JP5880941B2 - Method for producing reduced iron - Google Patents

Description

  The present invention relates to a method for producing reduced iron by briquetting a mixture of iron ore powder and carbonaceous material powder and subjecting the briquette to a reduction treatment.

Conventionally, the following methods are known as methods for reducing iron ore, and technical improvements have been made to increase productivity.
(1) Blast furnace method In the blast furnace method, iron ore and coke are charged in layers, and hot air (oxygen-enriched air) at about 1000 ° C is blown from the bottom of the furnace to produce hot metal. In this blast furnace method, technical improvements to improve productivity include increasing hot air temperature, increasing oxygen enrichment, charging reduced iron, and improving iron ore and coke charging methods. ing. Basically, iron ore that can be used in a blast furnace is not a powdered ore, but is a massive ore or sintered ore that can withstand the load in the blast furnace. Similarly, coke can withstand the load in the blast furnace. Quality is required.

Because iron ore and coke are charged in layers, the reduction reaction of iron ore depends on the reducing gas (CO, H ₂ ) generated by the gasification of coke generated in the lower part of the furnace. The reduction reaction at the contact cannot be expected very much. In order to further increase the productivity, the pressure in the furnace can be made higher than the normal operation level (3 to 4 kg / cm ² -G), but the coke gasification reaction (C + CO ₂ = On the contrary, 2CO) is inhibited, which is disadvantageous for the production of reducing gas. The blast furnace method is a process for producing hot metal from iron ore. Gas, solid and liquid coexist in the furnace, and reducing gas flows from the lower part of the furnace to the upper part of the furnace, reducing and melting hot metal and molten slag. Descends towards the bottom of the furnace. In such a process, when the pressure in the furnace is increased, the gas density and the viscosity are increased. Therefore, there is a possibility that the reduction and melting of molten iron and molten slag are hindered.

(2) Reduced iron production method using a shaft furnace This production method involves charging ore or iron ore pellets into a shaft furnace (these materials descend toward the bottom of the furnace) and reforming natural gas from the bottom of the furnace. In this method, reduced iron (CO, H ₂ ) at 800 to 950 ° C. is blown to produce reduced iron, and HYLIII, Midrex, and the like are known. Since this method uses high-cost natural gas as the reducing material, the plant location is limited to the country producing the natural gas. In this manufacturing method, as technical improvements for improving productivity, the reformed gas temperature to be blown is increased, the hydrogen concentration in the reducing gas is increased, and the like. This production method is also basically iron ore reduction with a reducing gas. Although high pressure is possible to improve productivity, high pressure is more advantageous for carbon deposition reaction (2CO = C + CO ₂ ) and methanation reaction (CO + 3H ₂ = CH ₄ + H ₂ O). It would be converted to C or CH _4. Moreover, since the methanation reaction is an exothermic reaction, it is difficult to control the reduction temperature.

Furthermore, in order to improve productivity, it is necessary to improve the iron ore reduction rate. Patent Documents 1 and 2 disclose a method of increasing the contact point between iron ore and carbonaceous material by mixing and agglomerating iron ore (iron oxide) and carbonaceous material. In addition, the method shown by these patent documents is a method of producing reduced iron by carrying out high temperature reduction of the manufactured agglomerate with a rotary hearth furnace.
Non-Patent Documents 1 to 3 disclose results of iron ore reduction reaction under high pressure.

JP 2010-53376 A JP 2002-167624 A

Nishikawa, 5 others, "Reduction experiment of powdered hematite ore using flow-type high-pressure differential thermal analyzer", Iron and Steel, 64 (1978), p.121-127 Black beans, 2 others, “Reduction reaction rate of iron oxide pellets with hydrogen gas under high pressure”, Iron and steel, 66 (1980), p.23-32 E. Kasai, 2 others, “Effect of Mixed-grinding Material and Iron Oxide on Reduction Composite”, ISIJ International, 35 (1995), p.1444-1451

Blast furnace process and reduced iron production method according to the shaft furnace, in which by using a reducing gas at a pressure of several kg / cm ² -G (about 5 kg / cm ² -G with reduced iron production process) perform the reduction of iron ore is there. As a measure for improving productivity (reduction rate), there is a method of increasing the temperature such as hot air temperature, but a method of increasing the pressure during reduction can be considered in order to further improve the reduction rate. However, when the pressure increases, the coke gasification reaction is hindered (blast furnace method), and it becomes a favorable condition for reactions such as carbon deposition and methanation, which conversely reduces productivity or causes operational troubles. It becomes a factor to do.

  The methods of Patent Documents 1 and 2 agglomerate a mixture of iron oxide and carbonaceous material, and produce reduced iron in a rotary hearth furnace. In this method, multiple layers (2 to 3 layers) of agglomerates are charged into the hearth of the rotary hearth furnace, and iron oxide is reduced by radiant heat from the furnace wall gas burner flame or the furnace inner wall. The upper part of the furnace is a combustion space, and the packing density of the agglomerated material is low, so that the productivity is low. In addition, the heat of the combustion gas is used for raising the temperature and reducing the agglomerated material, but most of it is discharged as exhaust gas through the upper space (low thermal efficiency). In addition, since a rotary hearth furnace is used, it is basically a reduction reaction at normal pressure, and operation at high pressure is difficult.

  Also, Non-Patent Documents 1 and 2 show a method of reducing iron ore at a pressure of about 1.3 MPa under a hydrogen stream (reduction of only iron ore particles, not mixing with carbonaceous materials). Non-Patent Document 3 shows a method in which iron ore and a carbonaceous material (graphite, coke) are simply mixed and pulverized, and the mixture is reduced under a pressure of 0.1 to 1.5 MPa. However, these methods cannot efficiently reduce iron ore with high productivity.

  Accordingly, an object of the present invention is to solve the above-described problems of the prior art, and to provide a method for producing reduced iron that can efficiently reduce iron ore with high productivity and obtain reduced iron at low cost. There is.

The present inventors have studied to solve the above problems, and as a result, the iron ore is reduced at a high reduction rate by reducing the briquette containing iron ore powder and biomass coal under a high temperature and high pressure of a predetermined level or higher. It has been found that reduced iron can be efficiently produced and reduced iron can be produced with high productivity. The present invention has been made based on such findings, and the gist thereof is as follows.
[1] In the method for producing reduced iron from iron ore, the iron ore powder is blended such that the mass ratio [C / O] of the fixed carbon in the carbonaceous material to the iron oxide-derived oxygen contained in the iron ore powder is 0.75 or more. Ratio (A) which adds and mixes granular biomass charcoal and press-molds this mixture into a briquette, and the briquette is at a high temperature and high pressure of 950 ° C. to 1100 ° C. and 2.0 Mpa or higher. A method for producing reduced iron, comprising a step (B) of obtaining reduced iron by performing a reduction treatment in step 1.
[2] The method for producing reduced iron according to the above [1], wherein in step (A), the iron ore powder is mixed with a biomass charcoal together with a binder.
[3] In the manufacturing method of [1] or [2] above, the step (B) is performed in the shaft furnace, and the briquette charged from the upper part of the shaft furnace is reduced to the lower part of the furnace. The method for producing reduced iron according to claim 1.

  According to the present invention, the briquette containing iron ore powder and biomass coal is reduced at a high temperature and high pressure of a predetermined level or higher, thereby efficiently reducing the iron ore at a high reduction rate and reducing iron with high productivity. Can be obtained. Moreover, since productivity can be maintained even if a low-grade raw material (iron ore, carbon material) is used, reduced iron can be manufactured at low cost.

Explanatory drawing which shows one Embodiment of the utilization method of the reduced iron obtained at the process (B) and this process (B) of this invention In an Example, the graph which shows the relationship between the pressure at the time of reducing the briquette which used charcoal powder as charcoal powder, and the briquette which used graphite powder at 950 degreeC, and the mass reduction rate of a briquette In an Example, the graph which shows the relationship between the temperature when the briquette which used charcoal powder as charcoal powder, and the briquette which used graphite powder reduced at various pressures, and the mass reduction rate of briquette In the examples, the relationship between the pressure when reducing briquettes using charcoal powder as the charcoal powder and the relative reduction rate at the gasification start temperature (reduction rate with a reduction rate of 1.0 at a pressure of 5 MPa). Graph showing

The method for producing reduced iron according to the present invention comprises a step (A) of adding biomass charcoal to iron ore powder, mixing the mixture, and press-molding the mixture to form a briquette; A step (B) of obtaining reduced iron by reducing treatment at a high temperature and high pressure of 0 Mpa or more. Since the reduction treatment in this step (B) is performed under a high pressure of 2.0 Mpa or more, the gas generated in the briquette due to the reaction is not easily released to the outside, and tends to stay inside the briquette. ) first CO occurs in the reduction reaction of the carbonaceous material and the iron oxide, the (b) produce a CO ₂ reacts with the CO is further oxidized iron, CO reacts with (c) the CO ₂ is carbonaceous material Then, the iron ore is reduced by a series of reactions in which the reaction of (b) → (c) is repeated, so that efficient reduction treatment is performed. Furthermore, by using biomass charcoal as the carbonaceous material powder, the rate at which CO ₂ and the carbonaceous material (c) react with each other to generate CO increases. As a result, the briquette reduction speed is also increased, and the efficiency of the reduction treatment is improved from this aspect. This is because biomass charcoal has a higher specific surface area than coal powder and coke powder, and carbon in biomass charcoal is not a strong graphite like carbon in coal or coke, but a highly reactive site. has many, because easily react with CO ₂ and iron ore. As a result, in the method for producing reduced iron of the present invention, a very efficient reduction treatment is performed, and high productivity is obtained.

In this invention, there is no special restriction | limiting in the iron ore powder briquetted by a process (A), You may use inferior quality powdered iron ore. The particle size of the iron ore powder is preferably 1/10 or less of the briquette size, although it depends on the size of the briquette to be produced. In general, a particle size of 3 mm or less is preferable.
Biomass charcoal, which is a charcoal material, may be a carbonized material such as wood, grass, sewage sludge, and the like, and charcoal is typical, but is not limited thereto. .
Biomass charcoal is granular, and the particle size thereof is preferably 1/10 or less of the briquette size, although it depends on the size of the briquette to be produced, and is preferably equal to or smaller than the particle size of the iron ore powder. In general, a particle size of 3 mm or less is preferable.
The mixing ratio of biomass charcoal to iron ore powder is determined in consideration of the amount of carbon necessary to reduce iron ore, but in general, the amount of fixed carbon in the carbonaceous material relative to iron oxide-derived oxygen contained in iron ore powder is limited. A blending ratio such that the mass ratio [C / O] is 0.75 or more is preferable.

  In order to briquette the raw material, a binder may be added to the iron ore powder together with biomass coal. Examples of the binder include organic binders such as starch, ethanol, higher alcohol, polyvinyl alcohol, carboxymethyl cellulose, polyacrylic acid, molasses, and lignin, cement, ground granulated blast furnace slag, gypsum, phosphoric acid, clay, bentonite. And inorganic binders such as magnesium sulfate, and one or more of these may be used. As for the compounding quantity of a binder, 1 mass part or more is preferable with respect to a total of 100 mass parts of iron ore powder and biomass charcoal. In addition, you may add a water | moisture content suitably in the case of briquetting.

In the step (A), biomass charcoal is added to the iron ore powder, a binder is further added if necessary (and water is added if necessary), and the mixture is pressure-molded to form a briquette. Usually, this pressure molding is performed using a briquette machine equipped with a molding die. The pressure molding conditions are appropriately selected according to the type of iron ore powder. After pressure molding, it is dried as necessary.
Although the briquette size depends on the furnace type for reduction, the briquette size may be a size that does not impair air permeability and that is industrially used. In general, a size of 6 cc or more is preferable.

In the subsequent step (B), the briquette is reduced at a predetermined high temperature and high pressure. Usually, this reduction process is performed in a shaft furnace, and in this case, the reduction process is performed in the process in which briquettes charged from the upper part of the shaft furnace descend to the lower part of the furnace.
As briquette reduction conditions, if the temperature is less than 950 ° C. and the pressure is less than 2.0 Mpa, a sufficient reduction rate cannot be obtained. Therefore, the reduction treatment temperature is 950 ° C. or more and the pressure is 2.0 Mpa or more.
Moreover, the upper limit of the temperature of reduction treatment shall be 1100 degrees C or less. This is because when the temperature of the reduction treatment exceeds 1100 ° C., the reduced briquettes are softened and melted, and the briquettes are fused (melting point is 1150 ° C. at a carbon concentration of 4.3%). Such fusion of briquettes causes troubles such as shelf hanging when reduction processing is performed in a shaft furnace as shown in FIG.
The time for the reduction treatment is the time required for raising the temperature and reducing the charged briquette, and usually requires 1 hour or more.
By this step (B), reduced iron having a reduction rate of 90% or more of iron oxide contained in the iron ore powder can be obtained.

  FIG. 1 shows an embodiment in which the step (B) of the present invention is carried out in a shaft furnace, and the briquette obtained in the step (A) is introduced into the furnace from the inlet 2 at the top of the shaft furnace 1. Is charged. The charged briquette descends in the furnace, is reduced in the process of descending to the lower part of the furnace, and finally is taken out from the outlet 3 at the lower end of the furnace. The shaft furnace is supplied with reducing gas such as CO that has been preheated to 900 ° C. or more from the inlet 4 to maintain the inside of the furnace at a high temperature. The reduced iron (briquette) taken out from the shaft furnace is melted in a melting furnace such as an electric furnace as shown in FIG. 1 to obtain molten iron.

  Two types of experimental samples were used: iron ore powder (hematite ore having a particle size of 44 to 100 μm) and hematite powder (average particle size 0.5 μm, purity 99.99%) as iron oxide, and purity 98% as carbonaceous material powder. Graphite powder (average particle size 20 μm) and charcoal powder carbonized at 450 ° C. (particle size 53 to 150 μm) were used. Table 1 shows the composition of iron ore powder, and Table 2 shows the composition of charcoal powder.

  Iron oxide and carbonaceous material are weighed so that the mass ratio [C / O] of carbon in the carbonaceous material relative to iron oxide-derived oxygen is 0.8, and then sufficiently mixed. For 30 seconds to produce a briquette (molded body) having a height of about 10 mm. In addition, when combining hematite powder and charcoal powder, since briquette strength was weak, a method of molding by adding ethanol as a binder to the mixed sample at the time of pressure molding was adopted. The briquette was sufficiently dried by holding at 105 ° C. for 6 hours or more, and then subjected to the experiment.

A reduction experiment was performed on the above briquettes using a normal electric furnace. In this reduction experiment, a predetermined amount of N ₂ was supplied into the furnace, and this N ₂ was discharged out of the furnace together with the gas generated in the furnace. N ₂ supplied into the furnace was controlled by a mass flow controller (˜20.0 NL / min), and the pressure in the furnace was controlled by a pressure regulator provided at the outlet of the electric furnace (˜10.0 MPa). In the reduction experiment, N ₂ (purity: 6N5) was introduced into the system, and after reaching a predetermined pressure, the flow rate was controlled to 0.5 NL / min, and heating was started to a predetermined temperature at a heating rate of 10 ° C./min. The exhausted gas was analyzed. The results of this gas analysis were used to confirm the reduction status. Further, the “reduction rate” in Test Example 1 and the “mass reduction rate” in Test Example 2 described below were determined by mass measurement and elemental analysis of the collected sample.

[Test Example 1]
The briquette described above was produced using iron ore powder as iron oxide and graphite powder as charcoal powder, and a reduction experiment of this briquette was conducted. The pressure in the reduction experiment was 0.3 MPa (No. 4), 1.0 MPa (No. 1), 3.0 MPa (No. 2), 5.0 MPa (No. 3), and the reduction experiment was performed at various temperatures. went. Table 3 shows the reduction rate of each briquette. According to Table 3, when graphite powder is used as charcoal powder, it can be seen that briquettes cannot be sufficiently reduced at a temperature of 1100 ° C. or lower.

[Test Example 2]
Briquette using charcoal powder as charcoal powder, hematite powder as iron oxide, briquette using graphite powder as charcoal powder, and hematite powder as iron oxide are manufactured as described above, and reduction of these briquettes The experiment was conducted. In this reduction experiment, for briquettes using charcoal powder as charcoal powder, the pressure was 0.3 MPa, 1.0 MPa, 2.0 MPa and 3.0 MPa, and for briquettes using graphite powder as charcoal powder, The pressure was 0.3 MPa, 1.0 MPa, 2.0 MPa, 3.0 MPa, and 5.0 MPa, and each was performed at a temperature of 950 ° C. The mass reduction rate of the briquette of each test example is shown in FIG. This mass reduction rate represents the theoretical maximum mass reduction rate from which all carbon and iron oxide-derived oxygen in the briquette are removed as 100% (the same applies to the mass reduction rate in FIG. 3 described later). .

According to FIG. 2, the briquette using the graphite powder as the carbonaceous material powder does not change in the mass reduction rate even when the pressure is increased. On the other hand, the briquette using charcoal powder as the charcoal powder increases the mass reduction rate as the pressure increases, and the mass reduction rate is 95% or more at 2.0 MPa or more. This shows that the reduction rate of iron ore is faster when charcoal powder is used.
Moreover, about the briquette similar to the above, the reduction test which changed temperature conditions in each pressure was done. The mass reduction rate of the briquette of each test example is shown in FIG. According to this, briquette using charcoal powder as charcoal powder has a faster reduction rate of iron oxide (iron ore) than briquette using graphite powder as charcoal powder, and it is reduced from the low temperature side by about 100 ° C. Has been shown to be.

[Test Example 3]
Using the charcoal powder as the charcoal powder and the iron ore powder as the iron oxide, the above briquette was manufactured, and the reduction experiment of this briquette was conducted. FIG. 4 shows the result of examining the relationship between the pressure during the reduction process and the relative reduction rate at the gasification start temperature in this reduction experiment. Here, the relative reduction rate is a reduction rate with a reduction rate of 1.0 at a pressure of 5 MPa. Further, the gasification start temperature is a temperature at which the following equation (2) occurs, since the reactions that can occur in the brickket are considered to be only the reduction reaction and the gasification reaction.
FeO _X + CO = FeO _X-1 + CO ₂ (1)
C + CO ₂ = 2CO (2)
FIG. 4 shows that the relative reduction rate is improved at 1.0 MPa as compared to the pressure of 0.3 MPa, but that the pressure is sufficiently reduced when the pressure is 2 MPa or more.

DESCRIPTION OF SYMBOLS 1 Shaft furnace 2 Loading port 3 Outlet 4 Inlet

Claims (3)

In a method for producing reduced iron from iron ore,
To the iron ore powder, the powdered biomass charcoal is added and mixed at a compounding ratio that the fixed carbon mass ratio [C / O] of the carbonaceous material relative to the iron oxide-derived oxygen contained in the iron ore powder is 0.75 or more , A step (A) of pressure-molding the mixture to form a briquette;
A method for producing reduced iron, comprising a step (B) of obtaining reduced iron by subjecting the briquette to reduction treatment at a high temperature and high pressure of 950 ° C. to 1100 ° C. and 2.0 Mpa or higher.   In a process (A), a binder is added to iron ore powder with biomass charcoal, and it mixes, The manufacturing method of reduced iron of Claim 1 characterized by the above-mentioned.   The reduced iron of claim 1 or 2, wherein the step (B) is performed in a shaft furnace, and the briquette charged from the upper part of the shaft furnace is reduced to the lower part of the furnace. Production method.

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