JPH10219314A - Method for using reduced iron in blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reduction efficiency and the ventilation and to stably execute the lowering of fuel ratio and the improvement of productivity by mixing iron raw material containing reduced iron in iron ore at a specific ratio and charging from the furnace top part, at the time of alternately charging the iron ore and coke layer by layer from the furnace top part and blowing auxiliary fuel from a tuyere part. SOLUTION: The iron ore is mainly used to a sintered ore variating about 1.7-2.1wt.% Al2 O3 . The reduced iron is used to >=50% to <95% reducing ratio as the object. Then, the iron ore is replaced at 5-35% into the reduced iron, and at the time of beforehand mixing both, since metallic iron is already produced in the reduced iron, the layer thickness of the iron ore is not too thick, and even in the case Al2 O3 content exceeds 1.80wt.% and the reduction speed of the iron ore is dropped causing to increase of fusing zone, since the metallic iron restrains shrinkage, the ventilation of the iron layer is secured and the reduction of remained FeO is smoothly progressed and the delay of the reduction is not developed. The abovementioned effect is further promoted by the metallic iron produced with the reduction of fuzed FeO.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention is to reduce the fuel ratio by maintaining good reducibility and softening shrinkage characteristics of the sinter ore, which occupies most of the iron ore charged from the furnace top,
The present invention relates to a blast furnace operation method with improved productivity.

[0002]

2. Description of the Related Art In the blast furnace operation, as a substitute for coke, a low-cost, highly flammable, and high calorific value fuel (pulverized coal, petroleum, heavy oil, naphtha, etc.) is blown from the tuyere to reduce hot metal production cost. Has been working to improve productivity,
The technology is disclosed in Japanese Patent Publication No. 233763. In particular, pulverized coal injection has become the mainstream in recent years in terms of price, greatly contributing to a reduction in fuel ratio (cost reduction) and an improvement in productivity.

[0003] The pulverized coal injected in this way burns instead of a part of coke in the blast furnace, and because of its good flammability and high calorific value, generates a large amount of reducing gas at a high temperature and efficiently. A simple reduction reaction can be performed. Therefore, the iron ore charged from the furnace top is quickly reduced to a metallic state, and at the same time, is melted to become hot metal at a high temperature.

[0004] In the conventional blast furnace operation, the proportion of sintered ore in the iron ore charged from the furnace top is usually 60 to 80.
wt%, which is very high, and the reduction efficiency and air permeability of the blast furnace are almost determined by the properties of the sinter such as reducibility and softening and shrinkage characteristics. Therefore, it is very important to improve the properties of the sinter such as reducibility, softening and shrinkage properties, etc., for reducing the fuel ratio and improving the productivity of the blast furnace.

On the other hand, pulverized coal is injected, especially 100 kg / t.
-Since a large amount of hot metal or more is injected, the heat flow ratio (ratio of the heat capacity of the solid to the heat capacity of the gas), which is an indicator of the heat reduction efficiency of the blast furnace, is reduced, so there is room for heat reduction, especially in the periphery of the blast furnace. . Therefore, the ratio of iron ore and coke charged into the peripheral portion (referred to as O / C) is increased to improve the reduction efficiency and air permeability in this region.

[0006]

By the way, the iron ore charged in the periphery of the blast furnace has a reaction heat transfer between it and the high-temperature reducing gas generated in the coke swirl combustion region (called a raceway) of the tuyere. Then, a cohesive zone is generated by softening and welding of the iron ore (the one generated in the peripheral portion is referred to as a root).
It is desirable that the roots exist stably around the lower part of the furnace in normal blast furnace operation, and do not change in position and thickness.

However, when the O / C in the peripheral portion is high and the thickness of the iron ore is too thick, or when the alumina (Al ₂ O ₃ ) content in the sintered ore is higher than 1.80 wt%. When the sinter decreases, the rate of reduction of the sinter decreases, so as the sinter is reduced while heating down the blast furnace,
A large amount of low-melting compound formed by the combination of SiO ₂ and FeO is generated. When Al ₂ O ₃ is high, Al ₂ O ₃ dissolves into the low-melting compound, and a melt is formed in the sinter from a lower temperature. Generate. When FeO further dissolves into this melt and Al ₂ O ₃ is high, the binding force between Al ₂ O ₃ and FeO is strong and the activity of FeO is small, so that the reducibility is poor and further reduction lag occurs. . For this reason, O /
We have to take action to lower C.

The Al ₂ O ₃ in the sinter is 1.80 wt.
%, The temperature at which the sintered ore is completely melted becomes high, and the temperature at which the melt starts to be formed is low, and the width of the cohesive zone is widened, and the O / C in the peripheral portion is increased. The occurrence of the same phenomenon as described above is also a reason for promoting a reduction delay in the peripheral portion. Therefore, when a large amount of pulverized coal is injected, the O / C
There is a limit to the rise, and Al ₂ O ₃ in the sinter is 1.
When it is higher than 80 wt%, the O / C increase limit in the peripheral portion is further reduced. As a result, the amount of gas in the peripheral area increases, the heat dissipated in the furnace increases, the fuel ratio increases, the charge drop abnormalities occur, and the productivity decreases. However, the margin of heat reduction in the above cannot be used effectively, and the amount of pulverized coal injected is limited.

Therefore, the present invention is to maintain the reducibility of the sinter, particularly the softening and shrinkage characteristics, in order to effectively utilize the margin of heat reduction in the peripheral portion caused by the injection of a large amount of pulverized coal. , Raise the O / C in the peripheral area,
Even when Al ₂ O ₃ in the sintered ore is higher than 1.80 wt%, the O / C in the peripheral portion is not reduced, and the reduction efficiency and air permeability in this region are improved to improve the blast furnace. The aim is to stably reduce the fuel ratio and improve productivity.

[0010]

According to the method of using reduced iron in the blast furnace of the present invention, iron ore and coke are charged alternately in layers from the top of the blast furnace to achieve the object.
When the auxiliary fuel is blown from the tuyere, the iron ore is mixed with 5-35 wt% of an iron raw material containing reduced iron and charged from the furnace top. When iron ore and coke are charged alternately in layers from the furnace top of the blast furnace and auxiliary fuel is blown from the tuyere, 30 to 45 watts of iron ore charged into the blast furnace are charged.
5% to 35% by weight of an iron raw material containing reduced iron to t%, and charging from the furnace top to the periphery of the furnace top, and charging of the remaining iron ore from the furnace top to parts other than the periphery of the furnace top. Features.

Further, iron ore and coke are charged alternately in layers from the furnace top of the blast furnace, and when auxiliary fuel is blown from the tuyere, 2-8 wt% of the iron ore charged into the blast furnace is The method is characterized in that an iron raw material containing reduced iron is mixed in an amount of 5 to 35 wt%, charged from the furnace top to the furnace center, and the remaining iron ore is charged from the furnace top to a part other than the furnace center. Furthermore, the average content of Al ₂ O _{3 in} the sintered ore charged from the furnace top of the blast furnace is more than 1.80 wt%. Further, as an iron raw material containing reduced iron, reduced iron having a reduction ratio of 50% or more and less than 90% is used. Furthermore, the present invention is characterized in that pig iron and / or scrap is used as an iron raw material containing reduced iron.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The iron ore in the present invention is a charge mainly composed of sintered ore in which Al ₂ O _3, which is usually used, varies from about 1.7 to 2.1 wt%. . The reduced iron in the present invention is a lump reduced iron manufactured using a lump ore and pellets as raw materials using a shaft furnace, and has a reduction rate of 5%.
The target is 0% or more and less than 95%. In addition, powdered reduced iron produced using a fluidized bed with fine ore as a raw material,
It is the one molded into a lump by a prequette making machine, and also has a reduction ratio of 50% or more and less than 95%.

[0013] 5-35 wt% of iron ore, the reduction rate is 50
% Or less and less than 95% of reduced iron, when pre-mixed with reduced iron and iron ore, metal iron is already formed in the reduced iron, so when the iron ore layer becomes too thick,
Alternatively, when the content of Al ₂ O ₃ in the sinter becomes higher than 1.80 wt%, even if the reduction rate of iron ore is reduced and the amount of generated melt is increased, metallic iron suppresses shrinkage. For,
The permeability of the iron ore layer mixed with reduced iron is ensured, and the residual F
The reduction of eO proceeds smoothly and does not cause a reduction delay. Melt F
When eO is reduced, solid metallic iron is generated, and the generated metallic iron further suppresses shrinkage, thereby improving the reduction rate and improving air permeability.

The reason for limiting the reduction ratio of reduced iron to 50% or more and less than 95% is that if it is less than 50%, when mixed with iron ore, the amount of metallic iron is too small and the effect of suppressing shrinkage is small. The reason is that almost no reduction in fuel ratio and improvement in production can be expected. If it is 95% or more, when mixed with iron ore, the effect of suppressing shrinkage is very large, the fuel ratio is reduced, and the production amount is greatly improved, but the cost of producing reduced iron becomes too high,
Because it is not economical.

The amount of reduced iron mixed with iron ore is 5 to 35 watts.
The reason for limiting the numerical value to t% is that if it is less than 5 wt%, when mixed with iron ore, the amount of metallic iron is too small, the effect of suppressing shrinkage is small, and a reduction in fuel ratio and improvement in production can hardly be expected. . If it exceeds 35 wt%, when mixed with iron ore, the effect of suppressing shrinkage is very large, but carburization of metallic iron is promoted, the melting temperature decreases, and the furnace heat of the blast furnace decreases. This is because the reduction and the increase in production volume cannot be expected much.

The iron ore mixed with the reduced iron is charged into the blast furnace from the top of the blast furnace alternately with coke in a layered manner. At this time, the iron ore mixed with the reduced iron is charged in all the blast furnace radial directions. In order to improve the reduction efficiency and air permeability of the peripheral portion of the blast furnace, 30 to 45 wt% of the iron ore charged from the furnace top is separately taken out for peripheral charging, and 5-35 wt% of the iron ore is charged.
The wt% is replaced with reduced iron having a reduction ratio of 50% or more and less than 95%, and the reduced iron and iron ore are mixed in advance. Then, the iron ore mixed with the reduced iron is charged into the periphery.

The term "peripheral portion" as used herein means 0.8 in the radial direction when the center is 0.0 and the furnace wall is 1.0.
It is defined as an area of ~ 1.0. The reason why the amount of iron ore separately taken out for peripheral charging is numerically limited to 30 to 45 wt% is that this amount corresponds to the amount that can be charged to the peripheral portion in the above range. The effect of the iron ore mixed with the reduced iron charged in the peripheral portion on the reduction of the fuel ratio and the improvement of the production amount is the same as the effect when the whole is charged.

In order to improve the reduction efficiency and air permeability at the center of the blast furnace, 2-8 wt% of the iron ore charged from the top of the furnace is required.
Separately for central charging, 5 to 3 of the iron ore
5 wt% is replaced with reduced iron having a reduction ratio of 50% or more and less than 95%, and the reduced iron and iron ore are mixed in advance. Then, the iron ore mixed with the reduced iron is charged into the center.

The center here is defined as 0.0 when the center is 0.0 and the furnace wall is 1.0 in the radial direction.
It is defined as an area of ０．２0.2. The reason why the amount of iron ore separately taken out for charging into the center is numerically limited to 2 to 8 wt% is that this amount corresponds to the amount that can be charged into the center in the above range. The effect of reducing the fuel ratio and improving the production of iron ore mixed with the reduced iron charged in the center,
The effect is the same as when the whole is charged. The effect of the reduced iron described above is substantially the same even when using a pig iron, scrap, or a mixture of both instead of the reduced iron having a reduction ratio of 50% or more and less than 95%.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below with reference to embodiments. Table 1 shows the blast furnace operation results according to the present invention in comparison with the conventional method. The target blast furnace was a medium-sized blast furnace having an inner volume of 3000 m ³ , and was operated with a sinter ratio of 75% by weight in iron ore and (80%) of (Al ₂ O ₃ ) in sinter. Pulverized coal injection rate 150kg / t-hot metal, fuel ratio 50
While maintaining the hot metal at 0 kg / t-hot metal,
Had been manufactured for days.

[0021]

[Table 1]

(Example 1) The raw material for sinter production was changed,
(Al ₂ O ₃ ) in the sinter increased to 2.0 wt%. At this time, a reduction rate of 7 wt%
This is an operation example according to the present invention in which 5% of reduced iron is replaced and coke is charged in layers from the furnace top alternately. Comparative Example 1
Compared to, the fuel ratio was low and the tapping amount was large.

Example 2 The pulverized coal injection rate was increased from 150 to 170 kg / t-hot metal. At this time, 35 wt% of the iron ore was separately taken out, 30 wt% of the iron ore was replaced with reduced iron having a reduction rate of 80%, and the iron ore was charged around the furnace top, according to the operation example of the present invention. Compared to Comparative Example 2, the fuel ratio was low and the tapping amount was large.

(Example 3) The raw material for sinter production was changed,
(Al ₂ O ₃ ) in the sinter increased to 2.1 wt%. At this time, an operation example according to the present invention in which 4 wt% of iron ore was separately taken out, 25 wt% of the iron ore was replaced with reduced iron having a reduction rate of 90%, and charged at the center of the furnace top. Compared to Comparative Example 3, the fuel ratio was low and the tapping amount was large.

(Example 4) The raw material for sinter production was changed,
(Al ₂ O ₃ ) in the sinter increased to 2.0 wt%. At this time, 15 wt% of the iron ore was replaced with pig iron and charged in layers from the furnace top alternately with coke.
It is an operation example by this invention. Compared with Comparative Example 1, the fuel ratio was low and the tapping amount was large.

(Example 5) The raw material for sinter production was changed,
(Al ₂ O ₃ ) in the sinter increased to 2.0 wt%. At this time, 10 wt% of the iron ore was replaced with scrap, and coke was charged alternately with coke from the furnace top in a layered manner. Compared with Comparative Example 1, the fuel ratio was low and the tapping amount was large.

(Comparative Example 1) The raw material for producing sinter changed.
This is an operation example according to the conventional method in which the operation is continued as it is when the content of the sintered ore (Al ₂ O ₃ ) rises to 2.0 wt%. As compared with Examples 1, 4, and 5, the fuel ratio had to be increased, and the production amount decreased.

(Comparative Example 2) This is an operation example according to the conventional method in which operation was continued as it was when the pulverized coal injection amount was increased from 150 to 170 kg / t-hot metal. As compared with Example 2, the fuel ratio had to be increased, and the production amount decreased.

(Comparative Example 3) The raw material for producing sinter changed.
This is an operation example according to the conventional method in which the operation is continued as it is when the content of the sintered ore (Al ₂ O ₃ ) rises to 2.1 wt%. As compared with Example 3, the fuel ratio had to be increased, and the production amount decreased.

[0030]

As described above, in the present invention, a part of iron ore is replaced with reduced iron in order to effectively utilize the margin of heat reduction in the peripheral part caused by the injection of a large amount of pulverized coal. By pre-mixing reduced iron and iron ore, when the layer thickness of iron ore becomes too thick,
Alternatively, when the Al ₂ O ₃ in the sinter becomes high, even if the reduction rate of the iron ore becomes slow and the amount of melt generated increases,
Since the metallic iron already generated in the reduced iron suppresses the contraction of the iron ore layer, the permeability of the iron ore layer mixed with the reduced iron is secured, and the reduction of the residual FeO proceeds smoothly, causing a reduction delay. Absent. When the molten FeO is reduced, solid metallic iron is generated, and the generated metallic iron further suppresses shrinkage, thereby improving the reduction rate and improving the air permeability. Therefore, the reduction efficiency and air permeability of the blast furnace can be improved, and the fuel ratio can be reduced and the productivity can be stably improved.

Claims (6)

[Claims] 1. An iron ore and a coke are alternately charged in layers from a furnace top of a blast furnace, and when an auxiliary fuel is blown from a tuyere, an iron raw material containing reduced iron is added to the iron ore in an amount of 5 to 35 wt. %. The method of using reduced iron in a blast furnace, wherein the reduced iron is charged from the furnace top. 2. When iron ore and coke are charged alternately in layers from the furnace top of the blast furnace and auxiliary fuel is blown from the tuyere, 30 to 45 wt% of iron ore charged into the blast furnace is added. A blast furnace characterized by mixing an iron raw material containing reduced iron in an amount of 5 to 35 wt%, charging the raw material from the furnace top to the furnace top periphery, and charging the remaining iron ore from the furnace top to other parts than the furnace top periphery. Use of reduced iron in Japan. 3. Iron ore and coke are charged alternately in layers from the furnace top of the blast furnace, and when auxiliary fuel is injected from the tuyere, 2-8 wt% of iron ore charged into the blast furnace is added. A blast furnace characterized by mixing an iron raw material containing reduced iron in an amount of 5 to 35 wt%, charging the iron ore from the furnace top to the center of the furnace, and charging the remaining iron ore from the furnace top to a part other than the center of the furnace top. Use of reduced iron in Japan. 4. A in the sintered ore charged from the furnace top of the blast furnace.
A method for using reduced iron in a blast furnace, wherein the average content of l ₂ O ₃ exceeds 1.80 wt%. 5. An iron raw material containing reduced iron having a reduction rate of 5
The method for using reduced iron in a blast furnace according to any one of claims 1 to 4, wherein 0% or more and less than 90% of reduced iron is used. 6. An iron raw material containing reduced iron, wherein pig iron and / or scrap is used.
5. The method for using reduced iron in a blast furnace according to any one of items 4 to 4.