Blast furnace operation method

Abstract

To reduce the emission of carbon dioxide by suppressing the increase of carbon consumption in an operation method of a blast furnace in which a large amount of hydrogen-based reducing gas is blown.SOLUTION: An operation method of a blast furnace in which a hydrogen-based reducing gas is blown so that a blown amount of hydrogen is 250 (Nm3 / pig-ton) or more includes a reduction step in which an iron source raw material is reduced to at least wustite in the reduction furnace to produce reduced iron, and a charging step in which the reduced iron obtained in the reduction step is charged from the top of the blast furnace.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace to produce pig iron by reducing an iron source material while injecting a hydrogen-based reducing gas. [Background technology]

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

[0003] In recent years, global warming has become a social issue, and as a countermeasure, there is a demand for reducing emissions of carbon dioxide, one of the greenhouse gases. As mentioned above, the blast furnace method uses carbonaceous materials to produce large amounts of pig iron, which results in the emission of large amounts of carbon dioxide. Therefore, reducing the amount of carbonaceous materials used is considered an important issue in the steel industry.

[0004] As a method for reducing the reducing agent ratio, a technique is known in which a hydrogen-based reducing gas is blown in together with hot air from the tuyere to promote the hydrogen reduction reaction using the hydrogen in the reducing gas, thereby reducing the direct reduction reaction.

[0005] Since hydrogen functions as a reducing gas in a blast furnace and not as a fuel, and the reduction reaction with hydrogen is an endothermic reaction, there is concern that injecting a large amount of hydrogen will disrupt the heat balance in the furnace. Specifically, in normal blast furnace operation using pulverized coal injection, if the injection rate of hydrogen-based reducing gas is increased while maintaining the molten iron temperature, iron tapping rate, blast temperature, and temperature before the tuyere constant, the hydrogen injection rate: 250 (Nm 3 The injection amount of hydrogen-based reducing gas reaches its limit at about 1 / pig-ton, and even if the blast rate, pulverized coal ratio, and oxygen enrichment rate are adjusted, the molten iron temperature cannot be maintained at the desired temperature, which causes problems in the production of pig iron. Therefore, a large amount of hydrogen-based reducing gas (hydrogen injection amount: 250 (Nm 3When blowing in air at a temperature of 1 / pig-ton or more, sensible heat compensation must be performed at the same time.

[0006] Here, known methods for sensible heat compensation include raising the blast temperature, decreasing the oxygen enrichment rate to increase the blast consumption rate, and injecting preheated reducing gas. However, current operating methods raise the blast temperature close to the upper limit, leaving almost no room for raising it. Furthermore, current operating methods lower the oxygen enrichment rate close to the lower limit, leaving almost no room for lowering it. Furthermore, injecting hydrogen-based reducing gas preheated to 1000°C or higher into a blast furnace that blows high-temperature air at 1200°C into the furnace will excessively increase the temperature in the combustion zone in front of the tuyere, increasing process operation risks and raising concerns about hydrogen embrittlement of the blast furnace equipment.

[0007] Patent Document 1 discloses a method for producing reduced iron by producing high-temperature gas mainly composed of CO and HO by combustion and gasification of coal-based fuel in a gasifier with a gas mainly composed of oxygen, and injecting this high-temperature gas into a reducing furnace. The technology disclosed in Patent Document 1 assumes the use of a coal-based reducing material, and does not assume the injection of a large amount of hydrogen-based reducing gas.

[0008] Patent Document 2 discloses a method of operating a blast furnace in which a reducing agent containing hydrogen is blown in and preheated gas is blown into the furnace from the shaft, thereby raising the furnace top gas temperature to 110°C or higher. However, the hydrogen blowing amount converted from the example disclosed in Table 1 of Patent Document 2 is 200 (Nm 3 / pig-ton) or less, and no consideration is given to the issues that arise when a large amount of hydrogen-based reducing gas is injected. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 58-171510 [Patent Document 2] Patent No. 4661890 [Patent Document 3] Japanese Patent Application Publication No. 8-253801 [Patent Document 4] Patent No. 5549227 [Patent Document 5] Japanese Patent Publication No. 2020-45508 [Non-patent literature]

[0010] [Non-Patent Document 1] Iron and Steel, Vol. 68 (1982), No. 15, p. 2369 (Haneda et al.) [Non-patent document 2] Iron and Steel, Vol. 62 (1976), No. 3, p. 315 (Hara et al.) [Non-patent document 3] Iron and Steel, Vol. 74 (1988), No. 12, p. 2254 (Yamaoka et al.) Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention aims to suppress an increase in carbon consumption and reduce carbon dioxide emissions in a blast furnace operation method in which a large amount of hydrogen-based reducing gas is injected. [Means for solving the problem]

[0012] In order to solve the above problems, the method of operating a blast furnace according to the present invention provides: (A1) a hydrogen injection rate of 250 (Nm 3 The method for operating a blast furnace includes injecting a hydrogen-based reducing gas into a reducing furnace so that the reduction ratio becomes equal to or greater than 1 / pig-ton. The method comprises a reduction step of reducing an iron source material to at least wustite in a reducing furnace to produce reduced iron, and a charging step of charging the reduced iron obtained in the reduction step into the blast furnace.

[0013] (A2) The reduction rate of the reduced iron obtained in the reduction step is X (%), and the amount of hydrogen injection is Y (Nm 3 / pig-ton), the hydrogen-based reducing gas is blown in within the range not exceeding the following formula (1), and the above formula (1) is defined as the hydrogen blowing amount (Nm 3 The method for operating a blast furnace according to (A1) above, characterized in that relationship information defining the relationship between the reduction rate (kg / pig-ton) and the blast furnace carbon consumption (kg / pig-ton) is acquired for each reduction rate, and the calculation is derived based on the acquired results. Y = aX + b (where a and b are constants) Equation (1)

[0014] (A3) From the above-mentioned related information, the hydrogen injection rate (Nm m) corresponding to the minimum value of the blast furnace carbon consumption (kg / pig-ton) 3 / pig-ton) was calculated, and the hydrogen injection amount (Nm 3 The method for operating a blast furnace according to (A2) above, characterized in that the formula (1) is derived based on the ratio of the total weight of slag to the total weight of slag (pig-ton) and the reduction rate.

[0015] (A4) The method for operating a blast furnace according to any one of (A1) to (A3), characterized in that the reduction step is carried out by injecting dehumidified blast furnace exhaust gas obtained by subjecting the blast furnace top exhaust gas to a dehumidification treatment into the reducing furnace.

[0016] (A5) The method for operating a blast furnace according to (A4), characterized in that the reduction step is carried out by further injecting into the reducing furnace, in addition to the dehumidified blast furnace exhaust gas, dehumidified reducing furnace gas obtained by subjecting the top exhaust gas of the reducing furnace to a dehumidification treatment.

[0017] (A6) The method for operating a blast furnace according to (A4) or (A5), characterized in that the reduction step is carried out by further injecting a hydrogen-based reducing gas into the reducing furnace from a supply source different from the blast furnace and the reducing furnace.

[0018] (A7) The method for operating a blast furnace according to (A4), characterized in that the reduction step is carried out by injecting dehumidified blast furnace exhaust gas obtained by subjecting blast furnace top exhaust gas to the dehumidification treatment and carbon dioxide separation treatment into the reducing furnace.

[0019] (A8) The method for operating a blast furnace according to (A5), characterized in that the reduction step is carried out by blowing into the reducing furnace a dehumidified blast furnace exhaust gas obtained by subjecting a top exhaust gas of the blast furnace to the dehumidification treatment and carbon dioxide separation treatment, and a dehumidified reducing furnace gas obtained by subjecting a top exhaust gas of the reducing furnace to the dehumidification treatment and carbon dioxide separation treatment.

[0020] (A9) The method for operating a blast furnace according to (A1) above, wherein the charging step is a step of charging reduced iron together with an iron source raw material that has not been subjected to a reduction treatment, and includes a pre-preparation step of determining a usage rate of reduced iron in the charging step in advance, and the pre-preparation step includes a first pre-preparation step of performing at least one of a step of obtaining a first relationship between the usage rate of reduced iron and a blast furnace carbon consumption reduction rate for each reduction rate of reduced iron and a step of obtaining a second relationship between the usage rate of reduced iron and a sole-loss carbon amount for each reduction rate of reduced iron, and a second pre-preparation step of determining a usage rate of reduced iron based on the first relationship and / or the second relationship obtained in the first pre-preparation step, and wherein the charging step is performed at the usage rate determined in the pre-preparation step. [Effects of the Invention]

[0021] According to the present invention, by charging reduced iron reduced to at least wüstite or higher into a blast furnace, the problem of heat shortage caused by the injection of a large amount of hydrogen-based reducing gas can be avoided, and as a result, an increase in carbon consumption can be suppressed, thereby reducing carbon dioxide emissions. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of a blast furnace body excluding auxiliary equipment. [Figure 2] 1 is a graph showing the relationship between the hydrogen injection amount and the blast furnace carbon consumption amount, organized for each reduction degree. [Figure 3] 1 is a graph showing how to achieve an optimum amount of hydrogen blown in accordance with the reduction rate. [Figure 4]FIG. 10 is a schematic diagram of a facility for carrying out a process for coupling a blast furnace and a reducing furnace (third embodiment). [Figure 5] 10 shows the results of a simulation of the relationship between the reduction rate of reduced iron obtained in a reduction furnace and that of reduced iron charged into a blast furnace (third embodiment). [Figure 6] FIG. 10 is a schematic diagram of a facility for carrying out a process for coupling a blast furnace and a reducing furnace (fourth embodiment). [Figure 7] 6 shows the results of a simulation corresponding to FIG. 5 (fourth embodiment). [Figure 8] 10 shows the results of an evaluation of whether or not operation is possible using a combined process of a blast furnace and a reduction furnace (fourth embodiment). [Figure 9] FIG. 1 is a schematic diagram of an equipment for realizing a blast furnace and reduction furnace coupling process. [Figure 10] 1 is a graph showing the amount of hydrogen blown in to achieve a desired reduction rate. [Figure 11] FIG. 10 is a schematic diagram of equipment for realizing a combined process of a blast furnace and a reducing furnace (sixth embodiment). [Figure 12] 8, and shows the results of an evaluation of whether or not operation is possible using a combined process of a blast furnace and a reduction furnace (sixth embodiment). [Figure 13] 10 shows the results of a simulation of the relationship between the reduced iron usage rate and the blast furnace carbon consumption reduction rate. [Figure 14] 10 shows the results of a simulation of the relationship between the reduced iron usage rate and the amount of solute-loss carbon. DETAILED DESCRIPTION OF THE INVENTION

[0023] (First embodiment) 1 is a schematic diagram of a furnace body excluding ancillary equipment of a blast furnace. The furnace body 100 includes a furnace throat K, a shaft L connected to the lower end of the furnace throat K, a furnace belly M connected to the lower end of the shaft L, a bosh N connected to the lower end of the furnace belly M, a tuyere O connected to the lower end of the bosh N, and a hearth bottom P connected to the lower end of the tuyere O. The shaft L is formed in a tapered shape that gradually expands in diameter from the top to the bottom.

[0024] A tuyere 101 is formed in the tuyere section O, and a hydrogen-based reducing gas and hot air can be blown into the furnace body 100 through this tuyere 101. The operating method of the blast furnace of this embodiment is premised on the injection of a large amount of hydrogen-based reducing gas, and the hydrogen injection rate is set to 250 (Nm 3 The blast furnace is operated so that the hydrogen injection rate required to produce 1 ton of pig iron is 250 Nm 3 The hydrogen-based reducing gas may be hydrogen gas itself, or may be a hydrogen-containing gas such as COG gas, natural gas, LPG gas, or methane gas. When a hydrogen-containing gas is used as the hydrogen-based reducing gas, the amount of hydrogen-containing gas injected is converted into the amount of hydrogen injected, and the amount of hydrogen injected is calculated to be 250 (Nm 3 Operate so that the net weight is at least 1 / pig-ton.

[0025] A rotating chute (not shown) that rotates around a vertical axis is provided at the furnace top 102 of the furnace body 100, and reduced iron and coke raw materials are charged alternately in layers from this rotating chute toward the interior of the furnace body 100. The reduced iron is obtained by reducing an iron source raw material to at least wustite (FeO) in advance. This may be wustite (FeO) or iron oxide with a higher reduction rate than wustite (FeO). The iron source raw material may be sintered ore, pellets, lump ore, or unsintered carbon-containing agglomerated ore. The reduction rate of reduced iron is defined by the following formula, and when a typical iron source raw material is reduced to wustite (FeO), the reduction rate is approximately 30 to 33%. (Reduction rate) = (1 - (amount of unreduced oxygen in reduced iron) / (amount of reduced oxygen in iron source material)) x 100 (%) However, the amounts of unreduced oxygen and reduced oxygen can be calculated from the analytical values ​​of the iron oxide components (Fe2O3, Fe3O4, FeO) in the reduced iron and iron source material, respectively, using the following formulas. (Amount of unreduced oxygen in reduced iron) ≡ (weight fraction of Fe2O3 in reduced iron) × 48 / 160 + (weight fraction of Fe3O4 in reduced iron) × 64 / 232 + (weight fraction of FeO in reduced iron) × 16 / 72 (Amount of oxygen to be reduced in the iron source raw material) ≡ (weight fraction of Fe2O3 in the iron source raw material) × 48 / 160 + (weight fraction of Fe3O4 in the iron source raw material) × 64 / 232 + (weight fraction of FeO in the iron source raw material) × 16 / 72 The meanings of reduced iron and reduction rate are the same in other embodiments. The coke raw material may contain ferro coke in addition to coke.

[0026] By charging reduced iron and coke raw materials into a blast furnace, a lumpy zone 103 can be formed at the top of the throat K and shaft L. The present invention can also be applied to a bell blast furnace that does not have a rotating chute. As the lumpy zone 103 descends within the furnace, it is heated by hot air blown in from the tuyere 101, and a roughly conical cohesive zone 104 is formed from the bosh N toward the bottom of the shaft L.

[0027] Iron 105 molten in the cohesive zone 104 passes through the dripping zone 106 and descends to become molten pig iron 107, which is accumulated at the hearth P. Coke and the like also pass through the dripping zone 106 and descend to pile up at the hearth P, forming a conical deadman 109 on top of the molten pig iron 107. A tap hole 108 is formed at the hearth P, and the molten pig iron 107 accumulated at the hearth P can be taken out of the blast furnace through the tap hole 108.

[0028] According to the operating method of this embodiment, the hydrogen injection amount: 250 (Nm 3 In a blast furnace operation method in which a hydrogen-based reducing gas is injected so that the total heat loss is at least 1 / pig-ton, the problem of heat shortage caused by the injection of a large amount of hydrogen-based reducing gas can be avoided by using reduced iron reduced to at least wüstite (FeO) as the burden material. As a result, the carbon consumption derived from coal used as a reducing agent can be reduced, thereby reducing carbon dioxide emissions in blast furnace operation.

[0029] (Second embodiment) As explained in the first embodiment, by charging reduced iron obtained by reducing the iron source material in advance into the blast furnace, the hydrogen injection amount (Nm3 This can avoid the problem of insufficient heat caused by an increase in the number of pigs. However, the hydrogen injection amount (Nm 3 If the hydrogen injection rate (Nm / pig-ton) is excessively increased, the endothermic reaction due to hydrogen reduction will exceed the effect of charging reduced iron (the effect of resolving the heat shortage), and the furnace top gas temperature and molten iron temperature will fall below the desired temperatures, so the carbon consumption of the blast furnace must be increased. 3 The critical point at which an increase in the reduction ratio (kg / pig-ton) no longer has the effect of reducing blast furnace carbon consumption (kg / pig-ton) was identified for each reduction ratio, and a method was investigated for injecting hydrogen-based reducing gas into the blast furnace within a range that does not exceed this critical point.

[0030] To quantitatively evaluate the effect of hydrogen-based reducing gas injection and reduced iron charging on reducing blast furnace carbon consumption (kg / pig-ton), the inventors conducted a simulation using a blast furnace mathematical model that theoretically estimates furnace conditions and predicts operational performance. The blast furnace mathematical model used was the one disclosed in Non-Patent Document 1. The simulation was based on the parameters shown in Table 1. The coke rate (however, the pulverized coal rate was fixed at 0) and the blast rate were used as adjustment means. The oxygen enrichment rate (in other words, the temperature before the tuyere) was adjusted so that the blast furnace carbon consumption (kg / pig-ton) was minimized for a given hydrogen gas consumption rate and reduction rate. The composition of the reduced iron corresponding to each reduction rate was set as shown in Table 2. A reduction rate of 32% corresponds to the case where all of the iron oxide contained in the reduced iron is wüstite (FeO). [Table 1] [Table 2]

[0031] The simulation results are organized by reduction rate and shown in Figure 2. The horizontal axis of Figure 2 is the amount of hydrogen injected into the blast furnace (Nm 3 / pig-ton), the left vertical axis is the blast furnace carbon consumption (kg / pig-ton), and the right vertical axis is the blast furnace carbon consumption reduction rate (%). The blast furnace carbon consumption reduction rate is the reduction rate compared to conventional operation (operation based on pulverized coal injection) without injecting hydrogen-based reducing gas, and the blast furnace carbon consumption in this conventional operation (hereinafter referred to as standard operation) is 425 (kg / pig-ton). Unreduced iron source raw materials are charged into the furnace, and the hydrogen injection rate is approximately 450 (Nm 3 When a blast furnace is operated under this condition, the reduction effect of blast furnace carbon consumption (kg / pig-ton) reaches a limit. On the other hand, reduced iron reduced to wustite (FeO) or more was charged into the furnace, and the hydrogen injection rate was 250 (Nm 3 When a blast furnace is operated under conditions of 1 / pig-ton or more, the hydrogen injection rate (Nm) is higher than when the blast furnace is operated with unreduced iron raw materials charged into the furnace. 3 When comparing carbon consumption (kg / pig-ton), it is possible to reduce carbon consumption (kg / pig-ton). 3 The graph defining the relationship between the amount of carbon consumed in a blast furnace (kg / pig-ton) and the amount of carbon consumed in a blast furnace (kg / pig-ton) corresponds to the "relationship information" set forth in claim 2. The data format of the relationship information is not limited to a graph, and may be in the form of a data table.

[0032] Also, from Figure 2, the hydrogen injection rate (Nm 3 / pig-ton) can be estimated for each reduction rate. Specifically, when the hydrogen injection rate is 250 (Nm 3 / pig-ton), the graph of each reduction rate is a downward convex graph (in other words, the blast furnace carbon consumption decreases as the hydrogen injection rate increases until it reaches a predetermined value, and increases as the hydrogen injection rate increases once it exceeds the predetermined value). Therefore, from this relationship information, it is possible to identify the minimum value of the blast furnace carbon consumption (kg / pig-ton) for each reduction rate. Then, the hydrogen injection rate (Nm 3 / pig-ton is read from Figure 2, and this hydrogen injection amount (Nm 3 By fitting the relationship between the reduction rate and the amount of hydrogen injected (Nm) to minimize the carbon consumption (kg / pig-ton) of the blast furnace for each reduction rate, 3 / pig-ton).

[0033] Equation (1) is a linear function derived from Figure 2. The correlation coefficient of the linear function was 0.9993. Y=-13.8X+1160...Formula (1) where Y is the amount of hydrogen blown (Nm 3 / pig-ton), and X is the reduction rate (%).

[0034] The reduction rate (%) of the reduced iron is substituted for X in equation (1) to calculate Y, and the hydrogen injection rate (Nm 3 By setting the hydrogen injection amount (Nm 3 The effect of reducing the blast furnace carbon consumption (kg / pig-ton) by increasing the hydrogen injection rate (Nm 3 / pig-ton) is 250 (Nm 3 The operation of this embodiment can be carried out within a range where the mass fraction is equal to or greater than the mass fraction of the pig-ton and does not exceed the value of formula (1). It goes without saying that if the specifications on which the simulation is based change, the constants in formula (1) will also change.

[0035] In this embodiment, when the reduction rate reaches 70%, the hydrogen injection rate (Nm m) corresponding to the minimum value of the blast furnace carbon consumption (kg / pig-ton) is 3 / pig-ton) is 250 (Nm 3 / pig-ton). Therefore, when the specifications shown in Tables 1 and 2 are used as a premise, the upper limit of the reduction rate must be set to 70% to carry out the operation of this embodiment. However, since this upper limit varies depending on the specifications, for example, even when the reduction rate is 70% or more, the hydrogen injection amount (Nm 3 / pig-ton) is 250 (Nm 3 / pig-ton) or more, the hydrogen injection amount (Nm 3 When the minimum value of (pig-ton / pig-ton) can be confirmed, the upper limit of the reduction rate can be set to more than 70%, and the operating method of this embodiment can be carried out.

[0036] (Third embodiment) As explained in the first and second embodiments, the carbon consumption of the blast furnace can be reduced by injecting a hydrogen-based reducing gas and charging reduced iron at the same time. However, if the carbon consumption during the reduction of the reduced iron increases, the benefit of reducing the carbon consumption of the blast furnace is diminished. Therefore, the present inventors have investigated a method of reducing reduced iron by using the top gas of the blast furnace (hereinafter also referred to as BFG gas).

[0037] FIG. 4 is a schematic diagram of equipment for realizing the process of connecting a blast furnace and a reducing furnace according to this embodiment. A reduction furnace 200 is provided upstream of the blast furnace 100. The reduction furnace 200 may be a shaft furnace. The BFG gas discharged from the top of the blast furnace 100 mainly contains carbon monoxide gas, carbon dioxide gas, hydrogen gas, nitrogen gas, and water vapor. By subjecting this BFG gas to a dehumidification treatment (cooling treatment), the water vapor contained in the BFG gas can be converted into HO and removed. Since the temperature of the BFG gas from which HO has been removed drops to less than 100°C, it is heated before being injected into the reduction furnace 200. Hereinafter, the BFG gas after the dehumidification treatment and injected into the reduction furnace 200 may be referred to as dehumidified blast furnace exhaust gas. Because the dehumidified blast furnace exhaust gas contains hydrogen gas, it can reduce the iron source material to reduced iron. The dehumidified blast furnace exhaust gas is subjected to a dust removal treatment before being injected into the reduction furnace 200.

[0038] Here, the present inventors used a mathematical model (see Non-Patent Documents 2 and 3) to verify whether or not the iron source raw material can be reduced to wüstite (FeO) or more by injecting dehumidified blast furnace exhaust gas as a reducing gas into the reduction furnace 200. This mathematical model is the same as the blast furnace mathematical model disclosed in Non-Patent Document 1 in that it theoretically estimates the state inside the furnace and predicts the operational performance.

[0039] Table 3 shows the prerequisites (operating conditions of the reduction furnace) for verification using the mathematical model. [Table 3] The calculation target for the simulation was a space equivalent to the reduction reaction zone of the reduction furnace 200, the reducing gas was the total amount of BFG gas after desorption, and the blast temperature was a typical temperature (900°C) for commercial shaft furnaces. In addition, as will be described in detail later, the simulation was also designed to take into account an operation of recycling a portion of the top exhaust gas, which is common in commercial shaft furnaces.

[0040] FIG. 5 shows the results of a simulation, with the horizontal axis representing the reduction rate (A%) of the reduced iron charged into the blast furnace 100, and the vertical axis representing the reduction rate (A'%) of the reduced iron obtained by injecting into the reducing furnace 200 dehumidified blast furnace exhaust gas derived from the BFG gas generated when the blast furnace 100 is operated with this reduced iron charged (temperature before the tuyere: 2000°C).

[0041] The coupling process of the blast furnace 100 and the reducing furnace 200 of this embodiment can be realized under the conditions plotted in the region above the dotted line (i.e., the region excluding the mismatch region indicated by hatching). In other words, it was found that there are operating conditions under which the iron source material can be reduced to reduced iron of wüstite (FeO) or higher by injecting dehumidified blast furnace exhaust gas as a reducing gas into the reducing furnace 200.

[0042] Referring to the same figure, 353 (Nm 3 When a blast furnace is operated with a hydrogen gas consumption rate of 1 / pig-ton, the reduction effect of the blast furnace carbon consumption compared to the standard operation described in the second embodiment is about 17%. In contrast, 353 (Nm 3 When a blast furnace is operated with a hydrogen gas consumption rate of 1 / pig-ton, the generated BFG gas is dehumidified, and the iron source raw material is reduced in the reduction furnace 200, reduced iron with a reduction rate of about 40% is obtained. By charging this reduced iron into the blast furnace, it is possible to reduce the carbon consumption of the blast furnace by about 27% compared to standard operation.

[0043] As described above, according to the present embodiment, the reducing furnace 200 is provided upstream of the blast furnace 100, and the dehumidified blast furnace exhaust gas obtained by dehumidifying the BFG gas generated from the blast furnace 100 is injected into the reducing furnace 200 as a reducing gas. This makes it possible to produce reduced iron that has been reduced to wüstite (FeO) or more without injecting a hydrogen-based reducing gas from outside the connection process between the blast furnace 100 and the reducing furnace 200. This makes it possible to effectively reduce carbon consumption.

[0044] (Fourth embodiment) A fourth embodiment of the present invention will be described with reference to Fig. 6. Fig. 6 is a schematic diagram of equipment for realizing a process for connecting a blast furnace and a reducing furnace according to this embodiment. The method for operating a blast furnace according to this embodiment is characterized in that it adds a technology for reusing, as reducing gas in the reducing furnace 200, gas obtained by dehumidifying the furnace top exhaust gas discharged from the reducing furnace 200 (hereinafter also referred to as dehumidified reducing furnace gas), as a reducing gas in the reducing furnace 200, compared to the method for operating a blast furnace according to the third embodiment. That is, as described in the third embodiment, when only dehumidified blast furnace exhaust gas is injected into the reducing furnace 200, operation is not possible in the mismatch region shown by hatching in Fig. 5. However, by further injecting dehumidified reducing furnace gas into the reducing furnace 200, the range of operation can be expanded.

[0045] The top flue gas of the reducing furnace 200 mainly contains carbon monoxide gas, carbon dioxide gas, hydrogen gas, nitrogen gas, and water vapor. By subjecting the top flue gas of the reducing furnace 200 to a dehumidification treatment (cooling treatment), the water vapor contained in the top flue gas is removed as HO, and a dehumidified reducing furnace gas can be obtained. Since the temperature of the dehumidified reducing furnace gas has been reduced by the cooling treatment, it is heated before being blown into the reducing furnace 200. As described above, in this embodiment, the reduction treatment of the iron source raw material is performed using the dehumidified blast furnace flue gas of the blast furnace 100 and the hydrogen gas contained in the dehumidified reducing furnace gas of the reducing furnace 200. The top flue gas of the reducing furnace 200 is subjected to a dedusting treatment before being recirculated to the reducing furnace 200.

[0046] When the amount of dehumidified blast furnace exhaust gas injected into the reducing furnace 200 is defined as S1 and the amount of recovered exhaust gas from the top of the reducing furnace 200 is defined as S2, the effect of exhaust gas circulation was evaluated by simulation using the "circulation rate" defined by the following equation (2). For the evaluation, the mathematical model described in the third embodiment was used. Circulation rate=S2 / S1·····························Formula (2)

[0047] 7 shows the results of a simulation corresponding to FIG. 5. Referring to FIG. 7, when dehumidified reducing furnace gas is not used (that is, when reduced iron is produced using only dehumidified blast furnace exhaust gas as shown in the third embodiment), for example, 353 (Nm 3 When the blast furnace is operated with a hydrogen gas consumption rate of 353 (Nm / pig-ton) and the iron source raw material is reduced by injecting dehumidified blast furnace exhaust gas into the reducing furnace 200, the reduction rate remains at about 40%. On the other hand, when dehumidified reducing furnace gas is further injected in addition to the dehumidified blast furnace exhaust gas under the condition of a circulation rate of 25%, reduced iron with a reduction rate of about 45% is obtained. In other words, in the third embodiment, 3Even if a blast furnace is operated with a hydrogen gas consumption rate of 1 / pig-ton, it is not possible to obtain reduced iron with a reduction rate of 45%. However, according to the operating method of this embodiment, reduced iron with a reduction rate of 45% can be obtained without changing the hydrogen gas consumption rate. In other words, compared to the third embodiment, reduced iron with a higher reduction rate can be produced without increasing the amount of hydrogen-based reducing gas injected from outside the consolidation process. Furthermore, as will be described later, the effect of reducing blast furnace carbon consumption can be further enhanced.

[0048] FIG. 8 shows the results of an evaluation of whether or not the blast furnace 100 and the reduction furnace 200 can be operated in a connected process according to this embodiment. The hatched area inside the dotted line is the range in which the connected operation described in this embodiment is possible. In other words, when reduced iron with a reduction rate of T% is charged into the blast furnace, the amount of hydrogen injected into the blast furnace 100 (Nm 3 This shows the range in which reduced iron with a reduction rate of T% can be obtained without changing the reduction ratio (pig-ton).

[0049] For example, 350 (Nm 3 When a blast furnace is operated with a hydrogen gas consumption rate of 1000 kJ / pig-ton, by using reduced iron with a reduction rate of 45% produced by applying the consolidation process of this embodiment, the reduction rate of carbon consumption in the blast furnace can be increased from 17% to 32% compared to the case where reduction is not performed.

[0050] Also, from Fig. 8, the hydrogen injection rate (Nm 3 The higher the H fraction in the exhaust gas from the reduction furnace 200, the higher the effect of recovering the reducing power of the dehumidified reduction furnace gas by dehumidification, and thus the higher the reduction rate of the reduced iron produced.

[0051] (Fifth embodiment) As described in the fourth embodiment, by injecting dehumidified blast furnace exhaust gas and dehumidified reducing furnace gas into the reducing furnace 200, it is possible to perform the coupled operation within the hatched region in FIG. 8 . However, in the coupled operation of the fourth embodiment, the coupled operation below this region cannot be performed due to a shortage of hydrogen-based reducing gas. For example, reduced iron with a reduction rate of 55%, indicated by an asterisk in FIG. 8 , cannot be produced in the coupled operation of the fourth embodiment due to a shortage of hydrogen-based reducing gas. Naturally, the same problem occurs in the coupled process of the third embodiment, in which only dehumidified blast furnace exhaust gas is injected into the reducing furnace 200.

[0052] The present embodiment aims to produce reduced iron with a higher reduction rate and expand the range of operation by supplementing the hydrogen-based reducing gas that is insufficient in the reducing furnace 200. Fig. 9 is an explanatory diagram illustrating the connection process of the blast furnace and the reducing furnace according to the present embodiment.

[0053] FIG. 9 is a schematic diagram of equipment for realizing the process of connecting a blast furnace and a reducing furnace according to this embodiment. In the connection process of this embodiment, three routes for blowing hydrogen-based reducing gas into the reduction furnace 200 are provided. (1) Injecting dehumidified blast furnace exhaust gas (injection route explained in the third embodiment) (2) Injecting dehumidified reduction furnace gas (injection route explained in the fourth embodiment) (3) Injecting hydrogen-based reducing gas from outside the connecting process (a route added in this embodiment) In this embodiment, a case where three routes are used simultaneously will be described, but route (2) may be omitted. As the injection route (3), a method of branching the hydrogen-based reducing gas injected into the blast furnace 100 and causing it to flow in may be considered.

[0054] The points marked with stars in Fig. 8 indicate the time when reduced iron with a reduction rate of 55% was charged into blast furnace 100 and the hydrogen injection rate was 352 (Nm 3In this operation, a hydrogen-based reducing gas is injected as a sintering gas (pig-ton). However, even if the BFG gas generated in this operation is dehumidified and injected into the reduction furnace 200, it is not possible to produce reduced iron with a reduction rate of 55%. Although the reduction rate can be increased by further injecting dehumidified reduction furnace gas, as shown in FIG. 10, by setting the circulation rate in the reduction furnace 200 described in the fourth embodiment to 50%, the hydrogen injection amount of the hydrogen-based reducing gas injected in the above route (3) can be reduced to 130 (Nm 3 This allows for the production of reduced iron with a reduction rate of 55%. That is, reduced iron with a high reduction rate, which cannot be obtained by the combined operation of the fourth embodiment, can be produced.

[0055] By charging reduced iron with a reduction rate of 55% into the blast furnace 100, the reduction rate of blast furnace carbon consumption can be increased to more than 40% compared to standard operation, as shown in FIG.

[0056] (Sixth embodiment) This embodiment is a modification of the fourth embodiment, and in addition to dehumidifying the BFG gas and the exhaust gas from the reducing furnace, it also separates carbon dioxide from these gases. FIG. 11 is a schematic diagram of equipment for implementing the process of connecting a blast furnace and a reducing furnace according to this embodiment. By separating carbon dioxide from the BFG gas and the exhaust gas from the reducing furnace, it is possible to remove oxidizing components from the gas injected into the reducing furnace 200. This allows reduced iron with a higher reduction rate to be charged into the blast furnace, and therefore the amount of hydrogen injection (Nm 3 This allows for a significant reduction in blast furnace carbon consumption while further reducing CO2 emissions (pig-tons). In other words, the decarbonation process can reduce hydrogen gas consumption.

[0057] 12 corresponds to FIG. 8, and the hatched area inside the dotted line is the range in which the combined operation of this embodiment is possible. In other words, when reduced iron with a reduction rate of T% is charged into the blast furnace, the amount of hydrogen injected into the blast furnace 100 (Nm 38 and 12 show the range in which reduced iron with a reduction rate of T% can be obtained by the operating method of this embodiment without changing the ratio (pig-ton). The hatched area inside the dotted line where combined operation is possible was identified based on the mathematical models described in Non-Patent Documents 2 and 3. By comparing and referring to FIGS. 8 and 12, it can be seen that this embodiment can significantly increase the reduction rate of blast furnace carbon consumption.

[0058] This embodiment can also be used as a modified example of Embodiment 3. Specifically, in addition to the dehumidification treatment of the BFG gas (an operation pattern in which exhaust gas from the reduction furnace is not blown in), a treatment to remove carbon dioxide may be added.

[0059] (Seventh embodiment)

[0060] As is well known, reducing CO2 emissions from blast furnace operation requires reducing the reducing agent ratio (RAR). Reducing agents function both as a heat source, raising the temperature of charge materials such as iron ore, and as a reducer of the charge materials. To reduce the RAR, the reduction efficiency within the furnace must be improved. The reduction reaction within the furnace can be expressed by various reaction equations. However, direct reduction (reaction equation: FeO + C → Fe + CO) is a large endothermic reaction, so reducing the RAR requires reducing direct reduction. Because direct reduction occurs in the lower part of the blast furnace, reducing direct reduction requires sufficient reduction of the charge materials using reducing gases such as CO and H2.

[0061] Known methods for solving this problem include a technique for improving the potential of the reducing gas injected from the tuyere, and a technique for charging reduced iron that has been reduced in advance in a shaft furnace or the like into the blast furnace to reduce the reduction load in the furnace (see Patent Documents 3 to 5).However, in a blast furnace operation method in which a mixed raw material consisting of reduced iron and unreduced iron source raw material is charged while a hydrogen-based reducing gas is injected from the tuyere, the conditions for more efficiently utilizing the reduced iron have not been considered in the prior art.

[0062] The present inventors have investigated the effect of blowing hydrogen-based reducing gas (however, the hydrogen blowing rate is ≥ 250 (Nm3 In a method for operating a blast furnace that charges the above-described mixed raw materials, it was discovered that when the usage rate of reduced iron in the mixed raw materials exceeds a predetermined rate, the effect of reducing the reducing agent ratio becomes saturated. Increasing the usage rate of reduced iron beyond this saturation point merely increases the energy required to produce reduced iron, and no further effect of reducing the reducing agent ratio can be obtained. Therefore, it is desirable to limit the usage rate so as not to exceed the saturation point. In other words, the present embodiment aims to enhance the effect of reducing the reducing agent ratio while reducing energy loss during the production of reduced iron.

[0063] The inventors conducted a simulation using a mathematical blast furnace model to examine the relationship between the reduced iron usage rate and the reduction rate of blast furnace carbon consumption, while varying the reduction rate for both pulverized coal injection operation and hydrogen injection operation. The mathematical blast furnace model used was that disclosed in Non-Patent Document 1. The simulation was performed on the assumptions shown in Table 4. The coke rate and blast rate were used as adjustment means. The oxygen enrichment rate (in other words, the temperature before the tuyere) was adjusted so that the blast furnace carbon consumption (kg / pig-ton) was minimized for a given hydrogen gas consumption rate and reduction rate. The hydrogen injection rate was 250 (Nm 3 / pig-ton) or more 290 (Nm) 3 The composition of the reduced iron corresponding to each reduction degree is shown in Table 2. [Table 4]

[0064] Pulverized coal injection operation is an operation in which pulverized coal is injected into a mixed raw material as a burden (in other words, no hydrogen-based reducing gas is injected). Hydrogen injection operation is an operation in which pulverized coal is injected into a mixed raw material as a burden, and a hydrogen-based reducing gas is injected.

[0065] 13 shows the simulation results, with the horizontal axis representing the reduced iron usage rate (%) and the vertical axis representing the blast furnace carbon consumption reduction rate (%). The data plotted as solid black corresponds to the pulverized coal injection operation, and the data plotted as open white corresponds to the hydrogen injection operation. In this embodiment, the usage rate (%) is defined as the mixing ratio of reduced iron when the mixed raw material is 100 mass %.

[0066] The blast furnace carbon consumption reduction rates (%) of the pulverized coal injection operation and the hydrogen injection operation were set as reduction rates relative to the standard operation (see the second embodiment). In this embodiment, the blast furnace carbon consumption in the standard operation was set to 426 (kg / pig-ton).

[0067] In pulverized coal injection operation, the blast furnace carbon consumption reduction rate (%) increased as the reduced iron usage rate (%) increased, and reached its maximum when the usage rate (%) reached 100%. In other words, no simulation results were obtained showing that the effect of increasing the blast furnace carbon consumption reduction rate (%) saturates before the reduced iron usage rate (%) reached 100%.

[0068] On the other hand, in hydrogen injection operation, the blast furnace carbon consumption reduction rate (%) increased until the reduced iron usage rate (%) reached 80%, but even when the reduced iron usage rate (%) was increased from 80% to 100%, the blast furnace carbon consumption reduction rate (%) did not increase. In other words, it was found that the effect of increasing the blast furnace carbon consumption reduction rate (%) saturates when the reduced iron usage rate (%) is in the range from 60% to 80% (hereinafter referred to as the first usage rate saturation range). Therefore, when determining the reduced iron usage rate (%) based on Figure 13, it is desirable to set an appropriate usage rate (%) within the first usage rate saturation range.

[0069] This makes it possible to reduce the energy loss during reduced iron production while enhancing the effect of reducing agent rate reduction (in other words, the same effect of reducing agent rate reduction as when the reduced iron usage rate (%) is 100% can be obtained). In this embodiment, the effect of reducing blast furnace carbon consumption when the reduced iron usage rate is increased by 20% increments is simulated, but the present invention is not limited to this. It is also possible to simulate the effect of reducing blast furnace carbon consumption when the reduced iron usage rate is increased by X% (where X<20%) increments. This makes it possible to grasp the usage rate saturation range more accurately. However, if X% is too small, the simulation becomes complicated, so it is desirable to set X% to 5% or more and 20% or less.

[0070] In the above example, the utilization rate saturation range was estimated from the relationship between the blast furnace carbon consumption reduction rate (%) and the utilization rate (%) (hereinafter also referred to as the "first relationship"), but the present invention is not limited to this. The utilization rate saturation range may also be estimated from the relationship between the solute loss carbon amount (kg / pig-ton) and the reduced iron utilization rate (%) (hereinafter also referred to as the "second relationship"). The second relationship can also be obtained using the above-mentioned blast furnace mathematical model, as in the first relationship.

[0071] Figure 14 shows the simulation results, with the horizontal axis representing the reduced iron usage rate (%) and the vertical axis representing the amount of solute-loss carbon (kg / pig-ton). The meanings of pulverized coal injection operation, hydrogen injection operation, and the blast furnace carbon consumption reduction rate (%) are the same as those in Figure 13, so explanations will be omitted. Note that the minimum value of the solute-loss carbon amount (kg / pig-ton) is generally less than 10 (kg / pig-ton) and is not necessarily 0 (kg / pig-ton).

[0072] In the pulverized coal injection operation with "reduced iron with a reduction rate of 70% (no hydrogen injection)," the amount of solute-loss carbon (kg / pig-ton) decreased as the reduced iron usage rate (%) increased, and reached a minimum when the usage rate (%) reached 100%. In other words, no simulation results were obtained showing that the effect of decreasing the solute-loss carbon amount (kg / pig-ton) saturates before the reduced iron usage rate (%) reached 100%.

[0073] On the other hand, in the hydrogen injection operation using reduced iron with a 70% reduction rate (with hydrogen injection), the amount of solute-loss carbon (kg / pig-ton) decreased until the utilization rate (%) of reduced iron reached 80%. However, the amount of solute-loss carbon (kg / pig-ton) did not decrease even when the utilization rate (%) of reduced iron was increased from 80% to 100%. In other words, when using reduced iron with a 70% reduction rate, the reduction effect of solute-loss carbon (kg / pig-ton) saturated when the utilization rate (%) was in the range of 60% to 80% (hereinafter referred to as the second utilization rate saturation range). Therefore, when determining the utilization rate (%) of reduced iron with a 70% reduction rate based on Figure 14, it is desirable to set an appropriate utilization rate (%) within the second utilization rate saturation range.

[0074] Furthermore, in the hydrogen injection operation using reduced iron with a 95% reduction rate (with hydrogen injection), the amount of solute-loss carbon (kg / pig-ton) decreased until the reduced iron usage rate (%) reached 60%. However, increasing the reduced iron usage rate (%) from 60% to 100% did not decrease the amount of solute-loss carbon (kg / pig-ton). In other words, when using reduced iron with a 95% reduction rate, the effect of reducing the amount of solute-loss carbon (kg / pig-ton) was saturated when the usage rate was in the range of 40% to 60%. Therefore, when determining the usage rate (%) of reduced iron with a 95% reduction rate based on Figure 14, it is desirable to set an appropriate usage rate (%) in the range of 40% to 60%.

[0075] This makes it possible to reduce energy loss during reduced iron production while enhancing the effect of reducing agent ratio reduction. In this embodiment, the effect of reducing the amount of sole-loss carbon when the reduced iron usage rate is increased by 20% is simulated for each reduction rate. However, the present invention is not limited to this, and it is also possible to simulate the effect of reducing the amount of sole-loss carbon when the reduced iron usage rate is increased by X% (where X<20%). This makes it possible to grasp the usage rate saturation range more accurately. However, if X% is too small, the simulation becomes complicated, so it is desirable to set X% to 5% or more and 20% or less.

[0076] To summarize the above findings, this embodiment includes the following steps 1 and 2 as preparatory steps for a charging step in which reduced iron is charged into a blast furnace together with an iron source raw material that has not been subjected to a reduction treatment. Step 1: Determine the relationship between (1) and / or (2) in advance. (1) Relationship between the reduced iron usage rate (%) and the blast furnace carbon consumption reduction rate (%) for each reduced iron reduction rate (2) Relationship between reduced iron usage rate (%) and solubilized carbon content (kg / pig-ton) for each reduction rate of reduced iron In the above-described embodiment, the simulation was performed for reduced iron with reduction rates of 70% and 95%, but the reduction rate is not limited to this.

[0077] Step 2: Determine the usage rate of reduced iron based on the relationship (1) and / or (2). Here, "based on the relationship (1) and (2)" includes, for example, checking whether the usage rate of reduced iron obtained from the relationship (1) is valid based on the relationship (2). For example, if the reduced iron usage rate (%) determined from the above-mentioned first usage rate saturation range is not included in the above-mentioned second usage rate saturation range, the usage rate (%) can be determined again from the overlapping range of the first usage rate saturation range and the second usage rate saturation range. [Explanation of symbols]

[0078] 100 Blast furnace 200 Reduction furnace

Claims

1. Hydrogen injection amount: 250 (Nm 3 In a blast furnace operation method in which a hydrogen-based reducing gas is injected so that the reduction ratio is equal to or greater than 1 / pig-ton, a reduction step of reducing the iron source material to at least wustite in a reduction furnace to produce reduced iron; a charging step of charging the reduced iron obtained in the reduction step into the blast furnace; and The relationship information defining the relationship between the hydrogen injection rate (Nm3 / pig-ton) and the blast furnace carbon consumption (kg / pig-ton) is acquired for each reduction rate, and based on the acquired results, the following formula (1) is derived using the hydrogen injection rate Y (Nm3 / pig-ton) and the reduction rate of reduced iron X (%) as parameters. When the reduction rate of the reduced iron obtained in the reduction step is substituted for X in the following formula (1), Y calculated is defined as a reference value, A method for operating a blast furnace, characterized by operating the blast furnace by adjusting at least one of the hydrogen injection rate (Nm 3 / pig-ton) and the reduction rate (%) of reduced iron so that the hydrogen injection rate (Nm 3 / pig-ton) does not exceed the reference value. Y = aX + b (where a and b are constants) Equation (1)

2. From the above-mentioned related information, the hydrogen injection rate (Nm m 3 / pig-ton) was calculated, and the hydrogen injection amount (Nm 3 2. The method for operating a blast furnace according to claim 1, wherein the formula (1) is derived based on the ratio of the total mass of iron ore to the total mass of iron ore (m / pig-ton) and the reduction rate.

3. 3. The method for operating a blast furnace according to claim 1, wherein the reduction step is carried out by injecting dehumidified blast furnace exhaust gas obtained by subjecting the blast furnace top exhaust gas to a dehumidification treatment into the reducing furnace.

4. 4. The method for operating a blast furnace according to claim 3, wherein the reduction step is carried out by further injecting into the reducing furnace, in addition to the dehumidified blast furnace exhaust gas, dehumidified reducing furnace gas obtained by subjecting the top exhaust gas of the reducing furnace to a dehumidification treatment.

5. 5. The method for operating a blast furnace according to claim 3, wherein the reduction step is carried out by further injecting a hydrogen-based reducing gas into the reducing furnace from a supply source different from that of the blast furnace and the reducing furnace.

6. 4. The method for operating a blast furnace according to claim 3, wherein the reduction step is carried out by injecting dehumidified blast furnace exhaust gas, which has been subjected to the dehumidification treatment and carbon dioxide separation treatment, into the reducing furnace.

7. 5. The method for operating a blast furnace according to claim 4, wherein the reduction step is carried out by injecting into the reducing furnace a dehumidified blast furnace exhaust gas obtained by subjecting the blast furnace top exhaust gas to the dehumidification treatment and the carbon dioxide separation treatment, and a dehumidified reducing furnace gas obtained by subjecting the reducing furnace top exhaust gas to the dehumidification treatment and the carbon dioxide separation treatment.

8. A method for operating a blast furnace in which a hydrogen-based reducing gas is injected so that the hydrogen injection rate is 250 (Nm 3 / pig-ton) or more, a reduction step of reducing the iron source material to at least wustite in a reduction furnace to produce reduced iron; a charging step of charging the reduced iron obtained in the reduction step into the blast furnace; and the charging step is a step of charging reduced iron together with an iron source raw material that has not been subjected to a reduction treatment, a preparation step of determining in advance a usage rate of reduced iron in the charging step, the advance preparation step includes a first advance preparation step of performing at least one of a step of obtaining a first relationship between a usage rate of reduced iron and a blast furnace carbon consumption reduction rate for each reduction rate of reduced iron, and a step of obtaining a second relationship between a usage rate of reduced iron and a blast furnace carbon consumption reduction rate for each reduction rate of reduced iron; a second advance preparation step of determining a usage rate of reduced iron based on the first relationship and / or the second relationship obtained in the first advance preparation step; and A method for operating a blast furnace, comprising carrying out the charging step at the usage rate determined in the advance preparation step.

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