Gas production device, gas production system, and gas production method

Abstract

To provide a gas production device capable of efficiently producing product gas including carbon monoxide from source gas including carbon dioxide while improving energy efficiency.SOLUTION: A gas production device 1 allowing source gas to contact with a reducing agent 4R reducing carbon dioxide to produce product gas, has: a connection unit 2 feeding source gas; a reduction gas feeder 3 feeding reduction gas including hydrogen reducing the reduction agent 4R in an oxidized state; and a plurality of reactors 4a, 4b each connected to the connection unit 2 and the reduction gas feeder 3 and capable of switching the source gas and the reduction gas to be supplied. Each of the reactors 4a, 4b is arranged in a housing to store the reduction agent 4R and has a separation cylinder capable of carrying out at least either separating water from hydrogen formed by contacting the reduction agent 4R or separating carbon monoxide from carbon dioxide.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas production apparatus, a gas production system, and a gas production method.

Background Art

[0002] In recent years, the concentration of carbon dioxide (CO2), which is a kind of greenhouse gas, has been continuously increasing in the atmosphere. The increase in the concentration of carbon dioxide in the atmosphere promotes global warming. Therefore, it is important to recover the carbon dioxide emitted into the atmosphere. Furthermore, if the recovered carbon dioxide can be converted into valuable substances and reused, a carbon recycling society can be realized. Also, as a global measure, as in the Kyoto Protocol of the United Nations Framework Convention on Climate Change, for carbon dioxide, which is the cause of global warming, the reduction rate in developed countries is determined for each country based on 1990, and it is stipulated that the reduction target value should be jointly achieved within the agreed period.

[0003] In order to achieve the reduction target, exhaust gases containing carbon dioxide generated from steel mills, refineries, or thermal power plants are also targeted, and various technical improvements have been made regarding the reduction of carbon dioxide in these industries. An example of such a technology is carbon dioxide capture and storage (CCS). However, this technology has a physical limit in storage and is not a fundamental solution. In addition, for example, Patent Document 1 discloses a technology for converting carbon dioxide into valuable substances. Specifically, a production apparatus for producing carbon monoxide from carbon dioxide using cerium oxide containing zirconium is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, according to the inventors' study, the invention described in Patent Document 1 is an invention that specifies a metal oxide that effectively converts carbon dioxide to carbon monoxide. In Patent Document 1, only conceptual or general information is disclosed regarding the production conditions and production apparatus for carbon monoxide, as shown in the figures. It was found that further technological improvements are required for industrial production of carbon monoxide. Also, from the perspective of industrial production of carbon monoxide, it is important to improve energy efficiency. In the production of carbon monoxide using the above metal oxide, the generated gas contains, in addition to carbon monoxide, unreacted carbon dioxide. Also, in order to regenerate the metal oxide in the oxidized state, hydrogen is brought into contact therewith, but the gas generated at this time contains, in addition to water vapor (water), unreacted hydrogen.

[0006] That is, the generated gas contains substances before and after contact with the metal oxide (reducing agent) (that is, substances before and after reaction with the metal oxide). In general, to separate these substances, the difference in temperature at which they condense (liquefy) by cooling is utilized. However, this requires a large amount of energy for cooling and is wasteful. Therefore, an object of the present invention is to provide a gas production apparatus (that is, an industrially advantageous production apparatus), a gas production system, and a gas production method that can efficiently produce a generated gas containing carbon monoxide from a raw material gas containing carbon dioxide while improving energy efficiency. Means for Solving the Problems

[0007] Such an object is achieved by the following present invention.

[0008] (1) The gas production apparatus of the present invention is a gas production apparatus that brings a raw material gas containing carbon dioxide into contact with a reducing agent containing a metal oxide that reduces the carbon dioxide to produce a generated gas containing carbon monoxide, a raw material gas supply unit that supplies the raw material gas, A reducing gas supply unit that supplies a reducing gas containing a reducing substance for reducing the reducing agent oxidized by contact with the carbon dioxide; It is connected to the raw material gas supply unit and the reducing gas supply unit respectively, and has a plurality of reactors capable of switching the supplied raw material gas and the reducing gas; Each of the reactors includes a reactor main body and a separation cylinder disposed in the reactor main body, which houses the reducing agent and is capable of separating at least one of the oxide of the reducing substance generated by contact with the reducing agent and the reducing substance, and separating the carbon monoxide and the carbon dioxide.

[0009] (2) In the gas production apparatus of the present invention, it is preferable that the separation cylinder has heat resistance. (3) In the gas production apparatus of the present invention, it is preferable that the separation cylinder is composed of a metal, an inorganic oxide or a metal organic structure. (4) In the gas production apparatus of the present invention, it is preferable that the separation cylinder is composed of a porous body having continuous pores in which adjacent pores communicate with each other. (5) In the gas production apparatus of the present invention, it is preferable that the separation cylinder has a porosity of 10 to 90%.

[0010] (6) In the gas production apparatus of the present invention, the reducing substance is hydrogen, the oxide of the reducing substance is water, It is preferable that the separation cylinder has an average pore diameter of 600 pm or less. (7) In the gas production apparatus of the present invention, it is preferable that the separation cylinder has hydrophilicity. (8) In the gas production apparatus of the present invention, it is preferable that the metal oxide contained in the reducing agent contains at least one selected from metal elements belonging to Groups 3 to 12. (9) The gas production apparatus of the present invention preferably further has a gas confluence unit that passes through the reactors and merges the separated gases to generate a mixed gas.

[0011] (10) The gas production apparatus of the present invention preferably further has gas lines that are connected to each of the reactors and are independent of each other for transferring the separated gas. (11) In the gas production apparatus of the present invention, further, a raw material gas heating unit that heats the raw material gas before being supplied to the reactor, and a reducing gas heating unit that heats the reducing gas before being supplied to the reactor are preferably provided. (12) The gas production system of the present invention, includes a raw material gas generation unit that generates a raw material gas containing carbon dioxide, and the gas production apparatus of the present invention, characterized in that the gas production apparatus is connected to the raw material gas generation unit via the raw material gas supply unit.

[0012] (13) The gas production method of the present invention is a gas production method for producing a product gas containing carbon monoxide by bringing a raw material gas containing carbon dioxide into contact with a reducing agent containing a metal oxide that reduces the carbon dioxide, including a plurality of reactors having a reactor main body and a separation cylinder disposed in the reactor main body for accommodating the reducing agent, preparing a reducing gas containing a reducing substance for reducing the reducing agent oxidized by contact of the raw material gas and the carbon dioxide, by switching the reactor that supplies the raw material gas and the reducing gas, alternately bringing the raw material gas and the reducing gas into contact with the reducing agent in the separation cylinder of each reactor to convert the carbon dioxide into carbon monoxide, and then reducing the oxidized reducing agent, wherein the separation cylinder is capable of at least one of separation of an oxide of the reducing substance generated by contact with the reducing agent and the reducing substance, and separation of the carbon monoxide and the carbon dioxide.

[0013] (14) In the gas production method of the present invention, the gases that have passed through the reactor and been separated are merged together to generate a mixed gas. It is preferable to recover the produced gas by using the mixed gas as it is or by purifying carbon monoxide from the mixed gas. (15) In the gas production method of the present invention, it is preferable to process the gases that have passed through each of the reactors and been separated independently of each other.

Advantages of the Invention

[0014] According to the present invention, it is possible to efficiently produce a produced gas containing carbon monoxide from a raw material gas containing carbon dioxide while enhancing energy efficiency.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the gas production apparatus, gas production system, and gas production method of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings. FIG. 1 is a schematic diagram showing an embodiment of the gas production system of the present invention, FIG. 2 is a cross-sectional view schematically showing the configuration of the reactor of FIG. 1, FIG. 3 is a view showing an enlarged part of FIG. 2, and FIG. 4 is a schematic diagram showing the configuration of the exhaust gas heating section of FIG. 1. The gas production system 100 shown in FIG. 1 includes a furnace (raw material gas generation unit) 20 that generates exhaust gas (raw material gas) containing carbon dioxide, and a gas production device 1 connected to the furnace 20 via a connection part 2. In addition, in this specification, the upstream side with respect to the gas flow direction is simply described as the "upstream side", and the downstream side is simply described as the "downstream side".

[0017] The furnace 20 is not particularly limited. For example, it is a furnace attached to a steel mill, a refining plant, or a thermal power plant, and preferably includes a combustion furnace, a blast furnace, a converter, etc. In the furnace 20, exhaust gas is generated (produced) during combustion, melting, refining, etc. of the contents. In the case of a combustion furnace (incinerator) in a waste incineration plant, examples of the contents (waste) include plastic waste, raw garbage, municipal solid waste (MSW), waste tires, biomass waste, household garbage (quilts, papers), building members, etc. Note that these wastes may contain one type alone or two or more types.

[0018] Exhaust gas usually contains, in addition to carbon dioxide, other gas components such as nitrogen, oxygen, carbon monoxide, water vapor, methane, etc. The concentration of carbon dioxide contained in the exhaust gas is not particularly limited, but considering the production cost of the produced gas (conversion efficiency to carbon monoxide), 1% by volume or more is preferable, and 5% by volume or more is more preferable. In the case of exhaust gas from a combustion furnace in a waste incineration plant, it contains 5 - 15% by volume of carbon dioxide, 60 - 70% by volume of nitrogen, 5 - 10% by volume of oxygen, and 15 - 25% by volume of water vapor.

[0019] The exhaust gas from a blast furnace (blast furnace gas) is the gas generated when producing pig iron in a blast furnace, and contains 10 - 15% by volume of carbon dioxide, 55 - 60% by volume of nitrogen, 25 - 30% by volume of carbon monoxide, and 1 - 5% by volume of hydrogen. In addition, the exhaust gas from a converter (converter gas) is the gas generated when producing steel in a converter, and contains 15 - 20% by volume of carbon dioxide, 50 - 60% by volume of carbon monoxide, 15 - 25% by volume of nitrogen, and 1 - 5% by volume of hydrogen. Note that, as the raw material gas, not only exhaust gas but also a pure gas containing 100% by volume of carbon dioxide may be used.

[0020] However, if exhaust gas is used as the raw material gas, the carbon dioxide that has been conventionally discharged into the atmosphere can be effectively utilized, and the environmental load can be reduced. Among these, from the viewpoint of carbon circulation, exhaust gas containing carbon dioxide generated in a steelworks or a refining plant is preferable. In addition, as for blast furnace gas and converter gas, the untreated gas discharged from the furnace may be used as it is, or for example, the treated gas after a treatment for removing carbon monoxide or the like may be used. The untreated blast furnace gas and converter gas have the gas compositions as described above, respectively, and the treated gas has a gas composition close to the gas composition shown by the exhaust gas from the combustion furnace. In this specification, any of the above gases (gases before being supplied to the gas manufacturing apparatus 1) is called exhaust gas.

[0021] <Overall Configuration> The gas manufacturing apparatus 1 brings the exhaust gas (raw material gas containing carbon dioxide) discharged from the furnace 20 and supplied via the connection part 2 into contact with a reducing agent containing a metal oxide that reduces carbon dioxide contained in the exhaust gas, thereby manufacturing a generated gas (synthesis gas) containing carbon monoxide. The gas manufacturing apparatus 1 mainly includes a connection part 2, a reducing gas supply part 3, two reactors 4a and 4b, a gas line GL1 connecting the connection part 2 and each of the reactors 4a and 4b, a gas line GL2 connecting the reducing gas supply part 3 and each of the reactors 4a and 4b, and a gas line GL4 connected to each of the reactors 4a and 4b. In the present embodiment, the connection part 2 constitutes a raw material gas supply part that supplies exhaust gas to the reactors 4a and 4b. Note that, if necessary, pumps for transferring gas may be arranged at predetermined positions in the middle of the gas line GL1, the gas line GL2, and the gas line GL4. For example, when the pressure of the exhaust gas is adjusted to be relatively low in the compression part 6 described later, the gas can be smoothly transferred in the gas manufacturing apparatus 1 by arranging the pumps.

[0022] The gas line GL1 is connected to the connection part 2 at one of its ends. On the other hand, at the other end of the gas line GL1, the reactors 4a and 4b provided in the reaction part 4 are respectively connected to the inlet ports of the reactors 4a and 4b via the gas switching part 8 and the two gas lines GL3a and GL3b. With such a configuration, the exhaust gas supplied from the furnace 20 via the connection part 2 passes through the gas line GL1 and is supplied to each of the reactors 4a and 4b. The gas switching part 8 can be configured to include, for example, a branched gas line and a flow path opening / closing mechanism such as a valve provided in the middle of this branched gas line.

[0023] As shown in FIG. 2, each of the reactors 4a and 4b is composed of a multi-tubular reaction device (fixed-bed reaction device) including a plurality of separation cylinders 41 each filled (accommodated) with a reducing agent 4R and a housing (reactor main body) 42 that houses the plurality of separation cylinders 41. According to such a multi-tubular reaction device, the opportunity for contact between the reducing agent 4R, the exhaust gas, and the reducing gas can be sufficiently ensured. As a result, the production efficiency of the product gas can be increased. The reducing agent 4R of the present embodiment is preferably, for example, in the form of particles (granules), flakes, pellets, or the like. With the reducing agent 4R having such a shape, the filling efficiency into the separation cylinder 41 can be increased, and the contact area with the gas supplied into the separation cylinder 41 can be further increased. When the reducing agent 4R is in the form of particles, its volume average particle diameter is not particularly limited, but is preferably 1 to 50 mm, and more preferably 3 to 30 mm. In this case, the contact area between the reducing agent 4R and the exhaust gas (carbon dioxide) can be further increased, and the conversion efficiency of carbon dioxide to carbon monoxide can be further improved. Similarly, the regeneration (reduction) of the reducing agent 4R by the reducing gas containing the reducing substance can also be performed more efficiently. The particulate reducing agent 4R is preferably a molded body produced by tumbling granulation because its sphericity is higher.

[0024] Further, the reducing agent 4R may be supported on a carrier. The constituent material of the carrier may be any material that is difficult to be denatured according to the exhaust gas (raw material gas), reaction conditions, etc., and is not particularly limited. For example, carbon materials (graphite, graphene, etc.), zeolite, montmorillonite, SiO2, ZrO2, TiO2, V2O5, MgO, alumina (Al2O3), silica, and composite oxides of these materials can be mentioned. Among these, zeolite, montmorillonite, SiO2, ZrO2, TiO2, V2O5, MgO, alumina (Al2O3), silica, and composite oxides of these materials are preferable. A carrier composed of such a material is preferable in that it does not adversely affect the reaction of the reducing agent 4R and has excellent supporting ability for the reducing agent 4R. Here, the carrier is not involved in the reaction of the reducing agent 4R and simply supports (holds) the reducing agent 4R. As an example of such a form, a configuration in which at least a part of the surface of the carrier is coated with the reducing agent 4R can be mentioned.

[0025] The metal oxide (oxygen carrier) contained in the reducing agent 4R is not particularly limited as long as it can reduce carbon dioxide, but preferably contains at least one selected from metal elements belonging to Groups 3 to 12, more preferably contains at least one selected from metal elements belonging to Groups 4 to 12, and still more preferably contains at least one of titanium, vanadium, iron, copper, zinc, nickel, manganese, chromium, cerium, etc. Metal oxides containing iron, metal oxides containing cerium, or composite oxides are particularly preferable. These metal oxides are useful because the conversion efficiency of carbon dioxide to carbon monoxide is particularly good.

[0026] The volumes of the two reactors 4a and 4b are set to be substantially equal to each other and are appropriately set according to the amount of exhaust gas to be treated (the size of the furnace 20 and the size of the gas production apparatus 1). In the present invention, a separation cylinder 41 capable of separating at least one of the oxide of the reducing substance generated by contact with the reducing agent 4R and the reducing substance, and carbon monoxide and carbon dioxide is disposed in the housing 42. This feature will be described in detail later.

[0027] In the middle of the gas line GL1, a concentration adjustment unit 5, a compression unit 6, a micro-component removal unit 7, and an exhaust gas heating unit (raw material gas heating unit) 10 are provided in order from the side of the connection part 2. The concentration adjustment unit 5 adjusts to increase the concentration of carbon dioxide contained in the exhaust gas (in other words, to concentrate carbon dioxide). The exhaust gas also contains unnecessary gas components such as oxygen. By increasing the concentration of carbon dioxide contained in the exhaust gas in the concentration adjustment unit 5, the concentration of unnecessary gas components contained in the exhaust gas can be made relatively low. Therefore, it is possible to prevent or suppress the adverse effect of unnecessary gas components on the conversion efficiency of carbon dioxide to carbon monoxide by the reducing agent 4R. The concentration adjustment unit 5 is preferably constituted by an oxygen removal device that removes oxygen contained in the exhaust gas. Thereby, the amount of oxygen introduced into the gas production apparatus 1 can be reduced (that is, the concentration of oxygen contained in the exhaust gas can be adjusted to be low). Therefore, the gas composition of the exhaust gas can be deviated from the explosion range, and ignition of the exhaust gas can be prevented. Among the gas production apparatuses 1, since the consumption of electric energy in the oxygen removal device is large, it is effective to use electric power as renewable energy as described later.

[0028] In this case, it is preferable to adjust the concentration of oxygen contained in the exhaust gas to less than 1% by volume with respect to the whole exhaust gas, more preferably to less than 0.5% by volume, and even more preferably to less than 0.1% by volume. Thereby, ignition of the exhaust gas can be more reliably prevented. The oxygen removal device that removes oxygen contained in the exhaust gas can be configured using one or more of a separator of a cryogenic separation method (cryogenic method), a separator of a pressure swing adsorption (PSA) method, a separator of a membrane separation method, a separator of a temperature swing adsorption (TSA) method, a separator of a chemical absorption method, a separator of a chemical adsorption method, etc. Note that in the concentration adjustment unit 5, the concentration of carbon dioxide may be adjusted to be high by adding carbon dioxide to the exhaust gas.

[0029] The compressor section 6 increases the pressure of the exhaust gas before it is supplied to the reactors 4a and 4b. As a result, the amount of exhaust gas that can be processed at one time in the reactors 4a and 4b can be increased. Therefore, the conversion efficiency of carbon dioxide to carbon monoxide in the reactors 4a and 4b can be further improved. Such a compressor section 6 can be composed of, for example, a turbo compressor such as a centrifugal compressor or an axial flow compressor, a reciprocating compressor (reciprocating compressor), a diaphragm compressor, a single screw compressor, a twin screw compressor, a scroll compressor, a rotary compressor, a rotary piston type compressor, a sliding vane type compressor, a positive displacement compressor, a roots blower (two-lobe blower) capable of handling low pressure, a centrifugal blower, etc.

[0030] Among these, from the viewpoint of ease of scaling up the gas production system 100, the compressor section 6 is preferably composed of a centrifugal compressor, and from the viewpoint of reducing the manufacturing cost of the gas production system 100, it is preferably composed of a reciprocating compressor. The pressure of the exhaust gas after passing through the compressor section 6 is not particularly limited, but is preferably 0 to 1 MPaG, more preferably 0 to 0.5 MPaG, and even more preferably 0.01 to 0.5 MPaG. In this case, the conversion efficiency of carbon dioxide to carbon monoxide in the reactors 4a and 4b can be further improved without increasing the pressure resistance of the gas production apparatus 1 more than necessary.

[0031] The fine component removal section 7 removes fine components (trace unwanted gas components, etc.) contained in the exhaust gas. Such a fine component removal section 7 can be composed of, for example, at least one type of processor among a gas-liquid separator, a protector (guard reactor), and a scrubber (absorption tower). When using a plurality of processors, the order of their arrangement is arbitrary. However, when using a combination of a gas-liquid separator and a protector, it is preferable to arrange the gas-liquid separator upstream of the protector. In this case, the removal efficiency of fine components from the exhaust gas can be further increased, and the service life (lifespan) of the protector can be extended.

[0032] The gas-liquid separator separates, for example, condensed water (liquid) generated when the exhaust gas is compressed by the compression unit 6 from the exhaust gas. In this case, unnecessary gas components remaining in the exhaust gas are also dissolved and removed in the condensed water. The gas-liquid separator can be composed of, for example, a simple container, a swirling flow type separator, a centrifugal separator, a surface tension type separator, etc. Among these, the gas-liquid separator is preferably composed of a simple container because of its simple structure and low cost. In this case, a filter that allows the passage of gas but blocks the passage of liquid may be arranged at the gas-liquid interface in the container. Also, in this case, a liquid line may be connected to the bottom of the container, and a valve may be provided in the middle thereof. According to such a configuration, the condensed water stored in the container can be discharged outside the gas production device 1 through the liquid line by opening the valve. Note that the liquid line may be connected to a tank 30 described later so that the discharged condensed water can be reused.

[0033] The exhaust gas from which the condensed water has been removed by the gas-liquid separator can be configured to be supplied to, for example, a protector. Such a protector preferably includes a substance capable of capturing a microcomponent contained in the exhaust gas and being a component (inactivating component) that reduces the activity of the reducing agent 4R by contact with the reducing agent 4R. According to such a configuration, when the exhaust gas passes through the protector, the substance in the protector reacts (captures) with the inactivating component, thereby preventing or suppressing the inactivating component from reaching the reducing agent 4R in the reactors 4a and 4b and protecting it (that is, preventing the decrease in activity). Therefore, it is possible to prevent or suppress the conversion efficiency of carbon dioxide to carbon monoxide by the reducing agent 4R from being extremely reduced due to the adverse effect of the inactivating component.

[0034] Such substances include those having a composition contained in the reducing agent 4R and capable of reducing the activity of the reducing agent 4R upon contact with an inactivating component. Specifically, metal oxides identical or similar to those contained in the reducing agent 4R can be used. Here, similar metal oxides refer to those having the same metal element contained therein but different compositions, or those having different types of metal elements contained therein but belonging to the same group in the periodic table of elements. Also, the inactivating component is preferably at least one selected from sulfur, mercury, sulfur compounds, halogen compounds, organosilicons, organic phosphorus, and organometallic compounds, and more preferably at least one selected from sulfur and sulfur compounds. By removing such an inactivating component in advance, it is possible to effectively prevent a sharp decrease in the activity of the reducing agent 4R. In addition, the above-mentioned substance may be any substance whose activity is reduced by the same component as the inactivating component of the reducing agent 4R, and metal oxides such as iron oxide and zinc oxide are preferable in that they have excellent capturing ability for the above-mentioned inactivating component.

[0035] The protector may be configured to dispose a mesh material in the housing and place the particles of the above-mentioned substance on the mesh material, or to dispose a honeycomb-shaped filter member or a cylindrical or particulate molded body composed of the above-mentioned substance in the housing. In particular, when the protector is disposed between the compression section 6 (gas-liquid separator) and the exhaust gas heating section 10, it is possible to improve the removal efficiency of the inactivating component while preventing deterioration of the above-mentioned substance due to heat.

[0036] The exhaust gas heating section 10 heats the exhaust gas before it is supplied to the reactors 4a and 4b. By preheating the exhaust gas before the reaction (before reduction) in the exhaust gas heating section 10, the conversion (reduction) reaction of carbon dioxide to carbon monoxide by the reducing agent 4R in the reactors 4a and 4b can be further promoted. The exhaust gas heating section 10 can be composed of, for example, an electric heater 101 and a heat exchanger (economizer) 102 as shown in FIG. 4. The heat exchanger 102 is configured by bending a part of the piping that constitutes the gas line GL4 (to be described later) that discharges the gas (mixed gas) after passing through the reactors 4a and 4b and approaching the piping that constitutes the gas line GL1. According to such a configuration, by utilizing the heat of the high-temperature gas (mixed gas) after passing through the reactors 4a and 4b, the exhaust gas before being supplied to the reactors 4a and 4b can be heated by heat exchange, so that effective utilization of heat can be achieved.

[0037] Such a heat exchanger 102 can be configured, for example, as a jacket type heat exchanger, an immersion coil type heat exchanger, a double pipe type heat exchanger, a shell & tube type heat exchanger, a plate type heat exchanger, a spiral type heat exchanger, etc. Also, in the exhaust gas heating unit 10, either one of the electric heater 101 and the heat exchanger 102 may be omitted. In the exhaust gas heating unit 10, instead of the electric heater 101, a combustion furnace or the like can also be used. However, if the electric heater 101 is used, electric power (electrical energy) as renewable energy can be used as its power source, so that the environmental load can be reduced. As the renewable energy, electrical energy utilizing at least one selected from solar power generation, wind power generation, hydroelectric power generation, wave power generation, tidal power generation, biomass power generation, geothermal power generation, solar heat, and ground heat can be used.

[0038] Also, on the upstream side of the exhaust gas heating unit 10 (for example, between the gas-liquid separator and the protector in the middle of the micro-component removal unit 7), an exhaust gas line may be branched from the gas line GL1, and a vent part provided outside the gas production apparatus 1 may be connected to the end thereof. In this case, a valve is preferably provided in the middle of the exhaust gas line. If the pressure in the gas production apparatus 1 (gas line GL1) rises more than necessary, by opening the valve, a part of the exhaust gas can be discharged (released) from the vent part through the exhaust gas line. Thereby, damage due to the pressure rise of the gas production apparatus 1 can be prevented in advance.

[0039] The gas line GL2 is connected to the reducing gas supply section 3 at one of its ends. On the other hand, the gas line GL2 is connected to the inlet ports of the reactors 4a and 4b provided in the reaction section 4 via the gas switching section 8 and two gas lines GL3a and GL3b, respectively. The reducing gas supply section 3 supplies a reducing gas containing a reducing substance that reduces the reducing agent 4R oxidized by contact with carbon dioxide. The reducing gas supply section 3 of the present embodiment is configured by a hydrogen generator that generates hydrogen by electrolysis of water, and a tank (reducing gas raw material storage section) 30 outside the gas production apparatus 1 that stores water in this hydrogen generator is connected. With such a configuration, the reducing gas containing hydrogen (reducing substance) supplied from the hydrogen generator (reducing gas supply section 3) passes through the gas line GL2 and is supplied to each of the reactors 4a and 4b. According to the hydrogen generator, a large amount of hydrogen can be generated relatively inexpensively and simply. There is also an advantage that the condensed water generated in the gas production apparatus 1 can be reused. Among the gas production apparatuses 1, since the consumption of electric energy in the hydrogen generator is large, it is effective to use electric power as the renewable energy as described above.

[0040] Note that a device that generates by-product hydrogen can also be used as the hydrogen generator. In this case, the reducing gas containing by-product hydrogen is supplied to each of the reactors 4a and 4b. Examples of the device that generates by-product hydrogen include a device that electrolyzes an aqueous sodium chloride solution, a device that steam reforms petroleum, a device that manufactures ammonia, and the like. Further, the gas line GL2 may be connected to a coke oven outside the gas production apparatus 1 via a connection section, and the exhaust gas from the coke oven may be used as the reducing gas. In this case, the connection section constitutes the reducing gas supply section. This is because the exhaust gas from the coke oven mainly contains hydrogen and methane and contains hydrogen in an amount of 50 to 60% by volume. In the middle of the gas line GL2, a reducing gas heating unit 11 is provided. This reducing gas heating unit 11 heats the reducing gas before it is supplied to the reactors 4a and 4b. By preheating the reducing gas before the reaction (before oxidation) in the reducing gas heating unit 11, the reduction (regeneration) reaction of the reducing agent 4R by the reducing gas in the reactors 4a and 4b can be further promoted.

[0041] The reducing gas heating unit 11 can be configured in the same manner as the exhaust gas heating unit 10. The reducing gas heating unit 11 is preferably composed of only an electric heater, only a heat exchanger, or a combination of an electric heater and a heat exchanger, and more preferably composed of only a heat exchanger or a combination of an electric heater and a heat exchanger. If the reducing gas heating unit 11 is equipped with a heat exchanger, the heat of the high-temperature gas (e.g., mixed gas) after passing through the reactors 4a and 4b can be used to heat the reducing gas before it is supplied to the reactors 4a and 4b by heat exchange, so that effective utilization of heat can be achieved.

[0042] According to the above configuration, by switching the gas line (flow path) in the gas switching unit 8, for example, exhaust gas can be supplied to the reactor 4a containing the reducing agent 4R before oxidation via the gas line GL3a, and reducing gas can be supplied to the reactor 4b containing the oxidized reducing agent 4R via the gas line GL3b. At this time, the reaction of the following formula 1 proceeds in the reactor 4a, and the reaction of the following formula 2 proceeds in the reactor 4b. In the following formulas 1 and 2, the case where the metal oxide contained in the reducing agent 4R is iron oxide (FeO x-1 ) is shown as an example. Formula 1: CO2 + FeO x-1 → CO + FeO x Formula 2: H2 + FeO x → H2O + FeO x-1 Thereafter, by switching the gas line in the gas switching unit 8 in the opposite manner to the above, the reaction of the above formula 2 can proceed in the reactor 4a, and the reaction of the above formula 1 can proceed in the reactor 4b.

[0043] Note that both the reactions shown in the above formulas (1) and (2) are endothermic reactions. Therefore, when the gas production apparatus 1 brings the exhaust gas or the reducing gas into contact with the reducing agent 4R (that is, during the reaction between the exhaust gas or the reducing gas and the reducing agent 4R), it is preferable that the gas production apparatus 1 further has a reducing agent heating unit (not shown in FIG. 1) that heats the reducing agent 4R. By providing such a reducing agent heating unit, the temperature in the reaction between the exhaust gas or the reducing gas and the reducing agent 4R can be maintained at a high temperature, preferably preventing or suppressing a decrease in the conversion efficiency of carbon dioxide to carbon monoxide, and further promoting the regeneration of the reducing agent 4R by the reducing gas.

[0044] However, depending on the type of the reducing agent 4R, the reactions shown in the above formulas (1) and (2) may be exothermic reactions. In this case, it is preferable that the gas production apparatus 1 has a reducing agent cooling unit that cools the reducing agent 4R instead of the reducing agent heating unit. By providing such a reducing agent cooling unit, during the reaction between the exhaust gas or the reducing gas and the reducing agent 4R, it is possible to preferably prevent the deterioration of the reducing agent 4R, preferably prevent or suppress a decrease in the conversion efficiency of carbon dioxide to carbon monoxide, and further promote the regeneration of the reducing agent 4R by the reducing gas. That is, it is preferable that the gas production apparatus 1 is provided with a reducing agent temperature control unit that adjusts the temperature of the reducing agent 4R according to the difference in the type (exothermic reaction or endothermic reaction) of the reducing agent 4R. The preferred configuration of the reducing agent temperature control unit will be described in detail later.

[0045] Branched gas lines GL4a and GL4b are respectively connected to the outlet ports of the reactors 4a and 4b, and these merge at the gas merging section J4 to form a gas line GL4. Further, valves (not shown) are respectively provided in the middle of the branched gas lines GL4a and GL4b as required. For example, by adjusting the opening degree of the valves, the passing speeds of the exhaust gas and the reducing gas passing through the reactors 4a and 4b (that is, the processing speed of the exhaust gas by the reducing agent 4R and the processing speed of the reducing agent 4R by the reducing gas) can be set. In this embodiment, the reaction unit 4 is constituted by reactors 4a and 4b and a gas switching unit 8.

[0046] With such a configuration, the gases (in this embodiment, mainly carbon monoxide and water vapor) that have passed through each of the reactors 4a and 4b are mixed by merging at the gas merging section J4, and after a mixed gas (merged gas) is generated, it passes through one gas line GL4. Therefore, if the flow path switching state (valve opening and closing state) of the gas switching unit 8 is changed to perform different reactions in each of the reactors 4a and 4b, a mixed gas can be continuously produced, and ultimately, a product gas can also be continuously produced. Also, since the same reaction is alternately repeated in the reactors 4a and 4b, the concentration of carbon monoxide contained in the mixed gas can be stabilized, and as a result, the concentration of carbon monoxide contained in the product gas can also be stabilized. Therefore, the above-described gas production apparatus 1 (gas production system 100) can continuously and stably produce carbon monoxide from carbon dioxide, which is industrially advantageous.

[0047] On the other hand, when the gas merging section J4 is not provided, when switching the supplied gas, it is necessary to shut off the gas switching unit 8 (temporarily close the valve), and each reactor 4a, 4b has to be operated in a batch mode. For this reason, depending on the concentration of carbon dioxide in the exhaust gas, the type of reducing agent 4R, the capacity of the reactors 4a and 4b, etc., the production time of carbon monoxide may become long, the conversion efficiency may be poor, and it may be industrially disadvantageous. Also, the components of the gas discharged from each of the reactors 4a and 4b are likely to change each time the supplied gas is switched. For this reason, the post-treatment process for the gas discharged from each of the reactors 4a and 4b may become complicated. Here, the concentration of carbon monoxide contained in the mixed gas is usually preferably adjusted within a specific range (a predetermined volume % with respect to the entire mixed gas). If this concentration is too low, although it depends on the performance of the gas purification unit 9 described later, it tends to be difficult to obtain a product gas containing carbon monoxide at a high concentration. On the other hand, even if the upper limit value of this concentration is increased beyond that, no further increase in the effect of further increasing the concentration of carbon monoxide contained in the finally obtained product gas can be expected.

[0048] At the opposite ends of the reactors 4a and 4b of the gas line GL4, a product gas discharge section 40 for discharging the product gas outside the gas production apparatus 1 is connected. Also, a gas purification unit 9 is provided in the middle of the gas line GL4. In the gas purification unit 9, carbon monoxide is purified from the mixed gas, and a product gas containing high-concentration carbon monoxide is recovered. Note that when the carbon monoxide concentration in the mixed gas is sufficiently high, the gas purification unit 9 may be omitted. Such a gas purification unit 9 can be composed of, for example, at least one type of processor among a cooler, a gas-liquid separator, a gas separator, a separation membrane, and a scrubber (absorption tower). When using a plurality of processors, their arrangement order is arbitrary. However, when combining and using a cooler, a gas-liquid separator, and a gas separator, it is preferable to arrange them in this order. In this case, the purification efficiency of carbon monoxide from the mixed gas can be further enhanced.

[0049] The cooler cools the mixed gas. Thereby, condensed water (liquid) is generated. Such a cooler can be configured to include a jacket-type cooling device having a jacket for passing a refrigerant around a pipe, a configuration similar to that of the reactors 4a and 4b (see Figure 2), a multi-tube type cooling device for passing the mixed gas through the pipe body and the refrigerant around the pipe body, an air fin cooler, etc.

[0050] The gas-liquid separator separates the condensed water generated when cooling the mixed gas in the cooler from the mixed gas. At this time, the condensed water has the advantage that unnecessary gas components remaining in the mixed gas (especially carbon dioxide) can be dissolved and removed. The gas-liquid separator can be configured in the same manner as the gas-liquid separator of the microcomponent removal unit 7, and preferably can be configured as a simple container. In this case, a filter that allows the passage of gas but blocks the passage of liquid may be arranged at the gas-liquid interface in the container. Also, in this case, a liquid line may be connected to the bottom of the container, and a valve may be provided in the middle thereof. According to such a configuration, the condensed water stored in the container can be discharged (released) outside the gas production device 1 through the liquid line by opening the valve.

[0051] Furthermore, it is preferable to provide a drain trap on the downstream side of the valve in the middle of the liquid line. Thereby, even if the valve malfunctions and carbon monoxide or hydrogen flows out into the liquid line, it can be stored in the drain trap and prevented from being discharged outside the gas production device 1. Instead of this drain trap, or together with the drain trap, a malfunction detection function of the valve and a redundancy measure when the valve malfunctions may be provided. Note that the liquid line may be connected to the above-described tank 30 so that the discharged condensed water can be reused.

[0052] The gas separator can be configured using one or more of, for example, a separator of a cryogenic separation method (cryogenic method), a pressure swing adsorption (PSA) method separator, a membrane separation method separator, a temperature swing adsorption (TSA) method separator, a porous coordination polymer (PCP) in which a metal ion (for example, copper ion) and an organic ligand (for example, 5-azidoisophthalic acid) are combined, a separator using amine absorption, and the like. Also, a valve may be provided between the gas-liquid separator and the gas separator of the gas line GL4. In this case, by adjusting the opening degree of the valve, the processing speed of the mixed gas (manufacturing speed of the generated gas) can be adjusted.

[0053] In this embodiment, the concentration of carbon monoxide contained in the mixed gas discharged from the gas-liquid separator is 75 to 90% by volume with respect to the whole mixed gas. Therefore, in fields where a generated gas containing carbon monoxide at a relatively low concentration (75 to 90% by volume) can be used, it can be directly supplied to the next process without purifying carbon monoxide from the mixed gas. That is, the gas separator can be omitted. Examples of such fields include a field of synthesizing valuable substances (such as ethanol, etc.) by fermentation with microorganisms (such as Clostridium, etc.) from the generated gas, a field of manufacturing steel using the generated gas as a fuel or a reducing agent, a field of manufacturing electric devices, a field of synthesizing chemicals (phosgene, acetic acid, etc.) using carbon monoxide as a synthesis raw material, and the like.

[0054] On the other hand, in fields where it is necessary to use a generated gas containing carbon monoxide at a relatively high concentration (more than 90% by volume), carbon monoxide is purified from the mixed gas to obtain a generated gas containing carbon monoxide at a high concentration. Examples of such fields include a field of using the generated gas as a reducing agent (blast furnace), a field of generating electricity by thermal power using the generated gas as a fuel, a field of manufacturing chemicals using the generated gas as a raw material, a field of fuel cells using the generated gas as a fuel, and the like.

[0055] In this embodiment, the separation cylinder 41 is configured to be capable of at least one of separating water (oxide of the reducing substance) and hydrogen (reducing substance) generated by contact with the reducing agent 4R, and separating carbon monoxide and carbon dioxide generated by contact of the separation cylinder 41 with the reducing agent 4R. In particular, the separation cylinder 41 is preferably configured to allow water (steam) or carbon monoxide to permeate through its wall and separate it from hydrogen or carbon dioxide. In this specification, water and carbon monoxide generated by the reaction upon contact with the reducing agent 4R may be referred to as "substances after contact with the reducing agent 4R", and hydrogen and carbon dioxide before contact (reaction) with the reducing agent 4R may be referred to as "substances before contact with the reducing agent 4R". According to such a configuration, since it is possible to remove the reaction product (substances after contact with the reducing agent 4R) from the inner cavity (reaction field) of the separation cylinder 41, that is, to separate the substances before and after contact with the reducing agent 4R, the activity of the reducing agent 4R can be maintained. For this reason, the reactions in the above formulas 1 and 2 can be continued for a long time, that is, the conversion efficiency from carbon dioxide to carbon monoxide and the reduction (regeneration) efficiency of the oxidized reducing agent 4R can be improved. As a result, a product gas containing carbon monoxide can be efficiently produced from a raw material gas containing carbon dioxide.

[0056] In this case, the water and carbon monoxide that have permeated through the separation cylinder 41 are discharged from the reactors 4a and 4b to the branch gas lines GL4a and GL4b. On the other hand, the unreacted hydrogen and unreacted carbon dioxide that have passed through the inside of the separation cylinder 41 are discharged to the gas lines GL9a and GL9b connected to the housing 42 (space 43). These gas lines GL9a and GL9b may be connected to the middle of the gas line GL1 and the gas line GL2 respectively. Thereby, unreacted hydrogen and unreacted carbon dioxide can be reused. The gas discharged to the branch gas lines GL4a and GL4b may contain gas components other than water or carbon monoxide, and the gas discharged to the gas lines GL9a and GL9b may also contain gas components other than hydrogen or carbon dioxide.

[0057] Incidentally, the separation of carbon monoxide and carbon dioxide, and the separation of water and hydrogen can also be achieved by cooling the gas discharged from each of the reactors 4a and 4b by utilizing the difference in the condensation (liquefaction) temperature. However, in this case, when using the separated gas components in a high-temperature state downstream of the reactors 4a and 4b (for example, when using in the heat exchanger 102), it is necessary to heat them again, resulting in waste of energy required for cooling and reheating. On the contrary, in the present invention, since the temperature drop of the separated gas components is unlikely to occur, it contributes to the reduction of thermal energy in the entire production of the product gas, that is, the energy efficiency can be improved.

[0058] As described above, from the viewpoint of preventing the reduction in the conversion efficiency of carbon dioxide to carbon monoxide, it is preferable to heat the reducing agent 4R. Therefore, the separation cylinder 41 preferably has heat resistance. Thereby, while preventing the alteration and deterioration of the separation cylinder 41, the reducing agent 4R can be sufficiently heated. Such a separation cylinder 41 is preferably composed of a metal, an inorganic oxide, or a metal organic framework (MOF). In this case, it is easy to impart excellent heat resistance to the separation cylinder 41. Here, examples of the metal include titanium, aluminum, copper, nickel, chromium, cobalt, or alloys containing these. Examples of the inorganic oxide include silica, zeolite, etc. Examples of the metal organic framework include a structure of zinc nitrate hydrate and terephthalic acid dianion, a structure of copper nitrate hydrate and trimesic acid trianion, etc. When using a metal, the separation cylinder 41 is preferably composed of a porous material having a porosity of 80% or more.

[0059] The separation cylinder 41 is preferably composed of a porous body having continuous pores (pores penetrating the cylinder wall) in which adjacent pores communicate with each other. With such a separation cylinder 41, the permeation rate of water or carbon monoxide can be increased, and the separation of water and hydrogen and / or the separation of carbon monoxide and carbon dioxide can be performed more smoothly and reliably. The porosity of the separation cylinder 41 is not particularly limited, but is preferably 10 to 90%, more preferably 20 to 60%. Thereby, while preventing the mechanical strength of the separation cylinder 41 from extremely decreasing, the permeability of water or carbon monoxide can be sufficiently maintained at a high level. In addition, the shape of the separation cylinder 41 is not particularly limited, and examples thereof include a cylindrical shape, a square shape, and a rectangular tube shape such as a hexagonal shape.

[0060] From the viewpoint of more reliably preventing or suppressing the decrease in the conversion efficiency of carbon dioxide to carbon monoxide, it is effective to increase the reduction (regeneration) efficiency of the reducing agent 4R in the oxidized state. That is, as shown in FIG. 3, it is preferable to configure the generated water (H2O) by bringing the supplied hydrogen (H2) into contact with the reducing agent 4R in the separation cylinder 41 to move through the separation cylinder 41 into the space 43 in the housing 42. In this case, the average pore diameter of the separation cylinder 41 is preferably 600 pm or less, more preferably 400 to 500 pm. Thereby, the separation efficiency between water and hydrogen can be further improved. In addition, the space 43 in the housing 42 may be depressurized or a carrier gas (sweep gas) may be passed through. Examples of the carrier gas include inert gases such as helium and argon.

[0061] Further, the separation cylinder 41 preferably has hydrophilicity. If the separation cylinder 41 has hydrophilicity, the affinity of water for the separation cylinder 41 increases, and water easily permeates the separation cylinder 41 more smoothly. As a method for imparting hydrophilicity to the separation cylinder 41, a method of improving the polarity of the separation cylinder 41 by changing the ratio of metal elements in the inorganic oxide (for example, increasing the Al / Si ratio), a method of coating the separation cylinder 41 with a hydrophilic polymer, a method of treating the separation cylinder 41 with a coupling agent having a hydrophilic group (polar group), a method of performing plasma treatment, corona discharge treatment, etc. on the separation cylinder 41, etc. can be mentioned. Furthermore, the affinity for water may be controlled by adjusting the surface potential of the separation cylinder 41.

[0062] On the other hand, in the separation cylinder 41, when preferentially separating carbon monoxide and carbon dioxide, or when simultaneously separating both water and hydrogen and carbon monoxide and carbon dioxide, the constituent material, porosity, average pore diameter, degree of hydrophilicity or hydrophobicity, surface potential, etc. of the separation cylinder 41 may be appropriately combined and set.

[0063] Next, the usage method (operation) of the gas production system 100 will be described. [1] First, by switching the gas line (flow path) in the gas switching unit 8, the connection unit 2 and the reactor 4a are communicated, and the reduction gas supply unit 3 and the reactor 4b are communicated. [2] Next, in this state, the supply of exhaust gas is started from the furnace 20 via the connection unit 2. The exhaust gas supplied from the furnace 20 is usually at a high temperature of 50 to 300°C, but is cooled to 30 to 50°C by the time it reaches the concentration adjustment unit 5.

[0064] [3] Next, the exhaust gas passes through the oxygen removal device (concentration adjustment unit 5). As a result, oxygen is removed from the exhaust gas, and the concentration of carbon dioxide contained in the exhaust gas increases. [4] Next, the exhaust gas passes through the compression unit 6. As a result, the pressure of the exhaust gas increases. [5] Next, the exhaust gas passes through the microcomponent removal unit 7. As a result, the condensed water generated when the exhaust gas is compressed by the compression unit 6 and the inactivating components that reduce the activity of the reducing agent 4R are removed from the exhaust gas.

[0065] [6] Next, the exhaust gas passes through the exhaust gas heating unit 10. As a result, the exhaust gas is heated. [7] Next, the exhaust gas is supplied to the reactor 4a. In the reactor 4a, carbon dioxide in the exhaust gas is reduced to carbon monoxide by the reducing agent 4R. At this time, carbon monoxide may move into the space 43 in the housing 42 through the separation cylinder 41. Also, at this time, the reducing agent 4R is oxidized. The heating temperature of the exhaust gas in the above step [6] is preferably 300 to 700 °C, more preferably 450 to 700 °C, still more preferably 600 to 700 °C, and particularly preferably 650 to 700 °C. If the heating temperature of the exhaust gas is set within the above range, for example, a rapid temperature drop of the reducing agent 4R due to the endothermic reaction when converting carbon dioxide to carbon monoxide can be prevented or suppressed, so that the reduction reaction of carbon dioxide in the reactor 4a can proceed more smoothly.

[0066] [8] In parallel with the above steps [2] to [7], water (raw material of reducing gas) is supplied from the tank 30 to the hydrogen generator (reducing gas supply unit 3) to generate hydrogen from water. [9] Next, the reducing gas containing hydrogen passes through the reducing gas heating unit 11. Thereby, the reducing gas is heated.

[10] Next, the reducing gas is supplied to the reactor 4b. In the reactor 4b, the reducing agent 4R in the oxidized state is reduced (regenerated) by the reducing gas (hydrogen). At this time, water is generated, and in this embodiment, it moves to the space 43 in the housing 42 through the separation cylinder 41 and is separated from hydrogen. The heating temperature of the reducing gas in the above step [9] is preferably 300 to 700 °C, more preferably 450 to 700 °C, still more preferably 600 to 700 °C, and particularly preferably 650 to 700 °C. If the heating temperature of the reducing gas is set within the above range, for example, a rapid temperature drop of the reducing agent 4R due to the endothermic reaction when reducing (regenerating) the reducing agent 4R in the oxidized state can be prevented or suppressed, so that the reduction reaction of the reducing agent 4R in the reactor 4b can proceed more smoothly.

[0067] Here, when the heating temperature of the exhaust gas by the exhaust gas heating unit 10 is X [°C] and the heating temperature of the reducing gas by the reducing gas heating unit 11 is Y [°C], it is preferable that |X - Y| (that is, the absolute value of the difference between X and Y) satisfies the relationship of 0 to 25, more preferably satisfies the relationship of 0 to 20, and even more preferably satisfies the relationship of 0 to 15. In other words, the heating temperature X of the exhaust gas and the heating temperature Y of the reducing gas may be the same or slightly different. By setting X and Y so as to satisfy the above relationship, the conversion of carbon dioxide to carbon monoxide and the reduction of the reducing agent 4R by the reducing gas can proceed with a good balance. In addition, when the heating temperature X of the exhaust gas and the heating temperature Y of the reducing gas are made different, since the amount of heat required for the reduction reaction of the reducing agent 4R by the reducing gas tends to be larger than the amount of heat required for the reduction reaction of carbon dioxide by the reducing agent 4R, it is preferable to set the heating temperature Y of the reducing gas higher than the heating temperature X of the exhaust gas.

[0068] In the present embodiment, the gas switching timing in the gas switching unit 8 (that is, the switching timing of the exhaust gas and the reducing gas supplied to the reactors 4a and 4b) is preferably the condition I: when a predetermined amount of exhaust gas is supplied to the reactor 4a or 4b, or the condition II: when the conversion efficiency of carbon dioxide to carbon monoxide falls below a predetermined value. Thereby, before the conversion efficiency of carbon dioxide to carbon monoxide significantly decreases, the reactors 4a and 4b are switched, so that the concentration of carbon monoxide contained in the mixed gas can be increased and stabilized. In addition, for the detection of the condition II, gas concentration sensors may be arranged near the inlet and outlet ports of the reactors 4a and 4b, respectively. Based on the detection values of these gas concentration sensors, the conversion efficiency of carbon dioxide to carbon monoxide can be obtained by calculation.

[0069] Also, from the viewpoint of further stabilizing the concentration of carbon monoxide contained in the mixed gas, it is preferable to set the supply amount of the exhaust gas to the reactors 4a and 4b and the supply amount of the reducing gas to the reactors 4a and 4b to be as close as possible. Specifically, when the supply amount of the exhaust gas to the reactors 4a and 4b is P [mL / min] and the supply amount of the reducing gas to the reactors 4a and 4b is Q [mL / min], it is preferable that P / Q satisfies the relationship of 0.9 to 2, and more preferably satisfies the relationship of 0.95 to 1.5. If the supply amount P of the exhaust gas is too large, depending on the amount of the reducing agent 4R in the reactors 4a and 4b, the amount of carbon dioxide discharged from the reactors 4a and 4b tends to increase without being converted to carbon monoxide.

[0070] The predetermined amount in the above condition I is preferably an amount of 0.01 to 3 moles of carbon dioxide per mole of the metal element having the largest mass ratio in the reducing agent 4R, and more preferably an amount of 0.1 to 2.5 moles. Also, the predetermined value in the above condition II is preferably 50 to 100%, more preferably 60 to 100%, and even more preferably 70 to 100%. Note that the upper limit of the predetermined value may be 95% or less, or may be 90% or less. In any case, before the conversion efficiency of carbon dioxide to carbon monoxide extremely decreases, the reactors 4a and 4b can be switched. As a result, a mixed gas containing carbon monoxide at a high concentration can be stably obtained, and thus, a product gas containing carbon monoxide at a high concentration can also be produced.

[0071] Note that the supply amount Q of the reducing gas (reducing substance) is preferably an amount of 0.1 to 3 moles of hydrogen per mole of the metal element having the largest mass ratio in the reducing agent 4R, and more preferably an amount of 0.15 to 2.5 moles. Even if the supply amount Q of the reducing gas is increased beyond the upper limit value, no further increase in the effect of reducing the reducing agent 4R in the oxidized state can be expected. On the other hand, if the supply amount Q of the reducing gas is too small, depending on the amount of hydrogen contained in the reducing gas, the reduction of the reducing agent 4R may be insufficient. Also, the pressure of the reducing gas supplied to the reactors 4a and 4b may be atmospheric pressure or may be pressurized (the same level as the exhaust gas).

[0072]

[11] Next, the gases that have passed through the reactors 4a and 4b merge to form a mixed gas. On the other hand, the water (or water and carbon monoxide) separated in the separation cylinder 41 is discharged from the gas lines GL9a and GL9b. At this point, the temperature of the mixed gas is usually 600 to 650°C. If the temperature of the mixed gas at this point is within the above range, it means that the temperature inside the reactors 4a and 4b is maintained at a sufficiently high temperature, and it can be judged that the conversion of carbon dioxide to carbon monoxide by the reducing agent 4R and the reduction of the reducing agent 4R by the reducing gas are proceeding efficiently.

[12] Next, the mixed gas is cooled to 100 to 300°C before reaching the gas purification unit 9.

[13] Next, the mixed gas passes through the gas purification unit 9. As a result, for example, the generated condensed water and carbon dioxide dissolved in the condensed water are removed. As a result, carbon monoxide is purified from the mixed gas, and a product gas containing carbon monoxide at a high concentration is obtained. Note that the temperature of the obtained product gas is 20 to 50°C.

[14] Next, the product gas is discharged from the product gas discharge unit 40 outside the gas production apparatus 1 and is used in the next process.

[0073] <Configuration of the reducing agent heating unit (reducing agent temperature control unit)> FIG. 5 is a schematic diagram showing the configuration of the reducing agent heating unit, and FIG. 6 is a schematic diagram showing another configuration of the reducing agent heating unit. The reducing agent heating unit 12 shown in FIG. 5 includes a medium supplied to a jacket (not shown) provided on the outer periphery of the housing 42, a transfer device 121 that transfers the medium to the jacket, and a heating device 122 that heats the medium.

[0074] The reducing agent heating unit 12 of this configuration example includes a circulating medium line ML1 connected to each of the reactors 4a and 4b, and this medium line ML1 is filled with a medium. The medium line ML1 branches midway, then is connected to each of the reactors 4a and 4b, and then merges again to become one. Also, a transfer device 121 and a heating device 122 are arranged midway in the merged medium line ML1. According to such a configuration, when the medium heated by the heating device 122 circulates through the medium line ML1, it is supplied to the jackets of the reactors 4a and 4b. As a result, the reducing agent 4R is indirectly heated via the housing 42 and the separation cylinder 41. Also, the heating temperatures of the reducing agent 4R in the two reactors 4a and 4b can be set to be substantially equal. The heating temperature of the reducing agent 4R is preferably 300 to 700°C, and more preferably 650 to 700°C. If the heating temperature is too high, although it depends on the type of metal oxide constituting the reducing agent 4R, the reducing agent 4R tends to deteriorate and its activity tends to decrease. On the other hand, if the heating temperature is too low, the time required to produce the product gas containing carbon monoxide at a high concentration tends to be long.

[0075] Examples of the medium include gases, liquids (including viscous liquids), etc. The heating device 122 can be composed only of an electric heater, or can also be composed of an electric heater and a heat exchanger similar to that described in the exhaust gas heating unit 10. According to the latter configuration, the heat of the high-temperature gas after passing through the reactors 4a and 4b is used to heat the medium before being supplied to the reactors 4a and 4b by heat exchange, so that effective utilization of heat can be achieved. In addition, when using a gas as the medium, the transfer device 121 can be composed of a blower. Also, when using a liquid as the medium, the transfer device 121 can be composed of a pump. Note that the reducing agent heating unit 12 can also be composed of an electric heater instead of the configuration using a medium (heating gas). In this case, the heating by the electric heater may be performed on the housing 42 of the reactors 4a and 4b, or may be performed separately on the separation cylinder 41 filled with the reducing agent 4R.

[0076] The reducing agent heating unit 12 shown in FIG. 6 is provided with a non-circulating medium line ML2 and is configured to use air (gas) as the medium. In this configuration example, a transfer device 121 (a blower), a first heat exchanger 123, and a heating device 124 composed of an electric heater are arranged in order from the air supply port side of the medium line ML2, and a second heat exchanger 125 is arranged on the air discharge port side. The first heat exchanger 123 and the second heat exchanger 125 preferably each have the same configuration as the heat exchanger 102. The first heat exchanger 123 performs heat exchange between the gas (for example, the mixed gas) after passing through the separation cylinders 41 of the reactors 4a and 4b and the air before being supplied to the jackets of the reactors 4a and 4b. On the other hand, the second heat exchanger 125 performs heat exchange between the air after passing through the jackets of the reactors 4a and 4b and the exhaust gas before being supplied to the reactors 4a and 4b.

[0077] By utilizing the heat of the high-temperature gas or air (medium) after passing through the reactors 4a and 4b to heat the air (medium) or exhaust gas before being supplied to the reactors 4a and 4b through heat exchange, effective utilization of heat can be achieved. Note that the second heat exchanger 125 may be configured to perform heat exchange with the reducing gas before being supplied to the reactors 4a and 4b instead of performing heat exchange with the exhaust gas before being supplied to the reactors 4a and 4b, or may be configured to perform heat exchange with both the exhaust gas and the reducing gas before being supplied to the reactors 4a and 4b. Also, according to the configuration example shown in FIG. 6, compared with the configuration example shown in FIG. 5, since the temperature of the medium in contact with the transfer device 121 is lower, there is an advantage that a relatively inexpensive transfer device with low heat resistance can also be used.

[0078] Here, if a combustion furnace or the like is used to heat the reactors 4a and 4b (the reducing agent 4R), it is necessary to burn fuel to maintain the heating temperature (reaction temperature) of the reducing agent 4R. For this reason, carbon dioxide is generated and has to be released into the atmosphere. On the other hand, by configuring the reducing agent heating unit 12 as shown in FIGS. 5 and 6, electric power (electrical energy) as the renewable energy as described above can be used as the power source of the transfer device 121 and the heating devices 122 and 124, so that the environmental load can be reduced. There is also an advantage that the possibility of ignition of the combustible gas existing in the gas production apparatus 1 can be more reliably reduced.

[0079] Note that, instead of the configuration shown in FIGS. 5 and 6, the reducing agent heating unit may be configured to include an irradiation device that irradiates the reducing agent 4R with microwaves. According to the configuration in which the reducing agent 4R is heated by irradiation with microwaves, the reducing agent 4R can be heated to the target temperature in a relatively short time. In addition, it is easy to heat not only the vicinity of the surface of the reducing agent 4R but also the central portion uniformly. Furthermore, it is easy to precisely control the heating temperature of the reducing agent 4R. Therefore, by using the irradiation device, the production efficiency of the produced gas can be further increased. In addition, such an irradiation device can be miniaturized as compared with the configuration shown in FIGS. 5 and 6. In addition, in the case of irradiation with microwaves, only the vicinity of the surface of the reducing agent 4R can be locally (preferably) raised to the target temperature. For this reason, when the reaction proceeds at a high temperature (in the case of an endothermic reaction), its efficiency can be easily increased. In this case, since only the energy for raising the temperature of only the vicinity of the surface of the reducing agent 4R needs to be input, the energy efficiency is also improved.

[0080] Microwaves mean electromagnetic waves with a frequency of 300 MHz to 300 GHz, and are classified into extremely high frequency (UHF) with a frequency of 300 to 3000 MHz, centimeter wave (SHF) with a frequency of 3 to 30 GHz, millimeter wave (EHF) with a frequency of 30 to 300 GHz, and submillimeter wave (SHF) with a frequency of 300 to 3000 GHz. Among them, as microwaves, extremely high frequency (UHF) is preferable. By using extremely high frequency (UHF), the reducing agent 4R can be heated to the target temperature in a shorter time. Note that when performing irradiation with microwaves, appropriate measures against leakage of radio waves in accordance with the Radio Law are taken.

[0081] Further, the microwave irradiation may be performed continuously or intermittently (pulsed). The inventors have found that when the microwave irradiation is performed continuously, the conversion efficiency of carbon dioxide to carbon monoxide and the regeneration (reduction) efficiency of the reducing agent 4R by the reducing gas are further enhanced. Although the reason is not necessarily clear, it is considered that carbon dioxide contained in the exhaust gas supplied into the reactors 4a and 4b, hydrogen contained in the reducing gas, and the reducing agent 4R are activated by the continuously irradiated microwaves. On the other hand, when the microwave irradiation is performed intermittently, the microwave may be irradiated at a predetermined timing so as to compensate only for the energy required for the endothermic reaction during the conversion of carbon dioxide to carbon monoxide and the regeneration (reduction) of the reducing agent 4R by the reducing gas, so that the energy efficiency can be increased.

[0082] In the case of heating by microwave irradiation, the heating temperature of the exhaust gas, the heating temperature of the reducing gas, and the heating temperature of the reducing agent 4R may be the same as or different from the above ranges, respectively. For example, each of the above heating temperatures can be set to 300 to 700°C. Note that the irradiation device may be disposed inside or outside the reactors 4a and 4b. As described above, if the gas composition of the exhaust gas is deviated from the explosion range by the concentration adjustment unit 5, it is possible to suitably prevent the exhaust gas from becoming an ignition source regardless of the microwave irradiation conditions. In addition, since electrical energy is used as the power source of the irradiation device, there is also an advantage that it is easy to switch this electrical energy to renewable energy.

[0083] As described above, when the reaction by the reducing agent 4R is an exothermic reaction, the reducing agent temperature control unit can be configured as a reducing agent cooling unit. In this case, for example, in the configurations shown in FIGS. 5 and 6, the first heat exchanger 123 and the second heat exchanger 125 may be omitted, and the heating devices 122 and 124 may be changed to cooling devices. Examples of the cooling device include a jacket-type cooling device and a multi-tube type cooling device. Also in this case, it is preferable that the cooling temperature (temperature after temperature control) of the reducing agent 4R is in the same range as described above.

[0084] <Configuration near the connection part> FIG. 7 is a schematic view showing a configuration near a connection part (raw material gas supply part) between the gas production apparatus of the present invention and a furnace. As shown in FIG. 7, the furnace 20 includes a chimney 21 that discharges exhaust gas to the atmosphere. One end of a gas line 23 is connected to a branch part 22 in the middle of the chimney 21 in the height direction. The other end of this gas line 23 is connected to the connection part 2 of the gas production apparatus 1.

[0085] In the configuration shown in FIG. 7, a cooling unit 13 is provided between the connection part 2 and the concentration adjustment unit 5. The cooling unit 13 includes a cooling device 131 and a container 132 connected to the cooling device 131. The cooling device 131 can be configured by a jacket-type cooling device or a multi-tube type cooling device as described above. The exhaust gas supplied from the furnace 20 contains, in addition to water vapor, oxidation gas components (SO x , HCl, etc.). Therefore, by cooling in the cooling unit 13, it is preferable to condense water vapor together with the oxidation gas components and remove them as condensed water (acidic aqueous solution) in which the oxidation gas components are dissolved. Thereby, corrosion of the piping constituting the gas line GL1 can be suitably prevented. In this configuration example, an acidic aqueous solution is generated by cooling the exhaust gas with the cooling device 131, and this acidic aqueous solution is stored in the container 132 and separated from the exhaust gas. Also, a filter that allows the passage of gas but blocks the passage of liquid may be arranged at the gas-liquid interface in the container 132. In the case of such a configuration, the separation distance (L1 in FIG. 7) between the branch portion 22 and the cooling device 131 is not particularly limited, but is preferably 10 m or less, and more preferably 1 to 5 m. If the separation distance L1 is set within the above range, it is possible to prevent the generation of condensed water (acidic aqueous solution) in which acidic gas is dissolved at a location not intended for the gas line GL1, and more reliably prevent the corrosion of the pipes constituting the gas line GL1.

[0086] Further, when the gas production system 100 is installed, for example, in a cold region or the like, particularly depending on the separation distance L2 between the furnace 20 and the gas production device 1, condensed water may be generated in the middle of the gas line 23 and may even freeze. This may cause the pipes constituting the gas line 23 to be damaged. Therefore, in order to prevent such troubles, it is preferable to heat the exhaust gas in the gas line 23. The heating temperature may be any temperature at which freezing does not occur, but is preferably at or above the acid dew point temperature (for example, 120°C), and more preferably 120 to 150°C. Thereby, while preventing the pipes constituting the gas line 23 from being damaged, it is also possible to suitably prevent the corrosion of the pipes due to the generation of condensed water in which acidic gas is dissolved. In addition, in order to heat the exhaust gas in the gas line 23, for example, an electric heating wire (heater) may be wound around the pipes constituting the gas line 23 and arranged. Further, for the purpose of corrosion resistance, instead of using a heater, a resin-lined pipe made of a corrosion-resistant resin material (for example, a fluorine-based resin material) may be used. In this configuration example, the container 132 may be omitted as necessary.

[0087] In the above embodiment, exhaust gas was described as an example of the raw material gas. However, as described above, the raw material gas is not particularly limited to exhaust gas as long as it is a gas containing carbon dioxide. Therefore, in the above embodiment, various treatment conditions of the exhaust gas (including the pressure of pressurization by the compression unit 6, the heating temperature before supplying to the reactors 4a and 4b, the supply amount to the reactors 4a and 4b, etc.) can be similarly applied to other raw material gases.

[0088] Using the gas production apparatus 1 and the gas production system 100 as described above, a product gas containing carbon monoxide can be produced from a raw material gas containing carbon dioxide. <Gas production method> The gas production method of the present embodiment is a method for producing a product gas containing carbon monoxide by bringing the exhaust gas (raw material gas) into contact with the reducing agent 4R. I: A plurality of reactors 4a and 4b having a separation cylinder 41 containing the reducing agent 4R disposed therein, an exhaust gas containing carbon dioxide, and a reducing gas containing hydrogen (reducing substance) for reducing the reducing agent 4R oxidized by contact with carbon dioxide are prepared. II: By switching the reactors 4a and 4b that supply the exhaust gas and the reducing gas, the exhaust gas and the reducing gas are alternately brought into contact with the reducing agent 4R in each of the reactors 4a and 4b (separation cylinder 41) to convert carbon dioxide into carbon monoxide, and then the oxidized reducing agent 4R is reduced. At this time, the separation cylinder 41 is capable of at least one of separating water (oxide of the reducing substance) and hydrogen (reducing substance) generated by contact with the reducing agent 4R, and separating carbon monoxide and carbon dioxide.

[0089] <Product> The product gas produced using the gas production apparatus 1 and the gas production system 100 usually has a carbon monoxide concentration of 60% by volume or more, preferably 75% by volume or more, and more preferably 90% by volume or more. In addition, the product gas as described above can be used in fields such as synthesizing valuable substances (such as ethanol) by fermentation with microorganisms (such as Clostridium), manufacturing steel using it as a fuel or a reducing agent, manufacturing electric devices, manufacturing chemicals (phosgene, acetic acid, etc.) using carbon monoxide as a synthesis raw material, using it as a reducing agent (blast furnace), using it as a fuel for power generation by thermal power, and using it in the field of fuel cells as a fuel.

[0090] Further, in the gas production system 100 (gas production apparatus 1) described above, the gas that has passed through the reactors 4a and 4b was configured to merge immediately after passing through the reactors 4a and 4b, but various treatments may be performed before merging. That is, at least one processor can be provided in the middle of the branch gas lines GL4a and GL4b for any purpose. Alternatively, the gas merging section J4 may be omitted, and the branch gas lines GL4a and GL4b may be used as independent gas lines. In this case, the gas (water or carbon monoxide) that has passed through each of the reactors 4a and 4b and has been separated is transferred through the independent branch gas lines GL4a and GL4b. For example, the gas containing water (steam) is subjected to waste treatment or conversion treatment to the tank 30, and the gas containing carbon monoxide is subjected to purification treatment as necessary and then to subsequent-stage treatment. According to such a configuration, the gas that has passed through each of the reactors 4a and 4b and has been separated can be processed independently of each other.

[0091] The gas production apparatus, gas production system, and gas production method of the present invention have been described above, but the present invention is not limited thereto. For example, the gas production apparatus and gas production system of the present invention may each have any other arbitrary additional configuration with respect to the above-described embodiment, may be replaced with any configuration that exhibits the same function, or some configurations may be omitted. Further, in the gas production method of the present invention, a process for any purpose may be added with respect to the above-described embodiment.

[0092] Also, in the above-described embodiment, a gas containing hydrogen as a reducing gas has been described as a representative, but as the reducing gas, a gas containing at least one selected from hydrocarbons (e.g., methane, ethane, acetylene, etc.) and ammonia as a reducing substance instead of or together with hydrogen can also be used. In the above embodiment, a heat exchanger configured to perform heat exchange between the exhaust gas (raw material gas), reduction gas, or heating medium before being supplied to the reactor and the mixed gas has been described. However, a heat exchanger configured to perform heat exchange with the gas discharged from each reactor and before being made into the mixed gas may be employed.

Example

[0093] Next, specific examples of the present invention will be described. Note that the present invention is not limited to the following specific examples. (Examples 1, 2 and Comparative Example) By setting the selectivity ratio between hydrogen and water (steam) in the separation cylinder, the change in the reduction (regeneration) efficiency of the oxidizing state reducing agent was simulated. Note that the constituent material of the reducing agent was cerium oxide. Also, by changing the porosity, average pore diameter, and hydrophilicity degree of the separation cylinder, the selectivity ratio of hydrogen to water in the separation cylinder was set to hydrogen:water = 1:10000 (Example 1), 1:100 (Example 2), and 1:0 (Comparative Example). The results of this simulation are shown in Table 1 below.

[0094]

Table 1

[0095] As shown in Table 1, by increasing the selectivity ratio of water to hydrogen in the separation cylinder, that is, by increasing the degree of separating hydrogen and water by allowing water to permeate through the separation cylinder, it can be seen that even at the same temperature, the conversion efficiency of hydrogen to water can be further increased.

Explanation of Reference Numerals

[0096] 100…Gas production system 1…Gas production apparatus 2…Connection part 3…Reduction gas supply part 4…Reaction part 4a, 4b…Reactor 41…Separation cylinder, 42…Housing, 43…Space, 44…Partition part, 4R…Reducing agent 5…Concentration adjustment unit 6…Compression unit 7…Micro-component removal unit 8…Gas switching unit 9…Gas purification unit 10…Exhaust gas heating unit 101…Electric heater, 102…Heat exchanger 11…Reduction gas heating unit 12…Reducing agent heating unit 121…Transfer device, 122…Heating device, 123…First heat exchanger, 124…Electric heater, 125…Second heat exchanger 13…Cooling unit 131…Cooling device, 132…Container 20…Furnace 21…Chimney, 22…Branching part, 23…Gas line 30…Tank 40…Generated gas discharge part GL1…Gas line GL2…Gas line GL3a, GL3b…Gas line GL4…Gas line GL4a, GL4b…Branched gas line, J4…Gas confluence part GL9a, GL9b…Gas line L1…Separation distance L2…Separation distance

Claims

1. A gas production apparatus for producing a product gas containing carbon monoxide by bringing a raw material gas containing carbon dioxide into contact with a reducing agent containing a metal oxide that reduces the carbon dioxide, comprising: a raw material gas supply unit that supplies the raw material gas; a reducing gas supply unit that supplies a reducing gas containing a reducing substance that reduces the reducing agent oxidized by contact with the carbon dioxide; a plurality of reactors respectively connected to the raw material gas supply unit and the reducing gas supply unit and capable of switching between the supplied raw material gas and the reducing gas; each of the reactors has a reactor main body that houses the reducing agent, and is configured to be capable of at least one of separating an oxide of the reducing substance generated by contact with the reducing agent from the reducing substance and separating the carbon monoxide from the carbon dioxide; wherein when the supply amount of the raw material gas to the reactor is P [mL / min] and the supply amount of the reducing gas to the reactor is Q [mL / min], P / Q satisfies the relationship of 0.9 to 2. The gas production apparatus is characterized by this.

2. A gas production apparatus for producing a product gas containing carbon monoxide by bringing a raw material gas containing carbon dioxide into contact with a reducing agent containing a metal oxide that reduces the carbon dioxide, comprising: a raw material gas supply unit that supplies the raw material gas; a reducing gas supply unit that supplies a reducing gas containing a reducing substance that reduces the reducing agent oxidized by contact with the carbon dioxide; a plurality of reactors respectively connected to the raw material gas supply unit and the reducing gas supply unit and capable of switching between the supplied raw material gas and the reducing gas; each of the reactors has a reactor main body that houses the reducing agent, and is configured to be capable of at least one of separating an oxide of the reducing substance generated by contact with the reducing agent from the reducing substance and separating the carbon monoxide from the carbon dioxide; the timing for switching between the raw material gas and the reducing gas supplied to the reactor is Condition I: when a predetermined amount of the raw material gas is supplied to the reactor, or Condition II: when the conversion efficiency of the carbon dioxide to carbon monoxide falls below a predetermined value, the predetermined amount in Condition I is an amount of 0.01 to 3 moles of carbon dioxide per mole of the metal element having the largest mass ratio in the reducing agent, and the predetermined value in Condition II is 50 to 100%. The gas production apparatus is characterized by this.

3. The reducing substance is hydrogen, and the oxide of the reducing substance is water. The separation cylinder has an average pore diameter of 600 pm or less, and the gas production apparatus according to claim 1 or 2.

4. The metal oxide contained in the reducing agent contains at least one selected from metal elements belonging to Groups 3 to 12, and the gas production apparatus according to any one of claims 1 to 3.

5. Furthermore, the gas production apparatus according to any one of claims 1 to 4, further comprising a gas merging section that merges the gases separated after passing through the reactor to generate a mixed gas.

6. Furthermore, the gas production apparatus according to any one of claims 1 to 5, further comprising independent gas lines connected to each of the reactors for transferring the separated gases.

7. Furthermore, a raw material gas heating section for heating the raw material gas before supplying it to the reactor, and a reducing gas heating section for heating the reducing gas before supplying it to the reactor, and the gas production apparatus according to any one of claims 1 to 6.

8. A raw material gas generation section for generating a raw material gas containing carbon dioxide, and the gas production apparatus according to any one of claims 1 to 7, and the gas production apparatus is connected to the raw material gas generation section via the raw material gas supply section, and a gas production system characterized by this.

9. A gas production method for producing a product gas containing carbon monoxide by bringing a raw material gas containing carbon dioxide into contact with a reducing agent containing a metal oxide for reducing the carbon dioxide, preparing a plurality of reactors having a reactor body for accommodating the reducing agent, the raw material gas, and a reducing gas containing a reducing substance for reducing the reducing agent oxidized by contact with the raw material gas and the carbon dioxide, by switching the reactor for supplying the raw material gas and the reducing gas, the raw material gas and the reducing gas are alternately brought into contact with the reducing agent in each reactor, and when reducing the oxidized reducing agent after converting the carbon dioxide to carbon monoxide, at least one of separation of the oxide of the reducing substance generated by contact with the reducing agent and the reducing substance, and separation of the carbon monoxide and the carbon dioxide is possible in the reactor, When the supply amount of the raw material gas to the reactor is P [mL / min] and the supply amount of the reducing gas to the reactor is Q [mL / min], P / Q satisfies the relationship of 0.9 to 2, and a gas production method characterized by this.

10. A gas production method for producing a product gas containing carbon monoxide by bringing a raw material gas containing carbon dioxide into contact with a reducing agent containing a metal oxide that reduces the carbon dioxide, a plurality of reactors each having a reactor body for accommodating the reducing agent, a raw material gas, and a reducing gas containing a reducing substance for reducing the reducing agent oxidized by contact with the raw material gas and the carbon dioxide are prepared, by switching the reactor to which the raw material gas and the reducing gas are supplied, in each reactor, the raw material gas and the reducing gas are alternately brought into contact with the reducing agent, and after converting the carbon dioxide to carbon monoxide, when reducing the oxidized reducing agent, the reactor is capable of at least one of separating the oxide of the reducing substance generated by contact with the reducing agent from the reducing substance and separating carbon monoxide from carbon dioxide, the timing for switching the raw material gas and the reducing gas supplied to the reactor is Condition I: when a predetermined amount of the raw material gas is supplied to the reactor, or Condition II: when the conversion efficiency of the carbon dioxide to carbon monoxide falls below a predetermined value, the predetermined amount in Condition I is an amount of 0.01 to 3 moles of carbon dioxide per mole of the metal element having the largest mass ratio in the reducing agent, the predetermined value in Condition II is 50 to 100%, characterized in that it is a gas production method. [

11. ] A gas production method for producing a product gas containing carbon monoxide by bringing a raw material gas containing carbon dioxide into contact with a reducing agent containing a metal oxide that reduces the carbon dioxide, a plurality of reactors each having a reactor body for accommodating the reducing agent, a raw material gas, and a reducing gas containing a reducing substance for reducing the reducing agent oxidized by contact with the raw material gas and the carbon dioxide are prepared, by switching the reactor to which the raw material gas and the reducing gas are supplied, in each reactor, the raw material gas and the reducing gas are alternately brought into contact with the reducing agent, and after converting the carbon dioxide to carbon monoxide, when reducing the oxidized reducing agent, the reactor is capable of at least one of separating the oxide of the reducing substance generated by contact with the reducing agent from the reducing substance and separating carbon monoxide from carbon dioxide, A gas production method characterized by adjusting the oxygen concentration contained in the raw material gas to less than 1% by volume and increasing the pressure of the raw material gas before the raw material gas is supplied to the reactor.

12. After passing through the reactor and being separated, the gases are merged together to produce a mixed gas. The gas production method according to any one of claims 9 to 11, wherein the mixed gas is recovered as the product gas as it is, or by purifying the carbon monoxide from the mixed gas.

13. The gas production method according to any one of claims 9 to 11, wherein the gases separated after passing through each of the reactors are processed independently of each other.

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