WO2025211235A1 - Method for producing unfired carbon-containing agglomerated ore and method for using silicic acid biomass in blast furnace - Google Patents

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

The present invention relates to a method for producing unfired carbon-containing agglomerates and a method for using silica biomass in a blast furnace.

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.

Traditionally, various types of iron-bearing dust and carbon-bearing dust recovered from various dust collectors at steelworks have been recycled. Because this leads to resource conservation, it is related to the method of reducing the carbon content of input (a) above. In order to reuse the recovered iron-bearing dust and carbon-bearing dust as blast furnace raw material (also known as blast furnace charge raw material), there is a technology in which a cement-based hydraulic binder is added to them, and they are mixed and molded into unfired agglomerates 8 to 16 mm in diameter. When these unfired agglomerates contain carbonaceous material as a reducing agent, they are also called unfired carbon-bearing agglomerates, to make it clear that they contain carbonaceous material.

In the manufacturing process of unsintered carbonaceous agglomerates, quicklime and CaO-based cement are often used 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 inside the blast furnace to become excessively high. This inhibits the coagulation and meltdown of the produced metal, causing problems with poor air and liquid permeability in the lower part of the blast furnace.

To address these problems, Patent Document 1 discloses an invention in which the melting point of slag generated in the lower part of the furnace is lowered and air and liquid permeability are improved by adjusting the basicity, CaO/ _SiO2, which is the ratio of gangue components in uncalcined 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 uncalcined carbon-bearing agglomerates to 1.0 to 2.0, it is preferable to adjust the blending amount of ore with a high _SiO2 content (also called silicic acid-containing ore).

Furthermore, in relation to the method (c) above of replacing conventional coal, oil, 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 PCI (Pulverized Coal Injection), a pulverized coal injection technology in which biochar obtained by carbonizing biomass is pulverized into pulverized coal PC (Pulverized Coal), which is then injected into the blast furnace through the blast tuyeres 3 (see Figure 2). The invention described in this document also gives examples of applicable biomass, such as cedar wood, palm trunks, and coconut shells, but also claims that any biomass that pyrolyzes to produce charcoal can be used, including those from agriculture, forestry, livestock, fisheries, waste, etc.

International Publication No. 2011/021577 JP 2011-117075 A

Incidentally, the expanded 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, is becoming a problem. This is because biochar derived from silicate biomass can be problematic due to its high ash content of around 30-50%. Furthermore, biochar derived from silicate biomass not only promises a stable supply, but also has sufficient properties as a carbon source, with a fixed carbon content of around 15-50% and a unit calorific value of around 14-28 MJ/kg.

Previous studies into the use 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. Even in the invention described in Patent Document 2, which utilizes biochar in pulverized coal injection (PC) technology, there is no explicit disclosure of 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 from the blast tuyeres 3 at the bottom along with hot air, as shown in Figure 2. It generates high-temperature reducing gas in the combustion zone 5, and the ash is absorbed into the surrounding slag, so the ash content in the pulverized coal (PC) is presumably not a problem. However, when using biochar with a high ash content as a carbonaceous material instead of pulverized coal (PC), it is important to note that the temperature in the lower furnace may drop, potentially destabilizing the furnace conditions.

On the other hand, whether biochar derived from high-ash silicic acid biomass can be used as the carbonaceous material in the unsintered carbonaceous agglomerates described in Patent Document 1 requires further investigation. This is because, with 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 addressed in Patent Document 1.

The present invention therefore aims to provide a method for producing unfired carbon-bearing agglomerates that utilizes biochar derived from silicate biomass, and a method for using silicate biomass in a blast furnace.

[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 it 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-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;
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.

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 a reduction in _CO2 emissions in the iron and 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 produced in large quantities in Japan every year, can be used as the raw material for 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 use 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 can provide a method for producing unsintered carbon-bearing agglomerates and a method for using 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.

FIG. 1 is a graph showing the relationship between CaO/SiO ₂ and metal dropping rate of unsintered carbon-containing agglomerates disclosed in Patent Document 1. 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. 1 is a flow chart for explaining a method for producing unburned carbon-containing agglomerates according to an embodiment of the present invention.

Unfired carbon-bearing agglomerates (hereinafter referred to simply as carbon-bearing agglomerates or simply as agglomerates) according to an embodiment of the present invention are one of the raw materials charged into the top of a blast furnace. Iron ore, a blast furnace raw material, can be efficiently used in various forms, including lump ore that can be charged as is, or by changing its 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 into sintered ore, and iron-bearing dust recovered within steelworks can be agglomerated with hydraulic cement to form unfired agglomerates.

Here, we will briefly explain, using Figure 2, the process of producing molten iron from iron ore in a blast furnace. 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 trying to maintain this layered state (not shown) as much as possible. Hot air and pulverized coal, a complementary reducing agent to the coke, are blown in through the blast tuyeres 3 at the bottom of the furnace. In the combustion zone (also known as 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 violent updraft that rises through the furnace, raising the temperature of the iron ore descending within the furnace, thereby promoting indirect reduction.

As the iron ore melts as it descends inside the furnace, a donut-shaped cohesive zone 4 is formed in a semi-molten state with 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 piled-up layers take on an inverted V shape. The high-temperature gas rising inside the furnace flows along the inverted V-shaped cohesive zone 4 toward the upper center, and the gas that has gathered at the central axis is evenly redistributed to the periphery of the furnace via the coke layer.

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 collects in the basin 6 at the bottom of the hearth. This molten iron is removed from the tap hole 7 located next to the bottom of the hearth and transported to the next steelmaking process. At the same time as the iron is tapped, slag, which is the dissolved and separated impurities in the iron ore such as silica and alumina, is also discharged and is reused as a by-product in cement and other applications.

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 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 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, the two methods will be described together without distinguishing between them.

In the example shown in Figure 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 silicic acid biomass-derived biochar of 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 of this embodiment is also mixed with other blended raw materials, such as iron-containing raw materials, while undergoing particle size adjustment through conventional processes. A binder and approximately 5 to 15% moisture, depending on the binder amount, are then added to the blended raw materials and kneaded in a mixer. The blended raw materials are then granulated using a pan pelletizer (also known as a disc pelletizer) and formed into pellets. The green pellets after molding are typically cured for approximately two weeks in the case of sun curing, but this is not limited to this period and can be adjusted to a period of approximately one to three weeks depending on the raw material blend ratio, curing conditions such as temperature and humidity, and the required properties of the agglomerated ore.

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, fine iron ore produced by crushing and/or sizing fine iron ore for sintering, etc. Recycling of 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.

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, such as blast furnace primary ash (dry dust collection), coke dust, pulverized 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 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.

Silicate biomass refers to plants containing silica (silica plants) or parts thereof such as their leaves and stems, and includes rice and wheat husks and straw, bamboo leaves, and corn leaves and stems. Biochar derived from siliceous biomass is a carbonaceous material obtained by dry distilling siliceous biomass. The dry distillation method is not important, but dry distillation using a rotary kiln is an example. As mentioned above, biochar derived from siliceous 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.

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. Therefore, the basicity of the molten liquid of all the raw materials charged to the blast furnace 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 the unsintered carbon-containing 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 other raw materials charged to the blast furnace, there are cases where adjustment of the unsintered carbon-containing agglomerates alone is not necessary.

Gangue components in gangue raw materials commonly used in non-calcined carbon-bearing agglomerates include CaO, SiO ₂ , Al ₂ O ₃ , MgO, etc. These components are also contained in the iron-bearing raw materials, the carbon-bearing raw materials, and the binder.

Normally, unsintered carbon-bearing agglomerates use hydraulic binders such as CaO-based cement to provide the agglomerates with sufficient cold crushing strength. In this embodiment, such binders can include commonly used fine powders primarily composed of granulated blast furnace slag, time-aging binders made from alkaline activators, quicklime, Portland cement, bentonite, and the like. The amount of binder (addition amount) can be determined appropriately, taking into account other blending conditions, etc. If the amount of binder is too small, it becomes difficult to maintain sufficient cold crushing strength of the unsintered carbon-bearing agglomerates. Furthermore, if the amount of binder is too large, the amount of slag in the unsintered carbon-bearing agglomerates increases, destabilizing the air permeability in the lower furnace area. As a result, a stable reducing agent rate reduction effect cannot be achieved.

As described above, the binder components of unsintered carbonaceous agglomerates increase the basicity CaO/ _SiO2 of the melt of the unsintered carbonaceous agglomerates, which may impair the air permeability and liquid permeability around the cohesive zone of the blast furnace. Although gangue components are also contained in the iron-bearing raw materials and the 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 unsintered carbonaceous agglomerates according to this embodiment as a gangue raw material to reduce this basicity. Silica stone is a typical example of the silicic acid-containing ore, but it is not limited thereto.

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

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.

This section describes a preferred embodiment of the method for producing uncalcined carbonaceous agglomerates that utilizes biochar derived from silicic acid biomass. 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 mix for uncalcined carbonaceous agglomerates, the entire amount is used. If the amount is insufficient, the biochar is changed to partial replacement, and the raw material mix ratio is determined. The silicon oxide content in the biochar that is ultimately included in the uncalcined carbonaceous agglomerates is used as part or all of the silicic acid 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, as it can also be adjusted using a separate auxiliary raw material in the blast furnace charge.

(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.

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

A typical reduction reaction of iron ore is as follows:
Fe 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 per mole of iron ore, but here, 3 moles of carbon are blended per mole of iron ore, taking into consideration reaction yield, etc. In addition, the calculation is premised on the atomic weight of carbon being 12 and the molecular weight of iron ore (Fe ₂ O ₃ ) being 160.

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 SiO ₂ : 33.6% by mass)

Based on the formula (2), the ratio of 3 moles of carbon to 1 mole of iron ore, taking into account the 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) is expressed by the following formula (3).
{A×28[%]÷12[g/mol]}×3=B÷160[g/mol]
B=11.2A... (3)

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)

Ultimately, the production amount D (tons) of unsintered carbon-containing agglomerates is 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 proportion s (mass %) of silicon oxide (SiO ₂ ) in the unfired carbonaceous agglomerate is expressed by the following formula (6) with reference to the amount of silicon oxide (SiO ₂ ) in the biochar.
s=A×33.6[%]÷D=A×33.6[%]÷13.4A
s=2.5[%] ... (6)
The proportion f (mass %) of iron ore (Fe ₂ O ₃ ) in the unburned carbon-containing agglomerate is expressed by the following formula (7).
f=B÷D=11.2A÷13.4A=83.6[%]... (7)

(Example of calculation for adjusting blast furnace feedstock using agglomerated ore 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.

Here, we estimate the case where sinter c1 (tons) is charged into a blast furnace together with silica stone (100% _SiO2 ) b (tons) as an auxiliary raw material, but replace it with sinter c2 (tons) and agglomerated ore a (tons) containing biochar derived from silicic acid biomass. Note that the biochar contained in the agglomerated ore here is the same as the rice husk charcoal used in the above calculation.
If the amount of silica stone b (tons) before substitution is equivalently substituted with the silicon oxide content in the agglomerated ore a (tons), the following equation (8) holds when referring to the above equation (6): That is, from equation (8), it can be seen that by charging into a blast furnace agglomerated ore a (tons) with a weight 40 times that of the silica stone b (tons) as an auxiliary material, the silica stone as an auxiliary material can be equivalently substituted.
b = a × 2.5 [%]
∴a=40b... (8)

Furthermore, if it is assumed that the iron ore content in the replaced agglomerates can be directly reduced from the amount of sintered ore charged, the following formula (9) is established 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 stone (33.4 times the weight of the auxiliary raw material silica stone b (ton)).
c1-c2=0.836a=0.836×40b=33.44b... (9)

1 Blast furnace 2 Furnace top 3 Blast tuyeres 4 Cohesive zone 5 Combustion zone (raceway)
6. Pond section 7. Tap hole

Claims (2)

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. 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;
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.