JP2013216943A - Method of producing reduced iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing reduced iron by which a briquette can be efficiently irradiated with a microwave and metallization with the irradiation of the microwave can be further promoted.SOLUTION: There is provided a method of producing reduced iron in which a burner arranged in a solid reducing furnace and radiant heat from a furnace wall of the solid reducing furnace are used as heat sources, and the reduced iron is produced by heating a briquette formed by mixing iron ore raw material and reducing material. In the method, a microwave with which the briquette is irradiated is further used as the heating sources, and the briquette is irradiated with the microwave in the solid reducing furnace when the internal temperature of the briquette is at least in the temperature range of 600-1,150°C.

Description

  The present invention relates to a method for producing reduced iron.

  As the production of steel materials by electric furnaces becomes popular, the demand for scrap, which is the main raw material, is tightened, and the demand for reduced iron is increasing due to the demand for high-grade steel production in electric furnaces.

  As one of the processes for producing reduced iron, powdered iron ore and powdered coal or coke are mixed into agglomerates such as pellets and briquettes. Is charged into a rotary hearth furnace and heated to a high temperature to reduce iron oxide in iron ore to obtain solid metallic iron (see, for example, Patent Documents 1 to 4 below). .

  In the above-described method, a burner is generally used for heating the rotary hearth, and the agglomerated material that is a raw material of reduced iron is heated by radiant heat from the burner and the furnace wall of the rotary hearth furnace. Heating by radiation is heating by light with a short wavelength near the infrared, and the very surface layer of the briquette is heated, and the heat is transferred to the inside so that the inside of the briquette is heated. Heating. Therefore, in the part where the raw material overlaps on the hearth, the heating on the back side is insufficient, resulting in nonuniform reduction of the entire agglomerated material, and the average reduction rate is reduced.

  Here, the heat necessary for the reduction reaction of the raw material composed of iron oxide and carbonaceous material is first supplied to the upper surface of the raw material layer by radiant heating by burner combustion in the space located in the upper part of the hearth, It will be supplied to the lower part of the raw material layer by conduction heat transfer in the raw material layer. Therefore, if the thickness of the raw material layer is increased in order to increase productivity, the heat transfer to the lower part of the raw material layer is delayed, the reduction rate of the lower part of the layer is reduced, and the residence time is increased, Productivity is reduced.

  In recent years, a technique has also been proposed in which the agglomerated material is heated not by a burner but by microwave irradiation (see Patent Document 5 below).

JP 11-248359 A JP-A-11-310832 JP 2004-315852 A JP 2011-112340 A JP 2008-214715 A

Yoichi Murase, Hiroshi Takashima, Hideki Nakano, Koji Koshiji, Hideaki Zhou, Tetsuo Kubota, "Electromagnetic Field Distribution in Microwave Cavity", IEICE Technical Report, The Institute of Electronics, Information and Communication Engineers, February 1996, MW 95-201 Pp. 67-72

  However, in the method described in Patent Document 5, as described in the document, the amount of microwave power to be irradiated needs to be 100 to 200 kWh per ton of agglomerates. However, the output of the microwave oscillation device is generally an upper limit for industrial use of about 100 kW / unit, and the microwave alone is a mass that requires a large amount of production of several tens of tons per day. It is extremely difficult to heat and reduce the compound.

  Therefore, the present inventors conducted extensive studies on a method capable of suppressing the occurrence of reduction defects on the back side of the agglomerated material that does not directly reach the radiant heating while suppressing an increase in operating cost. And the microwave heating that can reach the inside of the object and heat the object directly from the inside.

  Here, by irradiating microwaves over the entire area of the solid reduction furnace, it is considered possible to suppress the occurrence of defective heating on the back side of the agglomerate, but on the other hand, to irradiate microwaves There is a concern about the increase in cost required. Therefore, when both heating by a burner and heating by microwaves are used in combination, microwaves are irradiated under conditions where the metallization promoting efficiency of the agglomerates by microwave irradiation is high while suppressing an increase in operating costs. I realized that it was important.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to allow the agglomerated material to efficiently absorb microwaves, and to metallize by microwave irradiation. It is an object of the present invention to provide a method for producing reduced iron, which can further promote the process.

  In order to solve the above-described problems, according to one aspect of the present invention, an iron oxide raw material and a reducing material are mixed using a radiant heat from a burner provided in a solid reduction furnace and a furnace wall of the solid reduction furnace as a heat source. In the method for producing reduced iron in which reduced agglomerate is produced by heating the agglomerated product formed in this way, microwaves applied to the agglomerate are further used as the heat source in the solid reduction furnace. In addition, there is provided a method for producing reduced iron that irradiates the agglomerate with the microwave when at least the internal temperature of the agglomerate is in a temperature range of 600 ° C. to 1150 ° C.

  At least when the internal temperature of the agglomerate is 900 ° C., the agglomerate may be irradiated with the microwave.

  In the solid reduction furnace, a microwave irradiation member for irradiating the microwave is installed on the entire region in which the internal temperature of the agglomerated material is in the temperature range so as to be a microwave irradiable region. The microwave may be irradiated to the chemical compound in at least a part of the microwave irradiable region.

  In the solid reduction furnace, a microwave irradiation member for irradiating the microwave to at least a part of the region where the internal temperature of the agglomerated material is in the temperature range is provided, and the microwave irradiation region The agglomerated material may be irradiated with the microwave in the microwave irradiation region.

  As described above, according to the present invention, the agglomerate is irradiated with microwaves at least when the internal temperature of the agglomerate is somewhere in the temperature range of 600 ° C. to 1150 ° C. It is possible to efficiently irradiate the compound with microwaves, to efficiently absorb the microwaves with respect to the agglomerated material, and to further promote metallization by microwave irradiation.

It is explanatory drawing shown about the flow of the manufacturing method of a general reduced iron. It is explanatory drawing for demonstrating the rotary hearth furnace which is an example of a solid reduction furnace. It is explanatory drawing which showed the structure of the microwave irradiation apparatus which can be utilized with the manufacturing method of the reduced iron which concerns on the 1st Embodiment of this invention. It is explanatory drawing shown about the heating apparatus used for examination of the irradiation timing of a microwave. It is explanatory drawing shown about the heating apparatus used for examination of the irradiation timing of a microwave. It is the graph which showed the relationship between the agglomerate temperature at the time of a microwave irradiation start, and a metallization rate. It is the graph which showed the differential scanning calorimetry result of the agglomerate.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(About manufacturing process of reduced iron)
Prior to describing a method for producing reduced iron according to an embodiment of the present invention, first, a general process for producing reduced iron will be described in detail with reference to FIG. FIG. 1 is an explanatory diagram for explaining a general manufacturing process of reduced iron.

  First, iron oxide raw materials such as iron dust (iron oxide powder), iron ore, and powder ore, and reducing materials such as coal, coke, and fine carbon are stored in the hopper 1 and the like in advance. The iron oxide raw material and the reducing material are blended so as to have a preset blending ratio and charged into the pulverizer 2.

  A crusher 2 typified by a vibration mill such as a ball mill crushes the charged iron oxide raw material and the reducing material to a predetermined particle size while mixing them. The particle diameters of the iron oxide raw material and the reducing material after pulverization can be set to values suitable for a solid reduction furnace such as a rotary hearth furnace, a fluidized bed furnace, and a shaft furnace used for producing reduced iron. The mixture of the pulverized iron oxide raw material and the reducing material is conveyed to the kneader 3.

  The kneader 3 kneads the mixture pulverized to a predetermined particle size by the pulverizer 2. Moreover, the kneading machine 3 may perform a humidity control process for adding water to the mixture until the water content is suitable for a solid reduction furnace used for producing reduced iron. As an example of the kneading machine 3, for example, a mix muller can be cited. The mixture kneaded by the kneader 3 is conveyed to the molding machine 4.

  A molding machine 4 such as a pan pelletizer (dish granulator), a double roll compressor (briquette making machine), an extrusion molding machine or the like molds a mixture containing an iron oxide raw material and a reducing material, and agglomerates such as pellets. It is a chemical. Here, the agglomerated material refers to pellets, briquettes, extruded products that have been cut by extrusion molding, and granular materials / agglomerated materials such as mass-adjusted agglomerated materials. When the molding machine 4 is dried and heat-reduced, which will be described later, for example, when charged into the melting furnace 7 in the hot state, the above mixture is adjusted so as to have a size larger than the particle size so as not to be scattered by the rising gas flow in the furnace. Agglomerates. The produced agglomerated material is charged into the drying furnace 5.

  The drying furnace 5 dries the agglomerated material and has a moisture content suitable for the heating and reducing process described later (in other words, a moisture content suitable for each solid reduction furnace used for producing reduced iron: for example, 1% And so on. The agglomerated product having a predetermined moisture content is conveyed to a solid reduction furnace 6 to be described later.

  For example, the solid reduction furnace 6 such as a rotary hearth furnace (RHF), a fluidized bed furnace, a shaft furnace, etc., heats the agglomerate charged in a heating atmosphere such as an LNG burner or a COG burner. Reduce to iron reduced. The solid reduction furnace heats the agglomerate to, for example, about 1000 to 1300 ° C. to reduce the agglomerate and produce reduced iron. The manufactured reduced iron is conveyed to the melting furnace 7. In the melting furnace 7, the reduced iron produced in the solid reduction furnace 6 is melted to produce hot metal. The produced hot metal is processed into various steel products through a desulfurization / decarburization process, a secondary refining process, a continuous casting process, a rolling process, and the like.

  In the following, a rotary hearth furnace will be described as an example of the solid reduction furnace. However, the solid reduction furnace used in the method for producing reduced iron according to the embodiment of the present invention is not limited to the rotary hearth furnace.

(About rotary hearth furnace)
Next, a rotary hearth furnace which is an example of a solid reduction furnace used in the method for producing reduced iron will be described in detail with reference to FIG. FIG. 2 is an explanatory diagram for explaining a rotary hearth furnace which is an example of a solid reduction furnace.

  The rotary hearth furnace 21 has, for example, a substantially cylindrical shape as shown in the upper part of FIG. 2. For example, agglomerated material is charged from an inlet provided on the upper surface of the rotary hearth furnace 21 or the like. The The agglomerated material charged is heated and reduced while moving along the circumferential direction in the furnace to be reduced iron and taken out from the furnace.

A schematic diagram when the rotary hearth furnace 21 is developed along the circumferential direction is shown in the lower part of FIG.
Inside the rotary hearth furnace 21, a rotary hearth 25 that can move in the rotary hearth furnace 21 along the circumferential direction is provided. The briquette B charged from the charging port 27 is developed on the rotary hearth 25. The briquette B is leveled by the hot leveler 29 and moves in the furnace as the rotary hearth 25 moves. The briquette B is heated by the radiant heat of the high-temperature combustion gas generated by the furnace wall or the burner 31 on the furnace in the course of movement, and the iron oxide raw material is reduced by the reducing material in the briquette B. Reduced iron, which is a reduced iron oxide raw material, is discharged from the rotary hearth furnace 21 by the discharger 33.

The briquette B moving in the rotary hearth furnace 21 rises in temperature from the outside to the inside of the briquette B due to the radiant heat of the high-temperature combustion gas, and the briquette reduction reaction proceeds from the outer periphery of the briquette toward the center. proceed. At this time, inside the briquette B, iron oxide components (FeO, Fe ₂ O _3, etc.) contained in the briquette are reduced by the reducing material (carbon C) contained in the briquette to become reduced iron (Fe). Go.

  Here, the interior of the rotary hearth furnace 21 is divided into a plurality of zones by walls protruding from the furnace ceiling, called partition walls (or sag walls) 35, as shown in the lower part of FIG. There are many. In the rotary hearth furnace 21, reduced iron is manufactured by controlling the amount of heat of the burner, the gas atmosphere, the air ratio, the amount of secondary air, and the like for each zone. The height of the partition wall 35 (height from the ceiling position of the rotary hearth furnace 21 to the lower end of the partition wall 35) is appropriately set according to the size of the rotary hearth furnace 21, etc. It is formed so as to protrude from the furnace ceiling up to about 2/3 of the height of the rotary hearth furnace 21. Therefore, the separation distance between the bottom surface of the partition wall 35 (the bottom surface facing the hearth) and the hearth is about ３ with respect to the height of the rotary hearth furnace 21.

  The first zone located in the vicinity of the briquette inlet 27 and the second zone adjacent to the first zone are mainly intended for raising the temperature of the briquette B charged in the rotary hearth furnace 21. It is a zone to do. Further, the third and subsequent zones following the second zone are zones whose main purpose is the reduction of briquette B. Here, the first zone and the second zone are collectively referred to as the initial stage of heating / reduction, and the third and subsequent zones are referred to as the reduction period.

  Due to the high-temperature combustion gas generated by the burner 31, the temperature of the agglomerated product in the initial stage of heating / reduction is raised to about 1200 ° C., and after the reduction period, it is maintained at about 1200 to 1300 ° C.

(Combined use of burner heating and microwave heating)
Therefore, the present inventors conducted extensive studies on a method capable of suppressing the occurrence of reduction defects on the back side of the agglomerated material that does not directly reach the radiant heating while suppressing an increase in operating cost. And the microwave heating that can reach the inside of the object and heat the object directly from the inside.

  As a result of diligent studies to use both heating by a burner and heating by a microwave, the main raw material of the agglomerate charged into the solid reduction furnace can efficiently absorb microwaves. It became clear that. Hereinafter, this point will be described in detail with reference to equations.

The microwave energy P _abs per unit volume absorbed by the substance is expressed as the following Expression 11. As can be seen by referring to Equation 11 below, the microwave energy P _abs per unit volume absorbed by the substance to be heated (substance to be heated) depends on the conductivity, dielectric constant and permeability of the substance to be heated. You can see that Therefore, it can be said that P _abs represented by the following formula 11 is an amount related to the microwave absorption efficiency of the heated material.

Here, in Equation 11 above,
σ: Conductivity of heated material [S / m]
f: Microwave frequency [Hz]
ε ₀ : dielectric constant in vacuum [F / m]
ε ″: Imaginary part of relative permittivity of heated material μ ₀ : Permeability in vacuum [H / m]
μ ”: Imaginary part of relative permeability of heated material E: Electric field strength formed by microwave [V / m]
H: intensity of magnetic field formed by microwave [A / m]
π: Pi ratio.

  The values of the imaginary part ε ″ of the relative dielectric constant are collectively shown below for the iron oxide and carbon material (reducing material) that are the raw materials of the agglomerated material and the refractory furnace materials that are generally used.

Imaginary part of dielectric constant ε ”
Alumina, which is a typical refractory furnace material: 0.004 to 0.01
・ Powdered carbon powder: 10-50
・ Iron oxide: 0.1-10

  As is clear from the above, the iron oxide and carbon material used as the raw material for the agglomerate have a large value of the imaginary part ε ″ of the relative dielectric constant relative to the refractory furnace material generally used in a drying furnace or the like, The oxide and carbon material (reducing material) can absorb more microwave energy, and the value of alumina, which is a typical refractory furnace material, compared to the values of iron oxide and carbon powder, The value is about 1/1000, and it can be seen that the refractory furnace material does not absorb much microwave energy, so when the microwave is irradiated in the furnace in which the agglomerates are inserted, There is little energy supply to the furnace wall etc. which are coat | covered with the furnace material, and it becomes possible to raise only the temperature of the agglomerate which is a raw material efficiently, suppressing the raise in furnace temperature.

(About the microwave used)
Then, the microwave used with the manufacturing method of reduced iron which concerns on embodiment of this invention is demonstrated easily.

  The microwave generally refers to an electromagnetic wave having a wavelength of 1 mm to 1 m and a frequency of 300 MHz to 300 GHz. However, as noted in the method for heating an agglomerate according to the present embodiment, when microwaves are used as heating means (so-called microwave heating is performed), microwaves are so-called ISM (Industry- Science-Medical) refers to an electromagnetic wave in a frequency band belonging to the band.

  In the embodiment of the present invention described below, there is no particular limitation as long as the electromagnetic wave has a frequency belonging to the IMS band. For example, a 2.45 GHz band (2.40 GHz to 2.50 GHz), a 5.8 GHz band (5. 725 GHz to 5.875 GHz) and frequencies belonging to the 24 GHz band (24.0 GHz to 24.25 GHz) can be selected as appropriate. However, since the penetration of the microwave into the heated object is proportional to the wavelength of the microwave, the penetration depth of the 2.45 GHz band becomes the largest in the microwave of the ISM band, and the inside of the briquette or You can reach the lower briquettes that overlap. In addition, 2.45 GHz is widely used for microwave ovens and other microwave heating, and the device is inexpensive. From the point that a single oscillator can emit a large output up to several tens of kW, The equipment cost of the present invention that requires a large output of the kW class can also be introduced at a lower cost than the other two frequency devices. For this reason, the ISM band microwave device used in the present invention is preferably capable of oscillating 2.45 GHz microwave.

(About the configuration of the microwave irradiation device)
Next, the configuration of a microwave irradiation apparatus that can be used in the method for producing reduced iron according to the embodiment of the present invention will be described in detail with reference to FIG. Drawing 3 is an explanatory view for explaining the composition of the microwave irradiation device which can be used with the manufacturing method of reduced iron concerning the embodiment of the present invention.

  The microwave irradiation apparatus 100 according to the embodiment of the present invention is a solid reduction for producing reduced iron by heating an agglomerate formed by mixing an iron oxide raw material and a reducing material with radiant heat from a burner and a furnace wall. It is used for the furnace.

  As shown in FIG. 3, the microwave irradiation apparatus 100 according to the embodiment of the present invention mainly includes a microwave oscillator 101, a circulator 103, an automatic matching unit 107, and a microwave irradiation member 109. These devices are connected by a waveguide 111. In FIG. 3, a support mechanism for supporting each member such as the microwave irradiation member 109 and the waveguide 111 is not shown.

  The microwave oscillator 101 is a device that oscillates a microwave having a frequency belonging to, for example, an ISM band. The microwave oscillator 101 is preferably a device capable of oscillating microwaves having a kW class output. For example, a microwave having a frequency belonging to a 2.45 GHz band is output to the circulator 103 described later by the microwave oscillator 101. As this microwave oscillator 101, a publicly known one can be appropriately selected and used.

  The circulator 103 performs a microwave progress control using, for example, a magnet, so that the microwave input to the circulator 103 is changed from the incident wave output from the microwave oscillator 101 to the automatic matching unit 107 described later. It separates into the reflected wave that has returned. The circulator 103 guides the separated incident microwave toward the automatic matching unit 107 described later, and guides the reflected microwave toward the isolator 105 side. Thereby, the reflected microwave can be absorbed by a dummy load (for example, water) provided in the isolator 105 and can be prevented from returning to the microwave oscillator 101 side. By providing such a circulator 103, the microwave irradiation apparatus 100 according to the embodiment of the present invention can output a stable microwave. As this circulator 103, a known circulator can be appropriately selected and used.

  The automatic matching unit 107 reduces the reflected wave from the load side by matching the impedance on the incident side with the impedance on the load side (that is, the raw material layer side made of agglomerated material), and the reflected wave is almost zero. It is a device. The automatic matching unit 107 measures the phase and intensity of the reflected electric field and automatically performs impedance matching, thereby realizing the reduction of the reflected wave as described above. By providing an automatic matching unit 107 and realizing automatic matching processing according to the impedance on the load side, the agglomerated material can be stably and efficiently irradiated with microwave energy from a microwave irradiation member 109 described later. It becomes possible.

  The microwave irradiation member 109 is a member that irradiates the agglomerate charged in the solid reduction furnace 6 with microwaves. An inert gas such as nitrogen or argon has a predetermined flow rate / flow velocity to the microwave irradiation member 109 so that dust or the like existing in the solid reduction furnace 6 does not flow backward from the tip of the microwave irradiation member 109. It may be supplied so that. In this case, the inert gas supplied into the microwave irradiation member 109 is preferably a heated gas in order to prevent a temperature drop inside the solid reduction furnace 6. The waveguide 111 connecting the microwave irradiation member 109 and the automatic aligner 107 is provided with dustproof glass so that dust or the like existing in the solid reduction furnace does not flow into the automatic aligner 107. As the microwave irradiating member 109, it is possible to use all known ones such as various antennas, waveguides, and coaxial cables.

  The waveguide 111 is a tube that guides a microwave to a desired location. The shape of the waveguide 111 may be appropriately determined in consideration of the waveguide characteristics of the microwave, etc., and the waveguide 111 itself also depends on the frequency and output intensity of the microwave to be used. A well-known thing can be selected suitably.

(First embodiment)
<About the manufacturing method of reduced iron>
As explained above, the iron oxide raw material and the reducing material contained in the agglomerate that is the raw material of reduced iron are substances that absorb microwaves well, and by combining heating with a burner and heating with microwaves, It is considered possible to heat the agglomerated material efficiently. Here, when considering the combined use of heating with a burner and heating with a microwave, it is possible to suppress the occurrence of defective heating on the back side of the agglomerate by irradiating microwaves throughout the solid reduction furnace. On the other hand, there is a concern about an increase in cost required for irradiation with microwaves.

  For this reason, if there is an appropriate timing for irradiating the agglomerate with microwaves, the present inventors will increase the operating cost by irradiating the agglomerates with microwaves at that timing. We thought that it would be possible to efficiently absorb microwaves to the agglomerated material while suppressing the above, and intensively studied as shown below.

[Examination of microwave irradiation timing]
Below, the examination result of the irradiation timing of the microwave with respect to an agglomerate is demonstrated in detail, referring FIG. 4A-FIG. FIG. 4A and FIG. 4B are explanatory diagrams showing a heating apparatus used for examining the irradiation timing of microwaves. FIG. 5 is a graph showing the relationship between the agglomerate temperature and the metallization rate at the start of microwave irradiation. FIG. 6 is a graph showing the results of differential scanning calorimetry of the agglomerated material.

  In order to examine the timing of microwave irradiation, the present inventors conducted various experiments shown below using a heating apparatus as shown in FIGS. 4A and 4B simulating an actual solid reduction furnace 6. did.

  As shown in FIGS. 4A and 4B, the heating apparatus used for the examination of the microwave irradiation timing is a combination of the electric furnace and the microwave irradiation apparatus shown in FIG. ), And a front chamber provided in the front stage of the heating chamber, and a rear chamber provided in the rear stage of the heating chamber and used as a cooling chamber. In the experiment shown below, each atmosphere in the front chamber, the heating chamber, and the rear chamber is maintained in a nitrogen atmosphere that is an inert gas, and microwaves are irradiated into the heating chamber from a microwave irradiation device installed above the heating chamber. I did it.

  A partition door made of a heat insulating material and a metal plate is installed between the front chamber and the heating chamber, and between the heating chamber and the rear chamber, so that the heat in the heating chamber and the microscopic radiation radiated into the heating chamber. Waves were prevented from entering the front and rear chambers.

  In addition, an exhaust pipe is provided in the heating chamber so that reaction gases such as fumes and CO gas generated by heating the agglomerated material are exhausted to the outside of the heating chamber.

  Here, the agglomerate raw material is placed on a tray formed of a refractory material that does not absorb microwaves, so that it can be moved from the front chamber to the heating chamber to the rear chamber without touching the outside air. It has become.

  In the following experiment, after using the agglomerated material used in the operation in the actual solid reduction furnace 6 and moving the agglomerated material to a heating chamber that has been in a high temperature state in advance, after the elapse of time t1 (min) And microwave irradiation for time t2 (min). Thereafter, after the elapse of time t3 (minutes), the agglomerated material was moved to the rear chamber and rapidly cooled in a nitrogen atmosphere to fix the reduced state.

  That is, in the following experiment, the agglomerated material is heated for a total heating time T = t1 + t2 + t3 (minutes), and microwaves are irradiated for t2 time. Below, it tested about the difference in the reduction | restoration promotion effect by microwave irradiation by changing time t1, t2, t3 suitably.

  In addition, after embedding a 1.6 type K type sheath thermocouple in the center of each agglomerated material, the material was heated, and the temperature near the center of the agglomerated material was measured as the internal temperature of the agglomerated material.

○ Manufacture of used agglomerates (briquette) In addition to 79% by mass of iron-making dust having the composition shown below and 20% by mass of coal as a reducing material, 1% by mass of bentonite is further mixed as a binder to provide an appropriate amount of moisture. The added mixture was produced. Thereafter, the mixture was kneaded and then charged into a briquette machine to produce a raw briquette having an average diameter of 50 mm and a thickness of 20 mm. The produced raw briquette was dried using a dryer to obtain a dry briquette having a moisture content of 0.5% by mass.

  The size of the raw briquette is a general size of agglomerated material used when producing reduced iron, and is within a range of an outer diameter of 10 mm to 60 mmφ × thickness of 10 mm to 30 mm. .

[Example 1]
Experimental conditions and obtained results Table 2 below also shows the conditions of the conducted experiments and the obtained results.
In this experiment, the agglomerated material (briquette) was placed in the heating chamber of the composite heating apparatus shown in FIG. 4A for a total of 20 minutes to heat and reduce the agglomerated material. During the course of 3 minutes, 500 W of 2.45 GHz microwave was irradiated from the microwave irradiation apparatus. The electric power of the electric furnace was automatically controlled so that the temperature was maintained at 1200 ° C. by the temperature control operation.

  The agglomerated material was kept in a heating furnace at a constant temperature for a certain time, and then rapidly cooled in a nitrogen atmosphere in the rear chamber to fix the reduced state in the agglomerated material. Thereafter, the mass ratio of each iron oxide, metallic iron, and total iron component contained in the agglomerated material is identified by the fluorescent X-ray calibration curve method and the volume method (JIS M8213) and the obtained reduced iron The metallization rate was calculated. Here, the metalization rate (%) of the obtained reduced iron can be calculated by the following equation 101.

Metalization rate (%)
= {(Mass% of metallic Fe in the agglomerated material) ÷ (mass% of total Fe in the agglomerated material)} × 100
... (Formula 101)

  In Table 2 below, no. Sample 10 shows the result of heating for 20 minutes without performing microwave irradiation, which is a simulation of a general method for producing reduced iron without heating by microwave.

FIG. 5 shows the relationship between the metallization rate obtained by the above experiment and the temperature near the center of the agglomerated material at the start of microwave irradiation.
Referring to Fig. 5, when microwave irradiation is started when the temperature in the vicinity of the center of the agglomerated material is 600 ° C to 1150 ° C, there is no microwave irradiation (No. 10, metalization rate 85. It was found that the metallization of the agglomerated material was promoted compared to 1%).

  Further, in the low temperature state where the temperature near the center was less than 600 ° C., the effect of promoting metallization by microwave irradiation was not recognized. Also, when the temperature near the center exceeds 1000 ° C., the effect of promoting metallization by microwave irradiation decreases, and when the temperature near the center exceeds 1150 ° C., the effect of promoting metallization by microwave irradiation is not seen. .

  From the results shown in FIG. 5, it is clear that there is an appropriate irradiation start temperature condition when the agglomerated material being heated is irradiated with microwaves, and the temperature range is the internal temperature of the agglomerated material. It can be seen that is in the range of 600 ° C to 1150 ° C. Moreover, it can be seen from the results shown in FIG. 5 that when the temperature in the vicinity of the center of the agglomerated material is about 900 ° C., the effect of promoting the metallization rate by microwave irradiation is the greatest.

  From the knowledge described above, in the present invention, the microwave irradiation is preferably started under the condition that the temperature in the vicinity of the center of the agglomerated material is in the range of 600 ° C to 1150 ° C. It is considered more preferable to start under conditions where the temperature in the vicinity of the center is at least 900 ° C.

[Example 2]
Experimental conditions As in Example 1, using the composite heating apparatus shown in FIG. 4A, an agglomerated metallization test was performed by radiant heating and microwave composite heating. Similar to Example 1, the agglomerate was heated for a total heating time T = t1 + t2 + t3 (minutes), of which microwave irradiation was applied for t2 hours. In Example 1, the microwave irradiation time t2 was set to 3 minutes, but in Example 2, the evaluation of the metallization of the agglomerates at various times of t2 was performed. The component composition of the agglomerate used in the test is the same as in Example 1. By changing the heating time t1 until the start of microwave irradiation, the temperature near the center of the agglomerate at the start of microwave irradiation was changed to three levels of 700 ° C, 900 ° C, and 1000 ° C. The microwave irradiation time t2 was changed at three levels of 0.5 minutes, 1.0 minute, and 2.0 minutes. The total heating time t1 + t2 + t3 was 20 minutes, which was the same as the test conditions of Example 1.

○ Test results The test results obtained are shown in Table 3 below. Similar to Example 1, even when the microwave irradiation time was as short as 0.5 to 2.0 minutes, the metallization rate of the agglomerate was an example in which heating was performed for 20 minutes without microwave irradiation. As compared with No. 1 No. 1 (conditions without microwave irradiation), the effect of microwave irradiation promoting the metallization of the agglomerated material was confirmed.

  Acceleration amount Δη of metallization rate η (the metallization rate η after treatment under each condition and No. 1 of Example 1) based on the condition without microwave irradiation (No. 10 of Example 1). The difference between the metallization rate η of 10 conditions) was almost proportional to the microwave irradiation time. That is, when the temperature near the center of the agglomerate is in the range of 600 ° C. to 1150 ° C., and when the start of microwave irradiation is at the same timing, the metallization is accelerated according to the microwave irradiation time. Can do.

  Thus, in the test of starting microwave irradiation when the temperature in the vicinity of the center of the agglomerated material is 600 ° C. to 1150 ° C., the metal by microwave irradiation is independent of the value of the duration t2 of microwave irradiation. Acceleration effect was obtained. This result shows that the metallization promoting effect of the agglomerated material can be obtained by irradiating the agglomerated material with microwaves at least in a range where the internal temperature of the agglomerated material is 600 ° C. to 1150 ° C. It shows that it is obtained.

  Furthermore, the effect of promoting the metallization of the agglomerated material is increased by performing microwave irradiation under conditions where the temperature in the vicinity of the center of the agglomerated material is in a temperature range including 900 ° C. Here, the microwave irradiation is not limited to the case where the internal temperature of the agglomerated material is 600 ° C. to 1150 ° C., and the continuous irradiation is performed only once. Among them, microwave irradiation may be performed a plurality of times, for example, in two irradiations of a range of 700 ° C. to 800 ° C. and a range of 900 ° C. to 1000 ° C.

[Example 3]
Experimental conditions A microwave heating test similar to that in Example 1 was performed in a state where the agglomerated material to be heated was laminated in two layers. That is, as shown in FIG. 4B, the agglomerated material is placed on the upper and lower layers on the refractory material tray, subjected to radiant heating by a heating furnace and microwave combined heat treatment, and the metallization rate η after heating is evaluated. did. The test procedure except that the agglomerated raw material was divided into two layers was the same as in Example 1 and Example 2, and the agglomerate used in the test was the same as in Example 1 and Example 2. . In the test, thermocouples were installed for both the agglomerate located in the upper layer and the agglomerate located in the lower layer so that the internal temperature of the agglomerate located in each layer could be measured.

○ Test results The test results obtained are shown in Table 4 below. Even when microwaves are irradiated from above with the agglomerates stacked in two stages, the result is that the metalization of the lower agglomerates is promoted and the microwaves agglomerate from the surface of the agglomerated raw material to the lower layer. As a result, the lower layer agglomerated material was heated by deeply penetrating to the compound, and the metallization of the lower layer agglomerated material was promoted. In addition, the metallization promotion Δη (%) was larger in the lower layer agglomerate than in the upper layer agglomerate.

  For this reason, by using a heating method using a combination of a burner furnace and a microwave, metallization progresses on the back side of the agglomerated material where the radiant heating of the burner is difficult to reach, or on the overlapping lower agglomerated material. It became clear that the metallization can be promoted by microwave heating more effectively than the agglomerate on the surface of the delayed one.

  In addition, in the test of Example 1, it can be considered as follows that there exists an appropriate temperature condition about the microwave irradiation to the agglomerate under heating.

The relationship between the temperature of the agglomerated material, the content of each component in the agglomerated material, and the metallization rate was examined by the following method. That is, the agglomerate raw material is formed into a small pellet of 5 g, held in a heating furnace at a constant temperature for a certain period of time, and after reaching a uniform temperature (= equal to the furnace temperature) to the inside of the agglomerate, The agglomerated material was taken out and quenched in a nitrogen atmosphere to fix the reduced state. Analysis was then conducted to investigate the progress of metallization of the agglomerates and the change in the content of Fe ₂ O ₃ and FeO.

  The above investigation was carried out by changing the temperature at which the heating furnace was held for a certain period of time from 500 ° C. to 1300 ° C. in increments of 100 ° C.

[Progress of metallization of agglomerates]
According to the above investigation, when the temperature of the agglomerated material exceeded 900 ° C., the metal Fe (metal Fe) in the agglomerated material began to increase rapidly, and the metallization rate of the agglomerated material increased rapidly. Thereafter, when the temperature of the agglomerate approached 1200 ° C., the increase in the metallization rate was saturated, indicating that the agglomerate reduction reaction was almost terminated at a temperature of 1200 ° C.

[Change in content of Fe ₂ O _{3 in} agglomerated material]
The content of Fe ₂ O ₃ in the agglomerated material starts to decrease when the temperature of the agglomerated material reaches 600 ° C., and then continues to decrease from 1100 ° C. to 1200 ° C. It was found that the reduction of the Fe ₂ O ₃ component in the agglomerated material was almost completed in the temperature range of ° C.

[Change in content of FeO in agglomerates]
The content of FeO in the agglomerated material started to increase when the temperature of the agglomerated material reached 600 ° C, and then continued to increase to the agglomerate temperature of 1000 ° C. When the agglomerate temperature exceeds 1000 ° C., the FeO content in the raw material starts to decrease and continues to decrease until the agglomerate temperature reaches 1200 ° C., and the reduction of the FeO component in the agglomerate raw material is also 1200. It was found that the process was completed at around ° C.

  That is, from the above knowledge, when the agglomerated raw material being heated is irradiated with microwaves, even if the agglomerated raw material reaches 1200 ° C. or higher and is irradiated with microwaves, the reduction reaction of the agglomerated material Therefore, it is estimated that the contribution of the microwave irradiation to the reduction reaction cannot be expected.

  FIG. 6 shows the results of differential scanning calorimetry (DSC) for the agglomerates described above. The calorific values shown in FIG. 6 are normalized with the endothermic peak value near 900 ° C. being −1. Is displayed.

As is clear from FIG. 6 showing the DSC measurement result, in the DSC measurement result, a large endothermic reaction peak is observed in the range from about 650 ° C. to about 1150 ° C. It is thought that this peak endothermic reaction heat mainly indicates endothermic energy associated with a series of reactions in which the iron oxide component in the agglomerated raw material such as Fe ₂ O ₃ , Fe ₃ O ₄ , FeO and the like is reduced. It is done.

  Therefore, in the above experimental results, it was considered that the metallization promoting effect was obtained by irradiating microwaves at a temperature of 600 ° C. to 1150 ° C. The endotherm of DSC considered to be used for the reduction of iron oxide It is considered that the energy of the reaction could be supplied by microwave irradiation in addition to the energy supply by radiant heating of the raw material surface from the electric furnace and heat conduction from the surface to the inside of the raw material.

Here, it has been confirmed that, under the temperature conditions of 600 ° C. to 1150 ° C., most of the iron oxide is present in the agglomerated product as Fe ₂ O ₃ or FeO. Further, _Fe 2 _O 3, FeO, is a microwave heating of Fe powder ease per unit mass _is Fe ₂ O 3>FeO> Fe powder. Fe ₂ O ₃ has a low dielectric loss coefficient near room temperature and poor microwave heating characteristics, but has high microwave absorption characteristics at a high temperature of 200 ° C. or higher. FeO is a good absorber of microwaves over a wide range from room temperature to high temperature. That is, by irradiating microwaves at a timing when a large amount of Fe ₂ O _{3 in} a high temperature state in which microwave absorption is large due to radiation heating remains in the agglomerated raw material, the microwaves are agglomerated raw material. It is considered that it is efficiently absorbed by Fe ₂ O ₃ therein, FeO (further, a carbon component kneaded as a reducing agent, which is a good microwave absorber), and the like. Therefore, when the agglomerated material is irradiated with microwaves at a high temperature of 200 ° C. or higher, the microwave is efficiently absorbed when a large amount of Fe ₂ O ₃ remains in the agglomerated material. However, it can be said that this is one of the reasons why the present invention produces an effect.

  As described above, according to the present invention, the microwave absorptive energy is absorbed into the agglomerated material by irradiating the agglomerated material with microwaves under the condition that the metallization promoting efficiency of the agglomerated material by microwave irradiation is high. The microwave energy absorbed by the agglomerates can be efficiently reduced by irradiating microwaves in accordance with the temperature conditions under which the reduction reaction proceeds in the agglomerates. It can be consumed for the promotion of metallurgy, and the metallization of the agglomerated material can proceed efficiently. That is, if microwave irradiation is performed under the temperature conditions of the present invention, it can be expected that even a microwave device with a relatively small output scale will have a large effect of promoting metallization.

Even if the agglomerate raw material is 600 ° C. or less, although a large amount of Fe ₂ O ₃ remains, the microwave absorption efficiency to the agglomerate raw material is good, but the temperature is reduced by the reduction reaction as is apparent from the results of DSC analysis. Therefore, it is considered that energy is consumed to raise the temperature of the raw material, and the reduction is not promoted.

  Furthermore, when there is microwave irradiation in Example 3, the metallization promoting effect Δη1 of the upper layer agglomerates (when the metallization rate η of the upper layer agglomerates No24 in Table 4 is used as a reference, In contrast to the metallization rate η of the upper layer agglomerate when irradiated with microwaves, the metallization promoting effect Δη2 of the lower layer agglomerate (the metallization rate η of the lower agglomerate No24 in Table 4) The reason why the difference in the metallization rate η of the lower layer agglomerate when irradiated with microwaves is large is as follows.

Since the agglomerate located in the lower layer is difficult to receive radiant heat from the heating furnace, the temperature of the agglomerate in the lower layer is lower than the agglomerate located in the upper layer, and the metallization rate is higher than the agglomerate in the upper layer. (No. 24 in Table 4). That is, in this state, the lower layer agglomerates are in the process of reduction as compared with the upper layer agglomerates, and Fe ₂ O ₃ that easily absorbs microwaves in the agglomerates has a slight carbon content. A large amount remains, and the microwave absorption efficiency is better than that of the upper layer, and more microwave energy is absorbed. Therefore, it is considered that the effect of promoting metallization is great.

  Moreover, according to the test by the present inventors, the metallization of the agglomerated material proceeds rapidly due to the temperature rise of the agglomerated material in the range of the metallization rate from about 20% to about 80%. That is, in the agglomerate having a metallization rate of about 20% to 80%, the rate of increase of the metallization rate per 1 ° C. temperature rise of the raw material is large. On the other hand, if the metallization rate exceeds 80%, the progress of metallization becomes slow even if the temperature of the agglomerated material is increased. That is, in the agglomerate having a metallization rate of more than 80%, the rate of increase of the metallization rate per 1 ° C. of the raw material temperature increase is smaller than that in the case of the metallization rate of less than 80%. No. 3 in Example 3. Under 24 conditions, the metallization rate of the agglomerate in the upper layer is 80.2%, and it has reached a region where the increase in metallization per 1 ° C. temperature increase is small. On the other hand, the metallization rate of the lower agglomerate is 67.4%, which is a state in which the rate of increase of the metallization rate per 1 ° C. of temperature rise is large. Therefore, in No20-No23 of Example 3, when a microwave is irradiated from the upper part and the temperature of the agglomerate rose by the microwave, the lower agglomerate is more in comparison with the upper agglomerate. It is thought that metallization has advanced greatly.

[Application of the knowledge obtained to the production method of reduced iron]
As described above, when heating and reducing the agglomerate using both heat energy supplied by a burner or radiant heat and energy by microwaves, the internal temperature is somewhere between 600 ° C and 1150 ° C. It has been found that it is effective to irradiate microwaves on the agglomerated material in the state (more preferably, the agglomerated material in the state where the internal temperature is at least 900 ° C.). By irradiating the agglomerates at such an internal temperature with microwaves, the energy of the microwaves is effectively used for the reduction reaction of iron oxide in the agglomerates, and the operation cost is reduced, and more efficiency is achieved. It becomes possible to produce reduced iron well.

When the above knowledge is applied to an actual method for producing reduced iron, for example, the following may be performed.
First, in the solid reduction furnace 6 used for the operation, a portion where the internal temperature of the agglomerated product is 600 ° C. to 1150 ° C. under the actual operation conditions is specified. In addition, an experimental furnace simulating actual operating conditions was manufactured, and the time until the internal temperature of the agglomerated product reached 600 to 1150 ° C. (time required for temperature increase) was determined in the solid reduction furnace 6. You may specify the part from which the internal temperature of a compound becomes 600 to 1150 degreeC.

  Then, a microwave irradiation member (for example, various antennas, waveguides, coaxial cables, etc.) for irradiating the entire region where the internal temperature of the agglomerate falls within the above range is installed. What is necessary is just to irradiate a microwave with respect to the agglomerate to pass through at least a part of this microwave irradiation possible area | region as a microwave irradiation possible area | region.

  Further, the microwave irradiation member is installed in at least a part of the region where the internal temperature of the agglomerate falls within the above range to form a microwave irradiation region. Alternatively, microwaves may be irradiated.

  In addition, after installing the microwave irradiation member over the whole area of the solid reduction furnace 6 in the hearth traveling direction, the internal temperature of the agglomerated material is measured by various sensors, and the obtained measurement result is fed back to thereby microwave. The position of the microwave irradiation member used for irradiation may be variably controlled.

  Note that the microwave irradiation method as described above is merely an example, and in the solid reduction furnace, at least the agglomerate whose internal temperature is somewhere between 600 ° C. and 1150 ° C. is microwaved. The method of irradiating is not particularly limited.

  As described above, according to the method for producing reduced iron according to the present embodiment, at least the agglomerate in which the internal temperature is in a state of 600 ° C. to 1150 ° C. is irradiated with microwaves. The energy of the irradiated microwave can be effectively used for the reduction reaction of iron oxide. As a result, it becomes possible to efficiently heat and reduce the agglomerate just by irradiating the microwave at a specific part of the range where the internal temperature is in the range of 600 ° C. to 1150 ° C., while suppressing the operating cost, It becomes possible to irradiate microwaves efficiently. As a result, it becomes possible to further promote metallization of the agglomerated material by microwave irradiation.

  In the above, the manufacturing method of reduced iron which concerns on this embodiment was demonstrated in detail, referring FIGS. 4-6.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, not only a solid reduction furnace having only a solid reduction function for heating solid agglomerates obtained by mixing iron oxide powder such as iron ore and iron-making dust and a reducing material such as charcoal to obtain solid metallic iron The furnace having both the function of solid reduction and the function of separating metallic iron and slag belongs to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 100 Microwave irradiation apparatus 101 Microwave oscillator 103 Circulator 105 Isolator 107 Automatic matching device 109 Microwave irradiation member (waveguide)

Claims (4)

Reduction to produce reduced iron by heating the agglomerate formed by mixing the iron oxide raw material and the reducing material, using the radiant heat from the burner provided in the solid reduction furnace and the furnace wall of the solid reduction furnace as a heat source In the iron manufacturing method,
As the heat source, further utilizing the microwave irradiated to the agglomerate,
In the solid reduction furnace, the agglomerate is irradiated with the microwave when at least the internal temperature of the agglomerate is in a temperature range of 600 ° C. to 1150 ° C. Iron manufacturing method. 2. The method for producing reduced iron according to claim 1, wherein the microwave is irradiated to the agglomerated material when the internal temperature of the agglomerated material is 900 ° C. at least. In the solid reduction furnace, with respect to the entire region where the internal temperature of the agglomerated material is in the temperature range, a microwave irradiation member for irradiating the microwave is installed to be a microwave irradiable region,
The method for producing reduced iron according to claim 1, wherein the agglomerated material is irradiated with the microwave in at least a part of the microwave irradiable region. In the solid reduction furnace, a microwave irradiation member for irradiating the microwave to at least a part of the region where the internal temperature of the agglomerated material is in the temperature range is provided, and the microwave irradiation region age,
3. The method for producing reduced iron according to claim 1, wherein the agglomerated material is irradiated with the microwave in the microwave irradiation region.

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