Temperature-raising material for converter and temperature-raising method of molten metal in converter

Abstract

To provide a temperature-raising material for a converter and a temperature-raising method of molten metal in the converter, which can effectively utilize a volatile component in biomass coal as a heat source in the temperature-raising material for the converter including the biomass coal.SOLUTION: A temperature-raising material for a converter comprises biomass coal. The biomass coal comprises 10 mass% or more of volatile components. The temperature-raising material has an apparent concentration of 1000 kg / m3 or more. A temperature-raising method for raising the temperature of the molten metal in the converter uses the temperature-raising material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a temperature-raising material for a converter and a method for raising the temperature of molten metal in a converter. [Background technology]

[0002] In converter steelmaking, the charged iron sources are molten pig iron and pig iron produced in a blast furnace, as well as iron scrap. Molten pig iron and pig iron are produced in a blast furnace by reducing iron ore with coke as a reducing agent, resulting in the emission of large amounts of CO2 during the reduction process. Iron scrap, on the other hand, only requires the heat required to heat and melt it in the converter, resulting in less CO2 emissions than molten pig iron and pig iron.

[0003] To achieve carbon neutrality, reducing CO2 emissions from the steelmaking process is an important issue. To reduce CO2 emissions in converter steelmaking, increasing the ratio of cold iron sources, such as iron scrap, in the converter and reducing the ratio of molten pig iron and mold iron produced in the blast furnace is effective. Increasing the ratio of iron scrap in the converter's main raw material charge requires securing sufficient heat for heating and melting. In converter refining, the heat from the combustion of carbon and silicon contained in the molten pig iron and mold iron is used as a heat source. If the heat is insufficient, additional heating materials, such as amorphous graphite or ferrosilicon, are added to raise the molten metal in the converter to the desired temperature.

[0004] When carbonaceous materials such as soil graphite are used as a heat source in converter refining, the carbonaceous material burns in the converter, which generates CO2. On the other hand, if biomass charcoal made by carbonizing biomass is used as the raw material for the carbonaceous material, the amount of CO2 emitted from burning it can be considered to be zero, since biomass charcoal is made by carbonizing biological resources, and biomass, which is an organic resource derived from plants in particular, absorbs CO2 during the growth process.

[0005] Patent Document 1 discloses a converter heat-raising material made by carbonizing plant biomass to produce a carbonized material, and then using the carbonized material as the main raw material, adding a binder and moisture to mold the material, which has a composition in a dry state excluding moisture of 70% by mass or more of fixed carbon, 20% by mass or less of volatile components, 0.1% by mass or less of sulfur, the remainder being ash, and the moisture content being 5% by mass or less.Comparative Example 1 in the same document states that when the volatile components of the heat-raising material are high, the fixed carbon content decreases, and a large amount of heat-raising material must be added to obtain the required amount of heat.

[0006] Patent Document 2 discloses a heating material for converters, which is characterized by being produced by carbonizing plant biomass to produce a carbonized material, mixing the carbonized material as the main raw material with iron-containing dust, and then adding a binder and moisture to the mixture to form it.

[0007] Patent Document 3 discloses a method for manufacturing a heating material for a converter, which is characterized by extruding a mixture of carbonized plant biomass and plastic, where the plastic content is 25% by mass or more and the carbonized content is 75% by mass or less, without performing a subsequent drying process.

[0008] Patent Document 4 describes a converter heating material that is a carbide molded body formed by molding carbide powder and a binder, and the carbide molded body has a density of 500 to 1500 kg / m 3 The present invention discloses a converter heating material having a crushing strength of 490 N / piece or more and a predetermined outer shape. The carbonized material in the carbonized molded body can be a carbonized material obtained by carbonizing plant biomass.

[0009] Patent Document 5 discloses a converter heating material and a method for manufacturing the same, which is a carbide molded body made by mixing carbide powder particles with adjusted particle size with a binder, and which makes it possible to increase the carbide filling rate while reducing the amount of binder added.

[0010] One well-known steel refining method using a converter is the MURC process, which performs dephosphorization blowing, intermediate slag draining, and decarburization blowing in a single converter. By increasing the slag volume through slag foaming during dephosphorization blowing, the slag draining rate is increased when the slag is discharged from the throat during intermediate slag draining. After decarburization blowing, the converter is tilted and molten steel is tapped from the tap hole. Meanwhile, the LD-ORP and SRP processes are known as methods for performing dephosphorization blowing and decarburization blowing using two converters. In these processes, the molten pig iron after dephosphorization blowing is discharged from the tap hole into a ladle, and this molten pig iron is then recharged into the converter after slag draining for decarburization blowing. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. WO2013 / 128786 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-56412 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-108638 [Patent Document 4] Japanese Patent Application Publication No. 2023-133079 [Patent Document 5] Japanese Patent Application Publication No. 2023-132282 Summary of the Invention [Problem to be solved by the invention]

[0012] When biomass is carbonized to produce biomass charcoal, volatile matter is removed as the carbonization process progresses, increasing the fixed carbon content. The amount of volatile matter in biomass charcoal can be adjusted by adjusting the temperature and time of the carbonization process. Biomass charcoal with low volatile matter content is expensive and less productive due to the increased processing time and temperature.

[0013] Conventionally, when biomass charcoal is used as a heating material for converters, the volatile content cannot be effectively utilized as a heat source, so biomass charcoal with a high fixed carbon content has been used with the volatile content reduced as much as possible. If the volatile content in the carbonaceous material can be effectively utilized as a heat source, it will be possible to effectively use low-cost biomass charcoal with a high volatile content as a heating material for converters.

[0014] An object of the present invention is to provide a heating material for a converter containing biomass charcoal, which can effectively utilize the volatile matter in the biomass charcoal as a heat source, and a method for heating molten metal in a converter. [Means for solving the problem]

[0015] That is, the gist of the present invention is as follows. [1] A heating material for a converter containing biomass charcoal, The biomass charcoal contains 10% by mass or more of a volatile matter, and the temperature-raising material has an apparent density of 1000 kg / m 3 A temperature-raising material for a converter characterized by the above. However, the biomass charcoal means carbonized biomass. [2] A method for raising the temperature of molten metal in a converter, characterized by using the temperature-raising material for converters described in [1]. [Effects of the Invention]

[0016] As a heating material for a converter containing biomass coal, the volatile matter in the biomass coal is set to 10 mass% or more, and the apparent density of the heating material is set to 1000 kg / m 3 By doing so, the heating and temperature-raising effect of the volatile matter in the biomass charcoal is fully utilized, contributing to an increase in the blending ratio of iron scrap in converter refining, and also making it possible to use inexpensive temperature-raising materials. DETAILED DESCRIPTION OF THE INVENTION

[0017] This invention focuses on a heating agent for converters containing biomass charcoal. Biomass is used as the main raw material for the heating agent. There are various definitions of biomass, but in this invention, it is defined as "renewable, biologically derived organic resources excluding fossil resources." This is the definition in the "Biomass Japan Comprehensive Strategy," which was approved by the Cabinet in December 2002 and supervised by the Ministry of Agriculture, Forestry and Fisheries. Specific examples of biomass include wood (especially thinned wood), palm oil, and rice straw.

[0018] The biomass charcoal that constitutes the temperature-rising material of the present invention is formed by carbonizing biomass as a raw material. Biomass carbonization is a process in which biomass is heated in a non-oxidizing atmosphere to decompose carbon compounds. However, the present invention is characterized in that the carbonization process is terminated with volatile matter remaining, rather than completely removing the volatile matter from the biomass. Biomass that has been carbonized using biomass as a raw material is referred to as "biomass charcoal."

[0019] In the past, when biomass charcoal was left with volatile matter remaining in it and used as a heating material in a converter, the volatile matter in the biomass charcoal did not function as a heat source. Biomass charcoal has a lower density than amorphous graphite and tends to float on the molten slag when charged into a converter. The volatile matter desorbed from biomass charcoal does not contribute to combustion, and the gas desorbed from the biomass charcoal upon reaching the converter is sucked into the exhaust gas equipment, resulting in no heating effect. This is presumably because the amount of heating per unit weight is lower than that of amorphous graphite or biomass charcoal with low volatile matter.

[0020] The volatile matter contained in biomass charcoal contributes to the temperature rise of the molten metal in the converter by indirect combustion through the reaction of the volatile matter with the slag. The volatile matter is a hydrocarbon, and C * If you write, C * +(FeO)→CO+Fe (1) Fe+(1 / 2)O2→(FeO) (2) From (1)+(2), C *+(1 / 2)O2→CO (3) The volatile matter reduces the iron oxide (FeO) in the slag (Equation (1)), which is then oxidized again by the top-blown oxygen (Equation (2)). This indirectly burns the volatile matter (Equation (3)), generating heat and contributing to the temperature rise of the molten metal in the converter.

[0021] When biomass charcoal was forcibly immersed in molten slag using a small melting furnace and the gas generated was analyzed, it was found that the amount of CO and CO2 generated increased compared to simple desorption of volatiles, indicating that immersing biomass charcoal in molten slag causes the reaction described in equation (3) to occur, generating heat.

[0022] From the above results, even if biomass coal has a high volatile content, if it can be allowed to settle in the slag immediately after being charged into the converter, the volatile content will be burned by the above reaction and it can be effectively used as a heat source. However, biomass coal has a lower density (400-900 kg / m) than amorphous graphite. 3 ) and do not easily settle in the slag. This was found to be the reason why, in the past, when biomass charcoal was used as a heating material in a converter, the volatile matter in the biomass charcoal did not contribute as a heat source.

[0023] In contrast, biomass charcoal is crushed and mixed with binders and other materials to form a compact, and the apparent density is increased to 1000 kg / m 3 It was discovered that by using the above temperature-raising agent, it becomes easier to settle in the slag, and by promoting the reaction between the volatile matter and the slag, the temperature of the converter can be raised, leading to the completion of this invention. Cornstarch, water, etc. can be used as the binder. In addition, by mixing and molding high-density materials such as refractories, slag, dust, and concrete together, the density of the temperature-raising agent can be increased to 1000 kg / m 3 It can be more than that.

[0024] Hereinafter, the percentages representing the volatile matter and moisture content in biomass charcoal mean mass percentages.

[0025] The volatile matter content of biomass charcoal was varied to prepare temperature-raising materials for converter furnaces containing biomass charcoal. The apparent density of the temperature-raising materials was also varied by varying the materials and their contents included with the biomass charcoal. These temperature-raising materials were then added to the converter during converter refining, with the amount added being such that the biomass charcoal input rate in the temperature-raising materials was constant (30 kg / t-steel). In all experimental levels, the composition of the charged iron source and the temperature of the molten pig iron were constant, the carbon content of the molten iron at the end of converter refining (end-point C) was constant, and refining was performed without the addition of iron ore as a cooling material during converter refining. Under these conditions, the blending ratio of iron scrap in the main raw materials charged was adjusted so that the molten iron temperature at the end of converter refining was constant (1650°C).

[0026] As a result of the above tests, as will be clear from the examples described later, the density of the temperature-rising material was 1000 kg / m 3 When the density of the temperature-raising material is less than 1000 kg / m, the mixing ratio of the iron scrap must be reduced, and this becomes more pronounced as the volatile matter content increases. 3 When the content is set to the above, the blending ratio of iron scrap can be increased, and it has become clear that the effect is remarkable when the volatile matter content is 10% or more, which led to the present invention.

[0027] That is, the heating material for a converter containing biomass charcoal of the present invention is a material in which the biomass charcoal contains 10 mass% or more of a volatile matter, and the heating material has an apparent density of 1000 kg / m 3 The apparent density of the heating material is 1300 kg / m or more. However, biomass charcoal means carbonized biomass. The volatile content of the biomass charcoal is more preferably 15% by mass or more, and even more preferably 20% by mass or more. 3 More preferably, it is 1500 kg / m or more. 3 More preferably, it is equal to or greater than this.

[0028] The volatile matter in the biomass charcoal contained in the temperature-raising material can be analyzed as described in "JIS M 8812 (Methods for proximate analysis of coal)."

[0029] The apparent density of the temperature-rising material can be evaluated by the method described in JIS Z8807:2012.

[0030] The biomass charcoal in the temperature-rising material of the present invention is carbonized using biomass as the raw material, with some volatile matter remaining, and the volatile matter content after carbonization is adjusted to 10% or more and 50% or less. Since the moisture in the biomass is evaporated and removed in the early stages of the carbonization process, the moisture content is 0%. Even if left outdoors after carbonization, the moisture content is at most less than 10%.

[0031] Biomass itself, for example, wood, contains 60 to 80% volatile matter and 10 to 20% moisture.

[0032] It is preferable that the temperature-raising material be in the form of pellets or briquettes, as this makes it less likely to be sucked in along with the exhaust gas when introduced. It can be manufactured by crushing and mixing biomass charcoal and other materials and then compressing and molding them.

[0033] The method for raising the temperature of molten iron refined in a converter according to the present invention is characterized by using the above-mentioned temperature-raising agent for converters according to the present invention. This allows the blending ratio of iron scrap to be increased. The amount of the temperature-raising agent added is preferably 10 kg / t-steel or more, calculated as the unit consumption of biomass charcoal in the temperature-raising agent. More preferably, it is 30 kg / t-steel or more. [Example]

[0034] Wood was used as the biomass raw material for biomass charcoal. The wood contained 60-80% volatile matter and 10-30% moisture. This wood was used as the raw material for carbonization. The carbonization process involved carbonization by dry distillation in a nitrogen atmosphere at a temperature range of 300-600°C for 30 minutes to 1 hour, adjusting the volatile matter to a range of 8-50% as shown in Table 1.

[0035] The analysis of the volatile content listed in Table 1 was performed as described in "JIS M 8812 (Methods for Industrial Analysis of Coal)." When heated at 900°C for 7 minutes while avoiding contact with air, the mass fraction (%) of the sample was calculated for the weight loss on heating, and the moisture determined at the same time was subtracted from this to determine the volatile content. When analyzing the moisture content, the sample was heated and dried at 107°C for 1 hour in a dry air, helium, or nitrogen atmosphere, and the mass fraction (%) of the weight loss was calculated to determine the moisture content. For the biomass chars listed in Table 1, moisture content was essentially not detected.

[0036] The biomass charcoal prepared as described above was mixed with inorganic materials such as bricks and cement to adjust the apparent density, and a heating material (biomass charcoal mixed heating material) was used. The apparent density of the heating material was evaluated using the method described in JIS Z8807:2012, and the results are shown in Table 1.

[0037] Molten iron, iron scrap, and auxiliary materials are charged into a 300-ton converter, and oxygen is blown from the top lance at a rate of 30,000 Nm 3 MURC dephosphorization blowing, intermediate slag removal, and decarburization blowing were performed at a rate of 1 / h. In all examples, the hot metal temperature was constant at 1350°C, the hot metal composition was constant, and the carbon concentration at tapping was also constant. The amount of auxiliary materials charged during refining was also constant, and no iron oxide was added as a cooling material. The biomass-coal mixed heating material was charged so that the biomass-coal consumption rate was 30 kg / t-steel, and the iron scrap blending ratio was adjusted so that the tapping temperature was 1650°C. Table 1 lists the apparent density of the biomass-coal mixed heating material, the volatile matter content of the biomass-coal, and the iron scrap blending ratio. Since the biomass-coal consumption rate was constant, a higher iron scrap blending ratio means that the heating and temperature-raising effect of the biomass-coal in the heating material is better. Under the conditions of this example, it has been found that for every 1°C improvement in the temperature-raising effect of the molten metal due to the use of a temperature-raising agent, the mixing ratio of iron scrap can be increased by 0.05% while maintaining a constant final molten metal temperature.

[0038] [Table 1]

[0039] In Table 1, invention examples 1 to 10 are examples of the present invention. Comparative examples 1 to 6 are comparative examples. Numerical values ​​outside the range of the present invention are underlined. As is clear from the results of comparative examples 1 to 5 in Table 1, when the density of the temperature-rising material of the comparative example was 1000 kg / m 3 In Comparative Example 7, the density of the temperature-rising material was 1000 kg / m 3 Despite the above, the volatile matter content was less than 10% and the blending ratio of iron scrap was only 6.2%.

[0040] In contrast, in the present invention, the density of the temperature-rising material is set to 1000 kg / m 3 From the above, it is clear that the effect of increasing the mixing ratio of iron scrap becomes more pronounced when the volatile matter content is 10% or more, the iron scrap mixing ratio is 7.2% or more, and the apparent density of the temperature-rising material is higher.

Claims

1. A heating material for a converter containing biomass charcoal, The biomass charcoal contains 10% by mass or more of a volatile matter, and the temperature-raising material has an apparent density of 1000 kg / m ３ A temperature-raising material for a converter characterized by the above. However, the biomass charcoal means carbonized biomass.

2. A method for raising the temperature of molten metal in a converter, comprising using the temperature-raising material for a converter according to claim 1.

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