JPH05287338A - Method for operating blast furnace - Google Patents

Abstract

(57) [Summary] [Purpose] Even if pulverized coal of 170 kg / t or more is blown from the tuyere of the blast furnace, its combustibility is secured and the replacement rate with coke is kept high, while maintaining the production amount and fuel ratio. , The powdery iron source blown from the tuyere is completely reduced and melted in the raceway to maintain a constant production amount and a constant silicon content in the hot metal without increasing the coke ratio. [Composition] Two upper and lower tuyeres are installed in the lower part of the blast furnace, and at least one of a pulverized iron source or pulverized coal is blown into the blast furnace from the upper tuyeres and pulverized coal is blown into the blast furnace from the lower tuyeres. In addition, a plasma arc heater is installed at the tuyere, and the high temperature gas ejected from the plasma arc heater is blown into the blast furnace together with the powdery iron source or pulverized coal. [Effect] The powdery iron source blown from the upper tuyeres is completely reduced and melted before reaching the lower tuyeres, and the pulverized coal blown from the upper and lower tuyeres is completely burned in the raceway.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when a large amount of pulverized coal is blown from the tuyere, maintains its combustibility to maintain a high substitution rate with coke and is blown from the tuyere. The present invention relates to a blast furnace operating method for improving productivity and reducing a fuel ratio by stably reducing and melting a powdery iron source.

[0002]

2. Description of the Related Art In blast furnace operation, as an alternative to coke, an inexpensive fuel with good combustibility and high calorific value (pulverized coal, petroleum, heavy oil, naphtha, etc.) is blown from the tuyere to reduce the hot metal production cost. , Is trying to improve productivity,
The technology is disclosed in Japanese Patent Publication No. 23763. In particular, in recent years, pulverized coal injection has become the mainstream in terms of price, which greatly contributes to fuel ratio reduction (cost reduction) and productivity improvement.

The pulverized coal thus blown burns in the blast furnace instead of a part of the coke, and because of its good combustibility and high calorific value, it produces a large amount of reducing gas at high temperature and is efficient. A simple reduction reaction. Therefore, the iron ore charged from the top of the furnace is rapidly reduced to a metal state and is melted to form high-temperature hot metal, so that the furnace heat of the blast furnace is high and the productivity is improved.

Further, in recent blast furnace operation, low silicon operation is aimed at from the viewpoints of quality improvement and economical efficiency in the steelmaking process which is a post-process. As a typical operation mode of this kind, there is a method of blowing a powdered iron source such as iron oxide powder or reduced iron powder from the tuyere together with pulverized coal, which is disclosed in Japanese Patent Laid-Open No. 137402/1982. ing.

The powdered iron source such as the iron oxide powder and the reduced iron powder thus blown undergoes a reduction reaction in the blast furnace to be reduced to a metal state, and during the reduction, reacts with the hot metal in the blast furnace. 2 (Fe0) + [Si] = 2 [Fe] + (SiO
Silicon in the hot metal is reduced by the reaction of ₂ ). When the blast furnace operation is stable, the amount of iron ore charged from the top of the blast furnace can be reduced by the amount of the powdery iron source blown from the tuyere. Usually, iron ore charged from the top of the furnace is agglomerated to maintain the air permeability in the furnace, so iron ore that requires pretreatment is replaced with cheap powder. The use of the iron source is also effective in improving the economical efficiency of blast furnace operation.

[0006]

By the way, in the conventional blast furnace operation, when a large amount of pulverized coal is blown, the whole amount of the pulverized coal blown in is not burned and some unburned char is generated. This unburned char is discharged from the top of the furnace by riding the rising gas flow.
The replacement rate of pulverized coal for coke decreases, causing an increase in fuel ratio and a decrease in production. In addition, since this unburned char is captured in the coke layer (called the core) at the center of the lower part of the blast furnace, it impedes the liquid permeability of the molten pig iron flowing down in this part,
Eventually, the gas permeability of this portion will be hindered, and the production amount of the blast furnace will further decrease.

For the above reasons, there is an upper limit to the amount of pulverized coal blown in, and the following excess oxygen ratio is maintained at 1.0 or more during operation. (Excess oxygen ratio) = (Air blown from tuyere, pure oxygen, amount of oxygen in pulverized coal) /
(Amount of oxygen required to burn carbon and hydrogen in pulverized coal to CO ₂ and H ₂ O)

When the excess oxygen ratio is 1.0 or more, the total amount of carbon and hydrogen in the pulverized coal is C + O ₂ = CO ₂ , 2H + (1 /
2) CO ₂ and H ₂ O are formed by the reaction of O ₂ = H ₂ O,
This is the total amount of coke and CO ₂ + C = 2 in the raceway
CO, CO by the reaction of _{H 2 O + C = H 2} + CO, H 2
Therefore, unburned char is not generated. However, when the excess oxygen ratio is less than 1.0, the total amount does not become CO ₂ and H ₂ O, and some C (unburned char) is generated. As described above, this unburned char causes a decrease in the replacement rate and poor ventilation.

The pulverized coal injection amount when the excess oxygen ratio is 1.0 is as follows when the fuel ratio of the blast furnace is 500 kg / t-pig.
It is about 170 kg / t-pig, and this amount is the blowing limit. That is, this value is the limit of the blast furnace production amount and fuel ratio, and further improvement in productivity and reduction in fuel ratio cannot be expected.

Further, in the conventional blast furnace operation, the powdery iron source blown from the tuyere is reduced and melted into hot metal in a region called a raceway where the coke swirls and burns.
The amount of heat required for the reduction and melting is given in advance by raising the blast temperature, increasing the coke ratio, etc., but the time during which the powdery iron source stays in the raceway is extremely short, so that it cannot be completely reduced and melted. To reach the inside of the raceway (core surface layer). Then, since it accumulates in this area and a rapid reduction melting occurs, the temperature of this area is lowered, and the gas permeability and liquid permeability are impaired.

At this time, the ratio of ore and coke in the central portion (hereinafter abbreviated as O / C) is reduced, and the O / C in the intermediate portion to the peripheral portion is increased accordingly. If it is not possible to increase the O / C from the middle part to the peripheral part, reduce the O / C in the central part and the total O / C. This strengthens the gas flow in the central part and raises the temperature in this region, and maintains air permeability and liquid permeability. Reducing the overall O / C results in an increase in the coke ratio, a decrease in the production amount, and an increase in the silicon content in the hot metal, which is not preferable for blast furnace operation.

Further, the amount of the powdery iron source blown from the tuyere may be reduced or cut, which also leads to a decrease in the production amount and an increase in silicon in the hot metal. When pulverized coal is blown from the tuyere together with the pulverized iron source, the amount of heat required for the thermal decomposition of the pulverized coal is necessary in addition to the amount of heat required for the reduction and melting of the pulverized iron source. With a limited increase in blast temperature and an increase in coke ratio, there is a limit to the amount of pulverized iron source and pulverized coal injected.

Therefore, the present invention uses 170 kg / t of pulverized coal.
Even if it blows in more than that, it maintains its combustibility, maintains a high substitution rate with coke, maintains the production amount and fuel ratio, and
An object of the present invention is to completely reduce and melt a powdery iron source blown from a tuyere in a raceway and maintain a constant production amount and a constant silicon in hot metal without increasing a coke ratio.

[0014]

Means for Solving the Problems The present invention is to solve the above problems, in which a powdery iron source and pulverized coal are blown into the blast furnace from the tuyere, and iron ore and coke are alternated from the furnace top. In the blast furnace operating method of charging into the blast furnace, two upper and lower tuyeres are installed in the lower part of the blast furnace, and at least one of pulverized iron source and pulverized coal is blown from the upper tuyeres and pulverized coal is blown into the blast furnace from the lower tuyeres. It is characterized by including. Further, a plasma arc heater is installed at the tuyere, and the high temperature gas ejected from the plasma arc heater is blown into the blast furnace together with the powdery iron source or pulverized coal. The distance between the upper and lower tuyeres is 1.
It is characterized by being 0 m or more and 2.0 m or less.

[0015]

FIG. 1 shows the positions of tuyere installed in the upper and lower stages of the lower part of the blast furnace in the present invention. In FIG. 1, 1 is a blast furnace,
2 is the upper tuyeres and 3 is the lower tuyeres. The lower tuyeres are at the same height as the tuyeres installed in a normal blast furnace, but the upper tuyeres are installed 1.0 to 2.0 m above the lower tuyeres.

At least one of the powdery iron source and the pulverized coal is blown into the blast furnace from the upper tuyeres, but the blown powdery iron source is not completely reduced and melted in the raceway formed in the upper tuyeres. However, it is completely reduced and melted while reaching the lower stage tuyere installed 1.0 to 2.0 m below. The reason why the distance between the upper and lower tuyeres is 1.0 to 2.0 m is as follows.
If it is less than 0 m, the powdery iron source blown from the upper tuyeres is not completely reduced and melted while reaching the lower tuyeres, while 2.0 m
If it exceeds, the iron ore charged from the furnace top competes with the reducing and melting region, and the reduction or melting of the iron ore charged from the furnace top becomes insufficient due to the powdered iron source blown from the upper tuyeres. Because it will be.

Although pulverized coal is blown from the lower tuyeres, a part of the pulverized coal can be blown from the upper tuyeres, so that the amount of pulverized coal blown can be increased as a total amount. Therefore, the amount of pulverized coal blown when the excess oxygen ratio is less than 1.0 (170 kg /
A quantity of blow in excess of t) is achieved. This does not lead to poor air permeability, liquid permeability, increase in fuel ratio, decrease in productivity, and increase in hot metal silicon.

Further, in the present invention, a plasma arc heater may be installed at the tuyere in order to further increase the amounts of the powdery iron source and the pulverized coal blown from the upper and lower tuyeres. FIG. 2 shows a state of the plasma arc heater installed in the upper tuyeres or the lower tuyeres in the present invention. Figure 2
Here, 2 or 3 is an upper or lower tuyere, 4 is a blast branch pipe, 5 is a plasma arc heater, 6 is a powdered iron source or a pulverized coal blowing burner, 9 is an iron skin, and 10 is a brick.
Since the high temperature gas generated by the plasma arc heater can raise the blast temperature near the powder iron source or the pulverized coal injection position, the amount of heat required for the reduction and melting of the powder iron source,
The amount of heat required for the thermal decomposition of pulverized coal can be increased, and the amount of pulverized iron source and pulverized coal injected can be increased.

As another method of installing the plasma arc heater in the present invention, a probe equipped with the plasma arc heater is inserted from the lower tuyere, and pulverized coal is blown in front of the high temperature gas generated by the plasma arc heater. There is. FIG. 3 shows a probe equipped with a plasma arc heater inserted from the lower tuyere. In FIG. 3, 3 is a lower tuyere, 4 is a blast branch pipe, 7 is a probe equipped with a plasma arc heater, 9 is an iron skin, and 10 is a brick.

FIG. 4 is a sectional view showing the structure of a probe equipped with a plasma arc heater according to the present invention. In FIG. 4, 5 is a plasma arc heater, 7 is a probe, and 8 is a pulverized coal blowing port. In Fig. 4, the maximum blast temperature (1
A gas having a temperature higher than 300 ° C.) is generated, and pulverized coal is blown out in front of this high temperature gas. Thermal decomposition of pulverized coal occurs rapidly at high temperature above 1300 ℃,
As compared with the case of 0 ° C., the produced amount of gas (having a higher burning rate) increases (that is, the produced amount of char decreases), the produced char expands, and its burning rate increases.

Therefore, the gas with the increased amount of combustion almost completes combustion in the blast branch pipe, and the amount of char combustion in the blast branch pipe increases, so that the amount of char entering the raceway decreases. In addition, this char is flammable,
Since it is highly reactive, it easily reacts with CO ₂ and H ₂ O,
The reaction of CO ₂ + C = 2CO and H ₂ O + C = H ₂ + CO results in CO and H ₂ , so that unburned char is not generated even when the excess oxygen ratio is less than 1.0. In other words, all unburned chars disappear within the raceway and are discharged from the furnace top.
There is no trapping in the core. For this reason, the replacement rate of coke is not lowered and the ventilation failure does not occur.

As the kind of high-temperature gas generated by the plasma arc heater, N ₂ , Ar, air or the like is usually used, but a reducing gas such as CO or H ₂ or CO ₂ or H ₂ O is mixed with these. Gas can also be used.

[0023]

EXAMPLES The features of the present invention will be specifically described with reference to the following examples. Table 1 shows the operation results of Examples and Table 2 shows the operation results of Comparative Examples.

[0024]

[Table 1]

[0025]

[Table 2]

Example 1 The blast temperature of the upper tuyeres was set to 1250 ° C., 50 kg / t of fine ore without preliminary reduction was blown, and the blast temperature of the lower tuyeres was set to 1
This is an operation example in which the temperature is set to 250 ° C and 130 kg / t of pulverized coal is blown. Compared to Comparative Example 1, the blowing pressure was low, the coke ratio and the fuel ratio were low, the amount of tapped metal was large, and the amount of silicon in the hot metal was low.

Example 2 The plasma arc heater shown in FIG. 2 was installed in the upper tuyeres, the blowing temperature was set to 1300 ° C., and 50 kg / t of fine ore and 50 kg / t of pulverized coal having a preliminary reduction rate of 30% were blown in.
The plasma arc heater shown in Fig. 2 was installed in the lower tuyeres, the blast temperature was 1300 ° C, and pulverized coal was 150 kg / t.
It is an example of an operation in which

Example 3 The plasma arc heater shown in FIG. 2 was installed in the upper tuyeres, the blast temperature was 1300 ° C., and 75 kg / t of fine ore with a preliminary reduction rate of 60% and 50 kg / t of pulverized coal were blown in,
The plasma arc heater shown in Fig. 3 was installed in the lower tuyeres, the blast temperature was 1350 ° C, and pulverized coal was 175 kg / t.
It is an example of an operation in which

Example 4 The plasma arc heater shown in FIG. 2 was installed in the tuyere of the upper stage, the blast temperature was set to 1300 ° C., 100 kg / t of fine ore with a preliminary reduction rate of 90% and 50 kg / t of pulverized coal were blown into the lower stage. The plasma arc heater shown in Fig. 2 was installed in the tuyere, the blast temperature was 1300 ° C, and the pulverized coal was 150 kg /
This is an operation example in which t is blown.

Example 5 The blast temperature of the upper tuyeres was set to 1200 ° C. and pulverized coal 50 kg
/ T is blown, the plasma arc heater shown in FIG. 3 is installed in the lower tuyere, the blast temperature is set to 1350 ° C., and pulverized coal 1
This is an operation example in which 75 kg / t is blown.

In each case, since the powdery iron source is completely reduced and melted in the raceway to form hot metal, the production amount is high and the silicon content in the hot metal is decreased as compared with Comparative Examples 1 and 2. There is.

Comparative Example 1 is an operation example in which the blowing temperature was 1250 ° C. and 50 kg / t of fine ore without preliminary reduction and 130 kg / t of pulverized coal were blown from the same tuyere. Example 1
On the other hand, the blast pressure is high, the coke ratio and the fuel ratio are high, the amount of tapping is small, and the amount of silicon in the hot metal is high. In Comparative Example 2, the blast temperature was 1250 ° C., the blast pressure decreased, the amount of tapping increased,
This is an operation example in which the amount of fine ore blown from the same tuyere without pre-reduction (30 kg / t) and the amount of pulverized coal blown (100 kg / t) were reduced with the aim of reducing the amount of silicon in the hot metal.
Compared with Comparative Example 1, although the blast pressure was decreased, the amount of tapping was increased, and the silicon content in the hot metal was decreased, it was not as high as that of Example 1, and the coke ratio and the fuel ratio were higher than those of Example 1.

[0033]

As described above, the upper and lower parts of the blast furnace 2 are
By installing the tuyeres of the steps, blowing at least one of the pulverized iron source or pulverized coal from the upper tuyeres and the pulverized coal from the lower tuyeres into the blast furnace, and by installing a plasma arc heater at the tuyeres. It is possible to increase the total blowing amount of at least one of the powdery iron source and the pulverized coal by raising the blowing temperature near the powdery iron source or the pulverized coal blowing position by the high temperature gas generated by the plasma arc heater. As a result, it is possible to avoid gas permeability, poor liquid permeability, pulverized coal substitution rate, and increase in silicon in the hot metal, improve productivity, reduce fuel ratio, and provide stable hot metal supply.

[Brief description of drawings]

FIG. 1 is a diagram showing the positions of tuyeres installed in two stages, upper and lower, in the lower part of the blast furnace.

FIG. 2 is a diagram showing a state of a plasma arc heater installed in the upper tuyeres or the lower tuyeres.

FIG. 3 is a view showing a probe equipped with a plasma arc heater inserted from the lower tuyere.

FIG. 4 is a cross-sectional view showing the structure of a probe equipped with a plasma arc heater.

[Explanation of symbols]

 1 Blast furnace 2 Upper stage tuyeres 3 Lower stage tuyeres 4 Blower branch pipe 5 Plasma arc heater 6 Blow burner 7 Probe

Claims (3)

[Claims] 1. In a blast furnace operating method in which a pulverized iron source and pulverized coal are blown into a blast furnace from a tuyere, and iron ore and coke are alternately charged from the furnace top, upper and lower two-stage blades are placed in the lower part of the blast furnace. A blast furnace operating method characterized in that a mouth is installed and at least one of a powdery iron source or pulverized coal is blown into the blast furnace from the upper tuyeres and pulverized coal is blown into the blast furnace from the lower tuyeres. 2. The blast furnace operation according to claim 1, wherein a plasma arc heater is installed at the tuyere, and a high temperature gas ejected from the plasma arc heater together with the powdery iron source or pulverized coal is blown into the blast furnace. Law. 3. The distance between the upper and lower tuyeres is 1.0 m or more.2.
The blast furnace operating method according to claim 1 or 2, wherein the blast furnace operation is 0 m or less.