JP2000226608A - Operation of blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blast furnace operation method by which heat generation of a gas produced in a blast furnace can efficiently be controlled independently of the fuel ratio in the blast furnace. SOLUTION: Heat generation of a gas produced in a blast furnace is controlled by adjusting the reproducing ratio of charged raw material to be >=20% to <70%. Here, in the case that the weight average of the prereducing ratio of a charged raw material is >=20% to <30%, the heat generation of the gas is controlled while keeping the fuel ratio in the blast furnace almost constant, and in the case that the weight average of the prereducing ratio of the charged raw material is >=30% to <70%, the heat generation of the gas is controlled to almost constant regardlessly of the variation of the fuel ratio in the blast furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blast furnace operating method for controlling a calorific value of a gas generated from a blast furnace by changing a pre-reduction rate of a blast furnace raw material.

[0002]

2. Description of the Related Art Reduction of CO _2, which is a recent social need, imposes a reduction in the amount of gas generated in a blast furnace, that is, a reduction in the fuel ratio of a blast furnace in the steel industry. However, the blast furnace generated gas is often used as a fuel for a heating furnace or the like in an ironworks, and from such a viewpoint, a decrease in the fuel ratio is not preferable because it leads to a decrease in the calorific value (latent heat) of the blast furnace generated gas. Therefore, there is a need for a technique for maintaining the calorific value of the blast furnace generated gas irrespective of the fluctuation of the blast furnace fuel ratio or increasing the calorific value of the blast furnace generated gas while maintaining the fuel ratio of the blast furnace constant.

[0003]

In the conventional blast furnace operation, the calorific value of the gas generated from the blast furnace has a correlation with the fuel ratio. The higher the fuel ratio, the higher the calorific value of the gas generated by the blast furnace, and the lower the fuel ratio, the higher the calorific value. The amount is also low, and effective control of the calorific value of the gas generated from the blast furnace without depending on the fuel ratio of the blast furnace has not yet been performed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a blast furnace operating method capable of effectively controlling a calorific value of a blast furnace generated gas without depending on a blast furnace fuel ratio. I do.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have examined various wrist diagrams based on the overall material and heat balance, and found that the preliminary reduction rate of the blast furnace feedstock (ore oxidation degree) ), It was found that the calorific value of the gas generated from the blast furnace can be controlled without depending on the fuel ratio of the blast furnace.

More specifically, as a result of studying a wrist diagram based on the overall material and heat balance, for example, the preliminary reduction rate of iron ore charged into the blast furnace is 20% or more and less than 30% (iron oxide If the pre-reduction state is a pre-reduction state up to FeO when Fe ₂ O _{3 is} assumed), the calorific value of the gas generated from the blast furnace is substantially proportional to the pre-reduction rate of the iron ore while keeping the fuel ratio of the blast furnace constant. If the pre-reduction rate of the iron ore charged into the blast furnace is 30% or more and less than 70%,
The inventors have found that it is possible to change the fuel ratio while keeping the calorific value of the blast furnace generated gas constant, and have completed the present invention.

[0007] That is, the first invention is characterized in that the blast furnace operation is characterized by adjusting the pre-reduction rate of the blast furnace raw material to be at least 20% and less than 70% to control the calorific value of the blast furnace generated gas. Is the way.

According to a second aspect of the present invention, the calorific value of the gas generated from the blast furnace is adjusted while maintaining the fuel ratio of the blast furnace substantially constant by adjusting the pre-reduction rate of the raw material charged in the blast furnace to 20% or more and less than 30%. It is a blast furnace operating method characterized by controlling.

The third invention adjusts the pre-reduction rate of the blast furnace raw material to be 30% or more and less than 70% to keep the calorific value of the blast furnace generated gas substantially constant irrespective of fluctuations in the blast furnace fuel ratio. It is a blast furnace operating method characterized by controlling.

A fourth aspect of the invention is characterized in that the preliminary reduction rate of the blast furnace charge is adjusted to be 30% or more and less than 70%, and that high crystalline water ore is used as a part of the blast furnace charge. Is the blast furnace operating method. As a result, it is possible to suppress a rise in the furnace top gas temperature that occurs when the preliminary reduction rate of the blast furnace raw material exceeds 30%.

A fifth aspect of the present invention is the method according to any one of the first to fourth aspects, wherein at least a part of the blast furnace charge is reduced by adjusting the weight average of the preliminary reduction rate of the blast furnace charge. A blast furnace operating method characterized in that a pre-reduced sintered ore is blended in a ratio of 20% or more to less than 70%. The preliminary reduction rate of the blast furnace raw material is the average preliminary reduction obtained as a weighted average value of the reduction rates of the individual raw materials constituting the blast furnace raw material such as ordinary sinter, preliminary reduced sinter, and iron scrap. It can be obtained as a rate.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the calorific value of blast furnace generated gas is controlled by adjusting the preliminary reduction rate of the blast furnace raw material to be 20% or more and less than 70%. It is based on the knowledge that the inventors theoretically found from a list diagram based on the overall material and heat balance. Regarding this finding, that is, by changing the pre-reduction rate (degree of oxidation) of iron ore, which is a blast furnace charge, it is possible to control the calorific value of blast furnace generated gas without depending on the fuel ratio of the blast furnace. This will be described with reference to the drawings. FIG. 1 is a graph showing the gas temperature distribution inside the blast furnace, and FIG. 2 is a graph showing the relationship between the reduction equilibrium of iron oxide, the actual gas composition in the furnace, and the degree of iron oxide oxidation.

In FIG. 1, the gas temperature inside the blast furnace is about 150 to 200 ° C. at the top of the furnace and 2000 to 2400 ° C. at the tuyere. Further, the shaft portion has a so-called heat preservation zone, which is a constant temperature region of approximately 1000 ° C. In this heat preservation zone, iron oxide is present in the gas composition and reduction stage slightly deviating from the FeO-Fe reduction equilibrium. In FIG. 2, the horizontal axis in the upper part indicates the degree of oxidation of the gas in the blast furnace (in other words, the ratio of oxygen atoms to carbon atoms, O / C). The degree of oxidation of the gas is 1 when the gas composition is only CO in the lower part of the blast furnace, and the gas moves to the upper part while reducing iron oxide, and finally the total amount of CO is reduced.
₂ when it is ₂ (+ N ₂ ). On the other hand, the vertical axis indicates the oxygen atom ratio to the iron atom (O / Fe). The state with the highest degree of oxidation at the time of charging is Fe ₂ O ₃ (degree of oxidation = 1.5). As the reduction proceeds sequentially in the blast furnace, Fe ₃ O ₄ (degree of oxidation = 1.33), FeO ( The oxidation degree becomes 1.05), and finally becomes metallic iron (oxidation degree = 0). In addition, if this is represented by a reduction rate, Fe ₂ O ₃ (reduction rate = 0%), Fe ₃ O
₄ (reduction rate = 11.3%), FeO (reduction rate = 30)
%) And metallic iron (reduction rate = 100%).

The lower part of FIG. 2 is an equilibrium diagram of the reduction of iron oxide by CO. The horizontal axis represents the degree of oxidation of the gas as described above, and the vertical axis represents the reduction equilibrium temperature. According to FIG.
When the temperature is set to 00 ° C., the F at this temperature is lower than the lower stage in FIG.
The degree of gas oxidation (O / C) at the time of e-FeO reduction equilibrium is determined. Since the degree of oxidation of ore (FeO) is 1.05, the point W in the upper part of FIG. 2 is obtained.

On the other hand, an ore having an oxidation degree of 1.5 (Fe₂O₃)
Is charged from the furnace top, a straight line PT-PB (hereinafter referred to as an operation line)
Along with the degree of oxidation of ore and gas
I do. The fuel ratio of the blast furnace is determined by the gradient of this straight line (C / Fe).
Is determined. Operation of the blast furnace is ideal, and reduction equilibrium is reached.
If so, this line touches point W and the fuel ratio is
Take the minimum value. However, in actual blast furnaces, iron oxide reduction
The operation line does not pass through the point W because it deviates from the equilibrium.
Pass through a point. Where the straight line P₀−W and straight line P₀−P ₁Length of
Ratio (P₀−W) / (P₀−P₁) Is the reduction equilibrium of the blast furnace
It indicates the degree of achievement and is called shaft efficiency. Through
The shaft efficiency of a blast furnace is usually 0.90 to 0.95.
You.

When the preliminary reduction rate of the blast furnace charge is set to 20% or more and less than 30% as in the second invention, the oxidation degree of the blast furnace charge is lower than 1.5. It becomes P _{T ''} on behalf of the P _T. As a result, the gas composition (oxidation degree) also decreases, and as a result, the calorific value of the blast furnace generated gas increases. However, in this case, since the gradient of the operation line does not change, the fuel ratio does not change in principle. That is, it is possible to control the calorific value of the blast furnace generated gas while maintaining the fuel ratio of the blast furnace substantially constant.

Further, as in the third invention, the blast furnace charge
If the reserve rate exceeds 30%, the ordinate of point W is
It moves to the W 'point lower than 1.05. Constant shaft efficiency
Assuming that the operating line is the shaft efficiency (P₀−P₁’/
P₀-W ') is constant ₁’Point,
As a result, the slope of the operation line becomes smaller, and the fuel ratio decreases.
However, in this case, there is no decrease in the degree of oxidation of the gas.
It is assumed that the calorific value of the generated gas does not change. Sand
That is, the calorific value of the gas generated from the blast furnace regardless of the fluctuation of the blast furnace fuel ratio
Can be controlled to be substantially constant.

That is, the preliminary reduction rate of the blast furnace raw material is 3
If it is less than 0% (up to the FeO reduction stage), the degree of oxidation of the blast furnace generated gas decreases in accordance with the preliminary reduction rate, and as a result, the calorific value of the blast furnace generated gas increases. In this case, it is not possible to reduce the fuel ratio of the blast furnace, and consequently the amount of blast furnace generated gas (= carbon dioxide gas generation), but if the blast furnace generated gas is used as fuel for heating furnaces in steelworks, Since the calorific value of the gas generated from the blast furnace is improved, the total energy consumption of the steelworks can be reduced. In addition, the preliminary reduction rate is 20
%, The effect of increasing the calorific value of the blast furnace generated gas is small.

On the other hand, the preliminary reduction rate of the blast furnace raw material is 30%.
In the above (reduction stage in which FeO and some metallic iron are present), the fuel ratio of the blast furnace can be reduced according to the preliminary reduction rate, and as a result, the amount of gas generated from the blast furnace (= carbon dioxide gas generation amount) can be reduced. However, in this case, a decrease in the degree of oxidation of the blast furnace generated gas (= an increase in the calorific value) cannot be expected. The preliminary reduction rate of the blast furnace raw material is theoretically 100% by increasing the proportion of iron scrap or the like whose reduction rate is close to 100%.
Is possible. However, in the actual operation, when the preliminary reduction rate becomes 30% or more, the furnace top temperature rises, and it is necessary to take measures to decrease the furnace top temperature.
% Or more, the current measures cannot suppress the rise in furnace top temperature. Therefore, in the present invention, the preliminary reduction rate is set to less than 70%.

Next, a method of adjusting the pre-reduction rate of the blast furnace raw material to a predetermined range in the present invention will be described.
In a sintered ore, which is a normal blast furnace charge, FeO is 5 wt.
%, About 1 wt. %, But since Fe is almost in the state of Fe ₂ O ₃ , the degree of oxidation is close to 1.5, and the preliminary reduction rate of the entire blast furnace raw material is at most about 2%. Therefore, in order to adjust to the range of the preliminary reduction rate of the present invention, in addition to iron scrap and reduced iron close to metallic iron (reduction rate = 100%), the present inventors have disclosed in Japanese Patent Application No. 10-3.
What is necessary is just to mix and mix the pre-reduced sinters described in detail in US Pat.

Japanese Patent Application No. 10-369818 discloses that when sintering is produced by firing with an endless moving grate type sintering machine, at least the SiO ₂ content in the compounding raw material is 6 watts.
t. %, A primary granulation step of mixing a predetermined amount of the solid fuel (A) having a particle diameter adjusted to 1 mm to 10 mm with the compounded raw material to form a granulated product, A secondary granulation step of mixing and granulating a predetermined amount of the solid fuel (B) whose particle diameter has been adjusted to 5 mm or less to form pseudo-particles coated with the solid fuel (B) is carried out. A prereduction sinter having a reduction ratio of 20% or more and less than 30% or 30% or more and less than 90% is obtained. From the viewpoint of making the ratio of the solid fuel appropriate, the preliminary reduction rate is 70%.
The following are preferred. Therefore, in adjusting the weight-average value of the preliminary reduction rate of the blast furnace charge, at least a part of the blast furnace charge is mixed with the pre-reduced sintered ore having a reduction rate of 20% or more and less than 70%. Is preferred.

In this case, the ratio of the sum of the weights of the solid fuel (A) and the solid fuel (B) is 4.5 wt. % To 30.0w
t. %, And the value of the weight ratio (A) / (B) of the solid fuel (A) and the solid fuel (B) is preferably 0.8 or more. In addition, solid fuel (A) for 1t of product sintered ore
And the sum of the weights of the solid fuel (B) and the solid fuel (B) is 50 kg / t or more, and the ratio (A) of the weight of the solid fuel (A) to the weight of the solid fuel (B)
It is preferable to adjust the blending amount of the solid fuel so that the value of / (B) becomes 0.8 or more.

As the solid fuel (A) and the solid fuel (B), coke breeze is usually used. For example, when the target value of the preliminary reduction rate is set in the range of 20% or more and less than 30%, Of the coke breeze of 4.5 wt. % To 8.5 wt. %, The correlation between the preliminary reduction rate and the ratio of coke breeze in the mixed raw material is determined, and the ratio of coke breeze in the mixed raw material is determined based on the correlation. Similarly, when the pre-reduction rate is set in the range of 30% or more and less than 70%, the ratio of the solid fuel in the mixed raw material is set to 8.5 w
t. % To 30 wt. The correlation may be obtained by changing the correlation in the range of%.

The amount of coke breeze to be added may be represented by a coke ratio which is a ratio to a mixed raw material, or may be represented by a unit of coke per ton of sintering production. Using the following relational expression, conversion between the coke ratio and the coke intensity can be performed. Coke basic unit (kg / t) = ｛Coke ratio (%) ×
(Use of new raw materials (kg / t) + return of ore (kg / t)
t))｝ / (new material usage (kg / t) × sintering yield (%)) × 1000

The above-mentioned reduced iron is obtained, for example, by a shaft furnace type Midrex process, a Hyl-III process,
The rotary kiln type is manufactured by the SL / RN process or the like.
%, But the strength of the product reduced iron is low,
Since the production amount is small and it can be used as a raw material for blast furnace, it is not very suitable.
It is preferable to use the pre-reduced sintered ore described in No. 18.

In the present invention, the pre-reduction ratio of the pre-reduction sintered ore is 7
The reason for making the pre-reduction rate less than 0% is that if the pre-reduction rate is to be 70% or more, the solid fuel ratio such as coke breeze becomes too high, so that a melting phenomenon occurs in the sintering process, and as a result, the reduction is hindered by gas drift. This is because it is difficult to set the preliminary reduction rate to 70% or more, and there is a problem that the sintered ore having a high reduction rate is reoxidized when stored in the yard.

The preliminary reduction rate of the blast furnace raw material is 30%.
If the temperature exceeds the upper limit, the top gas temperature of the blast furnace rises and a new problem such as exceeding the upper limit temperature of equipment maintenance of 300 ° C. occurs. Thus, the endothermic reaction when the decomposition of the crystallization water occurs can suppress the rise in the furnace top gas temperature.

[0028]

EXAMPLES (First Example) In an operating blast furnace having an inner volume of 4300 m ^3, a part of or all of ordinary sinter in a charged material is replaced with pre-reduced sinter, and in some cases, further sinter is added. , Some of the pellets and lump ore in the charge were partially replaced to reduce the average preliminary reduction rate of the charge to 2
Changes were made in the range of 0% or more and less than 30% (up to 29.0%), and the changes in the blast furnace fuel ratio and the calorific value of the blast furnace generated gas at this time were investigated (Inventive Examples 1 to 4). Also, for comparison,
Similarly, the average pre-reduction rate of the raw material is reduced to 10% by partially replacing the normal sinter in the raw material with the preliminary reduced sinter.
The blast furnace fuel ratio and the change in the calorific value of the blast furnace generated gas at this time were also examined (Comparative Examples 1 to 3). The results are shown in Table 1.

The operating specifications of the blast furnace at that time are shown in Table 3, but conditions other than the charged raw materials were not changed as much as possible. The preliminary reduced sinter used was adjusted to have an average preliminary reduction ratio of about 30% by the production method of Japanese Patent Application No. 10-369818, as shown in Table 1. The values of the pre-reduction ratios of the pre-reduction sintered ores used in Comparative Examples 1 to 4 and Comparative Examples 1 to 3 slightly vary.

As shown in Table 1, in the case of Invention Examples 1 to 4 in which the average preliminary reduction rate of the charged raw material is 20% or more and less than 30%, the calorific value of the blast furnace generated gas is almost proportional to the preliminary reduction rate. It can be seen that it rises. On the other hand, in Comparative Examples 1 to 3 in which the average preliminary reduction rate is less than 20%, the change in the calorific value of the blast furnace generated gas is small even if the preliminary reduction rate of the charged material changes. It was also confirmed that the fuel ratio hardly changed even when the average pre-reduction rate of the charged raw material changed in the range of 20% or more and less than 30%.

Therefore, as the present inventors have reasoned theoretically, the fuel ratio of the blast furnace is substantially constant by adjusting the average preliminary reduction rate of the blast furnace feedstock to be 20% or more and less than 30%. It was confirmed that it was possible to control the calorific value of the blast furnace generated gas while maintaining the temperature.

Next, how to determine the preliminary reduction rate of the sinter ore and the average preliminary reduction rate of the charged material will be described. In generally Fe analysis of ores, total iron (T.Fe), 2-valent iron ^{(Fe 2} +), metal iron (M.Fe) is actually measured, trivalent iron ^{(Fe 3+)} All It can be obtained by subtracting divalent iron (Fe ²⁺ ) and metallic iron (M.Fe) from iron (T.Fe).
In the pre-reduced sinter less than 0%, the metallic iron content (M.Fe)
Is almost not contained, so that the trivalent iron (Fe ³⁺ ) can be obtained by subtracting the divalent iron (Fe ²⁺ ) from the total iron (T.Fe). The pellets and lump ores charging the raw material of the divalent iron ^{(Fe 2+)} in is hardly contained, 5～6W usually sinter divalent iron ^{(Fe 2+)} is in FeO in terms
t. %included. The pre-reduction ratios of the ordinary sinter and the pre-reduction sinter are respectively 30% × (Fe ²⁺ ) / (TF
e). Therefore, the average preliminary reduction rate of the raw material was determined as a weighted average value of the reduction rates of the ordinary sinter and the preliminary reduced sinter in the raw material.

(Second Embodiment) In order to change the average pre-reduction ratio of the charged raw material in the range of 30% or more and less than 60%, a pre-reduction sintered ore having a reduction ratio of approximately 60% was produced. In the blast furnace in operation with an internal volume of 4300 m ³ as in the case of the embodiment of the present invention, first, the normal sinter in the charged material is partially replaced with this pre-reduced sinter. ,
By partially replacing the pellets and lump ore in the charge with metal scrap, the average pre-reduction rate of the charge is changed from 30% to about 60%, and the blast furnace fuel ratio and the calorific value of the blast furnace generated gas are reduced. Changes were investigated (Examples 11 to 1 of the invention)
4). Table 2 shows the results. The operating parameters of the blast furnace at this time are as shown in Table 3, and the conditions other than the charged raw materials are not changed as much as possible, as in the first embodiment.

As a result, as shown in Table 2, Inventive Example 1 in which the average preliminary reduction rate of the charged material was 30% or more and less than 60%.
In the case of Nos. 1 to 14, the blast furnace fuel ratio was reduced (approximately 20%) almost in proportion to the average preliminary reduction rate, but the calorific value of the blast furnace generated gas was hardly changed. Therefore, it is possible to control the fuel ratio of the blast furnace while maintaining the calorific value of the gas generated from the blast furnace substantially constant by adjusting the preliminary reduction rate of the raw material charged in the blast furnace to be 30% or more and less than 60%. It was confirmed that.

In this embodiment, if the preliminary reduction ratio of the raw material charged in the blast furnace exceeds 30%, the temperature of the top gas of the blast furnace rises and exceeds the upper limit temperature of 300 ° C. for equipment maintenance. A part of the lump ore in the charged raw material has a water content of crystallization of 10 wt. % Of highly crystalline water ore (Pisolite). Crystal water content of 10 wt. % Of high-crystal water ore in the raw material is 15% to increase the furnace top gas temperature to 250 ° C.
The following could be suppressed. Further, although the average preliminary reduction ratio of the blast furnace charge is as high as 50% or more as in Invention Example 14, the ratio of the high crystalline water ore in the charge is 10%.
In the case of less than the following, the furnace top gas temperature was lowered by using the furnace top sprinkling which has been conventionally performed.

It is to be noted that the pre-reduction rate can be further increased by increasing the amount of iron scrap in the charged material as compared with Example 14 of the present invention. The furnace top temperature can be suppressed to 300 ° C. or lower by the combined use or the spraying of the furnace top. However, when the pre-reduction rate becomes 70% or more, these means reduce the furnace top temperature to 3%.
It is difficult to keep the temperature below 00 ° C.

In determining the pre-reduction rate of the charged raw material, in the pre-reduction sintered ore having a reduction rate of 30% or more as in this embodiment, metallic iron (M.Fe) is generated. Valent iron (Fe ³⁺ ) is determined by subtracting divalent iron (Fe ²⁺ ) and metallic iron (M.Fe) from total iron (T.Fe). The preliminary reduction rate of the preliminary reduction sinter is 30% ×
(Fe ²⁺ ) / (T.Fe) + 100% × (M.Fe)
/(T.Fe). The average pre-reduction rate of the raw material was determined as a weighted average of the reduction rates of the ordinary sinter, the pre-reduced sinter, and the metal scrap in the raw material. The pre-reduction rate of metal scrap in the charged raw material is 100%.
%.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

According to the present invention, by adjusting the preliminary reduction rate of the blast furnace raw material to be 20% or more and less than 30%, the blast furnace fuel gas can be maintained at a substantially constant value while maintaining the blast furnace fuel ratio at a substantially constant value. It is possible to control the amount of heat generated. Further, by adjusting the pre-reduction rate of the blast furnace raw material to be 30% or more and less than 70%, it is possible to control the fuel ratio of the blast furnace while maintaining the calorific value of the blast furnace generated gas substantially constant. is there. Therefore, the calorific value of the blast furnace generated gas can be controlled without depending on the fuel ratio of the blast furnace. In addition, by using high-crystal water ore, the preliminary reduction rate of the blast furnace raw material is reduced to 30 wt. % Or more, it is possible to suppress a rise in the furnace top gas temperature that occurs when the temperature is set to be equal to or more than 10%.

[Brief description of the drawings]

FIG. 1 is a view showing a gas temperature distribution in a blast furnace.

FIG. 2 is a diagram showing the relationship between the reduction equilibrium of iron oxide, the degree of oxidation of gas in a blast furnace, and the degree of oxidation of iron oxide.

Claims (5)

[Claims] 1. A method for operating a blast furnace, wherein a preliminary reduction ratio of a raw material charged to a blast furnace is adjusted to be 20% or more and less than 70% to control a calorific value of gas generated from a blast furnace. 2. A method for controlling a calorific value of gas generated from a blast furnace while maintaining a fuel ratio of the blast furnace substantially constant by adjusting a pre-reduction rate of a raw material charged in the blast furnace to be 20% or more and less than 30%. Characteristic blast furnace operating method. 3. The method according to claim 1, wherein the preliminary reduction rate of the raw material charged in the blast furnace is adjusted to be 30% or more and less than 70% so that the calorific value of the gas generated from the blast furnace is controlled to be substantially constant irrespective of a change in the blast furnace fuel ratio. Characteristic blast furnace operating method. 4. The method according to claim 1, wherein the preliminary reduction rate of the blast furnace charge is adjusted to be 30% or more and less than 70%, and high crystal water ore is used as a part of the blast furnace charge. 3. The blast furnace operating method according to 3. 5. A method for adjusting the preliminary reduction rate of the blast furnace charge, wherein at least a part of the blast furnace charge has a reduction rate of 2%.
The blast furnace operating method according to any one of claims 1 to 4, wherein the pre-reduced sintered ore is blended in a range of 0% or more and less than 70%.