JP4736541B2 - Method for producing reduced metal - Google Patents

Description

  The present invention relates to a method for producing a reduced metal from a substance containing a metal component using a mobile hearth furnace, and in particular, a metal-containing ore such as iron ore, an iron content generated in a steelworks, a smelter, a smelter, etc. And a method for producing reduced metals such as reduced iron from metal-containing raw materials such as dust, sludge or scale containing various metal components.

  Conventionally, steel is mainly produced by a blast furnace-converter method or an electric furnace method. Among these, the electric furnace method is a method in which scrap or reduced iron is used as a raw material, and these are heated and melted by electric energy, and further refined to make steel in some cases. At present, this method uses scrap as the main raw material. However, in recent years, the supply and demand of the scrap has been tight, and demand for iron-containing raw materials to replace scrap, such as reduced iron, has increased especially for the manufacture of high-grade products. It's getting on.

  As a process for producing the reduced iron (a method using a mobile hearth furnace), for example, as disclosed in Patent Document 1, an iron ore and a solid reducing agent are formed on a moving bed that rotates and moves in a horizontal direction. There is a rotary hearth furnace method in which the mixture is stacked and iron ore is heated and reduced by width radiation heat transfer from above to obtain reduced iron. The production of reduced iron by the rotary hearth method has the advantages that the construction cost of the equipment is relatively low, the operation trouble is relatively small, and the reduced iron can be produced stably.

  In such a method for producing reduced iron, the reduction reaction in the heating furnace is considered to proceed by direct reduction between the iron ore and the solid reducing agent. This direct reduction is an endothermic reaction, and the supply and reduction rate of this heat determines the productivity. The heat is supplied by using a burner as a heat source, and by means of a radiant heat transfer from a burner flame or a furnace inner wall. When the raw material supplied on the moving bed moves in a high-temperature atmosphere in the heating furnace, volatile matter is generated from the solid reducing agent in the raw material, and CO gas is generated by the reaction between the solid reducing agent and iron oxide. Combustible gas such as is generated. These gas components can be an important heat source. If this gas component can be used effectively in the furnace, it is considered that the fuel ratio is effective.

  In addition, with regard to the operation of the rotary hearth furnace, studies are being made on techniques for preventing reoxidation of reduced iron for the purpose of improving productivity. In the production of reduced iron in a rotary hearth furnace, there is little generation of flammable gas such as CO gas after the melting zone, so the atmosphere in the furnace is reduced by the intake air or the oxidizing gas generated during combustion of the main burner. This is because oxidation may occur, and in order to prevent this, fine adjustment of the pressure in the furnace and the gas flow is required.

  For example, Patent Document 2 and Patent Document 3 disclose a technique for reducing the fuel consumption rate by controlling the gas flow in the heating furnace to prevent reoxidation of the reduced metal and effectively using the gas containing CO. ing. In this technology, a partition wall that can move up and down is installed in the rotary hearth furnace, the structure of the exhaust gas duct is devised, or an exhaust gas pressure control valve is installed to make effective use of the gas. In addition to the high equipment costs, there is a problem that operability and equipment maintenance are poor.

  In Patent Document 4, in order to prevent reoxidation of the reduced metal, in addition to installing a partition wall that can move up and down in the middle of the moving floor, the partition wall itself is also provided with a flow rate adjusting opening. Discloses a method for controlling the gas flow in the furnace by adjusting the pressure for each heating / reducing step, melting step, cooling step, and discharging step. However, this technology is effective in preventing reoxidation of the reduced metal, but the structure of the partition wall is complicated, which increases the equipment cost and increases the maintenance cost, as well as stable operation. Make it difficult.

Further, Patent Document 5 discloses that a carbonaceous atmosphere modifier as an atmosphere modifier in the melting step is charged on the hearth at least before the raw material molded body is melted, and the atmospheric conditions at the end of production, particularly during carburizing / melting. It is a technology that prevents reoxidation of reduced iron by appropriate control. However, in order to put this technology into practical use, it is necessary to finely control the particle size of the atmosphere adjusting agent and its charging amount, and at the same time, it is indispensable to control to maintain a favorable state in terms of cost. there were.
Japanese Unexamined Patent Publication No. 63-108188 Japanese Patent Laid-Open No. 2001-107120 Japanese Patent Laid-Open No. 2001-107121 JP 2004-315910 A JP 2001-279315 A

  The present invention has been made in order to solve the above-mentioned various problems of the prior art, and the object of the present invention is to provide support in the furnace without causing reoxidation of the reduced metal. The purpose is to propose a technology capable of reducing the fuel consumption rate through the effective use of flammable gas. Another object of the present invention is to realize a reduction in the fuel consumption rate without requiring excessive capital investment. Still another object of the present invention is to provide a rotary furnace capable of reducing fuel consumption before the reduction process and preventing reoxidation of the reduced metal by effectively burning CO gas generated in the melting process with oxygen. It is to propose a method for operating the floor furnace.

In the present invention, in order to achieve the above object, as a result of intensive studies, a floor layer is formed by laying a solid reducing agent on a moving bed moving in a heating furnace, and a metal layer is formed on the floor layer. A raw material consisting of a mixture of the contained raw material and a solid reducing agent is charged and deposited, and while moving the raw material in the heating furnace, the raw material is heated by the combustion heat of the fuel supplied from the burner to the upper part of the moving bed and reduced. Further, in the method for producing a reduced metal by cooling after being guided to the melting zone and being melted , both the main burner and the secondary combustion burner to which fuel and combustion-supporting gas are supplied are supplied to the melting zone. was placed, the total amount of combustion assisting gas to the fuel to these burners, the supply amount corresponding to 1.01 to 1.5 times the stoichiometric combustion oxygen quantity of the fuel as the oxygen amount, within the range From the main burner I have found that is possible to adopt a method for producing a reduced metal, wherein the transfer of a part of the fee supply amount supplied from the secondary combustion burner is effective.

In such present invention, the position in the height direction of the 2 Tsugi燃Shoba Na, considered more effective solutions be positioned lower than the position of the main burner.

As described above, according to the present invention, firstly, the solid reducing agent is not only mixed with the reducing metal in the raw material such as the iron oxide-containing substance, but also separately on the moving floor as a floor covering material. In addition to protecting the moving bed, it is possible to prevent reoxidation of the reduced metal generated in the melting zone, and secondly, a secondary combustion burner in which excess combustible gas generated in the furnace is disposed in the melting zone By making it a heat source for the reduction zone (heating process) by burning in, it is possible to reduce the fuel consumption rate without requiring a complicated and expensive device. In particular, the combustible CO gas component generated until the reduction of the charged raw material can be effectively used as a heat source for the melting zone, which is extremely effective for reducing the fuel consumption rate.
Further, in the molten zone, the generated molten metal agglomerates, so that the solid reducing agent laid on the moving bed is exposed to the atmospheric gas, so that the solid on the moving bed is present even if there is excess oxygen. Since it comes to be used for combustion of a reducing agent, there is little possibility that the combustible gas component (oxygen) which generate | occur | produces in a furnace will flow out in a downstream direction wastefully.

  FIG. 1 shows a “rotary hearth furnace” as an example of a mobile hearth furnace preferably used for carrying out the method of the present invention. A reduction zone 10b, a melting zone 10c, and a cooling zone 10d are partitioned and a moving bed 11 that moves continuously is disposed in the furnace body 10. On the moving bed 11, a raw material 12 made of a mixture of a metal-containing raw material such as iron ore and a solid reducing agent such as coal is charged and deposited to a predetermined thickness. In addition, as this raw material 12, a carbonaceous material interior pellet may be used.

  Although the moving bed 11 is surrounded by a furnace body 10 having a refractory lining, the characteristic feature of the present invention is that a solid reducing agent, Prior to charging the raw materials, the carbon material is preliminarily deposited as a flooring material. In addition, two types of burners 13a and 13b are disposed on the upper side of the furnace body 10, and the iron ore on the moving bed 11 is heated and reduced by using the combustion heat of the burners 13a and 13b as a heat source. ing. In FIG. 1, 14 is a charging device for charging the raw material onto the moving bed 11, and 15 is a discharging device for discharging the reduced product. In addition, this rotary hearth furnace can maintain the atmospheric temperature in the furnace body 10 at about 1300 ° C. and recover unmelted reduced iron, while melting at a high temperature of about 1500 ° C. It is also possible to adopt a system in which the metal and slag are separated and collected.

  Even if any operation is performed, in this rotary hearth furnace, by using an agglomerated mixture containing an iron-containing material such as iron ore and a carbonaceous solid reducing agent such as coal, By increasing the contact area between these, the reaction rate during reduction may be promoted and the processing time may be shortened. Such shortening of the processing time leads to improvement in productivity and reduction in production cost. This is desirable to bring.

  FIG. 2 is a vertical sectional view in the circumferential direction in which the rotary hearth furnace is linearly developed between the raw material charging device and the product discharging device. The reference numerals indicate the same components as those shown in FIG. 1, but the charging device has a raw material charging device 14a and a reducing agent charging device 14b, and the burner is arranged from the reduction zone to the melting zone. There are a main burner 13a and a secondary combustion burner 13b arranged only in the melting zone. In addition, 16 of illustration is a cooling device.

  In the operation of this furnace, on the moving bed 11 moved at a predetermined speed, first, a solid reducing agent for flooring is supplied from the reducing agent charging device 14b to form a lower layer, and a metal-containing substance and a solid are formed on the lower layer. The raw material 12 made of a mixture with a reducing agent is supplied from the raw material charging device 14a to become an upper layer, and moves through the zones 10a to 10d in the furnace. Here, the mixture of the raw material containing the metal-containing substance and the solid reducing agent may be a powder or a lump such as a pellet or a briquette.

  As a raw material containing a metal-containing substance, metal-containing ores such as iron ore, iron generated in ironworks, smelters, etc., and dust, sludge, scale, etc. containing various metal components can be used. As the solid reducing agent, solid synthetic fuels synthesized from solid fuels such as coal and coke or wastes can be used. These solid reducing agents can be used as the solid reducing material layer 17 on the moving bed 11 or can be used as a constituent material of the raw material that is the mixture.

  As described above, in the rotary hearth furnace applied to the method of the present invention, a plurality of main burners 13a are installed on both side walls of the heating furnace, which is above the moving bed 11, from the reduction zone 10b to the melting zone 10c. In the main burner 13a, fuel (heavy oil, natural gas, propane gas, pulverized coal, etc.) and primary combustion air (or oxygen-enriched air) for burning the fuel supplied from the main burner are supplied. Is done. This main burner is provided in the entire region from the heating / reduction process to the melting process in the furnace. In addition, although the example which installed the main burner 13a in the furnace wall upper part is shown in FIG. 2, since the objective of this main burner 13a is to supply the heat | fever smoothly in a furnace, in this meaning, The main burner 13a may be provided downward on the ceiling portion of the furnace body.

Further, for the melting zone 10c, one to a plurality of secondary combustion burners 13b are installed together. FIG. 2 shows an example in which two secondary combustion burners 13b are installed. The secondary combustion burner 13b is supplied with secondary combustion air (or oxygen-enriched air) as a preferred combustion-supporting gas, that is, a gas for promoting the combustion of surplus CO gas generated in the furnace. To do. In the present invention, the secondary combustion means that the CO gas generated until the reduction of the metal content is completed in the reaction from the reduction zone to the melting zone, and the secondary combustion air, etc. The oxygen supplied from the combustion chamber burns the CO gas generated by oxidizing the solid reducing agent on the hearth.
However, in the combustion with a burner, there is a case where the combustion is not completely performed depending on the state of the mixture of fuel and oxygen, and even if an amount of oxygen equal to the theoretical combustion oxygen amount is supplied, a combustible gas such as CO gas remains. There is a case.

  Therefore, in the present invention, the secondary combustion burner 13b disposed in the melting zone 10c is used to cause secondary combustion above the melting zone, which is the environment in which the reduced metal is generated, so as to effectively use the heat energy. It was. The secondary combustion burner 13b may be disposed in the reduction zone 10b. However, in this case, the CO gas generated by the reduction of the raw material is combusted, so that the operational effects of the present invention are not hindered. Absent.

  As described above, in the present invention, in the stage of the melting zone 10c, the amount of the combustion-supporting gas such as oxygen supplied to this zone is supplied in excess of the amount necessary for the combustion of the fuel. The combustible gas generated in the band 10c was completely burned, and the furnace interior was changed to a high temperature atmosphere. Therefore, in the present invention, the total amount of oxygen in the combustion-supporting gas supplied from the main burner 13a and the secondary combustion burner 13b in the melting zone 10c is the theoretical combustion oxygen amount for the fuel supplied together from the main burner 13a. It was decided to supply an amount corresponding to the amount of oxygen corresponding to 1.01 to 1.5 times the amount. This theoretical amount of combustion oxygen means the amount of oxygen required for combustible gases such as carbon and hydrogen in the fuel to completely burn and become combustion products such as carbon dioxide and water. By supplying an equal or greater amount of oxygen, the combustible gas component can be completely burned.

  Therefore, in the present invention, the reason why the total amount of the combustion-supporting gas supplied to the melting zone 10c through the burners 13a and 13b is equivalent to 1.01 to 1.5 times the theoretical combustion oxygen amount of the fuel is defined as the oxygen amount. It is as follows. That is, for the lower limit of 1.01, if the amount of oxygen is less than this, there is almost no effect of oxidizing the solid reducing agent on the hearth and generating CO gas, so the temperature rise in the molten zone 10c cannot be expected. is there. Moreover, about upper limit 1.5, when excess oxygen is supplied exceeding this, oxygen which does not contribute to combustion of the solid reducing agent on a hearth will come to be generated. In this case, oxygen that does not contribute to combustion enters the melting zone 10c at room temperature and exits from the melting zone to the reduction zone at the temperature of the high-temperature atmosphere of the melting zone, so that the temperature of the melting zone 10c is lowered instead. . For this reason, it also causes a decrease in the productivity of the furnace, so the upper limit of the amount of oxygen in the combustion-supporting gas supplied to the melting zone 10c is preferably 1.5.

  In the mobile hearth furnace, the amount of combustible gas such as volatile matter and CO gas expected as a heat source is considerably reduced from the latter stage of the reduction zone 10b to the melting zone 10c, and the reducing atmosphere is reduced. Therefore, it is necessary to pay attention to the reoxidation of the produced reduced iron.

  However, the method of the present invention does not necessarily fall into this situation because a bed layer made of a solid reducing agent is provided under the raw material layer. That is, as shown in the concept of this situation in FIG. 3, on the moving bed 11 in the method of the present invention, in addition to the molten reduction product 18 composed of molten metal (metal) and molten slag which are melted and aggregated, Since the solid reducing agent layer is exposed on the surface, a part of excess oxygen in the furnace atmosphere gas is also consumed for burning the floor reducing solid reducing agent. In addition, some other excess oxygen may be consumed in the oxidation of the molten metal, but under the practice of the method of the present invention, the molten metal is present on the solid reducing agent layer. There is always a state in which carbon is supplied, and the oxidized metal is immediately reduced by the carbon and returned to the metal.

  In the present invention, the supply of fuel and combustion-supporting gas to the burners 13a and 13b disposed in the molten zone 10c may be performed using pulverized coal, heavy oil, or the like in combination with the above-described method. Note that the burners 13a and 13b to be used can be of any type such as a premix type and a postmix type.

  In adopting the above-mentioned secondary combustion burner 13b, the present invention shows the arrangement at the same level as the main burner 13a as shown in FIG. 2, but in addition, as shown in FIG. By setting the installation position of the combustion burner 13b in the height direction below the installation position of the main burner 13a, the excess oxygen is combustible gas such as CO gas generated from the solid reducing agent, raw material, and molten metal on the moving bed. If the contact with is accelerated, it can be used effectively due to the temperature rise of the melting zone 10c.

This example shows the result of a reduction iron production experiment using a rotary hearth furnace as shown in FIGS. In addition, Table 1 shows the operating conditions and the results when a reduced iron production experiment was conducted using LNG as the fuel and air and oxygen as the combustion-supporting gas.
An example in which LNG was burned at 70 m ³ (standard state) / h under the condition of an air-fuel ratio of 1.00 using only the main burner 13a as a heat supply source to the melting zone 10c was set as a comparative example.
This air-fuel ratio is expressed as 1 when the theoretical combustion oxygen amount necessary for complete combustion of LNG supplied to the melting zone 10c is supplied with enriched oxygen air having an oxygen concentration of 35 vol%.
At this time, 110 m ³ (standard state) / h of LNG was supplied to the reduction zone 10b, and a melting zone atmosphere temperature of 1510 ° C. and a reduction zone atmosphere temperature of 1505 ° C. were achieved, and stable operation could be continued.

On the other hand, as shown in FIG. 2, from the secondary combustion burner 13b installed at the same height level as the main burner of the melting zone 10c, 100 m ³ (standard state) / h, 150 m ³ (standard state) / Examples of supplying air h and setting the air-fuel ratio in the melting zone 10c to 1.3 and 1.5 were shown as Reference Examples 1 and 2, respectively. In addition, since the volatile component generated in the melting zone 10c and the solid reducing agent on the hearth were burned with excess oxygen, the temperature in the melting zone 10c increased. Therefore, in Reference Examples 1 and 2, the LNG supply amount in the reduction zone 10b could be reduced to 90 m ³ (standard state) / h and 60 m ³ (standard state) / h, respectively. Moreover, the temperature of the melting zone 10c and the reduction zone 10b could be maintained at a temperature almost equal to or higher than that of the comparative example.

Next, in Examples 1 and 2 , a part of the amount of LNG supplied from the main burner to the melting zone 10c was transferred to the supply from the secondary combustion burner for the conditions of Reference Examples 1 and 2, respectively. It is. Also in these examples, the temperatures of the melting zone 10c and the reduction zone 10b were almost the same as those of Reference Examples 1 and 2. Therefore, it has been found that there is no problem even when fuel is sent from the secondary combustion burner.

Further, Reference Example 3 is an example in which the same combustion conditions as in Example 1 are adopted. As shown in FIG. 4, the level in the height direction of the secondary combustion burner is set between the upper surface of the hearth and the main burner. This is an example in which reduced iron production was carried out with a configuration lowered to half the height.
In this case, since the CO gas generated by the combustion of the volatile component and the solid reducing agent on the hearth can be burned effectively, the temperature in the melting zone 10c can be further increased, as shown in Table 1. In addition, even if the amount of LNG supplied to the reduction zone 10b was further reduced from that in Example 1 , the reduction zone 10b and the melting zone 10c could maintain substantially the same temperature.

  The technology according to the present invention is employed for the production of reduced metals such as iron by a rotary hearth furnace, but this technology is also used for the production of sponge iron and iron powder as well as other metal powders. be able to.

It is a schematic diagram of a rotary hearth furnace. It is a vertical sectional view of the state where the rotary hearth furnace concerning an embodiment of the invention was developed. It is a conceptual diagram of reaction of excess oxygen in a melting process. It is a vertical sectional view of a state where a rotary hearth furnace according to another embodiment of the present invention is developed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Rotary hearth furnace 10a Pre-tropical zone 10b Reduction zone 10c Melting zone 11 Moving bed 12 Raw material 13a Main burner 13b Secondary combustion burner 14a Raw material charging device 14b Solid reductant charging device 15 Raw material discharge device 16 Cooling device 17 For flooring Solid reducing agent (layer)

Claims (2)

On the moving floor moving in the heating furnace, a solid reducing agent is spread to form a floor covering layer, and a raw material composed of a mixture of a metal-containing raw material and a solid reducing agent is charged and deposited on the floor covering layer. The reduced metal is heated by the combustion heat of the fuel supplied from the burner to the upper part of the moving bed while moving the raw material in the heating furnace, reduced, further led to the melting zone and cooled and then cooled. In the melting zone, both the main burner and the secondary combustion burner to which the fuel and the combustion supporting gas are supplied are arranged, and the total amount of the combustion supporting gas with respect to the fuel to these burners is determined. In addition, an oxygen amount corresponding to 1.01 to 1.5 times the theoretical combustion oxygen amount of the fuel is supplied, and a part of the fuel supply amount from the main burner within this range is supplied from the secondary combustion burner. especially the transfer of the supply Manufacturing method of reducing metal to. 2 Tsugi燃Shoba the position in the height direction of the Na, the production method of reduced metal according to claim 1, characterized in that is positioned lower than the position of the main burner.

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