JP2001032005A - Operation of rotary furnace hearth method for reduction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an explosive-cracking phenomenon caused by the vaporization of moisture and the loss of raw material tile into exhaust gas due to powdering and to improve product yield, when the powdery raw material containing the moisture is reduced in a rotary furnace hearth method. SOLUTION: Mixture of the powdery material containing metal oxide with the moisture and powdery reducing agent consisting essentially of carbon, is dehydrated, and after forming solid aggregate, this residual moisture in this solid aggregate is dried to <=2%, and this is supplied into the rotary furnace and reduced. The average grain diameter of the powdery material containing the metal oxide is made to <=80 micron. As the powdery material containing the metal oxide, dust and/or sludge produced in metal refining or working process, are used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing a metal oxide using a rotary hearth for reduction, and a process for reducing dust and sludge containing metal oxides generated in a metal refining and processing industry. How to do it.

[0002]

2. Description of the Related Art There are various processes for producing reduced iron and alloyed iron. Among them, a rotary hearth method is used as a process with high productivity. The rotary hearth method is a type of firing furnace (hereinafter referred to as a rotary furnace) in which a disc-shaped refractory hearth lacking a central portion rotates at a constant speed on rails under a fixed refractory ceiling and side walls. This process is mainly used for the reduction of metal oxide. Rotary furnaces usually have a disk-shaped hearth with a diameter of 1
It has a width of 0 to 50 meters and a width of 2 to 6 meters.

[0003] A powder containing a metal oxide as a raw material is mixed with a carbon-based reducing agent, then formed into raw material pellets and supplied to a rotary furnace. The raw material pellets are spread on this hearth, and since the raw material pellets are left on the hearth, there is an advantage that the raw material pellets are hard to collapse in the furnace, and the powdered raw material adheres to the refractory. Without any problems
In addition, there is an advantage that the product yield of lumps is high. Also,
In recent years, the number of practiced examples has been increasing because of the fact that high productivity and inexpensive coal-based reducing agents and powdered raw materials can be used.

Further, the rotary hearth method is also effective for the treatment of reduction and removal of impurities from the blast furnace, converter, electric furnace, and the thinner sludge in the rolling process, and is also used as a dust treatment process. This is an effective process for resource recycling.

[0005] The outline of the operation of the rotary hearth method is as follows. First, after a sufficient amount of a carbon-based reducing agent necessary for the reduction of this oxide is mixed with the ore, dust, and sludge metal oxides as raw materials, the average water content is reduced to about 10% by a granulator such as a pan pelletizer. % To produce pellets of several mm to several tens of mm with water. If the raw material ore or the reducing agent has a large particle size, it is pulverized by a pulverizer such as a ball mill, kneaded, and granulated.

The pellets are supplied in layers on a rotary hearth, and the pellets laid on the hearth are rapidly heated and
It is fired at a high temperature of around 1300 ° C. for a period of from 1 minute to 20 minutes. At this time, the metal oxide is reduced by the reducing agent mixed in the pellet, and a metal is generated. The metallization ratio depends on the metal to be reduced, but for iron, nickel and manganese, 9
5% or more, and even chromium which is difficult to reduce is 50% or more.
In the case of treating dust generated from the steel industry, impurities such as zinc, lead, alkali metals, and chlorine are volatilized and removed during the reduction reaction, so that it can be easily recycled to blast furnaces and electric furnaces. Become.

[0007] As described above, in the method of reducing metal and the method of reducing iron-making dust using a rotary hearth, it is essential that the raw material and the reducing agent are pelletized. It is important to bring the mixture of the metal powder and the reducing agent into a state of good granulation, and various methods such as pre-grinding of the raw materials and kneading in a ball mill have been performed.

[0008]

As described above, the method of reducing metal oxide by the rotary hearth method using the conventional method is excellent in productivity and production cost, and economically produces metal. How to However, it is important to make the raw material and the reducing agent into pellets, and it is important to select a raw material with high granulation performance or install an expensive pulverizer to improve the granulation by crushing the raw material. There was a problem that was necessary and costly for this.

That is, when using an ore such as iron ore as a raw material, the particle size of the raw ore is generally large.
After pulverizing so that the average particle size is tens of microns or less,
It was granulated to produce pellets. As a result, there are drawbacks in that the equipment for the pulverizing step is expensive, that power is required for operating the pulverizer, and that maintenance costs are required due to wear of the pulverizer.

[0010] Therefore, in order to save the cost of pulverization, a raw material of fine powder is sometimes used, but the selectivity of the raw material is strict and it is not a general-purpose method. Therefore, it is effective to use fine ore after the wet beneficiation, to use thickener dust in a blast furnace or a converter, to use sludge of scale pits in a rolling process, or to precipitate sediment in a pickling process. However, even in this case, there was a problem that it was difficult to granulate due to too much water content. That is, these raw materials are fine powder having a particle size of 1 micron or less to several tens of microns,
As a result, in a state containing water, these tend to be sludge-like, and even after dewatering with a vacuum dehydrator or filter press, the water content is 20% to 50%. Did not.

In order to solve this problem, there is a method of completely drying with a heat source such as hot air. However, the powdered raw material is quasi-agglomerated during the drying process and cannot be granulated as it is, so it is crushed, turned into fine particles again, and then watered together with other raw materials, and granulated. After doing
It was reduced on the rotary hearth.

As a result, even when used in the above method, water can be added again after drying using a large amount of heat source, so that a heat source is required again for evaporation of water during granulation. It was not an economical way to reduce metals.

[0013] In particular, when dust and sludge generated in the metal refining and processing industries such as the steel making industry are collected from a wet dust collector or a sedimentation tank, the generated products can reduce a large amount of water, up to 80%. When these products are to be reduced by the rotary hearth method, the problems of the drying step and the pulverization after drying have been remarkable.

In order to solve these problems, for example,
As disclosed in Japanese Patent Application Laid-Open No. H11-12619, as a method of using a raw material without granulation in a rotary hearth method, the raw material is tiled with a compression molding machine and used in a rotary hearth method. A method has been invented. However, this method still has a problem in using a raw material containing a large amount of water. That is, as shown in Japanese Patent Application Laid-Open No. H11-12624, it is necessary to adjust the water content of the raw material to 6 to 18%. For this purpose, a drying treatment is required in addition to a prior dehydration treatment. There is a problem that requires complicated moisture control. In addition, for the charging of the raw materials, as shown in JP-A-11-12621,
A complicated charging device is required, and there have been problems such as high maintenance costs for this equipment.

Further, when the raw material having such a shape is directly charged into a rotary furnace having a high temperature, the explosion phenomenon accompanying the evaporation of the water occurs due to the high water content, and the raw material tile becomes powdered. Thus, there is a problem that the product is lost in the exhaust gas and the product yield is extremely poor.

As described above, in the conventional method, there is an economical problem in reducing the powdery material containing water by the rotary hearth method, and a new technique for solving this problem is required. Was.

[0017]

The present invention is as described in (1) to (9). (1) After a mixture of a powder containing a metal oxide containing water and a powdery reducing agent mainly composed of carbon is dehydrated to form a solidified aggregate, the residual moisture of the solidified aggregate is reduced by 2%. An operation method of the rotary hearth method for reduction, characterized in that the material is dried to the following, supplied to a rotary furnace, and reduced. (2) The operation method of the rotary hearth method for reduction according to (1), wherein the average particle size of the powder containing the metal oxide is 80 μm or less. (3) The operating method of the rotary hearth method for reduction according to (1), wherein dust and / or sludge generated in a metal refining or processing step is used as the powder containing the metal oxide. (4) The operation method of the rotary hearth method for reduction according to (2), wherein dust and / or sludge generated in a metal refining or processing step is used as the powder containing the metal oxide. (5) The method for operating a rotary hearth for reduction according to (1), wherein dust or sludge collected from a wet dust collector or a sedimentation tank is used as the powder containing the metal oxide. (6) A mixture of a powder mainly composed of a metal oxide and a reducing agent mainly composed of powdered carbon is dehydrated by a dehydrator so as to form a plate or a flat sphere, and then dried. (7) Method for operating the rotary hearth for reduction described in (1) (7) Solidification and coagulation produced by drying a mixture of a powder containing a metal oxide containing water and a powdery reducing agent followed by drying. The method for operating a rotary hearth for reduction according to (1), wherein the thickness of the aggregate is 25 mm or less. (8) The reduction according to (2), wherein a mixture of a powder mainly composed of a metal oxide containing water and a powdery reducing agent is dehydrated and then dried at a temperature of 250 ° C. or less. Operating method of the rotary hearth. (9) A method for operating a rotary hearth for reduction, characterized in that a crude metal product produced on a rotary hearth is formed by a hot press.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a reduction process of a metal oxide by a rotary hearth method according to the present invention. This equipment includes a storage pit 1 for powdery raw materials containing water, a slurry transport device 2, a dewatering device 3, a belt conveyor 4, a raw material mixture thickness adjusting device 5, a dryer 6, a rotary furnace 7, an exhaust heat recovery air preheater. 8, a process including an exhaust gas dust collector 9 and a hot press machine 10.

First, the raw material powder containing water is mixed in the storage pit 1 with a powdered reducing agent mainly composed of carbon. Instead of the storage pit, it is also possible to mix well in a stirring vessel. The solid-liquid mixture is transported by the slurry transport device 2 to the dehydrating device 3, where it is dehydrated to form a raw material mixture. In this embodiment, a transmission filter is used, but a filter press or a centrifuge may be used. The water content after dehydration is desirably 10% to 30%. If the water content is too small, the raw material mixture is likely to fall apart before drying, and if the water content is too large, the amount of heat for drying becomes excessive.

The raw material mixture is sent to a raw material mixture thickness adjusting device 5 on a belt conveyor 4. Here, the raw material mixture is adjusted to have a thickness of 25 mm or less. For adjusting the thickness, a molding device or the like can be used, but a simple plate-shaped leveling device as shown in FIG. 2 may be used. If the thickness of the raw material mixture has been adjusted at the stage of dehydration, this may be omitted. FIG. 2 shows the raw material mixture thickness adjusting device 5 shown in FIG. The raw material mixture is sent to the raw material mixture supply unit 11 by the belt conveyor 4 of FIG. 1, and the raw material mixture before thickness adjustment 14 discharged from the raw material mixture is fed to the upper movable pressing device 12 and the lower movable pressing device 13 to have a thickness
It becomes the raw material mixture 15 after thickness adjustment adjusted to be equal to or less than mm.

Thereafter, the raw material mixture is dried with a pellet dryer 6 using hot air at 200 ° C. to 300 ° C. to form a solidified aggregate. As the hot air, it is effective to use preheated air obtained by recovering the sensible heat of the exhaust gas from the rotary hearth in the heat exchanger 8.

The present inventors have found that, in the pretreatment of the raw materials constituted by the apparatuses 1 to 6, the present invention can be applied to powdery raw materials. In the raw material 1 of the iron ore of the pellet feed, which is a relatively coarse raw material shown in Table 1, the strength of the solidified aggregate was relatively low. When all the raw materials in Table 1 were tested,
It has been found that the strength of the solidified aggregate increases as the particle size decreases. In the raw material 4 of the finest pickling sludge,
It became the maximum strength. The reason is that during the drying, the raw material mixture forms an agglomerate due to the adhesive force between the internal particles, and at this time, the smaller the particle size, the larger the specific surface area, and this adhesive force is found to be large. Was. As a result of the operation using various raw materials shown in Table 1, when the average particle size becomes 80 μm or less, the operation is affected by the strength of solidified aggregates such as the powdering rate during drying and the loss of the raw material scattering to exhaust gas. We found that the results were good. It is for this reason that the use of raw materials, particularly of 80 microns or less, is part of the invention in the present invention.

[0023]

[Table 1]

In the case of raw materials having a relatively coarse particle size, the influence of the drying temperature is small. In the case of raw materials having a fine particle size, if the drying temperature is too high, the internal pressure of the raw material mixture due to evaporation of water increases, and The inventors of the present invention have found that there is a phenomenon in which the raw material 5 described in Table 1 is used as a raw material having a small particle diameter. As a result, as shown in FIG. In addition, it has been found that when the drying temperature exceeds 250 ° C., the solidified aggregates are greatly powdered. It is for this reason that the drying temperature is set to 250 ° C. or less, particularly when using raw materials of 80 μm or less in the present invention.

The dried solidified agglomerates are charged into a rotary furnace 7. Although not shown in the figure, the loading device may be a simple device such as a swinging conveyor or a vibration feeder. The inside of the rotary furnace is controlled at a temperature of 900 ° C. to 1350 ° C. Generally, the raw material inlet should be between 900 ° C and 1 ° C.
At 000 ° C, in the firing zone, it is 1200 ° C to 1350 ° C. The charged solidified agglomerates ride on the rotating hearth, move in the furnace from the low-temperature part to the high-temperature part, and are reduced.
Depending on the type of metal to be reduced, operating temperature, raw material thickness, and other operating conditions, the time for reduction is from 8 minutes to 25 minutes.

When the solidified aggregate to be charged has a high moisture content,
Immediately after charging into the furnace, it was confirmed that the solidified aggregate exploded due to high temperature. The present inventors investigated the relationship between the residual moisture after drying and the explosion of the solidified agglomerate produced using the raw material 5 shown in Table 1 described above, and found that the residual moisture was about 2%.
And found that the explosion would become more severe after passing.

When explosion of the solidified agglomerates occurs, the
Since the amount of the raw material scattered in the exhaust gas increases, the ratio of the raw material scattered in the exhaust gas was investigated by changing the residual water content of the solidified aggregate produced using the raw material 5. The results are shown in FIG. 4, and it was also found that when the residual moisture exceeds about 2%, the scattering loss ratio of the solidified aggregate to the exhaust gas sharply increases. It is for this reason that in the present invention, the residual moisture after drying of the solidified aggregates is 2% or less.

In the rotary hearth method, the reduction itself proceeds very quickly because the particle size of the metal oxide material is small. Thus, the rate-limiting process of the reaction is heat transfer to the mixture.
The heat is transferred from the high-temperature furnace gas to the surface of the solidified aggregate by radiant heat transfer, and then conducted to the inside of the solidified aggregate. Therefore, in the rotary hearth method, the thickness of the solidified agglomerate affects the degree of reaction, that is, the metallization ratio. Then, the present inventors investigated the relationship between the thickness of the solidified aggregate and the metallization ratio. As the operating conditions, the raw material is supplied under the condition that the solidified aggregate forms one layer on the hearth,
A reduction for minutes was performed. The results are shown in FIG. 5, and it was clarified that when the thickness of the solidified aggregate exceeded 25 mm, the metallization ratio decreased. In the present invention, the thickness of the solidified aggregate is 2
It is for this reason that it is 5 mm or less.

The reduced metal produced by the reduction is discharged at a high temperature by a discharger. This reduced metal (hereinafter, referred to as a crude metal product) is put into a refractory-lined transfer machine with a chute, sent to a hot press machine 10, formed into briquettes, and then cooled using spray water. . When a hot press is not used, there is a method of using a rotary cooler or water cooling in a water cooling pit.
In particular, the crude metal product manufactured according to the present invention has a relatively small average particle size and a small crushing strength, so that problems of product pulverization and reoxidation during storage are likely to occur. Forming briquettes is an effective means.

[0030]

EXAMPLES The raw materials used in the operation of the present invention are shown in Table 1. Sample material 1 was a powdery iron ore called a pellet feed having an average particle size of 92 microns. Sample material 2 was made of iron chromium ore and had an average particle size of 74.
Micron. The sample raw material 3 is dust collected by a wet dust collector of a blast furnace and is called secondary gas ash. The moisture before dehydration is 69%. The average particle size was 53 microns. Sample raw material 4 is pickling sludge obtained from a thickener of a waste liquid for pickling the surface of a steel sheet in a rolling process at an ironworks, and has a water content of 85% before dehydration. The average particle size was very small, 7.8 microns. Sample material 5 was a mixture of sample material 3 and sample material 4 and had an average particle size of 22 microns.

Although coke flour was used as the reducing agent, powdered coal or oil coke may be used. The average particle size of the coke breeze was 127 microns. The mixing ratio of the coke breeze is calculated based on the reduction equivalent in the metal oxide in the raw material, and is 0.85 to 1.85 times the reduction equivalent in the premise that the fixed carbon amount in the coke reacts to carbon monoxide. Mix by setting to 2 times.

The raw material 1 was used to investigate the cost and operating results of the production of reduced iron according to the present invention and the conventional method.
It was shown to. The comparative conventional method 1 is a process using raw material pellets, in which raw materials are dehydrated and pre-dried (up to 4% moisture), granulated (pellet production), and pellet dried (1% moisture).
Until then, reduced iron is produced in a reduction process in a rotary hearth. The reason for reducing the water content to 4% by pre-drying is that it is necessary to send the water to the granulator in a smooth state for granulation, so the water content must be lower than the water content dehydrated by the dehydrator. That's why. The conventional method 2 is a process including a process of producing a tile-shaped molded product of the raw material, in which reduced iron is produced in a process of dehydrating and pre-drying the raw material (up to 8% moisture), molding, and reducing in a rotary hearth. It is a method. The moisture content of the pre-drying is to maintain the strength of the tile-shaped molded product at the time of molding, as shown in JP-A-11-12624.

[0033]

[Table 2]

Each production cost was represented by an index with the total cost per raw material charge of Conventional Method 1 being 100. Conventional method 1
In this case, since the process is long and, in particular, the drying is performed twice, the cost of the pretreatment of the raw material is as high as 24 in total, which is the main factor of the cost increase. In contrast, conventional method 2
Although the cost of the pretreatment of the raw material has been reduced to a total of 18, the raw material moisture at the time of supply to the rotary furnace is 8%.
%, The heat required to evaporate this moisture in the rotary furnace is required, and there is an increase in cost here, so that the total cost is reduced by only 3% from 97 to the conventional method 1. Not. Also, since the raw material moisture is 8%,
In the furnace, the tile-shaped raw material explodes, causing a large amount of raw material scattering loss to the exhaust gas, and insufficient reduction of the raw material accumulated on the hearth as powder, resulting in a low metallization rate. there were.

On the other hand, in the operation of the rotary hearth method for reduction using the present invention, the pretreatment is simple, the cost related to this part is only 13 in total, and the raw material for charging the rotary furnace is not used. Since there is almost no moisture, even the operation of the rotary furnace main body can be performed at the same cost as in the conventional method 1, so that the total cost was 89, which was 11% lower than that of the conventional method 1. Further, the raw material scattering loss to the exhaust gas and the metallization ratio were as good as the conventional method 1. As described above, in the rotary hearth method using the present invention, since simple pretreatment of the raw material is sufficient, the metal oxide can be reduced at a low cost, and the metalization rate and the raw material scattering loss to the exhaust gas can be reduced. The results were good and a high product yield was achieved.

Next, a reduction operation including a metal oxide was carried out using the raw materials shown in Table 1 with the equipment according to the present invention shown in FIG. The operating conditions are as shown in Table 3. The results are shown in Tables 4-1 and 4-2. Examples operated under the conditions within the range of the present invention are described as examples, and those operated under conditions outside the range are described as comparative examples.

[0037]

[Table 3]

[0038]

[Table 4]

Since raw material 1 is a coarse raw material having an average particle size of 92 microns, as shown in Table 4-1, Examples 1 and 2
As a result of operating at a different drying temperature, even at a drying temperature of 250 ° C. or more, the operation results such as powdering of the solidified aggregates were good, but the drying temperature was changed to 250 ° C. or more. In Example 2, which was the drying temperature, the powdering rate and the raw material scattering loss to the exhaust gas were slightly high. However, in Comparative Example 1, since the thickness of the solidified aggregate was 31 mm, which was outside the range of the present invention, the reduction reaction was delayed and the metallization rate of the crude metal product was 67%.
%.

The operation results of the raw material 2 are shown in Table 4-1 as an example of metals other than iron and as an example of chromium reduction. Chromium is less reducible than iron, so the reduction reaction has not progressed under the same conditions, but again, as shown in Example 3, by setting the thickness of the solidified aggregate to 19 mm and within the scope of the present invention, The metallization ratio was as good as 79%.

On the other hand, in Comparative Example 2, since the thickness of the solidified agglomerate was 30 mm, which was outside the range of the present invention, the reduction reaction was delayed, and the metallization rate of the crude metal product was as low as 52%. .

Next, as an example of a raw material having a small particle size, an example using secondary gas ash generated from a blast furnace is shown in Table 4-2.
In Example 4, since both the drying temperature and the residual moisture of the thickness of the solidified agglomerate were within the range of the present invention, good operation results were obtained. Compared with Example 1, which is an example of operation using iron ore with pellet feed, which is a relatively coarse raw material, in particular, powdered solidified agglomerates during drying and material scattering loss to exhaust gas were reduced to about half, resulting in improved operating results. are doing. In other words, it was demonstrated that the use of fine raw materials provided good operating results with less powdering.

Comparative Example 3 is an example of the effect of too high a drying temperature on the operation when a fine raw material of 80 microns or less is used. In this example, since the drying temperature was too high at 259 ° C., powdering at the time of drying was severe, reaching 4.6%, and as a result, the material scattering loss to the exhaust gas was 3.7.
%, And the ratio of powdered raw material that has fallen on the hearth has increased, making it difficult for the powdered raw material to react.
The metallization rate is also decreasing.

Next, Comparative Example 4 is an operation example in which the residual moisture after drying is high. 2.8% residual moisture after drying
Therefore, there was a problem that the explosion of the solidified aggregate occurred at the time of charging into the furnace, the raw material scattering loss was increased to 7.8%, and the metallization rate was lowered.

An operation example in which pickling sludge is used as a very fine raw material is described as Example 5, and an operation example in which the mixed raw material of the blast furnace secondary gas ash dust and the pickling sludge is used. Example 6 is shown in Table 4-2.
In all of these examples, good operation results were obtained for each evaluation item. As described above, the present invention can achieve sufficient results even with two types of mixed raw materials.

[0046]

According to the present invention, in the rotary hearth method for reduction, metal oxide can be economically reduced to produce metal. Further, it is possible to economically treat dust and sludge containing metal oxides generated from the metal manufacturing industry. In particular, it is an effective means for treating dust and sludge containing a large amount of water.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the overall configuration of equipment for a rotary hearth method for reduction according to the present invention.

FIG. 2 is a diagram showing an embodiment of a raw material mixture thickness adjusting device used in the facility of the present invention.

FIG. 3 is a diagram showing the influence of a drying temperature on powdering of a raw material mixture during drying when the particle size of the raw material is small.

FIG. 4 is a diagram showing the effect of residual moisture of solidified aggregates on loss of raw material scattering to exhaust gas.

FIG. 5 is a diagram showing the effect of the thickness of the solidified aggregate after drying on the metallization rate after the reduction reaction.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 raw material storage pit 2 slurry transport device 3 dehydrating device 4 belt conveyor 5 raw material mixture thickness adjusting device 6 pellet dryer 7 rotary furnace 8 waste heat recovery air preheater 9 exhaust gas dust collector 10 hot press machine 11 raw material mixture supply unit 12 upper movable Pressing device 13 Lower movable pressing device 14 Raw material mixture before thickness adjustment 15 Raw material mixture after thickness adjustment

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22B 7/00 C22B 7/00 H 7/02 7/02 A

Claims (9)

[Claims] 1. A mixture of a powder containing a metal oxide containing water and a powdery reducing agent mainly composed of carbon is dehydrated to form a solidified aggregate, and the residual moisture of the solidified aggregate is removed. A method for operating a rotary hearth method for reduction, characterized in that it is dried to 2% or less, supplied to a rotary furnace and reduced. 2. The method according to claim 1, wherein the average particle diameter of the powder containing the metal oxide is 80 μm or less. 3. The operating method of the rotary hearth method for reduction according to claim 1, wherein dust and / or sludge generated in a metal refining or processing step is used as the powder containing the metal oxide. . 4. The method according to claim 2, wherein dust and / or sludge generated in a metal refining or processing step is used as the powder containing the metal oxide. . 5. The method for operating a rotary hearth for reduction according to claim 1, wherein dust or sludge collected from a wet dust collector or a sedimentation tank is used as the powder containing the metal oxide. 6. A mixture of a powder mainly composed of a metal oxide and a reducing agent mainly composed of powdered carbon is dehydrated by a dehydrator so as to form a plate or a flat sphere, and then dried. The method for operating a rotary hearth for reduction according to claim 1. 7. The solidified aggregate produced by dehydrating a mixture of a powder mainly composed of a metal oxide containing water and a powdery reducing agent and then drying the mixture to have a thickness of 25 mm or less. The method for operating a rotary hearth for reduction according to claim 1. 8. The method according to claim 2, wherein a mixture of a powder mainly composed of a metal oxide containing water and a powdery reducing agent is dehydrated and then dried at a temperature of 250 ° C. or less. Operating method of rotary hearth for reduction 9. A method for operating a rotary hearth for reduction, characterized in that a crude metal product produced on a rotary hearth is formed by a hot press.