JPH05287339A - Method for operating blast furnace - Google Patents

Abstract

PURPOSE:To secure blowing quantity even in the case of a limitted raising blasting temp. at the time of injecting iron source and pulverized coal, to perfectly execute smelting reduction to the injected powdery iron source in a raceway and to increase the production quantity without rising coke ratio. CONSTITUTION:At the time of injecting the powdery iron source and the pulverized coal into the inner part of a blast furnace from a tuyere part, cementite is injected into the inner part of the blast furnace from the tuyere together with the powdery iron source and the pulverized coal. Since the cementite has 100% of pre-reduction ratio, it is unnecessary to compensate the reduction heat, and since the carbon is incorporated at 6.7%, the cementite can be replaced the injecting quantity of the pulverized coal by the content and it is unnecessary to compensate the decomposing heat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention, when blowing a powdery iron source and a pulverized coal from a tuyere, stably reduces and melts the blown powdery iron source and improves the combustibility of the pulverized coal. The present invention relates to a blast furnace operating method that secures a high rate of substitution with coke, reduces the coke ratio, and improves productivity.

[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]

In the conventional blast furnace operation, the powdery iron source blown from the tuyere is reduced and melted in a region called a raceway where the coke swirls and burns to form hot metal. The amount of heat required to compensate for the reduction melting is given in advance by raising the blast temperature, but since the time during which the powdered iron source stays in the raceway is extremely short, the raceway is not fully reduced and melted. Reach the inner part (furnace core surface layer). Then, because of the accumulation in this area and rapid reduction melting, the temperature in this area drops,
Impairs breathability and liquid permeability.

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 increases the coke ratio, which leads to a decrease in the production amount and is not preferable in the operation of the blast furnace.

Further, the amount of the powdery iron source blown from the tuyere may be reduced or cut, which also leads to a reduction in the production amount. In order to reduce the amount of heat required to compensate for the reduction and melting of the powdered iron source and to completely reduce and melt it in the raceway, the preliminary reduction rate of the powdered iron source should be increased. If the value is increased, the processing cost will increase rapidly, which is not economical. Usually, at most about 60% is the economic limit.

When pulverized coal is blown together with the pulverized iron source from the tuyere, it is necessary to compensate the thermal decomposition of the pulverized coal in addition to the amount of heat required to compensate the reduction melting of the pulverized iron source. With a certain amount of heat added, there is a limit to the amount of pulverized iron source and pulverized coal blown with a certain limited increase in blast temperature.

Therefore, according to the present invention, when the powdery iron source and the pulverized coal are blown, the blowing amount is secured even if the temperature of the blast is limited to a certain extent, and the blown powdery iron source is completely discharged in the raceway. The purpose is to reduce and melt and increase the production without increasing the coke ratio.

[0011]

Means for Solving the Problems The present invention is intended to solve the above problems, in which a powdered iron source and pulverized coal are blown into the blast furnace from the tuyere, and iron ore and coke are fed from the furnace top. In the blast furnace operating method in which the cement is alternately charged, the cementite is blown into the blast furnace from the tuyere along with the powdered iron source and the pulverized coal.

[0012]

The cementite used in the present invention is highly purified by reducing powdered ore with a mixed gas of methane, hydrogen and nitrogen in a fluidized bed reactor. Cementite is a powdery iron source with a pre-reduction rate of 100%, and contains 6.7% of carbon, so it is also effective as an alternative raw material for pulverized coal. Even when stored in the yard, it is chemically stable and does not undergo changes due to oxidation or heat generation, and it is stable even when transported by gas without sticking or clogging of pipes. It is an iron source.

Since cementite has a preliminary reduction rate of 100%, it is not necessary to compensate for its reduction heat, and the amount of iron blown in can be increased and the amount of production can be increased with a certain limited increase in blast temperature. Further, since it contains 6.7% of carbon, it can be replaced with the amount of pulverized coal blown by that amount, and since it is not necessary to compensate the decomposition heat, the amount of blown can be further increased. That is, the amount of carbon blown together with the pulverized coal can be increased, and the coke ratio can be reduced.

In the blast furnace operating method according to the present invention, an operation test is conducted in which cementite is blown during the blowing of the powdery iron source and the pulverized coal, and the powdery iron source and / or the pulverized coal is reduced by that amount. The results shown in FIGS. 1 to 3 were obtained. Fig. 1 shows the case where the powdered ore with a preliminary reduction rate of 60% was replaced with cementite with a constant amount of pulverized coal injected from the tuyere, and the coke ratio decreased and the production increased as the cementite injection increased. Has become.

FIG. 2 shows the case where the powdered ore with a pre-reduction rate of 30% was replaced with cementite while the amount of carbon blown from the tuyere was constant. As the amount of blown cementite increased, the coke ratio decreased and production increased. The quantity is rising.

FIG. 3 shows the case where the iron ore amount blown from the tuyere is constant and the powdered ore that has not been pre-reduced is replaced with cementite. As the amount of cementite blown increases, the coke ratio decreases and the production amount increases. Has become.

[0017]

EXAMPLES The features of the present invention will be specifically described with reference to the following examples. Table 1 shows the operation results of the blast furnace according to the present invention in which cementite is blown from the tuyere of the blast furnace in comparison with the conventional method.
The target blast furnace is a medium-sized blast furnace with an internal volume of 3000 m ³ , and iron ore and ordinary metallurgical coke were charged in layers at a ratio of O / C = 3.7 from the furnace top, and the pre-tuyere frame temperature was 2010 ° C.
(Blower temperature 1200 ° C, blast humidity 25g / Nm ³ -ai
r, oxygen enrichment rate 1.0%, pulverized coal injection amount 100 kg /
t-pig, powder ore with a preliminary reduction rate of 60% 100 kg / t
-Pig), hot metal is produced at 6000 t / day.

[0018]

[Table 1]

Example 1 Cementite 65 k was obtained with the blowing temperature set to 1300 ° C. and the pulverized coal blowing rate kept constant at 100 kg / t according to FIG.
Blowing in g / t, 65 kg of powdered ore with a preliminary reduction rate of 60%
/ T is an example of operation. Compared to Comparative Example 1, the coke ratio is low and the amount of tapped iron is large.

EXAMPLE 2 100 kg / t of powdered ore with a preliminary reduction rate of 60% and 100 kg of powdered ore with a preliminary reduction rate of 30% were used with a blast temperature of 1300 ° C.
Was replaced with / t. After that, according to FIG. 2, cementite 65 kg / t was blown, and the amount of pulverized coal blown was 95 kg / t so that the amount of carbon blown from the tuyere was constant (75 kg / t). Compared to Comparative Example 2, the coke ratio is low and the amount of tapped iron is large.

Example 3 100 kg / t of powdered ore having a pre-reduction rate of 60% and a blown temperature of 1300 ° C. and 105 kg of powdered ore not subjected to pre-reduction
replaced with t. After that, according to FIG. 3, 45 kg / t of cementite was blown, and the amount of powdered ore blown without pre-reduction was 45 kg / t so that the amount of iron blown from the tuyere was constant (67 kg / t). Here is an example. Compared with Comparative Example 3, the coke ratio is low and the amount of tapped iron is large.

Comparative Example 1 is an operation example by a conventional method in which the blowing temperature is 1300 ° C., the pulverized coal blowing rate is constant at 100 kg / t, and the fine ore having a preliminary reduction rate of 60% is 120 kg / t. The coke ratio is higher than in Example 1, and the amount of tapped iron is small.

Comparative Example 2 is an operation example according to the conventional method in which the blowing temperature is 1300 ° C. and 100 kg / t of the powder ore having the preliminary reduction rate of 60% is replaced with 100 kg / t of the powder ore having the preliminary reduction rate of 30%. The coke ratio is higher than in Example 2, and the amount of tapped iron is small.

Comparative Example 3 is an operation example of a conventional method in which the blowing temperature is 1300 ° C. and 100 kg / t of the powder ore having a preliminary reduction rate of 60% is replaced with 105 kg / t of the powder ore not subjected to the preliminary reduction. Compared to Example 3, the coke ratio is high and the amount of tapped iron is small.

[0025]

As described above, in the present invention, when the powdery iron source and the pulverized coal are blown from the tuyere, the preliminary reduction rate is 100% and the carbon content is 6.7%. By replacing cementite with a powdered iron source and / or pulverized coal and blowing it from the tuyere, the coke ratio decreases,
The production volume will increase and a stable hot metal supply will be possible.

[Brief description of drawings]

FIG. 1 is a graph showing changes in the relationship between the two when the pre-reduction rate of 60% blown from the tuyere is substituted with cementite and blown, and the coke ratio and the amount of tapping are changed.

FIG. 2 is a graph showing changes in the relationship between the two when the pre-reduction rate of 30% blown from the tuyere is replaced with semethanite, and the coke ratio and the amount of tapping are changed.

FIG. 3 is a graph showing changes in the relationship between the two when the powdered ore without pre-reduction blown from the tuyere is replaced with cementite and blown, and the coke ratio and the amount of tapped iron are changed.

Claims (1)

[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 charged alternately from the furnace top together with the pulverized iron source and pulverized coal. , Blast furnace operating method characterized by blowing cementite from the tuyere into the blast furnace.