Method for estimating the decrease in thermal reserve zone temperature

Abstract

To provide a method to estimate a decrease ΔTtrz in a thermal reserve zone temperature Ttrz by focusing on a mean distance LRS of special raw fuel.SOLUTION: A temperature drop ΔTtrz in a thermal reserve zone is estimated when a special raw fuel is charged into a blast furnace. The special raw fuel contains carbon particles or carbon substances and iron-based particles consisting of metallic iron or iron oxide. Using a correlation in which the logarithm of the mean distance LRS in the special raw fuel and the amount of decrease, ΔTtrz, are expressed as a linear function, the decrease in the temperature of the thermal reserve zone, ΔTtrz, is determined based on the mean distance LRS calculated from the special raw fuel charged into the blast furnace. As the special raw fuel, at least one of coal-bearing lump ore, ferro-coke and small lump coke may be used.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for estimating the amount of decrease in the thermal reserve zone temperature of a blast furnace. [Background technology]

[0002] In Patent Document 1, the fluctuation of the thermal reserve zone temperature is evaluated based on the fluctuation of the gasification reaction initiation temperature (measured value) and the correlation between the gasification reaction initiation temperature and the thermal reserve zone temperature, which is previously obtained. Here, the gasification reaction initiation temperature is the temperature at which the weight loss rate of the coke per unit time is 0.002 [min -1 ] is the coke temperature when it exceeds

[0003] In Patent Document 2, when coke or a charge having higher carbonaceous reactivity than coke is used, a first correspondence relationship is defined between the reaction temperature in iron / iron oxide equilibrium and the oxygen potential of the reducing gas, and a second correspondence relationship is defined between the gasification reaction initiation temperature of coke / charge (alone) and the oxygen potential of the reducing gas when the gasification reaction initiation temperature is determined. Then, in a temperature-gas utilization ratio diagram, the temperature at the intersection of the first correspondence relationship and the second correspondence relationship is estimated as the thermal reserve zone temperature of the blast furnace.

[0004] In Non-Patent Document 1, in order to consider the degree of proximity of carbon and iron oxide in carbon-containing agglomerates, the average distance L between carbon and iron oxide is considered. OC is calculated. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-196151 A [Patent Document 2] JP 2018-048376 A [Non-patent literature]

[0006] [Non-Patent Document 1] "Reaction characteristics of innovative agglomerates based on ores and their effect on blast furnace use", Materials and Processes (CAMP-ISIJ) 22 (2019), 722 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, in order to evaluate the fluctuation of the thermal reserve zone temperature, the gasification reaction start temperature must be measured by a test using a specified gasification test device for each high reactivity coke used. In Patent Document 2, too, in order to determine the second correspondence relationship for estimating the thermal reserve zone temperature, the gasification reaction start temperature must be measured by a test using a specified test device.

[0008] The inventors of the present application have used the average distance L OC It was found that there is a correlation between the amount of decrease in the thermal reserve zone temperature and the amount of decrease in the thermal reserve zone temperature, and this led to the completion of the present invention. [Means for solving the problem]

[0009] The present invention is a method for estimating the amount of decrease in the thermal reserve zone temperature when a special raw material is charged into a blast furnace. Here, the special raw material is a raw material used to reduce the blast furnace reducing agent ratio (RAR), such as small coke or carbon-containing agglomerated ore, other than general blast furnace charges such as coke or iron ore (sintered ore). A part of this special raw material contains carbon particles or a carbon matrix, and iron-based particles made of metallic iron or iron oxide. Using the correlation between the logarithm of the average distance and the amount of decrease in the thermal reserve zone temperature expressed as a linear function, which will be described below, the amount of decrease in the thermal reserve zone temperature is calculated based on the average distance calculated from the special raw material charged into the blast furnace.

[0010] The above-mentioned average distance is the average distance between the carbon particles in the special raw fuel or the pseudo-carbon particles in the carbon matrix and the iron-based particles (metallic iron / iron oxide), and is defined by the following formulas (I) and (II).

[0011]

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[0012] L RS is the average distance [mm], x is the average distance L RS Depending on the special raw fuel, one of the carbon particles (carbon particles contained in the special raw fuel or pseudo carbon particles in the carbon matrix) and the iron-based particles that specify the average distance is taken as the reference particle, and the other of the carbon particles and the iron-based particles that specify the average distance is taken as the surrounding particle. When the special raw fuel is regarded as an assembly of units that is composed of one reference particle contained in the special raw fuel and multiple surrounding particles that exist around the reference particle, d U is the diameter in units [mm], d R is the diameter of the reference particle [mm], V R is the volume of the reference particle contained in the unit [mm 3 ], V S is the volume of surrounding particles contained in the unit [mm 3 ].

[0013] The above correlation can be expressed by the following formula (III).

[0014]

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[0015] ΔT trz is the amount of decrease [℃], m is the carbon substitution rate [%], L RS is the average distance [mm], k is the average distance L at a carbon substitution rate of 1% (m = 1) RS Logarithm of and decrease amount ΔT trz is the constant [-] that maps

[0016] As the special raw fuel, at least one of carbon-containing agglomerated ore, ferro coke, and small coke mixed with ore can be used. When at least two of carbon-containing agglomerated ore, ferro coke, and small coke are used as the special raw fuel, the total value of the reduction amount calculated for each special raw fuel based on the correlation can be estimated as the reduction amount of the thermal reserve zone temperature. Effect of the Invention

[0017] According to the present invention, the average distance L of the special raw fuel RS By calculating the above, the amount of decrease in the thermal reserve zone temperature can be estimated. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram illustrating the average distance LRS for carbon-containing agglomerated ore and a mixture of small coke and ore. [Diagram 2] FIG. 2 is a diagram for explaining the average distance LRS for ferro-coke. [Diagram 3] 11 is a diagram showing the relationship between the average distance LRS of the special raw fuel and the amount of decrease ΔTtrz in the thermal reserve zone temperature Ttrz. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In this embodiment, the average distance L RS The logarithm of (lоg(L RS ) and the thermal reserve zone temperature T trz The decrease in ΔT trz Taking advantage of the fact that there is a linear correlation between the average distance L of the special raw material charged into the blast furnace RS The decrease from ΔT trz As described later, the average distance L RS From the above correlation (linear function), the decrease amount ΔT trz can be sought.

[0020] Special raw materials are materials other than general blast furnace materials such as coke and iron ore (sintered ore). They are charged into the blast furnace to reduce the blast furnace reducing agent ratio (RAR) and to reduce the thermal reserve zone temperature T trz The special raw fuel is, for example, a carbon-containing agglomerate, ferro-coke, and small coke. The carbon-containing agglomerate is an agglomerate of iron ore and carbonaceous material (carbon), the ferro-coke is a coke produced by mixing with iron oxide, and the small coke is a coke with a particle size smaller than that of the lump coke, and is mixed with the ore before use.

[0021] (average distance L RS About average distance L RS The idea behind this is explained below.

[0022] In special raw fuels, other particles (hereinafter referred to as "surrounding particles") exist around a reference particle (hereinafter referred to as "reference particle"), so it can be divided into units containing one reference particle. A collection of multiple units constitutes a special raw fuel. One unit is composed of one reference particle and multiple surrounding particles that surround the reference particle.

[0023] In carbon-bearing agglomerates, carbonaceous materials are dispersed in the iron ore, so the reference particle is a carbon particle (carbonaceous material particle), and the surrounding particles are iron-based particles made of iron oxide or metallic iron. The carbon particles and iron-based particles contained in the carbon-bearing agglomerates are distributed as shown in Figure 1, and each unit is an area (three-dimensional area) surrounded by a division line L with each carbon particle at its center. If the three-dimensional area surrounded by the division line L is approximated as a sphere, it will have a diameter d U In this unit, a carbon particle is located at the center, and iron-based particles are present around the carbon particle.

[0024] In the unit of carbon-containing agglomerates approximated as a sphere, the carbon particles and iron-based particles are regarded as spheres, and the carbon particles have a diameter (particle size) d RThe distance L between the carbon particles and each iron-based particle is RS_n is the shortest distance from the surface of the carbon particle to the surface of each iron-based particle. The distance L for all iron-based particles in the unit RS_n The average distance L RS It becomes.

[0025] If the entire ore layer in which small coke is mixed with ore is considered as a mixture of small coke and ore, carbon particles (coke particles) and iron-based particles (iron oxide and metallic iron particles) are distributed in the same way as in the carbon-containing agglomerated ore shown in Figure 1. The unit of this mixture, which is approximated as a sphere, has a diameter of d U and has a diameter (particle size) d R The carbon particle having the above structure is located at the center of the unit, and the iron-based particles are present around the carbon particle. The distance L between the carbon particle and each iron-based particle is RS_n is the shortest distance from the surface of the carbon particle to the surface of each iron-based particle. The distance L for all iron-based particles in the unit RS_n The average distance L RS It becomes.

[0026] In ferro-coke, as shown in Figure 2, iron-based particles consisting of iron oxide or metallic iron are dispersed in coke (carbon matrix), so the reference particle is the iron-based particle and the surrounding area is coke. Here, since it is not possible to distinguish the surrounding coke, the coke is treated as a pseudo particle (carbon particle) and considered as a surrounding particle. The unit of ferro-coke is the area (three-dimensional area) surrounded by the iron-based particle at the center. Here, if the three-dimensional area surrounded by the iron-based particle at the center is approximated as a sphere, the diameter d U In this unit, an iron-based particle is located at the center, and coke (pseudo carbon particles) is present around the iron-based particle.

[0027] In the unit of ferro-coke that approximates a sphere, the iron-based particles and the pseudo-carbon particles are each considered to be spherical, and the iron-based particles have a diameter (particle size) of d RThe distance L between the iron particles and the pseudo-carbon particles is RS_n is the shortest distance from the surface of the iron particle to the surface of each pseudo carbon particle. The distance L for all the pseudo carbon particles included in the unit RS_n The average distance L RS It becomes.

[0028] The average distance L mentioned above RS is calculated from the following formulas (1) and (2).

[0029]

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[0030] In the above formulas (1) and (2), L RS is the average distance [mm], and x is the distance L explained in Figures 1 and 2. RS_n Parameter in the direction that defines U is the diameter in units [mm], d R is the diameter of the reference particle (particle size) [mm], V R is the volume of the reference particle contained in the unit [mm 3 ], V S is the volume of surrounding particles contained in the unit [mm 3 The above formulas (1) and (2) are based on the premise that the reference particles are uniformly dispersed in the special raw fuel.

[0031] When using carbon agglomerates, the bulk density [mg / mm 3 ] and mass [mg], the volume V of the reference particle (carbon particle) R In addition, the bulk density [mg / mm 3 ] and mass [mg], the volume V of the surrounding particles (iron-based particles) S The diameter d can be calculated. R According to the above formula (2), the volume V R ,V Sand diameter d R From diameter d U Based on the above formula (1), the average distance L RS can be sought.

[0032] When using small coke, the bulk density [mg / mm 3 ] and mass [mg], the volume V of the reference particle (carbon particle) R In addition, the bulk density [mg / mm 3 ] and mass [mg], the volume V of the surrounding particle S The diameter d can be calculated. R According to the above formula (2), the volume V R ,V S and diameter d R From diameter d U Based on the above formula (1), the average distance L RS can be sought.

[0033] When ferro-coke is used, the true specific gravity [mg / mm 3 ] and mass [mg], the volume V of the reference particle (iron-based particle) R The apparent specific gravity [mg / mm 3 ] and mass [mg], the volume V of the surrounding particles (pseudo carbon particles) S The diameter d can be calculated. R As the volume V, the median diameter of the fine ore blended during the production of ferro coke may be used, or the median diameter taking into consideration the shrinkage of the ferro coke during the production (carbonization) of ferro coke may be used. R ,V S and diameter d R From diameter d U Based on the above formula (1), the average distance L RS can be sought.

[0034] (Thermal reserve zone temperature T trz The decrease in ΔT trz About average distance L RS and thermal reserve zone temperature T trz The decrease in ΔT trz The correlation is expressed by the following formula (3).

[0035]

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[0036] In the above formula (3), ΔT trz is the decrease in the thermal reserve zone temperature [℃], m is the carbon substitution rate [%], L RS is the average distance [mm], k is the average distance L at a carbon substitution rate of 1% RS Logarithm of and decrease amount ΔT trz The constant k is the average distance L while changing the carbon substitution rate m. RS and the decrease amount ΔT trz According to the embodiment described below, the constant k can be set to 1.2[-].

[0037] As shown in the above formula (3), the average distance L RS The logarithm of (lоg(L RS ) and the thermal reserve zone temperature T trz The decrease in ΔT trz According to the above formula (3), the average distance L RS If the carbon replacement rate m is calculated, the decrease in the amount of trz can be sought.

[0038] The carbon replacement ratio m is the ratio of the amount of carbon resulting from the charged special raw materials and fuels to the total amount of carbon used in the blast furnace operation before the special raw materials and fuels are used (hereinafter referred to as "standard operation"). Specifically, the carbon replacement ratio m can be calculated from the following formula (4).

[0039]

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[0040] In the above formula (4), m is the carbon replacement rate [%]. The numerator on the right side of the above formula (4) indicates the amount of carbon [kg / t] resulting from the special raw material fuel charged, and the denominator on the right side of the above formula (4) indicates the total amount of carbon [kg / t] used in the standard operation. CR is the coke ratio [kg / t] in the standard operation, PCR is the pulverized coal ratio [kg / t] in the standard operation, Cc is the carbon content [mass%] of the normal coke in the standard operation, and Cp is the carbon content [mass%] of the pulverized coal in the standard operation. RCA is the amount of special raw material fuel charged to the blast furnace [kg / t], and Cr is the carbon content [mass%] of the special raw material fuel charged to the blast furnace. The coke ratio CR and the pulverized coal ratio PCR can be obtained in the standard operation. The carbon contents Cc and Cp can be measured based on the provisions of JIS M8813.

[0041] For special raw materials charged into a blast furnace, the average distance L RS If the carbon replacement rate m is calculated, the decrease amount ΔT trz According to this embodiment, the thermal reserve zone temperature T can be calculated without performing the tests as in Patent Documents 1 and 2. trz The decrease in ΔT trz can be estimated.

[0042] Thermal reserve zone temperature T trz The decrease in ΔT trz In estimating the thermal reserve zone temperature T, it is preferable that the carbon substitution rate m is 15% or less. When the carbon substitution rate m is higher than 15%, trz The decrease in ΔT trz becomes difficult to change, and the relationship of the above formula (3) may become difficult to hold.

[0043] When one type of special raw material is charged into a blast furnace, as described above, the average distance L RSAfter calculating the carbon replacement rate m, the decrease amount ΔT trz On the other hand, when two or more types of special raw materials and fuels are charged into the blast furnace at the same time, the thermal reserve zone temperature T trz The decrease in ΔT trz can be sought.

[0044] First, the average distance L for each special raw material RS After calculating the carbon replacement rate m, the decrease amount ΔT trz (Here, the amount of decrease ΔT trz_n ") is calculated. The amount of decrease ΔT trz_n is the thermal reserve zone temperature T trz Next, the decrease in all special raw materials and fuels ΔT trz_n The total amount of the thermal reserve zone temperature T trz The decrease in ΔT trz Here, with regard to the carbon replacement rate m, it is preferable that the total of the carbon replacement rates m for all the special raw fuels is 15% or less.

[0045] In this embodiment, the thermal reserve zone temperature T trz The decrease in ΔT trz If it is possible to estimate, for example, the desired reduction amount ΔT trz The manufacturing conditions and charging conditions of special raw materials can be determined to achieve the above. trz As shown in the above formula (3), the average distance L RS and the carbon substitution rate m. The average distance L RS As can be seen from the above formulas (1) and (2), the diameter (particle size) of the reference particle d R and volume V R Therefore, as a manufacturing condition for the special raw fuel, the particle diameter of the standard particle d R or volume V R In addition, since the carbon replacement rate m depends on the amount of special raw fuel charged, as can be seen from the above formula (4), this amount can be determined as a charging condition.

[0046] The desired decrease ΔT trz can be determined taking into account the reducing agent ratio RAR. trz The decrease in ΔT trz is known to be proportional to the reduction amount ΔRAR of the reducing agent ratio RAR, so if the target reduction amount ΔRAR is determined, the reduction amount ΔT trz Based on the correlation of the reduction amount ΔRAR, the reduction amount ΔT corresponding to the reduction amount (target) ΔRAR trz This decrease amount ΔT trz is the desired reduction amount ΔT trz It becomes. EXAMPLES

[0047] Diameter (median diameter) of the reference particle d R Special fuels with different temperatures and chemical compositions were produced. Carbon-containing agglomerates (CCA) and ferro-coke (FC) were used as special fuels.

[0048] The carbon-containing agglomerates were produced by mixing industrial hematite powder, carbonaceous material, and high-early-strength Portland cement (15% by mass), molding the mixture with an extrusion molding machine, and then curing. Here, the particle diameter (median diameter) d of the carbonaceous material (standard particle) is R Six types of carbon-containing agglomerates (CCA1 to CCA6) were produced by varying the blending amount of carbon and carbonaceous material (standard particle). R The chemical composition of carbon-bearing agglomerates is shown in Table 1 below. The chemical composition of carbon-bearing agglomerates includes the carbon content (TC) and the total iron content (T.Fe).

[0049] Ferro-coke was produced by adding a certain amount of iron ore to crushed coal, forming the mixture into briquettes using a molding machine, and then carbonizing the mixture in a box-type carbonization furnace. Here, the particle diameter (median diameter) of the iron ore (standard particle) d RSix types of ferro-coke (FC1 to FC6) were produced by varying the blending amount of iron ore (standard particle). R The chemical composition of ferro-coke is shown in Table 1 below. The chemical components of ferro-coke include carbon content (TC), total iron content (T.Fe), metallic iron content (M.Fe), and iron oxide content (FeO).

[0050] For the small coke, coke with a particle size of 9 to 13 mm (47 kg / t) was mixed uniformly with the ore.

[0051] Table 1 below shows the volume ratios V for the carbon-containing agglomerates (CCA1 to CCA6), ferro-coke (FC1 to FC6), and small coke, as shown in the above formulas (1) and (2). S / V R , diameter d in units U and the average distance L RS The calculation results of are also shown. The standard conditions shown in Table 1 below are the standard conditions before using carbon-containing agglomerates (CCA1 to CCA6) and ferro-coke (FC1 to FC6). The average distance L RS was calculated based on the conditions when the lump coke layer and the ore layer are formed in normal operation.

[0052] [Table 1]

[0053] BIS furnace tests were carried out using carbon-containing agglomerates (CCA1-CCA6), ferro-coke (FC1-FC6) and small coke, and the thermal reserve zone temperature T trz The thermal reserve zone temperature T trz is defined as the temperature at which the rate of temperature rise is the minimum. In the BIS furnace test, for example, the device described in "Iron and Steel, Vol. 87 (2001), No. 5, pp. 357-364, 'Technology for Improving the Efficiency of Reactions in Blast Furnaces by Using Highly Reactive Coke'" can be used.

[0054] In the BIS furnace test, the particle size of the carbon-containing agglomerates (CCA1-CCA6) and ferro-coke (FC1-FC6) was set to 8-13 mm. trz In each measurement, the amount of sintered ore and normal coke was adjusted so that the carbon content (TC) and total iron content (T.Fe) per charge were constant. The carbon replacement rate m was also kept constant (10%).

[0055] Air temperature is 1178℃, moisture content is 18.6g / Nm 3 Under the condition of oxygen enrichment of 2.7%, the bosh gas composition (CO: 36.0%, H2: 7.0%, N2: 57.0%) and the bosh gas amount (1343 Nm3) were adjusted so that the reducing agent ratio (RAR) was 481 kg / t and the coke ratio (CR) was 349 kg / t. 3 The ore / coke (O / C) ratio was set at 4.63. Considering the alkaline circulation in the blast furnace, the reagent KOH was added in an amount of 1.8% relative to the amount of coke.

[0056] Thermal reserve zone temperature T when two types of special raw materials are used simultaneously trz The decrease in ΔT trz In order to verify this, the thermal reserve zone temperature T trz Here, the carbon replacement ratio m of the carbon-containing agglomerated ore (CCA3) alone was set equal to the carbon replacement ratio m of the ferro-coke (FC2) alone, and the total of these carbon replacement ratios m was set to 10%.

[0057] Thermal reserve zone temperature T trz The decrease in ΔT trz In order to verify the effect of the carbon replacement ratio m on the thermal reserve zone temperature T trz was measured.

[0058] The results of the above-mentioned BIS reactor test are shown in Table 2 below. trz is the thermal reserve zone temperature T trz From the above, the thermal reserve zone temperature T trz In addition, for the condition where carbon-containing agglomerates (CCA3) and ferro-coke (FC2) were mixed ("CCA+FC"), the decrease in the carbon-containing agglomerates (CCA3), ΔT trz and the decrease in the amount of ferro-coke (FC2) ΔT trz is the value calculated from the above formula (3) for reference.

[0059] [Table 2]

[0060] Figure 3 shows the average distance L RS and the thermal reserve zone temperature T trz The decrease in ΔT trz This shows the relationship between:

[0061] As can be seen from FIG. 3, when the carbon substitution rate m is 10%, the thermal reserve zone temperature T trz The decrease in ΔT trz Regardless of the type of special fuel, the average distance L RS The logarithm of (lоg(L RS )) and the straight line (linear function) LR shown in FIG. 3 is expressed by the following formula (5).

[0062]

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[0063] For the condition where carbon-containing agglomerates (CCA3) and ferro-coke (FC2) are mixed ("CCA+FC"), the reduction amount ΔT for each of the carbon-containing agglomerates (CCA3) and ferro-coke (FC2) is calculated based on the above formula (5). trzThe results were as shown in the parentheses in Table 2 (CCA: -21[℃], FC6: -16[℃]). trz The sum of these values ​​is the decrease in ΔT measured in the BIS reactor test. trz From this, when two or more types of special raw materials and fuels are charged into a blast furnace at the same time, the reduction amount ΔT trz_n The sum of these two values ​​is the thermal reserve zone temperature T trz The decrease in ΔT trz It can be seen that it is possible to estimate

[0064] For carbon-containing agglomerate (CCA3), when the carbon substitution rate m was changed to 5, 10, 15, and 20%, the thermal reserve zone temperature T trz The decrease in ΔT trz This resulted in a decrease in the amount of decrease ΔT trz It can be seen that depends on the carbon substitution rate m. Here, as can be seen from FIG. 3, the decrease in the amount of decrease ΔT trz The decrease in the carbon substitution rate m was 15 and 20%, but the decrease in the carbon substitution rate m was ΔT trz From this, it can be seen that for carbon-containing agglomerates (CCA3), the reduction in ΔT trz It is preferable to estimate [Explanation of symbols]

[0065] L: Lotteries, d U : diameter in units, d R : diameter of reference particle (particle size), L RS_n : Distance between the reference particle and the surrounding particle

Claims

1. A method for estimating a decrease in a thermal reserve zone temperature when a special raw fuel containing carbon particles or a carbon substrate and iron-based particles made of metallic iron or iron oxide is charged into a blast furnace, comprising: When the average distance between the carbon particles or the pseudo-carbon particles in the carbon matrix in the special raw fuel and the iron-based particles is defined by the following formulas (I) and (II), The reduction amount is calculated based on the average distance calculated from the special raw fuel charged into the blast furnace using a predetermined correlation in which the logarithm of the average distance and the reduction amount are expressed as a linear function when a carbon replacement rate, which is the ratio of the amount of carbon attributable to the special raw fuel charged to the total amount of carbon used in a standard operation that does not use the special raw fuel, is a predetermined value; The special raw fuel is at least one of carbon-containing agglomerated ore, ferro-coke, and a mixture of ore and small coke; a method for estimating an amount of decrease in thermal reserve zone temperature, the method comprising the steps of: determining an amount of decrease in each of the special raw fuels based on the carbon replacement ratio of each of the special raw fuels used and the correlation, under a condition that a sum of the carbon replacement ratios of all the special raw fuels is equal to or less than an upper limit value for establishing the correlation, when at least two of carbon-containing agglomerated ore, ferro coke, and the mixture are used as the special raw fuels; and estimating a total value of the amount of decrease in the thermal reserve zone temperature as an amount of decrease in the thermal reserve zone temperature. [0010] L ＲＳ is the average distance [mm], and x is the average distance L ＲＳ is a parameter in a direction that defines Depending on the carbon particles or the iron-based particles dispersed in the special raw fuel, one of the carbon particles and the iron-based particles that defines the average distance is taken as a reference particle and the other as a surrounding particle, and the special raw fuel is considered to be composed of one reference particle contained in the special raw fuel and a plurality of surrounding particles that exist around this reference particle, and the reference particle is considered to be an aggregate of units located at the center, d Ｕ is the diameter of the unit [mm], d Ｒ is the particle diameter of the reference particle [mm], V Ｒ is the volume [mm ３ ], V Ｓ is the volume [mm ３ ]

2. 2. The method for estimating the amount of decrease in thermal reserve zone temperature according to claim 1, wherein the correlation is expressed by the following formula (III): [0025] ΔT ｔｒｚ is the amount of decrease [°C], m is the carbon substitution rate [%], L ＲＳ is the average distance [mm], k is the average distance L ＲＳ Logarithm of the decrease amount ΔT ｔｒｚ is the constant [-] that corresponds to

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