Gas production system and method for operating the gas production system

Abstract

The system includes a reactor (2) having a reducing agent that reduces a raw material gas to generate a product gas, a hydrogen generator (3) that generates a reducing gas for reducing the reducing agent, a raw material gas supply path (41) that sends the raw material gas to the reactor, a reducing gas supply path (42) that sends a reducing gas from the hydrogen generator to the reactor, a product gas discharge path (43) that discharges the product gas generated in the reactor, a recycled gas discharge path (44) that discharges recycled gas generated from the reducing agent reduced by the reducing gas from the reactor and sends it to the hydrogen generator, a supply gas switching unit (60) that switches the path of the gas sent to the reactor, and an exhaust gas switching unit (70) that switches the path of the gas exhausted from the reactor.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to gas production systems and methods of operating gas production systems. [Background technology]

[0002] In recent years, in order to prevent global warming and realize a carbon-recycling society, research and development has been advanced into technologies for recovering carbon dioxide from exhaust gases or the atmosphere and converting the recovered carbon dioxide into valuable substances. For example, a gas production system has been disclosed that produces a product gas containing carbon monoxide from a raw material gas containing carbon dioxide (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-75447 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional gas production systems, water vapor generated in a reactor is condensed and converted into liquid water, which is temporarily stored in a tank and then supplied from the tank to a hydrogen generator. When the hydrogen generator is composed of a solid oxide electrolysis cell, a steam methane reformer, or a steam reformer using an oxygen carrier such as a metal oxide, the water stored in the tank is converted into water vapor and supplied to the hydrogen generator. As such, conventional gas production systems require energy to convert a feed gas containing carbon dioxide into a product gas containing carbon monoxide, as well as energy to condense the water vapor and energy to convert water into water vapor, resulting in low energy efficiency.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a gas production system with high energy efficiency. [Means for solving the problem]

[0006] The gas production system of the present disclosure includes a reactor having a reducing agent that reduces carbon dioxide contained in a raw material gas to produce a product gas containing carbon monoxide, a hydrogen generator that generates a reducing gas containing hydrogen for reducing the reducing agent, a raw material gas supply path that sends the raw material gas to the reactor, a reducing gas supply path that sends the reducing gas from the hydrogen generator to the reactor, a product gas discharge path that discharges the product gas produced in the reactor from the reactor, a recycled gas discharge path that discharges recycled gas containing water vapor generated from the reducing agent reduced by the reducing gas from the reactor and sends it to the hydrogen generator, a supply gas switching unit that switches the path of the gas sent to the reactor to either the raw material gas supply path or the reducing gas supply path, and an exhaust gas switching unit that switches the path of the gas discharged from the reactor to either the product gas discharge path or the recycled gas discharge path. [Effects of the Invention]

[0007] The gas production system of the present disclosure is equipped with a recycled gas discharge path that discharges recycled gas containing water vapor generated from the reducing agent reduced by the reducing gas from the reactor and sends it to the hydrogen generator, thereby improving energy efficiency. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a configuration diagram of a gas production system according to a first embodiment. [Figure 2] FIG. 2 is a diagram for explaining the operation of the gas production system according to the first embodiment. [Figure 3] FIG. 2 is a diagram for explaining the operation of the gas production system according to the first embodiment. [Figure 4] FIG. 10 is a configuration diagram of a gas production system according to a second embodiment. [Figure 5] FIG. 10 is a diagram for explaining the operation of the gas production system according to the second embodiment. [Figure 6]FIG. 10 is a diagram for explaining the operation of the gas production system according to the second embodiment. [Figure 7] FIG. 10 is a configuration diagram of a gas production system according to a third embodiment. [Figure 8] FIG. 10 is a diagram for explaining the operation of the gas production system according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a gas production system according to an embodiment of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same reference numerals indicate the same or corresponding parts.

[0010] Embodiment 1 1 is a configuration diagram of a gas production system according to a first embodiment. The gas production system 1 according to this embodiment includes a reactor 2 having a reducing agent that reduces a feed gas containing carbon dioxide to produce a product gas containing carbon monoxide, and a hydrogen generator 3 that generates a reducing gas containing hydrogen for reducing the reducing agent. The gas production system 1 according to this embodiment also includes a feed gas supply path 41 that sends the feed gas to the reactor 2, a reducing gas supply path 42 that sends a reducing gas from the hydrogen generator 3 to the reactor 2, a product gas discharge path 43 that discharges the product gas generated in the reactor 2 from the reactor 2, and a recycled gas discharge path 44 that discharges recycled gas containing water vapor generated from the reducing agent reduced by the reducing gas from the reactor 2 and sends the recycled gas to the hydrogen generator 3. Furthermore, the gas production system 1 according to this embodiment is equipped with a supply gas switching unit 60 that switches the path of the gas sent to the reactor 2 to either the raw material gas supply path 41 or the reducing gas supply path 42, and an exhaust gas switching unit 70 that switches the path of the gas exhausted from the reactor 2 to either the generated gas exhaust path 43 or the recycled gas exhaust path 44.

[0011] A raw material gas containing carbon dioxide is supplied to the raw material gas supply path 41 from an external raw material gas supply unit 4. The raw material gas supply path 41 is equipped with a blower 51 for pressurizing and feeding the raw material gas, and a raw material gas heater 31 for heating the raw material gas. The raw material gas heater 31 heats the raw material gas to a temperature close to the temperature of the reactor 2 described below. Note that if the temperature of the raw material gas supplied from the raw material gas supply unit 4 is high, or if the heat capacity of the reactor 2 is sufficiently large compared to the raw material gas, the raw material gas heater 31 may be omitted.

[0012] A reducing gas containing hydrogen is supplied to the reducing gas supply path 42 from the hydrogen generator 3. The reducing gas supply path 42 is provided with a blower 52 for pressurizing and feeding the reducing gas, and a reducing gas heater 32 for heating the reducing gas. The reducing gas heater 32 heats the reducing gas to a temperature close to the temperature of the reactor 2, which will be described later. Note that if the temperature of the reducing gas supplied from the hydrogen generator 3 is high, or if the heat capacity of the reactor 2 is sufficiently large compared to the reducing gas, the reducing gas heater 32 may not be necessary.

[0013] The produced gas discharge path 43 is connected to a produced gas discharge unit 5 for discharging the produced gas to the outside. The recycled gas discharge path 44 is provided with a blower 53 for pressure-transferring the recycled gas from the reactor 2 to the hydrogen generator 3. Note that if the wind power of the blower 53 that pressure-transfers the recycled gas to the hydrogen generator 3 is large, the blower 52 provided in the reducing gas supply path 42 may be omitted.

[0014] The supply gas switching unit 60 is composed of a raw material gas on-off valve 61 provided between the raw material gas supply path 41 and the reactor 2, and a reducing gas on-off valve 62 provided between the reducing gas supply path 42 and the reactor 2. When the supply gas switching unit 60 opens either the raw material gas on-off valve 61 or the reducing gas on-off valve 62, it closes the other valve. In this way, the supply gas switching unit 60 switches the path of the gas sent to the reactor 2 to either the raw material gas supply path 41 or the reducing gas supply path 42.

[0015] The exhaust gas switching unit 70 is composed of a produced gas on-off valve 71 provided between the produced gas discharge path 43 and the reactor 2, and a recycled gas on-off valve 72 provided between the recycled gas discharge path 44 and the reactor 2. When the exhaust gas switching unit 70 opens either the produced gas on-off valve 71 or the recycled gas on-off valve 72, it closes the other valve. In this way, the exhaust gas switching unit 70 switches the path for gas discharged from the reactor 2 to either the produced gas discharge path 43 or the recycled gas discharge path 44.

[0016] The reducing agent provided in the reactor 2 is composed of a material that is easily oxidized by carbon dioxide and easily reduced by hydrogen. For example, a material containing at least one metal element belonging to groups 3 to 12 can be selected as such a material. For example, iron is preferred because it has a high conversion efficiency for reducing carbon dioxide and converting it to carbon monoxide. The reducing agent is preferably in the form of granules, flakes, or pellets. A reducing agent in such a shape can increase the filling rate inside the reactor 2 and increase the contact area with the raw material gas. The reducing agent may be supported on a carrier such as alumina, silica, or activated carbon.

[0017] The reactor 2 is maintained at a temperature suitable for the oxidation-reduction reaction of the reducing agent by a temperature control mechanism (not shown). When the reducing agent is, for example, iron, the temperature of the reactor 2 is preferably 600 to 1000°C. The higher the temperature of the reactor 2, the faster the reaction rate of the oxidation-reduction reaction of the reducing agent, thereby increasing the amount of gas produced per unit time. On the other hand, the lower the temperature of the reactor 2, the less energy is required for the temperature control mechanism and the lower the heat resistance required for the components of the reactor 2. This reduces the running costs of the gas production system 1 and the manufacturing costs of the reactor 2. The temperature of the reactor 2 may be changed when the reducing agent undergoes an oxidation reaction and a reduction reaction. However, not changing the temperature during the oxidation and reduction reactions of the reducing agent reduces energy loss associated with temperature increases and decreases.

[0018] The hydrogen generator 3 has the function of generating hydrogen from water vapor. Examples of hydrogen generators with such a function include solid oxide electrolysis cells and steam methane reformers. Because solid oxide electrolysis cells can generate hydrogen using only steam as a raw material, it is preferable to use solid oxide electrolysis cells as the hydrogen generator 3. The hydrogen generator 3 is maintained at a temperature suitable for hydrogen generation by a temperature control mechanism (not shown). When the hydrogen generator 3 is a solid oxide electrolysis cell, the temperature of the hydrogen generator 3 is preferably 600 to 800°C. When the hydrogen generator 3 is a steam methane reformer, the temperature of the hydrogen generator 3 is preferably 500 to 1000°C. The lower the temperature of the hydrogen generator 3, the less energy is required for the temperature control mechanism, and the lower the heat resistance required for the components of the hydrogen generator 3. Therefore, the running costs of the gas production system 1 and the manufacturing costs of the hydrogen generator 3 can be reduced. Furthermore, the smaller the difference between the temperature of the hydrogen generator 3 and the temperature of the reactor 2, the less energy loss occurs due to temperature changes in the reducing gas and the recycled gas.

[0019] The reuse gas discharge path 44 is maintained at a high temperature to suppress condensation of water vapor contained in the reuse gas. The temperature of the water vapor generated inside the reactor 2 is 600 to 1000°C, the same as the temperature of the reactor 2. In the gas production system 1 of this embodiment, the temperature of the water vapor flowing through the reuse gas discharge path 44 is preferably equal to or higher than the temperature of the hydrogen generator 3. If the temperature of the water vapor flowing through the reuse gas discharge path 44 is equal to or higher than the temperature of the hydrogen generator 3, this is preferable because it allows for suppression of heating energy in the hydrogen generator 3. In order to maintain the temperature of the water vapor flowing through the reuse gas discharge path 44 at or higher than the temperature of the hydrogen generator 3, the reuse gas discharge path 44 is preferably covered with a heat insulating material. Furthermore, a heater may be provided as necessary.

[0020] Next, the operation of the gas production system 1 according to this embodiment will be described. 2 and 3 are diagrams for explaining the operation of the gas production system 1 according to the present embodiment. In Fig. 2 and Fig. 3, thick lines indicate a state in which gas flows through the corresponding path, and dotted lines indicate a state in which gas does not flow through the corresponding path.

[0021] The gas production system 1 according to this embodiment has two operation modes: a reducing agent regeneration mode in which the reducing agent provided in the reactor 2 is reduced and regenerated, and a gas production mode in which the raw material gas is reduced with the reducing agent to produce a useful gas. The gas production system 1 according to this embodiment generates a product gas from the raw material gas by repeating these two modes.

[0022] FIG. 2 is a diagram illustrating the operation of a reducing agent regeneration mode in which the reducing agent provided in the reactor 2 is regenerated. At this time, it is assumed that the reducing agent was oxidized in the gas generation mode. In this mode, the raw material gas on-off valve 61 of the supply gas switching unit 60 is closed, and the reducing gas on-off valve 62 is open. Furthermore, the product gas on-off valve 71 of the exhaust gas switching unit 70 is closed, and the recycled gas on-off valve 72 is open. In this mode, hydrogen is sent from the hydrogen generator 3 to the reactor 2 via the reducing gas supply path 42. The oxidized reducing agent is reduced and regenerated by this hydrogen. When the oxidized reducing agent is reduced, water vapor is generated. The water vapor generated inside the reactor 2 is sent to the hydrogen generator 3 via the recycled gas exhaust path 44. In this manner, the oxidized reducing agent can be regenerated in the gas generation mode.

[0023] FIG. 3 is a diagram illustrating operation in a gas production mode in which a raw material gas is reduced with a reducing agent provided in reactor 2 to produce a useful gas. In this mode, raw material gas on-off valve 61 of supply gas switching unit 60 is open, and reducing gas on-off valve 62 is closed. Furthermore, product gas on-off valve 71 of exhaust gas switching unit 70 is open, and recycled gas on-off valve 72 is closed. In this mode, a raw material gas containing carbon dioxide is sent from an external raw material gas supply unit 4 to reactor 2 via raw material gas supply path 41. The reducing agent provided in reactor 2 reduces carbon dioxide contained in the sent raw material gas and converts it into a product gas containing carbon monoxide. At this time, the reducing agent is oxidized. The product gas generated inside reactor 2 is sent to an external product gas discharge unit 5 via product gas discharge path 43. In this way, gas production system 1 according to this embodiment generates a product gas containing carbon monoxide from a raw material gas containing carbon dioxide during operation in the gas production mode.

[0024] The gas production system 1 configured in this manner sends the water vapor generated in the reducing agent regeneration mode to the hydrogen generator 3 without condensing it, eliminating the need for energy to convert water into water vapor and increasing energy efficiency.

[0025] In the gas production system of this embodiment, a heat exchanger may be provided between the raw material gas supply path 41 and the produced gas discharge path 43. This heat exchanger makes it possible to use the thermal energy of the produced gas flowing through the produced gas discharge path 43 to increase the temperature of the raw material gas flowing through the raw material gas supply path 41. Furthermore, a heat exchanger may be provided between the raw material gas supply path 41 and the recycled gas discharge path 44. This heat exchanger makes it possible to use the thermal energy of the recycled gas flowing through the recycled gas discharge path 44 to increase the temperature of the raw material gas flowing through the raw material gas supply path 41.

[0026] In the reducing agent regeneration mode, if hydrogen remains that has not reacted with the reducing agent, the remaining hydrogen is sent to the hydrogen generator 3 together with water vapor as recycled gas, and is used again to regenerate the reducing agent together with the hydrogen generated in the hydrogen generator 3. Therefore, the hydrogen utilization efficiency can be improved compared to when the gas generated in the reducing agent regeneration mode is not recycled. Even when the gas generated in the reducing agent regeneration mode is not recycled, hydrogen can be separated and purified from the gas generated in the reducing agent regeneration mode and reused to regenerate the reducing agent, but even in that case, it is difficult to separate and purify 100% of the hydrogen from the gas. Therefore, the hydrogen utilization efficiency can be improved even compared to when hydrogen is separated and purified.

[0027] Furthermore, if components that are easily oxidized by water vapor are used inside the hydrogen generator 3, deterioration of the components inside the hydrogen generator 3 can be suppressed by setting the gas flow rate so that a constant amount of hydrogen is always present in the recycled gas.

[0028] Embodiment 2 In the gas production system according to the first embodiment, when operating in the reducing agent regeneration mode, the source gas cannot be converted into the product gas, and therefore the product gas cannot be continuously produced. The gas production system according to the second embodiment is equipped with multiple reactors, and at least one reactor can always be operated in the gas production mode. Therefore, the gas production system according to the present embodiment can continuously produce the product gas.

[0029] FIG. 4 is a configuration diagram of a gas production system according to this embodiment. As shown in FIG. 4, in the gas production system 1 according to this embodiment, the first reactor 21 and the second reactor 22 are connected in parallel between the raw material gas supply path 41 and the reducing gas supply path 42 and the produced gas discharge path 43 and the recycled gas discharge path 44. In addition, in the gas production system 1 according to this embodiment, a first heat exchanger 81 is provided between the raw material gas supply path 41 and the produced gas discharge path 43, and a second heat exchanger 82 is provided between the raw material gas supply path 41 and the recycled gas discharge path 44. The first heat exchanger 81 uses the thermal energy of the produced gas flowing through the produced gas discharge path 43 to increase the temperature of the raw material gas flowing through the raw material gas supply path 41. The second heat exchanger 82 uses the thermal energy of the recycled gas flowing through the recycled gas discharge path 44 to increase the temperature of the raw material gas flowing through the raw material gas supply path 41.

[0030] Furthermore, in the gas production system 1 according to the present embodiment, a water-vapor separation unit 80 and a water vapor measurement unit 84 are provided between the second heat exchanger 82 of the reuse gas discharge path 44 and the hydrogen generator 3. The water-vapor separation unit 80 separates water vapor and liquid water contained in the reuse gas flowing through the reuse gas discharge path 44. The water separated by the water-vapor separation unit 80 is discharged to the outside from the drain discharge unit 6. Furthermore, in the gas production system 1 according to the present embodiment, a water vapor supply unit 85 is connected to the hydrogen generator 3, and a water vapor control unit 86 is connected to the water vapor measurement unit 84. The water vapor control unit 86 controls the amount of water vapor supplied from the water vapor supply unit 85 to the hydrogen generator 3, based on the amount of water vapor measured by the water vapor measurement unit 84.

[0031] The supply gas switching unit 60 is composed of a raw material gas on-off valve 61 provided between the raw material gas supply path 41 and the first reactor 21, a reducing gas on-off valve 62 provided between the reducing gas supply path 42 and the first reactor 21, a raw material gas on-off valve 63 provided between the raw material gas supply path 41 and the second reactor 22, and a reducing gas on-off valve 64 provided between the reducing gas supply path 42 and the second reactor 22. When the supply gas switching unit 60 opens one of the raw material gas on-off valve 61 and the reducing gas on-off valve 62, it closes the other valve. In this way, the supply gas switching unit 60 switches the path of the gas sent to the first reactor 21 to either the raw material gas supply path 41 or the reducing gas supply path 42. Furthermore, when the supply gas switching unit 60 opens one of the raw material gas on-off valve 63 and the reducing gas on-off valve 64, it closes the other valve. In this way, the supply gas switching unit 60 switches the path of the gas sent to the second reactor 22 to either the raw material gas supply path 41 or the reducing gas supply path .

[0032] The exhaust gas switching unit 70 is composed of a product gas on-off valve 71 provided between the product gas discharge path 43 and the first reactor 21, a reuse gas on-off valve 72 provided between the reuse gas discharge path 44 and the first reactor 21, a product gas on-off valve 73 provided between the product gas discharge path 43 and the second reactor 22, and a reuse gas on-off valve 74 provided between the reuse gas discharge path 44 and the second reactor 22. When the exhaust gas switching unit 70 opens either the product gas on-off valve 71 or the reuse gas on-off valve 72, it closes the other valve. In this way, the exhaust gas switching unit 70 switches the path for gas discharged from the first reactor 21 to either the product gas discharge path 43 or the reuse gas discharge path 44. Furthermore, when the exhaust gas switching unit 70 opens either the product gas on-off valve 73 or the reuse gas on-off valve 74, it closes the other valve. In this way, the exhaust gas switching unit 70 switches the route of the gas exhausted from the second reactor 22 to either the produced gas exhaust route 43 or the recycled gas exhaust route 44.

[0033] In the gas production system 1 configured as described above, the first heat exchanger 81 uses the thermal energy of the produced gas discharged to the outside to increase the temperature of the raw material gas, thereby making it possible to effectively utilize the thermal energy of the produced gas. As shown in Fig. 4, it is preferable to arrange the first heat exchanger 81 upstream of the second heat exchanger 82 in the raw material gas supply path 41. By arranging the first heat exchanger 81 upstream of the second heat exchanger 82, the temperature difference between the produced gas and the raw material gas increases, allowing for efficient heat exchange in the first heat exchanger 81.

[0034] Furthermore, in gas production system 1 of the present embodiment, water vapor control unit 86 controls the amount of water vapor supplied from water vapor supply unit 85 to hydrogen generator 3 based on the amount of water vapor measured by water vapor measurement unit 84, so water vapor can be replenished to hydrogen generator 3 even when the amount of water vapor flowing through reuse gas discharge path 44 decreases. Therefore, hydrogen generator 3 can be operated stably for a long period of time.

[0035] Furthermore, since the water-air separation unit 80 removes liquid water contained in the recycled gas, it is possible to prevent clogging of the recycled gas discharge path 44 and suppress deterioration of the blower 53 and the hydrogen generator 3. The water separated by the water-air separation unit 80 may be supplied to the water vapor supply unit 85 and reused as water vapor, instead of being discharged to the outside from the drain discharge unit 6.

[0036] Furthermore, since the gas production system 1 of this embodiment is equipped with two reactors, each reactor can be operated in a different mode. 5 and 6 are diagrams for explaining the operation of the gas production system 1 according to this embodiment. In FIGS. 5 and 6, thick lines indicate a state in which gas flows through the corresponding path, and dotted lines indicate a state in which gas does not flow through the corresponding path. Note that, in order to realize the gas flows shown in FIGS. 5 and 6, the opening and closing of each on-off valve of the supply gas switching unit 60 and the exhaust gas switching unit 70 is controlled.

[0037] 5 is a diagram for explaining the operation when the first reactor 21 is operating in the reducing agent regeneration mode and the second reactor 22 is operating in the gas generation mode. As shown in FIG. 5, a reducing gas is sent to the first reactor 21 from the hydrogen generator 3 via a reducing gas supply path 42. Inside the first reactor 21, the reducing agent is reduced and regenerated by the reducing gas. The water vapor generated when the reducing agent is reduced is sent to the hydrogen generator 3 via a recycled gas discharge path 44. In this way, the first reactor 21 can regenerate the reducing agent oxidized in the gas generation mode.

[0038] 5, a raw material gas is supplied to the second reactor 22 from a raw material gas supply path 41. Inside the second reactor 22, carbon dioxide contained in the raw material gas is reduced by a reducing agent to produce a product gas containing carbon monoxide. The product gas produced inside the second reactor 22 is sent to the external product gas discharge unit 5 via a product gas discharge path 43. In this way, in the second reactor 22, a product gas containing carbon monoxide can be produced from a raw material gas containing carbon dioxide.

[0039] FIG. 6 is a diagram illustrating the operation when the first reactor 21 is operating in the gas production mode and the second reactor 22 is operating in the reducing agent regeneration mode. As shown in FIG. 6, a raw material gas is supplied to the first reactor 21 from a raw material gas supply path 41. Inside the first reactor 21, carbon dioxide contained in the raw material gas is reduced by the reducing agent to produce a product gas containing carbon monoxide. The product gas produced inside the first reactor 21 is sent to the external product gas discharge unit 5 via a product gas discharge path 43. In this way, the first reactor 21 can produce a product gas containing carbon monoxide from a raw material gas containing carbon dioxide.

[0040] 6, a reducing gas is sent from the hydrogen generator 3 to the second reactor 22 via a reducing gas supply path 42. Inside the second reactor 22, the reducing agent is reduced and regenerated by the reducing gas. The water vapor generated when the reducing agent is reduced is sent to the hydrogen generator 3 via a recycled gas discharge path 44. In this way, the second reactor 22 can regenerate the reducing agent oxidized in the gas production mode.

[0041] In a gas production system configured in this manner, one of the two reactors can always be operated in gas production mode, allowing for continuous production of product gas. It is not necessary for the gas production system of this embodiment to operate the two reactors in different modes. Normally, both reactors can be operated in gas production mode, and one of the reactors can be operated in reducing agent regeneration mode as needed. Furthermore, the gas production system of this embodiment may include three or more reactors.

[0042] In the gas production system 1 configured as described above, the water vapor generated in the reducing agent regeneration mode is sent to the hydrogen generator 3 without condensing, eliminating the need for energy to convert water to water vapor, thereby improving energy efficiency. Furthermore, even if the amount of water vapor generated in the reducing agent regeneration mode is insufficient, water vapor to make up for the shortfall is supplied from the water vapor supply unit 85, thereby suppressing an increase in energy consumption.

[0043] In the gas production system of this embodiment, when a solid oxide electrolysis cell is used as the hydrogen generator, an oxygen-containing gas is generated from the oxygen electrode of the solid oxide electrolysis cell. Although not shown, a heat exchanger may be disposed between the path for discharging this oxygen-containing gas and the raw material gas supply path, and the thermal energy of the oxygen-containing gas may be used to increase the temperature of the raw material gas flowing through the raw material gas supply path 41. This can further improve the energy efficiency of the gas production system.

[0044] Embodiment 3 When the reducing agent provided inside the reactor reduces the raw material gas, carbon, organic matter, etc. may adhere to the surface of the reducing agent. If adhesions exist on the surface of the reducing agent, the contact area between the reducing agent and the raw material gas decreases, thereby reducing the reducing ability of the reducing agent. The gas production system according to the third embodiment can burn and remove adhesions on the surface of the reducing agent by sending oxygen generated by the hydrogen generator to the reactor.

[0045] FIG. 7 is a configuration diagram of a gas production system according to this embodiment. The gas production system 1 according to this embodiment includes three reactors. As shown in FIG. 7, in the gas production system 1 according to this embodiment, the first reactor 21, the second reactor 22, and the third reactor 23 are connected in parallel between the raw material gas supply path 41 and the reducing gas supply path 42 and the produced gas discharge path 43 and the recycled gas discharge path 44. In addition, in this embodiment, the hydrogen generator 3 is configured as a solid oxide electrolysis cell. In the solid oxide electrolysis cell, hydrogen is generated at the hydrogen electrode and an oxygen-containing gas is generated at the oxygen electrode. In order to supply this oxygen-containing gas to the first reactor 21, the second reactor 22, and the third reactor 23, the gas production system 1 according to this embodiment is provided with an oxygen gas supply path 45. The oxygen gas supply path 45 is provided with a blower 54 for pressurizing and feeding the oxygen-containing gas. Oxygen gas on-off valves 67, 68, and 69 are provided between oxygen gas supply path 45 and first reactor 21, second reactor 22, and third reactor 23, respectively. Note that if the wind power of blower 53 that pressurizes the recycled gas to hydrogen generator 3 is large, blower 54 provided in oxygen gas supply path 45 may not be necessary.

[0046] Furthermore, the gas production system 1 according to this embodiment is provided with a combustion gas discharge path 46 for discharging the combustion gas generated when deposits on the surface of the reducing agent are burned by oxygen. The combustion gas flowing through the combustion gas discharge path 46 is discharged to the outside from a combustion gas discharge unit 7. Combustion gas on-off valves 77, 78, and 79 are provided between the combustion gas discharge path 46 and the first reactor 21, the second reactor 22, and the third reactor 23, respectively. Furthermore, in the gas production system 1 according to this embodiment, the oxygen gas supply path 45 and the combustion gas discharge path 46 are connected via a bypass valve 87.

[0047] The supply gas switching unit 60 is composed of a raw material gas on / off valve 61 provided between the raw material gas supply path 41 and the first reactor 21, a reducing gas on / off valve 62 provided between the reducing gas supply path 42 and the first reactor 21, a raw material gas on / off valve 63 provided between the raw material gas supply path 41 and the second reactor 22, a reducing gas on / off valve 64 provided between the reducing gas supply path 42 and the second reactor 22, a raw material gas on / off valve 65 provided between the raw material gas supply path 41 and the third reactor 23, a reducing gas on / off valve 66 provided between the reducing gas supply path 42 and the third reactor 23, oxygen gas on / off valves 67, 68, 69, and a bypass valve 87.

[0048] The exhaust gas switching unit 70 is composed of a produced gas on-off valve 71 provided between the produced gas discharge path 43 and the first reactor 21, a recycled gas on-off valve 72 provided between the recycled gas discharge path 44 and the first reactor 21, a produced gas on-off valve 73 provided between the produced gas discharge path 43 and the second reactor 22, a recycled gas on-off valve 74 provided between the recycled gas discharge path 44 and the second reactor 22, a produced gas on-off valve 75 provided between the produced gas discharge path 43 and the third reactor 23, a recycled gas on-off valve 76 provided between the recycled gas discharge path 44 and the third reactor 23, and combustion gas on-off valves 77, 78, and 79.

[0049] Furthermore, in the gas production system 1 of the present embodiment, a third heat exchanger 83 is provided between the raw material gas supply path 41 and the combustion gas exhaust path 46. The third heat exchanger 83 uses the thermal energy of the combustion gas flowing through the combustion gas exhaust path 46 to increase the temperature of the raw material gas flowing through the raw material gas supply path 41. Similarly to the gas production system of the second embodiment, the gas production system 1 of the present embodiment also includes a steam-water separator 80, a water vapor measuring unit 84, a water vapor supply unit 85, and a water vapor control unit 86.

[0050] In the gas production system 1 of this embodiment, the reactor has an attachment removal mode in addition to a gas generation mode and a reducing agent regeneration mode as operation modes. FIG. 8 is a diagram for explaining the operation of the gas production system 1 according to this embodiment. In FIG. 8, thick lines represent a state in which gas flows through the corresponding path, and dotted lines represent a state in which gas does not flow through the corresponding path. FIG. 8 is a diagram for explaining the operation when the first reactor 21 is operated in the gas generation mode, the second reactor 22 is operated in the reducing agent regeneration mode, and the third reactor 23 is operated in the deposit removal mode. Note that, in order to realize the gas flow shown in FIG. 8, the opening and closing of each on-off valve of the supply gas switching unit 60 and the exhaust gas switching unit 70 is controlled.

[0051] As shown in Fig. 8, a raw material gas is supplied to the first reactor 21 from a raw material gas supply path 41. Inside the first reactor 21, carbon dioxide contained in the raw material gas is reduced by a reducing agent to produce a product gas containing carbon monoxide. The product gas produced inside the first reactor 21 is sent to the external product gas discharge unit 5 via a product gas discharge path 43. In this way, in the first reactor 21, a product gas containing carbon monoxide can be produced from a raw material gas containing carbon dioxide.

[0052] 8, a reducing gas is sent from the hydrogen generator 3 to the second reactor 22 via a reducing gas supply path 42. Inside the second reactor 22, the reducing agent is reduced and regenerated by the reducing gas. The water vapor generated when the reducing agent is reduced is sent to the hydrogen generator 3 via a recycled gas discharge path 44. In this way, the second reactor 22 can regenerate the reducing agent oxidized in the gas production mode.

[0053] 8, oxygen is supplied to the third reactor 23 from the hydrogen generator 3 via an oxygen gas supply path 45. Inside the third reactor 23, the oxygen burns deposits attached to the surface of the reducing agent. The combustion gas generated when the deposits are burned is sent to the combustion gas discharge section 7 via a combustion gas discharge path 46.

[0054] In the gas production system configured in this manner, the water vapor generated in the reducing agent regeneration mode is sent to the hydrogen generator 3 without condensing, eliminating the need for energy to convert water to water vapor and improving energy efficiency. Furthermore, even if the amount of water vapor generated in the reducing agent regeneration mode is insufficient, water vapor to make up for the shortfall is supplied from the water vapor supply unit 85, allowing the gas production system to operate stably while suppressing an increase in energy.

[0055] Furthermore, in a gas production system configured as described above, at least one of the multiple reactors can be operated in gas production mode at all times, allowing for continuous production of produced gas. Furthermore, in the gas production system of this embodiment, operation can be performed in deposit removal mode, allowing the gas production system to operate stably for long periods of time. Furthermore, since high-temperature oxygen generated in the hydrogen generator 3 is used instead of supplying oxygen from outside the gas production system, the energy efficiency of the gas production system is further improved.

[0056] In the operation of the gas production system shown in Figure 8, the three reactors are operated in different modes, but it is not necessary for each of the three reactors to operate in different modes. Normally, the three reactors are operated in gas production mode, and one or two of the reactors may be operated in reducing agent regeneration mode or deposit removal mode as needed. Furthermore, in each reactor, operation in the deposit removal mode may be performed every time after operation in gas production mode, or operation in the deposit removal mode may be performed intermittently only when the reducing ability of the reducing agent has decreased.

[0057] Although the gas production system of this embodiment includes three reactors, the present invention is not limited to this. The gas production system of this embodiment may include one or more reactors. Furthermore, since the combustion gas contains carbon dioxide, the combustion gas may be supplied from the combustion gas discharge unit to the raw material gas supply unit.

[0058] When at least one reactor is operated in the reducing agent regeneration mode, the hydrogen generator 3 generates hydrogen, and this hydrogen is supplied to the reactor operating in the reducing agent regeneration mode. At this time, if the other reactors are not operating in the deposit removal mode, the oxygen generated by the hydrogen generator 3 becomes unnecessary. In such a case, in the gas production system of the present embodiment, the unnecessary oxygen generated by the hydrogen generator 3 can be sent directly to the combustion gas exhaust path 46 by closing the oxygen gas on-off valves 67, 68, 69 and opening the bypass valve 87.

[0059] While the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not exemplified are conceivable within the scope of the technology disclosed in this specification, including, for example, cases where at least one component is modified, added, or omitted, and cases where at least one component is extracted and combined with components of another embodiment. [Explanation of symbols]

[0060] REFERENCE SIGNS LIST 1 gas production system, 2 reactor, 3 hydrogen generator, 4 raw material gas supply section, 5 produced gas discharge section, 6 drain discharge section, 7 combustion gas discharge section, 21 first reactor, 22 second reactor, 23 third reactor, 31 raw material gas heater, 32 reducing gas heater, 41 raw material gas supply path, 42 reducing gas supply path, 43 produced gas discharge path, 44 recycled gas discharge path, 45 oxygen gas supply path, 46 combustion gas discharge path, 51, 52, 53, 54 blower, 60 supply gas switching section, 61, 63, 65 raw material gas on / off valve, 62, 64, 66 reducing gas on / off valve, 67, 68, 69 oxygen gas on / off valve, 70 discharge gas switching section, 71, 73, 75 produced gas on / off valve, 72, 74, 76 recycled gas on / off valve, 77, 78, 79 Combustion gas on-off valve, 80 steam separation section, 81 first heat exchanger, 82 second heat exchanger, 83 third heat exchanger, 84 water vapor measurement section, 85 water vapor supply section, 86 water vapor control section, 87 bypass valve.

Claims

1. a reactor having a reducing agent that reduces carbon dioxide contained in the raw material gas to produce a product gas containing carbon monoxide; a hydrogen generator that generates a reducing gas containing hydrogen for reducing the reducing agent; a raw material gas supply path for transmitting the raw material gas to the reactor; a reducing gas supply path for transmitting the reducing gas from the hydrogen generator to the reactor; a product gas discharge path for discharging the product gas generated in the reactor from the reactor; a recycled gas discharge path for discharging recycled gas containing water vapor generated from the reducing agent reduced by the reducing gas from the reactor and sending the recycled gas to the hydrogen generator; a supply gas switching unit that switches a gas path sent to the reactor between the raw material gas supply path and the reducing gas supply path; and an exhaust gas switching unit that switches the path of the gas exhausted from the reactor to either the generated gas exhaust path or the recycled gas exhaust path.

2. 2. The gas production system according to claim 1, wherein a raw material gas heater for heating the raw material gas is provided in the raw material gas supply path, and a reducing gas heater for heating the reducing gas is provided in the reducing gas supply path.

3. 2. The gas production system according to claim 1, wherein a first heat exchanger is provided between the raw material gas supply path and the generated gas discharge path, and a second heat exchanger is provided between the raw material gas supply path and the recycled gas discharge path.

4. 4. The gas production system according to claim 3, wherein the first heat exchanger is provided upstream of the second heat exchanger in the raw material gas supply path.

5. 5. The gas production system according to claim 1, further comprising: a water vapor measuring unit that measures the amount of water vapor contained in the recycled gas in the recycled gas discharge path; and a water vapor supply unit that supplies water vapor to the hydrogen generator based on the amount of water vapor contained in the recycled gas measured by the water vapor measuring unit.

6. a plurality of the reactors are provided, and the plurality of reactors are connected in parallel between the raw material gas supply path and the reducing gas supply path, and the generated gas discharge path and the recycled gas discharge path; 5. The gas production system according to claim 1, wherein the supply gas switching unit switches the path of the gas sent to each of the reactors to one of the raw material gas supply path and the reducing gas supply path, and the exhaust gas switching unit switches the path of the gas exhausted from each of the reactors to one of the generated gas exhaust path and the recycled gas exhaust path.

7. 5. The gas production system according to claim 1, wherein the hydrogen generator is configured by a solid oxide electrolysis cell having a hydrogen electrode and an oxygen electrode, and hydrogen is generated at the hydrogen electrode and oxygen is generated at the oxygen electrode.

8. an oxygen gas supply path that supplies the oxygen generated at the oxygen electrode of the hydrogen generator to the reactor, and a combustion gas discharge path that discharges, from the reactor, a combustion gas that is generated when deposits attached to the reducing agent are combusted with the oxygen supplied to the reactor, 8. The gas production system according to claim 7, wherein the supply gas switching unit switches the path of the gas sent to the reactor to one of the raw material gas supply path, the reducing gas supply path, and the oxygen gas supply path, and the exhaust gas switching unit switches the path of the gas exhausted from the reactor to one of the generated gas exhaust path, the recycled gas exhaust path, and the combustion gas exhaust path.

9. 5. The gas production system according to claim 1, wherein the recycled gas contains hydrogen.

10. 5. The gas production system according to claim 1, wherein the temperature of the water vapor contained in the recycled gas flowing through the recycled gas discharge path is maintained at or above the temperature of the hydrogen generator.

11. 1. A method for operating a gas production system including a reactor having a reducing agent that reduces carbon dioxide contained in a raw material gas to produce a product gas containing carbon monoxide, and a hydrogen generator that generates a reducing gas containing hydrogen for reducing the reducing agent, comprising: a gas production mode in which the raw material gas is sent to the reactor and reduced with the reducing agent to produce the product gas; a reducing agent regeneration mode in which the reducing gas generated in the hydrogen generator is sent to the reactor to reduce and regenerate the reducing agent, and water vapor generated when the reducing agent is reduced is sent to the hydrogen generator.

12. 12. The method for operating a gas production system according to claim 11, wherein the hydrogen generator is composed of a solid oxide electrolysis cell having a hydrogen electrode and an oxygen electrode, and further comprises a deposit removal mode in which oxygen generated at the oxygen electrode of the hydrogen generator is sent to the reactor to burn and remove deposits attached to the reducing agent.

13. 13. The method for operating a gas production system according to claim 11 or 12, wherein, when the gas production system is operated in the reducing agent regeneration mode, the temperature of the steam sent to the hydrogen generator is maintained at or above the temperature of the hydrogen generator.

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