JP2014189858A - Method for producing reduced iron and production device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing reduced iron by efficiently reducing an agglomerated product including an iron oxide-containing substance and a carbonaceous reducing substance, and a production device therefor.SOLUTION: An agglomerated product including an iron oxide-containing substance and a carbonaceous reducing substance is heated at 100 to 660°C by a high frequency heating coil 8, and thereafter, the agglomerated product is heated at 1,000 to 1,400°C in a reducing furnace 9.

Description

  The present invention relates to a method for producing reduced iron by heating an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance, and a production apparatus therefor.

  In recent years, as a method of steelmaking in terms of the recycling and use of iron resources and simple equipment, after mixing iron oxide-containing materials such as ironmaking dust and iron ore generated in the steelmaking process and carbonaceous materials that are carbonaceous reducing materials, lump There has been proposed a method for producing reduced iron by subjecting the agglomeration to an agglomerate and reducing the agglomerate by heating.

For example, Patent Document 1 discloses a high-frequency induction heating apparatus that heats and reduces iron oxide contained in electric furnace dust generated by a steel maker using high-frequency induction and a reducing agent so that it can be reused as reduced iron, and electric furnace dust. A high frequency induction heating device is disclosed that can be recovered as zinc or zinc oxide when it contains zinc. However, the iron oxide cannot be heated above the Curie temperature of iron oxide simply by high frequency induction heating, so that the reduction does not proceed sufficiently and the reduced iron cannot be obtained. In addition, α-Fe ₂ O _3, which is a kind of iron oxide, is a paramagnetic substance and cannot be subjected to high-frequency heating. Therefore, it is necessary to specify the kind of iron oxide, but there is no such disclosure.

  In general, as a method for obtaining reduced iron from an iron oxide-containing substance, as disclosed in Patent Document 2, Patent Document 3, and Patent Document 4, an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance is used. A technique for reducing iron oxide by heating at a high temperature of about 1000 to 1400 ° C. in a reduction furnace such as a rotary hearth furnace or a rotary kiln is known. However, the iron oxide-containing substance or the carbonaceous reducing substance itself contains moisture, and moisture may be added together with the binder when these raw materials are agglomerated. If water in such agglomerates is brought into the furnace, the heat energy of the reduction furnace that should be used to reduce the iron oxide-containing material is used for water evaporation, so that energy utilization There is a drawback of low efficiency.

  Further, Patent Document 5 discloses a supply device including a hopper and a pipe as means for supplying an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance to a rotary hearth furnace. The feeding device is used only as a means for supplying the agglomerate, and the agglomerate cannot be heated.

JP 2008-291342 A Japanese Patent Laid-Open No. 2001-20005 JP 2001-181720 A Japanese Patent Laid-Open No. 10-226829 JP 2001-64711 A

  The present invention has been made in view of such disadvantages of the prior art, and its object is to efficiently reduce an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance. The object is to provide a method for producing reduced iron and a production apparatus therefor.

In order to achieve the above object, the present inventor supplies an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance to the reduction furnace so that the thermal energy of the reduction furnace can be effectively used for the reduction of the agglomerate. In order to reduce the water content in the agglomerate as much as possible, it was considered necessary to heat the water to a boiling point of 100 ° C. or higher. In addition, the dust generated in the iron making process of a steelworks usually contains a large amount of iron oxide in addition to metallic iron as a ferromagnetic material and carbon as a diamagnetic material. Examples of the iron oxide include γ-Fe ₂ O ₃ and Fe ₃ O ₄ that are ferrimagnetic materials, FeO that is an antiferromagnetic material, and α-Fe ₂ O ₃ that is a paramagnetic material. Therefore, the present inventor has considered applying high-frequency heating using a heat generation phenomenon caused by a high-frequency electromagnetic field. However, since these iron oxides are insulators, heat generation due to eddy current loss cannot be considered even through high-frequency current. Therefore, when these iron oxides are placed between two electrodes to which a high frequency voltage is applied, it can be expected that heat is generated due to dielectric loss (hysteresis loss).

The hysteresis loss corresponds to the size of the area surrounded by a so-called hysteresis loop. Among the iron oxides, α-Fe ₂ O ₃ which is a paramagnetic substance does not have a hysteresis loop, and γ-Fe ₂ O ₃ and Fe ₃ O ₄ which are ferrimagnetic substances and FeO which is an antiferromagnetic substance do not have a hysteresis loop. Since a hysteresis loop is observed, it is considered that γ-Fe ₂ O ₃ , Fe ₃ O _4, and FeO generate heat due to hysteresis loss.

The hysteresis loss _Ph is expressed by the following equation (1).
P _h = k _h fB _m ^1.6 (1)
k _h : proportional constant, f: frequency, B _m : maximum magnetic flux density The maximum magnetic flux density B _m is expressed by the following equation (2).
B _m = k (V / fA) (2)
k: proportionality constant, V: voltage, f: frequency, A: cross-sectional area of iron core If formula (2) is substituted into formula (1),
^{_{P h = k h 'f (}} V / f) 1.6 = k h' (V 1.6 / f 0.6) (3)
k _h ': proportionality constant

When a current is passed through the coil, the magnetic flux density rises, and eventually reaches the maximum magnetic flux density determined by the material and shape of the iron core. Until this maximum magnetic flux density is reached, the hysteresis loss is proportional to the frequency from the above equation (1). To do. On the other hand, from the above equation (3), the hysteresis loss is proportional to the voltage and inversely proportional to the frequency, but there is an upper limit to the voltage from the viewpoint of the specifications of the power supply equipment. That is, when leading a high-frequency current to the _γ-Fe 2 _{O 3} and _Fe 3 _{O 4} and FeO, although up to a certain frequency _{f 0} tends to increase the amount of heat generated by hysteresis losses when the frequency is increased, the frequency _{f 0} If it exceeds, the amount of heat generated by hysteresis loss tends to decrease.
The optimum frequency of high-frequency heating to obtain the maximum heat generation due to hysteresis loss varies depending on conditions such as the iron core material, shape, and equipment specifications (maximum voltage, maximum current). Select the optimal frequency according to the conditions. It is preferable.

This invention is made | formed based on the said knowledge, The place made into the summary is as follows.
[1] An agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance is heated to 100 ° C. or more and 660 ° C. or less by high-frequency heating, and then the agglomerate is heated to 1000 ° C. or more and 1400 ° C. in a reduction furnace. It is the manufacturing method of the reduced iron characterized.
[2] The above iron oxide-containing substance contains at least one substance in γ-Fe ₂ O ₃ , Fe ₃ O ₄ and FeO in an amount of 18% by mass to 100% by mass. 1]. The method for producing reduced iron according to 1).
[3] A high-frequency heating apparatus for high-frequency heating an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance, a rotary hearth rotating at a predetermined speed and a heating means for reducing the agglomerate It is the manufacturing apparatus of reduced iron characterized by adding to the agglomerate supply means of the rotary hearth type reduction furnace which has.

  According to the method and apparatus for producing reduced iron of the present invention, reduced iron can be produced by efficiently reducing an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance.

FIG. 1 shows the difference in heating time depending on the type of iron oxide, with the heating time (minutes) on the horizontal axis and the heating temperature (° C.) on the vertical axis when the iron oxide is heated at high frequency (10 kHz, 8 kW). It is. FIG. 2 shows that when the iron oxide-containing reagent is heated at high frequency (10 kHz, 3 kW), the horizontal axis represents the ratio of Fe ₃ O ₄ in the iron oxide-containing reagent (%: mass basis), and the heating temperature (° C.) is the vertical axis. as the shaft is a diagram showing the relationship between the most heated hard Fe ₃ O ₄ ratio and heating temperature. This iron oxide-containing reagent is composed of Fe ₃ O ₄ and a diamagnetic material. FIG. 3 is a diagram showing a schematic configuration of a production apparatus capable of carrying out the method for producing reduced iron of the present invention. FIG. 4 is a schematic configuration diagram showing a state in which a high-frequency heating coil is wound around the agglomerate supply pipe for supplying the agglomerate to the rotary hearth type reduction furnace.

(1) Types of iron oxide and heating time in high-frequency heating Normally, the dust generated in the iron making process at a steel mill contains up to about 15% by mass of metallic iron, and often contains carbon and a large amount of iron oxide. . Therefore, an agglomerate containing 15% by mass of metallic iron and the remaining 85% by mass of γ-Fe ₂ O ₃ , Fe ₃ O ₄ or FeO was high-frequency heated with a high-frequency heating device having a frequency of 10 kHz. The horizontal axis in FIG. 1 indicates the heating time (minutes), and the vertical axis indicates the heating temperature (° C.). In FIG. 1, line A represents γ-Fe ₂ O ₃ , line B represents Fe ₃ O ₄ , and line C represents FeO. As is apparent from FIG. 1, γ-Fe ₂ O ₃ is heated to 600 ° C. or higher earliest, and it takes the longest time to heat FeO to 600 ° C. or higher, and Fe ₃ O ₄ is heated to 600 ° C. or higher. It can be seen that the time required for this is a little longer than γ-Fe ₂ O ₃ . And γ-Fe ₂ O ₃ could be heated up to 629 ° C., Fe ₃ O _{4 up} to 620 ° C., and FeO up to 660 ° C., respectively. These iron oxides are said to have a Curie point of about 590 ° C to 600 ° C, but they contain 15% by mass of metallic iron, and as a result of heat generation due to eddy current loss, it seems that they could be heated to over 600 ° C. It is. It was confirmed that α-Fe ₂ O ₃ could not be heated at high frequency.
The heating temperature by high-frequency heating of the agglomerate containing the iron oxide-containing substance and the carbonaceous reducing substance is set to 100 ° C. or higher. Because it is necessary to do. The reason why the heating temperature is set to 660 ° C. or lower is that it is difficult to heat at a higher frequency.

(2) Ratio of FeO, γFe ₂ O ₃ , and Fe ₃ O _{4 in} the iron oxide-containing material At least one material among γFe ₂ O ₃ , Fe ₃ O _4, and FeO in the iron oxide-containing material When the content of is less than 18% by mass, it is difficult to heat to 100 ° C. or higher. Therefore, it is preferable that the iron oxide-containing substance contains 18% by mass or more and 100% by mass or less of at least one of γFe ₂ O ₃ , Fe ₃ O ₄ and FeO. In this case, the ratio of at least one substance in γFe ₂ O ₃ , Fe ₃ O _4, and FeO in the iron oxide-containing substance is the metal iron, carbonaceous reducing substance, moisture, binder in the agglomerate It means the mass% in iron oxide excluding the above.

FIG. 2 is a diagram showing the relationship between the ratio of Fe ₃ O ₄ in the iron oxide-containing reagent (%: mass basis) and the heating temperature (° C.) when the iron oxide-containing reagent is heated at high frequency. It can be seen that when Fe ₃ O ₄ is 18% or more, it is heated to 100 ° C. or more. As shown in FIG. 1, among γFe ₂ O ₃ , Fe ₃ O _4, and FeO, Fe ₃ O ₄ is most difficult to be heated. Therefore, among the iron oxide-containing materials, γFe ₂ O ₃ , Fe ₃ O ₄ It can be seen that by containing at least 18% by mass of at least one substance in FeO and FeO, it can be heated to 100 ° C. or higher by high-frequency heating.

  The optimum frequency of high-frequency heating to obtain the maximum heat generation due to hysteresis loss varies depending on conditions such as the iron core material, shape, and equipment specifications (maximum voltage, maximum current). It is preferable to select the optimum frequency from several kHz to 500 kHz.

(3) Reduced iron manufacturing apparatus The reduced iron manufacturing apparatus of this invention is demonstrated using FIG.
The present invention stores iron oxide-containing substances such as ironmaking dust and iron ore generated in the ironmaking process as raw materials, and carbonaceous materials that are carbonaceous reducing substances in silos 1 and 2, respectively. The iron oxide-containing substance and the carbonaceous material are discharged at a speed of 1 mm and supplied to a pulverizer 3 such as a ball mill which is the next process. In order to adjust the moisture content of the powder obtained by pulverization and to add a binder, the powder, the binder stored in the silo 5 and the water stored in the silo 6 are kneaded in the kneader 4 and obtained by kneading. The resulting kneaded product is molded by the molding machine 7, and the agglomerate obtained by molding is heated to a predetermined temperature of 100 ° C. or higher by the high-frequency heating coil 8, and then the agglomerated product is put into the rotary hearth type reduction furnace 9. Reduced iron can be obtained by reduction in a typical reduction furnace. Here, the reduction furnace is not necessarily limited to the rotary hearth type, and may be a rotary kiln, a shaft furnace, or the like. However, in the case of a rotary hearth type, it is only necessary to add a high frequency heating coil to the agglomerate supply path of a known rotary hearth type reducing furnace, and the high frequency heated agglomerate is directly charged into the reduction furnace. Therefore, there is an advantage that the equipment cost for that is relatively low. As the high-frequency heating coil, a generally known copper pipe type or water-cooled cable type can be used. The material of the apparatus for supplying the agglomerate is preferably a diamagnetic material typified by ceramics such as zirconia and silicon carbide so that it is not heated at high frequency by a high frequency heating coil.

  FIG. 4 is a view showing a state in which the high-frequency heating coil 16 is wound around the outer periphery of the agglomerate supply pipe 17 for supplying the agglomerate to the rotary hearth type reducing furnace 18. 15 is a hopper and 19 is a hearth.

"material"
As the iron oxide-containing substance, a substance containing iron oxide such as iron making dust or iron ore generated in the iron making process can be used. As the carbonaceous reducing material, coal particles represented by anthracite coal can be used.

≪Crushing process≫
The reduction reaction in the reduction device is promoted by refining the substance to be reduced. Therefore, in the grinding process of the iron oxide-containing substance and the carbonaceous reducing substance, a ball mill, a rod mill, a vibrating ball mill, an attritor, a jet crusher Etc. can be used.

≪Kneading process≫
The iron oxide-containing substance and carbonaceous reducing substance refined in the pulverization process are transferred to the subsequent molding process and molded in the presence of appropriate amounts of moisture and binder. Kneaded.

≪Molding process≫
An iron oxide-containing substance and a carbonaceous reducing substance containing appropriate amounts of moisture and a binder are molded by a molding method such as briquetting, pelletizing, and extrusion molding to obtain an agglomerate.

≪Drying heating process≫
If the agglomerate is charged into the reduction furnace as it is, problems such as loss of agglomerate recovery due to heat loss due to moisture evaporation and cracking will occur. It is preferable to sufficiently heat the product so that the moisture content is less than 1%. Therefore, it is preferable to perform high-frequency heating at a temperature of 100 ° C. or higher and 660 ° C. or lower for a predetermined time.

≪Reduction process≫
The agglomerate after drying is subjected to reduction treatment for about 10 to 20 minutes under a burner heating atmosphere condition of about 1000 to 1400 ° C. by a process described later using a reduction device (for example, rotary hearth type reduction furnace 9). Applied.
That is, the agglomerate charged into the rotary hearth type reduction furnace 9 is heated by a flame generated by a mixed gas of air supplied from the path 11 and liquefied natural gas supplied from the path 12 emitted from the burner 10. However, it is reduced in the reducing furnace 9 that rotates slowly. The reduced iron discharged from the reduction furnace 9 after one rotation of the reduction furnace 9 is transported to the melting furnace 14 by transport means 13 such as a truck, and is made into molten iron by the reaction heat of coal and oxygen.

≪Method for evaluating reduced iron≫
As a method for evaluating the characteristics of reduced iron produced in the rotary hearth type reducing furnace 9, the metal component (M.Fe) relative to the total iron content (T.Fe) obtained from the component analysis is used as an index indicating the degree of progress of reduction. A metallization ratio (M.Fe / T.Fe) that is a ratio of

  Examples of the present invention will be described below. However, the present invention is not limited to the following examples, and changes and modifications can be made as appropriate without departing from the technical scope of the present invention.

  Anthracite was used as the reducing material, and iron-making dust having the component composition (mass%) shown in Table 1 below was used as the iron oxide raw material. The iron dust, carbonaceous material, binder, and water are kneaded, and then a tablet with a diameter of 30 mm and a height of 20 mm is compression-molded with a load of 3.6 MPa. A heating coil (10 kHz, 8 kW) heated and unheated was manufactured, and the briquette was heated for a predetermined time in a 1250 ° C. resistance heating furnace simulating a rotary hearth type reducing furnace. Reduced iron was obtained. Table 2 below shows the high-frequency heating temperature, the heating time at 1250 ° C., the relative metallization rate, and the moisture in the briquette. A relative metallization rate shows the relative value which makes the metallization rate (metallic iron / total iron content) of the sample 1 1.00. The water | moisture content in a briquette shows the water | moisture content in the briquette before high frequency heating and resistance heating furnace insertion. This moisture content was measured by JSM8811 (coal and coke sampling method and total moisture / moisture measurement method).

  As shown in Table 2, when Sample 1 and Sample 2 are compared, it can be seen that the metallization rate can be improved only by high-frequency heating to 100 ° C. That is, it can be seen that the thermal energy of the resistance heating furnace can be effectively used for reduction of the agglomerates by reducing the moisture in the agglomerates.

  As shown in Table 2, when sample 2 and sample 3 are compared, when high-frequency heating is performed up to 590 ° C. compared to heating up to 100 ° C., in addition to the reduction of moisture in the agglomerate, preheating before charging the reducing furnace is performed. Therefore, it can be seen that the metallization rate can be significantly improved by effectively using the thermal energy of the resistance heating furnace as the reduction energy.

  As shown in Table 2, as can be seen by comparing Sample 2 and Sample 4, the metallization rate of reduced iron obtained by heating an agglomerate heated to 590 ° C. at a high frequency at 1250 ° C. for 8 minutes is 100 ° C. It was the same as the metallization rate of the reduced iron obtained by heating the agglomerate heated at high frequency to 1250 ° C. for 10 minutes. That is, heating time (reduction time) can be shortened by 20% by sufficiently reducing the moisture in the agglomerate and preheating by high-frequency heating.

DESCRIPTION OF SYMBOLS 1 Silo 2 Silo 3 Crusher 4 Kneading machine 5 Silo 6 Silo 7 Molding machine 8 High frequency heating coil 9 Rotary hearth type reducing furnace 10 Burner 11 Air supply path 12 Liquefied natural gas supply path 13 Conveying means 14 Melting furnace 15 Hopper 16 High frequency Heating coil 17 Agglomerate supply pipe 18 Rotary hearth reducing furnace 19 Hearth

Claims (3)

  An agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance is heated to 100 ° C. or more and 660 ° C. or less by high-frequency heating, and then the agglomerate is heated to 1000 ° C. or more and 1400 ° C. in a reduction furnace. A method for producing reduced iron. The iron oxide-containing substance contains at least one substance selected from FeO, γFe ₂ O ₃ and Fe ₃ O _{4 in} an amount of 18% by mass to 100% by mass. A method for producing reduced iron.   A high-frequency heating apparatus for high-frequency heating an agglomerate containing an iron oxide-containing substance and a carbonaceous reducing substance, a rotary furnace having a rotary hearth rotating at a predetermined speed and heating means for reducing the agglomerate An apparatus for producing reduced iron, characterized by being added to the agglomerate supply means of a bed type reduction furnace.