Method for producing unburned carbon-containing agglomerates and method for utilizing silica biomass in blast furnaces

Abstract

The present invention provides a method for producing uncalcined carbon-containing agglomerates using biochar derived from silicic acid biomass, and a method for utilizing silicic acid biomass in a blast furnace. In the method for producing uncalcined carbon-containing agglomerates, a blended raw material containing an iron-containing raw material, a carbon-containing raw material, a gangue raw material, and a binder is formed into agglomerates, which are then cured for a predetermined period to produce uncalcined carbon-containing agglomerates. Part or all of the carbon-containing raw material and part or all of the silicic acid-containing ore in the gangue raw material are replaced with fixed carbon and silicon oxide in biochar obtained by carbonizing silicic acid biomass. In the method for utilizing silicic acid biomass in a blast furnace, the uncalcined carbon-containing agglomerates obtained as described above are charged into the top of a blast furnace.

Description

[Technical Field]

[0001] The present invention relates to a method for producing unburned carbon-containing agglomerates and a method for utilizing silica biomass in a blast furnace. [Background technology]

[0002] Reducing CO2 emissions is an urgent issue from the perspective of preventing global warming, and technological development is being carried out in the steel industry to reduce CO2 emissions. Methods for reducing CO2 emissions include (a) reducing the amount of carbon in inputs, (b) capturing CO2 in outputs, and (c) replacing conventional coal, oil, etc. with carbon-free carbon sources.

[0003] Conventionally, various types of iron-bearing dust and carbon-bearing dust recovered from various dust collectors at steelworks have been recycled. This leads to resource conservation, and is related to the method of reducing the carbon content of inputs described in (a) above. To reuse the recovered iron-bearing dust and carbon-bearing dust as blast furnace raw material (also called blast furnace charge raw material), there is a technology in which they are mixed with a cement-based hydraulic binder, kneaded, and molded into unfired agglomerates with diameters of 8 to 16 mm. When these unfired agglomerates contain carbonaceous material as a reducing agent, they are also called unfired carbon-bearing agglomerates, to clarify that they contain carbonaceous material.

[0004] In the manufacturing process of unsintered carbonaceous agglomerates, quicklime and CaO-based cement are used in large amounts as binders, resulting in a high CaO content in the product. This causes the viscosity of the molten liquid produced from the unsintered carbonaceous agglomerates during the reaction process in the blast furnace to become excessively high. This inhibits the coagulation and meltdown of the produced metal, resulting in problems such as poor air and liquid permeability in the lower part of the blast furnace.

[0005] To address these problems, Patent Document 1 discloses an invention that lowers the melting point of slag generated in the lower part of the furnace and improves air and liquid permeability by adjusting the basicity, CaO / SiO2, which is the ratio of gangue components in unburned carbon-bearing agglomerates, to 1.0 to 2.0, as shown in Figure 1. Furthermore, this document states that in order to adjust the basicity, CaO / SiO2, of unburned carbon-bearing agglomerates to 1.0 to 2.0, it is preferable to adjust the blending amount of high-SiO2-containing ore (also called silicic acid-containing ore).

[0006] Furthermore, in relation to the method (c) for replacing conventional coal, petroleum, etc. with carbon-free carbon sources, various technologies are being developed to utilize biomass as a carbon-free carbon source in steelworks. For example, Patent Document 2 discloses an invention related to pulverized coal injection (PCI), a pulverized coal injection technology in which biomass is dry-distilled to produce biochar, which is then pulverized into pulverized coal (PC), which is then injected into a blast furnace through a blast tuyeres 3 (see Figure 2). The invention disclosed in this document gives examples of applicable biomass, such as cedar wood, palm trunks, and coconut shells, but also claims that any biomass that generates char upon pyrolysis, such as from agriculture, forestry, livestock, fisheries, and waste, can be used. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2011 / 021577 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-117075 Summary of the Invention [Problem to be solved by the invention]

[0008] Meanwhile, expanding the use of biomass (also known as silicate biomass due to its high ash content), such as rice husks and straw, which are carbon-free carbon sources and are generated in Japan in quantities exceeding 2 million tons each year, has become a problem. This is because biochar derived from silicate biomass can be problematic due to its high ash content of approximately 30-50%. Furthermore, biochar derived from silicate biomass not only promises a stable supply, but also possesses sufficient properties as a carbon source, with a fixed carbon content of approximately 15-50% and a unit calorific value of approximately 14-28 MJ / kg.

[0009] Previous studies of biochar as a carbon-free carbon source in steelworks have not fully addressed the issue of high ash content in biochar derived from silicate biomass. Patent Document 2, which describes the use of biochar in pulverized coal injection (PC), does not explicitly address the issue of high ash content in biochar derived from silicate biomass. The pulverized coal (PC) described in the document is blown into the blast furnace 1 through a blast tuyere 3 at the bottom, as shown in Figure 2, along with hot air. It generates high-temperature reducing gas in the combustion zone 5, and the ash is absorbed into the surrounding slag. Therefore, the ash content in the pulverized coal (PC) is likely not a problem. However, when using biochar with a high ash content as a substitute for pulverized coal (PC), it is important to note that the temperature in the lower furnace may drop, potentially destabilizing the furnace.

[0010] On the other hand, it is necessary to consider whether biochar derived from silicate biomass with a high ash content can be used as the carbonaceous material in the unsintered carbonaceous agglomerates described in Patent Document 1. This is because, in the case of unsintered carbonaceous agglomerates charged from the top 2 of a blast furnace, the ash content of the unsintered carbonaceous agglomerates directly affects the air and liquid permeability around the cohesive zone 4 in the lower part of the furnace, which is an issue in Patent Document 1.

[0011] Therefore, an object of the present invention is to provide a method for producing unfired carbon-containing agglomerates that utilizes biochar derived from silicic acid biomass, and a method for utilizing silicic acid biomass in a blast furnace. [Means for solving the problem]

[0012] [1] A method for producing unfired carbon-bearing agglomerates by forming a blend of raw materials containing an iron-bearing raw material, a carbon-bearing raw material, a gangue raw material, and a binder into agglomerates and curing them for a predetermined period of time, A method for producing unfired carbon-containing agglomerates, in which part or all of the carbon-containing raw material and part or all of the siliceous ore in the gangue raw material are replaced with fixed carbon and silicon oxide in biochar obtained by dry distillation of siliceous biomass. [2] Among blended raw materials containing an iron-bearing raw material, a carbon-bearing raw material, a gangue raw material, and a binder, part or all of the carbon-bearing raw material and part or all of the silicic acid-containing ore in the gangue raw material are replaced with fixed carbon and silicon oxide in biochar obtained by dry distillation of silicic acid biomass; The method for utilizing silica biomass in a blast furnace comprises forming the blended raw material into an agglomerate, curing the agglomerate for a predetermined period of time, and then charging the resulting uncalcined carbon-containing agglomerate into the top of the blast furnace.

[0013] According to the present invention, part or all of the carbon-containing raw materials for uncalcined carbon-bearing agglomerates can be replaced with fixed carbon from biochar derived from silicic acid biomass, thereby contributing to the reduction of CO2 emissions in the steel industry. Furthermore, according to the present invention, part or all of the silicic acid-containing ore in the gangue raw materials for uncalcined carbon-bearing agglomerates can be replaced with silicon oxide from biochar derived from silicic acid biomass, without changing the gangue content charged into the blast furnace. Therefore, there is no adverse effect on the air and liquid permeability around the cohesive zone in the lower part of the furnace. Furthermore, according to the present invention, biochar derived from silicic acid biomass, which is generated in large quantities in Japan every year, can be used as the raw material for the blending of uncalcined carbon-bearing agglomerates, containing both the carbon-bearing raw materials and the gangue raw materials, thereby providing an advantage in terms of procurement. Meanwhile, according to the present invention, a new application can be provided for biochar derived from silicic acid biomass, which has previously had limited uses due to its high ash content, by effectively utilizing both fixed carbon and silicon oxide. As described above, the present invention provides a method for producing uncalcined carbon-bearing agglomerates and a method for utilizing silica biomass in a blast furnace, which contribute to the procurement of biochar and the reduction of CO2 emissions in the steel industry without adversely affecting the air and liquid permeability in the cohesive zone at the bottom of the furnace. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a graph showing the relationship between CaO / SiO2 of unburned carbon-containing agglomerates and the metal dropping rate, as disclosed in Patent Document 1. [Figure 2] FIG. 1 is a schematic vertical cross-sectional view of a blast furnace for explaining an overview of the process for producing molten iron from iron ore in a blast furnace. [Figure 3] 1 is a flow chart for explaining a method for producing unburned carbon-containing agglomerates according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The non-calcined carbon-containing agglomerate ore (hereinafter, simply referred to as "carbon-containing agglomerate ore" or "agglomerate ore") according to an embodiment of the present invention is one of the raw materials charged into the blast furnace from the top. Iron ore as a blast furnace raw material can be efficiently used in various forms, such as lump ore that can be charged as is, or by changing the form depending on the state of the raw material. For example, fine ore (fine iron ore), which would impair the air permeability inside the furnace if used as is, can be burned and solidified to form sintered ore, or iron-containing dust recovered in a steelworks can be agglomerated with hydraulic cement to form non-calcined agglomerated ore.

[0016] Here, we will briefly explain the process of producing molten iron from iron ore in a blast furnace using Figure 2. In blast furnace operation, iron ore and coke are first charged into the furnace top 2 at the top of the blast furnace 1 in alternating layers, and then the ore is lowered through the furnace while minimizing disruption of this layered structure (not shown). Hot air and pulverized coal, a complementary reducing agent to the coke, are blown in through blast tuyeres 3 at the bottom of the furnace. In the combustion zone (also called the raceway) 5 formed by this hot air, the pulverized coal and coke burn, generating high-temperature reducing gases such as carbon monoxide and hydrogen. These reducing gases form a strong updraft that rises through the furnace, raising the temperature of the iron ore descending within the furnace, thereby promoting indirect reduction.

[0017] As the iron ore melts as it descends inside the furnace, it forms a donut-shaped cohesive zone 4, which is semi-molten and has a high density somewhere between solid and liquid. This cohesive zone 4 acts as a straightening plate for the high-temperature gas rising from below. Because a relatively large amount of high-temperature gas flows through the relatively thin iron ore layer in the center, the fused layer forms preferentially from the upper center of the furnace, and the accumulated layers take on an inverted V shape. The high-temperature gas rising inside the furnace flows toward the upper center along the inverted V-shaped cohesive zone 4, and the gas that once gathered at the central axis is evenly redistributed to the periphery of the furnace via the coke layer.

[0018] As the molten iron drips through the coke layer, it comes into contact with the carbon in the coke and is further directly reduced, becoming molten iron containing just under 5% carbon, which accumulates in a basin 6 at the bottom of the hearth. This molten iron is removed from a tap hole 7 located next to the bottom of the hearth and carried to the next step in the steelmaking process. At the same time as the iron is tapped, slag, which has been dissolved and separated from the iron ore, such as silica and alumina, is also discharged and reused as a by-product in cement and other applications.

[0019] As shown in Fig. 3, the unsintered carbon-containing agglomerates according to the embodiment of the present invention are produced by forming agglomerates from a blend of raw materials containing an iron-containing raw material, a carbon-containing raw material, a gangue raw material, and a binder, and curing the agglomerates for a predetermined period of time. The predetermined curing period can be, for example, about one to three weeks. In this process, some or all of the carbon-containing raw materials and some or all of the siliceous ore in the gangue raw material are replaced with fixed carbon and silicon oxide in biochar obtained by dry distillation of siliceous biomass. The method for utilizing silica biomass in a blast furnace, in which the uncalcined carbon-containing agglomerate produced in this manner is charged into the top of the blast furnace, is another embodiment of the present invention. Note that, here, both methods will be described together without distinguishing between them.

[0020] In the example shown in FIG. 3, a blend of iron-containing, carbon-containing, and gangue raw materials is mixed in a ball mill while adjusting the particle size distribution to an appropriate range before kneading. In the biochar derived from silicic acid biomass according to this embodiment, the fixed carbon of the carbon-containing raw material and the ash of the gangue raw material are already mixed, but this is not a problem. The biochar derived from silicic acid biomass according to this embodiment is also mixed with other blended raw materials, such as iron-containing raw materials, while adjusting the particle size through conventional processes. Then, a binder and approximately 5 to 15% moisture depending on the binder amount are added to the blended raw materials, and the mixture is kneaded in a mixer. The blended raw materials are then granulated and formed into pellets using a pan pelletizer (also called a disc pelletizer). The green pellets after molding are typically cured for about two weeks in the case of sun curing, but this is not limited to this period and can be adjusted to a period of about one to three weeks depending on the blending ratio of the raw materials, curing conditions such as temperature and humidity, and the required properties of the agglomerated ore.

[0021] Examples of iron-containing raw materials used in this embodiment include iron-containing dust such as sinter dust and blast furnace dust generated in the steelmaking process, pellet feed with a smaller particle size than fine iron ore for sintering, and fine iron ore produced by crushing and / or sizing fine iron ore for sintering. Recycling of such various iron-containing dusts recovered from steelworks and effective use of fine iron ore (fine iron ore) not used as sinter can contribute to reducing CO2 emissions.

[0022] The carbon-containing feedstock used in this embodiment, which is to be replaced with fixed carbon in biochar derived from silicic acid biomass, is the same as that generally used in non-sintered agglomerates: blast furnace primary ash (dry dust collection), coke dust, pulverized coke, anthracite, etc. In this embodiment, some or all of these are replaced with fixed carbon in biochar derived from silicic acid biomass and used as the carbon-containing feedstock. The fixed carbon in the biochar derived from silicic acid biomass used here is a carbon-free carbon source and serves as an alternative feedstock that directly reduces CO2 emissions.

[0023] Silica biomass refers to plants containing silica (silica plants) or parts thereof such as their leaves and stems, including rice and wheat husks and straw, bamboo leaves, and corn leaves and stems. Biochar derived from silica biomass is a carbonaceous material obtained by dry distillation of silica biomass. While any dry distillation method can be used, dry distillation using a rotary kiln is an example. As mentioned above, biochar derived from silica biomass has a fixed carbon content of approximately 15-50%, an ash content of approximately 30-50%, and a unit calorific value of approximately 14-28 MJ / kg.

[0024] In blast furnace operation, ensuring the air permeability and liquid permeability around the cohesive zone is one of the most important management issues. Therefore, the basicity of the molten liquid of all raw materials charged to the blast furnace, CaO / SiO2, is usually adjusted by increasing or decreasing the amount of auxiliary materials mixed with raw materials such as iron ore so that it falls within a predetermined range. It is also preferable to control the basicity of the molten liquid of unsintered carbon-bearing agglomerates alone so that it falls within a predetermined range, for example, as shown in Figure 1. However, since the basicity of the molten liquid in the blast furnace is also adjusted by the auxiliary materials of the blast furnace charge, adjustment of the basicity of the molten liquid of unsintered carbon-bearing agglomerates alone may not be necessary.

[0025] The gangue components in the gangue raw materials commonly used in unfired carbonaceous agglomerates are CaO, SiO2, Al2O3, MgO, etc. These components are also contained in the iron-bearing raw materials, carbon-bearing raw materials, and binders.

[0026] In general, a hydraulic binder such as CaO-based cement is used in unsintered carbon-containing agglomerates to provide the agglomerates with sufficient cold crushing strength. In this embodiment, such binders can be commonly used, such as fine powder containing granulated blast furnace slag as a main component, aging binders containing alkaline activators, quicklime, Portland cement, or bentonite. The amount of binder (added amount) can be determined appropriately, taking into account other blending conditions. If the amount of binder is too small, it becomes difficult to maintain sufficient cold crushing strength of the unsintered carbon-containing agglomerates. Furthermore, if the amount of binder is too large, the amount of slag in the unsintered carbon-containing agglomerates increases, destabilizing the permeability of the lower furnace. As a result, a stable reducing agent ratio reduction effect cannot be obtained.

[0027] As described above, the binder components of uncalcined carbonaceous agglomerates increase the basicity (CaO / SiO2) of the melt of the uncalcined carbonaceous agglomerates, which may worsen the air permeability and liquid permeability around the cohesive zone of a blast furnace. While gangue components are also contained in iron-bearing raw materials and carbonaceous raw materials, the basicity (CaO / SiO2) is increased mainly due to the binder components. Therefore, a silicic acid-containing ore such as silica stone is blended into the uncalcined carbonaceous agglomerates according to this embodiment as a gangue raw material to lower this basicity. Silica stone is a typical example of the silicic acid-containing ore, but it is not limited to this.

[0028] In this embodiment, part or all of this siliceous ore is used as the gangue raw material by replacing the silicon oxide in the biochar derived from siliceous biomass without changing the gangue charged into the blast furnace. Therefore, even if the biochar derived from siliceous biomass is used for the unfired carbon-bearing agglomerate ore, there is no adverse effect on the air and liquid permeability in the cohesive zone at the bottom of the furnace.

[0029] Here, since the content of gangue components such as SiO2 varies greatly depending on the brand of original ore, such as the ore that generates dust and the ore that is blended into sintered ore, it is preferable to adjust the CaO / SiO2 value by selecting the brand of ore used in the steelworks. In particular, the CaO / SiO2 value is greatly affected by the blending amount of ore with a high SiO2 content.

[0030] A preferred embodiment of the method for producing uncalcined carbonaceous agglomerates according to this embodiment, in which biochar derived from silicic acid biomass can be utilized, is described below. First, because the fixed carbon content and ash content per unit amount of biochar derived from silicic acid biomass are expected to fluctuate, the fixed carbon content and ash content per unit amount of the incoming biochar derived from silicic acid biomass are confirmed. Next, if the confirmed fixed carbon content is sufficient to replace the entire amount of the carbonaceous raw material in the raw material blend for the uncalcined carbonaceous agglomerates, the entire amount is replaced. If the confirmed fixed carbon content is insufficient, the biochar is partially replaced, and the raw material blending ratio is determined. The silicon oxide content in the biochar that is consequently included in the uncalcined carbonaceous agglomerates is used as part or all of the siliceous ore in the gangue raw material for the uncalcined carbonaceous agglomerates. The amount of silicon oxide in the biochar derived from silicic acid biomass may affect the basicity of the melt in the blast furnace. Therefore, adjusting the basicity of the uncalcined carbonaceous agglomerates alone is preferable, but is not essential, since adjustment can also be achieved using a separate auxiliary raw material for the blast furnace charge.

[0031] (Example of calculation of the composition of agglomerated ore containing biochar derived from silicate biomass) Here, we will explain the results of calculations for the case where the carbon-containing raw material of ordinary unfired carbon-containing agglomerates is replaced equivalently with fixed carbon in biochar derived from silicic acid biomass.

[0032] To simplify the calculation, the raw materials are assumed to consist of only three types: biochar (A (tons), iron ore powder (B (tons), and binder (C (tons)), and the sum of these amounts is assumed to be D (tons) of unfired carbon-bearing agglomerates. A+B+C=D (1)

[0033] A typical reduction reaction of iron ore is as follows: Fe2O3+3 / 2C → 2Fe+3 / 2CO2··· (2) From the reaction equation (2), we can see that theoretically, 3.5 moles of carbon are required for 1 mole of iron ore, but here we will blend 3 moles of carbon for 1 mole of iron ore, taking into account reaction yield, etc. In addition, the calculation is based on the assumption that the atomic weight of carbon is 12 and the molecular weight of iron ore (Fe2O3) is 160.

[0034] The biochar derived from silicate biomass is rice husk charcoal dry-distilled at 500°C, and its specific components are as follows: ·Fixed carbon: 28.0% by mass Volatile content: 34.5% by mass ·Ash content: 37.5% by mass (including SiO2: 33.6% by mass)

[0035] Based on Equation (2), the ratio of 3 moles of carbon to 1 mole of iron ore, taking into account reaction yield, the amount of fixed carbon in the biochar, etc., the quantitative relationship between the amount of biochar A (tons) and the amount of fine iron ore B (tons) can be expressed by the following Equation (3). {A×28[%]÷12[g / mol]}×3=B÷160[g / mol] B=11.2A (3)

[0036] The amount of binder to be mixed is usually about 3 to 10 mass% of the total amount of the carbonaceous material and the iron ore powder, but here it is set to 10 mass%, and taking into account formula (3), it is set as shown in the following formula (4). C = (A + B) × 0.1 = (1 + 11.2) × 0.1 × A C=1.22A (4)

[0037] Ultimately, the production volume of unfired carbon-bearing agglomerates D (tons) can be expressed by equation (5) using the amount of biochar A (tons) from equations (1), (3), and (4). D=A+B+C=A+11.2A+1.22A≒13.4A (5) The silicon oxide (SiO2) ratio s (mass%) of this unfired carbonaceous agglomerate is expressed by the following formula (6) with reference to the amount of silicon oxide (SiO2) in the biochar. s=A×33.6[%]÷D=A×33.6[%]÷13.4A s=2.5[%] (6) The ratio f (mass%) of iron ore (Fe2O3) in the unburned carbon-bearing agglomerate is expressed by the following formula (7). f=B÷D=11.2A÷13.4A=83.6[%] ··· (7)

[0038] (Example of calculation for adjusting blast furnace feedstock using agglomerates containing biochar derived from silicate biomass) Next, we will explain the results of calculations of the amount of silica stone, an auxiliary raw material that can be equivalently substituted, and the amount of sintered ore that can be reduced by using the unsintered carbon-containing agglomerated ore containing the silicon oxide content and iron ore content estimated above as a blast furnace charging raw material.

[0039] Here, we estimate the case where sinter c1 (ton) is charged into a blast furnace with silica stone (100% SiO2) b (ton) as an auxiliary raw material, but replace sinter c2 (ton) with agglomerated ore a (ton) containing biochar derived from silica biomass. Note that the biochar contained in the agglomerated ore here is the same as the rice husk charcoal used in the above calculations. If the silica stone b (tons) before replacement is equivalently replaced by the silicon oxide in the agglomerated ore a (ton), then the following equation (8) holds true, referring to equation (6) above. That is, equation (8) shows that by charging agglomerated ore a (tons) with a weight 40 times that of the silica stone b (tons) as an auxiliary material into a blast furnace, the silica stone as an auxiliary material can be equivalently replaced. b = a × 2.5 [%] ∴a=40b (8)

[0040] Furthermore, if we assume that the iron ore content in the replaced agglomerates can be directly reduced from the amount of sintered ore charged, then referring to equation (7), the following equation (9) holds: That is, equation (9) shows that it is possible to reduce the amount of sintered ore by 0.836 times the weight of agglomerated ore a (ton) that is replaced equivalently with silica (33.4 times the weight of sintered ore as auxiliary raw material silica b (ton)). c1-c2=0.836a=0.836×40b=33.44b (9) [Explanation of symbols]

[0041] 1 blast furnace 2 Hearth top 3 Blow tuyere 4 Cohesive zone 5 Combustion zone (raceway) 6. Bathtub 7 Taphole

Claims

1. A method for producing unfired carbon-bearing agglomerates by forming a blended raw material containing an iron-bearing raw material, a carbon-bearing raw material, a gangue raw material, and a binder into an agglomerate and curing the agglomerate for a predetermined period of time, comprising: A method for producing unfired carbon-containing agglomerates, in which part or all of the carbon-containing raw material and part or all of the siliceous ore in the gangue raw material are replaced with fixed carbon and silicon oxide in biochar obtained by dry distillation of siliceous biomass, which is a plant containing silica, including rice husks and straw of rice, wheat, etc., bamboo leaves, corn leaves and stalks, etc.

2. Among blended raw materials containing an iron-containing raw material, a carbon-containing raw material, a gangue raw material, and a binder, part or all of the carbon-containing raw material and part or all of the silicic acid-containing ore in the gangue raw material are replaced with fixed carbon and silicon oxide in biochar obtained by dry distillation of silicic acid biomass, which is a plant containing silica, including rice husks and straw of rice, wheat, etc., bamboo leaves, corn leaves and stalks, etc.; When the unburned carbon-containing agglomerates produced by molding the blended raw materials into agglomerates and curing them for a predetermined period are charged into the top of a blast furnace, The method for utilizing silicate biomass in a blast furnace comprises adjusting the amount of auxiliary materials added to the blast furnace so that the basicity CaO / SiO 2 of the molten liquid of all raw materials charged into the blast furnace falls within a predetermined range depending on the amount of silicon oxide contained in the uncalcined carbon-containing agglomerated ore.

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