Method for producing ferrocoke

Abstract

This invention provides a method for producing ferrocoke that exhibits sufficient coke-like properties in a blast furnace, even when using biomass raw materials as the carbon material for ferrocoke production. [Solution] A method for producing ferrocoke by mixing one or more coals and ores, molding the resulting molded product, and carbonizing the resulting product, characterized in that, in the above mixing, carbonized biomass obtained by heat-treating biomass raw materials is added as the char material, and coal, ore, and carbonized biomass are mixed.

Description

[Technical Field]

[0001] This invention relates to a method for producing ferrocoke. [Background technology]

[0002] To operate blast furnaces efficiently, coke, produced by carbonizing coal in a coke oven, is charged into the furnace. The coke charged into the blast furnace serves several purposes, including acting as a spacer to improve ventilation, as a reducing agent, and as a heat source.

[0003] In recent years, technologies for using highly reactive coke have been investigated from the perspective of improving the reactivity of coke. Because highly reactive coke initiates the reaction at a lower temperature in the blast furnace, the reaction efficiency is greatly improved, and a reduction in the reducing agent ratio can be expected. One example of highly reactive coke is ferrocoke, which has metallic iron embedded inside the coke. Ferrocoke can improve the reduction efficiency by promoting the gasification reaction of coke in the blast furnace through the catalytic effect of the embedded metallic iron.

[0004] Furthermore, in recent years, the need to reduce carbon dioxide (CO2) emissions has been increasing globally, and the steel industry is also required to replace conventional coal with carbon-neutral raw materials such as biomass in order to reduce emissions. Because biomass raw materials are highly reactive, further improvement in reactivity can be expected by blending them with ferrocoke. On the other hand, if the reactivity of ferrocoke increases, its post-reaction strength decreases, and it pulverizes in the furnace, obstructing the ventilation of the blast furnace, leading to decreased productivity and an increase in the reducing agent ratio. Therefore, there is a limit to how much the reactivity of ferrocoke can be improved, and it is necessary to maintain a minimum level of post-reaction strength.

[0005] Regarding the above problem, Patent Document 1 describes that it is possible to suppress the decrease in post-reaction strength by setting an upper limit for the iron ore blending for each particle size. However, the invention described in Patent Document 1 is for ordinary ferrocoke, and no studies have been conducted on blending biomass raw materials with ferrocoke.

[0006] Regarding the blending of biomass raw materials with ferrocoke, Patent Document 2 discloses a method for producing ferrocoke in which iron ore and biomass raw materials are mixed in advance, pre-carbonized and pre-reduced, and then mixed with coal.

[0007] Furthermore, Patent Document 3 describes a method for producing ferrocoke in which biomass is preheated to a temperature equal to or lower than that of iron ore before being mixed with iron ore. The document describes an example in which the biomass is preheated to 200-300°C and the iron ore to 400-500°C before mixing the biomass and iron ore. Patent Document 3 also states that when biomass is preheated at a high temperature, pyrolysis gas is generated, so it is desirable to keep the preheating temperature low. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 8-12975 [Patent Document 2] Japanese Patent Publication No. 2005-15700 [Patent Document 3] Japanese Patent Publication No. 2004-217914 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, in the method described in Patent Document 2, the highly reactive biomass raw material and the iron ore are placed in close proximity within the ferrocoke by pre-mixing the iron ore and biomass raw material. As a result, the reactivity around the iron ore is locally increased, making it easier for coarse defects to be generated, and it is thought that the strength of the ferrocoke will decrease.

[0010] Furthermore, the method described in Patent Document 3 involves preheating the biomass at a low temperature of around 200-300°C, which leaves volatile components in the biomass. This releases oxygen-containing gases during carbonization, hindering the softening and melting of the coal. Additionally, while the moldability of the ferrocoke raw material is improved by softening and melting the coal during molding, coal cannot be restored to its original state once softened and melted, resulting in poor softening and melting properties during carbonization.

[0011] Furthermore, while blending biomass raw materials with iron ore can be expected to improve the reactivity of ferrocoke, the mechanism of reactivity improvement differs: iron ore improves the reactivity of the surrounding coke substrate, while biomass raw materials react themselves. Therefore, it is thought that the reaction and pulverization behavior in the blast furnace will differ when reactivity is improved by blending biomass raw materials compared to when reactivity is improved by increasing the amount of iron ore.

[0012] The present invention has been made in view of the above problems, and its purpose is to provide a method for producing ferrocoke that exhibits sufficient coke-like effects in a blast furnace, even when biomass raw materials are used as carbon material for ferrocoke. [Means for solving the problem]

[0013] [1] A method for producing ferrocoke by mixing one or more coals and ores, molding the mixture, and then carbonizing the resulting molded material, A method for producing ferrocoke, characterized in that, in the above mixing, carbonized biomass obtained by heat-treating biomass raw materials is added as the carbon material, and the coal, the ore and the carbonized biomass are mixed.

[0014] [2] In the mixing, the manufacturing method of ferrocoke according to [1], wherein the amount of the carbonized biomass is blended such that the post-reaction strength of the produced ferrocoke is 38.6% or more.

[0015] [3] In the mixing, the manufacturing method of ferrocoke according to [2], wherein 15% by mass or less of the carbonized biomass is blended.

Advantages of the Invention

[0016] According to the present invention, even when a biomass raw material is used as a carbon material for ferrocoke, it is possible to produce ferrocoke that exhibits sufficient effects as coke in a blast furnace.

Brief Description of the Drawings

[0017] [Figure 1] It is a schematic diagram showing the gasification behavior during the reaction of ferrocoke without blending of a biomass raw material and ferrocoke with blending of a biomass raw material. (a) relates to ferrocoke produced by blending only coal and iron ore, and (b) relates to ferrocoke produced by blending coal, iron ore and a biomass raw material. [Figure 2] It is a diagram showing the relationship between the reaction time and the post-reaction strength for three levels of ferrocoke used in Example 1. [Figure 3] It is a diagram showing the relationship between the reaction temperature and the post-reaction strength for three levels of ferrocoke used in Example 2. [Figure 4] It is a diagram showing the relationship between the reactivity and the post-reaction strength of ferrocoke for Example 4.

Embodiments for Carrying Out the Invention

[0018] Embodiments of the present invention will be described below with reference to the drawings. The present invention relates to a method for producing ferrocoke, which involves mixing one or more coals and ores, molding the mixture, and then carbonizing the resulting molded product to produce ferrocoke, characterized in that, in the mixing, carbonized biomass obtained by heat-treating biomass raw materials is added as the carbon material, and the coal, ore, and carbonized biomass are mixed together.

[0019] The inventors diligently considered ways to solve the above problems. Figure 1 is a schematic diagram showing the gasification behavior during reaction of ferrocoke without biomass raw materials and ferrocoke with biomass raw materials. Here, Figure 1(a) relates to ferrocoke produced by blending only coal and iron ore, and Figure 1(b) relates to ferrocoke produced by blending coal, iron ore, and biomass raw materials. Figure 1 shows the difference in reaction behavior between ordinary coke and ferrocoke.

[0020] As shown in Figure 1(a), in the case of ordinary ferrocoke 10, the gasification reaction proceeds from the interface between the metallic iron 4 and the coke of the coke substrate 3. As a result, defects form around the metallic iron 4, leading to pulverization, and after the reaction, coarse defects 5 form around the metallic iron 4, reducing the strength of the ferrocoke 10.

[0021] On the other hand, as shown in Figure 1(b), in ferrocoke 1, which is blended with carbonized biomass, the biomass raw material itself is highly reactive, and the carbonized biomass-derived coke substrate 6, which is bonded to the relatively less reactive coke substrate 3, is considered to be even more reactive. Therefore, even as the reaction progresses, although the portion of the carbonized biomass-derived coke substrate 6 becomes pores 7, the defects formed are considered to have little effect on the strength. As a result, it is considered possible to produce ferrocoke with higher reactivity while maintaining minimum post-reaction strength.

[0022] To fully realize the effects described above, it is considered preferable that biomass raw materials are not in close proximity to each other, and that biomass raw materials are not in close proximity to iron ore. Therefore, the inventors conceived of mixing coal, ore, and carbonized biomass. This makes it possible to suppress the close proximity of biomass raw materials to iron ore.

[0023] Furthermore, the inventors conceived of incorporating carbonized biomass, obtained by heat-treating biomass raw materials, as the carbon material. This makes it possible to suppress the release of oxygen-containing gases during dry distillation.

[0024] As shown in the examples described later, ferrocoke blended with carbonized biomass exhibits higher post-reaction strength at the same reaction rate compared to ferrocoke without carbonized biomass. As a result, it was found that more reactive ferrocoke can be used in blast furnaces, enabling further reductions in CO2 emissions. Thus, the present invention was completed.

[0025] In this invention, one or more types of coal, ore, and carbonized biomass are mixed. The order in which these are mixed is not limited; coal, ore, and carbonized biomass may be mixed simultaneously, coal and carbonized biomass may be mixed first, and the resulting mixture may be mixed with ore, or coal and ore may be mixed first, and then carbonized biomass may be mixed. This mixing can be carried out using a high-speed agitator or the like.

[0026] The coal and ore used in this invention can be those known to have been used in conventional ferrocoke production methods.

[0027] Furthermore, the biomass raw material used for the carbonized biomass in this invention is an organic industrial resource derived from plants and animals present in the current ecosystem, and the organic matter that makes up the biomass circulates within the ecosystem while changing its form. The CO2 generated when biomass is burned originates from carbon that was originally taken in by living organisms when they grew, and therefore does not affect the increase or decrease in the total amount of CO2 in the atmosphere, and is considered to be in a state of so-called carbon neutrality. In contrast, the CO2 generated when fossil fuels are burned originates from underground resources isolated from the current ecosystem, and is therefore not considered to be in a state of carbon neutrality. For this reason, fossil fuels such as coal and oil are not included in the biomass in this embodiment.

[0028] Specifically, any type of biomass that can be used as an industrial resource from products produced in fields such as agriculture, forestry, livestock farming, and fisheries, as well as waste generated during the production process, is acceptable, but it is preferable that it includes at least one of palm kernel shell and woody biomass.

[0029] Palm kernel shells are a biomass produced as a by-product after extracting coconut oil from palm kernels. Palm kernel shells are suitable as a biomass to be used in this embodiment because they are inexpensive and have moderate strength. On the other hand, woody biomass consists of wood from coniferous trees such as cedar, pine, and cypress, and broad-leaved trees such as zelkova and birch. The part of the wood is not limited. Woody biomass also includes unused parts such as waste wood from construction and papermaking, and thinned wood generated in forestry. Sawdust produced in sawmilling is one of the typical woody biomass.

[0030] In this invention, carbonized biomass raw materials are blended with coal and ore as the carbon material. The carbonization of the biomass raw materials can be carried out by heat treatment of the biomass raw materials in an atmosphere where air is blocked. By making the atmosphere during the heat treatment of the biomass raw materials an atmosphere where air (oxygen) is blocked, i.e., a non-oxidizing atmosphere, the combustion of the biomass raw materials is inhibited, and the biomass raw materials can be carbonized. To create an atmosphere where air is blocked, for example, the biomass raw materials can be placed in a sealable container and heat treated, or the atmosphere can be made a vacuum or an inert gas atmosphere.

[0031] Untreated biomass raw materials have poor pulverizability and are difficult to use as raw materials for ferrocoke, but their pulverizability can be improved by heat treatment. The heat treatment temperature required for carbonization of biomass raw materials varies depending on the type of biomass raw material, but if it is 400°C or higher, carbonization will proceed sufficiently and pulverizability will improve. Therefore, it is preferable to set the heat treatment temperature for carbonization of biomass raw materials to 400°C or higher.

[0032] Furthermore, it is preferable to reduce the particle size of the biomass raw material by carbonizing it and then pulverizing it. The particle size of the carbonized biomass is preferably 3 mm or less, and more preferably 1 mm or less. On the other hand, there is no lower limit to the particle size of the carbonized biomass; the finer, the better.

[0033] Regarding the evaluation method for the reactivity and post-reaction strength of ferrocoke, the conventional method for general coke (not ferrocoke) first measures the mass C of the coke sample before reaction, measures the mass A of the coke sample reacted with CO2 at 1100°C for 2 hours, and measures the mass B of the sample on a 9.5 mm sieve after rotating the reacted sample 600 times in a Type I testing machine. Then, the reaction rate is evaluated based on the mass reduction rate of the sample after reaction with CO2 (i.e., ((mass C - mass A) / mass C) × 100 (%)), and the post-reaction strength of the coke is evaluated based on the ratio of mass B to mass A (i.e., (mass B / mass A) × 100 (%)) (see Shozo Murakami et al., Coke Circular, Vol. 23, 1974, pp. 82-87). However, the above method cannot evaluate the reactivity and post-reaction strength of ferrocoke because its reactivity is too high.

[0034] Ferrocoke is a type of coke that is particularly specialized for reaction, and its role in the blast furnace differs from that of ordinary coke. Therefore, the methods for evaluating the reactivity and post-reaction strength that can reproduce the gasification reaction of ferrocoke in a blast furnace are considered to be different from those for ordinary coke.

[0035] Therefore, the inventors diligently investigated methods for evaluating the reactivity and post-reaction strength of highly reactive ferrocoke. As a result, they found that the following method allows for a more accurate reproduction of the reaction state and the amount of powder when it reaches the bottom of the blast furnace. • Reactivity of ferrocoke: Mass loss rate after reaction at 1000°C in a CO2 atmosphere for 60 minutes. • Strength after ferro-coke reaction: The mass ratio on a 9.5 mm sieve after a sample reacted at 1000°C in a CO2 atmosphere for 60 minutes and rotated 600 times at a speed of 20 rpm in a Type I drum testing machine.

[0036] In other words, the inventors conducted reaction tests under various conditions to evaluate the reactivity and post-reaction strength of ferrocoke. As a result, it became clear that even for samples where the evaluation results were almost the same when evaluated using the conventional method of reacting coke with CO2 for 120 minutes, the difference could be detected by shortening the reaction time. Specifically, they found that by setting the reaction time to between 20 minutes and 110 minutes, it was possible to detect the difference between ferrocokes with different properties and evaluate the reactivity and post-reaction strength of ferrocoke. They also found that the difference in reactivity and post-reaction strength between ferrocokes with different properties was greatest when the reaction time was 60 minutes.

[0037] Furthermore, by setting the reaction temperature above the reaction start temperature of the ferrocoke charged into the reaction vessel, preferably between 900°C and 1100°C, it is possible to prevent most of the sample from becoming pulverized, allowing for good detection of differences in reactivity and post-reaction strength between samples. It was also found that setting the reaction temperature to 1000°C maximizes the difference in post-reaction strength between ferrocokes with different properties.

[0038] Based on the above findings, the inventors established a method for evaluating the post-reaction strength of ferrocoke by measuring the mass C of a coke sample before the reaction, measuring the mass A of a ferrocoke sample reacted with CO2 at 1000°C for 60 minutes, measuring the mass B of the sample on a 9.5 mm sieve after rotating the reacted sample 600 times in a Type I testing machine, evaluating the reaction rate based on the mass reduction rate of the sample after reaction with CO2 (i.e., ((mass C - mass A) / mass C) × 100 (%)), and evaluating the post-reaction strength of ferrocoke based on the ratio of mass B to mass A (i.e., (mass B / mass A) × 100 (%)).

[0039] The inventors evaluated the relationship between post-reaction strength and blast furnace operation for various ferrocokes with different properties. As shown in the examples described later, they found that if the post-reaction strength of ferrocoke is 38.6% (mass%) or higher, the gas utilization rate, which is an indicator of reduction efficiency, improves, and the reducing agent ratio can be reduced. Furthermore, they found that the ventilation in the blast furnace is equivalent to, or at least worse than, that when using general coke instead of ferrocoke, it does not cause problems for blast furnace operation. Therefore, it is preferable to blend the carbonized biomass raw material used as a carbon material in an amount such that the post-reaction strength of the ferrocoke produced is 38.6% or higher.

[0040] The amount of carbonized biomass needed to obtain ferrocoke with a post-reaction strength of 38.6% or higher cannot be determined definitively, as it is influenced by the properties and mixing ratios of coal and ore, but for example, it is 15% by mass or less.

[0041] Next, the mixed raw materials are molded as described above, and the resulting molded product is subjected to carbonization. The molding and carbonization of the raw materials can also be carried out by conventionally known methods.

[0042] In this way, ferrocoke containing carbonized biomass can be manufactured. [Examples]

[0043] (Example 1) In Example 1, the effect of the reaction time between ferrocoke and CO2 on the post-reaction strength was evaluated. The properties of the three types of ferrocoke used in the test are shown in Table 1. In Table 1, FC represents the fixed carbon ratio of the ferrocoke, and T.Fe represents the iron content.

[0044] [Table 1]

[0045] Three types of ferrocoke A, B, and C with different properties (all with a reaction initiation temperature of less than 900°C) were prepared, and the difference in post-reaction strength among the samples over time was investigated. Specifically, 20 egg-shaped ferrocoke pieces measuring 30 mm × 25 mm × 18 mm (6 cc) were placed in a cylindrical reaction vessel, and the samples were reacted with CO2 at 1000°C for 30 minutes. The mass A of the sample after the reaction was measured. Subsequently, the ferrocoke sample after the reaction was rotated at 600 rpm at 20 rpm using a Type I testing machine, then placed on a sieve with a mesh size of 9.5 mm and sieved. The mass B of the sample remaining on the sieve was measured. The ratio of mass B to mass A was then calculated from the measured masses A and B, and the resulting ratio was defined as the post-reaction strength. The same measurement of post-reaction strength was performed for reaction times of 0 minutes, 60 minutes, 90 minutes, and 120 minutes. Figure 2 shows the relationship between reaction time and post-reaction strength for ferrocoke A to C.

[0046] The post-reaction strength of ferrocoke showed an increase in the difference in post-reaction strength between samples up to 60 minutes of reaction time, but conversely, the difference narrowed after 60 minutes. As a result, it was found that the post-reaction strength evaluation method used in the present invention can detect differences in post-reaction strength between samples when the reaction time is between 20 minutes and 110 minutes, the difference in post-reaction strength between samples increases when the reaction time is between 30 minutes and 90 minutes, and the difference is largest when the reaction time is 60 minutes.

[0047] (Example 2) In Example 2, the effect of the reaction temperature between ferrocoke and CO2 on the post-reaction strength was evaluated. The three types of ferrocoke used in the test were the same as those used in Example 1. Three types of ferrocoke with different properties, A, B, and C, were used to investigate the difference in post-reaction strength between samples as the reaction temperature progressed. Specifically, 20 ferrocoke units were placed in a cylindrical reaction vessel, and the samples were reacted with CO2 at a temperature of 900°C for 60 minutes. The mass A of the sample after the reaction was measured. Subsequently, the ferrocoke sample after the reaction was placed in the drum of a Type I testing machine, the drum was rotated 600 times at 20 rpm, and then the sample was placed on a sieve with a mesh size of 9.5 mm and sieved. The mass B of the sample remaining on the sieve was measured. The ratio of mass B to mass A was then calculated from the measured masses A and B, and the value of the obtained ratio was defined as the post-reaction strength. The post-reaction strength measurements described above were also performed for reaction temperatures of 800°C, 1000°C, and 1100°C. Figure 3 shows the relationship between reaction time and post-reaction strength for ferrocokes A to C.

[0048] The post-reaction strength of ferrocoke showed almost no difference between samples at a reaction temperature of 700°C, but the difference widened above 800°C, reaching its greatest extent at 1000°C. Above 1000°C, the difference in post-reaction strength narrowed with increasing reaction temperature, but the difference remained detectable up to 1100°C. However, when the reaction temperature was set to 1200°C, almost no difference between samples was detectable. As a result of these findings, it was found that the post-reaction strength measurement method used in this invention is effective at reaction temperatures between 800°C and 1100°C, with the greatest difference occurring at 1000°C.

[0049] (Example 3) In Example 3, to evaluate the effect of post-reaction strength on aeration in the blast furnace based on the evaluation method used in the present invention, four types of ferrocoke with different post-reaction strengths were used in the blast furnace, and the operating results under each condition were compared with the conditions of the reference example to evaluate the reducing properties and permeability. As an air permeability resistance index, the K value (=(P B 2 -P T 2 ) / V 1.7 ) (PB : Blast pressure (g / cm 2 ), P T : Top pressure of the furnace (g / cm 2 ), V: Blast volume (Nm 3 / min)) were used. The measurement conditions for the strength after reaction were a reaction time of 60 minutes and a reaction temperature of 1000 °C. The results are shown in Table 2.

[0050]

Table 2

[0051] When ferrocoke with strength after reaction of 58.6%, 49.5% and 38.6% was used, the gas utilization rate, which is an index of reduction efficiency, improved and the reductant ratio decreased. The ventilation during this period was equivalent to the reference example or, even if it deteriorated, it was not a problem for blast furnace operation. On the other hand, when ferrocoke with a low strength after reaction of 28.7% was used, the ventilation resistance index increased significantly, and the tapping ratio decreased because the blast had to be reduced. From the above results, it was confirmed that the evaluation method of strength after reaction used in the present invention can evaluate the ventilation effect when ferrocoke is used in a blast furnace.

[0052] (Example 4) In Example 4, the relationship between the reactivity and post-reaction strength of ferrocoke in which carbonized biomass was incorporated as part of the carbon material was investigated. Two types of coal, one type of iron ore, and one type of biomass raw material were used as raw materials. First, coal and iron ore with particle size adjusted to 100% of 3 mm or less, and carbonized biomass obtained by carbonizing woody raw materials at 700°C and then adjusting the particle size to 100% of 1 mm or less were simultaneously mixed in the ratios shown in Table 3. Next, the mixed raw materials were kneaded in a high-speed agitator while heating to 160°C with asphalt pitch and soft pitch added as binders at 3.5% by mass and 5.0% by mass, respectively, relative to the total mass of the raw materials. After that, the mixture was molded in a molding machine with a roll size of 650 mmφ × 104 mm, with a rotation speed of 2 rpm and pressure applied at 2 tons per 1 cm in the width direction, to obtain an egg-shaped molded product of 30 mm × 25 mm × 18 mm (6 cc). Next, the obtained molded material was carbonized using the following laboratory-scale method (fixed bed). Specifically, the molded material was packed into a carbonization vessel measuring 200 mm in length, 60 mm in width, and 200 mm in height, and carbonized for 4 hours and 20 minutes using programmed heating at a maximum of 850°C, followed by cooling in a nitrogen atmosphere. The reactivity and post-reaction strength of the obtained ferrocoke were evaluated. The lower limit of the post-reaction strength of the ferrocoke was set at 38.6%, the same as the effect confirmed in the blast furnace as described above. Figure 4 shows the relationship between the reactivity and post-reaction strength of the obtained ferrocoke.

[0053] [Table 3]

[0054] Both iron ore and carbonized biomass show a decrease in post-reaction strength as their blending ratio increases. However, the decrease in post-reaction strength is smaller when carbonized biomass is blended, confirming that it is possible to produce more reactive ferrocoke while maintaining post-reaction strength. Furthermore, it was confirmed that the blending ratio of carbonized biomass can be up to 15% by mass without falling below the lower limit of post-reaction strength (38.6%). [Industrial applicability]

[0055] According to the present invention, even when biomass raw materials are used as carbon material for ferrocoke, it is possible to produce ferrocoke that exhibits sufficient coke-like effects in a blast furnace. [Explanation of Symbols]

[0056] 1. Carbonized biomass-blended ferrocoke 2. Pores in the coke matrix 3. Coke substrate 4 Metallic iron 5. Gross defects 6. Coke substrate derived from carbonized biomass 7. Pores in coke substrate derived from carbonized biomass 10. Standard ferrocoke

Claims

1. In a method for producing ferrocoke by mixing one or more coals and ores, molding the resulting molded material, and then carbonizing it, A method for producing ferrocoke, characterized in that, in the above mixing, carbonized biomass obtained by heat-treating biomass raw materials is added as the carbon material, and the coal, the ore and the carbonized biomass are mixed.

2. The method for producing ferrocoke according to claim 1, wherein in the mixing, an amount of carbonized biomass is added such that the post-reaction strength of the ferrocoke produced is 38.6% or more.

3. The method for producing ferrocoke according to claim 2, wherein the mixture contains 15% by mass or less of the carbonized biomass.

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