JPS5910411B2 - Pretreatment method for raw materials for direct steelmaking - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a pretreatment method for raw materials for direct steelmaking, and in particular, to effectively prevent so-called clustering, which is the sticking of raw materials to each other due to the diffusion of metallic iron that occurs on the surface of the raw materials in the main furnace. Regarding the processing method.

Among the ring iron production technologies, the so-called shaft produces reduced iron by reacting the raw material charged from the top of the furnace with the reducing gas introduced from the bottom of the furnace, based on the principle of counterflow between solid and gas. The furnace method is known as the most efficient process with excellent operational stability.

The production capacity of one shaft furnace is currently about 400,000 to 500,000 tons per year, but in recent years, direct steelmaking plants of 5 to 10 units have been built in natural gas producing regions of the Middle East and the Soviet Union. Increasingly, there is an increase in the number of cases in which steel is manufactured directly using the abundant natural gas that is built, so increasing the size of equipment and increasing productivity per unit are important considerations. This is becoming an issue.

Furthermore, even if the direct iron manufacturing method is replaced by the current blast furnace iron manufacturing method due to the use of nuclear heat for iron manufacturing in the future, larger equipment and higher productivity will inevitably be required.

The most effective method for increasing the productivity of this shaft furnace is to raise the temperature of the blown reducing gas.

Increasing the temperature of the reducing gas has a favorable effect not only in terms of productivity but also in preventing re-oxidation of the product (reduced iron).

However, increasing the temperature of the reducing gas injected from the slats in the lower part of the furnace, on the other hand, causes an undesirable phenomenon called clustering, in which the charged raw material lumps in the high temperature region of the lower part of the reduction zone in the furnace stick to each other.

If clusters of raw materials are formed in the furnace, not only will the flow (fall) of the raw materials in the furnace become uneven, but it will also cause an increase in gas pressure drop, making the operation extremely unstable, and in severe cases, the operation may become unstable. They are forced to stop.

In order to increase the productivity of shaft furnaces, it is absolutely necessary to develop means for effectively preventing the above-mentioned clustering caused by the increase in temperature of the reducing gas.

By the way, the above-mentioned adverse effects caused by the generated clusters depend on the cluster strength, that is, the degree of adhesion between the raw materials.If the cluster strength is extremely low, the raw materials filled in the furnace may separate due to their own weight. Although it does not cause any particular problem when it falls apart, if the adhesion force is strong, it causes various troubles as mentioned above.

The evaluation of this cluster strength was carried out using a rotating steel barrel 1, 1 drive stage 2, which rotates the barrel, as shown in Figure 1.
After the clusters are placed in the barrel and rotated at a constant speed for a certain period of time, the crushed clusters are removed and the amount of remaining clusters is weighed, and the remaining percentage represents the cluster strength. It is convenient.

According to experiments conducted by the present inventors, it has been found that the CS value (a) calculated by the following formula from the thruster residual amount after rotating at a rotational speed of 30 rpm for 5 minutes can be practically effectively used as the cluster strength. are doing.

CS(B/AXIOO) [wherein A represents the weight of the sample cluster before the rotation test, and B represents the weight of the cluster remaining on the sieve with a mesh corresponding to the raw material particle size after the rotation test and the test.

]. The generation of clusters is influenced by the reducing gas temperature as well as the properties of the charged raw material, and the strength of the clusters generated is particularly susceptible to the iron grade of the raw material.

For example, using iron ore pellets with various iron grades, H2 55, CO 36, CO2 5 and CH,
The cluster strength generated when reducing gas with a composition of 4% as a reducing gas at 910°C for 3 hours was measured using the rotating test shown in Figure 1 above. When measured using a testing device, a relationship as shown by curve a in FIG. 2 is established between iron quality and cluster strength.

As shown in the figure, as the iron grade increases, the cluster strength increases significantly, but when the iron grade is about 64 or less, the strength of the cluster increases significantly. After testing, all the clusters peeled off,
The cluster strength value becomes 0.

For this reason, it may be possible to use low-grade iron raw materials with a high gangue content as a means to prevent the formation of clusters, but this increases the gangue content that is carried over into the resulting reduced iron, resulting in subsequent steelmaking. The amount of electricity required for melting in the process is increased n
This causes the inconvenience of doing so.

Generally, it is said that the power consumption increases by 25 to 30 KWH per ton of steel when the power is increased by 1% gangue in reduced iron.

In addition, an increase in the amount of gangue 710 is undesirable because it causes an increase in the amount of lime used in the steelmaking furnace and destabilizes the melting operation due to expansion of slag.

Various other methods have been devised to suppress or alleviate cluster generation.

For example, there is a method of mixing alumina, ceramic, etc. with raw material in a shaft furnace (Japanese Patent Publication No. 35-6504), a method of mixing and charging molded coal coke into a shaft furnace (Japanese Patent Application Laid-open No. 51-96717), or Method of charging fine carbon particles with iron oxide (%Koshō 51-3536
6) have been proposed.

However, in this method of charging other materials in a mixed manner, the amount of iron raw material charged is reduced by the charging volume of other materials, sacrificing the productivity of the shaft furnace, and There is a drawback that separation of reduced iron and other substances is troublesome.

Furthermore, mixing other materials with different specific gravity, shape, particle size, etc. from the iron raw material (iron oxide) disturbs the uniform and smooth descent of the materials in the furnace and the flow of reducing gas, and especially the fine carbon particles. The mixing method involves problems such as significant gas pressure loss in the furnace and increased power loss of dust.

In addition, as another method, a method using lime-added pellets made by adding lime to iron ore has been proposed (Japanese Unexamined Patent Application Publication No. 1983-1981-1).
No. 42008).

In Figure 2, curve b shows the cluster strength when pellets formed by adding lime to ores of various iron grades are used as raw materials and reduced under the same conditions as peresoto in curve a in the figure. It is.

As shown in the figure, by adding lime, the iron grade was approximately 67.
%, the cluster strength is O, and even at higher grades, the strength value is extremely low, and it is recognized that it is very effective in suppressing and mitigating clusters.

However, this method has the drawback of worsening the reducibility of the raw material, as shown in FIG.

The figure shows the reduction rate and reduction when the iron grade is set at a constant value of approximately 67% and pellets manufactured by varying the amount of lime added are used as raw materials, and the same reducing gas as above is used for reduction at 860 ° C. It is a graph showing the relationship between time, and in the figure, curves a and b
and C, the lime addition rate is 0.12% and 0.9, respectively.
The cases of section 1.1 and section 1.1 are shown.

In direct steelmaking, the quality of the finished product (reduced iron) is generally one with a high reduction rate of 90 or higher, the so-called final reduction rate, but as shown in the figure, the value is higher than that in pellets. The higher the lime CaO content, the lower the content tends to be.

In addition to hematite, the calcined structure of lime-loaded pellets contains a solid solution of CaO-nFe203 or CaO-Fe2.
Slag phases such as 03 and Sio2 coexist, and the iron oxides fixed in the slag are difficult to reduce in the reduction range of the shaft furnace method, so lime is present in the pellet structure. Its presence impairs the reducibility of the raw material and lowers the final reduction rate.

The present inventors have devised a method for effectively preventing the clustering phenomenon while overcoming the drawbacks of the previously proposed cluster prevention measures as described above and providing stable and smooth operability and excellent reducibility. In order to develop this, we have been conducting intensive research on the relationship between reduction conditions, raw material properties, and cluster formation behavior.

As a result, we found that the metallographic cause of the clusters is 1.Ma, which is based on the sintering phenomenon caused by the surface diffusion of reduced metallic iron as a solid. It is extremely effective to form a film of CaO, MgO, or other foreign substances that do not adversely affect the steelmaking process on the surface of the charged raw material as a means of suppressing and alleviating the steelmaking process. We have found that it is effective and convenient to immerse the raw material in a solution containing a foreign substance or to spray the solution onto the surface of the raw material.

The present invention was completed based on this knowledge.

That is, the present invention provides that, prior to charging the direct steelmaking raw material into a direct steelmaking reduction furnace such as a shaft furnace, the raw material is subjected to the following steps:
By spraying a magnesium mercury solution or immersing the raw material in these solutions and drying, a coating film of about 0.05 to 2 stripes (based on the weight of the raw material before being sprayed or immersed) is formed on the surface of the raw material. The goal is to effectively prevent the raw materials from sticking to each other without impairing the reducibility of the raw materials or the stability of operation within the furnace.

The present invention will be explained in detail below.

According to the present invention, the charged raw material is coated with a foreign substance before being introduced into the furnace.

The foreign substance is preferably one that does not interfere with the steelmaking process that follows the reduction reaction in the reduction furnace, and CaO and MgO are preferable.

To form a film, for example, when using CaO or MgO, an aqueous solution of Ca(OH)2 or Mg(OH)2 is made, and this is sprayed onto the surface of the raw material, or it is immersed in the aqueous solution and then dried. This makes it possible to form a very thin film on the surface of the raw material.

The film of calcium hydroxide or magnesium hydroxide thus formed dissociates water as follows when heated by force.

C a (OH) 2 → C a O + H2
0 ”・-・(1) Mg(OH)2→MgO+H20
・・・・・・・・・(2) The reaction of Uero 1) is carried out under atmospheric pressure.
At 580°C, reaction (2) occurs at 350°C.

Therefore, the film of the raw material that has undergone film formation treatment is easily dehydrated by the above reaction during the drying process before charging into the shaft furnace or in the upper part of the shaft furnace, and as a result, the surface structure becomes appropriately porous. Therefore, the reduction reaction in the furnace proceeds smoothly without any hindrance.

The material particles that adhere to the surface of the raw material prevent the metallic iron produced by the reduction reaction from coming into contact with each other, and also play the role of suppressing the movement of atoms, which is one of the driving forces for surface diffusion between solids. Effectively prevent mutual sticking.

The film formation in the method of the present invention may be carried out in various ways, and for example, a large amount of raw material can be efficiently processed using an apparatus as shown in FIG.

In the figure, 1 is an endless band dryer with a mesh that is finer than the particle size of the raw material, 2 is a raw material hopper that supplies the raw material to the band dryer, and 4 is a spray nozzle, from which the treatment liquid for film formation is applied to the raw material above the dryer. is scattered.

7 and 8 are raw material drying devices.

The raw material 3 supplied from the raw material hopper 2 onto the band dryer 1 is first sprayed with a treatment liquid from the spray nozzle 4 while being sequentially transferred to the left by the band dryer 10 rotations.

As the treatment liquid, as mentioned above, C a (OH)2
An aqueous solution of Mg(OH)2 or Mg(OH)2 can be used.

The processing liquid permeates through the raw material layer 3 while sufficiently covering the surface of the raw material, and the remaining liquid is recovered in the lower recovery tank 5 and sent to the soubray nozzle 4 section by the circulation pump 6 for reuse.

The raw material on which a treatment liquid film has been formed on the surface by spraying the treatment liquid then reaches the hot air supply pipe 7 and the hood 8, where it is heated for about 15 minutes.
After being dried while being exposed to a gas flow of 0 to 500° C., the material reaches the terminal end of the belt dryer 1, falls into the material receiving hopper 9, and is stored therein.

In this way, a raw material having a film made of foreign substances contained in the treatment liquid is obtained.

By using such an apparatus, it is possible to efficiently form a uniform foreign substance film on the surface of the raw material by continuously processing a large amount of the raw material.

The raw material thus obtained maintains good reducibility in the reduction furnace and effectively prevents clustering.

Figure 5 shows the strength measurement results of clusters generated when iron oxide raw materials with a foreign material film were subjected to reduction treatment (reduction time 3 hours) in a shaft furnace at various reduction temperatures according to the method of the present invention. This is a graph.

In the figure, curves 1 and 2 are obtained by immersing raw material pellets in an aqueous calcium hydroxide solution and adding 0.2% and 0.0% CaO, respectively.
．． 5'% (based on the weight of the raw material before coating) was deposited.

Note that curve a shows the comparative materials of untreated pellets, and curve b shows the comparative materials of lime-added pellets.

As is clear from the figure, the cluster strength of the raw material pellets treated by the force method of the present invention is significantly higher than that of untreated pellets (curve a), although there are slight differences depending on the type and amount of coating material. It is recognized that the value is low and roughly equivalent to that of lime-added Calopellet (curve b).

FIG. 6 is a graph showing the final reduction rate of each pellet in the above treatment, and each symbol on each curve 2ta and b represents the same pellet as above.

As shown in the figure, the final reduction rate achieved with lime-added pellets (curve b) is less than 95%, whereas that with the method of the present invention (curve 2) is extremely high; ) is recognized as having a level equivalent to that of

As mentioned above, untreated pellets have a high final reduction rate (Fig. 6, curve a), but have the disadvantage that strong clusters are likely to form (Fig. 5, curve a), whereas lime-added pellets have Although it has the advantage of being less likely to form clusters and having low strength (Fig. 5, curve b), it has the disadvantage of poor reducibility and a low final reduction rate (Fig. 6, curve b).

On the other hand, according to the method of the present invention, the reducibility equivalent to that of untreated pellets is maintained (Fig. 6, curve 2), and the cluster prevention effect is equivalent to that of lime-added pellets (Fig. 6, curve 2). 5, curves 1 and 2).

As described above, according to the present invention, the reduced iron raw material is immersed in or sprinkled with a liquid containing a suitable foreign substance to form a film on its surface, which is a simple means of forming a film on the surface of the raw material, without impairing the reducibility of the raw material. Clustering in the reduction furnace can be effectively prevented, and stable and smooth operation can be guaranteed, especially when increasing the reaction content in the furnace for the purpose of improving productivity.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the appearance of the cluster strength measuring device, Figure 2 is a graph showing the influence of the iron grade of the raw material on cluster strength, Figure 3 is a graph showing the relationship between reduction rate and reduction time, and Figure 4. 5 is a schematic diagram showing a specific example of a raw material processing apparatus used in carrying out the present invention, FIG. 5 is a graph showing the relationship between cluster strength and reduction temperature, and FIG. 6 is a graph showing the relationship between final reduction rate and reduction temperature. This is a graph showing. 1... Band dryer, 2... Raw material supply hoch, 3
... Raw material, 4... Spray nozzle, 5... Processing liquid recovery tank, 6... Circulation pump, 7... Hot air supply pipe, 9
...Raw material receiving hopper.

Claims (1)

[Claims] 1. Prior to directly charging raw materials for steelmaking into a steelmaking reduction furnace, the raw materials are sprayed with a calcium hydroxide or magnesium hydroxide solution, or by immersing the raw materials in these liquids and then drying them. 0.05~ on the surface of the raw material
A method for pre-processing raw materials for direct steelmaking, characterized in that clustering of raw materials is prevented by forming a coating film of 2nd layer (based on the weight of raw materials before being sprayed or immersed).