JP2008189972A - Method for operating moving type hearth furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for economically operating a moving type hearth furnace with which reduced iron having the suitable size for industrial use can be collected in high yield and also, a facility is minimized and the frequency of repairing is little. <P>SOLUTION: This method for operating the moving type hearth furnace is performed as the followings. A part or the whole of reduction products and hearth carbonaceous materials generated in the moving type hearth furnace are exhausted and then classified. As to the carbonaceous material undersize, a magnetic-separation is applied only to a part or the whole of these materials under size, and the magnetically separated undersize carbonaceous materials are reused as the hearth carbonaceous material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mobile furnace in which raw materials and the like are stacked on a hearth that moves in the furnace in the horizontal direction, and the raw materials are heated and reduced to produce reduced iron while the mobile hearth moves in the furnace. The present invention relates to a method for operating a floor furnace.

  Steel is generally manufactured by refining in a converter or electric furnace. Among these, in the electric furnace method, scrap and reduced iron are heated and melted using electric energy and, depending on the case, further refined into steel. However, in recent years, there has been a tendency to use reduced iron instead of scrap due to the tight supply and demand of scrap and the demand for higher quality steel. Recently, new technology for producing reduced iron has been developed to meet these demands. In this technique, a mixture of an iron oxide-containing raw material such as iron ore and a solid reducing material is charged and deposited on a horizontal moving hearth, and the oxide is heated and reduced by radiant heat transfer from above. Alternatively, the reduced product is recovered by melting the reduced product on the same hearth and separating it into slag and metal (Patent Documents 1 and 2).

  In these prior arts, a mobile hearth furnace is used, which is a method in which the hearth moves horizontally in the furnace, and the raw material is heated in the course of the movement. In general, the hearth moving to the position of FIG. 1 rotates and moves as shown in FIG. Because of this type, the mobile hearth furnace is also called a rotary hearth furnace.

  Conventionally, as shown in FIG. 1, this rotary hearth furnace is an annular furnace body divided into a pre-tropical zone 10a, a reduction zone 10b, a melting zone 10c, and a cooling zone 10d from the raw material supply side to the discharge side. 10 and an annular hearth 11 is disposed in the furnace body so as to rotate. For example, a mixed raw material 2 made of a mixture of iron ore and a solid reducing material is charged on the rotating and moving hearth 11. As the mixed raw material, a carbonaceous material-containing pellet or a mixture of powdered iron ore and a solid reducing material is preferably used. The hearth 11 has a refractory applied on its surface, but may be formed by depositing a granular refractory, for example. A burner 13 is disposed on the upper portion of the furnace body 10, and a metal-containing oxide such as iron ore deposited on the furnace floor 11 is heated and reduced under the reducing material using the burner 13 as a heat source. Thus, a reduction product is obtained. In FIG. 1, reference numeral 14 denotes a charging device for charging the raw material onto the hearth, and reference numeral 15 denotes a discharging device for discharging the reduced product.

  In this mobile hearth furnace, the reduction product is melted and separated into slag and metal in order to protect the hearth from the molten slag and to reduce and carburize by increasing the reduction potential in the vicinity of the raw material. For the purpose of proceeding, a method of laying hearth charcoal on the hearth has been adopted. In this method, the melted and separated metal is discharged together with the slag and hearth charcoal laid on the hearth, but the metal, slag and charcoal are mainly made of only metal by magnetic separation or sieving. It is supposed to be separated and recovered (Patent Documents 2 and 3).

  Patent Document 4 discloses a method of recycling a carbonaceous material separated from metal and slag as a reducing material or hearth carbonaceous material mixed with iron oxide.

  Patent Document 5 discloses a method of separating slag and carbonaceous material from metal by magnetic separation or electrostatic separation, and recycling only the carbonaceous material. In this method, metal and slag less than 3 mm, which are not suitable for industrial use, are generated, and separated into granular metal having a particle size of 3 mm or more and carbon material mixed with metal and slag having a particle size of less than 3 mm, This is a method of recycling and using carbonaceous materials mixed with metal and slag of less than 3 mm. That is, in this method, when the recycled carbon material is supplied again into the furnace and subjected to heat treatment, the small particle size metal and slag in the carbon material are produced by reduction of the iron oxide raw material and Slag can be absorbed and the recovery rate can be increased.

  However, in this method, in order to separate the melted and separated metal from the hearth carbon material loaded on the slag or the hearth, it is necessary to cool these emissions in order to magnetically select the total amount. In this case, it is preferable to use an air-cooled cooler in order to prevent the carbonaceous material from getting wet. However, not only is the equipment large in size and not economical, but it is less than 3 mm, which is difficult to industrially use on the magnetized side. There is a problem that not only metal is generated in an amount of about 10 mass% or more, but also fine slag and carbon materials other than metal are mixed. In addition, in the method of recycling the carbonaceous material mixed with metal and slag less than 3 mm after sieving at 3 mm, the sieve size is fine, so that the size of the sieve becomes large for processing with realistic sieving efficiency. There's a problem.

  The hearth carbon material is consumed in a mobile hearth furnace, or part of it is discharged out of the system when it is reduced and / or separated from the molten product. In this regard, Patent Document 6 discloses that when a new carbon material is introduced, the new carbon material is merged with a high-temperature recycled carbon material to compensate for the decrease. It discloses a method for preventing the carbonaceous material stacking portion from entering and preventing the occurrence of large temperature unevenness in the hearth carbonaceous material.

  However, in this method, depending on the properties of the raw material, 20 mass% or more of the metal may be concentrated in the high-temperature recycled charcoal. If such charcoal is conveyed at a high temperature of 200 ° C. or higher, the conveying member may be worn. There is a problem that the frequency of replacement becomes high due to intensification.

As for the method of recovering the reduced metal without melting, the hearth carbon is charged and deposited on the hearth in order to prevent the iron oxide raw material from fusing and solidifying to the hearth (patent) Reference 7).
Japanese Patent Laid-Open No. 11-310832 Japanese Patent Application Laid-Open No. 11-172312 JP 2001-279315 A JP-A-11-106814 Japanese Patent Laid-Open No. 2003-213312 JP 2005-283011 A JP 2002-302710 A

This invention makes it a subject to solve the problem mentioned above which the prior art of patent documents 1-7 has.
That is, an object of the present invention is to provide a method for operating a mobile hearth furnace that can recover reduced iron having a size suitable for industrial use in a high yield, and reduce the size of the equipment and the frequency of repairing the equipment. It is to propose.

The inventors have developed the present invention by obtaining the knowledge that the operation method according to the gist configuration described below is effective as a result of intensive studies on a method that can solve the above problems and achieve the above object. .
That is, the present invention first forms a hearth carbon material layer by loading powder hearth carbon material on the moving hearth of the mobile hearth furnace, and oxidizes the hearth carbon material layer. The mixed raw material containing the iron-containing raw material and the carbonaceous reducing material is charged and / or agglomerated and then charged, heated while the hearth moves through the furnace, and reduced to produce a reduced product. In this method, after the reduction product and part or all of the hearth carbon material are discharged by the discharge device, they are classified, and part or all of the carbon material under the sieve is magnetically selected, and the magnetic force selection is performed. A method for operating a mobile hearth furnace, in which the later sieved carbon material is reused as the hearth carbon material, is effective.

  In the present invention, a powder hearth carbon material is first loaded on a moving hearth of a mobile hearth furnace to form a hearth carbon material layer, and an oxidation is performed on the hearth carbon material layer. The mixed raw material containing the iron-containing raw material and the carbonaceous reducing material is charged and / or agglomerated and then charged, heated while the hearth moves through the furnace, and reduced to produce a reduced product. In the method in which the reduced product is melted at least once and cooled and solidified, the reduced product after cooling and solidification and part or all of the hearth carbon material are discharged by a discharge device and then classified. A method for operating a mobile hearth furnace, wherein a part or all of the sieving carbon material is magnetically selected, and the sieving carbon material after the magnetic separation is reused as the hearth carbon material. Was also found to be an effective means for solving problems.

  In the present invention, the carbonaceous material that has not been subjected to magnetic separation among the sieving carbonaceous materials is used by mixing with the magnetic material after magnetic separation, and the hearth carbonaceous material recovered for reuse is all The Fe content is 20 mass% or less, the total Fe content of the hearth carbon material is adjusted by managing the bulk density of the carbon material, and the total Fe content of the hearth carbon material is: Providing a preferable solution by adjusting the blending of the carbonaceous material that does not undergo magnetic sorting and the carbonized material after magnetic sorting, and that the mobile hearth furnace is a rotary hearth furnace it can.

  According to the present invention having the above-described configuration, reduced iron having a size suitable for industrial use can be produced with high yield. In addition, according to the present invention, since the waste with a small amount of Fe is processed by magnetic separation, the frequency of repairing the equipment can be reduced and the equipment can be downsized. Therefore, according to this invention, the operating method of the mobile hearth furnace excellent in economical efficiency can be proposed.

  The operation method of the mobile hearth furnace according to the present invention forms a hearth carbon material layer by stacking a hearth carbon material on the mobile hearth, as seen in Japanese Patent Application Laid-Open No. 11-172131. The iron oxide-containing raw material and carbonaceous reducing material are agglomerated as needed on the hearth carbonaceous material layer, and then charged and deposited, and heat reduction is performed during the movement of the hearth to produce a reduced product. Further, the present invention is applied to a technique in which the reduced product is melted and agglomerated and then cooled and solidified to produce reduced iron.

  In the method of the present invention, when producing reduced iron (metallic iron) in a mobile hearth furnace, the hearth moving in the furnace is protected from the melt, or the powder containing the iron oxide raw material is fused. In order to prevent the formation of a sedimentary layer on the hearth by solidification, in order to increase the reduction potential in the vicinity of the raw material and promote reduction and carburization, the hearth carbon material layer is placed on the hearth by loading the hearth carbonaceous material. Then, the mixed raw material is charged on top of it and the operation is started.

  That is, the present invention classifies the reduction product and a part or all of the hearth charcoal with a discharge device after classifying them, and a part or all of the charcoal under the sieve is magnetically selected, The sieving carbon material from which metal (Fe) has been removed by the magnetic separation is recovered as the hearth carbon material and reused. In this method, when a part of the sieving carbon material is magnetically sorted, the remaining carbon material that is not magnetically sorted is at least magnetically sorted hearth carbonaceous material so that the total Fe content is 20 mass% or less. It is necessary to mix and use. Such operation of the mobile hearth furnace can reduce the size of the equipment, reduce the frequency of equipment repair, and recover high-yield reduced iron that is suitable for industrial use. In addition, the total Fe content in the hearth carbon material can be reduced.

  What is important in the above operation method of the present invention is to make the total Fe content contained in the recovered carbon material to be recycled 20 mass% or less. As described above, when the total Fe content in the recycling hearth carbon material treated in the moving hearth furnace is adjusted to 20 mass% or less, the wear of the conveying device can be greatly reduced. Here, FIG. 2 shows a carbon material containing fine metal, using a carbon material in which a part of the metal is removed by magnetic separation and the amount of metal (total Fe amount) is changed. And the relationship between the wear rate and the measurement result at different temperatures. As shown in this figure, it can be seen that when the total Fe content in the carbon material exceeds 20 mass%, the wear rate suddenly increases in the entire temperature range. On the other hand, it was also found that when the total Fe content was 20 mass% or less, the wear rate was not significantly different from that when the total Fe content was 1 mass%. Therefore, it turned out that it manages so that the total Fe content of the hearth charcoal collect | recovered may be 20 mass% or less.

  In addition, as one method for adjusting the total Fe content of the recovered carbon material recycled as the hearth carbon material to 20 mass% or less, a method of managing the bulk density of the recycled carbon material as an index can be used. In general, the bulk density of the carbonaceous material is affected by the bulk density of the base carbonaceous material and the particle size distribution of the carbonaceous material. A method of determining the total Fe content as the control value is preferable.

  It is not an industrial method to directly analyze and manage the total Fe content of hearth carbon material to be recycled. On the other hand, the bulk density of the carbon material to be recycled and the total Fe content show a strong correlation. Because. Therefore, if the bulk density of the carbonaceous material is measured, it is considered that the total Fe amount of the carbonaceous material can be easily estimated and managed.

That is, FIG. 3 shows the relationship with the bulk density of the carbonaceous material during the wear measurement. As shown in this figure, there is a strong correlation between the total Fe in the carbonaceous material and the bulk density of this carbonaceous material, and when the total Fe content = 20 mass%, the bulk density of the carbonaceous material is equivalent to 1.2 g / cm ³ . is there. In the present invention, the bulk density of the charcoal material is set with a funnel on a 1 liter container, and then the recycled charcoal material is fed through a 6 mm sieve and piled up on the container, and then the container surface is ground with a ruler. It is a value obtained by measuring the mass of the contents after making 1 liter.

  However, since the bulk density of the carbon material is also affected by the bulk density of the base carbon material and the particle size distribution of the carbon material, “bulk density: 1.2” is not an absolute index, and is an actual recycled carbon material. It is preferable to determine the control value after measuring the bulk density and taking the correlation.

  Next, the recycled hearth carbon material (hereinafter simply referred to as “recycled carbon material”) recovered from the discharge device of the mobile hearth furnace for reuse as the hearth carbon material is In order to perform magnetic separation, it is necessary to lower the temperature of the recycled carbon material to 500 ° C. or lower. As a method for lowering the temperature of this recycled carbon material, for example, a wet new carbon material and a high temperature recovered carbon material under a sieve separated on the fine grain side are mixed to evaporate water and There are people who lower the temperature.

  The recycled carbon material is magnetically separated after its temperature is suitable for magnetic separation, and part or all of the metal is separated and removed. The recycled carbon material having a low metal content thus obtained is recharged onto the hearth to form a hearth carbon material layer. In addition, such a processing method means that the recovered carbon material can be recycled without wasting sensible heat of the recovered carbon material. In addition, after classifying a product metal, reduced iron, etc. and a carbon material by classification operation, the recycled carbon material under the sieve may be made to lower the temperature of the recycled carbon material using a wet new carbon material.

  FIG. 4 shows a flow of an example in which the recycled carbon material is not magnetically selected when the collected carbon material is recycled. That is, this method classifies the high-temperature reduction product and the furnace discharge carbonaceous material discharged from the mobile hearth furnace (hereinafter, simply referred to as “reduction furnace”) 2 with the screen 3 to obtain a product (on a sieve) 4. And recycled carbon material, that is, hearth carbon material. However, in the case of this example, the carbon material also contains metal, slag, and the like that have passed through the screen 3, and is supplied to the reduction furnace 2 through the carbon material recycling line 5 as it is. Therefore, in this method, since carbon is included in the carbonaceous material, particularly when the amount of the metal exceeds 20 mass% in the total Fe content, the wear rate of various facilities increases and the facility renewal cycle becomes short. .

  Fig.5 (a)-(d) shows the carbonaceous material recycling flow adapted to the method of the present invention. In the example of FIG. 5A, a recycled charcoal storage tank 6 is installed at the exit of the screen 3, and the recovered charcoal is recycled from the recycled charcoal storage tank 6 to the reduction furnace 2 through the charcoal recycling line 5. This is the case. In this method, a part of the carbon material in the recycled carbon material storage tank 6 is sent to the magnetic separator 7, and the remaining carbon material from which the magnetic powder 8 has been removed is returned to the recycled carbon material storage tank 6 again. Further, in this method, a means for cooling the high-temperature recovered carbon is required in order to lower the temperature of the recycled carbon to 500 ° C. or lower suitable for magnetic separation. Therefore, it is desirable that the recycled charcoal storage tank 6 has a function of making the cooling means and the recycled charcoal temperature uniform. For example, as a preferable cooling means, water spray, a water cooling pipe, an inert gas blower, etc. may be sufficient, and there is no special restriction. The carbon material temperature may be equalized by using a stirrer, but the carbon material is moved by the movement of the conveyor that conveys the recycled carbon material from the recycled carbon material storage tank 6 to the magnetic separator 7 side or the carbon material recycling line 5 side. The structure may be agitated.

  The amount of the carbon material sent to the magnetic separator 7 is necessary for adjusting the bulk density of the carbon material so that the total Fe content in the recycled carbon material conveyed on the carbon material recycling line 5 is 20 mass% or less. Over the amount. Of course, even if the total amount of the recycled carbon material is magnetically selected, it is possible to reduce the wear of the conveying member due to Fe in the carbonaceous material. However, in order to magnetically select the total amount, a larger magnetic separator is required and the equipment becomes large. The recycled carbon material is sampled from the carbon material recycling line 5 periodically or irregularly so that the total Fe content in the recycled carbon material of the carbon material recycling line 5 is 20 mass% or less, and the bulk density is 20 mass% of the Fe content. When the value is higher than the equivalent value, it is possible to reduce the size of the facility by managing the magnetic selection amount so that it is easy and minimizing the magnetic selection amount. In addition, transportation of the recycled recovered coal from the screen 3 to the recycled coal storage tank 6 and from the recycled coal storage tank 6 to the magnetic separator 7 uses the fall of the recycled recovered coal to reduce the equipment wear as much as possible. Is preferred. The magnetic powder 8 separated by magnetic separation is not wasted if it is recycled in the same process as a raw material for reduced iron and metallic iron, and may be reused as a raw material for other processes such as sintering.

  FIG.1 (b) shows another embodiment of this invention, and the example of the flow from which the return from the magnetic separator 7 turns into the reduction furnace 2 instead of the recycle carbon | charcoal material storage tank 6 with respect to Fig.1 (a). It is. Also in this example, the amount of carbon material sent to the magnetic separator 7 is regular or irregular so that the total Fe content in the recycled carbon material conveyed through the carbon material recycling line 5 is 20 mass% or less. Recycled carbon material is sampled from the recycle line 5, and when the bulk density is higher than the value equivalent to 20 mass% of the total Fe content, the amount of magnetic separation is managed to be easy.

  FIG. 1 (c) shows still another embodiment of the present invention. In contrast to FIG. 1 (a), the supply of new carbon material from the wet carbon material hopper 1 is not the carbon material recycling line 5. This is an example of a recycled charcoal storage tank 6. In this example, in order to lower the temperature of the recycled carbon material to 500 ° C. or less suitable for magnetic separation, this is a preferable mode because latent heat of vaporization from the new wet carbon material can be used. It is desirable that the recycled carbon material storage tank 6 has a function of stirring the carbon material for making the temperature of the recycled carbon material uniform, but the recycled carbon material from the recycled carbon material storage tank 6 is supplied to the magnetic separator 7 side or the carbon material. A structure in which the carbonaceous material is agitated by the movement of the conveyor that conveys to the recycle line 5 side may be employed. Also in this case, the amount of carbon material sent to the magnetic separator 7 is regular or irregular so that the total Fe content in the recycled carbon material conveyed through the carbon material recycling line 5 is 20 mass% or less. Recycled carbon material is sampled from the recycle line 5, and when the bulk density is higher than the value equivalent to 20 mass% of the total Fe content, the amount of magnetic separation is managed to be easy.

  FIG. (D) shows still another embodiment of the present invention. In contrast to FIG. 1 (b), the supply of new carbon material from the wet carbon material hopper 1 is not the carbon material recycling line 5. Recycled charcoal storage tank 6 is provided. Also in this case, the amount of carbon material sent to the magnetic separator 7 is regular or irregular so that the total Fe content in the recycled carbon material conveyed through the carbon material recycling line 5 is 20 mass% or less. Recycled carbon material is sampled from the recycle line 5, and when the bulk density is higher than the value corresponding to Fe content of 20 mass%, the amount of magnetic separation is managed to be easy.

  In addition, the sieve mesh used for classification of the reduction product and the furnace discharge carbon is preferably about 3 to 15 mm. If the mesh size is small, the ratio of product metal, reduced iron, etc. mixed in the recycled recovered carbon will decrease, but the ratio of fine products that are difficult to use industrially will increase, and the product value will be relatively low. Also, at the same throughput, the smaller the sieve mesh, the larger the required sieve area. Conversely, if the sieve mesh is large, the product particle size becomes a size suitable for industrial use and the sieve size may be small. However, the ratio of product metal, reduced iron, etc. mixed in the recycled coal increases, and the recycled coal Equipment for transporting materials is subject to wear. The particle size of the hearth carbon material is preferably equal to or less than the screen mesh. This is because the coarse carbon material exceeding the screen mesh is mixed with the product and discharged.

  As described above, in the present invention, the minimum necessary equipment can be used, the frequency of repairing the equipment can be reduced, and reduced iron having a size suitable for industrial use can be recovered in a high yield. It becomes possible. Note that the mobile hearth furnace is applicable to the present invention as long as Fe accumulates in the recycled carbon material, and even if it is a reduction furnace that recovers the raw material without melting it, Further, the present invention can be applied to a reduction / melting furnace in which a raw material is reduced and then melted to recover metal and slag. However, it is recommended to use a rotary hearth furnace that can shorten the conveyance path for recycled carbon materials as a particularly preferable facility.

  The operation of producing reduced iron and metallic iron using a rotary hearth furnace with a diameter of 7m as shown in Fig. 1 is carried out, and the recovered material is treated with the treatment flow of Fig. 1 (c), and recycled charcoal with or without magnetic separation. The material properties and the wear rate of the recycled charcoal conveyor were investigated. The results are shown in Table 1. In addition, the sieve mesh of the screen 3 was 6 mm, and the replenishment wet fresh carbon material having a particle size adjusted to 5 mm or less was used.

Example 1
On the hearth carbon material layer formed on the hearth moving inside the furnace, a mixed powder material in which fine ore, fine coal and limestone were mixed in a ratio of 74: 22: 4 was charged, and the surface was made uneven. Thereafter, heating, reduction, and melting treatment were performed at a maximum furnace temperature of 1500 ° C. As the recovered carbon material (under sieve) 4b, 0.71 t / h carbon material and 0.25 t / h mixed Fe were generated, but 0.25 t / h out of the total 0.96 t / h was magnetically selected. However, 0.07 t / h magnetic deposits could be removed. The removed magnetic deposit was used as a sintering raw material. The bulk density of the recycled carbon material was 1.18 g / cm ³ and the total Fe was 19 mass%. The temperature of the carbonaceous material recycling line 5 was 450 ° C., and the wear rate of the conveying equipment was low (1: 1 relative value).

Comparative Example 1
Under the same conditions as in Example 1, heating, reduction, and melting treatment were performed. As the recovered carbon material (under sieve) 4b, 0.73 t / h carbon material and 0.26 t / h mixed Fe were generated, but magnetic separation was not performed. As a result, the recycled carbon material had a bulk density of 1.30 g / cm ³ and a total Fe of 25 mass%. The temperature of the carbonaceous material recycling line 5 was 480 ° C., and the wear rate of the conveying device was a large relative value of 3.5.

Example 2
Blast furnace dust and sintered ore are mixed at a ratio of 67:33, molded into a briquette of about 7 cc, charged on a hearth carbon material layer formed on the hearth, and at a maximum furnace temperature of 1500 ° C, Reduction and melting were performed. As the recovered carbon material (under sieve) 4b, 0.38 t / h carbon material and 0.19 t / h mixed Fe were generated, but when 0.25 t / h of the total 0.57 t / h was subjected to magnetic separation, 0 A magnetic deposit of 0.08 t / h could be removed. The removed magnetic deposit was used as a sintering raw material. The bulk density of the recycled carbonaceous material in 1.18 g / cm ^3, the total Fe was 19mass%. The temperature of the carbonaceous material recycling line 5 was 440 ° C., and the wear rate of the conveying equipment was low (relative value 1.0).

Example 3
Heating, reduction, and melting were performed under the same conditions as in Example 2 except that the magnetic deposits removed by magnetic separation were mixed and charged in the briquette. As the recovered carbon material (under sieve) 4b, 0.38 t / h carbon material and 0.19 t / h mixed Fe were generated, but 0.25 t / h of the total 0.57 t / h was magnetically selected. , 0.08 t / h magnetic deposits could be removed. The bulk density of the recycled carbon material was 1.19 g / cm ³ and the total Fe was 19 mass%. The temperature of the carbonaceous material recycling line 5 was 440 ° C., and the wear rate of the conveying equipment was low (1: 1 relative value). The recovered metal increased by 0.08 t / h compared to Example 2. After removal by magnetic separation, the magnetic deposits mixed with briquettes and re-inserted were recovered as metal on the sieve size.

Example 4
Blast furnace dust and converter dust are mixed at a ratio of 40:60, molded into a briquette of about 7 cm ³ , charged on the hearth carbon material layer formed on the hearth, and at a maximum furnace temperature of 1350 ° C, Reduction treatment was performed. As the recovered carbon material (under sieve) 4b, 0.30 t / h carbon material and 0.12 t / h mixed Fe were generated, but 0.15 t / h out of the total 0.42 t / h was magnetically separated. A magnetic deposit of 0.04 t / h could be removed. The removed magnetic deposit was used as a sintering raw material. The bulk density of the recycled carbon material was 1.14 g / cm ³ and the total Fe was 17 mass%. The temperature of the carbonaceous material recycling line 5 was 460 ° C., and the wear rate of the conveying equipment was low (1: 0 relative value).

Example 5
Heating and reduction treatment were performed under the same conditions as in Example 4 except that the magnetic deposits removed by magnetic separation were mixed with the mixed powder and subjected to briquette molding. As the recovered carbon material (under sieve) 4b, 0.31 t / h carbon material and 0.12 t / h mixed Fe were generated, but 0.15 t / h of the total 0.43 t / h was magnetically selected. , 0.04 t / h magnetic deposits could be removed. The bulk density of the recycled carbon material was 1.15 g / cm ³ and the total Fe was 17 mass%. The temperature of the carbonaceous material recycling line 5 was 460 ° C., and the wear rate of the conveying equipment was low (1: 1 relative value). The recovered reduced iron increased by 0.04 t / h compared to Example 4. After the removal by magnetic separation, the magnetic deposit mixed with the briquette powder and recharged was recovered as reduced-size iron on the sieve.

  The technique of the present invention is effective as an operation technique for a mobile hearth furnace such as a rotary hearth furnace.

It is a basic diagram which shows a mobile hearth furnace. It is a graph which shows the relationship between the total Fe amount in a carbonaceous material, and a wear rate. It is a graph which shows the relationship between the total Fe amount in a carbon material, and the bulk density of a recycled carbon material. It is a basic diagram which shows the example of the conventional method which does not carry out magnetic selection of the collection | recovery carbonaceous materials. It is a basic diagram which shows the example of the method of this invention which carries out magnetic selection of the collection | recovery carbonaceous materials.

Explanation of symbols

1 Carburized material hopper 2 Reduction furnace 3 Screen 4a Product (on sieve)
4b Collected charcoal (under sieve)
5 Carbon material recycling line 6 Recycled carbon material storage tank 7 Magnetic separator 8 Magnetic powder 9 Non-magnetic carbon material recycling line 10 Furnace 10a Pre-tropical 10b Reduction zone 10c Melting zone 10d Cooling zone 11 Hearth 13 Burner 14 Charging device 15 Discharge device

Claims (7)

First, powder hearth carbon material is loaded on the moving hearth of the mobile hearth furnace to form a hearth carbon material layer, and iron oxide-containing raw material and carbonaceous matter are formed on the hearth carbon material layer. In a method in which a mixed raw material containing a reducing material is charged and / or agglomerated and then charged, heated while the hearth moves in the furnace, and reduced to produce a reduced product.
After the reduction product and part or all of the hearth carbon material are discharged by a discharge device, they are classified, and part or all of the carbon material under the sieve is magnetically sorted, and the sieved after the magnetic separation A method for operating a mobile hearth furnace, wherein carbonaceous material is reused as the hearth carbonaceous material. First, powder hearth carbon material is loaded on the moving hearth of the mobile hearth furnace to form a hearth carbon material layer, and iron oxide-containing raw material and carbonaceous matter are formed on the hearth carbon material layer. The mixed raw material containing the reducing material is charged and / or agglomerated and then charged, heated while the hearth moves in the furnace, reduced to produce a reduced product, and the reduced product In a method of melting at least once and then cooling and solidifying,
The reduced product after cooling and solidification and part or all of the hearth carbon material are discharged by a discharge device, and then classified, and part or all of the carbon material under the sieve is magnetically selected, and the magnetic force is selected. A method for operating a movable hearth furnace, wherein a later sieved carbon material is reused as the hearth carbon material. The operation method of the mobile hearth furnace according to claim 1 or 2, wherein a carbon material not subjected to magnetic sorting among the sieved carbon materials is used by mixing with a carbon material after magnetic separation. 4. The mobile hearth furnace according to claim 1, wherein the hearth carbon material collected for reuse has a total Fe content of 20 mass% or less. 5. Operation method. The operation method of the mobile hearth furnace according to claim 4, wherein the total Fe content of the hearth carbonaceous material is adjusted by managing the bulk density of the carbonaceous material. The total Fe content of the hearth carbonaceous material is adjusted by blending adjustment of a carbonaceous material that has not undergone magnetic sorting and a carbonaceous material that has been subjected to magnetic sorting among the sieving carbonaceous materials. The operation method of the mobile hearth furnace described. The method for operating a mobile hearth furnace according to any one of claims 1 to 6, wherein the mobile hearth furnace is a rotary hearth furnace.

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