JPH0826416B2 - Steelmaking raw material with excellent clustering resistance for direct ironmaking or smelting reduction ironmaking - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a preliminary reduction using a vertical furnace typified by a shaft furnace (hereinafter sometimes simply referred to as a vertical furnace), that is, a direct iron-making method. Alternatively, when performing preliminary reduction in the smelting reduction ironmaking method, it relates to an ironmaking raw material excellent in clustering resistance that does not cause clustering in the vertical furnace even if the operating temperature is raised, and thereby heat loss It has achieved a reduction and an improvement in operational efficiency.

[Prior Art] The direct iron-making method or the smelting reduction iron-making method is suitable for small-scale production and has the versatility to use coal or natural gas as a reducing agent. It has been gradually increasing recently.

The mainstream of the direct iron making method or the smelting reduction iron making method at present is the Midrex method and the HyL method which use a vertical furnace represented by a shaft furnace as a reducing furnace. Bulk iron ore (lump ore) or pellets (solidified ore solidified into spheres) are used as the raw material for charging the shaft furnace. These often cause a phenomenon called clustering in the high temperature reducing atmosphere in the shaft furnace. It is known to significantly impair operability. That is, clustering is
A phenomenon in which lump ore and pellets are fused together in a high-temperature reducing atmosphere in a shaft furnace to form a large lump, and when such a phenomenon occurs, it becomes difficult to discharge reduced iron from the lower part of the shaft furnace, or In the shaft furnace, a bridging phenomenon of charged ores (hereinafter sometimes simply referred to as a load) called a shelving occurs, which hinders the smooth descent of the load, resulting in a marked decrease in operability. From such a point, in normal shaft furnace operation, the maximum reduction temperature is kept low to prevent the occurrence of clustering. Therefore, the reduction rate cannot be sufficiently increased and the productivity is satisfactory. Has not been able to improve. The maximum reduction temperature is determined by the temperature of the reducing gas blown into the shaft furnace, but the temperature of the reducing gas emitted from a general reducing gas generator is usually much higher than the above maximum reducing temperature. In order to supply the reducing gas to the shaft furnace, the temperature must be lowered to the maximum reducing temperature, which causes a loss of heat energy. Especially in the smelting reduction method which has been actively studied recently, the reducing gas generated is extremely high in temperature,
The loss of thermal energy caused by lowering the reducing gas to the maximum reducing temperature cannot be understated.

By the way, the maximum reduction temperature of the shaft furnace currently in operation is about 830 ° C in the case of the Midrex method, and almost all other methods operate at temperatures below this. On the other hand, the operating temperature of the reformer, which is a reducing gas production device, is approximately
At 1100 ℃, the reducing gas produced by this device is about 97
Since the temperature is 0 ° C, when it is blown into the shaft furnace, it must be cooled to 850 to 900 ° C, and a heat loss of about 100 ° C occurs during this.

In the smelting reduction method, the reducing gas is produced at a temperature above the melting temperature of metallic iron, so the temperature of the reducing gas generated is about
Although it may reach up to 1500 ℃, if a shaft furnace is adopted as the preliminary reduction furnace, the reducing gas should be reduced from about 1500 ℃ to 85 ℃.
The temperature must be lowered to about 0 to 900 ° C, and the heat loss during this period becomes enormous.

Furthermore, from the viewpoint of the reduction reaction rate of the raw material ore, theoretically, it has been confirmed that increasing the operating temperature by 100 ° C will increase the reduction reaction rate by a factor of about 1.3. If so, productivity can be improved by about 30%.

However, if an attempt is made to raise the maximum reduction temperature, clustering occurs as described above and operation stability is significantly impaired. Therefore, it is unavoidable that the reduction temperature is suppressed to a low level during the operation.

From this point of view, research is being conducted to increase the reduction reaction temperature while preventing clustering. For example, the method disclosed in Japanese Examined Patent Publication No. 59-10411 is composed of CaO or MgO by the following reaction after heat treatment after depositing an aqueous solution containing Ca (OH) ₂ or Mg (OH) ₂ on a raw iron ore. It is intended to prevent clustering by forming a film.

Ca (OH) ₂ → CaO + H ₂ O Mg (OH) ₂ → MgO + H ₂ O However, this method cannot obtain a satisfactory clustering prevention effect, as will be apparent from the examples described later.

[Problems to be Solved by the Invention] Therefore, the applicant of the present application has repeatedly studied clustering prevention means, and previously disclosed Japanese Patent Application No. 60-145641 (Japanese Patent Laid-Open No. 62-7806).
No.). That is, the proposal uses a raw material iron ore whose surface is coated with cement as an iron-making raw material in performing preliminary reduction in a vertical furnace, and succeeds in preventing clustering at reduction temperatures up to 1000 ° C. There is. However, with this level of clustering prevention effect, it cannot be said that the sensible heat of the reducing gas discharged from the smelting reduction furnace, which has an operating temperature of 1500 ° C, is still fully utilized (the temperature is reduced to 1000 ° C). Heat loss is still large.

The present invention was made in view of these circumstances, by increasing the operating efficiency in the furnace by providing an ironmaking raw material for direct ironmaking or smelting reduction ironmaking excellent in clustering prevention performance, and It is intended to reduce heat loss in the iron making process.

[Means for Solving Problems] However, the iron-making raw material of the present invention which has achieved the above-mentioned object is an iron-making raw material used in a direct iron-making method or a smelting reduction iron-making method, and a cement is formed on the surface of the massive or spherical iron-making raw material. The gist is that it is a coating of compound iron ore.

[Operation] As described above, the reduction temperature in the direct reduction using the vertical furnace depends on the clustering generation temperature. The gangue component and the pellet are affected by the basic components such as calcium compounds and magnesium compounds [CaO, Ca (OH) ₂ , CaCo ₃ , CaCO ₃ · MgCO ₃ ] added to the pellets. Especially for pellets,
It is known that the clustering temperature changes depending on the type and amount of additives, as well as the firing temperature. For example, adding lime (CaO) -based minerals to (CaO / SiO
₂ ) It has been confirmed that the temperature at which clustering occurs can be increased by increasing the ratio, that is, the basicity.
This method has a drawback that the iron quality is lowered by the addition of the lime mineral. However, as the iron ore raw material for direct iron making (method of melting in an electric furnace after reduction), there is a circumstance that originally high-grade iron ore is selected to reduce the operating cost of the electric furnace. There is little room to adjust the clustering temperature. That is, it is said that the minimum iron grade required as a raw material for direct ironmaking is 65 to 70% by weight, and under these restrictions, even if lime-based minerals are added, the amount added is naturally limited. , Clustering cannot be effectively prevented.

In addition, in the smelting reduction iron manufacturing method in which reduced iron is melted in the vertical furnace, the high-temperature reducing gas generated from the melting furnace is supplied to the vertical furnace, which is the preliminary reducing furnace, when it is used, as described above. Since the difference between the temperature and the operating temperature (reduction temperature) is large, heat loss is significant. Therefore, in order to reduce heat loss, it is necessary to develop a method that can prevent clustering even at a reduction temperature of over 1000 ° C.

Under such circumstances, the prior application method of "putting the iron-making raw material in which the surface of the raw iron ore is coated with cement into the vertical furnace and performing preliminary reduction" has achieved some success in preventing clustering. However, they have not fully answered the above request. The reason is that the amount of cement used is limited because it is necessary to maintain the iron quality above a certain level, and as a result, the cement coating thickness cannot be increased sufficiently and there is a limit to the prevention of clustering. It is considered to be a thing.
That is, fusion of the iron-making raw materials that occur in the latter stage of reduction of the iron-making raw material, interdiffusion of metal iron and entanglement of whiskers,
Or, it is considered that it is caused by melt adhesion due to the formation of low melting point slag.Therefore, the effect of coating the raw material surface with cement is to avoid direct contact between the iron-making raw material particle ground surfaces and to spread the above on the contact surface. It can be inferred that this is to prevent such problems as described above.
If the temperature exceeds 1000 ° C, it is impossible to completely prevent direct contact between the bare surfaces, and as a result, clustering may occur.

On the other hand, in the present invention, as shown in the above configuration, the iron-making raw material surface is provided with a cement-containing iron ore instead of the cement single component to achieve a sufficient coating thickness, and as a result, at an operating temperature exceeding 1000 ° C. But now it is possible to prevent clustering. That is, clustering has been confirmed in another experiment that the higher the iron content in the ironmaking raw material, the more likely it is to occur, but conversely, the result of the experiment is that the mutual diffusion of iron, which is the cause of clustering, is This means that the smaller the iron content is, the smaller the iron content is. Therefore, the purpose of preventing clustering does not necessarily mean that the iron content does not have to be zero. In other words, even if a small amount of iron ore is contained in the cement coating layer, it is possible to substantially prevent interdiffusion of iron if the amount is below a predetermined limit, and It is possible to suppress the deterioration of iron quality due to the formation. Therefore, we decided to adopt a means of coating cement-containing iron ore instead of cement single component, and conducted various studies. As a result, even if the coating thickness was increased, the overall deterioration of iron quality was suppressed, and as a result It is possible to reliably prevent contact between the raw materials and to prevent clustering even at an operating temperature of 1000 ° C or higher, and to perform efficient preliminary reduction while further suppressing heat loss.

Although the basic configuration of the present invention is as described above, in order to more reliably exert such a clustering prevention effect, the iron content of the massive or spherical iron-making raw material (core) is 66 to
The cement content of the cement-containing iron ore coating layer is 70% by weight, and the cement content is 6 to less than 80% by weight, or the coating layer has a thickness of 0.05.
It is desired to be in the range of ~ 4.5 mm, preferably 0.10-4.5 mm. That is, if the cement content is less than 6% by weight or the coating layer thickness is less than 0.05 mm, the clustering prevention effect cannot be effectively exhibited, and the iron content of the ironmaking raw material is less than 66% by weight or the coating layer thickness is 4.5 mm. If it exceeds the above range, the slag amount increases and the iron content decreases, and the productivity, the metallization rate, the reduction rate, etc. decrease, resulting in an undesirable situation. Further, when the cement content of the cement-containing iron ore coating layer exceeds 80% by weight, it becomes close to the cement single-component layer, and improvement in coating thickness cannot be expected. The upper limit of the iron content of the iron-making raw material is set to 70% by weight because it is adjusted to the upper limit of the usual high-grade raw material, and does not limit the use of the higher-grade iron-making raw material. The upper limit of the coating thickness and the amount of cement compounded in the coating layer can be further increased.

There are no particular restrictions on the type of cement that is mixed with iron ore, including self-hardening cement (boltland cement), latent hydraulic cement (such as blast furnace cement), blast furnace slag, blast furnace slag, and fine powder of steel slag. All of them can be used, but the most preferable is that they have high hydraulic properties in terms of adhesion to iron ore, contain a large amount of a compound (3CaO · SiO ₂ ) that exhibits a strong hydration reaction, and It is an inexpensive and easily available ordinary Portland cement, early strength Portland cement, high strength Portland cement, etc. The method for adhering cement to the surface of the raw material ore is not limited at all, but the most common methods include rolling method, spraying method, dipping method and the like.

[Example] d50 (50% passing particle system) = 30 μm (Blaine value: 2000 cm)
² / g) powdered iron ore (iron content 67.98% by weight) was granulated with a tire type pelletizer to a particle size of 12.7 mm ^φ , and the surface of the granulated product had the same purity as the above iron ore. 12 for iron ore
Cement-blended iron ore blended with wt% cement.
An iron agglomerated ore coated with a cement-containing iron ore under the conditions shown in Table 1 was produced by coating to a thickness of 15 mm. The structure is first
Table 2 shows the chemical analysis values of each part of the cement-containing iron ore-coated iron agglomerate when the amount of cement is changed. In addition, the chemical analysis results of the untreated iron agglomerate produced by plain iron ore having an iron content of 67 wt% or more and the coated iron agglomerated ore produced by coating with cement-containing iron ore
Shown in the table.

As is clear from Table 3, T.Fe in iron agglomerated ores from 67.98% by weight to 67.% by coating treatment of cement-containing iron ore.
It decreased by 0.53% by weight from 45% by weight. However, such a decrease in T / Fe is unlikely to cause a substantial hindrance to the quality of raw iron ore for direct ironmaking and smelting reduction ironmaking.

Next, using these two types of iron ore pellets, a clustering evaluation test was performed by the following method.

That is, assuming that a modified natural gas is used as the reducing gas, a reducing gas having the composition shown in Table 4 is prepared,
500 g of each of the above pellets is charged into a 75 ^φ × 165 ^l (mm) reaction tube (sample layer height is about 50 mm), and a reduction reaction is carried out for 3 hours while applying a load of ² kg / cm ² from above. Therefore, the sample pellets are fused with each other while contracting due to the pressure applied from the above. The reduction temperature at this time is usually 910 ° C, but 10% for cement-containing iron ore-coated iron agglomerates.
It was carried out at 50 to 1100 ° C. After completion of the reduction, the sample was cooled and taken out, put into a cylinder of 120 ^φ x 700 ^l (mm), rotated at 30 rpm for 5 minutes, taken out from the cylinder, and then the whole mass of two or more pellets fused together. The weight ratio to the pellet was calculated as a cluster index. The results are shown in Table 5.

As is clear from Table 5, when the coating treatment with cement-containing iron ore was performed in the granulation process of the iron agglomerate manufacturing stage, even when the reduction temperature was raised to 1050 ° C, the untreated pellets were heated to 910 ° C or the cement was coated. Shrinkage rate of pellets at each reduction temperature of 1050 ℃ (33.75% for the former and 57.65 for the latter)
%), And clustering does not occur at all. It also shows that the pressure loss is as low as 5.0 mmAq, and there is no problem with breathability.

Next, it is also disclosed in the aforementioned Japanese Patent Publication No. 59-10411.
In order to compare the clustering prevention effect of CaO surface-adhered pellets, limestone-added pellets, cement-coated pellets, and coated iron agglomerates of the cement-containing iron ore according to the present invention, the relationship between the reduction temperature and cluster index of each treated experimental sample And the results shown in FIG. 2 were obtained.

As is clear from Fig. 2, limestone-added pellets and Ca
The cluster index is 0% when the reduction temperature is 910 ° C and the cement-coated pellet is 1000 ° C for O surface-attached pellets, but the cluster index increases sharply when the temperature is raised to 1000-1050 ° C. On the other hand, in the case of a coated iron agglomerated ore containing cement-containing iron ore, the cluster index is 0% even when the reduction temperature is raised to 1050 ° C., and the superiority of the present invention can be confirmed. Further, Fig. 3 shows the relationship between the cement content of the coating and the cluster index in the reduction at 1050 ° C according to the above method using iron ore having an iron content of 67.98% by weight, and Fig. 4 shows the same iron ore. The results of investigating the relationship between the thickness of the coating and the cluster index are shown. At this reducing temperature, clustering is performed by coating the cement coating with a cement content of 6 wt% or more and a thickness of 0.05 mm or more. It turns out that it can be sufficiently prevented.

Next, based on the iron content of raw iron ore, which has a proven track record for direct iron making, the lower limit of the iron content that can be allowed as a raw material for direct iron making was set to 65% by weight, the iron content of the iron ore used, and the cement content of the coating The allowable values of the coating thickness when the cement-containing iron ore-coated iron agglomerates were produced by changing the amount as shown in Tables 6 and 7 were obtained, and the results shown in Figures 5 and 6 were obtained. .

As shown in FIG. 5, in A ₁ and A ₃ , the iron content in the coating layer is high, so even if the coating thickness is increased, the iron content in the coated iron agglomerate does not fall below 65% by weight. To prevent clustering, it is useless to increase the coating thickness more than necessary, and if the coating thickness is too high, the coating strength may decrease and the coating layer may peel off. On the other hand, for A ₂ and A _{4 to} A ₆ , when the coating thickness exceeds 3.5 mm, 4.5 mm, 3.0 mm and 0.6 mm, the iron content in the coated iron agglomerate becomes smaller than the lower limit value (65% by weight). From these data, the coating thickness of cement-containing iron ore should be 4.5 mm or less in order to prevent the content of iron content (lower limit value) allowable as a raw material for iron manufacturing directly from being exceeded while avoiding excessive thickening. Is desired.

Further, as shown in FIG. 6, when the iron content of the iron ore used is low, if the cement content of the coating layer exceeds 80% by weight, the relationship of ensuring the iron content of the coated iron agglomerate or more to be lower than the lower limit value is secured. The coating layer thickness is less than 0.05 mm. As a result, mutual diffusion of iron in iron ore cannot be prevented and clustering occurs. Therefore, it is desirable that the content of cement in the coating layer be 80% by weight or less.

[Effects of the Invention] The present invention is configured as described above, and the effects thereof are summarized as follows.

(1) Clustering can be prevented as much as possible by coating a very small amount of cement-containing iron ore, and the operational stability of the vertical furnace can be improved.

(2) The reduction temperature can be considerably increased along with the prevention of clustering, the reduction rate can be improved and the productivity can be improved accordingly, and the heat loss of the reducing gas from the reducing gas generator can be reduced (that is, the amount of high temperature can be reduced). ) Is possible.

(3) Since a sufficient effect can be obtained by coating a very small amount of cement-containing iron ore, the iron quality of the iron-making raw material is hardly deteriorated.

[Brief description of drawings]

Fig. 1 is a cross-sectional view of cement-mixed iron ore-coated granulated pellets, Fig. 2 is a graph showing the relationship between reduction temperature and cluster index when various iron ore pellets are used, and Fig. 3 is cement-mixed iron ore-coated granules. The graph which shows the relationship between the amount of cement and the cluster index for the iron ore in the coating part of the granular pellets, and FIG. 4 is the graph which shows the relationship between the thickness of the coating layer of the cement-mixed iron ore of the cement-coated granulated pellets and the cluster index, FIG. 5 is a graph showing the relationship between the coating thickness and the iron content contained in the coated iron agglomerated ore, and FIG. 6 is a graph showing the relationship between the coating layer thickness and the iron content contained in the coated iron agglomerated ore according to the cement content of the coating layer cement. Is.

Continuation of front page (56) References JP-A-49-89606 (JP, A)

Claims (1)

[Claims] 1. An iron-making raw material used in a direct iron-making method or a smelting reduction iron-making method, which is obtained by coating a cemented iron ore on the surface of a massive or spherical iron-making raw material, which is excellent in clustering resistance. Ironmaking raw materials for direct ironmaking or smelting reduction ironmaking.