JP4992257B2 - 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, for example, 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, but in recent years, the supply and demand of the scrap has been tight, and in particular, for the manufacture of high-grade products, there is a demand for an iron-containing raw material, such as reduced iron, as an alternative to scrap. It is growing.

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

  In such reduced iron production technology, the reduction reaction in the heating furnace is considered to proceed by direct reduction between the iron ore and the solid reducing agent. Since this direct reduction is an endothermic reaction, the reduction rate and productivity in the furnace are determined by the amount of heat supplied. 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. By the way, when the raw material supplied on the moving bed moves in the high-temperature atmosphere in the heating furnace, volatile matter is generated from the solid reducing agent in the raw material, and the solid reducing agent and iron oxide are contained in the furnace. Combustible CO gas is generated by the reaction. This CO gas can be an important heat source, and if it can be effectively used in the furnace, it is considered that it contributes to a reduction in the fuel ratio.

JP-A-63-108188

  The present invention has been made in order to solve the above-described various problems of the prior art, and the object of the present invention is to generate CO generated in the furnace without causing reoxidation of the reduced metal. It 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.

In the present invention, in order to achieve the above object, the result of intensive studies, the moving floor for moving the furnace, above the Taso paved solid reductant, the mixture of the metal-containing material and solid reducing agent The raw material is deposited and deposited, and while the metal-containing raw material moves in the heating furnace, it is heated and reduced by the combustion heat of the burner, and then melted at least once and then cooled to cool the reduced metal. In the manufacturing method, a main burner is disposed on the upper side of the heating furnace side wall from the heating / reduction zone to the melting zone, and below the main burner in the heating / reduction zone ,
When the interval obtained by dividing the distance between the heating / reducing zone entry side end and the melting zone exit side end by 10 is displayed as a dimensionless number (0 to 1.0), the interval from the heating / reduction zone entry end is 0. A moving direction position in the range of 2 to 0.5, and
When the interval obtained by dividing the distance between the center of the main burner and the surface of the raw material layer by 10 is represented by a dimensionless number (0 to 1.0), the distance from the surface of the raw material layer is within the range of 0.2 to 0.6. At the height position
It has been found that it is effective to employ a method for producing a reduced metal, which is characterized in that a combustion-supporting gas blowing nozzle is provided to burn a combustible gas.

Further, in the present invention, in the vicinity of the main burner described above may be arranged secondary combustion burner for supplying only the fuel and combustion assisting gas or combustion-supporting gas, the inlet side of the front Symbol heating and reduction zone It is considered that an exhaust gas duct at the top is a more effective solution.

  According to the present invention, by combusting excess combustible gas generated in the furnace, it can be used as a heat source for the heating / reduction zone (heating process), so that a complicated and expensive apparatus is not required. In addition, it is possible to reduce the fuel consumption rate.

  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 furnace body 10 of this rotary hearth furnace is divided into a pre-tropical zone 10a, a heating / reduction zone 10b, a melting zone 10c, and a cooling zone 10d in order from the raw material charging side. The moving floor 11 that moves continuously is disposed. 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 material, the carbon material is previously charged as a material for the flooring layer. A burner 13 is disposed on the upper side wall of the furnace body 10. The burner 13 includes a main burner 13a and, if necessary, a secondary combustion burner 13b. The metal-containing raw material such as iron ore on the moving bed 11 using the combustion heat of the burners 13a and 13b as a heat source. Is heated and reduced. 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, the operation of the rotary hearth furnace can be a system in which the atmospheric temperature in the furnace body 10 is maintained at about 1300 ° C. to recover unmelted reduced iron, while the temperature is increased to about 1500 ° C. It is also possible to use a system in which the metal is recovered after being melted and separated into metal and slag.

  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 mutual contact area, the reaction rate during reduction may be promoted and the processing time may be shortened. Such shortening of the processing time is desirable for improving productivity and reducing production cost.

  FIG. 2 is a circumferential longitudinal sectional view in which the rotary hearth furnace is linearly developed from the position of the raw material charging device to the product discharge device. The same reference numerals as those shown in FIG. 1 denote the same components. In this figure, among the charging devices, the raw material charging device is 14a, the reducing agent charging device is 14b, the main burner is arranged from the heating / reduction zone to the melting zone, and the secondary combustion burner 13b is required. Accordingly, the burner 13b is preferably disposed 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 reducing agent charging device 14b is used to supply a solid reductant for flooring into a lower layer, and a metal-containing substance is formed on the lower layer. The raw material 12 made of a mixture of the solid reducing agent is supplied from the raw material charging device 14a to become an upper layer (raw material 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 that is above the moving bed 11 from the heating / 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. The main burner 13a 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, if necessary, one or more secondary combustion burners 13b are installed on the side wall of the heating furnace together with the main burner 13a. The secondary combustion burner 13b is supplied with a combustion-supporting gas having secondary combustion air (or oxygen-enriched air) as a suitable example, that is, a gas for promoting combustion of surplus CO gas generated in the furnace. Is done. 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 heating / reduction zone to the melting zone and for secondary combustion. The oxygen supplied from air or the like burns CO gas generated by oxidizing the solid reducing agent on the hearth.
However, in the combustion using only the main burner 13a, complete combustion may not occur depending on the state of mixing of fuel and oxygen. Even if an amount of oxygen equal to the theoretical combustion oxygen amount is supplied, combustible gas such as CO gas is not generated. It may remain as it is.

  Therefore, in this case, it is preferable to arrange the secondary combustion burner 13b in the melting zone 10c to cause secondary combustion above the melting zone in which the reduced metal is generated and to effectively use the heat energy. . The secondary combustion burner 13b may also be disposed in the heating / reduction zone 10b.

  As described above, in the present invention, the combustion-supporting gas such as oxygen is supplied to the melting zone 10c and the heating / reduction zone 10b through the secondary combustion burner 13b in an amount more than necessary for the combustion of the fuel. The combustible gas generated in the melting zone 10c and the heat reduction zone 10b can be completely burned to make the furnace have a high temperature atmosphere. In this case, 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 for the fuel supplied from the main burner 13a and the secondary combustion burner 13b. It is preferable to supply an amount of oxygen corresponding to about 1.01 to 1.5 times the amount of oxygen. This theoretical combustion oxygen amount means the amount of oxygen necessary for combustible gas such as carbon and hydrogen in the fuel to burn completely to form combustion products such as carbon dioxide and water.

  The total amount of the combustion-supporting gas supplied to the melting zone 10c through the main burner 13a and the secondary combustion burner 13b is equivalent to 1.01 to 1.5 times the theoretical combustion oxygen amount of the fuel as an oxygen amount. The reason is as follows. The lower limit of 1.01 is because if the amount of oxygen is smaller than this, there is almost no effect of oxidizing the solid reducing agent on the hearth and generating CO gas, and therefore the temperature rise in the melting zone 10c cannot be expected. 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 the mobile hearth furnace, the amount of combustible gas such as volatile matter and CO gas expected as a heat source decreases from the latter stage of the heating / reduction zone 10b to the melting zone 10c. The reducing atmosphere near the hearth is reduced. Therefore, excessive injection of secondary combustion supporting gas into the zone using the secondary combustion burner 13b may cause reoxidation of the produced reduced iron. However, in the method of the present invention, since a floor layer made of a solid reducing agent is provided under the raw material layer, this situation does not necessarily occur.

  Next, FIG. 3 shows a conceptual diagram of the reaction in the heating / reduction zone, which is a hint for developing the present invention. As can be understood from this figure, the working environment of the method of the present invention is a large amount on this layer due to the reaction between the solid reducing agent and iron oxide embedded in the charged raw material, particularly in the reaction in the heating / reduction zone. It can be seen that a large amount of CO is generated, and most of it stays in that portion.

  Therefore, in the present invention, in order to effectively use a large amount of CO gas generated on the raw material layer in the heating / reduction process as heat energy, in addition to the main burner 13a and the secondary combustion burner 13b, the generation thereof A dedicated combustion-supporting gas blowing nozzle 13c for burning only CO gas is arranged. That is, in this heating / reduction zone, a large amount of CO gas is generated by the reaction (FeO + C → Fe + CO ↑) between the metal oxide in the raw material layer and the interior carbon material, but if this gas cannot be utilized effectively, This is because the exhaust gas is exhausted wastefully through the exhaust duct.

  As described above, in addition to the main burner 13a and the secondary combustion burner 13b, the reason for the purpose of disposing the combustion-supporting gas blowing nozzle 13c is that in the case of the main burner 13a, the combustion-supporting gas (air) is used. Even if it is supplied in excess, it is mainly used to completely fuel the fuel that is injected together, so that sufficient air is supplied to sufficiently burn the CO gas generated on the raw material layer in the heating / reduction zone. Because it cannot be said to do. The role of the secondary combustion burner 13b mainly has only an auxiliary role of the main burner 13a. Therefore, as described above, if the large amount of CO gas generated in the heating / reduction zone is to be used effectively, the former two burners 13a and 13b are not sufficient. A means of supply is required. In the present invention, in order to meet this requirement, the combustion-supporting gas blowing nozzle 13c is installed.

  However, according to the study by the present inventors, it has been found that the place where the combustion-supporting gas blowing nozzle 13c is disposed is not limited, and a suitable position must be selected and disposed. That is, the effect is low at a position that is too high in the furnace, and there is an effect of CO combustion at a position that is too low, but the powder loaded on the hearth blows up and is easily discharged out of the furnace together with the exhaust gas. This will increase the amount of dust. In addition, even if the reaction stage (the moving distance of the moving bed moving in the heating furnace, hereinafter referred to as “movement position”) is advanced too much or is not advanced, there is little effect.

  4, 5, and 6, the preferred position in the height direction of the combustion-supporting gas blowing nozzle 13 c is divided into 10 (1-1.0) distances from the raw material layer surface to the center position of the main burner. The relationship between the height position and the exhaust gas temperature and the amount of dust in the exhaust gas is expressed as the moving distance of the moving bed 0.1 (−), 0.4 (−), 0.7 ( -) Shows the results of the investigation in the three stages. As can be seen from these figures, the amount of dust flowing in the exhaust gas duct 18 affects the influence of the blown gas at a position below 0.2 (−) from the surface of the raw material layer at the level in the height direction in the heating furnace. This is not desirable because it increases rapidly. On the other hand, when the position from the surface of the raw material layer exceeds 0.6 (−), the exhaust gas temperature difference in the exhaust gas duct 18 rapidly decreases, and it is understood that the CO gas combustion efficiency is deteriorated. From these results, in the present invention, the level in the height direction of the combustion-supporting gas blowing nozzle 13c is in the range of 0.2 to 0.6, preferably in the range of 0.2 to 0.4.

  7, 8, and 9, the movement position of the combustion-supporting gas blowing nozzle 13 c in the furnace is divided into 10 (0 to 1) distances from the heating / reduction zone inlet side end to the melting zone outlet side end in the furnace. 0.0) to make it dimensionless, and the result of investigating the relationship between the moving position and the exhaust gas temperature and the amount of dust in the exhaust gas is the height level of this nozzle 0.1 (-), 0.5 (-) , 0.7 (−) three levels are displayed. From these figures, it was found that when the moving distance is in the range of 0.2 to 0.5, the combustion efficiency is particularly high and the amount of dust contained in the exhaust gas is small, which is preferable.

  In the present invention, when supplying the fuel and the combustion-supporting gas to the main burner 13a and the secondary combustion burner 13b disposed in the melting zone 10c, the above-described method is adopted, and pulverized coal, heavy oil is used. Etc. may be used in combination. The main burner 13a and the secondary fuel burner 13b to be used can be of any type such as a premix type or a postmix type.

Examples 1, 2, and 3 show the results of experiments for producing reduced iron using a rotary hearth furnace as shown in FIGS. Table 1 shows the operating conditions and results when reducing iron is produced using LNG as fuel and air and oxygen as fuel support.
Comparative Example 1 shows an example in which no flammable gas nozzle is arranged, and Comparative Examples 2 and 3 show examples in which the nozzle arrangement position (height position) is outside the conforming range of the present invention. Similarly, Comparative Examples 4 and 5 show examples in which the nozzle arrangement position (moving direction position) is at a position outside the applicable range of the present invention. In these examples and comparative examples, the main burner was burned under the conditions of an air-fuel ratio of 1.2 and an oxygen enrichment rate constant with respect to the amount of LNG used.
The amount of LNG used in the molten zone was constant at 75 m ³ _N / h, and the molten zone was blown in only with 180 m ³ _N / h for secondary combustion air (oxygen enrichment rate was constant). . On the contrary, the reduction zone was blown with only the combustion-supporting gas, the injection amount was constant 220 m ³ _N / h (the oxygen enrichment rate was constant), and the influence of the injection position of the combustion-supporting gas on the furnace temperature was investigated. The amount of LNG in the reduction zone was adjusted according to the effect of the combustion-supporting gas blowing nozzle so as to prevent the reduction zone temperature from deviating greatly.

  In Examples 1, 2, and 3, by supplying the combustion-supporting gas to a position where the amount of CO generated from the hearth is large, the CO gas generated from the raw material layer can be burned in the vicinity of the hearth as it is. It can be seen that the temperature difference (T35-T31) between the inside and the exhaust gas duct is larger than that of the comparative example. However, in Comparative Example 3, the effect of burning CO gas was greatly increased by arranging the nozzle height at a position of 0.1, but the blowing position was close to the raw material layer, so the powder on the raw material layer surface layer As a result, the amount of dust increased about four times and the load on the exhaust gas system increased.

  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 the reaction in a heating / reduction zone. It is a graph which shows the relationship between the combustion support gas blowing nozzle height in the movement position 0.4, exhaust gas temperature, and exhaust gas dust amount. It is a graph which shows the relationship between the combustion support gas blowing nozzle height in the movement position 0.7, exhaust gas temperature, and exhaust gas dust amount. It is a graph which shows the relationship between the combustion support gas blowing nozzle height in the movement position 0.1, exhaust gas temperature, and exhaust gas dust amount. It is a graph which shows the relationship between the movement position of combustion-supporting gas blowing in burner height 0.5, exhaust gas temperature, and exhaust gas dust amount. It is a graph which shows the relationship between the movement position of combustion support gas blowing in burner height 0.7, exhaust gas temperature, and exhaust gas dust amount. It is a graph which shows the relationship between the movement position of combustion-supporting gas blowing in burner height 0.1, exhaust gas temperature, and exhaust gas dust amount.

Explanation of symbols

10 Rotary hearth furnace 10a Pre-tropical zone 10b Heating / reduction zone 10c Melting zone 10d Cooling zone 11 Moving bed 12 Raw material 13a Main burner 13b Secondary combustion burner 13c Combustion gas injection nozzle 14a Raw material charging device 14b Solid reducing agent Charging device 15 Raw material discharging device 16 Cooling device 17 Solid reductant for flooring (layer)
18 Exhaust gas duct

Claims (3)

A moving floor for moving the furnace, above the Taso paved solid reductant, and charged raw material consisting of a mixture of metal-containing material and solid reducing agent is deposited, the metal-containing raw material in a heating furnace In the method of manufacturing reduced metal by heating and reducing with combustion heat of the burner while moving, and then cooling after melting at least once, in the side wall of the heating furnace from the heating and reduction zone to the melting zone A main burner is arranged at the top, and below the main burner in the heating / reduction zone ,
When the interval obtained by dividing the distance between the heating / reducing zone entry side end and the melting zone exit side end by 10 is displayed as a dimensionless number (0 to 1.0), the interval from the heating / reduction zone entry end is 0. A moving direction position in the range of 2 to 0.5, and
When the interval obtained by dividing the distance between the center of the main burner and the surface of the raw material layer by 10 is represented by a dimensionless number (0 to 1.0), the distance from the surface of the raw material layer is within the range of 0.2 to 0.6. At the height position
A method for producing a reduced metal, characterized in that a combustible gas is burned by disposing a combustion-supporting gas blowing nozzle.   2. The method for producing a reduced metal according to claim 1, wherein a secondary combustion burner that supplies only fuel and a combustion-supporting gas or only a combustion-supporting gas is disposed in the vicinity of the main burner.   The method for producing a reduced metal according to claim 1, wherein an exhaust gas duct is provided in an upper part on the entrance side of the heating / reduction zone.

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