Blast furnace plant operation method

Abstract

The present invention relates to a method for operating a blast furnace plant (1) including a blast furnace (10), at least one material hopper (20) having an upper seal valve (21) and a lower seal valve (22) for charging raw materials into the blast furnace (10), and at least one hot stove (30) for generating hot air for the blast furnace (10), the method including at least one charging cycle including the steps of opening the upper seal valve (21), introducing raw materials into the material hopper (20), closing the upper seal valve (21), equalizing the pressure between the material hopper and the top of the blast furnace, and opening the lower seal valve (22) to discharge the raw materials into the blast furnace (10). In order to provide a cost-effective method for minimizing the risk of explosion during operation of a top charging system, the present invention allows for the transfer of off-gas from at least one hot stove (30) by a transfer system (40) to at least one material hopper (20) and for the off-gas to be injected into the material hopper (20) before the bottom seal valve (22) is opened.

Description

[Technical Field]

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

[0002] Today, the blast furnace remains the most widely used process for steel production, although alternative methods exist, such as scrap melting in an electric arc furnace or direct reduction. One of the problems with blast furnace installations is the blast furnace gas (BFG). This gas is commonly referred to as "top gas" because it exits the top of the furnace. One component of BFG is CO2, which is harmful to the environment and often renders it useless for industrial purposes. BFG can contain high concentrations of CO2, ranging from 20% to 30% (v / v). Apart from this, BFG typically contains significant amounts of N2, CO, H2O, and H2. Summary of the Invention [Problem to be solved by the invention]

[0003] In connection with the reduction of CO2 emissions, efforts are being made to reduce the use of carbonaceous fuels for blast furnace operation. As an alternative, fuels with increased hydrogen concentrations are being used. Also, fuels such as coke oven gas can be used as reducing gas for iron ore. However, it is not possible to completely oxidize the reducing gas, and therefore a large amount of hydrogen gas exists in the reaction products. This also increases the H2 concentration in the top region of the blast furnace, where the material hopper of the top charging system is located. In modern blast furnaces, the material hopper is usually 40 to 120 m 3The material hopper has a volume of 1000 sq. m. When raw materials are charged into the material hopper, ambient air is also introduced and mixes with the blast furnace top gas, resulting in a gas mixture containing a large amount of oxygen (from the ambient air) and hydrogen (from the top gas). The resulting mixture may be flammable and even explosive, posing a high safety risk to the operation of the top charging facility. To avoid such risks, it has been proposed to inject N2 (or an N2-enriched gas mixture) into the material hopper together with or immediately after the input materials. While such nitrogen inerting is effective, it consumes a large amount of N2, which cannot be recovered or reused. This increases the operating costs of the blast furnace plant. Furthermore, N2 or N2-enriched gas is not always available. [Means for solving the problem]

[0004] It is therefore an object of the present invention to provide a cost-effective method for minimizing the risk of fire and explosion during operation of a top charging system.

[0005] This object is solved by a method according to claim 1 and a blast furnace plant according to claim 15. Preferred embodiments are covered by the dependent claims.

[0006] In particular, a method for operating a blast furnace plant is provided, the method comprising the steps of: opening the top sealing valve; introducing raw material into a material hopper; closing the top sealing valve; Opening the lower seal valve to discharge the raw material into the blast furnace; at least one charging cycle having Off-gas from the at least one hot stove is transferred to the at least one material hopper by a transfer system, and the off-gas is injected into the material hopper before a lower seal valve is opened to discharge the raw material into the blast furnace.

[0007] 1. A blast furnace plant comprising a blast furnace, at least one material hopper for charging raw materials into the blast furnace, the material hopper having an upper seal valve and a lower seal, and at least one hot stove adapted to generate hot air for the blast furnace, opening the top sealing valve; introducing raw material into a material hopper; closing the top sealing valve; Opening the lower seal valve to discharge the raw material into the blast furnace; and adapted to perform at least one charging cycle including a transfer system adapted to transfer off-gas from the at least one hot stove to the at least one material hopper, and adapted to inject the off-gas into the material hopper before the lower seal is opened and the raw material is discharged into the blast furnace; Blast furnace plants are also provided. General description of the invention

[0008] The present invention provides a method for operating a blast furnace plant. The blast furnace plant comprises a blast furnace. While this method can be applied to the production of other metals, such as lead or copper, blast furnaces are typically used to produce pig iron. Generally, a blast furnace has a suitable vertical shaft or furnace, typically with an outer wall having a refractory lining. This has an upper opening through which raw materials are introduced into the shaft and a lower opening through which slag and raw metal (e.g., pig iron) are removed. At the bottom of the blast furnace, the shaft is typically surrounded by an annular bustle, from which multiple tuyere tubes originate. Hot air is injected into the shaft through the tuyere tubes. In this context, "hot air" refers to hot air, but also to other O-containing gases or gas mixtures, such as oxygen-enriched air or (almost) pure oxygen. Optionally, other solid components (such as granular coal) or gases (such as coke oven gas, natural gas, or synthetic gas) can be injected into the shaft either at the tuyere level or at the shaft level (above the tuyere level). The tuyere level corresponds to the melting zone of the blast furnace, while the shaft level largely corresponds to the reduction zone of the blast furnace, which is usually significantly cooler than the melting zone.

[0009] Blast furnace plants also include at least one material hopper for charging raw materials into the blast furnace. The raw materials may also be referred to as charge materials or input materials. These are granular bulk materials that may contain particles of various sizes. The raw materials may also contain particles of various chemical compositions. Therefore, strictly speaking, such materials may be referred to as a material mixture. For simplicity, the term "material" is used in this context. As explained further below, blast furnace plants typically include multiple material hoppers for different raw materials. The raw materials may be, for example, iron ore or another iron-containing material, fuel, or reducing materials such as coal, coke, carbonaceous material, wood, charcoal, or mixtures thereof.

[0010] The material hopper, also known as a lock hopper, includes an upper seal valve and a lower seal valve. The upper seal valve, also known as a top seal valve, is located at or near the upper end of the material hopper, and the lower seal valve, also known as a bottom seal valve, is located at or near the lower end of the material hopper. Each seal valve is adapted to seal an opening in the material hopper. Correspondingly, the hopper includes an upper opening for receiving material and a lower opening for discharging material into the blast furnace. Each seal valve provides an airtight seal, although a small amount of gas leakage through the seal valve is acceptable. In addition to the upper and lower seal valves, the hopper may also include a lower material gate. The function of this material gate is not to provide an airtight seal but to regulate the flow of material into the blast furnace through the lower opening. At least one material hopper is typically part of a so-called "bellless top" charging system in a blast furnace plant.

[0011] Blast furnace plants also include at least one hot blast stove that generates hot air for the blast furnace. As mentioned above, "hot air" in this context can refer to any heated O2-containing gas, typically hot air. A hot blast stove, also known as a hot blast stove, cowper stove, or cowper, is a regenerative heat exchanger or regenerator that is heated during the combustion or heating stage, stores heat, and the heat is then transferred to cold air (i.e., cold air or another O2-containing gas) during the blowing or blasting stage. As explained below, blast furnace plants typically include multiple hot blast stoves that can alternately pass through each blowing stage to provide a nearly constant supply of hot air to the blast furnace. During the heating stage, fuel gas is combusted to generate heat, which is then (partially) stored by the hot blast stove (typically checker bricks within the furnace). Combustion of fuel gas often produces off-gas with negligible calorific value or calorific value, particularly with a very low O2 concentration. However, its high temperature can be utilized to transfer heat in a heat exchanger. In the prior art, the off-gas is typically released to the environment, for example through the chimney of a blast furnace plant.

[0012] The proposed method includes at least one charging cycle. Typically, multiple charging cycles are performed sequentially. Each charging cycle refers to one material hopper. If a blast furnace plant typically includes multiple material hoppers, the charging cycles for different material hoppers may be performed sequentially and / or simultaneously. Each charging cycle includes the following steps: opening the top seal valve, introducing material into the material hopper, closing the top seal valve, equalizing the material hopper with the top pressure of the blast furnace, and opening the bottom seal valve to discharge the material into the blast furnace. It is understood that material is introduced through the aforementioned top opening associated with the top seal valve and discharged into the blast furnace through the aforementioned bottom opening associated with the bottom seal valve. Note that these steps are typically performed in the order listed so that at least one seal valve is closed at any given time during the charging cycle. Although not mentioned above, it is understood that the pressure in the material hopper is released to the atmosphere before the top seal valve is opened. In addition, since the upper seal valve is open while the lower seal valve is closed, once the materials are discharged into the blast furnace, the lower seal valve is closed for the next charging cycle. Therefore, free gas exchange between the blast furnace and the environment through the material hopper is always prevented. Blast furnaces are usually operated at an overpressure relative to the environment to prevent blast furnace gases from freely escaping to the outside.

[0013] It will be appreciated that there may be a significant time interval between the closing of the top seal valve and the opening of the bottom seal valve during which material accumulates in the material hopper, and the bottom seal valve may be opened and closed several times to repeatedly discharge material before the top seal valve is again opened to introduce new material into the material hopper.

[0014] According to the present invention, off-gas from at least one hot blast stove is transferred to at least one material hopper by a transfer system, and the off-gas is injected into the material hopper before the lower seal valve is opened. The transfer system is adapted to transfer the off-gas from the hot blast stove to the material hopper. In the simplest case, the transfer system can include a single pipe connecting the hot blast stove to the material hopper. However, it will be understood that additional elements are required for controlled and efficient transfer, some of which are described below. The off-gas is, of course, the gas (or gas mixture) resulting from the aforementioned combustion during the heating phase of the hot blast stove. It is within the scope of the present invention for the off-gas to be combined or mixed with other gases before or during injection into the material hopper. Because the off-gas results from combustion, its O2 concentration is generally low, even negligible. Therefore, the off-gas can be considered an inert gas. By introducing the off-gas into the material hopper, the O2 concentration can be significantly reduced, ideally rendering the material hopper inert. Therefore, the risk of forming an explosive mixture when the bottom seal valve is opened and gas from inside the material hopper mixes with the blast furnace gas originating from the blast furnace is significantly reduced. This applies particularly in situations where the blast furnace gas contains significant amounts of H2, which can form explosive mixtures with O2 (commonly referred to as "oxyhydrogen" or "nargas").

[0015] The use of abundantly available gases from normal operation of blast furnace plants as inert gas is highly beneficial for the proposed method. Because the off-gas is available in large quantities and at no additional cost, effective and inexpensive inertization of the material hopper can be achieved.

[0016] Depending on various factors, such as the composition of the off-gas and the blast furnace gas, partial inerting of the material hopper may be sufficient. However, when the bottom seal valve is opened, the off-gas is preferably injected into the material hopper so that it constitutes more than 50% v / v of the gas. In other words, the original atmosphere in the material hopper is preferably replaced with more than 50% v / v of the off-gas before the bottom seal valve is opened. For example, if the original atmosphere in the material hopper consists of air with an O2 concentration of approximately 21% v / v and the air is replaced by only 70% v / v of the off-gas, which contains almost no O2, the resulting gas mixture has an O2 concentration of approximately 6% v / v, which may be acceptable to avoid the risk of explosion.

[0017] Furthermore, when the lower seal valve is opened, it is preferable to inject off-gas so that the O2 concentration in the gas in the raw material hopper is less than 4.5 v / v%. The O2 concentration in each case may be even lower, for example, less than 3 v / v%.

[0018] The flammability limits based on volume percent of hydrogen in air at 101 kPa (1 atmosphere) are 4.0 and 75.0. The flammability limits based on volume percent of hydrogen in oxygen at 101 kPa are 4.0 and 94.0. The explosive limits of hydrogen in air are 18.3 to 59 volume percent. Flames in and around tubes or structural assemblies can create turbulence that can cause a deflagration to develop into an explosion, even in the absence of total containment.

[0019] This method can be particularly useful when a blast furnace is operated with a fuel such as coke oven gas, which is used as a reducing gas for iron ore. As explained above, this results in a significant H concentration in the blast furnace gas. In such an embodiment, after the lower seal valve is opened, the gas in the material hopper at least partially mixes with blast furnace gas from the blast furnace, which has an H concentration of at least 5% v / v. Here, the "gas in the material hopper" may also be referred to as the "atmosphere in the material hopper." The H concentration of the blast furnace gas may be even higher, for example, at least 7% v / v. It will be appreciated that opening the lower seal valve removes the barrier between the gas in the material hopper and the blast furnace gas, allowing the two gases to at least partially mix with each other. A H concentration of at least 5% v / v, combined with an atmosphere containing at least 4.5% oxygen, may result in at least a flammable or even explosive mixture. However, when the gas in the material hopper is inerted using the method of the present invention, the formation of a flammable or explosive mixture may be suppressed.

[0020] As explained above, off-gas is a result of combustion in a hot blast stove, which typically consumes most of the oxygen present prior to combustion. Preferably, the off-gas has an O2 concentration of less than 2% v / v, more preferably less than 1% v / v. Under these circumstances, the off-gas can be considered substantially oxygen-free, and therefore, replacing a sufficient portion of the internal gases with the off-gas can effectively inert the material hopper.

[0021] Preferably, an overpressure is created in the material hopper between the time the upper valve is closed and the time the lower sealing valve is opened. In this context, "overpressure" refers to a pressure above the atmospheric pressure surrounding the blast furnace plant. Typically, there is also an overpressure in the blast furnace. Therefore, if the material hopper is at atmospheric pressure, a significant amount of blast furnace gas will enter the material hopper. The overpressure can be set to a value slightly higher than the pressure in the blast furnace, for example, from about 0 mbar to 100 mbar or more. In particular, this overpressure can be created by injecting offgas at high pressure or by using other pressurized gases.

[0022] There are various options regarding exactly when the off-gas is injected into the material hopper. According to one option, a portion of the off-gas is injected before the raw material is introduced into the material hopper. At this stage, the gas in the material hopper may include air, off-gas, and blast furnace gas from the previous charging cycle. Because the blast furnace gas also introduces air into the material hopper, it is particularly desirable to vent at least most of the blast furnace gas before new raw material is introduced. In this embodiment, the material hopper may be "flushed" with off-gas before new raw material is introduced. By "portion," we mean that at least a portion or a small amount of the total off-gas injected during one charging cycle is injected before the raw material is introduced into the material hopper.

[0023] Typically, the concentration of blast furnace gas in the material hopper is highest near the lower seal valve because this is the area closest to the blast furnace. Offgas can be advantageously injected into this area to effectively remove or at least dilute the blast furnace gas in the material hopper. In particular, a portion of the offgas is injected between the lower seal valve and the lower material gate. The lower material gate is typically used to regulate the flow of material from the material hopper to the blast furnace. It is sometimes referred to as a material flow regulation gate. The lower material gate is typically located inside the material hopper relative to the lower seal valve, i.e., upstream of the lower seal valve.

[0024] Instead of or in addition to injecting the off-gas before the raw material is introduced into the material hopper, a portion of the off-gas may be injected while the raw material is being introduced into the material hopper. This can reduce the amount of ambient air introduced with the raw material. In this embodiment, the off-gas may be injected into the top of the material hopper, for example, at or near the top seal valve.

[0025] As already mentioned above, each hot blast stove alternates between a heating phase, in which the hot blast stove is heated by combustion, which generates off-gas, and a blowing phase, in which the hot blast stove generates hot air. According to a preferred embodiment, off-gas is recovered from the hot blast stove between the start of a heating phase and the start of the next blowing phase. In other words, the recovery of off-gas is synchronized with the heating and blowing phases of each hot blast stove. By stopping the recovery of off-gas before the start of the blowing phase, the risk of recovering cold or hot air from the hot blast stove instead of off-gas is avoided. It will be appreciated that even the transfer of a small amount of cold or hot air to the material hopper can significantly impair inertization.

[0026] The transfer system, i.e., the system for transferring off-gas from the hot air stove to the material hoppers, includes a recovery pipe for each hot air stove, a discharge pipe for each material hopper, and an intermediate section connecting each recovery pipe to each discharge pipe. Each recovery pipe is connected to the hot air stove and the intermediate section. It can be said that off-gas from all the hot air stoves is collected in the intermediate section. In the intermediate section, the off-gas can be temporarily stored for further transfer to at least one material hopper, if necessary. The discharge pipes lead from the intermediate section to each material hopper, i.e., there is one discharge pipe for each material hopper. Therefore, the off-gas is transferred from the hot air stove through the recovery pipe, the intermediate section, and the discharge pipe to the material hopper.

[0027] Preferably, the off-gas recovered from the hot blast stove is cooled by a cooling device before being injected into the material hopper. Such a cooling device is typically a heat exchanger. Thus, the temperature of the off-gas can be reduced from an initial temperature of, for example, 300°C to 400°C to, for example, 30°C to 80°C. Furthermore, the heat contained in the off-gas can be transferred to other media and thus utilized to facilitate processes in the blast furnace plant or externally. Cooling the off-gas can, for example, prevent damage to the material hopper due to heat. Furthermore, even if a flammable gas mixture is formed, for example, locally and temporarily, in the material hopper, reducing the overall temperature in the material hopper reduces the risk of such a mixture igniting. Typically, the off-gas is cooled while being transported in the transport system from the hot blast stove to the material hopper. For example, the intermediate section described above can include a cooling device so that a single cooling device can be used to cool the off-gas from all the hot blast stoves.

[0028] In one embodiment, the off-gas can be transported passively, i.e., according to a pressure difference, from the hot air stove to the material hopper. However, such passive transport is ineffective and can lead to unpredictable off-gas supply. Therefore, it is preferable for the off-gas to be driven through the transport system by a blower unit. The blower unit may be incorporated into the aforementioned intermediate section of the transport system. The blower unit may include one or more blowers. Preferably, the off-gas flow rate is adjusted by controlling the output of at least one blower. Each blower may have a variable speed drive. The blowers may be arranged in parallel, i.e., the intermediate section may include multiple blower ducts parallel to the off-gas flow, each blower duct containing one blower. The parallel arrangement of blowers increases operational safety through redundancy and allows for higher gas flow rates to be achieved. A recirculation bypass line is added to each blower to improve each blower's response behavior to changing load points. Thus, the blowers operate in continuous operation, and adaptation to different load points is achieved by the recirculation bypass line.

[0029] When a blast furnace plant includes multiple material hoppers, the charging cycles of the different material hoppers are typically not performed simultaneously. Therefore, off-gas is typically only needed in one material hopper at a time. Therefore, it is preferable for the off-gas to be selectively directed to at least one of the material hoppers by a distribution valve unit. The distribution valve unit may include one or more valves that may be located in different discharge pipes. For example, if there are two discharge pipes, the off-gas can be directed to one material hopper by closing the valve in the discharge pipe of the other material hopper. Alternatively, each discharge pipe may be equipped with a check valve to prevent unwanted backflow of the off-gas.

[0030] The present invention also provides a blast furnace plant including a blast furnace, at least one material hopper having an upper seal valve and a lower seal valve for charging raw materials into the blast furnace, and at least one hot stove adapted to generate hot air for the blast furnace. The blast furnace plant is adapted to perform at least one charging cycle including the following steps: opening the upper seal valve, introducing raw materials into the material hopper, closing the upper seal valve, equalizing the pressure between the material hopper and the blast furnace top, and opening the lower seal valve to discharge the raw materials into the blast furnace. The blast furnace plant further includes a transfer system adapted to transfer off-gas from the at least one hot stove to the at least one material hopper, and the blast furnace plant is adapted to inject the off-gas into the material hopper before the lower seal valve is opened. In other words, the present invention relates to a blast furnace plant including a blast furnace and at least one material hopper for charging and introducing raw materials into the blast furnace. The (material) hopper includes an upper seal valve and a lower seal valve. At least one hot blast stove generates hot blast for the blast furnace. The blast furnace plant is configured to perform at least one charging cycle, each of which includes the following steps: opening the upper seal valve, introducing material into the material hopper via the upper seal valve, closing the upper seal valve, equalizing the pressure between the material hopper and the blast furnace top pressure, and opening the lower seal valve to discharge the material into the blast furnace. The blast furnace plant further includes a transfer system configured to transfer off-gas from the at least one hot blast stove to the at least one material hopper, and the blast furnace plant is configured to inject the off-gas into the material hopper. The material hopper can be pressurized to the blast furnace top pressure before the lower seal valve is opened to discharge the material into the blast furnace. It should be noted that the embodiments and advantages described in connection with the method according to the present invention also apply to the blast furnace plant according to the present invention.In one embodiment, the hopper's upper seal valve is configured to seal the hopper's upper opening, the lower seal valve is configured to seal the hopper's lower opening, and the hopper further includes a material gate disposed above the lower seal valve. A "seal valve" generally refers to a sealing mechanism configured to seal a pressurized (gas) volume from the adjacent environment. A "material gate" refers to an openable / closable device for regulating / controlling the passage (and amount) of material introduced into a (blast) furnace. This arrangement allows off-gas to be injected at least partially between the lower seal valve and the lower material gate.

[0031] All these terms have been explained with reference to the method of the invention and will not be explained again. Preferred embodiments of the blast furnace of the invention correspond to the embodiments of the method of the invention. [Brief explanation of the drawings]

[0032] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 1 is a schematic diagram of a blast furnace plant of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a portion of the blast furnace plant of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0033] FIG. 1 is a schematic diagram of a blast furnace plant 1 of the present invention, suitable for implementing the method of the present invention. The blast furnace plant includes a blast furnace 10, the general operation of which is known in the art and will not be described here. Two material hoppers 20, one of which is shown diagrammatically in FIG. 2, are disposed above the top of the blast furnace 10. Each material hopper 20 includes an upper seal valve 21 for sealing the upper opening, a lower seal valve 22 for sealing the lower opening, and a material gate 23 disposed above the lower seal valve 22. During operation, each of the material hoppers 20 receives raw material for the blast furnace 10. For example, one material hopper 20 may receive iron ore, while the other material hopper 20 may receive coke. Each raw material is temporarily stored in the material hopper 20 before being discharged into the blast furnace 10.

[0034] Each material hopper 20 sequentially goes through multiple charging cycles. At the start of each charging cycle, the lower seal valve 22 and material gate 23 are closed, and the upper seal valve 21 is opened. Material can then be charged into the material hopper 20 through the upper seal valve 21. Once a predetermined amount of material has been charged, the upper seal valve 21 is closed, providing an airtight seal toward the outside of the material hopper 20. Next, the pressure within the material hopper 20 is increased until it reaches an overpressure exceeding the pressure within the blast furnace 10. The lower seal valve 22 is then opened, and the material gate 23 does not provide an airtight seal even when the lower seal valve 22 is closed, allowing gas exchange between the material hoppers 20 of the blast furnace 10. To discharge the material into the blast furnace 10, the material gate 23 is opened to a certain extent, thereby controlling the flow of material. Finally, once all the material has been discharged into the blast furnace 10, the material gate 23 and the lower seal valve 22 are closed. The pressure in the material hopper 20 can then be adjusted to ambient pressure, after which the top seal valve 21 can be reopened and new material can be charged.

[0035] In industrial setups, semi-clean BF gas is often injected into the material hopper in the first step, bringing it to a pressure of BF gas -0.15 bar. This is called primary equalization, after which hot stove off-gas is injected to bring the hopper to BF top pressure (similar to secondary equalization, which is usually done with nitrogen).

[0036] Generally speaking, some components of blast furnace gas can form combustible or explosive mixtures with oxygen in the ambient air. In particular, blast furnace gas can contain significant concentrations of H, e.g., at least 7% v / v, which combine with O to form combustible mixtures. To minimize or eliminate this problem, off-gas is injected into the material hopper 20 during certain stages of the charging cycle, as described below. The off-gas has an O concentration of less than 2% v / v and can therefore generally be considered an inert gas. The off-gas is recovered from multiple hot stoves 30, which are typically used to supply hot air to the blast furnace 10. Each hot stove 30 alternates between a heating phase, in which the stove is heated by combustion, which generates off-gas, and a blowing phase, in which the hot stove produces hot air. The hot stoves 30 are lined with checker bricks, which temporarily store heat from combustion. When the off-gas in the hot stove 30 is replaced with cold air (i.e., air or another oxygen-containing gas at ambient temperature), heat is transferred to the cold air, generating hot air. A fuel gas suitable for combustion can be introduced into the hot stove 30 by a supply pipe, not shown for the sake of simplicity. The same applies to the cold air pipe for supplying the cold air and the hot air pipe for transporting the hot air from the hot stove 30 to the blast furnace 10.

[0037] The off-gas is partially transported through the off-gas pipe 31 to the chimney 33, from where it is released to the environment. A portion of the internal heat of the off-gas, which may initially have a temperature of 300°C to 400°C, is recovered by a first heat exchanger 32 within the off-gas pipe 31. Another portion of the off-gas is transported to the material hopper 20 via a transfer system 40, which will be described in detail below. A recovery pipe 41 begins at each hot blast stove 30. The gas flow through each recovery pipe 41 can be controlled by a control valve 42. The control valve 42 operates to recover off-gas from the hot blast stove 30 only when the hot blast stove 30 is in the heating phase, while preventing gas from being recovered from the hot blast stove 30 when the hot blast stove 30 is in the blowing phase, thereby avoiding the introduction of oxygen-enriched gas into the transfer system 40. Each recovery pipe 41 is connected to an intermediate section 50 of the transfer system 40, more specifically, to an intermediate pipe 51. In the second heat exchanger 52, the internal heat of the off-gas is recovered and it is cooled, for example to a temperature of 45°C. Downstream of the second heat exchanger 52, the off-gas reaches a reservoir 53, where it can be temporarily stored, which is used to smooth the gas flow and condense some of the residual moisture in the gas. The intermediate pipe 51 then reaches a blower section 54, where it branches into three blower pipes 55. Each blower pipe 55 contains a blower 56 that propels the off-gas through the transfer system 40. The output of each blower 56 can be adjusted to adapt the off-gas flow rate.

[0038] The intermediate section 50 is connected to two discharge pipes 60, each connected to one of the material hoppers 20. Each discharge pipe 60 includes a flow meter 61 that can monitor gas flow. Specifically, information from the gas flow meter 61 can be used to appropriately control the blower 56. A distribution valve unit 62 includes two control valves 63, one for each discharge pipe 60. The distribution valve unit 62 regulates the gas flow and can shut off the gas flow through one of the discharge pipes 60, particularly in situations where off-gas does not need to be injected into the corresponding material hopper 20. Furthermore, each distribution line 60 includes a check valve 64, a relief pipe 67, and two shutoff valves 65 and 66 located upstream and downstream of the relief pipe 67. For example, gas can be released from the discharge pipe 60 through the relief pipe 67 for maintenance purposes. The shutoff valves 65 and 66 can be used to isolate a portion of the transfer system 40 before the relief pipe 67 is opened.

[0039] As shown in the cross-sectional view of FIG. 2, the discharge pipe 60 enters the material hopper 20 between the bottom seal valve 22 and the material gate 23. Once all the material has been discharged into the blast furnace 10, the bottom seal valve 22 and the material gate 23 are closed as described above. However, the material gate 23 does not provide an airtight seal for the remainder of the material hopper 20. Before the top seal valve 21 is opened, off-gas is injected through the discharge pipe 60 to vent any remaining H2 in the blast furnace gas from the bottom of the material hopper 20. Injection can continue until at least 90% (v / v) of the gas in the material hopper 20 has been replaced with the off-gas. Gas already contained in the material hopper 20 can be released through a relief valve (not shown). Material can then be introduced through the top seal valve 21 as described above. At this point, the H2 concentration in the material hopper 20 is negligible, so an explosive mixture cannot be formed. However, ambient air is introduced with the material, thereby introducing a significant amount of O2 into the material hopper 20. This could pose a risk of causing an explosion when the lower seal valve 22 is reopened. This risk can be avoided in various ways. For example, after the raw material is introduced, off-gas injection via the discharge pipe 60 can be continued to move O2 from at least the lower part of the material hopper. Alternatively or additionally, an additional discharge pipe 70 may be provided to inject off-gas near the upper seal valve 21 at the top of the material hopper 20. This discharge pipe 70 allows off-gas to be injected while the raw material is being introduced. Therefore, the ambient air around the raw material becomes significantly thinner. Therefore, the O2 concentration in the material hopper can be reduced to, for example, less than 5% v / v. [Explanation of symbols]

[0040] 1 Blast furnace plant 10 blast furnace 20 Material hopper 21 Upper seal valve 22 Lower seal valve 23 Material Gate 30 hot stove 31 Offgas pipe 32,52 heat exchanger 33 Chimney 40 Transport System 41 Recovery pipe 42 Control 50 middle part 51 Intermediate tube 53 Reservoir 54 Blower unit 55 Air pipe 56 Blower 60,70 Discharge pipe 61 Flow meter 62 Distribution valve unit 63 Control valve 64 Check valve 65,66 Shut-off valve 67 Relief pipe

Claims

1. A method for operating a blast furnace plant (1) comprising a blast furnace (10), at least one material hopper (20) for charging raw materials into the blast furnace (10), the material hopper having an upper seal valve (21) and a lower seal valve (22), and at least one hot stove (30) for generating hot air for the blast furnace (10), the method comprising: opening the upper sealing valve (21); introducing raw material into said material hopper (20); closing the upper sealing valve (21); a pressure equalization step between the material hopper and the blast furnace top pressure; opening the lower seal valve (22) to discharge the raw material into the blast furnace (10); at least one charging cycle having off-gas from the at least one hot stove (30) is transferred to the at least one material hopper (20) by a transfer system (40), the off-gas is injected into the material hopper (20), and the material hopper is pressurized to a blast furnace top pressure before the bottom seal valve (22) is opened and the raw materials are discharged into the blast furnace; and When the bottom seal valve (22) is opened, the off-gas is injected so as to constitute at least 70 v / v % of the gas in the material hopper (20).

2. When the lower seal valve (22) is opened, the O 2 of the gas in the material hopper (20) is ２ 2. The method of claim 1, wherein the off-gas is injected to a concentration of less than 4.5% v / v.

3. After the lower seal valve (22) is opened, the gas in the material hopper (20) is at least 5 v / v % H ２ 3. The method according to claim 1 or 2, characterized in that the blast furnace gas is at least partially mixed with the blast furnace gas (10) having a concentration.

4. The off-gas is less than 2% v / v O ２ 4. The method according to claim 1, wherein the concentration is 0.01 to 0.

1.

5. 5. The method according to claim 1, wherein an overpressure is generated inside the material hopper (20) between the time when the upper sealing valve (21) is closed and the time when the lower sealing valve (22) is opened.

6. 6. The method according to any one of claims 1 to 5, characterized in that the off-gas is injected at least partially before the raw material is introduced into the material hopper (20).

7. 7. The method according to any one of claims 1 to 6, characterized in that the off-gas is injected at least partially between the lower sealing valve (22) and the lower material gate (23).

8. 8. The method according to any one of claims 1 to 7, characterized in that the off-gas is injected at least partially while the raw material is being introduced into the material hopper (20).

9. 9. The method according to claim 1, wherein each hot blast stove (30) alternately passes through a heating stage in which the hot blast stove (30) is heated by combustion that generates the off-gas, and a blowing stage in which the hot blast stove (30) generates hot air, and the off-gas is recovered from the hot blast stove (30) between the start of the heating stage and the start of the next blowing stage.

10. 10. The method according to any one of claims 1 to 9, characterized in that the transfer system (40) comprises a return pipe (41) for each hot stove (30), a discharge pipe (60) for each material hopper (20), and an intermediate section (50) connecting each return pipe (41) to each discharge pipe (60).

11. 11. The method according to any one of claims 1 to 10, characterized in that the off-gas recovered from the hot blast stove (30) is cooled by a cooling device (52) before being injected into the material hopper (20).

12. 12. The method according to any one of claims 1 to 11, characterized in that the off-gas is propelled through the transfer system (40) by a blower unit (54).

13. 13. The method according to any one of claims 1 to 12, characterized in that the off-gas is selectively directed to at least one of a plurality of material hoppers (20) by a distribution valve unit (62).

14. A blast furnace plant (1) comprising a blast furnace (10), at least one material hopper (20) for charging raw materials into the blast furnace (10), the material hopper having an upper seal valve (21) and a lower seal valve (22), and at least one hot stove (30) adapted to generate hot air for the blast furnace (10), The blast furnace plant (1) further comprises a transfer system (40) adapted to transfer off-gas from the at least one hot stove (30) to the at least one material hopper (20), wherein the blast furnace plant (1) is configured to inject the off-gas into the material hopper (20) and to perform at least one charging cycle as defined in the method of claim 1.

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