Blast furnace operation method

Abstract

A blast furnace operation method according to the present invention comprises: a first injection step for injecting a first reducing gas and biomass coal, or biomass coal together with pulverized coal, from a conventional tuyere into a blast furnace; and a second injection step for injecting, from the conventional tuyere into the blast furnace, a second reducing gas obtained by separating and removing at least some CO2 gas and H2O gas from the blast furnace gas. When injecting the biomass coal during the first injection step, the biomass coal to be injected from the conventional tuyere is selected using carbon content, hydrogen content, and decomposition heat as control parameters.

Description

Blast furnace operation methods

[0001] This disclosure relates to a method for operating a blast furnace. This application claims priority under Japanese Patent Application No. 2024-220590, filed in Japan on December 17, 2024, the contents of which are incorporated herein by reference.

[0002] In the blast furnace process, pig iron is produced by alternately charging iron-based raw materials and coke in layers from the top of the furnace to form ore layers, while blowing hot air together with pulverized coal from the tuyeres at the bottom of the blast furnace. Coke and pulverized coal are used as reducing agents.

[0003] In recent years, global warming has become a major social issue, and reducing emissions of carbon dioxide, one of the greenhouse gases, is a key measure. As mentioned above, the blast furnace method uses carbon to produce large quantities of pig iron, resulting in the emission of large amounts of carbon dioxide. Therefore, reducing the amount of carbon used is considered a crucial issue in the steel industry.

[0004] Reducing agents serve as a heat source to raise the temperature of the blast furnace charges, and also as a reducing agent to reduce the iron-based raw materials inside the furnace. In order to reduce the reducing agent ratio (the total mass of reducing agents required to produce one ton of molten iron), it is necessary to improve the reduction efficiency inside the furnace.

[0005] The reduction reaction of iron-based raw materials in a furnace is defined by various reaction equations, but among these reduction reactions, the direct reduction reaction (reaction equation: FeO + C → Fe + CO) is known to be an endothermic reaction accompanied by a large amount of heat absorption. Therefore, reducing the proportion of the direct reduction reaction is important in reducing the ratio of reducing agents. If the proportion of the direct reduction reaction can be reduced, the amount of reducing agent used in the direct reduction reaction and as a heat source can be reduced.

[0006] One known method for reducing the reducing agent ratio is to blow in a hydrogen-based reducing gas (such as COG gas, natural gas, LPG gas, methane gas, or hydrogen gas) along with hot air from a tuyer, thereby promoting a hydrogen reduction reaction using the hydrogen in the reducing gas and reducing the direct reduction reaction.

[0007] For example, Patent Document 1 describes a technique for improving the reducing gas potential inside a furnace by blowing hydrogen gas into it along with hot air from a tuyer. Patent Document 1 defines a parameter called the reduction rate of carbon consumption per unit (Input△C) as an indicator parameter for reducing the reducing agent ratio, and states that the larger the reduction rate of carbon consumption per unit (Input△C), the lower the reducing agent ratio, and consequently, CO ２ It has been disclosed that emissions will be reduced.

[0008] Furthermore, as an alternative method to reduce the reducing agent ratio, a method has been proposed in which biomass is charged into the blast furnace instead of a coal-derived reducing agent. For example, Patent Document 2 discloses a method in which biomass coal, obtained by carbonizing biomass under predetermined carbonization conditions (carbonization temperature: 450°C, carbonization time: 30 minutes or more), is blown into the tuyeres of a blast furnace. Patent Document 3 discloses a method in which a mixture of crushed biomass coal and pulverized coal, in which the volatile content is adjusted to 10 mass% or more, is blown into the tuyeres of a blast furnace.

[0009] However, by efficiently utilizing biomass coal, the CO2 emissions from blast furnaces can be reduced. ２ To reduce emissions, it is necessary to optimize the properties of biomass coal. However, the technologies described in Patent Documents 2 and 3 did not involve performance evaluation in blast furnaces linked to the properties of biomass coal, making it unclear whether the biomass was being utilized efficiently.

[0010] In response to the above-mentioned challenges in the utilization of biomass coal, Patent Document 4 discloses a method for operating a blast furnace in which crushed biomass coal, which is a carbonized product of biomass, is blown in from a tuyeres while reducing iron raw materials, characterized in that the lower heating value of the biomass coal is used as a control indicator to determine the biomass coal to be blown in from the tuyeres.

[0011] International Publication No. 2021 / 107091 Japanese Patent Publication No. 2011-117075 Japanese Patent Publication No. 2011-117074 Japanese Patent Publication No. 2023-038504

[0012] Kouji TAKATANI, Takanobu INADA, Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace", ISIJ International, Vol. 39 (1999), No. 1, p. 15-22

[0013] As described above, there are two methods for reducing the reducing agent ratio: injecting hydrogen-based reducing gas into the blast furnace and utilizing biomass coal. Although the operating method described in Patent Document 4 is an excellent technology, it does not anticipate injecting hydrogen-based reducing gas into the blast furnace. As a result of the inventors' investigation, it was found that when hydrogen-based reducing gas is injected, the correlation between the lower heating value and the amount of carbon replacement is small, and that biomass coal cannot be efficiently utilized using the lower heating value as a management indicator. Therefore, the object of this disclosure is to provide a blast furnace operating method in which biomass coal and hydrogen-based reducing gas are injected into the blast furnace, and which uses a management indicator that has a large correlation with the amount of carbon replaced from fossil fuels, contributing to the efficient utilization of biomass coal (utilization with a high replacement rate by biomass coal).

[0014] The inventors investigated the reason why the correlation between the lower heating value and the amount of carbon substitution decreases when a hydrogen-based reducing gas is injected, and then investigated new management indicators. As a result, by using the C content (carbon content), H content (hydrogen content), and decomposition heat in the carbon material of biomass coal as management indicators, the CO emissions from the blast furnace can be controlled. ２ We discovered that biomass charcoal, which can reduce emissions, can be used efficiently.

[0015] This disclosure has been made in view of the above findings. The gist of this disclosure is as follows: [1] A method of operating a blast furnace according to one aspect of this disclosure comprises a first blowing step in which biomass coal or the biomass coal and pulverized coal, and a first reducing gas are blown into the inside of the blast furnace from a tuyeres, and CO ２ Gas and H ２The blast furnace operation method described in [2] [1] includes a second blowing step in which a second reduced gas obtained by separating and removing at least a portion of the O gas is blown into the interior of the blast furnace from the normal tuyeres, wherein in the first blowing step, when blowing in the biomass coal, the biomass coal to be blown in from the normal tuyeres is selected using the carbon content, hydrogen content and decomposition heat as control indicators. [3] The blast furnace operation method described in [1] may involve, in the first blowing step, obtaining data on the carbon content, hydrogen content, and decomposition heat for each of the multiple biomass coals whose raw materials are different from each other, and selecting one or more types of biomass coal from the multiple biomass coals such that the carbon content is 0.50 or more, the hydrogen content is 0 or more and 0.05 or less, and the decomposition heat is 0 kcal / kg or more and 200 kcal / kg or less, and blowing the selected biomass coal from the normal tuyeres.

[0016] According to the above-described aspect of this disclosure, a blast furnace operation method is provided in which biomass coal and hydrogen-based reducing gas (first reducing gas) are injected into the blast furnace, and the method uses a management indicator that has a large correlation with the replacement rate and contributes to the efficient utilization of biomass coal. This operation method reduces CO emissions from the blast furnace. ２ It is effective in efficiently reducing [the amount].

[0017] It is a relational diagram evaluating the relationship between the pulverized coal carbon substitution rate (substitution rate) of biomass charcoal and the lower calorific value using a blast furnace mathematical model. It is a relational diagram evaluating the relationship between the pulverized coal carbon substitution rate (substitution rate) of biomass charcoal and the C content in a carbon material with a decomposition heat of 100 kcal / kg using a blast furnace mathematical model. It is a relational diagram evaluating the relationship between the pulverized coal carbon substitution rate (substitution rate) of biomass charcoal and the H (hydrogen) content in a carbon material with a decomposition heat of 100 kcal / kg and a C content of 78.4 mass% using a blast furnace mathematical model. It is a relational diagram evaluating the relationship between the pulverized coal carbon substitution rate (substitution rate) of biomass charcoal and the decomposition heat of a carbon material with a C content of 78.4 mass%. It is a diagram showing the relationship between the estimated substitution rate and the substitution rate in the examples. It is a schematic diagram of an example of a blast furnace used in the operation method of the blast furnace according to the present embodiment.

[0018] The operation method of the blast furnace according to an embodiment of the present disclosure (the operation method of the blast furnace according to the present embodiment) will be described. The operation method of the blast furnace according to the present embodiment includes a first blowing step of blowing biomass charcoal or biomass charcoal and pulverized coal, and a first reducing gas into the inside of the blast furnace from the normal tuyere, and from the blast furnace gas (BFG), CO ２ gas and H ２ A second blowing step of blowing at least a part of the O gas, which is obtained by separating and removing, into the inside of the blast furnace from the normal tuyere. In the present disclosure, as shown in FIG. 6, the normal tuyere 11 is a tuyere provided below the bosch part 12 of the blast furnace 10. The normal tuyere 11 is two places on the left and right in FIG. 6, but it may be one place, or may be provided at three or more places substantially evenly along the circumference of the blast furnace. Each step will be described.

[0019] [First Blowing Step] In the operation method of the blast furnace according to the present embodiment, as the first blowing step, biomass charcoal or biomass charcoal and pulverized coal, and a first reducing gas (that is, biomass charcoal and a first reducing gas, or biomass charcoal, pulverized coal and a first reducing gas) are blown into the inside of the blast furnace from the normal tuyere.

[0020] (Injection of Biomass Charcoal) The inventors focused on the properties of biomass charcoal (carbon content, hydrogen content, decomposition heat), and evaluated the relationship between these properties of biomass charcoal and the pulverized coal carbon substitution rate (hereinafter referred to as "substitution rate") using a blast furnace mathematical model. The outline of the blast furnace mathematical model used for the evaluation is as follows. Blast furnace mathematical model: By dividing the internal area of the blast furnace in the height direction, radial direction, and circumferential direction, a plurality of meshes (small areas) are defined, and the behavior of each mesh is simulated (see, for example, Non-Patent Document 1).

[0021] <Regarding Simulation Conditions> The simulation conditions will be explained. When injecting the first reducing gas into the blast furnace from the normal tuyere, taking the specifications shown in Table 1 as the basic operation (normal pulverized coal operation) conditions, completely stopping the pulverized coal injected from the normal tuyere of the blast furnace, and increasing the injection amount of biomass charcoal shown in Table 2, the blast volume, oxygen enrichment amount, and biomass charcoal ratio were adjusted so that the hot metal output, hot metal temperature, and top gas temperature were the same as those during the basic operation under the condition of a constant coke ratio. Hydrogen gas was used as the first reducing gas, and the hydrogen gas injection amount was 350 Nm ３ / t, and the temperature of the injected hydrogen gas (hydrogen gas injection temperature) was set at 1200°C. The size of the biomass charcoal was set to be under a 200-mesh sieve (74 μm), and it was assumed that the entire amount of biomass charcoal injected into the furnace would burn. The simulation was carried out for each case (C1, C2, H, Ash, HD) shown in Table 2.

[0022]

[0023]

[0024] In Table 2 (where % in the table represents mass%), Case C1 contains multiple biomass charcoals with varying C content (58.4% to 88.4% by mass), and equal H content, Ash content, and decomposition heat. Ash refers to the ash content. Case C2 contains multiple biomass charcoals with varying C content (75.0% to 95.7% by mass), and equal H content, Ash content, and decomposition heat. Case H contains multiple biomass charcoals with varying H content (0% to 6.0% by mass), and equal C content, Ash content, and decomposition heat. Case Ash contains multiple biomass charcoals with varying Ash content (0% to 15.0% by mass), and equal C content, H content, and decomposition heat. Case HD contains multiple biomass charcoals with varying decomposition heats (0 kcal / kg to 400 kcal / kg) and equal C, H, and ash content.

[0025] When the content of a certain component was changed relative to the base biomass charcoal, the change was adjusted by the oxygen content. For example, when evaluating the effect of reducing the carbon content by 10% by mass relative to the base biomass charcoal, it was assumed that the oxygen content would increase by 10% by mass.

[0026] In summary, the blast furnace mathematical model was subjected to a thermal balance calculation to simulate the question: "When biomass coal is injected in place of pulverized coal, using normal pulverized coal operation as the base operation, what amount of biomass coal should be injected to produce the same level of molten iron as in normal pulverized coal operation?" Based on the results of this thermal balance calculation, the "substitution rate" was calculated as follows.

[0027] <About the Replacement Rate> In blast furnace operations where biomass coal is injected from the tuyeres, the objective is to reduce carbon consumption derived from coal. Therefore, the amount of carbon reduction derived from pulverized coal per unit amount of biomass coal injected is used as the evaluation index. In this embodiment, the "replacement rate" is used as this evaluation index. The definition of the replacement rate is as follows: Replacement rate = (amount of pulverized coal reduction due to the use of biomass coal × carbon content in pulverized coal) / amount of biomass coal used ... Equation (1) Here, the unit of "amount of pulverized coal reduction due to the use of biomass coal" in the equation is "kg / pig-ton", which is the amount of pulverized coal reduced when producing 1 ton of molten iron. The unit of "amount of biomass coal used" is also "kg / pig-ton", which is the amount of biomass coal used to produce 1 ton of molten iron. The unit of "carbon content in pulverized coal" is dimensionless and is the ratio (-) of the weight of carbon contained in pulverized coal.

[0028] <Relationship between replacement rate, C and H ratio (content or content) in the charcoal material, and decomposition heat> Based on the above simulation, the inventors evaluated the relationship between the replacement rate of individual biomass charcoals calculated from the above simulation, the C content (mass%) (carbon content (-) in the charcoal material (biomass charcoal); here, for example, a C content of 50 mass% is equivalent to a carbon content of 0.50), and the decomposition heat of the biomass charcoal (kcal / kg). In this embodiment, based on the biomass charcoal property data in Table 2, the decomposition heat (kcal / kg) was estimated from the following equation (2). Decomposition heat (kcal / kg) = 78.375 × C content in biomass charcoal (mass%) + 289.25 × H content in biomass charcoal (mass%) - lower heating value of biomass charcoal (kcal / kg) .....Equation (2) Here, "78.375" and "289.25" are constants derived from thermodynamic constants. Furthermore, the lower heating value (kcal / kg) is the amount of heat generated when a fuel undergoes complete combustion (carbon is converted to carbon dioxide and hydrogen is converted to water vapor).

[0029] Furthermore, in the above simulation, the carbon content in the charcoal material is a set condition, but in the case of actual charcoal material, it can be measured in accordance with JIS M8819:1997 (Coal and coke - Method of elemental analysis by instrumental analyzer). Also, in the above simulation, the lower heating value was defined based on equation (2) from the relationship between the carbon content, hydrogen content and decomposition heat in the biomass charcoal. On the other hand, in the case of actual charcoal material, the lower heating value can be estimated in accordance with JIS M8814:2003. Specifically, when the lower heating value of biomass charcoal is H1 (MJ / kg), the higher heating value Hh of the biomass charcoal can be measured in accordance with JIS M8814:2003, and the lower heating value H1 (MJ / kg) can be estimated by substituting the measured higher heating value Hh into equation (3). H1 = Hh - r × (9H + w) ... Equation (3) In equation (3), H is the H content (mass%) in the biomass charcoal (sample) before combustion, and w is the moisture content (mass%) in the biomass charcoal (sample) before combustion. r is the latent heat of condensation of water vapor (MJ / kg), and in this embodiment it is set to 0.044 (constant). The H content in the biomass charcoal can be measured according to the elemental analysis method of JIS M8813:2006. The moisture content in the biomass charcoal can be measured according to the industrial analysis method of JIS M8812:2006.

[0030] The evaluation results for each case are shown in Figures 1 to 4. The vertical axis in Figures 1 to 4 represents the substitution rate obtained by the blast furnace mathematical model described above.

[0031] Figure 1 plots the relationship between the carbon replacement rate (substitution rate) of pulverized coal in biomass coal and its lower heating value (LHV). From Figure 1, it can be seen that the correlation between LHV and substitution rate is low, and that when LHV is used as an indicator, biomass coal may not be utilized effectively.

[0032] Figure 2 plots the relationship between the carbon content of a carbon material (biomass carbon) and the replacement rate for a carbon material (biomass carbon) with a decomposition heat of 100 kcal / kg. From the plot, a regression line (linear function) was obtained using the least squares method, and the correlation coefficient was calculated. The correlation coefficient was approximately 0.999, indicating a strong correlation. Furthermore, the above simulation shows that when the carbon content in the carbon material is increased, the replacement rate increases by 1.089 times for each increase in carbon content when the hydrogen content is 3.8 mass% (0.01089 for an increase of 0.01 (1%)), and by 1.175 times for each increase in carbon content when the hydrogen content is 0 mass%. On average, the replacement rate increases by 1.132 times for each increase in carbon content. Figure 3 plots the relationship between the carbon replacement rate (replacement rate) of biomass coal and the hydrogen (H) content in the coal material with a decomposition heat of 100 kcal / kg and a carbon content of 78.4 mass%. From the plot, it can be seen that increasing the H content in the coal material increases the replacement rate by 2.09 times the increase in H content. Figure 4 plots the relationship between the carbon replacement rate (replacement rate) of biomass coal and the decomposition heat of coal material with a carbon content of 78.4 mass%. From the plot, it can be seen that as the decomposition heat increases, the replacement rate increases by 2.69 × 10⁻¹⁴ times the increase in decomposition heat. －４ It can be seen that the replacement rate decreases by a factor of two. From the above simulations, it was found that the higher the C content and H content in the charcoal material, the higher the replacement rate. Furthermore, it was found that even if the C content and H content in the charcoal material are the same, the replacement rate decreases when the decomposition heat increases. In other words, it was found that a predetermined replacement rate can be obtained by controlling the C content, H content and decomposition heat in the charcoal material. Based on this relationship, for example, to achieve the same replacement rate as biomass charcoal with a C content of 85.4 mass%, an H content of 0 mass%, and a decomposition heat of 100 kcal / kg, it can be seen that the C content in the charcoal material should be 81.0 mass%, the H content 3.0 mass%, and the decomposition heat 148 kcal / kg.

[0033] Based on the above results, and assuming the above parameters, the estimated replacement rate can be calculated using the following formula: Estimated replacement rate = CP + 1.132 × (CB - CP) + 2.09 × (HB - HP) - 2.69 × 10 -４ × (HDB - HDP) Here, CP, HP, and HDP are the carbon content (-), hydrogen content (-), and decomposition heat (kcal / kg) of the standard pulverized coal, respectively, while CB, HB, and HDB are the carbon content (-), hydrogen content (-), and decomposition heat (kcal / kg) of the biomass coal, respectively.

[0034] Based on the above considerations, in the blast furnace operation method according to this embodiment, as the first injection step, the first reducing gas and pulverized biomass coal, which is an auxiliary reducing agent, are normally injected from the tuyeres. In this blast furnace operation method, the biomass coal to be injected from the tuyeres is selected using the carbon content (mass%), hydrogen content (mass%), and decomposition heat (kcal / kg) of the charcoal material (biomass coal) as control indicators. The biomass coal may be injected together with pulverized coal (partial substitution of pulverized coal) or injected in place of pulverized coal (complete substitution of pulverized coal).

[0035] The decomposition heat of the char material (biomass char) is preferably between 0 kcal / kg and 200 kcal / kg. If the decomposition heat is high, the replacement rate will decrease, and if it exceeds 200 kcal / kg, there is a concern that a sufficient replacement rate cannot be obtained, assuming other conditions are normal operating conditions.

[0036] The carbon content of the char material (biomass char) is preferably 50% by mass or more. If the carbon content is less than 50% by mass, there is a concern that a sufficient replacement rate cannot be obtained due to the high ash content in the char material. The hydrogen content of the biomass char is preferably 0% by mass or more and 5% by mass or less in order to ensure sufficient carbonization and reduction of decomposition heat.

[0037] The particle size of the biomass charcoal is preferably 500 μm or less. If it exceeds 500 μm, combustion may be insufficient. There is no lower limit, but considering the load of crushing, the particle size may be 30 μm or more.

[0038] The particle size of biomass charcoal can be measured using a method in accordance with JIS Z8815:1994 "General Rules for Sieving Test Methods".

[0039] In this embodiment, biomass char is a char material containing carbonized material obtained by dry distillation of biomass. Biomass includes all types of biomass that produce carbonized material through thermal decomposition, such as agricultural, forestry, livestock, fisheries, and waste materials. Woody biomass includes papermaking by-products such as pulp black liquor and chip dust, sawmilling by-products such as bark and sawdust, forest residues such as branches, leaves, twigs, and scraps, thinned timber from cedar, cypress, and pine, waste logs for edible fungi, and other special forest products, as well as forestry biomass such as fuelwood forests of oak, sawtooth oak, and pine, and short-rotation forests of willow, poplar, eucalyptus, and pine, and general waste such as pruned branches from street trees in municipalities and garden trees in private homes, and industrial waste such as pruned branches from street trees in national and prefectural governments and garden trees in companies, and construction waste. Agricultural biomass, including rice husks, wheat straw, rice straw, sugarcane residue, palm oil, etc., which are classified as agricultural biomass and originate from waste and by-products, as well as some agricultural biomass such as rice bran, rapeseed, and soybeans, which originate from energy crops, can also be suitably used as woody biomass.

[0040] Conventional batch, rotary kiln, and vertical furnace methods can be used for the carbonization of biomass. The carbonization gas generated during the carbonization of biomass can be used as a heat source during the carbonization process. However, a heat source may also be obtained by burning fuel gases other than carbonization gas, such as heavy oil or propane.

[0041] As a carbonization condition, the carbonization temperature can be set. The carbonization temperature is the final temperature reached in the furnace. For example, when blowing biomass obtained by carbonizing palm oil (hereinafter also called PKS charcoal) through a tuyer, the carbonization temperature of the palm oil can be set according to the following procedures (A) to (C). (A) Produce multiple PKS charcoals by carbonizing palm oil while changing the carbonization temperature. (B) After identifying the properties of each PKS charcoal (C content (mass%), H content (mass%), decomposition heat (kcal / kg), etc.), estimate the lower heating value (kcal / kg) and identify the PKS charcoal that meets the conditions. (C) Set the carbonization temperature at which the PKS charcoal identified in (B) was produced as the carbonization temperature of the palm oil (hereinafter also called the appropriate carbonization temperature). As a carbonization condition to be changed, the carbonization time can be used along with the carbonization temperature, or instead of the carbonization temperature. Changes in the carbon content, hydrogen content, and decomposition heat of biomass charcoal change depending on the carbonization conditions (carbonization temperature and / or carbonization time).

[0042] The carbonized biomass char is subjected to a crushing process, where it is crushed to a particle size of, for example, 500 μm or less, and is usually blown into the blast furnace through a tuyer. The crushing method is not particularly limited, but a roller mill can be used, for example.

[0043] <<Example of Selection Method>> This section describes a specific method for selecting biomass charcoal from multiple carbonized biomass charcoals to be blown in from the tuyere during the first blowing process. However, the selection method is not limited to the method described below.

[0044] (Selection Method 1) In Selection Method 1, when there are multiple biomass charcoals with the same raw material (biomass raw material) but different carbonization conditions, data on the C content (carbon content), H content (hydrogen content), and decomposition heat of each is obtained. Then, from among the multiple biomass charcoals, one or more types of biomass charcoals are selected as the biomass charcoals that should normally be blown in from the tuyeres, such that the average C content is 50% by mass or more (carbon content of 0.50 or more), the average H content is 0% by mass or more and 5% by mass or less (hydrogen content of 0 or more and 0.05 or less), and the average decomposition heat is 0 kcal / kg or more and 200 kcal / kg or less. The average C content, H content, and decomposition heat can be determined by a weighted average according to the respective content of the multiple biomass charcoals to be combined. In this embodiment, different carbonization conditions refer to conditions in which the average values ​​of the C content, H content, and decomposition heat of the biomass charcoal produced differ by 1.5% or more for C content, 0.75% or more for H content, and 25 kcal / kg or more for decomposition heat. By investigating the average values ​​of the C content, H content, and decomposition heat of the biomass charcoal produced under different carbonization conditions in advance, it is possible to determine whether the carbonization conditions are the same or different. Biomass charcoal produced under the same manufacturing conditions (same type of biomass material, carbonization conditions, and carbonization equipment) can be considered to have the same C content, H content, and decomposition heat. That is, when selecting one type of biomass charcoal, biomass charcoal produced under manufacturing conditions in which the C content is 50% by mass or more (carbon content of 0.50 or more), the H content is 0% by mass or more and 5% by mass or less (hydrogen content of 0 or more and 0.05 or less), and the decomposition heat is 0 kcal / kg or more and 200 kcal / kg or less is normally selected as the biomass charcoal to be blown in from the tuyere. Biomass charcoal may be a combination of two or more types. In this case, the combination should be selected based on the carbon content and decomposition heat of each type, in a predetermined mass ratio, such that the average carbon content, hydrogen content, and decomposition heat of the combined biomass charcoal meet the predetermined criteria.

[0045] (Selection Method 2) In Selection Method 2, data on the C content (carbon content), H content (hydrogen content), and decomposition heat are obtained for multiple biomass charcoals that have different raw materials (different types of raw materials). Then, one or more types of biomass charcoals are selected from the multiple biomass charcoals such that the average C content is 50% by mass or more, the average H content is 0% by mass or more and 5% by mass or less, and the average decomposition heat is 0 kcal / kg or more and 200 kcal / kg or less. Selection Method 2 is applied when commercially available biomass charcoal is used as an auxiliary reducing agent. Samples are obtained for each of the multiple biomass charcoals that have different raw materials. The properties of the obtained samples (C content (mass%), H content (mass%), lower heating value, decomposition heat (kcal / kg), etc.) are individually identified, and one or more types of biomass charcoal are selected such that the average C content is 50% by mass or more (carbon content of 0.50 or more), the average H content is 0% by mass or more and 5% by mass or less (hydrogen content of 0% or more and 0.05 or less), and the average decomposition heat is 0 kcal / kg or more and 200 kcal / kg or less.

[0046] The selected biomass coal is designated as the biomass coal to be blown in from the tuyeres. The raw material for the designated biomass coal is newly obtained, crushed, and then blown in from the tuyeres. This allows for the efficient use of commercially available biomass, etc., in a blast furnace operation method aimed at reducing carbon consumption from coal. The crushing method is not particularly limited as described above, but for example, a roller mill can be used.

[0047] (Selection Method 3) Selection Methods 1 and 2 may be combined. That is, if there are multiple biomass charcoals with different raw materials and different carbonization conditions, one or more types of biomass charcoals may be selected such that the average of the combined biomass charcoals has a C content of 50% by mass or more (carbon content of 0.50% or more), an H content of 0% by mass or more and 5% by mass or less (hydrogen content of 0% or more and 0.05% or less), and a decomposition heat of 0 kcal / kg or more and 200 kcal / kg or less.

[0048] (Injection of First Reducing Gas) Generally, hot air, pulverized coal, and enriched oxygen gas are blown into the blast furnace from the tuyeres. The hot air reacts with the pulverized coal blown in with it and with the coke in the blast furnace to generate high-temperature reducing gas (mainly CO gas in this case). In other words, the hot air gasifies the coke and pulverized coal. In some cases, pulverized coal is not blown into the blast furnace. The generated reducing gas rises inside the blast furnace, heating and reducing the iron-based raw materials. The iron-based raw materials descend inside the blast furnace, being heated and reduced by the reducing gas. Subsequently, the iron-based raw materials melt and are further reduced by the coke as they descend the blast furnace. The iron-based raw materials are ultimately stored in the hearth as molten pig iron containing slightly less than 5% by mass of carbon. The molten pig iron in the hearth is removed from the tap and used in the next steelmaking process.

[0049] In the operating method according to this embodiment, in addition to the hot air described above, a first reducing gas is blown into the blast furnace. By blowing the first reducing gas together with the hot air from the tuyeres, the reducing gas potential inside the furnace can be improved, and the reducing agent ratio can be reduced.

[0050] <First Reducing Gas> The first reducing gas is a gas (sometimes called a hydrogen-based reducing gas) that contains 30 mol% or more of H as an elemental composition and exists as a gas under standard conditions (0°C, 1 atm). For example, H ２ Gas, unsaturated hydrocarbon gas (C ２ H ４ , C ２ H ２ , C ３ H ６ (etc.), saturated hydrocarbon gases (CH ４ , C ２ H ６ , etc.), NH ３ Gas, coke oven gas, city gas, natural gas, etc., and mixtures thereof. Particularly preferred is H ２ Gas, unsaturated hydrocarbon gas (C ２ H ４ , C ２ H ２ , C ３ H ６ (etc.) H ２The gas is preferable from the viewpoint of reducing carbon consumption per unit, as it does not contain carbon and does not undergo thermal decomposition reactions at the tuyeres. Furthermore, its low viscosity and density make it preferable from the viewpoint of permeability within the blast furnace. Unsaturated hydrocarbon gases are preferable because they contain double and triple bonds in their gas molecules, resulting in a relatively high heat of combustion per mol of oxygen, and they also serve as a heat source at the tuyeres. It is more preferable that the elemental composition ratio of H in the first reducing gas is 50 mol% or more. Also, the first reducing gas may contain other gases (e.g., N) (without impairing the effects of this embodiment). ２ A mixed gas with (or other gas) is also acceptable. The amount of first reducing gas injected is 0 Nm. ３ / t over 600Nm ３ It is preferable that the amount is less than or equal to / t. Furthermore, the first reducing gas may be blown into the blast furnace at room temperature, but it is preferable that it be blown in after being heated in order to supply heat to the blast furnace. For example, 500°C or higher, 1000°C or higher, or 1200°C or higher. The first reducing gas is supplied from outside the blast furnace system. For example, it can be heated in a heater connected to a tuyere as needed from a tank that stores the first reducing gas, and then blown into the blast furnace from the tuyere.

[0051] [Second Injection Process] In the blast furnace operation method according to this embodiment, as the second injection process, CO is injected from blast furnace gas (BFG). ２ Gas and H ２ The second reduced gas, obtained by separating and removing at least a portion of the oxygen gas, is usually blown into the blast furnace through a tuyer. The order of the first and second blowing processes does not matter, and they may be performed simultaneously.

[0052] (Injection of secondary reducing gas from the tuyeres) In the operating method according to this embodiment, secondary reducing gas is injected into the blast furnace from the tuyeres. This has the effect of promoting reduction and heating inside the furnace.

[0053] <Secondary Reducing Gas> The secondary reducing gas that is normally blown in from the tuyer is a gas containing 20% ​​or more CO gas by volume fraction. The secondary reducing gas is, for example, a gas recovered and separated from the top exhaust gas of the furnace, or a CO gas and H obtained by reforming hydrocarbon gases using common methods such as partial oxidation. ２This includes gas containing other gases (so-called reforming furnace top circulation gas). The secondary reducing gas is typically blown into the blast furnace through tuyeres by any means. For example, the secondary reducing gas can be temporarily stored in a buffer tank, the secondary reducing gas introduced from the buffer tank can be pressurized by a compressor to the internal pressure of the blast furnace (approximately 4.5 to 5.0 atmospheres), heated in a secondary reducing gas heater introduced from the compressor, and the heated secondary reducing gas can then be blown into the blast furnace through tuyeres. Multiple tuyeres may be present, in which case the secondary reducing gas can be blown into the blast furnace from multiple tuyeres.

[0054] The amount of second reducing gas injected is 200 Nm³. ３ / t or more 600Nm ３ It is preferable that the amount is less than or equal to / t. Furthermore, it is preferable that the temperature at which the second reducing gas is injected is 800°C or higher.

[0055] CO in the second reducing gas ２ Gas and H ２ A lower O gas content is preferable. For example, H ２ The O gas is preferably 3% or less by volume fraction, more preferably 1% or less. Also, CO ２ The gas is preferably 3% or less by volume fraction, more preferably 1% or less. Keeping it below this value suppresses the influence of the endothermic gasification reaction. Also, CO ２ When the separation rate decreases, a large amount of CO enters the second reducing gas. ２ There are concerns that the inclusion of gas will lower the concentration of reducing gases (CO gas, hydrogen gas) in the second reducing gas, making it more difficult to promote reduction in the shaft. ２ The content is measured by a gas analyzer, such as a gas chromatograph. ２ Gas and H ２ O gas is discharged outside the system. The separation method is not particularly limited. Examples include chemical adsorption and physical adsorption (PSA).

[0056] CO2 from the top exhaust gas of the furnace ２ Gas and H ２When separating and removing oxygen gas to generate a second reducing gas, it is not necessary to separate and remove the entire amount of top exhaust gas. For example, it is possible to recover only the amount of top exhaust gas corresponding to the flow rate of the second reducing gas injected into the blast furnace and then remove the oxygen gas. ２ Gas and H ２ The oxygen gas may be separated and removed. The remaining top exhaust gas can be used as a heat source for the steel mill.

[0057] For the biomass coal types shown in Table 3, Nos. 1 to 3 (in the table, the percentage of content is in mass%), the replacement rate was evaluated using a blast furnace mathematical model. The outline of the blast furnace mathematical model used for the evaluation is as follows: Blast furnace mathematical model: Following the method in Non-Patent Literature 1, multiple meshes (small regions) were defined by dividing the internal region of the blast furnace in the height, radial, and circumferential directions, and the behavior of each mesh was simulated. As a simulation condition, the blast furnace operation method was assumed to involve injecting biomass coal and / or pulverized coal, as well as hydrogen gas as the first reducing gas, into the furnace through the tuyeres, and also injecting a second reducing gas through the tuyeres. Based on the pulverized coal injection operation parameters shown in Table 4 as a baseline, the injection of pulverized coal through the tuyeres was completely stopped, and the amount of biomass coal injected was increased. Under the condition of a constant coke ratio, the airflow rate, oxygen enrichment rate, and biomass coal ratio were adjusted so that the amount of pig iron produced, molten iron temperature, and furnace top gas temperature were the same as during basic operation. The size of the biomass coal was assumed to be below a 200-mesh sieve (74 μm), and it was assumed that all of the biomass coal injected into the furnace would burn. No. 0 in Table 3 represents the baseline pulverized coal properties.

[0058]

[0059]

[0060] Furthermore, the estimated replacement rate was calculated using the following formula based on the carbon content CP(-) of the standard pulverized coal, the hydrogen content HP(-) of the pulverized coal, the decomposition heat HDP (kcal / kg) of the pulverized coal, the carbon content CB(-) of the biomass coal, the hydrogen content HB(-) of the biomass coal, and the decomposition heat HDB (kcal / kg) of the biomass coal: Estimated replacement rate = CP + 1.132 × (CB - CP) + 2.09 × (HB - HP) - 2.69 × 10 -４× (HDB-HDP)

[0061] Figure 5 shows the relationship between the estimated replacement rate when using commercially available biomass coal calculated using the above formula and the replacement rate evaluated by the blast furnace mathematical model. As can be seen from Figure 5, the estimated replacement rate of biomass coal calculated using the above formula is in close agreement with the replacement rate evaluated by the blast furnace mathematical model. Therefore, in a blast furnace operation method in which biomass coal and / or pulverized coal, and the first reducing gas are normally blown into the blast furnace from the tuyere, and the second reducing gas is normally blown into the blast furnace from the tuyere, it has been shown that biomass coal can be efficiently utilized by selecting biomass coal using the carbon content, hydrogen content and decomposition heat of the biomass coal as management indicators when blowing biomass coal from the tuyere.

[0062] According to this disclosure, a blast furnace operation method is provided in which biomass coal and hydrogen-based reducing gas (first reducing gas) are injected into the blast furnace, and the method uses a management indicator that has a large correlation with the replacement rate and contributes to the efficient utilization of biomass coal. This operation method reduces CO emissions from the blast furnace. ２ It is effective in efficiently reducing and has high potential for industrial application.

[0063] 10 Blast furnace 11 Standard tuyeres 12 Bosch section

Claims

1. A first injection process in which biomass coal or the biomass coal and pulverized coal, and the first reducing gas are normally blown into the inside of the blast furnace from the tuyeres, and CO ２ Gas and H ２ A method for operating a blast furnace, comprising: a second injection step of blowing a second reduced gas obtained by separating and removing at least a portion of the O gas into the interior of the blast furnace from the normal tuyeres; wherein in the first injection step, when injecting the biomass coal, the biomass coal to be blown in from the normal tuyeres is selected using carbon content, hydrogen content and decomposition heat as control indicators.

2. The method for operating a blast furnace according to claim 1, characterized in that, in the first blowing step, data on the carbon content, hydrogen content, and decomposition heat are obtained for a plurality of biomass coals that are the same raw material but have different carbonization conditions, and one or more types of biomass coal are selected from the plurality of biomass coals such that the carbon content is 0.50 or more, the hydrogen content is 0 or more and 0.05 or less, and the decomposition heat is 0 kcal / kg or more and 200 kcal / kg or less, and the selected biomass coal is blown in from the normal tuyeres.

3. The method for operating a blast furnace according to claim 1, characterized in that, in the first blowing step, data on the carbon content, hydrogen content, and decomposition heat of a plurality of biomass coals, each of which is made from different raw materials, is obtained, and one or more types of biomass coal are selected from the plurality of biomass coals such that the carbon content is 0.50 or more, the hydrogen content is 0 or more and 0.05 or less, and the decomposition heat is 0 kcal / kg or more and 200 kcal / kg or less, and the selected biomass coal is blown in from the normal tuyeres.

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