Blast furnace operation method, and blast furnace

Abstract

In this blast furnace operation method in which a high-temperature reducing gas is blown into a blast furnace body, piping connecting a heating unit for heating the reducing gas and a blowing part of the blast furnace body has a multi-pipe structure having at least an inner pipe and an outer pipe, a heat insulation material is provided between the inner pipe and the outer pipe, and an inert gas is filled into the space between the inner pipe and the outer pipe.

Description

Operating method of blast furnace and blast furnace

[0001] This disclosure relates to an operating method of a blast furnace and a blast furnace. This application claims priority based on Japanese Patent Application No. 2025-025258 filed in Japan on February 19, 2025, and incorporates its content herein by reference.

[0002] In general blast furnace operation, iron-based raw materials and coke are charged into the furnace alternately and layer by layer from the top of the blast furnace, and reducing gas is blown into the blast furnace. This reducing gas reduces iron-based raw materials (mainly iron oxide) in the furnace.

[0003] In order to efficiently promote the reduction of iron-based raw materials in the furnace using reducing gas, in the operation of the blast furnace, the reducing gas is heated by a heating device such as a heater so that the reduction reaction proceeds efficiently, the reducing gas is blown into the blast furnace without the temperature dropping too much, and it is necessary to have safety measures in case the high-temperature reducing gas leaks from the pipe before being blown into the blast furnace. Since the reducing gas is heated to a high temperature, if the reducing gas leaks from the pipe before being blown into the blast furnace, it is necessary to stop the operation, which is not desirable. Also, if the reducing gas leaks from the pipe, the reducing material for the iron-based raw materials will be insufficient, which is not desirable.

[0004] For example, Patent Document 1 discloses a method for detecting leakage of a heat-insulated pipe, which is characterized by blowing gas into the annular space between an outer pipe and a heat-insulating material, discharging the gas from the annular space at a position away from the blowing point in the axial direction, and measuring the humidity of the discharged gas with a humidity detector to detect leakage. Patent Document 1 discloses that when the fluid being transported inside the inner pipe leaks or groundwater enters the annular space from the outer pipe, these evaporate and the humidity rises, so that the humidity detector indicates a high humidity.

[0005] Japanese Patent Application Laid-Open No. 58-021133

[0006] In the technology described in Patent Document 1, it is possible to detect leakage of the fluid being transported from the inner pipe or groundwater from the outer pipe, but it is not possible to detect leakage of the reducing gas heated to a high temperature. Therefore, the technology described in Patent Document 1 cannot be applied to the operation of a blast furnace.

[0007] This disclosure is made in view of the above circumstances and aims to provide a method for operating a blast furnace that allows for safe operation without leakage of reducing gas to the outside, in a method for injecting high-temperature reducing gas into a blast furnace, and a blast furnace used therein.

[0008] The gist of this disclosure is as follows: [1] A method for operating a blast furnace, wherein high-temperature reducing gas is injected into the blast furnace body, wherein the piping connecting a heating section for heating the reducing gas and the injection section of the blast furnace body is a multi-tube structure having at least an inner tube and an outer tube, has an insulating material between the inner tube and the outer tube, and fills the space between the inner tube and the outer tube with an inert gas. [2] The method for operating a blast furnace according to [1], wherein the outer tube has an exhaust section equipped with a gas concentration meter, and the gas concentration meter detects leakage of the reducing gas from the inner tube. [3] The method for operating a blast furnace according to [2], wherein the inert gas is constantly supplied between the inner tube and the outer tube. [4] The method for operating a blast furnace according to [2] or [3], wherein the exhaust section equipped with the gas concentration meter is located at the top of the outer tube. [5] A method for operating a blast furnace according to any one of [2] to [4], characterized in that if the amount of reducing gas leaking from the inner tube is small, the supply pressure of the inert gas is increased to prevent leakage of the reducing gas from the inner tube. [6] A blast furnace used in the method for operating a blast furnace according to [1], comprising: a blast furnace body; a heating section for heating reducing gas; and piping connecting the injection section of the blast furnace body and the heating section, wherein the piping has a multi-tube structure having at least an inner tube and an outer tube, and an insulating material is provided between the inner tube and the outer tube.

[0009] According to the above-described embodiment of this disclosure, it is possible to provide a method for operating a blast furnace in which high-temperature reducing gas is injected, enabling safe operation without leakage of the reducing gas to the outside, and a blast furnace used therein.

[0010] This is a schematic diagram of a blast furnace used in the blast furnace operation method according to this embodiment.

[0011] The following describes the operation method of a blast furnace according to the embodiment of this disclosure with reference to the drawings.

[0012] Figure 1 is a schematic diagram of a blast furnace 1 used in the blast furnace operation method according to this embodiment. As shown in Figure 1, the blast furnace 1 includes a blast furnace body 10, a heating section 20, and piping 30 as blast furnace ancillary equipment. More specifically, it includes a blast furnace body, a heating section for heating reducing gas, and piping connecting the injection section of the blast furnace body and the heating section, wherein the piping has a multi-tube structure having at least an inner tube and an outer tube, and an insulating material is provided between the inner tube and the outer tube.

[0013] The blast furnace body 10 is a cylindrical device into which iron-based raw materials and coke can be charged. Multiple blowing ports 11 for blowing air into the furnace are provided at regular intervals on the circumferential surface of the blast furnace body 10. In the example in Figure 1, the blowing ports 11 are shown as tuyeres.

[0014] The heating unit 20 is equipment for raising the temperature of the reducing gas supplied to the furnace. In the heating unit 20, the reducing gas is heated by heating means such as electric heating or gas combustion. The heating unit 20 may also be a hot stove.

[0015] The piping 30 is equipment connected to the blast furnace body 10. The piping 30 has a multi-tube structure having at least an inner tube 31 and an outer tube 32, with an insulating material 33 between the inner tube 31 and the outer tube 32. The reducing gas is sent from the heating section 20 on the upstream side through the inner tube 31 to the injection section 11 of the blast furnace body 10 on the downstream side. In this embodiment, the upstream and downstream sides are defined with respect to the reducing gas.

[0016] The reducing gas injected from the reducing gas inlet is a gas that functions as a reducing agent inside the blast furnace. That is, even if a gas does not function as a reducing agent before being injected into the blast furnace body 10, if it can generate reducing components by thermal decomposition inside the blast furnace, it is included in the "reducing gas" as defined in this embodiment. Furthermore, the specific gravity of the reducing gas is smaller than the specific gravity of the hot air injected into the blast furnace from the hot air tuyeres. Examples of such reducing gases include at least one selected from hydrogen gas, hydrocarbon gases (e.g., methane gas), carbon monoxide gas, ammonia gas, and alcohol gases (e.g., methanol gas and ethanol gas). In this embodiment, at least one selected from coke oven gas (COG), converter gas (LDG), blast furnace gas (BFG), natural gas (NG), and synthesis gas (Syngas) may be used as the reducing gas. These reducing gases may be used individually or in combination of two or more. Among these, the reducing gas is preferably hydrogen gas or a reducing gas containing hydrogen atoms. The reducing gas is heated to a high temperature before being blown in through the reducing gas inlet. The temperature of the heated reducing gas is preferably 530°C or higher, 550°C or higher, or 600°C or higher. From the viewpoint of improving the efficiency of the reduction reaction of iron-based materials in the furnace, it is preferably 800°C or higher, and more preferably 900°C or higher or 1000°C or higher.

[0017] The thermal insulation material 33 has the function of suppressing the temperature drop of the reducing gas inside the inner tube 31. Therefore, it is possible to suppress the temperature drop of the reducing gas heated in the heating section 20 until the reducing gas reaches the injection section 11. The thermal insulation material 33 has voids. The voids contain air, but when an inert gas is supplied between the inner tube 31 and the outer tube 32, the air is replaced with the inert gas, and the voids in the thermal insulation material 33 are filled with the inert gas. For example, organic or inorganic materials can be used as the thermal insulation material. As organic materials, synthetic resins (polyester resin, polyurethane resin, acrylic resin, epoxy resin) can be used, and as inorganic materials, glass fibers, ceramics, etc. can be used. As ceramics, ceramic fibers with low thermal conductivity can be used.

[0018] The piping 30 is not directly connected to the injection section 11 at the bottom of the furnace, but may extend to the vicinity of the injection section 11. In this case, the piping 30 may be connected to an annular pipe connected to multiple injection sections 11 provided circumferentially around the blast furnace body 10. Furthermore, the piping 30 only needs to be configured to inject reducing gas into the blast furnace body 10, and may be configured to blow reducing gas through a shaft (not shown). The bottom of the furnace refers to the area located between the furnace body, where the furnace diameter is largest, and the taphole in the height direction. Additionally, the radially outer side of the outer tube 32 may have another outer tube (a second outer tube if the outer tube 32 is the first outer tube) for the purpose of insulating the temperature of the reducing gas and protecting the outer tube 32.

[0019] The outer pipe 32 may have an air supply section 34 for supplying inert gas. If the outer pipe 32 has an air supply section 34, the inert gas is supplied from the air supply section 34 between the inner pipe 31 and the outer pipe 32. The outer pipe 32 may also have an exhaust section 35 for discharging the inert gas. In the example shown in Figure 1, the air supply section 34 is provided at the downstream end of the reducing gas and the exhaust section 35 is provided at the upstream end, but the opposite configuration is also possible.

[0020] The inner pipe 31 and the outer pipe 32 may be constructed by joining multiple steel pipes from the upstream side to the downstream side. In this embodiment, since the inner pipe 31 and the outer pipe 32 are required to function as piping for high-temperature reducing gas, it is preferable that they have appropriate heat resistance and corrosion resistance. The connections between the multiple steel pipes are connected, for example, by welding or flange connection.

[0021] In the blast furnace operation method according to this embodiment, an inert gas is filled between the inner tube 31 and the outer tube 32. The inert gas is, for example, helium, argon, or nitrogen gas. It is preferable to use nitrogen gas as the inert gas because it is easy to handle and readily available. A method for sufficiently filling the space between the inner tube 31 and the outer tube 32 with inert gas is to supply inert gas from the air supply section 34, stop supplying inert gas from the air supply section 34 when the oxygen concentration between the inner tube 31 and the outer tube 32 falls below 1%, and then close the air supply section 34 and the exhaust section 35.

[0022] By filling the space between the inner pipe 31 and the outer pipe 32 with inert gas, the air in the voids of the insulation material 33 is replaced by the inert gas. In this case, even if reducing gas leaks from the inner pipe 31, the leaked reducing gas is maintained between the inner pipe 31 and the outer pipe 32 and does not come into contact with air between the inner pipe 31 and the outer pipe 32 or outside the outer pipe 32. Therefore, even if a reducing gas that would spontaneously ignite upon contact with air is used, operation can continue safely.

[0023] In the blast furnace 1 described above, it is preferable that the exhaust section 35 be equipped with a gas concentration meter. Depending on the type of reducing gas, a concentration meter capable of detecting the concentration of the reducing gas components should be used. The concentration of the reducing gas components can be measured by opening the air supply section 34 and the exhaust section 35, and measuring the concentration of the reducing gas components while supplying inert gas from the air supply section 34. If reducing gas is leaking from the inner pipe 31, the leakage of reducing gas can be detected from the measurement value obtained by the gas concentration meter in the exhaust section 35. After measurement, the inert gas should be refilled using the method described above, and the air supply section 34 and the exhaust section 35 should be closed.

[0024] Furthermore, if the outer pipe 32 has an exhaust section 35 equipped with a gas concentration meter, it is preferable in the operation method of the blast furnace 1 to constantly supply inert gas between the inner pipe 31 and the outer pipe 32, and to constantly measure the concentration of the reducing gas components using the gas concentration meter provided in the exhaust section 35.

[0025] In this case, inert gas is constantly supplied from the air supply section 34, and inert gas is constantly discharged from the exhaust section 35. Furthermore, the concentration of the reducing gas components is constantly measured using a gas concentration meter. This allows for the rapid detection of reducing gas leakage from the inner pipe 31 based on the measurement value from the gas concentration meter in the exhaust section 35. Note that "constantly supplying inert gas" here also includes intermittently supplying inert gas. When supplying inert gas intermittently, the supply of inert gas is stopped for a certain period of time (for example, 5 to 10 seconds), and this operation is repeated.

[0026] The exhaust section 35, equipped with a gas concentration meter, is preferably located at the top of the outer tube 32. The top of the outer tube 32 refers to the upstream side of the reducing gas, i.e., the side of the heating section 20, when the outer tube 32 is arranged vertically (parallel to the axial direction of the blast furnace body 10) as shown in Figure 1, and to the upper vertical side when viewed from the axial direction of the outer tube 32, when the outer tube 32 is arranged horizontally (perpendicular to the axial direction of the blast furnace body 10). By equipping the exhaust section 35 and gas concentration meter at the top of the outer tube 32, the reducing gas, which has a lower specific gravity than the inert gas, can be more easily detected by the gas concentration meter. As a result, leakage of reducing gas from the inner tube 31 can be detected more quickly.

[0027] It is preferable to detect the leakage of reducing gas using a gas concentration meter, and if the amount of leaked reducing gas is small, to increase the supply pressure of the inert gas from the air supply section 34. It is preferable to increase the supply pressure of the inert gas until no more reducing gas leaks from the inner pipe 31. Whether or not there is a leakage of reducing gas can be determined by the gas concentration meter. Here, "small amount" means that the concentration of reducing gas is, for example, less than 10 volume%, less than 6 volume%, or less than 4 volume%. Note that if the reducing gas is hydrogen, the detection limit of the hydrogen concentration meter is 0.003 volume%. By increasing the supply pressure of the inert gas from the air supply section 34 until no more reducing gas leaks from the inner pipe 31, the blast furnace 1 can be operated continuously without stopping operations.

[0028] According to the above-described embodiment of this disclosure, it is possible to provide a method for operating a blast furnace in which high-temperature reducing gas is injected, enabling safe operation without leakage of the reducing gas to the outside, and a blast furnace used therein.

[0029] 1 Blast furnace 10 Blast furnace body 11 Injection section 20 Heating section 30 Piping 31 Inner pipe 32 Outer pipe 33 Insulation material 34 Air supply section 35 Exhaust section

Claims

1. A method for operating a blast furnace, wherein high-temperature reducing gas is injected into the blast furnace body, characterized in that the piping connecting the heating section for heating the reducing gas and the injection section of the blast furnace body has a multi-tube structure having at least an inner tube and an outer tube, an insulating material is provided between the inner tube and the outer tube, and an inert gas is filled between the inner tube and the outer tube.

2. The method for operating a blast furnace according to claim 1, characterized in that the outer tube has an exhaust section equipped with a gas concentration meter, and the leakage of the reducing gas from the inner tube is detected by the gas concentration meter.

3. The method for operating a blast furnace according to claim 2, characterized in that the inert gas is constantly supplied between the inner tube and the outer tube.

4. The method for operating a blast furnace according to claim 2 or 3, characterized in that the exhaust section on which the gas concentration meter is provided is located at the upper part of the outer tube.

5. The method for operating a blast furnace according to claim 2 or 3, characterized in that, if the amount of reducing gas leaking from the inner tube is small, the supply pressure of the inert gas is increased to prevent leakage of the reducing gas from the inner tube.

6. The method for operating a blast furnace according to claim 4, characterized in that, if the amount of reducing gas leaking from the inner tube is small, the supply pressure of the inert gas is increased to prevent leakage of the reducing gas from the inner tube.

7. A blast furnace used in the blast furnace operation method described in claim 1, comprising: a blast furnace body; a heating section for heating reducing gas; and piping connecting the blowing section of the blast furnace body and the heating section, wherein the piping has a multi-tube structure having at least an inner tube and an outer tube, and an insulating material is provided between the inner tube and the outer tube.

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