TWI859671B - Blast furnace operation method - Google Patents

Abstract

The present invention provides a blast furnace operation method, which can improve the properties of the slag generated in the lower part of the furnace and ensure the air permeability in the fusion zone and dripping zone in the furnace even if the FeO component in the slag is reduced when the blast furnace operation is implemented to generate a high-concentration reducing gas in the furnace in front of the tuyere. The blast furnace operation method of the present invention is to charge iron-based raw materials, auxiliary raw materials and coke from the top of the blast furnace, and blow gas from the tuyere of the blast furnace to generate a high-concentration reducing gas in the furnace in front of the tuyere, and the blast furnace operation method sets the alkalinity of the total raw material components of the iron-based raw materials and the auxiliary raw materials to a specified range. In this case, it is preferred to set the alkalinity of the total raw material components to a range of 1.0 or more and 1.7 or less.

Description

Blast furnace operation method

The present invention relates to a blast furnace operating method for generating high-concentration reducing gas in the blast furnace in front of the tuyere. More specifically, it relates to a blast furnace operating method for improving the properties of slag in the molten zone and dripping zone in the blast furnace to increase the permeability in the blast furnace.

In recent years, there has been a trend to reduce the emission of _CO2 gas (carbon dioxide gas), which is one of the greenhouse gases. In the iron smelting process using blast furnaces, carbon materials are used as reducing materials, so a large amount of _CO2 gas is generated. Therefore, the steel industry has become one of the major industries in terms of _CO2 gas emissions, and must respond to the social demand for reducing _CO2 gas emissions. Specifically, further reduction of the ratio of reducing materials derived from coal in blast furnace operations has become a top priority. The so-called ratio of reducing materials derived from coal refers to the combined mass of coke derived from coal and reducing gases derived from coal required to produce 1 ton of molten iron.

The reducing materials have the function of increasing the temperature of the charge by becoming heat in the furnace, and reducing the iron ore, sintered ore of iron ore, and iron ore particles in the furnace, which are iron-based raw materials. In order to reduce the reducing material ratio and reduce the emission of _CO2 gas, it is necessary to improve the reduction efficiency of the reducing materials while maintaining the heat in the furnace.

Hydrogen equipment has attracted much attention as a reducing material for reducing _CO2 gas emissions. The reduction of iron ore using hydrogen is an endothermic reaction, but its endothermic amount is smaller than that of a direct reduction reaction (reaction formula: FeO+C→Fe+CO), and the reduction rate based on hydrogen is faster than that based on CO gas. Therefore, by blowing hydrogen-based gas into a blast furnace, it is possible to simultaneously reduce _CO2 gas emissions and improve reduction efficiency.

For stable operation of the blast furnace, it is necessary to ensure the air permeability of the melting zone where the iron-based raw materials are melted in the blast furnace. However, in the blast furnace operation that generates high-concentration reducing gas in the furnace before the tuyere, and in the blast furnace operation that has a high concentration of reducing gas in the furnace and a faster reduction reaction rate than the previous operation, the air permeability in the blast furnace is not clear.

While producing ferromillite, blast furnaces also produce a large amount of blast furnace slag (containing oxides such as FeO, CaO, _Al2O3 , MgO, and _SiO2 ) as a by-product. In order to maintain good air permeability in the _furnace , it is necessary to design raw materials that can suppress the viscosity of the produced blast furnace slag to a low level and ensure liquid permeability.

As prior art for solving problems similar to the above-mentioned subject, the technologies disclosed in Patent Documents 1 to 3 are proposed.

Patent document 1 discloses a blast furnace operation in which _coke is charged from the furnace top and auxiliary fuel is blown in from the tuyere. According to Patent document 1, by setting the ratio of _Al2O3 to _SiO2 ( _Al2O3 / _{SiO2 )} of coke and auxiliary fuel to 0.6 or more, and setting the alkalinity of blast furnace slag ((CaO+ _Al2O3 +MgO ₎ / _SiO2 ) to 1.8 or more, the properties of blast furnace slag can be improved, and the gas permeability and liquid permeability can be increased.

Patent document 2 discloses a method for operating a blast furnace in which pulverized coal (150 kg or more per ton of iron produced) is blown into the blast furnace together with hot air from the tuyere. According to patent document 2, by using sintered ore having a _SiO2 component of 4.0 mass% to 4.8 mass%, a MgO component of 1.2 mass% to 2.4 mass%, a CaO component of 6.0 mass% to 9.0 mass%, and an _Al2O3 component of 1.9 mass% to 2.5 mass% as more than 80% of the charge other than coke charged from the _furnace top, the viscosity of the dripping slag can be suppressed to be low even if the FeO component of the slag composition is reduced.

Patent document 3 discloses a method for operating a blast furnace using a _{sintered ore} with high strength (shatter index (SI)>92%) and high reducibility (reducibility index (RI)>70%) by adjusting the blending ratio of auxiliary raw materials according to the amount of Al2O3 in the sintered ore commonly used. According to Patent document 3, by injecting an auxiliary raw material in an amount corresponding to the difference in the blending ratio of the auxiliary raw materials of the sintered ore with high strength and high reducibility and the sintered ore commonly used from the tuyere of the blast furnace, a high ore/reduced material ratio operation can be performed stably for a long period of time.

[Prior art literature]

[Patent Literature]

Patent document 1: Japanese Patent Publication No. 2004-10948

Patent document 2: Japanese Patent Publication No. 9-13107

Patent document 3: Japanese Patent Publication No. 2005-298923

However, these existing technologies all target the operation of a blast furnace in which by-raw materials such as _SiO2 powder, auxiliary fuels containing CaO or _SiO2 , or pulverized coal are blown into the furnace from the tuyere, and do not mention the raw material components or slag components in the blast furnace operation in which a high-concentration reducing gas is produced in the furnace in front of the tuyere.

In the blast furnace operation of the present invention, the concentration of the reducing gas generated in the furnace in front of the tuyere is very high. Therefore, the reduction rate of the iron-based raw materials in the furnace increases and the FeO concentration in the slag decreases, and the FeO component in the slag decreases to a range lower than the operating range described in the prior art. The prior art does not take into account the further reduction of the FeO component in the slag.

That is, when the operation is performed in such a manner that the high-concentration reducing gas generated in the furnace before the tuyere becomes within the range of region A in FIG. 1 (the description of FIG. 1 will be described later) (including the range of _H2 gas = 0 volume % to 100 volume %, _N2 gas = 0 volume % to 71 volume %, CO gas = 0 volume % to 100 volume %), the reduction of the iron-based raw materials from low temperatures is promoted more than in the previous operation, and the reduction rate of the iron-based raw materials reaching the lower part of the furnace is increased. In this case, if the state of the previous operation method is maintained, the slag permeability may be reduced due to the reduction of the FeO component in the slag, the slag may be retained in the gaps of the coke layer, the ventilation resistance in the furnace may increase, and fumes may be induced.

The present invention is made in view of the above situation, and its purpose is to provide a blast furnace operation method, which improves the slag properties when the blast furnace operation is implemented to generate high-concentration reducing gas in the furnace in front of the tuyere, and even if the FeO content in the slag is reduced, the air permeability in the molten zone and dripping zone in the blast furnace can be ensured.

The gist of the present invention for solving the above-mentioned problem is as follows.

[1] A blast furnace operation method, wherein iron-based raw materials, auxiliary raw materials and coke are charged from the top of the blast furnace, and gas is blown from the tuyere of the blast furnace to generate high-concentration reducing gas in the furnace in front of the tuyere, wherein the alkalinity of the total raw material component of the iron-based raw materials and the auxiliary raw materials is set within a specified range.

[2] A blast furnace operating method as described in [1], wherein the alkalinity of the total raw material components is set within a range of greater than 1.0 and less than 1.7.

[3] A blast furnace operating method as described in [1], wherein the high-concentration reducing gas has the following composition when expressed as a bosh gas composition, namely, it includes _H2 gas, _N2 gas and CO gas, and the ratio of _H2 gas, _N2 gas and CO gas is at a point where _{H2 gas} : 0 volume%, _{N2 gas} : 0 volume%, CO gas: 100 volume%, _H2 gas: 100 volume%, _N2 gas: 0 volume%, CO gas: 0 volume%, _H2 gas: 29 volume%, _N2 gas: 71 volume%, CO gas: 0 volume%, and _H2 gas: 0 volume%, N2 gas: 10 ... ₂ gas: 37 volume %, CO gas: 63 volume % The composition within the area surrounded by these four points includes H ₂ gas in the range of 0 volume %~100 volume %, N ₂ gas in the range of 0 volume %~71 volume %, and CO gas in the range of 0 volume %~100 volume %.

[4] A blast furnace operating method as described in [2], wherein the high-concentration reducing gas is a composition represented by a furnace gas composition, namely, comprising _H2 gas, _N2 gas and CO gas, and the ratio of _H2 gas, _N2 gas and CO gas is at a point in a ternary system diagram of _H2 gas- _N2 gas-CO gas where _H2 gas: 0 volume%, _N2 gas: 0 volume%, CO gas: 100 volume%, _H2 gas: 100 volume%, _N2 gas: 0 volume%, CO gas: 0 volume%, _H2 gas: 29 volume%, _N2 gas: 71 volume%, CO gas: 0 volume%, and _H2 gas: 0 volume%, N2 gas: 10 ... ₂ gas: 37 volume %, CO gas: 63 volume % The composition within the area surrounded by these four points includes H ₂ gas in the range of 0 volume %~100 volume %, N ₂ gas in the range of 0 volume %~71 volume %, and CO gas in the range of 0 volume %~100 volume %.

[5] The blast furnace operating method as described in any one of [1] to [4], wherein the amount of H ₂ gas in the high-concentration reducing gas is in the range of 0 Nm ³ /molten iron-ton to 500 Nm ³ /molten iron-ton.

In the present invention, when a blast furnace operation is performed to generate a high-concentration reducing gas in the furnace before the tuyere, the alkalinity (mass% CaO/mass% _SiO2 ) of the total raw material components of the iron-based raw materials and the auxiliary raw materials is set within a specified range. Thereby, the viscosity of the slag generated in the molten zone and the dripping zone in the blast furnace is optimized, and the liquid permeability of the slag in the blast furnace is controlled within the operable range. As a result, the gas permeability in the blast furnace can be well maintained, and the stable operation of the blast furnace is achieved.

The following is an explanation of the embodiment of the present invention. The blast furnace operation method of the present embodiment is a blast furnace operation method in which iron-based raw materials, auxiliary raw materials and coke are alternately and layeredly charged into the blast furnace from the top of the blast furnace, and gas is blown into the blast furnace from a tuyere provided at the bottom of the blast furnace, and a high-concentration reducing gas is generated in the blast furnace in front of the tuyere by the gas blown from the tuyere. The iron-based raw materials include, for example, iron ore, sintered ore of iron ore, iron ore particles, reduced iron and scrap iron. The auxiliary raw materials include SiO ₂ and CaO alone or in combination. The types of the iron-based raw materials, auxiliary raw materials, and coke used are not particularly limited. If they are iron-based raw materials, auxiliary raw materials, and coke used in the previous blast furnace operation, they can also be appropriately used in the present invention.

The gas used to generate the high-concentration reducing gas includes a reducing component that reduces the iron-based raw materials in the blast furnace. Here, the reducing component that reduces the iron-based raw materials in the blast furnace includes not only CO gas, _H2 gas, and hydrocarbon gas that can reduce the iron-based raw materials, but also _CO2 gas, _H2O gas, and other components that generate reducing gas by reaction or decomposition reaction with coke.

Fig. 1 is a diagram showing the composition range of the high-concentration reducing gas generated in the furnace before the tuyere by the blast furnace operation method of this embodiment in the gas component composition of the ternary system diagram of _H2 gas- _N2 gas-CO gas, using the belly gas composition. The so-called high-concentration reducing gas in this embodiment is a reducing gas in which the average reduction rate of the iron-based raw material is 80% or more when the high-concentration reducing gas is used to reduce the iron-based raw material at 900°C for 180 minutes. When the reducing gas is represented by the furnace gas composition, it is a composition including _H2 gas, _N2 gas and CO gas, and the ratio of _H2 gas, _N2 gas and CO gas (wherein the ratio is assumed to be _H2 gas + _N2 gas + CO gas = 100 volume %) is within the range of area A (the operating range of the present invention) represented by the oblique line portion in FIG. 1, and includes _H2 gas in the range of 0 volume % to 100 volume %, _N2 gas in the range of 0 volume % to 71 volume %, and CO gas in the range of 0 volume % to 100 volume %.

Region A is a range surrounded by _four points, namely, point O (H ₂ gas: 0 volume%, N ₂ gas: 0 volume%, CO gas: 100 volume%), point P (H ₂ gas: 100 volume%, N ₂ gas: 0 volume%, CO gas: 0 volume%), point Q (H ₂ gas: 29 volume%, N ₂ gas: 71 volume%, CO gas: 0 volume%), and point R (H ₂ gas: 0 volume%, N ₂ gas: 37 volume%, CO gas: 63 volume%), in the ternary system diagram of H ₂ gas-N 2 gas-CO gas. In addition, FIG. 1 shows a comparative gas composition of a general blast furnace operation range in the past. In the area A, within the range surrounded by the four points O (H ₂ gas: 0 volume %, N ₂ gas: 0 volume %, CO gas: 100 volume %), point P (H ₂ gas: 100 volume %, N ₂ gas: 0 volume %, CO gas: 0 volume %), point Q' (H ₂ gas: 43 volume %, N ₂ gas: 57 volume %, CO gas: 0 volume %) and point R' (H ₂ gas: 0 volume %, N ₂ gas: 14 volume %, CO gas: 86 volume %), the average reduction rate of the iron-based raw material when reduced at 900°C for 180 minutes is above 90%, so the FeO content in the slag component in the molten zone in the furnace is significantly reduced. Therefore, when a high-concentration reducing gas within this composition range is generated in the furnace before the tuyere, the effect of adjusting the alkalinity (mass% CaO/mass% SiO ₂ ) of the total raw material components for recovering the dripping amount of the molten material including slag becomes higher.

The inventors of the present invention used a small test furnace with a scale of 1/4 that simulated a blast furnace to conduct an experiment to generate a high-concentration reducing gas in the furnace in front of the tuyere and investigate the slag composition in the molten zone and dripping zone in the furnace. Table 1 shows an example of the composition of the iron-based raw materials used in the small test furnace.

In a small test furnace, the following test was conducted, i.e., the formula of the iron-based raw material, auxiliary raw material and coke was set to the same as the operation method described in Patent Document 2, and the alkalinity of the total raw material components of the iron-based raw material and auxiliary raw material was 2.0, and a high-concentration reducing gas was generated in the furnace before the tuyere. Under the test conditions, the slag components in the molten zone in the furnace were calculated to have an FeO component of less than 3.5% by mass, an _SiO2 component of 25.4% to 28.3% by mass, _{an Al2O3} component of 8.6% to 9.2% by mass, a CaO component of 52.5% to 56.7% by mass, and an MgO component of 5.3% to 7.3% by mass. Since the alkalinity of the slag increased to about 2.0 and the amount of slag dripping decreased to about one-tenth of that in the previous test, the gas permeability deteriorated to a level beyond the range in which the test could be continued stably.

It is believed that the alkalinity of the generated slag must be reduced when increasing the amount of slag dripping. Therefore, the alkalinity of the total raw material components of iron-based raw materials and auxiliary raw materials was changed within the range of 0.95~2.23, and a test was conducted to generate high-concentration reducing gas in the furnace before the tuyere to investigate the effect of the alkalinity of the total raw material components on the amount of molten material dripping and the ventilation resistance index KS.

Regarding the amount of molten material dripping, the molten material dripping during the test was recovered after the experiment, and its total weight was measured using a weight meter. The ventilation resistance index KS was calculated as the integral value of the ventilation resistance K value (1/m) calculated based on the pressure loss measured in the range of the furnace temperature above 1000°C and the physical property value estimated based on the operating conditions.

<Calculation method of ventilation resistance index KS>

The ventilation resistance K value (1/m) is calculated using the following formula (1).

K=(△P/H)/(ρ _gas ^0.7 ×μ _gas ^0.3 ×v _gas ^1.7 )...(1)

Here, ΔP is the pressure loss (Pa), H is the thickness of the filling layer in the furnace (m), ρ _gas is the gas density (kg/m ³ ), μ _gas is the gas viscosity (Pa.s), and v _gas is the gas flow rate (m/s). ΔP is obtained by installing a pressure gauge on the furnace wall at the tuyere and the upper part of the test furnace (the space above the filling layer) and calculating the pressure difference. Regarding H, a measuring jig is inserted from a hole drilled in the upper part of the test furnace, for example, to measure the position of the filling layer surface, and the distance in the height direction between the filling layer surface position and the position where the tuyere is installed is used as H. The position of the filling layer surface can be measured using a laser distance meter. ρ _gas can be calculated based on the composition of the gas introduced from the tuyere, the temperature in the furnace, and the pressure in the furnace. μ _gas can be calculated based on the composition of the gas introduced from the tuyere, and the temperature in the furnace. v _gas can be calculated based on the flow rate of the gas introduced from the tuyere, the temperature in the furnace, and the pressure in the furnace. Here, the temperature in the furnace is obtained by installing a plurality of thermometers on the furnace wall at a position corresponding to the filling layer, and using the average value of the measured values of the thermometers. Similarly, the pressure in the furnace is obtained by installing a plurality of pressure gauges on the furnace wall at a position corresponding to the filling layer, and using the average value of the measured values of the pressure gauges. The average value of the pressure at the tuyere used in the calculation of ΔP and the pressure on the top of the filling layer can also be used as the pressure in the furnace.

The ventilation resistance index KS is calculated using the following formula (2).

In formula (2), Tmax is the maximum temperature for measuring the pressure loss in the furnace. Although it is different for each measurement, it is around 1500℃~1650℃.

Figure 2 is a graph showing the effect of the alkalinity of the total raw material components on the amount of melt dripping in an experiment in which a high-concentration reducing gas is generated in the furnace before the tuyere. The horizontal axis of Figure 2 is the alkalinity of the total raw material components (mass%CaO/mass% _SiO2 ), and the vertical axis is the amount of melt dripping (g).

Fig. 3 is a graph showing the effect of the alkalinity of the total raw material components on the ventilation resistance index KS in an experiment in which a high-concentration reducing gas is generated in the furnace before the tuyere. The horizontal axis of Fig. 3 is the alkalinity of the total raw material components (mass%CaO/mass% _SiO2 ), and the vertical axis is the ventilation resistance index KS ( ¹⁰⁵ ℃/m).

As shown in Figure 2, the amount of molten material dripping increases when the alkalinity of the total raw material components of the iron-based raw materials and auxiliary raw materials is in the range of 1.0 to 1.7. In addition, as shown in Figure 3, it is confirmed that the ventilation resistance index KS decreases to below 2000, which is the target value, when the alkalinity of the total raw material components of the iron-based raw materials and auxiliary raw materials is in the range of 1.0 to 1.7. The target value of the ventilation resistance index KS of 2000 is the threshold value for the test to continue stably. The so-called stable test refers to a test in which the surface height of the filling layer decreases uniformly with respect to time, and no faults such as fumes occur.

Based on these results, it was confirmed that by setting the alkalinity of the total raw material components of the iron-based raw materials and auxiliary raw materials in the range of 1.0 to 1.7, it was possible to stably conduct an experiment to generate a high-concentration reducing gas in the furnace before the tuyere.

The blast furnace operation method of this embodiment is based on the test results, and is a blast furnace operation method in which iron-based raw materials, auxiliary raw materials and coke are charged from the top of the blast furnace, and gas is blown from the tuyere of the blast furnace to generate high-concentration reducing gas in the furnace in front of the tuyere, and the alkalinity of the total raw material components of the charged iron-based raw materials and the charged auxiliary raw materials is set within a specified range.

Here, the alkalinity of the total raw material components of the charged iron-based raw materials and the charged auxiliary raw materials is preferably within the range of 1.0 or more and 1.7 or less. This can improve the dripping and air permeability of the molten material in the lower part of the blast furnace. When the alkalinity of the total raw material components of the iron-based raw materials and the auxiliary raw materials is less than 1.0, and when the alkalinity of the total raw material components of the iron-based raw materials and the auxiliary raw materials exceeds 1.7, the viscosity of the slag increases and deviates from the stable operating range, which is not good.

Furthermore, the alkalinity of the total raw material components of the charged iron-based raw materials and auxiliary raw materials is preferably 1.1 or more and 1.7 or less, and further preferably 1.4 or more and 1.5 or less. Thereby, the viscosity of the slag is further reduced, and the dripping and air permeability of the molten material can be further improved. When adjusting the raw materials, it is preferred to set the slag amount to 400kg/molten iron-ton or less. By setting the slag amount to 400kg/molten iron-ton or less, the decrease in air permeability caused by the increase in the amount of molten material melted out from the low temperature area can be suppressed.

In addition, the high-concentration reducing gas preferably has an H ₂ gas amount (including hydrogen in hydrocarbons) in the range of 0 Nm ³ /molten iron-ton to 500 Nm ³ /molten iron-ton. This can suppress the decrease in the temperature in the furnace and the decrease in the reduction reaction rate. On the other hand, if the H ₂ gas amount in the high-concentration reducing gas exceeds 500 Nm ³ /molten iron-ton, the temperature in the furnace decreases and the reduction reaction rate decreases, which is not preferred. In addition, when H ₂ gas is blown in a single form, in order to keep the temperature before the tuyere within the operating range, it is preferred to blow the H ₂ gas after heating it.

As described above, in the blast furnace operation method of this embodiment, when the blast furnace operation is performed to generate high-concentration reducing gas in the furnace before the tuyere, the alkalinity of the total raw material components of the charged iron-based raw materials and the charged auxiliary raw materials is controlled within a specified range. Thereby, the viscosity of the slag generated in the molten zone and the dripping zone in the blast furnace is optimized, and the liquid permeability of the slag in the blast furnace is controlled within the range that can be operated, so that the gas permeability in the blast furnace can be well maintained, and stable operation can be achieved.

[Implementation example]

A large blast furnace was used to conduct the following blast furnace operation test, that is, iron-based raw materials, auxiliary raw materials and coke were alternately charged from the top of the furnace, the alkalinity of the total raw material composition of the iron-based raw materials and auxiliary raw materials charged from the top of the furnace was changed, and a high-concentration reducing gas was generated in the furnace in front of the tuyere. An example of the test results is shown in Table 2.

As shown in Table 2, it was confirmed that in Invention Examples 1 to 4, in which the alkalinity of the total raw material components of the iron-based raw materials and auxiliary raw materials charged from the top of the furnace was set within the range of the present invention, the dripping property and the ventilation property were good and stable operation was possible. On the other hand, in Comparative Examples 1 to 3, in which the alkalinity of the total raw material components of the iron-based raw materials and auxiliary raw materials charged from the top of the furnace was outside the range of the present invention, sufficient dripping amount could not be obtained and ventilation property was also poor.

FIG1 is a diagram showing the composition range of the high-concentration reducing gas generated in the furnace before the tuyere by the blast furnace operation method of the present embodiment, using the belly gas composition in the gas component composition of the _ternary system diagram of _H2 gas-N2 gas-CO gas.

Figure 2 is a graph showing the effect of the alkalinity of the total raw material composition on the amount of molten material dripping in an experiment in which a high-concentration reducing gas is generated in the furnace in front of the tuyere.

Figure 3 is a graph showing the effect of the alkalinity of the total raw material components on the ventilation resistance index KS in an experiment in which a high-concentration reducing gas is generated in the furnace in front of the tuyere.

Claims (3)

A method for operating a blast furnace, wherein iron-based raw materials, auxiliary raw materials and coke are charged from the furnace top of the blast furnace, and gas is blown into the furnace from the tuyere of the blast furnace so as to generate a high-concentration reducing gas in the furnace in front of the tuyere, wherein the _high -concentration reducing gas is composed of _H2 gas, _{N2 gas} and CO gas when expressed as a belly gas composition, and the ratio of _H2 gas, _N2 gas and CO gas is at a point where _H2 gas: 0 volume%, _N2 gas: 0 volume%, CO gas: 100 volume%, _H2 gas: 100 volume%, _N2 gas: 0 volume%, CO gas: ... The composition within the area surrounded by the four points of _H2 gas: 29 volume %, _N2 gas: 71 volume %, CO gas: 0 volume %, and _H2 gas: 0 volume %, _N2 gas: 37 volume %, CO gas: 63 volume %, and includes _H2 gas in the range of 0 volume %~100 volume %, _N2 gas in the range of 0 volume %~71 volume %, and CO gas in the range of 0 volume %~100 volume %, and the blast furnace operating method sets the alkalinity of the total raw material component of the iron-based raw material and the auxiliary raw material to within a specified range. A blast furnace operating method as described in claim 1, wherein the alkalinity of the total raw material composition is set within a range of greater than 1.0 and less than 1.7. The blast furnace operating method as described in claim 1 or 2, wherein the amount of H ₂ gas in the high-concentration reducing gas is in the range of 0 Nm ³ /molten iron-ton to 500 Nm ³ /molten iron-ton.