Method for determining charging area of iron ore raw material and method for operating blast furnace

Abstract

To improve reducibility of an iron ore raw material to be used in an operation of a blast furnace and to further reduce a ratio of reducing materials in the blast furnace.SOLUTION: The present invention relates to a method for determining a charging area of iron ore raw material when charging the iron ore raw material and coke into the furnace. A relation between two different temperatures, Tlow and Thigh (where Thigh>Tlow) as a reduction temperature to magnetite when the iron ore raw material is reduced to magnetite and the time required for the magnetite in the iron ore raw material to reach a predetermined reduction rate due to a reduction rate when the magnetite in the iron ore raw material is reduced to metallic iron, is determined in advance; and a charging area for the iron ore raw material in the furnace is determined using the relation.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for determining the charging area of an iron ore raw material when charging the iron ore raw material and coke into a furnace, and an operating method of a blast furnace.

Background Art

[0002] In recent years, in the steelmaking process, reduction of CO2 emissions and reduction of molten iron cost by low reductant ratio operation have been demanded. Particularly in the blast furnace method, since carbonaceous materials are responsible for important elements such as reduction reaction and heat supply, the contribution to reduction of CO2 emissions by reducing the amount of carbonaceous materials used and improving the utilization efficiency is very large, and various efforts are being directed. For example, improving the reducibility of iron ore raw materials such as pellets is effective in reducing the reductant ratio of a blast furnace.

[0003] For example, pellets, which are a kind of iron ore raw material, are classified into self-fluxing pellets and acidic pellets. The former is defined as having a ratio (CaO / SiO2) of CaO (mass%) to SiO2 (mass%) in the pellet exceeding 0.5, and the latter is defined as having CaO / SiO2 of 0.5 or less.

[0004] Patent Document 1 discloses a raw material charging method into a blast furnace for the purpose of improving the reducibility of acidic pellets in order to effectively utilize acidic pellets, which are easier to manufacture among these pellets. Specifically, a raw material charging method into a blast furnace is disclosed in which 10 mass% or more of the blast furnace charging raw material for one charge is acidic pellets, 60 to 75 mass% of the coke for one charge is a mixed layer, and the remaining 25 to 40 mass% is charged alone.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 discloses a method for effectively utilizing acidic pellets. On the other hand, self-dissolving pellets have the characteristic that reduction degradation is less likely to occur due to their high strength. Therefore, effective utilization that takes advantage of the characteristics of self-dissolving pellets and acidic pellets has been studied.

[0007] However, at present, many studies on the charging method according to the properties of pellets are related to the classification of acidic and self-dissolving types, and no charging method of pellets based on raw material properties other than these acidic and self-dissolving classifications has been proposed. In particular, when aiming to improve the reducibility of pellets under low reductant ratio operation, it is necessary to consider the change in the temperature distribution in the blast furnace, but no proposal has been made to charge pellets considering such a temperature distribution.

[0008] In addition, in recent years, due to the deterioration of resources, diversification of the charging materials used in the blast furnace has been demanded. In order to achieve a reduction in CO2 emissions in such an environment, improvement in reactivity by effective utilization is required for various iron ore raw materials such as pellets and sintered ore.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for determining a charging region of an iron ore raw material capable of improving the reducibility of the iron ore raw material used in operation and further reducing the reductant ratio of the blast furnace, and an operation method of the blast furnace using such a method for determining the charging region.

Means for Solving the Problems

[0010] In order to solve the above problems, the present inventor conducted reduction tests using a plurality of types of pellets, sintered ore, lump ore, etc. as iron ore raw materials, and examined the influence of the reduction temperature on the reduction behavior of the iron ore raw materials. As a result, it was obtained that when the pre-reduction temperature to magnetite is lowered, the reduction rate of the main reduction after magnetite is improved. More specifically, at the pre-reduction temperature T high as described in detail below, the reduction rate of the main reduction was improved for any iron ore raw material. On the other hand, at the pre-reduction temperature T highLower than T low When it is lowered to, in some iron ore raw materials, the reduction rate of this reduction improved as described above. On the contrary, there were also iron ore raw materials in which the reduction rate of this reduction decreased. Regarding the details of this reduction experiment, the reduction temperature T low and T high The suitable ranges of will be described in the embodiments below, including them.

[0011] From the above results, the present inventor regarded the pre-reduction temperature as a factor affecting the reduction rate when magnetite is reduced to metallic iron (that is, the reduction rate of this reduction), and the pre-reduction temperature was set to T high to T low When it is lowered to, it was found that it is preferable to change the arrangement of the iron ore raw materials in the blast furnace according to the change in the reduction rate of this reduction (that is, the relationship between the two pre-reduction temperatures and the reduction rate of this reduction). That is, iron ore raw materials in which the reduction rate of this reduction does not decrease or the degree of decrease is small even when the pre-reduction temperature is T low are arranged in the part where the temperature rise is slow in the blast furnace, while iron ore raw materials in which the reduction rate of this reduction decreases are preferably arranged in the part where the temperature rise is fast in the blast furnace. As a result, the conclusion was reached.

[0012] The present invention has been made based on such new findings. According to one aspect of the present invention, there is provided a method for determining the charging region of the iron ore raw material when charging the iron ore raw material and coke into the furnace, the method comprising: two different temperatures T as the reduction temperature to magnetite when the iron ore raw material is reduced to magnetite low and T high (Here, T high > T low Let it be.) and the time required for the magnetite to reach a predetermined reduction rate, due to the reduction rate when the magnetite in the iron ore raw material is reduced to metallic iron, are obtained in advance, and the charging region of the iron ore raw material in the furnace is determined using the relationship. A method for determining the charging region of an iron ore raw material is provided.

[0013] In the method for determining the charging region of the iron ore raw material, the temperature Tlow and T high preferably satisfies the following formulas (1) to (3). 400 ≦ T low <700 ···(1) 700 ≦ T high ≦ 900 ···(2) T high -T low ≧ 100 ···(3)

[0014] In the method for determining the charging region of the iron ore raw material, based on the above relationship, a reduction temperature influence index RTI may be calculated by the following formula (4), and the charging region of the iron ore raw material in the furnace may be determined using the reduction temperature influence index RTI. RTI = (the time to reach 50% of the magnetite standard reduction rate at T low ) / (the time to reach 50% of the magnetite standard reduction rate at T high ) ···(4)

[0015] In the method for determining the charging region of the iron ore raw material, the iron ore raw material may be arranged from the center of the furnace toward the furnace wall in order from the one with the largest reduction temperature influence index.

[0016] In the method for determining the charging region of the iron ore raw material, the iron ore raw material is a mixed raw material composed of a plurality of types of iron ore raw materials having different properties. When charging the mixed raw material into the furnace, the charging region of the mixed raw material in the furnace may be determined using the reduction temperature influence index of the iron ore raw material having the largest mass ratio among the mixed raw materials.

[0017] In the method for determining the charging region of the iron ore raw material, the iron ore raw material may be pellets, sintered ore, or lump ore.

[0018] Further, according to another aspect of the present invention based on the above new findings, in an operating method of a blast furnace for charging an iron ore raw material and coke into the furnace, a blast furnace operating method for determining the charging region of the iron ore raw material in the furnace by the above method for determining the charging region of the iron ore raw material is provided.

Advantages of the Invention

[0019] As described above, according to the present invention, since the suitable charging region of the iron ore raw material can be determined in consideration of the influence of the reduction temperature on the reduction rate, the reducibility of the iron ore raw material can be improved. Specifically, using the relationship between two different reduction temperatures T low and T high and the time required for magnetite to reach a predetermined reduction rate due to the reduction rate of the iron ore raw material, for example, even if the pre-reduction temperature is reduced from T high to T low , the iron ore raw material whose reduction rate of the main reduction does not decrease or the degree of decrease is small is arranged in the portion where the temperature rise is slow even in the blast furnace. On the other hand, the iron ore raw material whose reduction rate of the main reduction decreases is arranged in the portion where the temperature rise is fast even in the blast furnace. Thereby, the average reduction rate of the entire blast furnace charge is improved, and as a result, the reduction material ratio can be reduced.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0022] (Method for Determining Charging Region of Iron Ore Raw Material) First, in the method for determining the charging region of the iron ore raw material according to the present invention, the basic concept regarding the charging region of the iron ore raw material will be described. Note that the "charging region of the iron ore raw material" means the range where the iron ore raw material reaches the surface of the raw materials existing in a layered manner in the blast furnace. As described above, the inventor, in aiming to improve the reducibility of the iron ore raw material under low reductant ratio operation, conducted a reduction test in consideration of the change in the temperature distribution in the blast furnace, and investigated the influence of the reduction temperature on the reduction behavior of the iron ore raw material. Specifically, under the test conditions shown in FIG. 1, a test in which reduction is performed step by step was carried out. Note that the "reductant ratio" is one of the indicators representing the unit consumption of the reductant in the blast furnace, and is represented by the total mass of the reductants per ton of hot metal. The above "low reductant ratio operation" means an operation carried out under conditions where such a reductant ratio shows a low value.

[0023] Here, examples of the iron ore raw material to be focused on in the method for determining the charging region of the iron ore raw material according to the present invention include pellets, sintered ore, lump ore, and the like. In the present test, which will be described in detail below, different types of pellet-shaped iron ore raw materials A to D having the chemical compositions and CaO / SiO2 ratios shown in Table 1, and sintered ore (hereinafter referred to as iron ore raw material E) were used. Note that in the following iron ore raw materials A to E, the remainder of the chemical composition is trace elements.

[0024]

Table 1

[0025] In such a test, in the preliminary reduction stage, the reduction gas conditions are adjusted so as to be in the magnetite stable region, and the reduction is allowed to proceed until all of the iron oxide becomes magnetite. In the main reduction stage, the test conditions are set to evaluate only the reduction stage from magnetite to metallic iron. Therefore, in the preliminary reduction stage, the iron ore raw material is reduced until all of the iron oxide in the iron ore raw material becomes magnetite. Further, in the main reduction stage, magnetite is reduced by a reduction reaction showing a certain reduction rate to become metallic iron.

[0026] Here, as shown in Table 2, a test was conducted to simply evaluate the influence of the difference in the temperature rising conditions in the blast furnace on the reduction rate in the main reduction by changing the preliminary reduction temperature isothermally to 500°C, 700°C, 900°C, and 1000°C for different types of iron ore raw materials A to E. In this test, rather than focusing on the reduction rate itself in the main reduction, the evaluation was carried out by focusing on the time required for magnetite to reach a predetermined reduction rate, which is determined by such a reduction rate. In this test, the main reduction temperature was fixed at 1000°C. This is for comparing only the influence of the preliminary reduction.

[0027] Table 2 and Figure 2 show the relationship between the preliminary reduction temperature and the time required for the magnetite in the main reduction to reach a reduction rate of 50% for iron ore raw materials A to E. Hereinafter, the time required for magnetite to be reduced by a reduction reaction showing a certain reduction rate and reach a magnetite-based reduction rate of 50% in the main reduction stage will be referred to as the "time required for the magnetite in the main reduction to reach a reduction rate of 50%". The magnetite-based reduction rate is the reduction rate based on magnetite in the main reduction, where magnetite (Fe3O4) is defined as 0% and metallic iron (Fe) is defined as 100%.

[0028] Also, the reason for setting the magnetite standard reduction rate at 50% is mainly to consider the influence of indirect reduction with carbon monoxide (CO) gas. For example, until the temperature in the blast furnace reaches 1200°C, the reduction is mainly by carbon monoxide gas. The reduction reaction by this carbon monoxide gas is an exothermic reaction. On the other hand, for example, when the temperature in the blast furnace exceeds 1200°C, the influence of direct reduction by carbon (C) begins to increase significantly. The direct reduction reaction by this carbon is an endothermic reaction. In the blast furnace, heat is generated by charging and burning a carbon source. Here, if the exothermic reaction by the above-mentioned indirect reduction is increased, the carbon source for heat generation can be reduced. Therefore, it is preferable to increase the reduction reaction (exothermic reaction) up to 1200°C and decrease the reduction reaction (endothermic reaction) above 1200°C. From such a viewpoint, improvement of the reduction rate up to 1200°C is desired. And since it is considered that the reduction rate at which this 1200°C is reached in the blast furnace is about 50%, the magnetite standard reduction rate is set at 50%. The standard of the magnetite standard reduction rate is not particularly limited, but it is preferably 50% or less for the above reasons, and 50% is more preferable because the larger the reduction rate value, the easier it is to grasp the difference in the arrival time.

[0029] Referring to Table 2 and Figure 2, at a preliminary reduction temperature of 700 to 1000 °C, in all iron ore raw materials A to E, when the preliminary reduction temperature was decreased, the time to reach 50% of the magnetite standard reduction rate became shorter, and the reduction rate of the main reduction improved. On the other hand, when the preliminary reduction temperature was decreased to 500 °C, in iron ore raw material B, the reduction rate of the main reduction improved and did not decrease. Also, in iron ore raw material A, although the degree of decrease in the reduction rate was small, in iron ore raw materials C, D, and E, the reduction rate of the main reduction decreased. From these results, the preliminary reduction temperature in the range of 700 to 1000 °C is a temperature that brings about the relationship of "improving the reduction rate of the main reduction and shortening the time to reach 50% of the magnetite standard reduction rate" in all the iron ore raw materials A to E under consideration. On the other hand, the preliminary reduction temperature of 500 °C is a temperature that brings about the relationship of "as a result of differences in the behavior of the reduction rate of the main reduction among iron ore raw materials A to E, differences occur in the time to reach 50% of the magnetite standard reduction rate". Thus, it can be said that the preliminary reduction temperature is a factor that affects the reduction rate of the main reduction in which magnetite is reduced to metallic iron.

[0030] From the above results, it was concluded that it is preferable to change the arrangement of the iron ore raw materials in the blast furnace according to the change in the reduction rate of the main reduction when the preliminary reduction temperature is decreased to 500 °C. That is, iron ore raw materials A and B, for which the reduction rate of the main reduction does not decrease or the degree of decrease is small even when the preliminary reduction temperature is 500 °C, are arranged in regions in the blast furnace where the temperature rise is slow. Such iron ore raw materials A and B will not have an adverse effect on reduction even if they are arranged in regions with a low reduction temperature history. On the other hand, iron ore raw materials C, D, and E, for which the reduction rate of the main reduction decreases, are arranged in regions in the blast furnace where the temperature rise is fast.

[0031] Here, there is a temperature distribution in the radial direction inside the blast furnace. Since the temperature rise is slow on the furnace wall side, the burden charged in the furnace wall is reduced more slowly than the burden charged in the center of the furnace. Therefore, it is preferable to place the iron ore raw material, which is more likely to have a reduced reduction rate in this reduction, at the center of the blast furnace, and to place the iron ore raw material, which has a non-reduced or slightly reduced reduction rate in this reduction, at the furnace wall of the blast furnace. For example, in the case of the iron ore raw materials shown in Table 2, it is preferable to place iron ore raw materials A and B at the furnace wall of the blast furnace and iron ore raw materials C, D, and E at the center of the blast furnace.

[0032] Furthermore, the inventor of the present invention has set a reduction temperature influence index RTI as a criterion for determining the charging area of the iron ore raw material in this way. The reduction temperature influence index RTI is the ratio of the time to reach 50% of the magnetite standard reduction rate at a preliminary reduction temperature of 500°C to the time to reach 50% of the magnetite standard reduction rate at a preliminary reduction temperature of 700°C, as shown in the following formula (4'). By paying attention to such a reduction temperature influence index RTI, the charging area of the iron ore raw material can be determined more simply.

[0033] Reduction temperature influence index RTI = (Time to reach 50% of the magnetite standard reduction rate at a preliminary reduction temperature of 500°C) / (Time to reach 50% of the magnetite standard reduction rate at a preliminary reduction temperature of 700°C) ···(4')

[0034] Table 2 shows the reduction temperature influence index RTI for iron ore raw materials A to E. Based on the reduction temperature influence index RTI as shown in Table 2, the inventor of the present invention came up with the idea of arranging the iron ore raw materials in order from the one with a large reduction temperature influence index RTI, from the center of the furnace towards the furnace wall. For the iron ore raw materials A to E shown in Table 2, along the direction from the furnace wall towards the center of the furnace, in order from the side of the furnace wall, iron ore raw material B → iron ore raw material A → iron ore raw material E → iron ore raw material D → iron ore raw material C are arranged.

[0035] Thus, according to the method for determining the charging area of the iron ore raw material, the reduction temperature to magnetite (the reduction temperature of preliminary reduction) when the iron ore raw material is reduced to magnetite is regarded as a factor affecting the reduction rate when magnetite is reduced to metallic iron. The relationship between two relatively different preliminary reduction temperatures in the preliminary reduction and the time required for magnetite to reach a predetermined reduction rate due to the reduction rate (the reduction rate of final reduction) when magnetite in the iron ore raw material is reduced to metallic iron is obtained in advance. Then, according to the method for determining the charging area of the iron ore raw material, the charging area of the iron ore raw material in the furnace is determined using such a relationship. According to such a method for determining the charging area of the iron ore raw material, since the suitable charging area of the iron ore raw material can be determined in consideration of the influence of the reduction temperature on the reduction rate, the reduction rate (reducibility) of the iron ore raw material can be improved. As a result, the average reduction rate of the entire blast furnace charge is improved, and thereby the reduction material ratio can be reduced.

[0036] Also, as described above, even without determining the arrangement order of each iron ore raw material in more detail, for example, a threshold value can be set in advance for the reduction temperature influence index RTI, and based on such a threshold value, it is also possible to determine the charging area of the iron ore raw material. In this case, for the iron ore raw material having a reduction temperature influence index RTI less than the set threshold value, it may be arranged at the furnace wall part, and for the iron ore raw material having a reduction temperature influence index RTI exceeding the set threshold value, it may be arranged at the furnace center part. By performing the threshold determination based on such a reduction temperature influence index RTI, the determination of the charging area of the iron ore raw material can be performed more simply.

[0037] Based on the reduction temperature influence index RTI as shown in Table 2, for example, 1.10 can be set as the threshold value of the reduction temperature influence index RTI for determining the charging area of the iron ore raw material. Then, the iron ore raw materials A and B with a reduction temperature influence index RTI less than 1.10 may be arranged at the furnace wall part, and the iron ore raw materials C, D, and E with a reduction temperature influence index RTI of 1.10 or more may be arranged at the furnace center part.

[0038]

Table 2

[0039] According to the method for determining the charging area of the iron ore raw material described above, considering the influence of the reduction temperature on the reduction rate, the suitable charging area of the iron ore raw material can be determined more simply. Therefore, the reduction rate (reducibility) of the iron ore raw material can be improved more simply. That is, for the furnace wall part, which is an area where the temperature rise is slow in the blast furnace, charge the iron ore raw material with a reduction temperature influence index RTI < threshold value (for example, 1.10), and charge the iron ore raw material with a reduction temperature influence index RTI ≥ threshold value (for example, 1.10) at the furnace center part, which is an area where the temperature rise is fast. As a result, the average reduction rate of the entire blast furnace charge is improved, and thereby the reduction material ratio can be reduced.

[0040] Note that in the above, the preliminary reduction temperatures of 500 °C and 700 °C were used as the reference, but it is not limited to such preliminary reduction temperatures. For example, two different preliminary reduction temperatures T low and T high (where T high > T low shall be used). Note that the units of the following T low and T high are each °C. The T low shown in the following formula (1) corresponds to the temperature that brings about the relationship of "a difference occurs in the behavior of the reduction rate of the main reduction", and the T high shown in the following formula (2) corresponds to the temperature that brings about the relationship of "improving the reduction rate of the main reduction".

[0041] 400 ≤ T low < 700 ···(1) 700 ≤ T high ≤ 900 ···(2) T high - T low ≥ 100 ···(3)

[0042] Here, the lower and upper limits in the above formulas (1) to (3) will be described. As described above, in the preliminary reduction stage, the reduction reaction is allowed to proceed until all of the iron oxide becomes magnetite. Further, the reaction from iron oxide (hematite, Fe2O3) to magnetite becomes substantial at 400 °C or higher. For this reason, the lower limit of the preliminary reduction temperature T low is set to 400 °C.

[0043] As described above with reference to Table 2 and FIG. 2, in the range of the preliminary reduction temperature of 500 °C to 700 °C, the behavior of the magnetite-based reduction rate 50% arrival time (reduction rate) differs depending on the type of iron ore raw material. Such behavior means that the reduction rate differs depending on the type of iron ore raw material. Therefore, as the boundary between the two preliminary reduction temperatures T low and T high , a temperature of 700 °C is set. For T low , as shown in the above formula (1), the upper limit is less than 700 °C, while for T high , as shown in the above formula (2), the lower limit is 700 °C or higher.

[0044] Furthermore, if the difference between the preliminary reduction temperatures T low and T high is small, the difference in the magnetite-based reduction rate 50% arrival time becomes small, so that the criterion for determining the charging area of the iron ore raw material may not be clarified. For this reason, it is necessary to ensure a certain difference between the preliminary reduction temperatures T low and T high .

[0045] Also, for pellets, which are an example of an iron ore raw material, there are few differences in the physical and chemical properties between the pellets. However, for sintered ore and lump ore, which are examples of iron ore raw materials, individual differences in the physical and chemical properties are often observed among the samples. Therefore, from the viewpoint of eliminating the influence of such individual differences in the properties on the reduction rate of the main reduction and focusing only on the influence of the preliminary reduction temperature on the reduction rate of the main reduction, it is necessary to ensure a certain difference between the preliminary reduction temperatures T low and T high .

[0046] As a result of the present inventors' intensive studies, it has been found that, as the temperature difference described above, it is preferable to secure, for example, 100°C or higher. For this reason, as shown in the above formula (3), the preliminary reduction temperature T low and T high The difference between (T high -T low ) was set to 100°C or higher.

[0047] When the preliminary reduction temperature T high exceeds 900°C, since the time to reach 50% of the magnetite standard reduction rate at the preliminary reduction temperature T high is sufficiently long, the range of change in the reduction rate due to the decrease in the preliminary reduction temperature becomes ambiguous. For example, using the results in Table 2, when the ratio of the time to reach 50% of the magnetite standard reduction rate at a preliminary reduction temperature of 500°C to the time to reach 50% of the magnetite standard reduction rate at a preliminary reduction temperature of 1000°C is determined as the reduction temperature influence index RTI, the reduction temperature influence index RTI is less than 1.10 for all types of iron ore raw materials, and the criteria for determining the charging region of the iron ore raw material become unclear. For this reason, the upper limit value of the preliminary reduction temperature T high is set to 900°C.

[0048] Here, the above T low is more preferably, for example, 500°C or higher and 700°C or lower. Further, the difference between the preliminary reduction temperature T low and T high (T high -T low ) is more preferably 200°C or higher.

[0049] Also, when paying attention to the two types of preliminary reduction temperatures T low and T high as described above, the reduction temperature influence index RTI shown in the above formula (4') may be rewritten as in the following formula (4).

[0050] Reduction temperature influence index RTI = (Time to reach 50% of the magnetite standard reduction rate at the preliminary reduction temperature T low ) / (Time to reach 50% of the magnetite standard reduction rate at the preliminary reduction temperature T highMagnetite standard reduction rate reaching 50% in (time) ···(4)

[0051] Here, for the sake of caution, the present inventors performed pre-reduction while changing the pre-reduction temperature in the range of 500 to 900°C in the same manner as the examples shown in Tables 1 and 2 for other iron ore raw materials (self-fluxing pellets) different from the pelletized iron ore raw materials shown in Table 1 above, and then performed main reduction at 1000°C. As a result, further verification was carried out on the relationship between the pre-reduction temperature, the magnetite standard reduction rate, and the elapsed time from the start of the main reduction. The obtained results are shown in FIG. 3. In FIG. 3, the vertical axis represents the magnetite standard reduction rate (%), and the horizontal axis represents the elapsed time (seconds) from the start of the main reduction.

[0052] As is also clear from FIG. 3, it can be seen that when the pre-reduction temperature is changed, there is a difference in the elapsed time required for the magnetite standard reduction rate to reach 50% in the main reduction. More specifically, when the pre-reduction temperature is 500°C, the elapsed time required for the magnetite standard reduction rate to reach 50% is about 1350 seconds, while when the pre-reduction temperature is 600 to 900°C, the elapsed time required for the magnetite standard reduction rate to reach 50% is shorter than that when the pre-reduction temperature is 500°C. Also, the elapsed time required for the magnetite standard reduction rate to reach 50% was the shortest (about 980 seconds) when the pre-reduction temperature was 700°C. From such results, it can be understood that the pre-reduction temperature is a factor that affects the reduction rate in the main reduction, and the relationship between the pre-reduction temperature and the reduction rate in the main reduction as described above is not specific to the pelletized iron ore raw materials and sintered ore shown in Table 1.

[0053] Also, in the above method for determining the charging area of the iron ore raw material, the reduction temperature influence index RTI is not limited to the above formulas (4') and (4). In the above formulas (4') and (4), the reduction temperature influence index RTI is the time required for the magnetite standard reduction rate to reach 50% at the pre-reduction temperature of 700°C (or, T high ) with respect to the time required for the magnetite standard reduction rate to reach 50% at the pre-reduction temperature of 500°C (or, Tlow ) was the ratio of the time to reach 50% of the magnetite reduction rate, but as shown in the following formulas (5’) and (5), it may be defined as the difference in the time to reach 50% of the magnetite reduction rate at two pre-reduction temperatures.

[0054] Reduction temperature influence index RTI = (Time to reach 50% of the magnetite reduction rate at a pre-reduction temperature of 500°C) - (Time to reach 50% of the magnetite reduction rate at a pre-reduction temperature of 700°C) ···(5’) Reduction temperature influence index RTI = (Time to reach 50% of the magnetite reduction rate at a pre-reduction temperature T low ) - (Time to reach 50% of the magnetite reduction rate at a pre-reduction temperature T high ) ···(5)

[0055] In this case, the iron ore raw materials may be arranged from the center of the furnace towards the furnace wall in order of decreasing reduction temperature influence index RTI.

[0056] Also, for the reduction temperature influence index RTI as shown in the above formulas (5’) and (5), a threshold value may be set in advance, and based on such a threshold value, the charging area of the iron ore raw materials may be determined. Here, the threshold value of the reduction temperature influence index RTI in the above formulas (5’) and (5) can be set to, for example, 200 seconds. Then, the iron ore raw materials with a reduction temperature influence index RTI less than this threshold value of 200 seconds may be arranged at the furnace wall, and the iron ore raw materials with an RTI of 200 seconds or more may be arranged at the center of the furnace.

[0057] Furthermore, in the method for determining the charging area of the iron ore raw materials described above, when charging a mixed raw material in which multiple types of iron ore raw materials are mixed into the furnace, the charging area of the mixed raw material may be determined using the reduction temperature influence index RTI of the iron ore raw material with the largest mass ratio among the mixed raw materials. When charging a mixed raw material in which iron ore raw materials A and C are mixed into the blast furnace in the above reduction test, for example, if the proportion of iron ore raw material A is larger than that of iron ore raw material C, the mixed raw material may be arranged on the furnace wall side, and if the proportion of iron ore raw material C is larger than that of iron ore raw material A, the mixed raw material may be arranged at the center of the furnace.

[0058] In addition, in the above description, the explanation was given focusing on "the relationship between the reduction temperature when the iron ore raw material is reduced to magnetite and the time required for the magnetite in the iron ore raw material to reach a predetermined reduction rate", but the charging area of the iron ore raw material may be determined by focusing on "the relationship between the reduction temperature when the iron ore raw material is reduced to magnetite and the reduction rate when the magnetite in the iron ore raw material is reduced to metallic iron".

[0059] (Operating method of blast furnace) Next, an operating method of a blast furnace using the method for determining the charging area of the iron ore raw materials according to the present invention will be described. FIG. 4 shows the distribution of charged materials in the furnace according to the present embodiment.

[0060] Here, a range of 0 or more and less than 0.7 in terms of the dimensionless furnace throat radius is defined as the center of the furnace, and a range of 0.7 or more and 1.0 or less is defined as the furnace wall part, and a horizontal plane formed in the furnace wall part or in the vicinity of the furnace wall part is defined as a terrace. The dimensionless furnace throat radius is dimensionless with the radius of the blast furnace being 1.

[0061] According to the operating method of the blast furnace according to the present invention, using the method for determining the charging area of the iron ore raw materials as described above, the charging area of the iron ore raw materials used in the operation is determined in advance. Then, based on the obtained results, each of the iron ore raw materials used in the operation is charged into the blast furnace so as to reach the determined charging area.

[0062] In FIG. 4, reference numeral 1 denotes coke, reference numeral 2 denotes a mixed material of sintered ore and iron ore raw material C shown in Table 1, and reference numeral 3 denotes a layer formed of iron ore raw material A shown in Table 1. The coke layer 1 forms an inclined layer that slopes downward from the furnace wall side toward the center of the furnace. The mixed layer 2 of sintered ore and iron ore raw material C shown in Table 1 forms a terrace on the furnace wall side and an inclined layer that slopes downward from the inner tip of the terrace toward the center of the furnace. The iron ore raw material A layer 3 is disposed at the center of the furnace.

[0063] [Charging method] The above-described charge distribution can be realized by the following charging method. Note that the following charging method is a raw material charging method in a bell-less blast furnace, and all charging is performed while tilting from near the furnace wall toward the furnace center direction while rotating the swing chute. (1) Charge coke in the range of 0.4 or more and 1.0 or less in terms of dimensionless tuyere radius to form the coke layer 1. (2) Charge a mixed material of sintered ore and iron ore raw material C in the range of 0.1 or more and 1.0 or less in terms of dimensionless tuyere radius to form the mixed layer 2. Among the mixed layer 2, iron ore raw material C is present in a large amount at the furnace center. (3) Charge iron ore raw material A in the range of 0.6 or more and 1.0 or less in terms of dimensionless tuyere radius to form the iron ore raw material A layer 3.

[0064] Note that in the above-described embodiment, the raw material charging method in a bell-less blast furnace has been described, but the raw material charging method of the present invention can also be implemented in a bell-type blast furnace. In that case, the content and order of the charging batch are the same as those in the case of the bell-less blast furnace described above, and the control of the charging area is realized by adjusting the movable armor for each charging batch.

[0065] And also in the above-described embodiment, by charging iron ore raw material A at the furnace wall part which is a region where the temperature rise is slow in the furnace and charging iron ore raw material C at the furnace center part which is a region where the temperature rise is fast, the average reduction rate of the entire blast furnace charge is improved, and thereby it becomes possible to reduce the reduction material ratio.

Example

[0066] The calculation model shows that the reduction rate of the raw materials in the blast furnace is improved by the method for determining the charging area of the iron ore raw materials of the present invention.

[0067] (Verification Example 1) In this verification, the reduction rate of the ore layer was obtained using a simple mathematical model that examined the reduction behavior in the load softening test by Hisashi Nishimura et al. (Iron and Steel, The Iron and Steel Institute of Japan, 2016, Vol. 102, No. 2 (2016), pp. 61-67).

[0068] The temperature and gas pattern are as shown in FIGS. 5 and 6. The solid lines in FIGS. 5 and 6 are the patterns adopted as the representative reduction conditions for the furnace wall part with slow temperature rise. Also, the dashed lines in FIGS. 5 and 6 are the patterns adopted as the representative reduction conditions at the furnace center part.

[0069] In the mathematical model of Hisashi Nishimura et al., the phenomenon is treated as one-dimensional unsteady with uniform radial direction, and the reduction behavior of the raw material particles is expressed by the three-interface unreacted core model. In the calculation model used this time, the ore layer thickness is 70 mm, the coke layer thickness is 20 mm, and the coke layer is arranged above and below the ore layer. The porosity of the ore layer and the coke layer is constant at 0.4, the pellet particle size is 12.5 mm, and the coke particle size is 17.5 mm. Here, regarding the reduction of magnetite-iron, based on the two-interface unreacted core model, the reaction rate constant was calculated by the parameter fitting method by analyzing the results of the above reduction test and used as a parameter in the model. The calculation method of the parameter and the parameters regarding the reduction of hematite-magnetite were based on the literature (Takeaki Murayama et al., Iron and Steel, The Iron and Steel Institute of Japan, 1994, Vol. 80, No. 7 (1994), pp. 493-500).

[0070] Table 3 shows the average reduction rate (hereinafter simply referred to as the reduction rate) in the ore layer at the time of reaching 1200°C when the ore layer is made of a single pellet or sintered ore (pellet-shaped iron ore raw materials A to D and sintered ore (iron ore raw material E) shown in Table 1) calculated by model calculation. Here, the reduction rate assumes Fe2O3 is 0% and Fe is 100%.

[0071]

Table 3

[0072] As shown in Fig. 5, in the case of the furnace wall conditions, the region below 900 °C is long, so the reduction is in an unfavorable situation compared to the furnace center. Therefore, the reduction rate in the furnace wall is lower than that in the furnace center. However, due to the decrease in the reduction temperature up to magnetite, the reduction rate after magnetite changes. For iron ore raw materials A and B with a reduction temperature influence index RTI < 1.10 shown in Equation (4), the reduction rate after magnetite is improved due to the decrease in the reduction temperature up to magnetite. Therefore, the difference in the reduction rate between the furnace wall conditions and the furnace center conditions is small. On the other hand, for iron ore raw materials C, D, and E with a reduction temperature influence index RTI ≥ 1.10, the reduction rate after magnetite is not improved because the region below 700 °C becomes long. Therefore, the difference in the reduction rate between the furnace wall conditions and the furnace center conditions is large.

[0073] From the above results, it can be seen that by arranging iron ore raw materials with a low reduction temperature influence index RTI in the furnace wall and iron ore raw materials with a high reduction temperature influence index RTI in the furnace center, the average reduction rate of the entire blast furnace charge can be improved.

[0074] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings. However, the present invention is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims. Naturally, these are also understood to belong to the technical scope of the present invention.

[0075] The embodiments disclosed this time are illustrative in all respects and not restrictive. The above embodiments may be omitted, substituted, or changed in various forms without departing from the scope of the invention as defined in the appended claims and the gist of the invention as described hereinafter. For example, the constituent elements of the above embodiments can be arbitrarily combined within the range that does not impair their effects. Further, from such an arbitrary combination, the actions and effects of each constituent element involved in the combination can be naturally obtained, and other actions and other effects that are obvious to those skilled in the art from the description of this specification can also be obtained.

[0076] Also, the effects described in this specification are merely illustrative or exemplary and not limiting. That is, the technology according to the present invention can exhibit other effects that are obvious to those skilled in the art from the description of this specification, together with or instead of the above effects.

[0077] Note that the following configurations also belong to the technical scope of the present invention. [1] A method for determining the charging region of the iron ore raw material when charging the iron ore raw material and coke into the furnace, Two different temperatures T as the reduction temperature to magnetite when the iron ore raw material is reduced to magnetite low and T high (where T high >T low is set). And, the relationship between the time required for the magnetite to reach a predetermined reduction rate, which is caused by the reduction rate when the magnetite in the iron ore raw material is reduced to metallic iron, is obtained in advance, A method for determining the charging region of the iron ore raw material, which determines the charging region of the iron ore raw material in the furnace using the above relationship. [2] The temperatures T low and T high satisfy the following formulas (1) to (3). The method for determining the charging region of the iron ore raw material according to [1]. 400≦T low <700 ···(1) 700≦T high≤900 ···(2) T high -T low ≥100 ···(3) Here, the above T low and T high are each in °C. [3] Based on the above relationship, the reduction temperature influence index RTI is calculated by the following formula (4), and the charging area of the iron ore raw material in the furnace is determined using the reduction temperature influence index RTI. The method for determining the charging area of the iron ore raw material according to [2]. RTI = (Time to reach 50% magnetite standard reduction rate at T low ) / (Time to reach 50% magnetite standard reduction rate at T high ) ···(4) [4] The iron ore raw material is arranged from the center of the furnace towards the furnace wall in order of decreasing reduction temperature influence index. The method for determining the charging area of the iron ore raw material according to [3]. [5] The iron ore raw material is a mixed raw material composed of multiple types of iron ore raw materials with different properties. When charging the mixed raw material into the furnace, the charging area of the mixed raw material in the furnace is determined using the reduction temperature influence index of the iron ore raw material with the largest mass ratio in the mixed raw material. The method for determining the charging area of the iron ore raw material according to [3] or [4]. [6] The iron ore raw material is a pellet, sintered ore, or lump ore. The method for determining the charging area of the iron ore raw material according to any one of [1] to [5]. [7] In the operation method of a blast furnace for charging iron ore raw material and coke into the furnace, The charging area of the iron ore raw material in the furnace is determined by the method for determining the charging area of the iron ore raw material according to any one of [1] to [6]. The operation method of the blast furnace.

Industrial Applicability

[0078] The present invention can be applied when charging iron ore raw material and coke into a blast furnace.

Explanation of Symbols

[0079] 1 Coke layer 2 Mixed layer of sinter and iron ore raw material C 3 Iron ore raw material A layer

Claims

1. A method for determining the charging area of the iron ore raw material when charging the iron ore raw material and coke into the furnace, Two different temperatures T as the reduction temperature to magnetite when the iron ore raw material is reduced to magnetite ｌｏｗ and T ｈｉｇｈ where (here, T ｈｉｇｈ > T ｌｏｗ is set), and the relationship between the time required for the magnetite to reach a predetermined reduction rate and the reduction rate when the magnetite in the iron ore raw material is reduced to metallic iron is obtained in advance. A method for determining the charging area of the iron ore raw material, which determines the charging area of the iron ore raw material in the furnace using the relationship.

2. the temperature T ｌｏｗ and T ｈｉｇｈ The method for determining the charging area of the iron ore raw material according to claim 1, which satisfies the following formulas (1) to (3). 400 ≤ T ｌｏｗ < 700 ··· (1) 700 ≤ T ｈｉｇｈ ≤ 900 ··· (2) T ｈｉｇｈ -T ｌｏｗ ≥100 ··· (3) Here, the T ｌｏｗ and T ｈｉｇｈ are each in °C.

3. The method for determining the charging area of the iron ore raw material according to claim 2, wherein a reduction temperature influence index RTI is calculated by the following formula (4) based on the relationship, and the charging area of the iron ore raw material in the furnace is determined using the reduction temperature influence index RTI. RTI = (the time to reach 50% of the magnetite standard reduction rate at T ｌｏｗ ) / (the time to reach 50% of the magnetite standard reduction rate at T ｈｉｇｈ )... (4)

4. The method for determining the charging area of the iron ore raw material according to claim 3, wherein the iron ore raw materials are arranged from the center of the furnace toward the furnace wall in order of decreasing reduction temperature influence index.

5. The iron ore raw material is a mixed raw material composed of a plurality of types of iron ore raw materials with different properties, When charging the mixed raw material into the furnace, the charging area of the mixed raw material in the furnace is determined using the reduction temperature influence index of the iron ore raw material having the largest mass ratio among the mixed raw materials. The method for determining the charging area of the iron ore raw material according to claim 3.

6. The iron ore raw material is a mixed raw material composed of a plurality of types of iron ore raw materials with different properties, When charging the mixed raw material into the furnace, the charging area of the mixed raw material in the furnace is determined using the reduction temperature influence index of the iron ore raw material having the largest mass ratio among the mixed raw materials. The method for determining the charging area of the iron ore raw material according to claim 4.

7. The method for determining the charging area of the iron ore raw material according to claim 1, wherein the iron ore raw material is pellets, sintered ore, or lump ore.

8. In an operation method of a blast furnace for charging an iron ore raw material and coke into the furnace, An operation method of a blast furnace, which determines the charging area of the iron ore raw material in the furnace by the method for determining the charging area of the iron ore raw material according to any one of claims 1 to 7.

Images