JP2019116661A - Manufacturing method of carbonaceous material inner package sintered ore - Google Patents

Abstract

To provide a method for producing carbon material-embedded sintered ore capable of producing carbon material-embedded sintered ore with high reduction efficiency with high yield.
A method of producing a carbon material-embedded sintered ore, which comprises adding a coagulating material such that a compounding ratio of a coagulating material to a sintering material satisfies the following equation (1): Production method.
[(100−Z) × Y] / 100 ≦ X <Y (1)
However, X in the formula (1) is the blending ratio (mass%) of the coagulating material to the sintering raw material, and Y is the blending ratio (mass%) of the coagulating material necessary for sintering granulated particles, Z is the compounding ratio (mass%) of carbon material interior particles to sintering materials.
[Selected figure] Figure 7

Description

  The present invention relates to a technique for producing sintered ore used as a raw material for iron making in a blast furnace or the like, and more specifically, a charcoal produced by using granulated particles having a carbon material core inside as a part of the sintering raw material The present invention relates to a method for producing material-embedded sintered ore.

In the blast furnace iron making process, iron ore and sintered ore are mainly used as an iron source. Sinter is manufactured in the following procedure. First, an iron-containing raw material such as iron ore and dust having a particle size of 10 mm or less, a lime-containing raw material such as limestone, quick lime and steelmaking slag, and an MgO containing raw material such as refined nickel slag, dolomite and serpentine, and SiO ₂₎ Add an appropriate amount of water to a sintering material containing a secondary material containing a raw material and a coagulating material comprising coke breeze, anthracite etc., and mix and granulate using a drum mixer etc. to make pseudo particles. Next, the sintering raw material in the form of pseudo-particles is loaded on a circulating and moving pallet of a sintering machine, and the coagulating material contained in the sintering raw material is burned to form a sintered cake. Thereafter, the sinter cake is crushed, cooled and sized, and those having a certain particle diameter or more are recovered as product sintered ore. Sinter is a kind of agglomerated ore produced in this way.

  In recent years, attention has been focused on carbonaceous material-containing sintered ore in which an iron-containing raw material such as iron ore and dust and a carbonaceous material such as coke are closely arranged as the above-mentioned agglomerated ore. The reason for this is that the reduction efficiency can be improved by closely arranging the iron source and the carbonaceous material in the agglomerate ore, and furthermore, the temperature of the blast furnace upper portion can be lowered while maintaining the productivity.

  As a method for producing such agglomerated mineral, Patent Document 1 discloses a carbon material interior particle in which a carbon material is coated with an iron ore powder and a CaO-containing raw material, and this is used as a usual granulated particle having no carbon material. A method of producing a carbon material-embedded sintered ore by sintering the raw material into a sintered raw material using the lower suction type sintering machine is disclosed.

Patent No. 5790966

  As disclosed in Patent Document 1, in order to produce a carbon material-embedded sintered ore, the carbon material-embedded particles are mixed with ordinary granulated particles which do not have a carbon material as sintering raw materials, and the sintering is performed. The raw material is sintered by a sintering machine, but depending on the compounding amount of the coagulating material to be mixed with the sintering raw material, the carbon material core is melted and disappears by sintering by the sintering machine, and the reduction efficiency of the carbon material-embedded sintered ore Is greatly reduced. On the other hand, if the blending amount of the coagulating material is too small, the yield of the carbonaceous material-containing sintered ore decreases. However, patent document 1 does not describe anything about the compounding quantity of the coagulating material with respect to the sintering raw material which mix | blended the carbon material interior particle. This invention is made in view of the said subject, Comprising: The objective mix | blends the coagulating material of the quantity suitable for the sintering raw material containing a carbon material interior particle, and, thereby, the carbon material interior baking with high reduction efficiency It is to manufacture the ore with high yield.

The features of the present invention which can solve such problems are as follows.
[1] Carbon material interior particles in which an outer layer comprising a powdery iron-containing material and a lime-containing material is formed around a carbon material core, an iron-containing material, a secondary material, and a coagulating material A method for producing a carbon material-embedded sintered ore, which comprises sintering raw materials mixed with granulated particles obtained by granulating raw materials containing them and charging them into a pallet of a sintering machine for sintering. The manufacturing method of a carbon material interior sintering ore which mix | blends the said coagulating material so that the compounding ratio of the said coagulating material may satisfy following (1) Formula.
[(100−Z) × Y] / 100 ≦ X <Y (1)
However, X in the said (1) Formula is a compounding ratio (mass%) of the said coagulating material with respect to the said sintering raw material, Y is a compounding ratio (mass%) of the coagulating material required for sintering of the said granulated particle And Z is the blending ratio (mass%) of the carbonaceous material interior particles to the sintering raw material.
[2] The method for producing a carbon material-embedded sintered ore according to [1], wherein the coagulating material is blended so that the compounding ratio of the coagulating material satisfies the following formula (2).
[(100-Z) × Y] / 100 ≦ X ≦ [(100-Z) × Y] / 100 + (α × Z) / 100 (2)
However, X in the said (2) Formula is a compounding ratio (mass%) of the said coagulating material, Y is a compounding ratio (mass%) of the coagulating material required for sintering of the said granulated particle, Z Is the compounding ratio (mass%) of the carbon material interior particles to the sintering raw material, and α is the heat quantity necessary to raise the temperature of the carbon material interior particles divided by the combustion heat of the coagulating material It is a mass ratio (mass%) of the coagulating material with respect to the sintering raw material calculated.

  By carrying out the method for producing a carbon material-embedded sintered ore according to the present invention, it is possible to suppress the melting and disappearance of carbon material cores in the carbon material-embedded sintered ore, and it is possible to achieve a high reduction It can be manufactured by distillation.

It is a schematic diagram explaining an example of the manufacturing method of the carbon material internal sintering sinter which concerns on this embodiment. FIG. 2 is a schematic cross-sectional view of a sintering test pan 20. It is a photograph of carbon material interior particles after sintering the sintering materials which made the compounding rate of a condensation agent 4.0 mass%. It is a carbon material interior particle after sintering the sintering raw material which made the compounding ratio of the coagulating material 4.8 mass%, and a photograph of the circumference of it. It is a carbon material interior particle after sintering the sintering raw material which made the compounding ratio of the coagulating material 5.6 mass%, and a photograph of the circumference of it. It is a carbon material interior particle after sintering the sintering raw material which made the compounding ratio of the coagulating material 6.0 mass%, and a photograph of the circumference of it. It is a graph which shows the relationship between the compounding ratio of a coagulant, and the yield and RI.

  Hereinafter, the present invention will be described through embodiments of the present invention, but the following embodiments do not limit the invention according to the claims. FIG. 1: is a schematic diagram explaining an example of the manufacturing method of the carbon material internal sintering ore which concerns on this embodiment. A method of producing a carbon material-embedded sintered ore according to the present embodiment will be described with reference to FIG.

As shown in FIG. 1, first, using a kneader 10, raw materials containing iron ore powder and quick lime (CaO) are mixed into a mixture. Here, iron ore powder is an example of a powdery iron-containing raw material, and is, for example, pellet feed with a particle diameter of 10 to 1000 μm. In addition, quicklime is an example of a lime-containing material, and limestone may be used in place of quicklime and together with quicklime, and dolomite [CaMg (CO ₃ ) ₂ ], which increases the viscosity of the melt produced during sintering, And / or may be added to limestone. That is, the lime-containing raw material is a raw material containing any one or more of quick lime, limestone and dolomite. The mixture, coke particles having a particle diameter of 3 mm or more serving as a carbon material core, and a predetermined amount of water are supplied to the granulator 12. In the granulator 12, an outer layer made of a mixture of iron ore powder and quick lime is formed around the coke particles, and carbon material-embedded particles having a particle size of 5 mm or more are granulated.

  Although the carbon material interior particles are granulated in such a granulation process, not all the carbon material core particles are internally provided to all the granulated carbon material interior particles, but some carbon material nuclei are internally provided. Not contain granulated particles. In the present embodiment, the carbon material-embedded particles are granulated particles which are granulated in the above-mentioned granulation step and which contain granulated particles which incorporate carbon material nuclei and granulated particles which do not incorporate some carbon material nuclei. Means In addition, the particle size in this embodiment is a particle size sieved using the sieve of the nominal opening according to JIS (Japanese Industrial Standard) Z 8801-1, and for example, the particle size of 3 mm or more is The particle size to be sieved on a sieve using a sieve with a nominal opening of 3 mm in accordance with JIS Z 8801-1.

In parallel with the granulation process of the carbon material-embedded particles, an iron-containing material such as iron ore and dust having a particle size of 10 mm or less, which is a raw material of conventional sintered ore, The raw material containing the auxiliary material containing the contained material and the coagulating material made of powdered coke or anthracite having a particle diameter of less than 3 mm is granulated by a granulator 14 such as a drum mixer to make granulated particles. The auxiliary materials may include MgO-containing materials such as refined nickel slag, dolomite and serpentine, and SiO ₂ -containing materials made of silica stone or the like.

  Next, the carbon material-containing particles are blended with granulated particles obtained by granulating conventional sinter ore raw materials to obtain sinter raw materials. In the present embodiment, the carbon material-containing particles are blended such that the blending ratio of the carbon material-containing particles to the sintering material is 20% by mass. Here, the compounding ratio of the carbonaceous material interior particles to the sintering material is a percentage of the mass ratio of the carbonaceous material interior particles to the mass of the sintering material.

  The sintering raw material in which the carbon material interior particles are blended is carried into the surge hopper of the lower suction type sintering machine 16. The sintering material is charged from the surge hopper to an endless moving pallet to form a charging bed. The charge layer is ignited by an igniter installed at the upper side, and the charge layer is sequentially burned and sintered by sucking the upper gas downward from the wind box provided at the lower side. The charge layer is sintered by the heat of combustion generated by the combustion to form a sintered cake. The sinter cake obtained in this way is crushed and sized in a discharge section, and agglomerates of about 5 mm or more are recovered as a carbon-clad internal sinter ore. The carbon material-embedded sintered ore produced in this manner is used as a steelmaking material of the blast furnace 18.

  In the method for producing a carbon material-embedded sintered ore according to this embodiment, the compounding ratio of the coagulating material to the sintering material is lowered according to the compounding ratio of the carbon material-embedded particles to the sintering material. That is, the mixture ratio of the coagulating material to the sintering material is X (mass%), and the granulated material (hereinafter, referred to as ordinary granulated particles) obtained by granulating the sintering material which does not contain the carbon material interior particles Assuming that the compounding ratio of the coagulating material necessary for sintering is Y (mass%) and the compounding ratio of the carbon material interior particles to the sintering material is Z (mass%), the compounding ratio X of the coagulating material is the carbon material to the sintering material A coagulating material is blended so as to satisfy the following equation (1) including the blending ratio Z of the interior particles.

  [(100−Z) × Y] / 100 ≦ X <Y (1)

  By blending the coagulating material so that the compounding ratio X of the coagulating material satisfies the above equation (1), melting and disappearance of the carbonaceous material core embedded in the carbonaceous material interior particle due to excessive supply of heat are suppressed, and the carbonaceous material It is possible to suppress a reduction in the reduction efficiency of the internal sintered ore. That is, the technical significance of the above equation (1) is to lower the compounding ratio of the coagulating material in accordance with the compounding ratio of the carbon material internal particle to the sintering raw material, whereby the carbon material internal particle is internally It has achieved control of melting and disappearance of the carbon core.

  On the other hand, if the blending ratio of the coagulating material is too low, the sintering of the sintering material becomes insufficient and the yield of the carbon material-embedded sintered ore decreases. For this reason, the lower limit of the compounding ratio of the coagulating material was specified so that the compounding ratio of the carbonaceous material interior particles was reduced from the compounding ratio of the coagulating material necessary for sintering of the ordinary granulated particles. Therefore, by blending the coagulant so as to satisfy the above equation (1), it is possible to suppress the supply of heat being too small at the time of sintering of the sintering raw material, and as a result, It is possible to suppress the drop in oil residue.

  Furthermore, the compounding ratio of the coagulating material to the sintering material is X (mass%), and the compounding ratio of the coagulating material necessary for sintering the ordinary granulated particles is Y (mass%), and the carbon material interior to the sintering material The mass ratio of the coagulating material to the sintering raw material is calculated by dividing the amount of heat necessary to raise the temperature of the carbon material interior particles by setting the compounding ratio of the particles to Z (mass%) by the combustion heat of the coagulating material. Assuming that it is% by mass, it is preferable to blend the coagulating material so that the blending ratio X of the coagulating material satisfies the following formula (2) including the blending ratio Z of the carbon material-embedded particles to the sintering raw material.

  [(100-Z) × Y] / 100 ≦ X ≦ [(100-Z) × Y] / 100 + (α × Z) / 100 (2)

  By blending the coagulating material so that the compounding ratio X of the coagulating material satisfies the above equation (2), melting and disappearance of the carbon material core embedded in the carbon material-embedded particle due to excessive supply of heat are further suppressed, The reduction of the reduction efficiency of the material-embedded sinter can be further suppressed. That is, the technical significance of the equation (2) is that the carbon material-containing particles are raised to a compounding ratio obtained by subtracting the compounding ratio of the carbon material-containing particles from the compounding ratio of the coagulating material required for sintering of the ordinary granulated particles. The upper limit of the above (1) is to be defined so that the compounding rate is obtained by adding the coagulating material necessary for heating. Thereby, the yield of the carbon material-embedded sintered ore can be further improved while suppressing melting and disappearance of the carbon material core embedded in the carbon material-embedded particles. The gaseous fuel may be supplied from above the charging bed of the lower suction type sintering machine 16 instead of part of the coagulating material mixed in the sintering raw material. The gaseous fuel may be any one selected from blast furnace gas, coke oven gas, blast furnace / coke oven mixed gas, converter gas, city gas, natural gas, methane gas, ethane gas, propane gas, shale gas, and mixtures thereof. You may use the flammable gas of

Next, the carbon material-embedded sintered ore will be described. In the carbon material-embedded sintered ore produced by the method for producing a carbon material-embedded sintered ore according to the present embodiment, the carbon material and an iron source such as iron ore are closely arranged in the agglomerated ore. By arranging the carbon material and the iron source in close proximity in the agglomerate ore, CO generated by the gasification reaction (endothermic reaction) on the carbon material side is used for the reduction reaction (exothermic reaction) on the iron source side, The reduction efficiency is improved because these reactions occur repeatedly at a rapid rate within the agglomerated mineral, such as the CO ₂ generated by the reduction reaction is used in the gasification reaction, and so on. Furthermore, if the carbon material and the iron source are arranged close to each other, the heat required for the gasification reaction is supplied by the reduction reaction of the iron source, so the thermal efficiency is improved and the temperature of the blast furnace upper portion is lowered without reducing the reduction efficiency. You can also Thus, the reduction efficiency can be improved by using the carbon material-embedded sintered ore as the iron making material for blast furnace, and further, the temperature of the blast furnace upper portion can be lowered.

  In the method for producing a carbon material-embedded sintered ore according to the present embodiment, the compounding ratio of the coagulating material to the sintering material is not blended with the carbon material-embedded particles in accordance with the compounding ratio of the carbon material-embedded particles to the sintering material. It is in the range of the compounding ratio which satisfies the said (1) Formula or the said (2) Formula made lower than the compounding ratio of the coagulating material required for sintering of a sintering raw material. Thereby, melting and disappearance of the carbon material core embedded in the carbon material-embedded particle are suppressed, and the effect by arranging the carbon material and the iron source close to each other can be obtained.

  FIG. 2 is a schematic cross-sectional view of the sintering test pan 20. As shown in FIG. The result of the sintering experiment which simulates the manufacturing method of the carbon material internal sintering sinter which concerns on this embodiment is demonstrated using the sintering test pot 20 shown in FIG. Also in this sintering experiment, sintering raw material 22 which blended carbon material interior particles to usual granulated particles was used. The blending ratio of the carbonaceous material interior particles was 20% by mass with respect to the sintering material. Moreover, the compounding ratio of the coagulating agent required for sintering of the normal granulated particle was 6.0 mass%.

  In this sintering experiment, a sintering test pot is used to sinter the sintering raw material in which the mixing ratio of the coagulating material to the sintering raw material is adjusted to 4.0 mass%, 4.8 mass%, 5.6 mass%, and 6.0 mass%. 20 was charged, the upper end side was ignited, and the air 24 was vented from the upper side to the lower side to sinter the sintered raw material including the carbon material-embedded particles. Thereafter, the molten state of the carbon material-embedded particles after sintering is photographed to confirm the state of the carbon material-embedded particles after sintering, and the retention and RI of the produced carbon material-embedded sintered ore are measured. did. After the completion of the sintering experiment, the sintered cake taken out of the sintering test pan 20 is dropped once from a height of 2 m, and the yield of the carbon material-embedded sintered ore is a sieve with an opening of 10 mm with respect to the mass of the sintered cake. The percentage of mass fraction of sintered ore remaining on the Moreover, RI is a parameter | index which shows the reducibility of a sintered ore, Comprising: It is the value measured based on JISM 8713.

  In this sintering experiment, the compounding ratio Y of the coagulating material necessary for sintering of the ordinary granulated particles is 6.0 mass% as described above, and the compounding ratio Z of the carbonaceous material internal particle to the sintering raw material is It is 20.0 mass%. These values were substituted into equation (1) to obtain equation (3) below.

  4.8 ≦ X <6.0 (3)

  From the above equation (3), an example in which the blending ratio of the coagulating material to the sintering material is 4.0 mass% is an example below the lower limit of the range of X determined by the equation (3). An example in which the blending ratio of the coagulating material to the sintering raw material is 6.0 mass% is an example exceeding the upper limit of the range of X defined by the equation (3). An example in which the blending ratio of the coagulating material to the sintering raw material is 4.8% by mass and 5.6% by mass is an example satisfying the formula (3).

  Further, α, which is a mass ratio of the coagulating material to the sintering raw material calculated by dividing the heat amount necessary to raise the temperature of the carbon material internal particle in the above equation (2) by the combustion heat of the coagulating material, It can be calculated as follows. The amount of heat required to raise the temperature of the carbon-embedded particles includes heat for raising the temperature of the raw material (hematite) of the carbon-embedded particles from normal temperature (25 ° C.) to 1200 ° C. and the carbon-embedded particles. There are heat required for thermal decomposition of crystal water (0.3% by mass) and latent heat of vaporization of water (8.0% by mass) contained in carbon material-embedded particles. The amount of coagulating material required to raise the temperature of the raw material of the carbon material-embedded particles is 33.2 kg-coke / t, and the amount of the coagulating material required for thermal decomposition of the crystal water is 0.2 kg-coke / t. The latent heat of evaporation of water is 6.7 kg-coke / t.

  The amount of heat required to heat the hematite, which is a raw material of the carbon material-embedded particles, from normal temperature to 1200 ° C. can be calculated by the following equation (4).

However, the values of a, b and c in the equation (4) differ depending on the hematite phase. The values of a, b and c of the α phase, β phase and γ phase of hematite are shown in Table 1.

  Assuming that 40.1 kg-coke / t, which is the sum of the amounts of these coagulating agents, is the amount of the condensing agent necessary for raising the temperature of the carbon material-containing particles, the mass ratio α of the coagulating agent to the sintering material is approximately 4 . These values were substituted into the above equation (2) to obtain the following equation (5). The value of α may vary depending on the raw material of the carbon material-embedded particles and the granulation method, but is generally a value within the range of 1 ≦ α ≦ 6. In addition, it is conceivable to use quicklime, cement or other auxiliary raw material when producing carbon material-embedded particles, but in that case, the temperature rise of the auxiliary raw material and the heat quantity for the reaction may be similarly calculated.

  4.8 ≦ X ≦ 5.6 (5)

  From the above equation (5), an example in which the mixing ratio of the coagulating material to the sintering material in the sintering experiment is 4.8 mass% is an example of the lower limit of the equation (5). The example made into 5.6 mass% of compounding ratios is an example of the upper limit of (5) Formula.

  FIG. 3 is a photograph of carbon material-embedded particles after sintering the sintering raw material in which the mixing ratio of the coagulating material is 4.0 mass%. As shown in FIG. 3, in the case of using a sintering raw material in which the mixing ratio of the coagulating material was 4.0 mass%, the carbon material-containing particles were present without melting. For this reason, RI of the carbon material-embedded sintered ore of this example was as high as 81.8%, but the heat amount of sintering was insufficient because the blending ratio of the coagulating material was too low. The yield was as low as 60.7% by mass.

  FIG. 4 is a photograph of carbon material-embedded particles after sintering the sintering raw material having a blending ratio of the coagulating material of 4.8% by mass, and the surrounding area. As shown in FIG. 4, when using a sintering raw material having a blending ratio of 4.8% by mass of the coagulating material, the carbonaceous material interior particles do not melt away, and the carbonaceous material interior particles and the usual granulated particles are obtained. A carbon material-embedded sinter ore is produced, which is partially sintered. At this time, the yield of the carbon material-embedded sintered ore was 73.3% by mass, and the RI was 80.3%.

  FIG. 5 is a photograph of carbon material-embedded particles after sintering the sintering raw material having a blending ratio of the coagulating material of 5.6% by mass and the surrounding area. As shown in FIG. 5, when using a sintering raw material having a mixing ratio of the coagulating material of 5.6% by mass, the carbonaceous material interior particles do not melt away, and the carbonaceous material interior particles and ordinary granulated particles are obtained. A carbon material-embedded sinter ore which is sufficiently sintered is produced. At this time, the yield of the carbon material-embedded sintered ore was 75.3% by mass, and the RI was 78.6%.

  FIG. 6 is a photograph of carbon material-embedded particles after sintering the sintering raw material having a blending ratio of the coagulating material of 6.0% by mass, and the surrounding area. As shown in FIG. 6, when the sintering raw material which made the compounding ratio of the coagulating material 6.0 mass% was used, the heat became excessive, the carbon material interior particle melted, and the carbon material nucleus disappeared. . The retention rate of the carbon material-embedded sintered ore at this time was 76.1% by mass, and the RI was 57.2%. As described above, when the carbon material-embedded particles are melted, the effect of arranging the carbon material and the iron source close to each other in the agglomerated mineral can not be obtained, and the RI is greatly reduced. The results of these sintering experiments are shown in Table 2 below and in FIG.

  FIG. 7 is a graph showing the relationship between the compounding ratio of the coagulating material and the yield and RI. In FIG. 7, the horizontal axis is the blending ratio (mass%) of the coagulating material, and the vertical axis is the yield (mass%) or RI (%). In the case where the blending ratio Y of the coagulating material necessary for sintering of the ordinary granulated particles is 6.0 mass%, as shown in FIG. 7, the blending ratio of the coagulating material to the sintering raw material is 0.48 mass% A coagulating material is blended so as to satisfy at least 6.0 mass%. That is, the coagulating material is blended so that the blending ratio of the coagulating material to the sintering raw material satisfies the above-mentioned equation (1). As a result, it can be seen that melting and disappearance of the carbon material core in the carbon material-embedded sintered ore can be suppressed, and the carbon material-embedded sintered ore having a high reduction efficiency can be produced with high yield.

  Further, the coagulating material is blended so that the blending ratio of the coagulating material to the sintering raw material satisfies 0.48 mass% or more and 5.6 mass% or less. That is, the coagulating material is blended so that the blending ratio of the coagulating material to the sintering raw material satisfies the above equation (2). As a result, it is possible to further suppress melting and disappearance of the carbonaceous material core in the carbonaceous material-embedded sintered ore, and it is possible to produce the carbonaceous material-embedded sintered ore with high reduction efficiency with high yield.

DESCRIPTION OF SYMBOLS 10 Kneader 12 Granulator 14 Granulator 16 Lower suction type sintering machine 18 Blast furnace 20 Sinter test pot 22 Sintered raw material 24 Air

Claims (2)

A carbon material-containing particle in which an outer layer comprising a powdery iron-containing raw material and a lime-containing raw material is formed around a carbon material core, an iron-containing raw material, a secondary raw material, and a coagulating material A method for producing a carbon material-embedded sintered ore, which comprises sinter raw material mixed with granulated particles obtained by granulating the raw material and loaded into a pallet of a sintering machine for sintering.
The manufacturing method of a carbon material interior sintering ore which mix | blends the said coagulating material so that the compounding ratio of the said coagulating material with respect to the said sintering raw material may satisfy following (1) Formula.
[(100−Z) × Y] / 100 ≦ X <Y (1)
However, X in the said (1) Formula is a compounding ratio (mass%) of the said coagulating material with respect to the said sintering raw material,
Y is a blending ratio (mass%) of a coagulating material necessary for sintering the granulated particles,
Z is a compounding ratio (mass%) of the carbonaceous material interior particle to the sintering raw material. The method for producing a carbon material-embedded sintered ore according to claim 1, wherein the coagulating material is compounded such that a compounding ratio of the coagulating material satisfies the following formula (2).
[(100-Z) × Y] / 100 ≦ X ≦ [(100-Z) × Y] / 100 + (α × Z) / 100 (2)
However, X in said (2) Formula is a compounding ratio (mass%) of the said coagulating agent,
Y is a blending ratio (mass%) of a coagulating material necessary for sintering the granulated particles,
Z is a compounding ratio (mass%) of the carbon material internal particle to the sintering material,
α is a mass ratio (mass%) of the coagulating material to the sintering raw material calculated by dividing the heat amount required to raise the temperature of the carbon material-embedded particles by the heat of combustion of the coagulating material.