JP7560735B2 - Method for designing mixture of iron-containing raw materials and method for operating blast furnace - Google Patents

Description

The present invention relates to a method for designing the mix of iron-containing raw materials that form an ore layer in a blast furnace, and a method for operating a blast furnace in which iron-containing raw materials mixed according to this mix design method are charged into the blast furnace to form an ore layer.

In a blast furnace, iron-containing ore raw materials (sintered ore, pellets, lump ore, etc.) and coke as a reducing agent and fuel are charged alternately from the top of the furnace, and hot air is blown in from the tuyeres at the bottom of the furnace together with auxiliary fuel such as pulverized coal. The ore raw materials and coke (hereinafter collectively referred to as "charge") charged from the top of the furnace form ore layers and coke layers that are layered alternately. As the ore raw materials and coke are lowered in the blast furnace, they gradually descend toward the bottom of the furnace, and are heated by the reducing gas rising from the bottom of the furnace, raising their temperature.

The raw ore material descends while being heated and reduced in the blast furnace. When it reaches the bottom of the furnace, it begins to soften and melt, forming a fused ore layer. In the fused ore layer, the gaps between the raw ore material decrease, and the permeability of the reducing gas decreases. For this reason, the reducing gas passes through the coke layer adjacent to the fused ore layer and rises toward the top of the furnace. The area in the blast furnace where the fused ore layer exists (including the coke layer adjacent to the fused ore layer) is called the fused zone. Therefore, the shape of the fused zone has an extremely large effect on the permeability of the blast furnace.

Therefore, in the past, the air permeability inside the blast furnace was controlled by focusing on the reducibility of the raw ore.

For example, Patent Document 1 discloses a method of operating a blast furnace that suppresses deterioration of coke strength and powdering in the blast furnace and ensures good permeability within the furnace by maintaining the weighted average value of the coke reactivity index (CRI) of all charged coke, the weighted average value of the sinter reducibility index (RI) of all charged sinter, and the amount of blast furnace slag per ton of molten iron within a predetermined range.

Patent Document 2 discloses a blast furnace operation method in which the reduction rate of iron ores is maintained at ₅₀ % or more by adjusting one or more of the component ratios of FeO and _Al2O3 in the sintered ore charged to the blast furnace, the slag ratio of the blast furnace charge, and the blast moisture in the hot air blown from the tuyere of the blast furnace, thereby improving the permeability in the lower part of the furnace, stabilizing the blast furnace condition, and reducing the fuel rate.

In addition, a method is known that focuses on and manages the S value (the area of the portion where the pressure drop is 200 mmH ₂ O or more in a time-pressure drop curve obtained by heating and reducing sintered ore), which is one of the indexes (hereinafter also referred to as "high temperature property evaluation indexes") that represent the high temperature properties of iron-containing raw materials such as raw ore (Patent Document 3). More specifically, Patent Document 3 discloses a method of charging sintered ore into a blast furnace, in which sintered ore is divided into two types based on its high temperature properties (S value), and the sintered ore with poor high temperature properties is charged as a lower layer and the sintered ore with excellent high temperature properties is charged above it as an upper layer, thereby improving the reducibility of the entire ore layer.

JP 2005-272968 A Japanese Patent Application Publication No. 6-256818 JP 2002-309306 A

Iron and Steel, Vol. 83 (1997), pp. 97-102, "Development of a method for evaluating the softening and melting properties of sintered ore"

The high-temperature properties of iron-containing raw materials, such as ore raw materials, are one of the important factors that determine the shape of the cohesive zone. In addition to the S value mentioned above, conventional high-temperature property evaluation indices include the fusion start temperature (Ts), the drip start temperature (Te, Td), and the difference between the drip start temperature and the fusion start temperature (ΔT = Te - Ts) (for example, Non-Patent Document 1).

On the other hand, from the viewpoint of reducibility of iron-containing raw materials, the reduction ratio at the melting start temperature (Ts) is important, and therefore, in the present invention, this is defined as the melting start reduction ratio (Rs). A blending design method for designing the blending of iron-containing raw materials that form the iron-containing raw material layer in a blast furnace using the melting start reduction ratio (Rs) has not been reported so far.

The present invention aims to provide a method for designing the mix of iron-containing raw materials that form the iron-containing raw material layer in a blast furnace using the reduction rate (Rs) at the start of fusion.

In order to solve the above-mentioned problems, the blending design method of the present invention is (1) a blending design method for designing a blending of a plurality of types of iron-containing raw materials that form an iron-containing raw material layer in a blast furnace, _and is characterized in that the blending of a plurality of types of the iron-containing raw materials is designed so that a weighted average value Rs _av of the reduction rate at the start of fusion of the plurality of types of the iron-containing raw materials, represented by the following formula (I), is equal to or greater than a lower limit value Rs min, and the lower limit value Rs _min is a weighted average value Rs _{av that corresponds to a target value of at least one parameter selected from the air permeability index, coke ratio, and productivity in the blast furnace, which is determined in advance based on the track record during stable operation of the blast furnace, in a correlation between the weighted average value Rs av} and the weighted average value Rs _av .
In the above formula (I), i is the type of iron-containing raw material, Rs _i is the reduction rate [%] of the type i of iron-containing raw material at the start of fusion [%], and M _i R is the blending ratio [mass %] of the type i of iron-containing raw material to all types of iron-containing raw materials.

(2) The method for designing a blend of iron-containing raw materials according to (1), characterized in that the highest value among the weighted average values Rs _av corresponding to the target values of two or more of the parameters is determined as the lower limit value Rs _min .

(3) The blending design method of the iron-containing raw materials according to (1) or (2), further comprising designing a blend of the plurality of types of the iron-containing raw materials so that a variation σRs of reduction rates at the start of fusion of the plurality of types of the iron-containing raw materials, represented by the following formula (II), is 10% or less:
In the above formula (II), i is the type of iron-containing raw material, Rs _i is the reduction rate [%] of the type i of iron-containing raw material at the start of fusion, Rs _av is the weighted average value [%] of the reduction rates of multiple types of the iron-containing raw materials at the start of fusion, and M _i R is the blending ratio [mass %] of the type i of iron-containing raw material to all types of iron-containing raw materials.

(4) The method for designing a blend of iron-containing raw materials according to any one of (1) to (3), characterized in that one type of iron-containing raw material among the plurality of types of iron-containing raw materials is composed of a plurality of lump ores of different brands, the reduction ratio Rs _i of the lump ores at the start of fusion is the reduction ratio of each of the brands at the start of fusion, and the blending ratio M _i R of the lump ores is the blending ratio of each of the brands.

(5) The method for designing a blend of iron-containing raw materials according to any one of (1) to (4), characterized in that one type of iron-containing raw material among the plurality of types of iron-containing raw materials is composed of a plurality of pellets of different brands, the reduction ratio Rs _i at the start of fusion of the pellets is the reduction ratio at the start of fusion of each of the brands, and the blending ratio M _i R of the pellets is the blending ratio for each of the brands.

(6) The method for designing a blend of iron-containing raw materials according to any one of (1) to (5), characterized in that one type of iron-containing raw material among the plurality of types of iron-containing raw materials is composed of a plurality of sintered ores having different sintering raw materials and/or firing conditions, the reduction rate Rs _i of the sintered ores at the start of fusion is the reduction rate of each of the sintered ores having different sintering raw materials and/or firing conditions, and the blending ratio M _i R of the sintered ores is the blending ratio of each of the sintered ores having different sintering raw materials and/or firing conditions.

(7) A method for operating a blast furnace, comprising charging into the blast furnace a plurality of types of iron-containing raw materials whose mix has been designed by the method for designing the mix of iron-containing raw materials described in any one of (1) to (6) to form an iron-containing raw material layer.

According to the present invention, a method for designing the mix of iron-containing raw materials that form the iron-containing raw material layer in a blast furnace can be provided using the reduction rate (Rs) at the start of fusion.

FIG. FIG. 1 is a diagram showing an apparatus for measuring a reduction rate at the start of fusion. FIG. 2 is a diagram showing conditions for measuring the reduction rate at the start of fusion. FIG. 2 is a diagram showing an example of high-temperature properties of sintered ore. FIG. 13 is a diagram illustrating the correlation between the corrected airflow resistance index K2 _cor and the weighted average value Rs _av (lower limit value Rs _min ). FIG. 13 is a diagram illustrating the correlation between the coke ratio CR and the weighted average value Rs _av (lower limit value Rs _min ). FIG. 1 is a diagram illustrating the correlation between the productivity and the weighted average value Rs _av (lower limit value Rs _min ). FIG. 2 is a diagram illustrating the relationship between the reduction rate Rs at the start of fusion and the air permeability in a blast furnace. FIG. 13 is a graph showing the relationship between the corrected air resistance index K2 _cor and the weighted average value Rs _av before and after mix design. FIG. 1 is a diagram showing the relationship between the coke ratio CR and the weighted average value Rs _av before and after the blend design. FIG. 1 is a diagram showing the relationship between the productivity and the weighted average value Rs _av before and after the blend design. FIG. 11 is a diagram showing the relationship between the corrected airflow resistance index K2 _cor and the variation σRs in the reduction rate at the start of fusion.

First, the process by which the present invention was completed will be explained using Figure 1.

FIG. 1 is a diagram showing the inside of a blast furnace. As shown in FIG. 1, a charge 2 is charged into the blast furnace 1. The charge 2 is mainly coke and iron-containing raw materials (including ore raw materials described later), and the coke and iron-containing raw materials are charged alternately to form a coke layer 3 and an iron-containing raw material layer 4 that are alternately stacked. The iron-containing raw material layer 4 does not have to be composed of only iron-containing raw materials. For example, the iron-containing raw material layer 4 may contain coke. In the iron-containing raw material layer 4 that is heated and reduced and descends in the blast furnace, the iron-containing raw materials begin to soften and fuse, forming a fusion layer 5. The molten pig iron 9 that drips from the fusion layer 5 is stored in the hearth 10. The hot air blown into the blast _{furnace from the tuyere 7 burns the pulverized coal and coke in the raceway 8 in front of the tuyere, generating reducing gas (CO, H 2 )} , which rises in the furnace. In the cohesive zone 5, the iron-containing raw materials are fused together, so there are few gaps between the iron-containing raw materials, and the permeability of the reducing gas is poor. Therefore, the reducing gas passes through the coke layer 6 adjacent to the cohesive zone 5 and rises in the blast furnace 1. In other words, the permeability of the furnace gas in the cohesive zone is limited to the coke layer 6 adjacent to the cohesive zone 5, so the shape of the cohesive zone has a significant effect on the permeability of the blast furnace 1. The cohesive zone refers to the region in which the cohesive layers 5 are present, including the coke layers 6 between the cohesive layers 5.

The inventors considered that the high-temperature properties of the iron-containing raw materials affect the shape of the cohesive zone, and considered it important to grasp the high-temperature properties. As a result of intensive research focusing on an index representing the high-temperature properties (high-temperature property evaluation index), the inventors found that a value Rs av (hereinafter also simply referred to as "weighted average value Rs _av ") obtained by weighting the reduction ratios Rs at the start of fusion of the iron-containing raw materials of the plurality of types of iron-containing raw materials forming the iron-containing raw material layer ₄ according to the blending ratios (mass%) of the iron-containing raw materials correlates with the gas permeability in the blast furnace, and thus completed the present invention.

In this specification, the reduction rate Rs at the start of fusion refers to the reduction rate of the iron-containing raw material when a fusion layer is formed in the load-softening test described below. Whether or not a fusion layer is formed can be determined by whether or not the pressure loss of the iron-containing raw material layer reaches a predetermined value in the load-softening test described below. For example, it can be determined that a fusion layer is formed when the pressure loss of the iron-containing raw material layer reaches 200 x 9.8 Pa.

First Embodiment
A first embodiment of the present invention will now be described.

The blending design method of this embodiment is a method for designing the blending of multiple types of ore raw materials that form an ore layer (corresponding to the iron-containing raw material layer described above). The ore raw material is a raw material that contains 50% by mass or more of iron. At least two types of ore raw materials are used for the ore raw materials whose blending is designed by the blending design method of this embodiment, and for example, two or more types of ore raw materials selected from the group consisting of sintered ore, lump ore, and pellets are used.

In the blending design method of the present embodiment, the blending of multiple types of ore raw materials is designed so that the weighted average value Rs _av of the reduction rates Rs at the start of fusion of multiple types of ore raw materials is equal to or greater than the lower limit value Rs _min described below. The weighted average value Rs _av is expressed by the following formula (1).

In the above formula (1), Rs _av is the weighted average value [%] of the reduction rates at the start of fusion of multiple types of ore raw materials, i is the type of ore raw material, Rs _i is the reduction rate [%] of the ore raw material type i at the start of fusion, and M _i R is the blending ratio [mass %] of the ore raw material type i to all types of ore raw materials.

In the above formula (1), the reduction ratio Rs at the start of fusion measured for each type of ore raw material is used as the reduction ratio Rs _i of the ore raw material of type i. The reduction ratio Rs at the start of fusion is measured using the load-softening test described in Non-Patent Document 1, and the following measuring device and measuring conditions are used.

(Apparatus for measuring reduction rate Rs at the start of fusion)
FIG. 2 shows an apparatus for measuring the reduction rate Rs at the start of fusion. In this measuring apparatus, as shown in FIG. 2, Tamman electric furnaces are arranged in two stages, one above the other, and the two furnaces (upper furnace 12 and lower furnace 11) are connected by a flange. Gas 17 is introduced from the lower part of the lower furnace 11. In the lower furnace 11, the lower furnace heater H' is controlled by the lower furnace heater control means 16, and the gas 17 is preheated. Then, the gas 17 preheated to a high temperature is introduced into the upper reduction furnace (upper furnace 12). The gas 17 introduced into the upper furnace 12 is introduced into a graphite crucible 13 (inner diameter approximately 85 mm) with a perforated bottom, and the ore raw material in the ore layer 14 sandwiched between two coke layers 21 is heated and reduced. A load is applied to the coke layer 21 and the ore layer 14 by a load machine 19. When the gas 17 is introduced into the upper furnace 12 and the lower furnace 11 to heat and reduce the raw ore, the upper furnace heater H is controlled by the upper furnace heater control means 15 to perform adiabatic control so that the difference between the outer wall temperature of the reaction tube (a reaction tube provided between the graphite crucible 13 and the upper furnace heater H) of the upper furnace 12 and the temperature of the top of the sample layer (a layer composed of the coke layer 21 and the ore layer 14) is constant. The upper furnace heater control means 15 also performs heating control as described below. The post-reduced gas 18 is discharged from the top of the upper furnace 12. The molten iron generated by heating and reducing the raw ore in the ore layer 14 is received in the dripping molten iron receiver 20. According to this device, the reduction and melting behavior of the raw ore in the actual furnace can be accurately grasped by introducing the gas 17 preheated to a high temperature and performing adiabatic control.

(Conditions for measuring reduction rate Rs at the start of fusion)
The ore raw material forming the ore layer 14 is any one of a plurality of types of ore raw materials for which the blending is designed. A load-softening test is performed for each type of ore raw material for which the blending is designed, so that the reduction ratio Rs at the start of fusion can be measured for each type of ore raw material. The ore raw material forming the ore layer 14 is made of ore raw material sized to 10 mm to 15 mm. The ore layer 14 is formed to have a layer thickness of approximately 70 mm. The coke forming the coke layer 21 is made of coke sized to 10 mm to 15 mm. The coke layers 21 sandwiching the ore layer 14 are each made to have a layer thickness of approximately 20 mm.

The composition and temperature conditions of the gas 17 introduced into the above-mentioned measuring device are as shown in FIG. 3. Specifically, the heating rate of the gas 17 in the lower furnace 11 is set to 10° C./min, which is the maximum capacity of the furnace, and the temperature of the gas 17 is maintained at this temperature after it reaches the maximum normal temperature of the furnace (1700° C.). The heating rate of the gas 17 in the upper furnace 12 is set to 10° C./min up to 1000° C., and is set to 5° C./min, which is the average heating rate of an actual furnace, at 1000° C. or higher. Regarding the composition of the gas 17, N ₂ is introduced up to 800° C., and a reducing gas (CO: 29.4 vol.%-H ₂ : 3.6 vol.%-N ₂ : 67.0 vol.%) is introduced at 800° C. or higher. The gas flow rate is constant at 34 Nl/min, and a standard superficial velocity of 10 cm/sec is ensured. The composition of gas 17 was determined based on the bosh gas composition when the blast humidity was 15×10 ⁻³ kg/Nm ³ and the pulverized coal ratio was 100 kg/t-pig, by adjusting N 2 while keeping the H 2 /CO ratio constant so that the reduction rate of the _ore raw material at 1000 _° C would be 30%, which is almost the same as the results of an actual dismantling investigation (the results of an investigation after dismantling an actual furnace).

As shown in FIG. 3, the load applied to the ore layer 14 and the coke layer 21 is 0.098 MPa when the temperature of the gas 17 is 800°C or higher. At this load (0.098 MPa) or higher, the load dependency on shrinkage and ventilation is extremely small, so the above-mentioned conditions are used. Note that when the temperature is less than 800°C, no load is applied to the ore layer 14 and the coke layer 21. The upper furnace 12 performs heating control at the start of the test, switches to adiabatic control at around 1200°C, and switches back to heating control after molten iron has dripped into most of the sample layer (ore layer 14).

Figure 4 shows an example of the high-temperature property evaluation index of sintered ore measured by the load-softening test described in Non-Patent Document 1 using the above-mentioned measuring device and measuring conditions. In this embodiment, of the high-temperature property evaluation indexes shown in Figure 4, the reduction ratio when the fusion layer is formed (when the pressure loss in the ore layer reaches 200 x 9.8 Pa), that is, the reduction ratio at the start of fusion Rs, is used.

In addition to the reduction rate Rs at the start of fusion, FIG. 4 also shows, as high-temperature property evaluation indexes, the maximum value of the pressure loss in the ore layer (maximum pressure loss value ΔP _max ), the temperature when the fusion layer is formed (when the pressure loss in the ore layer reaches 200×9.8 Pa) (fusion start temperature Ts), the temperature width (temperature width ΔT) of the ore layer when the fusion layer is formed (when the pressure loss in the ore layer is 200×9.8 Pa or more), the integral value (S′) of the pressure loss when the fusion layer is formed (when the pressure loss in the ore layer is 200×9.8 Pa or more (i.e., within the temperature width ΔT)), the dripping start temperature of the ore raw material (dripping start temperature Td), and the temperature (Te) when the pressure loss in the ore layer decreases to the pressure loss when the fusion layer is formed (200×9.8 Pa).

In this embodiment, the above-mentioned test is performed for each type of raw ore, and the measured reduction ratio Rs at the start of fusion of each raw ore is used as the reduction ratio Rs _i at the start of fusion in the above formula (1).

In the above formula (1), the blending ratio M _i R of the ore raw material type i is the blending ratio MR (the mass ratio of each type of ore raw material to 100 mass% of all types of ore raw materials for which the blend is designed) obtained for each type of ore raw material. The method of obtaining the blending ratio MR is not particularly limited, and the mass of each type of ore raw material may be actually measured or the mass of each type of ore raw material may be predicted.

(Regarding the lower limit Rs _min )
The lower limit Rs _min is determined based on at least one parameter of the airflow resistance index K2 in the blast furnace, the coke ratio CR, and the productivity. A detailed description will be given below, but first, the airflow resistance index K2 will be described.

The airflow resistance index K2 is a known index that indicates airflow resistance (for example, see "Handbook of Steel Properties, Steelmaking Edition," p. 250, published by the Iron and Steel Institute of Japan and the 54th Ironmaking Committee of the Japan Society for the Promotion of Science, 2006), and the higher the airflow resistance (in other words, the lower the breathability), the higher the airflow resistance index K2. The airflow resistance index K2 can be calculated using the following formula (2).

In the above formula (2), K2 is the airflow resistance index [-], P _B is the blast pressure [hPa], P _T is the furnace top pressure [hPa], L is the effective height of the blast furnace (height from the tuyere to the surface of the charge) [m], V is the bosh gas amount [Nm ³ /min], and D is the hearth diameter [m].

Next, a method for determining the lower limit value Rs _min from the airflow resistance index K2 will be described.

If the correlation between the weighted average value Rs _av and the airflow resistance index K2 is determined in advance, the weighted average value Rs _av corresponding to the airflow resistance index K2 (target value) can be determined as the lower limit value Rs _min by specifying the target value of the airflow resistance index K2. The correlation between the weighted average value Rs _av and the airflow resistance index K2 can be determined by the method described below.

In a coordinate system with the weighted average value Rs _av and the airflow resistance index K2 as coordinate axes, the operation performance of the blast furnace is plotted, and the area where the operation performance of the blast furnace when stable operation is performed (hereinafter referred to as the "stable operation area") is plotted, and the area where the operation performance of the blast furnace when stable operation is not performed (hereinafter referred to as the "unstable operation area") is plotted is identified. Then, the boundary line dividing the stable operation area and the unstable operation area can be defined as the correlation between the weighted average value Rs _av and the airflow resistance index K2. The "division" here does not mean that the stable operation area and the unstable operation area are strictly divided, but it is sufficient if it can roughly divide the stable operation area and the unstable operation area.

The boundary between the stable operation region and the unstable operation region can be created, for example, by the following procedure. Among the operation records in which stable operation was performed, the operation record having the smallest value of the airflow resistance index K2 is extracted for each weighted average value Rs _av . Next, an approximation formula is created based on the extracted operation record and the weighted average value Rs _av , and this is used as the boundary line. In addition, since it is not necessary to strictly divide the stable operation region and the unstable operation region as described above, in identifying the stable operation region, it is not necessary to use the region in which all operation records in which stable operation was performed are plotted. In roughly dividing the stable operation region and the unstable operation region, for example, the region in which 90% or more of all operation records in which stable operation was performed are plotted can be regarded as the stable operation region.

In Fig. 5, the results of stable operation in four blast furnaces 1 to 4 are plotted, and the correlation (one example) between the weighted average value Rs _av and the corrected airflow resistance index K2 _cor is shown. In Fig. 5, the corrected airflow resistance index K2 _cor is used instead of the airflow resistance index K2. The "airflow resistance index" in the present invention includes the airflow resistance index K2 and the corrected airflow resistance index K2 _cor .

The corrected airflow resistance index K2 _cor is a value obtained by correcting the airflow resistance index K2 represented by the above formula (2) based on the coke ratio CR and coke strength DI in blast furnace operation. Since the airflow resistance index K2 is affected by the coke ratio CR and coke strength DI, it is preferable to understand the correlation with the weighted average value Rs _av after excluding the influence of the coke ratio CR and coke strength DI. Therefore, the corrected airflow resistance index K2 _cor was used instead of the airflow resistance index K2. Here, the airflow resistance index K2 was set to a value when the coke ratio CR was 320 kg/t (reference value) and the coke strength DI was 86% (reference value).

In the calculation of the corrected air permeability resistance index K2 _cor , a correction was made by adding 3 [-] to the air permeability resistance index K2 in response to an increase in the coke ratio CR in the blast furnace operation by 1 kg/t relative to the reference value (320 kg/t). In addition, a correction was made by subtracting 3 [-] from the air permeability resistance index K2 in response to a decrease in the coke ratio CR in the blast furnace operation by 1 kg/t relative to the reference value (320 kg/t). On the other hand, a correction was made by adding 120 [-] to the air permeability resistance index K2 in response to an increase in the coke strength DI in the blast furnace operation by 1% relative to the reference value (86%). In addition, a correction was made by subtracting 120 [-] from the air permeability resistance index K2 in response to a decrease in the coke strength DI in the blast furnace operation by 1% relative to the reference value (86%).

According to FIG. 5, the correlation between the weighted average value Rs _av and the corrected airflow resistance index K2 _cor is defined by a straight line (dotted line) shown as the lower limit Rs _min . According to the straight line (dotted line) of the lower limit Rs _min , the higher the corrected airflow resistance index K2 _cor , the lower the lower limit Rs _min , and the lower the corrected airflow resistance index K2 _cor , the higher the lower limit Rs _min . The region where the corrected airflow resistance index K2 _cor is high relative to the straight line (dotted line ₎ of the lower limit Rs _min is a stable operation region, and the region where the corrected airflow resistance index K2 _cor is low relative to the straight line (dotted line) of the lower limit Rs _{min includes an unstable operation region. Note that all the operational results plotted in FIG. 5 are operational results in which stable operation was performed, but some operational results are excluded to determine the straight line (dotted line) of the lower limit Rs min} .

5, if the correlation between the weighted average value Rs _av and the corrected airflow resistance index K2 _cor (i.e., the straight line of the lower limit Rs _min ) is determined, it is possible to specify the lower limit Rs _min corresponding to the target value of the corrected airflow resistance index K2 _cor . For example, when the target value of the corrected airflow resistance index K2 _cor is 800 [-], the lower limit Rs _min is 58 [%].

In the example shown in Fig. 5, the correlation between the weighted average value Rs _av and the corrected airflow resistance index K2 _cor is expressed as a linear function (a straight line with the lower limit value Rs _min ), but is not limited to this. As described above, the correlation between the weighted average value Rs _av and the corrected airflow resistance index K2 _cor may be defined as a boundary line dividing the stable operation region and the unstable operation region.

Next, a method for determining the lower limit value Rs _min from the coke ratio CR will be described.

If the correlation between the weighted average value Rs _av and the coke ratio CR is determined in advance, the weighted average value Rs _av corresponding to the coke ratio CR (target value) can be determined as the lower limit value Rs _min by specifying the target value of the coke ratio CR. The correlation between the weighted average value Rs _av and the coke ratio CR can be determined by the method described below.

In a coordinate system with the weighted average value Rs _av and the coke rate CR as the coordinate axes, the operation record of the blast furnace is plotted, and the stable operation region and the unstable operation region are identified as described above. Then, the boundary line dividing the stable operation region and the unstable operation region can be defined as the correlation between the weighted average value Rs _av and the coke rate CR.

The boundary line between the stable operation region and the unstable operation region can be created, for example, by the following procedure: Among the operational records in which stable operation was performed, the operational record having the lowest coke ratio CR is extracted for each weighted average value Rs _av . Next, an approximation formula is created based on the extracted operational records and the weighted average value Rs _av , and this is used as the boundary line.

In Fig. 6, the results of stable operation in four blast furnaces 1 to 4 are plotted, and the correlation between the weighted average value Rs _av and the coke ratio CR (one example) is shown. According to Fig. 6, the correlation between the weighted average value Rs _av and the coke ratio CR is defined by a straight line shown as the lower limit value Rs _min . According to this straight line of the lower limit value Rs _min , when the coke ratio CR is 330 [kg/t], the lower limit value Rs _min is 56 [%], and the lower limit value Rs _min increases by 2 [%] in response to a decrease in the coke ratio CR by 10 [kg/t].

According to the straight line of the lower limit Rs _min shown in Fig. 6, the higher the coke rate CR, the lower the lower limit Rs _min , and the lower the coke rate CR, the higher the lower limit Rs _min . The region on the side of the straight line of the lower limit Rs _min where the coke rate CR is high is a stable operation region, and the region on the side of the straight line of the lower limit Rs _min where the coke rate CR is low includes an unstable operation region. Note that all the operation results plotted in Fig. 6 are operation results where stable operation was performed, but some operation results are excluded to determine the straight line of the lower limit Rs _min (dotted line).

6, if the correlation between the weighted average value Rs _av and the coke ratio CR (i.e., the straight line of the lower limit value Rs _min ) is determined, it is possible to specify the lower limit value Rs _min corresponding to the target value of the coke ratio CR. For example, when the target value of the coke ratio CR is set to 290 [kg/t], the lower limit value Rs _min is 64 [%].

In the example shown in Fig. 6, the correlation between the weighted average value Rs _av and the coke rate CR is expressed as a linear function (a straight line of the lower limit value Rs _min ), but is not limited to this. As described above, the correlation between the weighted average value Rs _av and the coke rate CR may be defined as a boundary line dividing the stable operation region and the unstable operation region.

Next, a method for determining the lower limit value Rs _min from the productivity will be described.

If the correlation between the weighted average value Rs _av and the productivity is determined in advance, the weighted average value Rs _av corresponding to the productivity (target value) can be determined as the lower limit value Rs _min by specifying the target value of the productivity. The correlation between the weighted average value Rs _av and the productivity can be determined by the method described below.

In a coordinate system with the weighted average value Rs _av and the productivity as the coordinate axes, the operation record of the blast furnace is plotted, and the stable operation region and the unstable operation region are identified as described above. Then, the boundary line dividing the stable operation region and the unstable operation region can be defined as the correlation between the weighted average value Rs _av and the productivity.

The boundary line between the stable operation region and the unstable operation region can be created, for example, by the following procedure: Among the operational records in which stable operation was performed, the operational record having the highest productivity value is extracted for each weighted average value Rs _av . Next, an approximation formula is created based on the extracted operational records and the weighted average value Rs _av , and this is used as the boundary line.

In Fig. 7, the results of stable operation in four blast furnaces 1 to 4 are plotted, and the correlation between the weighted average value Rs _av and the productivity is shown (one example). According to Fig. 6, the correlation between the weighted average value Rs _av and the productivity is defined by a straight line shown as the lower limit value Rs _min . According to this straight line of the lower limit value Rs _min , the lower limit value Rs _min is 56% when the productivity is 1.8-, and the lower limit value Rs _min increases by 1% in response to an increase in the productivity by 0.1.

According to the straight line of the lower limit Rs _min , the higher the productivity, the higher the lower limit Rs _min , and the lower the productivity, the lower the lower limit Rs _min . The region on the lower productivity side of the straight line of the lower limit Rs _min is a stable operation region, and the region on the higher productivity side of the straight line of the lower limit Rs _min includes an unstable operation region. All the operational results plotted in FIG. 7 are operational results in which stable operation was performed, but some operational results are excluded to determine the straight line of the lower limit Rs _min (dotted line).

7, if the correlation between the weighted average value Rs _av and the productivity (i.e., the straight line of the lower limit value Rs _min ) is determined, the lower limit value Rs _min corresponding to the target value of the productivity can be specified. For example, when the target value of the productivity is set to 2.0 [−], the lower limit value Rs _min is 58 [%].

In the example shown in Fig. 7, the correlation between the weighted average value Rs _av and the productivity is expressed as a linear function (a straight line of the lower limit value Rs _min ), but is not limited thereto. As described above, the correlation between the weighted average value Rs _av and the productivity may be defined as a boundary line dividing the stable operation region and the unstable operation region.

The lower limit Rs _min can be determined based on two or more parameters among the air permeability index K2, the coke ratio CR, and the productivity. In this case, the lower limit Rs _min is determined for each parameter based on the above-mentioned method, and the lower limit Rs _min (candidate value) is generated as many times as the number of parameters. Among these lower limit Rs _min (candidate values), the lower limit Rs _min showing the highest value can be adopted as the lower limit Rs _min in the blending design method of this embodiment. As a result, when the blending design of the ore raw material is performed so that the weighted average value Rs _av is equal to or greater than the lower limit Rs _min , the weighted average value Rs _av can be equal to or greater than all the lower limit values Rs _min (candidate values). In addition, the lower limit Rs _min in the blending design method of this embodiment can also be the average value of multiple lower limit values Rs _min (candidate values).

(Regarding the mix design of mineral ore materials)
In the blending design method of this embodiment, a blending of multiple types of ore raw materials is designed so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min . As will be described in the examples below, when ore raw materials with blends designed to have different weighted average values Rs _av were used in an actual furnace as raw materials for forming an ore layer (hereinafter also referred to as "blast furnace raw materials"), the ventilation resistance in the blast furnace was stable at a low level if the weighted average value Rs _av was equal to or greater than the lower limit value Rs _min .

As can be understood from the above formula (1), the weighted average value Rs _av can be adjusted by changing the blending ratio M _i R and the reduction ratio Rs _i at the start of fusion. The blending ratio M _i R can be changed by changing the blending amount of each ore raw material. The reduction ratio Rs _i at the start of fusion can be changed by changing the type of ore raw material. Therefore, designing the blending of the ore raw materials so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min means, in other words, determining the blending ratio of the ore raw materials and the type of the ore raw materials that make the weighted average value Rs _av equal to or greater than the lower limit value Rs _min .

Table 1 below shows an example of the blending of the ore raw materials when calculating the weighted average value _Rsav . The results shown in Fig. 4 were obtained using the sintered ore shown in Table 1 below. σRs shown in Table 1 below is the variation in the reduction ratio Rs at the start of fusion of multiple types of ore raw materials, and the details will be described later.

The blending design method of this embodiment can be used when changing the blending ratio of the ore raw materials used in a blast furnace, or when changing the type of ore raw materials used in a blast furnace, as shown below.

When changing the blending ratio of the ore raw materials used in the blast furnace, for example, the reduction rate Rs at the start of fusion of each ore raw material already used is measured in advance, and when the blending ratio to be changed is set, it is judged whether the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min . If the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min , the blending ratio of the ore raw materials to be changed is adopted and the blending is designed (determined). If the weighted average value Rs _av is below the lower limit value Rs _min , the blending ratio is reviewed again and the blending is designed so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min . Note that if the weighted average value Rs _av is below the lower limit value Rs _min , the type of ore raw material may be reviewed and the blending may be designed so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min .

When changing the type of ore raw material used in the blast furnace, the reduction rate Rs at the start of fusion of the ore raw material to be changed (if there is any ore raw material that is not changed, the reduction rate Rs at the start of fusion of the ore raw material) is measured in advance, and when the type of ore raw material is changed without changing the blending ratio, it is determined whether the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min . If the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min , the blending is designed (determined) by adopting the change in type without changing the blending ratio already used. If the weighted average value Rs _av is below the lower limit value Rs _min , the blending ratio of the ore raw material is reviewed and the blending is designed so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min . Note that the type of ore raw material to be changed may be reviewed again to design the blending so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min .

The ore raw material, the composition of which is designed by the blending design method of this embodiment, is used as a blast furnace raw material. The blast furnace raw material may be composed only of the ore raw material, the composition of which is designed by the blending design method of this embodiment, but may contain, in addition to the ore raw material, for example, coke, ferro coke, carbon-containing agglomerates, and auxiliary materials. In this case, as described above, the composition of the ore raw material may be designed so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min, focusing only on the multiple types of ore raw materials (excluding coke, ferro coke, carbon-containing agglomerates, and auxiliary materials). By using the ore raw material, the composition of which is designed by the blending design method of this embodiment, as a blast furnace raw material for blast furnace operation, the permeability in the blast furnace is improved. The reason for this will be explained with reference to FIG. 8.

FIG. 8 is a diagram for explaining the relationship between the reduction rate Rs at the start of fusion and the air permeability in the blast furnace. As described above, since the fusion layer has poor air permeability, almost no reducing gas flows through the fusion layer, and passes through the coke layer adjacent to the fusion layer. In the process of forming the fusion layer from the ore layer, the main reduction form transitions from indirect reduction by reducing gas (FeO + CO (g) → Fe + CO ₂ (g) (exothermic reaction)) to direct reduction by solid carbon (FeO + C → Fe + CO (g) (endothermic reaction)). An increase in the reduction rate Rs at the start of fusion means that the indirect reduction rate (exothermic reaction) until the fusion layer is formed increases, and the direct reduction rate (endothermic reaction) in the lower part of the furnace decreases. Therefore, if the reduction rate Rs at the start of fusion increases, the amount of heat absorbed in the lower part of the furnace decreases (the endothermic reaction decreases), and the temperature rise of the ore raw material is promoted. When the temperature rise of the ore raw material is promoted, the carburization of the ore (iron) is promoted, and the dripping of the molten iron is promoted. As a result, the area of the cohesive zone on the furnace center side is reduced, and the reducing gas can easily pass through the cohesive layer. When the weighted average value Rs _av of the reduction rate Rs at the start of fusion of the ore raw material used as the blast furnace raw material is equal to or higher than the lower limit value Rs _min , this phenomenon occurs significantly, and it is considered that the gas permeability in the blast furnace is easily improved.

In the blending design method of this embodiment, it is preferable to design the blending of multiple types of raw ore materials so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min , and further, the variation σRs (hereinafter simply referred to as "variation σRs") of the reduction rates Rs at the start of fusion of multiple types of raw ore materials, expressed by the following formula (3), is 10% or less. The condition that the variation σRs is 10% or less has also been determined by the present inventor based on the examples described later.

In the above formula (3), σRs is the variation [%] of the reduction rate Rs at the start of fusion of multiple types of ore raw materials, i is the type of ore raw material, Rs _i is the reduction rate [%] of the ore raw material type i at the start of fusion, Rs _av is the weighted average value [%] of the reduction rate Rs _i at the start of fusion of multiple types of ore raw materials, and M _i R is the blending ratio [mass %] of the ore raw material type i to all types of ore raw materials.

The weighted average value Rs _av , the reduction rate Rs _i at the start of fusion, and the blending ratio M _i R in the above formula (3) are the same as the weighted average value Rs _av , the reduction rate Rs _i at the start of fusion, and the blending ratio M _i R in the above formula (1), respectively, and therefore detailed explanations are omitted.

The variation σRs can be adjusted by changing the blending amount of each raw ore and the type of raw ore, similarly to the weighted average value Rs _av . In other words, designing the blending of raw ore so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min and the variation σRs is equal to or less than 10% means determining the blending ratio of raw ore and the type of raw ore so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min and the variation σRs is equal to or less than 10%.

In addition to the weighted average value Rs _av being equal to or greater than the lower limit value Rs _min , the variation σRs being 10% or less further improves the air permeability in the blast furnace compared to the case where the variation σRs exceeds 10%.

In the above-described embodiment, the reduction rate Rs _i at the start of fusion and the blending ratio M _i R are set for each type of raw ore, but there are multiple brands of raw ore such as lump ore and pellets, and even if the type of raw ore is the same (lump ore or pellets), the reduction rate Rs at the start of fusion may differ between different brands. Therefore, in the blending design method of this embodiment, when multiple brands of raw ore are used as at least one type of raw ore among lump ore and pellets, it is preferable to use the reduction rate Rs at the start of fusion and the blending ratio MR set for each brand as the reduction rate Rs at the start of fusion and the blending ratio MR of the raw ore of that type.

Specifically, for example, in the case where sinter, lump ore, and pellets are used as the ore raw material, and lump ore of brand a and lump ore of brand b are used as the lump ores, the reduction ratio Rs at the start of fusion and the blending ratio MR set for the lump ore of brand a and the lump ore of brand b respectively become the reduction ratio Rs _i at the start of fusion and the blending ratio M _i R in the above formulas (1) and (3). That is, the subscript i shown in the above formulas (1) and (3) is defined not only to distinguish the type of ore raw material, but also to distinguish multiple brands belonging to one type.

For example, when sinter, lump ore, and pellets are used as raw ore materials, and when pellets of brand a and brand b are used as pellets, the reduction ratio Rs at the start of fusion and the blending ratio MR set for the pellets of brand a and the pellets of brand b are the reduction ratio Rs _i at the start of fusion and the blending ratio M _i R in the above formulas (1) and (3). That is, the subscript i shown in the above formulas (1) and (3) is defined not only to distinguish the type of raw ore materials, but also to distinguish multiple brands belonging to one type.

The brands include those named after the place of origin (mine) of the ore raw material or the manufacturer's company. The blending ratio MR set for each brand is the mass ratio of each brand of ore raw material to 100% mass of all types and brands (by type), and is not the mass ratio of each brand of lump ore to all brands of lump ore (i.e., the mass ratio of each brand of lump ore to 100% mass of lump ore) or the mass ratio of each brand of pellets to all brands of pellets (i.e., the mass ratio of each brand of pellets to 100% mass of pellets).

Similarly, there are multiple sintered ores with different sintering raw materials and/or firing conditions, and the reduction rate Rs at the start of fusion may differ between sintered ores with different sintering raw materials and/or firing conditions. When the sintering raw materials are different, the components or particle size of the sintering raw materials themselves may be different, or the blending ratio of the sintering raw materials may be different. When the sintering raw materials are different, for example, the components of the sintered ore will be different, and the reduction rate Rs at the start of fusion may be different. On the other hand, an example of a firing condition is the fuel ratio. When the firing conditions are different, the pore structure of the sintered ore will be different, and the reduction rate Rs at the start of fusion may be different.

For this reason, in the blending design method of this embodiment, when a plurality of sintered ores with different sintering raw materials and/or firing conditions are used as the fusion start reduction rate _Rs and blending ratio M _i R shown in the above formulas (1) and (3), it is preferable to use the fusion start reduction rate Rs and blending ratio MR set for each sintered ore with different sintering raw materials and/or firing conditions, respectively. In addition, the blending ratio MR set for each sintered ore with different sintering raw materials and/or firing conditions is the mass ratio of each sintered ore with different sintering raw materials and firing conditions to 100 mass% of all types of ore raw materials, and is not the mass ratio of each sintered ore with different sintering raw materials and firing conditions to all sintered ores with different sintering raw materials and firing conditions.

Even if the ore raw material is the same type, by setting the reduction ratio Rs at the start of fusion and the blending ratio MR for each sintered raw material and/or ore raw material (sintered ore) with different firing conditions or for each brand of ore raw material (lump ore, pellets), it becomes easier to obtain the weighted average value Rs _av and the variation σRs that more accurately reflect the actual high-temperature properties (reduction ratio Rs at the start of fusion) of the ore raw material.

When adjusting the weighted average value Rs _av and the variation σRs for sintering raw materials and/or ore raw materials (sintered ore) with different firing conditions or ore raw materials of different brands (lump ore, pellets) to perform blending design, in addition to the blending ratio of each type of ore raw material, it is possible to change the blending ratio of each sintering raw material and/or ore raw material (sintered ore) with different firing conditions or ore raw material of different brands (lump ore, pellets), and it is also possible to change the type of ore raw material, as well as the sintering raw material and/or the firing conditions and the brand.

(Blast furnace operation method)
In blast furnace operation, multiple types of ore raw materials whose mixes are designed by the mix design method of this embodiment are charged into the blast furnace to form an ore layer (corresponding to the iron-containing raw material layer in the present invention) in the blast furnace.

Second Embodiment
Next, a second embodiment of the present invention will be described.

This embodiment is a method for designing a blend of multiple types of iron-containing raw materials that form an iron-containing raw material layer. The iron-containing raw materials are raw materials that contain 15% or more by mass of iron, and specifically include sintered ore, pellets, lump ore, as well as carbon-containing agglomerated ore and ferro-coke. The iron-containing raw materials are a concept that includes ore raw materials. In addition, the types of iron-containing raw materials refer to classifications such as sintered ore, pellets, lump ore, carbon-containing agglomerated ore, and ferro-coke.

As described above, the cohesive layer is formed by softening and fusing the ore raw material contained in the iron-containing raw material layer, but when the iron-containing raw material layer contains iron-containing raw materials other than the ore raw material, the iron-containing raw materials may also contribute to the formation of the cohesive layer. In other words, they may affect the shape of the cohesive zone. Therefore, in this embodiment, a reduction ratio Rs at the start of fusing is set for each type of iron-containing raw material, and the blending of multiple types of iron-containing raw materials is designed so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min .

Two or more types of iron-containing raw materials are used for the iron-containing raw materials for which the blending design method of this embodiment is used, and for example, two or more types of iron-containing raw materials selected from the group consisting of sintered ore, lump ore, pellets, ferrocoke, and carbon-containing agglomerated ore can be used.

In the blending design method of the present embodiment, a blending of a plurality of types of iron-containing raw materials is designed so that a weighted average value Rs _av of the reduction ratios _Rs at the start of fusion of a plurality of types of iron-containing raw materials, which is expressed by the following formula (4), is equal to or greater than a lower limit value Rs _min . As described in the first embodiment, the lower limit value Rs min can be determined based on any one of the air permeability index K2 (or the corrected air permeability index K2 _cor ), the coke ratio CR, and the pig iron productivity, or can be determined based on two or more parameters of the air permeability index K2 (or the corrected air permeability index K2 _cor ), the coke ratio CR, and the pig iron productivity.

In the above formula (4), Rs _av is the weighted average value [%] of the reduction rates Rs _i of multiple types of iron-containing raw materials at the start of fusion, i is the type of iron-containing raw material, Rs _i is the reduction rate [%] of the type i of iron-containing raw material at the start of fusion, and M _i R is the blending ratio [mass %] of the type i of iron-containing raw material to all types of iron-containing raw materials.

In the above formula (4), the reduction ratio _Rs at the start of fusion of the iron-containing raw material of type i is the reduction ratio Rs at the start of fusion measured for each type of iron-containing raw material. The reduction ratio Rs at the start of fusion of the iron-containing raw material can be measured by the load-softening test described in Non-Patent Document 1, as in the first embodiment. The load-softening test described in Non-Patent Document 1 and the device and conditions used for the test are the same as those in the first embodiment, so a detailed description will be omitted. In addition, the blending ratio M _i R of the iron-containing raw material of type i in the above formula (4) is calculated in the same way as the blending ratio M _i R in the first embodiment (the blending ratio M _i R in the above formula (1)), so a detailed description will be omitted.

The weighted average value Rs _av expressed by the above formula (4) can be adjusted by changing the blending amount of each iron-containing raw material and the type of iron-containing raw material. Therefore, in this embodiment, designing the blending of the iron-containing raw materials so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min means determining the blending ratio of the iron-containing raw materials and the type of the iron-containing raw materials so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min .

The blending design method of this embodiment, like the blending design method of the first embodiment, can be used when changing the blending ratio of the iron-containing raw materials used in the blast furnace or when changing the type of iron-containing raw materials used in the blast furnace. The specific method is the same as in the first embodiment, so a detailed description is omitted.

The iron-containing raw materials whose composition is designed by the composition design method of this embodiment are used as raw materials (blast furnace raw materials) for forming an iron-containing raw material layer. The blast furnace raw materials may be composed only of the iron-containing raw materials whose composition is designed by the composition design method of this embodiment, but may contain, for example, coke and auxiliary raw materials in addition to the iron-containing raw materials. In this case, as described above, the composition of the iron-containing raw materials may be designed so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min, focusing only on the multiple types of iron-containing raw materials (excluding coke and auxiliary raw materials). By using the iron-containing raw materials whose composition is designed by the composition design method of this embodiment as blast furnace raw materials for blast furnace operation, the permeability in the blast furnace is improved. This is thought to be one of the reasons that, as described in the first embodiment, the cohesive zone on the furnace center side is reduced, and the phenomenon that the reducing gas in the furnace easily passes through the coke layer adjacent to the cohesive layer occurs significantly.

In the blending design method of the present embodiment, it is preferable to design the blending of the plurality of types of iron-containing raw materials so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min , and further, the variation σRs (hereinafter, simply referred to as "variation σRs") of the reduction rates Rs _i at the start of fusion of the plurality of types of iron-containing raw materials, which is expressed by the following formula (5), is 10% or less.

In the above formula (5), σRs is the variation [%] of the reduction rate Rs of the multiple types of iron-containing raw materials at the start of fusion, i is the type of iron-containing raw material, Rs _i is the reduction rate [%] of the type i of iron-containing raw material at the start of fusion, Rs _av is the weighted average value [%] of the reduction rates Rs _i of the multiple types of iron-containing raw materials at the start of fusion, and M _i R is the blending ratio [mass %] of the type i of iron-containing raw materials to all types of iron-containing raw materials.

The weighted average value Rs _av , the reduction rate Rs _i at the start of fusion, and the blending ratio M _i R in the above formula (5) are the same as the weighted average value Rs _av , the reduction rate Rs _i at the start of fusion, and the blending ratio M _i R in the above formula (4), respectively, and therefore detailed explanations are omitted.

The variation σRs can be adjusted by changing the blending amount of each iron-containing raw material and the type of iron-containing raw material. In other words, designing the blending of the iron-containing raw materials so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min and the variation σRs is equal to or less than 10% means determining the blending ratio of the iron-containing raw materials and the type of the iron-containing raw materials so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min and the variation σRs is equal to or less than 10%.

Regarding the blending of the iron-containing raw materials, when the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min and the variation σRs is equal to or less than 10%, the air permeability in the blast furnace is further improved compared to the case where the variation σRs exceeds 10%.

In the blending design method of the present embodiment, as in the first embodiment, when using iron-containing raw materials (sintered ore) with different sintering raw materials and/or firing conditions or different brands of iron-containing raw materials (lump ore, pellets, carbon-containing agglomerated ore, ferro-coke) even if they are the same type of iron-containing raw materials, it is preferable to set the reduction ratio Rs at the start of fusion and the blending ratio MR for each iron-containing raw material with different sintering raw materials and/or firing conditions or different brands of iron-containing raw materials. In this case, it becomes easier to obtain the weighted average value Rs _av and the variation σRs that more accurately reflect the actual high-temperature properties (reduction ratio Rs at the start of fusion) of the iron-containing raw materials.

(Blast furnace operation method)
In blast furnace operation, a plurality of types of iron-containing raw materials whose mixes are designed by the mix design method of the present embodiment are charged into the blast furnace to form an iron-containing raw material layer in the blast furnace.

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

For the ore raw material used as blast furnace raw material, multiple blends with different weighted average reduction rates at the start of fusion Rs _av were designed. The ore raw material of the designed blends was used as blast furnace raw material in three blast furnaces A to C with ^internal volumes of 3000 to 5500 m3. In each blast furnace, sintered ore, lump ore, and pellets were used as the ore raw material.

(Mixture design 1)
In the blast furnace A, a mix design of the blast furnace raw materials (ore raw materials) was carried out. When carrying out this mix design, first, the correlation between the weighted average value Rs _av and the corrected airflow resistance index K2 _cor (see FIG. 5) was used to specify the lower limit Rs _min corresponding to the target value of the corrected airflow resistance index K2 _cor . Here, when the target value of the corrected airflow resistance index K2 _cor was set to 550 [-], the lower limit Rs _min was 65 [%].

The ore raw material blending design was performed so that the weighted average value Rs _av was equal to or greater than the lower limit value Rs _min (65%). Specifically, among the above-mentioned three types of ore raw materials, the blending ratio MR of the lump ore having a low reduction rate Rs at the start of fusion was lowered, and the sintered ore was changed to a sintered ore having a higher reduction rate Rs at the start of fusion than the sintered ore before the blending design. The weighted average value Rs _av before the blending design was lower than the lower limit value Rs _min (65%), but the weighted average value Rs _av after the blending design was higher than the lower limit value Rs _min (65%). That is, the weighted average value Rs _av after the blending design increased by 2 to 5% compared to the weighted average value Rs _av before the blending design. This blending design significantly reduced the corrected air permeability resistance index K2 _cor as shown in FIG. 9. According to the results shown in FIG. 9, it was confirmed that the blending design improved the permeability of the blast furnace.

(Mixture Design 2)
In the blast furnace A, a blending design of the blast furnace raw materials (ore raw materials) was carried out. In carrying out this blending design, first, a lower limit value Rs _min corresponding to the target value of the coke ratio CR was specified using the correlation between the weighted average value Rs _av and the coke ratio CR (see FIG. 6). Here, when the target value of the coke ratio CR was set to 285 [kg/t], the lower limit value Rs _min was 65 [%].

The ore raw material blending design was performed so that the weighted average value Rs _av was equal to or higher than the lower limit value Rs _min (65%). Specifically, among the above-mentioned three types of ore raw materials, the blending ratio MR of the lump ore having a low reduction rate Rs at the start of fusion was reduced, and the sintered ore was changed to a sintered ore having a higher reduction rate Rs at the start of fusion than the sintered ore before the blending design. The weighted average value Rs _av before the blending design was lower than the lower limit value Rs _min (65%), but the weighted average value Rs _av after the blending design was higher than the lower limit value Rs _min (65%). That is, the weighted average value Rs _av after the blending design increased by 2 to 5% compared to the weighted average value Rs _av before the blending design. This blending design can reduce the coke ratio CR, and this reduction in the coke ratio CR is due to the improvement in permeability in the blast furnace.

(Mixture design 3)
In the blast furnace C, a blending design of the blast furnace raw materials (ore raw materials) was carried out. When carrying out this blending design, first, the correlation between the weighted average value Rs _av and the productivity (see FIG. 7) was used to specify the lower limit Rs _min corresponding to the target value of the productivity. Here, when the target value of the productivity was set to 2.7 [-], the lower limit Rs _min became 65 [%].

The ore raw material blending design was performed so that the weighted average value Rs _av was equal to or higher than the lower limit value Rs _min (65%). Specifically, among the above-mentioned three types of ore raw materials, the sintered ore was changed to one having a higher reduction rate Rs at the start of fusion than the sintered ore before the blending design, and the blending ratio of the sintered ore after the change was increased. The weighted average value Rs _av before the blending design was lower than the lower limit value Rs _min (65%), but the weighted average value Rs _av after the blending design was higher than the lower limit value Rs _min (65%). That is, the weighted average value Rs _av after the blending design increased by 4 to 5% compared to the weighted average value Rs _av before the blending design. This blending design can increase the productivity, and this increase in the productivity is due to the improvement in permeability in the blast furnace.

On the other hand, in the blast furnaces B and C, although the weighted average value Rs _av after the blending design was about the same, the corrected permeability resistance index K2 _cor of the blast furnace B tended to be larger than that of the blast furnace C. Therefore, regarding the blending of the ore raw materials in the blast furnaces B and C, the relationship between the variation σRs of the reduction degree at the start of fusion of the ore raw materials and the corrected permeability resistance index K2 _cor was investigated. The results are shown in FIG.

As shown in Fig. 12, in the blast furnace C, the variation σRs was 10% or less for all blends, whereas in the blast furnace B, the variation σRs exceeded 10% for most blends. From this result, it was understood that by designing the blend of the ore raw materials so that the weighted average value Rs _av is equal to or greater than the lower limit value Rs _min and the variation σRs is 10% or less, the permeability in the blast furnace is more likely to be improved than in the case where the blend of the ore raw materials is designed so that the variation σRs exceeds 10%.

Reference Signs List 1 Blast furnace 2 Charge material 3 Coke layer 4 Iron-containing raw material layer 5 Cohesive layer 6 Coke layer adjacent to the cohesive layer 7 Tuyere 8 Raceway 9 Dripped molten iron 10 Hearth 11 Lower furnace 12 Upper furnace 13 Graphite crucible 14 Ore layer 15 Upper furnace heater control means 16 Lower furnace heater control means 17 Gas 18 Post-reduced gas 19 Loading machine 20 Dripped molten iron receiver 21 Coke layer H Upper furnace heater H' Lower furnace heater

Claims (7)

A method for designing a mixture of a plurality of types of iron-containing raw materials forming an iron-containing raw material layer in a blast furnace, comprising:
A blend of the plurality of types of iron-containing raw materials is designed so that a weighted average value Rs _av of reduction rates at the start of fusion of the plurality of types of iron-containing raw materials, which is represented by the following formula (I), is equal to or greater than a lower limit value Rs _min ;
The method for designing a blending ratio of iron-containing raw materials, characterized in that the lower limit value Rs _min is a weighted average value Rs _av corresponding to a target value of at least one parameter selected from a permeability resistance index in a blast furnace, a coke ratio, and a productivity ratio, the weighted average value Rs _av being determined in advance based on a track record of stable operation of the blast furnace.
In the above formula (I), i is the type of iron-containing raw material, Rs _i is the reduction rate [%] of the type i of iron-containing raw material at the start of fusion [%], and M _i R is the blending ratio [mass %] of the type i of iron-containing raw material to all types of iron-containing raw materials. 2. The method for designing a blend of iron-containing raw materials according to claim 1, wherein the highest value among the weighted average values Rs _av corresponding to the target values of two or more of the parameters is determined as the lower limit value Rs _min . The blending design method of the iron-containing raw materials according to claim 1 or 2, further comprising designing a blend of the plurality of types of the iron-containing raw materials so that a variation σRs of the reduction rates at the start of fusion of the plurality of types of the iron-containing raw materials, represented by the following formula (II), is 10% or less.
In the above formula (II), i is the type of iron-containing raw material, Rs _i is the reduction rate [%] of the type i of iron-containing raw material at the start of fusion, Rs _av is the weighted average value [%] of the reduction rates of multiple types of the iron-containing raw materials at the start of fusion, and M _i R is the blending ratio [mass %] of the type i of iron-containing raw material to all types of iron-containing raw materials. One type of the iron-containing raw material among the plurality of types of iron-containing raw materials is composed of a plurality of lump ores of different brands,
The reduction ratio Rs _i of the lump ore at the start of fusion is the reduction ratio at the start of fusion for each brand,
The lump ore blending ratio M _i R is the blending ratio for each brand.
4. The method for designing a blend of iron-containing raw materials according to claim 1 . One type of iron-containing raw material among the plurality of types of iron-containing raw materials is composed of a plurality of pellets of different brands,
The reduction rate Rs _i of the pellets at the start of fusion is the reduction rate of each brand at the start of fusion,
The blending ratio M _i R of the pellets is the blending ratio for each brand.
5. The method for designing a blend of iron-containing raw materials according to claim 1 . One type of iron-containing raw material among the plurality of types of iron-containing raw materials is composed of a plurality of sintered ores having different sintering raw materials and/or sintering conditions,
The reduction rate Rs _i of the sintered ore at the start of fusion is a reduction rate at the start of fusion for each of the sintered ores having different sintering raw materials and/or firing conditions;
The blending ratio M _i R of the sintered ore is a blending ratio of each of the sintered ores having different sintering raw materials and/or firing conditions;
6. The method for designing a blend of iron-containing raw materials according to claim 1 . A method for operating a blast furnace, comprising charging a plurality of types of iron-containing raw materials, the composition of which is designed by the method for designing the composition of iron-containing raw materials according to any one of claims 1 to 6, into the blast furnace to form an iron-containing raw material layer.