JP5218196B2 - Method for reducing iron oxide-containing substances - Google Patents

Description

  The present invention relates to a method for reducing an iron oxide-containing substance containing iron oxide in a hematite state such as iron ore, dust, sludge, etc. to metallic iron so that it can be used as an iron source in an ironworks or the like.

  In recent years, various attempts have been made to apply a heating phenomenon (ie, microwave oven technology) by irradiating microwaves, which are a kind of electromagnetic waves, to various industrial processes. Compared with the conventional heating process, microwave heating can (1) quickly heat the substance itself that absorbs microwaves from the inside, and (2) select only the substance that absorbs microwaves. Because it has various features such as (3) non-thermal effects that can not be generated by heating with a normal electric furnace, etc. In recent years, not only in the drying field that has been studied, but in recent years, by applying microwave heating to the reduction reaction of various metal oxides including iron ore, let us establish a more efficient reduction process than before. There is a great deal of consideration.

  Patent Document 1 proposes a method for producing iron powder by reducing iron oxide by blending a powdery iron oxide raw material with a carbonizing agent and a carbonate as a reducing agent and irradiating with microwaves. Yes. Further, Patent Document 2 proposes a method for producing a metal by irradiating a container filled with a metal-containing material and a reducing agent with microwaves and additionally applying energy such as an electric arc.

JP-A-6-279824 JP-T-2004-526864

Saji et al. Saburo Izumi, Mitsuhiro Izumi, Junji Morimoto, Yukio Makino, Masashi Miyake “Powder and Powder Metallurgy”, Powder Powder Metallurgy Association, 2007, Vol. 54, no. 8, p585

When heating by microwaves is performed, the material to be heated (the material itself is heated from the inside) must be a material that absorbs microwaves. There are forms of iron oxide such as hematite (ferric oxide / Fe ₂ O ₃ ), magnetite (triiron tetroxide / Fe ₃ O ₄ ), and wustite (ferrous oxide / FeO). In general, it is known that it is difficult to perform heating by microwaves alone because of poor wave absorption. Therefore, in the case of iron ore, which is the main raw material in the iron and steel industry, heating with microwaves can be carried out without any problem if it is a magnetite mainly composed of magnetite. As for hematite mainly composed of hematite, or limonite composed mainly of trivalent iron-based iron hydroxide (goethite / Fe ₂ O ₃ .3H ₂ O) similar to hematite. Then, heating by microwaves cannot be performed effectively. In addition, by-products generated in steelworks (blast furnace dust, converter dust, neutralized sludge, etc.) are often reused as raw materials for iron making, but since these main components are also hematite or goethite, these are also used. Even the by-products of these products cannot be heated effectively by microwave alone.

  Therefore, in Patent Document 1 and Patent Document 2, it is stated that when hematite is used as a raw material, it is necessary to separately mix a substance having high microwave absorption (such as carbon or magnetite). In any case, it is necessary to add carbon as a reducing agent in order to reduce iron oxide. However, according to Patent Document 1, in order to perform microwave heating of hematite satisfactorily, In addition, it is stated that it is necessary to add more than twice as much extra carbon to the equivalent amount required for the reduction of iron oxide, and there has been a problem from the viewpoint of wasting costs related to the reducing agent. In addition, since excess carbon that does not contribute to the reduction reaction is heated to a temperature equal to or higher than that of iron oxide, it is necessary to increase the microwave output accordingly, and as a result, it is necessary to generate microwaves. There was also a problem of consuming large amounts of power.

  Further, it is known that even if a substance has poor microwave absorbability at room temperature, there is a substance that improves microwave absorbability as the temperature rises, and some documents (for example, non-patent documents) In 1), it is stated that hematite is also a substance having such a large temperature dependence. Therefore, Patent Document 2 proposes a method in which a heated material is preheated to a critical temperature at which microwave absorption is improved by a method such as electric furnace heating, and then heating by microwaves and metal reduction are performed. However, this method requires a separate preheating reactor that does not contribute to the reduction reaction in addition to the microwave heating reactor necessary for metal reduction, which increases both the equipment cost and energy consumption. There was a problem that.

  An object of the present invention is to reduce an iron oxide-containing substance mainly composed of hematite such as iron ore to a metallic iron level more efficiently than before, and use it as a raw material in an ironworks or the like.

In order to achieve the above object, the gist of the present invention is as follows.
(1) An iron oxide-containing substance containing at least one of hematite or goethite is reduced using a by-product gas generated from a steel mill as a reducing gas , and part or all of the hematite or goethite is reduced. As a reducing substance converted into magnetite, a reducing agent containing carbon is mixed with the reducing substance, the resulting mixture is heated by irradiation with microwaves, and iron oxide in the reducing substance contained in the mixture is changed. A method for reducing an iron oxide-containing substance, characterized in that the iron oxide-containing substance is further reduced to at least part of metallic iron.
( 2 ) The method for reducing an iron oxide-containing substance according to ( 1 ), wherein blast furnace gas (BFG) generated from a steel mill is used as the reducing gas.
( 3 ) The method for reducing an iron oxide-containing substance according to (1) or (2 ), wherein a fluidized bed is used as a reactor for carrying out the gas reduction.
( 4 ) The method for reducing an iron oxide-containing substance according to any one of (1) to ( 3 ), wherein neutralized sludge generated from an iron mill is used as the iron oxide-containing substance.

  It becomes possible to efficiently reduce an iron oxide-containing substance containing at least one of hematite such as iron ore and goethite to a metallic iron level and use it as a raw material in an ironworks or the like.

It is a flow sheet concerning the present invention. It is a flow sheet in the example of the present invention. It is a flow sheet in the example of the present invention. It is a flow sheet in a comparative example. It is a flow sheet in a comparative example.

Hereinafter, the present invention will be described in detail.
FIG. 1 is a flow sheet showing an embodiment of the present invention.
An iron oxide-containing substance whose main component is at least one of hematite (Fe ₂ O ₃ ) and goethite (Fe ₂ O ₃ .H ₂ O) (hereinafter also referred to as “hematite”) as a raw material for iron making 1 is initially charged into the gas reduction reactor 2. In the gas reduction reactor 2, the iron oxide-containing substance 1 and the high-temperature reducing gas 3 react to reduce part or all of the hematite to the magnetite (Fe ₃ O ₄ ) level.

When hematite is reduced by gas, the level of magnetite, wustite (FeO), or metallic iron (Fe) is reduced depending on the reduction temperature and the reducing gas (CO, H ₂ etc.) contained in the reducing gas. It is determined in equilibrium by the ratio. For example, when the reducing gas is a CO—CO ₂ mixed gas and the reduction temperature is 900 ° C., the reduction from hematite to magnetite proceeds easily if there is very little CO gas, but the reduction from magnetite to wustite. Does not proceed unless a reducing gas containing about 20% or more of CO (a ratio of CO / (CO + CO ₂ ), ie, CO ₂ of 80% or less) is used, and the reduction from wustite to metallic iron is CO 2. Will not proceed unless a gas containing about 70% or more is used.

A technology for producing a gas containing a reducing gas such as CO and H _{2 at} a high concentration from natural gas, petroleum, coal, etc. using means such as steam reforming, partial oxidation, etc. has been established. In the present invention, it is not preferable to newly establish such a gas production facility because it causes extreme enlargement of facility cost and running cost, and it is desirable to effectively use the by-product gas normally generated in the ironworks as a reducing gas. . As ironworks byproduct gas, there are coke oven gas (COG) generated from a coke oven, converter gas (LDG) generated from a converter, and blast furnace gas (BFG) generated from a blast furnace. Table 1 shows an example of the composition of each gas and the degree of gas oxidation (OD) defined by the following equation (1).
OD [%] = (H ₂ O [volume%] + CO ₂ [volume%]) / (H ₂ [volume%] + H ₂ O [volume%]
+ CO [volume%] + CO ₂ [volume%]) × 100 (1)

Since any gas contains a reducing gas (CO, H ₂ ), it can be used as the reducing gas of the present invention. However, in the gas reduction reactor of the present invention, hematite may be reduced to about magnetite, so it contains a reducing gas at a high concentration (that is, OD is low). It is not necessary to use high-priority COG and LDG that are used in all quantities as heating furnaces, power plant boilers, etc., and reduce BFG, which is treated as low-grade gas at present with high OD and is not effectively used. It is preferable to use it as a gas.

  That is, the BFG 4 is heated by burning (partially oxidizing) a part of combustible components contained therein by the air 6 in the partial oxidizer 5 installed in front of the gas reduction reactor 2, and the high-temperature reducing gas. 3 is introduced into the gas reduction reactor 2, and the hematite in the iron oxide-containing material 1 is rapidly reduced to the extent of magnetite. The percentage of hematite contained is reduced to magnetite depending on the reaction temperature and reaction time, that is, the specifications of the gas reduction reactor 2, but it is not necessary to reduce all of the hematite to magnetite. If it can reduce, it will not become a problem in the microwave heating reactor 10 of the latter stage.

  Further, the partial oxidizing gas of BFG4 used as the reducing gas 3 here cannot reduce hematite to metallic iron, but it can sufficiently reduce to the wustite level, so that part of the hematite is wustite. Even if it is reduced to the above, there is no problem in the microwave heating reactor 10 at the subsequent stage.

  Specifically, hematite may be reduced until the reduction rate becomes 5% or more. Here, the reduction rate is an index indicating how much oxygen is actually removed with respect to the theoretical oxygen amount removed when hematite is reduced to metallic iron. When all are hematite, the reduction rate is 0%, when all are magnetite, the reduction rate is 11.1%, when all are wustite (FeO), the reduction rate is 33.3%, and when all are metallic iron, it is reduced. Rate = 100%. (In other words, a reduction rate of 11.1% means that all hematite has been reduced to magnetite, and a reduction rate of 5% means that hematite and magnetite are mixed (assuming that no reduction after wustite occurs). Is the state). The reduction rate of 5% is a state in which 45% by mass of iron molecules (total Fe) is mixed as magnetite and 55% by mass as hematite, and more magnetite is contained in hematite. It is desirable. In addition, although wustite is inferior to magnetite, it has better microwave absorbability than hematite. Therefore, even if the total amount of hematite in iron oxide-containing substance 1 is reduced to wustite, in the subsequent microwave reduction reactor 10 It doesn't matter.

  As the iron oxide-containing substance 1 mainly composed of hematite used here, any of the above-mentioned iron ore (hematite, limonite), ironworks by-products (dust, sludge), etc. may be used. In order to perform good heating in the heating reactor 10, powder is desirable. This is because, for particles with a large particle size, even if it is a substance that absorbs a large amount of microwaves, microwaves can penetrate only near the particle surface and sufficiently heat the inside of the particles. This is because there is a possibility that cannot be done. Therefore, it is desirable to use a fine ore having a particle size of 10 mm or less as the iron ore used here. In addition, regarding the ironworks by-product, since it is already a fine powder having an average of about 20 to 100 μm at the time of occurrence, there is no particular limitation on the particle size.

  In the gas reduction reactor 2, it is possible to remove adhering water and crystal water associated with the iron oxide-containing substance 1 prior to the reduction reaction. Therefore, the iron ore used here is a pisolite ore or maramamba ore, which contains a large amount of water of crystallization, is difficult to use directly in existing sinter production facilities, and has a large proportion of fine powder in the particle size distribution. It is preferable to use (lobe river ore, Yandi kugina ore, etc.). In addition, there are many steelworks by-products that contain a large amount of adhering water or crystallization water, such as dust recovered in wet dust collection facilities or neutralized sludge recovered from acidic wastewater treatment processes. There is no particular problem in using the iron oxide-containing substance 1 in the invention. Of course, a dryer for removing adhering water may be installed before the gas reduction reactor, and the iron oxide-containing substance 1 after removing adhering water may be charged into the gas reduction reactor 2.

As a method of the gas reduction reactor 2, various types such as a shaft furnace type and a packed bed type can be used. As described above, it is preferable to use the powdered iron oxide-containing substance 1 in the present invention. Therefore, it is desirable to use a fluidized bed type reactor. There are various types of fluidized beds, but especially when using fine ore as the iron oxide-containing substance 1, the particle size distribution has a wide particle size distribution from 100 μm or less to about 20 mm. Therefore, it is desirable to use a circulating fluidized bed type reactor.
The use of a packed bed type reactor as the gas reduction reactor 2 is that when the reducing gas 3 is introduced, the pressure loss in the gas reducing reactor becomes too large, so that only a small amount of the reducing gas 3 can be introduced. When an attempt is made to increase the input amount by increasing the input pressure, there is a high possibility that the iron oxide-containing substance 1 cannot be satisfactorily reduced due to the occurrence of a bypass, and furthermore, fine ore with a particularly fine particle diameter is generated from the inside of the gas reduction reactor. Since there is a possibility of scattering, a fluidized bed type reactor is preferable from this point.

  The reaction temperature in the gas reduction reactor 2 may be 600 ° C. or higher at which a reaction rate (reduction reaction from hematite to magnetite) with no practical problem is obtained. If the reaction temperature is made as high as possible, the reaction rate increases, and there is an advantage that the gas reduction reactor can be made compact. 2 may cause sticking (a phenomenon in which particles adhere to and grow in the facility) and hinder a smooth operation, so the reaction temperature is desirably 900 to 1000 ° C.

  The partially reduced iron-containing material (reduced material at least partially converted to magnetite) 7 discharged from the gas reduction reactor 2 is necessary for causing the reduction reaction to the metallic iron raw material 12 in the microwave heating reactor 10. The reducing agent 9 is mixed with an appropriate means such as a mixer.

  As the reducing agent 9 used here, as long as the powder contains carbon, coal (pulverized coal), coal char, powdered coke, graphite powder, activated sludge, activated sludge dry distillate, wood powder, wood dry distillate ( Charcoal powder) and various dusts may be used. Further, the reducing agent may be added directly to the iron oxide-containing substance 1 before the gas reduction reactor 2 is charged. In particular, high water content by-products generated from each process as a reducing agent (sewage sludge generated from sewage treatment plants, activated sludge generated from biological wastewater treatment facilities such as ammonia effluent (safe water) at steelworks) When we want to make effective use of wet dust generated from steelworks, etc., dry these high water content by-products in the gas reduction reactor 2 and mix the partially reduced iron-containing substance 7 and the reducing agent sufficiently. It is desirable to add the reducing agent directly to the gas reduction reactor 2 because it can be done.

  As described so far, the partially reduced iron-containing substance 7 contains magnetite, and itself absorbs microwaves well and is heated. Therefore, the reducing agent (carbon) has a function as a so-called temperature increase accelerator. It is not necessary to have it. Therefore, the reducing agent is less than 2.0 of the theoretical equivalent required to reduce the oxide contained in the iron oxide-containing substance (including metal components other than iron when they are reduced). However, if the addition is about 1.0 to 1.5 times, the reduction reaction proceeds sufficiently, so that it is not necessary to add it excessively more than the theoretical equivalent. However, when it is desired to further increase the rate of temperature rise in the microwave heating reactor to shorten the processing time, a reducing agent may be added 2.0 times or more of the theoretical equivalent. The theoretical equivalent described here is a stoichiometric amount according to the reaction formula of oxygen + carbon = CO2 in the metal oxide. Further, the oxygen content ratio in the partially reduced iron-containing material is determined by an iron form analysis method such as a fluorescent X-ray analysis method or a volumetric method (JISM8213).

  In this way, the partially reduced iron-containing material 7 sufficiently mixed with the reducing agent is introduced into the microwave heating reactor 10. In the microwave heating reactor 10, the partially-reduced iron-containing material 7 charged by irradiating the microwave generated from the microwave oscillator 11 is heated.

  At this time, the atmosphere inside the microwave heating reactor 10 may be in any state, but in order to favorably reduce the oxide, the inside of the microwave heating reactor 10 is an oxygen-free atmosphere (nitrogen, argon, etc.). (Inert gas atmosphere). However, the partially reduced iron-containing material 7 mixed with the reducing agent is molded (granulated) into a pellet and then charged into the microwave heating reactor 10 to minimize the contact area between the atmospheric gas and the partially reduced iron-containing material 7. (The state where only the pellet surface is in contact with the atmosphere gas and the inside of the pellet is not in contact with the atmosphere gas) Even if the atmosphere gas is the atmosphere (air) containing oxygen, the partially reduced iron-containing substance 7 The reduction rate of can be sufficiently increased. Moreover, when the inside of a pellet becomes the sintering temperature (1100 ° C. to 1200 ° C.) or higher when microwave heating is performed, the inside of the pellet is melted and sintered, and the strength of the pellet itself is higher than that before microwave irradiation. Since it becomes possible to raise, there also exists a merit that handling after that will become favorable.

  Partially reduced iron-containing substance 7 is a metal that is efficiently reduced in a short time by heating iron oxide (magnetite, wustite) itself, which is a substance to be reduced, in the microwave heating reactor 10 (a phenomenon peculiar to microwave heating). The iron raw material 12 is reduced. In addition, metal oxides (Ni, Cr, etc.) other than iron may be contained in the oxide-containing substance 1 (especially when ironworks by-products are used as raw materials), but Ni is easier to reduce than iron. Of course, a part of Cr is also reduced.

  The frequencies of microwaves that are allowed to be used industrially in Japan are 0.915 GHz and 2.450 GHz, and it is better to use a long-wavelength 0.915 GHz microwave for heated objects of large lumps. Although there is a report that it is good, in the present invention, a microwave oscillator that emits either frequency may be used. Also, an oscillator that emits microwaves (millimeter wave, submillimeter wave) in the shorter wavelength range (10 to 300 GHz), which has recently been attracting attention (for example, a gyrotron that has been studied as a heating device for nuclear fusion) May be used.

  The heating temperature in the microwave heating reactor 10 varies depending on the degree of metallization in the metallic iron raw material 12, but is preferably 800 to 1600 ° C. A temperature lower than 800 ° C. is not preferable because even Fe reduction does not occur sufficiently, and conversely, even if the temperature is higher than 1600 ° C., the energy consumption in the microwave oscillator 11 only increases, and the merit is justified. Is not preferred because it cannot be obtained. Further, when the metallic iron raw material 12 is not melted, it is desirable that the temperature is 1100 ° C. or lower. The heating temperature is adjusted so as to reach the target temperature by controlling the microwave output (PID control, on / off control, etc.).

  The metal iron raw material 12 generated in this way is used as a reduced iron source in a steelmaking process such as a blast furnace, converter, electric furnace or the like. Further, since the exhaust gas 8 discharged from the gas reduction reactor still has a reducing gas component, it can be used as a fuel gas in a separate process or an accompanying waste heat recovery boiler.

Example 1
According to the flow shown in FIG.
As the iron oxide-containing substance mainly composed of hematite, lobe river powder ore 13 which is a kind of limonite (pisolite ore) was used. In addition, the adhesion water of the lobe river powder ore 13 was 4 mass%, the crystallization water was 8 mass% (adhesion water removal base), and the average particle diameter was 900 micrometers.

Robliber powder ore 13 (1 t) was treated in a circulating fluidized bed type gas reduction reactor 2. As the reducing gas 3, room temperature (25 ° C.) of BFG4 (blast furnace gas) in the partial oxidation unit 5 to 1000 Nm ^3, the air is preheated to 600 ° C. by the exhaust gas 8 and the heat exchanger in the air preheater 14 6 (350 Nm ³ ) Reducing gas 3 (1280 Nm ³ ) at 1000 ° C. produced by reacting with ³ ) was used. Table 2 shows each gas property.

  From the gas reduction reactor 2, a partially reduced iron-containing substance 7 having a reduction rate of iron of 10% (90% by mass of iron molecules (total Fe) mixed as magnetite and 10% by mass as hematite) is obtained. 850 kg was recovered. The average particle residence time in the gas reduction reactor 2 was 15 minutes.

  This partially reduced iron-containing substance 7 is mixed in a mixer 15 with a powder coke 16 having a particle size of 3 mm or less (120 kg, corresponding to 1.2 times the amount of carbon required for the equivalent of iron reduction) as a reducing agent. After that, it was introduced into the microwave reduction reactor 2 and irradiated with microwaves having a frequency of 2.450 GHz from a microwave oscillator 11 in a nitrogen atmosphere. The temperature was rapidly raised to 1300 ° C. in 10 minutes, and the temperature was kept as it was. Reduction to metallic iron was performed by heating for 1 hour. The temperature was measured using a thermocouple in a state where the powder sample and the thermocouple temperature measuring unit were in sufficient contact.

  After microwave heating, 660 kg of metal iron raw material 12 having an iron reduction rate of 95% (metalization rate of 95%) was produced. This metallic iron raw material 12 was utilized as an iron-making raw material by putting it into a converter in the steelworks.

(Example 2)
According to the flow shown in FIG.
As the iron oxide-containing substance mainly composed of hematite, neutralized sludge 17 generated from an acidic wastewater treatment process (neutralization treatment facility using alkali) at an ironworks was used. Table 3 shows the analysis values of the neutralized sludge 17 that was the subject of the present invention. The neutralized sludge 17 has properties after being processed by a dehydrator (filter press). Moreover, the unit [mass% -dry] in the table indicates the mass ratio of each component based on the weight excluding adhering moisture (including crystal water) (hereinafter the same). Furthermore, the average particle diameter of the neutralized sludge 17 was 30 μm.

  The neutralized sludge 17 (1 t) was treated by the dryer 18 to remove the adhering water, and then the dried neutralized sludge 19 was treated in the bubbling fluidized bed type gas reduction reactor 2. Also, blast furnace dust 20 (110 kg, corresponding to 1.3 times the amount of carbon necessary for iron reduction) as a reducing agent was charged into the gas reduction reactor 2 together with the dry neutralized sludge 19. Table 4 shows analysis values of the blast furnace dust 20. The average particle size of the blast furnace dust 20 was 25 μm.

As the reducing gas 3, a normal temperature (25 ° C.) of BFG4 (blast furnace gas) 1000 Nm ³ air 6 heated to 600 ° C. by the exhaust gas heat exchanger in advance air preheater in the partial oxidation unit 5 (350 Nm ³⁾ 1000 ° C. reducing gas 3 (1280 Nm ³ ) produced by the reaction was used. Table 5 shows each gas property.

  From the gas reduction reactor 2, a partially reduced iron-containing substance 7 having an iron reduction rate of 11% (a state in which 99% by mass of iron molecules (total Fe) is mixed as magnetite and 1% by mass as hematite) is obtained. 340 kg was recovered. The average particle residence time in the gas reduction reactor 2 was 15 minutes.

  This partially reduced iron-containing substance 7 is introduced into a microwave reduction reactor 10 and irradiated with microwaves having a frequency of 2.450 GHz from a microwave oscillator 11 in a nitrogen atmosphere. The temperature rapidly rises to 1300 ° C. in 10 minutes. The reduction to metallic iron was performed by heating at the same temperature for 1 hour. The temperature was measured using a thermocouple in a state where the powder sample and the thermocouple temperature measuring unit were in sufficient contact.

  After microwave heating, 240 kg of metallic iron raw material 12 having an iron reduction rate of 98% (metalization rate of 97%) was produced. The chlorine content contained in the neutralized sludge 17 was removed in a series of reduction steps, and was not contained in the metallic iron raw material 12. The nickel oxide contained in the neutralized sludge was also reduced and its metallization rate was 97%. This metallic iron raw material 12 was utilized as an iron-making raw material by putting it into a converter in the steelworks.

(Comparative Example 1)
The comparative example was implemented according to the flow shown in FIG.
As the iron oxide-containing substance mainly composed of hematite, lobe river powder ore 13 which is a kind of limonite (pisolite ore) was used. In addition, the adhesion water of the lobe river powder ore 13 was 4 mass%, the crystallization water was 8 mass% (adhesion water removal base), and the average particle diameter was 900 micrometers.

Robliber powder ore 13 (1 t) was treated in a circulating fluidized bed type gas reduction reactor 2. As the reducing gas 3, room temperature (25 ° C.) of BFG4 (blast furnace gas) in the partial oxidation unit 5 to 1000 Nm ^3, the air is preheated to 600 ° C. by the exhaust gas 8 and the heat exchanger in the air preheater 14 6 (350 Nm ³ ) Reducing gas 3 (1280 Nm ³ ) at 1000 ° C. produced by reacting with ³ ) was used. Table 6 shows each gas property.

  The average particle residence time in the gas reduction reactor 2 was 90 minutes, but the reduction rate of the recovered partially reduced iron-containing material 7 (840 kg) was only 15%.

(Comparative Example 2)
The comparative example was implemented according to the flow shown in FIG.
As the iron oxide-containing substance mainly composed of hematite, neutralized sludge 17 generated from an acidic wastewater treatment process (neutralization treatment facility using alkali) at an ironworks was used. Table 7 shows the analytical values of the neutralized sludge 17 that was the subject of this comparative example. The neutralized sludge 17 has properties after being processed by a dehydrator (filter press). Moreover, the unit [mass% -dry] in the table indicates the mass ratio of each component based on the weight excluding adhering moisture (including crystal water) (hereinafter the same). Furthermore, the average particle diameter of the neutralized sludge 17 was 30 μm.

  After the neutralized sludge 17 (1 t) is treated by the dryer 18 to remove the adhering water, the dried neutralized sludge 19 is converted into a blast furnace dust 20 (110 kg, equivalent to an amount necessary for iron reduction) generated from a blast furnace as a reducing agent. The mixture was mixed with the mixer 15 and then directly introduced into the microwave reduction reactor 10. Table 8 shows analysis values of the blast furnace dust 20. The average particle size of the blast furnace dust 20 was 25 μm.

  In the microwave reduction reactor 10, microwaves having a frequency of 2.450 GHz were irradiated from the microwave oscillator 11 in a nitrogen atmosphere, but it took 1.5 hours for the temperature to rise to 1300 ° C. Thereafter, the hematite contained in the sludge was reduced to metallic iron by heating at the same temperature for 1 hour. The temperature was measured using a thermocouple in a state where the powder sample and the thermocouple temperature measuring unit were in sufficient contact.

  After microwave heating, 240 kg of metallic iron raw material 12 with an iron reduction rate of 98% was produced. Further, the chlorine content contained in the neutralized sludge 17 was removed in the microwave reduction process, and was not contained in the metallic iron raw material 12. However, the processing time was significantly increased (microwave reduction 150 minutes) compared to the example (gas reduction 15 minutes + microwave reduction 70 minutes = total 85 minutes), and the power consumption was also increased accordingly.

1 Iron oxide-containing material 2 Gas reduction reactor 3 Reducing gas 4 BFG
5 Partial Oxidizer 6 Air 7 Partially Reduced Iron Containing Substance 8 Exhaust Gas 9 Reducing Agent 10 Microwave Heating Reactor 11 Microwave Oscillator 12 Metallic Iron Raw Material 13 Robliber Powder Ore 14 Air Preheater 15 Mixer 16 Powder Coke 17 Neutralized Sludge 18 Dryer 19 Dry neutralized sludge 20 Blast furnace dust

Claims (4)

An iron oxide-containing substance containing at least one of hematite or goethite is reduced using a by-product gas generated from a steel mill as a reducing gas , and part or all of the hematite or goethite is converted into magnetite. The converted reducing substance is mixed with a reducing agent containing carbon in the reducing substance, and the resulting mixture is heated by irradiating microwaves to further reduce iron oxide in the reducing substance contained in the mixture. A method of reducing an iron oxide-containing substance, characterized in that at least a part is metallic iron. 2. The method for reducing an iron oxide-containing substance according to claim 1, wherein blast furnace gas (BFG) generated from an ironworks is used as the reducing gas. The method for reducing an iron oxide-containing substance according to claim 1 or 2 , wherein a fluidized bed is used as a reactor for carrying out the gas reduction. The method for reducing an iron oxide-containing material according to any one of claims 1 to 3 , wherein neutralized sludge generated from an iron mill is used as the iron oxide-containing material.

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