JP5494121B2 - Method for producing reduced iron - Google Patents

Description

  The present invention relates to a method for producing reduced iron, and more particularly to a method for producing reduced iron capable of improving the metallization rate.

In recent years, a method for producing reduced iron using iron-making dust generated in an iron-making process has been widely used. As a method for producing such reduced iron, for example, as shown in Patent Document 1, iron-making dust or iron ore is used. A method is known in which stone and a carbonaceous material that is a reducing material are mixed and then agglomerated to give an agglomerated material, and this agglomerated material is heated and reduced on a hearth that continuously moves.
Further, in Patent Document 2, in order to increase the strength and reducibility of the agglomerated material charged into the rotary bed furnace, the particle size distribution of the particles constituting the agglomerated material is (cumulative sieve 30% ratio particle size) / A method for producing reduced iron is disclosed in which the particle size is adjusted so that (cumulative sieve 70% ratio particle size) is 1/3 or less.

In the invention of Patent Document 2, as described above, by increasing the strength and reducibility of the agglomerated material charged into the rotary bed furnace, the occurrence of equipment troubles due to the generation of agglomerated material and powder having a small particle size Furthermore, it aims at preventing the deterioration of productivity accompanying the extension of the baking time.
Certainly, it is important to increase the strength and reducibility of the agglomerated material, but the material described in Patent Document 2 is examined under the condition that the median particle size of the raw material to be blended including the reducing material is 62 μm or 110 μm. In order to adjust the particle size by crushing the raw material to such a level industrially, a considerable amount of energy is required, so that the problem is very large from the viewpoint of the economical efficiency of the reduced iron production process. In addition, in the case of coal used as a reducing material, there is a problem that a dust explosion countermeasure is required to finely pulverize to such a particle size.

JP 2003-293020 A Japanese Patent Laid-Open No. 11-12626

In view of the above, the present inventors have studied to enhance the productivity by promoting the reaction of the reduction process.
The particle size distribution of the iron-making dust generated in the iron-making process as a raw material is configured with a particle size from about 1000 μm to about 0.5 μm after crushing. On the other hand, coal used as a reducing material is difficult to be crushed, and is composed of particles having a particle size of about 1000 μm to about 10 μm after crushing, and has a feature that is slightly coarser than iron dust.
In general, an agglomerated product obtained by blending both of these is obtained and subjected to a reduction treatment. However, studies have been made focusing on an improvement for further increasing the reaction rate.
As a result, for the carbonaceous material used for the reducing material, as the specific surface area increases, the irregularities on the surface of the particles increase, and the fine particles of iron-making dust are buried in the dents, while the dents contribute to the reaction effectively, It was found that if the size is too large, the dent will be too small and fine particles of iron-making dust will not enter and the reduction rate will not increase easily.

  On the other hand, if a carbon material with a large specific surface area is used as the reducing material, the voids are substantially increased, so that a lot of voids remain in the agglomerated product after the reduction, and the contact part of the constituent particles forming reduced iron It has also been found that the strength decreases and the overall strength decreases.

  The present invention has been made in view of the above-described problems in the conventional reduced iron manufacturing technology, and its purpose is to define an optimum condition for the surface area of the reducing material in order to enhance the reducibility, and to provide a high strength and high metal An object of the present invention is to provide a method for producing reduced iron having a conversion rate.

In order to solve the above problems, the method for producing reduced iron according to the present invention includes an iron oxide raw material having a particle size distribution of 1000 μm to 0.5 μm and a coarser particle size distribution than 1000 μm. A method for producing reduced iron by agglomeration comprising a reducing material having a particle size of 10 μm in a reduction furnace, wherein the reducing material has a specific surface area of 10 to 300 (m ² / g). The first carbon material and the second carbon material having a specific surface area of less than 10 (m ² / g) are mixed and used, and the mass ratio in which the first carbon material is used is 5 of the total used mass of the reducing material. % Or more and 50% or less.

In the present invention, it is preferable that the first carbon material of the reducing material contains carbon-based particles obtained by dry distillation of a used product mainly containing a resin.
In this case, the used product mainly composed of the resin may include one or more of a waste tire, a waste belt, and a waste rubber.

  According to the present invention, the first carbon material having a specific surface area of a predetermined range and the second carbon material having a specific surface area smaller than that of the first carbon material are mixed, and the mass ratio using the first carbon material. By setting the amount to a predetermined range with respect to the total use mass of the reducing material, these two carbonaceous materials effectively act, and reduced iron having high strength and a high metallization rate can be obtained.

It is a process flow figure showing one embodiment of a manufacturing method of reduced iron of the present invention. It is the graph which compared the relationship between the temperature of 900 degreeC vicinity, and the weight reduction rate accompanying a reduction reaction about three types of carbon materials from which a specific surface area differs. It is a graph which shows the relationship between the specific surface area of a carbonaceous material, and the reduction | restoration rate parameter | index of 900 degreeC vicinity. It is a graph which shows the relationship between the specific surface area of a carbonaceous material, and the metallization rate after a reduction | restoration. It is a graph which shows the relationship between the use ratio of the carbonaceous material of specific surface area 50 (m < ² > / g), and the metallization rate after reduction | restoration. It is a graph which shows the relationship between the use ratio of the carbonaceous material of specific surface area 50 (m < ² > / g), and the intensity | strength after reduction | restoration. It is a graph which shows the relationship between the usage-ratio of the carbon material from which a specific surface area differs, and the oxygen basic unit of a cold iron source melting furnace.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a process flow diagram showing an embodiment of a method for producing reduced iron according to the present invention.
Specifically, when producing reduced iron, firstly, iron oxide raw materials such as iron dust and iron ore generated in the iron making process as raw materials, and carbon materials such as coal and dry distillate as reducing materials, respectively. A crushing and mixing step of crushing and mixing the iron oxide raw material and the carbonaceous material that are stored in separate silos and supplied at a constant speed from each silo is performed. After the crushing and mixing step, the mixture produced in the step is subjected to a kneading step in which the moisture content is adjusted and a binder is added and kneaded, and the mixture after the kneading step is agglomerated to form an agglomerated product. Perform the agglomeration process. The molded agglomerated product is further dried to a moisture content of less than 1%, and then the dried agglomerated product is put into a reduction furnace having a rotary hearth for reduction and reduction. Reduced iron is manufactured by performing the reduction process process made into iron.
In addition, a part of the reduced iron produced here is sent to the cold iron source melting furnace operation of the next process, coal and oxygen are blown and melted in the cold iron source melting furnace, and used for the production of hot metal. .

The crushing and mixing step is performed by introducing the iron oxide raw material and the reducing material into a crusher such as a ball mill. Since the reduction reaction of iron oxide is known to promote the reaction by making the constituent particles finer, by performing such a crushing and mixing step, the iron oxide raw material and the reducing material are made finer, The reduction reaction is promoted.
The kneading step is performed by a kneader such as a mix muller. However, when forming agglomerates in a wet state, it is important to optimize moisture and add an appropriate binder. The kneading process is a very important process for kneading the binder.

In the agglomeration step, a mixture of iron oxide raw material and reducing material (agglomerated material raw material) that has been moisture-adjusted and to which a binder has also been added, such as briquette, extrusion molding, pellets, etc. by rolling granulation or compression molding, etc. It is agglomerated by the molding method.
Further, in the drying step, if the agglomerated product that has been wet-formed enters the reduction furnace as it is, there is a possibility that problems such as a heat loss accompanying evaporation of moisture and a decrease in agglomerate recovery yield due to cracking may occur. Therefore, it is performed to prevent this, and as described above, the water content in the agglomerated material is reduced to less than 1%.
Furthermore, in the reduction treatment step, the dried agglomerated material is reduced using a rotary hearth furnace under an atmospheric temperature condition of about 1200 to 1300 ° C. for a treatment time of about 20 minutes, thereby reducing the reduced iron. Get.

As the iron oxide raw material used in the method for producing reduced iron, iron oxide such as iron making dust and iron ore generated in the iron making process is mainly used.
On the other hand, as a reducing material necessary for the reduction of the iron oxide material, carbon-based particles obtained by dry distillation of used products mainly composed of coal or resin are used.

  Here, as already mentioned, as for the carbonaceous material used for the reducing material, as the specific surface area increases, the irregularities on the surface of the particles increase, and the fine particles of iron-making dust are buried in the depressions, and the depressions are effective for the reaction. On the other hand, when the surface area is too large, the indentation becomes too small and the fine particles of the iron-making dust do not enter and the reduction rate is difficult to increase. This point will be specifically described.

That is, in order to investigate the influence of the specific surface area of the carbon material, a reduction experiment was performed by changing the specific surface area of the carbon material.
Specifically, iron oxide reduction experiments were performed using three levels of carbon materials with specific surface areas of 2 (m ² / g), 38 (m ² / g), and 1100 (m ² / g). However, as shown in FIG. 2, it was found that a carbon material having a specific surface area of 38 (m ² / g) starts a large reduction reaction at a lower temperature.
This is thought to be because the surface roughness of the aforementioned carbonaceous material particles increased, and the fine particles of iron-making dust were buried in the recesses, so that the recesses effectively contributed to the reaction and the reduction rate was increased.
On the other hand, if the specific surface area is too large, such as 1100 (m ² / g), the dent becomes too small and fine particles of iron-making dust do not enter the dent, so that the reduction rate increases due to the dent. It is thought that the influence of was small.

When measuring the specific surface area of carbonaceous materials, this time, a method was used to adsorb gas molecules whose adsorption occupancy area was clear on the powder particle surface at a low temperature and to determine the specific surface area of the sample from the amount. Used nitrogen as the gas. The specific surface area was calculated using a method known as the BET method.
Specifically, first weigh the sample without adsorbate, and then determine the change in the amount of adsorption with respect to the pressure change during the process of nitrogen gas adsorption on the sample surface. The amount of adsorbed gas molecules was determined from the BET adsorption isotherm. Since the adsorption area of nitrogen molecules is known, the surface area of the sample can be calculated from the amount of gas adsorption.

As a result of repeated experiments of this type, when a carbon material having a specific surface area of 10 to 300 (m ² / g) is used as the reducing material, the reduction rate is increased and the metallization rate of the reduced iron is increased. We found it appropriate to improve.
The range of the specific surface area of the carbon material is set to 10 to 300 (m ² / g), as described above, when the surface area exceeds 300 (m ² / g), the dent on the surface becomes too small, Fine particles are difficult to enter, and the contribution to the increase in the reduction rate due to the dents is reduced. On the other hand, when the ratio is less than 10 (m ² / g), the surface irregularities are small, and the dents into which fine particles of iron-making dust enter are reduced. This is because the influence on the increase in the reduction rate is reduced.

On the other hand, when a carbon material having a large specific surface area is used, voids are naturally increased in the agglomerated material, so that many voids remain in the agglomerated material after reduction. If it does so, since the contact part of the component particle | grains which form reduced iron will reduce, it is possible that the whole intensity | strength falls. If the strength of the agglomerated material after reduction is insufficient, the agglomerated material may break when it is transported to the next process, generating agglomerated material and powder with a small particle size, which may cause equipment troubles. There is also.
Therefore, in order to ensure the strength that can prevent the occurrence of such troubles, a carbonaceous material having a specific surface area of less than 10 (m ² / g) is mixed with the reducing material and used for the agglomerated material. It has been found that it is appropriate to ensure the strength of reduced iron (agglomerated product after reduction) by reducing the voids as much as possible.
Accordingly, as the reducing material, both the first carbon material having a specific surface area of 10 to 300 (m ² / g) and the second carbon material having a specific surface area of less than 10 (m ² / g) should be used. is necessary.
In addition, since it does not become 0 about the specific surface area of a carbon material, it is natural that the specific surface area of the 2nd carbon material to be used does not contain 0.

Furthermore, in order to achieve both the realization of the high metalization rate of reduced iron and the strength, the mass ratio using the first carbonaceous material having a specific surface area of 10 to 300 (m ² / g) It has been found that it is appropriate that the total mass used is 5% or more and 50% or less.
The reason why the mass ratio in which the first carbon material is used is in the range of 5% to 50% of the total used mass of the reducing material is that the mass ratio of the first carbon material is less than 5% of the total used mass of the reducing material. In some cases, the amount of the first carbon material that has a high function of improving the reduction rate is small, so that the contribution to the high metallization rate is small. On the other hand, when the mass ratio exceeds 50%, there are many voids in the agglomerated material. This is because the strength of the agglomerated product after the reduction is reduced and it becomes easy to break.

By the way, as a result of intensive studies in order to obtain a carbon material having a large specific surface area that is optimal as the first carbon material, the inventors obtained such a first carbon material by performing a carbonization treatment of organic matter. It was found that this is preferable.
The organic matter that is the subject of dry distillation is preferably a used product mainly composed of resin, for example, waste tires, waste belts, waste rubber are included, and these can be subjected to dry distillation treatment by mixing them alone or in combination. Thus, the first carbon material having a large specific surface area can be obtained relatively easily.
A common feature of these products is that they contain granular carbon black. Carbon black is generally a particle having a size of 0.1 μm or less, and it is considered that fine carbon black is present in an aggregated form in a used product mainly composed of resin. When this is carbonized, the resin around the carbon black is thermally decomposed, leaving a carbon black aggregated skeleton, and forming an uneven carbon material (carbonized carbonized) on the surface, presuming to increase the specific surface area of the carbon material Is done.

  As the dry distillation method, for example, an external heating type rotary kiln can be used. This external heat type rotary kiln has a structure that blocks the outside air, and can normally feed dry matter such as waste tires from one side while rotating at a rotational speed of about 1 to 5 rpm. Yes. The heating temperature of the externally heated part of the kiln is usually about 600 ° C. to 700 ° C., and the to-be-dried product is heated from the outside of the kiln cylinder and gradually rises in temperature, and the rubber part is heated up to the kiln outlet. If it is decomposed and gasified and the remaining carbon black and waste tires are used, wires and the like are separated as solids. The pyrolytic solid substance mainly composed of carbon black becomes the first carbon material having a specific surface area in the optimum range as the reducing material.

  As mentioned above, although the manufacturing method of the reduced iron of this invention was described, according to the manufacturing method of the above-mentioned reduced iron, the specific surface area which improves a reduction rate and contributes to a high metallization rate as a reducing material is large with a fixed range. The first carbon material is mixed with a second carbon material having a specific surface area effective for securing the strength of reduced iron (agglomerated material after reduction) smaller than that of the first carbon material. By setting the mass ratio at which the material is used within a predetermined range with respect to the total used mass of the reducing material, it is possible to stably obtain reduced iron with a high metalization rate and high strength.

In order to investigate the effect of the specific surface area of the carbon material on the reduction, reduction experiments were performed using a reducing material having a different specific surface area.
In the reduction experiment, the same steps as those in the above embodiment were performed. In other words, using iron-making dust generated in the iron-making process and carbon materials with various specific surface areas as raw materials, after crushing with a ball mill, adding corn starch as a binder, kneading and moisture adjustment, agglomerates molded by briquette method After manufacturing and making the moisture less than 1% in the drying step, reduction treatment was performed for 20 minutes in a rotary hearth furnace at a furnace temperature of 1250 ° C.
FIG. 3 shows the relationship between the reduction rate index (reduction rate at 900 ° C.) with respect to the specific surface area of the carbonaceous material used.
Moreover, the relationship with the metallization rate after reduction | restoration with respect to the specific surface area of the carbonaceous material used for FIG. 4 (ratio of metal iron content with respect to the total iron content density | concentration) is shown.

As shown in FIG. 3, when the specific surface area of the carbon material is in the range of 10 (m ² / g) to 300 (m ² / g), a reduction rate effective for improving the metallization rate of reduced iron is obtained. I understand.
Moreover, as shown in FIG. 4, when the specific surface area of a carbon material is the range of 10 (m < ² > / g) -300 (m < ² > / g), it turns out that a 83% or more high metalization rate is realizable. .
As a result, it was found that there is an optimum range for the specific surface area of the carbonaceous material used for the reducing material, considering the reduction rate and the high metalization rate. In particular, it was found that when the specific surface area of the carbon material is in the range of 10 (m ² / g) to 300 (m ² / g), a sufficient reduction rate and a high metallization rate can be obtained.

Use of the first carbon material in order to confirm the use ratio of the first carbon material having a specific surface area of 10 (m ² / g) to 300 (m ² / g), the metallization rate of reduced iron, and the strength. A reduction case was conducted with the ratio changed.
Specifically, as a reducing material, a first carbon material having a specific surface area of 50 (m ² / g) and a second carbon material having a specific surface area of 2 (m ² / g) are mixed and used. The reduction treatment was carried out in the same manner as above. In addition, about the 1st carbon material, it experimented by changing the mass ratio with respect to the total use mass of a reducing material.
FIG. 5 shows the relationship between the metallization ratio after reduction and the ratio using a specific surface area of 50 (m ² / g).
FIG. 6 shows the relationship between the reduced iron strength after reduction with respect to the ratio using a specific surface area of 50 (m ² / g).

As a result, as shown in FIG. 5, it was found that the metallization rate increases when the specific surface area is 50 (m ² / g), that is, the ratio of using the first carbon material is increased. Thereby, it was demonstrated that the 1st carbon material with a large specific surface area has had a great influence on the improvement of the metallization rate of reduced iron.
On the other hand, as shown in FIG. 6, it was found that the crushing strength of reduced iron (agglomerated product after reduction) decreased when the ratio of using the first carbon material was increased. Thereby, it turned out that the intensity | strength of reduced iron influences the ratio which uses a carbon material with a large specific surface area. Note that the reduction in the strength of reduced iron due to the use of a carbon material with a large specific surface area, as already mentioned, will naturally increase the number of voids when a carbon material with a large specific surface area is used in the agglomerate. It is thought that this is because the voids remain afterwards and the contact portions of the constituent particles forming the reduced iron are reduced and become brittle as a whole.

An experiment was conducted to examine in more detail the relationship between the ratio of the first carbon material having a specific surface area of 10 (m ² / g) to 300 (m ² / g) and the strength of reduced iron.
In this experiment, as a reducing material, a carbon material having a specific surface area of 5, 10, 50, 300 (m ² / g) and a carbon material having a specific surface area of 2 (m ² / g) are mixed and used. The reduced iron was melted in the cold iron source melting furnace operation (see FIG. 1), which is the next step after the reduction treatment step, and the oxygen intensity was examined.
Here, the cold iron source melting furnace remodels the converter, blows oxygen and coal while leaving the hot metal in the furnace, and melts the cold iron source such as reduced iron with its combustion heat to produce hot metal. It is. The oxygen basic unit tends to decrease as the metallization rate of the reduced iron is higher and the rate of staying in the cold iron source melting furnace is higher, and is an index indicating the quality of the reduced iron.
Note that the high rate of staying in the cold iron source melting furnace means that the strength of reduced iron is high, and when reduced iron is introduced from above the melting furnace, it falls into the melting furnace as a lump, so It shows that it stays in the furnace overcoming the gas updraft. On the other hand, when the strength of the reduced iron is low, when the reduced iron is introduced from the upper side of the melting furnace, it breaks and there are many small particles, so it gets out of the furnace on the rising air flow of the furnace gas For this reason, the rate of staying in the cold iron source melting furnace is lowered.
The result of this experiment is shown in FIG.

As a result, in the case of a carbonaceous material having a specific surface area of 10 to 300 (m ² / g), if the mixing ratio is 50% or less, the oxygen basic unit of the melting furnace has a specific surface area of 2 (m ² / g). It was found that when only the carbonaceous material was used, that is, below the oxygen consumption rate when the horizontal axis in FIG.
This is because when the use ratio of the carbonaceous material having a specific surface area of 10 to 300 (m ² / g) is 50% or more, the strength of the reduced iron is reduced, and the reduced iron pieces are cracked when carried to the next process. This is thought to be due to a decrease in the yield of charging into the melting furnace and a reduction in the metallization rate of the reduced iron at the time of charging into the melting furnace.
Moreover, if the usage rate of the carbonaceous material having a specific surface area of 10 to 300 (m ² / g) is less than 5%, the oxygen basic unit of the melting furnace is only the carbonaceous material having a specific surface area of 2 (m ² / g). Compared to the oxygen consumption rate when using. The reason for this is considered to be because the effect of improving the metallization rate is small with this amount of use.
Furthermore, when a specific surface area of 5 (m ² / g) is used, the improvement effect may be small compared to the case of using only a carbon material with a specific surface area of 2 (m ² / g). I understood.
Therefore, in the case of a carbonaceous material having a specific surface area of 10 to 300 (m ² / g), if the mixing ratio is 5% or more and 50% or less, reduced iron having a sufficient degree of strength for transportation or the like is obtained. It has been demonstrated that it can.

Claims (3)

An agglomerate comprising an iron oxide raw material having a particle size distribution of 1000 μm to 0.5 μm and a reducing material which is coarser than the iron oxide raw material and has a particle size distribution of 1000 μm to 10 μm. A method for producing reduced iron by reduction in a reduction furnace, wherein the reducing material is a first carbon material having a specific surface area of 10 to 300 (m ² / g) and a specific surface area of less than 10 (m ² / g). The second carbon material is mixed and used, and the mass ratio in which the first carbon material is used is 5% or more and 50% or less of the total used mass of the reducing material. Method. 2. The method for producing reduced iron according to claim 1, wherein the first carbon material of the reducing material contains carbon-based particles obtained by dry distillation of a used product mainly containing a resin. .   3. The method for producing reduced iron according to claim 2, wherein the used product mainly composed of the resin includes one or more of a waste tire, a waste belt, and a waste rubber.

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