JPH05255718A - Method for operating blast furnace - Google Patents

Abstract

PURPOSE:To avoid the reduction in productivity and the increase in fuel ratio in a blast furnace by preventing the deterioration of the reducibility of sintering ores when the content of alumina (Al2O3) in the sintering ore is high. CONSTITUTION:When the alumina (Al2O3) content in the sintering ore exceeds 1.9%, the basicity (CaO/SiO2) of the sintering ore is made to be >=2.0. By executing such an operation method, the reducibility of the sintering ore is secured and the O/C at the peripheral part of the furnace at the time of blowing a large quantity of pulverized coal is increased and reduction efficiency in this range can be improved. Therefore, the improvement of productivity and the reduction of the fuel ratio in the blast furnace area achieved, and the stable molten iron supply can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to alumina (Al ₂ O) in sinter which accounts for most of iron ore charged from the furnace top.
₃ ) It relates to a blast furnace operation method in which the productivity is stabilized and the fuel ratio is lowered by ensuring the reducibility of sinter when the content is high.

[0002]

2. Description of the Related Art In blast furnace operation, as an alternative to coke, an inexpensive, highly combustible, high calorific fuel (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. Various reduction reactions. 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.

[0004]

In the conventional blast furnace operation, the proportion of the sintered ore in the iron ore charged from the furnace top is usually as high as 60 to 80%, and the sinter ore is reduced. The operating efficiency of the blast furnace is almost determined by the characteristics of the blast furnace.
Therefore, the improvement of sinter ore properties was important for improving the productivity of the blast furnace and reducing the fuel ratio.

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

However, alumina (Al ₂ O) in the sintered ore
₃ ) When the content is high, especially when it exceeds 1.9%, Al ₂ O ₃ and FeO combine to form a low melting point compound as the sintered ore is heated and reduced while descending in the blast furnace. Therefore, a melt is generated in the sinter from a lower temperature.
When FeO is dissolved in 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 the reducibility is poor and reduction delay occurs. At this time, if the O / C in the peripheral area of the furnace is increased, the reduction delay is further promoted, and the delay of the fall of the charge in the furnace wall, the stagnation of the fall, and the formation of deposits decrease the productivity and increase the fuel ratio. I had no choice.

Therefore, alumina (Al ₂ O ₃ ) in the sintered ore
When the content is high, the O / C around the furnace cannot be increased, and as a result, the amount of gas around the furnace increases, the heat dissipated in the furnace increases, the fuel ratio increases, and Since an abnormal drop in the load occurs and productivity drops, the amount of pulverized coal injected is limited. Alumina in sintered ore (Al ₂ O
₃ ) When the content is high, the temperature at which the sinter completely dissolves becomes high, and the melt formation start temperature is low, and the width of the cohesive zone widens, and The occurrence of the same phenomenon as when the temperature was raised is also a reason for promoting the reduction delay in the peripheral area of the furnace.

Therefore, the present invention is directed to the alumina (A
When the content of l ₂ O ₃ ) is high, by ensuring the reducibility of the sinter, the O around the furnace when a large amount of pulverized coal is sucked
By increasing / C and improving the reduction efficiency in this region, the object is to improve the productivity of the blast furnace and stably reduce the fuel ratio.

[0009]

Means for Solving the Problems The present invention is intended to solve the above problems, in which pulverized coal is blown into the interior of a blast furnace from the tuyere, and iron ore and coke are alternately charged from the top of the blast furnace. In the operating method, when the content of alumina (Al ₂ O ₃ ) in the sintered ore charged from the furnace top exceeds 1.9%, the basicity (CaO / SiO ₂ ) of the sintered ore is 2.0 or more. It is characterized by

[0010]

In the present invention, the alumina (Al
_{Even if the} content of ₂ O ₃ ) exceeds 1.9%, by setting the basicity (CaO / SiO ₂ ) of the sintered ore to 2.0 or more, the reducibility of the sintered ore before the melt formation is improved. FeO because it is good
The amount of the low melting point compound formed by the combination of Al ₂ O ₃ and FeO is small, and the rise in the melt formation temperature does not decrease. Further, FeO is dissolved in the generated melt,
By setting the basicity (CaO / SiO ₂ ) of the sinter to 2.0 or more, the CaO content in the melt increases, and Al
The binding force of ₂ O ₃ and CaO is stronger than the binding force of Al ₂ O ₃ and FeO, the activity of FeO is maintained high, and the reduction property is high, so that no reduction delay occurs.

In the present invention, the basicity of the sintered ore (CaO
/ SiO ₂ ) is set to 2.0 or more because if the ratio is less than 2.0, the reducibility of the sinter is not so good and the CaO content in the melt is not so high. This is because the lowering of the liquid generation temperature and the lowering of FeO activity cannot be suppressed. Further, when the content of alumina (Al ₂ O ₃ ) in the sinter is 1.9% or less, the decrease in the melt generation temperature and the decrease in FeO activity due to Al ₂ O ₃ described above are not significant, and the blast furnace The operation is smooth and does not require the operation of the present invention.

Further, the slag composition (CaO / SiO ₂ , Al ₂ O ₃ , MgO) flowing out from the taphole of the blast furnace is usually kept almost constant (eg CaO / SiO).
₂ = 1.25, (Al ₂ O ₃ ) = 14.5%, (Mg
O) = 5.0%). Therefore, when the ratio of the sintered ore in the iron ore is high, the basicity of the sintered ore (CaO / Si
When O ₂ ) is 2.0 or more, CaO / SiO ₂ = 1.25 in the slag flowing out from the tap hole cannot be maintained, and the slag becomes high. In this case, the proportion of the sintered ore in the iron ore should be reduced while keeping the basicity (CaO / SiO ₂ ) of the sintered ore at 2.0 or higher, or the proportion of the soft ore should be kept constant. Such SiO ₂ content is charged from the furnace top.

FIG. 1 shows the alumina (Al ₂ O ₃ ) content in the sinter used in the present invention and the basicity (Ca) of the sinter.
The relationship of O / SiO ₂ ) is shown. Al ₂ O ₃ = 1.9-
Up to 2.0, CaO / SiO ₂ = 2.0, Al ₂
When O ₃ exceeds 2.0, CaO / SiO ₂ is proportionally increased. This figure was obtained by an operational test.

[0014]

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 comparison with the conventional method. The target blast furnace is a medium-sized blast furnace with an internal volume of 3000 m ³ , and the proportion of sinter in iron ore is 74%, the basicity of the sinter (CaO / SiO ₂ ) = 1.8, Al ₂ O ₃ in the sinter.
= 1.8% was operating. In order to set CaO / SiO ₂ = 1.25 in the slag composition flowing out from the tap hole, 9 kg / t-pig of limestone was charged from the furnace top, and (Al ₂ O
₃ ) = 13.5%, (MgO) = 5.9%, and the amount of slag was 319 kg / t-pig. Pulverized coal injection amount 18
Hot metal was produced at 6000 t / day while maintaining 0 kg / t-pig and a fuel ratio of 500 kg / t-pig. The O / C of the peripheral portion of the furnace was 6.0.

[0015]

[Table 1]

Example 1 When the ratio of Al ₂ O _{3 in the} sintered ore increased to 2.0%, as shown in FIG.
According to the basicity of the sinter (CaO / SiO ₂ ) =
2.0, the ratio of sinter in iron ore to 70%, pulverized coal 180 kg / t-pig (O / C 6.0 around the furnace)
This is an example of operation that maintained the above. At this time, the composition of slag flowing out from the tap hole is CaO / SiO ₂ = 1.25, (Al ₂
O ₃ ) = 14.5%, (MgO) = 5.0%, and the amount of slag was 310 kg / t-pig. As a result of ensuring the sinter reducibility in the peripheral portion of the furnace, Comparative Examples 1 and 2
Compared with, the amount of pulverized coal suction is large, the amount of tapping is large,
Low fuel ratio.

Example 2 When the ratio of Al ₂ O _{3 in the} sintered ore increased to 2.2%, as shown in FIG.
According to the basicity of the sinter (CaO / SiO ₂ ) =
2.2, the ratio of sintered ore in iron ore to 63%, O / C around the furnace was maintained at 5.5, and pulverized coal 160 kg / t
It is an example of operation in which −pig is blown. At this time, 3 kg / t-pig of soft silica was charged from the top of the furnace so that CaO / SiO ₂ = 1.25 in the slag composition flowing out from the tap hole. (Al ₂ O ₃ ) = 14.8%, (MgO) = 4.
It was 6%, and the amount of slag was 312 kg / t-pig.

[0018] When elevated to Example 3 sinter in Al ₂ O ₃ = 2.4%, Figure 1
According to the basicity of the sinter (CaO / SiO ₂ ) =
2.5, the ratio of sinter in iron ore to 60%, O / C around the furnace was maintained at 5.0, pulverized coal 150kg / t
It is an example of operation in which −pig is blown. At this time, 12 kg / t-pig of soft silica was charged from the furnace top in order to set CaO / SiO ₂ = 1.25 in the slag composition flowing out from the taphole. (Al ₂ O ₃ ) = 14.9%, (MgO) =
The amount was 4.3%, and the amount of slag was 320 kg / t-pig.

Comparative Example 1 is Al ₂ O ₃ = 2.0 in the sintered ore.
% Is an example of an operation by the conventional method in which the sinter ore property is used as it is, and the composition of slag flowing out from the tap hole is CaO / SiO ₂ = 1.25, and the limestone is 9 kg / t-pig was charged from the furnace top. (Al ₂
O ₃ ) = 14.2%, (MgO) = 5.1%, and the amount of slag was 319 kg / t-pig. I tried to maintain the O / C in the peripheral area of the furnace at 6.0, but a reduction delay occurred in the peripheral area of the furnace, which caused a delay in the falling of the charge in the furnace wall, stagnant fall, and the formation of deposits. O / C of 4.
5, the amount of pulverized coal injected was reduced compared to Example 1, the fuel ratio was inevitably increased, and the productivity was reduced.

Further, in Comparative Example 2, under the same operating conditions as in Comparative Example 1, the O / C in the peripheral area of the furnace was lowered to 4.0 in order to avoid the reduction delay in the peripheral area of the furnace, and the pulverized coal injection amount was reduced. It is an example of the operation by the conventional method in which the
As a result, production decreased and fuel ratio increased.

[0021]

As described above, in the present invention, the content of alumina (Al ₂ O ₃ ) in the sintered ore is 1.9.
%, The basicity of sinter (CaO / SiO ₂ ) =
By setting the ratio to 2.0 or more, the reducibility of the sintered ore can be secured, the O / C in the peripheral area of the furnace can be increased when a large amount of pulverized coal is injected, and the reduction efficiency in this region can be improved. It is possible to improve the productivity of the blast furnace, reduce the fuel ratio, and supply a stable hot metal.

[Brief description of drawings]

FIG. 1 shows the alumina (Al ₂ O ₃ ) content in the sintered ore,
Graph showing the relationship between the basicity of sintered ore in the present invention (CaO / SiO ₂₎

Claims (1)

[Claims] 1. In a blast furnace operating method in which pulverized coal is blown into the blast furnace from the tuyere and iron ore and coke are alternately charged from the furnace top, alumina in the sintered ore charged from the furnace top ( A blast furnace operating method characterized in that when the Al ₂ O ₃ ) content exceeds 1.9%, the basicity (CaO / SiO ₂ ) of the sinter is set to 2.0 or more.