Blast furnace operation method

Abstract

To increase the permeability inside a furnace while increasing the reducibility of pellets, without requiring large-scale capital investment or an increase in the cost of producing pig iron.SOLUTION: In an operation method of a blast furnace, the method includes a raw material charging step of forming a predetermined iron raw material layer in the furnace, the predetermined iron raw material layer consisting of iron raw materials including at least sintered ore and pellets, the predetermined iron raw material layer includes a first iron raw material layer and a second iron raw material layer, the second iron raw material layer is formed on the first iron raw material layer, the second iron raw material layer comprises 50 mass% or more of the pellets included in the predetermined iron raw material layer, and is formed in at least a portion of a range of 0.7 to 1.0 in terms of a dimensionless radius of the furnace diameter.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to a method for operating a blast furnace in which pellets are contained in the iron raw material charged into the blast furnace. [Background technology]

[0002] In blast furnace operation, iron raw materials such as sintered ore, pellets, and lump ore (hereinafter collectively referred to as "iron raw materials"), and coke as a reducing agent and fuel are charged alternately from the top of the furnace, and hot air is blown from the tuyeres at the bottom of the furnace, while auxiliary fuel such as pulverized coal is blown in. The iron raw materials and coke charged from the top of the furnace are layered alternately to form iron raw material layers and coke layers, which gradually descend inside the blast furnace toward the bottom of the furnace, and are heated and heated by the gas rising from the bottom of the furnace.

[0003] The layer of iron raw material that descends while being heated and reduced in the blast furnace begins to soften and melt when it reaches the bottom of the furnace, forming a cohesive layer. The area in the blast furnace where the cohesive layer exists is called the cohesive zone. The gas in the furnace that reaches the cohesive layer passes through the coke slits between the cohesive layers of the ore and heads toward the top of the furnace. Therefore, the shape of the cohesive zone has a huge impact on the permeability of the blast furnace, and the high-temperature properties of the ore are one of the important factors that determine the shape of the cohesive zone.

[0004] Conventionally, a load-softening test has been carried out to evaluate the high-temperature properties of ore using indices such as the reduction rate at the start of fusion (hereinafter also referred to as "Rs"), the start of fusion temperature (hereinafter also referred to as "Ts"), the start of dripping temperature (hereinafter also referred to as "Td"), or the difference between the start of fusion temperature and the start of dripping temperature (ΔT=Td-Ts) (see Non-Patent Document 1). Patent Documents 1 to 3 have made various studies on the use of pellets in blast furnace operation from the viewpoint of these high-temperature properties.

[0005] Patent Document 1 describes a blast furnace operation method and a method for designing the blending of ore raw materials, which maintain or improve the reducibility (Rs) of the ore layer by lowering the thermal reserve zone temperature when increasing the blending ratio of pellets, which have a lower reducibility (Rs) than sintered ore. As a means for adjusting the thermal reserve zone temperature, the injection of hydrogen-containing gas and the use of highly reactive coke or carbon-containing agglomerated ore are mentioned, but there is a problem in that all of these measures require large-scale capital investment and increase the cost of pig iron production.

[0006] Patent Document 2 describes a method of operating a blast furnace in which the ore contains 10% or more pellets, the ore charging is divided into two or more batches, 80% or more of the pellets are charged in the second batch and thereafter, and the pellets are segregated in the upper layer with a dimensionless radius of 0.2 to 0.8. Patent Document 3 describes a method of operating a blast furnace in which the ore charging is divided into two batches for an ore layer containing sintered ore and pellets, and the pellet ratio in the second ore batch is 60% to 80%. The methods described in Patent Documents 2 and 3 are techniques for suppressing clogging of the coke slit by molten ore by segregating pellets in the upper layer of the ore layer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2023-50036 A [Patent Document 2] Patent No. 6354708 [Patent Document 3] JP 2019-127628 A

[0008] [Non-Patent Document 1] Iron and Steel, Vol. 83 (1997), pp. 97-102, "Development of a method for evaluating the softening and melting properties of sintered ore" Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to improve the gas permeability inside the furnace while increasing the reducibility of the pellets in a method for operating a blast furnace, the method including a raw material charging step for forming a predetermined iron raw material layer inside the furnace, the layer being made of iron raw materials including at least sintered ore and pellets, without requiring large-scale capital investment or an increase in the cost of producing pig iron. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides a method for operating a blast furnace, which is characterized in that (1) in the method for operating a blast furnace including a raw material charging step of forming a predetermined iron raw material layer in the furnace, the predetermined iron raw material layer consisting of iron raw materials including at least sintered ore and pellets, the predetermined iron raw material layer includes a first iron raw material layer and a second iron raw material layer, the second iron raw material layer is formed on the first iron raw material layer, the second iron raw material layer contains 50 mass% or more of the pellets contained in the predetermined iron raw material layer, and is formed within a range of 0.7 to 1.0 in terms of a dimensionless radius of the furnace diameter.

[0011] (2) The method for operating a blast furnace according to (1) above, characterized in that the second iron raw material layer is formed on an ore terrace of the first iron raw material layer.

[0012] (3) A method for operating a blast furnace according to (1) or (2) above, characterized in that the first iron raw material layer and the second iron raw material layer are formed in different ore dumps.

[0013] (4) The method for operating a blast furnace according to any one of (1) to (23), characterized in that the pellets are basic pellets or mixed pellets obtained by mixing the basic pellets and acidic pellets, and at least a part of the second iron raw material layer is formed in a furnace diameter dimensionless radius in the range of 0.9 to 1.0. Effect of the Invention

[0014] According to the present invention, in a blast furnace operation method including a raw material charging step of forming a predetermined iron raw material layer in the furnace, the raw material layer is made of iron raw materials including at least sintered ore and pellets, and the permeability in the furnace can be improved while increasing the reducibility of the pellets without requiring a large-scale capital investment or an increase in the pig iron production cost. If the permeability is improved, the coke rate can be reduced. [Brief description of the drawings]

[0015] [Figure 1A] FIG. 2 is a schematic diagram of an iron raw material layer and a coke layer. [Figure 1B] FIG. 2 is another schematic diagram of an iron raw material layer and a coke layer (a second iron raw material layer is formed on the furnace wall side). [Figure 1C] FIG. 2 is another schematic diagram of an iron raw material layer and a coke layer (a second iron raw material layer is formed on the terrace shoulder side). [Figure 1D] FIG. 2 is another schematic diagram of an iron raw material layer and a coke layer (a second iron raw material layer is formed at a position avoiding the vicinity of the furnace wall and the vicinity of the terrace shoulder). [Diagram 2] 1 is a bar graph showing the relationship between the reduction rate and the pre-reduction temperature. [Diagram 3] 1 shows the results of a pellet dropping property test. [Figure 4] FIG. 1 is a schematic diagram of the iron raw material layer formed in one dump. [Diagram 5] This is data on ηCO obtained via the upper sonde. [Figure 6] This is data on ηH2 obtained via the upper sonde. [Figure 7] This is temperature distribution data obtained via the upper sonde. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 1A is a schematic diagram showing an iron raw material layer and a coke layer formed in a blast furnace. The iron raw material layer is formed by carrying out a raw material charging step in which iron raw materials including at least sintered ore and pellets are charged into the furnace. The iron raw materials may include lump ore, carbon-containing agglomerated ore, reduced iron, etc. in addition to sintered ore and pellets.

[0017] Sintered ore is produced by mixing powdered iron ore with limestone, coke powder, etc., and then carrying out a sintering reaction in a sintering machine. Pellets are produced by granulating crushed fine ore together with auxiliary materials into spherical pellets, which are then heated and molded with heavy oil or coal. The blast furnace may be a bell-less type blast furnace or a bell blast furnace.

[0018] The iron raw material layer includes a first iron raw material layer O1 and a second iron raw material layer O2. A coke layer C is formed below the iron raw material layer. An ore terrace OT is formed at the end of the first iron raw material layer O1 on the furnace wall FW side. The ore terrace OT is a surface portion of the iron raw material layer whose terrace angle is sufficiently smaller than the angle of repose of the iron raw material. The terrace angle is the inclination angle of the ore terrace OT with respect to the horizontal direction (furnace radial direction).

[0019] The terrace angle of the ore terrace OT may be positive or negative. A positive terrace angle means that the end of the ore terrace OT on the furnace wall FW side is located closer to the furnace top than the end on the furnace center CE side. A negative terrace angle means that the end of the ore terrace OT on the furnace center CE side is located closer to the furnace top than the end on the furnace wall FW side. Note that FIG. 1A shows an ore terrace OT with a negative terrace angle. The first iron raw material layer O1 extends from directly below the second iron raw material layer O2 toward the furnace center CE side.

[0020] Here, the end of the ore terrace OT on the furnace center CE side is defined as OTe (hereinafter, also referred to as terrace shoulder OTe). If the position of the terrace shoulder OTe is defined by the dimensionless radius of the furnace diameter when the furnace diameter is set to 1, it is generally 0.6 to 0.9.

[0021] When the pellets contained in the iron raw material layer consisting of the first iron raw material layer O1 and the second iron raw material layer O2 are taken as 100% by mass, the content of pellets contained in the second iron raw material layer O2 is 50% by mass or more, and preferably 60% by mass or more. In other words, the second iron raw material layer O2 is a pellet-rich layer containing 50% by mass or more of pellets. The effect of the present invention can be obtained as long as the pellets are contained at 50% by mass or more. When the iron raw material layer is taken as 100% by mass, the content of pellets contained in the iron raw material layer is preferably 5% by mass or more and less than 30% by mass.

[0022] The pellets may be basic pellets, acid pellets, or a mixture of these. If basic pellets and acid pellets are defined by the ratio of CaO (mass%) to SiO2 (mass%) in the pellets (CaO / SiO2), in other words, basicity, basic pellets are pellets with a basicity of more than 0.5, and acidic pellets are pellets with a basicity of 0.5 or less. In the following description, basicity may be expressed as "C / S".

[0023] The second iron raw material layer O2 is formed in at least a part of the range of the dimensionless radius of the furnace diameter of 0.7 to 1.0. The phrase "at least a part" means that the second iron raw material layer O2 may be deposited in the entire range or in a part of the range, as exemplified below. 1A illustrates a state in which the position of the terrace shoulder OTe is a dimensionless furnace radius of 0.7, and the second iron raw material layer O2 is formed over the entire ore terrace OT. That is, in FIG. 1A, the second iron raw material layer O2 is formed over the entire range of the dimensionless furnace radius of 0.7 to 1.0. In FIG. 1B to FIG. 1D, the second iron raw material layer O2 is formed in a part of the furnace diameter dimensionless radius of 0.7 to 1.0 (in other words, a part of the ore terrace OT). In FIG. 1B, a first iron raw material layer O1 is formed on a coke layer C1, and a second iron raw material layer O2 is formed on the furnace wall side on an ore terrace OT. In FIG. 1C, a first iron source layer O1 is formed on a coke layer C1, and a second iron source layer O2 is formed on the ore terrace OT on the terrace shoulder portion OTe side. In FIG. 1D, a first iron raw material layer O1 is formed on a coke layer C1, and a second iron raw material layer O2 is formed on an ore terrace OT at a position avoiding the vicinity of the furnace wall FW and the vicinity of the terrace shoulder OTe.

[0024] The reason why the pellets contained in the iron raw material layer are unevenly distributed on the furnace wall side in this way is because the reducibility of the pellets is improved. That is, in order to improve the reducibility of the pellets, it is important to secure the holding time in the temperature range of 700℃ to 900℃, and the temperature distribution on the FW side of the furnace wall is relatively suitable. By improving the reducibility of the pellets, the solution loss reaction, ηCO, and ηH2 of the blast furnace can be improved. The present inventors obtained this knowledge from a pellet reducibility test.

[0025] (Pellet reducibility test) The effect of reduction temperature on the reducibility of pellets was evaluated by a reduction test. Basic pellets A (C / S=0.96) were used. Specifically, the effect of the reduction temperature (pre-reduction temperature) from hematite (H) to magnetite (M) of basic pellet A (hereinafter also referred to as pellet A) on the reduction rate (reduction rate of main reduction) from magnetite (M) to metallic iron (F) was evaluated. In the pre-reduction (H → M) step, the gas composition was set to the magnetite stable region, and the material was heated at a temperature of 500 to 1000°C for 2 hours. In the main reduction step, the test was carried out at a temperature of 1000°C using a balance gas of CO-50% N2.

[0026] Fig. 2 is a bar graph showing the relationship between the reduction rate of pellet A 1 h after the start of the main reduction (in other words, the reduction rate based on magnetite) and the pre-reduction temperature, where the horizontal axis is the pre-reduction temperature (℃) and the vertical axis is the reduction rate (%). It was found from the same figure that when the pre-reduction temperature is lowered to 700℃ to 900℃, the reduction rate of the pellet increases, in other words, the reduction speed of the pellet increases.

[0027] The inventors of the present invention consider the reason why the above results were obtained in the pellet reducibility test as follows. As magnetite is generated at a lower temperature, the pore size decreases and the specific surface area increases, accelerating the reduction reaction. On the other hand, if the pore size becomes too small, gas diffusion (Knudsen diffusion) is thought to limit the reaction rate and inhibit the reduction reaction. Therefore, in order to improve the reducibility of the pellets, it is important to secure a holding time in the temperature range of 700 to 900°C, and it was considered that the temperature distribution on the FW side of the furnace wall (in the range of 0.7 to 1.0 in terms of the dimensionless radius of the furnace diameter) is relatively suitable for improving reducibility.

[0028] The second iron raw material layer O2 is desirably formed on the ore terrace OT of the first iron raw material layer O1. Since the terrace angle of the ore terrace OT is smaller than the angle of repose of the ore, the second iron raw material layer O2 can be easily deposited at a desired position.

[0029] Here, by stacking the second iron raw material layer O2 on the first iron raw material layer O1 (in other words, by making the pellet-rich iron raw material layer the upper layer), clogging of the coke slit is suppressed and air permeability is improved, and melting reduction by unreduced FeO is suppressed, thereby improving reducibility. The present inventors obtained this knowledge through a pellet dropping property test.

[0030] (Pellet Dropping Property Test) The effect of the pellet arrangement on the dropping temperature was evaluated using a load-softening test device. The evaluation results are shown in Figure 3. Case I, where pellets and sintered ore were uniformly mixed, Case II, where pellets and sintered ore were placed in the lower and upper layers, respectively, and Case III, where pellets and sintered ore were placed in the upper and lower layers, respectively, were compared. The pellets were a mixed raw material of pellets B and pellets C. The ratio was pellets B:pellets C:sintered ore = 29:21:50 (pellet ratio: 50 mass%). The pellet layer in Case II and Case III was a uniform mixture of pellets B and pellets C. The C / S of pellets B was 1.04, and the C / S of pellets C was 0.76. The temperature, reducing gas, and load during the test were given conditions simulating those of an actual blast furnace.

[0031] Referring to Fig. 3, the dripping temperatures of Case I, Case II, and Case III are shown, as well as the dripping temperatures of pellets B, C, and sintered ore. As is clear from the evaluation results in Fig. 3, it was found that the arrangement of Case III (pellets arranged in the upper layer) can most effectively suppress the drop in dripping temperature. The inventors of the present invention believe that the reason for this is that "in Case III, the pellets, which start dripping before the sintered ore, are trapped by the sintered ore in the lower layer." Therefore, by arranging the pellets in the upper layer, the drop in dripping temperature is suppressed, and therefore clogging of the coke slit can be prevented. In addition, smelting reduction by unreduced FeO is suppressed. Since smelting reduction is an endothermic reaction, suppressing smelting reduction can improve reducibility.

[0032] Here, it is desirable to deposit at least a portion of the second iron raw material layer O2 at a furnace diameter dimensionless radius of 0.9 to 1.0, and to limit the pellets contained in the second iron raw material layer O2 to basic pellets or mixed pellets (mixed pellets of basic pellets and acidic pellets). This increases the fluidity of the slag near the furnace wall, thereby further increasing the permeability of the blast furnace. Note that, since "at least a part" is used, a part of the second iron raw material layer O2 may be deposited in the range of the dimensionless radius of the furnace diameter of 0.7 to 0.8. The present inventors obtained this knowledge through thermodynamic calculations.

[0033] (thermodynamic calculation) The melting points (slag melting points) of gangue components (CaO+SiO2+Al2O3+MgO) in the iron raw materials of sintered ore and pellets were calculated using thermodynamic equilibrium calculation software (Factsage). Three types of pellets were used: pellet B (basic pellet), pellet C (basic pellet), and acidic pellet. The slag melting points of pellet B were 1420°C, pellet C were 1400°C, and both of the slag melting points of sintered ore and acidic pellets were over 1600°C.

[0034] The melting point of the gangue of the basic pellets (pellets B and C) is lower than that of the sintered ore and acidic pellets, and the pellets melt first in the upper layer, promoting the assimilation of the slag, which suggests an improvement in the fluidity of the slag in the dripping zone. Therefore, it was considered that by depositing at least a part of the second iron raw material layer O2 near the furnace wall FW (dimensionless radius of furnace diameter: 0.9 to 1.0) and limiting the pellets to basic pellets (including mixed pellets), the slag fluidity near the furnace wall is improved and the formation of deposits on the furnace wall is suppressed, thereby further improving the air permeability of the blast furnace.

[0035] In this embodiment, the ore dump is divided into an O1 dump and an O2 dump (in other words, an ore dump with an increased pellet ratio) to form the iron raw material layer. This makes it easier to control the iron raw material layer to a desired layer structure. The method for forming the coke layer is not particularly limited.

[0036] However, the iron raw material layer may be formed in one dump. FIG. 4 shows a schematic diagram of the iron raw material layer formed in one dump. Referring to FIG. 4, when the iron raw material layer O is formed in one dump, the raw material charging step may be carried out so that the ratio of pellets contained in the upper layer Oeu (the boundary of the upper layer Oeu is shown by a dotted line in FIG. 4) of the iron raw material layer near the furnace wall (dimensionless radius of furnace diameter 0.7 to 1.0) is 50 mass % or more of the pellets contained in the entire iron raw material layer O. The upper layer Oeu is preferably the upper layer when the iron raw material layer is divided into two equal parts in the furnace height direction. In the iron raw material layer O, the upper layer Oeu corresponds to the second iron raw material layer, and the portion excluding the upper layer Oeu corresponds to the first iron raw material layer. A raw material charging method for realizing such a layered structure can be explored using a model experimental device simulating a blast furnace or a numerical simulation model such as DEM. In such an experimental device, iron raw materials including sintered ore and pellets are charged into the furnace while changing the arrangement of the pellets in the furnace top hopper, and an iron raw material layer is formed. After the iron raw material layer is formed, a raw material charging method for realizing the above-mentioned layered structure can be explored by evaluating the distribution of the pellets in the iron raw material layer. In the numerical simulation model, the processing performed in the above-mentioned experimental device is simulated by information processing using software.

[0037] (Example) The present invention will now be described in detail with reference to examples. Furnace capacity 4500m 3 In a large blast furnace of the class, iron raw material rich in pellet C (C / S = 0.76) was charged into the upper layer of the ore layer on the wall side of the blast furnace. Specifically, the ore dump was divided into two, and the first dump (O1 dump) mixed 33 mass% of the total pellets C and charged the iron raw materials in the entire area except for the vicinity of the furnace center (furnace diameter dimensionless radius 0.0 to 1.0), and the second dump (O2 dump) mixed 67 mass% of the total pellets C and charged the iron raw materials on the ore terrace. That is, the first iron raw material layer O1 was formed by the O1 dump, and the second iron raw material layer O2 was formed on the ore terrace of the first iron raw material layer O1 by the O2 dump. If the position of the second iron raw material layer O2 is defined by the furnace diameter dimensionless radius, it is 0.7 to 1.0, and the second iron raw material layer O2 was formed over this entire range. That is, 67 mass% of the total pellets were distributed to the second iron raw material layer O2. In the comparative example, iron raw materials not containing pellets were charged in the O2 dump. Table 1 shows the main specifications of the comparative example in comparison with the embodiment. [Table 1]

[0038] In the examples, the pellet ratio in the O2 dump was changed as follows compared to the comparative example. - Pellets ratio in O2 dump to the entire iron raw material layer: Changed from 0% to 6% by mass Pellets to iron raw material ratio in O2 dump: Changed from 0% to 32% by mass The productivity and raw fuel quality index during the operation period of the comparative example and the operation period of the example were approximately the same, and there was no change in the amount of fine sintered ore used.

[0039] The middle K value and the lower K value are indicators for evaluating permeability, and both values ​​decreased by changing the operation from the comparative example to the example. Therefore, improvement in permeability and stabilization of gas flow were confirmed. In addition, CR (coke ratio) also decreased slightly due to the improvement in permeability. The TK value, upper K value, middle K value, and lower K value are defined by the following formulas.

number

number

number

number

[0040] The ηCO, ηH2 and temperature distributions obtained through the upper probe are shown in Figures 5 to 7. 0 corresponds to the position of the furnace center, and 1 corresponds to the position of the furnace wall. By changing from the comparative example operation to the example operation, ηCO and ηH2 in the middle of the furnace decreased, and ηCO and ηH2 on the furnace wall side increased. Therefore, it was confirmed that the reduction efficiency on the furnace wall side, where the pellet charging amount was increased, was improved. Regarding the temperature distribution, the temperature decreased especially from the middle of the furnace to the furnace wall, which is an advantageous temperature distribution for reducing pellets as described above.

[0041] As described above, by making the upper layer of the ore layer on the furnace wall side a pellet-rich iron raw material layer, it was confirmed that the permeability was improved, the CR (coke ratio) was reduced, and the reducibility was improved. [Explanation of symbols]

[0042] O1 First iron raw material layer O2 Second iron raw material layer Oeu Upper Layer (Second Iron Raw Material Layer) C Coke layer OT Coke Terrace OTe Terrace shoulder FW furnace wall CE furnace center

Claims

1. A method for operating a blast furnace, comprising a raw material charging step of forming a predetermined iron raw material layer in a furnace, the raw material layer being made of iron raw materials including at least sintered ore and pellets, the predetermined iron raw material layer includes a first iron raw material layer and a second iron raw material layer, the second iron raw material layer is formed on the first iron raw material layer, the second iron raw material layer contains 50 mass% or more of the pellets contained in the predetermined iron raw material layer, and is formed in at least a part of a furnace diameter dimensionless radius range of 0.7 to 1.

0. A method for operating a blast furnace comprising the steps of:

2. 2. The method for operating a blast furnace according to claim 1, wherein the second layer of iron raw material is formed on an ore terrace of the first layer of iron raw material.

3. 3. The method for operating a blast furnace according to claim 1 or 2, wherein the first iron raw material layer and the second iron raw material layer are formed in different ore dumps.

4. The pellets are basic pellets or a mixture of the basic pellets and the acidic pellets, At least a part of the second iron raw material layer is formed in a furnace diameter dimensionless radius in a range of 0.9 to 1.

0.

3. The method for operating a blast furnace according to claim 1 or 2.

5. The pellets are basic pellets or a mixture of the basic pellets and the acidic pellets, At least a part of the second iron raw material layer is formed in a furnace diameter dimensionless radius in a range of 0.9 to 1.

0.

4. The method for operating a blast furnace according to claim 3.

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