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

Abstract

To provide a rising heat material for a converter capable of feeding molten metal with high yield even if the degree of freedom of external dimensions is increased.SOLUTION: A rising heat material for a converter of a carbide molding formed by molding a carbide powder particle and a binder is characterized in that the carbide molding has (a) the density of 500-1500 kg / m3, (b) a collapse strength of 490 N / piece or more, and (c) an outer shape having a representative length d in which the gravity becomes larger from a balance relationship between the gravity applied to the carbide molding and the drag force received from the converter exhaust gas according to the outer shape of the carbide molding.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat-raising material for a converter and a method for manufacturing the same, and more particularly to a heat-raising material for a converter that can be fed into the molten metal with a high yield even with increased flexibility in external dimensions, and a method for manufacturing the same. [Background technology]

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

[0003] 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, phosphorus, and other substances from the molten iron in accordance with the material properties requirements of the steel products. In this case, there is a problem that the molten iron temperature decreases due to the pretreatment of the molten iron.

[0004] 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.

[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 after adjusting the moisture content to a specific level, then molded under high pressure and dried, making it possible to mold the carbon powder into a solid (briquette) with sufficient strength.

[0007] Furthermore, Patent Document 2 describes a converter heat booster made by molding carbonized plant-based biomass carbide with a binder. This material replaces conventional converter heat boosters made from fossil resources such as coal, coke, and graphite, thereby reducing fossil resource consumption and the generation of greenhouse gases such as CO2. In addition, by making the particle size of the carbide 3 mm or less, it is made into a solid (briquette) 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, since the carbon powder, which is the raw material of the heating material described in Patent Document 1, has a large proportion of particles with a particle size of 1 mm or less, at 30 to 70%, there is a problem that the processing load for adjusting the particle size, such as the pulverization treatment of the carbon raw material, is high.

[0010] In addition, the carbon powder, which is the raw material of the heating material described in Patent Document 2, needs to be sized 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 that the processing load for adjusting the particle size, such as the pulverization treatment of the carbon raw material, is high.

[0011] In addition, the heating materials targeted in Patent Document 1 and Patent Document 2 are only exemplified as being generally applicable to briquettes with a representative length of about 50 mm. Even if one tries to adopt a heating material with a pellet size having a representative length of about 20 mm, which has a small molding load, it is not clear whether the heating material to which these inventions are applied can be surely charged into the molten metal without being crushed or scattered.

[0012] The present invention has been made in view of the above circumstances, and aims to provide a heating material for a converter and a method for manufacturing the same, which have a density and a crushing strength within a predetermined range, and can be charged into the molten metal with a high yield even when the degree of freedom of the outer dimensions is increased under the condition of a representative length such that gravity overcomes the resistance received from the converter exhaust gas.

Means for Solving the Problems

[0013] [1] A heating material for a converter, which is a carbide molded body formed by molding carbide powder particles and a binder, wherein the carbide molded body (a) has a density of 500 to 1500 kg / m 3 and, (b) has a crushing strength of 490 N / piece or more, and further, (c) has an outer shape such that, from the balance relationship between the gravity applied to the carbide molded body and the resistance received from the converter exhaust gas according to the outer shape of the carbide molded body, the gravity is greater at a representative length d. A heating material for a converter, characterized by having such an outer shape. [2] The representative length d of the carbide molded body satisfies the formula (1), and is the heating material for a converter according to [1].

[0014] [Number] Here, d is the representative length [m] of the carbide molded body, and ρ lump is the density of the carbide molded body, which is 500 to 1500 [kg / m 3 , and ρ gas is the density of the converter exhaust gas, which is 0.17 to 0.21 [kg / m 3 , v gas is the flow velocity of the converter exhaust gas, which is 5 to 50 [m / s], C d is the resistance coefficient, which is 1.0 [-] for pellets and 1.6 [-] for briquettes, and g is the gravitational acceleration [m / s 2 .

[0015] [3] The carbide molded body contains iron, and is the heating material for a converter according to [1] or [2].

[0016] [4] The carbide in the carbide molded body (d) has a particle size with a maximum particle size less than 1 / 2 of the representative length d, (e) when classified so that the large particle size side is 70% by volume and the small particle size side is 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, and is the heating material for a converter according to any one of [1] to [3].

[0017] [5] The carbide in the carbide molded body is a carbide obtained by carbonizing at least one selected from the group consisting of coal, plant-based biomass, and waste plastic, and is the heating material for a converter according to any one of [1] to [4]. [6] A method for manufacturing a heating material for a converter according to any one of [1] to [5], characterized in that an extrusion molding machine or a compression molding machine is used in the molding step of the carbide molded body. [Advantages of the Invention]

[0018] According to the above configuration, for a heat-up material for a converter (hereinafter, also simply referred to as a heat-up material) formed by molding carbide powder particles and a binder, having a density of 500 to 1500 kg / m 3 , by using one having such a density and using one having an outer dimension in which its gravity is greater from the balance relationship between the gravity applied to the material and the resistance received from the converter exhaust gas according to the outer shape of the material, it is possible to surely make the material reach the molten metal until it is crushed. Further, since the crushing strength of the heat-up material is not less than 490 N / piece, the heat-up material does not break into dust and scatter with the converter exhaust gas before reaching the molten steel, so the heat-up material can be charged into the molten metal with a high yield. Furthermore, by selecting the representative length d at which the heat-up material surely falls without being crushed, as the heat-up material size, a wide size range from pellet size to briquette size can be used, so that it is easy to ensure the freedom of manufacturing for optimizing the molding load and the like during the manufacture of the heat-up material.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic cross-sectional view of an example of a converter facility used when implementing the present invention, and also a view schematically explaining the acting force received by the heat-up material when the heat-up material is charged. [Figure 2] It is a schematic cross-sectional view showing a state of pulverizing biomass charcoal by a roll crusher (cutter mill) used in preliminary experiments and examples leading to the present invention. [Figure 3] It is a schematic cross-sectional view showing a state of compression molding pulverized matter of biomass charcoal by a double-roll type briquette machine used in an example of the present invention. [Figure 4] It is a schematic cross-sectional view showing a state of extrusion molding pulverized matter of biomass charcoal by a pellet manufacturing machine (pelletizer) used in preliminary experiments leading to the present invention. [Figure 5]This figure, obtained in preliminary experiments leading to the present invention, compares the theoretical formula for the boundary between the fall and buoyancy of the converter heating element after it has been introduced from the auxiliary material input chute into the converter exhaust gas with the results of an offline buoyancy test. [Figure 6] This figure shows the results of an offline flotation test, similar to Figure 5, obtained in preliminary experiments leading to the present invention, where the density of the heat-raising material for the converter was increased by adding iron and adjusting the iron content. [Figure 7] 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 8] 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 9] This figure shows the measurement results of the particle size of the crushed biomass char material obtained in the embodiment of the present invention. [Modes for carrying out the invention]

[0020] 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.

[0021] 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. The molten iron 8 and slag 9 are stirred together, and the molten iron 8 is decarburized and refined. The decarburization and refinement of the molten iron 8 generates converter exhaust gas 10, mainly composed of CO gas, from inside the furnace.

[0022] 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 downstream of the flue 4 in that order. With this converter exhaust gas 10 treatment equipment, the converter exhaust gas 10 generated inside the converter body 1 during decarburization refining is cooled, dust removed, and recovered unburned in a gas holder (not shown) downstream of the induced draft fan (not shown).

[0023] 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.

[0024] The present invention relates to a heat-raising material for a converter, which is a carbide molded body formed from carbide powder and a binder, wherein the carbide molded body is (a) Density is 500-1500 kg / m³ 3 And, (b) The crush strength is 490 N / piece or more, and further, (c) The external shape is characterized in that, based on the balance between the gravity acting on the carbide molded body and the drag force received from the converter exhaust gas according to the external shape of the carbide molded body, the gravity is greater, and the external shape has a characteristic length d.

[0025] 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.

[0026] 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 transported out on a belt conveyor 29. As a molding device for the carbide molded body, a well-known twin-roll briquette machine, which is a typical compression molding machine, or a pelletizer, which is a typical extrusion molding machine, can be used. In Figure 3, the kneaded 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 molded material 24 (briquettes 24a), and then transported out on a belt conveyor 34. Figure 4 schematically shows how a similar mixture of carbon material 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 material 24 (pellets 24b), which is then transported out on a belt conveyor 45. It should be noted that there are differences in characteristics between compression molding machines and extrusion molding machines, and therefore, the choice of which molding machine to adopt should be made appropriately, taking into account the characteristics of both machines. For example, compression molding machines have the advantage of being able to handle a wide variety of raw materials for granulation applications and producing granulated material with relatively high crushing strength. On the other hand, due to their structure, compression molding machines have a relatively low production capacity per unit, and many units are needed to accommodate mass production. In terms of production capacity, extrusion molding machines, which have a different granulation mechanism than compression molding machines, have the advantage of being able to secure relatively high production volumes and are advantageous for mass production. However, since extrusion molding machines cannot apply the same amount of pressure as compression granulators, the crushing strength of granules produced by extrusion molding tends to be lower than that of granules produced by compression molding machines. Furthermore, it is important to note that in extrusion molding, the crushing strength decreases as the pressure applied to the die decreases with increasing particle size.

[0027] The carbide molded body (heat-raising material for converters) of the present invention has a density of 500 to 1500 kg / m³3 The density of the heat-raising material is 500 kg / m³. 3 If the density is less than 1500 kg / m³, it becomes difficult to select an external dimension in which the gravitational force acting on the heat-raising material itself is greater than the drag force from the converter exhaust gas, while ensuring sufficient carbide content as a heat-raising material. 3 This is because if the size exceeds a certain limit, it becomes difficult to ensure sufficient carbide content as a heat-raising material.

[0028] Herein, the carbide molded body (heat-raising material for converters) of the present invention may contain iron. This is preferable because, for example, when using a carbon material with a high amount of volatile components and low density after carbonization as the raw material for the carbide constituting the heat-raising material, it is possible to increase the density of the heat-raising material by mixing iron oxide powder such as steelmaking dust or iron scrap powder granules with a binder and molding it, thereby making the gravitational force of the heat-raising material greater than the drag force received from the converter exhaust gas.

[0029] The crushing strength of the carbide molded body (heat-raising material for converters) of the present invention is 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.

[0030] As shown in Figure 1, the carbide molded body (converter heating element) 11 of the present invention has a representative length d such that the gravitational force 12 is greater than the gravitational force 12 acting on it, based on the balance between the gravitational force 12 acting on it and the drag force 13 received from the converter exhaust gas 10 according to its external shape. If the representative length d determined by the external shape of the converter heating element 11 is not such that the gravitational force 12 of the converter heating element 11 is greater than the gravitational force 12 of the converter heating element 11, based on the balance between the gravitational force 13 received from the converter exhaust gas according to the external shape of the converter heating element 11, the converter heating element 11 will float up with the converter exhaust gas 10, and it will not be possible to feed the converter heating element 11 into the molten metal (molten iron or molten steel) 8. In the case of a pellet-shaped converter heating element 11, the representative length d can be represented by the pellet diameter, and in the case of a briquette-shaped converter heating element, the representative length d can be represented by the maximum diagonal length.

[0031] The characteristic length d of the carbide molded body (heat-raising material for converter) of the present invention preferably satisfies formula (1). This is because a heat-raising material having a characteristic length d that satisfies formula (1) can be reliably introduced into the molten metal without floating up with the converter exhaust gas.

number

[0032] The derivation process of equation (1) will be explained below. Before deriving equation (1), the inventors examined the balance between the gravitational force 12 acting on the converter heating element 11 itself and the drag force 13 received from the converter exhaust gas according to its external shape, as shown in the enlarged view in Figure 1, in order to determine the conditions under which the converter heating element could be reliably introduced into the molten metal without floating up with the converter exhaust gas. That is, from these balance relationships, the equation in which gravity is greater is given by the volume of the heating element Q [m 3 ], the projected area of ​​the heat-raising material with respect to the converter exhaust gas flow is A[m 2 Except for the variable ], the same variables as in equation (1) are used, and it can be expressed as in equation (2).

number

[0033] The validity of equations (1) and (2) was confirmed by offline flotation tests, and the results are shown in Figures 5 and 6. In Figure 5, the curves in which the inequalities of equations (1) and (2) are treated as equals are shown, and the experimental values ​​are plotted on these curves. Figure 6 is a graph showing the results of an offline flotation test similar to Figure 5, but in Figure 6, it is shown that the validity of equations (1) and (2) can be confirmed even when the density of the heat-raising material is increased by mixing carbide raw materials with iron oxide powder such as steelmaking dust or iron scrap powder particles together with a binder to form the heat-raising material.

[0034] The carbides in the carbide molded body (heat-boosting material for converters) of the present invention are (d) The maximum particle size is less than half of the characteristic length d, (e) When the area 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, it is preferable that 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. 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, where the horizontal axis represents particle size and the vertical axis represents the cumulative value of particle quantity as a percentage of volume (%).

[0035] The following describes the preliminary experimental results regarding the preferred range of carbide particle size. 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.

[0036] 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.

[0037] 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 7 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 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 that can be read from Figure 7 and a figure equivalent to Figure 7 (including data for particle size ratios not shown in Figure 7).

[0038] [Table 1]

[0039] Figure 7 shows that the porosity changes depending on the mixing ratio (mixing ratio) of large-particle-diameter carbides to small-particle-diameter carbides, and that it takes a minimum value when the volume proportion of small particles is around 0.3. Also from Figure 7, it can be seen that the change in porosity can be stratified and organized according to the ratio of particle sizes. Figure 8 is a diagram that summarizes the relationship between the particle size ratio of large-particle-diameter and small-particle-diameter carbides in the converter heating element, which can be organized in this stratified way, with the horizontal axis representing the ratio and the vertical axis representing the minimum porosity of the carbide molded body of the converter heating element. From Figure 8, it can be seen that the minimum porosity can be reduced by increasing the particle size ratio (large particle size / small particle size) of the carbides. From this, it can be expected that increasing the particle size ratio (large particle size / small particle size) of the carbides will increase the packing density (= 1 - porosity) and improve the crushing strength which is proportional to the packing density.

[0040] 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 7, 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, resulting in a failure to obtain a normal molded body and 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.

[0041] On the other hand, it was found that when large particles with a large diameter, such as 1 / 2A, were used as large particles, the required binder concentration increased. This is thought to be because, although it is expected that small particles will fill in between the large particles during granulation, there will inevitably be areas where small particles do not fill in between the large particles. Therefore, it was determined that particle sizes with a maximum particle diameter of 1 / 2 or more of the characteristic length d, which result in areas where small particles do not fill in between the large particles, are undesirable.

[0042] Based on the preliminary experimental results described above, the carbides contained in the carbide molded body (heat-boosting material for converters) of the present invention are, firstly, (d) to have a maximum particle size less than half of the characteristic length d, in order to ensure sufficient crushing strength of the carbide molded body, and at the same time, in order to ensure a favorable control range, (e) 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, it is preferable that 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.

[0043] The carbide molded body (heat boosting material for converters) of the present invention is a carbide obtained by carbonizing at least one selected from the group consisting of coal, plant-based biomass, and waste plastics. In particular, when the carbide molded body (heat boosting material for converters) is manufactured using carbides derived from plant-based biomass or waste plastics, it is desirable from an environmental protection standpoint as it substantially reduces CO2 emissions in the steelmaking process. [Examples]

[0044] The following describes embodiments of the present invention.

[0045] (Example 1) First, the particle size of the heat-raising material that can be introduced into the converter was calculated. Assuming the shape to be introduced is a pillow-shaped briquette and that it falls from the side of the briquette, according to page 100 of "Mechanical Engineering Handbook Basic Edition A5 Granular Engineering" published by the Japan Society of Mechanical Engineers in 1986, the briquette shape can be fitted to a cube, the drag coefficient Cd is 1.6, and the apparent density of the briquette is ρ lump 600 kg / m 3 , converter exhaust gas density ρ gas 0.17 kg / m 3 Assuming a gas flow velocity v of 42 m / s, the briquette size is calculated to be greater than 40 mm using equation (1).

[0046] Next, as the raw material for the carbonized material, we decided to use mainly woody biomass raw materials such as sawmill scraps and forest residues, with the exception of some coal. These materials were heated and carbonized at 650°C, and the resulting coke, derived from some coal, and the majority of the biomass carbon material were to be used for the molded product.

[0047] As described above, given that the briquette size of the heat-raising material for the converter was calculated to be over 40 mm, the target particle size of the crushed carbon material was set to 8 mm or less. The carbon material was passed through the roll crusher (cutter mill) shown in Figure 2 once or multiple times, and then sieved to prepare crushed carbon material of various average particle sizes. Furthermore, by combining these crushed carbon materials of various average particle sizes and dividing them so that the large particle size side accounts for 70 volume% and the small particle size side accounts for 30 volume%, a mixture of carbide powders was prepared in which 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 was in the range of approximately 1.5 to 2.3.

[0048] Next, 3% by mass of corn starch and 24% by mass of water were added to the prepared carbide powder and mixed, then compressed and molded into briquettes or pellets using the twin-roll briquette machine shown in Figure 3 or the pelletizer shown in Figure 4. After molding, the material was left to stand at room temperature for 5 days to dry until the moisture content reached approximately 3%, and then used as a heat-raising material for converters as shown in Table 2.

[0049] The prototype converter heating element shown in Table 2, developed as described above, was tested in a real converter with a maximum capacity of 360 tons / ch and a maximum output of 340 tons / ch. The molten iron temperature was set to 1350°C, and the amount of heating element added was set to 1000-3000 kg / ch. To prevent excessive temperature rise, 1000 kg of iron ore was added at the end of the smelting process when the heating element was added. Table 2 shows the heating effect of the converter heating material, indicated by ΔT(°C), based on Comparative Example 1, where no heating material was added. When 1000 kg of the heating material from Invention Example 1 was added, the tapping temperature shifted up by about 10°C. When 2000 kg of the carbon material from Invention Example 2 was added, the tapping temperature shifted up by about 20°C. Furthermore, when 3000 kg of the carbon material from Invention Example 3 was added, the tapping temperature shifted up by about 30°C. This confirms that the converter heating materials from Invention Examples 1 to 3 reliably made contact with the molten metal. In addition, Example 4 has conditions similar to Example 3, except that the carbide raw material was changed from woody biomass to coal. However, since the density and strength are higher than that of the heating material in Example 3, the tapping temperature shifted up by another 10°C. This suggests that yield loss due to crushing, etc., after the heating material was added was advantageously avoided. Furthermore, in Invention Example 5, where 50 mass% iron was mixed into the biomass charcoal to increase its density, although the amount of charcoal material decreased due to the addition of iron, the temperature rose by approximately 17°C compared to Comparative Example 1, where no heat-raising material was added. This confirms that increasing the density of the heat-raising material is effective in ensuring the molten metal contact efficiency of the heat-raising material in accordance with operating conditions such as when the rise rate of the converter exhaust gas is high. As described above, it was confirmed that in the present invention, the material reliably contacts the molten metal in the converter and contributes to heat contact.

[0050] On the other hand, in Comparative Example 2, 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 crushing strength is reduced too much when 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 (particle size ratio) is set to 3.0, resulting in a tapping temperature that is about 20°C lower compared to Invention Example 3. This is presumed to be because the crushing strength of the heating material decreased, making it impossible to maintain the shape of the heating material during the transport process, causing some of it to break and scatter, thus reducing the molten metal transfer efficiency. Furthermore, in Comparative Example 3, where the representative length d is about one-fifth of that of Invention Example, the tapping temperature is also 20°C lower compared to Invention Example 3. This is thought to be because the representative length d of the heating material is not large enough to withstand the upward flow of the converter exhaust gas, so most of the heating material scatters and contributes almost nothing to heat transfer.

[0051] [Table 2]

[0052] Figure 9 shows the particle size distribution of the biomass carbon carbide powders from Invention Examples 1-3, where the ratio of median particle size D50 of the large-particle-sized carbide to the median particle size D50 of the small-particle-sized carbide (particle size ratio) is 2.3, and the carbide powder from Comparative Example 2, where the ratio is 3.0, when the biomass carbon carbide powders are divided so that 70% by volume is large-particle-sized and 30% by volume is small-particle-sized. Table 2 shows that these differences in particle size distribution (particle size ratio) of the carbide powders result in differences in the crushing strength of the heat-raising material for converters.

[0053] (Example 2) Next, we will describe an example where the input material is in the form of pellets. In this case as well, similar to the briquette case in Example 1, we first calculated the particle size of the heat-raising material that could be introduced into the converter. Assuming that the pellets fall from the radial direction, the drag coefficient Cd is 1.0 according to the literature presented in Example 1. Also, similar to the briquette case in Example 1, the apparent density ρ of the pellets lump 600 kg / m 3 , converter exhaust gas density ρ gas 0.17 kg / m3 Let's assume the following. The gas flow velocity v is set to 37 m / s, assuming pellets are introduced during the initial decarburization phase of converter blowing when the exhaust gas volume is relatively low. Under these conditions, calculations using equation (1) yield that the pellet diameter is greater than 19 mm.

[0054] As described above, given that the pellet size of the heat-raising material for the converter was calculated to be over 19 mm, the target particle size of the crushed carbon material was set to 4 mm or less. In line with this target particle size, crushed carbon material of various average particle sizes was prepared by passing the carbon material through the roll crusher (cutter mill) shown in Figure 2 once or multiple times and then sieving it. Furthermore, when the material was divided so that the large particle size side accounted for 70% by volume and the small particle size side accounted for 30% by volume, a mixture of carbide powders was prepared in which 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 was in the range of approximately 1.5 to 2.3.

[0055] Next, 3% by mass of corn starch and 24% by mass of water were added to the prepared carbide powder and mixed, and then compressed into φ20 mm pellets using the pelletizer shown in Figure 4. After molding, the pellets were left to stand at room temperature for 5 days to dry until the moisture content was about 3%, and then used as a heat-raising material for converters as shown in Table 3.

[0056] The converter heating element shown in Table 3, which was prototyped as described above, was put into the converter in the same manner as in Example 1. The converter used in the test was a real converter with a maximum capacity of 360 ton / ch and a maximum output of 340 ton / ch. The molten iron temperature was set to 1350°C, and the amount of converter heating element added was set to 1000-3000 kg / ch. In order to prevent excessive temperature rise, 1000 kg of iron ore was added at the end of the smelting process in which the converter heating element was added. The temperature rise effect of the converter heating element is shown in Table 3 as ΔT (°C), based on the case of Comparative Example 1, in which no heating element was added. As shown in Table 3, when 3000 kg of the carbon material from Invention Example 6 was input, the tapping temperature shifted to approximately 30°C higher, confirming that the heat-raising material for the converter was reliably molten, similar to the briquette product. On the other hand, Comparative Example 4 is a case where the crushing strength was too low, and the tapping temperature was 15°C lower compared to Invention Example 6. The decrease in crushing strength in Comparative Example 4 is thought to be mainly due to the following two factors. The first factor is estimated to be that 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, 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, is large at 3.0, the same as in Comparative Example 2 in Table 2. The second factor is thought to be that the extrusion molding machine in Example 2 cannot increase the pressure as much as the compression granulator in Example 1. Thus, in Comparative Example 4, similar to Comparative Example 2 in Table 2, the crushing strength of the heating material decreased, making it impossible to maintain the shape of the heating material during the transport process. As a result, some of it broke and scattered, which is presumed to have reduced the molten metal fusion efficiency. Note that Comparative Example 1 in Table 3 is a reproduction of Comparative Example 1 shown in Table 2, which serves as a standard for not using heating material for the converter.

[0057] [Table 3] [Explanation of Symbols]

[0058] 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 (molten metal) 9 Slag 10 Converter exhaust gas 11. Carbide molded body (heat-raising material for converter) 12. Gravity of carbide molded bodies (heat-raising material for converters) 13. Drag of converter exhaust gas 21. Charcoal materials (biomass charcoal materials) (dry distillate) 22. Crushed charcoal material (biomass charcoal material) 23. Carbon material (biomass carbon material) mixture 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 molded body is (a) Density of 500 to 1500 kg / m³ ３ And, (b) The crush strength is 490 N / piece or more, and further, (c) A heat-raising material for a converter, characterized in that its external shape has a representative length d that satisfies formula (1). [Math 1] Here, d is the characteristic length [m] of the carbide molded body, ρ lump is the density of the carbide molded body [kg / m³], ρ gas is the converter exhaust gas density, which is 0.21 [kg / m³]. v gas is the flow velocity of the converter exhaust gas, which is 50 [m / s]. Cd is the drag coefficient, which is 1.0 [-] for pellets and 1.6 [-] for briquettes. g is the acceleration due to gravity [m / s²].

2. The converter heating element according to claim 1, characterized in that the carbide molded body contains iron.

3. The carbide in the aforementioned carbide molded body is (d) The maximum particle size is less than half of the characteristic length d, (e) The converter heating element according to claim 1 or claim 2, 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.

4. The converter heating element according to claim 1 or claim 2, characterized in that the carbide in the carbide molded body is a carbide obtained by carbonizing at least one selected from coal, plant-based biomass, and waste plastics.

5. A method for manufacturing a heat-boosting material for a converter according to claim 1 or claim 2, characterized in that an extrusion molding machine or a compression molding machine is used in the molding step of the carbide molded body.

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