JPH11335713A - Production of reduced iron briquette - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a reduced iron by which the reduced iron briquette having high average quality can be obtd in high productivity. SOLUTION: Iron oxide briquette containing carbonaceous material having almost 10-30 mm in the range of grain diameter, is laid on the furnace hearth of a shifting floor type heating furnace so that the laid density becomes <=1.4 kg/m<2> /mm, and thereafter, the iron oxide briquette is rapidly heated so that the surface temp. thereof becomes >=1200 deg.C within 1/3 of the staying time of this iron oxide briquette in the shifting floor type heating furnace. The, after making the reduced iron briquette by reducing until the metalloid ratio of the iron oxide briquette becomes >=85%, this reduced iron briquette is discharged from the moving floor type heating furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of producing reduced iron agglomerates by reducing iron oxide agglomerates containing a carbon material using a moving bed type heating furnace.

[0002]

2. Description of the Related Art As a method for producing reduced iron, the Midrex method is well known. In the Midrex method, reducing gas converted from natural gas is blown from the tuyere and raised in a shaft furnace to reduce iron ore and iron oxide pellets filled in the furnace to obtain reduced iron. It is. However, in this method, it is necessary to supply a large amount of natural gas as a fuel, and the location conditions are limited.

[0003] Therefore, attention has been focused on a method for producing reduced iron that can use relatively inexpensive coal as a reducing agent instead of natural gas. For example, U.S. Pat.
No. 01631 describes a process for producing reduced iron by mixing and ore fines with a carbonaceous material, pelletizing them, and reducing them by heating under a high-temperature atmosphere. According to this method,
In addition to the fact that the reducing agent is based on coal, it has advantages such as the ability to directly use fine ore, high-speed reduction, and the ability to adjust the carbon content in the product.

In the method described in these US Patent Publications, a dried iron oxide agglomerate is charged into a moving bed type heating furnace such as a rotary hearth furnace, and heated while moving in the furnace. Carbon oxides reduce iron oxide agglomerates.

[0005]

The reduction of iron oxide agglomerates by the carbonaceous material proceeds from the surface of the agglomerates due to heat transfer.
Therefore, in the latter half of the reduction, metallic iron is deposited on the surface layer of the upper surface of the agglomerate, but the reduction reaction does not proceed sufficiently in the central part or lower part where the temperature is low, and the quality of the reduced iron decreases. not enough. In addition, the temperature control of the rotary hearth furnace is performed by the secondary combustion of the combustible gas generated from the combustion burner or the agglomerate. It is necessary that the gas approach the complete combustion at the furnace exit. However,
If an appropriate reducing atmosphere is not maintained, the agglomerates are exposed to the oxidizing gas, particularly in the latter half of the reduction zone, and the metallic iron on the surface layer of the agglomerates is re-oxidized, thereby deteriorating the product quality.

Further, iron oxide agglomerates have a size suitable for operating conditions. Those having a size suitable for operating conditions have high quality after reduction, while those having a size smaller than the suitable size are reoxidized due to excessive heating, and those having a large size are insufficiently reduced due to insufficient heating. In addition, if the particle size of the agglomerates varies, both the reduction rate and the strength of the entire product decrease.

An object of the present invention is to provide a method for producing reduced iron capable of obtaining reduced iron agglomerates having high average quality with high productivity.

[0008]

According to the method for producing reduced iron agglomerates of the present invention, first, iron oxide agglomerates containing a carbonaceous material having a particle size of approximately 10 to 30 mm are produced. Next, the iron oxide agglomerate containing the carbon material is thinly spread on the hearth of the moving bed type heating furnace so that the spread density becomes 1.4 kg / m ² / mm or less. Thereafter, the iron oxide agglomerate is heated so that the surface temperature of the iron oxide agglomerate becomes 1200 ° C or more within one-third of the time the iron oxide agglomerate stays in the moving bed type heating furnace. Heat things quickly. Then, after reducing the iron oxide agglomerate to a reduced iron agglomerate until the metallization ratio becomes 85% or more, the reduced iron agglomerate is discharged from the moving bed type heating furnace.

[0009] In the step of producing the iron oxide agglomerate containing the carbonaceous material, at least 80% of the iron oxide agglomerate is included in the target particle size ± 80%.
It is desirable to make it within 2mm. Further, it is desirable that the maximum fluidity of the carbon material used in softening and melting be 0.8 or more.

The apparent density of the iron oxide agglomerate produced in the step of producing the iron oxide agglomerate containing the carbonaceous material is as follows:
Desirably, it is 2.3 g / cm ³ or more.

[0011] In the step of reducing the iron oxide agglomerate containing carbonaceous material, the amount of CO gas generated during the reduction from the iron oxide agglomerate may be reduced to less than one-fourth of the generation peak. It is desirable to control the degree of reduction of the exhaust gas from the burner for heating the iron oxide agglomerate to Fe or FeO equilibrium. Further, it is desirable that the apparent density of the reduced iron agglomerate after reduction is 2 g / cm ³ or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Radiation heat is dominant in the form of heat transfer in a furnace. For this reason, iron oxide agglomerates containing carbon material can be laid on the hearth without overlapping, thereby achieving uniform heating, improved productivity,
It is important from the point of quality improvement. For this reason, it is desirable that the floor density on the hearth be 1.4 kg / m ² / mm or less. Here, kg / m ² in the unit of the bedding density is the mass of iron oxide agglomerate per unit area of the hearth, and mm in the unit of the bedding density indicates the average particle size of the iron oxide agglomerate. ing.

Further, as shown in FIG. 5, when the temperature exceeds 1200 ° C., the degree of reduction (CO / (CO + CO ₂ )) (shown as collected data in the figure)
Therefore, it is important to rapidly heat the iron oxide agglomerate charged in the furnace to 1200 ° C. to promote the reduction of the agglomerate. Therefore, the shorter the heating time up to 1200 ° C., the better. However, there are restrictions from the point of actual operation, and the surface temperature of the
It is sufficient to heat to 1200 ° C within a time period of less than / 3.

During the reduction, when the amount of CO gas generated from the iron oxide agglomerate falls to 1/4 of the peak generation time,
The central part of the iron oxide agglomerate is reduced and the surface part is in a state where metallic iron is precipitated. For this reason, by controlling the degree of reduction of the exhaust gas of the burner to Fe or FeO equilibrium at this time, reoxidation of metallic iron on the surface layer can be prevented and reduction of the surface layer can be promoted.

The carbon material having a high fluidity is formed at the time of softening and melting to improve the thermal conductivity in the agglomerate by filling the voids between the iron oxides in the agglomerate with the carbon material. be able to. Therefore, it is desirable to use a carbon material with a maximum fluidity of 0.8 or more during softening and melting. Thus, even if the gas temperature in the furnace is increased to increase the productivity, the surface of the agglomerate does not melt in the furnace. Further, since the iron oxide agglomerate containing the carbon material is molded under pressure, the internal voids are also reduced and the thermal conductivity is improved. The improvement in the thermal conductivity of the iron oxide agglomerates speeds up the reduction reaction, thereby improving the productivity of the production of reduced iron.

Also, by increasing the apparent density of the iron oxide agglomerate containing the carbonaceous material, the mass of the iron oxide agglomerate per unit area of the hearth increases, and as a result, the productivity is improved.
Therefore, it is desirable that the apparent density of the iron oxide agglomerate be 2.3 g / cm ³ or more.

In dissolving the reduced iron agglomerate, if the apparent density of the reduced iron agglomerate is larger than the slag in the melting furnace, the reduced iron agglomerate does not float on the slag.
The dissolution of reduced iron agglomerates is faster. Therefore, it is desirable that the reduced iron agglomerates after reduction have an apparent density of 2 g / cm ³ or more, which is higher than the general apparent density of slag.

The particle size of the iron oxide agglomerate containing carbon material is as follows:
The more uniform it can be laid without overlapping on the hearth. In addition, quality deterioration due to overheating or underheating is eliminated, and a homogeneous product can be obtained. Therefore, it is desirable to control the particle size so that 80% or more of the iron oxide agglomerate containing carbon material is within ± 2 mm of the target particle size.

In the granulation of the iron oxide agglomerate containing the carbonaceous material, the gas generated in the heating and mixing step, the pressure forming step, and the degassing step of the raw material is recovered, and the recovered gas is used for a reducing burner. By using it as fuel, the fuel consumption rate can be reduced. In addition, by injecting the recovered gas into the final stage of reduction in the reduction furnace, reoxidation of the reduced iron agglomerates can be prevented.

In the reduction zone, combustible gases such as CO and H ₂ generated from the iron oxide agglomerate containing the carbon material are efficiently burned in the vicinity of the iron oxide agglomerate to be heated to the heated object. By using the supply heat source, the fuel supply to the moving bed type heating furnace can be reduced. For this reason, it is desirable to supply the secondary combustion air to burn the combustible gas.

[0021]

The present invention will be described in more detail with reference to the following examples.

Example 1 Iron ore (78.3%) and coal (20.0%) having the components shown in Table 1
In addition, binder: iron oxide agglomerate made by mixing 1.7%,
Spread on the hearth at a density of 1.0 kg / m ² / mm, productivity 100 kg / m
Reduction was performed using a rotary hearth furnace at ² / hr. The result is shown in FIG. In the comparative example in the figure, the spread density was changed to 1.5 kg / m ² / mm. As is evident from FIG. 1, when the bedding density of the agglomerate exceeds 1.4 kg / m ² / mm, a decrease in the metallization ratio is observed. In order to improve the quality of the reduced iron agglomerate, it is desirable that the layer thickness is smaller than 1 and, specifically, the spread density is 1.4 kg / m ² / mm or less.

[0023]

[Table 1]

Example 2 The iron oxide agglomerate containing the same carbonaceous material as in Example 1 was laid on the hearth so that the pile density was 1.1 kg / m ² / mm and the productivity was 80 kg / m ² /
Reduction was performed using a rotary hearth furnace at hr. The size of the agglomerates at this time was adjusted so that 80% of the agglomerates fell within the target particle size of ± 2 mm. As a result, a reduced iron agglomerate having the grade shown in FIG. 2 was obtained. The spread density of the comparative example is 1.5 to 1.75 kg / m ² / mm. As is clear from FIG. 2, the metal density of the reduced iron agglomerate in the portion where the agglomerate overlaps is reduced by about 30% as compared with the example of the present invention because the comparative example has a high spread density. I have.
On the other hand, in the example of the present invention, a reduced iron agglomerate of stable quality with a metallization ratio of 96% was obtained.

FIG. 3 shows the relationship between the particle size of the reduced iron agglomerate and the metallization ratio at this time. As shown in FIG. 3, the reduced iron agglomerate has a peak of the metallization ratio at a particle size of 13 to 16 mm,
If the particle size is out of this range, the metallization ratio decreases. From this result, it is best to put all of the target particle size ± 1.5 mm, but if the agglomerate was granulated with a pan pelletizer and sieved with a roller screen, this target particle size ± 1.5 mm was achieved. It is not easy to do. Therefore, by pressing the iron oxide agglomerate, 80% of the iron oxide agglomerate can be set within the target particle size of ± 2 mm. Usually, the particle size of the agglomerates is 10 to 30 mm, depending on the operating conditions.

Example 3 An iron oxide agglomerate containing the same carbonaceous material as in Example 1 was charged into a rotary hearth furnace, and reduced at an ambient temperature of 1300 ° C. for 9 minutes. The spread density at this time is 1.15 kg / m ² / mm. The oxidation degree of the combustion gas ((CO ₂ + H ₂ O) / (CO + H ₂ + CO ₂ + H ₂ O))
1.0 and the latter half ranged from 0 to 1.0. The switching time between the first half and the second half was also varied between 0 and 8 minutes. FIG. 4 shows the relationship between the oxidation degree of the combustion gas in the latter half and the metallization ratio.

As shown in FIG. 4, as the degree of reduction of the combustion gas decreases, and by quickly switching to a lower degree of oxidation, the metallization ratio increases. Oxidation degree of combustion gas in the second half to 0.53 6
If it is switched within minutes, the metallization rate is 85% or more. If it is switched within 4 minutes, the metallization rate is 90% or more. However, if the switching time is as slow as 8 minutes, the metallization rate is less than 85%. If the oxidation degree of the combustion gas after switching is 0, the metallization ratio can be maintained at 90% or more even if the switching time is as slow as 6 minutes. By the way, the amount of CO generated from the agglomerates at a switching time of 4 minutes is 80% of the peak at the time of generation, and 47 minutes at the peak of generation at 6 minutes.
% At 8 minutes was 13% of the peak. Therefore, even if the amount of CO generated from the agglomerates is reduced to less than 1/4 of the peak at the time of generation peak, the metallization rate cannot be improved even if the oxidation degree of the combustion gas is switched to a low reduction degree.

Example 4 The same iron oxide agglomerate containing the same carbon material as in Example 1 was spread at a density of 1.04 kg / m ² / mm in a rotary hearth furnace so as not to overlap, and reduced. Table 2 shows some of the reduction conditions and the grade of the reduced iron agglomerates. The burner exhaust gas reduction shown here is Fe ₂ O ₃ equilibrium. This reduction indicates that there are operating conditions under which a high metallization ratio can be obtained without controlling the degree of reduction of the burner exhaust gas to Fe or FeO equilibrium. This is assumed as follows. That is, as shown in FIG. 5, as the temperature in the furnace is increased, the temperature of the agglomerate is also increased, so that the solution loss reaction is activated and CO / (CO + CO ₂ )
The value is rising. The CO / (CO + CO ₂ ) value indicates the degree of reduction of the burner exhaust gas. The farther this value is from the boundary between Fe and FeO, the higher the reduction potential. Therefore, it is presumed that the atmosphere around the agglomerate becomes very highly reducing due to the high-temperature operation, and the influence of the degree of reduction of the exhaust gas from the burner is reduced.

[0029]

[Table 2]

Example 5 FIG. 6 shows five types of carbon materials A, C, E, H and I having different flow rates.
1 shows the relationship between the heating time and the central temperature of the agglomerate when the agglomerate was heated at an ambient temperature of 1300 ° C. As shown in FIG. 6, the high-flow carbonaceous materials (charcoal materials H and I)
The time required to reach 1300 ° C. is shorter than that of (carbon materials A and C). In addition, since the reduction reaction starts at about 800 ° C, the temperature history of the heating process is also important, and the temperature inside the agglomerate is fast when a highly fluid carbon material is used. From the observation of the cross-sectional structure of the agglomerate during the reduction process, it was confirmed that when a highly fluid carbonaceous material was used, a connection structure of solid carbonaceous iron oxide particles was formed. For this reason, it is desirable to use a carbon material having a maximum fluidity of 0.8 or more during softening and melting.

Example 6 Iron ore and pulverized coal shown in Table 1 were replaced with iron ore 78% and coal 22%
Then, the mixture was heated to 450 ° C., and 2 to 5 cm ³ of agglomerate was hot formed at a pressure of 39 MPa (hot formed briquette). As a comparative example, iron ore and pulverized coal were mixed at the same mixing ratio, and about 1% of bentonite was added as a binder to the mixture, and formed into an agglomerate having a volume of 2 cm ³ by a granulator (pellet). FIG. 7 shows the respective apparent densities. As shown in FIG. 7, the apparent density of the hot formed agglomerate is 40% higher.

Next, the hot formed agglomerate and the granulated agglomerate are
A reduction test was performed in a reduction furnace maintained at 1300 ° C. FIG. 8 shows the result. As is clear from the figure, at the same volume, the reduction time is shortened as the apparent density of the agglomerate increases. Therefore, productivity is improved by improving the apparent density of agglomerates. FIG. 9 shows the apparent density of the hot formed agglomerate after reduction. As shown in the figure, as the apparent density of the agglomerate before reduction increases, the apparent density of the agglomerate after reduction increases in proportion to this. Also,
FIG. 9 shows that when the hot formed agglomerate is subjected to a degassing treatment at 500 ° C. for 30 minutes, the agglomerate does not swell in the reduction step, and the apparent density of the reduced iron may be 2 g / cm ³ or more. Shows

FIG. 10 shows the results of experiments in which reduced iron agglomerates having apparent densities of 1.6 g / cm ³ and 2.4 g / cm ³ were melted in a crucible. Normally, the molten slag density is about 2 g / cm ³ , and if the apparent density of the reduced iron agglomerate is lower than this, the agglomerate floats on the slag surface as shown in the figure to delay dissolution. Conversely, if the apparent density of the reduced iron agglomerates is large, the agglomerates sink into the slag to promote dissolution. As a result of test, apparent density of agglomerate is 1.6 g
For / cm ^3, dissolution rate was 0.5 kg / min, an apparent density 2.
For 4 g / cm ³ , the dissolution rate is 2 kg / min. As described above, the melting rate is improved four times by making the apparent density of the reduced iron agglomerate larger than the apparent density of the slag in the melting furnace.

[0034]

As is apparent from the above description,
According to the present invention, an iron oxide agglomerate containing a carbonaceous material having a particle size within a range of ± 2 mm and an apparent density of 2.3 g / cm ³ or more is laid and the density is 1.4 kg / m ² / mm or less. Lay thinly on the hearth of the moving bed type heating furnace so that the iron oxide agglomerate containing carbon material stays in the moving bed type heating furnace within one-third of the time, and the surface temperature becomes lower. Since it is rapidly heated to 1200 ° C. or more to reduce the metallization rate to 85% or more, reduced iron agglomerates having high average quality can be obtained with high productivity. Furthermore, the apparent density of reduced iron agglomerates after reduction is 2 g / c
Since it is m ³ or more, the reduced iron agglomerates sink into the slag at the time of dissolution in the subsequent step, and dissolution is promoted.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the bedding density of agglomerates and the metallization ratio.

FIG. 2 is a graph showing the difference between the metallization ratio of reduced iron agglomerates in Example 2 and a comparative example.

FIG. 3 is a graph showing the relationship between the particle size of reduced iron agglomerates and the metallization ratio.

FIG. 4 is a diagram showing the relationship between the degree of reduction of the combustion gas in the latter half of the reduction and the metallization ratio in the third embodiment.

FIG. 5 is a view showing the relationship between the center temperature of agglomerates and the degree of gas oxidation in Example 4.

FIG. 6 shows an agglomerate using five types of carbon materials having different fluidities.
It is a figure which shows the relationship between the heating time at the time of heating at 1300 degreeC atmospheric temperature, and agglomerate center temperature.

FIG. 7 is a diagram showing a comparison of apparent densities of a hot-formed agglomerate (hot-formed briquette) of the present invention and a dried raw agglomerate (pellet) of a comparative example.

FIG. 8 is a diagram showing the results of a reduction test performed on a hot formed agglomerate and a granulated agglomerate having different apparent densities in a reduction furnace maintained at 1300 ° C.

FIG. 9 is a diagram showing a relationship between an apparent density of an agglomerate before reduction and an apparent density of a reduced iron agglomerate.

FIG. 10 is a view showing experimental results obtained by melting reduced iron agglomerates having apparent densities of 1.6 g / cm ³ and 2.4 g / cm ^{3 in} a crucible.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ken Sugiyama 1-6-14 Edobori, Nishi-ku, Osaka-shi, Osaka Industrial Service International Co., Ltd. (72) Inventor Yoshimichi Takenaka 1 Kanazawacho, Kakogawa-shi, Hyogo Address Kobe Steel Co., Ltd.Kakogawa Works (72) Inventor Kazuya Miyagawa 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel Co., Ltd.Kakogawa Works 1 (72) Inventor Shoji Jouchi 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel, Ltd.Kakogawa Works (72) Inventor Haruhisa Iwakiri 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel Works, Kakogawa Works (72) Inventor Makoto Nishimura 1-5-5, Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture No. 5 Kobe Steel, Ltd.Kobe Research Institute (72) Inventor Takao Umeki Hyogo 1 Kanazawa-cho, Kakogawa-shi Kobe Steel Works, Kakogawa Works (72) Inventor Sumito Hashimoto 1 Kanazawa-machi, Kakogawa-shi, Hyogo Prefecture Kobe Steel Works, Kakogawa Works (72) Inventor Teruhisa Uehara Kakogawa, Hyogo Prefecture 1 Kanazawa-cho, Kobe Kobe Steel Works Kakogawa Works

Claims (6)

[Claims] 1. A method for producing a reduced iron agglomerate, comprising the steps of: producing an iron oxide agglomerate containing a carbonaceous material having a particle size in a range of 10 to 30 mm;
On the moving bed type heating furnace hearth, spread it so that the spreading density is 1.4 kg / m ² / mm or less, and the iron oxide agglomerate stays in the moving bed type heating furnace within one-third of the time. In time, the surface temperature
A method for producing reduced iron agglomerates, comprising heating to 1200 ° C. or more and reducing the metallization rate to 85% or more. 2. The method for producing a reduced iron agglomerate according to claim 1, wherein 80% or more of the iron oxide agglomerate containing the carbon material is within ± 2 mm of a target particle size. 3. The method for producing a reduced iron agglomerate according to claim 1, wherein the carbon material used in the iron oxide agglomerate containing the carbon material has a maximum fluidity of 0.8 or more during softening and melting. 4. During the reduction of the iron oxide agglomerate containing the carbonaceous material, the oxidation of the iron oxide agglomerate before the amount of CO gas generated from the iron oxide agglomerate falls to less than one-fourth of the generation peak. 4. The method for producing reduced iron agglomerates according to claim 1, wherein the degree of reduction of the exhaust gas of the burner for heating the iron agglomerates is controlled in parallel with Fe or FeO. 5. The method for producing a reduced iron agglomerate according to claim 1, wherein the apparent density of the iron oxide agglomerate containing the carbonaceous material before reduction is 2.3 g / cm ³ or more. . 6. The reduced iron agglomerate obtained by reducing the iron oxide agglomerate containing the carbonaceous material has an apparent density of 2 g / cm ³ or more. For producing reduced iron agglomerates.