TWI889305B - Blast furnace operation method - Google Patents

Abstract

The present invention proposes a blast furnace operation method, which suppresses the reduction pulverization property by using a plurality of sintered ores with adjusted components, and can ensure the permeability in the furnace even in a blast furnace using a large amount of _H2 as a reducing material. As the sintered ores, a sintered ores including a sintered ores with high reduction pulverization property and a sintered ores with low reduction pulverization property compared to the sintered ores with high reduction pulverization property are used for operation. As a preferred embodiment, it can be applied to the blast furnace operation method using a large amount of _H2 as a reducing material.

Description

Blast furnace operation method

The present invention relates to a method for operating a blast furnace, which can improve the reduction pulverization resistance of sintered ore and ensure the permeability in the furnace during the operation of the blast furnace, preferably using a large amount of _H2 as a reducing material.

The steel industry is strongly required to reduce _CO2 emissions. The iron smelting step accounts for about 80% of _CO2 emissions. Therefore, the use of _H2 as a reducing material for iron oxide in blast furnaces is under review. If _H2 is used as a reducing material for iron oxide, _H2O is produced as a byproduct, and _CO2 emissions can be reduced by that amount. When _H2 is used as a reducing material, since the reduction of iron oxide by _H2 is an endothermic reaction, it is expected that the furnace temperature will be lowered. Therefore, the low temperature region of 400-550°C, which causes the reduction and pulverization of the sintered ore, will be significantly increased, and the reduction and pulverization of the sintered ore will be promoted, and there is a concern that the production efficiency will be reduced due to the deterioration of the permeability in the blast furnace (for example, see Patent Document 1). The reduction and pulverization of the sintered ore is caused by the volume expansion caused by the reduction of hematite to magnetite at low temperature, which causes turtle cracks inside the sintered ore. It is believed that the reduction rate of _H2 reduction is fast, so the reduction and pulverization increases.

Generally, as a technique to suppress the reduction pulverization of sintered ore, it is known that increasing FeO or reducing alkalinity (CaO/SiO ₂ ) is effective. In the former case, there is a problem that if FeO increases, the reduction property will deteriorate significantly. In the latter case, reducing alkalinity means reducing CaO or possibly increasing SiO ₂ . However, reducing CaO will reduce the amount of molten metal produced in the sintered ore manufacturing process, which will deteriorate the sintering productivity. In addition, increasing SiO ₂ will lead to an increase in the slag ratio in the blast furnace. From the perspective of reducing the reducing material ratio or cutting the slag treatment cost, it is sought to reduce SiO ₂ in the sintered ore as much as possible.

In low _SiO2 sintered ore, as a technology that has both high reducibility and resistance to reduction pulverization, the technology disclosed in Patent Document 1 is known. In the technology disclosed in Patent Document 1, _SiO2 is reduced to 4.2~4.9 mass%, and the FeO content is increased to the range of 7.0~9.0 mass%. Alternatively, in order to increase the alkalinity to the range of 1.8~2.2 and further improve the resistance to reduction pulverization, dolomite of a specific particle size is formulated as an MgO source, and the MgO content is increased to the range of 1.5~3.0 mass%. In addition, Patent Document 2 also proposes a technology for grouping sintered ore based on the quality of reduction pulverization and changing the charging position of the blast furnace.

[Prior Art Literature] [Patent Literature]

Patent document 1: Japanese Patent Publication No. 11-131151

Patent document 2: Japanese Patent Publication No. 1-188610

On the other hand, blast furnaces produce about 300 kg of by-product slag per ton of molten iron, which is used in civil engineering and building materials. In order to ensure the proper properties of blast furnace slag, the alkalinity of the slag must be managed between 1.0 and 1.35. Therefore, since the composition required for sintered ore is almost determined if the operating conditions are determined, the adjustment range of the technology disclosed in Patent Document 1 is limited. In addition, in the technology disclosed in Patent Document 2, there is no proposed method for reducing the quality of pulverization by adjusting the composition.

The purpose of the present invention is to solve the problems faced by the prior art and to propose a blast furnace operation method that suppresses reduction pulverization by using a plurality of sintered ores with adjusted compositions and ensures furnace permeability even in a blast furnace using a large amount of _H2 as a reducing material.

The blast furnace operation method of the present invention is characterized in that, as the sintered ore, a sintered ore is used which is a mixture of at least two types of sintered ore including a sintered ore with high reducibility and a sintered ore with lower reducibility than the sintered ore with high reducibility.

In addition, in the blast furnace operation method of the present invention, the following preferred embodiments are considered: (1) a large amount of _H2 is used as a reducing material for operation; (2) the sintered ore with low reduction pulverization property is prepared to account for 25-75% by mass of the whole sintered ore mixed as described above; (3) the reduction pulverization property is obtained by reducing 500 g of the sintered ore at 550°C for 40 minutes in an environment having a specific gas composition of 31 vol% CO gas concentration, 19 vol% _H2 gas concentration, and 50 vol% _N2 gas concentration, and then measuring the reduction pulverization property according to JIS M The pulverization of the rolling device specified in 8720 is evaluated by the reduction pulverization index represented by the powder rate below 2.8 mm. (4) The sintered ore with high reduction pulverization property is a sintered ore with a reduction rate of 11% or more when 500g of the sintered ore is reduced at 550℃ for 40 minutes in an environment with a specific gas composition of 31vol% CO gas concentration, 19vol% _H2 gas concentration and 50vol% _N2 gas concentration. The sintered ore with low reduction pulverization property is a sintered ore with a reduction rate of less than 11% when reduced under the same conditions. (5) The reduction rate of the sintered ore with high reduction pulverization property is more than 6 percentage points away from the reduction rate of the sintered ore with low reduction pulverization property.

According to the blast furnace operation method of the present invention, the blast furnace operation is performed using a sintered ore that is a mixture of at least two types of sintered ores, including a sintered ore with high reduction pulverization and a sintered ore with low reduction pulverization relative to the sintered ore with high reduction pulverization. In this way, the reduction pulverization can be reduced while maintaining the same reduction (reduction rate) as when a single raw material is used. In addition, since the blast furnace needs to maintain the slag alkalinity at 1.0~1.25, there is a component restriction when using a single sintered ore. Based on the present invention, the operation using heterogeneous sintered ores may also relax the restrictions on the composition of each sintered ore.

[Figure 1] is a graph showing the relationship between the reduction rate and the reduction powder index obtained as the foresight of the present invention.

[Figure 2] is a diagram used to illustrate the outline of the present invention.

[Figure 3] is a diagram showing Embodiment 3 of the present invention.

The following is a detailed description of the implementation of the present invention. The following implementation is an example of a device or method that embodies the technical idea of the present invention, and does not limit the structure to the following. In other words, the technical idea of the present invention can be modified in various ways within the technical scope of the patent application.

<The whole process of completing this invention>

The reduction pulverization mechanism of sintered ore was examined by the following method. First, the relationship between the reduction index (%) and the reduction rate (%) was examined for the sintered ore before reduction, the sintered ore reduced in an environment of 30%CO-70% _N2 , and the sintered ore reduced in an environment of 19%CO-11% _H2-70 % _N2 . The results are shown in Figure 1. As can be seen from the results in Figure 1, the reduction pulverization index of the sintered ore increases linearly before the reduction rate reaches 11%, and the increase rate of the reduction pulverization index stagnates after the reduction rate reaches 11%. If the reduction rate after 11% is regarded as the reduction pulverization stagnation zone, it can be seen that in a gas environment containing _H2 , the reduction is fast and it is easy to reach the reduction pulverization stagnation zone. After the reduction rate of 11%, the tendency of the reduction pulverization stagnation zone is the same when the sintered ore is reduced in the CO/ _N2 gas system and in the CO/ _H2 / _N2 gas system. The final reduction pulverization amount is determined by the reduction rate at that time. This is a new view. Since the reduction rate of ₀ ~11% is consistent with the region _{where Fe2O3} is reduced to _Fe3O4 , it can be seen that _the main cause of reduction pulverization is the reduction _{of Fe2O3} to _Fe3O4 .

Here, the reduction pulverization index and reduction rate are used as evaluation methods for low-temperature reduction pulverization. The reduction pulverization index is calculated as follows. First, 500g of sintered ore is reduced for 40 minutes at 550°C in an environment with a specific gas composition of 31vol% CO gas concentration, 19vol% _H2 gas concentration, and 50vol% _N2 gas concentration. Subsequently, pulverization is performed using a rolling device specified in JIS M 8720, and the powder rate below 2.8mm is taken as the reduction pulverization index. In addition, the reduction rate at this time is the value obtained by dividing the weight change (g) before and after the reduction test by the amount of reduced oxygen (g) assuming that all the iron in the sintered ore exists _{as Fe2O3} , and multiplying the result by 100%.

FIG2 is a graph obtained based on the above viewpoints to illustrate the concept of the present invention. As shown in FIG2, in the present invention, by mixing a sintered ore with high reduction pulverization (high pulverization sintered ore) and a sintered ore with low reduction pulverization (low pulverization sintered ore), the reduction pulverization of the entire sintered ore can be suppressed while the reduction rate is maintained to a certain extent. In the present invention, if the sintered ore includes at least one sintered ore with high reduction pulverization and one sintered ore with low reduction pulverization, for example, two or more sintered ores such as two sintered ores with high reduction pulverization and one sintered ore with low reduction pulverization can be mixed.

Furthermore, the blast furnace operation method of the present invention is also effective for a normal blast furnace, but if it is applied to a blast furnace operation using a large amount of _H2 as a reducing material, it is a better embodiment because the reduction pulverization of the sintered ore can be reduced and the ventilation in the furnace during operation can be ensured. Furthermore, in the blast furnace operation method of the present invention, by mixing the sintered ore with low reduction pulverization to form 25-75 mass% of the whole sintered ore, the purpose of reducing the reduction pulverization of the sintered ore of the present invention can be achieved, which is a better embodiment.

In the preferred embodiment of the present invention, the reduction pulverization property is evaluated by reducing 500 g of sintered ore at 550°C for 40 minutes in an environment with a specific gas composition of 31 vol% CO gas concentration, 19 vol% _H2 gas concentration, and 50 vol% _N2 gas concentration, and then pulverizing it in a rolling device specified in JIS M 8720, and the reduction pulverization index represented by the powder rate below 2.8 mm is used.

In a preferred embodiment of the present invention, the sintered ore with high reduction pulverization and the sintered ore with low reduction pulverization are defined as follows. The sintered ore with high reduction pulverization is a sintered ore with a reduction rate of 11% or more when 500 g of the sintered ore is reduced at 550°C for 40 minutes in an environment having a specific gas composition of 31 vol% CO gas concentration, 19 vol% _H2 gas concentration, and 50 vol% _N2 gas concentration. The sintered ore with low reduction pulverization is a sintered ore with a reduction rate of less than 11% when reduced under the same conditions. Furthermore, the reduction rate of the sintered ore with high reduction pulverization is preferably more than 6 percentage points away from the reduction rate of the sintered ore with low reduction pulverization.

[Implementation example]

Compared with CO reduction, the reduction reaction of the sintered ore by H2 reduction proceeds faster, and the reduction proceeds even at low temperatures. Therefore, compared with the conventional CO reduction, it is easy to reach the reduction pulverization stagnation zone of 11% even at 550°C. Therefore, in an environment containing _H2 , by mixing and using sintered ores with different reduction rates at 550°C, the effect of reducing the reduction pulverization property is significantly manifested while maintaining a certain degree of reduction rate. According to the present invention, by loading a plurality of sintered ores with different reduction rates at 550°C into a blast furnace, the reduction pulverization resistance of the sintered ore can be improved in the operation of the blast furnace using a large amount of _H2 as a reducing material, and the permeability in the furnace can be ensured.

Based on the above findings, in the following examples, high-reducibility sintered ore, low-reducibility sintered ore, and sintered ore mixed with the two were prepared, and the reduction pulverization properties were evaluated.

As a high-reducing sintered ore with a reduction rate of 15% or more at 550°C, by reducing the blending rate of powdered coke of the agglomerate and increasing the oxygen enrichment rate during sintering, a sintered ore with FeO reduced to 9.0-1.0 mass% was produced (sintered ores A-E in Example 1 below). And as a low-reducing sintered ore with a reduction rate of 11% or less at 550°C, a sintered ore with a blending rate of powdered coke of the agglomerate increased to 6.5 mass% (sintered ore F in Example 1 below) and a sintered ore with alkalinity increased to 2.5 or more was produced (sintered ores H-I in Example 2 below). Furthermore, by mixing the actually produced sintered ore and evaluating the low-temperature reduction pulverization property, it was confirmed that the reduction pulverization index was reduced (Example 3 below).

<Implementation Example 1>

By adjusting the mixing ratio of powdered coke in the agglomerate and performing oxygen enrichment during sintering, sintered ores with different reduction rates at 550°C are produced. The following Table 1 shows the results of the low-temperature reduction pulverization test of the produced sintered ores. Under the condition of oxygen enrichment, a high-reducing sintered ores with a mixing ratio of powdered coke below 5.5% and a reduction rate of more than 15% at 550°C are obtained.

<Implementation Example 2>

By increasing the alkalinity from 2.0 to 2.8, a low-reduction sintered ore with a reduction rate of less than 11% at 550°C was produced. Table 2 below shows the results of the low-temperature reduction pulverization test of the produced sintered ore. When the alkalinity is above 2.5, the reduction rate at 550°C becomes less than 11%, and the reduction pulverization index is also at a low level of less than 30%.

<Implementation Example 3>

In Examples 1 and 2, the prepared sintered ore A (high-reducing sintered ore) and sintered ore F (low-reducing sintered ore) or sintered ore I (low-reducing sintered ore) were mixed at a ratio of 1:1 to prepare a mixed sintered ore, and the mixed sintered ore was subjected to a low-temperature reduction pulverization test. The results are shown in Figure 3 below. The reduction rate and reduction pulverization index of the mixed sintered ore at 550°C are about the average value of the two sintered ores alone. The reduction pulverization index of the mixed sintered ore is about 5 percentage points lower than the quadratic approximate equation of the reduction rate and reduction pulverization index at 550°C. It was found that the reduction pulverization index can be reduced by mixing sintered ores.

[Industrial availability]

According to the blast furnace operation method of the present invention, not only the normal blast furnace operation but also the blast furnace which preferably uses a large amount of _H2 as a reducing material can suppress the reduction pulverization and ensure the air permeability in the furnace.

Claims (5)

A blast furnace operation method, characterized in that a sintered ore is used as a sintered ore, which is a mixture of at least two kinds of sintered ore, including a sintered ore with high reduction pulverization property and a sintered ore with low reduction pulverization property compared with the sintered ore with high reduction pulverization property, wherein 500 g of the sintered ore with high reduction pulverization property is sintered at 550°C to form a gas with a CO gas concentration of 31 vol%, a H ₂ gas concentration of 19 vol%, and a N _2. Sintered ores having a reduction rate of 11% or more when reduced for 40 minutes in an environment of a specific gas composition with a gas concentration of 50 vol%. The aforementioned sintered ores with low reduction pulverizability are sintered ores having a reduction rate of less than 11% when reduced under the same conditions. A blast furnace operating method as claimed in claim 1, wherein a large amount of _H2 is used as a reducing material for the operation. The blast furnace operation method of claim 1, wherein the sintered ore with low reducibility is mixed to account for 25-75% by mass of the entire mixed sintered ore. The blast furnace operation method of claim 1, wherein the reduction pulverization property is evaluated by reducing 500 g of sintered ore at 550°C for 40 minutes in an environment having a specific gas composition of 31 vol% CO gas concentration, 19 vol% _H2 gas concentration, and 50 vol% _N2 gas concentration, and then pulverizing the ore using a rolling device specified in JIS M 8720, and the reduction pulverization index represented by the powder ratio below 2.8 mm is used. A blast furnace operating method as claimed in claim 1, wherein the reduction rate of the sintered ore with high reducibility and pulverization is more than 6 percentage points away from the reduction rate of the sintered ore with low reducibility and pulverization.

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