Method for producing reducing gas and production equipment, as well as a system for producing and burning reducing gas.

Abstract

The present invention aims to provide a method for producing reducing gas and a production facility that can be used in existing facilities without modifying the equipment, as well as a reducing gas production and combustion system equipped with the production facility. [Solution] The present invention provides a method for producing a reducing gas, which includes a reducing gas production step of producing a reducing gas by electrolyzing exhaust gas containing at least CO2, the reducing gas production step of which includes a calorific value control step of which controls the calorific value of the reducing gas, and in the calorific value control step, the calorific value of the reducing gas is controlled according to the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas. The present invention provides a reducing gas production facility that produces a reducing gas by electrolyzing exhaust gas containing at least CO2, and includes a calorific value control unit configured to control the calorific value of the reducing gas according to the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas.

Description

[Technical Field]

[0001] This invention relates to a method for producing reducing gas, production equipment, and a system for producing and burning reducing gas. [Background technology]

[0002] In recent years, reducing greenhouse gas emissions has been called for as a measure against global warming. Much of our energy demand is met by burning fossil fuels, and the carbon dioxide produced as a result is a prime example of a greenhouse gas.

[0003] In heating furnaces and hot blast furnaces (furnaces that obtain heat through gas combustion), there is a need to reduce carbon dioxide emissions as exhaust gas. However, since heating furnaces and hot blast furnaces use coke gas, blast furnace gas (B gas), and a mixed gas (M gas) collected from the plant's internal gases, reducing carbon dioxide emissions may lead to a reduction in the scale of upstream processes due to factors such as the introduction of electric arc furnaces and a reduction in the coke ratio. There are also concerns about a shortage of energy needed for heating.

[0004] As a means of reducing emissions of greenhouse gases such as carbon dioxide, the use of fossil fuels is being considered, along with the use of renewable energy sources such as wind, solar, and geothermal energy as alternatives.

[0005] On the other hand, the use of renewable energy presents challenges in terms of cost, and meeting all energy demand with renewable energy is not realistic at present. Therefore, technologies such as Carbon Capture and Storage (CCS), which separates, captures, and stores carbon dioxide generated from the combustion of fossil fuels, and Carbon Capture and Utilization (CCU), which converts the separated and captured carbon dioxide into valuable materials such as fuels and chemical products, are also being considered.

[0006] The use of renewable energy is also being considered in heating furnaces and hot blast furnaces. By converting electricity derived from renewable energy into fuel gas, it can be stored and used, maximizing the potential of renewable energy. Hydrogen production by water electrolysis is a well-known technology for converting electricity derived from renewable energy into fuel gas. However, there are problems such as the combustion rate being too fast and difficult to control if the hydrogen concentration is too high, and leakage being likely due to the small molecular weight of hydrogen. Therefore, various methods have been proposed to convert hydrogen into other fuel gases that are easier to use (e.g., carbon monoxide, methane, etc.).

[0007] For example, Patent Document 1 proposes a method of receiving carbon dioxide and hydrogen, and using the heat generated by the oxidation of hydrogen contained in the raw material gas to produce carbon monoxide from the carbon dioxide contained in the raw material gas.

[0008] Furthermore, for example, Patent Document 2 proposes a hydrocarbon combustion system comprising: an electrolytic device that generates hydrogen using electricity generated from renewable energy; a hydrocarbon generator that generates hydrocarbons using the hydrogen generated in the electrolytic device and carbon dioxide; a hydrocarbon storage unit that stores the hydrocarbons generated in the hydrocarbon generator; a sealed combustor that burns the hydrocarbons taken out from the hydrocarbon storage unit; and a gas-liquid separation unit that separates carbon dioxide and water produced by the combustion of hydrocarbons, sending the carbon dioxide to the hydrocarbon generator and the water to the electrolytic device. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2022 / 264676 brochure [Patent Document 2] International Publication Brochure No. 2020 / 203087 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, combustion equipment in steel mills and similar facilities has a defined range of appropriate calorific value, and if the calorific value of the fuel gas falls outside this range, it may cause problems such as fires or equipment damage. The gas produced by the methods described in Patent Documents 1 and 2 has a different calorific value from the gas used in existing equipment in steel mills and similar facilities, so it cannot be directly applied to existing equipment, and modifications to the equipment are required, which presents a problem.

[0011] Therefore, the present invention aims to provide a method for producing reducing gas and a production facility that can be used in existing facilities without modifying the equipment, as well as a reducing gas production and combustion system equipped with the production facility. [Means for solving the problem]

[0012] The gist of the present invention is as follows: (1) A method for producing a reducing gas, which includes a reducing gas production step of electrolyzing exhaust gas containing at least CO2, The reducing gas production process includes a calorific value control process for controlling the calorific value of the reducing gas. The exhaust gas consists of one or more of the following: blast furnace combustion exhaust gas, hot blast furnace exhaust gas, coke oven exhaust gas, heating furnace exhaust gas, annealing furnace exhaust gas, and power generation equipment exhaust gas. A method for producing a reducing gas, characterized in that, in the calorific value control step, the calorific value of the reducing gas is controlled according to the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas.

[0013] (2) The method for producing the reducing gas described in (1), wherein the exhaust gas contains CO2 and H2O.

[0014] (3) The method for producing a reducing gas according to (1) or (2), wherein the heat generation control step includes controlling the amount of heat generated by adjusting at least one of the applied voltage and the electrode recirculation ratio of the electrolysis apparatus.

[0015] (4) The calorific value control step includes controlling the calorific value by adjusting the amount of water vapor added to the exhaust gas, and is the method for producing reducing gas according to any one of (1) to (3) above.

[0016] (5) It further includes an exhaust gas discharge combustion step of burning fuel gas in a fuel gas combustion facility, The fuel gas combustion facility consists of any one or more of a blast furnace gas combustion facility, a hot blast stove, a coke oven, a heating furnace, an annealing furnace, and a power generation facility, The exhaust gas used in the reducing gas production step is the gas discharged in the exhaust gas discharge combustion step, and is the method for producing reducing gas according to any one of (1) to (4) above.

[0017] (6) It further includes a reducing gas combustion step of burning the reducing gas in a reducing gas combustion facility, The reducing gas combustion facility consists of any one or more of a blast furnace gas combustion facility, a hot blast stove, a coke oven, a heating furnace, an annealing furnace, and a power generation facility, The exhaust gas used in the reducing gas production step is the gas discharged in the reducing gas combustion step, and is the method for producing reducing gas according to any one of (1) to (4) above.

[0018] (7) The exhaust gas discharge combustion step is a pure oxygen combustion step, and is the method for producing reducing gas according to (5) above.

[0019] (8) The exhaust gas has a hydrogen chloride concentration of 1 ppm or less by volume concentration, and is the method for producing reducing gas according to any one of (1) to (7) above.

[0020] (9) The exhaust gas has a hydrogen chloride concentration of more than 1 ppm by volume concentration, and the exhaust gas and a gas with a hydrogen chloride concentration of 1 ppm or less by volume concentration are alternately supplied to the reducing gas production step, and is the method for producing reducing gas according to any one of (1) to (7) above.

[0021] (10) A reducing gas production facility that produces a reducing gas by electrolyzing exhaust gas containing at least CO2, The exhaust gas consists of one or more of the following: blast furnace gas combustion exhaust gas, hot blast furnace exhaust gas, coke oven exhaust gas, heating furnace exhaust gas, annealing furnace exhaust gas, and power generation equipment exhaust gas. A reducing gas production apparatus characterized by comprising a calorific value control unit configured to control the calorific value of the reducing gas in accordance with the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas.

[0022] (11) The exhaust gas is a reducing gas production facility as described in (10), which contains CO2 and H2O.

[0023] (12) The reducing gas production apparatus according to claim (10) or (11), wherein the heat output control unit comprises at least one of an applied voltage adjustment unit for adjusting the applied voltage of the electrolysis apparatus and an electrode recirculation ratio adjustment unit for adjusting the electrode recirculation ratio.

[0024] (13) The reducing gas production equipment according to any one of (10) to (12), wherein the calorific value control unit is equipped with a water vapor amount adjustment unit for adjusting the amount of water vapor added to the exhaust gas.

[0025] (14) A fuel gas combustion facility for burning fuel gas, The equipment comprises a reducing gas production facility as described in any one of (10) to (13) above, The aforementioned fuel gas combustion equipment consists of one or more of the following: blast furnace gas combustion equipment, hot blast furnace, coke oven, heating furnace, annealing furnace, and power generation equipment. A reducing gas production and combustion system, wherein the exhaust gas used in the reducing gas production equipment is the gas discharged from the fuel gas combustion equipment.

[0026] (15) A reducing gas production facility described in any one of (10) to (14) above, The system includes a reducing gas combustion facility for burning the aforementioned reducing gas, The aforementioned reducing gas combustion equipment consists of one or more of the following: blast furnace gas combustion equipment, hot blast furnace, coke oven, heating furnace, annealing furnace, and power generation equipment. A reducing gas production and combustion system, wherein the exhaust gas used in the reducing gas production equipment is the gas discharged in the reducing gas combustion equipment.

[0027] (16) A reducing gas production and combustion system according to (14) or (15), wherein the fuel gas combustion equipment performs pure oxygen combustion. [Effects of the Invention]

[0028] According to the present invention, it is possible to provide a method for producing reducing gas and a production facility that can be used in existing facilities without modifying the equipment, as well as a reducing gas production and combustion system equipped with the production facility. [Brief explanation of the drawing]

[0029] [Figure 1] This is a flowchart showing a method for producing a reducing gas according to one embodiment of the present invention. [Figure 2] This is a flowchart of a method for producing reducing gas according to another embodiment of the present invention. [Modes for carrying out the invention]

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0031] <Method for producing reducing gas> First, a method for producing a reducing gas according to one embodiment of the present invention will be described. Figure 1 is a flowchart including a method for producing a reducing gas according to one embodiment of the present invention. As shown in Figure 1, the method for producing reducing gas according to this embodiment includes an exhaust gas combustion step (step S101), a reducing gas production step (step S102), and a calorific value control step (step S103).

[0032] The exhaust gas emission combustion process (step S101) is a process in which fuel gas is burned in a fuel gas combustion facility. The exhaust gas used in the reduction gas production process (step S102) is the gas emitted in the exhaust gas emission combustion process (step S101), and consists of one or more of the following: blast furnace gas combustion exhaust gas, hot blast furnace exhaust gas, coke oven exhaust gas, heating furnace exhaust gas, annealing furnace exhaust gas, and power generation equipment exhaust gas. In this embodiment, the fuel gas is supplied from an external source. As an example, the exhaust gas emission combustion process (step S101) can be a pure oxygen combustion process. This reduces the concentration of inert gas (such as nitrogen) in the exhaust gas, thereby expanding the range of calorific value adjustment. The exhaust gas emission combustion process (step S101) consists of one or more of the following: blast furnace gas combustion process, hot blast furnace combustion process, coke oven combustion process, heating furnace combustion process, annealing furnace combustion process, and power generation equipment combustion process. The exhaust gas contains at least carbon dioxide (hereinafter referred to as CO2). The exhaust gas may contain CO2 and H2O (water vapor). The fuel gas combustion equipment consists of one or more of the following: blast furnace gas combustion equipment, hot blast furnace, coke oven, heating furnace, annealing furnace, and power generation equipment. It may be the same equipment as the reducing gas combustion equipment described later, or it may be different equipment. Furthermore, if the exhaust gas contains hydrogen chloride, it is preferable to reduce the hydrogen chloride concentration in the exhaust gas to 1 ppm or less by volume. This is because a high concentration of hydrogen chloride in the exhaust gas reduces the current density during electrolysis in the reducing gas production process, thereby decreasing the efficiency of reducing gas production. This is thought to be because hydrogen chloride reacts with the nickel on the electrodes to form nickel chloride, which inhibits the electrolysis of the gas. Furthermore, even if the current density of electrolysis in the reducing gas production process decreases due to exhaust gas containing hydrogen chloride, the current density can be restored by subsequently flowing gas with a hydrogen chloride concentration of 1 ppm or less by volume. Therefore, the hydrogen chloride concentration in the exhaust gas does not always need to be 1 ppm or less by volume; exhaust gas with a high hydrogen chloride concentration and gas with a low hydrogen chloride concentration may be used alternately.

[0033] The reducing gas production process (step S102) is a process performed after the exhaust gas emission combustion process (step S101) in which a reducing gas is produced by electrolyzing exhaust gas containing at least CO2. At least a portion of the exhaust gas emitted in the exhaust gas emission combustion process (step S101) is sent to the reducing gas production facility. The amount of exhaust gas sent can be appropriately determined according to the scale of the reducing gas production facility.

[0034] The reducing gas production equipment is not particularly limited as long as it is equipped with an electrolysis device capable of reducing CO2 to CO (carbon monoxide) by electrolysis, provided that it is equipped with a calorific value control unit as described later. Therefore, as a basic configuration, for example, a solid oxide electrolyzer cell (SOEC) or a polymer electrolyte machine (PEM) can be used. An SOEC is a cell for obtaining CO by electrolyzing CO2. The basic configuration of an SOEC can be a normal configuration, and as an example, it can be a structure in which a solid electrolyte is sandwiched between a cathode and an anode. Since waste heat can be used to generate water vapor, it is preferable to use an SOEC for the reducing gas production equipment used in the reducing gas production process (step S102). In an SOEC, it is necessary to maintain the cell temperature at 600 to 900°C, so it is preferable to introduce the exhaust gas into the SOEC at a temperature range of 100 to 300°C so that the cell temperature does not drop when the exhaust gas is introduced. Since the reducing gas produced in SOEC is at a high temperature, it may be used as a heat source for generating steam in the reducing gas production process (step S102).

[0035] The reducing gas production process (step S102) includes a calorific value control process (step S103) for controlling the calorific value of the reducing gas. In the calorific value control process (step S103), an appropriate calorific value of the reducing gas is determined as the target calorific value according to the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas. In this embodiment, the determination of the target calorific value is performed as part of the calorific value control process (step S103), but the determination of the target calorific value can also be performed prior to the calorific value control process (step S103), and in this case, it can be performed at any timing prior to the calorific value control process (step S103).

[0036] The calorific value control step (step S103) includes controlling the calorific value by adjusting the reaction rate of electrolysis by adjusting at least one of the applied voltage and the electrode recirculation ratio of the electrolysis apparatus. Specifically, increasing the applied voltage can increase the reaction rate of electrolysis and thus increase the calorific value of the reduced gas produced, while decreasing the applied voltage can decrease the reaction rate of electrolysis and thus decrease the calorific value of the reduced gas produced. Furthermore, increasing the electrode recirculation ratio can increase the reaction rate of electrolysis and thus increase the calorific value of the reduced gas produced, while decreasing the electrode recirculation ratio can decrease the reaction rate of electrolysis and thus decrease the calorific value of the reduced gas produced. While not particularly limited, one example is that the applied voltage can have predetermined voltage ranges set for both increasing and decreasing the applied voltage. For example, when decreasing the applied voltage, the setting range can be set to 1.4 to 1.9V. Furthermore, although not particularly limited, one example is that the electrode recirculation ratio can be adjusted according to the single-pass reaction rate (one-pass conversion rate) of the SOEC.

[0037] Furthermore, the calorific value control step (step S103) includes controlling the calorific value by adjusting the amount of water vapor added to the exhaust gas. Specifically, increasing the amount of water vapor added can increase the reaction rate of electrolysis and thus increase the calorific value of the reduced gas produced, while decreasing the amount of water vapor added can decrease the reaction rate of electrolysis and thus decrease the calorific value of the reduced gas produced. The amount of water vapor can be appropriately determined according to the target calorific value. After adding water vapor to the exhaust gas, it may be introduced into the reduced gas production equipment, or the exhaust gas and the water vapor to be added may be introduced into the reduced gas production equipment separately so that the exhaust gas and water vapor are mixed inside the reduced gas production equipment.

[0038] For example, by producing reducing gas under predetermined conditions (e.g., under normal setting conditions) without controlling the calorific value, and measuring the calorific value of the produced reducing gas, it is possible to determine whether it is greater or less than the appropriate calorific value of the existing reducing gas combustion equipment (and therefore whether the calorific value should be controlled to decrease or increase). This can also be done by calculation based on the setting values ​​of each parameter under the predetermined conditions (e.g., normal setting conditions), rather than by actual measurement.

[0039] Returning to the explanation of the reducing gas production process (step S102), in the reducing gas production process (step S102), first, exhaust gas is introduced into the electrolysis cell (SOEC). Next, in order to control the calorific value (calorific value control process (step S103)), the following steps are performed. First, if necessary, an adjusted amount of steam can be added (step S103-1). The amount of steam added can be adjusted according to the target calorific value.

[0040] Adding water vapor allows for a further expansion of the adjustment range for the calorific value. For example, if the exhaust gas contains a large amount of inert gas such as nitrogen, the target calorific value cannot be reached even if the electrolytic reaction rate is increased to 100%. In such cases, adding water vapor to the exhaust gas makes it possible to produce a reducing gas with the target calorific value. To decrease the calorific value, the amount of water vapor is reduced to lower the reaction rate, and to increase the calorific value, the amount of water vapor is increased to promote electrolysis. Adding water vapor in the reducing gas production process (step S102) also has the effect of making it more difficult for carbon to precipitate on the electrodes, which contributes to extending the lifespan of the electrodes. By adjusting the amount of water vapor, it is also possible to freely adjust the ratio of CO to H2 (hydrogen) in the produced reducing gas.

[0041] The method of generating steam is not limited, but it can be produced in a steam production process, for example. Specifically, steam can be obtained by bubbling, or it can be produced by evaporating water using the waste heat of combustion exhaust gas. Instead of adding steam, the steam contained in the combustion exhaust gas can be introduced into the reducing gas production device without dewatering (adjusting the amount of dewatering) and used as a steam source in the reducing gas production process. Since the reducing gas produced in SOEC is at a high temperature, steam can also be generated using the sensible heat of the reducing gas.

[0042] Next, the applied voltage to the SOEC is adjusted (step S103-2). The magnitude of the applied voltage can be set appropriately according to the target heat generation.

[0043] Next, the electrode recirculation ratio of the SOEC is adjusted (step S103-3). The magnitude of the electrode recirculation ratio can be set appropriately according to the target heat generation amount. The order of steps S103-1 to S103-3 can be determined arbitrarily.

[0044] In this embodiment, all of the following are adjusted in the electrolysis apparatus: the applied voltage, the electrode recirculation ratio, and the amount of water vapor (including the case where no water vapor is added) (steps S103-1 to S103-3). However, it is sufficient to adjust one or more of these.

[0045] Next, using the SOEC operating conditions adjusted in the calorific value control process (step S103), the exhaust gas is reduced by electrolysis (step S102-1). This generates SOEC output gas (a mixture of reduced gas and water vapor) and oxygen.

[0046] Next, the SOEC output gas (a mixture of reducing gas and water vapor) is dehydrated to produce a reducing gas (step S102-2). The dehydration method is not particularly limited, but for example, it can be performed by cooling or membrane separation.

[0047] The calorific value of the output reducing gas can be measured as needed. Based on the measured calorific value, the operating conditions of the SOEC for the next calorific value control process (step S103) can be determined. Alternatively, the calorific value can also be calculated from the operating conditions.

[0048] Although not part of the process of this embodiment, the resulting reducing gas has its calorific value controlled and optimized, so it can be burned in (existing) reducing gas combustion equipment (step S104). The following describes the effects and advantages of the method for producing reducing gas according to this embodiment.

[0049] The method for producing reducing gas in this embodiment includes a reducing gas production step (step S102) in which reducing gas is produced by electrolyzing exhaust gas containing at least CO2, and the reducing gas production step includes a calorific value control step (step S103) in which the calorific value of the reducing gas is controlled according to the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas. According to the method for producing reducing gas of this embodiment, the calorific value of the reducing gas produced in the reducing gas production process (step S102) is controlled (step S103) to match the appropriate calorific value of the reducing gas combustion equipment, so that the obtained reducing gas can be used in (existing) reducing gas combustion equipment (step S104). As described above, the method for producing reducing gas according to this embodiment allows for the free setting of the calorific value of the reducing gas to be produced. Therefore, it is possible to produce reducing gas with the same calorific value as the fuel gas used in existing equipment (e.g., blast furnace gas), and thus it can be applied directly to existing equipment without modification.

[0050] Figure 2 is a flowchart of a method for producing reducing gas according to another embodiment of the present invention. The embodiment in Figure 2 differs from the embodiment in Figure 1 in that the exhaust gas is obtained by burning the reducing gas obtained by the method for producing reducing gas of the embodiment in Figure 2, without using an externally supplied fuel.

[0051] The method of the embodiment shown in Figure 2 includes a reducing gas combustion step (step S201) in which the reducing gas (obtained by the reducing gas manufacturing method of the embodiment shown in Figure 2) is burned in a reducing gas combustion facility. In the method of the embodiment shown in Figure 2, this reducing gas combustion step is the exhaust gas emission combustion step. That is, the exhaust gas used in the reducing gas production step (step S202) is the gas emitted in the reducing gas combustion step. In this case, the reducing gas combustion facility consists of one or more of the following: a blast furnace gas combustion facility, a hot blast furnace, a coke oven, a heating furnace, an annealing furnace, and a power generation facility.

[0052] The reducing gas production process (step S202) is the same as the reducing gas production process (step S102) in the embodiment of Figure 1, except that the exhaust gas used is obtained by burning the reducing gas obtained by the reducing gas production method of the embodiment of Figure 2, so a further explanation is omitted. Similarly, the calorific value control process (step S203) is the same as the calorific value control process (step S103) in the embodiment of Figure 1, so a further explanation is omitted.

[0053] As shown in the embodiment of Figure 2, the calorific value of the reducing gas produced can be freely set, so it is possible to produce reducing gas with the same calorific value as the fuel gas used in existing equipment (e.g., blast furnace gas), and therefore it can be applied as is without modifying existing equipment. Furthermore, in the embodiment shown in Figure 2, since the obtained reducing gas is used in step S201, it is not necessary to use an externally supplied fuel gas, energy can be reused, and greenhouse gas (CO2) emissions can be reduced. Furthermore, for the first cycle of this circulation process, an externally supplied fuel gas can be used, similar to the embodiment shown in Figure 1.

[0054] While not particularly limited, the method for producing the reducing gas in the embodiments shown in Figures 1 and 2 can, for example, be carried out using the reducing gas production equipment according to the following embodiment.

[0055] <Reducing gas production equipment> Next, a reducing gas production facility according to one embodiment of the present invention will be described. The reducing gas production facility of this embodiment is a reducing gas production facility that produces reducing gas by electrolyzing exhaust gas containing at least CO2. The exhaust gas consists of one or more of the following: blast furnace gas combustion exhaust gas, hot blast furnace exhaust gas, coke oven exhaust gas, heating furnace exhaust gas, annealing furnace exhaust gas, and power generation equipment exhaust gas, and may contain CO2 and H2O.

[0056] As described above, the reducing gas production equipment of this embodiment is not particularly limited as long as it includes an electrolysis device capable of reducing CO2 to CO by electrolysis, provided that it is equipped with a calorific value control unit described later. The basic configuration of the reducing gas production equipment can be, for example, a solid oxide electrolysis cell (SOEC) or a polymer electrolyte electrolysis device (PEM). In the case of SOEC, it can have a configuration similar to known SOECs, and as an example, it can have a structure in which a solid electrolyte is sandwiched between a cathode and an anode.

[0057] The reducing gas production equipment of this embodiment includes a calorific value control unit configured to control the calorific value of the reducing gas in accordance with the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas. Preferably, the calorific value control unit includes at least one of an applied voltage adjustment unit that adjusts the applied voltage of the electrolysis device and an electrode recirculation ratio adjustment unit that adjusts the electrode recirculation ratio. Preferably, the calorific value control unit also includes a water vapor amount adjustment unit that adjusts the amount of water vapor added to the exhaust gas. Preferably, the calorific value control unit includes one or more of the applied voltage adjustment unit, the electrode recirculation ratio adjustment unit, and the water vapor amount adjustment unit.

[0058] The heat output control unit can be configured using a processor. For example, the applied voltage adjustment unit can be a processor programmed to control the applied voltage of an electrolysis device such as an SOEC. Also, for example, the electrode recirculation ratio adjustment unit can be a processor programmed to control the electrode recirculation ratio of an electrolysis device such as an SOEC. Furthermore, for example, the water vapor amount adjustment unit can be a processor programmed to control the amount of water vapor added to the exhaust gas. The following describes the operation and effects of the reducing gas production equipment according to this embodiment.

[0059] The reducing gas production equipment of this embodiment is a reducing gas production equipment that produces reducing gas by electrolyzing exhaust gas containing at least CO2, and includes a calorific value control unit configured to control the calorific value of the reducing gas in accordance with the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas. According to the reducing gas production equipment of this embodiment, the calorific value control unit can control the calorific value of the reducing gas to match the appropriate calorific value of the reducing gas combustion equipment during production. Therefore, the resulting reducing gas can be used in (existing) reducing gas combustion equipment. As described above, the reducing gas production equipment of this embodiment allows for the free setting of the calorific value of the reducing gas to be produced. Therefore, it is possible to produce reducing gas with the same calorific value as the fuel gas used in existing equipment (e.g., blast furnace gas), and thus it can be applied to existing equipment without modification.

[0060] <Reducing gas production and combustion system> A reducing gas production and combustion system according to one embodiment of the present invention includes, for example, the reducing gas production equipment of the embodiment described above.

[0061] As an example, the system may further include a fuel gas combustion facility for burning fuel gas. The fuel gas combustion facility consists of one or more of the following: a blast furnace gas combustion facility, a hot blast furnace, a coke oven, a heating furnace, an annealing furnace, and a power generation facility. The exhaust gas used in the reducing gas production facility is the gas emitted from this fuel gas combustion facility. This fuel gas combustion facility can perform pure oxygen combustion or burn blast furnace gas.

[0062] Another example is the addition of a reducing gas combustion facility that burns the reducing gas. The exhaust gas used in the reducing gas production facility is the gas emitted from this reducing gas combustion facility.

[0063] Even with the reducing gas production and combustion system according to one embodiment of the present invention, the calorific value of the reducing gas can be controlled by the calorific value control unit of the reducing gas production equipment to match the appropriate calorific value of the reducing gas combustion equipment, and the resulting reducing gas can be used in (existing) reducing gas combustion equipment.

[0064] Although embodiments of the present invention have been described above, the present invention is not limited in any way to the above embodiments. For example, in the above embodiments, examples were given of exhaust gas being obtained by burning externally supplied fuel in a hot blast furnace, coke oven, heating furnace, annealing furnace, or power generation equipment (Embodiment of Figure 1), or of reducing gas being obtained by burning in a hot blast furnace, coke oven, heating furnace, annealing furnace, or power generation equipment (Embodiment of Figure 2). However, exhaust gas from blast furnace combustion, hot blast furnace, coke oven, heating furnace, annealing furnace, or power generation equipment may also be supplied from an external source. Various other modifications and changes are possible. The following describes embodiments of the present invention, but the present invention is not limited in any way to the following embodiments. [Examples]

[0065] Example 1 (Comparative Example 1) The exhaust gas obtained by burning blast furnace gas is electrolyzed without controlling its calorific value to produce reducing gas for a hot blast furnace. In this comparative example 1, where the calorific value is not controlled, the calorific value of the reducing gas is 6.56 MJ / Nm³. 3 Therefore, it cannot be used in existing equipment due to its excessively high heat output.

[0066] (Example of Invention 1) The exhaust gas obtained by burning blast furnace gas is electrolyzed to produce reducing gas for the hot blast furnace, after controlling the reaction rate by adjusting the applied voltage of the SOEC. Target calorific value: 4.6 MJ / Nm 3 It can produce reducing gas.

[0067] (Example of Invention 2) The exhaust gas obtained by burning blast furnace gas is electrolyzed using SOEC (Steam-Oxide Emission Control) with the reaction rate controlled by adding steam, in order to produce reducing gas for the hot blast furnace. Target calorific value: 4.6 MJ / Nm 3 It can produce reducing gas.

[0068] (Example of Invention 3) The exhaust gas obtained by burning blast furnace gas is electrolyzed using SOEC (Steam-Oxide-Conducted Gas) after controlling the reaction rate by adding steam to produce reduced gas for power generation. Target calorific value: 7.9 MJ / Nm 3 It can produce reducing gas.

[0069] (Example of Invention 4) The exhaust gas obtained by burning blast furnace gas is electrolyzed using SOEC (Steam-Oxide Emission Control) with the reaction rate controlled by adding steam, in order to produce reducing gas for the heating furnace. Target calorific value: 9.4 MJ / Nm 3 It can produce reducing gas.

[0070] (Example of Invention 5) Using the combustion exhaust gas of the hot blast stove, produce reduction gas for the hot blast stove, and burn the produced reduction gas to obtain exhaust gas and circulate it. In the production of reduction gas, control the reaction rate by adding water vapor to the SOEC and then perform electrolysis. Produce reduction gas with a target calorific value of 4.6 MJ / Nm 3 and perform process recirculation.

[0071] (Inventive Example 6) Using the exhaust gas obtained by burning blast furnace gas, produce reduction gas for the hot blast stove. Even when air combustion is performed, reduction gas with a target calorific value of 4.6 MJ / Nm 3 can be produced.

[0072] The details of this example are summarized in Table 1 below. In Table 1, the amount of water vapor is expressed as the volume% (outer number) of water vapor with respect to the combustion exhaust gas.

[0073]

Table 1

[0074] Example 2 To investigate the influence of the hydrogen chloride gas concentration in the exhaust gas, an SOEC electrolysis test was conducted using exhaust gas with different hydrogen chloride gas concentrations. The experimental conditions were as follows. ·SOEC: Ni-YSZ ·Applied voltage: 1.4 V ·SOEC temperature: 700 °C ·Exhaust gas flow rate: 250 mL / min

[0075] (Inventive Example 7) Set the exhaust gas composition to CO2: 40 volume%, H2O: 40 volume%, hydrogen chloride concentration: 0 ppm (volume concentration), and the current density to 1.4 A / cm 3

[0076] (Inventive Example 8) Set the exhaust gas composition to CO2: 40 volume%, H2O: 40 volume%, hydrogen chloride concentration: 1 ppm (volume concentration), and the current density to 1.4 A / cm 3 ​ The current density was equivalent to that of Invention Example 7, which did not contain hydrogen chloride.

[0077] (Example of Invention 9) The exhaust gas composition is assumed to be CO2: 40% by volume, H2O: 40% by volume, and hydrogen chloride concentration: 50 ppm (volume concentration). The current density is assumed to be 1.3 A / cm². 3 That's what I decided. The current density was lower than in Invention Example 7, which did not contain hydrogen chloride. Subsequently, when exhaust gas with 0 ppm (volume concentration) of hydrogen chloride was passed through, the current density was 1.4 A / cm². 3 He recovered.

[0078] (Example of Invention 10) The exhaust gas composition is assumed to be CO2: 40% by volume, H2O: 40% by volume, and hydrogen chloride concentration of 100 ppm (volume concentration). The current density is assumed to be 1.2 A / cm². 3 That's what I decided. The current density was lower than in Invention Example 7, which did not contain hydrogen chloride. Subsequently, when exhaust gas with 0 ppm (volume concentration) of hydrogen chloride was passed through, the current density was 1.4 A / cm². 3 He recovered.

Claims

1. At least CO ２ A method for producing a reducing gas, which includes a reducing gas production step, in which exhaust gas containing is electrolyzed to produce a reducing gas, The reducing gas production process includes a calorific value control process for controlling the calorific value of the reducing gas. The exhaust gas consists of one or more of the following: blast furnace combustion exhaust gas, hot blast furnace exhaust gas, coke oven exhaust gas, heating furnace exhaust gas, annealing furnace exhaust gas, and power generation equipment exhaust gas. A method for producing a reducing gas, characterized in that, in the calorific value control step, the calorific value of the reducing gas is controlled according to the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas.

2. The aforementioned exhaust gas is CO ２ and H ２ A method for producing a reducing gas according to claim 1, comprising oxygen (O).

3. The method for producing a reducing gas according to claim 1 or 2, wherein the heat output control step includes controlling the heat output by adjusting at least one of the applied voltage and the electrode recirculation ratio of the electrolysis apparatus.

4. The method for producing a reducing gas according to claim 1 or 2, wherein the calorific value control step includes controlling the calorific value by adjusting the amount of water vapor added to the exhaust gas.

5. The process further includes an exhaust gas emission combustion process in which fuel gas is burned in a fuel gas combustion facility, The aforementioned fuel gas combustion equipment consists of one or more of the following: blast furnace gas combustion equipment, hot blast furnace, coke oven, heating furnace, annealing furnace, and power generation equipment. The method for producing a reducing gas according to claim 1 or 2, wherein the exhaust gas used in the reducing gas production process is the gas discharged in the exhaust gas discharge combustion process.

6. The process further includes a reducing gas combustion step in which the reducing gas is burned in the reducing gas combustion equipment, The aforementioned reducing gas combustion equipment consists of one or more of the following: blast furnace gas combustion equipment, hot blast furnace, coke oven, heating furnace, annealing furnace, and power generation equipment. The method for producing a reducing gas according to claim 1 or 2, wherein the exhaust gas used in the reducing gas production process is the gas discharged in the reducing gas combustion process.

7. The method for producing a reducing gas according to claim 5, wherein the exhaust gas combustion step is a pure oxygen combustion step.

8. The method for producing a reducing gas according to claim 1 or 2, wherein the exhaust gas has a hydrogen chloride concentration of 1 ppm or less by volume.

9. The exhaust gas has a hydrogen chloride concentration of more than 1 ppm by volume. A method for producing a reducing gas according to claim 1 or 2, wherein the exhaust gas and a gas having a hydrogen chloride concentration of 1 ppm or less by volume are alternately supplied to the reducing gas production process.

10. At least CO ２ A reducing gas production facility that produces a reducing gas by electrolyzing exhaust gas containing the following: The exhaust gas consists of one or more of the following: blast furnace combustion exhaust gas, hot blast furnace exhaust gas, coke oven exhaust gas, heating furnace exhaust gas, annealing furnace exhaust gas, and power generation equipment exhaust gas. A reducing gas production apparatus characterized by comprising a calorific value control unit configured to control the calorific value of the reducing gas in accordance with the appropriate calorific value of the reducing gas combustion equipment that burns the reducing gas.

11. The aforementioned exhaust gas is CO ２ and H ２ A reducing gas production apparatus according to claim 10, comprising O.

12. The reducing gas production apparatus according to claim 10 or 11, wherein the heat output control unit comprises at least one of an applied voltage adjustment unit for adjusting the applied voltage of the electrolysis apparatus and an electrode recirculation ratio adjustment unit for adjusting the electrode recirculation ratio.

13. The reducing gas production apparatus according to claim 10 or 11, wherein the calorific value control unit comprises a water vapor amount adjustment unit for adjusting the amount of water vapor added to the exhaust gas.

14. A fuel gas combustion facility that burns fuel gas, The reducing gas production equipment according to claim 10 or 11 comprises, The aforementioned fuel gas combustion equipment consists of one or more of the following: blast furnace gas combustion equipment, hot blast furnace, coke oven, heating furnace, annealing furnace, and power generation equipment. A reducing gas production and combustion system, wherein the exhaust gas used in the reducing gas production equipment is the gas discharged from the fuel gas combustion equipment.

15. A reducing gas production apparatus according to claim 10 or 11, The system includes a reducing gas combustion facility for burning the aforementioned reducing gas, The aforementioned reducing gas combustion equipment consists of one or more of the following: blast furnace gas combustion equipment, hot blast furnace, coke oven, heating furnace, annealing furnace, and power generation equipment. A reducing gas production and combustion system, wherein the exhaust gas used in the reducing gas production equipment is the gas discharged in the reducing gas combustion equipment.

16. The reduction gas production and combustion system according to claim 14, wherein the fuel gas combustion equipment performs pure oxygen combustion.

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