Gas production system and method for operating gas production system

Abstract

The present invention comprises: a reactor (2) having a reducing agent for reducing a raw material gas to generate a product gas; a hydrogen generator (3) for generating a reducing gas for reducing the reducing agent; a raw material gas supply path (41) for sending the raw material gas to the reactor; a reducing gas supply path (42) for sending the reducing gas from the hydrogen generator to the reactor; a product gas discharge path (43) for discharging the product gas generated in the reactor; a reuse gas discharge path (44) for discharging, from the reactor, a reuse gas generated from the reducing agent reduced by the reducing gas, and sending the reuse gas to the hydrogen generator; a supply gas switching unit (60) for switching the path of the gas sent to the reactor; and a discharge gas switching unit (70) for switching the path of the gas discharged from the reactor.

Description

Gas production system and method for operating a gas production system

[0001] The present disclosure relates to a gas production system and a method for operating a gas production system.

[0002] In recent years, in order to prevent global warming and realize a carbon cycle society, research and development of technologies for recovering carbon dioxide from exhaust gas or the atmosphere and converting the recovered carbon dioxide into valuable substances have been promoted. For example, a gas production system for producing a product gas containing carbon monoxide from a raw material gas containing carbon dioxide has been disclosed (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2021-75447

[0004] In a conventional gas production system, water vapor generated in a reactor is aggregated to be converted into liquid water and temporarily stored in a tank, and the water is supplied from the tank to a hydrogen generator. When the hydrogen generator is composed of a solid oxide electrolysis cell, a steam methane reformer, a steam reformer using an oxygen carrier such as a metal oxide, etc., the water stored in the tank is converted into steam and supplied to the hydrogen generator. Thus, in a conventional gas production system, in addition to the energy for converting a raw material gas containing carbon dioxide into a product gas containing carbon monoxide, energy for aggregating water vapor and energy for converting water into steam are required, and there is a problem of low energy efficiency.

[0005] The present disclosure has been made to solve the above-described problems, and an object thereof is to provide a gas production system with high energy efficiency.

[0006] The gas production system of this 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 reuse gas discharge path that discharges reuse 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 gas path 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 gas path discharged from the reactor to either the product gas discharge path or the reuse gas discharge path.

[0007] The gas production system of this disclosure is equipped with a reuse gas discharge path that discharges the reuse gas, which contains water vapor generated from the reducing agent reduced by the reducing gas, from the reactor and sends it to the hydrogen generator, thereby increasing energy efficiency.

[0008] This is a diagram illustrating the configuration of the gas production system according to Embodiment 1. This is a diagram illustrating the operation of the gas production system according to Embodiment 1. This is a diagram illustrating the operation of the gas production system according to Embodiment 1. This is a diagram illustrating the configuration of the gas production system according to Embodiment 2. This is a diagram illustrating the operation of the gas production system according to Embodiment 2. This is a diagram illustrating the operation of the gas production system according to Embodiment 2. This is a diagram illustrating the configuration of the gas production system according to Embodiment 3. This is a diagram illustrating the operation of the gas production system according to Embodiment 3.

[0009] Hereinafter, a gas production system according to an embodiment for implementing this 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. Figure 1 is a diagram showing the configuration of a gas production system according to Embodiment 1. The gas production system 1 according to this embodiment includes a reactor 2 having a reducing agent that reduces a raw material 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 raw material gas supply path 41 for sending raw material gas to the reactor 2, a reducing gas supply path 42 for sending reducing gas from the hydrogen generator 3 to the reactor 2, a product gas discharge path 43 for discharging the product gas generated in the reactor 2 from the reactor 2, and a reuse gas discharge path 44 for discharging reuse gas containing water vapor generated from the reducing agent reduced by the reducing gas from the reactor 2 and sending it to the hydrogen generator 3. Furthermore, the gas production system 1 according to this embodiment includes a supply gas switching unit 60 that switches the gas path sent to the reactor 2 to either a raw material gas supply path 41 or a reducing gas supply path 42, and an exhaust gas switching unit 70 that switches the gas path discharged from the reactor 2 to either a generated gas discharge path 43 or a reused gas discharge path 44.

[0011] The raw material gas supply path 41 is supplied with raw material gas containing carbon dioxide from an external raw material gas supply unit 4. The raw material gas supply path 41 is equipped with a blower 51 for pressurizing 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 that of the reactor 2, which will be described later. However, 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 not be necessary.

[0012] The reducing gas supply path 42 is supplied with reducing gas containing hydrogen from the hydrogen generator 3. The reducing gas supply path 42 is equipped with a blower 52 for pressurizing 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 that of the reactor 2, which will be described later. However, 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 generated gas discharge path 43 is connected to the generated gas discharge section 5 for discharging the generated gas to the outside. The reused gas discharge path 44 is equipped with a blower 53 for pressurizing the reused gas from the reactor 2 to the hydrogen generator 3. If the airflow of the blower 53 that pressurizes the reused gas to the hydrogen generator 3 is strong, the blower 52 provided in the reduction gas supply path 42 may be omitted.

[0014] The supply gas switching unit 60 consists of a raw material gas shut-off valve 61 provided between the raw material gas supply path 41 and the reactor 2, and a reduction gas shut-off valve 62 provided between the reduction gas supply path 42 and the reactor 2. The supply gas switching unit 60 closes the valve when either the raw material gas shut-off valve 61 or the reduction gas shut-off valve 62 is opened. In this way, the supply gas switching unit 60 switches the gas path sent to the reactor 2 to either the raw material gas supply path 41 or the reduction gas supply path 42.

[0015] The exhaust gas switching unit 70 consists of a generated gas on-off valve 71 provided between the generated gas discharge path 43 and the reactor 2, and a reused gas on-off valve 72 provided between the reused gas discharge path 44 and the reactor 2. The exhaust gas switching unit 70 closes the valve when either the generated gas on-off valve 71 or the reused gas on-off valve 72 is opened. In this way, the exhaust gas switching unit 70 switches the path of the gas discharged from the reactor 2 to either the generated gas discharge path 43 or the reused gas discharge path 44.

[0016] The reducing agent provided in reactor 2 is composed of a material that is easily oxidized by carbon dioxide and easily reduced by hydrogen. As such a material, for example, a material containing at least one metal element belonging to Group 3 to Group 12 can be selected. Iron, for example, is preferred because it has a high conversion efficiency in reducing carbon dioxide to carbon monoxide. The shape of the reducing agent is preferably, for example, granular, flake-like, or pellet-like. Reducing agents in such shapes can increase the packing rate inside 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] 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 reactor 2 is preferably 600 to 1000°C. The higher the temperature of reactor 2, the faster the reaction rate of the oxidation-reduction reaction of the reducing agent, thus increasing the amount of product gas produced per unit time. On the other hand, the lower the temperature of reactor 2, the less energy is required for the temperature control mechanism, and the lower the heat resistance required for the components of reactor 2. Therefore, the running cost of the gas production system 1 and the manufacturing cost of reactor 2 can be suppressed. Note that the temperature of reactor 2 may be changed when the reducing agent is undergoing an oxidation reaction and when it is undergoing a reduction reaction. However, not changing the temperature during the oxidation and reduction reactions of the reducing agent reduces energy loss associated with heating and cooling.

[0018] The hydrogen generator 3 has the function of generating hydrogen from water vapor. As a hydrogen generator having such a function, for example, a solid oxide electrolytic cell or a steam methane reformer can be used. Since a solid oxide electrolytic cell can generate hydrogen using only water vapor as a raw material, it is preferable to use a solid oxide electrolytic cell 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 electrolytic 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 cost of the gas production system 1 and the manufacturing cost of the hydrogen generator 3 can be suppressed. In addition, the smaller the difference between the temperature of the hydrogen generator 3 and the temperature of the reactor 2, the less energy is lost due to temperature changes of the reducing gas and recycled gas.

[0019] The recycled gas discharge path 44 is maintained at a high temperature to suppress the condensation of water vapor contained in the recycled gas. The temperature of the water vapor generated inside the reactor 2 is the same as the temperature of the reactor 2, 600 to 1000°C. In the gas production system 1 of this embodiment, it is preferable that the temperature of the water vapor flowing through the recycled gas discharge path 44 is equal to or higher than the temperature of the hydrogen generator 3. It is preferable that the temperature of the water vapor flowing through the recycled gas discharge path 44 is equal to or higher than the temperature of the hydrogen generator 3 because it can suppress the heating energy in the hydrogen generator 3. In order to maintain the temperature of the water vapor flowing through the recycled gas discharge path 44 at or above the temperature of the hydrogen generator 3, it is preferable that the recycled gas discharge path 44 is covered with an insulating material. A heater may also be provided as needed.

[0020] Next, the operation of the gas production system 1 according to this embodiment will be described. Figures 2 and 3 are diagrams illustrating the operation of the gas production system 1 according to this embodiment. In Figures 2 and 3, thick lines represent the state in which gas is flowing through the path, and dotted lines represent the state in which gas is not flowing through the path.

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

[0022] Figure 2 is a diagram illustrating the operation of the reducing agent regeneration mode for regenerating the reducing agent provided in reactor 2. In this case, it is assumed that the reducing agent was oxidized in the gas generation mode. In this mode, the raw material gas shut-off valve 61 of the supply gas switching unit 60 is closed, and the reducing gas shut-off valve 62 is open. Also, the generated gas shut-off valve 71 of the exhaust gas switching unit 70 is closed, and the reuse gas shut-off valve 72 is open. In this mode, hydrogen is sent from the hydrogen generator 3 to 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 reactor 2 is sent to the hydrogen generator 3 via the reuse gas discharge path 44. In this way, the reducing agent oxidized in the gas generation mode can be regenerated.

[0023] Figure 3 is a diagram illustrating the operation of a gas production mode in which a reducing agent in the reactor 2 reduces a raw material gas to produce a useful gas. In this mode, the raw material gas shut-off valve 61 of the supply gas switching unit 60 is open, and the reducing gas shut-off valve 62 is closed. Also, the produced gas shut-off valve 71 of the exhaust gas switching unit 70 is open, and the reuse gas shut-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 the reactor 2 via the raw material gas supply path 41. The reducing agent in the reactor 2 reduces the carbon dioxide contained in the supplied raw material gas and converts it into a produced gas containing carbon monoxide. At this time, the reducing agent is oxidized. The produced gas generated inside the reactor 2 is sent to an external produced gas discharge unit 5 via the produced gas discharge path 43. In this way, the gas production system 1 according to this embodiment generates a produced gas containing carbon monoxide from a raw material gas containing carbon dioxide when operating in the gas production mode.

[0024] In this configuration, the gas production system 1 sends the water vapor generated in the reducing agent regeneration mode to the hydrogen generator 3 without condensation, thus eliminating the need for energy to convert water into water vapor and resulting in high energy efficiency.

[0025] In this gas production system, a heat exchanger may be provided between the raw material gas supply path 41 and the generated gas discharge path 43. This heat exchanger allows the thermal energy of the generated gas flowing through the generated gas discharge path 43 to be used to raise 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 allows the thermal energy of the recycled gas flowing through the recycled gas discharge path 44 to be used to raise the temperature of the raw material gas flowing through the raw material gas supply path 41.

[0026] In the reducing agent regeneration mode, if unreacted hydrogen remains with the reducing agent, the remaining hydrogen is sent to the hydrogen generator 3 as a reused gas along with water vapor and used again to regenerate the reducing agent along with the hydrogen generated in the hydrogen generator 3. Therefore, compared to not recycling the gas generated in the reducing agent regeneration mode, the efficiency of hydrogen utilization can be improved. Even if 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 for reducing agent regeneration, but even in that case, it is difficult to separate and purify 100% of the hydrogen from the gas. Therefore, compared to separating and purifying hydrogen, the efficiency of hydrogen utilization can be improved.

[0027] Furthermore, if components that are easily oxidized by water vapor are used inside the hydrogen generator 3, the deterioration of these components 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 Embodiment 1, the raw material gas cannot be converted into the product gas when operating in reducing agent regeneration mode, and therefore the product gas cannot be continuously produced. The gas production system according to Embodiment 2 is equipped with multiple reactors, and at least one reactor can always be operated in gas production mode. Therefore, the gas production system according to this embodiment can continuously produce the product gas.

[0029] Figure 4 is a diagram showing the configuration of the gas production system according to this embodiment. As shown in Figure 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 reduction gas supply path 42, and the generated gas discharge path 43 and the reused 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 generated gas discharge path 43, and a second heat exchanger 82 is provided between the raw material gas supply path 41 and the reused gas discharge path 44. The first heat exchanger 81 uses the thermal energy of the generated gas flowing through the generated gas discharge path 43 to raise 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 reused gas flowing through the reused gas discharge path 44 to raise 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 this embodiment, a gas-water separation unit 80 and a water vapor measurement unit 84 are provided between the second heat exchanger 82 and the hydrogen generator 3 in the reuse gas discharge path 44. The gas-water 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 gas-water separation unit 80 is discharged to the outside from the drain discharge unit 6. In addition, in the gas production system 1 according to this 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 consists of a raw material gas shut-off valve 61 provided between the raw material gas supply path 41 and the first reactor 21, a reduction gas shut-off valve 62 provided between the reduction gas supply path 42 and the first reactor 21, a raw material gas shut-off valve 63 provided between the raw material gas supply path 41 and the second reactor 22, and a reduction gas shut-off valve 64 provided between the reduction gas supply path 42 and the second reactor 22. The supply gas switching unit 60 closes the valve when either the raw material gas shut-off valve 61 or the reduction gas shut-off valve 62 is opened. In this way, the supply gas switching unit 60 switches the gas path sent to the first reactor 21 to either the raw material gas supply path 41 or the reduction gas supply path 42. The supply gas switching unit 60 also closes the valve when either the raw material gas shut-off valve 63 or the reduction gas shut-off valve 64 is opened. In this way, the supply gas switching unit 60 switches the gas path sent to the second reactor 22 to either the raw material gas supply path 41 or the reducing gas supply path 42.

[0032] The exhaust gas switching unit 70 consists of a generated gas on-off valve 71 provided between the generated gas discharge path 43 and the first reactor 21, a reused gas on-off valve 72 provided between the reused gas discharge path 44 and the first reactor 21, a generated gas on-off valve 73 provided between the generated gas discharge path 43 and the second reactor 22, and a reused gas on-off valve 74 provided between the reused gas discharge path 44 and the second reactor 22. The exhaust gas switching unit 70 closes the valve of either the generated gas on-off valve 71 or the reused gas on-off valve 72 when the other valve is opened. In this way, the exhaust gas switching unit 70 switches the gas discharge path from the first reactor 21 to either the generated gas discharge path 43 or the reused gas discharge path 44. The exhaust gas switching unit 70 also closes the valve of either the generated gas on-off valve 73 or the reused gas on-off valve 74 when the other valve is opened. In this way, the exhaust gas switching unit 70 switches the path of the gas discharged from the second reactor 22 to either the generated gas discharge path 43 or the reused gas discharge path 44.

[0033] In the gas production system 1 configured in this way, the thermal energy of the generated gas discharged to the outside by the first heat exchanger 81 is used to raise the temperature of the raw material gas, thus effectively utilizing the thermal energy of the generated gas. As shown in Figure 4, it is preferable to place the first heat exchanger 81 upstream of the second heat exchanger 82 in the raw material gas supply path 41. By placing the first heat exchanger 81 upstream of the second heat exchanger 82, the temperature difference between the generated gas and the raw material gas increases, allowing for efficient heat exchange in the first heat exchanger 81.

[0034] Furthermore, in the gas production system 1 of this embodiment, the steam control unit 86 controls the amount of steam supplied from the steam supply unit 85 to the hydrogen generator 3 based on the amount of steam measured by the steam measuring unit 84. Therefore, even if the amount of steam flowing through the recycled gas discharge path 44 decreases, steam can be supplied to the hydrogen generator 3. As a result, the hydrogen generator 3 can be operated stably for a long period of time.

[0035] Furthermore, since the gas-water 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 hydrogen generator 3. Alternatively, instead of discharging the water separated by the gas-water separation unit 80 to the outside through the drain discharge unit 6, it may be supplied to the steam supply unit 85 and reused as steam.

[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. Figures 5 and 6 are diagrams illustrating the operation of the gas production system 1 according to this embodiment. In Figures 5 and 6, thick lines represent the state in which gas is flowing through the path, and dotted lines represent the state in which gas is not flowing through the path. In order to realize the gas flow shown in Figures 5 and 6, the opening and closing of the on-off valves of the supply gas switching unit 60 and the exhaust gas switching unit 70 are controlled.

[0037] Figure 5 illustrates the operation when the first reactor 21 is operating in reducing agent regeneration mode and the second reactor 22 is operating in gas generation mode. As shown in Figure 5, reducing gas is supplied to the first reactor 21 from the hydrogen generator 3 via the 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 the reuse gas discharge path 44. In this way, the reducing agent oxidized in the gas generation mode can be regenerated in the first reactor 21.

[0038] As shown in Figure 5, raw material gas is supplied to the second reactor 22 from the raw material gas supply path 41. Inside the second reactor 22, the 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 section 5 via the product gas discharge path 43. In this way, the second reactor 22 can produce a product gas containing carbon monoxide from a raw material gas containing carbon dioxide.

[0039] Figure 6 illustrates the operation when the first reactor 21 is operating in gas generation mode and the second reactor 22 is operating in reducing agent regeneration mode. As shown in Figure 6, raw material gas is supplied to the first reactor 21 from the raw material gas supply path 41. Inside the first reactor 21, the 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 section 5 via the 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] Furthermore, as shown in Figure 6, reducing gas is supplied to the second reactor 22 from the hydrogen generator 3 via the 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 the reuse gas discharge path 44. In this way, the reducing agent oxidized in the gas generation mode can be regenerated in the second reactor 22.

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

[0042] In this configuration, the gas production system 1 sends the water vapor generated in the reducing agent regeneration mode to the hydrogen generator 3 without condensation, thus eliminating the need for energy to convert water into water vapor and resulting in high energy efficiency. Furthermore, even if the amount of water vapor generated in the reducing agent regeneration mode is insufficient, the water vapor supply unit 85 supplies the necessary amount of water vapor, thus suppressing the increase in energy consumption.

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

[0044] Embodiment 3. The reducing agent provided inside the reactor may have carbon, organic substances, etc. adhering to the surface of the reducing agent when reducing the raw material gas. When deposits exist on the surface of the reducing agent, the contact area between the reducing agent and the raw material gas decreases, so the reducing ability of the reducing agent decreases. The gas production system according to Embodiment 3 can burn and remove the deposits adhering to the surface of the reducing agent by sending the oxygen generated by the hydrogen generator to the reactor.

[0045] Figure 7 is a configuration diagram of the gas production system according to this embodiment. The gas production system 1 according to this embodiment includes three reactors. As shown in Figure 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 product gas discharge path 43 and the recycled gas discharge path 44. Also, in this embodiment, the hydrogen generator 3 is composed of a solid oxide electrolysis cell. In a solid oxide electrolysis cell, hydrogen is generated at the hydrogen electrode, and a gas containing oxygen is generated at the oxygen electrode. In order to supply this gas containing oxygen to the first reactor 21, the second reactor 22, and the third reactor 23, an oxygen gas supply path 45 is provided in the gas production system 1 of this embodiment. The oxygen gas supply path 45 is equipped with a blower 54 for pumping the gas containing oxygen. Oxygen gas on-off valves 67, 68, and 69 are respectively provided between the oxygen gas supply path 45 and the first reactor 21, the second reactor 22, and the third reactor 23. When the wind force of the blower 53 for pumping the recycled gas to the hydrogen generator 3 is large, the blower 54 provided in the oxygen gas supply path 45 may not be necessary.

[0046] Further, in the gas production system 1 according to the present embodiment, a combustion gas discharge path 46 is provided for discharging 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 the 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. Further, in the gas production system 1 according to the present embodiment, an 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 includes 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, and 69, and a bypass valve 87.

[0048] The exhaust gas switching unit 70 includes a product gas on-off valve 71 provided between the product 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 product gas on-off valve 73 provided between the product 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 product gas on-off valve 75 provided between the product 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 this embodiment, a third heat exchanger 83 is provided between the raw material gas supply path 41 and the combustion gas discharge path 46. The third heat exchanger 83 uses the thermal energy of the combustion gas flowing through the combustion gas discharge path 46 to raise the temperature of the raw material gas flowing through the raw material gas supply path 41. In addition, the gas production system 1 of this embodiment is equipped with a gas-water separation unit 80, a water vapor measurement unit 84, a water vapor supply unit 85, and a water vapor control unit 86, similar to the gas production system of Embodiment 2.

[0050] In the gas production system 1 of this embodiment, in addition to the gas generation mode and the reducing agent regeneration mode, there is also a deposit removal mode as an operating mode for the reactor. Figure 8 is a diagram illustrating the operation of the gas production system 1 according to this embodiment. In Figure 8, thick lines represent the state in which gas is flowing through the path, and dotted lines represent the state in which gas is not flowing through the path. Figure 8 is a diagram illustrating the operation when the first reactor 21 is operating in gas generation mode, the second reactor 22 is operating in reducing agent regeneration mode, and the third reactor 23 is operating in deposit removal mode. In order to achieve the gas flow shown in Figure 8, the opening and closing of the on-off valves of the supply gas switching unit 60 and the exhaust gas switching unit 70 are controlled.

[0051] As shown in Figure 8, raw material gas is supplied to the first reactor 21 from the raw material gas supply path 41. Inside the first reactor 21, the 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 section 5 via the 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.

[0052] Furthermore, as shown in Figure 8, reducing gas is supplied to the second reactor 22 from the hydrogen generator 3 via the 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 the reuse gas discharge path 44. In this way, the reducing agent oxidized in the gas generation mode can be regenerated in the second reactor 22.

[0053] Furthermore, as shown in Figure 8, oxygen is supplied to the third reactor 23 from the hydrogen generator 3 via the oxygen gas supply path 45. Inside the third reactor 23, deposits adhering to the surface of the reducing agent are burned by the oxygen. The combustion gas generated when the deposits are burned is sent to the combustion gas discharge section 7 via the combustion gas discharge path 46.

[0054] In this gas production system, the water vapor generated in the reducing agent regeneration mode is sent to the hydrogen generator 3 without condensation, thus eliminating the need for energy to convert water into water vapor and resulting in high energy efficiency. Furthermore, even if the amount of water vapor generated in the reducing agent regeneration mode is insufficient, the water vapor supply unit 85 supplies the necessary amount of water vapor, allowing the gas production system to operate stably while suppressing energy increases.

[0055] Furthermore, in a gas production system configured in this way, at least one of the multiple reactors can always be operated in gas production mode, allowing for continuous production of the generated gas. In addition, the gas production system of this embodiment can be operated in deposit removal mode, enabling the gas production system to operate stably for extended periods. Moreover, since the system utilizes high-temperature oxygen generated by the hydrogen generator 3 rather than supplying oxygen from an external source, the energy efficiency of the gas production system is further improved.

[0056] In the gas production system shown in Figure 8, the three reactors are operated in different modes, but it is not always necessary to operate the three reactors in different modes. Normally, all three reactors are operated in gas generation mode, and one or two reactors may be operated in reducing agent regeneration mode or deposit removal mode as needed. In addition, each reactor may be operated in deposit removal mode after every gas generation mode operation, or it may be operated intermittently only when the reducing capacity of the reducing agent decreases.

[0057] Although the gas production system in this embodiment is equipped with three reactors, it is not limited to this. In the gas production system of this embodiment, one or more reactors are sufficient. Furthermore, since the combustion gas contains carbon dioxide, the combustion gas may be supplied from the combustion gas discharge section to the raw material gas supply section.

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

[0059] While this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are envisioned within the scope of the art disclosed in this specification. For example, these include modifying, adding or omitting at least one component, or even extracting at least one component and combining it with a component from another embodiment.

[0060] 1. Gas production system, 2. Reactor, 3. Hydrogen generator, 4. Raw material gas supply unit, 5. Product gas discharge unit, 6. Drain discharge unit, 7. Combustion gas discharge unit, 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. Product gas discharge path, 44. Reused gas discharge path, 45. Oxygen gas supply path, 46. Combustion gas discharge path, 51, 52, 53, 54. Blower, 60. Supply gas switching unit, 61, 63, 65. Raw material gas shut-off valve, 62, 64, 66. Reducing gas shut-off valve, 67, 68, 69. Oxygen gas shut-off valve, 70. Exhaust gas switching unit, 71, 73, 75. Product gas shut-off valve, 72, 74, 76. Reused gas shut-off valve, 77, 78, 79. 80 Combustion gas shut-off valve, 81 Gas-water separation unit, 81 First heat exchanger, 82 Second heat exchanger, 83 Third heat exchanger, 84 Water vapor measuring unit, 85 Water vapor supply unit, 86 Water vapor control unit, 87 Bypass valve.

Claims

1. A gas production system comprising: 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 generated in the reactor from the reactor; a reuse gas discharge path that discharges a reuse 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 reuse gas discharge path.

2. The gas production system according to claim 1, characterized in that 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. The gas production system according to claim 1 or 2, characterized in that 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. The gas production system according to claim 3, characterized in that the first heat exchanger is located upstream of the second heat exchanger in the raw material gas supply path.

5. The gas production system according to any one of claims 1 to 4, further comprising a water vapor measuring unit in the recycled gas discharge path for measuring the amount of water vapor contained in the recycled gas, 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. The gas production system according to any one of claims 1 to 5, comprising a plurality of reactors, wherein the plurality of reactors are connected in parallel between the raw material gas supply path and the reduction gas supply path and the generated gas discharge path and the reused gas discharge path, the supply gas switching unit switches the gas path sent to each of the reactors to either the raw material gas supply path or the reduction gas supply path, and the exhaust gas switching unit switches the gas path discharged from each of the reactors to either the generated gas discharge path or the reused gas discharge path.

7. The gas production system according to any one of claims 1 to 6, characterized in that the hydrogen generator is composed of a solid oxide electrolytic 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. The gas production system according to claim 7, further comprising: an oxygen gas supply path for supplying the oxygen generated at the oxygen electrode of the hydrogen generator to the reactor; and a combustion gas discharge path for discharging the combustion gas generated when deposits attached to the reducing agent are burned by the oxygen supplied to the reactor, wherein the supply gas switching unit switches the gas path 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 gas path discharged from the reactor to one of the generated gas discharge path, the reused gas discharge path, and the combustion gas discharge path.

9. The gas production system according to any one of claims 1 to 8, characterized in that the recycled gas contains hydrogen.

10. The gas production system according to any one of claims 1 to 9, characterized in that 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. A method for operating a gas production system comprising 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, the method comprising: a gas production mode in which the raw material gas is sent to the reactor and the raw material gas is reduced with the reducing agent to produce the product gas; and a reducing agent regeneration mode in which the reducing gas generated by the hydrogen generator is sent to the reactor to reduce and regenerate the reducing agent, and the water vapor generated when the reducing agent is reduced is sent to the hydrogen generator.

12. The method for operating a gas production system according to claim 11, characterized in that the hydrogen generator is composed of a solid oxide electrolytic 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 off deposits attached to the reducing agent.

13. The method for operating a gas production system according to claim 11 or 12, characterized in that when the system is operating in the reducing agent regeneration mode, the temperature of the water vapor supplied to the hydrogen generator is maintained at or above the temperature of the hydrogen generator.

Images