JP2006307275A - Method for producing reduced iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a reduced iron having excellent quality together with the reduction of the input energy while improving the producing efficiency by using reducing gas, by making suitable of an operating method for iron oxide introduced into a shaft furnace. <P>SOLUTION: In a method for producing the reduced iron by reducing the iron oxide in the shaft furnace, (a) the iron oxide containing carbon so as to beforehand become ≥10 mass% in conversion into the carbon, is charged in the shaft furnace, and (b) the reduced iron is produced by blowing the reducing gas into the shaft furnace. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing reduced iron for obtaining reduced iron using an iron oxide such as iron ore as a raw material.

  As for the method of producing reduced iron from metal oxides such as iron oxide, conventionally, iron oxide is charged from above the shaft furnace, and reducing gas such as natural gas is introduced from below the shaft furnace. There was a way to reduce the oxide.

For example, Patent Document 1 discloses a method for directly reducing an iron oxide raw material to iron by introducing CO and H ₂ generated by thermal decomposition of a higher hydrocarbon gas such as pentane as a reducing gas into a shaft furnace. Is disclosed.

  On the other hand, in recent years, a system using a rotary hearth furnace as a preliminary reduction furnace has been proposed. A rotary hearth furnace is provided with an annular furnace body, a movable hearth is provided inside the furnace, and a granulated product obtained by mixing granulated metal oxide and a solid reducing agent is granulated. Place on the hearth as a raw material, and inject a fuel gas from a burner to burn the combustible gas in the furnace, and the combustion heat causes the metal oxide in the granulated product to react with the solid reducing agent for reduction. The metal is obtained.

  For example, Patent Document 2 discloses that a compact is formed by agglomerating fine iron ore and fine carbonaceous material, the compact is preliminarily reduced in a rotary hearth furnace, discharged at a temperature of at least 1000 ° C., and manufactured. A method is disclosed in which a molten metal bath is generated in a smelting reduction vessel, a fine carbonaceous material is introduced below the surface of the bath in the vessel, and the pre-reduced shaped body is reduced.

  In this method, the metallization rate of the raw material (the proportion of oxygen removed from the metal oxide oxygen in the raw material) is controlled to be maintained at a high rate of about 90% or more. . In other words, by thinly spreading the granulated material on the hearth, the distribution width of the metallization rate between the surface layer and the inside is reduced, and the hearth is slowly moved to create it in the furnace. The metallization rate is maintained at a high rate by allowing the grains to stay for a long time.

JP 61-73805 A Japanese Patent Publication No. 3-60883

  Although the method described in Patent Document 1 can surely produce reduced iron by introducing reducing gas into the shaft furnace, it is necessary to operate the furnace at a high temperature in order to increase productivity. On the other hand, the method is not necessarily an economical process because it requires a large amount of reducing gas.

  Further, in the method described in Patent Document 2, in order to promote reduction in the rotary hearth furnace, the iron oxide raw material is spread out thinly in the rotary hearth furnace. Despite the fact that the production volume is reduced and a large amount of heat is emitted as exhaust gas, the gas temperature in the furnace is considerably increased (to 1350-1450 ° C.) without directly contacting the burner flame with the raw material. Since the raw material is heated at a high temperature, there is a problem that the production efficiency is low.

  Therefore, in the present invention, by optimizing the operation method of the iron oxide introduced into the shaft furnace, while reducing the input energy stably while improving the production efficiency stably using the reducing gas, the excellent quality An object of the present invention is to provide a reduced iron production technique capable of producing reduced iron.

  The present invention has been made based on the above object, and the gist thereof is as follows.

(1) In a method for producing reduced iron by reducing iron oxide in a shaft furnace,
(A) An iron oxide containing carbon in advance so as to be 10% by mass or more in terms of carbon is charged into a shaft furnace,
(B) A method for producing reduced iron, comprising producing reduced iron by blowing a reducing gas into a shaft furnace.

  (2) The method for producing reduced iron according to (1), wherein carbon-containing powder is used as the iron oxide.

  (3) The method for producing reduced iron according to (1) or (2), wherein limestone is mixed in advance with the iron oxide before charging the iron oxide into the shaft furnace.

  According to the present invention, since the method for introducing iron oxide into the shaft furnace (operation method) is optimized, the production efficiency in the production of reduced iron can be improved and the input energy can be reduced.

  This inventor examined various methods about the method of optimizing the operating method of the iron oxide in a shaft furnace. As a result, when introducing an iron oxide into a shaft furnace, it was found that if an appropriate introduction method was selected, the reduction proceeded efficiently and the productivity of reduced iron was improved.

  In other words, if solid iron is appropriately contained in the iron oxide as a raw material in advance, after the iron oxide is charged into the shaft furnace, the iron oxide can be reduced by the reducing gas introduced into the furnace. As the process progresses, the reduction by the carbon contained in the iron oxide itself progresses in parallel, leading to the idea that the time required for the reduction of iron oxide is significantly reduced compared to the reduction by the conventional reducing gas alone. .

  However, the quality of the reduced iron is not stable if the iron oxide simply contains carbon, that is, the metalization rate of the reduced iron discharged from the shaft furnace is considered to vary greatly. The effect of carbon in iron oxide on the quality of iron was investigated.

Pelletized iron oxide granulated by adding the coal shown in Table 1 to the iron ore having the composition shown in Table 1 as a carbon source and changing the carbon content in a shaft furnace having a volume of 0.2 m ³ The product was charged and introduced as a reducing gas at a constant COG = 1500 Nm ³ / t-iron oxide from the bottom of the furnace to reduce the iron oxide.

  In Fig. 1, iron oxide, which has been pelletized by adding coal as a carbon source to iron ore, was charged into a shaft furnace, and the metallization rate of reduced iron (ratio of metallic iron in the obtained reduced iron) ) Shows the result of organizing the time required to reach the target of 85%.

  The vertical axis in FIG. 1 shows the time until reaching the target metallization rate of 85% until the target metallization rate is reached when iron oxide not containing carbon is reduced using only a reducing gas according to the conventional method. It is shown as dimensionless with reference to the time.

  As shown in FIG. 1, it can be seen that as the carbon content in the iron oxide increases, the time required to reach the target metallization rate tends to be shorter. Furthermore, it can be seen that when the ratio of carbon in the iron oxide is 10% by mass or more, not only the reduction completion time is shortened, but also the variation in the reduction time itself is drastically reduced.

  The reason for this is that when the average content of coal previously introduced as a carbon source into iron oxide is as small as less than 10% by mass, the coal tends to segregate in the iron oxide due to the mixing condition of the coal, and the shaft furnace In the distribution of iron oxides, in the case of positive segregation of coal (the carbon content is high), the reduction time with the reducing gas occurs in parallel with the reduction with carbon, so the time to reach the target metallization rate is shortened. On the contrary, when the carbon content is low due to the negative segregation of coal, reduction by the coal contained in the iron oxide hardly occurs, and the reduction by the reducing gas is the main, so the iron oxide charged in the shaft furnace is It is presumed that the overall reduction time to reach the target metallization rate is not so shortened.

  Therefore, when the average content ratio of coal previously introduced as a carbon source into iron oxide is less than 10% by mass, the target metallization rate is reached by coal segregation (mixing condition) as shown in FIG. The time to do is considered to vary.

  However, when the proportion of carbon in the iron oxide is as high as 10% by mass or more, the carbon content is poor, and even if negative segregation occurs, the carbon content of the negative segregation portion is relatively high. Because the amount of iron oxide reduced by reducing gas itself is reduced, it is less affected by segregation (mixing) of carbon in iron oxide, and the time required to reach the target metallization rate varies. Is considered to be small.

  From the above, in order to efficiently obtain reduced iron from the iron oxide charged together with the reducing gas in the shaft furnace, the iron oxide mixed in advance so that the carbon content is 10% by mass or more is charged into the shaft furnace. There is a need to.

  However, as shown in FIG. 1, when the carbon ratio in the iron oxide exceeds 30% by mass, the effect of reducing the reduction time is saturated. Therefore, in consideration of economy, the ratio of carbon in the iron oxide is , Less than 30% by mass is preferable.

  In addition to the above iron ore, iron oxides that are secondarily generated in the iron product manufacturing process, such as steelmaking dust (converter dust collection dust, etc.), blast furnace, etc. It is also possible to recycle the oxide powder scattered at the top of the furnace or the blast furnace cast floor and the falling oxide powder at the time of raw material transportation (belt conveyor or the like), which is preferable from the economical viewpoint.

  Moreover, as a carbon source, not only coal but coke etc. can be used. In particular, in the iron oxide, the oxide powder scattered at the top of the blast furnace furnace or the blast furnace cast floor and the falling oxide powder at the time of raw material transportation (such as a belt conveyor) are carbon-containing powder containing carbon. Since the step of mixing carbon and iron oxide can be simplified, the use of the oxide powder is economical and particularly preferable.

  On the other hand, when coal is used as a solid reducing agent, the sulfur contained in the coal may remain in iron products produced using reduced iron as a raw material, which may adversely affect quality. When mixing with the oxide, it is desirable to desulfurize the coal in advance.

  If limestone is mixed in advance with iron oxide as a desulfurizing agent, sulfur can be desulfurized when iron oxide is reduced in the shaft furnace, so mixing of limestone is preferable.

  Next, the preferable manufacturing process of the iron oxide charged in the shaft furnace of the present invention will be described.

  The iron oxide is not limited to iron ore, and as described above, various iron oxides can be used, and various iron oxide raw materials are divided into iron sources and accommodated in a plurality of hoppers. The raw material to be obtained is also stored in the hopper in advance. Further, if necessary, limestone as a desulfurizing agent is similarly stored in the hopper in advance.

  One or two or more iron oxide raw materials are cut out from the hopper, and a binder as a molding filler is added. If necessary, the raw material as a carbon source and limestone are cut out, and at least carbon is 10% by mass. The raw material is prepared so that it becomes the above.

  Then, the prepared raw materials are put into a mixer such as a ball mill, a kneader, a paddle mixer, and mixed for a certain period of time so that the components and the particle size are uniform. Next, the obtained mixed raw material is molded by a molding machine such as an extrusion molding machine, a briquette machine, a dish type granulator or the like so as to become a molded iron oxide having a particle size of about φ10 to 20 mm.

  The particle size, hardness, etc. may be changed as appropriate according to the reduced iron production conditions of the shaft furnace.

  Utilizing the carbon content in the iron oxide raw material as a carbon source, using the iron ore, the blast furnace top, the dust scattered from the casting floor, and the dust from the material transport as the iron oxide raw material, as shown in Table 1. Further, a binder as a molding filler was added to form a pellet. In addition, coke and coal are mixed as a carbon source separately as required in the iron oxide raw material, and further, in some conditions, limestone (100 kg / ton-iron oxide) is contained as a desulfurizing agent, Molded into pellets.

Then, the iron oxide raw material molded product was put into a shaft furnace having a volume of 0.2 m ³ from above the furnace.

  In the present invention example and the comparative example, as in the iron oxide production process described above, the iron oxide raw material and the like are cut out from the hopper, stirred and mixed with a paddle mixer, and then formed into a φ20 mm iron oxide with a briquette machine. The furnace was charged. In the conventional example, the iron oxide iron ore was directly charged into the shaft furnace without being formed.

The reduction of the iron oxide was performed by introducing COG = 1500 Nm ³ / t-iron oxide from the lower part of the furnace as a reducing gas in both the present invention example, the comparative example and the conventional example, and the metallization rate was 85. The time required to reach% or higher was measured. The results are shown in Table 2.

  Table 2 also shows the analysis result of the sulfur content in the reduced iron when a predetermined amount of limestone is mixed with the iron oxide.

  Note that the reduction time reaches the target metallization rate of 85% according to the conventional example (reduction using only reducing gas without including carbon in the iron oxide). Table 2 shows the evaluation that was made dimensionless based on the time required until.

  In Table 2, No. which is an example of the present invention. 1-No. 4, since the carbon content in the iron oxide is 10% or more, the time to reach the target metallization rate of 85% or more is 0.68 to the time of the conventional example regardless of the type of the iron oxide source. 0.8, which is greatly shortened.

  Further, the variation in the reduction time (standard deviation σ) was as small as 0.024 to 0.3. Moreover, No. which mixed limestone beforehand. In the case of 4, the sulfur content was desulfurized in the shaft furnace, and the sulfur content in the reduced iron was reduced by about 10% compared to the iron oxide before the reduction.

  On the other hand, in Table 2, No. of the comparative example whose carbon content in the iron oxide is less than 10% by mass. 5 and no. In FIG. 6, although the reduction time can be shortened compared to the conventional example, it takes more time than the example of the present invention, and the variation (standard deviation σ) is large, and the reduction time cannot be stably reduced. .

It is a figure which shows the relationship between carbon content (%) in an iron oxide, and the time (reduction time ratio) required to reach | attain a target metalization rate (85%).

Claims (3)

In a method for producing reduced iron by reducing iron oxide in a shaft furnace,
(A) An iron oxide containing carbon in advance so as to be 10% by mass or more in terms of carbon is charged into a shaft furnace,
(B) A method for producing reduced iron, comprising producing reduced iron by blowing a reducing gas into a shaft furnace.   The method for producing reduced iron according to claim 1, wherein carbon-containing powder is used as the iron oxide. The method for producing reduced iron according to claim 1 or 2, wherein limestone is mixed in advance with the iron oxide before charging the iron oxide into the shaft furnace.

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