Gas production system and method for operating gas production system

Abstract

This gas production system (100) comprises switching units (21, 22) that adjust the opening and closing of flow paths (L1, L4) and a hollow reaction unit (40A) that is connected to the flow paths (L1, L4) and has a reducing agent inside. The reaction unit (40A) is connected, via the flow paths (L1, L4), to a first supply unit (11) that supplies a gas No. 1A (G1A) containing carbon dioxide and oxygen and a second supply unit (13) that supplies a reducing gas, and is configured to enable switching of contact, respectively, between the gas No. 1A (G1A) supplied from the first supply unit (11) and a first reducing agent containing a metal oxide, contact between a second reducing agent, which is the first reducing agent that has been brought into contact with the gas No. 1A, and a reducing gas (G3), and contact between a third reducing agent, which is the second reducing agent that has been brought into contact with the reducing gas (G3), and a gas No. 1B (G1B), which is the gas No. 1A (G1A) that has been brought into contact with the first reducing agent, by means of the switching units (21, 22).

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 recycling society, research and development of technologies for recovering carbon dioxide CO2 from exhaust gases, the atmosphere, etc. and converting the recovered CO2 into valuable substances have been promoted. For example, a raw material gas containing CO2 is brought into contact with a reducing agent containing a metal oxide that reduces CO2 to produce a product gas containing carbon monoxide CO. In order to increase the production efficiency of the product gas, it is important to increase the CO2 concentration in the raw material gas. Therefore, the following gas production apparatuses provided with a configuration for removing unnecessary gas components mainly such as O2 contained in the raw material gas have been disclosed.

[0003] That is, a conventional gas production apparatus includes a concentration adjustment unit having an oxygen removal apparatus such as a cryogenic separation type separator, a pressure swing adsorption type separator, a temperature swing adsorption type separator, etc. for removing oxygen contained in the raw material gas. The raw material gas from which oxygen has been removed by passing through this concentration adjustment unit is brought into contact with a reducing agent containing a metal oxide in a reactor to produce a product gas containing carbon monoxide (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2021-`75447

[0005] In the above conventional gas production apparatus, in order to remove unnecessary gas components mainly such as oxygen O2 contained in the raw material gas, an oxygen removal apparatus such as a cryogenic separation type separator is provided in the front stage of the reactor. However, such an oxygen removal apparatus is relatively expensive and has a large power consumption. Therefore, in the conventional gas production apparatus, there is a problem that the energy when driving the oxygen removal apparatus is lost and the gas production efficiency is lowered.

[0006] The present disclosure discloses a technology for solving the above problems, and aims to provide a gas production system and a method for operating a gas production system that are inexpensive and have high gas production efficiency.

[0007] The gas production system of the present disclosure comprises a switching unit provided in a flow path and adjusting the opening and closing of the flow path, and a hollow reaction unit connected to the flow path and having a reducing agent inside, wherein the reaction unit is connected via the flow path to a first supply unit that supplies a first A gas containing carbon dioxide and oxygen, and a second supply unit that supplies a reducing gas, and the system is configured such that, by adjusting the opening and closing of the flow path by the switching unit, the following contacts can be switched within the reaction unit: contact between the first A gas supplied from the first supply unit and the first reducing agent containing a metal oxide, contact between the second reducing agent, which is the first reducing agent that has come into contact with the first A gas, and the reducing gas, and contact between the third reducing agent, which is the second reducing agent that has come into contact with the reducing gas, and the first B gas, which is the first A gas, that has come into contact with the first reducing agent. Furthermore, the method for operating the gas production system of the present disclosure comprises: an oxygen reaction step of contacting a first gas A containing carbon dioxide and oxygen with a first reducing agent containing a metal oxide to produce a first gas B from which the oxygen in the first gas A has been removed; a hydrogen reaction step of contacting a second reducing agent, which is the first reducing agent oxidized by the oxygen in the first gas A, with a reducing gas containing hydrogen to produce a third reducing agent from which the second reducing agent has been reduced; and a carbon dioxide reaction step of contacting the third reducing agent with the first gas B to reduce the carbon dioxide in the first gas B to produce a product gas containing carbon monoxide, and also producing the first reducing agent used in the oxygen reaction step, from which the third reducing agent has been oxidized.

[0008] According to the gas production system and operating method of the gas production system of this disclosure, an inexpensive and highly efficient gas production system and operating method of the gas production system can be obtained.

[0009] This is a block diagram showing the schematic configuration of the gas production system according to Embodiment 1. This is a flowchart showing the operating method of the gas production system according to Embodiment 1. This is a block diagram showing another schematic configuration of the gas production system according to Embodiment 1. This is a diagram showing the hardware configuration of the control unit of the gas production system according to Embodiment 1. This is a block diagram showing the schematic configuration of the gas production system according to Embodiment 2. This is a diagram illustrating the reaction state of each switching reactor in the first step in the gas production system according to Embodiment 2. This is a diagram illustrating the reaction state of each switching reactor in the second step in the gas production system according to Embodiment 2. This is a diagram illustrating the reaction state of each switching reactor in the third step in the gas production system according to Embodiment 2.

[0010] Embodiment 1. Figure 1 is a block diagram showing the schematic configuration of the gas production system 100 according to Embodiment 1. The gas production system 100 of this embodiment converts a raw material gas, such as exhaust gas containing carbon dioxide CO2 and oxygen O2, into a product gas which is a valuable substance containing carbon monoxide CO, using a reducing agent.

[0011] As shown in Figure 1, the gas production system 100 includes a first reactor 41 as the first reaction section, a second reactor 42 as the second reaction section, and a third reactor 43 as the third reaction section, each of which is a hollow reaction section containing a reducing agent. In the following description, when it is not necessary to distinguish between the first reactor 41, the second reactor 42, and the third reactor 43, they may simply be referred to as reactors.

[0012] Furthermore, the reaction section of this gas production system 100 is connected to a raw material gas supply unit 11 as a first supply unit that supplies raw material gas G1A as first A gas, a hydrogen generator 13 as a second supply unit that generates a gas containing hydrogen, which is the reducing gas G3, a generated gas discharge unit 12 that discharges the generated gas G2, and a water vapor discharge unit 14 that discharges water vapor G4.

[0013] Specifically, the raw material gas supply unit 11 and the first reactor 41 are connected by a raw material gas pipe L1, which serves as a flow path for supplying raw material gas G1A to the first reactor 41. The first reactor 41 and the second reactor 42 are connected by an oxygen removal pipe L2, which serves as a flow path. The product gas discharge unit 12 and the second reactor 42 are connected by a product gas pipe L3, which serves as a flow path for discharging product gas G2. The hydrogen generator 13 and the third reactor 43 are connected by a reducing gas pipe L4, which serves as a flow path for supplying reducing gas G3 to the third reactor 43. The steam discharge unit 14 and the third reactor 43 are connected by a steam discharge pipe L5, which serves as a flow path for discharging steam.

[0014] Furthermore, the gas production system 100 is equipped with circulation piping for circulating the reducing agent between each reactor. Specifically, the gas production system 100 includes circulation piping L6A as a first transfer section for transferring the reducing agent from the first reactor 41 to the third reactor 43, circulation piping L6B as a second transfer section for transferring the reducing agent from the third reactor 43 to the second reactor 42, and circulation piping L6C as a third transfer section for transferring the reducing agent from the second reactor 42 to the first reactor 41. With this configuration, the reducing agent can be circulated in the order of the first reactor 41, the third reactor 43, the second reactor 42, and the first reactor 41.

[0015] Furthermore, the gas production system 100 is equipped with control valves that act as switching units to control the opening and closing of each pipe before and after each reactor. Specifically, a control valve 21, which acts as a first switching unit, is provided between the raw material gas supply unit 11 and the first reactor 41. In addition, a control valve 22, which acts as a second switching unit, is provided between the hydrogen generator 13 and the third reactor 43.

[0016] Furthermore, a control valve 23 is provided in the oxygen removal piping L2 between the first reactor 41 and the second reactor 42. Also, a control valve 24 is provided in the product gas piping L3 between the second reactor 42 and the product gas discharge section 12. Furthermore, a control valve 25 is provided in the steam discharge piping L5 between the third reactor 43 and the steam discharge device 14. In addition, control valves 31 and 32 are provided in the circulation piping L6A. Also, control valves 33 and 34 are provided in the circulation piping L6B. Also, control valves 35 and 36 are provided in the circulation piping L6C. Note that although two control valves 31 and 32 are provided in the circulation piping L6A, it is also acceptable to provide only one of them. Similarly, although two control valves 33 and 34 are provided in the circulation piping L6B, it is also acceptable to provide only one of them. Similarly, although two control valves 35 and 36 are provided in the circulation piping L6C, it is also acceptable to provide only one of them.

[0017] In the following explanation, when it is not necessary to distinguish between each of the control valves 21-25 and 31-36, they may simply be referred to as control valves. Furthermore, the gas production system 100 is equipped with a control unit 50 that can control the open and closed states of each of these control valves, and controls each control valve according to the modes described later.

[0018] Furthermore, the raw material gas supply unit 11 is equipped with a blower (not shown) for pressurizing the raw material gas G1A. The raw material gas piping L1 is also equipped with a heater 1 for heating the raw material gas G1A. The oxygen removal piping L2 is also equipped with a heater 2 for heating the gas supplied from the first reactor 41. The reduction gas piping L4 is also equipped with a heater 3 for heating the reduction gas G3.

[0019] Here, the reducing agent is composed of a material that is oxidized by carbon dioxide and reduced by hydrogen. As such a material, for example, at least one metal element belonging to Group 3 to Group 12 can be selected. In particular, metal oxides and composite oxides containing iron are preferred because they have particularly good conversion efficiency of carbon dioxide CO2 to carbon monoxide CO.

[0020] Furthermore, the reducing agent is preferably in the form of granules, flakes, or pellets. Such forms of reducing agents allow for increased packing density inside each reactor, thereby improving the contact efficiency between the reducing agent and the gas. Alternatively, the reducing agent may be supported on a carrier.

[0021] Each reactor is maintained at a temperature suitable for the oxidation reaction of the reducing agent with carbon dioxide and the reduction reaction of the oxidized reducing agent with hydrogen. The temperature of each reactor is set according to the material of the reducing agent, for example, preferably 600 to 1000°C for metal oxides and composite oxides containing iron. The higher the temperature of each reactor, the higher the reaction rate, and therefore the amount of gas that can be processed can be increased.

[0022] On the other hand, the lower the temperature of each reactor, the less thermal energy is required to raise the temperature, and the lower the heat resistance required for the components of each reactor, which can reduce the manufacturing costs and running costs of the gas production system. Furthermore, the temperature of each reactor may or may not be different for oxidation and reduction reactions. If oxidation and reduction reactions are carried out at the same temperature, the exergy loss due to temperature changes in each reactor is reduced, improving the energy efficiency of the gas production system.

[0023] As mentioned above, the hydrogen generator 13 produces hydrogen as a reducing gas G3, and various methods can be selected for such a hydrogen generator 13, such as a solid oxide electrolytic cell or steam methane reforming. In particular, using a solid oxide electrolytic cell is preferable because it can produce hydrogen using only steam as a raw material.

[0024] The temperature of the hydrogen generator 13 is set to a temperature suitable for hydrogen production, depending on the method. For example, it is preferable to set it to 600 to 800°C for solid oxide type electrolytic cells and to 500 to 1000°C for steam methane reforming. The lower the temperature of the hydrogen generator 13, the less thermal energy is required to raise the temperature, and the lower the heat resistance required for the components of the hydrogen generator 13, which can reduce the equipment cost, running cost, etc. of the gas production system. Also, the closer the temperature of the hydrogen generator 13 is to the temperature of each reactor, the less exergy loss due to temperature changes of the reducing gas G3 is reduced, and the energy efficiency of the gas production system can be improved. In this embodiment, hydrogen is generated and supplied by the hydrogen generator 13, but the hydrogen generator 13 may be omitted, and hydrogen obtained by purchasing, for example, may be supplied.

[0025] The operation of the gas production system 100 configured as described above will be explained below. Figure 2 is a flowchart showing the operation method of the gas production system 100 according to Embodiment 1. The explanation will focus on the case where the reducing agent provided inside each reactor contains Fe, and where the first reducing agent Fe3O4 is provided inside the first reactor 41. In addition, before the operation of the gas production system 100, all control valves are controlled to the closed state.

[0026] <Mode 1: Oxygen reaction process S1> First, the control unit 50 controls the control valve 21 between the raw material gas supply unit 11 and the first reactor 41 to the open state. As a result, raw material gas G1A, which contains carbon dioxide CO2 and oxygen O2, is supplied from the raw material gas supply unit 11 into the first reactor 41. After the raw material gas G1A is supplied into the first reactor 41, the control unit 50 controls the control valve 21 to the closed state.

[0027] Inside the first reactor 41, the raw material gas G1A and the oxidized first reducing agent Fe3O4 come into contact and react, removing oxygen O2 from the raw material gas G1A and completely oxidizing the first reducing agent Fe3O4 to Fe2O3, as shown in (Equation 1) below. The oxygen concentration in the raw material gas after this reaction is not particularly limited, but the lower the better. Here, the oxygen concentration in the raw material gas after the reaction depends on various conditions such as the amount of the first reducing agent Fe3O4, the oxygen concentration in the raw material gas G1A at the time it is supplied to the first reactor 41, and the contact time between the first reducing agent Fe3O4 and the raw material gas G1A. Therefore, the oxygen concentration may be adjusted to optimize the overall efficiency of the system, taking these conditions into account.

[0028]

[0029] <Mode 2: First Transfer Process S2> The control unit 50 controls both the control valves 31 and 32 provided in the circulation pipe L6A to be in the open state, and transfers the completely oxidized Fe2O3 as the second reducing agent Fe2O3 into the third reactor 43 via the circulation pipe L6A. After the second reducing agent Fe2O3 has been transferred into the third reactor 43, the control unit 50 controls the control valves 31 and 32 to be in the closed state.

[0030] <Mode 3: Hydrogen Reaction Process S3> The control unit 50 controls the control valve 22 between the hydrogen generator 13 and the third reactor 43 to the open state. As a result, reducing gas G3 containing hydrogen is supplied from the hydrogen generator 13 into the third reactor 43. After the reducing gas G3 is supplied into the third reactor 43, the control unit 50 controls the control valve 22 to the closed state. Inside the third reactor 43, the reducing gas G3 containing hydrogen comes into contact with the completely oxidized second reducing agent Fe2O3 and reacts, so that the second reducing agent Fe2O3 is reduced to Fe as shown in equation (2) below, and water vapor G4 is generated.

[0031]

[0032] The control unit 50 controls the control valve 25 between the third reactor 43 and the steam exhaust device 14 to the open state, and after the generated steam G4 is discharged through the steam exhaust device 14, controls the control valve 25 to the closed state.

[0033] <Mode 4: Second Transfer Process S4> The control unit 50 controls both the control valves 33 and 34 provided in the circulation piping L6B to the open state, and transfers the Fe reduced by contact with the reducing gas G3 as the third reducing agent Fe into the second reactor 42 via the circulation piping L6B. After the third reducing agent Fe has been transferred into the second reactor 42, the control unit 50 controls the control valves 33 and 34 to the closed state.

[0034] <Mode 5: Carbon Dioxide Reduction Process S5> The control unit 50 controls the control valve 23 between the first reactor 41 and the second reactor 42 to the open state. As a result, the raw material gas G1B, which has been removed as the first B gas by contact with the first reducing agent Fe3O4, is supplied from the first reactor 41 into the second reactor 42. After the raw material gas G1B is supplied into the second reactor 42, the control unit 50 controls the control valve 23 to the closed state.

[0035] Inside the second reactor 42, the oxygen-free raw material gas G1B and the third reducing agent Fe come into contact and react, so that as shown in equation (3) below, the third reducing agent is oxidized to Fe3O4 and product gas G2 is generated in which the carbon dioxide CO2 in the raw material gas G1B is reduced to carbon monoxide CO.

[0036]

[0037] The control unit 50 controls the control valve 24 between the generated gas discharge unit 12 and the second reactor 42 to be in the open state, and after the generated gas G2 is discharged through the generated gas discharge unit 12, it controls the control valve 24 to be in the closed state.

[0038] <Mode 6: Third Transfer Process S6> The control unit 50 controls both the control valves 35 and 36 provided in the circulation piping L6C to be in the open state, and transfers the Fe3O4 oxidized by contact with the raw material gas G1B into the first reactor 41 as the first reducing agent Fe3O4. After the first reducing agent Fe3O4 has been transferred into the first reactor 41, the control unit 50 controls the control valves 35 and 36 to be in the closed state.

[0039] By repeating modes 1 through 6 described above, oxygen can be efficiently removed from the raw gas without the need for expensive, power-hungry devices such as oxygen removal equipment. This allows for the production of the generated gas at a low cost and with high production efficiency. In particular, the exhaust gas can be directly treated with a reducing agent, and the reducing agent is circulated between reactors using an oxidation-reduction reaction, allowing for effective utilization of the reducing agent in each reactor. This reduces costs and enables further improvements in gas production efficiency.

[0040] Furthermore, at the start of the above manufacturing process, which includes modes 1 through 6, if, for example, the third reducing agent Fe is already present in the second reactor 42, the carbon dioxide reduction process of mode 5 should be executed immediately after the oxygen reaction process of mode 1. Each of the above modes should be executed by appropriately adjusting the opening and closing order of each control valve so that oxidation-reduction reactions with circulating reducing agents are carried out in each reactor. In addition, although the above description assumes that the control unit 50 controls the opening and closing of each control valve, this is not the only option. The control unit 50 may be omitted, and the opening and closing of each control valve may be done manually by an operator. Furthermore, if the raw material gas contains substances that corrode the reducing agent, such as nitrogen oxides and sulfur oxides, it is desirable to reduce these substances in the raw material gas beforehand using a decontamination device or the like.

[0041] The following describes a gas production system 100A with a different configuration from the gas production system 100 shown in Figure 1 above. Figure 3 is a block diagram showing the schematic configuration of the gas production system 100A according to Embodiment 1.

[0042] The gas production system 100 shown in Figure 1 had three reactors, a first reactor 41, a second reactor 42, and a third reactor 43, each configured independently. This gas production system 100A has only one reactor 40A as the reaction section. Furthermore, this reactor 40A is not provided with circulation piping for circulating the reducing agent. The raw material gas supply unit 11, the product gas discharge unit 12, the hydrogen generator 13, and the steam discharge unit 14 are all connected to this reactor 40A.

[0043] The operation modes of Mode 1, Mode 3, and Mode 5 described below are the same as the operation modes shown in FIG. 2. When supplying gas in each mode, by opening and closing the regulating valve, the supply of other gases other than the reaction target is stopped for reaction. Specifically, the gas production system 100A performs the following operations. Here, the case where the first reducing agent Fe3O4 is provided as a reducing agent inside the reactor 40A will be described. Also, before the operation of the gas production system 100A, all the regulating valves are controlled to be in a closed state.

[0044] <Mode 1: Oxygen reaction step> First, the control unit 50 controls the regulating valve 21 between the raw material gas supply unit 11 and the reactor 40A to an open state. Thereby, the raw material gas G1A containing carbon dioxide CO2 and oxygen O2 is supplied into the reactor 40A from the raw material gas supply unit 11. After the raw material gas G1A is supplied into the reactor 40A, the control unit 50 controls the regulating valve 21 to a closed state.

[0045] Inside the reactor 40A, when the raw material gas G1A and the oxidized first reducing agent Fe3O4 come into contact and react, oxygen O2 is removed, and at the same time, the first reducing agent Fe3O4 is completely oxidized to the second reducing agent Fe2O3. The raw material gas G1B as the first B gas from which oxygen has been removed by contacting with the first reducing agent Fe3O4 is mainly stored in the oxygen removal pipe L2 from the first reactor 41.

[0046] <Mode 3: Hydrogen reaction step> The control unit 50 controls the regulating valve 22 between the hydrogen generator 13 and the reactor 40A to an open state. Thereby, the reducing gas G3 containing hydrogen is supplied into the reactor 40A from the hydrogen generator 13. After the reducing gas G3 is supplied into the reactor 40A, the control unit 50 controls the regulating valve 22 to a closed state. Inside the reactor 40A, when the reducing gas G3 containing hydrogen and the completely oxidized second reducing agent Fe2O3 come into contact and react, the second reducing agent Fe2O3 is reduced to the third reducing agent Fe, and at the same time, water vapor G4 is generated.

[0047] The control unit 50 controls the regulating valve 25 between the reactor 40A and the water vapor discharge device 14 to an open state, discharges the generated water vapor G4 through the water vapor discharge device 14, and then controls the regulating valve 25 to a closed state.

[0048] <Mode 5: Carbon Dioxide Reduction Process> The control unit 50 controls the control valve 23 to the open state. As a result, the raw material gas G1B, which has had oxygen removed by contact with the first reducing agent Fe3O4, is supplied from the oxygen removal pipe L2 into the reactor 40A. Inside the reactor 40A, the oxygen-free raw material gas G1B comes into contact with the third reducing agent Fe and reacts, causing the third reducing agent Fe to be oxidized to the first reducing agent Fe3O4, and generating product gas G2 in which carbon dioxide CO2 in the raw material gas G1B is reduced to carbon monoxide CO.

[0049] The control unit 50 controls the control valve 24 between the generated gas discharge unit 12 and the reactor 40A to be in the open state, and after the generated gas G2 is discharged through the generated gas discharge unit 12, it controls the control valve 24 to be in the closed state.

[0050] Here, the control valve 23 functions as a partition separating the raw material gas G1B from the second reducing agent Fe2O3 and the reducing gas G3 in contact with the second reducing agent Fe2O3 and the reducing gas G3. This allows for higher gas production efficiency. The diameter and length of the oxygen removal pipe L2 are adjusted to have a capacity to temporarily store the raw material gas G1B, which is the first B gas from which oxygen has been removed in contact with the first reducing agent Fe3O4.

[0051] Furthermore, as another example of a partition wall configuration to separate the raw material gas G1B, from the second reducing agent Fe2O3 and the reducing gas G3, after oxygen O2 has been removed by contact with the first reducing agent Fe3O4, a wall may be provided inside the reactor 40A. In the gas production system 100 described above, the walls of the containers constituting the second reactor 42 and the third reactor 43 function as the partition wall. However, even without the above-mentioned partition wall, it is still possible to carry out the oxygen reaction process, the hydrogen reaction process, and the carbon dioxide reduction process.

[0052] By adopting the above configuration, the manufacturing cost of the reactors, i.e., the cost of the entire gas production system, can be reduced compared to a configuration in which three independent reactors are provided and piping is provided to circulate the reducing agent between the reactors. Furthermore, the control of the regulating valve in the control unit 50 can be simplified.

[0053] The gas production system of this embodiment, configured as described above, comprises a switching unit provided in a flow path and adjusting the opening and closing of the flow path, and a hollow reaction unit connected to the flow path and having a reducing agent inside, wherein the reaction unit is connected via the flow path to a first supply unit that supplies a first A gas containing carbon dioxide and oxygen, and a second supply unit that supplies a reducing gas, and the system is configured so that, by adjusting the opening and closing of the flow path by the switching unit, the following contacts can be switched within the reaction unit: contact between the first A gas supplied from the first supply unit and the first reducing agent containing a metal oxide, contact between the second reducing agent, which is the first reducing agent that has come into contact with the first A gas, and the reducing gas, and contact between the third reducing agent, which is the second reducing agent that has come into contact with the reducing gas, and the first B gas, which is the first A gas, that has come into contact with the first reducing agent. Furthermore, the operating method of the gas production system of this embodiment configured as described above comprises: an oxygen reaction step of contacting a first gas A containing carbon dioxide and oxygen with a first reducing agent containing a metal oxide to produce a first gas B from which the oxygen in the first gas A has been removed; a hydrogen reaction step of contacting a second reducing agent, which is the first reducing agent oxidized by the oxygen in the first gas A, with a reducing gas containing hydrogen to produce a third reducing agent from which the second reducing agent has been reduced; and a carbon dioxide reaction step of contacting the third reducing agent with the first gas B to reduce the carbon dioxide in the first gas B and produce a product gas containing carbon monoxide, and also producing the first reducing agent used in the oxygen reaction step, from which the third reducing agent has been oxidized.

[0054] This eliminates the need for expensive, power-hungry equipment such as oxygen removal devices, allowing for efficient removal of oxygen from the raw gas. As a result, the product gas can be manufactured at a low cost and with high production efficiency. In particular, the exhaust gas can be directly treated using a reducing agent, and the reducing agent is effectively utilized within the reactor using an oxidation-reduction reaction, which reduces costs and further improves gas production efficiency.

[0055] Furthermore, in the gas production system of this embodiment configured as described above, the reaction section has a partition wall that separates the first B gas from the second reducing agent and the reducing gas during contact between the second reducing agent and the reducing gas. Furthermore, the operating method of the gas production system of this embodiment configured as described above involves separating the first B gas from the second reducing agent and the reducing gas before the hydrogen reaction step in which the second reducing agent and the reducing gas are brought into contact.

[0056] This improves the reaction efficiency in the hydrogen reaction process and the carbon dioxide reduction process, thereby increasing the efficiency of gas production.

[0057] Furthermore, in the gas production system of this embodiment configured as described above, the reaction unit comprises: a first reaction unit that brings the first A gas supplied from the first supply unit into contact with the first reducing agent; a second reaction unit connected downstream of the first reaction unit via the flow path, to which the first B gas is supplied and to bring the third reducing agent into contact with the first B gas; a third reaction unit that brings the second reducing agent into contact with the reducing gas; a first transfer unit that moves the second reducing agent from the first reaction unit to the third reaction unit; a second transfer unit that moves the third reducing agent from the third reaction unit to the second reaction unit; and a third transfer unit that moves the first reducing agent, which is the third reducing agent that has come into contact with the first B gas, from the second reaction unit to the first reaction unit. Furthermore, the operating method of the gas production system of this embodiment configured as described above comprises: a first transfer step of transferring the second reducing agent in the first reaction unit to a third reaction unit in which the second reducing agent is brought into contact with the reducing gas, after the oxygen reaction step in the first reaction unit in which the first gas A is brought into contact with the first reducing agent; a second transfer step of transferring the third reducing agent in the third reaction unit to a second reaction unit in which the third reducing agent is brought into contact with the first gas B, after the hydrogen reaction step; and a third transfer step of transferring the first reducing agent in the second reaction unit to the first reaction unit after the carbon dioxide reaction step.

[0058] In this way, by using oxidation-reduction reactions to circulate the reducing agent between reactors and effectively utilizing the reducing agent in each reactor, costs can be reduced and gas production efficiency can be improved.

[0059] The hardware configuration of the control unit 50 will be described below. Figure 4 is a diagram showing an example of the hardware configuration of the control unit 50 as a control device. As shown in Figure 4, the control device consists of a processor 51 and a storage device 52. The storage device 52 includes a volatile storage device such as random access memory (not shown) and a non-volatile auxiliary storage device such as flash memory. Alternatively, a hard disk may be provided as an auxiliary storage device instead of flash memory. The processor 51 executes a program input from the storage device 52. In this case, the program is input to the processor 51 from the auxiliary storage device via the volatile storage device. The processor 51 may also output data such as calculation results to the volatile storage device of the storage device 52, or it may store the data in the auxiliary storage device via the volatile storage device.

[0060] Embodiment 2. Hereinafter, Embodiment 2 will be described with reference to the figures, focusing on the differences from Embodiment 1. Parts similar to those in Embodiment 1 will be denoted by the same reference numerals and their description will be omitted. Figure 5 is a block diagram showing the schematic configuration of the gas production system 200 according to Embodiment 2. The gas production system 200 comprises three independently configured switching reaction units, each consisting of a hollow reaction section containing a reducing agent: switching reactor 245A, switching reactor 245B, and switching reactor 245C. In the following description, when it is not necessary to distinguish between switching reactor 245A, switching reactor 245B, and switching reactor 245C, they may simply be referred to as switching reactors.

[0061] The raw material gas supply unit 11 is connected to each of the switching reactors 245A, 245B, and 245C via the raw material gas piping L201, which serves as a flow path. The hydrogen generator 13 is connected to each of the switching reactors 245A, 245B, and 245C via the reducing gas piping L204, which serves as a flow path. Although the generated gas discharge unit 12 is not shown in Figure 5, it is provided in the same manner as in Embodiment 1, and this generated gas discharge unit 12 is connected to each of the switching reactors 245A, 245B, and 245C via the generated gas piping L203. Also, although the steam discharge device 14 is not shown in Figure 5, it is provided in the same manner as in Embodiment 1, and this steam discharge device 14 is connected to each of the switching reactors 245A, 245B, and 245C via the steam discharge piping L205. Furthermore, the switching reactors 245A, 245B, and 245C are connected to each other via the oxygen removal piping L202.

[0062] Furthermore, the gas production system 200 is equipped with control valves that act as switching sections to control the opening and closing of each pipe before and after each switching reactor. Specifically, control valves 261, 262, and 263 are provided between the raw gas supply unit 11 and the switching reactors 245A, 245B, and 245C, respectively, as first switching sections. In addition, control valves 264, 265, and 266 are provided between the hydrogen generator 13 and the switching reactors 245A, 245B, and 245C, respectively, as second switching sections. Furthermore, control valves 267, 268, and 269 are provided between the switching reactors 245A, 245B, and 245C, respectively, as third switching sections.

[0063] Note that in Figure 5, the heaters 1, 2, and 3 and the control unit 50 shown in Embodiment 1 are omitted from the illustration. In addition, control valves, which are switching parts (not shown), are provided on the generated gas piping L203 and the steam discharge piping L205 connected to each switching reactor.

[0064] The operation of the gas production system 200 configured as described above will now be explained. Figure 6 is a diagram illustrating the reaction state of each switching reactor in the first step in the gas production system 200 according to Embodiment 2. Figure 7 is a diagram illustrating the reaction state of each switching reactor in the second step in the gas production system 200 according to Embodiment 2. Figure 8 is a diagram illustrating the reaction state of each switching reactor in the second step in the gas production system 200 according to Embodiment 2.

[0065] Furthermore, we will describe the case where the reducing agent provided inside each switching reactor contains Fe, and where a first reducing agent Fe3O4 is provided inside switching reactor 245A, a third reducing agent Fe is provided inside switching reactor 245B, and a second reducing agent Fe2O3 is provided inside switching reactor 245C. In addition, before the operation of the gas production system 200, all control valves are controlled to the closed state.

[0066] First, in the first step shown in Figure 6, the control unit 50 controls the control valve 261 between the raw material gas supply unit 11 and the switching reactor 245A to the open state, and also controls the control valves 267 and 268 between the switching reactor 245A and the switching reactor 245B to the open state. At the same time, the control unit 50 controls the control valve 266 between the hydrogen generator 13 and the switching reactor 245C to the open state.

[0067] As a result, as shown by the solid line in Figure 6, raw material gas G1A containing carbon dioxide CO2 and oxygen O2 is supplied from the raw material gas supply unit 11 into the switching reactor 245A. Inside the switching reactor 245A, raw material gas G1A and the first reducing agent Fe3O4 come into contact and react, removing oxygen O2 from raw material gas G1A and completely oxidizing the first reducing agent Fe3O4 to the second reducing agent Fe2O3. In addition, raw material gas G1B, from which oxygen has been removed by contact with the first reducing agent Fe3O4, is supplied from the switching reactor 245A to the switching reactor 245B via the oxygen removal pipe L202.

[0068] Inside the switching reactor 245B, the raw material gas G1B and the third reducing agent Fe come into contact and react, causing the third reducing agent Fe to be oxidized to the first reducing agent Fe3O4, and the carbon dioxide CO2 in the raw material gas G1B to be reduced to carbon monoxide CO, thereby generating product gas G2. The product gas G2 is discharged from the product gas discharge section 12 via the product gas piping L203.

[0069] Furthermore, as shown by the dashed line in Figure 6, hydrogen-containing reducing gas G3 is supplied from the hydrogen generator 13 into the switching reactor 245C. Inside the switching reactor 245C, the hydrogen-containing reducing gas G3 and the second reducing agent Fe2O3 come into contact and react, reducing the second reducing agent Fe2O3 to the third reducing agent Fe, and generating water vapor G4. The water vapor G4 is discharged from the water vapor discharge device 14 via the water vapor discharge pipe L205.

[0070] As described above, in the first step, the control unit 50 controls the opening and closing of each control valve so that the switching reactor 245A functions as a first reaction unit that carries out an oxygen reaction step in which the raw material gas G1A is brought into contact with the first reducing agent Fe3O4. The switching reactor 245B functions as a second reaction unit that carries out a carbon dioxide reaction step in which the raw material gas G1B from which oxygen has been removed is brought into contact with the third reducing agent Fe. The switching reactor 245C functions as a third reaction unit that carries out a hydrogen reaction step in which the reducing gas G3 is brought into contact with the second reducing agent Fe2O3. After the first step is completed, the control unit 50 controls all the control valves to be in the closed state.

[0071] As a result of this first step, the second reducing agent Fe2O3 is provided inside the switching reactor 245A, the first reducing agent Fe3O4 is provided inside the switching reactor 245B, and the third reducing agent Fe is provided inside the switching reactor 245C.

[0072] Next, in the second step shown in Figure 7, the control unit 50 controls the control valve 262 between the raw material gas supply unit 11 and the switching reactor 245B to the open state, and also controls the control valves 268 and 269 between the switching reactor 245B and the switching reactor 245C to the open state. At the same time, the control unit 50 controls the control valve 264 between the hydrogen generator 13 and the switching reactor 245A to the open state.

[0073] As a result, as shown by the solid line in Figure 7, raw material gas G1A containing carbon dioxide CO2 and oxygen O2 is supplied from the raw material gas supply unit 11 into the switching reactor 245B. Inside the switching reactor 245B, raw material gas G1A and the first reducing agent Fe3O4 come into contact and react, removing oxygen O2 from raw material gas G1A and completely oxidizing the first reducing agent Fe3O4 to the second reducing agent Fe2O3. Furthermore, raw material gas G1B from which oxygen has been removed by contact with the first reducing agent Fe3O4 is supplied from the switching reactor 245B via the oxygen removal pipe L202 into the switching reactor 245C.

[0074] Inside the switching reactor 245C, the raw material gas G1B and the third reducing agent Fe come into contact and react, causing the third reducing agent Fe to be oxidized to the first reducing agent Fe3O4, and the carbon dioxide CO2 in the raw material gas G1B to be reduced to carbon monoxide CO, thereby generating product gas G2. The product gas G2 is discharged from the product gas discharge section 12 via the product gas piping L203.

[0075] Furthermore, as shown by the dashed line in Figure 7, hydrogen-containing reducing gas G3 is supplied from the hydrogen generator 13 into the switching reactor 245A. Inside the switching reactor 245A, the hydrogen-containing reducing gas G3 and the second reducing agent Fe2O3 come into contact and react, reducing the second reducing agent Fe2O3 to the third reducing agent Fe, and generating water vapor G4. The water vapor G4 is discharged from the water vapor discharge device 14 via the water vapor discharge pipe L205.

[0076] As described above, in the second step, the control unit 50 controls the opening and closing of each control valve so that the switching reactor 245B functions as a first reaction unit that carries out an oxygen reaction step in which the raw material gas G1A is brought into contact with the first reducing agent Fe3O4. The switching reactor 245C functions as a second reaction unit that carries out a carbon dioxide reaction step in which the raw material gas G1B from which oxygen has been removed is brought into contact with the third reducing agent Fe. The switching reactor 245A functions as a third reaction unit that carries out a hydrogen reaction step in which the reducing gas G3 is brought into contact with the second reducing agent Fe2O3. After the execution of this second step, the control unit 50 controls all the control valves to be in a closed state.

[0077] As a result of this second step, the third reducing agent Fe is provided inside the switching reactor 245A, the second reducing agent Fe2O3 is provided inside the switching reactor 245B, and the first reducing agent Fe3O4 is provided inside the switching reactor 245C.

[0078] Next, in the third step shown in Figure 8, the control unit 50 controls the control valve 263 between the raw material gas supply unit 11 and the switching reactor 245C to the open state, and also controls the control valves 267 and 269 between the switching reactor 245C and the switching reactor 245A to the open state. At the same time, the control unit 50 controls the control valve 265 between the hydrogen generator 13 and the switching reactor 245B to the open state.

[0079] As a result, as shown by the solid line in Figure 8, raw material gas G1A containing carbon dioxide CO2 and oxygen O2 is supplied from the raw material gas supply unit 11 into the switching reactor 245C. Inside the switching reactor 245C, raw material gas G1A and the first reducing agent Fe3O4 come into contact and react, removing oxygen O2 from raw material gas G1A and completely oxidizing the first reducing agent Fe3O4 to the second reducing agent Fe2O3. In addition, raw material gas G1B, from which oxygen has been removed by contact with the first reducing agent Fe3O4, is supplied from the switching reactor 245C to the switching reactor 245A via the oxygen removal pipe L202.

[0080] Inside the switching reactor 245A, the raw material gas G1B and the third reducing agent Fe come into contact and react, causing the third reducing agent Fe to be oxidized to the first reducing agent Fe3O4, and the carbon dioxide CO2 in the raw material gas G1B to be reduced to carbon monoxide CO, thereby generating product gas G2. The product gas G2 is discharged from the product gas discharge section 12 via the product gas piping L203.

[0081] Furthermore, as shown by the dashed line in Figure 8, hydrogen-containing reducing gas G3 is supplied from the hydrogen generator 13 into the switching reactor 245B. Inside the switching reactor 245B, the hydrogen-containing reducing gas G3 and the second reducing agent Fe2O3 come into contact and react, reducing the second reducing agent Fe2O3 to the third reducing agent Fe, and generating water vapor G4. The water vapor G4 is discharged from the water vapor discharge device 14 via the water vapor discharge pipe L205.

[0082] As described above, in the third step, the control unit 50 controls the opening and closing of each control valve so that the switching reactor 245C functions as a first reaction unit that carries out an oxygen reaction step in which raw material gas G1A is brought into contact with the first reducing agent Fe3O4. The switching reactor 245A functions as a second reaction unit that carries out a carbon dioxide reaction step in which oxygen has been removed from the raw material gas G1B is brought into contact with the third reducing agent Fe. The switching reactor 245B functions as a third reaction unit that carries out a hydrogen reaction step in which reducing gas G3 is brought into contact with the second reducing agent Fe2O3. After the third step is completed, the control unit 50 controls all control valves to the closed state.

[0083] As a result of this third step, the first reducing agent Fe3O4 is provided inside the switching reactor 245A, the third reducing agent Fe is provided inside the switching reactor 245B, and the second reducing agent Fe2O3 is provided inside the switching reactor 245C.

[0084] After the third step described above is performed, the first step shown in Figure 6 is performed. The switching from the first step to the second step, from the second step to the third step, and from the third step to the first step by switching the opening and closing of each control valve as described above is called the switching step. In other words, the switching step is the switching of each control valve so that the switching reaction unit that was functioning as the first reaction unit functions as the third reaction unit, the switching reaction unit that was functioning as the second reaction unit functions as the first reaction unit, and the switching reaction unit that was functioning as the third reaction unit functions as the second reaction unit. As a result, the reducing agent can be effectively utilized in each switching reactor using oxidation-reduction reactions, which reduces costs and improves gas production efficiency.

[0085] In this embodiment, although the control unit 50 is described as controlling the opening and closing of each adjustment valve, the invention is not limited to this, and the opening and closing of each adjustment valve may be performed manually by an operator.

[0086] In the gas production system of this embodiment configured as described above, the reaction unit is configured to have three independent switching reaction units, each of which is connected to the first supply unit and the second supply unit via the flow path, and the switching reaction units are connected to each other via the flow path, and each of the switching reaction units is configured to function as any of the following reaction units by adjusting the opening and closing of the flow path by the switching unit: a first reaction unit that brings the first A gas supplied from the first supply unit into contact with the first reducing agent, a second reaction unit that is supplied with the first B gas and brings the third reducing agent into contact with the first B gas, and a third reaction unit that brings the second reducing agent into contact with the reducing gas.

[0087] This achieves the same effects as in Embodiment 1, eliminating the need for expensive, power-hungry devices such as oxygen removal equipment, and efficiently removing oxygen from the raw material gas. As a result, the generated gas can be produced at a low cost and with high production efficiency. Furthermore, by adjusting the opening and closing of each flow path by the switching unit, each switching reaction unit can function almost simultaneously as a first reaction unit that carries out an oxygen reaction process by contacting the raw material gas containing carbon dioxide and oxygen with a first reducing agent, a second reaction unit that carries out a carbon dioxide reaction process by contacting the oxygen-free raw material gas with a third reducing agent, and a third reaction unit that carries out a hydrogen reaction process by contacting the reducing gas with a second reducing agent. This makes it possible to improve the gas production efficiency.

[0088] Furthermore, in the operation method of the gas production system of this embodiment configured as described above, after the step of making each of the switching reaction units function as either the first reaction unit, the second reaction unit, or the third reaction unit, a switching step is provided in which the switching reaction unit that functioned as the first reaction unit functions as the third reaction unit, the switching reaction unit that functioned as the second reaction unit functions as the first reaction unit, and the switching reaction unit that functioned as the third reaction unit functions as the second reaction unit by adjusting the opening and closing of the flow path by the switching unit.

[0089] This allows for the effective use of reducing agents within each switching reactor using oxidation-reduction reactions, thereby reducing costs and improving gas production efficiency.

[0090] 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 extracting at least one component and combining it with a component from another embodiment.

[0091] 11 Raw material gas supply unit (first supply unit), 13 Hydrogen generator (second supply unit), 21, 261, 262, 263 Control valve (first switching unit), 22, 264, 265, 266 Control valve (second switching unit), 267, 268, 269 Control valve (third switching unit), 40A Reactor (reaction unit), 41 First reactor (first reaction unit), 42 Second reactor (second reaction unit), 43 Third reactor (third reaction unit), 245A, 245B, 245C Switching reactor (switching reaction unit), L1, L201 Raw material gas piping (flow path), L4, L204 Reducing gas piping (flow path), L2, L202 Oxygen removal piping (flow path), 100, 100A, 200 Gas production system.

Claims

1. A gas production system comprising: a switching unit provided in a flow path for adjusting the opening and closing of the flow path; and a hollow reaction unit connected to the flow path and having a reducing agent inside, wherein the reaction unit is connected via the flow path to a first supply unit for supplying a first A gas containing carbon dioxide and oxygen, and a second supply unit for supplying a reducing gas, and the system is configured to allow switching of the following contacts within the reaction unit by adjusting the opening and closing of the flow path by the switching unit: contact between the first A gas supplied from the first supply unit and a first reducing agent containing a metal oxide; contact between the second reducing agent, which is the first reducing agent in contact with the first A gas, and the reducing gas; and contact between the third reducing agent, which is the second reducing agent in contact with the reducing gas, and the first B gas, which is the first A gas, in contact with the first reducing agent.

2. The gas production system according to claim 1, wherein the reaction section has a partition wall that separates the first B gas from the second reducing agent and the reducing gas in contact with the second reducing agent and the reducing gas.

3. The gas production system according to claim 1 or claim 2, wherein the reaction unit comprises: a first reaction unit that brings the first A gas supplied from the first supply unit into contact with the first reducing agent; a second reaction unit connected downstream of the first reaction unit via the flow path, which is supplied with the first B gas and brings the third reducing agent into contact with the first B gas; a third reaction unit that brings the second reducing agent into contact with the reducing gas; a first transfer unit that moves the second reducing agent from the first reaction unit to the third reaction unit; a second transfer unit that moves the third reducing agent from the third reaction unit to the second reaction unit; and a third transfer unit that moves the first reducing agent, which is the third reducing agent that has come into contact with the first B gas, from the second reaction unit to the first reaction unit.

4. The gas production system according to claim 1 or 2, wherein the reaction unit is configured to have three independent switching reaction units, each of the switching reaction units is connected to the first supply unit and the second supply unit via the flow path, and the switching reaction units are connected to each other via the flow path, and each of the switching reaction units is configured to function as any of the following reaction units by adjusting the opening and closing of the flow path by the switching unit: a first reaction unit that brings the first A gas supplied from the first supply unit into contact with the first reducing agent; a second reaction unit that is supplied with the first B gas and brings the third reducing agent into contact with the first B gas; and a third reaction unit that brings the second reducing agent into contact with the reducing gas.

5. The gas production system according to any one of claims 1 to 4, wherein the reducing gas contains hydrogen, and the reducing agent contains a metal that reduces carbon dioxide and is reduced by hydrogen.

6. A method for operating a gas production system, comprising: an oxygen reaction step of contacting a first gas A containing carbon dioxide and oxygen with a first reducing agent containing a metal oxide to produce a first gas B from which the oxygen in the first gas A has been removed; a hydrogen reaction step of contacting a second reducing agent, which is the first reducing agent oxidized by the oxygen in the first gas A, with a reducing gas containing hydrogen to produce a third reducing agent from which the second reducing agent has been reduced; and a carbon dioxide reaction step of contacting the third reducing agent with the first gas B to reduce the carbon dioxide in the first gas B to produce a product gas containing carbon monoxide, and also producing the first reducing agent used in the oxygen reaction step, from which the third reducing agent has been oxidized.

7. A method for operating a gas production system according to claim 6, wherein, before the hydrogen reaction step in which the second reducing agent and the reducing gas are brought into contact, the first B gas is separated from the second reducing agent and the reducing gas.

8. A method for operating a gas production system according to claim 6 or 7, comprising: a first transfer step of transferring the second reducing agent in the first reaction section to a third reaction section in which the second reducing agent is brought into contact with the reducing gas, after the oxygen reaction step in the first reaction section in which the first gas A is brought into contact with the first reducing agent; a second transfer step of transferring the third reducing agent in the third reaction section to a second reaction section in which the third reducing agent is brought into contact with the first gas B, after the hydrogen reaction step; and a third transfer step of transferring the first reducing agent in the second reaction section to the first reaction section, after the carbon dioxide reaction step.

9. A method for operating a gas production system using the gas production system described in claim 4, comprising the steps of first making each of the switching reaction units function as one of the first reaction unit, the second reaction unit, or the third reaction unit, and then a switching step of adjusting the opening and closing of the flow path by the switching unit to make the switching reaction unit that functioned as the first reaction unit function as the third reaction unit, the switching reaction unit that functioned as the second reaction unit function as the first reaction unit, and the switching reaction unit that functioned as the third reaction unit function as the second reaction unit.

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