JP7832466B2 - Heat-boosting material for converters and method for manufacturing the same - Google Patents

Description

This invention relates to a heat-raising material for converters, and more specifically, to a heat-raising material for converters and a method for producing the same, which increases the strength of the heat-raising material by increasing the packing ratio of carbides, which are the raw materials of the heat-raising material, while optimizing the amount of binder added.

The converter in the steelmaking process is a key process for producing molten steel by decarburizing molten iron extracted from the blast furnace by blowing high-purity oxygen at high speed. Simultaneously, auxiliary raw materials, primarily quicklime, are added to remove impurities (such as phosphorus) from the molten iron.

On the other hand, in some cases, a pretreatment of the molten iron is performed as a pre-processing step before the converter, to remove sulfur and phosphorus (S) from the molten iron according to the material properties requirements of the steel products. In this case, however, there is a problem in that the molten iron temperature decreases due to the pretreatment.

Furthermore, in recent years, from an environmental protection perspective, reducing _CO2 emissions in the steelmaking process has become a crucial issue. In the steelmaking process, attempts are being made to increase the proportion of cold iron sources, such as scrap iron, used as the iron source, while reducing the proportion of molten iron. This is because, in the production of steel products, the production of molten iron in a blast furnace requires a great deal of energy to reduce and melt the iron ore, and at the same time emits a large amount of _CO2. In contrast, cold iron sources only require the heat of dissolution. Therefore, by using cold iron sources in the steelmaking process, the amount of energy used for the reduction heat of iron ore can be reduced, and the amount of _CO2 emitted can be significantly reduced. However, in a converter, the heat source for dissolving the cold iron source is the sensible heat of the molten iron and the heat of oxidation of carbon and silicon in the molten iron, and there is naturally a limit to the amount of cold iron source that can be dissolved.

Therefore, in the dephosphorization and decarburization refining of molten iron, various heat-raising materials have been proposed to supply additional carbon sources to the molten iron, in order to increase the thermal margin of the molten iron and expand the proportion of cold iron sources. These materials include coal, coke powder, graphite, electrode powder, and SiC, which are formed into lumps. Furthermore, natural mineral-derived earthy graphite, which is relatively inexpensive, is sometimes used as a heat-raising material.

Regarding such heat-raising materials for converters, for example, Patent Document 1 describes a method that involves adding a binder consisting of polyvinyl alcohol, carboxymethylcellulose, α-starch, etc., in an amount ranging from 0.5 to 1.0% by weight of the carbon powder to carbon powder (coal, coke powder, graphite, etc.), with 30-70% of particles with a particle size of 1 mm or less and the rest having a particle size of 1-8 mm. After conditioning and kneading the mixture to a moisture content of 10% or less, it is then subjected to high-pressure molding and drying, making it possible to mold the carbon powder into a solid material with sufficient strength.

Furthermore, Patent Document 2 describes a converter heat booster made by molding carbonized plant-based biomass that is carbonized and a binder consisting of starch, carboxymethylcellulose, corn starch, 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.

Japanese Patent Application Publication No. 2-270922 Patent No. 5846289

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. This results in a high processing load for particle size adjustment, such as grinding the carbon raw material.

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, this presents a problem of high processing load for particle size adjustment, such as the pulverization of the carbon raw material.

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 carbide, 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 pressures 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 during the molding of heat-raising materials.

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 binder amount is addressed by ensuring the strength of the molded charcoal material by completely crushing the raw char, then the cost of crushing the char increases, impairing overall economic efficiency.

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, by optimizing the particle size distribution of the carbide, which is the raw material for the heat-raising material, increases the packing density of the carbide and thus increases the strength of the heat-raising material while reducing the amount of binder added.

[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 has (a) a maximum particle size of 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 volume% and the small particle size side accounts for 30 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 crushing strength of 490 N/piece or more.
[3] A method for producing a heat-boosting material for a converter, which is a carbide molded body formed from carbide powder and a binder, comprising: 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, wherein (a') the carbide powder is divided 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 (b') the obtained carbide powder is blended such that when the large particle size side is divided into 70% by volume and the small particle size side into 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 producing 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.

According to the present invention, by arranging the particle size distribution of carbides in a converter heat-raising material (carbide molded body) (hereinafter also simply referred to as "heat-raising material") such that the maximum particle size of the carbides is less than half of the representative length d of the converter heat-raising material, and by dividing the carbide particles so that 70% by volume is on the large particle size side and 30% by volume is on the small particle size side, and setting 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 to be in the range of 1.5 to 2.3, it is possible to provide a converter heat-raising material and a method for manufacturing the same that increases the packing density of carbides and thus increases the strength of the heat-raising material, while reducing the amount of binder added within an economically reasonable range.

This is a schematic cross-sectional view of an example of a converter equipment in which the converter heating element of the present invention is used. 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. 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. This figure shows a schematic cross-sectional view illustrating the process of extruding and molding crushed biomass charcoal using the pelletizer used in the preliminary experiments and examples leading to the present invention. 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. 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. This figure, obtained in preliminary experiments leading to the present invention, summarizes the relationship between the ratio of the median particle size D50 of the large-particle-sized carbide to the characteristic length d of the carbide molded body and the binder concentration required when molding the heat-raising material for the converter. This figure shows the measurement results of the particle size of the crushed biomass carbon material used in an example of the pellet-shaped carbonized body of the present invention. This figure shows the measurement results of the particle size of the crushed biomass char material used in an example of the briquette-shaped char molded body of the present invention.

The present invention will be described in detail below. First, a converter facility to which the present invention is applied will be described. Figure 1 is a schematic cross-sectional view of an example of a converter facility using the converter heating element of the present invention.

In Figure 1, an upward-blowing lance 2 is inserted from above into the converter body 1 containing the molten iron 8. Oxygen gas is blown onto the molten iron 8 from this upward-blowing lance 2, and at the same time, bottom-blowing gas for stirring is blown in from multiple bottom-blowing tuyeres 3 located at the bottom of the converter body 1. This stirs the molten iron 8 and slag 9, resulting in the decarburization and refining of the molten iron 8. The decarburization and refining of the molten iron 8 generates converter exhaust gas 10, mainly composed of CO gas, from inside the furnace.

A flue 4 is installed above the converter body 1. A primary dust collector (not shown), a secondary dust collector (not shown), and an induced draft fan (not shown) are installed downstream of the flue 4 in this order. This converter exhaust gas treatment system cools and removes dust from the converter exhaust gas 10 generated inside the converter body 1 during decarburization refining. The unburned gas is then collected in a gas holder (not shown) downstream of the induced draft fan (not shown).

The connection point of the flue 4 to the furnace opening of the converter body 1 is called the skirt 5. It has a structure that allows for vertical movement, and in principle, the skirt 5 and the furnace opening of the converter body 1 are in close contact when recovering exhaust gas. Furthermore, the flue 4 is equipped with a secondary material feeding device consisting of a hopper 6 and an input chute 7 for adding 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.) to the converter body 1. Slag 9 is formed from the quicklime, calcined dolomite, iron ore, mill scale, manganese ore, etc., introduced into the furnace from the secondary material feeding device.

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, characterized in that (a) the carbides in the carbide molded body have a maximum particle size less than half the characteristic length d of the carbide molded body, and (b) when the molded 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 carbides on the large particle side to the median particle size D50 of the carbides on the small particle side is 1.5 to 2.3.

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 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 (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 side to the median particle size D50 of the carbide on the small particle side is in the range of 1.5 to 2.3 to obtain the carbide powder before molding.

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 it using a known molding device (see Figures 3 and 4), and then drying it to a predetermined moisture content. The main raw material, carbide powder, 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-based biomass, or waste plastics. Next, the resulting carbide is crushed to various particle sizes by passing it through a known cutter mill one or more times as needed, and then the particle size is adjusted by sieving or other methods. As the binder, inorganic bentonite, organic carboxymethylcellulose, corn starch, etc., can be used.

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 by a belt conveyor 29. As a molding device for the carbonized material, a known twin-roll briquette machine or a pelletizer can be used. Figure 3 schematically shows how a mixture of carbonized 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 carbonized material molded product 24 (briquette 24a), and then discharged by a belt conveyor 34. Figure 4 schematically shows how a similar mixture of charcoal materials 23 is supplied from the hopper 42 of the pellet manufacturing machine (pelletizer) 41 to the screw feeder 43, where it is compressed and extruded. It is then cut to a predetermined length by a cutter 44 to form molded products 24 (pellets 24b), which are then transported out on a belt conveyor 45.

The reason why the carbides in the carbide molded body of this 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 production of the heat-raising material for converters. That is, when granulating carbide powder, contrary to the expectation that small particles will fill in between large particles to create dense packing, there may be areas where small particles do not fill between large particles. This phenomenon is particularly pronounced when the maximum particle size is half or more the characteristic length d of the carbide molded body, as explained in the preliminary experimental results described later. Therefore, although particles are bound together by the liquid cross-linking adhesion force of the 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, the gaps between large particles widen, requiring a large liquid cross-linking adhesion force, thus necessitating an increase in the binder concentration.

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

Furthermore, when the carbide in the carbide molded body of the present invention is divided so that the large-particle side accounts for 70% by volume and the small-particle side accounts for 30% by volume, the ratio of the median particle size D50 of the large-particle side carbide to the median particle size D50 of the small-particle side carbide is set to 1.5 to 2.3. This is because, as 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, abnormalities in the carbide molded body do not occur, and a high product yield can be maintained.

This section describes the measurement of the median particle size ratio 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. After filtration, the carbide is collected and washed with pure water or methanol. Then, the particle size distribution of the carbide particles is determined by laser diffraction particle size distribution measurement (JIS Z 8825:2013 Particle size analysis - Laser diffraction/scattering method). Next, by computer analysis of this particle size distribution, the ratio of the median particle size D50 of the carbide particles on the large particle side to the median particle size D50 of the carbide particles on the small particle side can be determined 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. Note that the median particle size D50 here is determined by reading the particle size at which the cumulative value reaches 50% on a volume-based cumulative distribution curve, where the horizontal axis is the particle size and the vertical axis represents the cumulative value of the particle amount as a percentage of volume (%).

On the other hand, in the method for manufacturing the heat-raising material for converters of the present invention, the ratio of median particle sizes of the 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 results of the median particle size ratio of the carbide powder used as the raw material for the carbide molded body and the measurement results of the median particle size ratio of carbide particles in the carbide molded body produced from that carbide powder can be treated as equivalent both in principle and statistically.

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 when the packing density is high, the capillary attraction force between particles increases and mechanical bonding effects such as particles joining to each other's uneven surfaces come into play, so the crushing strength and the packing density (= 1 - porosity) are proportional.

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 of 0.414φ (relative to the aforementioned particle size 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.

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 = 20 mm) (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 groups on the large particle size side being 1/2A, 1/3A, 1/4A, 1/4A, and 1/5A, and the charred material groups 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 ratio) for each sample, with varying volume proportions (mixing ratio) of small particles within each of the ten carbide combinations, representing four example combinations with particle size ratios (1.3, 2.0, 2.5, 3.0). Each sample under these conditions was prepared by adding 8% by mass of cornstarch and an appropriate amount of water as a binder to each carbide mixture with varying volume proportions of small particles within each combination, kneading the mixture, then molding it into pellets using a pelletizer, and finally drying it to a moisture content of 3% by mass or less to obtain the test material. Table 1 also includes the minimum porosity values that can be read from Figure 5 and equivalent figures (including data for particle size ratios not shown in Figure 5).

Figure 5 shows that the porosity changes depending on the mixing ratio of small and large particle sizes, and that it reaches its minimum value when the volume proportion of small particles is around 0.3. Figure 5 also shows that the change in porosity can be stratified and organized according to the particle size ratio. Figure 6 summarizes the relationship between the particle size ratio of large and small particles in the converter heating element, which can be organized in this stratified manner, 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 increasing the particle size ratio of the carbide (large particle size / small particle size) can reduce the minimum porosity. From this, it was inferred that the amount of water added to fill the voids can be further reduced.

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 the amount of added water being higher 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, 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. For this reason, the porosity of sets No. Although inferior to combinations 3 and 4, combinations 1, 2, 7, and 9 were deemed suitable because they reduced the porosity by 2-5% compared to the case without a mixture of large and small particles (porosity 0.39), and even considering manufacturing variations, no abnormalities occurred in the carbide molded body, resulting in no decrease in product yield.

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 estimated 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. Therefore, the amount of binder was lower in set No. 7 than in set No. 2.

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 less than half the representative length d of the converter heating element (carbide molded body), and simultaneously, 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.

The crushing strength of the heat-raising material for converters in this invention is preferably 490 N/piece or more. If the crushing strength of the heat-raising material is less than 490 N/piece, it will crush into dust before it can reach the molten steel, scattering with the converter exhaust gas. This makes it impossible to feed the heat-raising material into the molten metal with a high yield.

The following describes embodiments of the present invention.

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.

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 approximately 9 mm or less for the 20 mm diameter pellets and 22 mm or less for the 50 mm side briquettes, in order to satisfy the requirement that "the maximum particle size is less than half the characteristic length d of the carbide heating material."

According to 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 one or more times, as in the preliminary experiment described above, and then sieved to prepare crushed biomass char with various average particle sizes. Furthermore, these crushed biomass char with various average particle sizes were combined and divided so that the large particle size side accounted for 70% by volume and the small particle size side accounted for 30% by volume. Five sets of char powder mixtures were prepared, where the ratio of the median particle size D50 of the large-particle char to the median particle size D50 of the small-particle char was in the range of 1.3 to 2.5, as shown in Table 2. The particle size distributions of each of the five prepared sets of char powder mixtures are shown in Figures 8 and 9.

Next, under the mixing conditions shown in Table 2, cornstarch and water were added to each of the five sets of carbide powders and mixed. The mixtures were 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 mixtures were left to stand at room temperature for five days to dry until the moisture content reached approximately 3%, and then used as heat-raising material for the converter.

In Comparative Example 1, as shown in Table 2 and Figure 8(a), the particle size ratio was small at 1.3, resulting in few small particles filling the gaps between large particles. Therefore, the minimum porosity could hardly be reduced, leading to an increase in the amount of added water to fill the gaps between large particles, and consequently, the amount of added binder was the largest among the five sets. Furthermore, the crush strength of n=10 samples of the dried carbide molded body in Comparative Example 1 failed to achieve the crush strength of 490 N or more required for operation.

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 lowest 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). Because of variations during manufacturing, the amount of added water tended to exceed the appropriate value. As a result, 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 obtain a sufficient sample for crush strength testing.

On the other hand, in Examples 1 to 3 of the present invention, regardless of the difference in pellet or briquette shape, it was possible to reduce the amount of binder while maintaining the crushing strength and yield required for operation.

1. Converter body 2. Top-blowing lance 3. Bottom-blowing tuyeres 4. Flue 5. Skirt 6. Hopper 7. Input chute 8. Molten iron 9. Slag 10. Converter exhaust gas 21. Carbon material (biomass carbon material) (carbonized product)
22. Crushed carbon material (biomass carbon material) 23. Mixed carbon material (biomass carbon material) 24. Molded carbon material (biomass carbon material) 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 Forming Roll 34 Belt Conveyor 41 Pelletizer
42 Hopper 43 Screw feeder 44 Cutter 45 Belt conveyor

Claims (4)

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. The converter heating element according to claim 1, characterized in that the heating element has a crush strength of 490 N/piece or more. 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, the carbide powder is obtained, which is 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') A method for producing a heat-raising material for a converter, characterized in that when 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, 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 producing the carbide powder before molding. 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.