JP5131058B2 - Iron-containing dust agglomerate and hot metal production method - Google Patents

Description

  The present invention relates to an iron-containing dust agglomerate obtained by hydrating and hardening iron-containing dust generated in a steel production process or the like with a hydraulic binder, and a hot metal production method using the iron-containing dust agglomerate.

  In iron and steel manufacturing processes, iron-containing dust is generated in various steps, and there is a known method of agglomerating such iron-containing dust and recycling it into a vertical melting furnace such as a cupola as an iron source. (For example, Patent Document 1). The reason for the agglomeration of iron-containing dust is that in vertical melting furnaces, there is a gas flow from the bottom of the furnace to the top of the furnace. This is because it is discharged outside the furnace and hot metal cannot be obtained.

In the method of Patent Document 1, a predetermined amount of quick lime or slaked lime is blended with iron oxide powder, carbonaceous powder is blended as necessary, and during the period when the crushing strength per pellet is 20 kg or more, The agglomerates are obtained by curing in
JP-A-48-23613

However, according to the test conducted by the present inventor, when the dust agglomerate produced by the above prior art is charged into the vertical melting furnace, the ventilation resistance of the furnace increases and stable operation becomes difficult. I found out.
What is particularly important for stable operation of the vertical melting furnace is that the air blown from the lower part of the furnace passes through the in-furnace packed bed constituted by the charge and is constantly discharged from the top of the furnace. . For that purpose, it is necessary to take care not to fill the voids in the packed bed in the furnace and increase the airflow resistance. In order to prevent the deterioration of the airflow resistance, it is important to suppress the generation of powder. Further, it is considered necessary to prevent the melt generated during the reduction / melting from filling the voids in the packed bed in the furnace.

In the prior art, the strength of the agglomerated material can be increased to produce a material that does not easily break or pulverize, but the melt cannot prevent the melt from filling the gap during reduction / melting. It is thought that the operation has become unstable.
Accordingly, an object of the present invention is to provide an iron-containing dust agglomerate having a high strength that is difficult to break and pulverize, and has a performance such that the melt generated during reduction and melting does not fill the voids in the packed bed in the furnace. There is.
Another object of the present invention is to provide a hot metal production method capable of stably producing hot metal using such an iron-containing dust agglomerate as an iron source.

In the present invention, the iron-containing dust agglomerates (hereinafter simply referred to as dust agglomerates) produced from iron mill-generated dusts, etc., maintain the strength of the melt generated during reduction / melting in the furnace. A method for imparting performance not to fill the voids in the inner packed layer was studied, and as a result, the following knowledge was obtained.
First, it was found that the melting start temperature of the dust agglomerate should be as high as possible in order to prevent the melt of the dust agglomerate from filling the voids in the packed bed in the furnace. Since the viscosity of the melt generally decreases as the temperature rises, the effect of filling the voids by dripping the melt generated at a high temperature quickly is small. On the contrary, when the melt is generated from a low temperature, the gap is easily filled without dripping, and the ventilation of the packed bed in the furnace is hindered.

  The dust agglomerated material charged in the vertical melting furnace comes into contact with the high temperature gas when descending the furnace, and the temperature rises. At this time, since heat is supplied from the outside, a temperature distribution is generated in the dust agglomerate. That is, the temperature of the central part of the dust agglomerate is relatively low, and the outer part is relatively hot. When a dust agglomerate with a uniform composition has such a temperature distribution, the outer part starts to reduce and melt first, and a melt is generated from a relatively low temperature side (furnace upper side) region of the furnace. To do. On the other hand, since it takes time to raise the temperature in the center, the melt is generated only after reaching the relatively high temperature side (furnace lower side) region of the furnace. As a result, the melt is present in a wide region in the furnace height direction. Will be disturbed.

  In order to solve such a problem, the composition of the dust agglomerate may have a distribution in the radial direction. That is, by adjusting the composition of the outer layer part of the dust agglomerate and raising its melting start temperature higher than the inner layer part, when the temperature distribution occurs inside the dust agglomerate in the furnace, at the timing when the inner layer part melts In addition, the outer layer portion may be melted. Thereby, about the outer layer part and inner layer part of a dust agglomerate, a melt can be produced | generated in the same area | region (position) in a furnace, As a result, the area | region where the melt of a dust agglomerate exists in a furnace Therefore, it is possible to prevent the melt from filling the gaps in the packed bed in the furnace, and to prevent deterioration of air permeability.

The present invention has been made on the basis of the above-described findings and has the following gist.
[1] An agglomerate obtained by hydrating and hardening iron-containing dust mixed with a hydraulic binder, comprising an inner layer part and an outer layer part, and the Al ₂ O ₃ content of the binder in the inner layer part x An iron-containing dust agglomerated product characterized in that (mass%) and the Al ₂ O ₃ content y (mass%) of the binder in the outer layer portion satisfy y> x.
[2] In the iron-containing dust agglomerated product of [1], the binder in the outer layer portion is made of alumina cement, and the binder in the inner layer portion is made of a binder having a lower Al ₂ O ₃ content than alumina cement. Featuring iron-containing dust agglomerates.
[3] In the iron-containing dust agglomerated product of [1] or [2] above, the ratio of the outer layer portion in the iron-containing dust agglomerated product is 10 mass% as a lower limit, and is determined by 90 mass% or the following formula (1) An iron-containing dust agglomerated product characterized in that the smaller one of the obtained values α (mass%) is the upper limit.

[4] The iron-containing dust agglomerated product according to any one of [1] to [3] above, wherein the binder content in the outer layer part and the inner layer part is 2 to 25 mass%. Chemicals.
[5] The iron-containing dust agglomerated product according to any one of [1] to [4] above, wherein the outer layer part and / or the inner layer part further contains carbonaceous material powder. .
[6] In a vertical melting furnace, iron source and coke are charged from the top of the furnace, hot air is blown from a plurality of tuyere provided at the bottom of the furnace, and the iron source is melted by the combustion heat of the coke. A method for producing hot metal, wherein the iron-containing dust agglomerated product of any one of [1] to [5] is used as at least part of an iron source.

  The iron-containing dust agglomerate of the present invention has a higher melting start temperature of the composition constituting the outer layer part than that of the inner layer part, so when the temperature distribution is generated inside the agglomerate when charged in the furnace. Thus, the time difference in which the melt is generated between the outer layer portion and the inner layer portion can be reduced or substantially eliminated. Thereby, a melt can be produced | generated in the same area | region (position) in a furnace about the outer layer part and inner layer part of an iron containing dust agglomerate. As a result, the area where the melt of iron-containing dust agglomerates exists in the furnace can be reduced, and the melt can be prevented from filling the voids in the packed bed in the furnace, thereby preventing deterioration of air permeability. It becomes possible.

The iron-containing dust agglomerated product of the present invention (hereinafter simply referred to as dust agglomerated product) is an agglomerated product obtained by hydrating and hardening iron-containing dust mixed with a hydraulic binder, and has an inner layer portion and an outer layer. The Al ₂ O ₃ content x (mass%) of the binder in the inner layer part and the Al ₂ O ₃ content y (mass%) of the binder in the outer layer part satisfy y> x. is there. Such a dust agglomerate is composed of, for example, a binder in the outer layer portion made of alumina cement, and a binder in the inner layer portion made of a binder having a lower Al ₂ O ₃ content than alumina cement, such as Portland cement. can do.

In such a dust agglomerate of the present invention, since the Al ₂ O ₃ content x of the binder in the inner layer portion and the Al ₂ O ₃ content y of the binder in the outer layer portion are y> x, The melting start temperature of the constituent composition is higher than that of the inner layer portion. For this reason, when the temperature distribution is generated in the agglomerate by being charged into the furnace, the time difference in which the melt is generated between the outer layer portion and the inner layer portion is reduced or substantially no time difference is generated. As a result, the melt can be generated in the same region (position) in the furnace for the outer and inner layer portions of the dust agglomerate, and the region where the dust agglomerate melt exists is reduced in the furnace. Thus, it is possible to suppress the melt from filling the voids in the packed bed in the furnace.

In this dust agglomerated product, it is preferable that the ratio of the outer layer portion is 10 mass% as the lower limit, and 90 mass% or the value α (mass%) obtained by the formula (1) described later, whichever is smaller.
The initial melt in the vertical melting furnace (hereinafter simply referred to as vertical furnace) has a low melting point by adding unreduced iron (FeO) to slag composed of CaO, SiO ₂ , Al ₂ O _3, etc. Generated by producing a compound. In the operation of a vertical furnace, the basicity of the final slag is usually set in the range of 0.8 to 1.3. This slag basicity is set so that it is suitable for the discharge of slag from vertical furnaces from the viewpoint of fluidity, and impurities in hot metal do not concentrate (for example, sulfur is well absorbed by slag). Value. Here, the slag basicity is the ratio [% CaO /% SiO ₂ ] between the CaO content (mass%) and the SiO ₂ content (mass%) in the slag.

For the reasons described above, conventional dust agglomerate binders include hydraulic binders with relatively low Al ₂ O ₃ content, such as Portland cement, blast furnace cement, fine blast furnace slag powder, quick lime, fly ash, etc. alone. Or they were often used in combination. When these binders are used, the initial melt is 2CaO · FeO · 2SiO ₂ (melting point 1203 ° C.) or CaO · FeO · SiO _2.
A compound having a relatively low melting point such as (melting point 1208 ° C.) is likely to be produced.

On the other hand, when alumina cement is used as the binder for the dust agglomerated material, the slag composition produces a compound of 2CaO.Al ₂ O ₃ .SiO ₂ and FeO, but the initial melt production temperature is 1280 ° C., and Al ₂ The temperature can be increased by about 80 ° C. as compared with the case where a binder having a low O ₃ content is used (for a quaternary phase diagram of CaO—FeO—Al ₂ O ₃ —SiO ₂ , for example, reference “JF Schairer , “The system CaO-FeO-Al ₂ O ₃ -SiO ₂ .
I. Results of quenching experiments on five joins ”, J. Am. Ceram. Soc., 25 [10]
241-274 (1942) etc.)
In addition, the slag that is finally discharged together with the hot metal from the lower part of the vertical furnace is called the final slag. However, when Al ₂ O ₃ in the final slag increases, the fluidity deteriorates, so the Al ₂ O ₃ in the final slag is At most, it is adjusted to 25 mass% or less, desirably 19 mass% or less.

There is a concern that the Al ₂ O ₃ composition in 2CaO · Al ₂ O ₃ · SiO ₂ produced when alumina cement is used as a binder reaches 37.2 mass%, and the fluidity deteriorates. In order to make the Al ₂ O ₃ composition of the slag produced from the dust agglomerated material less than the desirable level of 19 mass%, the amount of Al ₂ O ₃ contained in the entire dust agglomerated material is changed to the total amount of the dust agglomerated material. From the condition that the amount of slag generated from slag is 19 mass% or less of the total amount of SiO ₂ , Al ₂ O ₃ , CaO, and MgO in the dust agglomerated material, the value α obtained by the following formula (1) is set to the outer layer portion. It is necessary to set the upper limit of the ratio.
In the following formula (1), when the amount of slag in the dust is large, Al ₂ O ₃ derived from alumina cement is easily diluted, so the calculated value may exceed 90 mass%. In such a case, the upper limit of the ratio of the outer layer portion is set to 90 mass% based on the result of FIG.

1 (a) to 1 (c) show the effect of the ratio of the outer layer portion of the dust agglomerated material on the pressure loss when the dust agglomerated material of the present invention is used for actual operation in a vertical furnace. It is. In FIG. 1, the pressure loss index is an index when the pressure loss of a conventional dust agglomerate having no composition distribution in the radial direction is set to “1”.
As shown in FIG. 1A, when the ratio of the outer layer portion decreases, the pressure loss increases, and the effect of the present invention decreases. When the ratio of the outer layer portion is approximately 20 mass% or less, the blowing pressure tends to increase. When the ratio of the outer layer portion is sufficiently large, the blowing pressure index decreases to about 0.6, but the ratio of the outer layer portion at which the blowing pressure index becomes a preferable upper limit of 0.8 is approximately 10 mass%. . Therefore, the ratio of the outer layer part is preferably 10 mass% or more.

On the other hand, as shown in FIG.1 (b), when the ratio of an outer layer part exceeds 80 mass%, there exists a tendency for blowing pressure to increase. It can be seen that the ratio of the outer layer portion at which the blowing pressure index is 0.8, which is the preferred upper limit, is 90 mass%, similarly to the lower side of the outer layer portion. Therefore, the ratio of the outer layer portion is preferably 90 mass% or less (provided that the value α calculated by the above equation (1) exceeds 90 mass%).
Further, as shown in FIG. 1C, when the value α calculated by the above equation (1) is 90 mass% or less (in this case, the value α calculated by the above equation (1) is 50 mass%). The pressure loss is greatly reduced when the ratio of the outer layer portion is in the range of 10 to 50 mass%. In this case, the ratio of the outer layer portion is increased by 50 mass% or more because the blowing pressure increases because Al ₂ O ₃ in the slag generated from the dust agglomerate exceeds 19 mass%, and thus the viscosity of the generated slag increases. It is presumed that it was not easily dropped. However, it can be seen that even when the ratio of the outer layer portion is greater than or equal to the value calculated by the above equation (1) and is 90 mass%, the blowing pressure can be kept small as compared with the case where the present invention is not carried out.

Here, the reason why the pressure loss increases when the ratio of the outer layer portion is 90 mass% or more can be explained with reference to FIG. FIG. 2 schematically shows the relationship between time and temperature after the dust agglomerates are charged in the vertical furnace for each of the inner layer portion and the outer layer portion. In the dust agglomerates of the prior art, when the point A is reached, the initial melt generation at the outer portion is started, and the melt at the center is generated at the point B. The time during which the initial melt exists is represented by (i), and it can be said that the melt exists for a relatively long time. On the other hand, in the dust agglomerate of the present invention, the initial melt of the outer layer portion is generated for the first time at the point C, and the initial melt of the inner layer portion starts at the point B. Is represented by (ii) and is shorter than (i). This is presumed to contribute to pressure loss reduction. On the other hand, when the ratio of the outer layer portion exceeds 90 mass%, the initial melt generation point of the outer layer portion is the C point, which is the same as above, but the initial melt generation point of the inner layer portion is originally B, Since the amount of Al ₂ O ₃ is large, an apparent D point is obtained. As a result, the initial melt generation start of the outer layer portion shifts to the high temperature portion, but the initial melt generation start of the inner layer portion also shifts to the high temperature side, so the time during which the melt exists is shortened. Indicates that it is not possible. Therefore, it is understood that the ratio of the outer layer portion is preferably 90 mass% or less.

It is preferable that the compounding quantity of the binder in an outer layer part and an inner layer part is 2-25 mass%.
If the blending amount of the binder is less than 2 mass%, the required strength is not expressed. On the other hand, if it exceeds 25 mass%, the strength of the dust agglomerate is sufficient, but the operation of the vertical furnace becomes unstable due to the generated slag. There is a case. The main components constituting the binder are CaO, SiO ₂ , Al ₂ O ₃ , CaSO _4, etc., which need to be dissolved in a vertical furnace and discharged as slag. Since slag is generally less fluid than hot metal, it becomes difficult to discharge the slag as it increases, and it tends to accumulate in the vertical furnace, making it difficult to balance the amount of dissolution and discharge. In addition, in order to recycle iron, it is better that the blending amount of the hydraulic binder is small, and it is more desirable to set it to 2 to 12 mass%.

The iron-containing dust is dust containing iron oxide and / or metallic iron, and the type thereof is not particularly limited, but typical examples include steel-making dust generated in a steel manufacturing process. The steelmaking dust includes hot metal pretreatment dust generated in the hot metal pretreatment process, converter dust generated in the converter decarburization process, electric furnace dust generated in the electric furnace, and the like. These steelmaking dusts are collected by collecting dust from the exhaust gas generated in the steelmaking process. Among these, converter dust generated in the converter decarburization step, so-called OG dust, is particularly preferable because it has a low impurity content and therefore a high iron content. Examples of iron-containing dust other than steelmaking dust include blast furnace dust and rolling dust.
It is also possible to use fine dust and high moisture content dust (called so-called sludge or filter cake, etc., such as rolling sludge and surface-treated sludge) that are wet-recovered in each step of the steelworks. However, since the production of the agglomerates is limited in moisture as described later, it is preferable to use the agglomerated product after it is dried until it reaches a predetermined moisture content or mixed with dried dust to lower the moisture content.

As the hydraulic binder, for example, one or more of various types of cement such as Portland cement, blast furnace cement, alumina cement, fly ash cement, ground granulated blast furnace slag, and quick lime can be used.
In the present invention, it is necessary that the Al ₂ O ₃ content x of the binder in the inner layer portion and the Al ₂ O ₃ content y of the binder in the outer layer portion satisfy y> x. Is selected. Generally, the binder of the outer layer portion is mainly composed of alumina cement or alumina cement, and the inner layer portion is made of a binder other than alumina cement (usually, Portland cement or Portland cement is the main component). It is done.

You may mix | blend carbonaceous powder with an outer layer part and / or an inner layer part as needed.
This carbonaceous material powder is a powder containing carbon as a main component and becomes a reducing material of iron oxide in a vertical furnace. In general, lump coke is used as a reducing material in a vertical furnace for iron making, but in addition to lump coke, carbonaceous powder such as coke powder is cheaper and more advantageous in terms of cost, as well as iron oxide and carbon. Therefore, there is an advantage that the reduction reaction of iron oxide proceeds rapidly. As the carbonaceous material powder, one or more types such as coke powder, coal powder (preferably anthracite coal powder), plastic powder and the like can be used, and those having a low volatile content such as coke powder are particularly preferable. Further, when a large carbon material is present in the dust agglomerated material, cracks are generated from the portion, which causes a decrease in strength. Therefore, the carbon material powder preferably has a particle size of 3 mm or less. In general, the blending amount of the carbonaceous powder in the raw material is preferably about 2 to 25 mass%.

Moreover, you may mix | blend components other than the iron-containing dust mentioned above, a hydraulic binder, and carbonaceous powder suitably as needed in a dust agglomerate. For example, a curing sieve, surfactant, bentonite, chloride for increasing the compressive strength of dust agglomerates, and a sintered sieve as a material for imparting an appropriate particle size distribution to the raw material to enhance moldability. You may mix | blend 1 or more types, such as granular materials, such as iron-containing granular materials, such as a lower powder and a mill scale, and limestone for adjusting the basicity of slag, and meteorite.
Further, from the viewpoint of reducing the amount of slag to be generated as much as possible, the total amount of SiO ₂ , Al ₂ O ₃ , CaO, and MgO in the raw material is preferably set to 25 mass% or less. Of course, these components include those contained in hydraulic binders.

In order to produce the dust agglomerated product of the present invention, water is usually added to the raw material for the inner layer (iron-containing dust, hydraulic binder, etc.) and mixed, and then this is agglomerated by a method such as molding or granulation. Naturalize. Separately, water is added to the raw material for the outer layer (iron-containing dust, hydraulic binder, etc.) and mixed, and this is coated on the outside of the agglomerated material for the inner layer by a method such as molding or granulation. To do. Or, conversely to this method, a part of the raw material for the outer layer part added with water is molded into a concave shape with a mold, and the concave part of the molded product is filled with the raw material for the inner layer part added with water, Then, the rest of the raw material for the outer layer portion is covered, and the whole is further molded.
Although the amount of water varies depending on the composition of the raw material, the maximum amount of water that does not ooze out even when compressed during molding is desirable. Quantitatively, it is preferable to adjust the slump so that the maximum water amount is zero in the measurement according to JIS-A-1101 (method of measuring concrete slump). If the amount of water is too small, it cannot be molded or granulated properly, and curing of the hydraulic binder does not proceed. On the other hand, if the amount of water is too large and water oozes out during molding, special measures are required for the treatment of the water.

When the agglomerated material is obtained by a molding method, the molding process can be performed by any method such as molding using a mold, extrusion molding, roll press molding, etc. Since the chemicals tend to increase in strength, it is preferable to form them as densely as possible. For this reason, it is preferable to compression-mold the mixture of raw material and water or to perform compression molding while vibrating. Specifically, it is preferable to perform molding using a compression molding machine such as a briquette molding machine, a press molding machine, an extrusion molding machine, or the like having a vibration function.
Although the shape of a molded product is arbitrary, in order to suppress powdering at the time of charging to a furnace as much as possible, it is preferable that there are few corners. Also, the size of the molded product is arbitrary, but if it is too small, the pressure loss of the furnace will increase when it is charged into the vertical furnace, while if it is too large, the agglomerated material will not be formed when charged in the vertical furnace. Since reduction and dissolution delay due to temperature rise delay in the center portion occurs, generally a size of about 20 to 2000 cm ^{3 in} volume is preferable.

When the agglomerated material is obtained by a granulation method, for example, the agglomerated material is obtained by using two pelletizers for granulating the raw material for the inner layer part and coating the raw material for the outer layer part.
The agglomerated product obtained by molding or granulating a mixture of raw material and water is cured for a certain period of time because it is hydrated and cured by a hydraulic binder. The curing method and period may be arbitrary. For example, after performing primary curing with steam, secondary curing in the atmosphere may be performed. The curing period is preferably as short as possible from the aspects of curing space and productivity, but may be appropriately selected according to the required strength after curing. Generally, about 1 to 7 days is preferable.

Hereinafter, an embodiment of a method for producing a dust agglomerated product of the present invention will be described.
FIG. 3 schematically shows an example of the production flow of the dust agglomerate of the present invention.
Reference numeral 1 denotes a storage facility for the inner layer raw material. This storage facility 1 stores a storage tank 1a for iron-containing dust and a hydraulic binder (a hydraulic binder having a low Al ₂ O ₃ content such as Portland cement). A tank 1b and a storage tank 1c for charcoal powder are provided. The storage tanks 1a to 1c have a function for quantitatively supplying each stored raw material. The raw materials supplied in a fixed amount from the storage tanks 1a to 1c onto the conveyor 3 are introduced into the humidification mixer 2 together with water supplied from a water supply line (not shown). The mixture of water and raw material sufficiently mixed by the humidifying mixer 2 is conveyed and charged into the storage tank 5 by the conveyor 4 and is primarily stored here. The mixture in the storage tank 5 is used as a raw material for the inner layer portion.

6 is a storage facility for the raw material for the outer layer. This storage facility 6 stores a storage tank 6a for iron-containing dust and a hydraulic binder (a hydraulic binder having a high content of Al ₂ O ₃ such as alumina cement). A tank 6b and a storage tank 6c for charcoal powder are provided. The storage tanks 6a to 6c have a function for quantitatively supplying each stored raw material. The raw materials supplied in a fixed amount from the storage tanks 6a to 6c onto the conveyor 8 are introduced into the humidification mixer 7 together with water supplied from a water supply line (not shown). The mixture of water and raw material sufficiently mixed by the humidifying mixer 7 is conveyed and charged into the storage tank 10 by the conveyor 9, and is primarily stored here. The mixture in the storage tank 10 is used as a raw material for the outer layer.
The raw material in the inner layer part cut out from the storage tank 5 and the raw material for the outer layer part cut out from the storage tank 10 are formed and agglomerated by the molding machine 11, for example, and an agglomerated product A is obtained. This agglomerated product A is allowed to stand in the curing place 12 as necessary, and is cured until it is used in a vertical furnace.

FIGS. 4A to 4E show an embodiment in which raw materials are agglomerated by a molding method (press molding using a mold), and molding is performed by the following steps. In addition, although each drawing has shown the cross section of a formwork, a press, and a raw material, the cross section line of a formwork and a press is abbreviate | omitted.
FIG. 4A: A mold 13 having a predetermined size and shape is prepared.
FIG. 4B: The mold 13 is filled with the outer layer raw material 14a (mixture of water and raw material).
FIG. 4 (c): The raw material 14 a is press-molded with a convex press die 15. By this press molding, a recess 140 is formed on the upper surface of the raw material 14a.
FIG. 4D: The inner layer portion raw material 16 (mixture of water and raw material) is filled in the recess 140 of the raw material 14a, and the outer layer portion raw material 14b (mixture of water and raw material) is further covered thereon.
FIG. 4E: The entire raw material is press-molded by a press die 17 having a flat pressed surface. Thereby, the agglomerate A is obtained.

FIG. 5 shows an embodiment in which raw materials are agglomerated by a granulation method (granulation by a disk pelletizer). Here, the inner layer raw material storage facility 1, the conveyor 3, the humidification mixer 2, the outer layer raw material storage facility 6, the conveyor 8, and the humidification mixer 7 are the same as in the embodiment of FIG.
The raw material for the inner layer part (mixture of water and raw material) sufficiently mixed by the humidifying mixer 2 is conveyed and charged into the first disk pelletizer 19 by the conveyor 18, where it is granulated (agglomerated) into a substantially spherical shape. ) The granulated material 23 is conveyed and charged into the second disk pelletizer 21 by the conveyor 20. On the other hand, the raw material for the outer layer (mixture of water and raw material) sufficiently mixed by the humidifying mixer 7 is conveyed and charged into the disk pelletizer 21 by the conveyor 22, and the raw material for the outer layer is produced in the disk pelletizer 21. The agglomerate A is obtained by coating the outside of the granules 23.

An iron-containing dust was agglomerated to produce a dust agglomerate, which was used in a vertical melting furnace (iron scrap melting furnace). Converter iron OG dust or blast furnace dust was used as the iron-containing dust, Portland cement or alumina cement was used as the hydraulic binder, and coke powder was used as the carbonaceous powder. Table 1 shows each component composition of the used blast furnace dust, converter OG dust, Portland cement, alumina cement, and coke powder. The slag content in Table 1 indicates the total amount of SiO ₂ , Al ₂ O ₃ , CaO, and MgO (main compounds constituting slag). Anything other than these burns, becomes part of the hot metal, or volatilizes and moves into the dust.
In Invention Examples 1 to 10 and Comparative Examples shown below, a dust agglomerate was produced according to the production flow shown in FIGS. 3 and 4, and the dust agglomerate was charged into a vertical melting furnace for operation. . The results are shown in Table 2 together with the raw material blending amount of the dust agglomerate, compressive strength, furnace operating conditions, and the like.
In Table 2, the “amount of impurities to slag” is the total amount of SiO ₂ , Al ₂ O ₃ , CaO, and MgO in the raw material. Other than this, it burns, becomes part of the hot metal, or volatilizes and moves into dust.

[Invention Example 1]
Blast furnace dust was used as the iron-containing dust, the mass ratio of the outer layer portion was 50 mass%, 10 mass% of Portland cement was blended as the binder of the inner layer portion, and 10 mass% of alumina cement was blended as the binder of the outer layer portion. Moreover, since the used blast furnace dust contained 33 mass% of carbon and it was judged that it was sufficient to reduce | restore the oxide in dust, carbonaceous powder, such as coke powder, was not mix | blended. Since the dust agglomerated material is allowed to stand for about one week after production and then used in a vertical furnace, the cold compressive strength after curing for 7 days was used as an index of the strength of the dust agglomerated material. It has been confirmed by experiments that the cold agglomerate has a cold strength of about 10 MPa or more. However, in this example, it was sufficiently strong at 22.1 MPa, and the air permeability of the vertical furnace deteriorated (air blowing Operation was also smooth without increasing pressure. In this example, the amount of impurities to be slag was 23.2 mass%, which was the limit value of 25 mass% or less, so that the generated slag was not accumulated in the furnace, and the vertical furnace could be operated smoothly. there were.

[Invention Example 2]
Converter OG dust was used as the iron-containing dust, the mass ratio of the outer layer portion was 50 mass%, 10 mass% of Portland cement was blended as the binder of the inner layer portion, and 10 mass% of alumina cement was blended as the binder of the outer layer portion. The carbon content in the converter OG dust is only 0.66 mass%, and it was judged that this would be insufficient to reduce the oxide in the dust. Therefore, the coke powder as carbon material powder was 15 mass in the inner layer portion and the outer layer portion, respectively. % Blended. The cold agglomerate of the dust agglomerated material was sufficiently strong at 25.1 MPa, and the operation was smooth without deteriorating the air permeability of the vertical furnace (increasing the blowing pressure). In this example, the amount of impurities to slag was 14.3 mass%, and the limit value was 25 mass% or less. Therefore, the generated slag was not accumulated in the furnace, and the vertical furnace could be operated smoothly. there were.

[Invention Example 3]
Blast furnace dust was used as the iron-containing dust, and the mass ratio of the outer layer portion was set to 11 mass%, which was slightly smaller. 10 mass% of Portland cement was blended as an inner layer binder, and 10 mass% of alumina cement was blended as an outer layer binder. Similarly to Invention Example 1, no carbon material powder for reduction was blended. The cold agglomerate of the dust agglomerated material was sufficiently strong at 22.5 Mpa, and the air permeability of the vertical furnace was not deteriorated (the blowing pressure was increased), and the operation was smooth. In this example, the amount of impurities to be slag was 22.9 mass%, and the limit value was 25 mass% or less, so that the generated slag was not accumulated in the furnace, and the vertical furnace could be operated smoothly. there were.

[Invention Example 4]
Blast furnace dust was used as the iron-containing dust, and the mass ratio of the outer layer portion was set to 88 mass%, which was a little larger. 10 mass% of Portland cement was blended as an inner layer binder, and 10 mass% of alumina cement was blended as an outer layer binder. Similarly to Invention Example 1, no carbon material powder for reduction was blended. The cold agglomerate of the dust agglomerate was sufficiently strong as 23.2 MPa, and the operation was smooth without deteriorating the air permeability of the vertical furnace (increasing the blowing pressure). In this example, the amount of impurities to be slag is 23.5 mass% and the limit value is 25 mass% or less, so that the generated slag does not accumulate in the furnace, and the vertical furnace can be operated smoothly. there were.

[Invention Example 5]
Blast furnace dust was used as the iron-containing dust, and the mass ratio of the outer layer portion was set to 5 mass%, which is slightly smaller. 10 mass% of Portland cement was blended as an inner layer binder, and 10 mass% of alumina cement was blended as an outer layer binder. Similarly to Invention Example 1, no carbon material powder for reduction was blended. The cold strength of the dust agglomerated material is sufficiently strong at 21.1 Mpa. Since the ratio of the outer layer portion was smaller than 10 mass%, the effect of increasing the generation temperature of the initial melt in the outer layer portion was small, so the air permeability of the vertical furnace was slightly deteriorated (the blowing pressure was slightly increased). However, the change was small and there was no problem in actual operation. Moreover, in the present Example, since the amount of impurities to slag was 22.9 mass%, which was a limit value of 25 mass% or less, it was considered that there was no problem with discharging the generated slag out of the furnace.

[Invention Example 6]
Blast furnace dust was used as the iron-containing dust, and the mass ratio of the outer layer portion was set to 95 mass%, which was a little larger. 10 mass% of Portland cement was blended as an inner layer binder, and 10 mass% of alumina cement was blended as an outer layer binder. Similarly to Invention Example 1, no carbon material powder for reduction was blended. The cold strength of the dust agglomerate is sufficiently strong at 24.6 Mpa. Since the ratio of the outer layer portion was a value larger than 90 mass%, the mass ratio of the inner layer portion was relatively small, and the initial melt generation temperature of the outer layer portion relative to the initial melt generation temperature of the inner layer portion. Although the effect of raising the temperature was slightly small and the air permeability of the vertical furnace was slightly deteriorated (the air pressure was slightly increased), the change was small and there was no problem in actual operation. Moreover, in the present Example, since the amount of impurities to slag was 23.6 mass%, which was a limit value of 25 mass% or less, it was considered that there was no problem with discharging the generated slag out of the furnace.

[Invention Example 7]
Converter OG dust was used as the iron-containing dust, the mass ratio of the outer layer portion was set to 70 mass%, the Portland cement was compounded as 10 mass% as the binder in the inner layer portion, and alumina mass was compounded as 10 mass% as the binder in the outer layer portion. The carbon content in the converter OG dust is only 0.66 mass%, and it was judged that this would be insufficient to reduce the oxide in the dust. Therefore, the coke powder as carbon material powder was 15 mass in the inner layer portion and the outer layer portion, respectively. % Blended. The cold strength of the dust agglomerate is sufficiently strong at 26.1 Mpa. Although the ratio of the outer layer portion is a value smaller than 90 mass%, the inner layer was slightly larger than the calculated outer layer portion ratio of 51 mass% calculated by the formula (1) from the limit of the Al ₂ O ₃ concentration. The mass ratio of the part is relatively small, the effect of increasing the initial melt generation temperature of the inner layer part relative to the initial melt generation temperature is slightly small, and the vertical furnace air permeability is slightly deteriorated ( The air pressure increased slightly). However, the change was small and there was no problem in actual operation. Moreover, in the present Example, since the amount of impurities to slag was 14.4 mass%, which was a limit value of 25 mass% or less, it was considered that there was no problem with discharging the generated slag out of the furnace.

[Invention Example 8]
Converter OG dust was used as the iron-containing dust, the mass ratio of the outer layer portion was 50 mass%, 1 mass% of Portland cement was blended as the binder of the inner layer portion, and 1 mass% of alumina cement was blended as the binder of the outer layer portion. The carbon content in the converter OG dust is only 0.66 mass%, and it was judged that this would be insufficient to reduce the oxide in the dust. Therefore, the coke powder as carbon material powder was 15 mass in the inner layer portion and the outer layer portion, respectively. % Blended. The cold strength of the dust agglomerate is as low as 8.8 Mpa because the amount of the binder is small. For this reason, since the dust agglomerate was pulverized in the vertical furnace, the air permeability of the vertical furnace was slightly deteriorated (the blowing pressure was slightly increased). However, since the initial melt generation temperature in the outer layer portion and the inner layer portion of the dust agglomerated material could be appropriately controlled, the increase in the blowing pressure was small and there was no problem in actual operation. Moreover, in the present Example, since the amount of impurities to slag was 6.6 mass%, which was a limit value of 25 mass% or less, it was considered that there was no problem in discharging the generated slag outside the furnace.

[Invention Example 9]
Converter OG dust was used as the iron-containing dust, the mass ratio of the outer layer portion was 35 mass%, 27 mass% of Portland cement was blended as the binder of the inner layer portion, and 27 mass% of alumina cement was blended as the binder of the outer layer portion. The carbon content in the converter OG dust is only 0.66 mass%, and it was judged that this would be insufficient to reduce the oxide in the dust. Therefore, the coke powder as carbon material powder was 15 mass in the inner layer portion and the outer layer portion, respectively. % Blended. The cold strength of the dust agglomerate is very high at 34.8 Mpa due to the large amount of binder. The ratio of the outer layer portion is also in a suitable range. However, in this example, the amount of impurities to slag was 28.4 mass%, which was a value exceeding the limit value of 25 mass%. As a result, it was somewhat difficult to discharge the generated slag out of the furnace. The air permeability of the furnace was slightly deteriorated (the air pressure was slightly increased). However, the increase in the blowing pressure was small and there was no problem in actual operation.

[Invention Example 10]
Converter OG dust was used as the iron-containing dust, the mass ratio of the outer layer portion was 50 mass%, 10 mass% of Portland cement was blended as the binder of the inner layer portion, and 10 mass% of alumina cement was blended as the binder of the outer layer portion. In the agglomeration, no carbon powder for reduction was added. At this time, the coke ratio had to be increased due to the lack of reducing carbon. This increase is not so large as to be a problem, but is considered to be slightly larger than when added to the dust agglomerate. For example, in Example 2, since the coke ratio is 162 kg / t · pig and 15 mass% of the dust agglomerate, that is, 15 kg / t · pig of coke powder is supplied, the total amount of coke used is 177 kg / t · pig. It is. In this example, the coke ratio required 185 kg / t · pig. This is presumably because the coke powder increased the contact area between the oxide and carbon in the dust agglomerate, so that the reduction reaction of the oxide proceeded efficiently. In general, since the amount of lump coke used is increased compared to the case where carbonaceous powder is added to the dust agglomerated product, the production cost seems to increase slightly. The carbon material to be used may be determined in consideration of the price of coke and the amount of inventory. On the other hand, the cold strength of the dust agglomerated material is as high as 27.3 MPa, and the ratio of the outer layer portion is also in a suitable range. The amount of impurities to be slag is 13.9 mass%, and it can be said that there was no problem in discharging the slag generated below the limit value of 25 mass% to the outside of the furnace.

[Comparative example]
The composition of the dust agglomerated material was made uniform throughout, and converter OG dust was used as iron-containing dust. 10 mass% of Portland cement was blended as a binder. Moreover, 15 mass% of coke powder was added as carbon material powder for reduction. The cold agglomerate has a high cold strength of 20.1 Mpa, the amount of impurities to slag is 14.7 mass%, and it can be said that there was no problem with the discharge of slag produced below the limit value of 25 mass% to the outside of the furnace. However, since the initial melt formation temperature in the outer and inner layer portions of the dust agglomerate is not properly controlled, the melt exists over a wide range in the vertical direction of the vertical furnace. The voids in the inner packing layer were reduced, and the increase in blowing pressure became significant. For this reason, the operation became unstable, and blow-throughs occurred frequently, and the coke ratio was greatly increased to 208 kg / t · pig.

The graph which shows the result of having investigated the influence which the ratio of the outer layer part of dust agglomerate has on pressure loss, using the dust agglomerate of the present invention for operation of a vertical furnace Explanatory diagram schematically showing the relationship between time and temperature after the dust agglomerates are charged in the vertical furnace for each of the inner layer and outer layer Explanatory drawing which shows typically an example of the manufacturing flow of the dust agglomerate of this invention Explanatory drawing which shows typically an example of the agglomeration process in manufacture of the dust agglomerate of this invention Explanatory drawing which shows typically the other example of the agglomeration process in manufacture of the dust agglomerate of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,6 Raw material storage equipment 1a-1c, 6a-6c Storage tank 5,10 Storage tank 2,7 Humidification mixer 3, 4, 8, 9 Conveyor 11 Molding machine 12 Curing equipment 13 Formwork 14a, 14b, 16 Raw material 15 , 17 Press mold 18, 20, 22 Conveyor 19, 21 Disc pelletizer 23 Granulated product 140 Concave part A Agglomerate

Claims (6)

An agglomerate obtained by hydrating and hardening iron-containing dust mixed with a hydraulic binder,
It consists of an inner layer part and an outer layer part, and Al ₂ O ₃ content x (mass%) of the binder in the inner layer part and Al ₂ O ₃ content y (mass%) of the binder in the outer layer part satisfy y> x. An iron-containing dust agglomerate characterized by satisfaction. The iron-containing dust agglomerated product according to claim 1, wherein the binder in the outer layer portion is made of alumina cement, and the binder in the inner layer portion is made of a binder having a lower Al ₂ O ₃ content than alumina cement. The ratio of the outer layer portion in the iron-containing dust agglomerated product is characterized in that 10 mass% is the lower limit, and 90 mass% or the value α (mass%) obtained by the following formula (1) is the lower limit. The iron-containing dust agglomerated product according to claim 1 or 2.

  The iron-containing dust agglomerated product according to any one of claims 1 to 3, wherein a blending amount of the binder in the outer layer portion and the inner layer portion is 2 to 25 mass%.   The iron-containing dust agglomerated product according to any one of claims 1 to 4, wherein the outer layer part and / or the inner layer part further contains carbonaceous powder. In a vertical melting furnace, a method of producing hot metal by charging an iron source and coke from the top of the furnace, blowing hot air from a plurality of tuyere provided at the lower part of the furnace, and melting the iron source with the combustion heat of the coke Because
A hot metal production method using the iron-containing dust agglomerated product according to any one of claims 1 to 5 as at least a part of an iron source.

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