JP2012153948A - Method for producing agglomerate for raw material for blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an agglomerate for the raw material for a blast furnace, in which an agglomerate for the raw material for a blast furnace having high strength can be produced even if coal having low softening-melting properties or hardly having softening-melting properties and high crystallization water-containing iron ore are combinedly used.SOLUTION: Powdery coal A having the maximum fluidity log MF of 0.3 to 2.5, containing a volatile matter VM of ≥10 mass% and containing ≥0.3 mass% sulfur S and powdery iron ore B containing crystallization water LOI of ≥3 mass% are subjected to cold mixing by a mixer 1 to be a mixed raw material C, thereafter, the mixed raw material C is heated to a heating temperature T1 of 350 to 550°C by a heating device 2, the heated raw material C' is hot-molded at a molding temperature T2 (=T1-ΔT) in which a temperature reduction ΔT from the heating temperature T1 lies within 20°C by a hot molding machine 4 to produce a molding D, and the molding D is subjected to heating treatment at 560 to 750°C for ≥10 min in an inert gas atmosphere by a heat treatment device 5 to produce an agglomerate E for the raw material for a blast furnace.

Description

  The present invention relates to a method for producing an agglomerated material for blast furnace raw material by hot forming, which can be used as a charging raw material for a blast furnace, and in particular, a combination of a high crystal water-containing iron ore and a fine non-caking coal blast furnace. The present invention relates to a method suitable for producing an agglomerated material.

  The applicant of the present invention is a conventional carbonaceous material-internal cold by hot-forming a mixture of fine ore and softening-melting carbonaceous material for the purpose of using as raw materials for vertical furnaces such as blast furnaces and cupolas. We have developed an agglomerate of carbonaceous material that can provide high strength without adding a binder such as cement, such as pellets.

  Such an agglomerated carbonaceous material agglomerate can be produced, for example, by a process as shown in FIG. That is, the powdered iron ore B is heated to 400 to 800 ° C. by the rotary kiln (raw material heating means) 12, and the powdered coal A having the softening and melting property (fluidity) is separately separated from the rotary dryer (carbon material heating means) 11. After drying at a temperature of less than 250 ° C. at which no softening and melting occurs, these heated pulverized coal A (hereinafter also simply referred to as “coal”) and pulverized iron ore B (hereinafter simply referred to as “iron ore”). Is also used as a heated mixture C ′ at 250 to 550 ° C., which is a temperature at which the powdered coal A is softened and melted. The heated mixture C ′ is hot-molded by a twin-roll type molding machine (molding means) 14 to form a briquette, and if necessary, the residual tar content is removed by a degassing tank (heat treatment means) 15 so that the interior of the carbonaceous material is contained. Agglomerated product E is obtained (see Patent Document 1).

  By the way, in the said patent document 1, in the Example, log MF (MF: highest fluidity | liquidity) highly soft meltable coal (refer coal A and B of Table 1) exceeding 3 and LOI (crystal water content) ) Is used in combination with 6% by mass or more of high-crystal water-containing iron ore (see ores A and D in Table 2), a high-strength vertical agglomerate is disclosed. However, high soft melting coal with a log MF of more than 3 is limited in raw material selection, so coal with lower softening melting property or little softening melting property and iron ore with high crystal water content Development of a technique capable of producing a high-strength agglomerate for blast furnace raw material that can be used as a charging raw material for the blast furnace has been desired.

JP 2007-2111296 A

  Therefore, the present invention can produce a high-strength agglomerate for a blast furnace raw material even when used in combination with coal having low softening meltability or little softening meltability and iron ore containing high crystal water. It aims at providing the manufacturing method of the agglomerated material for blast furnace raw materials.

  In order to find a solution to the above problems, the inventors first changed the combination of the coal type and the iron ore brand, and changed the mixing and heating methods to various hot forming methods. The effect on the strength of the agglomerated material for blast furnace (hereinafter also simply referred to as “agglomerated material”) was investigated.

  As a result, surprisingly, after low-flowing or almost non-flowing coal containing a predetermined amount of volatile matter and sulfur and iron ore containing a predetermined amount of water of crystallization are cold mixed, It was found that the strength of the agglomerates for blast furnace raw materials is improved by heating the mixed raw material to the hot forming temperature and hot forming it, and then heat-treating it at a temperature higher than the hot forming temperature (see below) See example).

  As described above, the inventors assume that the strength of the agglomerated material for blast furnace raw material is expressed based on the following hypothesis even when coal having low or hardly caking properties is used.

That is, it is a hot forming temperature of 350 to 550, which is a mixed raw material composed of coal containing a predetermined amount of volatile matter and sulfur and iron ore containing a predetermined amount of crystal water, although it is low fluidity or almost non-flowable. When heated to ° C., pyrolysis gas containing H ₂ S is generated together with hydrocarbon components when the volatile matter is vaporized (devolatilized) from coal containing volatile matter and sulfur.

On the other hand, from iron ore containing crystallization water (goethite; FeO (OH)), crystallization water (H ₂ O) is dissociated and removed by the chemical reaction formula shown in the following formula (1), and is extremely fine. Active hematite (Fe ₂ O ₃ ) having a significantly increased specific surface area is formed by forming nanopores.

2FeO (OH) → Fe ₂ O ₃ + H ₂ O Formula (1)

When H ₂ S in the pyrolysis gas comes into contact with the reaction site of active hematite (Fe ₂ O ₃ ) whose specific surface area has increased remarkably, the pilot reaction (Fe _{1 -X} S) is generated.

Fe ₂ O ₃ + H ₂ S → Fe _1-x S + H ₂ O Formula (2)

Further, methane (CH ₄ ) in the pyrolysis gas is gas-reformed with water vapor (H ₂ O) derived from crystal water removed from the iron ore, and H ₂ is converted by a chemical reaction represented by the following formula (3). Generate.

_{CH 4 + H 2 O → 3H} 2 + CO ... Equation (3)

When the mixed raw material heated to the hot forming temperature is immediately hot pressed, the iron ore particles and the coal particles come into close contact with each other. Then, the equation (2) pyrrhotite _{(Fe 1-x} S) produced by chemical reaction are known to act as a catalyst for coal liquefaction reaction (e.g., see Japanese Patent Laid-Open No. 11-228972) For this reason, the surface layer of coal is hydrogenated and gelled due to the presence of hydrogen (H ₂ ) generated by the chemical reaction of the above formula (3). In addition, when liquefying the whole coal, ultra high pressure hydrogen such as a temperature: 350 to 500 ° C. and a hydrogen partial pressure of 7 to 20 MPa is required (see [0037] of the above-mentioned JP-A-11-228972). In the present invention, since only the surface layer of coal needs to be gelled, as long as the temperature is secured at 350 to 550 ° C., the gelation reaction can be sufficiently caused even with partial pressure of hydrogen lower than normal pressure. it is conceivable that.

  In this way, by hot pressing the coal whose surface layer has been gelled and the iron ore whose specific surface area has significantly increased due to the phase transformation from goethite to hematite due to dissociation of crystal water, The gel-like coal surface layer portion functions as a binder for binding the iron ore particles and the coal particle main body, and a strong molded product is obtained. Then, by heat-treating the molded product at a temperature higher than the hot forming temperature after hot forming, the volatile matter remaining in the formed product is vaporized and removed sufficiently, and the heating up to hot forming is performed. The strength of the molded product (agglomerated material for blast furnace raw material) is further increased by further solidifying the reformed coal structure by condensation polymerization and rearrangement.

  The inventors have further studied based on the above findings and have completed the following invention.

  The invention described in claim 1 is a powdery state in which the Gieseler maximum fluidity MF is 0.3 to 2.5 in log MF, the volatile content VM is 10 mass% or more, and the sulfur S is 0.3 mass% or more. A mixing step of mixing coal and powdered iron ore containing 3% by mass or more of crystal water LOI to make a mixed raw material, and heating this mixed raw material to a heating temperature T1 of 350 to 550 ° C. to make a heated raw material A heating step, a hot forming step in which this heated raw material is hot formed at a forming temperature T2 to form a molded product, and this molded product is heat-treated at 560 to 750 ° C. for 10 minutes or more in an inert gas atmosphere to be a blast furnace And a heat treatment step for forming an agglomerate for raw material, and a temperature drop ΔT (= T1−T2) from the heating temperature T1 to the molding temperature T2 is set within 20 ° C. It is a manufacturing method of a chemical compound.

  The invention according to claim 2 is a powdery state in which the Gieseler maximum fluidity MF is 0.3 to 2.5 in log MF, the volatile content VM is 10 mass% or more, and the sulfur S is 0.3 mass% or more. A mixing step of mixing coal and powdered iron ore containing 3% by mass or more of crystal water LOI to form a mixed raw material, a granulating step of granulating all or part of the mixed raw material into pellets, A heating step of heating the pellet and the remainder of the mixed raw material to a heating temperature T1 of 350 to 550 ° C. to form a heated raw material, and a hot forming step of hot forming the heated raw material at a molding temperature T2 to form a molded product And a heat treatment step of heating the molded product at 560 to 750 ° C. for 10 minutes or more in an inert gas atmosphere to form an agglomerated material for a blast furnace raw material, from the heating temperature T1 to the molding temperature T2. Temperature drop ΔT (= T1- 2) a method of manufacturing blast furnace feedstock agglomerates, characterized in that the within 20 ℃.

  Invention of Claim 3 makes the required time (DELTA) t (= t2-t1) from the end time t1 of the said heating process to the start time t2 of the said hot forming process within 2 minutes. It is a manufacturing method of the agglomerated material for blast furnace raw materials.

  Invention of Claim 4 provided the cooling process which cools the said agglomerate for blast furnace raw materials to 300 degrees C or less in the atmosphere of oxygen concentration 5 volume% or less after the said heat processing process. It is a manufacturing method of the agglomerated material for blast furnace raw materials of any one of these.

  Invention of Claim 5 is a manufacturing method of the agglomerated material for blast furnace raw materials of any one of Claims 1-4 in which the said powdered coal mix | blends 2 or more types of coal.

According to the present invention, unlike the above-described prior art (the manufacturing method described in Patent Document 1), powdered coal having low softening meltability or little softening meltability but containing a predetermined amount of volatile matter and sulfur. And powdered iron ore containing a predetermined amount of water of crystallization are mixed in a cold state, and then heated to a heating temperature of 350 to 550 ° C., and the temperature decrease from the heating temperature is within 20 ° C. By performing hot forming at a temperature and further heat-treating at 560 to 750 ° C., which is higher than the above heating temperature, the pulverized iron ore after crystal water dissociation by H ₂ S in pyrolysis gas generated from pulverized coal As a result of being tightened and the surface layer portion of the powdered coal being hydrogenated and gelled by the catalytic action to act as a binder, a high-strength agglomerate for blast furnace raw material can be produced.

It is a flowchart which shows schematic structure of the manufacturing apparatus of the agglomerated material for blast furnace raw materials based on one Embodiment of this invention. It is a flowchart for demonstrating the procedure of the laboratory test of an Example. It is a graph which shows the relationship between the sulfur S content in a powder iron ore, and the tensile strength of the agglomerated material for blast furnace raw materials. It is a figure which shows the microstructure of the agglomerated material for blast furnace raw materials. It is a figure which shows the result of having identified the compound in the agglomerated material for blast furnace raw materials by micro part X-ray diffraction. It is a graph which shows the relationship between the added amount of pillowite and the tensile strength of a tablet. It is a graph which shows the relationship between the crystal water LOI content in a powder iron ore, and the tensile strength of the agglomerated material for blast furnace raw materials. It is a graph which shows the relationship between the temperature fall part from heating temperature to molding temperature, and the tensile strength of the agglomerated material for blast furnace raw materials. During the step temperature increase of coal is a graph showing the time course of H _{2 S} in the temperature and the exhaust gas of the coal. It is a graph which shows the relationship between the required time from the completion | finish time of a heating to the shaping | molding start time, and the tensile strength of the agglomerated material for blast furnace raw materials. It is a graph which shows the relationship between heat processing time and the tensile strength of the agglomerated material for blast furnace raw materials. It is a graph which shows the differential thermal analysis result of a tablet. It is a flowchart which shows schematic structure of the manufacturing apparatus of the carbonaceous material agglomerated material in a prior art.

(Embodiment)
FIG. 1 shows a schematic configuration of an apparatus for producing an agglomerated material for a blast furnace raw material according to an embodiment of the present invention. In addition, the same code | symbol was used for the substance in common with FIG. 11 demonstrated by the said prior art.

  As coal, the Gieseler maximum fluidity MF is 0.3 to 2.5 (preferably 0.3 to 1.0) in log MF, and the volatile content VM is 10 mass% or more (preferably 12 mass% or more). , Sulfur S containing 0.3% by mass or more (preferably 0.4% by mass or more, more preferably 0.5% by mass or more), for example, non-coking coal used in pulverized coal for blast furnace tuyere injection Anthracite with a low content of volatile matter (less than 10% by mass) is not suitable.

  The Gieseler maximum fluidity MF was set to 0.3 to 2.5 (preferably 0.3 to 1.0) in log MF. If the maximum fluidity is too low, the gelation of the coal surface layer does not occur sufficiently. On the other hand, if the maximum fluidity is sufficiently high, the above prior art may be applied, and the present invention does not need to be applied. The reason why the volatile matter VM is contained in an amount of 10% by mass or more (preferably 12% by mass or more) is that in the mechanism based on the above hypothesis, it is essential that a considerable amount of hydrogen for hydrogenation of coal is generated. Because there is. In addition, it is assumed that the sulfur S is contained in an amount of 0.3% by mass or more (preferably 0.4% by mass or more, more preferably 0.5% by mass or more) in the mechanism based on the above hypothesis. This is because it is essential to generate a quantity. The upper limit (allowable value) of the sulfur S content in the powdered coal is not particularly required from the viewpoint of securing the amount of pyrotite produced, but is naturally determined from the viewpoint of limiting the total amount of S charged to the blast furnace. Is done. This upper limit (allowable value) varies depending on the allowable amount of the total S charge to the blast furnace, the blending ratio of the agglomerated material for the blast furnace raw material in the blast furnace raw material, etc. What is necessary is as follows.

  Moreover, as iron ore, what contains 3 mass% or more of crystal water LOI (preferably 5 mass% or more, more preferably 7 mass% or more), for example, high crystal water ore, maramamba ore, limonite ore, or the like is used. However, hematite ore or magnetite ore with low crystal water content (less than 3% by mass) is not suitable.

  The reason why the crystal water LOI content is 3% by mass or more (preferably 5% by mass or more, more preferably 7% by mass or more) is that it is essential that a considerable amount of active hematite is generated in the mechanism based on the above hypothesis. Because there is.

  The coal and iron ore may be pulverized if necessary, for example, in a powder form of about -100 μm for coal and about −200 μm for iron ore.

[Mixing process]
The powdered coal A and the powdered iron ore B thus adjusted in particle size are cut out in a mass ratio of 20:80 to 50:50 and mixed with the mixer 1 to obtain a mixed raw material C.

  The reason why the blending ratio of the powdered coal A and the powdered iron ore B is set in the range of 20:80 to 50:50 is as follows. That is, when there are too few compounding of powdered coal A, the total amount of the gelatinized surface layer part which acts as a binder will run short, and the intensity | strength of an agglomerate will fall. On the other hand, if the amount of powdered coal A is too large, cracks are likely to occur in the coal structure in the agglomerated material after molding due to expansion and contraction of the coal accompanying heating and cooling, and the strength of the agglomerated material is also reduced. The iron content in the agglomerated product becomes too low and the meaning as an iron raw material is lost.

At the time of this mixing, it is necessary to avoid heating the powdered iron ore B to 250 ° C. or higher before mixing with the powdered coal A as in the prior art. That is, when the powdered iron ore B containing crystal water is heated to 250 ° C. or higher, the active hematite having very fine nanopores is generated by dissociating and removing the crystal water before mixing with the powdered coal A. End up. Even if heated again after mixing with pulverized coal A in this state, the nanopores become coarse and become micropores in the meantime, and the hematite loses its activity. This is because water vapor (H ₂ O) does not occur and the gas reforming reaction does not occur, so H ₂ also does not occur, and hydrogenation reaction to the coal surface layer, that is, gelation of the coal surface layer does not proceed. . However, for the purpose of removing adhering moisture, drying at less than 250 ° C., preferably 180 ° C. or less is not a problem because the crystal water does not separate.

Moreover, it is necessary to avoid heating the powdered coal A to 250 ° C. or higher as in the case of the above-described conventional technology. That is, when the powdered coal A containing volatile matter is heated to 250 ° C. or higher, the volatile matter is vaporized and H ₂ S and CH ₄ are removed. However, since the above-described pyrotiteization reaction and gas reforming reaction do not occur, gelation of the coal surface layer portion does not proceed. However, drying at a temperature lower than 250 ° C., preferably 180 ° C. or lower for the purpose of removing adhering moisture is not a problem because volatile components do not vaporize.

  As the mixer 1, a known drum mixer or the like can be used.

[Heating process]
The mixed raw material C is heated to a heating temperature T1 of 350 to 550 ° C., preferably 400 to 500 ° C., with a heating device (for example, an externally heated rotary kiln) 2 to obtain a heated raw material C ′.

  Thus, after mixing the powdered coal A having a low softening meltability or little softening meltability but containing a predetermined amount of volatile matter and the powdered iron ore A containing a predetermined amount of crystal water, a predetermined temperature is mixed. It is considered that the powdered coal A, which has essentially no softening and melting properties, is heated by the above-mentioned hypothesis and the surface layer is gelled to acquire a function as a binder.

  The reason for setting the heating temperature T1 to 350 to 550 ° C. (preferably 400 to 500 ° C.) is that if the heating temperature T1 is too low, the vaporization of the volatile matter VM from the pulverized coal A is also caused by the crystals from the pulverized iron ore B. This is because the vaporization of water LOI is slow, and the gelation of the surface layer portion of the powdered coal A is delayed. On the other hand, if the heating temperature T1 is too high, the powdered coal A does not stay in the gelled state of the surface layer portion, This is because the coal structure further progresses to condensation polymerization / rearrangement and solidifies, and in any case, the function as a binder is not sufficiently exhibited.

  The reason why the external heating type is employed as the heating device 2 is that when heated by the internal heating type heating device, the mixed raw material C is rapidly heated and bursting (explosion) is likely to occur.

  The exhaust gas discharged from the heating device 2 may contain a tar content generated from the pulverized coal A, which may condense and adhere in the exhaust gas system and block the piping and the like. In order to prevent this, although not shown in the figure, for example, a combustor is installed in the exhaust gas discharge duct of the heating device 2 to burn and decompose tar components and gasify, or a burner is installed in the exhaust duct. What is necessary is just to employ | adopt the method etc. which carry out partial combustion of the volatile matter (hydrocarbon gas) in waste gas, hold | maintain at the temperature which a tar part does not condense, and convey to a waste gas processing apparatus.

[Hot forming process]
The mixed raw material (heating raw material) C ′ heated to the heating temperature T1 by the heating device 2 is discharged from the heating device 2 and then is hot-molded by a hot molding machine (for example, a twin roll molding machine for hot molding) 4. The briquette (molded product) D is pressure-molded.

  Here, it is generally desirable that the heated raw material C ′ heated by the heating device 2 is pressure-molded by the hot molding machine 4 before the temperature is lowered as much as possible. It is installed as close as possible to the machine 4.

  However, in an actual facility, a certain distance is required between the heating device 2 and the hot forming machine 4 due to the arrangement of each device, etc., and therefore, from the heating device 2 to the hot forming machine 4. It is necessary to transfer the heating raw material C ′ through a transfer duct or the like. Further, in actual operation, there is a difference in processing speed between the heating device 2 and the hot molding machine 4, so that the heated raw material C ′ discharged from the heating device 2 is installed in the hot molding machine 4. For example, the surge hopper 3 needs to temporarily hold it before entering.

  For this reason, when the heating raw material C ′ heated to the heating temperature T 1 in the heating device 2 is discharged from the heating device 2 and reaches the hot forming machine 4, the heating raw material C ′ is heated due to heat loss from the transfer duct and the surge hopper 3 on the way. The temperature decreases (temperature decrease ΔT), and the actual molding temperature T2 in the hot molding machine 4 is a temperature (T2 = T1−ΔT) that is lower than the heating temperature T1 by ΔT.

This temperature drop ΔT needs to be within 20 ° C. (preferably within 15 ° C., more preferably within 10 ° C.). When the temperature drop ΔT exceeds 20 ° C., the speed of coal devolatilization reaction, which is an endothermic reaction, is greatly reduced during pressure molding, and the amount of H ₂ S generated in association with this devolatilization reaction is also reduced. This is because the amount of pyrotite represented by the above formula (2) is greatly reduced due to the drastic reduction, gelation of the coal surface layer is suppressed, and the strength of the molded product D is reduced.

  As specific means for setting the temperature drop ΔT within 20 ° C. (preferably within 15 ° C., more preferably within 10 ° C.), for example, the thickness of the heat insulating material of the transfer duct or the surge hopper 3 is increased to enhance the heat insulating property. It is conceivable that a heater is installed in the transfer duct or the surge hopper 3 to keep it warm.

Further, the end point of the above-described heating process (that is, the discharge point from the heating device 2; hereinafter, also referred to as “the end point of heating”) from t1 to the start point of the hot-forming step (that is, to the hot forming machine 4). Achieving time point; hereinafter, also referred to as “molding start time point”) It is preferable that the required time Δt (= t2−t1) until t2 is within 2 minutes (further within 1.5 minutes, particularly within 1 minute). If it takes too much time from the end of heating to the start of molding, the nanopores of active hematite generated by crystal water dissociation at the time of heating become coarse and become micropores, the activity of hematite is reduced, and the H ₂ S due to the above temperature decrease is reduced. This is because, together with the reduction in the generation amount, the formation of the pilotite represented by the above formula (2) is further suppressed.

  As specific means for making the required time Δt within 2 minutes (further within 1.5 minutes, particularly within 1 minute), for example, shortening the transfer duct as much as possible, or reducing the amount of the heating raw material C ′ held in the surge hopper 3 as small as possible. It is possible to do.

[Heat treatment process]
By charging the molded product D into a heat treatment apparatus (for example, a shaft furnace) 5 adjusted to a temperature range of 560 to 750 ° C., which is higher than the heating temperature range in the heating step, and performing heat treatment for 10 minutes or more, The volatile matter remaining in the molded product D is vaporized and removed sufficiently, and the condensation polymerization / rearrangement of the coal structure is promoted and solidified. As a result, the obtained agglomerated material E obtains high strength, and when charged in the blast furnace and heated, the coal is no longer softened and the strength of the agglomerated material E is maintained. Thus, a large amount of tar is not generated, and troubles such as sticking of tar to the exhaust gas system of the blast furnace can be prevented.

[Cooling process]
Since the molded product D heat-treated in the shaft furnace 5 may be ignited or burnt if discharged into the atmosphere while being hot, an oxygen concentration of 5% by volume or less (for example, nitrogen) in the lower part of the shaft furnace 5 or a cooler (not shown). It is desirable to cool it to 300 ° C. or lower in an atmosphere of gas or combustion exhaust gas after cooling, etc. before discharging.

  The molded product D after degassing is sieved with a screen 6, and the sieved powder F is returned to the mixer 1 and reused if possible, while the mass E on the sieve has a desired high strength. Collected as agglomerated material for blast furnace raw material.

(Modification)
In the said embodiment, although the mixed raw material C which consists of pulverized coal A and pulverized iron ore B was shown as the heating raw material C 'by heating as it is, without granulating (mixing process-> heating process), All or a part of the mixed raw material C is granulated into pellets by adding an appropriate amount of water with a granulator (for example, a disk-type pelletizer), and the pellets and the remainder of the mixed raw material C are heated to heat the raw material C ′. (Mixing process → granulation process → heating process). Thus, by heating after pelletizing all or part of the mixed raw material C, the granulated individual pellets were in close contact with the pulverized coal A and the pulverized iron ore B. Since it is in a state, by heating this, the surface layer portion of the powdered coal A is sufficiently gelled, and when pressed by the hot molding machine 4, individual pellets are crushed, and the gelled portion inside Is extruded to the surface, and the entire heating raw material C ′ is integrated, and a high-strength briquette (agglomerated product) E is obtained after cooling.

  The average particle size of the pellets is preferably 1 to 15 mm, more preferably 1.5 to 10 mm, and particularly preferably 2 to 5 mm. Here, the average particle size of the pellets is obtained by sieving the pellets having a particle size distribution for each particle size range, and weighted average the representative diameters of each particle size range by the mass ratio of the pellets present in each particle size range. This is the calculated value. If the particle size of the pellet is too small, the mass ratio of the powdered carbonaceous material A and the powdered iron ore B in each pellet tends to be non-uniform, while if the particle size of the pellet is too large, it is heated to the center of the pellet. Depending on the size of the molded product D, the total mass of pellets entering the pocket of the molding machine is likely to vary during molding, and bursting (explosion) occurs during heating. This is because the possibility of causing a decrease in strength of the agglomerate E increases. When the molding machine used in the hot molding process is a twin roll type molding machine, the average particle size of the pellets satisfies the above regulations, and more than the roll gap of the twin roll type molding machine, And it is preferable to make it below the pocket depth of this twin roll type molding machine. By making the average particle size of the pellets equal to or larger than the roll gap, the biting property to the molding machine is improved, the molding pressure can be increased, and by making the pocket depth or less, An apparent density can be made high and it leads to the strength improvement of the agglomerate E. As the granulator, a known disk type pelletizer or drum type pelletizer can be used.

  Moreover, in the said embodiment, as the powdered coal A and the powdered iron ore B, although the example using a single brand was shown, you may mix | blend and use 2 or more types of brands. In this case, it is natural that the composition and properties after blending should satisfy the conditions defined in claim 1 above. The log MF of the powdered coal A after blending is obtained by weighted averaging the log MF of each brand (each coal type) by their mass ratio. Moreover, when reusing the above sieve powder F, the sieve powder F may be regarded as one of a plurality of brands of iron ore and handled in the same manner.

  Moreover, although the example which uses only a powdered iron ore and powdered coal as a mixing raw material was shown in the said embodiment in a mixing process, you may contain powdery flux (limestone, dolomite, etc.) further. In this case as well, the flux may be regarded as one of a plurality of brands of iron ore and handled in the same manner as described above.

  Moreover, in the said embodiment, although the example using a twin roll type molding machine was shown as a hot molding machine, you may use an extrusion molding machine.

  In order to confirm the effect of the present invention, the following laboratory tests were conducted.

〔Test method〕
As a laboratory test method, the following procedures (1) to (6) were performed (see FIG. 2).

(1) Powdered coal and powdered iron ore are blended in a mass ratio of 40:60 so that the total mass is about 8 g and stirred in a mixer (vertical cylindrical container with stirring blades). The mixed raw material is prepared by cold mixing under the conditions of blade rotation speed: 180 rpm and mixing time of 1.0 min.
(2) Next, a doughnut mold with an external heater is stacked in two upper and lower stages, and a heating device configured so that the temperature can be controlled independently in the upper and lower stages, and the central cylindrical space (inner diameter) of the upper mold side 20 mm) is filled with the mixed raw material and heated to a predetermined temperature (heating temperature T1).
(3) Thereafter, the heating raw material is transferred to the lower mold adjusted to a temperature (forming temperature T2) lower by a predetermined temperature ΔT than the heating temperature T1 of the upper mold, and the upper mold is removed for a predetermined time. After the elapse of time, the heated raw material is pressed with a molding load of 2000 kgf (1 kgf≈9.8 N) with a pressure pin to produce a tablet (molded product).
(4) A tablet (molded product) is taken out from the lower mold, and is quickly charged into a heating furnace heated to a predetermined temperature under N ₂ flow and heat-treated for a predetermined time.
(5) Take out the tablet (molded product) after the heat treatment and cool to room temperature with N ₂ .
(6) According to the concrete tensile strength test method (JIS-A1113), the crushing strength of the tablet (agglomerated material for blast furnace raw material) is measured, and the tensile strength is calculated.

〔sample〕
The particle size of the powdered coal was about ₅₀ μm at d ₅₀ (50% average diameter, the same shall apply hereinafter), and the particle size of the powdered iron ore was about 25 μm at d ₅₀ . And the mixing raw material was made into the compounding ratio (constant) of powdered iron ore: powdered coal = 60: 40 (mass ratio).

〔Test results〕
[Test 1] (Effect of sulfur S content in powdered coal)
In order to investigate the influence of sulfur S content in the powdered coal on the tensile strength of the tablet (agglomerated material for blast furnace raw material), the following tests were carried out.

  As powdered iron ore, only Australian high crystal water ore (LOI: 10.38% by mass) is used, and as powdered coal, volatile matter VM is 10 to 35% by mass, log MF is 0 to 0.3, Using five types of coal with a sulfur S content in the range of 0.1 to 0.7% by mass, each of these coals is blended in a simple manner, and tablets (agglomerated for blast furnace raw material) are formed using the above test method. The crushing strength was measured and the tensile strength was calculated. The heating temperature T1 is 430 ° C., the molding temperature T2 is 430 ° C. (that is, the temperature drop ΔT = T1-T2 = 0 ° C.), the time required Δt from the end of heating to the molding start is 0 min, the heat treatment temperature is 650 ° C. The heat treatment time was constant at 20 min.

The test results are shown in FIG. 3 and FIG. As shown in FIG. 3, regardless of the type of coal, between coals with the same log MF, the tensile strength of the tablet (agglomerated material for blast furnace raw material) increases as the sulfur S content in the coal increases. It is clear that it rises linearly. Further, from the figure, when the log MF of coal is 0.3 or more and the sulfur S content in the coal is 0.3 mass% or more, the tensile strength is 23 kgf / cm, which is sufficient strength as a charge for blast furnace. ^It can be seen that ² or more (corresponding to 200 kgf or more in terms of crushing strength of a briquette having a volume of about 6 cm ³ suitable for a blast furnace raw material) can be obtained.

  FIG. 4 shows the result of observing the microstructure of the tablet after heat treatment (agglomerated material for blast furnace raw material). (A) is a coal with a high softening and melting property corresponding to the prior art (log MF = 2.59). ), And (b) is an example of the present invention using coal (log MF = 0.3) having almost no softening and melting property. As shown in the figure, in the reference example of (a), it is clear that most of the coal particles once melted, whereas in the present invention example of (b), most of the coal particles are square. In other words, there is no evidence of melting of the entire particle. Nevertheless, it was estimated that only the surface layer of the coal particles once gelled because the tablet after heat treatment of the present invention example exhibited a predetermined strength.

  Therefore, the tablet after heat treatment (agglomerated material for blast furnace raw material) was analyzed by micro X-ray diffraction to identify the compound. The result is shown in FIG. (A) is a comparative example in which the sulfur S content in coal is less than 0.2% by mass, and (b) is an example of the present invention in which the sulfur S content in coal exceeds 0.6% by mass. As shown in the figure, in the comparative example (a), the diffraction peak of pyrotite (Fe1-xS) was not visually recognized, and the presence of pyrotite was not observed in the tablet. On the other hand, in the present invention example of (b), since the diffraction peak of pyrotite (Fe1-xS) is clearly visually recognized, it was confirmed that pyrotite was present in the tablet. (In addition, although it identified also about the tablet before heat processing of the example of this invention, it confirmed that the pilotite did not exist.) From this, in this invention example, coal surface layer part is a pilotite. The belief that gelation occurred due to the catalytic action of was increased.

[Test 2] (Effect of added amount of pillow tightness on tablet tensile strength)
Therefore, in order to verify the gelation effect of the coal surface layer of the pilotite from another point of view, unlike the test 1 described above, the reagent pilotite is added to the powdered coal alone without using the powdered iron ore. The other conditions were the same as in Test 1 above, and heating, hot forming, and heat treatment were performed to produce tablets, and the influence of the added amount of pillowite on the tablet tensile strength was investigated.

  The test results are shown in FIG. As shown in the figure, it is apparent that the tensile strength of the tablet increases as the amount of added pilotite increases compared to the case where no added pilotite is added.

  By comprehensively judging the results of Test 1 and Test 2, it can be said that the existence of pyrotite has been substantially verified to have a catalytic action on the gelation of the coal surface layer.

[Test 3] (Effect of crystal water LOI content in powdered iron ore)
Next, in order to investigate the influence of the crystal water LOI content in the powdered iron ore on the tensile strength of the tablet (agglomerated material for blast furnace raw material), the following test was carried out.

  That is, as pulverized coal, only coal for blast furnace tuyere injection (volatile matter VM: 15.4 mass%, log MF: 0.4, sulfur S content: 0.45 mass%) is used, and pulverized iron ore is used. As the stone, Australian high crystal water ore (LOI: 10.38% by mass), limonite ore (LOI: 14.0% by mass), and the Australian high crystal water ore in air at 650 ° C. in advance Using the one that was heated for 2 hours and completely removing the crystal water, each of these iron ores was blended as a simple substance and heated under the same conditions as in Test 1 above, followed by hot forming → heat treatment to produce a tablet. The effect of the crystal water LOI content in the powdered iron ore on the tensile strength of the iron was investigated.

  The test results are shown in FIG. As shown in the figure, there is a positive correlation between the crystal water LOI content in the powdered iron ore and the tensile strength of the tablet (agglomerated material for blast furnace raw material), and in order to obtain a predetermined tablet strength It was confirmed that the crystal water LOI content above a certain level is necessary.

Here, the reason why the tablet strength is reduced when using powdered iron ore from which crystal water has been removed in advance is considered as follows. That is, when the mixed raw material is heated to the heating temperature, the active hematite generated during the prior removal of the crystal water is reheated over a long period of time, so that the nanopores in the active hematite become coarse and become micropores. The activity is lost, the amount of pyrotite produced is reduced, and since there is no generation of water vapor (H ₂ O) derived from crystal water, there is no production of H ₂ due to gas reforming reaction. It is thought that this does not happen.

[Test 4] (Influence of heating temperature)
Next, in order to investigate the influence of the heating temperature on the tensile strength of the tablet (agglomerated material for blast furnace raw material), the following test was carried out.

  That is, only Australian high crystal water ore (LOI: 10.38% by mass) is used as the powdered iron ore, and blast furnace tuyere blowing coal P (volatile matter VM: 23.1) is used as the powdered coal. Mass%, log MF: 0.6, sulfur S content: 0.51 mass%) and semi-strongly caking coal Q (volatile matter VM: 28.8 mass%, log MF: 2.47, sulfur S content: 0.54% by mass) each of the two types of coal is used in a simple manner, the heating temperature is changed variously, and the other conditions are the same as in Test 1 above, and a tablet is produced. The impact was investigated.

The test results are shown in Table 1 below. As shown in the same table, when the heating temperature is outside the range of 350 to 550 ° C. defined in the present invention, the tablet tensile strength does not reach the target strength of 23 kgf / cm ² , whereas the heating temperature is the present invention. In the range of 350-550 degreeC to prescribe | regulate, it turns out that the tensile strength of a tablet can achieve target strength 23kgf / cm < ² > or more.

[Test 5] (Effect of temperature drop from heating temperature to molding temperature)
In order to investigate the influence of the temperature drop ΔT = T1-T2 from the heating temperature T1 to the molding temperature T2 on the tensile strength of the tablet (agglomerated material for blast furnace raw material), the following test was performed.

  That is, Australian high crystal water ore (LOI: 10.38% by mass) is used as the powdered iron ore, and coal for blast furnace tuyere (volatile matter VM: 23.3% by mass) is used as the powdered coal. , Log MF: 0.6, sulfur S content: 0.4 mass%), heating temperature T1 is constant at 430 ° C., only molding temperature T2 (that is, only temperature decrease ΔT) is variously changed, and others The tablets were prepared under the same conditions as in Test 1 above, and the effect of temperature decrease from the end of heating to the start of molding on the tensile strength of the tablets was investigated.

The test results are shown in FIG. As shown in the figure, as the temperature decrease ΔT increases, the tensile strength of the tablet decreases. When the temperature decrease ΔT exceeds 20 ° C., the target tensile strength 23 kgf / cm ² cannot be stably achieved. .

Here, in order to grasp the degree of decrease in the amount of H ₂ S generated due to the temperature drop after the completion of heating, using an infrared image furnace, only the blast furnace coal for injecting blast furnace tuyere is used as a sample under heating with Ar gas. The H ₂ S concentration in the exhaust gas was measured when the temperature was sequentially raised (step temperature rise) while alternately repeating heating interruption. The result is shown in FIG. As shown in the figure, when there is heat input to the coal during heating, the H ₂ S concentration in the exhaust gas rapidly increases, whereas when heating is interrupted and the heat input to the coal is turned off. It can be seen that the H ₂ S concentration in the exhaust gas rapidly decreases. From this, it was confirmed that when the temperature drop after the heating of the heated raw material was excessive, the amount of H ₂ S generated decreased drastically.

[Test 6] (Effect of required time from the end of heating to the start of molding)
In order to investigate the influence of the required time Δt from the end of heating to the start of molding on the tensile strength of the tablet (agglomerated material for blast furnace raw material), the following test was conducted.

  That is, Australian high crystal water ore (LOI: 10.38% by mass) is used as the powdered iron ore, and coal for blast furnace tuyere (volatile matter VM: 25.3% by mass) is used as the powdered coal. Log MF: 0.7, sulfur S content: 0.5 mass%), heating temperature T1 is constant at 430 ° C., molding temperature T2 is constant at 415 ° C. (that is, temperature decrease ΔT = 15 ° C. constant) Only the time required from the end of heating to the start of molding is variously changed. Other conditions are the same as in Test 1 above, and a tablet is produced. The temperature drop from the end of heating to the start of molding affects the tensile strength of the tablet. The impact was investigated.

The test results are shown in FIG. As shown in the figure, it can be seen that as the required time Δt increases, the tensile strength of the tablet decreases, and when the required time Δt exceeds 2 min, the target tensile strength of 23 kgf / cm ² cannot be stably achieved.

[Test 7] (Effect of heat treatment time)
In order to investigate the effect of heat treatment time on the tensile strength of tablets (agglomerated materials for blast furnace raw materials), the following tests were conducted.

  That is, Australian high crystal water ore (LOI: 10.38% by mass) is used as the powdered iron ore, and coal for blast furnace tuyere (volatile matter VM: 24.2% by mass) is used as the powdered coal. Log MF: 0.8, sulfur S content: 0.5% by mass), only the heat treatment conditions were variously changed, and other conditions were used to produce tablets under the same conditions as in Test 1 above, and the tablet tensile strength The effect of heat treatment time on the effect was investigated.

The test results are shown in FIG. In the same figure, changes in H ₂ S concentration in the furnace exhaust gas during heat treatment are also shown. As shown in the figure, it can be seen that the tensile strength of the tablet increases as the heat treatment time is extended, and that the tablet tensile strength can achieve the target strength of 23 kgf / cm ² or more after the heat treatment time of 10 minutes or longer. Since the generation of H ₂ S from the tablet is completed within 10 minutes, the development of the strength of the tablet in the heat treatment process is based on the gelation of the coal surface layer by hydrogenation reaction using pyrotite as a catalyst. Rather, it is presumed that the coal structure that had been modified in the preceding heating process and molding process was solidified by condensation polymerization and rearrangement.

[Test 8] (Influence of cooling temperature)
Finally, after the heat treatment of the tablet (molded product), the tablet (molded product) after being heat-treated at 600 ° C. and 800 ° C. in order to confirm to what extent the tablet (molded product) can be safely taken out into the atmosphere is checked with N _2. Differential thermal analysis was performed in the atmosphere and in the atmosphere.

The measurement results are shown in FIG. As shown in the figure, heat generation is not observed in the N ₂ atmosphere, but in the air atmosphere, although the sample mass does not change much from around 300 ° C., the heat generation amount starts to increase, and 400 ° C. When it exceeds, the sample mass starts to decrease greatly, and the calorific value increases rapidly, and the calorific value becomes maximum at around 500 ° C., and when it exceeds 500 ° C., the calorific value decreases.

  From this, the volatile matter VM remaining in the tablet evaporates from around 300 ° C., and this begins to oxidize in the atmosphere and generates heat. At around 400 ° C., oxidation of carbon with a large exotherm begins, When the temperature exceeds 500 ° C., it is considered that in addition to the oxidation reaction of carbon, an endothermic reaction in which iron oxide is directly reduced by carbon starts and the calorific value decreases.

  From the above results, in order to more reliably avoid the vaporization of the volatile matter VM remaining in the tablet and the accompanying oxidative exothermic reaction due to the atmosphere, cooling the molded product in an inert gas atmosphere in the cooling step after the heat treatment It is recommended that the temperature be 300 ° C. or lower.

1: Mixer 2: Heating device (external heating type rotary kiln)
3: Surge hopper 4: Hot forming machine (double roll type forming machine)
5: Heat treatment equipment (shaft furnace)
6: Screen A: Powdered coal B: Powdered iron ore C: Mixed raw material C ': Heated raw material D: Molded product (briquette)
E: Agglomerated material for blast furnace raw material (lumped on sieve)
F: Sieve powder

Claims (5)

Gieseler maximum fluidity MF is 0.3 to 2.5 in log MF, pulverized VM containing 10 mass% or more, sulfur coal containing 0.3 mass% or more, and 3 mass of crystal water LOI A mixing step of mixing powdered iron ore containing at least 5% into a mixed raw material,
A heating step of heating the mixed raw material to a heating temperature T1 of 350 to 550 ° C. to obtain a heated raw material;
A hot forming step in which this heated raw material is hot formed at a forming temperature T2 to form a molded product;
A heat treatment step of heat-treating the molded product at 560 to 750 ° C. for 10 minutes or more under an inert gas atmosphere to obtain an agglomerated material for a blast furnace raw material,
A method for producing an agglomerate for a blast furnace raw material, characterized in that a temperature drop ΔT (= T1-T2) from the heating temperature T1 to the molding temperature T2 is within 20 ° C. Gieseler maximum fluidity MF is 0.3 to 2.5 in log MF, pulverized VM containing 10 mass% or more, sulfur coal containing 0.3 mass% or more, and 3 mass of crystal water LOI A mixing step of mixing powdered iron ore containing at least 5% into a mixed raw material,
A granulation step of granulating all or part of this mixed raw material into pellets;
A heating step of heating the pellet and the remainder of the mixed raw material to a heating temperature T1 of 350 to 550 ° C. to form a heated raw material;
A hot forming step in which this heated raw material is hot formed at a forming temperature T2 to form a molded product;
A heat treatment step of heat-treating the molded product at 560 to 750 ° C. for 10 minutes or more under an inert gas atmosphere to obtain an agglomerated material for a blast furnace raw material,
A method for producing an agglomerate for a blast furnace raw material, characterized in that a temperature drop ΔT (= T1-T2) from the heating temperature T1 to the molding temperature T2 is within 20 ° C.   The method for producing an agglomerate for a blast furnace raw material according to claim 1 or 2, wherein a required time Δt (= t2-t1) from the end time t1 of the heating step to the start time t2 of the hot forming step is set to 2 min or less. .   The blast furnace according to any one of claims 1 to 3, further comprising a cooling step of cooling the agglomerated material for blast furnace raw material to 300 ° C or less in an atmosphere having an oxygen concentration of 5% by volume or less after the heat treatment step. A method for producing an agglomerated material.   The method for producing an agglomerated material for a blast furnace raw material according to any one of claims 1 to 4, wherein the powdered coal is a mixture of two or more types of coal.