Heat-boosting material for converters and method for manufacturing the same

Abstract

To provide a converter heating material capable of reducing the addition amount of a binder while increasing the strength of the heating material by increasing the filling rate of a carbide, and a method for producing the same.SOLUTION: A converter heating material of a carbide molded body obtained by being molded with a carbide particulate body and a binder. A carbide in the carbide molded body has (a) a particle diameter in which the maximum particle diameter is below 1 / 2 of the typical length d of the carbide molded body, and (b) when it is classified so that a large particle diameter side reaches 70 vol.% and a small particle diameter side reaches 30 vol.%, a ratio between the median particle diameter D50 of the carbide on the large particle diameter side and the median particle diameter D50 of the carbide on the small particle diameter side is 1.5 to 2.3. Also provided is a method for producing a converter heating material in which a carbide raw material is subjected to one or plural screening treatments and one or plural breaking treatments so that the carbide particulate body has particulate size distributions similar to the (a) and (b).SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a heating material for a converter, and more particularly to a heating material for a converter that increases the filling rate of carbide, which is a raw material of the heating material, to increase the strength of the heating material while optimizing the addition amount of a binder, and a method for manufacturing the same.

Background Art

[0002] The converter in the steelmaking process is a main process for producing molten steel by decarburizing hot metal discharged from a blast furnace by spraying high-purity oxygen at high speed. At the same time, auxiliary raw materials mainly composed of quicklime are added to remove impurities (such as phosphorus) in the hot metal.

[0003] On the other hand, as a pre-treatment process for hot metal before the converter, in some cases, a treatment for removing S, P, etc. in hot metal is performed according to the requirements of the material properties of steel products. In this case, there is a problem that the hot metal temperature decreases due to the pre-treatment of hot metal. [[ID=十七]]

[0004] In recent years, from the perspective of environmental protection, reduction of CO2 emissions has become an important issue in the ironmaking process. In the steelmaking process, attempts have been made to increase the blending ratio of cold iron sources such as iron scrap (scrap iron) as the iron source to be used and reduce the blending ratio of hot metal. This is because in the production of steel products, in the production of hot metal in a blast furnace, a large amount of energy is required to reduce and melt iron ore, and at the same time, a large amount of CO2 is emitted, while a cold iron source only requires the heat of fusion. When a cold iron source is used in the steelmaking process, the energy consumption for the reduction heat of iron ore can be reduced, and the amount of CO2 generated can be significantly reduced. However, in a converter, the heat source for melting the cold iron source is the sensible heat of the hot metal and the oxidation heat of carbon and silicon in the hot metal, and there is naturally a limit to the melting amount of the cold iron source.

[0005] Therefore, in the dephosphorization and decarburization refining of molten iron, various heat-raising materials have been proposed to supply an additional carbon source to the molten iron, such as coal, coke powder, graphite, electrode powder, and SiC, which are formed into lumps, in order to increase the thermal margin of the molten iron and expand the proportion of cold iron sources. In addition, natural mineral-derived earthy graphite, which is not formed, is also sometimes used as a heat-raising material because it is relatively inexpensive.

[0006] Regarding such heat-raising materials for converters, for example, Patent Document 1 describes a method in which carbon powder (coal, coke powder, graphite, etc.) containing 30-70% of particles with a particle size of 1 mm or less and the rest with a particle size of 1-8 mm is mixed with a binder consisting of polyvinyl alcohol, carboxymethylcellulose, α-starch, etc., in a range of 0.5-1.0% by weight of the carbon powder, and after conditioning and kneading to a moisture content of 10% or less, it is molded under high pressure and dried, making it possible to mold the carbon powder into a solid with sufficient strength.

[0007] Furthermore, Patent Document 2 describes a converter heat booster made by molding carbonized plant-based biomass (carbonized) with a binder consisting of starch, carboxymethylcellulose, cornstarch, etc., in an amount of 1 to 15% by mass relative to the mass of the carbonized material. This material can be used as a substitute for conventional converter heat boosters made from fossil resources such as coal, coke, and graphite, thereby reducing the consumption of fossil resources and the generation of CO2, a greenhouse gas. In addition, by making the particle size of the carbonized material 3 mm or less, it is made into a solid with a crush strength of 490 N / piece or more, which is sufficient strength for a converter heat booster. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2-270922 [Patent Document 2] Patent No. 5846289 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the carbon powder used as a raw material for the heat-raising material described in Patent Document 1 has a high proportion (30-70%) of particles with a particle size of 1 mm or less, which presents a problem of high processing load for particle size adjustment, such as grinding the carbon raw material.

[0010] Furthermore, the carbon powder used as a raw material for the heat-raising material described in Patent Document 2 needs to be granulated to a relatively narrow particle size range of 3 mm or less. Similar to the invention described in Patent Document 1, there is a problem in that the processing load for particle size adjustment, such as pulverization of the carbon raw material, is high.

[0011] Furthermore, while the heat-raising material described in Patent Document 1 uses a binder in the range of 0.5 to 1.0% by weight of carbon powder, and the heat-raising material described in Patent Document 2 uses a binder in the range of 1 to 15% by mass of carbides, in recent years, the large price fluctuations of plant-derived binders, specifically cornstarch derived from corn, have become a problem. This is due to price fluctuations linked to poor corn harvests caused by abnormal weather, and upward price pressure due to increased demand for corn-derived bioethanol to reduce environmental impact. Therefore, there is an increasing need for technologies that reduce the amount of binder used when molding heat-raising materials.

[0012] On the other hand, if the amount of binder added is less than the required amount, abnormalities such as insufficient strength in the molded charcoal material will occur, leading to operational problems during transportation and reduced yield. Furthermore, if the problem of insufficient strength in molded charcoal material due to a reduction in the amount of binder is resolved by ensuring the strength of the molded charcoal material by finely crushing all of the raw charcoal material, then the cost of finely crushing the charcoal material will increase, resulting in an overall loss of economic efficiency.

[0013] This invention has been made in view of the above circumstances, and aims to provide a converter heat-raising material and a method for manufacturing the same that makes it possible to increase the packing density of carbides, which are the raw materials for the heat-raising material, thereby increasing the strength of the heat-raising material while reducing the amount of binder added, by optimizing the particle size distribution of the carbides that are the raw materials for the heat-raising material. [Means for solving the problem]

[0014] [1] A converter heat-raising material for a carbide molded body formed from carbide powder and a binder, wherein the carbide in the carbide molded body is characterized in that (a) the maximum particle size is less than half the characteristic length d of the carbide molded body, and (b) when the body is divided so that the large particle size side accounts for 70% by volume and the small particle size side accounts for 30% by volume, the ratio of the median particle size D50 of the carbide on the large particle side to the median particle size D50 of the carbide on the small particle side is 1.5 to 2.3. [2] The converter heating element according to [1], characterized in that the converter heating element has a crush strength of 490 N / piece or more. [3] A method for producing a heat-boosting material for a converter, comprising: producing a carbide molded body formed from carbide powder and a binder; producing a carbide raw material by carbonizing at least one selected from coal, plant biomass, and waste plastics; subjecting the carbide raw material to one or more sieving processes and one or more crushing processes to obtain carbide powder separated from the carbide raw material into a plurality of groups with different particle sizes, within a range where the maximum particle size is less than 1 / 2 of the characteristic length d of the carbide molded body; and further, (b') blending the obtained carbide powder so that when the large particle size side accounts for 70% by volume and the small particle size side accounts for 30% by volume, the ratio of the median particle size D50 of the carbide on the large particle size side to the median particle size D50 of the carbide on the small particle size side is in the range of 1.5 to 2.3, thereby obtaining the carbide powder before molding. [4] The method for manufacturing a converter heat booster according to [3], characterized in that the converter heat booster has a crush strength of 490 N / piece or more. [Effects of the Invention]

[0015] According to the present invention, the particle size distribution of carbides in a converter heating element (carbide molded body) (hereinafter also simply referred to as heating element) is such that the maximum particle size of the carbides is less than half the representative length d of the converter heating element, and when the carbide particles are divided so that 70% by volume are on the large particle size side and 30% by volume are on the small particle size side, the ratio of the median particle size D50 of the carbides on the large particle size side to the median particle size D50 of the carbides on the small particle size side is in the range of 1.5 to 2.3. This makes it possible to increase the packing density of carbides and increase the strength of the heating element while reducing the amount of binder added within an economically reasonable range. This provides a converter heating element and a method for manufacturing the same. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic cross-sectional view of an example of a converter facility in which the converter heating element of the present invention is used. [Figure 2] This figure shows a schematic cross-sectional view of the process of crushing biomass charcoal using the roll crusher (cutter mill) used in the preliminary experiments and examples leading to the present invention. [Figure 3] This figure shows a schematic cross-sectional view illustrating the compression molding of crushed biomass charcoal using the twin-roll briquette machine used in the preliminary experiments and examples leading to the present invention. [Figure 4] This diagram shows a schematic cross-sectional view of how crushed biomass charcoal is extruded and molded using the pelletizer used in the preliminary experiments and examples leading to the present invention. [Figure 5] This figure, obtained in preliminary experiments leading to the present invention, summarizes the relationship between the ratio of large and small particle sizes of carbides in the converter heating element and the porosity of the carbide molded body of the converter heating element, stratified by the particle size ratio of large to small particles. [Figure 6] This figure, obtained in preliminary experiments leading to the present invention, summarizes the relationship between the particle size ratio of large and small particles of carbides in the converter heating element and the minimum porosity of the carbide molded body of the converter heating element. [Figure 7]This is a diagram obtained from preliminary experiments leading to the present invention, which summarizes the relationship between the ratio of the median particle size D50 of carbides on the larger particle size side to the representative length d of the carbide compact and the binder concentration required for molding the heating material for a converter. [Figure 8] This is a diagram showing the measurement results of the particle size of the pulverized biomass charcoal used in an example of the pellet-shaped carbide compact of the present invention. [Figure 9] This is a diagram showing the measurement results of the particle size of the pulverized biomass charcoal used in an example of the briquette-shaped carbide compact of the present invention.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, the present invention will be specifically described. First, the converter equipment to which the present invention is applied will be described. FIG. 1 is a schematic cross-sectional view of an example of a converter equipment using the heating material for a converter of the present invention.

[0018] In FIG. 1, an upper blowing lance 2 is inserted into the converter body 1 that houses hot metal 8. At the same time that oxygen gas is blown onto the hot metal 8 from this upper blowing lance 2, stirring bottom blowing gas is blown in from a plurality of bottom blowing tuyeres 3 arranged at the bottom of the converter body 1, and while the hot metal 8 and slag 9 are stirred, decarburization refining of the hot metal 8 is performed. Converter exhaust gas 10 mainly composed of CO gas is generated from the furnace due to the decarburization refining of the hot metal 8.

[0019] A flue 4 is installed above the converter body 1, and a primary dust collector (not shown), a secondary dust collector (not shown), and an induced draft fan (not shown) are installed in this order at the rear stage of the flue 4. With such a treatment facility for the converter exhaust gas 10, the converter exhaust gas 10 generated inside the converter body 1 by decarburization refining is cooled, dust removed, and recovered as it is unburned to a gas holder (not shown) on the downstream side of the induced draft fan (not shown).

[0020] The side of the flue 4 that connects to the furnace opening of the converter body 1 is called the skirt 5, and it has a structure that allows it to move up and down. When recovering exhaust gas, the skirt 5 and the furnace opening of the converter body 1 are in principle in close contact. The flue 4 is also equipped with a secondary material feeding device consisting of a hopper 6 and an input chute 7 for feeding secondary materials such as quicklime, calcined dolomite, iron ore, mill scale, manganese ore, heat risers (carbon materials such as coke and soil graphite), and ferroalloys (Fe-Mn, Fe-Si, etc.) into the converter body 1. Slag 9 is formed from the quicklime, calcined dolomite, iron ore, mill scale, manganese ore, etc. that are fed into the furnace from the secondary material feeding device.

[0021] The converter heating element of the present invention is a converter heating element of a carbide molded body formed from carbide powder and a binder, wherein the carbide in the carbide molded body is characterized in that (a) the maximum particle size is less than 1 / 2 of the characteristic length d of the carbide molded body, and (b) when the body is divided so that the large particle size side accounts for 70% by volume and the small particle size side accounts for 30% by volume, the ratio of the median particle size D50 of the carbide on the large particle size side to the median particle size D50 of the carbide on the small particle size side is 1.5 to 2.3.

[0022] Furthermore, the present invention relates to a method for producing a heat-raising material for a converter, which is a heat-raising material for a converter made of a carbide molded body formed from carbide powder and a binder, and is characterized in that: at least one selected from the group consisting of coal, plant-based biomass, and waste plastics is carbonized to produce a carbide raw material; one or more sieving treatments and one or more crushing treatments are applied to the carbide raw material to obtain carbide powder separated from the carbide raw material into multiple groups with different particle sizes, within a range where the maximum particle size is less than 1 / 2 of the characteristic length d of the carbide molded body; and (b') the obtained carbide powder is blended such that when the obtained carbide powder is divided into a large particle size side of 70% by volume and a small particle size side of 30% by volume, the ratio of the median particle size D50 of the carbide on the large particle size side to the median particle size D50 of the carbide on the small particle size side is in the range of 1.5 to 2.3 to obtain the carbide powder before molding.

[0023] The carbide molded body (heat-raising material for converters) of the present invention is obtained by adding a binder and water to carbide powder as the main raw material, mixing and stirring in a known mixer (not shown), molding with a known molding device (see Figures 3 and 4), and then drying to a predetermined moisture content. The carbide powder, which is the main raw material, is first carbonized using a known carbonization device (not shown) such as a rotary kiln, batch furnace, or shaft furnace, using raw materials such as coal, plant biomass, or waste plastics. Next, the obtained carbide is crushed to various particle sizes by passing it through a known cutter mill once or multiple times as needed, and then the particle size is adjusted by sieving or the like. As the binder, inorganic bentonite, organic carboxymethylcellulose, corn starch, etc. can be used.

[0024] As a known cutter mill, Figure 2 schematically shows how carbon material 21, which has been carbonized in a rotary kiln or the like, is supplied from the hopper 27 of a roll crusher (cutter mill) 26 to the crusher rolls 28, crushed into pulverized material 22, and then discharged on a belt conveyor 29. As a molding device for the carbide molded body, known twin-roll briquette machines or pellet manufacturers (pelletizers) can be used. Figure 3 schematically shows how a mixture of carbon material 23, which has been mixed with a binder and water in a mixer after particle size adjustment, is supplied from the hopper 32 of a twin-roll briquette machine 31 to the molding rolls 33, compressed and molded into a molded carbon material product 24 (briquette 24a), and then discharged on a belt conveyor 34. Figure 4 schematically shows how a similar mixture of charcoal materials 23 is supplied from the hopper 42 of a pelletizer 41 to a screw feeder 43, where it is compressed and extruded, and then cut to a predetermined length by a cutter 44 to become molded products 24 (pellets 24b), which are then transported out on a belt conveyor 45.

[0025] The reason why the carbides in the carbide molded body of the present invention have a maximum particle size less than half the characteristic length d of the carbide molded body is to avoid unnecessarily increasing the binder concentration during the manufacture of the heat-raising material for converters. In other words, when granulating carbide powder, contrary to the expectation that small particles will fill in between large particles and create dense packing, there are cases where small particles do not fill in between large particles. As will be explained in the preliminary experimental results described later, this phenomenon is particularly pronounced when the maximum particle size is half or more the characteristic length d of the carbide molded body. Therefore, although particles are bound together by the liquid crosslinking adhesion force of water containing the binder even between such large particles, when the maximum particle size is half or more the characteristic length d of the carbide molded body and the gaps between large particles widen, a large liquid crosslinking adhesion force is required, and thus the binder concentration needs to be increased.

[0026] Here, the representative length d of the carbide molded body (heat booster for converter) of the present invention will be explained. That is, the representative length d is a length that represents the outer shape of the heat booster for converter when dealing with the balance relationship between gravity acting on the heat booster for converter and the drag force received from the converter exhaust gas according to its outer shape. Using this representative length, for example, if a heat booster with a representative length such that gravity is smaller than the drag force received from the converter exhaust gas is used, it can be considered in advance that the heat booster will float up with the converter exhaust gas, making it impossible to feed the heat booster into the molten metal. Note that when the heat booster for converter is in pellet shape, the representative length d can be represented by the pellet diameter, and when the heat booster for converter is in briquette shape, the representative length d can be represented by the maximum diagonal length.

[0027] Furthermore, when the carbide in the carbide molded body of the present invention is divided into a large particle size side of 70% by volume and a small particle size side of 30% by volume, the ratio of the median particle size D50 of the large particle size carbide to the median particle size D50 of the small particle size carbide is set to 1.5 to 2.3. This is because, as will be explained in the preliminary experiments and examples described later, the porosity is reduced compared to when large and small particles are not blended, and the rate of change in the porosity is small, resulting in a wide range of acceptable porosity. Therefore, even considering variations during manufacturing, no abnormalities occur in the carbide molded body, and a high product yield can be maintained.

[0028] Here, we will explain how to measure the ratio of median particle sizes of carbide particles in the converter heating element (carbide molded body) of the present invention. First, the converter heating element (carbide molded body) is immersed in water to dissolve the binder, then filtered to collect the carbide, which is washed with pure water or methanol. The particle size distribution of the carbide particles is then determined by laser diffraction particle size distribution measurement (JIS Z 8825:2013 Particle size analysis - Laser diffraction and scattering method). Next, by computer analysis of this particle size distribution, the ratio of the median particle size D50 of the carbide on the large particle side to the median particle size D50 of the carbide on the small particle side can be determined when the material is divided so that the large particle side accounts for 70% by volume and the small particle side accounts for 30% by volume. Here, the median particle size D50 is determined by reading the particle size at which the cumulative value reaches 50% on a volume-based cumulative distribution curve in which the particle size is plotted on the horizontal axis and the cumulative value of the particle amount is expressed as a volume percentage (%) on the vertical axis.

[0029] On the other hand, in the method for manufacturing a heat-raising material for a converter according to the present invention, the ratio of median particle sizes of carbide powder, which is the main raw material for the carbide molded body, can be measured by sieving the carbide powder for each predetermined particle size and determining the particle size distribution of the carbide powder. This particle size distribution can then be determined using the same method as for determining the ratio of median particle sizes of carbide particles in the carbide molded body described above. Furthermore, the measurement result of the ratio of median particle sizes of carbide powder, which is the raw material for the carbide molded body, and the measurement result of the ratio of median particle sizes of carbide particles in the carbide molded body produced from that carbide powder can be treated as equivalent both in principle and statistically.

[0030] The results of preliminary experiments regarding the range of carbide particle sizes are described below. The inventors first investigated the relationship between the crushing strength of a carbide molded body (heat-raising material for converters) obtained by molding carbide powder and the packing density of carbide particles. Generally, it is known that crushing strength and packing density (= 1 - porosity) are proportional because a higher packing density increases the capillary attraction force between particles and mechanical bonding effects such as particles joining to each other's uneven surfaces.

[0031] Regarding packing efficiency, Horsfield's packing model is known, and when perfectly spherical particles of a single particle size φ are packed in a hexagonal close-packed structure, the void ratio is 25.9%. Furthermore, by filling the remaining spaces between the perfectly spherical particles with perfectly spherical particles of a size 0.414φ relative to the aforementioned φ, the void ratio can be reduced to 20.7%. However, when molding carbides, the packing structure is not hexagonal close-packed, the particle shape is not perfectly spherical, and the particle size is not uniform but distributed, making it difficult to apply Horsfield's packing model.

[0032] Therefore, as a preliminary experiment to increase the crushing strength of the charred material molded body by increasing the packing density of the charred material, when molding biomass charred material into pellets, we first prepared groups of charred material with average particle sizes equivalent to integer divisions of pellet diameter A (A=20mm) (1 / 2A, 1 / 3A, 1 / 4A, 1 / 5A, 1 / 6A) by adjusting the particle size of the raw material charred material through crushing and sieving. Of these groups of charred material, we decided to examine the 10 combinations shown in Table 1, with the charred material group on the large particle size side being 1 / 2A, 1 / 3A, 1 / 4A, 1 / 4A, and 1 / 5A, and the charred material group on the small particle size side being 1 / 3A, 1 / 4A, 1 / 5A, and 1 / 6A. Figure 5 shows the results of measuring the porosity (=1-packing rate) for each sample, with varying volume proportions (mixing ratio) of small particles within each of the 10 combinations of carbides, representing four example combinations with particle size ratios (1.3, 2.0, 2.5, 3.0). For each sample under these conditions, each carbide mixture with varying volume proportions (mixing ratio) of small particles within each combination was prepared by adding 8% by mass of cornstarch and an appropriate amount of water as a binder, kneading, then molding into pellets using a pelletizer, and finally drying to a moisture content of 3% by mass or less to obtain the test material. Table 1 also includes the minimum porosity that can be read from Figure 5 and a figure equivalent to Figure 5 (including data for particle size ratios not shown in Figure 5).

[0033] [Table 1]

[0034] Figure 5 shows that the porosity changes depending on the mixing ratio of small and large particle sizes, and that it takes a minimum value when the volume proportion of small particles is around 0.3. Also from Figure 5, it can be seen that the change in porosity can be stratified and organized according to the ratio of particle sizes. Figure 6 is a diagram that summarizes the relationship between the particle size ratio of large and small particle sizes of carbides in the converter heating element, which can be organized in this stratified way, with the minimum porosity of the carbide molded body of the converter heating element on the horizontal axis. From Figure 6, it can be seen that the minimum porosity can be reduced by increasing the particle size ratio of carbides (large particle size / small particle size). From this, it was inferred that the amount of water added to fill the voids can be further reduced.

[0035] However, in sets No. 3 and 4, although the particle size ratio is large and the minimum porosity can be significantly reduced to 0.32 and 0.25 respectively, as can be seen in Figure 5, the porosity changes greatly depending on the mixing ratio of carbide particles. Therefore, there is a concern that variations during manufacturing may result in an amount of added water being greater than the appropriate value, causing abnormalities such as lamination in the carbide molded body before drying after molding, leading to a decrease in product yield. On the other hand, although sets No. 1, 2, and 5-10 have lower porosity than sets No. 3 and 4, the rate of change in porosity near the mixing ratio that results in the minimum porosity is small, and there is a wide range of acceptable porosity. Therefore, even considering variations during manufacturing, it is expected that no abnormalities will occur in the carbide molded body and a high product yield can be obtained. Therefore, although the porosity is inferior to sets No. 3 and 4, sets No. 1, 2, 7, and 9 were deemed appropriate because, even considering variations during manufacturing, no abnormalities occurred in the carbide molded bodies, and there was no reduction in product yield.

[0036] As described above, Figure 6 suggests that increasing the particle size ratio of the carbides can reduce the minimum porosity and further reduce the amount of water added to fill the voids. Therefore, we decided to take this a step further and investigate the possibility of reducing the amount of binder required when molding the heat-raising material for the converter. Figure 7 summarizes the relationship between the ratio of the median particle size D50 of the large-particle-sized carbides to the representative length d of the carbide molded body and the binder concentration required when molding the heat-raising material for the converter. According to Figure 7, it was found that when large-particle-sized particles such as 1 / 2A are used, the required binder concentration increases. The following is presumed to be the reason for this: During granulation, it is expected that small particles will fill in between the large particles, resulting in dense packing. However, in some places, there will inevitably be areas where small particles do not fill in between the large particles. In these areas, the particles are bound together by the liquid cross-linking adhesive force of the water containing the binder. It is presumed that the wider the spacing between large particles, the greater the liquid crosslinking adhesion force required, and therefore the higher the binder concentration. In fact, when 1 / 2A was used for the large particles, as in set No. 2, a higher binder concentration was required compared to when 1 / 3A was used for the large particles, as in set No. 7. For this reason, the amount of binder was lower in set No. 7 than in set No. 2.

[0037] Based on the preliminary experimental results described above and the examples described later, the carbides contained in the converter heating element of the present invention are, firstly, in order to avoid unnecessarily increasing the binder concentration, (a) having a maximum particle size of less than half the representative length d of the converter heating element (carbide molded body), and at the same time, in order to ensure a favorable control range, (b) when the material is divided so that the large particle size side accounts for 70% by volume and the small particle size side accounts for 30% by volume, the ratio of the median particle size D50 of the carbides on the large particle size side to the median particle size D50 of the carbides on the small particle size side is 1.5 to 2.3.

[0038] The crushing strength of the heat-raising material for converters according to the present invention is preferably 490 N / piece or more. If the crushing strength of the heat-raising material is less than 490 N / piece, the heat-raising material will crush into dust before it can reach the molten steel and will be scattered with the converter exhaust gas, making it impossible to feed the heat-raising material into the molten metal with a high yield. [Examples]

[0039] The following describes embodiments of the present invention.

[0040] As the raw material for the carbonized material, woody raw materials such as sawmill scraps and forest residues were used, and the biomass carbon material, heated and carbonized at 650°C, was to be used as the material to be molded.

[0041] The converter heating material used in the examples was in the form of pellets with a diameter of 20 mm and briquettes with sides of 50 mm. The target particle size of the crushed biomass carbon material was set to 9 mm or less for the 20 mm diameter pellets and 22 mm or less for the 50 mm side briquettes, in order to generally satisfy the requirement that "the maximum particle size is less than half the characteristic length d of the carbide heating material."

[0042] In accordance with the target particle size values ​​for the crushed material, the above-mentioned biomass char material was passed through the roll crusher (cutter mill) 26 shown in Figure 2 once or multiple times, as in the preliminary experiment described above, and then sieved to prepare crushed biomass char with various average particle sizes. Furthermore, five sets of char powder mixtures were prepared by combining these crushed biomass char with various average particle sizes and dividing them so that the large particle size side accounted for 70% by volume and the small particle size side accounted for 30% by volume. The ratio of the median particle size D50 of the char on the large particle side to the median particle size D50 of the char on the small particle side was in the range of 1.3 to 2.5, as shown in Table 2. The particle size distribution of each of the five sets of char powder mixtures is shown in Figures 8 and 9.

[0043] Next, under the mixing conditions shown in Table 2, each of the five sets of carbide powders was mixed with cornstarch and water as a binder, and then compressed into briquettes or pellets using the twin-roll briquette machine shown in Figure 3 or the pelletizer shown in Figure 4. After molding, the mixture was left to stand at room temperature for 5 days to dry to a moisture content of approximately 3% to be used as a heat-raising material for a converter.

[0044] In Comparative Example 1, as shown in Table 2 and Figure 8(a), the particle size ratio was small at 1.3, and there were few small particles to fill the gaps between the large particles, so it was almost impossible to reduce the minimum porosity. As a result, the amount of water added to fill the gaps between the large particles increased, and consequently, the amount of binder added became the largest among the five sets. Furthermore, the crush strength of n=10 samples taken from the dried carbide molded body in Comparative Example 1 did not achieve the crush strength of 490N or more required for operation.

[0045] Furthermore, in Comparative Example 2, as shown in Table 2 and Figure 9(b), the particle size ratio was large at 2.5, resulting in a low minimum porosity. This reduced the amount of added water needed to fill the gaps between large particles, and consequently, the amount of added binder was the smallest among the five sets, along with Example 3 of the present invention. However, due to the large particle size ratio, the porosity changed significantly depending on the mixing ratio of carbide particles (see Figure 5). As a result, variations during manufacturing made it easy for the amount of added water to exceed the appropriate value. Consequently, abnormalities such as lamination occurred in the charcoal material before drying after molding, significantly reducing the product yield to the point where it was impossible to prepare test materials for crushing strength.

[0046] On the other hand, in Examples 1 to 3 of the present invention, regardless of the difference in shape between pellets and briquettes, it was possible to reduce the amount of binder while maintaining the crushing strength and yield required for operation.

[0047] [Table 2] [Explanation of symbols]

[0048] 1. Converter body 2. Upward-blowing lance 3 Bottom-blown tuyere 4 Flue 5 Skirts 6 Hopper 7 Shots to be taken 8. Molten iron 9 Slag 10 Converter exhaust gas 21. Charcoal materials (biomass charcoal materials) (dry distillate) 22. Crushed charcoal material (biomass charcoal material) 23. Carbon material (biomass carbon material) blend 24. Molded products made from carbon materials (biomass carbon materials) 24a Briquettes 24b pellets 26 Roll Crusher (Cutter Mill) 27 Hopper 28 Crusher Roll 29 Belt conveyor 31. Twin-roll briquette machine 32 Hopper 33. Molding Rolls 34 Belt conveyor 41. Pelletizer 42 Hopper 43 Screw Feeder 44 Cutter 45 Belt conveyor

Claims

1. A heat-raising material for a converter, which is a carbide molded body formed from carbide powder and a binder, The carbide in the aforementioned carbide molded body is (a) The maximum particle size is less than half of the characteristic length d of the carbide molded body, (b) A heat-raising material for a converter, characterized in that when the material is divided so that the large particle size side accounts for 70 volume percent and the small particle size side accounts for 30 volume percent, the ratio of the median particle size D50 of the carbide on the large particle size side to the median particle size D50 of the carbide on the small particle size side is 1.5 to 2.

3.

2. The converter heating element according to claim 1, characterized in that the converter heating element has a crushing strength of 490 N / piece or more.

3. A method for manufacturing a heat-raising material for a converter, which is a carbide molded body formed by molding carbide powder and a binder, Carbonized raw materials are produced by carbonizing at least one selected from coal, plant-based biomass, and waste plastics. The carbonized raw material is subjected to one or more sieving processes and one or more crushing processes, (a') From the carbide raw material, obtain carbide powders divided into multiple groups with different particle sizes, within a range where the maximum particle size is less than half of the characteristic length d of the carbide molded body, and further, (b') The obtained carbide powder is divided so that the large particle size side accounts for 70% by volume and the small particle size side accounts for 30% by volume, and the ratio of the median particle size D50 of the carbide on the large particle size side to the median particle size D50 of the carbide on the small particle size side is in the range of 1.5 to 2.3, thereby obtaining the carbide powder before molding. A method for manufacturing a heat-raising material for a converter, characterized by the above.

4. The method for manufacturing a converter heat-raising material according to claim 3, characterized in that the converter heat-raising material has a crushing strength of 490 N / piece or more.

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