Method for operating blast furnace

Abstract

This method for operating a blast furnace includes an injection step for injecting biomass coal or biomass coal and pulverized coal, together with a hydrogen-based reducing gas, into the interior of the blast furnace from a normal tuyere. In the injection step, when the biomass coal is injected, the biomass coal to be injected from the normal tuyere is selected using a carbon content, a hydrogen content, and heat of decomposition as management indices.

Description

Operating method of blast furnace

[0001] This disclosure relates to an operating method of a blast furnace. This application claims priority based on Japanese Patent Application No. 2024-220592 filed in Japan on December 17, 2024, and incorporates its content herein by reference.

[0002] In the blast furnace method, pig iron is produced by alternately charging iron-based raw materials and coke for forming an ore layer from the furnace top in layers, and blowing hot air together with pulverized coal from the tuyere at the lower part of the blast furnace. Carbonaceous materials such as coke and pulverized coal are used as reducing agents.

[0003] In recent years, global warming has become a social problem, and as a countermeasure, reduction of the emission amount of carbon dioxide, which is one of the greenhouse gases, is required. As described above, in the blast furnace method, since a large amount of pig iron is produced using carbonaceous materials, a large amount of carbon dioxide is emitted. Therefore, in the steel industry, reducing the usage amount of carbonaceous materials has been regarded as an important issue.

[0004] The reducing agent has a role as a heat source for raising the temperature of the blast furnace charge and a role as a reducing agent for reducing iron-based raw materials in the furnace. In order to reduce the reducing agent ratio (total mass of reducing agents required to produce 1 ton of hot metal), it is necessary to improve the reduction efficiency in the furnace.

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

[0006] As a method for reducing the reducing agent ratio, a technique is known in which a hydrogen-based reducing gas (COG gas, natural gas, LPG gas, methane gas, hydrogen gas, etc.) is blown from the tuyere together with hot air to promote a hydrogen reduction reaction using hydrogen in the reducing gas and reduce 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] The present disclosure has been made in view of the above findings. The gist of the present disclosure is as follows. [1] A method for operating a blast furnace according to an aspect of the present disclosure includes a blowing step of blowing biomass charcoal or the biomass charcoal and pulverized coal, and a hydrogen-based reducing gas into the blast furnace from a normal tuyere. In the blowing step, when blowing the biomass charcoal, the biomass charcoal blown from the normal tuyere is selected using the carbon content, hydrogen content, and decomposition heat as management indicators. [2] In the method for operating a blast furnace according to [1], the blowing amount of the hydrogen-based reducing gas may be more than 365 Nm ２ converted to H ３ / t. [3] In the method for operating a blast furnace according to [1], the blowing amount of the hydrogen-based reducing gas may be more than 0 Nm ２ converted to H ３ / t and 365 Nm ３ / t or less. [4] In the method for operating a blast furnace according to [3], the blowing amount of the hydrogen-based reducing gas may be more than 0 Nm ２ converted to H ３ / t and 300 Nm ３ / t or less. [5] In the method for operating a blast furnace according to any one of [1] to [4], in the blowing step, data on the carbon content, hydrogen content, and decomposition heat of a plurality of the biomass charcoals with the same raw materials and different carbonization conditions are obtained, and one or more biomass charcoals are selected from the plurality of biomass charcoals 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 charcoal may be blown from the normal tuyere. [6] In the method for operating a blast furnace according to any one of [1] to [4], in the blowing step, data on the carbon content, hydrogen content, and decomposition heat of a plurality of the biomass charcoals with different raw materials are obtained, and one or more biomass charcoals are selected from the plurality of biomass charcoals 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 charcoal may be blown from the normal tuyere.

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

[0017] This diagram shows the relationship between the carbon replacement rate (replacement rate) of pulverized coal and the lower heating value of biomass coal, evaluated using a blast furnace mathematical model. The blast furnace mathematical model was used when the hydrogen gas injection rate was 650 Nm³. ３ This diagram shows the relationship between the carbon replacement rate (replacement rate) of pulverized biomass coal and the carbon content in the coal material with a decomposition heat of 100 kcal / kg, assuming a hydrogen gas injection rate of 650 Nm³ / t. ３ This diagram shows the relationship between the carbon replacement rate (replacement rate) of pulverized biomass coal and the hydrogen (H) content in the coal material, where the decomposition heat is 100 kcal / kg and the carbon content is 78.4% by mass, for a given amount of 650 Nm³ / t. Using a blast furnace mathematical model, the hydrogen gas injection rate was 650 Nm³ / t. ３ This diagram shows the relationship between the carbon replacement rate (replacement rate) of pulverized biomass coal and the decomposition heat of a carbon material with a carbon content of 78.4% by mass, for a given amount of 0 to 650 Nm³ / t. The results were obtained using a blast furnace mathematical model, for hydrogen gas injection rates of 0 to 650 Nm³. ３ This figure shows the change in coefficient 1 (Coef1) for the case of / t. The hydrogen gas injection rate was obtained using a blast furnace mathematical model from 0 to 650 Nm³. ３ This figure shows the change in coefficient 2 (Coef2) for the case of / t. The hydrogen gas injection rate was obtained using a blast furnace mathematical model from 0 to 650 Nm³. ３ This figure shows the change in coefficient 3 (Coef3) when / t. In the example, the hydrogen gas injection amount is 50 Nm ３ This figure shows the relationship between the estimated replacement rate and the actual replacement rate when / t is used. In the example, the hydrogen gas injection rate is 100 Nm³. ３ This figure shows the relationship between the estimated replacement rate and the actual replacement rate when / t is used. In the example, the hydrogen gas injection rate is 200 Nm. ３This figure shows the relationship between the estimated replacement rate and the actual replacement rate when / t is used. In the example, the hydrogen gas injection rate is 300 Nm. ３ This figure shows the relationship between the estimated replacement rate and the actual replacement rate in the case of / t. In the example, the hydrogen gas injection amount is 400 Nm. ３ This figure shows the relationship between the estimated replacement rate and the actual replacement rate in the case of / t. In the example, the hydrogen gas injection rate is 650 Nm. ３ This figure shows the relationship between the estimated replacement rate and the replacement rate in the case of / t. This is a schematic diagram of an example of a blast furnace used in the blast furnace operation method according to this embodiment.

[0018] A method for operating a blast furnace according to one embodiment of this disclosure (a method for operating a blast furnace according to this embodiment) will be described. The method for operating a blast furnace according to this embodiment includes a blowing step in which biomass coal or biomass coal and pulverized coal, and hydrogen-based reducing gas are blown into the inside of the blast furnace from a normal tuyeres. In this disclosure, as shown in Figure 6, the normal tuyeres 11 are tuyeres provided below the Bosch section 12 of the blast furnace 10. In Figure 6, there are two normal tuyeres 11, one on the left and one on the right, but there may be one, or three or more may be provided substantially evenly along the circumference of the blast furnace. Each step will be described.

[0019] [Injection Process] In the blast furnace operation method according to this embodiment, as an injection process, biomass coal or biomass coal and pulverized coal, and hydrogen-based reducing gas (i.e., biomass coal and hydrogen-based reducing gas, or biomass coal, pulverized coal and hydrogen-based reducing gas) are normally injected into the blast furnace from the tuyeres.

[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 replacement rate (hereinafter referred to as "replacement 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: Multiple meshes (small regions) are defined by dividing the internal region of the blast furnace in the height, radial, and circumferential directions, and the behavior of each mesh is simulated (see, for example, Non-Patent Document 1).

[0021] <Simulation Conditions> The simulation conditions are explained below. The parameters shown in Table 1 were used as the basic operating conditions (normal pulverized coal operation), with the pulverized coal normally blown in from the tuyeres completely stopped, and the amount of biomass coal and hydrogen-based reducing gas blown in, as shown in Table 2-1, were varied. At that time, the airflow rate, oxygen enrichment rate, and biomass coal ratio were adjusted so that the tapping rate, molten iron temperature, and furnace top gas temperature were the same as during basic operation. Hydrogen gas was used as the hydrogen-based reducing gas, and the hydrogen gas blowing rate, hydrogen gas blowing temperature, airflow temperature, and coke ratio were as shown in Table 2-2. 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 blown into the furnace would burn. The simulation was performed for each case (C1, C2, H, Ash, HD) shown in Table 2-1, for each hydrogen gas blowing rate of each pattern (1 to 6) shown in Table 2-2.

[0022]

[0023]

[0024]

[0025] In Table 2-1 (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.

[0026] 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.

[0027] In summary, the blast furnace mathematical model was subjected to a thermal balance calculation to simulate the question: "When biomass coal is injected instead of pulverized coal, assuming a certain hydrogen gas injection rate (one of patterns 1 to 6), how much biomass coal injection is needed to produce the same level of molten iron as in normal pulverized coal operations?" Based on the results of this thermal balance calculation, the "substitution rate" was calculated as follows.

[0028] <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.

[0029] <Relationship between replacement rate, C and H content (content or content rate) 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, the C content (mass%) in the charcoal material (biomass charcoal) (carbon content (-); 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).

[0030] 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, w is the moisture content (mass%) in the biomass charcoal (sample) before combustion, and r is the latent heat of condensation of water vapor (MJ / kg), which in this embodiment 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.

[0031] The evaluation results for each case in which the amount of hydrogen gas injected was varied, and for each case in which the biomass coal injected was varied, are shown below.

[0032] (Hydrogen gas injection volume: 650 Nm) ３(In the case of / t) First, Figure 1 shows the results of evaluating the relationship between the pulverized carbon replacement rate (replacement rate) and the lower heating value (LHV) of biomass coal, as previously proposed. Figure 1 is a plot of the relationship between the pulverized carbon replacement rate (replacement rate) and the lower heating value (LHV) of biomass coal, which is obtained by the blast furnace mathematical model described above. From Figure 1, it can be seen that the correlation with the replacement rate is low for the lower heating value, and that when the lower heating value is used as an indicator, biomass coal may not be able to be utilized sufficiently effectively. Therefore, the effects of C content, H content, Ash content, and decomposition heat were individually evaluated by simulation for each case.

[0033] Figure 2A plots the relationship between the carbon content and the replacement rate of a carbon material (biomass charcoal) 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 0.992, indicating a strong correlation. Furthermore, the above simulation shows that increasing the carbon content in the carbon material increases the replacement rate by 1.16 times (0.0116 for an increment of 0.01 (1%)) relative to the increase in carbon content in the carbon material. Figure 2B plots the relationship between the carbon replacement rate (replacement rate) of pulverized biomass charcoal and the hydrogen (H) content in a carbon 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 carbon material increases the replacement rate by 0.75 times relative to the increase in H content in the carbon material. Figure 2C plots the relationship between the carbon replacement rate (replacement rate) of pulverized biomass coal and the decomposition heat of a carbon material with a carbon content of 78.4% by mass. From the plot, it can be seen that as the decomposition heat increases, the decomposition heat increases by 4.01 × 10⁻¹⁰ for each increase in decomposition heat. －４It 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 30 kcal / kg.

[0034] 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 + 1.16 × (CB - CP) + 0.75 × (HB - HP) - 4.01 × 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.

[0035] (Hydrogen gas injection rate: 50-400 Nm) ３ (In the case of / t) Using the same procedure, if the amount of hydrogen gas injected is 50 Nm³ ３ / t, 100Nm ３ / t, 200Nm ３ / t, 300Nm ３ / t, 400Nm ３ For each case where the concentration is / t, the C content, H content, Ash content, and the effect of decomposition heat were evaluated individually.

[0036] As a result, in all cases of hydrogen gas injection, the amount of hydrogen-based reducing gas injected was 650 Nm³. ３It was found that the estimated replacement rate can be expressed by the following formula, similar to the case for / t. However, it was found that the coefficients (Coef1, Coef2, Coef3) (i.e., the degree of influence) shown in the following formula change depending on the amount of hydrogen gas injected. Estimated replacement rate = CP + Coef1 × (CB - CP) + Coef2 × (HB - HP) - Coef3 × (HDB - HDP)

[0037] The coefficients (Coef1, Coef2, Coef3) for each pattern, derived from the simulation, are shown in Table 3.

[0038]

[0039] Furthermore, the relationship between Coef1, Coef2, Coef3 and the hydrogen gas injection rate is shown in Figures 3A to 3C. As can be seen from these figures, Coef1, Coef2, and Coef3 change depending on the hydrogen gas injection rate. However, for Coef1, it can be seen that the value saturates at high hydrogen gas injection rates, although there is some variation. Upon investigating the reason for this, it was found that the hydrogen gas injection rate (H ２ The amount of hydrogen-based reducing gas injected (converted to a certain amount) is 365 Nm³. ３ At levels exceeding / t, CO gas and H ２ It was assumed that the reduction of the ore by gas would be almost 100%, and that differences in the carbon and hydrogen content of the coal material blown into the blast furnace would no longer contribute to the reduction. Therefore, in this embodiment, the amount of hydrogen gas blown into Coef1 was 365 Nm³. ３ Within the range greater than / t, it was assumed to be constant.

[0040] 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 + {Coef1 × (CB - CP) + Coef2 × (HB - HP) - Coef3 × (HDB - HDP)} where Coef1, Coef2, and Coef3 are the hydrogen gas injection rate X (Nm³) ３ When expressed as / t, it can be expressed as follows: Coef1 = 4.00 × 10 －４X + 1.02 (wherein hydrogen gas injection amount X ≤ 365 Nm) ３ / t) Coef1 = 1.16 (hydrogen gas injection rate > 365 Nm) ３ / t) Coef2=8.61×10 －９ X ３ +1.57 × 10 －５ X ２ -1.05 × 10 －２ X+3.27 Coef3=exp(5.65×10 －４ X-8.16) As described above, 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.

[0041] Based on the above considerations, in the blast furnace operation method according to this embodiment, in the blowing process, a hydrogen-based reducing gas and pulverized biomass coal, which is an auxiliary reducing agent, are normally blown in from the tuyeres. The biomass coal to be blown in from the tuyeres is selected based on the carbon content (mass%), hydrogen content (mass%), and decomposition heat (kcal / kg) of the charcoal material (biomass coal) as control indicators that affect the replacement rate. The biomass coal may be blown in together with pulverized coal (partial substitution of pulverized coal) or in place of pulverized coal (complete substitution of pulverized coal).

[0042] 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.

[0043] 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.

[0044] 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.

[0045] The particle size of biomass char can be measured using a method in accordance with JIS Z 8815:1994 "General Rules for Sieving Test Methods".

[0046] 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.

[0047] 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.

[0048] 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 produced 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).

[0049] 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.

[0050] <<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 tuyeres during the blowing process. However, the selection method is not limited to the method described below.

[0051] (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 carbon content, hydrogen content, and decomposition heat of the biomass charcoal produced differ by 1.5% or more for carbon content, 0.75% or more for hydrogen content, and 25 kcal / kg or more for decomposition heat. By investigating the average values ​​of the carbon content, hydrogen content, and decomposition heat of the biomass charcoal produced under each carbonization condition in advance, it is possible to determine whether the carbonization conditions are the same or different. Biomass charcoal produced under the same manufacturing conditions (the same type of biomass material, carbonization conditions, and carbonization equipment) can be considered to have the same carbon content, hydrogen content, and decomposition heat. That is, when selecting one type of biomass charcoal, biomass charcoal produced under manufacturing conditions in which the carbon content is 50% by mass or more (carbon content of 0.50 or more), the hydrogen 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, hydrogen content and decomposition heat of each type, in a predetermined mass ratio, so that the average carbon content, hydrogen content and decomposition heat of the combined biomass charcoal become the predetermined carbon content, hydrogen content and decomposition heat.

[0052] (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.

[0053] 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.

[0054] (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 carbon content of 50% by mass or more, a hydrogen content of 0% by mass or more and 5% by mass or less, and a decomposition heat of 0 kcal / kg or more and 200 kcal / kg or less.

[0055] (Injection of hydrogen-based 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.

[0056] In the operating method according to this embodiment, in addition to the hot air mentioned above, a hydrogen-based reducing gas is blown into the blast furnace. By blowing in the hydrogen-based reducing gas along 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.

[0057] <Hydrogen-based reducing gases> Hydrogen-based reducing gases are gases in which H is present in an elemental composition ratio of 30 mol% or more, and which exist 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 cause a thermal decomposition reaction 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 hydrogen-based reducing gas is 50 mol% or more. Also, the hydrogen-based reducing gas may contain other gases (e.g., N) (without impairing the effects of this embodiment). ２ A mixed gas with (gas) is also acceptable. The amount of hydrogen-based reducing gas injected is important in terms of improving the reduction rate of carbon consumption per unit, H ２ Converted to 0 Nm ３ It will be set to over / t. In terms of being able to blow in a large amount of biomass coal, it will be 365 Nm ３ / t or less or 300Nm ３ It is preferable that the amount is less than or equal to / t. On the other hand, when enjoying the carbon reduction effect of blast furnaces through hydrogen reduction and then adding the carbon reduction effect of using biomass coal, it is preferable that the amount is 300 Nm ３ / t or more than 365Nm ３ It is greater than / t. However, if the amount of material being blown in is too much, it becomes difficult to satisfy the constraints of the tuyeres tip combustion temperature and the furnace top gas temperature, so the amount of biomass coal that can be blown in is limited, and therefore preferably 900 Nm ３ The amount is less than or equal to / t. Furthermore, while the hydrogen-based reducing gas may be injected at room temperature, it is preferable that it be injected in a heated state for heat supply to the blast furnace. For example, 500°C or higher, 1000°C or higher, or 1200°C or higher. The hydrogen-based reducing gas is supplied from outside the blast furnace system. For example, it can be heated from a tank storing the hydrogen-based reducing gas using a heater normally connected to a tuyere as needed, and then injected into the blast furnace through the tuyere.

[0058] (Example 1) For the biomass coal types shown in No. 1 to 3 of Table 4 (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 of 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, assuming a blast furnace operation method in which biomass coal and / or pulverized coal, and hydrogen gas as a hydrogen-based reducing gas, are normally blown into the blast furnace from the tuyeres, the pulverized coal blowing operation parameters shown in Table 5 were used as a reference for each hydrogen gas blowing amount, and the pulverized coal normally blown in from the tuyeres was completely stopped, while the amount of biomass coal blown in was increased, and the airflow rate, oxygen enrichment rate, and biomass coal ratio were adjusted so that the amount of iron tapped, molten iron temperature, and top gas temperature were the same as during basic operation under the condition of a constant coke ratio. The biomass charcoal was assumed to be below the 200-mesh sieve size (74 μm), and it was assumed that all of the biomass charcoal blown into the furnace would be burned. No. 0 in Table 4 represents the standard pulverized charcoal properties.

[0059]

[0060]

[0061] 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), the carbon content CB(-) of the biomass coal, the hydrogen content HB(-) of the biomass coal, and the decomposition heat HDB (kcal / kg): Estimated replacement rate = CP + {Coef1 × (CB - CP) + Coef2 × (HB - HP) - Coef3 × (HDB - HDP)} where Coef1, Coef2, and Coef3 are the hydrogen gas injection rate X (Nm³). ３ When expressed as / t, it can be expressed as follows: Coef1 = 4.00 × 10 －４ X + 1.02 (Hydrogen gas injection rate ≤ 365 Nm) ３ / t) Coef1 = 1.16 (hydrogen gas injection rate > 365 Nm) ３ / t) Coef2=8.61×10 －９ X３ +1.57 × 10 －５ X ２ -1.05 × 10 －２ X+3.27 Coef3=exp(5.65×10 －４ X-8.16)

[0062] Figures 4A to 4F show the relationship between the estimated replacement rate calculated using the above formula when using commercially available biomass coal and the replacement rate evaluated by the blast furnace mathematical model, for each hydrogen gas injection rate. As can be seen from Figures 4A to 4F, 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 hydrogen-based reducing gas, are normally injected into the blast furnace from the tuyeres, 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 injecting biomass coal from the normal tuyeres.

[0063] According to this disclosure, a blast furnace operation method is provided in which biomass coal and hydrogen-based 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].

[0064] 10 Blast furnace 11 Standard tuyeres 12 Bosch section

Claims

1. A method for operating a blast furnace, comprising a blowing step in which biomass coal or the biomass coal and pulverized coal, and hydrogen-based reducing gas are blown into the inside of the blast furnace from a normal tuyeres, wherein in the blowing step, 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 amount of hydrogen-based reducing gas injected is H ２ Converted to 365 Nm ３ The method for operating a blast furnace according to claim 1, characterized in that the amount is greater than / t.

3. The amount of hydrogen-based reducing gas injected is H ２ Converted to 0 Nm ３ / t over 365Nm ３ The method for operating a blast furnace according to claim 1, characterized in that the amount is less than or equal to / t.

4. The amount of hydrogen-based reducing gas injected is H ２ Converted to 0 Nm ３ / t over 300Nm ３ The method for operating a blast furnace according to claim 3, characterized in that the amount is less than or equal to / t.

5. The method for operating a blast furnace according to any one of claims 1 to 4, characterized in that, in the 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 coals 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 coals are blown in from the normal tuyeres.

6. The method for operating a blast furnace according to any one of claims 1 to 4, characterized in that, in the blowing step, data on the carbon content, hydrogen content, and decomposition heat of a plurality of biomass coals whose raw materials are different from each other is obtained, one or more types of biomass coals 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 coals are blown in from the normal tuyeres.

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