Blast furnace operation methods

Abstract

This invention provides a blast furnace operation method that allows for a further reduction in the reducing agent ratio. [Solution] A blast furnace operation method is employed in which a first reducing gas, which is a gas containing 30 mol% or more of H as an elemental composition and exists as a gas under standard conditions, is injected into the blast furnace, and a second reducing gas, which is a gas recovered and separated from the top exhaust gas and contains at least 50% CO gas by volume fraction, is injected into the blast furnace, and before injecting the second reducing gas into the blast furnace, the second reducing gas is heated to the injection temperature, and the injection temperature of the second reducing gas is determined based on the amount of first reducing gas injected into the blast furnace and the amount of second reducing gas injected into the blast furnace.

Description

[Technical Field]

[0001] The present invention relates to a method for operating a blast furnace. [Background technology]

[0002] In the iron and steel industry, the blast furnace method is the dominant process for producing pig iron. In the blast furnace method, blast furnace iron-based raw materials (raw materials containing iron oxide, mainly sintered ore; hereinafter simply referred to as "iron-based raw materials") and coke are alternately and layered into the blast furnace from the top, while hot air is blown into the blast furnace from tuyeres at the bottom. The hot air reacts with the pulverized coal blown in with the hot air and 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. The 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 drip down the blast furnace while being further reduced by the coke. Iron-based raw materials are ultimately stored in the hearth as molten pig iron (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. Therefore, in the blast furnace method, carbon materials such as coke and pulverized coal are used as reducing agents.

[0003] Incidentally, in recent years, with calls for preventing global warming, reducing emissions of carbon dioxide (CO2 gas), one of the greenhouse gases, has become a social issue. As mentioned above, the blast furnace method uses carbon as a reducing agent, thus generating a large amount of CO2 gas. Therefore, the steel industry is one of the major industries in terms of CO2 gas emissions, and it must respond to this social demand. Specifically, further reduction of the reducing agent ratio (amount of reducing agent used per ton of molten iron) in blast furnace operation is urgently needed.

[0004] Reducing agents play two roles in the furnace: generating heat to raise the temperature of the charge and reducing the iron-based raw materials. To reduce the reducing agent ratio, it is necessary to increase the reduction efficiency in the furnace. The reduction reactions in the furnace can be expressed by various reaction equations. Of these reduction reactions, the direct reduction reaction with coke (reaction equation: FeO + C ⇒ Fe + CO) is an endothermic reaction that involves a large amount of heat absorption. Therefore, minimizing the occurrence of this reaction is important in reducing the reducing agent ratio. Since this direct reduction reaction occurs in the lower part of the blast furnace, if the iron-based raw materials can be sufficiently reduced by reducing gases such as CO and H2 before reaching the lower part of the furnace, the amount of iron-based raw materials subject to direct reduction can be reduced.

[0005] As a conventional technology to solve the above problems, for example, as disclosed in Patent Document 1, a technique is known in which a hydrogen-based reducing gas is blown in along with hot air from a tuyer to improve the reducing gas potential in the furnace. In this technique, a hydrogen-based reducing gas such as LNG (liquefied natural gas) is used as the reducing gas for iron-based raw materials to reduce the reducing agent ratio. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 4661890 [Overview of the project] [Problems that the invention aims to solve]

[0007] When large amounts of hydrogen-based reducing gas are injected into the blast furnace through the tuyeres, the thermal balance between the upper and lower parts of the furnace changes significantly. (Here, the lower part refers to the region where the furnace temperature is higher than the Sol-Roth reaction (C + CO2 → 2CO) initiation temperature. The upper part is the region above the lower part of the furnace.) Therefore, it is necessary to appropriately control the operational parameters to maintain a stable thermal balance between the upper and lower parts of the furnace. In other words, injecting large amounts of hydrogen-based reducing gas into the blast furnace through the tuyeres to enjoy a significant carbon reduction effect lowers the tuyere tip combustion temperature. Increasing the oxygen enrichment rate to suppress this decrease in tuyere tip combustion temperature increases the heat flow ratio. As a result, the furnace top gas temperature decreases, potentially falling below the lower limit of the furnace top gas temperature used as an operational control standard. This raises concerns that this may lead to a significant delay in the heating of the charges in the upper part of the furnace and poor ventilation due to insufficient dust discharge to the outside of the furnace.

[0008] Thus, simply increasing the oxygen enrichment rate makes it difficult to simultaneously maintain the tuyere combustion temperature and the furnace top gas temperature within the appropriate range. This is because the blast furnace process utilizes the exhaust gas (exhaust gas after the Sol-Roth reaction is completed in the lower furnace) after the heat balance in the lower furnace, where the reduction and thermal load are greatest, is established to establish the reduction and thermal balance in the upper furnace. In normal operation without the use of hydrogen-based reducing gas, the operation is carried out with appropriate parameters so that the heat balance in the upper and lower furnaces is simultaneously satisfied. On the other hand, in operation in which a large amount of hydrogen-based reducing gas is injected into the blast furnace, the ore reduction rate becomes almost 100% at the fusion zone level and the amount of molten reduction becomes almost zero, so the reduction and thermal load in the lower furnace is greatly reduced. Consequently, carbon consumption is reduced. However, since the temperature of the exhaust gas generated from the lower furnace decreases, establishing the heat balance in the upper furnace becomes the rate-limiting factor in blast furnace operation.

[0009] Therefore, in the technology disclosed in Patent Document 1, a preheated reducing gas is supplied from the shaft section as the reducing gas supplied to the upper part of the furnace, in addition to the hydrogen-based reducing gas supplied from the lower part of the furnace. This is thought to allow the heat balance of the upper and lower parts of the furnace to be controlled almost independently.

[0010] On the other hand, from the perspective of further reducing the reducing agent ratio, there was room for improvement regarding the type of reducing gas injected into the blast furnace and the temperature of said reducing gas.

[0011] Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide a method for operating a blast furnace that can further reduce the reducing agent ratio. [Means for solving the problem]

[0012] The gist of this invention is as follows: (1) A method for operating a blast furnace, A first reducing gas, which contains 30 mol% or more of H as an elemental composition and exists as a gas under standard conditions, is injected into the blast furnace. A second reducing gas, which is a gas recovered and separated from the top exhaust gas of the furnace and contains at least 50% CO gas by volume fraction, is injected into the blast furnace. Before injecting the second reducing gas into the blast furnace, the second reducing gas is heated to the injection temperature. The injection temperature of the second reducing gas is set as follows: The amount of the first reducing gas injected into the blast furnace, The amount of the second reducing gas injected into the blast furnace, The method of operating a blast furnace, determined based on [the specified criteria]. (2) In the blast furnace provided with a conventional tuyere mounted below the Bosch section and a shaft tuyere mounted at a higher position than the conventional tuyere, The first reducing gas is blown into the blast furnace from the normal tuyeres. The second reducing gas is blown into the blast furnace from the shaft tuyere. (1) The method of operating the blast furnace. (3) The relationship between the injection temperature of the second reducing gas and the carbon consumption per unit of carbon is obtained, From the obtained relationship, obtain the range of the blowing temperature of the second reducing gas that is the minimum value of the carbon consumption per unit + 10 kg / t or less, Heat up the second reducing gas to the range of the blowing temperature and blow it into the blast furnace. The operation method of the blast furnace according to (1) or (2). (4) When the blowing amount of the second reducing gas is more than 0 Nm 3 / t and 300 Nm 3 / t or less, The blowing temperature of the second reducing gas is 0°C or more and 1000°C or less, Heat up the second reducing gas to the range of the blowing temperature that falls within the minimum value of the carbon consumption per unit kg / t + 10 kg / t or less, and blow it into the blast furnace. The operation method of the blast furnace according to (1) or (2). (5) When the blowing amount of the first reducing gas is more than 0 Nm 3 / t and 200 Nm 3 / t or less, and When the blowing amount of the second reducing gas is more than 0 Nm 3 / t and 100 Nm 3 / t or less, set the blowing temperature to 25°C or more and 400°C or less, When the blowing amount of the second reducing gas is more than 100 Nm 3 ] / t and 200 Nm 3 / t or less, set the blowing temperature to 200°C or more and 600°C or less, When the blowing amount of the second reducing gas is more than 200 Nm 3 / t and 300 Nm 3 / t or less, set the blowing temperature to 400°C or more and 800°C or less. The operation method of the blast furnace according to (4). (6) When the blowing amount of the first reducing gas is more than 200 Nm 3 / t and 400 Nm 3 / t or less, and When the blowing amount of the second reducing gas is more than 0 Nm 3 / t and 100 Nm 3When the temperature is less than or equal to / t, the blowing temperature is set to 600°C or higher and 1000°C or lower. The amount of the second reducing gas injected is 100 Nm³. 3 / t super 200Nm 3 When the temperature is less than or equal to / t, the blowing temperature is set to 400°C or higher and 800°C or lower. The amount of the second reducing gas injected is 200 Nm³. 3 / t super 300Nm 3 When the temperature is less than or equal to / t, the blowing temperature is set to 600°C or higher and 1000°C or lower. (4) The method of operating the blast furnace. (7) The amount of the first reducing gas being injected is 400 Nm³. 3 / t super 650Nm 3 / t is less than or equal to The amount of the second reducing gas blown in is 0 Nm 3 / t over 100Nm 3 When the temperature is less than or equal to / t, the blowing temperature is set to 200°C or more and 600°C or less. The amount of the second reducing gas injected is 100 Nm³. 3 / t super 200Nm 3 When the temperature is less than or equal to / t, the blowing temperature is set to 400°C or higher and 800°C or lower. The amount of the second reducing gas injected is 200 Nm³. 3 / t super 300Nm 3 When the temperature is less than or equal to / t, the blowing temperature is set to 600°C or higher and 1000°C or lower. (4) The method of operating the blast furnace. [Effects of the Invention]

[0013] According to the present invention, the reducing agent ratio can be further reduced, thereby lowering the carbon consumption per unit. "Carbon consumption per unit (Input C)" is the amount of carbon required to produce 1 ton of molten iron (i.e., the amount of carbon consumed per ton of molten iron). [Brief explanation of the drawing]

[0014] [Figure 1] This is a flowchart showing the overall configuration of the blast furnace system used in this embodiment. [Figure 2] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 25°C and the injection rate is 200 Nm3 / t. [Figure 3] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 400°C and the injection rate is 200 Nm3 / t. [Figure 4] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 800°C and the injection rate is 200 Nm3 / t. [Figure 5] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 1200°C and the injection rate is 200 Nm3 / t. [Figure 6] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 25°C and the injection rate is 400 Nm3 / t. [Figure 7] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 400°C and the injection rate is 400 Nm3 / t. [Figure 8] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 800°C and the injection rate is 400 Nm3 / t. [Figure 9] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 1200°C and the injection rate is 400 Nm3 / t. [Figure 10] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 400°C and the injection rate is 650 Nm3 / t. [Figure 11] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 800°C and the injection rate is 650 Nm3 / t. [Figure 12] This graph shows the correlation between the temperature of the second reducing gas and the carbon consumption per unit of fuel when the injection temperature of the first reducing gas into the blast furnace is 1200°C and the injection rate is 650 Nm3 / t. [Figure 13] This graph shows the correlation between the temperature of the reducing gas (secondary reducing gas) injected into the blast furnace and the CO gas concentration and CO2 gas concentration. [Modes for carrying out the invention]

[0015] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In this specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0016] <1. Overall configuration of the blast furnace system> First, the overall configuration of the blast furnace system 1 and the first reducing gas supply system 2 connected to the blast furnace system 1 according to this embodiment will be described based on Figure 1. The blast furnace system 1 comprises a blast furnace 10, a CO2 separation and recovery device 20, a buffer tank 30, a compressor 40, a heater 50, and a flow meter 61.

[0017] The blast furnace 10 comprises a blast furnace body 10a, a normal tuyere 11, and a shaft tuyere 12. Inside the blast furnace body 10a, a reduction reaction of iron-based raw materials is carried out using the blast furnace method. Specifically, iron-based raw materials and coke are charged into the blast furnace 10 alternately and in layers from the top of the blast furnace 10, while hot air, pulverized coal, and enriched oxygen gas are blown into the blast furnace 10 from the normal tuyere 11. In the following description, "tuyere tip combustion temperature" refers to the temperature at the gas outlet of the normal tuyere 11. The hot air reacts with the pulverized coal blown in with the hot air and the coke inside the blast furnace 10 to generate high-temperature reducing gas (in this case, CO gas). The hot air gasifies the coke and pulverized coal. Note that pulverized coal does not necessarily have to be included in the hot air. The reducing gas rises inside the blast furnace 10, reducing the iron-based raw materials while heating them. The iron-based raw materials descend through the blast furnace 10, while being heated and reduced by reducing gas. The iron-based raw materials then melt and are further reduced by coke as they drip down through the blast furnace 10. Ultimately, the iron-based raw materials accumulate in the hearth as molten pig iron (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.

[0018] Typically, the tuyeres 11 are located below the Bosch section of the blast furnace 10, and the hot air and second reducing gas described above are blown into the blast furnace 10 from the tuyeres 11. In Figure 1, only the tuyeres 11 are depicted at both ends of the blast furnace 10, but two or more tuyeres 11 may be provided at equal intervals along the circumferential direction. Alternatively, the first reducing gas may be blown into the blast furnace 10 from the tuyeres 11.

[0019] The shaft tuyeres 12 are positioned higher than the normal tuyeres 11 of the blast furnace 10, and the first reducing gas is blown from the shaft tuyeres 12 into the shaft portion 10b of the blast furnace 10. In Figure 1, shaft tuyeres 12 are depicted only at both ends of the shaft portion 10b, but two or more shaft tuyeres 12 may be provided at equal intervals along the circumferential direction of the shaft portion 10b, and they may be attached to the Bosch portion or the Belly portion. In addition, the second reducing gas may be blown into the blast furnace 10 from the shaft tuyeres 12.

[0020] Furthermore, when the first reducing gas is normally blown into the blast furnace 10 from the tuyere 11, the second reducing gas may also be blown into the blast furnace 10 from either the normal tuyere 11 or the shaft tuyere 12, or both. Moreover, the second reducing gas may also be blown in from either the normal tuyere 11 or the shaft tuyere 12, or both, and both the first and second reducing gases may be blown in from the normal tuyere 11.

[0021] The CO2 separation and recovery unit 20 is a device that recovers the top flue gas (BFG, Blast Furnace Gas) and separates it into CO gas, hydrogen gas, and nitrogen gas, and CO2 gas and H2O gas. The separation method is not particularly limited, but examples include chemical adsorption and physical adsorption (PSA). It is preferable that the energy required for separation be supplied by renewable energy. The CO2 gas and H2O gas are discharged outside the system. The CO2 separation and recovery unit 20 does not necessarily have to recover the entire amount of top flue gas. For example, the CO2 separation and recovery unit 20 may recover only an amount of top flue gas corresponding to the flow rate of gas injected into the blast furnace.

[0022] The buffer tank 30 is a tank for temporarily storing CO gas, hydrogen gas, and nitrogen gas separated and recovered from the furnace top exhaust gas. A desired amount of second reducing gas is introduced from the buffer tank 30 to the compressor 40. The remaining gas is used, for example, as a heat source in a steel mill. The hydrogen gas may also be reused as part of the first reducing gas, as described later.

[0023] The second reducing gas is a gas separated from the furnace top exhaust gas and contains at least 50% CO gas by volume fraction. Specifically, it is preferable that the condition CO / (CO+CO2+H2+H2O+N2)≧0.50 is satisfied.

[0024] The compressor 40 pressurizes the second reducing gas. Here, the compressor 40 pressurizes the second reducing gas to, for example, the internal pressure of the blast furnace 10 (approximately 4.5 atmospheres). The pressurized second reducing gas is introduced into the heater 50. In this embodiment, the second reducing gas was obtained by separating and recovering the top exhaust gas of the furnace, but the second reducing gas may also be obtained from outside the system.

[0025] The heater 50 heats the second reducing gas to a predetermined temperature. Here, the predetermined temperature is preferably determined based on, for example, the amount of first reducing gas injected into the blast furnace 10, the temperature of the first reducing gas, and the amount of second reducing gas injected into the blast furnace 10. As shown in the example, the temperature range of the second reducing gas in which the carbon consumption per unit area is within +10 kg / t from the minimum value is determined according to the amount of first reducing gas injected into the blast furnace 10, the temperature of the first reducing gas, and the amount of second reducing gas injected into the blast furnace 10. Therefore, by simulating blast furnace operation based on the amount of first reducing gas injected, the temperature of the first reducing gas, and the amount of second reducing gas injected into the blast furnace 10, the temperature range of the second reducing gas in which the carbon consumption per unit area is within +10 kg / t from the minimum value can be determined. This makes it possible to reduce the carbon consumption per unit area. Furthermore, the temperature range of the second reducing gas may be within +8 kg / t from the minimum value of the carbon consumption reduction unit, more preferably within +5 kg / t from the minimum value, and even more preferably within +3 kg / t from the minimum value.

[0026] The inventors conducted a study using a blast furnace mathematical model to determine the appropriate injection temperature of the second reducing gas in the operation of the blast furnace according to this embodiment. As a result, they found that the temperature of the second reducing gas at which carbon consumption per unit is lowest tends to increase with increasing injection volume of the second reducing gas and the first reducing gas, but is less dependent on increasing injection temperature of the first reducing gas.

[0027] In other words, by selecting a temperature range for the second reducing gas that results in a carbon consumption rate of within +10 kg / t from the minimum value, depending on the amount of first reducing gas injected into the blast furnace 10 and the amount of second reducing gas injected into the blast furnace 10, it is possible to obtain blast furnace operating conditions that minimize carbon consumption.

[0028] For example, if the injection temperature of the first reducing gas is room temperature and the injection volume of the first reducing gas is 0 Nm³ 3 / t super 200Nm 3 If the amount is within / t, the injection temperature of the second reducing gas is obtained as follows. That is, the amount of second reducing gas injected into the blast furnace 10 is 100 Nm³. 3 If the amount is less than / t, the predetermined temperature shall be set to room temperature to 400°C or lower. In this embodiment, room temperature generally means between 25°C and 30°C. The amount of second reducing gas blown into the blast furnace 10 is 100 Nm³. 3 / t super 200Nm 3 If the amount is less than / t, the specified temperature shall be between 200°C and 600°C. The amount of second reducing gas injected into the blast furnace 10 shall be 200 Nm³. 3 / t super 300Nm 3 If the temperature is less than / t, the specified temperature shall be between 400°C and 800°C.

[0029] On the other hand, if the injection temperature of the first reducing gas is 400°C and the injection volume of the first reducing gas is 0 Nm³ 3 / t super 200Nm 3 When the amount of second reducing gas injected into the blast furnace 10 is within / t, the injection temperature of the second reducing gas is obtained as follows. That is, when the amount of second reducing gas injected into the blast furnace 10 is 100 Nm³ 3 If the amount is less than / t, the specified temperature will be set to room temperature to 400°C. The amount of second reducing gas injected into the blast furnace 10 will be 100 Nm³. 3 / t super 200Nm 3 If the amount is less than / t, the specified temperature shall be between 200°C and 600°C. The amount of second reducing gas injected into the blast furnace 10 shall be 200 Nm³. 3 / t super 300Nm 3If the temperature is less than / t, the specified temperature shall be between 400°C and 800°C.

[0030] Similarly, if the injection temperature of the first reducing gas is 800°C and the injection volume of the first reducing gas is 0 Nm³ 3 / t super 200Nm 3 When the amount of second reducing gas injected into the blast furnace 10 is within / t, the injection temperature of the second reducing gas is obtained as follows. That is, when the amount of second reducing gas injected into the blast furnace 10 is 100 Nm³ 3 If the amount is less than / t, the specified temperature will be set to room temperature to 400°C. The amount of second reducing gas injected into the blast furnace 10 will be 100 Nm³. 3 / t super 200Nm 3 If the amount is less than / t, the specified temperature shall be between 200°C and 600°C. The amount of second reducing gas injected into the blast furnace 10 shall be 200 Nm³. 3 / t super 300Nm 3 If the temperature is less than / t, the specified temperature shall be between 400°C and 800°C.

[0031] Similarly, if the injection temperature of the first reducing gas is 1200°C and the injection volume of the first reducing gas is 0 Nm³ 3 / t super 200Nm 3 When the amount of second reducing gas injected into the blast furnace 10 is within / t, the injection temperature of the second reducing gas is obtained as follows. That is, when the amount of second reducing gas injected into the blast furnace 10 is 100 Nm³ 3 If the amount is less than / t, the specified temperature is set to room temperature. The amount of second reducing gas injected into the blast furnace 10 is 100 Nm³. 3 / t super 200Nm 3 If the amount is less than / t, the specified temperature shall be between 200°C and 600°C. The amount of second reducing gas injected into the blast furnace 10 shall be 200 Nm³. 3 / t super 300Nm 3 If the temperature is less than / t, the specified temperature shall be between 400°C and 800°C.

[0032] As shown in the embodiments described later, when the second reducing gas is heated under the above temperature conditions and injected into the blast furnace 10, the carbon consumption per unit area becomes the minimum value or close to it, making it possible to further reduce the carbon consumption per unit area. Furthermore, the temperature range in which the minimum carbon consumption per unit area is obtained does not depend on the injection temperature of the first reducing gas.

[0033] The method for heating the second reducing gas is not particularly limited, but a direct heating method in which the second reducing gas is heated by burning a portion of it is preferred. This method involves heating the second reducing gas by bringing it into direct contact with the fuel gas. This method allows for a smaller equipment size compared to indirect heating (for example, heating by heat exchange using the sensible heat of the exhaust gas from the top of the furnace). Therefore, the length of the piping for the second reducing gas after heating can be shortened, and heat loss is reduced.

[0034] In the direct heating method, the secondary reducing gas is partially burned, generating CO2 and H2O gases. The higher the heating temperature, the higher the concentration of CO2 and H2O gases in the secondary reducing gas. Graph L1 in Figure 13 shows the correlation between the temperature of the secondary reducing gas injected into the blast furnace 10 and the CO and CO2 gas concentrations in the secondary reducing gas. While a higher temperature of the secondary reducing gas is advantageous for blast furnace operation from a thermal standpoint because it increases the amount of sensible heat introduced into the blast furnace, it is disadvantageous for blast furnace operation from a reduction standpoint because the CO2 and H2O gas concentrations increase and the reduction potential decreases. However, as described above, by determining a predetermined temperature based on the amount of first reducing gas injected into the blast furnace 10, the temperature of the first reducing gas, and the amount of second reducing gas injected into the blast furnace 10, the effect of the decrease in reduction potential can be suppressed, and consequently, the carbon consumption per unit can be reduced.

[0035] The first reducing gas supply system 2 comprises a first reducing gas tank 70, a heater 71, and a flow meter 72. The first reducing gas supply system 2 is a system that supplies the first reducing gas to the blast furnace system 1 from outside the blast furnace system 1.

[0036] The first reducing gas tank 70 is a tank for storing the first reducing gas. Here, the first reducing gas refers to a gas in which H is present in an elemental composition ratio of 30 mol% or more and which exists as a gas under standard conditions (0°C, 1 atm). For example, it is H2 gas, unsaturated hydrocarbon gases (C2H4, C2H2, C3H6, etc.), saturated hydrocarbon gases (CH4, C2H6, etc.), NH3 gas, coke oven gas, city gas, natural gas, etc. and mixtures thereof. Particularly preferred are H2 gas and unsaturated hydrocarbon gases (C2H4, C2H2, C3H6, etc.). H2 gas is preferable from the viewpoint of reducing carbon consumption per unit because it does not contain carbon and does not cause a thermal decomposition reaction at the tuyeres. It is also preferable from the viewpoint of permeability in the blast furnace because the viscosity and density of the gas are low. Unsaturated hydrocarbon gases are preferred because they contain double and triple bonds in their gas molecules, resulting in a relatively high heat of combustion per mole of oxygen, and they also serve as a heat source at the tuyere. Furthermore, it is more preferable that the elemental composition ratio of H in the first reducing gas is 50 mol% or more. The first reducing gas may also be a mixed gas with other gases (e.g., N2 gas) (without impairing the effects of this embodiment). The heater 71 is connected to the blast furnace 10, and the heated first reducing gas is blown into the blast furnace 10. The heater 71 may be used in conjunction with the heater 50. The flow meter 72 normally measures the flow rate (amount of first reducing gas blown) of the first reducing gas blown into the blast furnace 10 from the tuyere 11. Alternatively, the first reducing gas may be blown into the blast furnace 10 from the shaft tuyere 12.

[0037] <2. Blast Furnace Operation Method> Next, the operation method of the blast furnace 10 according to this embodiment will be described. In the operation method of the blast furnace 10 according to this embodiment, iron-based raw materials and coke are charged into the blast furnace 10 alternately and in layers from the top of the blast furnace 10, while heated first reducing gas is supplied to the blast furnace 10 from the first reducing gas supply system 2. Then, in addition to the first reducing gas, hot air, pulverized coal, and enriched oxygen gas are blown into the blast furnace 10. The hot air reacts with the pulverized coal blown in with the hot air and the coke in the blast furnace 10 to generate high-temperature reducing gas (mainly CO gas in this case). That is, the hot air gasifies the coke and pulverized coal. The reducing gas and first reducing gas rise inside the blast furnace 10, heating and reducing the iron-based raw materials. The iron-based raw materials descend inside the blast furnace 10, being heated and reduced by the reducing gas and first reducing gas. After that, the iron-based raw materials melt and drip down inside the blast furnace 10 while being further reduced by the coke. The iron-based raw materials are ultimately stored in the hearth as molten pig iron (pig iron) containing slightly less than 5% carbon by mass. The molten pig iron from the hearth is removed from the tap and used in the next steelmaking process.

[0038] Meanwhile, top exhaust gas from the blast furnace 10 is discharged. The CO2 separation and recovery unit 20 recovers the top exhaust gas and separates it into CO gas, hydrogen gas, and nitrogen gas, and CO2 gas and H2O gas. The CO2 gas and H2O gas are discharged outside the system.

[0039] CO gas, hydrogen gas, and nitrogen gas are temporarily stored in buffer tank 30. A desired amount of secondary reducing gas is introduced from buffer tank 30 to compressor 40. The secondary reducing gas introduced to compressor 40 is gas recovered and separated from furnace top exhaust gas and contains at least 50% CO gas by volume fraction. The specific composition is as described above. The remaining gas is discharged from the system and used, for example, as a heat source in a steel mill.

[0040] Next, the second reducing gas is pressurized by the compressor 40. Here, the compressor 40 pressurizes the second reducing gas to, for example, the internal pressure of the blast furnace 10 (approximately 4.5 atmospheres). The pressurized second reducing gas is then introduced into the heater 50.

[0041] Next, the second reducing gas is heated to a predetermined temperature by the heater 50. That is, the second reducing gas is heated to a predetermined temperature before being injected into the blast furnace 10. Preferably, the predetermined temperature is determined based on the amount of first reducing gas injected into the blast furnace 10 and the amount of second reducing gas injected into the blast furnace 10. After heating the second reducing gas to the determined predetermined temperature, it is injected into the blast furnace 10. The specific method for determining the predetermined temperature is as described above. Furthermore, it is preferable to determine the CO / CO2 gas concentration ratio of the second reducing gas based on the amount of first reducing gas injected into the blast furnace 10, the temperature of the first reducing gas, and the amount of second reducing gas injected into the blast furnace 10. The specific method for determining this is as described above. The flow meter 61 measures the flow rate of the second reducing gas injected into the blast furnace 10.

[0042] In blast furnace operation, it is preferable to maintain the tuyere combustion temperature, furnace top exhaust gas temperature, and molten iron temperature within predetermined ranges for reasons such as ensuring stable operation. For example, the tuyere combustion temperature is preferably maintained at around 2000°C to 2300°C, the furnace top exhaust gas temperature is preferably maintained at around 105°C or higher, and the molten iron temperature is preferably maintained at around 1520°C or higher. The upper limit of the tuyere combustion temperature is an upper limit assumed for normal operation (operation without injection of the first reducing gas or the second reducing gas). If the tuyere combustion temperature exceeds the upper limit, it is preferable to take measures such as strengthening the cooling capacity of the tuyere equipment or using materials with higher heat resistance to prevent wear on the tuyere equipment. The blast furnace operation parameters are preferably determined so that the tuyere combustion temperature, furnace top exhaust gas temperature, and molten iron temperature are maintained within predetermined ranges. Furthermore, as long as the tuyere combustion temperature, furnace top exhaust gas temperature, and molten iron temperature are maintained within the predetermined range, the blast furnace operation parameters can be freely designed. Also, as a result of the design, the tuyere combustion temperature may exceed the upper limit, but it is preferable to implement the aforementioned countermeasures separately. [Examples]

[0043] Next, an embodiment of this model will be described. In this embodiment, a simulation of the blast furnace operation method according to this embodiment was performed to verify the effectiveness of the blast furnace operation method according to this embodiment. The simulation model used was the so-called "blast furnace mathematical model" shown in Kouji TAKATANI, Takanobu INADA, Yutaka UJISAWA, "Three-dimensional Dynamic Simulator for Blast Furnace", ISIJ International, Vol.39 (1999), No.1, pp.15-22, etc. This blast furnace mathematical model basically defines multiple meshes (small regions) by dividing the internal region of the blast furnace in the height, radial, and circumferential directions, and simulates the behavior of each mesh.

[0044] In this simulation, hydrogen gas was used as the first reducing gas, and blast furnace simulations were performed with the injection temperature and injection rate of the first and second reducing gases within the ranges shown in Table 1. Specifically, one operation pattern was defined as fixing the injection rate and injection temperature of the first reducing gas and the injection rate of the second reducing gas to arbitrary values, while varying the injection temperature of the second reducing gas. Then, simulations of blast furnace operation were performed for 32 patterns of operating conditions, in which the injection rate and injection temperature of the first reducing gas and the injection rate of the second reducing gas were varied. The calculation conditions for all patterns are shown in Table 2. Note that the carbon consumption per unit is the amount of carbon required to produce 1 ton of molten iron, and it roughly corresponds to the reducing agent ratio.

[0045] [Table 1]

[0046] [Table 2]

[0047] During blast furnace operation, the pulverized coal ratio, oxygen enrichment rate, and hot air injection rate were adjusted to maintain constant iron tapping rate, molten iron temperature, and furnace top gas temperature. However, if the pulverized coal ratio was zero, the coke ratio was adjusted. The second reducing gas temperature (a predetermined temperature) and the injection rate of the second reducing gas into the blast furnace 10 were varied, and the effects of these parameters on carbon consumption per unit area were investigated. The results are shown in Figures 2 to 12.

[0048] Figure 2 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 25°C, and the injection volume of the first reducing gas is 200 Nm³. 3 Graphs L10 to L30 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3 This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3 For cases where the value is / t, graph L30 shows the amount of second reducing gas injected at 300 Nm³. 3 This handles cases where the value is / t.

[0049] Figure 3 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 400°C, and the injection volume of the first reducing gas is 200 Nm³. 3 Graphs L10 to L30 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3 This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3 For cases where the value is / t, graph L30 shows the amount of second reducing gas injected at 300 Nm³. 3 This handles cases where the value is / t.

[0050] Figure 4 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 800°C, and the injection volume of the first reducing gas is 200 Nm³. 3 Graphs L10 to L30 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3 For cases where the value is / t, graph L30 shows the amount of second reducing gas injected at 300 Nm³. 3 This handles cases where the value is / t.

[0051] Figure 5 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 1200°C, and the injection volume of the first reducing gas is 200 Nm³. 3 Graphs L10 to L30 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3 This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3 For cases where the value is / t, graph L30 shows the amount of second reducing gas injected at 300 Nm³. 3 This handles cases where the value is / t.

[0052] Figure 6 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 25°C, and the injection volume of the first reducing gas is 400 Nm³. 3 Graphs L10 to L30 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3 This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3 For cases where the value is / t, graph L30 shows the amount of second reducing gas injected at 300 Nm³. 3 This handles cases where the value is / t.

[0053] Figure 7 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 400°C, and the injection volume of the first reducing gas is 400 Nm³. 3 Graphs L10 to L30 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3 This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3For cases where the value is / t, graph L30 shows the amount of second reducing gas injected at 300 Nm³. 3 This handles cases where the value is / t.

[0054] Figure 8 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 800°C, and the injection volume of the first reducing gas is 400 Nm³. 3 Graphs L10 to L30 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3 This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3 For cases where the value is / t, graph L30 shows the amount of second reducing gas injected at 300 Nm³. 3 This handles cases where the value is / t.

[0055] Figure 9 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 1200°C, and the injection volume of the first reducing gas is 400 Nm³. 3 Graphs L10 to L30 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3 This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3 For cases where the value is / t, graph L30 shows the amount of second reducing gas injected at 300 Nm³. 3 This handles cases where the value is / t.

[0056] Figure 10 shows that the injection temperature of the first reducing gas into the blast furnace 10 is 400°C, and the injection volume of the first reducing gas is 650 Nm³. 3 Graphs L10-L20 show the correlation between the second reducing gas temperature (°C) and the carbon consumption per unit (kg / t) in the case of / t. Graph L10 shows the case where the amount of second reducing gas injected is 100 Nm³. 3 This corresponds to the case where the amount of second reducing gas injected is 200 Nm³. Graph L20 shows this case. 3 This handles cases where the value is / t.

[0057] Fig. 11 is a graph L10 - L30 showing the correlation between the temperature of the second reducing gas (°C) and the carbon consumption unit (kg / t) when the injection temperature of the first reducing gas injected into the blast furnace 10 is 800°C and the injection amount of the first reducing gas is 650 Nm 3 / t. Graph L10 corresponds to the case where the injection amount of the second reducing gas is 100 Nm 3 / t, graph L20 corresponds to the case where the injection amount of the second reducing gas is 200 Nm 3 / t, and graph L30 corresponds to the case where the injection amount of the second reducing gas is 300 Nm 3 / t.

[0058] Fig. 12 is a graph L10 - L30 showing the correlation between the temperature of the second reducing gas (°C) and the carbon consumption unit (kg / t) when the injection temperature of the first reducing gas injected into the blast furnace 10 is 1200°C and the injection amount of the first reducing gas is 650 Nm 3 / t. Graph L10 corresponds to the case where the injection amount of the second reducing gas is 100 Nm 3 / t, graph L20 corresponds to the case where the injection amount of the second reducing gas is 200 Nm 3 / t, and graph L30 corresponds to the case where the injection amount of the second reducing gas is 300 Nm 3 / t.

[0059] As shown in Figs. 2 - 12, depending on the injection amount of the first reducing gas injected into the blast furnace 10 and the injection amount of the second reducing gas injected into the blast furnace 10, the temperature range of the second reducing gas for which the carbon consumption unit is near the minimum value is different. On the other hand, when the injection amount of the first reducing gas and the injection amount of the second reducing gas do not change, it can be seen that the temperature range of the second reducing gas for which the carbon consumption unit is near the minimum value does not depend on the change in the injection temperature of the first reducing gas.

[0060] For example, in Figs. 2 - 5, the injection amount of the first reducing gas is 200 Nm 3 / t, and the injection amount of the second reducing gas is 100 Nm 3When comparing the graphs for each L10 value of / t, even when the injection temperature of the first reducing gas varies from 25°C to 1200°C, the temperature range of the second reducing gas, which is near the minimum value of carbon consumption per unit, is from room temperature to 400°C or below. Furthermore, the amount of first reducing gas injected is 200 Nm³. 3 The value is / t, and the amount of second reducing gas injected is 200 Nm³. 3 When comparing the graphs of each L20 value at / t, regardless of the injection temperature of the first reducing gas, the temperature range of the second reducing gas that is near the minimum value of carbon consumption per unit is between 200°C and 600°C. Furthermore, the amount of first reducing gas injected is 200 Nm³. 3 The value is / t, and the amount of second reducing gas injected is 300 Nm³. 3 When comparing the graphs for each L30 value of / t, regardless of the injection temperature of the first reducing gas, the temperature range for the second reducing gas that is near the minimum value of carbon consumption per unit is between 400°C and 800°C.

[0061] On the other hand, in Figures 6 to 9, the amount of first reducing gas injected is 400 Nm³. 3 The value is / t, and the amount of second reducing gas injected is 100 Nm³. 3 When comparing the graphs for each L10 value of / t, even when the injection temperature of the first reducing gas varies from 25°C to 1200°C, the temperature range of the second reducing gas, which is near the minimum value of carbon consumption per unit, is between 600°C and 1000°C. Furthermore, the amount of first reducing gas injected is 400 Nm³. 3 The value is / t, and the amount of second reducing gas injected is 200 Nm³. 3 When comparing the graphs of each L20 value at / t, regardless of the injection temperature of the first reducing gas, the temperature range of the second reducing gas that is near the minimum value of carbon consumption per unit is between 400°C and 800°C. Furthermore, the amount of first reducing gas injected is 400 Nm³. 3 The value is / t, and the amount of second reducing gas injected is 300 Nm³. 3 When comparing the graphs for each L30 value of / t, regardless of the injection temperature of the first reducing gas, the temperature range of the second reducing gas that is near the minimum value of carbon consumption per unit is between 600°C and 1000°C.

[0062] On the other hand, in Figures 10 to 12, the amount of first reducing gas injected is 650 Nm³. 3 The value is / t, and the amount of second reducing gas injected is 100 Nm³. 3 When comparing the graphs for each L10 value of / t, even when the injection temperature of the first reducing gas varies from 25°C to 1200°C, the temperature range of the second reducing gas, which is near the minimum value of carbon consumption per unit, is between 200°C and 600°C. Furthermore, the amount of first reducing gas injected is 650 Nm³. 3 The value is / t, and the amount of second reducing gas injected is 200 Nm³. 3 When comparing the graphs of each L20 value at / t, regardless of the injection temperature of the first reducing gas, the temperature range of the second reducing gas that is near the minimum value of carbon consumption per unit is between 400°C and 800°C. Furthermore, the amount of first reducing gas injected is 650 Nm³. 3 The value is / t, and the amount of second reducing gas injected is 300 Nm³. 3 When comparing the graphs for each L30 value of / t, regardless of the injection temperature of the first reducing gas, the temperature range of the second reducing gas that is near the minimum value of carbon consumption per unit is between 600°C and 1000°C.

[0063] Therefore, as described above, by determining a predetermined temperature and heating the second reducing gas to that predetermined temperature before injecting it into the blast furnace 10, the carbon consumption per unit area can be further reduced.

[0064] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention. [Explanation of Symbols]

[0065] 1. Blast furnace system 2. First Reduction Gas Supply System 10 blast furnace 10a Blast furnace body 10b Shaft section 11 Normal tuyere 12 Shaft section tuyere 20 CO2 Separation and Recovery Device 30 buffer tanks 40 Compressors 50, 71 heater 61, 72 Flowmeter 70 First reduction gas tank

Claims

1. A method for operating a blast furnace, A first reducing gas, which contains 30 mol% or more of H as an elemental composition and exists as a gas under standard conditions, is injected into the blast furnace. A second reducing gas, which is a gas recovered and separated from the top exhaust gas of the furnace and contains at least 50% CO gas by volume fraction, is injected into the blast furnace. Before injecting the second reducing gas into the blast furnace, the second reducing gas is heated to the injection temperature. The injection temperature of the second reducing gas is set as follows: The amount of the first reducing gas injected into the blast furnace, The amount of the second reducing gas injected into the blast furnace, The method of operating a blast furnace, determined based on [the specified criteria].

2. In the blast furnace provided with a conventional tuyere mounted below the Bosch section and a shaft tuyere mounted at a higher position than the conventional tuyere, The first reducing gas is blown into the blast furnace from the normal tuyeres. The second reducing gas is blown into the blast furnace from the shaft tuyere. The method for operating a blast furnace according to claim 1.

3. The relationship between the injection temperature of the second reducing gas and the carbon consumption per unit of carbon is obtained, From the relationship obtained, the range of the injection temperature of the second reducing gas that is less than or equal to the minimum value of the carbon consumption unit + 10 kg / t is obtained. The second reducing gas is heated to the range of the injection temperature and then injected into the blast furnace. A method for operating a blast furnace according to claim 1 or 2.

4. The amount of the second reducing gas blown in is 0 Nm ３ / t over 300Nm ３ When it is less than or equal to / t, The injection temperature of the second reducing gas is 0°C or higher and 1000°C or lower. The second reducing gas is heated to a temperature range such that the carbon consumption per unit weight (kg / t) is less than or equal to the minimum value plus 10 kg / t, and then blown into the blast furnace. A method for operating a blast furnace according to claim 1 or 2.

5. The amount of the first reducing gas blown in is 0 Nm ３ / t over 200Nm ３ / t is less than or equal to, The amount of the second reducing gas blown in is 0 Nm ３ / t over 100Nm ３ When the value is less than or equal to / t, the blowing temperature is set to 25°C or higher and 400°C or lower. The amount of the second reducing gas being blown in is 100 Nm ３ / t over 200Nm ３ When the temperature is less than or equal to / t, the blowing temperature is set to 200°C or more and 600°C or less. The blowing amount of the second reducing gas is more than 200 Nm ３ / t and not more than 300 Nm ３ / t, and the blowing temperature is set to 400°C or higher and 800°C or lower The method for operating a blast furnace according to claim 4.

6. The amount of the first reducing gas blown in is 200 Nm ３ / t over 400Nm ３ / t is less than or equal to, The amount of the second reducing gas blown in is 0 Nm ３ / t over 100Nm ３ When the value is less than or equal to / t, the blowing temperature is set to 600°C or more and 1000°C or less. The amount of the second reducing gas being blown in is 100 Nm ３ / t over 200Nm ３ When the value is less than or equal to / t, the blowing temperature is set to 400°C or more and 800°C or less. The amount of the second reducing gas blown in is 200 Nm ３ / t over 300Nm ３ When the temperature is less than or equal to / t, the blowing temperature is set to 600°C or higher and 1000°C or lower. The method for operating a blast furnace according to claim 4.

7. The amount of the first reducing gas being blown in is 400 Nm ３ / t over 650Nm ３ / t is less than or equal to, The amount of the second reducing gas blown in is 0 Nm ３ / t over 100Nm ３ When the temperature is less than or equal to / t, the blowing temperature is set to 200°C or more and 600°C or less. The amount of the second reducing gas being blown in is 100 Nm ３ / t over 200Nm ３ When the value is less than or equal to / t, the blowing temperature is set to 400°C or more and 800°C or less. The amount of the second reducing gas blown in is 200 Nm ３ / t over 300Nm ３ When the temperature is less than or equal to / t, the blowing temperature is set to 600°C or higher and 1000°C or lower. The method for operating a blast furnace according to claim 4.

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