JPH1192833A - Agglomerate for reduced iron and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing method of an agglomerate for reduced iron which shortens the reducing time of fine ore in the agglomerate, and further, shortens the melting time of the reduced iron after reducing and prevents reoxidation of the reduced iron. SOLUTION: The agglomerate for reduced iron is composed of mixed material of powdery ore and carbonaceous material and the apparent density is >=2.3 g/cm<3> . Further, the apparent density of the reduced iron after reducing is >=2 g/cm<3> . The producing method of the reduced iron is executed by recovering gas generated in a heat mixing process of the races materials of the agglomerate, pressure forming and degassing processes thereof and to prevent the reoxidation of the reduced iron, by blowing this recovered gas into reduced end stage zoge in a reducing 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 by reducing fine ore in an agglomerated carbonaceous material agglomerate. A method for producing reduced iron that reduces the reduction time, further increases the apparent density of the reduced iron after reduction, reduces the melting time in the ironmaking and steelmaking processes, and prevents reoxidation of the reduced iron. It belongs to the technical field.

[0002]

2. Description of the Related Art As a method for producing reduced iron, the Midrex method is well known. According to this method, a reducing gas transformed from natural gas is blown from a tuyere and raised in a shaft furnace, whereby Reduced iron ore or iron oxide pellets filled in the furnace can be reduced to obtain reduced iron.
However, this method requires a large amount of expensive natural gas to be supplied as fuel.

[0003] In recent years, attention has been paid to a reduced iron production process in which relatively inexpensive coal can be used as a reducing agent instead of the natural gas. For example, U.S. Pat. No. 3,443,931 describes a process for producing reduced iron by mixing and ore fines and a carbonaceous material into pellets 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, there are advantages such as the ability to directly use fine ore, high-speed reduction, and the ability to adjust the carbon content in the product. Have.

[0004]

In this process, the agglomerates (pellets, briquettes, etc.) are heated by radiant heat from the upper surface of the high-temperature reduction furnace, so that the height of the raw material layer is limited, and therefore the productivity is reduced. To improve it, it is necessary to increase the reaction rate itself of the reduction reaction. However, since the reduction rate of agglomerates for reduced iron is limited by the heat transfer in the agglomerates, raise the temperature of the reduction furnace above the heat transfer limit in the agglomerates in order to improve productivity. Then, the agglomerate melts from the surface and causes sticking in the furnace and damage to the furnace body.

[0005] The agglomerate for reduced iron is obtained by mixing fine ore with a carbon material (such as coal) as a reducing agent and a binder, and pelletizing with a granulator or briquetting with a compacting machine. Etc. The agglomerate for reduced iron formed by these methods is a porous body as shown in Fig. 14 (a) and has a small contact area between the carbonaceous material and the fine ore. Is low. In order to increase the contact area between the carbonaceous material and the fine ore in the reduction process, the maximum flow rate during softening and melting of the carbonaceous material in the reduction furnace is a method to increase the reduction rate.
Carbonaceous interior pellets of 0.8 or more are proposed in Japanese Patent Application No. 9-147732.

[0006] However, in the above method, a binder is required at the time of forming the agglomerate, and this binder also lowers the quality of reduced iron. In addition, the carbon material having the highest maximum fluidity during softening and melting contains a large amount of volatile matter, and the use of this kind of carbon material causes swelling of agglomerates in the process of removing volatile matter, which causes cracking. Also, as shown in FIG. 14 (a), the agglomerate which is a porous body has a small apparent density,
Therefore, the apparent density of the reduced iron generated after the reduction is also reduced. If the apparent density of the reduced iron is small, the reduced iron floats on the slag in the melting furnace when dissolving the reduced iron, and there is a problem that it takes a long time to dissolve the reduced iron.

[0007] In addition, sintering of the fine ore in the agglomerate starts when the reduction is almost completed, and the reduced iron has an increased strength.
However, due to the restriction of operating temperature, if the hysteresis time during reduction is short, sintering is insufficient, the strength of the reduced iron is low, and destruction powdering occurs in the handling process such as discharge from the reduction furnace, which lowers the product yield. There is. Furthermore, since the burner is burned as a heat source in the reduction furnace, preventing the reoxidation of the reduced iron generated by the reduction of agglomerates by the combustion gas also increases the productivity of metallic iron in the reduced iron. It is important from above. It can be said that this reoxidation is easier for the reduced iron which is insufficiently sintered.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been made to increase the apparent density of agglomerates, shorten the reduction time of fine ore in the agglomerates, and facilitate sintering. , Further increase the apparent density of reduced iron after reduction,
It is an object of the present invention to provide an agglomerate for reduced iron that shortens the dissolution time and a method for producing reduced iron that prevents reoxidation of reduced iron.

[0009]

SUMMARY OF THE INVENTION The gist of the invention is a reduced iron agglomerate made of a mixture of fine ore and carbonaceous material and having an apparent density of 2.3 g / cm ³ or more.

It is characterized in that fine ore is mixed with carbonaceous material, hot-formed at a forming pressure of 20 to 150 MPa in a temperature range of 260 to 550 ° C., and then degassed for 5 minutes or more in a forming temperature range. This is a method for producing an agglomerate for reduced iron having an apparent density of 2.3 g / cm ³ or more.

[0011] The carbon material is a caking coal having a volatile content of 16% or more and a ghee cellar fluidity of 2DDPM or more.
This is a method for producing an agglomerate for reduced iron of ³ g / cm ³ or more.

The above apparent density, wherein the carbonaceous material is a non-caking coal having a volatile content of 16% or less and / or a carbonaceous material which is not softened by heating and mixed with a caking coal to give a gee cellar fluidity of 20 DDPM or more. Is a method for producing an agglomerate for reduced iron of 2.3 g / cm ³ or more.

[0013] The carbon material is a non-coking coal having a volatile content of 35% or more or a volatile content of 40% or more, an ash content of 5% or less, and a sulfur content of 0.3%.
This is a method for producing the following lignite agglomerates for reduced iron having an apparent density of 2.3 g / cm ³ or more.

The reduced iron agglomerate described above, wherein the reduced iron has an apparent density of 2 g / cm ³ or more after reduction.

[0015] The gas generated in the heating and mixing step, the pressure forming step, and the degassing step of the raw material of the agglomerate is recovered, and the recovered gas is blown into a reduction terminal zone of the reduction furnace to prevent reoxidation of the reduced iron. It is a method of producing iron.

The carbon material as the reducing agent is 260 ° C. depending on the type of coal.
If the temperature exceeds 550 ° C., a dry distillation reaction starts and the material softens and melts. When the fine ore and the carbonaceous material are mixed and pressed under this temperature range, the molten carbonaceous material easily penetrates into the voids between the fine ore particles, and the fine ore is strongly connected to each other. For this reason, a binder is not required, and the quality of reduced iron can be improved. In the present invention, a carbon material having this softening and melting property is used.

The agglomerate formed by hot forming in the temperature range of 260 to 550 ° C. is degassed for 5 minutes or more in the forming temperature range to volatilize the carbonized material in the agglomerate. It is possible to increase the strength of the agglomerate by removing the component and prevent cracking due to swelling of the agglomerate during reduction. The apparent density of the agglomerate after the degassing treatment shrinks due to the loss of volatile components, and thus is almost the same as the apparent density of the agglomerate before the degassing treatment. However, by performing degassing,
The agglomerates in the reduction process no longer swell, and the apparent density of reduced iron after reduction increases. Therefore, when dissolving the reduced iron, the apparent density of the reduced iron becomes larger than the apparent density of the slag in the melting furnace, and the reduced iron quickly sinks into the slag to promote dissolution, thereby increasing the productivity during melting. improves. Especially effective in electric furnace smelting.

The volatile content is 16% or more,
When using caking coal of DDPM or more, 350-55
Although hot forming is performed in a temperature range of 0 ° C., it is preferable to change the forming temperature in proportion to the maximum flow temperature of the Giesser flow rate. The forming pressure during hot forming is 19.6MPa or more and 147.1MPa or less, and the degassing treatment after forming is performed for 5 minutes or more in the forming temperature range. In order to increase the degassing rate, the temperature of the degassing / solidification tank may be increased, and the degassing treatment may be performed in the temperature range from the molding temperature to 600 ° C. In this way, an agglomerate for reduced iron having an apparent density of 2.3 g / cm ³ or more can be obtained.

When a non-coking coal having a volatile content of 16% or less and / or a carbon material which does not soften by heating is used as the carbon material, the non-caking coal having a volatile content of 16% or more is mixed with the coking coal, and the greaser fluidity is weighted. Using a carbon material adjusted to have an average value of 20 DDPM or more, hot forming is performed in a temperature range of 350 to 550 ° C., and it is preferable to change the forming temperature in proportion to the maximum flow temperature of the Giesler flow rate. Molding pressure during hot forming is 40MPa
Above, it is performed at 150 MPa or less, and the degassing treatment after molding is performed for 5 minutes or more in the molding temperature range. In order to increase the degassing rate, degassing can be performed in a temperature range from the molding temperature to 600 ° C. In this way, an agglomerate for reduced iron having an apparent density of 2.3 g / cm ³ or more can be obtained.

The carbon material is a non-coking coal having a volatile content of 35% or more or a volatile content of 40% or more, an ash content of 5% or less, and a sulfur content of 0.3%
When the following lignite is used as the carbonaceous material, it is hot-formed in a temperature range of 260 to 450 ° C., which is the decomposition starting temperature of non-coking coal and lignite. The forming pressure during hot forming should be 20MPa or more and 150MPa or less, and degassing after forming should be performed for 5 minutes or more in the forming temperature range. In order to increase the degassing rate, degassing can be performed at a temperature in the range from the molding temperature to 500 ° C. In addition, the ash content of lignite is less than 5% and the sulfur content is 0.3%.
The reason for limiting to less than or equal to% is to obtain high quality reduced iron. In this way, an agglomerate for reduced iron having an apparent density of 2.3 g / cm ³ or more can be obtained.

Therefore, the carbonaceous material in the agglomerate adheres to the fine ore, the contact area between the carbonaceous material and the ore increases, and the apparent density also increases. For this reason, the thermal conductivity in the agglomerate is also improved, the direct reduction of the fine ore in the agglomerate by the carbonaceous material is promoted, and the reduction time is shortened. Further, since the apparent density of the agglomerate is large, the partial pressure of CO in the agglomerate is increased, so that the gas reduction of the fine ore by CO is promoted.

When the residence time in the reduction furnace is equal due to the reduction promotion, the residence time in the furnace after the reduction is extended, the sintering of the reduced iron is accelerated and the strength of the reduced iron increases, and It becomes difficult to react to oxidation. As a result, in the handling step such as discharge from the reduction furnace, the destruction and pulverization of the reduced iron is less likely to occur, the product yield is improved, and the oxidation loss of the metallic iron in the reduced iron is small.

The gas generated in the step of heating and mixing the raw material of the agglomerate, the step of pressing and the step of degassing are heavy hydrocarbons such as tar and the like. By blowing into the zone, the reduced iron acts as a catalyst to perform gas reforming, thereby enriching CO and H ₂ , adjusting the atmosphere in the end-of-reduction zone to reducibility, and preventing reoxidation of reduced iron. The apparent density of the reduced agglomerate (reduced iron) thus obtained is 2 g / cm ³ or more.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. FIG. 1 shows an example of a conceptual diagram of a process for producing reduced iron according to the present invention. As shown in the figure, first, carbonaceous material and ore are pulverized by a pulverizer. Ore and non-coking coal with a volatile content of 16% or less are pulverized so that particles of 74μm or less become 70% or more. The particle size of caking coal, non-caking coal and lignite with a volatile content of 16% or more is not particularly limited, but it is preferable to grind it to 1 mm or less in order to maintain a good mixed state with ore. Regarding drying and preheating of ore and carbon material after pulverization, the carbon material is dried with a rotary drier at a temperature of 200 ° C or less to remove adhering moisture in order to reduce temperature fluctuation when mixing with ore due to moisture fluctuation. I do. On the other hand, the ore is preheated in a rotary kiln so as to reach the target forming temperature when mixed with the carbonaceous material.

For mixing the dried or preheated ore and the carbonaceous material, for example, a two-shaft mixer commonly used in this industry, which can be mixed in a short time to prevent overheating of the carbonaceous material, is used. Also, the mixer is kept warm to secure the molding temperature. The ore and the carbonaceous material after mixing are pressed into agglomerates (briquettes) using a hot forming machine with an indenter. In the pressure molding, it is sufficient that the agglomerate has sufficient strength to withstand handling. Therefore, the molding pressure is 20 MPa or more. As shown in FIG. 14 (b), the agglomerate formed in this way, as shown in FIG. 14 (b), melted carbon material penetrates into the gaps between the ore particles, firmly connects the ores, and also forms the carbonaceous material with the ore. Are also large. Further, the mixer and the molding machine have a closed structure, and the gas generated by the mixer and the molding machine is sucked and collected by using an ejector or the like, and the collected gas is blown into a reduction terminal zone of the reduction furnace to be used as a reducing gas.

In the agglomerate after molding, thermoplasticity remains in the carbonaceous material and a large amount of volatile matter remains. When this is charged into the reduction furnace as it is, the agglomerates expand due to the generation of volatile components, and in some cases, cracks enter and become powdery. In order to prevent this and increase the strength of the agglomerate, the agglomerate is charged into a degassing / solidification tank maintained at a temperature near or above the molding temperature to solidify the carbonaceous material and at the same time reduce the volatile content Let it. As shown in FIG. 14 (c), the agglomerate from which volatile components have been removed has gas holes (fine pores) from which volatile components have been removed. The apparent density of the agglomerate produced in this way is
2.3 g / cm ³ or more. Therefore, this degassing and solidifying treatment is an important step for preventing the agglomeration of the agglomerates and obtaining reduced-density iron. The agglomerate thus obtained exits the degassing / solidifying tank and is then sieved, the upper part of the sieve is charged into a reduction furnace, and the powder under the sieve is returned to the mixer again as a raw material.

The pyrolysis gas of the carbonaceous material generated in the mixer, the molding machine and the degassing / solidifying tank is mainly composed of hydrocarbons. This is collected by suction using an ejector or the like. For the ejector, a part of the exhaust gas from the reduction furnace is used after being pressurized with a blower. Keep the suction gas piping at about 500 ° C to prevent tar adhesion. The recovered pyrolysis gas is blown into a reduction furnace and used as a reducing gas for adjusting the atmosphere in the furnace and as a fuel.

The agglomerates discharged from the degassing / solidifying tank and sieved are hot-charged to a reducing furnace at a temperature of about 400 to 500 ° C. Hot-charged agglomerates are:
It is reduced in a furnace heated to 1200 to 1400 ° C by heat from the burner combustion. Further, the recovered pyrolysis gas, CO reformed in a furnace and enriched H _2, utilized for finishing reduction to increase the metallization degree of the reduced iron, as a blown into the last stage of reduction zone of the reduction furnace the reduction gas I do.

The agglomerate (reduced iron) reduced and discharged from the reduction furnace is once charged into a bucket in which air is shut off, and then charged into a converter or an electric furnace as an iron source to be melted. Also, the agglomerate (reduced iron) discharged from the reduction furnace can be hot-formed to obtain hot briquette reduced iron.

[0030]

Example 1 After mixing carbonaceous materials A to D and lignite shown in Table 1 with fine ore shown in Table 2 at a ratio of 22% of carbonaceous material and 78% of fine ore, the forming temperature was changed and the forming temperature was changed to 44 MPa. Approximately 3cm ^{3 in} pressure
Was formed into a briquette (agglomerate), and the change in apparent density was examined. The result is shown in FIG. Carbon materials A to Table 1
D is a caking coal having a volatile content of 16% or more. The maximum flow rate was measured based on JIS M8801.

[0031]

[Table 1]

[0032]

[Table 2]

As shown in FIG. 2, as the molding temperature increases, the apparent density increases, and after reaching the highest point,
Further, as the molding temperature increases, the apparent density sharply decreases. This is because the higher the molding temperature, the more gas is generated from the carbon material, and the briquette opposes this gas pressure, and the carbon material rapidly loses thermoplasticity due to thermal decomposition. In case of lignite, pyrolysis starts at 250 ℃
The apparent density began to increase by pressure molding from around 4
If the temperature exceeds 50 ° C., agglomerates having an apparent density of 2.3 g / cm ³ or more cannot be obtained, and in some cases, molding becomes impossible.

FIG. 3 shows the relationship between the moldable temperature range, the optimum molding temperature and the volatile matter of the carbonaceous material. The optimum molding temperature (the molding temperature at which the apparent density of briquettes is highest) varies in the range of 400 to 540 ° C in proportion to the volatile matter including lignite, and the molding temperature needs to be lowered as the volatile matter increases. In this case, the guideline is to lower the molding temperature by 4.6 ° C every time the volatile matter increases by 1%. Looking at caking coal with a volatile content of 16% or more, Fig. 4 shows the relationship between temperature and time at which the carbon material retains fluidity with the Giesler fluidity tester. When the carbon material temperature reaches 550 ° C, Both coal types have a fluidity retention time of 5 minutes or less. In addition, when the carbon material is charred, the caking property is lost at all and a molded product cannot be obtained. For this reason, if the fluidity retention time from heating to molding is short, the stability of molding is lacking, so that the molding temperature is desirably set to 550 ° C. or less in practical use.

In the case of non-caking coal having a volatile content of 16% or less and a carbon material which does not soften by heating, a high density briquette can be obtained by mixing with a thermoplastic carbon material and performing heat molding. FIG. 5 shows that the mixture of the carbonaceous material C and the coke breeze shown in Table 1 was mixed with the fine ore shown in Table 2 and the molding pressure was reduced.
It shows the relationship between the fluidity of the carbonaceous material mixture (weighted average of the maximum fluidity of the carbonaceous material) and the crushing strength of briquettes when molded at 44 MPa and a molding temperature of 450 ° C. As shown in FIG. 5, the handling of up While any apparent density indicates a value higher than 2.3 g / cm ^3, crush strength is strongly influenced by the fluidity of the carbonaceous material is charged into the rotary hearth furnace Taking into account the required strength of 10kg / P to withstand the flow rate of the carbonaceous material mixture is 20DDPM
(1.3logDDPM) or more is required.

Non-coking coal and brown coal having a volatile content of 35% or more cannot show thermoplasticity by the index used for caking coal. When brown coal or the like is molded at room temperature or at a relatively low temperature, the particles are unlikely to be plastically deformed, so even if molded at a considerably high pressure, springback occurs and briquettes may collapse. When this is molded at a temperature of 150 ° C. or more, briquettes can be obtained without causing springback. As shown in FIG. 2, the apparent density of the briquette increases with the temperature, and the apparent density increases at a molding temperature of 260 ° C. or more.
Briquettes of ³ g / cm ³ or more can be obtained. Also,
As shown in FIG. 6, the strength of briquettes molded at a pressure of 44 MPa increased in proportion to the molding temperature. At 150 ° C. or higher, the required crushing strength was 10 kg / P or more. FIG. 6 shows that the lignite shown in Table 1 and the fine ore shown in Table 2 were mixed at a ratio of 22% of brown coal and 78% of fine ore, and the molding temperature was changed to obtain a volume of about 3 cm ^{3 at} a pressure of 44 MPa. It shows the crushing strength of what was formed into briquettes.

[0037] Compared with caking coal, lignite is rich in low ash and sulfur content, so high-grade reduced iron can be obtained by using lignite as a carbon material. Incidentally, the properties of the reduced briquettes obtained by mixing 26% of the lignite shown in Table 1 and 74% of the fine ore shown in Table 2 and reducing the briquettes obtained by hot forming are shown in Table 3. As shown in Table 3, when lignite is used (B in the table), the metallization ratio is not different from that when coking coal is used (A in the table), but S is about 1 / 3 to improve the quality of reduced briquettes.

[0038]

[Table 3]

FIG. 7 shows the relationship between the molding pressure and the apparent density of briquettes when the type of coal is changed, and FIG. 8 shows the relationship between the molding pressure and the crushing strength of the briquettes when the type of coal is changed. FIG.
As shown in the figure, the apparent density of briquettes increases rapidly with the forming pressure up to 39MPa, and the apparent density differs slightly depending on the type of coal. However, the apparent density hardly changes at a forming pressure of 54MPa or more. When caking coal is used as the carbonaceous material, the apparent density is 2.7 g in consideration of economy and productivity.
In order to obtain briquettes of not less than / cm ³ , the molding pressure is suitably from 39 to 88 MPa. A molding pressure of 20 MPa is sufficient to obtain an apparent density of 2.3 g / cm ³ and a crushing strength of 10 kg / P or more without requiring a high apparent density (see FIG. 8). This result indicates that when only caking coal is used, a certain degree of strength can be ensured unless expansion is suppressed and excessive porousness is obtained as in the case of ordinary coking. On the other hand, when coke breeze showing no thermoplasticity is mixed with caking coal and used, it is necessary to increase the molding pressure because it is necessary to firmly couple caking coal with fine ore and coke fine particles. . For example, as shown in FIG. 8, when a carbon material (flow rate: 30 DDPM) obtained by mixing 60% of coke breeze and 40% of carbon material C shown in Table 1 was used, the molding pressure required 39 MPa.

The caking coal softens when heated and has the property of firmly connecting the fine ore particles. However, at this temperature, it still has a large amount of volatile matter, and when it is charged into the rotary hearth furnace at this temperature, it becomes hot. Generated gas increases the gas pressure inside the briquette due to the generated gas, which causes expansion or cracking and collapses, causing problems in the operation of the rotary hearth furnace, reducing powdered iron, reducing reduced apparent density Becomes iron. This phenomenon occurs because the generated gas is not easily released from the inside of the briquette to the outside while the carbon material retains thermoplasticity. When the caking coal is kept in the softening and melting temperature range, the carbonization proceeds slowly, and a part of the volatile components is gasified to lose the plasticity and the strength of the carbon material portion is increased. At this time, the volatile matter is 50
%, But as shown in Fig. 14 (c), pores are generated in the briquette due to degassing, and the volatile gas and the gas generated due to the reduction reaction remain in this state even when charged into a rotary hearth furnace. Since the briquettes are easily released from the inside to the outside from the pores, reduced iron having high density without swelling or cracking can be obtained. As shown in FIG. 4, the softening state holding time (fluidity holding time) becomes shorter as the temperature becomes higher, and is about 3 to 40 minutes in the range of 400 to 550 ° C. Therefore, it is necessary to perform the degassing process near the molding temperature for 5 minutes to 40 minutes.

[0041]

Example 2 Fine ore having the chemical composition shown in Table 2 and carbonaceous material having the chemical composition shown in Table 4 were mixed in a ratio of 78% finer ore and 22% carbonaceous material, and then heated to 450 ° C and heated to 39 MPa. Volume 2-5 cm by pressure
^It was hot-formed into briquettes (agglomerated products) of No. ³ . As a comparative example, fine ore 78 having the chemical composition shown in Tables 2 and 4 was used.
% And 22% of carbonaceous material, 1% of bentonite was added as a binder, and the mixture was formed into pellets having a volume of 2 cm ³ by a granulator. The apparent densities of the hot-formed briquettes of the present invention and the pellets (hereinafter referred to as pellets) of the comparative examples after drying were compared. FIG. 9 shows the result.

[0042]

[Table 4]

As shown in FIG. 9, the apparent density of the pellets is 2.0 g / cm ³ , and the apparent density of the hot-formed briquettes is 2.8 g / cm ³ , which is about 40% larger. I have. The reason for this is that, as described above, in the hot-formed briquettes, the carbon material softened and melted at 450 ° C penetrates between the ore particles by pressure molding and fills the voids.
14 (b)).

Further, the hot-formed briquette is
Degassing was performed at 450 ° C. for 30 minutes. By performing the degassing treatment, the volatile matter is released from the carbon material in the hot-formed briquette, and the weight is reduced by 2 to 3% (about 10 to 15% as the carbon material). However, the apparent density of the briquette is almost the same as the apparent density of the briquette before degassing, as described above. As a result, pores are generated in the carbonaceous material portion, and gas generated in the briquette at the time of reduction is easily released (see FIG. 14 (c)). Therefore, it is possible to prevent cracking due to blistering caused by gas generated in the briquette during the reduction process.

Next, hot-formed briquettes and pellets subjected to degassing with different apparent densities and volumes were examined for 13%.
A reduction test was performed in a reduction furnace maintained at 00 ° C. The result is shown in FIG. As is clear from the figure, at the same volume, as the apparent density of the agglomerate increases, the reduction time decreases. Therefore, productivity is improved by an increase in apparent density. The productivity when these are reduced in a rotary hearth furnace increases in proportion to the apparent density of agglomerates, as shown in FIG. According to FIG. 11, when the apparent density of the agglomerate increases by 0.1 g / cm ^3, the productivity in the rotary hearth furnace increases by 5.5 kg / m ² h. Therefore, the reason why the apparent density of the agglomerate is limited to 2.3 g / cm ³ or more in claim 1 is as follows. The vertical axis in FIG. 10 is the time (seconds) until the fine ore is reduced by 98%. In addition, the vertical axis in Fig. 11 is the hearth 1m ² , the amount of 98% reduced iron production per hour
(t).

FIG. 12 shows the relationship between the apparent density of agglomerates before reduction and the apparent density of reduced iron. As shown in the figure, the apparent density of reduced iron increases almost in proportion to the apparent density of agglomerates before reduction. Further, if the hot formed briquette is subjected to degassing at 500 ° C. for 30 minutes, the briquette does not swell during the reduction process, and the apparent density of the reduced iron increases. Thus, by performing degassing on the hot-formed briquettes, the apparent density of the reduced iron can be made 2 g / cm ³ or more. By making the apparent density of the reduced iron 2 g / cm ³ or more, as shown in FIG. 13, when dissolving the reduced iron in the next step, the apparent density of the reduced iron is smaller than the apparent density of the slag in the melting furnace. Get bigger,
Reduced iron quickly sinks into the slag and promotes dissolution,
The productivity during dissolution is improved.

FIG. 13 shows the results of dissolution tests of reduced iron having apparent densities of 1.6 g / cm ³ and 2.4 g / cm ^{3 in} a crucible. Normally, the density of the molten slag is about 2 g / cm ^{3. If} the apparent density of the reduced iron is lower than this, as shown in FIG. 13 (a), the reduced iron floats on the surface of the slag and dissolution is delayed. On the other hand, if the apparent density of the reduced iron is higher than the density of the molten slag, as shown in FIG. 13 (b), the reduced iron quickly sinks into the slag to promote dissolution. The results of the test, the dissolution rate of the reduced iron when the apparent density is 1.6 g / cm ³ at 0.5 kg / min, an apparent density of 2.4g
The dissolution rate of reduced iron at / cm ³ is 2 kg / min. Thus, by making the apparent density of the reduced iron larger than the apparent density of the slag in the melting furnace, the melting rate is improved four times. Therefore, the reason for limiting the apparent density of reduced iron to 2 g / cm ³ or more in claim 6 is here.

[0048]

As is apparent from the above description,
According to the present invention, it is possible to prevent cracking of agglomerates caused by volatiles of carbonaceous materials in the reduction process, shorten the reduction time of fine ore in the agglomerates, and further dissolve time of reduced iron after reduction. Can be obtained. Also, reoxidation of reduced iron in the reduction furnace can be prevented.

[Brief description of the drawings]

FIG. 1 is an example of a conceptual diagram of a process for producing reduced iron according to the present invention.

[Fig. 2] 22% of carbonaceous material shown in Table 1 and 78 of fine ore shown in Table 2
5 is a diagram showing the relationship between the molding temperature and the apparent density of the agglomerate when the agglomerate is formed by changing the forming temperature after mixing at a% ratio.

FIG. 3 is a diagram showing a relationship between a moldable temperature range, an optimal molding temperature, and a volatile content of a carbon material.

FIG. 4 is a diagram showing the relationship between temperature and time at which a carbonaceous material maintains fluidity in a ghee cellar fluidity test device.

FIG. 5 shows the flowability of the carbonaceous material mixture obtained by mixing a mixture of carbonaceous material C and coke breeze shown in Table 1 with a fine ore shown in Table 2 and molding at a molding pressure of 44 MPa and a molding temperature of 450 ° C. It is a figure which shows the relationship with the crushing strength of a briquette.

FIG. 6 shows lignite shown in Table 1 and fine ore shown in Table 2
% And fine ore at a rate of 78%, changing the molding temperature
FIG. 4 is a diagram showing the relationship between the molding temperature and the crushing strength of briquettes when molded at a pressure of 44 MPa.

FIG. 7 is a diagram showing the relationship between the molding pressure and the apparent density of briquettes when the type of coal is changed.

FIG. 8 is a diagram showing the relationship between the molding pressure and the crushing strength of briquettes when the type of coal is changed.

FIG. 9 is a diagram showing a comparative example of apparent densities of hot-formed briquettes of the present invention and dried green pellets of a comparative example.

FIG. 10 is a diagram showing the results of a reduction test performed in a reduction furnace maintained at 1300 ° C. on hot-formed briquettes and pellets that have been subjected to degassing with different apparent densities.

11 is a diagram showing productivity when the agglomerate shown in FIG. 10 is reduced in a rotary hearth furnace.

FIG. 12 is a graph showing the relationship between the apparent density of agglomerates before reduction and the apparent density of reduced iron.

FIG. 13 is a diagram showing the results of dissolution tests of reduced iron having apparent densities of 1.6 g / cm ³ and 2.4 g / cm ^{3 in} a crucible.

FIG. 14 is a schematic view of the internal structure of the agglomerate, where (a) is a conventional agglomerate, (b) is a hot-formed agglomerate of the present invention, and (c) is a hot-formed agglomerate of the present invention. It is a schematic diagram of the internal structure after the degassing process of the formation material.

Continued on the front page (72) Inventor Shoji Shirouchi 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Inside Kobe Steel Co., Ltd. Kakogawa Works (72) Inventor Kazuya Miyagawa 1 Kanazawacho Kakogawa City, Hyogo Prefecture Kobe Steel Co., Ltd. Inside the Kakogawa Works (72) Inventor Osamu Tsushita 4-3-1, Bingo-cho, Chuo-ku, Osaka-shi, Osaka Kobe Steel, Ltd.Osaka branch office

Claims (7)

[Claims] 1. An agglomerate for reduced iron comprising a mixture of fine ore and carbonaceous material and having an apparent density of 2.3 g / cm ³ or more. 2. The method is characterized in that fine ore and carbonaceous material are mixed, hot-formed at a molding pressure of 20 to 150 MPa in a temperature range of 260 to 550 ° C., and then degassed for 5 minutes or more in a forming temperature range. A method for producing an agglomerate for reduced iron having an apparent density of 2.3 g / cm ³ or more. 3. The method for producing an agglomerated product for reduced iron according to claim 2, wherein the carbonaceous material is a caking coal having a volatile content of 16% or more and a ghee cellar fluidity of 2DDPM or more. 4. A carbonaceous material in which a non-caking coal having a volatile content of 16% or less and / or a carbonaceous material which does not soften by heating is mixed with the caking coal to have a Gieseller fluidity of 20 DDPM or more. A method for producing an agglomerate for reduced iron according to claim 2. 5. The carbonaceous material is a non-coking coal having a volatile content of 35% or more or a volatile content of 40% or more, an ash content of 5% or less, and a sulfur content of 0.3% or less.
The method for producing an agglomerate for reduced iron according to claim 2, which is lignite of not more than 10%. 6. The agglomerate for reduced iron according to claim 1, wherein the apparent density of the reduced iron after reduction is 2 g / cm ³ or more. 7. The gas generated in the heating and mixing step, the pressure forming step and the degassing step of the raw material of the agglomerate is recovered, and the recovered gas is blown into the last stage of the reduction furnace to prevent reoxidation of the reduced iron. A method for producing reduced iron.