JPS5837364B2 - Pellet for reduction furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to pellets for producing reduced iron used in a reduction furnace.

In recent years, the so-called direct iron manufacturing method, in which iron ore is reduced with gas or carbonaceous materials, has become popular.

This method has the advantages of having a higher degree of freedom in energy selection than the blast furnace and converter method, which currently dominates the steel manufacturing process, such as being suitable for small-scale equipment with small capital, and not requiring a high level of technology. , production volume is expected to increase further in the future.

Although a number of direct steelmaking processes have been proposed recently, the preferred reduction reaction of these processes is achieved by shaft furnaces.

For production in shaft furnaces, lump ore is also used as feed material, but pelletized iron ore is more frequently used.

The higher the quality of these beresoto-like raw materials, the more desirable they are from the viewpoint of productivity.

However, when using pellets with a high iron content, the pellets have an unfavorable property of sticking to each other and clumping together during the stage of being reduced by high-temperature reducing gas in the furnace, which is not desirable in terms of operation.

Once the pellets become sticky inside the furnace, this causes phenomena such as the charge being hung on a shelf or being unable to be discharged outside the furnace, resulting in a significant drop in productivity.

In order to improve the unloading condition of pellets in a shaft furnace, a method has been proposed in which a breaker is installed in the furnace to destroy the pellets when they become sticky, but this method is not only expensive but also Maintenance of equipment is difficult.

In addition, as a countermeasure to solve this problem, a method has been proposed in which the outer surface of the pellet is coated with at least one substance selected from the group consisting of lime, limestone, and dolomite in a shaft furnace during pellet production. However, with this method, the strength of the surface coating layer is weak, so it easily peels off and adhesion cannot be completely prevented.

The present invention provides a method for producing pellets that do not easily stick even under high-temperature reducing gas injection, which solves the above-mentioned problems in reducing pellets for producing reduced iron using a shaft furnace. It is characterized in that by coating the outer periphery of the pellet with ore having a low iron content, a layer is formed on the pellet surface that is less likely to cause adhesion and does not peel off, thereby preventing the pellet from adhesion.

When producing reduced iron using a shaft furnace, it is necessary to increase the blowing temperature of the reducing gas to increase the productivity of the shaft furnace, and to reduce the amount of gangue in the charge to reduce the energy consumption in the product melting process. It is advantageous to reduce the amount of iron, that is, to increase the iron content, but all of these methods tend to cause the charge to hang in the furnace and stick to the charge, which causes the inability to discharge. However, once adhesion occurs, productivity will be significantly reduced as a result.

The inventors conducted various experiments to find out the cause of this adhesion, and found that adhesion occurs when reduced iron on the pellet surface is sintered at high temperatures, causing the pellets to stick together. It has been found that when the amount is less than 63%, adhesion becomes less likely to occur.

The present invention is an innovative method that utilizes the above results to prevent high-quality pellets from sticking in a shaft furnace.

The ore used in the present invention has a particle size that is generally used for producing pellets for producing reduced iron (for example, -44μ is 60 to 70
%), and by adding 0.5 to 1.0% of bentonite as a binder to this, it is used for granulating pellets.

First, in order to reduce energy consumption in the melting process of the product, we produce iron ore powder (hereinafter sometimes referred to as high-grade iron ore) with a small amount of gangue and an iron content of 63% or more, more preferably 65% or more.

) to produce green pellets with an average particle size of 6 to 16TnTfL using a granulator.

Next, either stop ore feeding in the same granulator and restart it, or use another granulator to feed iron-containing ore powder that does not easily cause stickiness, and then Coating to produce double granulated pellets.

The ore for coating the outer periphery preferably has an iron content of less than 63% in order to prevent the pellets from sticking together due to sintering of the reduced metal iron.

On the other hand, it is preferable that the iron content is 10% or more from the viewpoint of not reducing the iron content of the peresoto and strengthening the adhesion between the inner core and the coating layer.

In view of the above points, the coating ore preferably has an iron content of 10% or more and less than 63%, more preferably an iron content of 55% or more and less than 63%.

The ore for coating the outer periphery is at least iron ore powder within the above iron content range, or iron ore and lime, limestone, serpentine, dolomite, blast furnace slag, converter slag, and electric furnace slag. For mixed powders made by mixing one type of substance so that the iron content is within the above range (the mixing ratio varies depending on the mixed substance), or for converter slag and electric furnace slag that contain iron, each slag single grade Use powder.

The thickness of the ore layer covering the outer periphery is 0 from the point of view of preventing adhesion.
．． As long as it is above 1 rItmJJ, it may be as thick as it is, but from the point of view of increasing the iron content of the pellets, the thinner it is, the more desirable it is, and from the above two points, 0.1 to 1.0 mm is most preferable.

The pellets granulated in this way are dried using ready-made equipment.
Perform preheating and burning to produce burnt pellets.

It has been revealed that the fired pellets produced according to the present invention have good adhesion, strength at room temperature, and strength after reduction, and do not stick even under high-temperature reducing gas injection in a shaft furnace.

Next, the present invention will be explained by examples.

Example 1 Table 1 shows the chemical composition of the ore used.

First, beresoto with a particle size of 11 to 12 is produced using Brazil ore mixed with 0.5% bentonite, and the outer periphery is granulated with Hamasley ore containing 0.5% bentonite, and coated for 1 hour. A double granulated pellet according to the present invention with a particle size of 12 to 13 was prepared by forming layers.

The pellets were dried at 300°C for 6 minutes in an air atmosphere, then preheated at 1000°C for 5 minutes, and then
It was baked at a temperature of 50° C. for 10 minutes and used in various tests.

Adhesive properties were examined using an apparatus and test method devised by the present inventors.

The test equipment and test conditions are shown in FIGS. 1, 2, and 3.

Regarding the adhesive properties of the pellets, the lower the adhesive strength between the pellets, the better.

The test results are shown in Table 2.

For comparison, Table 2 also shows the results for pellets made of Brazilian ore alone and not coated with Hamasley ore.

As shown in Table 2, the pellets according to the present invention exhibited a low adhesive force of 0.2 kg, whereas the untreated pellets exhibited a high adhesive force of 12.1 kg.

In addition, it was possible to produce Beresoto, which has high strength at room temperature and high strength after reduction, and is suitable for shaft furnaces.

Example 2 Pellets with a particle size of 11 to 12 were produced using Brazilian ore mixed with 0.5% bentonite, and Riodoce ore with 0.5% bentonite and 8.6% limestone added to the outer periphery was produced. A double granulated pellet with a particle size of 12 to 13 mm was produced by granulating the powder to form a one-layer coating layer (iron content of the coating layer: 58.4%).

This pellet was fired under the same conditions as in Example 1 and used in various tests.

The test results are shown in Table 2. As shown in Table 2, similar to Example 1, pellets with low adhesive strength and high strength at room temperature and strength after reduction were able to be produced compared to pellets made of Brazilian ore alone.

As a result of operating a shaft furnace using the above-mentioned pellets for producing reduced iron according to the present invention, smooth operation could be performed without causing sticking in the shaft furnace.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an ore adhesion testing device, FIG. 2 is an explanatory diagram of an ore adhesion measuring device, and FIG. 3 is a diagram showing adhesion test conditions. 1...sample, 2...crucible, 3...
...Push rod, 4...Alumina ball, 5...
...Reaction tube, 6...Electric furnace, 7...
Gas inlet, 8... Gas outlet, 9...
・Weight.

Claims (1)

[Claims] 1. A pellet for a reduction furnace, characterized in that the outer surface of the pellet for producing reduced iron is coated with ore containing less than 63% iron.