for sintered ore before reduction, sintered ore reduced in a 30% CO-70% N2 atmosphere, and sintered ore reduced in a 19% CO-11% H2-70% N2 atmosphere. The results are shown in Figure 1. From the results in Figure 1, it was found that the reduction and pulverization index of sintered ore increased linearly up to a reduction rate of 11%, and that the rate of increase of the reduction and pulverization index stagnated thereafter. If the reduction rate above 11% is considered the reduction and pulverization stagnation region, it was found that reduction is faster in a gas atmosphere containing H2, and that the reduction and pulverization stagnation region is easily reached. This tendency for the reduction and pulverization stagnation region to form above 11% is the same whether sintered ore is reduced with a CO / N2 gas system or a CO / H2 / N2 gas system, and it was newly discovered that the final amount of reduced pulverization is determined by the reduction rate at that time. Since the reduction rate range of 0-11% coincides with the range where Fe2O3 is reduced to Fe3O4, it was found that the main cause of reduction and powdering is the reduction from Fe2O3 to Fe3O4.

[0014] Here, the reduction pulverization index and reduction rate were used as evaluation methods for low-temperature reduction pulverization properties. The reduction pulverization index was determined as follows: First, 500g of sintered ore was reduced at 550°C for 40 minutes with a predetermined gas composition of 31 vol% CO gas concentration, 19 vol% H2 gas concentration, and 50 vol% N2 gas concentration. After that, it was pulverized using a rolling device specified in JIS M 8720, and the reduction pulverization index was defined as a powder content of 2.8 mm or less. The reduction rate at this time was expressed as a percentage obtained by dividing the weight change (g) before and after the reduction test by the amount of oxygen reduced (g) assuming that all the iron in the sintered ore exists as Fe2O3.

[0015] Fig. 2 is a graph obtained based on the above findings for explaining the concept of the present invention. As shown in Fig. 2, in the present invention, by mixing and using sintered ore with high reduction degradation propensity (high degradation sintered ore) and sintered ore with low reduction degradation propensity (low degradation sintered ore), the reduction degradation of the entire sintered ore is suppressed while maintaining the reduction rate to a certain extent. In the present invention, as long as the sintered ore includes at least one type of high reduction degradation propensity sintered ore and one type of low reduction degradation propensity sintered ore, two or more types of sintered ore can be mixed, for example, two types of high reduction degradation propensity sintered ore and one type of low reduction degradation propensity sintered ore.

[0016] Note that the blast furnace operating method of the present invention is effective even for conventional blast furnaces, but when applied to blast furnace operation using a large amount of H₂ as a reducing material, it is a preferred embodiment because it can reduce the reduction degradation propensity of sintered ore and secure the gas permeability in the furnace during operation. In addition, in the blast furnace operating method of the present invention, blending the low reduction degradation propensity sintered ore so that it accounts for 25 to 75 mass% of the entire mixed sintered ore is a preferred embodiment, since the object of reducing the reduction degradation propensity of the sintered ore of the present invention can be more achieved.

[0017] In a preferred embodiment of the present invention, the reduction degradation propensity is evaluated by the following method: 500 g of sintered ore is reduced at 550°C for 40 minutes in an atmosphere with a predetermined gas composition having a CO gas concentration of 31 vol%, an H₂ gas concentration of 19 vol%, and an N₂ gas concentration of 50 vol%, then pulverized by a tumbling device specified in JIS M 9720, and evaluated by a reduction degradation index expressed by the powder ratio of particles of 2.8 mm or less.

[0018] Further, in a preferred embodiment of the present invention, sintered ore with high reduction degradation propensity and sintered ore with low reduction degradation propensity are defined as follows. Sintered ore with high reduction degradation propensity refers to sintered ore whose reduction ratio reaches 11% or more when 500 g of the sintered ore is reduced at 550°C for 40 minutes in an atmosphere having a predetermined gas composition with a CO gas concentration of 31 vol%, H2 gas concentration of 19 vol%, and N2 gas concentration of 50 vol%. Sintered ore with low reduction degradation propensity refers to sintered ore whose reduction ratio is less than 11% when reduced under the same conditions. Further, it is preferable that the difference between the reduction ratio of the sintered ore with high reduction degradation propensity and that of the sintered ore with low reduction degradation propensity is 6 percentage points or more. Examples

[0019] When sintered ore is reduced by H2, the reduction reaction proceeds faster than in the case of reduction by CO, and the reduction proceeds even at lower temperatures. Therefore, compared with conventional CO reduction, the reduction ratio can easily reach 11% even at 550°C, resulting in a reduction degradation stagnation region. Accordingly, in the case of an atmosphere containing H2, the mixed use of sintered ores having different reduction ratios at 550°C can prominently exhibit the effect of reducing reduction degradation propensity while maintaining the reduction ratio to a certain extent. According to the present invention, charging a plurality of sintered ores having different reduction ratios at 550°C into a blast furnace can improve the reduction degradation resistance of the sintered ore and ensure air permeability in the furnace during blast furnace operation using a large amount of H2 as a reducing agent.

[0020] Based on the above findings, in the following examples, highly reducible sintered ore, lowly reducible sintered ore, and a mixture of the two sintered ores were prepared, and their reduction degradation propensity was evaluated.

[0021] As a highly reducible sintered ore with a reduction rate of 15% or more at 550°C, we created a sintered ore with FeO reduced to 9.0-1.0 mass% by lowering the proportion of powdered coke, which is the binder, and increasing the oxygen enrichment rate during firing (sintered ores A-E in Example 1 below). In addition, as a low-reducible sintered ore with a reduction rate of 11% or less at 550°C, we created a sintered ore with an increased proportion of powdered coke, which is the binder, to 6.5 mass% (sintered ore F in Example 1 below) and a sintered ore with a basicity of 2.5 or higher (sintered ores H-I in Example 2 below). Furthermore, by mixing the actually created sintered ores and evaluating their low-temperature reducibility and pulverization properties, we confirmed a decrease in the reducibility and pulverization index (example 3 below).

[0022] <Example 1> By adjusting the blending ratio of powdered coke, which acts as a binder, and enriching the mixture with oxygen during firing, sintered ores with different reduction rates at 550°C were created. Table 1 below shows the results of low-temperature reduction pulverization tests of the created sintered ores. Under oxygen-enriched conditions, highly reducible sintered ores were obtained with a powdered coke blending ratio of 5.5% or less, resulting in a reduction rate of 15% or more at 550°C.

[0023] [Table 1]

[0024] <Example 2> By increasing the basicity from 2.0 to 2.8, we created a low-reducing sintered ore with a reduction rate of 11% or less at 550°C. Table 2 below shows the results of the low-temperature reduction and pulverization test of the created sintered ore. At a basicity of 2.5 or higher, the reduction rate at 550°C was 11% or less, and the reduction and pulverization index was also low at 30% or less.

[0025] [Table 2]

[0026] <Example 3> In Examples 1 and 2, a mixed sintered ore was prepared by mixing sintered ore A (highly reducing sintered ore) with either sintered ore F (low reducing sintered ore) or sintered ore I (low reducing sintered ore) in a 1:1 ratio. A low-temperature reduction pulverization test was then performed on the mixed sintered ore. The results are shown in Figure 3 below. The reduction rate and reduction pulverization index of the mixed sintered ore at 550°C were approximately the average values ​​for the two individual sintered ores. The reduction pulverization index of all mixed sintered ores decreased by approximately 5 points compared to the quadratic approximation formula for the reduction rate and reduction pulverization index at 550°C. From this, it was found that the reduction pulverization index can be lowered by using a mixture of sintered ores. [Industrial applicability]

[0027] According to the blast furnace operation method of the present invention, it is possible to suppress reductive pulverization and ensure furnace permeability not only in normal blast furnace operation but also, preferably, in blast furnaces using a large amount of H2 as a reducing agent.

Claims

1. A blast furnace operation method using a sintered ore obtained by mixing at least two types of sintered ores, including a sintered ore with high reductive pulverization properties and a sintered ore with lower reductive pulverization properties than the aforementioned sintered ore with high reductive pulverization properties, The aforementioned reductive pulverization property is evaluated by reducing 500 g of sintered ore at 550°C for 40 minutes in an atmosphere with a predetermined gas composition such that the CO gas concentration is 31 vol%, the H2 gas concentration is 19 vol%, and the N2 gas concentration is 50 vol%, and then pulverizing it using a rolling device specified in JIS M 8720, and using a reductive pulverization index expressed as a powder content of 2.8 mm or less. The aforementioned highly reductive sintered ore was prepared by heating 500g of sintered ore at 550°C for 40 minutes, with a CO gas concentration of 31 vol%, H ２ Gas concentration 19 vol%, N ２ A blast furnace operation method characterized in that 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%, and the sintered ore with low reducibility to powdering has a reduction rate of less than 11% when reduced under the same conditions.

2. H as a reducing agent ２ A blast furnace operating method according to claim 1, characterized in that it is operated using [a specific method].

3. The blast furnace operation method according to claim 1, characterized in that the sintered ore with low reducibility to powdering is blended to constitute 25 to 75 mass% of the total sintered ore mixture.

4. The blast furnace operation method according to claim 1, characterized in that the reduction rate of the sintered ore with high reductive pulverization potential and the reduction rate of the sintered ore with low reductive pulverization potential are separated by 6 points or more.

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