Method for producing unfired carbon-containing agglomerated ore and method for using silicic acid biomass in blast furnace

Abstract

The present invention provides a method for producing unfired carbon-containing agglomerated ore and a method for using silicic acid biomass in a blast furnace in each of which biochar derived from silicic acid biomass is utilized. In the present invention related to a method for producing unfired carbon-containing agglomerated ore, a combined raw material containing an iron-containing raw material, a carbon-containing raw material, a gangue raw material, and a binder is used to mold an agglomerated article, the agglomerated article is cured for a prescribed period of time, and thus unfired carbon-containing agglomerated ore is produced. At that time, fixed carbon and silicon oxide in biochar which is obtained through carbonization of silicic acid biomass are used, in the combined raw material used, as a part or the whole of the carbon-containing raw material and a part or the whole of silicic acid-containing ore in the gangue raw material. In the present invention related to a method for using silicic acid biomass in a blast furnace, the unfired carbon-containing agglomerated ore obtained as described above is charged from the top of the blast furnace.

Description

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

[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.

[0002] From the perspective of preventing global warming, CO ２ Reducing CO emissions is an urgent issue, and the steel industry is also ２ Technology development is underway to reduce CO emissions. ２ There are two ways to reduce emissions: (a) reducing the amount of carbon in the input, and (b) reducing the amount of CO2 in the output. ２ (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 and the like at steelworks have been recycled. This leads to resource conservation, and is therefore related to the method (a) above for reducing the carbon content of inputs. In order to reuse the recovered iron-bearing dust and carbon-bearing dust as blast furnace raw materials (also referred to as blast furnace charge raw materials), there is a technology in which a cement-based hydraulic binder is added to the dust, and the dust is mixed and molded to produce unfired agglomerates with a diameter of 8 to 16 mm. When these unfired agglomerates contain carbonaceous material as a reducing agent, they are also referred to as unfired carbon-bearing agglomerates, in order to clarify that they contain carbonaceous material.

[0004] In the production of unsintered carbon-bearing agglomerates, quicklime and CaO-based cement are used in large amounts as binders, resulting in a high CaO content in the product. As a result, the viscosity of the molten liquid produced from the unsintered carbon-bearing agglomerates during the reaction process in the blast furnace becomes excessively high. This inhibits the coagulation and melt-through of the produced metal, resulting in a problem of poor air and liquid permeability in the lower part of the blast furnace.

[0005] To address this problem, Patent Document 1 describes a method for determining the basicity of the unburned carbon-bearing agglomerate ore, which is the ratio of gangue components, CaO / SiO ２ The invention discloses that by adjusting the ratio of CaO / SiO2 to 1.0 to 2.0, the melting point of the slag generated in the lower part of the furnace is lowered, thereby improving the air and liquid permeability. ２In order to make the value of SiO2 between 1.0 and 2.0, ２ It is preferable to adjust the blending amount of the silica-containing ore (also called silica-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) technology, in which biochar obtained by carbonizing biomass is pulverized into pulverized coal (PC), which is then injected into a blast furnace through a blast tuyere 3 (see FIG. 2). In the invention described in this document, while cedar wood, palm trunks, and coconut shells are given as examples of applicable biomass in the examples, the invention also states that any biomass that generates charcoal upon pyrolysis, such as from agriculture, forestry, livestock, fisheries, and waste, can be used.

[0007] International Publication No. 2011 / 021577 Japanese Patent Application Laid-Open No. 2011-117075

[0008] Meanwhile, the expanded use of biomass (also called silicic acid 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 amounts exceeding 2 million tons annually, has become a problem. This is because biochar derived from silicic acid biomass can be problematic due to its high ash content of approximately 30-50%. Furthermore, biochar derived from silicic acid biomass not only promises 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 not considered a problem. However, when using biochar with a high ash content as a substitute for the pulverized coal (PC), it is important to note that the temperature in the lower furnace may decrease, potentially destabilizing the furnace conditions.

[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 a problem 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.

[0012] [1] A method for producing uncalcined carbon-containing agglomerates by forming agglomerates from a blended raw material 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, wherein some or all of the carbon-containing raw materials and some or all of the siliceous ore contained in the gangue raw material are replaced with fixed carbon and silicon oxide in biochar obtained by carbonizing siliceous biomass. [2] A method for utilizing siliceous biomass in a blast furnace by forming agglomerates from the blended raw materials containing an iron-containing raw material, a carbon-containing raw material, a gangue raw material, and a binder, and replacing some or all of the carbon-containing raw materials and some or all of the siliceous ore contained in the gangue raw material with fixed carbon and silicon oxide in biochar obtained by carbonizing siliceous biomass, and curing the agglomerates for a predetermined period of time to produce uncalcined carbon-containing agglomerates, which are then charged into the top of a blast furnace.

[0013] According to the present invention, a part or all of the carbon-containing raw material of the unburned carbon-containing agglomerate is replaced with fixed carbon in biochar derived from silicate biomass, thereby reducing CO ２ This can contribute to reducing CO2 emissions. Furthermore, according to the present invention, part or all of the siliceous ore contained in the gangue raw material for uncalcined carbonaceous agglomerates can be replaced with silicon oxide contained in biochar derived from siliceous biomass, without changing the gangue content charged into the blast furnace. Therefore, there is no adverse effect on the air permeability and liquid permeability around the cohesive zone in the lower part of the furnace. Furthermore, according to the present invention, biochar derived from siliceous biomass, which is produced in large quantities in Japan every year, can be used as a raw material containing both the carbonaceous raw material and the gangue raw material in the raw material blend for uncalcined carbonaceous agglomerates, which has an advantageous effect in terms of procurement. Meanwhile, according to the present invention, a new application can be provided for biochar derived from siliceous biomass, the uses of which have been limited due to its high ash content, by effectively utilizing both fixed carbon and silicon oxide. As described above, according to the present invention, the procurement of biochar and CO2 emissions in the steel industry can be improved without adversely affecting the air permeability and liquid permeability in the cohesive zone in the lower part of the furnace. ２ It is possible to provide a method for producing unburned carbon-containing agglomerates and a method for utilizing silica biomass in a blast furnace, which contribute to reducing emissions.

[0014] The CaO / SiO of the unburned carbon-containing agglomerate disclosed in Patent Document 1 ２ 1 is a diagram illustrating the relationship between the metal dripping rate and the temperature at which hot metal is added. 2 is a diagram illustrating the relationship between the temperature at which hot metal is added and the temperature at which hot metal is added. 3 is a diagram illustrating the relationship between the temperature at which hot metal is added and the temperature at which hot metal is added. 4 is a diagram illustrating the relationship between the temperature at which hot metal is added and the temperature at which hot metal is added. 5 is a diagram illustrating the relationship between the temperature at which hot metal is added and the temperature at which

[0015] The non-calcined carbon-containing agglomerated ore (hereinafter, simply referred to as "carbon-containing agglomerated ore" or "agglomerated 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, a brief overview of the process of producing molten pig iron from iron ore in a blast furnace will be described with reference to 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 state (not shown). Hot air and pulverized coal, a complementary reducing agent to the coke, are blown into the 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 combust, generating high-temperature reducing gases such as carbon monoxide and hydrogen. The reducing gas forms 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, a doughnut-shaped cohesive zone 4 is formed in a semi-molten state with a high density 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 is formed 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] The molten iron drips through the coke layer and comes into contact with the carbon in the coke, where it is further directly reduced, becoming molten iron containing just under 5% carbon, which accumulates in a reservoir 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 uncalcined carbon-containing agglomerates according to an embodiment of the present invention are produced by forming an agglomerate from a blended raw material containing an iron-containing raw material, a carbon-containing raw material, a gangue raw material, and a binder, and curing the agglomerate for a predetermined period of time. The predetermined curing period can be, for example, about one to three weeks. In this case, some or all of the carbon-containing raw material 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 carbonizing siliceous biomass. Another embodiment of the present invention is a method for utilizing siliceous biomass in a blast furnace, in which the uncalcined carbon-containing agglomerates produced in this manner are charged into the top of the blast furnace. Here, the two methods will be described together without distinguishing between them.

[0020] In the example shown in FIG. 3 , a blend of iron-containing raw materials, carbon-containing raw materials, and gangue raw materials is mixed in a ball mill while adjusting the particle size distribution to an appropriate range before kneading. In the silicic acid biomass-derived biochar 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 silicic acid biomass-derived biochar 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 using a pan pelletizer (also called a disc pelletizer) and formed into pellets. 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 particle size smaller than that of fine iron ore for sintering, and fine iron ore produced by crushing and / or sizing fine iron ore for sintering. By recycling various iron-containing dusts collected from steelworks and effectively utilizing fine iron ore (fine iron ore) that is not used as sinter, CO ２ This can contribute to reducing emissions.

[0022] The carbon-containing raw material 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, such as blast furnace primary ash (dry dust collection), coke dust, fine coke, and anthracite. 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 raw material. The fixed carbon in the biochar derived from silicic acid biomass used here is a carbon-free carbon source and cannot be directly converted into CO ２ It will be an alternative raw material that will help reduce emissions.

[0023] Silica biomass refers to plants containing silica (silica plants) or parts thereof such as their leaves and stems, and includes rice husks and straw from plants such as rice and wheat, bamboo leaves, and corn leaves and stems. Biochar derived from silica biomass is a carbonaceous material obtained by dry distillation of silica biomass, and can be obtained by any dry distillation method, but 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 to 50%, an ash content of approximately 30 to 50%, and a unit calorific value of approximately 14 to 28 MJ / kg.

[0024] In the operation of a blast furnace, ensuring the air permeability and liquid permeability around the cohesive zone is one of the most important management issues. ２ The amount of the auxiliary materials blended together with the raw materials such as iron ore is adjusted to fall within a predetermined range. ２is preferably controlled to be within a predetermined range as shown in Fig. 1. However, since the basicity of the melt in the blast furnace is also adjusted by the auxiliary materials of the raw materials charged into the blast furnace, there are cases where adjustment by the unburned carbon-containing agglomerate ore alone is not necessary.

[0025] The gangue components in the gangue raw material generally used in non-burned carbon-bearing agglomerates are CaO, SiO ２ , Al ２ O ３ and MgO, etc. These components are also contained in the iron-containing raw material, the carbon-containing raw material and the binder.

[0026] In order to provide the unsintered carbon-containing agglomerates with sufficient cold crushing strength, hydraulic binders such as CaO-based cement are typically used. In this embodiment, such binders can include commonly used fine powders containing granulated blast furnace slag as a main component, aging binders containing alkaline activators, quicklime, Portland cement, and 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 achieved.

[0027] As described above, the binder components of the unsintered carbonaceous agglomerates are determined by the basicity CaO / SiO ２ Since this increases the temperature, there is a concern that it may worsen the air permeability and liquid permeability around the cohesive zone of the blast furnace. Although gangue components are also contained in the iron-containing raw materials and the carbon-containing raw materials, the binder components are the main cause of the basicity CaO / SiO ２ Therefore, the non-calcined carbon-bearing agglomerate ore according to this embodiment is blended with a silicic acid-containing ore such as silica stone as a gangue raw material for the purpose of lowering this. The silicic acid-containing ore is typically silica stone, but is not limited thereto.

[0028] In this embodiment, the siliceous ore is partially or entirely replaced with silicon oxide in biochar derived from siliceous biomass, without changing the gangue charged into the blast furnace. Therefore, even if biochar derived from siliceous biomass is used for unsintered carbon-bearing agglomerates, there is no adverse effect on the air and liquid permeability in the cohesive zone at the bottom of the furnace.

[0029] Here, depending on the brand of the original ore, such as the ore that generates the dust or the ore that is mixed into the sintered ore, the SiO ２ Since the content of gangue components such as CaO / SiO varies greatly, the content of gangue components such as CaO / SiO varies greatly depending on the ore brand used in the steelworks. ２ It is preferable to adjust the value. ２ The value is SiO ２ It is greatly affected by the amount of ore with a high 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 Estimation of Components of Agglomerates Containing Biochar Derived from Silica Biomass) Here, we will explain the results of estimations when the carbon-containing raw material of a normal unfired carbon-containing agglomerate is equivalently replaced with fixed carbon in biochar derived from silica biomass.

[0032] To simplify the calculation, the blended raw materials are assumed to consist of only three types: biochar (A (tons), iron ore fines (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] The typical reduction reaction of iron ore is as follows: ２ O ３ +3 / 2C → 2Fe+3 / 2CO ２ ... (2) From the reaction formula (2), it can be seen that theoretically, 3 / 2 moles of carbon are required for 1 mole of iron ore, but here, taking into consideration the reaction yield, etc., 3 moles of carbon are blended for 1 mole of iron ore. In addition, the atomic weight of carbon, which is the premise of the calculation, is 12, and the iron ore (Fe ２ O ３ ) has a molecular weight of 160.

[0034] The biochar derived from silicate biomass was rice husk charcoal dry-distilled at 500°C, and its specific components were as follows: Fixed carbon: 28.0% by mass; Volatile matter: 34.5% by mass; Ash: 37.5% by mass (including SiO ２ :33.6% by mass)

[0035] Based on Equation (2), the blending ratio of 3 moles of carbon per mole of iron ore, taking into account reaction yield, the amount of fixed carbon in the biochar, and other factors, the quantitative relationship between the amount of biochar A (tons) and the amount of fine iron ore B (tons) is 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 mixed is usually about 3 to 10 mass % of the total amount of carbonaceous material and iron ore powder, but here it is set to 10 mass %, and taking into account equation (3), it is set as follows: C = (A + B) × 0.1 = (1 + 11.2) × 0.1 × A C = 1.22A ... (4)

[0037] Finally, the production amount D (tons) of unburned carbon-bearing agglomerates can be expressed by the formula (5) using the amount of biochar A (tons) from formulas (1), (3), and (4): D = A + B + C = A + 11.2A + 1.22A ≒ 13.4A (5) The silicon oxide (SiO ２ The ratio s (mass%) of silicon oxide (SiO ２ ) amount in the unburned carbon-containing agglomerate ore, and is expressed by the following formula (6): s = A × 33.6 [%] ÷ D = A × 33.6 [%] ÷ 13.4A s = 2.5 [%] (6) ２ O ３ The ratio f (mass %) of B to D is expressed by the following formula (7): f = B ÷ D = 11.2A ÷ 13.4A = 83.6 [%] (7)

[0038] (Example of Estimation of Blast Furnace Raw Material Adjustment Using Agglomerated Ores Containing Biochar Derived from Silica Biomass) Next, we will explain the results of estimations 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 uncalcined carbon-containing agglomerated ores containing the silicon oxide content and iron ore content estimated above as blast furnace charging raw materials.

[0039] Here, when sinter c1 (ton) is charged into the blast furnace, silica (SiO ２ This calculation assumes that the blast furnace is charged with sintered ore c2 (tons) and agglomerated ore a (tons) containing biochar derived from silica biomass. The biochar contained in the agglomerated ore is the same as the rice husk charcoal used in the above calculation. If the silica b (tons) before replacement is equivalently replaced with the silicon oxide content in agglomerated ore a (tons), the following formula (8) holds true, based on formula (6) above. From formula (8), it can be seen that charging agglomerated ore a (tons) with 40 times the weight of the auxiliary material silica b (tons) into the blast furnace will result in an equivalent replacement of the auxiliary material silica. 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, the following formula (9) holds true by referring to formula (7). That is, formula (9) shows that it is possible to reduce the amount of sintered ore by 0.836 times the weight of the agglomerates a (ton) that are replaced with silica (33.4 times the weight of the auxiliary raw material silica b (ton)). c1 - c2 = 0.836a = 0.836 x 40b = 33.44b ... (9)

[0041] 1 Blast furnace 2 Furnace top 3 Blast tuyere 4 Cohesive zone 5 Combustion zone (raceway) 6 Melt reservoir 7 Tap hole

Claims

1. A method for producing unsintered carbon-bearing agglomerates by forming a mixture 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, wherein part or all of the carbon-bearing raw materials and part or all of the siliceous ore contained in the gangue raw material are replaced with fixed carbon and silicon oxide in biochar obtained by dry distillation of siliceous biomass.

2. A method for utilizing silica biomass in a blast furnace, comprising: substituting fixed carbon and silicon oxide in biochar obtained by carbonizing silica biomass for part or all of the carbon-containing raw materials and part or all of the silica-containing ore in the gangue raw materials, among a blend of raw materials containing an iron-bearing raw material, a carbon-bearing raw material, a gangue raw material, and a binder; forming the blend of raw materials into agglomerates; and curing the agglomerates for a predetermined period to produce uncalcined carbon-bearing agglomerates, which are then charged into the top of the blast furnace.

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