JP5303727B2 - Method for producing reduced iron agglomerates for steelmaking - Google Patents

Description

  The present invention relates to a reduced iron agglomerated ore for steelmaking, which agglomerates granular reduced iron produced by reducing and roasting iron-containing dust and iron-containing sludge generated in an integrated steelworks and using it as a raw material for steelmaking. It relates to the manufacturing method.

  Currently, most of the iron produced is produced by the blast furnace method at an integrated steelworks. In the blast furnace method, ensuring air permeability in the furnace is important, so the iron raw material depends on sintered ore agglomerated with iron ore, and the carbonaceous material used as fuel and reducing agent is strongly caking. Relies on coke processed from charcoal.

  These raw fuels require high quality such as appropriate reducibility and reactivity in addition to the particle size that can guarantee the breathability in the furnace and the strength above a certain level. Become. In addition, these raw fuels are difficult to secure at a stable price because of a large price fluctuation due to social conditions. Furthermore, since it is necessary to install ancillary equipment such as coke production equipment and sintering equipment in addition to the blast furnace, equipment-related costs also increase.

  In addition, a large amount of energy is consumed inside the blast furnace to reduce the iron ore, which is an oxide, so that a large amount of carbon dioxide, which is a greenhouse gas, is generated.

  In the integrated steelworks, particulate iron-containing dust and iron-containing sludge (hereinafter also referred to as “iron-based dust and sludge” or simply “dust”) are generated in each manufacturing process. As described above, since raw materials and fuels used in the blast furnace are required to have high quality, dusts cannot be used as blast furnace raw fuel as they are. Therefore, in order to effectively use resources, dusts are used as raw materials for a sintering process for producing raw materials for blast furnaces.

  However, some dusts contain a zinc component, and if this zinc component is contained in a sintered ore product, the blast furnace is used to form furnace wall deposits and damage the furnace wall refractory. The operation will be adversely affected.

  Therefore, in order to avoid the occurrence of such problems in blast furnace operation, dezincing treatment by reduction roasting treatment is performed on dusts containing zinc components. In the reduction roasting treatment, the inside of the furnace is maintained at 1273K or more by charging dust and carbonaceous material into a high-temperature furnace, blowing air from one end of the furnace and burning the carbonaceous material, In this method, iron contained in dusts is reduced and recovered, and at the same time, fine powder containing ZnO is recovered together with exhaust gas generated by combustion. Typical examples of high-temperature furnaces that perform reduction roasting treatment (hereinafter also referred to as “reduction roasting furnaces”) include rotary kiln furnaces that rotate a cylindrical drum-shaped furnace body, and rotary hearth furnaces that rotate a disk hearth horizontally. Take as an example.

  In the reduction roasting furnace, it is advantageous that the reduced iron produced is finely divided from the viewpoint of enhancing the separation of zinc and iron contained in the dusts. Since the inside of the reduction roasting furnace is maintained in a high temperature reducing atmosphere, most of the iron oxide in the dust becomes metallic iron. If reduced iron containing metallic iron can be used as an iron-making raw material, a great merit can be expected from the viewpoint of securing the raw material at a low cost.

  In order to use this reduced iron in a blast furnace, it is necessary to agglomerate and to suppress pulverization of the agglomerated material in order to ensure air permeability in the furnace as described above. . Therefore, the agglomerates also require a certain level of particle size and strength.

  Therefore, conventionally, in order to use this reduced iron in a blast furnace, hot agglomeration has been carried out at a high temperature of about 973 K for the purpose of agglomerating the reduced reduced iron.

  FIG. 1 is a configuration diagram of a double roll briquette molding machine. An example of the agglomeration method is a method using a double roll briquette molding machine. The double roll briquette molding machine has a structure in which two cylindrical rolls 12 are horizontally adjacent. The roll 12 rotates in a direction from above to the adjacent point. A large number of molds (pockets) 25 serving as a form of agglomerated material (briquette) are provided on the outer peripheral surfaces of both rolls 12. The mold 25 is arranged so as to be synchronized between both rotating rolls 12. The outer peripheries of both rolls 12 do not contact each other, and there is a gap of about 2 mm even at an adjacent point that is the closest part.

  A raw material supply apparatus 10 that holds and supplies a raw material (in this case, powdered reduced iron obtained by reducing dusts) is disposed immediately above a portion where both rolls 12 are close to each other. The raw material 22 supplied from the raw material supply apparatus 10 is sent out in a state of being bitten from the upper side toward the closest part of both rolls 12 by the rotation of the roll 12. The raw material 22 enters the gap between the two rolls 12 and the mold 25, receives a compressive force from the two rolls 12 in the mold 25, and is discharged as a briquette 13 having a shape that combines the mold 25 and the gap.

  The agglomeration by hot briquette molding machine has few limitations on molding itself, but has a drawback that the cost of equipment and operation becomes enormous because it is necessary to combine molding equipment and cooling equipment.

  For example, Patent Document 1 discloses a device for agglomerating reduced iron with a briquette molding machine at a high temperature, but this device requires a very advanced technique in a method for cooling the device, and therefore, It is considered that the structure of the apparatus is also complicated.

  Further, when a cooling method in which reduced iron briquette in a high temperature state is introduced into water and rapidly cooled is adopted, residual stress and fine cracks are generated inside the briquette, so that even a slight impact is likely to break. As an improvement measure, it is conceivable to gradually cool the briquettes, but in this case, the cooling time becomes longer, the productivity is lowered, and the reduced iron is reoxidized in the process of cooling to room temperature in the atmosphere. The problem also occurs.

  In order to solve such a problem, Patent Document 2 discloses a method of slowly cooling reduced iron briquettes in a high temperature state using spray water, or after gradually cooling using gas and spray water in order. A method of rapid cooling has been proposed. As the slow cooling condition, it is said that a cooling rate of about 150 to 250 K / min at the surface temperature of the briquette is preferable. However, with this method, it is considered extremely difficult to control the cooling rate of the surface of the reduced iron briquette produced in large quantities.

  In addition, reduced iron is used in refractory and blast furnaces for the purpose of reduction and melting for producing metallic iron, even though it already contains a lot of metallic iron through a reduction process. Making a raw material for a sintering machine intended for raw material agglomeration for charging and use is extremely wasteful in terms of thermal energy required for the processing.

  On the other hand, steelmaking raw materials used in steelmaking furnaces, particularly converters or electric furnaces, are required to have low volatile dissipation properties. Since the inside of the steelmaking furnace is in a high temperature state, the powder existing in the raw material tends to volatilize and dissipate before melting in the molten steel. For this reason, granular reduced iron cannot be carried in in a steelmaking furnace.

  In addition, the powdered reduced iron causes troubles such as biting into the belt conveyor during the conveyance process. Therefore, it is required to agglomerate as briquettes having such a strength that they are not easily pulverized when they are put into a steelmaking furnace, even though they do not require a strength that can withstand use in a blast furnace.

  Therefore, the inventors previously agglomerated briquettes with a briquette molding machine in Patent Document 3 after cooling the powdered reduced iron produced in the reduction roasting furnace while keeping it cold. It was proposed to be used as a raw material for steelmaking used in steelmaking furnaces such as converters. As a raw material for steel making, the metallization rate is desirably 40% or more. The metallization rate is represented by metal content (mass%) / total iron content (mass%) × 100 (%). Moreover, since metallic iron is excellent in ductility, it can be agglomerated into briquettes having a certain degree of strength even if cold, as long as the reduced iron has a metallization rate of 40% or more. As described above, the briquette used as a steelmaking raw material in a steelmaking furnace such as a converter is not required to be as strong as that used in a blast furnace, so this method is considered a realistic method.

  However, as the crushing strength per briquette, at least 150 N / briquette is necessary. Such adjustment of briquette strength can be performed by adjusting the compression pressure of the roll of the briquette molding machine.

  However, applying a high compression pressure to the roll advances the wear on the roll surface and significantly reduces the life of the roll. In the operating cost of the agglomeration process by the double roll briquette molding machine, since the ratio of the maintenance cost of the roll is remarkably large, it is an important problem to improve the roll life. In addition, a double roll briquette molding machine capable of applying a high compression pressure requires the strength of the shaft portion of the roll and the wear resistance of the roll surface, and therefore the apparatus price is expensive. Therefore, it is required to produce briquettes with high strength at low compression pressure.

  Addition of a binder is mentioned as a method of improving the strength of a briquette with a low compression pressure.

  For example, in Patent Document 4, after adding a water-soluble binder to a steelmaking raw material containing at least 10% by mass or more of CaO and kneading with a kneader, the product is formed (agglomerated) by pressure molding, and then cured. Thus, a method for producing briquettes for steelmaking raw materials has been proposed. In this method, it is said that the strength of briquettes can be improved even in the cold, and the powder rate of raw materials carried into a steelmaking facility such as an electric furnace can be reduced.

  In this method, steel material dust, converter dust, scale, waste acid sludge, coke, and other various materials are individually cut out from the hopper, and each material is cut into a kneader and added to the binder and moisture. After kneading, a briquette is manufactured by pushing into a pressure type dumper made up of a pair of rollers rotating in opposite directions, each of which has a recess having a semi-diamond cross section, and the kneaded product is agglomerated.

  In the examples of Patent Document 4, lignin is used as a binder. However, since lignin is an organic / resin-based substance, it is thermally decomposed when it is introduced into a steelmaking furnace as a raw material for steelmaking. There is a risk of being emitted as greenhouse gases such as carbon dioxide and harmful gases.

  In particular, in a steelmaking furnace, a raw material, a binder, and molten pig iron may be supplied into the furnace with the furnace open. When hydrocarbons are contained in the binder, hydrocarbon-based materials are decomposed by thermal decomposition of the binder. There is a risk that harmful gases such as gas and CO gas, as well as flammable gases such as hydrogen, are generated and diffused to the workplace, and the working environment is significantly deteriorated. Therefore, it is preferable not to use organic or resin binders such as lignin as much as possible.

  Moreover, when the binder which consists of an inorganic substance is used, the amount of slag discharged | emitted from a steelmaking furnace increases. The discharged slag can be used as a roadbed material or the like, but since the demand for the roadbed material or the like is small, there is a high possibility that the increase in the discharged amount will be discarded. This disposal process is also expensive and not economical.

  When the binder itself is expensive, the ratio of the binder cost to the briquette manufacturing cost is also increased. A step of kneading the binder and the raw material for producing briquettes to be supplied to the machine is also necessary. Thus, when using a binder, the cost concerning briquette manufacture and slag processing increases very much.

  Furthermore, in the method proposed in Patent Document 4, the raw material that did not harden in the clustering machine, the briquette ear piece formed during agglomeration, or the briquette having a target particle size or less is classified by a vibration sieve. It is separated under a sieve with a machine, returned to the kneader and agglomerated again. On the other hand, raw materials such as briquettes remaining on the sieve are transported to a curing yard by a belt conveyor, naturally dried in the curing yard, and then transported to and put into an electric furnace.

  According to Patent Document 4, briquettes agglomerated in this way are screened by a classifier, dropped by a collision at the time of belt conveyor transfer when transported by a belt conveyor, and further carried by a heavy machine in a curing yard, There is a possibility of mechanical destruction. Moreover, during curing, the briquette may collapse due to expansion due to a hydration reaction between the moisture contained in the briquette and CaO and MgO in the raw material.

  For this reason, briquettes usually collapse at a considerable rate when they are put into a steelmaking facility such as an electric furnace, and the amount of powder in the raw material put into the steelmaking facility is large. When the amount of powder in the raw material charged into the electric furnace is large, the frequency of occurrence of troubles such as a drop in productivity due to shelves hanging in the furnace or outgassing increases. In order to avoid such troubles, briquettes in the curing yard are classified again with a classifier, and then the raw material on the sieve is carried into a steelmaking facility, and the raw material under the sieve is returned to the kneader. In Patent Document 4, in order to improve the strength of the briquette after agglomeration, when the raw material under sieving is returned to the kneader, the raw material under sieving is in the range of 10 to 40% by mass of the total raw material of the group. Propose to do.

  As described above, in the method described in Patent Document 4, classification using a sieve needs to be performed at two locations after formation and curing.

JP-T 2008-506041 (Claims and paragraphs [0078] to [0099], [0111] to [0113] and [0122] to [0126]) JP-A-6-316718 (claims, paragraphs [0006] to [0009] and [0028]) Japanese Patent Application No. 2008-170937 (claims, paragraphs [0025] and [0036]) JP 2008-81759 A (claims, paragraphs [0003], [0004], [0006], [0008], [0009], FIG. 1 and FIG. 3)

  As described above, if a binder is used to improve the strength of briquettes formed at a low compression pressure, harmful gases and the like are generated during steelmaking, causing problems in safety, the cost of the binder itself, and the kneading process There was also a problem that the operation cost was high. Moreover, in order to agglomerate again the powder particles generated from the briquettes after agglomeration, classification had to be performed at two locations.

  The present invention has been made in view of the above problems, and its purpose is to reduce the briquette strength even when formed at a low compression pressure, and to be inexpensively used safely in a steelmaking furnace. Method for producing reduced iron agglomerates for steel making, in which a briquette can be obtained, and classification for agglomerating powder particles generated after agglomeration can be carried out at one place The purpose is to provide.

  This invention is made | formed in order to achieve said objective, The summary exists in the manufacturing method of the reduced iron agglomeration for steel manufacture shown to following (1).

(1) Carbonaceous material is mixed with at least one of granular iron-based dust and sludge (dust) having an average composition and a zinc component content of 1.0% by mass or more and 10% by mass or less, and then reduced roasting. After processing to reduce iron, the reduced iron is classified into coarse reduced iron and granular reduced iron, and then the briquette forming raw material mainly using the granular reduced iron is agglomerated in a cold by a briquetting machine. In the manufacturing method of reduced iron agglomerate for steel making, which forms and forms reduced iron briquette, the water content of the briquette molding raw material is 0.5 mass% or more and less than 6 mass%, for steelmaking A method for producing reduced iron agglomerates.

  In order to complete the above invention, the present inventors examined a method for improving the strength of briquettes in place of the special binder proposed in Patent Document 4 above.

  As a result, by adding moisture to the granular reduced iron obtained by subjecting the above-mentioned dusts to reduction roasting, it has sufficient strength for steelmaking furnaces including converters. It has been found that it is possible to produce a reduced iron agglomerated mineral (hereinafter also referred to as “reduced iron briquette”).

  This is considered to be due to the following actions. When water is added to reduced iron, iron ions dissolve in the added water. At the same time, water molecules and oxygen molecules dissolved in the water are combined with iron ions and changed to iron hydroxide. This iron hydroxide binds the reduced iron particles constituting the reduced iron briquette and improves the strength of the reduced iron briquette. Finally, iron hydroxide reacts with oxygen molecules dissolved in moisture to become iron oxide.

  Further, the reduced iron obtained by the reduction roasting treatment includes slag components such as calcia and alumina, but these slag components become hydraulic substances and may improve the strength of the reduced iron briquette.

  In any case, simply adding water to the reduced iron obtained by the reduction roasting treatment of the dust strengthens the bonds between the particles constituting the reduced iron briquette obtained by agglomeration, and rolls Even if the compression pressure is low, a strong briquette can be produced. Therefore, the roll life of the briquette molding machine can be improved.

  However, as the moisture content of the reduced iron briquettes increases, the energy required to evaporate the moisture in the steelmaking furnace increases accordingly. Thus, the addition of moisture contributes to improving the strength of the reduced iron briquette, but increases the amount of heat compensation required in the steelmaking furnace, and is not preferable from the viewpoint of furnace operation. Therefore, in this invention, the appropriate range of the moisture content of reduced iron briquette was prescribed | regulated as 0.5 mass% or more and less than 6 mass%.

  Moreover, said invention is a method of manufacturing reduced iron briquette from the high zinc dusts generated in an ironworks. Therefore, management of the zinc component content contained in dusts is important in defining the components of reduced iron briquettes.

  In a steelmaking furnace, operational problems often occur when the zinc content of reduced iron briquettes exceeds 1.0% by mass. Since the dezincification rate in reduction roasting can ensure 90% or more, in order to make the zinc component content of reduced iron 1.0 mass% or less, the zinc component content of dusts should be 10 mass% or less. It is enough. On the other hand, it is not necessary to perform a dezincing process for dusts having a zinc component content of 1.0 mass% or less. Therefore, in the present invention, the proper range of the zinc content of dusts is defined as 1.0% by mass or more and 10% by mass or less. And since dusts are mixed and reduced to roast, the zinc component content does not need to be uniform before reducing torrefaction, and may be partially biased. An appropriate range was defined.

  In the invention described in (1) above, the briquette molding raw material may be obtained by spraying water directly onto the granular reduced iron.

  When using briquette molding raw material with powdered reduced iron added with only water, the target moisture content of the briquette molding raw material is simply sprayed on the powdered reduced iron before being supplied to the briquetting machine. It can be controlled within the range, and the same effect as when stirring with a mixer can be expected.

  In this case, a kneader for kneading the reduced iron and the binder is also unnecessary. In addition, the cost of the binder is unnecessary, and there is no generation of toxic gas or flammable gas derived from the binder-containing material when it is put into the steelmaking furnace, and there is no increase in slag generated in the steelmaking furnace as compared with the conventional case.

  Also, in the invention described in (1) above, from the viewpoint of suppressing the amount of moisture brought into the steelmaking furnace, as the briquette molding raw material, the powdered reduced iron is mixed with a steelmaking auxiliary raw material containing moisture. The mixture may contain 0.5% by weight or more and less than 6% by weight of water.

  Here, the “steel making auxiliary material” is a steel raw material under 5 mm sieving in a steelmaking furnace operation or a steelmaking material under 5 mm sieving introduced for the purpose of component adjustment, melting point lowering of the melt, etc. Among the dust, slag, sludge, scale, etc. generated in any process, it means a material under a 5 mm sieve that can be used in a steelmaking furnace for the purpose of adjusting the iron raw material or components or lowering the melting point of the melt. Such a steelmaking auxiliary material can also be used in a steelmaking furnace by agglomerating.

  When a steelmaking auxiliary material having a low moisture content is used, adjustment to increase the moisture content of the briquette molding material can be easily performed by adding moisture. However, in order to reduce the moisture content of the steelmaking auxiliary material, it is necessary to perform heating, drying, and the like, which is difficult as compared with the case where the moisture content is increased. In addition, it is desirable to avoid introducing moisture in the steelmaking furnace operation from the viewpoint of reducing necessary thermal compensation and preventing steam explosion and the like. Therefore, it is desirable to use a steelmaking auxiliary material having a low water content in a conventional steelmaking furnace operation as usual, and the steelmaking auxiliary material used in the present invention already contains water, particularly 1% by mass or more of water. It is desirable to use one containing In addition, since it is desirable to avoid the introduction of moisture in the steelmaking furnace operation as described above, the moisture content of the briquette molding raw material is set so that the moisture content of the formed briquette does not affect the steelmaking furnace operation. Is preferably less than 6% by mass.

  If steelmaking auxiliary materials containing moisture are mixed with granular reduced iron, the amount of moisture brought into the steelmaking furnace is increased compared to the case where steelmaking auxiliary materials are directly used for steelmaking operation as usual. Without reducing the strength of the reduced iron briquette. Also in this case, the cost of the binder is unnecessary, and there is no generation of various gases due to the binder-containing material and no increase in slag generated in the steelmaking furnace. Furthermore, there is no possibility that harmful components and impurities are mixed in the steel produced in the steelmaking furnace.

  In the invention described in (1) above, it is preferable that the reduced iron briquette is allowed to stand for at least 2 hours after molding. This is because the molded reduced iron briquette is improved in strength by standing still. The standing is performed in a place (space for standing) that is off the transport line of the reduced iron briquette so as not to be exposed to moisture such as rain as much as possible.

  The reduced iron briquette immediately after being discharged from the briquetting machine does not have sufficient strength, and if it is supplied to the sieve classifier in that state, it is damaged and the yield of reduced iron briquette is reduced. Therefore, the stationary space is preferably located immediately after being discharged from the briquette molding machine.

  The crushing strength of the reduced iron briquette required for introducing the steelmaking furnace is at least 150 N / briquette as described above. However, in order to suppress re-pulverization during sieving classification and to maintain a high yield of reduced iron briquettes, it is preferable to be 200 N / briquette or more. This strength can be achieved by standing for at least 2 hours after agglomeration.

  There is a possibility that a part of the reduced iron briquette is collapsed and pulverized before the reduced iron briquette discharged from the briquette molding machine is moved to the stationary space and left still. However, if the process flow is to be supplied to a sieve classifier after standing, the powder is reliably separated from the reduced iron briquette before being put into the steelmaking furnace, even if the sieve classifier is provided only at one location. Can be removed.

  Further, the reduced iron briquette may not be left immediately after being discharged from the briquette molding machine but may be left still after being classified by a sieve classifier. However, in this case, there is a high possibility that reduced iron briquettes whose strength is not improved will be pulverized at the time of classification, so the yield of reduced iron briquettes is reduced. In addition, the reduced iron briquettes classified by sieving may be moved to a stationary space, and part of the reduced iron briquettes may be collapsed and pulverized before being left still. The converter raw material (steel making raw material) is required to have a low volatile dissipative property, and pulverized reduced iron cannot be brought into the steel making furnace. Therefore, in order to remove the generated powder, it is desirable to classify again after standing.

  In this specification and the like, the “zinc component” means zinc contained in the form of metal or compound in dusts.

  “Powder and granular” means powders, granules or a mixed state thereof having a particle size of 5 mm or less.

  “Iron-based dust” and “iron-based sludge” mean dust and sludge having an iron content of 20% by mass or more, such as metallic iron and iron oxide, respectively.

  “Reduction roasting treatment” means that the object to be treated such as ore and dust is heated to a temperature below the melting point, causing the object to be treated and reducing gas, carbon, etc. to interact with each other, causing a reduction reaction, It means a process of reducing the object to be processed.

  “Agglomeration” means forming ore, dust, reduced iron or the like into a lump containing briquettes for the purpose of adjusting particle size or improving quality.

  According to the method for producing reduced iron agglomerated ore for steelmaking of the present invention, after mixing carbonaceous material with at least one of powdered iron-based dust and sludge containing zinc, reduced iron by reduction roasting treatment, after classification, Since the powdered reduced iron is used as the main raw material and the moisture content is briquette-molded under the condition of 0.5 mass% or more and less than 6 mass%, Unfavorable zinc components can be removed, and high-strength reduced iron briquettes can be produced under low briquetting molding pressure without using a binder. Thereby, the reduced iron briquette which can be used safely without generating harmful gas in a steelmaking furnace can be supplied at low cost.

  Moreover, by setting it as the process flow supplied to the sieve classification apparatus after standing, even if the sieve classification apparatus is provided only at one place, before putting it into the steelmaking furnace, the powder is separated from the reduced iron briquette, Can be removed.

  As described above, the method for producing reduced iron agglomerates for steelmaking according to the present invention is at least one of granular iron-based dust and sludge having an average composition and a zinc component content of 1.0% by mass or more and 10% by mass or less. In addition, after mixing the carbonaceous material, reduction roasting treatment is performed to obtain reduced iron, and after the reduced iron is classified into coarse granular reduced iron and granular reduced iron, briquettes using the granular reduced iron as a main raw material In the method for producing reduced iron agglomerate for steel making, the raw material is cold agglomerated with a briquette molding machine and the reduced iron briquette is molded. The water content of the briquette molding raw material is 0.5% by mass or more 6 It is a manufacturing method of the reduced iron agglomerate for steel manufacture characterized by being less than the mass%. Hereinafter, the method of the present invention will be described in more detail.

  FIG. 2 is an example of a process flow of the method for producing reduced iron agglomerate for steelmaking according to the present invention. As shown in the figure, a reduction roasting furnace raw material 2 made of a mixture of dusts and carbon materials containing a zinc component is subjected to reduction roasting treatment in a reduction roasting furnace 1, and zinc oxide-containing fine powder 3, Separated into reduced iron 4. Since the reduction roasting furnace 1 is maintained in a reducing atmosphere by CO generated by the combustion of the carbonaceous material, the reduction roasting reaction of the reduced roasting raw material 2 proceeds. As the reduction roasting furnace 1, a rotary kiln can be used. The zinc component content of the dusts constituting the reduction roasting furnace raw material 2 is 1.0% by mass or more and 10% by mass or less as an average composition.

  The reduced iron 4 produced in the reduction roasting furnace 1 is classified by the sieving classifier 6 into coarse granular reduced iron 4a that is a sieved product 20 and granular reduced iron 4b that is a sieved product 21.

  The sieve refined product 20 is directly supplied to the steelmaking furnace 7. On the other hand, if the unsieved product 21 is supplied to the steelmaking furnace 7 in a high temperature state as it is, it will be easily volatilized and dissipated without being melted in the molten steel, which may cause troubles such as biting into the belt of the conveyor during conveyance. Therefore, the sieved product 21 is added with the additive 8, mixed by the mixer 9, supplied to the briquette molding machine 11 by a predetermined amount by the raw material cutting device 10, and agglomerated cold by the briquette molding machine 11, It is discharged as reduced iron briquette 13a.

  The additive 8 is for improving the strength of the reduced iron briquette 13a, and at least one of moisture and a steelmaking auxiliary material containing moisture can be used. The additive 8 may contain a steelmaking byproduct waste material. The addition amount of the additive 8 is adjusted so that the moisture content of the mixture of the sieved product 21 and the additive 8, that is, the briquette molding raw material is 0.5 mass% or more and less than 6 mass%.

  The mixer 9 is used to sufficiently mix the unsieved product 21 and the additive 8. However, in the case where the additive 8 is only water, it is possible to simply spray the unsieved product 21 without using the mixer 9.

  As the briquetting machine 11, the double roll briquetting machine shown in FIG. 1 can be used.

  In the present invention, since the additive 8 uses at least one of moisture and a steelmaking auxiliary raw material containing moisture, harmful gases and flammable gases are generated in the steelmaking furnace 7 as in the case of using a special binder. There is nothing to do.

  In addition to the reduced iron briquette 13a, the discharge 13 from the briquette molding machine 11 includes reduced iron 13b in a powder form. Therefore, these discharged substances are returned to the sieve classification device 6 in a mixed state, and are classified into reduced iron briquette 13a which is a sieved product 20 and granular reduced iron 4b which is a sieved product 21. At this time, since the reduced iron briquette 13a is pulverized while being conveyed from the briquette molding machine 11 to the sieving classifier 6, the generated powder is also classified as the unsieved product 21, so that the powder is put into the steelmaking furnace 7. Can be suppressed.

  The sieved product 20 is directly supplied to the steelmaking furnace 7, and the sieved product 21 is supplied to the briquette molding machine 11 through the mixer 9 and the raw material cutting device 10. At this time, you may supply to the briquette molding machine 11 with the granular reduced iron 4b which classified the reduced iron 4 produced | generated in the reduction roasting furnace 1. FIG.

  Further, the discharge 13 from the briquette molding machine 11 may be classified by the sieve classification device 6 together with the reduced iron 4 generated in the reduction roasting furnace 1. In this case, the sieved product 20 is a mixture of reduced iron briquette 13a and coarse granular reduced iron 4a, and the sieved product 21 is granular reduced iron 4b supplied from the reduction roasting furnace 1 and the granular reduced powder passed through the briquette molding machine 11. It is a mixture with iron 13b.

  Since the discharge from the briquette molding machine 11 is improved in strength when left standing, it is preferably left still before returning to the sieve classifier 6. As shown in FIG. 1, the standing is performed in a standing space 15 that is a place away from the briquette transport line so as not to be exposed to moisture such as rain as much as possible. Since the reduced iron briquette 13 a immediately after being discharged from the briquette molding machine 11 does not have sufficient strength, the stationary space 15 is preferably located in the vicinity of the briquette molding machine 11.

  By leaving the discharge from the briquette molding machine 11, the strength of the reduced iron briquette 13a can be improved, and the possibility of breakage and re-pulverization when classifying by the sieve classifier 6 is reduced. The yield of reduced iron briquette 13a can be improved.

  Thus, by adopting a process flow for classifying the discharged material from the briquette molding machine 11 after standing, classification by the sieve classifying device 6 can be performed at one place.

  The crushing strength of the reduced iron briquette 13a is preferably 150 N / briquette or more in order to be charged into the steelmaking furnace, and more preferably 200 N / briquette or more from the viewpoint of suppressing re-pulverization during sieving classification. A crushing strength of 200 N / briquette or more can be obtained by allowing the reduced iron briquette 13a to stand for at least 2 hours.

  Further, the reduced iron briquette may be put in a bag or the like, loaded in a transport vehicle, and transported over a long distance to a remote place. At this time, the reduced iron briquette stored in the lower part of the bag or the like may be pulverized. Therefore, it is preferable to extend the standing time to further improve the strength in order to suppress powdering.

  The discharged material from the briquetting machine 11 may be left still after being classified by the sieving classifier 6, but in this case, the reduced iron briquette 13a whose strength is not improved can be pulverized during classification. Since the property is high, the yield of reduced iron briquette 13a decreases.

  In order to confirm the effect of the present invention, the following production test of reduced iron agglomerates for steel making was performed, and the properties of reduced iron briquettes, which were obtained reduced iron agglomerates for steel making, were evaluated.

1. Manufacturing apparatus In order to agglomerate a mixture of granular reduced iron and an additive to form reduced iron briquettes, the double roll briquette molding machine shown in FIG. 1 was used.

The roll diameter of the briquette molding machine is 410 mm, and the effective roll width is 96 mm. On the outer peripheral surface of the roll, a total of 144 egg-shaped molds serving as molds for reduced iron briquettes are provided in three rows in the width direction and 48 rows in the circumferential direction. The mold dimensions are 30 mm long, 25 mm wide, and 6.8 mm deep, and the reduced iron briquette produced is designed to have a volume of about 5.7 cm ³ . The maximum rotation speed of the roll is 7 rpm.

2. Samples Table 1 shows the main base of the dry reduced powder and additive used in this test on a dry basis, and Table 2 shows their particle size composition. In Table 1, T.W. Fe means the total iron content. Fe means metallic iron. As the powdered reduced iron, one produced by a reduction roasting furnace made of a rotary kiln was cooled to room temperature and used as a 5 mm sieved product. Further, the powdered reduced iron was dried before agglomeration so that the water content was 0.1% by mass or less.

  As the additive, moisture, or converter sludge or steelmaking slag containing moisture was used. The moisture content of the converter sludge was 9% by mass, and the moisture content of the steelmaking slag was 5% by mass.

  As shown in Table 1, the converter sludge used contains iron with high quality and can be used as an iron raw material. However, as shown in Table 2, since it is granular like reduced iron, it was mixed with granular reduced iron and agglomerated for use as an auxiliary material for steelmaking in a steelmaking furnace.

  Moreover, the used steel-making slag was agglomerated by mixing a granular material mainly composed of calcia and alumina with granular reduced iron. In general, steel slag is used as a melting point lowering material for converter slag, but lump is not used.

  Powdered reduced iron and additives were mixed at eight blending ratios shown in Table 3, and stirred with a mixer, then supplied to a double roll briquette molding machine to mold reduced iron briquettes. The moisture content of each reduced iron briquette is less than 0.1% by mass in sample 1 which is a comparative example, 6.0% by mass in sample 4, and in samples 2, 3 and 5-8 which are examples of the present invention. It was 0.5 mass% or more and 4.0 mass% or less. In samples 5 to 8, moisture was not added, and the moisture content was adjusted by moisture contained in the steelmaking auxiliary material (converter sludge or steelmaking slag).

  The reduced iron briquette was formed cold with a roll gap of 2.6 mm and a rotational speed of 7 rpm.

5. Test results Table 3 shows the test results together with the mixing ratio of the samples. Evaluation items were compression linear pressure and crushing strength. Here, the compression linear pressure is a value obtained by converting the compression load applied to the entire roll per roll effective width. In addition, the crushing strength was defined as the load when the reduced iron briquette immediately after molding was subjected to a vertical load from above and destroyed.

5.1. Effect of Water Addition FIG. 3 is a graph using the test results shown in Table 3, with the horizontal axis representing the water content and the vertical axis representing the crushing strength. In the case of 100% reduced iron (sample 1) to which no moisture was added, the crushing strength was 88 N / briquette, which was a low value that was less than the steelmaking furnace required strength (150 N / briquette). However, by adding moisture, or converter sludge or steelmaking slag containing moisture, the crushing strength was improved and the effect of moisture addition was confirmed. However, when the moisture content is increased to 6.0% by mass (Sample 4), the reduced iron briquette adheres to the roll during molding of the reduced iron briquette, and a normal briquette molding machine can be operated. There wasn't. The crushing strength of the sample 4 was measured for a normally molded one of the reduced iron briquettes molded under such circumstances.

  FIG. 4 is a graph using the test results shown in Table 3, with the horizontal axis representing the compression linear pressure and the vertical axis representing the crushing strength. However, it is determined that the data is not valid for sample 4, and is not described.

  In the case of 100% reduced iron (sample 1) with a compression linear pressure of 26.5 kN / cm, the crushing strength was 88 N / briquette, which was a low value that was less than the steelmaking furnace required strength. In the case of 100% reduced iron (sample 2) with a compression linear pressure of 44.1 kN / cm, the crushing strength was 155 N / briquette, which is a high value that satisfies the required steelmaking furnace strength. Thus, in order to make the crushing strength more than the steel furnace required strength with 100% reduced iron, it was necessary to set the compression linear pressure to about 44.1 kN / cm or more.

  On the other hand, in the samples (samples 3 to 9) to which moisture, or converter sludge or steelmaking slag containing moisture was added, although the compression linear pressure was less than 44.1 kN / cm, the crushing strength Was greater than 150 N / briquette. From this, it was found that by adding moisture, reduced iron briquette having the required strength in a steelmaking furnace can be obtained even at a low compression pressure.

5.2. Effect of stillness The reduced iron briquette obtained by using granular reduced iron (sample 3) with only moisture added and having a water content of 2.0% by mass is allowed to stand by changing the standing time. The crushing strength was measured. Table 4 shows the results of this static test.

  FIG. 5 is a graph using the test results shown in Table 4, with the horizontal axis representing the standing time and the vertical axis representing the crushing strength. As shown in Table 4 and FIG. 5, the crushing strength after standing for 2 hours exceeded a preferable value of 200 N / briquette in order to suppress re-pulverization during sieving classification. After that, the crushing strength increased, and at 284 hours, it became 2.5 times or more immediately after agglomeration. However, after 284 hours, the change in crushing strength was saturated.

  In addition, powdered reduced iron (sample 3) having a moisture content of 2.0% by mass added, was left in the atmosphere for 20 days after the moisture content was adjusted, and the iron metalization rate was determined. investigated. Table 5 shows the content of total iron (T.Fe) and metallic iron (M.Fe) in the granular reduced iron containing moisture before and after standing, and the value of the metallization rate of iron. The metallization rate (%) is a value defined by (M.Fe (mass%)) / (T.Fe (mass%)) × 100 (%), and is used as an index of the oxidation state of iron. it can. In addition, it represents that oxidation is progressing, so that the value of a metalization rate is low.

  As shown in Table 5, although the metallization rate slightly decreased before and after being left on the 20th, the oxidation state of the iron component was negligible for the operation of the steelmaking furnace. Also, from this result, if the water content is less than 6% by mass, even if water is added and then left in the air, the metallization rate decreases little, and the metallization rate necessary as a raw material for steelmaking It is estimated that 40% (mass%) or more can be maintained. Therefore, if the moisture content of the briquette molding raw material is less than 6.0% by mass, the oxidation state is considered to be a level with no problem in steelmaking furnace operation.

  According to the method for producing reduced iron agglomerated ore for steelmaking of the present invention, after mixing carbonaceous material with at least one of granular iron-based dust and sludge containing a zinc component, reduced iron is obtained by reduction roasting treatment, and after classification Since the powdered reduced iron is used as the main raw material and the moisture content is briquette-molded under the condition of 0.5% by mass or more and less than 6% by mass, the components in the steelmaking raw material supplied to the steelmaking furnace such as a converter and an electric furnace As a result, it is possible to remove an undesirable zinc component, and it is possible to produce reduced-strength iron briquettes with a low briquetting pressure without using a binder. Moreover, by setting it as the process flow supplied to the sieve classification apparatus after standing, even if the sieve classification apparatus is provided only at one place, before putting it into the steelmaking furnace, the powder is separated from the reduced iron briquette, Can be removed.

  Therefore, the method for producing reduced iron agglomerate for steelmaking of the present invention is a steelmaking that can be safely used in a steelmaking furnace from granular iron-based dust generated in large quantities at an integrated steelworks by using simple equipment. It can be widely applied as an economical method capable of producing reduced iron agglomerates (reduced iron briquettes).

It is a block diagram of a double roll type briquette molding machine. It is an example of the process flow of the manufacturing method of the reduced iron agglomerate for steel manufacture which concerns on this invention. It is a graph which shows the relationship between the moisture content of reduced iron briquette, and crushing strength. It is a graph which shows the relationship between the compression linear pressure and crushing strength of reduced iron briquette. It is a graph which shows the relationship between the stationary time of reduced iron briquette and crushing strength.

Explanation of symbols

1: Reduction roasting furnace 2: Reduction roasting furnace raw material 3: Zinc oxide-containing fine powder 4: Reduced iron 4a: Coarse granular reduced iron 4b: Powdered granular reduced iron 6: Sieve classification apparatus 7: Steel making furnace 8: Additive 9: Mixer 10: Raw material cutting device 11: Briquette molding machine 12: Roll 13: Emission 13a: Reduced iron briquette 13b: Powdered reduced iron 15: Space for stationary 20: Fine product 21: Unfinished product 22: Briquette molding raw material 25 : Mold (pocket)

Claims (4)

After mixing carbonaceous materials with at least one of powdered iron-based dust and sludge having an average composition and a zinc component content of 1.0% by mass or more and 10% by mass or less, reduction roasting treatment is performed to obtain reduced iron. The reduced iron is classified into coarse reduced iron and granular reduced iron, and then the briquette forming raw material mainly composed of the granular reduced iron is agglomerated cold by a briquette forming machine, In the manufacturing method of the reduced iron agglomerate for steel making,
A method for producing a reduced iron agglomerate for steel making, wherein the briquette forming raw material has a water content of 0.5% by mass or more and less than 6% by mass.   The method for producing reduced iron agglomerates for steel making according to claim 1, wherein the briquette forming raw material is obtained by spraying water directly onto the granular reduced iron.   The briquette molding raw material is obtained by mixing the powdered reduced iron with a steelmaking auxiliary raw material containing moisture, and the moisture content of the mixture is 0.5% by mass or more and less than 6% by mass. The manufacturing method of the reduced iron agglomerate for steel manufacture of Claim 1 or 2.   The method for producing a reduced iron agglomerate for steel making according to any one of claims 1 to 3, wherein the reduced iron briquette is left to stand for at least 2 hours after molding.

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